**3. The molecular mechanism of oxidative stress in diabetic nephropathy**

There are four major biochemical pathways considered to lead to the development of diabet‐ ic complications associated with hyperglycemia, (1) the polyol pathway, glucose is convert‐ ed to sorbitol and then metabolized to fructose. Advanced glycation end products (AGE) and reactive oxygen species (ROS) formation also occurs via this pathway, (2) the hexosa‐ mine pathway, fructose-6-phosphate is converted to glucosamine intermediates and the pro‐ duction of ROS is subsequently increased, (3) the protein kinase C (PKC) pathway, glucose is converted to glyceraldehyde-3-phosphate and leads to the formation of diacylglycerol (DAG). The elevation of intracellular DAG levels activate PKC, and then activate NADPH oxidase to induce ROS, (4) the formation of advanced glycation end products (AGEs), inter‐ action of AGEs with the receptors of advanced glycation end-products (RAGE) results in ROS activation (Stirban et al., 2008; Shah et al., 2009; Forbes et al., 2008; Brownlee, 2005; Kan‐ war et al., 2008; Singh et al., 2011).

Increased oxidative stress has been a widely accepted participant in the development and progression of diabetes and its complications (Maritim et al., 2003). ROS are activated in glomerular mesangial and tubular epithelial cells by high glucose, AGE, and cytokines (Park et al., 1999). Hyperglycemia activates the glycolytic pathway and excess generation of mitochondrial ROS initiates a vicious circle by activating several signaling to increase protein kinase C (PKC), and stimulating NADPH oxidase to induce ROS generation (Jo‐ hansen et al., 2005). Free radicals has been found to be formed disproportionately in‐ crease in diabetic subjects by glucose oxidation, nonenzymaticglycation of proteins, and then oxidative degradation of glycated proteins. Excessively amount of free radicals in‐ duce damage to cellular proteins, membrane lipids, nucleic acids, and then cell death (Maritim et al., 2003). Besides, increased ROS can cause vascular endothelium abnormali‐ ties, reacting directly with nitric oxide (NO) to produce cytotoxic peroxynitrite and in‐ creasing reactivity to vasoconstrictors and modification of extracellular matrix proteins (Schnackenberg, 2002). ROS can also damage endothelial cells indirectly by stimulating expression of various genes involved in inflammatory pathway (Baldwin, 1996). Previous study finds that high glucose induces ROS and then up-regulates TGF-β1 and extracellu‐ lar matrix (ECM) expression in the glomerular mesangial cell (Lee et al., 2003). There are also evidences that antioxidants can effectively inhibit high glucose induced TGF-β1 and fibronectin up-regulation (Ha et al., 1997). Ha et al. (2002) reported that ROS mediate high glucose-induced activation of NF-κB and NF-κB dependent monocyte chemoattrac‐ tant protein (MCP)-1 expression. NF-κB, a nuclear transcription factor, can initiate the transcription of genes associated with inflammatory response. It is induced by various cell stress-associated stimuli including growth factors, vasoactive agents, cytokines, and oxidative stress (Kuhad and Chopra, 2009). Advanced glycation end products induced by hyperglycemia stimulate NF-κB activation, which sustains the activation of NF-κB in dia‐ betes (Gao et al., 2006). Increased steady-state mRNA levels of inflammatory genes have been shown to associate with interstitial fibrosis and progressive human diabetic nephr‐ opathy (Kuhad and Chopra, 2009).

**Figure 1.** The relation between oxidative stress and diabetic nephropathy\* \*PKC, protein kinase C; AGE, advanced gly‐ cation end products; ROS, reactive oxygen species; NF-κB, nulcear factor-kappa B; AP-1,activator protein-1; TGF-β,

Antioxidants in Decelerating Diabetic Nephropathy

http://dx.doi.org/10.5772/45927

391

There are many evidences suggest that ROS play an important role in the pathogenesis of diabetic nephropathy (Rosen et al., 2001). To prevent the development and progression of diabetic nephropathy, it would be effective in combing the strategies to prevent overproduc‐ tion of ROS and to increase the removal of preformed ROS. (Ha et al., 2008). Some natural products were proved to possess the ability to decelerate diabetic nephropathy via reducing oxidative status. The flower of *Hibiscus sabdariffa*Linnaeus calyx (family Malvaceae, local name Karkaday) is commonly used in cold and hot beverages and as a supplement due to its perceived potential of health benefits. The flower extract has been reported to decrease blood pressure, and have antitumor characteristics as well as immune-modulating and anti‐ leukemic effects (Haji Faraji and Haji Tarkhani, 1999; Tseng et al., 2000). *Hibiscus sabdariffa*L. extract contains polyphenolic acids, flavonoids, protocatechuic acid (PCA) and anthocya‐ nins. *Hibiscus sabdariffa*L. extract has been found to contain various polyphenols and was shown to have antioxidative potential to inhibit the development of atherosclerosis in cho‐

**4. Improvement of antioxidantive status in diabetic nephropathy**

transforming growth factor-beta; MCP-1, monocyte chemotactic protein-1

TGF-β plays an important role in the development of renal hypertrophy and accumula‐ tion of extracellular matrix (ECM) components in diabetes mellitus (Wolf and Ziyadeh, 1999). The expression of TGF-β was found increased in diabetic nephropathy of experi‐ mental animals and in humans (Park et al., 1997; Yamamoto et al., 1993; Sharma et al., 1997; Shankland et al., 1994). Treatment with anti-TGF-β antibody has been documented that it attenuated the effect of high glucose induced cellular hypertrophy *in vitro* and in streptozotocin-induced diabetic mice (Wolf et al., 1992; Ziyadeh et al., 1994; Sharma et al., 1996). TGF-β is also the key regulator of ECM remodeling in mesangium causing me‐ sangial expansion and inducing the process of epithelial-mesenchymal transition (EMT) causing tubulointerstitial fibrosis (Ziyadeh et al., 2000; Oldfield et al., 2001). As the accu‐ mulation of ECM and persistence of tubulointerstitial fibrosis, the renal function progress to end-stage renal disease (ESRD). The relation between oxidative stress and diabetic nephropathy are shown in Figure 1 (Shah et al, 2007).

Increased oxidative stress has been a widely accepted participant in the development and progression of diabetes and its complications (Maritim et al., 2003). ROS are activated in glomerular mesangial and tubular epithelial cells by high glucose, AGE, and cytokines (Park et al., 1999). Hyperglycemia activates the glycolytic pathway and excess generation of mitochondrial ROS initiates a vicious circle by activating several signaling to increase protein kinase C (PKC), and stimulating NADPH oxidase to induce ROS generation (Jo‐ hansen et al., 2005). Free radicals has been found to be formed disproportionately in‐ crease in diabetic subjects by glucose oxidation, nonenzymaticglycation of proteins, and then oxidative degradation of glycated proteins. Excessively amount of free radicals in‐ duce damage to cellular proteins, membrane lipids, nucleic acids, and then cell death (Maritim et al., 2003). Besides, increased ROS can cause vascular endothelium abnormali‐ ties, reacting directly with nitric oxide (NO) to produce cytotoxic peroxynitrite and in‐ creasing reactivity to vasoconstrictors and modification of extracellular matrix proteins (Schnackenberg, 2002). ROS can also damage endothelial cells indirectly by stimulating expression of various genes involved in inflammatory pathway (Baldwin, 1996). Previous study finds that high glucose induces ROS and then up-regulates TGF-β1 and extracellu‐ lar matrix (ECM) expression in the glomerular mesangial cell (Lee et al., 2003). There are also evidences that antioxidants can effectively inhibit high glucose induced TGF-β1 and fibronectin up-regulation (Ha et al., 1997). Ha et al. (2002) reported that ROS mediate high glucose-induced activation of NF-κB and NF-κB dependent monocyte chemoattrac‐ tant protein (MCP)-1 expression. NF-κB, a nuclear transcription factor, can initiate the transcription of genes associated with inflammatory response. It is induced by various cell stress-associated stimuli including growth factors, vasoactive agents, cytokines, and oxidative stress (Kuhad and Chopra, 2009). Advanced glycation end products induced by hyperglycemia stimulate NF-κB activation, which sustains the activation of NF-κB in dia‐ betes (Gao et al., 2006). Increased steady-state mRNA levels of inflammatory genes have been shown to associate with interstitial fibrosis and progressive human diabetic nephr‐

TGF-β plays an important role in the development of renal hypertrophy and accumula‐ tion of extracellular matrix (ECM) components in diabetes mellitus (Wolf and Ziyadeh, 1999). The expression of TGF-β was found increased in diabetic nephropathy of experi‐ mental animals and in humans (Park et al., 1997; Yamamoto et al., 1993; Sharma et al., 1997; Shankland et al., 1994). Treatment with anti-TGF-β antibody has been documented that it attenuated the effect of high glucose induced cellular hypertrophy *in vitro* and in streptozotocin-induced diabetic mice (Wolf et al., 1992; Ziyadeh et al., 1994; Sharma et al., 1996). TGF-β is also the key regulator of ECM remodeling in mesangium causing me‐ sangial expansion and inducing the process of epithelial-mesenchymal transition (EMT) causing tubulointerstitial fibrosis (Ziyadeh et al., 2000; Oldfield et al., 2001). As the accu‐ mulation of ECM and persistence of tubulointerstitial fibrosis, the renal function progress to end-stage renal disease (ESRD). The relation between oxidative stress and diabetic

opathy (Kuhad and Chopra, 2009).

390 Type 1 Diabetes

nephropathy are shown in Figure 1 (Shah et al, 2007).

**Figure 1.** The relation between oxidative stress and diabetic nephropathy\* \*PKC, protein kinase C; AGE, advanced gly‐ cation end products; ROS, reactive oxygen species; NF-κB, nulcear factor-kappa B; AP-1,activator protein-1; TGF-β, transforming growth factor-beta; MCP-1, monocyte chemotactic protein-1
