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Several proteins are known to modulate cholesterol crystallization. We recently demonstrated that haptoglobin has cholesterol crystallization promoting activity. However, this effect is still not well understood mechanistically. The current study examined the distribution of haptoglobin compared to apolipoprotein A-I (apo A-I) to micelles, vesicles and crystals as an initial step in providing a focus for further studies of the mechanism of cholesterol crystallization activity. Specific protein purification was accomplished by immunoaffinity chromatography. The crystallization-promoting activity of biliary haptoglobin, albumin and commercial apo A-I was measured by a photometric crystal growth assay. The distribution of micelles, vesicles and proteins in model bile was determined by Sepharose CL-6B column chromatography. Detection of the presence of test proteins in cholesterol crystals was determined using specific 125I-radiolabelled proteins. Haptoglobin (20 micrograms/mL) showed a significant crystallization promoting-activity, whereas apo A-I (30 micrograms/mL) only tended to show a slight inhibitory activity. The cholesterol crystal-bound protein in each case was found to be less than 1% of the total concentration of that protein that had been added to the model bile system. The elution profile of commercial apo A-I from a Sepharose CL-6B column was strikingly altered when it was added to model bile prior to elution. In contrast, the column elution profiles for both haptoglobin and albumin were unchanged when model bile was similarly added to the sample. Haptoglobin increased the amount of cholesterol found in the vesicular fraction when compared to apo A-I. Haptoglobin does not bind tightly to either biliary lipid particles or to cholesterol crystals but does increase the amount of cholesterol in vesicles by inducing a shift from micellar cholesterol (P = 0.046). This shift appears to explain in part its promoting effect on cholesterol crystallization.

Concanavalin A (Con A)-binding glycoproteins accelerate the rate of cholesterol crystal formation as a prelude to gallstone formation. Immunoglobulins (IgM, IgA, and IgG), aminopeptidase N (APN), phospholipase C (pcPLC), and alpha 1-acid glycoprotein from this Con A fraction have all been proposed as candidate promoters. We immunopurified each of the six putative promoters and examined their comparative effects by adding equal amounts to a cholesterol crystal growth assay. The effects of immunoabsorptive removal of each of the specific candidate promoters from native bile were also compared. In additional studies, the potency of these proteins was in the following order: IgM > IgA = AAG > IgG. APN and pcPLC showed no effect on cholesterol crystal growth at their apparent physiological concentrations. In subtractive experiments, only a minor loss (< 10%) of net promoting activity from that of the whole Con A-bound fraction was observed after immunoabsorptive removal of pcPLC, APN, or immunoglobulins. Total removal of AAG, however, showed a far greater loss (/33%) of the net promoting activity. These data indicate that AAG accounts for the greatest portion of net biliary Con A-bound promoting activity derived from currently defined and well-identified glycoproteins. However, more than 60% of total Con A-binding promoting activity remains unaccounted for, indicating the presence of other important and still unidentified promoters in human bile.

Pooled, normal human gallbladder biles were initially separated on a molecular sieving chromatography column to remove soluble mucin glycoproteins as well as high molecular weight proteins (greater than 200,000). The remaining lower molecular weight proteins and other bile components were then examined by lectin affinity chromatography with four different types of lectin. The separated bound fractions were compared for inhibiting and promoting activities with a newly devised sensitive cholesterol crystal growth assay and for differences in electrophoretic patterns on SDS-gels. Protein factors (presumably glycoproteins) were found to have both inhibiting and promoting activities, even in the absence of cholesterol gallstone disease. The promoting effect was indicated by shortened crystal detection times and increases in crystal growth rate; whereas the inhibiting effect was indicated by decreases in crystal growth rate and reductions in the final crystal concentration as determined by the growth assay. Affinity chromatography mitigated the major problems of removing both lipids and pigment from the glycoproteins. In addition, partial purification of bound fractions with potent cholesterol crystal nucleation-altering activity can be obtained by this technique.

Among the factors affecting the stability of supersaturated bile that culminates in the nucleation and growth of cholesterol crystals are biliary lipids. The abundance and composition of these lipids affect the composition of biliary vesicles that, if rich in cholesterol, are themselves unstable and that constitute precursor particles from which cholesterol crystals somehow arise. Kinetic factors can affect stability in either of two ways: They can inhibit cholesterol crystallization, thus stabilizing the system, or they can promote the process of cholesterol crystal nucleation, thus stabilizing the system.

Apolipoprotein A-I (Apo A-I), conventionally purified by several steps including organic solvent-delipidation from plasma, inhibits cholesterol crystallization in bile. To observe a significant effect in vitro, however, supraphysiological concentrations above 100 microg/mL are required. For this reason, this protein has not been considered to play a physiological role in vivo. In the present study, we examined the cholesterol crystal growth-inhibiting effect of biliary Apo A-I at its physiological concentration, the modification of transcellular transfer of biliary lipids through cultured human gall-bladder epithelial cells (GBEC) by Apo A-I at its physiological concentration and the binding and secretion of Apo A-I by GBEC.We purified biliary Apo A-I to near homogeneity using immobilized artificial membrane chromatography. At 5 microg/mL, biliary Apo A-I reduced cholesterol crystal mass by 50%, whereas plasma-derived, solvent-delipidated Apo A-I had no effect. Using an antibody-capture enzyme-linked immunosorbent assay, we found reduced Apo A-I concentrations in bile samples from gallstone patients when compared with bile samples from gallstone-free controls (medians, 2.35 and 9.4 microg/mL, respectively). In a GBEC line, Apo A-I (5 microg/mL) enhanced transfer of phospholipid and cholesterol from the mucosal to the serosal side of cell monolayers by approximately 50%. These cells appear to bind Apo A-I reversibly in a dose- and time-dependent manner, compatible with receptor-type binding. Cultured human gall-bladder epithelial cells also showed basal secretion of Apo A-I, which was greatly increased by exposure to model bile solutions.Apolipoprotein A-I in bile, thus, has both a direct effect on cholesterol crystal formation and enhances lipid removal from gall-bladder bile by GBEC. This effect may be specific and receptor mediated. These observations support two separate roles for human biliary Apo A-I and suggest that this protein may be important in preventing the formation of cholesterol crystals (the initial step in gallstone formation) in supersaturated bile.

Cholelithiasis is a frequent disease in developed countries with significant economical implications. While the multifactorial pathogenesis of cholesterol gallstones has been widely accepted, the relative importance of the various contributing factors is not yet clear. One focus of research in recent years has been the identification and functional analysis of biliary proteins. Few proteins are synthesized in the biliary tract itself, the majority reflect the composition of serum proteins. Many biliary proteins modify cholesterol crystallization, the initial step of cholesterol gallstone formation. In cholelithiasis, biliary concentration of many pronucleating proteins are increased. However, this may be a consequence rather than the cause of the disease, because a majority of these proteins are acute-phase reactants. They may be secreted into bile at increased concentrations because of--often asymptomatic--cholecystitis due to gallstone disease. A number of protein-lipid interactions have been observed in search of a mechanism of action of biliary effector proteins. Only recently the potential modification of lipid removal from gallbladder bile by Apo A-I was described in addition to its direct antinucleating effect. In conclusion, biliary proteins directly modify cholesterol crystallization by protein-lipid interactions and may influence lipid absorption from the gallbladder.

Crystallization-inhibiting proteins can explain longer nucleation times associated with bile from gallstone-free subjects as compared with bile from patients with cholesterol gallstones. We partially characterized and examined the crystallization inhibitory potency of a newly purified 15 kd human biliary protein. Gallbladder bile was passed through an anti-apolipoprotein A-I (apo A-I) immunoaffinity column to extract lipid-associated proteins. The bound fraction was separated by 30 kd ultrafiltration. Sodium dodecyl sulfate-polyacrylamide gel electrophesis (SDS-PAGE) was performed under nonreducing and reducing conditions. Cholesterol crystallization activity was tested in a photometric cholesterol crystal growth assay. Isoelectric focusing was performed by using a standard gel. The purified 15 kd protein was subjected to N-terminal amino acid sequencing. Although the whole apo AI-bound fraction contained a variety of proteins and lipids, its 30 kd filtrate yielded a nearly pure 15 kd protein with only minor contamination from apo A-I. Amino acid sequencing showed that the protein was unique. Enzymatic deglycosylation revealed no evidence for glycosylation. At a protein concentration of 10 μg/ml, crystallization time was delayed as compared with control and apo A-I, and final crystal mass was reduced to 75% of control. Its isoelectric point was 6.1 without isoforms. Under nonreducing conditions, the protein formed a 30 kd dimer and a 60 kd tetramer. We conclude that this protein is a novel potent biliary crystallization inhibitor protein.

Protein factors, primarily glycoproteins, present in native human bile, have been found to modify, e.g., retard/accelerate, the process of de novo monohydrate crystal formation and, by inference, the rate of formation of cholesterol "nuclei" in such metastable cholesterol supersaturated systems. Neither the process of nucleation itself or how these modifiers work is yet well understood. From the health standpoint, an inhibitor type of protein has been found that may help explain why about 50% of the population have biliary cholesterol supersaturation; whereas, only about 10% actually form gallstones. To date, only one inhibitor glycoprotein has been isolated and characterized. Its role thus seems clear. This is in contrast to the situation with so-called promoter glycoproteins which accelerate nucleation and crystal formation. A number of these proteins have now been identified. An understanding of the comparative roles of each of these proteins has not yet been established. This is partly because of conflicting results, insufficient potencies or lack of information about physiologic concentrations.

Several proteins present in human bile have been reported to promote cholesterol crystallization and thus are potentially important in the formation of cholesterol crystals as the initial stage in gallstone pathogenesis. To be physiologically relevant, such proteins must either be present in high concentration in bile or have a potent promoting activity. The current study explored several of the more abundant but unexamined biliary proteins based upon their also having sufficiently high serum concentrations that antibodies were available for both their isolation and quantitation.Protein purification was accomplished by immunoaffinity chromatography of bile followed by delipidation. Con A affinity chromatography of bile was used to obtain the bound fraction, a portion of which was delipidated. Crystallization-promoting activity of both the purified proteins and Con A-bound glycoprotein fractions (CABG) was measured by a photometric crystal growth assay. A competitive antibody-capture ELISA assay was developed to measure concentrations of alpha 1-antitrypsin, transferrin, and haptoglobin in native bile.At their relevant physiological concentrations, biliary haptoglobin (15 micrograms/ml) had a crystallization-promoting activity twice that of the biliary IgM (75 micrograms/ml) used as a reference standard (P0.05). Biliary transferrin (20 micrograms/ml) had only modest promoting activity (P0.05). Biliary alpha 1-antitrypsin (50 micrograms/ml), by contrast, showed no promoting activity. Delipidation of the CABG fraction decreased its promoting activity by 75%. Biliary haptoglobin accounts for about 30% of delipidated total CABG-promoting activity.Biliary haptoglobin at its physiological concentration has a highly potent crystallization-promoting activity and thus becomes a candidate for major attention in understanding gallstone pathogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)

We recently identified a promoting glycoprotein in the concanavalin A-bound fraction of gallbladder bile as a biliary form of alpha 1-glycoprotein (AAG). The concentration of biliary AAG appears to exert an important promoting effect on the speed of cholesterol nucleation in many patients with cholesterol gallstone disease. In the current study, we provide information about the biliary concentration of AAG as well as the amount and comparative potency of its subfractions in patients with and without cholesterol gallstone disease. The amount of total biliary AAG and the amounts of its different isoforms separated by concanavalin A affinity chromatography were measured by ELISA. Estimates of absolute concentrations of AAG for each sample were normalized to the sample total protein content to give relative AAG values. The promoting activity (potency) of immunopurified biliary AAG from gallstone patients and gallstone-free controls on cholesterol crystallization was compared by a crystal growth assay. The mean absolute concentration of AAG in gallstone-free controls was not significantly different from multiple stone patients. The relative concentration of AAG (micrograms per milligram total protein) was significantly increased in patients with multiple stones when compared to controls (P0.05), and both the absolute and relative concentrations of AAG (micrograms per milligram bile), were three- and to five fold higher in a number of these patients. The functional activity and distribution of AAG in different subfractions was similar in gallstone patients and gallstone-free controls. The relative concentration of biliary AAG is significantly greater in cholesterol gallstone patients with multiple stones than in gallstone-free controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Concanavalin A (Con A)-binding glycoproteins accelerate the rate of cholesterol crystal formation as a prelude to gallstone formation. Immunoglobulins (IgM, IgA, and IgG), aminopeptidase N (APN), phospholipase C (pcPLC), and alpha 1-acid glycoprotein from this Con A fraction have all been proposed as candidate promoters. We immunopurified each of the six putative promoters and examined their comparative effects by adding equal amounts to a cholesterol crystal growth assay. The effects of immunoabsorptive removal of each of the specific candidate promoters from native bile were also compared. In additional studies, the potency of these proteins was in the following order: IgMIgA = AAGIgG. APN and pcPLC showed no effect on cholesterol crystal growth at their apparent physiological concentrations. In subtractive experiments, only a minor loss (10%) of net promoting activity from that of the whole Con A-bound fraction was observed after immunoabsorptive removal of pcPLC, APN, or immunoglobulins. Total removal of AAG, however, showed a far greater loss (/33%) of the net promoting activity. These data indicate that AAG accounts for the greatest portion of net biliary Con A-bound promoting activity derived from currently defined and well-identified glycoproteins. However, more than 60% of total Con A-binding promoting activity remains unaccounted for, indicating the presence of other important and still unidentified promoters in human bile.

Non-bile salt cholephilic organic anions comprise a single class of nonhomologous ligands having a range of hydrophobicity. Hydrophobicity enhances the hepatic extraction of cholephiles as well as their partitioning into secreted biliary lipid particles. When hydrophobicity is correlated with patterns of biliary excretion for studying transcellular transport, however, the more hydrophobic probes are unsuitable. Specifically, with the isolated perfused rat liver technique, the excretory times for sulfobromophthalein and rose bengal were significantly longer compared with that for the much more hydrophilic analogue phenol red (PR), which showed only a single, nearly symmetrical excretory peak at 10 min. Colchicine affected the apparently well-defined PR pathway only at a saturation dose (10,000 times the tracer dose). In contrast, the effect of a different perturbant, monensin, was striking at a tracer dose of PR, but was less evident at a saturation dose. The combined administration of colchicine and monensin had no additive inhibitory effect on PR excretion at tracer doses. At a saturation dose of PR, where monensin is less inhibiting, however, a significant additive inhibitory effect was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Among the factors affecting the stability of supersaturated bile that culminates in the nucleation and growth of cholesterol crystals are biliary lipids. The abundance and composition of these lipids affect the composition of biliary vesicles that, if rich in cholesterol, are themselves unstable and that constitute precursor particles from which cholesterol crystals somehow arise. Kinetic factors can affect stability in either of two ways: They can inhibit cholesterol crystallization, thus stabilizing the system, or they can promote the process of cholesterol crystal nucleation, thus stabilizing the system.

Non-bile-salt cholephilic organic anions are efficiently taken up by the liver. Recent work from our group has suggested the possible importance of relative hydrophobicity among various organic anions in hepatic uptake. To further validate and clarify this, we studied hepatic extraction of five different cholephilic dyes using the isolated perfused rat liver in single-pass mode. Albumin binding affinities and capacities for each of the ligands were measured in vitro to permit evaluation of in vivo interactions for each of them over a spectrum of unbound ligand concentrations. As expected, a strong positive correlation was found between ligand hydrophobicity and the relative degree of albumin binding affinity and capacity. Using appropriate experimental conditions, we also found a strong positive correlation between hepatic extraction efficiency for a given ligand and both its hydrophobicity and its unbound concentration. These data indicate that where the unbound ligand concentration is significant, the greater the ligand hydrophobicity, the greater is its efficiency of hepatic extraction. We conclude that hepatic extraction efficiency for non-bile-salt cholephilic organic anions depends on a combination of ligand hydrophilic/hydrophobic balance and the availability of the unbound ligand for uptake.

We describe a novel, facile, and highly reproducible spectrophotometric technique to measure a cholesterol crystal growth curve. This method permits a quantitative estimate of the potency or comparative abundance of a given kinetic effector substance. In addition to several internal validation procedures, data are provided that support the usefulness of the technique in the assay of substances with either known promoting activity, i.e., human mucin glycoprotein, or those with known inhibitory activity, i.e., human apolipoprotein A-I.

Any substance capable of ultimately forming itself into a solid crystal must undergo an initial step of forming crystal nuclei. The nucleation step in crystallization for all such systems has been a difficult process to describe. Even the definition of what constitutes a "nucleus" remains elusive because one is dealing with a conceptual construct that is found only in the submicroscopic domain and therefore is inaccessible to direct measurement. Based on these considerations, the so-called nucleation time assay can at best only be taken as an empirical parameter. Nucleation (operationally defined) and growth of cholesterol monohydrate crystals in both model and native biles occurs rapidly after aggregation of supersaturated vesicles. Cholesterol made available for crystal growth also originates from the vesicular pathway and not directly from biliary micelles. The exact mechanism(s) governing this linked "precursor-product" relationship remains undefined.

The idea that biliary proteins somehow inhibit nucleation/crystal growth of cholesterol crystals in supersaturated human biles is not new, and some supportive, albeit preliminary, evidence has already been provided for this. Progress in purification of biliary effector proteins has been slow and hindered by the lack of a sensitive and convenient assay method. The formidable problems of removing large amounts of both mucin and lipids from the samples before isolation of biliary proteins has constituted another major obstacle. Recently, the combination of a newly developed nucleation and crystal growth assay and the systematic use of lectin affinity chromatography has enabled rapid progress to be made. With these approaches, glycoprotein fractions containing primarily inhibiting activity and other fractions containing primarily promoting activity have been isolated from normal human biles. Thus these opposing activities can coexist and influence a balance of effects potentially defining the presence of health or disease. The most recent studies have led to the isolation of a single glycoprotein having an extremely potent crystal growth-inhibiting activity.

Detection and characterization of vesicles in native and model biles can be achieved by both imaging and nonimaging methods. Imaging methods provide more directly interpretable information, but sample preparation problems, particularly for application of electron microscopy, are a source of serious concern. Several nonimaging methods have also been used to advantage in the study of vesicles. These methods all share the disadvantage of being model dependent, thus making data analysis indirect and inferential; this is in addition to constraints unique to each of the several nonimaging methods. It is suggested that to achieve optimal accuracy in vesicle studies, a combination of different structural methods should be used where possible.

The presence of vesicles in human bile probably accounts almost entirely for the frequently observed, but hitherto unexplained, phenomenon of metastable cholesterol supersaturation. This, in turn, largely explains the prolonged stability of cholesterol solubilized in supersaturated human bile. Under certain overall compositional conditions for a supersaturated native bile, the vesicular phase in its contribution to total cholesterol transport also becomes supersaturated in cholesterol. Because of this, the vesicles also become unstable, leading to formation of cholesterol crystals. A simple but common example of one factor affecting composition in this way is concentration of total solutes, especially the biliary lipids. Conversely, dilution of bile (e.g., hepatic bile) markedly reduces the cholesterol saturation level in biliary vesicles. The result is that such vesicles become much more stable. Under these conditions, cholesterol crystal formation becomes unlikely and rarely, if ever, occurs.

Organic anions have recently been found to partition in vitro into various biliary lipid particulate species according to their relative hydrophobicities. To establish the physiological relevance of these observations, we intravenously injected various radiolabeled organic anions and assessed the distributions of parent compounds and their metabolites to lipid particles in canine bile. Partitioning into various biliary lipid particles was determined by gel permeation chromatography. Relative hydrophobicities of the various organic anions and their radiolabeled conjugates were determined by reverse-phase high-pressure liquid chromatography. A strong positive correlation (P less than 0.001) was found between percent vesicular association and degree of hydrophobicity for a given organic anion and/or its more polar conjugate. We conclude that 1) the hydrophobic-hydrophilic balance of organic anions is a key factor governing their partitioning to lipid particles secreted in bile; 2) the present study agrees well with our previously published in vitro observations; and 3) other chemical constituents, e.g., proteins, mucin, etc., appear to have little or no effect on organic anion transport in bile.

The presence of small vesicles composed of phospholipid and cholesterol has recently been demonstrated in super-saturated model and in dilute native human biles by several groups using differing methods. Among compositional factors shown to favor spontaneous vesicle formation and prolong the cholesterol monohydrate nucleation time in model bile systems are dilution, a raised cholesterol saturation index (CSI), and a low bile salt/phospholipid ratio. Time-lapse video-enhanced microscopy of a series of model bile systems representing systematically designed variations in the above factors revealed strong evidence for an essential linkage between antecedent vesicle aggregation and subsequent crystal nucleation. Stability of vesicles was inversely related to their degree of cholesterol saturation, i.e., the greater the degree of vesicular cholesterol saturation, the less their stability (metastability). Instability of vesicles was reflected by their early aggregation followed by rapid cholesterol crystal nucleation. The lowest degree of vesicular cholesterol saturation was found in dilute systems which also exhibited the greatest metastability despite a high degree of cholesterol solubility (raised CSI). Conversely, the more concentrated and least metastable systems exhibited both rapid vesicle aggregation and rapid onset of crystal nucleation. These systems, while influenced by the other compositional factors, were found to have a high degree of vesicular cholesterol saturation, i.e., cholesterol/phospholipid molar ratio = 2.0. An additional finding was the extreme variability in the proportionate distribution of total solution cholesterol distributed to the vesicular phase, i.e., from zero to as high as 37%. Higher solute concentration, raised bile salt/lecithin ratio, and raised CSI were interactive and almost equally capable of increasing the proportionate amount of cholesterol in the vesicular phase. In conclusion, lipid compositional differences in model bile systems drastically affect the cholesterol saturation of spontaneously formed phospholipid-cholesterol vesicles. This effect, in turn, exerts a potent influence upon the metastability of vesicles, subsequently affecting the cholesterol crystal nucleation time.

Rapid nucleation of cholesterol crystals has previously been shown to provide a sharp discrimination between abnormal (cholesterol gallstone-associated) and normal human gallbladder bile. In the present study, we sought to further clarify the crystal nucleation process by time-lapse microscopy using a novel high-resolution video-enhanced microscopy technique. Using a previously described method for removal of particles from abnormal biles, we found a strikingly rapid rate of de novo formation of unilamellar vesicles, soon followed by massive vesicular aggregation, culminating in crystal formation. In normal biles, by contrast, this rapid aggregation process was not observed and the isolated unilamellar vesicles showed prolonged stability. Morphometric analysis of interval particle counts showed statistically significant differences. The process of cholesterol monohydrate crystal nucleation in supersaturated human bile is characterized by a sequential combination of vesicle formation, vesicle aggregation, and subsequent crystal formation. The primary distinction between abnormal and normal biles resides only in the consistent rapidity of onset and completion of these events in the abnormal biles.

The onset time for cholesterol crystal nucleation of supersaturated normal human gallbladder biles is consistently prolonged when compared with biles from patients with cholesterol gallstone disease. Investigation of the factor(s) responsible for the suspended supersaturation (metastability) of normal human biles revealed that model bile solutions of cholesterol saturation index (CSI) and molar lipid composition identical to individual gallbladder bile specimens had much shorter crystal nucleation times, i.e., exhibited decreased metastability. Unsaturated normal biles, after supplementation with lecithin, cholesterol, and sodium taurocholate to a 'standard' supersaturated lipid composition, also demonstrated nucleation times three- to 15-fold longer than the comparable standard model bile. Total lipid extracts of normal biles, however, when similarly supplemented, did not differ in nucleation time from the control model solution. Gallbladder biles were fractionated by gel chromatography and the eluted fractions were pooled into two fractions. The fractions eluting in about the first 25% of the included volume when mixed with the supersaturated standard model bile induced a modest increase in nucleation time of approximately 1.5 times the control value. The fractions eluting in the second 25% of the included volume and which contained all of the bile lipids, were concentrated and supplemented with lipids to the standard composition. The nucleation times of these supplements were 3-10 times longer than the control nucleation times. Delipidated bile protein mixtures, purified by discontinuous sucrose gradient centrifugation, were recombined with purified lipids at the standard composition used previously. The nucleation times of these mixtures were significantly prolonged to the same extent as those associated with the second chromatographic fraction. These observations demonstrate that the delayed onset (inhibition) of cholesterol crystal nucleation observed in normal human gallbladder bile is produced by a factor(s) present in the biliary protein fraction.

The development and validation of a direct method for measuring maximum cholesterol solubility in bile is described. Application of this method to five large mammalian species, including man, produced a micellar zone significantly smaller than that previously reported. Further studies on in vitro model solutions patterned after bile confirmed this new micellar zone. Thus, direct evidence demonstrates that the micellar zone boundary derived in vitro from model solutions is applicable to human gallbladder bile. Using the present criteria, normal human bile, in contrast to bile from other mammalian species, is commonly supersaturated with cholesterol. A male-female difference in bile composition is not demonstrable despite the well-established female preponderance of cholelithiasis. Bile from patients with cholesterol cholelithiasis has a micellar zone similar to normals but differs compositionally in that there is a greater excess of cholesterol above saturation. We conclude that cholesterol supersaturation may be a necessary but not solely sufficient cause for gallstone formation.

Apolipoproteins A-1 and A-2 were purified from human plasma. At concentrations present in human bile these proteins prolonged the nucleation time of cholesterol monohydrate crystals when added to model systems of supersaturated bile. In contrast, apolipoprotein C-3 and other serum proteins did not have this effect. Also, when human gallbladder bile was fractionated by gel filtration chromatography, apolipoproteins A-1 and A-2 were among the proteins present in a fraction of bile enriched in potent inhibitors of cholesterol crystal nucleation. These findings suggest that apolipoproteins A-1 and A-2 in supersaturated human gallbladder bile could inhibit the rate of formation of solid cholesterol crystals and thus help to prevent spontaneous cholesterol gallstone formation in humans.

6 patients with radiolucent cholelithiasis underwent randomized successive 3-week trials on each of the following medications: beta-glycerophosphate, linoleic acid, or purified soybean lecithin. Bile-rich duodenal fluid was obtained prior to the study and following each treatment period. Soybean lecithin feeding effected a qualitative change in biliary lecithin with increased fatty acid unsaturation, but no significant improvement in biliary cholesterol saturation or lipid composition changes including a proportionate increase in biliary phospholipids resulted from any treatment program. A 6-month therapeutic trial with soybean lecithin plus cholic acid failed to show a therapeutic response indicative of gallstone dissolution in the 6 patients.

About 20 years ago, an era of major advances in clinical and basic research into gallstone pathogenesis began when the principles of physical chemistry were applied to cholesterol solubilisation and transport. The major (experimental) outcome was the reasonably accurate clinical definition of cholesterol saturation and supersaturation. Supersaturation, the indispensable prerequisite to cholesterol crystallisation and precipitation, was the first key discovery of this era of advances.

The various forms and manifestations of drug-induced liver disease depend on the operation and interaction of several potential factors. First, there is metabolism by the hepatic microsomal mixed-function oxidase (MFO) enzyme system, the most important component of which is cytochrome P-450. The microsomal membranes and the MFO enzymes are capable of induction (increase in structure and function). Second, for drug-induced liver damage to ensue, the drug must have certain structural properties so that upon metabolic conversion, activated (toxic) metabolites are produced. Third, in certain instances the normal tissue glutathione level is critical for normal excretion of a water-soluble metabolite; otherwise, with depletion of tissue macromolecules (mostly proteins) occurs, resulting in irreversible tissue necrosis. Lastly, although still a point of some controversy, in some instances genetically determined, metabolic, predisposing factors that favor the toxicity pathway may be present in a given patient, such as a patient who is a rapid acetylator. There may be other genetically determined abnormalities in drug metabolism that produce either abnormal metabolites or immunochemically reactive substances from a given agent, but these have not yet been identified.

Diffusion coefficients of single bile salt micelles and mixed binary micelles consisting of single bile salts and phosphatidylcholine in the molar ratio 3 : 1 have been measured using quasielastic laser light scattering spectroscopy. Among single systems, marked concentration dependence of the diffusion coefficient was observed only in those containing sodium taurodeoxycholate. Micellar size correlates with bile salt molecular structure in a manner similar to thaobserved by earlier workers with some minor differences towards a more consistent ordering. Phosphatidylcholine produces small increases in micellar size in most systems depending on bile salt structure, and seems most plausibly interpreted as simple swelling of the single species micelles. In some systems, when phosphatidylcholine is added, size or shape changes are indicated. Diffusion coefficients were also studied in the ternary systems bile saltphosphatidylcholine-cholesterol which were saturated and metastably supersaturated with respect to cholesterol. The Stokes radii in both systems were the same within experimental error, 35 A. Our results indicate that intermicellar interactions significantly contributed to the measured diffusion coefficients in the ternary systems as well as in the single sodium taurodeoxycholate and binary sodium taurodeoxycholate-phosphatidylcholine systems in the concentration range studied.

The rapid induction of cholesterol cholelithiasis in a new experimental model, the prairie dog, has recently been reported by two groups. In this model they were able to induce gallstones in as brief a period as 2 weeks, using a 1.2 per cent cholesterol diet. This unprecedented time intensity or telescoping of the induction process provided a unique opportunity for observation of physicochemical changes occurring rapidly over a short period of time and to correlate these with degree of biliary cholesterol saturation. To make such observations, 97 adult male and female prairie dogs were used in the present study. Seventy-two were fed the high cholesterol diet and sacrificed at intervals over a 14-day period; the remaining 25 were used as controls. The primary objective of this work was to determine whether or not there was any relationship between the in vivo events induced in prairie dog bile and our recently reported detailed observations of cholesterol precipitation phenomena in synthetic bile analogs. In these studies, solutions of physiologically relevant composition were constructed, which, when plotted according to convention on a tri-linear graph, fell within the zone of metastable or suspended supersaturation. These solutions revealed a consistent and previously undescribed liquid crystal to solid crystal phase transition during their approach to equilibrium at 37 degrees C. The in vivo studies of prairie dog bile following rapid induction of supersaturation revealed identical changes. At first, the supersaturated biles were isotropic followed by a period of turbidity and invariable formation of mesophase. After a few days, the liquid crystals decreased and solid cholesterol crystallites appeared. The most striking aspect of these observations is that the in vitro work has now predicted not only static, but dynamic processes as well, with respect to cholesterol precipitation beginning with the metastably supersaturated state and eventuating in gallstone formation. Ancillary new findings, resulting from the high cholesterol diet, included the induction of human-like hyper-beta-lipoproteinemia and rapid hepatocyte degranulation shown by electron microscopy.

Three generations of a kindred comprising 50 individuals are described in which recurrent intrahepatic cholestasis of pregnancy has occurred with high frequency. A uniform expression and complete penetrance of the trait in the women of a limited "affected" portion of the kindred (6 affected of 10 women), along with the direct parent-to-child inheritance mode, supports the conclusion that the inheritance mode is Mendelian dominant in type. Male expression of the phenotype seems to be inhibited. This is derived from observations that unmasking of carriers in the kindred by normal challenge provided useful information only in women, and was unhelpful when applied to a male obligate carrier. A linkage analysis is presented that explores the possibility of a relationship between the syndrome and homologous leukocyte antibody histocompatibility antigens. On the basis of present data, no conclusion can presently be reached regarding this possibility.

The phase diagram approach to defining solute relations in solutions at equilibrium was originally conceived more than a century ago by Josiah Willard Gibbs, the great American physical chemist of the late 19th century (1). Small and co-workers in a series of papers published a decade or more ago (2–4) observed that applying such a plotting system to lipid solute containing analogs for native human bile could provide, for the first time, a means for defining in thermodynamic terms the maximum solubility limit of cholesterol in bile. Based on such a definition, it was concluded that a clear separation of normal from abnormal (choles­terol gallstone-associated) human biles was possible because the latter were supersaturated, whereas normals were not. Subsequent studies (5–7) failed to confirm the precision of the claimed sep­aration of normal from abnormal (cholesterol gallstone-associated) biles. In addition, results of studies using chenodeoxycholic acid therapy for patients with cholesterol gallstone disease demon­strated discrepancies in the saturation index definition of bile from untreated patients compared with post-treatment observations (8). The combination of these findings therefore necessitated a reassessment of this initial cholesterol saturation limit definition. An important outcome of this work (9) resulted in observations indicating the need for a significant reduction in the phase diagram boundary limit for maximum cholesterol solubility. This was based primarily on the recognized need in these later studies to take into account the factor of time-dependent equilibration. According to the revised view, the still somewhat puzzling observation that biliary cholesterol supersaturation, as defined by the new criteria, occurred frequently in healthy man also became apparent; whereas such was not the case in a variety of large mammals. Further studies have documented that cholesterol supersaturation is likely to be enhanced in the presence of physiologic factors such as obesity (10, 11) or the effects of estrogen (12, 13). Such enhance­ment has also been well documented as resulting from pathophysio­logic processes such as ileal disease or resection, wherein a broken enterohepatic circulation creates a deficiency of bile salts, important solubilizers for cholesterol in bile.

The incidence of several forms of liver disease associated with inflammatory bowel disease has been putatively ascribed to a toxic effect on the liver of portal vein bile acids abnormal in type or amount. To examine this possibility, total bile acid concentrations (sulphated and non-sulphated) were measured by gas-liquid chromatography in inferior mesentric vein serum of 19 patients undergoing colectomy for severe inflammatory bowel disease (IBD). Similar determinations were obtained on a control group of eight patients requiring colectomy for other non-inflammatory conditions. Mean values for mesenteric vein serum bile acid concentrations (muM/1) were 19.6+/-1.8 in controls and 16.3+/-2.0 in IBD. The mean sulphated bile acid fraction did not exceed 10% of total, although there was considerable variability (up to 40% of total). Lithocholic acid levels (entirely sulphated in all patients) were low. Although the IBD group showed a more than two-fold increase in mean lithocholate concentration (0.54+/-0.15 muM/1) over controls (0.21 +/- muM/1), this difference was not statistically significant. No significant intra-group difference was noted in the non-sulphated and sulphated fractions for cholic, chenodeoxycholic, and deoxycholic acid species, respectively. No unidentified or unusual bile acids were observed. There was no correlation between bile acid measurements and liver histology. These findings fail to support the hypothesis that liver disease often found in association with severe inflammatory bowel disease represents a form of bile acid toxicity. The invariable finding of total sulphation of the lithocholic acid fraction even in the presence of severe mucosal disease was unexpected.

In earlier studies, we concluded that biliary cholesterol supersaturation may be a necessary but not sufficient cause for gallstone formation. In the present studies, we calculated cholesterol saturation indices (CSI) for 120 bile specimens of cholesterol gallstone patients and controls, using the solubility boundaries of Carey and Small (J Clin Invest 61:998-1026, 1978) for artificial biles. The mean CSI + SD was 1.42 +/- 0.68 for controls and 1.80 +/- 1.02 for cholesterol gallstone patients. Of the control bile samples, 68% were supersaturated. Since the two groups could not be sharply distinguished by saturation index, we studied another property of bile samples: nucleation time for cholesterol crystal formation. The mean nucleation time for 16 control bile samples was 15 days, and a strong correlation (r = 0.84) was found between CSI and nucleation time. Twelve bile samples of cholesterol gallstone patients had a mean nucleation time of 3 days and no correlation between CSI and nucleation time. A discriminant analysis of the data, which took into account both the CSI and the nucleation time for each sample, allowed a sharp distinction between bile samples of cholesterol gallstone patients and controls. This distinction could not have been drawn from studies with artificial biles, since these differ only in their CSI.

The presence of small vesicles composed of phospholipid and cholesterol has recently been demonstrated in super-saturated model and in dilute native human biles by several groups using differing methods. Among compositional factors shown to favor spontaneous vesicle formation and prolong the cholesterol monohydrate nucleation time in model bile systems are dilution, a raised cholesterol saturation index (CSI), and a low bile salt/phospholipid ratio. Time-lapse video-enhanced microscopy of a series of model bile systems representing systematically designed variations in the above factors revealed strong evidence for an essential linkage between antecedent vesicle aggregation and subsequent crystal nucleation. Stability of vesicles was inversely related to their degree of cholesterol saturation, i.e., the greater the degree of vesicular cholesterol saturation, the less their stability (metastability). Instability of vesicles was reflected by their early aggregation followed by rapid cholesterol crystal nucleation. The lowest degree of vesicular cholesterol saturation was found in dilute systems which also exhibited the greatest metastability despite a high degree of cholesterol solubility (raised CSI). Conversely, the more concentrated and least metastable systems exhibited both rapid vesicle aggregation and rapid onset of crystal nucleation. These systems, while influenced by the other compositional factors, were found to have a high degree of vesicular cholesterol saturation, i.e., cholesterol/phospholipid molar ratio = 2.0. An additional finding was the extreme variability in the proportionate distribution of total solution cholesterol distributed to the vesicular phase, i.e., from zero to as high as 37%. Higher solute concentration, raised bile salt/lecithin ratio, and raised CSI were interactive and almost equally capable of increasing the proportionate amount of cholesterol in the vesicular phase. In conclusion, lipid compositional differences in model bile systems drastically affect the cholesterol saturation of spontaneously formed phospholipid-cholesterol vesicles. This effect, in turn, exerts a potent influence upon the metastability of vesicles, subsequently affecting the cholesterol crystal nucleation time.