Investigation of Anthocyanidins and Anthocyanins for Targeting α-Glucosidase in Diabetes Mellitus

Anthocyanidins are bioactive compounds found mostly in colored plants and fruits. Consumption of anthocyanidin-rich foods has been shown to reduce the risk of diabetes. However, limited information is available regarding the inhibitory effect and interactions of anthocyanidins on α-glucosidase, the key enzyme that controls diabetes through degrading carbohydrate. Therefore, we used computational docking analysis to investigate the degree and type of inhibition by α-glucosidase, and the structural interactions of enzyme-selected anthocyanidins. The results suggested that anthocyanidins exhibit half maximal inhibitory concentration of 4∼55 μM; the strongest and weakest α-glucosidase inhibitors were delphinidin and malvidin, respectively. Indeed, delphinidin inhibits α-glucosidase in a mixed type, close to non-competitive manner with an inhibitory constant of 78 nM. Addition of a glycoside (glucoside or galactoside) at C3 on the C ring of delphinidin significantly decreased inhibitory activity, and addition of glycosides at C3 on the C ring and C5 on the A ring of delphinidin prevented all inhibitory activity. Molecular docking and free binding energy accurately confirmed the mode of inhibition determined by enzyme kinetics. These data will inform the use of alternative sources of anthocyanidins in functional foods and dietary supplements for prevention of diabetes. The results provide useful information for evaluating possible molecular models using anthocyanins/anthocyanidins as templates and α-glucosidase as the key enzyme in management of diabetes.