Extracts of Rehmanniae radix, Ginseng radix and Scutellariae radix improve glucose-stimulated insulin secretion and beta-cell proliferation through IRS2 induction.

Recent studies have revealed that beta-cell dysfunction is an important factor in developing type 2 diabetes. beta-cell dysfunction is related to impairment of the insulin/IGF-1 signaling cascade through insulin receptor substrate-2 (IRS2). The induction of IRS2 in beta-cells plays an important role in potentiating beta-cell function and mass. In this study, we investigated whether herbs used for treating diabetes in Chinese medicine-Galla rhois, Rehmanniae radix, Machilus bark, Ginseng radix, Polygonatum radix, and Scutellariae radix-improved IRS2 induction in rat islets, glucose-stimulated insulin secretion and beta-cell survival. R. radix, Ginseng radix and S. radix significantly enhanced glucose-stimulated insulin secretion compared to the control, i.e., by 49, 67 and 58%, respectively. These herbs induced the expression of IRS2, pancreas duodenum homeobox-1 (PDX-1), and glucokinase. The increased level of glucokinase could explain the enhancement of glucose-stimulated insulin secretion with these extracts. Increased PDX-1 expression was associated with beta-cell proliferation, which was consistent with the cell viability assay. In conclusion, R. radix, Ginseng radix and S. radix had an insulinotropic action similar to that of exendin-4.