Effects of proteins on phospholipid vesicle aggregation and lipid vesicle-monolayer interactions

Ground squirrel model for cholelithiasis: role of epithelial glycoproteins

The cholesterol-fed Richardson's ground squirrel (Spermophilus richardsonii) has proven to be an effective animal model in which to study factors that influence cholesterol gallstone formation and associated alterations in the gallbladder epithelium. Ground squirrels of either sex, fed a 2% cholesterol-enriched diet, exhibit cholesterol monohydrate crystal precipitation within 24 hours and macroscopically visible cholesterol stones by 3 weeks. Data on bile chemistry, biliary cholesterol precipitation, and various mucosal alterations occurring prior to, during, and after stone formation were collected using sampling intervals from 6 hours to 20 weeks on the diet. The results indicate that mucin hypersecretion appears to be more closely related to the initiation of nucleation than does either bile calcium of pH. Mucus hypersecretion begins within 18 hours of diet initiation and continues throughout the 20 week experimental period. Apical excrescences became more common and were larger in size during the early stages of cholelithiasis. Administration of aspirin during the experimental period demonstrated an inhibition of mucin synthesis and release. Gallstones were not formed in these aspirin-treated animals. A lectin-binding panel for 10 epithelial glycoprotein-related sugars indicated the mucin secreted by the gallbladder epithelium of 7 day experimental animals differed from that of controls. The most obvious difference was the abolition of WGA binding in the experimental animals, suggesting an absence of sialic acid expression in the mucin during the lithogenic process. Ultrastructural histochemistry indicated that both sulphomucin and sialomucin were present in the secretory granules and within the surface mucus layer of both experimental and control animals. Experimental animals, however, exhibited a significant predominance for sulphomucin. This pattern varies from that typically seen in other regions of the gastrointestinal tract where sialomucins predominate during pathologic processes.

Altered bile composition during cholesterol gallstone formation: cause or effect?

Gallbladder stasis, increased gallbladder absorption, and elevated biliary levels of calcium, hydrogen ion, and bilirubin have been implicated as factors potentially critical to cholesterol crystal precipitation. Previous studies, however, have analyzed bile only when crystals or gallstones have already formed. Therefore, we tested the hypothesis that changes in bile composition are a late effect, occurring only after crystal formation. Adult male prairie dogs were fed a standard nonlithogenic control diet (n = 7) or a lithogenic 1.2% cholesterol diet for 5, 9, or 14 days to cause cholesterol saturation (n = 7), cholesterol monohydrate crystals (n = 7), or gallstones (n = 7). Gallbladder bile was examined microscopically for crystals, and analyzed for ionized calcium, bilirubin, pH, total protein, and biliary lipids. The ratio of gallbladder to hepatic bile radiolabeled cholic acid specific activity (Rsa) was calculated as an index of gallbladder stasis. Cholesterol saturation index was calculated. The results demonstrate that increased gallbladder bile cholesterol saturation and total protein concentration precede cholesterol monohydrate crystal precipitation. However, changes in gallbladder ionized calcium, unconjugated bilirubin, pH, stasis, and absorption were noted only after crystals and gallstones had already formed. These data indicate that alterations in gallbladder bile calcium, bilirubin, pH, stasis, and absorption are not early changes, but occur simultaneously with or after crystal formation. Increased biliary protein, however, which was elevated prior to nucleation, may be an important mediator of cholesterol precipitation in cholesterol-saturated bile.

Effect of binding of ionised calcium on the in vitro nucleation of cholesterol and calcium bilirubinate in human gall bladder bile

Biliary calcium may be a nucleating agent in cholesterol cholelithiasis. A study was designed to determine the effect of binding of ionised calcium on in vitro nucleation time. Ultracentrifuged and microscopically clear gall bladder bile from cholesterol gall stone patients was divided into two aliquots. One aliquot served as control and ionised calcium was bound in the second aliquot by addition of EDTA. Nucleation time was observed for the two groups. Addition of EDTA had no effect on lipid composition of the biles. EDTA bound all ionised calcium. Calcium bilirubinate precipitated from all controls on day 1 but was absent in all samples with EDTA. Addition of EDTA had no effect on cholesterol crystal nucleation time; nucleation time was rapid in both the controls and samples with EDTA. Ionised calcium is essential for calcium bilirubinate precipitation but is not responsible for the rapid nucleation time of bile from cholesterol gall stone patients.

Rapid vesicle formation and aggregation in abnormal human biles. A time-lapse video-enhanced contrast microscopy study

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.