Lithogenicity of human bile is reduced by freezing and thawing

We examined the effects of freezing and thawing upon the nucleation time and the distribution of cholesterol between micelles and vesicles in 9 human gallbladder and 7 hepatic biles. The nucleation time was significantly longer after freezing when compared to fresh samples (22.4 +/- 2.6 vs. 7.4 +/- 1.9 days, respectively). Concomitantly, a substantial shift of cholesterol from vesicles to micelles was noted, with the proportion of vesicular cholesterol decreasing from 26.5% +/- 6.0% in fresh biles to 8.6% +/- 2.3% after freezing. These effects were observed in all types of human biles, regardless of origin, cholesterol saturation or initial presence of cholesterol crystals, and were most notable after the first week of freezing. The decrease in vesicular cholesterol in all biles and the increase in nucleation time of gallbladder biles correlated with the time the samples had been in a frozen state. It is concluded that the lithogenic properties of human bile are not maintained during storage at -20 degrees C. Freezing results in a shift of cholesterol from vesicles to micelles and reduces the tendency of cholesterol to crystallize from bile samples.