A Novel Focal Duodenal Radiation Injury Model Reveals Dose-, Time-, and Spatially Dependent Microbiome Perturbations After Radiation Injury.

PURPOSE: The duodenum is a key organ at risk during sterotactic ablative radiotherapy (SABR). Understanding mechanisms of radiation-induced intestinal injury (RIII) could reveal novel strategies to reduce SABR toxicities. The gut microbiome contributes to RIII; however, existing preclinical models either require surgical manipulation or fail to recapitulate high-dose conformal treatment fields used during SABR, confounding microbiome studies. We developed a noninvasive focal bowel irradiation model to assess microbiome dynamics in both the duodenum and the stool after high-dose duodenal irradiation.

METHODS AND MATERIALS: C57BL/6J mice received sham treatment or focal irradiation (12 or 18 Gy) to the proximal duodenum using a small animal irradiator. Stool and duodenal tissue samples were collected at days 4, 14, and 91 after treatment and processed for bacterial 16S rRNA gene V4 region amplicon sequencing (Illumina MiSeq platform). Microbiome diversity metrics were calculated, and multivariable linear mixed modeling identified bacterial taxa associated with radiation therapy.

RESULTS

Oral iodine contrast enabled duodenum visualization, and 100% of mice survived until euthanasia. Focal duodenal irradiation led to dose- and time-dependent changes in duodenal bacterial community composition that were not observed in stool. At days 4 and 14 after treatment, 18 duodenal taxonomic groups were significantly perturbed, whereas only 2 taxa were significantly altered in the stool.

CONCLUSIONS

Our focal duodenal irradiation model is safe, well tolerated, and easy to implement. It enables characterization of microbiome perturbations during both the acute and late phases of injury and serves as a platform for testing new RIII mitigation strategies. Our findings reveal that irradiation-induced changes in the duodenal microbiome are dose-, time-, and spatially dependent and are not reflected in stool samples. These results underscore the imperative of directly assessing tissue-associated microbiota, as relying solely on stool samples risks overlooking critical, localized microbial dynamics that may drive injury and repair.