Cholesterol sulphate and Ca2+ modulate the
mixing properties of lipids in stratum corneum model mixtures
Marjolaine Arseneault 1 and Michel Lafleur 1*
1 Université de Montréal
* To whom correspondence should be addressed. E-mail: michel.lafleur{at}umontreal.ca.
Submitted on May 29, 2006
Revised on July 5, 2006
Accepted on 8 September 2006
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Abstract |
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The influence of cholesterol sulphate and calcium on the phase behavior of lipid mixtures mimicking the stratum corneum lipids was examined using vibrational spectroscopy. Raman microspectrocopy showed that equimolar mixtures of ceramide, palmitic acid, and cholesterol underwent a phase transition where, at low temperatures, lipids formed mainly a mosaic of
microcrystalline phase-separated domains, and above 45 °C, a more fluid and disordered phase where the 3 lipid species were more miscible. In the presence of Ca2+, there was the formation of fatty acid-Ca2+ complexes that led to domains stable upon heating. Consequently, these lipid mixtures remained heterogeneous and the fatty acid molecules were not extensively involved in the formation of the fluid lipid phase, which included mainly ceramide and cholesterol. However the presence of cholesterol sulphate displaced the association site of Ca2+ ions and inhibited the formation of domains formed by the fatty acid molecules complexed with Ca2+ ions. The present work reveals that the cholesterol sulphate and Ca2+ modulate the lipid mixing properties and the lipid order in SC lipid models. The balance in the equilibria involving Ca2+, cholesterol sulphate, and fatty acids is proposed to have an impact on the organization and the function of the epidermis.
Key Words:
Ceramides, Infrared spectroscopy, Raman spectroscopy, phase separations
