Nucleation of cholesterol from vesicles isolated from bile of patients with and without cholesterol gallstones

Bile was obtained from patients with and without cholesterol gallstones at surgery. Biliary vesicles were separated from micelles by gel filtration. The cholesterol/phospholipid ratio in vesicles was much higher than in micelles. Cholesterol crystals nucleated from vesicular fractions, but nucleation from the micellar fractions was slow or did not occur at all. Cholesterol nucleated from vesicles obtained from bile of control patients as rapidly (2.4 days ± 0.7) as from patients with stones (2.4 days ± 0.9) and there was no difference in the vesicular cholesterol/phospholipid ratio. The effect of alteration of the bile salt environment was studied by changing the concentration of sodium cholate in the eluting buffer. At low concentrations (5 mM) only vesicles were eluted from the column. These vesicles had a relatively low cholesterol/phospholipid ratio and cholesterol nucleated slowly from these vesicles. At higher concentrations the proportion of micelles increased. The proportion of vesicles decreased progressively but their cholesterol/phospholipid ratio increased and the nucleation time fell. These studies demonstrate that cholesterol nucleates from vesicles in the absence of micelles, that control vesicles are not protected by tightly bound antinucleating substances and that exposure of vesicles to micelles strips relatively more phospholipid than cholesterol from the vesicular fraction, resulting in vesicles with higher cholesterol/phospholipid ratios and shorter nucleation times.