Using Zebrafish G Protein-Coupled Receptors to Obtain a Better Appreciation of the Impact of Pharmaceuticals in Wastewater to Fish

Pharmaceutical discharge to the environment is of concern due to its potential adverse effects on aquatic species. It is estimated that around 40% of pharmaceuticals target G protein-coupled receptors (GPCRs). The <i>in vitro</i> transforming growth factor-<i>α</i> (TGF<i>α</i>) shedding assay was applied to measure the antagonistic activities of pharmaceuticals against human GPCRs. However, their ability to stimulate fish GPCRs remains unclear. Here, antagonistic activities of 30 pharmaceuticals against zebrafish dopamine (zD2a and zD2c), adrenergic family member (z<i>β</i>1), and histamine (zH1 and zH3) receptors were measured by the TGF<i>α</i> shedding assay. The study found an interspecies difference in binding affinities between human and zebrafish: pharmaceuticals more strongly inhibited the zD2c and zH1 receptors than human D2 (hD2) and hH1 receptors, while zD2a and z<i>β</i>1 receptors were less inhibited than hD2 and h<i>β</i>1 receptors. The potential molecular explanations for the observed interspecies differences in binding affinity for hydroxyzine and bisoprolol were investigated using molecular docking. Pharmaceutical potency against zebrafish GPCRs and predicted effluent concentrations were used to predict equivalent quantities (EQs), and these EQs were used to prioritize pharmaceuticals of concern in wastewater in England and Japan. This study highlights the use of the TGF<i>α</i> shedding assay adopting zebrafish GPCRs to better understand the ecological effects of pharmaceuticals on fish.