Abstract

S. O. Oyedemi, G. Bradley and A. J. Afolayan*

Strychnos henningsii Gilg is used traditionally for the treatment of various ailments in southern Africa traditional medicine. The antioxidant and free radical scavenging activity of aqueous extract of this plant was investigated both in -vivo and -vitro using spectroscopic method against 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide anions, hydrogen peroxide (H 2O2), nitric oxide (NO), 2,2’- azinobis [3-ethylbenzothiazoline-6-sulfonic acid] diammonium salt (ABTS) and the ferric reducing agent. Total phenols, flavonoid, flavonol and proanthocyanidin were also determined to assess their effects on the antioxidant activity of this plant. Free radical scavenging activity of the plant extract against H2O2, ABTS and NO was concentration dependent with IC50 value of 0.023, 0.089 and 0.49 mg/ml respectively. However, S. henningsii exhibited lower inhibitory activity against DPPH with IC50 value of 0.739 mg/ml. The reducing power of the extract was found to be concentration dependent. The administration of the aqueous extract at 250, 500 and 1000 mg/kg body weight to male Wistar rats significantly increased the percentage inhibition of reduced glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT). Whereas, lipid peroxidation level in hepatotoxic rats decreased significantly at the dose of 500 and 1000 mg/kg body weight at the end of 7 days. The extract yielded high phenol content (48 mg/g tannic acid equivalent) followed by proanthocyanidin (8.7 mg/g catechin equivalent) flavonol (5.5 mg/g quercetin equivalent) and flavonoids (4.8 mg/g quercetin equivalent) respectively. A positive linear correlation was observed between these polyphenols and the free radical scavenging activities.