Ex vivo and in vitro antiplasmodial activity and toxicity of Caesalpinia decapetala (Roth) Alston (Fabaceae)

Ethnopharmacological relevance: Malaria is among the most prevalent and devastating parasitic diseases globally with most cases reported in Sub-Saharan Africa. One of the major reasons for the high malaria prevalence is the ever-increasing emergence of resistant strains of malaria-causing parasites to the currently used antimalarial drugs. This, therefore, calls for the search for antimalarial compounds with alternative modes of action. Plants used in traditional medicine for the treatment of malaria offer possible sources of such compounds. Caesalpinia decapetala has been used traditionally for the treatment of various diseases including malaria. However, the antiplasmodial activity of the plant has never been reported. Aim of the study: To determine the ex vivo and in vitro antiplasmodial activities of the extracts of the roots, stem bark and leaves of Caesalpinia decapetala. Methodology: The roots, stem bark and leaves of Caesalpinia decapetala (Roth) Alston (Caesalpiniaceae) were collected and air-dried under a shade then extracted consecutively with dichloromethane and methanol (1:1 (v/ v) (4 x 0.8 L). The extracts were tested for antiplasmodial activities against four strains of Plasmodium falciparum (W2, DD2, 3D7, and D6) and fresh P. falciparum field isolates using the SYBR green I assay. The mean fifty percent inhibition concentration (IC50) was determined for each assay. An acute oral toxicity test was done based on the Organization for Economic Cooperation and Development (OECD 425) guidelines using Swiss albino mice. Results: The leaves and stem bark extracts showed good antiplasmodial activities with IC50 values of 4.54 and 4.86 mu g/ mL, respectively, when tested against the fresh field isolates ex vivo. Similarly, the roots extract showed an IC50 value of 6.49 mu g/mL when tested against field isolates ex vivo. The roots extract showed the highest antiplasmodial activities among the samples when tested against W2 (IC50 = 6.12 mu g/mL), DD2 (IC50 = 8.17 mu g/mL), and D6 (IC50 = 16.02 mu g/ mL) strains of P. falciparum whereas the leaves showed the highest activity (IC50 = 9.3 mu g/mL) when tested against the 3D7 strain of P. falciparum. No mortality was observed for the mice treated with 2000 mg/kg of the leaves and stem bark extracts. The mouse treated with 2000 mg/kg of the roots extracts regained weight by day 12 of the observation period. Conclusion: Caesalpinia decapetala has the potential to suppress the growth of P. falciparum thereby contributing to combating the recurrent emergence of antimalarial drug resistance.