PubMed · 7100482
The authors differentiate between the sonographic appearance to spurious echoes in the gallbladder (pseudo-sludge) and the similar appearance of echogenic bile.
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C E Fiske, R A Filly. 1982. Pseudo-sludge.. https://doi.org/10.1148/radiology.144.3.7100482
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Bile-model systems containing cholesterol (CH), phosphatidylcholine (PC) and sodium cholate (NaC) at concentrations similar to those found in supersaturated human gall bladder bile ([CH]/[PC] = 0.60 +/- 0.01; CH saturation index, CSI = 1.58 +/- 0.03) were prepared by mixing PC-CH vesicles with NaC micellar solutions. Following mixing, the dispersion became transparent and gave rise to high resolution 1H-NMR spectra typical of mixed micellar systems. Cryo-transmission electron micrographs of specimens vitrified at that stage support the conclusion that the vesicles had become completely micellized. Following micellization, the metastable (cholesterol-supersaturated) bile-models spontaneously underwent a series of reorganizational steps: first, cholesterol-rich vesicles with a [CH]/[PC] ratio of 1.57 +/- 0.69 were formed, in co-existence with a mixed micellar system with [CH]/[PC] = 0.43 +/- 0.01 and CSI = 1.12 +/- 0.03. The resultant cholesterol-rich vesicles subsequently aggregated and cholesterol crystals of varying sizes and shapes appeared within the aggregates: needle-like structures were first observed, followed by clusters of those crystals and of helical crystals. Eventually, typical plate-like cholesterol crystals appeared, at which time some of the PC returned to the non-particulate (isotropic) phase. Consequently, the system contained cholesterol crystals coexisting with mixed micelles, whose composition was close to the limit of saturation (CSI = 1.08). These findings confirm the sequence of events preceding the appearance of cholesterol crystals, as previously proposed in our less detailed studies ((1990) Hepatology 12, 149S) and support the relevance of the morphologically similar results of Konikoff et al. ((1992) J. Clin. Invest. 90, 1155) obtained in a very dilute supersaturated bile-model.
In a model bile solution composed of lecithin (L)-bile salt (B), the solubilization of lipid and the accessibility of enzyme to the lipid were examined by observation of EPR spectra and measurement of enzyme activity. The lifetime of the spin probe in the micellar phase was estimated to be approx. 1 microsecond by means of line shape analysis. Both population and lifetime increased with temperature and the molar ratio of lecithin to bile salt (L/B). The EPR data indicated that simple micelle of bile salt, mixed disk micelle of bile salt-lecithin, and multi-lamellar mixed disk micelle can exist in a model bile solution, depending on the L/B molar ratio across a range from 0 to 1.5. The maximal power of the mixed disk micelle to solubilize cholesteryl ester in the model bile at a L/B molar ratio of 1:1 was confirmed by EPR measurement of cholesteryl 12-DOXYL-stearate. Observation of the enzyme activity on a mixture of model bile and substrate at 37 degrees C revealed selective accessibility of cholesterol esterase (bovine pancreas) to mixed disk micelle, of cholesterol oxidase (Streptomyces cinnamomeus) to both simple and mixed disk micelle, and of pancreatic lipase (porcine pancreas) to both simple micelle and an oil droplet of substrate. The temperature-dependent activity of cholesterol oxidase to cholesterol in mixed disk micelle can be explained in terms of mesomorphic phase transition of lecithin side chains followed with fluidity of liquid crystal phase. Regarding phospholipase C from Bacillus cereus, though the selective accessibility to the micelles was not observed at 37 degrees C, a decrease in activity for mixed disk micelle could be found at lower temperatures.
The distribution of phospholipid and cholesterol between the vesicular and micellar phases in bile plays an important role in the formation of cholesterol gallstones. Conventional analytical procedures to determine the distribution are potentially unreliable because they disturb the distribution of these compounds between the two phases. In this work, we circumvent this problem by using NMR. 31P-NMR is used to quantify directly the micellar and the vesicular amount of lecithin. The previously described 1H-NMR method to determine directly the micellar lecithin (Groen et al., J Lipid Res 31: 1315-1321) has been optimized by the implementation of a spectral quantification method. The agreement between the 31P and 1H methods was excellent. In our hands, the method of Ellul et al. (FEBS Lett 300: 30-32) did not allow quantification of micellar cholesterol, although our fitting procedure offered the possibility of quantifying overlapping spectral peaks by the use of prior knowledge about all the parameters of the compounds visible in the spectrum. The micellar cholesterol concentration was so low compared to the overlapping lecithin peaks that no reliable quantification was possible. The same problem was encountered when using other characteristic cholesterol resonances for quantification. Our data suggest that cholesterol present in the vesicular phases is too immobile to give rise to high-resolution peaks and the amount of cholesterol present in the micellar phase is too low to allow quantitation by NMR. We conclude that 1H-NMR can be used to determine micellar lecithin, and 31P-NMR to determine micellar as well as vesicular lecithin in model bile.