You are here:
Relative Chemical Binding Affinities for Trout and Human Estrogen Receptor Using Different Competitive Binding Assays
Citation:
DENNY, J. S., M. W. HORNUNG, M. A. TAPPER, P. K. SCHMIEDER, J. PREGENZER, J. MCKIM, AND D. BLAKEMAN. Relative Chemical Binding Affinities for Trout and Human Estrogen Receptor Using Different Competitive Binding Assays. Presented at Annual Meeting of Midwesst Chapter of SETAC, La Crosse, WI, March 30 - April 01, 2009.
Impact/Purpose:
Knowledge of chemical parameters such as the free fraction of test chemical may be critical for accurately comparing the same endpoint among different assays.
Description:
Rainbow trout-based assays for estrogenicity are currently being used for development of predictive models based upon quantitative structure activity relationships. A predictive model based on a single species raises the question of whether this information is valid for other species. To partially address this question, relative binding affinities (RBA) for six alkylphenols, seven alkylanilines, and three mono-hydroxy parabens were compared among three separate ER binding assays. The ERs used were from rainbow trout hepatic cytosol, 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. RBAs determined using the trout hepatic cytosol were lower than those determined using the recombinant trout or recombinant human ERá. RBAs determined using the two recombinant ERs (trout and human) were more similar to each other, than either was to RBAs determined with the trout cytosolic ER. This suggests that interspecies differences in receptors may contribute less to differences in RBAs than the differences between other parameters of the 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 chemical parameters such as the free fraction of test chemical may be critical for accurately comparing the same endpoint among different assays.