Cholesterol saturation, not proteins or cholecystitis, is critical for crystal formation in human gallbladder bile

Transcriptomic profiles reveal differences in zinc metabolism, inflammation, and tight junction proteins in duodenum from cholesterol gallstone subjects

Cholesterol Gallstone Disease (GSD) is a common multifactorial disorder characterized by crystallization and aggregation of biliary cholesterol in the gallbladder. The global prevalence of GSD is ~10–20% in the adult population but rises to 28% in Chile (17% among men and 30% among women). The small intestine may play a role in GSD pathogenesis, but the molecular mechanisms have not been clarified. Our aim was to identify the role of the small intestine in GSD pathogenesis. Duodenal biopsy samples were obtained from patients with GSD and healthy volunteers. GSD status was defined by abdominal ultrasonography. We performed a transcriptome study in a discovery cohort using Illumina HiSeq. 2500, and qPCR, immunohistochemistry and immunofluorescence were used to validate differentially expressed genes among additional case-control cohorts. 548 differentially expressed genes between GSD and control subjects were identified. Enriched biological processes related to cellular response to zinc, and immune and antimicrobial responses were observed in GSD patients. We validated lower transcript levels of metallothionein, NPC1L1 and tight junction genes and higher transcript levels of genes involved in immune and antimicrobial pathways in GSD patients. Interestingly, serum zinc and phytosterol to cholesterol precursor ratios were lower in GSD patients. A significant association was observed between serum zinc and phytosterol levels. Our results support a model where proximal small intestine plays a key role in GSD pathogenesis. Zinc supplementation, modulation of proximal microbiota and/or intestinal barrier may be novel targets for strategies to prevent GSD.

Gallbladder bile supersaturated with cholesterol in gallstone patients preferentially develops from shortage of bile acids

Gallstone (GS) formation requires that bile is supersaturated with cholesterol, which is estimated by a cholesterol saturation index (CSI) calculated from gallbladder (GB) total lipids and the mol% (mole percent) of bile acids (BAs), cholesterol, and phospholipids (PLs). Whereas CSI indicates GS risk, we hypothesized that additional comparisons of GB lipid mol% data are inappropriate to identify why CSI is increased in GS disease. We anticipated that GB lipid mmol/l (millimole per liter) levels should instead identify that, and therefore retrieved GB mmol/l data for BAs, cholesterol, and PLs from a study on 145 GS and 87 GS-free patients and compared them with the corresponding mol% data. BA and PL mmol/l levels were 33% and 31% lower in GS patients, while cholesterol was unaltered. CSI was higher in GS patients and correlated inversely with GB levels of BAs and PLs, but not with cholesterol. A literature search confirmed, in 13 studies from 11 countries, that GB BA levels and, to a certain extent, PLs are strongly reduced in GS patients, while cholesterol levels are not elevated. Our findings show that a shortage of BAs is a major reason why GB bile is supersaturated with cholesterol in GS patients. These results are sustainable because they are also valid from a global perspective.

Role of the biliary microbiome in gallstone disease

Gallstone disease is caused by multiple pathogenic factors and is common worldwide. Most studies have focused on the significance of the biliary microbiome in gallstone pathogenesis. Areas covered: In this study, the epidemiology of gallstone diseases and the existence, composition, origin, and mechanisms of the biliary microbiota were reviewed. Mechanisms involved in promoting the formation of different types of gallstones were also emphasized. The antibiotic susceptibility of the biliary microbiota is briefly discussed because it may guide clinical strategies. Expert commentary: The biliary microbiome facilitates the formation of brown pigment stones. Although glycoprotein (mucin) may be pivotal for many promoting substances to coagulate and integrate relevant components, new mechanisms involving prostaglandins, oxysterols, oxygen free radicals, and lipopolysaccharides have been discovered. Furthermore, specific bacterial species such as Helicobacter and Salmonella are involved in the pathogenesis of cholesterol gallstones. Recently, metabolomics of the biliary microbiome has been used to determine the detailed mechanisms that promote gallstone formation. Previously, the bacterial effects involved in the pathogenesis of brown pigment stones have not been analyzed in detail. Whether the administration of antibiotics is related to prophylaxis for gallstone formation and gallstone-associated infections remains unclear.

The NPC1L1 Polymorphism 1679C>G Is Associated with Gallstone Disease in Chinese Patients

Niemann Pick Type C1 Like 1 (NPC1L1) protein plays a key role in intestinal and hepatic cholesterol metabolism in humans. Genetic variation in NPC1L1 has been widely studied in recent years. We analyzed NPC1L1 single nucleotide polymorphisms in Chinese gallstone disease patients to investigate their association with gallstone disease. NPC1L1 mRNA expression was also measured in liver biopsies from patients with cholesterol gallstone disease and compared between genotypes. The G allele of the g1679C>G (rs2072183) polymorphism was significantly more prevalent in patients with gallstones compared with gallstone-free subjects. Moreover, patients carrying the G allele had lower hepatic NPC1L1 mRNA expression and higher biliary cholesterol (molar percentages) and cholesterol saturation index. Our study suggests that the G allele of the NPC1L1 polymorphism g1679C>G may be a positive marker of gallstone formation risk.

Genetic and functional identification of the likely causative variant for cholesterol gallstone disease at the ABCG5/8 lithogenic locus

The sterolin locus (ABCG5/ABCG8) confers susceptibility for cholesterol gallstone disease in humans. Both the responsible variant and the molecular mechanism causing an increased incidence of gallstones in these patients have as yet not been identified. Genetic mapping utilized patient samples from Germany (2,808 cases, 2,089 controls), Chile (680 cases, 442 controls), Denmark (366 cases, 766 controls), India (247 cases, 224 controls), and China (280 cases, 244 controls). Analysis of allelic imbalance in complementary DNA (cDNA) samples from human liver (n = 22) was performed using pyrosequencing. Transiently transfected HEK293 cells were used for [(3) H]-cholesterol export assays, analysis of protein expression, and localization of allelic constructs. Through fine mapping in German and Chilean samples, an ∼250 kB disease-associated interval could be defined for this locus. Lack of allelic imbalance or allelic splicing of the ABCG5 and ABCG8 transcripts in human liver limited the search to coding single nucleotide polymorphisms. Subsequent mutation detection and genotyping yielded two disease-associated variants: ABCG5-R50C (P = 4.94 × 10(-9) ) and ABCG8-D19H (P = 1.74 × 10(-10) ) in high pairwise linkage disequilibrium (r(2) = 0.95). [(3) H]-cholesterol export assays of allelic constructs harboring these genetic candidate variants demonstrated increased transport activity (3.2-fold, P = 0.003) only for the ABCG8-19H variant, which was also superior in nested logistic regression models in German (P = 0.018), Chilean (P = 0.030), and Chinese (P = 0.040) patient samples.

CONCLUSION

This variant thus provides a molecular basis for biliary cholesterol hypersecretion as the mechanism for cholesterol gallstone formation, thereby drawing a link between "postgenomic" and "pregenomic" pathophysiological knowledge about this common complex disorder. (HEPATOLOGY 2012).

Comparative proteomic analysis of gallbladder bile proteins related to cholesterol gallstones

Background

Nucleation of cholesterol monohydrate crystals following the aggregation and fusion of cholesterol-enriched vesicles is a critical procedure in the formation of cholesterol gallstone. Biliary proteins play important roles in the process. It is inefficient to screen pro-nucleating or anti-nucleating proteins with routine physiochemical techniques, by which we discovered several pro-nucleating proteins.

Methodology/Principal Findings

Based on comparative proteomic technologies, we investigated the differentially expressed proteins between the cholesterol gallstone and control groups, and between the vesicular phase and micellar phase. There are 401±75 spots detected on the cholesterol gallstone group and 389±94 spots on the control group gels, 120±24 spots detected on vesicular phase and 198±37 on micellar phase gels, and accordingly 22 and 8 differentially expressed proteins were identified successfully, respectively. Three of them, HSA, Profilin and Retinol Binding Protein, were validated by Western blot.

Conclusion/Significance

Some of the identified proteins are in good agreement with proteins reported to be involved in the gallstone formation before. The information from this study might provide some important clues to uncover the key proteins involved in the formation of cholesterol gallstone.

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.

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.

Roles of infection, inflammation, and the immune system in cholesterol gallstone formation

Cholesterol gallstone formation is a complex process mediated by genetic and environmental factors. Until recently, the role of the immune system in the pathogenesis of cholesterol gallstones was not considered a valid topic of research interest. This review collates and interprets an extensive body of basic literature, some of which is not customarily considered to be related to cholelithogenesis, describing the multiple facets of the immune system that appear to be involved in cholesterol cholelithogenesis. A thorough understanding of the immune interactions with biliary lipids and cholecystocytes should modify current views of the pathogenesis of cholesterol gallstones, promote further research on the pathways involved, and lead to novel diagnostic tools, treatments, and preventive measures.

Gallstone disease: from genes to evidence-based therapy

The number of gallstone patients is increasing in ageing populations with a high prevalence of metabolic syndrome and obesity. Recently variants of hepatic ATP binding cassette transporters have been identified as genetic susceptibility factors for gallstone disease, pointing to novel means for risk assessment and prevention. Although laparoscopic cholecystectomy is the mainstay of therapy for symptomatic gallbladder stones, the clinical management of gallstone disease is changing rapidly, with an increase in day case surgery and the advent of transluminal endoscopic surgery. Here, we summarize the molecular and genetic mechanisms of gallstone formation as well as the current evidence-based algorithms for diagnosis and therapy of gallbladder and bile duct stones.

Genetic evidence that apolipoprotein E4 is not a relevant susceptibility factor for cholelithiasis in two high-risk populations

Apolipoprotein E (apoE) isoforms are genetic determinants of interindividual variations in lipid metabolism. To assess whether apoE is a genetic risk factor for cholesterol gallstone disease (GD), we analyzed apoE variants in populations from Chile and Germany, two countries with very high prevalence rates of this disease. ApoE genotypes were determined in Chilean gallstone patients (n = 117) and control subjects (n = 122) as well as in German gallstone patients (n = 184) and matched controls (n = 184). In addition, we studied apoE variants in subgroups of Chilean patients with strong differences in their susceptibility to acquire gallstones: 50 elderly subjects without gallstones in spite of well-known risk factors for this disease (gallstone-resistant) and 32 young individuals with gallstones but without risk factors (gallstone-susceptible). Furthermore, correlation analysis of apoE genotypes with cholesterol crystal formation times, biliary cholesterol saturation index (CSI), and gallstone cholesterol contents was performed in 81 cholecystectomized patients. In this study analyzing the largest sample set available, apoE4 genotype was not associated with an increased frequency of GD in either population. Moreover, in the Chilean population after adjusting for risk factors such as gender, age, body mass index, serum lipids, and glucose, the odds ratio for the association of the apoE4 allele and GD was significantly (P < 0.05) <1. Also, genotypes were not correlated with cholesterol crystal formation time, CSI, or gallstone cholesterol content. In contrast to previous smaller studies, apoE polymorphisms were not associated with susceptibility to cholesterol GD in high-risk populations.

Gallstone disease

Gallstone disease is one of the most prevalent gastrointestinal diseases with a substantial burden to health care systems that is supposed to increase in ageing populations at risk. Aetiology and pathogenesis of cholesterol gallstones still are not well defined, and strategies for prevention and efficient nonsurgical therapies are missing. This review summarizes current concepts on the pathogenesis of cholesterol gallstones with focus on the uptake and secretion of biliary lipids and special emphasis on recent studies into the genetic background.

Gender and gallstone disease

Gallstone disease is a common disorder all over the world. In the Western societies about 80 % of the gallstones are composed primarily of cholesterol. Several risk factors for gallstone formation have been identified. One of the most important risk factors is female gender. Rates of gallstones are two to three times higher among women than men. But this is primarily a phenomenon of the childbearing age. Pregnancy is also a major risk factor for gallstone formation. The risk is related to the number of pregnancies. Sex hormones are most likely to be responsible for the increased risk. Estrogen increases biliary cholesterol secretion causing cholesterol supersaturation of bile. Thus, hormone replacement therapy in postmenopausal women and oral contraceptives have also been described to be associated with an increased risk for gallstone disease. However, the effect of estrogen is dose-dependent and new oral contraceptives with a low estrogen dose do not seem to increase the rate of gallstone formation. The present article focuses on the mentioned risk factors associated with female sex hormones.

Critical role of cholic acid for development of hypercholesterolemia and gallstones in diabetic mice

We studied bile acid and cholesterol metabolism in insulin-dependent diabetes utilizing genetically modified mice unable to synthesize cholic acid (Cyp8b1-/-). Diabetes was induced in Cyp8b1-/- and wild type animals (Cyp8b1+/+) by alloxan, and the mice were fed normal or cholesterol-enriched diet for 10 weeks. The serum levels of cholesterol were strongly increased in diabetic Cyp8b1+/+ mice fed cholesterol, while diabetic Cyp8b1-/- mice did not show any aberrations regardless of the diet. Diabetic cholesterol-fed Cyp8b1+/+ mice had much higher biliary cholesterol and cholesterol saturation index than all other groups, their bile contained a large number of cholesterol crystals, and their canalicular cholesterol transporter Abcg5/g8 mRNA levels were much higher. Cyp7a1 mRNA levels were similar in all diabetic mice but higher compared to non-diabetic animals. The results indicate a critical role for cholic acid for the development of hypercholesterolemia and gallstones in our animal model.

NPC2 is expressed in human and murine liver and secreted into bile: potential implications for body cholesterol homeostasis

The liver plays a critical role in the metabolism of lipoprotein cholesterol and in controlling its elimination through the bile. Niemann-Pick type C 2 (NPC2), a cholesterol-binding protein, is key for normal intracellular trafficking of lipoprotein cholesterol, allowing its exit from the endolysosomal pathway into the metabolically active pool of the cell. In addition, NPC2 is a secretory protein from astrocytes and epididymal cells. Although NPC2 mRNA is detected in the liver, plasma and biliary NPC2 protein levels and function have not been reported. This study demonstrates that NPC2 is present in murine and human plasma and bile. In addition, hepatic NPC2 protein expression was dramatically increased in NPC1-deficient mice but not regulated by cholesterol feeding or pharmacological modulation of various nuclear receptors involved in cholesterol and bile acid metabolism. Interestingly, biliary NPC2 levels were 3-fold increased in gallstone-susceptible C57BL6/J versus gallstone-resistant BALB/c mice. Furthermore, NPC2 was exclusively found in the cholesterol pro-nucleating ConA-binding fraction of human bile. In conclusion, NPC2 is secreted from the liver into bile and plasma, where it may have a functional role in cholesterol transport in normal and disease conditions.

Biliary lipids, water and cholesterol gallstones

Cholesterol supersaturation, hydrophobic bile salts, pronucleating proteins and impaired gall-bladder motility may contribute to gallstone pathogenesis. We here show that both gallstone-susceptible C57L and gallstone-resistant AKR male inbred mice exhibit supersaturated gall-bladder biles during early lithogenesis, whereas bile-salt composition becomes hydrophobic only in susceptible C57L mice. In vitro, cholesterol crystallization occurs depending on relative amounts of lipids; excess cholesterol may exceed solubilizing capacity of mixed bile salt-phospholipid micelles, whereas excess bile salts compared with phospholipids leads to deficient cholesterol-storage capacity in vesicles. In vivo, bile lipid contents are mainly determined at the level of the hepatocyte canalicular membrane, where specific transport proteins enable lipid secretion [ABCG5/G8 (ATP-binding cassette transporter G5/G8) for cholesterol, MDR3 (multi-drug resistant 3) for phospholipid, BSEP (bile salt export pump)]. These transport proteins are regulated by farnesoid X and liver X nuclear receptors. After nascent bile formation, modulation of bile water contents in biliary tract and gall-bladder exerts critical effects on cholesterol crystallization. During progressive bile concentration (particularly in the fasting gall-bladder), cholesterol and, preferentially, phospholipid transfer occurs from cholesterol-unsaturated vesicles to emerging mixed micelles. The remaining unstable cholesterol-enriched vesicles may nucleate crystals. Various aquaporins have recently been discovered throughout the biliary tract, with potential relevance for gallstone formation.

Biliary sludge is formed by modification of hepatic bile by the gallbladder mucosa

BACKGROUND & AIMS

We studied 22 patients with symptomatic microlithiasis to determine whether a contributory role of the gallbladder in the early stage of cholesterol gallstone formation exists. We compared the merits of different methods (ultrasonography and microscopy) and sources (hepatic or gallbladder) of bile samples for diagnosing microlithiasis.

METHODS

Paired hepatic and gallbladder bile samples were studied with polarizing microscopy. Nucleation time, bile salts, phospholipid, cholesterol, cholesterol saturation index (CSI), bilirubin, total protein, albumin and mucin concentration were measured. All patients had abdominal ultrasound examination.

RESULTS

With polarizing microscopy as the standard, ultrasonography was positive in 13 patients (59%) and negative in 9 (41%). All gallbladder bile samples were positive for microlithiasis by microscopy. Only one hepatic bile sample was positive (P < .0001). There was a disproportional enrichment of total protein, albumin, and mucin (P < .05) in the gallbladder bile and a conversion of bilirubin diglucuronide to monoglucuronide (P < .01). Gallbladder samples had lower CSI but a faster nucleation time (P < .001), which correlates inversely with CSI, total protein, and mucin concentration.

CONCLUSION

Biochemical composition and physical chemical behavior of hepatic bile are modified during residence in the gallbladder, contributing to sludge formation. Gallbladder bile has a lower calculated CSI, higher deconjugation of bilirubin, protein and mucin concentration and crystals were present. Hepatic bile samples are inappropriate for microscopic detection of microlithiasis.

Solubility of cholesterol in the crystal-free gallbladder bile of gallstone patients

Supersaturation of bile with cholesterol is generally considered the driving force of cholesterol precipitation. However, in most investigations the amount of cholesterol crystals is included in the calculation of the cholesterol saturation index (CSI). We therefore studied the solubility of cholesterol in crystal-free gallbladder bile from gallstone patients. Our results demonstrate significantly ( P <.05) higher CSIs (1.4 +/- 0.5 and 1.4 +/- 0.4 vs 1.1 +/- 0.4, mean +/- SD) in crystal-free gallbladder bile from 66 patients with cholesterol stones and 21 patients with mixed stones compared with those in 30 patients with pigment stones and a significant difference ( P <.001) in the amount of cholesterol in vesicles (19.2% +/- 13.7% and 14.3% +/- 11.6 % vs 4.2% +/- 5.9%) and of the crystal-observation time (COT; 1-21 days, median 2 days and 1-21 days, median 3 days, vs 3-21 days, median 21 days). We detected a positive correlation ( r =.24, P <.01) between the percentage of cholesterol in vesicles and the CSI and a negative correlation between COT and CSI ( r = -.23, P <.02 ) and COT and the percentage of cholesterol in vesicles ( r = -.52, P <.001 ). However, in 14 of 30 gallbladder-bile specimens from patients with pigment stones but in just 5 of 21 specimens from patients with mixed stones patients and 12 of 66 specimens from patients with cholesterol stones, the distribution of cholesterol in different phases (mixed micelles, vesicles, and crystals) was within the limits of solubility determined in previous studies of model bile. Therefore, in addition to the relative composition of biliary lipids, nonlipid components exert considerable influence on the solubility of cholesterol in the gallbladder bile of gallstone patients.

Genetic analysis of cholesterol gallstone formation: searching for Lith (gallstone) genes

The genetics of cholesterol cholelithiasis is complex because a number of interacting genes regulate biliary cholesterol homeostasis. Quantitative trait locus (QTL) analysis is a powerful method for identifying primary rate-limiting genetic defects and discriminating them from secondary downstream lithogenic effects caused by mutations of the primary genes. The subsequent positional cloning of such genes responsible for QTLs may lead to the discovery of pathophysiologic functions of Lith (gallstone) genes. In this review, we present a map of candidate genes for Lith genes that may determine gallstone susceptibility in mice. The physical-chemical, pathophysiologic, and genetic studies of Lith genes in bile, liver, gallbladder, and intestine will be crucial for elucidating the genetic mechanisms of cholesterol gallstone disease in mice and in humans. Because exceptionally close homology exists between mouse and human genomes, the orthologous human LITH genes can often be recognized after mouse genes are identified.

Helicobacter pylori infection in pediatric population: epidemiology, pathophysiology, and therapy

Helicobacter pylori, one of the most commonly encountered human pathogens, has been recognized in more than half of adults and children with chronic nonspecific gastritis, and nearly all children with peptic ulcer disease demonstrate antral infection with H. pylori. A high prevalence and early colonization of H. pylori infection in childhood was described in developing countries in contrast to developed countries. The current diagnostic methods include histology, microbiological culture, urease activity detection, polymerase chain reaction, and stool antigen detection. The infection often presents with nausea, vomiting, and epigastric pain but may remain asymptomatic. The treatment modality options are multiple; however, the association of a proton-pump inhibitor and two antibiotics for 1 or 2 weeks gives the best eradication rates. Drug resistance is a growing problem in this microorganism and new therapeutic options are currently limited.

High level of deoxycholic acid in human bile does not promote cholesterol gallstone formation

AIM: To study whether patients with excess deoxycholic acid (DCA) differ from those with normal percentage of DCA with respect to biliary lipid composition and cholesterol saturation of gallbladder bile.

METHODS: Bile was collected during operation through puncturing into the gallbladder from 122 cholesterol gallstone patients and 46 gallstone-free subjects undergoing cholecystectomy. Clinical data, biliary lipids, bile acid composition, presence of crystals and nucleation time were analyzed.

RESULTS: A subgroup of gallstone patients displayed a higher proportion of DCA in bile than gallstone free subjects. By choosing a cut-off level of the 90th percentile, a group of 13 gallstone patients with high DCA levels (mean 50 percent of total bile acids) and a large group of 109 patients with normal DCA levels (mean 21 percent of total bile acids) were obtained. The mean age of the patients with high DCA levels was higher than that of the group with normal levels (mean age: 62 years vs 45 years) and so was the mean BMI (28.3 vs 24.7). Plasma levels of cholesterol and triglycerides were slightly higher in the DCA excess groups compared with those in the normal DCA group. There was no difference in biliary lipid composition, cholesterol saturation, nucleation time or occurrence of cholesterol crystals in bile between patients with high and normal levels of DCA.

CONCLUSION: Gallstone patients with excess DCA were of older age and had higher BMI than patients with normal DCA. The two groups of patients did not differ with respect to biliary lipid composition, cholesterol saturation, nucleation time or occurrence of cholesterol crystals. It is concluded that DCA in bile does not seem to contribute to gallstone formation in cholesterol gallstone patients.

Effect of apolipoprotein E polymorphism on bile lipid composition and the formation of cholesterol gallstone

OBJECTIVE

It remains a matter of controversy whether possession of the apolipoprotein E4 (apoE4) allele is a genetic risk factor for the formation of cholesterol gallstones. The aim of the present study was to test this hypothesis by investigating the effect of apoE4 on bile lipid composition in normal subjects and in patients with cholesterol gallstones and to evaluate the distributions of apoE alleles in these two groups.

METHODS

The study population consisted of 79 patients who underwent open or laparoscopic cholecystectomy for symptomatic cholesterol gallstone disease. The control group (n = 53) included 11 patients with benign gallbladder polyps and 42 normal subjects acting as donors in living donor liver transplantation. The apoE genotypes were assessed by dot blot hybridization with digoxigenin-labeled probes. Bile lipid composition was determined by enzymatic assays and high performance liquid chromatography.

RESULTS

Bile lipid composition and cholesterol saturation index (CSI) were similar in the control subjects harboring the apoE4 allele and those without apoE4 (mean CSI, 85.9% and 72.2%, respectively, p = 0.69). Likewise, in the cholesterol gallstone patients, bile lipid composition and CSI were similar in the patients with and without apoE4 allele (mean CSI, 134.9% vs 152.2%, p = 0.6). Furthermore, the prevalence of the apoE4 allele was similar in the patients with cholesterol gallstones and in the control group (8.5% vs 7.6%, p = 0.46, OR = 0.88; 95% CI = 0.64-1.22).

CONCLUSIONS

The apoE4 allele is not a contributory factor to cholesterol gallstone formation, at least in the Japanese population.

Pathways of cholesterol crystallization in model bile and native bile

Hypersecretion of hepatic cholesterol, chronic supersaturation of bile with cholesterol and rapid precipitation of cholesterol crystals in the gallbladder from cholesterol-enriched vesicles represent the primum movens in cholesterol gallstone formation. Physical-chemical factors and pathways leading to cholesterol crystallization can be investigated in artificial model biles and ex vivo in fresh human bile. Depending on modulatory factors (i.e., lipid concentration, bile salt or phospholipid species, humidity, mucins, etc.), cholesterol can precipitate in several forms (i.e., monohydrate, anhydrous) and habits (i.e., plate-like, needle-like, intermediate arcs, filaments, tubules, spirals). Careful analysis of biliary cholesterol crystals includes biochemical analysis of precipitated crystals, polarizing quantitative light microscopy, and turbidimetric methods. In this paper, recent concepts on cholesterol crystallization in artificial model biles as well as in human bile will be reviewed.

Phenotypic characterization of Lith genes that determine susceptibility to cholesterol cholelithiasis in inbred mice: soluble pronucleating proteins in gallbladder and hepatic biles

BACKGROUND/AIMS

Gallstone susceptibility is high in C57L inbred mice (males > females) and low in AKR mice, related to variant lithogenic (Lith) genes. We examined the relationship between biliary crystallization-promoting proteins and gallstone susceptibility.

METHODS

Biliary protein and lipid concentrations were determined at 0, 7,14, 21, 28 and 56 days on a lithogenic diet.

RESULTS

Protein and soluble mucin concentrations in gallbladder biles increased markedly in males, but remained low in females of both strains and correlated with the cholesterol saturation index (CSI). In all groups, IgA and IgM concentrations decreased initially, but increased at later stages. There were no consistent changes in IgG concentrations, but aminopeptidase-N levels were higher in AKR than in C57L. During the lithogenic diet period, the CSI was > or = 2 in C57L males, approximately 1.5 in AKR males, and 1 in females of both strains. Taurodeoxycholate and taurochenodeoxycholate rose sharply in C57L, but remained low in AKR.

CONCLUSIONS

Hydrophobic bile salts, cholesterol supersaturation, and possibly, high mucin concentrations are associated with gallstone formation. In vitro crystallization-promoting immunoglobulins and aminopeptidase-N do not appear to be major factors in murine gallstone pathogenesis, in line with the observation that genes encoding these proteins do not co-localize with any known Lith locus.

Cholesterol crystal binding of biliary immuno-globulin A: visualization by fluorescence light microscopy

AIM: To assess potential contributions of biliary IgA for crystal agglomeration into gallstones, we visualized cholesterol crystal binding of biliary IgA.

METHODS: Crystal binding biliary proteins were extracted from human gallbladder bile using lectin affinity chromatography. Biliary IgA was isolated from the bound protein fraction by immunoaffinity chromatography. Pure cholesterol monohydrate crystals were incubated with biliary IgA and fluoresceine isothiocyanate (FITC)conjugated anti IgA at 37 °C. Samples were examined under polarizing and fluorescence light microscopy with digital image processing.

RESULTS: Binding of biliary IgA to cholesterol monohydrate crystals could be visualized with FITC conjugated anti IgA antibodies. Peak fluorescence occurred at crystal edges and dislocations. Controls without biliary IgA or with biliary IgG showed no significant fluorescence.

CONCLUSION: Fluorescence light microscopy provided evidence for cholesterol crystal binding of biliary IgA. Cholesterol crystal binding proteins like IgA might be important mediators of crystal agglomeration and growth of cholesterol gallstones by modifying the evolving crystal structures in vivo.

Biliary lipid composition in patients with cholesterol and pigment gallstones and gallstone-free subjects: deoxycholic acid does not contribute to formation of cholesterol gallstones

BACKGROUND

Four main disturbances have been attributed to cholesterol gallstone disease: hypersecretion of cholesterol from the liver with cholesterol supersaturation in bile; disturbed motility with defective absorption and secretion by the gallbladder; increased crystallisation of cholesterol in the gallbladder bile; and slow intestinal transit with increased amount of deoxycholic acid in the bile acid pool. We aimed to evaluate the biliary lipid composition in a large series of gallstone patients, with emphasis on the amount of deoxycholic acid and with respect to number of stones, compared to gallstone free subjects.

MATERIALS AND METHODS

Bile was sampled during operations through puncture of the gallbladder from 145 cholesterol gallstone patients, 23 patients with pigment stones and 87 gallstone free patients undergoing cholecystectomy. Biliary lipid composition, cholesterol saturation, bile acid composition, nucleation time and cholesterol crystals were analysed.

RESULTS

The patients with cholesterol gallstones showed higher molar percentage of cholesterol, lower total biliary lipid concentration, higher cholesterol saturation, shorter nucleation time and higher proportion of crystals in bile than the other groups. The nucleation time was significantly shorter in multiple cholesterol gallstone patients, but this was not due to higher cholesterol saturation. Male cholesterol gallstone patients showed higher cholesterol levels, lower total biliary lipid concentration, and higher cholesterol saturation in bile than female patients. There was no difference in biliary content of deoxycholic acid, but significantly lower content of cholic acid in gallstone patients compared to gallstone free patients.

CONCLUSIONS

We conclude that deoxycholic acid does not contribute to gallstone formation in cholesterol gallstone patients. The short nucleation time in patients with multiple cholesterol stones is not due to higher cholesterol saturation.

Impaired human gallbladder lipid absorption in cholesterol gallstone disease and its effect on cholesterol solubility in bile

BACKGROUND & AIMS

The role of the gallbladder in gallstone pathogenesis is still unclear. We examined the effects of gallbladder mucosal lipid absorption on lipid composition and cholesterol crystallization in bile.

METHODS

The in vitro-isolated, intra-arterially perfused gallbladder model was used (1) to compare the absorption rates of lipids from standard bile by gallbladders obtained from 7 patients with cholesterol gallstones and 6 controls; and (2) to measure the microscopic cholesterol crystal detection time in cholesterol-enriched pig bile before and after lipid absorption by the pig gallbladder.

RESULTS

Control gallbladders, but not cholesterol gallstone gallbladders, significantly reduced cholesterol (P < 0.02) and phospholipid (P < 0.01) and increased bile salt (P < 0.01) molar percentages in bile over a 5-hour period by efficient and selective cholesterol and phospholipid absorption. A histomorphometric study of the epithelial cells showed significantly higher values for nuclear density (P < 0.01) and nuclear (P < 0.05) and cytoplasmic (P < 0.05) areas in the cholesterol gallstone than the control group. Sequential microscopy of cholesterol-enriched pig bile showed significantly shorter cholesterol filament (P < 0.01) and typical cholesterol plate (P < 0. 02) detection times before than after exposure of bile to the gallbladder lipid absorption.

CONCLUSIONS

In cholesterol gallstone disease, the human gallbladder epithelium loses its capacity to selectively and efficiently absorb cholesterol and phospholipids from bile, even if it is hyperplastic and hypertrophic. This epithelial dysfunction eliminates the positive effect that the normal gallbladder exerts on cholesterol solubility in bile and might be a pathogenetic cofactor for cholesterol gallstone formation.

Gallstones

This review summarizes the main advances made in the epidemiology, pathogenesis, and medical treatment of gallstone disease in the past year. Whether rapid weight reduction can precipitate gallstone formation is still debated. Phospholipase A(2)-II seems to play an interesting role in the pathogenesis of multiple cholesterol stone formation, and ursodeoxycholic acid may partially halt the formation of multiple cholesterol stones by mediating an anti-inflammatory effect on the gallbladder. Bacterial infections may contribute to gallstone formation, perhaps through secretion of biofilm. The combination of ursodeoxycholic acid and simvastatin for the resolution and prevention of gallstones is promising, but larger studies are needed.

Physical and metabolic factors in gallstone pathogenesis

Gallstones form when the tenuous balance of solubility of biliary lipids tips in favor of precipitation of cholesterol, unconjugated bilirubin, or bacterial degradation products of biliary lipids. For cholesterol gallstones, metabolic alterations in hepatic cholesterol secretion combine with changes in gallbladder motility and intestinal bacterial degradation of bile salts to destabilize cholesterol carriers in bile and produce cholesterol crystals. For black pigment gallstones, changes in heme metabolism or bilirubin absorption lead to increased bilirubin concentrations and precipitation of calcium bilirubinate. In contrast, mechanical obstruction of the biliary tract is the major factor leading to bacterial degradation and precipitation of biliary lipids in brown pigment stones. Further understanding of the physical and metabolic factors of cholesterol and black pigment formation is likely to provide interventions to interrupt the earliest stages of gallstone formation.

Genetic epidemiology of cholesterol cholelithiasis among Chilean Hispanics, Amerindians, and Maoris

BACKGROUND & AIMS

The etiology of cholesterol gallstones is multifactorial, with interactions of genes and the environment. The hypothesis that aborigine cholesterol lithogenic genes are widely spread among Chileans, a population with a high prevalence of gallstones, was tested.

METHODS

Medical history and anthropometric measurements were obtained and abdominal ultrasonography was performed in 182 Mapuche Indians, 225 Maoris of Easter Island, and 1584 Hispanics. Blood groups, DNA, lipids, and glucose were analyzed. The Amerindian Admixture Index and mitochondrial DNA (mtDNA) assessed the ethnicity and degree of racial admixture.

RESULTS

Amerindian Admixture Index was 0.8 in Mapuches and 0.4 in Hispanics. All Mapuches, 88% of Hispanics, but none of Maoris had Amerindian mtDNA haplotypes. Age- and sex-adjusted global prevalence of gallstone disease was higher in Mapuches (35%) than in Hispanics (27%) and Maoris (21%). Compared with Hispanics, the youngest group of Mapuches had the greatest corrected risk of gallstones: odds ratios of 6.0 in women and 2.3 in men. In contrast, the gallstone risk in Maoris was lower compared with Hispanics: odds ratios of 0.6 for women and 0.5 for men.

CONCLUSIONS

Cholesterol lithogenic genes appear widely spread among Chilean Indians and Hispanics. They could determine the early formation of gallstones and explain the high prevalence of gallbladder diseases among some South American populations.