Assessment of Antiplasmodial Activity and Toxicity of Crude Extracts and Isolated Compounds from Oncoba spinosa (Flacourtiaceae)

Aims: The medicinal plant Oncoba spinosa is used by the local communities in Butebo County in Eastern Uganda for treatment of malaria and other diseases. In vitro antiplasmodial activities of the crude extracts and isolated compounds were screened against chloroquine sensitive 3D7 and resistant Dd2 strains. In vivo acute toxicity of the extracts and structure elucidation were also determined in the study.

Experimental: Crude extracts of: n-hexane, dichloromethane, ethyl acetate and methanol were prepared. Isolation and purification of these extracts were done using chromatographic techniques which consisted of column and thin layer chromatography. The structures were elucidated on the basis of spectroscopic evidence. In vitro antiplasmodial activity was performed on chloroquine sensitive 3D7 and resistant Dd2 strains of Plasmodium falciparum using SYBR Green 1 assay technique. Lorke’s method of acute toxicity was used to determine the in vivo acute toxicity of the crude extracts in mice.

Results: The root ethyl acetate crude extract had highest antiplasmodial activity of IC50:4.69 ± 0.01 µg/mL and 3.52 ± 0.02 µg/mL against 3D7 and Dd2 strains respectively while the remaining three were inactive against both strains of Plasmodium. Isolation resulted in the identification of three known compounds which included: β-sitosterol, benzoic acid and chaulmoogric acid. Among the tested compounds β-sitosterol showed the highest activity of IC50 3D7: 5.51 µM. Dichloromethane and hexane extracts were non-toxic with LD50 > 5000 mg/kg while the EtOAc and MeOH extracts were slightly toxic with LD50 of 547.72 mg/kg. Statistically significance existed between the antiplasmodial activity of the crude extracts and compounds when compared with the controls at (p < 0.05). Extracts and compounds exerted a significant (P < 0.05) decrease in antiplasmodial activity compared to the positive controls.

Conclusion: The findings confirm the ethnobotanical use of O. spinosa by the local communities in Butebo County for the treatment of malaria. The results also suggest that the crude extract of this plant is safe and possesses antimalarial activity which can be used as a basis for in vivo and clinical studies to be done. Therefore the plant can offer a potential drug lead for developing a safe, effective and affordable antimalarial.