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.

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 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.

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.