Hepatic Responses of Juvenile Fundulus heteroclitus from Pollution-adapted and Nonadapted Populations Exposed to Elizabeth River Sediment Extract

Bioenergetic Effects of Polycyclic Aromatic Hydrocarbon Resistance Manifest Later in Life in Offspring of Fundulus heteroclitus from the Elizabeth River

Shifts in key physiological processes can confer resistance to chemical pollutants. However, these adaptations may come with certain trade-offs, such as altered energy metabolic processes, as evident in Atlantic killifish (Fundulus heteroclitus) in Virginia's Elizabeth River (ER) that have evolved resistance to polycyclic aromatic hydrocarbons (PAHs). We seek to understand the bioenergetic costs of PAH resistance among subpopulations of Atlantic killifish with differing contamination levels in order to examine how these changes manifest across multiple life stages and how these costs might be exacerbated by additional stressors. Bioenergetics data revealed differences in metabolic rates between offspring of PAH-resistant fish and reference fish were absent or minimal in both the embryo and larval stages but pronounced at the juvenile life stage, suggesting that bioenergetic changes in pollution-adapted killifish manifest later in life. We also provide evidence that killifish from remediated sites are more sensitive to PAH exposure than killifish from nonremediated sites, suggesting loss of PAH tolerance following relaxed selection. Collectively, our data suggest that the fitness consequences associated with evolved resistance to anthropogenic stressors may manifest differently over time and depend on the magnitude of the selection pressure. This information can be valuable in effective risk and remediation assessments as well as in broadening our understanding of species responses to environmental change.

Cardiac physiology and metabolic gene expression during late organogenesis among F. heteroclitus embryo families from crosses between pollution-sensitive and -resistant parents

BACKGROUND

The teleost fish Fundulus heteroclitus inhabit estuaries heavily polluted with persistent and bioaccumulative chemicals. While embryos of parents from polluted sites are remarkably resistant to toxic sediment and develop normally, embryos of parents from relatively clean estuaries, when treated with polluted sediment extracts, are developmentally delayed, displaying deformities characteristic of pollution-induced embryotoxicity. To gain insight into parental effects on sensitive and resistant phenotypes during late organogenesis, we established sensitive, resistant, and crossed embryo families using five female and five male parents from relatively clean and predominantly PAH-polluted estuaries each, measured heart rates, and quantified individual embryo expression of 179 metabolic genes.

RESULTS

Pollution-induced embryotoxicity manifested as morphological deformities, significant developmental delays, and altered cardiac physiology was evident among sensitive embryos resulting from crosses between females and males from relatively clean estuaries. Significantly different heart rates among several geographically unrelated populations of sensitive, resistant, and crossed embryo families during late organogenesis and pre-hatching suggest site-specific adaptive cardiac physiology phenotypes relative to pollution exposure. Metabolic gene expression patterns (32 genes, 17.9%, at p < 0.05; 11 genes, 6.1%, at p < 0.01) among the embryo families indicate maternal pollutant deposition in the eggs and parental effects on gene expression and metabolic alterations.

CONCLUSION

Heart rate differences among sensitive, resistant, and crossed embryos is a reliable phenotype for further explorations of adaptive mechanisms. While metabolic gene expression patterns among embryo families are suggestive of parental effects on several differentially expressed genes, a definitive adaptive signature and metabolic cost of resistant phenotypes is unclear and shows unexpected sensitive-resistant crossed embryo expression profiles. Our study highlights physiological and metabolic gene expression differences during a critical embryonic stage among pollution sensitive, resistant, and crossed embryo families, which may contribute to underlying resistance mechanisms observed in natural F. heteroclitus populations living in heavily contaminated estuaries.

The role of gut microbial community and metabolomic shifts in adaptive resistance of Atlantic killifish (Fundulus heteroclitus) to polycyclic aromatic hydrocarbons

Altered gut microbiomes may play a role in rapid evolution to anthropogenic change but remain poorly understood. Atlantic killifish (Fundulus heteroclitus) in the Elizabeth River, VA have evolved resistance to polycyclic aromatic hydrocarbons (PAHs) and provide a unique opportunity to examine the links between shifts in the commensal microbiome and organismal physiology associated with evolved resistance. Here, 16S rRNA sequence libraries derived from fish guts and sediments sampled from a highly PAH contaminated site revealed significant differences collected at similar samples from an uncontaminated site. Phylogenetic groups enriched in the libraries derived from PAH-resistant fish were dissimilar to their associated sediment libraries, suggesting the specific environment within the PAH-resistant fish intestine influence the gut microbiome composition. Gut metabolite analysis revealed shifts between PAH-resistant and non-resistant subpopulations. Notably, PAH-resistant fish exhibited reduced levels of tryptophan and increased levels of sphingolipids. Exposure to PAHs appears to impact several bacterial in the gut microbiome, particularly sphingolipid containing bacteria. Bacterial phylotypes known to include species containing sphingolipids were generally lower in the intestines of fish subpopulations exposed to high concentrations of PAHs, inferring a complex host-microbiome relationship. Overall, killifish microbial community shifts appear to be related to a suppression of overall metabolite level, indicating a potential role of the gut in organismal response to anthropogenic environmental change. These results on microbial and metabolomics shifts are potentially linked to altered bioenergetic phenotype observed in the same PAH-resistant killifish populations in other studies.

The In Vitro Proinflammatory Properties of Water Accommodated Sediment Extracts from a Creosote-Contaminated US Environmental Protection Agency Superfund Site

The southern branch of the Elizabeth River near Portsmouth, Virginia, USA, is one of the most creosote-polluted subestuaries in North America and the former location of the Atlantic Wood US Environmental Protection Agency Superfund site. We previously demonstrated that adult Atlantic Wood killifish collected in situ had severe hepatic lesions, including hepatoblastoma and hepatocellular carcinoma, as well as suppressed circulating antibody responses compared to a historical reference site. Moreover, several innate immune functions were higher in Atlantic Wood fish, including elevated expression of hepatic cyclooxygenase-2 (COX-2), suggesting a proinflammatory environment. To further examine the potential of Atlantic Wood contaminants to modulate innate immune function(s), the present study used RAW264.7 mouse macrophages as an in vitro model to develop new approach methodologies for rapid screening. Lipopolysaccharide (LPS)-stimulated nitric oxide secretion by macrophages is a rapid, sensitive, and predictive in vitro system for screening potentially immunotoxic contaminants as single compounds or as complex mixtures. Compared to the reference site, filter-sterilized Atlantic Wood sediment extracts (water accommodated fractions) induced nitric oxide and IL-6 secretion as well as inducible nitric oxide synthase and COX-2 proteins at levels comparable to or higher than those induced by LPS treatments alone. Extracts also increased phagocytic activity by macrophages. Using a limulus lysate assay, we show that bacterial endotoxin levels in Atlantic Wood extracts are higher than in reference extracts and that polymyxin-B chelation ameliorates proinflammatory effects. These findings illuminate the reality of sediment constituents other than toxic compounds previously associated with developmental abnormalities and carcinogenesis in killifish from the Atlantic Wood site. Perhaps these data also suggest the presence of contaminant-adapted consortia of sediment microbes at many heavily polluted sites worldwide compared to less contaminated sites. Environ Toxicol Chem 2021;40:1576-1585. © 2021 SETAC.

Heart development in two populations of Atlantic killifish (Fundulus heteroclitus) following exposure to a polycyclic aromatic hydrocarbon mixture

Historic industrial pollution of the Elizabeth River, Virginia resulted in polycyclic aromatic hydrocarbon (PAH) contamination in sediments. Atlantic killifish (Fundulus heteroclitus) inhabiting the Atlantic Wood (AW) industrial site adapted to complex PAH mixture at this Superfund site. Their embryos have proved highly resistant to cardiac abnormalities indicative of PAH toxicity. In this study, embryos spawned from adults collected at AW and King's Creek (KC), a reference site, were exposed at 24 h post fertilization (hpf) to Elizabeth River Sediment Extract (ERSE), a complex PAH mixture, in a range of concentrations (0, 5.04, 50.45, 100.90, 151.35, or 252.25 µg/L total PAHs). Embryos were processed for histology at 144 hpf to enable evaluations of hearts at tissue and cellular levels. Morphometry and severity scoring were used to evaluate the extent of alterations. Unexposed embryos were similar in both populations. ERSE exposure resulted in multiple changes to hearts of KC embryos but not AW. Alterations were particularly evident in KC embryos exposed to concentrations above 1% ERSE (50.45 µg/L), which had thinner ventricular walls and larger pericardial edema. Individuals with moderate pericardial edema maintained arrangement and proximity of heart chambers, but changes were seen in ventricular myocytes. Severe pericardial edema was prevalent in exposed KC embryos and typically resulted in tube heart formation. Ventricles of tube hearts had very thin walls composed of small, basophilic cells and lacked trabeculae. Edematous pericardial fluid contained small amounts of proteinaceous material, as did controls, and was free of cells. This fluid was primarily unstained, suggesting water influx due to increased permeability. The use of histological approaches provided more specific detail for tissue and cellular effects in hearts of embryos exposed to PAHs and enabled understanding of potential links to later life effects of early life exposure.

PAH SORPTION TO NANOPLASTICS AND THE TROJAN HORSE EFFECT AS DRIVERS OF MITOCHONDRIAL TOXICITY AND PAH LOCALIZATION IN ZEBRAFISH

Plastics are world-wide pollutants that pose a potential threat to wildlife and human health. Small plastic particles, such as microplastics and nanoplastics, are easily ingested, and can act as a Trojan Horse by carrying microorganisms and pollutants. This study investigated the potential role of the Trojan Horse effect in the toxicity of nanoplastics to the vertebrate model organism, zebrafish (Danio rerio). First, we investigated if this effect could affect the toxicity of nanoplastics. Second, we analyzed if it could contribute to the biodistribution of the associated contaminants. And third, we focused on its effect on the mitochondrial toxicity of nanoplastics. We incubated 44 nm polystyrene nanoparticles with a real-world mixture of polycyclic aromatic hydrocarbons (PAHs) for 7 days and removed the free PAHs by ultrafiltration. We dosed embryos with 1 ppm of nanoplastics (NanoPS) or PAH-sorbed nanoplastics (PAH-NanoPS). Neither type of plastic particle caused changes in embryonic and larval development. Fluorescence microscopy and increased EROD activity suggested the uptake of PAHs in larvae exposed to PAH-NanoPS. This coincided with higher concentrations in the yolk sac and the brain. However, PAH-only exposure leads to their accumulation in the yolk sac but not in the brain, suggesting that that the spatial distribution of bioaccumulated PAHs can differ depending on their source of exposure. Both nanoplastic particles affected mitochondrial energy metabolism but caused different adverse effects. While NanoPS decreased NADH production, PAH-NanoPS decreased mitochondrial coupling efficiency and spare respiratory capacity. In summary, the addition of PAHs to the surface of nanoplastics did not translate into increased developmental toxicity. Low levels of PAHs were accumulated in the organisms, and the transfer of PAHs seems to happen in tissues and possibly organelles where nanoplastics accumulate. Disruption of the energy metabolism in the mitochondria may be a key factor in the toxicity of nanoplastics, and the Trojan Horse effect may amplify this effect.

Zebrafish CYP1A expression in transgenic Caenorhabditis elegans protects from exposures to benzo[a]pyrene and a complex polycyclic aromatic hydrocarbon mixture

Polycyclic aromatic hydrocarbons (PAHs) are environmental toxicants primarily produced during incomplete combustion; some are carcinogens. PAHs can be safely metabolized or, paradoxically, bioactivated via specific cytochrome P450 (CYP) enzymes to more reactive metabolites, some of which can damage DNA and proteins. Among the CYP isoforms implicated in PAH metabolism, CYP1A enzymes have been reported to both sensitize and protect from PAH toxicity. To clarify the role of CYP1A in PAH toxicity, we generated transgenic Caenorhabditis elegans that express CYP1A at a basal (but not inducible) level. Because this species does not normally express any CYP1 family enzyme, this approach permitted a test of the role of basally expressed CYP1A in PAH toxicity. We exposed C. elegans at different life stages to either the PAH benzo[a]pyrene (BaP) alone, or a real-world mixture dominated by PAHs extracted from the sediment of a highly contaminated site on the Elizabeth River (VA, USA). This site, the former Atlantic Wood Industries, was declared a Superfund site due to coal tar creosote contamination that caused very high levels (in the [mg/mL] range) of high molecular weight PAHs within the sediments. We demonstrate that CYP1A protects against BaP-induced growth delay, reproductive toxicity, and reduction of steady state ATP levels. Lack of sensitivity of a DNA repair (Nucleotide Excision Repair)-deficient strain suggested that CYP1A did not produce significant levels of DNA-reactive metabolites from BaP. The protective effects of CYP1A in Elizabeth River sediment extract (ERSE)-exposed nematodes were less pronounced than those seen in BaP-exposed nematodes; CYP1A expression protected against ERSE-induced reduction of steady-state ATP levels, but not other outcomes of exposure to sediment extracts. Overall, we find that in C. elegans, a basal level of CYP1A activity is protective against the examined PAH exposures.

Quality screening of the Lagos lagoon sediment by assessing the cytotoxicity and toxicological responses of rat hepatoma H4IIE and fish PLHC-1 cell-lines using different extraction approaches

In this study, sediment samples from Makoko and Ikorodu sites of the Lagos lagoon (Nigeria) were screened for toxicological responses on mammalian and fish cell lines using different extraction methods. Rat hepatoma H4IIE and fish PLHC-1 cell-lines were exposed to serial dilutions of the elutriate, polar and non-polar extracts. We evaluated exposed cells for cytotoxicity and aryl hydrocarbon receptor (AhR)-mediated toxicity. Cells exposed to polar and water extracts from Makoko and Ikorodu showed viability percentage of >80% at 48 h. On the other hand, exposure to the non-polar extracts exhibited cell viability of 50-60% at all tested dilutions. For both cell lines, a significant concentration-dependent induction of cyp1a mRNA was observed after exposure to the different extracts from both sites. Interestingly, the extracts affected functional enzymes differently for both cell lines. For H4IIE cells, while EROD activity paralleled cyp1a mRNA expression patterns, MROD showed significant concentration-specific reduction in cells exposed to polar and water extracts. On the contrary, while the MROD activity paralleled cyp1a mRNA, EROD activity was significantly inhibited in PLHC-1 cells exposed to water-, polar and non-polar extracts from both sites. These observations paralleled sediments PAH contamination burden from the study sites as revealed by co-relation analysis. In conclusion, although the different extracts did not exert high cytotoxic effects (except the non-polar) at the tested concentrations, they significantly modulated phase I biotransformation responses, showing that the studied sediments contain complex chemical mixture in the different extracts, with potential for overt physiological and general health consequences.

Blinded Visual Scoring of Images Using the Freely-available Software Blinder

In nearly all subfields of biomedical sciences, there are phenotypes that are currently classified by expert visual scoring. In research applications, these classifications require the experimenter to be blinded to the treatment group in order to avoid unintentional bias in scoring. Currently, many labs either use laborious and tedious methods to manually blind the images, require multiple experimenters to gather and score the data blindly or fail to properly blind the data altogether. In this protocol, we present a simple, freely available software that we created that allows the experimenter to blindly score images. In our protocol, the user loads unblinded images and defines a scoring system. The software then shows the user the images in a random order, allowing the user to select a score from their defined scoring system for each image. Furthermore, the software has an optional "quality control" mechanism where the user will be shown some images multiple times to test the robustness of the visual scoring. Finally, the software summarizes the results in an exportable file that includes unblinded summary data for each group and a full list of images with their scores. In this protocol, we briefly present directions for using the software, potential applications, and caveats/limitations to this approach.

Later life swimming performance and persistent heart damage following subteratogenic PAH mixture exposure in the Atlantic killifish (Fundulus heteroclitus)

High-level, acute exposures to individual polycyclic aromatic hydrocarbons (PAHs) and complex PAH mixtures result in cardiac abnormalities in developing fish embryos. Whereas acute PAH exposures can be developmentally lethal, little is known about the later life consequences of early life, lower level PAH exposures in survivors. A population of PAH-adapted Fundulus heteroclitus from the PAH-contaminated Superfund site, Atlantic Wood Industries, Elizabeth River, Portsmouth, Virginia, United States, is highly resistant to acute PAH cardiac teratogenicity. We sought to determine and characterize long-term swimming performance and cardiac histological alterations of a subteratogenic PAH mixture exposure in both reference killifish and PAH-adapted Atlantic Wood killifish embryos. Killifish from a relatively uncontaminated reference site, King's Creek, Virginia, United States, and Atlantic Wood killifish were treated with dilutions of Elizabeth River sediment extract at 24 h post fertilization (hpf). Two proven subteratogenic dilutions, 0.1 and 1.0% Elizabeth River sediment extract (total PAH 5.04 and 50.4 µg/L, respectively), were used for embryo exposures. Then, at 5-mo post hatching, killifish were subjected to a swim performance test. A separate subset of these individuals was processed for cardiac histological analysis. Unexposed King's Creek killifish significantly outperformed the unexposed Atlantic Wood killifish in swimming performance as measured by Ucrit (i.e., critical swimming speed). However, King's Creek killifish exposed to Elizabeth River sediment extract (both 0.1 and 1.0%) showed significant declines in Ucrit. Histological analysis revealed the presence of blood in the pericardium of King's Creek killifish. Although Atlantic Wood killifish showed baseline performance deficits relative to King's Creek killifish, their pericardial cavities were nearly free of blood and atrial and ventricular alterations. These findings may explain, in part, the diminished swimming performance of King's Creek fish. Environ Toxicol Chem 2017;36:3246-3253. © 2017 SETAC.