Reduced ileal expression of OSTalpha-OSTbeta in non-obese gallstone disease

Bile acid diarrhoea and metabolic changes after cholecystectomy: a prospective case-control study

INTRODUCTION

Bile acid diarrhoea (BAD) can occur due to disruption to the enterohepatic circulation such as following cholecystectomy. However, the mechanism behind this is as yet unknown. The aim of this study was to determine the rate of post-cholecystectomy diarrhoea and to assess whether FGF19 within the gallbladder was associated with the development of BAD.

METHODS

This was a prospective case-control study in which patients were assessed pre- and post- cholecystectomy (study group) and compared with patients also having laparoscopic surgery but not cholecystectomy (control group). Their bowel habits and a GIQLI questionnaire was performed to compare the pre- and post-operative condition of the two groups. Gallbladder tissue sample was tested for FGF19 and PPARα in the study group patients. A subset had serum lipid levels, FGF19 and C4 measurements.

RESULTS

Gallbladder PPAR α was found to have a significant correlation with stool consistency, with the lower the PPARα concentration the higher the Bristol stool chart number (i.e. looser stool). There were no significant correlation when assessing the effect of gallbladder FGF19 concentration on bowel habit, stool consistency, lipid levels, BMI or smoking. The study group showed a significant increase in triglycerides post-operatively, however there were no changes in cholesterol, HDL and LDL levels. Correlation of the increased triglyceride levels with stool consistency and frequency showed no significant results DISCUSSION AND CONCLUSION: We did not find any direct evidence that FGF19 levels within the gallbladder impact the development of post-cholecystectomy diarrhoea. There was however a significant increase in triglycerides postoperatively. There was also no correlation of bowel habits with PPARα suggesting the observed rise is independent of this pathway. Further work is required particularly relating to the gut microbiome to further investigate this condition.

Predictive value of bile acids as metabolite biomarkers for gallstone disease: A systematic review and meta-analysis

BACKGROUND

The profiles of bile acids (BAs) in patients with gallstone disease (GSD) have been found to be altered markedly though in an inconsistent pattern. This study aims to characterize the variation of the BA profiles in GSD patients, thereby to discover the potential metabolite biomarkers for earlier detection of GSD.

METHODS

Literature search of eight electronic database in both English and Chinese was completed on May 11, 2023. The qualitative and quantitative reviews were performed to summarize the changes of BA profiles in GSD patients compared with healthy subjects. The concentrations of BAs were adopted as the primary outcomes and the weighted mean differences (WMDs) and 95% confidence interval (CI) were generated by random-effects meta-analysis models.

RESULTS

A total of 30 studies were enrolled which included 2313 participants and reported the 39 BAs or their ratios. Qualitative review demonstrated serum Taurocholic Acid (TCA), Glycochenodeoxycholic acid (GCDCA), Glycocholic acid (GCA), Taurochenodeoxycholic acid (TCDCA), Glycodeoxycholic acid (GDCA) and Deoxycholic acid (DCA) were significantly increased in GSD patients compared with healthy subjects. Meta analysis was performed in 16 studies and showed that serum Total BAs (TBA) (WMD = 1.36μmol/L, 95%CI = 0.33; 2.4) was elevated however bile TBA (WMD = -36.96mmol/L, 95%CI = -52.32; -21.6) was declined in GSD patients. GCA (WMD = 0.83μmol/L, 95%CI = 0.06; 1.6) and TCA (WMD = 0.51μmol/L; 95%CI = 0.18; 0.85) were both increased in serum sample; TCDCA (WMD = 2.64mmol/L, 95%CI = 0.16; 5.12) was rising, however GCDCA (WMD = -13.82mmol/L, 95%CI = -21.86; -5.78) was falling in bile sample of GSD patients. The level of serum DCA in the GSD patients was found to be increased by using chromatography, yet decreased by chromatography mass spectrometry.

CONCLUSION

The profiles of BAs demonstrated distinctive changes in GSD patients compared with healthy control subjects. Serum GCA, TCA and GCDCA, as the typically variant BAs, presented as a potential marker for earlier diagnosis of GSD, which could facilitate early prophylactic intervention. Yet, further validation of these biomarkers by longitudinal studies is still warranted in the future. PROSPERO registration number CRD42022339649.

Effects of essential oil of Origanum onites and its major component carvacrol on the expression of toxicity pathway genes in HepG2 cells

BACKGROUND

Origanum species have been used in various commercial constructions as a remedy against burns and wounds, agriculture, alcoholic drinks, fragrance, and flavoring substances of food products. The essential oil of Origanum onites L. (EOOO) and its component carvacrol (CV) possesses a wide range of biological activities including anti-cancer activity.

PURPOSE

The purpose of this study was to investigate the growth inhibitory activity of the essential oil and its major component CV and then hepatotoxicity pathway-related genes in HepG2 cells.

METHODS

The effects of the EOOO and CV on cell growth and mRNA expressions of 84 hepatotoxicity pathway-related genes were investigated in HepG2, using trypan blue exclusion/ bromodeoxyuridine (BrdU) incorporation tests and real-time-polymerase chain reaction (RT-PCR) array, respectively.

RESULTS

The EOOO and CV inhibited cell growth with IC50 values of 0.08 µg/mL and 45 µg/mL, respectively, after 24 h. Real-time, reverse-transcription-polymerase chain reaction (RT2-PCR) array analysis revealed that expressions of 32 genes out of 84 were changed at least 2-fold or more in the EOOO-treated cells. Among them, expression levels of 17 genes were elevated, while expression levels of 15 genes were diminished. Furthermore, after exposure of cells to 45 µg/mL of CV, the expression of 8 genes was increased while the other 8 genes were decreased. Both the EOOO and carvacrol affected the expression of 48 genes of HepG2 cells which are involved in the hepatotoxicity pathway, indicating their hepatoprotective and possible anti-hepatocarcinogenic effects.

CONCLUSION

The present study demonstrates that the essential oil of Origanum onites and carvacrol can be used in various applications such as anticancer or herbal drugs, since its non-hepatotoxicity.

Gallstone Disease and Its Correlation With Thyroid Disorders: A Narrative Review

Over the years, several studies have revealed an important link between thyroid disorders and gallstone disease. According to these studies, hypothyroidism and hyperthyroidism are associated with cholesterol gallstone disease. This association between thyroid hormone disorders and cholesterol gallstone disease is due to the importance of thyroid hormones on cholesterol synthesis, bile functioning and content, and gallbladder motility. Several genes and receptors have been found on the thyroid gland, liver, and gallbladder to verify this association. These genes affect thyroid hormone secretion, lipid metabolism, and bile secretion. Defects in these various gene expression and protein functions lead to bile duct diseases. Other causes that lead to cholesterol gallstone disease are supersaturation of the bile with cholesterol and impaired gallbladder motility, which leads to bile stasis. This article has discussed these factors in detail while highlighting the association between thyroid hormones and cholesterol gallstone disease.

Exposure to the mycotoxin deoxynivalenol reduces the transport of conjugated bile acids by intestinal Caco-2 cells

Conjugated bile acids are synthesized in liver and subsequently secreted into the intestinal lumen from which they are actively reabsorbed and transported back to liver. The efficient enterohepatic circulation of conjugated bile acids is important to maintain homeostasis. The mycotoxin deoxynivalenol (DON) is a fungal secondary metabolite that contaminates cereal food. Upon human exposure, it can cause intestinal dysfunction. We explored the effects of DON exposure on the intestinal absorption of conjugated bile acids and the expression of bile acid transporters using an in vitro model based on Caco-2 cell layers grown in transwells. Our study shows that the transport rate of taurocholic acid (TCA) is decreased after 48-h pre-exposure of the Caco-2 cells to 2 µM DON, which is a realistic intestinal DON concentration. Exposure to DON downregulates expression of the genes coding for the apical sodium-dependent bile acid transporter (ASBT), the ileal bile acid-binding protein (IBABP) and the organic solute transporter α (OSTα), and it counteracts the agonist activity of Farnesoid X receptor (FXR) agonist GW4064 on these genes. In addition, the transport of ten taurine or glycine-conjugated bile acids in a physiological relevant mixture by the intestinal Caco-2 cell layers was decreased after pre-exposure of the cells to DON, pointing at a potential for DON-mediated accumulation of the conjugated bile acids at the intestinal luminal side. Together the results reveal that DON inhibits intestinal bile acid reabsorption by reducing the expression of bile acid transporters thereby affecting bile acid intestinal kinetics, leading to bile acid malabsorption in the intestine. Our study provides new insights into the hazards of DON exposure.

The Regional-Specific Relative and Absolute Expression of Gut Transporters in Adult Caucasians: A Meta-Analysis

The aim of this study was to derive region-specific transporter expression data suitable for in vitro-to-in vivo extrapolation (IVIVE) within a physiologically based pharmacokinetic (PBPK) modeling framework. A meta-analysis was performed whereby literary sources reporting region-specific transporter expression obtained via absolute and relative quantification approaches were considered in healthy adult Caucasian individuals. Furthermore, intestinal total membrane protein yield was calculated to enable mechanistic IVIVE via absolute transporter abundances. Where required, authors were contacted for additional information. A refined database was constructed where samples were excluded based on quantification in, non-Caucasian subjects, disease tissue, subjects <18 years old, duplicated samples, non-total membrane matrix, pooled matrices, or cDNA. Demographic data were collected where available. The weighted and geometric mean, coefficient of variation, and between-study homogeneity was calculated in each of eight gut segments (duodenum, two jejunum, four ileum, and colon) for 16 transporters. Expression data were normalized to that in the proximal jejunum. From a total of 47 articles, the final database consisted of 2238 measurements for 16 transporters. The solute carrier peptide transporter 1 (PepT1) showed the highest jejunal abundance, while multidrug resistance-associated protein (MRP) 2 was the highest abundance ATP-binding cassette transporter. Transporters displaying significant region-specific expression included the ileal bile acid transporter, which showed 18-fold greater terminal ileum expression compared with the proximal jejunum, while MRP3, organic cation transporter type 1 (OCTN1), and OCT1 showed >2-fold higher expression in other regions compared with the proximal jejunum. This is the first systematic analysis incorporating absolute quantification methodology to determine region-specific intestinal transporter expression. It is expected to be beneficial for mechanistic transporter IVIVE in healthy adult Caucasians. SIGNIFICANCE STATEMENT: Given the burgeoning reports of absolute transporter abundances in the human intestine, the incorporation of such information into mechanistic IVIVE-PBPK models could offer a distinct advantage in facilitating the robust assessment of the impact of gut transporters on drug disposition. The systematic and formal assessment via a literature meta-analysis described herein, enables assignment of the regional-specific expression, absolute transporter abundances, interindividual variability, and other associated scaling factors to healthy Caucasian populations within PBPK models. The resulting values are available to incorporate into PBPK models, and offer a verifiable account describing intestinal transporter expression within PBPK models for persons wishing to utilize them. Furthermore, these data facilitate the development of appropriate IVIVE scaling strategies using absolute transporter abundances.

Fibroblast Growth Factor 15/19: From Basic Functions to Therapeutic Perspectives

Discovered 20 years ago, fibroblast growth factor (FGF)19, and its mouse ortholog FGF15, were the first members of a new subfamily of FGFs able to act as hormones. During fetal life, FGF15/19 is involved in organogenesis, affecting the development of the ear, eye, heart, and brain. At adulthood, FGF15/19 is mainly produced by the ileum, acting on the liver to repress hepatic bile acid synthesis and promote postprandial nutrient partitioning. In rodents, pharmacologic doses of FGF19 induce the same antiobesity and antidiabetic actions as FGF21, with these metabolic effects being partly mediated by the brain. However, activation of hepatocyte proliferation by FGF19 has long been a challenge to its therapeutic use. Recently, genetic reengineering of the molecule has resolved this issue. Despite a global overlap in expression pattern and function, murine FGF15 and human FGF19 exhibit several differences in terms of regulation, molecular structure, signaling, and biological properties. As most of the knowledge originates from the use of FGF19 in murine models, differences between mice and humans in the biology of FGF15/19 have to be considered for a successful translation from bench to bedside. This review summarizes the basic knowledge concerning FGF15/19 in mice and humans, with a special focus on regulation of production, morphogenic properties, hepatocyte growth, bile acid homeostasis, as well as actions on glucose, lipid, and energy homeostasis. Moreover, implications and therapeutic perspectives concerning FGF19 in human diseases (including obesity, type 2 diabetes, hepatic steatosis, biliary disorders, and cancer) are also discussed.

Prevention of cholesterol gallstone disease by schaftoside in lithogenic diet-induced C57BL/6 mouse model

Schaftoside (SS) is a bioactive compound present in the Herba Desmodii Styracifolii (DS), a herb that has been used to treat cholelithiasis and urolithiasis in Chinese medicine. Whether SS inhibits cholesterol (Ch) gallstone formation has not been investigated. This study examined the effects of oral intake of SS on Ch gallstone formation in C57BL/6 mice fed a lithogenic diet. The rate of gallstone formation was recorded. Levels of Ch, triglycerides (TG) and bile salts (BS) were measured in the bile and serum. Liver histopathology was examined microscopically, and mRNA expression levels of key genes involved in cholesterol and bile metabolism were determined by qPCR. Mice fed SS were protected against gallstone formation, had increased biliary levels of BS, and reduced biliary Ch levels, resulting in a lower Ch saturation index (CSI). In addition, mice fed SS had lower serum TG and Ch levels, increased mRNA expression of liver X receptor α, ATP binding cassette transporter 5/8 (ABCG5/8), and ileal bile acid binding protein (IBABP) in the ileum, and of farnesoid X receptor and bile salt export protein (BSEP) in the liver and ileum. SS also protected against histologically determined liver damage. Overall, these data indicate that SS protects against Ch gallstone formation in mice, and that the effect is mediated by activation of ileal liver X receptor α and hepatic farnesoid X receptor.

An important intestinal transporter that regulates the enterohepatic circulation of bile acids and cholesterol homeostasis: The apical sodium-dependent bile acid transporter (SLC10A2/ASBT)

The enterohepatic circulation of bile acids (BAs) is governed by specific transporters expressed in the liver and the intestine and plays a critical role in the digestion of fats and oils. During this process, the majority of the BAs secreted from the liver is reabsorbed in intestinal epithelial cells via the apical sodium-dependent bile acid transporter (ASBT/SLC10A2) and then transported into the portal vein. Previous studies revealed that regulation of the ASBT involves BAs and cholesterol. In addition, abnormal ASBT expression and function might lead to some diseases associated with disorders in the enterohepatic circulation of BAs and cholesterol homeostasis, such as diarrhoea and gallstones. However, decreasing cholesterol or BAs by partly inhibiting ASBT-mediated transport might be used for treatments of hypercholesterolemia, cholestasis and diabetes. This review mainly discusses the regulation of the ASBT by BAs and cholesterol and its relevance to diseases and treatment.

Association of FXR gene variants with cholelithiasis

BACKGROUND AND AIM

Impairment of bile acid homeostasis is the most important risk factor of gallstone disease. Thereby the bile acid sensor farnesoid X receptor (FXR) plays a pivotal role in hepatic and intestinal bile acid metabolism. In this explorative study, the FXR gene was investigated to identify gene variants, associated with gallstone formation in a Caucasian population.

METHODS

Sequencing of the FXR gene was conducted in a randomly selected cohort of gallstone carriers (n=30) and control subjects (n=16) from Stuttgart, Germany. Genomic DNA was obtained from blood leukocytes. Genotype frequencies were established in the total cohort (controls: n=133, gallstone carriers: n=74). For expression analysis, total RNA and protein were isolated from ileal biopsies.

RESULTS

The sequencing showed the sole appearance of 10 SNPs in gallstone carriers. Further genotype analysis revealed significant gender- and weight-dependent frequency differences of 3 SNPs between gallstone carriers and controls in males (rs35724: OR=4.73, P=0.022) and normal weight subjects (rs11110385: OR=3.67, P=0.027; rs11110386: OR=3.67, P=0.027) applying the 11+12<>22 allele model. Furthermore, rs11110385 carriers showed a significantly decreased FXR protein expression (11+12<>22: P=0.003). Significant mRNA expression differences between lean rs11110385 carriers and non-carriers were observed in FXR target genes (decrease: ILBP: P=0.042, OSTalpha: P=0.071, FGF19: P=0.011. Increase: LRH1: P=0.044).

CONCLUSIONS

Three FXR gene variants (rs35724, rs11110385, rs11110386) were identified as potential susceptibility factors for cholelithiasis in a German cohort in gender- and weight-dependent manners. Thereby the tag SNP rs11110385 seemed to influence the activation of the FXR gene.

Impact of global Fxr deficiency on experimental acute pancreatitis and genetic variation in the FXR locus in human acute pancreatitis

Background

Infectious complications often occur in acute pancreatitis, related to impaired intestinal barrier function, with prolonged disease course and even mortality as a result. The bile salt nuclear receptor farnesoid X receptor (FXR), which is expressed in the ileum, liver and other organs including the pancreas, exhibits anti-inflammatory effects by inhibiting NF-κB activation and is implicated in maintaining intestinal barrier integrity and preventing bacterial overgrowth and translocation. Here we explore, with the aid of complementary animal and human experiments, the potential role of FXR in acute pancreatitis.

Methods

Experimental acute pancreatitis was induced using the CCK-analogue cerulein in wild-type and Fxr^-/- mice. Severity of acute pancreatitis was assessed using histology and a semi-quantitative scoring system. Ileal permeability was analyzed in vitro by Ussing chambers and an in vivo permeability assay. Gene expression of Fxr and Fxr target genes was studied by quantitative RT-PCR. Serum FGF19 levels were determined by ELISA in acute pancreatitis patients and healthy volunteers. A genetic association study in 387 acute pancreatitis patients and 853 controls was performed using 9 tagging single nucleotide polymorphisms (SNPs) covering the complete FXR gene and two additional functional SNPs.

Results

In wild-type mice with acute pancreatitis, ileal transepithelial resistance was reduced and ileal mRNA expression of Fxr target genes Fgf15, SHP, and IBABP was decreased. Nevertheless, Fxr^-/- mice did not exhibit a more severe acute pancreatitis than wild-type mice. In patients with acute pancreatitis, FGF19 levels were lower than in controls. However, there were no associations of FXR SNPs or haplotypes with susceptibility to acute pancreatitis, or its course, outcome or etiology.

Conclusion

We found no evidence for a major role of FXR in acute human or murine pancreatitis. The observed altered Fxr activity during the course of disease may be a secondary phenomenon.

Upregulation of hepatic bile acid synthesis via fibroblast growth factor 19 is defective in gallstone disease but functional in overweight individuals

BACKGROUND

Fibroblast growth factor 19 (FGF19) is an enteric hormone regulating bile acid de novo synthesis by sensing ileal bile acid flux. However, the role of FGF19 in cholelithiasis has not yet been elucidated and therefore is investigated in the present study.

METHODS

Total mRNA and protein were isolated from ileal biopsies and used for tissue expression analysis. FGF19, 7α-hydroxycholesterol (7α-OH-Chol), 27-hydroxycholesterol (27-OH-Chol), and different bile acids were determined in the blood samples.

RESULTS

FGF19 serum levels did not differ between gallstone carriers and controls but were significantly decreased in the overweight individuals (-32%, p = 0.0002), irrespective of gallstone status (normalweight to overweight controls -29%, p = 0.0017; normalweight to overweight gallstone carriers -44%, p = 0.0338), and correlated inversely with bodyweight (p < 0.0001, ρ = -0.3317). Compared to non-overweight controls, apical sodium-dependent bile acid transporter expression was significantly diminished in the non-overweight gallstone carriers (-42%, P mRNA = 0.0393; -52%, p protein = 0.0169) as well as in the overweight controls (-24%, P mRNA = 0.0148; -43%, p protein = 0.0017). FGF19 expression varied widely and was similar in all groups. A significant negative correlation was noted between 7α-OH-Chol, 27-OH-Chol, and FGF19 serum levels (p < 0.01; ρ7α-OH-Chol = -0.2155; ρ27-OH-Chol = -0.2144) in obesity.

CONCLUSION

Upregulation of hepatic bile acid synthesis via FGF 19 is defective in gallstone disease but functional in overweight individuals.

The mechanism of enterohepatic circulation in the formation of gallstone disease

Bile acids entering into enterohepatic circulating are primary acids synthesized from cholesterol in hepatocyte. They are secreted actively across canalicular membrane and carried in bile to gallbladder, where they are concentrated during digestion. About 95 % BAs are actively taken up from the lumen of terminal ileum efficiently, leaving only approximately 5 % (or approximately 0.5 g/d) in colon, and a fraction of bile acids are passively reabsorbed after a series of modifications in the human large intestine including deconjugation and oxidation of hydroxy groups. Bile salts hydrolysis and hydroxy group dehydrogenation reactions are performed by a broad spectrum of intestinal anaerobic bacteria. Next, hepatocyte reabsorbs bile acids from sinusoidal blood, which are carried to liver through portal vein via a series of transporters. Bile acids (BAs) transporters are critical for maintenance of the enterohepatic BAs circulation, where BAs exert their multiple physiological functions including stimulation of bile flow, intestinal absorption of lipophilic nutrients, solubilization, and excretion of cholesterol. Tight regulation of BA transporters via nuclear receptors (NRs) is necessary to maintain proper BA homeostasis. In conclusion, disturbances of enterohepatic circulation may account for pathogenesis of gallstones diseases, including BAs transporters and their regulatory NRs and the metabolism of intestinal bacterias, etc.

Clinical application of transcriptional activators of bile salt transporters

Hepatobiliary bile salt (BS) transporters are critical determinants of BS homeostasis controlling intracellular concentrations of BSs and their enterohepatic circulation. Genetic or acquired dysfunction of specific transport systems causes intrahepatic and systemic retention of potentially cytotoxic BSs, which, in high concentrations, may disturb integrity of cell membranes and subcellular organelles resulting in cell death, inflammation and fibrosis. Transcriptional regulation of canalicular BS efflux through bile salt export pump (BSEP), basolateral elimination through organic solute transporters alpha and beta (OSTα/OSTβ) as well as inhibition of hepatocellular BS uptake through basolateral Na(+)-taurocholate cotransporting polypeptide (NTCP) represent critical steps in protection from hepatocellular BS overload and can be targeted therapeutically. In this article, we review the potential clinical implications of the major BS transporters BSEP, OSTα/OSTβ and NTCP in the pathogenesis of hereditary and acquired cholestatic syndromes, provide an overview on transcriptional control of these transporters by the key regulatory nuclear receptors and discuss the potential therapeutic role of novel transcriptional activators of BS transporters in cholestasis.

Repression of Farnesoid X receptor contributes to biliary injuries of liver grafts through disturbing cholangiocyte bile acid transport

Biliary epithelial damage is the critical point in the development of nonanastomotic strictures, a serious biliary complication after liver transplantation (LT). Current study focuses on the roles and mechanisms of unbalanced bile acid (BA) transporting of cholangiocytes in biliary epithelial damages following LT. Using rat LT models, we observed that biliary transit time (BTT) of BA was prolonged, and the degree and duration of BTT prolongation were related to the cold ischemia time of donor liver. Moreover, prolonged BTT was correlated with bile duct injury severity. The expression of Farnesoid X receptor (FXR) underwent a dramatic decrease after transplantation, and the decrease in FXR was related to cold ischemic time of donor liver. Negative correlation was observed between FXR expression and BTT. With in vitro cultured human biliary epithelial cells, it was observed that FXR expressions and DNA binding activities were repressed under hypoxic conditions. FXR repression by hypoxia mediated unparallel expressions of BA transporters and intracellular accumulation of BAs, which induced higher cell apoptosis rates and enhanced profibrotic factor expression in cholangiocytes. These findings indicated that FXR repression under ischemic/hypoxic conditions contributed to biliary epithelial damages by disturbing BA transporting of cholangiocytes after LT.

Role of the ABCG8 19H risk allele in cholesterol absorption and gallstone disease

BACKGROUND

Gallstone disease is associated with p.D19H of ABCG8 as well as alterations of cholesterol and bile acid metabolism. However, molecular mechanisms have not been fully elucidated. It is important to understand the link between the sterol transporters ABCG5/8 and NPC1L1 and intestinal cholesterol absorption as well as de novo synthesis in gallstone patients stratified according to 19H risk allele. Moreover, the functional importance of the 19H variant on intestinal ABCG8 feature remains to be clarified.

METHODS

Measurements of serum surrogate markers of cholesterol absorption (plant sterols: sitosterol, campesterol) and synthesis (cholesterol precursor: lathosterol) were carried out by gas chromatography/mass spectrometry (GC/MS). For expression studies, total RNA was isolated from 168 ileal biopsies of study participants with (34) and without gallstone disease (134). Messenger RNA was measured by LightCycler real-time PCR. Genomic DNA was obtained from blood leukocytes. Genotype frequencies of p.D19H were established using MALDI-TOF mass spectrometry.

RESULTS

Compared to controls, cholesterol absorption but not synthesis in gallstone carriers was diminished by about 21% based on low serum sitosterol (P = 0.0269) and campesterol (P = 0.0231) to cholesterol ratios. D19H was found to be significantly associated with gallstones (odds ratio [OR] = 2.9, P = 0.0220, 95% confidence interval [CI]:1.22-6.89), particularly in the overweight cohort (OR = 3.2, P = 0.0430, 95% CI:1.07-9.26). Cholesterol absorption was about 24% lower in individuals carrying p.D19H compared to wild type (Psitosterol = 0.0080, Pcampesterol = 0.0206). Moreover, irrespective of phenotype, carriers of p.D19H displayed a significant lower absorption than carriers of the major allele. The most pronounced effect on cholesterol absorption ratio was observed for serum campesterol levels (wild type controls to mutated controls 28%, P = 0.0347 and wild type controls to gallstone carriers with 19H allele 37%, P = 0.0030). Notably, ABCG5/8 and NPC1L1 expression was similar in gallstone carriers and controls regardless of p.D19H presence.

CONCLUSIONS

Both gallstone disease and p.D19H of ABCG8 are associated with diminished cholesterol absorption. However, p.D19H is not responsible for the differences in small intestinal sterol transporter expression.

Effects of SLC10A2 variant rs9514089 on gallstone risk and serum cholesterol levels- meta-analysis of three independent cohorts

Background

Recently, a single nucleotide polymorphism (SNP) rs9514089 in SLC10A2 (apical sodium-dependent bile acid transporter gene) has been identified as a susceptibility variant for cholelithiasis in humans.

Methods

Here we assessed the effects of rs9514089 on gallstone risk and related phenotypes of the metabolic syndrome in the self-contained population of Sorbs (183 cases with gallstones/826 controls). Furthermore, we performed a meta-analysis for effects of rs9514089 on susceptibility for cholelithiasis in three independent cohorts (Stuttgart: 56 cases/71 controls, Aachen: 184 cases/184 controls and Sorbs).

Results

There was no significant association of rs9514089 with gallstone risk, serum lipid parameters and BMI in the Sorbs and in the meta-analysis of all three cohorts (p > 0.05). There was an effect trend in the subgroup of lean subjects but based on different effect directions in the three cohorts there was no significant association in the meta-analysis.

Conclusions

We were not able to replicate the effect of rs9514089 on gallstone risk in the Sorbs. Further analyses in larger cohorts are required to finally assess the role of genetic variants in SLC10A2 in human gallstone development and lipid metabolism.

Molecular Mechanisms Underlying the Link between Nuclear Receptor Function and Cholesterol Gallstone Formation

Cholesterol gallstone disease is highly prevalent in western countries, particularly in women and some specific ethnic groups. The formation of water-insoluble cholesterol crystals is due to a misbalance between the three major lipids present in the bile: cholesterol, bile salts, and phospholipids. Many proteins implicated in biliary lipid secretion in the liver are regulated by several transcription factors, including nuclear receptors LXR and FXR. Human and murine genetic, physiological, pathophysiological, and pharmacological evidence is consistent with the relevance of these nuclear receptors in gallstone formation. In addition, there is emerging data that also suggests a role for estrogen receptor ESR1 in abnormal cholesterol metabolism leading to gallstone disease. A better comprehension of the role of nuclear receptor function in gallstone formation may help to design new and more effective therapeutic strategies for this highly prevalent disease condition.

Pathogenesis of cholesterol and pigment gallstones: an update

Phase separation of cholesterol crystals from supersaturated bile is still considered the key event in cholesterol gallstone formation. In this review, we will first provide a basal framework of the interactions between the sterol, bile salts and phospholipids in aqueous solutions and then summarize new developments. The hepatocytic apical membrane harbours specific transport proteins for these lipids. Polymorphisms in the gene encoding the cholesterol transporter ABCG5-G8 have been found to increase overall gallstone risk, whereas functional mutations in the gene encoding the phospholipid floppase ABCB4 lead to the rare clinical syndrome of low phospholipid associated cholelithiasis. Expression of bile salt and phospholipid transport proteins is regulated bij the bile salt nuclear receptor Farnesoid X receptor (FXR), while the Liver X Receptor (LXR) α regulates ABCG5-G8. Although data from murine experiments suggest a critical role of FXR in gallstone formation, its role in human lithogenesis remains controversial. Variants of the gene encoding UGT1A1 (uridine 5'-diphosphate (UDP)-glucuronosyltransferase 1A1) responsible for bilirubin conjugation were recently associated with risk of gallstones as well as stone bilirubin content, suggesting common factors in cholesterol and pigment gallstone pathogenesis.

Role of the intestinal bile acid transporters in bile acid and drug disposition

Membrane transporters expressed by the hepatocyte and enterocyte play critical roles in maintaining the enterohepatic circulation of bile acids, an effective recycling and conservation mechanism that largely restricts these potentially cytotoxic detergents to the intestinal and hepatobiliary compartments. In doing so, the hepatic and enterocyte transport systems ensure a continuous supply of bile acids to be used repeatedly during the digestion of multiple meals throughout the day. Absorption of bile acids from the intestinal lumen and export into the portal circulation is mediated by a series of transporters expressed on the enterocyte apical and basolateral membranes. The ileal apical sodium-dependent bile acid cotransporter (abbreviated ASBT; gene symbol, SLC10A2) is responsible for the initial uptake of bile acids across the enterocyte brush border membrane. The bile acids are then efficiently shuttled across the cell and exported across the basolateral membrane by the heteromeric Organic Solute Transporter, OSTα-OSTβ. This chapter briefly reviews the tissue expression, physiology, genetics, pathophysiology, and transport properties of the ASBT and OSTα-OSTβ. In addition, the chapter discusses the relationship between the intestinal bile acid transporters and drug metabolism, including development of ASBT inhibitors as novel hypocholesterolemic or hepatoprotective agents, prodrug targeting of the ASBT to increase oral bioavailability, and involvement of the intestinal bile acid transporters in drug absorption and drug-drug interactions.

Getting the mOST from OST: Role of organic solute transporter, OSTalpha-OSTbeta, in bile acid and steroid metabolism

The organic solute transporter (OST)(alpha)-OST(beta) is an unusual heteromeric carrier expressed in a variety of tissues including the small intestine, colon, liver, biliary tract, kidney, and adrenal gland. In polarized epithelial cells, OSTalpha-OSTbeta protein is localized on the basolateral membrane and functions in the export or uptake of bile acids and steroids. This article reviews recent results including studies of knockout mouse models that provide new insights to the role of OSTalpha-OSTbeta in the compartmentalization and metabolism of these important lipids.

Role of cholangiocyte bile Acid transporters in large bile duct injury after rat liver transplantation

BACKGROUND

The pathogenesis of nonanastomotic strictures with a patent hepatic artery remains to be investigated. This study focuses on the role of cholangiocyte bile acid transporters in bile duct injury after liver transplantation.

METHODS

Sprague-Dawley rats were divided into three groups (n=20 for each): the sham-operated group (Sham), the transplant group with 1-hr donor liver cold preservation (CP-1h), and the transplant group with 12-hr donor liver cold preservation (CP-12h). Bile was collected for biochemical analysis. The histopathologic evaluation of bile duct injury was performed and the cholangiocyte bile acid transporters apical sodium-dependent bile acid transporter (ASBT), ileal lipid binding protein (ILBP), and Ostalpha/Ostbeta were investigated. RESULTS.: The immunohistochemical assay suggested that ASBT and ILBP were expressed exclusively on large bile duct epithelial cells, whereas Ostalpha and Ostbeta were expressed on both small and large bile ducts. Western blot and quantitative polymerase chain reaction analysis showed that the expression levels of these transporters dramatically decreased after transplantation. It took seven to 14 days for ILBP, Ostalpha, and Ostbeta to recover, whereas ASBT recovered within 3 days and even reached a peak above the normal level seven days after operation. In the CP-12h group, the ratios of the ASBT/ILBP, ASBT/Ostalpha and ASBT/Ostbeta expression levels were correlated with the injury severity scores of large but not small bile ducts.

CONCLUSIONS

The results suggest that the unparallel alteration of cholangiocyte bile acid transporters may play a potential role in large bile duct injury after liver transplantation with prolonged donor liver preservation.

The genetic background of gallstone formation: an update

Gallstone disease is one of the most prevalent gastrointestinal diseases with a substantial burden to health care systems that is expected to increase in ageing populations at risk. This review summarizes recent data on the genetic background of cholesterol gallstones and the role of biliary lipid composition. Three previously unknown non-synonymous mutations in the ABCB4 gene encoding the hepatobiliary phospholipid-flippase MDR3 are presented.

Pathogenesis of gallstones

Cholesterol gallstone formation is a complex process and involves phase separation of cholesterol crystals from supersaturated bile. In most cases, cholesterol hypersecretion is considered the primary event in gallstone formation. The sterol is transported through the hepatocytic canalicular membrane by ABCG5-G8. Expression of this transport protein is regulated by transcription factor Liver X Receptor-alpha, which may be responsible for biliary hypersecretion. Hydrophobic bile salt pool, bile concentration, excess pronucleating mucin, and impaired gallbladder and intestinal motility are secondary phenomena in most cases but nevertheless may contribute to gallstone formation.

Organic solute transporter, OSTalpha-OSTbeta: its role in bile acid transport and cholestasis

Organic solute transporter alpha-beta (OSTalpha-OSTbeta) is a unique heteromeric transporter localized to the basolateral membrane of epithelial cells involved in sterol transport. It is believed to be the primary bile acid efflux transporter in the intestine of mammals and is therefore essential to bile acid homeostasis and the enterohepatic circulation. First described in the evolutionarily primitive small skate, LEUCORAJA ERINACEA, this facilitated transporter requires expression of both subunits for its function. It can transport a variety of bile acids, as well as estrone 3-sulfate, dehydroepiandrosterone 3-sulfate, digoxin, and prostaglandin E (2). Expression of both subunits is variable between species and tissues; in humans high expression is noted in the liver, small intestine, kidney, testis, and adrenal gland. OSTalpha-OSTbeta is directly regulated by the bile acid sensing nuclear receptor, farnesoid X receptor (FXR). Furthermore, it is part of the complex regulatory pathway that controls bile acid synthesis and homeostasis. Hepatic OSTalpha-OSTbeta is upregulated in cholestasis in both humans and rodents, where it appears to play a protective role. Additional studies are necessary to determine its role in liver injury, bile acid malabsorption, and lipid and glucose metabolism, as well as a potential protective role for kidney OSTalpha-OSTbeta in cholestasis.

Bile acids and their nuclear receptor FXR: Relevance for hepatobiliary and gastrointestinal disease

The nuclear receptor Farnesoid X Receptor (FXR) critically regulates nascent bile formation and bile acid enterohepatic circulation. Bile acids and FXR play a pivotal role in regulating hepatic inflammation and regeneration as well as in regulating extent of inflammatory responses, barrier function and prevention of bacterial translocation in the intestinal tract. Recent evidence suggests, that the bile acid-FXR interaction is involved in the pathophysiology of a wide range of diseases of the liver, biliary and gastrointestinal tract, such as cholestatic and inflammatory liver diseases and hepatocellular carcinoma, inflammatory bowel disease and inflammation-associated cancer of the colon and esophagus. In this review we discuss current knowledge of the role the bile acid-FXR interaction has in (patho)physiology of the liver, biliary and gastrointestinal tract, and proposed underlying mechanisms, based on in vitro data and experimental animal models. Given the availability of highly potent synthetic FXR agonists, we focus particularly on potential relevance for human disease.

Fecal bile acid excretion and messenger RNA expression levels of ileal transporters in high risk gallstone patients

BACKGROUND

Cholesterol gallstone disease (GS) is highly prevalent among Hispanics and American Indians. In GS, the pool of bile acids (BA) is decreased, suggesting that BA absorption is impaired. In Caucasian GS patients, mRNA levels for ileal BA transporters are decreased. We aimed to determine fecal BA excretion rates, mRNA levels for ileal BA transporter genes and of regulatory genes of BA synthesis in Hispanic GS patients.

RESULTS

Excretion of fecal BA was measured in seven GS females and in ten GS-free individuals, all with a body mass index < 29. Participants ingested the stool marker Cr2O3 (300 mg/day) for 10 days, and fecal specimens were collected on the last 3 days. Chromium was measured by a colorimetric method, and BA was quantitated by gas chromatography/mass spectroscopy. Intake of calories, nutrients, fiber and cholesterol were similar in the GS and GS-free subjects. Mean BA excretion levels were 520 +/- 80 mg/day for the GS-free group, and 461 +/- 105 mg/day for the GS group. Messenger RNA expression levels were determined by RT-PCR on biopsy samples obtained from ileum during diagnostic colonoscopy (14 GS-free controls and 16 GS patients) and from liver during surgery performed at 8 and 10 AM (12 GS and 10 GS-free patients operated on for gastrointestinal malignancies), all with a body mass index < 29. Messenger RNA level of the BA transporter genes for ileal lipid binding protein, multidrug resistance-associated protein 3, organic solute transporter alpha, and organic solute transporter beta were similar in GS and GS-free subjects. Messenger RNA level of Cyp27A1, encoding the enzyme 27alpha-hydroxylase, the short heterodimer partner and farnesoid X receptor remained unchanged, whereas the mRNA level of Cyp7A1, the rate limiting step of BA synthesis, was increased more than 400% (p < 0.01) in the liver of GS compared to GS-free subjects.

CONCLUSION

Hispanics with GS have fecal BA excretion rates and mRNA levels of genes for ileal BA transporters that are similar to GS-free subjects. However, mRNA expression levels of Cyp7A1 are increased in GS, indicating that regulation of BA synthesis is abnormal in Hispanics with GS.

A variant of the SLC10A2 gene encoding the apical sodium-dependent bile acid transporter is a risk factor for gallstone disease

Background

Cholelithiasis is a multifactorial process and several mechanisms of gallstone formation have been postulated. As one of these mechanisms, a decreased expression of the ileal apical sodium-dependent bile acid transporter gene SLC10A2 in gallstone carriers was described previously. In this study the SLC10A2 gene was investigated to identify novel genetic variants and their association with gallstone formation.

Methodology/Principal Findings

Study subjects were selected with the presence or absence of gallstones confirmed by ultrasound and medical history. Genomic DNA was obtained from blood leukocytes. Sequence analysis was performed of all six exonic and flanking regions as well as of 2,400 base pairs of the SLC10A2 promoter in a cohort of gallstone carriers and control subjects from Stuttgart, Germany. Genotype frequencies of newly identified genetic variants (n = 6) and known single nucleotide polymorphisms (n = 24) were established using MALDI-TOF mass spectrometry. Six new genetic variants were found within the SLC10A2 gene. Although none of the variants was linked to gallstone disease in the Stuttgart cohort overall, the minor allele of SNP rs9514089 was more prevalent in male non-obese gallstone carriers (p = 0.06680, OR = 11.00). In a separate population from Aachen, Germany, the occurrence of rs9514089 was two-fold higher in gallstone patients (22%) than in corresponding controls (11%) (p = 0.00995, OR = 2.19). In the pooled Aachen/Stuttgart cohort rs9514089 was highly significantly linked to cholelithiasis (p = 0.00767, OR = 2.04). A more frequent occurrence was observed for male gallstone carriers (22%) compared to controls (9%) (p = 0.01017, OR = 2.99), for the total normal weight group (p = 0.00754, OR = 2.90), and for male non-obese gallstone patients (p = 0.01410, OR = 6.85). Moreover, for the minor allele of rs9514089 an association with low plasma cholesterol levels was found especially in gallstone carriers (p = 0.05).

Conclusions/Significance

We have identified SLC10A2 as a novel susceptibility gene for cholelithiasis in humans. Comprehensive statistical analysis provides strong evidence that rs9514089 is a genetic determinant especially in male non-obese gallstone carriers. The minor allele of rs9514089 is related to differences in plasma cholesterol levels among the subjects.

Bile acid transporters

In liver and intestine, transporters play a critical role in maintaining the enterohepatic circulation and bile acid homeostasis. Over the past two decades, there has been significant progress toward identifying the individual membrane transporters and unraveling their complex regulation. In the liver, bile acids are efficiently transported across the sinusoidal membrane by the Na(+) taurocholate cotransporting polypeptide with assistance by members of the organic anion transporting polypeptide family. The bile acids are then secreted in an ATP-dependent fashion across the canalicular membrane by the bile salt export pump. Following their movement with bile into the lumen of the small intestine, bile acids are almost quantitatively reclaimed in the ileum by the apical sodium-dependent bile acid transporter. The bile acids are shuttled across the enterocyte to the basolateral membrane and effluxed into the portal circulation by the recently indentified heteromeric organic solute transporter, OSTalpha-OSTbeta. In addition to the hepatocyte and enterocyte, subgroups of these bile acid transporters are expressed by the biliary, renal, and colonic epithelium where they contribute to maintaining bile acid homeostasis and play important cytoprotective roles. This article will review our current understanding of the physiological role and regulation of these important carriers.

Bile acid transporters

In liver and intestine, transporters play a critical role in maintaining the enterohepatic circulation and bile acid homeostasis. Over the past two decades, there has been significant progress toward identifying the individual membrane transporters and unraveling their complex regulation. In the liver, bile acids are efficiently transported across the sinusoidal membrane by the Na(+) taurocholate cotransporting polypeptide with assistance by members of the organic anion transporting polypeptide family. The bile acids are then secreted in an ATP-dependent fashion across the canalicular membrane by the bile salt export pump. Following their movement with bile into the lumen of the small intestine, bile acids are almost quantitatively reclaimed in the ileum by the apical sodium-dependent bile acid transporter. The bile acids are shuttled across the enterocyte to the basolateral membrane and effluxed into the portal circulation by the recently indentified heteromeric organic solute transporter, OSTalpha-OSTbeta. In addition to the hepatocyte and enterocyte, subgroups of these bile acid transporters are expressed by the biliary, renal, and colonic epithelium where they contribute to maintaining bile acid homeostasis and play important cytoprotective roles. This article will review our current understanding of the physiological role and regulation of these important carriers.

Mutation screening of apical sodium-dependent bile acid transporter (SLC10A2): novel haplotype block including six newly identified variants linked to reduced expression

The apical sodium-dependent bile acid transporter (SLC10A2) plays a key role in the reabsorption of luminal bile acids into the enterohepatic circulation. Rare variations in SLC10A2 have been reported to be associated with Crohn's disease, primary bile acid malabsorption and familial hypertriglyceridemia; however, variants associated with reduced SLC10A2 expression have not been reported to date. In this study, we have performed a sequence analysis of SLC10A2 using genomic DNA of 93 individuals. A new haplotype structure was identified including ten variants with complete linkage disequilibrium (LD' = 1.0, r (2) = 1.0) of which six polymorphisms were novel. The sequence variants were confirmed in three independent cohorts (n = 1,290) by a recently established MALDI-TOF MS iPLEX assay. Remarkably, haplotype carriers with the minor allele exhibited significant reduced ileal SLC10A2 expression on mRNA levels (2.6-fold, P = 0.0009) and protein levels (2.4-fold, P = 0.0157). In future studies a single tag SNP selected of this haplotype block will provide reliable genetic testing to investigate systemically the influence of the SLC10A2 haplotype for disease susceptibility and/or drug response.

The role of FXR in disorders of bile acid homeostasis

As ligands for the nuclear receptor FXR, bile acids regulate their own synthesis, transport, and conjugation, thus protecting against bile acid toxicity. Recently, the role of genetic variants in FXR itself, FXR target genes, and regulators of FXR in the pathophysiology of the liver and intestine has become increasingly evident.