Identification of a novel a-glucosidase inhibitor from Melastoma dodecandrum Lour. fruits and its effect on regulating postprandial blood glucose

Melastoma dodecandrum Lour. (MDL) extracts have shown potent alpha-glucosidase inhibitory activity, suggesting MDL might be a good source of alpha-glucosidase inhibitors. The aim of the study was to identify compounds in MDL extracts with alpha-glucosidase inhibitory activities and evaluate their effect on postprandial blood glucose as well as elucidating the underlying mechanisms of inhibition. A total of 34 polyphenols were identified in MDL fruits, among which 10 anthocyanins and three proanthocyanidin derivatives were discovered for the first time. Dosing mice with MDL extracts (100 mg/kg body weight, by gavage) was associated with a significantly decrease in postprandial blood glucose concentrations after oral administration of maltose. The most potent alpha-glucosidase inhibitor was identified as casuarictin (IC50 of 0.21 mu g/mL). Casuarictin bound competitively to alpha-glucosidase, occupying not only the catalytic site but also forming strong hydrogen bonds with alpha-glucosidase residues. Therefore, casuarictin derived from MDL fruits might be used as novel alpha-glucosidase inhibitor in functional foods or other dietary products.