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

Suppression of α- amylase and α- glucosidase is favorable for improvement of postprandial hyperglycemia. Here, the inhibitory mechanisms of epicatechin gallate (ECG) on α- amylase and α- glucosidase are explored by enzyme kinetics , spectroscopy and molecular modeling approaches. ECG was found to have strong inhibitory efficiency against α- amylase and α- glucosidase in mixed−type manners with IC 50 values of 45.30 ± 0.22 and 4.03 ± 0.01 μg/mL, respectively. ECG bound to α- amylase and α- glucosidase forming ECG– α- amylase and ECG– α- 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 α- amylase, and Lys156, Ser157, Arg315 and Asp352 of α- glucosidase, which may prevent the entrance of substrate leading to a decline in enzyme activity . Meanwhile, at the constant IC 50 ratios of ECG to acarbose or epigallocatechin gallate, an obvious antagonism was observed in α- amylase inhibition , while additive and synergistic effects for α- glucosidase. These findings suggest that ECG may be a potential inhibitor of α- amylase and α- glucosidase, which could be used as a nutrient supplement for the prevention of diabetes mellitus.