Protective role of nitric oxide synthases in pulmonary emphysema in mice

Background: It has been reported that alveolar nitric oxide (NO) levels and lung expression levels of several types of NO synthase (NOS) isoforms are increased in patients with pulmonary emphysema. However, the roles of NO and NOSs in the development of pulmonary emphysema remain to be fully elucidated. In this study, we addressed this point in our mice lacking all three NOSs. Methods: Experiments were performed in wild-type (WT), single nNOS-/-, iNOS-/-, eNOS-/-, and triple n/i/eNOS-/- mice. They were treated with intratracheal instillation of either 0.05 unit porcine pancreatic elastase (PPE) or saline (control). Twenty-one days later, pulmonary emphysematous changes were evaluated. Results: At 21 days after intratracheal PPE administration, plasma NOx levels were by far lowest in the triple NOSs-/- mice as compared with the WT mice. Intratracheal PPE administration caused pulmonary emphysematous changes in all the mice studied. Notably, the extents of pulmonary emphysematous changes, as assessed by mean distance of alveolar space and by micro computed tomography value, were most aggravated in the triple n/i/eNOS-/- mice as compared with the WT mice. Those changes were associated with highest number of total cells, macrophages, and lymphocytes in bronchoalveolar lavage fluid. Long-term treatment with sodium nitrate significantly prevented PPE-induced pulmonary emphysematous changes in the triple NOSs-/- mice. Conclusion: These results provide the first evidence that genetic disruption of all NOSs results in markedly exacerbated pulmonary emphysematous changes in mice, indicating an important protective role of NO/NOSs in the pathogenesis of pulmonary emphysema.