New insights on cross-species differences in the modulation of human and zebrafish nuclear receptors by single chemicals and environmental mixtures

In the context of contamination of aquatic ecosystems by endocrine disrupting chemicals (EDCs), this work aims to provide new insights on cross-species differences in the modulation of nuclear receptors (NRs) and the aryl hydrocarbon receptor (AhR) by individual chemicals and environmental mixtures, in order to help further cross-species extrapolation in the frame of the environmental risks of EDCs. To this end, a panel of individual ligands and environmental mixtures from an urban waste water treatment plant (WWTP), were screened on a set of recently developed in vitro reporter cell lines based on both human (h) and zebrafish (zf) NRs and AhR. Our results revealed that for some of the receptors marked cross-species differences occurred (PXR, PPARγ, PR) while for other receptors the differences were lower (ER, AR, GR, MR) or almost absent (AhR, ERRγ). For instance, promegestone acts as a full agonist of the hPR but as partial agonist of the zfPR whereas the dihydroxy-4-pregnen-3-one -reference ligand of the zfPR- antagonizes the hPR. In the same way, none of the reference ligands of the hPXR (T0913117) modulates the zfPXR whereas the clotrimazole -reference ligand of zfPXR- modulates also the hPXR but with lower potency. Then the hAR was more sensitive to the agonist mifepristone and the antagonist OH-flutamide than the zfAR whereas the dexamethasone was a more potent agonist of the zfGR than the hGR. Also significant differences in selectivity were noted among h and zf ER subtypes. Finally, the in vitro profiling of an urban WWTP confirmed these cross-species differences in terms of level, type (agonist vs antagonist), distribution along the WWTP. For instance, h and zf estrogenic activity was differentially detected in the sludge and the suspended material. In the same way, strong zf anti-androgenic activity was detected in the effluent while no human one can be detected. Also, strong zf mineralocorticoidic activity was detected in both influent and effluent whereas only h anti-mineralocorticoid activity was detected. Alogether, our results showed that h and zf NRs are, for some of them, differentially modulated by individual chemicals and environmental mixtures. Also, interaction of EDCs towards NRs cannot always be extrapolated between these species highlighting the need to further document NRs modulation between human and fish and associated responses, to improve human health and environmental risk assessment of EDCs.