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

Mammalian alpha-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 mu M, 97 M and 36 l,mu M, respectively. The intestinal maltase inhibitory activities of 2 and 3 were even higher than that of 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG) (4, IC50=140 mu M), which is a known potent alpha-glucosidase inhibitor. Comparison of the activities of 1-4, 1,2,3-O-trigalloyl-beta-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 alpha-glucosidase, noncompetitively. This is the first report on mammalian alpha-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. (c) 2007 Elsevier Ltd. All rights reserved.