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ToxSci Advance Access originally published online on December 14, 2006
Toxicological Sciences 2007 96(1):145-153; doi:10.1093/toxsci/kfl185
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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

In Vitro and In Vivo Evaluation of the Estrogenic, Androgenic, and Progestagenic Potential of Two Cyclic Siloxanes

Anne L. Quinn1, Jane M. Regan, Joseph M. Tobin, Brian J. Marinik, Joan M. McMahon, Debra A. McNett, Christopher M. Sushynski, Steven D. Crofoot, Paul A. Jean and Kathleen P. Plotzke

Dow Corning Corporation, Midland, Michigan 48686

1 To whom correspondence should be addressed at Dow Corning Corporation, 2200 West Salzburg Road, Mail Stop: CO3101, Midland, Michigan 48686-0994. Fax: (989) 496-5595. E-mail: anne.quinn{at}dowcorning.com.

Received September 13, 2006; accepted November 21, 2006


  Abstract

The purpose of these experiments was to determine the potential estrogenic, androgenic, and progestagenic activity of two cyclic siloxanes, octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5). Receptor-binding experiments and a luciferase reporter gene assay were used to determine if the materials were able to bind and activate either the estrogen receptors (ERs) or progesterone receptors (PRs)—{alpha} or ß. The rat uterotrophic assay (RUA) for estrogenic activity and the Hershberger assay for androgenic activity were utilized as the in vivo assays. For the ER-binding studies, D4 was shown to bind to ER{alpha} but not to ERß. D5 did not bind to either of the two receptors. D4 activated the reporter gene at 10µM, while D5 was considered negative in the estrogen reporter gene assay. Neither material was a ligand for the PRs. Both the RUA and Hershberger assays were conducted using whole-body inhalation of the two materials for 16 h/day. D4 resulted in a small but significant increase in both wet and blotted uterine weight as well as increases in both luminal and glandular epithelial cell height in both Sprague Dawley and Fischer 344 rats. D5 was negative in both rat strains, indicating that D5 does not possess estrogenic activity. Neither material possessed any significant antiestrogenic activity. Both materials were negative in the Hershberger assay indicating that neither material possesses any significant androgenic activity. Our studies have shown that D4 exhibits a low affinity for ER{alpha} in vitro and a weakly estrogenic response in vivo.

Key Words: D4; D5; octamethylcyclotetrasiloxane; decamethylcyclopentasiloxane; silicone; siloxane; estrogen receptor {alpha} and ß; androgen; progesterone; luciferase reporter gene; RUA; estrogenic.


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