The GARD™skin assay: Investigation of the applicability domain for metals

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Andy Forreryd
Robin Gradin
Olivia Larne
Nissanka Rajapakse
Eliot Deag
Henrik Johansson


New approach methods (NAMs) for hazard identification of skin sensitizing chemicals have been adopted as test guidelines by the OECD during the last decade as alternatives to animal models. These models align to individual key events (KE) in the adverse outcome pathway (AOP) for skin sensitization for which the molecular initiating event (MIE) is covalent binding to proteins. As it currently stands, the AOP does not include mechanistic events of sensitization by metals, and limited information is available on whether NAMs accurately the predict sensitization potential of such molecules, which have been proposed to act via alternative mechanisms to organic chemicals. Methods for assessing the sensitization potential of metals would comprise valuable tools to support risk management within e.g., occupational settings during production of new metal salts or within the medical device industry to evaluate leachables from metal alloys. This paper describes a systematic evaluation of the applicability domain of the GARD™skin assay for assessment of metals. Hazard classifications were supplemented with an extended analysis of gene expression profiles induced by metal sensitizers to compare the induction of toxicity pathways between metals and organic sensitizers. Based on the results of this study, the accuracy, sensitivity, and specificity of GARD™skin for prediction of skin sensitizing hazard were 92% (12/13), 100% (7/7) and 83% (5/6), respectively. Thus, the performance of GARD™skin for assessment of metals was found to be similar to what is observed on conventional organic substances, providing support for inclusion of metals within the applicability domain of the test method.

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Forreryd, A., Gradin, R., Larne, O., Rajapakse, N., Deag, E. and Johansson, H. (2022) “The GARD™skin assay: Investigation of the applicability domain for metals”, ALTEX - Alternatives to animal experimentation. doi: 10.14573/altex.2203021.

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