Effect of l-leucine methyl ester on growth and ultrastructure of Trypanosoma cruzi

L-Amino acid methyl esters, such as L-leucine methyl ester (Leu-OMe), have been identified as agents targeting the lysosomal system of Leishmania amazonensis amastigotes, by a mechanism that involves ester hydrolysis by parasite enzymes located inside megasomes. We have here analyzed the effect of Leu-OMe on all three evolutive forms of Trypanosoma cruzi, in a search for potential targets of the compound in this protozoan. Treatment of epimastigote forms resulted in dose-dependent growth inhibition, with IC50/1 day = 0.55 +/- 0.21 mM. Incubation with 4-8mM/1 day led to 100% cell death. Treatment of bloodstream trypomastigotes resulted in cell lysis, with an IC50/1 day = 1.46 +/- 0.16 mM. Furthermore, infected macrophages treated with 0.125-1mM Leu-OMe showed a dose- and time-dependent decrease in the percent of amastigote infection. Morphological changes in macrophages were observed only at concentrations above 8mM, at the third day of treatment. Analysis of treated parasites by transmission electron microscopy demonstrated severe morphological alterations in cell shape, mitochondrion and nucleus, while kinetoplast and reservosomes (pre-lysosomal compartments) appeared to be not affected. Lysis of bloodstream trypomastigotes and intracellular amastigotes indicated that lysosomes of T. cruzi are the main target for the drug, since reservosomes occur only in epimastigote forms. The presence of lysosomes in T. cruzi epimastigotes was demonstrated by using ultrastructural cytochemistry.