Hyodeoxycholic acid

Metabolism

In rat intestinal microflora hyodeoxycholic acid is produced by a Gram-positive rod—termed HDCA-1—from several isomers of hyocholic acid and muricholic acid. In pigs with a normal gastrointestinal flora the majority of hyodeoxycholic acid found in bile is of secondary nature, but a small amount was also found in germ free pigs, which supports the hypothesis that HDCA may be a primary bile acid in this species. In healthy humans only traces of HDCA have been found in urine, but in patients with cholestatic liver disease or intestinal malabsorption a significant amount has been found excreted.

Hyodeoxycholic acid undergoes glucuronidation in human liver and kidneys. Glucuronidation of hyodeoxycholic and hyocholic acids was observed to occur extensively at the 6α-hydroxyl group, unlike primary bile acids which form 3α-hydroxy-linked glucuronides. This suggests an important pathway for the elimination of toxic and cholestatic bile acids, e.g. lithocholic and chenodeoxycholic acids which can form hyodeoxycholic and hyocholic acids, respectively, after 6α-hydroxilation. The enzyme family responsible for glucosidation of hyodeoxycholic acid in human liver is UDP-glucuronosyltransferase. Both the UGT2B4 and UGT2B7 isoforms are able to glucuronidate HDCA. This is an example of redundancy in protection against harmful endogenous compounds provided by UGT isoforms, which present distinct but frequently overlapping substrate specificity. A common amino-acid residue that confers these two isoforms specificity to HDCA has been identified in 2006.

Animal model studies support the concept that bile acids may play a role in the development of colon cancer. Deoxycholic acid (DCA) is believed to be tumor promoter, while ursodeoxycholic acid (UDCA) was found to suppress the development of colon tumors. The mechanism that accounts for this difference in function is not clear. In vitro studies found that DCA induces apoptosis in some colon cancer cell lines, while UDCA arrests cell proliferation without inducing apoptosis. In these studies HDCA exhibited biological activity that is intermediate to DCA and UDCA, arresting growth for a time, but causing apoptosis after extended exposure.

Applications

It was known since 1939 that HDCA could be used to synthesize progesterone.{{cite journal

In the 1980s, hyodeoxycholic acid was investigated for its propensity to prevent cholesterol-induced gallstones in animals fed with a lithogenic diet. Another animal study determined that oral administration of HDCA leads to a decrease in LDL-cholesterol concentration, a strong stimulation of hepatic cholesterol biosynthesis and an excessive loss of cholesterol in feces. Unlike ursodeoxycholic acid, which is an approved drug for the treatment of gallstones, HDCA is not marketed for any medical condition.

In supramolecular chemistry a molecular tweezer based on a hyodeoxycholic acid showed a high selectivity the towards the fluorine radical.

References

References

1. (July 1999). "Formation of hyodeoxycholic acid from muricholic acid and hyocholic acid by an unidentified gram-positive rod termed HDCA-1 isolated from rat intestinal microflora". Applied and Environmental Microbiology.
2. Haslewood GA. (June 1971). "Bile salts of germ-free domestic fowl and pigs". Biochemical Journal.
3. (May 1983). "Intestinal absorption, excretion, and biotransformation of hyodeoxycholic acid in man". Journal of Lipid Research.
4. (September 1987). "6 alpha-glucuronidation of hyodeoxycholic acid by human liver, kidney and small bowel microsomes". Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism.
5. (September 1985). "Glucuronidation of bile acids in human liver, intestine and kidney. An in vitro study on hyodeoxycholic acid". FEBS Letters.
6. (September 1991). "Isolation and characterization of hyodeoxycholic-acid: UDP-glucuronosyltransferase from human liver". European Journal of Biochemistry.
7. (December 1993). "Glucuronidation of hyodeoxycholic acid in human liver. Evidence for a selective role of UDP-glucuronosyltransferase 2B4". Journal of Biological Chemistry.
8. (February 2003). "Glucosidation of hyodeoxycholic acid by UDP-glucuronosyltransferase 2B7". Biochemical Pharmacology.
9. (March 2007). "Substrate specificity of the human UDP-glucuronosyltransferase UGT2B4 and UGT2B7. Identification of a critical aromatic amino acid residue at position 33". The FEBS Journal.
10. (June 2001). "Bile acid hydrophobicity is correlated with induction of apoptosis and/or growth arrest in HCT116 cells". Biochemical Journal.
11. (2006). "Resistance to ursodeoxycholic acid-induced growth arrest can also result in resistance to deoxycholic acid-induced apoptosis and increased tumorgenicity". [[BMC Cancer]].
12. (July 1999). "The steroid story of Jenapharm: from the late 1940s to the early 1970s". Steroids.
13. (June 1984). "Prevention of cholesterol-induced gallstones by hyodeoxycholic acid in the prairie dog". Journal of Lipid Research.
14. (July 1995). "Effects of hyodeoxycholic acid and alpha-hyocholic acid, two 6 alpha-hydroxylated bile acids, on cholesterol and bile acid metabolism in the hamster". Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism.
15. Kim, K. (2005). "A hyodeoxycholic acid-based molecular tweezer: a highly selective fluoride anion receptor". Tetrahedron.