THE EFFECT OF NITRIC-OXIDE AND PEROXYNITRITE ON APOPTOSIS IN HUMAN POLYMORPHONUCLEAR LEUKOCYTES

In acute lung injury, neutrophil apoptosis may be important in regulat ing the inflammatory process by controlling neutrophil numbers and thu s activity. Exogenous inhaled nitric oxide is now a widely used therap y in patients with acute lung injury, and its effects on apoptosis may be important. We investigated the effect of nitric oxide and peroxyni trite on apoptosis in lipopolysaccharide stimulated polymorphonuclear leukocytes as a model of nitric oxide-treated lung injury. Cells were incubated for up to 16 h with and without 1.7 mu g/ml lipopolysacchari de and the nitric oxide donor GEA-3162 or the peroxynitrite donor SIN- 1. Apoptosis was assessed using flow cytometry following annexin-V sta ining, after 4, 6, 8, and 16 h. Data were assessed using Kruskal-Walli s analysis of variance or Mann-Whitney U-test as appropriate. Annexin- V staining increased spontaneously over 16 h in untreated cells (p =.0 002) and incubation with either 1000 mu M SIN-1 or 10 mu M GEA-3162 in creased annexin staining at early time points in nonactivated cells. A poptosis was attenuated when cells were exposed to lipopolysaccharide and both nitric oxide and peroxynitrite dose dependently inhibited thi s suppression at all time points and was most apparent at 16 h (p =.00 4 and .001, respectively). Exposure of activated neutrophils to exogen ous nitric oxide or peroxynitrite has marked influences on apoptosis. This work has implications for the modulation of neutrophil function w ithin the lung in patients with lung injury who receive inhaled nitric oxide therapy. (C) 1998 Elsevier Science Inc.