Refinement of LabCyte EPI-MODEL24 Skin Irritation Test Method for Adaptation to the Requirements of OECD Test Guideline 439

A validation study of an in vitro skin irritation test (SIT) method using a reconstructed human epidermal (RhE) model for replacement of the Draize test was conducted by the European Centre for the Validation of Alternative Methods (ECVAM), and a protocol using an RhE model, EpiSkin^TM (SkinEthic, France), was approved as a validated reference method (VRM) in April, 2007. Structural and performance test criteria for skin models are defined in the ECVAM Performance Standards. We have performed several evaluations of our RhE model, LabCyte EPI-MODEL24 (Japan Tissue Engineering Co., Ltd, Japan), and have confirmed the original LabCyte EPI-MODEL24 SIT method defined by the ECVAM Performance Standards. However, the original LabCyte EPI-MODEL24 SIT might not meet with OECD test guideline 439 (OECD TG439) defining the SIT method used with a RhE model, which was newly adopted in July, 2010. This is because the original LabCyte EPI-MODEL24 SIT method predicted 1- bromohexane as a false-negative, which is one of the reference chemicals listed in OECD TG439 but OECD TG439 doesn't allow a SIT which predicts a false-negative except for some specific reference chemicals. In the present study, various modifications of the original LabCyte EPI-MODEL24 SIT have been examined in order to solve the misclassification of 1-bromohexane showing up as a false-negative, and it was found that the misclassification could be corrected by modifying the washing protocol for test chemicals (the modified LabCyte EPI-MODEL24 SIT). When the predictive potency of the modified LabCyte EPI-MODEL24 SIT was evaluated with the 20 reference chemicals listed in the new OECD TG439 for in vitro skin irritation testing, which was adopted in July 2010, the sensitivity, specificity and overall accuracy were 90 %, 70 %, and 80%, respectively. It is thought that these results meet the acceptance criteria described in OECD TG439.