J. Soc. Cosmetic Chemists, 19, 16 3-172 (Mar. 4, 1968) The Effect of Dimethyl Sulfoxide on Percutaneous Absorption: A Mechanistic Study. Part II STANLEY G. ELFBAUM, Ph.D., and KARL LADEN, Ph.D.* Presented before the Mid-A tlantic Chapter, February 1 •, 1067 Synopsis--Dimethyl sulfoxide (DMSO) has been found to be effective in enhancing the in vitro percutaneous absorption of picrate ion through intact guinea pig skin membranes. Observations reported here suggest that DMSO causes swdling or expansion of the protein fibers in the skin barrier. Excised skin membranes become grossly swollen, wrinkled, and turgid when exposed to large concentrations of DMSO. DMSO causes the reduced viscosi- ties of bovine serum albumin and beta lactoglobulin to increase on the acid sides of their iso- electric points. Such behavior would be expected of a protein chain undergoing unfolding or expansion. Dioxane which had been shown through viscosity studies to cause an expansion or swelling of soluble proteins also causes a marked enhancement of the diffusion of picrate ion through intact guinea pig skin membranes. The equilibrium liquid retention studies on hair in DMS0/Hs0 mixtures reveal that liquid retention and swelling increase with increasing concentrations of DMS0 up to 100% DMS0. The effect is similar to diffusion studies in which large concentrations of DMS0 were necessary to enhance the penetration process appreciably. INTRODUCTION In the preceding paper (1), the observation was reported that guinea pig skin membranes which had been subjected to high concentra- tions of dimethyl sulfoxide (DMSO) appeared more wrinkled, more stretched and swollen, and less pliable than skin membranes which had been in contact with aqueous buffers or lower concentrations of DMSO. Similar observations have been reported by others (2, 3). * Gillette Research Institute, 6220 Kansas Avenue, N.E., Washington, D.C. 20011. 163

164 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS These observations suggested to us that the enhanced percutaneous penetration produced by DMSO may be caused by a swelling ( or expan- sion) of the protein fibers in the skin. Because of the structural limita- tions of the skin matrix, the complete swelling or complete expansion of the protein fibers would have to be restrained. This could result in the turgid and wrinkled appearance of the skin. Other results in the literature indicate that DMSO is capable of mod- ifying or altering protein fibers. Russell and Winkelmann made the observation that DMSO caused the thermal shrinkage temperature of hu- man abdominal dermis to increase with increasing concentrations of DMSO and that this was accompanied by a decrease in the values of isometric tension and amount of isotonic contraction (4). Bradbury and Chapman have also observed that DMSO caused a 23% increase in diametrical swelling of wool (5). While it is well know that swelling skin via hydration dramatically enhances skin permeability (6, 7), the possibility does exist that hydra- tion does not exhaust the expansion potential of the skin. Other solvents have been reported to enhance the swelling or un- folding of proteins to a greater extent than does water alone. In 1961, Van Ho!de and Sun reported on the effect of dioxane upon the configura- tion of the globular protein, bovine serum albumin. Normally, the con- figuration of bovine serum albumin (BSA) is relatively insensitive to solvent environment in the region around the isoelectric point. On the acid side of the isoelectric point, the protein undergoes a well known and well documented reversible expansion. Van Holde and Sun found that the acid expansion of the BSA molecule, as evidenced by viscometric changes, was appreciably enhanced by the presence of dioxane. The results were attributed to the enhancement of electrostatic interactions within the molecular framework of the protein molecule due to the non- polar effects of dioxane (8). With these results in mind, it was decided to investigate whether the changes in permeability of the skin barrier induced by DMSO might be explained by virtue of its swelling action. Thus the effect of DMSO on swelling proteins was studied in detail. In addition, the effect of a different protein swelling solvent (dioxane) on altering the permeability of the skin was evaluated. MATERIALS AND METHODS "Certified" reagent grade 1,4-dioxane and "certified" reagent grade dimethyl sulfoxide were obtained from Fisher Scientific Company, Fair-