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Bile acid synthesis occurs in liver cells, which synthesize primary bile acids (cholic acid and chenodeoxycholic acid in humans) via cytochrome P450-mediated oxidation of cholesterol in a multi-step process. Approximately 600 mg of bile salts are synthesized daily to replace bile acids lost in the feces, although, as described below, much ...
Bacteria metabolize chenodeoxycholic acid into the secondary bile acid lithocholic acid, and they metabolize cholic acid into deoxycholic acid. There are additional secondary bile acids, such as ursodeoxycholic acid. Deoxycholic acid is soluble in alcohol and acetic acid. When pure, it exists in a white to off-white crystalline powder form.
Ursodeoxycholic acid (UDCA), also known as ursodiol, is a secondary bile acid, produced in humans and most other species from metabolism by intestinal bacteria. It is synthesized in the liver in some species, and was first identified in bile of bears of genus Ursus , from which its name derived. [ 8 ]
Hyodeoxycholic acid, also known as 3α,6α-Dihydroxy-5β-cholan-24-oic acid or HDCA, is a secondary bile acid, one of the metabolic byproducts of intestinal bacteria. It differs from deoxycholic acid in that the 6α-hydroxyl is in the 12 position in the former. The 6α-hydroxyl group makes HDCA a hydrophilic acid, a property it shares with ...
Due to the pH of the small intestine, most of the bile acids are ionized and mostly occur as their sodium salts which are then called “primary conjugated bile salts.” In the lower small intestine and colon , bacteria dehydroxylate some of the primary bile salts to form secondary conjugated bile salts (which are still water-soluble).
Unabsorbed CDCA can be metabolised by bacteria in the colon to form the secondary bile acid, lithocholic acid or the epimer, ursodeoxycholic acid. [3] CDCA is the most potent natural bile acid at stimulating the nuclear bile acid receptor, farnesoid X receptor (FXR). [5]
Bacterial 7α-dehydroxylation in the colon produces the secondary bile acid, hyodeoxycholic acid. Epimerization of the 7-hydroxyl to the β-position is found in ω-muricholic acid (also known as β-hyocholic acid). [4] The enzyme responsible for the 6-hydroxylation reaction of chenodeoxycholic acid in the pig is the cytochrome P450 CYP4A21. [5]
Lithocholic acid, also known as 3α-hydroxy-5β-cholan-24-oic acid or LCA, is a bile acid that acts as a detergent to solubilize fats for absorption. Bacterial action in the colon produces LCA from chenodeoxycholic acid by reduction of the hydroxyl functional group at carbon-7 in the "B" ring of the steroid framework.