Deconjugation conjugated bile acids

Deconjugation of bile acids may become excessive when bacterial overgrowth occurs in the small intestine. This condition is referred to as the stagnant loop or blind loop syndrome and is characterized by diarrhea, often accompanied by steatorrhea because of a decrease in the effective concentration of conjugated bile salts and a reduction in the fat-absorptive capacity of the small intestine. 

Bile acids and salts have been found to enhance the absorption of both calcium and vitamin D hence, to increase calcium absorption both directly and indirectly (3,37). However, the ability of some dietary fibers such as lignin and pectin to absorb conjugated and deconjugated bile salts onto their surfaces to be excreted in the feces (a mechanism credited to the hypocholesterolemic effect of some dietary fibers) may result in an overall decrease in calcium absorption from the gastrointestinal tract (7,33,38-40). 

Chromatography.—Considerable attention is being paid to chromatographic methods for the separation and recognition of bile acids and their derivatives. The analysis (g.l.c.) of mixtures of bile acids and their conjugates is reported to be simplified by direct conversion into heptafluorobutyrate derivatives, which occurs with simultaneous deconjugation.The carboxyl function is apparently converted into its volatile mixed cholanyl-heptafluorobutyryl anhydride. Ethyl-dimethylsilyl ethers of bile acid ethyl esters are also reported to be suitable for... 

Around one-quarter of the bile acid conjugates reaching the ileum have the amino acid moiety removed by the action of bacterial enzymes. A decon-jugating enzyme, choloylglycine hydrolase (EC 3.5.1.24) has been isolated from clostridial bacteria (Nl) and is used in methods for the analysis of bile acids. The majority of deconjugated bile acids are reabsorbed and return to the liver, where they are efficiently reconjugated with glycine or taurine (V7). 

To deconjugate bile acids for further analysis, particularly by gas-liquid chromatography, different methods are required for the hydrolysis of the peptide bonds in glycine and taurine conjugates than for hydrolysis of the ester sulfate and glucuronide bonds. Glycine and taurine may be removed by either alkaline or enzymatic hydrolysis (Rll). Alkaline hydrolysis is often... 

Taurine conjugates are not absorbed in the upper intestine of human subjects (31,32), the major transport taking place in the lower ileum by both an active mechanism and passive ionic diffusion. Glycine conjugates, particularly those of dihydroxy bile acids, on the other hand, are absorbed also in the jejunum by passive ionic diffusion (33). Negligible amounts of free bile acids are normally found in the upper small intestine (23), while deconjugation is known to occur in the lumen of the terminal ileum. Absorption of free bile acids appears to take place by both ionic and nonionic diffusion, the transport for dihydroxy bile acids being particularly rapid even in the upper intestine (33). 

In the normal individual the bile acids remain conjugated until they reach the colon, where they may be deconjugated by bacterial enzymes. If because of changes in the bacterial flora deconjugation occurs in the higher portion of the intestine, most of the free bile salts are rapidly reabsorbed, reconjugated, and partly excreted in the feces. Clearly, severe liver disease interferes with the complete conjugation of the bile salt pool. 

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