Genistein, a flavonoid in legumes and some herbal medicines, has various biological actions. However, studies on whether genistein has an effect on pancreatic (beta)cell function are very limited. In the present study, we investigated the effect of genistein on (beta)cell proliferation and cellular signaling related to this effect and further determined its antidiabetic potential in insulin-deficient diabetic mice. Genistein induced both INS1 and human islet (beta)cell proliferation after 24 h of incubation, with 5 µm genistein inducing a maximal 27% increase. The effect of genistein on (beta)cell proliferation was neither dependent on estrogen receptors nor shared by 17(beta)estradiol or a host of structurally related flavonoid compounds. Pharmacological or molecular intervention of protein kinase A (PKA) or ERK1/2 completely abolished genistein-stimulated (beta)cell proliferation, suggesting that both molecules are essential for genistein action. Consistent with its effect on cell proliferation, genistein induced cAMP/PKA signaling and subsequent phosphorylation of ERK1/2 in both INS1 cells and human islets. Furthermore, genistein induced protein expression of cyclin D1, a major cell-cycle regulator essential for (beta)cell growth. Dietary intake of genistein significantly improved hyperglycemia, glucose tolerance, and blood insulin levels in streptozotocin-induced diabetic mice, concomitant with improved islet (beta)cell proliferation, survival, and mass. These results demonstrate that genistein may be a natural antidiabetic agent by directly modulating pancreatic (beta)cell function via activation of the cAMP/PKA-dependent ERK1/2 signaling pathway. Genistein may be a natural anti-diabetic agent by directly modulating pancreatic (beta)cell function via activation of the cAMP/PKA-dependent ERK1/2 signaling pathway.
