7-Hydroxy-6-Methoxycoumarin 8-Glucoside (Fraxin) Confers Protection against Ionizing Radiation-Induced Intestinal Epithelial Cell Death Both In Vitro and In Vivo

The small intestine is highly sensitive to ionizing radiation. Radiation-induced intestinal injury (RIII) limits the therapeutic effect of tumor radiotherapy. However, there are currently few effective treatments available for the prevention or mitigation of RIII. Fraxin, structurally a derivative of a coumarin glucoside extracted from the herbal Cortex Qinpi, has the advantages of low toxicity and relatively low cost. Some studies have proven that Fraxin has anti-inflammatory and antibacterial effects. Our results show that Fraxin can not only promote the regeneration of intestinal stem cells and repair the intestinal structure caused by irradiation but also regulate the composition of gut microbiota and then play an immunomodulatory role through IL-22 signaling pathways, resulting in radioprotective effects.Human intestinal epithelial cells (HIECs) and intestinal organs were used as experimental models in vitro. The experimental group was irradiated with 6 Gy, detected by a cell counting kit, cell cloning, apoptosis, γ-H2AX and 8-OHdG IF. Male C57BL/6 mice aged 6-8 weeks were given a single dose of whole abdominal irradiation (WAI) at 13 Gy, detected by HE staining, IHC, IF and TUNEL methods, and survival and body weight changes were recorded, fecal samples and small intestinal tissue samples were collected 6 hours and 3 days after irradiation, and the gut microbiota was detected by 16S rRNA sequencing. Whole small intestinal tissue was analyzed by genomic transcript spectrum and RNA sequencing.Compared with vehicle treatment, Fraxin administration significantly improved the quality of life after WAI and maintained the body weight of mice. In addition, the crypt-villus architecture of the intestinal tracts in mice treated with Fraxin was well preserved, and the number of goblet cells, Lgr5+ intestinal stem cells (ISCs) and their daughter cells, Ki67+ proliferating cells increased significantly, reducing the structural damage caused by radiation. Meanwhile, Fraxin improved the expression of tight junction proteins such as E-cadherin and Claudin-3 after WAI, strikingly reduced the levels of FITC-dextran in serum, maintained the integrity of the intestinal barrier. In addition, we have confirmed that Fraxin can increase the cell viability of HIECs, reduce the 8OHdG fluorescence intensity induced by IR, and reduce γ H2AX lesions and apoptosis. Fraxin administration recovered the disorder of the structure of gut microbiota after irradiation and promoted the expression of probiotics, and KEGG pathway analysis suggested that it was related to immunity. Transcriptional sequencing showed that the IL-22 signaling pathway was significantly activated in the Fraxin treatment group, suggesting that Fraxin may have a protective effect on intestinal radiation through IL-22.In conclusion, Fraxin treatment attenuate RIII by modulating the composition of the gut microbiota and activate the IL-22 signaling pathway to reduce RIII.