Evaluation of model for stratum corneum lipid barrier against steroid diffusion

The ability of three matrices to model the barrier properties of the lipid domain of stratum corneum (SC) against permeation of seven steroids was stu died. Model matrices were water and oleic acid/oleate; a mixture of unsatur ated and saturated fatty acids/soap; or a more complex matrix also containi ng 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 ind ividual substances. Parabolic relationships were found between K values and octanol/water partition coefficients (P-oct) of the steroids, with an opti mum permeability at log P-oct of 3.0. All three models showed good resistan ce to permeability by steroids. The effects of cationic, anionic and non-ionic surfactants on the permeabil ity of hydrocortisone within the water oleic acid/oleate matrix were also i nvestigated. Permeability increased with anionic surfactants, decreased wit h cationic surfactants and varied little with non-ionic surfactants. The ma trices tested appeared able to model the effect of surfactants on the perme ability of hydrocortisone through the SC.