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.

Pathophysiological insights of methylglyoxal induced type-2 diabetes.

Diabetes mellitus is a metabolic disorder constituting a major health problem whose prevalence has gradually increased worldwide over the past few decades. Type 2 diabetes mellitus (T2DM) remains more complex and heterogeneous and arises as a combination of insulin resistance and inadequate functional ß-cell mass and comprises about 90% of all diabetic cases. Appropriate experimental animal models are essential for understanding the molecular basis, pathogenesis of complications, and the utility of therapeutic agents to abrogate this multifaceted disorder. Currently, animal models for T2DM are obtained as spontaneously developed diabetes or diabetes induced by chemicals or dietary manipulations or through surgical or genetic methods. The currently used diabetogenic agents have certain limitations. Recently, methylglyoxal (MG), a highly reactive compound derived mainly from glucose and fructose metabolism has been implicated in diabetic complications. MG is a major precursor of the advanced glycation end product (AGE) and promotes impaired functions of insulin signaling, GLUT transporters, anion channels, kinases, and endothelial cells and is finally involved in apoptosis. Recent array of literature also cited that higher concentrations of MG causes rapid depolarization, elevated intracellular Ca(2+) concentration, and acidification in pancreatic ß-cells. This review henceforth highlights the mechanism of action of MG and its implications in the pathophysiology of experimental diabetes.

Reporter protein complementation imaging assay to screen and study Nrf2 activators in cells and living animals.

NF-E2-related factor-2 (Nrf2) activators promote cellular defense mechanism and facilitate disease prevention associated with oxidative stress. In the present study, Nrf2 activators were identified using cell-based luciferase enzyme fragment complementation (EFC) assay, and the mechanism of Nrf2 activation was studied by molecular imaging. Among the various Nrf2 activators tested, pterostilbene (PTS) showed effective Nrf2 activation, as seen by luminometric screening, and validation in a high throughput-intact cell-imaging platform. Further, PTS increased the expression of Nrf2 downstream target genes, which was confirmed using luciferase reporter driven by ARE-NQO1 and ARE-GST1 promoters. Daily administration of PTS disturbed Nrf2/Keap1 interaction and reduced complemented luciferase signals in HEK293TNKS mouse tumor xenografts. This study reveals the potentials of Nrf2 activators as chemosensitizing agents' for therapeutic intervention in cancer treatment. Hence, the validated assay can be used to evaluate the identified activators preclinically in small animal models by noninvasive molecular imaging approach.

In vitro evaluation of free radical scavenging activity of Codariocalyx motorius root extract.

OBJECTIVE: To determine the phenolic content in Codariocalyx motorius root extract and to evaluate its antioxidant properties using various in vitro assay systems. METHODS: The antioxidant activity was evaluated based on scavenging of 1,1-diphenyl-2-picrylhydrazyl, hydroxyl radicals, superoxide anions, nitric oxide, hydrogen peroxide, peroxynitrite, reducing power and by inhibition of lipid peroxidation which was estimated in terms of thiobarbituric acid reactive substances. RESULTS: The root extract of the Codariocalyx motorius (C. motorius) exhibited potent total antioxidant activity that increased with increasing amount of extract concentration, which was compared with standard drug such as quercetin, butylated hydroxytoluene, tocopherol at different concentrations. The different concentrations of the extracts showed inhibition on lipid peroxidation. In addition, the extracts had effective reducing power, free radical scavenging, super oxide anion scavenging, nitric oxide scavenging, lipid peroxidation, and total phenolic content depending on concentration. High correlation between total phenolic contents and scavenging potential of different reactive oxygen species (r(2)=0.831-0.978) indicated the polyphenols as the main antioxidants. CONCLUSIONS: Codariocalyx motorius (C. motorius) root possess the highly active antioxidant substance which can be used for the treatment of oxidative stress-related diseases.