Benchmarking performance of SENS-IS assay against weight of evidence skin sensitization potency categories

Validation of a new 3D epidermis model for the SENS-IS assay to evaluate skin sensitization potency of chemicals

In vitro methods for evaluating skin sensitization are advancing as ethical alternatives to animal testing. The SENS-IS assay, based on genomic profiling, relies on robust biological models like 3D reconstructed human epidermis (RHE). The Rhe model from Episkin was typically used to performed the SENS-IS assay. This study validates the Skin+ model as an alternative to the established Episkin model in the SENS-IS assay. We tested 19 proficiency chemicals categorized by human and LLNA potency and compared results between Skin+ and Episkin. The Skin+ model demonstrated over 93 % intra- and inter-batch reproducibility, closely matching Episkin's performance. Additionally, barrier function tests and gene expression analyses confirmed the consistency of the Skin+ model in response to SLS, TNBS, and DMSO treatments. The Skin+ model proved to be a reliable and reproducible alternative to the EpiSkin model, maintaining strong barrier integrity and delivering comparable sensitization predictions. This validation broadens the options for laboratories and industries seeking versatile 3D RHE models for in vitro skin sensitization testing, supporting the transition to more ethical and precise methods.

In Vitro Prediction of Skin-Sensitizing Potency Using the GARDskin Dose-Response Assay: A Simple Regression Approach

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.

A novel three-dimensional Nrf2 reporter epidermis model for skin sensitization assessment

Skin sensitization assessment has progressed from the use of animal models towards the application of New Approach Methodologies (NAMs). Several skin sensitization NAMs are accepted for regulatory use, but a majority relies on submerged in vitro cell cultures that limit their applicability domain, posing challenges for testing hydrophobic chemicals and mixtures. A newly developed three-dimensional (3D) Nrf2 reporter epidermis model for skin sensitization assessment is reported. This NAM may help to overcome these limitations. The NAM combines the in vivo-like biology and exposure conditions of 3D epidermis models with the reliability, convenience, and cost-effectiveness of secreted reporter gene technology. The Keap1-Nrf2-ARE pathway was chosen as the reporter gene read-out, as it is induced by most skin sensitizers and already adopted in OECD Test guideline 442D. Immortalized human primary keratinocytes (Ker-CT) were stably transfected with the pIGB-Nrf2-SEAP vector to construct a Nrf2 reporter cell line. Ker-CT Nrf2 reporter cells showed negligible basal expression of the Secreted Embryonic Alkaline Phosphatase (SEAP) reporter, which was induced 13.5-fold by exposure to the skin sensitizer cinnamic aldehyde (CA). Co-exposure to CA and the Nrf2 inhibitor glucocorticoid clobetasol propionate significantly suppressed the CA-induced SEAP expression, confirming dependance of the SEAP expression on Nrf2 activation. Using air-liquid interface and animal constituent free culture conditions, the Ker-CT Nrf2 reporter cells differentiated to stratified 3D epidermis models with an in vivo-like skin architecture and functional skin barrier. Evaluation of a Ker-CT Nrf2 reporter cell-based 2D assay by testing 10 conventional reference chemicals showed a predictive accuracy for skin sensitization potential of 80% and 70% compared to LLNA and human data in two independent laboratories and a high intra- and interlaboratory reproducibility. Moreover, the 3D epidermis models predicted 3 sensitizing and 2 non-sensitizing reference chemicals correctly in a first proof-of-concept study. Further investigations foresee the testing of additional chemicals, including hydrophobic compounds and mixtures to confirm the potential of the 3D epidermis models to broaden the applicability domain for NAM-based skin sensitization assessment.

Common fragrance chemicals activate dendritic cells in coculture with keratinocytes

BACKGROUND

Fragrances are important contact allergens; however, investigation of their skin sensitization potency has been challenging in new approach methods (NAMs). Many fragrance chemicals are susceptible to autoxidation or can be metabolized by enzymes constitutively expressed in skin keratinocytes. Strong sensitizers can be formed in both of these processes. Further, keratinocytes can modulate the dendritic cell (DC) activation and maturation potential, a key event in the acquisition of contact allergy.

OBJECTIVES

To evaluate the 2D coculture model consisting of keratinocytes and DCs using different weak to moderate sensitizing fragrance chemicals. Further, to investigate fragrances and related oxidation products in the in vitro model and compare to in vivo data.

METHODS

Chemicals were tested in the coculture activation test (COCAT), consisting of HaCaT keratinocytes and THP-1 cells. THP-1 cell surface expression of costimulatory and adhesion molecules (CD86 and CD54) collected after 24 h incubation with the chemicals was analysed using flow cytometry.

RESULTS

Twenty-four molecules were tested positive, three were negative (n = 27). Four pairs were evaluated, with aldehydes showing a 6- to 13-fold stronger responses compared to their corresponding alcohols.

CONCLUSIONS

Results provide insight into the activation of DC in their natural environment of keratinocytes. α,β-Unsaturated alcohols were classified as weaker sensitizers compared to their corresponding aldehydes. In sum, testing of fragrances retrieved results in good agreement with in vivo data.

Reference Chemical Potency List (RCPL): A new tool for evaluating the accuracy of skin sensitisation potency measurements by New Approach Methodologies (NAMs)

Considerable progress has been made in the design of New Approach Methodologies (NAMs) for the hazard identification of skin sensitising chemicals. However, effective risk assessment requires accurate measurement of sensitising potency, and this has proven more difficult to achieve without recourse to animal tests. One important requirement for the development and adoption of novel approaches for this purpose is the availability of reliable databases for determining the accuracy with which sensitising potency can be predicted. Some previous approaches have relied on comparisons with potency estimates based on either human or animal (local lymph node assay) data. In contrast, we here describe the development of a carefully curated Reference Chemical Potency List (RCPL) which is based on consideration of the best available human and animal data. The RCPL is comprised of 33 readily available chemicals that span a wide range of chemistry and sensitising potency, and contain examples of both direct and indirect (pre- and pro-) haptens. For each chemical a potency value (PV) was derived, and chemicals ranked according to PV without the use of potency categories. It is proposed that the RCPL provides an effective resource for assessment of the accuracy with which NAMs can measure skin sensitising potency.

Skin Sensitization Testing: The Ascendancy of Non-Animal Methods

A century ago, toxicology was an empirical science identifying substance hazards in surrogate mammalian models. Over several decades, these models improved, evolved to reduce animal usage, and recently have begun the process of dispensing with animals entirely. However, despite good hazard identification, the translation of hazards into adequately assessed risks to human health often has presented challenges. Unfortunately, many skin sensitizers known to produce contact allergy in humans, despite being readily identified as such in the predictive assays, continue to cause this adverse health effect. Increasing the rigour of hazard identification is inappropriate. Regulatory action has only proven effective via complete bans of individual substances. Since the problem applies to a broad range of substances and industry categories, and since generic banning of skin sensitizers would be an economic catastrophe, the solution is surprisingly simple—they should be subject to rigorous safety assessment, with the risks thereby managed accordingly. The ascendancy of non-animal methods in skin sensitization is giving unparalleled opportunities in which toxicologists, risk assessors, and regulators can work in concert to achieve a better outcome for the protection of human health than has been delivered by the in vivo methods and associated regulations that they are replacing.