Evaluation of α-amylase inhibitory activities of selected antidiabetic medicinal plants

Inhibitors of carbohydrate hydrolyzing enzymes such as α-amylase play an important role for the control of diabetes mellitus especially in patients with type 2 diabetes. In this study we selected ten antidiabetic medicinal plants, because they have been recommended to treat diabetes in traditional Iranian medicine, and screened them for α-amylase inhibitory activities. Among the tested samples, Camellia sinensis (Theaceae) leaf (IC50 = 1.54 mg/mL), Trigonella foenum-graecum (Leguminosae) seed (IC50 = 1.87 mg/mL) and leaf (IC50 = 1.92 mg/mL), and Urtica dioica (Urticaceae) leaf (IC50 = 1.89 mg/mL) revealed appreciable α-amylase inhibitory activities in a concentration-dependent manner. Furthermore, the most active sample, Camellia sinensis leaf, was partitioned by stepwise solvent–solvent extraction process and the inhibitory effect of each fraction on the α-amylase was tested. According to the results, the ethyl acetate fraction (IC50 = 0.53 mg/mL) and the residue (IC50 = 0.52 mg/mL) had the highest α-amylase inhibitory activities.