59. Regeneration of Beta Cells

Epicatechin potentiation of glucose-stimulated insulin secretion in INS-1 cells is not dependent on its antioxidant activity

Kaiyuan YANG1, Catherine B CHAN1, 2, *
1Department of Agricultural, Food and Nutritional Science, University of Alberta Edmonton, Alberta, T6G 2E1 Canada; 2Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2P5, Canada

Abstract
Epicatechin (EC) is a monomeric flavan-3-ol. We have previously demonstrated that glucose-intolerant rats fed flavan-3-ols exhibit improved pancreatic islet function corresponding with an increase in circulating EC-derived metabolites. Thus, we speculate that EC may act as a cellular signaling molecule in vivo to modulate insulin secretion. In this study we further examined the effects of different concentrations of EC on H2O2 or hyperglycemia-induced ROS production, as well as on saturated fatty acid (SFA)-impaired glucose-stimulated insulin secretion (GSIS) in INS-1 cell line in vitro. We showed that EC at a high concentration (30 μmol/L), but not a low concentration (0.3 μmol/L), significantly decreased H2O2 or hyperglycemia-induced ROS production in INS-1 cells. However, EC (0.3 μmol/L) significantly enhanced SFA-impaired GSIS in INS-1 cells. Addition of KN-93, a CaMKII inhibitor, blocked the effect of EC on insulin secretion and decreased CaMKII phosphorylation. Addition of GW1100, a GPR40 antagonist, significantly attenuated EC-enhanced GSIS, but only marginally affected CaMKII phosphorylation. These results demonstrate that EC at a physiological concentration promotes GSIS in SFA-impaired β-cells via activation of the CaMKII pathway and is consistent with its function as a GPR40 ligand. The findings support a role for EC as a cellular signaling molecule in vivo and further delineate the signaling pathways of EC in β-cells.
Keywords: epicatechin; flavonoids; hyperglycemia; oxidative stress, insulin secretion; CaMKII signaling pathway; GPR40; KN-93; GW1100
Acta Pharmacologica Sinica advance online publication, 8 Feb 2018; doi: 10.1038/aps.2017.174

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