Influence of cholesterol crystallization effector proteins on vesicle fusion in supersaturated model bile

Abstract

Background: In lithogenic bile, cholesterol-rich vesicles rapidly aggregate and fuse to eventually form cholesterol crystals. This process is modulated by cholesterol crystallization effector substances. In this study, we developed a method for quantitative assessment of vesicle fusion and used it to partly characterize the mechanisms of action of cholesterol crystallization effector proteins.

Methods: Cholesterol:phospholipid (1:1) liposomes were prepared and labelled with octadecyl rhodamine B chloride (R18). Fusion of these liposomes was detected by the increase of R18 fluorescence after incubation with various proteins, such as albumin, concanavalin-A bound glycoprotein, immunoglobulins, apolipoprotein A-I and apolipoprotein B (all at 100 microg/mL).

Results: Fusion of cholesterol/phospholipid liposomes was increased by 16 and 14% in the presence of concanavalin-A bound glycoprotein and immunoglobulins, respectively, and decreased by 21 and 9% after addition of apolipoprotein A-I and apolipoprotein B, respectively. The effect of each protein on vesicle fusion was correlated with its hydrophobicity.

Conclusions: These results suggest that nucleation effector proteins modulate the stability of vesicles and, thus, affect cholesterol crystallization. Such modulation is based upon protein-vesicle association, which defines the physico-chemical metastability of vesicular cholesterol.