Toxicological assessments of skin sensitizers have progressed towards a higher reliance on non-animal methods. Current technological trends aim to extend the utility of non-animal methods to accurately characterize skin-sensitizing potency. The GARDskin Dose–Response assay has previously been described; it was shown that its main readout, cDV₀ concentration, is associated with skin-sensitizing potency. The ability to predict potency from cDV₀ in the form of NESILs derived from LLNAs or human NOELs was evaluated. The assessment of a dataset of 30 chemicals showed that the cDV₀ values still correlated strongly and significantly with both LLNA EC3 and human NOEL values (ρ = 0.645–0.787 [p < 1 × 10⁻³]). A composite potency value that combined LLNA and human potency data was defined, which aided the performance of the proposed model for the prediction of NESILs. The potency model accurately predicted sensitizing potency, with cross-validation errors of 2.75 and 3.22 fold changes compared with NESILs from LLNAs and humans, respectively. In conclusion, the results suggest that the GARDskin Dose–Response assay may be used to derive an accurate quantitative continuous potency estimate of skin sensitizers.

Non-animal methods for identification and characterization of skin sensitizers are continuously evolving, advancing towards more effective, accurate, and informational assays. The GARDskin assay is a scientifically and regulatory recognized assay for the assessment of skin sensitizers. It currently relies on targeted gene expression measurement to derive hazard classifications. With the progression of next generation sequencing technologies, whole transcriptome analysis provides an interesting alternative to the currently implemented targeted gene expression approach. RNA-seq was evaluated for its use in the GARDskin assay as a gene expression quantification method. Based on 24 paired samples acquired on both RNA-seq and the NanoString nCounter platform (the currently standard GARDskin acquisition method), gene expression profiles were found to be highly similar. Comparisons of treatment effects yielded a Spearman’s correlation coefficient of 0.95 and a Lin’s concordance correlation coefficient of 0.87. RNA-seq data was also used to classify the sensitizing hazard of 24 treatments using the standard GARDskin analysis pipeline. The classifications corresponded completely with references, rendering correct classifications for all treatments. In conclusion, it was found that the RNA-seq data strongly resembled NanoString nCounter data, and that it could be used to derive reliable hazard classifications in the GARDskin assay.

Pre-clinical toxicological evaluation is an essential component of ensuring the safety and compatibility of wearable devices with biological systems. Along with the local endpoints of cytotoxicity and irritation, skin sensitization is a core toxicological endpoint. Testing wearable devices, which are often solid and composed of multiple components, presents new challenges for New Approach Methods. In the current proof-of-concept study, we propose a strategy for conducting risk assessment of the individual components and the leachables from wearable devices. The GARDskin Dose-Response assay (OECD TGP 4.106) was used to predict the skin sensitization potency of three acrylate monomers, two acrylamide monomers, and one reactive dye. The GARDskin Medical Device (ISO 10993-10:2021, Annex C) was used to classify MED-2000 extracts spiked with isobornyl acrylate. All chemicals were classified as skin sensitizers. The quantitative potency predictions correlated well with available data from defined approaches and produced near-identical potency rankings. Available human and animal reference data were too sparse and heterogenous to substantiate agreement in potency. Finally, the GARDskin Medical Device assay correctly classified the spiked extract as skin sensitizing. In conclusion, the GARDskin assay and associated applications are well adapted to address the testing requirements for wearable devices.