LSC Abstract – Pleural inflammation is essential in bleomycin-induced lung toxicity

Abstract

Introduction: In patients, the therapeutic use of bleomycin (BLM), a potent anticancerous drug, is strongly restrained because of its lung toxicity with pulmonary fibrosis (PF) being the most devastating form. Toxic and Idiopathic PF start classically in the subpleural area. It is know that 1) Pleural mesothelial cells (PMCs) acquire a TGF-β1-induced myofibroblast phenotype and 2) inflammation plays a significant role in fibrogenesis. The role of mesothelial cells in PF and in BLM lung toxicity has still to be investigated. Methods: C57Bl/6 mice were intravenously (IV) injected with BLM or NaCl. In vitro , human pleural mesothelial cells (Met5A) were treated with BLM. Results: Repeated IV BLM induces a peculiar lung fibrotic response with 1) an histological peripheral distribution, 2) a collagen accumulation in pleural and subpleural area, 3) an overexpression in PMCs of MMP-2, -9, HSP27, all involved in myofibroblast tranformation and 4) a migration of PMCs into the lung. This process was associated with an inflammatory profile with an increase 1) in neutrophils in pleural lavage fluid (PLF) and 2) an enhanced caspase-1 activity (total lung tissue). TGF-β1 was overexpressed in PLF. TGF-β1 and collagen accumulations were hampered after pleural inhibition of IL-1β (Anakinra intrapleural injection). IV administration of BLM triggered cell death in pleural and subpleural area (TUNEL). In vitro , BLM-induced cell death correlated with an increase in caspase-1 activity. Conclusion: IV BLM in rodent induces subpleural PF as observed in toxic and idiopathic PF in human. Our results demonstrate a key role of PMCs and suggest a caspase-1 dependent inflammation in this fibrogenesis process.