Fig. 1

Bile acid (BA) biosynthesis and metabolism. Schematic representation of synthetic pathways of primary BAs in hepatocytes (tawny color) and secondary BAs in the intestine (dark brown color). The formation of BAs occurs in the liver via 2 pathways: the classical (or neutral) and the alternative (or acidic) pathways. BAs in the liver are then conjugated with glycine (G) or taurine (T). Primary BAs are metabolized by certain gut bacteria by deconjugation, dehydroxylation, conjugation, and epimerization, generating secondary BAs. The majority of BAs in the gut (90-95%) are reabsorbed in the ileum and recirculate to the liver through the portal vein. The remaining BAs are eliminated through the feces. CA, cholic acid. DCA, deoxycholic acid. CDCA, chenodeoxycholic acid. LCA, lithocholic acid. UDCA, ursodeoxycholic acid