Mechanistic Investigations Into the Developmental Toxicity of Nitrated and Heterocyclic PAHs

Abstract

Nitrated polycyclic aromatic hydrocarbons (NPAHs) and heterocyclic PAHs (HPAHs) are recognized environmental pollutants. However, the health risks of NPAHs and HPAHs to humans and environmental systems are not well-studied. The developmental zebrafish (Danio rerio) model was used to evaluate the toxicity of a structurally diverse set of 27 NPAHs and 10 HPAHs. The individual activity of each compound towards the aryl hydrocarbon receptor (AHR), including the role of the AHR in observed toxicity, and genetic markers of oxidative stress and cardiac toxicity were evaluated. Zebrafish embryos were exposed from 6 to 120 hours post fertilization (hpf), to a broad concentration range of individual compounds, and evaluated for 22 developmental endpoints. The potential role of AHR was determined using the transgenic Tg(cyp1a:nls-egfp) reporter zebrafish line. All compounds were screened computationally through molecular docking using a previously developed AHR models of zebrafish isoforms 1A, 1B, and 2. Some compounds did not induce observable developmental toxic responses, whereas others produced statistically significant concentration-dependent toxicity. The tested compounds also exhibited a range of predicted AHR binding and cyp1a/GFP induction patterns, including cyp1a expression in the liver, vasculature, skin, and yolk, which we determined to be due to distinct isoforms of the AHR, using morpholino oligonucleotide knockdown. Furthermore, we investigated mRNA expression of oxidative and cardiac stress genes at 48 and 120 hpf, which indicated several potential mechanisms-of-action for NPAHs. Overall, we observed a range of developmental toxicities, cyp1a/GFP expression patterns, and gene expression profiles, suggestive of several potential mechanisms of action.

Signaling Events Downstream of AHR Activation That Contribute to Toxic Responses: The Functional Role of an AHR-Dependent Long Noncoding RNA ( slincR ) Using the Zebrafish Model

“…Developmental exposure to TCDD or PAHs can produce blood circulation defects and cyp1a1 expression in the vasculature (Andreasen et al. 2002; Chlebowski et al. 2017; Henry et al.…”

“…The AHR is ligand-activated by numerous PAHs, which pose a major concern due to their potential toxic effects on ecosystems and human health (Chlebowski et al. 2017; Geier et al.…”

“…2014). In zebrafish, the activation of the AHR by 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD) and numerous PAHs results in the dysregulation of hundreds of genes and is associated with lethality, wasting, hemorrhaging, and defects in the skeletal and cardiovascular systems (Chlebowski et al. 2017; Denison and Nagy 2003; Garcia et al.…”

Zebrafish as a Model for Toxicological Perturbation of Yolk and Nutrition in the Early Embryo

“…Compounds including TCDD classically induce “blue sac syndrome,” a pathology characterized by yolk sac and pericardial edema [61]. However, a wide array of toxicants including polycyclic aromatic hydrocarbons [63, 64], polychlorinated biphenyls [65, 66], polybrominated flame retardants [67], poly- and perfluorinated compounds [68, 69] (unpublished data), organophosphates [70–73], herbicides [74–76], and nanoparticles [67, 77–79] among others have been demonstrated to cause yolk sac edema in zebrafish embryos. The wide range of chemical properties demonstrated by these chemicals suggests that yolk sac edema is an especially sensitive toxicological outcome for embryonic evaluation.…”

Investigating the application of a nitroreductase-expressing transgenic zebrafish line for high-throughput toxicity testing

“…Zebrafish are not believed to have nitroreductase activity. This is supported by the distinctly different toxicological profiles for the corresponding pairs of amino- and nitro- compounds in zebrafish [8]. Some evidence suggests zebrafish may have nitroreductase activity in the yolk [9], and it is possible that zebrafish, like humans and other model organisms, may have nitroreductase activity in the intestine due to the presence of microbiota [10], [11].…”