Phagocytic cells are believed to play a crucial role in the development of inflammatory lung diseases. We assumed that the oxidation of methionine (met) to methionine sulfoxide [met(O)] by oxygen-derived free radicals released from phagocytes is one parameter to identify the oxidative mechanisms of lung injury. To test this hypothesis we determined the molar ratio of met(O)/met in the soluble protein fraction of bronchoalveolar lavage (BAL) fluids from healthy nonsmokers and from nonsmoking patients with idiopathic pulmonary fibrosis (IPF) or sarcoidosis. The met(O)/met ratio of the healthy nonsmoker group (n = 11) was 0.046 +/- 0.008 (mean +/- SEM). In contrast, the met(O)/met ratio of the nonsmoking IPF group (n = 11) was significantly increased to 0.223 +/- 0.053 (p less than 0.0002). The BAL fluids of this group showed strongly increased numbers of neutrophils but normal numbers of alveolar macrophages (AM). In the sarcoidosis group (n = 10) the met(O)/met ratio (0.048 +/- 0.010) was not significantly different from control values. A close relationship was found between the met(O)/met ratios and the relative as well as the absolute neutrophil counts (r = 0.86; p less than 0.0002; n = 22). In contrast, no significant correlation was found between the met(O)/met ratios and the absolute AM counts (r = 0.22; p = 0.32; n = 22). We conclude that mechanisms of oxidative lung injury in IPF can be characterized by oxidation of met and that this oxidation may be mediated by neutrophils.

myeloperoxidase/H,O,/chloride system and the related compound NH,CI. With taurine monochloramine, another myeloperoxidase-related oxidant, 1.05 mol Met(O) were generated per mol a-l-PI during inactivation. These oxidants attack preferentially one Met residue in a-l-PI, which is identical with Met 358, as concluded from the parallelism of loss of elastase inhibitory activity and oxidation of Met. A similar high specificity for Met oxidation was determined for the xanthine oxidase-derived oxidants. In contrast, the ratio found for ozone and m-chloroperoxybenzoic acid was 6.0 and 5.0, respectively, indicating oxidation of additional Met residues besides the reactive site Met in a-l-PI, i.e. unselective action of these oxidants. Further studies were performed on the efficiency of oxidants for total depletion of the elastase inhibitory capacity of a-l-PI. Ozone and m-chloroperoxybenzoic acid were IO-fold less effective and the superoxide anion/hydroxyl radicals were 3&50-fold less effective to inactivate the elastase inhibitory activity as compared to the myeloperoxidase-derived oxidants. The myeloperoxidase-related oxidants are discussed as important regulators of a-l-PI activity in vivo.

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In proteins released from quiescent human neutrophils during incubation, 21% of the methionine (Met) residues were found to be oxidized. However, the portion of oxidized Met in extracellular proteins increased to 66% after stimulating the cells with zymosan and to 75% after stimulation with phorbol myristate acetate (PMA). Generation of such high levels of oxidized Met in native proteins by activated neutrophils has, so far, not been observed. The presence of superoxide dismutase during incubation of PMA‐stimulated cells produced a negligible effect on methionine oxidation, while the presence of catalase resulted in a methionine suifoxide (Met(O)) content of only 28% in the released proteins. It is proposed that the conversion of Met to Met(O) in these proteins predominantly occurs by action of the myeloperoxidase/ H2O2/Cl− system in the extracellular space.

Eight beagle dogs were exposed for 290 d to a low concentration of sulfur(/\/) aerosol 10.3 mg m -3 S(IQ corresponding to 0.6 mg m -3 sulfur dioxide]. No clinical symptoms were found that could be correlated with the pollutant. However, significant changes were observed in some of the biochemical and cellular parameters determined in sequential bronchoalveolar lavage (EAL) fluids. The protein and albumin concentration increased (p < .05) in the second half of the exposure period, indicating changes in the transudation kinetics of serum proteins into the alveolar lumen. The relative levels of methionine sulfoxide and carbonyl groups in the BAL protein, indicators for oxidative reactions in the respiratory tract, were lowered (p < .03) immediately after the beginning of chronic sulfur(/\/) exposure. This indicates either a lowered oxidant burden andlor an increased antioxidant capacity in the lungs. The enzyme @-Nacetylglucosaminidase increased significantly (p < .05) in the EAL fluid. This increase might be due to enhanced release of lysosomal compounds mediated by sulfite. It did not result from damage of BAL cells, since their viability was not impaired during exposure. Alveolar macrophages (AM) showed a lowered in vitro phagocytosis rate (p < .05) for polystyrene particles and a reduced production (p < .05) of oxygen-derived free radicals after stimulation with opsonized zymosan. These results indicate a reduction in the nonspecific defense capacity of the AM. In conclusion, chronic exposure to an S(IV) aerosol at low concentration might initiate pathobiochemical pathways in the lungs, indicating a potential health hazard.