Macrophage-derived peroxynitrite diffusion and toxicity to Trypanosoma cruzi

We studied the capacity of macrophage-derived peroxynitrite to diffuse into and exert cytotoxicity against Trypanosoma cruzi, the causative agent of Chagas’ disease. In two types of macrophage–T. cruzi co-cultures, one with a fixed separation distance between source and target cells, and another involving cell-to-cell interactions, peroxynitrite resulted in significant oxidation of intracellular dihydrorhodamine and inhibition of [3H]thymidine incorporation in T. cruzi, which were not observed by superoxide or nitric oxide alone. The effects were attenuated in the presence of bicarbonate, in agreement with the extracellular consumption of peroxynitrite by its fast reaction with CO2. However, studies using different T. cruzi densities, which allow to modify average diffusion distances of exogenously added peroxynitrite to target cells, indicate that at distances <5 μm, the diffusion process outcompetes the reaction with CO2 and that the levels of peroxynitrite formed by macrophages would be sufficient to cause toxicity to T. cruzi during cell-to-cell contact and/or inside the phagosome.