Kunka Mohanram Ramkumar

Antidiabetic effect of Gymnema montanum leaves: effect on lipid peroxidation induced oxidative stress in experimental diabetes

Gymnema montanum is widely used in ancient medicine for the ailment of various diseases. Oral administration of 200 mg kg(-1) (body weight) BW of the alcoholic extract of the leaf for 3 weeks resulted in a significant reduction in blood glucose and an increase in plasma insulin, whereas the effect of 50 and 100 mg kg(-1) BW was not significant. The alcoholic extract also resulted in decreased free radical formation in plasma of diabetic rats. Thus, this study shows that Gymnema montanum leaf extract (GLEt) possess antihyperglycemic and antiperoxidative effect. The decrease in lipid peroxides and increase in reduced glutathione (GSH), ascorbic acid (Vitamin C) and alpha-tocopherol (Vitamin E) clearly show the antioxidant properties of GLEt. The effect of GLEt was most prominently seen in the case of animals given 200 mg kg(-1) BW. In addition, the results suggest that GLEt was highly effective than the reference drug glibenclamide.

Luteolin ameliorates cisplatin-induced acute kidney injury in mice by regulation of p53-dependent renal tubular apoptosis

BACKGROUND Cisplatin chemotherapy often causes acute kidney injury in cancer patients. The causative mechanisms of cisplatin-induced acute kidney injury include renal inflammation, activation of p53 tumour suppressor protein and tubular apoptosis. Luteolin, a flavone found in medicinal herbs and plants, has been reported to exhibit anti-inflammatory, antioxidant and anticarcinogenic activities. The purpose of this study was to investigate the anti-apoptotic effect of luteolin on cisplatin-induced acute kidney injury and the molecular mechanism. METHODS C57BL/6 mice were treated with cisplatin (20 mg/kg) with or without treatment with luteolin (50 mg/kg for 3 days). Renal function, histological changes, degree of oxidative stress and tubular apoptosis were examined. The effects of luteolin on cisplatin-induced expression of renal p53, PUMA-α and Bcl-2 family proteins were evaluated. RESULTS Treatment of mice with cisplatin resulted in renal damage, showing an increase in blood urea nitrogen and creatinine levels, tubular damage, oxidative stress and apoptosis. Treatment of cisplatin-treated mice with luteolin significantly improved renal dysfunction, reducing tubular cell damage, oxidative stress and apoptosis. Examination of molecules involving apoptosis of the kidney revealed that treatment of cisplatin increased the levels of p53 and its phosphorylation, PUMA-α, Bax and caspase-3 activity that were significantly decreased by treatment with luteolin. CONCLUSION These results indicate that cisplatin induces acute kidney injury by regulation of p53-dependent renal tubular apoptosis and that luteolin ameliorates the cisplatin-mediated nephrotoxicity through down-regulation of p53-dependent apoptotic pathway in the kidney.

Modulatory effects of morin on hyperglycemia by attenuating the hepatic key enzymes of carbohydrate metabolism and β-cell function in streptozotocin-induced diabetic rats

The present study was aimed to evaluate the effect of morin on blood glucose, insulin level, hepatic glucose regulating enzyme activities and glycogen level in experimental diabetes. Diabetes mellitus was induced by a single intraperitoneal injection of streptozotocin (STZ) (50 mg/kg b.w.). Five days after STZ injection, diabetic rats received morin (25 and 50 mg/kg b.w.) orally for 30 days. Glibenclamide was used as reference drug. Morin treatment significantly reduced the blood glucose and improved the serum insulin levels. Further, a dose-dependent reduction in glucose-6-phosphatase and fructose-1,6-bisphosphatase was observed along with the increase in liver hexokinase and glucose-6-phosphate dehydrogenase activities. Morin supplement were found to be effective in preserving the normal histological appearance of pancreatic islets as well as to preserve insulin-positive β-cells in STZ-rats. Therefore, these findings suggest that morin displays beneficial effects in the treatment of diabetes, mediated through the regulation of carbohydrate metabolic enzyme activities.

Quercetin ameliorates tunicamycin-induced endoplasmic reticulum stress in endothelial cells

Endothelial dysfunction highlights that it is a potential contributor in the pathogenesis of vascular complications arising from endoplasmic reticulum stress (ER stress) and has been emerging as a main causative factor in vascular failure. Here, we hypothesize that the natural flavonoid, quercetin plays an effective role in reducing ER stress in human umbilical vein endothelial cells.

Anti-hyperlipidemic and anti-peroxidative role of pterostilbene via Nrf2 signaling in experimental diabetes

Nuclear factor erythroid 2-related factor (Nrf2), a key transcription factor triggers the expression of antioxidant and detoxification genes thereby providing cellular protective functions against oxidative stress-mediated disorders. Recent research has identified that pharmacological activation of Nrf2 also regulates the largest cluster of genes associated with lipid metabolism. With this background, this paper highlights the anti-hyperlipidemic and anti-peroxidative role of pterostilbene (PTS), an Nrf2 activator, in streptozotocin (STZ)-induced diabetic model. PTS administration to diabetic mice for 5 weeks significantly regulated blood glucose levels through the elevation of insulin secretion. The circulatory and liver lipid profiles of total cholesterol (TC), triglycerides (TG) and non-esterified fatty acids (NEFA) were maintained to normal levels upon PTS treatment. Moreover, PTS administration also normalized the circulatory levels of very low-, low- and high density lipoprotein cholesterols (VLDL-, LDL-, HDL-C) and also reduced lipid peroxidation in STZ-induced diabetic mice. In addition, Nrf2 and its downstream targets, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) enzyme activities and glutathione (GSH) levels were significantly elevated in liver tissues of diabetic mice upon PTS administration. Further, H&E staining of diabetic mouse liver showed collapse in hepatic microvesicles due to altered lipid metabolism. Both structural and functional alterations were attenuated by PTS indicating its role in diabetic dyslipidemia through Nrf2-mediated mechanism that could be considered as a promising therapeutic agent.

Reversibility of endothelial dysfunction in diabetes: role of polyphenols.

The endothelium, a thin single sheet of endothelial cells, is a metabolically active layer that coats the inner surface of blood vessels and acts as an interface between the circulating blood and the vessel wall. The endothelium through the secretion of vasodilators and vasoconstrictors serves as a critical mediator of vascular homeostasis. During the development of the vascular system, it regulates cellular adhesion and vessel wall inflammation in addition to maintaining vasculogenesis and angiogenesis. A shift in the functions of the endothelium towards vasoconstriction, proinflammatory and prothrombic states characterise improper functioning of these cells, leading to endothelial dysfunction (ED), implicated in the pathogenesis of many diseases including diabetes. Major mechanisms of ED include the down-regulation of endothelial nitric oxide synthase levels, differential expression of vascular endothelial growth factor, endoplasmic reticulum stress, inflammatory pathways and oxidative stress. ED tends to be the initial event in macrovascular complications such as coronary artery disease, peripheral arterial disease, stroke and microvascular complications such as nephropathy, neuropathy and retinopathy. Numerous strategies have been developed to protect endothelial cells against various stimuli, of which the role of polyphenolic compounds in modulating the differentially regulated pathways and thus maintaining vascular homeostasis has been proven to be beneficial. This review addresses the factors stimulating ED in diabetes and the molecular mechanisms of natural polyphenol antioxidants in maintaining vascular homeostasis.

Pterostilbene-mediated Nrf2 activation: Mechanistic insights on Keap1:Nrf2 interface

The discovery of Keap1-Nrf2 protein-protein interaction (PPI) inhibitors has become a promising strategy to develop novel lead molecules against variety of stress. Hence, Keap1-Nrf2 system plays an important role in oxidative/electrophilic stress associated disorders. Our earlier studies identified pterostilbene (PTS), a natural analogue of resveratrol, as a potent Nrf2 activator and Keap1-Nrf2 PPI inhibitor as assessed by luciferase complementation assay. In this study, we further identified the potential of PTS in Nrf2 activation and ARE-driven downstream target genes expression by nuclear translocation experiments and ARE-luciferase reporter assay, respectively. Further, the luciferase complementation assay identified that PTS inhibits Keap1-Nrf2 PPI in both dose and time-dependent manner. Computational studies using molecular docking and dynamic simulation revealed that PTS directly interacts with the basic amino acids of kelch domain of Keap1 and perturb Keap1-Nrf2 interaction pattern. This manuscript not only shows the binding determinants of Keap1-Nrf2 proteins but also provides mechanistic insights on Nrf2 activation potential of PTS.

Pterostilbene Ameliorates Streptozotocin-Induced Diabetes through Enhancing Antioxidant Signaling Pathways Mediated by Nrf2.

Nuclear factor erythroid 2-related factor 2 (Nrf2) remains a master regulator of cytoprotective and antioxidant genes. In this study, we investigated the antidiabetic role of pterostilbene (PTS) in streptozotocin (STZ)-induced diabetic model through Nrf2-mediated antioxidant mechanisms. The ability of PTS to activate Nrf2 in MIN6 cells was assessed by dissociation of the Nrf2-Keap1 complex at different time points and by expression of ARE-driven downstream target genes of Nrf2. Immunoblot experiments examining Nrf2 activation and phosphorylation indicated that it conferred cytoprotection against STZ-induced cellular damage. In STZ-induced diabetic mice, PTS administration significantly decreased blood glucose levels through the improvement of insulin secretion. In addition, we also observed insulin-positive cells with recovered islet architecture in the pancreas of STZ-induced diabetic mice after treatment with PTS. The activation of Nrf2 and expression of its downstream target genes were observed upon PTS treatment, thereby reducing oxidative damage to pancreas. Furthermore, PTS treatment significantly reverted the abundance of key glucose metabolism enzymes, such as hexokinase, glucose-6-phosphatase, glucose-6-phosphate dehydrogenase, and fructose-1,6-bisphosphatase, to near-normal levels in liver tissue of STZ-induced diabetic mice. These results clearly indicate that PTS maintains glucose homeostasis, suggesting the possibility that it is a future candidate for use in diabetes management.

Protective effect of gallic acid on alloxan-induced oxidative stress and osmotic fragility in rats

In the present study, we investigated the antioxidant effect of gallic acid (GA) on membrane lipid peroxidation and osmotic fragility in alloxan-induced diabetic Wistar rats. GA was administered orally at doses of 5, 10, and 20 mg/kg body weight for 45 days, after which liver and kidney tissues were analyzed for the degree of lipid peroxidation, reduced glutathione, and the activities of antioxidants such as catalase, superoxide dismutase, and glutathione peroxidase. Administration of GA to alloxan-induced diabetic rats reduced the blood glucose level with an increase in the level of insulin. Liver and kidney tissues from diabetic animals exhibited disturbances in antioxidant defense compared with normal rats. GA at a dose of 20 mg/kg b.w. showed a significant effect than that of the other doses. In addition, the results revealed that GA protected the integrity of erythrocyte membrane in diabetic rats as demonstrated by lower percentage of hemolysis and resistance to hydrogen peroxide-induced peroxidation. The anti-hyperglycemic activity of GA in alloxan-induced diabetic rats was also comparable with glibenclamide, a reference drug. These results suggest that GA could provide a beneficial effect on diabetes by decreasing oxidative stress-related diabetic complications.

The Impact of Oxidative Stress on Islet Transplantation and Monitoring the Graft Survival by Non-Invasive Imaging

Islet transplantation is an attractive strategy to treat severe diabetic conditions in patients suffering from autoimmune derived diabetes, and it has currently been considered a forefront research arena in diabetes. Major aim of islet transplantation is to achieve successful insulin independent disease free survival. The key challenges in transplanted islets are the generation of reactive oxygen species (ROS) and associated oxidative stress, pro-inflammatory cytokine - (TNFα) mediated apoptotic induction, attack by immune cells, and achieving revascularization with minimal hypoxic microenvironment. Free radicals and their derivatives are constantly produced in living systems, but at relatively low level, and in a balanced state. Oxidative stress, which occurs as a result of an imbalance between the intracellular free radicals production and the cellular antioxidant defense mechanisms in the transplanted islets, can lead to cell death. The balance between oxidants and antioxidants in a cell can be easily disturbed by increase in ROS production or reduction in the level of cellular antioxidant defensive substances, which can cause many metabolic complications, including pancreatic β-cell damage. Antioxidants function as blockers of radical processes by eliminating harmful ROS produced during normal cellular metabolism. A complex antioxidant defense mechanism has been developed by nature in cells to protect the cellular homeostasis. This system mainly includes antioxidant enzymes, vitamins and minerals. As transplanted islet survival is crucial for achieving successful therapy, most of these antioxidants can be used as a supplement to scavenge the local ROS thereby improving the survival of transplanted islets. Currently, very few techniques have been routinely used to qualitatively and quantitatively assess the survival and function of islet grafts, especially to confirm the success of treatment, which includes metabolic parameters such as blood glucose, insulin and C-peptide levels. These biochemical measurements provide markers at only the late stages of islet rejection. Use of molecular imaging techniques has the potential for real-time non-invasive monitoring of the functional status and viability of transplanted islet grafts in living animals. This review mainly focuses on the current status of islet transplantations, potential preventive strategies used to reduce oxidative stress-mediated toxicity in islet grafts, and use of molecular imaging as a tool to quantitatively evaluate the functional status of the transplanted islets in living animals.