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.
Mesenchymal stem cell–secreted extracellular vesicles carrying TGF‐β1 up‐regulate miR‐132 and promote mouse M2 macrophage polarization
