Changes of gut microbiome and metabolome in the AOM/DSS mouse model of colorectal cancer with FLASH radiation

Objective:To investigate the differences in small intestinal toxicity and taxonomic composition,diversity,and functional pathways of gut microbiome and metabolome after different radiotherapies in mouse colorectal cancer(CRC)model.Methods:Azoxymethane/dextran sodium sulfate(AOM/DSS)-induced mouse CRC model was treated with single pulse FLASH-RT(dose rate 100 Gy/s)or CONV-RT(dose rate 2 Gy/min)at whole abdomen.At 12 d after radiotherapy,sections of small intestinal tract tissue were dissected for hematoxylin and eosin(HE)staining and the fresh feces were collected for 16S ribosomal RNA(rRNA)microbiome sequencing and liquid chromatography and mass spectrometry(LC-MS)metabolomics sequencing to assess changes in the gut microbiota and metabolites.Microbial high-throughput 16S rRNA data was analyzed with QIIME2 and LEfSe softwares.ProteoWizard,XCMS and Ropls softwares were used for LC-MS analysis.Results:HE staining showed that FLASH-RT maintained small intestinal integrity and reduced the radiotherapyinduced injury.Sequencing analysis of gut fecal microbiome showed that phylum Bacteroidetes and genera Prevotella and Lactobacillus of microbial community were increased after FLASH-RT.Metabolomics sequencing analysis revealed that the metabolites after FLASH-RT were enriched in amino acid metabolism,while cholesterol metabolism was top enriched after CONV-RT.Conclusions:FLASH-RT significantly mitigates the small intestine tissue damage compared with CONV-RT.FLASHRT and CONV-RT have different impact on gut microbiota and its metabolites.Our results provide a theoretical basis for the early evaluation,prediction and individualized treatment of the irradiation effect after novel FLASHRT on tumors through the evaluation of intestinal microbiota and metabolites.