Fig. 1

The synthesis of primary and secondary bile acids. a CDCA and CA are predominantly synthesized through the classical pathway in the hepatic endoplasmic reticulum, contributing to more than 90% of total bile acid synthesis under normal physiological conditions. This synthesis process is regulated by CYP7A1, and CDCA is produced in the absence of CYP8B1. Subsequently, these primary bile acids are converted into conjugated forms, primarily glycine or taurine-conjugated (in a 3:1 ratio in humans), with the assistance of BAAT. b Within the intestine, BSH plays a predominant role in deconjugating bile acids (TCA, GCA, TCDCA, and GCDCA), converting them back into unconjugated forms. Subsequently, 7-α-dehydroxylase enzymes catalyze the conversion of these unconjugated bile acids into DCA and LCA. Additionally, a minor fraction of deoxycholic acid can be further converted into UDCA by intestinal bacteria's 7-β-hydroxysteroid Dehydrogenase enzymes