title: Omega-hydroxyceramides are required for corneocyte lipid envelope (CLE) formation and normal epidermal permeability barrier function.
abstract: Omega-hydroxyceramides (omega-OHCer) are the predominant lipid species of the corneocyte lipid envelope in the epidermis. Moreover, their omega-esterified-derivatives (acylCer) are major components of the stratum corneum extracellular lamellae, which regulate cutaneous permeability barrier function. Because epidermal omega-OHCer appear to be generated by a cytochrome P450-dependent process, we determined the effects of a mechanism-based inhibitor of omega-hydroxylation, aminobenzotriazole (ABT), on epidermal omega-OH Cer formation and barrier function. We first ascertained that ABT, but not hydroxybenzotriazole (OHBT), a chemical relative with no P450 inhibitory activity, inhibited the incorporation of [14C]-acetate into the omega-OH-containing Cer species in cultured human keratinocytes (68.1% +/- 6.9% inhibition versus vehicle-treated controls; p < 0.001), without altering the synthesis of other Cer and fatty acid species. In addition, ABT significantly inhibited the omega-hydroxylation of very long-chain fatty acids in cultured human keratinocytes. Topical application of ABT, but not OHBT, when applied to the skin of hairless mice following acute barrier disruption by tape-stripping, resulted in a significant delay in barrier recovery (e.g., 38.3% delay at 6 h versus vehicle-treated animals), assessed as increased transepidermal water loss. The ABT-induced barrier abnormality was associated with: (i) a significant decrease in the quantities of omega-OHCer in both the unbound and the covalently bound Cer pools; (ii) marked alterations of lamellar body structure and contents; and (iii) abnormal stratum corneum extracellular lamellar membrane structures, with no signs of cellular toxicity. Furthermore, pyridine-extraction of ABT- versus vehicle-treated skin, which removes all of the extracellular lamellae, leaving the covalently attached lipids, showed numerous foci with absent corneocyte lipid envelope in ABT- versus vehicle-treated stratum corneum. These results provide the first direct evidence for the importance of omega-OHCer for epidermal permeability function, and suggest further that acylCer and/or corneocyte lipid envelope are required elements in permeability barrier homeostasis.
authors.affiliation: Department of Dermatology, School of Medicine, University of California, San Francisco, USA.
authors.forename: M
authors.initials: M
authors.lastname: Behne
authors.forename: Y
authors.initials: Y
authors.lastname: Uchida
authors.forename: T
authors.initials: T
authors.lastname: Seki
authors.forename: P O
authors.initials: PO
authors.lastname: de Montellano
authors.forename: P M
authors.initials: PM
authors.lastname: Elias
authors.forename: W M
authors.initials: WM
authors.lastname: Holleran
mesh_terms: D000287:Administration, Topical; D000818:Animals; D002518:Ceramides / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D000078404:Epidermal Cells; D004817:Epidermis / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D006900:Hydroxylation / Q000187:drug effects; D015603:Keratinocytes / Q000378:metabolism / Q000502:physiology*; D008055:Lipids / Q000502:physiology*; D008297:Male; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D008812:Mice, Hairless; D009685:Nuclear Envelope / Q000502:physiology; D015388:Organelles / Q000187:drug effects; D010539:Permeability / Q000187:drug effects; D012016:Reference Values; D014230:Triazoles / Q000494:pharmacology
chemical_list: D002518:Ceramides; D008055:Lipids; D008565:Membrane Proteins; D014230:Triazoles; C033020:1-aminobenzotriazole