Mechanism of cholesterol gallstones formation

Interindividual variability of canalicular ATP-binding-cassette (ABC)-transporter expression in human liver

Interindividual variability in hepatic canalicular transporter expression might predispose to the development of hepatic disorders such as acquired forms of intrahepatic cholestasis. We therefore investigated expression patterns of bile salt export pump (BSEP, ABCB11), multidrug resistance protein 3 (MDR3, ABCB4), multidrug resistance associated protein 2 (MRP2, ABCC2) and multidrug resistance protein 1 (MDR1, ABCB1) in healthy liver tissue of a white population. Protein expression levels were correlated with specific single nucleotide polymorphisms (SNPs) in the corresponding transporter genes. Hepatic protein expression levels from 110 individuals undergoing liver resection were assessed by Western blot analysis of liver plasma membranes enriched in canalicular marker enzymes. Each individual was genotyped for the following synonymous (s) and nonsynonymous (ns) SNPs: ABCB11: (ns:1457T>C and 2155A>G), ABCB4: (ns:3826A>G) and ABCC2 (ns:1286G>A,3600T>A and 4581G>A) and ABCB1 (ns:2677G>T/A and s:3435C>T). Transporter expression followed unimodal distribution. However, of all tested individuals 30% exhibited a high expression and 32% a low or very low expression phenotype for at least one of the four investigated transport proteins. Transporter expression levels did not correlate with age, sex, underlying liver disease, or presurgery medication. However, low BSEP expression was associated with the 1457C-allele in ABCB11 (P = .167) and high MRP2 expression was significantly correlated with the 3600A and 4581A ABCC2 variants (P = .006). In conclusion, the results demonstrate a considerable interindividual variability of canalicular transporter expression in normal liver. Furthermore, data suggest a polymorphic transporter expression pattern, which might constitute a risk factor for the development of acquired forms of cholestatic liver diseases.

Estrogen-induced gallstone formation in males. Relation to changes in serum and biliary lipids during hormonal treatment of prostatic carcinoma

To assess if and by which mechanisms pharmacological estrogen treatment induces gallstone disease, we examined patients with recently diagnosed prostatic cancer randomly allocated to estrogen therapy (n = 37) or orchidectomy (n = 35). According to gallbladder ultrasonography, after 1 yr new gallstones had developed in 5 of 28 estrogen-treated patients, compared with 0 of 26 orchidectomized patients (P = 0.03). Estrogen therapy for 3 mo increased the relative concentration of cholesterol and cholesterol saturation of bile by approximately 30% (n = 10). Serum LDL cholesterol was reduced by approximately 40%, and its relative change related inversely to that of bile cholesterol (Rs = -0.77). There were no changes in biliary or serum lipids after orchidectomy (n = 9). Secretion rates of biliary lipids were measured with a duodenal perfusion technique. Patients on chronic estrogen therapy (n = 5) had approximately 40% higher biliary excretion rates of cholesterol than age-matched controls (n = 7). Phospholipid secretion was also higher, but no difference in bile acid secretion was found. We conclude that an increased hepatic secretion of cholesterol results in increased cholesterol saturation of bile and an enhanced rate of gallstone formation during estrogen treatment. The changes in bile cholesterol seem to be related to the induced changes in serum lipoprotein metabolism.

Mucin in gall bladder bile of gall stone patients: influence of treatment with chenodeoxycholic acid and ursodeoxycholic acid

The concentration of hexosamine, a marker for mucin, was determined and related to the degree of cholesterol saturation and to the occurrence of cholesterol crystals in gall bladder bile of gall stone patients (n = 40) and gall stone free subjects (n = 25). Ten of the gall stone patients had been treated with chenodeoxycholic acid (CDCA) and eight with ursodeoxycholic acid (UDCA) three to four weeks before cholecystectomy. The hexosamine content was significantly higher in gall stone patients (137 (19) ng/ml, mean (SE) than in gall stone free subjects (83 (9) ng/ml, p less than 0.02). Treatment with CDCA or UDCA decreased cholesterol saturation, but did not significantly affect the hexosamine concentration. There was no difference in hexosamine concentration between gall stone patients with and without cholesterol crystals. The results do not support the hypothesis that the degree of cholesterol saturation is important for the mucin content of gall bladder bile in man. Neither do the data indicate that the formation and occurrence of cholesterol crystals in gall bladder bile from gall stone patients is caused by an increased concentration of mucin. As the studies were conducted on patients who had already had gall stones for several years, however, an effect of mucin in the very early stage of gall stone formation cannot be completely excluded.

Bezafibrate therapy and biliary lipids: effects of short-term and long-term treatment in patients with various forms of hyperlipoproteinaemia

Several hypolipidaemic drugs increase biliary cholesterol saturation and induce the formation of cholesterol gallstones. In order to determine the influence of bezafibrate, a clofibrate analogue with hypolipidaemic properties, on bile lipid composition, we studied twelve patients with various forms of hyperlipoproteinaemia (six type IIA, three type IIB and three type IV hyperlipoproteinaemia; six had a genetic diagnosis of familial hypercholesterolaemia and five familial combined hyperlipidaemia). After 4 weeks of therapy, when serum lipids were significantly reduced, the relative proportion of cholesterol in stimulated fasting duodenal bile was increased by 28% (P less than 0.001). Phospholipids were concomitantly increased and bile acids decreased, resulting in an increase in biliary cholesterol saturation from 89 +/- 4% to 105 +/- 8% (SEM, P less than 0.02). The changes induced were similar in patients with familial hypercholesterolaemia and familial combined hyperlipidaemia. After 1 year of continued treatment, serum lipid responses were unaltered. The changes in biliary lipids were also persistent as the relative cholesterol concentration remained increased by 33% (P less than 0.01) and cholesterol saturation averaged 106 +/- 8% (P less than 0.02). Although the effect on bile cholesterol appeared to be transient in some patients, the results of the present study suggest that the risk of cholesterol gallstone formation may be increased during bezafibrate therapy.

Influence of increased fibre intake on biliary lipids

Influence of increased fibre intake on biliary lipids. The influence of dietary fibres (30 g wheat bran per day) on the lithogenicity of the bile was studied in ten healthy persons, whose body weight was 76.8 +/- 2.3 kg, height 189.9 +/- 2.1 cm, age 25.5 +/- 0.26 years. These 10 young male volunteers were given twice daily 15 g wheat bran additionally for six weeks in addition to their normal diet. The bile was obtained endoscopically prepapillarily following stimulation of the gallbladder with ceruletid. The contraction of the gallbladder was controlled sonographically. Increased dietary fibre intake resulted in significant lowering of cholesterol concentration in the bile from 3.27 +/- 0.89 mmol/1 to 2.50 +/- 0.67 mmol/1. The lithogenic index (Admirand and Small, 1968) decreased statistically significant from 1.01 +/- 0.14 to 0.67 +/- 0.11. Total cholesterol and HDL and LDL cholesterol remained unchanged; likewise, there was no change in serum triglyceride and phospholipid concentrations. Hence, an increased intake of dietary fibres of the wheat bran type should be the first dietary measure in both prevention and treatment of cholesterol gallstone disease.

Influence of age on secretion of cholesterol and synthesis of bile acids by the liver

Supersaturation of bile with cholesterol predisposes to the development of cholesterol gallstones. To identify the factors determining cholesterol saturation of bile, we analyzed the lipid composition of stimulated duodenal bile in 60 healthy subjects of various ages (31 men and 29 women) who were not obese and were free of gallstones. A positive correlation between age and cholesterol saturation of bile was found (P less than 0.001). To analyze the relation between age and cholesterol saturation, we studied the rates of hepatic secretion of biliary lipids and the kinetics of cholic acid and chenodeoxycholic acid in 22 and 18 of the subjects, respectively. Age was positively correlated with the cholesterol secretion rate (r = 0.48) and negatively correlated with bile acid synthesis (r = -0.60) and the size of the cholic acid pool (r = -0.54). We conclude that cholesterol saturation of bile increases with age as a consequence of enhanced hepatic secretion of cholesterol and decreased bile acid synthesis. These findings may explain why age is a risk factor for the development of cholesterol gallstones.

Evidence for distinct precursor pools for biliary cholesterol and primary bile acids in cebus and cynomolgus monkeys

The abnormal metabolism and distribution of plasma lipoproteins have been associated with atherosclerosis and gallstones. To better understand the process of cholesterol excretion, a study was designed to determine whether the contribution of lipoprotein free 14C-cholesterol (as LDL or HDL) to biliary cholesterol or primary bile acids differs in two species of nonhuman primates, cebus and cynomolgus monkeys, having opposite plasma LDL/HDL ratios. Since amino acid conjugation might influence bile acid synthesis or secretion, the taurine and glycine conjugates of newly synthesized primary bile acids, cholic acid (CA) and chenodeoxycholic acid (CDCA), were measured in the species capable of conjugating with taurine or glycine (cynomolgus). After total bile acid pool washout, monkeys were infused with human LDL or HDL labeled with free 14C-cholesterol, and the specific activities (SA) of biliary cholesterol and primary bile acid conjugates were determined. In both species, regardless of the lipoprotein infused, the SA of biliary cholesterol and CA were greater than those for total bile acids and CDCA, respectively. In cynomolgus, the SA of glycine conjugates was higher for CA than CDCA, while the SA of taurine conjugates was greater for CDCA than CA. Under these conditions, (i) infused lipoprotein free cholesterol (as either LDL or HDL) contributed more to biliary cholesterol than to bile acids and more to CA than to CDCA; (ii) glycine conjugated preferentially with CA rather than CDCA, while taurine was the preferred conjugate for CDCA.