Structural and functional effects of oleic acid and iontophoresis on hairless mouse stratum corneum

The aim of this study was to assess the effects of chemical and electrical modes of percutaneous penetration enhancement on the intercellular lipid lamellae of the stratum corneum. Hairless mice were treated with either oleic acid/propylene glycol and iontophoresis separately or together. Permeability barrier function was evaluated by measuring transepidermal water loss and correlated with the structure of stratum corneum intercellular lamellae, as evaluated by electron microscopy, using ruthenium tetroxide postfixation. Transepidermal water loss levels did not change following 1 h iontophoresis alone. In contrast, topical applications of 0.3 M oleic acid in propylene glycol for 1 h increased transepidermal water loss significantly. Moreover, the combined use of iontophoresis plus 0.3 M oleic acid for 1 h further increased transepidermal water loss at equivalent time points. Ultrastructural observations demonstrated both marked disorganization of the intercellular lipid lamellae, as well as the presence of distended lacunae within the stratum corneum in oleic acid/propylene glycol plus or minus iontophoresis-treated stratum corneum. This study provides direct evidence that the oleic acid/propylene glycol system can disrupt the stratum corneum lipid lamellar structures, and that coapplications of oleic acid with iontophoresis further enhance the effects of oleic acid. The synergy between chemical and physical enhancement may afford a new approach to promote transdermal drug delivery.