Modulatory effects of Moringa oleifera extracts against hydrogen peroxide-induced cytotoxicity and oxidative damage

Studies have demonstrated that the induction of oxidative stress may be involved in oxidative DNA damage. The present study examined and assessed the hydrogen peroxide (H2O2)-mediated DNA damage in human tumor KB cells and also assessed the ability of Moringa oleifera leaf extracts to inhibit the oxidative damage. H2O2 imposed a stress on the membrane lipids which was quantified by the extent of thiobarbituric acid reactive substances (TBARS) formed. The leaf extracts caused a very significant inhibition of the extent of LPO formation and enhanced the activity of antioxidative enzymes such as superoxide dismutase (SOD) and catalase (CAT) in KB cells. The comet assay was employed to study the DNA damage and its inhibition by the leaf extracts. H2O2 caused a significant increase in the number of cells bearing comets, resulting in significant DNA damage. The leaf extracts significantly reduced the incidence of comets in the oxidant stressed cells. The extent of cytotoxicity of H2O2 in the presence and the absence of leaf extracts studied in KB tumor cells by the MTT assay showed that H2O2 caused a marked decrease in the viability of KB cells where as the leaf extracts effectively increased the viability of assaulted KB cells. The observed cytoprotective activity is probably due to the antioxidant properties of its constituents, mainly phenolics. Total phenolics showed higher correlation with antioxidant activity. The leaf extracts showed higher antioxidant activity than the reference compound. These results suggest that the inhibition by the leaf extracts on oxidative DNA damage could be attributed to their free radical scavenging activities and the effect evidenced in KB cells can be in part correlated to a modulation of redox-sensitive mechanisms.