Cytotoxicity and antiplasmodial activity of alkaloid extracts prepared from eight african medicinal plants used in Nigeria

Abstract

Objectives: Malaria morbidity and mortality rates are worsening, despite the dedicated commitment to eradicate the infestation, principally because of failing chemotherapy, the mainstay of treatment, and lack of registered vaccine. Therefore, the search for more potent antimalarial agents has become urgent and imperative. Hence, in this study, the cytotoxicity and antiplasmodial activity of the ethanolic leaf extracts and alkaloid fractions of eight 8African medicinal plants used in Nigerian traditional medicine were evaluated using standard methods and documented procedures. Materials and Methods: In vitro antiplasmodial activity was assessed using 3D7 chloroquine-sensitive strain of Plasmodium falciparum maintained at 5% hematocrit (human type O-positive red blood cells) in complete RPMI 1640 medium, while cytotoxicity was determined by the microassay technique using L929 animal cell fibroblasts by the lactate dehydrogenase method. Results: Results indicate that the ethanolic leaf extracts of six out of the eight plants (Tridax procumbens, Ipomoea purpurea, Sida acuta, Senna alata, Phyllanthus amarus, Azadirachta indica, Nauclea latifolia, and Polyalthia longifolia) studied were non-toxic (CC50 range: 33.88–954.99 µg/ml; and Chloroquine, CQ: 79.43µg/ml), but T. procumbens and S. acuta showed mild toxicity (CC50 =23.99µg/ml for each plants) as judged by the standard reference (CC50: 30µg/ml= non-toxic). However, all leaf extracts of the eight plants demonstrated significant (P < 0.05) growth inhibition of P. falciparum (IC50 range: 0.05–0.28µg/ml, CQ: 0.03 µg/ml, standard reference: ≤5 µg/ml=highly active) with very highly rated selectivity index, (SI), values (range: 343–3990, CQ: 2648, reference: >10=selectable). In addition, the alkaloid fractions of the eight plants showed no toxicity (CC50:44.67–954.99 µg/ml) and had very active antiplasmodial activity (IC50: 0.23–2.04µg/ml) with great SI figures (22–2942). Alkaloids from P. amarus, A. indica, N. latifolia, and P. longifolia were particularly reputable (SI=2942, 1361, 2081, and 1516, respectively) for selection. Conclusion: This in vitro study confirms the antiplasmodial activity of these plants and justifies their use in the Nigerian tradomedicine, but further identified the alkaloid constituent as the medicinal phytochemical responsible for the observed antiplasmodial activity. Alkaloids from especially the four notable plants with high SI should, therefore, be characterized with the hope of discovering novel agent(s) against malaria.