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

Differential scanning calorimetry (DSC) and H-2-NMR experiments were p erformed on lipid vesicles prepared from a lipid mixture resembling th e lipid composition of stratum corneum lipids in the epidermis. This l ipid mixture showed a broad phase transition with a transition range f rom 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 dip almitoylphosphatidylcholine vesicles with the vesicles made from the m odel mixture for stratum corneum lipids resulted in the mixing of lipi d 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. T he mixing of lipid components apparently proceeds by monomer exchange through the water phase. H-2-NMR spectroscopy showed that the resultin g mixed lipid system has different phase characteristics, being in a l iquid-crystalline state at 37-degrees-C and transforming apparently to an inverted hexagonal phase at higher temperature. The consequences f or the penetration of liposomes through the stratum corneum of the ski n are discussed. Mixing of liposomes with the lipids in the intercellu lar layers could be one mechanism contributing to the enhancement of t he permeability of the skin to lipid vesicles.