Berberine inhibits glucose oxidation and insulin secretion in rat islets

Glucose promotes insulin secretion primarily via its metabolism and the production of metabolic coupling factors in beta-cells. The activation of AMP-activated protein kinase (AMPK), an energy sensor, results in a decrease in insulin secretion from beta-cells, but its mechanism remains largely unknown. Berberine, an oral anti-diabetic drug, has been shown to activate AMPK in multiple peripheral tissues. Here, we examined the effects of berberine and AMPK activation on insulin secretion and glucose oxidation in rat islets. Our results showed that berberine inhibited glucose-stimulated insulin secretion from rat islets with AMPK activation. When glucose concentration was elevated to 25 mmol/L, the inhibitory action of berberine on insulin secretion disappeared. Furthermore, berberine significantly decreased oxygen consumption rate (OCR) and ATP production induced by high glucose in rat islets. Although adenovirus-mediated overexpression of constituent-activated AMPK markedly decreased GSIS and OCR in rat islets, the inhibition of AMPK by compound C did not reverse berberine-suppressed OCR. In addition, berberine attenuated glucose-stimulated expression of fatty acid synthase. These results indicate that berberine-mediated deceleration of glucose oxidation is tightly link to the decreased insulin secretion in islets independent of AMPK activation and inhibition of fatty acid synthesis may also contribute to the effect of berberine on insulin secretion.