Inhibitory effect of cadmium on estrogen signaling in zebrafish brain and protection by zinc.

The present study was conducted to assess the effects of Cd exposure on estrogen signaling in the zebrafish brain, as well as the potential protective role of Zn against Cd-induced toxicity. For this purpose, the effects on transcriptional activation of the estrogen receptors (ERs), aromatase B (Aro-B) protein expression and molecular expression of related genes were examined in vivo using wild-type and transgenic zebrafish embryos. For in vitro studies, an ER-negative glial cell line (U251MG) transfected with different zebrafish ER subtypes (ERα, ERß1 and ERß2) was also used. Embryos were exposed either to estradiol (E2 ), Cd, E2 +Cd or E2 +Cd+Zn for 72 h and cells were exposed to the same treatments for 30 h. Our results show that E2 treatment promoted the transcriptional activation of ERs and increased Aro-B expression, at both the protein and mRNA levels. Although exposure to Cd, does not affect the studied parameters when administered alone, it significantly abolished the E2 -stimulated transcriptional response of the reporter gene for the three ER subtypes in U251-MG cells, and clearly inhibited the E2 induction of Aro-B in radial glial cells of zebrafish embryos. These inhibitory effects were accompanied by a significant downregulation of the expression of esr1, esr2a, esr2b and cyp19a1b genes compared to the E2 -treated group used as a positive control. Zn administration during simultaneous exposure to E2 and Cd strongly stimulated zebrafish ERs transactivation and increased Aro-B protein expression, whereas mRNA levels of the three ERs as well as the cyp19a1b remained unchanged in comparison with Cd-treated embryos. In conclusion, our results clearly demonstrate that Cd acts as a potent anti-estrogen in vivo and in vitro, and that Cd-induced E2 antagonism can be reversed, at the protein level, by Zn supplement. Copyright © 2016 John Wiley & Sons, Ltd.

Aryl hydrocarbon receptor-independent toxicity of weathered crude oil during fish development.

Polycyclic aromatic hydrocarbons (PAHs), derived largely from fossil fuels and their combustion, are pervasive contaminants in rivers, lakes, and nearshore marine habitats. Studies after the Exxon Valdez oil spill demonstrated that fish embryos exposed to low levels of PAHs in weathered crude oil develop a syndrome of edema and craniofacial and body axis defects. Although mechanisms leading to these defects are poorly understood, it is widely held that PAH toxicity is linked to aryl hydrocarbon receptor (AhR) binding and cytochrome P450 1A (CYP1A) induction. Using zebrafish embryos, we show that the weathered crude oil syndrome is distinct from the well-characterized AhR-dependent effects of dioxin toxicity. Blockade of AhR pathway components with antisense morpholino oligonucleotides demonstrated that the key developmental defects induced by weathered crude oil exposure are mediated by low-molecular-weight tricyclic PAHs through AhR-independent disruption of cardiovascular function and morphogenesis. These findings have multiple implications for the assessment of PAH impacts on coastal habitats.