Developmental toxicity,EROD, and CYP1A mRNA expression in zebrafish embryos exposed to dioxin‐like PCB126

Dioxin‐like PCB126 is a persistent organic pollutant that causes a range of syndromes including developmental toxicity. Dioxins have a high affinity for aryl hydrocarbon receptor (AhR) and induce cytochrome P4501A (CYP1A). However, the role of CYP1A activity in developmental toxicity is less clear. To better understand dioxin induced developmental toxicity, we exposed zebrafish (Danio rerio) embryos to PCB126 at concentrations of 0, 16, 32, 64, and 128 μg L^?1 from 3‐h post‐fertilization (hpf) to 168 hpf. The embryonic survival rate decreased at 144 and 168 hpf. The fry at 96 hpf displayed gross developmental malformations, including pericardial and yolk sac edema, spinal curvature, abnormal lower jaw growth, and non‐inflated swim bladder. The pericardial and yolk sac edema rate significantly increased and the heart rate declined from 96 hpf compared with the controls. PCB126 did not alter the hatching rate. To elucidate the mechanism of PCB126‐induced developmental toxicity, we conducted ethoxyresorufin‐O‐deethylase (EROD) in vivo assay to determine CYP1A enzyme activity, and real‐time PCR to study the induction of CYP1A mRNA gene expression in embryo/larval zebrafish at 24, 72, 96, and 132 hpf. In vivo EROD activity was induced by PCB126 at 16 μg L^?1 concentration as early as 72 hpf but significant increases were observed only in zebrafish exposed to 64 and 128 μg L^?1 doses (p < 0.005) at 72, 96, and 132 hpf. Induction of CYP1A mRNA expression was significantly upregulated in zebrafish exposed to 32 and 64 μg L^?1 at 24, 72, 96, and 132 hpf. Overall, the severe pericardial and yolk sac edema and reduced heart rate suggest that heart defects are a sensitive endpoint, and the general trend of dose‐dependent increase in EROD activity and induction of CYP1A mRNA gene expression provide evidence that the developmental toxicity of PCB126 to zebrafish embryos is mediated by activation of AhR. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 201–210, 2016.     

TBBPA induces developmental toxicity,oxidative stress,and apoptosis in embryos and zebrafish larvae (Danio rerio)

Tetrabromobisphenol A (TBBPA) is currently one of the most frequently used brominated flame retardants and can be considered as a high production volume chemical. In this study, zebrafish embryos and larvae served as a biological model to evaluate TBBPA‐induced developmental toxicity, oxidative stress, oxidant‐associated gene expression, and cell apoptosis. Abnormalities, including hyperemia and pericardial edema, were induced in zebrafish larvae. The results showed that toxicity endpoints such as hatching rate, survival rate, malformation rate, and growth rate had a significant dose–response relationship with TBBPA. Further studies revealed that TBBPA did not alter the enzyme activities of Copper/Zinc Superoxide dismutase (Cu/Zn‐SOD), catalase (CAT), and glutathioneperoxidase (GPx) at 0.10 mg/L, but decreased activities following exposure to 0.40, 0.70, and 1.00 mg/L. Despite the significantly decreased gene expression of Cu/Zn‐SOD, CAT, and GPx1a in the 1.00 mg/L treatment group, other treatments (0.10, 0.40, 0.70 mg/L) did not alter gene expression. Moreover, Acridine orange staining results showed that apoptotic cells mainly accumulated in the brain, heart, and tail, indicating possible TBBPA‐induced brain, cardiac, and blood circulation system impairment in zebrafish embryos and larvae. Histological analysis also showed evidence of obvious heart impairment in TBBPA‐treated groups. This study provides new evidence on the developmental toxicity, oxidative stress, and apoptosis of embryos and zebrafish larvae, which is important for the evaluation of environmental toxicity and chemical risk. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1241–1249, 2016.     

Thiamethoxam induces oxidative stress and antioxidant response in zebrafish (Danio Rerio) livers

Thiamethoxam, a second‐generation neonicotinoid insecticide, was found to be toxic to nontarget aquatic organisms. The purpose of this study was to investigate the toxicity of thiamethoxam (0.30, 1.25, and 5.00 mg/L) on zebrafish (Danio rerio) livers at the 7th, 14th, 21st, and 28th days. The reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), glutathione‐s‐transferase (GST), malondialdehyde (MDA) content, and DNA damage were used to evaluate the toxic effects of thiamethoxam on zebrafish. Compared to control groups, ROS levels were ascended in the exposure period; SOD and CAT activities were dramatically increased during early exposure and then inhibited. GST activity only increased on days 28. MDA content was slightly elevated on days 21 and 28. Additionally, a clear dose‐response relationship was found for DNA damage. In conclusion, thiamethoxam could induce oxidative stress and DNA damage on the exposed zebrafish. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 2006–2015, 2016.     

Food colorant Sunset Yellow (E110) intervenes developmental profile of zebrafish (Danio rerio)

In this study, we tested the teratogenic/embryotoxic potentials of food colorant, Sunset Yellow (E110) using zebrafish embryos as a model. Laboratory‐raised developing embryos of Danio rerio were exposed to graded concentrations (00, 0.1, 1.0, 2.0, 3.0, 4.0, 5.0, 10, 20, 30, 40, 50 and 100 mm ) of E110 from gastrulation stage (~6 hours post‐fertilization [hpf]) up until hatching. The developmental trajectory of each embryo and post‐hatched larva was traced from 24 to 168 hpf. The no observed effect concentration (NOEC), median effective concentration (EC₅₀), median lethal concentration (LC₅₀) and teratogenic index were determined. In the 0.1 mm E110‐exposed embryos, the development proceeded as in controls (NOEC), while, exposure of embryos to 1‐5 mm of E110 led to a decrease in body size, dry body mass of resultant larvae along with appearance of morphological deformities such as, microphthalmia, pericardial edema, yolk sac edema and spinal curvature. Larvae of 10‐50 mm E110‐exposed embryos exhibited increased cellular apoptosis in the cardiac region with significantly declined heartbeats and elevated mortality rates, in addition to the above‐mentioned abnormalities. In the 100 mm exposure group, all embryos succumbed to death within 24 hpf. The NOEC and LC₅₀ recorded were at 0.1 and 42.57 mm respectively. EC₅₀ (96 hpf) recorded for pericardial edema and yolk sac edema was 19.41 and 39.84 mm with teratogenic index quotient 2.1 and 1.06 respectively The study provides direct evidence for the developmental toxicity/teratogenic potential of E110.     

DNA damage and effects on glutathione‐S‐transferase activity induced by atrazine exposure in zebrafish (Danio rerio)

This study was undertaken to investigate the protective effect of atrazine (2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐S‐triazine) on the activity of glutathione‐S‐transferase (GST) and DNA damage in males and females of adult zebrafish (Danio rerio). Zebrafish were exposed to control and three treatments (0.01, 0.1, and 1 mg/L) of atrazine for 5, 10, 15, 20, and 25 days. The results indicated that, for males, the GST activity at lower atrazine concentrations (0.01 and 0.1 mg/L) was markedly higher than that of the controls throughout the duration of the experiment while there was a significant inhibition of the GST activity at 1 mg/L atrazine at days 5 and 20. For females, a significant increase was detected at 0.1 mg/L on the days 5 and 15 and at 0.01 mg/L on day 20. The DNA damage in zebrafish was evaluated using the comet assay; the olive tail moments obtained for hepatopancreas were enhanced after treatment with different concentrations of atrazine on days 5, 10, 15, 20, and 25. The DNA damage increased with increasing atrazine concentrations, indicating that genotoxicity of atrazine and significant differences was found compared to the controls. In conclusion, these findings provide further evidence of the effects of atrazine on aquatic ecosystems. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2010.     

佐匹克隆及其杂质对斑马鱼胚胎发育毒性的比较研究

目的 对佐匹克隆及其主要杂质的斑马鱼胚胎发育毒性进行比较研究.方法 以斑马鱼胚胎为实验对象,在体视光学显微镜下观察佐匹克隆及其主要杂质(杂质A、B、C和2-氨基-5-氯吡啶)在不同暴露浓度时对斑马鱼胚胎发育情况的影响,包括胚胎致畸、致死情况的检测与统计.结果 佐匹克隆及其4个杂质对斑马鱼胚胎发育的毒性表型类似;毒性作用...     

Four-dimensional imaging and quantification of gene expression in early developing zebrafish (Danio rerio) embryos.

Four-dimensional (4D) imaging is a powerful tool for studying three-dimensional (3D) changes in an organism through time. Different imaging systems for obtaining 3D data from in vivo specimens have been developed but usually involved large and expensive machines. We successfully used a simple inverted compound microscope and a commercially available program to study and quantify in vivo changes in sonic hedgehog (shh) expression during early development in a green fluorescence protein (GFP) transgenic zebrafish (Danio rerio) line. We applied the 4D system to study the effect of 100 microM cadmium exposure on shh expression. In control zebrafish embryos, shh:GFP expression was detected at about 9 h post-fertilization (hpf) and increased steadily in the next 7 h, peaking at about 17 hpf and decreasing in the following 4 h. In the same time period, different shh expression volumes were observed in cadmium-treated and control embryos. Embryos affected by cadmium-exposure demonstrated a down-regulation in shh expression. The number of GFP-expressing cells measured by flow cytometry decreased, and expression of neurogenin-1, a downstream target of the shh signaling pathway, was down-regulated, providing additional supporting data on the effects of cadmium on shh. In summary, we demonstrated the setup of a 4D imaging system and its application to the quantification of gene expression.     

Fluorinated diiodine alkanes exert developmental toxicity on embryo‐larval stages of zebrafish strain AB via regulating the expression of the specific endocrine‐related genes

Fluorinated diiodine alkanes (FDIAs) are environmental pollutants, including octafluoro‐1,4‐diiodobutane (PFBDI), hexadecafluoro‐1,8‐diiodooctane (PFODI) and dodecafluoro‐1,6‐diiodohexane (PFHxDI). They showed an estrogenic effect in in vitro studies. However, little information is currently available regarding the toxicity of FDIAs in in vivo studies. Zebrafish (Danio rerio) is a vertebrate animal model that is increasingly used for toxicity and efficacy screening as well as for assessing the toxicity and safety of novel compounds, pollutants and pharmaceuticals. In the present study, we investigated the developmental toxicity of FDIAs (PFBDI, PFHxDI and PFODI) and the specific endocrine‐related gene expression in zebrafish embryos. The results revealed that all three FDIAs showed developmental toxicity on zebrafish embryos. The half‐maximal effective concentration values for PFBDI, PFHxDI and PFODI were 0.89 ± 0.07, 0.53 ± 0.04 and 0.04 ± 0.007 mm , respectively. PFHxDI exhibited the highest developmental toxicity compared with the other FDIAs. In addition, all three FDIAs significantly upregulated the expression of estrogen receptor (esr)1 and cytochrome P450 (CYP) 19b (CYP19b), but did not significantly affect the expression of esr2b, CYP17 and CYP19a in zebrafish. The upregulation effect of PFHxDI was greater than the effect of PFBDI and PFODI. This study furthers our knowledge on the effects of FDIAs on the developmental toxicity and the specific endocrine‐related gene expression in the embryo‐larval stages of zebrafish. Our results provided a preliminary insight into the toxicity of FDIAs in zebrafish, which will be of great relevance regarding future studies on FDIAs in the environment.     

Determination of acute and early life stage toxicity of fat-plant effluent using zebrafish (Danio rerio)

The present study examines the effects of an effluent from a fat plant (FP) on zebrafish (Danio rerio) embryos and larvae using the whole effluent toxicity testing methods (WET). The method is based on acute toxicity using 96-h larval mortality and chronic toxicity using endpoints such as the time to hatch, hatching success, deformity, growth rate, swim-up failure, accumulative mortality, and sex ratio. On the basis of larval mortality the 96-h LC(50) (the concentration was lethal to 50% of newly hatching zebrafish larvae) was 68.9%. In chronic toxicity test, newly fertilized embryos (<5-h old) were exposed to 1, 6, 12, 25, 50% effluent concentrations in a 24-h static renewal system at (27 +/- 0.5) degrees C until 15-day posthatch. The results showed that all chronic endpoints were significantly different from the control at 50% dilution. Embryos began to show lesions on third day at higher concentrations (12, 25, 50% FP effluent concentrations). Treatment group of 25% dilution showed delayed time to hatch. Morphological abnormalities were observed in newly hatched larvae at 25 and 50% FP effluent concentrations. At 25% dilution, sex ratio of larvae was alternated and there was feminization phenomenon. On the basis of the study, the FP effluent tested here may cause increasing embryotoxicity in the zebrafish embryos. We conclude that the test using zebrafish is feasible to evaluate both acute and chronic toxicities of industrial effluents.     

Cardiotoxicity evaluation of anthracyclines in zebrafish (Danio rerio)

Drug‐induced cardiotoxicity is a leading factor for drug withdrawals, and limits drug efficacy and clinical use. Therefore, new alternative animal models and methods for drug safety evaluation have been given great attention. Anthracyclines (ANTs) are widely prescribed anticancer agents that have a cumulative dose relationship with cardiotoxicity. We performed experiments to study the toxicity of ANTs in early developing zebrafish embryos, especially their effects on the heart. LC₅₀ values for daunorubicin, pirarubicin, doxorubicin (DOX), epirubicin and DOX‐liposome at 72 h post‐fertilization were 122.7 μM, 111.9 μM, 31.2 μM, 108.3 μM and 55.8 μM, respectively. At the same time, zebrafish embryos were exposed to ANTs in three exposure stages and induced incomplete looping of the heart tube, pericardia edema and bradycardia in a dose‐dependent manner, eventually leading to death. DOX caused the greatest heart defects in the treatment stages and its liposome reduced the effects on the heart, while daunorubicin produced the least toxicity. Genes and proteins related to heart development were also identified to be sensitive to ANT exposure and downregulated by ANTs. It revealed ANTs could disturb the heart formation and development. ANTs induced cardiotoxicity in zebrafish has similar effects in mammalian models, indicating that zebrafish may have a potential value for assessment of drug‐induced developmental cardiotoxicity. Copyright © 2014 John Wiley & Sons, Ltd.     

Oxidative stress‐mediated developmental toxicity induced by isoniazide in zebrafish embryos and larvae

Isoniazide (INH) is an important first‐line drug that is used to treat tuberculosis. However, the effect of INH on fetal growth has not yet been elucidated, and the mechanism of INH‐induced developmental toxicity is still unknown. In the present study, we employed zebrafish embryos and larvae to investigate the developmental toxicity of INH. The survival rates of the embryos and larvae as well as the hatching rates of embryos were significantly reduced. Morphological abnormalities, including spinal curvature, yolk retention, swimming bladder absence, tail bending and shorter body lengths were induced by INH. Histopathological analysis showed loose cell‐to‐cell contacts and large vacuoles in the larval hepatocytes. Thin intestinal walls, frayed gut villi and widespread cell lysis were observed in the intestines of the larvae in the higher concentration (8, 16 mm ) exposure groups. In addition, exposure to high doses (≥ 6 mm ) of INH significantly reduced the locomotor capacity of the zebrafish larvae. INH significantly increased the levels of reactive oxygen species and malondialdehyde and decreased the superoxide dismutase activity in zebrafish larvae, which suggested that oxidative stress was induced and that the antioxidant capacity was inhibited. Superoxide dismutase 1 and liver fatty acid‐binding protein mRNA levels were significantly downregulated, while the GSTP2 and cytochrome P450 3A mRNA levels were significantly upregulated in the INH‐exposed zebrafish larvae. The overall results indicated that INH caused a dose‐ and time‐dependent increase in developmental toxicity and that oxidative stress played an important role in the developmental toxicity induced by INH in zebrafish larvae. Copyright © 2017 John Wiley & Sons, Ltd.     

Thymol exposure mediates pro-oxidant shift by regulating Nrf2 and apoptotic events in zebrafish (Danio rerio) embryos

The biochemical process of oxidative stress is an integral mechanism of chemical toxicity, contributing to complex pathological disorders. Thymol (THY) has a wide range of therapeutic applications for several ailments, although a better understanding of signaling cues regulated by this compound is needed to address the mechanism of its action. To better perceive the mode of action, we investigated the potential impact of THY on zebrafish embryos, with special emphasis on ROS biogenesis. In this study, we exposed the zebrafish embryos to 25, 50 and 100μM of THY for 96 hours post fertilization (hpf). Noticeable teratogenic effects were observed upon assessing the survival rate (LC₅₀ = 42.35μM), hatching process, morphological exam and cardiac functions, thereby verifying the toxicity of THY on zebrafish embryos. Furthermore, we analyzed the effect of THY on the levels of ROS, mitochondrial membrane potential (ΔΨm) and immunofluorescence by DCFH-DA, JC-1, Casp-3-FITIC staining, respectively. Furthermore, we preformed the expressional analysis of Nrf2, superoxide dismutase-1 (SOD-1), catalase (CAT), Cytochrome P450 (CYP450) and apoptotic marker proteins (AIF, p53, Bax, Bcl-2, Casp-3 and Casp-9) in zebrafish embryos. As expected, we noticed a significant modulatory effect on the above-mentioned activities by THY. Collectively, our findings suggest that ROS might be the prime mediator responsible for THY-induced oxidative damage, thereby affecting the cellular defense mechanism and apoptotic events in zebrafish embryos.     

Mechanism of TiO2 nanoparticle‐induced neurotoxicity in zebrafish (Danio rerio)

Zebrafish (Danio rerio) has been used historically for evaluating the toxicity of environmental and aqueous toxicants, and there is an emerging literature reporting toxic effects of manufactured nanoparticles (NPs) in zebrafish embryos. Few researches, however, are focused on the neurotoxicity on adult zebrafish after subchronic exposure to TiO₂ NPs. This study was designed to evaluate the morphological changes, alterations of neurochemical contents, and expressions of memory behavior‐related genes in zebrafish brains caused by exposures to 5, 10, 20, and 40 μg/L TiO₂ NPs for 45 consecutive days. Our data indicated that spatial recognition memory and levels of norepinephrine, dopamine, and 5‐hydroxytryptamine were significantly decreased and NO levels were markedly elevated, and over proliferation of glial cells, neuron apoptosis, and TiO₂ NP aggregation were observed after low dose exposures of TiO₂ NPs. Furthermore, the low dose exposures of TiO₂ NPs significantly activated expressions of C‐fos, C‐jun, and BDNF genes, and suppressed expressions of p38, NGF, CREB, NR1, NR2ab, and GluR2 genes. These findings imply that low dose exposures of TiO₂ NPs may result in the brain damages in zebrafish, provide a developmental basis for evaluating the neurotoxicity of subchronic exposure, and raise the caution of aquatic application of TiO₂ NPs. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 163–175, 2016.     

DNA damage and oxidative stress induced by endosulfan exposure in zebrafish (Danio rerio)

Endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzo-dioxathiepin-3-oxide), an organochlorine pesticide, is prevalently used all around the world. It is considered to be a new candidate for the persistent organic pollutants group. Endosulfan residues in the environment may cause serious damage to ecosystems, especially in aquatic environments. The present study was conducted to investigate the effect of endosulfan on antioxidant enzymes [catalase (CAT) and superoxide dismutase (SOD)], reactive oxygen species (ROS) generation and DNA damage in zebrafish. Male and female zebrafish were separated and exposed to a control solution and four concentrations of endosulfan (0.01, 0.1, 1, and 10 μg L^?1) and were sampled after 7, 14, 21, and 28 days. It is noteworthy that the present research explored the correlation among the three indicators induced by endosulfan. Low endosulfan concentrations (0.01 μg L^?1) induced a slight increase of SOD and CAT activity, which kept ROS in a stable level. High endosulfan concentration (10 μg L^?1) induced excessive ROS production which exceeded the capacity of the cellular antioxidants and exhausted the enzyme including CAT and SOD. The DNA damage of zebrafish was evaluated by single-cell gel electrophoresis and was enhanced with increasing endosulfan concentration. In conclusion, the present study showed that endosulfan (0.01–10 μg L^?1) has toxic effects on zebrafish.     

Xenoestrogenic effects of ethinylestradiol in zebrafish (Danio rerio)

To assess the estrogenic effects of ethinylestradiol on zebrafish, zebrafish at different developmental stages (embryos, juveniles, and adults) were exposed to the synthetic hormone ethinylestradiol (EE2) in concentrations of 1, 10, and 100 ng/L for up to 33 days. Survival, hatching, length, weight, growth, condition, hepatosomatic index, gonadosomatic index, and vitellogenin (VTG) production were examined. Exposure of zebrafish juveniles and embryos to 100 ng EE2/L for up to 33 days had significant effects on survival, growth, and hatching. Two VTG fragments with molecular weights of approximately 140 and 170 kDa were detected with protein electrophoresis and Western blotting in the blood of exposed males and exposed and unexposed females, as well as in whole-body homogenates of exposed and unexposed juveniles. Significantly higher VTG concentrations (compared to controls) were measured in adults exposed to 10 and 100 ng EE2/L for 14 days, but not in fish exposed to 1 ng EE2/L. This study demonstrated that (1) zebrafish juveniles, larvae, and embryos are sensitive to the toxic effects of the endocrine disrupter EE2; (2) the effects on VTG production in adults are detected after exposure to environmentally relevant concentrations of EE2; (3) unexposed juvenile zebrafish produce measurable concentrations of VTG.     

Lack of Effect of 3,3′4,4′,5-Pentachlorobiphenyl (PCB 126) Throughout Gestation and Lactation on Multiple Fixed Interval–Fixed Ratio and DRL Performance in Rats

There is evidence that polychlorinated biphenyl (PCB) congeners have differential effects on endpoints of neurotoxicity depending on their chemical structure: specifically, that ortho-substituted congeners are neurotoxic while coplanar (dioxin-like) congeners are relatively inactive in producing neurotoxic effects. This study extends research on the effects of developmental exposure to the coplanar congener 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126) in Long–Evans rats. Dams were dosed with 0, 0.25, or 1 μg/kg/day Monday to Friday beginning 5 weeks before and continuing through gestation and lactation. The first 2-week breeding period produced 10, 7, and 13 litters in the three dose groups, respectively, used in behavioral assessment. Breeding females from the control and low-dose group that did not conceive were rebred after 76 days of dosing, producing 6 and 6 litters used in behavioral testing. One female and male from each litter were tested on a multiple fixed interval–fixed ratio schedule of reinforcement beginning at about 200 days of age, followed immediately by performance on a DRL schedule. There were no compelling indications of a treatment-related effect on either schedule. These same rats failed to exhibit PCB-induced impairment on a spatial delayed alternation task performed prior to the current experiments. This regimen of PCB exposure produced reduced weight gain between birth and weaning in Cohort 1, and decreased thyroxine levels and changes in hematology and serum biochemistry parameters in both cohorts. These data provide further evidence for absence of behavioral toxicity as a result of gestational and lactational exposure to a dioxin-like PCB congener. Published by Elsevier Science Inc.     

Oxidative stress induced by fluoroquinolone enrofloxacin in zebrafish (Danio rerio) can be ameliorated after a prolonged exposure

The purpose of our experiment was to evaluate the effect of enrofloxacin on biotransformation, oxidative stress and mRNA expression of related genes in fish as a non-target organisms. Zebrafish (Danio rerio) juveniles were treated with enrofloxacin at concentrations of 5, 10 and 500 μg/L for 14 days. A three-day-long test caused changes of catalytic activity of glutathione peroxidase and glutathione-S-transferase. Moreover, lipid peroxidation was observed at the highest concentration. No significant changes either in catalytic activity of antioxidant enzymes or elevated lipid peroxidation were observed from sampling day 7 on. mRNA expression of genes encoding antioxidant enzymes was also not affected by enrofloxacin after a 14-day exposure. This suggests the ability of D. rerio juveniles to adapt to enrofloxacin in a short time period. Moreover, enrofloxacin was not shown to affect collagen, cathepsin K, optic atrophy 1 and pyruvate kinase L/R mRNA expression in this study.     

Neurodevelopmental defects in zebrafish (Danio rerio) at environmentally relevant dioxin (TCDD) concentrations.

Persistent ecotoxicants, such as dioxin and PCBs, are thought to pose one of the greatest threats to public and ecological health in the industrial world. These compounds cause a range of macroscopic malformations, particularly to the craniofacial apparatus and cardiovascular system during vertebrate development. However, little is known about microscopic effects, especially on the sensitive early life stages or on the molecular basis of developmental neurotoxicity. Using zebrafish (Danio rerio), we have explored neurological deficits caused by early-life exposure to environmentally relevant concentrations of dioxin. We show, using a quantitative stereological technique, that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) substantially reduces the capacity for embryonic brain development, causing a 30% reduction in total neuronal number in the 168-h larval brain. Using transgenic GFP-expressing zebrafish lines, we link this to decreased expression of key developmentally regulated genes, namely neurogenin and sonic hedgehog. This disruption of neuronal development provides the basis for understanding the neurotoxic effects of these compounds.     

Acute alteration of cardiac ECG, action potential, I(Kr) and the human ether-a-go-go-related gene (hERG) K+ channel by PCB 126 and PCB 77

Polychlorinated biphenyls (PCBs) have been known as serious persistent organic pollutants (POPs), causing developmental delays and motor dysfunction. We have investigated the effects of two PCB congeners, 3,3′,4,4′-tetrachlorobiphenyl (PCB 77) and 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126) on ECG, action potential, and the rapidly activating delayed rectifier K⁺ current (I_Kr) of guinea pigs' hearts, and hERG K⁺ current expressed in Xenopus oocytes. PCB 126 shortened the corrected QT interval (QTc) of ECG and decreased the action potential duration at 90% (APD₉₀), and 50% of repolarization (APD₅₀) (P < 0.05) without changing the action potential duration at 20% (APD₂₀). PCB 77 decreased APD₂₀ (P < 0.05) without affecting QTc, APD₉₀, and APD₅₀. The PCB 126 increased the I_Kr in guinea-pig ventricular myocytes held at 36 °C and hERG K⁺ current amplitude at the end of the voltage steps in voltage-dependent mode (P < 0.05); however, PCB 77 did not change the hERG K⁺ current amplitude. The PCB 77 increased the diastolic Ca²⁺ and decreased Ca²⁺ transient amplitude (P < 0.05), however PCB 126 did not change. The results suggest that PCB 126 shortened the QTc and decreased the APD₉₀ possibly by increasing I_Kr, while PCB 77 decreased the APD₂₀ possibly by other modulation related with intracellular Ca²⁺. The present data indicate that the environmental toxicants, PCBs, can acutely affect cardiac electrophysiology including ECG, action potential, intracellular Ca²⁺, and channel activity, resulting in toxic effects on the cardiac function in view of the possible accumulation of the PCBs in human body.