Molecular interactions of penetration enhancers within ceramides organization: A FTIR approach

The barrier function of the skin is related to the unique composition of the stratum corneum (SC) lipids and their complex structural arrangement. The high content of ceramides would seem to be ideally suited for the formation of ordered impermeable membrane.Skin penetration enhancers (PE) are molecules which reversibly remove the barrier resistance of the SC. Interactions with SC intercellular lipids are of crucial importance for the effectiveness of PE action. Their mode of action on the lipid bilayer may involve interactions at two sites, i.e., at or near the polar head groups of the lipid bilayer and/or between the hydrophobic tails of the bilayer. This paper discusses the local effect of four PE, among the most investigated, limonene, ethanol, oleic acid and DMSO.FTIR is used in this study to highlight the local effect of the PE on ceramides films. Lipophilic PE, i.e., oleic acid and limonene, both present a direct fluidizing action on the alkyl chains and an indirect action on the polar head groups resulting in a more spacing lipid packing. Hydrophilic PE, i.e., ethanol and DMSO, have no interaction on the lipid bilayer but show a complex action on the polar headgroup, weakening the H-bonds.Our most significant finding is that each PE we investigated interacted with the ceramide packing, depending of these structures. Such modifications contribute a share to interpretation, at the molecular level, of the decrease of skin barrier properties with PE described in published data.