Influence of cholesterol on the structure of stratum corneum lipid model membrane

This study describes the influence of cholesterol on a model membrane consisting of four stratum corneum (SC) lipids in three different states at 32 and 85 °C. Using small-angle X-ray diffraction on multilamellar vesicles, the lamellar repeat distance, D, was determined. Small-angle neutron scattering on unilamellar vesicles was used to calculate the membrane thickness, average area of the membrane surface per molecule, average volume per molecule in the membrane, and membrane density. After the sample preparation, the membranes show one lamellar phase. Over 10 days, the systems separate into two lamellar phases and crystalline cholesterol. On heating the samples to 85 °C, the domains merge into one phase, the D-value of which increases slightly with increasing cholesterol concentration. On cooling the samples back to 32 °C, only one phase is observable again. The increasing cholesterol concentration in the membrane causes a decrease in the D-value, membrane thickness, and membrane density. Simultaneously, the area of the membrane surface and membrane volume per molecule increase. In conclusion, cholesterol fluidises the SC lipid membranes in the state below the main phase transition and condenses above it. This effect can have an important impact on the pathologic skin states such as the recessive X-linked ichthyosis.