J. Cosmet. Sci., 70, 247–257 (September/October 2019) 247 In Vitro Penetration of Petrolatum in Stratum Corneum from Bodywash Formulation APIPA WANASATHOP, ZHANQUAN SHI, Q. CHING STELLA, KARL S. WEI, PETER B. STYCZYNSKI, CHUIYING LI, and S. KEVIN LI , Division of Pharmaceutical Sciences, James L. Winkle College of Pharmacy, University of Cincinnati, Cincinnati, Ohio (A.W., Z.S., S.K.L.) , Procter & Gamble Co., Mason, Ohio (Q.C.S., K.S.W., P.B.S., C.L.) Accepted for publication July 16, 2019. Synopsis Petrolatum is a mixture of hydrocarbons that is widely used as a moisturizer. It is incorporated in bodywash formulations to help hydrate and maintain healthy skin appearance. The aim of this study was to investigate skin deposition and penetration of petrolatum from an experimental bodywash system consisting of petrolatum in vitro. Experiments were performed using cadaver split-thickness skin and Franz diffusion cells. Radiolabeled 14 C-dotriacontane (C32-alkane) was used as a model permeant for petrolatum. The bodywash was applied on the skin and subsequently rinsed. At predetermined time points, the skin was wiped to remove the residual material on the surface, and tape-stripping was performed. Petrolatum was observed to deposit from the bodywash when applied on split-thickness skin with simulated rinsing. Petrolatum then penetrated into the stratum corneum and was detected at the depth of 12 tape-stripping and in the epidermis. The bodywash formulation could provide signifi cant deposition and penetration of petrolatum into the stratum corneum at 1–72 hours postapplication. INTRODUCTION Bodywash is a widely used cosmetic product and is directly applied to the human skin. Its purpose is to cleanse and condition the skin. The active ingredients in bodywash are surfactants that remove dirt and soil on the skin. Surfactants also remove protective oils that are naturally present. This can lead to dry and uncomfortable skin after washing (1). Therefore, moisturizing bodywashes are formulated to improve skin hydration and main- tain a healthy skin surface condition. Petrolatum is a semisolid widely used in cosmetics as a moisturizer. It is a complex mixture of hydrocarbons obtained from dewaxing paraffi nic residual oil (2). It was suggested that petrolatum can accelerate the skin surface barrier recovery and replace intercellular lipids by fi lling in the stratum corneum interstices (3). Petrolatum was also found to induce Address all correspondence to Apipa Wanasathop at wanasaaa@mail.uc.edu .
JOURNAL OF COSMETIC SCIENCE 248 expression of key barrier differential markers such as fi laggrin and loricrin and upregulate antimicrobial peptides and innate immune genes, modulating skin antimicrobial activity (4). Petrolatum in bodywash formulation could therefore benefi t the function of the skin surface barrier. The aim of this in vitro study was to investigate skin deposition and penetration of petro- latum into the stratum corneum from a bodywash system consisting of petrolatum. The experiments were performed with human cadaver skin in Franz diffusion cell in vitro. Radiolabeled 14 C-dotriacontane (C32-alkane) was the model permeant for petrolatum that was mixed with the bodywash before the study. After bodywash application and rinse-off from the skin surface, the amount of petrolatum deposited on the skin was de- termined by the amount in the rinse-off solution and mass balance. Tape-stripping was then performed to determine the amount and depth of petrolatum penetration into the stratum corneum. The epidermis was separated from the dermis by dissection to deter- mine the amounts of petrolatum in these skin layers. MATERIALS AND METHODS MATERIALS 14 C-dotriacontane (specifi c activity 10 mCi/mmol) was purchased from American Radio- labeled Chemicals (Saint Louis, MO). 3 H-water (specifi c activity 1 mCi/g) was purchased from Moravek Biochemicals (Brea, CA). Ultima Gold scintillation cocktail was purchased from PerkinElmer (Waltham, MA). Glyceryl monooleate was purchased from BASF Cor- poration (Florham Park, NJ). Petrolatum was purchased from Sonneborn (Petrolia, PA). An experimental bodywash base without petrolatum and glyceryl monooleate was obtained from the Procter & Gamble Co . (P&G). Hexane and bovine serum albumin, fraction V (BSA) were purchased from Fisher Scientifi c (Fair Lawn, NJ). Ethanol was purchased from Pharmco-Aaper (Shelbyville, KY). Polysorbate 20 (Tween 20) was purchased from Uniqema (Wilmington, DE). Sodium azide (NaN3) was purchased from Acros Organics (Morris Plains, NJ). Phosphate-buffered saline (PBS: 0.01 M phosphate buffer, 0.0027 M potassium chloride, and 0.137 M sodium chloride), pH 7.4, was prepared using PBS tablets and deionized water as described by the manufacturer (MP Biomedicals, Solon, OH) and preserved using 0.02% NaN3. FRANZ DIFFUSION CELL SETUP Posterior torso split-thickness cadaver skin (thickness ~0.01–0.04 cm) from eight skin donors was obtained from the New York Firefi ghters Skin Bank (New York, NY) in pack- ages at -80°C. The ages of the skin donors were between 45 and 70 years. The split- thickness skin was thawed in PBS according to the instructions on the skin packages and stored at -20°C until use. Before use, the skin sample was cut into 1.5 × 1.5 cm pieces and equilibrated in PBS at room temperature for 2 h. The vertical Franz diffusion cell used in this study had a diffusional area of 0.71 cm2. The fully hydrated skin sample was mounted on the cell between the donor and receptor chambers, with the stratum corneum side of the skin facing upward to the environment. The dermis side of the skin sample
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