The anti-diabetic mechanisms by isoflavone genistein
In the present study, we first investigated the effect of genistein on Î²-cell insulin secretion and proliferation and cellular signaling related to these effects in vitro and in vivo. We then determined its anti-diabetic potential in insulin-deficient and obese diabetic mouse models. The results in our study showed that exposure of clonal insulin secreting (INS1E) cells or isolated pancreatic islets to genistein at physiologically relevant concentrations (1-10 Î¼M) enhanced glucose-stimulated insulin secretion (GSIS), whereas insulin content was not altered, suggesting that genistein-enhanced GSIS is not due to a modulation of insulin synthesis. This genisteinâ s effect is protein tyrosine kinase- and KATP channel-independent. In addition, genistein had no effect on glucose transporter-2 expression or cellular ATP production, but similarly augmented pyruvate-stimulated insulin secretion in INS1E cells, indicating that genistein improvement of insulin secretion in Î²-cells is not related to an alternation in glucose uptake or the glycolytic pathway. Further, genistein (1-10 Î¼M) induced both INS1 and human islet Î²-cell proliferation following 24 h of incubation, with 5 ÂµM genistein inducing a maximal 27% increase. The effect of genistein on Î²-cell proliferation was neither dependent on estrogen receptors, nor shared by 17Î²-estradiol or a host of structurally related flavonoid compounds. Pharmacological or molecular intervention of PKA or ERK1/2 completely abolished genistein-stimulated Î²-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 Î²-cell growth. Dietary intake of genistein significantly improved hyperglycemia, glucose tolerance, and blood insulin levels in both insulin deficient type 1 and obese type 2 diabetic mice, concomitant with improved islet Î²-cell proliferation, survival, and mass. These changes were not due to alternations in animal body weight gain, food intake, fat deposit, plasma lipid profile, or peripheral insulin sensitivity. Collectively, these findings provide better understanding of the mechanism underlying the anti-diabetic effects of genistein.
Loss of functional Î²-cell mass through apoptosis is central to the development of both T1D and T2D and islet Î²-cell preservation and regeneration are very important components of Î²-cell adaptation to increased apoptosis and insulin resistance and therefore holds promise as a treatment for this disease. In this context, these findings may potentially lead to the development of novel low-cost natural agents for prevention and treatment of diabetes.
- Doctoral Dissertations