Interaction mechanism of carnosic acid against glycosidase (α-amylase and α-glucosidase).

Inhibition the activity of glycosidase is an effective method for the treatment and prevention of diabetes. In this study, enzymatic kinetics, fluorescence spectrum experiment, starch granule digestion, molecular docking studies and animal's studies were used to investigate the interaction mechanism of carnosic acid against two glycosidase (α-amylase and α-glucosidase). Enzymatic kinetics showed that carnosic acid inhibited α-amylase activity in a competitive manner and α-glucosidase activity in a non-competitive manner. The half inhibitory concentrations (IC50) of carnosic acid to α-amylase and α- glucosidase were (1.12 ± 0.31) and (0.08 ± 0.17), respectively. The fluorescence quenching experiments showed that the intrinsic fluorescence of α-amylase or α-glucosidase was quenched by forming a complex with carnosic acid, and there was only one binding site between carnosic acid and glycosidase. The starch granules were no longer hydrolyzed by α-amylase after the addition of carnosic acid, which indicated that carnosic acid inhibited the activity of α-amylase. Molecular docking study showed that carnosic acid binds to the amino acid residues of glycosidase through hydrogen bond and van der Waals force, which leads to the change of the molecular conformation of glycosidase and thus reduces the activity of glycosidase. The experiment on mice showed that carnosic acid could effectively reduce postprandial blood glucose in mice.