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Comparison of Relative Binding Affinities for Trout and Human Estrogen Receptor Based upon Different Competitive Binding Assays
Citation:
DENNY, J. S., M. W. 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. Presented at SETAC Annual Meeting, Tampa, FL, November 16 - 20, 2008.
Impact/Purpose:
Knowledge of not only the biological variables involved, but also chemical parameters such as the free fraction of test chemical, may be critical for accurately comparing the same endpoint among different assays.
Description:
The development of a predictive model based upon a single aquatic species inevitably raises the question of whether this information is valid for other species. To partially address this question, relative binding affinities (RBA) for six alkylphenols (para-substituted, n- and branched-alkyl), seven alkylanilines (para-substituted n-alkyl), and three mono-hydroxy parabens were compared among three separate competitive ER binding assays. The ERs used for these assays were from a rainbow trout hepatic cytosol preparation, a recombinant rainbow trout ERá, and a recombinant human ERá. The two trout-based assays used displacement of 3H-estradiol from the ER, and the human ERá-based assay used displacement of a flourescent ligand as the measure of ER binding. For all chemicals tested, the RBA determined using the trout hepatic cytosol was lower than that 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 in comparison to that in purified recombinant receptor assays, may lead to differences in the bioavailability of a test chemical to interact with the receptor. Thus, knowledge of not only the biological variables involved, but also chemical parameters such as the free fraction of test chemical, may be critical for accurately comparing the same endpoint among different assays.