Objective A radioactive pulmonary fibrosis model of SD rats was established to explore the application of fibrosis-related proteins and cytokines as the evaluation degree of tissue fibrosis and serve as the basis for studies on radioactive pulmonary fibrosis.

Method Thirty-seven male SD rats weighing 180-200 g were randomly divided into the control (n=5) and irradiation groups (n=32). The irradiation groups were irradiated by an X-ray line characterized by a single exposure dose of 13 Gy (n=10), 15 Gy (n=10), and 17 Gy (n=12). After exposure for 4 and 6 months, hematoxylin-eosin staining and Masson staining were used to evaluate pulmonary fibrosis in the rats. Fibronectin 1 (FN1), matrix metalloproteinase 2 (MMP2), and α-smooth muscle actin (α-SMA) expression levels in lung tissues were detected by Western blot analysis. Hydroxyproline content in the lung tissue were evaluated the lung tissue collagen protein expression levels. ELISA was employed to detect the change of cytokines, such as the transforming growth factor β (TGF-β), interleukin 6, tumor necrosis factor α (TNF-α), and interferon γ (INF-γ), in the bronchoalveolar lavage fluid. Independent sample t-test was used for the intergroup comparison.

Results Compared with the control group, the model group developed pulmonary fibrosis after 4-6 months, and the degree of fibrosis increased with the irradiation dose and time. The protein expression level of FN1 and α-SMA in the lung tissues of the model group was higher than that of the control group, and the protein expression level of MMP2 was lower than that of the control group. The hydroxyproline content in the 6-month model group was higher than that of the control group, increased from (514.19±282.20) μg/mg to (886.13±145.01), (1188.70±273.84), (1700.70±590.95) μg/mg respectively (t=2.621, 3.609, 4.004, all P<0.05). The TGF-β, interleukin 6, and TNF-α levels in the bronchoalveolar lavage fluid of the model group were up-regulated compared with those in the normal control group (t=4.030–12.780, all P<0.05), whereas the IFN-γ was down-regulated (t=2.498–4.303, all P<0.05).

Conclusions The SD rat model of radiation pulmonary fibrosis was successfully constructed. The fibrin content of the rat lung tissues failed to reflect the degree of lung tissue fibrosis. The hydroxyproline content in the lung tissue and the cytokines in the bronchoalveolar lavage fluid can be used as evaluation indexes in severe fibrosis.