CHOLESTEROL PRECIPITATION FROM CHOLESTEROL-SUPERSATURATED BILE MODELS

Bile-model systems containing cholesterol (CH), phosphatidylcholine (P C) and sodium cholate (NaC) at concentrations similar to those found i n supersaturated human gall bladder bile ([CH]/[PC] = 0.60 +/- 0.01; C H saturation index, CSI = 1.58 +/- 0.03) were prepared by mixing PC-CH vesicles with NaC micellar solutions. Following mixing, the dispersio n became transparent and gave rise to high resolution H-1-NMR spectra typical of mixed micellar systems. Cryo-transmission electron microgra phs of specimens vitrified at that stage support the conclusion that t he 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-e xistence with a mixed micellar system with [CH]/[PC] = 0.43 +/- 0.01 a nd CSI = 1.12 +/- 0.03. The resultant cholesterol-rich vesicles subseq uently aggregated and cholesterol crystals of varying sizes and shapes appeared within the aggregates: needle-like structures were first obs erved, followed by clusters of those crystals and of helical crystals. Eventually, typical plate-like cholesterol crystals appeared, at whic h time some of the PC returned to the non-particulate (isotropic) phas e. Consequently, the system contained cholesterol crystals coexisting with mixed micelles, whose composition was close to the limit of satur ation (CSI = 1.08). These findings confirm the sequence of events prec eding the appearance of cholesterol crystals, as previously proposed i n our less detailed studies ((1990) Hepatology 12, 149S) and support t he relevance of the morphologically similar results of Konikoff et al. ((1992) J. Clin. Invest. 90, 1155) obtained in a very dilute supersat urated bile-model.