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ToxSci Advance Access published online on February 16, 2006
Toxicological Sciences, doi:10.1093/toxsci/kfj136
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© The Author 2006. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received January 10, 2006
Accepted February 13, 2006

Endocrine Toxicology

Brain Cytochrome P450 Aromatase Gene Isoforms and Activity Levels in Atlantic Salmon after Waterborne Exposure to Nominal Environmental Concentrations of the Pharmaceutical Ethynylestradiol and Antifoulant Tributyltin

Angeliki Lyssimachou 1, Bjørn Munro Jenssen 1, and Augustine Arukwe 1 *

1 Department of Biology, Norwegian University of Science and Technology (NTNU) Høgskoleringen 5, 7491 Trondheim, Norway

* To whom correspondence should be addressed.
Augustine Arukwe, E-mail: arukwe{at}bio.ntnu.no


  Abstract

In this study, the effects of two environmental endocrine-disruptors, the synthetic pharmaceutical estrogen (ethynylestradiol) and antifoulant (tributyltin) representing two different modes of action on the endocrine system, were studied on brain steroidogenic pathway of juvenile Atlantic salmon (Salmo salar). Neurosteroidogenesis was studied using brain aromatase gene isoforms and enzyme activity, in parallel with typical xenoestrogen responses such as brain estrogen receptor (ER{alpha}) and plasma vitellogenin (Vtg) levels. Fish were exposed to nominal waterborne ethynylestradiol (EE2; 5 and 50ng/L) and tributyltin (TBT; 50 and 250ng/L) concentrations dissolved in dimethylsulfoxide (DMSO), singly and in combination. Gene expressions were quantified using real-time PCR with gene-specific primers, aromatase activity was analyzed using the tritiated water release assay and plasma vitellogenin was analyzed using competitive ELISA. Our data show that EE2 induced a concentration-specific modulation of P450aromA, P450aromB and aromatase activity in addition to ER{alpha} and plasma Vtg levels in juvenile salmon at day 3 post exposure. TBT exposure caused both the elevation and inhibition of P450aromA, P450aromB and aromatase activity levels, depending on concentration, at day 7 post-exposure. TBT elevated and inhibited ER{alpha} and plasma Vtg, and also antagonized EE2-induced expression of the studied variables at day 7 post-exposure. Interestingly, the carrier vehicle DMSO modulated the receptor and non-receptor mediated estrogenic responses at day 7 post-exposure, compared to day 3. In general, these findings suggest that the exposed animals are experiencing impaired steroidogenesis and modulations of receptor-mediated endocrine responses. Given the integral role of neurosteroids in homeostatic process, growth, metabolism, reproduction and development of central nervous system and function, these effects may have serious impact on this endocrine pathway and potentially affect organismal reproductive performance and health. In conclusion, the regulation of steroidogenesis is a fundamental mechanism involved in the biosynthesis of important biological compounds, irrespective of organ, therefore the search for the molecular targets of xenoestrogens, given singly and also in combination, in these pathways will increase our understanding on organismal endocrine disruption and potential consequences.

Keywords: Neurosteroidogenesis; Aromatase Genes; Pharmaceutical; Antifouling agent; Endocrine disruption; Fish.
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