The role of receptor‐mediated activities of 4‐ and 5‐ring unsubstituted and methylated polycyclic aromatic hydrocarbons (PAHs) in developmental toxicity

Abstract

The present study evaluated the aryl hydrocarbon receptor (AhR), estrogen receptor‐α (ER‐α), and retinoic acid receptor (RAR) mediated activities of nine 4‐ and 5‐ring unsubstituted and monomethylated polycyclic aromatic hydrocarbons (PAHs) using a series of Chemical‐Activated LUciferase gene eXpression (CALUX) assays. The potential role of these aforementioned receptors in relation to the developmental toxicity of these PAHs was further assessed in the zebrafish embryotoxicity test (ZET). The results show that all nine tested PAHs were AhR agonists, benz[a]anthracene (BaA) and 8‐methyl‐benz[a]anthracene (8‐MeBaA) were ER‐α agonists, and none of the tested PAHs induced ER‐α antagonistic or RAR (ant)agonistic activities. In the AhR CALUX assay, all the methylated PAHs showed higher potency (lower EC50) in activating the AhR than their respective unsubstituted PAHs, implying that the addition of a methyl substituent on the aromatic ring of PAHs could enhance their AhR‐mediated activities. Co‐exposure of zebrafish embryos with each individual PAH and an AhR antagonist (CH223191) counteracted the observed developmental retardations and embryo lethality to a certain extent, except for 8‐methyl‐benzo[a]pyrene (8‐MeBaP). Co‐exposure of zebrafish embryos with either of the two estrogenic PAHs (i.e., BaA and 8‐MeBaA) and an ER‐α antagonist (fulvestrant) neutralized embryo lethality induced by 50 μM BaA and the developmental retardations induced by 15 μM 8‐MeBaA. Altogether, our findings suggest that the observed developmental retardations in zebrafish embryos by the PAH tested may partially be AhR‐ and/or ER‐α‐mediated, whereas the RAR seems not to be relevant for the PAH‐induced developmental toxicity in the ZET.

Evaluating the in vitro developmental toxicity potency of a series of petroleum substance extracts using new approach methodologies (NAMs)

“…As a result, the EC50 values obtained following 24 h exposure to BaP and PAH-containing materials in the AhR CALUX assay are higher than those upon 6 h exposure (EC50 BaP_6h: 6 × 10 –4 μg/ml; EC50 BaP_24h: 1.8 × 10 –2 μg/ml). In line with this observation, it was previously reported that BaP induction is higher after 6 h than after 24 h in the AhR CALUX assay, whereas the reverse was observed for more persistent compounds like TCDD (Hamers et al 2000 ; Machala et al 2001 ; Vrabie et al 2009 ; Fang et al 2023 ). On the contrary, for base oil samples tested (SN100-LBO, SN500-LBO, SN100-BO), the AhR activity was observed only after 6 h but not 24 h exposure, implying a transient or short-lived AhR activation.…”