Anti-leishmanial activity of allicin (=diallyl thiosulphinate) has been tested in vitro against promastigotes and intracellular amastigotes of Leishmania donovani and Leishmania infantum. Macrophage infections have been carried out in vitro in the murine cell line J774 and ex vivo with peritoneal macrophages from BALB/c mice with a modified method to isolate metacyclic promastigotes. The compound has shown a significant in vitro effect on the multiplication of promastigotes of L. donovani and L. infantum in a time- and dose-dependent manner. It has been shown for the first time the inhibition of multiplication of intracellular amastigotes of Leishmania by allicin. Inhibitory concentrations of the compound were in the micromolar range (10-30 μM) for both Leishmania species. Antileishmanial effect of allicin apparently was not related to products of degradation of the molecule as assessed by mass spectrometry analysis. Inhibitory activity of allicin against promastigotes and intracellular amastigotes increased when the compound was added to the cultures every 24 h. Two administrations of 5 μM allicin inhibited by ca. 50% the proliferation of Leishmania amastigotes. Low toxicity for mammalian cells of this compound suggests the interest of exploring the value of allicin in combined therapy against leishmanial infections.
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