Physicochemical characterisation of human stratum corneum lipid liposomes

Abstract

Liposomes were prepared from an extract of all human stratum corneum lipids (hSCL) and characterised in terms of temperature and the presence of Ca 2+ by different physicochemical methods. Vesicle aggregation and lateral phase separation were induced by divalent cations with Ca 2+ being more efficient than Mg 2+. At 24.1°C, i.e. well below physiological temperatures the suspensions consisted of a lamellar phase and crystalline cholesterol. At and above 37°C, this cholesterol surplus was dissolved in the hSCL membranes. However, melting of the hSCL was not completed up to 60°C. The presence of Ca 2+ (≥9 mM) induced lateral phase separation and fusion of vesicles into extended multilamellar lipid sheets (MLLS) at and above 32.5°C. Upon a subsequent cooling cycle recrystallisation of cholesterol occurred within the MLLS. Finally, membrane mixing of hSCL liposomes with vesicles made of synthetic lipids was investigated. No mixing was observed between either of DPPE/oleic acid, DPPC/DPPE, DPPC/lyso-PC and hSCL liposomes. Mixtures of DPPC/cholesterol hemisuccinate showed a temperature-dependent membrane mixing behaviour, whilst hSCL liposomes and phosphatidylserine liposomes fused temperature-independently with hSCL liposomes.