Reconstructed Skin Micronucleus Assay (RSMN)
The micronucleus test is increasingly used for testing of substances since it is a central component of many current genotoxicity testing batteries. In this assay dividing cells are evaluated with regard to the appearance of small extra nuclei, i.e. micronuclei, which either comprise chromosome fragments or entire chromosomes, thereby detecting clastogenic as well as aneugenic effects. Micronuclei can be evaluated in vivo (OECD TG 474) or in various primary cells or cell lines (OECD TG 487). In general, the in vivo micronucleus test is optimized to predict results that represent the oral route of exposure. For dermally applied compounds like household products and a growing number of pharmaceuticals or cosmetics, a dermal in vivo micronucleus test was developed. However, it is not considered by the respective OECD TG and cannot be used for cosmetics since animal experiments are prohibited for cosmetic ingredients in Europe. Therefore, a skin-based in vitro micronucleus assay has been developed which utilizes human 3D reconstructed skin models, namely EpiDerm™ (MatTek, Ashland, MA). This Reconstructed Skin MicroNucleus assay (RSMN) considers the barrier function of the skin and the organ- and species-specific metabolism, enabling exposure of chemicals relevant for the situation of use. After first proof-of-concept studies with model genotoxins and initial favourable assessment of transferability and intra- and inter-laboratory reproducibility, a validation program was designed and funded by Cosmetics Europe thereby expanding the program to an international scale. While the formal validation is yet unpublished, data generated to date suggest a good predictive capacity and broad applicability of the assay. In consequence, the RSMN is considered a valuable new in vitro method for the assessment of genotoxicity of dermally exposed chemicals and drugs. The RSMN is intended to be used for following-up positive or equivocal results generated in the standard in vitro genotoxicity tests, thereby filling a critical gap in the test battery.
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