IN VITRO ANTIOXIDANT ABILITIES AND INHIBITION OF RABBIT MUSCLE LACTATE DEHYDROGENASE BY AQUEOUS EXTRACT OF HANNOA KLAINEANA STEM BARK.

This study was aimed at investigating antioxidant properties and inhibitory effect on Lactate dehydrogenase by aqueous extract of Hannoa klaineana stem bark. The bark of the stem was assessed for its antioxidant activity by determining the ability of the extract to scavenge 2, 2-diphenyl-1-picrylhydrazyl (DPPH.) radical, superoxide anion (O2.-) and nitric oxide radicals. The stem bark showed a significant (p<0.05) maximal inhibition of DPPH. Radical value of 55.23 ± 1.34% at 10,000 µg/ml of extract compared to ascorbic acid which inhibited 72.30 ± 3.12% at the concentration of 10,000 µg/ml. Maximal superoxide anion (O2.-) inhibition was 103.42 µg/ml at the 1000 µg/ml of extract. The IC50 for the stem bark extract inhibition of DPPH and O2.- anion radical were found to be 103.42 µg/ml and 94.21 µg/ml respectively compared to ascorbic acid and quercetin (8.35µg/ml and 10.87µg/ml). The extract was also found to rapidly scavenge nitric oxide at different time intervals. Also, the Km and Vmax of LDH were 27.8 µg/ml and 11.1 µmol/min.mg-1 protein respectively. The double reciprocal plot for the aqueous extract revealed a non competitive type of inhibition based on their doses. The inhibition Constant (Ki) was 14.5 µg/ml which indicates high inhibitory capability of the extract on lactate dehydrogenase in dose-dependent manner. Hence, this plant extract could be use as sources of natural antioxidant, enzyme inhibitory agent and as a promising opportunity in designing a novel drug with high efficacy to slow down the rate at which malaria parasite and tumour cells proliferate.