The trypanothione-thiol system in Trypanosoma cruzi as a key antioxidant mechanism against peroxynitrite-mediated cytotoxicity

Peroxynitrite, the reaction product between superoxide (O(*2)) and nitric oxide (*NO), is a powerful oxidizing species that contributes to macrophage competence against pathogens. In this context, peroxynitrite appears to play an important role in controlling infection by Trypanosoma cruzi, the unicellular parasite responsible for Chagas disease. T. cruzi contains various enzyme systems for the decomposition of hydroperoxides, all of which involve the participation of the low-molecular-weight dithiol trypanothione (N(1),N(8)-bis(glutathionyl)spermidine) as a critical redox partner. A large fraction of the trypanothione-dependent antioxidant capacity of T. cruzi is linked to the tryparedoxin-tryparedoxin peroxidase system which has critical protein thiol groups. In this report we demonstrate that dihydrotrypanothione is readily consumed during peroxynitrite challenge to cells to yield the corresponding trypanothione disulfide. On the other hand, glutathione, which is present in T. cruzi at lower concentrations than trypanothione, is consumed to a much lesser extent and mainly evolves to glutathione-protein mixed disulfides. The inhibition of glutathione biosynthesis by buthionine sulfoximine, which decreases glutathione concentration to 10% of control after 20 h, neither affects the concentration of dihydrotrypanothione nor sensitizes T. cruzi to peroxynitrite-mediated cytotoxicity. On the other hand, pretreatment of T. cruzi with diamide, which leads to a significant depletion (>70%) of dihydrotrypanothione, largely increases the extent of cellular nitration and inhibition of cell growth caused by peroxynitrite. Altogether, our findings support a key protective role for dihydrotrypanothione and the trypanothione-dependent antioxidant system in T. cruzi against peroxynitrite, which may facilitate the survival of trypanosomes within the oxidative environment of activated macrophages.