Antiplasmodial and Cytotoxic Activities of Extracts of Selected Medicinal Plants Used to Treat Malaria in Embu County, Kenya

Malaria is a deadly disease caused by a protozoan parasite whose mode of transmission is through a female Anopheles mosquito. It affects persons of all ages; however, pregnant mothers, young children, and the elderly suffer the most due to their dwindled immune state. The currently prescribed antimalarial drugs have been associated with adverse side effects ranging from intolerance to toxicity. Furthermore, the costs associated with conventional approach of managing malaria are arguably high especially for persons living in low-income countries, hence the need for alternative and complementary approaches. Medicinal plants offer a viable alternative because of their few associated side effects, are arguably cheaper, and are easily accessible. Based on the fact that studies involving antimalarial medicinal plants as potential sources of efficacious and cost-effective pharmacotherapies are far between, this research was designed to investigate antiplasmodial and cytotoxic activities of organic and aqueous extracts of selected plants used by Embu traditional medicine practitioners to treat malaria. The studied plants includedErythrina abyssinica(stem bark),Schkuhria pinnata(whole plant),Sterculia africana(stem bark),Terminalia brownii(leaves),Zanthoxylum chalybeum(leaves),Leonotis mollissima(leaves),Carissa edulis(leaves),Tithonia diversifolia(leaves and flowers), andSenna didymobotrya(leaves and pods).In vitroantiplasmodial activity studies of organic and water extracts were carried out against chloroquine-sensitive (D6) and chloroquine-resistance (W2) strains ofPlasmodium falciparum.In vivoantiplasmodial studies were done by Peter's four-day suppression test to test for theirin vivoantimalarial activity againstP. berghei. Finally, cytotoxic effects and safety of the studied plant extracts were evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) rapid calorimetric assay technique. The water and methanolic extracts ofT. browniiandS. africanaand dichloromethane extracts ofE. abyssinica,S. pinnata, andT. diversifolialeaves revealed highin vitroantiplasmodial activities (IC50 <= 10 mu g/ml). Further, moderatein vivoantimalarial activities were observed for water and methanolic extracts ofL. mollissimaandS. africanaand for dichloromethane extracts ofE. abyssinicaandT. diversifolialeaves. In this study, aqueous extracts ofT. browniiandS. africanademonstrated high antiplasmodial activity and high selectivity indices values (SI >= 10) and were found to be safe. It was concluded thatT. browniiandS. africanaaqueous extracts were potent antiplasmodial agents. Further focused studies geared towards isolation of active constituents and determination ofin vivotoxicities to ascertain their safety are warranted.