Report from the BfR expert hearing on practicability of hormonal measurements: recommendations for experimental design of toxicological studies with integrated hormonal end points

Abstract

This publication summarizes discussions that were held during an international expert hearing organized by the German Federal Institute for Risk Assessment (BfR) in Berlin, Germany, in October 2017. The expert hearing was dedicated to providing practical guidance for the measurement of circulating hormones in regulatory toxicology studies. Adequate measurements of circulating hormones have become more important given the regulatory requirement to assess the potential for endocrine disrupting properties for all substances covered by the plant protection products and biocidal products regulations in the European Union (EU). The main focus was the hypothalamus-pituitary-thyroid axis (HPT) and the hypothalamuspituitary-gonadal axis (HPG). Insulin, insulin-like growth factor 1 (IGF-1), parathyroid hormone (PTH) and vitamins A and D were also discussed. During the hearing, the experts agreed on specific recommendations for design, conduct and evaluation of acceptability of studies measuring thyroid hormones, thyroid stimulating hormone and reproductive hormones as well as provided some recommendations for insulin and IGF-1. Experts concluded that hormonal measurements as part of the test guidelines (TGs) of the Organisation for Economic Cooperation and Development (OECD) were necessary on the condition that quality criteria to guarantee reliability and reproducibility of measurements are adhered to. Inclusion of the female reproductive hormones in OECD TGs was not recommended unless the design of the study was modified to appropriately measure hormone concentrations. The current report aims at promoting standardization of the experimental designs of hormonal assays to allow their integration in OECD TGs and highlights research needs for better identification of endocrine disruptors using hormone measurements.

Prenatal test cohort of a modified rat comparative thyroid assay adding brain thyroid hormone measurements and histology but lowering group size appears able to detect disruption by sodium phenobarbital

“…Recently, not only for US but also European registration, the CTA may be required if existing data for the pesticide provides evidence of a treatment-related effect on thyroid structure or function in other studies ( ECHA/EFSA, 2018 , Kucheryavenko et al, 2019 ). However, acceptable ranges of serum THs alterations in rats (i.e., ranges not considered causally related to adverse effects) are not currently described by either USEPA or OECD.…”

“…Our hypothesis was that the CTA can be conducted with 50 % less animals without losing the power to detect TH disruption. Statistical power is a critical point for defining the limits of the selected study type to detect changes in hormone concentrations under the chosen experimental conditions with the necessary sensitivity ( Kucheryavenko et al, 2019 , Li et al, 2019 , Marty et al, 2021 ).…”

Data collection in support of the Endocrine Disruption (ED) assessment for non‐target vertebrates

“…Recommendations for hormonal studies, more specifically measurements of thyroid and reproductive hormones, in mammalian (usually rodent) test systems have previously been described (European Chemicals Agency (ECHA) and European Food Safety Authority (EFSA) with support from the Joint Research Centre (JRC). 2018; Kucheryavenko et al 2019). Using non-mammalian vertebrates to study thyroid or reproductive toxicity of chemicals can provide important insights for wildlife species.…”