Development of a ModifiedIn vitroSkin Absorption Method to Study the Epidermal/Dermal Disposition of a Contact Allergen in Human Skin

Abstract

In vitro skin absorption methods exist in Organisation for Economic Co-operation and Development (OECD) guideline form (No. 428) and are used to estimate the degree of systemic penetration of chemicals through skin. More detailed kinetics of permeation through skin compartments are not described well by existing methods. This study was designed to assess the practical feasibility of generating compartmental (stratum corneum/epidermal/dermal) disposition and kinetic data of topically applied chemicals. For chemically induced effects initiated in the skin (e.g., skin allergy), the delivery of tissue concentrations of chemical will impact the incidence and severity of biological effect. Explicit data on the kinetics of chemical disposition in skin have not traditionally been needed for skin allergy risk assessment: current in vivo assays embody delivery implicitly. Under the 7th Amendment to the European Cosmetics Directive, in vivo assays (such as the local lymph node assay for skin sensitization) will not be permitted to assess cosmetic ingredients. New in vitro and in silico alternative approaches and ways of predicting risk of adverse effects in humans need to be developed, and new methods such as that described here provide a way of estimating delivered concentrations and the effect of formulation changes on that delivery. As we continue to deconstruct the contributing factors of skin allergy in humans, it will be useful to have methods available that can measure skin tissue compartment exposure levels delivered from different exposure use scenarios. Here we provide such a method. The method could also be used to generate useful data for developing in silico kinetic models of compartmental skin delivery and for refining data for skin delivery in relation to the evaluation of systemic toxicity.

Measuring the Penetration of a Skin Sensitizer and Its Delivery Vehicles Simultaneously with Confocal Raman Spectroscopy

“…The overall findings of this study are in good agreement with the work by Pendlington et al [26] , who examine the penetration rates of cinnamaldehyde in these same vehicles in vitro with radiolabelling methods. The two methods provide complementary data, the radiolabelling method giving the amount of penetration to the receptor solution, the Raman method giving more details about the penetration into the top layers of the skin and more time points.…”

“…In practice the Raman signal from each chemical needs to be above a certain working limit of detection, and as more components are added to the mixture, the resolution of each chemical becomes more challenging. Cinnamaldehyde was observed to penetrate at different rates from four different vehicles, the order of which, acetone 1 aqueous ethanol 1 absolute ethanol 1 propylene glycol 1 olive oil, matches a previous study using different methods [26] . Also it was found that the vehicle of preference for the LLNA assay, acetone:olive oil, phase separates on the skin surface with subsequent consequences for adsorption rates into the skin.…”

“…A model skin sensitizer of moderate potency, trans -cinnamaldehyde, is applied to the skin in a range of different solvents (vehicles): absolute ethanol, 50% aqueous ethanol, propylene glycol and a 4: 1 acetone:olive oil mixture. These have been chosen because they are currently used in in vivo skin sensitization protocols and enable a comparison with a previous study [26] . The acetone:olive oil combination is of particular interest in characterizing skin sensitizer hazard as it is the vehicle of choice for LLNA.…”

Evaporation of decamethylcyclopentasiloxane (D5) from selected cosmetic products: Implications for consumer exposure modeling

“…The disposition of volatile organic compounds (VOCs) after dermal application has been studied in the past (Gilpin et al, 2009;Kasting et al, 2007;Pendlington et al, 2008). Acknowledging the fact that consumer products designed for topical applications are usually complex and often non-aqueous systems containing multiple ingredients, researchers attempted to investigate the influence of the formulation on dermal absorption (Reifenrath and Robinson, 1982;Saiyasombati and Kasting, 2003) and evaporation (Nihi et al, 2009;Vuilleumier et al, 1995) for a range of VOCs.…”

Assuring safety without animal testing: Unilever’s ongoing research programme to deliver novel ways to assure consumer safety

“…A key element of this work is to improve our current estimates of dermal exposure to ingredients for which we have detailed information on both formulation effects and consumer habits and use patterns. A new experimental approach based on ex vivo human skin has been investigated to determine skin compartmental concentrations and the delivery kinetics of a chemical in vitro (Pendlington et al, 2008). Techniques like this aim to establish a relationship between the exposure on the skin and the chemical bioavailability at the target site assumed to be the epidermis and dermis.…”