SEAZIT: Systematic Evaluation of the Application of Zebrafish in Toxicology
The small size and rapid development of the zebrafish make it a useful vertebrate model for assessing the potential effects of substances on growth and development through the use of high-throughput screening methods. The embryonic zebrafish model has been used for this purpose in pharmaceutical development and in high-throughput screening programs at NTP and the EPA. However, deficits in the following key areas hinder the broader adoption of the zebrafish model for toxicological screening:
- Consistent experimental protocol elements
- Clear understanding of mechanisms of chemical absorption, distribution, metabolism, and excretion in zebrafish
- Consistent informatics approaches used for classification of outcomes
Thus, to enable the broader adoption of zebrafish for toxicological screening, NTP established the Systematic Evaluation of the Application of Zebrafish in Toxicology (SEAZIT) program, jointly led by NTP and NICEATM scientists. Summarized below are four key SEAZIT program activities:
- Zebrafish information gathering
- A webinar series focused on the use of informatics to improve data analysis for zebrafish screening studies (2017)
- An interlaboratory zebrafish study (2019)
- A zebrafish best practices workshop
In 2016, SEAZIT team members conducted a series of interviews with experts in the use of zebrafish in toxicology studies. These interviews identified the following:
- Areas key to developing a harmonized testing protocol for zebrafish studies
- Sources of variability among laboratories
As a result, in April 2017, a meeting with zebrafish researchers and data scientists was conducted to discuss how to improve zebrafish screening data analysis using ontologies, which are standardized nomenclature systems. The meeting discussions supported planning of an interlaboratory study to examine effects on toxicity estimates of renewing exposure media and removing the chorion, a permeable membrane enclosing the zebrafish embryo.
- A flash report of the meeting summarizes the presentations, discussions, and recommendations.
- Information about current research practices gathered from this effort are summarized in Hamm et al. 2018.
Key issues being addressed by SEAZIT include the variability among laboratories in the endpoints measured and the nomenclature used for each endpoint. On behalf of SEAZIT, NICEATM presented a webinar series in 2017 that considered how these issues might be addressed by implementing ontologies (i.e., standardized nomenclature systems).
The goals of the webinar series were to:
- Summarize some of the barriers to routine use of zebrafish in toxicological evaluations
- Review the concept of ontologies
- Consider how ontologies could be applied to harmonize procedures used for zebrafish screening studies
A webinar series in fall 2018 examined three case studies that illustrated the utility of zebrafish models for toxicology.
The interlaboratory study conceived during the Information Gathering phase will begin in 2019. It will be designed to determine the effect of chorion removal and exposure media renewal on study outcomes. Participating laboratories will use in-house protocols to test a defined chemical set while varying the two protocol elements under investigation. The chemical set, which was designed to provide overlap with other NTP studies, includes chemicals with a range of physicochemical properties and developmental effects. Many of the chemicals have in vivo reference data available from rodent and other zebrafish studies. The interlaboratory study will also include a pilot effort on chemical kinetics in support of future studies of absorption, distribution, metabolism, and excretion in zebrafish.
The primary goal of SEAZIT is to develop best practices for data analysis. To this end, the data generated in this study will be made publicly available. This will allow interested investigators to collaborate to establish a means by which all data generated by the study can contribute to a consensus toxicity value for each chemical.
Best Practices Workshop
A 2020 best practices workshop will serve as a public forum where experts from various fields can discuss continued development and standardization of assays, as well as practices for collecting, analyzing, and reporting data. A report from the workshop will be published in the peer-reviewed literature and will provide recommendations on how to conduct zebrafish screening assays and report the data.