Inhibitory effect on α-glucosidase by the fruits of Terminalia chebula Retz.

Mammalian α-glucosidase inhibitory activity by Terminalia chebula Retz. fruits was investigated. The aqueous methanolic extract was found to have potent rat intestinal maltase inhibitory activity, whereas neither intestinal sucrase nor isomaltase activity was inhibited by this extract. Using bioassay-guided separation, three active ellagitannins were identified as chebulanin (1), chebulagic acid (2) and chebulinic acid (3) and were shown to possess potent intestinal maltase inhibitory activity, with the IC50 values of 690 μM, 97 μM and 36 μM, respectively. The intestinal maltase inhibitory activities of 2 and 3 were even higher than that of 1,2,3,4,6-penta-O-galloyl-β-d-glucose (PGG) (4, IC50=140 μM), which is a known potent α-glucosidase inhibitor. Comparison of the activities of 1–4, 1,2,3-O-trigalloyl-β-d-glucose (5), neochebulagic acid (6) and corilagin (7) suggested that the positions of chebulloyl and galloyl groups mostly affected the potency. Kinetic studies revealed that 2, 3, and 4 inhibited maltose-hydrolyzing activity of intestinal α-glucosidase, noncompetitively. This is the first report on mammalian α-glucosidase inhibition by 1, 2 and 3 isolated from T. chebula fruits. These results suggest a use of the extract of T. chebula fruits for managing Type 2 diabetes.