The role of CYP1A inhibition in the embryotoxic interactions between hypoxia and polycyclic aromatic hydrocarbons (PAHs) and PAH mixtures in zebrafish (Danio rerio)

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants with elevated concentrations in waters that may also experience hypoxia. Previous research has shown interactions between hypoxia and some PAHs (fluoranthene, α-naphthoflavone) but no interaction with others (benzo[a]pyrene (BaP), β-naphthoflavone). Here we examine how hypoxia (7.4% oxygen, ~35% of normoxia) affects the embryotoxicity of PAHs that act through different mechanisms and the role that CYP1A inhibition may play in these interactions. 500 μg/L BaP and 1-200 μg/L benzo[k]fluoranthene (BkF) interacted synergistically with hypoxia to induce pericardial edema in developing zebrafish (Danio rerio). Hypoxia protected from the embryotoxicity of pyrene (PY) and had no effect on the toxicity of polychlorinated biphenyl-126. Despite previous reports of other CYP1A inhibitors interacting with hypoxia, up to 2000 μg/L dibenzothiophene, 2-aminoanthracene (AA), and carbazole (CB) all failed to induce embryotoxicity under normoxic or hypoxic conditions. The toxicity of PAH mixtures—including binary mixtures of BaP/AA and BaP/CB and two environmentally relevant, complex mixtures—were exacerbated severely by hypoxia to induce or worsen pericardial edema and cause mortality. The interactions between hypoxia and BkF and PY were closely mimicked by morpholino knockdown of CYP1A, indicating a potential role for metabolism of these compounds in their toxicity. Our results indicate that various PAHs may exhibit synergistic, antagonistic or additive toxicity with hypoxia. The enhanced toxicity of environmental mixtures of PAHs under hypoxia suggests that risk assessments that do not take into account potential interactions with hypoxia may underestimate the threat of PAHs to fish in contaminated sites.

Effects of elevated dissolved carbon dioxide and perfluorooctane sulfonic acid, given singly and in combination, on steroidogenic and biotransformation pathways of Atlantic cod

“…Elsewhere, hypoxia was also shown to decrease CYP1A-mediated ethoxyresorufin-O-deethylase (EROD) activity in zebrafish embryos (Fleming and Di Giulio, 2011) and cyp1a mRNA levels in Atlantic cod liver (Olsvik et al, 2006). Mammalian in vivo studies using rabbit, and rodent in vitro hepatocyte studies also showed decreases in cyp1a and cyp1a2 mRNA and protein expression by hypoxia, whose effects on CYP1As are mediated through HIF-1α, cellular cytokines and reactive oxygen species (ROS) (Fradette et al, 2007;Fradette and Du Souich, 2004).…”

Distribution and sources of the polycyclic aromatic hydrocarbons in the sediments of the Pearl River estuary, China

“…PAHs are primarily aroused by the incomplete consumption/burning of wood, coal, petroleum and natural gas (Lima et al 2003), spill of petroleum or petroleum products (Boehm and Farrington 1984) and discharge of the traffic exhausts (Naes et al 1995). PAHs can be detected in almost all environmental medias including air, water and soil (sediment) (Fleming and Di Giulio 2011;Huang et al 2012;Zhao et al 2012). The sediments are considered as a primary reservoir of PAHs in aquatic systems.…”

Early life co-exposures to a real-world PAH mixture and hypoxia result in later life and next generation consequences in medaka (Oryzias latipes)

“…All scenarios were run with 5 embryos in each of 3 replicates, and exposures were performed in a Heraeus Heracell 150 Tri-Gas Cell Culture Incubator (Thermo Scientific, Waltham, MA) with oxygen adjustment by nitrogen injection. As described by Fleming and Di Giulio (2011), initial oxygen adjustment of this incubator takes approximately 6–8 hours. Therefore, all equipment and materials were prepared in advance in preparation for rapid placement of vials in the incubator.…”

“…Because oxygen saturation requirements exist for biodegradation of PAHs, hypoxia may prolong the persistence of PAHs resulting in synergistic, antagonistic or additive effects (Boyd et al, 2005; Fleming and Di Giulio, 2011; Matson et al, 2008; Wassenberg and Di Giulio, 2004). Hypoxia should be considered in evaluations of natural waterways because of the possibility of underestimating ecotoxicity of PAHs.…”