[Therapeutic effects of different doses of methylprednisolone on smoke inhalation-induced acute lung injury in rats].

OBJECTIVE:To investigate the therapeutic effect of different doses of methylprednisolone (MP) in smoke inhalation-induced acute lung injury (SI-ALI). METHODS:Adult male Sprague-Dawley (SD) rats were divided into control group (group A, n = 6), smoke inhalation group (group B, smoke inhalation 30 minutes, n = 30) and smoke + MP 40, 4, 0.4 mg/kg intervention group (groups C, D, E; intraperitoneal injection of MP at 1 hour before smoke inhalation, n = 30) according to random number table method. The survival status of rats in each group was observed at 24 hours, and murine smoke inhalation induced trauma score (MSITS) according to the symptoms and signs of rats at 3 hours after smoke inhalation were scored. The blood of abdominal aorta of rats was collected. Then the rats were sacrificed to harvest bronchoalveolar lavage fluid (BALF) and lung tissue. The levels of interleukin (IL-6, IL-17a) in plasma and BALF were detected by enzyme linked immunosorbent assay (ELISA); the total number of white blood cells and the proportion of leukocytes or macrophages in BALF were calculated; the histopathological changes of lung were observed and the lung injury score was given; the expression of myeloperoxidase (MPO) and high mobility group protein B1 (HMGB1) in lung tissue were detected by Western Blot. RESULTS:The 24-hour survival rate of group B rats was 33.67%. The survival rate of groups C, D and E (65.73%, 85.17%, 60.07%) were significantly higher than that of group B (all P < 0.05), and the survival rate of group D was significantly higher than that of groups C and E. Diffuse inflammatory cell infiltration, intra-alveolar hemorrhage and a large amount of edema fluid were seen in the lung tissue of group B; and the lung injury score was significantly higher than that of group A. Compared with group B, the lung injury in different doses of MP group were decreased to different degrees, while the lung injury scores in groups C and D were significantly decreased (3.31±1.37, 2.62±0.98 vs. 5.52±0.97, both P < 0.01); correlation analysis showed that MSITS score was significantly and positively correlated with lung injury score (r = 0.862, P < 0.001). The levels of plasma inflammatory factors and BALF protein, inflammatory cells and inflammatory factors, and the expression of MPO, HMGB1 in group B were significantly higher than those in group A. Compared with group B, the levels of inflammatory factors in plasma, and protein content, inflammatory cells and inflammatory factors in BALF in different doses of MP group were decreased to different degrees, with significant differences in groups C and D [plasma: IL-17a (pg/L): 49.28±27.12, 36.57±16.52 vs. 191.79±88.21; IL-6 (ng/L): 206.47±109.96, 197.52±113.86 vs. 669.00±299.60; BALF: protein content (mg/L): 892.0±164.5, 566.1±120.9 vs. 1 838.0±145.8; white blood cell count (×109/L): 5.40±1.67, 2.81±1.20 vs. 9.02±2.06; neutrophil ratio: 0.315±0.081, 0.273±0.080 vs. 0.590±0.096; IL-17a (ng/L): 22.63±8.62, 18.92±8.43 vs. 43.31±19.17; IL-6 (ng/L): 156.49±46.94, 123.66±64.91 vs. 253.43±80.03; all P < 0.01]; in addition, the expression of MPO and HMGB1 protein in lung tissues of MP groups with different doses were significantly decreased, the expression of MPO in group D was significantly lower than that in group E [MPO/β-actin (fold increase from group A): 2.14±0.97 vs. 4.35±0.87, P < 0.01], the expression of HMGB1 in groups C and D were significantly lower than that in group E [HMGB1/β-actin (fold increase from group A): 1.77±0.73, 1.23±0.67 vs. 3.65±1.08, both P < 0.05]. CONCLUSIONS:MP can significantly improve the survival rate of SI-ALI rats and reduce the acute pulmonary and systemic inflammatory response. The MP effect of 4 mg/kg was better than 40 mg/kg and 0.4 mg/kg.