Pirfenidone Suppresses Pulmonary Fibrosis Through Regulation of Alveolar Macrophage Polarization

Purpose The etiology of idiopathic pulmonary fibrosis (IPF) is still largely unknown and effective treatment is difficult. Pirfenidone (PFD) is a representative medication used to treat IPF, although its anti-fibrotic mechanism is unclear. Researchers reported PFD (u003e 100 µg/ml) significantly suppressed fibroblast growth in vitro. However, clinically, the Cmax of PFD in the blood is approximately 10 µg/ml. From this discrepancy, we hypothesized that there might be an additional mechanism of PFD action besides the direct effect on fibroblasts. Macrophages (Mϕ) control fibrosis via the regulation of M1/M2 polarization. M1 Mϕ exhibit proinflammatory properties, whereas M2 Mϕ promote fibrogenesis and tissue remodeling. Therefore, the aim of this study was to investigate the effects of PFD on M1/M2 polarization. Method Rat alveolar Mϕ (NR8383) were stimulated in vitro with LPS (5 ng/ml) and IFN-γ (10 U/ml), or IL-10 (10 ng/ml) to induce M1 and M2 phenotypes, respectively. Expression of M1 markers, iNOS, SOCS3 and TNF-α, and M2 markers, mannose receptor and arginase-1, was assessed by western blotting after 24 hours in the absence or presence of PFD (10, 100 µg/ml). Additionally, 7-week-old male Wistar rats were randomly divided into sham, bleomycin (BLM), 10 and 100 mg/kg PFD groups. Following intratrachial instillation of BLM (3 mg/kg) or saline, rats were orally administered PFD daily. Rats were killed at 14 days post-BLM and the polarization of Mϕ in pulmonary tissues analyzed. Results Treatment with LPS+INF-γ or IL-10 significantly increased the level of M1 or M2 markers respectively. PFD significantly reduced M2 marker expression at both 10 and 100 µg/ml, whereas it showed no significant effect on M1 marker expression. Moreover, M2 marker expression was increased in the rats of the BLM-treated groups. Notably, the level of M2 markers decreased significantly in the 10 and 100 mg/kg PFD groups compared with that of the BLM groups. Conclusions These results suggest PFD suppresses lung fibrosis through regulation of M2 Mp at clinically relevant concentrations.