Role of oxidative stress and antioxidant defense in 3,3',4,4',5-pentachlorobiphenyl-induced toxicity and species-differential sensitivity in chicken and duck embryos

Al2O3 nanoparticles trigger the embryonic hepatotoxic response and potentiate TNF-α-induced apoptosis-modulatory effect of p38 MAPK and JNK inhibitors

Recent evidences illustrated that the release of aluminum oxide nanoparticles (Al₂O₃-NPs) into the biosphere may pose risk to the environment and cause adverse effects on living organisms including humans. The current study assessed the hepatotoxic effects of Al₂O₃-NPs on developing chicken embryo and cell culture models. Results demonstrated that Al₂O₃-NPs exposure causes histological abnormalities and increased the level of tissue damage markers (ALP, AST, and ALT) in the embryonic liver. Furthermore, increased oxidative stress (TBARS) and impaired function of antioxidant enzymes (SOD, CAT, and GPx) were also observed. Moreover, it adversely affects red blood cells (RBC) morphology, liver metabolism, and stress response gene expression (HO-1 and NQO-1). Dose-dependent ROS generation and cytotoxic response in addition to potentiating effect on tumor necrosis factor alpha (TNF-α)-induced apoptosis (caspase-3 activity) were also observed. Inhibition of p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinase (JNK) pathways modulates Al₂O₃-NPs-induced apoptosis in HepG2 cells. Novel mechanisms behind embryonic hepatotoxicity, cytotoxic potentiating effects, and possible prevention strategies have been explored.

Bioaccumulation and physiological responses of the turtle Chelydra serpentina exposed to polychlorinated biphenyls during early life stages

Despite the North American production ban of polychlorinated biphenyls (PCBs), PCBs are ubiquitous in the environment and in wildlife tissues. Chelydra serpentina serpentina (common snapping turtle) have been used as environmental indicators of PCB pollution upwards of 40 years given their high site fidelity and high trophic position. Despite their long use as indicators of PCB contamination, the effects of PCBs in reptiles remain largely unknown. In this study, we performed two experiments to assess i) bioaccumulation and ii) toxicity of PCBs to 1-month-old C. s. serpentina, to aid in interpretation of PCB burdens. Food pellets were spiked at an environmentally relevant concentration (0.45 μg/g) of the PCB mixture Aroclor 1254 to model hepatic bioaccumulation and depuration, through feeding, for 31 days and clean food for 50 days, respectively. No significant differences in PCB concentrations were observed in liver tissue over the course of the experiment, suggesting that juvenile turtles can likely metabolize low environmentally occurring concentrations of PCBs. Additionally, a dose-response experiment, performed to determine hepatic toxicity and bioaccumulation in juvenile C. s. serpentina, showed a 1.8-fold increase in hepatic expression of cyp1a when fed A1254-spiked pellets (12.7 μg/g; range 0-12.7 μg/g). This gene induction correlates with the significant increase of group 3 PCB congeners measured in the turtle liver, which are known to be metabolized by CYP1A. This study indicates that C. s. serpentina may be a good environmental indicator for PCBs, while more research is needed to assess the effects of body burdens in wild C. s. serpentina.

Nutritional modulation of the antioxidant capacities in poultry: the case of selenium

Natural antioxidants play important roles in maintaining chicken health, productive and reproductive performance of breeders, layers, rearing birds, and growing broilers. There is a wide range of antioxidant molecules in the body: vitamin E, carotenoids, selenium, ascorbic acid, coenzyme Q, carnitine, taurine, antioxidant enzymes, etc. In the body all antioxidants work together to create the antioxidant network called "antioxidant systems" with Se being the "chief-executive." Analysis of the current data on selenium roles in antioxidant defenses in poultry clearly showed its modulatory effect at the level of breeders, developing embryos, newly hatched chicks, and postnatal chickens. On the one hand, Se is involved in the expression and synthesis of 25 selenoproteins, including GSH-Px, TrxR, and SepP. On the other hand, Se affects non-enzymatic (vitamin E, CoQ, and GSH) and enzymatic (SOD) antioxidant defense mechanisms helping build strong antioxidant defenses. Se efficiency depends on the level of supplementation and form of dietary Se, organic Se sources being more effective modulators of the antioxidant systems in poultry than sodium selenite. Moreover, Se levels in eggs from some wild avian species are close to those found in chicken eggs after 0.3 ppm organic Se supplementation and a search for most effective dietary form of organic Se is a priority in poultry nutrition. Antioxidant/prooxidant (redox) balance of the gut and the role/interactions of Se and microbiota in maintaining gut health would be a priority for future poultry research.

α-Tocopherol-ascorbic acid hybrid antioxidant based cationic amphiphile for gene delivery: Design, synthesis and transfection

Natural antioxidants and vitamins have potential to protect biological systems from peroxidative damage induced by peroxyl radicals, α-tocopherol (Vitamin E, lipid soluble) and ascorbic acid (vitamin C, water soluble), well known natural antioxidant molecules. In the present study we described the synthesis and biological evaluation of hybrid of these two natural antioxidants with each other via ammonium di-ethylether linker, Toc-As in gene delivery. Two control cationic lipids N14-As and Toc-NOH are designed in such a way that one is with ascorbic acid moiety and no tocopherol moiety; another is with tocopherol moiety and no ascorbic acid moiety respectively. All the three cationic lipids can form self-assembled aggregates. The antioxidant efficiencies of the three lipids were compared with free ascorbic acid. The cationic lipids (Toc-As, N14-As and Toc-NOH) were formulated individually with a well-known fusogenic co-lipid DOPE and characterization studies such as DNA binding, heparin displacement, size, charge, circular dichroism were performed. The biological characterization studies such as cell viability assay and in vitro transfection studies were carried out with the above formulations in HepG2, Neuro-2a, CHO andHEK-293T cell lines. The three formulations showed their transfection efficiencies with highest in Toc-As, moderate inN14-As and least in Toc-NOH. Interestingly, the transfection efficiency observed with the antioxidant based conjugated lipid Toc-As is found to be approximately two and half fold higher than the commercially available lipofectamine 2000 at 4:1 charge ratio in Hep G2 cell lines. In the other cell lines studied the efficiency of Toc-As is found to be either higher or similarly active compared to lipofectamine 2000. The physicochemical characterization results show that Toc-As lipid is showing maximum antioxidant potency, strong binding with pDNA, least size and optimal zeta potential. It is also found to be least toxic in all the cell lines studied especially in Neuro-2a cell lines when compared to other two lipids. In summary, the designed antioxidant lipid can be exploited as a delivering system for treating ROS related diseases such as malignancy, brain stroke, etc.

EROD activity, chromosomal damage, and oxidative stress in response to contaminants exposure in tree swallow (Tachycineta bicolor) nestlings from Great Lakes Areas of Concern

Tree swallow, Tachycineta bicolor, nestlings were collected from 60 sites in the Great Lakes, which included multiple sites within 27 Areas of Concern (AOCs) and six sites not listed as AOCs from 2010 to 2014. Nestlings, approximately 12 days-of-age, were evaluated for ethoxyresorufin-O-dealkylase (EROD) activity, chromosomal damage, and six measures of oxidative stress. Data on each of these biomarkers were divided into four equal numbered groups from the highest to lowest values and the groups were compared to contaminant concentrations using multivariate analysis. Contaminant concentrations, from the same nestlings, included polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), perfluorinated compounds (PFCs), and 17 elements. Alkylated polycyclic aromatic hydrocarbons (aPAHs) and parent PAHs (pPAHs) were measured in pooled nestling dietary samples. Polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and pesticides were measured in sibling eggs. Concentrations of aPAHs, pPAHs, chlordane, dieldrin, heptachlor, and PCBs, in that order, were the major contributors to the significant differences between the lowest and highest EROD activities; PFCs, PBDEs, the remaining pesticides, and all elements were of secondary importance. The four categories of chromosomal damage did not separate out well based on the contaminants measured. Concentrations of aPAHs, pPAHs, heptachlor, PCBs, chlordane, and dieldrin were the major contributors to the significant differences between the lowest and highest activities of two oxidative stress measures, total sulfhydryl (TSH) activity and protein bound sulfhydryl (PBSH) activity. The four categories of thiobarbituric acid reacting substances (TBARS), oxidized glutathione (GSSG), reduced glutathione (GSH), and the ratio of GSSG/GSH did not separate well based on the contaminants measured.

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, oxidative stress, and related gene expression induced by dioxin-like PCB 126 in zebrafish (Danio rerio)

3,3',4,4',5-Pentachlorobiphenyl (PCB126) cause multiple adverse effects in organisms including animals and humans. Although PCB toxicities are linked to oxidative damage in rodents, the mechanism in early life stages of zebrafish is not clear. To explore the developmental toxicity mechanism of PCB126, three paradigms (toxicological phenotypes, biochemical changes, and molecular changes) were studied in 3-h postfertilization (hpf) zebrafish (Danio rerio) embryos exposed to different PCB126 concentrations (0, 16, 32, 64, and 128 μg/L) until 168 hpf. Developmental malformations, including pericardial and yolk sac edema, impaired lower jaw growth, spinal curvature, head edema and failure to inflate the swim bladder were observed, some as early as 72 hpf. Mortality was not apparent in early stages but significantly increased in a dose-dependent manner from 144 hpf onward. A dose-dependent significant increase in malformation rate was observed from 72 hpf onward with up to 100% at 132 hpf in embryos exposed to 128 μg/L of PCB126. Higher doses of PCB126 significantly decreased the copper-zinc superoxide dismutase (CuZn-Sod), catalase (Cat), and glutathione peroxidase (Gpx) enzyme activities at 96, 132 hpf, but markedly declined from thereafter. PCB126 at 128 μg/L significantly increased the malondialdehyde content at 72, 96, and 132 hpf. The transcriptional gene expression of antioxidant enzymes Cat and Gpx was upregulated in embryos exposed to 64 μg/L of PCB126 at 24 and 96 hpf. Sod1 messenger RNA (mRNA) was low in embryos exposed to 32 μg/L at 72 and 96 hpf but was induced in embryos exposed to 64 and 128 μg/L doses at 132 hpf. Collectively, the results suggest oxidative stress as a major factor in the induction of multiple developmental abnormalities in early life stages of zebrafish exposed to PCB126. However, the relationship between the antioxidant enzyme activity and the mRNA expression was not clear and the potential reasons for this are discussed.

Chromosomal damage and EROD induction in tree swallows (Tachycineta bicolor) along the Upper Mississippi River, Minnesota, USA

The health of tree swallows, Tachycineta bicolor, on the Upper Mississippi River (UMR) was assessed in 2010 and 2011 using biomarkers at six sites downriver of Minneapolis/St. Paul, MN metropolitan area, a tributary into the UMR, and a nearby lake. Chromosomal damage was evaluated in nestling blood by measuring the coefficient of variation of DNA content (DNA CV) using flow cytometry. Cytochrome P450 1A activity in nestling liver was measured using the ethoxyresorufin-O-dealkylase (EROD) assay, and oxidative stress was estimated in nestling livers via determination of thiobarbituric acid reacting substances (TBARS), reduced glutathione (GSH), oxidized glutathione (GSSG), the ratio GSSG/GSH, total sulfhydryl, and protein bound sulfhydryl (PBSH). A multilevel regression model (DNA CV) and simple regressions (EROD and oxidative stress) were used to evaluate biomarker responses for each location. Chromosomal damage was significantly elevated at two sites on the UMR (Pigs Eye and Pool 2) relative to the Green Mountain Lake reference site, while the induction of EROD activity was only observed at Pigs Eye. No measures of oxidative stress differed among sites. Multivariate analysis confirmed an increased DNA CV at Pigs Eye and Pool 2, and elevated EROD activity at Pigs Eye. These results suggest that the health of tree swallows has been altered at the DNA level at Pigs Eye and Pool 2 sites, and at the physiological level at Pigs Eye site only.

Potency of polycyclic aromatic hydrocarbons (PAHs) for induction of ethoxyresorufin-O-deethylase (EROD) activity in hepatocyte cultures from chicken, Pekin duck, and greater scaup

The potency of tetrachlorodibenzo-p-dioxin (TCDD) and 18 polycyclic aromatic hydrocarbons (PAHs) for induction of ethoxyresorufin-O-deethylase (EROD) activity was assessed in primary hepatocyte cultures prepared from chicken (Gallus domesticus), Pekin duck (Anas platyrhynchos domesticus), and greater scaup (Aythya marila). TCDD and 8 of the PAHs induced EROD activity in a concentration-dependent manner. Seven of these were previously shown to be acutely toxic to avian embryos, while the 10 congeners that did not produce an EROD response caused limited mortality. The rank order potency of the EROD-active congeners in all three species was as follows: TCDD>dibenz[ah]anthracene>benzo[k]fluoranthene>indeno[1,2,3-cd]pyrene>benzo[a]pyrene>chrysene≈benz[a]anthracene≈benz[ghi]perylene>benzo[b]naphtho[2,3-d]thiophene. Chicken hepatoctyes were more sensitive than duck hepatocytes to EROD induction by all test compounds, but the gap in species sensitivity was 100-fold for TCDD, and generally ≤10-fold for PAHs. This study is the first to use in vitro methods to rank the AHR-mediated potency of PAHs in birds. These data may be useful for assessing risks associated with exposure to PAHs in the environment.

Incubation stage and polychlorinated biphenyl (PCB) congener patterns in an altricial and precocial bird species

The composition of polychlorinated biphenyl (PCB) congeners was compared between non-incubated and embryonated eggs of tree swallows (Tachycineta bicolor) and little terns (Sterna albifrons) to determine if measurable changes in PCB congeners occurred during the embryonic period. There was no indication of changes in PCB congener patterns over the incubation period in tree swallows in 1999 and 2000 at a site with very high PCB exposure or a site with more modest PCB exposure. Additionally, congeners known to be either quickly metabolized or conserved based on experimental studies did not generally respond as predicted. Similarly, PCB congener patterns in eggs of little terns from Bottsand, Schleswig-Holstein, Germany, did not differ between non-incubated and embryonated eggs. The results from both species suggest that the stage of incubation is not an important consideration when evaluating PCB congener patterns; comparisons and assessments can be made with eggs collected at all stages of incubation.

Dietary antioxidants (selenium and N-acetylcysteine) modulate paraoxonase 1 (PON1) in PCB 126-exposed rats

Environmental pollutants polychlorinated biphenyls (PCBs), especially dioxin-like PCBs, cause oxidative stress and associated toxic effects, including cancer and possibly atherosclerosis. We previously reported that PCB 126, the most potent dioxin-like PCB congener, not only decreases antioxidants such as hepatic selenium (Se), Se-dependent glutathione peroxidase, and glutathione (GSH) but also increases levels of the antiatherosclerosis enzyme paraoxonase 1 (PON1) in liver and serum. To probe the interconnection of these three antioxidant systems, Se, GSH, and PON1, we examined the influence of varying levels of dietary Se and N-acetylcysteine (NAC), a scavenger of reactive oxygen species (ROS) and precursor for GSH synthesis, on PON1 in the absence and presence of PCB 126 exposure. Male Sprague-Dawley rats, fed diets with differing Se levels (0.02, 0.2, or 2 ppm) or NAC (1%), were treated with a single intraperitoneal injection of corn oil or various doses of PCB 126 and euthanized 2 weeks later. PCB 126 significantly increased liver PON1 mRNA, protein level and activity, and serum PON1 activity in all dietary groups but did not consistently increase thiobarbituric acid levels (thiobarbituric acid reactive substances, TBARS), an indicator of lipid oxidation and oxidative stress, in liver or serum. Inadequate (high or low) dietary Se decreased baseline and PCB 126-induced aryl hydrocarbon receptor (AhR) expression but further increased PCB 126-induced cytochrome P450 1A1 (CYP1A1) expression, the enzyme believed to be the cause for PCB 126-induced oxidative stress. In addition, a significant inverse relationship was observed not only between dietary Se levels and PON1 mRNA and PON1 activity but also with TBARS levels in the liver, suggesting significant antioxidant protection from dietary Se. NAC lowered serum baseline TBARS levels in controls and increased serum PON1 activity but lowered liver PON1 activities in animals treated with 1 μmol/kg PCB 126, suggesting antioxidant activity by NAC primarily in serum. These results also show an unexpected predominantly inverse relationship between Se or NAC and PON1 during control and PCB 126 exposure conditions. These interactions should be further explored in the development of dietary protection regimens.

Dioxin sensitivity-related two critical amino acids of arylhydrocarbon receptor may not correlate with the taxonomy or phylogeny in avian species

There are two arylhydrocarbon receptor (AhR) isoforms in birds, AhR1 and AhR2. The varying sensitivity of AhR is reported to be related to two critical amino acids at positions 325 and 381 in the AhR1 ligand-binding domain. In this study, seven avian species whose in vivo dioxin sensitivity was known, and 13 species with no data regarding their in vivo dioxin sensitivity were examined. The two critical amino acids in the ligand-binding domain were investigated in avian species, and the results were compared with the taxonomy or phylogenetic trees for the bird AhR proteins. We found that the two critical amino acids did not correlate with the taxonomy or phylogeny of these proteins, suggesting that dioxin sensitivity was independent of taxonomy.

Accumulation of mercury, selenium and PCBs in domestic duck brain, liver and egg from a contaminated area with an investigation of their redox responses

PCBs and methylmercury (MeHg) are two of the most ubiquitous contaminants in the Qingzhen (QZ) area of Guizhou province. The estimated tolerable daily intakes (TDIs) of total mercury (T-Hg), MeHg, PCBs and Se from contaminated rice, eggs and fish by Chinese people in QZ showed that both MeHg and PCBs exceeded the corresponding safety limits. Pearson's correlation analyses of mercury and Se in all duck tissues showed that there were high correlations with T-Hg or MeHg and Se in QZ samples. However, the molar ratio between T-Hg and Se in brain tissues was close to 1, suggesting that Se is antagonistic to mercury toxicity only in brain tissues. Biochemical analyses showed that both superoxide dismutase and glutathione peroxidase increased in the brain, whereas in the liver and egg these enzymes decreased. However, lipid peroxidation and H2O2 generation in liver and egg tissues showed contrary responses, where significant increases in these tissues were seen relative to controls. Mercury and PCBs co-accumulation in liver and egg tissues gave rise to large numbers of free radicals as well as aggravated alkyl free radicals, superoxide radical and nitric oxide, thereby resulting in oxidative stress in these tissues. It can be concluded that an adaptive response of the redox defense system is present in brain tissues, as opposed to a general break down of the redox defense system in liver and egg. The results obtained in this study will provide basic information on exposure and risk assessment in local residents.

Relative potency of PCB126 to TCDD for sublethal embryotoxicity in the mummichog (Fundulus heteroclitus)

The relative potency (ReP) of 3,3',4,4',5-pentachlorobiphenyl (PCB126) to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for sublethal responses was assessed in Fundulus heteroclitus embryos. Eggs were treated with intravitelline injections of graded sublethal doses of PCB126 (312-5000 pg g(-1) wet weight, ww) or TCDD (5-1280 pg g(-1) ww). At 16 days post-fertilization (DPF), craniofacial deformities were observed in larvae hatched from eggs treated with the two highest doses of PCB126 (2500-5000 pg g(-1) ww). Both compounds caused a dose-responsive reduction of larval growth and prey capture ability (at ≥1250 pg g(-1) ww), and induction of ethoxyresorufin-O-deethylase (EROD) activity (at ≥80 pg g(-1) ww). The dose-response relationships for EROD activity for PCB126 and TCDD had similar slopes and the ReP of PCB126 to TCDD for EROD activity was estimated at 0.71. This is 140-fold higher than the World Health Organization (WHO) TCDD equivalency factor (TEF) of PCB126 for fish (0.005), which is based on rainbow trout (Oncorhynchus mykiss) embryolethality data. The slope of the dose-response relationship for prey capture ability for PCB126 was steeper than for TCDD, suggesting different mechanisms of action. Expression levels of several genes were also studied by quantitative real-time polymerase chain reaction (qPCR) following exposure to single doses of TCDD or PCB126 (1280 and 1250 pg g(-1) ww, respectively) causing similar EROD induction. A different pattern of responses was observed between PCB126 and TCDD: PCB126 appeared to induce antioxidant responses by inducing sod2 expression, while TCDD did not. These results suggest that relative potencies are species-specific and that the current ReP for PCB126 underestimates its toxicity for some fish species. It is recommended to develop species-specific RePs for a variety of sublethal endpoints and at environmentally relevant doses.

Pansteatitis associated with high levels of polychlorinated biphenyls in a wild loggerhead sea turtle Caretta caretta

We describe the morphologic and toxicological findings in a case of pansteatitis in a stranded loggerhead sea turtle Caretta caretta. At necropsy, a large amount of adipose tissue in the celomic cavity showing very firm, yellow to orange irregular formations was observed. Histological lesions ranged from the infiltration of necrotic fat by scarce multinucleated giant cells and numerous macrophages containing xylene-insoluble lipopigment inclusions to the presence of several granulomas characterized by an irregular central necrotic area consisting of lipopigment surrounded by numerous multinucleated giant cells. Microbiological cultures were negative. Celomic fat was analyzed for PCBs and DDTs, resulting in very high levels of PCB 138, 153, 180 209 (3170, 2830, 980 and 1190 ng g-1, respectively). Although a nutritional cause cannot be ruled out, the high levels of PCBs detected in the celomic fat could have induced lipid peroxidation in adipocytes, resulting in cell damage, deposition of ceroid pigment and inflammatory response. This is the first report of pansteatitis in a wild sea turtle.

Antioxidative defense and oxidative stress in ringed seals (Pusa hispida) from differently polluted areas

High contaminant levels detected in Baltic seals have been associated with various health effects. In this study several parameters related to antioxidative defense and oxidative stress (concentrations of reduced and oxidised glutathione, lipid hydroperoxide and vitamin E, activities of glutathione reductase, peroxidase and S-transferase, glucose-6-phosphate dehydrogenase, catalase, and superoxidedismutase) were measured in the livers of ringed seals from the Baltic Sea and from a less contaminated reference area, Svalbard, Norway. Seals were caught during two different time periods 1996-1997 and 2002-2007, which represent different levels of contamination. No signs of oxidative damage were found in the Baltic seals. However, glutathione metabolism was enhanced in the ringed seals from the Baltic Sea compared to the seals from Svalbard. The adaptation to dive where repetitive ischemia/reperfusion occurs naturally may contribute to the resistance of oxidative stress and to the capacity to increase enzymatic antioxidant defense in phocid seals. This could explain the similarities in oxidative stress levels despite the differences in antioxidant responses between the ringed seals from the Baltic Sea and Svalbard.

Effects of in ovo exposure of white leghorn chicken, common pheasant, and Japanese quail to 2,3,7,8-tetrachlorodibenzo-p-dioxin and two chlorinated dibenzofurans on CYP1A induction

In birds, activation of the aryl hydrocarbon receptor (AhR) by some polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) results in induction of cytochrome P4501A (CYP1A) expression. This response has been useful for predicting relative sensitivity of birds to dioxin-like compounds. To further investigate species-sensitivity to dioxins and dioxin-like compounds induction of cytochrome P450 1A4 and 1A5 (CYP1A4 and CYP1A5) mRNA and ethoxyresorufin O-deethylase (EROD) activity were quantified in liver of posthatch white leghorn chicken, common pheasant, and Japanese quail exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), or 2,3,7,8-tetrachlorodibenzofuran (TCDF) via air cell injection. The rank-order of sensitivity of TCDD- and TCDF-exposed birds, based on CYP1A, was chicken>pheasant>quail. Based on CYP1A5 mRNA expression and EROD induction, the order of sensitivity of PeCDF-exposed birds was identical to that for TCDD and TCDF. However, based on CYP1A4 mRNA expression the rank-order was pheasant>chicken>quail. When comparing the potency of the three compounds in each species, based on CYP1A4 mRNA expression, TCDD was the most potent compound in chicken. However, PeCDF was equally potent to TCDD in quail and was more potent than TCDD in pheasant. These results suggest that quantitative real-time polymerase chain reaction (Q-PCR) analysis of CYP1A expression, particularly CYP1A4 mRNA expression, may be a more sensitive biomarker of exposure than analysis of EROD induction, especially in less responsive avian species. Based on these findings future risk assessments should consider the sensitivity of the species inhabiting a site and the congeners of concern that are present.

Effects of Aroclor 1254 on oxidative stress in developing Xenopus laevis tadpoles

Over the last decades, amphibians decline has been reported worldwide. Exposure to polychlorinated biphenyls (PCBs) is one of the possible causes in addition to climate changes, UV-radiation or habitat destruction. In the present study, we tested the hypothesis that PCBs could induce oxidative stress in young tadpoles. Developing Xenopus laevis were exposed from 2- to 5-d postfertilization (pf) to 0.1 or 1 mg/l of Aroclor 1254. Lipid peroxidation and antioxidant systems (SOD, CAT, GST, GPx, GR activities and t-GSH level) were investigated in whole organisms. Exposure to both concentrations did not impact on the survival and development whereas the average body weight decreased. Exposure to 1 mg/l of Aroclor 1254 induced a significant (p<0.05) increase of GST activity when compared to controls 0 and DMSO. The other antioxidant enzymes and LPO evaluation remained unchanged. Our results demonstrate that exposure of X. laevis tadpoles to environmental concentrations of Aroclor 1254 interfere with normal growth. They also highlight that very young X. laevis tadpoles express antioxidant systems.

Protein expression profiling in the African clawed frog Xenopus laevis tadpoles exposed to the polychlorinated biphenyl mixture aroclor 1254

Exposure to environmental pollutants such as polychlorinated biphenyls (PCBs) is now taken into account to partly explain the worldwide decline of amphibians. PCBs induce deleterious effects on developing amphibians including deformities and delays in metamorphosis. However, the molecular mechanisms by which they express their toxicity during the development of tadpoles are still largely unknown. A proteomics analysis was performed on developing Xenopus laevis tadpoles exposed from 2 to 5 days postfertilization to either 0.1 or 1 ppm Aroclor 1254, a PCB mixture. Two-dimensional DIGE with a minimal labeling method coupled to nanoflow liquid chromatography-tandem mass spectrometry was used to detect and identify proteins differentially expressed under PCBs conditions. Results showed that 59 spots from the 0.1 ppm Aroclor 1254 condition and 57 spots from the 1 ppm Aroclor 1254 condition displayed a significant increase or decrease of abundance compared with the control. In total, 28 proteins were identified. The results suggest that PCBs induce mechanisms against oxidative stress (peroxiredoxins 1 and 2), adaptative changes in the energetic metabolism (enolase 1, glycerol-3-phosphate dehydrogenase, and creatine kinase muscle and brain types), and the implication of the unfolded protein response system (glucose-regulated protein, 58 kDa). They also affect, at least at the highest concentration tested, the synthesis of proteins involved in normal cytogenesis (alpha-tropomyosin, myosin heavy chain, and alpha-actin). For the first time, proteins such as aldehyde dehydrogenase 7A1, CArG binding factor-A, prolyl 4-hydroxylase beta, and nuclear matrix protein 200 were also shown to be up-regulated by PCBs in developing amphibians. These data argue that protein expression reorganization should be taken into account while estimating the toxicological hazard of wild amphibian populations exposed to PCBs.

Embryo toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin to the wood duck (Aix sponsa)

We examined the sensitivity of the wood duck (Aix sponsa) embryo to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) by injecting the toxicant into their eggs. Six groups of wood duck eggs (n = 35 to 211 per trial) were injected with 0 to 4600 pg TCDD/g egg between 2003 and 2005. Injections were made into yolk prior to incubation, and eggs were subsequently incubated and assessed weekly for mortality. Significant TCDD-induced mortality was not observed through day 25 (90% of incubation). Liver, heart, eye, and brain histology were generally unremarkable. Hepatic ethoxyresorufin-O-deethylase activity, a biomarker of dioxin-like compound exposure, was induced by 12-fold in the 4600 pg/g treatment relative to controls. The median lethal dose for chicken (Gallus domesticus) eggs we dosed identically to wood duck eggs was about 100 pg/g, similar to other assessments of chickens. Among dioxin-like compound embryo lethality data for 15 avian genera, the wood duck 4600 pg/g no-observed-effect level ranks near the middle. Because no higher doses were tested, wood ducks may be like other waterfowl (order Anseriformes), which are comparatively tolerant to embryo mortality from polychlorinated dibenzo-p-dioxins and dibenzofurans when exposed by egg injection.

Key amino acids in the aryl hydrocarbon receptor predict dioxin sensitivity in avian species

Dioxin-like compounds are toxic to most vertebrates, but significant differences in sensitivity exist among species. A recent study suggests that the amino acid residues corresponding to Ile324 and Ser380 in the chicken aryl hydrocarbon receptor 1 (AHR1) are important determinants of differential biochemical responses to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in chickens and common terns. Here, we investigate whether the identity of these amino acid residues can predict embryonic sensitivity to dioxin-like compounds in a wide range of birds. AHR1 sequences were determined in species for which sensitivity data were available. Of all the species surveyed, chickens were unique in having the Ile/Ser genotype and were also the most sensitive to dioxin-like compounds. Turkeys, ring-necked pheasants, and Eastern bluebirds (intermediate Ile/Ala genotype) were less sensitive than chickens but more sensitive than American kestrels, common terns, double-crested cormorants, Japanese quail, herring gulls, or ducks (Val/ Ala genotype). Our work suggests that key amino acids in the AHR1 ligand binding domain are predictive of broad categories of dioxin sensitivity in avian species. Given the large degree of variation in species sensitivity and the paucity of species-specific toxicity data, a genetic screen based on these findings could substantially improve risk assessment for dioxin-like compounds in wild birds.

Reactive oxygen species from the uncoupling of human cytochrome P450 1B1 may contribute to the carcinogenicity of dioxin-like polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are classified by the International Agency for Research on Cancer as probable human carcinogens. A subset of PCBs are described as 'dioxin like' because of similarities to 2,3,7,8-tetrachlorodibenzo-p-dioxin. Dioxin-like PCBs have been shown to tightly bind the active site of cytochrome P450 (CYP) 1A isoforms, primarily CYP1A1, resulting in inhibition of CYP activity and the generation of reactive oxygen species (ROS) as a result of uncoupling of the catalytic cycle. Human CYP1B1 (hCYP1B1) is an extrahepatic CYP closely related to hCYP1A1 and is overexpressed in the lungs of smokers. Moreover, hCYP1B1 has been found to be overexpressed in cancers derived from a number of tissue types, as well as in pre-malignant prostate tumours, implicating overexpression of hCYP1B1 as a risk factor for extrahepatic carcinogenesis. It has been demonstrated previously that hCYP1B1 is inhibited by dioxin-like PCBs, but whether or not it is uncoupled has not been investigated. In the current study, the ability of three dioxin-like PCBs 3,3',4,4'-tetrachlorobiphenyl, 3,3',4,4',5-pentachlorobiphenyl and 3,3',4,4',5,5'-hexachlorobiphenyl (PCB169) to inhibit hCYP1B1 and stimulate the formation of ROS in V79MZ cells (which lack endogenous CYPs) expressing hCYP1B1 was demonstrated. Moreover, the generation of ROS was also associated with increases in parameters of oxidative stress related to genotoxicity (DNA oxidation and lipid peroxidation). For PCB169, these effects were time and concentration dependent. These data identify a novel mechanism of genotoxicity for dioxin-like PCBs, as well as providing further evidence that overexpression of hCYP1B1 is a risk factor for extrahepatic carcinogenesis.

A possible role of multidrug resistance-associated protein 2 (Mrp2) in hepatic excretion of PCB126, an environmental contaminant: PBPK/PD modeling

3,3',4,4',5'-Pentachlorobiphenyl (PCB126) is a carcinogenic environmental pollutant and its toxicity is mediated through binding with aryl hydrocarbon receptor (AhR). Earlier, we found that PCB126 treated F344 rats had 110-400 times higher PCB126 concentration in the liver than in the fat. Protein binding was suspected to be a major factor for the high liver concentration of PCB126 despite its high lipophilicity. In this research, we conducted a combined pharmacokinetic/pharmacodynamic study in male F344 rats. In addition to blood and tissue pharmacokinetics, we use the development of hepatic preneoplastic foci (glutathione-S-transferase placental form [GSTP]) as a pharmacodynamic endpoint. Experimental data were utilized for building a physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) model. PBPK/PD modeling was consistent with the experimental PK and PD data. Salient features of this model include: (1) bindings between PCB126 and hepatic proteins, particularly the multidrug resistance-associated protein (Mrp2), a protein transporter; (2) Mrp2-mediated excretion; and (3) a relationship between area under the curve of PCB126 in the livers and % volume of GSTP foci. Mrp2 involvement in PCB126 pharmacokinetics is supported by computational chemistry calculation using a three-dimensional quantitative structure-activity relationship model of Mrp2 developed by S. Hirono et al. (2005, Pharm. Res. 22, 260-269). This work, for the first time, provided a plausible role of a versatile hepatic transporter for drugs, Mrp2, in the disposition of an important environmental pollutant, PCB126.

Activity patterns of biotransformation enzymes in juvenile chickens after in ovo dosage of PCB126

Little is known about the correlations between biotransformation enzymes in juvenile birds after exposure to environmental toxicants like PCBs. In this study eggs of domestic chicken (Gallus domesticus) were dosed with PCB126 in concentrations of 0.175-0.325 ng/g egg weight. Liver subcellular fractions were analyzed for activities of Phase 1 and Phase 2 biotransformation enzymes 2 and 5 weeks post-hatch. Ethoxyresorufin O-deethylase (EROD) activity was increased in both the 2-week and 5-week samples. Glutathione-S-transferase (GST) activity was increased in the 2-week samples only, but the 5-week samples showed an overall much higher GST activity, probably as a result of a still developing enzyme expression in maturing chickens. The same pattern was seen in the phenol-type UDP-glucuronosyltransferase (UGT) activity of the control animals. The week two samples showed a positive dose-response relationship for the UGT activity, but after 5 weeks this was reversed, possibly caused by inhibition of hydroxylated PCB metabolites. Phenol-type sulfotransferase (SULT) activities were not significantly correlated with time or dose. There was a strong positive regression between the Ah-receptor mediated EROD and UGT activities. The EROD activities were also positively correlated to the GST activities. Most interesting was a negative correlation between the UGT and SULT activities: an inhibited UGT activity appeared to be compensated by an increased SULT activity.

Suppression of endogenous antioxidant enzymes by 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced oxidative stress in chicken liver during development

Domestic chickens (Gallus gallus) are an excellent model in which to evaluate developmental toxicity and oxidative stress because of their high sensitivity to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The goal of this study was to measure the effects of environmentally relevant doses of TCDD on endogenous hepatic antioxidant enzyme activity in hatchling chickens. The vehicle (sunflower oil) or 2, 20, or 200 pg/g TCDD was injected into chicken eggs before incubation. On hatching, livers were harvested and quickly frozen. The changes in activity of antioxidant enzymes, including glutathione peroxidase (GPx), glutathione reductase (GRx), copper zinc superoxide dismutase (SOD), and catalase (CAT) were determined as indicators of oxidative stress. TCDD exposure was associated with a significant suppression of the activities of the protective endogenous enzymes GPx, GRx, and SOD in the liver, even at the lowest dose. CAT activity was also suppressed, but not significantly. The measured decreases were 37% to 63% for GPx, 50% to 58% for GRx, 30% to 40% for SOD, and 16% to 24% for CAT. Noncomplex dose-response relationships were evident in GPx and GRx, whereas SOD and CAT curves were U-shaped. These results demonstrate that a decreased ability to scavenge reactive oxygen species may result from developmental TCDD exposure at very low doses, contributing to oxidative stress and thus to the embryotoxicity of TCDD.

Oxidative stress as a mechanism of teratogenesis

Emerging evidence shows that redox-sensitive signal transduction pathways are critical for developmental processes, including proliferation, differentiation, and apoptosis. As a consequence, teratogens that induce oxidative stress (OS) may induce teratogenesis via the misregulation of these same pathways. Many of these pathways are regulated by cellular thiol redox couples, namely glutathione/glutathione disulfide, thioredoxinred/thioredoinox, and cysteine/cystine. This review outlines oxidative stress as a mechanism of teratogenesis through the disruption of thiol-mediated redox signaling. Due to the ability of many known and suspected teratogens to induce oxidative stress and the many signaling pathways that have redox-sensitive components, further research is warranted to fully understand these mechanisms.

Potential role for oxidative stress in 2,2'-dichlorobiphenyl-induced inhibition of uterine contractions but not myometrial gap junctions

Previously, we reported that 2,2'-dichlorobiphenyl (2,2'-DCB)-induced decreases of amplitude and synchronization of uterine contractions are dependent on MAPK-induced phosphorylation of Connexin43 (Cx43) and inhibition of myometrial gap junctions. Recent studies show that oxidative stress inhibits uterine contractions and myometrial gap junctions also. The present study examines the hypothesis that 2,2'-DCB-induced modification of uterine contraction is dependent on oxidative stress-mediated inhibition of myometrial gap junctions via activation of mitogen-activated protein kinase (MAPK) and phosphorylation of Cx43. In uterine strips treated with alpha-tocopherol (100 microM), deferoxamine mesylate (Def, 50 microM), or superoxide dismutase (SOD, 1000 U) after a 1-h exposure to 100 microM 2,2'-DCB, modification of uterine contractions reversed 1 h after initiating antioxidant treatment. Treatment of uterine strips with 100 microM 2,2'-DCB for 1 h lowered total SOD activity and also induced a surge of superoxide generation after 5 min of exposure. However, myometrial cells exposed in culture to 100 microM 2,2'-DCB did not produce reactive oxygen species as determined by the lack of superoxide anion generation measured by the cytochrome c reduction assay, reactive species by the formazan assay, hydrogen peroxide by the 2',7'-dichlorofluorescein assay, and lipid peroxidation by the thiobarbituric acid-reactive substance assay. Furthermore, cotreatment with SOD or Def was unable to prevent 2,2'-DCB-induced phosphorylation of Cx43, activation of MAPK, and inhibition of myometrial gap junctions. Although antioxidants reversed 2,2'-DCB-induced inhibition of uterine contraction force and synchronization, the myometrial cell culture experiments failed to support oxidative stress as a mechanistic link between 2,2'-DCB-induced inhibition of myometrial gap junctions and modification of uterine contraction.

Ovotransferrin is a redox-dependent autoprocessing protein incorporating four consensus self-cleaving motifs flanking the two kringles

Embryos of avian eggs and mammals are highly sensitive to oxidative stress and hence maintaining a steady reducing environment during the embryonic development is known to confer protection. Although information is completely lacking, proteins of avian egg albumin which have been suggested to play various biological functions, are the major targets for such reducing state during embryogenesis. In this study, we found that ovotransferrin (OTf), the second major protein in egg albumin, undergoes autocleavage at distinct sites upon reduction with thiol-reducing agent or thioredoxin-reducing system. Mass spectral and microsequencing analysis indicated that OTf is able to cleave itself through the unique chemical reactivity of four tripeptides motifs, HTT (residues 209-211), HST (residues 542-544) and two CHT (residues 115-117 and 454-456). Intriguingly, these self-cleavage sites were uniquely located upstream and downstream of the two disulfide kringle domains (residues 115-211 and 454-544) of OTf. These reduction-scissile sequences, His/Cys-X-Thr, are evolutionary conserved self-cleavage motifs found in several autoprocessing proteins including hedgehog proteins. Interestingly, reduction of other two members of transferrin family induced autocleavage patterns, similar to that of OTf, in bovine lactoferrin (bLf) while human lactoferrin (hLf) showed much less self-cleaving activity. This finding is the first to describe that transferrins are a new subset in the class of proteins able to carry out autoprocessing, providing insight into this unusual biochemical process that appears to be a molecular switch involved in triggering a yet unidentified function(s) of OTf as well as bLf.

Protective effects of antioxidant vitamins on Aroclor 1254-induced toxicity in cultured chicken embryo hepatocytes

Primary culture of chicken embryo hepatocytes (CEHs) was established to reveal toxicity of polychlorinated biphenyls (PCBs) and attenuating effects of antioxidants vitamin E (VE), vitamin C (VC) and vitamin A (VA) on PCBs-induced cytotoxicity. CEHs were dispersed from 14-day-old chicken embryo livers and exposed to Aroclor 1254 (A1254) in the range of 0.1-10 microg/ml, A1254 (10 microg/ml) and each vitamin (10 microg/ml) for 24 h. Cell viability was evaluated by determinations of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) leakage. The antioxidant status, namely cellular lipid peroxidation, was evaluated by measuring the thiobarbituric acid reactive substances (TBARS) and glutathion (GSH) levels and superoxide dismutase (SOD) activities. The cultured CEHs maintained normal polygonal cell shape and formed confluent monolayer after 24-h culture. A1254 (10 microg/ml) caused irreversible damage to cell membrane integrity and induced cell death in a dose-dependent manner. It induced increased TBARS production, decreased SOD activity and GSH concentration. VE, VC and VA alone or combinations of VE+VC and VE+VA significantly attenuated A1254-induced toxic effects, which suggested that lipid peroxidation was involved in the sequence of events leading to A1254-induced damage or death of the cultured CEHs. These results indicated that CEHs in serum-free culture represented a suitable model for rapid toxicity assessment of environmental pollutants such as PCBs in a visible manner. Antioxidant vitamins displayed protective effects on CEHs from A1254-induced damage through preventing lipid peroxidation.

Environmental toxicity studies using chickens as surrogates for wildlife: effects of vehicle volume

Domestic chicken embryos are frequently used for avian developmental toxicity studies of polyhalogenated aromatic hydrocarbons, which are often injected into eggs with oil-based vehicles. The volume of toxicant and vehicle injected ranges from relatively low volumes (0.1-0.5 microl/g egg) to relatively high volumes (1.0 microl/g egg and above). Previous research from our laboratory suggested that high volumes of vehicle oil may disrupt normal growth of chicken embryos, possibly from hypoxia-like effects. This analysis explored the potential effects of vehicle volume on developing chicken embryos. We assessed standard measures of mortality, organ growth, body growth, and behavior from chickens developmentally exposed in ovo prior to incubation to low (0.1 microl/g egg) or high volumes (1.0 microl/g egg) of corn oil injected into airsacs or to no injection. The chickens receiving high volumes of oil showed increases in overall embryonic mortality and early embryo mortality compared to chickens receiving low volumes of oil or no injection. The chickens receiving high volumes of oil showed decreased activity during righting reflex, running time, visual discrimination, and olfactory aversion tests, and increased activity during an open-field activity test compared to chickens receiving low volumes of oil or no injection. Somatic endpoints do not appear to be affected by high volume injections. These results suggest that high volumes of vehicle injected into airsacs of eggs may lead to hypoxia-like conditions that increase embryonic mortality and disrupt simple behaviors. However, some effects of volume may diminish when injections are performed later in incubation.

Environmental toxicity studies using chickens as surrogates for wildlife: effects of injection day

Domestic chicken embryos are frequently used for avian developmental toxicity studies of polyhalogenated aromatic hydrocarbons, which are often injected into eggs with oil-based vehicles. Injection times range from immediately prior to incubation (embryonic day zero, E0) to after 4 days of incubation (E4) and beyond. Because the majority of organogenesis in chicken embryos occurs during the first 4 days of development, injection after E0 may miss critical, sensitive, developmental periods. We evaluated whether differences in the day of vehicle administration would lead to differences in standard measures of embryotoxicity. We assessed embryotoxicity using mortality, organ somatic indices, teratogenesis, and behavior in hatchling chickens developmentally exposed to a high volume (1.0 microl/g egg) of corn oil vehicle, which was injected into the airsac at E0 or E4. The E0 vehicle group had 76.5% higher overall embryo mortality, embryos died earlier in development, and hatchlings took more than two times longer to right in a righting reflex test compared to the E4 vehicle group. Other behavioral results demonstrated that hatchling chickens from the E0 vehicle group performed differently from their respective no-inject controls, whereas hatchling chickens from the E4 vehicle group did not. The bursal somatic index differed statistically by injection day and weighed 23.7% more in the E0 vehicle group than the E4 vehicle group. These results suggest that the embryonic day of contaminant injection is an important consideration, particularly when using a high volume of vehicle to evaluate developmental toxicity of a contaminant on embryo mortality or behavior.

3,3',4,4',5-Pentachlorobiphenyl (PCB 126) impacts hepatic lipid peroxidation, membrane fluidity and beta-adrenoceptor kinetics in chick embryos

Polychlorinated biphenyls (PCB) and other aryl hydrocarbon receptor (AHR) agonists induce oxidative stress and alter membrane lipid peroxidation and fluidity. This study tested the hypothesis that PCB-induced changes in membrane properties impact membrane beta-adrenoceptor (beta-AR) affinity and capacity in chick embryo hepatocytes. Embryos were injected into the air cell with 1.6 microg 3,3',4,4',5-pentachlorobiphenyl (PCB 126)/kg egg at day 0, and incubated to day 19 when livers were removed. This dose resulted in hepatic PCB 126 levels of 0.67 ng/g liver or 10.2 ng/g liver lipid; levels in untreated embryos were non-detectable. Hepatic microsomal EROD activity was elevated by approximately 12-fold and embryo mortality was significantly increased compared with the untreated group. Hepatic lipid peroxidation increased and membrane order (steady-state fluorescence anisotropy values) decreased with in ovo PCB 126 exposure. Consistent with changes in membrane structure, hepatic beta-AR affinity for CGP 12177 significantly decreased (Kd increased) without changes in receptor numbers. This study demonstrates that in ovo exposure to PCB 126 in chick eggs significantly impacted embryo survival, and this was correlated with altered hepatic membrane structure and ultimately membrane function.

Effects of the mosquito larvicide GB-1111 on bird eggs

Golden Bear Oil (GB-1111; legal trade name for GB-1313) is a petroleum distillate used in the United States and other countries as a mosquito larvicide. As part of an evaluation of the potential effects of GB-1111 on birds, fertile eggs of mallards (Anas platyrhynchos) and bobwhite (Colinus virginianus) were incubated in the laboratory, and treated on day 4 of incubation with external applications equivalent to either 0, 1/3, 1, 3 or 10 times the maximum rate (X) of 47 l/ha (5 gal/A) of field application of GB-1111. Hatching success was significantly reduced in mallards treated at 3 and 10 times the maximum field application, with a calculated approximate LD50 of 1.9 times the maximum field application. Most mortality occurred within a week of treatment. Hepatic P450-associated monooxygenase activity (ethoxyresorufin-O-dealkylase; EROD) was negatively related to dose. In the 3X group there was a significant increase in the concentration of hepatic reduced glutathione (GSH) but a decrease in protein-bound thiols (PBSH). Hatching success of bobwhite was marginally reduced at the highest level of treatment (10X). Other effects at this level in bobwhite included a significant increase in incidence of abnormal embryos or hatchlings, lower body and liver weights, and a two-fold increase in hepatic microsomal EROD activity in hatchlings. The recommended maximum rate of field application of GB-1111 is unlikely to impair the survival or development of bobwhite embryos but is potentially toxic to mallard embryos under conditions of larvicide drift or spray overlap.

Oxidative stress in liver and brain of the hatchling chicken (Gallus domesticus) following in ovo injection with TCDD

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was injected into chicken eggs prior to incubation to study possible mechanisms of toxicity and teratogenicity. One of the suggested mechanisms of teratogenicity is oxidative stress. Eggs were injected simultaneously with TCDD and cotreatment compounds in an attempt to prevent oxidative stress or to block cytochrome P450 activity. Indicators of oxidative stress were assessed in livers and brains of hatchling chicks. In ovo, exposure to TCDD caused significant effects on indicators of oxidative stress in liver, but not in the brain of the hatchling chicks. TCDD did not significantly affect superoxide production. In liver, TCDD treatment caused a decrease in glutathione content and glutathione peroxidase activity and an increase in the ratio of oxidized to reduced glutathione. TCDD increased the susceptibility to lipid peroxidation and oxidative DNA damage in liver. Administration of the antioxidants vitamin E and vitamin A provided partial protection against TCDD-induced oxidative stress in liver. The lack of effect of TCDD in chicken brain could be due to the low cytochrome P4501A activity in this tissue and little accumulation of TCDD in brain compared to liver. Phenytoin, a known inducer of oxidative stress, caused a decrease in glutathione content and an increase in susceptibility to lipid peroxidation in both liver and brain and increased oxidative DNA damage in brain. Responsiveness varied among individual animals, but measures of the oxidative stress were correlated.

Mechanisms of TCDD-induced abnormalities and embryo lethality in white leghorn chickens

The toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds in birds has been well-established in laboratory and field studies. Observed effects of TCDD and related chemicals in birds include developmental deformities, reproductive failure, liver damage, wasting syndrome and death. The mechanism of action of TCDD at the cellular level is primarily mediated through the aryl hydrocarbon receptor (AhR). However, the mechanism of toxic action at the organism level is poorly understood. In this study, the role of radical oxygen species and mixed function oxidize (MFO; cytochrome P4501A) in the mechanism of TCDD-induced abnormalities and lethality were examined by co-injecting radical scavengers and an MFO inhibitor (piperonyl butoxide). Egg injection studies were conducted to determine if in ovo TCDD exposure can cause oxidative stress in white leghorn chicken eggs. Test agents were injected into the yolk prior to incubation. Treatments included TCDD (150 ng/kg), triolein (vehicle control), and various co-treatments including MnTBAP (a mimetic of superoxide dismutase), piperonyl butoxide, piroxicam, vitamin A acetate, and vitamin E succinate. Phenytoin, which is known to cause teratogenesis through oxidative stress was used as a positive control. Eggs were incubated until hatch and then the following parameters were assessed: mortality, hatching success, abnormalities, weights for whole body, liver, heart and brain, and biochemical endpoints for oxidative stress. As a measure of exposure, concentrations of TCDD and ethoxyresorufin-O-deethylase (EROD) activities were measured in tissues of hatchlings. While greater mortality and abnormalities were observed in the TCDD treatment groups, the number of the replicates were not great enough to detect statistically significant differences in abnormality rates for the co-treatments. Some of the observed developmental abnormalities included edema, liver necrosis and bill, eye and limb deformities with TCDD treatments, bill and brain deformities with phenytoin treatments, eye abnormalities with Vitamin E treatments, and abnormal feather pigmentation with piperonyl butoxide treatments.

Effect of a single dose of polychlorinated biphenyls on hepatic cell proliferation and the DNA binding activity of NF-kappaB and AP-1 in rats

Polychlorinated biphenyls (PCBs) are environmental pollutants that, because of their persistence and biomagnification, raise concerns about the health consequences of long-term exposure. PCB mixtures induce hepatocellular carcinomas in rodents, but the mechanism of their promoting activity is not clear. Previous studies have shown that oxidative stress occurs after PCB administration, with the induction of lipid peroxidation and oxidative DNA damage, which may contribute to their promoting activity. In this study, we examined whether the oxidative stress-sensitive transcription factors NF-kappaB or AP-1 were activated by PCBs in the liver. Male Sprague-Dawley rats were injected i.p. with corn oil, 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153, 30, 150, or 300 micromol/kg), 3,3',4,4'-tetrachlorobiphenyl (PCB-77, 30, 150, or 300 micromol/kg), or both PCBs (each 30 or 150 micromol/kg). Rats were euthanized 2, 6, or 24 h, or 2, 6, and 10 d after the PCB injection. Electrophoretic mobility shift assays (EMSAs) were performed to determine NF-kappaB and AP-1 DNA binding activities. The highest NF-kappaB DNA binding activity was observed in rats receiving higher doses of PCB-153 (150 and 300 micromol/kg), with peak activation occurring 2 d after injection. AP-1 activation was not detected at any timepoint. Hepatocyte proliferation, as measured by the labeling index, was increased only in groups receiving the highest dose of PCB-153 or the combination of two PCBs (150 micromol/kg each) at day 2, and not by any other PCB treatment at any timepoint. These results show that PCB-153, but not PCB-77, can induce hepatocyte proliferation and hepatic NF-kappaB activation after a single dose.

Proinflammatory properties of coplanar PCBs: in vitro and in vivo evidence

So-called coplanar polychlorinated biphenyls (PCBs), as well as other environmental contaminants that are aryl hydrocarbon receptor (AhR) agonists, may compromise the normal functions of vascular endothelial cells by activating oxidative stress-sensitive signaling pathways and subsequent proinflammatory events critical in the pathology of atherosclerosis and cardiovascular disease. To test this hypothesis, porcine endothelial cells were exposed to PCB 153 and to three coplanar PCBs (PCB 77, PCB 126, or PCB 169). In contrast to PCB 153, which is not a ligand for the Ah receptor (AhR), all coplanar PCBs disrupted endothelial barrier function. All coplanar PCBs increased expression of the CYP1A1 gene, oxidative stress (DCF fluorescence), and the DNA-binding activity of nuclear factor kappaB (NF-kappaB). PCB-induced oxidative stress was concentration-dependent, with PCB 126 exhibiting a maximal response at the lowest concentration (0.5 microM) tested. The increase in NF-kappaB-dependent transcriptional activity was confirmed in endothelial cells by a luciferase reporter gene assay. In contrast to PCB 153, coplanar PCBs that are AhR ligands increased endothelial production of interleukin-6. At 3.4 microM, expression of the adhesion molecule VCAM-1 was most sensitive to PCB 77 and 169. We also provide in vivo evidence, suggesting that binding to the AhR is critical for the proinflammatory properties of PCBs. Twenty hours after a single administration of PCB 77, VCAM-1 expression was increased only in wild-type mice, while mice lacking the AhR gene showed no increased staining for VCAM-1. These data provide evidence that coplanar PCBs, agonists for the AhR, and inducers of cytochrome P450 1A1, produce oxidative stress and an inflammatory response in vascular endothelial cells. An intact AhR may be necessary for the observed PCB-induced responses. These findings suggest that activation of the AhR can be an underlying mechanism of atherosclerosis mediated by certain environmental contaminants.