**8. Prevention of beta cell dysfunction and apoptosis**

Islet beta-cells are almost completely destroyed when patients with type 1 diabetes are diag‐ nosed. To date, insulin substitute therapy is still one of the main treatments. The cure of type 1 diabetes requires beta-cell regeneration from islet cell precursors and prevention of recurring autoimmunity. Therefore, beta-cell replacement, regeneration and proliferation emerge as a new research focus on therapy for type 1 diabetes; however, its application is limited by the shortage of pancreas donors. In-vitro expansion of human cadaveric islet beta cells represents an attractive strategy for generation of abundant beta-like cells. Human beta cells patent a very low proliferation capacity in vivo, and intact isolated islets cultured in suspension do not proliferate, although they remain functional for months. When islets are allowed to attach, limited replication of beta cells can be induced by growth factors or ex‐ tracellular matrix components before the beta-cell phenotype is lost. Previous accepting of the determinants of tissue mass during adult life is still rudimentary. Insights into this prob‐ lem may suggest novel approaches for the treatment of neoplastic as well as degenerative diseases. In the case of the pancreas, elucidating the mechanisms that govern β cell mass will be important for the design of regenerative therapy for both type 1 and type 2 diabetes, diseases characterized by an insufficient mass of β cells. It is clear that β cell mass increase during pregnancy and in insulin-resistant states, but evidence on the ability of β cells to re‐ generate from a severe, diabetogenic injury is conflicting. Whereas autoimmune diabetes is normally irreversible, recent evidence from both humans and rodents suggests that β cell function (i.e., insulin production and the maintenance of glucose homeostasis) can partly re‐ cover if autoimmunity is blocked.

sulin secretion in a glucose-dependent manner. Due to their dependence on ambient glucose for action, they are emerging as important new therapeutic agents to promote insulin secretion without accompanying hypoglycemia (a common complication of sulfonylurea treatment). Unlike sulfonylureas, incretins act by activating Gs (a G-protein that activates adenylyl cy‐ clase) to increase cAMP in beta cells. cAmp, like ATP, is an important signal that regulates insulin release. Typically, the main mechanism of action of cAMP is by activation of an en‐ zyme called protein kinase A (PKA) that, in turn, phosphorylates other substrates to turn on (or off) vital cell functions. Using a biochemical assay called the yeast hybrid screening method to identify and isolate new proteins, some researchers identified a novel protein, cAMP-GEF II, a cAMP sensor (cAMPS) that forms a complex with other intracellular pro‐ teins (Rim2 and Rab3) to directly regulate insulin exocytosis. Then, using molecular reagents that antagonize the effects of cAMPS, they observed that incretin-potentiated insulin secre‐ tion is attenuated. These results provide a mechanism whereby cAMP can directly promote exocytosis of insulin granules without activation of PKA (ie, a PKA-independent pathway),

and thereby provide additional molecular targets for therapeutic intervention.

system but by some other factor, such as cystic fibrosis or pancreatic surgery.

ta-cell mass but rather from an impairment of insulin secretion.

**8. Prevention of beta cell dysfunction and apoptosis**

**Type one diabetes:** Islet beta-cells are almost completely destroyed when patients with type 1 diabetes are diagnosed. Type 1 diabetes occurs when the bodies own immune system de‐ stroys the beta cells. Some people develop a type of diabetes – called secondary diabetes - which is similar to type 1 diabetes, but the beta cells are not destroyed by the immune

**Type two diabetes:** Defects in insulin action and insulin secretion are both present in type 2 diabetes, and both are believed to be genetically predetermined. In the absence of a defect in beta-cell function, individuals can compensate indefinitely for insulin resistance with appro‐ priate hyperinsulinemia, as observed even in obese populations. Both insulin secretion and insulin action are impaired in type 2 diabetes. However, when allowance is made for the hy‐ perglycaemia and the fact that glucose stimulates insulin secretion, it becomes apparent that the insulin levels in diabetic patients are lower than in healthy controls and inadequate betacell function therefore represents a key feature of the disease. Theoretically, the insulin se‐ cretory defect could result from either defects of beta-cell function or a reduction in beta-cell mass. Most quantitative estimates indicate that type 2 diabetes associates with either no change or < 30% reduction in beta-cell mass. Moreover, the secretion defect is more severe than can be accounted for solely by the reduction in beta-cell mass. It therefore appears that the insulin secretory defect in type 2 diabetes does not primarily result from insufficient be‐

Islet beta-cells are almost completely destroyed when patients with type 1 diabetes are diag‐ nosed. To date, insulin substitute therapy is still one of the main treatments. The cure of

**7. Beta cell dysfunction and apoptosis**

120 Type 1 Diabetes

Islet beta-cell regeneration and development are controlled by many growth factors, espe‐ cially insulin-like growth factor-1 (IGF-1). Pancreatic islets produce Igf1 and Igf2, which bind to specific receptors on β-cells. Igf1 has been shown to influence β-cell apoptosis, and both Igf1 and Igf2 increase islet growth; Igf2 does so in a manner additive with fibroblast growth factor 2. Some study showed that IGF-1 can protect beta-cells from the destruction of apoptosis factors and promoting beta-cell survival and proliferation. Interleukin-1beta (IL-1 beta) is a potent pro-inflammatory cytokine that has been shown to inhibit islet beta cell function as well as to activate Fas-mediated apoptosis in a nitric oxide-dependent manner. Furthermore, this cytokine is effective in recruiting lymphocytes that mediate beta cell de‐ struction in type one diabetes. IGF-I has been shown to block IL-1beta actions in vitro.

Glucagon like peptide 1 (GLP-1) is a potent insulin secretagogue released by L-cells of the distal large intestine in response to meal ingestion and, together with glucose-dependent in‐ sulinotropic polypeptide (GIP), account for 90% of the incretin effect. Type 2 diabetic pa‐ tients are characterized by severely impaired β-cell function, reduced plasma GLP-1 response to meal/glucose ingestion that correlates with reduced insulin secretion, and severe β-cell resistance to the stimulatory effect of GLP-1 on insulin secretion. GLP-1 also inhibits glucagon secretion, delays gastric emptying, and promotes weight loss by its appetite-sup‐ pressant effect. GLP-1 analogs also stimulate islet neogenesis and β-cell replication and in‐ hibit islet apoptosis. The gluco-incretin hormones GLP-1 and GIP can protect beta-cell against apoptosis induced by cytokines or glucose and free fatty acids. Both hormones bind to specific Gs-coupled receptors, which trigger cAMPformation. In beta-cells, basal cAMP levels controls glucose competence, i.e., the magnitude of the insulin secretion response to a given increase in extracellular glucose concentration. Increases in cAMP levels, for instance as stimulated by GLP-1 or GIP action, potentiate glucose-stimulated insulin secretion by both protein kinase A (PKA)-dependent and independent mechanisms; they also stimulate gene transcription through PKA dependent phosphorylation of the transcription factor CREB. In beta-cells, increased cAMP levels also activate the MAP kinase cascade, leading to rapid phosphorylation of Erk1/2. An activation of the PI3Kinase/Akt pathway is also ob‐ served. PI3kinase may be directly activated by the ßγ subunit of Gs, be secondary to transac‐ tivation of the EGF receptor by betacellulin, or may follow transcriptional induction of IRS-2 through the PKA/CREB pathway. The IRS- 2/PI3kinase/Akt pathway is known to have antiapoptotic effects; however, it is unclear why increased expression of IRS-2 leads to activa‐ tion of its signaling pathway. IRS-2 may be downstream of the insulin (IR) or IGF-1 (IGF-1R) receptors. Studies of mice with beta-cell specific inactivation of either receptor indicated that the insulin receptor was important for compensatory growth of the beta-cells in response to insulin resistance whereas the IGF-1 receptor was involved in the control of glucose compe‐ tence. Although these properties make GLP-1 an ideal antidiabetic agent, it is rapidly cleaved (*T*1/2 = 1–2 min) by dipeptidyl peptidase-4. GLP-1 enhances beta cell function with an increase in the ability to secrete insulin and restore first phase insulin release. Our pervious study showed that a novel GLP-1 analogue consisting of the fusion of active GLP-1 and IgG heavy chain constant regions (GLP-1/IgG-fc) therapy can enhances beta cell mass. It also could increase insulin secretion. Within the pancreas, GLP-1 expands β-cell mass via promo‐ tion of β-cell growth and reduction of β-cell death.

tion of insulin secretion. In addition, GABA or its metabolites may regulate proinsulin syn‐ thesis. These new observations provide insight into the complex nature of GABAergic neurons and β-cell GABA in regulation of islet function. Our study showed that GABA ex‐ erts has protective and regenerative effects on islet beta cells and reverses diabetes. GABA therapy increased beta cell proliferation and decreased beta cell apoptosis, which in turn in‐ crease beta cell mass and induced the reversal of hyperglycemia in the different kind of mice. Our data suggest that GABA exerts has ani-inflammatory effects, and is directly inhib‐

Beta-Cell Function and Failure http://dx.doi.org/10.5772/52153 123

Magnesium deficiency has recently been proposed as a novel factor implicated in the patho‐ genesis of the diabetic complications. In our previous study we showed that oral chronic Mg

Another potential treatment is the combination of two growth factors called gastrin and epider‐

Many traditional treatments have been recommended in the alternative system of medicine for treatment of diabetes mellitus and regeneration of beta cells such as Garlic, Teucriumpolium, Cinnamon and Psidium guava leaves. Photochemical analysis of those herbs have revealed the presence of flavonoids, which include quercetin and its derivatives. It is concluded that querce‐ tin, a flavonoid with antioxidant properties brings about the regeneration of the pancreatic is‐

Connective tissue growth factor (CTGF), to induce adult β cell mass expansion. Some study showed that CTGF is required for embryonic β cell proliferation3, and that CTGF overex‐

The mouse pancreas develops from ventral and dorsal evaginations of the posterior foregut endoderm at embryonic day, a process dependent on the transcription factors Pdx1 and Ptf1. Differentiation of all pancreatic endocrine cell types (α, β, Δ and PP) is dependent on the transcription factor, neurogenin 3 (Ngn3). *Ngn3* expression is controlled by a variety of factors, including the Notch signaling pathway and the transcriptional regulators pancreatic and duodenal homeobox 1 (Pdx1), SRY-box 9 (Sox9) and hepatic nuclear factor 6 (Hnf6). Al‐ though β cell neogenesis begins, these early insulin-positive cells do not contribute to ma‐ ture islets. Instead, endocrine cells that will go on to contribute to the mature islets begin to differentiate period known as the secondary transition. Some transcription factors critically involved in β cell differentiation include NK2 homeobox 2 (Nkx2.2), Nkx6.1, islet 1 (Isl-1), neuronal differentiation 1 (NeuroD1), motor neuron and pancreas homeobox 1(Mnx1),

In adults, physiological stimuli can enhance β cell proliferation during development. Al‐ though several factors have been identified that play a role in the regulation of embryonic and neonatal β cell proliferation. One cell cycle regulator that does play a role in embryonic β cell proliferation is the cell cycle inhibitor, p27Kip1. Inactivation of *p27Kip1* during em‐ bryogenesis results in an increase in β cell proliferation and subsequently β cell mass. There was no change, however, in early postnatal β cell proliferation, suggesting that p27Kip1 is

mal growth factor (EGF), which has been shown to promote beta-cell regeneration in rats.

administration could improve islet structure and decrease the blood glucose.

lets and probably increases insulin release in streptozocin-induced diabetic rats.

pression in embryonic cells increases β cell proliferation and β cell mass.

itory to T cells and macrophages.

paired box gene 4 (Pax4) and Pdx1.

not crucial to postnatal proliferation.

γ-Aminobutyric acid (GABA), a prominent inhibitory neurotransmitter, is present in high concentrations in β-cells of islets of Langerhans. The GABA shunt enzymes, glutamate de‐ carboxylase (GAD) and GABA transaminase (GABA-T) have also been localized in islet βcells. With the recent demonstration that the 64,000-Mr antigen associated with insulindependent diabetes mellitus is GAD, there isincreased interest in understanding the role of GABA in islet functions. Only a small component of β-cell GABA is contained in insulin se‐ cretory granules, making it unlikely that GABA, co-released with insulin, is physiologically significant. Our immunohistochemical study of GABA in β-cells of intact islets indicates that GABA is associated with a vesicular compartment distinctly different from insulin secretory granules. Whether this compartment represents a releasable pool of GABA has yet to be de‐ termined. GAD in β-cells is associated with a vesicular compartment, similar to the GABA vesicles. In addition, GAD is found in a unique extensive tubular cisternal complex (GAD complex). It is likely that the GABA-GAD vesicles are derived from this GAD-containing complex. Physiological studies on the effect of extracellular GABA on islet hormonal secre‐ tion have had variable results. Effects of GABA on insulin, glucagon, and somatostatin se‐ cretion have been proposed. The most compelling evidence for GABA regulation of islet hormone secretion comes from studies on somatostatin secretion, where it has an inhibitory effect. Some researchers present new evidence demonstrating the presence of GABAergic nerve cell bodies at the periphery of islets with numerous GABA-containing processes ex‐ tending into the islet mantle. This close association between GABAergic neurons and islet αand δ-cells strongly suggests that GABA inhibition of somatostatin and glucagon secretionis mediated by these neurons. Intracellular β-cell GABAA and its metabolismmay have a role in β-cell function. New evidence indicates that GABA shunt activity is involved in regula‐ tion of insulin secretion. In addition, GABA or its metabolites may regulate proinsulin syn‐ thesis. These new observations provide insight into the complex nature of GABAergic neurons and β-cell GABA in regulation of islet function. Our study showed that GABA ex‐ erts has protective and regenerative effects on islet beta cells and reverses diabetes. GABA therapy increased beta cell proliferation and decreased beta cell apoptosis, which in turn in‐ crease beta cell mass and induced the reversal of hyperglycemia in the different kind of mice. Our data suggest that GABA exerts has ani-inflammatory effects, and is directly inhib‐ itory to T cells and macrophages.

as stimulated by GLP-1 or GIP action, potentiate glucose-stimulated insulin secretion by both protein kinase A (PKA)-dependent and independent mechanisms; they also stimulate gene transcription through PKA dependent phosphorylation of the transcription factor CREB. In beta-cells, increased cAMP levels also activate the MAP kinase cascade, leading to rapid phosphorylation of Erk1/2. An activation of the PI3Kinase/Akt pathway is also ob‐ served. PI3kinase may be directly activated by the ßγ subunit of Gs, be secondary to transac‐ tivation of the EGF receptor by betacellulin, or may follow transcriptional induction of IRS-2 through the PKA/CREB pathway. The IRS- 2/PI3kinase/Akt pathway is known to have antiapoptotic effects; however, it is unclear why increased expression of IRS-2 leads to activa‐ tion of its signaling pathway. IRS-2 may be downstream of the insulin (IR) or IGF-1 (IGF-1R) receptors. Studies of mice with beta-cell specific inactivation of either receptor indicated that the insulin receptor was important for compensatory growth of the beta-cells in response to insulin resistance whereas the IGF-1 receptor was involved in the control of glucose compe‐ tence. Although these properties make GLP-1 an ideal antidiabetic agent, it is rapidly cleaved (*T*1/2 = 1–2 min) by dipeptidyl peptidase-4. GLP-1 enhances beta cell function with an increase in the ability to secrete insulin and restore first phase insulin release. Our pervious study showed that a novel GLP-1 analogue consisting of the fusion of active GLP-1 and IgG heavy chain constant regions (GLP-1/IgG-fc) therapy can enhances beta cell mass. It also could increase insulin secretion. Within the pancreas, GLP-1 expands β-cell mass via promo‐

γ-Aminobutyric acid (GABA), a prominent inhibitory neurotransmitter, is present in high concentrations in β-cells of islets of Langerhans. The GABA shunt enzymes, glutamate de‐ carboxylase (GAD) and GABA transaminase (GABA-T) have also been localized in islet βcells. With the recent demonstration that the 64,000-Mr antigen associated with insulindependent diabetes mellitus is GAD, there isincreased interest in understanding the role of GABA in islet functions. Only a small component of β-cell GABA is contained in insulin se‐ cretory granules, making it unlikely that GABA, co-released with insulin, is physiologically significant. Our immunohistochemical study of GABA in β-cells of intact islets indicates that GABA is associated with a vesicular compartment distinctly different from insulin secretory granules. Whether this compartment represents a releasable pool of GABA has yet to be de‐ termined. GAD in β-cells is associated with a vesicular compartment, similar to the GABA vesicles. In addition, GAD is found in a unique extensive tubular cisternal complex (GAD complex). It is likely that the GABA-GAD vesicles are derived from this GAD-containing complex. Physiological studies on the effect of extracellular GABA on islet hormonal secre‐ tion have had variable results. Effects of GABA on insulin, glucagon, and somatostatin se‐ cretion have been proposed. The most compelling evidence for GABA regulation of islet hormone secretion comes from studies on somatostatin secretion, where it has an inhibitory effect. Some researchers present new evidence demonstrating the presence of GABAergic nerve cell bodies at the periphery of islets with numerous GABA-containing processes ex‐ tending into the islet mantle. This close association between GABAergic neurons and islet αand δ-cells strongly suggests that GABA inhibition of somatostatin and glucagon secretionis mediated by these neurons. Intracellular β-cell GABAA and its metabolismmay have a role in β-cell function. New evidence indicates that GABA shunt activity is involved in regula‐

tion of β-cell growth and reduction of β-cell death.

122 Type 1 Diabetes

Magnesium deficiency has recently been proposed as a novel factor implicated in the patho‐ genesis of the diabetic complications. In our previous study we showed that oral chronic Mg administration could improve islet structure and decrease the blood glucose.

Another potential treatment is the combination of two growth factors called gastrin and epider‐ mal growth factor (EGF), which has been shown to promote beta-cell regeneration in rats.

Many traditional treatments have been recommended in the alternative system of medicine for treatment of diabetes mellitus and regeneration of beta cells such as Garlic, Teucriumpolium, Cinnamon and Psidium guava leaves. Photochemical analysis of those herbs have revealed the presence of flavonoids, which include quercetin and its derivatives. It is concluded that querce‐ tin, a flavonoid with antioxidant properties brings about the regeneration of the pancreatic is‐ lets and probably increases insulin release in streptozocin-induced diabetic rats.

Connective tissue growth factor (CTGF), to induce adult β cell mass expansion. Some study showed that CTGF is required for embryonic β cell proliferation3, and that CTGF overex‐ pression in embryonic cells increases β cell proliferation and β cell mass.

The mouse pancreas develops from ventral and dorsal evaginations of the posterior foregut endoderm at embryonic day, a process dependent on the transcription factors Pdx1 and Ptf1. Differentiation of all pancreatic endocrine cell types (α, β, Δ and PP) is dependent on the transcription factor, neurogenin 3 (Ngn3). *Ngn3* expression is controlled by a variety of factors, including the Notch signaling pathway and the transcriptional regulators pancreatic and duodenal homeobox 1 (Pdx1), SRY-box 9 (Sox9) and hepatic nuclear factor 6 (Hnf6). Al‐ though β cell neogenesis begins, these early insulin-positive cells do not contribute to ma‐ ture islets. Instead, endocrine cells that will go on to contribute to the mature islets begin to differentiate period known as the secondary transition. Some transcription factors critically involved in β cell differentiation include NK2 homeobox 2 (Nkx2.2), Nkx6.1, islet 1 (Isl-1), neuronal differentiation 1 (NeuroD1), motor neuron and pancreas homeobox 1(Mnx1), paired box gene 4 (Pax4) and Pdx1.

In adults, physiological stimuli can enhance β cell proliferation during development. Al‐ though several factors have been identified that play a role in the regulation of embryonic and neonatal β cell proliferation. One cell cycle regulator that does play a role in embryonic β cell proliferation is the cell cycle inhibitor, p27Kip1. Inactivation of *p27Kip1* during em‐ bryogenesis results in an increase in β cell proliferation and subsequently β cell mass. There was no change, however, in early postnatal β cell proliferation, suggesting that p27Kip1 is not crucial to postnatal proliferation.

As mentioned above Pdx1expressed in multipotent pancreatic progenitors in the early stages of pancreas development, but, Pdx1 expression becomes enhanced in insulin-positive cells and is found at only low levels in exocrine cells. This expression pattern is maintained into adulthood and Pdx1 plays a critical rolein maintenance of the mature β cell phenotype. Inactivation of *Pdx1* in embryonic insulin-expressing cells results in a dramatic decrease in β cell proliferation at late gestation, leading to decreased β cell mass at birth and early onset diabetes. Two large Maf (musculoaponeuroticfibrosarcoma oncogene homolog) transcrip‐ tion factors that are closely related to one another, MafA and MafB, are critical for β cell dif‐ ferentiation and embryonic *Pdx1* expression22 and therefore may have an indirect effect on embryonic β cell replication.

[7] Cornu M, Yang GY, Jaccard E, Poussin C, Widmann C, Thorens B. Glp-1 Protects Be‐ ta-Cells Against Apoptosis By Increasing The ActivtiyOfAn Igf-2/Igf1-Receptor Au‐

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[12] Gunasekaran U, Hudgens CW, Wright BT, Maulis MF, Gannon M. Differential regu‐

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[14] Kashima Y, Shibasaki T, Miki T, Seino S. Importance of the cAMP-GEFII/Rim2 com‐ plex in incretin-potentiated insulin secretion. Program and abstracts of the 62nd Sci‐ entific Sessions of the American Diabetes Association, 14(18), 2002, San Francisco,

[15] LeRoith D. Beta-cell dysfunction and insulin resistance in type 2 diabetes: role of

[16] Mansoori A, Zaheri H, Soltani N, Kharazmi F, Keshavarz M, Kamalinajad M. Effect of the administration of Psidium guava leaves on lipid profiles and sensitivity of the vascular mesenteric bed to phenylephrine in STZ-induced diabetic rats. JMD, 2(1):

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[18] Miki T, Liss B, Minami K, et al. KATP channels in the maintenance of glucose homeo‐ stasis. Program and abstracts of the 62nd Scientific Sessions of the American Diabetes Association, 14(18), 2002, San Francisco, California. Poster 1492-P. Diabetes, Volume

[19] Mirghazanfari SM, Keshavarz M, Nabavizadeh F, Soltani N, Kamalinejad M. 2010. The effect of Teucriumpolium L. Extracts on insulin release from in situ isolated per‐

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Association; 14(18), 2002, San Francisco, California.

California. 265-OR. Diabetes, Volume 51, Supplement 2.

beta-cell K (ATP) channel.BiochemSoc Trans. 30(2):323-7, 2002

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ol. 77:269-303, 2001

138-145, 2012

51, Supplement 2.

Inactivation of the eIF2α endoplasmic reticulum resident kinase, PERK (proteinkinase RNAlike endoplasmic reticulum kinase), specifically in embryonic β cells (PERKΔbeta) results in a 2-fold decrease in β cell proliferation, which persists through postnatal day (P).
