Article

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

Authors: Kaiyuan YANG1, Catherine B CHAN1,2
1 Department of Agricultural, Food and Nutritional Science, University of Alberta Edmonton, Alberta, T6G 2E1 Canada
2 Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2P5, Canada
Corresponding to: Catherine B CHAN: cbchan@ualberta.ca,
DOI: 10.1038/aps.2017.174
Received: 27 October 2017
Accepted: 26 November 2017
Advance online: 1 February 2018

Abstract

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