Background: Silicosis is a chronic, irreversible occupational pulmonary disorder characterized by persistent inflammation and fibrotic remodeling, with endoplasmic reticulum (ER) stress implicated in its pathogenesis. Fluorofenidone (AKF-PD), an anti-fibrotic agent, has shown protective properties in pulmonary fibrosis. This study aimed to evaluate the therapeutic effects of AKF-PD on silica-induced pulmonary fibrosis and elucidate its underlying molecular mechanisms.

Methods: A murine silicosis model was established through intratracheal instillation of a silica suspension. Mice were randomly divided into three groups: control, silica, or silica + AKF-PD (24 mice per group). Lung tissues were collected at 7, 14, and 28 days for histopathological analysis (hematoxylin and eosin (HE) and Masson staining), inflammation and fibrosis scoring, enzyme-linked immunosorbent assay (ELISA), reverse transcription quantitative real-time PCR (RT-qPCR), and western blotting. In vitro, MLE-12 cells were treated with silica in the presence or absence of AKF-PD or the ER stress inhibitor 4-PBA (4-PBA). Oxidative stress indices (malondialdehyde (MDA), reactive oxygen species (ROS), superoxide dismutase (SOD), glutathione (GSH)), inflammatory cytokines (interleukin (IL)-6, IL-1β), fibrosis markers (α-SMA, Fibronectin 1, Collagen IV), and ER stress-related proteins (Grp78, Chop, Xbp1, phospho-Ire1a, phospho-Eif2a) were quantified.

Results: In vivo, AKF-PD significantly attenuated alveolitis and fibrosis scores compared with the silica group, with Masson staining confirming reduced collagen deposition (p < 0.001). ELISA and RT-qPCR analyses showed decreased IL-6 (Il6) and IL-1β (Il1b) expression, while western blotting revealed downregulation of α-SMA, Fibronectin 1, and Collagen IV. ER stress markers (Grp78, Chop, Xbp1, phospho-Ire1a, phospho-Eif2a) and oxidative stress indices (MDA, ROS) were suppressed, accompanied by elevated GSH levels and SOD activity (p < 0.05). In vitro, AKF-PD reduced silica-induced production of inflammatory cytokines, fibrotic proteins, and ER stress mediators in MLE-12 cells (p < 0.05). These effects were comparable to those of 4-PBA, indicating that modulation of ER stress and oxidative stress contributed to the observed protection.

Conclusions: AKF-PD alleviates silica-induced pulmonary inflammation and fibrosis in vivo and in vitro. Its protective effects are associated with the regulation of ER stress and oxidative stress pathways, highlighting AKF-PD as a promising therapeutic candidate for silicosis.