Exogenous sphinganin derived sphingolipid increases epidermal ceramide content in human reconstructed skin

Sphingolipids are major constituents of the human stratum corneum in an equimolar ratio with free fatty acids and cholesterol. Arranged as intercellular membrane bilayers, they play a central role in permeability barrier homeostatis. It has been shown that qualitative and/or quantitative changes in stratum corneum lipids may result in defective barrier function and the appearance of dry skin. We assumed that supplementation of dry skin with a ceramide precursor could improve the sphingolipid content of the stratum corneum. In the present study, we investigated the ability of human skin to transform a sphinganin derived sphingolipid into endogenous ceramides. Since human reconstructed epidermis has been shown to provide a valuable model for studying skin lipogenesis, we decided to investigate the effect of medium supplementation with N-(2-hydroxyhexadecanoyl) sphinganin on the epidermal lipid synthesis and composition of an in vitro skin model, EPISKIN< trademark >. The reconstructed epidermis was cultured for 7 to 14 days at the air-liquid interface in the presence of N-(2-hydroxyhexadecanoyl) sphinganin (10^-7M). The incorporation of [¹⁴C]-acetate revealed no modification of the lipid synthetic pathways in the presence of ceramide precursor. HPTLC quantification exhibited an increase in the epidermal total ceramide content. This change in lipid composition could not be attributed to the incorporation of exogenous sphinganin in stratum corneum bilayers since no specific increase in a-hydroxylated sphinganin occurred. On the other hand, ceramide fractions 1, 2 and 3 increased, showing a possible metabolization of the exogenous sphingolipid by reconstructed epidermis. The results obtained in this study, using EPISKIN< trademark > as skin model, show that an exogenous, suitable lipid precursor is able to enhance endogenous total ceramide content.