Role for enhanced faecal excretion of bile acid in hydroxysteroid sulfotransferase-mediated protection against lithocholic acid-induced liver toxicity

The efficient clearance of toxic bile acids such as lithocholic acid (LCA) requires drug-metabolizing enzymes. We therefore assessed the influence of pregnenolone 16 alpha- carbonitrile (PCN) treatment on LCA-induced hepatotoxicity and disposition of LCA metabolites using female farnesoid X receptor (FXR)-null and wild-type mice. Marked decreases in serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities, and hepatic tauroLCA (TLCA) concentrations were found in LCA- fed wild-type mice co-treated with PCN. Whereas induction of Cyp3a and hydroxysteroid sulfotransferase (Sult2a) proteins was observed in FXR-null and wild-type mice, clear increases in biliary 3 alpha- sulfated TLCA but not total 6 alpha-hydroxy LCA (taurohyodeoxycholic acid and hyodeoxycholic acid) were only observed in PCN-treated wild-type mice. Biliary 3 alpha- sulfated TLCA output rate was increased 7.2-fold, but accounts for only 4.2% of total bile acid output rate in LCA and PCN-co-treated wild-type mice. Total 3 alpha- sulfated LCA (LCA and TLCA) was, however, the most abundant bile acid component in faeces suggesting that efficient faecal excretion of biliary 3 alpha- sulfated TLCA through escape from enterohepatic circulation. FXR-null mice, which have constitutively high levels of the Sult2a protein, were fed a diet supplemented with 1% LCA and 0.4% dehydroepiandrosterone (DHEA), a typical Sult2a substrate/inhibitor. The faecal total 3 alpha- sulfated bile acid excretion was reduced to 62% of FXR-null mice fed only the LCA diet. Hepatic TLCA concentration and serum AST activity were significantly higher in FXR-null mice fed DHEA and LCA diet than in FXR-null mice fed the LCA diet or DHEA diet. These results suggest that hepatic formation of 3 alpha- sulfated TLCA is a crucial factor for protection against LCA- induced hepatotoxicity.