Taurine conjugated bile acids

FI GURE 4.3 Structures of allocholic acid (petromyzonol sulfate is identical apart from replacement of the carboxyl group with sulfate), taurine-conjugated bile acid, and geosmin. 

Fig. 5.4.15a,b Parts of two-dimensional total correlated spectroscopy spectra of human bile (a) and a mixture of standard solutions of GCA, GDCA, TCA and TDCA (b). These spectra show the connectivity of amide proton signals to H-25 and/or H-26 protons of glycine and/or taurine conjugated bile acids (reprinted from [40])... 

Fig. 5.4.16 Typical room temperature nuclear magnetic resonance spectra of human BA and standards of glycine- and taurine-conjugated bile acid, (reprinted from [40])...

Ijare OB, Somashekar BS, Gowda GA, Sharma A, Kapoor VK, Khetrapal CL (2005) Quantification of glycine and taurine conjugated bile acids in human bile using H NMR spectroscopy. Magn Reson Med 53 1441-1446... 

GIO. Goswami, S. K., and Frey, C. F., A method for the separatimi ofglydne-conjugated bile acids as a group from taurine-conjugated bile acids. Biochem. Med. 17, 20-23 (1977). 

Onishi, S., Itoh, S., and Ishida, Y., Assay of free, glycine- and taurine-conjugated bile acids in serum by high-pressure liquid chromatography by using post-column reaction after group separation, Biochem. J. 204, 135-139 (1982). 

The microsomal 12a-hydroxylase seems to be influenced by the flux of bile acids through the liver in a similar way as cholesterol 7a-hydroxylase. Biliary drainage in rats leads to a 2-fold stimulation of 12a-hydroxylase [44] perhaps due to reduced intake of food [252]. However, it was shown later that 12a-hydroxylation of 7a-hydroxy-4-cholesten-3-one was inhibited by feeding rats different taurine-conjugated bile acids at the 1% level [110]. Ahlberg et al. showed that the microsomal 12a-hydroxylase in human liver was inhibited by about 50% after treatment for 8 weeks with chenodeoxycholic acid, 15 mg/kg body weight [HI]. The increased ratio between cholic acid and chenodeoxycholic acid observed after treatment with cholestyramine is also consistent with an inhibitory effect of reabsorbed bile acids on the 12a-hydroxylase [219]. 

The mechanism by which the lipolytic products pass from the micellar phase into the mucosal cell is unknown, and an extensive discussion of the possibilities is inappropriate here. Since lipolytic products are extensively absorbed whereas taurine-conjugated bile acids are not absorbed in jejunal perfusion experiments (23), and since exchange rates of lipolytic products between micelles are thought to be quite rapid (78), molecular collision of lipolytic products with the cell membrane, resulting in reversible or partially reversible adsorption, has been proposed as the mechanism of fat absorp-... 

The efficient intestinal absorption of bile acids involves both active and passive absorption, but little information on the relative sites and mechanisms of absorption and on their contribution to the entire enterohepatic cycle of bile acids exists. Although the contribution of passive and active absorption of bile acids in the rat small intestine has been measured (20), no data are available for other species. The major site of absorption in all vertebrates appears to be the ileum, where an active transport site exists (14,15). Free bile acids are absorbed passively in the jejunum by nonionic diffusion, dihydroxy acids being absorbed more rapidly than trihydroxy acids (21,22). Perfusion studies in the human jejunum have suggested that glycine dihydroxy bile acids may be absorbed to some extent, and additional evidence for jejunal absorption of bile acids has been obtained in patients and animals with ileal resection (97,98). No information exists on the importance of jejunal bile acid absorption in health in man. Taurine-conjugated bile acids do not appear to be absorbed in the human jejunum (24). 

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). 

Norman (3) demonstrated that the types of bile acids found in normal rat bile were not the same as those which were excreted in the feces. However, when the rats were fed high levels of antibiotics, the fecal bile acids were excreted essentially unchanged from the biliary bile acids (4). The intestinal bacteria were responsible for the hydrolysis of the biliary taurine-conjugated bile acids to the free bile acids found in the feces. Norman also showed that the dehydroxylation of cholic acid to deoxycholic acid could be prevented by Inhibiting the intestinal bacteria. The total amount of fecal bile acid excreted by conventional chicks has been found to be significantly lowered (5) by incorporation of an antibiotic into the diet. 

D water 300 A7-butanol 100 Taurine-conjugated bile acids... 

In a short note Hanaineh and Brooks describe separation of methyl ester trimethylsilyl ethers of glycine-conjugated bile acids (55). This could perhaps serve as a basis for direct analysis of bile and a similar method has been employed by M. and E. Horning (56). It is not yet possible to separate taurine-conjugated bile acids by gas chromatography. 

For the identification of bile acids in bile from man and different animals, Kuksis (13) and co-workers have used ion-exchange chromatography for the separation of glycine- and taurine-conjugated bile acids. After alkaline hydrolysis, extraction, and methylation, the bile acids were analyzed on SE-30 and QF-1 columns. Tentative identifications were supported by additional gas-liquid chromatographic analysis of methyl ester acetates and methyl ester trifluoroacetates. The latter derivatives were also analyzed on OV-17 columns (117). 

The strong-base anion-exchange paper has been employed (38) in the hydroxide form for the separation of free and taurine-conjugated bile acids with diisobutyl ketone-acetic acid-water (4 5 1, v/v/v) or chloroform-methanol-ammonia (4 1 0.1, v/v/v) as developing solvents. It would be anticipated that these systems would also be capable of resolving glycine-and taurine-conjugated bile acids. 

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