Estrogen-Like Activity of Perfluoroalkyl Acids In Vivo and Interaction with Human and Rainbow Trout Estrogen Receptors In Vitro

Abstract

The objectives of this study were to determine the structural characteristics of perfluoroalkyl acids (PFAAs) that confer estrogen-like activity in vivo using juvenile rainbow trout (Oncorhynchus mykiss) as an animal model and to determine whether these chemicals interact directly with the estrogen receptor (ER) using in vitro and in silico species comparison approaches. Perfluorooctanoic (PFOA), perfluorononanoic (PFNA), perfluorodecanoic (PFDA), and perfluoroundecanoic (PFUnDA) acids were all potent inducers of the estrogen-responsive biomarker protein vitellogenin (Vtg) in vivo, although at fairly high dietary exposures. A structure-activity relationship for PFAAs was observed, where eight to ten fluorinated carbons and a carboxylic acid end group were optimal for maximal Vtg induction. These in vivo findings were corroborated by in vitro mechanistic assays for trout and human ER. All PFAAs tested weakly bound to trout liver ER with half maximal inhibitory concentration (IC(50)) values of 15.2-289 μM. Additionally, PFOA, PFNA, PFDA, PFUnDA, and perlfuorooctane sulfonate (PFOS) significantly enhanced human ERα-dependent transcriptional activation at concentrations ranging from 10-1000 nM. Finally, we employed an in silico computational model based upon the crystal structure for the human ERα ligand-binding domain complexed with E2 to structurally investigate binding of these putative ligands to human, mouse, and trout ERα. PFOA, PFNA, PFDA, and PFOS all efficiently docked with ERα from different species and formed a hydrogen bond at residue Arg394/398/407 (human/mouse/trout) in a manner similar to the environmental estrogens bisphenol A and nonylphenol. Overall, these data support the contention that several PFAAs are weak environmental xenoestrogens of potential concern.

Assessment of Estrogenic Activity of Perfluoroalkyl Acids Based on Ligand-induced Conformation State of Human Estrogen Receptor

“…This is in good agreement with the results of a radio-labeled competitive ligand binding assay with trout liver ER. 17 The reason for the different binding affinity with ER among the six PFAAs will be discussed later after computer modeling. For the measurement of ligand-induced hERα conformational change, a conformation-specific peptide was immobilized on SPR sensor chip through biotin-streptavidin interaction.…”

“…Differences in estrogenic activities among various PFAAs were also observed in previous in vivo and cell assays. 15,17 To understand the structural basis of these differences, molecular modeling on the interactions between PFAAs and hERα was performed. E2 (the endogenous ligand) and OHT (a known ER antagonist) were first docked to hERα-LBD using the Autodock software.…”

“…Several PFAAs including PFOS and PFOA were assessed to be weak environmental xenoestrogens. 17 Putting together, these different results indicate that the estrogenic effect of PFAAs may depend on the animal species and route of exposure. Consequently, a mechanistic study on the interactions between PFAAs and hERα at molecular level is highly desired.…”

Structure–activity relations in binding of perfluoroalkyl compounds to human thyroid hormone T3 receptor

“…Second, TR binding potency is also dependent on the end group in the order of sulfonate > carboxylate > alcoholic hydroxyl. Several previous studies assessed the binding potency of PFCs with some other proteins, including nuclear receptors such as ER and peroxisome PPARs, transport proteins such as transthyretin, human serum albumin, and fatty acid-binding protein (Benninghoff et al 2011;Chen and Guo 2009;Luebker et al 2002;Weiss et al 2009;Zhang et al 2013). As far as we know, there was no previous study on the binding interaction between PFCs and TR.…”

“…Direct binding and activation to PPARs have been demonstrated (Wolf et al 2012;Takacs and Abbott 2007). Recently, some other nuclear receptors, such as estrogen receptor (ER), constitutive androstane receptor, pregnane X receptor, androgen receptor, and aryl hydrocarbon receptor have also been identified as possible targets of PFCs (Benninghoff et al 2011;Bjork et al 2011;Gao et al 2013).…”