HPLC profile, <i>in vitro</i> alpha-amylase, alpha-glucosidase inhibitory and antioxidant activities of <i>Gymnema sylvestre</i> ethyl acetate leaf extract

Abstract

Gymnema sylvestre (GS) has been used locally as antidiabetic, antioxidant, antihyperlipidemic and anticancer medicinal plant. Oxidative stress has been implicated in pathogenesis of various diseases including diabetes and antioxidants play a leading role in preventing the progression of the disease. This study aimed to determine antidiabetic potential relative to carbohydrate hydrolyzing enzymes (alpha-amylase and alpha-glucosidase) and antioxidant activities towards oxidative stress and lipid peroxidation (MDA) of Gymnema sylvestre ethyl acetate leaves extract (GSEALE). The extract was found to inhibit α-glucosidase than α-amylase with Inhibitory concentration (IC₅₀) values of 170.45±13.61 and 130.77±3.15 respectively. The extract was also found to scavenge DPPH (53.87±17.12%), hydroxyl (28.10±14.35%) and hydrogen peroxide (34.26±20.12%) radicals. The activities of superoxide dismutase (SOD) was found to be significantly lower (p<0.05) when the extract-treated and extract+H₂O₂-treated were compared with the normal control (untreated group). Levels of reduced glutathione (GSH) in the extract- treated was found to be significantly lower (p<0.05) when compared with both normal and positive controls while the extract+H₂O₂-treated was significantly lower than the positive control but higher than extract-treated group. Levels of MDA was significantly higher in extract-treated and extract+H₂O₂-treated than the positive control (p<0.05). The total flavonoids (9.29±0.76) and total phenolics (6.18±0.52) and saponins (62.98±0.31) were found to be present in the leaves in high amount with tannins, steroids, soluble starch and carbohydrates also present. High Performance Liquid Chromatography profile revealed Resorcinol/Catechol to be one of the phenolics detected and may be responsible for GSEALE’s inhibition of α-amylase and α-glucosidase and antioxidant properties. This shows that GS can probably be used for antidiabetic purpose due to significant antioxidant and carbohydrate hydrolyzing enzymes inhibitory properties.

Keywords: Antioxidants, HPLC, Gymnema sylvestre, carbohydrate hydrolyzing enzymes, lipid peroxidation, Diabetes mellitus