[Mechanisms of Akkermansia muciniphila in regulating bile acid metabolism of cholestatic model mice].

Objective: To investigate the therapeutic effects of Akkermansia muciniphila (AKK) on liver injury induced by cholestasis and its mechanisms in regulating bile acid metabolism. Methods: The cholestatic mouse model was established by bile duct ligation (BDL). A total of 35 male C57BL/6J mice (8 weeks old) were divided into 5 groups using a random numder table method (7 mice per group): group A (control group), group B (BDL group), group C (BDL+AKK group), group Z (BDL+AKK+Z/E-guggulsterone group), and group G (BDL+AKK+Gly-β-muricholic acid group). Preoperative and postoperative changes in liver function and bile acid metabolism indicators was observed of mice in groups A, B, and C. The liver function and fibrosis markers were compared between groups, as well as serum, liver, and fecal total bile acid levels, fecal bile acid composition, liver histopathology, and the mRNA expression of key proteins involved in the bile acid enterohepatic circulation and the farnesoid X receptor (FXR) signaling pathway were compared. Multiple groups of data were compared using analysis of variance or nonparametric Kruskal Wallis H test. Results: Twelve days after BDL, in groups A, B, and C, mice in group C exhibited milder postoperative jaundice and their body weights on postoperative days 4-5 and 7-11 were heavier than those in group B mice (all P<0.05). The liver tissues of mice in group C were milder than those in group B in terms of appearance, histopathology, inflammation and liver fibrosis (all P<0.05). The levels of serum alanine aminotransferase, aspartate aminotransferase, as well as the expression levels of liver α-smooth muscle actin and type Ⅰ collagen, and the levels of total liver bile acid and fecal β-murine bile acid in the C group mice were all lower than those of group B mice ((46±20) vs. (90±34) U/L, (96±17) vs.(122±31) U/L, (2.01±0.11)% vs. (7.55±0.21)%, (1.92±0.10)% vs. (7.28±0.51)%, (62±14) vs. (124±39) μmol/mg, 3 052 (1 522, 6 406) vs. 14 756 (6 582, 33 474) ng/g, all P<0.05). And the mRNA expression levels of cholesterol 7α-hydroxylase and bile salt export pump of the ileum, etc. in group C mice were lower than those in group B mice (all P<0.05), while the mRNA expression levels of FXR and fibroblast growth factor 15 in the intestine were higher than those in group B mice (all P<0.05). In groups B, C, Z, and G, compared with group C, mice in groups Z and G had aggravated liver injury and fibrosis, increased total bile acid levels in the liver, and increased serum alanine aminotransferase, total bilirubin, and expression levels of liver α-smooth muscle activator protein and type I collagen (all P<0.05). There was no statistically difference in the above indicators between group Z and group G (all P<0.05). Conclusion: AKK reduces liver bile acid synthesis, regulates bile acid metabolism, alleviate liver function damage and fibrosis, and improves clinical phenotypes by activating the intestinal FXR-fibroblast growth factor 15 signaling pathway.