PHYSICOCHEMICAL CHARACTERIZATION OF HUMAN STRATUM-CORNEUM LIPID LIPOSOMES

Liposomes were prepared from an extract of all human stratum corneum l ipids (hSCL) and characterised in terms of temperature and the presenc e of Ca2+ by different physicochemical methods, Vesicle aggregation an d lateral phase separation were induced by divalent cations with Ca2being more efficient than Mg2+. At 24.1 degrees C, i.e. well below phy siological temperatures the suspensions consisted of a lamellar phase and crystalline cholesterol, At and above 37 degrees C, this cholester ol surplus was dissolved in the hSCL. membranes. However, melting of t he hSCL was not completed up to 60 degrees C. The presence of Ca2+ (gr eater than or equal to 9 mM) induced lateral phase separation and fusi on of vesicles into extended multilamellar lipid sheets (MLLS) at and above 32.5 degrees C. Upon a subsequent cooling cycle recrystallisatio n of cholesterol occurred within the MLLS. Finally, membrane mixing of hSCL liposomes with vesicles made of synthetic lipids was investigate d. No mixing was observed between either of DPPE/oleic acid, DPPC/DPPE , DPPC/lyso-PC and hSCL liposomes, Mixtures of DPPC/cholesterol hemisu ccinate showed a temperature-dependent membrane mixing behaviour, whil st hSCL liposomes and phosphatidylserine liposomes fused temperature-i ndependently with hSCL liposomes. (C) 1998 Elsevier Science Ireland Lt d. All rights reserved.