Bile acid conjugation, taurine

Cystine) Taurine Bile acid conjugation, neuronal cell undernutrition, inflammatory diseases Reduces contrast-induced nephropathy in... 

The taurine residue can also be found as an amide derivative of the 26-carboxylic acid function in the 3p,5a,6p,15a-polyhydroxylated steroids 328 and 329, which were obtained from the starfish Myxoderma platyacanthum [245]. The structures of both compounds were determined from spectral data and chemical correlations. The bile of the sunfish Mola mola has been shown to contain a new bile acid conjugated with taurine (330) together with sodium taurocholate. Compound 330 was identified as sodium 2-[3a,7a, 11 a-trihydroxy-24-oxo-5P-cholan-24-yl]amino]ethane-sulfonate on the basis of its physicochemical data and chemical transformations [246]. 

In addition to bile acid conjugation, a variety of other compounds may also be excreted as taurine conjugates, including retinoic acid (Section 2.2.1.3) and a number of xenobiotics. 

Several mechanisms have been proposed to explain the cholestasis that occurs during parenteral nutrition, but there is little direct evidence to support any of them. Nutrient deficiencies that may be critical for hepatic uptake, biotransformation, and secretion of bile may be involved. Deficiency of taurine, which is important for bile acid conjugation, may cause cholestasis in premature infants. Certain amino acids may act as toxins. Reduced... 

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). 

Bile acids conjugated with either taurine or glycine may be transported indeed, the ileal system can transport cholic acid itself. When an analogue of taurocholate containing a positively charged group (compound 8, Fig. 3)... 

In addition to changing the physical properties of bile acids, conjugation also alters their physiological properties. On the basis of extremely limited evidence, it seems likely that the bile acid pool of animals with exclusively taurine conjugates is maintained chiefly by active absorption from the ileum. 

Thyroid activity also influences bile acid conjugation. In ten hypothyroid patients, the mean ratio of glycine-conjugated/taurine-conjugated bile acids was 8.8. The mean value after treatment with desiccated thyroid or thyroxine to restore a euthyroid state was 3.4, corresponding quite closely to the mean value of 3.1 for normal subjects (8). 

The terminal step in the biosynthesis of bile acids from cholesterol is represented by the enzymatic synthesis of water-soluble bile acid conjugates of taurine and/or glycine through a peptide bond, as shown in Fig. 1. 

The demonstration by Bergstrom et al. (4,5) in 1953 of the conversion of deoxycholic acid to taurocholic acid in the rat in vivo and by rat liver slices paved the way for studies on 7a-hydroxylation and conjugation of bile acids. The early work on the synthesis of bile acid conjugates in vitro utilized slices or homogenates of rat and human liver, and the enzymatic reaction was followed by the incorporation of radioactivity from carboxyl- C-labeled bile acids into the corresponding taurine and glycine conjugates (6,7). The... 

Szepesi et al. (1982) designed a TLC method for the isolation and determination of chenodeoxycholic acid and related compounds using silica gel 60 plates with the mobile phase chloroform-ethyl acetate-acetic acid-2 methoxyethanol (9 9 2 1). Van den Ende et al. (1983) combined TLC and in situ fluorometry to determine 0.05-0.1 pg of free bile acids and bile acids conjugated with glycine or taurine. 

Cysteine Precursor of taurine (used in bile acid conjugation and for other functions) reducing... 

A.S. Truswell, S. McVeigh, W.D. Mitchell, and B. Bronte-Stewart, Effect in man of feeding taurine on bile acid conjugation and serum cholesterol levels, J. Atherosclerosis Res. 5s526 (1965). 

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