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Free keywords:
stratum corneum lipids; model membrane; transdermal drug delivery; penetration enhancer; mode of action
Abstract:
To optimize transdermal application of drugs, the barrier function of the skin, especially the stratum corneum (SC), needs to be reduced reversibly. For this purpose, penetration enhancers like urea or taurine are applied. Until now, it is unclear if this penetration enhancement is caused by an interaction with the \SC\} lipid matrix or related to effects within the corneocytes. Therefore, the effects of both hydrophilic enhancers on \{SC\} models with different dimensionality, ranging from monolayers to multilayers, have been investigated in this study. Many sophisticated methods were applied to ascertain the mode of action of both substances on a molecular scale. The experiments reveal that there is no specific interaction when 10 urea or 5 taurine solutions are added to the \{SC\ model systems. No additional water uptake in the head group region and no decrease of the lipid chain packing density have been observed. Consequently, we suppose that the penetration enhancing effect of both substances might be based on the introduction of large amounts of water into the corneocytes, caused by the enormous water binding capacity of urea and a resulting osmotic pressure in case of taurine.
