J. Soc. Cosmet. Chem., 29, 265-282 (May 1978) Autoradiographic study on percutaneous absorption of several oils useful for cosmetics M. SUZUKI, K. ASABA, H. KOMATSU and M. MOCHIZUKA Pola Laboratories, 27-1, Takashimadai, Kanagawa-Ku, Yokohama, Japan. Received September 9, 1977. Synopsis PERCUTANEOUS ABSORPTION of five 14C-labelled OILS, n-octadecane, decanoxy decane, 2-hexyldecanoxy octane, isopropyl myristate and glyceryl tri-(oleate), generally used in COSMETICS were studied from the point of view of their safety. In whole body AUTORADIOGRAPHY with hairless mice, there was no visible penetration into the skin and organs, whereas microautoradiography with guinea pigs showed local penetration. Isopropyl myristate penetrated to the greatest extent, whereas 2-hexyldecanoxy octane was hardly absorbed. Percutaneous absorption of these two oils, therefore, was examined in Angora rabbits by microautora- diography simultaneously with skin irritation potential by histological method from the following aspects: 1. patterns of penetration and irritation according to application time and 2. fate within the skin and pattern of irritation after application. In addition, intradermal metabolic fate was also studied in vito. INTRODUCTION Skin irritations or eruptions caused by cosmetics are very serious problems from a social viewpoint. Skin penetration of irritants in cosmetics used topically is a prerequi- site of their causing responses in the living cells of the epidermis and underlying dermis. Thus, cosmetic chemists have long been interested in percutaneous absorption as a very important phenomenon. From the standpoint mentioned above, the authors have been studying percutaneous absorption of cosmetic constituents not only to examine their permeability, but also to evaluate its relationship to the occurrence of irritation and toxicity. The findings re- garding these relations are expected to improve the quality of cosmetics in terms of their safety. Though percutaneous absorption has been measured on some available materials used in small amounts in cosmetics, e.g., germicides (1-4), hormones (5-7), vitamins (8,9) and surfactants (10-12), little data have been reported on the base materials of cos- metics. In this paper, percutaneous absorption of several oils used as bases in cosmetics were studied in hairless mice, guinea pigs and Angora rabbits. 265

266 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Methods of measuring percutaneous absorption have been reviewed by Ainsworth (13), Barr (14), Tregear (15), Grasso and Lansdown (16) and Idson (17). In this study, the technique of microautoradiography was employed together with that of whole body autoradiography developed by Ullberg (18). Simultaneously, primary irritation potentials were observed histologically on the same substances. In addition, intradermal metabolic fates of the oils were also examined radiochromato- graphically. MATERIALS Isopropyl myristate-•4C (•4C-IPM), decanoxy decane-•C (•C-DD) and 2-hexylde- canoxy octane-•C ( TM C-HDO) were synthesized from 1-•4C-myristic acid, 1-1•C-decyl bromide and 1-•C-octanol respectively in our laboratory. The above starting materials, glyceryl tri-(oleate-1-•C) (•C-GTO) and 1-•4C-octadecane (•C-OD) were obtained from Daiichi Pure Chemicals. These labelled compounds were chemically and radio- chemically pure as checked by thin layer chromatography using several different solvent systems and scanning with a radiochromatogram scanner Aloka TLC-2D. Specific activities of these five oils were adjusted approximately to 0.2/•Ci/mg suitable for this study. An oil-containing hydrophilic ointment was prepared in the following formula: •C- labelled oil 5%, white petrolatum 30%, stearyl alcohol 15%, propylene glycol 12%, sodium lauryl sulfate 2% and distilled water 36%. METHODS WHOLE BODY AUTORADIOGRAPHY WITH HAIRLESS MICE Male hairless mice (hr/hr strain) weighing 25 g (average) were used. Applied to the dorsal skin of animals under occlusion were 0.01 ml of the radioactive oils on 2.5 cm diameter Japanese papers backed with Lumirror © film (Toray Industries, Inc.) or 50 mg of the oil-containing hydrophilic ointments on 2.5 cm diameter filter papers (Toyo Roshi Co., Ltd.). The treated areas of skins were covered with 3M Co.'s Micropore sur- gical tape. The mice were anesthesized with diethyl ether and immersed immediately in a dry ice- acetone bath (-78øC) at different intervals (1, 6, 24 and 48 hr). Subsequently, whole body autoradiography was carried out according to the Ullberg method (18). Forty sagittal sections adhering to Scotch © Tape No. 810 (Sumitomo-3M Co., Ltd.) were prepared with a Jung type microtome from Yamatokoki Co., Ltd., in a freezing room (- l 5øC). The sections were allowed to dry in that room, then brought into contact with Sakura X-ray film Industrial Type N (Konishiroku Photo Ind. Co., Ltd.), and exposed for 40 days. The film development was according to the usual procedure recommended by the manufacturer. MICROAUTORADIOGRAPHY WITH GUINEA PIGS Male guinea pigs (Hartley strain) weighing 340 g (average) were used. The hair on the dorsal region of animals was removed with a hair clipper and an electric shaver one day