Use of chemical mixtures to differentiate mechanisms of endocrine action in a small fish model

Abstract

a b s t r a c tVarious assays with adult fish have been developed to identify potential endocrine-disrupting chemicals (EDCs) which may cause toxicity via alterations in the hypothalamic-pituitary-gonadal (HPG) axis. These assays can be sensitive and highly diagnostic for key mechanisms such as agonism of the estrogen and androgen receptors (ERs, ARs) and inhibition of steroid synthesis. However, most of the tests do not unambiguously identify AR antagonists. The purpose of this work was to explore the utility of a mixture test design with the fathead minnow (Pimephales promelas) for detecting different classes of EDCs including AR antagonists. Adults of both sexes were exposed via the water to EDCs with diverse mechanisms of action in the absence or presence of 17␤-trenbolone (TB), a potent AR agonist which masculinizes female fathead minnows. Similar to previous studies with the model AR antagonists flutamide and vinclozolin, exposure of females to the AR antagonist cyproterone acetate in the presence of TB decreased expression of an easily-observed masculinization response, nuptial tubercle formation. Mixture studies with TB and the model ER agonists, 17␣-ethinylestradiol and bisphenol A, also showed inhibition of tubercle formation in the females, but unlike the AR antagonists, the estrogens markedly induced synthesis of vitellogenin (VTG: egg yolk protein), particularly in males. The ER agonists also offset TB-induced depressions in plasma VTG concentrations in female fish. Additional mixture experiments were conducted with TB and triclocarban, an anti-microbial reported to enhance AR-mediated responses, or ammonia, a "negative control" with no known direct effects on HPG function. Neither chemical affected VTG status in males or females in the absence or presence of TB; however, both slightly enhanced TB-induced tubercle formation in females. Based on studies described herein and elsewhere with the fathead minnow, a TB co-exposure assay appears to be an effective approach for clearly identifying AR antagonists as well as potential EDCs with other relevant mechanisms of action.Published by Elsevier B.V.

Effects of the antimicrobial contaminant triclocarban, and co‐exposure with the androgen 17β‐trenbolone, on reproductive function and ovarian transcriptome of the fathead minnow (Pimephales promelas)

“…In vivo studies in rats have supported the in vitro evidence that TCC augments, but does not directly elicit, androgen action . Similarly, in a previous study with fathead minnow, TCC (10 µg/L) enhanced 17β trenbolone (TRB)‐induced formation of nuptial tubercles (a male secondary sex characteristic) in females exposed to mixtures of the 2 chemicals for 21 d . Augmentation of estrogenic action has also been reported in vivo.…”

An approach to detecting estrogenic endocrine disruption via choriogenin expression in an estuarine model fish species

“…Although EDCs currently impact a wide array of fish species, most EDC studies continue to use a few standard laboratory denizens to assess their impact (e.g., zebrafish, medaka, fathead minnow) (Scholz and Mayer 2008;Segner 2009;Ankley et al 2010). As such, environmental risk assessment and assumptions about sensitivity to EDCs are primarily based on these few species.…”

On‐Site Exposure to Treated Wastewater Effluent Has Subtle Effects on Male Fathead Minnows and Pronounced Effects on Carp

“…The often counterintuitive effects of estrogenic exposure are also highlighted by their impact on secondary sex characteristics (Figure ). Laboratory studies have documented reduction in these characteristics by some EEs (Ankley et al ., ), but also stronger expression of secondary sex characteristics even in female fathead minnows exposed to androgens (Pawlowski et al ., ). Previous literature demonstrates quick plasticity to tubercle development in female fathead minnows exposed to androgens in six days (Ankley et al ., ).…”