Effect of mucous glycoprotein on nucleation time of human bile

Morphological and elemental mapping of gallstones using synchrotron microtomography and synchrotron X-ray fluorescence spectroscopy

BACKGROUND AND AIM

Regional differences in gallstone (GS) composition are well documented in the Indian subcontinent. The reasons for the same are unknown. Etiopathogenesis of GS remains elusive despite advances in instrumentation. This was an in-depth analysis of the chemical, structural, and elemental composition of GS with special reference to synchroton studies.

METHODS

We used high-end sensitive analytical complementary microscopic and spectroscopic methods techniques, such as X-ray diffraction, scanning electron microscopy, Fourier transform infrared, synchrotron X-ray fluorescence spectroscopy (SR-XRF), and 2D and 3D synchrotron microtomography (SR-μCT), to study the ultra structure and trace element composition of three major types of GS (cholesterol, mixed, and pigment). SR-XRF quantified the trace elements in GS.

RESULTS

The cholesterol GS (monohydrate and anhydrate) were crystalline, with high calcium content. The pigment GS were amorphous, featureless, black, and fragile, with high calcium bilirubinate and carbonate salts. They had the highest concentration of iron (average 31.50 ppm) and copper (average 92.73 ppm), with bacterial inclusion. The mixed stones had features of both cholesterol and pigment GS with intermediate levels of copper (average 20.8 ppm) and iron (average 17.78 ppm).

CONCLUSION

SR-μCT has, for the first time, provided cross-sectional computed imaging delineating the framework of GS and mineral distribution. It provided excellent mapping of cholesterol GS. SR-XRF confirmed that pigment GS had high concentrations of copper and iron with bacterial inclusions, the latter possibly serving as a nidus to the formation of these stones.

MUC Expression in Gallbladder Epithelial Tissues in Cholesterol-Associated Gallbladder Disease

Background/Aims

Gallstone pathogenesis is linked to mucin hypersecretion and bacterial infection. Several mucin genes have been identified in gallbladder epithelial cells (GBECs). We investigated MUC expression in cholesterol-associated gallbladder disease and evaluated the relationship between mucin and bacterial infection.

Methods

The present study involved 20 patients with cholesterol stones with cholecystitis, five with cholesterol stones with cholesterolosis, six with cholesterol polyps, two with gallbladder cancer, and six controls. Canine GBECs treated with lipopolysaccharide were also studied. MUC3, MUC5AC, MUC5B, and MUC6 antibodies were used for dot/slot immunoblotting and immunohistochemical studies of the gallbladder epithelial tissues, canine GBECs, and bile. Reverse-transcription polymerase chain reaction was performed to evaluate MUC3 and MUC5B expression.

Results

MUC3, MUC5AC, MUC5B, and MUC6 were expressed in the normal gallbladder epithelium, and of those, MUC3 and MUC5B exhibited the highest expression levels. Greatly increased levels of MUC3 and MUC5B expression were observed in the cholesterol stone group, and slightly increased levels were observed in the cholesterol polyp group; MUC3 and MUC5B mRNA was also upregulated in those groups. Canine GBECs treated with lipopolysaccharide also showed upregulation of MUC3 and MUC5B.

Conclusions

The mucin genes with the highest expression levels in gallbladder tissue in cholesterol-associated diseases were MUC3 and MUC5B. Cholesterol stones and gallbladder infections were associated with increased MUC3 and MUC5B expression.

New Evidences of Key Factors Involved in "Silent Stones" Etiopathogenesis and Trace Elements: Microscopic, Spectroscopic, and Biochemical Approach

The knowledge of the key factors involved in etiopathogenesis of the gallstone disease requires chemical, structural, and elemental composition analysis. The application of different complementary analytical techniques, both microscopic and spectroscopic, are aimed to provide a more comprehensive determination of the gallbladder calculi ultrastructure and trace element identification. High sensitivity techniques such as electron microscopy (SEM), Fourier transform infrared (FTIR), electron paramagnetic resonance (EPR) spectroscopy, and X-ray diffraction (XRD) along with biochemical analysis are used in a new attempt to investigate various factors which play a regulatory role in the pathogenesis of gallstones. The microstructure of different types of gallbladder stones has specific characteristics which are related to the elemental composition. The binding of metal ions with bile salts and bilirubin plays important roles in gallstone formation as revealed by FTIR spectrum of calcium bilirubinate complex in pigment gallstones. The EPR results demonstrated the generation of bilirubin free radicals and variation of its electronic structure and conjugation system in the skeleton of bilirubin molecule during complex formation. EPR spectra of pigment gallstones demonstrate the coexistence of four paramagnetic centers including stable bilirubin free radical, Mn2+, Cu2+, and Fe3+ with distinct magnetic parameters and well-resolved hyperfine structure in the case of Mn2+ ions. The result confirms a macromolecular network structure with proteins and the formation of bilirubin-coordinated polymer. Bilirubin and bilirubinate free radical complexes may play an important role in pigment gallstone formation.

Regression of preestablished cholesterol gallstones by dietary garlic and onion in experimental mice

We have recently reported the health beneficial potential of dietary garlic and onion in reducing the incidence and severity of cholesterol gallstone (CGS) during its experimental induction in mice. In the current study, the efficacy of dietary garlic and onion in regressing preestablished CGS was investigated in experimental mice. After inducing CGS in mice with a lithogenic diet for 10 weeks, they were maintained on basal diets containing 0.6% dehydrated garlic or 2% dehydrated onion for a further 10 weeks. Dietary garlic and onion, either raw or heat processed, regressed preformed CGS in mice up to 53% to 59%, whereas the regression in the basal control diet group was only 10%. The antilithogenic potency of garlic was decreased by its heat processing, but not in the case of onion. Biliary cholesterol was significantly decreased in garlic- and onion-fed animals. Biliary cholesterol saturation index and hydrophobicity index were significantly lowered by dietary garlic and onion. Serum and liver cholesterol levels were decreased by feeding these spices during post-CGS induction period. Hepatic hydroxymethylglutaryl-coenzyme A reductase activity was increased after feeding garlic and onion, whereas activities of the cholesterol-degrading enzymes cholesterol-7α-hydroxylase and sterol-27-hydroxylase were increased in spice-fed groups. These results indicate that feeding garlic and onion effectively accelerates the regression of preformed CGS by promoting cholesterol desaturation in bile. This observation is significant in the context of evolving dietary intervention strategy to address regression of existing CGS and stopping the possible recurrence.

Ursodeoxycholic acid reduces lipid peroxidation and mucin secretagogue activity in gallbladder bile of patients with cholesterol gallstones

BACKGROUND

Recently it has been postulated that gallbladder mucin hypersecretion observed in the pathogenesis of cholesterol gallstone disease may be induced by biliary lipid peroxidation. Ursodeoxycholic acid treatment reduces mucin concentration and the formation of cholesterol crystals in the gallbladder bile of patients with cholesterol gallstones and this effect might be mediated by a decrease of biliary lipid peroxidation.

MATERIAL AND METHODS

In a double-blind, placebo-controlled trial patients with symptomatic cholesterol gallstones received either ursodeoxycholic acid (750 mg daily) (n = 10) or placebo (n = 12) 10-12 days prior to cholecystectomy. As a marker for lipid peroxidation malondialdehyde was measured in bile together with mucin concentration. In addition, the mucin secretagogue activity of the individual bile samples was assessed in cultured dog gallbladder epithelial cells.

RESULTS

Ursodeoxycholic acid therapy resulted in a significant reduction of lipid peroxidation in bile as determined by the biliary malondialdehyde concentration (1.36 +/- 0.28 vs. 2.05 +/- 0.38 micromol L(-1); P < 0.005) and the malondialdehyde (micromol L(-1))/total bile acid (mmol L(-1)) ratio (0.02 +/- 0.005 vs. 0.06 +/- 0.01; P < 0.001). Furthermore, a decrease in mucin concentrations (0.7 +/- 0.3 vs. 1.3 +/- 0.5 mg mL(-1); P < 0.005) and of the mucin secretagogue activity of gallbladder bile (0.9 +/- 0.2 vs. 2.2 +/- 0.3 times control; P < 0.001) was observed.

CONCLUSIONS

The reduction of lipid peroxidation and mucin secretagogue activity of gallbladder bile induced by ursodeoxycholic acid treatment may contribute to the beneficial effects of this drug on gallbladder bile composition and symptoms in cholesterol gallstone patients.

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.

Effect of gallbladder mucin on the crystallization of cholesterol in bile

OBJECTIVES

Mucin is supposed to accelerate the crystallization of cholesterol in model bile while studies in native human gallbladder bile revealed conflicting results.

METHODS

Therefore, we determined the relation of mucin concentration and cholesterol crystal observation time in gallbladder bile of 73 patients with cholesterol and mixed and 21 patients with pigment stones. In addition, bile samples of 20 patients with cholesterol gallstones were supplemented with either 0 (control) or 0.5-4.0 mg/ml purified bovine mucin or human mucin isolated from gallbladder bile, to study the effect of variable mucin concentrations on the crystallization of cholesterol.

RESULTS

Rapid nucleating biles (</= 4 days, n = 59) showed higher mucin concentrations (0.73 +/- 0.1 mg/ml vs 0.43 +/- 0.07 mg/ml) than biles with longer (> 4 days, n = 35) cholesterol crystal observation times (P < 0.05), but no correlation between mucin concentration and cholesterol crystal observation time was observed. Supplementation experiments with bovine purified mucin (up to 4.0 mg/ml) showed no significant effect on the total amount of newly formed cholesterol crystals within 21 days. However, higher amounts of newly formed cholesterol crystals were seen in bile samples supplemented with human mucin in comparison to negative controls.

CONCLUSIONS

Our results demonstrate a dose-dependent effect of human but not of bovine gallbladder mucin on the formation of cholesterol monohydrate crystals in gallbladder bile of patients with cholesterol stones. Therefore, studies of cholesterol crystallization in model bile systems may be valuable but should always be confirmed in native gallbladder bile as the more physiological effector system.

Gallbladder mucin plays a role in gallstone formation

Mucin is a high-molecular-weight glycoprotein that is synthesized, stored, and secreted by epithelial mucosal cells, especially goblet cells. Mucin proteins are derived from many different genes, termed MUC genes. Several lines of evidence point to a biological role for mucin in cholesterol gallstone formation. Mucin serves as a pronucleating agent in experimental and human gallstone disease, and the hydrophobic binding sites in the polypeptide core of mucin may provide a favorable environment for nucleation of cholesterol monohydrate from supersaturated bile. Mucin hypersecretion is prominent in many animal models of gallstone formation, thus contributing by its pronucleating quality to gallstone formation. According to some research, mucin hypersecretion may also contribute to the formation of brown pigment stones. This may be explained in part by the findings that lipopolysaccharides derived from certain bacteria are effective stimulants of mucin secretion. Aspirin and nonsteroidal anti-inflammatory drugs inhibit gallbladder mucin secretion and prevent gallstone formation in animal models. Expanding our knowledge on mucin research may improve our understanding of the natural history of gallstone formation and enable the development of new treatment strategies.

Purification and characterization of 33.5 kDa vesicular protein in human bile

AIM: The present study was undertaken to purify and partially characterize the 33.5-kilodalton (33.5 kDa) vesicular protein in human bile and to explore the possible molecular mechanisms of the initial crystal nucleation process.

METHODS: The 33.5 kDa vesicular protein was isolated by ultracentrifugation and further purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing conditions. The purified 33.5 kDa vesicular protein was subjected to N-terminal amino acid sequencing and amino acid analysis. Cholesterol crystallization activity was detected by cholesterol crystal growth assay. The sugar chain of the 33.5 kDa vesicular protein was analyzed by dot-immunobinding assay of lectin coupled to a peroxidase (HRP-DSA, HRP-ConA, HRP-WGA) and was deglycosylated using two different enzymatic approaches (N-deglycosylation and O-deglycosylation) to determine the molecular weight of the protein component, the type of linkage between polypeptide and carbohydrate components.

RESULTS: The 33.5 kDa vesicular protein with complicated glycan was an extensively glycosylated (37.3%) monomer and these sugar chains strongly bound to DSA, but did not bind to ConA. Amino acid sequencing indicated that the protein was unique. The 33.5 kDa vesicular protein exhibited potent cholesterol crystallization promoting activity in vitro with derived crystal growth curve indices It, Ig, Ic presented as 0.57, 1.52, and 1.63 respectively. Both enzymatic proteolysis and N-deglycosylation of the protein removed all activity.

CONCLUSION: These data suggest the 33.5 kDa vesicular protein may be responsible for the pathogenesis of cholesterol gallstone disease, and the sugar chains play an important role in pro-nucleating process.

Evaluation of gallbladder volume and motility in non-insulin-dependent diabetes mellitus patients using real-time ultrasonography

AIMS

The prevalence of cholelithiasis is 2 to 3 times higher in patients with diabetes mellitus than in the normal population, especially in a group of patients with non-insulin-dependent diabetes mellitus (NIDDM). We investigated the pathogenesis of this increased prevalence by ultrasonography with a brief comparison of demographic features.

MATERIALS AND METHODS

The study group was consisted of NIDDM patients (41 males and 47 females, mean age 53.5 +/- 11 years), and the control group included healthy volunteers (33 males and 34 females, mean age 50.3 +/- 18 years). All patients were investigated after 12 hours of fasting and 30 minutes after a standard test meal. Pre-meal and post-meal gallbladder volumes were used for calculation of the ejection fraction of the gallbladder and fasting gallbladder volume.

RESULTS

In the study group, there was no correlation between the fasting gallbladder volume and age, parity, and body mass index. However, fasting gallbladder volume and duration of diabetes mellitus showed significant correlation (r = 0.212, P < 0.05). The mean ejection fraction of gallbladders in the study group was 48.48%, whereas that of the control group was 56.32%. There was a significant reduction of ejection fraction in the study group (P = 0.003).

CONCLUSION

Our study indicated that there were an increased fasting gallbladder volume and impaired ejection fraction in NIDDM patients. This may be the initiator of bile stasis in the gallbladder and subsequent cholesterol crystal and stone formation.

Cholesterol crystallite nucleation in supersaturated model biles from a thermodynamic standpoint

A rapid, silicone polymer film uptake method was used to determine the cholesterol (Ch) thermodynamic activity (A(T)) in taurocholate (TC)-lecithin (L) and taurochenodeoxycholate (TCDC)-L model biles supersaturated with Ch. Also, time-dependent quasielastic light scattering (QLS) measurements and microscopic observations were made to determine the nature of particle species and the Ch nucleation times. In all cases in which Ch-L vesicles were present, a linear relationship between the logarithm of Ch nucleation times and Ch A(T) was found. These findings support that Ch A(T) is the appropriate parameter that represents the Ch nucleation tendency and that vesicles are catalytic sites in the Ch nucleation process. When Ca2+, a nucleation promoter ion, was present in the supersaturated model biles, the increased values of Ch A(T) quantitatively correlated with shorter Ch nucleation times. These latter findings further demonstrate that Ch A(T) is the dominant factor in explaining the Ch nucleation tendencies in supersaturated model biles.

Role of bile mucin in bacterial adherence to biliary stents

Biliary stent placement is a well-established method of relieving obstructive jaundice. However, a frequent complication is occlusion of the stent caused by bacterial biofilm formation and sludge accumulation. In this study we investigated the possible effect of bile mucin on bacterial adherence to biliary stents at the initial stage of biofilm formation. By means of an in vitro bile-perfusion system, polyethylene stents were perfused with pig gallbladder bile infected with Escherichia coli. The concentrations of mucin in the pig bile were adjusted with purified mucin. The amount of bacteria adhering to the inner surface of the stents was measured and compared for stents perfused with bile containing various concentrations of mucin. Furthermore, we conditioned the stent inner surface with purified pig bile mucin and observed the effect of the conditioning on subsequent bacterial adherence. In addition, a common method for assaying bacterial adhesion with polystyrene microtiter plates was also used in this study. The results demonstrated that more bacteria adhered to the inner surface of stents perfused with bile containing 5 mg/mL mucin than of those perfused with bile containing 0.5 and 0 mg/mL mucin. Increased bacterial adherence was demonstrated on the stent surfaces conditioned with purified mucin compared with that seen on the nonconditioned stent surfaces. The optical densities indicating bacterial adhesion in the microtiter plate wells precoated with mucin were higher than those in non-coated plate wells. The in vitro results indicate that when a biliary stent is implanted in vivo, mucin in bile may condition the stent inner surface, modulate subsequent bacterial adherence to the surface, and participate in stent occlusion.

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.

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.

Lipopolysaccharide from Escherichia coli stimulates mucin secretion by cultured dog gallbladder epithelial cells

Biliary infection is associated with mucin hypersecretion by the biliary epithelium. Mucins have been identified as potent pronucleators of cholesterol in bile. The aim of the present study was to determine whether lipopolysaccharides (LPS) from different bacteria are capable of stimulating mucin secretion by cultured dog gallbladder epithelial (DGBE) cells, and to investigate the mechanism by which LPS stimulate mucin secretion. Mucin secretion by confluent monolayers of DGBE cells was quantified by measuring the secretion of [3H]-N-acetyl-D-glucosamine-labeled glycoproteins. Cell viability was evaluated by measuring the leakage of the enzyme, lactate dehydrogenase (LDH), into the culture medium. LPS, derived from Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa (200 microg/mL), all caused an increase in mucin secretion by the DGBE cells, without causing concomitant cell lysis. LPS from E. coli was found to be the most potent stimulator of mucin secretion, and increased mucin secretion by the DGBE cells to 252% +/- 14% of control. LPS from E. coli had no effect on intracellular cyclic adenosine monophosphate (cAMP) levels in the DGBE cells. Addition of the nitric oxide (NO)-releasing compound, NOR-4 (0.125-1 mmol/L), to the cells did not result in increased mucin secretion, and the NO synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME) (4 or 10 mmol/L), did not inhibit the LPS-stimulated mucin secretion. Exogenous tumor necrosis factor alpha (TNF-alpha) (1-10 ng/mL) did cause a minor increase in mucin secretion by the DGBE cells, but the effect of LPS from E. coli on mucin secretion could not be inhibited by preincubation with a TNF-alpha antibody (10 microg/mL). We conclude that LPS stimulates mucin secretion by the gallbladder epithelium. Whether this stimulation is mediated by TNF-alpha remains to be determined.

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.

Effect of beta-cyclodextrin dietary supplementation on biliary proteins and their resulting cholesterol nucleating activity in pigs

We explored the possibility that the biliary protein fraction may support part of the variation in the nucleating activity previously measured in gallbladder biles of pigs. Eighteen gallbladder aspirates freshly obtained from three dietary groups (0, 5, or 10% beta-cyclodextrin) of six pigs were chromatographed to purify their total protein fraction. Proteins were quantified, and analysed through electrophoresis and immunoblotting or enzyme-linked immunosorbent assay for albumin, and five putative effectors of cholesterol crystallisation, mucins, immunoglobulin A, 130 kDa, apolipoprotein A-I, and anionic polypeptide fraction. Each total protein fraction was also assayed for its ability to influence cholesterol precipitation, when added to supersaturated model bile. The current data provided evidence that the cholesterol crystallisation-promoting activity of biliary proteins in model biles increased with the beta-cyclodextrin dietary content. This occurred without any significant change in the total biliary protein content, but was associated with a significant decrease in the concentration of albumin and apolipoprotein A-I, resulting in changes in the overall balance of proteins in bile. Comparison of these results with the crystallisation figures previously obtained from the corresponding native biles led us to conclude that biliary proteins might influence the outcome of the crystallisation process, namely the final crystal concentration at equilibrium, but would not systematically represent a major driving force for determining the velocity of crystal formation in native bile of pigs.

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.

Mechanism of bile salt-induced mucin secretion by cultured dog gallbladder epithelial cells

1. Hypersecretion of gallbladder mucin has been proposed to be a pathogenic factor in cholesterol gallstone formation. Using cultured gallbladder epithelial cells, we demonstrated that bile salts regulate mucin secretion by the gallbladder epithelium. In the present study we have investigated whether established second messenger pathways are involved in bile salt-induced mucin secretion. 2. The effect of activators and inhibitors on mucin secretion was studied by measuring the secretion of [3H]N-acetyl-D-glucosamine-labelled glycoproteins. Intracellular cAMP content of the cells was measured using a radioimmunoassay. 3. Incubation of the cells with 10 mM taurocholate did not increase the intracellular cAMP content (25.7 versus control 22.8 pmol of cAMP/mg of protein). No stimulation of mucin secretion was observed after incubation with 1-100 microM concentrations of the calcium ionophores ionomycin and A23187. The stimulatory effect of 10 mM tauroursodeoxycholate (TUDC) on mucin secretion could not be inhibited by the addition of EDTA. Activation of protein kinase C (PKC) by 1 microgram/ml phorbol 12-myristate 13-acetate (PMA) caused an increase in mucin secretion (342% versus control 100%), comparable with the effect of 40 mM TUDC. The effect of 10 ng/ml PMA could partially be inhibited by a concentration of 2 microM of the PKC inhibitor staurosporin. Staurosporin had no inhibitory effect on mucin secretion induced by TUDC. 4. In gallbladder epithelial cells bile salts do not stimulate mucin secretion via one of the classical signal transduction pathways. We hypothesize that bile salts act on mucin secretion via a direct interaction with the apical membrane.

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.

Sedimentation of biliary sludge: effect on composition of gallbladder bile from patients with cholesterol, mixed, or pigment stones

BACKGROUND

Ultracentrifugation of bile has been used extensively to remove insoluble material such as sludge from bile before further studies of cholesterol nucleation. Although it has been recognized that this procedure may affect the composition of gallbladder bile, it has not been studied systematically in different gallstone populations. Therefore, we investigated the concentration of biliary lipids, protein, mucin, and bilirubin before and after ultracentrifugation.

METHODS

Gallbladder bile samples were aspirated during laparoscopic surgery from 66 patients (35 with cholesterol, 16 with mixed, and 15 with pigment stones).

RESULTS

Whereas the concentrations of bile acids, phospholipids, protein, and bilirubin in gallbladder bile did not change significantly after ultracentrifugation, cholesterol (20.6 +/- 1.6 to 14.8 +/- 1.2 mmol/l) and mucin concentrations (0.99 +/- 0.2 to 0.67 +/- 0.1 mg/ml) and the cholesterol saturation index (1.68 +/- 0.12 to 1.31 +/- 0.10) decreased significantly in gallbladder bile from patients with cholesterol stones.

CONCLUSIONS

Sedimentation of biliary sludge may profoundly affect the composition of gallbladder bile, which has to be considered in studies of cholesterol saturation and nucleation. The cholesterol concentration difference between native and ultracentrifuged bile reflects the insoluble crystalline fraction of cholesterol and may be useful for quantitation of the mass of cholesterol crystals in gallstone-associated bile samples.

Effect of NSAIDs on gallbladder bile composition

Secretion of gallbladder mucin is an important step in gallstone pathogenesis. Previous studies have demonstrated that aspirin and other nonsteroidal antiinflammatory drugs (NSAIDs) can both inhibit gallbladder mucin secretion and prevent gallstone formation in animal models of cholesterol gallstone disease. The present study was performed to determine if chronic NSAID use was associated with a reduction in the mucin content or affected the lipid components of human gallbladder bile. Four groups of patients were identified retrospectively from a cohort of 230 morbidly obese patients who underwent gastric bypass surgery. The index group consisted of 18 patients who were found to have gallstones at gastric bypass surgery and had a history of chronic NSAID use. Three other patient groups were identified from the cohort by matching this index population for sex, race, and age according to the following criteria: (1) patients with gallstones who had not utilized NSAIDs, (2) patients without gallstones but with chronic NSAID use, and (3) patients without gallstones and without a history of NSAID use. Gallbladder bile was obtained from all patients by direct aspiration from the gallbladder at the time of surgery. Patients with gallstones had a significantly (P < 0.02) greater concentration of gallbladder mucin in their gallbladder bile compared to patients without gallstones (0.897 +/- 0.226 vs 0.173 +/- 0.039 mg/ml). Among gallstone patients, gallbladder mucin was reduced in those patients with a history of chronic NSAID use (1.18 +/- 0.43 vs 0.74 +/- 0.19 mg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Model bile and bile salts accelerate mucin secretion by cultured dog gallbladder epithelial cells

BACKGROUND & AIMS

Hypersecretion of gallbladder mucin has been proposed as a pathogenic factor in gallstone formation. We investigated whether mucin secretion is modulated by biliary constituents using normal, well-differentiated dog gallbladder epithelial cells.

METHODS

Model biles or bile salts were applied to monolayers of epithelial cells. Mucin secretion was studied by measuring the secretion of [3H]N-acetyl-D-glucosamine-labeled glycoproteins.

RESULTS

Model biles with different cholesterol saturation indices increased mucin secretion by the cells to an average 251% after 5 hours of incubation (P < 0.01). Mucin secretion remained elevated during a 24-hour period, suggesting a sustained effect on mucin secretion. There was no relation between the cholesterol or phospholipid concentration and the extent of stimulation of mucin secretion. Taurocholate caused a dose-dependent increase in mucin secretion, suggesting that bile salt was the bile component responsible for the stimulatory effect. At a concentration of 0.5 mmol/L, only the more hydrophobic bile salts taurochenodeoxycholate and taurodeoxycholate, but not the hydrophylic bile salts taurocholate and tauroursodeoxycholate, stimulated mucin secretion (P < 0.01).

CONCLUSIONS

Bile salts play an important role in the regulation of mucin secretion. A shift in the bile salt composition of bile towards the more hydrophobic bile salts may cause mucin hypersecretion, thereby initiating cholesterol gallstone formation.

Primary dual defect of cholesterol and bile acid metabolism in liver of patients with intrahepatic calculi

BACKGROUND/AIMS

Intrahepatic calculi, which are characterized by cholesterol-rich pigment stones, are highly prevalent in East Asia. Their pathogenesis remains unknown. To elucidate the etiological factors underlying the formation of cholesterol-supersaturated bile, which leads to the formation of cholesterol-rich pigment stones cholesterol and bile acid de novo syntheses in the liver were studied.

METHODS

Liver specimens were assayed for the catalytic activities and steady-state messenger RNA levels of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase and cholesterol 7 alpha-hydroxylase.

RESULTS

The activity of HMG-CoA reductase, consistent with the messenger RNA level, was significantly higher in 13 patients with intrahepatic grown pigment stones (11.2 +/- 1.3 pmol.min-1.mg protein-1 [mean +/- SEM; P < 0.0001] for affected hepatic lobes and 13.4 +/- 1.7 [P < 0.0001] for unaffected ones [P < 0.0001]) than in 19 control subjects (6.4 +/- 0.4) and in 29 patients with gallbladder cholesterol stones (2.1 +/- 0.1). On the other hand, the activity of 7 alpha-hydroxylase, consistent with the messenger RNA level, was significantly lower in patients with intrahepatic brown pigment stones (2.8 +/- 0.5 pmol.min-1.mg protein-1 [P < 0.0001] for affected lobes and 2.6 +/- 0.5 [P < 0.0001] for unaffected ones) than in control subjects (6.0 +/- 0.6) and in patients with cholesterol stones (5.1 +/- 0.5).

CONCLUSIONS

In intrahepatic calculi, the formation of supersaturated bile and cholesterol-rich pigment stones may be attributed to the primary dual defect of up-regulated cholesterogenesis and down-regulated bile acid synthesis in the liver.

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.

Increased biliary protein precedes gallstone formation

Although nucleation is critical to the pathogenesis of cholesterol gallstones, the factors responsible for this process are poorly defined. Numerous potential nucleating agents have been identified in the bile of humans and animals with cholelithiasis, including mucus, calcium, and bilirubin. Recent studies have shown that patients with cholesterol crystals and gallstones have increased biliary total protein, suggesting that protein may be a previously unrecognized nucleating factor. We tested the hypothesis that biliary total protein is increased prior to cholesterol gallstone formation. Prairie dogs were maintained on either control (N = 22) or 0.4% cholesterol-enriched chow (N = 18) for up to 18 weeks. Cholesterol-fed animals were classified as pregallstone (N = 12) or gallstone (N = 6) based on gross examination of the gallbladder bile. Both hepatic and gallbladder biles were then analyzed for lipid, bile acid, calcium, and protein content. Cholesterol feeding was associated with increased gallbladder concentrations of cholesterol, phospholipids, and calcium in the pregallstone and gallstone groups. Biliary total protein was significantly elevated in the pregallstone (5.8 +/- 0.4 mg/ml, P < 0.001) and gallstone animals (6.0 +/- 0.6 mg/ml, P < 0.001) as computed to controls (3.8 +/- 0.3 mg/ml). Regression analysis showed positive correlations between gallbladder bile total protein and the gallbladder bile cholesterol saturation index (CSI) (P < 0.001), as well as between gallbladder total protein and calcium (P < 0.001). Although the hepatic bile CSI was elevated in cholesterol-fed animals, total protein remained unchanged, suggesting that the alteration in biliary protein is a gallbladder phenomenon.(ABSTRACT TRUNCATED AT 250 WORDS)

Subcellular characterization of glycoproteins in the principal cells of human gallbladder. A lectin cytochemical study

Gallbladder mucus is mainly composed of glycoproteins, which seem to play a critical role in cholesterol nucleation during gallstone formation. The biosynthetic pathway and sequential processing as well as the characterization of the oligosaccharide side-chains of human gallbladder secretory glycoproteins have not been completely defined. The aim of the present study is the subcellular characterization of the glycoproteins in the principal cells of human gallbladder. Principal cells of normal human gallbladder were studied by means of a variety of cytochemical techniques, including lectin histochemistry, enzyme and chemical treatments, immunocytochemistry and lectin-gold technology. Fucose, galactose, N-acetylglucosamine, N-acetylgalactosamine and N-acetylneuraminic acid residues were detected in mucous granules, Golgi apparatus and apical membrane of principal cells. Mannose residues were only observed in dense bodies. Oligosaccharide side-chains of the glycoproteins contained in the biliary mucus are synthesized in the Golgi apparatus of the principal cells of the gallbladder epithelium and are also contained in the mucous granules of these cells. Terminal N-acetylneuraminic acid(alpha 2-3)galactose(beta 1-3)N-acetylgalactosamine, N-acetylneuraminic acid(alpha 2-3)galactose(beta 1-4)N-acetylglucosamine and galactose(beta 1-4)N-acetylglucosamine sequences are contained in the oligosaccharide chains of gallbladder mucus glycoproteins. The dense bodies detected in the cytoplasm of the principal cells contained N-linked glycoproteins. Mucin-type O-linked glycoproteins were the main components of the mucous granules although some N-linked chains were also detected.

Identification of a 130-kilodalton human biliary concanavalin A binding protein as aminopeptidase N

BACKGROUND/AIMS

Human gallbladder bile contains a group of nonmucin glycoproteins that binds to the lectin concanavalin A (con A) and has been reported to promote cholesterol monohydrate crystal nucleation, an event preceding the formation of gallstones. Several of these proteins, including a 130-kilodalton protein, have been isolated and shown to promote nucleation in vitro. The aim of this study was to identify this and other major biliary con A binding glycoproteins.

METHODS

Gallbladder bile was chromatographed on con A agarose, and the eluted proteins were electrophoresed, blotted, and subjected to amino-terminal sequence analysis.

RESULTS

The major con A binding proteins were identified as aminopeptidase N (a 130-kilodalton protein), alpha 2 macroglobulin, hemopexin, immunoglobulin heavy chains, and the beta chain of haptoglobin. After further purification, aminopeptidase N was found to be enzymatically active and to promote cholesterol crystallization at its approximate physiological concentration in bile.

CONCLUSIONS

It is likely that aminopeptidase N is the previously characterized 130-kilodalton biliary crystallization promoting protein. Aminopeptidase N is probably released from the biliary canalicular membrane by the detergent activity of bile salts and may be one factor that promotes cholesterol crystallization in the gallbladder.

Artificial bile inhibits bile salt-induced gallbladder glycoprotein release in vitro

The more hydrophobic bile salts cause rapid release of preformed gallbladder mucin and other glycoproteins by gallbladder explants in vitro, whereas the less hydrophobic bile salts elicit a lesser response. This study was designed to determine (a) whether this short-term effect was matched by a sustained increase in glycoprotein secretion over 24 hr and (b) whether it occurred when bile salts were presented in model biles rather than aqueous solution. Although 3 mmol/L taurodeoxycholate in aqueous solution increased release of preformed gallbladder glycoprotein to 843% of control values after 30 min incubation (p < 0.001), no significant increase was observed after 24 hr. The more prolonged exposure also reduced precursor uptake by 32% (p < 0.05) and inhibited synthesis of new glycoprotein by 24% (p < 0.05). Moreover, the stimulatory effect of taurodeoxycholate on release of gallbladder glycoprotein was much reduced when it was presented in model biles rather than in aqueous solution. Nor was there any difference between the effects of more hydrophobic vs. less hydrophobic bile salts when presented in model biles. Aqueous solutions of the more hydrophobic bile salts induce a rapid release of gallbladder glycoprotein in vitro but do not produce a sustained increase in glycoprotein secretion. Their effect is liable to be prevented in vivo by interaction between bile salts and the other lipids in gallbladder bile.

Human gallstones contain pronucleating nonmucin glycoproteins that are immunoglobulins

OBJECTIVE

Pronucleating nonmucin glycoproteins in human cholesterol and black gallstones were isolated and identified.

SUMMARY BACKGROUND DATA

Gallbladder bile contains nonmucin glycoproteins that are pronucleating of cholesterol monohydrate crystals. Little is known about the presence or activity of these proteins within gallstones.

METHODS

Nonmucin glycoproteins were isolated from single cholesterol (n = 8), multiple cholesterol (n = 8), and black pigment (n = 8) gallstones by concanavalin A lectin-affinity chromatography. The proteins were separated by sodium dodecyl sulfate gradient electrophoresis. Western blot analysis was performed for Fab immunoglobulin fragments, and heavy chains from the immunoglobulin G, A, E, and M subclasses. A crystal observation time assay was performed on the combination of isolated nonmucin glycoproteins from gallstones and isolated Fab fragments.

RESULTS

Nonmucin glycoproteins of molecular weights 10, 15, 17, 22, 28, and 208 kD were identified in gallstones. These six nonmucin glycoproteins shortened the crystal observation time by more than 50% (p < 0.01) compared with model bile. Western blot analysis confirmed the identity of the 22- and 28-kD proteins as immunoglobulin Fab fragments. These were seen in all gallstones, irrespective of the gallstone type. The isolated Fab 28-kD fragment from the gallstones of 23 patients shortened the extrapolated crystal observation time by 78% (p < 0.01). However, commercially available Fab fragments had no effect on either cholesterol crystal appearance or growth.

CONCLUSIONS

Nonmucin glycoproteins that are pronucleating for cholesterol monohydrate crystals are also found in human cholesterol and black pigment gallstones. Fab immunoglobulin fragments were found in all gallstones irrespective of the gallstone type. Fab immunoglobulin fragments from gallstones shortened the crystal observation time but not crystal growth or total crystal content compared with model bile or commercially available Fab fragments. These data suggest that an antigen-immune (Fab) complex may contribute to cholesterol crystal function.

Gallbladder mucin, arachidonic acid, and bile lipids in patients who develop gallstones during weight reduction

BACKGROUND

Arachidonic acid (AA) and hydrophobic bile salts (BS) stimulate gallbladder mucin (GBM) secretion, which is thought to be an essential step in gallstone pathogenesis. The present study was performed to evaluate the relationship between AA, BS, and GBM in patients who develop gallstones following weight reduction.

METHODS

Eleven patients who underwent gastric bypass, developed symptomatic gallstones, and then underwent cholecystectomy were evaluated. Gallbladder bile was obtained for analysis during each procedure. Matched patients who did not develop gallstones following gastric bypass served as controls.

RESULTS

GBM increased in every patient who developed stones (mean increase: 5000%). The largest increase was observed soon after gastric bypass, and this declined curvilinearly with time. Gallbladder bile cholesterol was initially elevated but then rapidly declined before increasing back to pregastric bypass levels after weight loss was complete. No significant changes in phosphatidylcholine molecular species (including AA) or BS composition were observed following weight reduction. Concentrations of cholesterol, phospholipids, and changes in [AA] over time were each a linear function of [BS]. No relationship between GBM and any of these bile constituents was apparent.

CONCLUSIONS

These observations strongly suggest that increases in GBM, which occur with gallstone formation in humans, are not the result of alterations in biliary AA or BS composition.

Bile and plasma lipid composition in non-obese normolipidemic subjects with and without cholesterol gallstones

A two-stage study was carried out to characterize the bile and plasma lipid composition in normolipidemic non-obese patients with and without cholesterol gallstones. The first stage involved 11 patients with cholesterol gallstones admitted for elective cholecystectomy and a control group of 16 patients without cholesterol gallstones undergoing elective laparotomy. Bile samples were obtained intraoperatively by aspiration from the gallbladder. The bile of all the gallstone patients was supersaturated with cholesterol and its nucleation time was much shorter than that of bile in the control group (2.5 days vs 22.5 days, respectively, P < 0.001). The biliary fatty acid profile of phosphatidylcholine (PC) and free fatty acids (FFA) of gallstone patients was similar to that of the control group. C-22 fatty acids were found in a higher concentration in the FFA than in the PC fatty acids (P < 0.05) in both groups of patients. Plasma triglyceride levels in the gallstone patients were significantly higher than those in the control group and the biliary cholesterol level correlated with that of plasma triglycerides. In the second stage of the study, plasma lipid profiles were obtained in two additional groups of patients, 20 patients with and 24 patients without cholesterol gallstones, for an in-depth characterization of the differences in plasma lipid profiles. The gallstone patients were found to have not only significantly higher concentrations of plasma triglycerides but increased cholesterol and phospholipid level as well. These differences were essentially due to a higher lipid content of the plasma VLDL fraction, similar to the pattern of patients with type IV hyperlipoproteinemia.

A rapid method for the measurement of cholesterol thermodynamic activity in bile salt-lecithin-cholesterol solutions

Earlier work from this laboratory suggested that the cholesterol (Ch) thermodynamic activity is a more meaningful measure of the degree of Ch supersaturation in human bile than the widely known cholesterol saturation index. An early version of a method for determining thermodynamic activity based on Ch uptake from bile salt (BS)-lecithin (LE) solutions into silicone polymer particles, but requiring 12-24 h for reaching equilibrium, was considered unsatisfactory because Ch nucleation and crystal formation frequently occurred within a few hours. The aim of the present work was to develop a method that would reduce equilibration times to the order of 1 h. Changing the thickness of the silicone film alone did not result in the desired reduction of equilibration times and it was soon deduced that the uptake of Ch by the silicone film from the BS-LE solution was a surface-controlled transport process involving the transport of Ch by negatively charged BS and BS-LE micelles at the interface. Three different approaches were tried to modify the silicone film to make its surface positively charged, thereby reducing and/or eliminating the presumed electrical repulsion barrier for the interfacial transport of Ch. The film was treated with different concentrations of aminopropyl methyl-dimethylsiloxane (AMDS) in cyclohexane, octadecyldimethyl-[3-(trimethoxysilyl)-propyl] ammonium chloride (ODTOP) in methanol, and octadecylamine solution in ethanol. Films treated with 1-1.5% ODTOP and 5-10% AMDS reduced the Ch equilibration times for model BS-LE solutions to < 1 h.

Isolation and characterization of a cholesterol crystallization promoter from human bile

BACKGROUND

Recent studies on the pathogenesis of cholesterol gallstone disease have focused on the potential importance of an imbalance between biliary proteins having either inhibitory or promoting activities on nucleation and/or growth of cholesterol crystals as the initial stage in stone formation. The current study describes the purification and partial characterization of a 42-kilodalton biliary glycoprotein that shows concentration-dependent cholesterol crystallization-promoting activity.

METHODS

Chromatographic methods were used for separation and purification. Characterization steps included electrophoresis, deglycosylation, amino acid and carbohydrate analysis, and activity analysis by crystal growth assay.

RESULTS

The 42-kilodalton purified glycoprotein is an extensively glycosylated (37%) monomer with an acidic isoelectric point (pl < 4.1) that is probably based on the sialic acid content of the carbohydrate moiety. Enzymatic N-deglycosylation removes the carbohydrate moiety and inactivates the promoting activity. Furthermore, enzymatic proteolysis results in both its complete structural degradation and functional inactivation. Although the glycoprotein was isolated from normal human gallbladder biles, its presence in gallstone-associated samples is clearly shown.

CONCLUSIONS

This report outlines biochemical features of a human biliary glycoprotein that may be of major pathophysiological significance in gallstone disease.

Extracellular matrix proteins in bile and serum of patients with gallstone disease

The relationship of basement membrane to interstitial collagen-related protein metabolism was investigated in a sample of 100 consecutive patients undergoing surgery for gallstone disease. The measurements were performed on both sera and bile specimens using specific radioimmunoassays for type IV collagen, laminin, endogenous intact human type III collagen aminopropeptide and its degradation product, Col. 1. While basement membrane related proteins, type IV collagen and laminin were dominant in the bile, type III collagen related proteins were lower than in the corresponding serum samples. Both the intact type III procollagen peptide and its Col. 1 fragment were, however, found in the bile. The highest bile laminin concentrations were observed in patients with gallbladder fibrosis, whereas type III aminopropeptides were elevated not only in fibrosis and cancer but, most markedly, in acute inflammation of the gallbladder. Bile type IV collagen concentration was also found to vary according to the cholesterol content of gallstones. The results point to differences in the metabolism of various extracellular matrix proteins during the development of gallstone disease. The association between such proteins, the histological alterations in the gallbladder wall and the cholesterol content of gallstones may have implications for the pathogenesis of gallstone disease.

Management of recurrent gallstones

The risk of gallstone recurrence following non-surgical treatment has been overestimated in the past for two reasons: (1) diagnosis of primary gallstone dissolution was based on oral cholecystography; and (2) gallstone recurrence was expressed as a cumulative recurrence rate. Results based on better methodologies for diagnosis of gallstones (ultrasonography) and for calculation of results (life-table analysis) have indicated that gallstones recur in about 50% of patients, and that the risk of recurrence is confined mainly to the first 5 years after dissolution. Pretreatment gallstone characteristics, but not patient characteristics, are important risk factors for gallstone recurrence. Multiple stones are more likely to recur than solitary stones, a phenomenon attributable to the presence of a potent pronucleating factor in the bile of patients with multiple stones. This observation, and the finding that NSAID administration may reduce gallstone recurrence via inhibition of mucin secretion, suggests that the nucleation defect might be a key factor in the pathogenesis of recurrent gallstones. Prophylaxis with low-dose CDCA or UDCA has proven ineffective for preventing gallstone recurrence, although it may reduce it. Since the majority of recurrent gallstones are small when first seen because of regular ultrasonographic follow-up, multiple, radiolucent and in functioning gallbladders, they are amenable to bile acid retreatment, and intermittent bile acid therapy is probably a viable strategy for long-term management of cholesterol cholelithiasis.

Gallstones during octreotide therapy

Gallbladder stones (GBS) are found in up to 50% of patients receiving octreotide, but the reported prevalence of cholecystolithiasis in patients treated with octreotide is variable and little is known about gallstone incidence, composition, pathogenetic mechanisms, dissolvability, and primary prevention. Octreotide treatment apart, in industrialised societies most GBS are mixed in composition, cholesterol-rich (arbitrarily greater than 70% cholesterol by weight), radiolucent (70%), and, given a patent cystic duct (70%), dissolvable in bile rendered unsaturated in cholesterol by oral ursodeoxycholic (UDCA) +/- chenodeoxycholic (CDCA) acid treatment. They form when (1) GB bile becomes supersaturated with cholesterol (as the molar ratio of cholesterol to phospholipids in biliary vesicles approaches 1:1, the vesicles become unstable); (2) there is an imbalance between pro- and anti-nucleating factors, which favors cholesterol crystal precipitation; and (3) there is stasis within the GB as a result of altered motor function and/or excess mucus that traps the crystals. These changes may be associated with altered (4) biliary bile acid composition (more DCA and less CDCA than normal), and/or (5) phospholipid fatty acid composition (arachidonyl-rich lecithin acting as a substrate for mucosal prostaglandin synthesis which, in turn, may influence both gallbladder motility, and mucus glycoprotein synthesis and secretion). During octreotide treatment, meal-stimulated cholecystokinin (CCK) release is impaired leading to GB hypomotility, but little is known about the effects of octreotide on biliary cholesterol saturation, crystal nucleation time, mucus glycoprotein concentration, bile acid or phospholipid fatty acid composition. Most, but not all, reports suggest that the prevalence of GBS in octreotide-treated patients is considerably greater than that in age-, sex-, and weight-matched controls, but proof (by pre-treatment and on-treatment ultrasound) that the GBS were absent before, but developed during, therapy is not always available. Furthermore, there are few data on analysis of GBS composition in patients developing stones during treatment, although initial reports suggest that octreotide-associated GBS are also radiolucent, cholesterol-rich, and dissolve with oral bile acid treatment. Maximum GBS attenuation values, measured in Hounsfield Units (HU) by localized computerized tomography scanning of the GB, predict stone composition and dissolvability: GBS with scores of less than 100 HU are cholesterol-rich and dissolve well with oral bile acid treatment. However, preliminary results in 11 acromegalic patients treated with 200 to 600 micrograms octreotide/d for 29 to 68 months show that the HU scores range from 23 to 490 (mean +/- SEM, 116 +/- 41), suggesting that at least four of these 11 patients have non-cholesterol stones.(ABSTRACT TRUNCATED AT 400 WORDS)