Fluorescence high-performance liquid chromatographic determination of free and conjugated bile acids in serum and bile using 1-bromoacetylpyrene as a pre-labeling reagent

Quantitative-profiling of bile acids and their conjugates in mouse liver, bile, plasma, and urine using LC-MS/MS

The differences among individual bile acids (BAs) in eliciting different physiological and pathological responses are largely unknown because of the lack of valid and simple analytical methods for the quantification of individual BAs and their taurine and glycine conjugates. Therefore, a simple and sensitive LC-MS/MS method for the simultaneous quantification of 6 major BAs, their glycine, and taurine conjugates in mouse liver, bile, plasma, and urine was developed and validated. One-step sample preparation using solid-phase extraction (for bile and urine) or protein precipitation (for plasma and liver) was used to extract BAs. This method is valid and sensitive with a limit of quantification ranging from 10 to 40 ng/ml for the various analytes, has a large dynamic range (2500), and a short run time (20 min). Detailed BA profiles were obtained from mouse liver, plasma, bile, and urine using this method. Muricholic acid (MCA) and cholic acid (CA) taurine conjugates constituted more than 90% of BAs in liver and bile. BA concentrations in liver were about 300-fold higher than in plasma, and about 180-fold higher in bile than in liver. In summary, a reliable and simple LC-MS/MS method to quantify major BAs and their metabolites was developed and applied to quantify BAs in mouse tissues and fluids.

Enhancement of atmospheric pressure chemical ionization for the determination of free and glycine-conjugated bile acids in human serum

A highly sensitive and accurate method based on the precolumn derivatization of bile acids (BA) with a high ionization efficiency labeling reagent 1,2-benzo-3,4-dihydrocarbazole-9-ethyl-benzenesulfonate (BDEBS) coupled with LC/MS has been developed. After derivatization, BA molecules introduced a weak basic nitrogen atom into the molecular core structure that was readily ionized in commonly used acidic HPLC mobile phases. Derivatives were sufficiently stable to be efficiently analyzed by atmospheric pressure chemical ionization (APCI)-MS/MS in positive-ion mode. The MS/MS spectra of BA derivatives showed an intense protonated molecular ion at m/z [M + H]+. The collision-induced dissociation of the molecular ion produced fragment ions at [MH-H2O]+, [MH-2H2O]+, [MH-3H2O]+. The characteristic fragment ions were at m/z 320.8, 262.8, and 243.7 corresponding to a cleavage of N-CO, O-CO, and C-OCO, respectively, and bonds of derivatized molecules. The selected reaction monitoring, based on the m/z [M+H]+ --> [MH-H2O]+, [MH-2H2O]+, [MH-3H2O]+, 320.8, 262.8, and 243.7 transitions, was highly specific for the BA derivatives. The LODs for APCI in a positive-ion mode, at an S/N of 5, were 44.36-153.6 fmol. The validation results showed high accuracy in the range of 93-107% and the mean interday precision for all standards was <15% at broad linear dynamic ranges (0.0244-25 nmol/mL). Good linear responses were observed with coefficients of > 0.9935 in APCI/MS detection. Therefore, the facile BDEBS derivatization coupled with mass spectrometric analysis allowed the development of a highly sensitive and specific method for the quantitation of trace levels of the free and glycine-conjugated BA from human serum samples.

Ursodeoxycholate further increases bile-duct cell proliferative response induced by partial bile-duct ligation in rats

BACKGROUND

Bile salts (BSs) stimulate cholangiocyte proliferation in vitro and in vivo in normal rats. In this study, we evaluated the effects of BS-enriched diets on cholangiocyte proliferative activity already triggered by partial bile-duct ligation (pBDL), a surgical model that induces mild cholestatic conditions, focusing our attention on ursodeoxycholate (UDC).

METHODS

Animals (n=45) were fed either a standard diet, or a 0.2% deoxycholate- or 0.2% UDC-enriched diet for 4 weeks. Then, in each group, ten animals underwent pBDL and five underwent sham operation. Serum and biliary BS levels, serum cholestasis and cytolysis indexes, as well as liver conventional histology, apoptosis and proliferative activity were evaluated 48 h after the operation.

RESULTS

Animals that underwent pBDL showed sustained proliferative response compared with sham-operated rats. BS-enriched diets did not influence cholangiocyte proliferation in sham-operated rats. However, significantly increased proliferation was observed in pBDL rats fed a UDC-enriched diet. The evaluation of humoral and histological parameters excluded the possibility that the increased proliferation induced by UDC-enriched diet could be related to concomitant liver cell damage.

CONCLUSION

A UDC-enriched diet is able to amplify the magnitude of the cholangiocyte hyperplastic process, which occurs by a stimulatory mechanism after partial bile-duct ligation.

Influence of ursodeoxycholate-enriched diet on liver tumor growth in HBV transgenic mice

Hepatitis B virus (HBV) transgenic mice (official designation, Tg [Alb-1 HBV] Bri 44) invariably develop macroscopically evident tumors within the 20th month of life. Sustained proliferative activity seems to play an important role in the development of these lesions. We previously showed that ursodeoxycholate (UDC) stimulates hepatocyte proliferation in various experimental settings. Herein, we tested the assumption that biological factors able to further increase liver cell proliferation, such as UDC, could accelerate tumor development in this animal model. For this study, 22 eight-week-old male transgenic mice were divided into 2 groups; 11 animals received a standard diet, and 11 received a UDC-enriched diet. The 2 groups were further divided into 2 subgroups of 5 and 6 animals each and were sacrificed at 3 and 15 months of age, respectively. These different times were chosen to exclude diet-related toxicity (in 3-month-old mice) and evaluate tumor growth (in 15-month-old mice). In addition, hepatocyte proliferation was assessed in all animals. In 3-month-old mice receiving UDC, cholestatic and cytolytic indices as well as liver histology were comparable to those in controls. At 15 months, all UDC-treated mice showed large multinodular tumors whereas only 33% of controls developed smaller uninodular neoplasms. Hepatocyte proliferation was increased in all animals receiving UDC compared with controls. In conclusion, the increase in serum UDC (undetectable in mice fed a standard diet), in the absence of any toxic effect on the liver, suggests the involvement of this bile salt in the stimulation of hepatocyte proliferation and tumor growth.

High-performance liquid chromatographic determination of ursodeoxycholic acid after solid phase extraction of blood serum and detection-oriented derivatization

Ursodeoxycholic acid (3 alpha,7 beta-dihydroxy-5 beta-cholanoic acid, UDCA) is a therapeutically applicable bile acid widely used for the dissolution of cholesterol-rich gallstones and in the treatment of chronic liver diseases associated with cholestasis. UDCA is more hydrophilic and less toxic than another therapeutically valuable bile acid, chenodeoxycholic acid (CDCA), the 7 alpha-epimer of UDCA. Procedures for sample preparation and HPLC determination of UDCA in blood serum were developed and validated. A higher homologue of UDCA containing an additional methylene group in the side chain was synthetized and used as an internal standard (IS). Serum samples with IS were diluted with a buffer (pH=7). The bile acids and IS were captured using solid phase extraction (C18 cartridges). The carboxylic group of the analytes was derivatized using 2-bromo-2'-acetonaphthone (a detection-oriented derivatization), and reaction mixtures were analyzed (HPLC with UV 245 nm detection; a 125--4 mm column containing Lichrospher 100 C18, 5 microm; mobile phase: acetonitrile--water, 6:4 (v/v)). Following validation, this method was used for pharmacokinetic studies of UDCA in humans.

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.

Structure-retention correlation of isomeric bile acids in inclusion high-performance liquid chromatography with methyl beta-cyclodextrin

The structure-retention correlation of various C24 bile acid isomers was studied by the addition of methyl beta-cyclodextrin (Me-beta-CD) to mobile phases in reversed-phase high-performance liquid chromatography (HPLC). The compounds examined include a series of monosubstituted bile acids related to cholanoic acids differing from one another in the position and configuration of an oxygen-containing function (hydroxyl or oxo group) at the position C-3, C-6, C-7, or C-12 and the stereochemistry of the A/B-ring fusion (trans 5 alpha-H and cis 5 beta-H) in the steroid nucleus. The inclusion HPLC with Me-beta-CD was also applied to biologically important 4 beta- and 6-hydroxylated bile acids substituted by three to four hydroxyl groups in the 5 beta-steroid nucleus. These bile acid samples were converted into their fluorescence prelabeled 24-pyrenacyl ester derivatives and chromatographed on a Capcell Pak C18 column eluted with methanol-water mixtures in the presence or absence of 5 mM Me-beta-CD. The effects of Me-beta-CD on the retentions of each compound were correlated quantitatively to the decreasing rate of capacity factors and the relative strength of host-guest interactions. On the basis of the retention data, specific and nonspecific hydrogen-bonding interactions between the bile acids and the Me-beta-CD were discussed.

Determination of simvastatin and its active metabolite in human plasma by column-switching high-performance liquid chromatography with fluorescence detection after derivatization with 1-bromoacetylpyrene

By using a fluorescent derivatization and column-switching technique, a highly sensitive and selective high-performance liquid chromatographic (HPLC) method has been developed for the determination of simvastatin (I, beta-hydroxy-delta-lactone form) and its active hydrolyzed metabolite (II, beta,delta-dihydroxy acid form of I) in human plasma. A plasma sample spiked with internal standards was applied to a C8 solid-phase extraction column. Compounds I and II were separately extracted from plasma into two fractions. Compound I in one of the fractions was hydrolyzed to II. A fluorescent derivative was prepared by esterification of II with 1-bromoacetylpyrene in the presence of 18-crown-6 for both fractions. The pyrenacyl ester of II thus obtained was purified on a phenylboronic acid (PBA) solid-phase extraction column, and was measured by column-switching HPLC with fluorescence detection. The calibration curves for both I and II were linear in the concentration range of 0.1-10 ng/ml. The intra-day coefficients of variation were less than 11.0%, and the accuracies were between 91.7% and 117% within the concentration range for both analytes. The limits of quantification (LOQ) for both analytes were set to 0.1 ng/ml. This assay method has adequate sensitivity and selectivity to measure the concentrations of I and II in human plasma from clinical studies.

Sensitive analytical method for the novel H1-receptor antagonist HSR-609 in human plasma and urine by high-performance liquid chromatography with pre-column fluorescent derivatization

A simple and sensitive method for quantitation of HSR-609 (I) in human plasma and urine was developed using HPLC with the fluorescence labelling reagent 4-(N,N-dimethylaminosulfonyl)-7-N-piperazino-2,1,3-benzox adi azole (DBD-PZ). Compound I was extracted from human plasma and urine, and derivatized by reaction with DBD-PZ in the presence of Mukaiyama reagent A, an equimolar solution of 2,2'-dipyridyl disulfide (DPDS) and triphenylphosphine (TPP) in acetonitrile. The reaction mixture was cleaned up by liquid liquid extraction following the derivatization. The conjugate was analyzed by ion-pair-HPLC with fluorometric detection. The quantitation limits for I were 0.5 ng/ml in plasma and 5 ng/ml in urine. Using this method, plasma concentration and urinary excretion of I were studied after oral administration of I to human volunteers.

Ultraviolet and fluorescence derivatization reagents for carboxylic acids suitable for high performance liquid chromatography: a review

Pre- and postcolumn derivatization with a suitable chromophore or fluorophore have often been utilized to enhance the sensitivity and selectivity of detection for analytes possessing a carboxyl group. The major classes of UV and fluorescent derivatization reagents include the coumarin analogues, alkyl halides, diazoalkanes, and amines. The derivatization reaction conditions, HPLC systems for separation of the conjugates and detection limits of various analytes are presented in this review. High mass sensitivity for various carboxylic acids have been achieved with the hydrazides, anthracenes, and diazoalkanes.

Determination of carboxylic acid salts in pharmaceuticals by high-performance liquid chromatography after pre-column fluorogenic labelling

2-Bromoacetyl-6-methoxynaphthalene (Br-AMN) was used as a fluorogenic labelling reagent for high-performance liquid chromatographic (HPLC) analyses of pyroglutamic acid, 4-hydroxybutyric acid and thioctic acid in pharmaceutical formulations. The reaction was carried out in aqueous medium in the presence of a cationic surfactant to obtain the direct derivatization of the salts of 4-hydroxybutyric acid and thioctic acid or in acetonitrile for pyroglutamic acid. The resulting naphthacylesters were then chromatographed under reversed-phase (C-18) conditions and detected fluorimetrically (lambda exc, 300 nm; lambda em, 460 nm). The method proved to be suitable for the sensitive and selective analysis of commercial formulations of the cited acidic drugs.

Tauroursodeoxycholate increases rat liver ursodeoxycholate levels and limits lithocholate formation better than ursodeoxycholate

BACKGROUND & AIMS

To explain the greater hepatoprotective effect of tauroursodeoxycholic acid vs. ursodeoxycholic acid, the absorption, hepatic enrichment, and biotransformation of these bile acids (250 mg/day) were compared in rats.

METHODS

Bile acids were determined in intestinal contents, feces, urine, plasma, and liver by gas chromatography-mass spectrometry.

RESULTS

The concentration of ursodeoxycholate in the liver of animals administered tauroursodeoxycholic acid (175 +/- 29 nmol/g) was greater (P < 0.05) than in animals administered ursodeoxycholic acid (79 +/- 19 nmol/g). Hepatic lithocholate was substantially higher after ursodeoxycholic acid administration (21 +/- 10 nmol/g) than after tauroursodeoxycholic acid administration (12 +/- 1 nmol/g). A concomitant reduction in the proportion of hydrophobic bile acids occurred that was greatest during tauroursodeoxycholic acid administration. In the intestinal tract, the mass of ursodeoxycholate and its specific metabolites was greater in rats administered tauroursodeoxycholic acid (27.2 mg) than those administered ursodeoxycholic acid (13.2 mg). In feces, the proportion of lithocholate was 21.9% +/- 4.9% and 5.4% +/- 4.0% after ursodeoxycholic acid and tauroursodeoxycholic acid administration, respectively.

CONCLUSIONS

Compared with ursodeoxycholic acid, tauroursodeoxycholic acid induces a greater decrease in the percent composition of more hydrophobic bile acids within the pool, limits lithocholate formation, and increases hepatic ursodeoxycholate concentration. These differences are explained by increased hepatic extraction and reduced intestinal biotransformation and not by enhanced absorption of the amidated species.

High-performance liquid chromatographic-electrospray mass spectrometric analysis of bile acids in biological fluids

The present work describes the development of HPLC-mass spectrometric systems equipped with an electrospray interface for the quantitative analysis of bile acids. Good separation of free as well as glycine- and taurine-conjugated bile acids was achieved with a C18 reversed-phase column (3 microns particle size, 70 x 4.6 mm I.D.) employing methanol-15 mM ammonium acetate as the mobile phase for both isocratic and gradient mode, at a flow-rate of 0.3 ml/min. This system permits post-column splitting of the eluate for analysis by two different detectors: (1) electrospray-mass spectrometer with a flow-rate of 18 microliters/min; and (2) a complementary evaporative light scattering mass detector. When bile salts were ionized in the electrospray interface operating in the negative-ion mode, only [M-H]- molecular ions were generated; the detection limit was 15 pg injected for all bile acids studied. In the second system, a semi-micro pre-column splitting apparatus (Acurate, LC Packings) was utilized: with this device the flow-rate from the HPLC pump was reduced to 1.4 microliters/min and bile acids were separated with a micro-bore C18 column (3 microns particle size, 150 x 0.30 I.D.), using the same mobile phase as above. With this latter system, a head-column enrichment technique can be used: the amount injected can be increased from 60 to 200 nl, permitting an improvement in the detection limit to 5 pg injected. Application of the HPLC-electrospray-mass spectrometric method to bile and serum bile acid analysis is described; preliminary data on the ability of the first system to determine the 13C/12C isotope ratio in 13C-labeled bile acid enriched serum is also critically discussed.

Fluorogenic reactions for biomedical chromatography

A number of fluorogenic reactions, which have been used for HPLC detection systems by means of pre- and/or postcolumn derivatization, are surveyed with respect to both sensitivity and selectivity for the determination of biomedically important substances. For the derivatization of the substances, two types of fluorogenic reactions, fluorescence-generating and fluorescence-tagging, have been studied. The former are usable in most instances for both pre- and postcolumn derivatization methods, and the latter only for precolumn derivatization methods. HPLC methods utilizing the fluorogenic reactions allow analytes to be detected at picomole-subfemtomole levels. In the fluorescence-generating reactions, several fluorogenic reagents possessing two or more reactive sites in the molecule, which show molecular recognition for a variety of analytes, permit facile and reproducible detection in HPLC because there are fewer interferences from biological matrices.

Determination of conjugated and unconjugated serum 3 alpha-OH bile acids by high-performance liquid chromatography

A simple reverse-phase liquid chromatographic method has been developed for the quantitative measurement of 11 3 alpha-OH bile acids in paediatric serum samples. Bile acids are enzymatically reduced to the corresponding 3-keto compound and then derivatized with the fluorophore dansyl hydrazine. Preliminary fractionation of bile acids is not required. The limit of detection is 0.1 mumol/L using a sample size of 200 microL. One hundred and twenty-three serum samples were analysed by the high-performance liquid chromatography (HPLC) method and the results compared with a commercial kit method (Enzabile) presently used in many laboratories for the measurement of total bile acids. There was a good correlation between the two methods (r = 0.96). The method is suitable for use in a clinical laboratory for the further investigation of those patients with abnormally high total bile acid levels where quantification of bile acid fractions is required.

Quinoxalinone derivatization of biological carboxylic acids for detection by peroxyoxalate chemiluminescence with high-performance liquid chromatography

A quinoxalinone fluorescent tag is evaluated as a carboxylic acid derivatizing reagent for detection by peroxyoxalate chemiluminescence. The synthetic procedure for the quinoxalinone was modified to give a yield that is significantly increased over that reported previously. The new conditions use less hazardous reagents, and produce a final product greater than 97% pure, without the need for intermediate clean-up steps. The derivatization reaction is also modified to give increased yields of greater than 85% compared to 74% obtained previously. The post-column chemiluminescence reaction conditions are optimized to give detection limits of 500 attomole/injection-10 times lower than the fluorescence previously obtained. The reagent is used for the first time on a plasma sample extract. Typical method precision is 4%.

HPLC-fluorescence determination of bile acids in pharmaceuticals and bile after derivatization with 2-bromoacetyl-6-methoxynaphthalene

2-Bromoacetyl-6-methoxynaphthalene was used as a pre-chromatographic fluorescent labelling reagent for the high-performance liquid chromatographic (HPLC) analysis of bile acids. The derivatization reaction was performed in an aqueous medium in the presence of tetrahexylammonium bromide by ultrasonication at 40 degrees C to give fluorescent esters which were separated by reversed-phase HPLC and detected fluorimetrically (lambda ex = 300 nm, lambda em = 460 nm). Applications to the determination of ursodeoxycholic acid (UDCA) and chenodeoxycholic acid (CDCA) in their pharmaceutical formulations are described. The method was also applied to the determination of free and conjugated bile acids in human bile samples.

High performance liquid chromatographic determination of free and conjugated bile acids in serum, liver biopsies, bile, gastric juice and feces by fluorescence labeling

Separation and measurement of commonly occurring free and conjugated bile acids in serum, liver biopsies, bile, gastric juice and feces have been successfully accomplished using high performance liquid chromatography with fluorescence labeling. Free and conjugated bile acids were extracted from pretreated samples using Sep-Pak C18 cartridges and then fractionated on a piperidinohydroxypropyl Sephadex LH-20 column. Free and glycine conjugated bile acids were labelled with 4-bromomethyl-7-methoxycoumarin. Taurine conjugated bile acids were hydrolysed with cholylglycine hydrolase prior to derivatization with 4-bromomethyl-7-methoxycoumarin. Labelled bile acids were eluted using an acetonitrile/methanol/water gradient on an ultrasphere ODS column. The eluate was monitored by a fluorophotometer at 360 nm (excitation) and 410 nm (emission). Linearity was obtained between 50 and 400 nmol. Recoveries from serum, gastric juice and feces were greater than 87%. This is therefore a sensitive method for the precise quantification of bile acids in serum, liver biopsies, bile, gastric juice and feces.

Liquid chromatographic monitoring of pseudocholinesterase activity: comparison of methods

In order to study the activity of pseudocholinesterase in vitro, two liquid chromatographic techniques have been developed. One is based on phase transfer-catalyzed (PTC) esterification of the carboxylic acid formed during hydrolysis of the substrate, and the other on the use of a radioisotopically labeled substrate. In both cases, the substrate used was a long-chain choline ester. The PTC method, utilizing (N-9-acridinyl)bromoacetamide as a fluorogenic labeling reagent in an aqueous-organic two-phase system, gives esters with very high fluorescence intensity. The radiochromatographic method makes use of on-line radioactivity monitoring of the substrate and product in order to follow the hydrolysis reaction. In both methods reversed-phase liquid chromatography is used. A method for the synthesis of 3H-labeled choline esters is also described. Both techniques are compared with regard to sensitivity, reproducibility and practical considerations.

High-performance liquid chromatographic separation of bile acid pyrenacyl esters with cyclodextrin-containing mobile phase

The high-performance liquid chromatographic separation of bile acid pyrenacyl esters with cyclodextrin-containing mobile phase is presented. Compared with conventional methods, inclusion chromatography gives much more satisfactory separation of derivatized bile acids in a short time. The application of this method to the separation of glycine-conjugated bile acids in human bile is also described.

High-performance liquid chromatographic determination of cortolic and cortolonic acids as pyrenyl ester derivatives

A new procedure is described for the detection of the acidic metabolites of cortisol (cortoic acids) as the pyrenylmethyl-21-oic esters. The derivatizing reagent, diazomethylpyrene, was prepared by an improved procedure. The reagent was used at room temperature, required no catalyst, and was not restricted by stoichiometric requirements. The steroid esters were separated by reversed-phase high-performance liquid chromatography and analyzed simultaneously by their ultraviolet absorbance and fluorescence characteristics. Identities of the products were confirmed using the photodiode array detector to determine spectral profiles, absorbance maxima, and absorbance ratios. Further confirmation of identity of the cortoic acid esters used mass spectrometry under normal and collision-activated dissociation conditions. With the method described, a linear spectral response was obtained between 8 and 1680 fmol. Application of the technique to the analysis of steroid acids in human urine indicated the presence of cortoic acids.

Pre-column derivatization of free bile acids for high-performance liquid chromatographic and gas chromatographic-mass spectrometric analysis

Pentachlorophenyl (PCP) esters of five free bile acids (FBA) were obtained by reacting the FBA and Kovacs' complex (KC) in a 1:8 molar ratio in acetone at 65 degrees C, and were purified by column chromatography on silica gel. The esters were crystallized from benzene-hexane, derivatized as trimethylsilyl ethers for gas chromatography on a DB-1 capillary column and for gas chromatography-mass spectrometry with a DB-5 column, and mass spectrometry (MS) in the electron-impact (EI) positive-ion mode at 70 eV. The reaction is specific for FBA even in the presence of glycine and taurine conjugates of bile acids. The PCP esters were treated with benzylamine in chloroform or methanol to produce N-benzyl derivatives of FBA. The N-benzylamides were separated by high-performance liquid chromatography (HPLC) on a 4-microns Nova-Pak C18 column, studied by thermospray-LC-MS, and in the direct insertion probe-EI positive-ion mode.

Elevation of individual serum bile acids on exposure to trichloroethylene or alpha-naphthylisothiocyanate

Rats were treated with trichloroethylene via intraperitoneal (ip) injection or inhalation, or with ip alpha-naphthylisothiocyanate (ANIT). Serum samples were assayed for indices of liver injury including alanine aminotransferase (ALT), sorbitol dehydrogenase (SDH), alkaline phosphatase (AP), and bilirubin. Liver from some rats was examined for histological appearance. These data were compared to levels of individual serum bile acids (SBA) determined by high-performance liquid chromatography. Trichloroethylene and ANIT, each at their highest dose only, caused elevations in ALT, but not SDH or AP. The highest dose of ANIT also caused elevated serum bilirubin and cholangitis in the liver. SBA were also elevated in response to both trichloroethylene and ANIT, but at doses below those at which other parameters of liver function were increased. For both chemicals, taurocholic acid was the most sensitive of the bile acids assayed, being elevated at the lowest doses tested of 10 mumols/kg for trichloroethylene and 5 mumols/kg for ANIT. As the doses were raised more of the individual bile acids showed increases. On exposure to trichloroethylene via inhalation taurocholic acid was one of two SBA to show elevation. Thus, both trichloroethylene and ANIT cause elevation in SBA at doses well below those which cause an increase in standard indicators of liver dysfunction. This suggests that SBA and perhaps taurocholic acid, in particular, may provide a sensitive tool for studying hepatobiliary effects of chemicals.

Determination of individual bile acids in serum by high performance liquid chromatography

A high performance liquid chromatographic (HPLC) method for analysis of 4 free and 8 conjugated bile acids in submicromolar quantities in serum is described using precolumn derivatization with 4-bromomethyl-7-methoxycoumarin (BMC) and fluorescence detection. Bile acids were extracted from serum with 0.4 M sodium bicarbonate, adsorbed onto a Sep-Pak C18 cartridge and eluted with methanol. The extract was derivatized with BMC in acetonitrile using 18-crown-6 crown ether as catalyst and the BMC labelled glycine conjugates and free bile acids were analysed using acetonitrile + methanol + water gradient elution and detection at 320/385 nm. Using a novel and simple approach, taurine conjugates were isolated by extracting the dried, derivatized material with water, in contrast to previous methods which required column chromatography cleanup to isolate the taurine conjugates prior to derivatization. The isolated taurine conjugates were then hydrolysed enzymatically, extracted, derivatized and analysed as free-bile acids. Recoveries of individual bile acids varied from 83-96% for free and glycine conjugates and 72-83% for taurine conjugates. Coefficients of variation were in the range of 5.1-12.5%. In addition to the simpler and shorter procedure for taurine conjugates, this method has increased sensitivity over most other procedures and improved HPLC separation for the various bile acids and conjugates with equivalent recovery and reproducibility compared with other published methods.

N-(9-acridinyl)-bromoacetamide--a powerful reagent for phase-transfer-catalyzed fluorescence labeling of carboxylic acids for liquid chromatography

Phase-transfer-catalyzed esterification of various carboxylic acids has been carried out on a microanalytical scale with a new reagent, N-(9-acridinyl)-bromoacetamide, in aqueous/organic two-phase systems. The procedure gives esters showing very high fluorescence intensity in acid solution. The large Stokes' shift (greater than 120 nm) means that a low background can be achieved even when using a large emission bandwidth. These derivatives show very good chromatographic behavior on reversed-phase liquid chromatographic columns with the use of aqueous acetonitrile, containing 0.2% of phosphoric acid, as the mobile phase. Detection limits (S/N = 2) as low as 10 fmol can be obtained under optimal conditions.

Group separation of free and conjugated bile acids by pre-packed anion-exchange cartridges

A rapid and simple procedure for the group separation of the major free and conjugated bile acids of man is described. After initial extraction with Bond Elut C18 cartridges, the analytes are fractionated into the unconjugated, glycine- and taurine-conjugated forms using disposable Bond Elut SAX columns and methanol-acetate buffer eluents. The method is found to be accurate and reproducible and to afford complete resolution between fractions. Free and conjugated bile acids present in human bile and gastric juice are assayed by high-performance liquid chromatography, after extraction and group separation according to the described procedure.

Determination of 17-oxosteroid sulphates in serum by ion-pair extraction, prelabelling with dansylhydrazine and high-performance liquid chromatography with fluorescence detection

A new high-performance liquid chromatographic (HPLC) method with fluorescence detection is described for the direct determination of four serum 17-oxosteroid sulphates. Each serum sample was deproteinated with methanol, the methanol was evaporated and 17-oxosteroid sulphates in the residue were extracted with benzene as ion pairs in the presence of tetrapentylammonium ion. The ion pairs were labelled with dansylhydrazine and the hydrazones were separated by HPLC on a Capcell-Pak C8 (silicone polymer-coated silica gel modified with octyl groups) reversed-phase column using methanol-0.5% (w/v) sodium acetate-50% (v/v) acetic acid (57:42:1, v/v/v) as the mobile phase. The eluent was monitored with a fluorometric detector at an excitation wavelength of 330 nm and an emission wavelength of 540 nm.

Chemiluminescent assay of co-factors

Bioluminescent methods are widely used for the assay of the co-factors, NADH and ATP. Although the bioluminescent method is highly sensitive, the enzymes used are unstable and expensive. Therefore a chemiluminescent method would be valuable in clinical routine assay. We have developed a chemiluminescent method for the assay of NADH using the 1-methoxy-5-methylphenazinium methyl sulphate (1-MPMS)/isoluminol(IL)/microperoxidase(m-POD) system. In order to increase the sensitivity of this method, enzymatic cycling system was coupled to the chemiluminescent assay of NADH. Alcohol dehydrogenase and malate dehydrogenase were used as the cycling enzyme. The standard curve was obtained in the range from 3 X 10(-14) to 5 X 10(-12) mol/assay. The detection limit of NADH was 30 fmol/assay which was comparable to that of the bioluminescent method using bacterial luciferase. Two chemiluminescent methods for the assay of ATP have been developed. Method 1 is the system using hexokinase/G6PDH and 1-PMS/IL/m-POD, and method 2 is the system based on the enzymatic cycling reaction of ATP using hexokinase/pyruvate kinase. Method 2 is 1000/fold more sensitive than the method 1. The detection limit of ATP was 10 fmol/assay.