A mouse model of progressive lung fibrosis with cutaneous involvement induced by a combination of oropharyngeal and osmotic minipump bleomycin delivery.

Systemic sclerosis (SSc) with interstitial lung disease (SSc-ILD) lacks curative pharmacological treatments, thus necessitating effective animal models for candidate drug discovery. Existing bleomycin (BLM)-induced SSc-ILD mouse models feature spatially limited pulmonary fibrosis, spontaneously resolving after 28 days. Here, we present an alternative BLM administration approach in female C57BL/6 mice, combining oropharyngeal aspiration (OA) and subcutaneous mini-pump delivery (pump) of BLM to induce a sustained and more persistent fibrosis, while retaining stable skin fibrosis. A dose-finding study was performed with BLM administered as 10 µg (OA) +80 mg/kg (pump) (10 + 80), 10 + 100, and 15 + 100. Forty-two days after OA, micro-computed tomography (micro-CT) imaging and histomorphometric analyses showed that the 10 + 100 and 15 + 100 treatments induced significant alterations in lung micro-CT-derived readouts, Ashcroft score, and more severe fibrosis grades compared with saline controls. In addition, a marked reduction in hypodermal thickness was observed in the 15 + 100 group. A time-course characterization of the BLM 15 + 100 treatment at days 28 , 35 , and 42 , including longitudinal micro-CT imaging, revealed progressing alterations in lung parameters. Lung histology highlighted a sustained fibrosis accompanied by a reduction in hypodermis thickness throughout the explored time-window, with a time-dependent increase in fibrotic biomarkers detected by immunofluorescence analysis. BLM-induced alterations were partly mitigated by Nintedanib treatment. Our optimized BLM delivery approach leads to extensive and persistent lung fibrotic lesions coupled with cutaneous fibrotic alterations: it thus represents a significant advance compared with current preclinical models of BLM-induced SSc-ILD. NEW & NOTEWORTHY This study introduces an innovative approach to enhance the overall performance of the mouse bleomycin (BLM)-induced model for systemic sclerosis with interstitial lung disease (SSc-ILD). By combining oropharyngeal aspiration and subcutaneous mini-pump delivery of BLM, our improved model leads to sustained lung fibrosis and stable skin fibrosis in female C57BL/6 mice. The optimized 15 + 100 treatment results in extensive and persistent lung fibrotic lesions and thus represents a significant improvement over existing preclinical models of BLM-induced SSc-ILD.