Cyp1a reporter zebrafish reveals target tissues for dioxin

Putting advanced materials to the test: Ti3C2 MXenes alleviate the hazardous effects of the environmental pollutant benzo[a]pyrene

Advanced materials are materials that have been engineered to exhibit novel or enhanced properties that confer superior performance when compared to conventional materials. Here, we evaluated the impact of Ti3C2 MXenes, a two-dimensional (2D) material, on the adverse effects caused by polycyclic aromatic hydrocarbons. To this end, we studied benzo[a]pyrene denoted here as B[a]P as a model compound. B[a]P was found to adsorb to MXenes as evidenced by UV-Vis spectroscopy. MXenes in the presence or absence of natural organic matter (NOM) were well tolerated by zebrafish embryos. The uptake (ingestion) of MXenes by zebrafish was determined by quantifying the Ti content using inductively coupled plasma mass spectrometry (ICP-MS) while Raman confocal mapping was applied for the label-free identification of MXenes in situ in exposed zebrafish. The body burden of B[a]P was determined by gas chromatography-mass spectrometry (GC-MS). The potential impact of MXenes on B[a]P triggered aryl hydrocarbon receptor (AhR) induction was assessed by evaluating the induction of downstream genes including cyp1a, and results were validated by using the transgenic zebrafish reporter tg(cyp1a-eGFP). The potential impact of MXenes on the genotoxicity caused by B[a]P was also assessed. MXenes were shown to ameliorate AhR induction and DNA damage caused by B[a]P. This was corroborated by using the human colon-derived cell line HT-29. Taken together, MXenes were found to be non-hazardous and alleviated the adverse effects caused by B[a]P in vitro and in vivo.

TnP and AHR-CYP1A1 Signaling Crosstalk in an Injury-Induced Zebrafish Inflammation Model

Aryl Hydrocarbon Receptor (AHR) signaling is crucial for regulating the biotransformation of xenobiotics and physiological processes like inflammation and immunity. Meanwhile, Thalassophryne nattereri Peptide (TnP), a promising anti-inflammatory candidate from toadfish venom, demonstrates therapeutic effects through immunomodulation. However, its influence on AHR signaling remains unexplored. This study aimed to elucidate TnP's molecular mechanisms on the AHR-cytochrome P450, family 1 (CYP1) pathway upon injury-induced inflammation in wild-type (WT) and Ahr2-knockdown (KD) zebrafish larvae through transcriptomic analysis and Cyp1a reporters. TnP, while unable to directly activate AHR, potentiated AHR activation by the high-affinity ligand 6-Formylindolo [3,2-b]carbazole (FICZ), implying a role as a CYP1A inhibitor, confirmed by in vitro studies. This interplay suggests TnP's ability to modulate the AHR-CYP1 complex, prompting investigations into its influence on biotransformation pathways and injury-induced inflammation. Here, the inflammation model alone resulted in a significant response on the transcriptome, with most differentially expressed genes (DEGs) being upregulated across the groups. Ahr2-KD resulted in an overall greater number of DEGs, as did treatment with the higher dose of TnP in both WT and KD embryos. Genes related to oxidative stress and inflammatory response were the most apparent under inflamed conditions for both WT and KD groups, e.g., Tnfrsf1a, Irf1b, and Mmp9. TnP, specifically, induces the expression of Hspa5, Hsp90aa1.2, Cxcr3.3, and Mpeg1.2. Overall, this study suggests an interplay between TnP and the AHR-CYP1 pathway, stressing the inflammatory modulation through AHR-dependent mechanisms. Altogether, these results may offer new avenues in novel therapeutic strategies, such as based on natural bioactive molecules, harnessing AHR modulation for targeted and sustained drug effects in inflammatory conditions.

Burn pit-related smoke causes developmental and behavioral toxicity in zebrafish: Influence of material type and emissions chemistry

Combustion of mixed materials during open air burning of refuse or structural fires in the wildland urban interface produces emissions that worsen air quality, contaminate rivers and streams, and cause poor health outcomes including developmental effects. The zebrafish, a freshwater fish, is a useful model for quickly screening the toxicological and developmental effects of agents in such species and elicits biological responses that are often analogous and predictive of responses in mammals. The purpose of this study was to compare the developmental toxicity of smoke derived from the burning of 5 different burn pit-related material types (plywood, cardboard, plastic, a mixture of the three, and the mixture plus diesel fuel as an accelerant) in zebrafish larvae. Larvae were exposed to organic extracts of increasing concentrations of each smoke 6-to-8-hr post fertilization and assessed for morphological and behavioral toxicity at 5 days post fertilization. To examine chemical and biological determinants of toxicity, responses were related to emissions concentrations of polycyclic hydrocarbons (PAH). Emissions from plastic and the mixture containing plastic caused the most pronounced developmental effects, including mortality, impaired swim bladder inflation, pericardial edema, spinal curvature, tail kinks, and/or craniofacial deformities, although all extracts caused concentration-dependent effects. Plywood, by contrast, altered locomotor responsiveness to light changes to the greatest extent. Some morphological and behavioral responses correlated strongly with smoke extract levels of PAHs including 9-fluorenone. Overall, the findings suggest that material type and emissions chemistry impact the severity of zebrafish developmental toxicity responses to burn pit-related smoke.

Exposure to the aryl hydrocarbon receptor agonist dioxin disrupts formation of the muscle, nerves, and vasculature in the developing jaw

Human exposure to environmental pollutants can disrupt embryonic development and impact juvenile and adult health outcomes by adversely affecting cell and organ function. Notwithstanding, environmental contamination continues to increase due to industrial development, insufficient regulations, and the mobilization of pollutants as a result of extreme weather events. Dioxins are a class of structurally related persistent organic pollutants that are highly toxic, carcinogenic, and teratogenic. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most potent dioxin compound and has been shown to induce toxic effects in developing organisms by activating the aryl hydrocarbon receptor (AHR), a ligand activated transcription factor targeted by multiple persistent organic pollutants. Contaminant-induced AHR activation results in malformations of the craniofacial cartilages and neurocranium; however, the mechanisms mediating these phenotypes are not well understood. In this study, we utilized the optically transparent zebrafish model to elucidate novel cellular targets and potential transcriptional targets underlying TCDD-induced craniofacial malformations. To this end, we exposed zebrafish embryos at 4 h post fertilization to TCDD and employed a mixed-methods approach utilizing immunohistochemistry staining, transgenic reporter lines, fixed and in vivo confocal imaging, and timelapse microscopy to determine the targets mediating TCDD-induced craniofacial phenotypes. Our data indicate that embryonic TCDD exposure reduced jaw and pharyngeal arch Sox10+ chondrocytes and Tcf21+ pharyngeal mesoderm progenitors. Exposure to TCDD correspondingly led to a reduction in collagen type II deposition in Sox10+ domains. Embryonic TCDD exposure impaired development of tissues derived from or guided by Tcf21+ progenitors, namely: nerves, muscle, and vasculature. Specifically, TCDD exposure disrupted development of the hyoid and mandibular arch muscles, decreased neural innervation of the jaw, resulted in compression of cranial nerves V and VII, and led to jaw vasculature malformations. Collectively, these findings reveal novel structural targets and potential transcriptional targets of TCDD-induced toxicity, showcasing how contaminant exposures lead to congenital craniofacial malformations.

Generation and application of a novel transgenic zebrafish line Tg(GAcyp1a:eGFP/Luc) as an in vivo assay to sensitive and specific monitoring of DLCs in the environment

CYP1A is the most commonly used biomarker and transgenic fish which carrying a cyp1a promoter to drive a reporter gene can be used as reliable way to monitor dioxin/dioxin-like compounds (DLCs) in the environment. Here, we cloned the cyp1a promoter of Gambusia affinis and this promoter showed stronger transcriptional activity than that of zebrafish. Then, a Tg(GAcyp1a:eGFP/Luc) transgenic zebrafish line was first constructed with the G. affinis cyp1a promoter driving eGFP expression using meganuclease I-SceI mediated transgenesis technology. The Tg(GAcyp1a:eGFP/Luc) larvae at 72 h post-fertilization (hpf) were tested by exposing to TCDD for 72 h, and induced GFP was mainly expressed in the liver with low background. The Tg(GAcyp1a:eGFP/Luc) zebrafish showed high sensitivity (limit of detection of 0.322 ng/L TCDD and 0.7 TEQ-ng/L PCDD/Fs) and specificity (insensitive to responses to PAHs and PCBs). In addition, the transgenic line showed a low detection concentration of the DLCs contaminated environmental samples (as low as 1.8 TEQ-ng/L), and the eGFP fluorescence intensity and the chemical-TEQ values were closely correlated. In conclusion, a sensitively and specifically transgenic zebrafish line was established to convenient and effective to detect DLCs in the environment.

Exposure to the persistent organic pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) disrupts development of the zebrafish inner ear

Dioxins are a class of highly toxic and persistent environmental pollutants that have been shown through epidemiological and laboratory-based studies to act as developmental teratogens. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most potent dioxin congener, has a high affinity for the aryl hydrocarbon receptor (AHR), a ligand activated transcription factor. TCDD-induced AHR activation during development impairs nervous system, cardiac, and craniofacial development. Despite the robust phenotypes previously reported, the characterization of developmental malformations and our understanding of the molecular targets mediating TCDD-induced developmental toxicity remains limited. In zebrafish, TCDD-induced craniofacial malformations are produced, in part, by the downregulation of SRY-box transcription factor 9b (sox9b), a member of the SoxE gene family. sox9b, along with fellow SoxE gene family members sox9a and sox10, have important functions in the development of the otic placode, the otic vesicle, and, ultimately, the inner ear. Given that sox9b is a known target of TCDD and that transcriptional interactions exist among SoxE genes, we asked whether TCDD exposure impaired the development of the zebrafish auditory system, specifically the otic vesicle, which gives rise to the sensory components of the inner ear. Using immunohistochemistry, in vivo confocal imaging, and time-lapse microscopy, we assessed the impact of TCDD exposure on zebrafish otic vesicle development. We found exposure resulted in structural deficits, including incomplete pillar fusion and altered pillar topography, leading to defective semicircular canal development. The observed structural deficits were accompanied by reduced collagen type II expression in the ear. Together, our findings reveal the otic vesicle as a novel target of TCDD-induced toxicity, suggest that the function of multiple SoxE genes may be affected by TCDD exposure, and provide insight into how environmental contaminants contribute to congenital malformations.

Comparative analysis of two new zebrafish models: The cyp1a low-expression line and cyp1a knockout line under PAHs exposure

Cytochrome P450 1 (CYP1) is an important enzyme family involved in the metabolism of pollutants, and used as a biomarker to monitor environmental pollution. In this study, a fluorescence-labeled cyp1a zebrafish line, named as KI (cyp1a^+/+-T2A-mCherry) (KICM), was originally constructed to monitor dioxin-like compounds in the environment. However, the cyp1a gene expression in the KICM line was inhibited by the fluorescence labeling, thus leading to a significantly increased sensitivity of KICM zebrafish line to PAHs. Then, a cyp1a knockout zebrafish line, named KOC, were constructed for comparative analysis with the cyp1a low-expression line. Interestingly, knockout of the cyp1a gene did not increase the sensitivity of zebrafish to PAHs as significantly as the cyp1a low-expression line. So, the expression levels of related genes in the aryl hydrocarbon receptor pathway were analyzed and the results showed that the expression level of cyp1b in KOC group was significantly higher than that of wild type and KICM under the same PAH exposure. This indicated that the effect of losing cyp1a was compensated by inducing expression of cyp1b. In conclusion, two new zebrafish models including cyp1a low-expression line and cyp1a knockout line were constructed in this study, which may provide a convenient model for subsequent studies on the toxicity mechanism of PAHs and the role of cyp1a in detoxification.

Toxicity and ecological risk assessment for two AhR agonistic pesticides mepanipyrim and cyprodinil and their metabolites

Mepanipyrim and cyprodinil are widely used to control and/or prevent fungal diseases in fruit culture. They are frequently detected in the aquatic environment and some food commodities. Different from TCDD, mepanipyrim and cyprodinil are more easily metabolised in the environments. However, the risk of their metabolites to the ecological environment is unclear and needs to be further confirmed. In this study, we investigated the temporal pattern of mepanipyrim- and cyprodinil-induced CYP1A and AhR2 expression and EROD enzyme activity at different time frames during zebrafish embryonic and larval development. Then, we assessed the ecological risk of mepanipyrim, cyprodinil, and their metabolites to aquatic organisms. Our results showed that mepanipyrim and cyprodinil exposure could increase the expression level of cyp1a and ahr2 genes and EROD activity by a dynamic pattern in different developmental stages of zebrafish. Besides, their several metabolites showed strong AhR agonistic activity. Importantly, these metabolites could cause potential ecological risks to aquatic organisms and should be paid more attention to. Our results would provide an important reference value for environmental pollution control and the use management of mepanipyrim and cyprodinil.

Exposure to the persistent organic pollutant 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, dioxin) disrupts development of the zebrafish inner ear

Dioxins are a class of highly toxic and persistent environmental pollutants that have been shown through epidemiological and laboratory-based studies to act as developmental teratogens. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most potent dioxin congener, has a high affinity for the aryl hydrocarbon receptor (AHR), a ligand activated transcription factor. TCDD-induced AHR activation during development impairs nervous system, cardiac, and craniofacial development. Despite the robust phenotypes previously reported, the characterization of developmental malformations and our understanding of the molecular targets mediating TCDD-induced developmental toxicity remains limited. In zebrafish, TCDD-induced craniofacial malformations are produced, in part, by the downregulation of SRY-box transcription factor 9b ( sox9b ), a member of the SoxE gene family. sox9b , along with fellow SoxE gene family members sox9a and sox10 , have important functions in the development of the otic placode, the otic vesicle, and, ultimately, the inner ear. Given that sox9b in a known target of TCDD and that transcriptional interactions exist among SoxE genes, we asked whether TCDD exposure impaired the development of the zebrafish auditory system, specifically the otic vesicle, which gives rise to the sensory components of the inner ear. Using immunohistochemistry, in vivo confocal imaging, and time-lapse microscopy, we assessed the impact of TCDD exposure on zebrafish otic vesicle development. We found exposure resulted in structural deficits, including incomplete pillar fusion and altered pillar topography, leading to defective semicircular canal development. The observed structural deficits were accompanied by reduced collagen type II expression in the ear. Together, our findings reveal the otic vesicle as a novel target of TCDD-induced toxicity, suggest that the function of multiple SoxE genes may be affected by TCDD exposure, and provide insight into how environmental contaminants contribute to congenital malformations.

Highlights

The zebrafish ear is necessary to detect changes in motion, sound, and gravity.Embryos exposed to TCDD lack structural components of the developing ear.TCDD exposure impairs formation of the fusion plate and alters pillar topography.The semicircular canals of the ear are required to detect changes in movement.Following TCDD exposure embryos fail to establish semicircular canals.

Graphene oxide elicits microbiome-dependent type 2 immune responses via the aryl hydrocarbon receptor

The gut microbiome produces metabolites that interact with the aryl hydrocarbon receptor (AhR), a key regulator of immune homoeostasis in the gut1,2. Here we show that oral exposure to graphene oxide (GO) modulates the composition of the gut microbiome in adult zebrafish, with significant differences in wild-type versus ahr2-deficient animals. Furthermore, GO was found to elicit AhR-dependent induction of cyp1a and homing of lck+ cells to the gut in germ-free zebrafish larvae when combined with the short-chain fatty acid butyrate. To obtain further insights into the immune responses to GO, we used single-cell RNA sequencing to profile cells from whole germ-free embryos as well as cells enriched for lck. These studies provided evidence for the existence of innate lymphoid cell (ILC)-like cells3 in germ-free zebrafish. Moreover, GO endowed with a 'corona' of microbial butyrate triggered the induction of ILC2-like cells with attributes of regulatory cells. Taken together, this study shows that a nanomaterial can influence the crosstalk between the microbiome and immune system in an AhR-dependent manner.

Non-additive mixture effects of benzo[a]pyrene and pesticides in vitro and in vivo: Role of AhR signaling

Polycyclic aromatic hydrocarbons (PAHs) and pesticides are two major groups of environmental contaminants which humans are simultaneously exposed to. However, potential mixture interactions of these groups of chemicals are not well-studied. In this study, the effects of binary mixtures of the PAH benzo[a]pyrene (B[a]P) and the commonly used pesticides chlorpyrifos, paraquat and tebuconazole on human liver HepG2 cells were investigated. The results showed that binary mixtures of B[a]P and paraquat or tebuconazole mainly caused additive effects on cell viability and cytochrome P4501a1 (CYP1A1) expression compared to single compound exposures. In contrast, the binary mixture with chlorpyrifos interacted antagonistically on cell viability and ROS production, whereas synergistic effects were observed for induction of CYP1A1 expression. B[a]P and chlorpyrifos also inhibited the activity of recombinant human CYP1A1 enzyme. To verify the synergistic in vitro results, zebrafish (Danio rerio) embryos were exposed to binary mixtures of B[a]P and chlorpyrifos. The mixtures caused synergistic induction of CYP1A expression, as well as synergistic developmental toxicity on multiple endpoints including non-inflated swim bladder, yolk-sac and pericardial edema, and spinal deformation. The effects were reduced upon morpholino-mediated knockdown of the aryl hydrocarbon receptor (AhR), indicating an AhR-dependence of the synergistic toxicity. Altogether, these data suggest that the combination of AhR activation and CYP1A1 inhibition is responsible for the underlying non-additive interaction between B[a]P and chlorpyrifos in vitro and in vivo.

Damage to Olfactory Organs of Adult Zebrafish Induced by Diesel Particulate Matter

Particulate matter (PM) is an environmental hazard that is associated with various human health risks. The olfactory system is directly exposed to PM; therefore, the influence of PM exposure on olfactory function must be investigated. In this study, we propose a zebrafish olfactory model to evaluate the effects of exposure to diesel particulate matter (DPM), which was labeled Korean diesel particulate matter (KDP20). KDP20 comprises heavy metals and polycyclic aromatic hydrocarbons (PAHs). KDP20 exposed olfactory organs exhibited reduced cilia and damaged epithelium. Olfactory dysfunction was confirmed using an odor-mediated behavior test. Furthermore, the olfactory damage was analyzed using Alcian blue and anti-calretinin staining. KDP20 exposed olfactory organs exhibited histological damages, such as increased goblet cells, decreased cell density, and calretinin level. Quantitative real-time polymerase chain reaction (qRT-PCR) revealed that PAHs exposure related genes (AHR2 and CYP1A) were upregulated. Reactive oxidation stress (ROS) (CAT) and inflammation (IL-1B) related genes were upregulated. Furthermore, olfactory sensory neuron (OSN) related genes (OMP and S100) were downregulated. In conclusion, KDP20 exposure induced dysfunction of the olfactory system. Additionally, the zebrafish olfactory system exhibited a regenerative capacity with recovery conditions. Thus, this model may be used in future investigating PM-related diseases.

Cytochrome P450-dependent biotransformation capacities in embryonic, juvenile and adult stages of zebrafish (Danio rerio)-a state-of-the-art review

Given the strong trend to implement zebrafish (Danio rerio) embryos as translational model not only in ecotoxicological, but also toxicological testing strategies, there is an increasing need for a better understanding of their capacity for xenobiotic biotransformation. With respect to the extrapolation of toxicological data from zebrafish embryos to other life stages or even other organisms, qualitative and quantitative differences in biotransformation pathways, above all in cytochrome P450-dependent (CYP) phase I biotransformation, may lead to over- or underestimation of the hazard and risk certain xenobiotic compounds may pose to later developmental stages or other species. This review provides a comprehensive state-of-the-art overview of the scientific knowledge on the development of the CYP1-4 families and corresponding phase I biotransformation and bioactivation capacities in zebrafish. A total of 68 publications dealing with spatiotemporal CYP mRNA expression patterns, activities towards mammalian CYP-probe substrates, bioactivation and detoxification activities, as well as metabolite profiling were analyzed and included in this review. The main results allow for the following conclusions: (1) Extensive work has been done to document mRNA expression of CYP isoforms from earliest embryonic stages of zebrafish, but juvenile and adult zebrafish have been largely neglected so far. (2) There is insufficient understanding of how sex- and developmental stage-related differences in expression levels of certain CYP isoforms may impact biotransformation and bioactivation capacities in the respective sexes and in different developmental stages of zebrafish. (3) Albeit qualitatively often identical, many studies revealed quantitative differences in metabolic activities of zebrafish embryos and later developmental stages. However, the actual relevance of age-related differences on the outcome of toxicological studies still needs to be clarified. (4) With respect to current remaining gaps, there is still an urgent need for further studies systematically assessing metabolic profiles and capacities of CYP isoforms in zebrafish. Given the increasing importance of Adverse Outcome Pathway (AOP) concepts, an improved understanding of CYP capacities appears essential for the interpretation and outcome of (eco)toxicological studies.

An inadvertent issue of human retina exposure to endocrine disrupting chemicals: A safety assessment

Endocrine disrupting chemicals (EDCs) are a group of chemical compounds that present a considerable public health problem due to their pervasiveness and associations with chronic diseases. EDCs can interrupt the endocrine system and interfere with hormone homeostasis, leading to abnormalities in human physiology. Much attention has been focused on the adverse effects EDCs have on the reproductive system, neurogenesis, neuroendocrine system, and thyroid dysfunction. The eye is usually directly exposed to the surrounding environment; however, the influences of EDCs on the eye have received comparatively little attention. Ocular diseases, such as ocular surface diseases and retinal diseases, have been implicated in hormone deficiency or excess. Epidemiologic studies have shown that EDC exposure not only causes ocular surface disorders, such as dry eye, but also associates with visual deficits and retinopathy. EDCs can pass through the human blood-retinal barrier and enter the neural retina, and can then accumulate in the retina. The retina is an embryologic extension of the central nervous system, and is extremely sensitive and vulnerable to EDCs that could be passed across the placenta during critical periods of retinal development. Subtle alterations in the retinal development process usually result in profound immediate, long-term, and delayed effects late in life. This review, based on extensive literature survey, briefly summarizes the current knowledge about the impact of representative manufactured EDCs on retinal toxicity, including retinal structure alterations and dysfunction. We also highlight the potential mechanism of action of EDCs on the retina, and the predictive retinal models of EDC exposure.

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.

Generation and application of a Tg(cyp1a:egfp) transgenic marine medaka (Oryzias melastigma) line as an in vivo assay to sensitively detect dioxin-like compounds in the environment

Large-range environmental pollution by dioxin and dioxin-like compounds (DLCs) is becoming a serious problem. To establish an in vivo method for the detection of DLCs in seawater, a Tg(cyp1a-12DRE:egfp) transgenic marine medaka (Oryzias melastigma) line was first developed with the modified cyp1a-12DRE promoter driving enhanced green fluorescent protein (EGFP) expression using Tol2 transgenesis technology. With increasing concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), the EGFP fluorescence intensity increased significantly. The Tg(cyp1a-12DRE:egfp) medaka possessed high sensitivity (limit of detection of 1 ng/L TCDD) and specificity and low background. This transgenic line is capable of detecting DLCs in environmental seawater in which the concentration of DLCs is at least 0.12207 ng/L TCDD after sample enrichment. The fluorescence-toxic equivalency (TEQ) values from EGFP intensity were closely correlated with the chemical-TEQ values obtained from chemical analyses. Furthermore, the Tg(cyp1a-12DRE:egfp) medaka can directly detect DLCs in seawater samples after a serious pollution accident and screen unknown aryl hydrocarbon receptor (AhR) agonists for risk assessment. For the first time, a convenient method has been established that sensitively and specifically responds to DLCs using the Tg(cyp1a-12DRE:egfp) marine medaka, which could be a highly efficient tool for detecting seawater DLCs in the future.

A zebrafish model of nondystrophic myotonia with sodium channelopathy

Nondystrophic myotonias are disorders of Na⁺ (Na_v1.4 or SCN4A) and Cl^- (CLCN1) channels in skeletal muscles, and frequently show phenotype heterogeneity. The molecular mechanism underlying their pathophysiology and phenotype heterogeneity remains unclear. As zebrafish models have been recently exploited for studies of the pathophysiology and phenotype heterogeneity of various human genetic diseases, a zebrafish model may be useful for delineating nondystrophic myotonias. Here, we generated transgenic zebrafish expressing a human mutant allele of SCN4A, referred to as Tg(mylpfa:N440K), and needle electromyography revealed increased number of myotonic discharges and positive sharp waves in the muscles of Tg(mylpfa:N440K) than in controls. In addition, forced exercise test at a water temperature of 24 °C showed a decrease in the distance moved, time spent in and number of visits to the zone with stronger swimming resistance. Finally, a forced exercise test at a water temperature of 18 °C exhibited a higher number of dive-bombing periods and drifting-down behavior than in controls. These findings indicate that Tg(mylpfa:N440K) is a good vertebrate model of exercise- and cold-induced human nondystrophic myotonias. This zebrafish model may contribute to provide insight into the pathophysiology of myotonia in sodium channelopathy and could be used to explore a new therapeutic avenue.

AhR Agonist Activity Confirmation of Polyhalogenated Carbazoles (PHCZs) Using an Integration of in Vitro, in Vivo, and in Silico Models

Polyhalogenated carbazoles (PHCZs) are a kind of rising environmental pollutant that has been reported to pose high risk to human beings and the natural environment. PHCZs are of a similar molecular structure with of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and exhibited some dioxin-like toxicity. Dioxin-like compounds (DLCs) are banned by the Stockholm Convention due to their potential adverse impacts to the environment and public health. However, a few efforts have been made toward the regulation of PHCZs. Herein, we initiated multimodels to systematically determine and validate the dioxin-like effects of PHCZs on a large scale. Transgenic zebrafish line-Tg(cyp1a-12DRE:EGFP) and stably transfected HepG2 cell line with luciferase reporter plasmids were used to screen and evaluate the aryl hydrocarbon receptor (AhR) agonist effects of the target PHCZs, which were then verified by application of molecular docking and expression levels of AhR downstream genes. Results of the two bioassays showed that most of the tested PHCZs could pose dioxin-like AhR agonist effects, change the expression levels of AhR downstream genes, and interact with AhR in accordance with TCDD. In summary, data presented here can help to guide the safe use and regulation of PHCZs.

Identification of new aryl hydrocarbon receptor (AhR) antagonists using a zebrafish model

A new series of 1,3-diketone, heterocyclic and α,β-unsaturated derivatives were synthesized and evaluated for their AhR antagonist activity using zebrafish and mammalian cells. Compounds 1b, 2c, 3b and 5b showed significant AhR antagonist activity in a transgenic zebrafish model. Among them, compound 3b, and 5b were found to have excellent AhR antagonist activity with IC₅₀ of 3.36 nM and 8.3 nM in a luciferase reporter gene assay. In stem cell proliferation assay, compound 5b elicited marked HSC expansion.

Generation of a Tg(cyp1a-12DRE:EGFP) transgenic zebrafish line as a rapid in vivo model for detecting dioxin-like compounds

Dioxin-like compounds (DLCs) are extremely stable toxic organic compounds and can cause serious health risks. To develop a convenient biomonitoring tool for the detection of DLCs in the environment, we generated a transgenic line-Tg(cyp1a-12DRE:EGFP)-with a zebrafish cyp1a promoter recombined with multiple dioxin-responsive elements (DREs) that drive EGFP expression. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced EGFP expression was observed in the head cartilage (most sensitive), gut, otic vesicle, pectoral fin bud and eye of larvae. The lowest observed effect concentration of TCDD was estimated to be approximately 1 ng/L. Compared with existing zebrafish lines, our transgenic fish displayed comparable or even higher detection sensitivity to DLCs and could serve as an improved and rapid assay in an in vivo context. The Tg(cyp1a-12DRE:EGFP) transgenic zebrafish line also had higher stability for inducing EGFP expression (nearly 100% of our zebrafish induced EGFP at approximately 1 ng/L TCDD) than other lines. In addition, Tg(cyp1a-12DRE:EGFP) zebrafish could serve as a convenient and straightforward tool to assess potential cranial malformations and related health effects.

Immune response induced by major environmental pollutants through altering neutrophils in zebrafish larvae

Environmental pollutants may cause adverse effects on the immune system of aquatic organisms. However, the cellular effects of pollutants on fish immune system are largely unknown. Here, we exploited the transgenic zebrafish Tg(lysC:DsRed2) larva as a preliminary screening system to evaluate the potential inflammatory effects of environmental pollutants. Tg(lysC:DsRED2) larvae aged 7-day-postfertilization (7 dpf) were treated with selected environmental chemicals for 24 h (24 h) and the number of neutrophils were quantified using both image analysis and fluorescence activated cell sorting (FACS). We found that the numbers of neutrophils in the Tg(lysC:DsRED2) larvae were significantly increased by most of the organic chemicals tested, including E2 (17β-estradiol), BPA (Bisphenol-A), NDEA (N-nitrosodiethylamine), 4-NP (4-Nitrophenol) and Lindane (γ-hexachlorocyclohexane). Neutrophil numbers were also increased by all the metals tested (Na2HAsO4· 7H2O, Pb(NO3)2, HgCl₂, CdCl2, CuSO₄·5H₂O, ZnSO4, and K2Cr2O7). The only exception was TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), which significantly reduced the number of neutrophils after exposure. Additionally, the transcription of genes (lyz, mpo, tnfα and il8) related to fish immune system were significantly modulated upon exposure to some of the selected chemicals such as E2, TCDD, Cu and Cd. This study revealed that representatives of major categories of environmental pollutants could cause an acute inflammatory response in zebrafish larvae as shown by alterations in the neutrophils, which may imply a common immunotoxicity mechanism for most environmental pollutants. This study has also demonstrated that Tg(lyz:DsRed2) transgenic zebrafish is an excellent tool for screening environmental chemicals with potential inflammatory effects through FACS-facilitated neutrophil counting.

Mechanistic Investigations Into the Developmental Toxicity of Nitrated and Heterocyclic PAHs

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

Hypersensitive assessment of aryl hydrocarbon receptor transcriptional activity using a novel truncated cyp1a promoter in zebrafish

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent organic pollutant (POP), an unintentional byproduct of various industrial processes, and a human carcinogen. The expression of the cytochrome P450 1A (cyp1a) gene is upregulated in the presence of TCDD through activating the aryl hydrocarbon receptor pathway in a dose-dependent manner. Several essential response elements, including the 8 potential xenobiotic response elements in the cyp1a promoter region, have been identified to be the main functional parts for the response to TCDD. Thus, we aimed to develop a convenient and sensitive biomonitoring tool to examine the level of POPs in the environment and evaluate its potential human health risks by TCDD. Here, we established a transgenic zebrafish model with a red fluorescent reporter gene ( mCherry) using the truncated cyp1a promoter. Under exposure to TCDD, the expression pattern of mCherry in the reporter zebrafish mirrored that of endogenous cyp1a mRNA, and the primary target tissues for TCDD were the brain vessels, liver, gut, cloaca, and skin. Our results indicated that exposure of the embryos to TCDD at concentrations as low as 0.005 nM for 48 h, which did not elicit morphologic abnormalities in the embryos, markedly increased mCherry expression. In addition, the reporter embryos responded to other POPs, and primary liver cell culture of zebrafish revealed that Cyp1a protein was mainly expressed in the cytoplasm of liver cells. Furthermore, our transgenic fish embryos demonstrated that TCDD exposure can regulate the expression levels of several tumor-related factors, including epidermal growth factor, TNF-α, C-myc, proliferating cell nuclear antigen, TGF-β, serine/threonine kinase (Akt), and phosphorylated Akt, suggesting that our transgenic fish can be used as a sensitive model to evaluate the carcinogenicity induced by TCDD exposure.-Luo, J.-J., Su, D.-S., Xie, S.-L., Liu, Y., Liu, P., Yang, X.-J., Pei D.-S. Hypersensitive assessment of aryl hydrocarbon receptor transcriptional activity using a novel truncated cyp1a promoter in zebrafish.

Development of a high-throughput in vivo screening platform for particulate matter exposures

Particulate matter (PM) exposure is a public health burden with poorly understood health effect mechanisms and lacking an efficient model to compare the vast diversity of PM exposures. Zebrafish (Danio rerio) are amenable to high-throughput screening (HTS), but few studies have investigated PM toxicity in zebrafish, despite the multitude of advantages. To develop standardized exposure procedures, the urban PM standard reference material (SRM) 1649b was used to systematically determine sample preparation methods, design experimental controls, determine concentration ranges and evaluation procedures. Embryos (n = 32/treatment) were dechorionated and placed into 96-well plates containing SRM1649b (0-200 μg/mL) at 6 h post fertilization (hpf). Developmental toxicity was assessed at 24 and 120 hpf by evaluating morphological changes, embryonic/larval photomotor behavior, and mortality. Differences from blank medium and particle controls were observed for all biological responses measured. Differences due to SRM1649b concentration and preparation method were also observed. Exposure to SRM1649b from DMSO extraction was associated with changes in morphology and mortality and hypoactivity in photomotor responses compared to the DMSO control for the whole particle suspension (76, 68%) and soluble fraction (59, 54%) during the embryonic and larval stages, respectively. Changes in behavioral responses were not observed following exposure to the insoluble fraction of SRM1649b from DMSO extraction. The toxicity bias from PM preparation provided further impetus to select a single HTS exposure method. Based on the biological activity results, the soluble fraction of SRM1649b from DMSO extraction was selected and shown to have concentration dependent cyp1a/GFP expression. This rapid, sensitive and consistently scalable model is a potentially cost-effective vertebrate approach to study the toxicology of PM from diverse locations, and provides a path to identifying the toxic material(s) in these samples, and discover the mechanisms of toxicity.

An integrated approach with the zebrafish model for biomonitoring of municipal wastewater effluent and receiving waters

Comprehensive monitoring of water pollution is challenging. With the increasing amount and types of anthropogenic compounds being released into water, there are rising concerns of undetected toxicity. This is especially true for municipal wastewater effluents that are discharged to surface waters. This study was designed to integrate zebrafish toxicogenomics, targeted gene expression, and morphological analyses, for toxicity evaluation of effluent discharged from two previously characterized wastewater treatment plants (WWTPs) in Pima County, Arizona, and their receiving surface water. Zebrafish embryos were exposed to organic extracts from the WWTP1 effluent that were reconstituted to represent 1× and 0.5× of the original concentration. Microarray analyses identified deregulated gene probes that mapped to 1666, 779, and 631 unique human homologs in the 1×, 0.5×, and the intersection of both groups, respectively. These were associated with 18 cellular and molecular functions ranging from cell cycle to metabolism and are involved in the development and function of 10 organ systems including nervous, cardiovascular, haematological, reproductive, and hepatic systems. Superpathway of cholesterol biosynthesis, retinoic acid receptor activation, glucocorticoid receptor and prolactin signaling were among the top 11 perturbed canonical pathways. Real-time quantitative PCR validated the expression changes of 12 selected genes. These genes were then tested on zebrafish embryos exposed to the reconstituted extract of water sampled downstream of WWTP1 and another nearby WWTP2. The expression of several targeted genes were significantly affected by the WWTP effluents and some of the downstream receiving waters. Morphological analyses using four transgenic zebrafish lines revealed potential toxicity associated with nervous, hepatic, endothelial-vascular and myeloid systems. This study demonstrated how information can be obtained using adverse outcome pathway framework to derive biological effect-based monitoring tools. This integrated approach using zebrafish can supplement analytical chemistry to provide more comprehensive monitoring of discharged effluents and their receiving waters.

Editor's Highlight: Transgenic Zebrafish Reporter Lines as Alternative In Vivo Organ Toxicity Models

Organ toxicity, particularly liver toxicity, remains one of the major reasons for the termination of drug candidates in the development pipeline as well as withdrawal or restrictions of marketed drugs. A screening-amenable alternative in vivo model such as zebrafish would, therefore, find immediate application in the early prediction of unacceptable organ toxicity. To identify highly upregulated genes as biomarkers of toxic responses in the zebrafish model, a set of well-characterized reference drugs that cause drug-induced liver injury (DILI) in the clinic were applied to zebrafish larvae and adults. Transcriptome microarray analysis was performed on whole larvae or dissected adult livers. Integration of data sets from different drug treatments at different stages identified common upregulated detoxification pathways. Within these were candidate biomarkers which recurred in multiple treatments. We prioritized 4 highly upregulated genes encoding enzymes acting in distinct phases of the drug metabolism pathway. Through promoter isolation and fosmid recombineering, eGFP reporter transgenic zebrafish lines were generated and evaluated for their response to DILI drugs. Three of the 4 generated reporter lines showed a dose and time-dependent induction in endodermal organs to reference drugs and an expanded drug set. In conclusion, through integrated transcriptomics and transgenic approaches, we have developed parallel independent zebrafish in vivo screening platforms able to predict organ toxicities of preclinical drugs.

Generation and application of a novel transgenic zebrafish line Tg(cyp1a:mCherry) as an in vivo assay to sensitively monitor PAHs and TCDD in the environment

The polycyclic aromatic hydrocarbons (PAHs) and 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) are classified as human carcinogens, and can also cause serious health problems. To develop a convenient bio-monitoring tool for the detection of PAHs and TCDD in the environment, we generated a transgenic zebrafish line Tg(cyp1a:mCherry) with cyp1a promoter driving mCherry expression. Here, Tg(cyp1a:mCherry) embryos were treated with different concentrations of TCDD and five US EPA priority PAHs congeners. The results showed that the expressions of mCherry and endogenous cyp1a were consistent with the PAHs exposure concentrations and were largely induced by TCDD and ≥4-ring PAHs. Moreover, the sensitivity of Tg(cyp1a:mCherry) embryos was also evaluated through monitoring of the PAHs contamination in the water and soil samples. The elevated red fluorescent signals and cyp1a expression levels were observed in Tg(cyp1a:mCherry) zebrafish after exposure to water samples and soil organic extracts with higher concentrations of ≥4-ring PAHs. These results further strengthen our findings of concentration- and congener-dependent response of the newly established zebrafish. Taken together, the newly established zebrafish line will prove as a sensitive, efficient and convenient tool for monitoring PAHs and TCDD contamination in the environment.

Differential sensitivities to dioxin-like compounds PCB 126 and PeCDF between Tg(cyp1a:gfp) transgenic medaka and zebrafish larvae

It has been intensively documented that there are species-differences in the sensitivity to dioxin-like compounds (DLCs) in mammalian and avian. However, this issue is still unclear in fish. This study aimed at evaluating the differential sensitivities to DLCs in fish larvae. Here, larvae of Tg(cyp1a:gfp) medaka and Tg(cyp1a:gfp) zebrafish were tested with 2,3,7,8-Tetrachlorodibenzodioxin (TCDD), polychlorinated biphenyl 126 (PCB 126) and 2,3,4,7,8,-Pentachlorodibenzofuran (PeCDF). Comparative analyses were performed on induction of GFP fluorescence, expression of endogenous cyp1a mRNAs and EROD activity between the two species after exposure to these chemicals. We found that PCB 126 and PeCDF exposure at high concentrations induced strong GFP expression in multiple organs (liver, head kidney and gut) in both medaka and zebrafish larvae. Moreover, the expression of endogenous cyp1a mRNA was significantly elevated in the zebrafish larvae exposed to TCDD, PCB 126 and PeCDF at different concentrations. Likewise, almost all the exposure conditions could cause prominent elevation of EROD activity in the zebrafish larvae, while the EROD activities were just slightly elevated in the medaka larvae exposed to 1 nM and 0.5 nM of TCDD as well as to 1.5 nM and 15 nM of PeCDF, but not in the medaka larvae exposed to PCB 126. Taken together, zebrafish was proved to be more sensitive than medaka to PCB 126 and to PeCDF in this study. The findings suggested species-specific sensitivity to DLCs in fish and will facilitate choosing a sensitive and reliable fish model or tool to evaluate the risk of dioxins and DLCs exposure.

Comparative developmental toxicity of a comprehensive suite of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants that occur in complex mixtures. Several PAHs are known or suspected mutagens and/or carcinogens, but developmental toxicity data is lacking for PAHs, particularly their oxygenated and nitrated derivatives. Such data are necessary to understand and predict the toxicity of environmental mixtures. 123 PAHs were assessed for morphological and neurobehavioral effects for a range of concentrations between 0.1 and 50 µM, using a high throughput early-life stage zebrafish assay, including 33 parent, 22 nitrated, 17 oxygenated, 19 hydroxylated, 14 methylated, 16 heterocyclic, and 2 aminated PAHs. Additionally, each PAH was evaluated for AHR activation, by assessing CYP1A protein expression using whole animal immunohistochemistry (IHC). Responses to PAHs varied in a structurally dependent manner. High-molecular weight PAHs were significantly more developmentally toxic than the low-molecular weight PAHs, and CYP1A expression was detected in five distinct tissues, including vasculature, liver, skin, neuromasts and yolk.

Graphene oxide nanosheets induce DNA damage and activate the base excision repair (BER) signaling pathway both in vitro and in vivo

Graphene oxide (GO) has widespread concerns in the fields of biological sciences and medical applications. Currently, studies have reported that excessive GO exposure can cause cellular DNA damage through reactive oxygen species (ROS) generation. However, DNA damage mediated response of the base excision repair (BER) pathway due to GO exposure is not elucidated yet. Therefore, we exposed HEK293T cells and zebrafish embryos to different concentrations of GO for 24 h, and transcriptional profiles of BER pathway genes, DNA damage, and cell viability were analyzed both in vitro and in vivo. Moreover, the deformation of HEK293T cells before and after GO exposure was also investigated using atomic force microscopy (AFM) to identify the physical changes occurred in the cells' structure. CCK-8 and Comet assay revealed the significant decrease in cell viability and increase in DNA damage in HEK293T cells at higher GO doses (25 and 50 μg/mL). Among the investigated genetic markers in HEK293T cells, BER pathway genes (APEX1, OGG1, CREB1, UNG) were significantly up-regulated upon exposure to higher GO dose (50 μg/mL), however, low exposure concentration (5, 25 μg/mL) failed to induce significant genetic induction except for CREB1 at 25 μg/mL. Additionally, the viscosity of HEK293T cells decreased upon GO exposure. In zebrafish, the results of up-regulated gene expressions (apex1, ogg1, polb, creb1) were consistent with those in the HEK293T cells. Taken all together, the exposure to elevated GO concentration could cause DNA damage to HEK293T cells and zebrafish embryos; BER pathway could be proposed as the possible inner response mechanism.

Functional validation of novel MKS3/TMEM67 mutations in COACH syndrome

COACH syndrome is an autosomal recessive developmental disorder, a subtype of Joubert syndrome and related disorders, characterized by cerebellar vermis hypoplasia, oligophrenia, ataxia, coloboma, and hepatic fibrosis. Although mutations in TMEM67 (transmembrane protein 67)/MKS3 (Meckel-Gruber syndrome, type 3) were reported to cause COACH syndrome, this causality has not verified by functional studies. In a 20-year-old Korean man, we found cerebellar ataxia, isolated elevation in serum γ-glutamyl transpeptidase (γ-GTP) activity, oligophrenia, the molar tooth sign (MTS) in the brain MR images and congenital hepatic fibrosis (CHF). Two novel compound heterozygous mutations were found in TMEM67 in the patient: i) missense mutation (c.395 G > C and p.Gly132Ala) in exon 3, and ii) deletion in exon 26 (c.2758delT and p.Tyr920ThrfsX40). Western blotting showed that the p.Tyr920ThrfsX40 mutation accelerates turnover of the TMEM67 protein. Although wild-type human TMEM67 RNA rescued phenotypes of zebrafish embryos injected with anti-sense oligonucleotide morpholinos against tmem67, the two human TMEM67 RNAs individually harboring the two mutations did not. Finally, Wnt signaling, but not Hedgehog signaling, was suppressed in tmem67 morphants. To the best of our knowledge, this is the first report verifying the causality between COACH syndrome and TMEM67, which will further our understanding of molecular pathogenesis of the syndrome.

A novel forward osmosis system in landfill leachate treatment for removing polycyclic aromatic hydrocarbons and for direct fertigation

Landfill leachate (LL) is harmful to aquatic environment because it contains high concentrations of dissolved organic matter, inorganic components, heavy metals, and other xenobiotics. Thus, the remediation of LL is crucial for environmental conservation. Here, a potential application of the forward osmosis (FO) filtration process with ammonium bicarbonate (NH₄HCO₃) as a draw solution (DS) was investigated to remediate membrane bioreactor-treated LL (M-LL). After the leachate treatment, the toxicity and removal efficiencies of polycyclic aromatic hydrocarbons (PAHs) were evaluated using zebrafish and cultured human cells. The water recovery rate was improved using the current protocol up to 86.6% and 91.6% by both the pressure retarded osmosis (PRO) mode and the forward osmosis (FO) mode. Water flux increased with the increasing DS concentrations, but solution velocities decreased with the operation time. Toxicity tests revealed that the M-LL treated by NH₄HCO₃ had no toxic effect on zebrafish and human cells. Moreover, green fluorescent protein (GFP) expression in the transgenic zebrafish Tg(cyp1a:gfp) induced by PAHs was very weak compared to the effects induced by untreated M-LL. Since the diluted DS met local safety requirements of liquid fertilizer, it could be directly applied as the liquid fertilizer for fertigation. In conclusion, this novel FO system using NH₄HCO₃ as the DS provides a cheap and efficient protocol to effectively remove PAHs and other pollutants in LL, and the diluted DS can be directly applied to crops as a liquid fertilizer, indicating that this technique is effective and eco-friendly for the treatment of different types of LL.

Partial Gene Sequencing of CYP1A, Vitellogenin, and Metallothionein in Mosquitofish Gambusia yucatana and Gambusia sexradiata

Ground characteristics in the Yucatan Peninsula make recovery and treatment of wastewater very expensive. This situation has contributed to an increase of pollutants in the aquifer. Unfortunately, studies related to the effects of those pollutants in native organisms are scarce. The aim of this work was to obtain partial sequences of widely known genes used as biomarkers of pollutant effect in Gambusia yucatana and Gambusia sexradiata. The studied genes were: cytochrome P450 1A (CYP1A); vitellogenin (VTG); metallothionein (MT), and two housekeeping genes, 18S and β-actin. From reported sequences of Gambusia affinis, primers were designed and amplification was done in the local Gambusia species exposed for 48 h to gasoline (100 µL/L, stirred for 24 h pre-exposure). Preliminary results revealed partial sequences of all genes with an approximate average length of 200 bp. BLAST analysis of found sequences indicated a minimum of 97% identity with reported sequences for G. affinis or Gambusia holbrooki showing great similarity.

Hepatoprotective and antioxidant effects of dietary Glycyrrhiza polysaccharide against TCDD-induced hepatic injury and RT-PCR quantification of AHR2, ARNT2, CYP1A mRNA in Jian Carp (Cyprinus carpio var. Jian)

To evaluate the protective effects of Glycyrrhiza polysaccharide (GPS) against 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced hepatotoxicity in Jian carp, the fish were fed diets containing GPS at doses of 0.1, 0.5 and 1.0g/kg for 60days before an intraperitoneal injection of 0.6μg/kg TCDD at a volume of 0.05mL/10g body weight. At 72hr post-injection, blood and liver samples were taken for biochemical analysis and the fish liver samples were used for the preparation of pathological slices. The results showed that increases in alanine aminotransferase (GPT), aspartate aminotransferase (GOT), lactate dehydrogenase (LDH), and alkaline phosphatase (AKP) in serum induced by TCDD were significantly inhibited by pre-treatment with 1.0g/kg GPS. Following the 1.0g/kg GPS pre-treatment, total protein (TP), albumin (Alb), catalase (CAT), glutathione peroxidase (GPx), total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) activities in liver tissue increased significantly, malondialdehyde (MDA) formation (P<0.05 or P<0.01) was significantly inhibited, and the expression of cytochrome P4501A (CYP1A), aryl hydrocarbon receptor 2 (AHR2) and aryl hydrocarbon receptor nuclear translocator 2 (ARNT2) mRNA (P<0.05) was significantly enhanced. Histological observations on fish liver were obtained by preparing paraffin tissue sections via HE staining, and the results showed that histological changes were obviously reduced by 0.5 and 1.0g/kg GPS. GPS significantly reduced liver tissue damage caused by TCDD. Overall, these results proved the hepatoprotective effect of GPS in protecting against fish liver injury induced by TCDD, and supported the use of GPS (1.0g/kg) as a hepatoprotective and antioxidant agent in fish.

Zebrafish in Toxicology and Environmental Health

As manufacturing processes and development of new synthetic compounds increase to keep pace with the expanding global demand, environmental health, and the effects of toxicant exposure are emerging as critical public health concerns. Additionally, chemicals that naturally occur in the environment, such as metals, have profound effects on human and animal health. Many of these compounds are in the news: lead, arsenic, and endocrine disruptors such as bisphenol A have all been widely publicized as causing disease or damage to humans and wildlife in recent years. Despite the widespread appreciation that environmental toxins can be harmful, there is limited understanding of how many toxins cause disease. Zebrafish are at the forefront of toxicology research; this system has been widely used as a tool to detect toxins in water samples and to investigate the mechanisms of action of environmental toxins and their related diseases. The benefits of zebrafish for studying vertebrate development are equally useful for studying teratogens. Here, we review how zebrafish are being used both to detect the presence of some toxins as well as to identify how environmental exposures affect human health and disease. We focus on areas where zebrafish have been most effectively used in ecotoxicology and in environmental health, including investigation of exposures to endocrine disruptors, industrial waste byproducts, and arsenic.

Mechanistic Evaluation of Benzo[a]pyrene's Developmental Toxicities Mediated by Reduced Cyp19a1b Activity

Benzo[a]pyrene (BaP) is a ubiquitous environmental contaminant that is both an endocrine disruptor and a carcinogen. Aromatase (CYP19) is a key enzyme in steroidogenesis that is responsible for conversion of androgens to estrogens and thus plays a key role in steroid homeostasis. We hypothesized that some of the adverse outcomes of early developmental exposure to BaP are the result of reduced Cyp19a1b activity. Our goal was to investigate the role of estrogen homeostasis during early development and determine the role of aromatase inhibition as a relevant mechanism in BaP's developmental toxicities. One-cell zebrafish embryos were injected with a Cyp19a1b-morpholino (MO) or control-MO. Other non-injected embryos were exposed to waterborne BaP, fadrozole (a Cyp19 inhibitor), estradiol (E2), BaP + E2, Cyp19a1b MO + E2, or fadrozole + E2 for 96 hours post-fertilization (hpf). Adverse outcomes were compared between treatments, and the ability of E2 co-exposure to rescue each observed dysmorphology was assessed. BaP significantly decreased cyp19a1b gene expression in 96 hpf zebrafish larvae homogenates. Concentrations of E2 in 48 hpf larvae were significantly decreased by BaP, fadrozole and Cyp19a1b-MO. Cumulative mortality of zebrafish larvae was significantly increased following BaP or fadrozole exposure or Cyp19a1b knockdown compared to controls. E2 co-treatment rescued mortality caused by 10 μg/L BaP, 10 μg/L fadrozole, or Cyp19a1b-MO. In a treatment-blinded morphological assessment of larvae at 96 hpf, several phenotypes were negatively impacted by BaP, fadrozole, or Cyp19a1b knockdown and rescued by exogenous E2 co-treatment; these included body length, optic vesicle size, swim bladder inflation, pericardial and abdominal edema, and incidence of normal larval tail shape. Abnormal pectoral fins were caused by BaP exposure only. Uninflated swim bladders were caused by all treatments including E2 alone. Our results indicate that certain BaP-mediated adverse developmental outcomes were mechanistically in accordance with BaP-mediated Cyp19a1b inhibition.

Zebrafish biosensor for toxicant induced muscle hyperactivity

Robust and sensitive detection systems are a crucial asset for risk management of chemicals, which are produced in increasing number and diversity. To establish an in vivo biosensor system with quantitative readout for potential toxicant effects on motor function, we generated a transgenic zebrafish line TgBAC(hspb11:GFP) which expresses a GFP reporter under the control of regulatory elements of the small heat shock protein hspb11. Spatiotemporal hspb11 transgene expression in the musculature and the notochord matched closely that of endogenous hspb11 expression. Exposure to substances that interfere with motor function induced a dose-dependent increase of GFP intensity beginning at sub-micromolar concentrations, while washout of the chemicals reduced the level of hspb11 transgene expression. Simultaneously, these toxicants induced muscle hyperactivity with increased calcium spike height and frequency. The hspb11 transgene up-regulation induced by either chemicals or heat shock was eliminated after co-application of the anaesthetic MS-222. TgBAC(hspb11:GFP) zebrafish embryos provide a quantitative measure of muscle hyperactivity and represent a robust whole organism system for detecting chemicals that affect motor function.

Generation of Tg(cyp1a:gfp) Transgenic Zebrafish for Development of a Convenient and Sensitive In Vivo Assay for Aryl Hydrocarbon Receptor Activity

Both dioxins/dioxin-like compounds and polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants and cause multiple adverse health effects on human and wildlife. Cyp1a is the most commonly used biomarker induced by these pollutants through activation of the aryl hydrocarbon receptor (AhR) pathway. Here we generated Tg(cyp1a:gfp) transgenic zebrafish for establishing a convenient in vivo assay for analysing these xenobiotic compounds. The Tg(cyp1a:gfp) larvae at 4 day post-fertilization were tested with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and GFP induction was observed mainly in the kidney, liver and gut. Similar GFP expression was also induced strongly by two dioxin-like chemicals, co-planar polychlorinated biphenyl (PCB126) and polychlorinated dibenzo-p-furan (PeCDF) and relatively weakly by two PAHs, 3-methylcholanthrene (3-MC) and benzo[a]pyrene (BAP). The lowest observed effective concentration (LOEC) of TCDD was estimated to be ∼1 pM and the EC50 (effective concentration to induce GFP in 50 % of Tg(cyp1a:gfp) larvae) was ∼10 pM. PCB126 and PeCDF had ∼10× lower potencies in GFP induction than TCDD, while the potencies for 3-MC and BAP were at least 1000× lower. The sensitivity of Tg(cyp1a:gfp) larvae to respond TCDD was also favourable compared to that of ethoxyresorufin-O-deethylase (EROD) assay in both zebrafish larvae and adult livers. As GFP-based assay in transgenic zebrafish can be easily accommodated in multi-well dishes, the Tg(cyp1a:gfp) zebrafish should provide not only a valuable biomonitoring tool for aquatic contaminants but also a potential high-throughput chemical screening platform for identification of new AhR agonists.

Ligand-Specific Transcriptional Mechanisms Underlie Aryl Hydrocarbon Receptor-Mediated Developmental Toxicity of Oxygenated PAHs

Polycyclic aromatic hydrocarbons (PAHs) are priority environmental contaminants that exhibit mutagenic, carcinogenic, proinflammatory, and teratogenic properties. Oxygen-substituted PAHs (OPAHs) are formed during combustion processes and via phototoxidation and biological degradation of parent (unsubstituted) PAHs. Despite their prevalence both in contaminated industrial sites and in urban air, OPAH mechanisms of action in biological systems are relatively understudied. Like parent PAHs, OPAHs exert structure-dependent mutagenic activities and activation of the aryl hydrocarbon receptor (AHR) and cytochrome p450 metabolic pathway. Four-ring OPAHs 1,9-benz-10-anthrone (BEZO) and benz(a)anthracene-7,12-dione (7,12-B[a]AQ) cause morphological aberrations and induce markers of oxidative stress in developing zebrafish with similar potency, but only 7,12-B[a]AQ induces robust Cyp1a protein expression. We investigated the role of the AHR in mediating the toxicity of BEZO and 7,12-B[a]AQ, and found that knockdown of AHR2 rescued developmental effects caused by both compounds. Using RNA-seq and molecular docking, we identified transcriptional responses that precede developmental toxicity induced via differential interaction with AHR2. Redox-homeostasis genes were affected similarly by these OPAHs, while 7,12-B[a]AQ preferentially activated phase 1 metabolism and BEZO uniquely decreased visual system genes. Analysis of biological functions and upstream regulators suggests that BEZO is a weak AHR agonist, but interacts with other transcriptional regulators to cause developmental toxicity in an AHR-dependent manner. Identifying ligand-dependent AHR interactions and signaling pathways is essential for understanding toxicity of this class of environmentally relevant compounds.

Beta-naphthoflavone-inducedCYP1A expression in the guppy Jenynsia multidentata: Time-dependent response, anesthetic MS-222 effect and fin analysis

Cytochrome P450 1A (CYP1A) expression in fish is used as a biomarker of exposure to organic contaminants, such PAHs, PCBs and dioxins, in the aquatic environment. South American guppy fish Jenynsia multidentata were exposed to the prototypical aryl hydrocarbon receptor (AHR) agonist beta-naphthoflavone (BNF; 1μM) and the fins were biopsied to characterize different aspects of CYP1A induction. RTq-PCR was used to quantify CYP1A mRNA levels in fish tissues. CYP1A induction in the gill, liver and anal fin (gonopodium) occurred within the first hour of waterborne exposure to BNF and persisted throughout 2, 4, 8, 24, 48 and 96h compared to controls (DMSO vehicle; p<0.05). The organ-specific temporal pattern of induction was marked by mRNA levels consistently augment as duration of exposure increases and tend to a sustained induction from 24h to 96h for gill and liver (∼15-fold and ∼50-fold over control, respectively). In gonopodium, there was a maximum CYP1A mRNA level at 4h (∼34-fold over control). Basal CYP1A mRNA levels and its induction following BNF exposure were not affected by administration of a chemical anesthetic (fish immersion in 100mgl(-1) MS-222 for 2-5min) in the gill, liver, gonopodium, dorsal or tail fin (p<0.05). In an ex vivo assay, in which small pieces of biopsied fins were exposed to BNF for 4h, high CYP1A induction was observed in the tail and gonopodium (∼49-fold and ∼69-fold, respectively) but not in the dorsal fin compared to controls. To our knowledge, this is the first study to show that a 1h waterborne exposure to an AHR agonist is sufficient to cause CYP1A induction in fish organs and fins. The present study added new information to the field regarding the use of MS-222 as an anesthetic on fish and the analysis of biopsied fins as an alternative non-lethalex vivo assay for evaluating the CYP1A biomarker in fish. This observation could be useful for planning fish toxicological bioassays and biomonitoring studies on the aquatic environments in South America.

Transgenic fish systems and their application in ecotoxicology

The use of transgenics in fish is a relatively recent development for advancing understanding of genetic mechanisms and developmental processes, improving aquaculture, and for pharmaceutical discovery. Transgenic fish have also been applied in ecotoxicology where they have the potential to provide more advanced and integrated systems for assessing health impacts of chemicals. The zebrafish (Daniorerio) is the most popular fish for transgenic models, for reasons including their high fecundity, transparency of their embryos, rapid organogenesis and availability of extensive genetic resources. The most commonly used technique for producing transgenic zebrafish is via microinjection of transgenes into fertilized eggs. Transposon and meganuclease have become the most reliable methods for insertion of the genetic construct in the production of stable transgenic fish lines. The GAL4-UAS system, where GAL4 is placed under the control of a desired promoter and UAS is fused with a fluorescent marker, has greatly enhanced model development for studies in ecotoxicology. Transgenic fish have been developed to study for the effects of heavy metal toxicity (via heat-shock protein genes), oxidative stress (via an electrophile-responsive element), for various organic chemicals acting through the aryl hydrocarbon receptor, thyroid and glucocorticoid response pathways, and estrogenicity. These models vary in their sensitivity with only very few able to detect responses for environmentally relevant exposures. Nevertheless, the potential of these systems for analyses of chemical effects in real time and across multiple targets in intact organisms is considerable. Here we illustrate the techniques used for generating transgenic zebrafish and assess progress in the development and application of transgenic fish (principally zebrafish) for studies in environmental toxicology. We further provide a viewpoint on future development opportunities.

Zebrafish: A marvel of high-throughput biology for 21st century toxicology

The evolutionary conservation of genomic, biochemical and developmental features between zebrafish and humans is gradually coming into focus with the end result that the zebrafish embryo model has emerged as a powerful tool for uncovering the effects of environmental exposures on a multitude of biological processes with direct relevance to human health. In this review, we highlight advances in automation, high-throughput (HT) screening, and analysis that leverage the power of the zebrafish embryo model for unparalleled advances in our understanding of how chemicals in our environment affect our health and wellbeing.

Zebrafish transgenic line huORFZ is an effective living bioindicator for detecting environmental toxicants

Reliable animal models are invaluable for monitoring the extent of pollution in the aquatic environment. In this study, we demonstrated the potential of huORFZ, a novel transgenic zebrafish line that harbors a human upstream open reading frame of the chop gene fused with GFP reporter, as an animal model for monitoring environmental pollutants and stress-related cellular processes. When huORFZ embryos were kept under normal condition, no leaked GFP signal could be detected. When treated with hazardous chemicals, including heavy metals and endocrine-disrupting chemicals near their sublethal concentrations (LC50), huORFZ embryos exhibited different tissue-specific GFP expression patterns. For further analysis, copper (Cu²⁺), cadmium (Cd²⁺) and Chlorpyrifos were applied. Cu²⁺ triggered GFP responses in skin and muscle, whereas Cd²⁺ treatment triggered GFP responses in skin, olfactory epithelium and pronephric ducts. Moreover, fluorescence intensity, as exhibited by huORFZ embryos, was dose-dependent. After surviving treated embryos were returned to normal condition, survival rates, as well as TUNEL signals, returned to pretreatment levels with no significant morphological defects observed. Such results indicated the reversibility of treatment conditions used in this study, as long as embryos survived such conditions. Notably, GFP signals decreased along with recovery, suggesting that GFP signaling of huORFZ embryos likely reflected the overall physiological condition of the individual. To examine the performance of the huORFZ line under real-world conditions, we placed huORFZ embryos in different river water samples. We found that the huORFZ embryos correctly detected the presence of various kinds of pollutants. Based on these findings, we concluded that such uORF^chop-based system can be integrated into a first-line water alarm system monitoring the discharge of hazardous pollutants.