Pushing the Limits: Expanding the Applicability Domain of EpiSensA for Skin Sensitization Assessment

Introduction:

Skin sensitization is an immune-mediated process leading to allergic contact dermatitis following dermal exposure to chemicals. The Epidermal Skin Sensitization Assay (EpiSensA) is an in vitro assay adopted in 2024 by OECD to assess skin sensitization potential. The assay evaluates keratinocyte activation, which is the second key event in the skin sensitization adverse outcome pathway. The current applicability of the assay is limited by a minimum solubility requirement (≥0.0122% w/v) in validated vehicles such as 4:1 acetone:olive oil (AOO), distilled water, or 50% ethanol. Chemicals not meeting this criterion are considered incompatible with the test system.

Methods:

The EpiSensA quantifies changes of expression in marker genes (ATF3, GCLM, DNAJB4, and IL-8) following topical chemical exposure to a reconstructed human epidermis (RhE) model. Our experiments assessed strategies to expand the applicability domain of EpiSensA by evaluating alternative solvents, conducting testing of neat materials (to mimic consumer exposure), and assessing the skin sensitization potential of medical device extracts.

Results:

Alternative solvents including mineral oil, olive oil, dimethyl sulfoxide (DMSO), saline, and acetonitrile were evaluated. Of these, mineral oil and olive oil were identified as compatible with the EpiSensA, maintaining tissue viability >95% and gene induction below established positivity thresholds (ATF3 <15‑fold; GCLM and DNAJB4 <2‑fold; IL‑8 <4‑fold). A body lotion and a perfume were tested neat and predicted to be positive, based on increased expression of ATF3 and IL-8 in both products, and DNAJB4 in the lotion. Olive oil-based extracts of latex gloves and non‑latex condoms, prepared according to ISO 10993‑12, did not exceed classification thresholds and thus were classified as negative in the assay.

Conclusion:

These findings suggest the potential to expand the EpiSensA applicability domain to include alternative solvents, neat materials, and medical device extracts, while highlighting key considerations and the need for further evaluation for regulatory application.