Purification of isopropyl fatty acids markedly changed the skin permeation of a model hydrophilic chemical

Abstract

We determined the difference in the skin-penetration enhancing effects of conventional (C-) and super-refined (SR-) isopropyl fatty acids (IPFAs) including isopropyl myristate (IPM), isopropyl palmitate (IPP), and isopropyl oleate (IPO). In vitro permeation experiments were performed with excised hairless rat skin using a model mal-absorbed chemical, calcein. As a result, SR-IPM pretreatment markedly increased the skin permeation of calcein from aqueous solution more than C-IPM pretreatment, in spite of a small difference in IPM purity (98.78 vs 99.96%). Similar phenomena were recorded even when using SR-IPM emulsion compared with C-IPM emulsion without pretreatment. In contrast, C-IPP pretreatment showed higher skin permeation than SR-IPP. In addition, no difference was observed in skin permeation between C-IPO and SR-IPO. Skin impedance was also determined as an index of skin barrier function. SR-IPM changed the skin barrier function more than C-IPM, which supported the penetration-enhancing order of C-IPM and SR-IPM shown above. It was unexpected to find such a big difference in the skin-penetration enhancing effect of C-IPM vs SR-IPM and C-IPP vs SR-IPP. The present results suggested that SR-IPM could be a promising ingredient in pharmaceutical and cosmetic products for topical use.