Elevated Serum Superoxide Dismutase Levels Correlate with Disease Severity and Neutrophil Degranulation in Idiopathic Pulmonary Fibrosis

1. Tissue damage in idiopathic pulmonary fibrosis is due in part to oxidant-antioxidant imbalance.

2. We evaluated the serum levels of the antioxidant enzyme Cu/Zn superoxide dismutase (EC 1.15.1.1) in 25 patients with idiopathic pulmonary fibrosis, 34 patients with sarcoidosis and 40 healthy control subjects by an enzyme immunometric assay.

3. We found that patients with idiopathic pulmonary fibrosis have higher serum Cu/Zn superoxide dismutase levels than control subjects and patients with sarcoidosis. In addition, serum Cu/Zn superoxide dismutase levels correlate with disease severity indexes in patients with idiopathic pulmonary fibrosis.

4. The increase in serum Cu/Zn superoxide dismutase level in idiopathic pulmonary fibrosis could depend on degranulation of activated neutrophils or release from damaged cells. To elucidate the contribution of neutrophil degranulation we determined the polymorphonuclear cell elastase level in the same specimens. We found a strong correlation between serum Cu/Zn superoxide dismutase and polymorphonuclear cell elastase activities, and, in patients with idiopathic pulmonary fibrosis, we observed higher levels of polymorphonuclear cell elastase than in control subjects and patients with sarcoidosis, which correlated positively with disease severity indexes.

5. Cu/Zn superoxide dismutase can catalyse the dismutation of O₂ into H₂O_z and generate OH · These oxygen radicals are probably the major factors responsible for tissue damage (in particular, alveolar and endothelial cells) and fibrosis in experimental lung injury.

6. Taking into account: (a) the specific enzymic activity of Cu/Zn superoxide dismutase (i.e. production of H₂O₂ and OH ·), (b) the possible enhancement of the effect of reduced glutathione deficiency (high H₂O₂) by increased Cu/Zn superoxide dismutase activity, and (c) the correlation that we found between disease severity and Cu/Zn superoxide dismutase and polyphorphonuclear cell elastase levels, we suggest that, in idiopathic pulmonary fibrosis, increased activities of Cu/Zn superoxide dismutase and polymorphonuclear cell elastase can achieve a pro-inflammatory pathogenic effect.

7. However, the results of this study of serum Cu/Zn superoxide dismutase and polymorphonuclear cell elastase concentrations in individual patients does not support a clear-cut cause-effect relationship between these enzyme levels and the clinical changes in the patients.