PHYTOCHEMICAL SCREENING, EVALUATION OF IN-VITRO ANTIOXIDANT ACTIVITIES AND ACUTE TOXICITY EFFECT OF ORGANIC EXTRACTS OF DORSTENIA MANNII (MORACEAE)

Abstract

Background: Many oxidative stress related diseases are as a result of accumulation of free radicals in the body. A lot of researches are going on worldwide directed towards finding natural antioxidants of plants origins. The aims of this study were to screen for phytochemical constituents, evaluate their in vitro antioxidant activities and acute toxicity effect of the crude organic extracts of D. mannii.

Methods: The phytochemical screening was done using the method of Trease and Evans. 1989, The flavonoid, proanthocyanidin, tannins and phenolic contents of the extracts were also determined using standard phytochemical reaction methods. Antioxidant potential of crude organic extract of D. mannii was assessed using tests involving inhibition of, DPPH, NO and metal chelating. The acute toxicity study was performed according to the OECD,  2004 protocol.

Results: Phytochemical screening revealed the presence of alkaloids, saponines, tannins, and flavonoids in all plant extracts. Glycosides and phlobatannins were also present in all plant extracts except, ethanolic Leaves (EL). Twig extracts had the highest polyphenol content (ET= 815.51 ± 0.57 mg EqCat vs HT= 727.27± 0.36 mg EqCat; P< 0.05), compared to leaves (P< 0.05), thus retaining twigs as the best plant part. The antioxidant activity measurement revealed that, both twig extracts had a comparable scavenging activities of DPPH free radical; IC₅₀ (ET= 5.58 mg/ml vs HT= 6.82 mg/ml) and NO; IC₅₀ (ET= 0.08 mg/ml vs HT= 0.10 mg/ml) respectively, with ET being the most active compared to HT respectively. Both extracts were also observed to significantly chelate metals best at concentrations 0,5 mg/ml and 0,75 mg/ml, for HT and ET respectively, with IC₅₀ (HT= 1.03 x 10^-10 mg/ml vs ET= 5.04 x 10^-10mg/ml; P< 0.05), with HT being the most active compared to ET. For the acute toxicity studies, no death of rats was neither recorded in the control nor in the treated groups indicating that the LD₅₀ > 5000 mg/kg BW. The animals exhibited no changes in general behaviour or physiopatological activities. Although there was a change in the weights of rats in the treated groups, this was significantly reduced in the HT group and statistically not significant in the ET group though higher compare to the control (P< 0.05). Results of blood parameters indicated a significant decrease in AST and ALT levels between the negative control and the treated groups (P< 0.05), with HT lowering AST more than ET.

Conclusions: Our findings provide evidence that the crude extract of D. mannii is a potential source of natural antioxidants, and this justified its uses in folkloric medicines.