Levels of 7 alpha-hydroxy-4-cholesten-3-one in plasma reflect rates of bile acid synthesis in man

Prospective comparison of diagnostic tests for bile acid diarrhoea

BACKGROUND

Bile acid diarrhoea is often missed because gold standard nuclear medicine tauroselcholic [75-Se] acid (SeHCAT) testing has limited availability. Empirical treatment effect has unknown diagnostic performance, whereas plasma 7α-hydroxy-4-cholesten-3-one (C4) is inexpensive but lacks sensitivity.

AIMS

To determine diagnostic characteristics of empirical treatment and explore improvements in diagnostics with potential better availability than SeHCAT.

METHODS

This diagnostic accuracy study was part of a randomised, placebo-controlled trial of colesevelam. Consecutive patients with chronic diarrhoea attending SeHCAT had blood and stool sampled. Key thresholds were C4 > 46 ng/mL and SeHCAT retention ≤10%. A questionnaire recorded patient-reported empirical treatment effect. We analysed receiver operating characteristics and explored machine learning applied logistic regression and decision tree modelling with internal validation.

RESULTS

Ninety-six (38%) of 251 patients had SeHCAT retention ≤10%. The effect of empirical treatment assessed with test results for bile acid studies blinded had 63% (95% confidence interval 44%-79%) sensitivity and 65% (47%-80%) specificity; C4 > 46 ng/mL had 47% (37%-57%) and 92% (87%-96%), respectively. A decision tree combining C4 ≥ 31 ng/mL with ≥1.1 daily watery stools (Bristol type 6 and 7) had 70% (51%-85%) sensitivity and 95% (83%-99%) specificity. The logistic regression model, including C4, the sum of measured stool bile acids and daily watery stools, had 77% (58%-90%) sensitivity and 93% (80%-98%) specificity.

CONCLUSIONS

Diagnosis of bile acid diarrhoea using empirical treatment was inadequate. Exploration suggested considerable improvements in the sensitivity of C4-based testing, offering potential widely available diagnostics. Further validation is warranted.

CLINICALTRIALS

gov: NCT03876717.

An integrated analysis of fecal microbiome and metabolomic features distinguish non-cirrhotic NASH from healthy control populations

BACKGROUND AND AIMS

There is great interest in identifying microbiome features as reliable noninvasive diagnostic and/or prognostic biomarkers for non-cirrhotic NASH fibrosis. Several cross-sectional studies have reported gut microbiome features associated with advanced NASH fibrosis and cirrhosis, where the most prominent features are associated with cirrhosis. However, no large, prospectively collected data exist establishing microbiome features that discern non-cirrhotic NASH fibrosis, integrate the fecal metabolome as disease biomarkers, and are unconfounded by BMI and age.

APPROACH AND RESULTS

Results from shotgun metagenomic sequencing performed on fecal samples prospectively collected from 279 US patients with biopsy-proven NASH (F1-F3 fibrosis) enrolled in the REGENERATE I303 study were compared to those from 3 healthy control cohorts and integrated with the absolute quantification of fecal bile acids. Microbiota beta-diversity was different, and BMI- and age-adjusted logistic regression identified 12 NASH-associated species. Random forest prediction models resulted in an AUC of 0.75-0.81 in a receiver operator characteristic analysis. In addition, specific fecal bile acids were significantly lower in NASH and correlated with plasma C4 levels. Microbial gene abundance analysis revealed 127 genes increased in controls, many involving protein synthesis, whereas 362 genes were increased in NASH many involving bacterial environmental responses (false discovery rate < 0.01). Finally, we provide evidence that fecal bile acid levels may be a better discriminator of non-cirrhotic NASH versus health than either plasma bile acids or gut microbiome features.

CONCLUSIONS

These results may have value as a set of baseline characteristics of non-cirrhotic NASH against which therapeutic interventions to prevent cirrhosis can be compared and microbiome-based diagnostic biomarkers identified.

Bile acid metabolism regulatory network orchestrates bone homeostasis

Bile acids (BAs), synthesized in the liver and modified by the gut microbiota, have been widely appreciated not only as simple lipid emulsifiers, but also as complex metabolic regulators and momentous signaling molecules, which play prominent roles in the complex interaction among several metabolic systems. Recent studies have drawn us eyes on the diverse physiological functions of BAs, to enlarge the knowledge about the "gut-bone" axis due to the participation about the gut microbiota-derived BAs to modulate bone homeostasis at physiological and pathological stations. In this review, we have summarized the metabolic processes of BAs and highlighted the crucial roles of BAs targeting bile acid-activated receptors, promoting the proliferation and differentiation of osteoblasts (OBs), inhibiting the activity of osteoclasts (OCs), as well as reducing articular cartilage degradation, thus facilitating bone repair. In addition, we have also focused on the bidirectional effects of BA signaling networks in coordinating the dynamic balance of bone matrix and demonstrated the promising effects of BAs on the development or treatment for pathological bone diseases. In a word, further clinical applications targeting BA metabolism or modulating gut metabolome and related derivatives may be developed as effective therapeutic strategies for bone destruction diseases.

Loose ends in the differential diagnosis of IBS-like symptoms

Two thirds of the patients we believed to have IBS in the 1970's have since been possible to diagnose with treatable conditions like bile acid diarrhea, inflammatory bowel disease, microscopic colitis, celiac disease, disaccharide malabsorption, exocrine pancreatic insufficiency, or rare genetic variants. Despite advances in diagnostic techniques a substantial proportion of patients continue suffering from IBS-like symptoms that cannot be explained by current knowledge. Although it is likely that further research will reveal small but important subgroups of patients with treatable mechanisms for IBS-like symptoms, we propose that only two large groups remain for being addressed in the clinic: those with connective tissue disorders such as Ehlers-Danlos syndrome or hypermobility spectrum disorders and those with autism spectrum disorders. Patients with connective tissue disorders exhibit identifiable disturbances of gut motor function and possibly increased gut permeability as underlying mechanisms for IBS-like symptoms. Autism spectrum disorders pose a much more difficult problem in the clinic. Disturbances of perception combined with anxiety and excessive worry about signals from the gut can lead to an endless but futile search for something being wrong. The search can involve large numbers of care givers, no one understanding the patient's suffering. Others may try to change their diet to lessen symptoms, only to find that almost all foods may cause worrying perceptions from the gut. Early recognition of autism spectrum disorders is essential for finding better ways to help patients with gastrointestinal and, as is often the case, extraintestinal symptoms.

The regulatory role of bile acid microbiota in the progression of liver cirrhosis

Bile acids (BAs) are synthesized in liver tissue from cholesterol and are an important endocrine regulator and signaling molecule in the liver and intestine. It maintains BAs homeostasis, and the integrity of intestinal barrier function, and regulates enterohepatic circulation in vivo by modulating farnesoid X receptors (FXR) and membrane receptors. Cirrhosis and its associated complications can lead to changes in the composition of intestinal micro-ecosystem, resulting in dysbiosis of the intestinal microbiota. These changes may be related to the altered composition of BAs. The BAs transported to the intestinal cavity through the enterohepatic circulation are hydrolyzed and oxidized by intestinal microorganisms, resulting in changes in their physicochemical properties, which can also lead to dysbiosis of intestinal microbiota and overgrowth of pathogenic bacteria, induction of inflammation, and damage to the intestinal barrier, thus aggravating the progression of cirrhosis. In this paper, we review the discussion of BAs synthesis pathway and signal transduction, the bidirectional regulation of bile acids and intestinal microbiota, and further explore the role of reduced total bile acid concentration and dysregulated intestinal microbiota ratio in the development of cirrhosis, in order to provide a new theoretical basis for the clinical treatment of cirrhosis and its complications.

Gentamicin alleviates cholestatic liver injury by decreasing gut microbiota-associated bile salt hydrolase activity in rats

Intrahepatic cholestasis lacks effective therapeutic drugs. The gut microbiota-associated bile salt hydrolases (BSH) may be a potential therapeutic target. In this study, oral administration of gentamicin (GEN) decreased the serum and hepatic levels of total bile acid in 17α-ethynylestradiol (EE)-induced cholestatic male rats, significantly improved the serum levels of hepatic biomarkers and reversed the histopathological changes in the liver. In healthy male rats, the serum and hepatic levels of total bile acid were also decreased by GEN, the ratio of primary to secondary bile acids, and conjugated to unconjugated bile acids was significantly increased, and the urinary excretion of total bile acid was elevated. 16S rDNA sequencing of the ileal contents revealed that GEN treatment substantially reduced the abundance of Lactobacillus and Bacteroides both of which expressed BSH. Consistently, BSH activity analysis by the generation of d5-chenodeoxycholic acid from d5-taurochenodeoxycholic acid in situ showed BSH was significantly inhibited in the ileal contents of rats treated with GEN. This finding led to an increased proportion of hydrophilic conjugated bile acids and facilitated the urinary excretion of total bile acids, thereby decreasing serum and hepatic total bile acids and reversing liver injury related to cholestasis. Our results provide important evidence that BSH can be a potential drug target for treating cholestasis.

Pharmacological inhibition of MEK1/2 signaling disrupts bile acid metabolism through loss of Shp and enhanced Cyp7a1 expression

The RAS-MAPK signaling pathway is one of the most frequently dysregulated pathways in human cancer. Small molecule inhibitors directed against this pathway have clinical activity in patients with various cancer types and can improve patient outcomes. However, the use of these drugs is associated with adverse effects, which can result in dose reduction or treatment interruption. A better molecular understanding of on-target, off-tumor effects may improve toxicity management. In the present study, we aimed to identify early initiating biological changes in the liver upon pharmacological inhibition of the RAS-MAPK signaling pathway. To this end, we tested the effect of MEK inhibitor PD0325901 using mice and human hepatocyte cell lines. Male C57BL/6 mice were treated with either vehicle or PD0325901 for six days, followed by transcriptome analysis of the liver and phenotypic characterization. Pharmacological MEK inhibition altered the expression of 423 genes, of which 78 were upregulated and 345 were downregulated. We identified Shp, a transcriptional repressor, and Cyp7a1, the rate-limiting enzyme in converting cholesterol to bile acids, as the top differentially expressed genes. PD0325901 treatment also affected other genes involved in bile acid regulation, which was associated with changes in the composition of plasma bile acids and composition and total levels of fecal bile acids and elevated predictive biomarkers of early liver toxicity. In conclusion, short-term pharmacological MEK inhibition results in profound changes in bile acid metabolism, which may explain some of the clinical adverse effects of pharmacological inhibition of the RAS-MAPK pathway, including gastrointestinal complications and hepatotoxicity.

Bile acid conjugation deficiency causes hypercholanemia, hyperphagia, islet dysfunction, and gut dysbiosis in mice

Bile acid-CoA: amino acid N-acyltransferase (BAAT) catalyzes bile acid conjugation, the last step in bile acid synthesis. BAAT gene mutation in humans results in hypercholanemia, growth retardation, and fat-soluble vitamin insufficiency. The current study investigated the physiological function of BAAT in bile acid and lipid metabolism using Baat-/- mice. The bile acid composition and hepatic gene expression were analyzed in 10-week-old Baat-/- mice. They were also challenged with a westernized diet (WD) for additional 15 weeks to assess the role of BAAT in bile acid, lipid, and glucose metabolism. Comprehensive lab animal monitoring system and cecal 16S ribosomal RNA gene sequencing were used to evaluate the energy metabolism and microbiome structure of the mice, respectively. In Baat-/- mice, hepatic bile acids were mostly unconjugated and their levels were significantly increased compared with wild-type mice. Bile acid polyhydroxylation was markedly up-regulated to detoxify unconjugated bile acid accumulated in Baat-/- mice. Although the level of serum marker of bile acid synthesis, 7α-hydroxy-4-cholesten-3-one, was higher in Baat-/- mice, their bile acid pool size was smaller. When fed a WD, the Baat-/- mice showed a compromised body weight gain and impaired insulin secretion. The gut microbiome of Baat-/- mice showed a low level of sulfidogenic bacteria Bilophila. Conclusion: Mouse BAAT is the major taurine-conjugating enzyme. Its deletion protected the animals from diet-induced obesity, but caused glucose intolerance. The gut microbiome of the Baat-/- mice was altered to accommodate the unconjugated bile acid pool.

Circadian Rhythms Coordinated With Gut Microbiota Partially Account for Individual Differences in Hepatitis B-Related Cirrhosis

Cirrhosis is the end stage of chronic liver diseases like chronic hepatitis B. In China, hepatitis B accounts for around 60% of cases of cirrhosis. So far, clinical and laboratory indexes for the early diagnosis of cirrhosis are far from satisfactory. Nevertheless, there haven’t been specific drugs for cirrhosis. Thus, it is quite necessary to uncover more specific factors which play their roles in cirrhosis and figure out the possible therapeutic targets. Among emerging factors taking part in the initiation and progression of cirrhosis, gut microbiota might be a pivot of systemic factors like metabolism and immune and different organs like gut and liver. Discovery of detailed molecular mechanism in gut microbiota and gut liver axis leads to a more promising prospect of developing new drugs intervening in these pathways. Time-based medication regimen has been proofed to be helpful in hormonotherapy, especially in the use of glucocorticoid. Thus, circadian rhythms, though haven’t been strongly linked to hepatitis B and its complications, are still pivotal to various pathophysiological progresses. Gut microbiota as a potential effective factor of circadian rhythms has also received increasing attentions. Here, our work, restricting cirrhosis to the post-hepatitis B one, is aimed to summarize how circadian rhythms and hepatitis B-related cirrhosis can intersect via gut microbiota, and to throw new insights on the development of new and time-based therapies for hepatitis B-related cirrhosis and other cirrhosis.

From Dietary Cholesterol to Blood Cholesterol, Physiological Lipid Fluxes, and Cholesterol Homeostasis

Dietary cholesterol (C) is a major contributor to the endogenous C pool, and it affects the serum concentration of total C, particularly the low-density lipoprotein cholesterol (LDL-C). A high serum concentration of LDL-C is associated with an increased risk for atherosclerosis and cardiovascular diseases. This concentration is dependent on hepatic C metabolism creating a balance between C input (absorption and synthesis) and C elimination (conversion to bile acids and fecal excretion). The daily C absorption rate is determined by dietary C intake, biliary C secretion, direct trans-intestinal C excretion (TICE), and the fractional C absorption rate. Hepatic C metabolism coordinates C fluxes entering the liver via chylomicron remnants (CMR), LDL, high-density lipoproteins (HDL), hepatic C synthesis, and those leaving the liver via very low-density lipoproteins (VLDL), biliary secretion, and bile acid synthesis. The knowns and the unknowns of this C homeostasis are discussed.

Modulation of Bile Acid Metabolism to Improve Plasma Lipid and Lipoprotein Profiles

New drugs targeting bile acid metabolism are currently being evaluated in clinical studies for their potential to treat cholestatic liver diseases, non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). Changes in bile acid metabolism, however, translate into an alteration of plasma cholesterol and triglyceride concentrations, which may also affect cardiovascular outcomes in such patients. This review attempts to gain insight into this matter and improve our understanding of the interactions between bile acid and lipid metabolism. Bile acid sequestrants (BAS), which bind bile acids in the intestine and promote their faecal excretion, have long been used in the clinic to reduce LDL cholesterol and, thereby, atherosclerotic cardiovascular disease (ASCVD) risk. However, BAS modestly but consistently increase plasma triglycerides, which is considered a causal risk factor for ASCVD. Like BAS, inhibitors of the apical sodium-dependent bile acid transporter (ASBTi’s) reduce intestinal bile acid absorption. ASBTi’s show effects that are quite similar to those obtained with BAS, which is anticipated when considering that accelerated faecal loss of bile acids is compensated by an increased hepatic synthesis of bile acids from cholesterol. Oppositely, treatment with farnesoid X receptor agonists, resulting in inhibition of bile acid synthesis, appears to be associated with increased LDL cholesterol. In conclusion, the increasing efforts to employ drugs that intervene in bile acid metabolism and signalling pathways for the treatment of metabolic diseases such as NAFLD warrants reinforcing interactions between the bile acid and lipid and lipoprotein research fields. This review may be considered as the first step in this process.

Circulating bile acids concentration is predictive of coronary artery disease in human

Synthetized by the liver and metabolized by the gut microbiota, BA are involved in metabolic liver diseases that are associated with cardiovascular disorders. Animal models of atheroma documented a powerful anti-atherosclerotic effect of bile acids (BA). This prospective study examined whether variations in circulating BA are predictive of coronary artery disease (CAD) in human. Consecutive patients undergoing coronary angiography were enrolled. Circulating and fecal BA were measured by high pressure liquid chromatography and tandem mass spectrometry. Of 406 screened patients, 80 were prospectively included and divided in two groups with (n = 45) and without (n = 35) CAD. The mean serum concentration of total BA was twice lower in patients with, versus without CAD (P = 0.005). Adjusted for gender and age, this decrease was an independent predictor of CAD. In a subgroup of 17 patients, statin therapy doubled the serum BA concentration. Decreased serum concentrations of BA were predictors of CAD in humans. A subgroup analysis showed a possible correction by statins. With respect to the anti-atherosclerotic effect of BA in animal models, and their role in human lipid metabolism, this study describe a new metabolic disturbance associated to CAD in human.

Chyme Reinfusion Restores the Regulatory Bile Salt-FGF19 Axis in Patients With Intestinal Failure

BACKGROUND AND AIMS

Automated chyme reinfusion (CR) in patients with intestinal failure (IF) and a temporary double enterostomy (TDE) restores intestinal function and protects against liver injury, but the mechanisms are incompletely understood. The aim was to investigate whether the beneficial effects of CR relate to functional recovery of enterohepatic signaling through the bile salt-FGF19 axis.

APPROACH AND RESULTS

Blood samples were collected from 12 patients, 3 days before, at start, and 1, 3, 5, and 7 weeks after CR initiation. Plasma FGF19, total bile salts (TBS), 7-α-hydroxy-4-cholesten-3-one (C4; a marker of bile salt synthesis), citrulline (CIT), bile salt composition, liver tests, and nutritional risk indices were determined. Paired small bowel biopsies prior to CR and after 21 days were taken, and genes related to bile salt homeostasis and enterocyte function were assessed. CR induced an increase in plasma FGF19 and decreased C4 levels, indicating restored regulation of bile salt synthesis through endocrine FGF19 action. TBS remained unaltered during CR. Intestinal farnesoid X receptor was up-regulated after 21 days of CR. Secondary and deconjugated bile salt fractions were increased after CR, reflecting restored microbial metabolism of host bile salts. Furthermore, CIT and albumin levels gradually rose after CR, while abnormal serum liver tests normalized after CR, indicating restored intestinal function, improved nutritional status, and amelioration of liver injury. CR increased gene transcripts related to enterocyte number, carbohydrate handling, and bile salt homeostasis. Finally, the reciprocal FGF19/C4 response after 7 days predicted the plasma CIT time course.

CONCLUSIONS

CR in patients with IF-TDE restored bile salt-FGF19 signaling and improved gut-liver function. Beneficial effects of CR are partly mediated by recovery of the bile salt-FGF19 axis and subsequent homeostatic regulation of bile salt synthesis.

Manipulating the Microbiome: An Alternative Treatment for Bile Acid Diarrhoea

Bile acid diarrhoea (BAD) is a widespread gastrointestinal disease that is often misdiagnosed as irritable bowel syndrome and is estimated to affect 1% of the United Kingdom (UK) population alone. BAD is associated with excessive bile acid synthesis secondary to a gastrointestinal or idiopathic disorder (also known as primary BAD). Current licensed treatment in the UK has undesirable effects and has been the same since BAD was first discovered in the 1960s. Bacteria are essential in transforming primary bile acids into secondary bile acids. The profile of an individual’s bile acid pool is central in bile acid homeostasis as bile acids regulate their own synthesis. Therefore, microbiome dysbiosis incurred through changes in diet, stress levels and the introduction of antibiotics may contribute to or be the cause of primary BAD. This literature review focuses on primary BAD, providing an overview of bile acid metabolism, the role of the human gut microbiome in BAD and the potential options for therapeutic intervention in primary BAD through manipulation of the microbiome.

Biochemical Diagnosis of Bile Acid Diarrhea: Prospective Comparison With the 75Seleno-Taurohomocholic Acid Test

INTRODUCTION

The diagnosis of bile acid diarrhea is often missed because the availability of the seleno-taurohomocholic acid (SeHCAT) test is limited. We aimed to compare the biomarkers 7α-hydroxy-4-cholesten-3-one (C4) and fibroblast growth factor 19 (FGF19) with the SeHCAT test.

METHODS

Patients with chronic diarrhea without intestinal resection referred for SeHCAT were prospectively recruited for this diagnostic accuracy study. Blood was sampled at fasting and after a stimulation meal with chenodeoxycholic acid. SeHCAT retention ≤10% defined bile acid diarrhea and >10% defined miscellaneous diarrhea. Receiver operating characteristics (ROC) were analyzed with SeHCAT as the gold standard. www.clinicaltrials.gov (NCT03059537).

RESULTS

Patients with bile acid diarrhea (n = 26) had mean C4 of 30 ng/mL (95% confidence interval: 19-46) vs 8 (7-11; P < 0.001) in the miscellaneous diarrhea group (n = 45). Area under the ROC curve (ROCAUC) for C4 was 0.83 (0.72-0.93). C4 < 15 ng/mL had 85% (74%-96%) negative predictive value; C4 > 48 ng/mL had 82% (59%-100%) positive predictive value. Twenty patients had C4 values 15-48 ng/mL, of whom 11/20 had SeHCAT ≤10%. Median fasting FGF19 was 72 pg/mL (interquartile range: 53-146) vs 119 (84-240) (P = 0.004); ROCAUC was 0.71 (0.58-0.83). Stimulated FGF19 responses did not differ (P = 0.54).

DISCUSSION

We identified C4 thresholds with clinically useful predictive values for the diagnosis of and screening for bile acid diarrhea in patients with chronic watery diarrhea. Further validation of the cutoff values with the placebo-controlled effect of sequestrant therapy is warranted (see Visual Abstract, Supplementary Digital Content 2, http://links.lww.com/AJG/B603).

Bile acid metabolism and circadian rhythms

Circadian rhythms are biological systems that synchronize cellular circadian oscillators with the organism's daily feeding-fasting or rest-activity cycles in mammals. Circadian rhythms regulate nutrient absorption and utilization at the cellular level and are closely related to obesity and metabolic disorders. Bile acids are important modulators that facilitate nutrient absorption and regulate energy metabolism. Here, we provide an overview of the current connections and future perspectives between the circadian clock and bile acid metabolism as well as related metabolic diseases. Feeding and fasting cycles influence bile acid pool size and composition, and bile acid signaling can respond to acute lipid and glucose utilization and mediate energy balance. Disruption of circadian rhythms such as shift work, irregular diet, and gene mutations can contribute to altered bile acid metabolism and heighten obesity risk. High-fat diets, alcohol, and gene mutations related to bile acid signaling result in desynchronized circadian rhythms. Gut microbiome also plays a role in connecting circadian rhythms with bile acid metabolism. The underlying mechanism of how circadian rhythms interact with bile acid metabolism has not been fully explored. Sustaining bile acid homeostasis based on circadian rhythms may be a potential therapy to alleviate metabolic disturbance.

Bile Acids and FXR: Novel Targets for Liver Diseases

Bile acids (BAs) are evolutionally conserved molecules synthesized in the liver from cholesterol and have been shown to be essential for lipid homeostasis. BAs regulate a variety of metabolic functions via modulating nuclear and membrane receptors. Farnesoid X receptor (FXR) is the most important nuclear receptor for maintaining BA homeostasis. FXR plays a tissue-specific role in suppressing BA synthesis and promoting BA enterohepatic circulation. Disruption of FXR in mice have been implicated in liver diseases commonly occurring in humans, including cholestasis, non-alcoholic fatty liver diseases, and hepatocellular carcinoma. Strategically targeting FXR activity has been rapidly used to develop novel therapies for the prevention and/or treatment of cholestasis and non-alcoholic steatohepatitis. This review provides an updated literature review on BA homeostasis and FXR modulator development.

Effect of single and multiple doses of elobixibat, an ileal bile acid transporter inhibitor, on chronic constipation: A randomized controlled trial

AIMS

Elobixibat is a minimally absorbed ileal bile acid transporter inhibitor. This study aimed to investigate the safety, tolerability, efficacy, pharmacokinetics and pharmacodynamics of elobixibat in Japanese patients with chronic constipation.

METHODS

This study consisted of single-dose and multiple-dose tests with a dose-escalating design. Sixty patients including females and males were randomized into five dose levels of elobixibat (2.5, 5, 10, 15 or 20 mg, n = 10 per level) and corresponding placebo (n = 2 per group). A crossover design was used to examine food effect in single-dose test. Patients received test tablets once daily for 14 days in multiple-dose test. We assessed pharmacokinetic-dose proportionality, levels of serum high- and low-density lipoprotein cholesterol and plasma 7α-hydroxy-4-cholesten-3-one (C4), food effect and sex-specific effect. Adverse events and bowel functions such as bowel movements, stool consistency and straining were also evaluated.

RESULTS

Food consumption reduced systemic exposure by around 80% [e.g. least squares mean (ratio of breakfast/no breakfast) maximum plasma concentration: 0.2085 (90% confidence interval, 0.1371-0.3172) at 15 mg] while increased plasma C4 level (P < 0.001). In the multiple-dose test, elobixibat reduced low-density lipoprotein cholesterol and increased C4 whilst unaltering high-density lipoprotein cholesterol level. The increased spontaneous bowel movement frequency was correlated with higher dosage and higher C4 level (R²  = 0.5929 at Week 2). Adverse events were mainly gastrointestinal symptoms, most of which were mild.

CONCLUSIONS

Elobixibat should be taken before breakfast. Once-daily administration of elobixibat was found to be safe and tolerated up to 20 mg in female and male patients with chronic constipation.

Bile Acid Metabolism in Liver Pathobiology

Bile acids facilitate intestinal nutrient absorption and biliary cholesterol secretion to maintain bile acid homeostasis, which is essential for protecting liver and other tissues and cells from cholesterol and bile acid toxicity. Bile acid metabolism is tightly regulated by bile acid synthesis in the liver and bile acid biotransformation in the intestine. Bile acids are endogenous ligands that activate a complex network of nuclear receptor farnesoid X receptor and membrane G protein-coupled bile acid receptor-1 to regulate hepatic lipid and glucose metabolic homeostasis and energy metabolism. The gut-to-liver axis plays a critical role in the regulation of enterohepatic circulation of bile acids, bile acid pool size, and bile acid composition. Bile acids control gut bacteria overgrowth, and gut bacteria metabolize bile acids to regulate host metabolism. Alteration of bile acid metabolism by high-fat diets, sleep disruption, alcohol, and drugs reshapes gut microbiome and causes dysbiosis, obesity, and metabolic disorders. Gender differences in bile acid metabolism, FXR signaling, and gut microbiota have been linked to higher prevalence of fatty liver disease and hepatocellular carcinoma in males. Alteration of bile acid homeostasis contributes to cholestatic liver diseases, inflammatory diseases in the digestive system, obesity, and diabetes. Bile acid-activated receptors are potential therapeutic targets for developing drugs to treat metabolic disorders.

Spexin Acts as Novel Regulator for Bile Acid Synthesis

Spexin is a novel hormone involved in obesity and diabetes while its biofunctional significance in lipid metabolism is still to be comprehended. Global metabolomic analysis in the present study revealed multiple metabolic pathways altered by spexin intraperitoneal (i.p.) injection in rat serum, which are highlighted by the changes in several bile acid metabolites. In rats, spexin (300 μg/kg) could dramatically reduce hepatic and circulating total bile acids (TBA) level compared with the controls. Correspondingly, treatment with spexin by i.p. injection for 28 days led to significant decrease in serum TBA and gallbladder weight in C57BL/6J mice. In enterohepatic circulation system, spexin effectively reduced TBA levels in mouse liver and gallbladder but not the intestine. Hepatic cholesterol 7α-hydroxylase 1 (CYP7A1) expression, unsurprisingly, was suppressed by spexin injection. Both GALR2 and GALR3 antagonists reversed the inhibitory effects of spexin on concentrations of serum TBA and 7 α-hydroxy-4-cholesten-3-one (C4), and hepatic CYP7A1 expression. Finally, negative correlations were observed between serum spexin and total cholesterol (TC), total bile acid (TBA), tauro-chenodeoxycholate (TCDCA), as well as glycochenodeoxycholate (GCDCA) in 91 healthy volunteers. These findings illuminate the intrinsic importance of spexin in the regulation of bile acid synthesis and metabolism.

The Role of the Gut Microbiota in Bile Acid Metabolism

The gut microbiota has been considered a cornerstone of maintaining the health status of its human host because it not only facilitates harvesting of nutrients and energy from ingested food, but also produces numerous metabolites that can regulate host metabolism. One such class of metabolites, the bile acids, are synthesized from cholesterol in the liver and further metabolized by the gut microbiota into secondary bile acids. These bioconversions modulate the signaling properties of bile acids through the nuclear farnesoid X receptor and the G protein-coupled membrane receptor 5, which regulate diverse metabolic pathways in the host. In addition, bile acids can regulate gut microbial composition both directly and indirectly by activation of innate immune response genes in the small intestine. Therefore, host metabolism can be affected by both microbial modifications of bile acids, which leads to altered signaling via bile acid receptors, and by alterations in the composition of the microbiota. In this review, we mainly describe the interactions between bile acids and intestinal microbiota and their roles in regulating host metabolism, but we also examine the impact of bile acid composition in the gut on the intestinal microbiome and on host physiology.

LC-MS/MS quantification of 7α-hydroxy-4-cholesten-3-one (C4) in rat and monkey plasma

7α-hydroxy-4-cholesten-3-one (C4) is an oxidative enzymatic product of cholesterol metabolism via cholesterol 7α-hydroxylase, an enzyme also known as cholesterol 7-alpha-monooxygenase or cytochrome P450 7A1 (CYP7A1). C4 is a stable intermediate in the rate limiting pathway of bile acid biosynthesis. Previous studies showed that plasma C4 levels correlated with CYP7A1 enzymatic activity and could serve as a biomarker for bile acid synthesis. Here we developed and qualified a simple and robust high-throughput method using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) to quantify C4 in rat and monkey plasma. As C4 being an endogenous compound, this method used calibration standards in 50/50: acetonitrile/water (v/v). In order to mimic the incurred samples, quality control samples were prepared in the authentic plasma. Stable isotope labeled C4 (C4-d₇) was used as the internal standard. The sample volume for analysis was 20μL and the sample preparation method was protein precipitation with acetonitrile. The average endogenous C4 concentrations, from 10 different lots of rat and monkey plasma, were 53.0±16.5ng/mL and 6.8±5.6ng/mL, respectively. Based on these observed endogenous C4 levels, the calibration curve ranges were established at 1-200ng/mL and 0.5-100ng/mL for rat assay and monkey assay, respectively. The method was qualified with acceptable accuracy, precision, linearity, and specificity. Matrix effect, recovery, and plasma stability of bench-top, freeze-thaw, and long-term frozen storage were also evaluated. The method has been successfully applied to pre-clinical studies.

Acute caloric restriction counteracts hepatic bile acid and cholesterol deficiency in morbid obesity

BACKGROUND

Bile acid (BA) synthesis is regulated by BA signalling in the liver and by fibroblast growth factor 19 (FGF19), synthesized and released from the intestine. In morbid obesity, faecal excretion and hepatic synthesis of BAs and cholesterol are strongly induced and caloric restriction reduces their faecal excretion considerably. We hypothesized that the high intestinal food mass in morbidly obese subjects promotes faecal excretion of BAs and cholesterol, thereby creating a shortage of both BAs and cholesterol in the liver.

METHODS

Ten morbidly obese women (BMI 42 ± 2.6 kg m^-2 ) were monitored on days 0, 3, 7, 14 and 28 after beginning a low-calorie diet (800-1100 kcal day^-1 ). Serum was collected and liver size and fat content determined. Synthesis of BAs and cholesterol was evaluated from serum markers, and the serum levels of lipoproteins, BAs, proprotein convertase subtilisin/kexin type 9 (PCSK9), insulin, glucose and FGF19 were monitored. Fifty-four nonobese women (BMI <25 kg m^-2 ) served as controls.

RESULTS

At baseline, synthesis of both BAs and cholesterol and serum levels of BAs and PCSK9 were elevated in the obese group compared to controls. Already after 3 days on a low-calorie diet, BA and cholesterol synthesis and serum BA and PCSK9 levels normalized, whereas LDL cholesterol increased. FGF19 and triglyceride levels were unchanged, and liver volume was reduced by 10%.

CONCLUSIONS

The results suggest that hepatic BAs and cholesterol are deficient in morbid obesity. Caloric restriction rapidly counteracts these deficiencies, normalizing BA and cholesterol synthesis and circulating PCSK9 levels, indicating that overproduction of cholesterol in enlarged peripheral tissues cannot explain this phenotype. We propose that excessive food intake promotes faecal loss of BAs and cholesterol contributing to their hepatic deficiencies.

The ascending pathophysiology of cholestatic liver disease

In this review we develop the argument that cholestatic liver diseases, particularly primary biliary cholangitis and primary sclerosing cholangitis (PSC), evolve over time with anatomically an ascending course of the disease process. The first and early lesions are in "downstream" bile ducts. This eventually leads to cholestasis, and this causes bile salt (BS)-mediated toxic injury of the "upstream" liver parenchyma. BS are toxic in high concentration. These concentrations are present in the canalicular network, bile ducts, and gallbladder. Leakage of bile from this network and ducts could be an important driver of toxicity. The liver has a great capacity to adapt to cholestasis, and this may contribute to a variable symptom-poor interval that is often observed. Current trials with drugs that target BS toxicity are effective in only about 50%-60% of primary biliary cholangitis patients, with no effective therapy in PSC. This motivated us to develop and propose a new view on the pathophysiology of primary biliary cholangitis and PSC in the hope that these new drugs can be used more effectively. These views may lead to better stratification of these diseases and to recommendations on a more "tailored" use of the new therapeutic agents that are currently tested in clinical trials. Apical sodium-dependent BS transporter inhibitors that reduce intestinal BS absorption lower the BS load and are best used in cholestatic patients. The effectiveness of BS synthesis-suppressing drugs, such as farnesoid X receptor agonists, is greatest when optimal adaptation is not yet established. By the time cytochrome P450 7A1 expression is reduced these drugs may be less effective. Anti-inflammatory agents are probably most effective in early disease, while drugs that antagonize BS toxicity, such as ursodeoxycholic acid and nor-ursodeoxycholic acid, may be effective at all disease stages. Endoscopic stenting in PSC should be reserved for situations of intercurrent cholestasis and cholangitis, not for cholestasis in end-stage disease. These are arguments to consider a step-wise pathophysiology for these diseases, with therapy adjusted to disease stage. An obstacle in such an approach is that disease stage-defining biomarkers are still lacking. This review is meant to serve as a call to prioritize the development of biomarkers that help to obtain a better stratification of these diseases. (Hepatology 2017;65:722-738).

Biomarkers for bile acid diarrhoea in functional bowel disorder with diarrhoea: a systematic review and meta-analysis

There is no universally available laboratory test to diagnose bile acid diarrhoea (BAD).

OBJECTIVE

To conduct a systematic review and meta-analysis to identify a biomarker for idiopathic BAD in patients with functional bowel disorder (FBD) with diarrhoea.

DESIGN

We searched multiple databases through 15 May 2015. Data were only available to estimate the diagnostic yield of each test (the prevalence of a positive test). Estimates were pooled across studies using the random effects model.

RESULTS

We included 36 studies, enrolling 5028 patients (24 using ⁷⁵selenium homotaurocholic acid test (⁷⁵SeHCAT) retention of <10%, 6 using fasting serum C4, 3 using fasting serum fibroblast growth factor 19 (FGF19) and 2 based on total faecal bile acid (BA) excretion over 48 h). The diagnostic yields (and 95% CI) of abnormal tests were: 0.308 (0.247 to 0.377) for ⁷⁵SeHCAT retention (<10%), 0.171 (0.134 to 0.217) for serum C4, 0.248 (0.147 to 0.385) for serum FGF19 and 0.255 (0.071 to 0.606) for total faecal BA excretion over 48 h. The majority of the analyses were associated with substantial heterogeneity. Performance characteristics relative to a gold standard test could not be estimated.

CONCLUSIONS

Overall, the test with the highest diagnostic yield conducted in the largest number of studies was ⁷⁵SeHCAT retention, which is not widely available in many countries outside Europe and Canada. Using different diagnostic tests, 25% (average) of patients with lower FBD with diarrhoea has evidence of idiopathic BAD. These tests serve to identify idiopathic BAD among patients with FBD with diarrhoea. Further studies are required to appraise the performance characteristics of tests for idiopathic BAD.

Cholic acid therapy in Zellweger spectrum disorders

INTRODUCTION

Zellweger spectrum disorders (ZSDs) are characterized by a failure in peroxisome formation, caused by autosomal recessive mutations in different PEX genes. At least some of the progressive and irreversible clinical abnormalities in patients with a ZSD, particularly liver dysfunction, are likely caused by the accumulation of toxic bile acid intermediates. We investigated whether cholic acid supplementation can suppress bile acid synthesis, reduce accumulation of toxic bile acid intermediates and improve liver function in these patients.

METHODS

An open label, pretest-posttest design study was conducted including 19 patients with a ZSD. Participants were followed longitudinally during a period of 2.5 years prior to the start of the intervention. Subsequently, all patients received oral cholic acid and were followed during 9 months of treatment. Bile acids, peroxisomal metabolites, liver function and liver stiffness were measured at baseline and 4, 12 and 36 weeks after start of cholic acid treatment.

RESULTS

During cholic acid treatment, bile acid synthesis decreased in the majority of patients. Reduced levels of bile acid intermediates were found in plasma and excretion of bile acid intermediates in urine was diminished. In patients with advanced liver disease (n = 4), cholic acid treatment resulted in increased levels of plasma transaminases, bilirubin and cholic acid with only a minor reduction in bile acid intermediates.

CONCLUSIONS

Oral cholic acid therapy can be used in the majority of patients with a ZSD, leading to at least partial suppression of bile acid synthesis. However, caution is needed in patients with advanced liver disease due to possible hepatotoxic effects.

Prolonged fibroblast growth factor 19 response in patients with primary sclerosing cholangitis after an oral chenodeoxycholic acid challenge

Background

Bile salts likely contribute to liver injury in patients with primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC). Fibroblast growth factor 19 (FGF19) is a bile salt-induced enterokine with hepatoprotective potential as it suppresses de novo bile salt synthesis. Here, we evaluated the bile salt receptor FXR/FGF19 gut–liver axis in PSC and PBC patients.

Methods

Fasted patients with PSC (n = 12) and PBC (n = 10), and healthy controls (HC; n = 10) were orally challenged with the natural FXR agonist chenodeoxycholic acid (CDCA 15 mg/kg). Blood was sampled hourly until 8 h afterwards. Serum FGF19 and bile salt excursions were determined. Serum levels of 7α-hydroxy-4-cholesten-3-one (C4), reflecting bile salt synthesis, were measured as a biomarker of FGF19 response.

Results

Baseline serum FGF19 levels were comparable between groups, while fasted bile salt levels in PSC patients were elevated. Upon CDCA challenge, HC and PBC patients showed a serum FGF19 peak after 4 h followed by a decline. PSC patients showed a prolonged and elevated serum FGF19 response up to 8 h, combined with a sustained serum elevation of CDCA and other bile salts. In general, C4 levels declined following FGF19 elevation. In PSC patients with less favorable prognosis, baseline C4 levels were drastically suppressed and did not further decline.

Conclusion

Following an oral CDCA challenge, PSC patients showed an impaired clearance of CDCA and a prolonged serum FGF19 response. FXR agonist therapy in PSC could cause prolonged exposure to elevated levels of FGF19, and we propose careful monitoring for detrimental side effects in patient studies.

Electronic supplementary material

The online version of this article (doi:10.1007/s12072-016-9769-7) contains supplementary material, which is available to authorized users.

Review article: bile acid diarrhoea - pathogenesis, diagnosis and management

BACKGROUND

Bile acid diarrhoea results from imbalances in the homoeostasis of bile acids in the enterohepatic circulation. It can be a consequence of ileal disease/dysfunction, associated with other GI pathology or can be idiopathic.

AIMS

To summarise the different types of bile acid diarrhoea and discuss the currently available diagnostic methods and treatments.

RESULTS

Bile acid diarrhoea is found in up to 40% of patients diagnosed as having functional diarrhoea/IBS-D, and in up to 80% of patients who have undergone ileal resection. It is likely under-diagnosed and under-treated. In idiopathic disease, errors in regulation feedback of fibroblast growth factor 19 contribute to the development of the condition. Clinical therapeutic trials for bile acid diarrhoea have been used to diagnose it, but the ⁷⁵ SeHCAT test is the primary current method. It is sensitive, specific and widely available, though not in the USA. Other diagnostic methods (such as serum measurement of the bile acid intermediate 7α-hydroxy-4-cholesten-3-one, or C4) have less widespread availability and documentation, and some (such as faecal measurement of bile acids) are significantly more complex and costly. First-line treatment of bile acid diarrhoea is with the bile acid sequestrant cholestyramine, which can be difficult to administer and dose due to gastrointestinal side effects. These side effects are less prominent in newer agents such as colesevelam, which may provide higher efficacy, tolerability and compliance.

CONCLUSION

Bile acid diarrhoea is common, and likely under-diagnosed. Bile acid diarrhoea should be considered relatively early in the differential diagnosis of chronic diarrhoea.

Bile acids synthesis decreases after laparoscopic sleeve gastrectomy

BACKGROUND

Bariatric surgery is the most effective treatment alternative in morbid obesity. The mechanisms contributing to these benefits remain poorly understood. Bile acids (BAs) are mediators of different regulatory functions in glucose and cholesterol homeostasis and energy expenditure. Recent evidence suggests that BAs are critically important for the beneficial effects of sleeve gastrectomy (SG).

OBJECTIVES

The aim of this study was to evaluate the effect of SG on BA synthesis.

SETTING

University Hospital. Santiago, Chile.

METHODS

Obese patients were evaluated before and after SG (1, 3, 6, and 12 months). BA synthesis was evaluated through the serum marker, 7 α-hydroxy-4-cholesten-3-one (C4). Primary and secondary BA and C4 were determined by high performance liquid chromatography coupled with tandem mass spectrometry detection (HPLC-MS/MS).

RESULTS

From June 2013 to January 2014, 19 patients (age 37.6±7.8 years; BMI 35.8±3.5 kg/m(2); 79% female) were included in this study. Mean weight loss at 1, 3, 6, and 12 months was 11.3, 17.5, 23.6, and 25.4 kg, respectively, equivalent to 11.8, 18.6, 24.8, and 26.9 of total body water percentage (%TBW) (P<.0001), respectively and 43.2, 68.2, 91, and 98.8 of percentage of excess weight loss (%EWL), respectively (P<.001). Serum C4 levels at baseline, 1, 3, 6, and 12 months were 23.4±21.1, 4.9±8.2, 8.7±12.1, 13.8±12.9, and 18.8±16.8 ng/mL (P<.0001), respectively. Fibroblast growth factor 19 (FGF19) levels at baseline, 1, 3, 6, and 12 months were 71±33.3, 130.5±66.2, 117.8±57.2, 134.6±91.7, and 124.3±85.9 pg/mL (P = .019), respectively.

CONCLUSION

Serum levels of C4 decrease after SG, indicating a reduction in the synthesis of BA. FGF19 may play a role in decreasing BA synthesis. Further studies are necessary to characterize the effect of bariatric surgery on BA homeostasis.

Effect of different fat-enriched meats on non-cholesterol sterols and oxysterols as markers of cholesterol metabolism: Results of a randomized and cross-over clinical trial

BACKGROUND AND AIM

Different kinds of fatty acids can affect the synthesis, absorption, and elimination of cholesterol. This study was carried out to assess the associations of cholesterol metabolism with the intake of two meats with different fatty acid composition in healthy volunteers.

METHODS AND RESULTS

The study group was composed of 20 subjects (12 males and eight females; age, 34.4 ± 11.6 years; body mass index (BMI), 23.5 ± 2.3 kg/m(2); low-density lipoprotein (LDL) cholesterol, 2.97 ± 0.55 mmol/l; high-density lipoprotein (HDL) cholesterol, 1.61 ± 0.31 mmol/l; triglycerides (TG), 1.06 ± 0.41 mmol/l) who completed a 30-day randomized and cross-over study to compare the cholesterol metabolism effect of 250 g of low-fat lamb versus 250 g of high-fat lamb per day in their usual diet. Cholesterol absorption, synthesis, and elimination were estimated from the serum non-cholesterol sterol and oxysterol concentrations analyzed by a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). No changes in weight, plasma lipids, or physical activity were observed across the study. Cholesterol intestinal absorption was decreased with both diets. Cholesterol synthesis and elimination decreased during the low-fat lamb dietary intervention (ρ = 0.048 and ρ = 0.005, respectively).

CONCLUSION

Acute changes in the diet fat content modify the synthesis, absorption, and biliary elimination of cholesterol. These changes were observed even in the absence of total and LDL cholesterol changes in plasma.

REGISTRATION NUMBER FOR CLINICAL TRIALS

ClinicalTrials.gov PRS, NCT02259153.

Bile acid signaling in metabolic disease and drug therapy

Bile acids are the end products of cholesterol catabolism. Hepatic bile acid synthesis accounts for a major fraction of daily cholesterol turnover in humans. Biliary secretion of bile acids generates bile flow and facilitates hepatobiliary secretion of lipids, lipophilic metabolites, and xenobiotics. In the intestine, bile acids are essential for the absorption, transport, and metabolism of dietary fats and lipid-soluble vitamins. Extensive research in the last 2 decades has unveiled new functions of bile acids as signaling molecules and metabolic integrators. The bile acid-activated nuclear receptors farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, vitamin D receptor, and G protein-coupled bile acid receptor play critical roles in the regulation of lipid, glucose, and energy metabolism, inflammation, and drug metabolism and detoxification. Bile acid synthesis exhibits a strong diurnal rhythm, which is entrained by fasting and refeeding as well as nutrient status and plays an important role for maintaining metabolic homeostasis. Recent research revealed an interaction of liver bile acids and gut microbiota in the regulation of liver metabolism. Circadian disturbance and altered gut microbiota contribute to the pathogenesis of liver diseases, inflammatory bowel diseases, nonalcoholic fatty liver disease, diabetes, and obesity. Bile acids and their derivatives are potential therapeutic agents for treating metabolic diseases of the liver.

Bile acid malabsorption assessed by 7 alpha-hydroxy-4-cholesten-3-one in pediatric inflammatory bowel disease: correlation to clinical and laboratory findings

BACKGROUND AND AIMS

Measurement of 7 alpha-hydroxy-4-cholesten-3-one (C4) in serum is a semiquantitative test for bile acid malabsorption (BAM). We have previously established pediatric normal values for C4 with an upper limit of normal of 66.5 ng/mL, independent of age and sex. Here we performed the C4 test in 58 pediatric patients with Crohn's disease (CD) and ulcerative colitis (UC).

METHODS

C4 was measured using high performance liquid chromatography (HPLC) in fasting serum samples of 44 patients with CD (range 7-19 years) and 14 with UC (4-18 years). Disease activity was assessed by the pediatric CD and UC activity indices (PCDAI and PUCAI, respectively) plus serum (CRP, ESR) and fecal inflammatory markers (calprotectin).

RESULTS

C4 concentrations were increased in 10 CD (23%) (range: 70.8-269.3 ng/mL) but only one UC patient (72.9 ng/mL). CD patients with diarrhea (n=12) had higher C4-values compared to those without (76.9 vs. 30.4 ng/mL; p=0.0043). Ileal resection in CD patients (n=10) was associated with increased C4 concentrations (81.2 vs. 24.3 ng/mL, p=0.0004). No correlation was found between C4 values and inflammatory markers. Six of 7 CD patients with persistent diarrhea but quiescent disease (PCDAI ≤12.5) had C4 values indicating BAM.

CONCLUSION

Elevated C4 concentrations indicating BAM are common in children with CD. They are associated with ileal resection and non-bloody diarrhea in the absence of active disease or elevated inflammatory markers. The C4-test identifies a subgroup of CD patients with persistent diarrhea in spite of clinical remission which may benefit from bile acid binding therapy.

Thyroid hormone reduces PCSK9 and stimulates bile acid synthesis in humans

Reduced plasma LDL-cholesterol is a hallmark of hyperthyroidism and is caused by transcriptional stimulation of LDL receptors in the liver. Here, we investigated whether thyroid hormone (TH) actions involve other mechanisms that may also account for the reduction in LDL-cholesterol, including effects on proprotein convertase subtilisin/kexin type 9 (PCSK9) and bile acid synthesis. Twenty hyperthyroid patients were studied before and after clinical normalization, and the responses to hyperthyroidism were compared with those in 14 healthy individuals after 14 days of treatment with the liver-selective TH analog eprotirome. Both hyperthyroidism and eprotirome treatment reduced circulating PCSK9, lipoprotein cholesterol, apoB and AI, and lipoprotein(a), while cholesterol synthesis was stable. Hyperthyroidism, but not eprotirome treatment, markedly increased bile acid synthesis and reduced fibroblast growth factor (FGF) 19 and dietary cholesterol absorption. Eprotirome treatment, but not hyperthyroidism, reduced plasma triglycerides. Neither hyperthyroidism nor eprotirome treatment altered insulin, glucose, or FGF21 levels. TH reduces circulating PSCK9, thereby likely contributing to lower plasma LDL-cholesterol in hyperthyroidism. TH also stimulates bile acid synthesis, although this response is not critical for its LDL-lowering effect.

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

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

Diacylglycerol acyltransferase 1 inhibition with AZD7687 alters lipid handling and hormone secretion in the gut with intolerable side effects: a randomized clinical trial

AIM

Inhibition of diacylglycerol acyltransferase 1 (DGAT1) is a potential treatment modality for patients with type 2 diabetes mellitus and obesity, based on preclinical data suggesting it is associated with insulin sensitization and weight loss. This randomized, placebo-controlled, phase 1 study in 62 overweight or obese men explored the effects and tolerability of AZD7687, a reversible and selective DGAT1 inhibitor.

METHODS

Multiple doses of AZD7687 (1, 2.5, 5, 10 and 20 mg/day, n = 6 or n = 12 for each) or placebo (n = 20) were administered for 1 week. Postprandial serum triacylglycerol (TAG) was measured for 8 h after a standardized 45% fat meal. Glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) were measured and a paracetamol challenge was performed to assess gastric emptying.

RESULTS

Dose-dependent reductions in postprandial serum TAG were demonstrated with AZD7687 doses ≥5 mg compared with placebo (p < 0.01). Significant (p < 0.001) increases in plasma GLP-1 and PYY levels were seen at these doses, but no clear effect on gastric emptying was demonstrated at the end of treatment. With AZD7687 doses >5 mg/day, gastrointestinal (GI) side effects increased; 11/18 of these participants discontinued treatment owing to diarrhoea.

CONCLUSIONS

Altered lipid handling and hormone secretion in the gut were demonstrated during 1-week treatment with the DGAT1 inhibitor AZD7687. However, the apparent lack of therapeutic window owing to GI side effects of AZD7687, particularly diarrhoea, makes the utility of DGAT1 inhibition as a novel treatment for diabetes and obesity questionable.

Age-associated alterations in cholesterol homeostasis: evidence from a cross-sectional study in a Northern Italy population

Background

The modifications of cholesterol metabolism associated with aging are ill-defined. The objective of this study was to define age-associated alterations of the different metabolic pathways controlling cholesterol homeostasis by analyzing circulating sterols.

Methods

We analyzed serum samples collected from 201 adult (75 male, 126 female) subjects within the epidemiological MICOL study (Multicentrica Italiana Colelitiasi). The age range was 38–79 years; 103 had evidence of gallstones. The concentrations of the different sterols, recognized as markers of the main pathways of cholesterol homeostasis, were analyzed by gas chromatography-mass spectrometry, including lathosterol (synthesis), campesterol and sitosterol (absorption), and 7α-hydroxy-4-cholesten-3-one (degradation to bile acids).

Results

A significant direct correlation was detected between age and cholesterol levels (r =0.34, P<0.01). The lathosterol/cholesterol ratio was lower in older age quartiles (P<0.05 by analysis of variance), with an inverse correlation between the lathosterol/cholesterol ratio and age (r=−0.32, P<0.01). Such correlation was particularly evident in females. The campesterol/cholesterol and sitosterol/cholesterol ratios were inversely correlated with aging in control, but not in gallstone patients. The levels of 7α-hydroxy-4-cholesten-3-one were not correlated with age.

Conclusion

These data show a reduction of cholesterol synthesis with aging which is associated with increased circulating cholesterol levels. The finding might be related to a reduced metabolic need for cholesterol in advancing age, leading to a downregulation of the main mechanisms of cholesterol intake in the liver. A different age-related behavior was observed in gallstone-free versus gallstone patients regarding cholesterol absorption. The possible implications in terms of the pharmacological management of hypercholesterolemia in the elderly remain to be defined.

Serum 7-alpha-hydroxy-4-cholesten-3-one as a marker for bile acid loss in children

OBJECTIVE

To establish age-related reference values for 7-alpha-hydroxy-4-cholesten-3-one (C4) in a pediatric population and to investigate bile acid malabsorption in children with short bowel syndrome (SBS).

STUDY DESIGN

Serum was obtained between 8:00 a.m. and 11:00 a.m. from 100 healthy children (52% males, 9 months to 18 years of age) after 10 hours of fasting. Pediatric patients with SBS served as disease controls (n = 12). Following solid-phase extraction and purification, C4 was determined by high-performance liquid chromatography using a ultraviolet detector at a wavelength of 241 nm. The upper limit of normal for C4 concentrations was defined as the mean plus 2 SD of the log-normal distribution.

RESULTS

The mean concentration and SD of C4 in healthy children was 22.8 ± 15.8 ng/mL with no relation to age or sex and an upper limit of normal of 66.5 ng/mL. Normal C4 values were found in 97 of 100 healthy children, and all 12 patients with SBS had C4 concentrations above 100 ng/mL (mean 299.6 ± 167.8 ng/mL; range 105.7-562.1 ng/mL, P < .0001 compared with controls).

CONCLUSIONS

The determined upper limit of normal for C4 concentration in healthy children corresponds to previously published levels in healthy adults and is independent of age and sex. The consistently elevated C4 concentrations in our patients with SBS confirm the reliability of this noninvasive, nonisotopic method to assess bile acid malabsorption in children.

Methods for diagnosis of bile acid malabsorption in clinical practice

Altered concentrations of bile acid (BA) in the colon can cause diarrhea or constipation. More than 25% of patients with irritable bowel syndrome with diarrhea or chronic diarrhea in Western countries have BA malabsorption (BAM). As BAM is increasingly recognized, proper diagnostic methods are needed to help direct the most effective course of treatment for the chronic bowel dysfunction. We review the methodologies, advantages, and disadvantages of tools that directly measure BAM: the (14)C-glycocholate breath and stool test, the (75)selenium homotaurocholic acid test (SeHCAT), and measurements of 7 α-hydroxy-4-cholesten-3-one (C4) and fecal BAs. The (14)C-glycocholate test is laborious and no longer widely used. The (75)SeHCAT has been validated but is not available in the United States. Measurement of serum C4 is a simple and accurate method that can be used for most patients but requires further clinical validation. Assays to quantify fecal BA (total and individual levels) are technically cumbersome and not widely available. Regrettably, none of these tests are routinely available in the United States; assessment of the therapeutic effects of a BA binder is used as a surrogate for diagnosis of BAM. Recent data indicate the advantages to studying fecal excretion of individual BAs and their role in BAM; these could support the use of the fecal BA assay, compared with other tests. Measurement of fecal BA levels could become a routine addition to the measurement of fecal fat in patients with unexplained diarrhea. Availability ultimately determines whether the C4, SeHCAT, or fecal BA test is used; more widespread availability of such tests would enhance clinical management of these patients.

Alterations in bile acid synthesis in carriers of hepatocyte nuclear factor 1α mutations

OBJECTIVES

Heterozygous mutations in hepatocyte nuclear factor 1α (HNF1α) cause maturity onset diabetes of the young 3 (MODY3), an autosomal dominant form of diabetes. Deficiency of HNF1α in mice results in diabetes, hypercholesterolaemia and increased bile acid (BA) and cholesterol synthesis. Little is known about alterations in lipid metabolism in patients with MODY3. The aim of this study was to investigate whether patients with MODY3 have altered cholesterol and BA synthesis and intestinal cholesterol absorption. A secondary aim was to investigate the effects of HNF1α mutations on the transcriptional regulation of BA metabolism.

METHODS

Plasma biomarkers of BA and cholesterol synthesis and intestinal cholesterol absorption were measured in patients with MODY3 (n = 19) and in matched healthy control subjects (n = 15). Cotransfection experiments were performed with several promoters involved in BA metabolism along with expression vectors carrying the mutations found in these patients.

RESULTS

Plasma analysis showed higher levels of BA synthesis in patients with MODY3. No differences were observed in cholesterol synthesis or intestinal cholesterol absorption. Cotransfection experiments showed that one of the mutations (P379A) increased the induction of the cholesterol 7α-hydroxylase promoter compared with HNF1α, without further differences in other studied promoters. By contrast, the other four mutations (L107I, T260M, P291fsinsC and R131Q) reduced the induction of the farnesoid X receptor (FXR) promoter, which was followed by reduced repression of the small heterodimer partner promoter. In addition, these mutations also reduced the induction of the apical sodium-dependent bile salt transporter promoter.

CONCLUSIONS

BA synthesis is increased in patients with MODY3 compared with control subjects. Mutations in HNF1α affect promoters involved in BA metabolism.

Free fatty acids repress small heterodimer partner (SHP) activation and adiponectin counteracts bile acid-induced liver injury in superobese patients with nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease in industrialized countries and may proceed to steatohepatitis (NASH). Apoptosis and free fatty acid (FFA)-induced lipotoxicity are important features of NASH pathogenesis. We have shown a hepatoprotective effect of adiponectin in steatotic livers of hepatitis C virus (HCV) patients and recent data links bile acid (BA) metabolism to the pathogenesis of NAFLD. The aim of this study was to identify potential interactions between BA and FFA metabolism in NAFLD. Liver biopsies and serum samples from 113 morbidly obese patients receiving bariatric surgery, healthy individuals, and moderately obese NAFLD patients were studied. Serum FFA, BA, and M30 were increased in NASH versus simple steatosis, while adiponectin was significantly decreased. The NAFLD activity score (NAS) score correlated with BA levels and reversely with adiponectin. Adiponectin reversely correlated with CD95/Fas messenger RNA (mRNA) and hepatocellular apoptosis. The BA transporter high-affinity Na+ /taurocholate cotransporter (NTCP) and the BA synthesizing enzyme cholesterol 7 alpha-hydroxylase (CYP7A1) were significantly up-regulated in obese patients and hepatoma cells exposed to FFA. Up-regulation of NTCP and CYP7A1 indicate failure to activate small heterodimer partner (SHP) upon farnesoid X receptor (FXR) stimulation by increasing BA concentrations. In line with the NAS score, adiponectin levels were reversely correlated with BA levels. Adiponectin correlated with NTCP and affects Cyp7A1 expression both in vivo and in vitro.

CONCLUSION

BA synthesis and serum BA levels correlated with disease severity in NAFLD, while adiponectin is reversely correlated. FFA exposure prevented SHP-mediated repression of NTCP and Cyp7A1 expression, which lead to increased BA synthesis and uptake. In NASH, BA accumulation induced hepatocyte cell death and late FXR activation failed to prevent hepatocyte injury due to decreased adiponectin levels. Early treatment with FXR ligands and/or adiponectin-receptor agonists might prevent NASH.

Fibroblast Growth Factor 19 and 7α-Hydroxy-4-Cholesten-3-one in the Diagnosis of Patients With Possible Bile Acid Diarrhea

OBJECTIVES:

Increased colonic bile acids can cause chronic diarrhea. Bile acid diarrhea (BAD) is treatable by sequestrants, and may be secondary to ileal disease or primary BAD. It is underdiagnosed, partly because the selenium-75-homocholic acid taurine (SeHCAT) retention test is not available in many countries, and is underutilized in others. Serum 7α-hydroxy-4-cholesten-3-one (C4), a measure of bile acid synthesis, is available for diagnosis in specialist centers. Recently, deficiency of the ileal hormone fibroblast growth factor 19 (FGF19) has been shown in BAD. Our aim is to evaluate the diagnostic value of FGF19 in a large and prospective group of patients with chronic diarrhea, previously investigated with C4.

METHODS:

Patients undergoing routine investigation provided fasting blood samples. C4 was determined by high-performance liquid chromatography, and used to stratify two groups: group 1 (n=119), consisting of patients with normal C4 (≤ 28 ng/ml), and group 2 (n=139), consisting of patients with high C4 (>28 ng/ml), including any of the possible causes of BAD. Serum FGF19 was measured in stored samples by enzyme-linked immunosorbent assay.

RESULTS:

FGF19 and C4 were significantly inversely related (r_s=−0.64, P<0.001). Patients with raised C4 had significantly lower median FGF19 values. Both of these were more marked when secondary to ileal disease, in particular ileal resection, than in primary BAD. The sensitivity and specificity of FGF19 at 145 pg/ml for detecting a C4 level >28 ng/ml were 58% and 79%, respectively. For C4 >60 ng/ml, these were 74% and 72% on receiver-operating characteristic analysis, the area under the curve was 0.80 (95% confidence interval 0.74–0.87).

CONCLUSIONS:

Serum FGF19 could be developed as a simple blood test to increase the diagnostic rates of BAD.

The use of stable and radioactive sterol tracers as a tool to investigate cholesterol degradation to bile acids in humans in vivo

Alterations of cholesterol homeostasis represent important risk factors for atherosclerosis and cardiovascular disease. Different clinical-experimental approaches have been devised to study the metabolism of cholesterol and particularly the synthesis of bile acids, its main catabolic products. Most evidence in humans has derived from studies utilizing the administration of labeled sterols; these have several advantages over in vitro assay of enzyme activity and expression, requiring an invasive procedure such as a liver biopsy, or the determination of fecal sterols, which is cumbersome and not commonly available. Pioneering evidence with administration of radioactive sterol derivatives has allowed to characterize the alterations of cholesterol metabolism and degradation in different situations, including spontaneous disease conditions, aging, and drug treatment. Along with the classical isotope dilution methodology, other approaches were proposed, among which isotope release following radioactive substrate administration. More recently, stable isotope studies have allowed to overcome radioactivity exposure. Isotope enrichment studies during tracer infusion has allowed to characterize changes in the degradation of cholesterol via the "classical" and the "alternative" pathways of bile acid synthesis. Evidence brought by tracer studies in vivo, summarized here, provides an exceptional tool for the investigation of sterol metabolism, and integrate the studies in vitro on human tissue.

An evaluation of the use of serum 7-alpha-hydroxycholestenone as a diagnostic test of bile acid malabsorption causing watery diarrhea

BACKGROUND

Bile acid malabsorption (BAM) is a recognized cause of watery diarrhea, often diagnosed empirically based on clinical response to cholestyramine. The radionuclide selenium-labelled homocholic acid-taurine whole body retention test is expensive, labour intensive and of limited availability.

OBJECTIVE

To report on the clinical performance of serum 7-alphahydroxy-4-cholesten-3-one (7HCO) as a test of BAM in adult patients with unexplained diarrhea.

METHODS

Patients with unexplained diarrhea were investigated over a three-year period. Final diagnosis was determined based on medical history and investigations, serum levels of 7HCO and response to cholestyramine. ROC analysis was used to determine the ideal upper reference range cut-off value to optimize sensitivity/specificity for BAM. Time of blood specimen collection was recorded to investigate possible variation in results throughout the working day.

RESULTS

ROC analysis yielded a sensitivity/specificity of 90%/77% for type 1 BAM (ileal disease/resection) and 97%/74% for type 2 BAM (idiopathic) using 30 ng/mL as the upper limit of normal for serum 7HCO when compared with all other patients. Of 813 patients, 196 tested positive. Serum 7HCO levels were significantly higher in blood specimens that were collected between 12:00 and 13:00 (median 24 ng/mL) than in specimens collected between 09:00 and 10:00 (median 17 ng/mL) (P<0.05).

CONCLUSION

Serum 7HCO testing is a simple, sensitive, noninvasive, inexpensive alternative to other more commonly used tests for BAM. Time of specimen collection, however, resulted in small but significant result variations and, although unlikely to have much impact on test value, it should ideally be standardized.

Role of thyroid receptor β in lipid metabolism

Thyroid hormones (THs) exert their actions by binding to thyroid hormone receptors (TRs) and thereby affect tissue differentiation, development, and metabolism in most tissues. TH-deficiency creates a less favorable lipid profile (e.g. increased plasma cholesterol levels), whereas TH-excess is associated with both positive (e.g. reduced plasma cholesterol levels) and negative (e.g. increased heart rate) effects. TRs are encoded by two genes, THRA and THRB, which, by alternative splicing, generate several isoforms (e.g. TRα1, TRα2, TRβ1, and TRβ2). TRα, the major TR in the heart, is crucial for heart rate and for cardiac contractility and relaxation, whereas TRβ1, the major TR in the liver, is important for lipid metabolism. Selective modulation of TRβ1 is thus considered as a potential therapeutic target to treat dyslipidemia without cardiac side effects. Several selective TH analogs have been tested in preclinical studies with promising results, but only a few of these compounds have so far been tested in clinical studies. This review focuses on the role of THs, TRs, and selective and non-selective TH analogs in lipid metabolism. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

Thyroid hormones and thyroid hormone receptors: Effects of thyromimetics on reverse cholesterol transport

Reverse cholesterol transport (RCT) is a complex process which transfers cholesterol from peripheral cells to the liver for subsequent elimination from the body via feces. Thyroid hormones (THs) affect growth, development, and metabolism in almost all tissues. THs exert their actions by binding to thyroid hormone receptors (TRs). There are two major subtypes of TRs, TRα and TRβ, and several isoforms (e.g. TRα1, TRα2, TRβ1, and TRβ2). Activation of TRα1 affects heart rate, whereas activation of TRβ1 has positive effects on lipid and lipoprotein metabolism. Consequently, particular interest has been focused on the development of thyromimetic compounds targeting TRβ1, not only because of their ability to lower plasma cholesterol but also due their ability to stimulate RCT, at least in pre-clinical models. In this review we focus on THs, TRs, and on the effects of TRβ1-modulating thyromimetics on RCT in various animal models and in humans.