Comparative effects on biliary concanavalin A-bound glycoproteins and calcium ion on cholesterol crystal nucleation and growth in model bile

Abstract

The concanavalin A-bound glycoproteins in human gallbladder bile have recently been demonstrated to be strong promoters of cholesterol crystal nucleation. In the present study, we investigated the mechanism(s) whereby such promoters affect cholesterol crystal nucleation and/or growth, and compared these mechanisms with those of another promoter, calcium ion. Concanavalin A-bound glycoproteins were isolated from the Helix pomatia-unbound fraction of gallbladder bile from stone-free patients, and determined by electrohoresis to consist of six subclasses (MW 143, 98, 80, 58, 50, and 40 kDa). A cholesterol crystal growth assay showed that concanavalin A-bound glycoproteins both accelerated nucleation time and increased growth rate, whereas calcium ion affected nucleation time only. In the presence of both concanavalin A-bound glycoproteins and calcium ion, both cholesterol nucleation and growth were markedly enhanced. A gel permeation chromatographic study revealed that concanavalin A-bound glycoproteins shifted a considerable amount of cholesterol from micelles to vesicles, whereas calcium ion did not. These results suggest that concanavalin A-bound glycoproteins promote cholesterol crystal nucleation and growth, partly by shifting cholesterol from stable micelles to metastable nonmicellar fractions in bile. In contrast, calcium ion promotes these processes by other mechanisms and, therefore, enhances the effect of concanavalin A-bound glycoproteins.