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

Separation of bile acid isomer plays a pivotal role in bioequivalence evaluation of ursodeoxycholic acid

Based on our experiences in bile acid profiling, this work developed and validated a liquid chromatography electrospray ionization tandem mass spectrometry method to separate endogenous bile acid isomers and quantitatively determine ursodeoxycholic acid (UDCA), glycoursodeoxycholic acid (GUDCA) and tauroursodeoxycholic acid (TUDCA) in human plasma. The separation was performed on a CORTECS C18 column with the mobile phase consisting of 1.0 mM ammonium acetate and acetonitrile-methanol (80:20, v/v). UDCA, GUDCA and TUDCA were detected in the negative mode on a triple-quadrupole mass spectrometer at the ion transitions of m/z 391 > 391, m/z 448 > 74, m/z 498 > 80, respectively. Phosphate buffer was employed as the surrogate matrix to establish the isotope internal standard corrected calibration curves of analytes. The background-method with a linearity range of 10-200 ng/mL was partially validated to determine the endogenous levels of analytes in blank human plasma, which was incorporated into the validation of bioequivalence-method with a linearity range of 50-10000 ng/mL. The bioequivalence (BE)-method was fully validated with special focus on matrix effects, which have been critically evaluated using the precision and accuracy of quality control samples prepared from the blank human plasma of 12 individuals. It is disclosed for the first time that the BE results of UDCA formulation may yield false results when the method is insufficient to separate UDCA from isoursodeoxycholic acid, a microbial metabolite of both endogenous and exogenous UDCA. The present method has established a milestone for the evaluation of UDCA formulations and is expected to provide a valuable reference for the bioanalytical development of endogenous medicinal products.

Simultaneous determination of UDCA and its major metabolites in human plasma with surrogate matrix by a rapid and specific LC-MS/MS method

A rapid, convenient, and specific liquid chromatography-tandem mass spectrometry method was developed and validated for the simultaneous quantification of ursodeoxycholic acid (UDCA), and its major metabolites, glycoursodeoxycholic acid (GUDCA) and tauroursodeoxycholic acid (TUDCA) in human plasma. Methanol was chosen as surrogate matrix for preparation the calibrators to establish calibration curves. Isotope internal standard was used for each analyte. After plasma samples were deproteinized with methanol, the post-treatment samples were analyzed on a ZORBAX SB-C18 column (2.1 × 50 mm, 1.8 μm) with 2 mM ammonium acetate and acetonitrile as mobile phase at a flow rate of 0.5 mL/min. Detection was performed on a triple quadrupole mass spectrometer operating in multiple reaction monitoring (MRM) employing negative ESI interface using API5500 triple quadrupole tandem mass spectrometer system, with the transitions set at m/z 391.4 → m/z 391.4, m/z 448.3 → m/z 73.9, m/z 498.4 → m/z 80.1, m/z 395.3 → m/z 395.3, m/z 453.3 → m/z 74.0, and m/z 503.2 → m/z 79.9 for UDCA, GUDCA, TUDCA, UDCA-d4, GUDCA-d5, and TUDCA-d5, respectively. The calibration curve ranges were 5.00-2500 ng/mL for UDCA and GUDCA and 0.500-250 ng/mL for TUDCA. The intra- and inter-day precision was within 7.00% in terms of relative standard deviation (RSD%) and the accuracy within 11.75% in terms of relative error. The selectivity, sensitivity, extraction recovery, matrix effect, dilution reliability, and stability were within the acceptable range. The method was successfully applied to a pharmacokinetic study in 12 healthy Chinese volunteers after oral administration of 250 mg UDCA.

Fibroblast Growth Factor 19 modulates intestinal microbiota and inflammation in presence of Farnesoid X Receptor

BACKGROUND

Disruption of bile acid (BA) homeostasis plays a key role in intestinal inflammation. The gut-liver axis is the main site for the regulation of BA synthesis and BA pool size via the combined action of the nuclear Farnesoid X Receptor (FXR) and the enterokine Fibroblast Growth Factor 19 (FGF19). Increasing evidence have linked derangement of BA metabolism with dysbiosis and mucosal inflammation. Thus, here we aimed to investigate the potential action of an FGF19 analogue on intestinal microbiota and inflammation.

METHODS

A novel engineered non-tumorigenic variant of the FGF19 protein, M52-WO 2016/0168219 was generated. WT and FXRnull mice were injected with AAV-FGF19-M52 or the control AAV-GFP and subjected to Sodium Dextran Sulphate-induced colitis.

FINDINGS

FGF19-M52 reduced BA synthesis and pool size, modulated its composition and protected mice from intestinal inflammation. These events were coupled with preservation of the intestinal epithelial barrier integrity, inhibition of inflammatory immune response and modulation of microbiota composition. Interestingly, FGF19-M52-driven systemic and local anti-inflammatory activity was completely abolished in Farnesoid X Receptor (FXR)null mice, thus underscoring the need of FXR to guarantee enterocytes' fitness and complement FGF19 anti-inflammatory activity. To provide a translational perspective, we also show that circulating FGF19 levels are reduced in patients with Crohn's disease.

INTERPRETATION

Reactivation of the FXR-FGF19 axis in a murine model of intestinal inflammation could bona fide provide positive changes in BA metabolism with consequent reduction of intestinal inflammation and modulation of microbiota. These results point to the therapeutic potential of FGF19 in the treatment of intestinal inflammation with concomitant derangement of BA homeostasis.

FUNDING

A. Moschetta is funded by MIUR-PRIN 2017 <- 2017J3E2W2; Italian Association for Cancer Research (AIRC, IG 23239); Interreg V-A Greece-Italy 2014-2020-SILVER WELLBEING, MIS5003627; HDHL-INTIMIC EuJPI-FATMAL; MIUR PON "R&I" 2014-2020-ARS01_01220. No money has been paid by NGM Biopharmaceuticals or any other agency to write this article.

Suppression of Hepatic Bile Acid Synthesis by a non-tumorigenic FGF19 analogue Protects Mice from Fibrosis and Hepatocarcinogenesis

Critical regulation of bile acid (BA) pool size and composition occurs via an intensive molecular crosstalk between the liver and gut, orchestrated by the combined actions of the nuclear Farnesoid X receptor (FXR) and the enterokine fibroblast growth factor 19 (FGF19) with the final aim of reducing hepatic BA synthesis in a negative feedback fashion. Disruption of BA homeostasis with increased hepatic BA toxic levels leads to higher incidence of hepatocellular carcinoma (HCC). While native FGF19 has anti-cholestatic and anti-fibrotic activity in the liver, it retains peculiar pro-tumorigenic actions. Thus, novel analogues have been generated to avoid tumorigenic capacity and maintain BA metabolic action. Here, using BA related Abcb4^-/- and Fxr^-/- mouse models of spontaneous hepatic fibrosis and HCC, we explored the role of a novel engineered variant of FGF19 protein, called FGF19-M52, which fully retains BA regulatory activity but is devoid of the pro-tumoral activity. Expression of the BA synthesis rate-limiting enzyme Cyp7a1 is reduced in FGF19-M52-treated mice compared to the GFP-treated control group with consequent reduction of BA pool and hepatic concentration. Treatment with the non-tumorigenic FGF19-M52 strongly protects Abcb4^-/- and Fxr^-/- mice from spontaneous hepatic fibrosis, cellular proliferation and HCC formation in terms of tumor number and size, with significant reduction of biochemical parameters of liver damage and reduced expression of several genes driving the proliferative and inflammatory hepatic scenario. Our data bona fide suggest the therapeutic potential of targeting the FXR-FGF19 axis to reduce hepatic BA synthesis in the control of BA-associated risk of fibrosis and hepatocarcinoma development.

Long-term Administration of Nuclear Bile Acid Receptor FXR Agonist Prevents Spontaneous Hepatocarcinogenesis in Abcb4-/- Mice

Altered bile acid (BA) signaling is associated with hepatotoxicity. The farnesoid X receptor (FXR) is a nuclear receptor that transcriptionally regulates BA homeostasis. Mice with FXR ablation present hepatocarcinoma (HCC) due to high toxic BA levels. Mice with Abcb4 ablation accumulate toxic BA within the bile ducts and present HCC. We have previously shown that intestinal specific activation of FXR by transgenic VP16-FXR chimera is able to reduce BA pool size and prevent HCC. Here we tested chemical FXR activation by administering for 15 months the dual FXR/ membrane G protein-coupled receptor (TGR5) agonist INT-767 (6α-ethyl-3α,7α,23-trihydroxy-24-nor-5β-cholan-23-sulphate) to Fxr-/- and Abcb4-/- mice. HCC number and size were significantly reduced by INT-767 administration. In contrast, no changes in HCC tumor number and size were observed in Fxr-/- mice fed with or without INT-767. Notably, INT-767 preserved the hepatic parenchyma, improved hepatic function and down-regulated pro-inflammatory cytokines. Moreover, in Abcb4-/- mice INT-767 prevented fibrosis by reducing collagen expression and deposition. Thus, long term activation of FXR is able to reduce BA pool, reprogram BA metabolism and prevent HCC. These data provide the impetus to address the bona fide therapeutic potential of FXR activation in disease with BA-associated development of HCC.

Promotion of classic neutral bile acids synthesis pathway is responsible for cholesterol-lowing effect of Si-miao-yong-an decoction: Application of LC-MS/MS method to determine 6 major bile acids in rat liver and plasma

Si-miao-yong-an decoction (SMYAD), a traditional Chinese medicine formula, significantly reduced plasma TC, LDL-c levels and increased HDL-c level in hyperlipidemia rats. Liver function test and tissue section examination indicated that SMYAD improved liver function and reduced fat accumulation in hyperlipidemia rat liver. A LC-MS/MS method was established and well validated to evaluate major bile acids derived from cholesterol metabolism through the classic neutral pathway and the alternative acidic pathway (cholic acid, chenodeoxycholic acid and their taurine and glycine conjugates) in liver and plasma. Increased total 6 bile acids concentrations in both liver and plasma were observed after oral administration of 12g/kg/d, 24g/kg/d and 36g/kg/d of SMYAD in a dose dependent manner which contributed to eliminate of cholesterol. Cholic acid, taurocholic acid and glycocholic acid act as the main products of bile acid classic neutral synthesis pathway and show sharp increase (p<0.01) after treatment of SMYAD at dosage of 24-36g/kg/d. For liver samples, taurocholic acid level act as the largest growth section, while in plasma samples, cholic acid act as the largest growth section after SMYAD treatment, compared with Model group. By contrast, the main products of alternative acidic pathway (chenodeoxycholic acid and its glycine and taurine conjugates) show no significant increase after treatment of SMYAD. In conclusion, the cholesterol lowing effect of SMYAD may be related with the accelerated transformation of cholesterol into bile acids through the classic neutral pathway.

Antiinflammatory effect of phytosterols in experimental murine colitis model: prevention, induction, remission study

Phytosterols, besides hypocholesterolemic effect, present anti-inflammatory properties. Little information is available about their efficacy in Inflammatory Bowel Disease (IBD). Therefore, we have evaluated the effect of a mixture of phytosterols on prevention/induction/remission in a murine experimental model of colitis. Phytosterols were administered x os before, during and after colitis induction with Dextran Sodium Sulfate (DSS) in mice. Disease Activity Index (DAI), colon length, histopathology score, 18F-FDG microPET, oxidative stress in the intestinal tissue (ileum and colon) and gallbladder ileum and colon spontaneous and carbachol (CCh) induced motility, plasma lipids and plasma, liver and biliary bile acids (BA) were evaluated. A similar longitudinal study was performed in a DSS colitis control group. Mice treated with DSS developed severe colitis as shown by DAI, colon length, histopathology score, 18F-FDG microPET, oxidative stress. Both spontaneous and induced ileal and colonic motility were severely disturbed. The same was observed with gallbladder. DSS colitis resulted in an increase in plasma cholesterol, and a modification of the BA pattern. Phytosterols feeding did not prevent colitis onset but significantly reduced the severity of the disease and improved clinical and histological remission. It had strong antioxidant effects, almost restored colon, ileal and gallbladder motility. Plasmatic levels of cholesterol were also reduced. DSS induced a modification in the BA pattern consistent with an increase in the intestinal BA deconjugating bacteria, prevented by phytosterols. Phytosterols seem a potential nutraceutical tool for gastrointestinal inflammatory diseases, combining metabolic systematic and local anti-inflammatory effects.

Key discoveries in bile acid chemistry and biology and their clinical applications: history of the last eight decades

During the last 80 years there have been extraordinary advances in our knowledge of the chemistry and biology of bile acids. We present here a brief history of the major achievements as we perceive them. Bernal, a physicist, determined the X-ray structure of cholesterol crystals, and his data together with the vast chemical studies of Wieland and Windaus enabled the correct structure of the steroid nucleus to be deduced. Today, C24 and C27 bile acids together with C27 bile alcohols constitute most of the bile acid "family". Patterns of bile acid hydroxylation and conjugation are summarized. Bile acid measurement encompasses the techniques of GC, HPLC, and MS, as well as enzymatic, bioluminescent, and competitive binding methods. The enterohepatic circulation of bile acids results from vectorial transport of bile acids by the ileal enterocyte and hepatocyte; the key transporters have been cloned. Bile acids are amphipathic, self-associate in solution, and form mixed micelles with polar lipids, phosphatidylcholine in bile, and fatty acids in intestinal content during triglyceride digestion. The rise and decline of dissolution of cholesterol gallstones by the ingestion of 3,7-dihydroxy bile acids is chronicled. Scientists from throughout the world have contributed to these achievements.

Curcuma longa L. as a therapeutic agent in intestinal motility disorders. 2: Safety profile in mouse

BACKGROUND

Curcuma extract exerts a myorelaxant effect on the mouse intestine. In view of a possible use of curcuma extract in motor functional disorders of the gastrointestinal tract, a safety profile study has been carried out in the mouse.

METHODS

Thirty mice were used to study the in vitro effect of curcuma on gallbladder, bladder, aorta and trachea smooth muscular layers and hearth inotropic and chronotropic activity. The myorelaxant effect on the intestine was also thoroughly investigated. Moreover, curcuma extract (200 mg/Kg/day) was orally administered to twenty mice over 28 days and serum liver and lipids parameters were evaluated. Serum, bile and liver bile acids qualitative and quantitative composition was were also studied.

RESULTS

In the intestine, curcuma extract appeared as a not competitive inhibitor through cholinergic, histaminergic and serotoninergic receptors and showed spasmolytic effect on K(+) induced contraction at the level of L type calcium channels. No side effect was observed on bladder, aorta, trachea and heart when we used a dose that is effective on the intestine. An increase in gallbladder tone and contraction was observed. Serum liver and lipids parameters were normal, while a slight increase in serum and liver bile acids concentration and a decrease in bile were observed.

CONCLUSIONS

Although these data are consistent with the safety of curcuma extract as far as its effect on the smooth muscular layers of different organs and on the heart, the mild cholestatic effect observed in absence of alteration of liver function tests must be further evaluated and the effective dose with minimal side effects considered.

Method development and validation of six bile acids for regulated bioanalysis: improving selectivity and sensitivity

BACKGROUND

Quantification of bile acids using LC-MS has previously been very challenging on triple quadrupole MS systems due to the absence of a primary fragment ion for unconjugated bile acids.

RESULTS

A LC-high-resolution/accurate mass MS method for the analysis of six bile acids (cholic acid, chenodeoxycholic acid, taurocholic acid, deoxycholic acid, lithocholic acid and ursodeoxycholic acid) was developed and successfully validated. The method includes a single extraction and a single injection with all analytes separated using target-selected ion monitoring (SIM) mode in two periods with a resolution of 70,000 and 140,000, respectively.

CONCLUSION

This is the first LC-high-resolution/accurate mass assay fully validated to quantify six bile acids for regulated bioanalysis.

Reduced biliary sterol output with no change in total faecal excretion in mice expressing a human apolipoprotein A-I variant

BACKGROUND/AIMS

Apolipoprotein (apo)A-I(M) (ilano), is a molecular variant of apoA-I(wild-type), associated with dramatically low HDL-cholesterol levels, but no increased risk for cardiovascular disease. In view of the present uncertainties on the role of apoA-I in liver cholesterol removal by way of bile acids and neutral sterols, and of the greater capacity of apoA-I(M) (ilano) to remove arterial cholesterol, biliary sterol metabolism was evaluated in transgenic mice expressing apoA-I(M) (ilano).

METHODS

ApoA-I(M) (ilano) mice were fed a high-cholesterol/high-fat diet, and compared with human apoA-I(wild-type) mice. Plasma lipid levels, hepatic bile flow and composition, hepatic and intestinal cholesterol and bile acid content, and faecal sterol content were measured. Moreover, the expression of hepatic ABCA1, SR-B1 and that of hepatic and intestinal genes involved in bile acid metabolism were evaluated.

RESULTS

The dietary treatment led to a strong elevation in HDL-cholesterol levels in A-I(M) (ilano) mice, associated with an increased expression of hepatic ABCA1. ApoA-I(M) (ilano) mice showed lower cholesterol output from the liver compared with apoA-I(wild-type) mice, in the absence of liver sterol accumulation. Faecal excretion of neutral sterols and bile acids was similar in the two mouse lines.

CONCLUSIONS

In spite of a different response to the dietary challenge, with an increased ABCA1 expression and a lower hepatic cholesterol output in apoA-I(M) (ilano) mice, the net sterol excretion is comparable in the two transgenic lines.

Beneficial effect of sulphate-bicarbonate-calcium water on gallstone risk and weight control

AIM: To investigate the effect of drinking sulphate-bicarbonate-calcium thermal water (TW) on risk factors for atherosclerosis and cholesterol gallstone disease.

METHODS: Postmenopausal women with functional dyspepsia and/or constipation underwent a 12 d cycle of thermal (n = 20) or tap (n = 20) water controlled drinking. Gallbladder fasting volume at ultrasound, blood vitamin E, oxysterols (7-β-hydroxycholesterol and 7-ketocholesterol), bile acid (BA), triglycerides, total/low density lipoprotein and high density lipoprotein cholesterol were measured at baseline and at the end of the study. Food consumption, stool frequency and body weight were recorded daily.

RESULTS: Blood lipids, oxysterols and vitamin E were not affected by either thermal or tap water consumption. Fasting gallbladder volume was significantly (P < 0.005) smaller at the end of the study than at baseline in the TW (15.7 ± 1.1 mL vs 20.1 ± 1.7 mL) but not in the tap water group (19.0 ± 1.4 mL vs 19.4 ± 1.5 mL). Total serum BA concentration was significantly (P < 0.05) higher at the end of the study than at baseline in the TW (5.83 ± 1.24 μmol vs 4.25 ± 1.00 μmol) but not in the tap water group (3.41 ± 0.46 μmol vs 2.91 ± 0.56 μmol). The increased BA concentration after TW consumption was mainly accounted for by glycochenodeoxycholic acid. The number of pasta (P < 0.001), meat (P < 0.001) and vegetable (P < 0.005) portions consumed during the study and of bowel movements per day (P < 0.05) were significantly higher in the TW than in the tap water group. Body weight did not change at the end of the study as compared to baseline in both groups.

CONCLUSION: Sulphate-bicarbonate-calcium water consumption has a positive effect on lithogenic risk and intestinal transit and allows maintenance of a stable body weight despite a high food intake.

Dual farnesoid X receptor/TGR5 agonist INT-767 reduces liver injury in the Mdr2-/- (Abcb4-/-) mouse cholangiopathy model by promoting biliary HCO⁻₃ output

Chronic cholangiopathies have limited therapeutic options and represent an important indication for liver transplantation. The nuclear farnesoid X receptor (FXR) and the membrane G protein-coupled receptor, TGR5, regulate bile acid (BA) homeostasis and inflammation. Therefore, we hypothesized that activation of FXR and/or TGR5 could ameliorate liver injury in Mdr2(-/-) (Abcb4(-/-)) mice, a model of chronic cholangiopathy. Hepatic inflammation, fibrosis, as well as bile secretion and key genes of BA homeostasis were addressed in Mdr2(-/-) mice fed either a chow diet or a diet supplemented with the FXR agonist, INT-747, the TGR5 agonist, INT-777, or the dual FXR/TGR5 agonist, INT-767 (0.03% w/w). Only the dual FXR/TGR5 agonist, INT-767, significantly improved serum liver enzymes, hepatic inflammation, and biliary fibrosis in Mdr2(-/-) mice, whereas INT-747 and INT-777 had no hepatoprotective effects. In line with this, INT-767 significantly induced bile flow and biliary HCO 3- output, as well as gene expression of carbonic anhydrase 14, an important enzyme able to enhance HCO 3- transport, in an Fxr-dependent manner. In addition, INT-767 dramatically reduced bile acid synthesis via the induction of ileal Fgf15 and hepatic Shp gene expression, thus resulting in significantly reduced biliary bile acid output in Mdr2(-/-) mice.

CONCLUSION

This study shows that FXR activation improves liver injury in a mouse model of chronic cholangiopathy by reduction of biliary BA output and promotion of HCO 3--rich bile secretion.

Engineered three-dimensional liver mimics recapitulate critical rat-specific bile acid pathways

A critical hepatic function is the maintenance of optimal bile acid (BA) compositions to achieve cholesterol homeostasis. BAs are rarely quantified to assess hepatic phenotype in vitro since existing analytical techniques have inadequate resolution. We report a detailed investigation into the biosynthesis and homeostasis of eight primary rat BAs in conventional in vitro hepatocyte cultures and in an engineered liver mimic. The three-dimensional (3D) liver mimic was assembled with layers of primary rat hepatocytes and liver sinusoidal endothelial cells. A high-pressure liquid chromatography and mass spectrometry technique was developed with a detection limit of 1 ng/mL for each BA, which is significantly lower than previous approaches. Over a 2-week culture, only 3D liver mimics exhibited the ratio of conjugated cholic acid to chenodeoxycholic acid that has been observed in vivo. This ratio, an important marker of BA homeostasis, was significantly higher in stable collagen sandwich cultures indicating significant deviation from physiological behavior. The biosynthesis of tauro-β-muricholic acid, a key primary rat BA, doubled only in the engineered liver mimics while decreasing in the other systems. These trends demonstrate that the 3D liver mimics provide a unique platform to study hepatic metabolism.

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.

Rapid quantification of bile acids and their conjugates in serum by liquid chromatography-tandem mass spectrometry

Beside their role as lipid solubilizers, bile acids (BAs) are increasingly appreciated as signaling factors. As ligands of G-protein coupled receptors and nuclear hormone receptors BAs control their own metabolism and act on lipid and energy metabolism. To study BA function in detail, it is necessary to use methods for their quantification covering the structural diversity of this group. Here we present a simple, sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the analysis of bile acid profiles in human plasma/serum. Protein precipitation was performed in the presence of stable-isotope labeled internal standards. In contrast to previous LC-MS/MS methods, we used a reversed-phase C18 column with 1.8microm particles and a gradient elution at basic pH. This allows base line separation of 18 bile acid species (free and conjugated) within 6.5min run time and a high sensitivity in negative ion mode with limits of detection below 10nmol/L. Quantification was achieved by standard addition and calibration lines were linear in the tested range up to 28micromol/L. Validation was performed according to FDA guidelines and overall imprecision was below 11% CV for all species. The developed LC-MS/MS method for bile acid quantification is characterized by simple sample preparation, baseline separation of isobaric species, a short analysis time and provides a valuable tool for both, routine diagnostics and the evaluation of BAs as diagnostic biomarkers in large clinical studies.

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.

Spectrofluorimetric determination of bile acid using a europium-doxycycline probe

A new spectrofluorimetric method was developed for the determination of trace amounts of bile acid (BA). Using europium ion (Eu(3+))-doxycycline (DC) as a fluorescent probe, in a buffer solution of pH=7.0, BA can remarkably reduce the fluorescence intensity of the DC-Eu(3+) complex at lambda=612 nm; the reduced fluorescence intensity of the Eu(3+) is proportional to the concentration of BA. Optimum conditions for the determination of BA were also investigated. The linear range and detection limit for the determination of BA were 5.0 x 10(-8) mol/L to 5.5 x 10(-7) mol/L and 1.1 x 10(-8) mol/L, respectively. This method is practical and relatively free of interference from coexisting substances, and can be successfully applied to assess BA in serum samples.

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.

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.

Ursodeoxycholic acid improves gastrointestinal motility defects in gallstone patients

AIM: To simultaneously evaluate the presence of defects in gallbladder and gastric emptying, as well as in intestinal transit in gallstone patients (GS) and the effect of chronic ursodeoxycholic acid (UDCA) administration on these parameters and on serum bile acids and clinical outcome in GS and controls (CTR).

METHODS: After a standard liquid test meal, gallbla-dder and gastric emptying (by ultrasound), oroileal transit time (OITT) (by an immunoenzymatic technique) and serum bile acids (by HPLC) were evaluated before and after 3 mo of UDCA (12 mg/kg bw/d) or placebo administration in 10 symptomatic GS and 10 matched healthy CTR.

RESULTS: OITT was longer in GS than in CTR (P < 0.0001); UDCA significantly reduced OITT in GS (P < 0.0001), but not in CTR. GS had longer gastric half-emptying time (t_1/2) than CTR (P < 0.0044) at baseline; after UDCA, t_1/2 significantly decreased (P < 0.006) in GS but not in CTR. Placebo administration had no effect on gastric emptying and intestinal transit in both GS and CTR.

CONCLUSION: The gallstone patient has simultaneous multiple impairments of gallbladder and gastric emptying, as well as of intestinal transit. UDCA administration restores these defects in GS, without any effect in CTR. These results confirm the pathogenetic role of gastrointestinal motility in gallstone disease and suggest an additional mechanism of action for UDCA in reducing bile cholesterol supersaturation.

A direct method for the separation and quantification of bile acid acyl glycosides by high-performance liquid chromatography with an evaporative light scattering detector

A direct method for the separation and quantification of a series of bile acid acyl glycosides using high-performance liquid chromatography coupled to an evaporative light scattering detector (HPLC-ELSD) is described. Complete separation of each of 15 bile acid acyl 24-alpha-glucosides and their 24-beta-anomers and 24-beta-galactosides was achieved by the stepwise gradient elution mode on a C18 column using a mixture of acetonitrile-methanol (8:2, v/v) and 1% aqueous acetic acid as the mobile phase. 24-beta-Galactosides were always eluted faster than the corresponding 24-beta-glucosides, which eluted after the corresponding 24-alpha-anomers. Calibration curves of different 24-beta-galactosides were linear over a range of 0.2-40 nmol of injected amount and the detection limits (S/N > 3) were from 0.08 to 0.1 nmol. The present HPLC-ELSD method may provide an insight into the separation and quantification of the biologically interesting neutral bile acids.

Tandem mass spectrometry in the study of fatty acids, bile acids, and steroids

Over the last 50 years, the mass spectrometry of lipids has evolved to become one of the most mature techniques in biomolecule analysis. Many volatile and non-polar lipids are directly amenable to analysis by gas-chromatography-mass spectrometry (GC-MS), a technique that combines the unsurpassed separation properties of gas-chromatography with the sensitivity and selectivity of electron ionization mass spectrometry. Less volatile and/or thermally labile lipids can be analyzed by GC-MS, following appropriate sample derivatization. However, many complex lipids are not readily analyzed by GC-MS, and it is these molecules that are the subject of the current review. Since the early 1970s, there have been three outstanding developments in mass spectrometry that are particularly appropriate in lipid analysis; i.e., the introduction of (i) fast atom bombardment (FAB); (ii) electrospray (ES); and (iii) tandem mass spectrometry (MS/MS). The FAB and ES ionization techniques will be discussed in relation to MS/MS, and examples of their application in biochemical studies will be presented. The review will concentrate on the analysis of fatty acids, bile acids, steroid conjugates, and neutral steroids.

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.

Separation and quantitation of bile acids using an isocratic solvent system for high performance liquid chromatography coupled to an evaporative light scattering detector

We developed a quantitative method for the analysis of bile acids using a high performance liquid chromatograph coupled to an evaporative light scattering detector. An isocratic solvent system was used to resolve in a single run conjugated and unconjugated bile acid species relevant in human and rodent physiology. The detection of various bile acids was linear over a range of 0.08 to 10 nmol of injected molecules. The developed system is a convenient and cost-effective method for the routine analysis of a wide variety of bile acids.

Clinical applications of tandem mass spectrometry: ten years of diagnosis and screening for inherited metabolic diseases

This paper reviews the clinical applications of tandem mass spectrometry (MS-MS) in diagnosis and screening for inherited metabolic diseases in the last 10 years. The broad-spectrum of diseases covered, specificity, ease of sample preparation, and high throughput provided by the MS-MS technology has led to the development of multi-disorder newborn screening programs in many countries for amino acid disorders, organic acidemias, and fatty acid oxidation defects. Issues related to sample acquisition, sample preparation, quantification of metabolites, and validation are discussed. Our current experience with the technique in screening is presented. The application of MS-MS in selective screening has revolutionized the field and made a major impact on the detection of certain disease classes such as the fatty acid oxidation defects. New specific and rapid MS-MS and LC-MS-MS methods for highly polar small molecules are supplementing or replacing some of the classical GC-MS methods for a multitude of metabolites and disorders. New exciting applications are appearing in fields of prenatal, postnatal, and even postmortem diagnosis. Examples for pitfalls in the technique are also presented.

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.

Application of evaporative light scattering detection to the characterization of combinatorial and parallel synthesis libraries for pharmaceutical drug discovery

The advent of combinatorial and parallel synthesis methodologies in drug discovery have necessitated the development of analytical techniques which permit high throughput quantitative analysis of mixtures of small organic molecules. High pressure liquid chromatography with evaporative light scattering detection has become the major tool for this task. In this article we briefly review the theory of evaporative light scattering detection and the design of commercial instruments, as well as discuss the operational constraints imposed by the exigency of analyzing en masse the product libraries generated by these new drug discovery methods. The application of evaporative light scattering detection to library analysis is illustrated using examples from our library synthesis program. Complemented by ultraviolet absorbance detection for purity assessment and mass spectrometry for product identification, evaporative light scattering detection is the only technique affording sufficient accuracy and sensitivity for high throughput library analysis.

A simple liquid-liquid extraction with hexane for low-picogram determination of drugs and their metabolites in plasma by high-performance liquid chromatography with positive ion electrospray tandem mass spectrometry

Four sensitive, specific and accurate methods, based on high-performance liquid chromatography (HPLC) with positive ion electrospray tandem mass spectrometry (MS/MS) coupled with liquid-Liquid extraction (LLE), have been developed and validated for the low-picogram determination of two drug candidates and a metabolite (compounds I-III) in human, monkey and rat plasma. In the LLE procedure, hexane or a mixture of hexane and methyl t-butyl ether was used to isolate these compounds from plasma of the different species after basification of each biological sample with sodium carbonate. The reconstituted extracts were then injected into a positive ion electrospray LC/MS/MS system for the quantitative analysis. The lower limit of quantitation of the methods ranged from 20 to 200 pg/mL. The use of hexane for the LLE proved to be simple, rapid and reproducible, and provided very clean extracts with little interference. The inter- and intra-day precision for the four methods was within 9%, and the accuracy was in the range 94-107%. The effect of pH on the isomerization of I (E-isomer) to its Z-isomer (II) showed that the rate of isomerization increased with decrease in pH and that there was no isomerization at pH >/=6.

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.

Analytical development of electrospray and nanoelectrospray mass spectrometry in combination with liquid chromatography for the characterization of proteins

Mass spectrometry has significantly extended its applicability in the area of characterization of protein structures. Electrospray ionization enables on-line coupling with liquid chromatography which has become a powerful tool for the characterization of peptide and protein mixtures. The most recent development of a nanoelectrospray source, using capillary forces for a particularly mild analyte transport and ionization into the mass spectrometer, opens a wide field for applications to protein structure analysis. In this paper, the analytical development of liquid chromatography-electrospray ionization mass spectrometry and nano-electrospray ionization mass spectrometry, adapted to an electrospray ionization quadrupole mass spectrometer and its application to the characterization of noncovalent protein complexes are described.

Taurohyodeoxycholic acid protects against taurochenodeoxycholic acid-induced cholestasis in the rat

The prevention of the hepatotoxic effects produced by intravenous infusion of taurochenodeoxycholic acid (TCDCA) by coinfusion with taurohyodeoxycholic acid (THDCA) was evaluated in bile fistula rats; the hepatoprotective effects of the latter were also compared with those of tauroursodeoxycholic acid (TUDCA). Rats infused with TCDCA at a dose of 8 micromol/min/kg showed reduced bile flow and calcium secretion, as well as increased biliary release of alkaline phosphatase (AP) and lactate dehydrogenase (LDH). This was associated with a very low biliary secretion rate of TCDCA (approximately 1 micromol/min/kg). Simultaneous infusion of THDCA or TUDCA at the same dose preserved bile flow and almost totally abolished the pathological leakage of the two enzymes into bile. The effect was slightly more potent for THDCA. The maximum secretion rate of TCDCA increased to the highest value (8 micromol/min/kg) when coinfused with either of the two hepatoprotective bile acids (BA), which were efficiently and completely secreted in the bile, without metabolism. Calcium output was also restored and phospholipid (PL) secretion increased with respect to the control saline infusion. This increase was higher in the THDCA study. These data show that THDCA is highly effective in the prevention of hepatotoxicity induced by intravenous infusion of TCDCA by facilitating its biliary secretion and reducing its hepatic residence time; this was associated with selective stimulation of PL biliary secretion.

Comparative analysis of conjugated bile acids in human serum using high-performance liquid chromatography and capillary electrophoresis

This paper describes the analysis of conjugated bile acids in human serum using reversed-phase high-performance liquid chromatography (HPLC) and micellar electrokinetic capillary electrophoresis (CE). Samples of healthy subjects and patients with different hepatic diseases were pretreated with a simple preparation procedure using a solid-phase extraction technique. The optimal analytical conditions of both chromatographic methods were investigated for the convenience and reliability for routine analysis. Both HPLC and CE methods were found to be reliable and compatible. The recoveries of nine bile acid conjugates using both methods were generally >85% and reproducibility >90%. The day-to-day variation of retention time was <5% for HPLC, while the variation of migration time for CE was <3%. Although the detection limit of the HPLC method (1 nmol/ml) was five times more sensitive than that of the CE method, the CE method was considered to be more time and cost effective.

Quantitative determination of BMS-186716, a thiol compound, in rat plasma by high-performance liquid chromatography-positive ion electrospray mass spectrometry after hydrolysis of the methyl acrylate adduct by the native esterases

During method development in support of non-clinical studies in animal models, BMS-186716 was found to be extremely unstable in blood and plasma. Stabilization of the compound was achieved by reacting the compound with methyl acrylate (MA) in blood, from which the plasma was then prepared. While the resulting BMS-186716-MA adduct was found to be stable in dog plasma, and hence it was used as the basis for the method developed for analysis of dog plasma samples, the BMS-186716-MA adduct was found to be unstable in rat plasma as it was readily hydrolyzed to BMS-186716-acrylic acid (AA) by native esterases found in rat plasma. Although the finding of the instability of BMS-186716-MA in rat plasma was not the result of prospective planning, we were able to successfully develop a quantitative bioanalytical method using BMS-186716-AA as the analyte instead of the originally planned BMS-186716-MA analyte. The standard and quality-control (QC) samples were prepared by spiking blank plasma with BMS-186716-MA, and then allowing them to stand at room temperature for 1 h to convert BMS-186716-MA to BMS-186716-AA. After adding the internal standard BMS-188035-AA, each sample was acidified with HCl and then extracted with methyl tert.-butyl ether. The reconstituted extract was injected into a HPLC-electrospray ionization mass spectrometric system for detection by positive ion electrospray ionization. A lower limit of quantitation (LLQ) of 5 ng/ml was achieved, using 0.1 ml plasma and a standard curve range of 5-5000 ng/ml.

Highly sensitive method for the determination of tamsulosin hydrochloride in human plasma dialysate, plasma and urine by high-performance liquid chromatography-electrospray tandem mass spectrometry

A highly sensitive method for the determination of tamsulosin hydrochloride, a structurally new type of sulphamoile derivative, in human plasma dialysate, plasma and urine has been developed by using liquid chromatography-electrospray tandem mass spectrometry (LC-MS-MS). Plasma dialysate, plasma and urine samples were extracted by brief liquid-phase extraction and analyzed using an HPLC system coupled to a mass spectrometer via an electrospray ionization interface. Selected reaction monitoring was used for the detection of tamsulosin and its internal standard. This method was validated in the concentration range 10-1000 pg/ml in plasma dialysate, 0.5-50 ng/ml in plasma, and 1-100 ng/ml in urine with sufficient specificity, accuracy and precision. The in vivo protein binding study demonstrated that the unbound tamsulosin in human plasma obtained by the equilibrium dialysis after 0.4-mg oral dosing was measurable. In addition, the percentage of unbound tamsulosin in an in vitro study (0.71-0.91%) obtained by using spiked 14C-labelled tamsulosin was slightly larger than that of the in vivo study (0.68-0.86%), indicating that the unbound concentration calculated by the product of the plasma concentration and the in vitro unbound fraction (fu) was unfavorably overestimated. These results suggest that the combination of LC-MS-MS and equilibrium dialysis method has enough sensitivity to determine the unbound concentration in clinical use and gives the concentration more exactly than the in vitro fu.

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.

Quantitative determination of BMS186716, a thiol compound, in dog plasma by high-performance liquid chromatography-positive ion electrospray mass spectrometry after formation of the methyl acrylate adduct

As it is extremely unstable in blood, the thiol compound BMS186716 was stabilized by the addition of methyl acrylate (MA) to blood samples. The blood samples were then kept in ice for 10-15 min for completion of the Michael addition reaction to occur between the thiol group of BMS186716 and MA, after which the plasma was separated by centrifugation under refrigeration. For sample analysis, the standard and quality control samples were prepared by spiking blank plasma with the BMS186716-MA adduct. After addition of the internal standard, BMS 188035-MA, each sample was acidified with HCI and then extracted with methyl tert.-butyl ether. Each reconstituted extract was injected into a high-performance liquid chromatography-positive ion electrospray ionization mass spectrometric system. The electrospray condition was chosen to enhance the [M+NH4]+ signal at the expense of the [M+H]+ signal. Monitoring the [M+NH4]+ signal, a lower limit of quantitation of 2.5 ng/ml was achieved, with 0.5 ml plasma. We have thus shown that a sulfhydryl compound (BMS186716) in blood can successfully be stabilized by reacting it with MA and that the adduct produced is adequately stable in blood and plasma to allow the development of a rugged quantitative bioanalytical method.

Quantitative determination of a nonpeptide antithrombotic in dog plasma by microbore high-performance liquid chromatography-tandem mass spectrometry utilizing pneumatically assisted electrospray ionization

A method has been developed and is described for the quantitative determination of a nonpeptide antithrombotic in dog plasma. The assay employs reversed phase microbore high-performance liquid chromatography in conjunction with tandem mass spectrometry utilizing pneumatically assisted electrospray ionization. The analyte and internal standard are isolated from the plasma matrix by solid-phase extraction. The mass spectrometer is operated in the positive ion multiple reaction monitoring mode and is set to detect the presence of a precursor-product ion pair for both the analyte and internal standard to generate product ion chromatograms for both species. The analyte is quantified by using weighted least-squares regression of the peak height ratio of drug:internal standard. The method provides linear response for plasma concentrations ranging from 5 ng/mL (25 pg on-column) to 2500 ng/mL. Statistical evaluation and examples of authentic sample assays are also presented.