RESUMO
Leishmaniasis is one of the major infectious diseases affecting the poorest regions of the world. The present study evaluated the antileishmanial activity of a guaianolide purified from the hydroalcoholic extract of aerial parts of Tanacetum parthenium (L.) Schultz Bip. The isolated compound showed activity against the promastigote form of Leishmania amazonensis, with 50% inhibition (IC(50)) of cell growth at a concentration of 2.6 µg/ml. For the intracellular amastigote form, this guaianolide reduced by 10% the survival index of parasites in macrophages when it was used at 20.0 µg/ml. The selective index (SI) ratio (CC(50) for J774G8 cells/IC(50) for protozoans) was 385, showing that it is more selective against the parasite than mammalian cells. Morphological alterations of protozoans treated with IC(50) included changes in size, shape, and structure (more than one nucleus and flagellum) under both light and scanning electron microscopies.