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Evaluation of Thyroid Hormone System Disrupting Potential of Resorcinol in Fish Using an AOP-Based Approach
Citation:
Van Dingenen, I., E. Andersen, J. Novak, M. Christiansen, A. Haigis, S. Volz, B. Blackwell, E. Stacy, D. Villeneuve, L. Vergauwen, K. Hilscherova, H. Holbech, AND D. Knapen. Evaluation of Thyroid Hormone System Disrupting Potential of Resorcinol in Fish Using an AOP-Based Approach. SETAC EU, Dublin, IRELAND, April 30 - May 04, 2023. https://doi.org/10.23645/epacomptox.26042086
Impact/Purpose:
Per- and polyfluorinated alkyl substances (PFAS) are a large class of compounds of concern to the Agency and the public. Molecular screening approaches are being applied as part of a tiered testing strategy to assess potential hazards of PFAS to human health and the environment. Adverse outcome pathways (AOPs) are a framework for organizing scientific knowledge concerning the links between specific biological activities measured in molecular screening assays and adverse effects considered relevant for risk assessment and environmental safety decision-making. The present presentation reports on testing of network of AOPs for a thyroid disrupting chemical, and demonstrates how AOPs can support similar hazard characterization for PFAS that are identified to act as thyroid disrupting chemicals. Results help to establish the scientific credibility and utility of hazard screening approaches employing a combination of new approach methodologies and targeted testing anchored to AOPs.
Description:
1. Introduction A growing number of pollutants are reported to negatively affect the hypothalamus-pituitary-thyroid (HPT) axis. Resorcinol is currently under consideration as a substance of very high concern in the European Union. It is used for a variety of purposes, such as the synthesis of resins used in the rubber industry, but also as a substance in pharmaceuticals such as in acne treatments. There is in vitro evidence that resorcinol can inhibit thyroperoxidase (TPO), an enzyme crucial in the synthesis of thyroid hormones (THs) and case studies have linked resorcinol exposure to hypothyroidism in humans. Evidence linking resorcinol to thyroid hormone system disruption (THSD) in the environment is currently lacking. In the current study, the potential of resorcinol to interfere with the THS both in vitro and in vivo (in the zebrafish model) was assessed using the adverse outcome pathway (AOP) conceptual framework. The adverse effects of THSD on swim bladder inflation and eye development in fish have recently been described in a set of AOPs [1-3]. In vitro data were gathered to predict the possible molecular initiating events (MIEs) through which resorcinol could affect the THS in fish. TH levels and effects on two robust endpoints of THSD, swim bladder and eye development, were assessed in zebrafish embryos following resorcinol exposure. 2. Materials and Methods In vitro assays were performed to predict the different MIEs through which resorcinol can possibly affect the THS: deiodinase (DIO) 1/2 and TPO inhibition, NIS inhibition, AhR agonism, thyroid receptor (TR) (ant)agonism and transthyretin (TTR) displacement assays. Effects on TH levels, the swim bladder and eye development were assessed through zebrafish embryo exposures. Whole-body TH levels were measured at 5 days post fertilization (dpf) using an established LC-MS method. At both 5 and 7 dpf, swim bladder inflation was assessed using a binary scoring system and swimming activity was analysed using a Zebrabox video tracking device. All larvae were photographed and larval length and swim bladder surface was assessed using the free image processing software ImageJ. Histological analyses were performed to determine the effects on eye development in 8 day old zebrafish larvae. Resorcinol concentrations in the exposure medium were quantified. Additional qPCR analyses are being performed to further elucidate the effect of resorcinol on the HPT axis. All statistical analyses were performed in Graphpad Prism and R. 3. Conclusions In vitro data showed that resorcinol can interfere with the HPT-axis through TPO inhibition, DIO1 inhibition, TTR displacement and TR antagonism. TPO inhibition could explain the decreased T4 levels, but not the impaired inflation of the swim bladder. The effect of the swim bladder is therefore probably a result of one of the other possible MIEs. The current study illustrates how an AOP-based approach can be used to consider the contributions of multiple mechanisms when evaluating the THSD potential of a chemical.
URLs/Downloads:
DOI: Evaluation of Thyroid Hormone System Disrupting Potential of Resorcinol in Fish Using an AOP-Based Approach
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