Membrane stabilization and kinetics of carbohydrate metabolizing enzymes (α-amylase and α-glucosidase) inhibitory potentials of Eucalyptus obliqua L. ethanolic leaf extract

Eucalyptus spp. are important herbs finding therapeutic application in many parts of the world against a number of disorders including diabetes mellitus. Inhibitors of α-amylase and α-glucosidase offer an effective strategy to modulate levels of postprandial hyperglycemia via control of starch metabolism. The GC-MS analysis, membrane stabilization and mechanism(s) of inhibitory potential of Eucalyptus obliqua ethanolic extract on α-amylase and α-glucosidase were evaluated. The α-amylase inhibitory potential of the extract was investigated by reacting different concentrations of the extract with α-amylase and starch solution, while α-glucosidase inhibition was determined by pre-incubating α-glucosidase with different concentrations of the extracts followed by the addition of p-nitrophenylglucopyranoside. The mode(s) of inhibition of the enzymes were determined using the Lineweaver-Burke plot. The extract exhibited potent and moderate inhibitory potential against α-amylase and α-glucosidase, respectively. The inhibition was dose-dependent with respective half-maximal inhibitory concentration (IC50) values of 2.19 and 0.45 mg mL-1. The extract also had respective membrane stabilization potentials of 86.58% and 76% on bovine erythrocytes against hypotonic solution and heat-induced hemolysis. The effect elicited by the extract at the investigated doses could be ascribed to the presence of active metabolites as revealed by the analytical chromatogram. Overall, the non-competitive mechanism of action of E. obliqua extract is due to its inhibitory effects on both α-amylase and α-glucosidase. This concomitantly extenuates the rate of starch hydrolysis leading to ameliorated glucose levels, thus lending support to hypoglycemic candidature of E. oblique.