Stratum Corneum Lipids of Human Epidermal Keratinocyte Air-Liquid Cultures: Implications for Barrier Function

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Abstract
Purpose. The purpose of this study is to investigate the permeability barrier, i.e., the stratum corneum (SC) lipids, of human epidermal keratinocyte air-liquid cultures and compare them with those of human SC. Methods. The SC lipids composition was analyzed by TLC technique, the organization by electron microscopic procedure, and the phase transition temperature by Infrared spectroscopic method. Results. Electron microscopy demonstrated that The SC lipids of cultures were largely retained inside the corneocytes, and that the intercellular lipids lack both the basic unit repetition (i.e., broad : narrow : broad : broad : narrow : broad of electron lucent bands) and the covalently-bound lipid envelope normally found in human SC. These characteristics are similar to those found in SC from patients with atopic dermatitis or psoriasis, or from animals with essential fatty acid deficiency, suggesting that the cultures may be hyperproliferative. In addition, the high free sterol content and the altered fatty acid/ceramide composition of these cultures argue that the compromised barrier function is linked to hyperproliferation and lipid synthesis, or vice versa. Infrared spectroscopic analyses confirm that there are major conformational differences between the lipids of human and cultured SC. Conclusions. The profound differences in SC lipid composition, organization and conformational properties attest that permeability alone is not a sufficiently sensitive marker to define barrier equivalence between cultures and human skin.