Increased oxidized methionine residues in BAL fluid proteins in acute or chronic bronchitis

Abstract

Phagocytic cells such as alveolar macrophages (AM) or polymorphonuclear neutrophils (PMN) in the bronchoalveolar tract are a potential source of the oxygen-derived free radicals which are presumed to be involved in lung tissue damage. Previous results have shown that the methionine sulphoxide (MET(O)) content of bronchoalveolar lavage fluid (BALF) protein is a reliable parameter to indicate oxidative processes in idiopathic pulmonary fibrosis (IPF). We measured the molar ratio between MET(O) and methionine (MET) in the BALF protein from healthy nonsmokers (control group), healthy smokers and patients with acute or chronic bronchitis (AB or CB). The MET(O)/MET ratio of the nonsmoking group (n = 11) was 0.046 ± 0.008 (mean ± SEM). Healthy smokers (n = 8) had similar values (0.042 ± 0.008), even though they had strongly increased AM counts in BALF. Patients with AB (n = 12) showed an increased MET(O)/MET ratio (0.191 ± 0.031) and had high PMN but normal AM counts in BALF. Patients with CB (n = 13) showed an increase in the MET(O)/MET ratio (0.086 ± 0.010) and moderately increased PMN and markedly increased AM counts. Taking all results together, the MET(O)/MET ratio correlated positively with the relative PMN number (r = 0.70; p < 0.0002) and inversely with the relative AM number (r = -0.67; p < 0.0002). In the group with CB, the MET(O)/MET ratio correlated inversely with forced expiratory volume in one second (FEV1) % pred. (r = -0.77) and FEV1/inspiratory vital capacity (IVC) % pred. (r = -0.89). We conclude that oxidative pulmonary processes in AB and CB are reflected in an increase of the MET(O) content in the BALF protein, which is predominantly mediated by PMN.