Antioxidant and hypoglycemic activities of various solvent fractions of methanol extract of Terminalia alata Heyne ex Roth trunk-bark

The antioxidant and hypoglycemic capacities of various solvent fractions from the trunk-bark methanol extract of Terminalia alata Heyne ex Roth (T. alata) were investigated. The DPPH radical scavenging assay was used to evaluate the antioxidant activity, and the methods for determination of digestive enzymes inhibitory activity and fasting blood glucose reduction capacity in diabetic rats were used to determine the hypoglycemic activity of the extract fractions. The results indicated that higher total phenolics content was measured with increasing polarity of extraction solvent and DPPH radical scavenging activity coincided with phenolics content. Ethyl acetate fraction (EAF), n-butanol fraction (BF), and water fraction (WF) were obtained. They possessed α-amylase inhibition with the IC50 values of 0.056 ± 0.001, 0.138 ± 0.005, and 0.022 ± 0.001 mg.mL-1, respectively, which were lower than acarbose (IC50 = 0.154 ± 0.02 mg.mL-1). In contrast, IC50 values of α-glucosidase inhibitory activities of these fractions were higher than those of acarbose. In addition, these fractions also lowered fasting blood glucose concentrations in streptozotocin induced diabetic rats at a dose of 200 mg.kg-1 bw (body weight) without inducing body weight loss, which was not observed when treating with acarbose. The EAF and WF of trunk-bark of T. alata are recommended as potent sources for further research on antioxidant and hypoglycemic activities.