Proteins of guinea-pig bile: selective resorption in the gall bladder

Hepatic bile versus gallbladder bile: a comparison of protein and lipid concentration and composition in cholesterol gallstone patients

Many studies have demonstrated that gallbladder bile (but not hepatic bile) of animals or patients with cholesterol gallstones contains higher protein concentrations than does gallbladder bile of control patients without stones or with pigment stones. The underlying defect has not been elucidated. To establish whether there is net production or net absorption/degradation of protein by gallbladder epithelium for different classes of protein, paired samples of hepatic and gallbladder bile were obtained from fourteen patients with cholesterol gallstones during elective cholecystectomy. In these paired samples, lipid and protein composition were determined. To obtain the concentration ratio (CR) of protein and lipid, its concentration in the gallbladder was divided by the concentration determined in the paired hepatic bile sample. The CR of bile salts was used as a parameter for water absorption in the gallbladder. Of the biliary proteins that were determined only mucin, albumin, immunoglobulin (Ig) G, and aminopeptidase N appeared to increase in the gallbladder from another cause than water absorption. A strong correlation was found between mucin, albumin, and IgG. Haptoglobin, alpha1-acid glycoprotein, IgM, and IgA appeared to be absorbed by gallbladder epithelium in the majority of patients. In cholesterol gallstone patients, total protein concentration in gallbladder bile of cholesterol gallstone patients is increased when compared with hepatic bile. The increase in protein concentration cannot be explained for all bile samples solely by water absorption. In this study we show that the defect is largely caused by a selective increase in albumin, mucin, and IgG. All other proteins which were investigated are taken up by the gallbladder.

Gallbladder mucosal protein secretion during development of experimental cholecystitis

The development of experimental cholecystitis produced by lysophosphatidylcholine is associated with reversal of the normal absorptive characteristics of gallbladder mucosa, resulting in the intraluminal accumulation of water, glycoprotein, and protein. The purpose of the present study was to attempt to ascertain if the protein leaks into the lumen because of the cytolytic properties of lysophosphatidylcholine or if it is due to an active secretory process and to characterize the protein produced. Experiments were performed on anesthetized cats undergoing gallbladder perfusion with and without lysophosphatidylcholine. The amount of protein in the perfusate was measured and albumin clearance from blood to gallbladder lumen was calculated with and without the administration of vesicular transport inhibitors. In separate experiments, control and lysophosphatidylcholine (LPC) produced gallbladder perfusates were collected and the protein subjected to SDS-PAGE to ascertain the nature of the protein secreted. Inhibitors of both microtubular and microfilament activity decreased the protein accumulation and clearance produced by lysophosphatidylcholine. Gallbladder white blood cell accumulation and inflammation as evaluated by beta-glucuronidase and prostaglandin E levels were not significantly altered by cytochalasin or colchicine administration. Lysophosphatidylcholine also produced significant increases in perfusate LDH levels. The protein produced was primarily a 66-kDa protein. Transfer of the protein to a nitrocellulose membrane and immunoblotting with anti-albumin antibody demonstrated that the protein was albumin. The results suggest that during the development of cholecystitis, lysophosphatidylcholine produces albumin accumulation in the gallbladder primarily by inducing an active secretory process resulting in gallbladder distension.

Increased biliary protein precedes gallstone formation

Although nucleation is critical to the pathogenesis of cholesterol gallstones, the factors responsible for this process are poorly defined. Numerous potential nucleating agents have been identified in the bile of humans and animals with cholelithiasis, including mucus, calcium, and bilirubin. Recent studies have shown that patients with cholesterol crystals and gallstones have increased biliary total protein, suggesting that protein may be a previously unrecognized nucleating factor. We tested the hypothesis that biliary total protein is increased prior to cholesterol gallstone formation. Prairie dogs were maintained on either control (N = 22) or 0.4% cholesterol-enriched chow (N = 18) for up to 18 weeks. Cholesterol-fed animals were classified as pregallstone (N = 12) or gallstone (N = 6) based on gross examination of the gallbladder bile. Both hepatic and gallbladder biles were then analyzed for lipid, bile acid, calcium, and protein content. Cholesterol feeding was associated with increased gallbladder concentrations of cholesterol, phospholipids, and calcium in the pregallstone and gallstone groups. Biliary total protein was significantly elevated in the pregallstone (5.8 +/- 0.4 mg/ml, P < 0.001) and gallstone animals (6.0 +/- 0.6 mg/ml, P < 0.001) as computed to controls (3.8 +/- 0.3 mg/ml). Regression analysis showed positive correlations between gallbladder bile total protein and the gallbladder bile cholesterol saturation index (CSI) (P < 0.001), as well as between gallbladder total protein and calcium (P < 0.001). Although the hepatic bile CSI was elevated in cholesterol-fed animals, total protein remained unchanged, suggesting that the alteration in biliary protein is a gallbladder phenomenon.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Albumin absorption and protein secretion by the gallbladder in man and in the pig

To study albumin absorption by the gallbladder in man, an in vitro model was first established in the pig and compared with in vivo function in the same species. Water and electrolyte transport and 125I-albumin absorption and protein secretion in vivo and in vitro were compared. Then similar in vitro studies were performed on human gallbladders obtained at surgery. The in vivo study in the pig was performed without disturbing the gallbladder except to tie a cannula in the cystic duct end. The in vitro model was identical in the pig and human gallbladders. Gallbladders were excised using a technique causing minimal injury and anoxia. They were oxygenated on both mucosal and serosal surfaces in a temperature-controlled environment. Luminal and external bath test solutions consisted of modified Ringers bicarbonate with added glucose; luminal solutions also contained 125I-albumin from different species, depending on the study. Active absorption of sodium and water occurred in both types of studies in the pig but in vivo absorption rates were considerably greater than in vitro rates. Albumin absorption in vivo was substantial; although present in vitro, the absorption of albumin was diminished relatively more than electrolyte transport rates. Protein secretion rates into the gallbladder were similar in vitro and in vivo. The results of studies in the human gallbladders in vitro were similar to the pig, except albumin absorption was greater. Some human gallbladders were obtained from control patients and some from patients with cholesterol gallstones. There were no significant differences between the two groups for any of the variables studied; however, the numbers were small and some control gallbladders were not normal gallbladders.

Apolipoprotein localization in the human bile duct and gallbladder

Apolipoproteins AI, AII and B were identified in the normal and pathological human bile duct and the gallbladder epithelium using an avidin-biotin immunoperoxidase technique. Small intestine and stomach sections served as positive and negative controls respectively. Staining was focal for apolipoproteins AI and AII, and continuous for apolipoprotein B. In addition to homogenous and granular cytoplasmic staining, foamy cytoplasmic staining, particularly for apolipoproteins AI and AII, was observed around lipid droplets in cells containing much lipid. No correlation between a particular pathological condition of the gallbladder (acute cholecystitis, mucocele, chronic cholecystitis, cholesterolosis) and staining pattern or intensity of staining was found for any of the apolipoproteins, although both apolipoproteins AI and AII stained more intensely than apolipoprotein B in each group. Positive staining was also found for all apolipoproteins in epithelial cells which had invaded the underlying connective tissue (gallbladder carcinoma), suggesting that the epithelial cells are capable of synthesizing apolipoproteins de novo. In this latter case, apolipoprotein B stained more intensely than for either AI or AII, and significantly (p less than 0.05) more strongly than that found in the other pathological groups. The identification of apolipoproteins in the gallbladder epithelium raises the interesting question of their origin and functional role.

Biliary proteins and the nucleation defect in cholesterol cholelithiasis

A study was performed to determine whether differences in gallbladder proteins might be present in patients with rapidly nucleating bile. Gallbladder and hepatic bile protein concentrations were measured using a fluorometric assay. The method was validated by an independent technique, i.e., hydrolysis and amino acid analysis. Persons with cholesterol gallstones had significantly higher gallbladder bile protein concentrations than patients without gallbladder disease or patients with pigment stones. The protein concentration correlated with the in vitro nucleation time in the cholesterol stone group. Gallbladder bile proteins were also purified by chromatography and gradient ultracentrifugation. Proteins from patients with cholesterol gallstones accelerated the nucleation time of control bile, whereas protein from controls had little effect. Hepatic bile protein concentrations were similar in persons with and without cholesterol gallstones. The gallbladder-to-hepatic bile ratios of a variety of solutes were examined. The ratio for protein in the cholesterol gallstone group can be explained straightforwardly by water reabsorption in the gallbladder, whereas the very low ratio in patients without cholesterol gallstones suggests that their gallbladders reduce protein mass by a process such as protein absorption or degradation during water absorption in the gallbladder.

Receptor-mediated uptake of asialoglycoprotein by the primate liver initiates both lysosomal and transcellular pathways

The degradation of asialoglycoproteins in hepatocytes has been well described in several animal models, but no direct evidence has yet been obtained for asialoglycoprotein processing in the primate liver. A double radiolabeling strategy was employed in the experiments described in this paper to evaluate the fate of asialoorosomucoid in the squirrel monkey. Intravenously injected asialoorosomucoid was taken up by the liver with a half-time of 1 min. Electron microscopic autoradiography showed progression of asialoorosomucoid from the hepatocyte plasma membrane through vesicles to multivesicular bodies and then to secondary lysosomes near the Golgi-rich area of the cell. Over 75% of the grains initially associated with clear endocytic compartments after injection had moved to these later organelles within 20 min. Following degradation of asialoorosomucoid labeled with the Bolton and Hunter reagent, radiocatabolites were secreted into bile, peaking approximately 47 min after injection. We also found that 7 to 8% of the injected protein entered an alternative pathway which led to resecretion of the ligand at the bile canaliculus. This was considerably more than in rats (1 to 3%), but roughly comparable to the amount in guinea pigs (10 to 17%). Intact asialoorosomucoid peaked in monkey bile approximately 27 min after injection and was 3 to 4 times more concentrated than the initial plasma concentration, indicating receptor-mediated transport. Gel filtration chromatography and polyacrylamide gel analysis of the secreted protein indicated that it had arrived in bile unaltered. Since less than 1% of the autoradiographic grains were localized to nonparenchymal cells, the hepatocyte was identified as the cell type simultaneously responsible for both pathways. We propose that missorting of some of the asialoglycoprotein to bile reflects diffusion within intracellular sorting compartments to areas primarily dedicated to the processing of unrelated ligands, such as those newly synthesized for biliary secretion.

1-Naphthylisothiocyanate-induced permeability of hepatic tight junctions to proteins

We have studied the early action of 1-naphthylisothiocyanate (ANIT) in relation to its effect on the permeability barrier formed by hepatic tight junctions. Materials having different Mr values [inulin (5000), horseradish peroxidase (HRP) (40,000), ovalbumin (also 40,000) and pig gamma-globulin (IgG) (160,000)] were individually pulsed, within 1 min, into perfused rat livers operating under single-pass conditions. In untreated rats, a small peak of HRP and ovalbumin and a comparatively larger peak of inulin were observed in the bile at 7 min. In rats treated with ANIT, with increasing duration of ANIT treatment the inulin peak increased proportionally, whereas the HRP and ovalbumin peaks remained unchanged until after 10 h of ANIT exposure; gamma-globulin was not detected in the 7 min bile sample until after 14 h of ANIT treatment. Bile flow in all rats remained approximately the same until after 14 h of ANIT pretreatment, when substantial bile-flow reduction was observed. Phenobarbitone pretreatment increased the effect of ANIT and massively elevated the first HRP peak; it also shortened the time (to 4 h) at which the increase in permeability to this protein was observed. In contrast, the first HRP peak was virtually abolished in rats that had received the mixed-function-oxidase inhibitor SKF 525A. These experiments suggest that (i) ANIT progressively increased the permeability of the junctional barrier before the reduction in bile flow, (ii) the ANIT-increased permeability change seems to be inversely dependent upon the Mr of the infused proteins, and (iii) metabolites of ANIT were involved in the development of the junctional permeability change.

Sources of proteins in human bile

The proteins of 46 human bile specimens, collected by several different routes have been studied by crossed immunoelectrophoresis, by rocket immunoelectrophoresis and by radioimmunoassay. The results were analysed by plotting the variation in the bile: plasma ratio of particular proteins against molecular weight and by examination of the correlation between the concentrations of different proteins in the biles of different patients. Our results show that the majority of human bile proteins derive from plasma although bile specific proteins are always present. The majority of plasma proteins appear to enter bile by a 'sieving' mechanism which results in an inverse relationship between the bile: plasma ratio and the molecular weight. In addition there was a very high degree of correlation between the biliary concentrations of alpha 2-macroglobulin, IgG, haptoglobin, haemopexin, albumin, prealbumin, and orosomucoid. A number of other proteins namely thyroxine binding globulin, GC globulin and alpha 2HS-glycoprotein appeared in bile at concentrations greater than those expected if entry is by the sieving mechanism. These three proteins, however, are of rather low molecular weight and the reason for the lack of correlation appears to be individual variation in the 'pore size', presumably reflecting variation in the porosity of tight junction between hepatocytes. Although the majority of human bile proteins would appear to enter bile by a molecular weight-dependent pathway, four proteins, namely secretory IgA, IgM, haemoglobin and caeruloplasmin, showed significant deviation from the predicted relationship and probably enter bile at least partly by transport across cells. The concentration of beta 2-glycoprotein I was also much greater than expected from its molecular weight. The reason for this is not yet clear but may well reflect a very efficient and specific transport mechanism.