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Bile acids are produced from cholesterol only in hepatocytes. As amphipathic steroid acids, they are detergents (natural surfactants) secreted into the bile ducts, enter the small intestine, and are partially absorbed in the terminal ileum with different functions.
Bile acids play an important role in Fat digestion and vitamin absorption.
Highly toxic bile acids are DCA and LCA. Non-toxic bile acids / bile salts are CA and ursodeoxycholic acid (UDCA )
The conjugated bile acids are called bile salts
The circulating bile salts / bile acids pool composition consists of Primary bile acids (PBAs) produced from cholesterol in the liver, and secondary bile acids formed by specific gut bacteria
Signaling means:
Bile acids are now widely reported to play an important role as a signaling molecule in cell proliferation, metabolism, and differentiation of cells such as hepatocytes (), gastric cancer cells (), and colon cancer cells ()
Bile acids are involved in lipid metabolism (Hofmann 1999 Arch Intern Med. 159: 2647-2658; ), cholesterol elimination, bile flow
Bile acids are involved in protein kinase cascades, cyclic AMP (cAMP) synthesis, and calcium mobilization
Bile acids are ligands for several nuclear hormone receptors, including farnesoid X-receptor (FXR)
Bile acids signals have also been elucidated in other nonclassical BA pathways, such as sphingosine-1-phosphate and BK (large-conductance calcium- and voltage-activated potassium) channels
It has been shown in the last few decades that bile acids are hormones, ligands for receptors, and transcription factors
Some are more hydrophobic than others, a physiochemical property that accounts for their functional differences
Bile acids are divided into two great classes C 27 bile acids (with a C 8 (isooctanoic acid) side chain) and C 24 bile acids (with a C5 ( isopentanoic acid) side chain)
C27 bile acids (named cholestanoic acids) occur in reptiles, ancient birds, and some amphibians, but are only trace constituents of the circulating bile acids in healthy mammals
C 24 bile acids (named cholanoic acids) occur in reptiles, birds, bony fish, and mammals
The bile acid pool consists of multiple species of bile acids, which differ in the position and configuration of hydroxyl groups on their sterol rings and side-chain conjugates
Structure of cholesterol and bile acids : CA, cholic acid; UDCA, ursodeoxycholic acid; CDCA, chenodeoxycholic acid; DCA, deoxycholic acid; LCA, lithocholic acid; Muricholic acid (MCA)
Bile acids are synthesized in the liver, where cholesterol is converted via 7 alfa-hydroxylase (CYP7A1) and, to a lesser extent, 27alfa-hydroxylase (CYP27A1) and 24-hydroxylase (CYP46A1), to the primary bile acids cholic acid (CA) and chenodeoxycholic acid (CDCA) in humans (CA and muricholic acid in rodents)
The hydrophobic ring structure of the cholesterol is digested into more water-soluble amphipathic compounds
Bile acids hepatic lost to the large intestine are replenished by de novo hepatic synthesis, which is regulated by fibroblast growth factor-19 (FGF19) signaling in the small intestine in humans (or FGF15 in rodents).
Bile acids / Bile salts are critical molecules for life, and disruption of Bile Acids / Bile Salts homeostasis has been closely linked to hepatic, intestinal, and systemic diseases, including cholestasis, Fatty liver disease / Hepatic Steatosis, and hepatic and colon tumors
see also:
Bile salts / Bile acids & Cancer
Bile Acids / Bile Salts & Diseases / Disorders
Bile Acids / Bile Salts & Enterohepatic circulation
Primary bile acids (PBAs)
Secondary bile salts / Secondary bile acids (SBAs)