Letters to the Editor
LETTER TO THE EDITOR Tremendous ex vivo child skin absorption and permeation of eucalyptol KEYWORDS Skin absorption; Skin permeation; Terpenes; Eucalyptol
Some of drug products intended for application onto children’s healthy skin contain eucalyptol (1,8-cineol) or eucalyptus essential oil in which eucalyptol can appear even up to 90% concentration. The aim of this study was to determine quantitative absorption of this compound into and through the child skin after its application in hydrogel form. As comparison, the absorption of eucalyptol into the adult skin was investigated. Eucalyptol (purity 98%, Fluka, Buchs, Switzerland) was incorporated in concentration of 5% (w/w) into carbomer (Carbopol 974P NF, Noveon Inc., Cleveland, OH, USA) hydrogel using 0.5% of polysorbate 80 (Tween 80) (Fluka, Buchs, Switzerland) as surfactant. Full cadaver skin from the region of thorax of a oneyear-old full-term Caucasian child and a 43-year-old Caucasian woman (the subjects did not have skin diseases) was placed in the flow-through diffusion chamber (Crown Glass, USA) with the diffusion area of 0.65 cm2. An isotonic pH 7.3 phosphate buffer, 10 ml, as sink-condition-ensuring acceptor fluid (AF) was recirculated beneath the skin at a rate of 10 ml/ h, and the system was maintained at 37 0.5 8C. 100 mg/cm2 of the preparation was applied onto the skin, covered with Parafilm1 (Sigma—Aldrich, Steinheim, Germany) and left for 15, 30 and 60 min. After the preparation was removed, the stratum corneum (SC) was separated by a tape-stripping method (3M Medica Pharma, St. Paul, MN, USA) . The first three fragments were discarded, and the remaining fragments were finally merged into three fractions (seven fragments each): outer (SC I), middle (SC II) and inner (SC III). Eucalyptol in SC fractions and in the remaining skin (epidermis with dermis, ED), and in AF, was analyzed by gas chromatography, after extraction with methanol . The amounts of eucalyptol determined in the skin layers were expressed per 1 cm2 area. Statistical analysis was performed using the Wilcoxon test and the differences were considered significant at p < 0.05. Rapid saturation of the child skin SC with eucalyptol can be observed just after 15 min of application (Fig. 1a, Table 1), and thus the total maximal amount of penetrant in the SC (712 mg/cm2) was noted at this time point. The increasing amount of eucalyptol in ED during application was indicated, reaching the maximum amount of 1248 mg/cm2 after
30 min; therefore the total content of eucalyptol in the child skin was as much as 2 mg/cm2 after only 30 min of application. Unless after 15 min of the permeation process, the presence of eucalyptol in the AF could not be ascertained, the extension of the application time up to 30 min caused permeation of 45 mg/cm2 of terpene, and after 60 min—73 mg/cm2. The appearance of eucalyptol in the AF took place when the saturation of ED by terpene occurred. This is the most important observation the study presented. During our long-standing investigations of the penetration of terpenes into adult skin, terpene (namely citronellol) was detected only once in the AF. It happened when citronellol was applied in the multi-co-enhancer carrier — essential oil . In adult skin, the saturation of the SC by terpene also appeared after 15 min of application (Fig. 1b, Table 1). The extension of application time had no effect on the increase of the amount of terpene in the SC fractions. The total content of eucalyptol in the SC during the study was about 550 mg/cm2. Significantly slower rate of eucalyptol penetration into ED could be observed for adult skin than for the child skin. The maximum concentration of permeant in these layers (845 mg/cm2) was reached not before 60 min; therefore, maximal total absorption in the adult skin (1.4 mg/cm2) could be recorded after 60 min of the test. The permeation of eucalyptol into AF was not demonstrated, even after 60 min of application. To avoid the influence of other active compounds on the penetration process, only the pure eucalyptol was incorporated into the vehicle. However, the influence of the surfactant present in the vehicle on the skin absorption of eucalyptol cannot be omitted. Eucalyptol has a log P value 2.8 that predisposes it for ready penetration into the SC, and the relatively good aqueous solubility (2.6 mg/ml) implies easy penetration into viable skin layers . Case studies on why the differences between eucalyptol’ skin penetration profiles are so great indicate the difference in the structure of one-yearold child skin and adult skin. Studies performed by Fluhr et al.  demonstrated different transepidermal-water-loss for children and adults skin; thereby the faster and higher penetration of eucalyptol through the SC of child skin can be justified by the smaller cohesion of corneocytes and wider intercellular spaces. The strong saturation of ED with eucalyptol suggests also the incomplete formation of the dermal-epidermal border. On the other hand, most sources maintain that properties of the skin barrier in full-term born children do not essentially differ from those of an adult [6,7].
Letters to the Editor
Table 1 Ex vivo skin penetration and permeation of eucalyptol (mg/cm2; mean S.D.; n = 4) Amount of eucalyptol Stratum corneum total Epidermis with dermis Skin total Acceptor fluid
712 43 460 184 1172 98 0
763 40 1248 281 2011 170 45 16
698 78 1357 158 2055 193 73 17
564 46 319 120 883 138 0
549 59 543 54 1092 108 0
575 127 845 98 1420 161 0
References  Cal K, Krzyzaniak M. Stratum corneum absorption and retention of linalool and terpinen-4-ol applied as gel or oily solution in humans. J Dermatol Sci 2006;42:265—7.  Cal K. How does the type of vehicle influence the in vitro skin absorption and elimination kinetics of terpenes? Arch Dermatol Res 2006;297:311—5.  Cal K. Skin penetration of terpenes from essential oils and topical vehicles. Planta Med 2006;72:311—6.  Cal K, Kupiec K, Sznitowska M. Effect of physicochemical properties of cyclic terpenes on their ex vivo skin absorption and elimination kinetics. J Dermatol Sci 2006;41:137—42.  Fluhr JW, Pfisterer S, Gloor M. Direct comparison of skin physiology in children and adults with bioengineering methods. Pediatr Dermatol 2000;17:436—9.  Ginsberg G, Hattis D, Miller R, Sonawane B. Pediatric pharmacokinetic data: implications for environmental risk assessment for children. Pediatrics 2004;113:973—83.  Mancini AJ. Skin. Pediatrics 2004;113:1114—9.  Bos JD, Meinardi MM. The 500 Dalton rule for the skin penetration of chemical compounds and drugs. Exp Dermatol 2000;9:165—9.
Fig. 1 Absorption of eucalyptol (mean S.D., n = 4). (a) In child skin layers. (b) In adult skin layers. Abbreviations: ED, epidermis with dermis; SC III, inner stratum corneum; SC II, middle stratum corneum; SC I, outer stratum corneum.
Even if side effects for eucalyptol are sporadically reported, the possibility of their appearance when using eucalyptol containing drug products should be appreciated. The molecular mass of eucalyptol (<500 Da) predicts it to have a possible allergenic factor . This seems to be essential for the application of eucalyptol containing preparations onto the skin of young children because their skin can be outright ‘‘open’’ for exogenous substances.
Krzysztof Cal* Monika Sopala Medical University of Gdansk, Department of Pharmaceutical Technology, Hallera 107, 80-416 Gdansk, Poland *Corresponding author. Tel.: +48 58 349 3183; fax: +48 58 349 3190 E-mail address: [email protected]
(K. Cal) 31 December 2007 doi:10.1016/j.jdermsci.2008.06.004
LETTER TO THE EDITOR Evaluation of photoallergic potential of chemicals using THP-1 cells
KEYWORDS Photoallergy; Photohapten; Prohapten; THP-1
Both systemic and topical exogenous photosensitizers evoke cutaneous photosensitivity and clinically recognized drug photosensitivity and photocontact dermatitis, respectively. The action spectrum of these two types of photosensitivity is mainly ultraviolet A (UVA) . Photosensitive chemicals have both phototoxic and photoallergic potentials. Phototoxic reaction is mainly mediated by free