The mechanism of interactions between flavan-3-ols against a-glucosidase and their in vivo antihyperglycemic effects.

Catechin and epicatechin are flavan-3-ols, with (+)-catechin (C) and (-)-epicatechin (EC) being the most common optical isomers found in nature. In this study, we found that C and EC showed notable inhibitory activity against a-glucosidase (AGH), and that both inhibition activities reversible and competitive. Additionally, we observed that C and EC quenched the intrinsic fluorescence of AGH through a static quenching mechanism, and that the electrostatic force was the predominant driving factor in the binding reaction. Molecular docking studies indicated that the benzene-ring-4'-hydroxyphenyl construct on flavan-3-ol plays an important role in AGH inhibition, and that the inhibition increases along with increased binding of amino acid residues at this site. Furthermore, C and EC inhibited glucose absorption in everted intestine sleeves in vitro and suppressed increases in postprandial blood glucose levels in vivo. Our results suggest that C and EC are useful to protect against hyperglycemia through inhibiting the activity of a-glucosidase.