Current concepts in cholesterol gallstone pathogenesis

Osteopontin Deficiency Alters Biliary Homeostasis and Protects against Gallstone Formation

The precipitation of excess biliary cholesterol as solid crystals is a prerequisite for cholesterol gallstone formation, which occurs due to disturbed biliary homeostasis. Biliary homeostasis is regulated by an elaborate network of genes in hepatocytes. If unmanaged, the cholesterol crystals will aggregate, fuse and form gallstones. We have previously observed that the levels of osteopontin (OPN) in bile and gallbladder were reduced in gallstone patients. However, the role and mechanism for hepatic OPN in cholesterol gallstone formation is undetermined. In this study, we found that the expression of hepatic OPN was increased in gallstone patients compared with gallstone-free counterparts. Then, we observed that OPN-deficient mice were less vulnerable to cholesterol gallstone formation than wild type mice. Further mechanistic studies revealed that this protective effect was associated with alterations of bile composition and was caused by the increased hepatic CYP7A1 expression and the reduced expression of hepatic SHP, ATP8B1, SR-B1 and SREBP-2. Finally, the correlations between the expression of hepatic OPN and the expression of these hepatic genes were validated in gallstone patients. Taken together, our findings reveal that hepatic OPN contributes to cholesterol gallstone formation by regulating biliary metabolism and might be developed as a therapeutic target for gallstone treatments.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

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

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

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

Mechanism for the transit-induced increase in colonic deoxycholic acid formation in cholesterol cholelithiasis

BACKGROUND & AIMS

Many patients with cholesterol gallbladder stones (GBS) have a high percentage of deoxycholic acid (DCA) in gallbladder bile (all of which are in the conjugated form), probably as a result of prolonged large bowel transit times (LBTT). However, whether the prolonged LBTT increases DCA formation, solubilization, or absorption (or all 3) is not known.

METHODS

In 40 subjects (20 with GBS; age range, 24-74 years), we measured LBTT using radiopaque markers, and intestinal luminal pH by radiotelemetry. We also measured quantitative anaerobic bacteriology and the activities of 2 bile acid-metabolizing enzymes in fresh cecal aspirates obtained during clinically indicated unprepared colonoscopy, and related these results to the percentage of DCA in fasting serum measured by gas chromatography-mass spectrometry.

RESULTS

Compared with controls, GBS patients had longer LBTT (mean 23.1 +/- SEM 2.8 h vs. 36.5 +/- 3.3 h; P < 0.01); more total (2.7 +/- 0.6 x 10(9) vs. 5.9 +/- 1.5 x 10(9) cfu/mL) and Gram-positive (9.5 +/- 3.1 x 10(8) vs. 18.0 +/- 4.1 x 10(8) cfu/mL; P < 0.05) anaerobes; and greater 7alpha-dehydroxylating (7alpha-DH) activity (3.39 +/- 0.59 vs. 10.37 +/- 1.15 x 10(-4) U/mg protein) in the cecal aspirates. They also had higher intracolonic pH values (P < 0.02) and increased percentages of DCA in fasting serum (13.4% +/- 1.52% vs. 21.8% +/- 2. 19%; P < 0.005). Results of univariate and multivariate analyses confirmed that LBTT was critical in determining the percentage of DCA in serum and showed that 7alpha-DH activity and apparent distal colonic pH were also significant independent variables.

CONCLUSIONS

Slow colonic transit (more time), increased Gram-positive anaerobes (more bacteria), and greater 7alpha-DH activity (more enzyme) favor enhanced DCA formation; transit-induced increases in distal colonic luminal pH favor enhanced DCA solubilization/bioavailability; and increases in LBTT (more time) again favor DCA absorption.

Changes of lipid metabolism in plasma, liver and bile during cholesterol gallstone formation in rabbit model

AIM: To find out the relationship between the disturbances of lipid metabolism and the formation of cholesterol gallstones by studying the changes of lipid metabolism in plasma, liver tissue and the bile.

METHODS: Male and female white Japanese rabbits were divided randomly into a control group (Con) and four experimental groups of 10 rabbits each fed with a diet containing 1.2% cholesterol for one, two, three and four weeks (1 wk, 2 wk, 3 wk and 4 wk group). The measurement of plasma triglyceride (TG), total cholesterol (TC), high density lipoprotein cholesterol (HDL-C) and its subfractions (HDL2-C, HDL3-C), very low and low density lipoprotein cholesterol (VLDL-C, LDL-C) was taken with standard enzymatic techniques. Apolipoprotein (apo) concentrations in plasma were measured by radial immunodiffusion assay for apoA1, apoB100, aopC¢ò and apoC II. Total cholesterol of liver was measured by the enzymatic procedure for each animal. Bile acids, mainly glycocholate (GCA) and glycodeoxycholate (GDCA) were detected by dual wavelength thin layer scanner.

RESULTS: In all the experimental groups fed with dietary cholesterol, cholesterol crystal was found in the gallbladder in 2/10 cases of the 1 wk group, 4/10 of the 2 wk group,6/10 of the 3 wk group and 7/10 of the 4 wk group respectively. The concentration of plasma total cholesterol (TC), triglyceride (TG), phospholipid (pl), VLDL-C, LDL-C, apoB100, apoC II, apoC III gradually increased (P < 0.05)with the prolonged feeding time of dietary cholesterol. High density lipoprotein cholesterol and its subfractions (HDL-C, HDL2-C, HDL3-C) showed a tendency to decrease, but without statistical significance (P > 0.05). ApoA1 was reduced with increased feeding time of dietary cholesterol (P < 0.05). The hepatic and biliary cholesterol increased 1-1.5 times as compared with the control group (t = 5.221 and 3.445, P < 0.05). The GCA gradually decreased beginning from the control group to the 4 wk group (P < 0.05).

CONCLUSION: Owing to the high cholesterol diet, the increased concentrations of plasma TC, TG, VLDL-C, LDL-C, hepatic TC and TG, apoB100, apoC II and apoC III possibly enhanced the secretion of biliary cholesterol into bile; the decreased plasma apoA1 level might reduce the secretion of antinucleating factor into bile. All those factors mentioned above probably contribute to the formation of cholesterol gallstones.

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

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

Gallbladder motility, gallstones, and the surgeon

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

Influence of bile salt molecular species on cholesterol crystallization from supersaturated model biles

Time-sequential enzymatic determination of cholesterol (CH) crystals harvested by ultrafiltration, and concomitant polarizing light microscopy observations corroborated the striking importance of the bile salts (BS) species in determining CH crystals formation rate from supersaturated model biles incubated in vitro. The more hydrophilic tauroursodeoxycholate, taurohyocholate, glycohyocholate, taurohyodeoxycholate, glycohyodeoxycholate and glyco-3 alpha, hydroxy-6 oxo-5 beta-cholanate inhibited CH precipitation through the formation of a stabilized liquid-crystalline phase. In contrast, in all hydrophobic systems (taurine (T) and glycine (G) conjugates of cholate (C), deoxycholate (DC) and chenodeoxycholate (CDC)), CH crystals precipitated with time. When crystallized CH concentrations were plotted vs. time, the figures showed a sigmoidal pattern, consistent with the transition from metastable systems to stable equilibrium states. Over the equilibration period, the nucleation kinetics (as inferred from enzymatic measurements) and all crystallization events (as microscopically observed) were both shifted in time, depending on the BS species: they were earliest in CDC systems, then in DC systems, and finally in C systems. In the latter, the delay was clearly due to the formation of a transient labile liquid-crystalline phase. G-conjugation also induced a significant delay in CH precipitation, compared to T-conjugation. At last, maximum crystallized CH concentrations at equilibrium were in the decreasing order: C > CDC > DC and T-conjugates > G-homologues. All data are discussed in connection with BS hydrophobicities, with predictions from the phase equilibria of aqueous biliary lipid systems and with new insights into CH crystal habits.

Effects of ethanol on contractile response of gall bladder isolated from guinea pig

The effects of ethanol treatment in vitro and in vivo on gall bladder contraction were investigated using gall bladder strips isolated from guinea pigs. In vitro pretreatment of the strips with ethanol at a concentration of over 50 mM significantly attenuated the reactivity and sensitivity of contractile responses to KCl, acetylcholine and histamine in a concentration-dependent manner. Indomethacin treatment or removal of extracellular calcium remarkably reduced gall bladder contractile response to acetylcholine. The depressive effect of ethanol in vitro on gall bladder contraction was also noted in the presence of indomethacin or absence of calcium in the medium. The concentration-response curve of calcium-induced contraction in 40 mM KCl-depolarized gall bladder strip shifted to the right on pretreatment with ethanol. In the case of strips following the chronic administration of 3% ethanol solution ad libitum for 4 weeks, contractile responses to KCl, acetylcholine and histamine did not differ, compared to those in the pair-fed group. This chronic ethanol administration induced tolerance to the acute inhibitory effect of ethanol on gall bladder contractile responses to the agonists. Ethanol is thus shown to exert direct inhibitory action on gall bladder contraction by lowering the calcium sensitivity of the contractile apparatus of smooth muscle; it is unlikely that ethanol consumption would affect gall bladder motility in vivo, owing to the tolerance produced toward the acute inhibitory action of ethanol.

Gallstone cholesterol content is related to apolipoprotein E polymorphism

BACKGROUND

The genetically determined phenotypes of apolipoprotein E are related to variations in lipoprotein levels and in the enterohepatic metabolism of cholesterol and bile acids. The present study was designed to elucidate the role of apolipoprotein E polymorphism in gallstone formation.

METHODS

Apolipoprotein E phenotype was determined in 169 consecutive cholecystectomy patients and in 200 controls. The cholesterol content of the gallstones (n = 169), the presence of cholesterol monohydrate crystals of fresh gallbladder bile (n = 142), and the nucleation time (n = 35) were also analyzed.

RESULTS

The median cholesterol content of the gallstones was higher in the apolipoprotein E4 category (phenotypes E4/4 and E4/3, 97%) than in the E3 (E3/3, 78%) and E2 patients (E2/2 and E2/3, 76%, P = 0.0003). In E4 patients, cholesterol crystals were found immediately after surgery in 27 of 40 (68%), whereas in E3 and E2 groups in 36 of 88 (41%), and 4 of 14 (29%) of the patients (P = 0.0001). The median nucleation time in E4 patients (2.5 days) was shorter than in patients with E3 (5.5 days) or E2 (6.0 days) (P = 0.0016).

CONCLUSIONS

These data indicate that apolipoprotein E polymorphism affects cholesterol content of cholelithiasis. We suggest that this phenomenon is mediated by the altered formation of cholesterol monohydrate crystals in different apolipoprotein E phenotypes.