Increasing evidence suggests that oxidative damage to cell components has an important pathophysiological role in many human diseases. The free radicals formed in cells can readily attack protein, DNA and unsaturated lipids resulting in their loss of function and damage. Red blood cells are highly susceptible to oxidative damage which results in cell lysis. A natural antioxidant could be a potential therapeutic intervention. Thus, we examined the antioxidant activity of Clinacanthus nutans (CN). An ethanolic extract of dried leaves of CN was used in this study. The free radical (1,1-diphenyl-2-picrylhydrazyl; DPPH) scavenging activity, the ferric reducing antioxidant power (FRAP) and the intracellularly antioxidant activity of the extract were determined. The protective effect of the extract against 2,2′-azobis(2-amidinopropane) hydrochloride (AAPH)-induced rat red blood cell lysis was also evaluated. It was found that the extract could scavenge DPPH with the maximum scavenging activity of 67.65±6.59% and with an IC50 of 110.4±6.59 µg/ml. The FRAP value was 17 mg ascorbate equivalent to one gram of the extract. The extract demonstrated a significant inhibition of peroxide production in rat macrophages stimulated by phorbol myristate acetate (PMA) and protected red blood cell against AAPH-induced hemolysis with an IC50 of 359.38±14.02 mg/ml. In conclusion, the ethanolic extract of CN had an antioxidant activity and protective effect against freeradical-induced hemolysis.
