Screening and evaluation of α-glucosidase inhibitors from indigenous medicinal plants in Dak Lak Province, Vietnam

alpha-Glucosidase inhibitors have received much attention due to their important use in treating diabetes mellitus. Although some synthetic alpha-glucosidase inhibitors have been available for a long time, they often cause various unexpected side effects. Thus, the present study was aimed at finding a safe, natural source of alpha-glucosidase inhibitors. Twenty-six samples of 22 medicinal plants were collected in the Dak Lak province of Vietnam and evaluated for alpha-glucosidase inhibitory activity. Trunk bark extract from Euonymus laxiflorus Champ (ELC extract) was selected as the best alpha-glucosidase inhibitor with the smallest IC50 = 0.36 mg/mL against rat-derived alpha-glucosidase. This extract had a stronger inhibitory activity against alpha-glucosidase from Saccharomyces cerevisiae (IC50 = 1.32 A mu g/mL) and Bacillus stearothermophilus (IC50 = 5.15 A mu g/mL). The potential inhibition against some other enzymes were tested, and the results showed that the ELC extract did not inhibit fungal cellulase but strongly inhibited porcine alpha-amylase (IC50 = 6.7 A mu g/mL). The ELC extract also inhibited the proteases papain and bromelain, with IC50 = 339 A mu g/mL and IC50 = 226 A mu g/mL, respectively. The thermal and pH stabilities of the ELC extract were also investigated.