Role of bile salt hydrophobicity in distribution of phospholipid species to carriers in supersaturated model bile solutions

Background: Phospholipid species modulate cholesterol-holding capacity and, therefore, regulate bile metastability. Methods: In this study, we investigated the effect of bile salt hydrophobic ity on the distribution of phospholipids among lipid particles in supersatu rated model bile solutions (total lipid concentration, 9 g/dL; taurocholate /phospholipid ratio 3.0, cholesterol saturation index 1.3), by using gel pe rmeation chromatography. Results: With an increase of bile salt hydrophobicity in the elution buffer , the uptake of cholesterol and phospholipids into bile salt micelles was i ncreased, associated with an increased cholesterol/phospholipid molar ratio of the vesicles. In contrast,there was an inverse correlation between the hydrophobicity of the phospholipid species in the vesicles and that of bile salts in the elution buffer, suggesting that hydrophobic bile salts induce d preferential uptake of hydrophobic phospholipids into bile salt micelles, while less hydrophobic phospholipids, with a relatively low cholesterol-ho lding capacity, remained in the vesicles. Conclusions: These data indicate that bile salt hydrophobicity regulates ve sicular cholesterol metastability by modulating the hydrophobicity of phosp holipids in vesicles, as well as the lipid distribution among various bilia ry lipid particles.