Exposure time–dependent effects on the relative potencies and additivity of PAHs in the Ah receptor‐based H4IIE‐luc bioassay

Abstract

In the present study, relative potency factors (REPs) of 16 individual polycyclic aromatic hydrocarbons (PAHs) were investigated using the H4IIE-luc bioassay. Exposure time-dependent effects on the REPs were examined using 24, 48, and 72 h of exposure. Seven different mixtures of PAHs were tested for additivity at an exposure time of 24 h. Three of the PAH mixtures were also studied at 48 and 72 h of exposure. The mixture toxicities were predicted using the REP concept and the concentration addition (CA) model. Relative potency factor values investigated in the present study were similar to those reported in earlier studies. Declining REPs with an increasing exposure time were shown for all PAHs, indicating that this bioassay approach could be developed to assess the persistency of aryl hydrocarbon receptor (AhR) agonistic PAHs and in the risk assessment of complex PAH mixtures. The results from the mixture studies indicated that additive interactions of PAHs are time dependent. Generally, 48- and 72-h exposures resulted in biological effects that were similar to the CA and REP model predictions, while these models tended to underestimate the effect, to some extent, in the 24-h exposure, at least for the mixtures containing two to four PAHs. Thus, it cannot be ruled out that in the 24-h exposures, the tested PAH mixtures had slight synergistic effects. Further research is needed to identify and test additional AhR activating PAHs and investigate whether the effects in the H4IIE-luc bioassay are additive for more complex samples containing both PAHs and other AhR-activating contaminants. Also, the observed superinduction of luciferase by PAH-mixes warrants studies of whether this also can occur for relevant AhR-mediated endpoints in vivo.

Time‐dependent relative potency factors for polycyclic aromatic hydrocarbons and their derivatives in the H4IIE‐luc bioassay

“…Oxidation of the PAHs seems to reduce the AhR agonistic potency and efficacy of the compounds. Except for benzo[a]fluorenone, all oxy‐PAHs in the present study had lower efficacy compared to their parent PAHs (Tables and ).…”

“…Data points represent the mean value of 2 to 4 experiments for each of the individual PACs. Asterisk indicates data from Larsson et al . ( B ) Relationships between measured concentrations in the wells and exposure duration for 3 PACs in the H4IIE‐luc bioassay.…”

Measured and predicted affinities of binding and relative potencies to activate the AhR of PAHs and their alkylated analogues

“…One example is chrysene. The ReP 50 estimate for chrysene determined in this study was 9.7 Â 10 À7 which is 1.3-and 2.4-fold different from the previous estimates using the H4IIE-luc system, reported by Villeneuve et al (2002) and Larsson et al (2012), respectively.…”

“…The AhR protein, which belongs to the basic helix-loop-helix protein family, plays an important role in the toxicity pathway of dioxin-like compounds including PAHs (Eichbaum et al, 2014;Larsson et al, 2012). This ligand-dependent transcription factor responds to diverse ligands and plays a critical role not only in toxicity, but also in immune function, cardiovascular physiology, and xenobiotic metabolism (Ma, 2001;Motto et al, 2011;Xing et al, 2012).…”

Genotoxicity of Heterocyclic PAHs in the Micronucleus Assay with the Fish Liver Cell Line RTL-W1

“…The biological effects so far cover, e.g. toxicity to Daphnia and green algae, mutagenicity in the Ames assay, embryotoxicity to embryos of the zebrafish ( Danio rerio ) or effects mediated by the aryl hydrocarbon and retinoid receptor, respectively [12], [13], [14], [15], [16], [17], [18].…”