Interaction of liposome formulations with human skin in vitro

The interaction of liposome formulations consisting of Phospholipon (R) 80 and sphingomyelin with human skin was investigated. These formulations were shown previously to have a composition-dependent effect on the penetration of Heparin into the skin. Fluorescence labelled phosphatidylethanolamine ( PE-NBD) was incorporated in the liposomes and the depth in which the fluore scent phospholipid label enters into epidermal membrane and full thickness skin was studied by confocal laser scanning microscopy (CLSM). Confocal. se ctions parallel to the surface of the skin were recorded in heat separated epidermis. An even distribution of phospholipid in the lipid matrix of the stratum corneum surrounding the corneocytes was observed with Phospholipon 80 but not when sphingomyelin was included in the formulation. The addition of Heparin which formed a coating around the liposomes, caused a strong lo calization of fluorescence within the epidermis. For full thickness skin, m echanical cross sections of skin were made and optical sections were record ed parallel to the plane of cut. Phospholipid penetrated and was distribute d fairly homogeneously in the lower dermis layers within 30 min of applicat ion regardless of liposome composition and the presence of Heparin. This ra ther quick penetration process seemed to follow distinct pathways along the epidermis and the upper dermis, notably the hair follicle route. Thus, a s trong and in some respects composition-dependent interaction of phospholipi ds with skin is evident. These observations, however, are limited to the le vel of phospholipid molecules, rather than of entire liposomes interacting with skin. (C) 2001 Elsevier Science B.V. All rights reserved.