Quantitative analysis of cholesterol nucleation with time in supersaturated model bile

The amount of cholesterol (Ch) crystals formed in supersaturated taurochenodeoxycholate (TCDC) - lecithin (L) solutions of the same Ch saturation index (CSI) but at different Ch thermodynamic activities (Ch A(T)) was quantified at different time intervals. The initial Ch nucleation rate (i.e., amount of Ch crystals formed with respect to time) in a Ch A(T) = 1.73 and TCDC to L molar ratio (TCDC:L) = 5.1 system was faster than that in a Ch A(T) = 1.42 and TCDC:L = 3.4 system. Shaking could enhance the early appearance of Ch crystals and cause the fast initial Ch nucleation rates for the TCDC:L = 5.1 and the TCDC:L = 3.4 systems. The final Ch nucleation rates were faster than the initial Ch nucleation rates for the TCDC:L = 5.1 and the TCDC:L = 3.4 systems. According to a light scattering analysis of vesicle concentration in supersaturated TCDC-L solutions, vesicles provide nucleation sites only in the Ch nucleation process and the vesicle concentration may not be an important factor for the Ch nucleation rate. A model of a mixed TCDC-L micelle releasing Ch molecules together with the surface area of Ch crystals formed was used in the interpretation of the Ch nucleation.