Stratum corneum lipid organization as observed by atomic force, confocal and two-photon excitation fluorescence microscopy.
Skin moisturization is largely a function of stratum corneum barrier capacity, which in turn is a function of the physical state and structural organization of the stratum corneum extracellular lipid matrix [J. Invest. Dermatol.18, 433 (1952); AIChE J. 21, 985 (1975); Acta Derm. Venereol.74, 1 (1994); J. Invest. Dermatol.117, 830 (2001)]. Three unsolved key questions with respect to this lipid matrix' structural organization [Acta Derm. Venereol.74, 1 (1994); J. Invest. Dermatol.117, 830 (2001); J. Invest. Dermatol.118, 897 (2002); J. Invest. Dermatol.118, 899 (2002)] are: i) whether the lipid matrix is constituted by a single-gel phase or by co-existing solid (crystalline or gel) domains, ii) whether a separate fluid (liquid crystalline) phase is present and iii) whether the local pH has a direct effect on the lipid matrix' phase behaviour. Using an array of complementary visual-related biophysical techniques (e.g. atomic force microscopy and confocal/two-photon excitation fluorescence microscopy), it was recently shown that reconstituted membranes composed of extracted decontaminated human stratum corneum lipids do not form a fluid phase, but exclusively a single-gel phase that segregates into co-existing microscopic domains below pH 6 [Biophys. J.93, 3142 (2007)]. It was further shown that the role of cholesterol is related to dispersion of ceramide-enriched domains. This effect is counteracted by the presence of free fatty acids, which mix with skin ceramides but not with cholesterol.
Norlén
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Department of Cell and Molecular Biology (CMB), Medical Nobel Institute, Karolinska Institute, Stockholm, Sweden. lars.norlen@ki.se
Plasencia
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Bagatolli
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D000818:Animals; D002518:Ceramides / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D005109:Extracellular Matrix / Q000737:chemistry / Q000378:metabolism*; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D006801:Humans; D050356:Lipid Metabolism / Q000502:physiology*; D018625:Microscopy, Atomic Force; D018613:Microscopy, Confocal; D036641:Microscopy, Fluorescence, Multiphoton; D012867:Skin / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure
D002518:Ceramides; D005230:Fatty Acids, Nonesterified; D002784:Cholesterol