The Regulatory Effect And Mechanism Of Taurochenodeoxycholic Acid On Acute Lung Injury In Staphylococcus Aureus-infected Mice

Acute lung injury（ALI）is an uncontrolled inflammatory reaction,which is caused by many factors,including bacterial infection,pneumonia and traumatic lung parenchyma injury.Acute respiratory distress syndrome（Ards）is the main symptom in the diseased animals.Studies have shown that Taurochenodeoxycholic acid（TCDCA）has significant anti-inflammatory,antipyretic,analgesic,antitussive,antiasthmatic,expectorant,antibacterial and antioxidant activities.However,the regulatory mechanism of S.Aureus infection on acute lung injury in mice is still unclear.In this study,the mechanisms of TCDCA in the regulation of acute lung injury induced by Staphylococcus aureus infection in mice were investigated in vitro and in vivo.The peritoneal macrophages of C57BL/6J mice were pretreated with TCDCA at different concentrations for 1 h before or after Staphylococcus aureus infection The activation of inflammatory signaling pathways in mouse macrophages was detected by Western blot,and the production of TLR2 was detected by Flow cytometry.In addition,the binding mode and binding energy between TCDCA and TLR2 were predicted by molecular docking technique.In the in vivo study,mice were intraperitoneally injected with TCDCA for 1 h before or after Staphylococcus aureus infection.Acute lung injury was induced by intranasal Staphylococcus aureus in mice.The levels of inflammatory mediators in the lungs of mice were detected by ELISA,and the expression of injury-associated protein HMGB1 in the lungs of mice was detected by immunofluorescence.The results showed that TCDCA pretreatment or treatment could regulate the secretion of inflammatory cytokines（TNF-α,IL-1β,IL-6 and PGE₂）and anti-inflammatory cytokines（IL-10）in macrophages induced by Staphylococcus aureus infection（P<0.05）.In addition,TCDCA also Staphylococcus aureus the phosphorylation levels of NF-κB p65,MAPKs p38 and ERK in the inflammatory signaling pathways induced by infection（P<0.05）.Molecular docking results showed that TCDCA and TLR2 receptors could hydrogen bond via THR-153 and GLU-178 amino residues,which were verified by Flow cytometry.The results of in vivo experiments showed that pretreatment or treatment with TCDCA could down-regulate the secretion of TNF-α,IL-1β,IL-6 and IL-10 in the lungs of Staphylococcus aureus infected mice（P<0.05）.In addition,pretreatment or treatment with TCDCA down-regulated the expression of HMGB1 protein,a marker of lung tissue damage,in mice infected with Staphylococcus aureus.This study suggests that TCDCA,as an immunomodulator,plays an important role in the regulation and protection of host inflammatory response and lung injury induced by Staphylococcus aureus infection,the elucidation of this mechanism provides a scientific and effective theoretical basis for the use of TCDCA and its analogues in the prevention and treatment of host lung injury and inflammatory diseases caused by Staphylococcus aureus infection.