IN-VITRO HUMAN SKIN BARRIER PERTURBATION BY OLEIC-ACID - THERMAL-ANALYSIS AND FREEZE-FRACTURE ELECTRON-MICROSCOPY STUDIES

This study aims to elucidate the working mechanism Df oleic acid (OA) on isolated human stratum corneum (SC) sheets using two in vitro techn iques, differential thermal analysis and freeze-fracture electron micr oscopy. Differential thermal analysis on SC after the application of O A in propylene glycol revealed significant changes in the thermal prof iles of SC compared to that of the untreated SC. The changes occurred generally on the lipid phase transitions by both shifting the temperat ures to a lower degree and reducing the enthalpies of the transitions normally observed between 40 degrees and 90 degrees C. Another newly o bserved change took place in the temperature range below O degrees C, referred to as the subzero region. The subzero transition of OA has pr ofoundly influenced the subzero SC lipid transition (normally observed at around -10 degrees C) by shifting it to a lower temperature. The i nteresting observation was that the subzero transition of SC lipid and of OA became a single transition after the SC is heated to 120 degree s C, which indicates a close interaction between oleic acid and SC lip ids. Electron micrographs obtained by freeze-fracture electron microsc opy revealed the formation of a new structure in the intercellular lip id regions of SC in the presence of OA. These findings may prove that oleic acid acts as a skin penetration enhancer by forming together wit h SC lipid a new type of lipid domain which are responsible for the de creased capacity of skin barrier function after oleic acid treatment. (C) 1997 Elsevier Science B.V.