Predicting the results of a 24-hr human patch test for surfactants: utility of margin-setting in a reconstructed human epidermis model

To predict the results of a 24-hr closed human patch test, we previously recommended the use of in vitro test with a reconstructed human epidermis (RhE) model adopted in OECD TG 439, and proposed the margin method, which includes evaluation of twice the concentration to avoid a false positive for surfactants. Therefore, in this study, we used LabCyte EPI-MODEL as a RhE model, and confirmed the reproducibility of this method using five surfactants, including benzalkonium chloride (BC), sodium lauryl sulfate (SLS), and lauryl betaine (LB), for which false negative results have previously been reported, and three different surfactants. For all surfactants, prediction of patch test results using a margin of two revealed that human tests could be performed safely, confirming the utility of the margin method. In addition, we examined the relationship with critical micellar concentration (CMC). The IC50 for cell viability in the RhE model for three types of surfactants (BC, SLS, and LB) was 2.7- to 49.7-times the CMC. Therefore, the range of concentrations in which tests were performed with the present method was within the range of concentrations with high cleansing. Furthermore, we examined the relationship between cell viability and release of the inflammatory mediator interleukin-1α (IL-1α). IL-1α release was associated with cell viability, supporting the results of the human patch test.