OECD GUIDELINE FOR THE TESTING OF CHEMICALS DRAFT PROPOSAL FOR A NEW GUIDELINE In Vitro Skin Irritation: Reconstructed Human Epidermis (RhE) Test Method

INTRODUCTION 1. Skin irritation refers to the production of reversible damage to the skin following the application of a test chemical for up to 4 hours [as defined by the United Nations (UN) Globally Harmonized System of Classification and Labelling of Chemicals (GHS)](1). This Test Guideline provides an in vitro procedure that may be used for the hazard identification of irritant chemicals (substances and mixtures) in accordance with UN GHS and EU CLP Category 2 (1)(2)(3), as well as non-classified chemicals, i.e. UN GHS No-Category, for member countries or regions that do not adopt the optional UN GHS Category 3 (mild irritants). Depending on the regulatory framework and the classification system in use, this test method may be used to determine the skin irritancy of chemicals as a stand-alone replacement test for in vivo skin irritation testing, or as a partial replacement test, within a tiered testing strategy (4). 2. The assessment of skin irritation has typically involved the use of laboratory animals [OECD Test Guideline 404; adopted in 1981 and revised in 1992 and 2002](4). In relation to animal welfare concerns, TG 404 was revised in 2002, allowing for the determination of skin corrosion/irritation by applying a tiered testing strategy, using validated in vitro or ex vivo test methods, thus avoiding pain and suffering of animals. Three validated in vitro test methods have been adopted as OECD Test Guidelines 430, 431 and 435 (5)(6)(7), to be used for the corrosivity part of the tiered testing strategy of TG 404 (4). 3. This Test Guideline addresses the human health endpoint skin irritation. It is based on reconstructed human epidermis (RhE), which in its overall design (the use of human derived non-transformed epidermis keratinocytes as cell source and use of representative tissue and cytoarchitecture) closely mimics the biochemical and physiological properties of the upper parts of the human skin, i.e. the epidermis. This Test Guideline also includes a set of Performance Standards (PS) developed by EC-ECVAM (8) (Annex 2) for the assessment of similar and modified RhE-based test methods developed by EC-ECVAM (8), in accordance with the principles of Guidance Document No. 34 (9). 4. Prevalidation, optimisation and validation studies have been completed for an in vitro test method an RhE model, commercially available as EpiSkin™ (designated the Validated Reference Method – VRM). Two other commercially available in vitro skin irritation RhE test methods have shown similar results to the VRM …