THE FORMATION OF COMPETENT BARRIER LIPIDS IN RECONSTRUCTED HUMAN EPIDERMIS REQUIRES THE PRESENCE OF VITAMIN-C

Our analysis of epidermal lipids revealed that (glucosyl)ceramide prof iles in various human skin equivalents are different from those of nat ive tissue, The main difference is the reduced content in skin equival ents of ceramides 4-7 and especially the very low content of the most polar ceramides 6 and 7, which contain hydroxylated sphingoid base and /or fatty acid. To facilitate hydroxylation, the culture medium was su pplemented with vitamins C and E, Although in vitamin E-supplemented m edium lipogenesis was not affected, in vitamin C-supplemented medium t he content of glucosylceramides and of ceramides 6 and 7 was markedly increased, both in the presence and absence of serum and irrespective the substrate used (inert or natural, populated or not with fibroblast s), The improvement of the lipid profile was accompanied by a marked i mprovement of the barrier formation as judged from extensive productio n of lamellar bodies, their complete extrusion at the stratum granulos um/stratum corneum interface, and the formation of multiple broad lipi d lamellar structures in the intercorneocyte space, The presence of we ll-ordered lipid lamellar phases was confirmed by small-angle x-ray di ffraction. Some differences between native and reconstructed epidermis , however, were noticed, Although the long-range lipid lamellar phase was present in both the native and the reconstructed epidermis, the sh ort lamellar phase was present only in native tissue, It remains to be established whether these differences can be ascribed to small differ ences in relative amounts of individual ceramides, to differences in f atty acid profiles, or to differences in cholesterol sulfate, pH, or c alcium gradients, The results indicate the key role vitamin C plays in the formation of stratum corneum barrier lipids.