Antiplasmodial Properties of Alstonia boonei Stem-Bark and Picralima nitida Seed in Different Combinations

Abstract

The use of mixtures of plants in form of decoctions is common practice in African ethnomedicine.The study evaluated the antiplasmodial activities of the freeze-dried decoctions of different combination ratios of the stem-bark of Alstonia boonei De Wild (Apocynaceae) and dry seed of Picralima nitida (Stapf) T.&H.Dur. (Apocynaceae) against chloroquine-sensitive Plasmodium bergheiberghei NK65 strain.Thus, the decoctions of the mixtures of A. boonei stem-bark (A) and P. nitida seed (P) were prepared in three different ratios 1:1 (AP1), 1:2 (AP2) and 2:1 (AP3), were separately filtered, concentrated in vacuo and freeze-dried to obtain the corresponding extractive for each ratio. The acute toxicity test was carried out on each of the ratios using Lorke’s method. The antiplasmodial activity of each ratio was assessed using 4-day test at 1.5-100 mg/kg. The ratio with the best chemosuppressive activity was subjected to prophylactic and established malaria infection tests at 6.25–50 mg/kg, with pyrimethamine (1.25 mg/kg) and chloroquine (5 mg/kg) as positive controls, respectively. The LD₅₀ of each extractive was greater than 5000 mg/kg. The chemosuppressions of AP1, AP2 and AP3 at 12.5 mg/kg were 55.7%, 64.4% and 57.2%, respectively, with AP2 being comparable to chloroquine. The ED₅₀ for AP1, AP2 and AP3 were 27.8, 26.0 and 29.7 mg/ kg, respectively.Furthermore, AP2 exhibited curative activity with parasite clearance between 82.6% and 84% at 12.5 - 50 mg/kg while it showed prophylactic activities between 46.5% and 55.3% at the same doses. The observed antiplasmodial activities of the freeze-dried extractive (AP2) from the decoction of A. boonei stem-bark and P. nitida seed in ratio 1:2 can therefore be exploited for herbal antimalarial drug development.

Keywords: Antimalarial, Parasitaemia, Pyrimethamine, Chemosuppression