IN VITRO ANTIOXIDANT AND FREE SCAVENGING ACTIVITIES OF EXTRACTS AND FRACTIONS, ACUTE AND SUB-ACUTE TOXICITY OF AQUEOUS EXTRACT FROM MORINDA NORINDOIDES (BAKER) MILNE-REDHEAD (RUBIACEAE) LEAVES IN EXPERIMENTAL WISTAR RATS

Cimanga K. R.*, Kapanda M. P., Vlietinck A. J., Pieters L.

ABSTRACT

Aqueous extract, its soluble fractions chloroform, ethylacetate, n-butanol and residual aqueous, as well as 80% methanol extract and polysaccharides from Morinda morindoides leaves were submitted to the evaluation of their potential antioxidant activity against some selected reactive oxygen species (ROS) including DPPH (2,2’ diphenyl-1-picrylhydrazyl), ABTS (2,2-azino-bis-3-ethylbenzothiazoline-6-sulphonate or 2,2-azino-bis-ethylbenzothiasoline sulfonic acid), superoxide anion O2●-, hydroxyl HO● and hydrogen peroxide H2O2. Acute and sub-acute toxicity of aqueous extract was also evaluated in experimental Wistar rats. Results showed that aqueous extract and its soluble fractions, and 80% methanol extract exerted pronounced antioxidant activity by inhibiting the activity of selected reactive oxygen species with IC50 values < 10 µg/ml. 80% methanol extract exhibited high activity with IC50 values ranging from 2.05±0.00 to 3.52±0.01 µg/ml compared to aqueous extract and its soluble fractions with IC50 values from 3.25±0.01 to 9.81±0.02 µg/ml. All soluble fractions displayed this activity with IC50 values ranging from 4.16±0.02 to 9.81±0.02 µg/ml. Polysaccharides exhibited this activity with IC50 values from 15.05±0.03 to 52.06±0.02 µg/ml. Flavonoids quercetin, rutin and quercetrin exhibited antioxidant activity with IC50 values from 3.15±0.03 to 25.60±0.01 µg/ml while kaempferol, kaempferol-3-O-rutinoside and kaempferol-7-O-rhamnosylsophoroside displayed this activity with IC50 values ranging from 7.82±0.01 to 25.06±0.03 µg/ml. In acute and sub-acute toxicity, aqueous extract did not induce mortality in treated animals at the highest oral dose of 5000 mg/kg body weight [(LD50) > 5000 mg/kg body weight)]. It was devoid with considerable influence on vital organ weights, serum electrolytes, haematological and biochemical parameters of treated rats. Thus, it was found to be practically non-toxic and safe by oral route. Thus, the aqueous extract from M. morindoides leaves can be used for the prevention of the occurring of some diseases mainly cardiovascular in humans.

Keywords: Morinda morindoides, leaves, extracts, fractions, polysaccharides, antioxidant activity, acute and sub-acute toxicity.