Cocoa flavonoids attenuate high glucose-induced insulin signalling blockade and modulate glucose uptake and production in human HepG2 cells

Abstract

Insulin resistance is the primary characteristic of type 2 diabetes. Cocoa and its main flavanol, (-)-epicatechin (EC), display some antidiabetic effects, but the mechanisms for their preventive activities related to glucose metabolism and insulin signalling in the liver remain largely unknown. In the present work, the preventive effect of EC and a cocoa polyphenolic extract (CPE) on insulin signalling and on both glucose production and uptake are studied in insulin-responsive human HepG2 cells treated with high glucose. Pre-treatment of cells with EC or CPE reverted decreased tyrosine-phosphorylated and total levels of IR, IRS-1 and -2 triggered by high glucose. EC and CPE pre-treatment also prevented the inactivation of the PI3K/AKT pathway and AMPK, as well as the diminution of GLUT-2 levels induced by high glucose. Furthermore, pre-treatment of cells with EC and CPE avoided the increase in PEPCK levels and the diminished glucose uptake provoked by high glucose, returning enhanced levels of glucose production and decreased glycogen content to control values. These findings suggest that EC and CPE improved insulin sensitivity of HepG2 treated with high glucose, preventing or delaying a potential hepatic dysfunction through the attenuation of the insulin signalling blockade and the modulation of glucose uptake and production.