The present study was performed to determine whether the degree of
lecithin hydrophobicity regulates bile metastability and, therefore, affects the process of
cholesterol crystallization. Supersaturated model bile (MB) solutions were prepared with an identical composition on a molar basis (
taurocholate/
lecithin/
cholesterol, 73:19.5:7.5; total
lipid concentration 9 g/dl) except for the
lecithin species; egg yolk
phosphatidylcholine, soybean
phosphatidylcholine, 1-palmitoyl-2-linoleoyl-sn-phosphatidylcholine,
dilinoleoyl phosphatidylcholine and
dipalmitoyl phosphatidylcholine. Each MB
solution was incubated and sequentially examined. Video-enhanced contrast microscopy demonstrated that the rate of vesicular aggregation and fusion correlated with the degree of
lecithin hydrophobicity, and that the rate of
cholesterol crystal nucleation correlated with the degree of
lecithin hydrophilicity. In MBs containing less hydrophobic
lecithin, needle-like crystals developed and transformed into mature plate-like crystals, whereas classical plate-like crystals were consistently observed in MBs composed of hydrophobic
lecithin.
Laser-diffraction particle size analysis demonstrated that the increase in
lecithin hydrophobicity enlarged the vesicle dimension, enhancing its
cholesterol-holding capacity. Correlation between vesicular
cholesterol packing density and
lecithin hydrophobicity suggests that the process of bile
cholesterol nucleation and growth is regulated, in part, by acyl chain unsaturation in
lecithin. Since the composition of biliary
lecithins is responsive to dietary manipulations, this study provides new insights into the prevention of
cholesterol gallstones.