Determination of conjugated bile acids in human urine by high-performance liquid chromatography with chemiluminescence detection

The profile of bile acids and their sulfate metabolites in human urine and serum

The role of sulfation in ameliorating the hepatotoxicity of bile acids (BAs) in humans remains unknown due to the lack of proper analytical methods to quantify individual BAs and their sulfate metabolites in biological tissues and fluids. To this end, a simple and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to characterize the detailed BA profile in human urine and serum. The limit of quantification was 1ng/mL and baseline separation of all analytes was achieved within in a run time of 32min. The method was validated over the dynamic range of 1-1000ng/mL. The LC-MS/MS method was more accurate, precise, and selective than the commercially available kits for the quantification of sulfated and unsulfated BAs, and the indirect quantification of individual sulfated BAs after solvolysis. The LC-MS/MS method was applied to characterize the BA profile in urine and serum of healthy subjects. Thirty three percent of serum BAs were sulfated, whereas 89% of urinary BAs existed in the sulfate form, indicating the role of sulfation in enhancing the urinary excretion of BAs. The percentage of sulfation of individual BAs increased with the decrease in the number of hydroxyl groups indicating the role of sulfation in the detoxification of the more hydrophobic and toxic BA species. Eighty percent of urinary BAs and 55% of serum BAs were present in the glycine-amidated form, whereas 8% of urinary BAs and 13% of serum BAs existed in the taurine-amidated form.

Measurement of transport activities of bile acids in human multidrug resistance-associated protein 3 using liquid chromatography-tandem mass spectrometry

A method has been developed for the measurement of transport activities in membrane vesicles obtained from human multidrug resistance-associated protein 3-expressing Sf9 cells for 1beta-hydroxy-, 6alpha-hydroxy- and unsaturated bile acids by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry. Calibration curves for the bile acids were linear over the range of 10 to 2000 pmol/mL, and the detection limit was less than 2 pmol/mL for all bile acids using selected reaction monitoring analysis. The method was applied to measurements of adenosine triphosphate-dependent transport activities of the membrane vesicles for the above-mentioned hydroxylated and unsaturated bile acids. The present study demonstrated that the human multidrug resistance-associated protein 3 vesicles accepted 1beta-, 6alpha-hydroxylated and unsaturated bile acids along with common bile acids, such as glycocholic acid and taurolithocholic acid 3-sulfate. The developed method is useful for measurements of bile acid transport activities.

Bile acids: analysis in biological fluids and tissues

The formation of bile acids/bile alcohols is of major importance for the maintenance of cholesterol homeostasis. Besides their functions in lipid absorption, bile acids/bile alcohols are regulatory molecules for a number of metabolic processes. Their effects are structure-dependent, and numerous metabolic conversions result in a complex mixture of biologically active and inactive forms. Advanced methods are required to characterize and quantify individual bile acids in these mixtures. A combination of such analyses with analyses of the proteome will be required for a better understanding of mechanisms of action and nature of endogenous ligands. Mass spectrometry is the basic detection technique for effluents from chromatographic columns. Capillary liquid chromatography-mass spectrometry with electrospray ionization provides the highest sensitivity in metabolome analysis. Classical gas chromatography-mass spectrometry is less sensitive but offers extensive structure-dependent fragmentation increasing the specificity in analyses of isobaric isomers of unconjugated bile acids. Depending on the nature of the bile acid/bile alcohol mixture and the range of concentration of individuals, different sample preparation sequences, from simple extractions to group separations and derivatizations, are applicable. We review the methods currently available for the analysis of bile acids in biological fluids and tissues, with emphasis on the combination of liquid and gas phase chromatography with mass spectrometry.

Serum C24 bile acids in the developing human fetus

The C24 bile acids (BA) in the serum of 22 healthy human fetuses between weeks 20 and 37 of gestation were determined by capillary GC-MS. Fetal blood samples were taken in utero from the umbilical cord monitored by echography. There was no correlation between total bile acids (TBA) and gestational age. The TBA concentration was 5.14 +/- 2.13 microM. Primary BA (cholic acid and chenodeoxycholic acid) were the main BA (66.78 +/- 13.47%) with chenodeoxycholic acid being the main one. There were low concentrations of secondary BA (deoxycholic acid and lithocholic acid) (10.28 +/- 7.85%), which formed by intestinal bacterial 7 alpha-dehydroxylation of primary BA in the adult, despite the germ-free gut. The tertiary BA (ursodeoxycholic acid) was also detected (12.06 +/- 9.64%). There was 6 alpha-hydroxylation of chenodeoxycholic acid and of lithocholic acid to produce hyocholic acid and hyodeoxycholic acid respectively. Two 1 beta-hydroxylated BA were detected at different times of gestation. Cholic acid was rarely found in the 6 alpha- and 1 beta-hydroxylated forms. These additional hydroxylations could help to protect the fetal liver against the accumulation of cytotoxic bile acids at a time when other detoxification pathways are poorly developed. Traces of unsaturated bile acids like 3 beta-hydroxy-5-cholenoic acid were detected, showing that 27-hydroxylation of cholesterol does occur.

Label-free biochemical detection coupled on-line to liquid chromatography

The on-line coupling of a label-free optical biosensor to a HPLC system is described by combining the separation power of HPLC with the specificity of the biosensor system. A highly cross-reactive antibody against the pesticide isoproturon was used as model for affinity proteins. The binding strength of the antibody to the utilized pesticides was characterized with the biosensor, first. In the on-line coupling setup, the eluate of the HPLC was mixed continuously with the antibodies. The presence of antigens was detected by a reduction of the antibody binding to the transducer. This reduced binding was quantified by a differentiation of the sensor signal by applying a Savitzky-Golay algorithm. Limits of detection were found to be in the femtomole range without preconcentration, which is comparable to a study using fluorescence-based biochemical detection.

Retention and separation studies of cholesterol and bile acids using thermostated thin-layer chromatography

The influence of temperature on retention and separation of cholesterol and bile acids, using reversed-phase thin-layer chromatography, was studied. As mobile phases methanol-water mixtures of various compositions were used. Chromatographic experiments were performed using vapor-saturated chambers at temperatures ranging from 5 to 60 degrees C. A linear relationship between R(M) values and temperature (1/T) as well as mobile phase composition was observed. The elution order of steroids under the conditions investigated was discussed. Each chromatogram was evaluated using simple optimization parameters and the best chromatographic conditions for the separation of multicomponent samples were chosen.

Review of progress in sterol oxidations: 1987-1995

Material dealing with the chemistry, biochemistry, and biological activities of oxysterols is reviewed for the period 1987-1995. Particular attention is paid to the presence of oxysterols in tissues and foods and to their physiological relevance.

Enzyme immunoassay for conjugated cholic and 1 beta-hydroxycholic acids in urine of early infancy

A direct competitive heterologous enzyme immunoassay (EIA) for conjugated cholic acid (CA) was developed using horseradish peroxidase labeled antigen having a shorter bridge length than that of the immunogen. An appropriate dose-response curve for conjugated CA was obtained in the range of 0.05-50 ng/well. Specificity of the EIA proved satisfactory in terms of cross-reactivities to 23 kinds of related bile acids. The proposed method was evaluated to be useful for the determination of conjugated CA in urine with acceptable accuracy and inter- and intra-assay precision. The results of analysis showed a reverse relationship between age and urinary excretion ratio of conjugated 1 beta-hydroxy-CA to conjugated CA in the first 9 months after birth.