In vivo and in vitro anti-diabetic activity of extracts of Anthoclestia vogelii planch and isolation of decussatin, a new α-amylase inhibitor from its stem bark and leaves

Abstract

The aqueous methanol crude extracts of Anthocleista vogelii, Planch were investigated for their anti-diabetic activities in normoglycaemic and alloxan-induced diabetic rats. Bioassay guided fractionation in vitro was used to investigate the α-amylase inhibitory activities. The leaves and stem bark crude extracts at 1 g/kg body weight (BW) gave 60.35 % and 69.68 % (p < 0.05) peak reduction in blood glucose levels on day-7 and day-5 respectively, which was higher than the 58.43 % for the reference group, glibenclamide given on day-7. Decussatin, a xanthone at 1 mg/mL with a 78.0 % (p < 0.001) α-amylase inhibition was isolated with comparable anti-diabetic activity to acarbose, a known synthetic α-glucosidase drug, which gave a 54.9 % inhibition at the same concentration. Spectral characterization of the isolated compound using IR, GC-MS, and NMR established the structure of the compound to be decussatin. In addition, computational calculations further confirmed the structure as decussatin with spectroscopic data that matched the experiment. The anti-diabetic activity as revealed by the results further validates, scientifically, the traditional use of the plant in managing diabetes. As such, we provide evidence of a probable mode of operation by α-amylase inhibition due to the presence of decussatin isolated from the leaves and stem bark.