Proliferative responses in the local lymph node assay associated with concomitant exposure to 1,4-phenylenediamine and methyldibromo glutaronitrile: evidence for synergy?

Using new approach methodologies for the identification of a sensitizing co-formulant in a plant protection product

According to Regulation (EC) No 1272/2008, plant protection products (PPPs) can be classified for skin sensitisation by either considering the full formulation or the individual components. For a fraction of PPPs, an application of both assessment strategies results in discrepant classification results. We here aimed to resolve this discrepancy for PPP 1, an exemplary product, which was classified as sensitizing by a positive local lymph node assay but scored negative by the component-based method. We collected further data, as suggested by the regulation, based on a combination of new approach methodologies (NAMs) covering several key events (KEs) in the adverse outcome pathway model for skin sensitisation. Precisely, we employed quantitative structure activity relationship (QSAR) analysis (KE 1), the human cell line activation test (h-CLAT) complemented by Interleukin-8 release measurements (KE 3) and a novel short-term T cell test that is based on the induced expression of activation markers (KE 4). We tested the complete product, individual co-formulants (CFs) or single substances. PPP 1 tested positive in all in vitro assays. QSAR analysis revealed two CFs containing sensitizing chemicals. Only CF 1 was tested positive in the h-CLAT at a minimal induction threshold of 1.5 mg/mL, being less potent than PPP 1. In the T cell assay, both PPP 1 and CF 1 were tested positive at around 0.1 mg/mL. In conclusion, our results propose a novel integrated NAM-based strategy that should be explored further for skin sensitisation hazard identification of complex mixtures, such as PPPs.

Updating exposure assessment for skin sensitization quantitative risk assessment for fragrance materials

In 2008, a proposal for assessing the risk of induction of skin sensitization to fragrance materials Quantitative Risk Assessment 1 (QRA1) was published. This was implemented for setting maximum limits for fragrance materials in consumer products. However, there was no formal validation or empirical verification after implementation. Additionally, concerns remained that QRA1 did not incorporate aggregate exposure from multiple product use and included assumptions, e.g. safety assessment factors (SAFs), that had not been critically reviewed. Accordingly, a review was undertaken, including detailed re-evaluation of each SAF together with development of an approach for estimating aggregate exposure of the skin to a potential fragrance allergen. This revision of QRA1, termed QRA2, provides an improved method for establishing safe levels for sensitizing fragrance materials in multiple products to limit the risk of induction of contact allergy. The use of alternative non-animal methods is not within the scope of this paper. Ultimately, only longitudinal clinical studies can verify the utility of QRA2 as a tool for the prevention of contact allergy to fragrance materials.

Harnessing co-operative immune augmentation by contact allergens to enhance the efficacy of viral vaccines

Although the development of successful vaccines against coronaviruses may be achieved, for some individuals the immune response that they stimulate may prove to be insufficient for effective host defence. The principle that a relatively strong contact allergen will have an enhancing effect on sensitization compared with a less potent contact allergen if they are co-administered, may not, at first, appear relevant to this issue. However, this augmentation effect is thought to be due to the sharing of common or complementary pathways. Here, we briefly consider aspects of the shared and complementary pathways between skin sensitization induced by exposure to a contact allergen and the immune response to viruses, with particular reference to COVID-19. The relationship leads us to explore whether this principle, which we name here as "co-operative immune augmentation" may be extended to include viral vaccination. We consider evidence that even relatively weak contact allergens, used in vaccines for other purposes, can show enhanced sensitization, which is in keeping with a co-operative augmentation principle. Finally, we consider how the potent contact allergen diphenylcyclopropenone could be employed safely as an enhancer of vaccine responses.

A Dose-Response Modeling Approach Shows That Effects From Mixture Exposure to the Skin Sensitizers Isoeugenol and Cinnamal Are in Line With Dose Addition and Not With Synergism

Currently, hazard characterization of skin sensitizers is based on data obtained from studies examining single chemicals. Many consumer products, however, contain mixtures of sensitizers that might interact in such a way that the response induced by a substance is higher than predicted in the hazard assessment. To assess interaction of skin sensitizers in a mixture, a dose-response modeling approach is applied. With this approach, it is possible to assess whether or not responses from mixtures of sensitizers can be predicted from the dose-response information obtained from individual chemicals using dose addition. We selected the skin sensitizers isoeugenol and cinnamal, frequently occurring together in consumer products, to be examined in an adjusted local lymph node assay (LLNA). Cell number and cytokine production (IL-10 and IFN-γ) of the auricular lymph nodes were measured as hallmarks of the skin sensitization response. We found that dose addition for these 2 skin sensitizers closely predicted the effects from mixtures of both chemicals across the broad dose range tested. Hence, isoeugenol and cinnamal show no synergistic effects in the LLNA. Therefore, hazard assessment and risk assessment of these substances can be performed without taking into account mixture exposure.