Solubilisation of cholesterol in human bile.

Two non-disruptive separation techniques (gel filtration, and CsCl density gradient ultracentrifugation) were used to characterise the mode of cholesterol transport in human bile. Both methods showed that biliary cholesterol is solubilised as a high--Mr non-micelle (lipoprotein) complex as well as the mixed micelle. The lipoprotein complex was separated between the densities 1.01 and 1.08, had a cholesterol to phospholipid ratio of 0.95 +/- 0.41 and contained protein (7-20% by wt). The mixed micelle on the other hand sedimented at d greater than or equal to 1.18, and had a cholesterol to phospholipid ratio of 0.41 +/- 0.13. Eighteen bile samples, obtained from either T-tube, gallbladder or endoscopy, were analysed, and without exception they all contained a fraction of biliary cholesterol in the non-micelle form. The results indicate that cholesterol is secreted, at least in part, as a lipoprotein complex independently of bile acids (mixed micelles).