Alterations in stratum corneum lipid liposomes due to the action of TritonX-100 - Influence of the level of ceramides on this process

The role played by the ceramides (Cer) in the interaction of Triton X-100 ( TX-100) with liposomes modeling the stratum corneum (SC) lipid composition was studied. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined at sublytic level by moni toring the changes in the fluorescence intensity of liposomes due to the 5( 6)-carboxyfluorescein (CF) released from the interior of vesicles. Higher a nd lower Cer proportions than those existing in the SC (40%) led respective ly to a fall and to a rise in the surfactant ability to alter these liposom es. However, the surfactant partitioning between bilayers and water (bilaye r affinity with vesicles) exhibited a maximum for 40% Cer. Thus, at low Cer proportions the ability of TX-100 molecules to alter these bilayers was ma ximum despite their reduced partitioning into bilayers, in line with the re ported interaction of the anionic surfactant model sodium dodecyl sulfate w ith these vesicles. These findings underline the fragility of these bilayer s as an effective barrier and could explain in part the reported dependenci es of low level of Cer in skin lipids and function barrier abnormalities. T he fact that the free surfactant concentration needed to achieve the two in teraction levels investigated was lower than the surfactant CMC indicates t hat permeability alterations were mainly ruled by the action of surfactant monomers, regardless of Cer proportion in bilayers. (C) 2000 Elsevier Scien ce B.V. All rights reserved.