Rb2 inhibits α-glucosidase and regulates glucose metabolism by activating AMPK pathways in HepG2 cells

Five ginsenosides were evaluated as α-glucosidase and α-amylase inhibitors by enzymatic kinetics analysis, compared with the market diabetes healer, acarbose. The results indicated that Rb2 and Rd exhibited strong α-glucosidase and α-amylase inhibition. Concentration of Rb2 and Rd to inhibit 50% of α-glucosidase (IC50) were 32.2 and 38.8 μM, IC50 for α-amylase were 128 and 167.4 μM, respectively. The enzyme kinetic studies revealed that, in the presence of the most potent α-glucosidase inhibitors, Rb2 and Rd, the Michaelis-Menton constant (Km) remained constant but the maximal velocity (Vmax) decreased, revealing a non-competitive type of inhibition. Moreover, Rb2 and Rd were shown to be reversible inhibitors of yeast α-glucosidase with Ki values of 19.4 and 24.5 μM, respectively. Moreover, we investigated the effects of Rb2 on metabolism and demonstrated that Rb2 significantly increased glucose consumption in HepG2 cells. The phosphorylation of AMP-activated protein kinase (AMPK) was increased by treatment with Rb2.