Mass spectrometry of bile acids

Bile Acid Detection Techniques and Bile Acid-Related Diseases

Bile acid is a derivative of cholinergic acid (steroidal parent nucleus) that plays an important role in digestion, absorption, and metabolism. In recent years, bile acids have been identified as signaling molecules that regulate self-metabolism, lipid metabolism, energy balance, and glucose metabolism. The detection of fine changes in bile acids caused by metabolism, disease, or individual differences has become a research hotspot. At present, there are many related techniques, such as enzyme analysis, immunoassays, and chromatography, that are used for bile acid detection. These methods have been applied in clinical practice and laboratory research to varying degrees. However, mainstream detection technology is constantly updated and replaced with the passage of time, proffering new detection technologies. Previously, gas chromatography (GS) and gas chromatography-mass spectrometry (GC-MS) were the most commonly used for bile acid detection. In recent years, high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) has developed rapidly and has gradually become the mainstream bile acid sample separation and detection technology. In this review, the basic principles, development and progress of technology, applicability, advantages, and disadvantages of various detection techniques are discussed and the changes in bile acids caused by related diseases are summarized.

Standardizing and increasing the utility of lipidomics: a look to the next decade

Introduction: We present our views on the current application of mass spectrometry (MS) based lipidomics and how lipidomics can develop in the next decade to be most practical use to society. That is not to say that lipidomics has not already been of value. In-fact, in its earlier guise as metabolite profiling most of the pathways of steroid biosynthesis were uncovered and via focused lipidomics many inborn errors of metabolism are routinely clinically identified. However, can lipidomics be extended to improve biochemical understanding of, and to diagnose, the most prevalent diseases of the 21^st century? Areas covered: We will highlight the concept of 'level of identification' and the equally crucial topic of 'quantification'. Only by using a standardized language for these terms can lipidomics be translated to fields beyond academia. We will remind the lipid scientist of the value of chemical derivatization, a concept exploited since the dawn of lipid biochemistry. Expert opinion: Only by agreement of the concepts of identification and quantification and their incorporation in lipidomics reporting can lipidomics maximize its value.

Serum bile acids profiling by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and its application on pediatric liver and intestinal diseases

Background

A method for bile acid profiling measuring 21 primary and secondary bile acids in serum samples was developed and validated with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Sample preparation included spiking with internal standards followed by protein precipitation, centrifugation, drying under nitrogen gas and reconstitution. Extracted samples were injected onto a Phenomenex Kinetex C18 column (150 × 4.60 mm, 2.6 μm).

Methods

Data was collected with LC-MS/MS operated in negative ion mode with multiple reaction monitoring (MRM) and single reaction monitoring (SRM). The analytical run time was 12 min.

Results

The method showed excellent linearity with high regression coefficients (>0.99) over a range of 0.05 and 25 μM for all analytes tested. The method also showed acceptable intra-day and inter-day accuracy and precision. As a proof of concept, the analytical method was applied to patients with neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), biliary atresia (BA), and necrotizing enterocolitis (NEC), and distinct bile acids profiles were demonstrated.

Conclusions

The method could be poised to identify possible biomarkers for non-invasive early diagnosis of these disorders.

Sterolomics in biology, biochemistry, medicine

In mammalian systems "sterolomics" can be regarded as the quantitative or semi-quantitative profiling of all metabolites derived from cholesterol and its cyclic precursors. The system can be further complicated by metabolites derived from ingested phytosterols or pharmaceuticals, but this is beyond the scope of this article. "Sterolomics" can be performed on either an unbiased global format, or more usually, exploiting a targeted format. Here we discuss the different mass spectrometry-based analytical techniques used in "sterolomics" giving specific examples in the context of neurodegenerative disease and for the diagnosis of inborn errors of metabolism. We pay particular attention to the profiling of cholesterol metabolites in the bile acid biosynthesis pathways, although the analytical techniques discussed are also appropriate for analysis of hormonal steroids.

Mass spectrometry techniques in the survey of steroid metabolites as potential disease biomarkers: a review

Mass spectrometric approaches have been fundamental to the identification of metabolites associated with steroid hormones, yet this topic has not been reviewed in depth in recent years. To this end, and given the increasing relevance of liquid chromatography-mass spectrometry (LC-MS) studies on steroid hormones and their metabolites, the present review addresses this subject. This review provides a timely summary of the use of various mass spectrometry-based analytical techniques during the evaluation of steroidal biomarkers in a range of human disease settings. The sensitivity and specificity of these technologies are clearly providing valuable new insights into breast cancer and cardiovascular disease. We aim to contribute to an enhanced understanding of steroid metabolism and how it can be profiled by LC-MS techniques.

Metabolomics approaches for characterizing metabolic interactions between host and its commensal microbes

It is increasingly evident that the gut microbiota is involved in the regulation of multiple mammalian metabolic pathways through a series of interactive host-microbiota metabolic, signaling, and immune-inflammatory axes that physiologically connect the gut, liver, brain, and other organs. Correlation of the metabotypes with the gut microbial profiles derived from culture-independent molecular techniques is increasingly useful for deciphering inherent and intimate host-microbe relationships. Real-time analysis of the small molecule metabolites derived from gut microbial-host co-metabolism is essential for understanding the metabolic functions of the gut microbiome and has tremendous implications for personalized healthcare strategies. Metabolomics, an array of analytical techniques that includes high resolution NMR spectroscopy and chromatography-MS in conjunction with chemometrics and bioinformatics tools, enables characterization of the metabolic footprints of mammalian hosts that correlate with the microbial community in the intestinal tract. The metabolomics approach provides important information of a complete spectrum of metabolites produced from the gut microbial-mammalian co-metabolism and is improving our understanding of the molecular mechanisms underlying multilevel host-microbe interactions. In this review, the interactions of gut microbiota with their host are discussed and some examples of NMR- or MS-based metabolomics applications for characterizing the metabolic footprints of gut microbial-host co-metabolism are described. Advances in the metabolomic analysis of bile acids, short-chain fatty acids, and choline metabolism are also summarized.

The expanding role of mass spectrometry in metabolite profiling and characterization

Mass spectrometry has a strong history in drug-metabolite analysis and has recently emerged as the foremost technology in endogenous metabolite research. The advantages of mass spectrometry include a wide dynamic range, the ability to observe a diverse number of molecular species, and reproducible quantitative analysis. These attributes are important in addressing the issue of metabolite profiling, as the dynamic range easily exceeds nine orders of magnitude in biofluids, and the diversity of species ranges from simple amino acids to lipids to complex carbohydrates. The goals of the application of mass spectrometry range from basic biochemistry to clinical biomarker discovery with challenges in generating a comprehensive profile, data analysis, and structurally characterizing physiologically important metabolites. The precedent for this work has already been set in neonatal screening, as blood samples from millions of neonates are tested routinely by mass spectrometry as a diagnostic tool for inborn errors of metabolism. In this review, we will discuss the background from which contemporary metabolite research emerged, the techniques involved in this exciting area, and the current and future applications of this field.

Quantitative Analysis of Bile Acids in Human Plasma by Liquid Chromatography-Electrospray Tandem Mass Spectrometry: A Simple and Rapid One-Step Method

Bile acids play a pivotal role in the metabolism of cholesterol and lipids. Their blood concentrations are important prognostic and diagnostic indicators of hepatobiliary and intestinal dysfunction. This class of molecules comprises a heterogeneous group of compounds with a common cholesterol scaffold. Recently, the introduction of liquid chromatography coupled to tandem mass spectrometry methods has revealed an innovative path in the quantisation of specific bile acids in biological specimens. A robust and sensitive method has been developed based on high performance liquid chromatography separation coupled to an electrospray triple-quadrupole mass spectrometer. Human plasma samples were analysed on a C18 reverse-phase column. The elution profiles were monitored in multiple reaction-monitoring mode, quantifying and identifying each analyte by its own unique precursor to product patterns. A linear correlation over a broad range of bile acid concentrations (0.1-100 microM) was observed. The average recovery period for all of the analysed bile acids was 98 +/- 3%. Intra-day and inter-day precision averages were 2% and 5.4%, respectively. The determination was achieved within a single chromatographic run for all unconjugated, glycine- and taurine-conjugated isomeric forms of bile acids. As a proof of principle this method has been validated on a small subset of cholestatic patients (n = 7) and compared to appropriate clinical controls (n = 10). Based upon our encouraging experimental results, the described HPLC separation coupled to tandem mass spectrometry method for the analysis of bile acids in biological samples is deemed a robust and accurate procedure. Consequently, we propose this technique as a suitable candidate method for the identification and quantitation of bile acids in routine analysis.

North American Indian cirrhosis in children: a review of 30 cases

BACKGROUND

North American Indian childhood cirrhosis (NAIC) is a distinct, rapidly evolving form of familial cholestasis found in aboriginal children from northwestern Quebec. This is a retrospective review of the 30 patients treated in Quebec since the discovery of NAIC in 1970.

METHODS

The clinical records and histologic samples from 30 patients were reviewed. Extensive metabolic, biochemical, viral, genetic, and radiologic studies were performed in most patients.

RESULTS

Genetic analysis suggests autosomal recessive inheritance and a carrier frequency of 10% in this population. Gene mapping studies showed that the NAIC gene is located on chromosome 16q22. Typically, patients have neonatal cholestatic jaundice (70%) or hepatosplenomegaly (20%) with resolution of clinical jaundice by age 1 year but persistent direct hyperbilirubinemia. Portal hypertension was documented in 29 patients (91%). Variceal bleeding (15 patients, 50%) occurred as early as age 10 months. Surgical portosystemic shunting was performed in 13 of these 15 patients (87%); 4 (31%) rebled after 1 to 5 years. Fourteen patients died (47%). In 10 (71%), liver disease was the cause. Four children died of liver failure before liver transplantation became available. In transplanted livers, no recurrence of NAIC was observed after 1 to 10 years. Recognized infectious, metabolic, toxic, autoimmune, and obstructive causes of cirrhosis have been eliminated. The histologic features of NAIC show early bile duct proliferation and rapid development of portal fibrosis and biliary cirrhosis, suggesting a cholangiopathic phenomenon.

CONCLUSION

Together with gene mapping studies showing that the NAIC gene is different from those of other familial cholestases, these observations suggest that NAIC is a distinct entity that could be classified as "progressive familial cholangiopathy."

Separation techniques for bile salts analysis

The analysis of bile salts in biological samples has remained a difficult task, due to the complex nature of the salts and also to their low concentration in common sample fluids such as plasma and urine. Given their importance, the development of accurate and sensitive methods of instrumental analysis has been the subject of intensive research, and recent advances have eliminated or lessened some of the difficulties. Currently available techniques are the following: thin-layer chromatography, gas chromatography, high-performance liquid chromatography, supercritical fluid chromatography, gas chromatography-mass spectrometry and capillary electrophoresis. Liquid chromatography coupled with mass spectrometry (thermospray, fast atom bombardment, electrospray and ionspray), a method undergoing continuous improvement, is also being applied to bile salts analysis. In this paper, these various techniques, which differ greatly in specificity, accuracy and simplicity, are reviewed and discussed, in terms of analytical performance, applicability to a given sample fluid, major limitations, ability to identify uncommon bile salts, including unsaturated oxo derivatives, glucuronides, sulfates, glycosides and bile alcohols.

Effects of ursodeoxycholic acid on conjugated bile acids and progesterone metabolites in serum and urine of patients with intrahepatic cholestasis of pregnancy

BACKGROUND/AIMS AND METHODS

The mechanism(s) behind the effects of ursodeoxycholic acid on serum steroid sulphate profiles in patients with intrahepatic cholestasis of pregnancy is not clear. Conjugated progesterone metabolites and bile acids have therefore been analysed in serum and urine of patients with intrahepatic cholestasis of pregnancy before and during treatment with ursodeoxycholic acid using chromatographic and mass spectrometric methods.

RESULTS

The concentration of glycine-/taurine-conjugated bile acids decreased from 8.9+/-3 micromol/l (mean+/-SEM) before treatment to 1.8+/-0.6 micromol/l during treatment with ursodeoxycholic acid. The total bile acid excretion in urine decreased from 56+/-14 to 32+/-5.6 micromol/g creatinine. The proportion of cholic acid in serum and urine, and of 1beta-, 2beta- and 6alpha-hydroxylated cholic acids in urine decreased markedly during ursodeoxycholic acid while the percentages of 3alpha,12alpha-dihydroxy-3-oxo-4-cholenoic acid and chenodeoxycholic acid were unchanged. The levels in serum and excretion in urine of sulphated steroids decreased during ursodeoxycholic acid, by 45-49% for disulphates and 33-35% for monosulphates. The ratios of 3alpha- to 3beta-hydroxysteroid disulphates were lowered by ursodeoxycholic acid from 1.1 (mean) to 0.68 in serum, and from 1.2 to 0.70 in urine. The corresponding ratios for monosulphates before and during ursodeoxycholic acid were 6.9 and 4.5, respectively, in serum, and 21 and 5.2, respectively, in urine. The major monosulphates in urine, dominated by 5alpha-pregnane-3alpha, 20alpha-diol, were also conjugated with N-acetylglucosamine. The excretion of these double conjugates decreased from 27+/-8.4 to 15+/-5.3 micromol/g creatinine during ursodeoxycholic acid. In contrast to sulphated steroids, the concentrations of glucuronides were unchanged in serum and their excretion in urine tended to increase during ursodeoxycholic acid. The metabolism of ursodeoxycholic acid was similar to that described in nonpregnant subjects. In addition to metabolites hydroxylated in the 1beta-, 5beta-, 6alpha/beta and 22-positions, a 4-hydroxy-ursodeoxycholic acid was tentatively identified. This occurred predominantly as a double conjugate with glycine/taurine and glucuronic acid, as did other 4-hydroxylated bile acids of probable foetal origin.

CONCLUSIONS

The results are compatible with the contention that ursodeoxycholic acid stimulates the biliary excretion of sulphated progesterone metabolites, particularly those with a 3alpha-hydroxy-5alpha(H) configuration and disulphates. The effect(s) appears to be independent of the stimulation of bile acid secretion. An effect of ursodeoxycholic acid on the reductive metabolism of progesterone cannot be excluded.

Bile acid secretion during synchronized rat liver regeneration

One major difficulty in interpreting the changes occurring during liver regeneration is the co-existence of non-activated cells and proliferating hepatocytes at all stages of differentiation. The aim of this study was to investigate bile acid (BA) secretion into bile during normal (NLR) and synchronized (SLR) liver regeneration in rats. Regeneration was synchronized by reversible inhibition of ribonucleotide reductase by 10 h treatment with hydroxyurea (HU) shortly after two-third partial hepatectomy. Total BA output as measured by GC-MS increased immediately after partial hepatectomy. This was followed by a further transient enhancement during the next day in the NLR. HU treatment did not significantly modify total BA output, but after releasing synchronized regeneration a marked reduction was observed. This was followed by a recovery to reach values close to those of NLR on day 7 of the regenerative process in SLR. Amidated BA output as measured by HPLC analysis revealed an early enhancement in the proportion of non-conjugated BAs in bile in NLR. However, the profile of conjugated BAs, which was not affected by HU treatment, matched that of total BAs during the first stage of SLR. By contrast, the increase in BA output observed on day 3 of the regenerative process in this group was accounted for by an enhancement in non-conjugated BA secretion. On day 7 of the regenerative process, the proportion of conjugated BA in bile was restored to approximately 100% in this group. Most BA molecules were conjugated with taurine rather than with glycine in all experimental groups, during both NLR and SLR. GC-MS determinations indicated that the magnitude of the cholic acid predominance in all bile samples was significantly modified during liver regeneration. This was increased early after partial hepatectomy and declined toward control values after few (2-3) days. Enhancement in the cholic acid predominance was due to a reduction in the proportion of all other major BAs, above all ursocholic acid and omega-muricholic acid. By contrast, minor BAs in normal control rat bile such as allo-cholic acid were increased during both NLR and SLR, and remained at detectable levels up to day 7. Changes in the proportion of secreted BA species were similar in SLR and NLR except that the early reduction in the proportion of BAs other than cholic acid was more pronounced in SLR and the quantitative importance of the diversity in BA species was recovered earlier in SLR than in NLR. In summary, these results indicate that profound changes in BA secretion during rat liver regeneration do occur. Most of them are probably related to the existence of retro-differentiation/re-differentiation processes which are speeded up by hydroxyurea-induced synchronization of the wave of hepatocyte proliferation.

Analysis of bile acids and bile alcohols in urine by capillary column liquid chromatography-mass spectrometry using fast atom bombardment or electrospray ionization and collision-induced dissociation

Solid-phase extraction and group separation by anion exchange chromatography were combined with capillary column liquid chromatography-mass spectrometry (LC/MS) to permit a thorough characterization of bile acids and intact conjugates of bile alcohols in human urine. Groups of compounds were separated according to acid strength and were analysed on a capillary column, 0.25 x 500 mm, packed with 5 microns particles of Chromasil C18, and connected via a fused silica capillary to the continuous-flow fast atom bombardment (CF-FAB) or electrospray (ES) sources of an AutoSpec-TOFFPD hybrid mass spectrometer. Acetonitrile:water mixtures containing 30 mM ammonium acetate pH 7.2 were used as mobile phases, with 5% glycerol added for FAB Ionisation. Bile acids were analysed directly or after derivatization of carboxyl groups with 4-aminobenzenesulphonic acid. Negative-ion spectra (m/z 1000 or 800 to 300 or 100) were recorded using the point detector or, in the case of ES ionization, the focal plane array detector (FPD). Deprotonated molecules of bile acids containing a sulphonic acid group were detected with a spectral signal to noise ratio of 5:1 when about 90 fmol were injected onto the column of the LC/CF-FAB system. The corresponding peak in the reconstructed ion chromatogram gave a signal-to-noise ratio of about 25:1. The sensitivity could be increased 20-50 times by using ES ionization and the FPD. Bile acids without a sulphonic acid group gave about 70% of the signal of sulphonic acids using ES ionization. The capillary column LC/MS systems were evaluated by analyses of urine from an infant with cholestatic liver disease. More than 150 different bile acids and bile alcohol conjugates were detected, some of which were partially characterized using collision induced dissociation (CID) of the deprotonated molecules and B/E linked scans. A number of compounds were detected for the first time, e.g. di-, tri-, and tetra-hydroxycholestanoic acids conjugated with N-acetylhexosamine and cholestenediol, cholestenetriol and cholestanetriol doubly conjugated with sulphuric acid and glucuronic acid. The relative merits of ES and FAB ionization are discussed.

Byler-like familial cholestasis in an extended kindred

Progressive familial intrahepatic cholestasis (PFIC) occurs in many communities and races. A form of PFIC in five children from two consanguineous marriages in an Irish kindred is described. In addition, a review of clinical information from the records of three deceased members of the kindred strongly implies that they also suffered from PFIC. The children had a history of neonatal diarrhoea, sepsis, and intermittent jaundice that ultimately became permanent. They suffered intractable pruritus and growth retardation. Despite evidence of severe cholestasis, serum gamma-glutamyl transferase and cholesterol were normal in these children. Sweat sodium concentration were raised in three children. Liver histology showed severe intrahepatic cholestasis and hepatocellular injury. Urinary bile acid analysis revealed a non-specific pattern consistent with chronic cholestasis. These children suffer from a form of PFIC remarkably similar to that occurring in members of the Byler kindred.

The major metabolites of ursodeoxycholic acid in human urine are conjugated with N-acetylglucosamine

Ursodeoxycholic acid (750 mg/day) was administered orally to ten healthy subjects over a period of 10 days; 24 hr urine samples were collected the day before and on the last day of the study. Urinary bile acids were extracted, separated into groups of conjugates and analyzed by gas chromatography-mass spectrometry and fast atom bombardment mass spectrometry. Excretion of ursodeoxycholic acid rose from 70 to 2,915 micrograms/24 h. The highest increase was observed among N-acetylglucosamine conjugates, 90% of which constituted the previously unknown double conjugate of ursodeoxycholic acid with N-acetylglucosamine and glycine. Excretion of isoursodeoxycholic acid increased from 50 to 738 micrograms/24 h. This isomerization product of ursodeoxycholic acid was excreted almost exclusively as N-acetylglucosamine conjugate. In total, N-acetylglucosamine conjugates constituted 50% of urinary metabolites of ursodeoxycholic acid. In addition, metabolites of ursodeoxycholic acid hydroxylated at carbon atoms 1, 6, 22 and possibly 21 were observed. These compounds were also found as conjugates with N-acetylglucosamine. Their formation from ursodeoxycholic acid was definitely demonstrated by 13C-labeling after giving [24-13C]ursodeoxycholic acid to one of the healthy subjects and to a patient with extrahepatic cholestasis in whom hydroxylation of ursodeoxycholic acid at C-23 was also observed. The patient was also found to excrete the double conjugate of ursodeoxycholic acid with N-acetylglucosamine and taurine. The N-acetylglucosaminidation of ursodeoxycholic acid in vivo was shown to occur at C-7.(ABSTRACT TRUNCATED AT 250 WORDS)

A new cause of progressive intrahepatic cholestasis: 3 beta-hydroxy-C27-steroid dehydrogenase/isomerase deficiency

There have been a few reports of infants with severe neonatal cholestasis related to a defect in primary bile acid synthesis. To assess the importance of such deficiency among children with progressive intrahepatic cholestasis (Byler disease), screening for inborn errors in bile acid synthesis was performed by fast atom bombardment ionization-mass spectrometry of urine samples from 30 affected children. Bile acid analysis revealed a specific fast atom bombardment ionization-mass spectrometry profile for 3 beta-hydroxy-C27 steroid dehydrogenase/isomerase deficiency in five children who had jaundice, hepatosplenomegaly, and fatty stools beginning at ages ranging from 4 to 46 months. None of them had pruritus. Liver function tests showed persistently normal serum gamma-glutamyltransferase activity, low serum cholesterol and vitamin E levels, normal serum bile acid concentrations despite raised serum bilirubin levels, and decreased prothrombin time and clotting factor V. In four of the cases a similar disease was observed in siblings. Liver function returned to normal after oral ursodeoxycholic acid therapy. We conclude that 3 beta-hydroxy-C27-steroid dehydrogenase/isomerase deficiency should be considered when idiopathic cholestatic liver disease with clinical features akin to Byler disease is characterized by the association of normal serum gamma-glutamyltransferase activity, normal serum bile acid concentration, absence of pruritus, and a return to normal liver function during ursodeoxycholic acid therapy. Early identification of these children is essential because they benefit from bile acid therapy and might thus avoid the need for liver transplantation.

The urinary bile acid excretion in healthy premature and full-term infants during the neonatal period

The 24h urinary bile acid excretion was prospectively studied during the neonatal period in healthy, fully breastfed, premature and full-term infants. The urinary bile acids were identified by gas-liquid chromatography (GLC)-mass spectrometry and quantified by GLC. The excretion of bile acids in urine increased after birth, reaching maximum levels by the 3-4th day. Taurine conjugates predominated and the excretion of bile acid sulphates was remarkably low. Cholic acid and atypical bile acids were the main bile acids in urine during the first week. Tetrahydroxylated bile acids carrying hydroxyl groups at C-1, C-2 and C-6 were common, and also other 1- and 6-hydroxylated bile acids, including hyocholic and hyodeoxycholic acids. Three tentatively identified 4-hydroxylated bile acids, including one ketonic bile acid, were also found. Ketonic bile acids constituted an average of 16% of total urinary bile acids during the first week. Unsaturated bile acids were scantily found only during the first days. The excretion of atypical bile acids decreased to 1 month of age, parallel with the total bile acid excretion. The data support earlier hypothesis of a physiological cholestasis in the newborn. Atypical hydroxylated and ketonic bile acids, as well as cholic acid, constituted the major part of the urinary bile acids. The persistent atypical pattern of bile acids in urine during the first month of life indicates a longer period of immaturity of bile acid metabolism in healthy infants than previously described.

Synthesis of potential C27-intermediates in bile acid biosynthesis and their deuterium-labeled analogs

In connection with studies of alternative pathways in bile acid biosynthesis, potential intermediates in a pathway starting with 27-hydroxylation of cholesterol have been prepared in natural and deuterated forms. Established methods were used to prepare 27-hydroxycholesterol and 3 beta-hydroxy-5-cholestenoic acid. Clemmensen reduction of kryptogenin in unlabeled and deuterated solvents yielded 27-hydroxy-cholesterol and 16-oxo-5-cholestene-3 beta,27-diol, which were separated by adsorption chromatography on Unisil. The labeled 27-hydroxycholesterol and 3 beta-hydroxy-5-cholestenoic acid derived from it consisted of molecules with seven (50%), six (20%), and eight (20%) deuterium atoms, and unlabeled molecules were not detected. The acetates of 27-hydroxycholesterol and methyl 3 beta-hydroxy-5-cholestenoate were 7 alpha-hydroxylated in a copper-catalyzed reaction with tert-butylperbenzoate, and the products were purified by chromatography on Unisil. The 7 beta-epimers were obtained as side products. Labeled 3 beta,7 alpha-dihydroxy-5-cholenoic acid was prepared in the same way from 3 beta-hydroxy-5-[2,2,4,4,23-2H5]-cholenoic acid. The 3-oxo-delta 4 analogs of the 3 beta-hydroxy-delta 5 compounds were prepared by oxidation with cholesterol oxidase. The labeled products had the same isotopic composition as the starting materials. Gas chromatographic retention indices and mass spectral characteristics of the trimethylsilyl ether derivatives of the neutral steroids and the methylated acids are given for all compounds.

Ion spray liquid chromatographic/mass spectrometric characterization of bile acids

The ion spray mass spectra of selected bile acid standards are presented. Full-scan positive ion spectra obtained in solutions of acetonitrile-water-trifluoroacetic acid and methanol-water-trifluoroacetic acid show the presence of intense [M + S + H]+ and [M + 2S + H]+ ions (where S is either methanol or acetonitrile, depending on the solvent system) in addition to [M + H]+ ions. The relative abundance of the protonated and solvent adduct ions are reproducible and unique for several of the bile acids, and provide a means of identifying isomeric bile salts. Adduct ions are most abundant for free acids and weaker for glycine and taurine conjugates. On-line ion spray liquid chromatography/mass spectrometry (LC/MS) using a 3 cm x 4.6 mm cartridge column containing 3 microns particle size C18 packing was utilized for the separation and identification of components of monkey bile. Eight common bile acid conjugates were separated in less than 8 min utilizing a water-acetonitrile gradient with 0.1% trifluoroacetic acid as the mobile-phase modifier. Full-scan data were acquired from 1 microliter of untreated bile injected on-column. Identification of component bile acids from the equivalent of 1 nl injected on-column was obtained with the use of a 1 mm diameter microbore column. Limits of detection for bile acid conjugates using a microbore column and selected ion monitoring (SIM) range from 40 to 100 fmol.

Bile acid N-acetylglucosaminidation. In vivo and in vitro evidence for a selective conjugation reaction of 7 beta-hydroxylated bile acids in humans

The aim of this study was to define whether N-acetylglucosaminidation is a selective conjugation pathway of structurally related bile acids in humans. The following bile acids released enzymatically from N-acetylglucosaminides were identified: 3 alpha,7 beta-dihydroxy-5 beta-cholanoic (ursodeoxycholic), 3 beta, 7 beta-dihydroxy-5 beta-cholanoic (isoursodeoxycholic), 3 beta,7 beta-dihydroxy-5 alpha-cholanoic (alloisoursodeoxycholic), 3 beta,7 beta-dihydroxy-5-cholenoic, 3 alpha,7 beta,12 alpha-trihydroxy-5 beta-cholanoic, and 3 alpha,6 alpha,7 beta-trihydroxy-5 beta-cholanoic acids. The selectivity of conjugation was studied by administration of 0.5 g ursodeoxycholic (UDCA) or hyodeoxycholic (HDCA) acids, labeled with 13C, to patients with extrahepatic cholestasis, and of 0.5 g of 13C-labeled chenodeoxycholic acid (CDCA) to patients with extra- or intrahepatic cholestasis. After administration of [24-13C]-CDCA, labeled glucosides, and the glucuronide of CDCA were excreted in similar amounts. Labeled N-acetylglucosaminides of UDCA and isoUDCA were also formed. When [24-13C]-UDCA was given, 13C-label was detected in the N-acetylglucosaminide, the glucosides, and the glucuronide of UDCA, and in the N-acetylglucosaminide of isoUDCA. In the patient studied, 32% of the total UDCA excreted in urine was conjugated with N-acetylglucosamine. In contrast, 96% of the excreted amount of [24-13C]HDCA was glucuronidated, and 13C-labeled glucosides but no N-acetylglucosaminide were detected. The selectivity of N-acetylglucosaminidation towards bile acids containing a 7 beta-hydroxyl group was confirmed in vitro using human liver and kidney microsomes and uridine diphosphate glucose (UDP)-N-acetylglucosamine. These studies show that N-acetylglucosaminidation is a selective conjugation pathway for 7 beta-hydroxylated bile acids.

Synthesis of 13C-labeled chenodeoxycholic, hyodeoxycholic, and ursodeoxycholic acids for the study of bile acid metabolism in liver disease

In order to study the glycosidic conjugation of chenodeoxycholic, hyodeoxycholic, and ursodeoxycholic acids in patients with cholestasis after oral administration of pharmacological amounts of the respective bile acids avoiding the application of radioactive tracers we synthesized [24-13C]chenodeoxycholic, [24-13C]hyodeoxycholic, and [24-13C]ursodeoxycholic acids. The reaction intermediates of the bile acid syntheses were characterized by infrared spectroscopy. Purity was confirmed using thin-layer chromatography as well as gas chromatography-mass spectrometry. The 13C atom excess of approximately 90% of the synthesized bile acids was the same as the 13C atom excess of the sodium [13C]cyanide used for the labeling reaction confirming the successful synthesis. After oral administration of 0.5 g of [24-13C]ursodeoxycholic acid to a healthy volunteer, 13C label was detected in the nonamidated and glycine- or taurine conjugated glucosides and the N-acetylglucosaminide of ursodeoxycholic acid in urine. This establishes ursodeoxycholic acid as the first bile acid so far known to undergo both of the recently described glycosidic conjugation reactions in humans.

Bile acids. LXXXI. Synthesis and structural assignment of E/Z isomers of substituted methyl hydroxy-5 beta-cholest-24-en-26-oates

Syntheses of the E and Z isomers of methyl 3 alpha-,3 alpha,7 alpha-,3 alpha,12 alpha-, and 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholest-24-en-26-oates are reported. Mass spectral studies show fragmentation patterns in support of assignment as the E or Z isomers, especially in differences in loss of the side chain. Chromatographic procedures, primarily gas chromatography and high-performance liquid chromatography, support these assignments. The E isomer predominates in either of two methods of synthesis.

Delta 4-3-oxosteroid 5 beta-reductase deficiency described in identical twins with neonatal hepatitis. A new inborn error in bile acid synthesis

A new inborn error in bile acid synthesis, manifest in identical infant twins as severe intrahepatic cholestasis, is described involving the delta 4-3-oxosteroid 5 beta-reductase catalyzed conversion of the key intermediates, 7 alpha-hydroxy-4-cholesten-3-one and 7 alpha,12 alpha-dihydroxy-4-cholesten-3-one for chenodeoxycholic and cholic acid synthesis, to the respective 3 alpha-hydroxy-5 beta (H) products. This defect was detected by fast atom bombardment ionization-mass spectrometry from an elevated excretion and predominance of taurine conjugated unsaturated hydroxy-oxo-bile acids. Gas chromatography-mass spectrometry confirmed these to be 7 alpha-hydroxy-3-oxo-4-cholenoic and 7 alpha,12 alpha-dihydroxy-3-oxo-4-cholenoic acids (75-92% of total). Fasting serum bile acid concentrations were greater than 37 mumol/liter; chenodeoxycholic acid was the major bile acid, but significant amounts of allo(5 alpha-H)-bile acids (approximately 30%) were present. Biliary bile acid concentration was less than 2 mumol/liter and consisted of chenodeoxycholic, allo-chenodeoxycholic, and allo-cholic acids. These biochemical findings, which were identical in both infants, indicate a defect in bile acid synthesis involving the conversion of the delta 4-3-oxo-C27 intermediates into the corresponding 3 alpha-hydroxy-5 beta(H)-structures, a reaction that is catalyzed by a delta 4-3-oxosteroid-5 beta reductase enzyme. This defect resulted in markedly reduced primary bile acid synthesis and concomitant accumulation of delta 4-3-oxo-and allo-bile acids. These findings indicate a pathway in bile acid synthesis whereby side chain oxidation can occur despite incomplete alterations to the steroid nucleus, and lend support for an active delta 4-3-oxosteroid 5 alpha-reductase catalyzing the conversion of the delta 4-3-oxosteroid intermediates to the respective 3 alpha-hydroxy-5 alpha(H)-structures.

Detergent and ion-pair extraction of bile acids in liver tissue for analysis by fast atom bombardment mass spectrometry

Methods for detergent and ion-pair extraction and group separation of bile salts in liver tissue using decyltrimethylammonium bromide (DTMAB), Lipidex 1000 and octadecyl-bonded silica were studied. Samples of rat liver were homogenized in 0.1 M DTMAB and the supernatants were diluted to 0.03 M DTMAB and passed through a column of Lipidex 1000/Sep-Pak C18. After washing with water, the bile salts were eluted with 70% aqueous methanol. The recovery of endogenous bile acids labelled with 14C in vivo was quantitative. Part of the extracted lipids and remaining DTMAB was removed by a second extraction on Sep-Pak C18, resulting in 84% recovery of bile acids in an extract suitable for analysis by fast atom bombardment mass spectrometry. The amount of extract required for this analysis corresponded to 5-10 mg of rat liver tissue. The ion-pairs of unconjugated and conjugated mono-, di- and trihydroxy bile acids could be separated into groups by reversed-phase chromatography on mu Bondapak C18 prior to mass spectrometric analysis.

Omega-oxidation of cysteine-containing leukotrienes by rat-liver microsomes. Isolation and characterization of omega-hydroxy and omega-carboxy metabolites of leukotriene E4 and N-acetylleukotriene E4

Leukotriene E4 was metabolized to two polar products by rat liver microsomes. These products were characterized by physico-chemical and chemical techniques. The chemical structures, (5S, 6R)-5,20-dihydroxy-6S-cysteinyl-7,9-trans-11,14-cis-icosatetraenoic acid (omega-hydroxy-leukotriene E4) and (5S, 6R)-5-hydroxy-6S-cysteinyl-7,9-trans-11,14-cis-icosatetraen-1,20-d ioic acid (omega-carboxy-leukotriene E4) suggested that leukotriene E4 was transformed by an omega-hydroxylase and omega-hydroxyleukotriene E dehydrogenase in sequence. N-Acetyl-leukotriene E4 was also transformed by these enzymes, but at a rate six times lower than leukotriene E4. The products formed from N-acetylleukotriene E4 were characterized as being N-acetyl-omega-hydroxy-leukotriene E4 and N-acetyl-omega-carboxy-leukotriene E4. Other substrates were 11-trans-leukotriene E4 and N-acetyl-11-trans-leukotriene E4. In contrast, leukotrienes C4 and D4 were not converted into omega-oxidized metabolites. The leukotriene E omega-hydroxylase reaction required NADPH and molecular oxygen as cofactors, and was most rapidly catalyzed by liver microsomes. Liver cytosol, fortified with NAD+, converted omega-hydroxyleukotriene E4 and N-acetyl-omega-hydroxy-leukotriene E4 into omega-carboxy metabolites. Microsomes contained at least 18 times less omega-hydroxy-leukotriene E dehydrogenase activity than did cytosol. Liver microsomes supplemented with acetyl-coenzyme A converted omega-hydroxy and omega-carboxy-leukotriene E4 into the corresponding N-acetyl derivatives. The novel enzyme, leukotriene E omega-hydroxylase, which is described here is distinct from a previously described leukotriene B omega-hydroxylase based on substrate competition and kinetic data.

Familial giant cell hepatitis associated with synthesis of 3 beta, 7 alpha-dihydroxy-and 3 beta,7 alpha, 12 alpha-trihydroxy-5-cholenoic acids

Urinary bile acids from a 3-mo-old boy with cholestatic jaundice were analyzed by ion exchange chromatography and gas chromatography-mass spectrometry (GC-MS). This suggested the presence of labile sulfated cholenoic acids with an allylic hydroxyl group, a conclusion supported by analysis using fast atom bombardment mass spectrometry (FAB-MS). The compounds detected by FAB-MS were separated by thin layer chromatography and high performance liquid chromatography. The sulfated bile acids could be solvolyzed in acidified tetrahydrofuran, and glycine conjugates were partially hydrolyzed by cholylglycine hydrolase. Following solvolysis, deconjugation, and methylation with diazomethane, the bile acids were identified by GC-MS of trimethylsilyl derivatives. The major bile acids in the urine were 3 beta,7 alpha-dihydroxy-5-cholenoic acid 3-sulfate, 3 beta,7 alpha,12 alpha-trihydroxy-5-cholenoic acid monosulfate, and their glycine conjugates. Chenodeoxycholic acid and cholic acid were undetectable in urine and plasma. The family pedigree suggested that abnormal bile acid synthesis was an autosomal recessive condition leading to cirrhosis in early childhood.

Plasma bile acids in patients with peroxisomal dysfunction syndromes: analysis by capillary gas chromatography-mass spectrometry

Six patients with disorders of peroxisomal function have been studied. Two presented in the neonatal period with the classical features of the Zellweger syndrome, two had incomplete Zellweger phenotypes, one infantile Refsum's disease and one rhizomelic chondrodysplasia punctata. Plasma bile acid profiles were determined using capillary gas chromatography-mass spectrometry. In all patients, except the case of chondrodysplasia punctata, 27-carbon and 29-carbon bile acids were present. The compounds identified included trihydroxycoprostanic acid (THCA), dihydroxycoprostanic acid (DHCA), C24-, C25- and C26-hydroxylated derivatives of THCA, a 27-carbon acid with four nuclear hydroxy groups and 3 alpha,7 alpha,12 alpha-trihydroxy-27a,27b-dihomo-5 beta-cholestan-26, 27b-dioic acid (C29-dicarboxylic acid). THCA was present at a low concentration in the patient with infantile Refsum's disease; the concentration of DHCA and the C29 dicarboxylic acid were considerably higher. The presence of abnormal bile acids in patients with Zellweger syndrome and infantile Refsum's disease could be explained by the absence of peroxisomes from their hepatocytes. In chondrodysplasia punctata the cause of peroxisomal dysfunction must be different, since normal bile acid synthesis is preserved.

Rapid diagnosis of Zellweger syndrome and infantile Refsum's disease by fast atom bombardment--mass spectrometry of urine bile salts

A method is described for the rapid determination of urinary bile salt profiles by fast atom bombardment--mass spectrometry (FAB-MS). Urine was passed through a reverse-phase octadecylsilane bonded silica cartridge and the bile salts eluted with methanol. Negative ion FAB spectra could be obtained from the equivalent of 10 microliter of urine loaded onto the target probe with glycerol as matrix. In samples from normal infants and children bile salt peaks were rarely detectable above the background whereas peaks produced by steroid sulphates and glucuronides and bile alcohol glucuronides could usually be identified. In samples from infants and children with cholestasis the major peaks were produced by the taurine and glycine conjugates of di-, tri- and tetrahydroxycholanoic acids (and their monosulphates). In samples from patients with Zellweger syndrome and infantile Refsum's disease, a unique ion at m/z 572 indicated the presence of taurine-conjugated tetrahydroxy-cholestanoic acid(s). The amide linkage to taurine was cleaved by alkaline hydrolysis but not by cholylglycine hydrolase. Capillary gas chromatography--mass spectrometry (GC-MS) of the bile acids liberated by alkaline hydrolysis indicated the presence of at least two nuclear-tetrahydroxylated cholestanoic acids, probably the 6 alpha- and 1 beta-hydroxylated derivatives of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestan-26-oic acid.

Fast atom bombardment combined with tandem mass spectrometry for determination of bile salts and their conjugates

Fast atom bombardment desorption of bile salts produces negative ions which show little fragmentation. The lack of fragmentation limits the utility of the method for resolving questions regarding specific structural features. This paper is a report of negative ion fast atom bombardment mass spectra and collision-activated decomposition spectra of cholate, chenodeoxycholate, lithocholate, taurocholate, taurochenodeoxycholate, taurolithocholate, 3 beta-ol-5-cholenate, taurolithocholate-3-sulfate and glycolithocholate-3-sulfate. The collision-activated decomposition spectra are useful for distinguishing bile salt structural features and for quantifying relative amounts of isomeric ions in a mixture. The negative ion mode is well suited for generating anions of bile salts and, when coupled with collisional activation, provides complementary information to the positive ion mode. The collision-activated fragmentation is also unusual as it appears to be an example of reactions occurring remote from the charge site. Furthermore, on the basis of the fragmentations, the charge site can be located in the amphiprotic form of some gas-phase diprotic bile acids such as taurolithocholate-3-sulfate and glycolithocholate-3-sulfate.

Serum bile acid composition in patients with cystic fibrosis

Serum bile acid composition was examined in detail using capillary column gas chromatography and mass spectrometry in 10 children with cystic fibrosis (CF) and 4 healthy children. The mean total bile acid concentration in fasting serum of CF patients was 2.33 +/- 0.84 mumol/l, slightly lower than but not statistically significantly different from healthy controls (mean 2.86 +/- 0.98 mumol/l) and appeared to show no relationship to the degree of exocrine pancreatic insufficiency. Analysis of individual serum bile acids in these children showed that cholic acid represented less than 10% of the total bile acids. Chenodeoxycholic acid was the predominant serum bile acid; the mean concentration in CF patients was 0.98 +/- 0.51 mumol/l, lower than for the healthy controls (1.69 +/- 0.84 mumol/l). Concentrations of lithocholic acid, 3 beta-hydroxy-5-cholenoic, ursodeoxycholic and 3 beta, 7 alpha, 12 alpha-trihydroxy-5 beta-cholanoic acids in fasting serum samples of the CF patients were not significantly different from the healthy control sera but were higher than those normally found in adults. Measurements of fecal bile acid excretion indicated an increased loss of primary bile acids in patients with CF consistent with an impairment of the enterohepatic circulation of bile acids.

Bile acids in deermice lacking liver alcohol dehydrogenase

Liver alcohol dehydrogenase (EC 1.1.1.1) is believed to catalyze the oxidation of 26-hydroxylated intermediates in the biosynthesis of bile acids from cholesterol. We have therefore analyzed the composition and size of the bile acid pool in deer-mice genetically lacking alcohol dehydrogenase. Cholic acid was found to be the major primary bile acid accompanied by small amounts of chenodeoxycholic acid. Variable amounts of secondary bile acids were also present, mainly deoxycholic acid and 3 alpha, 12 alpha-dihydroxy-7-oxo-5 beta-cholanoic acid. The same bile acids were found in animals with normal levels of alcohol dehydrogenase. The pool of bile acids in the gallbladder, small intestine and large intestine varied between 4.2 and 8.4 mumol in four animals lacking alcohol dehydrogenase and between 6.0 and 8.4 mumol in four control animals. Ethanol did not influence pool size or composition of bile acids in the animal studied. It is concluded that alcohol dehydrogenase is not obligatory for normal bile acid biosynthesis.