Effect of nitric oxide donors on oxygen-dependent cytotoxic responses mediated by neutrophils

We analyzed the effect of nitric oxide (NO) on oxygen-dependent cytotoxic r esponses mediated by neutrophils against unopsonized erythrocytes using thr ee NO donors: S-nitrosoglutathione (GSNO), S-nitroso-N-acetylpenicillamine (SNAP), and sodium nitroprusside (SNP), Neutrophils were treated with these compounds for 1-2 min at 37 degrees C and cytotoxicity was then triggered in the presence of NO donors by precipitating immune complexes, aggregated IgG, the chemotactic peptide FMLP, or opsonized zymosan, GSNO induced, in a ll cases, a marked increase in cytotoxic responses, while SNAP moderately i ncreased cytotoxicity triggered by immune complexes, aggregated IgG, or, op sonized zymosen, without modifying those responses induced by FMLP, By cont rast, SNP dramatically suppressed cytotoxicity triggered by all of the stim uli assessed. The enhancing effects mediated by GSNO and SNAP did not depen d on the stimulation of guanylyl cyclase and mere prevented by the NO scave ngers hemoglobin and PTIO (2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide), The inhibitory activity of SNP, on the other hand, was not preven ted by NO scavengers, suggesting that it cannot be ascribed to the release of NO. In another set of experiments, neutrophils were pretreated with GSNO or SNAP for different times. Then cells were washed to remove NO donors fr om the culture medium, and cytotoxicity was triggered by different stimuli. It was found that neutrophils must be pretreated with NO donors for at lea st 4 h to increase cytotoxic responses, and pretreatment for longer periods (i.e,, 8 or 18 h) further increased cytotoxicity. Not only cytotoxic respo nses, but also the production of O-2(-) and H2O2, and the release of myelop eroxidase were increased under these conditions.