Cholesterol monohydrate dissolution rate studies in aqueous micellar solutions of alpha-(nonylphenyl)-omega-hydroxydeca(oxyethylene), n-alkylamines, and fatty acids

Formation of Cholesterol Crystals at a Mucin Coated Substrate

PURPOSE

High-resolution, tapping-mode atomic force microscopy (AFM) was used to monitor the early stage of the formation of cholesterol crystals under simulated conditions of the gallbladder environment.

METHODS

AFM images of phosphatidylcholine/cholesterol vesicles were obtained using a mucin-coated mica substrate.

RESULTS

The vesicles appeared flattened with diameters from 100 to 300 nm and heights that varied from 10 to 100 nm. Phosphatidylcholine/cholesterol vesicles were mixed with bile salt solutions to yield supersaturated (with respect to cholesterol) dispersions, which were then placed onto mica, silanized mica, and mucin-covered mica substrates. After equilibration, sub-micron sized, plate-like structures were observed at the mica and mucin covered surface, but none were seen at the silanized surface. The morphology was characterized as it pertains to the relative growth rates of the crystal faces.

CONCLUSION

The comparison of these results with literature reports of cholesterol crystals grown in solution suggests that the physical chemical properties of the surface have an important influence in determining the nucleation and subsequent crystal growth of cholesterol.

Cholesterol monohydrate dissolution rate studies in aqueous micellar sodium chenodeoxycholate solutions

The dissolution rate of cholesterol monohydrate in various concentrations of sodium chenodeoxycholate (1) was significantly influenced by the addition of strong electrolytes. The mass transfer resistances decreased with increasing electrolyte concentrations and attained an asymptotic minimum value predicted and experimentally established for the convective/diffusion-controlled situation. Reduction of the interfacial barrier to dissolution was many times more sensitive to Mg2+ than to Na+ at equimolar concentrations. Cholesterol monohydrate solubilities increased nonlinearly with increasing 1 in 0.01 M phosphate buffer at pH 8.0 and was not influenced by the presence of strong electrolytes. Measured diffusion coefficients gave supporting evidence that the effective micellar size remained the same within the various experimental systems up to 116 mM chenodeoxycholate. The experimental findings indicated that the interfacial barrier is electrostatic in character. They are consistent with the phenomenon of diffusion of negatively charged micelles toward a negatively charged cholesterol monohydrate surface and the subsequent collision complex transfer of cholesterol molecules at the crystal surface. The results and mechanistic interpretations are also in accord with the previous model studies on cholesterol monohydrate dissolution in the presence of mixed micelles composed of nonionic and ionic surfactants.