Use of Dermal Equivalent and Skin Equivalent Models for in Vitro Cutaneous Irritation Testing of Cosmetic Products: Comparison with in Vivo Human Data

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Abstract
The development of new cosmetic formulations requires precise assessment of their safety and efficacy. Today, legislation imposes increasing measures of safety as well as the limitation of animal use for such testing (European Community directive 93/35/CEE). Subsequently, safety assessment protocols now focus on in vivo human volunteer tests and in vitro methods. In this study, in vivo testing consisted of 48 h patch tests on human volunteers followed by a clinical evaluation of irritation based on a visual scoring system including evaluation of erythema, edema, dryness, and vesicles. For in vitro testing to substantiate the safety of cosmetic products, we propose two three-dimensional models, a dermal equivalent (DE) and a skin equivalent (SE). The DE is composed of a porous collagen-glycosaminoglycans-chitosan dermal substrate populated by normal human fibroblasts. The SE is completed by a fully differentiated epidermis made by seeding normal human keratinocytes onto the DE. To evaluate the usefulness of such in vitro models for cytotoxicity trials, 14 cosmetic products reflecting a range of galenic forms (oil, mascara, cream, lotion) were tested both in vivo and in vitro. In vitro testing consisted of a topical application (10μl) of pure or appropriate dilution of cosmetic products, reflecting future use, onto DEs and SEs (n = 6). After a 24 h contact, measurement of residual cellular viability using the MTT test as well as LDH and IL-1α release measurement allowed an evaluation of the skin irritation potential. The in vitro results were compared to the in vivo data using a binary correlation based on the irritation potential prediction (nonirritating/irritating). A concordance of 71% and 79%, respectively, for the DE model and the SE model were obtained versus in vivo data.

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