Effects of somatostatin against oxidative stress in mouse model of acute lung injury

Abstract

Objective To investigate the effects and potential mechanisms of somatostatin (SST)against oxidative stress in a mouse model of lipopolysaccharide (LPS)-induced acute lung injury (ALI).Methods A total of 96 ICR male mice of specific pathogen free (SPF) were divided randomly (random number) into four groups:normal control group (n =24),SST control group (n =24),ALI group (n =24) and SST treated group (n =24).The mice of ALI group were given the intra-peritoneal injection of LPS in dose of 12 mg in solution of 40 mL/kg.Mice of normal control group were given the intra-peritoneal injection of equivalent volume of normal saline (NS 40 mL/kg) instead,and mice of SST control group were given the intra-peritoneal injection of equivalent volume of normal saline (40 mL/kg) instead,then hypodermic injection of SST (20 μg:20 mL/kg) at 0.5,2,6 or 12 h after normal saline administration,and mice of SST treated group were given the intra-peritoneal injection of LPS (12 mg:40 mL/kg),then hypodermic injection of SST (20 μg:20 mL/kg) at 0.5,2,6 or 12 h after LPS administration.All mice were sacrificed at 3,8 h or 16 h after the first injection of LPS or NS.The lung wet/dry ratios were calculated.Pathological changes of lung tissues were observed under light microscope after HE staining.The levels of malondialdehyde (MDA),superoxide dismutase (SOD) and catalase (CAT) in the lung tissues were determined by chemical colorimetry; quinone oxidoreductase (NQO-1) levels in the lung tissues were measured by ELISA ; the expressions of nuclear factor-E2-related factor2 (Nrf2) and its protein levels in the lung tissues were measured by RT-PCR and Western blotting,respectively.One-way analysis of variance (ANOVA) was employed for statistical analysis by using SPSS version 19.0 to compare values among all groups.Results There were no significant differences in all biomarker variables between normal control group and SST control group (P ＜ 0.05).Lung wet/dry ratios in ALI group at 8 h and 16 h were significantly higher than those in normal control group (P =0.000) and obviously lower in SST treated group (5.21 ±0.13) vs.(5.78±0.20),(5.39±0.29) vs.(6.17 ±0.17) (P=0.000).Compared with normal control group,the damage of lung tissues in ALI group was more severe.In contrast,histopathological lesions observed in SST treated group were milder significantly.The MDA and NQO-1 in the lung tissues were much higher in ALI group than those in normal control group,while the activities of SOD and CAT were much lower in ALI group (P =0.000).Compared with ALI group,the MDA level (ng/mg) in SST treated group decreased remarkably (2.66 ±0.18) vs.(3.58 ±0.26),(3.52 ±0.31)vs.(4.37 ±0.19),(3.81 ±0.38) vs.(4.92 ±0.25) (P=0.000),whereas CAT activity (U/mg)increased significantly (9.21± 0.47) vs.(7.90±0.32),(10.06±0.51) vs.(8.39±0.41),(10.98 ± 0.33) vs.(9.52 ± 0.55) (P =0.000) ; SOD activity and NQO-1 level at 3 h had no obvious increase (P =0.359、0.111),but SOD activities and NQO-1 levels were markedly increased at 8 h and 16 h [SOD (U/mg):(75.34±5.5) vs.(67.89±3.8),P=0.021; (64.82±4.2) vs.(50.31 ±5.0),P=0.000],[NQO-1 (ng/mg):(1.052 ±0.041) vs.(0.715±0.038),(1.338±0.027)vs.(0.532 ± 0.028),P =0.000].Compared with normal control group,the Nrf2 mRNA and protein levels in ALI group were higher markedly (P =0.000),and Nrf2 mRNA in SST treated group were much higher (P =0.023-0.000),while Nrf2 protein level at 3 h showed no significant difference (P =0.101)but increased obviously at 8 h,16 h (P =0.000).Conclusions Our study has shown that SST can upregulate Nrf2 signal pathway,which may have the effects on regulating the immune response and protections against oxidative damages in ALI. Key words: Lipopolysaccharide ;  Acute lung injury;  Somatostatin ;  Oxidative Stress ;  Nuclear factor-E2-related factor 2 ;  Mice