Developmental effects of dioxins and related endocrine disrupting chemicals

Protective effects of Korean Red Ginseng against toxicity of endocrine-disrupting chemicals

Several chemicals have been developed owing to the progression of industrialization, among which endocrine-disrupting chemicals (EDCs; essential for plastic production) are used as plasticizers and flame retardants. Plastics have become an essential element in modern life because they provide convenience, thus increasing EDCs exposure to humans. EDCs cause adverse effects such as deterioration of reproductive function, cancer, and neurological abnormalities by disrupting the endocrine system and hence are classified as "dangerous substances." Additionally, they are toxic to various organs but continue to be used. Therefore, it is necessary to review the contamination status of EDCs, select potentially hazardous substances for management, and monitor the safety standards. In addition, it is necessary to discover substances that can protect against EDC toxicity and conduct active research on the protective effects of these substances. According to recent research, Korean Red Ginseng (KRG) exhibits protective effects against several toxicities caused by EDCs to humans. In this review, the effects of EDCs on the human body and the role of KRG in protection against EDC toxicity are discussed.

The Association between Blood Concentrations of PCDD/DFs, DL-PCBs and the Risk of Type 2 Diabetes Mellitus and Thyroid Cancer in South Korea

Background and Objectives: Epidemiological studies have inconsistently shown an association between dioxin and risk of type 2 diabetes mellitus (T2DM) and cancer. This study aims to examine the effects of blood concentration of dioxin-like polychlorinated biphenyls (DL-PCBs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/DFs) on T2DM and thyroid cancer. Methods: We conducted a nested case–control study within the Korean cancer prevention study-II (KCPS-II) consisting of 15 thyroid cancer cases, 30 T2DM cases, and 55 controls. A total of 500 samples were used in 100 pooling samples. An average value of a pooled sample was calculated weighted by the blood volume of each sample. Results: The study population included 100 participants from the KCPS-II (median (IQR) baseline age, 54.06 [21.04] years; 48 women). The toxic equivalents of PCDD/DFs showed a significant positive association with T2DM and thyroid cancer, after adjustments for potential confounders (T2DM ORs  =  1.23; 95% CI  =  1.05–1.43; thyroid cancer ORs  =  1.34; 95% CI  =  1.12–1.61). Conclusion: In this study, both T2DM and thyroid cancer were associated with the blood concentrations of PCDD/DFs. The association between PCDD/DFs and T2D was found among women but not among men. Our findings suggest that further biochemical in vivo research and epidemiologic studies are needed to clarify the association between dioxins concentrations and diseases.

The combined effects of Map3k1 mutation and dioxin on differentiation of keratinocytes derived from mouse embryonic stem cells

Epithelial development starts with stem cell commitment to ectoderm followed by differentiation to the basal keratinocytes. The basal keratinocytes, first committed in embryogenesis, constitute the basal layer of the epidermis. They have robust proliferation and differentiation potential and are responsible for epidermal expansion, maintenance and regeneration. We generated basal epithelial cells in vitro through differentiation of mouse embryonic stem cells (mESCs). Early on in differentiation, the expression of stem cell markers, Oct4 and Nanog, decreased sharply along with increased ectoderm marker keratin (Krt) 18. Later on, Krt 18 expression was subdued when cells displayed basal keratinocyte characteristics, including regular polygonal shape, adherent and tight junctions and Krt 14 expression. These cells additionally expressed abundant Sca-1, Krt15 and p63, suggesting epidermal progenitor characteristics. Using Map3k1 mutant mESCs and environmental dioxin, we examined the gene and environment effects on differentiation. Neither Map3k1 mutation nor dioxin altered mESC differentiation to ectoderm and basal keratinocytes, but they, individually and in combination, potentiated Krt 1 expression and basal to spinous differentiation. Similar gene-environment effects were observed in vivo where dioxin exposure increased Krt 1 more substantially in the epithelium of Map3k1^+/- than wild type embryos. Thus, the in vitro model of epithelial differentiation can be used to investigate the effects of genetic and environmental factors on epidermal development.

Genetic Control of MAP3K1 in Eye Development and Sex Differentiation

The MAP3K1 is responsible for transmitting signals to activate specific MAP2K-MAPK cascades. Following the initial biochemical characterization, genetic mouse models have taken center stage to elucidate how MAP3K1 regulates biological functions. To that end, mice were generated with the ablation of the entire Map3k1 gene, the kinase domain coding sequences, or ubiquitin ligase domain mutations. Analyses of the mutants identify diverse roles that MAP3K1 plays in embryonic survival, maturation of T/B cells, and development of sensory organs, including eye and ear. Specifically in eye development, Map3k1 loss-of-function was found to be autosomal recessive for congenital eye abnormalities, but became autosomal dominant in combination with Jnk and RhoA mutations. Additionally, Map3k1 mutation increased eye defects with an exposure to environmental agents such as dioxin. Data from eye developmental models reveal the nexus role of MAP3K1 in integrating genetic and environmental signals to control developmental activities. Here, we focus the discussions on recent advances in understanding the signaling mechanisms of MAP3K1 in eye development in mice and in sex differentiation from human genomics findings. The research works featured here lead to a deeper understanding of the in vivo signaling network, the mechanisms of gene-environment interactions, and the relevance of this multifaceted protein kinase in disease etiology and pathogenesis.

Dioxin exposure associated with fecundability and infertility in mothers and daughters of Seveso, Italy

STUDY QUESTION

Is there an association between 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure and fecundability and infertility among Seveso women and their daughters?

SUMMARY ANSWER

TCDD exposure is associated with a decrease in fecundability and increased risk of infertility in women, as well as their daughters.

WHAT IS KNOWN ALREADY

In animal studies, maternal exposure to TCDD is associated with decreased fertility in offspring. Effects of TCDD are mediated by activation of the aryl hydrocarbon receptor (AHR) pathway.

STUDY DESIGN, SIZE, DURATION

The Seveso Women's Health Study (SWHS) has followed 981 women exposed to TCDD in a 1976 accident since 1996. In 2014, we initiated the Seveso Second Generation Study to follow-up their children.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We obtained information on pregnancy history including time of trying to conceive from SWHS women and their daughters who were 18 years or older. We considered TCDD exposure as initial 1976 serum TCDD concentration and estimated TCDD at pregnancy. We examined relationships of TCDD exposure with time to pregnancy (TTP, the monthly probability of conception within the first 12 months of trying) and infertility (≥12 months of trying to conceive). We also assessed contributions of polymorphisms in the AHR pathway via genetic risk score.

MAIN RESULTS AND THE ROLE OF CHANCE

Among SWHS women (n = 446), median TTP was 3 months and 18% reported taking ≥12 months to conceive. Initial 1976 TCDD (log10) was associated with longer TTP (adjusted fecundability odds ratio = 0.82; 95% CI 0.68-0.98) and increased risk of infertility (adjusted relative risk = 1.35; 95% CI 1.01-1.79). TCDD at pregnancy yielded similar associations. Among SWHS daughters (n = 66), median TTP was 2 months and 11% reported taking ≥12 months to conceive. Daughters showed similar, but non-significant, associations with maternal TCDD exposure.

LIMITATIONS, REASONS FOR CAUTION

A limitation of this study is time to pregnancy was reported retrospectively, although previous studies have found women are able to recall time to conception with a high degree of accuracy many years after the fact. The number of SWHS daughters who had a live birth was small and we were unable to examine fecundability of SWHS sons.

WIDER IMPLICATIONS OF THE FINDINGS

Consistent with previous findings in animal studies, our study found that TCDD exposure may be associated with decreased fertility in Seveso mothers and potentially in their daughters exposed in utero. There may be susceptible genetic subgroups. The literature has largely considered the genetics of the AHR pathway in the context of male fertility but not female fertility, despite strong biological plausibility. These findings should be replicated in larger populations and of different ancestry. Future studies in Seveso should examine the sons and the grandchildren of exposed mothers given the animal literature suggesting potential heritable epigenetic effects.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by grant numbers F06 TW02075-01 from the National Institutes of Health, R01 ES07171 and 2P30-ESO01896-17 from the National Institute of Environmental Health Sciences, R82471 from the U.S. Environmental Protection Agency and #2896 from Regione Lombardia and Fondazione Lombardia Ambiente, Milan, Italy. J.A. was supported by F31ES026488 from the National Institutes of Health. The authors declare they have no actual or potential competing financial interests.

TRIAL REGISTRATION NUMBER

N/A.

Parental exposure to azoxystrobin causes developmental effects and disrupts gene expression in F1 embryonic zebrafish (Danio rerio)

The fungicide azoxystrobin induces reproductive toxicity in adult zebrafish. However, data are lacking regarding the impact of azoxystrobin in the F1 generation after parental exposure. To address this knowledge gap, parental zebrafish (F0) were exposed to 2, 20 and 200 μg/L azoxystrobin for 21 days. Following this, fertilized F1 embryos from the exposed parents were either exposed to the same concentration as their corresponding exposed parents (F0+/F1+) or were reared in clean water (F0+/F1-) for 96 h ("+", exposed; "-" unexposed). Likewise, F1 embryos from the non-exposed parents were either reared in clean water (F0-/F0-) as the control group or were exposed to 2, 20 and 200 μg/L azoxystrobin (F0-/F1+) for 96 h. Mortality, deformities, hatching rate, body length, and the expression of transcripts related to the endocrine system, oxidative stress, and apoptosis were measured. Increased mortality, higher malformation rate, decreased hatching rate, and a shorter total body length, as well as up-regulated cyp19b, vtg1, vtg2, p53, casp3, and casp9 mRNA and down-regulated sod1 and sod2 mRNA were detected in F1 embryos from the F0 and F1 exposure group at 20 and 200 μg/L azoxystrobin (F0+/F1+) when compared with the group from the F0 exposure alone (F0+/F1-). Interestingly, F1 exposure alone (F0-/F1+) did not induce mortality, developmental impairments, nor morphological deformations compared to the control group, but it did increase expression level of sod1, sod2, cat, p53, and casp9 at 200 μg/L azoxystrobin. Taken together, these data suggest that azoxystrobin affects survivability, development, and genes involved in the endocrine system, oxidative stress, and apoptosis in F1 embryos if their parents are initially exposed to this fungicide compared to embryos from non-exposed parents. Moreover, the effects are more severe if the offspring are continuously exposed to azoxystrobin similar to their parents.

Application of sandwich spatial estimation method in cancer mapping: A case study for breast cancer mortality in the Chinese mainland, 2005

High-accuracy spatial distribution estimation is crucial for cancer prevention and control. Due to their complicated pathogenic factors, the distributions of many cancers' mortalities appear blocky, and spatial heterogeneity is common. However, most of the commonly used cancer mapping methods are based on spatial autocorrelation theory. Sandwich estimation is a new method based on spatial heterogeneity theory. A modified sandwich estimation method suitable for the estimation of cancer mortality distribution is proposed in this study. The variances of cancer mortality data are used to fuse sandwich estimation results from various auxiliary variables, the feasibility of which in estimating cancer mortality distributions is explained theoretically. The breast cancer (BC) mortality of the Chinese mainland in 2005 was taken as a case, and the accuracy of the modified sandwich estimation method was compared with that of the Hierarchical Bayesian (HB), the Co-Kriging (CK) and the Ordinary Kriging (OK) methods. The accuracy of the modified sandwich estimation method was better than the HB, the CK and the OK methods, and the estimation result from the modified sandwich estimation method was more likely to be acceptable. Therefore, this study represents an attempt to apply the sandwich estimation method to the estimation of cancer mortality distributions with strong spatial heterogeneity, which holds great potential for further application.

Hepatocyte-Specific Deletion of TIPARP, a Negative Regulator of the Aryl Hydrocarbon Receptor, Is Sufficient to Increase Sensitivity to Dioxin-Induced Wasting Syndrome

The aryl hydrocarbon receptor (AHR) mediates the toxic effects of dioxin (2, 3, 7, 8-tetrachlorodibenzo-p-dioxin; TCDD), which includes thymic atrophy, steatohepatitis, and a lethal wasting syndrome in laboratory rodents. Although the mechanisms of dioxin toxicity remain unknown, AHR signaling in hepatocytes is necessary for dioxin-induced liver toxicity. We previously reported that loss of TCDD-inducible poly(adenosine diphosphate [ADP]-ribose) polymerase (TIPARP/PARP7/ARTD14), an AHR target gene and mono-ADP-ribosyltransferase, increases the sensitivity of mice to dioxin-induced toxicities. To test the hypothesis that TIPARP is a negative regulator of AHR signaling in hepatocytes, we generated Tiparpfl/fl mice in which exon 3 of Tiparp is flanked by loxP sites, followed by Cre-lox technology to create hepatocyte-specific (Tiparpfl/flCreAlb) and whole-body (Tiparpfl/flCreCMV; TiparpEx3-/-) Tiparp null mice. Tiparpfl/flCreAlb and TiparpEx3-/- mice given a single injection of 10 μg/kg dioxin did not survive beyond days 7 and 9, respectively, while all Tiparp+/+ mice survived the 30-day treatment. Dioxin-exposed Tiparpfl/flCreAlb and TiparpEx3-/- mice had increased steatohepatitis and hepatotoxicity as indicated by greater staining of neutral lipids and serum alanine aminotransferase activity than similarly treated wild-type mice. Tiparpfl/flCreAlb and TiparpEx3-/- mice exhibited augmented AHR signaling, denoted by increased dioxin-induced gene expression. Metabolomic studies revealed alterations in lipid and amino acid metabolism in liver extracts from Tiparpfl/flCreAlb mice compared with wild-type mice. Taken together, these data illustrate that TIPARP is an important negative regulator of AHR activity, and that its specific loss in hepatocytes is sufficient to increase sensitivity to dioxin-induced steatohepatitis and lethality.

Prenatal exposure to TCDD and atopic conditions in the Seveso second generation: a prospective cohort study

BACKGROUND

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a toxic environmental contaminant that can bioaccumulate in humans, cross the placenta, and cause immunological effects in children, including altering their risk of developing allergies. On July 10, 1976, a chemical explosion in Seveso, Italy, exposed nearby residents to a high amount of TCDD. In 1996, the Seveso Women's Health Study (SWHS) was established to study the effects of TCDD on women's health. Using data from the Seveso Second Generation Health Study, we aim to examine the effect of prenatal exposure to TCDD on the risk of atopic conditions in SWHS children born after the explosion.

METHODS

Individual-level TCDD was measured in maternal serum collected soon after the accident. In 2014, we initiated the Seveso Second Generation Health Study to follow-up the children of the SWHS cohort who were born after the explosion or who were exposed in utero to TCDD. We enrolled 677 children, and cases of atopic conditions, including eczema, asthma, and hay fever, were identified by self-report during personal interviews with the mothers and children. Log-binomial and Poisson regressions were used to determine the association between prenatal TCDD and atopic conditions.

RESULTS

A 10-fold increase in 1976 maternal serum TCDD (log10TCDD) was not significantly associated with asthma (adjusted relative risk (RR) = 0.93; 95% CI: 0.61, 1.40) or hay fever (adjusted RR = 0.99; 95% CI: 0.76, 1.27), but was significantly inversely associated with eczema (adjusted RR = 0.63; 95% CI: 0.40, 0.99). Maternal TCDD estimated at pregnancy was not significantly associated with eczema, asthma, or hay fever. There was no strong evidence of effect modification by child sex.

CONCLUSIONS

Our results suggest that maternal serum TCDD near the time of explosion is associated with lower risk of eczema, which supports other evidence pointing to the dysregulated immune effects of TCDD.

Prenatal concentrations of Perfluoroalkyl substances and early communication development in British girls

Perfluoroalkyl substances (PFAS), found in many household products and classed as endocrine disrupting chemicals, can be transferred through the placenta and are associated with multiple developmental deficits in offspring. Using data from the Avon Longitudinal Study of Parents and Children (ALSPAC), we investigated the association between intrauterine exposure to PFAS and early communication development in 432 mother-daughter dyads at 15 and 38months of age. Concentrations of perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), perfluorohexane sulfonate (PFHxS), and perfluorononanoate (PFNA) were measured in maternal serum collected during pregnancy. Early communication development was measured with the ALSPAC-adapted MacArthur Communicative Development Inventories for Infants and Toddlers. The infant questionnaire measured verbal comprehension, vocabulary comprehension and production, nonverbal communication, and social development. The toddler questionnaire measured language, intelligibility, and communicative sub-scores. Multivariable linear regression was used to examine associations between each PFAS exposure and each communication sub-scale score. The association between maternal PFAS concentrations and early communication development at 15 and 38months of age varied by maternal age at delivery. In daughters of younger mothers (<25years of age), every 1ng/mL of PFOS was associated with a 3.82 point (95% confidence interval (CI): -6.18, -1.47) lower vocabulary score at 15months and a 0.80 point (95% CI: -1.74, 0.14) lower language score at 38months. Prenatal exposure to select PFAS was positively and negatively associated with communication development among girls, with inconsistent pattern of association across all measured PFAS and endpoints.

Association between dioxin and cancer incidence and mortality: a meta-analysis

The objective of the present study was to systematically assess the association between dioxin/2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and cancer incidence and mortality. Systematic literature searches were conducted until July 2015 in Pubmed, Embase and Cochrane library to identify relevant studies. A random-effects model was applied to estimate the pooled odds ratio (OR), risk ratio (RR), standard incidence ratio (SIR) or standard mortality ratio (SMR) for cancer incidence or mortality. In addition, dose-response, meta-regression, subgroup, and publication bias analyses were conducted. Thirty-one studies involving 29,605 cancer cases and 3,478,748 participants were included. Higher external exposure level of TCDD was significantly associated with all cancer mortality (pooled SMR = 1.09, 95% CI: 1.01-1.19, p = 0.04), but not all cancer incidence (pooled RR = 1.01, 95% CI: 0.97-1.06, p = 0.49). Higher blood level of TCDD was both significantly associated with all cancer incidence (pooled RR = 1.57, 95% CI: 1.21-2.04, p = 0.001) and all cancer mortality (pooled SMR = 1.45, 95% CI: 1.25-1.69, p < 0.001). Subgroup analysis suggested that higher external exposure and blood level of TCDD were both significantly associated with the mortality caused by non-Hodgkin's lymphoma. In conclusion, external exposure and blood level of TCDD were both significantly associated with all cancer mortality, especially for non-Hodgkin's lymphoma.

Compound- and sex-specific effects on programming of energy and immune homeostasis in adult C57BL/6JxFVB mice after perinatal TCDD and PCB 153

Early life exposure to endocrine disrupting compounds has been linked to chronic diseases later in life, like obesity and related metabolic disorders. We exposed C57BL/6JxFVB hybrid mice to the aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the constitutive androstane receptor/pregnane X receptor agonist polychlorinated biphenyl 153 (PCB 153) in an experimental design relevant for human exposure. Exposure occurred during gestation and lactation via maternal feed to a wide dose range (TCDD: 10-10,000 pg/kg body weight/day; PCB 153: 0.09-1406 μg/kg body weight/d). Then exposure was ceased and offspring were followed up to 1 year of age. Metabolic parameters like body weight, fat pad weights, glucose tolerance, endocrine serum profile, and neurobehavioral and immunological parameters were determined. Body weight was transiently affected by both compounds throughout the follow-up. TCDD-exposed males showed decreased fat pad and spleen weights and an increase in IL-4 production of splenic immune cells. In contrast, females showed increased fat pad weights and production of IFNγ. PCB 153-exposed males showed an increase in glucose, whereas females showed an increase in glucagon, a decrease in pancreas weight, and an increase in thymus weight. In conclusion, early life exposure to TCDD appears to affect programming of energy and immune homeostasis in offspring, whereas the effects of perinatal PCB 153 were mainly on programming of glucose homeostasis. Both compounds act sex-specifically. Lowest derived BMDLs (lower bounds of the (two sided) 90%-confidence interval for the benchmark dose) for both compounds are not lower than current tolerable daily intakes.

Gene-Environment Interactions Target Mitogen-activated Protein 3 Kinase 1 (MAP3K1) Signaling in Eyelid Morphogenesis

Gene-environment interactions determine the biological outcomes through mechanisms that are poorly understood. Mouse embryonic eyelid closure is a well defined model to study the genetic control of developmental programs. Using this model, we investigated how exposure to dioxin-like environmental pollutants modifies the genetic risk of developmental abnormalities. Our studies reveal that mitogen-activated protein 3 kinase 1 (MAP3K1) signaling is a focal point of gene-environment cross-talk. Dioxin exposure, acting through the aryl hydrocarbon receptor (AHR), blocked eyelid closure in genetic mutants in which MAP3K1 signaling was attenuated but did not disturb this developmental program in either wild type or mutant mice with attenuated epidermal growth factor receptor or WNT signaling. Exposure also markedly inhibited c-Jun phosphorylation in Map3k1(+/-) embryonic eyelid epithelium, suggesting that dioxin-induced AHR pathways can synergize with gene mutations to inhibit MAP3K1 signaling. Our studies uncover a novel mechanism through which the dioxin-AHR axis interacts with the MAP3K1 signaling pathways during fetal development and provide strong empirical evidence that specific gene alterations can increase the risk of developmental abnormalities driven by environmental pollutant exposure.

Loss of the Mono-ADP-ribosyltransferase, Tiparp, Increases Sensitivity to Dioxin-induced Steatohepatitis and Lethality

The aryl hydrocarbon receptor (AHR) mediates the toxic effects of the environmental contaminant dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD). Dioxin causes a range of toxic responses, including hepatic damage, steatohepatitis, and a lethal wasting syndrome; however, the mechanisms are still unknown. Here, we show that the loss of TCDD-inducible poly(ADP-ribose) polymerase (Tiparp), an ADP-ribosyltransferase and AHR repressor, increases sensitivity to dioxin-induced toxicity, steatohepatitis, and lethality. Tiparp(-/-) mice given a single injection of 100 μg/kg dioxin did not survive beyond day 5; all Tiparp(+/+) mice survived the 30-day treatment. Dioxin-treated Tiparp(-/-) mice exhibited increased liver steatosis and hepatotoxicity. Tiparp ADP-ribosylated AHR but not its dimerization partner, the AHR nuclear translocator, and the repressive effects of TIPARP on AHR were reversed by the macrodomain containing mono-ADP-ribosylase MACROD1 but not MACROD2. These results reveal previously unidentified roles for Tiparp, MacroD1, and ADP-ribosylation in AHR-mediated steatohepatitis and lethality in response to dioxin.

Very low-dose (femtomolar) 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) disrupts steroidogenic enzyme mRNAs and steroid secretion by human luteinizing granulosa cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic congener of the polyhalogenated aromatic hydrocarbons (PAH), which causes anatomical abnormalities and developmental defects, impairs ovulation and reduces fertility. TCDD's endocrine-disrupting effects are, in part, caused by a direct action at the ovary. Herein we investigated the in-vitro effects of environmentally relevant doses of TCDD on estradiol-17β (E2) production by human luteinizing granulosa cells (hLGC) obtained from women stimulated for in-vitro fertilization (IVF). TCDD at all concentrations tested (3.1fM, 3.1pM and 3.1nM) significantly decreased E2 secretion when assayed for by radioimmunoassay (RIA). Herein we confirm that TCDD alters E2 secretion by hLGC in a time-, not dose-dependent fashion and are the first to show decreases in E2 secretion with fM concentrations of TCDD. Using real-time quantitative PCR (RT-qPCR), the decreased E2 secretion correlates with a decrease in the mRNA expression levels two enzymes in the estrogen biosynthesis pathway: CYP11A1 and CYP19A1.

Serum TCDD and TEQ concentrations among Seveso women, 20 years after the explosion

The Seveso Women's Health Study (SWHS) is a historical cohort study of the female population residing near Seveso, Italy, on 10 July 1976, when a chemical explosion resulted in the highest known residential exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Individual TCDD concentration was measured in serum collected near the time of the explosion, and in 1996, we collected adequate blood for TCDD and total dioxin toxic equivalent (TEQ) measurement. Polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls were measured in 1996 serum for a sample (n=225, 23%) of the SWHS cohort and WHO 2005 TEQs were calculated. We examined characteristics that predict 1996 TCDD concentrations and estimated TCDD elimination half-life over the 20-year period since the explosion. Median lipid-adjusted TCDD and total TEQ concentrations in 1996 serum were 7.3 and 26.2 p.p.t., respectively. Initial 1976 TCDD and age at explosion were the strongest predictors of 1996 TCDD. The TCDD elimination half-life was 7.1 years for women older than 10 years in 1976, but was shorter in those who were younger. Twenty years after the explosion, TCDD concentrations in this SWHS sample, the majority of who were children in 1976, remain elevated relative to background. These data add to the limited data available on TCDD elimination half-life in children.

Maternal dioxin exposure and pregnancy outcomes over 30 years of follow-up in Seveso

Animal evidence suggests an association between exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and adverse pregnancy outcomes. Epidemiologic studies report inconsistent results, but are limited by narrow range of exposure, small sample size, and lack of a biologic measure of highest lifetime exposure. On July 10, 1976, a chemical explosion in Seveso, Italy resulted in the highest known residential exposure to TCDD. In 1996, we initiated the Seveso Women's Health Study (SWHS), a retrospective cohort of TCDD exposure and reproductive health. Individual-level TCDD was measured in serum collected soon after the explosion. After 20years of follow-up, we found no association between maternal TCDD in 1976 serum or estimated at pregnancy and spontaneous abortion (SAB), fetal growth, or gestational length. Here, we present an updated analysis of TCDD exposure and adverse pregnancy outcomes from a subsequent follow-up of the SWHS cohort in 2008-2009. SWHS women had 1211 post-explosion pregnancies through the 2008-2009 follow-up. We found no association between TCDD estimated at pregnancy and SAB, fetal growth, or gestational length. However, we found a non-significant inverse association between maternal 1976 serum TCDD and birthweight (adjusted β=-22.8, 95% CI: -80.1, 34.6). The association was stronger among first post-explosion births, but remained non-significant (adjusted β=-47.7, 95% CI: -107.3, 11.9). SWHS is the first study to be able to consider two potentially relevant measures of TCDD exposure: highest lifetime dose and in utero. Our results, although non-significant, suggest that highest dose may be more relevant in epidemiologic studies of TCDD and pregnancy outcomes.

Serum dioxin concentrations and bone density and structure in the Seveso Women's Health Study

BACKGROUND

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a widespread environmental contaminant, is a known endocrine disruptor. In animal studies, TCDD exposure impairs bone metabolism and increases fragility. To our knowledge, no epidemiologic studies have examined this association.

OBJECTIVES

On 10 July 1976, a chemical explosion in Seveso, Italy, resulted in the highest known residential exposure to TCDD. In 1996, we initiated the Seveso Women's Health Study, a retrospective cohort study of the health of the women. In 2008, we followed up the cohort. Here, we evaluated the association between TCDD exposure and bone structure and geometry in adulthood, and considered whether timing of TCDD exposure before achievement of peak bone mass (assumed to occur 2 years after onset of menarche) modified the association.

METHODS

Individual TCDD concentration was measured in archived serum collected soon after the explosion. In 2008, 350 women who were <20 years old in 1976 underwent a dual-energy X-ray absorptiometry (DXA) bone scan. Bone mineral density was measured at the lumbar spine and hip, and hip geometry was extracted from hip DXA scans using the hip structural analysis method.

RESULTS

Among premenopausal women, TCDD serum levels were associated with some indexes indicating better bone structure in women exposed before peak bone mass (n=219), with stronger associations in those exposed before 5 years of age (n=46). In contrast, among postmenopausal women, TCDD levels were associated with evidence of better bone structure in women exposed after peak bone mass (n=48) than in other women (n=18).

CONCLUSIONS

Our current results do not support the hypothesis that postnatal TCDD exposure adversely affects adult bone health. Continued follow-up of women who were youngest at exposure is warranted. Future studies should also focus on those exposed in utero.

Ultrahigh resolution mass spectrometry-based metabolic characterization reveals cerebellum as a disturbed region in two animal models

In the previous reports about cognitive dysfunction, cerebellum was thought to be a less affected tissue by genetic or environmental alterations in comparison to other tissues in the brain including hippocampus under the same conditions. In this work, we investigated two types of metabolomic alterations inside the cerebellum tissue. The first one addressed the differences in the metabolomics profiles between Transgenic (Tg) CRND8 of Alzheimer's disease mice and non-transgenic (non-Tg) littermates. The second one addressed the metabolic differences between wild type mice exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and wild type mice which are not exposed to this toxic compound. For these two investigations, ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS) was implemented. As a result, the significant changes of each comparison were tentatively annotated by the high mass accuracy generated from the measurements in the negative ion mode. The biosynthesis of amino acids was also enhanced pronouncedly, and perturbation of purine metabolism was also observed in Tg mice compared to non-Tg littermates. In another animal model, the reduced levels of amino acids were found whereas the intermediate levels in purine metabolism and fatty acids including fatty acid conjugated metabolites were elevated in cerebellar tissues of mice exposed to TCDD compared to control group. Collectively, it was demonstrated that FT-ICR/MS was a powerful tool for interpretation of the elemental compositions of the peaks, revealing that the metabolic perturbations in cerebellar tissues of mice were induced by either genetic manipulation or environmental factor. Therefore, the non-targeted approach, alternatively, provides various metabolic phenotypes for the systems-level mirror of the complex etiology of neurotoxicity in the cerebellum.

In utero exposure to dioxins and dioxin-like compounds and anogenital distance in newborns and infants

BACKGROUND

Anogenital distance in animals is used as a measure of fetal androgen action. Prenatal exposure to dioxins and dioxin-like compounds in rodents causes reproductive changes in male offspring and decreases anogenital distance.

OBJECTIVE

We assessed whether in utero exposure to dioxins and dioxin-like compounds adversely influences anogenital distance in newborns and young children (median age, 16 months; range, 1-31 months).

METHODS

We measured anogenital distance among participants of the "Rhea" mother-child cohort study in Crete and the Hospital del Mar (HMAR) cohort in Barcelona. Anogenital distance (AGD; anus to upper penis), anoscrotal distance (ASD; anus to scrotum), and penis width (PW) were measured in 119 newborn and 239 young boys; anoclitoral (ACD; anus to clitoris) and anofourchetal distance (AFD; anus to fourchette) were measured in 118 newborn and 223 young girls. We estimated plasma dioxin-like activity in maternal blood samples collected at delivery with the Dioxin-Responsive Chemically Activated LUciferase eXpression (DR CALUX®) bioassay.

RESULTS

Anogenital distances were sexually dimorphic, being longer in males than females. Plasma dioxin-like activity was negatively associated with AGD in male newborns. The estimated change in AGD per 10 pg CALUX®-toxic equivalent/g lipid increase was -0.44 mm (95% CI: -0.80, -0.08) after adjusting for confounders. Negative but smaller and nonsignificant associations were observed for AGD in young boys. No associations were found in girls.

CONCLUSIONS

Male infants may be susceptible to endocrine-disrupting effects of dioxins. Our findings are consistent with the experimental animal evidence used by the Food and Agriculture Organization/World Health Organization to set recommendations for human dioxin intake.

Maternal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin and the body burden in offspring of long-evans rats

OBJECTIVES

In utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) results in a wide variety of developmental effects in pups at doses much lower than those causing overt toxicity in adult animals. We investigated the relationship between tissue concentrations of TCDD in dams and fetuses and developmental effects on pups.

MATERIALS AND METHODS

Pregnant Long-Evans rats were given TCDD at a single oral dose of 12.5, 50, 200, or 800 ng of TCDD or [(3)H]-TCDD/kg bw on gestation day (GD) 15. Dams were sacrificed on GD16 and GD21, and the tissue concentrations of TCDD were measured in dams and fetuses. Pups were sacrificed on postnatal day (PND) 49 and PND63 for males and PND70 for females, and the reproductive effects and tissue concentrations of TCDD were determined.

RESULTS

The sex ratio (male/female) on GD21 was significantly reduced at 50 ng TCDD/kg and at 12.5 and 50 ng TCDD/kg at birth, but not at other doses. Delayed puberty was observed in males at 200 ng TCDD/kg and in males and females at 800 ng TCDD/kg. Anogenital distance, testis weight, epididymal sperm count, sperm motility, and ejaculated sperm count were not affected. Estrous cyclicity was not different from that of the control in any treatment group. A dose-dependent decrease in weight of seminal vesicle and prostate on PND49 was observed. Prostate weight was significantly decreased at 800 ng TCDD/kg. At this dose, maternal body burden and TCDD concentration in fetuses were 290 pg TCDD/g and 52 pg TCDD/g on GD16, respectively. Reduced prostate weight is a sensitive and commonly observed endpoint so that the body burdens of dams and fetuses at the LOAEL of this endpoint could be served as the basis for establishing TDI for dioxins.

Dioxin exposure and cancer risk in the Seveso Women's Health Study

BACKGROUND

2,3,7,8-Tetrachlorodibenzo-para-dioxin (TCDD), a widespread environmental contaminant, disrupts multiple endocrine pathways. The International Agency for Research on Cancer classified TCDD as a known human carcinogen, based on predominantly male occupational studies of increased mortality from all cancers combined.

OBJECTIVES

After a chemical explosion on 10 July 1976 in Seveso, Italy, residents experienced some of the highest levels of TCDD exposure in a human population. In 1996, we initiated the Seveso Women's Health Study (SWHS), a retrospective cohort study of the reproductive health of the women. We previously reported a significant increased risk for breast cancer and a nonsignificant increased risk for all cancers combined with individual serum TCDD, but the cohort averaged only 40 years of age in 1996. Herein we report results for risk of cancer from a subsequent follow-up of the cohort in 2008.

METHODS

In 1996, we enrolled 981 women who were 0-40 years of age in 1976, lived in the most contaminated areas, and had archived sera collected near the explosion. Individual TCDD concentration was measured in archived serum by high-resolution mass spectrometry. A total of 833 women participated in the 2008 follow-up study. We examined the relation of serum TCDD with cancer incidence using Cox proportional hazards models.

RESULTS

In total, 66 (6.7%) women had been diagnosed with cancer. The adjusted hazard ratio (HR) associated with a 10-fold increase in serum TCDD for all cancers combined was significantly increased [adjusted HR = 1.80; 95% confidence interval (CI): 1.29, 2.52]. For breast cancer, the HR was increased, but not significantly (adjusted HR = 1.44; 95% CI: 0.89, 2.33).

CONCLUSIONS

Individual serum TCDD is significantly positively related with all cancer incidence in the SWHS cohort, more than 30 years later. This all-female study adds to the epidemiologic evidence that TCDD is a multisite carcinogen.

Environmental pollutants and type 2 diabetes: a review of mechanisms that can disrupt beta cell function

The prevalence of diabetes mellitus is currently at epidemic proportions and it is estimated that it will increase even further over the next decades. Although genetic predisposition and lifestyle choices are commonly accepted reasons for the occurrence of type 2 diabetes, it has recently been suggested that environmental pollutants are additional risk factors for diabetes development and this review aims to give an overview of the current evidence for this. More specifically, because of the crucial role of pancreatic beta cells in the development and progression of type 2 diabetes, the present work summarises the known effects of several compounds on beta cell function with reference to mechanistic studies that have elucidated how these compounds interfere with the insulin secreting capacity of beta cells. Oestrogenic compounds, organophosphorus compounds, persistent organic pollutants and heavy metals are discussed, and a critical reflection on the relevance of the concentrations used in mechanistic studies relative to the levels found in the human population is given. It is clear that some environmental pollutants affect pancreatic beta cell function, as both epidemiological and experimental research is accumulating. This supports the need to develop a solid and structured platform to fully explore the diabetes-inducing potential of pollutants.

Metabolomic analysis of liver and skeletal muscle tissues in C57BL/6J and DBA/2J mice exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been demonstrated to have the adverse effects on human health. In this study, we applied a metabolomic approach in conjunction with unsupervised and supervised machine learning methods to investigate the toxic effects of TCDD. By using liquid chromatography/quadrupole time-of-flight mass spectrometry, non-targeted metabolomic analysis revealed the metabolic signatures of the toxicity in aryl hydrocarbon receptor (AhR)-high affinity C57BL/6J (C6) mice as well as low affinity strain-DBA/2J (D2) mice. Lysophospholipids and long chain fatty acids were strikingly elevated in the C6 mice exposed to TCDD in both liver and skeletal muscle tissues. Meanwhile, the level of palmitoylcarnitine, which is one of the important indicators in fatty acid β-oxidation, increased significantly. Moreover, several nucleosides and amino acids decreased markedly. On the other hand, much less differentiating metabolites were highlighted in another strain-D2 mouse model. Taking liver and skeletal muscle tissues together, the levels of inosine, valine and glutamine decreased significantly. One lysophospholipid and two fatty acids were found to be enhanced. The principal components analysis and support vector machine clustering results also exhibited discriminations in the liver and skeletal muscle tissues of the mice. The obtained results indicated that TCDD could disrupt several metabolic pathways, including fatty acid biosynthesis and amino acid metabolism in both C6 and D2 mice. The increased rate of fatty acid beta-oxidation, however, was only observed in the liver and skeletal muscle tissues of C6 mice. The perturbation of the tricarboxylic acid (TCA) cycle was testified in two strains but the change was much slighter in D2 mice. It was of particular interest to note that the succinate level was enhanced in the liver tissues of both strains, and particularly, the change was up to 11.49-fold in the liver of C6 mice treated with TCDD. Collectively, the discrimination of D2 mice was not as distinct as that of C6 mice when exposed to the same dosage. Furthermore, D2 was confirmed to be less-sensitive rather than resistant to a high dose of TCDD.

Neural precursor cell proliferation is disrupted through activation of the aryl hydrocarbon receptor by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Neurogenesis involves the proliferation of multipotent neuroepithelial stem cells followed by differentiation into lineage-restricted neural precursor cells (NPCs) during the embryonic period. Interestingly, these progenitor cells express robust levels of the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor that regulates expression of genes important for growth regulation, and xenobiotic metabolism. Upon binding 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a pervasive environmental contaminant and potent AhR ligand, AhR, is activated and disrupts gene expression patterns to produce cellular toxicity. Because of its widespread distribution in the brain during critical proliferative phases of neurogenesis, it is conceivable that AhR participates in NPC expansion. Therefore, this study tested the hypothesis that AhR activation by TCDD disrupts signaling events that regulate NPC proliferation. The C17.2 NPC line served as a model system to (1) assess whether NPCs are targets for TCDD-induced neurotoxicity and (2) characterize the effects of TCDD on NPC proliferation. We demonstrated that C17.2 NPCs express an intact AhR signaling pathway that becomes transcriptionally active after TCDD exposure. (3)H-thymidine and alamar blue reduction assays indicated that TCDD suppresses NPC proliferation in a concentration-dependent manner without the loss of cell viability. Cell cycle distribution analysis by flow cytometry revealed that TCDD-induced growth arrest results from an impaired G1 to S cell cycle transition. Moreover, TCDD exposure altered p27( kip1) and cyclin D1 cell cycle regulatory protein expression levels consistent with a G1 phase arrest. Initial studies in primary NPCs isolated from the ventral forebrain of embryonic mice demonstrated that TCDD reduced cell proliferation through a G1 phase arrest, corroborating our findings in the C17.2 cell line. Together, these observations suggest that the inappropriate or sustained activation of AhR by TCDD during neurogenesis can interfere with signaling pathways that regulate neuroepithelial stem cell/NPC proliferation, which could adversely impact final cell number in the brain and lead to functional impairments.

The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin disturbs the establishment and maintenance of cell polarity in preimplantation rat embryos

Maternal exposure to the environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces a variety of defects in compaction-stage embryos, including monopolar spindle formation, errors in chromosome segregation, and fragmentation resulting from aberrant cytokinesis. In this study, we investigated the possibility that a failure in centrosome duplication, separation, or positioning within blastomeres might underlie the observed effects of TCDD on early embryos. The subcellular localization of the centrosomal marker TUBG1 was analyzed in preimplantation embryos collected from female rats exposed to either chronic (50 ng kg(-1) wk(-1) for 3 wk) or acute (50 ng/kg or 1 microg/kg at proestrus) doses of TCDD. In treated embryos, interphase TUBG1 foci were more abundant and cortically displaced when compared to those in controls. At prophase, some blastomeres exhibited a single large perinuclear TUBG1 aggregate, suggesting a failure in centrosome duplication or separation. Furthermore, the presence of monopolar spindles at metaphase was confirmed by the localization of TUBG1 to the single spindle pole. Therefore, the misregulation of centrosome number and localization, as indicated by TUBG1 staining, may contribute to errors in chromosome segregation and cytokinesis in embryos following maternal TCDD exposure.

The inhibition effect of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin-induced aryl hydrocarbon receptor activation in human hepatoma cells with the treatment of cadmium chloride

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), considered as endocrine disruptors, tend to accumulate in fatty tissues. Dioxin-responsive element chemical activated luciferase gene expression assay (DRE-luciferase assay) has been recognized as a semi-quantitative method for screening dioxins for its fast and low-cost as compared with HRGC/HRMS. However, some problems with the bioassay, including specificity, detection variation resulted from different cleanup strategies, and uncertainty of false-negative or false-positive results, remain to be overcome. Cadmium is a prevalent environmental contaminant around the world. This study was aimed to examine the effects of cadmium on the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced activation of aryl hydrocarbon receptor (AhR)-mediated gene expression in human hepatoma cells (Huh7-DRE-Luc cells and Huh7 cells). Ethoxyresorufin-O-deethylase (EROD) and DRE-luciferase assay were employed to determine the enzyme activity of cytochrome P450 1A1 (CYP1A1) and activation of AhR, respectively. The results showed that Cd(2+) levels significantly inhibited the induction of TCDD-induced CYP1A1 and DRE luciferase activation in hepatoma cells. The 50% inhibited concentrations (IC(50)) of CdCl(2) were 0.414 microM (95% confidence interval (C.I.): 0.230-0.602 microM) in Huh7-DRE-Luc cells and 23.2 microM (95% C.I.: 21.7-25.4 microM) in Huh7 cells. Accordingly, prevention of interference with non-dioxin-like compounds in a DRE-luciferase assay is of great importance in an extensive cleanup procedure.

Estrogen and TCDD influence RLN2 gene activity in estrogen receptor-positive human breast cancer cells

Expression of relaxin is increased in human breast cancer, and relaxin was shown to increase in vitro invasiveness through increased production and secretion of matrix metalloproteinases in human breast cancer cells. The role of estrogen in the promotion of breast cancer is well-known. The environmental toxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a known carcinogen but has been shown to have antiestrogenic effects in human breast cancer cells. In this study, we have employed real-time PCR and chromatin immunoprecipitation (ChIP) assays to investigate the influence of estrogen and TCDD on relaxin-1 (RLN1) and relaxin-2 (RLN2) gene expression in MCF-7 and T47D human breast cancer cells. Estrogen increased RLN2 transcripts in T47D and MCF-7 cells after just 4 h of exposure, whereas TCDD did not. RLN1 transcripts were only induced after 24 h of estrogen exposure. TCDD did have antiestrogenic activity and reduced the estrogen-mediated increase in RLN2 and RLN1 mRNA. The estrogen-mediated increase in RLN2 mRNA levels was not caused by changes in the mRNA stability. ChIP analysis revealed binding of estrogen receptor-alpha (ERalpha) to promoter sequences of the RLN2 gene. Thus, we provide evidence that RLN2 gene activity is directly regulated by activated ERalpha in human breast cancer cells and we show that activation of the arylhydrocarbon receptor by TCDD inhibits this regulation by estrogen.

Concentrations of PCDD/PCDFs and PCBs in spent foundry sands

Approximately 10 million tons of spent foundry sand (SFS) are generated in the United States each year, and their beneficial use in agricultural and horticultural applications is being considered. Other studies have demonstrated that trace elements are low enough in sands from iron, steel, and aluminum foundries to allow their beneficial use. Because data were not available on polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and polychlorinated biphenyls in SFSs, we analyzed representative spent sands from 10 foundries to assess the potential for these compounds to limit their use in soil-related applications. The total TEQ (toxicity equivalent) concentrations ranged from 0.01 to 3.13 ng TEQ kg(-1), with an average concentration of 0.58 ng TEQ kg(-1). These concentrations are within the range of natural background in soils.

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the mortality and growth of two amphibian species (Xenopus laevis and Pseudacris triseriata)

We observed a slight drop in the growth of Xenopus laevis and Pseudacris triseriata larvae following acute exposure (24-48 h) during egg development to three concentrations of TCDD (0.3, 3.0, 30.0 microg/l). Our exposure protocol was modeled on a previous investigation that was designed to mimic the effects of maternal deposition of TCDD. The doses selected were consistent with known rates of maternal transfer between mother and egg using actual adult body burdens from contaminated habitats. Egg and embryonic mortality immediately following exposure increased only among 48 h X. laevis treatments. Control P. triseriata and X. laevis completed metamorphosis more quickly than TCDDtreated animals. The snout-vent length of recently transformed P. triseriata did not differ between treatments although controls were heavier than high-dosed animals. Likewise, the snout-vent length and weight of transformed X. laevis did not differ between control and TCDD treatments. These findings provide additional evidence that amphibians, including P. triseriata and X. laevis are relatively insensitive to acute exposure to TCDD during egg and embryonic development. Although the concentrations selected for this study were relatively high, they were not inconsistent with our current understanding of bioaccumulation via maternal transfer.

Spatial variations in the incidence of breast cancer and potential risks associated with soil dioxin contamination in Midland, Saginaw, and Bay Counties, Michigan, USA

BACKGROUND

High levels of dioxins in soil and higher-than-average body burdens of dioxins in local residents have been found in the city of Midland and the Tittabawassee River floodplain in Michigan. The objective of this study is threefold: (1) to evaluate dioxin levels in soils; (2) to evaluate the spatial variations in breast cancer incidence in Midland, Saginaw, and Bay Counties in Michigan; (3) to evaluate whether breast cancer rates are spatially associated with the dioxin contamination areas.

METHODS

We acquired 532 published soil dioxin data samples collected from 1995 to 2003 and data pertaining to female breast cancer cases (n = 4,604) at ZIP code level in Midland, Saginaw, and Bay Counties for years 1985 through 2002. Descriptive statistics and self-organizing map algorithm were used to evaluate dioxin levels in soils. Geographic information systems techniques, the Kulldorff's spatial and space-time scan statistics, and genetic algorithms were used to explore the variation in the incidence of breast cancer in space and space-time. Odds ratio and their corresponding 95% confidence intervals, with adjustment for age, were used to investigate a spatial association between breast cancer incidence and soil dioxin contamination.

RESULTS

High levels of dioxin in soils were observed in the city of Midland and the Tittabawassee River 100-year floodplain. After adjusting for age, we observed high breast cancer incidence rates and detected the presence of spatial clusters in the city of Midland, the confluence area of the Tittabawassee, and Saginaw Rivers. After accounting for spatiotemporal variations, we observed a spatial cluster of breast cancer incidence in Midland between 1985 and 1993. The odds ratio further suggests a statistically significant (alpha = 0.05) increased breast cancer rate as women get older, and a higher disease burden in Midland and the surrounding areas in close proximity to the dioxin contaminated areas.

CONCLUSION

These findings suggest that increased breast cancer incidences are spatially associated with soil dioxin contamination. Aging is a substantial factor in the development of breast cancer. Findings can be used for heightened surveillance and education, as well as formulating new study hypotheses for further research.

Mid-gestation Exposure of C57BL/6 Mice to 2,3,7,8-Tetrachlorodibenzo-p-dioxin Causes Postnatal Morphologic Changes in the Spleen and Liver

Pregnant C57BL/6 mice were exposed to 5 μg/kg 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) or vehicle by oral gavage between gestation days (GDs) 11 and 13. The thymus, spleen, and liver of the pups were examined histologically, and cell surface antigen expression was assessed on postnatal days (PNDs) 1, 14, 25, and 46. In addition to the expected decrease in thymic weight on PND 1, TCDD caused an increase in splenic weight on PND 14 and in hepatic weight on PNDs 14 and 25. The apoptotic index was increased and the corticomedullary border poorly defined in thymuses of TCDD-exposed mice on PND 1, but not at later endpoints. T lymphocytes were increased and B lymphocytes decreased in spleens of the TCDD-exposed mice on PND 46. TCDD-exposed mice had a nearly significant ( p =.051) decrease in the number of splenic germinal centers on PND 46. Foci of extramedullary hematopoiesis (EMH) were increased in number in the livers of TCDD-exposed mice on PND 14, suggesting possible increased production of immune cells of unknown phenotype and function in this organ. These results suggest that late-gestation thymic architectural changes caused by TCDD resolve shortly after birth: however, abnormalities in other immunologically important areas may appear later in postnatal life.

Autoradiographic localization of aromatic hydrocarbon receptor (AHR) in rhesus monkey ovary

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic congener of a large class of manmade pollutants that persist in the environment. TCDD exerts its toxic effects, in part, by binding to its receptor known as the aromatic hydrocarbon receptor (AHR). TCDD is estrogen modulatory and in some systems its receptor associates directly with estrogen receptors via co-activator molecules. TCDD inhibits steroid synthesis in human ovarian granulosa cells and AHR is found in these cells. We have previously shown that AHR is found in whole rhesus monkey ovary, but have yet to establish its location. In the present study, we set out to show that radiolabeled TCDD binds to monkey ovarian follicles and that this binding is receptor mediated. Ovaries from Macaca mulatta were sectioned on a cryostat at 10 micro m; and sections were incubated with either control vehicle, (3)H-TCDD, or (3)H-TCDD plus alpha-naphthoflavone (ANF), a known receptor-blocking agent. Here, we show for the first time specific binding of TCDD to the granulosa cells of antral follicles and other regions of the rhesus monkey ovary. Our data indicate a 60-fold increase in binding with (3)H-TCDD over that of control, and that this binding is reduced to the levels seen in controls with the addition of the competitive antagonist ANF. These findings support the hypothesis that TCDD directly affects primate ovarian function via the AHR.

Weibliche und männliche Fertilitätsstörungen und Risiken der assistierten Fertilisation

Ca. 10–15% der Paare im reproduktionsfähigen Alter bleiben ungewollt kinderlos. Der Anteil steigt tendentiell durch den zunehmend „späten Kinderwunsch“. Das durchschnittliche Alter der Erstgebärenden hat sich u.a. aus Gründen der Ausbildungszeit und Berufstätigkeit der Frau zwischen 1970 und 2000 vom 24. auf das 30. Lebensjahr verschoben. Eine gewollte Kinderlosigkeit kommt in ca. 10% der Ehen vor.

Dioxin affects glucose transport via the arylhydrocarbon receptor signal cascade in pluripotent embryonic carcinoma cells

Intoxication by dioxins such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) leads, among other damages, to early embryo loss, fetal malformations, and cardiovascular toxicity. Apart from binding to the arylhydrocarbon receptor (AhR), the mechanism of TCDD-mediated embryo toxicity is still unclear. We investigated possible modes of a TCDD-mediated toxicity, particularly in glucose metabolism, in pluripotent P19 mouse embryonic carcinoma cells. Undifferentiated P19 cells were exposed to 1-100 nM TCDD and characterized for AhR signaling. For studying cell differentiation, P19 cells were exposed to 10 nM TCDD at stage of embryoid body formation, and analyzed on glucose metabolism and cardiac differentiation during the next 3 wk. TCDD treatment activated the AhR-signaling cascade within 1 h, confirmed by AhR translocation, induction of cytochrome P450 1A1 expression, and activation of the xenobiotic response element. Although cell viability and transcription of the cardiac marker protein alpha-myosin heavy chain were affected, TCDD did not inhibit the differentiation of P19 cells to pulsating cardiomyocytes. TCDD significantly down-regulated the expression levels of the glucose transporter (GLUT) isoforms 1 and 3. After 24-h TCDD treatment, GLUT1 was no longer localized in the plasma membrane of P19 cells. The impaired GLUT expression correlated with a lower glucose uptake in 5-d-old embryoid bodies. The TCDD effects were mediated by AhR, as shown by preculture with the AhR antagonist alpha-naphthoflavone. Our data demonstrate that an AhR-mediated disturbance in GLUT expression and insufficient glucose uptake may be major mechanisms in TCDD embryo toxicity.

Panax ginseng effects on DNA damage, CYP1A1 expression and histopathological changes in testes of rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effects of Panax ginseng extracts on DNA damage, expression of cytochrome P450 (CYP) 1A1 and reproductive toxicity were evaluated in the testis of rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxinthe (TCDD). Fifty rats were divided into five groups according to treatment with 2,3,7,8-TCDD and P. ginseng extracts. Single cell gel electrophoresis assays were performed to evaluate DNA damage that occurred in the lymphocytes of rats. Histological changes in the seminiferous tubules of the testis were determined using Johnsen's scoring system and Real Time-PCR was performed to evaluate the mRNA expression of CYP1A1. Significant pathological effects were observed in the 2,3,7,8-TCDD treated rats including a reduced seminiferous tubular diameter, an increased number of damaged tubules (maturation arrest, eosinophilic degeneration and spermatid giant cells) and increased Johnsen's score. DNA damage and the expression of CYP1A1 mRNA were significantly increased in rat testes. There were no significant differences between the control and animals treated with P. ginseng extracts. However, a significantly decreased level of DNA damage, decreased CYP1A1 expression and reduced pathological effects were observed in the 2,3,7,8-TCDD with P. ginseng extracts treated groups when compared with the TCDD treated group. In summary, our study demonstrates that 2,3,7,8-TCDD induces the pathological and genotoxical damage in rat testes, while P. ginseng extract treatment exhibits a therapeutic capacity to reduce these effects via reduction of CYP1A1 mRNA.

Short-Term Hormone Release from Adult Female Rat Hypothalamic and Pituitary Explants is not Altered by 2,3,7,8-Tetrachlorodibenzo-p-dioxin

2, 3, 7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has adverse effects on reproduction, in part due to direct actions at the ovary. It is unclear whether effects are further mediated by glands that regulate ovarian function. We investigated whether effects of TCDD are mediated via the hypothalamic-pituitary axis. Hypothalamic and pituitary tissues were cultured in medium with and without TCDD. TCDD did not alter GnRH release from hypothalamic samples. It continued to be pulsatile with no differences in the average peak frequency, average peak amplitude, or baseline GnRH release. TCDD did not alter GnRH-induced release of gonadotropins from pituitary samples. There were no differences in average peak amplitude or baseline release. AhR, ARNT or ER alpha mRNA copy numbers in cultured pituitaries were not affected by TCDD. Our data suggest that TCDD effects on ovarian function are not mediated through the hypothalamic or pituitary release parameters tested in this study.

Placental transfer of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls in Taiwanese mothers in relation to menstrual cycle characteristics

The aim was to determine the body burden of dioxins and polychlorinated biphenyls (PCBs) and whether they are associated with variables influencing reproduction. Our subjects were healthy women (mean age of 29 [SD=4.5]) from central Taiwan. The congeners of dioxins and dioxin-like PCBs in placentas (n=119) were identified using gas chromatography/high resolution mass spectrometry. The median levels of polychlorinated dibenzo-p-dioxins/dibenzofurans and PCBs were 10.2 (geometric mean [GM]: 9.8, 95% confidence interval [95% CI]: 8.8-10.9) and 2.7 (GM: 2.7, 95% CI: 2.3-3.1) pg WHO-TEQ/g lipid, respectively. Total TEQ level in placentas was significantly correlated with mothers' arm circumference (r=0.22, p=0.043). Increased body fat percentage was associated with higher total TEQ level in placentas. After adjustment for maternal age, pre-pregnant body mass index (BMI), and parity, placental dioxin-TEQ level higher in women (age 19 years) with irregular menstrual cycle than in those (age <18 years) with regular menstrual cycle (p=0.032) and placental PCB-TEQ level was higher in women with menstrual cycles longer than 33 days versus less than 33 days (p=0.006). Thus, environmental exposure to dioxins and PCBs may be related to changes in current menstrual cycle characteristics.

The effects of maternal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin on testicular steroidogenesis in infantile male rats

Exposure of adult male animals to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) decreases serum androgen concentrations. Reduction in androgen levels after maternal exposure has also been reported, but these results have not been reproduced. We have earlier shown that TCDD stimulates rather than inhibits testosterone synthesis in the prenatal rat testis. The aim of the present study was to elucidate in utero-induced effects of TCDD on testicular steroidogenesis in the 14-day-old infant rats. At that time the foetal Leydig cell population is still the prevailing source of androgens. Pregnant Sprague-Dawley dams were given a single oral dose of TCDD (0, 0.04, 0.2, or 1.0 microg/kg) on day 13 of pregnancy. On postnatal day 14, the body weight of male offspring was reduced after exposure to 1.0 microg/kg TCDD (from 33.9 +/- 1.66 g to 31.6 +/- 2.67 g). Relative testis weight, plasma testosterone, luteinizing hormone and follicle-stimulating hormone levels remained unaltered in all exposure groups. Moreover, in ex vivo incubations, testosterone and cAMP production was not affected. StAR protein level in the freshly isolated testes was increased in the 0.2 microg/kg group, and seminiferous cord diameter in the 0.04 microg/kg group. The present study confirms our earlier findings in in utero TCDD-exposed foetal testis indicating that maternal TCDD exposure does not negatively influence the developmental testosterone production of foetal type Leydig cells in rats.

The aryl hydrocarbon receptor pathway and sexual differentiation of neuroendocrine functions

Historically, much of the research on health effects of environmental pollutants focused on ascertaining whether compounds were carcinogenic. More recent findings show that environmental contaminants also exert insidious effects by disrupting hormone action. Of particular concern are findings that developmental exposure to dioxins, chemicals that act through the aryl hydrocarbon receptor pathway, permanently alters sexually differentiated neural functions in animal models. In this review, we focus on mechanisms through which dioxins disrupt neuroendocrine development as exemplified by effects on a brain region critical for ovulation in rodents. We also provide evidence that dysregulation of GABAergic neural development may be a general mechanism underlying a broad spectrum of effects seen after perinatal dioxin exposure.

Differential susceptibilities of Holtzman and Sprague–Dawley rats to fetal death and placental dysfunction induced by 2,3,7,8-teterachlorodibenzo-p-dioxin (TCDD) despite the identical primary structure of the aryl hydrocarbon receptor

A single oral dose of 2,3,7,8-tetrachlorodibenzo-p-dioin (TCDD) administered to pregnant Holtzman (HLZ) rats on gestational days 15 (GD15) caused placental dysfunction, resulting in fetal death (Ishimura, R., Ohsako, S., Miyabara, Y., Sakaue, M., Kawakami, T., Aoki, Y., Yonemoto, J., Tohyama, C., 2002a. Increased glycogen content and glucose transporter 3 mRNA level in the placenta of Holtzman rats after exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin. Toxicol. Appl. Pharmacol. 178, 161-171; Ishimura, R., Ohsako, S., Kawakami, T., Sakaue, M., Aoki, Y., Tohyama, C., 2002b. Altered protein profile and possible hypoxia in the placenta of 2,3,7,8-tetrachlorodibenzo-p-dioxin-exposed rats. Toxicol. Appl. Pharmacol. 185, 197-206). In order to investigate the mechanism underlying the TCDD-induced fetal death, we compared two outbred strains of rats, namely, the HLZ and the Sprague-Dawley International Genetic Standard rats (SD-IGS), a strain with characteristics resembling those of the HLZ rats. Pregnant HLZ and SD-IGS rats were administered TCDD as a single dose by gavage on GD15, as described within the parentheses (HLZ, 0, 1.6 mug TCDD/kg; SD-IGS, 0, 2, 5, 10 microg TCDD/kg). Whereas a high incidence (14%) of fetal death was observed on GD20 in the HLZ rats, no fetal deaths occurred in the SD-IGS rats, even at the highest dose of TCDD. A histological marker of cellular abnormality at the placental junctional zone, i.e., delay in the disappearance of the glycogen cells and cysts filled with an eosinophilic material (GC-EM), which normally disappear by GD20, was observed in the HLZ rats after exposure to the lowest dose of TCDD (1.6 microg TCDD/kg), but not in the SD-IGS rats even after exposure to the highest dose of TCDD. Furthermore, maternal blood sinusoids in the labyrinth zone were constricted following exposure to TCDD in the HLZ, but not SD-IGS rats. These observations indicate that HLZ rats are more susceptible to the adverse effects of TCDD on fetal growth and placental function, than SD-IGS rats. Direct sequencing analysis of the aryl hydrocarbon receptor (AhR) gene revealed no difference in the primary structure of the receptor between the HLZ and SD-IGS rats. In addition, no significant differences were observed between the two strains of rats in the levels of induction of placental cytochrome P450 1A1, 1B1, AhR, and AhRR mRNAs following administration of serially increasing doses of TCDD (0.0125, 0.05, 0.2, 0.8, and 1.6 microg TCDD/kg), indicating that the activity of TCDD-AhR complex in the placenta is similar between the HLZ and SD-IGS rats. Taken together, the above-described findings indicate that the higher susceptibility of HLZ rats to TCDD-induced placental dysfunction and fetal death may be modulated by other factor(s) in the genetic background of HLZ rats than the AhR.

INDUCTION OF DETOXIFYING ENZYMES IN RODENT WHITE ADIPOSE TISSUE BY ARYL HYDROCARBON RECEPTOR AGONISTS AND ANTIOXIDANTS

The liver is the main organ of drug metabolism, but the expression and induction by xenobiotics of drug-metabolizing enzymes is also often observed in extrahepatic tissues. Recently, we reported that lipophilic cytochrome P450 inducers, beta-naphthoflavone (BNF), phenobarbital, and dexamethasone, induced CYP1, CYP2B, and CYP3A enzymes, respectively, in rat epididymal white adipose tissue (WAT) at both mRNA and protein levels. To further confirm the xenobiotic-induced expression of drug-metabolizing enzymes in adipose tissue, we studied the induction of CYP1A1 and other detoxifying enzymes by aryl hydrocarbon receptor (AhR) agonists and antioxidants. BNF increased CYP1A1 mRNA levels in several visceral WATs (epididymal, perirenal, and mesenteric) to a greater degree than in subcutaneous WAT in rats. Using C57BL/6 and DBA/2 mice with different responsiveness to aryl hydrocarbons and detecting cytoplasmic levels of AhR proteins, we have demonstrated that AhR mediates this CYP1A1 induction by BNF in WAT. Moreover, the NF-E2-related factor 2 (Nrf2)/antioxidant responsive element pathway is also functional in WAT, since BNF, which is known to activate both AhR and Nrf2, and antioxidants including tert-butylhydroquinone, 1-chloro-2,4-dinitrobenzene, and menadione induced the expression of Nrf2-target genes (NAD-(P)H:quinone oxidoreductase, glutathione S-transferase A subunits, and heme oxygenase-1) in rats and mice. These results suggest that both AhR and Nrf2 pathways are active in WAT and that lipophilic compounds accumulated in WAT can activate these transcription factors to increase detoxification capability in the tissue.

Suppressive effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on vascular remodeling that takes place in the normal labyrinth zone of rat placenta during late gestation

The maintenance of the placental vasculature is essential for sustaining normal fetal growth. On the basis of our previous observation that fetal death was accompanied by placental hypoxia upon exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (R. Ishimura et al., 2002a, Toxicol. Appl. Pharmacol. 185, 197-206), we here investigated the effects of TCDD on the placenta, focusing on the development of the labyrinth zone. Holtzman rats were administered a single oral dose of 1.6 mug of TCDD/kg body weight or an equivalent volume of vehicle (control) on gestation day (GD) 15, and placental tissues were analyzed on GD20. Immunohistochemical staining showed that the exposure to TCDD decreased the size of maternal blood sinusoids and caused the constriction of fetal capillaries in the placenta. In contrast, we found that vascular remodeling occurred in the labyrinth zone of normal rat placenta; that is, the vascular development in the normal labyrinth zone during the late gestation (from GD16 to GD20) showed dilated maternal blood sinusoids and fetal capillaries accompanied by a decrease in thickness and the apoptosis of trophoblasts. The present results demonstrate that this remodeling is suppressed by TCDD, which is further supported by the decreased expression level of Tie2 mRNA, the gene which is associated with vascular remodeling, and also by the decrease in the number of apoptotic trophoblasts in TCDD-exposed rats. The present study provided a new finding on the development of the vasculature in the labyrinth zone during the late gestation under normal conditions and showed the inhibition of vascular remodeling in TCDD-exposed rats.

In utero and lactational exposure to TCDD; steroidogenic outcomes differ in male and female rat pups

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) has a potency to induce decreased fertility and structural reproductive anomalies in male and female mammals. While the activity profile of sex steroid hormone production distinctly differs in developing males and females, we wanted to analyze sex-specific effects of TCDD introduced in utero and via lactation on gonadal steroidogenesis and gonadotropin levels in male and female rat infant pups. One oral dose of TCDD (0, 0.04, 0.2, or 1.0 microg/kg) was given to dams on gestational day (GD) 13. Plasma testosterone, estradiol, progesterone, follicle stimulating hormone (FSH), luteinizing hormone (LH), and gonadal mRNA levels for steroid acute regulatory protein (StAR), cytochrome P-450 cholesterol side-chain cleavage (P450scc), 3beta-hydroxy-steroid-dehydrogenase/Delta(5)-Delta(4) isomerase type I (3beta-HSD1), P-450 17alpha-hydroxylase/17,20-lyase (P450-17alpha), and cytochrome P-450 aromatase (P450arom) were determined on postnatal days (PND) 10-16. TCDD 1.0 mug/kg reduced body weights but did not affect relative testis weight or alter testicular and ovarian histology. Plasma estradiol levels in dams and female pups were reduced on PND 14 and 16. Progesterone levels remained unaltered, and FSH levels were increased in female pups. In males, testosterone levels were elevated on PND 10. Gonadal mRNA levels for StAR and steroidogenic enzymes increased during the postnatal growth. TCDD caused no changes in relatively low testicular mRNA levels. However, significant reductions in StAR and P450arom mRNA levels were seen in PND 14 ovaries, and P450arom activity was decreased in isolated ovarian follicles. We conclude that developing testis and male gonadotropin secretion are resistant to TCDD-induced toxicity. In female pups, reduced estradiol, ovarian P450arom expression and enzyme activity levels, and elevated FSH levels may have a role in the development of ovarian dysfunction reported in TCDD-exposed females.

Bone resorption by aryl hydrocarbon receptor-expressing osteoclasts is not disturbed by TCDD in short-term cultures

Polychlorinated dibenzo-p-dioxins (PCDDs) are highly toxic environmental contaminants, and 2,3,7,8-tetrachlorobenzo-p-dioxin (TCDD) is the most potent dioxin. Dioxins bind specifically to the cytosolic aryl hydrocarbon receptor (AHR), which is a ligand-activated transcription factor, and a majority of toxic effects of dioxins are mediated via AHR. We have recently demonstrated that TCDD disrupts bone modeling and decreases bone mechanical strength, and that partial resistance to these effects is related to an altered transactivation domain in AHR structure. In order to better understand the effects of dioxins on bone, we studied the presence and precise localization of AHR and also the number and activity of osteoclasts after TCDD treatments. Total RNA was extracted from mixed bone cell population cultures and expression of AHR mRNA was studied using RT-PCR. Bone cells expressed a considerable amount of AHR mRNA. To see which bone cells express AHR, immunostainings were performed in primary rat bone cell cultures, pure human osteoclast cultures and histological sections from AHR knockout and wild type bones. Immunostaining revealed a strong expression of AHR both in osteoclasts and osteoblasts with an especially prominent stain in bone resorbing osteoclasts. Effects of dioxin on primary bone cells were evaluated after TCDD treatment in the pit formation assay. The activity of osteoclasts was not affected measured as the percentage of active osteoclasts and the actual area of resorbed bone. These data indicate that even though TCDD-treated bones show decreased mechanical strength and size, this is not a direct result from increased osteoclastic bone resorption.

Dioxin-Like TEQ of women from the Seveso, Italy area by ID-HRGC/HRMS and CALUX

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) are widespread environmental contaminants that exist as complex mixtures and are frequently detected at part-per-trillion (ppt) levels in humans. Using isotope dilution high-resolution gas chromatography/ high-resolution mass spectrometry (HRGC/HRMS), we measure the PCDDs, PCDFs, and PCBs in serum of a population of 78 women residing in an area near Seveso, Italy where a TCDD explosion occurred in 1976 and where furniture is manufactured. The average total dioxin-like toxic equivalents (TEQ) of these women was 25.3 ppt, lipid-adjusted, comparable to other parts of Europe. TCDD levels, however, were higher among the few women who resided in the exposed area in 1976. We examined the possibility of using the CALUX (chemical-activated luciferase gene expression) bioassay to estimate total TEQ in a small volume of plasma from this population. A total of 32 archived plasma specimens were selected for CALUX bioassay, based on the distribution of Total TEQ by HRGC/HRMS. The CALUX bioassay was performed blind to HRGC/HRMS results with 2 ml plasma per replicate analysis. Of 32 samples, 10 were below detection limits in the CALUX bioassay. For the 32 samples, the CALUX-TEQ averaged 25.4 ppt, lipid-adjusted (range: 0-127.6) and was not significantly different from the HRGC/HRMS Total TEQ average of 31.2 ppt, lipid-adjusted (range: 12.7-88.3) (t = 0.88, P = 0.38), however, the two measures were not significantly correlated (R(s) = 0.04, P=0.82). More validation of the CALUX bioassay with larger sample volume is needed before application as an exposure measure in large-scale epidemiologic studies of health effects of dioxin-like compounds.

Transcriptional activation of the membrane-bound progesterone receptor (mPR) by dioxin, in endocrine-responsive tissues

We originally identified the membrane-bound progesterone receptor (mPR) using a screening for genes differentially expressed in liver of rats exposed to dioxin. Recent findings have suggested a role for the mPR in sperm cells, ovary, and brain; however, its mechanisms of action are largely unknown. In this study, we examined the expression pattern of the mPR in liver of rats exposed to dioxin and identified possible mechanisms of its regulation. We observed that mPR expression was induced by dioxin, but was also dependent on the hormonal responsiveness of the tissue. In particular, in male, but not female liver, dioxin induced the expression of the mPR. However, in control, untreated female liver the level of mPR transcript was higher than in control males. Moreover, in breast cancer cells MCF-7 dioxin induced mPR expression. Promoter studies using the luciferase assay indicated that a fragment of approximately 350 bp of the mPR promoter was able to induce luciferase activity in the presence of dioxin, suggesting that the presumptive XREs sites contained in this mPR promoter region are responsive to dioxin. Analysis of mPR protein level confirmed the results observed at the RNA level, both in rat liver and MCF-7 cells. Taken together, these observations suggest the existence of a novel cross-talk between steroid and aromatic hydrocarbon receptors (AhR), and underline the importance of the mPR as a mediator of physiologic effects of the sex hormones.

Expression of the arylhydrocarbon receptor in the peri-implantation period of the mouse uterus and the impact of dioxin on mouse implantation

The arylhydrocarbon receptor (AhR) is a nuclear transcription factor mediating toxic effects of chemicals such as dioxins. The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a member of polyhalogenated aromatic hydrocarbons family, exerts a wide-variety of toxic effects in a tissue- and species-specific manner including the reproduction process. Recently, AhR-mediated direct effects of TCDD on a cell-specific interaction with ovarian steroids have been shown. However, information regarding the effects of TCDD on the mouse implantation is limited. We therefore examined the expression and localization of AhR in the pregnant mouse uterus from 4 to 10 days of gestation (day 4 to day 10) using immunohistochemistry to investigate the effect of TCDD on uterine tissue during the peri-implantation period. Intense AhR expression was detected in the uterine vasculature throughout the periods examined. We also found that implanted blastocysts and their surrounding luminal epithelia and decidualized stroma expressed AhR on day 5. On days 6 and 7, persistent AhR expression was found in the transitional zone between the invading embryonic tissue and decidual tissue. On days 9 to 10, placental vasculature and spongiotrophoblasts displayed AhR immunoreactivity. The administration of TCDD on day 4 decreased the number of surviving implanted embryos on day 7 in a dose-dependent manner. This effect of TCDD was inhibited by the simultaneous administration of an AhR antagonist, alpha-naphthoflavone (alpha-NF). The spatio-temporal expression of AhR during the peri-implantation phase of the mouse uterus may indicate functional roles of this orphan receptor in fetomaternal interactions as well as substantiate the risk of exposure to chemicals such as dioxins during the reproductive period.