Idiopathic pulmonary fibrosis: clinical impact of different phenotypes

Abstract

Background. Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, irreversible disease and carries a bad prognosis with median survival ranging from 2.5 to 3.5 years. No proven effective treatment is available other than lung transplantation. IPF occurs in middle-aged and elderly adults and is associated with the histopathologic and/or radiologic pattern of usual interstitial pneumonia (UIP). Acute exacerbation, lung cancer and pulmonary hypertension (PH) are the main complications which adversely affect the survival of IPF patients. Different from acute exacerbation which can occur at any stage of the disease, lung cancer and pulmonary hypertension (PH) are more likely in advanced disease. IPF is reported to be associated with an increased risk of lung cancer (8–14-fold compared to the general population) which represents the cause of death in up to 10% of patients with IPF. Focal areas of neoplastic transformation are difficult to recognise by computed tomography (CT) and are often an unexpected finding in autoptic and explanted lungs. Type I alveolar epithelial cells are highly vulnerable to injury and several works have shown extensive loss of these cells in IPF, mainly by apoptotic cell death. Abnormal epithelial renewal results in the presence of different transitional reactive phenotypes. Serpin B3 and B4 [squamous cell carcinoma antigen (SCCA) 1/2] displays inhibitory activities on serine proteinases. Both isoforms protect injured cells from apoptosis induced by several kinds of stimuli, and in vivo experiments demonstrate that these Serpins can promote tumour growth. On the other side Pulmonary hypertension (PH) represents an important complication of idiopathic pulmonary fibrosis (IPF) with a negative impact on patient survival. A frequency of 20-90% has been reported and it carries severe consequences including decreased exercise capacity and increased mortality before and after lung transplantation. The complex biological processes that underlie pulmonary fibrosis might directly contribute to the pathogenesis of vascular remodelling which is equally patchy and heterogeneous. Endothelial injury, usually occurring through apoptotic cell death is another crucial aspect in the pathogenesis of IPF-associated PH as reported in recent studies. Several studies have implicated viral infection as a cause of epithelial injury and therefore an important factor in its pathogenesis. Among viral agents herpes viruses, in particular Epstein Barr virus (EBV), have been suggested as principal cofactors (as initiating or exacerbating agents) of fibrotic lung disease. The influence of viruses on PH associated with IPF is unknown. In this study we aimed to investigate two main complications/comorbidities that influence so far the natural history of IPF patients and have a negative prognostic impact on survival. We decided to study IPF patients associated to lung cancer (first study) and IPF patients associated to pulmonary hypertension (second study) in order to explore their patho-biological features and the clinical impact. First study Aim. Given that Serpin B3/B4 related to epithelial proliferation in IPF patients remains to be investigated. The aim of the work was to study the expression of Serpin B3/B4 tissue in relation to different clinicopathological data of IPF patients. Materials and methods. Explanted lungs from 48 IPF patients (including cases with cancer or high-grade epithelial dysplasia) were studied and compared with other diffuse parenchymal diseases and normal lungs. Immunohistochemistry for Serpin B3/B4 and Ki-67 was quantified in all cases, distinguishing stained metaplastic cells. In IPF patients correlations between Serpin expression and several clinicopathological data, including fibrotic remodelling were performed. Results. Serpin B3/B4 and Ki-67 were significantly overexpressed in many metaplastic cells in IPF patients compared to control cases. Higher Serpin B3/B4 was found in older patients and cases with more impaired respiratory function. Serpin B3/B4 expression was related to both TGF-b and Ki-67 and was higher in patients with cancer/high-grade dysplasia. Serpin B3 was expressed in all cases, whereas Serpin B4 was expressed only in IPF. Conclusions. Serpin B3/B4, particularly Serpin B4, appears to play an important role in aberrant epithelial proliferation. Evaluation of Serpin B3/B4 could have prognostic value in predicting disease progression, especially in patients with increased susceptibility to lung cancer. Second study Aim. The influence of viruses on PH associated with IPF is unknown. We aimed to investigate the influence of viruses in IPF patients focusing on aspects related to PH. A laboratory mouse model of gamma-herpesvirus (MHV-68) induced pulmonary fibrosis was also assessed. Methods. 55 IPF explanted lung 41 controls were studied by molecular analysis to detect several viral genomes. Viral molecular data were correlated with mean pulmonary arterial pressure (mPAP) and arterial remodelling. Different clinical and morphological variables were studied by univariate and multivariate analyses at time of transplant. The same lung tissue analyses were performed in MHV-68 infected mice. Results. A higher frequency of virus positive cases was found in IPF patients than in controls (p=0.0003) and only herpes virus genomes were detected. Viral cases showed higher mPAP (p=0.01) and poorer performance in the six minute walking test (6MWT; p=0.002). Increased arterial thickening, particularly of the intimal layer (p=0.002 and p=0.004) and higher TGF-β expression (p=0.002) were demonstrated in viral cases. The remodelled vessels showed increased vessel cell proliferation (Ki-67 positive cells) in the proximity to metaplastic epithelial cells and macrophages. Viral infection was associated with higher mPAP (p=0.003) and poorer performance in the 6MWT (p=0.001) after adjusting for other covariates/intermediate factors. In MHV-68 infected mice, morphological features were similar to those of patients. Conclusion. Herpesviral infections may contribute to the development of PH in IPF patients.