Antioxidant Enhancing Effect of Azadirachta indica A. Juss. Leaf Fractionated Extracts on Naja nigricollis Reinhardt Venom in Albino Rats

The lethality of snake venom is mainly attributed to its phospholipase A2 component that hydrolyzes cellular phospholipids, leading to the release of arachidonic acid that generates potentially toxic reactive oxygen species (ROS). Imbalance between excessive generation and poor removal of ROS causes lipid peroxidation leading to cellular damage. Hence, this research was aimed at evaluating the antioxidant-enhancing effect of Azadirachta indica leaf fractionated extracts on Naja nigricollis venom in albino rats. A. indica leaf was collected, authenticated and extracted using 95% methanol followed by fractionation using hexane and ethyl acetate. Ferric reducing antioxidant power assay was used for the in vitro test, while, in vivo experiments were conducted using Albino rats. The in vitro antioxidant effect of the hexane and ethyl acetate fractions presented ferric reducing power of 68.80 ± 1.40% and 71.54 ± 2.12% respectively. This are closely related to those of ascorbic acid (78.50 ± 2.80%) and α-tocopherol (75.00 ± 1.85%). The results of the in vivo tests indicated that a single injection (0.195 mg/kg b. wt.) of N. nigricollis venom caused significant (P<0.05) elevation of hepatic and renal ROS levels (7 and 8 folds respectively) with a concomitant increase in lipid peroxidation (LPO) compared to the control group. The ROS levels were decreased significantly leading to the decrease in the level of LPO in the envenomed rats treated with the hexane and ethyl acetate fractions compared to the venom control. The treatments significantly (P<0.05) increased the activities of superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) in both the hepatic and renal homogenates compared to the venom control. The degree of protection against LPO by reducing the levels of ROS as well as increasing the activities of the antioxidant enzymes has significantly (P<0.05) increased when combine treatment of standard antivenin and any of the hexane or ethyl acetate fractions was considered compared to when each of them was used alone. Based on these findings, it has been established that, the tested extracts have antioxidant as well as antioxidant-enhancing effects against the oxidative toxicity of N. nigricollis venom.