Effect of the γ-IFN on radiation damage and radiation fibrosis of the rabbit rectum after cavitas pelvisrute fractionated irradiation

Objective: To investigate the effect of γ-IFN on the radiation-induced injury and fibrosis of the rabbit rectum after the fractionated irradiation to pelvic cavity. Methods: The animal model of radiation rectum injury was established. 52 New Zealand rabbits were divided into 3 groups as the normal control group, the conventional radiation group, and γ-IFN group. Except the normal control group, the pelvic cavity of the two other groups were irradiated with 6 MV X-rays. At 5 d post-irradiatio the γ-IFN group was administered with 250 000 U/kg of γ-IFN once a week, while the conventional radiation group with 5 ml of saline solution. The rabbits were executed after 4, 8, 12 and 16 weeks, and the recta in the irradiated field were taken out. HE dyeing, in-situ hybridization and immuno-histochemical methods were used to analyze the radiation-induced rectrum injury and fibrosis. Results: At 4, 8, and 12 weeks post-irradiation, the radiation rectum injury and fibrosis were significantly different between the conventional radiation group and γ-IFN group(P < 0.05), but not at 16 weeks (P > 0.05) . At 4, 8, 12 and 16 weeks post-irradiation, the expression of TGF-β1 mRNA in-situ hybridization in the γ-IFN group were significantly different compared to the conventional radiation group and the normal control group (P <0.05) . The immuno-histochemical results of Col III showed the significant difference among the γ-IFN group and both the normal control group and conventional radiation group ( P < 0.05). Conclusions: γ-IFN could reduce the radiation rectum injury, suppress the expression of TGF-β1 mRNA in the rectum mucosa, inhibit the expression of Col III, and delay the formation of radiation-induced fibrosis. (authors)