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

Transgenic overexpression of Niemann-Pick C2 protein promotes cholesterol gallstone formation in mice

BACKGROUND & AIMS

Niemann-Pick C2 (NPC2) is a lysosomal protein involved in the egress of low-density lipoprotein-derived cholesterol from lysosomes to other intracellular compartments. NPC2 has been detected in several tissues and is also secreted from the liver into bile. We have previously shown that NPC2-deficient mice fed a lithogenic diet showed reduced biliary cholesterol secretion as well as cholesterol crystal and gallstone formation. This study aimed to investigate the consequences of NPC2 hepatic overexpression on liver cholesterol metabolism, biliary lipid secretion, gallstone formation and the effect of NPC2 on cholesterol crystallization in model bile.

METHODS

We generated NPC2 transgenic mice (Npc2.Tg) and fed them either chow or lithogenic diets. We studied liver cholesterol metabolism, biliary lipid secretion, bile acid composition and gallstone formation. We performed cholesterol crystallization studies in model bile using a recombinant NPC2 protein.

RESULTS

No differences were observed in biliary cholesterol content or secretion between wild-type and Npc2.Tg mice fed the chow or lithogenic diets. Interestingly, Npc2.Tg mice showed an increased susceptibility to the lithogenic diet, developing more cholesterol gallstones at early times, but did not show differences in the bile acid hydrophobicity and gallbladder cholesterol saturation indices compared to wild-type mice. Finally, recombinant NPC2 decreased nucleation time in model bile.

CONCLUSIONS

These results suggest that NPC2 promotes cholesterol gallstone formation by decreasing the cholesterol nucleation time, indicating a pro-nucleating function of NPC2 in bile.

Changes in gallbladder bile composition and crystal detection time in morbidly obese subjects after bariatric surgery

The aim of the present study was to elucidate the mechanisms of development of cholesterol crystals and gallstones during weight reduction in obese subjects. Twenty-five morbidly obese, gallstone-free subjects underwent vertical-banded gastroplasty. Gallbladder bile was collected at the time of the operation via needle aspiration and 1.1-7.3 months after the operation via ultrasound-guided transhepatic puncture of the gallbladder. The mean weight loss was 17 kg. Two patients developed gallstones and 10 patients displayed cholesterol crystals in their bile. In patients with a follow-up time of less than 2 months (n = 13), cholesterol saturation increased from 90% to 114% but tended to decrease in the patients with a follow-up time of more than 2 months. The extraction of the concanavalin-A-binding fraction from gallbladder bile obtained after weight reduction in 7 patients prolonged crystallization detection time from 6 to 10 days. The hexosamine concentration, a marker for mucin, was increased by about 100% in bile obtained in 6 of 7 patients after weight reduction. In conclusion, the results indicate that crystallization-promoting compounds (mucin) are of great importance in the development of cholesterol crystals and gallstones in obese subjects during weight reduction, probably because of defective gallbladder emptying.

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

BACKGROUND & AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Concanavalin A-binding cholesterol crystallization inhibiting and promoting activity in bile from patients with Crohn's disease compared to patients with ulcerative colitis

BACKGROUND/AIMS

Crohn's disease is a risk factor for gallstone formation. In contrast, patients with ulcerative colitis have an incidence of gallstone formation comparable to the general population. The reason for this difference is not known. The aim of this study was to elucidate the factors controlling cholesterol crystallization in gallbladder bile of Crohn's disease and ulcerative colitis patients.

METHODS

Gallbladder bile was obtained by aspiration during bowel resections (26 Crohn's disease patients, 20 ulcerative colitis patients). Biliary lipid composition, crystal detection time and the effect of extraction of the concanavalin A-binding fraction on crystal formation were determined.

RESULTS

Cholesterol crystals were present in seven of the 26 bile samples of Crohn's disease-patients and one of the 20 ulcerative colitis patients. Four of the bile samples of Crohn's disease patients were fast nucleating. None of the 20 ulcerative colitis patients had fast nucleating bile. Lipid composition, total lipid concentration and CSI were not significantly different between the two groups. In Crohn's disease patients extraction of concanavalin A-binding fraction decreased crystallization in 10 bile samples but accelerated crystallization in one bile sample. In eight bile samples from ulcerative colitis patients crystallization increased after concanavalin A-binding fraction extraction.

CONCLUSIONS

Compared to ulcerative colitis patients, gallbladder bile of Crohn's disease patients showed increased cholesterol crystallization despite comparable lipid composition and cholesterol saturation index. This difference is caused by increased cholesterol crystallization-promoting activity. Bile from ulcerative colitis patients contains a Con A-binding factor which inhibits cholesterol crystallization.

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

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