Abstract

Dr. Cimanga K. R.*, Ndala K. N., Mutambele H. D., Vlietinck A. J. and Pieters L.

ABSTRACT

The present investigation reported for the first time the antioxidant activity of extracts and fractions as well as acute and sub-acute toxicity of aqueous extract from Urena lobata (Malvaceae) leaves from Demoratic Republic of Congo. Results revealed that all samples inhibited the activities of all selected reactive oxygen species (ROS) with inhibitory concentrations 50 (IC50,) ?g/ml from 2.16 ± 0.00 to 6.06±0.01 ?g/ml against DPPH (2,2?-diphenyl-31-picrylhydrazyl), 5.22 ± 0.00 to 13.± 0.01 ?g/ml against ABTS (2, 2? - azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid, 12.36 ±0.03 to 24.65± 0.00 ?g/ml against superoxide anion (O2?-), 6.25 ± 00 to 21.50 ± 00 ?g/ml against OH? (hydroxyl) and 14.62±0.02 to 25.003 ?g/ml against hydrogen peroxide (H2O2). The most active sample was 80% methanol extract exhibiting the antioxidant activity with IC50 values of 2.16±0.00, 12.56±0.02, 12.36±0.03, 6.25±0.00 and 14.68±0.02 ?g/ml against DPPH, ABTS, O2?, OH? and H2O2 radicals respectively, followed by aqueous extract with IC50 values of 3.52±0.02, 7.15±0.03, 15.06±0.02, 8.26±0.08 and 10.15±0.10 against the same ROS in same order. Among soluble fractions, ethylacetate soluble fraction was the most active exhibiting antioxidant action with IC50 values of 4.15±0.02, 8.62±0.00, 18.36±0.05, 1025±0.012 and 16.25±0.02 ?g/ml against DPPH, APTS, O2?-, OH? and H2O2 radicals respectively. Chloroform, n-butanol and residual aqueous soluble fractions showed appreciable antioxidant activity against all selected ROS with IC50 values ranging from 4.15±0.02 to 24.65±0.10 ?g/ml. U. lobata leaves aqueous and 80% methanol extracts showed a content of total phenols (TP) of 25.86 and 28.62 mg of gallic acid equivalent and 7.52 and 9.06 mg flavonoids (TF) of quercetin equivalent respectively. They exhibited antioxidant activity against these selected ROS with IC50 values ranging from 4.01±0.03 to 8.65±0.06 for TP and 4.27±0.02 to 9.03±0.01 ?/ml for TF. In acute and sub-acute toxicity, aqueous extract did not induced mortality at the highest oral dose of 5000 m/kg body weight, i.e LD50 > 5000 g/kg body weight. It did not influence the levels of organ weights, haematological and biochemical parameters of treated animals compared to untreated. This finding showed that aqueous extract was found safe and well tolerated in animals. U. batatas was considered as a good source of phenolic and flavonoids compounds exerting significant antioxidant activity associated to that of extracts beneficials for human health in the preventing cardiovascular diseases.