Low-level pyrene exposure causes cardiac toxicity in zebrafish (Danio rerio) embryos

Bioconcentration of polycyclic aromatic hydrocarbons in different tissues of zebrafish (Danio rerio) investigated with PBTK model

Due to the lipophilicity, polycyclic aromatic hydrocarbons (PAHs) are easily accumulated in fish. However, the research on PAH bioaccumulation process in different fish tissues and the relevant effect mechanisms are still deficient. The bioconcentration of PAHs (phenanthrene, anthracene, fluoranthene, and pyrene) in different zebrafish tissues (skin, fish muscle, gill, digestive tract, liver, gonad, and residual) was studied. It was found that there was a difference in the PAH concentrations in different zebrafish tissues. Compared with other tissues, the PAH concentration was highest in the skin and lowest in the fish muscle. For example, the steady-state concentration of phenanthrene in the skin was nearly five times higher than that in the muscle. PAH distribution was related with the lipid contents in different zebrafish tissues; however, the correlation was not significant (p > 0.05), indicating that the lipid content was not the determining factor for the PAH distribution. The distribution was also affected by the bioconcentration kinetics of PAHs in different zebrafish tissues, and the PAH hydrophobic properties. In addition, the physiological based toxicokinetic (PBTK) model showed good performance in predicting PAH internal concentrations, and it may be used to predict the concentrations of PAHs in different fish tissues in future.

The valence state of iron-based nanomaterials determines the ferroptosis potential in a zebrafish model

Many nanomaterials containing different valences of iron have been designed for applications in biomedicine, energy, catalyzers, nanoenzymes, and so on. However, the toxic effects of the valence state of iron in iron-based nanomaterials are still unclear. Here, three different-valence iron-based nanomaterials (nFe@Fe₃O₄, nFe₃O₄ and nFe₂O₃) were synthesized and exposed to zebrafish embryos and mammalian cardiomyocytes. All of them induced ferroptosis along with an increase in valence through iron overload and the Fenton reaction. Specifically, we exposed Tg (cmlc2:EGFP) zebrafish to the three iron-based nanomaterials and found that nFe@Fe₃O₄ treatments led to enlarged ventricles, while nFe₃O₄ and nFe₂O₃ increased atrial size, which was consistent with the results from hematoxylin-eosin staining and in situ hybridization. Moreover, we used ferroptosis inhibitors (ferrostatin-1 or deferoxamine) to treat zebrafish along with nanoparticles exposure and found that the cardiac developmental defects caused by nFe₃O₄ and nFe₂O₃, but not nFe@Fe₃O₄, could be completely rescued by ferroptosis inhibitors. We further found that nFe@Fe₃O₄, rather than nFe₃O₄ and nFe₂O₃, reduced the dissolved oxygen in the medium, which resulted in hypoxia and acceleration of heart tube formation and ventricular enlargement, and both were fully rescued by oxygen donors combined with ferroptosis inhibitors. Consistently, these findings were also observed in mammalian cardiomyocytes. In summary, our study demonstrates that the valence state of iron-based nanomaterials determines the ferroptosis potential. Our study also clarifies that high-valence iron-based nanomaterials induce an enlarged atrium via ferroptosis, while low-valence ones increase the ventricular size through both hypoxia and ferroptosis, which is helpful to understand the potential adverse effects of different valences of iron-based nanomaterials on environmental health and assure the responsible and sustainable development of nanotechnology.

Latent impacts on juvenile rainbow trout (Oncorhynchus mykiss) cardio-respiratory function and swimming performance following embryonic exposures to hydraulic fracturing flowback and produced water

Technologies associated with hydraulic fracturing continue to be prevalent in many regions worldwide. As a result, the production of flowback and produced water (FPW) - a wastewater generated once pressure is released from subterranean wellbores - continues to rise in regions experiencing fracturing activities, while waste management strategies attempt to mitigate compounding burdens of increased FPW production. The heightened production of FPW increases the potential for release to the environment. However, relatively few studies have directly investigated how ecosystems and organisms may be latently affected long after exposures occur. The current study examines rainbow trout exposed in ovo at select critical cardiac developmental time points to differing dilutions and lengths of time (acute versus chronic) to determine how FPW-mediated exposure in ovo may alter later cardiac function and development. After exposure, we allowed fish to grow for ∼ 8 months post-fertilization and measured fish swimming performance, aerobic scope, and cardiac structure of juvenile trout. Acute 48 h embryonic 5% FPW exposure at either 3 days post-fertilization (dpf) or 10 dpf significantly reduced later swimming performance and aerobic scope in juvenile trout. In ovo exposure to 2.5% FPW at 3 dpf yielded significant decreases in these metrics as well, while exposing trout to 2.5% FPW at 10 dpf did not induce as significant effects. Morphometric analyses of heart muscle tissue in all treatments decreased compact myocardium thickness. Chronic 1% FPW in ovo exposure for 28 days induced similar reductions in swimming performance, aerobic scope, and decreased compact myocardium thickness as acute exposures. Overall, our results demonstrate that FPW exposure during egg development ultimately results in persistently impaired heart morphology and resulting physiological (swimming) performance.

Titanium dioxide nanoparticles decreases bioconcentration of azoxystrobin in zebrafish larvae leading to the alleviation of cardiotoxicity

Interactions between titanium dioxide nanoparticles (n-TiO₂) and pollutants in the aquatic environment may alter the bioavailability of pollutants, and thus altering their toxicity and fate. In order to investigate the bioconcentration of azoxystrobin (AZ) and its mechanism of cardiotoxicity in the presence of n-TiO₂, the experiment was divided into control, n-TiO₂ (100 μg/L), AZ (40, 200 and 1000 μg/L) and AZ (40, 200, 1000 μg/L) + n-TiO₂ groups, and the zebrafish embryos were exposed to the exposure solution until 72 h post-fertilization. Results suggested the presence of n-TiO₂ notably reduced the accumulation of AZ in larvae compared with exposure to AZ alone, thereby significantly decreasing AZ-induced cardiotoxicity, including heart rate changes, pericardium edema, venous thrombosis, increased sinus venosus and bulbus arteriosus distance and changes in cardiac-related gene expression. Further studies showed that AZ + n-TiO₂ together restrained total-ATPase and Ca²⁺-ATPase activities, while the activity of Na⁺K⁺-ATPase increased at first and then decreased. Furthermore, there were significant changes in the expressions of oxidative phosphorylation and calcium channel-related genes, suggesting mitochondrial dysfunction may be the potential mechanism of cardiotoxicity induced by AZ and n-TiO₂. This study supplies a new perspective for the joint action of AZ and environmental coexisting pollutants and provides a basis for ecological risk management of pesticides.

Insights into the hepatotoxicity of pyrene and 1-chloropyrene using an integrated approach of metabolomics and transcriptomics

The toxicity of pyrene (Pyr) and its chlorinated species have not be comprehensively and clearly elucidated. In this study, an integrated approach of metabolomics and transcriptomics were applied to evaluate the hepatotoxicity of Pyr and 1-chloropyrene (1-Cl-Pyr) at human exposure level, using human L02 hepatocytes. After 24 h exposure to Pyr and 1-Cl-Pyr at 5-500 nM, cell viability was not significantly changed. Transcriptomics results showed that exposure to Pyr and 1-Cl-Pyr at 5 and 50 nM obviously altered the gene expression profiles, but did not significantly induce the expression of genes strongly related to the activation of aryl hydrocarbon receptor (AhR), such as CYP1A1, CYP1B1, AHR, ARNT. Pyr and 1-Cl-Pyr both induced a notable metabolic perturbation to L02 cells. Glycerophospholipid metabolism was found to be the most significantly perturbed pathway after exposure to Pyr and 1-Cl-Pyr, indicating their potential damage to the cell membrane. The other significantly perturbed pathways were identified to be oxidative phosphorylation (OXPHOS), glycolysis, and fatty acid β oxidation, all of which are related to energy production. Exposure to Pyr at 5 and 50 nM induced the up-regulation of fatty acid β oxidation and OXPHOS. The similar result was observed after exposure to 5 nM 1-Cl-Pyr. In contrast, exposure to 50 nM 1-Cl-Pyr induced the down-regulation of OXPHOS by inhibiting the activity of complex I. The obtained results suggested that the modes of action of Pyr and 1-Cl-Pyr on energy production remarkably varied not only with molecular structure change but also with exposure concentration.

Polycyclic aromatic hydrocarbon and its effects on human health: An overeview

Polycyclic aromatic hydrocarbons (PAHs) are a class of chemicals of considerable environmental significance. PAHs are chemical contaminants of fused carbon and hydrogen aromatic rings, basically white, light-yellow, or solid compounds without color. Natural sources of pollution are marginal or less significant, such as volcanic eruptions, natural forest fires, and moorland fires that trigger lightning bursts. The significant determinants of PAH pollution are anthropogenic pollution sources, classified into four groups, i.e., industrial, mobile, domestic, and agricultural pollution sources. Humans can consume PAHs via different routes, such as inhalation, dermal touch, and ingestion. The Effect of PAHs on human health is primarily based on the duration and route of exposure, the volume or concentration of PAHs to which one is exposed, and the relative toxicity of PAHs. Many PAHs are widely referred to as carcinogens, mutagens, and teratogens and thus pose a significant danger to human health and the well-being of humans. Skin, lung, pancreas, esophagus, bladder, colon, and female breast are numerous organs prone to tumor development due to long-term PAH exposure. PAH exposure may increase the risk of lung cancer as well as cardiovascular disease (CVD), including atherosclerosis, thrombosis, hypertension, and myocardial infarction (MI). Preclinical studies have found a relationship between PAH exposure, oxidative stress, and atherosclerosis. In addition, investigations have discovered a relationship between PAH exposure at work and CVD illness and mortality development. This review aims to explain PAH briefly, its transportation, its effects on human health, and a relationship between environmental exposures to PAHs and CVD risk in humans.

Establishment of cytochrome P450 1a gene-knockout Javanese medaka, Oryzias javanicus, which distinguishes toxicity modes of the polycyclic aromatic hydrocarbons, pyrene and phenanthrene

Cytochrome P450 1a (Cyp1a) is an important enzyme for metabolism of organic pollutants. To understand its reaction to polycyclic aromatic hydrocarbons (PAHs), we knocked out this gene in a marine model fish, Javanese medaka, Oryzias javanicus, using the CRISPR/Cas 9 system. A homozygous mutant (KO) strain with a four-base deletion was established using an environmental DNA (eDNA)-based genotyping technique. Subsequently, KO, heterozygous mutant (HT), and wild-type (WT) fish were exposed to model pollutants, pyrene and phenanthrene, and survivorship and swimming behavior were analyzed. Compared to WT, KO fish were more sensitive to pyrene, suggesting that Cyp1a transforms pyrene into less toxic metabolites. Conversely, WT fish were sensitive to phenanthrene, suggesting that metabolites transformed by Cyp1a are more toxic than the original compound. HT fish showed intermediate results. Thus, comparative use of KO and WT fish can distinguish modes of pollutant toxicity, providing a deeper understanding of fish catabolism of environmental pollutants.

Influences of petroleum hydrocarbon pyrene on the formation, stability and antibacterial activity of natural Au nanoparticles

The effect of pyrene on the formation of naturally Au nanoparticles (AuNPs) in the presence of humic acid (HA) under UV irradiation is described. TEM, EDS, FTIR and XPS were carried out to prove the formation of AuNPs and display their morphologies and formation mechanism. There are little differences between size, morphology and function groups of surface coated materials of AuNPs formed with and without pyrene. With the presence of HA, pyrene showed an inhibiting effect on the reduction of Au ion via competition for O₂^•-, thereby decreasing the production of AuNPs. However, AuNPs formed by HA-pyrene showed higher stability than AuNPs formed by HA with the sedimentation rates of 4.13% and 13.68% respectively after 30-d standing. As for the antibacterial activities against Staphylococcus aureus and Escherichia coli, AuNPs formed by HA-pyrene were more toxic than AuNPs formed by HA. Meanwhile, changes of environmental factors such as temperature, pH and ionic strength exhibited similar influence trend on the formation of AuNPs in the presence and absence of pyrene. The results suggest that the typical petroleum hydrocarbon pyrene contained in spilled oil could influence the formation, fate and ecotoxicity of AuNPs.

Mitigation of arsenic induced developmental cardiotoxicity by ferulic acid in zebrafish

We investigated whether ferulic acid (FA), a nutraceutical could mitigate the arsenic (As) induced cardiotoxicity. Zebrafish larvae (60 and 72 h post-fertilization [hpf]) were used to study the effect of FA on As at different time points (24 and 48 h after exposure). The FA exposure was given as pre-treatment (60 hpf) and simultaneous treatment (72 hpf) to translate the results for As contaminated areas. To accomplish this, the lethality assay was done, and based on the results, the dosage for As (1 mM) and FA (30 μM) was fixed. The FA intervention (30 μM) as 12 h pre-treatment (60 hpf) and simultaneous treatment along with As (72 hpf) decreased the As content in zebrafish larvae as evidenced by inductively coupled plasma-mass spectrometry. As exposure showed congenital deformities especially cardiac malformations in zebrafish larvae after 24 and 48 h. These teratogenic effects induced by As were reduced by FA supplementation in both groups. Also, o-dianisidine staining demonstrated that As treated larvae encountered abnormal cardiac function with reduced blood circulation, while FA supplementation reversed these effects. The acetylcholinesterase activity, a biomarker of As-induced cardiotoxicity was also found to be decreased in As group, which was rescued by FA. The modulation in the expression of the genes involved in cardiogenesis (nkx2.5, bmp2b, gata4, gata5, myh6, myl7, and tnnt2) further confirmed the ameliorative effect of FA on As induced malformations.

Retene, pyrene and phenanthrene cause distinct molecular-level changes in the cardiac tissue of rainbow trout (Oncorhynchus mykiss) larvae, part 2 - Proteomics and metabolomics

Polycyclic aromatic hydrocarbons (PAHs) are global contaminants of concern. Despite several decades of research, their mechanisms of toxicity are not very well understood. Early life stages of fish are particularly sensitive with the developing cardiac tissue being a main target of PAHs toxicity. The mechanisms of cardiotoxicity of the three widespread model polycyclic aromatic hydrocarbons (PAHs) retene, pyrene and phenanthrene were explored in rainbow trout (Oncorhynchus mykiss) early life stages. Newly hatched larvae were exposed to sublethal doses of each individual PAH causing no detectable morphometric alterations. Changes in the cardiac proteome and metabolome were assessed after 7 or 14 days of exposure to each PAH. Phase I and II enzymes regulated by the aryl hydrocarbon receptor were significantly induced by all PAHs, with retene being the most potent compound. Retene significantly altered the level of several proteins involved in key cardiac functions such as muscle contraction, cellular tight junctions or calcium homeostasis. Those findings were quite consistent with previous reports regarding the effects of retene on the cardiac transcriptome. Significant changes in proteins linked to iron and heme metabolism were observed following exposure to pyrene. While phenanthrene also altered the levels of several proteins in the cardiac tissue, no clear mechanisms or pathways could be highlighted. Due to high variability between samples, very few significant changes were detected in the cardiac metabolome overall. Slight but significant changes were still observed for pyrene and phenanthrene, suggesting possible effects on several energetic or signaling pathways. This study shows that early exposure to different PAHs can alter the expression of key proteins involved in the cardiac function, which could potentially affect negatively the fitness of the larvae and later of the juvenile fish.

Zebrafish (Danio rerio) as an excellent vertebrate model for the development, reproductive, cardiovascular, and neural and ocular development toxicity study of hazardous chemicals

In the past decades, the type of chemicals has gradually increased all over the world, and many of these chemicals may have a potentially toxic effect on human health. The zebrafish, as an excellent vertebrate model, is increasingly used for assessing chemical toxicity and safety. This review summarizes the efficacy of zebrafish as a model for the study of developmental toxicity, reproductive toxicity, cardiovascular toxicity, neurodevelopmental toxicity, and ocular developmental toxicity of hazardous chemicals, and the transgenic zebrafish as biosensors are used to detect the environmental pollutants.

A Review of the Functional Roles of the Zebrafish Aryl Hydrocarbon Receptors

Over the last 2 decades, the zebrafish (Danio rerio) has emerged as a stellar model for unraveling molecular signaling events mediated by the aryl hydrocarbon receptor (AHR), an important ligand-activated receptor found in all eumetazoan animals. Zebrafish have 3 AHRs-AHR1a, AHR1b, and AHR2, and studies have demonstrated the diversity of both the endogenous and toxicological functions of the zebrafish AHRs. In this contemporary review, we first highlight the evolution of the zebrafish ahr genes, and the characteristics of the receptors including developmental and adult expression, their endogenous and inducible roles, and the predicted ligands from homology modeling studies. We then review the toxicity of a broad spectrum of AHR ligands across multiple life stages (early stage, and adult), discuss their transcriptomic and epigenetic mechanisms of action, and report on any known interactions between the AHRs and other signaling pathways. Through this article, we summarize the promising research that furthers our understanding of the complex AHR pathway through the extensive use of zebrafish as a model, coupled with a large array of molecular techniques. As much of the research has focused on the functions of AHR2 during development and the mechanism of TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) toxicity, we illustrate the need to address the considerable knowledge gap in our understanding of both the mechanistic roles of AHR1a and AHR1b, and the diverse modes of toxicity of the various AHR ligands.

Retene, pyrene and phenanthrene cause distinct molecular-level changes in the cardiac tissue of rainbow trout (Oncorhynchus mykiss) larvae, part 1 - Transcriptomics

Polycyclic aromatic hydrocarbons (PAHs) are contaminants of concern that impact every sphere of the environment. Despite several decades of research, their mechanisms of toxicity are still poorly understood. This study explores the mechanisms of cardiotoxicity of the three widespread model PAHs retene, pyrene and phenanthrene in the rainbow trout (Oncorhynchus mykiss) early life stages. Newly hatched larvae were exposed to each individual compound at sublethal doses causing no significant increase in the prevalence of deformities. Changes in the cardiac transcriptome were assessed after 1, 3, 7 and 14 days of exposure using custom Salmo salar microarrays. The highest number of differentially expressed genes was observed after 1 or 3 days of exposure, and retene was the most potent compound in that regard. Over-representation analyses suggested that genes related to cardiac ion channels, calcium homeostasis and muscle contraction (actin binding, troponin and myosin complexes) were especially targeted by retene. Pyrene was also able to alter similar myosin-related genes, but at a different timing and in an opposite direction, suggesting compound-specific mechanisms of toxicity. Pyrene and to a lesser extent phenanthrene were altering key genes linked to the respiratory electron transport chain and to oxygen and iron metabolism. Overall, phenanthrene was not very potent in inducing changes in the cardiac transcriptome despite being apparently metabolized at a slower rate than retene and pyrene. The present study shows that exposure to different PAHs during the first few days of the swim-up stage can alter the expression of key genes involved into the cardiac development and function, which could potentially affect negatively the fitness of the larvae in the long term.

Multi-walled carbon nanotubes functionalized with pyrene-PEG via π-π interactions: toxicological assessment in zebrafish embryos

Multi-walled carbon nanotubes (MWCNT) have many promising biological applications, even though functionalization is needed for better biocompatibility. Functionalization of MWCNT with polyethylene glycol (PEG) is a promising and widely studied approach, but the best PEGylation method is still under investigation. In this work, we have tested the biological implications of MWCNT functionalized via π-stacking with pyrene-PEG (MWCNT-Pyr-PEG) in zebrafish embryos. As Pyr toxicity is well documented and represents a major concern for the safety of the proposed approach, we have also tested the effects of the exposure to the isolated conjugate (Pyr-PEG). The resulting suspensions were stable in saline medium and well dispersed. Zebrafish embryos at 24 h post-fertilization (hpf) were dechorionated and randomly assigned to seven experimental groups (n = 50 per group): control, MWCNT-Pyr-PEG at 0.2, 2.0, and 20.0 mg l^-1, and Pyr-PEG at the same concentrations, and exposures were performed in 96-well plates. Specimens were observed for heart rate, malformations, body length, mortality, traveled distance, and number of new movements. Heart rate was reduced in embryos exposed to any tested concentration of MWCNT-Pyr-PEG, while this effect was observed with Pyr-PEG from 2 mg l^-1. The highest concentration of MWCNT-Pyr-PEG also led to increased occurrence of malformations, shortened body length and reduced traveled distance. The functionalization approach shows promise due to the stability in saline media, even though toxic effects were observed in the highest tested concentrations, being the MWCNT the main actors underlying these outcomes.

Acute fluorene-9-bisphenol exposure damages early development and induces cardiotoxicity in zebrafish (Danio rerio)

Fluorene-9-bisphenol (BHPF) is a substitute for bisphenol A (BPA), which is widely used to manufacture plastic products. Previous studies indicate that BHPF has an anti-estrogenic effect and induces cytotoxicity in mice oocytes. However, the effects of acute BHPF exposure on the aquatic organism obtain little attention. In this study, a series of BHPF concentrations (1 μM, 2 μM, 5 μM, 10 μM, 20 μM) was used to exposed zebrafish embryos from 2 h post-fertilization (hpf). The results showed the LC₅₀ at 96hpf was 2.88 μM (1.01 mg/L). Acute exposure induced malformation in morphology, and retarded epiboly rate at 10hpf, increased apoptosis. Moreover, acute BHPF exposure led cardiotoxicity, by impeding cardiac looping, decreasing cardiac contractility (reducing the stroke volume and cardiac output, decreasing fractional shortening of ventricle). Besides that, BHPF exposure altered the expression of cardiac transcriptional regulators and development related genes. In conclusion, acute BHPF exposure induced developmental abnormality, retarded cardiac morphogenesis and injured the cardiac contractility. This study indicated BHPF would be an unneglected threat for the safety of aquatic organisms.

Teratogenic effects of environmentally relevant concentrations of phenanthrene on the early development of marine medaka (Oryzia melastigma)

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants in marine environments and have arouse great concern since they pose adverse effects to marine ecosystem. To determine the potential impacts of environmentally relevant PAHs on early life stages of marine fish, this study exposed embryos of marine medaka (Oryzias melastigma) to 0, 2, 10, 50, and 250 μg/L of phenanthrene (Phe), one of the most abundant PAHs. The results demonstrated that Phe exposure decreased hatching rates, delayed hatching time of embryos, and increased deformity rate of newly-hatched larvae. Exposure to 10 and 50 μg/L Phe decreased the survival rate of marine medaka larvae at 28 days post-fertilization (dpf), and no embryo successfully hatched in 250 μg/L Phe exposure group. Morphology results showed that 10, 50, and 250 μg/L Phe exposure significantly retarded the development of embryos, and 2, 10, and 50 μg/L caused yolk sac edema and pericardial edema in newly-hatched larvae, indicating that low concentrations of Phe could induce developmental cardiac toxicity. Furthermore, the changes in the expression of heart development-related genes were determined, and the results showed that Phe-induced cardiac malformation might be related with fgf8, bmp4, smyd1, ATPase and gata4 genes. Overall, environmentally relevant PAHs could disrupt heart morphogenesis and hatching process of marine medaka, which might have profound consequences for sustainability of fish population.

Cardiac toxicity of acrolein exposure in embryonic zebrafish (Danio rerio)

Acrolein is a widely distributed pollutant produced from various sources such as industrial waste, organic combustion, and power plant emissions. It is also intentionally released into irrigation canals to control invasive aquatic plants. Zebrafish (Danio rerio) has a good reputation for being an attractive model organism for developmental and toxicological research. In this study, zebrafish embryos were exposed to acrolein to investigate the cardiotoxic effects. The 96-h LC₅₀ (median lethal concentration) value of acrolein was determined as 654.385 μg/L. Then, the embryos were treated with the sublethal experimental concentrations of acrolein (1, 4, 16, 64, and 256 μg/L) for 96 h. Embryos were examined at 48, 72, and 96 h post-fertilization (hpf). Acrolein affected the cardiac morphology and function of the embryos. Sinus venosus-bulbus arteriosus (SV-BA) distance of 64 μg/L and 256 μg/L acrolein groups was elongated compared with the control samples. Immunostaining with MF20 antibody clearly exhibited that the atrium positioned posterior to the ventricle which indicated cardiac looping inhibition. Histological preparations also showed the mispositioning and the lumens of the chambers narrowed. Acrolein-induced increased heart rate was noted in the 4, 16, 64, and 256 μg/L treatment groups. Taken together, these results indicated that acrolein disrupted the heart development and cardiac function in zebrafish, suggesting that its water-borne risks should be considered seriously.

Using Zebrafish to Analyze the Genetic and Environmental Etiologies of Congenital Heart Defects

Congenital heart defects (CHDs) are among the most common human birth defects. However, the etiology of a large proportion of CHDs remains undefined. Studies identifying the molecular and cellular mechanisms that underlie cardiac development have been critical to elucidating the origin of CHDs. Building upon this knowledge to understand the pathogenesis of CHDs requires examining how genetic or environmental stress changes normal cardiac development. Due to strong molecular conservation to humans and unique technical advantages, studies using zebrafish have elucidated both fundamental principles of cardiac development and have been used to create cardiac disease models. In this chapter we examine the unique toolset available to zebrafish researchers and how those tools are used to interrogate the genetic and environmental contributions to CHDs.

The effects of Deepwater Horizon crude oil on ammonia and urea handling in mahi-mahi (Coryphaena hippurus) early life stages

Many ecologically important fishes, including mahi-mahi (Coryphaena hippurus), and their offspring were directly exposed to crude oil following the Deepwater Horizon (DWH) oil spill. Early life stage fish are especially vulnerable to the toxicity of crude oil-derived polycyclic aromatic hydrocarbons (PAHs). In teleosts, yolk sac proteins are the main energy source during development and are usually catabolized into ammonia or urea among other byproducts. Although excretion of these waste products is sensitive to oil exposure, we know little about the underlying mechanisms of this process. In this study, we examined the effects of crude oil on ammonia and urea handling in the early life stages of mahi. Mahi embryos exposed to 30-32 μg L^-1 ∑PAH exhibited increased urea excretion rates and greater accumulation of urea in the tissues before hatch suggesting that ammonia, which is highly toxic, was converted into less-toxic urea. Oil-exposed embryos (6.3-32 μg L^-1 ∑PAH) displayed significantly increased tissue ammonia levels at 42 hpf and upregulated mRNA levels of ammonia transporters (Rhag, Rhbg and Rhcg1) from 30 to 54 hpf. However, despite increased accumulation and higher expression of ammonia transporters, the larvae exposed to higher ∑PAH (30 μg L^-1 ∑PAH) showed reduced ammonia excretion rates after hatch. Together, the increased production of nitrogenous waste reinforces previous work that increased energy demand in oil-exposed embryos is fueled, at least in part, by protein metabolism and that urea synthesis plays a role in ammonia detoxification in oil-exposed mahi embryos. To our knowledge, this study is the first to combine physiological and molecular approaches to assess the impact of crude-oil on both nitrogenous waste excretion and accumulation in the early life stages of any teleosts.

Developmental effects in fish embryos exposed to oil dispersions - The impact of crude oil micro-droplets

During accidental crude oil spills and permitted discharges of produced water into the marine environment, a large fraction of naturally occurring oil components will be contained in micron-sized oil droplets. Toxicity is assumed to be associated with the dissolved fraction of oil components, however the potential contribution of oil droplets to toxicity is currently not well known. In the present work we wanted to evaluate the contribution of oil droplets to effects on normal development of Atlantic cod (Gadus morhua) through exposing embryos for 96 h to un-filtered (dispersions containing droplets) and filtered (water soluble fractions) dispersions in a flow-through system at dispersion concentrations ranging from 0.14 to 4.34 mg oil/L. After exposure, the embryos were kept in clean seawater until hatch when survival, development and morphology were assessed. The experiment was performed at two different stages of embryonic development to cover two potentially sensitive stages (gastrulation and organogenesis). Exposure of cod embryos to crude oil dispersions caused acute and delayed toxicity, including manifestation of morphological deformations in hatched larvae. Oil droplets appear to contribute to some of the observed effects including mortality, larvae condition (standard length, body surface, and yolk sac size), spinal deformations as well as alterations in craniofacial and jaw development. The timing of exposure may be essential for the development of effects as higher acute mortality was observed when embryos were exposed from the start of gastrulation (Experiment 1) than when exposed during organogenesis (Experiment 2). Even though low mortality was observed when exposed during organogenesis, concentration-dependent mortality was observed during recovery.

Potential role of polycyclic aromatic hydrocarbons as mediators of cardiovascular effects from combustion particles

Air pollution is the most important environmental risk factor for disease and premature death, and exposure to combustion particles from vehicles is a major contributor. Human epidemiological studies combined with experimental studies strongly suggest that exposure to combustion particles may enhance the risk of cardiovascular disease (CVD), including atherosclerosis, hypertension, thrombosis and myocardial infarction.In this review we hypothesize that adhered organic chemicals like polycyclic aromatic hydrocarbons (PAHs), contribute to development or exacerbation of CVD from combustion particles exposure. We summarize present knowledge from existing human epidemiological and clinical studies as well as experimental studies in animals and relevant in vitro studies. The available evidence suggests that organic compounds attached to these particles are significant triggers of CVD. Furthermore, their effects seem to be mediated at least in part by the aryl hydrocarbon receptor (AhR). The mechanisms include AhR-induced changes in gene expression as well as formation of reactive oxygen species (ROS) and/or reactive electrophilic metabolites. This is in accordance with a role of PAHs, as they seem to be the major chemical group on combustion particles, which bind AhR and/or is metabolically activated by CYP-enzymes. In some experimental models however, it seems as PAHs may induce an inflammatory atherosclerotic plaque phenotype irrespective of DNA- and/or AhR-ligand binding properties. Thus, various components and several signalling mechanisms/pathways are likely involved in CVD induced by combustion particles.We still need to expand our knowledge about the role of PAHs in CVD and in particular the relative importance of the different PAH species. This warrants further studies as enhanced knowledge on this issue may amend risk assessment of CVD caused by combustion particles and selection of efficient measures to reduce the health effects of particular matters (PM).

Toxic effects of a methanolic coal dust extract on fish early life stage

Coal dust is a contaminant that impacts the terrestrial and aquatic environment with a complex mixture of chemicals, including PAHs and metals. This study aims to evaluate the toxic effect of a methanolic coal dust extract on a fish early life stage by analyzing phenotypic alterations, transcriptome changes, and mortality in zebrafish (ZF) embryos. ZF embryos were exposed to methanolic coal dust extract at 1-5000 mg·L-1 and monitored using bright field microscopy 24 and 48 hpf to determine malformations and mortality. In situ hybridization, RNA sequencing, and qRT-PCR were employed to identify transcriptome changes in malformed embryos. Three malformed phenotypes were generated in a dose-dependent manner. In situ hybridization analysis revealed brain, somite, dorsal cord, and heart tube development biomarker alterations. Gene expression profile analysis identified changes in genes related to structural constituent of muscle, calcium ion binding, actin binding, melanin metabolic process, muscle contraction, sarcomere organization, cardiac myofibril assembly, oxidation-reduction process, pore complex, supramolecular fiber, striated muscle thin filament, Z disc, and intermediate filament. This study shows, for the first time, the malformations generated by a mixture of pollutants from a methanolic coal dust extract on a fish early life stage, constituting a potential risk for normal embryonic development of other aquatic vertebrate organisms. Furthermore, we establish that phenotypes and changes in gene expression induced by the extract constitute a target for future studies about mechanical toxicity and their utility as sensitive tools in environmental risk assessments for biota and humans exposed to coal mining activities.

Determination and toxicity evaluation of the generated byproducts from sulfamethazine degradation during catalytic oxidation process

Sulfamethazine (SMZ), a kind of sulfonamide antibiotics, can exist for a long periods of time and has been widely detected in the environment, which could pose a potential health threat to human beings. In this study, sludge-derived carbon (SC) catalyst was modified and applied to degrade SMZ during catalytic oxidation process. Degradation products and possible transformation pathways were investigated based on data of GC-MS. The toxicity evolution of SMZ degradation after catalytic oxidation process was tested with zebrafish and microbial degradation respirometer. As a consequence, SC modified with nitric acid (SCHNO₃) exhibited highly catalytic efficiency reached 92.2% SMZ conversion and 75.2% total organic carbon (TOC) removal rate after 480 min. Ten kinds of possible products were identified by GC-MS during degradation process of SMZ, indicating two possible pathways. No pronounced malformation was observed in the toxicity experiments with zebrafish until 120 h post fertilization (hpf). However, further analysis showed that zebrafish incubated with SMZ solution had higher mortality, lower hatching rate, slower spontaneous movement and shorter body length, compared with the group used normal nutrient solution, while the water after treatment had lower toxicity effects on zebrafish. The toxicity experiments with microbial degradation respirometer showed that SMZ solution had lower value of oxygen uptake, which indicated that SMZ solution had higher values of toxicity and inhibition of pharmaceutical compounds. This study provides a catalyst with low cost and high catalytic efficiency for degradation process of SMZ and gives a deeper insight into the ecotoxicity of treated water.

Assessment of environmentally contaminated sediment using a contact assay with early life stage zebrafish (Danio rerio)

Lake Saint-Louis, a shallow fluvial lake near the western tip of the island of Montreal, QC, Canada is an important spawning ground for many species of fish. Sediments in certain areas of the lake are known to be contaminated with high levels of metals and legacy organic chemicals. To improve our understanding of risk to native fish populations, we conducted a study evaluating levels of sediment contamination and potential effects on early life stage fish. Concentrations of PAHs, PCBs, PCDDs and PCDFs were several orders of magnitude higher at two industrial sites (B1 and B2) than at a nearby reference site (IP). Concentrations of 32 metals and metalloids were at least 5-fold higher at B1 and B2 than at IP. Moreover, all available interim sediment quality guidelines (ISQGs) were exceeded at the two contaminated sites, while none were exceeded at the reference site. Biological effects were evaluated using a sediment contact assay. Zebrafish (Danio rerio) embryos were exposed to clean water (control), or to sediment from IP, B1, and B2 until 120 h post fertilization (hpf). Mortality was significantly elevated in fish exposed to the B1, but not the B2 sediment. The frequency of deformities increased with increasing contamination, but this trend was not statistically significant (p > 0.05). Genes that are implicated in the response to PAHs, PCBs, dioxins and furans (cyp1a, cyp1b1, ahr2) were significantly elevated in the 120 hpf larvae exposed to the B1 and B2 sediments. Global DNA methylation, and mRNA expression of genes related to oxidative stress (maft, cat, hmox1, sod2), embryonic development (bmp2b, baf60c), metal exposure (mt2), and DNA repair (gadd45b) were unaffected. Our results suggest that the Beauharnois sector of Lake Saint-Louis is poor quality spawning habitat due to high levels of contamination, and the potential for harmful effects on early life stage fish.

Assessment of raw and ozonated oil sands process-affected water exposure in developing zebrafish: Associating morphological changes with gene expression

With the ever-increasing amounts of oil sands process-affected water (OSPW) accumulating from Canada's oil sands operations, its eventual release must be considered. As OSPW has been found to be both acutely and chronically toxic to aquatic organisms, remediation processes must be developed to lower its toxicity. Ozone treatment is currently being studied as a tool to facilitate the removal of organic constituents associated with toxicity. Biomarkers (e.g. gene expression) are commonly used when studying the effects of environmental contaminants, however, they are not always indicative of adverse effects at the whole organism level. In this study, we assessed the effects of OSPW exposure on developing zebrafish by linking gene expression to relevant cellular and whole organism level endpoints. We also investigated whether or not ozone treatment decreased biomarkers and any associated toxicity observed from OSPW exposure. The concentrations of classical naphthenic acids in the raw and ozonated OSPW used in this study were 16.9 mg/L and 0.6 mg/L, respectively. Ozone treatment reduced the total amount of naphthenic acids (NAs) in the OSPW sample by 92%. We found that exposure to both raw and ozonated OSPW had no effect on the survival of zebrafish embryos. The expression levels of biotransformation genes CYP1A and CYP1B were induced by raw OSPW exposure, with CYP1B being more highly expressed than CYP1A. In contrast, ozonated OSPW exposure did not increase the expression of CYP1A and only slightly induced CYP1B. A decrease in cardiac development and function genes (NKX2.5 and APT2a2a) was not associates with large changes in heart rate, arrhythmia or heart size. We did not find any indications of craniofacial abnormalities or of increased occurrence of apoptotic cells. Overall, our study found that OSPW was not overtly toxic to zebrafish embryos.

Polycyclic Aromatic Hydrocarbons (PAHs) in inland aquatic ecosystems: Perils and remedies through biosensors and bioremediation

Polycyclic Aromatic Hydrocarbons (PAHs) are among the most ubiquitous environmental pollutants of high global concern. PAHs belong to a diverse family of hydrocarbons with over one hundred compounds known, each containing at least two aromatic rings in their structure. Due to hydrophobic nature, PAHs tend to accumulate in the aquatic sediments, leading to bioaccumulation and elevated concentrations over time. In addition to their well-manifested mutagenic and carcinogenic effects in humans, they pose severe detrimental effects to aquatic life. The high eco-toxicity of PAHs has attracted a number of reviews, each dealing specifically with individual aspects of this global pollutant. However, efficient management of PAHs warrants a holistic approach that combines a thorough understanding of their physico-chemical properties, modes of environmental distribution and bioaccumulation, efficient detection, and bioremediation strategies. Currently, there is a lack of a comprehensive study that amalgamates all these aspects together. The current review, for the first time, overcomes this constraint, through providing a high level comprehensive understanding of the complexities faced during PAH management, while also recommending future directions through potentially viable solutions. Importantly, effective management of PAHs strongly relies upon reliable detection tools, which are currently non-existent, or at the very best inefficient, and therefore have a strong prospect of future development. Notably, the currently available biosensor technologies for PAH monitoring have not so far been compiled together, and therefore a significant focus of this article is on biosensor technologies that are critical for timely detection and efficient management of PAHs. This review is focussed on inland aquatic ecosystems with an emphasis on fish biodiversity, as fish remains a major source of food and livelihood for a large proportion of the global population. This thought provoking study is likely to instigate new collaborative approaches for protecting aquatic biodiversity from PAHs-induced eco-toxicity.

Evidence of selective activation of aryl hydrocarbon receptor nongenomic calcium signaling by pyrene

In its classical genomic mode of action, the aryl hydrocarbon receptor (AhR) acts as a ligand activated transcription factor regulating expression of target genes such as CYP1A1 and CYP1B1. Some ligands may also trigger more rapid nongenomic responses through AhR, including calcium signaling (Ca²⁺). In the present study we observed that pyrene induced a relatively rapid increase in intracellular Ca²⁺-concentrations ([Ca²⁺]_i) in human microvascular endothelial cells (HMEC-1) and human embryonic kidney cells (HEK293) that was attenuated by AhR-inhibitor treatment and/or transient AhR knockdown by RNAi. In silico molecular docking based on homology models, suggested that pyrene is not able to bind to the human AhR in the agonist conformation. Instead, pyrene docked in the antagonist conformation of the AhR PAS-B binding pocket, although the interaction differed from antagonists such as GNF-351 and CH223191. Accordingly, pyrene did not induce CYP1A1 or CYP1B1, but suppressed CYP1-expression by benzo[a]pyrene (B[a]P) in HMEC-1 cells, confirming that pyrene act as an antagonist of AhR-induced gene expression. Use of pharmacological inhibitors and Ca²⁺-free medium indicated that the pyrene-induced AhR nongenomic [Ca²⁺]_i increase was initiated by Ca²⁺-release from intracellular stores followed by a later phase of extracellular Ca²⁺-influx, consistent with store operated calcium entry (SOCE). These effects was accompanied by an AhR-dependent reduction in ordered membrane lipid domains, as determined by di-4-ANEPPDHQ staining. Addition of cholesterol inhibited both the pyrene-induced [Ca²⁺]_i-increase and alterations in membrane lipid order. In conclusion, we propose that pyrene binds to AhR, act as an antagonist of the canonical genomic AhR/Arnt/CYP1-pathway, reduces ordered membrane lipid domains, and activates AhR nongenomic Ca²⁺-signaling from intracellular stores.

Fenbuconazole exposure impacts the development of zebrafish embryos

Fenbuconazole (FBZ), a triazole-containing fungicide, is widely used in agriculture and horticulture. In the present study, the development and cardiac functioning were observed and determined in zebrafish embryos exposed to FBZ at 5, 50 and 500 ng/L nominal concentrations for 72 h. The results showed that 500 ng/L FBZ significantly increased pericardial edema rate, spine curvature rate, disturbed cardiac function, and led a shortened lower jaw. The transcription of genes such as tbx5, nkx2.5, tnnt2, gata4, bmp2b, myl7 was altered, which might be responsible for the cardiac developmental and functioning defects in the larvae. The deformation in bone development might be related with the impaired transcription levels of shh and bmp2b. The transcription of cyp26a1 (encoding retinoic acid metabolism enzyme) was significantly up-regulated in the 500 ng/L group, which might be a reason causing the teratogenic effect of FBZ. These results suggest that FBZ could have toxic effects on embryonic development, which should be considered in the risk evaluation of FBZ application.

Microplastic does not magnify the acute effect of PAH pyrene on predatory performance of a tropical fish (Lates calcarifer)

Microplastic (MP) leads to widespread pollution in the marine ecosystem. In addition to the physical hazard posed by ingestion of microplastic particles, concern is also on their potential as vector for transport of hydrophobic contaminants. We experimentally studied the single and interactive effects of microplastic and pyrene, a polycyclic aromatic hydrocarbon, on the swimming behaviour and predatory performance of juvenile barramundi (Lates calcarifer). Juveniles (18+ days post hatch) were exposed to MPs, or pyrene (100 nM), or combination of both, and feeding rate and foraging activity (swimming) were analysed. Exposure to MPs alone did not significantly influence feeding performance of the juveniles, while a dose-effect series of pyrene showed strong effect on fish behaviour when concentrations were above 100 nM. In the test of combined MP and pyrene exposure, we observed no effect on feeding while swimming speed decreased significantly. Thus, our results confirm that short-time exposure to pyrene impacts the performance of fish juveniles, while additional exposure to microplastic at the given conditions influenced their activity only and not their feeding rate. Further studies of the combined effects of microplastics and pollutants on tropical fish behaviour are encouraged.

The developmental effects of low-level procymidone towards zebrafish embryos and involved mechanism

Procymidone (PCM), a dicarboximide fungicide, is widely used in agriculture to control plant diseases. In the present study, zebrafish embryos were exposed to PCM at 0, 10, 100 and 1000 ng/L for 72 h, the development and cardiac functioning of larvae were observed and determined. The results showed that hatching rate was significantly decreased in the 1000 ng/L treatment, and pericardial edema rate and spine curvature rate were significantly increased in the 100 and 1000 ng/L groups. The PCM-treated larvae exhibited an increased heart rate as well as arrhythmia, and shortened low jaw. The transcription levels of cardiac development-related genes tbx5, nkx2.5, tnnt2, gata4, myh6, myl7, cdh2, ryr2 were altered, which might be responsible for the cardiac developmental and functioning defects in the larvae. The deformation in bone development might be related with the impaired transcription levels of ihh, shh, bmp2b, bmp4, gh, igf1, sox9, gli2. The activities of Na⁺/K⁺-ATPase and Ca²⁺-ATPase were significantly inhibited by 100 ng/L and 1000 ng/L PCM exposure, which might be a cause for the occurrence of pericardial edema and skeletal deformation. The results of this study will be helpful in evaluating the potential threat of PCM to fish population in the aquatic environment.

Cardio-respirometry disruption in zebrafish (Danio rerio) embryos exposed to hydraulic fracturing flowback and produced water

Hydraulic fracturing to extract oil and natural gas reserves is an increasing practice in many international energy sectors. Hydraulic fracturing flowback and produced water (FPW) is a hyper saline wastewater returned to the surface from a fractured well containing chemical species present in the initial fracturing fluid, geogenic contaminants, and potentially newly synthesized chemicals formed in the fracturing well environment. However, information on FPW toxicological mechanisms of action remain largely unknown. Both cardiotoxic and respirometric responses were explored in zebrafish (Danio rerio) embryos after either an acute sediment-free (FPW-SF) or raw/sediment containing (FPW-S) fraction exposure of 24 and 48 h at 2.5% and 5% dilutions. A 48 h exposure to either FPW fraction in 24-72 h post fertilization zebrafish embryos significantly increased occurrences of pericardial edema, yolk-sac edema, and tail/spine curvature. In contrast, larval heart rates significantly decreased after FPW fraction exposures. FPW-S, but not FPW-SF, at 2.5% doses significantly reduced embryonic respiration/metabolic rates (MO₂), while for 5% FPW, both fractions reduced MO₂. Expression of select cardiac genes were also significantly altered in each FPW exposure group, implicating a cardiovascular system compromise as the potential cause for reduced embryonic MO₂. Collectively, these results support our hypothesis that organics are major contributors to cardiac and respiratory responses to FPW exposure in zebrafish embryos. Our study is the first to investigate cardiac and respiratory sub-lethal effects of FPW exposure, demonstrating that FPW effects extend beyond initial osmotic stressors and verifies the use of respirometry as a potential marker for FPW exposure.

Assessing the toxicity of triphenyltin to different life stages of the marine medaka Oryzias melastigma through a series of life-cycle based experiments

Toxic effects of triphenyltin (TPT) to different life stages of the marine medaka Oryzias melastigma were investigated through a series of life-cycle based exposure experiments. In embryo stage, TPT exposure could elevate the heartbeat rate at Day 6-8 post-fertilization and increase the expression levels of five heart development related genes (i.e., ATPase, COX2, BMP4, GATA4 and NKX2.5). In larval stage, TPT shortened the body length at ≥10μg/L and suppressed the swimming activity of the fish larvae at Day 1 post-hatching at 50μg/L. In reproductive stage, TPT exposure resulted in a male-biased sex ratio (2μg/L) and reduced the gonadosomatic index (GSI) in females (≥ 0.1μg/L), which might in turn lead to a decline in their population fitness. The reproductive stage of O. melastigma was more sensitive to TPT than other stages, while the GSI of female medaka was the most sensitive endpoint.

In vivo cardiovascular toxicity induced by acetochlor in zebrafish larvae

The risk of acetochlor to human health is still unclear, prompting concern over its risk, especially to pesticide suicides population, occupational population (farmers, retailers and pharmaceutical workers), and special population (young children and infants, pregnant women, older people, and those with compromised immune systems). This study was to explore the toxic effect and the possible mechanism of toxic action of acetochlor using zebrafish larvae whose toxicity profiles have been confirmed to be strikingly similar with mammalian. The result indicated that the toxic target organ of acetochlor was cardiovascular system. Thus, cardiovascular toxicity evaluation was investigated systematically. The main phenotypes of cardiovascular toxicity induced by acetochlor were bradycardia, pericardial edema, circulation defect, and thrombosis; Malformed heart was confirmed by histopathological examination. Thrombosis which maybe triggered by bradycardia was further studied using o-dianisidine for erythrocyte staining; Substantial thrombus in the caudal vein and significantly reduced heart red blood cells (RBCs) intensity which can reflect the thrombosis degree were observed in zebrafish in a concentration-dependent manner. Additionally, the mRNA expression level of Nkx2.5 and Gata4 related to induction of cardiac program were down-regulated significantly by quantitative real-time polymerase chain reaction (qRT-PCR), which could cause defects in the cardiovascular system. For the first time, our results demonstrated that acetochlor induced cardiovascular toxicity, and down-regulation of Nkx2.5 and Gata4 might be its possible molecular basis. Our data generated here might provide novel insights into cardiovascular disease risk following acetochlor exposure to human, especially to pesticide suicides population, occupational population and special population.

Developmental toxicity in flounder embryos exposed to crude oils derived from different geographical regions

Crude oils from distinct geographical regions have distinct chemical compositions, and, as a result, their toxicity may be different. However, developmental toxicity of crude oils derived from different geographical regions has not been extensively characterized. In this study, flounder embryos were separately exposed to effluents contaminated by three crude oils including: Basrah Light (BLO), Pyrenees (PCO), and Sakhalin Vityaz (SVO), in addition to a processed fuel oil (MFO-380), to measure developmental toxicity and for gene expressions. Each oil possessed a distinct chemical composition. Edema defect was highest in embryos exposed to PCO and MFO-380 that both have a greater fraction of three-ring PAHs (33% and 22%, respectively) compared to BLO and SVO. Observed caudal fin defects were higher in embryos exposed to SVO and MFO-380, which are both dominated by naphthalenes (81% and 52%, respectively). CYP1A gene expressions were also highest in embryos exposed to SVO and MFO-380. Higher incidence of cardiotoxicity and lower nkx 2.5 expression were detected in embryos exposed to PCO. Unique gene expression profiles were observed in embryos exposed to crude oils with distinct compositions. This study demonstrates that crude oils of different geographical origins with different compositional characteristics induce developmental toxicity to different degrees.

A Novel Danshensu Derivative Prevents Cardiac Dysfunction and Improves the Chemotherapeutic Efficacy of Doxorubicin in Breast Cancer Cells

Doxorubicin (Dox) is an anthracycline antibiotic widely used in clinics as an anticancer agent. However, the use of Dox is limited by its cardiotoxicity. We have previously shown that a Danshensu (DSS) derivative, ADTM, displayed strong cardioprotective effects. With improved chemical stability and activity, a novel DSS derivative, D006, based on the structure of ADTM, was synthesized. In the present study, the protective effects of D006, indexed by attenuation of the cardiotoxicity induced by Dox as well as chemosensitizing effects that increase the antitumor activity of Dox, were investigated. Our results showed that D006 was more potent than either parental compound, or their use in combination, in ameliorating Dox-induced toxicity in H9c2 cells. In our zebrafish model, D006, but not DSS, alone significantly preserved the ventricular function of zebrafish after Dox treatment. Moreover, D006 upregulated mitochondrial biogenesis and increased mtDNA copy number after Dox treatment of H9c2 cells. D006 promoted the expression of HO-1 protein in a time-dependent manner while the HO-1 inhibitor, Znpp, reversed the protective effects of D006. In human breast tumor MCF-7 cells, D006 enhanced Dox-induced cytotoxicity by increasing apoptosis. In conclusion, our results indicate that a new DSS derivative exhibits promising protective effects against Dox-induced cardiotoxicity both in vivo and in vitro, an effect at least partially mediated by induction of HO-1 expression and the activation of mitochondrial biogenesis. Meanwhile, D006 also potentiated the anti-cancer effects of Dox in breast tumor cells.

Effects of Deepwater Horizon crude oil exposure, temperature and developmental stage on oxygen consumption of embryonic and larval mahi-mahi (Coryphaena hippurus)

The timing and location of the 2010 Deepwater Horizon (DWH) incident within the Gulf of Mexico resulted in crude oil exposure of many commercially and ecologically important fish species, such as mahi-mahi (Coryphaena hippurus), during the sensitive early life stages. Previous research has shown that oil exposure during the embryonic stage of predatory pelagic fish reduces cardiac function - a particularly important trait for fast-swimming predators with high aerobic demands. However, it is unclear whether reductions in cardiac function translate to impacts on oxygen consumption in these developing embryos and larvae. A 24-channel optical-fluorescence oxygen-sensing system for high-throughput respiration measurements was used to investigate the effects of oil exposure, temperature and developmental stage on oxygen consumption rates in embryonic and larval mahi-mahi. Oil-exposed developing mahi-mahi displayed increased oxygen consumption, despite clear cardiac deformities and bradycardia, confirming oxygen uptake and delivery from a source other than the circulatory system. In addition to metabolic rate measurements, nitrogenous waste excretion was measured to test the hypothesis that increased energy demand was fueled by protein catabolism. This is the first study to our knowledge that demonstrates increased energy demand and energy depletion in oil-exposed developing mahi-mahi.

Lagos lagoon sediment organic extracts and polycyclic aromatic hydrocarbons induce embryotoxic, teratogenic and genotoxic effects in Danio rerio (zebrafish) embryos

An expansion of anthropogenic activity around Lagos lagoon, Nigeria, has raised concerns over increasing contaminants entering the lagoon's ecosystem. The embryotoxicity, teratogenicity and genotoxicity of sediment organic extracts from four sampling zones around Lagos lagoon, Ilaje, Iddo, Atlas Cove and Apapa, as well as the dominant polycyclic aromatic hydrocarbons (PAHs) identified in water measured during the wet season (naphthalene, phenanthrene, pyrene, benzo[a]pyrene and a mixture of these), were assessed with Danio rerio embryos. Embryos were exposed to varying concentrations of toxicants from 0-72 h post-fertilization (hpf). Embryotoxicity at 72 hpf showed a dose-dependent increase in mortality upon exposure to extracts from all zones, except Atlas Cove. Similarly, higher levels of teratogenic effects, such as increased oedema, and haemorrhage and developmental abnormalities resulted from exposure to extracts from Ilaje, Iddo and Apapa zones. Treatment with single PAHs revealed that significant levels of detrimental effects were obtained only for phenanthrene. The modified comet assay revealed that the oxidative damage to DNA was generally low (<12 %) overall for all sediment extracts, but was significantly elevated with Ilaje and Iddo sediment extracts when compared with solvent controls. Oxidative damage was observed with the single PAHs, phenanthrene and benzo[a]pyrene, as well as with the PAH mixture. This study highlights that Lagos lagoon sediment extracts have teratogenic, embryotoxic and genotoxic properties, which are likely due to the high molecular weight PAHs present in the extracts, some of which are known or are suspected human carcinogens.

Application of molecular endpoints in early life stage salmonid environmental biomonitoring

Molecular endpoints can enhance existing whole animal bioassays by more fully characterizing the biological impacts of aquatic pollutants. Laboratory and field studies were used to examine the utility of adopting molecular endpoints for a well-developed in situ early life stage (eyed embryo to onset of swim-up fry) salmonid bioassay to improve diagnostic assessments of water quality in the field. Coastal cutthroat trout (Oncorhynchus clarki clarki) were exposed in the laboratory to the model metal (zinc, 40μg/L) and the polycyclic aromatic hydrocarbon (pyrene, 100μg/L) in water to examine the resulting early life stage salmonid responses. In situ field exposures and bioassays were conducted in parallel to evaluate the water quality of three urban streams in British Columbia (two sites with anthropogenic inputs and one reference site). The endpoints measured in swim-up fry included survival, deformities, growth (weight and length), vitellogenin (vtg) and metallothionein (Mt) protein levels, and hepatic gene expression (e.g., metallothioneins [mta and mtb], endocrine biomarkers [vtg and estrogen receptors, esr] and xenobiotic-metabolizing enzymes [cytochrome P450 1A3, cyp1a3 and glutathione transferases, gstk]). No effects were observed in the zinc treatment, however exposure of swim-up fry to pyrene resulted in decreased survival, deformities and increased estrogen receptor alpha (er1) mRNA levels. In the field exposures, xenobiotic-metabolizing enzymes (cyp1a3, gstk) and zinc transporter (zntBigM103) mRNA were significantly increased in swim-up fry deployed at the sites with more anthropogenic inputs compared to the reference site. Cluster analysis revealed that gene expression profiles in individuals from the streams receiving anthropogenic inputs were more similar to each other than to the reference site. Collectively, the results obtained in this study suggest that molecular endpoints may be useful, and potentially more sensitive, indicators of site-specific contamination in real-world, complex exposure scenarios in addition to whole body morphometric and physiological measures.

Severe Coal Tar Sealcoat Runoff Toxicity to Fish Is Prevented by Bioretention Filtration

Coal tar sealcoats applied to asphalt surfaces in North America, east of the Continental Divide, are enriched in petroleum-derived compounds, including polycyclic aromatic hydrocarbons (PAHs). The release of PAHs and other chemicals from sealcoat has the potential to contaminate nearby water bodies, reducing the resiliency of aquatic communities. Despite this, relatively little is known about the aquatic toxicology of sealcoat-derived contaminants. We assessed the impacts of stormwater runoff from sealcoated asphalt on juvenile coho salmon (Oncorhynchus kisutch) and embryo-larval zebrafish (Danio rerio). We furthermore evaluated the effectiveness of bioretention as a green stormwater method to remove PAHs and reduce lethal and sublethal toxicity in both species. We applied a coal tar sealcoat to conventional asphalt and collected runoff from simulated rainfall events up to 7 months postapplication. Whereas sealcoat runoff was more acutely lethal to salmon, a spectrum of cardiovascular abnormalities was consistently evident in early life stage zebrafish. Soil bioretention effectively reduced PAH concentrations by an order of magnitude, prevented mortality in juvenile salmon, and significantly reduced cardiotoxicity in zebrafish. Our findings show that inexpensive bioretention methods can markedly improve stormwater quality and protect fish health.

Confirmation of Stormwater Bioretention Treatment Effectiveness Using Molecular Indicators of Cardiovascular Toxicity in Developing Fish

Urban stormwater runoff is a globally significant threat to the ecological integrity of aquatic habitats. Green stormwater infrastructure methods such as bioretention are increasingly used to improve water quality by filtering chemical contaminants that may be harmful to fish and other species. Ubiquitous examples of toxics in runoff from highways and other impervious surfaces include polycyclic aromatic hydrocarbons (PAHs). Certain PAHs are known to cause functional and structural defects in developing fish hearts. Therefore, abnormal heart development in fish can be a sensitive measure of clean water technology effectiveness. Here we use the zebrafish experimental model to assess the effects of untreated runoff on the expression of genes that are classically responsive to contaminant exposures, as well as heart-related genes that may underpin the familiar cardiotoxicity phenotype. Further, we assess the effectiveness of soil bioretention for treating runoff, as measured by prevention of both visible cardiac toxicity and corresponding gene regulation. We find that contaminants in the dissolved phase of runoff (e.g., PAHs) are cardiotoxic and that soil bioretention protects against these harmful effects. Molecular markers were more sensitive than visible toxicity indicators, and several cardiac-related genes show promise as novel tools for evaluating the effectiveness of evolving stormwater mitigation strategies.

The effects of weathering and chemical dispersion on Deepwater Horizon crude oil toxicity to mahi-mahi (Coryphaena hippurus) early life stages

To better understand the impact of the Deepwater Horizon (DWH) incident on commercially and ecologically important pelagic fish species, a mahi-mahi spawning program was developed to assess the effect of embryonic exposure to DWH crude oil with particular emphasis on the effects of weathering and dispersant on the magnitude of toxicity. Acute lethality (96 h LC50) ranged from 45.8 (28.4-63.1) μg l(-1) ΣPAH for wellhead (source) oil to 8.8 (7.4-10.3) μg l(-1) ΣPAH for samples collected from the surface slick, reinforcing previous work that weathered oil is more toxic on a ΣPAH basis. Differences in toxicity appear related to the amount of dissolved 3 ringed PAHs. The dispersant Corexit 9500 did not influence acute lethality of oil preparations. Embryonic oil exposure resulted in cardiotoxicity after 48 h, as evident from pericardial edema and reduced atrial contractility. Whereas pericardial edema appeared to correlate well with acute lethality at 96 h, atrial contractility did not. However, sub-lethal cardiotoxicity may impact long-term performance and survival. Dispersant did not affect the occurrence of pericardial edema; however, there was an apparent reduction in atrial contractility at 48 h of exposure. Pericardial edema at 48 h and lethality at 96 h were equally sensitive endpoints in mahi-mahi.

Silver nanoparticles affect the neural development of zebrafish embryos

Silver nanoparticles (AgNPs) have been widely used in commercial products. This study aims to understand the impact of AgNPs on the early developmental stages in zebrafish (Danio rerio) embryos. Embryos were exposed to two sizes of AgNPs at three dose levels, as well to free Ag(+) ions, for a range of 4-96 h post-fertilization (hpf). The acute exposure study showed that exposure to AgNPs affected the neurological development, and the exposed embryos exhibited anomalies such as small head with hypoplastic hindbrain, small eye and cardiac defects. At the molecular level, AgNPs altered the expression profiles of neural development-related genes (gfap, huC and ngn1), metal-sensitive metallothioneins and ABCC genes in exposed embryos. The expression of AhR2 and Cyp1A, which are usually considered to mediate polycyclic aromatic hydrocarbon toxicity, were also significantly changed. A size-dependent uptake of AgNPs was observed, whereby 4 nm AgNPs were more efficiently taken up compared with the 10 nm-sized particles. Importantly, the head area accumulated AgNPs more efficiently than the trunk area of exposed zebrafish embryos. No free Ag(+) ions, which can be potentially released from the AgNP solutions, were detected. This study suggests that AgNPs could affect the neural development of zebrafish embryos, and the toxicity of AgNPs may be partially attributed to the comparatively higher uptake in the head area. These results indicate the potential neurotoxicity of AgNPs and could be extended to other aquatic organisms.

Reproductive and transgenerational toxicities of phenanthrene on female marine medaka (Oryzias melastigma)

Phenanthrene (PHE) is one of the most abundant polycyclic aromatic hydrocarbons in the aquatic environment and often results from oil spills. To assess the effects of PHE on fish, marine medaka (Oryzias melastigma) was exposed to PHE at 0.06, 0.6, 6 and 60 μg/L. The reproductive functions and transgenerational effects were investigated. After 80 days exposure, the percentage of previtellogenic and vitellogenic oocytes in the ovary showed a significant decrease in the 0.06 and 60 μg/L groups. The mRNA levels of salmon-type gonadotropin releasing hormone, the follicle-stimulating hormone FSHβ, and the luteinizing hormone LHβ in the brain; the cytochrome P450 aromatase gene CYP19A and the estrogen receptor α (ERα) in the ovary; and ERα and vitellogenin VTG1 and 2 in the liver all exhibited significant down-regulation in the 0.06 and 60 μg/L groups, but did not significantly change in the 6 μg/L group compared to the control, which was quite consistent with development of the oocytes. A significant elevation of PHE accumulation in the brain in the 0.06 and 60 μg/L groups gave a reasonable explanation for the nonmonotonic dose-response and also elucidated the action pathway via the brain-pituitary-gonadal axis. The reduction of the time to hatch and the increased cardiac rhythm of embryos were in accord with the PHE accumulative levels in the eggs. The results demonstrated that exposure to PHE at both low and high concentrations can inhibit ovary development. In addition, PHE can be maternally transferred to embryos and influence the health and sustainability of the next generation.

Aryl organophosphate flame retardants induced cardiotoxicity during zebrafish embryogenesis: by disturbing expression of the transcriptional regulators

As a result of the ban on some brominated flame retardants (BFRs), the use of organophosphate flame retardants (OPFRs) increases, and they are detected in multi-environment media at higher frequency and concentrations. However, the toxicity data of OPFRs, especially those on developmental toxicology are quite limited, which prevents an accurate evaluation of their environmental and health risk. Because a previous study reported that two aryl-OPFRs induced cardiotoxicity during zebrafish embryogenesis, we designed experiments to compare the heart developmental toxicity of a series of aryl-OPFRs with alkyl-OPFRs and explored possible internal mechanism. First, acute toxicity of 9 frequently used OPFRs were studied with zebrafish embryos (2-96 hpf). By comparing the LC50 and EC50 (pericardium edema) data, two aryl-OPFRs, triphenyl phosphate (TPhP) and cresyl diphenyl phosphate (CDP) showed greater heart developmental toxicity than the others. It was also found that the acute toxicity of OPFRs varied mainly depending on their hydrophobicity. Further study on the cardiotoxicity of TPhP and CDP showed that the cardiac looping progress can be impeded by 0.10mg/L TPhP or CDP exposure. Bradycardia and reduction of myocardium were also observed in 0.50 and 1.0mg/L TPhP groups and 0.10, 0.50, and 1.0mg/L CDP groups. 0-48 hpf is the vulnerable window of zebrafish cardiogenesis that can be easily affected by TPhP and CDP. RT-qPCR measurement on the expressions of key transcriptional regulators in cardiogenesis showed that BMP4, NKX2-5, and TBX5 were significantly inhibited at the exposure points of 12 hpf and 24 hpf which may be the internal factors related to the heart developmental toxicity. As zebrafish is a good model organism for human health study, the present results call for a greater attention to the health risk of fetus in pregnant women exposed to such OPFRs.

Zebrafish and clean water technology: assessing soil bioretention as a protective treatment for toxic urban runoff

Urban stormwater contains a complex mixture of contaminants that can be acutely toxic to aquatic biota. Green stormwater infrastructure (GSI) is a set of evolving technologies intended to reduce impacts on natural systems by slowing and filtering runoff. The extent to which GSI methods work as intended is usually assessed in terms of water quantity (hydrology) and quality (chemistry). Biological indicators of GSI effectiveness have received less attention, despite an overarching goal of protecting the health of aquatic species. Here we use the zebrafish (Danio rerio) experimental model to evaluate bioinfiltration as a relatively inexpensive technology for treating runoff from an urban highway with dense motor vehicle traffic. Zebrafish embryos exposed to untreated runoff (48-96h; six storm events) displayed an array of developmental abnormalities, including delayed hatching, reduced growth, pericardial edema, microphthalmia (small eyes), and reduced swim bladder inflation. Three of the six storms were acutely lethal, and sublethal toxicity was evident across all storms, even when stormwater was diluted by as much as 95% in clean water. As anticipated from exposure to cardiotoxic polycyclic aromatic hydrocarbons (PAHs), untreated runoff also caused heart failure, as indicated by circulatory stasis, pericardial edema, and looping defects. Bioretention treatment dramatically improved stormwater quality and reversed nearly all forms of developmental toxicity. The zebrafish model therefore provides a versatile experimental platform for rapidly assessing GSI effectiveness.

Evaluating toxicity of heavy fuel oil fractions using complementary modeling and biomimetic extraction methods

The toxicity of chemically dispersed heavy fuel oil (HFO) and 3 distillate fractions to rainbow trout (Oncorhynchus mykiss) embryos was evaluated using the PETROTOX model and a biomimetic extraction technique that involved passive sampling of oil-contaminated test media with solid-phase microextraction (SPME) fibers. Test solutions for toxicity testing were generated using a combination of dispersant and high-energy mixing. The resulting water accommodated fractions (WAF) provided complex exposure regimens that included both dissolved hydrocarbons and oil droplets. The toxicity of the various fractions differed by approximately 3 orders of magnitude when expressed on the basis of WAF dilution. Using detailed compositional data, the PETROTOX model predicted the speciation of hydrocarbons between dissolved and oil droplet phases and explained observed toxicity based on computed dissolved phase toxic units (TUs). A key finding from model calculations was that dissolved hydrocarbon exposures and associated TUs were a nonlinear function of WAF dilution, because dissolved hydrocarbons were largely controlled by the dissolution of oil droplets that were transferred in WAF dilutions. Hence, oil droplets served to "buffer" dissolved concentrations in WAF dilutions at loadings greater than 1 mg/L, resulting in higher dissolved concentrations and TUs than expected based on dilution. The TUs computed at each WAF dilution explained the observed toxicity among the HFO and fractions to within a factor of 3. Dissolved material measured by SPME showed a consistent relationship with model-predicted TUs, confirming the utility of this approach for providing an integrated measure of exposure to bioavailable hydrocarbons. These 2 approaches provide complementary tools for better defining bioavailability of complex petroleum substance.

Developmental toxicity of diclofenac and elucidation of gene regulation in zebrafish (Danio rerio)

Environmental pollution by emerging contaminants, e.g. pharmaceuticals, has become a matter of widespread concern in recent years. We investigated the membrane transport of diclofenac and its toxic effects on gene expression and the development of zebrafish embryos. The association of diclofenac with the embryos conformed to the general partition model at low concentration, the partition coefficient being 0.0033 ml per embryo. At high concentration, the interaction fitted the Freundlich model. Most of the diclofenac remained in the extracellular aqueous solution with less than 5% interacting with the embryo, about half of which was adsorbed on the membranes while the rest entered the cytoplasm. Concentrations of diclofenac over 10.13 μM were lethal to all the embryos, while 3.78 μM diclofenac was teratogenic. The development abnormalities at 4 day post treatment (dpt) include shorter body length, smaller eye, pericardial and body edema, lack of liver, intestine and circulation, muscle degeneration, and abnormal pigmentation. The portion of the diclofenac transferred into the embryo altered the expression of certain genes, e.g. down-regulation of Wnt3a and Gata4 and up-regulation of Wnt8a. The alteration of expression of such genes or the regulation of downstream genes could cause defects in the cardiovascular and nervous systems.

Multigenerational effects of benzo[a]pyrene exposure on survival and developmental deformities in zebrafish larvae

In the aquatic environment, adverse outcomes from dietary polycyclic aromatic hydrocarbon (PAH) exposure are poorly understood, and multigenerational developmental effects following exposure to PAHs are in need of exploration. Benzo[a]pyrene (BaP), a model PAH, is a recognized carcinogen and endocrine disruptor. Here adult zebrafish (F0) were fed 0, 10, 114, or 1,012 μg BaP/g diet at a feed rate of 1% body weight twice/day for 21 days. Eggs were collected and embryos (F1) were raised to assess mortality and time to hatch at 24, 32, 48, 56, 72, 80, and 96 h post fertilization (hpf) before scoring developmental deformities at 96 hpf. F1 generation fish were raised to produce the F2 generation followed by the F3 and F4 generations. Mortality significantly increased in the higher dose groups of BaP (2.3 and 20 μg BaP/g fish) in the F1 generation while there were no differences in the F2, F3, or F4 generations. In addition, premature hatching was observed among the surviving fish in the higher dose of the F1 generation, but no differences were found in the F2 and F3 generations. While only the adult F0 generation was BaP-treated, this exposure resulted in multigenerational phenotypic impacts on at least two generations (F1 and F2). Body morphology deformities (shape of body, tail, and pectoral fins) were the most severe abnormality observed, and these were most extreme in the F1 generation but still present in the F2 but not F3 generations. Craniofacial structures (length of brain regions, size of optic and otic vesicles, and jaw deformities), although not significantly affected in the F1 generation, emerged as significant deformities in the F2 generation. Future work will attempt to molecularly anchor the persistent multigenerational phenotypic deformities noted in this study caused by BaP exposure.