Mutual Inhibition Between Farnesoid X Receptor And Hepatic Inflammation In LPS-induced Acute Liver Injury

Background In adult's liver,a key nuclear receptor named farnesoid X receptor(FXR),crucially involves in the metabolism of cholesterol in the body.Not only that,FXR has been thought of as a key factor in anti-inflammation.Obeticholic acid(OCA)as a synthetic FXR agonist has been used clinically.We suspected that FXR activated by OCA had a role in nuclear factor ?B(NF-?B),which is a nuclear transcription factor in inflammatory respond,thus alleviated acute liver injury.On the other hand,NF-?B activated by LPS supposed to inhibit FXR and its target genes.Objective The aim of the present study was to investigate the effects of obeticholic acid(OCA),a synthetic FXR agonist,on lipopolysaccharide(LPS)-induced acute liver injury.Methods Eight-week-old female ICR mice,weighing 28-30 g,were purchased from Beijing Vital River(Beijing,China),whose foundation colonies were all introduced from Charles River Laboratories.The animals were always allowed free access to water and food and placed in an environment with temperature(20-25 ?)and humidity(50±5 %)on12-hour light/dark cycle for a period of one week before experiment.Total 48 mice were randomly divided into six groups.All mice except controls were intraperitoneally injected with LPS(2.0 mg/kg).In the OCA and LPS+OCA groups,mice were pretreated with three doses of OCA(5.0 mg/kg,dissolved in corn oil)at 48,24,and 1 h before LPS injection.In the Control and LPS groups,mice were pretreated with three time of corn oil.Mice were sacrificed either 2 h or 8 h after LPS injection.Serum samples were collected for measurement of biochemical parameters.Some liver samples were collected for morphological examination to count inflammatory cells.The remainingliver tissues were collected and frozen immediately in lipid nitrogen for real-time RT-PCR and Western Blot.The interaction between nuclear protein FXR and nuclear factor NF-?B were analyzed.This study followed the guidelines for humane treatment set by the Association of Laboratory Animal Sciences at Anhui Sciences and the Center for Laboratory Animal Sciences at Anhui Medical University(Permit Number: 15-0011).Adequate measures were taken to minimize pain or discomfort of mice.Results The results showed that the serum alanine aminotransferase(ALT)and aspartate aminotransferase(AST)increased slightly 2 hours after LPS injection,and increased significantly after 8 hours.Pretreatment with OCA reduced the elevation of ALT.At the same time,Pretreatment with OCA alleviated the increase of liver weight and liver coefficient as well as focal hepatocyte necrosis and inflammatory cell infiltration in acute liver injury induced by LPS.In addition,OCA down-regulated the up-regulation of LPS-induced hepatic inflammatory cytokines(such as il-1? and il-6)and chemokines(such as mip-2,kc,and cox-2).In addition,OCA inhibited the activation of liver nuclear factor ?B(NF-?B)p65 and p50 subunits.Another experiment showed that pretreatment of OCA activated FXR in hepatocytes.However,FXR in livers of mice injected with LPS was down-regulated at 2 and 8 hours,and nuclear translocation of FXR activated by OCA was suppressed.Correspondingly,LPS down-regulated the two target genes of FXR in liver bsep and mrp2,while pretreatment with OCA alone could significantly up-regulate the target gene expression.In addition,OCA reinforces interaction between hepatic FXR and NF-?B p65 subunit.These results indicate that in LPS-induced acute liver injury,there is a mutual inhibitory effect between the nuclear receptor FXR and the liver NF-?B p65 subunit.ConslusionPretreatment of OCA reduced liver inflammation in LPS-induced acute liver injury.Correspondingly,LPS activates liver NF-?B signaling and also inhibits hepatic FXR and its target genes.