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An AOP-based alternative testing strategy to predict the impact of thyroid hormone disruption on swim bladder inflation in zebrafish
Citation:
Stinckens, E., L. Vergauwen, G. Ankley, R. Blust, V. Darras, Dan Villeneuve, H. Witters, D. Volz, AND D. Knapen. An AOP-based alternative testing strategy to predict the impact of thyroid hormone disruption on swim bladder inflation in zebrafish. AQUATIC TOXICOLOGY. Elsevier Science Ltd, New York, NY, 200:1-12, (2018).
Impact/Purpose:
To support acceptance of in vitro, high throughput, pathway-based data as viable alternatives to costly whole animal testing, there is need to demonstrate that chemicals can be effectively prioritized with regard to probable in vivo hazards. The adverse outcome pathway (AOP) framework was developed to aid this process by describing the scientific basis for associating apical hazards with specific biological activities. The present paper demonstrates how a pathway-based assay for deiodinase inhibition could be linked with an AOP to effectively prioritize a group of 51 chemicals with regard to their ability to impair swimbladder inflation in fish. This work both strengthens the foundation of empirical support for the AOP linking deiodinase inhibition to decreased young of year survival in fish and supports the EDSP program’s on-going pivot away from in vivo tier 1 screening assays to greater reliance on high throughput screening tools. This case study shows how high throughput data and AOPs can be coupled to generate actionable information that helps to inform regulatory decisions relevant to EDSP and other programs.
Description:
Within the field of chemical safety assessment, there is a desire to replace costly whole organism testing with more efficient and cost-effective alternatives based on in vitro test systems. Disruption of thyroid hormone signaling via inhibition of enzymes called deiodinases is one way chemicals can cause a variety of adverse developmental outcomes in vertebrates. In this paper, 51 chemicals were screened for deiodinase inhibition using a simple in vitro assay. Hazard predictions for 14 of those chemicals were then evaluated in whole organism assays. Results suggest that in most cases, the alternative assays were effective in prioritizing chemicals with regard to their potential hazards.The adverse outcome pathway (AOP) framework can be used to help support the development of alternative testing strategies aimed at predicting adverse outcomes caused by triggering specific toxicity pathways. In this paper, we present a case-study demonstrating the selection of alternative in chemico assays targeting the molecular initiating events of established AOPs, and evaluate use of the resulting data to predict higher level biological endpoints. Based on two AOPs linking inhibition of the deiodinase (DIO) enzymes to impaired posterior swim bladder inflation in fish, we used in chemico enzyme inhibition assays to measure the molecular initiating events for an array of chemicals. Zebrafish embryos were then exposed to 14 compounds with different measured inhibition potentials. Effects on posterior swim bladder inflation, predicted based on the information captured by the AOPs,were evaluated. By linking the two datasets and setting thresholds, we were able to demonstrate that the in chemico dataset can be used to predict biological effects on posterior chamber inflation, with only a few outliers. Our results show how information organized using the AOP framework can be employed to develop or select alternative assays, and successfully forecast downstream key events along the AOP. In general, such in chemico assays could serve as a first-tier high-throughput system to screen and prioritize chemicals for subsequent acute and chronic fish testing, potentially reducing the need for long-term and costly toxicity tests requiring large numbers of animals.
