Basic studies on cholesterol solubilization in bile salt solution

Summary

Previous studies on cholesterol solubilization by bile salts have often shown inconsistencies. To obtain basic informations on this problem, cholesterol solubilization in the aqueous solution of several bile salts have been reexamined. Kinetic studies revealed that not only the rate but also the magnitude of solubilization depended on the amount of excess cholesterol and the concentration of bile salt. An appropriate proportion of added cholesterol to bile salt was evaluated as 1: 5–10 (w/w), corresponding to about 200% excess amount to approximate supposed solubility. The solubilization equilibrium was rather difficult to fix and must be checked by the procedure used. A linear relation was obtained between the quantity of solubilized cholesterol and the concentration of bile salt. The slope of the straight line was designated k. As the solubilizing power could be given by the ratio of the solubilizate to the solubilizer, it was expressed numerically by k value as well as graphically by the molar ratio of cholesterol to bile salt as ordinale and the molar concentration of bile salt as abscissa in which the above relation was hyperbolic, k being as asymptote. k values obtained for cholate, chenodeoxycholate, deoxycholate and equimolar cholate-deoxycholate mixture were 3.72 × 10^-2, 6.79 × 10^-2, 8.10 × 10^-2 and 6.55 × 10^-2 respectively.