Gut-to-bile transfer of microbially amidated minor bile acids in patients with hepatopancreatobiliary disorders

During bile acid (BA) intestinal transit, microbially amidated BAs (MABAs) are produced. This study investigated their cholephilic behavior and their presence in the bile of patients with hepatopancreatobiliary diseases.

Bile samples were collected during surgical or endoscopic procedures and analyzed using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), with cholic acid (CA) and chenodeoxycholic acid (CDCA) chemically amidated with leucine (Leu), phenylalanine (Phe), or tyrosine (Tyr) as standards. Gut-to-bile transfer was investigated in cellular and animal models.MABAs (Leu>Phe>Tyr) were detected (<1 µM) in the bile of ≈50% of patients with hepatopancreatobiliary disorders. Their levels were positively correlated with total BA concentrations and inversely correlated with the proportion of major conjugated BAs, but not with age, fat-soluble vitamin levels, or disease outcomes. Oral gavage of D - and L -enantiomers of Tyr-CA in mice resulted in intestinal hydrolysis and limited access of L -Tyr-CA to the enterohepatic circulation. In rats, the intravenous injection of glycocholic acid (GCA) and MABAs resulted in similarly rapid biliary outputs. The time course of biliary secretion after infusing MABAs and GCA into the microbiota-free rat ileum in situ was also similar. Docking studies predicted the interaction of BA transporters and MABAs with binding energies comparable to those of taurocholic acid (TCA) and GCA. In cells expressing BA transporters, MABA uptake was efficient (NTCP>ASBT>OATP1B3) and inhibitable by TCA.

Like major conjugated BAs, MABAs are transferred from the gut, where they are produced, to the bile of patients with hepatopancreatobiliary diseases, suggesting gut dysbiosis that favors species generating these compounds.