Avian-Specific Evidence for an Estrogen Receptor Agonism Adverse Outcome Pathway Based on Chicken Embryos and LMH 3D Spheroids Exposed to Ethinylestradiol and Bisphenol A

Several adverse outcome pathways (AOPs) describe the effects of endocrine disrupting compounds on estrogen signaling. Substantial data support an AOP related to estrogen receptor (ER) antagonism, leading to decreased fecundity in fish. In this study, data were generated for an ER agonism AOP leading to reduced fecundity in avian species (AOP537). Chicken embryos and the chicken leghorn male hepatoma cell line, LMH, were used to elucidate key events associated with estrogen signaling following exposure to 17α-ethinylestradiol (EE2) and bisphenol A (BPA). Embryos were exposed via egg injection. Viability and hepatic estrogen-responsive gene expression data were collected at midincubation (embryonic day [ED] 11). Changes in plasma vitellogenin (VTG), gonad morphology and growth were evaluated prior to pipping (ED20). Both chemicals dysregulated estrogen-responsive genes in hepatic tissue and increased plasma VTG concentrations. In LMH spheroids, EE2 and BPA altered estrogen-responsive genes and VTG concentrations at 24 and 48 h, respectively. Gonadal histology revealed oocyte-type cells and loss of testicular cords in male embryos exposed to EE2 and BPA. Overall, EE2 and BPA upregulated VTG mRNA expression, increased plasma VTG, and caused impairments in gonadal development. These results contribute avian-specific evidence to support an endocrine disruption AOP describing the relationship between disrupted VTG synthesis and impaired reproduction.