Protective effects of epicatechin against the toxic effects of streptozotocin on rat pancreatic islets: in vivo and in vitro.

Abstract

Green tea catechins have diverse pharmacological effects such as anticarcinogenic and antioxidant activities. To study the protective effects of green tea (-)-epicatechin (EC) against the toxic effects of streptozotocin (STZ), a selective beta cell toxin, on pancreatic islets in vivo and in vitro. Rats were randomly divided into four groups: control, EC (30 mg/kg)-treated, STZ (60 mg/kg)-treated, and EC plus STZ (same doses; EC+STZ)-treated rats. EC was administered twice a day for 6 days, and a single injection of STZ was used. In EC+STZ-treated rats, EC was administered 6 hours prior to STZ since posttreatment with EC had no beneficial effects on fully developed diabetes in our unpublished study. Insulin and insulin mRNA were detected by immunohistochemical analysis and in situ hybridization, respectively, and physiologic parameters including blood glucose concentration were measured daily. Following isolation of the islets, insulin release, nitrite levels, and islet morphology were observed in the four groups: control, EC (0.8 mM)-treated, STZ (5 mM)-treated, and EC+STZ (same doses)-treated islets. In EC+STZ-treated rats, hyperglycemia and weight loss were not observed and islet morphology was well preserved compared with STZ-treated rats. Compared with STZ treatment alone, insulin release was increased and nitrite production was decreased in EC+STZ-treated islets. EC appears to be helpful in protecting pancreatic islets against exposure to STZ in both in vivo and in vitro systems.