(368bw) Unravelling Complex Pathways of Cholesterol Crystallization in Biomimetic Systems

• Studying polymorphism using state-of-the-art characterization techniques to probe crystal growth at multiple length scales
• Designing potential therapeutic approaches for pathological diseases in areas ranging from atherosclerosis and gallstones to mineralization in kidney stones.
• Elucidating mechanisms of classical and nonclassical crystal nucleation and growth using high resolution techniques such as in situ atomic force microscopy.

Related Presentations:

1. (#690931) In Situ Characterization of Cholesterol Crystallization in BiomimeticSolvents

2. (#691406) Understanding Cholesterol Precipitation in Biomimetic Environments

Abstract Text:

Numerous pathological conditions are characterized by the excessive crystallization of cholesterol, a molecule that plays a crucial role in human physiology. Cholesterol is prominently involved in the development of atherosclerotic plaque in arteries, and the formation of gallstones from bile, resulting in various ailments such as jaundice and Bouveret's syndrome. Despite these global healthcare challenges, there is a paucity of research exploring the underlying mechanisms of cholesterol crystallization. Nevertheless, it is widely recognized that unraveling approaches to control the precipitation of cholesterol holds immense potential in the development of novel pharmaceutical interventions for the treatment of these conditions.

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 alcohol as a lipid surrogate to examine cholesterol crystallization. We discovered that some water-alcohols lead to the formation of cholesterol monohydrates whereas others lead to formation of solvates. We used a combination of oblique illumination microscopy (OIM) and dynamic light scattering (DLS) to show that cholesterol nucleation involves a two-step process involving the assembly of clusters, which are present in both undersaturated and supersaturated media. Using a binary mixture of water and isopropanol, we demonstrated that cholesterol monohydrate growth involves classical layer nucleation and spreading. Time-resolved imaging confirmed that layer generation originates from defects (dislocations) where monomer incorporation into advancing steps occurs by a surface diffusion pathway, leading to macrosteps that reduce growth by a self-inhibition mode of action not commonly observed in other crystalline systems. We also studied the dissolution of cholesterol crystal surfaces and identified unique nonclassical pathways that differ from conventional layer-by-layer step recession or etch pit formation. These collective findings reveal complex mechanisms of cholesterol monohydrate crystallization that contribute to a deeper understanding of cholesterol-related pathological conditions and offer potential avenues for the development of targeted therapeutic interventions.