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Approaches for predicting effects of unintended environmental exposure to an endocrine active pharmaceutical, tamoxifen
Citation:
Mills, Lesley J., W. Matthew Henderson Henderson, Saro Jayaraman, R. Gutjahr-Gobell, G. Zaroogian, Doranne Borsay Horowitz, AND Susan C. Laws. Approaches for predicting effects of unintended environmental exposure to an endocrine active pharmaceutical, tamoxifen. ENVIRONMENTAL TOXICOLOGY. John Wiley & Sons, Ltd., Indianapolis, IN, 31(12):1834–1850, (2016).
Impact/Purpose:
The overarching purpose of the research reported in this manuscript is to reduce uncertainties associated with assessing the environmental impact of emerging endocrine-active pharmaceuticals (EAPs) on human and ecological health, specifically the EAP tamoxifen and its active metabolites. Tamoxifen is used world-wide to treat certain breast cancers. Because tamoxifen is a ubiquitous pharmaceutical and interacts with estrogen receptors, a case study was conducted with this pharmaceutical to 1) determine the effect of tamoxifen on reproductive endpoints in a non-target species (i.e., a fish), 2) compare its potential for toxicological effects through biologically-active metabolites across species, 3) assess whether in vitro assays predict in vivo results, and 4) investigate formation of biologically-active metabolites in aquatic sediments.
Description:
Tamoxifen is an endocrine-active pharmaceutical (EAP) that is used world-wide. Because tamoxifen is a ubiquitous pharmaceutical and interacts with estrogen receptors, a case study was conducted with this compound to (1) determine effects on reproductive endpoints in a nontarget species (i.e., a fish), (2) compare biologically-active metabolites across species, (3) assess whether in vitro assays predict in vivo results, and (4) investigate metabolomic profiles in tamoxifen-treated fish to better understand the biological mechanisms of tamoxifen toxicity. In reproductive assays, tamoxifen exposure caused a significant reduction in egg production and significantly increased ovarian aromatase activity in spawning adult cunner fish (Tautogolabrus adspersus). In plasma from tamoxifen-exposed cunner, the predominant metabolite was 4-hydroxytamoxifen, while in rats it was N-desmethyltamoxifen. Because 4-hydroxytamoxifen is a more biologically active metabolite than N-desmethyltamoxifen, this difference could result in a different level of risk for the two species. The results of in vitro assays with fish hepatic microsomes to assess tamoxifen metabolism did not match in vivo results, indicating probable differences in excretion of tamoxifen metabolites in fish compared with rats. For the first time, a complete in vitro characterization of the metabolism of tamoxifen using fish microsomes is presented. Furthermore, a metabolomic investigation of cunner gonad extracts demonstrates that tamoxifen alters the biochemical profile in this nontarget species. Understanding the consequence of tamoxifen exposure in nontarget species, and assessing the discrepancies between sex- and species-mediated endpoints, is a step toward understanding how to accurately assess the risks posed by EAPs, such as tamoxifen, in the aquatic environment.
