Antiplasmodial and toxicity activities and characterization of chemical compounds extracted from selected medicinal plants in Uganda

Abstract

Malaria caused by Plasmodium parasite is at the moment the one of the highest killer disease in the tropics. In developing countries, where malaria is one of the most prevalent diseases, some people still rely on traditional medicine for the treatment of this disease. In the present study an ethnobotanical survey was conducted to document antimalarial medicinal plants. In vitro antiplasmodial and in vivo toxicity activities were carried out on crude root extracts and on the isolated pure compounds from Oncoba spinosa, Acacia sieberiana and Euclea latideus. Structure elucidation was also carried out on the isolated pure compounds. The ethnobotanical survey was conducted by use of semi-structured interviews and a guided questionnaire. The characterization of the isolated compounds was determined using NMR technique only. The antiplasmodial activity was performed using a fluorescence based SYBR Green 1 assay technique on 3D7 and Dd2 Plasmodium strains. Lorke’s method was used to determine the in vivo acute toxicity of the extracts on mice. Thirty three plant species from 30 genera belonging to 23 families were documented, of these ten species (30.3 %) were recorded for the first time as antimalarial plants. Acute toxicity studies showed that all crude extracts of E. latideus and A. sieberiana had LD50 > 5000 mg/kg. The LD50 for hexane and CH2Cl2 extracts of O. spinosa were > 5000 mg/kg while the EtOAc and MeOH had 547.72 mg/kg. The EtOAc extract of O. spinosa had high activity of (IC50) 3D7: 4.69 ± 0.01 μg/mL and Dd2: 3.52 ± 0.02 μg/mL. Extracts of E. latideus had high activity (IC50) 3D7: (9.75-38.21) μg/mL and Dd2: (2.78-38.93) μg/mL. A. sieberiana extracts had the highest activity of (IC50) 3D7: (4.45-27.32) μg/mL and Dd2: (3.38-21.87) μg/mL. Isolation resulted in the identification of eight known compounds which included; three triterpenoids Lupeol, betulin, 3β-(5-methoxyferuloyl)lup-20(30)-ene; two steroids β-sitosterol, stigmasitosterol; benzoic acid and an aliphatic acid chaulmoogric acid. Betulin and β-sitosterol had the highest activity (IC50) 3D7: 3.71 and 5.51 μM, respectively. Antiplasmodial activities of the extracts (IC50: 2.76- > 50) μg/mL, pure compounds (IC50: 3.71- > 120.77) μM of the three plants and the controls (IC50: 0.0056-0.0440) μg/mL showed significance among themselves at (P < 0.05). Extracts and compounds exerted a significant (P < 0.05) decrease in antiplasmodial activity compared to the standard controls. The findings show that the crude extracts and pure compounds have got high antiplasmodial activity and lack toxicity. Therefore the local communities can continue to use the three plants for the treatment of malaria and this justifies the ethanomedicinal use of the plants for the management of malaria.