Abstract
Background:Radiation-induced lung injury (RILI) mainly contributes to the complications of thoracic radiotherapy. RILI can be divided into early-stage radiation pneumonia (RP) and late-stage radiation-induced lung fibrosis (RILF). Once RILF occurs, patients will eventually develop irreversible respiratory failure; thus, a new treatment strategy to prevent RILI is urgently needed. This study explored the therapeutic effect of pirfenidone (PFD), a Food and Drug Administration (FDA)-approved drug for idiopathic pulmonary fibrosis (IPF) treatment, and its mechanism in the treatment of RILF. Methods:A series of in vitro and in vivo assays were performed to explore the role and mechanism of PFD in the prevention and treatment of RILF. Results:Collagen deposition and fibrosis in the lung were reversed by PFD treatment, which was associated with reduced M2 macrophage infiltration and inhibition of the transforming growth factor-β1(TGF-β1) /drosophila mothers against decapentaplegic 3 (Smad3) signaling pathway. Moreover, PFD treatment decreased the radiation-induced expression of TGF-β1 and phosphorylation of Smad3 in alveolar epithelial cells (AECs) and vascular endothelial cells (VECs). Furthermore, IL-4- and IL13-induced M2 macrophage polarization was suppressed by PFD treatment in vitro, resulting in reductions in the release of arginase-1(ARG-1), chitinase 3-like 3 (YM-1) and TGF-β1. Notably, the PFD-induced inhibitory effects on M2 macrophage polarization were associated with downregulation of nuclear factor kappa-B (NF-κB) p50 activity. Additionally, PFD could significantly inhibit ionizing radiation-induced chemokine secretion in MLE-12 cells and consequently impair the migration of RAW264.7 cells. PFD could also eliminate TGF-β1 from M2 macrophages by attenuating the activation of TGF-β1/Smad3. Conclusion:PFD is a potential therapeutic agent to ameliorate fibrosis in RILF by reducing M2 macrophage infiltration and inhibiting the activation of TGF-β1/Smad3.