Biliary proteins. Unique inhibitors of cholesterol crystal nucleation in human gallbladder bile

Acute cholangitis: a state-of-the-art review

Acute cholangitis is a potentially life-threatening bacterial infection of the intra and/or extrahepatic bile ducts. It remains the second and third cause of community-acquired and hospital-acquired bacteremia, respectively, and is associated with mortality rates of up to 15%, despite advances in broad-spectrum antimicrobial therapy and improved access to emergency biliary tract decompression procedures. Even though not much has changed in recent years in terms of diagnosis or treatment, new data have emerged regarding multidrug-resistant bacteria that serve as etiologic agents of cholangitis. Moreover, different approaches in antibiotic regimes depending on severity grading and bile sample cultures as well as novel minimally invasive endoscopic procedures that can help when consecrated treatments such as endoscopic retrograde cholangiopancreatography (ERCP) fail, cannot be performed, or are unavailable have been proposed. This state-of-the-art review aims to offer a complete and updated assessment of the epidemiology, novel diagnostic and therapeutic methods, complications, and prognostic variables of acute cholangitis. The authors will review the prognostic implications of unusual complications, the relevance of regular bile samples and antibiograms, and their new role in guiding antibiotic therapy and limiting antibiotic resistance to present an organized and comprehensive approach to the care of acute cholangitis.

Mouse models of gallstone disease

PURPOSE OF REVIEW

The establishment of mouse models of gallstones, and the contribution of mouse models to genetic studies of gallstone disease, as well as the latest advances in the pathophysiology of gallstones from mouse experiments are summarized.

RECENT FINDINGS

The combined uses of genomic strategies and phenotypic studies in mice have successfully led to the identification of many Lith genes, which pave the way for the discovery of human LITH genes. The physical-chemical, genetic, and molecular biological studies of gallstone disease in mice with knockout or transgene of specific target genes have provided many novel insights into the complex pathophysiological mechanisms of this very common hepatobiliary disease worldwide, showing that interactions of five primary defects play a critical role in the pathogenesis of cholesterol gallstones. Based on mouse studies, a new concept has been proposed that hepatic hypersecretion of biliary cholesterol is induced by multiple Lith genes, with insulin resistance as part of the metabolic syndrome interacting with cholelithogenic environmental factors to cause the phenotype.

SUMMARY

The mouse model of gallstones is crucial for elucidating the physical-chemical and genetic mechanisms of cholesterol crystallization and gallstone formation, which greatly increase our understanding of the pathogenesis of this disease in humans.

Analytic Reviews : Nonsurgical Alternatives in the Management of Gallstones

Until recently, the only therapeutic option for patients with symptomatic gallstones was surgery. However, sev eral new and innovative nonsurgical approaches are cur rently available, including oral dissolution therapy with the bile salts, ursodeoxycholic and chenodeoxycholic acids, instillation of liquid solvents such as methyl tert- butyl ether directly into the gallbladder or the common bile duct, and extracorporeal shock-wave lithotripsy. We review the role of each of these methods in the management of patients with gallstones as well as the epidemiology, pathogenesis, natural history, and radi ological characteristics of gallstones, all important con siderations when choosing appropriate treatment for the individual patient.

Gallstones

Gallstones grow inside the gallbladder or biliary tract. These stones can be asymptomatic or symptomatic; only gallstones with symptoms or complications are defined as gallstone disease. Based on their composition, gallstones are classified into cholesterol gallstones, which represent the predominant entity, and bilirubin ('pigment') stones. Black pigment stones can be caused by chronic haemolysis; brown pigment stones typically develop in obstructed and infected bile ducts. For treatment, localization of the gallstones in the biliary tract is more relevant than composition. Overall, up to 20% of adults develop gallstones and >20% of those develop symptoms or complications. Risk factors for gallstones are female sex, age, pregnancy, physical inactivity, obesity and overnutrition. Factors involved in metabolic syndrome increase the risk of developing gallstones and form the basis of primary prevention by lifestyle changes. Common mutations in the hepatic cholesterol transporter ABCG8 confer most of the genetic risk of developing gallstones, which accounts for ∼25% of the total risk. Diagnosis is mainly based on clinical symptoms, abdominal ultrasonography and liver biochemistry tests. Symptoms often precede the onset of the three common and potentially life-threatening complications of gallstones (acute cholecystitis, acute cholangitis and biliary pancreatitis). Although our knowledge on the genetics and pathophysiology of gallstones has expanded recently, current treatment algorithms remain predominantly invasive and are based on surgery. Hence, our future efforts should focus on novel preventive strategies to overcome the onset of gallstones in at-risk patients in particular, but also in the population in general.

Bile proteome in health and disease

The study of bile proteins could improve the understanding of physiological processes involved in the regulation of the hepato-biliary system. Researchers have tried for years to investigate the bile proteome but, until recently, only a few tens of proteins were known. The advent of proteomics, availing of large-scale analytical devices paired with potent bioinformatic resources, lately allowed the identification of thousands of proteins in bile. Nevertheless, the knowledge of their role in the hepato-biliary system still represents almost a "blank page in the book of physiology." In this review, we first guide the reader through the historical phases of the analysis of bile protein content, emphasizing the recent progresses achieved through the use of proteomic techniques. Thereafter, we deeply explore the involvement of bile proteins in health and disease, with a particular focus on the discovery of biomarkers for biliary tract malignancies.

Osteopontin plays an anti-nucleation role in cholesterol gallstone formation

AIM

  To investigate the role of osteopontin in cholesterol gallstone formation.

METHODS

  Nucleation time was determined in model and human gallbladder bile in vitro. Effect of osteopontin on vesicles of bile was investigated via transmission electron microscopy. The mRNA and protein expression of osteopontin were detected in human calculus and normal gallbladder tissues, and then lipid compositions of human bile were determined via commercial kits.

RESULTS

  Osteopontin could prolong the nucleation time in a dose-dependent manner, and inhibit the pro-nucleation effect induced by calcium ion. Cholesterol crystal growth was inhibited by osteopontin in a dose-dependent manner in model and human gallbladder bile, but not affected by calcium. Furthermore, the formation, aggregation and fusion of vesicles were suppressed by osteopontin in model and human bile as demonstrated by transmission electron microscopy. The mRNA and protein expression of osteopontin in calculus gallbladder tissues were lower than those in normal tissues. The concentrations of cholesterol, phospholipid and bile acids, and cholesterol saturated index were higher and the contents of osteopontin and calcium, nevertheless, were found to be lower in lithogenic bile than those in normal controls.

CONCLUSION

  These findings indicated that osteopontin could inhibit the cholesterol gallstone formation as an anti-nucleation factor, which may be involved in the pathogenesis of cholesterol gallstone formation.

Effect of dietary garlic and onion on biliary proteins and lipid peroxidation which influence cholesterol nucleation in bile

Formation of cholesterol gallstones in gallbladder is controlled by procrystallizing and anticrystallizing factors present in bile. Dietary garlic and onion have been recently observed to possess anti-lithogenic potential in experimental mice. In this investigation, the role of biliary proteins from rats fed lithogenic diet or garlic/onion-containing diet in the formation of cholesterol gallstones in model bile was studied. Cholesterol nucleation time of the bile from lithogenic diet group was prolonged when mixed with bile from garlic or onion groups. High molecular weight proteins of bile from garlic and onion groups delayed cholesterol crystal growth in model bile. Low molecular weight (LMW) proteins from the bile of lithogenic diet group promoted cholesterol crystal growth in model bile, while LMW protein fraction isolated from the bile of garlic and onion groups delayed the same. Biliary LMW protein fraction was subjected to affinity chromatography using Con-A and the lectin-bound and unbound fractions were studied for their influence on cholesterol nucleation time in model bile. Major portion of biliary LMW proteins in lithogenic diet group was bound to Con-A, and this protein fraction promoted cholesterol nucleation time and increased cholesterol crystal growth rate, whereas Con-A unbound fraction delayed the onset of cholesterol crystallization. Biliary protein from garlic/onion group delayed the crystallization and interfered with pronucleating activity of Con-A bound protein fraction. These data suggest that apart from the beneficial modulation of biliary cholesterol saturation index, these Allium spices also influence cholesterol nucleating and antinucleating protein factors that contribute to their anti-lithogenic potential.

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.

Large-scale identification of human biliary proteins from a cholesterol stone patient using a proteomic approach

Gallbladder bile, one of the most important body fluids, is composed of water, inorganic ions, conjugated bile salts, phospholipids, cholesterol, bilirubin, mucin and proteins. The separation and identification of bile proteins remain difficult due to the complexity of this matrix. In the present study, human gallbladder bile was obtained from a cholesterol stone patient, and the proteins were isolated and purified by dialysis, precipitation and delipidation procedures. The resulting proteins were divided into several aliquots. One aliquot was subjected to two-dimensional gel electrophoresis (2DE). The protein spots were then in-gel digested and analyzed by liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS). Another aliquot was directly digested and analyzed by a combination of strong cation-exchange (SCX) and reversed-phase (RP) chromatography prior to tandem mass spectrometry (2D-LC/MS/MS). Eventually, 48 and 218 unique proteins were identified from 2DE/MS and 2D-LC/MS/MS, respectively, resulting in a total of 222 unique identified proteins. Of the 218 proteins identified by 2D-LC/MS/MS, 92 were identified based on more than one unique tryptic peptide, and, of the total 222 proteins, 98 were identified based on more than one unique tryptic peptide.

Apolipoprotein E polymorphism and lithogenic factors in gallbladder bile

BACKGROUND

Associations between the polymorphism of apolipoprotein E, which plays an important role in cholesterol metabolism and cholesterol gallstone formation, have been reported recently. Patients with the apo E4 isoform showed increased numbers and cholesterol contents of their stones, a higher frequency of cholesterol crystals in bile, increased susceptibility to gallstone fragmentation by extracorporeal shock-wave lithotripsy and an increase in recurrence rate after dissolution. A recent study, however, showed that fast cholesterol crystallization in bile is associated with multiple stones but not with apo E4. Therefore the mechanism for an increased risk of gallstone formation in patients with the apo E4 isoform still remains under debate.

DESIGN

To clarify this issue we investigated 37 patients with gallstones (10 with the apo E4 allele and 27 without the allele). Gallbladder biles were examined for total cholesterol and other lipids, cholesterol saturation index, crystal observation time, crystal mass, total protein and mucin. Moreover, number of gallstones and cholesterol in gallstones was compared in both groups.

RESULTS

The crystal observation time (2.5 vs. 2.0 days, median) and the cholesterol saturation index (1.34 +/- 0.45 vs. 1.43 +/- 0.74) did not differ significantly between the apo E4 and the non apo E4 group. Total biliary lipids (11.6 +/- 3.8 vs. 9.3 +/- 3.9 g 100 mL-1, P = 0.126) and total biliary cholesterol (21.8 +/- 9.7 vs. 15.7 +/- 7 mmol L-1, P = 0.067) tended to be elevated in the apo E4 group. Crystal mass (3.60 +/- 4.10 vs. 2.38 +/- 2.70 mmol L-1), biliary total protein (8.6 +/- 3.5 vs. 8.3 +/- 6.6 mg mL-1) and mucin (0.55 +/- 0.38 vs. 0.66 +/- 0.67 mg mL-1), number (solitary/multiple) of gallstones and cholesterol in gallstones were not different in both groups of patients.

CONCLUSIONS

In comparison to the non apo E4 patients the apo E4 group showed a trend to elevated biliary cholesterol whereas crystal observation time, cholesterol saturation index, crystal mass, number of gallstones, cholesterol content of gallstones and total protein and mucin were not different. These findings do not suggest an association of the apo E isoform and the formation of cholesterol gallstones

Cholelithiasic disease and associated factors in a Spanish population

In order to analyze the factors associated with cholelithiasic disease, 1268 participants of a population sample were studied. On univariate analysis, 11 of the 23 variables included showed a statistically significant association (P < 0.05). Five of these variables, including obesity, triglyceride level, intake of hypolipidemic drugs, and a diet rich in cholesterol and saturated fats in women, and physical exercise in men, remained significantly associated after controlling for age. On multivariate analysis among women, a positive association was found with age (P < 0.001), obesity, and the use of hypolipidemic agents (P < 0.05) and a negative one with a diet rich in cholesterol and saturated fats (P < 0.05). Among men, the same analysis revealed there was a positive association with age (P < 0.001) and triglycerides (P < 0.05) and a negative one with physical exercise (P < 0.05). In conclusion, obesity and the use of hypolipidemic agents in women and triglycerides in men, were positively associated with cholelithiasic disease, independent of age, while negative associations included the intake of cholesterol and saturated fats in women and physical exercise in men.

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.

Fatty acid bile acid conjugates (FABACs)--new molecules for the prevention of cholesterol crystallisation in bile

BACKGROUND

Cholesterol gall stones are a frequent disease for which at present surgery is the usual therapy. Despite the importance of bile acids it has become evident that phospholipids are the main cholesterol solubilisers in bile. Even phospholipid components, such as fatty acids, have anticrystallising activity.

AIM

To synthesise fatty acid bile acid conjugates (FABACs) and study their effects on cholesterol crystallisation in bile in vitro and in vivo.

METHODS

FABACs were prepared by conjugation of cholic acid at position 3 with saturated fatty acids of variable chain length using an amide bond. Cholesterol crystallisation and its kinetics (crystal observation time, crystal mass) were studied in model bile, pooled enriched human bile, and fresh human bile using FABACs with saturated fatty acids of varying chain length (C-6 to C-22). Absorption of FABACs into blood and bile was tested in hamsters. Prevention of biliary cholesterol crystallisation in vivo was tested in hamsters and inbred mice.

RESULTS

FABACs strongly inhibited cholesterol crystallisation in model as well as native bile. The FABACs with longer acyl chains (C-16 to C-22) were more effective. At a concentration of 5 mM, FABACs almost completely inhibited cholesterol crystallisation in fresh human bile for 21 days. FABACs were absorbed and found in both portal and heart blood of hamsters. Levels in bile were 2-3 times higher than in blood, indicating active secretion. Appreciable levels were found in the systemic circulation 24-48 hours after a single administration. Ingested FABACs completely prevented the formation of cholesterol crystals in the gall bladders of hamsters and mice fed a lithogenic diet.

CONCLUSIONS

FABACs are potent inhibitors of cholesterol crystallisation in bile. They are absorbed and secreted into bile and prevent the earliest step of cholesterol gall stone formation in animals. These compounds may be of potential use in cholesterol gall stone disease in humans.

Antidenaturant drugs for cataract and other condensation diseases

'Condensation diseases' are heterogeneous pathological conditions in which the primary pathogenetic step is the loss of solubility of specific substances, resulting in the formation of a condensed phase. Typical examples are cataract, nephrolithiasis, gallstone disease and certain rheumatic conditions in which protein denaturation, aggregation and precipitation may occur. Since the condensing molecules are often proteins, antidenaturant agents should be considered rational drugs for the treatment of these diseases. Surprisingly, however, only a few molecules with these properties are currently available for therapeutic use, including bendazac for cataract.

Composition and immunofluorescence studies of biliary "sludge" in patients with cholesterol or mixed gallstones

BACKGROUND/AIMS

Gallbladder bile from patients with cholesterol or mixed gallstones frequently contains biliary "sludge", a suspension of cholesterol monohydrate crystals and pigment granules embedded in mucin and proteins. The composition of biliary "sludge" and the preferential localization of mucin and proteins could be an indicator for its potential role in gallstone formation.

METHODS

Ultracentrifugation (100000 g/l h) was used to precipitate "sludge" from bile, and the concentration difference of its main components between native bile and ultracentrifuged bile samples was calculated. After purification of the sediment, immunolocalization was performed for the detection of mucin, IgA, albumin, aminopeptidase, and anionic polypeptide fraction using polyclonal and monoclonal antibodies.

RESULTS

The amount of sludge in gallbladder bile was 4.26 mg/ml-0.78 (mean+/-SEM) in patients with cholesterol and 2.51 mg/ml+/-0.39 in patients with mixed stones and cholesterol was the main component (48.9+/-4.6% and 44.4+/-7.1%). The sediment appeared as a mixture of vesicular aggregates and pigment particles which were linked by a gel matrix of mucin containing cholesterol crystals. While anionic polypeptide fraction and aminopeptidase were associated to pigments, IgA was uniformly spread in the crystalline parts of "core-like" structures, and albumin, when it was present, appeared as randomly located small spots.

CONCLUSIONS

Our study demonstrates that the cholesterol content and the distribution pattern of mucin and different proteins is similar in the sediments of biliary "sludge" to that previously shown in cholesterol and mixed gallstones. This suggests that biliary "sludge" represents an early stage of gallstone formation in these patients.

Genetic determinants of variation in gallbladder disease in the Mexican-American population

Since there have not been any studies that quantify the influence of genetic factors on gallbladder disease (GBD) in humans using information from families, we utilized pedigree data to explore the genetic control of variation in liability to GBD. Using an extension of a variance components approach, we performed genetic analyses of GBD using information from 32 low-income Mexican-American families with two slightly different general models incorporating several sex-specific GBD risk factors. After evaluating the relative magnitudes of the covariate effects from these two models, we identified a parsimonious model including only significant predictors of GBD. According to this model, heritability for GBD was high (h2 = 0.44+/-0.18), after accounting for the significant effects of age, leptin in both sexes, total cholesterol, and HDL cholesterol in males only. We have shown quantitatively that variation in GBD is under strong genetic control. However, there are two major limitations to our findings: (1) since GBD was defined by a self-reported clinical history rather than an ultrasound examination, the prevalence of GBD could have been underestimated; and (2) since our design did not allow for shared environmental effects, our estimate of heritability may have been inflated.

Microstructural evolution of lipid aggregates in nucleating model and human biles visualized by cryogenic transmission electron microscopy

Obtaining reliable information on the physical state and ultrastructure of bile is difficult because of its mixed aqueous-lipid composition and thermodynamic metastability. We have used time-lapse cryogenic transmission electron microscopy (cryo-TEM) combined with video-enhanced light microscopy (VELM) to study microstructural evolution in nucleating bile. A well-characterized model bile and gallbladder biles from cholesterol and pigment gallstone patients were studied sequentially during cholesterol nucleation and precipitation. In model bile, cholesterol crystallization was preceded by the appearance of the following distinct microstructures: spheroidal micelles (3-5 nm), discoidal membrane patches (50-150 nm) often in multiple layers (2-10), discs (50-100 nm), and unilamellar (50-200 nm) and larger multilamellar vesicles (MLVs). The membrane patches and discs appeared to be short-lived intermediates in a micelle-to-vesicle transition. Vesicular structures formed by growth and closure of patches as well as by budding off from vesicles with fewer bilayers. MLVs became more abundant, uniform, and concentric as a function of time. In native bile, all the above microstructures, except discoidal membrane patches, were observed. However, native MLVs were more uniform and concentric from the beginning. When cholesterol crystals appeared by light microscopy, MLVs were always detected by cryo-TEM. Edges of early cholesterol crystals were lined up with micelles and MLVs in a way suggesting an active role in feeding crystal growth from these microstructures. These findings, for the first time documented by cryo-TEM in human bile, provide a microstructural framework that can serve as a basis for investigation of specific factors that influence biliary cholesterol nucleation and crystal formation.

Isolation and characterization of hydrophobic polypeptides in human bile

Polypeptides were isolated from human bile by extraction with chloroform/methanol, followed by reversed-phase chromatography in methanol/ethylene chloride and gel filtration in chloroform/methanol. Peptides were characterized by SDS/PAGE, sequence analysis and matrix-assisted laser desorption ionization/time-of-flight mass spectrometry. This identified haemoglobin alpha chain, ATP synthase lipid-binding protein subunit 9, an N-terminal fragment of mac25/insulin-like growth factor-binding protein 7 and an internal fragment of monocyte differentiation antigen CD14, all not described previously in bile. In addition, alpha1-antitrypsin, known in bile from previous work, was also identified. The hydrophobic character of haemoglobin alpha chain is not apparent from its amino acid sequence, but the other polypeptides all have major hydrophobic segments. These results show that several proteins are removed upon organic solvent extraction used for delipidation during the preparation of samples for proteome analysis. Several of the polypeptides found are unexpectedly present in bile, suggesting that specific excretion mechanisms may be involved.

Sluggish small bowel motility is involved in determining increased biliary deoxycholic acid in cholesterol gallstone patients

OBJECTIVE

Our aim was to establish whether small intestine transit time is defective in subjects with cholesterol gallstones.

METHODS

We enrolled 10 patients (eight women, two men; mean age, 48.7 yr; mean body mass index [BMI], 22.4 Kg/m2) with recently diagnosed cholelithiasis, with no liver pathology, who were not taking any drugs, and 11 comparable healthy volunteers (eight women, three men; mean age, 46.2 yr; mean BMI, 22.7 Kg/m2), who served as controls. All subjects underwent orocecal (by starch breath test technique and serum assays of salazopyrin), oroileal (by serum assays of tauroursodeoxycholic acid), and duodenoileal (by serum assays of taurocholic acid) transit times; cholesterol saturation index; and bile acid composition and gallbladder motility studies (by ultrasound). For serum assays, blood samples were collected over a period of 7 h. Gallbladder motility and orocecal transit time were evaluated simultaneously.

RESULTS

All four means of assessing transit time gave longer times in cholesterol gallstone patients than in controls: orocecal transit time (salazopyrin) = 366 +/- 13 vs 258 +/- 16 min, p < 0.0005; orocecal transit time (starch breath test) = 415 +/- 139 vs 290 +/- 15 min, p < 0.01; duodenoileal transit time: 272 +/- 23 vs 205 +/- 23 min, p < 0.03; and oroileal transit time: 308 +/- 18 vs 230 +/- 19 min, p < 0.009. Cholesterol gallstone patients showed an increase in percent molar biliary deoxycholic acid (30% +/- 4.5% vs 16% +/- 1.3%, p < 0.02) and a decrease in percent molar cholic acid 32% +/- 2.2% vs 40% +/- 1.3%, p < 0.03) and chenodeoxycholic acid (34% +/- 3% vs 41% +/- 1.8%, p < 0.03), compared with controls; patients also had greater percent molar biliary cholesterol. A linear relationship (r2 = 0.6324, p = 0.0012) between biliary deoxycholic acid and small bowel transit time was found. Residual gallbladder volumes were larger in cholesterol gallstone patients (11.38 +/- 1.27 vs 7.55 +/- 0.39 ml, p < 0.04), whereas basal gallbladder volumes, although higher, did not reach statistical significance (24.25 +/- 2.41 vs 19.98 +/- 1.63 ml; p = ns).

CONCLUSIONS

This study confirms that patients with cholesterol gallstones have delayed small bowel transit, defective gallbladder motor function, and increased biliary deoxycholic acid. Delayed small bowel transit may contribute to supersaturation of bile with cholesterol by increasing deoxycholic acid production.

Progressive familial intrahepatic cholestasis

Progressive familial intrahepatic cholestasis (PFIC), also known as Byler disease, is an inherited disorder of childhood in which cholestasis of hepatocellular origin often presents in the neonatal period and leads to death from liver failure before adolescence. The pattern of appearance of affected children within families is consistent with autosomal recessive inheritance. Several studies have provided support for the heterogeneity of this clinical entity suggesting the existence of different types due to different disorders affecting the hepatocyte and related to defects of bile acid secretion or bile acid metabolism. Recent molecular and genetic studies have identified genes responsible for three types of PFIC and have shown that PFIC was related to mutations in hepatocellular transport system genes involved in bile formation. These findings now provide specific diagnostic tools for the investigation of children with PFIC and should allow prenatal diagnosis in the future. Genotype-phenotype correlations performed in patients treated with ursodeoxycholic acid or biliary diversion should allow those PFIC patients who could benefit from these therapies to be precisely identified. In the future, other therapies, such as cell and gene therapies, might be considered and could also represent an alternative to liver transplantation.

Apolipoprotein A-I in bile inhibits cholesterol crystallization and modifies transcellular lipid transfer through cultured human gall-bladder epithelial cells

BACKGROUND

Apolipoprotein A-I (Apo A-I), conventionally purified by several steps including organic solvent-delipidation from plasma, inhibits cholesterol crystallization in bile. To observe a significant effect in vitro, however, supraphysiological concentrations above 100 microg/mL are required. For this reason, this protein has not been considered to play a physiological role in vivo. In the present study, we examined the cholesterol crystal growth-inhibiting effect of biliary Apo A-I at its physiological concentration, the modification of transcellular transfer of biliary lipids through cultured human gall-bladder epithelial cells (GBEC) by Apo A-I at its physiological concentration and the binding and secretion of Apo A-I by GBEC.

METHODS AND RESULTS

We purified biliary Apo A-I to near homogeneity using immobilized artificial membrane chromatography. At 5 microg/mL, biliary Apo A-I reduced cholesterol crystal mass by 50%, whereas plasma-derived, solvent-delipidated Apo A-I had no effect. Using an antibody-capture enzyme-linked immunosorbent assay, we found reduced Apo A-I concentrations in bile samples from gallstone patients when compared with bile samples from gallstone-free controls (medians, 2.35 and 9.4 microg/mL, respectively). In a GBEC line, Apo A-I (5 microg/mL) enhanced transfer of phospholipid and cholesterol from the mucosal to the serosal side of cell monolayers by approximately 50%. These cells appear to bind Apo A-I reversibly in a dose- and time-dependent manner, compatible with receptor-type binding. Cultured human gall-bladder epithelial cells also showed basal secretion of Apo A-I, which was greatly increased by exposure to model bile solutions.

CONCLUSIONS

Apolipoprotein A-I in bile, thus, has both a direct effect on cholesterol crystal formation and enhances lipid removal from gall-bladder bile by GBEC. This effect may be specific and receptor mediated. These observations support two separate roles for human biliary Apo A-I and suggest that this protein may be important in preventing the formation of cholesterol crystals (the initial step in gallstone formation) in supersaturated bile.

Gallstone formation. Local factors

Bile supersaturation is necessary for cholesterol gallstones to form. Not all people with supersaturated bile form gallstones, however, and additional factors must be present. The role of pronucleating substances has been extensively studied. Of these, proteins, especially mucin, are best understood. Mucin is secreted by the gallbladder epithelium and may act as a nidus for crystal nucleation. Other proteins that may act as pronucleators include alpha 1-acid glycoprotein, alpha 1-antichymotrypsin, phospholipase C, and a small calcium binding protein. The role of antinucleating factors is less well understood. Certain drugs, including octreotide and ceftriaxone, may also predispose to stone formation. Another local factor is gallbladder stasis, a well-known risk factor for pigment stone formation. More recent research has focused on the role of bacterial infection, which has long been believed to be a factor in pigment gallstone formation. Newer data also support a role for infection in cholesterol gallstone pathogenesis. Additionally, genetic factors that may predispose a patient to cholesterol gallstones have been identified in mice and in humans.

Biliary secretory immunoglobulin A is a major constituent of the new group of cholesterol crystal-binding proteins

BACKGROUND & AIMS

Recently we described a new group of lectin-bound biliary proteins that bind to cholesterol crystals, modify crystal morphology, and inhibit cholesterol crystallization. The aim of the current study was to characterize and identify individual members of this group of cholesterol crystal-binding proteins.

METHODS

Crystal-binding proteins were purified from human gallbladder bile by lectin affinity chromatography and preparative gel electrophoresis. Purified crystal-binding proteins were characterized by using cholesterol crystal-growth assays, immunoblotting, and amino acid analysis. For comparison, identified biliary proteins were isolated from gallbladder bile by lectin affinity and immunoaffinity chromatography.

RESULTS

The individual crystal-binding proteins with molecular weights of 74, 63, and 28 kilodaltons inhibited cholesterol crystallization in a dose-dependent manner (2.5-10 micrograms/mL). Immunoblotting with specific antibodies and N-terminal amino acid sequences revealed that the 74-kilodalton crystal-binding protein is the secretory component, the 63-kilodalton protein is the heavy chain, and the 28-kilodalton protein is the light chain of human secretory immunoglobulin (Ig) A. Isolated biliary IgA showed a potent inhibitory effect on cholesterol crystallization in model bile even at levels less than physiological concentrations (1-100 micrograms/mL).

CONCLUSIONS

Biliary secretory IgA is a major constituent of the previously described group of cholesterol crystal-binding proteins. Crystal-binding IgA may be an important modulator of crystal agglomeration into stones and stone growth in vivo.

Cholesterol crystallization in human gallbladder bile: relation to gallstone number, bile composition, and apolipoprotein E4 isoform

Patients with multiple cholesterol gallstones are at increased risk of recurrence after nonsurgical therapy, possibly because of fast biliary cholesterol crystallization. Serum apolipoprotein E4 (apo E4) is a risk factor for primary cholesterol gallstone formation as well as recurrence. We examined potential effects of stone number and apolipoprotein E genotype on crystallization and on various crystallization-influencing factors in gallbladder biles of 36 cholesterol stone patients (25 multiple stones: 10 carrying the epsilon4 allele). Biliary cholesterol saturation, bile salt composition or concentrations of total protein, immunoglobulin (Ig)A, IgG, alpha1-acid glycoprotein, haptoglobin, or mucin--all crystallization promoters--did not differ between multiple and solitary stone patients, apparently not explaining different speed of crystallization (crystal observation time 3.5 +/- 0.6 days vs. 12.7 +/- 2.4 days, respectively; P = .0003). In contrast, biliary aminopeptidase-N activities (2,607 +/- 592 mU/mL vs. 947 +/- 185 mU/mL; P = .04) were higher and IgM levels (179 +/- 39 vs. 65 +/- 8 mg/L; P = .09) tended to be higher in the case of multiple stones. Although patients carrying the epsilon4 allele had similar stone numbers and crystallization as patients without the epsilon4 allele, their cholesterol saturation index (CSI) was lower (1.08 +/- 0.09 vs. 1.54 +/- 0.13; P = .01), whereas total protein and bile salt concentrations tended to be higher with preferential taurine-conjugation. In conclusion, fast cholesterol crystallization is associated with multiple stones but not with apolipoprotein E4. Whereas fast crystallization may contribute to high recurrence rates after nonsurgical therapy in case of multiple gallstones, the mechanism for increased risk of gallstone formation in patients carrying the epsilon4 allele remains unknown.

Gallbladder volume: comparison of diabetics and controls

Diabetics are known to have an increased prevalence of gallstones. The aim of this study was to investigate whether diabetics have increased gallbladder volumes that would predispose to stasis, nucleation of cholesterol crystals, and gallstone formation. The gallbladder volume of 271 diabetic subjects and 277 controls was determined by ultrasound using the ellipse formula. Gallbladder volume was also determined by the sum of the cylinders method in 143 cases with a strong correlation (r = 0.89) between the two methods. Using analysis of variance, gallbladder volume was influenced by both diabetic type (NIDDM = 33.68 cm3, IDDM = 26.84 cm3, controls = 29.05 cm3; P = 0.018) and the presence of gallstones (gallstones = 32.04 cm3, no gallstones = 27.58 cm3; P = 0.018). The variation in gallbladder volume between NIDDM, IDDM, and control subjects was influenced by the presence of gallstones (P = 0.024, interaction term from ANOVA). Significant differences (P < 0.001) were only found between NIDDM vs IDDM and NIDDM vs control in the nongallstone group (NIDDM = 34.33 cm3, IDDM = 25.08 cm3, control = 25.17 cm3). Males had significantly larger gallbladder volumes than females: 31.98 cm3 vs 27.74 cm3 (P = 0.023). After the inclusion of BMI, HDL cholesterol, triglyceride, and age in a statistical model with gender and diabetic type in those without gallstones, significant differences were still found between NIDDM and IDDM (P = 0.013) and NIDDM and controls (P = 0.005), demonstrating that NIDDM is an independent predictor for increased gallbladder volume.

The role of the Concanavalin A-binding fraction in cholesterol crystallization in native human bile

BACKGROUND/AIMS

Many Concanavalin A-binding glycoproteins have been proposed to influence cholesterol crystallization in human bile. This has been studied mainly by addition of the Concanavalin A-binding fraction to model bile. The physiological relevance of the proteins in native bile is not yet known. The aim of this study was to establish the role of the Concanavalin A-binding fraction in cholesterol crystallization in native human gallbladder bile.

METHODS

To determine the effects of the removal of Concanavalin A-binding fraction, fresh human gallbladder bile was incubated with either Concanavalin A-Sepharose or Sepharose alone. Beads were sedimented and crystallization was studied in the supernatant.

RESULTS

Extraction of Concanavalin A-binding fraction decreased crystallization in fast-nucleating biles (Crystal Detection Time < or =4 days). Slow-nucleating biles were not affected. The effect could not be related to the content of known pronucleating proteins (IgA, IgM, haptoglobin, aminopeptidase N and alpha1-acid glycoprotein), since the slow-nucleating biles contained similar amounts of these proteins.

CONCLUSIONS

Although Concanavalin A-binding fraction always accelerated crystallization when added to model bile, removal of the same fraction from native bile often had no effect. We conclude that slow-nucleating biles in particular contain undetermined factors which regulate the activity of pronucleators.

Distinct immuno-localization of mucin and other biliary proteins in human cholesterol gallstones

BACKGROUND/AIMS

Cholesterol gallstones consist of cholesterol crystals and smaller amounts of pigments and calcium salts, arrayed on a mucin plus protein matrix. The localization of the various biliary proteins in the stones has not been characterized. We aimed to localize several biliary proteins in gallstones in order to determine their possible role in stone formation and growth.

METHODS

The distribution of several matrix proteins and their relationships to the minerals were determined using immunostaining and EDAX microanalysis on hemisected cholesterol gallstones.

RESULTS

Pigment areas were rich in calcium and contained Cu, P and S. These elements were absent in cholesterol regions. Mucin was identified in a three-dimensional network intercalated between cholesterol crystals and as septa between deposits of pigments and cholesterol; APF/CBP and ApN coated only the pigment deposits. No specific topographical localization was found for albumin or IgA.

CONCLUSIONS

This suggests a role for mucin, APF/ CBP and ApN in the formation of cholesterol gallstones. We propose that cholesterol crystals bind directly to mucin, whereas calcium salts and pigments deposit on APF/CBP and ApN bind to the mucin.

Lithogenicity of human bile is reduced by freezing and thawing

We examined the effects of freezing and thawing upon the nucleation time and the distribution of cholesterol between micelles and vesicles in 9 human gallbladder and 7 hepatic biles. The nucleation time was significantly longer after freezing when compared to fresh samples (22.4 +/- 2.6 vs. 7.4 +/- 1.9 days, respectively). Concomitantly, a substantial shift of cholesterol from vesicles to micelles was noted, with the proportion of vesicular cholesterol decreasing from 26.5% +/- 6.0% in fresh biles to 8.6% +/- 2.3% after freezing. These effects were observed in all types of human biles, regardless of origin, cholesterol saturation or initial presence of cholesterol crystals, and were most notable after the first week of freezing. The decrease in vesicular cholesterol in all biles and the increase in nucleation time of gallbladder biles correlated with the time the samples had been in a frozen state. It is concluded that the lithogenic properties of human bile are not maintained during storage at -20 degrees C. Freezing results in a shift of cholesterol from vesicles to micelles and reduces the tendency of cholesterol to crystallize from bile samples.

Electrophoretic analysis of biliary proteins: application of high resolution two-dimensional polyacrylamide gel electrophoresis with immobilized pH gradient in the first dimension

Native bile samples, dialyzed against double distilled water, fractionated by Sepharose 2B column chromatography, concentrated by ultrafiltration and lyophilized, were solubilized in lysis buffer and studied by two-dimensional electrophoresis (2-DE) with immobilized pH gradients in the first dimension. We counted 70, and 7 spots in 2-DE patterns of bile from patients with cholesterol gallstones and pigment gallstones, respectively.

A new subgroup of lectin-bound biliary proteins binds to cholesterol crystals, modifies crystal morphology, and inhibits cholesterol crystallization

Biliary proteins inhibiting or promoting cholesterol crystallization are assumed to play a major role in cholesterol gallstone pathogenesis. We now report a new group of biliary proteins that bind to cholesterol crystals, modify crystal morphology, and inhibit cholesterol crystallization. Various glycoprotein mixtures were extracted from abnormal human gallbladder bile using lectin affinity chromatography on concanavalin A, lentil, and Helix pomatia columns and were added to supersaturated model bile. Independent of the protein mixtures added, from the cholesterol crystals harvested, the same four GPs were isolated having molecular masses of 16, 28, 63, and 74 kD, respectively. Each protein was purified using preparative SDS-PAGE, and influence on cholesterol crystallization in model bile was tested at 10 microg/ml. Crystal growth was reduced by 76% (GP63), 65% (GP16), 55% (GP74), and 40% (GP28), respectively. Thus, these glycoproteins are the most potent biliary inhibitors of cholesterol crystallization known so far. Evidence that the inhibiting effect on cholesterol crystallization is mediated via protein-crystal interaction was further provided from scanning electron microscopy studies. Crystals grown in presence of inhibiting proteins showed significantly more ordered structures. Incidence of triclinic crystals and regular aggregates was shifted from 30 to 70% compared with controls. These observations may have important implications for understanding the role of biliary proteins in cholesterol crystallization and gallstone pathogenesis.

Gallbladder motility, gallstones, and the surgeon

Cholecystectomy is one of the commonest surgical procedures in the Western world, with more than half a million procedures performed annually in the United States alone. In recent years, studies of gallstone pathogenesis and gallbladder disease have increasingly focused on abnormal gallbladder motility in the pathogenesis of some, if not all, gallbladder conditions. The control of gallbladder motility is complex and depends on an intricate interplay of neural and hormonal factors. An understanding of the control of gallbladder motility is crucial to the understanding of the mechanisms of gallstone formation and may help to explain the failure to cure symptoms after cholecystectomy in up to one third of patients. The purpose of this article is to outline mechanisms controlling gallbladder motility, examine recent developments in our understanding of this complex process, and relate changes in motility to common disease conditions of the gallbladder. The role of altered motility in the pathogenesis of gallstones is discussed and the effects of commonly performed surgical procedures such as truncal vagotomy and cholecystectomy on upper gut physiology are reviewed.

Dietary fish oil inhibits cholesterol monohydrate crystal nucleation and gallstone formation in the prairie dog

BACKGROUND

Epidemiologic studies suggest that populations consuming a diet rich in fish oil have lower rates of both atherosclerotic heart disease and gallstones. The mechanisms underlying this inhibitory effect on cholesterol gallstone formation remain unclear. We therefore studied the effect of dietary fish oil on bile composition and cholesterol precipitation in an animal model of gallstone disease.

METHODS

Adult male prairie dogs were fed a standard control diet (n = 12) or a lithogenic 1.2% cholesterol diet (n = 16). One half of the animals in each group had their diet supplemented with concentrated fish oil.

RESULTS

After 14 days animals receiving the cholesterol diet all developed biliary cholesterol monohydrate crystals and gallstones. When fish oil was added to this high cholesterol diet, solid cholesterol crystal precipitation and gallstone formation were completely inhibited. This inhibition of gallstone formation was accompanied by a significant decrease in biliary calcium and total protein concentration. Microscopic cholesterol liquid crystals were evident in the bile of all of the animals fed the cholesterol plus fish oil diet. Dietary fish oil also significantly prolonged cholesterol monohydrate crystal observation time in animals receiving the lithogenic diet.

CONCLUSIONS

These data suggest that dietary fish oil exerts a potent antilithogenic effect on cholesterol gallstone disease and may induce a stable liquid crystalline phase retarding nucleation.

Biliary alpha 1-acid glycoprotein concentrations in gallstone-free controls and in patients with multiple or solitary cholesterol gallstones

We recently identified a promoting glycoprotein in the concanavalin A-bound fraction of gallbladder bile as a biliary form of alpha 1-glycoprotein (AAG). The concentration of biliary AAG appears to exert an important promoting effect on the speed of cholesterol nucleation in many patients with cholesterol gallstone disease. In the current study, we provide information about the biliary concentration of AAG as well as the amount and comparative potency of its subfractions in patients with and without cholesterol gallstone disease. The amount of total biliary AAG and the amounts of its different isoforms separated by concanavalin A affinity chromatography were measured by ELISA. Estimates of absolute concentrations of AAG for each sample were normalized to the sample total protein content to give relative AAG values. The promoting activity (potency) of immunopurified biliary AAG from gallstone patients and gallstone-free controls on cholesterol crystallization was compared by a crystal growth assay. The mean absolute concentration of AAG in gallstone-free controls was not significantly different from multiple stone patients. The relative concentration of AAG (micrograms per milligram total protein) was significantly increased in patients with multiple stones when compared to controls (P < 0.05), and both the absolute and relative concentrations of AAG (micrograms per milligram bile), were three- and to five fold higher in a number of these patients. The functional activity and distribution of AAG in different subfractions was similar in gallstone patients and gallstone-free controls. The relative concentration of biliary AAG is significantly greater in cholesterol gallstone patients with multiple stones than in gallstone-free controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Gallbladder emptying in vivo, bile composition, and nucleation of cholesterol crystals in patients with cholesterol gallstones

BACKGROUND/AIMS

Impaired postprandial gallbladder emptying may provide time for progressive bile concentration with formation of instable cholesterol-rich vesicles and fast nucleation of cholesterol crystals. The aim of this study was to assess postprandial gallbladder emptying, bile composition, and nucleation of cholesterol crystals in the same patient.

METHODS

In 30 patients with cholesterol gallstones, postprandial gallbladder emptying was measured ultrasonographically. In each patient, gallbladder bile composition (obtained at cholecystectomy) and nucleation of cholesterol crystals was determined. Patients were divided in 22 strong contractors (> 50% postprandial gallbladder emptying) and 8 weak contractors.

RESULTS

In weak contractors, bile salt and phospholipid concentrations were much higher than in strong contractors (234.6 +/- 24.7 vs. 130.3 +/- 10.8 mmol/L [P < 0.001] and 44.5 +/- 3.5 vs. 30.2 +/- 3.1 mmol/L [P < 0.05], respectively). Cholesterol concentrations were comparable in strong and weak contractors. Consequently, total lipid concentration was significantly higher (15.5 +/- 1.4 and 9.2 +/- 0.7 g/dL; P < 0.001) and cholesterol saturation index significantly lower (0.90 +/- 0.08 and 1.61 +/- 0.17; P < 0.001) in weak contractors. Nucleation time, percentage of cholesterol in vesicles, bile salt species, and molecular species of phosphatidylcholine were not significantly different.

CONCLUSION

Differences in bile composition can be linked to different patterns of postprandial gallbladder emptying and may point to two different pathways of gallstone formation.

The effect of albumin on the state of aggregation and phase transformations in phosphatidylcholine-sodium cholate mixtures

Dilution of phospholipid-detergent mixed micellar systems results in an increase of the fraction of monomeric detergent and, consequently, in a decrease of the effective ratio Re between non-monomeric detergent and phospholipid. The value of Re has been previously shown to be the main determinant of the state of aggregation in such mixtures: at Re values below a critical value ReSAT, the mixture is vesicular; at Re values higher than ReSOL, the mixture is micellar, whereas within the range of ReSAT-ReSOL, vesicles and micelles co-exist. Albumin binds bile salts. Therefore, in PC-cholate mixtures, Re is reduced by the presence of albumin in the system. Within the range of PC concentrations of 2-23 mM, cholate concentrations of 2-15 mM and BSA concentrations of 0-100 mg/ml, binding of cholate to BSA results in reduction of the effective cholate concentration to the extent of 0.11 mM cholate per 1 mg/ml BSA, namely up to 7 cholate molecules bind to each BSA molecule. Yet, the values of ReSAT and ReSOL are essentially independent of BSA. In addition, at any given Re value, the size of vesicles made by dilution of mixed micelles is a complex function of albumin and PC concentrations. Possible mechanistic details which may cause this effect are discussed. These effects of albumin on the state of aggregation of PC-cholate mixtures must be taken into account in studies of such mixtures in the presence of albumin when other effects of albumin (e.g., on phospholipolysis) are investigated. Practical conclusions are reached with respect to the procedures that can be used to prepare vesicles of identical composition and size in the presence of different concentrations of albumin.

Electrophoretic analysis of bile proteins from patients with and without gallstones

Bile proteins from 82 cases with various types of gallstones (pure cholesterol stones, cholesterol stones with a small amount of other substances, mixed stones and pigment stones) and 9 controls without gallstones were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A unique bile protein with a molecular mass of 32 kDa was identified. The 32 kDa protein could be stained on immunoblotting membranes using immunoperoxidase with concanavalin A. The 32 kDa protein was found in all controls but only in a portion (22.2-36.4%) of the patients with gallstones of various types. Following electrophoretic elution from the SDS-PAGE gels, the 32 kDa protein was analyzed by reversed phase--high-performance liquid chromatography, yielding three peaks for controls and only two peaks for patients with gallstones.

Role of nutrient fat and cholecystokinin in regulation of gallbladder emptying in man

Postprandial gallbladder contraction is mainly regulated by cholecystokinin (CCK), but little is known about the dose-response relationship between CCK release and gallbladder contraction, in particular after meals with differing fat content. Decreased postprandial gallbladder emptying has been suggested to play a major role in the development of gallstones in man, and dietary factors may therefore be important in the pathogenesis of gallbladder stasis. We studied, in a randomized order, the effect of three isocaloric meals (250 ml) with identical osmolality on CCK release and gallbladder contraction in six healthy volunteers: (1) a pure fat meal (25 g triglycerides); (2) a mixed meal containing fat (8 g, 29% of caloric content), protein (10 g, 17%), and dextrose (32 g, 54%); and (3) a fat-free meal containing albumin (25 g, 46%) and dextrose (32 g, 54%). Gallbladder volumes and antral cross-sectional areas were determined by ultrasonography and plasma CCK and PP levels by RIA. The pure fat meal caused the highest CCK release (187 +/- 27; mean +/- SEM) and maximal (> 85% of fasting volume) gallbladder contraction (3172 +/- 361; AUC) as compared to the other two meals (P < 0.05). The mixed and the fat-free meal caused similarly low (< 50% of fasting volume) gallbladder contraction (6052 +/- 342 and 6134 +/- 500, respectively), although they induced markedly different CCK levels (157 +/- 12 and 87 +/- 13, respectively; P < 0.05). Gastric emptying rates were similar for all meals (18,500 +/- 3300, 18,600 +/- 2700 and 19,800 +/- 3100, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of apolipoprotein A1 in cholesterol gallstones and gallbladder bile of patients with gallstones

Biliary apolipoprotein A1 in bile inhibits the nucleation of cholesterol crystals from bile super-saturated with cholesterol. In the present study, using an enzyme-linked immunosorbent assay of apolipoprotein A1, we determined the content of apolipoprotein A1 in cholesterol gallstones and samples of gallbladder bile collected simultaneously from 23 patients during cholecystectomy. Protein content in cholesterol gallstones ranged from 50 to 5700 micrograms/g, with median, quartile, and three quartile values being 250, 111, and 740; apolipoprotein A1 content ranged from 9 to 9000 ng/g (200, 41, 647). The gallbladder bile samples contained protein at concentrations of 0.4-9.0 mg/ml (2.0, 1.1, 3.2), while apolipoprotein A1 was present at concentrations of 2.0-136.0 micrograms/ml (30.0, 10.0, 90.0). A notable finding was that the A1/total protein (TP) values for gallbladder bile, which ranged from 0.13% to 6.80% (1.62, 0.89, 3.34), were several times higher than those determined for gallstone samples, which ranged from 0.01% to 1.2%, 2% (0.06, 0.02, 0.25). The results of sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that the protein profile in cholesterol gallstones was similar to that in gallbladder bile. It was concluded that: (1) the protein contained in gallstones may originate from bile, (2) the content of apolipoprotein A1 in cholesterol gallstones is only a trace amount, compared with that in gallbladder bile, and (3) biliary apolipoprotein A1 may be retained in a soluble phase in gallbladder bile, with minimal precipitation onto the surfaces of gallstones.