Isolation, characterisation and antimalarial activity of four selected South African plants

Abstract

Malaria, an infectious disease affecting both human beings and other animals, is transmitted by parasitic protozoans belonging to the Plasmodium genus. Malaria is commonly treated with drugs such as quinine, chloroquine, and artesunate. However, the incidence of treatment failure due to drug-drug interactions and parasite resistance is increasing. Therefore, the rich medicinal potential of plants found in nature in Africa is increasingly being explored. The traditional use of Lippia javanica, Sclerocarya birrea, Melia azedarach and Capparis tomentosa for the treatment of malaria is well-known, but the phytochemistry of these four plants is not fully known. Parts of these plants were extracted and column chromatography was used to fractionate the extracts. The antioxidant activities of the fractions were determined using free radical scavenging and reducing power assays, while the cytotoxic, antiplasmodial and antitrypanosomal activities were determined using cell toxicity assay, parasite lactate dehydrogenase (pLDH) and trypanosome assay. The methanol stem bark extract of Melia azedarach (Fraction 2) had the highest phenolic content (59.39 mg GAE/g), while the methanol leaf extract of Melia azedarach had the highest flavonoid content of 188.65 mg QE/g. In the reducing power tests and DPPH free radical scavenging activity, the methanol stem bark extract of Melia azedarach had the lowest IC50 value of 0.1074 μg/mL and an IC0.5 value of 0.5296 μg/mL, respectively. Furthermore, the methanol stem bark extract of Melia azedarach at a concentration of 50 μg/mL showed significant cytotoxicity against HeLa cells (-1.22±0.07 %). The methanol stem bark extract of Melia azedarach at the tested concentration (250 μg/mL) decreased the viability of Plasmodium falciparum to 36.38±11.96 % with an IC50 value of 6.5 μg/mL. Concerning the antitrypanosomal activity, the methanol stem bark extract of Melia azedarach affected the viability of the trypanosomes at the tested concentration (250 μg/mL), giving a viability of 14.05 ± 0.59 %, with an IC50 value of 0.4 μg/mL. The presence of epicatechin (29) and catechin (31) in this extract was confirmed using several spectroscopic techniques (IR, NMR, UPLC-MS and HRMS).