Lipid solubilization in human gallbladder versus hepatic biles

BACKGROUND/AIMS: Cholesterol crystallizes more rapidly in gallbladder than in hepatic biles, supposedly due to formation of cholesterol-supersaturated vesicles in concentrated gallbladder biles because of preferential micellization of phospholipids compared to cholesterol. We therefore aimed to compare lipid solubilization in hepatic and gallbladder biles. METHODS: Mixed micellar and vesicular phases were separated from hepatic and associated gallbladder biles of seven cholesterol gallstone patients by using state-of-the-art gel filtration with bile salts at intermixed micellar/intervesicular compositions and concentrations in the eluant. RESULTS: Vesicles were found in 6 out of 7 hepatic biles, but only in 2 of the corresponding gallbladder biles. Both percentage (7.8+/-5.1 vs. 36.3+/-7.6%; p = 0.01) and amount (0.9+/-0.2 vs. 1.7+/-0.3 mM; p = 0.06) of vesicular cholesterol were lower in gallbladder biles. Similar results were found for vesicular phospholipids (1.3+/-0.8 vs. 11.6+/-6.0%; p = 0.05; and 0.3+/-0.1 vs. 1.1+/-0.5 mM; p = 0.07). The vesicular cholesterol/ phospholipid ratio was 1.7+/-0.5 in hepatic bile but 4.3 and 1.8 in the 2 gallbladder biles which contained vesicles. Mixed micelles in gallbladder biles had a higher cholesterol saturation index than mixed micelles in hepatic biles (1.43+/-0.11 vs. 1.15+/-0.07; p = 0.02). CONCLUSIONS: Concentration of bile in the gallbladder leads to decreased vesicular lipid contents. The finding of supersaturated mixed micelles in the absence of vesicles in a significant number of patients points to the possibility of non-vesicular modes of crystallization.     

Cholesterol nucleation from its carriers in human bile

This study was performed to determine whether biliary cholesterol nucleates primarily from vesicles or micelles. Twenty gallbladder biles and 12 hepatic biles from patients with gallstones as well as 16 model biles were examined. The nucleation times (days) of the biles as well as their isolated vesicular and micellar fractions were determined and their lipid composition was analyzed. In 41 of 46 comparisons, cholesterol nucleated faster from vesicles than micelles; in only one case was the opposite found. The mean (+/- S.D.) nucleation times of vesicles and micelles in gallbladder biles were 8.9 +/- 5.4 vs. 15.4 +/- 8.6, in hepatic biles 14.6 +/- 9.4 vs. 20.6 +/- 9.1, and in model biles 9.0 +/- 3.7 vs. 18.9 +/- 9.1 days, respectively. All these differences were significant (p less than 0.005). Gallbladder biles (n = 7) devoid of vesicles nucleated more slowly (9.0 +/- 9.5 days), as compared to gallbladder biles (n = 13) containing vesicles (3.8 +/- 2.2 days). The nucleation time of gallbladder and hepatic biles was significantly correlated with the nucleation time of the vesicles from these biles (r = 0.847, p less than 0.05). There was no correlation with the nucleation time of micelles from the same biles. The percentage of cholesterol carried by vesicles in bile was positively correlated to the molar percentage of biliary cholesterol and the cholesterol saturation index and negatively correlated to the molar percentage of bile salts. Our data suggest that phospholipid vesicles are the major vehicle for cholesterol precipitation in bile as well as an important determinant of the nucleation time of bile.     

Lipid solubilization in human gallbladder versus hepatic biles

Background/Aims: Cholesterol crystallizes more rapidly in gallbladder than in hepatic biles, supposedly due to formation of cholesterol-supersaturated vesicles in concentrated gallbladder biles because of preferential micellization of phospholipids compared to cholesterol. We therefore aimed to compare lipid solubilization in hepatic and gallbladder biles.Methods: Mixed micellar and vesicular phases were separated from hepatic and associated gallbladder biles of seven cholesterol gallstone patients by using state-of-the-art gel filtration with bile salts at intermixed micellar/intervesicular compositions and concentrations in the eluant.Results: Vesicles were found in 6 out of 7 hepatic biles, but only in 2 of the corresponding gallbladder biles. Both percentage (7.8±5.1 vs. 36.3±7.6%; p=0.01) and amount (0.9±0.2 vs. 1.7±0.3 mM; p=0.06) of vesicular cholesterol were lower in gallbladder biles. Similar results were found for vesicular phospholipids (1.3±0.8 vs. 11.6±6.0%; p=0.05; and 0.3±0.1 vs. 1.1±0.5 mM; p=0.07). The vesicular cholesterol/phospholipid ratio was 1.7±0.5 in hepatic bile but 4.3 and 1.8 in the 2 gallbladder biles which contained vesicles. Mixed micelles in gallbladder biles had a higher cholesterol saturation index than mixed micelles in hepatic biles (1.43±0.11 vs. 1.15±0.07; p=0.02).Conclusions: Concentration of bile in the gallbladder leads to decreased vesicular lipid contents. The finding of supersaturated mixed micelles in the absence of vesicles in a significant number of patients points to the possibility of non-vesicular modes of crystallization.     

Ultracentrifugation systematically overestimates vesicular cholesterol levels in bile

To accurately determine the cholesterol (Ch) distribution between mixed micelles and vesicles in lithogenic bile, both ultracentrifugation and gel chromatography with the correct intermixed micellar/vesicular bile salt concentration (IMC) have been proposed. We have systematically compared both separation techniques with physiological model biles to ascertain their quantitative separation ability. After determination of optimal ultra-centrifugation conditions in systems containing only micelles or vesicles, Ch-supersaturated model biles [3-10 g/dL, 10 mol percent Ch, taurocholate (TC)]/([TC + egg yolk phosphatidylcholine (EYPC)] = 0.6 and 0.7) were adjusted to a density of 1.03 g/mL, and ultracentrifuged at 42,000 rpm and 37 degrees C for 13 hours. Identical model biles were subjected to gel chromatography with the correct IMC, either directly or after remixing and incubation at 37 degrees C after ultracentrifugation. By ultracentrifugation, 31 percent +/- 2 percent (TC/(TC + EYPC) = 0.6) and 40 percent +/- 5 percent (TC/(TC + EYPC) = 0.7) of total Ch were found in vesicles (Ch/EYPC molar ratios = 1.0 and 1.3, respectively). However, by gel chromatography, only 19 percent +/- 2 percent (Ch/EYPC = 1.0) and 22 percent +/- 2 percent (Ch/EYPC = 1.5) of total Ch were found in the corresponding biles. Gel chromatography of biles (TC/(TC + EYPC) = 0.7) ultracentrifuged for various durations showed a progressive increase in vesicular Ch to 41 percent after 13 hours. On incubation for 11.5 hours after ultracentrifugation, vesicular Ch decreased to 31 percent, thus approaching the initial (gel chromatography) value. Quasielastic light scattering also demonstrated formation of vesicles in ultracentrifuged Ch-unsaturated model bile (cholesterol saturation index (CSI) approximately 0.97). As compared with gel chromatography, ultracentrifugation systematically elevates vesicular Ch, possibly because of induced shifts in lipids between lipid aggregates caused by variation in local bile salt concentration. Because ultracentrifugation can alter the phases present in bile, gel chromatography with the correct IMC more accurately represents the distribution of Ch in biliary lipid aggregates. (Hepatology 1996 Apr;23(4):896-903)     

Cholesterol and pigment gallstone disease: comparison of the reliability of three bile tests for differentiation between the two stone types

Gallbladder biles and stones were obtained at 116 cholecystectomies for symptomatic gallstone disease. All 33 patients younger than 50 years had cholesterol stones, whereas 40% of the older patients had pigment stones. We compared the reliability of three different bile tests for the differentiation between cholesterol and pigment stone patients. Whereas both the presence of cholesterol monohydrate crystals in fresh gallbladder bile and a nucleation time less than or equal to 20 days in ultrafiltered gallbladder bile had a specificity of 100% for cholesterol gallstone disease, biliary supersaturation with cholesterol (cholesterol saturation index greater than 1.0) had a low specificity. The sensitivity of nucleation time less than or equal to 20 days for cholesterol gallstone disease was 78% in concentrated gallbladder biles (biliary total lipid concentration greater than or equal to 5 g/dl) but only 21% in dilute biles (biliary total lipid concentration less than 5 g/dl). In contrast, examination for the presence of cholesterol crystals in fresh bile was reasonably sensitive both in concentrated and dilute gallbladder biles (sensitivity, 84% and 72%, respectively). In addition, duodenal bile obtained from 16 patients (10 cholesterol, 6 pigment) before cholecystectomy showed cholesterol crystals in 7 of the cholesterol but in none of the pigment stone patients. We conclude that examination of fresh bile for cholesterol crystals is a specific and reasonably sensitive test for cholesterol gallstone disease.     

Distribution of cholesterol between vesicles and micelles in human gallbladder bile: influence of treatment with chenodeoxycholic acid and ursodeoxycholic acid

The present study aimed at determining the relative distribution of cholesterol between the vesicular and micellar phases in gallbladder bile of gallstone patients (n = 23) and gallstone-free subjects (n = 7). Nine of the gallstone patients were treated with chenodeoxycholic acid and seven were treated with ursodeoxycholic acid, 15 mg/kg/day, for 3 wk before cholecystectomy. The vesicular and micellar fractions in bile were separated by sucrose density gradient ultracentrifugation, and a clear separation between the two phases was obtained. The vesicles were further identified by quasielastic light scattering spectroscopy and appeared to be of a uniform size with a mean hydrodynamic radius of 760 A. The proportion of cholesterol in the vesicular fraction was significantly higher in the untreated gallstone group (40% +/- 4%) compared with the gallstone-free (28% +/- 3%), ursodeoxycholic acid (28% +/- 3%) and chenodeoxycholic acid (18% +/- 4%) groups. Despite a low cholesterol saturation of bile in the latter three groups (88% +/- 12%, 51% +/- 9% and 65% +/- 5%, respectively), a considerable part of the biliary cholesterol was carried in the vesicular fraction. The cholesterol/phospholipid ratio in the vesicular fraction averaged between 0.49 and 0.58 in the gallstone, gallstone-free and chenodeoxycholic acid groups, whereas the ursodeoxycholic acid group had a significantly lower ratio of 0.24. The nucleation time of bile from the gallstone group was short (2 +/- 1 days) compared with the gallstone-free, chenodeoxycholic acid and ursodeoxycholic acid groups (23 +/- 3, 24 +/- 6 and 14 +/- 3 days, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pathways of cholesterol crystallization in model bile and native bile

Hypersecretion of hepatic cholesterol, chronic supersaturation of bile with cholesterol and rapid precipitation of cholesterol crystals in the gallbladder from cholesterol-enriched vesicles represent the primum movens in cholesterol gallstone formation. Physical-chemical factors and pathways leading to cholesterol crystallization can be investigated in artificial model biles and ex vivo in fresh human bile. Depending on modulatory factors (i.e., lipid concentration, bile salt or phospholipid species, humidity, mucins, etc.), cholesterol can precipitate in several forms (i.e., monohydrate, anhydrous) and habits (i.e., plate-like, needle-like, intermediate arcs, filaments, tubules, spirals). Careful analysis of biliary cholesterol crystals includes biochemical analysis of precipitated crystals, polarizing quantitative light microscopy, and turbidimetric methods. In this paper, recent concepts on cholesterol crystallization in artificial model biles as well as in human bile will be reviewed.     

Supersaturated bile from obese patients without gallstones supports cholesterol crystal growth but not nucleation

Cholesterol crystal formation was studied in gallbladder bile samples collected from 18 patients with cholesterol gallstones, 6 patients with black pigment stones, and 14 obese patients without gallstones. In the absence of seed crystals, bile from patients with cholesterol stones showed a much greater tendency to form cholesterol crystals in vitro than bile of similar cholesterol saturation from patients without cholesterol stones. The ability to form crystals was not related to the biliary hexosamine concentration, an indicator of mucin content. When small seed crystals of cholesterol monohydrate were added to each bile, the seed crystals dissolved in all biles (n = 8) with a cholesterol saturation index less than 0.76. In contrast, 29 of 30 biles with a cholesterol saturation index greater than 0.76 supported crystal growth, even when collected from patients without gallstones. These results indicate that the difference between supersaturated biles in the ability to form cholesterol crystals resides at the nucleation, rather than the growth, stage of crystal formation.     

Stabilization of biliary lipid particles by ursodeoxycholic acid

We evaluated the effect of ursodeoxycholic acid on the metastability of human bile as reflected by nucleation time and also assessed the mechanism of its action in an ultrastructural study. Ursodeoxycholic acid significantly prolonged the nucleation time of gallbladder bile from cholesterol gallstone patients without causing either drastic changes in the distribution of cholesterol between the nonmicellar and micellar fractions of bile or biliary choiesterol desaturation. Gel permeation chromatography resolved two distinct components of the nonmicellar fraction: vesicles and phospholipid lamellae (identified by electron microscopy). Nonmicellar cholesterol was predominantly carried by vesicles in the bile of untreated gallstone patients, whereas it was chiefly carried by phospholipid lamellae in patients treated with ursodeoxycholic acid. Furthermore, phospholipid lamellae from untreated gallstone patients showed rapid transformation and cholesterol microcrystal formation within seven days, whereas the lamellae from ursodeoxycholic acid-treated patients were stabilized and showed little change. On the other hand, biliary mucin concentration was reduced by the treatment with ursodeoxycholic acid. These findings suggest that ursodeoxycholic acid stabilizes phospholipid lamellae and consequently prolongs nucleation time. It is also possible that the reduction of biliary mucin plays a role in this process.     

Mucin and phospholipids determine viscosity of gallbladder bile in patients with gallstones

AIM: An increased viscosity of gallbladder bile has been considered an important factor in the pathogenesis of gallstone disease. Besides lipids and proteins, mucin has been suggested to affect the viscosity of bile. To further clarify these issues we compared mucin, protein and the lipid componEnts of hepatic and gallbladder bile and its viscosity in patients with gallstones. METHODS: Viscosity of bile (mPa.s) was measured using rotation viscosimetry in regard to the non Newtonian property of bile at low shear rates. RESULTS: Biliary viscosity was markedly higher in gallbladder bile of patients with cholesterol (5.00 +/- 0.60 mPa.s, mean +/- SEM, r= 28) and mixed stones (3.50 +/- 0.68 mPa.s; r= 8) compared to hepatic bile (0.92 +/- 0.06 mPa.s, r= 6). A positive correlation between mucin and viscosity was found in gallbladder biles (r = 0.65; P < 0.001) but not in hepatic biles. The addition of physiologic and supraphysiologic amounts of mucin to gallbladder bile resulted in a dose dependent non linear increase of its viscosity. A positive correlation was determined between phospholipid concentration and viscosity (r = 0.34, P < 0.005) in gallbladder biles. However, no correlation was found between total protein or the other lipid concentrations and viscosity in both gallbladder and hepatic biles. CONCLUSION: The viscosity of gallbladder bile is markedly higher than that of hepatic bile in patients with gallstones. The concentration of mucin is the major determinant of biliary viscosity and may contribute by this mechanism to the role of mucin in the pathogenesis of gallstones.     

Role of high total protein in gallbladder bile in the formation of cholesterol gallstones

While it is generally accepted that cholesterol supersaturation of bile is of key importance in the rapid formation of cholesterol crystals, the role of total biliary protein and pH in the pathogenesis of cholesterol gallstones is less well understood. The relation of cholesterol saturation, total protein, and pH was studied in 73 gallbladder bile samples with and 35 gallbladder bile samples without cholesterol crystals. In samples containing crystals, a trend to higher values of cholesterol and to a higher cholesterol saturation index was observed. However, significantly (P = 0.02) higher concentrations of total protein were found in samples with crystals [0.80 +/- 0.40 g/dL (8.0 +/- 4.0 g/L)] than in samples without crystals [0.63 +/- 0.26 g/dL (6.3 +/- 2.6 g/L)]. Moreover, of 22 bile samples with total protein concentrations greater than 10.0 g/L, cholesterol crystals were detected in all but 2. Total lipids, bile acids, phospholipids, and pH values were not significantly different in the two groups of bile samples. It was concluded that high biliary protein concentrations are frequently associated with cholesterol crystals and may, therefore, be a possible risk factor in the pathogenesis of cholesterol gallstones.     

Effect of phospholipids and their molecular species on cholesterol solubility and nucleation in human and model biles.

Much research in the pathophysiology of gall stones has been devoted to various molecular species of bile salts. Recent findings have shown the importance of phospholipids in biliary pathophysiology. In the present study the addition of increasing doses of egg lecithin to human and model biles progressively prolonged the nucleation time. Concurrently biliary cholesterol was shifted from the vesicular to the non-vesicular carrier(s) while the cholesterol/phospholipid ratio of the remaining vesicles was progressively lowered. Model bile solutions of identical lipid concentration were prepared using phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine as the only phospholipid. With phosphatidylethanolamine most of the cholesterol was shifted to the vesicular carrier while phosphatidylserine shifted most of the cholesterol to the non-vesicular carrier(s). With phosphatidylcholine the cholesterol was distributed in both carriers. Phosphatidyl choline species composed of various acyl fatty acids in the sn-1 and sn-2 positions were used as the sole phospholipid in otherwise identical model bile solutions. With palmitic acid in the sn-1 position and arachidonic acid in the sn-2 position most of the cholesterol was found in the non-vesicular carrier. When stearic acid was used in sn-2 position instead of arachidonic acid most of the cholesterol was found in the vesicular carrier. These and other variations in phospholipid molecular species shifted cholesterol among its carriers and also modified the nucleation time of model biles. Most of these effects were also found upon addition of the various phospholipid species to human biles. These findings show the importance of phospholipid species in biliary pathophysiology and may be useful when trying to manipulate cholesterol carriers and solubility in bile.     

Diurnal variation in cholesterol metastability of hepatic bile and its acute modulation with ursodeoxycholic acid in humans.

We studied the alteration of cholesterol metastability of hepatic bile caused by diurnal variations in hepatic biliary lipid excretions and acutely induced changes following ursodeoxycholic acid (UCDA) administration. Hepatic bile was collected at 6-h intervals for 24 h from 6 patients with an indwelling choledochal drainage before and after UDCA administration. A basal diurnal variation showed the highest cholesterol saturation index (p < 0.05) and cholesterol distribution in vesicles (p < 0.01) and the shortest nucleation time (p < 0.05) in the early morning. After the ingestion of ursodeoxycholic acid for 1 day, early morning biliary cholesterol concentrations were reduced. Interestingly, significant decreases in vesicular cholesterol concentrations (1.0 +/- 0.2 to 0.1 +/- 0.04 mM, p < 0.01) and in the vesicular cholesterol/phospholipid ratio (1.6 +/- 0.1 to 0.7 +/- 0.1, p < 0.05) were associated with prolongation of the nucleation time (11.5 +/- 1.2 to 18.7 +/- 1.5 days, p < 0.01). Biliary protein had no diurnal variations and did not decrease significantly with UCDA. These results indicate that during a day the early morning hepatic bile is the most unstable and that UCDA acutely enhances hepatic biliary metastability mainly by decreasing the rate of vesicular cholesterol saturation.     

Decreased protein concentration and improved metastability of bile induced by ursodeoxycholate

Previous studies demonstrated that higher biliary protein is associated with reduced metastability of bile. This study attempted to examine the induced effect of ursodeoxycholate on metastability of bile by measuring the nucleation time and biliary protein in cholesterol gallstone patients. Thirty-seven patients with functioning gallbladders were studied 10 control patients without gallstones and 27 with cholesterol gallstones. Ten of 27 cholesterol gallstone patients were treated with ursodeoxycholate (600 mg/ day) prior to surgery. Twelve of 17 untreated gallstone patients had cholesterol crystals in gallbladder bile while cholesterol crystals were absent in the ursodeoxycholate-treated gallstone patients and in the controls. Total protein concentration and cholesterol saturation index were significantly greater in the untreated gallstone patients with crystals than in those without crystals in bile. The treatment with ursodeoxycholate significantly decreased biliary protein concentration and cholesterol saturation index associated with the prolonged nucleation time. Cholesterol nucleation time correlated with biliary total protein concentration and cholesterol saturation index but not with total lipid concentration. It is concluded from the present study that ursodeoxycholate decreases biliary protein thereby partly increasing metastability of gallbladder bile.     

Matrix metalloproteinase inhibition protects rat livers from prolonged cold ischemia-warm reperfusion injury

Although many putative sterol transporters influencing cholesterol absorption and physical-chemical factors affecting dietary cholesterol absorption have been extensively investigated, it is still unclear how biliary cholesterol contributes to the regulation of intestinal cholesterol absorption. We studied whether the gallbladder can modulate the microaggregates of cholesterol carriers, which may in turn influence the intestinal absorption of biliary cholesterol. Supersaturated, crystallized, or micellar model biles were delivered via a duodenal catheter to conscious, freely moving C57L mice daily for 2 days. Intestinal uptake and absorption of biliary cholesterol and its fecal excretion, as well as expression levels of intestinal sterol transporters, were analyzed. Cholesterol uptake and absorption by the enterocyte were dramatically reduced in mice treated with crystallized biles compared with supersaturated biles. This correlated with the higher cumulative radioactivity of cholesterol recovered in the feces at 24 hours. Such findings were absent with the added reference compound sitostanol. After removing cholesterol crystals from crystallized biles, micellar biles showed essentially identical effects on intestinal absorption but with lower fecal cholesterol excretion compared with the original samples containing crystals. Expression levels of the jejunal Abcg5 (ATP-binding cassette transporter G5) and Abcg8, but not Npc1l1 (Niemann-Pick C1 like 1), were significantly increased by supersaturated biles compared with crystallized biles. CONCLUSION: Different physical forms of biliary cholesterol dramatically determine intestinal uptake and absorption of cholesterol. Solid plate-like cholesterol monohydrate crystals in bile are probably not absorbed and are totally excreted in feces from the body. The gallbladder may have a role in regulating cholesterol homeostasis by modulating the physical forms of biliary cholesterol.     

Decreased protein concentration and improved metastability of bile induced by ursodeoxycholate.

Previous studies demonstrated that higher biliary protein is associated with reduced metastability of bile. This study attempted to examine the induced effect of ursodeoxycholate on metastability of bile by measuring the nucleation time and biliary protein in cholesterol gallstone patients. Thirty-seven patients with functioning gallbladders were studied 10 control patients without gallstones and 27 with cholesterol gallstones. Ten of 27 cholesterol gallstone patients were treated with ursodeoxycholate (600 mg/day) prior to surgery. Twelve of 17 untreated gallstone patients had cholesterol crystals in gallbladder bile while cholesterol crystals were absent in the ursodeoxycholate-treated gallstone patients and in the controls. Total protein concentration and cholesterol saturation index were significantly greater in the untreated gallstone patients with crystals than in those without crystals in bile. The treatment with ursodeoxycholate significantly decreased biliary protein concentration and cholesterol saturation index associated with the prolonged nucleation time. Cholesterol nucleation time correlated with biliary total protein concentration and cholesterol saturation index but not with total lipid concentration. It is concluded from the present study that ursodeoxycholate decreases biliary protein thereby partly increasing metastability of gallbladder bile.     

Ursodeoxycholic acid decreases viscosity and sedimentable fractions of gallbladder bile in patients with cholesterol gallstones

OBJECTIVES: Ursodeoxycholic acid (UDCA) therapy is associated with reduced risk of biliary pain and acute cholecystitis or pancreatitis in patients with cholesterol gallstones. The underlying mechanisms are understood incompletely, which prompted us to study the influence of UDCA treatment on composition, viscosity and sedimentable fractions of gallbladder bile in 25 patients with symptomatic cholesterol gallstones. METHODS: In two randomised groups, either UDCA (750 mg daily) or placebo was given to each patient 10-12 days before cholecystectomy. Gallbladder bile was collected intraoperatively and analysed for protein, mucin, lipid composition, cholesterol crystal observation time, amount of cholesterol in vesicles, viscosity and sedimentable fractions (cholesterol, protein, mucin, bilirubin). RESULTS: UDCA-treated patients showed longer cholesterol crystal observation times and lower concentrations of total cholesterol and percentages of vesicular cholesterol in gallbladder bile. The concentrations of protein and mucin in gallbladder bile tended to be lower in the UDCA-treated group, but phospholipids, bile acids and bilirubin did not differ between the groups. Viscosity and the total sedimentable fractions of gallbladder bile decreased in the UDCA-treated patients. CONCLUSIONS: UDCA treatment reduces total and vesicular cholesterol, the formation of cholesterol crystals, viscosity, and the total amount of sedimentable fractions in gallbladder bile. These observations might explain, at least partially, why UDCA treatment attenuates the occurrence of biliary pain and complications in gallstone patients.     

The effect of bilirubin on biliary lipid secretion: analysis by horseradish peroxidase associated intrahepatic vesicular transport system

The mechanism of biliary lipid secretion is still controversial and there is no definite information regarding how bilirubin inhibits biliary phospholipid and cholesterol secretions without affecting bile salt secretion. In this study, the effects of bilirubin on intrahepatic vesicular transport and biliary lipid secretion were examined using bile-fistula rats. Horseradish peroxidase (HRP) was used as a tracer of intrahepatic vesicular transport. Bilirubin (5 mg/100 g BW) and/or HRP (5 mg/100 gBW) were injected through the mesenteric vein. Bile flow, biliary bile acid, biliary phospholipid and cholesterol outputs were examined in saline, HRP and HRP + bilirubin groups, respectively. Bile flow and biliary bile acid output were not affected by bilirubin administration. Biliary phospholipid and cholesterol as well as biliary HRP outputs were inhibited just after bilirubin administration, 42.8 +/- 6.1 SD% 47.7 +/- 5.1 SD%, and 33.4 +/- 3.8 SD%, respectively. These results suggested the participation of intrahepatic vesicular transport system in the inhibition of biliary lipid secretion by bilirubin and in its secretory mechanism.     

Low-dose ursodeoxycholic acid prolongs cholesterol nucleation time in gallbladder bile of patients with cholesterol gallstones

The high rate of stone recurrence represents a drawback of non-surgical therapy of cholesterol gallstone disease. Although most studies report that long-term bile acid treatment does not have protective effects, preliminary results suggest that low-dose ursodeoxycholic acid decreases the rate of gallstone recurrence in a subgroup of younger patients. To clarify the underlying mechanism we investigated whether low-dose ursodeoxycholic acid treatment influences biliary cholesterol saturation and/or nucleation time of cholesterol. Ten patients with cholesterol gallstones and functioning gallbladder received 250 mg ursodeoxycholic acid/day at bedtime 6-10 days prior to cholecystectomy. Eleven patients with cholesterol gallstones without treatment served as controls. Cholesterol crystals were present in the gallbladder bile of 7 out of the 10 patients receiving ursodeoxycholic acid and in all control biles. Ursodeoxycholic acid treatment significantly (P less than 0.02) decreased the cholesterol saturation index (mean +/- S.E.: 0.94 +/- 0.05 vs. 1.43 +/- 0.18) and led to an approximately 5-fold prolongation (P less than 0.005) of the cholesterol nucleation time (mean +/- S.E.: 12.0 +/- 2.4 vs. 2.3 +/- 0.7 days). We conclude that low-dose ursodeoxycholic acid might be effective in the prevention of post-dissolution gallstone recurrence by both decreasing cholesterol saturation and prolonging cholesterol nucleation time.     

Role of bile salt hydrophobicity in distribution of phospholipid species to carriers in supersaturated model bile solutions

BACKGROUND: Phospholipid species modulate cholesterol-holding capacity and, therefore, regulate bile metastability. METHODS: In this study, we investigated the effect of bile salt hydrophobicity on the distribution of phospholipids among lipid particles in supersaturated model bile solutions (total lipid concentration, 9 g/dL; taurocholate/phospholipid ratio 3.0, cholesterol saturation index 1.3), by using gel permeation chromatography. RESULTS: With an increase of bile salt hydrophobicity in the elution buffer, the uptake of cholesterol and phospholipids into bile salt micelles was increased, associated with an increased cholesterol/phospholipid molar ratio of the vesicles. In contrast, there was an inverse correlation between the hydrophobicity of the phospholipid species in the vesicles and that of bile salts in the elution buffer, suggesting that hydrophobic bile salts induced preferential uptake of hydrophobic phospholipids into bile salt micelles, while less hydrophobic phospholipids, with a relatively low cholesterol-holding capacity, remained in the vesicles. CONCLUSIONS: These data indicate that bile salt hydrophobicity regulates vesicular cholesterol metastability by modulating the hydrophobicity of phospholipids in vesicles, as well as the lipid distribution among various biliary lipid particles.