East African medicinal plants as a source of lead compounds for the development of new antimalarial drugs

Four traditional medicinal plants of east and central Africa, Emilia discifolia (Oliv.) C. Jeffrey, Senecio stuhlmannii, Indigofera emarginella A. Rich. and Aspilia africana (Pers) C.D. Adams, were screened for in vitro antimalarial activity using the nitro-tetrazolium blue-based parasite lactate dehydrogenase assay. The plant parts were collected in two batches: one in the wet season and the other in the dry season. The ethyl acetate extract of A. africana had the highest antiplasmodial activity against both the chloroquine-sensitive D10 [inhibitory concentration (IC)(50) = 9.3; 7.7-10.9 mu g ml(-1)] and the chloroquine-resistant K1 (IC50 = 11.5; 8.7-14.3 mu g ml(-1)) strains of P. falciparum. There was a positive correlation between the antiplasmodial activity of the extracts against the D10 and K1 strains of P. falciparum (Pearsons' coefficient, r = 0.9691, P =0.05). Yields of extracts and their antiplasmodial activity varied with season in some plant species. This study shows that some East African medicinal plants can serve as a source of lead compounds for the development of new drugs against the chloroquine-sensitive and chloroquine-resistant strains of P. falciparum. The need for optimization of the conditions of harvest to maximize yields is also highlighted.