A Novel Extract of Gymnema sylvestre Improves Glucose Tolerance In Vivo and Stimulates Insulin Secretion and Synthesis In Vitro

Herbal medicines, especially plant-derived extracts, have been used to treat Type 2 diabetes mellitus (T2DM) for many centuries, and offer the potential of cheap and readily available alternatives to conventional pharmaceuticals in developing countries. Extracts of Gymnema sylvestre (GS) have anti-diabetic activities and have been used as a folk medicine in India for centuries. We have investigated the effects of a novel high molecular weight GS extract termed OSA® on glucose tolerance in insulin-resistant ob/ob mice, and on insulin secretion and synthesis by isolated mouse islets. Single administration of OSA® (500 mg/kg) to ob/ob mice 30 min before an intraperitoneal glucose load improved their abnormal glucose tolerance. In vitro studies indicated that OSA® (0.25 mg/ml) initiated rapid and reversible increases in insulin secretion from isolated mouse islets at substimulatory (2 mM) and stimulatory (20 mM) glucose concentrations. In addition, prolonged treatment (24-48 h) of mouse islets with OSA® elevated the expression of preproinsulin mRNA and maintained the total insulin content of mouse islets in the presence of stimulated insulin secretion. These effects of OSA® are consistent with its potential use as a therapy for the hyperglycemia associated with obesity-related T2DM.