In Vitro Anti-Plasmodial and In Vivo Anti-Malarial Activity of Some Medicinal Plants Used by the Meru Community in Kenya for Treatment of Malaria
Gathirwa, Jeremiah Waweru
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Malaria is a serious disease affecting approximately 500 million people worldwide resulting in 3 million deaths every year. Increasing resistance to the commonly used antimalarial drugs has impacted negatively to its treatment. Concequently, there is an urgent need to develop new drugs. Plants have been considered to be a possible alternative and a rich source of new drugs. Most traditional healers in Africa use medicinal plants in combination and not singly. Research to justify use of medicinal plants in treatment of malaria alone and in combination is a priority. The objective of this study was to investigate the efficacy and safety of traditional anti-malarial plant extracts individually and in combination. Aqueous and methanol extracts of 15 plants traditionally used for treatment of malaria in Meru District, Kenya were tested in vitro and in vivo against Plasmodium falciparum (06 and W2 clones) and P. berghei. Toxicity of the active extracts was evaluated in vitro and in vivo, while their interactions in combination were tested by the sum-FIC method. Of the plants tested in vitro, 25.0% were highly active (ICso <10 ug/ml), 45.59% moderately active (ICso 10-50 ug/ml), 16.18% had weak activity of 50-100 ug/ml while 13.24% were not active ICso >100 ug/ml. Both the water and methanol extracts of Boscia salicifolia Olivo and Artemisia afra Jacq. ex Willd. were the most active against both the chloroquine (CQ) sensitive (D6) and the CQ resistant (W2) P. falciparum clones. When tested in vivo in a mouse model, A. afra and Rhus natalensis Bernh. ex Krauss. depicted the highest percent parasite clearance and a chemossupresion greater than 70%. Evaluating effect of combining some of these extracts with one another or with CQ against the multi-drug resistant P. falciparum clone W2 revealed some synergistic effect. Marked synergy/additive effect was among blends of plant extracts as opposed to blends with CQ that in many cases was antagonistic. The highest synergy was between Sclerocarya birrea (A.Rich.) Hochst + Lannea schweinfurthii (Engl.) Engl., A. afra + Clausena anisata (Willd.) Hook. f. ex. Benth., A. afra + L. sweinfurthii, and A. afra + Clutia robusta Pax, E, FZ. The interaction between Tabernaemontana holstii K. Schum + chloroquine was largely additive. Impressive cytotoxicity results were obtained with most of the plants tested revealing high selectivity indices an indication of enabling achievement of therapeutic doses at safe concentrations. In vivo acute toxicity on these medicicinal plants revealed that most were not toxic at a high dose of 5000 mg/kg body weight. The plants with low ICso values, high percent chemossupresion and low toxicity profiles are potential sources for novel antiplasmodial agents. These findings also justify use of combined medicinal plants in traditional medicine practices.