Activation of gut FXR improves the metabolism of bile acids, intestinal barrier, and microbiota under cholestatic condition caused by GCDCA in mice

Abnormal bile acid (BA) metabolism is involved in liver fibrosis. In a previous study, we discovered that the hydrophobic BA glycochenodeoxycholate (GCDCA) induced liver fibrosis and that GW4064, an agonist of farnesoid X receptor (FXR), alleviated liver fibrosis caused by GCDCA. However, the impacts of GCDCA on liver BAs, gut BAs, the intestinal barrier, and the gut microbiota are unclear, and obtaining this information would provide additional information into the role of GCDCA in the development of liver fibrosis. In the present study, ultra-performance liquid chromatography-tandem mass spectrometry revealed that mice administered GCDCA by gavage had higher levels of total and primary liver BAs than those in the control group, and a significant reduction in primary liver BAs was observed in the GCDCA + GW4064 group compared with those in the GCDCA group. Compared with those in the control group, the mice administered GCDCA by gavage had greater levels of total and primary BAs in the gut, especially T-alpha-MCA and T-beta-MCA, and no significant differences in the terminal ileum were observed between the GCDCA and GCDCA + GW4064 groups. Immunohistochemistry indicated that GCDCA administration inhibited gut FXR and FGF15 expression, whereas GW4064 activated gut FXR and promoted FGF15 expression. Moreover, immunohistochemistry revealed that GCDCA administration decreased mucin2, claudin-1, occludin, and ZO-1 expression, whereas GW4064 restored their expression. 16S rDNA sequencing revealed that the alpha diversity of the microbiota did not significantly differ among the three groups, but differences in the beta diversity of the microbiota were observed among the three groups. At the phylum level, GCDCA significantly disturbed the gut microbiota, as indicated by reductions in Desulfobacterota, Bacteroidota, and Actinobacteria in the GCDCA group compared with those in the control group. However, significantly increased abundances of Proteobacteria, Cyanobacteria, and Patescibacteria were noted in the GCDCA group compared with the control group. GW4064 administration significantly improved the microbiota structure at the phylum level. The efficacy of GW4064 was also observed at the genus level. Correlation analyses revealed fewer relationships between the gut microbiota and gut BAs, whereas the gut microbiota was more closely related to liver BAs in the GCDCA and GW4064 intervention groups. Together, GCDCA induced cholestasis and disturbed BA metabolism in the gut and liver, as well as the intestinal barrier and structure of the gut microbiota. Activation of gut FXR improved intestinal barrier injury and alleviated BA metabolism dysfunction and dysbacteriosis caused by GCDCA under cholestatic conditions.