INTERACTION OF PHOSPHOLIPID LIPOSOMES WITH LIPID MODEL MIXTURES FOR STRATUM-CORNEUM LIPIDS

Differential scanning calorimetry (DSC) and H-2-NMR experiments were performed on lipid vesicles prepared from a lipid mixture resembling the lipid composition of stratum corneum lipids in the epidermis. This lipid mixture showed a broad phase transition with a transition range from 40 to approx. 80-degrees-C. H-2-NMR spectroscopy revealed that the transition occurs from a lamellar gel-like phase to a cubic phase at high temperature. Both phases coexist over a broad temperature range. Mixing of populations of different soy bean phosphatidylcholine or dipalmitoylphosphatidylcholine vesicles with the vesicles made from the model mixture for stratum corneum lipids resulted in the mixing of lipid components, induced either by heating the vesicles to 95-degrees-C, or by incubation of the vesicle mixtures at 37-degrees-C for 2-24 h. The mixing of lipid components apparently proceeds by monomer exchange through the water phase. H-2-NMR spectroscopy showed that the resulting mixed lipid system has different phase characteristics, being in a liquid-crystalline state at 37-degrees-C and transforming apparently to an inverted hexagonal phase at higher temperature. The consequences for the penetration of liposomes through the stratum corneum of the skin are discussed. Mixing of liposomes with the lipids in the intercellular layers could be one mechanism contributing to the enhancement of the permeability of the skin to lipid vesicles.