Pathogenetic Significance of Reactive Oxygen Species in Diffuse Fibrosing Alveolitis

Excessive release of reactive oxygen metabolites (ROM) from lung inflammatory cells has been claimed to be of major pathogenetic significance in diffuse fibrosing alveolitis. In the present study, the content of oxidized methionine residues [Met(O)] as a percentage of total methionine (Met) in BAL-derived proteins was used to assess the biologic effect of ROM. In addition, procollagen-III-peptide was measured in BAL fluid as a marker of fibroblast activation. We investigated bronchoalveolar lavage (BAL) samples from seven control patients without evidence of interstitial lung disease and from 42 patients with fibrosing alveolitis caused by idiopathic pulmonary fibrosis (IPF), n = 20, or by collagen vascular disease (CVD), n = 22. Met(O) was elevated in the patients with IPF or CVD compared with that in the control subjects (8.86 ± 1.26 and 8.13 ± 1.44% versus 3.36 ± 0.49%, p < 0.01 and p < 0.05, respectively; mean ± SEM). A positive correlation was found between percentage of neutrophils in BAL and Met(O) in both groups separately and combined (IPF, r = 0.84; p < 0.001; CVD, r = 0.44; p < 0.05; IPF and CVD, r = 0.60; p < 0.001), whereas an inverse relationship existed between Met(O) and the percentage of alveolar macrophages in BAL (IPF, r = −0.59; p < 0.01; CVD, r = −0.24; NS; IPF and CVD, r = −0.41; p < 0.05). Inverse correlations were found in both groups combined between Met(O) and VC (r = −0.52; p < 0.01), Met(O) and diffusing capacity (Dl CO) (r = −0.40; p < 0.05), Met(O) and resting PaO2 (r = −0.47; p < 0.01), and Met(O) and exercise PaO2 (r = −0.51; p < 0.01). When the patients were assigned to two groups according to their Met(O) value being lower or higher than 5.97% (= mean value of the controls + 2 × SD), it was revealed that high Met(O) was associated with elevated percentage of BAL neutrophils (14.9 ± 3.2 versus 6.1 ± 3.0%; p < 0.005), with reduced percentage of alveolar macrophages in BAL (68.9 ± 3.6 versus 81.7 ± 5.2%; p < 0.01), and with increased procollagen-III-peptide concentration in BAL fluid (1.72 ± 1.29 ng/ml versus 0.23 ± 0.08 ng/ml; p < 0.05). Moreover, lung function parameters representative of interstitial lung disease (VC, Dl CO, resting PaO2, and exercise PaO2) were significantly reduced in patients with high Met(O) values. These data suggest that neutrophils are the major cause of oxidation of methionine residues in extracellular, BAL-derived proteins. The inverse relationship between Met(O) and various lung function parameters implies that these oxidation processes may also cause injury of parenchymal tissue. The association of high Met(O) and elevated procollagen-III-peptide indicates that fibroblast activation, at least in part, may be due to stimulation by ROM.