Guanine nitration in idiopathic pulmonary fibrosis and its implication for carcinogenesis

Rationale: Nitric oxide (NO)-induced nitrative stress of nucleic acids, as evidenced by guanine nitration, appears to be involved in inflammation-induced carcinogenesis. A high incidence of lung cancer in idiopathic pulmonary fibrosis (IPF) is the major reason for poor prognosis in patients with IPF. Objectives and Methods: We immunolhistochemically analyzed the formation and localization of 8-nitroguanine in lung tissues from control subjects, patients with IPF, and patients with lung cancer. Main Results: Immunolhistochernical analysis of control smoker and nonsmoker lungs showed weak immunoreactivity for 8-nitroguanine, mainly in cytoplasm of bronchial epithelial cells. In addition to the bronchial epithelial cells, metaplastic regenerated epithelial cells overlying dense fibrotic lesions in IPF showed strong 8-nitroguanine staining in the cytoplasm. The staining in these metaplastic cells colocalized with staining of inducible and endothelial NO synthases and 8-oxodeoxyguanosine, as evidenced by doubleimmuno-staining analysis. Confocal and immunoelectron microscopy revealed localization of 8-nitroquanine in metaplastic epithelial cytoplasm, mostly in mitochondria. Appreciable 8-nitroguanine immunostaining was also observed in both nuclei and cytoplasm of malignant epithelial cells in squamous cell carcinoma. No significant difference was found in the epithelial 8-nitroguanine formation between control smokers and nonsmokers, but much higher guanine nitration was observed in patients with IPF than in control subjects and patients with lung cancer, via a quantitative immunofluorescence image analysis. Conclusions: The present study indicates that not only oxidative stress but also nitrative stress induced by NO may participate in the pathogenesis of epithelia[ cell damage and aberrant regeneration occurring in IPF. Thus, guanine nitration may be a major risk factor for lung cancer development in IPF.