Search results
Results From The WOW.Com Content Network
Synthesis of bile acids is a major route of cholesterol metabolism in most species other than humans. The body produces about 800 mg of cholesterol per day and about half of that is used for bile acid synthesis producing 400–600 mg daily. Human adults secrete between 12 and 18 g of bile acids into the intestine each day, mostly after meals.
It is metabolized by the enzyme 7α-hydroxycholest-4-en-3-one 12α-hydroxylase to 7α,12α-dihydroxycholest-4-en-3-one and then to cholic acid, the major primary bile acid in humans. Alternatively, it can be converted into 5β-cholestane-3α,7α-diol and then to chenodeoxycholic acid, the other major primary bile acid in humans. [1]
Cholesterol 7 alpha-hydroxylase is the rate-limiting enzyme in the synthesis of bile acid from cholesterol via the classic pathway, catalyzing the formation of 7α-hydroxycholesterol. The unique detergent properties of bile acids are essential for the digestion and intestinal absorption of hydrophobic nutrients. [8]
This enzyme is involved in the initial stages of the synthesis of bile acids from cholesterol and a member of the short-chain dehydrogenase/reductase superfamily. This enzyme is a membrane-associated endoplasmic reticulum protein which is active against 7-alpha hydrosylated sterol substrates.
Cholic acid downregulates cholesterol-7-α-hydroxylase (rate-limiting step in bile acid synthesis), and cholesterol does the opposite. This is why chenodeoxycholic acid, and not cholic acid, can be used to treat gallstones (because decreasing bile acid synthesis would supersaturate the stones even more). [6] [7]
In the case of BSHs, deconjugated bile acids can interact with host cellular receptors, thus altering aspects of host physiology. [1] [12] A key human cellular receptor is the farnesoid X receptor (FXR), a bile acid-activated transcription factor, which regulates bile acid synthesis and transport.
Chenodeoxycholic acid (CDCA; also known as chenodesoxycholic acid, chenocholic acid and 3α,7α-dihydroxy-5β-cholan-24-oic acid) is a bile acid. Salts of this carboxylic acid are called chenodeoxycholates. Chenodeoxycholic acid is one of the main bile acids.
In the human liver, bile is composed of 97–98% water, 0.7% bile salts, 0.2% bilirubin, 0.51% fats (cholesterol, fatty acids, and lecithin), and 200 meq/L inorganic salts. [ 2 ] [ 3 ] The two main pigments of bile are bilirubin , which is orange-yellow, and its oxidised form biliverdin , which is green.