(424f) Investigating the Molecular Mechanisms of Cholesterol Crystallization in Biomimetic Systems

There are many severe pathological diseases that involve the crystallization of cholesterol, a ubiquitous molecule in human physiology. Cholesterol is a key component in heart plaque (atherosclerosis) and the imbalance of cholesterol supersaturation promotes the formation of gallstones from bile, leading to several diseases such as jaundice and Bouveret’s syndrome. Cholesterol is both essential to physiological processes and a key component of severe pathological diseases. Despite its relevance to worldwide healthcare problems, few studies have examined fundamental mechanisms of cholesterol crystallization. It is recognized, however, that elucidating methods to control cholesterol precipitation can be highly valuable for the development of new drugs to treat these diseases.

Prior studies have used lipids as biomimetic media to study bulk cholesterol crystallization; however, these systems are not amenable to facile in situ characterization techniques. To this end, we selected a binary mixture of water and ethanol as a lipid surrogate to examine cholesterol crystallization. Here, we will discuss our preliminary findings showing the impact of biomimetic ethanol-water mixtures on cholesterol monohydrate crystallization. We used a combination of oblique illumination microscopy (OIM) and dynamic light scattering (DLS) to prove that cholesterol nucleation involves a two-step process involving the assembly of clusters, which are present in both undersaturated and supersaturated media. These species are also directly involved in surface growth. Scattering measurements confirmed that cluster size is a function of temperature and water content, but is independent of cholesterol concentration. DLS data also revealed that solvent composition has a notable impact on the induction time and rate of crystal growth. We will also discuss the results of in situ atomic force microscopy measurements, which were used to confirm surface growth involves a combination of a classical layer-by-layer mechanism governed by diffusion-limited monomer incorporation and a nonclassical pathway involving cluster attachment. The presence of these clusters also has a unique impact on the dynamics of layer propagation during cholesterol monohydrate crystal surface growth that differs from any crystal growth mechanisms reported in literature.