Augmentation of human neutrophil and alveolar macrophage LTB4 production by N‐acetylcysteine: role of hydrogen peroxide

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Abstract
1 The actions of N‐acetylcysteine (NAC) on hydrogen peroxide (H2O2) and leukotriene B4 (LTB4) production by human resting and stimulated peripheral blood neutrophils and alveolar macrophages were investigated. 2 At a concentration of 100 μM, NAC significantly (P2O2 in the incubation medium of resting and opsonized zymosan (OZ; 0.5 mg ml−1)‐ or N‐formylmethionyl‐leucyl‐phenylalanine (fMLP; 1 μM)‐stimulated neutrophils and of resting and OZ‐stimulated macrophages. At concentrations of 10 μM and above, NAC augmented significantly the level of LTB4 in the supernatants of OZ‐ and fMLP‐stimulated neutrophils (PPPPP2O2 when incubated with exogenous H2O2 concentrations equivalent to those released from OZ‐stimulated neutrophils and macrophages. At no concentration did NAC affect quantitites of measurable LTB4 when incubated with exogenous LTB4. 4 Superoxide dismutase (SOD), which catalyzes the conversion of superoxide anion to H2O2 had no significant effect on LTB4 production by human neutrophils. In contrast, catalase, which catalyzes the conversion of H2O2 to H2O and O2, caused a pronounced, statistically significant (P4 measured in the supernatants of OZ‐ and fMLP‐stimulated neutrophils. 5 H2O2 (12.5 μM and 25 μM, concentrations equivalent to those measured in the supernatants of activated neutrophils and alveolar macrophages, respectively) caused a small (13%) decrease in the quantity of measurable LTB4 (P=0.051 and P−1). 6 In conclusion, the anti‐oxidant drug, NAC, increases LTB4 production by human neutrophils and alveolar macrophages, probably through the elimination of cell‐derived H2O2. LTB4 undergoes a H2O2‐dependent oxidation that is inhibited by NAC but this is unlikely to account 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. British Journal of Pharmacology (1997) 122, 758–764; doi:10.1038/sj.bjp.0701428