Objective  Radiation proctitis (RP) is the most common complication of radiotherapy for pelvic irradiation receivers. In this study, we investigated the changes in gut microbial profiles and their association with inflammation in patients with RP.

  Methods  Fecal samples were collected from 18 patients with cervical cancer undergoing radiotherapy, with 10 samples being obtained from patients with RP and 8 being used as control samples. Microbiota profiles were characterized by 16S rRNA sequencing using the Illumina HiSeq platform. An epithelial monolayer cell co-culture model was used to investigate the effects of radiation-induced microbial dysbiosis on the epithelial inflammatory response. Additionally, the serum cytokine levels of inflammatory indicators are evaluated. Furthermore, a radiation-induced mouse colitis model was used to analyze changes in fecal microbiota and tissue pathology, tight junction, and cytokine secretion.

  Results  Dysbiosis was observed among RP patients, and was characterized by a relatively higher abundance of Prevotella-9, Serratia, Rothia, Prevotella-2, and Veillonella and lower abundance of Bacteroides and Parasoidetes. The alpha diversity of the patients with RP was markedly reduced and the beta diversity analyses showed that the RP and control cohorts were differed substantially. Proteobacteria, Gammaproteobacteria, and Enterobacteriales were clearly enriched in patients with RP at the phylum, class, and order levels, respectively. Additionally, the levels of inflammatory markers were remarkably increased. Furthermore, RP-patient?derived microbiota induced the secretion of IL-1β, TNF-α, and IL-4, phosphorylation of p65, and the upregulation of COX, iNOS, MCP1, and CRP. Moreover, serum TNF-α, IL-1β, and CXCL-1 levels were significantly higher in patients with RP. In the RP mouse model, the quantities of total 16S rRNA gene and abundance of Bacteroides were significantly decreased, while the abundance of Prevotella was increased. The colons of RP mice were characterized by the destruction of epithelial architecture, mucus gland damage, and intense inflammatory cell infiltration. Meanwhile, the tight junctions were smaller, looser, and indistinct. Additionally, serum levels of TNF-α, IL-1β, and CXCL-1 were higher.

  Conclusions  We presented the overall picture of the gut microbiota in patients with RP. Our re-sults suggest that dysbiosis of the gut microbiota may be correlated with intestinal inflammation. Hence, gut microbiota may offer a set of biomarkers for prediction, disease activity evaluation, and treatment selection for RP.