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.

Proteomic identification of pterostilbene-mediated anticancer activities in HepG2 cells.

In the present study, we attempt to shed light on the underlying molecular mechanism of the anticancer activity of pterostilbene (PTS) in HepG2 cells through the proteomic approach. PTS was found to induce apoptosis by altering the expression of apoptotic genes and the G2/M phase of cell cycle arrest. Further, the 2-DE map showed the expression of 72 differentially regulated proteins in PTS-treated HepG2 cells, of which 8 spots with >2 fold up- or down-regulated level were identified by MALDI-TOF analysis, which has a regulatory role in apoptosis. These findings for the first time offer valuable insights into the mechanism of apoptotis by PTS in HepG2 cells.

Quercetin ameliorates tunicamycin-induced endoplasmic reticulum stress in endothelial cells.

OBJECTIVE: 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. MATERIALS AND METHODS: Human umbilical vein endothelial cells were pre-treated with different concentrations of quercetin (0-100 µm) before inducing ER stress using tunicamycin (TUN) (0.75 µg/ml); cytotoxicity was assessed by MTT assay. Expression levels of ER stress responsive genes, antioxidant enzymes and apoptotic markers were assessed by qRT-PCR, while roles of caspase-3 and PARP cleavage were measured by western blot analysis. RESULTS: Quercetin pre-treatment at 25 and 50 µm had a cytoprotective effect on cells against TUN-induced toxicity. Quercetin administration modulated expression level of ER stress genes coding for glucose-regulated protein 78 (GRP78) and C/EBP-homologous protein (CHOP), and antioxidant enzymes such as superoxide dismutase and catalase, along with free radical generation assessed by malondialdehyde assay. Induction of apoptosis was prevented with reduction in expression level of Bax, and concomitant increase in Bcl-2 levels, thus proving its potential against ER stress. CONCLUSION: The current study indicates that quercetin modulated stress responsive genes GRP78 and CHOP, helping endothelial cells prevent TUN-induced ER stress.

Modulatory effects of morin on hyperglycemia by attenuating the hepatic key enzymes of carbohydrate metabolism and ß-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 ß-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.

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 ß-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.