2025 SETAC Europe Presentations
Smithers Ecotoxicology and Environmental Fate & Metabolism scientists will present during the SETAC Europe Annual Meeting in Vienna. View the list of posters
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2025 SETAC Europe Poster: An Extended Amphibian Metamorphosis Assay (EAMA) with the reference compound Propylthiouracil (PTU)
The Amphibian Metamorphosis Assay (AMA) is a key in vivo screening assay intended to identify substances which may interfere with the normal function of the hypothalamic-pituitary-thyroid (HPT) axis. The Extended Amphibian Metamorphosis Assay (EAMA) is a recently proposed, modified design that was created to better evaluate thyroid-related endpoints using elements from the Larval Amphibian Growth and Development Assay (LAGDA); specifically, the development endpoint as a time-to-stage evaluation instead of stage determination at study day 21. There are several advantages to this change in design vs. the AMA. For instance, the robustness of the statistical and histological analyses is improved and extending to NF stage 62 encompasses exposure during metamorphic climax, when thyroid hormone plasma concentrations dramatically increase.
While regulatory studies have been performed with this extended design, no studies with reference chemicals have been conducted. Therefore the goal of this study was to evaluate EAMA endpoints after exposure to a reference toxicant and compare responses of thyroid-mediated endpoints vs. the fixed-time design. To this end, two extended AMA studies were conducted with propylthiouracil (PTU). Study #1 utilized the concentration range from the OECD test guideline 231 validation exercise: 2.5, 5.0, 10, and 20 mg/L and a dilution water control. A follow-up study employed a 40 mg/L treatment group and a dilution water control.
Statistically significant delays in development were observed between the control and the 20 mg/L treatment group at test termination. Metamorphic developmental arrest was observed at the 40 mg/L treatment group, as tadpoles did not develop past NF stage 56. In addition, statistically significant increases in wet body weight, snout-vent length (SVL), and hind limb length normalized by SVL were observed in 40 mg/L-exposed tadpoles compared to the control. Findings in the thyroid glands at 10, 20, and 40 mg/L included concentration-dependent increases in the prevalence and severity of follicular cell hypertrophy and follicular cell hyperplasia as well as decreased colloid. Thyroid hypertrophy was observed at 20 and 40 mg/L.
The results were in line with the expected outcome based on the mode of action of PTU as a thyroid hormone synthesis inhibitor and provide data for validation of the EAMA as a reduction and refinement alternative method to the AMA or the LAGDA.
Joseph Marini will present this research during the SETAC Europe 35th Annual Meeting, May 11-15, in Vienna, Austria. Meet with the Smithers team at stand 33 during the conference.