Filamentous Crystallization of Cholesterol and Its Dependence on Lecithin Species in Bile

Abstract

Abstract Cholesterol crystallization is a poorly understood obligatory step in cholesterol gallstone formation. We have studied early stages of cholesterol crystallization in a model bile system composed of an aqueous solution of taurocholate/cholesterol/lecithin (97.5/1.7/0.8 moles%). Nucleation of cholesterol crystals was induced by dilution of a micellar solution to achieve supersaturation. Following spontaneous vesicle formation, thin filamentous structures were observed by electron and light microscopy. The filaments were composed of a core of >95% cholesterol and a surface layer of < 5% lecithin, which was preferentially enriched in hydrophobic molecular species. The filaments had a buoyant density of 1.03 g/ml, and revealed an x-ray diffraction pattern compatible with crystalline cholesterol monohydrate with an additional Bragg reflection at 4.9A, suggesting a polymorph of cholesterol monohydrate, or early anhydrous crystallization. The filaments grew and transformed via intermediate spiral, helica...