Objective:To compare the dose-response effects of single-fraction ultra-high dose rate (FLASH) and conventional dose rate (CONV) whole abdominal irradiation (WAI) with X-rays on acute radiation-induced intestinal injury in mice, in order to identify optimal dose parameters and potential mechanisms.Methods:A total of 186 male C57BL/6J mice were randomly assigned to a non-irradiation group ( n=6), FLASH irradiation groups ( n=90), and CONV irradiation groups ( n=90). Acute radiation-induced intestinal injury models were established using single-fraction WAI with 11, 12, 13, 14, and 15 Gy X-rays (200 Gy/s for FLASH and 4 Gy/min for CONV). Changes in body weight, stool characteristics, and disease activity index (DAI) scores were assessed at 9 d post-irradiation. At 7 d post-irradiation at 11, 12, and 13 Gy, the intestines were collected for macroscopic examination and length measurement. The small intestine was selected for HE staining and quantitative analysis of intestinal crypt number and mucosal epithelial thickness. The survival of mice was assessed at 15 d post-WAI across all dose groups. Results:After single-fraction WAI at 11, 12, and 13 Gy, the body weight was higher in the FLASH group than that in the CONV group ( t=10.17, 12.65, 10.16, P<0.05). The DAI scores for the FLASH group were 1.00±1.10, 3.17±0.75, and 2.83±1.17, respectively, which were lower than those of the CONV group (4.33±0.52, 7.00±0.00, 8.60±0.55; t=8.70, 11.71, 14.99, P<0.05). However, after WAI at 14 Gy and 15 Gy, there were no significant differences in body weight and DAI between the FLASH group and the CONV group ( P>0.05). At 7 d after single-fraction WAI at 11, 12, and 13 Gy, mice in the FLASH group exhibited less intestinal congestion, edema, and shortening compared with the CONV group. The difference between the FLASH and CONV groups were statistically significant in small intestine length at 11 and 13 Gy ( t=4.42, 3.78, P<0.05), and in colorectal length at 11 and 12 Gy ( t=3.97, 3.12, P<0.05). Small intestine HE staining revealed superior preservation of intestinal architecture in the FLASH group compared with the CONV group, characterized by longer villi, increased crypt numbers, thicker mucosal epithelium, and enhanced structural integrity. The differences in crypt number and mucosal epithelial thickness were statistically significant ( tcrypt=13.10, 23.80, 11.90; tmucosal=5.75, 2.64, 7.74; P<0.05). At 15 d post-irradiation, the survival rate in the 15 Gy FLASH group was higher than that in the CONV group (50% vs. 10%, χ2=5.39, P<0.05), with a median survival extension of 6 d ( HR=0.340, 95% CI: 0.115 4-0.999 9). No significant survival differences were observed between the FLASH group and the CONV group at 11, 12, 13, and 14 Gy ( P>0.05). Conclusions:FLASH irradiation significantly alleviated acute radiation-induced intestinal injury from medium single-fraction WAI with 11, 12, and 13 Gy X-rays compared with CONV irradiation, and showed potential to improve mouse survival after single-fraction WAI at 15 Gy. This effect is likely associated with the preservation of intestinal crypts and exhibits a dose-dependent relationship.

Objective:To compare the dose-response effects of single-fraction ultra-high dose rate (FLASH) and conventional dose rate (CONV) whole abdominal irradiation (WAI) with X-rays on acute radiation-induced intestinal injury in mice, in order to identify optimal dose parameters and potential mechanisms.Methods:A total of 186 male C57BL/6J mice were randomly assigned to a non-irradiation group ( n=6), FLASH irradiation groups ( n=90), and CONV irradiation groups ( n=90). Acute radiation-induced intestinal injury models were established using single-fraction WAI with 11, 12, 13, 14, and 15 Gy X-rays (200 Gy/s for FLASH and 4 Gy/min for CONV). Changes in body weight, stool characteristics, and disease activity index (DAI) scores were assessed at 9 d post-irradiation. At 7 d post-irradiation at 11, 12, and 13 Gy, the intestines were collected for macroscopic examination and length measurement. The small intestine was selected for HE staining and quantitative analysis of intestinal crypt number and mucosal epithelial thickness. The survival of mice was assessed at 15 d post-WAI across all dose groups. Results:After single-fraction WAI at 11, 12, and 13 Gy, the body weight was higher in the FLASH group than that in the CONV group ( t=10.17, 12.65, 10.16, P<0.05). The DAI scores for the FLASH group were 1.00±1.10, 3.17±0.75, and 2.83±1.17, respectively, which were lower than those of the CONV group (4.33±0.52, 7.00±0.00, 8.60±0.55; t=8.70, 11.71, 14.99, P<0.05). However, after WAI at 14 Gy and 15 Gy, there were no significant differences in body weight and DAI between the FLASH group and the CONV group ( P>0.05). At 7 d after single-fraction WAI at 11, 12, and 13 Gy, mice in the FLASH group exhibited less intestinal congestion, edema, and shortening compared with the CONV group. The difference between the FLASH and CONV groups were statistically significant in small intestine length at 11 and 13 Gy ( t=4.42, 3.78, P<0.05), and in colorectal length at 11 and 12 Gy ( t=3.97, 3.12, P<0.05). Small intestine HE staining revealed superior preservation of intestinal architecture in the FLASH group compared with the CONV group, characterized by longer villi, increased crypt numbers, thicker mucosal epithelium, and enhanced structural integrity. The differences in crypt number and mucosal epithelial thickness were statistically significant ( tcrypt=13.10, 23.80, 11.90; tmucosal=5.75, 2.64, 7.74; P<0.05). At 15 d post-irradiation, the survival rate in the 15 Gy FLASH group was higher than that in the CONV group (50% vs. 10%, χ2=5.39, P<0.05), with a median survival extension of 6 d ( HR=0.340, 95% CI: 0.115 4-0.999 9). No significant survival differences were observed between the FLASH group and the CONV group at 11, 12, 13, and 14 Gy ( P>0.05). Conclusions:FLASH irradiation significantly alleviated acute radiation-induced intestinal injury from medium single-fraction WAI with 11, 12, and 13 Gy X-rays compared with CONV irradiation, and showed potential to improve mouse survival after single-fraction WAI at 15 Gy. This effect is likely associated with the preservation of intestinal crypts and exhibits a dose-dependent relationship.

Objective:To investigate the radiosensitizing effect and underlying mechanism of STING agonist (c-di-AMP) on cutaneous melanoma cells.Methods:Human cutaneous melanoma cells (A375) were divided into four groups: the control group, 10 μmol/L c-di-AMP group, X-ray irradiation group and X-ray irradiation combined with c-di-AMP group. The radiosensitizing effect of c-di-AMP on A375 cells was detected by CCK-8-based viability assay, lactate dehydrogenase (LDH) release assay, flow cytometry-based apoptosis assay, and colony formation assay. Western blot analysis was used to determine the expressions of cell death-related proteins.Results:In combination with 10 Gy X-ray irradiation, 10 μmol/L c-di-AMP showed significant radiosensitization effect in A375 cells, which was evidenced by decreased cell activity ( t=5.11, P<0.05), increased cytotoxicity ( t=10.15, P<0.05) and cell apoptosis ( t=4.41, P<0.05) and reduced clone viability( t=6.30, 3.55, 5.45, 3.55, P<0.05). The calculated radiosensitization ratio of c-di-AMP to A375 cells was 1.88. Moreover, 10 μmol/L c-di-AMP further increased the expressions of cell death-related proteins induced by radiation in A375 cells. Conclusions:The STING agonist c-di-AMP can be used as a radiosensitizer for cutaneous melanoma, which may provide a novel strategy for radiotherapy.