Preface

The main and preferred source of energy for the body is glucose. Therefore, most tissues and organs need a constant supply of glucose. The low blood concentrations of glucose can cause several pathologies and diseases such as seizures and loss of consciousness. Hypoglycemia may also cause death. On the other hand, long-term high glucose levels, hyperglycemia, can cause blindness, renal failure, cardiac and peripheral vascular disease, and neuropathy. Therefore, blood glucose concentrations need to be maintained within narrow limits and are carefully regulated to around 90 mg/mL (5 mM). The process of maintaining blood glucose at a steady state is called glucose homeostasis. This is achieved through a balance of the rate of consumption of dietary carbohydrates, utilization of glucose by peripheral tissues, and the loss of glucose through the kidney tubule. The liver and kidney also play a role in glucose homeostasis. A major role in glucose homeostasis is played by the liver by maintaining a balance between the uptake and storage of glucose via glycogenesis, and the release of glucose via glycogenolysis and gluconeogenesis. The body can adjust blood glucose levels by a variety of cellular mechanisms. In this process, a very important role is played by external signals conveyed by hormones, cytokines, and so on. In the past several years, the knowledge of regulation of blood glucose levels, glucose homeostasis, and diseases due to disturbances in glucose homeostasis, has been growing. This book aims to provide an overview on the topic of blood glucose levels in health and diseases. The authors discuss this process from different aspects to enhance the understanding of glucose homeostasis in the human body.

This book contains four sections. Section 1 contains only one chapter and describes the general characteristics of glucose transporters. Section 2 contains chapters in which authors describe mechanisms of regulation of blood glucose levels. These chapters include information on the molecular basis of blood glucose regulation, and role of PI3K/AKT in insulin-mediated glucose uptake. Section 3 focuses on low blood glucose levels (hypoglycemia). The authors describe pathologies due to hypoglycemia, as well as the symptoms and signals of this pathological state. Section 4 presents the influence of lifestyle on metabolic syndromes. This dependence is described on the basis of Ramadan fasting.

I would like to thank Mr. Gordan Tot for his great efforts in the book planning and editing during the process of book publication.

**II**

**Section 4**

*by Khalid S. Aljaloud*

Lifestyle and Metabolic Syndrome **109**

**Chapter 8 111**

The Effect of Ramadan Fasting on Metabolic Syndrome (MetS)

**Leszek Szablewski** Professor, Chair and Department of General Biology and Parasitology, Medical University of Warsaw, Poland

**1**

Section 1

Introduction

Section 1 Introduction

**3**

**Chapter 1**

Transporters

by diffusion. For cations such as K+

*Leszek Szablewski*

**1. Introduction**

Introductory Chapter: Glucose

The major source of energy for mammalian cells is glucose. Glucose derived from the diet and synthesized within the body is transported from the circulation into target cells. The transfer of glucose across the plasma membrane is necessary. Cell membrane is composed by lipid bilayer, which is hydrophobic. Glucose has hydrophilic nature. Therefore, cell membranes act as barriers to most molecules. For water molecules and a few other small molecules, such as oxygen and carbon dioxide, the lipid bilayer is permeable. These molecules move spontaneously down their concentration gradient

, and Ca2+; anions such as Cl<sup>−</sup> and HCO3

<sup>−</sup>; and

, Na+

bers. These transporters transport variety of molecules.

in the transport of several different molecules, not just glucose.

**2. Characteristics of glucose transporters**

**2.1 Characteristics of GLUT proteins**

hydrophilic molecules and macromolecules such as proteins and RNA, lipid bilayer is impermeable. Therefore, these molecules and ions need specific transport system. There are two general classes of membrane transporters: channels and carriers. Glucose transporters belong to the major facilitator superfamily (MFS). MFS contains 74 families of membrane transporters including more than 10,000 mem-

Glucose as well as other monosaccharides cannot penetrate the lipid bilayer because they are hydrophilic in nature; therefore, they require specific carrier proteins to undergo diffusion through the bilayer. In humans, there are three families of

genes that encode for glucose transporters: *SLC2A*, *SLC5A*, and *SLC50A* [1]. Glucose is transported across the cell membranes and tissue barriers by a sodium-independent glucose transporter (facilitated transport, GLUT proteins, and *SLC2* genes), sodium-dependent glucose symporters (secondary active transport, SGLT proteins, and *SLC5* genes), and glucose uniporter—SWEET protein (*SLC50* genes). Most cells express more than one kind of glucose transporters. However, these membrane carrier proteins are called glucose transporters; they are involved

In humans, 14 members of GLUT proteins have been identified. They are encoded by the solute-linked carrier family 2, subfamily A gene family, and *SLC2A* [2, 3]. All GLUT proteins are predicted to contain 12 hydrophobic membrane spanning, α-helical transmembrane (TM) domains. These domains are connected by hydrophilic loop between TM6 and TM7 of the protein [4–6]. GLUTs contain a site for single glycosylation on the exofacial end, either in the large loop between TM1 and TM2 (first extracellular loop) or between TM9 and TM10 (fifth extracellular

#### **Chapter 1**

## Introductory Chapter: Glucose Transporters

*Leszek Szablewski*

#### **1. Introduction**

The major source of energy for mammalian cells is glucose. Glucose derived from the diet and synthesized within the body is transported from the circulation into target cells. The transfer of glucose across the plasma membrane is necessary. Cell membrane is composed by lipid bilayer, which is hydrophobic. Glucose has hydrophilic nature. Therefore, cell membranes act as barriers to most molecules. For water molecules and a few other small molecules, such as oxygen and carbon dioxide, the lipid bilayer is permeable. These molecules move spontaneously down their concentration gradient by diffusion. For cations such as K+ , Na+ , and Ca2+; anions such as Cl<sup>−</sup> and HCO3 <sup>−</sup>; and hydrophilic molecules and macromolecules such as proteins and RNA, lipid bilayer is impermeable. Therefore, these molecules and ions need specific transport system. There are two general classes of membrane transporters: channels and carriers.

Glucose transporters belong to the major facilitator superfamily (MFS). MFS contains 74 families of membrane transporters including more than 10,000 members. These transporters transport variety of molecules.

Glucose as well as other monosaccharides cannot penetrate the lipid bilayer because they are hydrophilic in nature; therefore, they require specific carrier proteins to undergo diffusion through the bilayer. In humans, there are three families of genes that encode for glucose transporters: *SLC2A*, *SLC5A*, and *SLC50A* [1].

Glucose is transported across the cell membranes and tissue barriers by a sodium-independent glucose transporter (facilitated transport, GLUT proteins, and *SLC2* genes), sodium-dependent glucose symporters (secondary active transport, SGLT proteins, and *SLC5* genes), and glucose uniporter—SWEET protein (*SLC50* genes). Most cells express more than one kind of glucose transporters. However, these membrane carrier proteins are called glucose transporters; they are involved in the transport of several different molecules, not just glucose.

#### **2. Characteristics of glucose transporters**

#### **2.1 Characteristics of GLUT proteins**

In humans, 14 members of GLUT proteins have been identified. They are encoded by the solute-linked carrier family 2, subfamily A gene family, and *SLC2A* [2, 3]. All GLUT proteins are predicted to contain 12 hydrophobic membrane spanning, α-helical transmembrane (TM) domains. These domains are connected by hydrophilic loop between TM6 and TM7 of the protein [4–6]. GLUTs contain a site for single glycosylation on the exofacial end, either in the large loop between TM1 and TM2 (first extracellular loop) or between TM9 and TM10 (fifth extracellular

loop) [7]. As was proposed for GLUT1, helices 1, 2, 4, 5, 7, 8, 10, and 11 form an inner bundle that is stabilized by the outer helices 3, 6, 9, and 12 [8].

Based on the phylogenetic analysis of sequence similarity and characteristic elements, the GLUT family of sugar transporters is divided into three classes [4, 5, 9, 10]: an N-linked glycosylation site for GLUTs of class I and II is positioned in the first exofacial loop between TM1 and TM2, and family members of class III contain the glycosylation site between TM9 and TM10 [5].

Class I GLUTs include GLUT1–GLUT4 and GLUT14, which are 48–63% identical in humans. Class II GLUTs comprise of GLUT5, GLUT7, GLUT9, and GLUT11. These transporters are 36–40% identical. Class III GLUTs include GLUT6, GLUT8, GLUT10, GLUT12, and GLUT13 (HMIT). GLUTs in this class are only 19–41% identical.

The human GLUTs are involved in the transport of the several hexoses in addition to myoinositol, urate, glucosamine, and ascorbate [7]. All the members of the GLUT family are facilitative transporters except for GLUT13 (HMIT), which is an H+ /myoinositol symporter [11].

#### **2.2 Pseudogenes**

To date, four pseudogenes of *SLC2A* family were described [5, 7]:


#### **2.3 Characteristics of sodium-dependent glucose symporters**

Crane [12] showed that active glucose absorption by hamster's small intestine required sodium ions in the bathing medium. He proposed that these symporters have two binding sites: one for glucose and one for sodium [13].

The sodium-dependent glucose cotransporters belong to the gene family (*SLC5A*), the SGLTs, or sodium/substrate symporters family (SSSF), containing over 450 members [14–16]. In humans, 12 members of sodium-dependent glucose cotransporters have been identified. Amino acid comparison of the human sodiumdependent glucose cotransporters shows the range of identity from 57 to 71% [17]. The members of the SGLT family also share considerable homology among the proteins (21–70% amino acid identity with SGLT1) [10, 16]. These proteins contain of 580–718 amino acid residues, with a predicted mass of 60–80 kDa. There is a diversity in gene structure. In eight genes, the coding sequences are found in 14–15 exons (*SLC5A1, SLC5A2, SLC5A4–SLC5A6,* and *SLC5A9–SLC5A11*), and the coding sequence for *SLC5A7* and *SLC5A3* are present in exons 8 and 1, respectively. In *SLC5A9–SLC5A11* and *SLC5A3*, there is evidence for alternative splicing. These proteins contain 14 TM α-helices (TMHs) in all but not in sodium-iodide symporter (NIS) and SMCT1, which lack TMH14 [18]. Both the hydrophilic N- and C-termini are located on the extracellular side of the cell membrane [1]. SGLTs are

**5**

**Author details**

Leszek Szablewski

provided the original work is properly cited.

Medical University of Warsaw, Warsaw, Poland

\*Address all correspondence to: leszek.szablewski@wum.edu.pl

*Introductory Chapter: Glucose Transporters DOI: http://dx.doi.org/10.5772/intechopen.82263*

encoded by the gene *SLC50A1* [1].

in mice missing the GLUT2 transporter [21, 22].

highly glycosylated membrane proteins; however, glycosylation is not required in the functioning of the protein. The human *SLC5A* genes are expressed in different tissues, and all of them code for sodium-dependent glucose cotransporter proteins, except for SGLT3 (*SLC5A4*), which acts as a glucose sensor [19]. These carrier proteins transport substrates such as glucose, myoinositol, and iodide; one is a Na+

Cl<sup>−</sup>/choline cotransporter, and another is a glucose-activated ion channel [16].

SWEETs transport mono- and disaccharides across vacuolar and plasma membranes. A new class of glucose transporters, SWEET, was first identified by expressing candidate *Arabidopsis* genes coding for polytopic membrane proteins in HEK293T cells [20]. SWEETs are ubiquitously expressed in plants. In contrast to *Arabidopsis thaliana*, in which up to two dozen SWEETs have been identified, animals usually have only one SWEET, except for *Caenorhabditis elegans*, where seven SWEET-encoding genes have been found. Homologs of the SWEETs are widespread in metazoan genomes, and there is a single homolog in human genome (SWEET1)

Human SWEET1 (RAG1AP1), encoded by *SLC50A1*, comprises 221 amino acids with a molecular weight of 25 kDa. Human SWEET1 did not promote glucose uptake but instead mediated a weak efflux. Human SWEET1 when expressed in HEK293T cells was predominantly found to be localized in the Golgi with minimum expression also found in the plasma membrane. Chen et al. [20] discovered the highest level of expression in the oviduct, epididymis, and intestine, and its expression was induced in mouse mammary gland during lactation. The authors suggest that the human SWEET1 serves to supply glucose for lactose synthesis in the mammary gland. Human SWEET1 glucose transporter is the missing glucose transporter in the basolateral membrane of enterocytes where it may account for the exit of glucose from the cell into the blood in patients with Fanconi-Bickel syndrome and

**2.4 Characteristics of SWEET glucose transporters**

/

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Introductory Chapter: Glucose Transporters DOI: http://dx.doi.org/10.5772/intechopen.82263*

*Blood Glucose Levels*

identical.

**2.2 Pseudogenes**

sequences.

H+

loop) [7]. As was proposed for GLUT1, helices 1, 2, 4, 5, 7, 8, 10, and 11 form an

Based on the phylogenetic analysis of sequence similarity and characteristic elements, the GLUT family of sugar transporters is divided into three classes [4, 5, 9, 10]: an N-linked glycosylation site for GLUTs of class I and II is positioned in the first exofacial loop between TM1 and TM2, and family members of class III contain

Class I GLUTs include GLUT1–GLUT4 and GLUT14, which are 48–63% identical in humans. Class II GLUTs comprise of GLUT5, GLUT7, GLUT9, and GLUT11. These transporters are 36–40% identical. Class III GLUTs include GLUT6, GLUT8, GLUT10, GLUT12, and GLUT13 (HMIT). GLUTs in this class are only 19–41%

The human GLUTs are involved in the transport of the several hexoses in addition to myoinositol, urate, glucosamine, and ascorbate [7]. All the members of the GLUT family are facilitative transporters except for GLUT13 (HMIT), which is an

1.*SLC2A3P1* (alias GLUT6 or GLUT3 pseudogene) is located on chromosome

2.*SLC2A3P2* (alias GLUT3 pseudogene 2) is located on chromosome 1p31.3 and

3.*SLC2A3P4* (alias GLUT3 pseudogene 4) is located on chromosome 8q21.3 and

Crane [12] showed that active glucose absorption by hamster's small intestine required sodium ions in the bathing medium. He proposed that these symporters

The sodium-dependent glucose cotransporters belong to the gene family (*SLC5A*), the SGLTs, or sodium/substrate symporters family (SSSF), containing over 450 members [14–16]. In humans, 12 members of sodium-dependent glucose cotransporters have been identified. Amino acid comparison of the human sodiumdependent glucose cotransporters shows the range of identity from 57 to 71% [17]. The members of the SGLT family also share considerable homology among the proteins (21–70% amino acid identity with SGLT1) [10, 16]. These proteins contain of 580–718 amino acid residues, with a predicted mass of 60–80 kDa. There is a diversity in gene structure. In eight genes, the coding sequences are found in 14–15 exons (*SLC5A1, SLC5A2, SLC5A4–SLC5A6,* and *SLC5A9–SLC5A11*), and the coding sequence for *SLC5A7* and *SLC5A3* are present in exons 8 and 1, respectively. In *SLC5A9–SLC5A11* and *SLC5A3*, there is evidence for alternative splicing. These proteins contain 14 TM α-helices (TMHs) in all but not in sodium-iodide symporter (NIS) and SMCT1, which lack TMH14 [18]. Both the hydrophilic N- and C-termini are located on the extracellular side of the cell membrane [1]. SGLTs are

4.*SLC2AXP1* is located on chromosome 2q11.2 and contains internal stop

**2.3 Characteristics of sodium-dependent glucose symporters**

have two binding sites: one for glucose and one for sodium [13].

To date, four pseudogenes of *SLC2A* family were described [5, 7]:

inner bundle that is stabilized by the outer helices 3, 6, 9, and 12 [8].

the glycosylation site between TM9 and TM10 [5].

5q35.1 and is a retroposon of *SLC2A3*.

/myoinositol symporter [11].

is a retroposon of *SLC2A3*.

is a retroposon of *SLC2A3*.

**4**

highly glycosylated membrane proteins; however, glycosylation is not required in the functioning of the protein. The human *SLC5A* genes are expressed in different tissues, and all of them code for sodium-dependent glucose cotransporter proteins, except for SGLT3 (*SLC5A4*), which acts as a glucose sensor [19]. These carrier proteins transport substrates such as glucose, myoinositol, and iodide; one is a Na<sup>+</sup> / Cl<sup>−</sup>/choline cotransporter, and another is a glucose-activated ion channel [16].

#### **2.4 Characteristics of SWEET glucose transporters**

SWEETs transport mono- and disaccharides across vacuolar and plasma membranes. A new class of glucose transporters, SWEET, was first identified by expressing candidate *Arabidopsis* genes coding for polytopic membrane proteins in HEK293T cells [20]. SWEETs are ubiquitously expressed in plants. In contrast to *Arabidopsis thaliana*, in which up to two dozen SWEETs have been identified, animals usually have only one SWEET, except for *Caenorhabditis elegans*, where seven SWEET-encoding genes have been found. Homologs of the SWEETs are widespread in metazoan genomes, and there is a single homolog in human genome (SWEET1) encoded by the gene *SLC50A1* [1].

Human SWEET1 (RAG1AP1), encoded by *SLC50A1*, comprises 221 amino acids with a molecular weight of 25 kDa. Human SWEET1 did not promote glucose uptake but instead mediated a weak efflux. Human SWEET1 when expressed in HEK293T cells was predominantly found to be localized in the Golgi with minimum expression also found in the plasma membrane. Chen et al. [20] discovered the highest level of expression in the oviduct, epididymis, and intestine, and its expression was induced in mouse mammary gland during lactation. The authors suggest that the human SWEET1 serves to supply glucose for lactose synthesis in the mammary gland. Human SWEET1 glucose transporter is the missing glucose transporter in the basolateral membrane of enterocytes where it may account for the exit of glucose from the cell into the blood in patients with Fanconi-Bickel syndrome and in mice missing the GLUT2 transporter [21, 22].

#### **Author details**

Leszek Szablewski Medical University of Warsaw, Warsaw, Poland

\*Address all correspondence to: leszek.szablewski@wum.edu.pl

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **References**

[1] Wright EM. Glucose transport families SLC5 and SLC50. Molecular Aspects of Medicine. 2013;**34**:183-196

[2] Long W, Cheeseman CI. Structure of, and functional insight into the GLUT family of membrane transporters. Cell Health and Cytoskeleton. 2015;**7**:167-183

[3] Thorens B, Mueckler M. Glucose transporters in the 21st century. American Journal of Physiology. Endocrinology and Metabolism. 2010;**298**:E141-E145

[4] Joost HG, Bell GI, Best JD, Birnbaum MJ, Charron MJ, Chen YT, et al. Nomenclature of the GLUT/SLC2A family of sugar/polyol transport facilitators. American Journal of Physiology. Endocrinology and Metabolism. 2002;**282**:E974-E976

[5] Joost H-G, Thorens B. The extend GLUT-family of sugar-polyol transport facilitators: Nomenclature, sequence characteristics, and potential function of its novel members. Molecular Membrane Biology. 2001;**18**:247-256

[6] Uldry M, Thorens B. The SLC2 family of facilitative hexose and polyol transporters. Pflügers Archiv: European Journal of Physiology. 2004;**447**:480-489

[7] Mueckler M, Thorens B. The SLC2 (GLUT) family of membrane transporters. Molecular Aspects of Medicine. 2013;**34**:121-138

[8] Mueckler M, Makepeace C. Model of the exofacial substrate-binding site and helical folding of the human Glut1 glucose transporter based on scanning mutagenesis. Biochemistry. 2009;**48**:5934-5942

[9] Manolescu AR, Witkowska K, Kinnaird A, Cessford T, Cheeseman C. Facilitated hexose transporters: New perspectives on form and function. Physiology. 2007;**22**:234-240

[10] Zhao F-Q, Keating AF. Functional properties and genomic of glucose transporters. Current Genomics. 2007;**8**:113-128

[11] Uldry M, Ibberson M, Horisberger J-D, Rieder BM, Thorens B. Identification of a mammalian H+ -myo-inositol symporter expressed predominantly in the brain. The EMBO Journal. 2001;**20**:4467-4477

[12] Crane RK. Hypothesis for mechanism of intestinal active transport of sugars. Federation Proceedings. 1962;**21**:891-895

[13] Crane RK. Na<sup>+</sup> -dependent transport in the intestine and other animal tissues. Federation Proceedings. 1965;**24**:1000-1006

[14] Wright EM. Renal Na<sup>+</sup> /glucose cotransporters. The American Journal of Physiology. 2001;**280**:F10-F18

[15] Wright EM, Loo DDF, Hirayama BA, Turk E. Surprising versatility of Na<sup>+</sup> /glucose cotransporters: SLC5. Physiology. 2004;**19**:370-376

[16] Wright EM, Turk E. The sodium/ glucose cotransport family SLC5. Pflügers Archiv: European Journal of Physiology. 2004;**447**:510-518

[17] Woods IS, Trayhurn P. Glucose transporters (GLUT and SGLT): Expressed families of sugar transport protein. The British Journal of Nutrition. 2003;**89**:3-9

[18] Turk E, Wright EM. Membrane topology motifs in the SGLT cotransporter family. The Journal of Membrane Biology. 1997;**159**:1-20

**7**

*Introductory Chapter: Glucose Transporters DOI: http://dx.doi.org/10.5772/intechopen.82263*

[19] Bianchi L, Diez-Sampedro A. A single amino acid change converts the sugar sensor SGLT3 into a sugar transporter. PLoS One. 2010;**5**:e10241

[20] Chen LQ, Hou BH, Lalonde S, Takanaga H, Hartung ML, Qu XO, et al. Sugar transporters for intracellular exchange and nutrition of pathogens.

[21] Santer R, Hillebrand G, Steinmann B, Schaub J. Intestinal glucose transport: Evidence for a membrane traffic- based pathway in humans. Gastroenterology.

[22] Stumpel F, Burcelin R, Jungermann K, Thorens B. Normal kinetics of intestinal glucose absorption in the absence of GLUT2: Evidence for a transport pathway requiring glucose phosphorylation and transfer into the endoplasmic reticulum. Proceedings of the National Academy of Sciences of the United States of America.

Nature. 2010;**468**:527-532

2003;**124**:34-39

2001;**98**:11330-11335

*Introductory Chapter: Glucose Transporters DOI: http://dx.doi.org/10.5772/intechopen.82263*

[19] Bianchi L, Diez-Sampedro A. A single amino acid change converts the sugar sensor SGLT3 into a sugar transporter. PLoS One. 2010;**5**:e10241

[20] Chen LQ, Hou BH, Lalonde S, Takanaga H, Hartung ML, Qu XO, et al. Sugar transporters for intracellular exchange and nutrition of pathogens. Nature. 2010;**468**:527-532

[21] Santer R, Hillebrand G, Steinmann B, Schaub J. Intestinal glucose transport: Evidence for a membrane traffic- based pathway in humans. Gastroenterology. 2003;**124**:34-39

[22] Stumpel F, Burcelin R, Jungermann K, Thorens B. Normal kinetics of intestinal glucose absorption in the absence of GLUT2: Evidence for a transport pathway requiring glucose phosphorylation and transfer into the endoplasmic reticulum. Proceedings of the National Academy of Sciences of the United States of America. 2001;**98**:11330-11335

**6**

*Blood Glucose Levels*

**References**

[1] Wright EM. Glucose transport families SLC5 and SLC50. Molecular Aspects of Medicine. 2013;**34**:183-196

[2] Long W, Cheeseman CI. Structure of, and functional insight into the GLUT family of membrane transporters. Cell Health and Cytoskeleton. 2015;**7**:167-183

Facilitated hexose transporters: New perspectives on form and function. Physiology. 2007;**22**:234-240

[10] Zhao F-Q, Keating AF. Functional properties and genomic of glucose transporters. Current Genomics.

Horisberger J-D, Rieder BM, Thorens B. Identification of a mammalian


mechanism of intestinal active transport of sugars. Federation Proceedings.

cotransporters. The American Journal of

[15] Wright EM, Loo DDF, Hirayama BA, Turk E. Surprising versatility of

/glucose cotransporters: SLC5.

[16] Wright EM, Turk E. The sodium/ glucose cotransport family SLC5. Pflügers Archiv: European Journal of


/glucose

2007;**8**:113-128

1962;**21**:891-895

[13] Crane RK. Na<sup>+</sup>

1965;**24**:1000-1006

[14] Wright EM. Renal Na<sup>+</sup>

Physiology. 2001;**280**:F10-F18

Physiology. 2004;**19**:370-376

Physiology. 2004;**447**:510-518

Nutrition. 2003;**89**:3-9

[17] Woods IS, Trayhurn P. Glucose transporters (GLUT and SGLT): Expressed families of sugar transport protein. The British Journal of

[18] Turk E, Wright EM. Membrane topology motifs in the SGLT

cotransporter family. The Journal of Membrane Biology. 1997;**159**:1-20

H+

Na<sup>+</sup>

[11] Uldry M, Ibberson M,

Journal. 2001;**20**:4467-4477

[12] Crane RK. Hypothesis for

in the intestine and other animal tissues. Federation Proceedings.

[3] Thorens B, Mueckler M. Glucose transporters in the 21st century. American Journal of Physiology. Endocrinology and Metabolism.

[4] Joost HG, Bell GI, Best JD, Birnbaum

[5] Joost H-G, Thorens B. The extend GLUT-family of sugar-polyol transport facilitators: Nomenclature, sequence characteristics, and potential function of its novel members. Molecular Membrane Biology. 2001;**18**:247-256

[6] Uldry M, Thorens B. The SLC2 family of facilitative hexose and polyol transporters. Pflügers Archiv: European Journal of Physiology.

[7] Mueckler M, Thorens B. The SLC2 (GLUT) family of membrane transporters. Molecular Aspects of

[8] Mueckler M, Makepeace C. Model of the exofacial substrate-binding site and helical folding of the human Glut1 glucose transporter based on scanning mutagenesis. Biochemistry.

[9] Manolescu AR, Witkowska K, Kinnaird A, Cessford T, Cheeseman C.

Medicine. 2013;**34**:121-138

2004;**447**:480-489

2009;**48**:5934-5942

MJ, Charron MJ, Chen YT, et al. Nomenclature of the GLUT/SLC2A family of sugar/polyol transport facilitators. American Journal of Physiology. Endocrinology and Metabolism. 2002;**282**:E974-E976

2010;**298**:E141-E145

Section 2

Regulation of Glucose

Levels

9

Section 2

## Regulation of Glucose Levels

Chapter 2

Abstract

Regulation

or decrease lipid peroxidation.

1. Introduction

2.1.1 Location

11

Asma Ahmed and Noman Khalique

Molecular Basis of Blood Glucose

Blood glucose level is regulated by multiple pancreatic hormones, which regulate

it by different pathways in normal and abnormal conditions by expressing or suppressing multiple genes or molecular or cellular targets. Multiple synthetic drugs and therapies are used to cure glucose regulatory problems, while many of them are used to cure other health issues, which arise due to disturbance in blood glucose regulations. Many new approaches are used for the development of phytochemicalbased drugs to cure blood glucose regulation problems, and many of the compounds have been isolated and identified to cure insulin resistance or regulate beta cell function or glucose absorption in the guts or GLP-1 homoeostasis or two/more pathways (e.g., either cure hyperglycemia or raise insulin resistance or cure pancreatic beta cell regeneration or augmentation of GLP-1, production of islet cell, production and increased insulin receptor signaling and insulin secretion or decreased insulin tolerance or gluconeogenesis and insulin-mimetic action or production of α-glucosidase and α-amylase inhibitor or conserve islet mass or activate protein kinase A (PKA) and extracellular signal regulated kinases (ERK) or activate AMPK and reduce insulin sensitivity or suppress α-glucosidase activity and activate AMPK and downstream molecules or prevents cell death of pancreatic β-cell and activates SIRT1 or lower blood glucose due to their insulin-like chemical structures

Keywords: genes, molecular and cellular targets, hormones, pathways

blood glucose regulation problems and their associated diseases.

2. Hormones for the regulation of blood glucose levels

It is located at the back of stomach, within left upper abdominal cavity.

2.1 Pancreas: an exocrine and endocrine organ

Blood glucose is regulated by the pancreatic hormones alone or in combination with other endocrine glands and all this is controlled by one or more gene or cellular or molecular targets. If any problem occurs in the normal pathway(s), then multiple drugs or therapies are used to cure it. Moreover with the emerging technologies, multiple plant based formulations has been synthesized or in process to cure all

#### Chapter 2

## Molecular Basis of Blood Glucose Regulation

Asma Ahmed and Noman Khalique

#### Abstract

Blood glucose level is regulated by multiple pancreatic hormones, which regulate it by different pathways in normal and abnormal conditions by expressing or suppressing multiple genes or molecular or cellular targets. Multiple synthetic drugs and therapies are used to cure glucose regulatory problems, while many of them are used to cure other health issues, which arise due to disturbance in blood glucose regulations. Many new approaches are used for the development of phytochemicalbased drugs to cure blood glucose regulation problems, and many of the compounds have been isolated and identified to cure insulin resistance or regulate beta cell function or glucose absorption in the guts or GLP-1 homoeostasis or two/more pathways (e.g., either cure hyperglycemia or raise insulin resistance or cure pancreatic beta cell regeneration or augmentation of GLP-1, production of islet cell, production and increased insulin receptor signaling and insulin secretion or decreased insulin tolerance or gluconeogenesis and insulin-mimetic action or production of α-glucosidase and α-amylase inhibitor or conserve islet mass or activate protein kinase A (PKA) and extracellular signal regulated kinases (ERK) or activate AMPK and reduce insulin sensitivity or suppress α-glucosidase activity and activate AMPK and downstream molecules or prevents cell death of pancreatic β-cell and activates SIRT1 or lower blood glucose due to their insulin-like chemical structures or decrease lipid peroxidation.

Keywords: genes, molecular and cellular targets, hormones, pathways

#### 1. Introduction

Blood glucose is regulated by the pancreatic hormones alone or in combination with other endocrine glands and all this is controlled by one or more gene or cellular or molecular targets. If any problem occurs in the normal pathway(s), then multiple drugs or therapies are used to cure it. Moreover with the emerging technologies, multiple plant based formulations has been synthesized or in process to cure all blood glucose regulation problems and their associated diseases.

#### 2. Hormones for the regulation of blood glucose levels

#### 2.1 Pancreas: an exocrine and endocrine organ

#### 2.1.1 Location

It is located at the back of stomach, within left upper abdominal cavity.

#### 2.1.2 Parts

Its parts are head, body and tail. Majority of this secretory organ consists of:

a. Acinar/exocrine cells: Which secrete pancreatic juice (containing digestive enzymes i.e. amylase, pancreatic lipase and trypsinogen) into main and accessory pancreatic duct.

3. Pathways involved to regulate blood glucose levels in normal and

Pancreas maintains blood glucose levels within a very narrow range (4–6 MM) through glucagon and insulin by their opposing and balanced actions by the phenomenon of glucose homeostasis. During sleep/between meals/when blood glucose levels are low/during prolonged fasting, α-cells release glucagon and promote hepatic glycogenolysis. Along with this, glucagon do hepatic and renal gluconeogenesis and increase endogenous blood glucose levels. In elevated exogenous glucose levels, after a meal, insulin secretion is stimulated from β-cells and after docking to its receptor on muscle and adipose tissue, insulin enables insulindependent uptake of glucose into tissues and lowers blood glucose levels by removing the exogenous glucose from the blood stream (Figure 2). Moreover insulin enhances glycogenesis, lipogenesis and incorporation of amino acids into proteins; thus it performs its anabolic action as compared to glucagon which is catabolic. Along with pancreas, other organs also regulate blood glucose levels (Figure 3).

4. Genes, molecular and cellular targets to regulate blood glucose levels

Genetics is identifying a whole new set of genes, proteins and pathways that are

related to diabetes and blood sugar control. Till now, scientist have identified a genetic disorder in MafA (it controls the production of insulin in β-cells). Surprisingly, this genetic defect was present in an unrelated family along with diabetic and insulinoma family members. The link of this gene with a defect was detected for the first time and a stable resultant mutant protein was found with a longer life in the cell, and found to be significantly more abundant in β-cells than its normal version [2].

in normal and abnormal conditions

Maintenance of blood glucose levels by glucagon and insulin.

4.1 Genes to regulate blood glucose levels

Figure 2.

13

abnormal conditions

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

	- i. Glucagon-producing α-cells: They are 15–20% of the total islet cells and releases Glucagon to increase blood glucose levels.
	- ii. Amylin-, C-peptide- and insulin-producing β-cells: They are 65–80% of the total cells and produces insulin to decrease glucose.
	- iii. Pancreatic polypeptide (PP)-producing γ-cells: 3–5% of the total islet cells, to regulate the exocrine and endocrine secretion activity of the pancreas, is made of them.
	- iv. Somatostatin-producing δ-cells: Constitute 3–10% of the total cells and releases Somatostatin which inhibits both, glucagon and insulin release.
	- v. Ghrelin-producing ɛ-cells: Comprise <1% of the total islet cells.

Figure 1. Anatomical organization of the pancreas.

2.1.2 Parts

Blood Glucose Levels

accessory pancreatic duct.

Its parts are head, body and tail. Majority of this secretory organ consists of:

a. Acinar/exocrine cells: Which secrete pancreatic juice (containing digestive enzymes i.e. amylase, pancreatic lipase and trypsinogen) into main and

b. Endocrine cells: Which secrete pancreatic hormones directly in blood stream (in endocrine way). These cells cluster together and form the so-called islets of Langerhans (small, island-like structures within the exocrine pancreatic tissue and accounts for only 1–2% of the entire organ) (Figure 1). These are

i. Glucagon-producing α-cells: They are 15–20% of the total islet cells

five different types of cells and release various hormones [1]:

the pancreas, is made of them.

release.

Figure 1.

12

Anatomical organization of the pancreas.

and releases Glucagon to increase blood glucose levels.

ii. Amylin-, C-peptide- and insulin-producing β-cells: They are 65–80% of the total cells and produces insulin to decrease glucose.

iii. Pancreatic polypeptide (PP)-producing γ-cells: 3–5% of the total islet cells, to regulate the exocrine and endocrine secretion activity of

iv. Somatostatin-producing δ-cells: Constitute 3–10% of the total cells and releases Somatostatin which inhibits both, glucagon and insulin

v. Ghrelin-producing ɛ-cells: Comprise <1% of the total islet cells.

#### 3. Pathways involved to regulate blood glucose levels in normal and abnormal conditions

Pancreas maintains blood glucose levels within a very narrow range (4–6 MM) through glucagon and insulin by their opposing and balanced actions by the phenomenon of glucose homeostasis. During sleep/between meals/when blood glucose levels are low/during prolonged fasting, α-cells release glucagon and promote hepatic glycogenolysis. Along with this, glucagon do hepatic and renal gluconeogenesis and increase endogenous blood glucose levels. In elevated exogenous glucose levels, after a meal, insulin secretion is stimulated from β-cells and after docking to its receptor on muscle and adipose tissue, insulin enables insulindependent uptake of glucose into tissues and lowers blood glucose levels by removing the exogenous glucose from the blood stream (Figure 2). Moreover insulin enhances glycogenesis, lipogenesis and incorporation of amino acids into proteins; thus it performs its anabolic action as compared to glucagon which is catabolic. Along with pancreas, other organs also regulate blood glucose levels (Figure 3).

Figure 2. Maintenance of blood glucose levels by glucagon and insulin.

#### 4. Genes, molecular and cellular targets to regulate blood glucose levels in normal and abnormal conditions

#### 4.1 Genes to regulate blood glucose levels

Genetics is identifying a whole new set of genes, proteins and pathways that are related to diabetes and blood sugar control. Till now, scientist have identified a genetic disorder in MafA (it controls the production of insulin in β-cells). Surprisingly, this genetic defect was present in an unrelated family along with diabetic and insulinoma family members. The link of this gene with a defect was detected for the first time and a stable resultant mutant protein was found with a longer life in the cell, and found to be significantly more abundant in β-cells than its normal version [2].

iii. Only one variant, near IGF1 which is associated with insulin resistance

iv. β-cell impairment, which may play a larger role in type 2 diabetes than

v. Environment which may contribute to insulin resistance more than it does to

By using high-density microarray analysis, more than 31,000 genes, linked with pancreas, have been discovered and main aim was to find which gen(s) were most sensitive to glucose and fatty acids particularly from the products of high fat and sugar diets. It was found that TNFR5 gene had maximum compassion to glucose and fatty acids and due to high levels of fat and sugar, beta cells are destroyed due to its over expression. These findings suggested that people with type-II diabetes, primarily with poor blood glucose management/who have not been diagnosed, are more likely to over express this gene that leads to β cell damage. But blocking of TNFR5 in beta-cells, especially when glucose and fatty acids consumption is high, halted their obliteration which shows that reticence of TNFR5 activity could be a

To identify genetic variants responsible for blood sugar control, a genome-wide association study was done to find SNPs which could be correlated with Fasting Plasma Glucose levels. It was found that most strongly associated SNP was rs560887 in initial sampling of 650 non-obese French people. Same SNP was correlated with FPG levels in a secondary sample of 3400 same people, approximately 5000 Finns and a group of 860 obese French children. When results of all studied samples were combined, researchers found that each copy of T version of rs560887 leads to a 0.06 mmol/L reduction in FPG while rs560887 did not correlate with insulin levels or BMI of subjects. Moreover even after a 9 year follow-up period in French samples, this SNP also could not correlate with the risk of type 2 diabetes. Moreover two other SNPs; rs1260326 and rs1799884 (previously found to be associated with FPG) were also found to be significantly associated with FPG levels in same study and it was concluded that genes affected by these SNPs affect the threshold level of glucose in the bloodstream and triggered secretion of insulin by pancreas. When threshold will be higher, level of blood glucose increase even before insulin starts to

These are class B-GPCRs which are important targets for drugs of type 2 diabetes, obesity and blood glucose regulation problems. Structures of several class A-GPCRs have been solved, but class B receptors have not been well studied because of technical challenges. Their structures were identified and reported by four international research teams; NIDDK, NIGMS, FDA and NIDA. Structure of Glucagon receptor helps to understand how different domains cooperate in modulating the receptor function at molecular level. GLP-1 receptor, identified by cryo-electron microscopy, examined structure of receptor in complex with GLP-1 and its coupled G-protein while detailed structure of GLP-1 receptor, when bound by small molecules (that affect receptor's activity) has also been given and it is difficult to expect the importance of GPCRs which are targeted by about half of all drugs. Structural information about these receptors is crucial for further drug discovery efforts [6].

previously recognized

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

promising treatment strategy against type 2 diabetes [4].

4.2 Molecular pathway for blood glucose regulation

4.2.1 Glucagon and GLP-1 receptors

insulin secretion.

regulate it [5].

15

Figure 3. Maintenance of blood glucose levels by different organs (a) during well fed state (b) during post-prandial state.

Gene on chromosome-2 {encodes glucose-6-phosphatase catalytic 2 (G6PC2)} is linked with fasting glucose levels and is primarily expressed in pancreatic β-cells to convert glucose-6-phosphate back to glucose. Its genetic variation may be responsible for reduction in insulin secretion that increases glucose concentration. Chronically elevated levels of glucose may be a precursor for type 2 diabetes [3].

13 new genetic variants has been discovered by an international research consortium and these variants can manipulate blood glucose regulation, insulin resistance and function of insulin-secreting β-cells in European descent populations, in which 05 of the following newly discovered variants raised the risk of developing type 2 diabetes:


#### Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978


By using high-density microarray analysis, more than 31,000 genes, linked with pancreas, have been discovered and main aim was to find which gen(s) were most sensitive to glucose and fatty acids particularly from the products of high fat and sugar diets. It was found that TNFR5 gene had maximum compassion to glucose and fatty acids and due to high levels of fat and sugar, beta cells are destroyed due to its over expression. These findings suggested that people with type-II diabetes, primarily with poor blood glucose management/who have not been diagnosed, are more likely to over express this gene that leads to β cell damage. But blocking of TNFR5 in beta-cells, especially when glucose and fatty acids consumption is high, halted their obliteration which shows that reticence of TNFR5 activity could be a promising treatment strategy against type 2 diabetes [4].

To identify genetic variants responsible for blood sugar control, a genome-wide association study was done to find SNPs which could be correlated with Fasting Plasma Glucose levels. It was found that most strongly associated SNP was rs560887 in initial sampling of 650 non-obese French people. Same SNP was correlated with FPG levels in a secondary sample of 3400 same people, approximately 5000 Finns and a group of 860 obese French children. When results of all studied samples were combined, researchers found that each copy of T version of rs560887 leads to a 0.06 mmol/L reduction in FPG while rs560887 did not correlate with insulin levels or BMI of subjects. Moreover even after a 9 year follow-up period in French samples, this SNP also could not correlate with the risk of type 2 diabetes. Moreover two other SNPs; rs1260326 and rs1799884 (previously found to be associated with FPG) were also found to be significantly associated with FPG levels in same study and it was concluded that genes affected by these SNPs affect the threshold level of glucose in the bloodstream and triggered secretion of insulin by pancreas. When threshold will be higher, level of blood glucose increase even before insulin starts to regulate it [5].

#### 4.2 Molecular pathway for blood glucose regulation

#### 4.2.1 Glucagon and GLP-1 receptors

These are class B-GPCRs which are important targets for drugs of type 2 diabetes, obesity and blood glucose regulation problems. Structures of several class A-GPCRs have been solved, but class B receptors have not been well studied because of technical challenges. Their structures were identified and reported by four international research teams; NIDDK, NIGMS, FDA and NIDA. Structure of Glucagon receptor helps to understand how different domains cooperate in modulating the receptor function at molecular level. GLP-1 receptor, identified by cryo-electron microscopy, examined structure of receptor in complex with GLP-1 and its coupled G-protein while detailed structure of GLP-1 receptor, when bound by small molecules (that affect receptor's activity) has also been given and it is difficult to expect the importance of GPCRs which are targeted by about half of all drugs. Structural information about these receptors is crucial for further drug discovery efforts [6].

Gene on chromosome-2 {encodes glucose-6-phosphatase catalytic 2 (G6PC2)} is linked with fasting glucose levels and is primarily expressed in pancreatic β-cells to convert glucose-6-phosphate back to glucose. Its genetic variation may be responsible for reduction in insulin secretion that increases glucose concentration. Chron-

Maintenance of blood glucose levels by different organs (a) during well fed state (b) during post-prandial state.

13 new genetic variants has been discovered by an international research consortium and these variants can manipulate blood glucose regulation, insulin resistance and function of insulin-secreting β-cells in European descent populations, in which 05 of the following newly discovered variants raised the risk of developing

i. SNPs in the region of ADCY5 which influence fasting and postprandial

ii. FADS1 which is linked with fasting glucose as well as lipid traits.

ically elevated levels of glucose may be a precursor for type 2 diabetes [3].

type 2 diabetes:

14

Figure 3.

Blood Glucose Levels

glucose levels.

Control of blood glucose depends heavily on G-protein-coupled receptors (GPCRs) which can span cell membranes to communicate signals from the outside to inside of cell and starts a cascade of reactions in cell when once activated by binding of a substance which had made these receptors an important target for drug development. When blood glucose drops after an overnight fast, pancreas releases glucagon which binds a GPCR, glucagon receptor, on liver and muscle cells and stimulates cells to release glucose in blood. Moreover glucagon-like peptide-1 (GLP-1) hormone works by binding to another GPCR, GLP-1 receptor, on pancreatic cells. After a meal, intestine produces GLP-1, which leads to the production of insulin from pancreas to stimulate cells to pick glucose from blood [7].

soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor

ii. Syntaxin-1 and synaptobrevin 2 (or vesicle-associated membrane protein

Sec1/Munc18-like (SM) proteins, glucose vesicles form SNARE complex. To initiate

Several proteins are disturbed in the insulin signaling pathways in different conditions of insulin resistance, particularly obesity, type-II diabetes mellitus, metabolic syndrome, cardiovascular diseases, inflammatory disorders, and cancer [11].

It is tetramer protein, composed of 02 extracellular α- subunits and two trans membrane β-subunits. α-subunits have a binding site to insulin while the β-subunits contain an intrinsic tyrosine kinase activity towards intracellular side. Insulin

fusion, synaptobrevin 2, a vesicle (v-) SNARE fuses with the target (t-) SNAREs syntaxin-1 and SNAP-25, which are located in the target cell membrane (Figure 4) [9]. Numerous SNARE isoforms [syntaxin-1, 3 and 4, SNAP-25 and -23, synaptobrevins 2 and 3 (VAMP2 and 3)] are involved in glucose-stimulated insulin secretion whereas VAMP 8 (a non-essential SNARE protein for glucose-stimulated insulin secretion) has its role to regulate glucagon-like peptide-1-potentiated insulin secretion. In addition to SNARE and SM proteins, a calcium sensor is required to initiate membrane fusion. Synaptotagmins (highly expressed in neurons and endocrine cells) participated in Ca2+-dependent exocytosis processes. Seventeen synaptotagmins (Syts 1–17) have been identified while only eight (Syt-1, 2, 3, 5, 6, 7, 9 and 10) are able to bind Ca2+ and form a complex with the SNAREs to smooth the progress of and activate vesicle-membrane fusion process. Only Syt-3, 5, 7, 8 and 9 are concerned with insulin exocytosis [10].

i. Synaptosomal-associated protein of 25kDa (SNAP-25)

proteins (SNAREs).which are:

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

4.3.2 Mechanism of insulin action

4.3.2.1 Insulin receptor

Figure 4.

17

Glucose-stimulated insulin release from a pancreatic β-cell.

VAMP2)

#### 4.2.2 Heterocyclic scaffolds

For many years, heterocyclic scaffolds were the basis of anti-diabetic chemotherapies as bioactive scaffolds and have been evaluated for their biological response as inhibitors against their respective anti-diabetic molecular targets over past 5 years (2012–2017). Results revealed a diverse target sets of these scaffolds including protein tyrosine phosphatase 1 B (PTP1B), dipeptidyl peptidase-4 (DPP-4), free fatty acid receptors 1 (FFAR1), G protein-coupled receptors (GPCR), peroxisome proliferator activated receptor-γ (PPARγ), sodium glucose cotransporter-2 (SGLT2), α-glucosidase, aldose reductase, glycogen phosphorylase (GP), fructose-1,6-bisphosphatase (FBPase), glucagon receptor (GCGr) and phosphoenolpyruvate carboxykinase (PEPCK) [8].

#### 4.2.3 Incretin and adipokines

In addition to other several even newer therapies in development, Incretinbased therapies, like dipeptidyl peptidase- 4 (DPP- 4) inhibitor and glucagon like peptide-1 (GLP-1) analogues/mimetic offer a new therapeutic means for the treatment of T2DM. Moreover a great attention has been focused by many researchers on a number of potential molecular targets in adipocytes e.g. adipokines [8].

#### 4.3 Insulin secretion signaling pathway

#### 4.3.1 Molecular pathways for the insulin secretion

In β-cells, main stimulus for insulin release increases blood glucose levels after a meal. This blood glucose is taken up by facilitative glucose transporter GLUT2 (SLC2A2) on the surface of β-cells. Once inside the cell, glucose undergoes glycolysis and an amplified ATP/ADP ratio and this distorted ratio leads to close ATPsensitive K+ -channels (KATP-channels). While in non-stimulated circumstances, these channels open to ensure the maintenance of resting potential by transporting K+ -ions down their concentration gradient out of the cell. Upon closure, succeeding decrease in potency of externally moved K<sup>+</sup> -current elicits depolarization of membrane, followed by opening of voltage-dependent Ca+ -channels (VDCCs). Increase in intracellular Ca<sup>+</sup> concentrations ultimately triggers fusion of insulin-containing granules with membrane and succeeding release of their content. Whole secretory process is biphasic and 1st phase lasts for around 5 minutes after the glucose stimulus with the release of majority of insulin while in 2nd phase, which is somewhat slower, the remaining insulin is released. This insulin is stored in large densecore vesicles which are recruited near plasma membrane immediately after stimulation so that it should be readily available. Key molecules that mediate the fusion of the insulin-containing large dense-core vesicles belong to the superfamily of the

Control of blood glucose depends heavily on G-protein-coupled receptors (GPCRs) which can span cell membranes to communicate signals from the outside to inside of cell and starts a cascade of reactions in cell when once activated by binding of a substance which had made these receptors an important target for drug development. When blood glucose drops after an overnight fast, pancreas releases glucagon which binds a GPCR, glucagon receptor, on liver and muscle cells and stimulates cells to release glucose in blood. Moreover glucagon-like peptide-1 (GLP-1) hormone works by binding to another GPCR, GLP-1 receptor, on pancreatic cells. After a meal, intestine produces GLP-1, which leads to the production of insulin

For many years, heterocyclic scaffolds were the basis of anti-diabetic chemo-

In addition to other several even newer therapies in development, Incretinbased therapies, like dipeptidyl peptidase- 4 (DPP- 4) inhibitor and glucagon like peptide-1 (GLP-1) analogues/mimetic offer a new therapeutic means for the treatment of T2DM. Moreover a great attention has been focused by many researchers on a number of potential molecular targets in adipocytes e.g. adipokines [8].

In β-cells, main stimulus for insulin release increases blood glucose levels after a




meal. This blood glucose is taken up by facilitative glucose transporter GLUT2 (SLC2A2) on the surface of β-cells. Once inside the cell, glucose undergoes glycolysis and an amplified ATP/ADP ratio and this distorted ratio leads to close ATP-

these channels open to ensure the maintenance of resting potential by transporting

in intracellular Ca<sup>+</sup> concentrations ultimately triggers fusion of insulin-containing granules with membrane and succeeding release of their content. Whole secretory process is biphasic and 1st phase lasts for around 5 minutes after the glucose stimulus with the release of majority of insulin while in 2nd phase, which is somewhat slower, the remaining insulin is released. This insulin is stored in large densecore vesicles which are recruited near plasma membrane immediately after stimulation so that it should be readily available. Key molecules that mediate the fusion of the insulin-containing large dense-core vesicles belong to the superfamily of the


therapies as bioactive scaffolds and have been evaluated for their biological response as inhibitors against their respective anti-diabetic molecular targets over past 5 years (2012–2017). Results revealed a diverse target sets of these scaffolds including protein tyrosine phosphatase 1 B (PTP1B), dipeptidyl peptidase-4 (DPP-4), free fatty acid receptors 1 (FFAR1), G protein-coupled receptors (GPCR), peroxisome proliferator activated receptor-γ (PPARγ), sodium glucose cotransporter-2 (SGLT2), α-glucosidase, aldose reductase, glycogen phosphorylase (GP), fructose-1,6-bisphosphatase (FBPase), glucagon receptor (GCGr) and phos-

from pancreas to stimulate cells to pick glucose from blood [7].

phoenolpyruvate carboxykinase (PEPCK) [8].

4.3 Insulin secretion signaling pathway

4.3.1 Molecular pathways for the insulin secretion

decrease in potency of externally moved K<sup>+</sup>

brane, followed by opening of voltage-dependent Ca+

4.2.2 Heterocyclic scaffolds

Blood Glucose Levels

4.2.3 Incretin and adipokines

sensitive K+

K+

16

soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor proteins (SNAREs).which are:


Sec1/Munc18-like (SM) proteins, glucose vesicles form SNARE complex. To initiate fusion, synaptobrevin 2, a vesicle (v-) SNARE fuses with the target (t-) SNAREs syntaxin-1 and SNAP-25, which are located in the target cell membrane (Figure 4) [9].

Numerous SNARE isoforms [syntaxin-1, 3 and 4, SNAP-25 and -23, synaptobrevins 2 and 3 (VAMP2 and 3)] are involved in glucose-stimulated insulin secretion whereas VAMP 8 (a non-essential SNARE protein for glucose-stimulated insulin secretion) has its role to regulate glucagon-like peptide-1-potentiated insulin secretion. In addition to SNARE and SM proteins, a calcium sensor is required to initiate membrane fusion. Synaptotagmins (highly expressed in neurons and endocrine cells) participated in Ca2+-dependent exocytosis processes. Seventeen synaptotagmins (Syts 1–17) have been identified while only eight (Syt-1, 2, 3, 5, 6, 7, 9 and 10) are able to bind Ca2+ and form a complex with the SNAREs to smooth the progress of and activate vesicle-membrane fusion process. Only Syt-3, 5, 7, 8 and 9 are concerned with insulin exocytosis [10].

#### 4.3.2 Mechanism of insulin action

Several proteins are disturbed in the insulin signaling pathways in different conditions of insulin resistance, particularly obesity, type-II diabetes mellitus, metabolic syndrome, cardiovascular diseases, inflammatory disorders, and cancer [11].

#### 4.3.2.1 Insulin receptor

It is tetramer protein, composed of 02 extracellular α- subunits and two trans membrane β-subunits. α-subunits have a binding site to insulin while the β-subunits contain an intrinsic tyrosine kinase activity towards intracellular side. Insulin

Figure 4. Glucose-stimulated insulin release from a pancreatic β-cell.

#### Blood Glucose Levels

binding to α-subunit leads to conformational change and activation of β-subunit which results in tyrosyl autophosphorylation of the insulin receptor. After being activated and phosphorylated, several major and better characterized insulin signaling intracellular docking proteins {Src homology collagen (SHC), associated protein substrate (APS) and insulin receptor substrates- 1 & 2 (IRS-1 and IRS-2)} binds to insulin receptor for tyrosyl phosphorylation. All these proteins activate glucose uptake and metabolism, protein synthesis, gene expression, cell survival, growth, development, and differentiation. IRS proteins are phosphorylated on various tyrosine residues of the C-terminal region and generate specific sites for binding of proteins containing Src homoly-2 (SH2) domains [phosphatidylinositol-3 kinase (PI-3 K), Nck, and Grb-2.

#### 4.3.2.2 Pi-3 K

It is composed by a catalytic subunit (p110) and a regulatory subunit (p85) and mediate metabolic effects of the insulin. Binding of p85 subunit to phosphorylated tyrosine residues of IRS proteins activate catalytic activity of p110 subunit and subsequent rise in the generation of phosphatidylinositol 3,4-bisphosphate (PIP2) and phosphatidylinositol 3,4,5-trisphosphate (PIP3) content. Downstream proteins from PI3K pathway figure out several serine/threonine kinases e.g. phosphoinositide-dependent protein kinase-1 (PDK-1), protein kinase B (PKB/ Akt), protein kinase C (PKC), p70 S6 kinase (p70S6K) and glycogen synthase kinase-3 (GSK-3). All these kinases are involved in translocation of glucose transporter-4 (GLUT-4) from intracellular vesicles to plasma membrane, glycogen and protein synthesis, antiapoptotic effects and gene expression (Figure 4).

#### 4.3.2.3 Cbl

Signaling pathways which are involved in glucose uptake due to insulin induction starts with the recruitment of APS to activated insulin receptor and subsequent association and tyrosine phosphorylation of Cbl which interacts with Cbl associated protein (CAP) through an SH3 domain and with flotillin (a constituent of lipid raft, through a sorbin domain). Complex CrkII/C3G then binds to the phosphorylated tyrosine and residues of Cbl and activate C3G activity that exchanges GDP for GTP of TC10 (a small G-protein that belongs to the Rho family). After being activated, TC10 participates in GLUT-4 translocation (Figure 5) [12].

4.3.3 Molecular basis of insulin resistance

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

Figure 5.

Sevenless.

4.3.3.1 Increased plasma-free fatty acid level

iii. Modulation of gene transcription

i. Randle cycle

19

ii. Oxidative stress

It occurs when insulin-sensitive tissues (skeletal muscle, adipose tissue and liver) cannot respond properly to hormones which cause several chronic diseases, particularly those which are linked to obesity (type-II diabetes mellitus, metabolic syndrome, dyslipidemias, cardiovascular diseases, cancer and neurodegenerative diseases). However precise mechanisms of insulin resistance are not fully understood. Following factor have been proposed to participate in its development;

Summary of the main insulin signaling pathways. GLUT-1 and -4: Glucose transporter-1 and -4; Grb-2: Growth receptor binding-2; GSK-3: Glycogen synthase kinase-3; IR: Insulin receptor; IRS-1 and -2: Insulin receptor substrate-1 and -2; MAPK: Mitogen-activated protein kinase; PDK-1: Phosphoinositide-dependent kinase-1; PIP2: Phosphatidyl-inositol diphosphate; PI3: Phosphatidyl-inositol triphosphate; P: Phosphate; PKC: Protein kinase C; PP-1: Phosphoprotein phosphatase-1; p70S6K: Protein 70 S6 kinase; p90rsk: Protein 90 ribosomal S6 kinase; Shc: Src homology collagen; SHP-2: Phosphatase with Src homology 2 domain; SoS: Son of

As free fatty acids are elevated in obesity and related illness, they are supposed to be responsible for insulin action impairment but still complete mechanisms are not known. More availability of long chain saturated fatty acids results leads to insulin resistance in liver, skeletal muscle and adipose tissue. Various hypotheses proposed to explain insulin resistance induced by saturated fatty acids [14] are;

#### 4.3.2.4 Mitogen-activated protein kinase (MAPK)

This cascade starts with


This complex leads to the activation of c-Ras and raf, starting the MAPK cascade. MAPK pathway is involved in insulin induced differentiation, cell growth, and development, along with some metabolic effects e.g. glycogen synthesis and GLUT-4 translocation to plasma membrane (Figure 4). However, this cascade is not enough or even required to this later effect [13].

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

#### Figure 5.

binding to α-subunit leads to conformational change and activation of β-subunit which results in tyrosyl autophosphorylation of the insulin receptor. After being activated and phosphorylated, several major and better characterized insulin signaling intracellular docking proteins {Src homology collagen (SHC), associated protein substrate (APS) and insulin receptor substrates- 1 & 2 (IRS-1 and IRS-2)} binds to insulin receptor for tyrosyl phosphorylation. All these proteins activate glucose uptake and metabolism, protein synthesis, gene expression, cell survival, growth, development, and differentiation. IRS proteins are phosphorylated on various tyrosine residues of the C-terminal region and generate specific sites for binding of proteins containing Src homoly-2 (SH2) domains [phosphatidylinositol-3

It is composed by a catalytic subunit (p110) and a regulatory subunit (p85) and mediate metabolic effects of the insulin. Binding of p85 subunit to phosphorylated tyrosine residues of IRS proteins activate catalytic activity of p110 subunit and subsequent rise in the generation of phosphatidylinositol 3,4-bisphosphate (PIP2) and phosphatidylinositol 3,4,5-trisphosphate (PIP3) content. Downstream proteins

from PI3K pathway figure out several serine/threonine kinases e.g.

protein synthesis, antiapoptotic effects and gene expression (Figure 4).

TC10 participates in GLUT-4 translocation (Figure 5) [12].

4.3.2.4 Mitogen-activated protein kinase (MAPK)

1.The association of Shc to insulin receptor

enough or even required to this later effect [13].

2.Binding of Grb-2 to Shc or to IRS-1

This cascade starts with

phosphoinositide-dependent protein kinase-1 (PDK-1), protein kinase B (PKB/ Akt), protein kinase C (PKC), p70 S6 kinase (p70S6K) and glycogen synthase kinase-3 (GSK-3). All these kinases are involved in translocation of glucose transporter-4 (GLUT-4) from intracellular vesicles to plasma membrane, glycogen and

Signaling pathways which are involved in glucose uptake due to insulin induction starts with the recruitment of APS to activated insulin receptor and subsequent association and tyrosine phosphorylation of Cbl which interacts with Cbl associated protein (CAP) through an SH3 domain and with flotillin (a constituent of lipid raft, through a sorbin domain). Complex CrkII/C3G then binds to the phosphorylated tyrosine and residues of Cbl and activate C3G activity that exchanges GDP for GTP of TC10 (a small G-protein that belongs to the Rho family). After being activated,

3.Formation of the Grb-2/SoS (Son of Seven less) in the plasma membrane.

MAPK pathway is involved in insulin induced differentiation, cell growth, and development, along with some metabolic effects e.g. glycogen synthesis and GLUT-4 translocation to plasma membrane (Figure 4). However, this cascade is not

This complex leads to the activation of c-Ras and raf, starting the MAPK cascade.

kinase (PI-3 K), Nck, and Grb-2.

4.3.2.2 Pi-3 K

Blood Glucose Levels

4.3.2.3 Cbl

18

Summary of the main insulin signaling pathways. GLUT-1 and -4: Glucose transporter-1 and -4; Grb-2: Growth receptor binding-2; GSK-3: Glycogen synthase kinase-3; IR: Insulin receptor; IRS-1 and -2: Insulin receptor substrate-1 and -2; MAPK: Mitogen-activated protein kinase; PDK-1: Phosphoinositide-dependent kinase-1; PIP2: Phosphatidyl-inositol diphosphate; PI3: Phosphatidyl-inositol triphosphate; P: Phosphate; PKC: Protein kinase C; PP-1: Phosphoprotein phosphatase-1; p70S6K: Protein 70 S6 kinase; p90rsk: Protein 90 ribosomal S6 kinase; Shc: Src homology collagen; SHP-2: Phosphatase with Src homology 2 domain; SoS: Son of Sevenless.

#### 4.3.3 Molecular basis of insulin resistance

It occurs when insulin-sensitive tissues (skeletal muscle, adipose tissue and liver) cannot respond properly to hormones which cause several chronic diseases, particularly those which are linked to obesity (type-II diabetes mellitus, metabolic syndrome, dyslipidemias, cardiovascular diseases, cancer and neurodegenerative diseases). However precise mechanisms of insulin resistance are not fully understood. Following factor have been proposed to participate in its development;

#### 4.3.3.1 Increased plasma-free fatty acid level

As free fatty acids are elevated in obesity and related illness, they are supposed to be responsible for insulin action impairment but still complete mechanisms are not known. More availability of long chain saturated fatty acids results leads to insulin resistance in liver, skeletal muscle and adipose tissue. Various hypotheses proposed to explain insulin resistance induced by saturated fatty acids [14] are;


iv. Accumulation of intracellular lipid derivatives (diacylglycerol and ceramides)

1.Metformin (Glucophage, Glumetza, others): It is generally 1st medication for type-II diabetes and works by reducing gluconeogenesis in liver and improves body's sensitivity to insulin so that body utilizes insulin in more effective way.

2.Sulfonylureas: They help patients body to secrete more insulin. Its examples are glyburide (DiaBeta, Glynase), glipizide (Glucotrol) and glimepiride (Amaryl) and its possible side effects are low blood sugar and weight gain.

3.Meglitinides: Repaglinide (Prandin) and nateglinide (Starlix) works like sulfonylureas by stimulation of pancreas to secrete more insulin but they are faster acting with short duration of their effect in the body and have risk of

4.Thiazolidinediones: Along with Metformin, it include rosiglitazone (Avandia) and pioglitazone (Actos). They make the body's tissues more sensitive to insulin but these drugs causes weight gain and increased risk of heart failure and anemia that's why, these medications generally aren't 1st

5.DPP-4 inhibitors: Sitagliptin (Januvia), saxagliptin (Onglyza) and linagliptin (Tradjenta) are its different forms and help to lessen blood sugar levels but tend to have very unassuming effect as they do not cause weight gain but may

6.GLP-1 receptor agonists: These are injections to sluggish digestion and lower blood sugar levels. They often cause weight loss and its possible side effects are nausea and increased risk of pancreatitis. It includes Exenatide (Byetta, Bydureon), liraglutide (Victoza) and semaglutide (Ozempic). Current research has shown that liraglutide and semaglutide may reduce risk of heart

7.SGLT2 inhibitors: They prevent kidneys from reabsorbing sugar into blood and leads to its excretion via urine. It includes canagliflozin (Invokana), dapagliflozin (Farxiga) and empagliflozin (Jardiance). They may reduce the risk of heart attack and stroke in people with a high risk of these conditions while its side effects may include vaginal yeast infections, urinary tract infections, low blood pressure and a higher risk of diabetic ketoacidosis. Only Canagliflozin in this drug class has been associated with increased risk of lower

8.Insulin: People with type-II diabetes need insulin therapy. In past, insulin therapy was used as a last option but today it's often prescribed due to its instant benefits. It's possible side effects are low blood sugar (hypoglycemia)

last for a shorter time of 2–4 hours and include:

i. Insulin lispro (Humalog)

ii. Insulin aspart (NovoLog)

iii. Insulin glulisine (Apidra)

a. Rapid-acting injections: They take their effect within 5–15 minutes but

causing hypoglycemia and weight gain.

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

cause joint pain and increase pancreatitis risk.

attack and stroke (in people at high risk).

choice treatments.

limb amputation.

21

and its different forms are:


#### 4.3.3.2 Subclinical chronic inflammation

Chronic state of inflammation in insulin responsive tissues is major contributor to insulin resistance in obesity and related diseases. However, precise mechanisms as well as mediators involved in this interaction are not completely defined yet. Intracellular redox balance is delicately synchronized process that includes multiple generating pathways and degrading systems. Physiologically, ROS contribute in essential biological responses but their accumulation causes oxidative stress condition because of their highly oxidant nature to oxidize multiple intracellular components particularly membrane phospholipids, proteins, and DNA. In insulin resistance, increased ROS production and/or decreased ROS degradation is observed that leads to an oxidative stress condition and activation of signaling pathways related to stress. Oxidative stress is also responsible for muscle disorders and contributes to insulin resistance process. Transgenic mice expressing human ubiquitin protein E3 ligase (a protein that binds and promotes degradation of superoxide dismutase-1) leads to reduced superoxide degradation and as a result increased oxidative stress in the form of atrophy and sclerosis [15].

#### 4.3.3.3 Oxidative and nutritive stress

Activation of signaling pathways to stress is another reason of insulin resistance. Several serine/threonine kinases activated by oxidative stress pathways (JNK, PKC, GSK-3, NF-kB, and p38 MAPK) have been suggested to impair insulin signaling pathways [16].

#### 4.3.3.4 Altered expression of several genes and mitochondrial dysfunctioning

Expression of genes involved in lipid and glucose metabolism, insulin signaling, inflammation, redox balance and mitochondrial function is modified in insulin signaling, which shows that these processes participate in the pathophysiology of insulin resistance. Disturbed mitochondrial function has been suggested to have a central role in these alterations, since this organelle participates in all these processes [17].

#### 5. Current scenario of drugs and therapies to cure blood glucose regulation problems

#### 5.1 Drugs

#### 5.1.1 Drugs to manage type I and type II diabetes or its complications

Many of the drugs have a combination of effects. If a person needs two or more treatments to manage glucose levels, insulin treatment may be necessary. Possible treatments for type 1 diabetes include [18]:

iv. Accumulation of intracellular lipid derivatives (diacylglycerol and

Chronic state of inflammation in insulin responsive tissues is major contributor to insulin resistance in obesity and related diseases. However, precise mechanisms as well as mediators involved in this interaction are not completely defined yet. Intracellular redox balance is delicately synchronized process that includes multiple generating pathways and degrading systems. Physiologically, ROS contribute in essential biological responses but their accumulation causes oxidative stress condition because of their highly oxidant nature to oxidize multiple intracellular compo-

Activation of signaling pathways to stress is another reason of insulin resistance. Several serine/threonine kinases activated by oxidative stress pathways (JNK, PKC, GSK-3, NF-kB, and p38 MAPK) have been suggested to impair insulin signaling

Expression of genes involved in lipid and glucose metabolism, insulin signaling, inflammation, redox balance and mitochondrial function is modified in insulin signaling, which shows that these processes participate in the pathophysiology of insulin resistance. Disturbed mitochondrial function has been suggested to have a central role in these alterations, since this organelle participates in all these processes [17].

Many of the drugs have a combination of effects. If a person needs two or more treatments to manage glucose levels, insulin treatment may be necessary. Possible

nents particularly membrane phospholipids, proteins, and DNA. In insulin resistance, increased ROS production and/or decreased ROS degradation is observed that leads to an oxidative stress condition and activation of signaling pathways related to stress. Oxidative stress is also responsible for muscle disorders and contributes to insulin resistance process. Transgenic mice expressing human ubiquitin protein E3 ligase (a protein that binds and promotes degradation of superoxide dismutase-1) leads to reduced superoxide degradation and as a result

increased oxidative stress in the form of atrophy and sclerosis [15].

4.3.3.4 Altered expression of several genes and mitochondrial dysfunctioning

5. Current scenario of drugs and therapies to cure blood glucose

5.1.1 Drugs to manage type I and type II diabetes or its complications

ceramides)

Blood Glucose Levels

vi. Inflammation

v. Mitochondrial dysfunction

4.3.3.2 Subclinical chronic inflammation

4.3.3.3 Oxidative and nutritive stress

regulation problems

treatments for type 1 diabetes include [18]:

5.1 Drugs

20

pathways [16].

	- a. Rapid-acting injections: They take their effect within 5–15 minutes but last for a shorter time of 2–4 hours and include:

i. Insulin lispro (Humalog)


b. Short-acting injections: Its effect starts between 30 minutes to 1 hour but it last for 3–8 hours e.g.

lifestyle measures to bring them down, doctors can prescribe non-

1.Sulfonylureas: They improve insulin secretion by the pancreas into blood and people use following newer medicines most often because

insulin drugs to lower blood glucose. These drugs are:

c. Glyburide (DiaBeta, Micronase, Glynase)

d. The older, less common sulfonylureas are:

Today these drugs are less prescribed than in the past as they can cause hypo-

i. Meglitinides: They improves insulin secretion and might also improve the effectiveness of body to release insulin during meals. Its different forms are:

ii. Biguanides: They boost the effect of insulin, reduce the amount of glucose

iii. Metformin: It is the only licensed biguanide in the US and is available in the form of Glucophage, Glucophage XR, Glumetza, Riomet, and Fortamet.

iv. Thiazolidinediones: They reduce the resistance of tissues to the effects of insulin and are associated with serious side effects so they need monitoring for potential safety issues. People with heart failure should not use these

from liver and increase uptake of blood glucose into cells.

1.Chlorpropamide (Diabinese)

2.Tolazamide (Tolinase)

3.Tolbutamide (Orinase)

glycemia, leading to other health issues:

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

1.Nateglinide (Starlix)

2.Repaglinide (Prandin)

medications. They include:

1.pioglitazone (Actos)

4.acarbose (Precose)

5.miglitol (Glyset)

23

2.rosiglitazone (Avandia)

3.Alpha-glucosidase inhibitors

6.Dipeptidyl peptidase inhibitors

of their less adverse effects. These are:

a. Glimepiride (Amaryl)

b. Glipizide (Glucotrol)

i. Regular insulin (Humulin R and Novolin R)

c. Intermediate-acting injections: It is effective after 1–4 hours and last for 12–18 hours. e.g.

i. Insulin isophane, also called NPH insulin (Humulin N and Novolin N)

d. Long-acting injections: They are effective after 1/2 hours and last for between 14 and 24 hours. Its different forms are:

i. Insulin glargine (Toujeo)

ii. Insulin detemir (Levemir)

iii. Insulin degludec (Tresiba)

	- i. Insulin lispro protamine and insulin lispro (Humalog Mix 50/50 and Humalog Mix 75/25)
	- ii. Insulin aspart protamine and insulin aspart (NovoLog Mix 50/50 and NovoLog Mix 70/30)
	- iii. NPH insulin and regular insulin (Humulin 70/30 and Novolin 70/30)

i. Insulin human powder (Afrezza)

#### 9.Non-Inulin Injectables:

	- i. Amylin analogs: Pramlintide (Symlin) which mimics another hormone, amylin, that plays a role in glucose regulation.
	- ii. Glucagon which can reverse blood sugar levels when they fall too low as a result of insulin treatment.
	- i. Insulin: It can also manage high blood glucose levels in type-II diabetes but doctors typically prescribe it only when other treatments have not had the desired effect. Type-II diabetic pregnant women may also use it for the reduction of disease effects on fetus while for people with high blood glucose levels, in-spite of applying

b. Short-acting injections: Its effect starts between 30 minutes to 1 hour

c. Intermediate-acting injections: It is effective after 1–4 hours and last

d. Long-acting injections: They are effective after 1/2 hours and last for

e. Premixed injections: These are combinations of the above types of insulin and all takes effect from 5 minutes to 1 hour and last for 10–

i. Insulin lispro protamine and insulin lispro (Humalog Mix 50/50 and

ii. Insulin aspart protamine and insulin aspart (NovoLog Mix 50/50 and

iii. NPH insulin and regular insulin (Humulin 70/30 and Novolin 70/30)

f. People can breathe in rapid-acting inhalable insulin which produces its

a. For Patients with Type-1 Diabetes: These drugs are common for type 1

i. Amylin analogs: Pramlintide (Symlin) which mimics another hormone, amylin, that plays a role in glucose regulation.

ii. Glucagon which can reverse blood sugar levels when they fall too

i. Insulin: It can also manage high blood glucose levels in type-II diabetes but doctors typically prescribe it only when other

treatments have not had the desired effect. Type-II diabetic pregnant women may also use it for the reduction of disease effects on fetus while for people with high blood glucose levels, in-spite of applying

effects within 12–15 minutes and lasts for 2–3 hours e.g.

i. Insulin isophane, also called NPH insulin (Humulin N and Novolin N)

i. Regular insulin (Humulin R and Novolin R)

between 14 and 24 hours. Its different forms are:

but it last for 3–8 hours e.g.

i. Insulin glargine (Toujeo)

ii. Insulin detemir (Levemir)

iii. Insulin degludec (Tresiba)

Humalog Mix 75/25)

NovoLog Mix 70/30)

9.Non-Inulin Injectables:

22

24 hours and its different forms are:

i. Insulin human powder (Afrezza)

diabetic patients and its different forms are:

low as a result of insulin treatment.

b. For patients with Type-II Diabetes:

for 12–18 hours. e.g.

Blood Glucose Levels

lifestyle measures to bring them down, doctors can prescribe noninsulin drugs to lower blood glucose. These drugs are:

	- a. Glimepiride (Amaryl)
	- b. Glipizide (Glucotrol)
	- c. Glyburide (DiaBeta, Micronase, Glynase)
	- d. The older, less common sulfonylureas are:
		- 1.Chlorpropamide (Diabinese)
		- 2.Tolazamide (Tolinase)
		- 3.Tolbutamide (Orinase)

Today these drugs are less prescribed than in the past as they can cause hypoglycemia, leading to other health issues:

	- 1.Nateglinide (Starlix)
	- 2.Repaglinide (Prandin)
	- 1.pioglitazone (Actos)
	- 2.rosiglitazone (Avandia)
	- 3.Alpha-glucosidase inhibitors
	- 4.acarbose (Precose)
	- 5.miglitol (Glyset)
	- 6.Dipeptidyl peptidase inhibitors

11. saxagliptin and metformin (Kombiglyze XR)

5.1.2 Drugs that may help to prevent the complications of diabetes.

5.1.2.1 ACE inhibitors or angiotensin-II receptor blockers

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

cations of diabetes.

5.1.2.2 Statins and aspirin

doctors recommendation.

5.1.2.3 Drug for weight loss

help to treat diabetic obesity.

and also support weight loss.

antihyperglycemic treatment:

25

appetite to treat obesity.

12. sitagliptin and metformin (Janumet and Janumet XR)

viii.Alternatives: U.S. Food and Drug Administration has permitted ergot alkaloid, bromocriptine (Cycloset) to treat type-II diabetes. Doctors do not often propose/ set down this medication. Moreover people use bile acid sequestrants to manage cholesterol levels which can also help to maintain steady blood sugar levels. Along with these, only colesevelam (Welchol) is approved for type-II diabetes.

They are used to treat high blood pressure to prevent or manage kidney compli-

It is key part of diabetes management and prevention and doctors might suggest

i. Lorcaserin (Belviq): It enhances the feeling of being packed after food and

ii. Orlistat (Alli and Xenical): This drug decreases absorption of fat from diet

iii. Phentermine and topiramate (Qsymia): It is a grouped drug and reduce

5.1.3 Current guidelines at each person's situation and best approach for the individual

There are many guide lines for each person's health situation and each can

a. Sodium-glucose cotransporter 2 inhibitors (SGLT2)

b. Glucagon-like peptide 1 receptor agonists (GLP1-RA)

i. For people with type 2 diabetes and atherosclerotic cardiovascular disease (CVD), 2018 guidelines recommend following drugs as part of the

ii. Type-II diabetic people with atherosclerotic CVD and heart failure or a high

choose best one according to their health conditions [20] e.g.

risk of heart failure should be prescribed with:

a. Sodium-glucose cotransporter 2 inhibitors

medicines to cure it without effective lifestyle measures [19]. These drugs are

People can manage cardiovascular risks of diabetes (like heart disease and stroke) by taking them to lower cholesterol levels at a dozen of once per day on

	- 1.exenatide (Byetta, Bydureon)
	- 2.liraglutide (Victoza)
	- 3.dulaglutide (Trulicity)
	- 4.lixisenatide (Adlyxin)
	- 5. semaglutide (Ozempic)

1.alogliptin and metformin (Kazano)


8. repaglinide and metformin (PrandiMet)


7.alogliptin (Nesina)

Blood Glucose Levels

8.linagliptin (Tradjenta)

9. sitagliptin (Januvia)

10. saxagliptin (Onglyza)

1.canagliflozin (Invokana)

2.dapagliflozin (Farxiga)

3.empagliflozin (Jardiance)

4.ertugliflozin (Steglatro)

insulin release after meals are:

2.liraglutide (Victoza)

3.dulaglutide (Trulicity)

4.lixisenatide (Adlyxin)

5. semaglutide (Ozempic)

1.alogliptin and metformin (Kazano)

2.alogliptin and pioglitazone (Oseni)

3.glipizide and metformin (Metaglip)

4.glyburide and metformin (Glucovance)

5.linagliptin and metformin (Jentadueto)

6.pioglitazone and glimepiride (Duetact)

8. repaglinide and metformin (PrandiMet)

9. rosiglitazone and glimepiride (Avandaryl)

10. rosiglitazone and metformin (Avandamet)

of previous drugs include:

24

1.exenatide (Byetta, Bydureon)

patients. These include:

v. Sodium-glucose co-transporter 2 (SGLT2) inhibitors: They cause body to release more glucose into the urine from the bloodstream and might also lead to a modest amount of weight loss, which can be a benefit for type-II diabetic

vi. Incretin mimetics: The drugs that imitate incretin hormone and stimulate

vii. Oral combination drugs: Drugs that are obtained after combination of some

7.pioglitazone and metformin (Actoplus MET, Actoplus MET XR)

11. saxagliptin and metformin (Kombiglyze XR)

12. sitagliptin and metformin (Janumet and Janumet XR)


They are used to treat high blood pressure to prevent or manage kidney complications of diabetes.

#### 5.1.2.2 Statins and aspirin

People can manage cardiovascular risks of diabetes (like heart disease and stroke) by taking them to lower cholesterol levels at a dozen of once per day on doctors recommendation.

#### 5.1.2.3 Drug for weight loss

It is key part of diabetes management and prevention and doctors might suggest medicines to cure it without effective lifestyle measures [19]. These drugs are


There are many guide lines for each person's health situation and each can choose best one according to their health conditions [20] e.g.

	- a. Sodium-glucose cotransporter 2 inhibitors (SGLT2)
	- b. Glucagon-like peptide 1 receptor agonists (GLP1-RA)
	- a. Sodium-glucose cotransporter 2 inhibitors

iii. To treat people with type-II diabetes and chronic kidney disease, doctors urged to consider following guidelines to stop chronic kidney disease, CVD or both, from getting worse.:

6. New approaches to drug development and therapies, with a

blood glucose regulation problems

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

Figure 6.

27

(b) The selected.

particular focus on drug development by green synthesis to cure

Bioactive molecules from Natural products have been proved to improve insulin resistance and its associated complications by suppressing inflammatory signaling pathways [26]. Medicinal plants cannot be obsolete and still play a prominent role in human health care. Among natural sources, over 1200 plants have been claimed as antidiabetic remedies. While over 400 plants along with its 700 recipes and compounds have been scientifically evaluated for type-II diabetes. Metformin was developed on the basis of

Mechanisms underlying herbal therapies using antidiabetic plants and phytocompounds. (a) Different types of medicinal herbs can be classified based on their modes of action such as insulin resistance (type 1 herbs), -cell function (type 2 herbs), and GLP-1 (type 3 herbs) and glucose (re) absorption (type 4 herbs),


#### 5.2 Therapies

When medicines and lifestyle changes are not enough to manage diabetes, a less common treatment can become an option. Other treatments include different surgical procedures for treating type-I or type-II diabetes [21–25] which are as follows:

#### 5.2.1. Bariatric surgery

It is also called weight-loss surgery or metabolic surgery and it help obese and type-II diabetic patients to lose a large amount of weight and regain normal blood glucose levels. Even some people with diabetes may no longer need their diabetes medicine after it. Efficacy of this surgery can be checked by the variations in blood glucose level, type of weight-loss surgery and the amount of lost weight by the patients. Moreover it can also be monitored by the time occurrence of diabetes and on duration of usage of insulin. Current research suggested that weight-loss surgery also may help to improve blood glucose control in obese type-I diabetic people but still scientists are finding long-term results of this in type-I and II diabetic patients [21].

#### 5.2.2 Artificial pancreas

NIDDK has leading role to develop artificial pancreas technology. Artificial pancreas replaces manual blood glucose levels by the shots or pumping of insulin. Single system monitors blood glucose levels throughout the patient's life and provide insulin or a combination of insulin and glucagon routinely. The system can also be monitored remotely by parents or by medical staff. In 2016, FDA approved a type of artificial pancreas system, called a hybrid closed-loop system which tested blood glucose level after every 5 minutes throughout the day and night and automatically provided right amount of insulin to body. But when person still needed manual adjustment of insulin amount, pump delivered it at meal times. But artificial pancreas make patient free from some of daily tasks which are needed to keep blood glucose level steady or help to sleep through the night without need of wake and test blood glucose or to take medicine. Hybrid closed loop system was available in the U. S. in 2017. NIDDK has funded several important projects on different types of artificial pancreas devices for the better help of Type- I diabetic people for proper management of disease. These devices may also help type-II diabetic and gestational diabetic people to cure their disease [22, 23].

#### 5.2.3 Pancreatic islet transplantation

This is an experimental treatment for poorly controlled type-I diabetes as in this condition immune system attacks islet cells. Pancreatic islet transplant replace shattered islets with new ones to make and release insulin. In this process, islets are donated from the pancreas of donor of pancreas and are transferred to a type 1 diabetic patient. As researchers are still doing work on pancreatic islet transplantation, so procedure is only accessible to volunteers of research studies [24, 25].

iii. To treat people with type-II diabetes and chronic kidney disease, doctors urged to consider following guidelines to stop chronic kidney disease, CVD

When medicines and lifestyle changes are not enough to manage diabetes, a less common treatment can become an option. Other treatments include different surgical procedures for treating type-I or type-II diabetes [21–25] which are as follows:

It is also called weight-loss surgery or metabolic surgery and it help obese and type-II diabetic patients to lose a large amount of weight and regain normal blood glucose levels. Even some people with diabetes may no longer need their diabetes medicine after it. Efficacy of this surgery can be checked by the variations in blood glucose level, type of weight-loss surgery and the amount of lost weight by the patients. Moreover it can also be monitored by the time occurrence of diabetes and on duration of usage of insulin. Current research suggested that weight-loss surgery also may help to improve blood glucose control in obese type-I diabetic people but still scientists are finding long-term results of this in type-I and II diabetic patients [21].

NIDDK has leading role to develop artificial pancreas technology. Artificial pancreas replaces manual blood glucose levels by the shots or pumping of insulin. Single system monitors blood glucose levels throughout the patient's life and provide insulin or a combination of insulin and glucagon routinely. The system can also be monitored remotely by parents or by medical staff. In 2016, FDA approved a type of artificial pancreas system, called a hybrid closed-loop system which tested blood glucose level after every 5 minutes throughout the day and night and automatically provided right amount of insulin to body. But when person still needed manual adjustment of insulin amount, pump delivered it at meal times. But artificial pancreas make patient free from some of daily tasks which are needed to keep blood glucose level steady or help to sleep through the night without need of wake and test blood glucose or to take medicine. Hybrid closed loop system was available in the U. S. in 2017. NIDDK has funded several important projects on different types of artificial pancreas devices for the better help of Type- I diabetic people for proper management of disease. These devices may also help type-II diabetic and gestational

This is an experimental treatment for poorly controlled type-I diabetes as in this

condition immune system attacks islet cells. Pancreatic islet transplant replace shattered islets with new ones to make and release insulin. In this process, islets are donated from the pancreas of donor of pancreas and are transferred to a type 1 diabetic patient. As researchers are still doing work on pancreatic islet transplantation, so procedure is only accessible to volunteers of research studies [24, 25].

a. Sodium-glucose co transporter 2 inhibitor

b. Glucagon-like peptide 1 receptor agonist

or both, from getting worse.:

5.2 Therapies

Blood Glucose Levels

5.2.1. Bariatric surgery

5.2.2 Artificial pancreas

diabetic people to cure their disease [22, 23].

5.2.3 Pancreatic islet transplantation

26

#### 6. New approaches to drug development and therapies, with a particular focus on drug development by green synthesis to cure blood glucose regulation problems

Bioactive molecules from Natural products have been proved to improve insulin resistance and its associated complications by suppressing inflammatory signaling pathways [26]. Medicinal plants cannot be obsolete and still play a prominent role in human health care. Among natural sources, over 1200 plants have been claimed as antidiabetic remedies. While over 400 plants along with its 700 recipes and compounds have been scientifically evaluated for type-II diabetes. Metformin was developed on the basis of

#### Figure 6.

Mechanisms underlying herbal therapies using antidiabetic plants and phytocompounds. (a) Different types of medicinal herbs can be classified based on their modes of action such as insulin resistance (type 1 herbs), -cell function (type 2 herbs), and GLP-1 (type 3 herbs) and glucose (re) absorption (type 4 herbs), (b) The selected.


29

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978 Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

28

Blood Glucose Levels


biguanide compound from an antidiabetic herb, French lilac and is now its a first-line drug against type-II diabetes. Medicinal plants also contains a diverse bioactive compounds and can have multiple actions on insulin action, insulin production, or both. With a focus on scientific studies of selected glucose-lowering herbs, phyto compounds

Active compounds and biological actions of antidiabetic herbs.

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

Table 1.

31

Table 1. Active compounds and biological actions of antidiabetic herbs.

biguanide compound from an antidiabetic herb, French lilac and is now its a first-line drug against type-II diabetes. Medicinal plants also contains a diverse bioactive compounds and can have multiple actions on insulin action, insulin production, or both. With a focus on scientific studies of selected glucose-lowering herbs, phyto compounds

30

Blood Glucose Levels

and their ability to target insulin resistance, cell function, incretin related pathways and glucose (re)absorption (Figure 6a and b), multiple studies have been done.

IGF1 insulin-Like Growth Factor 1 B-GPCRs class B G protein-coupled receptors class A-GPCRs class A G protein-coupled receptors

Shc Src homology and collagen protein

raf rapidly Accelerated Fibrosarcoma

p38 MAPK p38 mitogen-activated protein kinases ACE inhibitors acetylcholine Esterase Inhibitors

NF-kB nuclear factor kappa-light-chain-enhancer of activated B cells

NIDDK National Institute of Diabetes and Digestive and Kidney

NIGMS National Institute of General Medical Sciences

GDP guanosine diphosphate, GTP guanosine diphosphate,

JNK c-Jun N-terminal kinase

GSK-3 glycogen synthase kinase-3

Diseases FDA Food and Drug Administration

NIDA National Institute on Drug Abuse

\* and Noman Khalique<sup>2</sup>

1 Institute of Molecular Biology and Biotechnology (IMBB), The University of

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 Department of Zoology, University of the Punjab, Lahore, Pakistan

\*Address all correspondence to: asma.ahmed@imbb.uol.edu.pk;

Cbl cannabinoid 1

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

c-Ras rat sarcoma

Author details

Lahore, Lahore, Pakistan

asma.ahmad.aridian@gmail.com

provided the original work is properly cited.

Asma Ahmed<sup>1</sup>

33

PKC protein kinase C

While more than 400 plants and compounds have shown In-vitro and/or In-vivo antidiabetic activities. Instead of listing each extract/compound, here, selected chemicals from plants and/or their extracts with the ability to control blood glucose levels as well as to modulate mechanisms involved in insulin resistance or cell function or incretin-related pathways or glucose (re)absorption can be tabulated (Table 1) along with chemical structure, antidiabetic activity and action in cells/ animal models and the results of administration of the plant extracts and compounds to diabetic patients [27].

#### 7. Conclusions

All hormones for the regulation of blood glucose levels along with their source organ up to the level of cell have been discussed in first section of chapter. Then different Pathways involved in regulating blood glucose levels in normal and abnormal conditions has been explained. Genes, Molecular and cellular targets to regulate blood glucose levels in normal and abnormal conditions has been discussed with particular focus on molecular basis of insulin signaling pathways and this pathway has been linked with Mechanism of Insulin Action and Molecular Basis of Insulin Resistance which is may be due to fatty acids, inflammation, stress and altered expression of several genes. Current scenario of Drugs and therapies to cure blood glucose regulation problems for the management of type 1 and type 2 diabetes has been explained. At the end New approaches to drug development and therapies by green synthesis to have been mentioned.

#### Acknowledgements

All authors are highly acknowledged to the host institutions for providing a forum for the publication of this data.

#### Conflict of interest

All authors declare that they do not have any conflict of interest with any company or organization or person.

#### Vote of thanks

All authors are highly acknowledged to their parents and teachers who contributed their whole life for making their siblings and students a successful person.

#### Abbreviations


Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

and their ability to target insulin resistance, cell function, incretin related pathways and

antidiabetic activities. Instead of listing each extract/compound, here, selected chemicals from plants and/or their extracts with the ability to control blood glucose levels as well as to modulate mechanisms involved in insulin resistance or cell function or incretin-related pathways or glucose (re)absorption can be tabulated (Table 1) along with chemical structure, antidiabetic activity and action in cells/ animal models and the results of administration of the plant extracts and com-

While more than 400 plants and compounds have shown In-vitro and/or In-vivo

All hormones for the regulation of blood glucose levels along with their source organ up to the level of cell have been discussed in first section of chapter. Then different Pathways involved in regulating blood glucose levels in normal and abnormal conditions has been explained. Genes, Molecular and cellular targets to regulate blood glucose levels in normal and abnormal conditions has been discussed with particular focus on molecular basis of insulin signaling pathways and this pathway has been linked with Mechanism of Insulin Action and Molecular Basis of Insulin Resistance which is may be due to fatty acids, inflammation, stress and altered expression of several genes. Current scenario of Drugs and therapies to cure blood glucose regulation problems for the management of type 1 and type 2 diabetes has been explained. At the end New approaches to drug development and therapies

All authors are highly acknowledged to the host institutions for providing a

All authors declare that they do not have any conflict of interest with any

All authors are highly acknowledged to their parents and teachers who contributed their whole life for making their siblings and students a successful person.

MafA musculoaponeurotic Fibrosarcoma Oncogene Family, A MafB musculoaponeurotic Fibrosarcoma Oncogene Family, B

SNPs single Nucleotide Polymorphism

ADCY5 adenylate cyclase 5 FADS1 fatty acid desaturase 1

glucose (re)absorption (Figure 6a and b), multiple studies have been done.

pounds to diabetic patients [27].

by green synthesis to have been mentioned.

forum for the publication of this data.

company or organization or person.

7. Conclusions

Blood Glucose Levels

Acknowledgements

Conflict of interest

Vote of thanks

Abbreviations

32


#### Author details

Asma Ahmed<sup>1</sup> \* and Noman Khalique<sup>2</sup>

1 Institute of Molecular Biology and Biotechnology (IMBB), The University of Lahore, Lahore, Pakistan

2 Department of Zoology, University of the Punjab, Lahore, Pakistan

\*Address all correspondence to: asma.ahmed@imbb.uol.edu.pk; asma.ahmad.aridian@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### References

[1] Betts GJ, Desaix P, Johnson E, Korol O, Kruse D, Poe B. Human Anatomy and Physiology. Houston, TX, USA: OpenStax College; 2013

[2] Queen Mary University of London. Diabetes gene found that causes low and high blood sugar levels in the same family. 2018

[3] Watanabe. University of Southern California. Gene That Regulates Glucose Levels Identified. 2008

[4] Marta B, Babatunji WO, Catriona M, Carmen T, Katie H, Tania AJ, et al. Glucolipotoxicity initiates pancreatic β-cell death through TNFR5/CD40 mediated STAT1 and NF-κB activation. Cell Death & Disease. 2016;7:e2329. DOI: 10.1038/cddis.2016.203

[5] Lyssenko V, Jonsson A, Almgren P, Pulizzi N, Isomaa B, Tuomi T, et al. Clinical risk factors, DNA variants, and the development of type 2 diabetes. The New England Journal of Medicine. 2008;359(21):2220-2232. DOI: 10.1056/ NEJMoa0801869

[6] Harrison W. The structures of receptors involved in blood sugar control. NIH Research Matters. 2017

[7] Bouatia-Naji N, Bonnefond A, Cavalcanti-Proença C, Sparso T, Holmkvist J, Marchand M, et al. A variant near MTNR1B is associated with increased fasting plasma glucose levels and type 2 diabetes risk. Nature Genetics. 2009;41(1):89-94. DOI: 10.1038/ng.277.Epub 2008 Dec 7

[8] Kerru N, Singh-Pillay A, Awolade P, Singh P. Current anti-diabetic agents and their molecular targets: A review. European Journal of Medicinal Chemistry. 2018;152:436-488. DOI: 10.1016/j.ejmech.2018.04.061

[9] Paola L, Contreras-Ferrat A, Genaro B, Marco V, David M, Cecilia H. Glucose-dependent insulin secretion in pancreatic β-cell islets from male rats requires Ca2+ release via ROSstimulated ryanodine receptors. PLoS One. 2015;10(10):e0140198. DOI: 10.1371/journal.pone.0140198

[16] Justin LR, Sushil KJ. Oxidative stress, insulin signaling and diabetes. Free Radical Biology and Medicine. 2013;50(5):567-575. DOI: 10.1016/j.

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

> [25] Rodolfo AMD, David BMD, Ana AAPRN. Pancreatic Islets Transplantation. 2018. The National Institute of Diabetes and Digestive and Kidney Diseases Health Information

[26] Gothai S, Ganesan P, Park S-Y, Fakurazi S, Choi D-K, Arulselvan P. Natural Phyto-bioactive compounds for

the treatment of type 2 diabetes: Inflammation as a target. Nutrients.

evidence. Evidence-based Complementary and Alternative Medicine. 2019;2019:6021209. DOI:

10.1155/2019/6021209

[27] Michael BA, Rosemary A, Daniel B, William E, Lydia EK, Emmanuel EB, et al. Phytomedicines used for diabetes mellitus in Ghana: A systematic search and review of preclinical and clinical

Center

2016;8(8):461

[17] Al-Zubairi AS, Eid EEM. Molecular

[18] Diabetes Health Center. Type 2

[19] Patient Care and Health Informa tion; Diseases & Conditions. Type 2 Diabetes (Diagnosis and Treatment). 2018. Mayo Clinic Minute: Get the facts

[20] American Diabetes Association. Lifestyle Management. Diabetes Care. 2017;40(Supplement 1):S33-S43. DOI:

[21] Chrysi K, Stavros L, Carel WIR, Alexander K. The role of bariatric surgery to treat diabetes: Current challenges and perspectives. BMC Endocrine Disorders. 2017;17:50. DOI:

[22] Tim N. Artificial pancreas: game changer for diabetes treatment? (News Letter). 2016. MedicalNewsToday. ISSN

[23] Boris K, William VT, William TC, Claudio C. The artificial pancreas in 2016: A digital treatment ecosystem for diabetes. Diabetes Care. 2016;39(7): 1123-1126. DOI: 10.2337/dc16-0824

[24] Foster ED, Bridges ND, Feurer ID,

Eggerman TL, Hunsicker LG, Alejandro R, et al. Improved healthrelated quality of life in a phase 3 islet transplantation trial in type 1 diabetes complicated by severe hypoglycemia. Diabetes Care. 2018;41(5):1001-1008.

DOI: 10.2337/dc17-1779

35

10.1186/s12902-017-0202-6

freeradbiomed.2010.12.006

targets in the development of Antidiabetic drugs. International Journal of Pharmacology. 2010;6:

Diabetes Treatments. 2017

on Type 2 diabetes

10.2337/dc17-S007

2375-9593

784-795

[10] Zhiping PP, Thomas CS. Cell biology of Ca2+triggered exocytosis. Current Opinion in Cell Biology. 2010;22(4): 496-505. DOI: 10.1016/j.ceb.2010.05.001

[11] Cicero LTC, Lin Y, Bartolome AP, Chen Y-C, Chiu S-C, Yang W-C. Herbal therapies for type 2 diabetes mellitus: Chemistry, biology, and potential application of selected plants and compounds. Evidence-based Complementary and Alternative Medicine. 2013;2013:33

[12] Colin W, Mike L. Insulin signaling pathways. 2014. Diapedia 51040851481 rev. no. 14. Available from: https://doi. org/10.14496/dia.51040851481.14

[13] Francesca W, Akiko K, Jorge G, Margaret LH, Normand P, Alexander L, et al. Activation of the Ras/mitogenactivated protein kinase pathway by kinase-defective epidermal growth factor receptors results in cell survival but not proliferation. Molecular and Cell Biology. 1998;18(12):7192-7204

[14] Chongben Z, Eric LK, Rosalind AC. Lipid signals and insulin resistance. Journal of Clinical Lipidology. 2013; 8(6):659-667. DOI: 10.2217/clp.13.67

[15] Young-Don K, Bin W, Jing JL, Ruishan W, Qiyue D, Shiyong D, et al. Upregulation of the E3 ligase NEDD4-1 by oxidative stress degrades IGF-1 receptor protein in Neurodegeneration. Journal of Neuroscience. 2012;32(32): 10971-10981. DOI: 10.1523/ JNEUROSCI.1836-12.2012

Molecular Basis of Blood Glucose Regulation DOI: http://dx.doi.org/10.5772/intechopen.89978

[16] Justin LR, Sushil KJ. Oxidative stress, insulin signaling and diabetes. Free Radical Biology and Medicine. 2013;50(5):567-575. DOI: 10.1016/j. freeradbiomed.2010.12.006

References

Blood Glucose Levels

family. 2018

Levels Identified. 2008

NEJMoa0801869

2017

34

[6] Harrison W. The structures of receptors involved in blood sugar control. NIH Research Matters.

[7] Bouatia-Naji N, Bonnefond A, Cavalcanti-Proença C, Sparso T, Holmkvist J, Marchand M, et al. A variant near MTNR1B is associated with increased fasting plasma glucose levels and type 2 diabetes risk. Nature Genetics. 2009;41(1):89-94. DOI: 10.1038/ng.277.Epub 2008 Dec 7

[8] Kerru N, Singh-Pillay A, Awolade P, Singh P. Current anti-diabetic agents and their molecular targets: A review. European Journal of Medicinal Chemistry. 2018;152:436-488. DOI: 10.1016/j.ejmech.2018.04.061

[1] Betts GJ, Desaix P, Johnson E, Korol O, Kruse D, Poe B. Human Anatomy and Physiology. Houston, TX, [9] Paola L, Contreras-Ferrat A,

Genaro B, Marco V, David M, Cecilia H. Glucose-dependent insulin secretion in pancreatic β-cell islets from male rats requires Ca2+ release via ROSstimulated ryanodine receptors. PLoS One. 2015;10(10):e0140198. DOI: 10.1371/journal.pone.0140198

[10] Zhiping PP, Thomas CS. Cell biology of Ca2+triggered exocytosis. Current Opinion in Cell Biology. 2010;22(4): 496-505. DOI: 10.1016/j.ceb.2010.05.001

[11] Cicero LTC, Lin Y, Bartolome AP, Chen Y-C, Chiu S-C, Yang W-C. Herbal therapies for type 2 diabetes mellitus: Chemistry, biology, and potential application of selected plants and compounds. Evidence-based Complementary and Alternative

[12] Colin W, Mike L. Insulin signaling pathways. 2014. Diapedia 51040851481 rev. no. 14. Available from: https://doi. org/10.14496/dia.51040851481.14

[13] Francesca W, Akiko K, Jorge G, Margaret LH, Normand P, Alexander L, et al. Activation of the Ras/mitogenactivated protein kinase pathway by kinase-defective epidermal growth factor receptors results in cell survival but not proliferation. Molecular and Cell

Biology. 1998;18(12):7192-7204

[15] Young-Don K, Bin W, Jing JL, Ruishan W, Qiyue D, Shiyong D, et al. Upregulation of the E3 ligase NEDD4-1 by oxidative stress degrades IGF-1 receptor protein in Neurodegeneration. Journal of Neuroscience. 2012;32(32):

10971-10981. DOI: 10.1523/ JNEUROSCI.1836-12.2012

[14] Chongben Z, Eric LK, Rosalind AC. Lipid signals and insulin resistance. Journal of Clinical Lipidology. 2013; 8(6):659-667. DOI: 10.2217/clp.13.67

Medicine. 2013;2013:33

[2] Queen Mary University of London. Diabetes gene found that causes low and high blood sugar levels in the same

[3] Watanabe. University of Southern California. Gene That Regulates Glucose

[4] Marta B, Babatunji WO, Catriona M, Carmen T, Katie H, Tania AJ, et al. Glucolipotoxicity initiates pancreatic β-cell death through TNFR5/CD40 mediated STAT1 and NF-κB activation. Cell Death & Disease. 2016;7:e2329. DOI: 10.1038/cddis.2016.203

[5] Lyssenko V, Jonsson A, Almgren P, Pulizzi N, Isomaa B, Tuomi T, et al. Clinical risk factors, DNA variants, and the development of type 2 diabetes. The New England Journal of Medicine. 2008;359(21):2220-2232. DOI: 10.1056/

USA: OpenStax College; 2013

[17] Al-Zubairi AS, Eid EEM. Molecular targets in the development of Antidiabetic drugs. International Journal of Pharmacology. 2010;6: 784-795

[18] Diabetes Health Center. Type 2 Diabetes Treatments. 2017

[19] Patient Care and Health Informa tion; Diseases & Conditions. Type 2 Diabetes (Diagnosis and Treatment). 2018. Mayo Clinic Minute: Get the facts on Type 2 diabetes

[20] American Diabetes Association. Lifestyle Management. Diabetes Care. 2017;40(Supplement 1):S33-S43. DOI: 10.2337/dc17-S007

[21] Chrysi K, Stavros L, Carel WIR, Alexander K. The role of bariatric surgery to treat diabetes: Current challenges and perspectives. BMC Endocrine Disorders. 2017;17:50. DOI: 10.1186/s12902-017-0202-6

[22] Tim N. Artificial pancreas: game changer for diabetes treatment? (News Letter). 2016. MedicalNewsToday. ISSN 2375-9593

[23] Boris K, William VT, William TC, Claudio C. The artificial pancreas in 2016: A digital treatment ecosystem for diabetes. Diabetes Care. 2016;39(7): 1123-1126. DOI: 10.2337/dc16-0824

[24] Foster ED, Bridges ND, Feurer ID, Eggerman TL, Hunsicker LG, Alejandro R, et al. Improved healthrelated quality of life in a phase 3 islet transplantation trial in type 1 diabetes complicated by severe hypoglycemia. Diabetes Care. 2018;41(5):1001-1008. DOI: 10.2337/dc17-1779

[25] Rodolfo AMD, David BMD, Ana AAPRN. Pancreatic Islets Transplantation. 2018. The National Institute of Diabetes and Digestive and Kidney Diseases Health Information Center

[26] Gothai S, Ganesan P, Park S-Y, Fakurazi S, Choi D-K, Arulselvan P. Natural Phyto-bioactive compounds for the treatment of type 2 diabetes: Inflammation as a target. Nutrients. 2016;8(8):461

[27] Michael BA, Rosemary A, Daniel B, William E, Lydia EK, Emmanuel EB, et al. Phytomedicines used for diabetes mellitus in Ghana: A systematic search and review of preclinical and clinical evidence. Evidence-based Complementary and Alternative Medicine. 2019;2019:6021209. DOI: 10.1155/2019/6021209

**37**

**2.1 Insulin**

**Chapter 3**

**Abstract**

**1. Introduction**

Role of PI3K/AKT Pathway in

*Ewa Świderska, Justyna Strycharz, Adam Wróblewski,* 

**Keywords:** insulin, PI3K, AKT, glucose uptake, GLUT4, insulin resistance

hormones with insulin being the most important one.

**2. Mechanism of insulin action**

Nowadays, when society is leading an increasingly sedentary lifestyle with constant access to food without the need for effort, we observe the raising occurrence of diseases with metabolic dysregulation. This financial and social burden has caused the great need for understanding mechanistic details of metabolic response pathways, causes of their impairment, and following consequences. Carbohydrate metabolism is mainly related to glucose. Its level should remain in a narrow range (4–7 mM) by balancing glucose release into the circulation, its absorption from the intestine, the breakdown of stored glycogen in liver, and the uptake of blood glucose by peripheral tissues. These processes are regulated by a few metabolic

Insulin is an anabolic peptide hormone secreted by pancreatic β cells, whose mature form arises in two stages [1]. First, preproinsulin is processed via cutting of the signal fragment and forming proinsulin [2]. This is followed by the excision of the middle fragment (C chain—35 aa), which gives dipeptide made up of two chains (A—21 aa, B—30 aa) connected by two disulfide bonds [3]. Insulin is a multitask

*Janusz Szemraj, Józef Drzewoski and Agnieszka Śliwińska*

Glucose uptake is regulated by several mechanisms, where insulin plays the most prominent role. This powerful anabolic hormone regulates the transport of glucose into the cell through translocation of glucose transporter from an intracellular pool to the plasma membrane mainly in metabolically active tissues like skeletal muscles, adipose tissue, or liver (GLUT4). This translocation occurs through multiple steps of PI3K/AKT signaling pathway. In this chapter, we will focus on molecular events leading to GLUT4 translocation, starting with activation of insulin receptors through signaling cascade involving phosphatidylinositol 3-kinase (PI3K) and protein kinase B (PKB) and finally, the action of their effectors. We will present regulatory mechanisms and modulators of insulin-mediated glucose uptake.

Insulin-Mediated Glucose Uptake

#### **Chapter 3**

## Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake

*Ewa Świderska, Justyna Strycharz, Adam Wróblewski, Janusz Szemraj, Józef Drzewoski and Agnieszka Śliwińska*

#### **Abstract**

Glucose uptake is regulated by several mechanisms, where insulin plays the most prominent role. This powerful anabolic hormone regulates the transport of glucose into the cell through translocation of glucose transporter from an intracellular pool to the plasma membrane mainly in metabolically active tissues like skeletal muscles, adipose tissue, or liver (GLUT4). This translocation occurs through multiple steps of PI3K/AKT signaling pathway. In this chapter, we will focus on molecular events leading to GLUT4 translocation, starting with activation of insulin receptors through signaling cascade involving phosphatidylinositol 3-kinase (PI3K) and protein kinase B (PKB) and finally, the action of their effectors. We will present regulatory mechanisms and modulators of insulin-mediated glucose uptake.

**Keywords:** insulin, PI3K, AKT, glucose uptake, GLUT4, insulin resistance

#### **1. Introduction**

Nowadays, when society is leading an increasingly sedentary lifestyle with constant access to food without the need for effort, we observe the raising occurrence of diseases with metabolic dysregulation. This financial and social burden has caused the great need for understanding mechanistic details of metabolic response pathways, causes of their impairment, and following consequences. Carbohydrate metabolism is mainly related to glucose. Its level should remain in a narrow range (4–7 mM) by balancing glucose release into the circulation, its absorption from the intestine, the breakdown of stored glycogen in liver, and the uptake of blood glucose by peripheral tissues. These processes are regulated by a few metabolic hormones with insulin being the most important one.

#### **2. Mechanism of insulin action**

#### **2.1 Insulin**

Insulin is an anabolic peptide hormone secreted by pancreatic β cells, whose mature form arises in two stages [1]. First, preproinsulin is processed via cutting of the signal fragment and forming proinsulin [2]. This is followed by the excision of the middle fragment (C chain—35 aa), which gives dipeptide made up of two chains (A—21 aa, B—30 aa) connected by two disulfide bonds [3]. Insulin is a multitask


**Table 1.**

*Metabolic functions of insulin.*

protein involved, among others, in the regulation of carbohydrate and lipid metabolism (**Table 1**). The most important stimulus for insulin production is a postprandial increase of blood glucose level. By increasing insulin production and its impact on effector cells (myocytes, adipocytes, and hepatocytes), glucose transport to the inside of the cells gets increased while reducing blood glucose level. This is achieved by an increased translocation of the insulin-dependent glucose carriers (GLUT), with GLUT-4 being found in skeletal muscle, hepatocytes, and adipocytes [4].

When glucose concentration exceeds 30 mM in the small intestine, glucose transport to the inside of the pancreatic β cells is initiated in an insulin-independent way *via* GLUT2 (**Figure 1**). GLUT2 facilitates transport with a concentration gradient. Inside the cell, glucose is converted into glucose-6-phosphate, which prevents the equalization of glucose levels and sustained transport to the cell. Glucose-6-phosphate enters the glycolysis, which results in the production of ATP molecules. As a result of a continuous glucose supply, the level of ATP is constantly increasing. This causes an inhibition of the potassium channel with the outflow of K+ ions from the cell being blocked. K+ ions concentration increases inside the cell, which becomes electropositive until the charges on the membrane are aligned and membrane becomes depolarized. Depolarization activates the voltage-dependent calcium channel, promoting the influx of Ca2+ ions to the cell. Ca2+ ions activate the ryanodine channel located in the membrane of insulin-accumulating vesicles, inducing their migration into the cell membrane and releasing their content [5].

#### **2.2 Insulin signaling pathway**

Released insulin participates in many metabolic actions, such as glycogen deposition in liver and skeletal muscles, a stimulation of lipogenesis and inhibition of lipolysis, and repression of gluconeogenesis in liver, but mainly in increased glucose uptake through insulin receptor signaling pathway [6]. Signal transmission from the blood to the inside of the cell is a complicated and strongly integrated process. It begins with binding of the hormone to the insulin receptor (IR), eliciting the large protein signal complex formation just below the surface of the cell membrane around IR's cytoplasmic domains (**Figure 2**) [7]. IRs are heterotetrameric glycoproteins containing two extracellular (α) and two intracellular (β) subunits. They occur mainly on the cell surface of metabolically active tissues like muscles, liver, and fat. The binding of insulin by extracellular subunits leads to IR dimerization, which allows ATP binding to β-subunits [8]. This causes the activation of the catalytic domains of tyrosine kinases in the cytoplasm [9]. In the first stage, there is an autophosphorylation of the receptor followed by phosphorylation of several substrate proteins, where IRS (insulin receptor substrate) proteins seem

**39**

**Figure 2.**

*cellular membrane and glucose inflow.*

**Figure 1.**

*Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake*

*Insulin release. Glucose is transported into β-cells via GLUT2 in an insulin-independent way with concentration gradient. Then, glucose is phosphorylated by glucokinase to glucose-6-phosphate, which allows for its inclusion to metabolic processes and ATP production. Raised ATP level triggers accumulation of K<sup>+</sup>*

*Ca2+ ions inside the cell and consequent release of insulin from vesicles. For details see text.*

*along with membrane depolarization. The latter activates Ca2+ channels, leading to increased concentration of* 

 *ions* 

to be most significant ones. The phosphorylation occurs on tyrosine residues, and then, phosphorylated IRS proteins can trigger two major signaling pathways. First pathway leads from Ras to mitogen-activated kinases (MAPK), being involved in the expression regulation of genes playing a role in cell growth and differentiation.

*Insulin signaling pathway. Insulin attaches to insulin receptors triggering its dimerization and intracellular autophosphorylation of their tyrosine residues, which constitute an attachment for IRS proteins. These molecules also undergo phosphorylation and form a complex with PI3K utilizing SH2 domains. PI3K phosphorylates PIP2, which results in PIP3 formation and activation of PDK1/2. AKT gets phosphorylated and activated by PDK1/2, subsequently eliciting phosphorylation of AS160. The latter is responsible for GLUT4 translocation to* 

*DOI: http://dx.doi.org/10.5772/intechopen.80402*

#### **Figure 1.**

*Blood Glucose Levels*

Carbohydrate metabolism

*Metabolic functions of insulin.*

**Table 1.**

protein involved, among others, in the regulation of carbohydrate and lipid metabolism (**Table 1**). The most important stimulus for insulin production is a postprandial increase of blood glucose level. By increasing insulin production and its impact on effector cells (myocytes, adipocytes, and hepatocytes), glucose transport to the inside of the cells gets increased while reducing blood glucose level. This is achieved by an increased translocation of the insulin-dependent glucose carriers (GLUT), with GLUT-4 being found in skeletal muscle, hepatocytes, and adipocytes [4]. When glucose concentration exceeds 30 mM in the small intestine, glucose transport to the inside of the pancreatic β cells is initiated in an insulin-independent way *via* GLUT2 (**Figure 1**). GLUT2 facilitates transport with a concentration gradient. Inside the cell, glucose is converted into glucose-6-phosphate, which prevents the equalization of glucose levels and sustained transport to the cell. Glucose-6-phosphate enters the glycolysis, which results in the production of ATP molecules. As a result of a continuous glucose supply, the level of ATP is constantly increasing. This causes an inhibition of the potassium channel with the outflow of

**Upregulation Downregulation**

Glycogenolysis Gluconeogenesis

Lipids oxidation Triglycerides breakdown

energy stores release

Transcription of proteins involved in

Glucose uptake via GLUT4 Glycogen synthesis Glycolysis

Triglycerides synthesis Cholesterol synthesis

energy stores generation

Protein metabolism Transcription of proteins involved in

Conversion of pyruvate to acetyl CoA

which becomes electropositive until the charges on the membrane are aligned and membrane becomes depolarized. Depolarization activates the voltage-dependent calcium channel, promoting the influx of Ca2+ ions to the cell. Ca2+ ions activate the ryanodine channel located in the membrane of insulin-accumulating vesicles, inducing their migration into the cell membrane and releasing their content [5].

Released insulin participates in many metabolic actions, such as glycogen deposition in liver and skeletal muscles, a stimulation of lipogenesis and inhibition of lipolysis, and repression of gluconeogenesis in liver, but mainly in increased glucose uptake through insulin receptor signaling pathway [6]. Signal transmission from the blood to the inside of the cell is a complicated and strongly integrated process. It begins with binding of the hormone to the insulin receptor (IR), eliciting the large protein signal complex formation just below the surface of the cell membrane around IR's cytoplasmic domains (**Figure 2**) [7]. IRs are heterotetrameric glycoproteins containing two extracellular (α) and two intracellular (β) subunits. They occur mainly on the cell surface of metabolically active tissues like muscles, liver, and fat. The binding of insulin by extracellular subunits leads to IR dimerization, which allows ATP binding to β-subunits [8]. This causes the activation of the catalytic domains of tyrosine kinases in the cytoplasm [9]. In the first stage, there is an autophosphorylation of the receptor followed by phosphorylation of several substrate proteins, where IRS (insulin receptor substrate) proteins seem

ions concentration increases inside the cell,

**38**

K+

ions from the cell being blocked. K+

Lipid metabolism Fatty acids synthesis

**2.2 Insulin signaling pathway**

*Insulin release. Glucose is transported into β-cells via GLUT2 in an insulin-independent way with concentration gradient. Then, glucose is phosphorylated by glucokinase to glucose-6-phosphate, which allows for its inclusion to metabolic processes and ATP production. Raised ATP level triggers accumulation of K<sup>+</sup> ions along with membrane depolarization. The latter activates Ca2+ channels, leading to increased concentration of Ca2+ ions inside the cell and consequent release of insulin from vesicles. For details see text.*

#### **Figure 2.**

*Insulin signaling pathway. Insulin attaches to insulin receptors triggering its dimerization and intracellular autophosphorylation of their tyrosine residues, which constitute an attachment for IRS proteins. These molecules also undergo phosphorylation and form a complex with PI3K utilizing SH2 domains. PI3K phosphorylates PIP2, which results in PIP3 formation and activation of PDK1/2. AKT gets phosphorylated and activated by PDK1/2, subsequently eliciting phosphorylation of AS160. The latter is responsible for GLUT4 translocation to cellular membrane and glucose inflow.*

to be most significant ones. The phosphorylation occurs on tyrosine residues, and then, phosphorylated IRS proteins can trigger two major signaling pathways. First pathway leads from Ras to mitogen-activated kinases (MAPK), being involved in the expression regulation of genes playing a role in cell growth and differentiation. The second one, phosphatidylinositol 3 kinase (PI3K) pathway, elicits AKT/PKB kinase phosphorylation, and it is responsible for the metabolic action of insulin.

#### **3. PI3K/AKT pathway**

As shown in **Figure 2**, activation of PI3K/AKT pathway starts with binding of IRS proteins via SH2 domains to PI3 kinase regulatory subunits. This results in the activation of PI3K that phosphorylates phosphatidylinositol 4,5-biphosphate (PIP2) to phosphatidylinositol(3,4,5)-triphosphate (PIP3). This, in turn, leads to the activation of PIP3-dependent kinases: PDK-1 and PDK-2 and eventually to the activation of AKT/PKB kinase and atypical PKCs [10]. Subsequently, AKT catalyzes the phosphorylation of AS160 substrate protein that stimulates the translocation of GLUT glucose transporters from the cytoplasmic vesicles onto the cell membrane surface and thereby increases the insulin-dependent transport of glucose into the cell. GLUT4 occurs mainly in the interior of the nonstimulated cell, due to the proper proportion of two actions: slow exocytosis and rapid endocytosis. AS160 increases GLUT4 exocytosis and inhibition of its endocytosis via its downstream target, Rab10, in adipocytes. This results in GLUT4 accumulation in the plasma membrane [11]. Besides the activation of insulin-dependent glucose uptake via GLUT4, AKT has many intracellular targets and mediates numerous metabolic effects. For instance, AKT triggers phosphorylation of glycogen synthase kinase 3 (GSK3), which leads to stimulation of glycogen synthesis in liver and skeletal muscle [12].

#### **4. PI3K/AKT regulation**

The PI3K/AKT pathway is under strict control, and its disturbances are the cause of many diseases, including primarily insulin resistance. Further knowledge of the mechanisms regulating this signaling is one of the most important challenges of modern science. Currently, three specific signaling nodes have been distinguished: (a) IRS proteins, (b) regulatory-PI3K kinase subunits, and (c) kinase isoform Akt/ PKB [13]. Disturbances of any of these nodes are mainly responsible for the reduction of the signal transmission efficiency and related diseases.

#### **4.1 IRS protein node**

IRS family consists of six proteins (IRS1–6), where two representatives, IRS1 and IRS2, are crucial in insulin signaling transduction. IRS proteins show tissuespecific expression and functionality [14]. They have three characteristic domains: (a) pleckstrin homology domain at N-terminus, (b) a phosphotyrosine-binding domain enabling binding to IR in the center, and (c) several sites of phosphorylation on tyrosine and serine residues at C-terminus. After tyrosine residues become phosphorylated, IRS binds by C-terminus domain to molecules containing an Srchomology-2 domain (SH2) [15]. IRS-1 and IRS-2 are widely expressed in all tissues, playing major roles in the maintenance of energy balance: muscle, liver, fat, and pancreatic islets. However, it seems that IRS1 plays the main role in myocytes and adipose tissue, while IRS2 is a key player in hepatocytes and islet cells [16, 17].

Generally, there are three ways allowing the regulation of IRS (**Figure 3**). Crucial control occurs mainly by multiple serine and threonine residues, which may be phosphorylated by different kinases. The phosphorylation of serine residues may inhibit insulin signaling by blocking tyrosine phosphorylation, which is necessary for

**41**

**Figure 3.**

*Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake*

signal transduction. However, the details of this inhibitory mechanism are still not well understood. Indeed, there is a strong correlation among serine phosphorylation, decreased tyrosine phosphorylation, and insulin resistance, which is closely related to abnormalities within PI3K pathway. Most critical enzymes being able to phosphorylate IRS in serine residue are stress-induced kinases like ERK, JNK, and AMPK along with inflammatory kinase IKK and other downstream kinases, such as AKT, atypical PKC isoforms, mTOR, or S6K [18, 19]. Blockage of IRS causes the reduced cell response for stimulation with insulin and formation of insulin resistance, the first step toward diabetes. This inhibitory phosphorylation mostly occurs because of low-grade inflammation state, which is caused by lipid accumulation [20]. Studies on palmitate showed that it significantly decreased the insulin-stimulated Ser phosphorylation of Akt and Tyr phosphorylation of IRS-1 [21]. Some drugs exert similar effect. The prominent example is simvastatin, which is commonly used in the prevention and treatment of cardiovascular diseases. Simvastatin reduces the phosphorylation of insulin-induced IR at Tyr, IRS-1 at Tyr, and AKT at Thr [22, 23]. Therefore, therapy with simvastatin or other statins might be a risk factor for the development of insulin resistance or diabetes. This effect can be decreased by many natural substances like silibinin (principal flavonoid contained in silymarin, a mixture of flavonolignans extracted from *Silybum marianum* seeds). Silibinin prevents PI3K/AKT pathway inhibition by decreasing IRS1 phosphorylation on Tyr [24]. Similar mechanism is typical of PTP1B (protein-tyrosine phosphatase 1B), whose overexpression can inactivate the whole PI3K pathway [25]. Since this protein was found to be overexpressed in insulinsensitive peripheral tissues (fat, muscle) and in hepatic cells during insulin-resistant state, searching for PTP1B inhibitors has become an important area of research in the treatment of impairment of insulin transmission pathway. FYGL (Fudan-Yueyang *G. lucidum* extract) appears to be a promising substance showing PTP1B inhibitory

*to suppress phosphorylation of its tyrosine, which is indispensable for signal transduction.*

*Overview of three major mechanisms affecting IRS-dependent signal transduction. Signaling via IR may be modulated simply by the decreased rate of IRS gene transcription. Second, proteins with PTB domains may compete with IRS for binding to phosphotyrosines of IR. Finally, IRS phosphorylation of serine residue is known* 

activity with weak cell permeability and bioavailability [26, 27].

tyrosine phosphorylation of IR [28, 29].

IRS function can be also regulated by competitively inhibiting the binding of IR to IRS, primarily by proteins containing phosphotyrosine-binding (PTB) domain. One of them, NYGGF4, is highly expressed in obese individuals. Studies on skeletal myotubes showed the reduced insulin-induced phosphorylation of IRS1 at Tyr and Akt phosphorylation at Ser residue without changes in the insulin-stimulated

*DOI: http://dx.doi.org/10.5772/intechopen.80402*

*Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake DOI: http://dx.doi.org/10.5772/intechopen.80402*

#### **Figure 3.**

*Blood Glucose Levels*

muscle [12].

**4. PI3K/AKT regulation**

**4.1 IRS protein node**

**3. PI3K/AKT pathway**

The second one, phosphatidylinositol 3 kinase (PI3K) pathway, elicits AKT/PKB kinase phosphorylation, and it is responsible for the metabolic action of insulin.

As shown in **Figure 2**, activation of PI3K/AKT pathway starts with binding of IRS proteins via SH2 domains to PI3 kinase regulatory subunits. This results in the activation of PI3K that phosphorylates phosphatidylinositol 4,5-biphosphate (PIP2) to phosphatidylinositol(3,4,5)-triphosphate (PIP3). This, in turn, leads to the activation of PIP3-dependent kinases: PDK-1 and PDK-2 and eventually to the activation of AKT/PKB kinase and atypical PKCs [10]. Subsequently, AKT catalyzes the phosphorylation of AS160 substrate protein that stimulates the translocation of GLUT glucose transporters from the cytoplasmic vesicles onto the cell membrane surface and thereby increases the insulin-dependent transport of glucose into the cell. GLUT4 occurs mainly in the interior of the nonstimulated cell, due to the proper proportion of two actions: slow exocytosis and rapid endocytosis. AS160 increases GLUT4 exocytosis and inhibition of its endocytosis via its downstream target, Rab10, in adipocytes. This results in GLUT4 accumulation in the plasma membrane [11]. Besides the activation of insulin-dependent glucose uptake via GLUT4, AKT has many intracellular targets and mediates numerous metabolic effects. For instance, AKT triggers phosphorylation of glycogen synthase kinase 3 (GSK3), which leads to stimulation of glycogen synthesis in liver and skeletal

The PI3K/AKT pathway is under strict control, and its disturbances are the cause of many diseases, including primarily insulin resistance. Further knowledge of the mechanisms regulating this signaling is one of the most important challenges of modern science. Currently, three specific signaling nodes have been distinguished: (a) IRS proteins, (b) regulatory-PI3K kinase subunits, and (c) kinase isoform Akt/ PKB [13]. Disturbances of any of these nodes are mainly responsible for the reduc-

IRS family consists of six proteins (IRS1–6), where two representatives, IRS1 and IRS2, are crucial in insulin signaling transduction. IRS proteins show tissuespecific expression and functionality [14]. They have three characteristic domains: (a) pleckstrin homology domain at N-terminus, (b) a phosphotyrosine-binding domain enabling binding to IR in the center, and (c) several sites of phosphorylation on tyrosine and serine residues at C-terminus. After tyrosine residues become phosphorylated, IRS binds by C-terminus domain to molecules containing an Srchomology-2 domain (SH2) [15]. IRS-1 and IRS-2 are widely expressed in all tissues, playing major roles in the maintenance of energy balance: muscle, liver, fat, and pancreatic islets. However, it seems that IRS1 plays the main role in myocytes and adipose tissue, while IRS2 is a key player in hepatocytes and islet cells [16, 17].

Generally, there are three ways allowing the regulation of IRS (**Figure 3**). Crucial

control occurs mainly by multiple serine and threonine residues, which may be phosphorylated by different kinases. The phosphorylation of serine residues may inhibit insulin signaling by blocking tyrosine phosphorylation, which is necessary for

tion of the signal transmission efficiency and related diseases.

**40**

*Overview of three major mechanisms affecting IRS-dependent signal transduction. Signaling via IR may be modulated simply by the decreased rate of IRS gene transcription. Second, proteins with PTB domains may compete with IRS for binding to phosphotyrosines of IR. Finally, IRS phosphorylation of serine residue is known to suppress phosphorylation of its tyrosine, which is indispensable for signal transduction.*

signal transduction. However, the details of this inhibitory mechanism are still not well understood. Indeed, there is a strong correlation among serine phosphorylation, decreased tyrosine phosphorylation, and insulin resistance, which is closely related to abnormalities within PI3K pathway. Most critical enzymes being able to phosphorylate IRS in serine residue are stress-induced kinases like ERK, JNK, and AMPK along with inflammatory kinase IKK and other downstream kinases, such as AKT, atypical PKC isoforms, mTOR, or S6K [18, 19]. Blockage of IRS causes the reduced cell response for stimulation with insulin and formation of insulin resistance, the first step toward diabetes. This inhibitory phosphorylation mostly occurs because of low-grade inflammation state, which is caused by lipid accumulation [20]. Studies on palmitate showed that it significantly decreased the insulin-stimulated Ser phosphorylation of Akt and Tyr phosphorylation of IRS-1 [21]. Some drugs exert similar effect. The prominent example is simvastatin, which is commonly used in the prevention and treatment of cardiovascular diseases. Simvastatin reduces the phosphorylation of insulin-induced IR at Tyr, IRS-1 at Tyr, and AKT at Thr [22, 23]. Therefore, therapy with simvastatin or other statins might be a risk factor for the development of insulin resistance or diabetes. This effect can be decreased by many natural substances like silibinin (principal flavonoid contained in silymarin, a mixture of flavonolignans extracted from *Silybum marianum* seeds). Silibinin prevents PI3K/AKT pathway inhibition by decreasing IRS1 phosphorylation on Tyr [24]. Similar mechanism is typical of PTP1B (protein-tyrosine phosphatase 1B), whose overexpression can inactivate the whole PI3K pathway [25]. Since this protein was found to be overexpressed in insulinsensitive peripheral tissues (fat, muscle) and in hepatic cells during insulin-resistant state, searching for PTP1B inhibitors has become an important area of research in the treatment of impairment of insulin transmission pathway. FYGL (Fudan-Yueyang *G. lucidum* extract) appears to be a promising substance showing PTP1B inhibitory activity with weak cell permeability and bioavailability [26, 27].

IRS function can be also regulated by competitively inhibiting the binding of IR to IRS, primarily by proteins containing phosphotyrosine-binding (PTB) domain. One of them, NYGGF4, is highly expressed in obese individuals. Studies on skeletal myotubes showed the reduced insulin-induced phosphorylation of IRS1 at Tyr and Akt phosphorylation at Ser residue without changes in the insulin-stimulated tyrosine phosphorylation of IR [28, 29].

Among other IRS modulatory mechanisms, it is worth mentioning about expression regulation of IRS mediated by hyperinsulinemia and other hormones [30]. Anjali et al. showed that FSH (follicle stimulating hormone) induces expression of IRS2 in granulosa cells [31]. Also, some natural medicines like Tangzhiqing formula, a mix of five herbs, modulate IRS expression level in HEPG2 cells (IR1 and IRS2) and L-6 myotubes (IRS1) [32].

#### **4.2 PI3K kinase subunits**

PI3 kinases constitute protein family, which exhibits activity of phosphorylation of lipids and proteins. They are divided into three groups according to their structural features and substrate preferences (**Table 2**). Members of I class are the most crucial in insulin signaling pathway. PI3K-1 are heterodimers made up of regulatory and catalytic subunits. The regulatory subunit is generally referred to as p85. They all have a similar domain structure: SH3 domain, breakpoint cluster region homology (BH), and two SH2 domains with iSH2 (interSH2) domain in between [33]. Signaling is initiated by p85 interacting through the SH2 domain with IRS phosphotyrosine motif. Subsequently, p85 is joined through its iSH2 domain to the adapter binding domain (ABD) of catalytic subunit called p110. Besides ABD, p110 also contains Ras-binding domain (RBD), which is involved in interaction with Ras protein superfamily, C2 and the helical scaffolding domains, along with kinase domain participating in PIP3 formation [34].

p85 protects p110 from degradation by forming a heterodimer. Furthermore, this binding allows p110 translocation to the cell membrane, where catalytic subunit is able to send a signal via phosphorylation of PIP2 to PIP3, a lipid second messenger. Interestingly, p110α is the most prominent one from all PI3K catalytic subunits in insulin-dependent pathway [35]. Cells with its deletion exhibit hyperglycemia and glucose intolerance [36]. While p110β seems to play a secondary role, its presence is necessary for p110α activity and thus maintenance of basal threshold of PIP3 [37, 38]. PIP3 is bound by proteins with PH domain such as AKT and PDK1. This critical event allows further signal transduction to downstream proteins.

In this control node, a few aspects are taken into account. Firstly, signaling via PI3K is critically dependent upon PI3K regulatory subunit with p85 mediating either its restriction or promotion. In cells deprived of upstream stimuli, p85 reduces p110 activity. It is executed through C2 and helical scaffolding domains, which form inhibitory contacts with p85. Furthermore, monomeric p85 binds to phosphorylated sites of IRS, thus blocking p85-p110 heterodimer attached to IRS [39]. p110, another


**43**

*Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake*

essential regulatory molecule, undergoes spatial regulation in some types of human cancer. Studies on HepG2 cells demonstrated that PAQR3 (progestin and adipoQ receptor family member 3) associates with p110α by attracting it to Golgi apparatus, a place of PAQR3 exclusive localization. This event inhibits the interaction between

There are two other possible PI3K activation pathways, both being dependent on ligand-membrane receptor binding. The first mechanism is based on binding the adaptor protein GRB2 to RTK (receptor tyrosine kinase). When GRB2 is already attached to GAB protein, it is allowed to bind p85. By contrast, the second way of PI3K activation is not dependent on p85 subunit. In this scenario, GRB2 binds to SOS, which activates RAS, leading to activation of p110α subunit. In addition, the p110β catalytic subunit may be stimulated in a similar, p85-independent way via G

Another critical regulatory mechanism is associated with the control of PIP3

Last but not least, PI3K dysregulation can be also underlain by gene mutations of p110α and p85 subunits or PI3K negative regulators. For instance, loss of function or deletion of PTEN is known to occur in numerous types of cancer. Therefore, enormous attempts are put into research focused on searching compounds targeting PI3K. The most common PI3K regulators are Wortmannin (steroid fungal metabolite) and LY294002 (morpholine-containing chemical compound) [51]. Moreover, there are multiple members of a new generation of more stable molecules such as SF-1126, CAL101, GSK615, XL147, and PF-4989216, which evoke the suppression of

AKT (also named PKB) occurs in mammals in three isoforms (AKT1, AKT2, and AKT3). Although they share a similar domain structure (N-terminal PH domain, a central kinase domain, and C-terminal domain), AKT isoforms exhibit target specificity and play divergent roles. AKT2 is the most essential in glucose uptake [53]. The PH domain enables AKT to be attracted by PIP3 just as PDK1. After binding to PIP3, AKT undergoes conformational changes that allow revealing the phosphorylation site. While they are in nearby, PDK is able to phosphorylate AKT on Thr308. Nevertheless, for full activation of AKT (besides AKT3), second phosphorylation on Ser residue is necessary (AKT1-Ser473 and Ser-474 AKT2). Ser473 is modified by PDK-2/mTORC2 (mammalian target of rapamycin complex 2) [54]. AKT activation is terminated through the action of PP2 (protein phosphatase 2) and PHLPP (PH domain leucine rich repeat phosphatase), which perform dephosphorylation of

While phosphorylation status of both of these sites is fundamental for AKT activity, there is plethora of other posttranslational modifications affecting its

level. There are several well-known inhibitors which dephosphorylate PIP3 with phosphatase and tensin homolog (PTEN) being the most well-known one. Undoubtedly, PTEN is an intriguing protein for research in the context of diseases with PI3K signaling impairment. For instance, in adipose tissue, it can be blocked by H2S or its precursor, l-cysteine. Diet supplementation of l-cysteine increases PIP3 level and mediates the activation of PI3K, resulting in improvement of glucose metabolism [43, 44]. Expression level of PTEN is also regulated epigenetically in adipocytes via several miRNAs such as miR-21, miR-23a-3p, miR-26a, miR-26b, and miR-181a-5p [45–49]. Another widely known PIP3 inhibitor is SHIP (SH2 containing inositol 5′-phosphatase). SHIP dephosphorylates PIP3 at 5′-inositol position (in contrast to PTEN targeting 3′-inositol position) and inhibits AKT primarily

*DOI: http://dx.doi.org/10.5772/intechopen.80402*

p85a and p110α [40, 41].

protein-coupled receptors [42].

through regulation of its cellular localization [50].

overactive PI3K signaling particularly in cancer [52].

**4.3 Kinase isoform AKT/PKB**

Thr308 and Ser473, respectively [55].

#### **Table 2.** *Classification of PI3K family members.*

*Blood Glucose Levels*

IRS2) and L-6 myotubes (IRS1) [32].

domain participating in PIP3 formation [34].

**Class Members Catalytic** 

Ia PI3Kα

II PI3K-C2α

PI3Kβ PI3Kδ

PI3K-C2β PI3K-C2γ

*Classification of PI3K family members.*

allows further signal transduction to downstream proteins.

**subunit**

Ib PI3Kγ p110γ p101

**4.2 PI3K kinase subunits**

Among other IRS modulatory mechanisms, it is worth mentioning about expression regulation of IRS mediated by hyperinsulinemia and other hormones [30]. Anjali et al. showed that FSH (follicle stimulating hormone) induces expression of IRS2 in granulosa cells [31]. Also, some natural medicines like Tangzhiqing formula, a mix of five herbs, modulate IRS expression level in HEPG2 cells (IR1 and

PI3 kinases constitute protein family, which exhibits activity of phosphorylation of lipids and proteins. They are divided into three groups according to their structural features and substrate preferences (**Table 2**). Members of I class are the most crucial in insulin signaling pathway. PI3K-1 are heterodimers made up of regulatory and catalytic subunits. The regulatory subunit is generally referred to as p85. They all have a similar domain structure: SH3 domain, breakpoint cluster region homology (BH), and two SH2 domains with iSH2 (interSH2) domain in between [33]. Signaling is initiated by p85 interacting through the SH2 domain with IRS phosphotyrosine motif. Subsequently, p85 is joined through its iSH2 domain to the adapter binding domain (ABD) of catalytic subunit called p110. Besides ABD, p110 also contains Ras-binding domain (RBD), which is involved in interaction with Ras protein superfamily, C2 and the helical scaffolding domains, along with kinase

p85 protects p110 from degradation by forming a heterodimer. Furthermore, this binding allows p110 translocation to the cell membrane, where catalytic subunit is able to send a signal via phosphorylation of PIP2 to PIP3, a lipid second messenger. Interestingly, p110α is the most prominent one from all PI3K catalytic subunits in insulin-dependent pathway [35]. Cells with its deletion exhibit hyperglycemia and glucose intolerance [36]. While p110β seems to play a secondary role, its presence is necessary for p110α activity and thus maintenance of basal threshold of PIP3 [37, 38]. PIP3 is bound by proteins with PH domain such as AKT and PDK1. This critical event

In this control node, a few aspects are taken into account. Firstly, signaling via PI3K is critically dependent upon PI3K regulatory subunit with p85 mediating either its restriction or promotion. In cells deprived of upstream stimuli, p85 reduces p110 activity. It is executed through C2 and helical scaffolding domains, which form inhibitory contacts with p85. Furthermore, monomeric p85 binds to phosphorylated sites of IRS, thus blocking p85-p110 heterodimer attached to IRS [39]. p110, another

> **Regulatory subunit**

p50α, p85β, p55γ

Monomeric PtdIns(4)P → PtdIns

p84/87

III PI3K-C3 Vps34 Vps15 PtdIns → PtdIns (3)P3 [77]

p110 (α/β/δ) p85α, p55α,

**Main reaction Reference**

[33]

[33]

[76]

PtdIns(4,5)P2 → PtdIns

PtdIns(4,5)P2 → PtdIns

(3,4,5)P3

(3,4,5)P3

(3,4)P2

**42**

**Table 2.**

essential regulatory molecule, undergoes spatial regulation in some types of human cancer. Studies on HepG2 cells demonstrated that PAQR3 (progestin and adipoQ receptor family member 3) associates with p110α by attracting it to Golgi apparatus, a place of PAQR3 exclusive localization. This event inhibits the interaction between p85a and p110α [40, 41].

There are two other possible PI3K activation pathways, both being dependent on ligand-membrane receptor binding. The first mechanism is based on binding the adaptor protein GRB2 to RTK (receptor tyrosine kinase). When GRB2 is already attached to GAB protein, it is allowed to bind p85. By contrast, the second way of PI3K activation is not dependent on p85 subunit. In this scenario, GRB2 binds to SOS, which activates RAS, leading to activation of p110α subunit. In addition, the p110β catalytic subunit may be stimulated in a similar, p85-independent way via G protein-coupled receptors [42].

Another critical regulatory mechanism is associated with the control of PIP3 level. There are several well-known inhibitors which dephosphorylate PIP3 with phosphatase and tensin homolog (PTEN) being the most well-known one. Undoubtedly, PTEN is an intriguing protein for research in the context of diseases with PI3K signaling impairment. For instance, in adipose tissue, it can be blocked by H2S or its precursor, l-cysteine. Diet supplementation of l-cysteine increases PIP3 level and mediates the activation of PI3K, resulting in improvement of glucose metabolism [43, 44]. Expression level of PTEN is also regulated epigenetically in adipocytes via several miRNAs such as miR-21, miR-23a-3p, miR-26a, miR-26b, and miR-181a-5p [45–49]. Another widely known PIP3 inhibitor is SHIP (SH2 containing inositol 5′-phosphatase). SHIP dephosphorylates PIP3 at 5′-inositol position (in contrast to PTEN targeting 3′-inositol position) and inhibits AKT primarily through regulation of its cellular localization [50].

Last but not least, PI3K dysregulation can be also underlain by gene mutations of p110α and p85 subunits or PI3K negative regulators. For instance, loss of function or deletion of PTEN is known to occur in numerous types of cancer. Therefore, enormous attempts are put into research focused on searching compounds targeting PI3K. The most common PI3K regulators are Wortmannin (steroid fungal metabolite) and LY294002 (morpholine-containing chemical compound) [51]. Moreover, there are multiple members of a new generation of more stable molecules such as SF-1126, CAL101, GSK615, XL147, and PF-4989216, which evoke the suppression of overactive PI3K signaling particularly in cancer [52].

#### **4.3 Kinase isoform AKT/PKB**

AKT (also named PKB) occurs in mammals in three isoforms (AKT1, AKT2, and AKT3). Although they share a similar domain structure (N-terminal PH domain, a central kinase domain, and C-terminal domain), AKT isoforms exhibit target specificity and play divergent roles. AKT2 is the most essential in glucose uptake [53].

The PH domain enables AKT to be attracted by PIP3 just as PDK1. After binding to PIP3, AKT undergoes conformational changes that allow revealing the phosphorylation site. While they are in nearby, PDK is able to phosphorylate AKT on Thr308. Nevertheless, for full activation of AKT (besides AKT3), second phosphorylation on Ser residue is necessary (AKT1-Ser473 and Ser-474 AKT2). Ser473 is modified by PDK-2/mTORC2 (mammalian target of rapamycin complex 2) [54]. AKT activation is terminated through the action of PP2 (protein phosphatase 2) and PHLPP (PH domain leucine rich repeat phosphatase), which perform dephosphorylation of Thr308 and Ser473, respectively [55].

While phosphorylation status of both of these sites is fundamental for AKT activity, there is plethora of other posttranslational modifications affecting its

performance [56]. For instance, oxidation of Cys124 triggered by PDGF-induced (platelet-derived growth factor) ROS leads to the blockage of AKT2 activity [57]. Besides PI3K-dependent activation, AKT may be switched on by alternative modulators. Namely, two groups of uncommon AKT activators are distinguished: tyrosine kinases (e.g., ACK1, SRC, PTK6) and serine/threonine kinases (e.g., TBK1, IKBKE). ACK1, a non-receptor tyrosine kinase, is capable of regulating AKT recruitment to the plasma membrane due to AKT phosphorylation on Tyr176, making it preferentially binding to phosphatidic acid—a membrane phospholipid. This elicits AKT attachment to plasma membrane even in the presence of some specific PI3K inhibitors. The increase of AKT2 activity occurs in many cancers, which may be underlain by auto-activating mutations of ACK1. Another nonreceptor kinase involved in AKT regulation is Src. Its action takes place on Tyr315 and 326. By contrast, PTK6 responds to epidermal growth factor (EGF), whose overexpression is typical of many cancers, via phosphorylating Tyr215 and 326. Modifications triggered by Src and PTK6 are resistant to some popular PI3K inhibitors. The second group of AKT activators, Ser/ Thr kinases, modifies Thr195, Ser378, and Ser473 (TBK1), as well as Ser137, Thr308, and Ser473 (IKBKE). These alternative activation modes may suggest that under some particular conditions, cells can turn on AKT signaling in quick response [58].

Due to the fact that AKT, just like PI3K, is one of the most commonly deregulated molecules in human cancers, AKT inhibitors development constitutes an important field of research. Currently tested molecules utilize two major mechanisms. First group acts as competitors for ATP-binding site of AKT (e.g., GSK690693, GDC-0068, GSK2110183, and GSK2141795). They share features of major pharmacophore with minor differences. The second group is composed of allosteric AKT inhibitors (e.g., 2,3-diphenylquinoxaline and analogs, alkylphospholipids). Many of these molecules are in clinical trial phase and have a potential in the treatment of AKT dysregulations [59].

#### **5. Environmental insulin signaling modulating factors**

The relationship between environmental factors like diet, drugs, lifestyle in general, and PI3K pathway remains undeniable. Herein, we will discuss major agents responsible for PI3K modulation. In terms of mediated effect, they can be divided into two types: insulin sensitizing factors and insulin-resistance inducing factors. They do not usually affect a specific protein, but through their action, they dysregulate the entire pathway and the overall metabolism.

#### **5.1 Factors inducing insulin resistance**

Due to the fact that insulin is one of the key regulators of metabolism, it is not surprising that the most important factor modulating its action is diet. Impairment of PI3K signaling is well known to be connected with obesity. Depending on the tissue, the mechanism of obesity-induced insulin resistance seems to differ, but it is in general connected with lipid overload. In liver and muscles, the most crucial is elevation of FFA level, which is characteristic for the obese. In consequence, toxic lipids, mainly ceramides and diacylglycerol (DAG), do accumulate. The increased amount of ceramides causes PP2A stimulation, which terminates insulin pathway via AKT dephosphorylation. On the other hand, DAG activates PKC isoforms (ε and θ) [60]. The latter ones are able to obstruct signaling either by IRS (muscles) or IR (liver). PKC isoforms activation leads to increased expression of NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells), which takes part

**45**

*Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake*

in inflammatory cell response. Subsequently, NFκB activates pro-inflammatory cytokines and stress-induced serine-threonine kinases like JNK, which are able to block insulin signaling pathway via improper IRS phosphorylation. Furthermore, the increasing concentration of lipids in the cells leads to the aggregation of toxic metabolites derived from the incomplete oxidation, and, as a result, the elevated synthesis of free radicals. This is also correlated with increased activation of stressinduced kinases. In overall, these events lead to PI3K pathway impairment and the

The mechanism of obesity-induced insulin resistance formation in adipose tissue is also related to lipid overload but has a different course. It is connected to the constant enlargement of adipocytes, which along with dysregulation of adipogenesis leads to the introduction of hypoxia. Reduced oxygen supply introduces cellular stress response, which includes activation of stress-induced kinases, pro-inflammatory cytokines, and tissue infiltration by pro-inflammatory macrophages. These events result in low-grade inflammation state characteristic of PI3K impairment. Adipose tissue is not only an energy reservoir but also an active endocrine organ, which produces hormones called adipocytokines. They are sensors of nutritional and metabolic homeostasis. Accumulation of visceral fat and inflammation development alters the secretary profile of adipocytokines. Adipocytes start to send pro-inflammatory signals like TNF-α and interleukin1 (IL1). Other typical insulin resistance-inducing cytokines are resistin and IL-6, which activate proinflammatory pathways of NFκB and JNK kinase, leading to defective response to

While prolonged high-calorie diet undeniably leads to insulin resistance, proper dietary style can be a sensitizing factor as well. There are many diet supplements improving insulin signaling. Herein, we will point out only a few members of this enormous group. For instance, glutamine (Gln) supplementation Gln increases the expression of key PI3K signaling molecules (PI3K, PDK1, and GLUT4) and promotes AKT phosphorylation, GLUT4 translocation, and glucose uptake in the presence of insulin during exposure to hyperglycemia [64]. An epidemic of obesity and numerous side effects of drugs that increase insulin sensitivity has caused the great interest among scientists to search for natural sensitizers. They include dieckol (an extract from a brown seaweed), which enhances translocation of GLUT4 in peripheral tissues [65]. Another seaweed improving glucose uptake is *Gelidium amansii*. It exhibits antihyperglycemic, antioxidant, and antiobesity effects potentially *via* PI3K/AKT/GLUT4 signaling [66]. Also, carnosol, a compound found in spices such as sage or rosemary, increases glucose uptake *via* GLUT4 [67]. Interestingly, it has been proven that 1,25-dihydroxyvitamin D3 (active form of vitamin D3), which is mainly provided with food, can improve glucose uptake and has a potential in acting as an anti-inflammatory factor [68]. It seems that an alternative for typical drugs like metformin or pioglitazone, which cause side effects, may be products containing natural substances like Jiangtang Xiaoke granule. The latter is composed of 10 herbs, and it can significantly increase the expression of vast PI3K proteins in

Components of the diet are not the only ones able to improve the signaling via discussed pathway. Studies on rat model demonstrated that long-term caloric restriction may enhance AKT2-dependent mechanism for improving insulin-stimulated glucose uptake. Moreover, a lot of research has been carried out to indicate

that physical exertion has a positive effect on insulin [70–73].

*DOI: http://dx.doi.org/10.5772/intechopen.80402*

emergence of insulin resistance [60–62].

insulin [63].

**5.2 Insulin-sensitizing factors**

mice even upon hyperglycemia [69].

#### *Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake DOI: http://dx.doi.org/10.5772/intechopen.80402*

*Blood Glucose Levels*

performance [56]. For instance, oxidation of Cys124 triggered by PDGF-induced (platelet-derived growth factor) ROS leads to the blockage of AKT2 activity [57]. Besides PI3K-dependent activation, AKT may be switched on by alternative modulators. Namely, two groups of uncommon AKT activators are distinguished: tyrosine kinases (e.g., ACK1, SRC, PTK6) and serine/threonine kinases (e.g., TBK1, IKBKE). ACK1, a non-receptor tyrosine kinase, is capable of regulating AKT recruitment to the plasma membrane due to AKT phosphorylation on Tyr176, making it preferentially binding to phosphatidic acid—a membrane phospholipid. This elicits AKT attachment to plasma membrane even in the presence of some specific PI3K inhibitors. The increase of AKT2 activity occurs in many cancers, which may be underlain by auto-activating mutations of ACK1. Another nonreceptor kinase involved in AKT regulation is Src. Its action takes place on Tyr315 and 326. By contrast, PTK6 responds to epidermal growth factor (EGF), whose overexpression is typical of many cancers, via phosphorylating Tyr215 and 326. Modifications triggered by Src and PTK6 are resistant to some popular PI3K inhibitors. The second group of AKT activators, Ser/ Thr kinases, modifies Thr195, Ser378, and Ser473 (TBK1), as well as Ser137, Thr308, and Ser473 (IKBKE). These alternative activation modes may suggest that under some

particular conditions, cells can turn on AKT signaling in quick response [58].

lated molecules in human cancers, AKT inhibitors development constitutes an important field of research. Currently tested molecules utilize two major mechanisms. First group acts as competitors for ATP-binding site of AKT (e.g., GSK690693, GDC-0068, GSK2110183, and GSK2141795). They share features of major pharmacophore with minor differences. The second group is composed of allosteric AKT inhibitors (e.g., 2,3-diphenylquinoxaline and analogs, alkylphospholipids). Many of these molecules are in clinical trial phase and have a potential in

the treatment of AKT dysregulations [59].

**5.1 Factors inducing insulin resistance**

**5. Environmental insulin signaling modulating factors**

dysregulate the entire pathway and the overall metabolism.

Due to the fact that AKT, just like PI3K, is one of the most commonly deregu-

The relationship between environmental factors like diet, drugs, lifestyle in general, and PI3K pathway remains undeniable. Herein, we will discuss major agents responsible for PI3K modulation. In terms of mediated effect, they can be divided into two types: insulin sensitizing factors and insulin-resistance inducing factors. They do not usually affect a specific protein, but through their action, they

Due to the fact that insulin is one of the key regulators of metabolism, it is not surprising that the most important factor modulating its action is diet. Impairment of PI3K signaling is well known to be connected with obesity. Depending on the tissue, the mechanism of obesity-induced insulin resistance seems to differ, but it is in general connected with lipid overload. In liver and muscles, the most crucial is elevation of FFA level, which is characteristic for the obese. In consequence, toxic lipids, mainly ceramides and diacylglycerol (DAG), do accumulate. The increased amount of ceramides causes PP2A stimulation, which terminates insulin pathway via AKT dephosphorylation. On the other hand, DAG activates PKC isoforms (ε and θ) [60]. The latter ones are able to obstruct signaling either by IRS (muscles) or IR (liver). PKC isoforms activation leads to increased expression of NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells), which takes part

**44**

in inflammatory cell response. Subsequently, NFκB activates pro-inflammatory cytokines and stress-induced serine-threonine kinases like JNK, which are able to block insulin signaling pathway via improper IRS phosphorylation. Furthermore, the increasing concentration of lipids in the cells leads to the aggregation of toxic metabolites derived from the incomplete oxidation, and, as a result, the elevated synthesis of free radicals. This is also correlated with increased activation of stressinduced kinases. In overall, these events lead to PI3K pathway impairment and the emergence of insulin resistance [60–62].

The mechanism of obesity-induced insulin resistance formation in adipose tissue is also related to lipid overload but has a different course. It is connected to the constant enlargement of adipocytes, which along with dysregulation of adipogenesis leads to the introduction of hypoxia. Reduced oxygen supply introduces cellular stress response, which includes activation of stress-induced kinases, pro-inflammatory cytokines, and tissue infiltration by pro-inflammatory macrophages. These events result in low-grade inflammation state characteristic of PI3K impairment. Adipose tissue is not only an energy reservoir but also an active endocrine organ, which produces hormones called adipocytokines. They are sensors of nutritional and metabolic homeostasis. Accumulation of visceral fat and inflammation development alters the secretary profile of adipocytokines. Adipocytes start to send pro-inflammatory signals like TNF-α and interleukin1 (IL1). Other typical insulin resistance-inducing cytokines are resistin and IL-6, which activate proinflammatory pathways of NFκB and JNK kinase, leading to defective response to insulin [63].

#### **5.2 Insulin-sensitizing factors**

While prolonged high-calorie diet undeniably leads to insulin resistance, proper dietary style can be a sensitizing factor as well. There are many diet supplements improving insulin signaling. Herein, we will point out only a few members of this enormous group. For instance, glutamine (Gln) supplementation Gln increases the expression of key PI3K signaling molecules (PI3K, PDK1, and GLUT4) and promotes AKT phosphorylation, GLUT4 translocation, and glucose uptake in the presence of insulin during exposure to hyperglycemia [64]. An epidemic of obesity and numerous side effects of drugs that increase insulin sensitivity has caused the great interest among scientists to search for natural sensitizers. They include dieckol (an extract from a brown seaweed), which enhances translocation of GLUT4 in peripheral tissues [65]. Another seaweed improving glucose uptake is *Gelidium amansii*. It exhibits antihyperglycemic, antioxidant, and antiobesity effects potentially *via* PI3K/AKT/GLUT4 signaling [66]. Also, carnosol, a compound found in spices such as sage or rosemary, increases glucose uptake *via* GLUT4 [67]. Interestingly, it has been proven that 1,25-dihydroxyvitamin D3 (active form of vitamin D3), which is mainly provided with food, can improve glucose uptake and has a potential in acting as an anti-inflammatory factor [68]. It seems that an alternative for typical drugs like metformin or pioglitazone, which cause side effects, may be products containing natural substances like Jiangtang Xiaoke granule. The latter is composed of 10 herbs, and it can significantly increase the expression of vast PI3K proteins in mice even upon hyperglycemia [69].

Components of the diet are not the only ones able to improve the signaling via discussed pathway. Studies on rat model demonstrated that long-term caloric restriction may enhance AKT2-dependent mechanism for improving insulin-stimulated glucose uptake. Moreover, a lot of research has been carried out to indicate that physical exertion has a positive effect on insulin [70–73].

#### **6. PI3K/AKT pathway impairment**

PI3K pathway impairment is related to many diseases, among which the most common and worth attention are insulin resistance and numerous types of cancers.

Insulin resistance may be defined as a subnormal glucose response to endogenous and/or exogenous insulin. Peripheral tissues are not able to respond to the hormone by increasing glucose uptake from the bloodstream. Initially, pancreatic β-cells are not harmed yet, and in response to high glucose level, they synthesize more and more insulin. However, if this state lasts for a long time, islet cells start to overgrow, and deterioration of their function and/or decline of β-cell mass do occur. As normalization of glucose level does not occur, cells are becoming more and more resistant to insulin simultaneously forming a vicious circle of insulin resistance. The most affected tissues are the most metabolically active ones like liver, muscles, and fat. Although the pathogenesis of insulin resistance is getting better understood, the exact mechanism is still not clear. The causes may be connected to abnormal insulin production, but in most cases, the changes in insulin receptors and their substrates along with defects in post-receptor signaling play the role.

PI3K pathway is one of the most frequently deregulated signaling pathways in human cancers. As it plays an essential role in many biological processes like cell survival, proliferation, migration and differentiation, its dysregulation may result in tumorigenesis. The most common changes are mutations (*PIK3CA*, *AKT1*, and *PTEN*), genes amplification (*PIK3CA*, *AKT1*, and *AKT2*), and loss of expression or deletion of the tumor suppressor PTEN [74]. The highest prevalence of mutations within PI3K pathway is typical of lung cancer, breast cancer, endometrial cancer, and head and neck cancer along with glioblastoma [75].

#### **7. Conclusions**

Insulin is the most crucial agent in glucose metabolism. It stimulates glucose uptake from the bloodstream to peripheral tissues. Furthermore, it is responsible for energy storage through accelerating glycogen synthesis and lipogenesis. In general, it promotes cellular events leading to energy storage and represses processes of energy release (**Figure 4**). Insulin action takes place mainly through PI3K pathway and results not only in metabolic effects but also in mitotic response. Insulin is also

**47**

*Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake*

involved in phenomena connected with cell survival. Multitasking nature of this hormone causes that any abnormality in its signal transmission can result in serious consequences, such as diabetes and cancer. These two diseases are the scourge of the modern world. The steadily increasing percentage of people suffering from insulin resistance or full-blown diabetes and the high incidence of cancer have caused scientists to focus on seeking therapeutic goals that may contribute to the prevention or treatment of these disorders. In insulin-resistance, the main target constitutes the improvement of insulin sensitivity. Among common approaches, it is worth to highlight two of them: increasing fatty acids oxidation and elongation of IR activation state by blocking PTP1B activity. Promising therapeutic targets seem to be also pro-inflammatory cytokines and other proteins involved in inflammation response. On the other hand, cancer cells show mainly hyperactivity of PI3K pathway and the increased glucose uptake. Therefore, it seems that blockage of impaired signal transduction may contribute to suppression of the growth of the tumor. For this reason, intensive search for selective inhibitors or silencers of the insulin pathway are underway. Conducting further research may become the basis for the development of new methods of prevention and more effective treatment strategies for these diseases.

This paper was supported by a grant no. 503/2-159-01/503-21-002 from the Medical University of Lodz and by The Polish Society of Metabolic Disease.

The authors declare that there is no conflict of interest regarding the publication

*DOI: http://dx.doi.org/10.5772/intechopen.80402*

**Acknowledgements**

**Conflict of interest**

**List of abbreviation**

ABD adapter binding domain ACK-1 activated CDC42 kinase 1

EGF epidermal growth factor

FSH follicle stimulating hormone FYGL Fudan-Yueyang *G. lucidum* extract GAB GRB2-associated binding protein GLUT1–4 glucose transporter type 1–4 GSK3 glycogen synthase kinase 3

HEPG2 human liver cancer cell line

IRS insulin receptor substrate JNK c-Jun N-terminal kinase

IKK IκB kinase IR insulin receptor

AMPK 5'AMP-activated protein kinase AS160 Akt substrate of 160 kDa

ERK extracellular signal-regulated kinase

GRB2 growth factor receptor-bound protein 2

IKBKE inhibitor of nuclear factor kappa-B kinase subunit epsilon

BH domain breakpoint cluster region homology domain

AKT (PKB) protein kinase B

of this paper.

**Figure 4.** *Critical actions and pathways controlled by insulin.*

#### *Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake DOI: http://dx.doi.org/10.5772/intechopen.80402*

involved in phenomena connected with cell survival. Multitasking nature of this hormone causes that any abnormality in its signal transmission can result in serious consequences, such as diabetes and cancer. These two diseases are the scourge of the modern world. The steadily increasing percentage of people suffering from insulin resistance or full-blown diabetes and the high incidence of cancer have caused scientists to focus on seeking therapeutic goals that may contribute to the prevention or treatment of these disorders. In insulin-resistance, the main target constitutes the improvement of insulin sensitivity. Among common approaches, it is worth to highlight two of them: increasing fatty acids oxidation and elongation of IR activation state by blocking PTP1B activity. Promising therapeutic targets seem to be also pro-inflammatory cytokines and other proteins involved in inflammation response. On the other hand, cancer cells show mainly hyperactivity of PI3K pathway and the increased glucose uptake. Therefore, it seems that blockage of impaired signal transduction may contribute to suppression of the growth of the tumor. For this reason, intensive search for selective inhibitors or silencers of the insulin pathway are underway. Conducting further research may become the basis for the development of new methods of prevention and more effective treatment strategies for these diseases.

### **Acknowledgements**

*Blood Glucose Levels*

**7. Conclusions**

**6. PI3K/AKT pathway impairment**

along with defects in post-receptor signaling play the role.

and head and neck cancer along with glioblastoma [75].

PI3K pathway impairment is related to many diseases, among which the most common and worth attention are insulin resistance and numerous types of cancers. Insulin resistance may be defined as a subnormal glucose response to endogenous and/or exogenous insulin. Peripheral tissues are not able to respond to the hormone by increasing glucose uptake from the bloodstream. Initially, pancreatic β-cells are not harmed yet, and in response to high glucose level, they synthesize more and more insulin. However, if this state lasts for a long time, islet cells start to overgrow, and deterioration of their function and/or decline of β-cell mass do occur. As normalization of glucose level does not occur, cells are becoming more and more resistant to insulin simultaneously forming a vicious circle of insulin resistance. The most affected tissues are the most metabolically active ones like liver, muscles, and fat. Although the pathogenesis of insulin resistance is getting better understood, the exact mechanism is still not clear. The causes may be connected to abnormal insulin production, but in most cases, the changes in insulin receptors and their substrates

PI3K pathway is one of the most frequently deregulated signaling pathways in human cancers. As it plays an essential role in many biological processes like cell survival, proliferation, migration and differentiation, its dysregulation may result in tumorigenesis. The most common changes are mutations (*PIK3CA*, *AKT1*, and *PTEN*), genes amplification (*PIK3CA*, *AKT1*, and *AKT2*), and loss of expression or deletion of the tumor suppressor PTEN [74]. The highest prevalence of mutations within PI3K pathway is typical of lung cancer, breast cancer, endometrial cancer,

Insulin is the most crucial agent in glucose metabolism. It stimulates glucose uptake from the bloodstream to peripheral tissues. Furthermore, it is responsible for energy storage through accelerating glycogen synthesis and lipogenesis. In general, it promotes cellular events leading to energy storage and represses processes of energy release (**Figure 4**). Insulin action takes place mainly through PI3K pathway and results not only in metabolic effects but also in mitotic response. Insulin is also

**46**

**Figure 4.**

*Critical actions and pathways controlled by insulin.*

This paper was supported by a grant no. 503/2-159-01/503-21-002 from the Medical University of Lodz and by The Polish Society of Metabolic Disease.

#### **Conflict of interest**

The authors declare that there is no conflict of interest regarding the publication of this paper.

#### **List of abbreviation**



#### **Author details**

Ewa Świderska1 \*, Justyna Strycharz1 , Adam Wróblewski1 , Janusz Szemraj1 , Józef Drzewoski<sup>2</sup> and Agnieszka Śliwińska<sup>3</sup>

1 Department of Medical Biochemistry, Medical University of Lodz, Lodz, Poland

2 Central Teaching Hospital of the Medical University of Lodz, Lodz, Poland

3 Department of Nucleic Acids Biochemistry, Medical University of Lodz, Lodz, Poland

\*Address all correspondence to: ewa.swiderska@stud.umed.lodz.pl

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**49**

*Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake*

[10] Manna P, Jain SK. PIP3 but not PIP2 increases GLUT4 surface expression and glucose metabolism mediated by AKT/PKCzeta/lambda phosphorylation in 3T3L1 adipocytes. Molecular and Cellular Biochemistry.

[11] Sano H, Eguez L, Teruel MN, Fukuda M, Chuang TD, Chavez JA, et al. Rab10, a target of the AS160 Rab GAP, is required for insulin-stimulated translocation of GLUT4 to the adipocyte plasma membrane. Cell Metabolism.

[12] Friedrichsen M, Birk JB, Richter EA, Ribel-Madsen R, Pehmoller C, Hansen BF, et al. Akt2 influences glycogen synthase activity in human skeletal muscle through regulation of NH(2) terminal (sites 2 + 2a) phosphorylation. American Journal of Physiology. Endocrinology and Metabolism.

2013;**381**(1-2):291-299

2007;**5**(4):293-303

2013;**304**(6):E631-E639

[15] Gustafson TA, He W, Craparo A, Schaub CD, O'Neill TJ. Phosphotyrosine-dependent

1995;**15**(5):2500-2508

2006;**7**(2):85-96

[13] Taniguchi CM, Emanuelli B, Kahn CR. Critical nodes in signalling pathways: Insights into insulin action. Nature Reviews. Molecular Cell Biology.

[14] Cai D, Dhe-Paganon S, Melendez PA, Lee J, Shoelson SE. Two new substrates in insulin signaling, IRS5/DOK4 and IRS6/DOK5. The Journal of Biological Chemistry. 2003;**278**(28):25323-25330

interaction of SHC and insulin receptor substrate 1 with the NPEY motif of the insulin receptor via a novel non-SH2 domain. Molecular and Cellular Biology.

[16] Thirone ACP, Huang C, Klip A. Tissue-specific roles of IRS proteins in insulin signaling and glucose

*DOI: http://dx.doi.org/10.5772/intechopen.80402*

[1] Banting FG, Best CH. The internal secretion of the pancreas. The Journal of Laboratory and Clinical Medicine.

biosynthesis: Evidence for a precursor. Science. 1967;**157**(3789):697-700

[3] Dodson G, Steiner D. The role of assembly in insulin's biosynthesis. Current Opinion in Structural Biology.

[4] Olson AL, Pessin JE. Structure, function, and regulation of the mammalian facilitative glucose

of Nutrition. 1996;**16**:235-256

transporter gene family. Annual Review

[5] Kellett GL, Brot-Laroche E, Mace OJ, Leturque A. Sugar absorption in the intestine: The role of GLUT2. Annual Review of Nutrition. 2008;**28**:35-54

[6] Newsholme EA, Dimitriadis G. Integration of biochemical and physiologic effects of insulin on glucose metabolism. Experimental and Clinical Endocrinology & Diabetes. 2001;**109**(Suppl 2):S122-S134

[7] Ullrich A, Schlessinger J. Signal transduction by receptors with tyrosine kinase activity. Cell. 1990;**61**(2):203-212

[8] Perlman R, Bottaro DP, White MF, Kahn CR. Conformational changes in the alpha- and beta-subunits of the insulin receptor identified by anti-peptide antibodies. The Journal of Biological Chemistry.

1989;**264**(15):8946-8950

1992;**267**(32):23290-23294

[9] Baron V, Kaliman P, Gautier N, Van Obberghen E. The insulin receptor activation process involves localized conformational changes. The Journal of Biological Chemistry.

[2] Steiner DF, Cunningham D, Spigelman L, Aten B. Insulin

1922;**7**(5):251-266

**References**

1998;**8**(2):189-194

*Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake DOI: http://dx.doi.org/10.5772/intechopen.80402*

#### **References**

*Blood Glucose Levels*

NYGGF4 (PID1)

MAPK mitogen-activated protein kinase mTOR mammalian target of rapamycin kinase mTORC2 mammalian target of rapamycin complex 2

PDGF platelet-derived growth factor

PH domain pleckstrin homology domain

PKC protein kinase C PP2 protein phosphatase 2

PAQR3 progestin and adipoQ receptor family member 3

PHLPP PH domain leucine rich repeat phosphatase PI3K phosphatidylinositol-4,5-bisphosphate 3-kinase

PIP2 phosphatidylinositol 4,5-bisphosphate PIP3 phosphatidylinositol (3,4,5)-trisphosphate

SHIP SH2-containing inositol 5′-phosphatase

SRC proto-oncogene tyrosine-protein kinase Src

SOS son of sevenless, guanine nucleotide exchange factor

PTB domain phosphotyrosine-binding domain PTB1 polypyrimidine tract binding protein-1 PTEN phosphatase and tensin homolog

PTK6 tyrosine-protein kinase 6 PTP1B protein-tyrosine phosphatase 1B

RBD Ras-binding domain ROS reactive oxygen species S6K ribosomal S6 kinase SH2 domain Src-homology-2 domain

TBK1 TANK binding kinase 1

PDK1 pyruvate dehydrogenase lipoamide kinase isozyme 1

**48**

Poland

**Author details**

Ewa Świderska1

Józef Drzewoski<sup>2</sup>

provided the original work is properly cited.

\*, Justyna Strycharz1

and Agnieszka Śliwińska<sup>3</sup>

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

1 Department of Medical Biochemistry, Medical University of Lodz, Lodz, Poland

3 Department of Nucleic Acids Biochemistry, Medical University of Lodz, Lodz,

2 Central Teaching Hospital of the Medical University of Lodz, Lodz, Poland

\*Address all correspondence to: ewa.swiderska@stud.umed.lodz.pl

, Adam Wróblewski1

phosphotyrosine interaction domain-containing protein 1

, Janusz Szemraj1

,

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[3] Dodson G, Steiner D. The role of assembly in insulin's biosynthesis. Current Opinion in Structural Biology. 1998;**8**(2):189-194

[4] Olson AL, Pessin JE. Structure, function, and regulation of the mammalian facilitative glucose transporter gene family. Annual Review of Nutrition. 1996;**16**:235-256

[5] Kellett GL, Brot-Laroche E, Mace OJ, Leturque A. Sugar absorption in the intestine: The role of GLUT2. Annual Review of Nutrition. 2008;**28**:35-54

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[7] Ullrich A, Schlessinger J. Signal transduction by receptors with tyrosine kinase activity. Cell. 1990;**61**(2):203-212

[8] Perlman R, Bottaro DP, White MF, Kahn CR. Conformational changes in the alpha- and beta-subunits of the insulin receptor identified by anti-peptide antibodies. The Journal of Biological Chemistry. 1989;**264**(15):8946-8950

[9] Baron V, Kaliman P, Gautier N, Van Obberghen E. The insulin receptor activation process involves localized conformational changes. The Journal of Biological Chemistry. 1992;**267**(32):23290-23294

[10] Manna P, Jain SK. PIP3 but not PIP2 increases GLUT4 surface expression and glucose metabolism mediated by AKT/PKCzeta/lambda phosphorylation in 3T3L1 adipocytes. Molecular and Cellular Biochemistry. 2013;**381**(1-2):291-299

[11] Sano H, Eguez L, Teruel MN, Fukuda M, Chuang TD, Chavez JA, et al. Rab10, a target of the AS160 Rab GAP, is required for insulin-stimulated translocation of GLUT4 to the adipocyte plasma membrane. Cell Metabolism. 2007;**5**(4):293-303

[12] Friedrichsen M, Birk JB, Richter EA, Ribel-Madsen R, Pehmoller C, Hansen BF, et al. Akt2 influences glycogen synthase activity in human skeletal muscle through regulation of NH(2) terminal (sites 2 + 2a) phosphorylation. American Journal of Physiology. Endocrinology and Metabolism. 2013;**304**(6):E631-E639

[13] Taniguchi CM, Emanuelli B, Kahn CR. Critical nodes in signalling pathways: Insights into insulin action. Nature Reviews. Molecular Cell Biology. 2006;**7**(2):85-96

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[31] Anjali G, Kaur S, Lakra R, Taneja J, Kalsey GS, Nagendra A, et al. FSH stimulates IRS-2 expression in human granulosa cells through cAMP/ SP1, an inoperative FSH action in PCOS patients. Cellular Signalling. 2015;**27**(12):2452-2466

[32] Gao J, Li J, An Y, Liu X, Qian Q, Wu Y, et al. Increasing effect of Tangzhiqing formula on IRS-1-dependent PI3K/ AKT signaling in muscle. BMC Complementary and Alternative Medicine. 2014;**14**:198

[33] Fruman DA. Regulatory subunits of class IA PI3K. Current Topics in Microbiology and Immunology. 2010;**346**:225-244

[34] Jimenez C, Hernandez C, Pimentel B, Carrera AC. The p85 regulatory subunit controls sequential activation of phosphoinositide 3-kinase by Tyr kinases and Ras. The Journal of Biological Chemistry. 2002;**277**(44):41556-41562

[35] Bi L, Okabe I, Bernard DJ, Wynshaw-Boris A, Nussbaum RL. Proliferative defect and embryonic lethality in mice homozygous for a deletion in the p110alpha subunit of phosphoinositide 3-kinase. The Journal of Biological Chemistry. 1999;**274**(16):10963-10968

[36] Nelson VL, Jiang YP, Dickman KG, Ballou LM, Lin RZ. Adipose tissue insulin resistance due to loss of PI3K p110alpha leads to decreased energy expenditure and obesity. American Journal of Physiology. Endocrinology and Metabolism. 2014;**306**(10):E1205-E1216

[37] Yu J, Zhang Y, McIlroy J, Rordorf-Nikolic T, Orr GA, Backer JM. Regulation of the p85/p110 phosphatidylinositol 3′-kinase: Stabilization and inhibition of the p110alpha catalytic subunit by the p85 regulatory subunit. Molecular and Cellular Biology. 1998;**18**(3):1379-1387

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[45] Ling HY, Hu B, Hu XB, Zhong J, Feng SD, Qin L, et al. MiRNA-21 reverses high glucose and high insulin induced insulin resistance in 3T3-L1 adipocytes through targeting phosphatase and tensin homologue. Experimental and Clinical Endocrinology & Diabetes: Official Journal, German Society of Endocrinology [and] German Diabetes Association. 2012;**120**(9):553-559

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[48] Li G, Ning C, Ma Y, Jin L, Tang Q, Li X, et al. miR-26b promotes 3T3-L1 adipocyte differentiation through targeting PTEN. DNA and Cell Biology. 2017;**36**(8):672-681

[49] Lozano-Bartolome J, Llaurado G, Portero-Otin M, Altuna-Coy A, Rojo-Martinez G, Vendrell J, et al. Altered expression of miR-181a-5p and miR-23a-3p is associated with obesity and TNFalpha-induced insulin resistance. The Journal of Clinical Endocrinology and Metabolism. 2018;**103**(4):1447-1458

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[52] Maira SM, Stauffer F, Schnell C, Garcia-Echeverria C. PI3K inhibitors for cancer treatment: Where do we stand? Biochemical Society Transactions. 2009;**37**(Pt 1:265-272

[53] Hanada M, Feng J, Hemmings BA. Structure, regulation and function of PKB/AKT—A major therapeutic target. Biochimica et Biophysica Acta. 2004;**1697**(1-2):3-16

[54] Guertin DA, Stevens DM, Thoreen CC, Burds AA, Kalaany NY, Moffat J, et al. Ablation in mice of the mTORC components raptor, rictor, or mLST8 reveals that mTORC2 is required for signaling to Akt-FOXO and PKCalpha, but not S6K1. Developmental Cell. 2006;**11**(6):859-871

[55] Chen R, Kim O, Yang J, Sato K, Eisenmann KM, McCarthy J, et al. Regulation of Akt/PKB activation by tyrosine phosphorylation. The Journal of Biological Chemistry. 2001;**276**(34):31858-31862

[56] Risso G, Blaustein M, Pozzi B, Mammi P, Srebrow A. Akt/PKB: One kinase, many modifications. The Biochemical Journal. 2015;**468**(2):203-214

[57] Wani R, Qian J, Yin L, Bechtold E, King SB, Poole LB, et al. Isoformspecific regulation of Akt by PDGFinduced reactive oxygen species.

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protein kinase B (AKT)/glucose transporter 4 (GLUT4) signaling pathway. Medical Science Monitor.

[65] Kang J, Ge C, Yu L, Li L, Ma H. Long-term administration of dehydroepiandrosterone accelerates glucose catabolism via activation of PI3K/Akt-PFK-2 signaling pathway in rats fed a high-fat diet. PLoS ONE.

[66] Choi J, Kim KJ, Koh EJ, Lee BY. *Gelidium elegans* extract ameliorates type 2 diabetes via regulation of MAPK and PI3K/Akt signaling. Nutrients.

Vlachogiannis IA, MacPherson REK, Tsiani E. Carnosol increases skeletal muscle cell glucose uptake via AMPKdependent GLUT4 glucose transporter translocation. International Journal of Molecular Sciences. 2018;**19**(5):1321

[68] Jin W, Cui B, Li P, Hua F, Lv X, Zhou J, et al. 1,25-Dihydroxyvitamin D3 protects obese rats from metabolic syndrome via promoting regulatory T cell-mediated resolution of

inflammation. International Journal of Molecular Sciences. 2018;**8**(2):178-187

[69] Yu N, Fang X, Zhao D, Mu Q, Zuo J, Ma Y, et al. Anti-diabetic effects of Jiang Tang Xiao Ke granule via PI3K/Akt signalling pathway in Type 2 diabetes KKAy mice. PLoS ONE.

[70] Cao S, Li B, Yi X, Chang B, Zhu B, Lian Z, et al. Effects of exercise on AMPK signaling and downstream components to PI3K in rat with type 2 diabetes. PLoS ONE. 2012;**7**(12):e51709

[71] Cao SC, Zhao G, Chang B, Zhang H. Effects of exercise on expression and phosphorylation of PI3K and PKB in insulin signaling in the skeletal muscles of type 2 diabetic rats. Nan fang yi ke da xue xue bao = Journal

2017;**12**(1):e0168980

[67] Vlavcheski F, Baron D,

2018;**24**:1241-1250

2016;**11**(7):e0159077

2018;**10**(1):51

*DOI: http://dx.doi.org/10.5772/intechopen.80402*

Proceedings of the National Academy of Sciences of the United States of America. 2011;**108**(26):10550-10555

[58] Mahajan K, Mahajan NP. PI3Kindependent AKT activation in cancers: A treasure trove for novel therapeutics.

[59] Nitulescu GM, Margina D, Juzenas P, Peng Q, Olaru OT, Saloustros E, et al. Akt inhibitors in cancer

treatment: The long journey from drug discovery to clinical use (review). International Journal of Oncology.

Journal of Cellular Physiology.

[60] Szendroedi J, Yoshimura T, Phielix E, Koliaki C, Marcucci M, Zhang D, et al. Role of diacylglycerol activation of PKCtheta in lipid-induced muscle insulin resistance in humans. Proceedings of the National Academy of Sciences of the United States of

[61] Birkenfeld AL, Shulman GI. Nonalcoholic fatty liver disease, hepatic insulin resistance, and type 2 diabetes. Hepatology. 2014;**59**(2):

[62] Goetze S, Blaschke F, Stawowy P, Bruemmer D, Spencer C, Graf K, et al. TNFalpha inhibits insulin's antiapoptotic signaling in vascular smooth muscle cells. Biochemical and Biophysical Research Communications.

2012;**227**(9):3178-3184

2016;**48**(3):869-885

America. 2014;**111**(26):

2001;**287**(3):662-670

[63] Stafeev IS, Vorotnikov AV, Ratner EI, Menshikov MY,

Parfyonova YV. Latent inflammation and insulin resistance in adipose tissue. International Journal of Endocrinology. 2017;**2017**:5076732

[64] Wang C, Deng Y, Yue Y, Chen W, Zhang Y, Shi G, et al. Glutamine

phosphatidylinositol-3-kinase (PI3K)/

enhances the hypoglycemic effect of insulin in L6 cells via

9597-9602

713-723

*Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake DOI: http://dx.doi.org/10.5772/intechopen.80402*

Proceedings of the National Academy of Sciences of the United States of America. 2011;**108**(26):10550-10555

*Blood Glucose Levels*

serine/threonine protein kinase (AKT)/protein kinase Czeta/lambda (PKCzeta/lambda) in 3T3l1 adipocytes. The Journal of Biological Chemistry.

The Journal of Clinical Endocrinology and Metabolism. 2018;**103**(4):1447-1458

[50] Carver DJ, Aman MJ, Ravichandran KS. SHIP inhibits Akt activation in B cells through regulation of Akt membrane localization. Blood.

2000;**96**(4):1449-1456

1995;**20**(8):303-307

2009;**37**(Pt 1:265-272

2004;**1697**(1-2):3-16

2006;**11**(6):859-871

[51] Ui M, Okada T, Hazeki K, Hazeki O. Wortmannin as a unique probe for an intracellular signalling protein, phosphoinositide 3-kinase. Trends in Biochemical Sciences.

[52] Maira SM, Stauffer F, Schnell C, Garcia-Echeverria C. PI3K inhibitors for cancer treatment: Where do we stand? Biochemical Society Transactions.

[53] Hanada M, Feng J, Hemmings BA. Structure, regulation and function of PKB/AKT—A major therapeutic target. Biochimica et Biophysica Acta.

[54] Guertin DA, Stevens DM, Thoreen CC, Burds AA, Kalaany NY, Moffat J, et al. Ablation in mice of the mTORC components raptor, rictor, or mLST8 reveals that mTORC2 is required for signaling to Akt-FOXO and PKCalpha, but not S6K1. Developmental Cell.

[55] Chen R, Kim O, Yang J, Sato K, Eisenmann KM, McCarthy J, et al. Regulation of Akt/PKB activation by tyrosine phosphorylation. The Journal of Biological Chemistry. 2001;**276**(34):31858-31862

[56] Risso G, Blaustein M, Pozzi B, Mammi P, Srebrow A. Akt/PKB: One kinase, many modifications.

[57] Wani R, Qian J, Yin L, Bechtold E, King SB, Poole LB, et al. Isoformspecific regulation of Akt by PDGFinduced reactive oxygen species.

The Biochemical Journal. 2015;**468**(2):203-214

[44] Manna P, Jain SK. L-cysteine and hydrogen sulfide increase PIP3 and AMPK/PPARgamma expression and decrease ROS and vascular inflammation markers in high glucose treated human U937 monocytes. Journal of Cellular Biochemistry.

2011;**286**(46):39848-39859

2013;**114**(10):2334-2345

2012;**120**(9):553-559

[46] Seeger T, Fischer A, Muhly-Reinholz M, Zeiher AM, Dimmeler S. Long-term inhibition of miR-21 leads to reduction of obesity in db/db mice. Obesity (Silver Spring, Md). 2014;**22**(11):2352-2360

[47] Xu G, Ji C, Song G, Zhao C, Shi C, Song L, et al. MiR-26b modulates insulin sensitivity in adipocytes by interrupting the PTEN/PI3K/AKT pathway. International Journal of Obesity (2005). 2015;**39**(10):

[48] Li G, Ning C, Ma Y, Jin L, Tang Q, Li X, et al. miR-26b promotes 3T3-L1 adipocyte differentiation through targeting PTEN. DNA and Cell Biology.

[49] Lozano-Bartolome J, Llaurado G, Portero-Otin M, Altuna-Coy A, Rojo-Martinez G, Vendrell J, et al. Altered expression of miR-181a-5p and miR-23a-3p is associated with obesity and TNFalpha-induced insulin resistance.

[45] Ling HY, Hu B, Hu XB, Zhong J, Feng SD, Qin L, et al. MiRNA-21 reverses high glucose and high insulin induced insulin resistance in 3T3-L1 adipocytes through targeting phosphatase and tensin homologue. Experimental and Clinical Endocrinology & Diabetes: Official Journal, German Society of Endocrinology [and] German Diabetes Association.

**52**

1523-1530

2017;**36**(8):672-681

[58] Mahajan K, Mahajan NP. PI3Kindependent AKT activation in cancers: A treasure trove for novel therapeutics. Journal of Cellular Physiology. 2012;**227**(9):3178-3184

[59] Nitulescu GM, Margina D, Juzenas P, Peng Q, Olaru OT, Saloustros E, et al. Akt inhibitors in cancer treatment: The long journey from drug discovery to clinical use (review). International Journal of Oncology. 2016;**48**(3):869-885

[60] Szendroedi J, Yoshimura T, Phielix E, Koliaki C, Marcucci M, Zhang D, et al. Role of diacylglycerol activation of PKCtheta in lipid-induced muscle insulin resistance in humans. Proceedings of the National Academy of Sciences of the United States of America. 2014;**111**(26): 9597-9602

[61] Birkenfeld AL, Shulman GI. Nonalcoholic fatty liver disease, hepatic insulin resistance, and type 2 diabetes. Hepatology. 2014;**59**(2): 713-723

[62] Goetze S, Blaschke F, Stawowy P, Bruemmer D, Spencer C, Graf K, et al. TNFalpha inhibits insulin's antiapoptotic signaling in vascular smooth muscle cells. Biochemical and Biophysical Research Communications. 2001;**287**(3):662-670

[63] Stafeev IS, Vorotnikov AV, Ratner EI, Menshikov MY, Parfyonova YV. Latent inflammation and insulin resistance in adipose tissue. International Journal of Endocrinology. 2017;**2017**:5076732

[64] Wang C, Deng Y, Yue Y, Chen W, Zhang Y, Shi G, et al. Glutamine enhances the hypoglycemic effect of insulin in L6 cells via phosphatidylinositol-3-kinase (PI3K)/ protein kinase B (AKT)/glucose transporter 4 (GLUT4) signaling pathway. Medical Science Monitor. 2018;**24**:1241-1250

[65] Kang J, Ge C, Yu L, Li L, Ma H. Long-term administration of dehydroepiandrosterone accelerates glucose catabolism via activation of PI3K/Akt-PFK-2 signaling pathway in rats fed a high-fat diet. PLoS ONE. 2016;**11**(7):e0159077

[66] Choi J, Kim KJ, Koh EJ, Lee BY. *Gelidium elegans* extract ameliorates type 2 diabetes via regulation of MAPK and PI3K/Akt signaling. Nutrients. 2018;**10**(1):51

[67] Vlavcheski F, Baron D, Vlachogiannis IA, MacPherson REK, Tsiani E. Carnosol increases skeletal muscle cell glucose uptake via AMPKdependent GLUT4 glucose transporter translocation. International Journal of Molecular Sciences. 2018;**19**(5):1321

[68] Jin W, Cui B, Li P, Hua F, Lv X, Zhou J, et al. 1,25-Dihydroxyvitamin D3 protects obese rats from metabolic syndrome via promoting regulatory T cell-mediated resolution of inflammation. International Journal of Molecular Sciences. 2018;**8**(2):178-187

[69] Yu N, Fang X, Zhao D, Mu Q, Zuo J, Ma Y, et al. Anti-diabetic effects of Jiang Tang Xiao Ke granule via PI3K/Akt signalling pathway in Type 2 diabetes KKAy mice. PLoS ONE. 2017;**12**(1):e0168980

[70] Cao S, Li B, Yi X, Chang B, Zhu B, Lian Z, et al. Effects of exercise on AMPK signaling and downstream components to PI3K in rat with type 2 diabetes. PLoS ONE. 2012;**7**(12):e51709

[71] Cao SC, Zhao G, Chang B, Zhang H. Effects of exercise on expression and phosphorylation of PI3K and PKB in insulin signaling in the skeletal muscles of type 2 diabetic rats. Nan fang yi ke da xue xue bao = Journal

of Southern Medical University. 2010;**30**(6):1217-1221

[72] Liu Y, Liu C, Lu ML, Tang FT, Hou XW, Yang J, et al. Vibration exercise decreases insulin resistance and modulates the insulin signaling pathway in a type 2 diabetic rat model. International Journal of Clinical and Experimental Medicine. 2015;**8**(8):13136-13144

[73] Maarbjerg SJ, Sylow L, Richter EA. Current understanding of increased insulin sensitivity after exercise— Emerging candidates. Acta Physiologica. 2011;**202**(3):323-335

[74] Li A, Qiu M, Zhou H, Wang T, Guo W. PTEN, insulin resistance and cancer. Current Pharmaceutical Design. 2017;**23**(25):3667-3676

[75] Faes S, Dormond O. PI3K and AKT: Unfaithful partners in cancer. International Journal of Molecular Sciences. 2015;**16**(9):21138-21152

[76] Falasca M, Maffucci T. Regulation and cellular functions of class II phosphoinositide 3-kinases. The Biochemical Journal. 2012;**443**(3):587-601

[77] Backer JM. The regulation and function of Class III PI3Ks: Novel roles for Vps34. The Biochemical Journal. 2008;**410**(1):1-17

**55**

**Chapter 4**

**Abstract**

Cardiovascular and Biochemical

The objective of this study was to assess the cardiovascular and biochemical responses during aerobic exercise recuperation in diabetic rats. There were utilized 12 animals, of 60 days, divided in two groups: control and diabetic. On the test day, the animals performed a 60 minutes' session of predominantly aerobic exercise, using an overload of 6% of their body's weight. After and before the exercise, the animals had their systolic blood pressure (SBP) and heart rate (HR), lactate, glycerol and glucose measured. The animals were trained during 30 days by swimming tank, with an extra weight equivalent to 4% extra weight a 40-min session. A decrease in glucose value occurred in the diabetic animals after exercising, as well as an increase of lactate in the same group. 1', 3', 5' and 7' after the exercise, a significant reduction of HR in the diabetic group was noticed when compared with the control group, such behavior was also observed with double product (DP) together with SBP values 1', 3' and 5' after the exercise. The diabetic animals' recovery has been possibly affected by a reduction of blood flow and a reduction

Diabetes mellitus (DM) is a complication that triggers problems to public health all around the world [1]. It most frequently type, diabetes mellitus type 2 (T2DM), face to hyperglycemia impact, may evolve to cardiovascular, neuromuscular and degenerative complications [2], being able to rise considerably the morbidity and

During DM complications' evolution, cardiac dysfunctions or diabetic cardiomyopathies occur, independent of the presence of vascular diseases, arteriosclerosis or heart attack [4, 5]. The development of diabetic condition alters the hemodynamic balance and, as a consequence, triggers a reduction of physical capacities of

With regard to the muscular system, a good functioning of it causes the action of insulin which connects itself to its receptor leading to the phosphorylation of its tyrosine receptor to the substrate of the insulin's receptor (IRS-1 and 2). IRS-1 and 2 mediate the effects over glucose metabolism, through the activation of

of energetic substrates contribution, as well as lactate clearance.

**Keywords:** exercise, glycemia, recuperation

**1. Introduction**

mortality [3].

the organism [6, 7].

Recuperation in Diabetic Rats

Responses in Exercise

*Luiz Augusto da Silva, Jéssica Wouk and* 

*Vinicius Muller Reis Weber*

#### **Chapter 4**

*Blood Glucose Levels*

2010;**30**(6):1217-1221

2015;**8**(8):13136-13144

2011;**202**(3):323-335

2017;**23**(25):3667-3676

of Southern Medical University.

[72] Liu Y, Liu C, Lu ML, Tang FT, Hou XW, Yang J, et al. Vibration exercise decreases insulin resistance and modulates the insulin signaling pathway in a type 2 diabetic rat model. International Journal of Clinical and Experimental Medicine.

[73] Maarbjerg SJ, Sylow L, Richter EA. Current understanding of increased insulin sensitivity after exercise— Emerging candidates. Acta Physiologica.

[74] Li A, Qiu M, Zhou H, Wang T, Guo W. PTEN, insulin resistance and cancer. Current Pharmaceutical Design.

[75] Faes S, Dormond O. PI3K and AKT: Unfaithful partners in cancer. International Journal of Molecular Sciences. 2015;**16**(9):21138-21152

[76] Falasca M, Maffucci T. Regulation

[77] Backer JM. The regulation and function of Class III PI3Ks: Novel roles for Vps34. The Biochemical Journal.

2008;**410**(1):1-17

and cellular functions of class II phosphoinositide 3-kinases. The Biochemical Journal. 2012;**443**(3):587-601

**54**

## Cardiovascular and Biochemical Responses in Exercise Recuperation in Diabetic Rats

*Luiz Augusto da Silva, Jéssica Wouk and Vinicius Muller Reis Weber*

#### **Abstract**

The objective of this study was to assess the cardiovascular and biochemical responses during aerobic exercise recuperation in diabetic rats. There were utilized 12 animals, of 60 days, divided in two groups: control and diabetic. On the test day, the animals performed a 60 minutes' session of predominantly aerobic exercise, using an overload of 6% of their body's weight. After and before the exercise, the animals had their systolic blood pressure (SBP) and heart rate (HR), lactate, glycerol and glucose measured. The animals were trained during 30 days by swimming tank, with an extra weight equivalent to 4% extra weight a 40-min session. A decrease in glucose value occurred in the diabetic animals after exercising, as well as an increase of lactate in the same group. 1', 3', 5' and 7' after the exercise, a significant reduction of HR in the diabetic group was noticed when compared with the control group, such behavior was also observed with double product (DP) together with SBP values 1', 3' and 5' after the exercise. The diabetic animals' recovery has been possibly affected by a reduction of blood flow and a reduction of energetic substrates contribution, as well as lactate clearance.

**Keywords:** exercise, glycemia, recuperation

#### **1. Introduction**

Diabetes mellitus (DM) is a complication that triggers problems to public health all around the world [1]. It most frequently type, diabetes mellitus type 2 (T2DM), face to hyperglycemia impact, may evolve to cardiovascular, neuromuscular and degenerative complications [2], being able to rise considerably the morbidity and mortality [3].

During DM complications' evolution, cardiac dysfunctions or diabetic cardiomyopathies occur, independent of the presence of vascular diseases, arteriosclerosis or heart attack [4, 5]. The development of diabetic condition alters the hemodynamic balance and, as a consequence, triggers a reduction of physical capacities of the organism [6, 7].

With regard to the muscular system, a good functioning of it causes the action of insulin which connects itself to its receptor leading to the phosphorylation of its tyrosine receptor to the substrate of the insulin's receptor (IRS-1 and 2). IRS-1 and 2 mediate the effects over glucose metabolism, through the activation of

phosphatidylinositol (PI)-3 kinase, PKA/AKt and the increase of glucose transporter type 4 (GLUT4), from intracellular compartments into plasma membrane. However, the non-functioning of the insulin's receptor with its respective hormone cause its resistance over the cell, in that way, glucose metabolism does not occur [8, 9], what entails blood's hyperglycemia and fatigue of the skeletal muscle involved.

It is well accepted that physical exercise may be related to the enhancement of insulin sensibility, GLUT4 expression and to the glycogen synthase enzyme activity in muscular cells of patients with DMT2, and that this stimulus may remain for up to 48 h [10, 11]. The physical exercise causes important changes in glucose homeostasis, actuating in specific proteins such as adenosine monophosphate-activated protein kinase (AMPK) that assists in the stimulus of liberation of glucose transporter 4 (GLUT4) of its cellular vesicles, in order to actuate in the glucose's input in the cell [12]. In this way, the exercise might rapidly decrease the glucose level in hyperglycemia condition.

There is the necessity of comprehending the way in which physical exercise may act in the physiological behavior of the organism, and the cardiovascular and biochemical responses bring along directions to understand how the organism reacts to physical exercise, in detriment of training variables as volume and intensity. In this way, the objective of this study was to evaluate the cardiovascular and biochemical responses during the recovering of aerobic exercise in diabetic rats.

#### **2. Material and methods**

#### **2.1 Animals**

Twelve male Wistar rats at 60 days of age were used in the study. The animals were kept in cages with controlled temperature (23 ± 2°C) and humidity (55 ± 10% humidity), and a light/dark cycle of 12 h. This study was approved by the Ethics Committee of research studies using animals (015/2015 Protocol).

#### **2.2 Diabetes induction and experimental design**

The animals were divided into two groups: [1] control (weights of 393 ± 44 g), [2] diabetic (weights of 308 ± 40 g). Alloxan (ALX) (Sigma, St. Louis, USA) dissolved in sodium chloride solution (0.9%) was administered intraperitoneally (ip) (120 mg/kg), after 12 h of fasting. Rats with fasting BG values between 150 and 250 mg/dL were considered diabetic. With 90 days old, the animals were submitted to an oral glucose tolerance test (OGTT) to verify their glycemic curve. Thus, a maximal exercise test (MET) was performed to evaluate the biochemical (glucose, lactate and glycerol) and cardiovascular (HR and SBP) responses before and after the exercise.

#### **2.3 Effort exercise test and training**

All animals were adapted to an aquatic environment to be able to swim during the test, through one daily session of 10 min, for 7 days prior to the experiment. On testing days, the animals performed a 60-min session of predominantly aerobic exercise by carrying an extra weight equivalent to 6% of their body weight in a swimming tank with 40 cm in depth, 70 cm in diameter, and water heated to 30 ± 1°C, according to the protocol proposed by Gobatto et al. [13]

Post testing, the animals were trained during 30 days by swimming tank, with an extra weight equivalent to 4% extra weight a 40-min session, according to the

**57**

*Cardiovascular and Biochemical Responses in Exercise Recuperation in Diabetic Rats*

procedures were always conducted at the same time of the day (08:00 am).

protocol modified proposed by Scariot et al. [14]. Exercise sessions and laboratory

Blood was collected from the tail vein in animals that fasted for 12 h to a posterior glucose analysis. These animals subsequently received one single dose of glucose (1 mg/kg of body weight) by gavage, and new blood samples were collected at times 30, 60, and 120 min. Blood glucose levels were determined in a glucometer

Blood glucose, lactate, and glycerol doses were performed in a glucometer (ACCU-CHEK® Active®) using approximately 25 μl of blood collected through

Heart rate values (HR) and systolic blood pressure (SBP) were obtained using a tail plethysmograph that transmitted data to a software that codified the results (Insight®, Ribeirão Preto, Brazil). In order to adapt animals to this device, it was attached to animals' tails three times a day for 5 days before the test. On test day, HR and SBP were obtained in triplicate for all animals, by the same evaluator, before and after treatments and prior to exercise. The Double Product index was used as an

All results are presented as mean ± E.P.M. Statistical analysis was performed using a Student's t-test for unpaired sample or one-way ANOVA. Values were considered statistically significant based on *P* < 0.05. The post hoc Student-Newman-Keuls test was used, when appropriate, to identify differences between groups.

**Figure 1** represents the blood glucose values during OGTT of the rats from different groups. The glycemic curve was significantly higher to the diabetic group, when comparing with the values related to the controls and diabetes post trained

**Figure 2** represents the blood glucose values before and after exercise. The glucose values were significantly different between control and diabetes groups, and intragroup a significant reduction occurred to the diabetic group after exercising (*P* < 0.05). Furthermore, the glucose post training, pre and post exercise was

smaller than the same diabetes group pre-training (*P* < 0.05).

DP = Systolic pressure × Heart rate (1)

indirect indicator of the cardiac work, calculated through the formula:

*DOI: http://dx.doi.org/10.5772/intechopen.79084*

caudal puncture, before and after the effort test.

**2.4 Oral glucose tolerance test**

(Accu-chek Advantage®).

**2.5 Biochemical analyses**

**2.6 Cardiovascular analyses**

**2.7 Statistical analyses**

**3.1 Oral glucose tolerance test**

**3.2 Biochemical responses**

groups at times 0, 30, 60 and 120 min.

**3. Results**

protocol modified proposed by Scariot et al. [14]. Exercise sessions and laboratory procedures were always conducted at the same time of the day (08:00 am).

#### **2.4 Oral glucose tolerance test**

*Blood Glucose Levels*

hyperglycemia condition.

**2. Material and methods**

**2.1 Animals**

the exercise.

phosphatidylinositol (PI)-3 kinase, PKA/AKt and the increase of glucose transporter type 4 (GLUT4), from intracellular compartments into plasma membrane. However, the non-functioning of the insulin's receptor with its respective hormone cause its resistance over the cell, in that way, glucose metabolism does not occur [8, 9], what entails blood's hyperglycemia and fatigue of the skeletal muscle involved. It is well accepted that physical exercise may be related to the enhancement of insulin sensibility, GLUT4 expression and to the glycogen synthase enzyme activity in muscular cells of patients with DMT2, and that this stimulus may remain for up to 48 h [10, 11]. The physical exercise causes important changes in glucose homeostasis, actuating in specific proteins such as adenosine monophosphate-activated protein kinase (AMPK) that assists in the stimulus of liberation of glucose transporter 4 (GLUT4) of its cellular vesicles, in order to actuate in the glucose's input in the cell [12]. In this way, the exercise might rapidly decrease the glucose level in

There is the necessity of comprehending the way in which physical exercise may act in the physiological behavior of the organism, and the cardiovascular and biochemical responses bring along directions to understand how the organism reacts to physical exercise, in detriment of training variables as volume and intensity. In this way, the objective of this study was to evaluate the cardiovascular and biochemical

Twelve male Wistar rats at 60 days of age were used in the study. The animals were kept in cages with controlled temperature (23 ± 2°C) and humidity (55 ± 10% humidity), and a light/dark cycle of 12 h. This study was approved by the Ethics

The animals were divided into two groups: [1] control (weights of 393 ± 44 g), [2] diabetic (weights of 308 ± 40 g). Alloxan (ALX) (Sigma, St. Louis, USA) dissolved in sodium chloride solution (0.9%) was administered intraperitoneally (ip) (120 mg/kg), after 12 h of fasting. Rats with fasting BG values between 150 and 250 mg/dL were considered diabetic. With 90 days old, the animals were submitted to an oral glucose tolerance test (OGTT) to verify their glycemic curve. Thus, a maximal exercise test (MET) was performed to evaluate the biochemical (glucose, lactate and glycerol) and cardiovascular (HR and SBP) responses before and after

All animals were adapted to an aquatic environment to be able to swim during the test, through one daily session of 10 min, for 7 days prior to the experiment. On testing days, the animals performed a 60-min session of predominantly aerobic exercise by carrying an extra weight equivalent to 6% of their body weight in a swimming tank with 40 cm in depth, 70 cm in diameter, and water heated to

Post testing, the animals were trained during 30 days by swimming tank, with an extra weight equivalent to 4% extra weight a 40-min session, according to the

responses during the recovering of aerobic exercise in diabetic rats.

Committee of research studies using animals (015/2015 Protocol).

30 ± 1°C, according to the protocol proposed by Gobatto et al. [13]

**2.2 Diabetes induction and experimental design**

**2.3 Effort exercise test and training**

**56**

Blood was collected from the tail vein in animals that fasted for 12 h to a posterior glucose analysis. These animals subsequently received one single dose of glucose (1 mg/kg of body weight) by gavage, and new blood samples were collected at times 30, 60, and 120 min. Blood glucose levels were determined in a glucometer (Accu-chek Advantage®).

#### **2.5 Biochemical analyses**

Blood glucose, lactate, and glycerol doses were performed in a glucometer (ACCU-CHEK® Active®) using approximately 25 μl of blood collected through caudal puncture, before and after the effort test.

#### **2.6 Cardiovascular analyses**

Heart rate values (HR) and systolic blood pressure (SBP) were obtained using a tail plethysmograph that transmitted data to a software that codified the results (Insight®, Ribeirão Preto, Brazil). In order to adapt animals to this device, it was attached to animals' tails three times a day for 5 days before the test. On test day, HR and SBP were obtained in triplicate for all animals, by the same evaluator, before and after treatments and prior to exercise. The Double Product index was used as an indirect indicator of the cardiac work, calculated through the formula:

DP = Systolic pressure × Heart rate (1)

#### **2.7 Statistical analyses**

All results are presented as mean ± E.P.M. Statistical analysis was performed using a Student's t-test for unpaired sample or one-way ANOVA. Values were considered statistically significant based on *P* < 0.05. The post hoc Student-Newman-Keuls test was used, when appropriate, to identify differences between groups.

### **3. Results**

#### **3.1 Oral glucose tolerance test**

**Figure 1** represents the blood glucose values during OGTT of the rats from different groups. The glycemic curve was significantly higher to the diabetic group, when comparing with the values related to the controls and diabetes post trained groups at times 0, 30, 60 and 120 min.

#### **3.2 Biochemical responses**

**Figure 2** represents the blood glucose values before and after exercise. The glucose values were significantly different between control and diabetes groups, and intragroup a significant reduction occurred to the diabetic group after exercising (*P* < 0.05). Furthermore, the glucose post training, pre and post exercise was smaller than the same diabetes group pre-training (*P* < 0.05).

#### **Figure 1.**

*Oral glucose tolerance test results of control and diabetes groups rats pre and post 30 days of training. The data represent the average ± E.P.M, n = 6, (a,b,c) difference letters = P < 0.05 (Student-Newman-Keuls after one-way ANOVA).*

#### **Figure 2.**

*Plasma concentration of glucose levels before and after the exercise protocol and 30 days of training. The data represent the average ± E.P.M, n = 6, \* = P < 0.05 when compared with the control group, # = P < 0.05 when compared with the same group,* & *= P < 0.05 when compared with the same group post-training (Student-Newman-Keuls after one-way ANOVA).*

**Figure 3** represents the glycerol and lactate values before and after exercise. No difference was observed in glycerol values between groups. Concerning the lactate values, a significant difference occurred between groups, both for pre and posttraining and diabetes pre-training groups.

#### **3.3 Cardiovascular responses**

**Figure 4** represents the HR, SBP and double product in rats of different groups. No statistical difference was noticed concerning the hemodynamic measures during resting. 1, 3, 5 and 7 min after the exercise, a significant reduction of HR in the diabetic group was noticed when compared with the control group, such behavior was also observed with DP together with SBP values 1, 3 and 5 min after the exercise. After 30 days of training, the diabetes and control groups maintained their HR similar between the time of 1, 4, 5 and 7 min, being that they were different

**59**

**4. Discussion**

**Figure 3.**

exercise with the intensity in question.

related to the diseases [16].

animal to face physical stress.

*Cardiovascular and Biochemical Responses in Exercise Recuperation in Diabetic Rats*

from their respective groups before the training. Significant reduction of SBP and DP values was observed for the control group after training compared to the same

*Plasma concentration of (A) lactate and (B) glycerol levels after the exercise protocol pre and post 30 days of training. The data represent the average ± E.P.M, n = 6, \* = P < 0.05 when compared with the control group, # = P < 0.05 when compared with the same group (Student-Newman-Keuls after one-way ANOVA).*

This study demonstrates that the HR analysis post-exercise presents intensity and performance information as well as the physical condition of the organism. The relation between the recuperation time and HR must be characterized, investigated and explained in order to obtain a better understanding of the whole picture, in other words, the clinical condition or hemodynamic/metabolic balance to the

The HR revealed a better recuperation in the diabetic animals, what may be related to the quantity of muscle present in these animals. According to Polito and Farinatti [15], this happens because in dynamic exercises, a greater volumetric load occurs in the left ventricle and the cardiac and hemodynamic responses are proportional to the intensity and to the muscular mass involved in this activity. In this case, this event would trigger a reduction of muscular mass in these animals due to the metabolic deregulation and consequent atrophy displayed in this clinical condition

The lactate increased after exercise in diabetic animals compared to the healthy ones, what would have related to the muscular metabolic capacity, because with a smaller consumption of glucose due to its reduced input in the muscle, the utilization of existent substrates or reutilization of resulting metabolites that derive lactate is necessary [17], in this situation, a better recuperation and a greater lactate removal from bloodstreams occurs, that demonstrates a better capacity of the

The heart of a patient with a diabetic condition has lower metabolic capacity because the main glucose capturer in cardiac muscle is also GLUT-4 [17], tending to have a lower response to recuperation after exercising due to the minor consumption of glucose. Some conditions associated with this response, such as the metabolic acidosis, general fatigue and reduction of neuronal function are due to hyperglycemia [18], causing a reduction of prompt reply to exercise in the body's systems. Although this phase of exercise may be starting to be investigated, the results still diverge about the necessary time to a total restoration to the rest levels after exercise, and the autonomic nervous system (ANS) might be involved in this event

group (*P* < 0.05). The diabetic groups did not show significant differences.

*DOI: http://dx.doi.org/10.5772/intechopen.79084*

*Cardiovascular and Biochemical Responses in Exercise Recuperation in Diabetic Rats DOI: http://dx.doi.org/10.5772/intechopen.79084*

**Figure 3.**

*Blood Glucose Levels*

**Figure 1.**

**Figure 2.**

*one-way ANOVA).*

**58**

**Figure 3** represents the glycerol and lactate values before and after exercise. No difference was observed in glycerol values between groups. Concerning the lactate values, a significant difference occurred between groups, both for pre and post-

 *= P < 0.05 when compared with the same group post-training (Student-*

*Plasma concentration of glucose levels before and after the exercise protocol and 30 days of training. The data represent the average ± E.P.M, n = 6, \* = P < 0.05 when compared with the control group, # = P < 0.05 when* 

*Oral glucose tolerance test results of control and diabetes groups rats pre and post 30 days of training. The data represent the average ± E.P.M, n = 6, (a,b,c) difference letters = P < 0.05 (Student-Newman-Keuls after* 

**Figure 4** represents the HR, SBP and double product in rats of different groups. No statistical difference was noticed concerning the hemodynamic measures during resting. 1, 3, 5 and 7 min after the exercise, a significant reduction of HR in the diabetic group was noticed when compared with the control group, such behavior was also observed with DP together with SBP values 1, 3 and 5 min after the exercise. After 30 days of training, the diabetes and control groups maintained their HR similar between the time of 1, 4, 5 and 7 min, being that they were different

training and diabetes pre-training groups.

&

**3.3 Cardiovascular responses**

*compared with the same group,* 

*Newman-Keuls after one-way ANOVA).*

*Plasma concentration of (A) lactate and (B) glycerol levels after the exercise protocol pre and post 30 days of training. The data represent the average ± E.P.M, n = 6, \* = P < 0.05 when compared with the control group, # = P < 0.05 when compared with the same group (Student-Newman-Keuls after one-way ANOVA).*

from their respective groups before the training. Significant reduction of SBP and DP values was observed for the control group after training compared to the same group (*P* < 0.05). The diabetic groups did not show significant differences.

#### **4. Discussion**

This study demonstrates that the HR analysis post-exercise presents intensity and performance information as well as the physical condition of the organism. The relation between the recuperation time and HR must be characterized, investigated and explained in order to obtain a better understanding of the whole picture, in other words, the clinical condition or hemodynamic/metabolic balance to the exercise with the intensity in question.

The HR revealed a better recuperation in the diabetic animals, what may be related to the quantity of muscle present in these animals. According to Polito and Farinatti [15], this happens because in dynamic exercises, a greater volumetric load occurs in the left ventricle and the cardiac and hemodynamic responses are proportional to the intensity and to the muscular mass involved in this activity. In this case, this event would trigger a reduction of muscular mass in these animals due to the metabolic deregulation and consequent atrophy displayed in this clinical condition related to the diseases [16].

The lactate increased after exercise in diabetic animals compared to the healthy ones, what would have related to the muscular metabolic capacity, because with a smaller consumption of glucose due to its reduced input in the muscle, the utilization of existent substrates or reutilization of resulting metabolites that derive lactate is necessary [17], in this situation, a better recuperation and a greater lactate removal from bloodstreams occurs, that demonstrates a better capacity of the animal to face physical stress.

The heart of a patient with a diabetic condition has lower metabolic capacity because the main glucose capturer in cardiac muscle is also GLUT-4 [17], tending to have a lower response to recuperation after exercising due to the minor consumption of glucose. Some conditions associated with this response, such as the metabolic acidosis, general fatigue and reduction of neuronal function are due to hyperglycemia [18], causing a reduction of prompt reply to exercise in the body's systems.

Although this phase of exercise may be starting to be investigated, the results still diverge about the necessary time to a total restoration to the rest levels after exercise, and the autonomic nervous system (ANS) might be involved in this event

#### **Figure 4.**

*Heart rate (A), systolic blood pressure (B), and double product (C) pre and post exercise in control and diabetes group rats pre and post 30 days of training. The data represent the average ± E.P.M, n = 6, (a,b,c) difference letters = P < 0.05 (Student-Newman-Keuls after one-way ANOVA).*

[19–21]. The time spent to the HR to return to resting levels depends on the interaction between the autonomic functions, the level of physical conditioning and the exercise intensity as well [22]. Evaluation post-effort show a hypotension after exercise in a gradual way, as it can be observed in the healthy animals [23]; however, the ANS reduced the resting values of the diabetic animals, demonstrating a failure in the hemodynamic involvement to a muscular recuperation and a desirable lactate removal, what could be hindered with the reduction of the bloodstream [24] due to the diabetic condition, demonstrating that after exercise complication are visible.

**61**

*Cardiovascular and Biochemical Responses in Exercise Recuperation in Diabetic Rats*

What must be observed is the recuperation of the diabetic animals that was harmed by a possible reduction of bloodstream, a reduction in the contribution of energetic substrates, as well as a lactate removal, that demonstrate the effects of the diseases upon the organism. This information demonstrates how homeostasis is unregulated due to a clinical condition that triggers complications in many tissues of the body. Yet, if the progression of the disease is slow, the complication of diabetes would also be reduced and the beginning of its limitations in tissues could

In this way, exercise is an important tool to glucose control for the animals because it may enhance systems that are essential to metabolic balance, such as the skeletal muscle, which has an important function in the movement, increasing the physical capability of the organism to resist to situations that aim to adapt the

This chapter showed which diabetic animals' recovery has been possibly affected by a reduction of blood flow and a reduction of energetic substrates contribution as well as lactate clearance. This information demonstrates how homeostasis is dysregulated due to a clinical condition that triggers complications in several body

The authors are thankful to CAPES (Brazil) and Fundação Araucaria of Paraná

There are no issues to disclose. There is no potential conflict of interest with the

*DOI: http://dx.doi.org/10.5772/intechopen.79084*

be prevented or eliminated.

tissues to a better function.

**Acknowledgements**

**Declaration of interest**

mentioned trademarks.

(Brazil) for the financial support to this study.

**5. Conclusion**

tissues.

*Cardiovascular and Biochemical Responses in Exercise Recuperation in Diabetic Rats DOI: http://dx.doi.org/10.5772/intechopen.79084*

What must be observed is the recuperation of the diabetic animals that was harmed by a possible reduction of bloodstream, a reduction in the contribution of energetic substrates, as well as a lactate removal, that demonstrate the effects of the diseases upon the organism. This information demonstrates how homeostasis is unregulated due to a clinical condition that triggers complications in many tissues of the body. Yet, if the progression of the disease is slow, the complication of diabetes would also be reduced and the beginning of its limitations in tissues could be prevented or eliminated.

In this way, exercise is an important tool to glucose control for the animals because it may enhance systems that are essential to metabolic balance, such as the skeletal muscle, which has an important function in the movement, increasing the physical capability of the organism to resist to situations that aim to adapt the tissues to a better function.

#### **5. Conclusion**

*Blood Glucose Levels*

**60**

**Figure 4.**

[19–21]. The time spent to the HR to return to resting levels depends on the interaction between the autonomic functions, the level of physical conditioning and the exercise intensity as well [22]. Evaluation post-effort show a hypotension after exercise in a gradual way, as it can be observed in the healthy animals [23]; however, the ANS reduced the resting values of the diabetic animals, demonstrating a failure in the hemodynamic involvement to a muscular recuperation and a desirable lactate removal, what could be hindered with the reduction of the bloodstream [24] due to the diabetic condition, demonstrating that after exercise complication are visible.

*Heart rate (A), systolic blood pressure (B), and double product (C) pre and post exercise in control and diabetes group rats pre and post 30 days of training. The data represent the average ± E.P.M, n = 6, (a,b,c)* 

*difference letters = P < 0.05 (Student-Newman-Keuls after one-way ANOVA).*

This chapter showed which diabetic animals' recovery has been possibly affected by a reduction of blood flow and a reduction of energetic substrates contribution as well as lactate clearance. This information demonstrates how homeostasis is dysregulated due to a clinical condition that triggers complications in several body tissues.

#### **Acknowledgements**

The authors are thankful to CAPES (Brazil) and Fundação Araucaria of Paraná (Brazil) for the financial support to this study.

#### **Declaration of interest**

There are no issues to disclose. There is no potential conflict of interest with the mentioned trademarks.

*Blood Glucose Levels*

#### **Author details**

Luiz Augusto da Silva1,2\*, Jéssica Wouk1 and Vinicius Muller Reis Weber1

1 Midwest State University of Paraná, Guarapuava, Paraná, Brazil

2 Physical Education Department, Guaraicá College, Guarapuava, Paraná, Brazil

\*Address all correspondence to: lasilva7@hotmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**63**

*Cardiovascular and Biochemical Responses in Exercise Recuperation in Diabetic Rats*

2010;**69**(1):33-41. DOI: 10.1016/j.

[9] D'Agostino Sr RB, Grundy S, Sullivan LM, et al. Validation of the Framingham coronary heart disease prediction scores: Results of a multiple ethnic groups investigation. Journal of the American Medical Association.

[10] Howarth FC, Al-Ali S, Al-Sheryani S, Al-Dhaheri H, Al-Junaibi SS, Almugaddum FA, et al. Effects of voluntary exercise on heart function in streptozotocin (STZ)-induced diabetic rat. International Journal of Diabetes and Metabolism. 2007;**15**(2):32-37

[11] Greenberg JA, Owen DR, Geliebter A. Decaffeinated coffee and glucose metabolism in young men. Diabetes

[12] Conde SV, Silva TN, Gonzalez C, Carmo MM, Monteiro EC, Guarino MP. Chronic caffeine intake decreases circulating catecholamines and prevents diet-induced insulin resistance and hypertension in rats. The British Journal

of Nutrition. 2012;**107**(1):86-95

[13] Gobatto CA, Mello MAR, Sibuya CY, Azevedo JRM, Santos LA, Kokubun E. Maximal lactate steady state in rats submitted to swimming exercise. Comparative Biochemistry & Physiology Part A. 2001;**130**:21-27

[14] Scariot PP, Manchado-gobatto FB, Torsoni AS, Dos\_reis IM, Beck WR, Gobatto CA. Continuous aerobic training in individualized intensity avoids spontaneous physical activity decline and improves MCT1 expression

Care. 2010;**33**(2):278-280

[8] DeFronzo RA. Current issues in the treatment of type 2 diabetes. Overview of newer agents: Where treatment is going. The American Journal of Medicine. 2010;**123**(3 Suppl):S38-S48

jpsychores.2010.01.021

2001;**286**:180-187

*DOI: http://dx.doi.org/10.5772/intechopen.79084*

[1] American Diabetes Association. Classification and Diagnosis of Diabetes. Diabetes Care. Jan 2016:**39**(Suppl 1):S13-S22

[2] Gujral UP, Mohan V, Pradeepa R, Deepa M, Anjana RM, Mehta NK, Gregg EW, Narayan KM. Ethnic variations in diabetes and prediabetes prevalence and the roles of insulin resistance and β-cell function: The CARRS and NHANES studies. Journal of Clinical & Translational Endocrinology.

[3] Stevens JW, Khunti K, Harvey R, Johnson M, Preston L, Woods HB, Davies M, Goyder E. Preventing the progression to type 2 diabetes mellitus in adults at high risk: A systematic review and network meta-analysis of lifestyle, pharmacological and surgical interventions. Diabetes Research and Clinical Practice. Mar

[4] Qi D, Rodrigues B. Glucocorticoids produce whole body insulin resistance with changes in cardiac metabolism. American Journal of Physiology. Endocrinology and Metabolism.

[5] Malfitano C, de Souza Junior AL, Irigoyen MC. Impact of conditioning hyperglycemic on myocardial infarction rats: Cardiac cell survival factors. World Journal of Cardiology.

[6] Faulkner MS, Quinn L, Fritschi C. Microalbuminuria and heart rate variability in adolescents with diabetes. Journal of Pediatric Health Care. 2010;**24**(1):34-41. DOI: 10.1016/j.

[7] Fritschi C, Quinn L. Fatigue in patients with diabetes: A review. Journal of Psychosomatic Research.

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2016;**4**:19-27

2015;**107**(3):320-331

2007;**292**:E654-E667

2014;**6**(6):449-454

pedhc.2009.01.002

*Cardiovascular and Biochemical Responses in Exercise Recuperation in Diabetic Rats DOI: http://dx.doi.org/10.5772/intechopen.79084*

#### **References**

*Blood Glucose Levels*

**62**

**Author details**

provided the original work is properly cited.

Luiz Augusto da Silva1,2\*, Jéssica Wouk1

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 Physical Education Department, Guaraicá College, Guarapuava, Paraná, Brazil

1 Midwest State University of Paraná, Guarapuava, Paraná, Brazil

\*Address all correspondence to: lasilva7@hotmail.com

and Vinicius Muller Reis Weber1

[1] American Diabetes Association. Classification and Diagnosis of Diabetes. Diabetes Care. Jan 2016:**39**(Suppl 1):S13-S22

[2] Gujral UP, Mohan V, Pradeepa R, Deepa M, Anjana RM, Mehta NK, Gregg EW, Narayan KM. Ethnic variations in diabetes and prediabetes prevalence and the roles of insulin resistance and β-cell function: The CARRS and NHANES studies. Journal of Clinical & Translational Endocrinology. 2016;**4**:19-27

[3] Stevens JW, Khunti K, Harvey R, Johnson M, Preston L, Woods HB, Davies M, Goyder E. Preventing the progression to type 2 diabetes mellitus in adults at high risk: A systematic review and network meta-analysis of lifestyle, pharmacological and surgical interventions. Diabetes Research and Clinical Practice. Mar 2015;**107**(3):320-331

[4] Qi D, Rodrigues B. Glucocorticoids produce whole body insulin resistance with changes in cardiac metabolism. American Journal of Physiology. Endocrinology and Metabolism. 2007;**292**:E654-E667

[5] Malfitano C, de Souza Junior AL, Irigoyen MC. Impact of conditioning hyperglycemic on myocardial infarction rats: Cardiac cell survival factors. World Journal of Cardiology. 2014;**6**(6):449-454

[6] Faulkner MS, Quinn L, Fritschi C. Microalbuminuria and heart rate variability in adolescents with diabetes. Journal of Pediatric Health Care. 2010;**24**(1):34-41. DOI: 10.1016/j. pedhc.2009.01.002

[7] Fritschi C, Quinn L. Fatigue in patients with diabetes: A review. Journal of Psychosomatic Research. 2010;**69**(1):33-41. DOI: 10.1016/j. jpsychores.2010.01.021

[8] DeFronzo RA. Current issues in the treatment of type 2 diabetes. Overview of newer agents: Where treatment is going. The American Journal of Medicine. 2010;**123**(3 Suppl):S38-S48

[9] D'Agostino Sr RB, Grundy S, Sullivan LM, et al. Validation of the Framingham coronary heart disease prediction scores: Results of a multiple ethnic groups investigation. Journal of the American Medical Association. 2001;**286**:180-187

[10] Howarth FC, Al-Ali S, Al-Sheryani S, Al-Dhaheri H, Al-Junaibi SS, Almugaddum FA, et al. Effects of voluntary exercise on heart function in streptozotocin (STZ)-induced diabetic rat. International Journal of Diabetes and Metabolism. 2007;**15**(2):32-37

[11] Greenberg JA, Owen DR, Geliebter A. Decaffeinated coffee and glucose metabolism in young men. Diabetes Care. 2010;**33**(2):278-280

[12] Conde SV, Silva TN, Gonzalez C, Carmo MM, Monteiro EC, Guarino MP. Chronic caffeine intake decreases circulating catecholamines and prevents diet-induced insulin resistance and hypertension in rats. The British Journal of Nutrition. 2012;**107**(1):86-95

[13] Gobatto CA, Mello MAR, Sibuya CY, Azevedo JRM, Santos LA, Kokubun E. Maximal lactate steady state in rats submitted to swimming exercise. Comparative Biochemistry & Physiology Part A. 2001;**130**:21-27

[14] Scariot PP, Manchado-gobatto FB, Torsoni AS, Dos\_reis IM, Beck WR, Gobatto CA. Continuous aerobic training in individualized intensity avoids spontaneous physical activity decline and improves MCT1 expression in oxidative muscle of swimming rats. Frontiers in Physiology. 2016;**7**:132

[15] Polito MD, Farinatti PTV. Respostas de frequência cardíaca, pressão arterial e duplo-produto ao exercício contraresistência: uma revisão da literatura. Revista Portuguesa de Ciências do Desporto. 2003;**3**(1):79-91

[16] Chiu CY, Yang RS, Sheu ML, Chan DC, Yang TH, Tsai KS, Chiang CK, Liu SH. Advanced glycation end-products induce skeletal muscle atrophy and dysfunction in diabetic mice via a RAGE-mediated, AMPK-downregulated, Akt pathway. The Journal of Pathology. 2016;**238**(3):470-482

[17] Nikooie R, Rajabi H, Gharakhanlu R, Atabi F, Omidfar K, Aveseh M, Larijani B. Exercise-induced changes of MCT1 in cardiac and skeletal muscles of diabetic rats induced by high-fat diet and STZ. Journal of Physiology and Biochemistry. 2013;**69**:865-877

[18] Silva MJ, Brodt MD, Lynch MA, McKenzie JA, Tanouye KM, Nyman JS, Wang X. Type 1 diabetes in young rats leads to progressive trabecular bone loss, cessation of cortical bone growth, and diminished whole bone strength and fatigue life. Journal of Bone and Mineral Research. 2009;**24**(9):1618-1627

[19] Freeman JV, Dewey FE, Hadley DM, Myers J, Froelicher VF. Autonomic nervous system interaction with the cardiovascular system during exercise. Progress in Cardiovascular Diseases. Mar–Apr 2006;**48**(5):342-362

[20] Yilmaz OH, Karakulak UN, Tutkun E, Bal C, Gunduzoz M, ErcanOnay E, Ayturk M, TekOzturk M, Alaguney ME. Assessment of cardiac autonomic nervous system in mercury exposed individuals via post-exercise heart rate recovery. Medical Principles and Practice. 2016;**25**(4):343-349. DOI: 10.1159/000445322

[21] Jae SY, Kurl S, Laukkanen JA, Zaccardi F, Choi YH, Fernhall B, Carnethon M, Franklin BA. Exercise heart rate reserve and recovery as predictors of incident type 2 diabetes. American Journal of Medicine. 2016;**129**(5):536

[22] Terziotti P, Schena F, Gulli G, Cevese A. Post-exercise recovery of autonomic cardiovascular control: A study by spectrum and cross-spectrum analysis in humans. European Journal of Applied Physiology. 2001;**84**:187-194

[23] Guasch E, Benito B, Qi X, et al. Atrial fibrillation promotion by endurance exercise: Demonstration and mechanistic exploration in an animal model. Journal of the American College of Cardiology. 2013;**62**(1):68-77

[24] Kuo YR, Wang CT, Wang FS, Chiang YC, Wang CJ. Extracorporeal shock-wave therapy enhanced wound healing via increasing topical blood perfusion and tissue regeneration in a rat model of STZ-induced diabetes. Wound Repair and Regeneration. 2009;**17**(4):522-530

**65**

Section 3

Hypoglycemia
