'The two primary bile
acids, Cholic acid and Chenodeoxycholic acid, are oxidised from cholesterol in
the liver. In the intestine, the primary bile acids are then dehydroxylated to
the secondary bile acids; Cholic acid to Deoxycholic acid and Chenodeoxycholic
acid to Lithocholic acid and Ursodeoxycholic acid. The two primary and
secondary bile acids can also be converted to their glycine and taurine
conjugates to increase water solubility. By choosing deuterium labelled
Chenoxycholic acid, Deoxycholic acid and Ursodeoxycholic acid it is possible to
differentiate the three bile acids even though the unlabelled forms all share
the same molecular weight. This allows for clear determination and identification
of each bile acid, as well as the glycine and taurine conjugates.
'