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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. [ABSTRACT FROM AUTHOR]

Background: People are exposed to mixtures containing allergens and irritants often causing contact dermatitis. Therefore, regulatory authorities require systematic information on the effects of mixtures on the sensitization threshold. In this study a moderate (cinnamal) and a weak (ethylene glycol dimethacrylate) allergen were combined with irritants covering different mechanisms of action (sodium dodecyl sulfate, salicylic acid, and α‐pinene). For a systematic approach, the single substances were initially tested using the KeratinoSens assay. Thereafter, each allergen was combined with noncytotoxic concentrations of the irritants. Method: The KeratinoSens assay was applied for the single substances according to OECD (Organisation for Economic Co‐operation and Development) Test Guideline 442D. Based on these results, three noncytotoxic concentrations of the irritants were selected and applied simultaneously with 12 concentrations of the allergens to the KeratinoSens cells. Sensitization threshold and cytotoxicity were measured and compared with the individual testing. Results: The combinations of allergens and irritants differed from the effects of the single substances and lowered the sensitization threshold. The quantitative approach allowed a clear description of the changes which varied by factors between 1.1 and 10.3. Conclusions: Overall, the allergen was the prominent compound in the mixture and its nature appeared to determine the degree of the response. [ABSTRACT FROM AUTHOR]

Background: Allergic contact dermatitis caused by henna‐based hair‐colouring products has been associated with adulteration of henna with p‐phenylenediamine (PPD). Objectives: To develop a testing approach based on in vitro techniques that address key events within the skin sensitization adverse outcome pathway in order to evaluate the allergenic potential of hair‐colouring products. Methods: The following in vitro assays were used to test the sensitizing capacity of hair dye ingredients: the micro‐direct peptide reactivity assay (mDPRA); the HaCaT keratinocyte‐associated interleukin (IL)‐18 assay; the U937 cell line activation test (U‐SENS)/IL‐8 levels; the blood monocyte‐derived dendritic cell test; and genomic allergen rapid detection (GARD skin). Those techniques with better human concordance were selected to evaluate the allergenic potential of 10 hair‐colouring products. Results: In contrast to the information on the label, chromatographic analyses identified PPD in all products. The main henna biomarker, lawsone, was not detected in one of the 10 products. Among the techniques evaluated by testing hair dye ingredients, the mDPRA, the IL‐18 assay, GARD skin and the U‐SENS correlated better with human classification (concordances of 91.7%‐100%) and were superior to the animal testing (concordance of 78.5%). Thus, these assays were used to evaluate hair‐colouring products, which were classified as skin sensitizers by the use of different two‐of‐three approaches. Conclusions: Our findings highlight the toxicological consequences of, and risks associated with, the undisclosed use of PPD in henna‐based "natural" "real‐life" products. [ABSTRACT FROM AUTHOR]

Background: Over 4000 small chemicals have been identified as allergens capable of inducing skin sensitization. Many sensitizers are hypothesized to act as haptens producing novel antigens, which can be presented to T cells by human leukocyte antigens (HLAs). Recent studies suggest that some chemical allergens use hapten‐independent mechanisms. Objective: To determine whether molecular docking can identify HLA molecules that bind skin‐sensitizing chemical allergens. Methods: Structural models of HLA molecules were used as the basis for molecular docking of 22 chemical allergens. Allergens predicted to bind HLA‐B*57:01 were tested for their ability to stimulate T cells by the use of proliferation and interferon‐gamma enzyme‐linked immunospot assays. Results: Chemical allergens that did not satisfy the criteria for hapten activity in vitro were predicted to bind more strongly to common HLA isoforms than those with known hapten activity. HLA‐B*57:01, which is an HLA allele required for drug hypersensitivity reactions, was predicted to bind several allergens, including benzyl benzoate, benzyl cinnamate, and benzyl salicylate. In in vitro T cell stimulation assays, benzyl salicylate and benzyl cinnamate were found to stimulate T cell responses from HLA‐B*57:01 carriers. Conclusions: These data suggest that small‐molecule skin sensitizers have the potential to interact with HLA, and show that T cell‐based in vitro assays may be used to evaluate the immunogenicity of skin‐sensitizing chemicals. [ABSTRACT FROM AUTHOR]

At the ESCD congress held in Manchester in 2016, a session was organized to encourage more dialogue between clinicians with expertise in skin sensitization and toxicologists seeking to provide effective risk assessment to prevent human health issues. That session focused on the remaining uncertainties regarding the induction and regulation of skin sensitization in humans, and the opportunities and challenges associated with the refinement and improvement of risk assessment methodologies. This short article, prompted by those discussions, debates what the authors regard as being among the most important and most intriguing uncertainties about skin sensitization and allergic contact dermatitis in humans, and the most significant opportunities for improving risk assessment. The aim has been to provide a basis for mapping out the areas that might benefit from a closer alignment between the relevant clinical community and toxicologists charged with the responsibility of ensuring that skin sensitization risks are understood and managed. [ABSTRACT FROM AUTHOR]