Cytochrome P4501 a induction in avian hepatocyte cultures: A promising approach for predicting the sensitivity of avian species to toxic effects of halogenated aromatic hydrocarbons

Wildlife ecological risk assessment in the 21st century: Promising technologies to assess toxicological effects

Despite advances in toxicity testing and the development of new approach methodologies (NAMs) for hazard assessment, the ecological risk assessment (ERA) framework for terrestrial wildlife (i.e., air-breathing amphibians, reptiles, birds, and mammals) has remained unchanged for decades. While survival, growth, and reproductive endpoints derived from whole-animal toxicity tests are central to hazard assessment, nonstandard measures of biological effects at multiple levels of biological organization (e.g., molecular, cellular, tissue, organ, organism, population, community, ecosystem) have the potential to enhance the relevance of prospective and retrospective wildlife ERAs. Other factors (e.g., indirect effects of contaminants on food supplies and infectious disease processes) are influenced by toxicants at individual, population, and community levels, and need to be factored into chemically based risk assessments to enhance the "eco" component of ERAs. Regulatory and logistical challenges often relegate such nonstandard endpoints and indirect effects to postregistration evaluations of pesticides and industrial chemicals and contaminated site evaluations. While NAMs are being developed, to date, their applications in ERAs focused on wildlife have been limited. No single magic tool or model will address all uncertainties in hazard assessment. Modernizing wildlife ERAs will likely entail combinations of laboratory- and field-derived data at multiple levels of biological organization, knowledge collection solutions (e.g., systematic review, adverse outcome pathway frameworks), and inferential methods that facilitate integrations and risk estimations focused on species, populations, interspecific extrapolations, and ecosystem services modeling, with less dependence on whole-animal data and simple hazard ratios. Integr Environ Assess Manag 2024;20:725-748. © 2023 His Majesty the King in Right of Canada and The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Reproduced with the permission of the Minister of Environment and Climate Change Canada. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Avian Pathogenic Escherichia coli (APEC) Strain-Dependent Immunomodulation of Respiratory Granulocytes and Mononuclear Phagocytes in CSF1R-Reporter Transgenic Chickens

Avian pathogenic Escherichia coli (APEC) cause severe respiratory and systemic disease in chickens, commonly termed colibacillosis. Early immune responses after initial infection are highly important for the outcome of the infection. In this study, the early interactions between GFP-expressing APEC strains of serotypes O1:K1:H7 and O2:K1:H5 and phagocytic cells in the lung of CSF1R-reporter transgenic chickens were investigated. CSF1R-reporter transgenic chickens express fluorescent protein under the control of elements of the CSF1R promoter and enhancer, such that cells of the myeloid lineage can be visualized in situ and sorted. Chickens were separately inoculated with APEC strains expressing GFP and culled 6 h post-infection. Flow cytometric analysis was performed to phenotype and sort the cells that harbored bacteria in the lung, and the response of the sorted cells was defined by transcriptomic analysis. Both APEC strains were mainly detected in CSF1R-transgene^neg (CSF1R-tg^neg) and CSF1R-tg^low MHC II^neg MRC1L-B^neg cells and low numbers of APEC were detected in CSF1R-tg^high MHC II^pos MRC1L-B^pos cells. Transcriptomic and flow cytometric analysis identified the APEC^pos CSF1R-tg^neg and CSF1R-tg^low cells as heterophils and the APEC^pos CSF1R-tg^high cells as macrophages and dendritic cells. Both APEC strains induced strong inflammatory responses, however in both CSF1R-tg^neg/low and CSF1R-tg^high cells, many immune related pathways were repressed to a greater extent or less activated in birds inoculated with APEC O2-GFP compared to APEC O1-GFP inoculated birds. Comparison of the immune pathways revealed the aryl hydrocarbon receptor (AhR) pathway, IL17 and STAT3 signaling, heterophil recruitment pathways and the acute phase response, are modulated particularly post-APEC O2-GFP inoculation. In contrast to in vivo data, APEC O2-GFP was more invasive in CSF1R-tg^high cells in vitro than APEC O1-GFP and had higher survival rates for up to 6 h post-infection. Our data indicate significant differences in the responses induced by APEC strains of prevalent serotypes, with important implications for the design and interpretation of future studies. Moreover, we show that bacterial invasion and survival in phagocyte populations in vitro is not predictive of events in the chicken lung.

The aryl hydrocarbon receptor 2 potentially mediates cytochrome P450 1A induction in the jungle crow (Corvus macrorhynchos)

To understand the role of aryl hydrocarbon receptor (AHR) isoforms in avian species, we investigated the functional characteristics of two AHR isoforms (designated as jcAHR1 and jcAHR2) of the jungle crow (Corvus macrorhynchos). Two amino acid residues corresponding to Ile³²⁴ and Ser³⁸⁰ (high sensitive type) in chicken AHR1 that are known to determine dioxin sensitivity were Ile³²⁵ and Ala³⁸¹ (moderate sensitive type) in jcAHR1 and Val³⁰⁶ and Ala³⁶² (low sensitive type) in jcAHR2. The quantitative comparison of the two jcAHR mRNA expression levels in a Tokyo jungle crow population showed that jcAHR2 accounted for 92.4% in the liver, while jcAHR1 accounted for only 7.6%. Both in vitro-expressed jcAHR1 and jcAHR2 proteins exhibited a specific binding to [³H]-labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Transactivation potencies for jcAHR1 and jcAHR2 in in vitro reporter gene assays were measured in jcAHR-expressed cells exposed to 16 dioxins and related compounds (DRCs). Both jcAHR1 and jcAHR2 were activated in a congener- and an isoform-specific manner. EC₅₀ value of TCDD for jcAHR2 (0.61 nM) was six-fold higher than that for jcAHR1 (0.098 nM), but jcAHR2 had higher transactivation efficacy than jcAHR1 in terms of the magnitude of response. The high transactivation efficacy of jcAHR2 in DRCs is in contrast to that of AHR2s in other avian species with low transactivation efficacy. Molecular docking simulations of TCDD with in silico jcAHR1 and jcAHR2 homology models showed that the two sensitivity-decisive amino acids indirectly controlled TCDD-binding modes through their surrounding amino acids. Deletion assays of jcAHR2 revealed that 736-805 amino acid residues in the C-terminal region were critical for its transactivation. We suggest that jcAHR2 plays a critical role in regulating the AHR signaling pathway, at least in its highly expressed organs.

Interindividual variation in the cytochrome P4501A response to 2,3,7,8-tetrachlorodibenzo-p-dioxin in herring gull embryo hepatocytes

Exposure to dioxin-like compounds is consistently associated with concentration-dependent induction of cytochrome P4501A (CYP1A) enzymes in primary cultures of avian hepatocytes. We have previously demonstrated that the median effective concentration (EC50) for induction of this response is predictive of in vivo sensitivity to dioxin-like compounds in birds. We investigated sources of interindividual variation in the CYP1A response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in wild herring gulls and considered how this variation may complicate dioxin sensitivity estimates based on the CYP1A bioassay. Concentration-dependent effects of TCDD on CYP1A mRNA expression were characterized in 55 hepatocyte cultures prepared from individual herring gull embryos. A large degree of variability was observed among the hepatocyte culture preparations. For example, 1) basal CYP1A4 and CYP1A5 mRNA expression varied by 20- and 126-fold, respectively, among individuals, and 2) exposure to TCDD induced CYP1A4 mRNA expression by 57-fold in the most responsive sample but did not significantly induce CYP1A4 mRNA expression above baseline values in 42% of hepatocyte culture preparations. Environmental and genetic factors contributing to the observed variability are discussed. Despite the large amount of interindividual variation, we conclude that reproducible EC50-based estimates of species sensitivity can be obtained from the CYP1A cell culture bioassay when samples are collected from relatively uncontaminated colonies. Environ Toxicol Chem 2019;38:660-670. © 2019 SETAC.

Risk for animal and human health related to the presence of dioxins and dioxin-like PCBs in feed and food

The European Commission asked EFSA for a scientific opinion on the risks for animal and human health related to the presence of dioxins (PCDD/Fs) and DL-PCBs in feed and food. The data from experimental animal and epidemiological studies were reviewed and it was decided to base the human risk assessment on effects observed in humans and to use animal data as supportive evidence. The critical effect was on semen quality, following pre- and postnatal exposure. The critical study showed a NOAEL of 7.0 pg WHO2005-TEQ/g fat in blood sampled at age 9 years based on PCDD/F-TEQs. No association was observed when including DL-PCB-TEQs. Using toxicokinetic modelling and taking into account the exposure from breastfeeding and a twofold higher intake during childhood, it was estimated that daily exposure in adolescents and adults should be below 0.25 pg TEQ/kg bw/day. The CONTAM Panel established a TWI of 2 pg TEQ/kg bw/week. With occurrence and consumption data from European countries, the mean and P95 intake of total TEQ by Adolescents, Adults, Elderly and Very Elderly varied between, respectively, 2.1 to 10.5, and 5.3 to 30.4 pg TEQ/kg bw/week, implying a considerable exceedance of the TWI. Toddlers and Other Children showed a higher exposure than older age groups, but this was accounted for when deriving the TWI. Exposure to PCDD/F-TEQ only was on average 2.4- and 2.7-fold lower for mean and P95 exposure than for total TEQ. PCDD/Fs and DL-PCBs are transferred to milk and eggs, and accumulate in fatty tissues and liver. Transfer rates and bioconcentration factors were identified for various species. The CONTAM Panel was not able to identify reference values in most farm and companion animals with the exception of NOAELs for mink, chicken and some fish species. The estimated exposure from feed for these species does not imply a risk.

Effects of in ovo exposure to 3,3',4,4'-tetrachlorobiphenyl (PCB 77) on heart development in tree swallow (Tachycineta bicolor)

Tree swallow (Tachycineta bicolor) eggs from 2 uncontaminated sites, the Patuxent Research Refuge (Laurel, MD, USA) and the Cobleskill Reservoir (Cobleskill, NY, USA) were dosed with polychlorinated biphenyl (PCB) 77 to evaluate effects on the developing cardiovascular system. To ensure embryonic viability, treatments were administered into the air cell at embryonic day 2.5 including: untreated (control), vehicle (filtered sterilized fatty acid mixture), 100 ng/g and 1000 ng/g egg. Eggs were dosed in the field with 0.2 μL/egg, returned to the nest, collected at embryonic day 13, hatched in the laboratory, and necropsied. The PCB 77-treated hatchlings were compared with uninjected, vehicle-injected, and environmentally exposed hatchlings collected from a PCB-contaminated Upper Hudson River (NY, USA) site. The PCB 77-treated embryos showed no effects on hatching success or hatchling mortality, heart index, or morphological measures of 4 distinct heart layers (heart width, length, septal thickness, total and ventricular cavity area) compared with controls. Hatchlings that had received PCB 77 exhibited increased incidence of a cardiomyopathy and absence of the ventricular heart wall compact layer (Chi square test; p < 0.001); environmentally exposed embryos showed no apparent effects. The compact layer is essential in development and overall heart function for ventricular cardiomyocyte proliferation and normal heart contraction. The finding that in ovo exposure to PCB 77 resulted in distinct cardiomyopathy has implications for long-term individual fitness. Environ Toxicol Chem 2018;37:116-125. © 2017 SETAC.

Ras oncogene and Hypoxia-inducible factor-1 alpha (hif-1α) expression in the Amazon fish Colossoma macropomum (Cuvier, 1818) exposed to benzo[a]pyrene

Benzo[a]pyrene (B[a]P) is a petroleum derivative capable of inducing cancer in human and animals. In this work, under laboratory conditions, we analyzed the responses of Colossoma macropomum to B[a]P acute exposure through intraperitoneal injection of four different B[a]P concentrations (4, 8, 16 and 32 μmol/kg) or corn oil (control group). We analyzed expression of the ras oncogene and the Hypoxia-inducible factor-1 alpha (hif-1α) gene using quantitative real-time PCR. Additionally, liver histopathological changes and genotoxic effects were evaluated through the comet assay. Ras oncogene was overexpressed in fish exposed to 4, 8 of 16 μmol/kg B[a]P, showing 4.96, 7.10 and 6.78-fold increases, respectively. Overexpression also occurred in hif-1α in fish injected with 4 and 8 μmol/kg B[a]P, showing 8.82 and 4.64-fold increases, respectively. Histopathological damage in fish liver was classified as irreparable in fish exposed to 8, 16 and 32 μmol/kg μM B[a]P. The genotoxic damage increased in fish injected with 8 and 16 μmol/kg in comparison with the control group. Acute exposure of B[a]P was capable to interrupt the expression of ras oncogene and hif-1α, and increase DNA breaks due to tissue damage.

Intrinsic Clearance of Xenobiotic Chemicals by Liver Microsomes: Assessment of Trophic Magnification Potentials

The use of trophic magnification factors (TMFs) to characterize the bioaccumulation potentials of chemicals was encouraged; however, the method for the assessment of trophic magnification potentials is still lacking. We optimized the in vitro assays used for the measurement of intrinsic clearance in liver microsomes by incorporating benzo[a]pyrene (B(a)P) as a benchmark compound. The intrinsic clearance of 40 compounds was then measured in microsomes from fish (weevers) and birds (quail); the characteristics of the trophic transfer of these 40 compounds were previously investigated in an aquatic food web in Bohai in northern China. Chemicals that are biotransformed at a rate similar to or higher than that of B[a]P in the microsomes of both weevers and quail (in vitro intrinsic clearance values, CL; CL/CLB[a]P: 0.1 to 2.4) generally exhibited no significant trophic magnification or dilution in the food web (TMF ≈ 1 or < 1), whereas chemicals that are biotransformed at extremely slow rates compared with B[a]P (CL/CLB[a]P: 0 to 0.2) showed significant trophic magnification in the food web (TMF > 1). The in vitro intrinsic clearance values of the target chemicals were found to be consistent with their respective trophic transfer behavior in the aquatic food web. Significant negative correlations were also found between the TMFs and the intrinsic clearance values of all target chemicals obtained in microsomes from both weevers and quail. Multiple linear regression analysis showed that biotransformation rates (CL/CLB[a]P) are a more important factor compared with the lipophilicity of the chemicals (log Kow) in the assessment of the trophic magnification of chemicals in the aquatic food web.

Time-dependent transcriptomic and biochemical responses of 6-formylindolo[3,2-b]carbazole (FICZ) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are explained by AHR activation time

6-Formylindolo[3,2-b]carbazole (FICZ) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are ligands of the aryl hydrocarbon receptor (AHR) and bind to the AHR with high affinity. Until recently, TCDD was considered to be the most potent AHR agonist, but several recent studies indicate that FICZ binds with greater affinity to the AHR than TCDD. To advance our understanding of the similarities and differences of the effects of FICZ and TCDD exposure in chicken embryo hepatocyte (CEH) cultures, we compared relative expression changes of 27 dioxin-responsive genes by the use of a chicken PCR array, porphyrin accumulation and ethoxyresorufin-O-deethylase (EROD) activity at different time points. In addition, an egg injection study was performed to assess the effects of FICZ on the developing chicken embryo. The results of the current study showed: (1) mean EROD-derived relative potency values for FICZ compared to TCDD changed as a function of time (i.e. 9, 0.004, 0.0008 and 0.00008 at 3, 8, 24, and 48h, respectively) in CEH cultures; (2) FICZ exposure did not result in porphyrin accumulation in CEH cultures; (3) concordance between gene expression profiles for FICZ and TCDD was time- and concentration-dependent, and (4) no mortality or morphological abnormalities were observed in chicken embryos injected with 0.87ng FICZ/g egg into the air cell. The results presented herein suggest that while FICZ and TCDD share similar molecular targets, transient versus sustained AHR activation by FICZ and TCDD result in differential transcriptomic responses. Moreover, rapid metabolism of FICZ in hepatocytes resulted in a significant decrease in the induction of EROD activity.

Relative sensitivities among avian species to individual and mixtures of aryl hydrocarbon receptor-active compounds

Dioxins and dioxin-like compounds (DLCs) are potent toxicants to most vertebrates. Sensitivities to DLCs vary among species. In the present study, the sensitivities of avian species (chicken [Gallus gallus], ring-necked pheasant [Phasianus colchicus], and Japanese quail [Coturnix japonica]) to some polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) were determined by using species-specific, in vitro, transactivation assays based on a luciferase reporter gene under control of species-specific aryl hydrocarbon receptors. In ring-necked pheasant and Japanese quail, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was not the most potent inducer of toxic effects. Especially for Japanese quail, the relative potency values of most of 9 PCDD/Fs tested were greater than for TCDD. The rank order of avian species sensitivities to DLCs was chicken > ring-necked pheasant > Japanese quail. Effects of binary mixtures of TCDD, 2,3,7,8-tetrachlorodibenzofuran, and 2,3,4,7,8-pentachlorodibenzofuran were strictly additive. Moreover, we also found that the primary DLCs that were responsible for most of the potency of the DLC mixtures can be deduced by using ordination in a multidimensional space defined by the avian species sensitivities. Overall, the relative potency and the species sensitivities of these chemicals could guide risk assessments to wild species when exposure to mixtures of DLCs in the environment.

In vitro dioxin-like potencies of HO- and MeO-PBDEs and inter-species sensitivity variation in birds

Due to their bioaccumulative properties, hydroxylated and methoxylated polybrominated diphenyl ethers (HO-/MeO-PBDEs) may pose ecological risks to wild life, including birds. However, their toxicity potencies in avian species are largely unknown. In the present study, an avian AHR1 luciferase reporter gene (LRG) assay with luciferase probes from chicken, pheasant and quail was used to test activations of avian aryl hydrocarbon receptor (AHR)-mediated pathways by 19 HO- or MeO-PBDEs in different avian species. Species-specific relative potencies (RePs) of HO-/MeO-PBDEs to tetrachlorodibenzo-p-dioxin (TCDD) and relative sensitivities of various species to each chemical were estimated. The results indicated that the ReP of the most potent HO-/MeO-PBDEs, 5-Cl-6-HO-BDE-47, was 7.8×10(-4) for chicken, 1.1×10(-2) for pheasant, and 1.7×10(-1) for quail comparing to TCDD. In addition, it was found that avian species with the greatest sensitivity to TCDD did not always have the greatest sensitivity to HO-/MeO-PBDEs and vice versa. This study contributed to filling in the knowledge gap regarding the dioxin-like activity of HO-/MeO-PBDEs in birds, and provided beneficial information for the prioritization of HO-/MeO-PBDEs for further research.

CAPSULE ABSTRACT

HO-/MeO-PBDEs activate avian AHR-mediated pathways in a congener- and species- specific manner. 5-Cl-6-HO-BDE-47 was the most potent among the nineteen HO-/MeO-PBDEs tested.

The Aryl Hydrocarbon Receptor: A Key Bridging Molecule of External and Internal Chemical Signals

The aryl hydrocarbon receptor (AhR) is a highly evolutionary conserved, ligand-activated transcription factor that is best known to mediate the toxicities of dioxins and dioxin-like compounds. Phenotype of AhR-null mice, together with the recent discovery of a variety of endogenous and plant-derived ligands, point to the integral roles of AhR in normal cell physiology, in addition to its roles in sensing the environmental chemicals. Here, we summarize the current knowledge about AhR signaling pathways, its ligands and AhR-mediated effects on cell specialization, host defense and detoxification. AhR-mediated health effects particularly in liver, immune, and nervous systems, as well as in tumorgenesis are discussed. Dioxin-initiated embryotoxicity and immunosuppressive effects in fish and birds are reviewed. Recent data demonstrate that AhR is a convergence point of multiple signaling pathways that inform the cell of its external and internal environments. As such, AhR pathway is a promising potential target for therapeutics targeting nervous, liver, and autoimmune diseases through AhR ligand-mediated interventions and other perturbations of AhR signaling. Additionally, using available laboratory data obtained on animal models, AhR-centered adverse outcome pathway analysis is useful in reexamining known and potential adverse outcomes of specific or mixed compounds on wildlife.

Characterization of AhR agonists reveals antagonistic activity in European herring gull (Larus argentatus) eggs

European herring gull (Larus argentatus) eggs from two Norwegian islands, Musvær in the south east and Reiaren in Northern Norway, were screened for dioxins, furans, and dioxin-like and selected non-dioxin-like polychlorinated biphenyls (PCBs), and subjected to non-target analysis to try to identify the aryl hydrocarbon receptor (AhR) agonists, responsible for elevated levels measured using the dioxin responsive chemically activated luciferase expression (DR-CALUX) assay. Eggs from Musvær contained chemically calculated toxic equivalent (WHO TEQ) levels of between 109 and 483 pg TEQ/g lw, and between 82 and 337 pg TEQ/g lw was determined in eggs from Reiaren. In particular PCB126 contributed highly to the total TEQ (69-82%). In 19 of the 23 samples the calculated WHO TEQ was higher than the TEQCALUX. Using CALUX specific relative effect potencies (REPs), the levels were lower at between 77 and 292 pg/g lw in eggs from Musvær and between 55 and 223 pg/g lw in eggs from Reiaren, which was higher than the TEQCALUX in 16 of the 23 samples. However, the means of the REP values and the TEQCALUX were not significantly different. This suggests the presence of compounds that can elicit antagonist effects, with a low binding affinity to the AhR. Non-target analysis identified the presence of hexachlorobenzene (HCB) (quantified at 9.6-185 pg/g lw) but neither this compound nor high concentrations of PCB126 and non-dioxin-like PCBs could explain the differences between the calculated TEQ or REP values and the TEQCALUX. Even though, for most AhR agonists, the sensitivity of herring gulls is not known, the reported levels can be considered to represent a risk for biological effects in the developing embryo, compared to LC50 values in chicken embryos. For human consumers of herring gull eggs, these eggs contain TEQ levels up to four times higher than the maximum tolerable weekly intake.

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.

Activation of avian aryl hydrocarbon receptor and inter-species sensitivity variations by polychlorinated diphenylsulfides

It was hypothesized that polychlorinated diphenyl sulfides (PCDPSs) can potentially interact with an aryl hydrocarbon receptor (AHR) and thereby cause adverse effects in wildlife like birds. A recently developed avian AHR1-luciferase report gene (LRG) assay was used to assess the interaction between avian AHR1 and 18 PCDPSs and to compare the interspecies sensitivity among chicken, ring-necked pheasant, and Japanese quail by PCDPSs. Most of the tested PCDPSs could activate the AHR1-mediated pathways in avian species, and the relative potency (ReP) of the PCDPSs increased with the increasing number of substituted Cl atoms. The rank orders of PCDPSs potency were generally similar among birds, although the ReP varied. In addition, not all the sensitivity rank orders of avian AHR1 constructs for PCDPSs were consistent with that of TCDD. ReP values of PCDPSs suggested that some PCDPSs like 2,3,3',4,5,6-hexa-CDPS and 2,2',3,3',4,5,6-hepta-CDPS are higher than the avian WHO-TEFs of OctaCDD, OctaCDF, and most of the coplanar PCBs. Our results report for the first time the activation of an AHR1-mediated molecular toxicological mechanism by PCDPSs, and provide the ranking of ReP and relative sensitivity values of different congeners, which could guide the further toxicity test of this group of potential high priority environmental pollutants.

PCBs and DDTs in light-vented bulbuls from Guangdong Province, South China: levels, geographical pattern and risk assessment

Thirty-two light-vented bulbuls (Pycnonotus sinensis) were collected from six sampling sites in Guangdong Province, South China to investigate the geographical variation on the occurrence of polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane and its metabolites (DDTs). Concentrations of PCBs and DDTs in the pectoral muscle of light-vented bulbul ranged from 140 to 73,000 ng/g lipid weight (lw) and 12 to 4600 ng/g lw, respectively. PCB concentrations were significantly higher in birds from e-waste site compared to other sampling sites (mean, 18,000 vs 290 ng/g lw, p<0.0001), implying that PCBs mainly came from e-waste recycling activities. No significant differences for DDT levels were observed among the sampling sites (p=0.092). Differences in PCB homologue profiles among the sampling sites were found and can be probably ascribed to different local contamination sources. p,p'-DDE (>80%) was the most abundant component of DDTs in birds. Compositional pattern of DDTs suggested that historical residue was the main source of DDT. The toxic equivalent (TEQ) concentrations had significant positive correlations with PCB concentrations, indicating that elevated PCB levels may have adverse effects on light-vented bulbuls.

In vitro bioassays for detecting dioxin-like activity--application potentials and limits of detection, a review

Use of in vitro assays as screening tool to characterize contamination of a variety of environmental matrices has become an increasingly popular and powerful toolbox in the field of environmental toxicology. While bioassays cannot entirely substitute analytical methods such as gas chromatography-mass spectrometry (GC-MS), the increasing improvement of cell lines and standardization of bioassay procedures enhance their utility as bioanalytical pre-screening tests prior to more targeted chemical analytical investigations. Dioxin-receptor-based assays provide a holistic characterization of exposure to dioxin-like compounds (DLCs) by integrating their overall toxic potential, including potentials of unknown DLCs not detectable via e.g. GC-MS. Hence, they provide important additional information with respect to environmental risk assessment of DLCs. This review summarizes different in vitro bioassay applications for detection of DLCs and considers the comparability of bioassay and chemical analytically derived toxicity equivalents (TEQs) of different approaches and various matrices. These range from complex samples such as sediments through single reference to compound mixtures. A summary of bioassay derived detection limits (LODs) showed a number of current bioassays to be equally sensitive as chemical methodologies, but moreover revealed that most of the bioanalytical studies conducted to date did not report their LODs, which represents a limitation with regard to low potency samples.

Ethoxyresorufin-O-deethylase (EROD) induction by TCDD, PeCDF and PCB 126 in bobwhite quail hepatocytes

World Health Organization (WHO) toxic equivalency factors are used to calculate toxic equivalent (TEQ) concentrations of complex mixtures of dioxin-like compounds (DLCs), such as polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and polychlorinated biphenyls (PCBs), for mammals, fish and birds. The TEQ concept assumes that all species of a taxa respond with similar sensitivity to individual DLCs, but several reports do not support this assumption for birds. Our laboratory is conducting research to attempt to uncover the fundamental mechanism(s) underlying the reasons why avian species differ in sensitivity to DLCs. The present study determined concentration-dependent effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) and 3,3',4,4',5-pentachlorobiphenyl (PCB 126) on ethoxyresorufin-O-deethylase (EROD) activity in primary cultures of northern bobwhite quail (Colinus virginianus) hepatocytes. Bobwhite quail were studied because (1) this species is used in the laboratory for toxicity testing and (2) the amino acids at all locations within the ligand binding domain (LBD) of aryl hydrocarbon receptor 1 (AHR1) in bobwhite quail and ring necked pheasant (Phasianus colchicus) are identical. Because earlier work indicated the importance of the identity of amino acids at key sites within the AHR1 LBD, we hypothesized that bobwhite quail and ring necked pheasant hepatocytes should have similar sensitivity to EROD induction by DLCs. ECthreshold-based relative sensitivity of the bobwhite quail compared to chicken for TCDD, PeCDF and PCB 126 was 0.11, 0.17 and 0.02, respectively. The rank order of potency was PeCDF > TCDD > PCB 126. The results confirm that bobwhite quail and ring-necked pheasant hepatocytes have similar sensitivity to EROD induction by TCDD, PeCDF and PCB 126.

Species-specific relative AHR1 binding affinities of 2,3,4,7,8-pentachlorodibenzofuran explain avian species differences in its relative potency

Results of recent studies showed that 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are equipotent in domestic chicken (Gallus gallus domesticus) while PeCDF is more potent than TCDD in ring-necked pheasant (Phasianus colchicus) and Japanese quail (Coturnix japonica). To elucidate the mechanism(s) underlying these differences in relative potency of PeCDF among avian species, we tested the hypothesis that this is due to species-specific differential binding affinity of PeCDF to the aryl hydrocarbon receptor 1 (AHR1). Here, we modified a cell-based binding assay that allowed us to measure the binding affinity of dioxin-like compounds (DLCs) to avian AHR1 expressed in COS-7 (fibroblast-like cells). The results of the binding assay show that PeCDF and TCDD bind with equal affinity to chicken AHR1, but PeCDF binds with greater affinity than TCDD to pheasant (3-fold) and Japanese quail (5-fold) AHR1. The current report introduces a COS-7 whole-cell binding assay and provides a mechanistic explanation for differential relative potencies of PeCDF among species of birds.

Protective role of cytochrome P450 1A1 (CYP1A1) against benzo[a]pyrene-induced toxicity in mouse aorta

Benzo[a]pyrene (BaP) is an environmental pollutant produced by combustive processes, such as cigarette smoke and coke ovens, and is implicated in the pathogenesis of atherosclerosis. Cytochrome P450 1A1 (CYP1A1) plays a role in both metabolic activation and detoxication of BaP in a context-dependent manner. The role of CYP1A1 in BaP-induced toxicity in aorta remains unknown. First, we fed Apoe⁻/⁻ mice an atherogenic diet plus BaP and found that oral BaP-enhanced atherosclerosis is associated with increased reactive oxygen species (ROS) and inflammatory markers, such as plasma tumor necrosis factor levels and aortic mRNA expression of vascular endothelial growth factor A (Vegfa). We next examined the effect of an atherogenic diet plus BaP on ROS and inflammatory markers in Cyp1a1⁻/⁻ mice. Although this treatment was not sufficient to induce atherosclerotic lesions in Cyp1a1⁻/⁻ mice, plasma antioxidant levels were decreased in Cyp1a1⁻/⁻ mice even in the absence of BaP treatment. The atherogenic diet plus BaP effectively elevated plasma ROS levels and expression of atherosclerosis-related genes, specifically Vegfa, in Cyp1a1⁻/⁻ mice compared with wild-type mice. BaP treatment increased Vegfa mRNA levels in mouse embryonic fibroblasts from Cyp1a1⁻/⁻ mice but not from wild-type mice. BaP-induced DNA adduct formation was increased in the aorta of Cyp1a1⁻/⁻ mice, but not wild-type or Apoe⁻/⁻ mice, and the atherogenic diet decreased BaP-induced DNA adducts in Cyp1a1⁻/⁻ mice compared with mice on a control diet. These data suggest that ROS production contributes to BaP-exacerbated atherosclerosis and that CYP1A1 plays a protective role against oral BaP toxicity in aorta.

Aryl hydrocarbon receptor agonists in European herring gull (Larus argentatus) eggs from Norway

Herring gull eggs from two locations in Norway, an island situated in the north (Musvær, 69.88° N, 18.55° E) and an island in the southeast (Reiaren, 59.15° N, 10.46° E) of the country, were analyzed for the presence of aryl hydrocarbon receptor (AhR) agonists. AhR agonist activity was determined using the dioxin-responsive chemically activated luciferase expression (DR-CALUX) assay to calculate the toxic equivalent quotient (TEQ)CALUX. TEQCALUX ranged from 16 to 401 pg TEQ/g lipid in the samples from the north (n = 11) and between 6 and 360 pg TEQ/g lipid (n = 12) in the southeastern samples. The large variance between the individual samples is postulated to be due to different feeding habits of individual birds. The levels of AhR agonists detected might lead to adverse effects for the developing embryo or to a significant increase of contaminant load for human consumers of eggs.

Toxicity reference values for protecting aquatic birds in China from the effects of polychlorinated biphenyls

PCBs are typical of persistent, bioaccumulative and toxic compounds (PBTs) that are widely distributed in the environment and can biomagnify through aquatic food webs, because of their stability and lipophilic properties. Fish-eating birds are top predators in the aquatic food chain and may suffer adverse effects from exposure to PCB concentrations. In this review, we address the toxicity of PCBs to birds and have derived tissue residue guidelines (TRGs) and toxic reference values (TRVs) for PCBs for protecting birds in China. In deriving these protective indices, we utilized available data and three approaches, to wit: species sensitivity distribution (SSD), critical study approach (CSA) and toxicity percentile rank method (TPRM). The TRGs and TRVs arrived at by using these methods were 42.3, I 0. 7, 4.3 pg TEQs/g diet wm and 16.7, 15.5, and 5.5 pg TEQs/g tissue wm for the CSA SSD and TPRM approaches, respectively. These criteria values were analyzed and compared with those derived by others. The following TRG and TRY, derived by SSD, were recommended as avian criteria for protecting avian species in China: 10.7 pg TEQs/g diet wm and 15.5 pg TEQs/g tissue wm, respectively. The hazard of PCBs to birds was assessed by comparing the TRVs and TRGs derived in this study with actual PCB concentrations detected in birds or fish. The criteria values derived in this study can be used to evaluate the risk of PCBs to birds in China, and to provide indices that are more reasonable for protecting Chinese avian species. However, several sources of uncertainty exists when deriving TRGs and TRVs for the PCBs in birds, such as lack of adequate toxicity data for birds and need to use uncertainty factors. Clearly, relevant work on PCBs and birds in China are needed in the future. For example, PCB toxicity data for resident avian species in China are needed. In addition, studies are needed on the actual PCB levels in birds and fish in China. Such information is needed to serve as a more firm foundation for future risk assessments.

Relative potencies of aroclor mixtures derived from avian in vitro bioassays: comparisons with calculated toxic equivalents

The World Health Organization toxic equivalency factors (WHO-TEFs) for birds were developed to simplify risk assessments of environmental mixtures of dioxin-like compounds (DLCs). Under this framework, toxic equivalents (TEQs) are used to represent the toxic potency of DLC mixtures as an equivalent concentration of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Recently, a luciferase reporter gene (LRG) assay, measuring aryl hydrocarbon receptor 1 (AHR1)-mediated gene expression, accurately predicted the relative potency of individual polychlorinated biphenyl (PCB) congeners in different avian species. The study presented here used the LRG assay to predict the relative potency of Aroclors 1016, 1221, 1242, 1248, 1254, and 1260 on induction of LRG activity in cells transfected with chicken, ring-necked pheasant, or Japanese quail AHR1 constructs. LRG assay results were compared to (1) results of ethoxyresorufin-O-deethylase (EROD) assays conducted in chicken hepatocytes and (2) calculated TEQs from the literature. The relative potencies of Aroclors were similar between the LRG and EROD assays, and bioassay-derived TEQs for the chicken closely resembled calculated TEQs. However, LRG assay-derived TEQs for the Japanese quail construct were 1-2 orders of magnitude higher than calculated TEQs for Aroclors 1254 and 1016. These results suggest that the WHO-TEFs are not representative of relative PCB potency for all avian species.

Alternative in vitro approach for assessing AHR-mediated CYP1A induction by dioxins in wild cormorant (Phalacrocorax carbo) population

Our line of papers revealed that the common (great) cormorant (Phalacrocorax carbo) possesses two isoforms of the aryl hydrocarbon receptor (ccAHR1 and ccAHR2). This paper addresses in vitro tests of the ccAHR signaling pathways to solve two questions: (1) whether there are functional differences in the two ccAHR isoforms, and (2) whether a molecular perturbation, cytochrome P450 1A (ccCYP1A) induction, in the population-level can be predicted from the in vitro tests. The transactivation potencies mediated by ccAHR1 and ccAHR2 were measured in COS-7 cells treated with 15 selected dioxins and related compounds (DRCs), where ccAHR1 or ccAHR2 expression plasmid and ccCYP1A5 promoter/enhancer-linked luciferase reporter plasmid were transfected. For congeners that exhibited dose-dependent luciferase activities, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) relative potencies (REPs) and induction equivalency factors (IEFs) were estimated. ccAHR1-IEF profile was similar to WHO avian TCDD toxic equivalency factor (TEF) profile except for dioxin-like polychlorinated biphenyls that showed lower IEFs in ccAHR1-driven reporter assay. ccAHR2-IEF profile was different from WHO TEFs and ccAHR1-IEFs. Notably, 2,3,4,7,8-PeCDF was more potent than TCDD for ccAHR2-mediated response. Using ccAHR1- and ccAHR2-IEFs and hepatic DRC concentrations in the Lake Biwa cormorant population, total TCDD induction equivalents (IEQs) were calculated for each ccAHR-mediated response. Nonlinear regression analyses provided significant sigmoidal relationships of ccAHR1- and ccAHR2-derived IEQs with hepatic ccCYP1A5 mRNA levels, supporting the results of in vitro ccAHR-mediated TCDD dose-response curves. Collectively, our in vitro AHR reporter assay potentially could be an alternative to molecular epidemiology of the species of concern regarding CYP1A induction by AHR ligands.

The effects of an environmentally relevant 58-congener polychlorinated biphenyl (PCB) mixture on cardiac development in the chick embryo

Chicken (Gallus domesticus) embryonic exposure in ovo to a 58-congener polychlorinated biphenyl (PCB) mixture resulted in teratogenic heart defects in chick embryos at critical heart developmental stages Hamburger-Hamilton (HH) stages 10, 16, and 20. The 58-congener mixture contained relative proportions of primary congeners measured in belted sandpiper (Megaceryle alcyon) and spotted sandpiper (Actitis macularia) eggs collected along the upper Hudson River, New York, USA, and chicken doses were well below observed environmental exposure levels. Embryos were injected with 0.08 µg PCBs/g egg weight and 0.50 µg PCBs/g egg weight (0.01 and 0.064 ng toxic equivalent/g, respectively) at embryonic day 0, prior to incubation. Mortality of exposed embryos was increased at all developmental stages, with a marked rise in cardiomyopathies at HH16 and HH20 (p < 0.05). Heart abnormalities occurred across all treatments, including abnormal elongation and expansion of the heart tube at HH10, improper looping and orientation, indentations in the emerging ventricular wall (HH16 and HH20), and irregularities in overall heart shape (HH10, HH16, and HH20). Histology was conducted on 2 cardiac proteins critical to embryonic heart development, ventricular myosin heavy chain and titin, to investigate potential mechanistic effects of PCBs on heart development, but no difference was observed in spatiotemporal expression. Similarly, cellular apoptosis in the developing heart was not affected by exposure to the PCB mixture. Conversely, cardiomyocyte proliferation rates dramatically declined (p < 0.01) at HH16 and HH20 as PCB exposure concentrations increased. Early embryonic cardiomyocyte proliferation contributes to proper formation of the morphology and overall thickness of the ventricular wall. Therefore, in ovo exposure to this 58-congener PCB mixture at critical stages adversely affects embryonic heart development.

Effects of an environmentally relevant polychlorinated biphenyl (PCB) mixture on embryonic survival and cardiac development in the domestic chicken

A 58-congener polychlorinated biphenyl (PCB) mixture based on contaminant analysis of spotted sandpiper eggs collected along the upper Hudson River, New York, USA, in 2004 was used to study in ovo PCB effects on cardiac development in the domestic chicken. Fertile eggs were injected prior to incubation with the following doses of the PCB mixture: untreated, sham, 0, 0.03, 0.08, 0.3, 0.5, 0.7, and 2.06 µg PCBs/g egg weight (toxic equivalent quotient [TEQ] range of 0.004-0.266 ng/g). In addition, there were untreated and sham-control groups. Embryonic development was monitored throughout incubation and chicks were necropsied at hatch. Hatchability followed a dose-dependent curve with significant (p < 0.05) mortality above the 0.5 µg PCBs/g egg weight treatment compared with controls. The median lethal dose (LD50) of this PCB mixture in hatchling chicks was estimated as 0.4 µg/g egg weight (0.052 ng TEQ/g egg wt) based on the lethality curve. Cardiac arrhythmia was observed at embryonic day 14 of development in embryos treated at concentrations of 0.5 µg/g egg weight and above. Histological analysis was utilized to characterize any cardiac abnormalities. Cardiomyopathies increased across treatments in a dose-dependent manner compared with control groups. Identified abnormalities included the absence of the trabeculated layer of the ventricular wall, ventricular dilation, thinning of the ventricular walls, malformation of the septal wall, and most commonly, absence of the compact layer of the ventricular wall. Chick heart width, depth, total area, compact layer depth, septal width, chamber area, and ventricular wall dimensions did not differ across treatments. The present study supports prior reports of adverse developmental effects of PCBs on cardiovascular systems in birds. Although the eggs hatched, measured cardiomyopathies suggest potential deleterious long-term impacts on individual health and fitness.

Cytochrome P4501A induction in primary cultures of embryonic European starling hepatocytes exposed to TCDD, PeCDF and TCDF

Novel methods that predict the sensitivity of avian embryos to the toxic effects of dioxin-like compounds (DLCs) using either (1) knowledge of the identity of amino acids at key sites within the ligand binding domain of aryl hydrocarbon receptor 1 (AHR1) or (2) a luciferase reporter gene assay that measures AHR1 activation were recently reported. Results from both methods predict that European starling (Sturnus vulgaris) and domestic chicken (Gallus gallus domesticus) embryos have similar sensitivity to the biochemical and toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) and 2,3,7,8-tetrachlorodibenzofuran (TCDF). Chicken embryos are highly sensitive to DLC toxicity, and the prediction that starlings are equally sensitive is surprising given their widespread distribution and large population size. In an attempt to learn more about starling sensitivity to DLCs, we determined concentration-dependent effects of TCDD, PeCDF and TCDF on cytochrome P4501A4 and 1A5 (CYP1A4 and 1A5) mRNA levels in primary cultures of hepatocytes prepared from embryonic European starlings. It has been demonstrated that the sensitivity of avian hepatocytes to CYP1A4/5 induction is well correlated with LD50 values of DLCs for several avian species. The results of the present study indicate that European starling hepatocytes are indeed as sensitive as chicken hepatocytes to CYP1A4/5 induction after exposure to TCDD. However, starling hepatocytes are less sensitive than chicken hepatocytes to CYP1A4/5 induction by PeCDF and TCDF.

Modulation of aryl hydrocarbon receptor target genes in circulating lymphocytes from dairy cows bred in a dioxin-like PCB contaminated area

Animal productions (i.e. fish, eggs, milk and dairy products) represent the major source of exposure to dioxins, furans, and dioxin-like (DL) polychlorobiphenyls for humans. The negative effects of these highly toxic and persistent pollutants are mediated by the activation of the aryl hydrocarbon receptor (AHR) that elicits the transcriptional induction of several genes, including those involved in xenobiotic metabolism. Previously we demonstrated the presence and functioning of the AHR signaling pathway in primary cultures of bovine blood lymphocytes. The aim of the present study was to investigate by real time PCR the expression and the inducibility of selected target genes (i.e. AHR, AHR nuclear translocator (ARNT), AHR repressor, CYP1A1 and CYP1B1) in uncultured cells from dairy cows naturally exposed to DL-compounds. The study was carried out on two groups of animals bred in a highly polluted area and characterized by a different degree of contamination, as assessed by bulk milk TEQ values, and a control group reared in an industry free area. Bovine lymphocytes expressed only AHR, ARNT and CYP1B1 genes to a detectable level; moreover, only CYP1B1 expression appeared to be correlated to TEQ values, being higher in the most contaminated group, and decreasing along with animal decontamination. Finally, lymphocytes from exposed cows displayed a lower inducibility of both CYP1A1 and CYP1B1 after the in vitro treatment with a specific AHR ligand. In conclusion, our results indicate that DL-compound contaminated cows may display significant changes in AHR-target gene expression of circulating lymphocytes.

Aryl hydrocarbon receptor activation leads to impairment of estrogen-driven chicken vitellogenin promoter activity in LMH cells

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates most of the toxic effects of environmental contaminants. Among the multiple pleiotropic responses elicited by AHR agonists, the antiestrogenic and endocrine-disrupting action of the receptor activation is one of the most studied. It has been demonstrated that some AHR agonists disrupt estradiol-induced vitellogenin synthesis in the fish liver via a mechanism that involves crosstalk between the AHR and the estrogen receptor (ER). Chicken hepatocytes have become a model for the study of AHR action in birds and the induction of the signal and its effect in these cells are well established. However, the impact of AHR activation on estradiol-regulated responses in the chicken liver remains to be demonstrated. The aim of the present study was, therefore, to determine the effect of AHR action on ER-driven transcription in a convenient model of chicken liver cells. For this purpose, we designed a reporter construct bearing the 5' regulatory region of the chicken vitellogenin II gene and used it to transfect chicken hepatoma LMH cells. We found that β-naphthoflavone represses ER-driven vitellogenin promoter activity and that this action is mediated by the AHR. This inhibitory crosstalk between both pathways appears to be unidirectional, since estradiol did not alter the transcript levels of an AHR target gene. Besides, and highly relevant, we show that LMH cell line transfected with a reporter construct bearing the chicken vitellogenin promoter sequence is a useful and convenient model for the study of AHR-ER interaction in chicken liver-derived cells.

Cytochrome P4501A induction in avian hepatocyte cultures exposed to polychlorinated biphenyls: comparisons with AHR1-mediated reporter gene activity and in ovo toxicity

Avian-specific toxic equivalency factors (TEFs) were developed by the World Health Organization to simplify environmental risk assessments of dioxin-like compounds (DLCs), but TEFs do not account for differences in the toxic and biochemical potencies of DLCs among species of birds. Such variability may be due to differences in species sensitivity to individual DLCs. The sensitivity of avian species to DLCs was recently associated with the identity of amino acids 324 and 380 in the aryl hydrocarbon receptor 1 (AHR1) ligand binding domain. A luciferase reporter gene (LRG) assay, measuring AHR1-mediated induction of a cytochrome P450 1A5 (CYP1A5) reporter gene, in combination with a species' AHR1 ligand binding domain sequence, were also shown to predict avian species sensitivity to polychlorinated biphenyls (PCBs) and PCB relative potency in a given species. The goals of the present study were to (1) characterize the concentration-dependent effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and PCBs 126, 77, 105 and 118 on induction of ethoxyresorufin O-deethylase (EROD) activity and CYP1A4/5 mRNA in chicken, ring-necked pheasant and Japanese quail embryo hepatocytes and (2) compare these in vitro results to those previously generated by the LRG assay and in ovo toxicity studies. EROD activity and CYP1A4/5 mRNA expression data support and complement the findings of the LRG assay. CYP1A enzyme activity and mRNA expression were significantly correlated both with luciferase activity and in ovo toxicity induced by PCBs. Relative potency values were generally similar between the LRG and EROD assays and indicate that the relative potency of some PCBs may differ among species.

Amino acid sequence of the ligand-binding domain of the aryl hydrocarbon receptor 1 predicts sensitivity of wild birds to effects of dioxin-like compounds

The sensitivity of avian species to the toxic effects of dioxin-like compounds (DLCs) varies up to 1000-fold among species, and this variability has been associated with interspecies differences in aryl hydrocarbon receptor 1 ligand-binding domain (AHR1 LBD) sequence. We previously showed that LD(50) values, based on in ovo exposures to DLCs, were significantly correlated with in vitro EC(50) values obtained with a luciferase reporter gene (LRG) assay that measures AHR1-mediated induction of cytochrome P4501A in COS-7 cells transfected with avian AHR1 constructs. Those findings suggest that the AHR1 LBD sequence and the LRG assay can be used to predict avian species sensitivity to DLCs. In the present study, the AHR1 LBD sequences of 86 avian species were studied, and differences at amino acid sites 256, 257, 297, 324, 337, and 380 were identified. Site-directed mutagenesis, the LRG assay, and homology modeling highlighted the importance of each amino acid site in AHR1 sensitivity to 2,3,7,8-tetrachlorodibenzo-p-dioxin and other DLCs. The results of the study revealed that (1) only amino acids at sites 324 and 380 affect the sensitivity of AHR1 expression constructs of the 86 avian species to DLCs and (2) in vitro luciferase activity of AHR1 constructs containing only the LBD of the species of interest is significantly correlated (r (2) = 0.93, p < 0.0001) with in ovo toxicity data for those species. These results indicate promise for the use of AHR1 LBD amino acid sequences independently, or combined with the LRG assay, to predict avian species sensitivity to DLCs.

Reciprocal inhibiting interactive mechanism between the estrogen receptor and aryl hydrocarbon receptor signaling pathways in goldfish (Carassius auratus) exposed to 17β-estradiol and benzo[a]pyrene

In the aquatic environment, both the estrogen receptor (ER) and aryl hydrocarbon receptor (AhR) responses are established biomarkers for assessing exposure to pollutants. These receptor responses can also be affected by the presence of other classes of pollutants and may result in misinterpretation of existing pollution. In this study, we investigated the interaction between ER-vitellogenin (VTG) and AhR-cytochrome P450 1A (CYP1A) signaling pathways in goldfish (Carassius auratus) after 10 days exposure to pollutants. 17β-Estradiol (E(2)) and benzo[a]pyrene (BaP) were selected as the ER and AhR agonists, respectively. The messenger RNA (mRNA) expression of ER-VTG and AhR-CYP1A in liver was determined using quantitative real-time polymerase chain reaction (QRT-PCR). VTG, endogenous E(2) and 7-ethoxyresorufin-O-deethylase (EROD) were also studied. Exposure to E(2) and BaP alone significantly induced the gene expression of ERα-VTG and AhR2-CYP1A, respectively. Moreover, the obvious expression of related proteins was also observed. However, these inductions were significantly reduced after combined exposure to E(2) and lower concentrations of BaP (20 and 50 μg/L), indicative of a reciprocal inhibiting ER-AhR interaction. However, high concentrations (100 μg/L) of BaP did not affect the E(2)-induced gene expression. Changes in VTG protein were in accordance with the expression of VTG mRNA, and more VTG protein was observed in liver than in serum. The induced endogenous E(2) levels were suppressed by the presence of BaP. While the gene expression of CYP1A showed a concentration-dependent increase, EROD induction exhibited a bell-shaped concentration-response curve. Taken together, these results demonstrate a reciprocal inhibiting mode of ER-AhR interactions and may lead to a possible underestimation of actual exposure.

Induction of cytochrome P4501A by highly purified hexachlorobenzene in primary cultures of ring-necked pheasant and Japanese quail embryo hepatocytes

Primary cultures of ring-necked pheasant (Phasianus colchicus) and Japanese quail (Coturnix japonica) embryo hepatocytes were used to compare the potencies of highly purified hexachlorobenzne (HCB-P), reagent-grade HCB (RG-HCB) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) as inducers of ethoxyresorufin O-deethylase (EROD) activity, cytochrome P4501A (CYP1A4) messenger ribonucleic acid (mRNA) and CYP1A5 mRNA. HCB-P, RG-HCB and TCDD all induced EROD activity and up-regulated CYP1A4 and CYP1A5 mRNA. Induction was not caused by contamination of HCB with polychlorinated dibenzo-p-dioxins, dibenzofurans or biphenyls. Based upon a comparison of the EC(50) and EC(threshold) values for EROD and CYP1A4/5 concentration-response curves, the potency of HCB relative to TCDD was 0.001 in ring-necked pheasant and 0.01 in Japanese quail embryo hepatocytes. Differences in species sensitivity to HCB were found to be mainly dictated by differences in species sensitivity to TCDD rather than differences in the absolute potency of HCB. Consequently, ring-necked pheasant and Japanese quail embryo hepatocytes were found to be equally sensitive to HCB exposure. Species sensitivity comparisons were also made with chicken (Gallus gallus domesticus) and revealed that chicken embryo hepatocytes were less responsive to EROD induction (lower maximal response) by HCB compared to the embryo hepatocytes of pheasant and quail.

Variation of basal EROD activities in ten passerine bird species--relationships with diet and migration status

Inter-specific differences in animal defence mechanisms against toxic substances are currently poorly understood. The ethoxyresorufin-O-deethylase (EROD) enzyme plays an important role in defence against toxic chemicals in a wide variety of animals, and it is an important biomarker for environmental contamination. We compared basal hepatic EROD activity levels among ten passerine species to see if there is inter-specific variation in enzyme activity, especially in relation to their diet and migration status. Migratory insectivores showed higher EROD activity compared to granivores. We hypothesize that the variable invertebrate diet of migratory insectivores contains a wider range of natural toxins than the narrower diet of granivores. This may have affected the evolution of mixed function oxidases (MFO) system and enzyme activities. We further tested whether metabolic rates or relative liver size were associated with the variation in detoxification capacity. We found no association between EROD activity and relative (per mass unit) basal metabolic rate (BMR). Instead, EROD activity and relative liver mass (% of body mass) correlated positively, suggesting that a proportionally large liver also functions efficiently. Our results suggest that granivores and non-migratory birds may be more vulnerable to environmental contaminants than insectivores and migratory birds. The diet and migration status, however, are phylogenetically strongly connected to each other, and their roles cannot be fully separated in our analysis with only ten passerine species.

In vitro transactivation potencies of black-footed albatross (Phoebastria nigripes) AHR1 and AHR2 by dioxins to predict CYP1A expression in the wild population

Our previous studies have detected high levels of dioxins and related compounds (DRCs) including polychlorinated dibenzo-p-dioxins (PCDDs), furans (PCDFs), and coplanar PCBs (Co-PCBs) in the black-footed albatross (BFA), Phoebastria nigripes, from the North Pacific region. We have also cloned two aryl hydrocarbon receptors, AHR1 and AHR2, of the BFA. To evaluate the sensitivity to DRCs in the BFA and to assess the status of cytochrome P450 1A (CYP1A) induction in the wild population, this study investigated the mRNA expression levels of BFA AHR1 and AHR2 and also the transactivation potencies of each AHR by 15 selected DRC congeners. Quantitative real-time PCR of BFA AHR mRNAs showed that hepatic AHR1 is more highly expressed than AHR2. Transactivation by graded concentrations of individual DRCs was measured in COS-7 cells, where BFA AHR1 or AHR2 was transiently transfected. For congeners that exhibited AHR-mediated dose-dependent activities, 50% effective concentration (EC(50)) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) relative potencies (REPs) were estimated. Based on the estimates of the REPs, TCDD induction equivalency factors (IEFs) were determined. For BFA AHR1, PeCDF was equipotent to TCDD, but other congeners exhibited lower IEFs. For BFA AHR2, PCDD/F congeners except OCDD/F showed IEFs ≥ 1.0. Using BFA AHR1- or AHR2-IEFs and hepatic concentrations of DRCs in North Pacific BFAs, TCDD induction equivalents (IEQs) were calculated. We further constructed nonlinear regression models on the relationships between BFA AHR1- or AHR2-IEF derived total IEQ or WHO-TEF derived total TEQ and ethoxyresorufin-O-deethylase activity (EROD) in the liver of wild BFAs. The results indicated that the relationships of BFA AHR1- and AHR2-based IEQs and EROD were predictable from BFA AHR1- and AHR2-mediated transactivation by TCDD, respectively. Collectively, these results suggest that the in vitro assay incorporating the AHR of species of concern would be a useful tool to predict the sensitivity to DRCs in the species and CYP1A induction in the wild population.

Differential display system with vertebrate-common degenerate oligonucleotide primers: uncovering genes responsive to dioxin in avian embryonic liver

To assess possible impacts of environmental pollutants on gene expression profiles in a variety of organisms, we developed a novel differential display system with primer sets that are common in seven vertebrate species, based on degenerate oligonucleotide-primed PCR (DOP-PCR). An 8-mer inverse repeat motif was found in most transcripts from the seven vertebrates including fish to primates with detailed transcriptome information; more than 10,000 motifs were recognized in common in the transcripts of the seven species. Among them, we selected 275 common motifs that cover about 40-70% of transcripts throughout these species, and designed 275 DOP-PCR primers that were common to seven vertebrate species (common DOP-PCR primers). To detect genes responsive to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in developing embryos, differential display with common DOP-PCR primers was applied to embryonic liver of two avian species, the chicken (Gallus gallus) and the common cormorant (Phalacrocorax carbo), which were exposed in ovo to TCDD. The cDNA bands that showed differences between the control and TCDD-treated groups were sequenced and the mRNA expression levels were confirmed by real-time RT-PCR. This approach succeeded in isolating novel dioxin-responsive genes that include 10 coding genes in the chicken, and 1 coding gene and 1 unknown transcript in the cormorant, together with cytochrome P450 1As that have already been well established as dioxin markers. These results highlighted the usefulness of systematically designed novel differential display systems to search genes responsive to chemicals in vertebrates, including wild species, for which transcriptome information is not available.

Gene expression and inducibility of the aryl hydrocarbon receptor-dependent pathway in cultured bovine blood lymphocytes

The exposure to dioxin-like (DL) compounds, an important class of persistent environmental pollutants, results in the altered expression of target genes. This occurs through the binding to the aryl hydrocarbon receptor (AhR), the subsequent dimerization with the AhR nuclear translocator (ARNT), and the binding of the complex to DNA responsive elements. A number of genes are up-regulated, including, among others, the AhR repressor (AHRR) and several biotransformation enzymes, such as the members of CYP1 family and NAD(P)H-quinone oxidoreductase (NOQ1). The expression and the inducibility of the above genes were investigated in mitogen-stimulated cultured blood lymphocytes from cattle, which represent a notable source of DL-compound human exposure through dairy products and meat. As assessed by real-time PCR, all the examined genes except CYP1A2 and NQO1 were detected under basal conditions. Cell exposure to the DL-compounds PCB126 or PCB77 in the 10(-6)-10(-9)M concentration range resulted in a 2-4-fold induction of CYPIA1 and CYP1B1, which was antagonized by α-naphthoflavone or PCB153. This study demonstrates for the first time the presence and inducibility of the AhR pathway in easily accessible cells like bovine peripheral lymphocytes and prompts further investigations to verify whether similar changes could occur under in vivo conditions.

Developmental and posthatch effects of in ovo exposure to 2,3,7,8-TCDD, 2,3,4,7,8-PECDF, and 2,3,7,8-TCDF in Japanese quail (Coturnix japonica), common pheasant (Phasianus colchicus), and white leghorn chicken (Gallus gallus domesticus) embryos

An egg injection study was conducted to confirm a proposed model of relative sensitivity of three avian species to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like chemicals. It was previously reported that the order of species sensitivity to in ovo exposure to TCDD, 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), or 2,3,7,8-tetrachlorodibenzofuran (TCDF) at doses ranging from 0.044 to 37 picomoles (pmol)/g egg was the chicken (Gallus gallus domesticus), common pheasant (Phasianus colchicus), and Japanese quail (Coturnix japonica) based on embryo mortality and hepatic enzyme induction. In the present study, the incidence of developmental deformities, changes in body and relative organ masses, and organ pathology of hatchlings as additional indicators of species sensitivity were assessed; in addition, embryo mortality in the three species was categorized by stage of development. Embryo mortality varied temporally with significant increases generally occurring after organogenesis and just prior to hatching. A significant increase in the percentage of developmental deformities was observed only in Japanese quail exposed to TCDF. Body and relative organ masses of quail, pheasants, and chickens dosed in ovo with TCDD, PeCDF, or TCDF were not consistently affected. Chemical-related pathology occurred only in livers of quail at the greatest doses of each compound. These results indicated that the incidence of developmental deformities, changes in body and relative organ masses and organ pathology could not be used as indicators of species sensitivity or chemical potency.

2,3,4,7,8-pentachlorodibenzofuran is a more potent cytochrome P4501A inducer than 2,3,7,8-tetrachlorodibenzo-p-dioxin in herring gull hepatocyte cultures

Concentration-dependent effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), and 2,3,7,8-tetrachlorodibenzofuran (TCDF) on cytochrome P4501A (CYP1A) induction were determined in primary cultures of embryonic herring gull (Larus argentatus) hepatocytes exposed for 24 h. Based on the concentration that induced 50% of the maximal response (EC50), the relative potencies of TCDD and TCDF did not differ by more than 3.5-fold. However, also based on the EC50, PeCDF was 40-fold, 21-fold, and 9.8-fold more potent for inducing ethoxyresorufin-O-deethylase (EROD) activity, CYP1A4 mRNA expression, and CYP1A5 mRNA expression than TCDD, respectively. The relative CYP1A-inducing potencies of PeCDF and of other dioxin-like chemicals (DLCs) in herring gull hepatocytes (HEH RePs), along with data on concentrations of DLCs in Great Lakes herring gull eggs, were used to calculate World Health Organization toxic equivalent (WHO-TEQ) concentrations and herring gull embryonic hepatocyte toxic equivalent (HEH-TEQ) concentrations. The analysis indicated that, when using avian toxic equivalency factors (TEFs) recommended by the WHO, the relative contribution of TCDD (1.1-10.2%) to total WHO-TEQ concentration was higher than that of PeCDF (1.7-2.9%). These results differ from the relative contribution of TCDD and PeCDF when HEH RePs were used; PeCDF was a major contributor (36.5-52.9%) to total HEH-TEQ concentrations, whereas the contribution by TCDD (1.2-10.3%) was less than that of PeCDF. The WHO TEFs for avian species were largely derived from studies with the domestic chicken (Gallus gallus domesticus). The findings of the present study suggest that it is necessary to determine the relative potencies of DLCs in wild birds and to re-evaluate their relative contributions to the biochemical and toxic effects previously reported in herring gulls and other avian species.

Effects of in ovo exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin on hepatic AHR/ARNT-CYP1A signaling pathways in common cormorants (Phalacrocorax carbo)

Our previous studies have isolated multiple isoforms of aryl hydrocarbon receptors (AHRs) and AHR nuclear translocators (ARNTs) in avian species. However, roles of such genes on cytochrome P450 1A (CYP1A) expression are not fully understood. To investigate the effects of dioxins on the hepatic expression profiles of AHR1, AHR2, ARNT1 and ARNT2 in avian species, and whether the expression levels of AHRs and ARNTs affect the transcriptions of CYP1A4 and CYP1A5 genes, the eggs of common (great) cormorants (Phalacrocorax carbo) collected from Lake Biwa, Japan, were in ovo administrated with 0, 1500 and 4500pg/g egg of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and the hepatic expression levels of AHRs, ARNTs and CYP1As in embryos were monitored with two-step real-time RT-PCR. In young and adult cormorants collected from the same location, the hepatic expressions of these genes were also measured to understand the effects of growth stage. The residue levels of TCDD and other chlorinated dioxin-like congeners (DLCs) in the body of cormorants were quantified with high-resolution gas chromatography equipped with mass-spectrometry. There was no observable effect of in ovo TCDD treatment even at the highest dosage on mortality, body weight and morphology of the liver, heart, spleen, kidney and lung in the embryos. The mRNA expression of ARNT2 was slightly suppressed by the treatment with TCDD, while no alteration was observed for the expression of AHR1, AHR2 and ARNT1. Expressions of CYP1A4 and CYP1A5 were dose-dependently enhanced by TCDD, but CYP1A4 mRNA level increased more prominently than CYP1A5, indicating the difference in induction efficiency between the CYP1A isozymes. Comparison of hepatic mRNA levels of these genes among embryonic, young and adult cormorants revealed that young and adult cormorants had greater CYP1A5 expression levels than embryos, independently of the accumulation levels of DLCs. These results suggest that the hepatic induction of each CYP1A by DLCs in cormorants occurs in an isoform-specific manner and CYP1A5 expression, at least partially, depends on the factors related to the growth of cormorants, but the transcriptional processes of CYP1As are not related to the expression levels of AHRs and ARNTs. This study yielded results supporting our previous observations that in reality, high accumulation of DLCs induces hepatic CYP1A4 and 1A5 expressions in the wild cormorant population.

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.

Hepatic CYP1A induction by chlorinated dioxins and related compounds in the endangered black-footed albatross from the North Pacific

The present study assesses effects of dioxins and related compounds (DRCs) including polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls (DL-PCBs) on cytochrome P450 1A (CYP1A) expression level in liver of black-footed albatrosses (Phoebastria nigripes) collected from the North Pacific. Total 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-T(4)CDD) toxic equivalents (TEQs) derived from toxic equivalency factor for birds proposed by World Health Organization were in the range of 2100 to 10 000 pg/g lipid wt (120-570 pg/g wet wt). Simultaneously, microsomal alkoxyresorufin O-dealkylase (AROD) activities, including methoxy-, ethoxy-, pentoxy-, and benzyloxy-resorufin O-dealkylase activities were also measured in the same specimens. Total TEQs and TEQ (on wet wt basis) from some individual DRC congeners had significant positive correlations with AROD activities, suggesting induction of CYP1A by DRCs. Congeners like 2,3,7,8-T(4)CDD and most of the DL-PCBs that showed no significant positive correlations between the concentrations and AROD activities, exhibited significant negative correlations between AROD activities and the concentration ratio of the congener to a recalcitrant CB169, suggesting preferential metabolism of these congeners by induced CYP1A. As far as we know, this is the first direct evidence revealing that hepatic CYP1A level is elevated with the accumulation of DRCs in the wild black-footed albatross population. The present study gives more robust estimate of impacts of DRCs on CYP1A induction in this rare pelagic species than indexes like hazard quotient and TEQ-threshold comparison that have been so far carried out.