Elevation of nitrotyrosine and nitrate concentrations in cystic fibrosis sputum

Nitric oxide (NO) is increased in the exhaled air of some patients with inf lammatory lung disorders, but not in others. NO may combine with superoxide to form peroxynitrite, which lowers NO gas concentrations, increases forma tion of nitrate, and increases nitration of tyrosine residues on proteins. We hypothesized that superoxide released from neutrophils in the lower resp iratory tract of cystic fibrosis (CF) results in increased nitrate and nitr otyrosine levels in sputum. In order to test this hypothesis, exhaled NO wa s collected from 5 stable adult CF subjects and from 5 nonsmoking normal co ntrols. Consistent with previous reports, exhaled NO concentrations were not increa sed in CF exhaled air (22.6 +/- 1.5 ppb vs. 28.6 +/- 1.5 ppb in normals, P > 0.05). Sputum was collected from 9 adult CF subjects and the same 5 norma l controls and evaluated for nitrite, nitrate, and nitrotyrosine. Nitrate a nd nitrotyrosine levels, but not nitrite, were significantly elevated in CF . Recently, myeloperoxidase has also been implicated as a mechanism of nitr otyrosine formation. Therefore, myeloperoxidase was measured and found to b e elevated in the CF sputum (64.2 +/- 35.9 vs. 0.73 +/- 0.16 U/ml, P < 0.00 1), and was found to correlate with concentrations of nitrotyrosine (r = 0. 87, P < 0.05). However, in vitro studies with myeloperoxidase and murine lu ng epithelial cells did not demonstrate a reduction of NO gas with nitrotyr osine or an increase in nitrate formation. These data demonstrate that nitrate and nitrotyrosine are elevated in the s puta of CF subjects and suggest increased production of NO in the lower res piratory tract of OF patients, despite the relatively low exhaled NO levels . Published 2000 Wiley-Liss, Inc.(dagger)