Protein nitration in cutaneous inflammation in the rat: essential role of inducible nitric oxide synthase and polymorphonuclear leukocytes

1 We have examined the relationship between neutrophil accumulation, NO. production and nitrated protein levels in zymosan-mediated inflammation in rat skin in vivo. 2 Rats were anaesthetized and cutaneous inflammation was induced by zymosan (injected intradermally, i.d.). Experiments were carried out up to 48 h, in recovery procedures as appropriate. Assays for neutrophil accumulation (measurement of myeloperoxidase), nitric oxide (assessment of NO2-/NO3-) and nitrated proteins (detected by ELISA and Western blot) were performed in skin extracts. 3 The results demonstrate a close temporal relationship between these parameters. Samples were assayed at 1, 4, 8, 24 and 48 h after i.d. injection of zymosan. The highest levels measured of each parameter (P < 0.001 compared with vehicle) were found at 4-8 h, with a reduction towards basal levels by 24 It. 4 Selective depletion of circulating neutrophils with anti-neutrophil antibody abolished neutrophil accumulation and protein nitration. In addition substantially decreased NO levels were found. 5 A selective inducible nitric oxide synthase (iNOS) inhibitor, N-3-aminomethyl-benzylacetamidine-dihydrochloride (1400W) also significantly reduced neutrophil levels and NO production and substantially inhibited protein nitration. 6 We conclude that the neutrophil leukocyte plays an essential role in the formation of iNOS-derived NO and nitrated proteins in inflammation, in a time-dependent and reversible manner. The NO-derived iNOS also has a role in stimulating further neutrophil accumulation into skin. This suggests a close mechanistic coupling between neutrophils, NO production and protein nitration.