| Combining Xenoestrogens at Levels below Individual No-Observed-Effect Concentrations Dramatically Enhances Steroid Hormone Action Nissanka Rajapakse, Elisabete Silva, and Andreas Kortenkamp Centre for Toxicology, School of Pharmacy, London, United Kingdom Abstract
The low potency of many man-made estrogenic chemicals, so-called xenoestrogens, has been used to suggest that risks arising from exposure to individual chemicals are negligible. Another argument used to dismiss concerns of health effects is that endogenous steroidal estrogens are too potent for xenoestrogens to contribute significantly to estrogenic effects. Using a yeast reporter gene assay with the human estrogen receptor  , we tested these ideas experimentally by assessing the ability of a combination of 11 xenoestrogens to affect the actions of 17ß-estradiol. Significantly, each xenoestrogen was present at a level well below its no-observed-effect concentration (NOEC) . To derive accurate descriptions of low effects, we recorded concentration-response relationships for each xenoestrogen and for 17ß-estradiol. We used these data to predict entire concentration-response curves of mixtures of xenoestrogens with 17ß-estradiol, assuming additive combination effects. Over a large range of concentrations, the experimentally observed responses decisively confirmed the model predictions. The combined additive effect of the 11 xenoestrogens led to a dramatic enhancement of the hormone's action, even when each single agent was present below its NOEC. Our results show that not even sub-NOEC levels of xenoestrogens can be considered to be without effect on potent steroidal estrogens when they act in concert with a large number of similarly acting chemicals. It remains to be seen to what degree these effects can be neutralized by environmental chemicals with antiestrogenic activity. Nevertheless, potential human and wildlife responses induced by additive combination effects of xenoestrogens deserve serious consideration. Key words: 17ß-estradiol, additivity, mixture effects, xenoestrogens, yeast estrogen screen (YES) . Environ Health Perspect 110:917-921 (2002) . [Online 12 August 2002] http://ehpnet1.niehs.nih.gov/docs/2002/110p917-921rajapakse/ abstract.html Address correspondence to A. Kortenkamp, Centre for Toxicology, School of Pharmacy, 29-39 Brunswick Square, London WC1N 1AX UK. Telephone/Fax: +44 20 7753 5908. E-mail: andreas.kortenkamp@ulsop.ac.uk We thank J. Sumpter and N. Beresford, Brunel University, UK, for providing the recombinant yeast cells. E.S. is funded by Programa Praxis XXI, Fundação para a Ciência e Tecnologia, Portugal, and N.R. is funded by a School of Pharmacy studentship. Received 15 January 2002 ; accepted 8 March 2002.
The full version of this article is available for free in HTML or PDF formats. |
