Neutron diffraction studies of oral stratum corneum model lipid membranes.

In this work we have investigated model lipid mixtures simulating a lipid component of oral stratum corneum (OSC). Neutron diffraction experiments on oriented samples have revealed that SM (bovine brain)/dipalmitoylphosphatidylethanolamine/dipalmitoylphosphatidylcholine (DPPE/DPPC) mixtures at molar ratios of 1/2/1 and 1/1/1 are one-phase membranes. The incorporation of low concentrations of ceramide 6 and cholesterol into SM/DPPC/DPPE bilayers does not result in a phase separation, affecting membrane hydration. The model OSC membrane composed of ceramide 6/cholesterol/fatty acids/cholesterol sulfate/SM (bovine brain)/DPPE/DPPC is characterized by coexistence of several lamellar phases, that behave differently during their hydration in water excess. The phase with lamellar repeat distance of about 45 Å is likely a ceramide-rich phase and shows a restricted swelling in water, while another phase with repeat distance of 50 Å swells very quickly on 15 Å and then disappears. Our results indicate that phospholipid-rich and ceramide-rich domains could possibly coexist in the intercellular space of oral epithelium.

Investigation of stratum corneum lipid model membranes with free fatty acid composition by neutron diffraction.

The outermost epidermal layer, the stratum corneum (SC), is the main skin barrier. Studies of SC model systems enable characterization of the influence of individual lipids on the organization of the SC lipid matrix, which is the main pathway of water through the skin. This work presents a neutron diffraction study of the SC model membranes based on short-chain ceramide 6 with nearly realistic composition of free fatty acids (FFA) at physiological temperature of the SC. The influence of FFA and the effect of cholesterol-cholesterol sulfate substitution on the structure and hydration of the SC model membranes are described. The structure of the SC membrane with FFA is close to the structure of the earlier studied SC membrane based on short-chain palmitic acid (PA) and does not vary significantly under changes of the ratio of the main membrane components. FFA accelerates membrane swelling at the same low level of hydration of both PA- and FFA-containing membranes. The substitution of cholesterol sulfate by cholesterol in the membrane composition decreases membrane swelling and leads to phase separation in the model system.