The chlorinated AHR ligand 3,3',4,4',5-pentachlorobiphenyl (PCB126) promotes reactive oxygen species (ROS) production during embryonic development in the killifish (Fundulus heteroclitus)

Dioxin-like polychlorinated biphenyl 126 (PCB126) disrupts gut microbiota-host metabolic dysfunction in mice via aryl hydrocarbon receptor activation

Exposure to environmental pollutants, including dioxin-like pollutants, can cause numerous health issues. A common exposure route to pollutants is through contaminated foods, and thus the gastrointestinal system and gut microbiota are often exposed to high amounts of pollutants. Multiple studies have focused on the imbalance in intestinal microbiota composition caused by dioxin-like pollutants. Here, we examined the effects of polychlorinated biphenyl 126 (PCB126) on the composition and functions of gut microbes through metagenomic sequencing, and explored the correlations between microflora dysbiosis and aryl hydrocarbon receptor (AHR) signaling. Adult male wild-type and Ahr^-/- mice with a C57BL/6 background were weekly exposed to 50 μg/kg body weight of PCB126 for 8 weeks. Results showed that PCB126 had the opposite effect on gut microbiota composition and diversity in the wild-type and Ahr^-/- mice. Functional prediction found that PCB126 exposure mainly altered carbon metabolism and signal regulatory pathways in wild-type mice but impacted DNA replication and lipopolysaccharide biosynthesis in Ahr^-/- mice. In wild-type mice, PCB126 exposure induced liver injury, decreased serum lipid content, and delayed gastrointestinal motility, which were significantly correlated to several specific bacterial taxa, such as Helicobacter. Following AHR knockout, however, the holistic effects of PCB126 on the host were lessened or abolished. These results suggest that PCB126 may disrupt host metabolism and gut microbiota dynamics via AHR activation. Overall, our findings provide new insight into the complex interactions between host metabolism and gut microbiota, which may contribute to grouped assessment of environmental pollutants in the future.

2,3'4,4',5-Pentachlorobiphenyl induces hepatocellular carcinoma cell proliferation through pyruvate kinase M2-dependent glycolysis

Polychlorinated biphenyls (PCBs) are classic persistent organic pollutants (POPs) and are associated with the progression of many cancers, including liver cancer. The present study investigated the effect of 2,3'4,4',5-pentachlorobiphenyl (PCB118) on hepatocellular carcinoma cell proliferation and its underlying mechanisms. The results indicated that PCB118 exposure promotes the proliferation and glycolysis of hepatocellular carcinoma SMMC-7721 cells. Moreover, PCB118 exposure increased the expression level of pyruvate kinase M2 (PKM2) and its nuclear translocation, whereas treatment with PKM2 shRNA suppressed the induction of cell proliferation and glycolysis by PCB118. PCB118 stimulated reactive oxygen species (ROS) production by activating nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Treatment with the antioxidants N-acetyl-L-cysteine (NAC) and superoxide dismutase (SOD) prevented PCB118-induced effects on PKM2, cell proliferation and glycolysis. Furthermore, we found that PCB118 activated NADPH oxidase through the aryl hydrocarbon receptor (AhR) in SMMC-7721 cells. Consistently, treatment with AhR shRNA suppressed PCB118-induced effects on PKM2, cell proliferation and glycolysis. Overall, these results indicated that PCB118 promotes HCC cell proliferation via PKM2-dependent upregulation of glycolysis, which is mediated by AhR/NADPH oxidase-induced ROS production.

Modification and quantification of in vivo EROD live-imaging with zebrafish (Danio rerio) embryos to detect both induction and inhibition of CYP1A

The visualization of specific activation of the aryl hydrocarbon receptor (AhR) directly in the zebrafish embryo (Danio rerio) via live-imaging is a reliable tool to investigate the presence of dioxin-like substances in environmental samples. The co-existence of inducers and inhibitors of cytochrome P450-dependent monooxygenases (CYP1A) is typical of complex environmental mixtures and requires modifications of the in vivo EROD assay: For this end, zebrafish embryos were used to evaluate the EROD-modifying potentials of common single-compound exposures as well as binary mixtures with the PAH-type Ah-receptor agonist β-naphthoflavone. For chemical testing, chlorpyrifos and Aroclor 1254 were selected; β-naphthoflavone served as maximum EROD induction control. Chlorpyrifos (≤EC₁₀) could be documented to be a strong CYP1A inhibitor causing characteristic edema-related toxicity. Aroclor 1254 resulted in inhibition of CYP1A catalytic activity in a concentration- and specific time-dependent manner. Next to a fast CYP1A induction, CYP1A inhibition could also be detected after 3h short-term exposure of zebrafish embryos to chlorpyrifos. This communication also describes techniques for the quantification of fluorescence signals via densitometry as a basis for subsequent statistical assessment. The co-exposure approach with zebrafish embryos accounts for the nature of potential interaction between CYP1A inducers and inhibitors and thus pays tribute to the complexity of environmental mixtures. The co-exposure EROD live-imaging assay thus facilitates a better understanding of mixture effects and allows a better assessment and interpretation of (embryo) toxic potentials.

Molecular mechanisms of 3,3'4,4',5-pentachlorobiphenyl-induced epithelial-mesenchymal transition in human hepatocellular carcinoma cells

Polychlorinated biphenyls (PCBs) are classic persistent organic pollutants (POPs). Many studies have found a positive association between the progression of hepatocellular carcinoma (HCC) and PCBs exposure. However, the influence of PCBs on epithelial-mesenchymal transition (EMT) of HCC remains to be unclear. In this study, we explored the effect of PCB126 on EMT in HCC cells and its underlying mechanisms. The data showed that PCB126, exposing both Bel-7402 and SMMC-7721 cells for 48h, promoted EMT that was demonstrated by E-cadherin repression, up-regulation of N-cadherin and vimentin, and morphological alteration. We found that signal transducer and activator of transcription 3 (STAT3)/Snail1 signaling was activated after PCB126 exposure, and the addition of STAT3 inhibitor WP1066 blocked PCB126-induced down-regulation of E-cadherin as well as up-regulation of N-cadherin and vimentin. Moreover, PCB126 exposure increased pyruvate kinase M2 (PKM2) expression and its nuclear translocation, whereas treatment with PKM2 shRNA suppressed the activation of STAT3/Snail1 signaling and the alternation of EMT-related molecules (E-cadherin, N-cadherin and vimentin). Furthermore, this study indicated estrogen receptor (ER) and aryl hydrocarbon receptor (AhR) were involved in PCB126-induced effects on PKM2, STAT3/Snail1 signaling and EMT by according treatment using ER inhibitor ICI and AhR shRNA. Notably, PCB126-increased reactive oxygen species (ROS) production via AhR is associated with activation of PKM2/STAT3/Snail1 cascades and contributes to EMT. Taken together, these results indicated that PCB126 promotes EMT process of HCC cells via PKM2/STAT3/Snail1 signaling which is mediated by ER and AhR.

Polychlorinated Biphenyls Induce Oxidative DNA Adducts in Female Sprague-Dawley Rats

Polychlorinated biphenyls (PCBs) are organic chemicals that were traditionally produced and widely used in industry as mixtures and are presently formed as byproducts of pigment and dye manufacturing. They are known to persist and bioaccumulate in the environment. Some have been shown to induce liver cancer in rodents. Although the mechanism of the toxicity of PCBs is unknown, it has been shown that they increase oxidative stress, including lipid peroxidation. We hypothesized that oxidative stress-induced DNA damage could be a contributor for PCB carcinogenesis and analyzed several DNA adducts in female Sprague-Dawley rats exposed to 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153), and a binary mixture (PCB 126 + 153) for 14, 31, and 53 wks. Eight adducts were measured to profile oxidative DNA lesions, including 8-oxo-deoxyguanosine (8-oxo-dG), 1,N(6)-ethenodeoxyadenosine (1,N(6)-εdA), N(2),3-ethenoguanine (N(2),3-εG), 1,N(2)-ethenodeoxyguanosine (1,N(2)-εdG), as well as malondialdehyde (M1dG), acrolein (AcrdG), crotonaldehyde (CrdG), and 4-hydroxynonenal-derived dG adducts (HNEdG) by LC-MS/MS analysis. Statistically significant increases were observed for 8-oxo-dG and 1,N(6)-εdA concentrations in hepatic DNA of female rats exposed to the binary mixture (1000 ng/kg/day + 1000 μg/kg/day) but not in rats exposed to PCB 126 (1000 ng/kg/day) or PCB 153 (1000 μg/kg/day) for 14 and 31 wks. However, exposure to PCB 126 (1000 ng/kg/day) for 53 wks significantly increased 8-oxo-dG, 1,N(6)-εdA, AcrdG, and M1dG. Exposure to PCB 153 (1000 μg/kg/day) for 53 wks increased 8-oxo-dG, and 1,N(6)-εdA. Exposure to the binary mixture for 53 wks increased 8-oxo-dG, 1,N(6)-εdA, AcrdG, 1,N(2)-εdG, and N(2),3-εG significantly above control groups. Increased hepatic oxidative DNA adducts following exposure to PCB 126, PCB 153, or the binary mixture shows that an increase in DNA damage may play an important role in hepatic toxicity and carcinogenesis in female Sprague-Dawley rats.

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.

Regulation of Ahr signaling by Nrf2 during development: Effects of Nrf2a deficiency on PCB126 embryotoxicity in zebrafish (Danio rerio)

The embryotoxicity of co-planar PCBs is regulated by the aryl hydrocarbon receptor (Ahr), and has been reported to involve oxidative stress. Ahr participates in crosstalk with another transcription factor, Nfe2l2, or Nrf2. Nrf2 binds to antioxidant response elements to regulate the adaptive response to oxidative stress. To explore aspects of the crosstalk between Nrf2 and Ahr and its impact on development, we used zebrafish (Danio rerio) with a mutated DNA binding domain in Nrf2a (nrf2a(fh318/fh318)), rendering these embryos more sensitive to oxidative stress. Embryos were exposed to 2 nM or 5 nM PCB126 at 24 h post fertilization (prim-5 stage of pharyngula) and examined for gene expression and morphology at 4 days post fertilization (dpf; protruding - mouth stage). Nrf2a mutant eleutheroembryos were more sensitive to PCB126 toxicity at 4 dpf, and in the absence of treatment also displayed some subtle developmental differences from wildtype embryos, including delayed inflation of the swim bladder and smaller yolk sacs. We used qPCR to measure changes in expression of the nrf gene family, keap1a, keap1b, the ahr gene family, and known target genes. cyp1a induction by PCB126 was enhanced in the Nrf2a mutants (156-fold in wildtypes vs. 228-fold in mutants exposed to 5 nM). Decreased expression of heme oxygenase (decycling) 1 (hmox1) in the Nrf2a mutants was accompanied by increased nrf2b expression. Target genes of Nrf2a and AhR2, NAD(P)H:quinone oxidoreductase 1 (nqo1) and glutathione S-transferase, alpha-like (gsta1), showed a 2-5-fold increase in expression in the Nrf2a mutants as compared to wildtype. This study elucidates the interaction between two important transcription factor pathways in the developmental toxicity of co-planar PCBs.

Evolved resistance to PCB- and PAH-induced cardiac teratogenesis, and reduced CYP1A activity in Gulf killifish (Fundulus grandis) populations from the Houston Ship Channel, Texas

The Houston Ship Channel (HSC), connecting Houston, Texas to Galveston Bay and ultimately the Gulf of Mexico, is heavily industrialized and includes several areas that have historically been identified as containing significant levels of mercury, dioxins, furans, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). Gulf killifish, Fundulus grandis, inhabit this entire estuarine system, including the most contaminated areas. F. grandis is the sister species of the well-established estuarine model organism Fundulus heteroclitus, for which heritable resistance to both PCB and PAH toxicity has been documented in several populations. F. grandis collected from two Superfund sites on the HSC and from a reference population were used to establish breeding colonies. F1 embryos from HSC populations were approximately 1000-fold more resistant to PCB126- and 2-5-fold more resistant to coal tar-induced cardiovascular teratogenesis, relative to embryos from the reference population. Reciprocal crosses between reference and contaminated populations exhibit an intermediate level of resistance, confirming that observed protection is genetic and biparentally inherited. Ethoxyresorufin-O-deethylase (EROD) data confirm a reduction in basal and induced cytochrome P4501A (CYP1A) activity in resistant populations of F. grandis. This result is consistent with responses previously described for resistant populations of F. heteroclitus, specifically a recalcitrant aryl hydrocarbon receptor (AHR) pathway. The decreased levels of cardiovascular teratogenesis, and decrease in CYP1A inducibility in response to PCB126 and a PAH mixture, suggest that HSC F. grandis populations have adapted to chronic contaminants exposures via a mechanism similar to that previously described for F. heteroclitus. To the best of our knowledge, this is the first documentation of evolved pollution resistance in F. grandis. Additionally, the mechanistic similarities between the population adaptation observed in this study and previous work in F. heteroclitus suggest that genetic variation predating the evolutionary divergence of these two species may best explain the apparent rapid parallel evolution of pollution resistance in genetically and geographically distinct species and populations.

Applicability of the TCDD-TEQ approach to predict sublethal embryotoxicity in Fundulus heteroclitus

The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxic equivalent quantity (TCDD-TEQ) approach was used successfully to predict lethal embryotoxicity in salmonids, but its applicability to sublethal effects of mixtures of organohalogenated compounds in other fish species is poorly known. The sublethal toxicity of two dioxin-like compounds (DLCs), 3,3',4,4'-tetrachlorobiphenyl (PCB77) and 2,3,4,7,8-pentachlorodibenzofuran (2,3,4,7,8-PnCDF), two non-dioxin-like (NDL) polychlorinated biphenyls (PCBs), 2,2',5,5'-tetrachlorobiphenyl (PCB52) and 2,3,3',4',6-pentachlorobiphenyl (PCB110), and of Aroclor 1254, a complex commercial mixture of PCBs, was assessed in Fundulus heteroclitus embryos exposed by intravitelline injection. At 16 days post-fertilization, the two DLCs and Aroclor 1254 altered prey capture ability in addition to inducing classical aryl hydrocarbon receptor-mediated responses: ethoxyresorufin-O-deethylase (EROD) induction, craniofacial deformities and reduction in body length. None of these responses was induced by the two NDL PCBs, at doses up to 5400 ng g(-1)wet weight. Dose-response curves for prey capture ability for the 2 DLCs tested were not parallel to that of TCDD, violating a fundamental assumption for relative potency (ReP) estimation. Dose-response curves for EROD induction were parallel for 2,3,4,7,8-PnCDF and TCDD, but the ReP of 2,3,4,7,8-PnCDF for F. heteroclitus was 5-fold higher than the World Health Organization (WHO) fish toxic equivalent factor (TEF) based on embryolethality in salmonids. The chemically derived TCDD-TEQs of Aroclor 1254, calculated using 3,3',4,4',5-pentachlorobiphenyl (PCB126) concentrations and it ReP for F. heteroclitus, overestimated its potency to induce EROD activity possibly due to antagonistic interactions among PCBs. This study highlights the limitations of using TEFs based on salmonid toxicity data alone for risk assessment to other fish species. There is a need to assess the variability of RePs of DLCs in different species for a variety of endpoints and to better understand interactions between DLCs and other toxic chemicals.

Environmental contaminant effects on juvenile striped bass in the San Francisco Estuary, California, USA

The decline of pelagic organisms in the San Francisco Estuary (SFE) (California, USA) is attributed to several factors, including water diversions, invasive species, and exposure to environmental toxicants. The present study evaluated the effects of environmental contaminants on liver vitellogenin, metallothionein, 7-ethoxyresorufin-O-deethylase (EROD), and benzyloxyresorufin O-deethylase (BROD) activity in juvenile striped bass (Morone saxitilis) in the SFE. Analysis of juvenile striped bass liver extracts revealed site-specific elevations of vitellogenin, metallothionein, and EROD biomarkers across the estuary. Although some striped bass in the estuary showed EROD activity similar to unhandled hatchery controls, several sites in the estuary showed significantly higher EROD activity that was in the range of beta-naphthoflavone (BNF)-injected, positive controls. Overall, EROD activity averaged 283% higher in estuary fish than in hatchery controls. Chemical analyses of extracts from semipermeable membrane devices (SPMDs) deployed in the estuary for one month showed elevated polyaromatic hydrocarbon (PAH) levels. Semipermeable membrane devices extract injections-induced metallothionein and BROD in striped bass livers. These data show that environmental exposures are impacting EROD and other biomarkers in the SFE striped bass population. Previous studies in our laboratory have associated poor larval development with maternal transfer of environmental contaminants. Further studies are needed to monitor contaminant exposures by the use of biomarkers and to integrate them into a more effective pelagic species recovery plan in the SFE.

Decontamination trends in the aquacultured fish gilthead seabream (Sparus aurata) after feeding long-term a PCDD/F spiked feed

Aquacultured fish gilthead seabream (Sparusaurata), previously exposed to low levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) trough the diet for a 13 months period, were fed on a clean feed for another 22 months. Gilthead seabream is a protandrous hermaphrodite species and this "decontamination" period coincided with the stages of sex differentiation, maturity and reproduction of the fish. PCDD/F levels in the fish tissues (i.e. muscle, liver, perivisceral fat and gonads), expressed in pg WHO-TEQg⁻¹ fresh weight, showed a general decreasing trend during the "decontamination" period. However, this general trend varied among tissues and was also dependent on sex and lipid contents. Toxicological effects affecting fish behaviour and hepatic marker responses were also evaluated. The results pointed out that exposure to PCDD/Fs did not have an impact on fish development and reproduction, since the proportion of sexes found after the sex reversal process was within the normal range described for this species. In addition, long-term exposure to low PCDD/F levels did not significantly affect the response of most of the biochemical markers considered. On the contrary, some of them (e.g. EROD activity) showed variations in their responses during the sex differentiation process and onwards. Finally, the hepatic AhR mRNA levels increased during dioxin exposure but they returned to values typical for non-exposed fish after the "decontamination" period.

Precision-Cut Liver Slices of Salmo salar as a tool to investigate the oxidative impact of CYP1A-mediated PCB 126 and 3-methylcholanthrene metabolism

Fish isolated cell systems have long been used to predict in vivo toxicity of man-made chemicals. In present study, we tested the suitability of Precision-Cut Liver Slices (PCLS) as an alternative to these models that allows the evaluation of a global tissue response to toxicants, to investigate oxidative stress response to cytochrome P450 1A (CYP1A) induction in fish liver. PCLS of Salmo salar were exposed for 21 h to increasing doses of 3-methylcholanthrene (3-MC) and Polychlorobiphenyl 126 (PCB 126). 3-MC (25 μM) strongly induced CYP1A transcription. In dose-response analysis (25-100 μM), EROD activity was strongly increased at intermediate 3-MC concentrations. We found the counter-intuitive decline of EROD at the highest 3-MC doses to result from reversible competition with ethoxyresorufin. No increases of H(2)O(2) production, antioxidant enzymes activities or oxidative damage to lipids were found with 3-MC treatments. PCLS subjected to PCB 126 (2-200 nM) showed increased contamination levels and a parallel increased CYP1A mRNA synthesis and EROD activity. H(2)O(2) production tended to increase but no oxidative damage to lipids was found. As antioxidant enzymes activities declined at the highest PCB 126 dose, it is suggested that longer incubation periods could be required to generate oxidative stress in PCLS.

Hydroethidine- and MitoSOX-derived red fluorescence is not a reliable indicator of intracellular superoxide formation: another inconvenient truth

Hydroethidine (HE; or dihydroethidium) is the most popular fluorogenic probe used for detecting intracellular superoxide radical anion. The reaction between superoxide and HE generates a highly specific red fluorescent product, 2-hydroxyethidium (2-OH-E(+)). In biological systems, another red fluorescent product, ethidium, is also formed, usually at a much higher concentration than 2-OH-E(+). In this article, we review the methods to selectively detect the superoxide-specific product (2-OH-E(+)) and the factors affecting its levels in cellular and biological systems. The most important conclusion of this review is that it is nearly impossible to assess the intracellular levels of the superoxide-specific product, 2-OH-E(+), using confocal microscopy or other fluorescence-based microscopic assays and that it is essential to measure by HPLC the intracellular HE and other oxidation products of HE, in addition to 2-OH-E(+), to fully understand the origin of red fluorescence. The chemical reactivity of mitochondria-targeted hydroethidine (Mito-HE, MitoSOX red) with superoxide is similar to the reactivity of HE with superoxide, and therefore, all of the limitations attributed to the HE assay are applicable to Mito-HE (or MitoSOX) as well.

Polluted-site killifish (Fundulus heteroclitus) embryos are resistant to organic pollutant-mediated induction of CYP1A activity, reactive oxygen species, and heart deformities

Exposure to coplanar polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) can adversely affect fish embryonic development, induce expression of cytochrome P4501A (CYP1A), and increase reactive oxygen species (ROS) production, effects believed to be mediated by the aryl hydrocarbon receptor (AHR). Killifish (Fundulus heteroclitus) populations in New Bedford Harbor, Massachusetts, USA (NBH) and Newark Bay, New Jersey, USA (NB) are generationally exposed to coplanar PCBs and PAHs and have developed resistance to PCB mediated induction of CYP1A. We hypothesized that fish resistant to CYP1A induction would also exhibit resistance to PCB and PAH induced ROS production and teratogenesis. Killifish embryos from two contaminated (NB, NBH) and two reference-site populations were exposed to vehicle or 3,3'4,4'5-pentachlorobiphenyl (PCB126) or 3-methylcholanthrene (3-MC) and evaluated for in ovo CYP1A activity, heart deformities, and ROS production. Both chemicals significantly increased in ovo ethoxyresorufin-O-deethylase (EROD) and ROS production in reference-site embryos. These chemicals provoked only moderate induction of in ovo EROD in NBH and NB embryos, and neither PCB126 nor 3-MC induced ROS production in these populations. Similarly, heart deformities were significantly induced by PCB126 in reference-site embryos, but had no significant effects on NB and NBH animals. These results indicate that fish resistant to CYP1A induction also exhibit decreased sensitivity to PCB126 and 3-MC-induced ROS production and teratogenesis. These findings further our understanding of toxicant resistance by demonstrating that reduced response to coplanar PCBs and PAHs extends beyond resistance to CYP1A induction to resistance to the physiological and teratogenic effects of these toxicants, responses that undoubtedly contribute to the increased survival of killifish inhabiting contaminated sites.

Development of ecotoxicoproteomics on the freshwater amphipod Gammarus pulex: identification of PCB biomarkers in glycolysis and glutamate pathways

PCBs are persistent organic pollutants largely distributed in the biosphere. Although their effects on vertebrates are well described, little is known about their action on freshwater invertebrate's metabolism. Gammarus pulex (Linné) was selected as an indicator model to develop a proteomic approach in order to characterize the effects of PCBs on the protein profile of this freshwater crustacean. Sublethal coplanar PCBs exposition and related 2D gel were performed. More than 560 spots were detected and a total of 21 proteins exhibiting significant expression differences in PCB exposed to G. pulex were identified by mass spectrometry. Database searches were conducted to relate the results to well-known metabolic pathways (pentose phosphate, cytoskeleton, energy, etc.). In particular, glyceraldehyde 3-phosphate dehydrogenase and arginine kinase were found to be sensitive to the PCB exposition of G. pulex. The aim of the present study was to assess the biochemical responses and the metabolic changes in G. pulex following intoxication to coplanar PCB congeners CB77 and CB169 by a proteomic approach. This approach allowed us, by the identification of key proteins, to highlight important biochemical mechanisms disturbed by the presence of these contaminants in G. pulex.

Induction of gene pattern changes associated with dysfunctional lipid metabolism induced by dietary fat and exposure to a persistent organic pollutant

Environmental modulators of chronic diseases can include nutrition, lifestyle, as well as exposure to environmental toxicants such as persistent organic pollutants. A study was designed to explore gene expression changes as affected by both dietary fat and exposure to the polychlorinated biphenyl PCB77. Mice were fed for 4 months diets enriched with high-linoleic acid oils (20% and 40% as calories), and during the last 2 months half of each group was exposed to PCB77. Ribonucleic acids (RNA) were extracted from liver tissue to determine gene expression changes using DNA microarray analysis. Our microarray data demonstrated a significant interaction between dietary fat and PCB exposure. Deregulated genes were organized into patterns describing the interaction of diet and PCB exposure. Annotation of the deregulated genes matching these probe sets revealed a significant high-fat mediated induction of genes associated with fatty acid metabolism, triacylglycerol synthesis and cholesterol catabolism, which was down-regulated in animals exposed to PCB77. Many of these genes are regulated by the peroxisome proliferator activated receptor-alpha (PPARalpha), and changes in PPARalpha gene expression followed the same gene pattern as described above. These results provide insight into molecular mechanisms of how dietary fat can interact with environmental pollutants to compromise lipid metabolism.

Protective effects of vitamin E against 3,3',4,4',5-pentachlorobiphenyl (PCB126) induced toxicity in zebrafish embryos

3,3',4,4',5-Pentachlorinated biphenyls 126 (PCB126) is a global environmental contaminant that can induce cellular oxidative stress. We investigated whether vitamin E can protect against toxicity from PCB126 during zebrafish (Danio rerio) development. Zebrafish embryos were exposed to 100nM PCB126 and compared with a second group that was co-exposed with 100muM vitamin E until 5 days post fertilization. PCB126 induced pericardial sac edema, yolk sac edema, and growth retardation in zebrafish embyos. In contrast, vitamin E co-exposure group did not show any gross changes. Real-time PCR results showed that vitamin E co-exposure group were restored to control group for the expression levels of heat shock protein 70 Cognate, aryl hydrocarbon receptor type-2, cytochrome P450 1A, and superoxide dismutase-1. These data give insights into the use of vitamin E to reduce PCB126-mediated toxicity and into the use of zebrafish embryos for exploring mechanisms underlying the oxidative potential of AHR agonists.

PCB77 (3,3',4,4'-tetrachlorobiphenyl) co-exposure prolongs CYP1A induction, and sustains oxidative stress in B(a)P-exposed turbot, Scophthalmus maximus, in a long-term study

Cytochrome P4501A (CYP1A), benzo(a)pyrene (B(a)P) activation and biliary elimination, phase II activities, and peroxisomal and antioxidant activities of turbot (Scophthalmus maximus) were studied in a long-term controlled experiment. Fish were serially exposed in water on day 1 and on completion of months 3, 6 and 9 to 0.1, 0.2, 0.1 and 0.1mg B(a)P/l, respectively, while another group was identically treated with additional PCB77 (3,3',4,4'-tetrachlorobiphenyl) at 1% of concomitant B(a)P (w/w). Temporally persistent responses were obtained by sampling on week 3 and 3 months from each latest exposure. Serial exposure to B(a)P+PCB77 progressively induced liver 7-ethoxyresorufin O-deethylase (EROD) activity and CYP1A protein levels (ELISA, western blotting) towards months 9, 12 and gill EROD activity on month 12. It associated with an apparent increase in liver benzo(a)pyrene diol epoxide (BPDE)-DNA adduct levels (ultrasensitive enzyme radioimmunoassay), and elevated bile B(a)P metabolite levels on month 9 females as compared to males. In contrast, B(a)P alone did not cause (p>0.05) comparable effects on liver EROD, CYP1A, adducts nor on bile metabolites. Both exposed groups demonstrated evidence for lasting oxidative stress as hepatic superoxide dismutase, catalase and glutathione peroxidase activities were significantly altered (p<0.05) with symptomatic pro-oxidant associations among them. Both treatments affected liver somatic index similarly (increase on month 3, decrease on month 9 in males). Continued exposure on month 18 (0.2mg B(a)P/l, 1% PCB77) followed by sampling 6 months later showed sustained induction (p<0.001) of hepatic EROD in B(a)P+PCB77 group, which was not seen in B(a)P alone treatment. Thus, PCB77 co-exposure prolonged CYP1A induction and contributed to a persistent oxidative challenge in B(a)P-exposed turbot. The results indicate synergistic effects of polycyclic aromatic hydrocarbon (PAH) and polychlorinated biphenyl (PCB) exposure in the aquatic environment.

Effects of diazinon on mummichog (Fundulus heteroclitus) larvae produced from eggs differentially treated with PCB126

During their formation, fish eggs receive a load of contaminants including polychlorinated biphenyls (PCBs) from their mother and then, after spawning, are exposed to pesticides present in water. This is the first study investigating the interaction between PCBs and organophosphorous pesticides in fish. The effect of diazinon was evaluated in mummichog (Fundulus heteroclitus) larvae produced from eggs differentially treated with 3,3',4,4',5 pentachlorobiphenyl (PCB126). A few hours after fertilization, eggs were treated topically with a solution of PCB126 (100 pg/microl) in dimethyl sulfoxide (DMSO) (Group P), DMSO (Group D), or not treated (Group N). Newly hatched larvae from Groups P and D were exposed to diazinon (125-12,900 ng/L) in saltwater and Group N larvae to saltwater alone. Diazinon caused a dose-responsive inhibition of cholinesterase (ChE) activity at environmentally realistic concentrations (> or =361 ng/L), with up to 85% inhibition at 12,900 ng/L. Body length was also inversely related to diazinon at concentrations > or =361 ng/L and was significantly reduced (by 4%) at 12,900 ng/L compared to controls. Mummichog larvae were highly sensitive to PCB126 with an eightfold induction of the activity of ethoxyresorufin-O-deethylase at a dose of 710 pg PCB126 or 3.6 pg TCDD-TEQ/g wet weight. Treatment with PCB126 also caused a slight reduction in body length but no effect on ChE activity. This study indicates that the effects of PCB126 and diazinon on body length are cumulative because no significant synergistic or antagonistic interactions were observed. Longer term studies with several doses of PCB126 are needed to fully assess the overall impact of joint exposure to diazinon and PCB126 on growth and survival of fish larvae.

Fundulus as the premier teleost model in environmental biology: opportunities for new insights using genomics

A strong foundation of basic and applied research documents that the estuarine fish Fundulus heteroclitus and related species are unique laboratory and field models for understanding how individuals and populations interact with their environment. In this paper we summarize an extensive body of work examining the adaptive responses of Fundulus species to environmental conditions, and describe how this research has contributed importantly to our understanding of physiology, gene regulation, toxicology, and ecological and evolutionary genetics of teleosts and other vertebrates. These explorations have reached a critical juncture at which advancement is hindered by the lack of genomic resources for these species. We suggest that a more complete genomics toolbox for F. heteroclitus and related species will permit researchers to exploit the power of this model organism to rapidly advance our understanding of fundamental biological and pathological mechanisms among vertebrates, as well as ecological strategies and evolutionary processes common to all living organisms.

The role of caveolin-1 in PCB77-induced eNOS phosphorylation in human-derived endothelial cells

Polychlorinated biphenyls (PCBs) may contribute to the pathology of atherosclerosis by activating inflammatory responses in vascular endothelial cells. Endothelial nitric oxide synthase (eNOS) is colocalized with caveolae and is a critical regulator of vascular homeostasis. PCBs may be proatherogenic by causing dysfunctional eNOS signaling. The objective of this study was to investigate the role of caveolin-1 in PCB-induced endothelial dysfunction with a focus on mechanisms associated with eNOS signaling. Cells derived from an immortalized human vascular endothelial cell line were treated with PCB77 to study nitrotyrosine formation through eNOS signaling. Phosphorylation studies of eNOS, caveolin-1, and kinases, such as Src, phosphatidylinositol 3-kinase (PI3K), and Akt, were conducted in cells containing either functional or small-interfering RNA-silenced caveolin-1 protein. We also investigated caveolin-1-regulated mechanisms associated with PCB-induced markers of peroxynitrite formation and DNA binding of NF-kappaB. Cellular exposure to PCB77 increased eNOS phosphorylation and nitric oxide production, as well as peroxynitrite levels. A subsequent PCB-induced increase in NF-kappaB DNA binding may have implications in oxidative stress-mediated inflammatory mechanisms. The activation of eNOS by PCB77 treatment was blocked by inhibitors of the Src/PI3K/Akt pathway. PCB77 also increased phosphorylation of caveolin-1, indicating caveolae-dependent endocytosis. Caveolin-1 silencing abolished both the PCB-stimulated Akt and eNOS phosphorylation, suggesting a regulatory role of caveolae in PCB-induced eNOS signaling. These findings suggest that PCB77 induces eNOS phosphorylation in endothelial cells through a Src/PI3K/Akt-dependent mechanism, events regulated by functional caveolin-1. Our data provide evidence that caveolae may play a critical role in regulating vascular endothelial cell activation and toxicity induced by persistent environmental pollutants such as coplanar PCBs.

The effects of copper and benzo[a]pyrene on retinoids and reproduction in zebrafish

This study examines whether a link exists between toxicant exposure, retinoids and reproduction in fish. Zebrafish were fed a control diet (8.1 microg Cu/g diet, 0 microg benzo[a]pyrene/g diet) or diets containing elevated copper (100 microg, 500 microg and 1000 microg Cu/g diet) or benzo[a]pyrene (B[a]P; 30 and 150 microg B[a]P/g diet) for 260 days. Toxicant-supplemented diets did not affect growth or mortality rates. While whole body retinoid levels in control zebrafish decreased during the experiment, females exposed to Cu or B[a]P for 200 days or more experienced additional losses of retinyl esters (45-100% depleted) and retinal (45% depleted in B[a]P-fed fish). Despite the reduced retinoids, Cu and B[a]P did not effect reproduction with respect to the number of eggs spawned, fertilization rates or egg retinal content (retinal was instead increased 55-65% in eggs from B[a]P-fed fish). There were no apparent deformities observed in 36 h post fertilization embryos from any treatment. It appears that although internal retinoid stores were depleted in adults, dietary retinoids were sufficient to meet the daily requirement for retinal deposition in the eggs and retinoic acid synthesis. This study has shown that retinoid levels in female zebrafish are sensitive to Cu and B[a]P, and are a good indicator of long-term exposure. It also brings to light the resiliency of the retinoid system in fish and the importance of the diet on the toxicological response. Specifically that dietary retinoids appear to support normal reproduction in the absence of internal retinoid stores.