In Vitroandin SilicoDerived Relative Effect Potencies of Ah-Receptor-Mediated Effects by PCDD/Fs and PCBs in Rat, Mouse, and Guinea Pig CALUX Cell Lines

Abstract

For a better understanding of species-specific relative effect potencies (REPs), responses of dioxin-like compounds (DLCs) were assessed. REPs were calculated using chemical-activated luciferase gene expression assays (CALUX) derived from guinea pig, rat, and mouse cell lines. Almost all 20 congeners tested in the rodent cell lines were partial agonists and less efficacious than 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). For this reason, REPs were calculated for each congener using concentrations at which 20% of the maximal TCDD response was reached (REP20TCDD). REP20TCDD values obtained for PCDD/Fs were comparable with their toxic equivalency factors assigned by the World Health Organization (WHO-TEF), while those for PCBs were in general lower than the WHO-TEF values. Moreover, the guinea pig cell line was the most sensitive as indicated by the 20% effect concentrations of TCDD of 1.5, 5.6, and 11.0 pM for guinea pig, rat, and mouse cells, respectively. A similar response pattern was observed using multivariate statistical analysis between the three CALUX assays and the WHO-TEFs. The mouse assay showed minor deviation due to higher relative induction potential for 2,3,7,8-tetrachlorodibenzofuran and 2,3,4,6,7,8-hexachlorodibenzofuran and lower for 1,2,3,4,6,7,8-heptachlorodibenzofuran and 3,3',4,4',5-pentachlorobiphenyl (PCB126). 2,3,7,8-Tetrachlorodibenzofuran was more than two times more potent in the mouse assay as compared with that of rat and guinea pig cells, while measured REP20TCDD for PCB126 was lower in mouse cells (0.05) as compared with that of the guinea pig (0.2) and rat (0.07). In order to provide REP20TCDD values for all WHO-TEF assigned compounds, quantitative structure-activity relationship (QSAR) models were developed. The QSAR models showed that specific electronic properties and molecular surface characteristics play important roles in the AhR-mediated response. In silico derived REP20TCDD values were generally consistent with the WHO-TEFs with a few exceptions. The QSAR models indicated that, e.g., 1,2,3,7,8-pentachlorodibenzofuran and 1,2,3,7,8,9-hexachlorodibenzofuran were more potent than given by their assigned WHO-TEF values, and the non-ortho PCB 81 was predicted, based on the guinea-pig model, to be 1 order of magnitude above its WHO-TEF value. By combining in vitro and in silico approaches, REPs were established for all WHO-TEF assigned compounds (except OCDD), which will provide future guidance in testing AhR-mediated responses of DLCs and to increase our understanding of species variation in AhR-mediated effects.

Influence of Co-Dosed Lipids from Biota Extracts on the Availability of Chemicals in In Vitro Cell-Based Bioassays

“…The two AhR-activating chemicals, PCB 126 38 and βnaphthoflavone, 39 were tested in the AhR-CALUX assay at the same Vf triolein in the range 0.25−4%. The f triolein ranged between 81 and 99% for the more hydrophobic PCB 126 and from 28 to 87% for the less hydrophobic β-naphthoflavone.…”

Consensus Toxicity Factors for Polychlorinated Dibenzo-p-dioxins, Dibenzofurans, and Biphenyls Combiningin SilicoModels and Extensivein VitroScreening of AhR-Mediated Effects in Human and Rodent Cells

“…Dose−Response Modeling. Dose−response modeling was conducted as described by Ghorbanzadeh et al for all data except those relating to lymphocytes and splenic cells (Table S1), where separate curves were fitted for each human donor due to the high variation in the individual responses 15,32 the maximum 2378-TCDD response (BMR 20TCDD ) was calculated to establish in vitro REPs. The benchmark response approach was chosen above calculating REPs based on 50% effect concentration (EC 50 ), as the Hill slope and efficacy between the individual congeners and 2378-TCDD were not for all congeners comparable.…”

“…The three outliers are all highly chlorinated and thus on the range of the applicability domain, and we have earlier identified outliers among these compounds. 15 Notably, OCDF showed very low membership score in both models but was defined as member on a 99% confidence level. The three compound classes share chemical characteristics of the chlorine atoms and aromatic rings but differ in flexibility where the PCBs are able to rotate over the biphenyl ring.…”

Elucidating the aryl hydrocarbon receptor antagonism from a chemical-structural perspective

“…These models are the first QSARs for AhR antagonistic activity of which we are aware. Previous QSAR models reported in the literature focused on AhR agonism or non-specific AhR-ligand binding [28,45]. Moreover, the models presented herein were built over a diverse dataset of chemicals and were observed to be consistent with the OECD validation principles [46].…”