Comparative developmental toxicity of eight typical organic pollutants to red sea bream (Pagrosomus major) embryos and larvae

Comparative effects of different metals on the Japanese medaka embryos and larvae

Rapid evaluation of the toxicity of metals using fish embryo acute toxicity is facilitative to ecological risk assessment of aquatic organisms. However, this approach has seldom been utilized for the comparative study on the effects of different metals to fish. In this study, acute and sub-chronic tests were used to compare the toxicity of Se(IV) and Cd in the embryos and larvae of Japanese medaka (Oryzias latipes). The embryos with different levels of dechorionation and/or pre-exposure were also exposed to Se(IV) and Cd at various concentrations. The results showed that the LC50-144 h of Cd was 1.3-5.2 folds higher than that of Se(IV) for the embryos. In contrast, LC50-96 h of Se(IV) were 200-400 folds higher than that of Cd for the larvae. Meanwhile, dechorionated embryos were more sensitive to both Se and Cd than the intact embryos. At elevated concentrations, both Se and Cd caused mortality and deformity in the embryos and larvae. In addition, pre-exposure to Cd at the embryonic stages enhanced the resistance to Cd in the larvae. However, pre-exposure to Se(IV) at the embryonic stages did not affect the toxicity of Se(IV) to the larvae. This study has distinguished the nuance differences in effects between Se(IV) and Cd after acute and sub-chronic exposures with/without chorion. The approach might have a potential in the comparative toxicology of metals (or other pollutants) and in the assessment of their risks to aquatic ecosystems.

Chronic exposure to environmental concentrations of benzo[a]pyrene causes multifaceted toxic effects of developmental compromise, redox imbalance, and modulated transcriptional profiles in the early life stages of marine medaka (Oryzias melastigma)

Polycyclic aromatic hydrocarbons (PAHs) accumulate and integrate into aquatic environments, raising concerns about the well-being and safety of aquatic ecosystems. Benzo[a]pyrene (BaP), a persistent PAH commonly detected in the environment, has been extensively studied. However, the broader multifaceted toxicity potential of BaP on the early life stages of marine fish during chronic exposure to environmentally relevant concentrations needs further exploration. To fill these knowledge gaps, this study assessed the in vivo biotoxicity of BaP (1, 4, and 8 μg/L) in marine medaka (Oryzias melastigma) during early development over a 30-day exposure period. The investigation included morphological, biochemical, and molecular-level analyses to capture the broader potential of BaP toxicity. Morphological analyses showed that exposure to BaP resulted in skeletal curvatures, heart anomalies, growth retardation, elevated mortality, delayed and reduced hatching rates. Biochemical analyses revealed that BaP exposure not only created oxidative stress but also disrupted the activities of antioxidant enzymes. This disturbance in redox balance was further explored by molecular level investigation. The transcriptional profiles revealed impaired oxidative phosphorylation (OXPHOS) and tricarboxylic acid (TCA) cycle pathways, which potentially inhibited the oxidative respiratory chain in fish following exposure to BaP, and reduced the production of adenosine triphosphate (ATP) and succinate dehydrogenase (SDH). Furthermore, this investigation indicated a potential connection to apoptosis, as demonstrated by fluorescence microscopy and histological analyses, and supported by an increase in the expression levels of related genes via real-time quantitative PCR. This study enhances our understanding of the molecular-level impacts of BaP's multifaceted toxicity in the early life stages of marine medaka, and the associated risks.

Shoaling, boldness, anxiety-like behavior and locomotion in zebrafish (Danio rerio) are altered by acute benzo[a]pyrene exposure

Environmental exposure to crude oil and/or its derivatives in fishes can negatively impact survival, morphology and physiology, but relatively little focus has been on behavior. Exposures can influence prey-predator interactions, courtship and other vital behaviors, leading to individual or population disruption at toxicant levels well below those producing morphological or physiological changes. The few behavioral studies of polycyclic aromatic hydrocarbons (PAHs) on fish behavior have yielded highly inconsistent results, likely relating to chronic vs. acute treatment. A few studies report lethargy and decreased exploratory behavior, while others indicate increased anxiety and greater exploratory behavior with PAH exposure. In our study on zebrafish (Danio rerio), we hypothesized that even relatively brief (30 min) exposure to the PAH benzo[a]pyrene (B[a]P) would impact group shoaling and individual behaviors in open field and novel object exploration tests. Exposures comprised measured concentrations of 1.0 μM, 10 μM, or 100 μM, B[a]P. Compared to controls, inter-individual distance (IID) was significantly increased by 100 μM B[a]P, but not by 1.0 μM or 10 μM B[a]P. Total distance moved by shoals was decreased significantly at B[a]P concentrations of 1.0 μM, 10 μM and 100 μM. In the open field test of individual locomotion and anxiety-like behavior, time spent in the thigmotaxis zone along the walls of the circular test arena (a proxy for anxiety-like behavior), was decreased at 100 μM. In the novel object approach test to investigate boldness, time spent near the object was significantly increased by both 10 μM and 100 μM B[a]P. Collectively, these data indicate a complex suite of changes in zebrafish including altered shoal dynamics, decreased anxiety, increased boldness, and decreased locomotion associated with exposure to B[a]P.

Ancient Sturgeons Possess Effective DNA Repair Mechanisms: Influence of Model Genotoxicants on Embryo Development of Sterlet, Acipenser ruthenus

DNA damage caused by exogenous or endogenous factors is a common challenge for developing fish embryos. DNA damage repair (DDR) pathways help organisms minimize adverse effects of DNA alterations. In terms of DNA repair mechanisms, sturgeons represent a particularly interesting model due to their exceptional genome plasticity. Sterlet (Acipenser ruthenus) is a relatively small species of sturgeon. The goal of this study was to assess the sensitivity of sterlet embryos to model genotoxicants (camptothecin, etoposide, and benzo[a]pyrene), and to assess DDR responses. We assessed the effects of genotoxicants on embryo survival, hatching rate, DNA fragmentation, gene expression, and phosphorylation of H2AX and ATM kinase. Exposure of sterlet embryos to 1 µM benzo[a]pyrene induced low levels of DNA damage accompanied by ATM phosphorylation and xpc gene expression. Conversely, 20 µM etoposide exposure induced DNA damage without activation of known DDR pathways. Effects of 10 nM camptothecin on embryo development were stage-specific, with early stages, before gastrulation, being most sensitive. Overall, this study provides foundational information for future investigation of sterlet DDR pathways.

Polycyclic aromatic compounds (PACs) in the Canadian environment: The challenges of ecological risk assessments

Ecological risk assessments (ERAs) of polycyclic aromatic compounds (PACs), as single congeners or in mixtures, present technical challenges that raise concerns about their accuracy and validity for Canadian environments. Of more than 100,000 possible PAC structures, the toxicity of fewer than 1% have been tested as individual compounds, limiting the assessment of complex mixtures. Because of the diversity in modes of PAC action, the additivity of mixtures cannot be assumed, and mixture compositions change rapidly with weathering. In vertebrates, PACs are rapidly oxygenated by cytochrome P450 enzymes, often to metabolites that are more toxic than the parent compound. The ability to predict the ecological fate, distribution and effects of PACs is limited by toxicity data derived from tests of a few responses with a limited array of test species, under optimal laboratory conditions. Although several models are available to predict PAC toxicity and rank species sensitivity, they were developed with data biased by test methods, and the reported toxicities of many PACs exceed their solubility limits. As a result, Canadian Environmental Quality Guidelines for a few individual PACs provide little support for ERAs of complex mixtures in emissions and at contaminated sites. These issues are illustrated by reviews of three case studies of PAC-contaminated sites relevant to Canadian ecosystems. Interactions among ecosystem characteristics, the behaviour, fate and distribution of PACs, and non-chemical stresses on PAC-exposed species prevented clear associations between cause and effect. The uncertainties of ERAs can only be reduced by estimating the toxicity of a wider array of PACs to species typical of Canada's diverse geography and environmental conditions. Improvements are needed to models that predict toxicity, and more field studies of contaminated sites in Canada are needed to understand the ecological effects of PAC mixtures.

On being the right shape: Roles for motile cilia and cerebrospinal fluid flow in body and spine morphology

How developing and growing organisms attain their proper shape is a central problem of developmental biology. In this review, we investigate this question with respect to how the body axis and spine form in their characteristic linear head-to-tail fashion in vertebrates. Recent work in the zebrafish has implicated motile cilia and cerebrospinal fluid flow in axial morphogenesis and spinal straightness. We begin by introducing motile cilia, the fluid flows they generate and their roles in zebrafish development and growth. We then describe how cilia control body and spine shape through sensory cells in the spinal canal, a thread-like extracellular structure called the Reissner fiber, and expression of neuropeptide signals. Last, we discuss zebrafish mutants in which spinal straightness breaks down and three-dimensional curves form. These curves resemble the common but little-understood human disease Idiopathic Scoliosis. Zebrafish research is therefore poised to make progress in our understanding of this condition and, more generally, how body and spine shape is acquired and maintained through development and growth.

Benzo[a]pyrene constrains embryo development via oxidative stress induction and modulates the transcriptional responses of molecular biomarkers in the marine medaka Oryzias javanicus

Embryos from the marine medaka fish Oryzias javanicus were treated with eight concentrations of benzo[a]pyrene (BaP) (0.001, 0.01, 0.1, 1, 2, 5, 10, or 20 μg L^--1) after they had been fertilized. Significant mortality and hatching delays were detected in embryos that had been exposed to 10 and 20 μg L^-1 BaP for 4 weeks. The mortality rate after hatching was higher in the medaka that had been previously exposed to > 2 μg L^-1 BaP. Significant elevations in intracellular reactive oxygen species and malondialdehyde contents were measured and the mRNA expressions of the antioxidant defense system genes (gst, sod, cat, and gpx) increased in the embryos exposed to 10 and 20 μg L^-1 BaP for 1 week. The hsp70, ahr, and cyp1a transcriptional responses were also significantly upregulated in the exposed groups after 1 week. The alterations to the in vivo parameters and molecular components suggested that waterborne BaP had a toxic effect on marine medaka embryos. Finally, fin defects, spinal curvature, and cardiac edema were highly induced when the embryos were exposed to > 5 μg L^-1 BaP.

Histological, biochemical and transcriptomic analyses reveal liver damage in zebrafish (Danio rerio) exposed to phenanthrene

Phenanthrene (PHE) is a common polycyclic aromatic hydrocarbon (PAH) in aquatic environments, and this contaminant can cause adverse effects on teleostean performance. In this study, we exposed the model freshwater fish (zebrafish; Danio rerio) to 300 μg/L PHE for 15 days. Histological analysis demonstrated that liver morphology deteriorated in PHE-exposed zebrafish, and cellular damage in the liver increased. Biological analysis revealed that exposure to PHE elicited significant changes in glutathione S-transferases (GST) and superoxide dismutase (SOD) activities. 476 differentially expressed genes (DEGs) were identified in liver between control and PHE treated groups through the transcriptomic analysis. Gene Ontology enrichment analysis (GO) suggested that PHE exposure induced changes in the expression of genes associated with "lipid transporter activity", "catalytic activity", "metal ion binding", "lipid transport" and "transmembrane transport". Furthermore, the "vitamin digestion and absorption" and "fat digestion and absorption" pathways enriched in Kyoto Encyclopedia of Genes and Genomes analysis (KEGG). Additionally, five candidate biomarkers associated with the PHE response in zebrafish were identified. In conclusion, our results elucidate the physiological and molecular responses to PHE exposure in the liver of zebrafish, and provide a framework for further studies of the mechanisms underlying the toxic effects of polycyclic aromatic hydrocarbons (PAHs) on aquatic organisms.

In vitro and in silico AHR assays for assessing the risk of heavy oil-derived polycyclic aromatic hydrocarbons in fish

In the aftermath of the Great East Japan Earthquake of March 11, 2011, marine fish in Kesennuma Bay, Japan, have been contaminated with heavy oil containing polycyclic aromatic hydrocarbons (PAHs). To estimate the risk of six PAHs (benzo[α]pyrene, dibenzothiophene, phenanthrene, 2,3,5-trimethylnaphthalene, acenaphthene, and 1-methylphenanthrene), which have been detected at high levels in the tissues of fish from Kesennuma Bay, we attempted to evaluate the effects of these PAHs on the fish aryl hydrocarbon receptor (AHR) signaling pathway. We initially measured PAH concentrations and cytochrome P4501A catalytic activities (EROD: ethoxyresorufin-O-deethylase and MROD: methoxyresorufin-O-demethylase) as markers of AHR activation in greenlings (Hexagrammos otakii) collected from Kesennuma Bay in 2014. The results showed that alkylated PAH concentrations and EROD/MROD activities were higher in sites close to the oil-spilled sites than in the control site, suggesting AHR activation by spilled alkylated PAHs. We then investigated AHR-mediated responses to these PAHs in the in vitro reporter gene assay system where red seabream (Pagrus major) AHR1 (rsAHR1) or rsAHR2 expression plasmids were transiently transfected into COS-7 cells. The in vitro assay showed rsAHR isoform-, PAH-, and dose-dependent transactivation potencies. The relative effective concentrations of benzo[α]pyrene, dibenzothiophene, phenanthrene, 2,3,5-trimethylnaphthalene, acenaphthene, and 1-methylphenanthrene that induce 20% of the maximum benzo[α]pyrene response (REC_20-BaP) for rsAHR1 activation were 0.052, 38, 79, 88, 270 nM, and no response, respectively, and those for rsAHR2 activation were 0.0049, 32, 53, 88, 60 nM, and no response, respectively. The results showed that the REC_20-BaP values of benzo[α]pyrene for both the rsAHR1 and rsAHR2 isoforms were lower than the concentrations (0.041-0.20 nM) detected in the muscle tissue of fish from Kesennuma Bay, while the REC_20-BaP values of other PAHs were higher than their tissue concentrations. In silico rsAHR homology modeling and subsequent ligand docking simulation analyses indicated that the rsAHR activation potencies of PAHs could be predicted from a rsAHR2 model. This study shows that in vitro and in silico rsAHR analyses may be a useful tool for assessing the risks to fish contaminated with PAHs.

Protective effects of genistein on cytochrome P-450 and vitellogenin expression in liver of zebrafish after PCB-126 exposure

The objective of the research is to study the action of Vitellogenin and P-4501A1 following coexposure at different times to genistein and PCB-126 using zebrafish as a model system. Polychlorinated biphenyls are ubiquitous substances in environment. The genistein is a phytoestrogen extracted from soybeans and it's contained in food for humans and animals. For this study, 200 adult zebrafish were used. Our findings show a marked immunoreactivity of Vtg at 12h in liver than the control with only PCB-126. Regarding effects of PCB-126 on Vtg after pretreatment with genistein in fishes, the immunohistochemistry results show a minor increase at 12h. After 24h the immunoreactivity is lower than 12h and then slightly increased at 72h with only PCB-126 and PCB-126 and genistein together. CYP1A1 progressively increases from 12h to 72h in all groups with minor immunoreactivity when we treated fish with genistein and PCB-126. We show a reduction in the estrogenic effect when the fishes were treated with genistein and PCB-126 together at 12h than the group treated with only PCB-126. Moreover, low concentrations of genistein decrease the marked P450 expression induced by PCB-126. This shows that genistein decreases the expression of P450 target genes mediated by AhR.