Establishment of a Standardized Rat Model of Chronic Radiation Proctitis and Preliminary Evaluation of Its Association with Tubulin

Background Chronic radiation proctitis, a major complication of pelvic radiotherapy, lacks effective treatments and a standardized animal model that recapitulates its late fibrotic and angiogenic pathologies. Aim This study aimed to establish a chronic radiation injury model resembling the progression of human radiation proctitis. Serial endoscopic observations were conducted to examine long-term rectal mucosal changes in rats post-irradiation, and the relationship with cytoskeletal proteins was preliminarily assessed. Methods The rats were randomly divided into 12 groups, including radiation dose groups of 12.5–37.5 Gy and a control group. A single-batch irradiation method was used to establish the model. The degree of rectal injury and progression over six months were assessed using endoscopic observations, the modified Vienna rectal endoscopic scoring system, and histological methods. Results Below 20 Gy, mucosal injury was negligible following resolution of acute inflammation.20–35 Gy, marked capillary dilation appeared around the eighth week post-irradiation, ultimately resulting in persistent radiation-induced proctitis. At 20 Gy, a sharp decrease in cytoskeletal proteins, particularly tubulin, was observed. This reduction correlated with the eventual development of chronic radiation injury in the 20–35 Gy groups. Moreover, VEGF was upregulation in the chronic phase. Conclusions A single rectal irradiation of 25 Gy is recommended to simplify the model establishment process and achieve successful induction of chronic radiation proctitis in rats while ensuring survival. When assessing pharmacological interventions for radiation proctitis, the observation period should be extended to at least eight weeks.