Relationship between the results of in vitro receptor binding assay to human estrogen receptor α and in vivo uterotrophic assay: Comparative study with 65 selected chemicals

Department of Human Environmental Science, Ochanomizu University, 2-1-1, Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan.
Toxicology in Vitro (Impact Factor: 3.21). 03/2008; 22(1):225-31. DOI: 10.1016/j.tiv.2007.08.004
Source: PubMed

ABSTRACT For screening chemicals possessing endocrine disrupting potencies, the uterotrophic assay has been placed in a higher level in the OECD testing framework than the ER binding assay to detect ER-mediated activities. However, there are no studies that can demonstrate a clear relationship between these assays. In order to clarify the relationship between the in vitro ER binding and in vivo uterotrophic assays and to determine meaningful binding potency from the ER binding assay, we compared the results from these assays for 65 chemicals spanning a variety of chemicals classes. Under the quantitative comparison between logRBAs (relative binding affinities) and logLEDs (lowest effective doses), the log RBA was well correlated with both logLEDs of estrogenic and anti-estrogenic compounds at r(2)=0.67 (n=28) and 0.79 (n=23), respectively. The RBA of 0.00233% was found to be the lowest ER binding potency to elicit estrogenic or anti-estrogenic activities in the uterotrophic assay, accordingly this value is considered as the detection limit of estrogenic or anti-estrogenic activities in the uterotrophic assay. The usage of this value as cutoff provided the best concordance rate (82%). These findings are useful in a tiered approach for identifying chemicals that have potential to induce ER-mediated effects in vivo.

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    • "Additionally, BPF has been shown to exhibit in vitro androgenic and anti-androgenic effects (Cabaton et al., 2009; Kitamura et al., 2005; Stroheker et al., 2004). BPF was shown to have estrogenic and anti-estrogenic activity in some in vivo studies with female rats (Akahori et al., 2008). For D-8 there is only limited evidence of endocrine activity. "
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    Regulatory Toxicology and Pharmacology 01/2015; 22(3). DOI:10.1016/j.yrtph.2015.01.002 · 2.14 Impact Factor
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    • "Tetrabromo-bisphenol A (TBBPA) is used primarily as a flame retardant in epoxy resin circuit boards, electronic enclosures, paper, plastic, and textiles (NTP, 2002; Olsen et al., 2003) and bisphenol AF (BPAF) is used in fluoroelastomers, polyamides, polyesters, polycarbonate copolymers , and other specialty polymers (Akahori et al., 2008; NTP, 2008; Perez et al., 1998). BPA and BPAF have been shown to induce estrogen-dependent responses in vivo and in vitro via binding to estrogen receptor (ER) ERa and ERb (Akahori et al., 2008; Bay et al., 2004; Wetherill et al., 2007; Yamasaki et al., 2003), whereas studies on the estrogenicity of TBBPA in vitro are inconsistent. Both BPAF and TBBPA have been nominated for toxicological characterization by the NTP, National Institute of Environmental Health Sciences (NTP, 2002, 2008). "
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    Toxicological Sciences 05/2010; 116(2):477-87. DOI:10.1093/toxsci/kfq156 · 4.48 Impact Factor
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    • "Although the automated approach is efficient and requires minimal manual preparation, a compound can only be identified as ER ligand with the MALDI methodology if its RBA is in the range of several percent. RBAs are determined in a competition experiment with a labelled ligand and expressed relative to the concentration of E2 required to induce a 50% drop of the signal (Kuiper et al., 1998; Blair et al., 2000; Okubo et al., 2004; Akahori et al., 2008). Therefore, a ligand with a 7% RBA requires a concentration ca. "
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    ABSTRACT: High-mass matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) combined with chemical cross-linking has the ability to monitor the ligand-dependent dimerization of the human estrogen receptor alpha ligand binding domain (hERalpha LBD) in solution. Because only ER ligands enhance the homodimer abundance, we evaluated the ability of this label-free approach for identifying endocrine disrupting compounds (EDCs) in a high-throughput manner. This was achieved by combining an automated liquid handler with an automated MS acquisition procedure, which allowed a five-fold gain in operator time compared to a fully manual approach. To detect ligand binding with enough confidence, the receptor has to be incubated with at least a 10 microM concentration of the test compound. Based on the increase of the measured homodimer intensity, eight compounds with a relative binding affinity (RBA, relative to the natural hormone estradiol) >7% were identified as ER ligands among the 28 chemicals tested. Two other compounds, quercetin and 4-tert-amylphenol, were also identified as ER ligands, although their RBAs have been reported to be only 0.01% and 0.000055%, respectively. This suggests that these two ligands have a higher affinity for hERalpha LBD than reported in the literature. The high-mass MALDI approach thus allows identifying high affinity EDCs in an efficient way.
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