Infrared spectroscopic study of stratum corneum model
membranes prepared from human ceramides, cholesterol and
fatty acids
Gert Gooris 1 and Joke Bouwstra 1*
1 Leiden University
* To whom correspondence should be addressed. E-mail: bouwstra{at}chem.leidenuniv.nl.
Submitted on August 2, 2006
Revised on September 11, 2006
Accepted on 17 November 2006
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Abstract |
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The outermost layer of the skin, the stratum corneum, consists of corneocytes surrounded by lipid domains. The main lipid classes in stratum corneum are cholesterol, ceramides and free fatty acids forming two crystalline lamellar phases. However, only limited information is available on whether the various lipid classes participate in the same crystalline lattices or that separate domains are formed within the lipid lamellae. In this paper infrared spectroscopic studies are reported of hydrated mixtures prepared from cholesterol, human ceramides and free fatty acids. Evaluation of the methylene stretching vibrations revealed a conformational disordering starting at around 60°C for all mixtures. Examining the rotational ordering (scissoring and rocking vibrations) of mixtures prepared from equimolar cholesterol and ceramides with a variation in the level of free fatty acids showed that at lower free fatty acid content orthorhombic and hexagonal domains coexist in the lipid lamellae. Increasing the fatty acid level to an equimolar cholesterol:ceramides:fatty acid mixture reveals the dominant present of an orthorhombic lattice, confirming x-ray diffraction studies. Replacing the protonated free fatty acid chains by its perdeuterated counterparts demonstrate that free fatty acids and ceramides participate in the same orthorhombic lattice up to a level of slightly less than 1:1:0.75 cholesterol:ceramides:free fatty acids molar ratio, but that free fatty acids form also separate domains within the lipid lamellae at equimolar ratios at room temperature. However, no evidence for this has been observed at 32°C. Extrapolating these findings to the situation in stratum corneum led us conclude that in stratum corneum but that fatty acids and ceramides participate in the orthorhombic lattice at 32°C, the skin temperature.
Key Words:
ceramides, crystalline lipid domains, infrared spectroscopy, skin
