Objective To investigate the preventive and therapeutic effects of normal mouse serum (NMS) on radiation-induced lung injury (RILI) in mice.

Methods Radiation pneumonitis models were established by whole-lung irradiation with 13 Gy, and radiation-induced fibrosis models were established by right-lung irradiation with 17 Gy in mice. The mice were randomly divided into the control group, the serum group, the irradiation group and the irradiation+serum group by stratified randomization, with 6 mice in each group. Mice in the serum group and irradiation+serum group received intravenous injections of 100 μL of normal mouse serum via the tail vein following irradiation, whereas mice in the control group and irradiation group received 100 μL of normal saline via the same route. Injections were administered every other day for a total of eight times. Tissue and blood samples were collected at 1.5 months and 7 months post-irradiation to evaluate relevant biological indicators. Levels of inflammatory factors in both serum and lung tissue were measured using ELISA kits. Morphological alterations and collagen deposition in lung tissue were assessed using hematoxylin-eosin (H&E) and Masson’s trichrome staining methods. Expression levels of fibrosis-related genes in the lungs were analyzed by qRT-PCR, while the expression levels of corresponding fibrosis-associated proteins were evaluated using immunohistochemistry and Western blot analysis. For statistical comparison, the independent-sample t-test assuming equal variances was applied to normally distributed measurement data between two groups.

Results Compared with the irradiation group, the lung organ coefficient in the irradiation+serum group was significantly reduced (0.649±0.050) vs. (0.766±0.076) 1.5 months after whole-lung irradiation with 13 Gy, and the difference was statistically significant (t=2.626, P<0.05), The pulmonary inflammatory phenotype was ameliorated. The levels of pneumonia-related inflammatory factors TGF-β, TNF-α, IL-1α, and IL-6 in the supernatant of mouse lung tissue were decreased (382.500±24.700 pg/ml) vs. (457.100±46.900 pg/ml), (349.600±41.830 pg/ml) vs. (426.200±56.250 pg/ml), (14.550±0.523 pg/ml) vs. (16.680±1.015 pg/ml), (32.830±3.640 pg/ml) vs. (40.650±4.345 pg/ml) (t=2.667 ~ 3.226, all P<0.05), and the levels of TGF-β, TNF-α, IL-1α, and IL-6 in the serum were also decreased (401.900±53.980 pg/ml) vs. (482.800±41.190 pg/ml), (403.500±39.990 pg/ml) vs. (492.300±38.690 pg/ml), (15.83±1.028 pg/ml) vs. (18.740±2.172 pg/ml), (32.980±3.193 pg/ml) vs. (41.920±2.865 pg/ml) (t=2.464~5.104, all P<0.05). Furthermore, compared with the irradiation group, the pathological manifestations of collagen deposition and morphological alterations in the right lung tissue of the irradiation+serum group were markedly improved 7 months after 17 Gy irradiation. Additionally, the expression levels of fibrosis-related genes, including Mmp2, Fibronectin, Mcp1, TNF-α, Col1a1, and Mmp13 (1.240±0.2449) vs. (1.862±0.456), (2.681±1.115) vs. (5.314±2.022), (1.608±0.283) vs. (3.123±0.573), (1.192±0.352) vs. (1.975±0.365), (1.473±0.677) vs. (2.646±0.551), (1.136±0.475) vs. (2.492±0.444) (t=2.550~5.236, all P<0.05), as well as the expression levels of fibrosis-related proteins Col1a1 and Alpha-SMA (1.433±0.282) vs. (2.732±0.612), (1.220±0.372) vs. (1.888±0.174) (t=3.340, 2.819, all P<0.05), were significantly downregulated.

Conclusions NMS can effectively alleviate the severity of radiation pneumonia and radiation pulmonary fibrosis in mice, demonstrating a certain preventive and therapeutic potential for radiation-induced lung injury. Early intervention during the early phase of radiation pneumonitis may effectively reduce and delay the progression of radiation-induced pulmonary fibrosis.