Divergent responsiveness of two isoforms of the estrogen receptor to mixtures of contaminants of emerging concern in four vertebrates

Abstract

Contaminants of emerging concern (CECs) are ubiquitous in aquatic environments with well-established endocrine-disrupting effects. A data matrix of 559 water samples was queried to identify two commonly occurring CECs mixtures in Great Lakes tributaries. One mixture consisted of eight agricultural CECs (AG), while another contained 11 urban CECs (UB). The known estrogenic compounds bisphenol A, estrone and nonylphenol were present in both mixtures. According to the EPA Tox21 in ToxCast database, AG and UB mixture at an environmentally relevant concentration were estimated to account for 6.5% and 3.4% estrogenicity of the model endocrine disruptor estradiol-17β, respectively. Two isoforms of the estrogen receptor (Esr1 and -2, former Erα and Erβ) cloned from fathead minnow, bluegill sunfish, American alligator and human, responded differently to AG and UB mixtures. Human and bluegill Esr1 were the most sensitive to AG and UB mixtures, respectively. Fathead minnow Esr1 and Esr2b were the least sensitive to 10× AG and UB in estrogen dose equivalents, respectively. Even at environmentally documented concentrations, UB significantly activated bluegill Esr1. Moreover, 100× concentrated UB hyperstimulated fathead minnow Esr1 beyond the maximum induction of estradiol-17β. These results indicate that efficacious receptors and species differ in their response to CEC mixtures. Furthermore, estrogenicity may be present in some CECs not previously considered estrogenic, or, alternatively, estrogenicity of a mixture may be enhanced through chemical interactions. Our study highlights the need for further studies of CECs utilizing a variety of receptors cloned from diverse species.

Land Use Contributions to Adverse Biological Effects in a Complex Agricultural and Urban Watershed: A Case Study of the Maumee River

“…Further analysis of plasma Vtg, an egg‐yolk precursor protein expressed in males only in the presence of estrogenic exposure and often used as a biomarker for endocrine disruption (Purdom et al ; Harries et al , ), demonstrates the estrogenic nature of the positive control (MIX) used in our experiment, as has been shown previously (Kohno et al ). Despite the known estrogenic potential of many agricultural (Xie et al ; Hoskins and Boone ) and urban/effluent chemicals (Hemming et al ), the lack of upregulation of Vtg in exposed males suggests that aqueous chemical concentrations were too low to induce synthesis of Vtg, which was highlighted by both the paucity of changes to cell viability with transfected fathead minnow estrogen receptor and the lack of detections of known estrogenic contaminants in surface water samples.…”

“…Estrogenicity in surface water samples was quantified using a transactivation assay as previously described (Kohno et al, 2018). Culture medium, Dulbecco's modified Eagle's medium (DMEM; D2902; Sigma) was prepared at 4× concentration with supplemental 3.7 g/250 mL sodium bicarbonate and 100 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid.…”

Indicators of exposure to estrogenic compounds at Great Lakes Areas of Concern: species and site comparisons

“…Conversely, fathead minnow erα was only induced by the highest concentration of the agricultural mixture and the highest two concentrations of the urban mixture. However, the fathead minnow erβ was more responsive to the urban mixture than the bluegill erβ (Kohno et al 2017 ). Interestingly, a survey of centrarchids at 20 riverine sites in North Carolina showed a distinct difference between Lepomis and Micropterus .…”

Critical assessment and integration of separate lines of evidence for risk assessment of chemical mixtures

“…Several in vitro lines are accepted by regulatory organizations for the assessment of single compounds and/or mixtures taking into account their ability to envisage in vivo results. For example, the US EPA has accepted the Tox-Cast Estrogen Receptor model as a substitute for the in vivo uterotrophic assay (Browne et al 2015;Kohno et al 2018).…”