Cécile Robert

A catch-up validation study on reconstructed human epidermis (SkinEthic™ RHE) for full replacement of the Draize skin irritation test

Efforts to fully replace the in vivo Draize skin irritation test, according to the Directive 67/548/ECC or OECD TG 404, were reinforced with the seventh Amendment of the Cosmetic Directive and the REACh regulation. In 2007, the EpiSkin test method was scientifically validated and recognized as the stand alone method to discriminate skin irritants (R38) from non-irritants (no label) according to the definition of the EU risk phrases. An ECVAM performance standards (PS) document was defined to evaluate the accuracy and reliability of other analogous test methods (ECVAM SIVS, May 2007). The present test was designed to determine the reliability and relevance of the Reconstructed Human Epidermis (RHE) model commercialized by SkinEthic. The RHE skin irritation test method consisted to topically apply topically the test substances for 42min followed by a 42h post-incubation. The main selected endpoint was the cell viability (MTT reduction), with a threshold of 50% viability. The RHE test method showed a good intra and inter-laboratory reproducibilities in a multicentric study involving three independent laboratories. The SkinEthic RHE test method showed to be relevant and reliable with a sensitivity of 90% and a specificity of 80% (MTT only) and was not improved by integrating another endpoint such as IL-1alpha. The overall accuracy was 85% resulting in the recognition of the SkinEthic RHE test method, by the ECVAM Scientific Advisory Committee in November 2008, as a stand alone replacement test method for the Draize rabbit in vivo test, as a screen, or as part of a sequential testing strategy in a weight of evidence approach, for classifying non-irritant and irritant test substances, depending on country requirements.

Low to moderate doses of infrared A irradiation impair extracellular matrix homeostasis of the skin and contribute to skin photodamage.

Human skin is daily exposed to sun rays, which include not only ultraviolet radiation, but also an important quantity of infrared (IR) radiation. In the past few years, many publications have underlined the negative impact of IR radiation on the human skin, particularly when the skin and/or the cells are exposed to high sun irradiance and significant doses of IR. In the present study, we demonstrate, in vitro on normal human fibroblasts, that even under low irradiance with single or very few repeated doses, infrared A irradiation (IRA) produces free radicals, triggers major changes in the expression of the type I collagen and elastin network, impairs the dermal-epidermal junction, upregulates several matrix metalloproteinases and has an impact on the expression of key genes of the extracellular matrix. We conclude that chronic or discretionary exposure to IRA could play a role that is more important than expected in premature skin aging.