Abstract
Bile acids are biosynthesized from cholesterol in the liver. Cholic acid (CA), chenodeoxycholic acid (CDCA), and deoxycholic acid (DCA) are major bile acids in humans. Neutral (classical) pathway is the major pathway of the bile acid biosynthesis in adult humans, which starts from 7ɑ-hydroxylation of cholesterol, catalyzed by cholesterol 7ɑ-hydroxylase (CYP7A1), the rate-limiting step of bile acid biosynthesis. In the liver, farnesoid X receptor (FXR) induces the negative nuclear receptor, small heterodimer partner (SHP), which inhibits CYP7A1 and CYP8B1 gene transcription. FXR and SHP are activated by bile acids in the liver. In the intestine, FXR agonists induce fibroblast growth factor 15 (FGF15; FGF19 in humans), which activates the liver FGF receptor in the liver to inhibit CYP7A1 and CYP8B1 expression. Most bile acids in the bile and serum are conjugated with glycine or taurine. In addition, sulfate and glucuronide conjugates of bile acids also exist, which are hydrophilic and useful for urinary excretion. Bile acids with less hydroxyl groups are subjected to these conjugations, which are appropriate for the detoxication of toxic bile acids.
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Takikawa, H. (2017). Metabolism of Bile Acids. In: Tazuma, S., Takikawa, H. (eds) Bile Acids in Gastroenterology. Springer, Tokyo. https://doi.org/10.1007/978-4-431-56062-3_1
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DOI: https://doi.org/10.1007/978-4-431-56062-3_1
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