Objective       To evaluate the effect of genistein as a protecting agent on the radiation-induced pulmonary fibrosis in mice.       Methods        The thoraces of female 8-week-old C57BL/6J mice were exposed to either sham irradiation or single fraction of 8MV X ray radiation of (12.0±0.2) Gy. A total of 60 mice were divided as Sham (C group

n=10)

radiation (R group

n=10)

genistein+radiation (Gen+R group

n=30)

amifostine+radiation (Ami+R group

n=10). The mice of Gen+R group were administered with genistein (200 mg/kg) in 8

16 and 24 h respectively before irradiation (n=10) and then administered once per day until 4 weeks. While the mice of Ami+R group was injected subcutaneously by 100 mg/kg amifostine in 30 min before irradiation and in every day until 4 weeks. Mice were sacrificed at 4

8

and 12 weeks post-irradiation. The lung tissues were removed and processed for definitive analysis

including hydroxypmline content and HE staining. ELISA was used to measure the serum level of transforming growth factor β1 (TGF-β1).       Results       Pathological study showed that pulmonary fibrosis became more severe along with the time after irradiation

and genistein attenuated lung inflammation and fibrosis. Radiation increased the expression of TGF-β1 and hydroxyprolin content in lung tissue in a time-dependent manner

and genistein reduced TGF-β1 expression and hydroxyprolin content (P0.05).       Conclusion       Genistein attenuates the progress of radiation-induced lung fibrosis

and exerts significant effect on prevention against radiation.