Effects of TCDD and its congeners 3,3',4,4'-tetrachloroazoxybenzene and 3,3',4,4'-tetrachlorobiphenyl on lymphoid development in the thymus of avian embryos

Metabolic and Hematological Responses to Endotoxin-Induced Inflammation in Chicks Experiencing Embryonic 2,3,7,8-Tetrachlorodibenzodioxin Exposure

Dioxin exposure during bird embryonic development disrupts immunity as well as mechanisms involved in energy metabolism, potentially affecting negatively acute-phase responses to pathogens. Thus, we hypothesized that embryonic exposure to 2,3,7,8-tetrachlorodibenzodioxin (TCDD) changes the metabolism and blood physiology of domestic chicks, affecting their physiological competence for responding to immune challenges. To test this hypothesis, we injected doses of 0, 1.5, and 3 ng TCDD/egg (based on survival experiments) on embryonic day 4 and then measured O₂ consumption and CO₂ production for metabolic rate, ventilation, and body temperature (T_B ) in 5-d-old chicks. Then, chicks were injected with lipopolysaccharide (LPS, endotoxin) or saline prior to repeating the physiological measurements. A second chick group exposed to identical TCDD and LPS treatments had blood partial pressure of oxygen, partial pressure of carbon dioxide, pH, bicarbonate concentration, lactate concentration, osmolality, hemoglobin concentration, red blood cell concentration, and hematocrit, as well as T_B , analyzed at 1 and 5 h after LPS injection. Metabolism in chicks embryonically exposed to 1.5 and 3 ng TCDD/egg was up to 37% higher, whereas body mass of chicks exposed to 3 ng TCDD/egg was approximately 6% lower. Chicks embryonically exposed to 3 ng TCDD/egg challenged with LPS showed a relative persistent hypometabolism accompanied by elimination of the normal hematological and osmotic responses to LPS. We conclude that embryonic exposure to TCDD affects posthatching metabolism as well as impairs metabolic, hematological, and osmotic responses to LPS. Environ Toxicol Chem 2020;39:2208-2220. © 2020 SETAC.

Effects of PCB 126 on primary immune organs and thymocyte apoptosis in chicken embryos

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyl (PCB) 126 produce thymic atrophy and immunosuppression. This study explored the hypothesis that the thymic atrophy produced by developmental exposure to PCB 126 is associated with an increase in apoptotic thymocytes at the end of incubation in chicken embryos. Eggs were injected via the air cell with PCB 126 (0.05, 0.13, 0.32, 0.64, and 0.80 ng/g egg) on d 0 of incubation, and tissues were collected on d 20. Controls included noninjected and vehicle-injected (sunflower oil) eggs. Thymocytes were cultured for 6 h and analyzed by flow cytometry for decreased DNA content (propidium iodide staining) and cell size (forward scatter), which indicate apoptosis. PCB 126 induced dose-dependent mortality with an LD50 of 1.01 ng/g and lowest-observed-effect concentration (LOEC) of 0.32 ng/g. Teratogenic effects commonly associated with TCDD and planar PCBs, including cranial and foot deformities and subcutaneous edema, tended to increase with dose of PCB 126. PCB 126 reduced thymus mass by approximately 20% at 0.64 and 0.8 ng/g, the number of viable thymocytes by approximately 20-24% at and above 0.13 ng/g, and the number of bursal lymphoid cells by 57% at 0.64 ng/g. The percentage of apoptotic thymocytes increased with dose, reaching levels 2 times greater than controls at 0.8 ng/g. Electrophoresis of low-molecular-weight DNA from thymocytes of all doses demonstrated fragments in multiples of 180 bp. This DNA laddering is a hallmark of apoptosis. At all doses, thymocytes exhibited caspase-3 activation, another indicator of apoptosis. The results of this experiment supported the hypothesis that the thymic atrophy produced by developmental exposure to PCB 126 in chicken embryos is associated with an increase in apoptotic thymocytes on embryonic d 20.

Effects of an extract of oystercatcher (Haematopus ostralegus) eggs from the Zeehavenkanaal in The Netherlands, and of its major contaminant, hexachlorobenzene, on the chicken embryo

Oystercatchers (Haematopus ostralegus) foraging on the canal 'Zeehavenkanaal' in the Netherlands have been shown to accumulate appreciable amounts of contaminants, especially hexachlorobenzene. The present study was performed to assess the embryotoxic effects of the present contaminants. To this end, a two step approach was followed. In step one, the toxic effects of hexachlorobenzene were studied in the chicken embryo bioassay, using concentrations realistic for the field situation. In step two, yolks of oystercatcher eggs were extracted and the embryotoxic potency of this extract was studied in the same bioassay, using doses of 1, 10 and 100% of the contaminant load in one average egg. The extract contained hexachlorobenzene and PCBs. However, presence of other compounds could not be excluded, since these were not analysed. Hexachlorobenzene induced a nonsignificant decrease in lymphocyte density in the bursa of Fabricius. The egg extract caused a 3.5 fold induction of EROD activity at the highest dose applied, and decreased lymphocyte density in the bursa of Fabricius.

Detection and localization of 3,3',4,4'-tetrachlorobiphenyl-induced P4501A protein in avian primary immune tissues

P4501A can be detected in thymic and bursal microsomes from chickens pretreated with 3,3',4,4'-tetrachlorobiphenyl (TCB) using a polyclonal antibody against purified P4501A from 3-methylcholanthrene (3-MC)-induced chicken embryo liver. A dose-response for induction by TCB of P4501A protein was detected by Western blotting in both bursal and thymic microsomes. Ethoxyresorufin-O-deethylase (EROD), a specific catalytic activity of P4501A, was also induced in a dose-response fashion. More TCB-induced P4501A was detected in thymus than bursa by both methods. No EROD was detected in bursal or thymic microsomes from untreated chickens, although P4501A protein was detected at very low levels in thymic microsomes from untreated chickens. P4501A was detected by immunohistochemistry in scattered patches of non-lymphocytic cells residing in medullary regions of the TCB-induced thymus but was not detected in lymphocytes. This result supports previous work demonstrating that TCB-inducible EROD is much higher in the supporting tissue cell fractions than in lymphocyte fractions of the primary immune tissues. Although EROD was induced by TCB in the late stage embryo after 20 h exposure, no effect of TCB on the cell cycle in thymic or bursal lymphocytes was observed over the same period. The same TCB exposure resulted in bursal but not thymic cellular depletion. Thymic and bursal supporting tissue cells may be primary sites of immunosuppression within these organs by P4501A inducers or substrates whether immunosuppression occurs subsequent to metabolism or through interaction with Ah receptors.

Monitoring biological effects of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls in great blue heron chicks (Ardea herodias) in British Columbia

The Canadian Wildlife Service monitors levels of polychlorinated aromatic hydrocarbons in great blue heron (Ardea herodias) eggs in British Columbia as indicators of environmental contamination. The present project assessed the temporal effects of environmental contamination with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) on hepatic microsomal ethoxyresorufin O-deethylase (EROD) activities and several morphological parameters in heron hatchlings. Between 1990 and 1992, eggs were collected from two great blue heron colonies in British Columbia that had elevated levels of contamination in 1988: Vancouver in 1990 and 1992, and Crofton in 1991. Biological parameters in the hatchlings and chemical contaminant levels in matched eggs from the same clutch were measured and compared with the findings from the same colonies studied in 1988. Levels of TCDD and other PCDDs and PCDFs had decreased significantly in both colonies since 1988. A concomitant decrease in EROD activity and incidence of chick edema, increase in body weight, and improvement of the reproductive success of the Crofton colony was observed. Body, yolk-free body, stomach, and intestine weights, tibia wet, dry, and ash weights, and tibia length regressed negatively on TCDD level (p < .01; n = 54). Hepatic EROD activity regressed positively on TCDD level (r2 = .49; p = .00005; n = 54). Regression of these parameters on the sum of TCDD toxic equivalents (TEQ) resulted in similar relationships. The reduction in severity of the effects observed in the contaminated colonies in the recent collections, accompanied by the declines in levels of PCDDs and PCDFs, was consistent with the dose-response relationships determined in 1988.

Biological effects of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls in double-crested cormorant chicks (Phalacrocorax auritus)

The present project assessed the effect of environmental contamination with polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) on hepatic microsomal ethoxyresorufin O-deethylase (EROD) activities and morphological parameters in matched double-crested cormorant (Phalacrocorax auritus) hatchlings from egg clutches chosen for chemical analysis. Double-crested cormorant eggs were collected from five colonies across Canada, with differing levels of contamination. Levels of contamination expressed in sum of 2,3,7,8-tetrachlorodibenzo-p-dioxin-toxic equivalents (TCDD-toxic equivalents or TEQ, ng/kg egg; mean +/- SEM) were: Saskatchewan, 250 +/- 50; Chain Islands, 672 +/- 73; Christy Islet, 276 +/- 14; Crofton, 131, n = 1; and Lake Ontario, 1606 +/- 118. In the hatchlings, hepatic EROD activities (pmol/min/mg protein; mean +/- SEM) were: Saskatchewan, 283 +/- 42; Chain Islands, 516 +/- 98; Christy Islet, 564 +/- 91; Crofton, 391 +/- 52; and Lake Ontario, 2250 +/- 156. Hepatic microsomal EROD activity (pmol/min/mg protein) regressed positively on TEQ (r2 = .69; p < .00005; n = 25). Yolk weight (g) regressed negatively on TEQ (r2 = .44; p = .00005). Wing length (mm) regressed negatively on PCB-169 (r2 = .28; p = .007). Monospecific antibodies raised against rat cytochrome P-450 1A1 recognized a protein in the hepatic microsomes of the double-crested cormorant, and also in those of the great blue heron (Ardea herodias), using immunoblotting. The intensity of the stained band increased with increased EROD activity, supporting the assumption that ethoxyresorufin is a suitable substrate for avian cytochrome P-450 1A1. These results validate the use of avian hepatic microsomal EROD activity as an index of cytochrome P-450 1A1 induction by environmental levels of polychlorinated aromatic hydrocarbons and as a useful screening tool to determine the extent of exposure to such chemicals. Furthermore, the induction of cytochrome P-450 1A1 observed in the cormorant indicates that the Ah receptor-mediated process, by which TCDD and related chemicals exert many of their toxicities, has been activated.

Polychlorinated biphenyls (PCBs): environmental impact, biochemical and toxic responses, and implications for risk assessment

Commercial polychlorinated biphenyls (PCBs) and environmental extracts contain complex mixtures of congeners that can be unequivocally identified and quantitated. Some PCB mixtures elicit a spectrum of biochemical and toxic responses in humans and laboratory animals and many of these effects resemble those caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related halogenated aromatic hydrocarbons, which act through the aryl hydrocarbon (Ah)-receptor signal transduction pathway. Structure-activity relationships developed for PCB congeners and metabolites have demonstrated that several structural classes of compounds exhibit diverse biochemical and toxic responses. Structure-toxicity studies suggest that the coplanar PCBs, namely, 3,3',4,4'-tetrachlorobiphenyl (tetraCB), 3,3',4,4',5-pentaCB, 3,3',4,4',5,5'-hexaCB, and their monoortho analogs are Ah-receptor agonists and contribute significantly to the toxicity of the PCB mixtures. Previous studies with TCDD and structurally related compounds have utilized a toxic equivalency factor (TEF) approach for the hazard and risk assessment of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) congeners in which the TCDD or toxic TEQ = sigma([PCDFi x TEFi]n)+sigma([PCDDi x TEFi]n) equivalent (TEQ) of a mixture is related to the TEFs and concentrations of the individual (i) congeners as indicated in the equation (note: n = the number of congeners). Based on the results of quantitative structure-activity studies, the following TEF values have been estimated by making use of the data available for the coplanar and monoortho coplanar PCBs: 3,3',4,4',5-pentaCB, 0.1; 3,3',4,4',5,5'-hexaCB, 0.05; 3,3',4,4'-tetraCB, 0.01; 2,3,3',4,4'-pentaCB, 0.001; 2,3',4,4',5-pentaCB, 0.0001; 2,3,3',4,4',5-hexaCB, 0.0003; 2,3,3',4,4',5'-hexaCB, 0.0003; 2',3,4,4',5-pentaCB, 0.00005; and 2,3,4,4',5-pentaCB, 0.0002. Application of the TEF approach for the risk assessment of PCBs must be used with considerable caution. Analysis of the results of laboratory animal and wildlife studies suggests that the predictive value of TEQs for PCBs may be both species- and response-dependent because both additive and nonadditive (antagonistic) interactions have been observed with PCB mixtures. In the latter case, the TEF approach would significantly overestimate the toxicity of a PCB mixture. Analysis of the rodent carcinogenicity data for Aroclor 1260 using the TEF approach suggests that this response is primarily Ah-receptor-independent. Thus, risk assessment of PCB mixtures that uses cancer as the endpoint cannot solely utilize a TEF approach and requires more quantitative information on the individual congeners contributing to the tumor-promoter activity of PCB mixtures.

Developmental and reproductive toxicity of dioxins and related compounds: cross-species comparisons

Developmental toxicity to TCDD-like congeners in fish, birds, and mammals, and reproductive toxicity in mammals are reviewed. In fish and bird species, the developmental lesions observed are species dependent, but any given species responds similarly to different TCDD-like congeners. Developmental toxicity in fish resembles "blue sac disease," whereas structural malformations can occur in at least one bird species. In mammals, developmental toxicity includes decreased growth, structural malformations, functional alterations, and prenatal mortality. At relatively low exposure levels, structural malformations are not common in mammalian species. In contrast, functional alterations are the most sensitive signs of developmental toxicity. These include effects on the male reproductive system and male reproductive behavior in rats, and neurobehavioral effects in monkeys. Human infants exposed during the Yusho and Yu-Cheng episodes, and monkeys and mice exposed perinatally to TCDD developed an ectodermal dysplasia syndrome that includes toxicity to the skin and teeth. Toxicity to the central nervous system in monkey and human infants is a potential part of the ectodermal dysplasia syndrome. Decreases in spermatogenesis and the ability to conceive and carry a pregnancy to term are the most sensitive signs of reproductive toxicity in male and female mammals, respectively.

Distribution and inducibility of a P450I activity in cellular components of the avian immune system

The level of expression of the cytochrome P450 system in an immune tissue could influence the sensitivity of that immune tissue to damage by xenobiotics. The capacity of immune organs and their cellular components for P450I-catalyzed metabolism was assayed in the 4-week-old chicken using the P450I-specific ethoxyresorufin-O-deethylase (EROD) assay and the P450I-inducer, 3,4,3',4'-tetrachlorobiphenyl (TCB). After induction by TCB, EROD was detectable in microsomes from whole thymus, bursa and in peritoneal exudate cells (containing primarily macrophages) at levels of 28.3, 7.2 and 1.3 pmol/mg microsomal protein/min, respectively; the level in control liver was 89.9 pmol/mg microsomal protein/min. No activity was detected in these immune tissues without induction. The P450I specific in vitro inhibitor, alpha-naphthoflavone (NF) inhibited the TCB-induced liver and immune tissue EROD by 50% at concentrations in the range of 0.07-0.1 microM. The cellular distribution of EROD in the bursa and thymus was studied in lymphocytes and supporting tissue cells after their separation by density gradient centrifugation. Much higher TCB-induced EROD was detected in immune tissue supporting cells than in lymphocytes, particularly in the thymus. The P450I in the supporting tissue of the bursa and thymus at 1 week post-hatch was also measured after eradication of the lymphocytes in both immune tissues by in ovo administration of CP. TCB-induced EROD was 12-fold higher in the lymphocyte-depleted thymus than in normal thymus, with a less marked but similar pattern in the bursa.(ABSTRACT TRUNCATED AT 250 WORDS)

Genotoxic potential of the organochlorine insecticide lindane (gamma-BHC): an in vivo study in chicks

The purpose of this work was to evaluate the genotoxic potential of lindane (gamma-isomer of benzene hexachloride (BHC)) in chicken in vivo tests: the bone marrow chromosome aberration and micronucleus tests. With the highest dose (100 mg/kg) a significant enhancement of chromosome aberrations was noticed after 24 and 48 h and with the second highest dose (75 mg/kg) after 24 h. A significant increase in the incidence of micronuclei in bone marrow cells was induced by all three doses (100, 75 and 50 mg/kg) given either intraperitoneally or orally while in peripheral erythrocytes only the two higher intraperitoneal doses (100 and 75 mg/kg) gave significant increases. On the basis of these results, lindane may be considered genotoxic in this test system and it is suggested that the chick in vivo system may be used as an alternative to a mammalian system for screening environmental chemicals for genotoxicity.

Roles of dosage, pharmacokinetics, and cellular sensitivity to damage in the selective toxicity of cyclophosphamide towards B and T cells in development

Cyclophosphamide (CP) is a known immunomodulating agent. When presented to either late stage chick embryos (e.g. 18 days of incubation (DI] or neonatal chicks. CP induces selective B cell damage resulting in humoral immunosuppression in chickens. The present study was undertaken in order to provide further insights into CP's selective immunotoxic effects. We investigated the influences of age, CP-dose, and drug distribution on CP-induced cytotoxicity in the B and T cell compartments of the developing chick. In this test system, differential immunotoxicity was strongly dosage-dependent; at all ages tested, B cell depletion predominated at low CP dosages (50 and 100 mg/kg) whereas equally extensive lymphocyte toxicity was observed in both thymus and bursa at 200 mg/kg drug levels. Furthermore, while immunotoxicity profiles were similar at the two later developmental timepoints (18 DI and 1 day post-hatch), significantly higher CP dosages were required to induce lymphoid damage at 12 DI. Pharmacokinetic studies with radiolabeled CP revealed that approximately two-fold higher levels of CP and its metabolites are taken up in bursal tissue as compared to the thymus. Experiments concerning the possible inherent differences in susceptibility to CP-induced mitotic inhibition and cell killing mediating selective toxicity towards B cells versus T cells showed that B cell mitosis was inhibited at CP dosages as low as 5 mg/kg. No such inhibition of T cell mitosis was observed at this same low dosage. However, mitosis was completely arrested in both B and T cells at 50 mg/kg CP. Observations of cellularity in immune organs shortly after CP exposure revealed that the bursa is at least ten times more sensitive than the thymus to CP-induced mitotic inhibition and killing of resident lymphocytes. These studies reveal that multiple factors are involved in modulating CP selective immunotoxicity in the developing embryo. These include the dosage level, preferential distribution of the drug to the bursa, and a much greater sensitivity of B cells to CP-mediated mitotic inhibition and cell killing.

2,3,7,8-Tetrachlorodibenzo-p-dioxin increases reliance on fats as a fuel source independently of diet: evidence that diminished carbohydrate supply contributes to dioxin lethality

The environmental toxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes a wasting syndrome marked by hypophagia, loss of body fat, changes in intermediary metabolism and death. Use of conventional laboratory animals has not resolved whether or not TCDD affects intermediary metabolism independently of hypophagia. We used the chick embryo, which does not require an exogenous food supply for energy, to answer this question. Our results show that TCDD treatment increases dependence on fats as a fuel source independently of changes in food intake and therefore can affect intermediary metabolism independently of hypophagia. Results of experiments using aminocarnitine to inhibit fatty acid oxidation suggest that TCDD treatment impairs carbohydrate production rather than its utilization and that the former effect contributes to TCDD lethality.

Cyclophosphamide metabolism in the primary immune organs of the chick: assays of drug activation, P450 expression, and aldehyde dehydrogenase

Several diagnostic catalytic assays were used to determine whether organ-specific metabolic activation or detoxification of cyclophosphamide (CP) contributes to the selective toxicity of CP directed towards differentiating B cells as compared to T cells in the developing chicken. An assay for the alkylation of 4-[p-nitrobenzyl] pyridine (NBP) was used to assess comparative levels of CP activation products generated from microsomal preparations from liver, bursa of Fabricius (B cells), and thymus (T cells) of day-old chicks. Three catalytic assays were used to characterize and compare cytochrome P450-associated enzyme activities in neonatal hepatic and lymphoid tissues. Aldrin epoxidase (AE) was used to detect phenobarbital (PB)-inducible P450 activity. Ethoxyresorufin-O-deethylase (EROD) and aryl hydrocarbon hydroxylase (AHH) were used for the evaluation of polycyclic aromatic hydrocarbon (PAH)-inducible P450 activities in control and PB- or 3,3',4,4'-tetrachlorobiphenyl (TCB)-induced animals. Using the NBP assay, basal and PB-induced CP activation were observed using chick liver microsomes. However, no evidence of CP activation from immune organ microsomes was observed in control, PB-, or TCB-induced chicks. Basal and PB-induced AE activities were observed in thymus, but not bursa, and represented less than 1% of basal liver activity. EROD activity was detected in TCB-induced samples from both thymus and bursa, the thymus having the greater activity. Activities of aldehyde dehydrogenase (ALDH), an enzyme involved in CP detoxification, were about equal in cytosolic fractions from the bursa and thymus. These studies suggest strongly that tissue-specific differences in metabolic capacities are not the major factors governing the selective toxicity of CP directed towards differentiating B lymphocytes in vivo.

TCDD inhibits the support of B-cell development by the bursa of Fabricius

The toxic effects produced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and its congeners include inhibition of lymphoid development. We have previously found an inhibition of B-cell development in the bursa of Fabricius of chick embryos treated with TCDD congeners in ovo. In the present study, the bursae of ten-day-old chick embryos were removed and cultured on filter paper for 24 hr in media with or without TCDD or 3,3',4,4'-tetrachlorazoxybenzene (TCAOB). Following culture, the bursae were transplanted onto the chorioallantoic membrane (CAM) of ten-day-old eggs of the same strain or of a strain expressing a different B-cell surface alloantigen. After 5 days on the CAM the number of B-cells was determined or the grafts were sectioned for subsequent immunohistochemistry. Results were as follows: 1) A lower number of lymphoid cells (dose dependent) was observed in the TCDD-treated transplants amounting to 40-50% of that in the controls at 10(-9) M TCDD. Higher concentrations of TCDD compromised survival of the grafts. A single concentration of TCAOB (10(-8) M) was tested, resulting in a lymphoid cell number of 60% of that of the controls. 2) The bursal epithelium showed relatively normal development even in cases where B-cell development was affected. 3) Lymphoid cells in the grafted bursae originated from the embryo of the host egg. These findings suggest that the TCDD congeners had a direct effect on the bursa of Fabricius, leading to an inhibition of lymphoid development. It is likely that the microenvironment is affected by these compounds, thus resulting in a decrease in the attraction of stem cells and/or in the capacity to induce proliferation of the colonizing cells.

Differences between chick and turkey embryos in sensitivity to 3,3',4,4'-tetrachloro-biphenyl and in concentration/affinity of the hepatic receptor for 2,3,7,8-tetrachlorodibenzo-p-dioxin

1. 3,3',4,4'-Tetrachlorobiphenyl (TCB) was 20-100 times more toxic in chick embryos than in turkey embryos when injected into eggs. 2. The ED50-value for induction of AHH activity by TCB in the liver of early chick and turkey embryos was estimated to be 0.6 and 6 micrograms/kg egg, respectively. 3. In both species alpha-naphthoflavone was more effective than metyrapone at inhibiting basal and TCB-induced AHH activities. 4. The TCDD receptor was detected in the liver of 7-day-old chick embryos, while it was not found in 9-day-old turkey embryo liver.