Evaluation of the antimalarial activity of extracts of carob tree (Ceratonia siliqua L.)
Over the twentieth century, the worldwide area of land affected by malaria decreased from 54 to 27% [1[. In spite of this reduction, malaria still remains the most important parasitic disease in the world: the worldwide morbidity and mortality caused by this disease is overwhelming, with 300–500 million cases and 1.5–2.7 million deaths each year . The malaria problem is also worsening due to parasite drug resistance, with strains of Plasmodium falciparum becoming progressively more resistant to antimalarials such as chloroquine . In order to attenuate the effects of the disease, a search for new antimalarial compounds is increasing. Since plants have proved to be potential sources for new antimalarial drugs, in the present study methanolic and aqueous extracts of pulp, seed coat + germ, bark and leaves from carob tree were tested in different concentrations (125, 62.5, 15.6, 7.8 and 0.975µg.ml-1) against two strains of Plasmodium falciparum: the 3D7 chloroquine – sensitive, and the Dd2 chloroquine – resistant. The inhibitory activity was evaluated by flow cytometry. The results were expressed as inhibition of parasite growth with increasing concentration of the extracts, and by IC50 (half maximal inhibitory concentration), which was used for the classification of the activity of the extracts as high, moderate or weak . Extracts having activity beyond this range were considered inactive . Based on this classification, active extracts were found, namely aqueous leaf extracts on strain 3D7 (IC50=3µg.ml-1), methanolic extracts from seed coat + germ on both strains (IC50 =6.1µg.ml-1) and aqueous extracts from bark, also on both strains (3D7: IC50 =5.7 and Dd2: IC50 =3.4µg.ml-1). The results obtained in this work suggest that some of the extracts tested may have antimalarial interest, and work is in progress aiming the fractionation of the extracts, their chemical characterization and study of their activity, in order to understand which compound or group of compounds are responsible for the antimalarial activity detected.
Acknowledgements: L. Marques thanks a Leonardo Da Vinci grant, and L. Custódio a post-doctoral grant (SFRH/BPD/20736/2004) from Portuguese Foundation for Science and Technology (FCT).
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