Oxidative stress injury and subsequent inflammatory response are considered to play critical roles in radiation-induced lung injury (RILI). Nuclear factor erythroid 2-related factor 2 (Nrf2) is a key transcription factor that regulates oxidative stress response and represses inflammation, but its therapeutic value in RILI remains elusive. Our previous studies have shown that the near-infrared (NIR) IR-61 dye evokes intracellular antioxidant defense by enhancing Nrf2 signaling and promoting anti-inflammatory effects. We established a model of RILI in mice exposed to whole-thoracic irradiation. The results showed that IR-61 treatment notably improved pulmonary functions by decreasing lung density and diminishing airway resistance. In addition, IR-61 significantly ameliorated radiation-induced inflammatory cell infiltration and proinflammatory cytokine (IL-1β, IL-6, and TNF-α) release, thereby mitigating inflammatory response. Furthermore, IR-61 mitigated radiation-induced lung fibrosis by decreasing the collagen deposition and the levels of fibrogenesis-related factors (collagen I, collagen III, α-SMA, and fibronectin). More importantly, IR-61 was found to accumulate in the mitochondria of macrophages in irradiated lung tissues. Therefore, the functions of IR-61 in macrophages were further studied in irradiated macrophage cell lines, MH-s and RAW 264.7 in vitro. The results indicated that IR-61 upregulated the expression of Nrf2 and heme oxygenase-1 (HO-1) and decreased the levels of reactive oxygen species (ROS) and pro-inflammatory cytokines (IL-1β and IL-6) in macrophages after radiation. In summary, our study suggests that IR-61 effectively mitigates RILI by activating Nrf2 signaling in irradiated lung tissues. In particular, Nrf2-mediated anti-inflammatory and antioxidant effects in irradiated lung tissue macrophages play critical roles in protecting against RILI.
Keywords: IR-61; Nrf2; macrophages; oxidative stress; radiation-induced lung injury.