Biliary proteins. Unique inhibitors of cholesterol crystal nucleation in human gallbladder bile

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.

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.

Effects of bile salt and phospholipid hydrophobicity on lithogenicity of human gallbladder bile

Increased biliary bile salt and phospholipid hydrophobicity may promote nucleation of cholesterol crystals and gallstone formation. We therefore compared bile salt composition (determined by gas-liquid chromatography) in patients with cholesterol (n = 35) and pigment (n = 16) gallstones (group A). Bile salt composition and cumulative bile salt hydrophobicity index were not different between both stone types. Hydrophobicity index or % of individual bile salts did not correlate with cholesterol saturation index or nucleation time. In an additional 21 cholesterol stone patients (group B) biliary bile salt and phospholipid hydrophobicity as determined by high-pressure liquid chromatography did not correlate with cholesterol saturation index or nucleation time. In both group A and group B, cholesterol stone patients with cholesterol crystals in their fresh biles had a higher % deoxycholic acid, a lower % cholic acid and a higher bile salt hydrophobicity index than crystal-negative patients. This study indicates the need for further research on the role of bile salt hydrophobicity in the pathogenesis of gallstones.

Development and validation of a quantitative assay for cholesterol crystal growth in human gallbladder bile

Crystal observation time is a rough estimate of the first microscopic appearance of cholesterol monohydrate crystals in an isotropic bile, and does not provide information on crystal growth kinetics. We have developed a method for quantitating cholesterol crystal growth in gallbladder bile. Crystals were separated from other biliary particles by ultracentrifugation on a discontinuous NaBr gradient, after bile density adjustment to d = 1.060 g/ml. More than 95% of crystals, both of native or synthetic source, floated in the density range 1.045-1.055. This density fraction was collected and crystal mass was measured by photometric turbidity, after calibration with suspensions of different-sized cholesterol crystals. The recovery of crystals added to original bile samples averaged 96.0 +/- 2.8%. Contamination with vesicles, which may potentially interfere with the turbidimetric assay, was excluded by gel-chromatography. The method was sequentially applied, until the 20th day of incubation, to biles obtained at surgery from patients with (A, n = 6) or without cholesterol gallstone (B, n = 4), and from gallstone patients pretreated for 1 week with oral ursodeoxycholic acid (C, n = 5). Crystal growth curves greatly differed, being much steeper in group A and almost flat in patients receiving ursodeoxycholic acid. The mean percent mass of biliary cholesterol in crystalline form at the 20th day was 19.2 +/- 13.5%, 1.2 +/- 0.8% and 2.7 +/- 1.1% in A, B and C, respectively (A vs. B: P = 0.014; A vs. C: P = 0.008). We conclude that the method allows a precise estimate of cholesterol crystal growth and can be usefully applied to human gallbladder biles.

The effect of bile acid hydrophobicity on nucleation of several types of cholesterol crystals from model bile vesicles

Nucleation of cholesterol crystals is thought to occur from cholesterol-phospholipid vesicles. We tested the hypothesis that bile acids are necessary for nucleation of cholesterol crystals. Model bile vesicles were prepared by KBr density ultracentrifugation of supersaturated model bile and mixed with one of the following bile acids: ursodeoxycholate, taurocholate, cholate, chenodeoxycholate or deoxycholate in final concentrations of 3, 30 and 100 mM. Vesicles were also mixed with various combinations of ursodeoxycholate and deoxycholate. Nucleation was assessed semi-quantitatively with polarizing microscopy. After 5 days, samples were again subjected to ultracentrifugation. Addition of 3 and 30 mM taurocholate, cholate, chenodeoxycholate and deoxycholate to vesicles induced nucleation. The extent of nucleation increased significantly with increasing bile acid hydrophobicity: deoxycholate > chenodeoxycholate > cholate > taurocholate (p < 0.05). At 100 mM bile acid this order was reversed (p < 0.05) because most of the cholesterol was solubilized in micelles as shown by ultracentrifugation after 5 days. Percentages of vesicular cholesterol decreased with increasing hydrophobicity: deoxycholate < chenodeoxycholate < cholate < taurocholate (p < 0.05). Ursodeoxycholate did not induce nucleation. At least seven cholesterol crystal shapes could be distinguished and all crystal types could be found after addition of various combinations of ursodeoxycholate+deoxycholate. We conclude that in this model: (a) bile acid species play an important role in the precipitation of cholesterol crystals from model bile vesicles; (b) the more hydrophobic bile acids induce more cholesterol crystal precipitation; and (c) the hydrophobicity of bile acids influences cholesterol crystal morphology.

Direct visualization of lipid aggregates in native human bile by light- and cryo-transmission electron-microscopy

The evolution of microstructures present in human gallbladder and hepatic bile was observed simultaneously by video-enhanced light microscopy (VELM) and transmission electron microscopy of vitrified specimens (cryo-TEM), as a function of time after withdrawal from patients. Fresh centrifuged gallbladder bile samples contained small (6 nm) spherical micelles in coexistence with vesicles (40 nm). Out of the seven bile samples investigated four contained, in addition, two types of elongated aggregates that have not been previously described. Uncentrifuged gallbladder bile also contained a mixture of ribbon- and plate-like crystals seen by VELM, but not by cryo-TEM. In aged (3-6-week-old) gallbladder bile samples VELM also revealed spiral and helical crystal structures. No such crystals were present in hepatic bile samples, although microcrystals, not observable by VELM were seen by cryo-TEM in addition to micelles and vesicles. The similarity of these observations to those observed in bile models lends strong support for the validity of the model systems. Furthermore, the presence of microcrystals in hepatic bile samples, apparently devoid of crystals by light microscopy, indicates that under certain conditions the common criterion of 'nucleation time' (NT), based on light microscopy, does not represent the real time of nucleation. In the human bile samples investigated in this study the dissociation between NT and the time of observation of microcrystals was seen in hepatic but not in gallbladder bile samples. Hence, crystal growth may be rate limiting only in dilute biles.

Human gallstones contain pronucleating nonmucin glycoproteins that are immunoglobulins

OBJECTIVE

Pronucleating nonmucin glycoproteins in human cholesterol and black gallstones were isolated and identified.

SUMMARY BACKGROUND DATA

Gallbladder bile contains nonmucin glycoproteins that are pronucleating of cholesterol monohydrate crystals. Little is known about the presence or activity of these proteins within gallstones.

METHODS

Nonmucin glycoproteins were isolated from single cholesterol (n = 8), multiple cholesterol (n = 8), and black pigment (n = 8) gallstones by concanavalin A lectin-affinity chromatography. The proteins were separated by sodium dodecyl sulfate gradient electrophoresis. Western blot analysis was performed for Fab immunoglobulin fragments, and heavy chains from the immunoglobulin G, A, E, and M subclasses. A crystal observation time assay was performed on the combination of isolated nonmucin glycoproteins from gallstones and isolated Fab fragments.

RESULTS

Nonmucin glycoproteins of molecular weights 10, 15, 17, 22, 28, and 208 kD were identified in gallstones. These six nonmucin glycoproteins shortened the crystal observation time by more than 50% (p < 0.01) compared with model bile. Western blot analysis confirmed the identity of the 22- and 28-kD proteins as immunoglobulin Fab fragments. These were seen in all gallstones, irrespective of the gallstone type. The isolated Fab 28-kD fragment from the gallstones of 23 patients shortened the extrapolated crystal observation time by 78% (p < 0.01). However, commercially available Fab fragments had no effect on either cholesterol crystal appearance or growth.

CONCLUSIONS

Nonmucin glycoproteins that are pronucleating for cholesterol monohydrate crystals are also found in human cholesterol and black pigment gallstones. Fab immunoglobulin fragments were found in all gallstones irrespective of the gallstone type. Fab immunoglobulin fragments from gallstones shortened the crystal observation time but not crystal growth or total crystal content compared with model bile or commercially available Fab fragments. These data suggest that an antigen-immune (Fab) complex may contribute to cholesterol crystal function.

Identification of human biliary alpha 1-acid glycoprotein as a cholesterol crystallization promoter

BACKGROUND/AIMS

We have recently outlined the biochemical features of a human 42-kilodalton biliary glycoprotein that shows concentration-dependent cholesterol crystallization-promoting activity. The goal in this work was to establish its identity and to examine some aspects of its biochemical properties relative to its activity.

METHODS

Internal amino acid sequencing following tryptic digestion was performed. Based upon this result, immunoreactivity against the 42-kilodalton glycoprotein was examined using a relevant antibody. With the same antibody, the 42-kilodalton glycoprotein was isolated from bile and assayed for activity. Sequential enzymatic deglycosylation of successive terminal glycans of the purified glycoprotein was performed, and the effects on both reductions in molecular radius (M(r)) and on comparative promoter activities were examined.

RESULTS

Both amino acid sequence and immunochemical data identify the 42-kilodalton glycoprotein as a biliary form of alpha 1-acid glycoprotein. When purified by immunoaffinity chromatography, potent promoting activity shown was proportionately reduced by successive removal of terminal glycans that also reduced the M(r)s.

CONCLUSIONS

The 42-kilodalton cholesterol crystallization-promoting glycoprotein is now identified as a biliary form of alpha 1-acid glycoprotein. Further, some aspects of the important role of glycans in this extensively glycosylated protein have been explored.

Total protein in common duct bile measured by acetonitrile precipitation and a micro bicinchoninic acid (BCA) method

Bile protein assays are complicated due to interference by other bile substances. In the present study we describe a microtiter plate method for the purification and quantification of bile proteins. The method is based on addition of acetonitrile in three steps to reconstituted freeze-dried bile, followed by ethanol washing of the precipitated proteins. Finally, protein in the precipitate is quantitated by two-point colour development using micro BCA reagents. Overall recoveries of protein in reconstituted bile spiked with exogenous protein (Seronorm) ranged from 91.0% (coefficient of variation; CV = 7.0%) to 97.1% (CV = 2.4%) by recoveries of 125I-Fibrinogen and 125I-Albumin. Bile pigments were largely removed during precipitation and washing, as verified by high pressure liquid chromatography (HPLC). Preferably the samples should be freeze-dried initially, as this lowered the blank readings. Two-point colour development with the BCA reagents were identical for standards assayed directly and standards added to protein depleted bile, and processed through all steps. Hence, no interference by either residual bile constituents nor the reagents upon the BCA protein assay could be detected. Standard curves ranged from 0.05 to 5.0 gl-1 (r > 0.98). Within day reproducibility (n = 15) was 7.8% (CV) and day to day (n = 10) was 12.1% (CV). Mean protein concentration in common duct bile from 30 patients was 1.20 gl-1 (range 0.34-3.87 gl-1). The method appears suitable for assay of bile protein, requires only limited sample volumes and allows processing of many samples within a short time.

Age, sex and source of hamster affect experimental cholesterol cholelithiasis

In the present study, we examined the effect of the following factors on a hamster model of cholesterol cholelithiasis: (i) the source of the golden Syrian hamsters (Sasco, Omaha, NE or Charles River, Wilmington, MA), (ii) the sex of the experimental animals and (iii) their age (4 wk vs. 8 wk of age). All hamsters were fed a semipurified diet which contained cholesterol (0.3%) and palmitic acid (1.2%). No cholesterol gallstones formed in any of the female hamsters regardless of age or source. The 4-week-old male hamsters from Sasco had the greatest incidence of gallstones (93%). The 8-week-old male hamsters tended to have a lower incidence of cholesterol gallstones than the younger ones, regardless of the commercial supplier (67 vs. 93% for Sasco and 27 vs. 40% for Charles River). Female hamsters had higher liver and serum cholesterol levels than the male hamsters; Charles River hamsters had lower serum cholesterol concentrations than the Sasco animals. Total biliary lipid concentrations were highest in Sasco male hamsters, but biliary cholesterol (mol%) was lower in the males than in the females (4.2-4.5% vs. 6.1-7.1%) regardless of age. The cholesterol saturation indices were higher in the Sasco females than the corresponding males; these values were lower in the Sasco hamsters than the Charles River animals, regardless of age or sex. The male Sasco hamsters had a higher total biliary bile acid concentration (98.9 mg/mL) than the Sasco females (58.9 mg/mL) and the Charles River animals (24.6 mg/mL for males and 38.2 mg/mL for females). The percentage of chenodeoxycholic acid in bile was significantly lower, and the percentage of cholic acid was higher in all females as compared to males.(ABSTRACT TRUNCATED AT 250 WORDS)

Congenital dyserythropoietic anaemia type II (HEMPAS) and its molecular basis

Congenital dyserythropoietic anaemia type II (CDA II) is a rare genetic anaemia in humans, inherited in an autosomally recessive mode. CDA II is also called HEMPAS as this disease is characterized by hereditary erythroblastic multinuclearity with positive acidified serum lysis test. Analyses of CDA II erythrocyte membranes showed that the band 3 glycoprotein is underglycosylated. An aberrant glycosylation pattern is seen in the polylactosamine carbohydrates which are normally attached to the band 3 and band 4.5 glycoproteins. The polylactosamines are, however, accumulated in the form of glycolipids. Therefore a genetic factor in CDA II appears to block the glycosylation of protein acceptors and shift these carbohydrates to the lipid acceptors. Structural analysis of CDA II band 3 carbohydrates identified truncated hybrid-type oligosaccharides and suggests that the Golgi glycosylation enzyme(s), alpha-mannosidase II or N-acetylglycosaminyltransferase II is defective in CDA II. By using a cDNA probe for alpha-mannosidase II, one CDA II case has been identified as being defective in the gene encoding alpha-mannosidase II. At present, it is not clear whether CDA II is a genetically heterogenous collection of glycosylation deficiencies, or genetically homogenous but apparently heterogenous in phenotype expression. Freeze-fracture electron microscopy and immunoelectron microscopy revealed that the band 3 glycoproteins are clustered in CDA II erythrocyte membranes. The abnormal distribution of band 3 might cause an unstable membrane organization. In CDA II erythroblasts, the membrane proteins might also be underglycosylated and abnormally distributed. When normal erythroblasts were cultured in vitro in the presence of swainsonine (alpha-mannosidase inhibitor) the erythroblasts became multinucleared. It is, therefore, quite possible that the enzymic defect of alpha-mannosidase II could cause various morphological anomalies including multinuclearity. Because the genes encoding glycosylation enzymes are housekeeping genes, the enzyme defect of CDA II is not restricted to erythroid cells and there is also an abnormal glycosylation of hepatocyte glycoproteins. On the other hand, there are many types of cells and tissues which appear not to be affected by the CDA II defect. A mechanism for the erythroid-specific manifestation of CDA II and its tissue specificity are also discussed.

Reduced cholesterol metastability of hepatic bile and its further decline in gall bladder bile in patients with cholesterol gall stones

The reduced metastability of biliary cholesterol in the gall bladder bile of patients with cholesterol gall stones has been well shown. The purpose of this study was to examine the hypothesis that such a difference in metastability already exists in hepatic bile. Paired hepatic and gall bladder bile samples were collected from 10 patients with cholesterol gall stones and six patients without gall stones. Cholesterol nucleation time, biliary lipid concentration, vesicular cholesterol distribution, and biliary protein concentration were measured and compared. The nucleation time in the hepatic bile of patients with cholesterol gall stones was significantly shorter than the gall stone free patients (8.2 (7.2) v 15.7 (5.8) days, p < 0.05), and was associated with a greater concentration of biliary lipid despite the lack of a difference in the cholesterol saturation index (CSI) and total protein concentration. During the storage of bile in the gall bladder, the nucleation time became quicker in the patients with cholesterol gall stone (2.9 (1.7) days) while it was similar in the gall stone free patients (17.3 (5.7) days) compared with that of the corresponding hepatic bile. These differences were associated with a higher CSI (1.44 (0.33) v 1.13 (0.14), p < 0.05) and a greater vesicular cholesterol distribution (19.7 (11.9) v 4.4 (1.4)%, p < 0.01) in the patients with cholesterol gall stones than the gall stone free patients. The concentrations of total lipid and protein in gall bladder bile were not significantly different between the two groups. In conclusion, patients with cholesterol gall stones produce less metastable hepatic bile by the evidence of shorter nucleation time. During the storage of the bile in the gall bladder, the metastability is reduced further only in the cholesterol gall stone patients but not in the gall stone free patients.

Bile concentration promotes nucleation of cholesterol monohydrate crystals by increasing the cholesterol concentration in the vesicles

Cholesterol in bile is solubilized in mixed micelles and cholesterol-phospholipid vesicles. Biliary cholesterol supersaturation and increased concentration of bile in the gallbladder promotes nucleation of cholesterol monohydrate crystals and gallstone formation, possibly by creating unstable vesicles with a high cholesterol/phospholipid ratio. In the present study super-saturated and unsaturated biles (cholesterol saturation index (CSI) 1.4 and 0.8 respectively) were prepared with concentrations typical of gallbladder and more dilute hepatic bile (total lipid concentration (TLCo) 10 and 2.5 g dl-1 respectively). The distribution of cholesterol between vesicles and micelles, and vesicular cholesterol/phospholipid ratio were studied using ultracentrifugation and gel-permeation chromatography. The nucleation time of cholesterol crystals was determined in whole model bile, and in the vesicular and micellar peak fractions. Increased CSI and bile dilution led to an increased proportion of cholesterol solubilized in vesicles. The concentration of bile did not influence vesicular cholesterol/phospholipid ratio. The vesicular cholesterol/phospholipid ratio found in gel-permeation chromatography experiments was similar at high and low CSI, whereas the ratio was significantly higher in supersaturated than in unsaturated biles in ultracentrifugation studies. Nucleation of cholesterol crystals from whole model bile was more rapid at the higher bile concentration and higher cholesterol saturation. Nucleation time in whole model bile correlated significantly with nucleation time in the corresponding vesicular peak fraction obtained by gel-permeation chromatography (r = 0.58: P < 0.01) and with the cholesterol concentration in this vesicular peak (r = -0.77; P < 0.002) but not with vesicular peak cholesterol/phospholipid ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Stabilization of biliary lipid particles by ursodeoxycholic acid. Prolonged nucleation time in human gallbladder bile

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 cholesterol 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.

Apolipoprotein A-I stabilizes phospholipid lamellae and thus prolongs nucleation time in model bile systems: an ultrastructural study

To explore the mechanisms whereby apolipoprotein A-I inhibits the nucleation of cholesterol crystals, we performed an ultrastructural study using supersaturated model bile systems. Vesicles, micelles and phospholipid lamellae were consistently separated by gel permeation chromatography either in the absence or presence of apolipoprotein A-I. Furthermore, apolipoprotein A-I coeluted with phospholipid lamellae. A sequential study using transmission electron microscopy revealed that phospholipid lamellae without apolipoprotein A-I showed a rapid transformation, with formation of multilamellae and fusion followed by microcrystal nucleation. In contrast, lamellae with apolipoprotein A-I showed little transformation. In conclusion, apolipoprotein A-I stabilizes the phospholipid lamellae, thereby inhibiting the nucleation of cholesterol crystals in supersaturated model bile systems.

Isolation of a human biliary glycoprotein inhibitor of cholesterol crystallization

BACKGROUND

About 50% of populations in developed countries have bile supersaturated with cholesterol, which is a major risk factor for cholesterol gallstone formation. Despite the prevalence of supersaturated bile, only about 10% of these populations develop gallstones. The existence of a biliary protein that inhibits cholesterol crystallization was hypothesized to explain this discrepancy. This report outlines the purification and characterization of such a human biliary glycoprotein.

METHODS

Chromatographic methods were used for separation and characterization. Additional steps included activity analysis by crystal growth assay, electrophoresis, and deglycosylation.

RESULTS

The glycoprotein consists of a heterodimer, M(r) of 120 kilodalton, with subunits of M(r) of 63 kilodalton and 58 kilodalton. Each of the subunits is characterized by an isoelectric point of 6.6 and shows comparable inhibitory activity. Deglycosylation of the subunits show that they share a similar polypeptide backbone (M(r) of 35 kilodalton) based upon a highly similar amino acid profile. This suggests that differential subunit glycosylation alone may account for the apparent heterodimeric structure.

CONCLUSIONS

No other human biliary glycoprotein has been found thus far that shows cholesterol crystal growth-inhibiting activity. Thus, it may be of importance in preventing gallstone formation in healthy populations.

Isolation and characterization of a cholesterol crystallization promoter from human bile

BACKGROUND

Recent studies on the pathogenesis of cholesterol gallstone disease have focused on the potential importance of an imbalance between biliary proteins having either inhibitory or promoting activities on nucleation and/or growth of cholesterol crystals as the initial stage in stone formation. The current study describes the purification and partial characterization of a 42-kilodalton biliary glycoprotein that shows concentration-dependent cholesterol crystallization-promoting activity.

METHODS

Chromatographic methods were used for separation and purification. Characterization steps included electrophoresis, deglycosylation, amino acid and carbohydrate analysis, and activity analysis by crystal growth assay.

RESULTS

The 42-kilodalton purified glycoprotein is an extensively glycosylated (37%) monomer with an acidic isoelectric point (pl < 4.1) that is probably based on the sialic acid content of the carbohydrate moiety. Enzymatic N-deglycosylation removes the carbohydrate moiety and inactivates the promoting activity. Furthermore, enzymatic proteolysis results in both its complete structural degradation and functional inactivation. Although the glycoprotein was isolated from normal human gallbladder biles, its presence in gallstone-associated samples is clearly shown.

CONCLUSIONS

This report outlines biochemical features of a human biliary glycoprotein that may be of major pathophysiological significance in gallstone disease.

Nucleation time and fatty acid composition of lecithin in human gallbladder bile

We investigated the relationship between bile nucleation time and the fatty acid composition of biliary lecithin in human gallbladder bile. Bile samples from patients with cholesterol gallstones nucleated more rapidly than those from patients with noncholesterol gallstones or no stones. The biliary cholesterol concentration was highest in the cholesterol gallstone group and was correlated with the molar percentage of linoleic acid and arachidonic acid, with these percentages also being higher in bile from the cholesterol gallstone patients than in bile from the other two groups. In addition, the mucous glycoprotein concentration in bile was also significantly higher in the cholesterol gallstone group. Thirty-three patients in the no-stone group showed bile nucleation times of less than 21 days. Higher concentrations of cholesterol and mucous glycoprotein and higher molar percentages of arachidonic and linoleic acid were noted in these patients. These findings suggest that in humans, hepatic cholesterol hypersecretion is associated with the increased unsaturated fatty acid proportion in biliary phospholipids and gallbladder mucin hypersecretion, thereby causing rapid cholesterol crystal nucleation.

Gall-bladder sludge: lessons from ceftriaxone

Ceftriaxone-associated sludge has been a fascinating story. The occurrence is novel and unique. It has produced a model of gall-bladder sludge in humans. This phenomenon has taught us a great deal about biliary lipid and organic anion excretion by the liver, and the physical chemistry of calcium and calcium sensitive anions. It has added further insights into the pathophysiology of gall-bladder sludge formation. It points to a combination of a hepatic effect where the liver secretes a biochemically abnormal bile, and a gall-bladder effect which provides an environment for precipitation, in order for sludge to develop. The precipitated calcium ceftriaxone has prompted us to re-evaluate the imaging criteria for the diagnosis of gall-bladder sludge versus gallstones. Above all, the rapid onset and rapid disappearance of ceftriaxone sludge has mirrored in a compressed, encapsulated form, the natural history of gall-bladder sludge. It has reminded us that, like gallstones, biliary sludge is usually benign and asymptomatic. However just because it is smaller than gallstones does not mean it cannot cause problems. It can disappear or it can become a calcium ceftriaxone gallstone.

Dietary fat and fatty acids modulate cholesterol cholelithiasis in the hamster

We tested two hypotheses, i) whether the type and the amount of fat in the diet will affect the formation of cholesterol gallstones in the hamsters, and ii) whether palmitic acid, a major fatty acid component of butterfat, can act as a potentiator of cholesterol cholelithiasis in the hamster. Young, male golden Syrian hamsters (Sasco) were fed a semipurified diet containing casein, corn starch, cellulose and cholesterol (0.3%) to which various types and amounts of fat (butterfat, olive oil, menhaden oil, corn oil) were added. All diets contained 2% corn oil to supply essential fatty acids to the growing hamsters. No deaths or illness occurred during the experiment. Animals fed the semipurified diet plus 4% butterfat (group 1) had a gallstone incidence of 63%. Replacement of butterfat with either olive oil, corn oil or menhaden oil prevented the formation of cholesterol gallstones entirely (groups 2-4). When total butterfat was increased from 4% to 8% (group 8), the incidence of cholesterol gallstones increased to 80%. Substitution of 4% olive oil (group 5), corn oil (group 6), or menhaden oil (group 7) for the additional 4% butterfat significantly reduced gallstones to 35%, 45% and 30%, respectively. The replacement of 4% butterfat with 1.2% palmitic acid gave the highest incidence of cholesterol gallstones (95%). These results suggest that butterfat (and one of its components, palmitic acid) intensifies gallstone formation in this model whereas mono- and polyunsaturated fats act as inhibitors of cholesterol cholelithiasis. A fatty acid, possibly palmitic acid, appears to act as lithogen in our model.

Gallbladder emptying stimuli in obese and normal-weight subjects

Gallbladder stasis may be an important factor in the pathogenesis of cholesterol-gallstone formation in some individuals. We investigated gallbladder function in a group of nondieting, gallstone-free, healthy subjects with normal (22 +/- 1 kg/m2) and high (36 +/- 1 kg/m2) body mass indexes. Fasting gallbladder volume (28.2 +/- 4.4 ml) and residual volume after maximal emptying (8.4 +/- 2.3 ml) in high-body-mass index subjects were not significantly different from those of normal-body-mass index subjects (20.5 +/- 2.5 ml and 4.2 +/- 1.3 ml, respectively). The percentage of gallbladder emptying (71% +/- 5%) and the rate of gallbladder emptying (-1.9 +/- 0.3 x 10(-2) min-1) in high-body-mass index subjects in response to a maximal emptying stimulus was similar to the percentage of emptying (78% +/- 6%) and rate of emptying (-2.3 +/- 0.6 x 10(-2) min-1) in normal-body-mass index subjects. A liquid meal containing less than 1 gm fat, 14 gm protein and 6 gm carbohydrate resulted in both a decreased rate of gallbladder emptying and an increased residual gallbladder emptying and an increased residual gallbladder volume in both groups. The addition of 10 or 20 gm (but not 4 gm) of fat to the liquid meal restored gallbladder emptying to the maximal-stimulus level. These results demonstrate that gallbladder emptying in response to a single liquid meal stimulus is not altered in obesity and that dose-response relationships to fat are similar in obese and normal-weight individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence of hydrogen ion secretion from the human gall bladder in vitro

Gall bladder bile is more acid that hepatic bile and this has been attributed to bicarbonate absorption by the gall bladder epithelium. The aim of this study was to investigate in vitro the acid base changes that occur across the human gall bladder mucosa. Fresh gall bladder tissue was obtained at cholecystectomy and placed in an Ussing Chamber and perfused with Ringer-Krebs glucose bicarbonate solution. The viability of the gall bladder was assessed by measuring the potential differences across the epithelium and by the morphology of the epithelial cells at the end of the experiments. Aliquots from the solutions were taken at two, 45 and 70 minutes and pCO2, hydrogen ion and bicarbonate concentrations were measured. In the mucosal side of the chamber a consistent and significant decrease was observed from two minutes to 70 minutes in bicarbonate concentration while pCO2 and hydrogen ion concentrations significantly increased. The degree of inflammation correlated well with the ability for acidification, the more inflamed the tissue the less its ability to acidify. When the gall bladder was exposed to amiloride or sodium free solution acidification was abolished in the mucosal side. When tissue metabolism was irreversibly inhibited by exposure to formaldehyde, hydrogen ion concentration and pCO2 were significantly decreased in the mucosal side of the chamber compared with the viable gall bladder. The human gall bladder is capable of secreting acid and this may be an important mechanism for preventing calcium precipitation and gall stone formation.

Possible factors affecting the cholesterol nucleation time in human bile: a filtration study

This study examined the hypothesis that filtration through the MW 300 kD cut-off membrane (XM-300) may influence factors affecting the cholesterol nucleation time (the appearance time of cholesterol monohydrate crystal). Differences in biliary lipids, biliary protein, mucous glycoprotein and vesicular composition were examined before and after the XM-300 filtration in control and cholesterol gallstone patients. The nucleation time in the cholesterol gallstone patients was significantly faster than that in the control patients. However, the nucleation time in the gallstone patients was significantly prolonged following the XM-300 filtration resulting in a similar value to that of the control patients. No differences in concentrations of total protein, mucous glycoprotein or lipids composition were observed. The nucleation time did not correlate with the total lipid concentration, the concentrations of biliary mucous glycoprotein or total protein. The prolonged nucleation time of gallstone bile by the XM-300 filtration was primarily ascribed to the removal of vesicles, which was confirmed by gel chromatography. It was concluded that vesicles greater than MW 300 kD are primarily responsible for the rapid nucleation time.

Gallbladder volume and emptying in diabetics: the role of neuropathy and obesity

Gallbladder (GB) volume was monitored by real-time sonography in diabetics (n = 21) and healthy volunteers (n = 55) after a test meal. Seventeen controls and seven diabetics were obese; six patients had both autonomous and somatic neuropathy, and four had somatic neuropathy. Fasting GB volume was similar in controls and diabetics with and without autonomic neuropathy; it was correlated with body mass index (controls, r = 0.43, P less than 0.002; diabetics, r = 0.46, P less than 0.04), and was increased in obese subjects. Post-prandial GB emptying was decreased in diabetics. Those with autonomous neuropathy exhibited larger residual volumes than controls (P less than 0.03). Post-prandial GB emptying was slower and less complete in (non-diabetic) obese subjects and deteriorated further in diabetic obese subjects. GB fasting tone was normal, but GB kinetics were impaired in diabetics; obesity and autonomous neuropathy were correlated with GB hypomotility.

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.

The validity of the cholesterol nucleation assay

The validity of the cholesterol nucleation assay rests on the assumption that all cholesterol crystals are removed at the start of the assay so that de novo formation of crystals can be studied. In this paper we have tested the validity of this assumption. Cholesterol crystals were added to supersaturated model bile. Subsequently the mixtures were either filtered over a 0.22 micron filter or centrifuged at 37 degrees C for 2 h at 100,000 x g. After ultracentrifugation the isotropic interphase was collected. Using polarized light microscopy no crystals could be visualized in this fraction. However, the nucleation time of the isotropic interphase decreased from 6.8 +/- 1.1 days to 1.8 +/- 0.2 days (mean +/- S.E., P less than 0.01, n = 5) when 10-100 micrograms/ml crystals were added prior to centrifugation. Similar results were observed when instead of centrifugation the mixtures containing crystals were filtered. After filtration over a 0.22 micron filter no crystals could be detected in the filtrate. Yet the nucleation time of the filtrate decreased from 6.4 +/- 0.7 days to 3.1 +/- 0.5 days (mean +/- S.E.) when 10 micrograms/ml cholesterol crystals were added before filtration (n = 10, P less than 0.01). Since no cholesterol crystals could be detected at the start of the assay the reduction in nucleation time must have been brought about by cholesterol microcrystals that passed through the filter. Supplementation of cholesterol crystals to model bile did not accelerate the nucleation time when the samples were passed over a 0.02 micron filter, indicating that the size of the microcrystals was larger than 20 nm. The effect of addition of cholesterol crystals prior to filtration over a 0.22 micron filter was also tested in the crystal growth assay recently developed by Busch et al. ((1990) J. Lipid Res. 31, 1903-1909). Addition of crystals had only a minor effect on the assay. In conclusion, the reduced nucleation time of biles from gallstone patients is probably not only due to the presence of promoting or the absence of inhibiting proteins, but can be caused by the presence of small cholesterol crystals in these biles.

Biliary proteins in patients with and without gallstones

BACKGROUND

Nucleation from supersaturated bile of calcium salts of cholesterol and bilirubinate is essential in the formation of gallstone. Nucleation requires gallbladder mucin and its main component, glycoprotein, may contribute to gallstone formation by providing a nidus or matrix for precipitation of lipid components. However, biliary protein patterns of patients with gallstones have not been completely explored.

METHODS

We have tried to extract, isolate and characterize the proteins in patients with gallstones and without gallstones. 21 bile samples were obtained from patients with different types of gallstones and with no stones at cholecystectomy. Biliary protein concentrations were measured by Lowry and Bensadoun methods, and individual glycoproteins from each of the patients were compared by silver staining and densimetric quantification of Sodium Dodesyl Sulfate Polyacrylamide Gel Electrophoresis.

RESULTS

1) Among 16 gallstones, 5 were cholesterol stones, 5 were calcium bilirubinate stones, and 6 were black pigment stones. 2) The mean protein concentration was highest in bile with cholesterol stones (47.6 mg/ml), 24.2 mg% in bile without gallstones, and 15.9 mg/ml in brown pigment stones. 3) Cholesterol gallstones were found to have 14.2 KD glycoproteins, whereas pigment stones were found to have 66 KD glycoproteins.

CONCLUSIONS

Gallbladder proteins from both cholesterol and pigment stones play an important role in the nucleation and growth of calcium salt crystals.

Effect of phospholipase C on cholesterol solubilization in model bile. A concanavalin A-binding nucleation-promoting factor from human gallbladder bile

Human bile contains a phospholipase C activity. To examine its pathophysiological importance, the effect of phospholipase C on the dynamics of lipid solubilization and nucleation (cholesterol crystal formation) were investigated in model bile. Phospholipase C from gallbladder bile from patients with gallstones was partially purified by competitively eluting from a concanavalin A (con A)-Sepharose (Sigma, St. Louis, MO) column and incubating with Pronase (Calbiochem, Behring Diagnostics, La Jolla, CA). Phospholipase C activity was resistant to Pronase digestion. When this fraction (concentrated to half the original volume) was mixed with model bile (1:1, vol/vol), a transfer of cholesterol and phospholipid from the micellar to the vesicular phase and an accelerate nucleation time were found concomitant with phospholipid hydrolysis. These effects were prevented by inhibiting the phospholipase C activity with ethylenediaminetetraacetic acid. To confirm that the results were caused by phospholipase C activity and not some other nucleation-promoting factor within the biliary con A preparation, model bile was incubated with bacterial phospholipase C. An identical cascade of events to that found with the partially purified biliary enzyme was observed. Further purification of the con A-bound proteins on DEAE-Sephadex (Pharmacia, Uppsala, Sweden) did not resolve any separate nucleation-promoting activity to that associated with phospholipase C activity. In conclusion, this study has identified phospholipase C as a/the con A nucleation-promoting activity in human gallbladder bile and has characterized a possible molecular mechanism by which cholesterol nucleation is stimulated by this fraction.

Differential patterns of lipid-protein association in fast and slow cholesterol nucleating human gallbladder biles: implications for cholesterol nucleation from biliary lipid carriers

We compared the protein/lipid structure and Ch-nucleating capacity of individual lipid carriers in two groups of human gallbladder biles: 11 with Fast cholesterol nucleation (2.2 +/- 1.3 days) and 10 with Slow cholesterol nucleation (19.2 +/- 4.4 days). The groups had comparable cholesterol-saturation (1.31 vs. 1.28), total lipids (9.9 vs. 8.5 g/dl) and proteins (8.5 vs. 7.6 mg/ml). Bile was ultracentrifuged (2 h at 150,000 x g) and the resulting isotropic phase was incubated with [3H]Ch and [14C]lecithin and gel-chromatographed on a Superose 6 column with a buffer containing 7.0 mM sodium-taurocholate. Seven protein peaks were identified (280 nm and biochemistry), with the following molecular mass ranges (kDa): 1 (Void volume), 2 (155-205), 3 (50-79), 4 (20-29), 5 (6-15), 6 (3.5-6), 7 (2-3.5). Peaks 2 and 3 were identified as vesicles and micelles, respectively. Fast vs. Slow Ch nucleating biles had: (a) more (P less than 0.02) cholesterol coeluting with vesicles, (b) more (P less than 0.01) lecithin coeluting with low m.w. peaks (Nos. 5-6), (c) less (P less than 0.01) cholesterol and lecithin coeluting with micelles. An inverse correlation (P less than 0.001) was observed between the amount of proteins coeluting with the micellar peak and the cholesterol nucleation of both whole bile and isolated micellar fractions. A marked shift of cholesterol and lecithin from micelles to vesicles was apparent, in the whole bile, after cholesterol nucleation had occurred. Incubation and sequential analysis of isolated and radiolabeled micelles showed a progressive transfer of lecithin and cholesterol molecules to low molecular weight fractions and to vesicles before cholesterol nucleation. We conclude that pro-nucleating biliary vesicles develop from micelles, due to the phasing out and redistribution of micellar cholesterol and lecithin, which are probably induced by biliary proteins.

Fibronectin: a possible factor promoting cholesterol monohydrate crystallization in bile

To examine the hypothesis that fibronectin physiologically present in bile might be a possible nucleating factor, the concentrations of fibronectin in gallbladder bile were determined and its induced effect on nucleation time and on the form of vesicle were examined in bile-model and human gallbladder bile. The gallbladder bile samples taken from patients with cholesterol gallstone had a significantly higher concentration of fibronectin and the faster nucleation time than the control. However, no significant correlation was found between nucleation time and endogenous fibronectin concentration. The addition of 0.5, 1.2, 10 micrograms/ml of fibronectin into two kinds of bile-model significantly shortened the nucleation time in a dose-related manner. Nucleation time was significantly shortened by the addition of 1 microgram/ml exogenous fibronectin into abnormal bile while such an effect was absent in the control. The addition of fibronectin increased the size of vesicles observed by the electron microscope. The results suggest that fibronectin physiologically present in bile may be one of the possible nucleating factors.

Aspirin does not inhibit cholesterol cholelithiasis in two established animal models

The effect of aspirin on cholesterol cholelithiasis was examined in the hamster and the prairie dog. In the prairie dog, diets were composed of semipurified components of chow, plus cholesterol (1.2%), with and without aspirin. Animals were studied for either 2 weeks or 4 weeks. Cholesterol gallstones were present in all groups at the end of each period; aspirin did not alter the incidence of cholelithiasis. All animals studied had cholesterol crystals in the bile when they were killed. Liver cholesterol levels in prairie dogs with and without aspirin tended to be lower in animals fed chow than in animals fed semipurified diets. There were no significant differences in cholesterol levels in the plasma or bile. The cholesterol saturation index of all biles approached unity when animals were fed chow with aspirin; animals fed the semipurified diets had cholesterol saturation indices of less than 1.0. The prairie dogs fed aspirin plus cholesterol in the semipurified diet showed increased levels of biliary chenodeoxycholic acid amidates and concomitant decreased levels of cholic acid amidates compared with animals fed the same diet without aspirin. Hamsters fed aspirin plus cholesterol in a semipurified diet tended to have a greater incidence of gallstones than animals given no aspirin (80% vs. 55%). Liver and bile cholesterol levels were similar with and without aspirin; plasma cholesterol levels increased significantly with aspirin [14.20 vs. 7.80 mmol/L (549 vs. 301 mg/dL)]. Lithogenic indices in all hamsters were above unity; biliary lipids, total lipid concentration, and biliary bile acid composition were similar. These results show that the addition of aspirin to a lithogenic diet does not reduce the incidence of cholelithiasis.

Bile acid and phospholipid fatty acid composition in bile of patients with cholesterol and pigment gallstones

It has been previously reported that patients with cholesterol gallstones have increased biliary deoxycholate and arachidonate content as compared with normal subjects without gallstones. Increased biliary deoxycholate and arachidonate content might be a primary factor in the pathogenesis of cholesterol gallstones or merely an epiphenomenon due to the presence of gallstones. We therefore compared biliary bile acid composition in 46 patients with cholesterol gallstones and 22 patients with pigment stones. In addition, biliary phospholipid fatty acid composition was determined in 44 of these patients (30 cholesterol and 14 pigment stone patients). No significant differences were detected. In particular, the percentage deoxycholic acid (mean +/- SD: 20.3 +/- 8.8% and 21.5 +/- 10.9% respectively) and the percentage arachidonic acid (4.4 +/- 2.0% and 4.5 +/- 2.2%, respectively) were very similar. A significant correlation between age and biliary cholesterol saturation index was found only for the group of patients with pigment stones (R = 0.52, p less than 0.02). In conclusion, the present study does not support a primary role for increased biliary deoxycholic acid or arachidonic acid in the pathogenesis of cholesterol gallstones.

Non-mucin proteins in the matrix of human cholesterol gallstones

Human cholesterol gallstones contain a pigmented organic matrix that may originate from biliary sludge. The cholesterol gallstone matrix contains mucin, bile pigments, and calcium salts. The goal of this study was to examine whether non-mucin proteins are present in the matrix of cholesterol gallstones. Matrix was prepared from cholesterol gallstones from 18 patients. Proteins were identified by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and by molecular sieve high-performance liquid chromatography (HPLC). Two proteins were present in each gallstone and migrated with or just adjacent to standards of bovine serum albumin on SDS-PAGE. Several additional lower molecular weight proteins were identified, but not in every gallstone. Protein fractions contained visible pigment after chloroform extraction, and pigment co-eluted with proteins on HPLC, suggesting binding of pigments to proteins in the matrix. We conclude that low molecular weight proteins are present in the cholesterol gallstone matrix. The major protein appears to be serum albumin, although definitive identification has not been established. The origin of these matrix proteins and their possible significance in the pathogenesis of cholesterol cholelithiasis is unknown.

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

The concentrations of total protein, mucus glycoprotein, cyclic-AMP, and apolipoproteins A-I, A-II, and B were determined in the gallbladder bile of patients with cholesterol gallbladder stones and in stone-free controls. The total protein content was significantly increased in gallstone patients (2.03 +/- 0.6 versus 1.31 +/- 0.67 mg/ml; p less than 0.05), as was the mucus glycoprotein concentration (380 +/- 88.5 versus 128 +/- 57.2 micrograms/ml; p less than 0.05). The cyclic-AMP concentration in the gallbladder fluid was increased up to 91 +/- 20 pmol/100 microliters in the gallstone subjects, as compared with 46 +/- 26 pmol/100 microliters (p less than 0.01) in stone-free controls. Cyclic-AMP concentrations correlated positively with the glycoprotein content of the bile in cholesterol gallstone patients (r = 0.66; p less than 0.05). The apolipoprotein concentrations were determined by the radial immundiffusion technique. The corresponding values for patients with stones and controls were 7.5 +/- 0.8 versus 3.0 +/- 0.8 for Apo A-I (p less than 0.025), 10.4 +/- 0.6 versus 6.3 +/- 1.3 for Apo A-II (p less than 0.02), and 1.9 +/- 0.5 versus 1.6 +/- 0.2 mg/dl for Apo B (NS), respectively. Biliary proteins probably play an important role in the nucleation process during the pathogenesis of cholesterol gallbladder stones.

Bilirubin monoglucuronide promotes cholesterol gallstone formation

Recent evidence suggests that cholesterol (Ch) solubility in bile is determined by a complex interaction of mixed micelles and lecithin-cholesterol vesicles. Bilirubin monoglucuronide (BMG), which binds to bile salts and incorporates into mixed micelles, may displace cholesterol from micelles into vesicles, thus favoring cholesterol monohydrate crystal precipitation. Therefore, we designed an experiment to test the hypothesis that BMG may enhance cholesterol gallstone formation without inducing cholesterol supersaturation. For 8 weeks, 28 adult male prairie dogs were fed either a control, nonlithogenic diet (0.03% Ch), a high carbohydrate diet (CHO) which has no cholesterol but increases hepatic bilirubin secretion, or the same CHO diet plus 0.03% Ch. Cholecystectomy was then performed, and bile was examined microscopically for stones or crystals and analyzed for BMG and biliary lipids. Cholesterol saturation index was calculated. Cholesterol gallstones were found in none of the control animals and in 13% of the CHO-fed animals. However, the addition of trace cholesterol to the CHO diet resulted in an 88% incidence of cholesterol gallstones (P less than 0.001 vs control, P less than 0.01 vs CHO, respectively). Gallbladder bile was unsaturated with cholesterol in all groups. (control = 0.65 +/- 0.05, CHO = 0.46 +/- 0.05, CHO + 0.03% Ch = 0.70 +/- 0.03). CHO feeding alone or with trace cholesterol significantly elevated gallbladder bilirubin monoglucuronide, phospholipid, and cholesterol concentrations when compared to controls. These data suggest that in the prairie dog a high carbohydrate diet with only trace amounts of cholesterol increases bilirubin monoglucuronide in gallbladder bile and causes cholesterol gallstone formation without inducing cholesterol supersaturation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary ethanol on gallbladder absorption and cholesterol gallstone formation in the prairie dog

Dietary ethanol has been reported to protect against cholesterol gallstone formation. Because enhanced gallbladder absorption of water is important in cholesterol cholelithiasis, we examined the hypothesis that ethanol acts by inhibiting the absorptive function of the gallbladder. Eighteen adult male prairie dogs were fed a lithogenic liquid diet containing 0.4% cholesterol. Half of the animals received 30% of total calories as ethanol, whereas their pair-fed controls received equicaloric amounts of maltose-dextrin. After 3 months, the gallbladders were inspected for gallstones and crystals, and gallbladder and hepatic bile were analyzed. Cholesterol stones and crystals were present in all nine controls. None of the alcohol-fed animals had stones, but four had cholesterol crystals. Gallbladder cholesterol, phospholipids, and total calcium were significantly decreased in alcohol-fed animals. In both gallbladder and hepatic bile, the cholesterol saturation index was significantly lower in alcohol-fed animals, as was the ratio of trihydroxy to dihydroxy bile salts. The ethanol-supplemented diet produced a significant decrease in the absorption of water by the gallbladder as indicated by changes in the gallbladder bile to hepatic bile ratios of the total bile salt concentration (7.29 +/- 1.25 versus 3.84 +/- 0.56; p less than 0.05) and the total calcium (3.37 +/- 0.24 versus 2.43 +/- 0.29; p less than 0.05). These findings indicate that the protective effect of ethanol may be related to its ability both to inhibit gallbladder absorption of water and to alter the composition of biliary lipids.