Circulating Bile Acid Pool Research Articles

Absence of gut microbiota reduces neonatal survival and exacerbates liver disease in Cyp2c70-deficient mice with a human-like bile acid composition.

Mice with deletion of Cyp2c70 have a human-like bile acid composition, display age- and sex-dependent signs of hepatobiliary disease and can be used as a model to study interactions between bile acids and the gut microbiota in cholestatic liver disease. In the present study, we rederived Cyp2c70-/- mice as germ-free (GF) and colonized them with a human or a mouse microbiota to investigate whether the presence of a microbiota can be protective in cholangiopathic liver disease associated with Cyp2c70-deficiency. GF Cyp2c70-/- mice showed reduced neonatal survival, liver fibrosis, and distinct cholangiocyte proliferation. Colonization of germ-free breeding pairs with a human or a mouse microbiota normalized neonatal survival of the offspring, and particularly colonization with mouse microbiota from a conventionally raised mouse improved the liver phenotype at 6-10 weeks of age. The improved liver phenotype in conventionalized (CD) Cyp2c70-/- mice was associated with increased levels of tauro-ursodeoxycholic acid (TUDCA) and UDCA, resulting in a more hydrophilic bile acid profile compared with GF and humanized Cyp2c70-/- mice. The hydrophobicity index of biliary bile acids of CD Cyp2c70-/- mice was associated with changes in gut microbiota, liver weight, liver transaminases, and liver fibrosis. Hence, our results indicate that neonatal survival of Cyp2c70-/- mice seems to depend on the establishment of a gut microbiota at birth, and the improved liver phenotype in CD Cyp2c70-/- mice may be mediated by a larger proportion of TUDCA/UDCA in the circulating bile acid pool and/or by the presence of specific bacteria.

Perinatal exposure to UDCA prevents neonatal cholestasis in Cyp2c70-/- mice with human-like bile acids

BackgroundCyp2c70-/- mice with a human-like bile acid (BA) composition display features of neonatal cholestasis. We assessed whether perinatal ursodeoxycholic acid (UDCA) exposure prevents neonatal cholestasis in Cyp2c70-/- mice and reduces cholangiopathy development later in life.MethodsCyp2c70+/- males were crossed with Cyp2c70+/- females fed either a regular chow diet or a 0.1% UDCA-containing diet during breeding, gestation, and suckling. Cholestasis and liver function parameters were assessed in their Cyp2c70-/- and wild-type offspring at 3 and 8 weeks of age.ResultsThree-week-old Cyp2c70-/- pups showed features of neonatal cholestasis, including elevated plasma BAs and transaminases, which were completely prevented in Cyp2c70-/- pups upon perinatal UDCA exposure. In addition, UDCA administration to the dams corrected altered hepatic gene expression patterns in Cyp2c70-/- pups, reduced markers of fibrogenesis and inflammation, and prevented cholangiocyte proliferation. Yet, these beneficial effects of perinatal UDCA exposure were not retained into adulthood upon discontinuation of treatment.ConclusionPerinatal exposure of Cyp2c70-/- mice to UDCA has beneficial effects on liver function parameters, supporting a direct role of BA hydrophobicity in the development of neonatal cholestasis in these mice. However, prevention of neonatal cholestasis in Cyp2c70-/- mice has no long-lasting effects on liver pathophysiology.ImpactThis is the first study showing that perinatal UDCA exposure prevents features of neonatal cholestasis that are observed in mice with a human-like bile acid composition, i.e., Cyp2c70-/- mice.Perinatal UDCA exposure of Cyp2c70-/- pups leads to UDCA enrichment in their circulating bile acid pool and, consequently, to a reduced hydrophobicity of biliary bile acids.Perinatal UDCA exposure of Cyp2c70-/- pups has no long-lasting effects on the development of cholangiopathy after discontinuation of treatment.The results in this study expand current knowledge regarding acute and long-lasting effects of UDCA treatment in early life.

Abstract PS6-59: Impact of Cholecystectomy in Breast Cancer Recurrence

Abstract Background: Several published studies demonstrate that bile acid metabolites may influence the growth of breast cancer cells in vitro. Our group has shown reduced plasma concentrations of cholic acid and chenodeoxycholic acid (primary bile acids) and deoxycholic acid and lithocholic acid (secondary bile acids) in breast cancer patients that later on develop tumor recurrence. Cholecystectomy reduces the circulating bile acid pool. In patients with prior cholecystectomy, changes in bile acid metabolites may contribute to breast cancer tumorigenesis and recurrence. This study investigates our institutional rate of cholecystectomy in women diagnosed with breast cancer and its impact on breast cancer recurrence. Methods: A retrospective review of patients with an invasive breast cancer diagnosis between 2014-2015 was conducted. Demographics, preoperative variables, surgical history and clinical outcome data was collected. 5-year disease-free survival (DFS) was compared using a Log-rank (Mantel-Cox) test. Results: The study included 264 patients with mean age of 60.9. Most were Caucasian (83.5%). The majority were diagnosed at Stage II or lower (80.3%) and had hormone receptor positive, HER2 negative breast cancer (72.9%). Approximately 22.7% of patients had prior cholecystectomy surgery. The only statistically significant heterogeneity in demographic data between patients with and without cholecystectomy was body mass index (BMI). Patients with cholecystectomy had a mean BMI of 33.3, versus 29.1 in patients with intact gallbladders. The 5-year DFS in breast cancer patients with cholecystectomy was 91.6%, versus 97.1% in patients with intact gallbladders (p=0.06). Conclusion: Women with breast cancer who had a history of cholecystectomy had increased rates of breast cancer recurrence over a 5-year period compared to women with breast cancer with intact gallbladders. Although this result was not statistically significant, a trend was seen. Future study of a larger patient sample size sample may lead to a statistical significant difference. The statistically significant difference in BMI between the two patient groups is likely a confounding factor, given increased BMI is a known risk factor for developing cholecystitis and breast cancer. This data supports existing in vitro studies that bile acids may influence the growth of breast cancer cells. There may be utility in closer follow-up of women with breast cancer and a history of cholecystectomy given the increased rate of breast cancer recurrence in this population. Citation Format: Isheeta Madeka, Rohin Gawdi, Katherine L Cook, Akiko Chiba. Impact of Cholecystectomy in Breast Cancer Recurrence [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS6-59.

Bile Acid and Cholesterol Metabolism in Atherosclerotic Cardiovascular Disease and Therapy

Dysregulation of lipid metabolism is a major factor contributing to atherosclerotic cardiovascular disease (ACVD), which is the number one cause of death in western countries. The liver plays a central role in maintaining whole body cholesterol homeostasis via catabolism of cholesterol to bile acids, as well as biliary cholesterol excretion. The liver synthesizes lipoproteins that transport dietary cholesterol and fats to muscle and adipose tissue, directs reverse cholesterol transport of excess cholesterol from extrahepatic tissues and macrophages to the liver to convert to bile acids, and thus, protects against metabolism-related nonalcoholic fatty liver disease (NAFLD) and ACVD. Liver fibrosis/nonalcoholic steatohepatitis increases the risk and prevalence of cardiovascular disease morbidity and mortality. Bile acids are signaling molecules and metabolic regulators that activate farnesoid X receptor and G protein-coupled bile acid receptor-1 to regulate lipid, glucose, and energy metabolism. The bidirectional regulation of bile acids and the gut microbiota determine the rate of bile acid synthesis, the bile acid pool size, and the composition of the circulating bile acid pool. The liver-intestine-heart axis regulates lipid metabolism, inflammation, and the pathogenesis of metabolic diseases such as ACVD, NAFLD, diabetes, and obesity. This review focuses on the roles of liver-to-intestine, liver-to-heart and intestine-to-heart axes in cholesterol, lipoprotein, and bile acid metabolism; signaling in heart health and ACVD; and drug therapies for atherosclerosis.

A review of analytical platforms for accurate bile acid measurement.

Bile acids are acidic steroids which help in lipid absorption, act as signaling molecules, and are key intermediate molecules between host and gut microbial metabolism. Perturbations in the circulating bile acid pool can lead to dysregulated metabolic and immunological function whichmay be associated withliver and intestinal disease. Bile acids have chemically diverse structures and are present in abroad range of concentrations in a wide variety of samples with complex biological matrices. Advanced analytical methods are therefore required to identify and accurately quantify individual bile acids. Though enzymatic determination of total bile acid is most popular in clinical laboratories, these methods provide limited information about individual bile acids. Advanced analytical methods such as gas chromatography- and liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy arehighly informative techniques which help in identification and quantification of individual bile acids in complex biological matrices. Here, we review the detection technologies currently used for bile acid identification and quantification. We further discuss the advantages and disadvantages of these analytical techniques with respect to sensitivity, specificity, robustness, and ease of use. Graphical abstract.

Intestinal Bacteria Interplay With Bile and Cholesterol Metabolism: Implications on Host Physiology.

Bile is a biological fluid synthesized in the liver, mainly constituted by bile acids and cholesterol, which functions as a biological detergent that emulsifies and solubilizes lipids, thereby playing an essential role in fat digestion. Besides, bile acids are important signaling molecules that regulate key functions at intestinal and systemic levels in the human body, affecting glucose and lipid metabolism, and immune homeostasis. Apart from this, due to their amphipathic nature, bile acids are toxic for bacterial cells and, thus, exert a strong selective pressure on the microbial populations inhabiting the human gut, decisively shaping the microbial profiles of our gut microbiota, which has been recognized as a metabolic organ playing a pivotal role in host health. Remarkably, bacteria in our gut also display a range of enzymatic activities capable of acting on bile acids and, to a lesser extent, cholesterol. These activities can have a direct impact on host physiology as they influence the composition of the intestinal and circulating bile acid pool in the host, affecting bile homeostasis. Given that bile acids are important signaling molecules in the human body, changes in the microbiota-residing bile biotransformation ability can significantly impact host physiology and health status. Elucidating ways to fine-tune microbiota-bile acids-host interplay are promising strategies to act on bile and cholesterol-related disorders. This manuscript summarizes the current knowledge on bile and cholesterol metabolism by intestinal bacteria, as well as its influence on host physiology, identifying knowledge gaps and opportunities to guide further advances in the field.

TGR5 contributes to glucoregulatory improvements after vertical sleeve gastrectomy in mice

ObjectiveVertical sleeve gastrectomy (VSG) produces high rates of type 2 diabetes remission; however, the mechanisms responsible remain incompletely defined. VSG increases circulating bile acid concentrations and bile acid signalling through...

Intestinal FXR-mediated FGF15 production contributes to diurnal control of hepatic bile acid synthesis in mice

Hepatic bile acid synthesis is subject to complex modes of transcriptional control, in which the bile acid-activated nuclear receptor farnesoid X receptor (FXR) in liver and intestine-derived, FXR-controlled fibroblast growth factor 15 (Fgf15) are involved. The Fgf15 pathway is assumed to contribute significantly to control of hepatic bile acid synthesis. However, scientific evidence supporting this assumption is primarily based on gene expression data. Using intestine-selective FXR knockout mice (iFXR-KO), we show that contribution of intestinal FXR-Fgf15 signalling in regulation of hepatic cholesterol 7α-hydroxylase (Cyp7A1) expression depends on time of the day with increased hepatic Cyp7A1 expression in iFXR-KO mice compared with controls exclusively during the dark phase. To assess the physiological relevance hereof, we determined effects of intestine-selective deletion of FXR on physiological parameters such as bile formation and kinetics of the enterohepatic circulation of bile acids. It appeared that intestinal FXR deficiency leads to a modest but significant increase in cholic acid pool size, without changes in fractional turnover rate. As a consequence, bile flow and biliary bile acid secretion rates were increased in iFXR-KO mice compared with controls. Feeding a bile acid-containing diet or treatment with a bile acid sequestrant similarly affected bile formation in iFXR-KO and control mice and induced similar changes in Cyp7A1 and Cyp8B1 expression patterns. In conclusion, this study is the first to demonstrate the physiological relevance of the contribution of the intestinal FXR-Fgf15 signalling pathway in control of hepatic bile acid synthesis. Fgf15 contributes to the regulation of hepatic bile acid synthesis in mice mainly during the dark phase. Expansion of the circulating bile acid pool as well as bile acid sequestration diminishes the contribution of intestinal FXR-Fgf15 signalling in control of hepatic bile acid synthesis and bile formation.

The stimulatory effect of LXRα is blocked by SHP despite the presence of a LXRα binding site in the rabbit CYP7A1 promoter

The transcription of the cholesterol 7alpha-hydroxylase gene (CYP7A1) is greatly decreased in cholesterol-fed rabbits. To determine whether the molecular structure of the promoter is responsible for this downregulation, we cloned the rabbit CYP7A1 promoter, identified the binding sites for alpha-fetoprotein transcription factor (FTF) and liver X receptor (LXRalpha), and studied the effects of FTF, LXRalpha, and SHP on its transcription. Adding LXRalpha/retinoid X receptor together with their ligands (L/R) to the promoter/reporter construct transfected into HepG2 cells greatly increased its activity. FTF did not increase promoter activity, nor did it enhance the stimulatory effect of L/R. Mutating the FTF binding site abolished the promoter baseline activity. Increasing amounts of SHP abolished the effect of L/R, and FTF enhanced the ability of SHP to decrease promoter activity below baseline levels. Thus, downregulation of CYP7A1 in cholesterol-fed rabbits is attributable secondarily to the activation of farnesoid X receptor, which increases SHP expression to override the positive effects of LXRalpha. Although FTF is a competent factor for maintaining baseline activity, it does not further enhance and may suppress CYP7A1 transcription.

Nasobiliary drainage for cholestatic pruritus

To the Editor: Stapelbroek et al.1 describe the remarkable efficacy of nasobiliary drainage in treating the pruritus associated with an incipient attack of acute cholestasis in 3 patients with benign recurrent intrahepatic cholestasis (BRIC). The rationale of such an approach is to remove the circulating bile acid pool, decrease intestinal absorption of bile acids, and thereby lower plasma bile acids. Multiple lines of evidence indicate that bile acid retention in cholestasis contributes directly or indirectly to pruritus. In their paper, the Utrecht group cites prior studies going back to 1988 that used partial biliary drainage or ileal bypass to successfully treat cholestatic pruritus, again with the same rationale. The purpose of this letter is to point out that there are several much older studies reporting that cholestatic pruritus can be treated by biliary drainage. The utility of surgical drainage of the biliary tract as a treatment of nonobstructive cholestatic liver disease was discussed and practiced in the early 1930′s in France.2 Still, earlier B. B. Vincent Lyon proposed duodenal drainage of bile to treat liver disease3 and described several patients who appeared to benefit from the procedure. In 1947, Richard Varco, a young cardiovascular surgeon at the University of Minnesota reported that in 5 of 6 patients with cholestatic pruritus, biliary drainage by cholecystostomy or T-tube abolished pruritus.4 In 3 of 6 patients, oral bile administration induced recurrence of pruritus (Varco subsequently had a distinguished career as a cardiovascular surgeon).5 In 1957, in a French review article discussing therapy for intrahepatic cholestasis (“medical jaundice”), it was recognized that several publications had shown that external biliary drainage relieves pruritus.6 In 1970, one of us (P-M. H.), as part of his doctoral thesis under the mentorship of Jacques Caroli, often considered to be the father of French hepatology, summarized the clinical experience of the Caroli group. Huet et al. reported that in14 of 17 patients biliary drainage induced relief of pruritus.7 The paper suggested that the only established indication for biliary drainage in liver in non-obstructive cholestatic liver disease was to relieve pruritus, and this view is probably valid today. For obstructive cholestatic liver disease, there is an extensive surgical-endoscopic literature reporting that biliary drainage either externally or internally reduces pruritus.8-10 The rationale here is different that than in intrahepatic cholestasis. In complete cholestasis caused by extrahepatic obstruction, there is no circulating bile acid pool. Presumably, biliary secretion has been down regulated by the high pressure in the biliary tree; biliary drainage increases canalicular transport function with the result that levels of bile acids (and possibly other pruritogens) are decreased. Thus, the useful report of Stapelbroek not only confirms the much older reports showing the utility of surgical biliary drainage to treat cholestatic pruritus, but also provides valuable information in showing that such intervention can be achieved conveniently by endoscopic biliary drainage. Alan F. Hofmann M.D*, Pierre-Michel Huet M.D , * Division of Gastroenterology, Department of Medicine, University of California, San Diego, San Diego, CA, Fédération d'Hepato-Gastroentérologie, Centre universitaire de Nice, Hôpital L'Árchet 2, Nice, France.

Resistance of SHP-null Mice to Bile Acid-induced Liver Damage

The orphan nuclear hormone receptor SHP (gene designation NROB2) is an important component of a negative regulatory cascade by which high levels of bile acids repress bile acid biosynthesis. Short term studies in SHP null animals confirm this function and also reveal the existence of additional pathways for bile acid negative feedback regulation. We have used long term dietary treatments to test the role of SHP in response to chronic elevation of bile acids, cholesterol, or both. In contrast to the increased sensitivity predicted from the loss of negative feedback regulation, the SHP null mice were relatively resistant to the hepatotoxicity associated with a diet containing 0.5% cholic acid and the much more severe effects of a diet containing both 0.5% cholic acid and 2% cholesterol. This was associated with decreased hepatic accumulation of cholesterol and triglycerides in the SHP null mice. There were also alterations in the expression of a number of genes involved in cholesterol and bile acid homeostasis, notably cholesterol 12alpha-hydroxylase (CYP8B1), which was strongly reexpressed in the SHP null mice, but not the wild type mice fed either bile acid containing diet. This contrasts with the strong repression of CYP8B1 observed with short term bile acid feeding, as well as the effects of long term feeding on other bile acid biosynthetic enzymes such as cholesterol 7alpha-hydroxylase (CYP7A1). CYP8B1 expression could contribute to the decreased toxicity of the chronic bile acid treatment by increasing the hydrophilicity of the bile acid pool. These results identify an unexpected role for SHP in hepatotoxicity and suggest new approaches to modulating effects of chronically elevated bile acids in cholestasis.

Suppression of sterol 12alpha-hydroxylase transcription by the short heterodimer partner: insights into the repression mechanism.

Cholesterol conversion to bile acids is subject to a feedback regulatory mechanism by which bile acids down-regulate their own synthesis. This regulation occurs at the level of transcription of several genes encoding enzymes in the bile acid biosynthetic pathway. One of these enzymes is sterol 12alpha-hydroxylase/CYP8B1 (12alpha-hydroxylase), the specific enzyme required for cholic acid synthesis. The levels of this enzyme determine the ratio of cholic acid to chenodeoxycholic acid and thus the hydrophobicity of the circulating bile acid pool. Previous studies from this laboratory showed that fetoprotein transcription factor (FTF) is required for 12alpha-hydroxylase promoter activity and bile acid-mediated regulation. Here, we report that the short heterodimer partner (SHP) suppresses 12alpha-hydroxylase promoter activity via an interaction with FTF. Hepatic nuclear factor-4 (HNF-4) binds and activates the 12alpha-hydroxylase promoter and is required for 12alpha-hydroxylase promoter activity. Although HNF-4 interacts with SHP, it is not involved in SHP-mediated suppression of 12alpha-hydroxylase promoter activity. FTF and not HNF-4 is the factor involved in regulation of 12alpha-hydroxylase promoter activity by bile acids through its interaction with SHP. Finally, interaction of SHP with FTF displaces FTF binding to its sites within the 12alpha-hydroxylase promoter. These results provide insights into the mechanism of action of bile acid-mediated regulation of sterol 12alpha-hydroxylase transcription.

α1-Fetoprotein Transcription Factor Is Required for the Expression of Sterol 12α-Hydroxylase, the Specific Enzyme for Cholic Acid Synthesis: POTENTIAL ROLE IN THE BILE ACID-MEDIATED REGULATION OF GENE TRANSCRIPTION

Cholesterol conversion to bile acids occurs via the "classic" (neutral) or the "alternative" (acidic) bile acid biosynthesis pathways. Sterol 12alpha-hydroxylase/CYP8b1 is the specific enzyme required for cholic acid synthesis. The levels of this enzyme determine the ratio of cholic acid to chenodeoxycholic acid and thus the hydrophobicity of the circulating bile acid pool. Expression of the 12alpha-hydroxylase gene is tightly down-regulated by hydrophobic bile acids. In this study, we report the characterization of two DNA elements that are required for both the 12alpha-hydroxylase promoter activity and bile acid-mediated regulation. Mutation of these elements suppresses 12alpha-hydroxylase promoter activity. Mutations of any other part of the promoter do not alter substantially the promoter activity or alter regulation by bile acids relative to the wild type promoter. These two DNA elements bind alpha(1)-fetoprotein transcription factor (FTF), a member of the nuclear receptor family. We also show that overexpression of FTF in a non-liver cell line activates the sterol 12alpha-hydroxylase promoter. These studies demonstrate the crucial role of FTF for the expression and regulation of a critical gene in the bile acid biosynthetic pathways.

Increased Fecal Bile Acid Excretion and Changes in the Circulating Bile Acid Pool Are Involved in the Hypocholesterolemic and Gallstone-Preventive Actions of Psyllium in Hamsters

The lipid-lowering effect of psyllium (PSY) is well established. Enhanced fecal bile acid excretion and a stimulation of hepatic bile acid synthesis are discussed as primary mechanisms of this action. To further examine the effect of bile acid excretion and specifically of compositional alterations in the bile acid pool on the cholesterol-lowering and gallstone-preventing action of PSY, male golden Syrian hamsters were fed lithogenic diets containing 5 g/100 g fat, 0.4 g/100 g cholesterol and 0 (control), 4 or 6% PSY or 1% cholestyramine (CHY). PSY significantly lowered plasma total cholesterol and triacylglycerol at a magnitude comparable to that induced by CHY. Although hepatic cholesteryl ester accumulation was completely inhibited by CHY, PSY did not prevent the hepatic storage of esterified cholesterol. PSY and CHY caused distinct alterations in the bile acid profile. PSY caused a selective reduction of taurine-conjugated bile acids, especially of taurochenodeoxycholate. As a result, the glycine:taurine conjugation and the cholate:chenodeoxycholate ratios were significantly higher in PSY-fed hamsters. PSY and CHY normalized the lithogenic index and prevented cholesterol gallstone formation compared with controls. Daily fecal bile acid excretion was ∼400% greater in hamsters fed 6% PSY, whereas CHY caused an 11-fold increase. Daily neutral sterol excretion did not differ in PSY-fed hamsters but was >100% greater in those fed CHY than in controls. These data emphasize the potent lipid-lowering effect of PSY. Increased fecal bile acid excretion and alterations of the circulating bile acid pool by removal of dihydroxy bile acids (e.g., taurochenodeoxycholate) appear to be main modulators of the hypocholesterolemic action of PSY by leading to an up-regulation of hepatic bile acid synthesis.

Liver transplantation and bile analysis: a parallel evolution.

Liver transplantation and bile analysis: a parallel evolution.

Biliary lipid composition and bile acid profiles during and after enteral fast of total parenteral nutrition in the rabbit.

Feeding and fasting influence biliary lipid composition. With total parenteral nutrition (TPN), it is possible to study the effects of a long-term "enteral fast" on biliary lipid composition without the metabolic ill-effects of nutrient deprivation. We compared the lipid and bile acid (BA) contents of hepatic and gallbladder biles in rabbits on completion of a 14-day regimen of TPN with those in rabbits returned to oral feeds for 6 weeks after a similar spell of TPN. Chow-fed rabbits served as controls. With TPN, plasma phospholipid and cholesterol levels were elevated. Basal bile flow and the secretion of bile acids and phospholipids were decreased in the TPN and post-TPN groups, while the cholesterol secretion rate was essentially unchanged. During TPN, the molar percent of cholesterol (relative to bile acids and phospholipid) in hepatic bile was increased. Biliary glycolithocholic acid (GLCA; as a percent of total conjugated BA) in hepatic bile increased from 1.7% (0.9% SEM) in the chow-fed to 8.5% (1.5% SEM) during TPN. In TPN and post-TPN groups, the gallbladder was enlarged to more than twice normal (chow-fed) size, and contained a dark, mucoid bile (biliary sludge). In this bile, (a) there was a 2.5-fold increase in bile acid concentration; and (b) the molar percent of cholesterol decreased while that of bile acids increased. TPN produced a state of functional cholestasis, which extended into the post-TPN period. Gallbladder distension was the common denominator of the hepatobiliary dysfunction in the TPN and post-TPN rabbits. With sequestration of bile acids in the gallbladder during and after TPN, the circulating bile acid pool was constricted, and the enterohepatic circulation impaired. As cholesterol secretion was low at all times, cholesterol supersaturation did not occur. The molar percent of cholesterol in gallbladder bile decreased, while that of bile acids increased; this suggests absorption of cholesterol by gallbladder mucosa. The increase in biliary GLCA probably resulted from bacterial biotransformation of glycochenodeoxycholic acid to lithocholic acid and its increased absorption from the cecum during TPN.

Cholylsarcosine, a new bile acid analogue: Metabolism and effect on biliary secretion in humans

Background: Cholylsarcosine, the synthetic conjugate of cholic acid and sarcosine, is resistant to deconjugation-dehydroxylation during enterohepatic cycling in rodents and improves lipid absorption in a canine model of intestinal bile acid deficiency caused by distal intestinal resection. Experiments were performed to define its metabolism and effect on biliary secretion in humans. Methods: The circulating bile acid pool was labeled with [14C]cholylsarcosine, and its turnover rate and biotransformation were determined by sampling bile daily. Cholylsarcosine (or cholyltaurine) was infused into the duodenum for 8 hours to define its effect on bile flow and biliary lipid secretion. Results: Cholylsarcosine was lost rapidly from the enterohepatic circulation with a t1/2 of 0.5 days. The compound was not biotransformed by hepatic or bacterial enzymes. Cholylsarcosine had choleretic activity similar to that of cholyltaurine but induced more phospholipid and cholesterol secretion than cholyltaurine in four of five subjects. Infusion of cholylsarcosine (or cholyltaurine) at a rate averaging 0.6 μmol · min−1 · kg−1 gave a biliary recovery of 0.2 μmol · min−1 · kg−1; this value is the Tmax for active ileal transport of conjugated bile acids in humans. Laboratory tests for liver injury remained within normal limits. Conclusions: In humans, cholylsarcosine is not metabolized, is nontoxic, and has similar effects on biliary secretion as cholyltaurine. It appears safe to test in long-term studies the effect of cholylsarcosine on bile acid-deficiency states in humans.

Bacterial deconjugation and enterohepatic circulation of norursocholic acid conjugates in rats

Experiments were performed to define the metabolism of norusocholic acid (nUC) conjugates and to quantify to what extent the bile acid pool can be enriched in these bile acids. In vitro incubations of norusocholylglycine (nUCG) and -taurine (nUCT) with small intestinal or cecal content showed deconjugation with only cecal content. Cholylglycine (CG) was deconjugated by small intestinal and cecal content. Infusion of nUCG and CG showed that only a small proportion of nUCG was deconjugated after 24 h of enterohepatic circulation, whereas all CG was deconjugated. When nUCT was administered orally, deconjugation was shown to take place mainly in the cecum. Chronic feeding of nUCT enriched the bile acid pool with only 20% nUCT. We conclude that nUC conjugates are deconjugated primarily by bacteria in the cecum and colon, in contrast to CG, which, in addition to cecum and colon, is deconjugated in the distal small intestine. nUCT and its metabolites do not enrich in the circulating bile acid pool mainly for the following reasons: 1) nUC conjugates have a low affinity for the ileal transport system; 2) nUC, even if formed by deconjugation, is not passively absorbed at a sufficient rate; 3) the small amount of norursodeoxycholic acid formed from nUC is glucuronidated in the liver and glucuronide conjugates do not undergo enterohepatic circulation; and 4) nUC conjugates do not suppress bile acid biosynthesis.

Changes in bile acid composition in patients with primary biliary cirrhosis induced by ursodeoxycholic acid administration

We describe a detailed study of the effects of ursodeoxycholic acid administration on bile acid composition of the serum and bile of patients with primary biliary cirrhosis. Gas chromatography-mass spectrometry was used to analyze bile acids from 10 patients with primary biliary cirrhosis before and during ursodeoxycholic acid administration (500 mg/day, corresponding to approximately 8 mg/kg body wt), after group separation of the unconjugated and conjugated fractions by lipophilic anion exchange chromatography. These studies were directed at assessing whether the beneficial role of ursodeoxycholic acid in primary biliary cirrhosis was the consequence of a shift in the hydrophobic/hydrophilic balance of the bile acid pool and whether the hypercholeresis might result from the cholehepatic circulation of unconjugated ursodeoxycholic acid in bile. In basal conditions, the unconjugated bile acids accounted for only 5.5% and 2.5%, respectively, of the total bile acids of serum and bile; cholic acid was the major component of the conjugated fraction of serum and bile (56.0% ± 4.0%, mean ± S.E.M.), and ursodeoxycholic acid was present in only trace amounts. The conjugated fraction contained many unusual bile acids (representing 16.5% ± 1.3% of total) including C 25 bile acids, iso-chenodeoxycholic acid and several oxo-bile acids. After ursodeoxycholic acid administration biochemical indices of liver function all improved, but the proportions of the unconjugated bile acids in serum and bile did not significantly change. Ursodeoxycholic acid became the predominant biliary bile acid of conjugated bile acid fraction (33.4% ± 1.4%) and significant decreases occurred (p < 0.05) in biliary levels of cholic acid (28.3% ± 2.3%) and the unusual bile acids (9.2% ± 0.8%), but no changes occurred in the proportions of chenodeoxycholic acid (from 19.4% ± 2.7% to 19.4% ± 1.3%) and deoxycholic acid (from 5.4% ± 1.4% to 6.8% ± 1.3%). The proportions of biliary lithocholic acid increased significantly after ursodeoxycholic acid administration (from 0.7% ± 0.1% to 2.9% ± 0.9%; p < 0.05). In serum, ursodeoxycholic acid concentrations attained levels of 64 μmol/L. Serum lithocholic acid concentrations increased, whereas cholic and chenodeoxycholic acids decreased. Relative percentages of individual biliary bile acids in the unconjugated fraction were similar to the conjugated fraction before and after ursodeoxycholic acid treatment. The proportions of biliary unconjugated ursodeoxycholic acid did not change significantly after its administration (from 0.6% to 0.9% of the total). These data provide little support for a significant shift in the hydrophilicity of the circulating bile acid pool after ursodeoxycholic acid administration. However, because the detergency and hepatotoxicity of a bile salt appears to correlate well with the retention index determined by reverse-phase liquid chromatography, the qualitative changes observed in the biliary pool (i.e., a displacement of cholic acid by ursodeoxycholic acid), suggests that a relative lowering of the hepatotoxicity index of the bile acid pool occurs after ursodeoxycholic acid therapy. Furthermore, our findings indirectly suggest that a hypercholeresis related to the biliary secretion of unconjugated ursodeoxycholic acid does not play a role in the beneficial effects of ursodeoxycholic acid therapy in primary biliary cirrhosis.

Role of bile acids in splanchnic hemodynamic response to chronic portal hypertension

Previous studies from our laboratory suggest that humoral factors, namely glucagon, can account for approximately 30% of the splanchnic vasodilation in rats with prehepatic portal hypertension. A reduced vascular sensitivity to norepinephrine, vasopressin, and angiotensin II may contribute to the splanchnic vasodilation. However, neither glucagon nor an altered vasoconstrictor sensitivity can fully account for the splanchnic vasodilation observed in portal hypertensive subjects. Therefore, the present study was designed to examine the role of bile acids in the splanchnic hyperemia of portal hypertension since (1) serum bile acids are elevated in portal hypertensive subjects and (2) bile acids are potent intestinal vasodilators. Prehepatic portal hypertension was induced in Sprague-Dawley rats by surgical constriction of the portal vein. Ten to 14 days after the induction of portal hypertension, the enterohepatic circulation of control and portal hypertensive rats was surgically interrupted. The animals were placed in Bollman restraint cages and allowed to recover. Eighteen to 24 hr later, the rats were anesthetized with sodium pentobarbital and regional blood flow measured with radiolabeled microspheres. Normal and portal hypertensive animals without bile fistula served as controls. Plasma bile acid levels measured by radioimmunoassay were approximately 3.8 times higher in portal hypertensive animals than in control. Bile duct cannulation effectively depleted both normal and portal hypertensive animals of their circulating bile acid pool and significantly reduced portal venous inflow in portal hypertensive but not in control rats. A role for bile acids as partial mediators of the splanchnic hyperemia of portal hypertension is suggested since bile acid depletion did not completely abolish the gastrointestinal hyperemia.