International ring trial of the epidermal equivalent sensitizer potency assay: reproducibility and predictive capacity

Abstract

Summary This study describes the international ring trial of the epidermal-equivalent (EE) sensitizer potency assay. This assay does not distinguish a sensitizer from a non-sensitizer, but may classify known skin sensitizers according to their potency. It assesses the chemical concentration resulting in 50% cytotoxicity (EE-EC50)or the 2-fold increase in Abbreviations: AOO, acetone:olive oil (4:1); BD, broad dose; EE, epidermal equivalent; EC 50 , chemical concentration in mg/ml that results in a decrease in cell viability to 50% compared to vehicle treated epidermal equivalents; DiSFeB, Dipartimento di Scienze Farmacologiche e Biomolecolari, Milan University, Milan; DMSO, 1% dimethylsulfoxide; DSA 05 , chemical dose per skin area in µg/cm 2 leading to a sensitization incidence of 5% in the human tested population; FD, fine dose; GPMT, Guinea Pig Maximization Test; HU, University of Applied Sciences, Utrecht; HRIPT, Human Repeat Insult Patch Test; IL-1α 2x , Chemical concentration in mg/ml resulting in a 2-fold increase in IL-1α release into culture supernatant of EE compared to supernatant of vehicle-exposed EE; LLNA, Local Lymph Node Assay; NOEL, human threshold level (no observed effect level) expressed in µg/cm 2 ; OECD, Organisation for Economic Co-operation and Development; SOP, standard operating procedure; VUMC, VU University Medical Center, Amsterdam

Alternative Approach for Potency Assessment: In Vitro Methods

“…As TLRs evolved to sense microbial pathogens, the inflammation induced by contact allergens would thus appear to be an accident in nature, but it raises the possibility that the activation of these pathways in keratinocytes and dendritic cells is a trait shared by all compounds with skin sensitizing potential. In line with these observations are our data, which show the possibility of discriminating contact allergens using the selective induction of IL-18 in keratinocytes, including reconstructed human epidermis [21,[28][29][30][31][32]. The argument is that more potent contact allergens will provoke at lower concentrations a stronger innate inflammatory reaction than will less potent allergens, which will in turn influence the migration of skin dendritic cells and their degree of activation and, therefore, the quality of immune responses elicited [33].…”

The GARD platform for potency assessment of skin sensitizing chemicals

“…In addition to hazard identification, information on skin sensitizer potency is imperative in order to allow quantitative risk assessment and to define exposure limits. Approaches for the prediction of skin sensitizer potency have been published and were recently reviewed by Ezendam et al (2016), such as assays targeting KE2 (epidermal equivalent sensitizer potency assay (Teunis et al, 2014), SENS-IS (Cottrez et al, 2015)) and the U-SENS assay modelling KE3 (Piroird et al, 2015). Furthermore, in silico models, often combining information from several in vitro methods, have been described, for example QSAR (Dearden et al, 2015), artificial neural networks (Tsujita-Inoue et al, 2014), probabilistic models and integrated testing strategy (ITS) approaches including a Bayesian model (Jaworska et al, 2013(Jaworska et al, , 2015Luechtefeld et al, 2015;Natsch et al, 2015).…”

Preliminary performance data of the RHE/IL‐18 assay performed on SkinEthic™RHE for the identification of contact sensitizers

“…In these test models, exposure to an irritant produces a decrease in cell viability which is proportional to the inflammatory potency of the tested substance. Most sensitizing compounds also being primary irritants [1,4,5,18], cell viability was demonstrated to reflect the sensitizing potency of a substance [25,26].…”