Screening for antimalarial activity of crude extracts from African medicinal plants

Malaria is still one of the most important diseases in this century. It has been estimated that in the last 20 years mortality from malaria has doubled (it is currently 3 millions deaths annually), and a major factor responsible for this increase is the resistance of malaria parasites to antimalarial drugs. [1] For this reason, there is an urgent need to discover new and affordable antimalarials. Antimalarial drugs derived from plants appear to be promising therapeutic candidates as exemplified by artemisinin and quinine, two of the most effective drugs against Plasmodium falciparum.

The aim of this study was to carry out a scientific evaluation of the claimed antimalarial properties of plants used in traditional medicine against malaria and fever, in order to validate their use. Therefore, 53 crude extracts from fourteen plants used in traditional medicine, mainly from Southern African regions, were screened for their in vitro antimalarial activity against the 3D7 P. falciparum strain. The air-dried powdered plant parts (roots, leaves, seeds or bark) or whole plants were extracted, sequentially, with solvents of increased polarity (hexane, dichloromethane, ethyl acetate and methanol). Schizontocidal activity was measured using a standard in vitro assay, with chloroquine as positive control. From the 53 extracts tested, one of them (2%) showed a significant activity (IC₅₀ <5µg/ml), 13 extracts (25%) showed moderate activity (10 <IC₅₀ <50 µg/ml), 21 (40%) weak activity (50 <IC₅₀ <100 µg/ml) and 18 extracts (34%) were inactive (IC₅₀ >100µg/ml). Further investigation of the most active extracts (Momordica balsamina L) is clearly warranted.

Acknowledgements: The authors wish to thank the Science and Technology Foundation, (FCT, grant SFRH/BD/22321/2005).

References: 1. WHO and Bloland, PB., 2001. Drug resistance in malaria. Geneva. WHO/CDS/CSR/DRS/2001.4 Ed. 2001.4,27p.