Cytosolic ferritin and lipid-associated ferritin are metabolically different in guinea-pig livers.

1. Using a human hepatoma (Hep G2) cell line that continually synthesizes 3 beta-hydroxy-5-cholenoic acid, lithocholic acid, chenodeoxycholic acid and cholic acid we have determined the metabolism and biological effects of 26-hydroxycholesterol and 7 alpha-hydroxycholesterol. 2. Addition of 26-hydroxycholesterol to the medium (6 microM) downregulated cholesterol and chenodeoxycholic acid synthesis. 3. The predominant metabolite of 26-hydroxycholesterol was 3 beta-hydroxy-5-cholenoic acid. 4. Cholesterol synthesis was not affected by the addition of 7 alpha-hydroxycholesterol (6 and 12 microM). The predominant metabolite of 7 alpha-hydroxycholesterol was chenodeoxycholic acid. 5. In Hep G2 cells 7 alpha-hydroxylation of 26-hydroxycholesterol is not well expressed.     

Bioconversion of 3beta-hydroxy-5-cholenoic acid into chenodeoxycholic acid by rat brain enzyme systems

We have previously demonstrated that the rat brain contains three unconjugated bile acids, and chenodeoxycholic acid (CDCA) is the most abundantly present in a tight protein binding form. The ratio of CDCA to the other acids in rat brain tissue was significantly higher than the ratio in the peripheral blood, indicating a contribution from either a specific uptake mechanism or a biosynthetic pathway for CDCA in rat brain. In this study, we have demonstrated the existence of an enzymatic activity that converts 3beta-hydroxy-5-cholenoic acid into CDCA in rat brain tissue. To distinguish marked compounds from endogenous related compounds, 18O-labeled 3beta-hydroxy-5-cholenoic acid, 3beta,7alpha-dihydroxy-5-cholenoic acid, and 7alpha-hydroxy-3-oxo-4-cholenoic acid were synthesized as substrates for in vitro incubation studies. The results clearly suggest that 3beta-hydroxy-5-cholenoic acid was converted to 3beta,7alpha-dihydroxy-5-cholenoic acid by microsomal enzymes. The 7alpha-hydroxy-3-oxo-4-cholenoic acid was produced from 3beta,7alpha-dihydroxy-5-cholenoic acid by the action of microsomal enzymes, and Delta4-3-oxo acid was converted to CDCA by cytosolic enzymes. These findings indicate the presence of an enzymatic activity that converts 3beta-hydroxy-5-cholenoic acid into CDCA in rat brain tissue. Furthermore, this synthetic pathway for CDCA may relate to the function of 24S-hydroxycholesterol, which plays an important role in cholesterol homeostasis in the body.     

Bile acid synthesis. Metabolism of 3 beta-hydroxy-5-cholenoic acid to chenodeoxycholic acid

Metabolism of 3 beta-hydroxy-5-cholenoic acid to chenodeoxycholic acid has been found to occur in rabbits and humans, species that cannot 7 alpha-hydroxylate lithocholic acid. This novel pathway for chenodeoxycholic acid synthesis from 3 beta-hydroxy-5-cholenoic acid led to a reinvestigation of the pathway for chenodeoxycholic acid from 3 beta-hydroxy-5-cholenoic acid in the hamster. Simultaneous infusion of equimolar [1,2-3H]lithocholic acid and 3 beta-hydroxy-5-[14C]cholenoic acid indicated that the 14C enrichment of chenodeoxycholic acid was much greater than that of lithocholic acid. Thus, in all these species, a novel 7 alpha-hydroxylation pathway exists that prevents the deleterious biologic effects of 3 beta-hydroxy-5-cholenoic acid.     

Determination of 3 beta-hydroxy-5-cholenoic acid in serum of hepatobiliary diseases--its glucuronidated and sulfated conjugates

3 beta-Hydroxy-5-cholenoic acid in the serum of control subjects and 62 patients with various hepatobiliary diseases was quantitated by mass fragmentography after separation into nonglucuronidated-nonsulfated, glucuronidated, and sulfated fractions. Deuterium-labeled deoxycholic acid and its glucuronide and sulfate were used as internal standards. Mean concentrations of total 3 beta-hydroxy-5-cholenoic acid in serum (mumole/liter) were as follows: Control subjects (14), 0.184; obstructive jaundice (15), 6.783; liver cirrhosis, compensated (12), 0.433, and decompensated (12), 1.636; chronic hepatitis (12), 0.241; and acute hepatitis (11), 2.364. Most of the 3 beta-hydroxy-5-cholenoic acid was glucuronidated or sulfated. Only in patients with obstructive jaundice did glucuronidation (60 +/- 14%) exceed sulfation (31 +/- 14%), sulfation exceeding glucuronidation in the others. The UDP-glucuronyltransferase might have different substrate specificities for 3 beta-hydroxy-5-cholenoic acid and other common bile acids, especially in the cholestatic state.     

Radioimmunological determination of serum 3 beta-hydroxy-5-cholenoic acid in normal subjects and patients with liver disease.

A radioimmunoassay for the determination of 3 beta-hydroxy-5-cholenoic acid in human serum has been developed, using 3 beta-hydroxy-5-cholenoyl-thyroglobulin as immunogen and 3 beta-hydroxy-5-cholenoylglycyl-125I histamine as radioactive ligand. The association constant was 6.3 X 10(8) l/mol. Cross reactivity with other bile acids of human serum was not detectable, but was 5.6% with cholesterol. Serum sample preparation included extraction of 3 beta-hydroxy-5-cholenoic acid from serum, solvolysis of sulfates, hydrolysis of conjugates, and separation from cholesterol by thin-layer chromatography. Serum concentrations of 3 beta-hydroxy-5-cholenoic acid were 0.23 +/- SD 0.12 mumol/l and 0.21 +/- SD 0.09 mumol/l in healthy males and females, respectively. In patients with primary biliary cirrhosis the serum concentration of 3 beta-hydroxy-5-cholenoic acid and the quotient 3 beta-hydroxy-5-cholenoic acid over total 3 alpha-hydroxy-bile acids (measured enzymatically) were significantly higher (P less than 0.02) than in patients with chronic active hepatitis or alcoholic cirrhosis. Analysis of 17 sera with elevated concentration of 3 beta-hydroxy-5-cholenoic acid by radioimmunoassay and capillary gas-liquid chromatography showed a close correlation (r = 0.91, slope = 0.97) between the results of the two methods.     

Bile acid and sterol solubilization in 2-hydroxypropyl-beta-cyclodextrin.

The use of 2-hydroxypropyl-beta-cyclodextrin has made it possible to prepare stable aqueous solutions of cholesterol, 26-hydroxycholesterol, 7 alpha-hydroxycholesterol, and monohydroxy bile acids such as lithocholic and 3 beta-hydroxy-5-cholenoic acids. These solutions are suitable for cell culture studies and for parenteral administration to animals.     

Mitochondrial and Peroxisomal β-Oxidation of Stearic and Lignoceric Acids by Rat Brain

Crude subcellular fractions were prepared from adult rat brains by differential centrifugation of brain homogenates. Greater than 98% of the cellular mitochondrial marker enzyme activity sedimented in the heavy and light mitochondrial pellets, and less than 1% of the activity sedimented in microsomal pellets. Lysosomal marker enzyme activities mainly (71-78% of cellular activity) sedimented in the heavy and light mitochondrial pellets. Significant amounts of the lysosomal marker enzyme activity also sedimented in the crude microsomal pellets (9-13% of total) and high-speed supernatants (14-16% of total). The specific activities of microsomal and peroxisomal marker enzyme activities were highest in the crude microsomal pellets. Fractionation of the crude microsomal pellets on Nycodenz gradients resulted in the separation of the bulk of the remaining mitochondrial, lysosomal, and microsomal enzyme activities from peroxisomes. Fatty acyl-CoA synthetase activities separated on Nycodenz gradients as two distinct peaks, and the minor peak of the activities was in the peroxisomal enriched fraction. Fatty acid beta-oxidation activities also separated as two distinct peaks, and the activities were highest in the peroxisomal enriched fractions. Mitochondria were purified from the heavy mitochondrial pellets by Percoll density gradients. Fatty acyl-CoA synthetase and fatty acid beta-oxidation activities were present in both the purified mitochondrial and peroxisomal enriched fractions. Stearoyl-CoA synthetase activities were severalfold greater compared to lignoceroyl-CoA synthetase, and stearic acid beta-oxidation was severalfold greater compared to lignoceric acid beta-oxidation in purified mitochondrial and peroxisomal enriched fractions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bile acid synthesis in cell culture

Confluent cultures of Hep G2 cells were found to synthesize chenodeoxycholic and cholic acids continually. Chenodeoxycholic acid was synthesized at the rate of 58 +/- 8.6 micrograms/96 h, a rate more than 7-fold greater than that for cholic acid. Addition of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol but not the -3 alpha, 7 alpha-diol was followed by an increase in cholic acid synthesis, thus indicating a relatively low 12 alpha-hydroxylase activity. Endogenous synthesis of monohydroxy bile acid ester sulfates was found, with maximum rates of 135 and 74 micrograms/96 h for lithocholic and 3 alpha-hydroxy-5-cholenoic acids, respectively. Incubation of Hep G2 cells in medium containing 25% D2O permitted a comparison of the precursor/product relationship of cholesterol with 3 beta-hydroxy-5-cholenoic acid. The pattern of incorporation of deuterium was in accordance with that expected, thus allowing the conclusion that this monohydroxy bile acid is derived from cholesterol and should be considered together with chenodeoxycholic and cholic acids as a primary bile acid.     

Bile acid synthesis: down-regulation by monohydroxy bile acids

The regulation of bile acid synthesis was studied in rabbits after interruption of the enterohepatic circulation by choledochoureteral anastomosis. Total daily bile acid output was 772 +/- 130 (SD) mumol/24 h, of which greater than 95% was glycocholic acid. Administration of deoxycholic or cholic acid or their conjugates (300-800 mumol) or gall-bladder bile failed to down-regulate endogenous bile acid synthesis. In contrast, chenodeoxycholic acid administration did down-regulate bile acid synthesis, but this effect was related to the formation and excretion of lithocholic acid. This observation was confirmed by the finding that i.v. infusion of 10-20 mumol of either lithocholic acid or 3 beta-hydroxy-5-cholenoic acid significantly reduced cholic acid synthesis. Thus monohydroxy bile acids, derived from either hepatic or intestinal sources, participate in the down-regulation of bile acid synthesis.     

Cholic acid synthesis from 26-hydroxycholesterol and 3-hydroxy-5-cholestenoic acid in the rabbit

Intravenous administration of 26-hydroxycholesterol to the rabbit with a bile fistula yielded cholic acid in proportions (84 and 86%) not significantly different from that derived from cholesterol. By contrast, the naturally occurring C27 bile acid 3 beta-hydroxy-5-cholestenoic acid yielded not more than 8% cholic acid. Thus initial 26-hydroxylation of cholesterol followed by 7-alpha-hydroxylation can provide sufficient amounts of cholic acid to be considered a quantitatively significant pathway for bile acid synthesis, and in addition it is the only pathway that can be the source of the circulating levels of C24 and C27 monohydroxy bile acids.     

Subcellular localization of 3 alpha, 7 alpha-dihydroxy- and 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoyl-coenzyme A ligase(s) in rat liver

Liver peroxisomes from both rat and humans have previously been shown to contain enzymes that catalyze the oxidative cleavage of the C27-steroid side chain in the formation of bile acids. It has not been clear, however, whether the initial step, formation of the CoA-esters of the 5 beta-cholestanoic acids, also occurs in these organelles. In the present work the subcellular localization of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoyl-CoA (THCA-CoA) ligase (THCA-CoA synthetase) and of 3 alpha,7 alpha-dihydroxy-5 beta-cholestanoyl-CoA (DHCA-CoA) ligase in rat liver has been investigated. Main subcellular fractions and peroxisome-rich density gradient fractions from rat liver were incubated with THCA or DHCA, CoA, ATP, and Mg2+. Formation of THCA-CoA and DHCA-CoA was determined after high pressure liquid chromatography of the incubation extracts. The microsomal fraction contained the highest specific (and also relative specific) activity both for the formation of THCA-CoA and DHCA-CoA. The rates of THCA-CoA formation were further increased from 124-159 nmol/mg.hr-1 in crude microsomal fractions to 184-220 nmol/mg.hr-1 when studied in purified rough endoplasmic reticulum fractions. Formation of THCA-CoA in peroxisomal fractions prepared in Nycodenz density gradients could be accounted for by a small contamination (3-7%) by microsomal protein. The distribution of THCA-CoA ligase was different from that of palmitoyl-CoA ligase that was found to be localized also to the peroxisomal fractions.     

Clostridium scindens baiCD and baiH genes encode stereo-specific 7alpha/7beta-hydroxy-3-oxo-delta4-cholenoic acid oxidoreductases

Secondary bile acids, formed by intestinal bacteria, are suggested to play a significant role in cancers of the gastrointestinal tract in humans. Bile acid 7alpha/beta-dehydroxylation is carried out by a few species of intestinal clostridia which harbor a multi-gene bile acid inducible (bai) operon. Several genes encoding enzymes in this pathway have been cloned and characterized. However, no gene product(s) has yet been assigned to the production of 3-oxo-Delta4-cholenoic acid intermediates of cholic acid (CA), chenodeoxycholic acid (CDCA) or ursodeoxycholic acid (UDCA). We previously reported that the baiH gene encodes an NADH:flavin oxidoreductase (NADH:FOR); however, the role of this protein in bile acid 7-dehydroxylation is unclear. Homology searches and secondary structural alignments suggest this protein to be similar to flavoproteins which reduce alpha/beta-unsaturated carbonyl compounds. The baiH gene product was expressed in Escherichia coli, purified and discovered to be a stereo-specific NAD(H)-dependent 7beta-hydroxy-3-oxo-Delta4-cholenoic acid oxidoreductase. Additionally, high sequence similarity between the baiH and baiCD gene products suggests the baiCD gene may encode a 3-oxo-Delta4-cholenoic acid oxidoreductase specific for CDCA and CA. We tested this hypothesis using cell extracts prepared from E. coli overexpressing the baiCD gene and discovered that it encodes a stereo-specific NAD(H)-dependent 7alpha-hydroxy-3-oxo-Delta4-cholenoic acid oxidoreductase.     

Effect of bile duct ligation on bile acid and cholesterol metabolism in rats

The effects of bile duct ligation on bile acid and cholesterol metabolism were examined in male Wistar strain rats. Quantitative and qualitative changes of bile acids and cholesterol in serum and urine occurred; beta-muricholic acid predominantly increased in serum and urine and the ratio of urinary cholic acid and beta-muricholic acid changed from about 5:3 on day 1 to about 1:8 on day 5 under biliary obstruction. The form of the increased urinary bile acids was mainly taurine-conjugated and partly sulfated. Under conditions of bile duct ligation on day 5, 14C-labeled 3 beta-hydroxy-5-cholenoic, lithocholic, and chenodeoxycholic acids were intragastrically administered to the rats after pretreatment with antibiotics and the metabolites of these three acids were investigated. 3 beta-Hydroxy-5-cholenoic acid was most efficiently converted to beta-muricholic acid. The present study strongly suggested the presence of an alternative metabolic pathway induced by bile duct ligation, which caused the change in composition of urinary bile acids, and especially the marked increase in beta-muricholic acid formation. A possible alternative pathway for bile acid biosynthesis under biliary obstruction in rats is postulated.     

Partial purification and immunoreactivity of an 80000-molecular-weight polypeptide associated with peroxisome proliferation in rat liver

Hypolipidaemic drugs and industrial plasticizers such as di-(2-ethylhexyl) phthalate, which cause proliferation of hepatic peroxisomes, also cause an increase in an 80000-mol.wt. polypeptide in the liver of rats and mice. This polypeptide has been designated as PPA-80 (PPA, for peroxisome-proliferation-associated; 80 for 80000mol.wt.). The polypeptide PPA-80 was purified to over 90% purity from livers of rats treated with the peroxisome proliferators Wy-14,643, nafenopin, tibric acid and clofibrate by a single-step preparative sodium dodecyl sulphate/polyacrylamide-gel-electrophoretic procedure. The antibodies raised against the PPA-80 polypeptide isolated from livers of rats treated with Wy-14,643 cross-reacted with polypeptide PPA-80 purified from the livers of rats treated with Wy-14,643, as well as from the livers of rats treated with nafenopin, tibric acid and clofibrate. The anti-(polypeptide PPA-80) antibodies did not cross-react with catalase, a marker enzyme for peroxisomes, or with NADPH–cytochrome P-450 reductase, which has the same approximate mol.wt., 80000. The intensity of immunoprecipitin bands formed with microsomal, large-particle and postnuclear fractions from livers of animals pretreated with peroxisome proliferators was significantly greater compared with equal amounts of protein from corresponding fractions obtained from control animals, suggesting that these agents all enhance the synthesis of the same 80000-mol.wt. polypeptide. Although the polypeptide PPA-80 was increased in the postnuclear, large-particle and microsomal fractions of livers of rats pretreated with peroxisome proliferators, the relative abundance of this peptide in the peroxisome-rich light-mitochondrial fraction and its lack in highly purified mitochondrial fractions suggest the localization of this polypeptide in peroxisomes and/or microsomal fraction. Additional studies are needed to establish unequivocally the subcellular localization of the polypeptide PPA-80 and to ascertain if this polypeptide is identical with the multi-functional protein displaying enoyl-CoA hydratase and β-hydroxyacyl-CoA dehydrogenase activities that was purified by Osumi & Hashimoto [(1979) Biochem. Biophys. Res. Commun. 89, 580–584].     

Evidence for peroxisomal hydroxylase activity in rat liver

This study presents evidence for the first time that rat liver peroxisomes contain a hydroxylase capable of converting 3 alpha, 7 alpha, 12 alpha,- trihydroxy-5 beta-cholestane to a cholestanetetrol. Furthermore, this hydroxylase differs from both the mitochondrial and microsomal enzymes in its response to various co-factors. Highly purified peroxisomal, mitochondrial, and microsomal fractions from cholestryamine-treated rats were incubated with [22(23)-3H]3 alpha,7 alpha,12 alpha,-trihydroxy-5 beta-cholestane under a variety of conditions. The products were acidified, extracted, and subjected to thin-layer chromatography to determine the amount of cholestanetetrol produced. The identification of the 25- and 26-hydroxylated products from the incubations with the microsomes was confirmed by gas chromatography-mass spectrometry. Peroxisomal fractions incubated with a NADPH-generating system, Mg2+, and ATP showed a rate of 40 pmol/min/mg conversion of 3 alpha,7 alpha,12 alpha,-trihydroxy-5 beta-cholestane to a cholestanetetrol. Co-factor studies indicated that both the peroxisomal and mitochondrial hydroxylase activities were dependent on NADPH, Mg2+, and ATP (with different concentration requirements) whereas the microsomal hydroxylase(s) required only NADPH. An abstract of this work has been published (1).     

ANALYTICAL STUDY OF MICROSOMES AND ISOLATED SUBCELLULAR MEMBRANES FROM RAT LIVER : II. Preparation and Composition of the Microsomal Fraction

Liver homogenates have been submitted to quantitative fractionation by differential centrifugation. Three particulate fractions: N (nuclear), ML (large granules), and P (microsomes), and a final supernate (S) have been obtained. The biochemical composition of the microsomal fraction has been established from the assay and distribution pattern of 25 enzymatic and chemical constituents. These included marker enzymes for mitochondria (cytochrome oxidase), lysosomes (acid phosphatase and N-acetyl-β-glucosaminidase), and peroxisomes (catalase). The microsomal preparations were characterized by a moderate contamination with large cytoplasmic granules (only 6.2% of microsomal protein) and by a high yield in microsomal components. Enzymes such as glucose 6-phosphatase, nucleoside diphosphatase, esterase, glucuronyltransferase, NADPH cytochrome c reductase, aminopyrine demethylase, and galactosyltransferase were recovered in the microsomes to the extent of 70% or more. Another typical behavior was shown by 5'-nucleotidase, alkaline phosphatase, alkaline phosphodiesterase I, and cholesterol, which exhibited a "nucleomicrosomal" distribution. Other complex distributions were obtained for several constituents recovered in significant amount in the microsomes and in the ML or in the S fraction.     

Formation of cholic acid from 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid by rat liver peroxisomes

In a previous study, it was shown that the peroxisomal fraction of rat liver, isolated by Percoll gradient centrifugation of a light mitochondrial fraction, was able to catalyze conversion of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) into cholic acid (Pedersen, J. I., and J. Gustafsson, 1980. FEBS Lett. 121: 345-348). In the present work, this peroxisomal THCA-oxidizing system has been studied in more detail. The peroxisomes were prepared by sucrose gradient centrifugation. By use of different marker enzymes, it was confirmed that the major part of the activity in the light mitochondrial fraction was located in the peroxisomes. The reaction was absolutely dependent on the presence of Mg2+, CoA, ATP, and NAD+ in the reaction medium. In addition to cholic acid, small amounts of 3 alpha, 7 alpha, 12 alpha, 24-tetrahydroxy-5 beta-cholestanoic acid were detected as product. Provided the peroxisomes were preincubated with ATP and CoA, the reaction was linear with time up to 75 min. It was linear with peroxisomal protein and the pH optimum was 8. The reaction was stimulated by FAD (ca. 50%), by cytosolic protein (about twofold), by microsomal protein (about twofold), bovine serum albumin (about sevenfold), and by KCN (75% at 1 mM). In the absence of bovine serum albumin in the medium the K'm for the overall reaction was 1.4 X 10(-6) M and the maximum rate was 4.3 nmol X mg-1 X hr-1. In the presence of bovine serum albumin, the K'm increased to 6.3 X 10(-6) M and the maximum rate to about 32 nmol X mg-1 X hr-1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Source of the hepatic microsomal trans-2-enoyl CoA hydratase bifunctional protein: endoplasmic reticulum or peroxisomes

The present study was designed to investigate the hepatic localization of the microsomal bifunctional trans-2-enoyl CoA hydratase. Despite the low activity (less than 10%) of peroxisomal marker enzymes in isolated hepatic microsomes (acyl CoA oxidase (this study), catalase, and urate oxidase (L. Cook, M. N. Nagi, J. Piscatelli, T. Joseph, M. R. Prasad, D. Ghesquier, and D. L. Cinti, 1986, Arch. Biochem. Biophys. 245, 24-26), additional evidence in this study suggests that the microsomal enzyme is derived from peroxisomes. For example, the microsomal hydratase activity was associated with the ribosomal fractions but not with the smooth endoplasmic reticulum. In addition, when an extract of the peroxisomal enzyme was incubated with either free ribosomes or membrane-bound ribosomes, marked binding was observed with each of the fractions. Furthermore, the ease of release of the bifunctional enzyme from both free ribosomes and membrane-bound ribosomes by only KCl suggests that the bound enzyme is not a nascent protein. Labeling of liver tissue from DEHP-treated rats with rabbit immune IgG made to the purified microsomal hydratase followed by gold conjugated goat anti-rabbit IgG suggested a single subcellular site for the bifunctional hydratase--the peroxisomal organelle.     

Bile acid metabolism in early life: studies of amniotic fluid

Bile acid metabolism of the human fetus was examined in early gestation (weeks 13-19) and compared with the full-term fetus from the analysis of amniotic fluid collected from healthy pregnant women. Total individual bile acids were determined by gas-liquid chromatography-mass spectrometry after solvolysis and hydrolysis of bile acid conjugates. Additionally, bile acids were separated according to their mode of conjugation by lipophilic anion exchange chromatography. Qualitatively the bile acid profiles of amniotic fluid in early gestation were similar and markedly different from those of full-term fetuses. Chenodeoxycholic acid was the major bile acid identified in early gestation and concentrations exceeded those of cholic acid, but by full term this relationship was reversed. Over 50 bile acids were identified in the amniotic fluids, these included C-1, C-4, and C-6 hydroxylated species and reflected primary hepatic synthesis by the fetus. At full term, 7 alpha,12 alpha-dihydroxy-3-oxo-4-cholenoic acid was one of the major bile acids identified in amniotic fluid. The monohydroxy bile acids lithocholic and 3 beta-hydroxy-5-cholenoic acids were present in significant proportions during early gestation, but by full term these accounted for only a few percent of the total bile acids. Quantitatively the total bile acid concentration of amniotic fluid was less than 4 mumol/l. The majority of bile acids were found to be glyco-, tauro-, and sulfate-conjugates. The more hydrophobic bile acids tended to be preferentially sulfated. These data indicate that significant and major changes in bile acid metabolism take place between early and late gestation in the human fetus.     

Mechanism of intestinal 7 alpha-dehydroxylation of cholic acid: evidence that allo-deoxycholic acid is an inducible side-product

We previously reported that the 7 alpha-dehydroxylation of cholic acid appears to be carried out by a multi-step pathway in intestinal anaerobic bacteria both in vitro and in vivo. The pathway is hypothesized to involve an initial oxidation of the 3 alpha-hydroxy group and the introduction of a double bond at C4-C5 generating a 3-oxo-4-cholenoic bile acid intermediate. The loss of water generates a 3-oxo-4,6-choldienoic bile acid which is reduced (three steps) yielding deoxycholic acid. We synthesized, in radiolabel, the following putative bile acid intermediates of this pathway 7 alpha,12 alpha-dihydroxy-3-oxo-4-cholenoic acid, 7 alpha,12 alpha-dihydroxy-3-oxo-5 beta-cholanoic acid, 12 alpha-dihydroxy-3-oxo-4,6-choldienoic acid, and 12 alpha-hydroxy-3-oxo-4-cholenoic acid and showed that they could be converted to 3 alpha,12 alpha-dihydroxy-5 beta-cholanoic acid (deoxycholic acid) by whole cells or cell extracts of Eubacterium sp. VPI 12708. During studies of this pathway, we discovered the accumulation of two unidentified bile acid intermediates formed from cholic acid. These bile acids were purified by thin-layer chromatography and identified by gas-liquid chromatography-mass spectrometry as 12 alpha-hydroxy-3-oxo-5 alpha-cholanoic acid and 3 alpha,12 alpha-dihydroxy-5 alpha-cholanoic (allo-deoxycholic acid). Allo-deoxycholic acid was formed only in cell extracts prepared from bacteria induced by cholic acid, suggesting that their formation may be a branch of the cholic acid 7 alpha-dehydroxylation pathway in this bacterium.