Total biliary protein, mucus glycoproteins, cyclic-AMP, and apolipoproteins in the gallbladder bile of patients with cholesterol stones and stone-free controls

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.

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.

Hepatic bile versus gallbladder bile: a comparison of protein and lipid concentration and composition in cholesterol gallstone patients

Many studies have demonstrated that gallbladder bile (but not hepatic bile) of animals or patients with cholesterol gallstones contains higher protein concentrations than does gallbladder bile of control patients without stones or with pigment stones. The underlying defect has not been elucidated. To establish whether there is net production or net absorption/degradation of protein by gallbladder epithelium for different classes of protein, paired samples of hepatic and gallbladder bile were obtained from fourteen patients with cholesterol gallstones during elective cholecystectomy. In these paired samples, lipid and protein composition were determined. To obtain the concentration ratio (CR) of protein and lipid, its concentration in the gallbladder was divided by the concentration determined in the paired hepatic bile sample. The CR of bile salts was used as a parameter for water absorption in the gallbladder. Of the biliary proteins that were determined only mucin, albumin, immunoglobulin (Ig) G, and aminopeptidase N appeared to increase in the gallbladder from another cause than water absorption. A strong correlation was found between mucin, albumin, and IgG. Haptoglobin, alpha1-acid glycoprotein, IgM, and IgA appeared to be absorbed by gallbladder epithelium in the majority of patients. In cholesterol gallstone patients, total protein concentration in gallbladder bile of cholesterol gallstone patients is increased when compared with hepatic bile. The increase in protein concentration cannot be explained for all bile samples solely by water absorption. In this study we show that the defect is largely caused by a selective increase in albumin, mucin, and IgG. All other proteins which were investigated are taken up by the gallbladder.

Characterization of glycoproteins in the epithelial cells of human and other mammalian gallbladder. A review

The mammalian gallbladder mucosa is lined by a simple columnar epithelium. Typical surface epithelial cells (principal cells) contain short microvilli, secretory granules, dense bodies, mitochondria and Golgi apparatus. Dense bodies are thought to be lysosomes. Secretory granules contain mucous glycoproteins which are released to the lumen by exocytosis. Oligosaccharide side chains of mucous glycoproteins may provide a favorable environment for nucleation of cholesterol in gallstone formation; therefore they have been studied during the past decades. Histochemical techniques allow the in situ identification of carbohydrates at both the cellular and subcellular levels. The oligosaccharide chains of principal cell mucous glycoproteins have been studied by classical histochemical techniques (PAS, alcian blue, HID, etc). These techniques indicate that mammalian gallbladder mucous glycoproteins are heavily sulphated, whereas sialic acid residues are scarce. Neutral mucins have not been described in the mammalian gallbladder. Electron microscopic studies have located the oligosaccharide chains in secretory granules and Golgi apparatus. More recently, lectins (molecules which specifically recognize and bind with different saccharides or saccharide sequences) have been applied for the intracellular localization of carbohydrate residues. Lectin histochemistry has detected fucose, galactose, N-acetylglucosamine, N-acetylgalactosamine and N-acetylneuraminic acid residues in mucous granules, Golgi apparatus and apical membrane of human principal cells. Mannose residues were observed only in dense bodies. The combined use of deglycosylation procedures and lectin histochemistry has revealed a variety of terminal sequences in oligosaccharide chains of gallbladder mucous glycoproteins: Neu5Ac(alpha 2-3)Gal(beta 1-3)GalNAc, Neu5Ac(alpha 2-3)Gal(beta 1-4)GlcNAc and Gal(beta 1-4)GlcNAc. This technology also suggested the occurrence of N-linked oligosaccharides in the dense bodies of principal cells. Mucous granules mainly contained mucin-type O-linked oligosaccharides although some N-linked chains have also been detected. Gallstone formation is probably a complex process depending on multiple factors. Mucous glycoproteins are one of the factors involved in this process. Histochemical methods offer an excellent research tool for the characterization of glycoproteins in the epithelial cells of the gallbladder, thus contributing to the elucidation of the pathophysiology of gallstone formation.

Variations in pigment and carbohydrate content of gallbladder bile affect accurate quantitation of total protein when using the fluorescamine method

BACKGROUND

Despite solute dilution and reduced total lipid concentrations, an unexplained increase in protein concentration has been reported to occur in the gallbladder bile of cholesterol gallstone patients.

METHODS

Solutes in gallbladder bile from gallstone-free controls and from four study groups were measured using standard methods. Total proteins were measured using amino acid analysis and a conventional fluorescamine method.

RESULTS

Bile salts and pigment content were greater in gallstone-free controls than in all other study groups, including morbidly obese gallstone-free subjects. Total biliary protein concentration, as determined by amino acid analysis in the gallstone-free control group was higher than in non-obese gallstone patients with multiple stones and in morbidly obese gallstone-free subjects. Total biliary proteins as measured with fluorescamine, however, did not show intergroup differences. A major problem of the conventional fluorescamine assay is shown to be an artefact arising from the high pigment content of the more concentrated samples.

CONCLUSIONS

Very dilute gallbladder bile samples are often found in the presence of gallstone disease. This also occurs in morbidly obese subjects, even in the absence of gallstones. Although the contribution of protein secretion/absorption by the gallbladder can also be relevant, especially in the presence of morbid obesity, the protein concentration in gallbladder bile, when accurately measured, generally parallels the concentrations of non-absorbed biliary solutes, reflecting the efficiency of fluid absorption. Measurement of biliary proteins by the conventional fluorescamine method is unreliable in clinical studies in which intergroup differences in pigment content are commonly present.

Lysosomal enzyme activities in gallbladder mucosa of gallstone-free subjects and patients with gallstones

BACKGROUND/AIMS

Gallstone patients have a reduced cellular lysosome content in the gallbladder mucosa cells compared with gallstone-free subjects. The purpose of the study was to further evaluate the possible role of lysosomes in the pathogenesis of cholesterol gallstone formation in humans.

METHODS

Lysosomal enzyme activities were assayed in gallbladder mucosa and for comparison in liver specimens of 19 gallstone-free subjects and 24 gallstone patients undergoing cholecystectomy.

RESULTS

Gallstone patients had 25-50% lower activities of the lysosomal proteases cathepsin B, D and L in their gallbladder mucosa compared with gallstone-free subjects. The activity of acid phosphatase also tended to be decreased in gallstone patients. The liver lysosomal enzyme activities were not significantly different between the two groups.

CONCLUSIONS

The results show that gallstone patients have diminished lysosomal enzyme activities in the gallbladder mucosa, a finding which may be related to decreased intracellular degradation of proteins and/or mucin in the mucosal cells. This may lead to a higher concentration of mucin in gallbladder bile and thus an increased risk of precipitation of cholesterol crystals and gallstone formation.

Comparison of haptoglobin and apolipoprotein A-I on biliary lipid particles involved in cholesterol crystallization

Several proteins are known to modulate cholesterol crystallization. We recently demonstrated that haptoglobin has cholesterol crystallization promoting activity. However, this effect is still not well understood mechanistically. The current study examined the distribution of haptoglobin compared to apolipoprotein A-I (apo A-I) to micelles, vesicles and crystals as an initial step in providing a focus for further studies of the mechanism of cholesterol crystallization activity. Specific protein purification was accomplished by immunoaffinity chromatography. The crystallization-promoting activity of biliary haptoglobin, albumin and commercial apo A-I was measured by a photometric crystal growth assay. The distribution of micelles, vesicles and proteins in model bile was determined by Sepharose CL-6B column chromatography. Detection of the presence of test proteins in cholesterol crystals was determined using specific 125I-radiolabelled proteins. Haptoglobin (20 micrograms/mL) showed a significant crystallization promoting-activity, whereas apo A-I (30 micrograms/mL) only tended to show a slight inhibitory activity. The cholesterol crystal-bound protein in each case was found to be less than 1% of the total concentration of that protein that had been added to the model bile system. The elution profile of commercial apo A-I from a Sepharose CL-6B column was strikingly altered when it was added to model bile prior to elution. In contrast, the column elution profiles for both haptoglobin and albumin were unchanged when model bile was similarly added to the sample. Haptoglobin increased the amount of cholesterol found in the vesicular fraction when compared to apo A-I. Haptoglobin does not bind tightly to either biliary lipid particles or to cholesterol crystals but does increase the amount of cholesterol in vesicles by inducing a shift from micellar cholesterol (P = 0.046). This shift appears to explain in part its promoting effect on cholesterol crystallization.

Purification and characterization of a novel human 15 kd cholesterol crystallization inhibitor protein in bile

Crystallization-inhibiting proteins can explain longer nucleation times associated with bile from gallstone-free subjects as compared with bile from patients with cholesterol gallstones. We partially characterized and examined the crystallization inhibitory potency of a newly purified 15 kd human biliary protein. Gallbladder bile was passed through an anti-apolipoprotein A-I (apo A-I) immunoaffinity column to extract lipid-associated proteins. The bound fraction was separated by 30 kd ultrafiltration. Sodium dodecyl sulfate-polyacrylamide gel electrophesis (SDS-PAGE) was performed under nonreducing and reducing conditions. Cholesterol crystallization activity was tested in a photometric cholesterol crystal growth assay. Isoelectric focusing was performed by using a standard gel. The purified 15 kd protein was subjected to N-terminal amino acid sequencing. Although the whole apo A-I-bound fraction contained a variety of proteins and lipids, its 30 kd filtrate yielded a nearly pure 15 kd protein with only minor contamination from apo A-1. Amino acid sequencing showed that the protein was unique. Enzymatic deglycosylation revealed no evidence for glycosylation. At a protein concentration of 10 micrograms/ml, crystallization time was delayed as compared with control and apo A-I, and final crystal mass was reduced to 75% of control. Its isoelectric point was 6.1 without isoforms. Under nonreducing conditions, the protein formed a 30 kd dimer and a 60 kd tetramer. We conclude that this protein is a novel potent biliary crystallization inhibitor protein.

Gallstone recurrence after successful dissolution therapy

After successful dissolution therapy of cholesterol gallbladder stones bile again becomes supersaturated and recurrent gallstones may develop. Three different postdissolution treatments [500 mg ursodeoxycholic acid (UDCA) per day (N = 14, group I), 100 mg aspirin per day (N = 14, group II) and diet (N = 15, group III) versus a control group (no treatment, N = 15, group IV) aimed at preventing recurrence of gallstones were investigated in a prospective, randomized study in 58 gallstone patients (33 female, 25 male) after complete stone clearance. Bile samples (prior to dissolution therapy and at stone recurrence) were investigated for biliary cholesterol (C), phospholipids (PL), total bile acid concentration (BA), cholesterol saturation index (CSI), total lipid concentration (TLC), total biliary protein concentration (TP), and nucleation time (NT). In group IV multiple gallstones tended to recur more often than solitary stones (66.7% vs 16.7%) whereas in groups I-III only solitary stones recurred. Recurrent gallbladder stones were detectable in 10 patients (eight patients in group IV and one each in groups I and II, respectively) within one year after dissolution and in two patients (one each in groups III and IV, respectively) after 15 months. Furthermore, the probability of stone recurrence was significantly higher in untreated patients as compared to treated patients. In nine (group IV) of 12 patients with recurrent stones NT, C, CSI, PL, BA, TLC, TP, and bile acid spectrum remained nearly unchanged as compared to their pretreatment values, whereas in three (groups I-III) of 12 cases a decrease in C, CSI, and TP was observed during therapy. However, in each of these three patients, initial and after-treatment TP was significantly higher and NT shorter as compared to groups I-IV. Furthermore, in these cases (N = 3) NT was prolonged, whereas no significant changes were found in PL, BA, TLC, and bile acid spectrum. Recurrence of gallstones, which seems to occur more likely in patients with multiple stones as compared to solitary stones, will happen in the early stage after stone clearance, again causing biliary pain. UDCA, aspirin or diet will reduce the probability for recurrent stones after complete gallstone dissolution.

Lysophosphatidylcholine-stimulated protein and glycoprotein production by human gallbladder mucosal cells

It has been demonstrated in experimental cholecystitis in cats produced by lysophosphatidylcholine that the development of inflammation is associated with the exsorption of a large amount of protein into the gallbladder lumen. It was subsequently demonstrated that in feline experimental cholecystitis the protein produced was albumin and that its production was decreased by vesicular transport inhibitors, suggesting an active secretory process. In the present study, the effect of lysophosphatidylcholine on protein production by fresh, isolated human gallbladder mucosal cells was evaluated. Isolated gallbladder mucosal cells were incubated with [14C]leucine for 24 hr in tissue culture medium. The cells readily incorporated the radioactive label into cellular protein, a process inhibited by cycloheximide. Exposure of the cells to lysophosphatidylcholine for 1 hr in buffer solution resulted in loss of intracellular protein into the buffer solution. Exposure of the cells for 1 hr prior to lysophosphatidylcholine administration to vesicular transport inhibitors, colchicine, and cytochalasin B and to 4 degrees C culture conditions failed to alter the lysophosphatidylcholine-produced passage of the 14C label extracellularly. SDS-PAGE evaluation of the protein produced demonstrated that human gallbladder mucosal cells continuously produced a 66-kDa protein that was not increased by increasing concentration of lysophosphatidylcholine and a 14-kDa protein that increased with increasing concentrations of lysophosphatidylcholine. Employing Western blotting with specific antibodies, the 66-kDa protein was demonstrated to not be albumin but a 66-kDa glycoprotein, and the 14-kDa protein was demonstrated to contain phospholipase A2. Human gallbladder mucosal cells produced a protein and glycoprotein in response to lysophosphatidylcholine by a mechanism not related to vesicular transport.

Concanavalin-A-extractable non-mucous glycoprotein concentrations in gallbladder bile of cholesterol gallstone patients

BACKGROUND

The relationship between protein concentrations and the nucleation activity of bile in cholesterol gallstone patients has already been investigated. Nucleation promoters are mucins and concanavalin A (Con-A)-extractable glycoproteins. Nucleation inhibitors are apolipoproteins. We wanted to investigate whether a change in concentration of apolipoprotein A-I (Apo A-I) or Con-A in the bile of cholesterol stone carriers is dependent on the nucleation time.

METHODS

Total protein was measured by fluorescence photometry, and Con-A-extractable glycoproteins were separated by their affinity to lectins and measured by photometry. Apolipoproteins were measured by radioactive competitive protein binding assay.

RESULTS

The protein concentrations in our bile samples were 2.41 +/- 1.08 mg/ml for the whole group, 2.73 +/- 1.07 mg/ml for a nucleation time less than 3 days, and 2.04 +/- 1.00 for a longer nucleation time. The concentration of the Con-A fraction accounted for 0.289 +/- 0.096 mg/ml, 0.306 +/- 0.081 mg/ml, and 0.274 +/- 0.109, respectively. The Apo A-I concentration was 52 +/- 64 micrograms/ml; 50 +/- 56 micrograms/ml for a nucleation time less than 3 days and 85 +/- 133 micrograms/ml for a longer nucleation time.

CONCLUSIONS

Obviously, individual protein fractions have an effect on the nucleation behaviour of gallbladder bile in cholesterol gallstone patients.

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)

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)