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In vitro-to-in vivo extrapolation of xenoestrogens using an estrogen responsive in vitro transcriptional activation assay and the in vivo uterotrophic assay
Citation:
Conley, J., B. Hannas, N. Evans, J. Furr, V. Sutherland, P. Foster, E. Gray, AND V. Wilson. In vitro-to-in vivo extrapolation of xenoestrogens using an estrogen responsive in vitro transcriptional activation assay and the in vivo uterotrophic assay. Triangle Consortrium for Reproductive Biology, Research Triangle Park (RTP), NC, February 06, 2016.
Impact/Purpose:
This abstract will be presented at the Triangle Consortium for Reproductive Biology 25th Annual Meeting Research Triangle Park, NC February 6, 2016
Description:
Widespread contamination of waters with both natural and synthetic estrogens is a concern for potential adverse ecological and human health effects. In vitro assays are valuable screening tools for identifying contaminated environmental samples and chemical specific mechanisms of toxicity, such as estrogen receptor activation. However, in vitro effect concentrations cannot necessarily be extrapolated to similar estimates in vivo because most in vitro assays do not account for toxicokinetics. To explore this issue further, we utilized data from the T47D-KBluc estrogen receptor transactivation assay to predict rat uterotrophic assay response following oral administration of individual chemicals and mixtures. 17B- estradiol (E2), ethinyl-estradiol (EE2), benzyl-butyl phthalate (BBP), bisphenol-A (BPA), bisphenol-AF (BPAF), bisphenol-C (BPC), bisphenol-S (BPS), and methoxychlor (MET) were tested individually, while BPS+MET and BPAF+MET were tested as equipotent mixtures. The observed in vivo EDso values were lower (3 - 1261-fold lower) than those predicted using in vitro data for all compounds except BBP, which is metabol ically deactivated. Interestingly, BPS (ECso=6.4e-7M) was less potent in vitro than BPA (ECso=1.2e-7M)by a factor of ~5, however in vivo BPS (EDso= 150 mg kg-1d-1)was ~7-fold more potent than BPA (EDso= 1118 mg kg-1 d-1). Further, we demonstrated that the uterotrophic response to mixtures of BPAF+MET and BPS+MET could be predicted from the individual in vivo data for those compounds using the dose addition model, however predictions using in vitro data resulted in EDso estimates that were 26- and 297-fold greater than observed, respectively. Overall, these data illustrate the potential risk of underestimating in vivo potency from predictions made with in vitro data for compounds that undergo significant disposition following oral administration. In vitro assays will continue to be valuable for screening, however increasing the complexity of in vitro models to account for aspects of toxicokinetics, notably metabolism, and alternative signaling pathways will be necessary to improve the prediction accuracy of in vitro-to-in vivo extrapolations. Abstract does not reflect U.S. EPA policy.