Captopril alleviates radiation-induced pulmonary fibrosis by suppressing PAI-1 expression and cytoskeleton-dependent epithelial-to-mesenchymal transition.

Radiation-induced lung injury (RILI) remains a significant complication of thoracic radiotherapy, with radiation-induced pulmonary fibrosis (RIPF) representing a serious and irreversible outcome. Epithelial-mesenchymal transition (EMT) has emerged as a critical contributor to RIPF progression; however, the underlying mechanisms remain poorly understood. Captopril (Cap), an angiotensin-converting enzyme inhibitor with established cardiovascular benefits, has been demonstrated to show protective effects against RILI. In this study, we investigated the role of Cap in facilitating RIPF using in vivo and in vitro models. A RIPF model was established by delivering a single 20 Gy dose of thoracic irradiation to male C57BL/6 mice using a Varian linear accelerator. A549 cells were exposed to 8 Gy of 6 MV X-ray radiation to mimic epithelial injury. Cap alleviated pulmonary edema, preserved alveolar structure, and reduced fibrosis in irradiated mice. In vitro, Cap suppressed radiation-induced changes in cellular morphology and multinucleation formation. Immunofluorescence analyses revealed that Cap reversed radiation-induced F-actin depolymerization, cytokinesis failure, and multinucleation. Network pharmacology identified PAI-1 as a potential target of Cap. Cap suppressed radiation-induced cell swelling and PAI-1 expression. For the mechanism, Cap downregulated the JNK/c-Jun signaling axis, a known regulator of PAI-1 transcription. Inhibition of JNK/c-Jun recapitulated the effects of Cap, leading to reduced multinucleation, lower PAI-1 levels, and downregulation of EMT markers. In summary, Cap prevented RIPF by down regulating PAI-1 to suppress EMT via JNK/c-Jun pathway. It provided a novel and potential therapeutic strategy for the clinical prevention and treatment of RIPF.