Characterization of the cholesterol crystallization-promoting low-density particle isolated from human bile.

Background & Aims: Biliary concanavalin A-binding glycoprotein (CABG) contains cholesterol crystallization-promoting activity that is not accounted for by the pronucleators that have been characterized in this fraction. The aim of this study was to isolate and characterize the missing activity.

Methods: Biliary glycoprotein was isolated using concanavalin A-Sepharose. Promoting activity in CABG was purified using density gradient ultracentrifugation.

Results: Activity in CABG separated into two fractions at low (1.08) and high (1.29) density, which showed different crystallization kinetics in a model bile. The high-density fraction had a late onset time (49.2 +/- 17.8 hours) but a high crystal growth rate (13.4 +/- 5.2 micrograms. mL-1.h-1). The low-density fraction had a rapid onset time (33.9 +/- 20.9 hours) but a slower growth rate (6.5 +/- 3.8 micrograms.mL-1 .h-1). The high-density fraction was not further characterized in this study. The low-density fraction contained solid particles consisting of lipid and very little protein, and the activity was fully pronase resistant. Delipidation of the low-density fraction removed all activity.

Conclusions: A potent pronase-resistant nucleation-promoting activity was activated from human bile and characterized. The low-density fraction may be responsible for the rapid nucleation in bile from typical patients with fast-nucleating gallstones.