Interaction of Epicutaneously Applied Lipids with Stratum Corneum Depends on the Presence of either Emulsifiers or Hydrogenated Phosphatidylcholine

The barrier function of the stratum corneum (SC) significantly determines the interaction of epicutaneously applied substances with the skin organ. Although the exact molecular processes are still unclear, it is undoubted that the intercellular lipid composition and order of the SC is significantly involved in this interaction. Topically substituted phases, especially those of lipophilic composition, seem to interact very intensely with lipid membranes; they can be integrated, form separate phases, or even permeate through the SC into the viable skin. The latter is not desired, especially in barrier-protective preparations with a lipophilic phase. The present paper investigates the penetration behavior of topically applied, Dil-labeled lipids into human ex vivo skin depending on the phase organization of different o/w emulsifiers compared to emulsifier-free preparations containing hydrogenated phosphatidylcholine by means of fluorescence indication. Results are presented for intact and defined damaged epidermal barrier. In addition, the washout effect based on skin samples treated by artificial watering after lipid incubation, and the influence of the phase transition temperature of the SC membrane were studied. The results show that in intact and damaged skin, the penetration depth of the lipids increases directly proportionally with the hydrophilic-lipophilic balance (HLB value), while the washout effect and the HLB value proved to be inversely related. An increase in penetration depth with higher HLB values was also apparent when the phase transition temperature of the physiological membranes was exceeded. Altogether, the results clearly demonstrate that the characteristics of the emulsifying phase of a preparation significantly determine the interaction of a substituted lipophilic phase with the SC. Especially bipolar lipids, like phosphatidylcholines, showed intradermal dispersion patterns which hint at an especially intense interaction with physiological membranes. Copyright (C) 2010 S. Karger AG, Basel