[Metformin protects against bleomycin-induced pulmonary fibrosis in mice]

Objective: To explore the effect of metformin on murine model of bleomycin (BLM)-induced lung injury and fibrosis. Methods: A total of 30 mice were divided into 3 groups: control, BLM, and BLM with metformin, in accordance with the random number table and each group had 10 mice. To induce the pulmonary fibrosis model, a concentration of 2 mg/ml bleomycin was intratracheally administered in the BLM group and BLM with metformin group with a volume of 1.75 μl/g, while the control group accepted saline with the same volume. Metformin (200 mg/kg) was given to the mice orally once a day from the day before intratracheal instillation of bleomycin to day 14. The daily survival condition of mice was recorded during 14 days. At day 14, HE-staining was used to assess the severity of fibrosis according to the method proposed by Ashcroft. Total lung collagen content was determined by hydroxyproline assay and Masson's trichrome staining. To examine the expression of fibronectin we used the method of immunohistochemistry staining. The changes of Transforming Growth Factor beta 1 (TGF-β(1)) in plasm, bronchoalveolar lavage fluid (BALF) and lung were measured by ELISA. Results: The survival rates of control group, BLM group and BLM with metformin group at day 14 were 10/10, 4/10 and 7/10 respectively. According to the method proposed by Ashcroft the score of metformin treated mice was significantly lower than that of the bleomycin model mice[(3.82±0.58) vs (7.79±0.06), (P<0.05)]. The hydroxyproline level in lung tissue were markedly attenuated in metformin treated mice compared with bleomycin model mice [(0.40±0.05) vs (0.73±0.10) μg/mg, (P<0.05)]. The level of TGF-β(1) in plasma, BALF and lung tissue were also decreased in mice treated with metformin compared with bleomycin model mice [(2.32±0.68) vs (4.59±0.45) ng/ml, (0.81±0.09) vs (1.40±0.06) ng/ml, (17.12±0.83) vs (21.25±0.69) ng/mg, all P<0.05]. Conclusion: Metformin can reduce the severity of pulmonary fibrosis in mice induced by bleomycin.