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AOP-informed assessment of endocrine disruption in freshwater crustaceans
Citation:
Tollefsen, K., M. Cronin, O. Evensen, L. Evenseth, F. Falciani, T. Iguchi, C. LaLone, Y. Li, C. Mellor, E. Perkins, J. Rundberget, B. Salbu, I. Sylte, Dan Villeneuve, N. Vinas, AND Y. Song. AOP-informed assessment of endocrine disruption in freshwater crustaceans. SETAC Europe, Rome, ITALY, May 13 - 17, 2018.
Impact/Purpose:
Development of high throughput toxicology (HTT) programs (e.g., ToxCast, Tox21) and potential application of those data has been heavily focused on human health. However, protecting ecosystems from harmful impacts of chemicals is another central aspect of EPA’s mission. At present, there are gaps in the HTT program with regard to biological pathways and molecular targets which are not relevant to humans but are none the less critical to the survival, growth/development, and/or reproduction in other species. This paper reviews the critical role of ecdysteroid signaling in the endocrine control of molting behavior in arthropods, a phylum representing over a million described species. It details evidence that disruption of ecdysone receptor-mediated signaling can lead to fatal failures in molting across a broad range of arthropod species and that there are chemicals present in the environment that can cause these effects. Review of the basic biology underlying the molting process in arthropods provides a foundation for describing a series of adverse outcome pathways (AOPs) linking perturbation of various targets involved in arthropod endocrine signaling to adverse phenotypic outcomes of ecological significance. The AOPs, in turn, provide a scientific foundation for development of high throughput assays and/or in silico tools that can be used to screen chemicals for their ability to interact with and perturb key targets in these arthropod endocrine pathways. Thus, this work can help to address the gap in HTT programs relative to coverage of critical pathways involved in invertebrate endocrine function. The content of this review and the resulting AOPs and assay development will have direct relevance to the Endocrine Disruptor Screening Program, the Office of Pesticide Programs, as many pesticides are designed to target and impair arthropod molting, and the Office of Water relative to expedited criteria development.
Description:
To date, most research focused on developing more efficient and cost effective methods to predict toxicity have focused on human biology. However, there is also a need for effective high throughput tools to predict toxicity to other species that perform critical ecosystem functions. The present work focuses on the development of cost effective and efficient tools for identifying chemicals with potential to adversely affect crustaceans through interactions with invertebrate endocrine systems. This work aims to improve our ability to protect invertebrates, as critical foundations of aquatic and terrestrial food-webs, from adverse effects of chemicals. 1. Introduction A number of exogenous compounds have the potential to interfere with the endocrine system of animals and may perturb vital endocrine processes to a degree causing an adverse effect (outcome) on ecologically relevant endpoints such as growth, development and reproduction. These endocrine disrupting (ED) effects have been well characterised in aquatic vertebrates and mammals due to a well-defined endocrine system and substantial research effort in the last decades, but knowledge on ED effects in a larger range of species are still poorly characterized. Lack of knowledge on ED effects in invertebrates is currently a major limiting factor to properly perform risk assessment of endocrine disrupting chemicals (EDCs) across taxa. The present project have focussed on developing Adverse Outcome Pathways (AOPs) for EDs in aquatic crustaceans, and applying these to assess the hazard and risk of ecologically relevant complex mixtures of pollutants. Although several ED mechanisms have been proposed to be of relevance for crustaceans, perturbations of endocrine processes related to chemical interactions with the ecdysone receptor (EcR) and the Juvenile Hormone (methyl farnesoid) receptor (MfR) have been identified to be of particular concern (Song et al., 2017; Fay et al. 2017). The present paper focus on the application of AOPs to 1) develop linkage between endocrine mechanisms and adverse outcomes, 2) identify knowledge gaps and inform testing strategies, 3) identify sensitive species/taxa, 4) identify likely define toxicity endpoints suitable for Integrated Approaches for Testing and Assessment, IATA (Tollefsen et al., 2014), 5) identify potential EDCs and 6) practical implementation of AOP information into cumulative hazard and risk assessment of ecologically relevant exposure scenarios. 2. Materials and methods A combination of literature surveys, in silico, in vitro and in vivo approaches was used to assemble AOPs for EcR agonists in arthropods, perform weight of evidence (WoE) considerations, and identify knowledge gaps as basis for experimental studies with the models freshwater crustacean D. magna (fig. 1). The data generated was used to define the chemical and taxonomic applicability domain and deploy a suite of methods covering the AOP continuum to evaluate the suitability and robustness for future IATA initiatives. The chosen endpoints ranging from the Molecular initiating Event (MiE), selected Key Events (KEs) and Adverse Outcomes (AOs) were used in Cumulative Hazard (CHA) and risk (CRA) Assessments of typical pollution profiles of European surface waters receiving agricultural, muncipal and industrial pollutants. 3. Results and discussion 3.1. Assembly and evaluation of a conceptual AOP An AOPs were succesfuly assembled using available data, weight of evidence (WoE) considerations performed (Song et al. 2016) and the resulting conceptual AOP submitted to the AOPwiki, www.aopwiki.org (AOP#4, fig. 2). The taxonomic applicability domain (susceptible species) was defined by the Sequence Alignment to Predict Across Species Susceptibility (SeqAPASS; fig. 2) tool (Lalone et al. 2016) and over 100 potential EcR binders were identified from available chemical inventories usin