Elango Bhakkiyalakshmi

Therapeutic potential of pterostilbene against pancreatic beta-cell apoptosis mediated through Nrf2

Nuclear factor erythroid 2‐related factor 2 (Nrf2) is considered to be a ‘master regulator’ of the antioxidant response as it regulates the expression of several genes including phase II metabolic and antioxidant enzymes and thus plays an important role in preventing oxidative stress‐mediated disorders, including diabetes. In this study, for the first time, we investigated the protective properties of a naturally available antioxidant, pterostilbene (PTS), against pancreatic beta‐cell apoptosis and the involvement of Nrf2 in its mechanism of action.

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.

Antidiabetic activity of alcoholic stem extract of Gymnema montanum in streptozotocin-induced diabetic rats.

In the present study, the effect of alcoholic stem extract of Gymnema montanum (GMSt) on blood glucose, plasma insulin, and carbohydrate metabolic enzymes were studied in experimental diabetes. Diabetes mellitus was induced by a single intraperitoneal injection of STZ (60 mg/kg bw). Five days after STZ induction, diabetic rats received GMSt orally at the doses of 25, 50, 100 and 200mg/kg daily for 3 weeks. Graded doses of stem extract showed a significant reduction in blood glucose levels and improvement in plasma insulin levels. The effect was more pronounced in 100 and 200mg/kg than 50mg/kg. GMSt showed significant increase in hexokinase, Glucose-6-phosphate dehydrogenase and glycogen content in liver of diabetic rats while there was significant reduction in the levels of glucose-6-phosphatase and fructose-1,6-bisphosphatase. The present study clearly indicated significant antidiabetic effect with the stem extract of G. montanum and lends support for its traditional usage.

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.

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.

Targeting SUMOylation cascade for diabetes management.

Post-translational modifications (PTMs) play important roles in regulating protein stability, trafficking, folding conformation, and functional activity. Small ubiquitin-like modifier (SUMO) protein mediates a distinct type of PTM called SUMOylation in which the SUMO protein is covalently ligated to the target protein and modifies its activities through a series of enzymatically-catalyzed reactions. SUMOylation regulates many cellular processes like transcription, the maintenance of the ion gradient across the cell membrane, stress response, autoimmunity, etc. Several target proteins of SUMOylation are involved in the biological pathways related to various human diseases, including cardiovascular diseases, diabetes, cancer, and neurodegenerative disorders. This review focuses on the SUMOylation process, regulatory roles of SUMOylation in diabetes, and prospects of developing novel anti-diabetic drugs targeting the SUMOylation process.

Carvacrol induces mitochondria-mediated apoptosis in HL-60 promyelocytic and Jurkat T lymphoma cells.

The aim of the present study was to investigate the effect of carvacrol, a phenolic monoterpenoid on the induction of apoptosis in HL-60 (Human acute promyelocytic leukemia cells) and Jurkat (human T lymphocyte cells) cells. Carvacrol showed a potent cytotoxic effect on both cells with dose-dependent increase in the level of free radical formation as measured by an oxidation sensitive fluorescent dye, 2,7-dichlorodihydrofluorescein diacetate (H2DCFDA) levels. The reduction in the level of antioxidants such as catalase (CAT) and superoxide dismutase (SOD) (P<0.05) was observed in carvacrol-treated cells. The major cytotoxic effect appears to be intervened by the induction of apoptotic cell death as assessed by annexin-V labeling assay using flow cytometry. Western blot analysis showed that Bax expression was increased, whereas Bcl-2 expression was significantly decreased in carvacrol exposed HL-60 cells and Jurkat cells. Further studies revealed that the dissipation of mitochondrial membrane potential of intact cells was accompanied by the activation of caspase-3. Our results found that the potential mechanism of cellular apoptosis induced by carvacrol is mediated by caspase-3 and is associated with the collapse of mitochondrial membrane potential, generation of free radicals, and depletion of the intracellular antioxidant pool.