Partial characterization of a nonmicellar system of cholesterol solubilization in bile

We have shown that there were two distinctly separate cholesterol-containing fractions in human hepatic and gallbladder bile. In addition to mixed micelles that were composed of bile salts, cholesterol, and phospholipids and measured at approximately 25 A by quasi-elastic light scattering spectroscopy, there was a nonmicellar fraction made up of cholesterol and phospholipids with no, or only trace amount of bile salts. This fraction had a mean hydrodynamic radius of 600 A. When studied with electron microscopy, the fraction consisted of particle spherical in shape that measured 900–1,300 A in diameter and were monodisperse. This form of cholesterol had a low buoyant density of less than 1.05 g/ml by density gradient ultracentrifugation and eluted as a macromolecular aggregate (mol wt greater than 200,000) employing Sephadex G-75 chromatography. The quantity of nonmicellar cholesterol in bile correlated positively with the cholesterol saturation index (r = 0.649; P less than 0.001) and inversely with relat...