Simultaneous determination of bile acids in rat bile and serum by high-performance liquid chromatography

Comparative profiling of serum, urine, and feces bile acids in humans, rats, and mice

Bile acids (BAs) play important pathophysiological roles in both humans and mammalian animals. Laboratory rats and mice are widely used animal models for assessing pharmacological effects and their underlying molecular mechanisms. However, substantial physiological differences exist in BA composition between humans and murine rodents. Here, we comprehensively compare BA profiles, including primary and secondary BAs, along with their amino acid conjugates, and sulfated metabolites in serum, urine, and feces between humans and two murine rodents. We further analyze the capabilities in gut microbial transform BAs among three species and compare sex-dependent variations within each species. As a result, BAs undergo amidation predominately with glycine in humans and taurine in mice but are primarily unamidated in rats. BA sulfation is a unique characteristic in humans, whereas rats and mice primarily perform multiple hydroxylations during BA synthesis and metabolism. For gut microbial transformed BA capabilities, humans are comparable to those of rats, stronger than those of mice in deconjugation and 7α-dehydroxylation, while humans are weak than those of rats or mice in oxidation and epimerization. Such differences enhance our understanding of the divergent experimental outcomes observed in humans and murine rodents, necessitating caution when translating findings from these rodent species to humans.

Comparative electrophysiological analysis of the bile acid-sensitive ion channel (BASIC) from different species suggests similar physiological functions

Despite the identification of cholangiocytes in the liver and unipolar brush cells in the cerebellum as sites of expression, the physiological function of the bile acid-sensitive ion channel (BASIC) remains unknown. Rat BASIC (rBASIC) and mouse BASIC (mBASIC) share 97% of their amino acid sequence but show strikingly different biophysical properties. rBASIC is inactive at rest while mBASIC is constitutively active, when expressed in Xenopus oocytes. This conundrum rendered the identification of the physiological function even more difficult. In this study, we investigated the electrophysiological and pharmacological properties of BASIC from rat, mouse, and human in Hek293 cells using the patch clamp technique. Surprisingly, in Hek293 cells, rBASIC and mBASIC showed almost completely identical properties. Both are blocked by extracellular Ca²⁺ and thus are inactive at rest; both are selective for Na⁺, show similar affinities for extracellular Ca²⁺, were inhibited by diminazene, and activated by various bile acids. This is in contrast to previous results derived from Xenopus oocytes as expression system and suggests that the cell type is important for shaping the biophysical properties of BASIC. Furthermore, we compared hBASIC with rBASIC and mBASIC and observed similar properties between these channels with one exception: the bile acid sensitivity profile of hBASIC is different from rBASIC and mBASIC; hBASIC is more sensitive to bile acids which are abundant in human bile but not in rodent bile. Taken together, these results suggest similar physiological roles for BASIC in different species.

Review article: therapeutic bile acids and the risks for hepatotoxicity

BACKGROUND

Bile acids play important roles in cholesterol metabolism and signal through farnesoid X receptor and G protein-coupled receptors. Given their importance in liver biology, bile acid therapy enables therapeutic applications beyond the treatment of cholestatic liver disease. However, predicting hepatotoxicity of bile acids in humans is obscured due to inconsistent extrapolations of animal data to humans.

AIM

To review the evidence that could explain discordant bile acids hepatotoxicity observed in humans and animals.

METHOD

Literature search was conducted in PubMed using keywords "bile acid," "transporter," "hepatotoxicity," "clinical study," "animal study," "species difference," "mechanism," "genetic disorder." Relevant articles were selected for review.

RESULTS

Clinically significant hepatotoxicity was reported in response to certain bile acids, namely chenodeoxycholic acid, which was given a boxed warning for potential hepatotoxicity. The chemical structure, specifically the number and orientation of hydroxyl groups, significantly affects their hydrophobicity, an important factor in bile acid toxicity. Experimental studies show that hydrophobic bile acids can lead to liver injury through various mechanisms, such as death receptor signalling, mitochondrial dysfunction and inflammation. Although animal studies play a central role in investigating bile acid safety, there are considerable differences in bile acid composition, metabolism and hepatobiliary disposition across species. This does not allow appropriate safety inference, especially for predicting hepatotoxicity in humans. Exploring evidences stemming from inborn errors, genetic models of disease and toxicology studies further improves an understanding of bile acid hepatotoxicity.

CONCLUSION

Species differences should be considered in the development of bile acid related therapeutics. Although the mechanism of bile acid hepatotoxicity is still not fully understood, continued mechanistic studies will deepen our understanding.

Cysteine sulfinic acid decarboxylase regulation: A role for farnesoid X receptor and small heterodimer partner in murine hepatic taurine metabolism

AIM

Bile acid synthesis is regulated by nuclear receptors including farnesoid X receptor (FXR) and small heterodimer partner (SHP), and by fibroblast growth factor 15/19 (FGF15/19). We hypothesized that hepatic cysteine sulfinic acid decarboxylase (CSAD) (a key enzyme in taurine synthesis) is regulated by bile acids (BA). The aim of this study was to investigate CSAD regulation by BA dependent regulatory mechanisms.

METHODS

Mice were fed a control diet or a diet supplemented with either 0.5% cholate or 2% cholestyramine. To study BA dependent pathways, we utilized GW4064 (FXR agonist), FGF19 or T-0901317 (liver X receptor [LXR] agonist) and Shp-/- mice. Tissue mRNA was determined by quantitative reverse transcription polymerase chain reaction. Amino acids were measured by high-performance liquid chromatography.

RESULTS

Mice supplemented with dietary cholate exhibited reduced hepatic CSAD mRNA while those receiving cholestyramine exhibited increased mRNA. Activation of FXR suppressed CSAD mRNA expression whereas CSAD expression was increased in Shp-/- mice. Hepatic hypotaurine concentration (the product of CSAD) was higher in Shp-/- mice with a corresponding increase in serum taurine conjugated BA. FGF19 administration suppressed hepatic cholesterol 7-α-hydroxylase (CYP7A1) mRNA but did not change CSAD mRNA expression. LXR activation induced CYP7A1 mRNA yet failed to induce CSAD mRNA expression.

CONCLUSION

BA regulate CSAD mRNA expression in a feedback fashion via mechanisms involving SHP and FXR but not FGF15/19 or LXR. These findings implicate BA as regulators of CSAD mRNA via mechanisms shared with CYP7A1.

Correlation between postprandial bile acids and body fat mass in healthy normal-weight subjects

BACKGROUND

Bile acids (BAs) play important roles in glucose regulation and energy homeostasis via G protein-coupled receptors, such as enteroendocrine L cell TGR5. The aim of the present study was to investigate the relationship between postprandial BA levels and body composition after ingestion of a standard test meal.

METHODS

Eleven healthy subjects of normal weight (body-mass index, 22.0 ± 1.6 kg/m(2) [mean ± SD]), ingested a 400-kcal test meal, and blood samples were obtained from them before ingestion and every 30 min for 120 min after ingestion. The BA fractions were measured with high-performance liquid chromatography. To evaluate body composition, body impedance analysis was performed 1h before ingestion of the test meal.

RESULTS

Concentrations of both total BA and total glycine-conjugated BA (GCBA) at 30, 60, 90, and 120 min after test-meal ingestion were significantly higher than those at baseline. The body-mass index was correlated with total GCBA at baseline. Moreover, body fat mass was correlated with total GCBA at 30 min (r=-0.688, P=0.019) and 60 min (r=-0.642, P=0.033) and with total BA at 30 min (r=-0.688, P=0.019) and 60 min (r=-0.642, P=0.033).

CONCLUSION

The postprandial BA response is inversely related with body fat mass in healthy subjects of normal weight.

Vitamin D and energy homeostasis: of mice and men

The vitamin D endocrine system has many extraskeletal targets, including adipose tissue. 1,25-Dihydroxyvitamin D₃, the active form of vitamin D, not only increases adipogenesis and the expression of typical adipocyte genes but also decreases the expression of uncoupling proteins. Mice with disrupted vitamin D action--owing to gene deletion of the nuclear receptor vitamin D receptor (Vdr) or the gene encoding 1α-hydroxylase (Cyp27b1)--lose fat mass over time owing to an increase in energy expenditure, whereas mice with increased Vdr-mediated signalling in adipose tissue become obese. The resistance to diet-induced obesity in mice with disrupted Vdr signalling is caused at least partially by increased expression of uncoupling proteins in white adipose tissue. However, the bile acid pool is also increased in these animals, and bile acids are known to be potent inducers of energy expenditure through activation of several nuclear receptors, including Vdr, and G-protein-coupled receptors, such as GPBAR1 (also known as TGR5). By contrast, in humans, obesity is strongly associated with poor vitamin D status. A causal link has not been firmly proven, but most intervention studies have failed to demonstrate a beneficial effect of vitamin D supplementation on body weight. The reasons for the major discrepancy between mouse and human data are unclear, but understanding the link between vitamin D status and energy homeostasis could potentially be very important for the human epidemic of obesity and the metabolic syndrome.

Bile acids increase the activity of the epithelial Na+ channel

The epithelial Na(+) channel (ENaC) is a key regulator of Na(+) absorption in various epithelia including the distal nephron and the distal colon. ENaC is a constitutively active channel, but its activity is modulated by a number of mechanisms. These include proteolytic activation, ubiquitination and cell surface expression, phosphorylation, intracellular Na(+) concentration, and shear stress. ENaC is related to the bile acid-sensitive ion channel (BASIC), a channel that is expressed in the epithelial cells of bile ducts. BASIC is activated by millimolar concentrations of extracellular bile acids. Bile acids are synthesized by the liver and secreted into the duodenum to aid lipolysis. A large fraction of the secreted bile acids is absorbed by the ileum and recirculated into the liver, but a small fraction passes the colon and is excreted. Bile acids can influence the ion transport processes in the intestinal tract including the colon. In this study, we show that various bile acids present in rat bile potently and reversibly increase the activity of rat ENaC expressed in Xenopus oocytes, suggesting that bile acids are natural modulators of ENaC activity.

Bile salts and their importance for drug absorption

Bile salts are present in the intestines of humans as well as the animals used during the development of pharmaceutical products. This review provides a short introduction into the physical chemical properties of bile salts, a description of the bile concentration and composition of bile in different animal species and an overview of the literature investigating the influence of bile salts on the in vivo performance of different compounds and drug formulations. Generally, there is a positive effect on bioavailability when bile is present in the gastro-intestinal tract, independent of the formulation systems, e.g. suspensions, solutions, cyclodextrin complexes or lipid based formulations, but a few exceptions have also been reported.

Bile acid binding resin improves metabolic control through the induction of energy expenditure

BACKGROUND

Besides well-established roles of bile acids (BA) in dietary lipid absorption and cholesterol homeostasis, it has recently become clear that BA is also a biological signaling molecule. We have shown that strategies aimed at activating TGR5 by increasing the BA pool size with BA administration may constitute a significant therapeutic advance to combat the metabolic syndrome and suggest that such strategies are worth testing in a clinical setting. Bile acid binding resin (BABR) is known not only to reduce serum cholesterol levels but also to improve glucose tolerance and insulin resistance in animal models and humans. However, the mechanisms by which BABR affects glucose homeostasis have not been established. We investigated how BABR affects glycemic control in diet-induced obesity models.

METHODS AND FINDINGS

We evaluated the metabolic effect of BABR by administrating colestimide to animal models for the metabolic syndrome. Administration of BABR increased energy expenditure, translating into significant weight reduction and insulin sensitization. The metabolic effects of BABR coincide with activation of cholesterol and BA synthesis in liver and thermogenesis in brown adipose tissue. Interestingly, these effects of BABR occur despite normal food intake and triglyceride absorption. Administration of BABR and BA had similar effects on BA composition and thermogenesis, suggesting that they both are mediated via TGR5 activation.

CONCLUSION

Our data hence suggest that BABR could be useful for the management of the impaired glucose tolerance of the metabolic syndrome, since they not only lower cholesterol levels, but also reduce obesity and improve insulin resistance.

Bile acid binding resin improves metabolic control through the induction of energy expenditure

BACKGROUND

Besides well-established roles of bile acids (BA) in dietary lipid absorption and cholesterol homeostasis, it has recently become clear that BA is also a biological signaling molecule. We have shown that strategies aimed at activating TGR5 by increasing the BA pool size with BA administration may constitute a significant therapeutic advance to combat the metabolic syndrome and suggest that such strategies are worth testing in a clinical setting. Bile acid binding resin (BABR) is known not only to reduce serum cholesterol levels but also to improve glucose tolerance and insulin resistance in animal models and humans. However, the mechanisms by which BABR affects glucose homeostasis have not been established. We investigated how BABR affects glycemic control in diet-induced obesity models.

METHODS AND FINDINGS

We evaluated the metabolic effect of BABR by administrating colestimide to animal models for the metabolic syndrome. Administration of BABR increased energy expenditure, translating into significant weight reduction and insulin sensitization. The metabolic effects of BABR coincide with activation of cholesterol and BA synthesis in liver and thermogenesis in brown adipose tissue. Interestingly, these effects of BABR occur despite normal food intake and triglyceride absorption. Administration of BABR and BA had similar effects on BA composition and thermogenesis, suggesting that they both are mediated via TGR5 activation.

CONCLUSION

Our data hence suggest that BABR could be useful for the management of the impaired glucose tolerance of the metabolic syndrome, since they not only lower cholesterol levels, but also reduce obesity and improve insulin resistance.

BASIC--a bile acid-sensitive ion channel highly expressed in bile ducts

Brain liver intestine Na+ channel (BLINaC) is an ion channel of the DEG/ENaC gene family of unknown function. BLINaC from rats (rBLINaC) and humans (INaC) is inactive at rest, and its mode of activation has remained unclear. Here, we show that the BLINaC protein localizes to cholangiocytes, epithelial cells that line bile ducts. Moreover, we provide evidence that rBLINaC and INaC are robustly activated by bile acids, in particular chenodeoxycholic acid and hyodeoxycholic acid (EC50=2.1±0.05 mM). Thus, BLINaC appears to be an epithelial cation channel of bile ducts sensitive to physiological concentrations of bile acids. BLINaC is related to acid-sensing ion channels (ASICs) and to the epithelial Na+ channel (ENaC) and shares ligand activation with ASICs and epithelial localization with ENaC. Therefore, based on the close homology of BLINaC to ASICs and its activation by bile acids, we propose to rename BLINaC bile acid-sensitive ion channel (BASIC).

Effects of bile-acid-binding resin (colestimide) on blood glucose and visceral fat in Japanese patients with type 2 diabetes mellitus and hypercholesterolemia: an open-label, randomized, case-control, crossover study

OBJECTIVE

The objective was to examine the effects of colestimide on blood glucose, visceral fat, adipocytokines, and bile acid conjugate fractions in Japanese patients.

METHODS

This study was an open-label, randomized, case-control, crossover study of colestimide 3 g/day in 40 Japanese patients with type 2 diabetes mellitus (T2D) and hypercholesterolemia. Patients were assigned to the colestimide group in which pravastatin and colestimide were administered orally and to the statin group in which pravastatin alone was administered orally. The principal outcome measures were serum lipid levels, fasting plasma glucose level in the early morning, hemoglobin A1c (HbA(1c)), visceral fat area (VFA), and serum 1,5-anhydroglucitol (1,5-AG) level.

RESULTS

Serum low-density lipoprotein cholesterol levels significantly decreased from 113±38 mg/dl at baseline to 90±20 mg/dl (P=.009) at week 12 of colestimide administration. HbA(1c) significantly decreased from 7.4%±0.9% at baseline to 6.9%±0.9% (P=.001) at week 12 of colestimide administration. Serum 1,5-AG levels increased from 9.4±10.1 μg/ml to 12.4±9.5 μg/ml (P=.05) at week 12 of colestimide administration. The statin group showed no significant changes in lipids and 1,5-AG. However, ΔVFA was inversely correlated with Δcholic acid, and multivariate analysis revealed that ΔVFA was a significant explanatory variable.

CONCLUSIONS

Colestimide holds promise not only for the treatment of hypercholesterolemia but also for the possible improvement of T2D and visceral fat obesity.

Identification of S-acyl glutathione conjugates of bile acids in human bile by means of LC/ESI-MS

Previous work from this laboratory has reported the biotransformation of bile acids (BA) into the thioester-linked glutathione (GSH) conjugates via the intermediary metabolites formed by BA:CoA ligase and shown that such GSH conjugates are excreted into the bile in healthy rats as well as rats dosed with lithocholic acid or ursodeoxycholic acid. To examine whether such novel BA-GSH conjugates are present in human bile, we determined the concentration of the GSH conjugates of the five BA that predominate in human bile. Bile was obtained from three infants (age 4, 10, and 13 months) and the BA-GSH conjugates quantified by means of liquid chromatography (LC)/electrospray ionization (ESI)-linear ion trap mass spectrometry (MS) in negative-ion scan mode, monitoring characteristic transitions of the analytes. By LC/ESI-MS, only primary BA were present in biliary BA, indicating that the dehydroxylating flora had not yet developed. GSH conjugates of chenodeoxycholic and lithocholic acid were present in concentrations ranging from 27 to 1120 pmol/ml, several orders of magnitude less than those of natural BA N-acylamidates. GSH conjugates were not present, however, in the ductal bile obtained from 10 adults (nine choledocholithiasis, one bile duct cancer). Our results indicate that BA-GSH conjugates are formed and excreted in human bile, at least in infants, although this novel mode of conjugation is a very minor pathway.

Dietary cholesterol reduces plasma triacylglycerol in apolipoprotein E-null mice: suppression of lipin-1 and -2 in the glycerol-3-phosphate pathway

Background

Cholesterol metabolism is tightly regulated by both cholesterol and its metabolites in the mammalian liver, but the regulatory mechanism of triacylglycerol (TG) synthesis remains to be elucidated. Lipin, which catalyzes the conversion of phosphatidate to diacylglycerol, is a key enzyme involved in de novo TG synthesis in the liver via the glycerol-3-phosphate (G3P) pathway. However, the regulatory mechanisms for the expression of lipin in the liver are not well understood.

Methodology/Principal Findings

Apolipoprotein E-knock out (apoE-KO) mice were fed a chow supplemented with 1.25% cholesterol (high-Chol diet). Cholesterol and bile acids were highly increased in the liver within a week. However, the amount of TG in very low-density lipoprotein (VLDL), but not in the liver, was reduced by 78%. The epididymal adipose tissue was almost eradicated in the long term. DNA microarray and real-time RT-PCR analyses revealed that the mRNA expression of all the genes in the G3P pathway in the liver was suppressed in the high-Chol diet apoE-KO mice. In particular, the mRNA and protein expression of lipin-1 and lipin-2 was markedly decreased, and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), which up-regulates the transcription of lipin-1, was also suppressed. In vitro analysis using HepG2 cells revealed that the protein expression of lipin-2 was suppressed by treatment with taurocholic acid.

Conclusions/Significance

These data using apoE-KO mice indicate that cholesterol and its metabolites are involved in regulating TG metabolism through a suppression of lipin-1 and lipin-2 in the liver. This research provides evidence for the mechanism of lipin expression in the liver.

Lowering bile acid pool size with a synthetic farnesoid X receptor (FXR) agonist induces obesity and diabetes through reduced energy expenditure

We evaluated the metabolic impact of farnesoid X receptor (FXR) activation by administering a synthetic FXR agonist (GW4064) to mice in which obesity was induced by a high fat diet. Administration of GW4064 accentuated body weight gain and glucose intolerance induced by the high fat diet and led to a pronounced worsening of the changes in liver and adipose tissue. Mechanistically, treatment with GW4064 decreased bile acid (BA) biosynthesis, BA pool size, and energy expenditure, whereas reconstitution of the BA pool in these GW4064-treated animals by BA administration dose-dependently reverted the metabolic abnormalities. Our data therefore suggest that activation of FXR with synthetic agonists is not useful for long term management of the metabolic syndrome, as it reduces the BA pool size and subsequently decreases energy expenditure, translating as weight gain and insulin resistance. In contrast, expansion of the BA pool size, which can be achieved by BA administration, could be an interesting strategy to manage the metabolic syndrome.

Activation of aldo-keto reductase family member 1B14 (AKR1B14) by bile acids: Activation mechanism and bile acid-binding site

Aldo-keto reductase (AKR) 1B14, a rat ortholog of mouse androgen-dependent vas deferens protein (AKR1B7), is involved in the synthesis of prostaglandin F(2α) and detoxification of 4-oxononenal formed by lipid peroxidation. The NADPH-linked reductase activity of AKR1B14 was activated by various bile acids. Although the activation was increased by decreasing pH from 9.0 to 6.0, the concentrations giving maximum stimulation (2- to 18-fold) were 0.2-6.0 μM for bile acids at pH 7.4. Kinetic analyses of the activation by glycochenodeoxycholic acid in the forward and reverse reactions, together with fluorescence changes and protection against 4-oxononenal-induced inactivation by bile acid, indicate that the bile acid binds to the enzyme and its coenzyme binary complex as a non-essential activator. The bile acid binding to AKR1B14 mainly accelerates the NADP(+) dissociation, the rate-limited step of the enzyme reaction. AKR1B7 was also activated by bile acids, but the activation was low and independent of pH. The mutagenesis of His269 and Leu267 of AKR1B14 into the corresponding residues (Arg and Pro, respectively) of AKR1B7 resulted in low and pH-independent activation by bile acids. The results, together with the docking of the bile acid in the recently determined crystal structure of AKR1B14, identify the bile acid-binding site of which His269 plays a key role in significant activation through its electrostatic interaction with the carboxyl group of bile acid, facilitating the release of NADP(+).

Identification of bile acid S-acyl glutathione conjugates in rat bile by liquid chromatography/electrospray ionization-linear ion trap mass spectrometry

Acyl-adenylates and acyl-CoA thioesters of bile acids (BAs) are reactive acyl-linked metabolites that have been shown to acylate the thiol group of glutathione (GSH); the reaction is catalyzed by glutathione S-transferase (GST) and the product is a thioester-linked BA-GSH conjugate. Such GSH conjugates are present in bile in lithocholic acid and ursodeoxycholic acid dosed-rats. To determine whether such novel BA-GSH conjugates are present in the bile of normal rats, we first synthesized the GSH conjugates of the major and minor biliary BAs of the rat and defined their MS and proton NMR properties. We then analyzed the BA-GSH composition in the bile of anesthetized biliary fistula rats by means of liquid chromatographic separation and electrospray ionization-linear ion trap mass spectrometric detection in negative- and positive-ion scan modes, monitoring characteristic transitions of the analytes. GSH conjugates of cholic, ω-muricholic, hyodeoxycholic, deoxycholic, 12-oxolithocholic, and lithocholic acids were present with concentrations in the range of 1.4-2.8 nmol/ml, some four orders of magnitude less than those of natural BA N-acyl amidates. Our results indicate that BA-GSH conjugates are formed and excreted in bile in the healthy rat, although this novel mode of BA conjugation is a very minor pathway.

Combined deletion of Fxr and Shp in mice induces Cyp17a1 and results in juvenile onset cholestasis

Bile acid homeostasis is tightly regulated via a feedback loop operated by the nuclear receptors farnesoid X receptor (FXR) and small heterodimer partner (SHP). Contrary to current models, which place FXR upstream of SHP in a linear regulatory pathway, here we show that the phenotypic consequences in mice of the combined loss of both receptors are much more severe than the relatively modest impact of the loss of either Fxr or Shp alone. Fxr-/-Shp-/- mice exhibited cholestasis and liver injury as early as 3 weeks of age, and this was linked to the dysregulation of bile acid homeostatic genes, particularly cytochrome P450, family 7, subfamily a, polypeptide 1 (Cyp7a1). In addition, double-knockout mice showed misregulation of genes in the C21 steroid biosynthesis pathway, with strong induction of cytochrome P450, family 17, subfamily a, polypeptide 1 (Cyp17a1), resulting in elevated serum levels of its enzymatic product 17-hydroxyprogesterone (17-OHP). Treatment of WT mice with 17-OHP was sufficient to induce liver injury that reproduced many of the histopathological features observed in the double-knockout mice. Therefore, our data indicate a pathologic role for increased production of 17-hydroxy steroid metabolites in liver injury and suggest that Fxr-/-Shp-/- mice could provide a model for juvenile onset cholestasis.

Immunosuppression in the livers of mice with obstructive jaundice participates in their susceptibility to bacterial infection and tumor metastasis

Although patients with obstructive jaundice are susceptible to bacterial infections and cancers, the mechanisms remain to be elucidated. In the present study, liver mononuclear cells (MNCs) of bile duct-ligated (BDL) mice were immunologically assessed. Liver natural killer T cells were greatly decreased within 24 h after BDL. Upon injection of Escherichia coli (E. coli; 10 colony-forming units) at 7 days after the procedure, all BDL mice had died, but no sham mice died. Consistently, an overgrowth of E. coli was seen in the livers of BDL mice. Although the serum IL-12 and IL-18 levels after E. coli challenge in BDL mice were higher than those in sham mice, the IFN-gamma level was greatly suppressed. However, exogenous IFN-gamma injection significantly increased BDL mouse survival after E. coli challenge. Furthermore, liver MNC of BDL mice exhibited a lower cytotoxic activity against tumors, and BDL mice intravenously injected with liver metastatic EL-4 cells showed markedly increased EL-4 metastases. The total bile acids, as well as the bile acid fractions, increased in the sera and liver. IFN-gamma production by liver MNC from normal mice stimulated with LPS in vitro was inhibited by the addition of bile acids, whereas, conversely, the production of IL-12 and IL-18 increased. In conclusion, liver natural killer T cells were diminished in BDL mice, and the function of liver MNC (IFN-gamma production) was also impaired presumably due to increased bile acids. This may partly explain the increased susceptibility of BDL mice to bacterial infections and tumor metastasis.

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.

Bile acids metabonomic study on the CCl4- and alpha-naphthylisothiocyanate-induced animal models: quantitative analysis of 22 bile acids by ultraperformance liquid chromatography-mass spectrometry

Bile acids (BAs) are crucial for the diagnosis, follow-up, and prognostics of liver and intestinal disorders and other diseases affecting BA metabolism. A rapid, simple, and sensitive analytical method is needed to demonstrate the full metabolic profile and simultaneously determine the individual BAs in biological samples. In our present study, an ultraperformance liquid chromatography-mass spectrometry (UPLC-MS) method has been established and validated for simultaneous quantitation of 22 BAs and a metabonomic study was performed based on the chemometric analysis of the serum samples from carbon tetrachloride (CCl4)- and alpha-naphthylisothiocyanate (ANIT)-induced liver failure rats. The optimal chromatographic condition was effected by UPLC (Acquity UPLC BEH column, 1.7 microm, 2.1 mm x 100 mm) using a linear gradient elution system of methanol-5 mM ammonium acetate containing 0.01% acetic acid after a simple-step deproteinization by precipitation. The separation of the 22 BAs can be finished in less than 12 min, and the concentrations of these BAs in rat serums were simultaneously determined using a selective ions monitoring mode. The method was validated with respect to repeatability (relative standard deviation < 9.78%) and accuracy (relative errors from -13.55 to 9.58%). The range of each BA was found from not detected (nd) to 8301 ng mL(-1), respectively. Furthermore, the developed method was successfully applied to the metabonomics analysis of BAs in CCl4- and ANIT-induced liver failure rats, using principle component analysis and canonical discriminant analysis. The serum samples from the two types of rat liver injury could be distinguished from each other and from the untreated animals according to the varieties of BAs. It indicated that the level of BAs could be considered as a sensitive parameter of hepatotoxicity induced by different chemical toxins. This novel metabonomics study of BAs based on the UPLC-MS profile provides not only an accurate quantitative assay of the serum concentrations of biomarkers but also a promising methodology for evaluation of liver injury.

Bear bile: dilemma of traditional medicinal use and animal protection

Bear bile has been used in Traditional Chinese Medicine (TCM) for thousands of years. Modern investigations showed that it has a wide range of pharmacological actions with little toxicological side effect and the pure compounds have been used for curing hepatic and biliary disorders for decades. However, extensive consumption of bear bile made bears endangered species. In the 1980's, bear farming was established in China to extract bear bile from living bears with "Free-dripping Fistula Technique". Bear farming is extremely inhumane and many bears died of illness such as chronic infections and liver cancer. Efforts are now given by non-governmental organizations, mass media and Chinese government to end bear farming ultimately. At the same time, systematic research has to be done to find an alternative for bear bile. In this review, we focused on the literature, laboratory and clinical results related to bear bile and its substitutes or alternative in English and Chinese databases. We examined the substitutes or alternative of bear bile from three aspects: pure compounds derived from bear bile, biles from other animals and herbs from TCM. We then discussed the strategy for stopping the trading of bear bile and issues of bear bile related to potential alternative candidates, existing problems in alternative research and work to be done in the future.

Effect of ursodeoxycholic acid on serum liver enzymes and bile acid metabolism in chronic active hepatitis C virus infection

AIM

Many reports have revealed ursodeoxycholic acid (UDCA) to be effective against chronic hepatitis C virus (HCV). However, some cases resist this therapy and the mechanism of action remains unclear. In this study, UDCA was administered to patients with chronic HCV and the correlation between the bile acids of the biliary bile and serum and the drug efficacy was investigated.

METHODS

Fifteen patients were given 600 mg/day of UDCA for more than 24 weeks. The serum bile acid concentrations and biliary and serum bile acid were collected before and after 24 weeks of UDCA treatment, and composition determined by high-performance liquid chromatography.

RESULTS

The treatment was effective in nine cases (ALT decreased to less than twice the normal values 80 IU/L) and ineffective in six cases. There was no significant difference in the serum bile acid concentrations before and after UDCA treatment between the values of both cases. After UDCA treatment, the serum percentage of UDCA (effective, 62.5 +/- 2.0; ineffective, 53.5 +/- 2.5, (P = 0.02)) and the percentage of chenodeoxycholic acid (CDCA) showed no remarkable changes. In the biliary bile the percentage of CDCA (effective, 30.9 +/- 2.0; ineffective, 20.0 +/- 3.0, (P = 0.007)) and the percentage of UDCA showed no remarkable changes.

CONCLUSION

In the effective cases, the percentage of UDCA in the serum and the percentage of CDCA in biliary bile were significantly higher than in the ineffective cases. This indicates that, when effective, CDCA decreases in hepatocytes and this reduction contributes to hepatoprotection.

Loss of orphan receptor small heterodimer partner sensitizes mice to liver injury from obstructive cholestasis

The orphan nuclear hormone receptor small heterodimer partner (SHP) regulates the expression of several genes involved in bile acid homeostasis in the liver. Because bile acid toxicity is a major source of liver injury in cholestatic disease, we explored the role of SHP in liver damage induced by common bile duct ligation (BDL). Shp(-/-) mice show increased sensitivity in this model of acute obstructive cholestasis, with greater numbers of bile infarcts and higher mortality than wild-type C57BL/6 mice. This increased sensitivity could not be accounted for by differences in expression of bile acid homeostatic genes 2 or 5 days after BDL. Instead, higher basal expression of such genes, including the key biosynthetic enzyme cholesterol 7alpha hydroxylase (Cyp7A1) and the bile salt export pump, is associated with both an increase in bile flow prior to BDL and an increase in acute liver damage at only 1.5 hours after BDL in Shp(-/-) mice, as shown by bile infarcts. At 3 hours, Cyp7A1 expression still remained elevated in Shp(-/-) with respect to wild-type mice, and the hepatic and serum bile acid levels and total hepatobiliary bile acid pool were significantly increased. The increased sensitivity of mice lacking SHP contrasts with the decreased sensitivity of mice lacking the farnesoid X receptor (FXR; nuclear receptor subfamily 1, group H, member 4) to BDL, which has been associated with decreased intraductal pressure and fewer bile infarcts.

CONCLUSION

We propose that differences in acute responses to BDL, particularly the early formation of bile infarcts, are a primary determinant of the differences in longer term sensitivity of the Fxr(-/-) and Shp(-/-) mice to acute obstructive cholestasis.

Protective effects of ursodeoxycholic acid on chenodeoxycholic acid-induced liver injury in hamsters

AIM: To investigate the effects of ursodeoxycholic acid (UDCA) on chenodeoxycholic acid (CDCA)-induced liver injury in hamsters, and to elucidate a correlation between liver injury and bile acid profiles in the liver.

METHODS: Liver injury was induced in hamsters by administration of 0.5% (w/w) CDCA in their feed for 7 d. UDCA (50 mg/kg and 150 mg/kg) was administered for the last 3 d of the experiment.

RESULTS: At the end of the experiment, serum alanine aminotransferase (ALT) increased more than 10 times and the presence of liver injury was confirmed histologically. Marked increase in bile acids was observed in the liver. The amount of total bile acids increased approximately three-fold and was accompanied by the increase in hydrophobic bile acids, CDCA and lithocholic acid (LCA). UDCA (50 mg/kg and 150 mg/kg) improved liver histology, with a significant decrease (679.3 ± 77.5 U/L vs 333.6 ± 50.4 U/L and 254.3 ± 35.5 U/L, respectively, P < 0.01) in serum ALT level. UDCA decreased the concentrations of the hydrophobic bile acids, and as a result, a decrease in the total bile acid level in the liver was achieved.

CONCLUSION: The results show that UDCA improves oral CDCA-induced liver damage in hamsters. The protective effects of UDCA appear to result from a decrease in the concentration of hydrophobic bile acids, CDCA and LCA, which accumulate and show the cytotoxicity in the liver.

Rat NAD+-dependent 3α-hydroxysteroid dehydrogenase (AKR1C17): A member of the aldo-keto reductase family highly expressed in kidney cytosol

Mammalian 3alpha-hydroxysteroid dehydrogenases (3alpha-HSDs) have been divided into two types: Cytosolic NADP(H)-dependent 3alpha-HSDs belonging to the aldo-keto reductase family, and mitochondrial and microsomal NAD(+)-dependent 3alpha-HSDs belonging to the short-chain dehydrogenase/reductase family. In this study, we characterized a rat aldo-keto reductase (AKR1C17), whose functions are unknown. The recombinant AKR1C17 efficiently oxidized 3alpha-hydroxysteroids and bile acids using NAD(+) as the preferred coenzyme at an optimal pH of 7.4-9.5, and was inhibited by ketamine and organic anions. The mRNA for AKR1C17 was detected specifically in rat kidney, where the enzyme was more highly expressed as a cytosolic protein than NADP(H)-dependent 3alpha-HSD (AKR1C9). Thus, AKR1C17 represents a novel NAD(+)-dependent type of cytosolic 3alpha-HSD with unique inhibitor sensitivity and tissue distribution. In addition, the replacement of Gln270 and Glu276 of AKR1C17 with the corresponding residues of NADP(H)-dependent 3alpha-HSD resulted in a switch in favor of NADP(+) specificity, suggesting their key roles in coenzyme specificity.

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.

Effect of Barley Endoprotease EP-B2 on Gluten Digestion in the Intact Rat

Celiac Sprue is a multifactorial disease characterized by an intestinal inflammatory response to ingested gluten. Proteolytically resistant gluten peptides from wheat, rye, and barley persist in the intestinal lumen and elicit an immune response in genetically susceptible individuals. Here, we demonstrate the in vivo ability of a gluten-digesting protease ("glutenase") to accelerate the breakdown of a gluten-rich solid meal. The proenzyme form of endoprotease B, isoform 2 from Hordeum vulgare (EP-B2), was orally administered to adult rats with a solid meal containing 1 g of gluten. Gluten digestion in the stomach and small intestine was monitored as a function of enzyme dose and time by high-performance liquid chromatography and mass spectrometry. In the absence of supplementary EP-B2, gluten was solubilized and proteolyzed to a limited extent in the stomach and was hydrolyzed and assimilated mostly in the small intestine. In contrast, EP-B2 was remarkably effective at digesting gluten in the rat stomach in a dose- and time-dependent fashion. At a 1:25 EP-B2/gluten dose, the gastric concentration of the highly immunogenic 33-mer gliadin peptide was reduced by more than 50-fold within 90 min with no overt signs of toxicity. Evaluation of EP-B2 as an adjunct to diet control is therefore warranted in celiac patients.

Bile acids induce energy expenditure by promoting intracellular thyroid hormone activation

While bile acids (BAs) have long been known to be essential in dietary lipid absorption and cholesterol catabolism, in recent years an important role for BAs as signalling molecules has emerged. BAs activate mitogen-activated protein kinase pathways, are ligands for the G-protein-coupled receptor (GPCR) TGR5 and activate nuclear hormone receptors such as farnesoid X receptor alpha (FXR-alpha; NR1H4). FXR-alpha regulates the enterohepatic recycling and biosynthesis of BAs by controlling the expression of genes such as the short heterodimer partner (SHP; NR0B2) that inhibits the activity of other nuclear receptors. The FXR-alpha-mediated SHP induction also underlies the downregulation of the hepatic fatty acid and triglyceride biosynthesis and very-low-density lipoprotein production mediated by sterol-regulatory-element-binding protein 1c. This indicates that BAs might be able to function beyond the control of BA homeostasis as general metabolic integrators. Here we show that the administration of BAs to mice increases energy expenditure in brown adipose tissue, preventing obesity and resistance to insulin. This novel metabolic effect of BAs is critically dependent on induction of the cyclic-AMP-dependent thyroid hormone activating enzyme type 2 iodothyronine deiodinase (D2) because it is lost in D2-/- mice. Treatment of brown adipocytes and human skeletal myocytes with BA increases D2 activity and oxygen consumption. These effects are independent of FXR-alpha, and instead are mediated by increased cAMP production that stems from the binding of BAs with the G-protein-coupled receptor TGR5. In both rodents and humans, the most thermogenically important tissues are specifically targeted by this mechanism because they coexpress D2 and TGR5. The BA-TGR5-cAMP-D2 signalling pathway is therefore a crucial mechanism for fine-tuning energy homeostasis that can be targeted to improve metabolic control.

High sensitive analysis of rat serum bile acids by liquid chromatography/electrospray ionization tandem mass spectrometry

Sensitive liquid chromatography (LC)/electrospray ionization (ESI) tandem mass spectrometry (MS) can be used to analyze the bile acid composition of rat serum. This method can analyze eight common bile acids and their glycine and taurine conjugates in 100 microl rodent serum by gradient elution on a reversed-phase column using a mixture of 20mM ammonium acetate buffer (pH 8.0), acetonitrile and methanol as a mobile phase. Selected reaction monitoring analysis under negative ion detection mode allowed the achievement of a high sensitive assay with a simple solid phase extraction using an ODS cartridge column. We used this method to investigate the effect of a one-day fast on the concentration and composition of serum bile acids in rats. The results suggested that the method described here is useful for the dynamic analysis of serum bile acids in rats.

Presence of protein-bound unconjugated bile acids in the cytoplasmic fraction of rat brain

Using liquid chromatography/electrospray ionization mass spectrometry, we have found three unconjugated bile acids [cholic acid (CA), chenodeoxycholic acid (CDCA), and deoxycholic acid (DCA)] in the rat brain cytoplasmic fraction. CDCA was detected only upon extraction with high concentrations of guanidine, indicating that it is bound noncovalently to protein in the brain. The most abundant of the three, it was present at a concentration of 1.6 nmol/g wet weight (approximately 15 mg of protein) of brain, corresponding to almost 30 times its serum concentration. CA and DCA were present at 1/30th the concentration of CDCA. Bile acids conjugated with amino acids, sulfuric acid, and glucuronic acid were not detected. These data clearly demonstrate that unconjugated CDCA and, to a lesser extent, CA and DCA, exists in the rat brain.

Chemoprevention of N-methylnitrosourea-induced colon carcinogenesis by ursodeoxycholic acid-5-aminosalicylic acid conjugate in F344 rats

Bile acids enhance colon carcinogenesis in animal models, whereas ursodeoxycholic acid (UDCA) suppresses it. Nonsteroid anti-inflammatory drugs prevent colon cancer development in animals and humans. The aim of the present study was to explore the inhibitory effect of UDCA conjugate with 5-aminosalicylic acid (5-ASA), UDCA-5-ASA conjugate (UDCA-5-ASA), against colon carcinogenesis in rats. One-hundred-and-twenty-nine 7-week-old F344 rats received an intrarectal instillation of 2 mg of N-methylnitrosourea 3 times a week for 3 weeks, and were fed a 0% (control), 0.11% or 0.02% UDCA-5-ASA-, 0.08% UDCA- or 0.03% 5-ASA-supplemented diet for the next 27 weeks. The test diets contained an equimolar amount of a test agent, 2.0 mmol/kg diet, except for the 0.02% UDCA-5-ASA diet. The tumor incidence and the mean number of tumors/rat at week 30 were significantly lower and smaller in the UDCA-5-ASA diet groups, 48% and 0.7 in both, and marginally lower in the UDCA and 5-ASA diet groups, 56% and 0.9, and 64% and 0.8, compared to the control group, 83% and 1.3. All the tumors were polypoid in shape, and most of them were differentiated adenocarcinomas restricted to the mucosa or submucosa. An analysis by HPLC for bile acids and 5-ASA in the feces and serum collected at week 30 showed that one-half of ingested UDCA-5-ASA was cleaved into UDCA and 5-ASA in the colon. Thus, the two moieties may have independently affected the promotion stage of carcinogenesis.

Effect of bile acids on formation of azoxymethane-induced aberrant crypt foci in colostomized F344 rat colon

The effect of bile acids on the formation of azoxymethane induced aberrant crypt foci (ACF) was investigated using the fecal stream-excluded colons of colostomized F344 rats. The excluded colon was irrigated with saline or bile acids (1 mg/0.5 ml per day, 5 days/week) for 4 weeks. The mean numbers of ACF per colon in rats given cholic acid, deoxycholic acid (DCA), chenodeoxycholic acid (CDCA), lithocholic acid, and ursodeoxycholic acid (UDCA) were 160.8, 118.2, 227.8, 150.7 and 87.3, respectively, while that of the control was 174.0. The number of ACF was significantly larger in CDCA, but smaller in UDCA and DCA-treated rats than the control (P<0.01). DCA did not induce apoptosis in the colon under the present conditions.

Changes in the composition of serum bile acid as a predictor of small bowel allograft rejection in rats

Composition of bile acid was studied as a noninvasive rejection marker after small bowel transplantation (SBT). Orthotopic SBT were performed in rats, and they were divided into four groups: group 1, sham-operated rats; group 2, recipients with isografts; group 3, recipients with allografts treated with FK506; and group 4, recipients with untreated allografts. On postoperative days (POD) 5 and 7, the graft histology, intraluminal bacterial overgrowth, individual bile acids concentration of the recipient serum and bile were examined. On POD 5, early histological findings of acute rejection were observed in group 4, and the ratio of secondary bile acids of this group were significantly higher than the other groups. The bile acid changes were enhanced by bacterial overgrowth on POD 7. The ratio of secondary bile acids changed in relation to acute rejection after SBT, suggesting that they can be useful for early diagnosis of acute SBT allograft rejection.

Transformation of bile acids and sterols by clostridia (fusiform bacteria) in Wistar rats

The effects on bile acid and sterol transformation of clostridia (fusiform bacteria), the dominant intestinal bacteria in rodents (ca. 10(10) counts per g wet feces) were examined in Wistar rats. After inoculation of clostridia into germ-free rats and into rats previously inoculated solely with Escherichia coli, most of the endogenous bile acids were deconjugated, and cholic acid and chenodeoxycholic acid were 7alpha-dehydroxylated to deoxycholic acid and lithocholic acid, respectively. Tauro-beta-muricholic acid, another major bile acid in rats, was deconjugated, but only part of it (ca. 30%) was transformed into hyodeoxycholic acid. Cholesterol and sitosterol were also reduced to coprostanol and sitostanol, respectively. Escherichia coli transformed neither bile acids nor sterols. These data suggest that clostridia play an important role in the formation of secondary bile acids and coprostanol in rats.

The choleretic effects of N-acetylglucosaminides, major urinary metabolites of ursodeoxycholic acid, in bile fistula rats

We investigated the effects of three bile acids conjugated with N-acetylglucosamine, ursodeoxycholate N-acetylglucosaminide, tauroursodeoxycholate N-acetylglucosaminide and glycoursodeoxycholate N-acetylglucosaminide, on bile flow and biliary excretion of various markers in comparison with ursodeoxycholic acid, tauroursodeoxycholic acid and glycoursodeoxycholic acid in bile fistula rats. These bile acids were infused intravenously at a constant rate of 0.3 or 0.6 micromol/min/100 g b.w. for 2 h. All bile acids examined increased bile flow in a dose-dependent manner. In particular, ursodeoxycholate N-acetylglucosaminide has a longer-lasting effect after its infusion on bile flow than the other bile acids. Furthermore, these bile acids markedly increased biliary total bile acid excretion. At a higher dose level, the coefficient of determination (r2) between the biliary total bile acid excretion and bile flow for ursodeoxycholate N-acetylglucosaminide (r2 = 0.39) was lower than that for the other bile acids (r2 = 0.75-0.92). The ursodeoxycholate N-acetylglucosaminide, as well as tauroursodeoxycholic acid, glycoursodeoxycholic acid, tauroursodeoxycholate N-acetylglucosaminide and glycoursodeoxycholate N-acetylglucosaminide, was mostly excreted in an unchanged form in bile, whereas ursodeoxycholic acid was excreted as a conjugate with taurine. The three N-acetylglucosaminides as well as ursodeoxycholic acid, tauroursodeoxycholic acid and glycoursodeoxycholic acid significantly increased the biliary excretion of cholesterol, phospholipid, bilirubin and total Ca2+. In contrast, the N-acetylglucosaminides significantly decreased in biliary bicarbonate concentration, whereas ursodeoxycholic acid significantly increased biliary bicarbonate concentration. However, tauroursodeoxycholic acid and glycoursodeoxycholic acid did not significantly change the biliary bicarbonate concentration. The results indicate that N-acetylglucosaminides have a choleretic effect in bile fistula rats. Our present study also demonstrates that N-acetylglucosaminides, but not ursodeoxycholic acid, tauroursodeoxycholic acid or glycoursodeoxycholic acid, can significantly reduce the biliary bicarbonate concentration. Furthermore, our findings suggest that ursodeoxycholate N-acetylglucosaminide may partly exert a choleretic effect via mechanisms different from those of the other bile acids.

Simultaneous determination of bile acids in rat liver tissue by high-performance liquid chromatography

A method for the simultaneous determination of bile acids in rat liver tissue by high-performance liquid chromatography was developed. Without prior fractionation and alkaline hydrolysis, 30 unconjugated, glycine- and taurine-conjugated bile acids were detected by post-column enzymatic reaction and fluorescence detection. They were separated on a reversed-phase column using a linear gradient solvent system of 10 mM tribasic ammonium phosphate-acetonitrile-methanol (44:12:5, v/v/v) and 20 mM dibasic ammonium phosphate-acetonitrile-methanol (2:1:2, v/v/v). The limits of detection were 1-5 pmol, and calibration curves were linear for concentrations ranging between 10 and 4000 pmol per 10 microl injection. This rapid and reliable method is effective for measuring bile acid levels in liver tissue not only of rats but also of patients with hepatobiliary and other diseases.

Prevention of N-methylnitrosourea-induced colon tumorigenesis by ursodeoxycholic acid in F344 rats

Bile acids are known to promote colon carcinogenesis. However, there is one study showing that ursodeoxycholic acid (UDCA) supplemented in the diet at the concentration of 0.4% prevented azoxymethane-induced rat colon tumorigenesis. The aim of our study was to explore the inhibitory effect of a much smaller dose of UDCA on colon carcinogenesis in rats. One hundred 7-week-old F344 rats were given 2 mg of N-methylnitrosourea 3 times a week for 3 weeks by intrarectal instillation, and were fed a 0% (control), 0.4% or 0.08% UDCA-supplemented diet for the next 27 weeks. All the rats were killed and examined for tumor development at week 30. The tumor incidence and number were significantly lower and smaller, respectively, in the UDCA-fed rats than in the control rats: 40% and 36% vs. 68%; 0.5 +/- 0.1 (mean +/- SEM) and 0.4 +/- 0.1 vs. 1.0 +/- 0.2. All the tumors were located in the distal half of the colon and were plaque-shaped or polypoid, being well-differentiated adenocarcinomas restricted to the mucosa or submucosa. Bile acids in the feces and the blood obtained at weeks 20 and 30, respectively, were analyzed by HPLC. A significant increase of UDCA was confirmed in both the feces and the blood of the UDCA-fed rats compared with the control rats. The results suggest that the continuous feeding of a small dose of UDCA may prevent colon carcinogenesis.

Polyethylene glycol-modified bilirubin oxidase improves hepatic energy charge and urinary prostaglandin levels in rats with obstructive jaundice

BACKGROUNDS/AIMS

No study has so far been conducted to clarify whether the presence of hyperbilirubinemia is detrimental to liver and renal functions. In the present study, the effects of polyethylene glycol-modified bilirubin oxidase (PEG-BOX) therapy on liver and renal function tests, hepatic energy charge and urinary prostaglandin levels were evaluated in a rat model of obstructive jaundice.

METHODS

Sprague-Dawley rats were used in the experimental model of obstructive jaundice. PEG-BOX or an equivalent amount of PEG alone was intravenously injected into the animals and sampling of blood and urine, and liver harvesting were done sequentially after bile duct ligation.

RESULTS

Conventional liver function tests showed no difference between PEG-BOX and control groups. However, bilirubin concentrations in the peripheral blood and liver tissue specimens markedly decreased, and the hepatic energy charge significantly increased in the PEG-BOX group as compared to controls. The blood concentration of bile acid was lower, but its urinary excretion was higher in the PEG-BOX group than in the control group. In vitro incubation of PEG-BOX with serum from rats with obstructive jaundice decreased the concentration of bilirubin but not that of bile acid. The urinary levels of prostaglandin E2 and the thromboxane B2/6-keto-prostaglandin Fla ratio were significantly lower in the PEG-BOX group than in the control group.

CONCLUSIONS

The systemic reduction of bilirubin concentration may contribute to normalization of the urinary levels of prostaglandins and thromboxane B2, to decrease in serum bile acid levels, and to improvement of the hepatic energy charge in obstructive jaundice. These findings suggest that preoperative improvement of jaundice may be beneficial to patients with obstructive jaundice.

Improvement of estradiol-17 beta-D-glucuronide-induced cholestasis by sodium tauroursodeoxycholate therapy in rats

BACKGROUND

Estradiol-17 beta-D-glucuronide (E-17G), a metabolite of natural estrogen, is well known to cause intrahepatic cholestasis in humans. We therefore investigated the effect of sodium tauroursodeoxycholate (T-UDCA), on E-17G-induced cholestasis in female rats.

METHODS

For the evaluation of the drug, animals given E-17G (10 mumol/kg) were divided into three groups, and T-UDCA was administered intravenously at various doses after E-17G treatment.

RESULTS

T-UDCA significantly prevented a marked reduction of bile flow in E-17G-treated rats in all experimental schedules. Furthermore, T-UDCA significantly increased in the biliary E-17G excretion rate at an early stage after E-17G treatment in rats. However, this drug caused no significant change in the biliary excretion rate of estradiol-3-sulfate-17 beta-D-glucuronide (E-3S-17G), which is identified as the major biliary metabolite with E-17G throughout the recovery periods.

CONCLUSION

These results suggest that T-UDCA can improve E-17G induced acute cholestasis by rapidly increasing the biliary E-17G excretion rate. Thus our finding may provide a useful approach for attempts to prevent drug-induced acute cholestasis in humans.