Preliminary mechanistic study of mitochondrial function in intestinal protection mediated by high-energy X-ray FLASH radiotherapy

Ultra-high dose rate (UHDR) radiation retains tumor-killing efficacy while mitigating toxicity to normal tissues, holding a promising transformative radiotherapy paradigm. This study aimed to explore the potential role of mitochondria in intestinal protection conferred by high-energy X-ray FLASH radiotherapy (FLASH-RT) and the associated signaling pathways. Healthy female C57BL/6 mice were subjected to whole-abdominal irradiation using three modalities: ultra-high dose rate radiotherapy (FLASH-RT), conventional dose rate radiotherapy (CONV-RT), and sham irradiation (Control). Mouse survival status and body weight changes were monitored within 15 days post-irradiation. At 72 h post-irradiation, whole blood samples were collected for hematological analysis, and intestinal tissues were harvested for pathological detection, transmission electron microscopy (TEM)-based observation of mitochondrial alterations, and two types of mitochondria-targeted metabolomic assays. A Compact single High-energy X-ray Source FLASH-RT device (CHEX-FLASH) was used, with a dose rate of 200 Gy/s. At 15 days post-irradiation, the survival rates of the Control group (100%, 10/10) and FLASH-RT group (80%, 8/10) were significantly higher than those of the CONV-RT group (30%, 3/10). Body weight decreased in the early post-irradiation period in all groups; however, the decline was milder in the FLASH-RT group with greater late-stage recovery. Hematological results at 72 h showed that CONV-RT induced similar marrow suppression compared to FLASH-RT. Intestinal histopathological analysis revealed that FLASH-RT alleviated intestinal inflammation and promoted enterocyte proliferation, whereas DNA double-strand breaks and apoptosis levels did not differ significantly between the two irradiated groups. FLASH-RT mitigated mitochondrial damage, reduced reactive oxygen species (ROS) levels and slightly activated mitophagy. Mitochondria-related energy metabolomics detection of intestinal tissues showed that the mitochondrial damage marker malonic acid was significantly lower in FLASH-RT than in CONV-RT, and differentially expressed metabolites were primarily enriched in mitochondrial antioxidant pathways. Additionally, upregulated expression of the antioxidant protein nuclear factor erythroid 2-related factor 2 (NRF2) and decreased total superoxide dismutase (SOD) activity were verified. CHEX-FLASH achieves UHDR irradiation and alleviates radiation-induced intestinal injury. The protective effect of FLASH-RT on intestinal tissues may be mediated by mitigating mitochondrial damage and enhancing antioxidant pathways through the improvement of mitochondrial energy metabolism.