Regulatory hazard and risk assessment of endocrine-active substances currently specifies four modes of action: interference with sex hormone (oestrogen, androgen) pathways, steroidogenesis, and thyroid hormone signalling. This does not encompass the full complexity of the endocrine system and its extended interfaces with environmental pollutants that can potentially disrupt the carefully maintained balance. Here we take the retinoid signalling pathway as a European case study for both, under- and unregulated endocrine pathways and outline the different levels of interference, discuss their adversity, and indicate crosstalk to other signalling pathways. Retinoid compounds already exist in drinking water sources, occur naturally in cyanobacterial blooms and/or enter surface waters via wastewater discharge, where they pose a potential hazard to the environment and human health - a situation that can be expected to worsen due to water shortages induced by climate-change and population growth. We briefly review relevant aspects of current endocrine disruptor (ED) testing for regulatory purposes and then expand upon the needs for inclusion of disruption of retinoid signalling in (ED) regulatory safety assessment contributing to adverse health outcomes that include cognitive function and neurological disease. An overview of developmental effects of retinoid signalling disruption across species highlights critical processes and potential crosstalk with other signalling pathways. A focused weight of evidence-based evaluation of the biologically plausible associations between neurological disorders and altered retinoid signalling highlights the evidence gaps. We show that monitoring only a limited number of anthropogenic priority chemicals in water is insufficient to address the environmental risks of retinoid signalling disruption. To comprehensively assess impacts on the endpoints, processes, and pathways of the endocrine system that are most vulnerable to chemical interference we need further investigation of the true mixture composition in environmental matrices. On a weight of evidence-basis this information can then be integrated into a reliable, inclusive, quantitative approach that ultimately accommodates all the critical pathways. By focusing on the retinoid signalling pathway, we intend to improve the scope and relevance of an integrated approach for the risk assessment of endocrine disruptors.
Bibliographical noteFunding Information:
The research has received funding from the Czech Science Foundation, Czechia, project No. 18-15199S, the RECETOX Research Infrastructure (Projects LM2018121 and the CETOCOEN EXCELLENCE Teaming 2 project supported by European Union’s Horizon 2020 (857560) and the Czech Ministry of Education, Youth and Sports (02.1.01/0.0/0.0/18_046/0015975)), the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 722493 NaToxAq (BK), and grant agreement No. 825,753 ERGO (KH). MNJ was supported by Public Health England, CR did not receive specific funding for this study. The European Union’s Research Executive Agency was not involved in any step of the study design.
The opinions are those of the authors’ and not necessarily the organisations’ involved. The European Union’s Research Executive Agency cannot be held responsible for any use that may be made of the information it contains.
© 2021, The Author(s).
- Endocrine disruptors
- Hazard and risk assessment
- Learning impairment
- Natural toxin
- Neurological disorder
- Retinoid signalling pathway