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ABSTRACT
The ability of three matrices to model the barrier properties of the lipid domain of stratum corneum (SC) against permeation of seven steroids was studied. Model matrices were water and oleic acid/oleate; a mixture of unsaturated and saturated fatty acids/soap; or a more complex matrix also containing phospholipids, sphingolipids, cholesterol and ceramides.
Permeability coefficients (K.) were similar in the three models, supporting the hypothesis that the barrier to steroid permeation is determined by the structural organization of the lipids, not by the chemical structure of individual substances. Parabolic relationships were found between K values and octanol/water partition coefficients (Poct) of the steroids, with an optimum permeability at log Poct, of 3·0. All three models showed good resistance to permeability by steroids. The effects of cationic, anionic and non-ionic surfactants on the permeability of hydrocortisone within the water oleic acid/oleate matrix were also investigated. Permeability increased with anionic surfactants, decreased with cationic surfactants and varied little with non-ionic surfactants. The matrices tested appeared able to model the effect of surfactants on the permeability of hydrocortisone through the SC