A comparative study of the effects of 7 beta-hydroxycholesterol, 25-hydroxycholesterol, and cholesterol on the structural and thermal phase behavior of multilamellar dipalmitoylphosphatidylcholine bilayer vesicles

摘要

The effects of 7 beta-hydroxycholesterol (7 beta OH) and 25-hydroxycholesterol (25OH) on the phase behavior and the structural properties of the multilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) bilayers were investigated with comparing to the effects of cholesterol (Chol). Differential scanning calorimetry (DSC) measurements showed these three sterols have slightly but distinctly different effects on the thermal behavior of DPPC bilayers. X-ray diffraction data analysis on DPPC bilayers containing 30 mol% sterols with the aid of molecular volume data estimated by the neutral buoyancy method indicated that the order of apparent occupied surface area per molecule is DPPC/7 beta OH > DPPC/25OH > DPPC/Chol at both 25 degrees C and 50 degrees C, suggesting that the strength of the condensation effect of these sterols follows inversely this order. Based on the findings in this study, we inferred the molecular orientations of Chol, 7 beta OH, and 25OH in DPPC bilayers.