Inhibitory mechanism of epicatechin gallate on α-amylase and α-glucosidase and its combinational effect with acarbose or epigallocatechin gallate

Suppression of alpha-amylase and alpha-glucosidase is favorable for improvement of postprandial hyperglycemia. Here, the inhibitory mechanisms of epicatechin gallate (ECG) on alpha-amylase and alpha-glucosidase are explored by enzyme kinetics, spectroscopy and molecular modeling approaches. ECG was found to have strong inhibitory efficiency against alpha-amylase and alpha-glucosidase in mixed-type manners with IC50 values of 45.30 +/- 0.22 and 4.03 +/- 0.01 mu g/mL, respectively. ECG bound to alpha-amylase and alpha-glucosidase forming ECG-alpha-amylase and ECG-alpha-glucosidase complexes, causing the conformational changes of the enzymes. Molecular simulation exhibited that ECG located into the active pocket of the enzymes likely contributed by some major amino acid residues Gln63 and Asp197 of alpha-amylase, and Lysl 56, Ser157, Arg315 and Asp352 of alpha-glucosidase, which may prevent the entrance of substrate leading to a decline in enzyme activity. Meanwhile, at the constant IC50 ratios of ECG to acarbose or epigallocatechin gallate, an obvious antagonism was observed in alpha-amylase inhibition, while additive and synergistic effects for alpha-glucosidase. These findings suggest that ECG may be a potential inhibitor of alpha-amylase and alpha-glucosidase, which could be used as a nutrient supplement for the prevention of diabetes mellitus. (C) 2019 Elsevier B.V. All rights reserved.