Nitric oxide production by activated human neutrophils exposed to sodium azide and hydroxylamine: the role of oxygen radicals.

The occurrence of a nitric oxide-generating system in human neutrophils has been controversial and the detection of nitric oxide rendered more difficult due to the capacity of oxygen radicals and other compounds to scavenge this molecule. Our results demonstrate that human neutrophils, when stimulated by adherence or by phorbol myristate acetate generate nitrite upon exposure to NaN3 or hydroxylamine. NaN3-dependent nitrite production was further increased by the addition of superoxide dismutase (SOD). The generation of nitrite was also stimulated by exogenous added H202 in resting neutrophils and could be induced in a cell-free system containing heme-enzymes, H202 and NaN3, suggesting a requirement for H202-mediated oxidation of NaN3 in nitrite formation by the stimulated cells. Treatment of the neutrophils with hydroxylamine led to the production of even larger quantities of nitrite (> 25 nmol/h.10(6) cells), an effect that was prevented by SOD, pointing to superoxide as a metabolite possibly involved in nitrite formation. These results emphasize the importance of oxygen radicals or other intermediates in the generation of nitrite by stimulated neutrophils exposed to the above compounds.