Environmental toxicology of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans

Comprehensive metabolic profiling of dioxin-like compounds exposure in laying hens: Implications for toxicity assessment

The evaluation of toxicity related to polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) is crucial for a comprehensive risk assessment in real-world exposure scenarios. This study employed a controlled feeding experiment to investigate the metabolic effects of dioxin-like compounds (DLCs) on laying hens via feed exposure. Diets enriched with two concentrations (1.17 and 5.13 pg toxic equivalents (TEQ)/g dry weight (dw)) were administered over 14 days, followed by 28 days of clean feed. Metabolomics analyses of blood samples revealed significant metabolic variations between PCDD/Fs and DL-PCBs exposed groups and controls, reflecting the induced metabolic disruption. Distinct changes were observed in sphingosine, palmitoleic acid, linoleate, linolenic acid, taurocholic acid, indole acrylic acid, and dibutyl phthalate levels, implying possible connections between PCDD/Fs and DL-PCBs toxic effects and energy-neuronal imbalances, along with lipid accumulation and anomalous amino acid metabolism, impacting taurine metabolism. Moreover, we identified three differential endogenous metabolites-L-tryptophan, indole-3-acetaldehyde, and indole acrylic acid-as potential ligands for the aryl hydrocarbon receptor (AhR), suggesting their role in mediating PCDD/Fs and DL-PCBs toxicity. This comprehensive investigation provides novel insights into the metabolic alterations induced by PCDD/Fs and DL-PCBs in laying hens, thereby enhancing our ability to assess risks associated with their exposure in human populations.

In silico prediction of nuclear receptor binding to polychlorinated dibenzofurans and its implication on endocrine disruption in humans and wildlife

Polychlorinated dibenzofurans (PCDFs) are known to cause endocrine disruption in humans and wildlife but the mechanisms underlying this disruption have not been adequately investigated. In this paper, the susceptibility of the endocrine system to disruption by PCDF congeners via nuclear receptor binding was studied using molecular docking simulation. Findings revealed that some PCDF congeners exhibit high probabilities of binding to androgen receptor in its agonistic and antagonistic conformations. In depth molecular docking analysis of the receptor-ligand complexes formed by PCDFs with androgen receptor in its agonistic and antagonistic conformations showed that, these complexes were stabilized by electrostatic, van der Waals, pi-effect and hydrophobic interactions. It was also observed that PCDF molecules mimic the modes of interaction observed in androgen-testosterone and androgen-bicalutamide complexes, utilizing between 65 and 83% of the amino acid residues used by the co-crystallized ligands for binding. This computational study suggests that some PCDF congeners may act as agonists and antagonists of androgen receptor in humans and wildlife via inapproprate binding to the receptor.

The Aryl Hydrocarbon Receptor as a Modulator of Anti-viral Immunity

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor, which interacts with a wide range of organic molecules of endogenous and exogenous origin, including environmental pollutants, tryptophan metabolites, and microbial metabolites. The activation of AHR by these agonists drives its translocation into the nucleus where it controls the expression of a large number of target genes that include the AHR repressor (AHRR), detoxifying monooxygenases (CYP1A1 and CYP1B1), and cytokines. Recent advances reveal that AHR signaling modulates aspects of the intrinsic, innate and adaptive immune response to diverse microorganisms. This review will focus on the increasing evidence supporting a role for AHR as a modulator of the host response to viral infection.

[Molecular Mechanism Whereby Maternal Exposure to Dioxin Suppresses Sexual Maturation of the Offspring after Growing Up]

 Dioxins, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are responsible for producing serious toxic effects in the next generation, such as sexual immaturity. Our laboratory found that treating pregnant rats on gestational day 15 with TCDD (1 μg/kg orally) targets pituitary luteinizing hormone (LH) to attenuate testicular steroidogenesis in fetuses. Because sex steroids during a short window ("the critical period") in the perinatal stage stimulate brain differentiation closely linked to sexual maturation, it is likely that TCDD imprints sexual immaturity on the offspring due to the lowered expression of LH during the fetal period. To address this hypothesis, we first investigated the effect of supplementation of equine chorionic gonadotropin (eCG), an LH-mimicking hormone, in fetuses exposed to TCDD. The result showed that eCG ameliorated defects in sexual behavior in adulthood as well as in steroidogenesis during the fetal stage. We also found that maternal exposure to TCDD induced the pituitary expression of histone deacetylases (HDACs) in fetuses. In agreement with this, TCDD deacetylated the histones wrapped around the LHβ gene, and valproic acid, an HDAC inhibitor, blocked the reduced level of LHβ caused by TCDD. These observations strongly suggest that TCDD induces the expression of HDACs to attenuate fetal LH production. Finally, such a transient reduction in steroidogenesis of the pituitary-gonadal axis causes a decrease in the expression of hypothalamic gonadotropin-releasing hormone, resulting in defects in sexual behavior in adulthood. This review increases our understanding of the developmental toxicities caused by endocrine disruptors including dioxins.

Sex-Dependent Influence of Developmental Toxicant Exposure on Group B Streptococcus-Mediated Preterm Birth in a Murine Model

Infectious agents are a significant risk factor for preterm birth (PTB); however, the simple presence of bacteria is not sufficient to induce PTB in most women. Human and animal data suggest that environmental toxicant exposures may act in concert with other risk factors to promote PTB. Supporting this "second hit" hypothesis, we previously demonstrated exposure of fetal mice (F1 animals) to the environmental endocrine disruptor 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) leads to an increased risk of spontaneous and infection-mediated PTB in adult animals. Surprisingly, adult F1_males also confer an enhanced risk of PTB to their control partners. Herein, we used a recently established model of ascending group B Streptococcus (GBS) infection to explore the impact of a maternal versus paternal developmental TCDD exposure on infection-mediated PTB in adulthood. Group B Streptococcus is an important contributor to PTB in women and can have serious adverse effects on their infants. Our studies revealed that although gestation length was reduced in control mating pairs exposed to low-dose GBS, dams were able to clear the infection and bacterial transmission to pups was minimal. In contrast, exposure of pregnant F1_females to the same GBS inoculum resulted in 100% maternal and fetal mortality. Maternal health and gestation length were not impacted in control females mated to F1_males and exposed to GBS; however, neonatal survival was reduced compared to controls. Our data revealed a sex-dependent impact of parental TCDD exposure on placental expression of Toll-like receptor 2 and glycogen production, which may be responsible for the differential impact on fetal and maternal outcomes in response to GBS infection.

The protracted waste crisis and physical health of workers in Beirut: a comparative cross-sectional study

BACKGROUND

Since July 2015, Lebanon has been experiencing a waste management crisis. Dumpsites in inhabited areas and waste burning have emerged due to the waste accumulation, further adding to the gravity of the situation. However, the association between the crisis and health of the population has not been scientifically reported.

METHODS

A comparative cross-sectional study was conducted to assess whether exposure to open dumpsites and waste burning is associated with acute health symptoms. The study sample included 221 male workers between the ages of 18-60 years selected from two areas chosen based on their proximity to a garbage dumpsite and waste burning. 110 workers were exposed to a garbage dumpsite and waste burning, and 111 workers were not. Data were collected via a face-to-face interview using a newly developed validated structured questionnaire. Chi-square tests were used to check for statistically significant differences between exposure and covariates. Multivariable analyses using multiple logistic regression were used to compare health symptoms between exposed and unexposed workers adjusting for potential confounders.

RESULTS

The prevalence of acute health symptoms was greater among the exposed workers than the non-exposed workers, including gastrointestinal, respiratory, dermatological and constitutional symptoms. Controlling for confounding variables, such as age, insurance, family support, residence near dumpsite, work site, and smoking, a minimum odds ratio (OR) of 4.30 was obtained when comparing the exposed population to those non-exposed.

CONCLUSION

The strong association between improper waste management and physical health calls for immediate attention by the government, stakeholders and community members to find optimal solutions for this waste management crisis and set immediate priority interventions such as regular waste collection, volume reduction and recycling performance improvement. However, the long recall period may have underestimated our results.

2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced hypertension

Objective:

The purpose of the present study was to evaluate the effects of melatonin on biochemical and cardiovascular changes resulting from exposure to 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD), a polychlorinated dibenzo- para-dioxin.

Methods:

A total of 24 Sprague-Dawley rats were divided equally into the following four groups: (1) control group was administered with 0.5 mL corn oil by gavage and 0.5 cc vehicle of melatonin (proportionally nine parts physiological serum + one part ethyl alcohol) intraperitoneally for 4 weeks, (2) the melatonin group was given 5 mg/kg/day melatonin intraperitoneally for 4 weeks, (3) the TCDD group was given 500 ng/kg/day TCDD by gavage for 4 weeks and (4) the TCDD + melatonin group was given TCDD (500 ng/kg/day) by gavage and melatonin (5 mg/kg/day) intraperitoneally simultaneously for 4 weeks. Systolic blood pressure was evaluated by the tail-cuff method. Vascular responses to phenylephrine and acetylcholine were evaluated in the isolated thoracic aortas.

Results:

TCDD not only augmented the systolic blood pressure but also increased the contractile responses to phenylephrine in aorta. Melatonin reversed the blood pressure augmented by TCDD and decreased the contractile responses to phenylephrine in aorta. TCDD induced an increase in the malondialdehyde levels in kidney tissue and melatonin did not change it. Therefore, TCDD caused a decrease in glutathione levels in kidney tissues and melatonin reversed it.

Conclusion:

Present data demonstrated that TCDD may lead to an increase in blood pressure via increased renal oxidative stress and vascular reactivity. However, melatonin might ameliorate the blood pressure disturbed by TCDD in part by decreasing the oxidant activity induced by TCDD.

Immunoanalysis methods for the detection of dioxins and related chemicals

With the development of biotechnology, approaches based on antibodies, such as enzyme-linked immunosorbent assay (ELISA), active aryl hydrocarbon immunoassay (Ah-I) and other multi-analyte immunoassays, have been utilized as alternatives to the conventional techniques based on gas chromatography and mass spectroscopy for the analysis of dioxin and dioxin-like compounds in environmental and biological samples. These screening methods have been verified as rapid, simple and cost-effective. This paper provides an overview on the development and application of antibody-based approaches, such as ELISA, Ah-I, and multi-analyte immunoassays, covering the sample extraction and cleanup, antigen design, antibody preparation and immunoanalysis. However, in order to meet the requirements for on-site fast detection and relative quantification of dioxins in the environment, further optimization is needed to make these immuno-analytical methods more sensitive and easy to use.

Xenobiotic metabolism of bank vole (Myodes glareolus) exposed to PCDDs

Previous studies in bank vole (Myodes glareolus) and field vole (Microtus agrestis) living at the old sawmill area contaminated by chlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) showed that these two relatively close species have a significant difference in their body burden of PCDD/Fs, bank voles having significantly higher concentrations. The aim of this study was to clarify more comprehensively the basic xenobiotic metabolism in wild bank voles and examine whether PCDD exposure would affect xenobiotic metabolism in bank voles more generally. The activity of cytochrome P450 enzymes was studied by fluorometric analyzes as well as by the aid of an earlier developed N-in-one CYP-selective activity cocktail, and immunoblotting assay. Several CYP-associated activities were considerably and statistically significantly elevated in the liver of animals living in the contaminated area. Increases in several CYP1A- and CYP2A/B-associated activities are probably due to the exposure to variable dioxin- and PCB-class inducers. The results of this comprehensive screening seemed to be in agreement with the existing knowledge of CYP enzyme induction by dioxin-like substances.

Chemical contaminants in feedlot wastes: concentrations, effects and attenuation

Commercial feedlots for beef cattle finishing are potential sources of a range of trace chemicals which have human health or environmental significance. To ensure adequate protection of human and environmental health from exposure to these chemicals, the application of effective manure and effluent management practices is warranted. The Australian meat and livestock industry has adopted a proactive approach to the identification of best management practices. Accordingly, this review was undertaken to identify key chemical species that may require consideration in the development of guidelines for feedlot manure and effluent management practices in Australia. Important classes of trace chemicals identified include steroidal hormones, antibiotics, ectoparasiticides, mycotoxins, heavy metals and dioxins. These are described in terms of their likely sources, expected concentrations and public health or environmental significance based on international data and research. Androgenic hormones such as testosterone and trenbolone are significantly active in feedlot wastes, but they are poorly understood in terms of fate and environmental implications. The careful management of residues of antibiotics including virginiamycin, tylosin and oxytetracycline appears prudent in terms of minimising the risk of potential public health impacts from resistant strains of bacteria. Good management of ectoparasiticides including synthetic pyrethroids, macrocyclic lactones, fluazuron, and amitraz is important for the prevention of potential ecological implications, particularly towards dung beetles. Very few of these individual chemical contaminants have been thoroughly investigated in terms of concentrations, effects and attenuation in Australian feedlot wastes.

The aryl hydrocarbon receptor complex and the control of gene expression

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that controls the expression of a diverse set of genes. The toxicity of the potent AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin is almost exclusively mediated through this receptor. However, the key alterations in gene expression that mediate toxicity are poorly understood. It has been established through characterization of AhR-null mice that the AhR has a required physiological function, yet how endogenous mediators regulate this orphan receptor remains to be established. A picture as to how the AhR/ARNT heterodimer actually mediates gene transcription is starting to emerge. The AhR/ARNT complex can alter transcription both by binding to its cognate response element and through tethering to other transcription factors. In addition, many of the coregulatory proteins necessary for AhR-mediated transcription have been identified. Cross talk between the estrogen receptor and the AhR at the promoter of target genes appears to be an important mode of regulation. Inflammatory signaling pathways and the AhR also appear to be another important site of cross talk at the level of transcription. A major focus of this review is to highlight experimental efforts to characterize nonclassical mechanisms of AhR-mediated modulation of gene transcription.

Dioxin exposure in contaminated sawmill area: the use of molar teeth and bone of bank vole (Clethrionomys glareolus) and field vole (Microtus agrestis) as biomarkers

Developmental disorders of teeth are among the most sensitive targets of polychlorinated dibenzo-p-dioxin and -furan (PCDD/F) exposure. In rats, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) reduces dose-dependently the size of molars, most severely the third lower molars. Dioxins also have effects on developing bone, including altered bone mineral density as well as reduced bending breaking force and stiffness. The aim of this study was to evaluate the use of the third lower molar and long bones as biomarkers of PCDD/F exposure in two wild vole species, the bank vole (Clethrionomys glareolus) and the field vole (Microtus agrestis) collected from a PCDD/F contaminated former sawmill area. Survey of soil and biota of the sawmill area indicated a PCDD/F contamination with a congener profile characteristic for the chlorophenol wood preservative Ky-5. The PCDD/F concentration in the bank vole was notably higher than in the field vole. The third molar of the bank vole was significantly smaller in dioxin-exposed animals compared to control group, while there was no difference between these two groups in the field vole. No significant alterations were observed in bone density and strength in either species except for reduced bending strength of the femur neck in bank vole males exposed to dioxins. Even though the bone changes are among the sensitive endpoints of dioxin-exposure, high variability due to age, size and gender limits their use as biomarkers of wildlife exposure. In conclusion, the size of molar teeth seems to be a sensitive and robust biomarker for PCDD/F exposure in wild bank vole populations and thus worth of further studies.

7H-Dibenzo[c,g]carbazole and 5,9-dimethyldibenzo[c,g]carbazole exert multiple toxic events contributing to tumor promotion in rat liver epithelial 'stem-like' cells

Immature liver progenitor cells have been suggested to be an important target of hepatotoxins and hepatocarcinogens. The goal of the present study was to assess the impact of 7H-dibenzo[c,g]carbazole (DBC) and its tissue-specific carcinogenic N-methyl (N-MeDBC) and 5,9-dimethyl (DiMeDBC) derivatives on rat liver epithelial WB-F344 cells, in vitro model of liver progenitor cells. We investigated the cellular events associated with both tumor initiation and promotion, such as activation of aryl hydrocarbon receptor (AhR), changes in expression of enzymes involved in metabolic activation of DBC and its derivatives, effects on cell cycle, cell proliferation/apoptosis and inhibition of gap junctional intercellular communication (GJIC). N-MeDBC, a tissue-specific sarcomagen, was only a weak inhibitor of GJIC or inducer of AhR-mediated activity, and it did not affect either cell proliferation or apoptosis. DBC was efficient GJIC inhibitor, while DiMeDBC manifested the strongest AhR inducing activity. Accordingly, DiMeDBC was also the most potent inducer of cytochrome P450 1A1 (CYP1A1) and CYP1A2 expression among the three compounds tested. Both DBC and DiMeDBC induced expression of CYP1B1 and aldo-keto reductase 1C9 (AKR1C9). N-MeDBC failed to significantly upregulate CYP1A1/2 and it only moderately increased CYP1B1 or AKR1C9. Only the potent liver carcinogens, DBC and DiMeDBC, caused a significant increase of p53 phosphorylation at Ser15, an increased accumulation of cells in S-phase and apoptosis at micromolar concentrations. In addition, DiMeDBC was found to stimulate cell proliferation of contact-inhibited WB-F344 cells at 1 microM concentration, which is a mode of action that might further contribute to its hepatocarcinogenicity. The present data seem to suggest that the AhR activation, induction of enzymes involved in metabolic activation, inhibition of GJIC or stimulation of cell proliferation might all contribute to the hepatocarcinogenic effects of DBC and DiMeDBC.

TCDD induces c-jun expression via a novel Ah (dioxin) receptor-mediated p38-MAPK-dependent pathway

The aryl hydrocarbon receptor (AhR) has a fundamental role during postnatal liver development and is essential for mediating dioxin toxicity. However, the genetic programs mediating, both, the toxic and physiological effects downstream of the transcription factor AhR are in major parts unknown. We have identified the proto-oncogene c-jun as a novel target gene of AhR. Induction of c-jun depends on activation of p38-mitogen-activated protein kinase (MAPK) by an AhR-dependent mechanism. None of the kinases that are known to phosphorylate p38-MAPK is activated by AhR. Neither the dephosphorylation rate of p38-MAPK is reduced. Furthermore, increased p38-MAPK phosphorylation in response to dioxins does not require ongoing transcription. These findings establish activating 'cross-talk' with MAPK signaling as a novel principle of AhR action, which is apparently independent of the AhR's function as a DNA-binding transcriptional activator.

Inhibition of the MEK-1/p42 MAP kinase reduces aryl hydrocarbon receptor–DNA interactions

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces expression of the cytochrome P450 1A1 gene, cyp1a1, by binding to its receptor, aryl hydrocarbon receptor (AhR). TCDD-bound AhR translocates to the nucleus and forms a heterodimer with its partner protein, AhR nuclear translocator (Arnt). The AhR/Arnt heterodimer then binds to the dioxin-response elements (DREs) in the cyp1a1 enhancer and stimulates transcription of cyp1a1. We tested whether kinase pathways are involved in this process by treating Hepa1c1c7 cells with kinase inhibitors. The MEK-1 inhibitor PD98059 reduced TCDD-induced transcription of cyp1a1. TCDD treatment results in phosphorylation of p44/p42 mitogen-activated protein kinase (MAPK), a substrate of MEK-1. Overexpression of dominant negative form of p42 MAPK suppressed TCDD-dependent transcription of a reporter gene controlled by dioxin-response elements (DREs), and pretreatment with PD98059 also blocked this transcription. PD98059 pretreatment also inhibited TCDD-induced DRE binding of the AhR/Arnt heterodimer. Together these results indicate that TCDD activates the MEK-1/p44/p42 MAPK pathway, which in turn activates AhR and so facilitates binding of AhR to the cyp1a1 DRE.

Polycyclic aromatic hydrocarbons modulate cell proliferation in rat hepatic epithelial stem-like WB-F344 cells

Although many polycyclic aromatic hydrocarbons (PAHs) are recognized as potent mutagens and carcinogens, relatively little is known about their role in the tumor promotion. It is known that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) can induce release of rat hepatic oval epithelial cells from contact inhibition by a mechanism possibly involving the aryl hydrocarbon receptor (AhR) activation. Many PAHs are AhR ligands and are known to act as transient inducers of AhR-mediated activity. In this study, effects of 19 selected PAHs on proliferation of confluent rat liver epithelial WB-F344 cells were investigated. Non-mutagens that are weak activators or nonactivators of AhR-mediated activity had no effect on cell proliferation. Relatively strong or moderate AhR ligands with low mutagenic potencies, such as benzofluoranthenes, benz[a]anthracene, and chrysene, were found to increase cell numbers, which corresponded to an increased percentage of cells entering S-phase. Strong mutagens, including benzo[a]pyrene and dibenzo[a,l]pyrene, increased a percentage of cells in S-phase without inducing a concomitant increase in cell numbers. The treatment with mutagenic PAHs was associated with an increased DNA synthesis and induction of cell death, which corresponded with the activation of p53 tumor suppressor. Apoptosis was blocked by pifithrin-alpha, the chemical inhibitor of p53. Both weakly and strongly mutagenic PAHs known as AhR ligands were found to induce significant increase of cytochrome P4501A activity, suggesting a presence of functional AhR. The results of the present study seem to suggest that a release from contact inhibition could be a part of tumor promoting effects of AhR-activating PAHs; however, the genotoxic effects of some PAHs associated with p53 activation might interfere with this process.

Evidence of aryl hydrocarbon receptor ligands in Presque Isle Bay of Lake Erie

The purpose of the present studies was to use a biomarker approach to examine xenobiotic exposure of brown bullhead in Presque Isle Bay, Lake Erie (USA). In particular, the presence of compounds that act through the aryl hydrocarbon receptor (AhR) was of interest due to its central role in gene regulation and carcinogenesis of dioxins and certain polycyclic aromatic hydrocarbons (PAHs). Initial screening of Presque Isle Bay sediment samples by gene expression microarray in mouse hepatocytes revealed prototypical dioxin-response genes such as cytochrome P450 1A1 and 1B1 (CYP1A1 and CYP1B1). The presence of AhR ligands in sediment samples was confirmed and quantified using an in vitro assay, the Chemical Activated Luciferase Expression (CALUX) assay. The CALUX assay system, by using different incubation times, allows for determination of total dioxin induction equivalents (IEQ) for less persistent compounds such as PAHs as well as for stable compounds such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and certain polychlorinated biphenyls (PCBs). Parts of Presque Isle Bay have significant concentrations of AhR ligands in sediment ranging from 200 to 1400 parts per trillion (ppt) dioxin IEQ equivalents (dry weight). This is much higher than levels of dioxin equivalents found in similar sediment samples (approximately 10 ppt). Cascade Creek appears to be a major source of dioxin-like contaminants as IEQs in sediments taken from various regions of this tributary ranged from 1300 to 42000 ppt IEQ. In addition, the CALUX assay indicated that the majority of the IEQs (>90%) in PIB samples were in fact derived from less stable compounds. To determine if brown bullhead are exposed and respond to these high levels of AhR ligands, CYP1A cDNA was cloned from this species and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) was used to examine mRNA levels. The CYP1A mRNA concentration was lower and less variable in fish taken from Presque Isle Bay than from a body of water with much lower AhR ligand concentration. Taken together, these studies show that sediment in Presque Isle Bay is highly contaminated with AhR ligands including dioxins and PAHs, but the brown bullhead are either not exposed or are non-responsive to these carcinogenic compounds.

Characteristics and application of established luciferase hepatoma cell line that responds to dioxin-like chemicals

AIM: To establish a luciferase reporter cell line that responds dioxin-like chemicals (DLCs) and on this basis to evaluate its characteristics and application in the determination of DLCs.

METHODS: A recombinant luciferase reporter plasmid was constructed by inserting dioxin-responsive element (DREs) and MMTV promoter segments into the pGL₃-promoter plasmid immediately upstream of the luciferase gene, which was structurally demonstrated by fragment mapping analysis in gel electrophoresis and transfected into the human hepatoma cell line HepG₂, both transiently and stably, to identify the inducible expression of luciferase by 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). The time course, responsive period, sensitivity, structure-inducibility and dose-effect relationships of inducible luciferase expression to DLCs was dynamically observed in HepG₂ cells stably transfected by the recombinant vector (HepG₂-Luc) and compared with that assayed by ethoxyresorufin-O-deethylase (EROD) in non-transfected HepG₂ cells (HepG₂-wt).

RESULTS: The inducible luciferase expression of HepG₂-Luc cells was noted in a time-, dose-, and AhR-dependent manner, which peaked at 4 h and then decreased to a stable level at 14 h after TCDD treatment. The responsiveness of HepG₂-Luc cells to TCDD induction was decreased with culture time and became undetectable at 10^th month of HepG₂-Luc cell formation. The fact that luciferase activity induced by 3, 3', 4, 4'-PCB in HepG₂-Luc cells was much less than that induced by TCDD suggests a structure-inducibility relationship existing among DLCs. Within the concentrations from 3.5 × 10^-12 to 5 × 10^-9 mol/L, significant correlations between TCDD doses and EROD activities were observed in both HepG₂-luc and HepG₂-wt cells. The correlation between TCDD doses from 1.1 × 10^-13 to 1 × 10^-8 mol/L and luciferase activities was also found to be significant in HepG₂-luc cells (r = 0.997, P < 0.001), but not in their HepG₂-wt counterparts. For the comparison of the enzyme responsiveness between cell lines to TCDD, the luciferase sensitivity and reproducibility in HepG₂-luc cells were both better than that of EROD in HepG₂-wt cells, the former was at 1.1 × 10^-13 mol/L and 3.5 × 10^-12 mol/L, and the coefficients of variation (CV) of the latter was 15%-30% and 22%-38%, respectively.

CONCLUSION: The luciferase expression of HepG₂-luc cells established in the present study could sensitively respond to the DLCs stimulation and might be a prospective tool for the determination of DLCs.

2,3,7,8-tetrachlorodibenzo-p-dioxin affects size and shape, but not asymmetry, of mandibles in mice

Fluctuating asymmetry (FA), the random differences between the left and right sides of a bilaterally symmetrical character, is often purported to be a sensitive measure of developmental instability particularly in populations exposed to environmental stressors. As the level of developmental instability increases, often too does the level of FA. In this study we tested the hypothesis that exposure of pregnant mice to low doses of 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) would increase the level of FA in the mandibles of their offspring. We used ten landmark coordinates around the mandible to create a single size variable (centroid size) and 20 Procrustes shape variables. These were used to test for effects of dioxin on mandible size and shape and their asymmetries. We found no detectable effect of TCDD on levels of FA in either size or shape of the mandible, but TCDD did produce a significant decrease in mandible size, and a significant effect on the overall shape.

Molecular basis of dioxin actions: evidence supporting chemoprotection

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD or dioxin), a highly publicized environmental contaminant, was shown to be chemoprotective against breast cancer in both rats and mice in bioassays conducted in the late 1970s. This finding went largely unnoticed as investigators focused on animal tumors that were increased by dioxin. The position that dioxin causes human tumors remains a subject for debate; however, recent epidemiological studies of a population highly exposed to dioxin in 1976 as a result of an industrial accident suggest that women with higher dioxin body burdens may have a lower incidence of breast cancer. With the growth of new knowledge about the molecular basis of dioxin actions in humans and animals, it is clear that most of the responses produced by this agent are initiated by a specific recognition protein (designated the Ah receptor) found in almost all animal and human tissues and organs. The recognition event between the Ah receptor and environmental agents like dioxin is due to the formation of a complex. We have observed that in the presence of dioxin, the Ah receptor turns off proliferation in tumor cells and suppresses the ability of these cells to invade normal tissue. We believe that these findings provide a molecular and biochemical basis for understanding the chemoprotective mechanisms suggested by the findings of rodent bioassays and could lead to the development of novel therapeutic agents targeting the Ah receptor.

Adrenocorticotropin (ACTH) and corticosterone secretion by perifused pituitary and adrenal glands from rodents exposed to 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD)

Although in utero maternal stress has been shown to have lasting effects on rodent offspring, fetal effects of chemically-induced alterations of the maternal hypothalamic-pituitary-adrenal axis (HPA) have not been well studied. This study examined the effects of in vivo 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure on pituitary-adrenal function in the male rat, pregnant female rat and pregnant female mouse. The secretion of adrenocorticotropin (ACTH) and corticosterone (CORT) in pituitary and adrenal glands, respectively, was assessed in ex vivo perifusion cultures. Male and pregnant female (gestation day 8) Sprague-Dawley rats were gavaged once with 10 microgram/kg TCDD, pregnant female mice once with 24 microgram/kg TCDD, and euthanized 10 days later. Hemi-pituitary (rat) or whole anterior pituitaries (mice) and right adrenal glands from the same animal were quartered, perifused under baseline and stimulated conditions. In both males and pregnant females, TCDD did not affect corticotropin releasing hormone (CRH)-stimulated ACTH secretion. Neither total pituitary ACTH nor plasma ACTH was altered in either sex or species by TCDD treatment. ACTH-stimulated CORT secretion was not affected by TCDD in either sex or species, and adrenal tissue and plasma CORT levels were unchanged in males and pregnant females by TCDD. However, the plasma ACTH:CORT ratio was decreased about 46% in male rats treated with TCDD. Plasma CORT levels were 23-fold higher and plasma ACTH levels were 1.5-fold higher in pregnant females than in male rats. In male versus female rats, adrenal CORT and anterior pituitary ACTH tissue levels were about 7.5- and 1.75-fold higher and ACTH, respectively. Female mouse adrenal tissue CORT was about 4-fold greater than female rat. The reduced plasma ACTH:CORT ratio in the male rat suggests that TCDD disturbs HPA function. Exposure of male rat to a 5-fold higher dose in earlier studies clearly demonstrated effects of TCDD on male rat HPA. The present study identified substantial HPA performance differences between male and pregnant female rats. The failure to detect a response to TCDD in pregnant female rat and mouse could be a function of both TCDD dose and the high level of secretion of both ACTH and CORT in pregnant animals. For the rat or mouse, a single exposure to TCDD during pregnancy does not appear sufficient to induce maternally-mediated developmental, reproductive and behavioral toxicity via the HPA axis.

Ethoxyresorufin-O-deethylase (EROD) activity in fish as a biomarker of chemical exposure

This review compiles and evaluates existing scientific information on the use, limitations, and procedural considerations for EROD activity (a catalytic measurement of cytochrome P4501A induction) as a biomarker in fish. A multitude of chemicals induce EROD activity in a variety of fish species, the most potent inducers being structural analogs of 2,3,7,8-tetracholordibenzo-p-dioxin. Although certain chemicals may inhibit EROD induction/activity, this interference is generally not a drawback to the use of EROD induction as a biomarker. The various methods of EROD analysis currently in use yield comparable results, particularly when data are expressed as relative rates of EROD activity. EROD induction in fish is well characterized, the most important modifying factors being fish species, reproductive status and age, all of which can be controlled through proper study design. Good candidate species for biomonitoring should have a wide range between basal and induced EROD activity (e.g., common carp, channel catfish, and mummichog). EROD activity has proven value as a biomarker in a number of field investigations of bleached kraft mill and industrial effluents, contaminated sediments, and chemical spills. Research on mechanisms of CYP1A-induced toxicity suggests that EROD activity may not only indicate chemical exposure, but also may also precede effects at various levels of biological organization. A current research need is the development of chemical exposure-response relationships for EROD activity in fish. In addition, routine reporting in the literature of EROD activity in standard positive and negative control material will enhance confidence in comparing results from different studies using this biomarker.

Aromatic hydrocarbon receptor interaction with the retinoblastoma protein potentiates repression of E2F-dependent transcription and cell cycle arrest

Polyhalogenated aromatic hydrocarbons, of which 2,3,7, 8-tetrachloro-p-dioxin (TCDD) is the prototype compound, elicit a variety of toxic, teratogenic, and carcinogenic responses in exposed animals and in humans. In cultured cells, TCDD shows marked effects on the regulation of cell cycle progression, including thymocyte apoptosis, induction of keratinocyte proliferation and terminal differentiation, and inhibition of estrogen-dependent proliferation in breast cancer cells. The presence of an LXCXE domain in the dioxin aromatic hydrocarbon receptor (AHR), suggested that the effects of TCDD on cell cycle regulation might be mediated by protein-protein interactions between AHR and the retinoblastoma protein (RB). Using the yeast two-hybrid system, AHR and RB were in fact shown to bind to each other. In vitro pull-down experiments with truncated AHR peptides indicated that at least two separate AHR domains form independent complexes with hypophosphorylated RB. Coimmunoprecipitation of whole cell lysates from human breast carcinoma MCF-7 cells, which express both proteins endogenously, revealed that AHR associates with RB in vivo only after receptor transformation and nuclear translocation. However, the AHR nuclear translocator and transcriptional heterodimerization partner, is not required for (nor is it a part of) the AHR.RB complexes detected in vitro. Ectopic expression of AHR and RB in human osteosarcoma SAOS-2 cells, which lack endogenous expression of both proteins, showed that AHR synergizes with RB to repress E2F-dependent transcription and to induce cell cycle arrest. Furthermore, AHR partly blocked T-antigen-mediated reversal of RB-dependent transcriptional repression. These results uncover a potential function for the AHR in cell cycle regulation and suggest that this function may be that of serving as an environmental sensor that signals cell cycle arrest when cells are exposed to certain environmental toxicants.

Characterization of 2,3,7,8-tetrachlorodibenzofuran-dependent suppression and AH receptor pathway gene expression in the developing mouse mammary gland

The AH receptor (AHR) is a ligand-activated transcription factor and member of a growing family of homologous proteins implicated in development. In this study we have characterized the actions of 2,3, 7,8-tetrachlorodibenzofuran (TCDF), a well-studied AHR ligand, and the expression of AHR and selected AHR signal transduction pathway genes in the developing mouse mammary gland. High levels of AHR protein were observed in the mammary glands of C57Bl/6J (AHR +/+) mice during estrous-stimulated growth and branching of terminal end buds (TEBs). Comparative analysis of mammary gland development in AHR -/- and +/+ littermates revealed a 50% reduction in TEBs and an increase in blunt-ended terminal ducts in the AHR null animals. Treatment of mammary glands, removed from estrogen/progesterone-primed C57Bl/6J mice and maintained in organ culture, with TCDF suppressed lobule development (greater than twofold decreases in lobule number and size), with a concomitant suppression of DNA synthesis, as judged by a 35 to 45% decrease in [3H]thymidine incorporation in the TEBs. Immunohistochemical staining patterns for AHR, aryl hydrocarbon nuclear translocator (ARNT; the heterodimerization partner of AHR), and two AHR-regulated genes, Cyp1A1 and Cyp1B1, were similar and not altered by treatment of mammary glands in organ culture with TCDF. The observed differences in the development of mammary glands from AHR +/+ and -/- mice, associated expression of the AHR protein with hormone-dependent lobule development, and suppressive actions of TCDF support the position that, in C57Bl/6J mice, development of the mammary gland is at least in part AHR dependent. Development occurs in the absence of exogenous AHR ligand, suggesting that the unoccupied receptor may function to support the proliferative stages required for full lobule development.

Dioxin exposure and non-malignant health effects: a mortality study

OBJECTIVE

To investigate, in a population heavily exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the possible unusual occurrence of diseases other than cancer.

METHODS

Five year extension of the follow up of the cohort involved in the Seveso accident. Soil measurements identified three exposure zones: (A) highest contamination, (B) substantial, and (R) low but higher than background contamination. Blood TCDD measurements, although limited in number, confirmed zone exposure ranking. The 15 year mortality in the exposed cohort was compared with that of a large population in the surrounding non-contaminated territory. Relative risks (RRs) and 95% confidence intervals (95% CIs) were estimated with Poisson regression techniques.

RESULTS

The already noted increased occurrence of cardiovascular deaths was confirmed, in particular in zone A, among males for chronic ischaemic heart disease (five deaths, RR 3.0, 95% CI 1.2 to 7.3), and among females for hypertensive disease (three deaths, RR 3.6, 95% CI 1.2 to 11.4) and chronic rheumatic heart disease. Novel findings were the increase of chronic obstructive pulmonary disease, most notably among males in zone A (four deaths, RR 3.7, 95% CI 1.4 to 9.9) and females in zone B (seven deaths, RR 2.4, 95% CI 1.1 to 5.1); and from diabetes, which was significantly increased in females in zone B (13 deaths, RR 1.9, 95% CI 1.1 to 3.2). In zone R, chronic ischaemic heart disease (males and females), hypertension (females), and diabetes (females) showed less pronounced, although significant excesses.

CONCLUSIONS

As well as high TCDD exposure, the accident caused a severe burden of strain in the population. Both these factors might have contributed to the noted increased risks (in particular, circulatory and respiratory). The cardiovascular and immune toxicity of TCDD, as well as its complex interaction with the endocrine system, might be relevant to the explanations of these findings. These results, although not conclusive, concur with previous data in suggesting cardiopulmonary and endocrine effects in humans highly exposed to TCDD.

Resistance to thyroid hormone: implications for neurodevelopmental research on the effects of thyroid hormone disruptors

Thyroid hormones are essential for normal behavioral, intellectual, and neurological development. Congenital hypothyroidism, if not treated, can result in irreversible mental retardation, whereas thyroid diseases with more moderate impairment of thyroid function, such as resistance to thyroid hormone, cause less severe intellectual and behavioral abnormalities, including attention deficit hyperactivity disorder. There is increasing evidence that exposure to certain synthetic compounds, including dioxins and polychlorinated biphenyls (PCBs), during the perinatal period can also impair learning, memory, and attentional processes in offspring. Animal and human studies suggest that exposure to these environmental toxicants impair normal thyroid function. Although the precise mechanisms of action of the adverse effects these toxicants have on neurodevelopment have not yet been elucidated, it is possible that they are partially or predominantly mediated by alterations in hormone binding to the thyroid hormone receptor. The convergence of studies that examine the neurodevelopmental consequences of moderate impairment of thyroid function, such as is found in resistance to thyroid hormone, with those studies that demonstrate the adverse behavioral and cognitive effects of perinatal exposure to dioxins and PCBs serves to generate new hypotheses to test in a research setting. Such studies may provide new insights into the basic pathogenesis of developmental neurotoxicity following exposure to thyroid-disrupting synthetic compounds.

Interactions of persistent environmental organohalogens with the thyroid hormone system: mechanisms and possible consequences for animal and human health

Several classes of environmental contaminants have been claimed or suggested to possess endocrine-disrupting potency, which may result in reproductive problems and developmental disorders. In this paper the focus is on the multiple and interactive mechanisms of interference of persistent polyhalogenated aromatic hydrocarbons (PHAHs) and their metabolites with the thyroid hormone system. Evidence suggests that pure congeners or mixtures of PHAHs directly interfere with the thyroid gland; with thyroid hormone metabolizing enzymes, such as uridine-diphosphate-glucuronyl transferases (UGTs), iodothyronine deiodinases (IDs), and sulfotransferases (SULTs) in liver and brain; and with the plasma transport system of thyroid hormones in experimental animals and their offspring. Changes in thyroid hormone levels in conjunction with high PHAH exposure was also observed in captive as well as free ranging wildlife species and in humans. Maternal exposure to PHAHs during pregnancy resulted in a considerable fetal transfer of hydroxylated PHAHs, which are known to compete with thyroxine (T4) for plasma transthyretin (TTR) binding sites, and thus may be transported to the fetus with those carrier proteins that normally mediate the delivery of T4 to the fetus. Concomitant changes in thyroid hormone concentrations in plasma and in brain tissue were observed in fetal and neonatal stages of development, when sufficient thyroid hormone levels are essential for normal brain development. Alterations in structural and functional neurochemical parameters, such as glial fibrillary acidic protein (GFAP), synaptophysin, calcineurin, and serotonergic neurotransmitters, were observed in the same offspring up to postnatal day 90. In addition, some changes in locomotor and cognitive indices of behavior were observed in rat offspring, following in utero and lactational exposure to PHAHs. Alterations in thyroid hormone levels and subtle changes in neurobehavioral performance were also observed in human infants exposed in utero and through lactation to relatively high levels of PHAHs. Overall these studies indicate that persistent PHAHs can disrupt the thyroid hormone system at a multitude of interaction sites, which may have a profound impact on normal brain development in experimental animals, wildlife species, and human infants.

Dioxinlike components in incinerator fly ash: a comparison between chemical analysis data and results from a cell culture bioassay

Potent polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxinlike polychlorinated biphenyls (PCBs) are among the most relevant toxic emissions from incinerators. Induction of cytochrome P450 1A1-catalyzed 7-ethoxyresorufin O-deethylase (EROD) activity in mammalian cell culture (EROD bioassay) is thought to be a selective and sensitive parameter used for the quantification of dioxinlike compounds. Fly ash extracts from municipal waste incinerators (MWI), a crematorium, wood combustors, and a noble metal recycling facility were analyzed in the EROD bioassay using rat hepatocytes in primary culture. Fractions containing 2,3,7,8-substituted PCDDs/PCDFs, dioxinlike PCBs, and 16 major polycyclic aromatic hydrocarbons (PAHs) were isolated from the extract and analyzed by gas chromatography-mass spectrometry (GC-MS) and by the EROD bioassay. It was found that with MWI samples the bioassay of the extract resulted in a two- to fivefold higher estimate of TCDD equivalents (TEQ) than the chemical analysis of PCDDs/PCDFs and PCBs. However, the outcome of both methods was significantly correlated, making the bioassay useful as a rough estimate for the sum of potent PCDDs/PCDFs and dioxinlike PCBs in extracts from MWI fly ash samples and in a fly ash sample from a crematorium. In noble metal recycling facility and wood combustor samples, higher amounts of PAHs were found, contributing to more pronounced differences between the results of both methods. The remaining unexplained inducing potency in fly ash samples probably results from additional dioxinlike components including certain PAHs not analyzed in this study. The hypothesis that emissions from MWI of hitherto unidentified dioxinlike compounds are higher by orders of magnitude than emissions of potent PCDDs/PCDFs and dioxinlike PCBs could not be confirmed. We found no indication for a marked synergistic interaction of dioxinlike fly ash components in the bioassay.

Retinoids in eggs and embryos of birds fed fish from the Great Lakes

Retinoids were analyzed in 11-day chick embryos and eggs from white Leghorn hens (Gallus domesticus) fed environmentally-derived polychlorinated biphenyls (PCB) in carp (Cyprinus carpio) from Saginaw Bay. The yolks and the embryos contained all-trans-retinol, 3,4-didehydroretinol and retinyl esters. There was no significant difference in the total retinoid content in the yolks of 11-day incubated eggs among hens fed for 7 weeks diets containing 0.5-6.6 mg PCB/kg diet. However, the proportional amount of retinols in the high (6.6 mg) PCB group was significantly less than that in low (0.5 mg) PCB controls, while the amount of retinyl palmitate in the high PCB group was significantly greater than that in the controls. Retinoids in the embryos were not affected by any of the PCB levels fed to hens for 7 weeks prior to laying the eggs. The 50% reduction in the molar ratio of retinols to retinyl palmitate in the yolks of eggs as the result of the high PCB level fed to hens for 7 weeks can serve as an indicator for chronic exposure to PCB contamination at the level of 6.6 mg or higher PCB/kg diet.

Environmental toxins and endometriosis

The effect of natural, environmental, or manufactured substances on endocrine organs is a current topic of discussion. Recently, some toxicants have been suggested to promote endometriosis; therefore, attention has turned to the role of environmental factors as a stimulant for endometriosis growth and maintenance. This article reviews the influence of various toxicants on endometriosis.

Aryl hydrocarbon receptor-mediated signal transduction

The aryl hydrocarbon (or dioxin) receptor (AhR) is a ligand-activated basic helix-loop-helix (bHLH) protein that heterodimerizes with the bHLH protein ARNT (aryl hydrocarbon nuclear translocator) forming a complex that binds to xenobiotic regulatory elements in target gene enhancers. Genetic, biochemical, and molecular biology studies have revealed that the AhR mediates the toxic and biological effects of environmentally persistent dioxins and related compounds. Cloning of the receptor and its DNA-binding partner, ARNT, has facilitated detailed efforts to understand the mechanisms of AhR-mediated signal transduction. These studies have determined that this unique receptor consists of several functional domains and belongs to a subfamily of bHLH proteins that share a conserved motif termed the PAS domain. In addition, recent genetic studies have revealed that expression of the AhR is a requirement for proper embryonal development, which appears to be a common function shared by many other bHLH proteins. This review is a summary of recent molecular studies of AhR-mediated gene regulation.

Reinventing public health

This chapter is a review of the current state of public health in light of the social, political, economic, scientific, and technological changes buffeting the United States. As an assessment of progress in current public health efforts, we address the five major issues in public health for the 1990s raised by Breslow (8): reconstruction of public health; setting objectives for public health; from disease control to health promotion; determinants of health and health policy; continuing social inequities and their impacts on health; and the health implications of accelerating developments in technology. Finally, we look to the twenty-first century and provide five clear paths necessary to strengthen the capacity of public health agencies to protect and improve the health status of the population.

Overlapping but unique DNA binding specificities of the Ah receptor and constitutive dioxin-responsive element binding proteins from human keratinocytes

To understand the relationships between the protein architecture assembled on dioxin-responsive elements (DRE) and transcriptional regulation by dioxin in human keratinocytes, the nuclear DRE-binding proteins from human keratinocytes were identified and characterized. In addition to the aryl hydrocarbon receptor (AHR) complex inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), nuclear extracts from 3 human keratinocyte cell lines also contained one or more proteins that bound specifically to the DRE but whose levels were unaffected by TCDD or by anti-AHR antibody pretreatment. Alteration of a conserved T, within the core DRE sequence needed for transcriptional activation by the AHR complex, did not affect AHR binding but severely affected the ability of the constitutive proteins to bind. These data suggest that the nonidentical interplay of the AHR and constitutive DRE-binding proteins on the DRE is important in the regulation of genes whose expression is controlled by DRE.

DNA binding by the heterodimeric Ah receptor. Relationship to dioxin-induced CYP1A1 transcription in vivo

The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin induces the microsomal enzyme cytochrome P4501A1 by increasing the transcription rate of the CYP1A1 gene. Induction requires two basic helix-loop-helix proteins, the ligand-binding aromatic hydrocarbon receptor (AhR) and its heterodimerization partner, the AhR nuclear translocator (Arnt). The AhR/Arnt heterodimer induces transcription by binding to dioxin-responsive elements (DREs) within an enhancer upstream of the CYP1A1 gene. The basic regions of AhR and Arnt are crucial for DRE binding. We have mutated these regions in order to analyze the relationship between DRE binding (determined in vitro using an electrophoretic mobility shift assay) and induction of CYP1A1 transcription (determined in vivo by genetic complementation of AhR-defective and Arnt-defective mouse hepatoma cells, using an RNase protection assay to measure mRNA accumulation). Our findings reveal the amino acids in the basic regions of AhR/Arnt that are important for both DRE binding and induction of transcription. This information provides biological background for the interpretation of structural (e.g. crystallographic) studies of the interactions between AhR/Arnt and the DRE. Our findings also indicate that the in vitro behavior of the mutants does not consistently predict their functional activity in vivo. Thus, genetic complementation constitutes an important and stringent test for analyzing the effects of mutations on AhR/Arnt function.

Exposure of laboratory animals to polychlorinated dibenzodioxins and polychlorinated dibenzofurans from commerical rodent chow

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) are ubiquitous low level environmental contaminants. Present finding of PCDDs and PCDFs in the human food supply suggested that laboratory animals maintained under controlled conditions may also receive unwanted exposure to these compounds from food. In this study, a commercial rodent chow, Prolab-RMH 1000, was analyzed for the toxicologically active 2,3,7,8-substituted PCDDs and PCDFs. The results show that the feed had a total PCDD/F dioxin toxic equivalence (I-TEq) of 0.13 pg/kg (ppt) wet weight. OCDD was the most abundant congener present, followed by 1,2,3,4,6,7,8-HpCDD, with these congeners representing the 5th and 6th greatest contributors to the calculated TEq. Daily ingestion of I-TEqs for the rats is calculated to be 3.9-6.5 pg/kg/day, and 13.0-32.5 pg/kg/day for mice. It is therefore important to consider the potential for background exposure to PCDDs and PCDFs from the diet when conducting studies with laboratory animals. This is particularly important when sensitive responses, such as enzyme induction, immunotoxicity, and developmental/reproductive toxicity are being investigated at very low exposures to this class of compounds.

Biomarkers for Great Lakes priority contaminants: halogenated aromatic hydrocarbons

One of the major goals of the Great Lakes Action Plan is to actively accumulate and assess toxicological information on persistent toxic substances found in the Great Lakes basin. As part of Health Canada's commitment to this plan, a review of biomarkers for the environmental contaminants polychlorinated biphenyls (PCBs) and polychlorinated dibenzodioxins/dibenzofurans (PCDDs/PCDFs) was conducted. In general, while food consumption was identified as the major source of human exposure to both contaminant groups, certain commodities, such as fish, milk and dairy products, and meat, were found to predominate. Due to the ubiquitous nature of these environmental contaminants and their propensity to bioaccumulate, all humans will have detectable body burdens, which in certain cases can be positively associated with the consumption of particular foods (i.e., PCBs and freshwater fish from the Great Lakes). When dealing with environmental exposure only, relating specific effect biomarkers to contaminant exposure or tissue levels was difficult, due in part to the complex nature of the exposure and the nonspecific nature of the effect. For PCBs, the most likely biomarkers of effect included some form of alteration in lipid metabolism (serum triglyceride/cholesterol levels) and elevation of hepatic-related enzymes, aspartate aminotransferase (AST) and gamma-glutamyltransferase (GGT). Cross-species extrapolation also indicates the potential for neurotoxicologic effects to occur in humans. For PCDDs/PCDFs, dermatologic lesions (chloracne) and indications of hepatic enzyme induction have been documented, but primarily due to occupational or high acute accidental exposures. Recent evidence suggests that neonates may represent a potential at-risk population due to relatively high exposure to PCDDs/PCDFs, as with PCBs, during breast feeding as compared to standard adult dietary intake. Future areas of potential benefit for biomarker development include immunologic and endocrine effects, primarily based on biologic plausibility from experimental animal research.

Hazard to man and the environment posed by the use of urban waste compost: a review

This review presents the current state of knowledge on the relationship between the environment and the use of municipal waste compost in terms of health risk assessment. The hazards stem from chemical and microbiological agents whose nature and magnitude depend heavily on the degree of sorting and on the composting methods. Three main routes of exposure can be determined and are quantified in the literature: (i) The ingestion of soil/compost mixtures by children, mostly in cases of pica, can be a threat because of the amount of lead, chromium, cadmium, PCDD/F and fecal streptococci that can be absorbed. (ii) Though concern about contamination through the food chain is weak when compost is used in agriculture, some authors anticipate accumulation of pollutants after several years of disposal, which might lead to future hazards. (iii) Exposure is also associated with atmospheric dispersion of compost organic dust that convey microorganisms and toxicants. Data on hazard posed by organic dust from municipal composts to the farmer or the private user is scarce. To date, microorganisms are only measured at composting plants, thus raising the issue of extrapolation to environmental situations. Lung damage and allergies may occur because of organic dust, Gram negative bacteria, actinomycetes and fungi. Further research is needed on the risk related to inhalation of chemical compounds.

Analysis of toxicological risks from local contamination by PCDDs and PCDFs: importance of isomer distributions and toxic equivalents

The concentrations of 2,3,7,8-chlorinated dibenzo-p-dioxins and furans (PCDD/PCDFs) at Finnish contaminated sites associated with chlorophenolic (CP) wood preservatives were measured by isomer-specific GC/HRMS methods, and the implications of the spatial and structural distributions of the isomers and of toxic equivalent (TEF) systems for toxicological risks were investigated. High concentrations (maximum value of over 90 ppb and arithmetic mean value of 19 ppb I-TEQs in dry weight) of PCDD/Fs were found in soil samples from sites where wood preservative consisting of 2346-TeCP, PeCP and 246-TCP have been used. The PCDD/Fs were distributed heterogeneously between soil layers, the concentrations in topsoil samples being generally smaller (mean 9.1 ppb I-TEQ d.w.) than those in subsoil (mean 28 ppb I-TEQ d.w.). Concentrations of PCDD/Fs were unrelated to the CP contents in the soil samples. Hexa-, hepta- and octachlorinated dibenzofurans were the dominant congeners by concentration in these and in most other samples, also in the wood preservative. The isomer distribution differed considerably between study sites, and even between samples of soil and waste at the same site. The relative importance of the samples and isomers was affected by the selection of TEFs; the importance of some of the CP-related samples was increased when applying TEFs based on lethality to juvenile fish, due to the abundance of 123478-HxCDF.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for two functionally distinct forms of the human Ah receptor

The Ah receptor (AhR) was visualized using monoclonal antibody Rpt 1 on protein blots of HeLa cell cytosol; two bands were detected at 104 and 106 kDa. The photoaffinity ligand, 2-azido-3-[125I]iodo-7,8-dibromodibenzo-p-dioxin, was added to HeLa cells in culture, and after 1 hour the cells were UV irradiated. Cytosolic and high salt nuclear preparations were isolated and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), followed by transfer of the protein to membrane. The AhR was visualized on the membrane, revealing two bands. Alignment of an autoradiogram with the membrane revealed that only the 106 kDa (upper) band was photoaffinity labeled. The nuclear fraction contained only the photoaffinity-labeled 106 kDa form of the AhR. The 104 kDa AhR does not appear to be a proteolytic product of the 106 kDa form. Cyanogen bromide fragmentation revealed that both forms contain the same size N-terminal fragment. Sucrose density gradient analysis of HeLa cell cytosol indicated that both forms cosedimented at 9 S. Both the 106 and 104 kDa AhR bands were detected in four different human cell lines. Together, these results would indicate that the AhR in human cell lines exists in two distinct forms.

Chemicals and cancer in humans: first evidence in experimental animals

Certain human diseases have been traced to exposure to environmental and occupational chemicals. In many instances the first evidence of potential adverse effects came from experimental studies and were subsequently discovered in humans. Associations of human cancers, as a diverse group of diseases, and chemicals have been made since the middle 1700s. Since then, nearly 100 chemicals, mixtures of chemicals, or exposure circumstances are now recognized as being or strongly implicated as being carcinogenic to humans. Of the less than 1000 agents evaluated adequately for carcinogenicity in laboratory animals, a varying spectrum of data from studies on humans are available for only about 20-25%. So far, more than 60 agents are linked unequivocally as causing cancer in humans, and another 50 or so are strongly suspected of being carcinogenic to humans. Not all of these have been or can be evaluated in animals because some are industrial processes or "occupations," some are environmental and cultural risk factors, and some are mixtures of agents. For those that can be studied experimentally, the qualitative concordance between humans and animals approaches unity, and in every case there is at least one common organ site of cancer in both species. The evidence of carcinogenicity in experimental animals preceded that observed in humans for nearly 30 agents and is the subject of this paper.