Exposure and Recovery from Environmentally Relevant Levels of Waterborne Polycyclic Aromatic Hydrocarbons from Deepwater Horizon Oil: Effects on the Gulf Toadfish Stress Axis

Endocrine disruptors, aryl hydrocarbon receptor and cortisol secretion

PURPOSE

Endocrine disruptors exert a plethora of effects in endocrine tissues, from altered function to carcinogenesis. Given its lipophilic nature, the adrenal cortex represents an ideal target for endocrine disruptors and thus, possibly, xenobiotic-induced adrenocortical dysfunction. However, there is no clear understanding of the effect of endocrine disruptors on adrenal steroidogenesis, in particular as regards the aryl hydrocarbon receptor (AHR) pathway, one of the key mediators.

METHODS

The present review recapitulates available evidence on the effects of AHR ligands on adrenal steroidogenesis, with focus on cortisol secretion.

RESULTS

Short-term exposure to AHR ligands most often induced a stress-like corticosteroid response followed by decreased responsiveness to stressors with long-term exposure. This was observed in several experimental models across species as well as in animals and humans in real-life settings. Prenatal exposure led to different effects according to sex of the offspring, as observed in murine models and in children from mothers in several countries. In vitro findings proved highly dependent on the experimental setting, with reduced cortisol response and steroidogenic enzyme synthesis mostly observed in fish and increased cortisol synthesis and secretion observed in murine and human adrenal cell lines. Of note, no AHR-binding element was detected in steroidogenic enzyme promoters, suggesting the involvement of additional factors.

CONCLUSION

Our review provides evidence for the impact of AHR ligands on adrenocortical function and indicates further avenues of research to better clarify its effects.

2,2',4,4'-Tetrabromodiphenyl ether and cadmium co-exposure activates aryl hydrocarbon receptor pathway to induce ROS and GSDME-dependent pyroptosis in renal tubular epithelial cells

We have previously found that a mixture exposure of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and cadmium (Cd) causes kidney damage; however, the mechanism was not fully understood. The aryl hydrocarbon receptor (AhR) is a ligand-receptor transcription factor that plays an important role in the adaptive response or metabolic detoxification of environmental toxins. Thus, this study aimed to examine the role of AhR in kidney toxicity. BDE-47 (50 μM) or Cd (5 μM) exposure reduced cell viability in renal tubular epithelial cells (HKC), with a larger effect observed in co-treatment. The cell morphology presented pyroptotic changes, including swollen cells, large bubbles, and plasma membrane pore formation. The gene expressions of AhR, heat shock protein 90 (Hsp90), AhR nuclear translocator (ARNT), and cytochrome P450 1B1 (CYP1B1) were increased, while CYP1A1 was decreased. Reactive oxygen species (ROS) were generated, which was reduced by the AhR antagonist CH223191. The apoptosis, necrosis, and intracellular lactated hydrogenase (LDH) release was elevated, and this was attenuated by N-acetylcysteine (NAC). Furthermore, the pyroptosis pathway was activated with increased protein levels of cleaved-caspase-3 and gasdermin E N-terminal (GSDME-NT), while caspase-8, caspase-3, and GSDME were decreased. These effects were alleviated by NAC and CH223191. Our data demonstrate a combined effect of BDE-47 and Cd on nephrotoxicity by activating AhR to induce ROS contributing to GSDME-dependent pyroptosis, and retardation of the AhR pathway could reduce this toxicity.

A multi-targeted investigation of Deepwater Horizon crude oil exposure impacts on the marine teleost stress axis

The toxicity of the polycyclic aromatic hydrocarbons (PAHs) in Deepwater Horizon (DWH) oil is well-established, but a knowledge gap exists regarding how this combination of PAHs affects the vertebrate stress axis. We hypothesized that (1) marine vertebrates exposed to DWH PAHs experience stress axis impairment, and co-exposure to an additional chronic stressor may exacerbate these effects, (2) serotonin (5-hydroxytryptamine; 5-HT) may act as a secondary cortisol secretagogue in DWH PAH-exposed fish to compensate for impairment, and (3) the mechanism of stress axis impairment may involve downregulation of cyclic adenosine monophosphate (cAMP; as proxy for melanocortin 2 receptor (MC2R) functionality), total cholesterol, and/or mRNA expression of CYP1A and steroidogenic proteins StAR, P450scc, and 11β-h at the level of the kidney. We found that in vivo plasma cortisol and plasma adrenocorticotropic hormone (ACTH) concentrations in Gulf toadfish exposed to an environmentally relevant DWH PAH concentration (ΣPAH₅₀= 4.6 ± 1.6 μg/L) for 7 days were not significantly different from controls, whether fish were chronically stressed or not. However, the rate of cortisol secretion by isolated kidneys after acute stimulation with ACTH was significantly lower in PAH-exposed toadfish compared to clean seawater (SW) controls. 5-HT does not appear to be acting as a secondary cortisol secretagogue, rather, PAH-exposed + stressed toadfish exhibited significantly lower plasma 5-HT concentrations than clean SW + stressed fish as well as a reduced sensitivity to 5-HT at the level of the kidney. There was a tendency for kidney cAMP concentrations to be lower in PAH-exposed fish (p = 0.069); however, mRNA expression of steroidogenic proteins between control and PAH-exposed toadfish were not significantly different and a significant elevation in total cholesterol concentration in PAH-exposed toadfish compared to controls was measured. Future work is needed to establish whether the slower cortisol secretion rate by isolated kidneys of PAH-exposed fish is detrimental, to determine the potential role of other secretagogues in compensating for the impaired kidney interrenal cell function, and to determine whether there is a reduction in MC2R mRNA expression or an impairment in the function of steroidogenic proteins.

Recommendations for advancing test protocols examining the photo-induced toxicity of petroleum and polycyclic aromatic compounds

Photo-induced toxicity of petroleum products and polycyclic aromatic compounds (PACs) is the enhanced toxicity caused by their interaction with ultraviolet radiation and occurs by two distinct mechanisms: photosensitization and photomodification. Laboratory approaches for designing, conducting, and reporting of photo-induced toxicity studies are reviewed and recommended to enhance the original Chemical Response to Oil Spills: Ecological Research Forum (CROSERF) protocols which did not address photo-induced toxicity. Guidance is provided on conducting photo-induced toxicity tests, including test species, endpoints, experimental design and dosing, light sources, irradiance measurement, chemical characterization, and data reporting. Because of distinct mechanisms, aspects of photosensitization (change in compound energy state) and photomodification (change in compound structure) are addressed separately, and practical applications in laboratory and field studies and advances in predictive modeling are discussed. One goal for developing standardized testing protocols is to support lab-to-field extrapolations, which in the case of petroleum substances often requires a modeling framework to account for differential physicochemical properties of the constituents. Recommendations are provided to promote greater standardization of laboratory studies on photo-induced toxicity, thus facilitating comparisons across studies and generating data needed to improve models used in oil spill science.

Early life-stage Deepwater Horizon crude oil exposure induces latent osmoregulatory defects in larval red drum (Sciaenops ocellatus)

Crude oil is known to induce developmental defects in teleost fish exposed during early-life stages (ELSs). A recent study has demonstrated that zebrafish (Danio rerio) larvae acutely exposed to Deepwater Horizon (DHW) crude oil showed transcriptional changes in key genes involved in early kidney (pronephros) development and function, which were coupled with pronephric morphological defects. Given the osmoregulatory importance of the kidney, it is unknown whether ELS effects arising from short-term crude exposures result in long-term osmoregulatory defects, particularly within estuarine fishes likely exposed to DWH oil following the spill. To address this knowledge gap, an acute 72 h exposure to red drum (Sciaenops ocellatus) larvae was performed using high-energy water-accommodated fractions (HEWAFs) of DWH weathered oil to analyze transcriptional changes in genes involved in pronephros development and function by quantitative PCR. To test the latent effects of oil exposure on osmoregulation ability, red drum larvae were first exposed to HEWAF for 24 h. Larvae were then reared in clean seawater for two weeks and a 96 h acute osmotic challenge test was performed by exposing the fish to waters with varying salinities. Latent effects of ELS crude oil exposure on osmoregulation were assessed by quantifying survival during the acute osmotic challenge test and analyzing transcriptional changes at 14 dpf. Results demonstrated that ELS crude oil exposure reduced survival of red drum larvae when challenged in hypoosmotic waters and that latent transcriptional changes in some target pronephric genes were evident, indicating that an affected kidney likely contributed to the increased mortality.

Urinary polycyclic aromatic hydrocarbon metabolites and depression: a cross-sectional study of the National Health and Nutrition Examination Survey 2005-2016

BACKGROUND

The adverse effects of polycyclic aromatic hydrocarbon (PAHs), a group of common environmental pollutants, on mental health are unclear. This study is developed to evaluate the potential association of urinary PAH metabolites with depression in US adults.

METHODS

Measurement of 8 urinary PAH metabolites and assessment of depression were available for 9625 adults in the National Health and Nutritional Examination Survey 2005-2016. Multiple logistic regression models and weighted quantile sum (WQS) regression models were applied to evaluate the association between urinary PAH metabolites and depression.

RESULTS

Among 9625 individuals with a weighted geometric mean age of 42.63 years, 801 participants suffered from depression. Significant positive dose-response relationships were observed between specific urinary PAH metabolites and the risk of depression after adjusting for potential confounders. Urinary 1-hydroxynaphthalene was positively and dose-dependently associated with the risk of depression among total participants (odds ratio: 1.188; 95% confidence interval: 1.096-1.288). In addition, each 1-unit increase of ln-transformed urinary 1-hydroxynaphthalene, 2-hydroxynaphthalene, 3-hydroxyfluorene, 2-hydroxyfluorene, 1-hydroxyphenanthrene, 2&3-hydroxyphenanthrene, 1-hydroxypyrene, and total PAH metabolites was associated with a 23.3%, 32.6%, 23.3%, 29.4%, 30.8%, 22.8%, 29.4%, and 31.7% increment in the risk of depression in smokers, respectively (all P and P _trend < 0.05). Of note, the positive WQS index was also significantly associated with the increased risk of depression in smokers (1.122, 1.059-1.188).

CONCLUSION

Exposure to PAHs may elevate the risk of depression among US adults. More studies are warranted to investigate the underlying mechanism by which PAHs induce the development of depression.

Exposure of zebrafish larvae to water accommodated fractions of weathered crude oil alters steroid hormone concentrations with minimal effect on cholesterol

Crude oil has multiple toxic effects in fish, particularly during their early life stages. Recent transcriptomics studies have highlighted a potential effect on cholesterol homeostasis and biosynthesis, but have not investigated effects on steroid hormones, which are biosynthetically downstream metabolites of cholesterol. We exposed zebrafish (Danio rerio) embryos and larvae to 3 concentrations of a high energy water accommodated fraction (HEWAF) of crude oil and measured effects on cholesterol and steroid hormones at 48 and 96 h post fertilization (hpf). HEWAF exposure caused a small decrease in cholesterol at 96 hpf but not 48 hpf. HEWAF-exposed larvae had higher levels of androstenedione, testosterone, estradiol, cortisol, corticosterone, and progesterone at 96 hpf compared to controls, while effects at 48 hpf were more modest or not present. 2-Methoxyestradiol was lower following HEWAF exposure at both time points. Dihydrotestosterone was elevated in one HEWAF concentration at 48 hpf only. Our results suggest that hormone imbalance may be an important toxic effect of oil HEWAF exposure despite no major effect on their biosynthetic precursor cholesterol.

Exposure and Recovery of the Gulf Toadfish (Opsanus beta) to Weathered Deepwater Horizon Slick Oil: Impacts on Liver and Blood Endpoints

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants that can be responsible for a variety of deleterious effects on organisms. These adverse outcomes are relatively well studied, but at concentrations rarely found in the environment. Among the documented effects of sublethal acute PAH exposure are reductions in osmoregulatory capacity and immune function, and changes in the function of critical metabolic organs such as the liver. Gulf toadfish (Opsanus beta) were exposed to control seawater (0.006 µg tPAH₅₀ /L) or water accommodated fractions of Deepwater Horizon spill oil diluted to 3 flow-through exposure regimes (0.009, 0.059, and 2.82 µg tPAH₅₀ /L) for 7 d, with a recovery period of equal duration. We hypothesized that these chronic exposures would induce the aryl hydrocarbon receptor (AhR)-mediated pathways and result in significant impacts on markers of osmoregulatory, immune, and metabolic function. We further hypothesized that measurable reversal of these impacts would be observed during the recovery period. Our results indicate that activation of cytochrome P 450 (CYP)1A1 was achieved during exposure and reversed during the recovery phase. The only significant deviations from controls measured were a reduction in plasma glucose in fish exposed to medium and high levels of PAH after 7 d of exposure and a reduction in plasma osmolality fish exposed to high levels of PAHs after 7 d of recovery, when CYP1A1 messenger (m)RNA levels had returned to control levels. Our study illustrates a disconnect between the activation of CYP1A1 in response to environmentally realistic PAHs concentrations and several physiological endpoints and supports the idea that the AhR might not be associated with mediating osmoregulatory, immune, and metabolic changes in Gulf toadfish. Environ Toxicol Chem 2021;40:1075-1086. © 2020 SETAC.