Read-across to rank skin sensitization potential: subcategories for the Michael acceptor domain

Background: Eliminating animal testing for skin sensitization is a significant challenge in consumer safety risk assessment. To be able to perform resilient risk assessments in the future, one will need alternative approaches to fill the data gaps. Objectives: To this end, we propose a subcategory-based read-across approach to estimate and rank skin sensitization potential of chemicals. The example described here is for the mechanism of Michael-type nucleophilic addition with subcategories being limited to carbonyl-containing compounds. Patients/Methods: In this approach, in silico tools based on structural alerts were used to determine both the mechanism of protein binding and the relative subcategories within that mechanism. Results: Fifty compounds previously evaluated in the in vivo mouse local lymph node assay (LLNA) were placed in 10 subcategories defined by their polarized alpha, beta-unsaturated substructure. To offset the limitations and skewness of the published in vivo data, in chemico glutathione (GSH) depletion data also were included. Conclusions: It was shown that the read-across approach can be successfully used to rank qualitatively skin sensitization potential of an untested carbonyl-containing Michael acceptor chemical by using subcategories. Moreover, the use of the more resilient in chemico GSH depletion data added further support to the read-across result.