[A role for mesothelial cells in the genesis of idiopathic pulmonary fibrosis?]. / Rô1e de la cellule mésothéliale dans la genèse de la fibrose pulmonaire idiopathique?

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive and lethal process of unknown etiology. The sub-pleural localization of fibrosis is a hallmark of early IPF but no link between the pleura and IPF has been established yet. We developed an experimental model of pleural fibrosis induced by adenovirus-mediated gene transfer of transforming growth factor (TGF)-beta1 to mesothelial cells and observed collagen accumulation within the pleura but also in the sub-pleural parenchyma. This sub-pleural fibrosis was associated, in vivo, with a mesothelial--to--myofibroblast transformation (mesothelio-fibroblastoid transformation), a process similar to the epithelial-mesenchymal transition. This phenotypic modification was also observed in vitro in mesothelial cells treated with recombinant TGF-beta1. These results suggest that mesothelial cells may have a central role not only in pleural fibrosis but also in the onset and progression of IPF.

Metabolism of nilutamide in rat lung.

Nilutamide is a non-steroidal anti-androgen drug proposed in the treatment of metastatic prostatic carcinoma. Its therapeutic effects are overshadowed by the occurrence of adverse reactions, mediated by mechanisms that remain elusive. To elucidate possible mechanisms for nilutamide toxicity, we investigated the metabolism of nilutamide in rat lung homogenates, in subcellular fractions and in freshly isolated cells. In whole lung homogenates, the nitro group of nilutamide was reduced to the amine and hydroxylamine moieties. These conversions occurred exclusively in the absence of dioxygen, were increased by the addition of FMN, FAD, or NADPH. Reductive metabolism of nilutamide to the amine and hydroxylamine was further evidenced in subcellular fractions obtained by differential ultracentrifugation. It was found to take place mainly in the cytosol of rat lung and to be stimulated, strongly, upon co-addition of NADPH and FMN. Addition of inhibitors of enzymes involved in the reductive metabolism of nitroaromatic compounds indicated that reduction of nilutamide involved, mainly, soluble flavoproteins. Incubations with freshly isolated lung cells revealed that macrophages were the main players in nitroreduction of nilutamide whereas the epithelial type II cells and the non-ciliated Clara cells were less efficient in catalyzing this reaction. Our results show that nilutamide is extensively reduced by lung tissues in the absence of oxygen, especially by enzymes found in alveolar macrophages. In accordance with recent findings, subcellular localization, oxygen sensitivity, cofactor requirements and inhibitor studies lead us to suggest the involvement of a soluble nitric oxide synthase in lung cytosolic nitroreduction.

Deglycosylated bleomycin has the antitumor activity of bleomycin without pulmonary toxicity.

Bleomycin (BLM) is a potent anticancer drug used to treat different malignancies, mainly lymphomas, germ cell tumors, and melanomas. Unfortunately, BLM has major, dose-dependent, pulmonary toxicity that affects 20% of treated individuals. The most severe form of BLM-induced pulmonary toxicity is lung fibrosis. Deglyco-BLM is a molecule derived from BLM in which the sugar residue d-mannosyl-l-glucose disaccharide has been deleted. The objective of this study was to assess the anticancer activity and lung toxicity of deglyco-BLM. We compared the antitumor activity and pulmonary toxicity of intraperitoneally administrated deglyco-BLM and BLM in three rodent models. Pulmonary toxicity was examined in depth after intratracheal administration of both chemotherapeutic agents. The effect of both drugs was further studied in epithelial alveolar cells in vitro. We demonstrated in rodent cancer models, including a human Hodgkin's lymphoma xenograft and a syngeneic melanoma model, that intraperitoneal deglyco-BLM is as effective as BLM in inducing tumor regression. Whereas the antitumor effect of BLM was accompanied by a loss of body weight and the development of pulmonary toxicity, deglyco-BLM did not affect body weight and did not engender lung injury. Both molecules induced lung epithelial cell apoptosis after intratracheal administration, but deglyco-BLM lost the ability to induce caspase-1 activation and the production of ROS (reactive oxygen species), transforming growth factor-ß1, and other profibrotic and inflammatory cytokines in the lungs of mice and in vitro. Deglyco-BLM should be considered for clinical testing as a less toxic alternative to BLM in cancer therapy.

TGF-beta1 induces progressive pleural scarring and subpleural fibrosis.

Pleural fibrosis is a misunderstood disorder which can cause severe restrictive lung disease with high morbidity and even mortality. The condition can develop in response to a large variety of diseases and tissue injury, among them infectious disease, asbestos, drugs, and radiation therapy. There is no efficient treatment to reverse established pleural fibrosis. TGF-beta1 is suspected, even if not proven, as a key cytokine in this process. In this study, we used adenoviral gene transfer of TGF-beta1 to the pleural mesothelium in rats. We show that local and transient TGF-beta1 overexpression induces homogenous, prolonged, and progressive pleural fibrosis without pleurodesis, associated with severe impairment of pulmonary function. We further demonstrate that pleural fibrosis can expand into the lung parenchyma from the visceral layer, but not into the muscle from the parietal layer. We provide evidence that matrix accumulation and fibrosis within the parenchyma evolved through a process involving "mesothelial-fibroblastoid transformation" and suggest that the pleural mesothelial cell may be an important player involved in the development of the subpleural distribution pattern known to be a hallmark of pulmonary fibrosis. This new model of pleural fibrosis will allow us to better understand the mechanisms of progressive fibrogenesis, and to explore novel antifibrotic therapies in the pleural cavity.

Distribution of nitroreductive activity toward nilutamide in rat.

Nilutamide is a pneumotoxic and hepatotoxic nitroaromatic (R-NO2) antiandrogen used in the treatment of prostate carcinoma in man. Previously, we established that in the rat lung, the drug is metabolized into the corresponding hydroxylamine (R-NHOH) and amine (R-NH2) derivatives. These results evidenced a cytosolic oxygen-sensitive (type II) nitroreductase activity in lung. In the present studies, we extended the characterization of nilutamide metabolism in liver, brain, kidney, heart, blood, intestine (small, cecum, and large, and their respective luminal contents) of male Sprague-Dawley rats. Subcellular fractions for all tissues (except blood) examined (postmitochondrial, cytosolic, and microsomal) were prepared by differential ultracentrifugation. Blood and intestinal contents were sonicated before investigation. Incubations were run in the presence or absence of O2 to assess type I and II nitroreductase activities. Organic extracts were analyzed by HPLC methods and results were expressed as pmoles of R-NH2 formed per milligram protein per minute. Four distinct nitroreductive activities were evidenced. Cytosolic and microsomal type II nitroreductase activities were detected in all tissue samples studied. Type I NR activity was not observed in any of the cytosols, but was detected in the small intestine, lung, kidney, and liver microsomes. Nilutamide was also reduced in the intestinal lumen, possibly by a bacterial type I nitroreductase. Highest activities were observed in cytosols and were oxygen sensitive. These results evidence and characterize previously unknown nitroreductive activities toward nilutamide in rat tissues that might provide some explanation to the side effects of nilutamide and other nitroaromatic compounds observed in human therapeutics.