Effect of Nintedanib in a Rat Model of Bleomycin-Induced Lung Fibrosis: A Transcriptome Analysis

INTRODUCTION: Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease with a poor prognosis, causing irreversible lung parenchymal damage. Pirfenidone and nintedanib exhibit some benefits on IPF, although they cannot cure or reverse its progression. Moreover, the molecular mechanisms responsible for their effects remain not entirely comprehended. Nintedanib, a multi-kinase receptor modulator, suppresses diverse proliferative pathways and displays antifibrotic effects in lung fibrosis models. However, the effects of its administration on the lung transcriptome have not yet been deeply investigated in in vivo models of lung fibrosis. This study aims to assess nintedanib's comprehensive transcriptomic profile in a rat model of bleomycin-induced lung fibrosis. MATERIALS & METHODS: Lung fibrosis was induced by two intratracheal administrations of bleomycin. Nintedanib “curative” protocol included three weeks of daily oral treatments (100 mg/kg) beginning seven days after the first bleomycin dose. At the end of the experiment, left lungs were processed for histological fibrosis evaluation by using an automated quantification system and the Ashcroft Score assessment. Right lungs were employed for RNA sequencing to undertake Differential Expression Analysis (DEGs) and a correlation network analysis (WGCNA). WGNA modules were thoroughly examined by cell and pathway enrichment analysis. Moreover, lipid peroxidation was assessed through the measurement of malondialdehyde (MDA) amount in right lung lysates. RESULTS: Bleomycin induced significant fibrotic lesions, as confirmed by the automated quantification and the Ashcroft Score. Nintedanib reduced the size of fibrotic lesions (?15%) and the incidence of severe Ashcroft scores. The number of differentially expressed genes decreased from over 2000 in fibrotic animals to barely more than 400 in nintedanib-treated rats, when compared to controls. WGCNA identified two gene clusters correlated to histological parameters, both characterized by gene expression patterns where nintedanib-treated animals resemble the profile observed in control animals. One cluster was associated with mesenchymal cells and focused on epithelial to mesenchymal transition and extracellular matrix organization pathways, in line with the exhibited anti-fibrotic effect of nintedanib. The second cluster, involving resident macrophages and inflammatory pathways, was specifically related to lipid homeostasis, potentially uncovering a new mechanistic role of nintedanib in modulating lung fibrosis. CONCLUSIONS: The mechanisms involving macrophages and lipid metabolism, both of which were influenced by nintedanib treatment in this in vivo study, may open new research directions to better inquire about the role of this cellular type in the regulation of lipid homeostasis and fibrosis, influencing both tissue repair and pathological lung fibrosis. Overall design: The samples belonged to three experimental groups: BLM, NINT, and SAL. The lung fibrosis model (BLM and NINT groups) consisted of two intratracheal administrations of BLM. The nintedanib curative protocol (NINT group) included three weeks of once-daily oral treatment beginning seven days after the first bleomycin administration. Control animals were given saline solution (SAL group). The right lung mRNA of four animals per group was subjected to trascriptomic analysis.