Role of Aryl Hydrocarbon Receptor and Oxidative Stress in the Regioselective Toxicities of Hydroxychrysenes in Embryonic Japanese Medaka (Oryzias latipes)

Abstract

AbstractOxygenated polycyclic aromatic hydrocarbons (oxy‐PAHs) are environmental contaminants that can be created through oxidation of parent PAHs. Previous studies have found that 2‐hydroxychrysene (2‐OHCHR) caused anemia in embryonic Japanese medaka whereas 6‐hydroxychrysene (6‐OHCHR) did not, an example of regioselective toxicity. Anemia was prevented by cytochrome P450 (CYP) inhibition, which reduced the formation of the potential oxidatively active metabolite, 1,2‐catechol, from 2‐OHCHR. 2‐OHCHR has also been found to be a four‐fold more potent aryl hydrocarbon receptor (AhR) agonist compared with 6‐OHCHR. These findings led us to hypothesize that AhR activation and/or oxidative stress play an important role in 2‐OHCHR toxicity. Although treatments with the AhR agonists polychlorinated biphenyl (PCB)126 and 2‐methoxychrysene (2‐MeOCHR) did not cause significant toxicity, pretreatments with the AhR antagonist, CH‐223191, reduced anemia by 97.2 ± 0.84% and mortality by 96.6 ± 0.69%. Aryl hydrocarbon receptor inhibition by the antagonist was confirmed by significant reductions (91.0 ± 9.94%) in induced ethoxyresorufin‐O‐deethylase activity. Thiobarbituric acid reactive substances concentrations were 32.9 ± 3.56% higher (p < 0.05) in 2‐OHCHR treatments at 100 hours postfertilization compared with controls. Staining 2‐OHCHR‐treated embryos with the reactive oxygen species (ROS) scavenger 2′,7′‐dichlorofluorescin diacetate revealed 32.6 ± 2.69% of 2‐OHCHR‐treated embryos exhibiting high concentrations of ROS in caudal tissues, which is a site for embryonic hematopoiesis in medaka. Pretreatment with antioxidants, N‐acetylcysteine (NAC) or vitamin E (Vit E) significantly reduced 2‐OHCHR‐induced anemia (NAC: 80.7 ± 1.12% and Vit E: 99.1 ± 0.43%) and mortality (NAC: 67.1 ± 1.69% and Vit E: 98.9 ± 0.66%). These results indicate that AhR may mediate 2‐OHCHR toxicity through canonical signaling by up‐regulating CYP1, enhancing the formation of reactive metabolites of 2‐OHCHR that generate ROS within caudal hematopoietic tissues, potentially disrupting hematopoiesis, leading to anemia and subsequent mortality. Environ Toxicol Chem 2023;42:698–706. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.