Macrophages are among the first cellular actors facing the invasion of microorganisms. These cells are able to internalize pathogens and destroy them by means of toxic mediators, many of which are produced enzymatically and have strong oxidizing capacity. Indeed, macrophages count on the NADPH oxidase complex activity, which is triggered during pathogen invasion and leads to the production of superoxide radical inside the phagosome. At the same time, the induction of nitric oxide synthase results in the production of nitric oxide in the cytosol which is able to readily diffuse to the phagocytic vacuole. Superoxide radical and nitric oxide react at diffusion controlled rates with each other inside the phagosome to yield peroxynitrite, a powerful oxidant capable to kill microorganisms. Peroxynitrite toxicity resides on oxidations and nitrations of biomolecules in the target cell. The central role of peroxynitrite as a key effector molecule in the control of infections has been proven in a wide number of models. However, some microorganisms and virulent strains adapt to survive inside the potentially hostile oxidizing microenvironment of the phagosome by either impeding peroxynitrite formation or rapidly detoxifying it once formed. In this context, the outcome of the infection process is a result of the interplay between the macrophage-derived oxidizing cytotoxins such as peroxynitrite and the antioxidant defense machinery of the invading pathogens.

No abstract

No abstract

Trypanosoma cruzi, the causative agent of Chagas disease (CD), contains exclusively Fe-dependent superoxide dismutases (Fe-SODs). During T. cruzi invasion 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. cruzi cytosolic 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], to T. cruzi at 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.

No abstract

Nitration of arachidonic acid (AA) to nitroarachidonic acid (AANO2) leads to anti-inflammatory intracellular activities during macrophage activation. However, less is known about the capacity of AANO2 to regulate the production of reactive oxygen species (ROS) under pro-inflammatory conditions. One of the immediate responses upon macrophage activation involves the production of superoxide radical (O2·−), due to the NADPH dependent univalent reduction of oxygen to O2·− by the phagocytic NADPH-oxidase isoform (NOX2), being the activity of NOX2 the main source of O2·− in monocytes/macrophages. Since NOX2 and AA pathways are connected, we propose that AANO2can modulate macrophage activation by inhibiting O2·− formation by NOX2. When macrophages were activated in the presence of AANO2, a significant inhibition of NOX2 activity was observed as evaluated by cytochrome c reduction, luminol chemiluminescence, Amplex Red fluorescence and flow cytometry; this process also occurs in physiological mimic conditions within the phagosomes. AANO2 decreased O2·− production in a dose-(IC50= 4.1 ± 1.8 μM AANO2) and time-dependent manner. The observed inhibition was not due to a decreased phosphorylation of the cytosolic subunits (e.g. p40phox and p47phox), as analyzed by immunoprecipitation and western blot. However, a reduction of the migration to the membrane of p47phox was obtained suggesting that the protective actions involve the prevention of the correct assembly of the active enzyme in the membrane. Finally, the observed in vitro effects were confirmed in an in vivo inflammatory model, where subcutaneous injection of AANO2 was able to decrease NOX2 activity in macrophages from thioglycolate treated mice.

No abstract

No abstract