Applied chemical safety assessment case study for repeated dose toxicity integrating non-animal methods

Historically, the prediction of reproductive and developmental toxicity has largely relied on the use of animals. The adverse outcome pathway (AOP) framework forms a basis for the development of new non-animal test methods. It also provides biological context for mechanistic information from existing assays. However, a single AOP may not capture all events that contribute to any relevant toxic effect, even in single chemical exposure scenarios. AOP networks, defined as sets of AOPs sharing at least one common element, are capable of more realistically representing potential chemical effects. They provide information on interactions between AOPs and have the potential to reveal previously unknown links between biological pathways. Analysis of these AOP networks can aid the prioritization of assay development, whether the goal is to develop a single assay with predictive utility of multiple outcomes, or development of assays that are highly specific for a particular mode of action. This paper provides a brief overview of the AOPs related to reproductive and developmental toxicity currently available in the AOP Wiki (http://aopwiki.org), and gives an example of an AOP network based on five reproductive and developmental toxicity-related AOPs for fish to illustrate how AOP networks can be used for assay development and refinement.