ABSTRACTS 291 Influence of solvents on paraben permeation through idealized skin model membranes John N. Twist, and Joel L. Zatz, Ph.D., Rutgers College of Pharmacy, P.O. Box 789, Pis- cataway, NJ 08854 The effect of various solvents on permeation of methylpropyl -- and butylparaben through polydi- methylsiloxane membranes, a model for skin, has been investigated. Flux from saturated solution should theoretically be the same, independent of solvent, in the absence of membrane-solvent inter- action. This was experimentally observed for water, various glycols and glycol-water mixtures, despite enormous differences in paraben solubility in these vehicles. However, there was significant increase in flux from solutions containing various aliphatic al- cohols. The nature of solvent-membrane interaction was investigated through studies of solvent uptake, paraben partitioning, and diffusivity within the membrane. The results indicated that an increase in partition coefficient was the major effect responsible for enhanced flux. Physical chemical properties af- fecting solvent activity influenced the results. The variables investigated here are also expected to de- termine solvent interaction with skin. SESSION F PRODUCT EFFICACY An in vivo system to evaluate efficacy of anti- aging products Peter P. Pugliese, M.D., and Kathleen Klinger, Xienta, Inc., Box 98, Bernville, PA 19506 The purpose of this study was to develop an in vivo model to determine the efficacy of anti-aging products designed to inhibit lipid peroxidation for- mulation by functioning as antioxidants. The system employs the hairless mouse model and utilizes ultraviolet radiation to induce lipid peroxi- dation. The test product is applied prior to irradia- tion and the animal sacrificed after a predetermined period. The epidermis is removed and assayed for malonyldialdehyde by the thiobarbituric acid method. Experience with tocopheryl acetate and betacarotene at various concentrations indicates that these substances are effective anti-aging ingre- dients. A dose-response curve of ultraviolet radia- tion and malonyldialdehyde production will be pre- sented. Pros and cons of the methodology will also be discussed. Single fiber studies of hair depilation R. R. Wickett, Ph.D.,* and Robert Mermel- stein,* S.C. Johnson & Son, 1525 Howe Street (M/S #136), Racine, WI 53403 A single-fiber method for investigating reduction kinetics in hair has been applied to the study of hair depilation. Time required to reduce the tensile stress supported by a hair was found to correlate to in vivo depilation times with commerical depila- tories. Reaction of hair with several reducing agents under depilating conditions was investigated by this method. Depilation rates were increased by in- creasing pH or adding guanidine salts. Rates were decreased by the addition of n-propanol, triacetin, glycerin, or propylene glycol. Emulsion state was also found to affect reduction kinetics. An experi- ment with a central composite design was used to produce a response surface for the effect of TGA concentration, pH, and guanidine hydrochloride concentration on depilation rate. A new procedure to characterize the surface topography of skin Harold Lipshitz, Ph.D., Dermametrics, Box 27, Carlisle, MA 01741 This paper describes an optical method that permits precise quantitative topographical mappings and the calculation of characteristic statistical param- eters of the skin's surface. The procedure utilizes instrumentation (patent pending) that allows mea- surements to be made on the skin or on replicas thereof. The instrumentation consists of a light re- flective optical system, a stage precisely position- able in the three orthogonal directions, and a data acquisition system. Using this system, a procedure was developed to measure the distances from an ar- bitrary reference plane to closely spaced points on the surface of the skin as a function of its x,y coor- dinates in the reference plane. Computerized three- dimensional plots of the data result in picturizations of the skin's surface, whose resolution is greater than that obtained with mechanical profilometry. The computerized image, so obtained, is in excel- lent agreement with scanning electron micrographs (SEMs) of replicas of the same surface. The depths of depressions on replicas of the skin's surface, as determined from stereoscopic SEM data, were within 2% of that measured by this procedure. Using this data, a number of statistical parameters characteristic of the skin's topography were calcu- lated. The methodology promises to be a valuable tool for evaluating the efficacy of emollients. Substantivity to keratins as measured by ESCA W. C. Harris and E. D. Goddard, Specialty Chem- icals Division, Union Carbide Corp., Old Saw Mill River Road, Tarrytown, NY 10591 It is well known that the composition of the outer- most layer of skin and hair is very important in re- lation to their perceived condition. Thus, to assess the effects of various topical treatments, it is desir-

292 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS able to have tools which have the high level of sensi- tivity needed to determine the presence of condi- tioning agents which may be present only in mono- layer or even submonolayer quantities on the surface of these substrates. The search for such tools is on- going. Here we report an investigation of electron spectroscopy for chemical analysis (ESCA), also known as X-ray photoelectron spectroscopy, for this purpose. In our study, emphasis was given to water soluble conditioning agents which were either poly- meric or cationic, or both. Substantivity was also emphasized, i.e., the ability of the agent to absorb from aqueous solution and resist rinse-off by water. The substrates were neonatal rat stratum corneum membranes and virgin brown human hair. ESCA, which probes the outermost 25-50 A of the substrate, is shown clearly to have the sensitivity to detect adsorbed layers of cationic polymers, al- lowing quantitative estimates of surface coverage from the increase in concentration of elements con- stituting the adsorbing species (or, indeed, from a reduction in measured concentration of elements constituting the original substrate surface). High resolution spectra, which are sensitive to the state of chemical bonding of the constituent elements, pro- vide characterizing information on the adsorbed species even when present in submonolayer amounts. Using the technique, we show that deposition can vary considerably along the surface of hair fibers but not with all conditioning polymers. The ability of anionic surfactants to strip deposited material is also demonstrated. Data obtained with isolated stratum corneum membranes show that deposition of polymers may be asymmetric, i.e., the uptake on the outside of the membrane may be different from that on the inside. Results from experiments where the membranes are preexposed to surfactant imply a role of surface lipids in this deposition inequality. Experiments on the effect of various protective skin emollients are also reported. We conclude that ESCA, with its unusually high sensitivity, provides a potentially very powerful tool for use in cosmetic science. An original predictive method for in vivo per- cutaneous absorption studies A. Rougier, D. Dupuis, C. Lotte, and R. Roguet, Laboratoires L'Oreal, 1 Avenue de Saint Germain, 93601 Aulany Sous Bois, France A relationship between stratum corneum (SC) reser- voir function and percutaneous absorption has been shown in human volunteers and in hairless rats. In the hairless rat (back), 10 radiolabeled molecules (200 n.mol) were applied (1 cm2). The quantity (x) of drug within the SC reservoir was determined at the end of application time (30 min) using the stripping technique, and the total amount pene- trated (y) was measured after 4 days. A linear correlation exists between these two param- eters and is given by y = 1.644 x -0.536 (r = 0.998, p inf. 0.001). In both rat (back) and human (arm), such relation is still valid when the same molecule (benzoic acid) is applied at different doses (125, 250, 500 and 1000 n.mol). This allows to establish in human, the correlation curve valid for all types of molecules, with only one compound. The relation obtained may be written as follow: y = 1.82 x -0.52 (r = 0.998, p inf. 0.001). It is worth noting that this relation has been found inde- pendent from the application time, the dose ap- plied, and the vehicle used. Thus, the quantity of drug penetrating through rat or human skin in vivo can be predicted by only mea- suring its horny layer concentration. Moreover, the relatively large amounts of product present in the SC at the end of application time should allow per- cutaneous absorption studies using nonradioactive techniques. Cell proliferation rate studies as efficacy indi- cators Fred Burmeister, Tri-K Industries, Inc., 466 Old Hook Road, P.O. Box 312, Emerson, NJ 07630 The use of human cell cultures in cell proliferation rate studies has been accepted as an in vitro model in the evaluation of antitumor agents' cytotoxic ac- tivity. The potential to look directly at cell prolifer- ation and viability led researchers to believe that a properly modified method could yield valuable in vitro data in the assessment of the efficacy of cos- metic agents and whole products. Tri-K industries, in conjunction with Alfacel Cor- poration, has developed a colorimetric method by which the viability and proliferative profile of human epidermal fibroblast cultures can be quanti- fied. As the culture medium is changed by the ad- dition of chemicals or cosmetic products, so is the specific proliferative profile of the cells in culture. We sought to eliminate the handling and storage problems associated with tritiated thymidine in the choice of this colorimetric assay. This assay utilizes a reagent which is cleaved only by active mitochon- dria. Dead or dying cells do not metabolize the re- agent and will not yield the blue chromophore which is read colorimetrically. We are looking at the physiological responses of cells to the modified media as they replicate . . . not factors associated with the synthesis of DNA . . . as is the case with the 'Warburg' assay of oxygen uptake.