**3. Oxidative stress induced by hyperglycaemia in type 1diabetes**

### **3.1. Pathways involved in the production of oxidants**

Moreover, pancreatic β-cells are sensitive to cytotoxic damage caused by reactive oxygen species as gene expression and activity of antioxidant enzymes such as glutathione peroxi‐

Increasing evidence in both experimental and clinical studies suggests that oxidative stress plays a central role in the onset of diabetes mellitus as well as in the development of vascu‐ lar and neurologic complications of the disease (Niedowicz & Daleke, 2005). Studies advanc‐ ing the role of oxidative stress in vascular endothelial cells proposed that oxidative stress mediate the diversion of glycolytic intermediates into pathological pathways (Rolo & Pal‐ meira, 2006; Turk, 2010). Oxidative stress is increased in diabetes mellitus owing to an in‐ crease in the production of oxygen free radicals and a deficiency in antioxidant defense mechanisms. Free radicals are formed disproportionately in diabetes by glucose oxidation, non-enzymatic glycation of proteins, and the subsequent oxidative degradation of glycated proteins (Rodiño-Janeiro et al., 2010). Abnormally high levels of free radicals and the simul‐ taneous decline of antioxidant defense mechanisms can lead to damage of cellular organ‐ elles and enzymes, increased lipid peroxidation, and development of insulin resistance

This review will explore recent evidence in the literature of the use of biomarkers to assess oxidative stress which is recognized as a significant mediator in the development of macro‐ vascular or cardiovascular complication in type 1 diabetes mellitus, as well as the potential for prevention of complications through the use of antioxidants. There is also a search for other biomarker of oxidative stress which might be clinically useful in patients with diabetes mellitus. Such a biomarker could potentially indicate the severity of disease, identify those

Impairment in the oxidant/antioxidant equilibrium creates a condition known as oxidative stress. There is a complex interaction between antioxidants and oxidants such as reactive oxygen species, which modulates the generation of oxidative stress. Oxidative stress takes place in a cellular system when the generation of reactive oxygen species increases and over‐ whelms the body's antioxidant capacity and defenses (Baynes, 1991). If the free radicals are not removed by the cellular antioxidants, they may attack and damage lipids, carbohy‐

Oxidative stress is known to be a component of molecular and cellular tissue damage mecha‐ nisms in a wide spectrum of human diseases (Maritim et al., 2003; Isabella et al., 2006). There is growing evidence that have connected oxidative stress to a variety of pathological conditions, including cancer, cardiovascular diseases, chronic inflammatory disease, post-ischaemic or‐ gan injury, diabetes mellitus, xenobiotic/drug toxicity, and rheumatoid arthritis (El Farama‐ wy & Rizk, 2011; Samanthi et al., 2011). In recent years, much attention has been focused on the role of oxidative stress. It has been reported that oxidative stress participates in the pro‐ gression and pathogenesis of secondary diabetic complications. This includes impairment of

at increased risk of complications and monitor response to treatment.

**2. Oxidative stress and beta-cell destruction**

drates, proteins and nucleic acids (Baynes & Thorpe, 1999).

dase activity is decreased in these cells (Lenzen et al., 1996).

(Ceriello, 2006).

224 Type 1 Diabetes

There are multiple sources of reactive oxygen species production in diabetes including those of non-mitochondrial and mitochondrial origins. Reactive oxygen species accelerates four important molecular mechanisms that are involved in oxidative tissue damage induced by hyperglycemia. These four pathways are increased advanced glycation end product, in‐ creased hexosamine pathway flux, activation of protein kinase C, and increased polyol path‐ way flux (also known as the sorbitol-aldose reductase pathway) (Rolo & Palmeira, 2006).

In the polyol pathway, the two enzymes aldose reductase and sorbitol dehydrogenase cause reactive oxygen species production. Glucose is reduced to sorbitol through the use of re‐ duced nicotinamide adenine dinucleotide phosphate, a reaction catalyzed by aldose reduc‐ tase. This pathway metabolizes 30 - 35% of the glucose present during hyperglycemia. The available reduced nicotinamide adenine dinucleotide phosphate is depleted resulting in the reduction of glutathione regeneration and nitric oxide synthase activity (Ramana et al., 2003). The oxidation of sorbitol to fructose with the concomitant production of reduced nico‐ tinamide adenine dinucleotide is catalyzed by sorbitol dehydrogenase. The reduced nicoti‐ namide adenine dinucleotide phosphate may be used by nicotinamide adenine dinucleotide phosphate oxidases to generate superoxide anion (Moore & Roberts, 1998). Vitamin C sup‐ plementation has been found to be effective in reducing sorbitol accumulation in the red blood cells of diabetic patients. In a study conducted by Cunningham et al. (1994) who in‐ vestigated the effect of two different doses of vitamin C supplements (100 and 600 mg) dur‐ ing a 58 day trial on young adults with type 1 diabetes mellitus, vitamin C supplementation at either dose within 30 days normalized sorbitol levels.

Advanced glycation end product in high concentration in body is toxic and can modify the structure of intracellular proteins especially those involved in gene transcription, and can cause damage to biological membranes and the endothelium. It may diffuse to the extracel‐ lular space and directly modify extracellular proteins such as laminin and fibronectin to dis‐ turb signaling between the matrix and cells that act via receptor for advanced glycation end products, which is present on many vascular cells (Bierhaus et al. 1998). In addition, ad‐ vanced glycation end products can modify blood proteins such as albumin, causing them to bind to advanced glycation end product receptors on macrophages/mesangial cells and in‐ crease the production of growth factors and proinflammatory cytokines (Brownlee, 2005). Kostolanská et al. (2009) observed significantly higher glycated hemoglobin, serum ad‐ vanced glycation end products and advanced oxidation protein products concentrations in 81 patients with type 1 diabetes mellitus compared with controls. They suggest that the measurement of glycated hemoglobin, serum advanced glycation end products and ad‐ vanced oxidation protein products may be useful to predict the risk of development of dia‐

Biochemical Evaluation of Oxidative Stress in Type 1 Diabetes

http://dx.doi.org/10.5772/52836

227

Antioxidants or antibodies against receptor for advanced glycation end product prevent both oxidative stress and the downstream signaling pathways that can be activated by liga‐ tion of receptor for advanced glycation end product. Advanced glycation end product-medi‐ ated reaction oxygen species production is implicated in diabetic vascular complications and in blood vessel endothelial activation (Cameron & Cotter, 1999; Mullarkey et al., 1990). The formation and accumulation of advanced glycation end products have been involved in the development and progression of diabetic micro- and macroangiopathy. The advanced glyca‐ tion end product-receptor for advanced glycation end product interaction produces oxida‐ tive stress and subsequently evokes thrombosis and vascular inflammation, thereby playing an important role in diabetic vascular complications (Yamagishi, 2009; Niiya et al., 2006). In a recent study, median levels of malondialdehyde and increased plasma levels of soluble re‐ ceptor for advanced glycation end product were found in 42 type 1 diabetic patients during the early years after diagnosis (0-10 years). These findings suggest that increased plasma levels of soluble receptor for advanced glycation end product in type 1diabetes may provide protection against cell damage and may be sufficient to eliminate excessive circulating ma‐

londialdehyde during early years after disease onset (Reis et al., 2012).

Reactive oxygen species consist of oxygen free radicals such as superoxide anion (O2

thione peroxidase, catalase, and small molecule substances such as vitamins C and E.

drogen peroxide (H2O2), hydroxyl radical (•OH), singlet oxygen, nitric oxide, and peroxyni‐ trite (Chong et al., 2005). Most of these free radicals are produced at low concentrations during normal physiological conditions in the body and are scavenged by endogenous en‐ zymatic and non-enzymatic antioxidant systems that include superoxide dismutase, gluta‐

•−), hy‐

**4. Free radicals formed during oxidative stress**

**4.1. Reactive oxygen species in type 1 diabetes**

betic complications (Kostolanská et al., 2009).

Glucose at high concentrations undergoes non-enzymatic reactions with primary amino groups of proteins to form glycated residues called Amadori products. These early glycation products undergo further complex reactions, such as rearrangement, dehydration, and con‐ densation, to become irreversibly cross-linked, heterogeneous fluorescent derivatives called advanced glycation end products (Thornalley, 2002). The advanced glycation end products binds to a cell surface receptor known as receptor for advanced glycation end product. As a result of interaction of advanced glycation end products, with receptor for advanced end product, there is the induction of the synthesis of reactive oxygen species via a mechanism which involves localization of pro-oxidant molecules at the cell surface (Yan et al., 1994) and the participation of activated nicotinamide adenine dinucleotide phosphate oxidase (Wauti‐ er et a., 2001). The reactive aldehydes methylglyoxal and glyoxal are produced from enzy‐ matic and non-enzymatic degradation of glucose, lipid and protein catabolism, and lipid peroxidation. These aldehydes form advanced glycation end products with proteins that are implicated in diabetic complications. Han et al. (2007) assessed plasma methylglyoxal and glyoxal using a novel liquid chromatography-mass spectrophotometry method in 56 young patients (6 - 22 years) with type 1 diabetes mellitus without complications. They found that mean plasma methylglyoxal and glyoxal levels were higher in the diabetic patients com‐ pared with their non-diabetic counterparts. They suggest that increased plasma methyl‐ glyoxal and glyoxal levels give an indication of future diabetic complications and emphasized the need for aggressive management (Han et al., 2007).

It has been shown that through receptor for advanced glycation end products mediated ef‐ fects, advanced glycation end product induces reactive oxygen species production possibly through an nicotinamide adenine dinucleotide phosphate oxidase, and the subsequent ex‐ pression of inflammatory mediators and activation of redox-sensitive transcription factors (Wautier et al., 2001; Schmidt et al., 1996). Furthermore, advanced glycation end products, binding to receptor for advanced glycation end product activate protein kinase C-α-mediat‐ ed activation of nuclear factor-κB (NFκβ) and nicotinamide adenine dinucleotide phosphate oxidase. This may cause the generation of mitochondrial reactive oxygen species and induce the production of various inflammatory cytokines further aggravating oxidative stress (Simm et al., 1997).

Advanced glycation end product in high concentration in body is toxic and can modify the structure of intracellular proteins especially those involved in gene transcription, and can cause damage to biological membranes and the endothelium. It may diffuse to the extracel‐ lular space and directly modify extracellular proteins such as laminin and fibronectin to dis‐ turb signaling between the matrix and cells that act via receptor for advanced glycation end products, which is present on many vascular cells (Bierhaus et al. 1998). In addition, ad‐ vanced glycation end products can modify blood proteins such as albumin, causing them to bind to advanced glycation end product receptors on macrophages/mesangial cells and in‐ crease the production of growth factors and proinflammatory cytokines (Brownlee, 2005). Kostolanská et al. (2009) observed significantly higher glycated hemoglobin, serum ad‐ vanced glycation end products and advanced oxidation protein products concentrations in 81 patients with type 1 diabetes mellitus compared with controls. They suggest that the measurement of glycated hemoglobin, serum advanced glycation end products and ad‐ vanced oxidation protein products may be useful to predict the risk of development of dia‐ betic complications (Kostolanská et al., 2009).

Antioxidants or antibodies against receptor for advanced glycation end product prevent both oxidative stress and the downstream signaling pathways that can be activated by liga‐ tion of receptor for advanced glycation end product. Advanced glycation end product-medi‐ ated reaction oxygen species production is implicated in diabetic vascular complications and in blood vessel endothelial activation (Cameron & Cotter, 1999; Mullarkey et al., 1990). The formation and accumulation of advanced glycation end products have been involved in the development and progression of diabetic micro- and macroangiopathy. The advanced glyca‐ tion end product-receptor for advanced glycation end product interaction produces oxida‐ tive stress and subsequently evokes thrombosis and vascular inflammation, thereby playing an important role in diabetic vascular complications (Yamagishi, 2009; Niiya et al., 2006). In a recent study, median levels of malondialdehyde and increased plasma levels of soluble re‐ ceptor for advanced glycation end product were found in 42 type 1 diabetic patients during the early years after diagnosis (0-10 years). These findings suggest that increased plasma levels of soluble receptor for advanced glycation end product in type 1diabetes may provide protection against cell damage and may be sufficient to eliminate excessive circulating ma‐ londialdehyde during early years after disease onset (Reis et al., 2012).
