Investigation of liposomes as carriers of sodium ascorbyl phosphate for cutaneous photoprotection

Long-term exposure of the skin to UV-A and UV-B radiation causes degenerative effect which can be decreased by scavenging reactive photochemical intermediates with antioxidants. In this study sodium ascorbyl phosphate (SAP), a very effective oxygen species scavenger, was encapsulated into liposomes in order to improve its penetration through the stratum corneum into the deeper layers of the skin. Two types of multilamellar vesicles were prepared, one from non-hydrogenated and the other from hydrogenated soybean lecithin, together with cholesterol, by the thin films method. They were characterized for size, polydispersity index, and zeta potential. In vitro diffusion of SAP and ex vivo penetration experiments were performed on pig ear epidermis membrane in a Franz diffusion cell. The size and zeta potential of liposomes containing SAP are significantly greater than those of empty liposomes. The upper limit of SAP entrapment efficiency was 8-10% in both types of liposomes. The stability of SAP in liposome formulations is much more influenced by storage temperature than by liposome composition. SAP penetrated through epidermis membrane significantly better from liposome dispersions than from water solution. The amount penetrating is much more influenced by the concentration of SAP in the formulation than by the lipid composition of liposomes. The SAP that penetrates through the epidermis reflects the active compound available to prevent or slow down the complex process of photodamage in the skin.