Protective Effect And Mechanism Of Caffeic Acid On Lipopolysaccharide-induced Acute Lung Injury

Acute lung injury(ALI)is an uncontrolled inflammatory response that simultaneously causes oxidative stress and cell death with complex etiology and pathogenesis and high mortality rate.In severe cases,it can lead to Acute Respiratory Distress Syndrome or multiple organ failure syndrome.Caffeic acid is a natural phenolic acid compound widely distributed in honeysuckle,yellow flower,eucommia and other traditional Chinese medicine plants.It can reduce blood sugar,reduce vascular permeability,enhance blood coagulation,increase the number of white blood cells and platelets,which is commonly used in the prevention and treatment of various medical and surgical bleeding diseases.In addition,caffeic acid also has various pharmacological activities such as anti-inflammatory,antibacterial,antioxidant,and anti-apoptosis,however,the regulatory effect of caffeic acid on ALI is rarely reported.Therefore,this study established a mice model of lipopolysaccharide-induced ALI and explored the protective effect of caffeic acid on ALI and the possible regulatory mechanism.The model of ALI in mice was established.Caffeic acid(15/30/60 mg/kg)or dexamethasone(5 mg/kg)was intraperitoneally injected 1h after intratracheal instillation of LPS(2 mg/kg).24 h after LPS administration,lung histopathological changes,lung wet/dry ratio,total cell count,neutrophil count,macrophage count and ROS levels in bronchoalveolar lavage fluid(BALF),myeloperoxidase(MPO)activity,oxidative stress indicators(MDA,CAT,SOD,GSH-Px),Nrf2 protein immunohistochemistry and TUNEL cell apoptosis were detected in lung tissue.The expression of pro-inflammatory factors(TNF-α,IL-6 and IL-1β),genes related to Nrf2 and mitochondria-mediated apoptosis pathways were detected by RT-q PCR.The expression of proteins related to NF-κB,MAPKs,NLRP3 inflammasome,Nrf2 and mitochondria-mediated apoptosis pathways were detected by Western blot.The results showed:Caffeic acid attenuated lung histopathological damage,decreased lung wet/dry ratio,decreased lung tissue MPO activity,decreased the count of total cells,neutrophils and macrophages in BALF,decreased TNF-α,IL-6,IL-1β m RNA expression,inhibited LPS-induced phosphorylation of NF-κB pathway related proteins IκBα,p65,p50 and MAPKs pathway related proteins p38,ERK,JNK,inhibited the activation of NLRP3 inflammasome,and downregulared the protein expression of ASC,pro-/cleased-caspase 1,pro-/mature-IL-1β,then attenuated inflammatory damage.Caffeic acid decreased ROS levels in BALF and MDA levels in lung tissue,increased CAT,SOD,GSH-Px activities,promoted nuclear translocation of Nrf2,activated Nrf2 pathway and upregulared the expression of downstream gene HO-1,NQO1,GCLC,GCLM,then attenuated inflammatory damage.Caffeic acid reduced the number of apoptotic-like cells in the lung,increased the expression of Bcl-2,decreased the expression of Bax,caspase3,caspase 9,Cytochrome C,p53,inhibited mitochondria-mediated apoptosis.In conclusion,LPS induced acute lung injury in mice and induced inflammation,oxidative stress,apoptosis.However,CA alleviated the inflammatory response by inhibiting the activation of NF-κB,MAPKs,and NLRP3 inflammasome pathways,improved oxidative damage by reducing ROS levels and activating Nrf2 antioxidant pathway,inhibited apoptosis by regulating mitochondrial-mediated apoptotic pathway,thereby protected against LPSinduced ALI.This study confirmed the protective effect of caffeic acid on ALI mice,and provided a theoretical basis for further understanding of the pharmacological activities of caffeic acid and elucidation of the the possible protective mechanism of caffeic acid against acute lung injury.