Effect of organic solvents on in vitro human skin water barrier function.

Skin barrier disruption caused by organic solvents to human cadaver dermatomed skin was evaluated using an in vitro model system. Resultant changes in transepidermal water loss (TEWL), as measured with an evaporimeter, were recorded after topical application of either acetone, chloroform:methanol 2:1, hexane, hexane:methanol 2:3, or the control, water, for exposure times of 1, 3, 6, and 12 min. The resultant lipid/solvent mixture was removed and analyzed for its lipid content. The ability of the different solvents to induce changes in the skin's barrier function was assessed by comparing pre- to post-solvent exposure TEWL (delta TEWL). When compared to the controls, water and unexposed skin, chloroform:methanol 2:1 caused the greatest significant increase in TEWL, followed by hexane:methanol 2:3. Acetone and hexane showed no difference in TEWL from the controls. Besides solvent, exposure time was a significant independent variable for predicting delta TEWL, and the interaction of the two (exposure time and solvent type together) was the strongest predictor. Lipid analysis of the extracts revealed that all the solvents removed comparable quantities of the surface lipids (triglycerides, wax esters, squalene, cholesterol esters). Stratum lipids--ceramides, free fatty acids, and cholesterol--extracted by chloroform:methanol 2:1 and hexane:methanol 2:3 were comparable and significantly greater than those extracted by acetone and hexane. These two solvents failed, however, to induce comparable changes in TEWL, as chloroform:methanol 2:1 induced a significantly greater delta TEWL than hexane:methanol 2:3. Additionally, no individual lipid class extracted by either chloroform:methanol 2:1 or hexane:methanol 2:3 proved to be a significant or accurate variable for predicting delta TEWL. This suggests that the mechanism by which topical chloroform:methanol 2:1 and hexane:methanol 2:3 exposure induce a delta TEWL involves more than pure lipid extraction.