Imaging and Monitoring Cholesterol Crystallization in Bile

Characterizing the microstructural evolution of lipid aggregates and precipitates in lithogenic bile is pivotal for understanding the process of cholesterol crystallization, leading to cholesterol gallstone formation. We have studied cholesterol precipitation in bile models and in human bile samples by the combined use of lightand cryotransmission electron microscopy with density gradient separation of lipid aggregates and other physical chemical techniques. Supersaturated unilamellar vesicles and spherical micelles precede the formation of filamentous cholesterol crystals in a dilute bile model. The filaments are replaced by intermediate crystal structures, before the formation of thermodynamically stable plate-like cholesterol monohydrate crystals. In concentrated synthetic bile models and in native bile, cholesterol crystallization is preceded by and partly concurrent with the appearance of supersaturated oligoand multilamellar vesicles of varying sizes and numbers of bilayers. The vesicular structures become desaturated while intermediate type crystals, and cholesterol monohydrate plates form. The available data indicate that biliary cholesterol crystallization is a multi-phase process, involving several intermediate lipid and microcrystalline structures.