α-Glucosidase inhibitors from abelmoschus esculentus seeds and Schinus terebinthifolius leaves

Abstract

Discovery of α-glucosidase inhibitors has been actively pursued with the aim of developing therapeutics for the treatment of type 2 diabetes mellitus. In examining inhibitory effect of edible plants, extracts of Abelmoschus esculentus seeds and Schinus terebinthifolius leaves revealed promising results, and they thus were selected for further investigation. The methanol crude extracts from seeds of A. esculentus afforded two flavonoid glycosides named, quercetin-3-O-β-glucoside or isoquercetin and quercetin-3-O-β-glucosyl (1'''→6'') glucoside. The isolated compounds selectively inhibited α-glucosidase whereas their inhibition against α-glucosdase from baker’s yeast was not observed. Isoquercetin inhibited maltase and sucrase 6-10 times more potent than its related diglucoside, thus indicating that increased hydrophilicity by glucose moiety reduced inhibitory effect and aglycone quercetin is critical for enzyme inhibition. Quercetin prepaed from commercially available rutin was also examined for α-glucosidase inhibition. It showed board inhibition against α-glucosidase from baker’s yeast, maltase and sucrose with IC₅₀ value of 62.8, 12.32 and 31.69 µM, respectively. The kinetic study of quercetin showed competitive inhibition in sucrase whereas mixed type inhibition against maltase was observed. The methanol crude extracts from Schinus terebinthifolius leaves afford 3 hydrolysable tannins named methyl gallate, b-glucogallin, 1,2,3,4,6-pentagalloyl-O-β-D-glucopyranoside (PGG) and inositol. PGG revealed highest inhibition against maltase and sucrose with IC₅₀ values of 27.21 and 37.53 µM, respectively. The kinetic analysis of PGG showed mixed type inhibition against maltase and sucrase. In addition, PGG showed dominant synergistic effect in rat intestinal maltase, thus leading to 7.1% and 7.9% higher inhibition. Notably, the kinetic analysis and synergistic effect of PGG is first report herein.