Repetitive installations of bleomycin induce persistent progressive lung fibrosis in a mouse model of IPF

<bold>Aims and objectives:</bold> The bleomycin (BLEO) mouse model of pulmonary fibrosis is extensively used in preclinical drug discovery for idiopathic pulmonary fibrosis (IPF). A major limitation of the standard BLEO-IPF model, using a single bleomycin instillation, is spontaneous resolution of lung fibrosis. The aim of this study was to establish a BLEO-IPF mouse model with persistent progressive pulmonary fibrosis using repetitive bleomycin instillations. <bold>Methods:</bold> 12-week-old C57BL/6JRj male mice received bi-weekly intratracheal instillations of either bleomycin (1.75 mg/kg, 50 µL) or saline (control, 50 µL) for a total of six weeks. A BLEO-IPF baseline group was terminated at 6 weeks post-BLEO administration. Remaining BLEO-IPF and control mice were terminated after an additional 8 weeks. Terminal pulmonary endpoints included spirometry, hydroxyproline (HP), Ashcroft score, quantitative histological markers of fibrogenesis and fibrosis as well as transcriptome signatures. <bold>Results:</bold> Compared to control mice, the BLEO-IPF baseline group showed impaired lung function and increased pulmonary fibrosis as indicated by increased total lung HP levels, Ashcroft score and %-area of α-SMA, PSR, Col1a1, and Col3. Following 8 weeks of saline dosing, BLEO-IPF mice demonstrated a persistent decline in lung function and a sustained lung fibrotic phenotype with maintained (HP, Col1a1) and further increased levels of fibrosis markers (Col3, PSR) as compared to baseline. <bold>Conclusions:</bold> Repetitive bleomycin installations lead to persistent progressive pulmonary fibrosis and impaired lung function in mice. The chronic BLEO-IPF model is highly suitable for testing novel antifibrotic drug candidates for IPF.