Biliary lipids and cholesterol gallstone formation

Biliary secretory immunoglobulin A is a major constituent of the new group of cholesterol crystal-binding proteins

BACKGROUND & AIMS

Recently we described a new group of lectin-bound biliary proteins that bind to cholesterol crystals, modify crystal morphology, and inhibit cholesterol crystallization. The aim of the current study was to characterize and identify individual members of this group of cholesterol crystal-binding proteins.

METHODS

Crystal-binding proteins were purified from human gallbladder bile by lectin affinity chromatography and preparative gel electrophoresis. Purified crystal-binding proteins were characterized by using cholesterol crystal-growth assays, immunoblotting, and amino acid analysis. For comparison, identified biliary proteins were isolated from gallbladder bile by lectin affinity and immunoaffinity chromatography.

RESULTS

The individual crystal-binding proteins with molecular weights of 74, 63, and 28 kilodaltons inhibited cholesterol crystallization in a dose-dependent manner (2.5-10 micrograms/mL). Immunoblotting with specific antibodies and N-terminal amino acid sequences revealed that the 74-kilodalton crystal-binding protein is the secretory component, the 63-kilodalton protein is the heavy chain, and the 28-kilodalton protein is the light chain of human secretory immunoglobulin (Ig) A. Isolated biliary IgA showed a potent inhibitory effect on cholesterol crystallization in model bile even at levels less than physiological concentrations (1-100 micrograms/mL).

CONCLUSIONS

Biliary secretory IgA is a major constituent of the previously described group of cholesterol crystal-binding proteins. Crystal-binding IgA may be an important modulator of crystal agglomeration into stones and stone growth in vivo.

Effects of age and diet on the lipid content and composition of gallbladder bile, liver and serum in laying strains of hen

1. Changes in lipid content and composition of liver and bile during pre- and post-laying periods were investigated in hens of a laying strain. 2. The large increase in liver lipid concentration, particularly triacylglycerols, at the onset of laying was accompanied by the appearance of triacylglycerols in the bile. 3. Accumulation of triacylglycerol in the liver was increased by a diet containing maize and soyabean meal. This was associated with increases in the triacylglycerol concentration in both serum and bile. 4. Liver microsomal phosphatidate phosphohydrolase activity was positively correlated with liver triacylglycerol content in birds given the maize/soyabean meal diet. 5. The time course of triacylglycerol accumulation in the liver and associated changes in the bile triacylglycerol concentration in laying strain hens were different to those previously observed in broiler hens. 6. Over the lifetime of the bird, secretion of triacylglycerols into bile may play an important role in the prevention of fatty liver syndromes.

Different susceptibilities to the formation of cholesterol gallstones in mice

In the search for an animal model of genetic determinants of cholesterol cholelithiasis, we found strain, gender and individual differences in mice. Male black (C57BL6J) mice had a 50% incidence of cholesterol gallstones after they consumed lithogenic food similar to that used by Tepperman et al. for 2 weeks, whereas similarly treated male agouti (CBA/J) mice and females of both strains were free of gallstones. The male and female mice of both strains were fertile at 8 weeks of age, and the male black mice were first susceptible to induction of gallstones at 24 weeks of age. Male agouti mice of the same age did not form gallstones until they had consumed the lithogenic food for 8 weeks. The gallbladder biles of both strains were supersaturated with cholesterol during the lithogenic regimen. The male agouti mice had much higher fractional turnover rates of [24-14C]cholic acid than did the male black mice. In spite of their small total cholate pools, the agouti mice had higher rates of new cholate synthesis than did the black mice. The rate of disappearance of [1,2-3H]cholesterol from the blood was higher in the male agouti than in the black mice. The gallbladders of the agouti mice contained less bile and weighed less empty than gallbladders of the black mice. They also did not increase in volume in response to the lithogenic diet as much as gallbladders of the black mice. The difference in gallstone induction times between male and female black mice was as great as the difference between the two strains.(ABSTRACT TRUNCATED AT 250 WORDS)

A unique lipid pattern associated with the gall bladder bile of the chick embryo

A study has been made of the lipid and fatty acid composition of the gall bladder bile of the chick embryo during the last week of incubation. The lipids and their fatty acid composition showed a unique pattern when compared to other animal species. Of the total lipid present, phospholipid accounted for less than half, and there were substantial proportions of both cholesteryl ester and triglyceride. In the cholesteryl ester, the proportion of which increased significantly over the last week of incubation, there was a very high level of oleic acid. The phospholipid contained a high level of arachidonic acid. The results are discussed in relation to observations on the biliary lipids of other animal species and the major features of the lipid metabolism of the chick embryo during the last week of incubation.

Aspirin prevention of cholesterol gallstone formation in prairie dogs

When prairie dogs (Cynomys ludovicianus) are fed a diet containing cholesterol, a marked increase in gallbladder mucin secretion parallels the evolution of cholesterol supersaturated bile. Gelation of mucin precedes the precipitation of cholesterol liquid and solid crystals and the development of gallstones. Aspirin given to prairie dogs inhibited mucin hypersecretion and gel accumulation and prevented gallstone formation without influencing the cholesterol content of supersaturated bile. This suggests that gallbladder mucin is a nucleation matrix for cholesterol gallstones.

Tupaias (tree shrews)--a new animal model for gallstone research. II. Influence of fat, sugar, and cholesterol on bile composition

The lipid composition of bile obtained from the gallbladder and from the liver of tupaias was determined. Compared to the gallbladder bile of man, the gallbladder bile of tupaias contains the same percentage of phospholipids (PL), one third of the cholesterol (CH), and 50% more total bile acids (TBA). The lithogenic index (LI) of the bile is about 0.2--0.3. No significant sex differences or diurnal variations are found in the composition of bile. The concentration of PL, CH, and TBA is found 5 to 8 times higher in the gallbladder bile than in the liver bile. The bile acid spectrum in tupaias equals that in man qualitatively and is similar quantitatively. In a feeding experiment, the influences of butter, cholesterol, butter plus cholesterol and sucrose on bile composition, clinicochemical serum values, and liver and gallbladder histology were studied. Groups of six animals each were fed the different diets over a 10-week period. In group A: 20% butter added to the standard diet, PL content was higher, the LI was unchanged. In group B: 2% cholesterol added to the standard diet, the CH value and the LI were elevated, CH crystals but no stones were found. In group C: 2% cholesterol and 20% butter in the standard diet, stone formation was observed. PL and CH values were higher than in group A and B, TBA values were lower. In group D: 50% sucrose added to the standard diet very low PL and TBA values were determined in the liver bile, resulting in elevated LIs. It is concluded that all three components of a diet, which had proven lithogenic in a preceding experiment (Schwaier, 1979a), contribute to gallstone formation.

The effect of polyunsaturated fats on bile acid metabolism and cholelithiasis in squirrel monkeys

Squirrel monkeys (Saimiri sciureus) were fed diets containing safflower oil, butter, or coconut oil and 1 mg cholesterol/cal for 15--17 mo to examine the effect of type of fat on cholelithiasis and bile acid metabolism. Controls were fed low cholesterol diets containing an isocaloric mixture of the three fats. Cholic acid fractional catabolic rate, pool size, chenodeoxycholic acid pool size, and total bile acid pool size and excretion rate were estimated using a modification of Lindstedt's isotopic turnover procedure. The animals fed the safflower oil diet had the highest incidence of cholelithiasis (9/10) when compared to those fed butter (3/7) and coconut oil (1/7). Animals consuming the low cholesterol control diet did not develop gallstones. The butter- and coconut oil-fed groups had significantly (p less than 0.05) expanded bile acid pools when compared to controls, and the butter-fed group had a significantly increased (p less than 0.05) cholic acid fractional catabolic rate. The safflower oil group had the smallest mean bile acid pool and the highest mean lithogenic index of the cholesterol-fed groups. It was concluded that the safflower oil-fed animals had a higher incidence of cholelithiasis than the butter group because, unlike the latter group, they did not compensate for a high cholesterol intake by stimulating bile acid synthesis. The animals consuming coconut oil apparently did not absorb cholesterol to the extent of the other groups and as a result their bile did not become saturated with cholesterol.