Farnesoid X receptor contributes to oleanolic acid-induced cholestatic liver injury in mice

Farnesoid X receptor (FXR) is a nuclear receptor involved in the metabolism of bile acid. However, the molecular signaling of FXR in bile acid homeostasis in cholestatic drug-induced liver injury remains unclear. Oleanolic acid (OA), a natural triterpenoid, has been reported to produce evident cholestatic liver injury in mice after a long-term use. The present study aimed to investigate the role of FXR in OA-induced cholestatic liver injury in mice using C57BL/6J (WT) mice and FXR knockout (FXR^-/- ) mice. The results showed that a significant alleviation in OA-induced cholestatic liver injury was observed in FXR^-/- mice as evidenced by decreases in serum alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase as well as reduced hepatocyte necrosis. UPLC-MS analysis of bile acids revealed that the contents of bile acids decreased significantly in liver and serum, while increased in the bile in FXR^-/- mice compared with in WT mice. In addition, the mRNA expressions of hepatic transporter Bsep, bile acid synthesis enzymes Bacs and Baat, and bile acids detoxifying enzymes Cyp3a11, Cyp2b10, Ephx1, Ugt1a1, and Ugt2b5 were increased in liver tissues of FXR^-/- mice treated with OA. Furthermore, the expression of membrane protein BSEP was significantly higher in livers of FXR^-/- mice compared with WT mice treated with OA. These results demonstrate that knockout of FXR may alleviate OA-induced cholestatic liver injury in mice by decreasing accumulation of bile acids both in the liver and serum, increasing the export of bile acids via the bile, and by upregulation of bile acids detoxification enzymes.