Glucocorticoid attenuating pulmonary fibrosis in rats with acute lung injury induced by smoke inhalation / 第二军医大学学报

ABSTRACT

Objective To explore the effect of methylprednisolone (MP) with different durations on pulmonary fibrosis in rats with acute lung injury induced by smoke inhalation. Methods A total of 178 male SD rats were randomized into 5 groups control group (n＝18), simple smoke inhalation group (smoke group, n＝40), smoke inhalation＋ MP treatment for 1 d, 3 d and 7 d groups, naming smoke＋MP (1D) group (n＝40), smoke＋MP (3D) group (n＝40) and smoke＋MP (7D) group (n＝40), respectively. The rats were exposed to smoke for 30 min in the smoke box to meet the criteria of acute lung injury. MP (4 mg/kg per day) was injected intraperitoneally at 1 d, 1-3 d and 1-7 d after smoke inhalation. Survival rates were calculated at 28 d after smoke inhalation. At 7 d, 14 d and 28 d after smoke inhalation, the lung tissues were stained with Masson’s trichrome staining and Sirius Red staining to evaluate pulmonary fibrosis. The mRNA expression levels of transforming growth factor β1 (TGF-β1) and α-smooth muscle actin (α-SMA) were detected by real-time fluorescent quantitative PCR, and the expression levels of myeloperoxidase (MPO), connective tissue growth factor (CTGF), high mobility group box 1 (HMGB1) and interleukin 6 (IL-6) were detected by Western blotting. Results The survival rate of the rats in the smoke group was 47.50%, and the survival rates were significantly improved to more than 80% after MP treatment with different durations (all P0.01). Masson’s trichrome staining and Sirius Red staining staining showed that the lung fibrosis of the rats in the smoke group was aggravated, and the fibrosis and collagen deposition in the smoke＋MP (3D) and smoke＋ MP (7D) groups were significantly attenuated compared with the smoke and smoke＋MP (1D) groups (P0.05 or P0.01). As time progressed, the mRNA expression levels of TGF-β1 and α-SMA after smoke inhalation were increased in the smoke and smoke＋MP (1D) groups. At 28 d after smoke inhalation, the TGF-β1 and α-SMA mRNA levels were significantly higher in the smoke and smoke＋MP (1D) groups compared with the smoke＋MP (3D) and smoke＋MP (7D) groups (P0.05 or P0.01). At 28 d after smoke inhalation, the protein expression levels of MPO, CTGF, HMGB1 and IL-6 were significantly reduced in smoke＋MP (3D) and smoke＋MP (7D) groups compared with the smoke and smoke＋MP (1D) groups (P0.05, P0.01). However, the above indicators have no significant difference between smoke＋MP (3D) group and smoke＋MP (7D) group (all P0.05). Conclusion MP can significantly improve survival rate of rats with smoke inhalation injury. MP treatment for 3 d or 7 d can significantly attenuate smoke inhalation induced pulmonary fibrosis at 28 d after smoke inhalation, but there is no significant difference between these two treatment protocols.