IMAGING SUPRAMOLECULAR AGGREGATES IN BILE MODELS AND HUMAN BILE

Investigation of cholesterol crystallization is essential for the unde rstanding of gallstone formation. Previous work has revealed a variety of aggregates of different sizes and shapes prior to the appearance o f ''classical'' plate-like cholesterol monohydrate crystals both in na tive biles and model systems. In this article, we review existing data based on various microscopic techniques and present data on microstru ctural pathways leading to cholesterol crystal formation in two differ ent bile models and in native bile. In continuation of our recent inve stigation of the microstructures in nucleating human bile, we now pres ent data suggesting that polymorphism is not limited to complex native bile, but also appears in two, simplified model systems. These studie s employed cryo-transmission electron microscopy (cryo-TEM) and video- enhanced light microscopy, using Nomarski optics (VELM). Only the comb ined use of these two complementary, non-perturbing direct methods can cover the whole range of microstructures ranging from a few nanometer s to several microns. Concentrated isotropic solutions of bile models, composed of cholesterol, lecithin and taurocholate, were diluted to i nduce cholesterol supersaturation and start an evolution of microstruc tures, leading to cholesterol crystallization. Initially, small sphero idal micelles were observed by cryo-TEM. Subsequently, uni-, oligo-and multilamellar vesicles, compatible with structures seen at the same t ime by VELM, appeared in coexistence with micelles. Thereafter, during a dynamic phase of cholesterol crystallization, filaments, tubular an d helical microstructures, as well as classical plate-like cholesterol monohydrate crystals were noted by light microscopy, Eventually, larg e plate-like crystals were observed by VELM, while cryo-TEM revealed o nly small spheroidal micelles. The crystallization process in native h uman bile during ex vivo incubation was found to bear close resemblanc e to the findings in the model systems, further supporting the applica bility of these systems to the exploration of microstructural aspects of nucleating human bile. (C) 1997 Wiley-Liss, Inc.