Membrane stabilization and kinetics of carbohydrate metabolizing enzymes (α-amylase and α-glucosidase) inhibitory potentials of Eucalyptus obliqua L.Her. (Myrtaceae) Blakely ethanolic leaf extract: An in vitro assessment

• Membrane stabilization and in vitro antidiabetic effects of E. obliqua was evaluated.
• Its extract was tested on RBC hemolysis (RH) and carbohydrate metabolizing enzymes.
• The mode of inhibition of the enzymes were determined using Lineweaver–Burke plot.
• The extract had respective potent and moderate effect on α-amylase and α-glucosidase.
• Its effect on RH was also significant and may be adduced to its phytonutrients.

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. obliqua.