AUGMENTATION OF HUMAN NEUTROPHIL AND ALVEOLAR MACROPHAGE LTB4 PRODUCTION BY N-ACETYLCYSTEINE - ROLE OF HYDROGEN-PEROXIDE

1 The actions of N-acetylcysteine (NAG) on hydrogen peroxide (H2O2) an d leukotriene B-4 (LTB4) production by human resting and stimulated pe ripheral blood neutrophils and alveolar macrophages were investigated. 2 At a concentration of 100 mu M, NAC significantly (P<0.01) suppress ed the accumulation of H2O2 in the incubation medium of resting and op sonized zymosan (OZ; 0.5 mg ml(-1))- or N-formylmethionyl-leucyl-pheny lalanine (fMLP; 1 mu M)-stimulated neutrophils and of resting and OZ-s timulated macrophages. At concentrations of 10 mu M and above, NAC aug mented significantly the level of LTB4 in the supernatants of OZ-and f MLP-stimulated neutrophils (P<0.01 and P<0.05, respectively) and OZ-st imulated macrophages (P<0.05 at 10 mu M, P<0.01 at 100 mu M NAG). 3 NA C (100 mu M) caused a significant (P<0.01) reduction in the quantity o f measurable H2O2 when incubated with exogenous H2O2 concentrations eq uivalent to those released from OZ-stimulated neutrophils and macropha ges.;it no concentration did NAC affect quantitites of measurable LTB4 when incubated with exogenous LTB4. 4 Superoxide dismutase (SOD), whi ch catalyzes the conversion of superoxide anion to H2O2 had no signifi cant effect on LTB4 production by human neutrophils. In contrast, cata lase, which catalyzes the conversion of H2O2 to H2O and O-2, caused a pronounced, statistically significant (P<0.01) increase in the levels of LTB4 measured in the supernatants of OZ-and fMLP-stimulated neutrop hils. 5 H2O2 (12.5 mu M and 25 mu M, concentrations equivalent to thos e measured in the supernatants of activated neutrophils and alveolar m acrophages, respectively) caused a small (13%) decrease in the quantit y of measurable LTB4 (P=0.051 and P<0.05 at 12.5 mu M and 25 mu M, res pectively) that was inhibited by NAC (100 mu M) but not by catalase (4 00 u ml(-1)). 6 In conclusion, the anti-oxidant drug, NAG, increases L TB4 production by human neutrophils and alveolar macrophages, probably through the elimination of cell-derived H2O2. LTB4 undergoes a H2O2-d ependent oxidation that is inhibited by NAC but this is unlikely to ac count fully for the increased levels of LTB4, suggesting that NAC may increase LTB4 production by blocking the H2O2-dependent inhibition of a synthetic enzyme, such as 5-lipoxygenase.