Oleanolic acid alleviates ANIT-induced cholestatic liver injury by activating Fxr and Nrf2 pathways to ameliorate disordered bile acids homeostasis

Cholestasis is a clinical syndrome with high incidence and few effective treatments. Oleanolic acid (OA) is a triterpenoid compound with anti-cholestatic effects. Studies using bile duct ligation or lithocholic acid modeling have shown that the alleviating effect of OA on cholerosis is related to the regulation of nuclear factor erythroid 2 related factor (Nrf2) or farnesoid X receptor (Fxr). This study aims to investigate the underlying mechanism of OA against alpha-naphthylisothiocyanate (ANIT)-induced cholestatic liver injury based on Nrf2 and Fxr dual signaling pathways. The ANIT-induced rats model was used with or without OA treatment. Serum biochemical indexes, liver histopathological changes and glutathione level were examined. Bile acids (BAs) targeted metabolomics based on UHPLC-MS/MS were performed. siRNA, RT-qPCR and western blot analysis were used to prove the role of Fxr and Nrf2 pathway in OA's anti-cholestatic liver injury in vivo and in vitro. OA significantly alleviated ANIT-induced liver injury in rats, reduced primary bile acids, accelerated metabolism of BAs and reduced the intrahepatic accumulation of BAs. The expressions of bile salt export pump (Bsep), Na+-taurocholic cotransport polypeptide (Ntcp), UDP-glucuronyl transferase 1a1 (Ugt1a1) and Fxr in rat liver were markedly up-regulated, the activation of Nrf2 was promoted, and the expression of cholesterol 7α-hydroxylase (Cyp7a1) was decreased after OA treatment. Moreover, Fxr or Nrf2 silencing attenuated the regulation of OA on BAs homeostasis related transporters and enzymes in rat primary hepatocytes. OA may regulate BAs-related transporters and metabolic enzymes by activating Fxr and Nrf2 pathways, thus alleviating the cholestatic liver injury induced by ANIT.