A Provocation on Formation of the Corneocyte Lipid Envelope

The major carriers of linoleic acid in the epidermis are an acylglucosylceramide in the viable portion of the epidermis and an analogous acylceramide in the stratum corneum. The acylglucosylceramide and acylceramide are the precursors of the corneocyte lipid envelope (CLE).

Oxidation of the ester-linked linoleate by two lipoxygenases working in tandem has been shown to be involved in CLE formation. Acylglucosylceramide appears to be the substrate for initial CLE formation at the bottom of the stratum corneum, while acylceramide is the precursor for the covalently attached ω-hydroxyceramide thereafter. It would be expected that consumption of linoleate in CLE formation would decrease the linoleate content of the remaining acylceramide; however, this is not observed for total acylceramide. When acylceramide from only the outer layers of stratum corneum has been analyzed, the linoleate content is notably reduced compared to the values found for these lipids from full thickness stratum corneum or epidermis. This is consistent with a major role for the linoleate-containing acylceramide in the later stages of CLE maturation. This also suggests that a mechanism that is not selective for ester-linked linoleate may also be involved in early CLE formation, while the oxygen-dependent mechanisms are essential in the later stage of envelope maturation.

This review proposes an oxygen-independent mechanism that may contribute to the early stages of CLE formation. The lipoxygenase-dependent contribution to the formation of the CLE would be more prominent in the later stages of maturation.