Global profiling and identification of bile acids by multi-dimensional data mining to reveal a way of eliminating abnormal bile acids

Bile acids (BAs), as crucial endogenous metabolites, are closely related to cholestasis, metabolic disorders, and cancer. To better understand their function and disease pathogenesis, global profiling of BAs is necessary. Here, multidimensional data mining was developed for the discovery and identification of potentially unknown BAs in cholestasis rats. Based on an in-house theoretical BA database and using a newly established liquid chromatography-tandem high-resolution mass spectrometry (LC-HRMS/MS) method, four-dimensional (4D) data including the retention times (RT), abundances, HRMS, and HRMS/MS spectra were acquired and elucidated. And 491 BAs were totally profiled. Then, the relationships between RT with different conjugation types, different positions and configurations of hydroxyl/ketone groups as well as fragmentation rules of hydroxyl, ortho-hydroxyl, ketone, and conjugated groups of BAs were summarized to assist BA identification for the first time. Finally, 292 BAs were assigned with molecular formulas, 201 of which were putatively identified by integrating the 4D data, applying structure-driven relative retention time rules, and a comparison with synthetic BAs. The estimated concentrations of 201 BAs, including 93 reported and 108 newly identified BAs, were quantified by using surrogate standards with similar structure. Among 201 BAs, 38 BAs were detected in both humans and rats for the first time. Our strategy has expanded the scope of BAs and provides a way to identify a class of metabolites. Compared to normal rats, the significantly increased sulfated and glucuronide conjugated BAs in urine and feces from experimentally cholestatic rats may reveal a way to diagnose intrahepatic cholestasis.

Quantitative bile acid profiling by liquid chromatography quadrupole time-of-flight mass spectrometry: monitoring hepatitis B therapy by a novel Na(+)-taurocholate cotransporting polypeptide inhibitor

A novel analytical approach for the targeted profiling of bile acids (BAs) in human serum/plasma based on liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) is presented. Reversed-phase chromatography enabled the baseline separation of 15 human BA species which could be readily detected by accurate mass analysis in negative ion mode. Blood proteins were removed by methanol precipitation in the presence of deuterium-labeled internal standards which allowed BA quantification in 50 μl plasma/serum. The assay was validated according to FDA guidance achieving quantification limits from 7.8 to 156 nM. Calibration curves prepared in charcoal-stripped serum/plasma showed excellent regression coefficients (R (2) > 0.997) and covered quantities from 7.8 to 10,000 nM depending on the analyzed species. Intra- and inter-day accuracy and precision were below 15 % for all analytes. Apparent extraction recoveries were above 97 %, and ion suppression rates were between 4 and 53 %. Mean BA level in serum/plasma from healthy volunteers ranged from 11 ± 4 nM (tauroursodeoxycholic acid) to 1321 ± 1442 nM (glycochenodeoxycholic acid). As a proof of concept, the assay was applied to plasma samples derived from a clinical phase I study of myrcludex B, a novel first-in-class virus entry inhibitor for the treatment of chronic hepatitis B and D. The results demonstrate that myrcludex-induced inhibition of the hepatic BA transporter Na(+)-taurocholate cotransporting polypeptide (NTCP) significantly affects plasma BA level. These observations provide novel insights into drug-induced metabolic responses and will be indispensable for the assessment of side effects and dose-finding processes during future clinical trials.

Isolation and determination of bile acids

In this article, the methods of isolation and determination of bile acids are reviewed. Methods for separation of bile acids from cattle and pig bile are given in detail. Isolation of a mixture of cholic acid and deoxycholic acids from cattle bile and their subsequent purification are described. The isolation and purification of hyodeoxycholic acid and other components of pig bile are also included. Methods for the determination of bile acids in various biological samples are reviewed, including enzyme assays, radioimmunoassay, enzyme immunoassay and chromatographic methods. Among chromatographic methods, separation and determination of bile acids by thin-layer chromatography, gas chromatography and high performance liquid chromatography are reviewed. Particular attention is given to the use of high performance liquid chromatography since this has recently been the most commonly applied method for the separation and determination of bile acids.

Benign recurrent intrahepatic cholestasis: a long-term follow-up study of two patients

Two brothers with benign recurrent intrahepatic cholestasis were studied over a period of 6 years. During this period, 11 episodes of cholestasis were observed, with a mean duration of 2.6 months (range: 2 weeks to 6 months). Once, both brothers developed cholestasis simultaneously. There was a prevalence for episodes of cholestasis in wintertime. The postprandial rise in serum sulfated glycolithocholic acid was increased in the patients, and the bile acid pool was enriched with secondary bile acids. In periods prior to cholestasis, the urinary 3 alpha OH-bile acid concentration was often elevated (greater than 50 mumoles per liter) without a clear correlation with the clinical prodromata. However, it could not be used as a predictor of cholestasis. In contrast, the postprandial rise in serum 3 alpha OH-bile acids was always grossly elevated in periods just before cholestasis. An increase both in fecal bile acid excretion as well as secondary bile acids in the bile acid pool indicated an increased spillover of bile acids into the large bowel. Cholestyramine administered directly after the first signs of cholestasis appeared to shorten an episode of cholestasis. On the other hand, withdrawal of cholestyramine in a cholestasis-free period may have resulted in an episode of cholestasis. Neither taurine supplementation for 3 and 7 weeks nor calcium phosphate, which binds sulfated bile acids in vitro, for 3 weeks could prevent an episode of cholestasis, although the latter normalized the bile acid pool composition. There is a rationale for a fat-restricted diet and cholestyramine therapy only as maintenance treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum bile acids: reference values in healthy dogs and comparison of two kit methods

Serum bile acid (SBA) reference intervals were established by use of a radioimmunoassay method for fasting dogs to be 0.2 to 4.3 micro mol/L (n = 60) and for 2 hour postprandial samples to be 0.6 to 24.2 micro mol/L (n = 37). The SBA reference intervals estimated using an enzymatic method were 0 to 8.6 micro mol/L for fasting (n = 26) and 0 to 29.8 micro mol/L for 2 hour postprandial samples (n = 36). The correlation between the two methods including samples from healthy dogs and clinical cases is good (n = 128, r = 0.82, p < 0.0001). The radioimmunoassay method is linear to 50 micro mol/L and the enzymatic method is linear to 100 micro mol/L, thus both methods require serum dilutions to be made in many cases of primary liver disease. The enzymatic method is less expensive and more convenient for use in a clinical laboratory but requires a greater sample volume (400 micro I) than the RIA method (50 micro I). Both methods have adequate precision and accuracy to be useful as diagnostic tests of liver function in dogs.

Sulphated lithocholic acid conjugates in serum from children with hepatic and intestinal diseases

Sulphated lithocholic acid conjugates (SGLC) were measured in the sera of 268 children with various hepatic and intestinal disorders. Two groups were distinguished: (I) SGLC concentration less than or equal to 1.2 mumol/l, n = 198, and (II) SGLC concentration greater than 1.2 mumol/l, n = 70. In 28 patients of the latter group the SGLC concentration was less than 25% of the concentration of glycocholic acid (GC) in the same serum sample. This group (IIA) consisted predominantly of patients with cholestasis, as characterized by high serum bile acid levels and deviating liver function tests. The rest of the group (IIB), with SGLC levels exceeding 25% of the GC concentration and relatively low serum bile acid concentrations, showed no clear cholestatic symptoms. A postprandial increase in serum SGLC (delta SGLC) greater than 1.0 mumol/l was found in only 1 of 32 patients of group I (3%), in 1 of 6 patients of group IIA (17%), but in 9 of 11 patients of group IIB (81%). delta SGLC did not correlate with delta GC in the same test, which indicated that a general hepatic bile acid clearance defect was not responsible. In two patients with intermittent cholestasis, the distinct postprandial rise in serum SGLC that was always found during anicteric periods could be prevented by adding cholestyramine to the test meal. We conclude that elevated serum concentrations of SGLC develop during the course of cholestasis but may also be caused by influx of this bile acid from the intestine. Because of its hepatotoxic properties, SGLC may be involved in the initiation or perpetuation of specific cholestatic phenomena.

Serum unconjugated bile acids: qualitative and quantitative profiles in ileal resection and bacterial overgrowth

Qualitative and quantitative profiles of unconjugated bile acids in the serum obtained over a 24-h period from three patients with ileal resections and one with a bacterial overgrowth are described. Unconjugated serum bile acids were determined using the high sensitivity and resolution of capillary column gas liquid chromatography after their rapid extraction and isolation using reverse phase octadecylsilane bonded silica cartridges and the lipophilic gel Lipidex 1000. Unconjugated serum bile acid concentrations were elevated throughout the day in both ileum resected patients and in conditions involving bacterial overgrowth when compared to healthy subjects. Total conjugated cholic acid concentrations were expectedly low in both intestinal disorders and were without the postprandial increases generally observed in healthy subjects. Qualitative gas chromatographic profiles of serum unconjugated bile acids in bacterial overgrowth distinctly revealed a predominance of deoxycholic acid and other secondary bile acids in all samples, while, in conditions of an impaired enterohepatic circulation, deoxycholic acid was absent or present in only trace amounts. The potential significance of measuring serum unconjugated bile acids in intestinal disorders is discussed.

Chemistry and enterohepatic circulation of bile acids

A brief review is given of the chemistry of bile acids, emphasizing the relationship between chemical structure, physical properties and enterohepatic cycling of the major primary and secondary bile acids. Features of the enterohepatic circulation of primary and secondary bile acids in man are summarized. The effects of bile acid feeding on the composition of the enterohepatic circulation in man are reviewed. Methods for characterizing the enterohepatic circulation of bile acids in man are tabulated.

Enzymic measurement of primary bile acids and the primary bile acid ratio in serum with the IL-Multistat III Fluorescence Light-Scattering Centrifugal Analyzer

Enzymic fluorimetric methods are described for the determination of primary bile acids and of chenodeoxycholic acid (CDC) and cholic acid (C) in serum. Bile acids are extracted from 0.3 mL of serum in a simple 5-min step with use of Sep-Pak C cartridges. Total primary bile acids are measured by an equilibrium technique after reaction with beta-NAD in the presence of 7 alpha-hydroxysteroid dehydrogenase. Chenodeoxycholic acid (and its conjugates) is measured by a reaction-rate technique employing the same reaction as above but under different experimental conditions. A small contribution of cholic acid (and its conjugates) to the reaction rate is eliminated by simple calculations. Cholic acid is calculated by difference of the two determinations. In both assays NADH fluorescence is measured with the Multistat centrifugal analyzer. Absolute recovery of bile acids from serum was about 87%. Day-to-day standard deviations for CDC and C were 1.6 and 2.0 mumol/L at serum concentrations of 22.1 and 24.1 mumol/L respectively. Comparison data with a cholylglycine RIA procedure gave the following correlation coefficients (x = RIA, y = proposed method): r = 0.980 (RIA vs total primary bile acids), r = 0.918 (RIA vs CDC) and r = 0.989 (RIA vs C). The methods described appear more practical for use on a routine basis than methods in the literature for the calculation of the primary bile acid ratio.

A bioluminescence assay for total 3 alpha-hydroxy bile acids in serum using immobilized enzymes

A bioluminescence assay for bile acids was developed using a co-immobilized 3 alpha-hydroxysteroid dehydrogenase, diaphorase, and bacterial luciferase. The assay was specific for bile acids containing a free 3 alpha-hydroxyl group, as well as androsterone. Light output was linear over a bile acid concentration range of 1-20 000 pmol. Intra-assay precision was 6.2-8.2% and the recovery of added standards was 92-110%. Comparison of results using the bioluminescence assay with those using gas liquid chromatography revealed an excellent correlation (r = 0.99, n = 31). Since the bioluminescence assay is rapid, sensitive, specific, and uses inexpensive reagents, it appears to be an ideal method for the measurement of total bile acids in serum.

Continuous-flow automated assay of steroids with nylon-tube-immobilized hydroxysteroid dehydrogenases

Several NAD(P)+-dependent hydroxysteroid dehydrogenases, namely 3 alpha-hydroxysteroid dehydrogenase, beta-hydroxysteroid dehydrogenase, 7 alpha-hydroxysteroid dehydrogenase, and 12 alpha-hydroxysteroid dehydrogenase were separately immobilized on nylon tubes for the continuous-flow automated assay of hydroxysteroids. 3 alpha-Hydroxysteroid dehydrogenase was also immobilized on pore glass. Spectrophotometric monitoring in the visible region, where blank values were markedly reduced, was achieved through the Meldola blue catalyzed transfer of hydrogen from NAD(P)H to a tetrazolium salt. Nylon-tube-immobilized enzymes maintained 45-55% of the original activity after 1 month of intermittent use. The operational range, using the "end point" approach, was 1-25 nmol of steroid and the assay speed 10-15 samples/h. Reliable results were obtained in the determination of 3 alpha-hydroxysteroids and 3 beta, 17 beta-hydroxysteroids in urine and total bile acids in serum.

Caffeine: a model compound for measuring liver function

The effects of liver disease on caffeine plasma clearance (Cl) and on exhalation of 14CO2 following i.v. injection of 2 mu Ci of [3-methyl-14C]caffeine together with 125 mg of the unlabeled compound were measured in 15 patients with cirrhosis, 11 subjects with miscellaneous liver disease, and 10 normal volunteers. Compared to mean values for Cl (2.02 +/- S.D. 0.68 ml per min per kg) and t1/2 (3.8 +/- 0.9 hr) in normal volunteers, cirrhotics were characterized by highly significant reductions in Cl (to 0.76 +/- 0.40) and prolongation in t1/2 (to 13.7 +/- 13.0), whereas the volume of distribution (VD) remained relatively unchanged (0.57 +/- 0.16 vs. 0.64 +/- 0.13 liter per kg in normals). Cumulative 14CO2 production and specific activity of 14CO2 in breath decreased in parallel (r = 0.83) with Cl. Patients with miscellaneous liver disease exhibited only small changes in Cl and t1/2; however, 14CO2 parameters in breath appeared more sensitive in indicating the slight functional derangement. In view of the correlation (Rs = 0.83) of cumulative 14CO2 excretion with the initial disappearance constant for bromosulfophthalein, the caffeine breath test may be considered as a quantitative measure of hepatic microsomal activity; based on a surprisingly close, hyperbolic relationship between Cl and fasting caffeine plasma concentrations, the latter might serve as a simple guide to severity of liver disease.

Microanalysis of free and conjugated bile acids by thin-layer chromatography and in situ spectrofluorimetry

A combination of thin-layer chromatography (TLC) and in situ spectrofluorimetry for the determination of free bile acids and bile acids conjugated with glycine or taurine is described. This method makes it possible to determine bile acids concentrations as low as 0.15-0.25 nmol (0.05-0.1 microgram) in a simple and reproducible way. Moreover, information can be obtained about conjugation patterns and relative concentrations of mono-, di-, and trihydroxy bile acids as well as about the presence of abnormal bile acids. After TLC the bile acids are made visible in uv light by dipping the layer in sulfuric acid in diethyl ether and warming it under well-described conditions. The fluorescence of the bile acids on the thin layer can be measured and makes it possible to quantitate them. The method presented here is applicable to bile acid-containing extracts from serum, bile, and feces, and the results are in good agreement with those obtained by enzymatic and gas-liquid chromatographic techniques.

A bioluminescent assay for 12-alpha-hydroxy bile acids using immobilized enzymes

A bioluminescent assay for 12-alpha-hydroxy bile acids was developed using enzymes coimmobilized onto Sepharose 4B. The immobilized enzymes used were a bacterial 12-alpha-hydroxysteroid dehydrogenase, bacterial luciferase, and NADPH:FMN oxidoreductase or bacterial diaphorase. The assay was specific for 12-alpha-hydroxy bile acids and the lower limit of detection was 4 pmol/0.5 ml assay volume with a linear range of 4 to 2000 pmol. Intraassay precision was from 7.8 to 8.2%. Values obtained with this assay showed good agreement with those obtained by gas-liquid chromatography. The system using diaphorase was not stable at 4 degrees C in the absence of added thiol compounds, but could be stabilized by the addition of glutathione (0.5 mM). The assay is a convenient, a rapid, and an extremely sensitive method for the measurement of 12-alpha-hydroxy bile acid concentrations in the serum of patients or experimental animals.

Postprandial plasma concentrations of glycine and taurine conjugated bile acids in healthy subjects

Fasting and postprandial plasma concentrations of glycine and taurine conjugates of cholic, chenodeoxycholic, and deoxycholic acid were measured by a high pressure liquid chromatography-enzymatic assay in nine healthy subjects. The mean value of each bile acid concentration increased significantly (2.4-4.7 times) in the postprandial period. The total glycine taurine ratio of 2.5 in the fasting state increased significantly to a maximum value of 3.3 at one to 1 1/2 hours postprandially and then declined. This shift in glycine taurine ratio shows, that the relative increase in concentrations of glycine conjugates exceeds the relative increase in concentrations of taurine conjugates in the early postprandial period, and supports the view that there is significant absorption of glycine conjugated bile acids from the proximal small intestine.

The patterns of glycine and taurine conjugates of bile acids in serum in hepatobiliary disease

Fasting serum concentrations of glycine and taurine conjugates of cholic, chenodeoxycholic, and deoxycholic acid were measured with a high-pressure liquid chromatography-enzymatic assay in patients with hepatobiliary disease. The total glycine to taurine ratio was significantly lower in extrahepatic cholestasis (median 1.1) than in cirrhosis (median, 2.0) and controls (median, 1.7). In patients with cirrhosis the ratio was significantly correlated with the S-bilirubins, P-coagulation factors (II + VII + X), and S-total conjugated bile acids. Because of large overlaps of the ratio between the groups the glycine to taurine ratio is of hardly any diagnostic value. The ratio of cholic acid conjugates to chenodeoxycholic acid conjugates was over 1.5 in 10 of 12 cholestasis patients and below this value in all but 1 patient with cirrhosis; the separation of the groups was not improved by splitting the ratio in glycine and taurine conjugates. This study does not suggest that separate determination of glycine and taurine conjugates of bile acids in serum adds diagnostic information in hepatobiliary disease.