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Comparison of Relative Binding Affinities for Trout and Human Estrogen Receptor Based upon Different Competitive Binding Assays, oral
Citation:
DENNY, J. S., M. HORNUNG, M. A. TAPPER, P. K. SCHMIEDER, J. PREGENZER, J. MCKIM, IV, AND D. BLAKEMAN. Comparison of Relative Binding Affinities for Trout and Human Estrogen Receptor Based upon Different Competitive Binding Assays, oral. Presented at Joint Meeting of the Minnesota, Ontario, and Wisconsin Chapters of the American Fisheries Society, Duluth, MN, February 02 - 04, 2009.
Impact/Purpose:
The US EPA has been mandated to screen industrial chemicals and pesticides for potential endocrine activity.
Description:
The US EPA has been mandated to screen industrial chemicals and pesticides for potential endocrine activity. To evaluate the potential for chemicals to cause endocrine disruption in fish we have previously measured the affinity of a number of chemicals for the rainbow trout estrogen receptor (ER). To partially address the question of interspecies differences, relative binding affinities (RBA) for sixteen chemicals were compared among three separate competitive ER binding assays. The ERs were from rainbow trout hepatic cytosol, recombinant rainbow trout ERá, and recombinant human ERá. The two trout-based assays used displacement of 3H-estradiol from ER, and the human ERá-based assay used displacement of a flourescent ligand from ER. The RBAs determined using the trout hepatic cytosol were lower than those determined using the recombinant trout or recombinant human ERá. In all cases but one, RBAs determined using the trout recombinant ERá and the human recombinant ERá were more similar to each other, than either was to RBAs determined with the trout cytosolic ER preparation. This suggests that interspecies differences in receptors may contribute less to differences in RBAs than the differences between other parameters of the competitive binding assays. Matrix differences such as higher protein concentration in the cytosolic preparation may lead to differences in the bioavailability of a test chemical to interact with the receptor. Thus chemical parameters such as the free fraction of test chemical may be critical for accurately comparing the same endpoint among different assays.