Jenny Odum

Obstacles to the prediction of estrogenicity from chemical structure: assay-mediated metabolic transformation and the apparent promiscuous nature of the estrogen receptor.

Information on structure-activity relationships (SAR) and pathways of metabolic activation would facilitate the preliminary screening of chemicals for estrogenic potential. Published crystallographic studies of the estrogen receptor (ER) imply an essential role of the two hydroxyl groups on estradiol (17beta-E(2)) for its binding to ER. The influence of these hydroxyl groups on ER binding and estrogenicity was evaluated by the study of 17beta-E(2) with one or both of these hydroxyl groups removed (17beta-desoxyestradiol and 3, 17beta-bisdesoxyestradiol, respectively). 6-Hydroxytetralin (17beta-E(2) with its C- and D-rings removed) and other synthetic estrogens were also studied. The estrogenicity assays comprised a yeast ER-mediated transcription assay, mammalian cell transcription assays incorporating either ER alpha or ER beta, and the immature rat uterotrophic assay. With the exception of 6-hydroxytetralin in the uterotrophic assay, all the chemicals were active in all the assays. Hydroxylation of the two desoxy compounds to estradiol was shown to occur in immature female rats, but metabolism was not implicated in the responses observed in the ER-binding and yeast systems. It is concluded that the 3-hydroxyl and 17beta-hydroxyl groups of 17beta-E(2) are not absolute requirements for estrogenicity. It would therefore be of value to the derivation of SAR for estrogenicity were the crystal structure of the bisdesoxy-E(2)/ER complex to be evaluated.

The importance of protocol design and data reporting to research on endocrine disruption.

Several recent articles have discussed the doubts expressed by some scientists regarding the validity of endocrine disruption studies conducted by industrial scientists or sponsored by the chemical industry (1-3). The last of these articles (3) recounted personal attacks made on the integrity of Stephen Safe ofTexas A&M University. It is in the nature of any new branch of toxicology that, at least initially, adverse effects may be discovered for chemicals by those academic laboratories working in the new area. The chemical industry is then left to confirm and extend the findings of others. Such confirmatory studies are usually necessary because the initial publications often describe the results of limited or unreplicated experiments (4). The articles mentioned above (1-3) concerned the prospect that repeat studies conducted by or sponsored by the chemical industry are designed in order not to confirm the original observation. We wish to discuss the complementary concern that many new findings in this area are either inadequately described or are based on data derived using inadequate test protocols. This makes it difficult to conduct faithful repeat experiments, however well-motivated the responsible scientists are. We recently decided to confirm and extend adverse endocrine toxicities reported for nonylphenol (NP) and bisphenol-A (BPA). For both of these chemicals, we experienced problems when attempting to design repeat experiments due to inadequacies of the original publications. These inadequacies may seem to be relatively minor, but when the outcomes of the repeat experiments are likely to be challenged, they become important. Three influential papers using the Noble rat have been published by Colerangle and Roy over the past 4 years (5-7). The papers in question report the results of implanting the estrogens estrone, diethylstilbestrol (DES), NP, or BPA into Noble rats and monitoring the consequent changes in cell growth in the mammary gland. Either pellets or mini-pumps were used to deliver the test chemicals over 11 days. In each case growth of the mammary gland was reported. A significant aspect of these results is that estrogenic effects were found for NP and BPA at much lower dose levels than would have been expected based on the results of earlier studies (8-11), in particular, rat uterotrophic assays conducted using three daily administrations of the test chemicals. To resolve the uncertainties created by this apparent difference in assay sensitivities , we embarked on full repeats of the DES and NP Noble rat mammary gland assays (5-7). …