Gut Microbiota-Bile Acid Crosstalk in Diarrhea-Irritable Bowel Syndrome

Figure 1

Bile acids biosynthesis, metabolism, and its relationship with gut microbiota. In humans, bile acids (BAs) mainly consist of primary BAs and secondary BAs. The primary BAs include CA and CDCA, which are synthesized by cholesterol in hepatocytes through the classical pathway and the alternative pathway. The secondary BAs mainly include DCA and LCA, which are converted from primary BAs by gut microbiota. The major genera of gut microbiota take part in secondary BA production which includes Lactobacillus, Bifidobacterium, Clostridium, Listeria, Bacteroides, and enterococcus in deconjugation and Eubacterium and Clostridium in 7α-dehydroxylation. Abbreviations: CA: cholic acid; CDCA: chenodeoxycholic acid; DCA: deoxycholic acid; LCA: lithocholic acid; TCA: taurocholic acid; TCDCA: taurochenodeoxycholic acid; GCA: glycocholic acid; GCDCA: glycochenodeoxycholic acid; CYP7A1: cholesterol 7α-hydroxylase; CYP8B1: sterol 12α-hydroxylase; CYP27A1: sterol 27-hydroxylase; CYP7B1: oxysterol 7a-hydroxylase.