In vivo antimalarial activity of Keetia leucantha twigs extracts and in vitro antiplasmodial effect of their constituents.

Ethnopharmacological Relevance: The West African tree Keetia leucantha (Rubiaceae) is used in traditional medicine in Benin to treat malaria. The twigs dichloromethane extract was previously shown to inhibit in vitro Plasmodium falciparum growth with no cytotoxicity (>100µg/ml on human normal fibroblasts).

Materials And Methods: The dichloromethane and aqueous extracts of twigs of K. leucantha were evaluated in vivo against Plasmodium berghei NK 173 by the 4-day suppressive test and in vitro against a chloroquine-sensitive strain of Plasmodium falciparum (3D7) using the measurement of the plasmodial lactate dehydrogenase activity. Bioguided fractionations were realized and compounds were structurally elucidated using extensive spectroscopic analysis.

Results: The in vivo antimalarial activity of K. leucantha dichloromethane and aqueous twigs extracts were assessed in mice at the dose of 200mg/kg/day. Both extracts exhibited significant effect in inhibiting parasite growth by 56.8% and 53.0% (p<0.0001) on day 7-postinfection. An LC-MS analysis and bioguided fractionations on the twigs dichloromethane extract led to the isolation and structural determination of scopoletin (1), stigmasterol (2), three phenolic compounds: vanillin (3), hydroxybenzaldehyde (4) and ferulaldehyde (5), eight triterpenic esters (6-13), oleanolic acid and ursolic acid. The antiplasmodial activity of the mixture of the eight triterpenic esters showed an antiplasmodial activity of 1.66 ± 0.54 µg/ml on the 3D7 strain, and the same range of activity was observed for isolated isomers mixtures.

Conclusions: This is the first report on the in vivo activity of K. leucantha extracts, the isolation of thirteen compounds and analysis of their antiplasmodial activity. The results obtained may partially justify the traditional use of K. leucantha to treat malaria in Benin.