Naltrexone reduces bleomycin-induced lung fibrosis in rats by attenuating fibrosis, inflammation, oxidative stress, and extracellular matrix remodeling.

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease characterized by excessive extracellular matrix (ECM) accumulation, fibroblast activation, and chronic inflammation. This study examined the antifibrotic effects of naltrexone (NTX), an opioid receptor antagonist, in a bleomycin (BLM)-induced pulmonary fibrosis model in Wistar rats. Daily administration of NTX significantly reduced alveolar wall thickening, collagen deposition, and histopathological injury scores. At higher doses, NTX markedly decreased levels of pro-inflammatory cytokines (TNF-α, IL-6, TGF-β), oxidative stress markers (MPO, NO), and key fibrotic markers including α-SMA and delta opioid receptor (DOR). Additionally, NTX restored antioxidant defenses (GSH, TAC) and enhanced GSK-3β phosphorylation, thereby modulating the Wnt/β-catenin and NF-κB signaling pathways. To further investigate the cellular mechanisms underlying NTX's antifibrotic activity, in vitro experiments were conducted using BLM-stimulated NIH-3 T3 fibroblasts. NTX inhibited the production of collagen type I and III, tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2), and matrix metalloproteinases (MMP-2 and MMP-9) in a dose- and time-dependent manner. This dual regulation of ECM synthesis and degradation suggests a more balanced therapeutic strategy compared to merely inhibiting collagen accumulation. Molecular docking analyses revealed strong interactions between NTX and key proteins involved in inflammatory and fibrotic signaling cascades. Notably, NTX at a dose of 20 mg/kg demonstrated antifibrotic efficacy comparable to that of pirfenidone. Collectively, these findings suggest that NTX exerts protective effects in pulmonary fibrosis by simultaneously targeting inflammation, oxidative stress, and ECM remodeling. Given its favorable tolerability and potential cost-effectiveness, NTX emerges as a promising candidate for IPF therapy. Further clinical investigations are warranted to evaluate its translational potential.