Comparative study on phytochemical constituents, antioxidant activity and acute toxicity of extracts of <i>Alstonia boonei</i> de Wild and <i>Anthocleista djalonensis</i>

Abstract

The phytochemical constituents, in vitro antioxidant activity and acute toxicity of the aqueous and ethanol stem-bark extracts of Alstonia boonei and Anthocleista djalonensis were investigated. Phytochemical quantification test revealed that the aqueous extract of A. djalonensis had a significantly higher (p<0.05) amount of total phenol than other extracts. The ethanol extract of A. boonei however had significantly higher levels (p<0.05) of total flavonoid and proanthocyanidin. DPPH’s radical scavenging activity of the aqueous extract of A. djalonensis (IC₅₀ of 8.75±0.22) was better than that of the other extracts and close to that of ascorbic acid standard (IC₅₀ 1.12±0.23). The extracts had significantly higher (p<0.05) ability to reduce ferric ions to the ferrous form when compared with the ascorbic acid standard. Although the extracts possessed significantly lower (p<0.05) reducing potential than the ascorbic acid standard, both extracts of A. djalonensis were able to inhibit lipid peroxidation with the aqueous counterpart proving to be more superior. The acute toxicity study involved the administration of a single oral dose of the extracts at varying concentrations. LD₅₀ of both extracts of A. djalonensis and the ethanol extract of A. boonei were beyond 5000 mg/kg body weight of the extract. However, for the aqueous extract of A. boonei some signs of toxicity were observed. These included increase in respiratory rate for the animals that received 3000 and 5000 mg/kg and eventual death at the latter dose. These results suggest that the aqueous extract of A. djalonensis possess better antioxidant property than the other extracts studied.

Keywords: Alstonia boonei; Anthocleista djalonensis; Phytochemical constituents; Antioxidant capacity; Acute toxicity