Study of alpha-amylase and urease inhibitory activities of Melilotus indicus (Linn.) All.

Melilotus indicus (Linn.) All. is a small herb distributed throughout Pakistan and has a number of ethnomedicinal uses. It is also consumed as a vegetable. In the present work, we are reporting the alpha-amylase and urease inhibitory activities of methanolic extract of M. indicus and its sub-fractions in different solvents. Both the methanolic extract and its fractions in chloroform, ethyl acetate, n-butanol and water showed remarkable inhibitory activities against alpha-amylase with the IC50 values being 1.29, 1.45, 1.07, 1.45 and 2.10 mg/mL respectively. The efficacy of the methanolic extract was comparable with that of acarbose (1.20 mg/mL), while the ethyl acetate fraction was more potent. The urease inhibitory activities of methanolic extract and chloroform, ethyl acetate, n-butanol and water fractions were more prominent with IC50 values being 0.95, 0.89, 1.53, 0.98 and 4.90 μg/mL respectively. The activity of methanolic extract was slightly higher than that of thiourea (0.97 μg/mL) which in turn was slightly higher than that of n-butanolic fraction. The chloroform fraction showed the highest anti-urease activity. All the plant samples showed enzyme inhibitory activity in a dose-dependent manner. Moreover, they were manifold more effective against urease than alpha-amylase. The combination of the plant extract with acarbose considerably increased the potency of the latter. The findings suggest that enzyme inhibitory activities of the vegetable M. indicus may have pharmacological significance against diabetes mellitus and gastrointestinal ulcers.