Trypanosoma cruzi, the causative agent of Chagas disease (CD), contains exclusively Fe-dependent superoxide dismutases (Fe-SODs). DuringT. cruziinvasion to macrophages, superoxide radical (O2•−) is produced at the phagosomal compartment toward the internalized parasite via NOX-2 (gp91-phox) activation. In this work,T. cruzicytosolic Fe-SODB overexpressers (pRIBOTEX–Fe-SODB) exhibited higher resistance to macrophage-dependent killing and enhanced intracellular proliferation compared with wild-type (WT) parasites. The higher infectivity of Fe-SODB overexpressers compared with WT parasites was lost in gp91-phox−/−macrophages, underscoring the role of O2•−in parasite killing. Herein, we studied the entrance of O2•−and its protonated form, perhydroxyl radical [(HO2•); pKa= 4.8], toT. cruziat the phagosome compartment. At the acidic pH values of the phagosome lumen (pH 5.3 ± 0.1), high steady-state concentrations of O2•−and HO2•were estimated (∼28 and 8 µM, respectively). Phagosomal acidification was crucial for O2•−permeation, because inhibition of the macrophage H+-ATPase proton pump significantly decreased O2•−detection in the internalized parasite. Importantly, O2•−detection, aconitase inactivation, and peroxynitrite generation were lower in Fe-SODB than in WT parasites exposed to external fluxes of O2•−or during macrophage infections. Other mechanisms of O2•−entrance participate at neutral pH values, because the anion channel inhibitor 5-nitro-2-(3-phenylpropylamino) benzoic acid decreased O2•−detection. Finally, parasitemia and tissue parasite burden in mice were higher in Fe-SODB–overexpressing parasites, supporting the role of the cytosolic O2•−-catabolizing enzyme as a virulence factor for CD.
Reactions of superoxide dismutases with HS − /H 2 S and superoxide radical anion: An in vitro EPR study