Sodium Butyrate Alleviates LPS-induced Acute Lung Injuryin Mice Via Inhibiting HMGB1 Release

Acute lung injury(ALI)is a common clinical disease caused by various direct and indirect injury factors.It is called acute respiratory distress syndrome(ARDS)when it develops to a serious stage.The mortality rate of ALI is as high as 30%-40%,which seriously endangers humans' health.However,there is a lack of effective therapeutic drugs for ALI at present.The main pathological manifestation of ALI is inflammatory infiltration.Lipopolysaccharide(LPS)is one of the important factors that cause lung and systemic inflammation.High mobility group box-1 protein(HMGB1)exists in eukaryotic cells and is considered as a proinflammatory cytokine.Much evidence have shown that the extracellular HMGB1 plays role as a late mediator of endotoxin-induced acute lung injury.Sodium butyrate(SB)is an effective inhibitor of HMGB1,which can inhibit inflammation in many disease models,such as sepsis,hemorrhagic shock,ischemic stroke and Con-A-induced liver injury in mice,but this function has not been reported in acute lung injury model.In the present study,we try to explore whether sodium butyrate can inhibit the release of inflammatory cytokines by establishing a bacterial LPS-induced acute lung injury model.Furthermore,provide new direction for the research and treatment of acute lung injury,and find new ideas and strategies for the long-term clinical treatment of acute lung injury.Objective: This study try to discuss the mechanism of HMGB1 in acute lung injury induced by bacterial LPS and to determine whether sodium butyrate can inhibit the release of inflammatory factors,especially HMGB1.Furthermore,elucidateing the regulatory effects of LPS-induced acute lung injury(ALI)and its possible mechanism,so as to provide experimental basis for basic and clinical intervention strategies based on HMGB1.Methods: 100 male BALB/c mice aged 6-8 weeks and weighing 20-22 grams were purchased from the Animal Laboratory Center of Wuhan University.All mice were randomly divided into three groups after one week of adaptive feeding: model group(LPS model group),normal control group(PBS treatment),and pretreatment group(LPS model + sodium butyrate treatment before LPS).Modeling: The mice were anesthetized by ether anesthesia for modeling.LPS was injected into trachea with the concentration 10 mg/kg,and sodium butyrate solution was injected intraperitoneally half an hour before LPS treatment with the concentration 500 mg/kg.After 24 hours of modeling,lung tissue and alveolar lavage fluid were collected for the detection of related indicators:(1)wet/dry(W/D)weight ratio of lung;(2)myeloperoxidase activity(MPO);(3)collection of bronchoalveolar lavage fluid and cell count to detect the levels of IL-6 and TNF-alpha;(4)histological examination,paraffin section to check the degree of lung injury in mice;(5)the levels of TNF-alpha and IL-6 were detected by ELISA;(6)Western bolt was used to detect the expression of HMGB1 and NF-kappa B protein.Statistical processing: All data were expressed by x_tantalum s(mean standard deviation)and analyzed by SPSS 17.0 statistical software.One-way ANOVA and significant Student-t test were used to analyze the data.P < 0.05 indicated that the difference had statistical significance.Results:(1)Sodium butyrate pretreatment alleviated acute lung injury induced by LPS in mice: the wet/dry weight ratio,the severity score of lung injury and the number of BALF cells in LPS group increased significantly(p<0.01)compared with PBS group,while these items in sodium butyrate pretreatment group was significantly lower than that in LPS group(p<0.01).(2)Sodium butyrate pretreatment inhibited MPO activity in LPS-induced acute lung injury: MPO activity in LPS group was significantly increased(p<0.01)compared with PBS group;and MPO activity in sodium butyrate pretreatment group was significantly decreased compared with LPS group(p<0.01).(3)Sodium butyrate pretreatment inhibited the production of TNF-a and IL-6 in LPS-induced acute lung injury: the expression levels of TNF-a and IL-6 in BALF in LPS group increased significantly(p<0.01)compared with PBS group;and the expression levels of TNF-a and IL-6 in sodium butyrate pretreatment was decreased significantly(p<0.01)compared with LPS group.(4)Sodium butyrate pretreatment inhibited the activation of HMGB1 and NF-kappa B in LPS-induced acute lung injury: the expression levels of HMGB1 and NF-kappa B protein in LPS group were significantly higher than that in PBS group;and the expression levels of HMGB1 and NFkappa B protein in sodium butyrate pretreatment group were significantly lower than that in LPS group.(5)Sodium butyrate can alleviate acute lung injury induced by LPS in mice: to explore the therapeutic effect of sodium butyrate,SB was given half an hour after LPS modeling,24 hours later,compared with LPS treatment group,total cells,neutrophils and macrophages in BALF in sodium butyrate treatment group were significantly reduced,pathological changes of acute lung injury were significantly reduced,and neutrophil infiltration,interstitial edema and pulmonary hemorrhage were significantly improved.Conclusion:(1)Sodium butyrate pretreatment can significantly reduce acute lung injury,manifested in significantly reducing lung dry-wet weight ratio,MPO activity and inflammatory cell infiltration.(2)The protective effect of sodium butyrate may be related to its inhibition of TNF-alpha and IL-6.(3)The protective effect of sodium butyrate on inflammation is related to inhibiting the expression of HMGB1 and NF-kappa B.(4)The application of sodium butyrate provides an important idea for clinical treatment of acute lung injury.