Nitric Oxide Synthases and Reactive Oxygen Species Damage in Pleural and Lung Tissues and Neoplasia

Reactive nitrogen species (RNS) and reactive oxygen species (ROS) have been linked with the pathogenesis of lung malignancies and chronic obstructive pulmonary disease (COPD). In vitro studies indicated that mesothelioma and lung carcinoma cell lines synthesize nitric oxide synthases (NOS) mRNA. The Comet-assay indicated that asbestos fibers caused DNA single -strand breaks in mesothelial cells, and this effect was enhanced by glutathione depletion. The use of FPG in the Comet assay indicated that the asbestos induced DNA strand breaks were oxidant mediated. In vivo non-neoplastic pleura was mostly negative for inducible NOS (iNOS), while inflamed pleura was positive. The immunohistochemical expression of iNOS was detected in 74% and 96% of malignant mesotheliomas and metastatic pleural adenocarcinomas, respectively. Epithelial and mixed mesotheliomas expressed more often intense iNOS immunoreactivity compared to the sarcomatoid subtype. Normal mesothelial cells showed occasional positivity for endothelial NOS (eNOS), but reactive mesothelial cells were strongly stained. eNOS was found in 89% of mesotheliomas. Vascular endothelial growth factor (VEGF) was identified in 47%, a VEGF receptor FLK1 in 69% and the VEGF receptor, FLT1, in 71% of mesotheliomas. FLK1 or FLT1 immunoreactivities were more often seen in epithelioid and biphasic mesotheliomas than in sarcomatoid mesotheliomas. In lung samples of non-smokers, smokers and COPD patients, the levels of nitrotyrosine were higher in alveolar macrophages of smokers and COPD patients than in the non-smokers and in the alveolar epithelium of smokers and COPD patients than in the non-smokers. The iNOS expression was weak in the bronchial and alveolar epithelium in all groups but eNOS was most prominently expressed in alveolar macrophages while neuronal NOS (nNOS) was negative in all of the major cell types of the lung. Bronchial metaplasia-dysplasia-sequence was clearly positive for iNOS, nNOS and nitrotyrosine. Thus, smoking can cause protein nitration also in normal lung. Prominent iNOS and nNOS immunoreactivity in metaplasia-dysplasia-lesions suggests a divergent role of NOSs in carcinogenesis and destruction of alveolar epithelium in emphysematous lung. In lung cancer samples, iNOS was detected in 40% cases, while 89% and 81% cases were positive for eNOS and nNOS, respectively. Intense eNOS staining was seen more often in adenocarcinomas than in squamous cells carcinomas, and iNOS immunoreactivity was seen more often in grade I-II tumors than in grade III tumors. The patients with tumors showing high expression of iNOS, eNOS and nNOS, exhibited better survival, but this was not an independent prognostic factor.