Bone toxicity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the retinoid system: A causality analysis anchored in osteoblast gene expression and mouse data

Dioxin exposures impact on bone quality and osteoblast differentiation, as well as retinoic acid metabolism and signaling. In this study we analyzed associations between increased circulating retinol concentrations and altered bone mineral density in a mouse model following oral exposure to 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD). Additionally, effects of TCDD on differentiation marker genes and genes involved with retinoic acid metabolism were analysed in an osteoblast cell model followed by benchmark dose-response analyses of the gene expression data. Study results show that the increased trabecular and decreased cortical bone mineral density in the mouse model following TCDD exposure are associated with increased circulating retinol concentrations. Also, TCDD disrupted the expression of genes involved in osteoblast differentiation and retinoic acid synthesis, degradation, and nuclear translocation in directions compatible with increasing cellular retinoic acid levels. Further evaluation of the obtained results in relation to previously published data by the use of mode-of-action and weight-of-evidence inspired analytical approaches strengthened the evidence that TCDD-induced bone and retinoid system changes are causally related and compatible with an endocrine disruption mode of action.

Endocrine, metabolic and apical effects of in utero and lactational exposure to non-dioxin-like 2,2',3,4,4',5,5'-heptachlorobiphenyl (PCB 180): A postnatal follow-up study in rats

PCB 180 is a persistent and abundant non-dioxin-like PCB (NDL-PCB). We determined the developmental toxicity profile of ultrapure PCB 180 in developing offspring following in utero and lactational exposure with the focus on endocrine, metabolic and retinoid system alterations. Pregnant rats were given total doses of 0, 10, 30, 100, 300 or 1000 mg PCB 180/kg bw on gestational days 7-10 by oral gavage, and the offspring were sampled on postnatal days (PND) 7, 35 and 84. Decreased serum testosterone and triiodothyronine concentrations on PND 84, altered liver retinoid levels, increased liver weights and induced 7-pentoxyresorufin O-dealkylase (PROD) activity were the sensitive effects used for margin of exposure (MoE) calculations. Liver weights were increased together with induction of the metabolizing enzymes cytochrome P450 (CYP) 2B1, CYP3A1, and CYP1A1. Less sensitive effects included decreased serum estradiol and increased luteinizing hormone levels in females, decreased prostate and seminal vesicle weight and increased pituitary weight in males, increased cortical bone area and thickness of tibial diaphysis in females and decreased cortical bone mineral density in males. Developmental toxicity profiles were partly different in male and female offspring, males being more sensitive to increased liver weight, PROD induction and decreased thyroxine concentrations. MoE assessment indicated that the 95^th percentile of current maternal PCB 180 concentrations do not exceed the estimated tolerable human lipid-based PCB 180 concentration. Although PCB 180 is much less potent than dioxin-like compounds, it shares several toxicological targets suggesting a potential for interactions.

Role of aryl hydrocarbon receptor (AHR) in overall retinoid metabolism: Response comparisons to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure between wild-type and AHR knockout mice

Young adult wild-type and aryl hydrocarbon receptor knockout (AHRKO) mice of both sexes and the C57BL/6J background were exposed to 10 weekly oral doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; total dose of 200 μg/kg bw) to further characterize the observed impacts of AHR as well as TCDD on the retinoid system. Unexposed AHRKO mice harboured heavier kidneys, lighter livers and lower serum all-trans retinoic acid (ATRA) and retinol (REOH) concentrations than wild-type mice. Results from the present study also point to a role for the murine AHR in the control of circulating REOH and ATRA concentrations. In wild-type mice, TCDD elevated liver weight and reduced thymus weight, and drastically reduced the hepatic concentrations of 9-cis-4-oxo-13,14-dihydro-retinoic acid (CORA) and retinyl palmitate (REPA). In female wild-type mice, TCDD increased the hepatic concentration of ATRA as well as the renal and circulating REOH concentrations. Renal CORA concentrations were substantially diminished in wild-type male mice exclusively following TCDD-exposure, with a similar tendency in serum. In contrast, TCDD did not affect any of these toxicity or retinoid system parameters in AHRKO mice. Finally, a distinct sex difference occurred in kidney concentrations of all the analysed retinoid forms. Together, these results strengthen the evidence of a mandatory role of AHR in TCDD-induced retinoid disruption, and suggest that the previously reported accumulation of several retinoid forms in the liver of AHRKO mice is a line-specific phenomenon. Our data further support participation of AHR in the control of liver and kidney development in mice.

Toxicity of colloidal silver products and their marketing claims in Finland

AIMS

The aim was to investigate the marketing practices, beliefs and health claims regarding the use of colloidal silver in Finland. Silver nanoparticles (AgNPs) are potentially toxic due to their small size and Ag+-release capabilities, and the use of colloidal silver products containing AgNPs can cause a wide variety of adverse effects such as argyria.

METHODS

Contents of three company websites selling colloidal silver were reviewed, and the claims used in the marketing of colloidal silver were compared to the scientific information about silver. In Facebook posts and discussion about colloidal silver were analyzed.

RESULTS

In Finland, the marketing of colloidal silver products on websites selling the products did not follow the regulations of authorities; several scientifically unfounded claims about the efficacy and medical use of colloidal silver were found. After the Finnish Broadcasting Company (Yle) documentary and an intervention by authorities, contents of the websites were changed, but still questionable information and misleading claims could be found. In the analyzed Facebook groups attitudes towards medical use of colloidal silver were uncritically positive, internal use was highly promoted and the restrictions of use were considered unjustified.

CONCLUSIONS

The use of quackery products such as colloidal silver can be dangerous, and their use and marketing should be controlled and restricted.

Estimated PCDD/F TEQ and total TEQ concentrations in the serum of 7-10 year old Finnish children

Polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and polychlorinated biphenyls (PCBs) are persistent organic pollutants that have detrimental health effects. As people are exposed to them mainly through the diet, EU has set maximum food dioxin and PCBs levels. EFSA CONTAM Panel made new risk assessment in 2018 that lowered the tolerable weekly intake (TWI) from 14 pg-TEQ/kg bw/week to 2 pg-TEQ/kg bw/week. Critical effect was decreased semen count at the age of 18-19 years if serum total TEQ at the age of 9 years exceeded the No Observed Adverse Effect Level (NOAEL) of 7 pg/g lipid. However, it is largely unknown to what extent NOAEL is exceed in European boys currently. We thus measured PCBs from small volume of serum in 184 Finnish children 7-10 years of age. To estimate the TEQ levels of children from measured PCB levels, we used our existing human milk PCDD/F and PCB concentrations to create a hierarchical Bayesian regression model that was used to estimate TEQs from measured PCBs. For quality control (QC), three pooled blood samples from 18 to 20 year old males were measured for PCDD/Fs and PCBs, and estimated for TEQs. In QC samples measured and estimated TEQs agreed within 84%-106%. In our estimate for 7-10 year old children, PCDD/F TEQ exceeded NOAEL only in 0.5% and total TEQ in 2.7% of subjects. Risk management following the decreased TWI proposed by the CONTAM Panel should be carefully considered if total TEQ in children is already largely below the NOAEL.

Transgenerational epigenetic and transcriptomic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure in rat

In rats, direct exposure to TCDD causes myriad toxicities. Exposed rats experience hepatotoxicity, wasting syndrome and immune suppression, amongst others. "Inherited exposure", as occurs in the F3 generation of directly exposed F0 animals, has also been shown to cause toxicity: both male and female F3 rats demonstrate an increased incidence of adult onset disease, females also display reproductive abnormalities and increased incidence of ovarian diseases while males show increased incidence of kidney disease and an altered sperm epigenome. Here, we explore the hepatic transcriptomic profile of male and female F3 Sprague-Dawley rats bred through the paternal germ line from F0 dams exposed to a single dose of TCDD (0, 30, 100, 300 or 1000 ng/kg body weight) by oral gavage. We hypothesize that RNA transcripts with altered abundance in livers of unexposed F3 progeny of treated F0 Sprague-Dawley rats may result from epigenetic modifications to the genome. We further survey patterns of differential methylation within male F3 rat testis. Female F3 rats demonstrated more TCDD-mediated hepatic transcriptomic changes than males, with differences primarily in the lowest dose group. In testis from male F3 rats, multiple olfactory receptors displayed patterns of differential methylation. Hypermethylation of Egfr and Mc5r among testes from TCDD lineage rats was observed, but without corresponding changes in hepatic mRNA abundance. Further studies examining these differences in other tissue types are warranted.

Novel Aspects of Toxicity Mechanisms of Dioxins and Related Compounds

Dioxins and related compounds are common environmental contaminants. Although their levels have gone down, they are still of concern, in particular regarding developmental toxicity. The adverse effects of these compounds are mediated by the aryl hydrocarbon receptor (AHR), whose canonical signaling pathway has been unveiled in fair detail. The alternative (non-genomic) pathways are much more obscure. AHR has also proven to be a master regulator of numerous physiological phenomena, which has led to the search of selective AHR modulators with low toxicity. Papers of this Special Issue address the developmental toxicity of dioxins and related compounds as well as selective modulators of AHR and both its canonical and alternative signaling pathways. In addition, new optical and stereoscopic methods for the detection of dioxins are presented. As a whole, this Special Issue provides an up-to-date view on a wide variety of aspects related to dioxin toxicity mechanisms from both original research articles and reviews.

Chained Risk Assessment for Life-Long Disease Burden of Early Exposures - Demonstration of Concept Using Prenatal Maternal Smoking

Traditional risk factors and environmental exposures only explain less than half of the disease burden. The developmental origin of the health and disease (DOHaD) concept proposes that prenatal and early postnatal exposures increase disease susceptibility throughout life. The aim of this work is to demonstrate the application of the DOHaD concept in a chained risk assessment and to provide an estimate of later in life burden of disease related to maternal smoking. We conducted three systematic literature searches for meta-analysis and reviewed the literature reporting meta-analyses of long-term health outcomes associated with maternal smoking and intermediate risk factors (preterm birth, low birth weight, childhood overweight). In the chained model the three selected risk factors explained an additional 2% (34,000 DALY) of the total non-communicable disease burden (1.4 million DALY) in 2017. Being overweight in childhood was the most important risk factor (28,000 DALY). Maternal smoking was directly associated with 170 DALY and indirectly via the three intermediate risk factors 1000 DALY (1200 DALY in total). The results confirm the potential to explain a previously unattributed part of the non-communicable diseases by the DOHAD concept. It is likely that relevant outcomes are missing, resulting in an underestimation of disease burden.

Effects of maternal smoking on body size and proportions at birth: a register-based cohort study of 1.4 million births

OBJECTIVES

The aim of our work was to analyse the effect of maternal smoking on body size and body proportions of newborns when the mother had smoked only during the first trimester, in comparison with continued smoking after the first trimester. Furthermore, we have evaluated how growth restriction associated with maternal smoking contributes to changes in body proportions.

DESIGN

Register-based cohort study SETTING: Maternal Exposure (MATEX) cohort identified from the Finnish Medical Birth Register.

PARTICIPANTS

Singleton births without congenital anomalies and missing data (1.38 million) from 1 January 1991 to 31 December 2016.

METHODS

Logistic regression was used to quantify the effect of maternal smoking, stratified by the maternal smoking status.

OUTCOME MEASURES

Body proportions indicated by low brain-to-body ratio (defined as <10th percentile); high ponderal index and high head-to-length ratio (defined as >90th percentile); small body size for gestational age at birth (defined as weight, length or head circumference <10th percentile) and preterm birth (<37 weeks) and low birth weight (2500 g).

RESULTS

Continued smoking after the first trimester was associated with high ponderal index (OR 1.26, 95% CI 1.23 to 1.28), low brain-to-body ratio (1.11, 1.07-1.15) and high head-to-length ratio (1.22, 1.19-1.26), corresponding with absolute risks of 22%, 10% and 19%, respectively). The effects were slightly lower when smoking had been quit during the first trimester. Similar effects were seen for the body size variables and low birth weight. Preterm birth was not associated with smoking only during first trimester.

CONCLUSIONS

Maternal smoking, independent of smoking duration during pregnancy, was associated with abnormal body proportions resulting from larger reduction of length and head circumference in comparison to weight. The effects of having quit smoking during the first trimester and having continued smoking after the first trimester were similar, suggesting the importance of early pregnancy as a sensitive exposure window.

Multigenerational and Transgenerational Effects of Dioxins

Dioxins are ubiquitous and persistent environmental contaminants whose background levels are still reason for concern. There is mounting evidence from both epidemiological and experimental studies that paternal exposure to the most potent congener of dioxins, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), can lower the male/female ratio of offspring. Moreover, in laboratory rodents and zebrafish, TCDD exposure of parent animals has been reported to result in reduced reproductive performance along with other adverse effects in subsequent generations, foremost through the paternal but also via the maternal germline. These impacts have been accompanied by epigenetic alterations in placenta and/or sperm cells, including changes in methylation patterns of imprinted genes. Here, we review recent key studies in this field with an attempt to provide an up-to-date picture of the present state of knowledge to the reader. These studies provide biological plausibility for the potential of dioxin exposure at a critical time-window to induce epigenetic alterations across multiple generations and the significance of aryl hydrocarbon receptor (AHR) in mediating these effects. Currently available data do not allow to accurately estimate the human health implications of these findings, although epidemiological evidence on lowered male/female ratio suggests that this effect may take place at realistic human exposure levels.

Smoking during pregnancy in Finland - Trends in the MATEX cohort

Aims: In Finland, smoking rates in the general population are decreasing due to increased awareness of the adverse effects and tightened tobacco legislation. However, previous studies have shown that smoking in pregnant Finnish women remained as high as in the general Finnish female population at around 15% in 2010. Our aim was to describe temporal and spatial trends in smoking behaviour, and determinants of changes in smoking behaviour between first and second pregnancy. Methods: Self-reported smoking from the Finnish Medical Birth Register covered the years 1991-2015 (N=1,435,009). The association of maternal age and socioeconomic status with smoking rate was analysed. Spatial trends were assessed at municipality level. Results: The overall smoking rate during early pregnancy remained fairly stable at around 15% from 1991 to 2015, but increased in teenage and young women below 25 years of age. The mean smoking rate (36%) was higher in these age groups than in older pregnant women (11%). Through the study period the smoking rate remained higher in blue collar workers compared with higher socioeconomic groups. Between the first and second child, on average only 4% of women started to smoke and 41% quitted. Smoking rates developed less favourably in Eastern Finland. Conclusions: The observed increase in smoking rate during pregnancy in teenage and young women is concerning. Pregnancy is a trigger point for smoking cessation in a big fraction of pregnant women. More studies are needed to explain the opposite trends of smoking rates in Northern and Western Finland compared with Eastern Finland.

Behavioural phenotypes in mice after prenatal and early postnatal exposure to intermediate frequency magnetic fields

Electromagnetic fields are ubiquitous in the environment. Human exposure to intermediate frequency (IF) fields is increasing due to applications like electronic article surveillance systems, wireless power transfer, and induction heating cooking hobs. However, there are limited data on possible health effects of exposure to IF magnetic fields (MF). In the present study, we set out to assess cognitive and behavioural effects of IF MF in mice exposed during prenatal and early postnatal periods. Pregnant female mice were exposed continuously to 7.5kHz MFs at 12 and 120μT, from mating until weaning of pups. Sham exposed pregnant mice were used as a control group. A behavioural teratology study was conducted on the male offspring at two months of age to detect possible effects on the developing nervous system. Body weight development did not differ between the exposure groups. The exposure did not alter spontaneous motor activity when exploring a novel cage or anxiety in novelty-suppressed feeding or marble burying tests. Improved performance in the Rotarod task was observed in the 12µT group, while the 120μT exposure group swam more slowly than the sham exposed group in the Morris swim navigation task. However, indices of learning and memory (path length and escape latency during task acquisition and search bias during the probe test) did not differ between the exposure groups. Furthermore, the passive avoidance task did not indicate any impairment of long-term memory over a 48h interval in the exposed groups. In a post-mortem histopathological analysis, there was no evidence for an effect of IF MF exposure on astroglial reactivity or hippocampal neurogenesis. The results suggest that the IF MF used did not have detrimental effects on spatial learning and memory or histological markers of tissue reaction. The two statistically significant findings that were observed (improved performance in the Rotarod task in the 12µT group and decreased swimming speed in the 120µT group) are likely to be chance findings, as they do not form an internally consistent, dose-dependent pattern indicative of specific developmental effects.

Behavioral testing of mice exposed to intermediate frequency magnetic fields indicates mild memory impairment

Human exposure to intermediate frequency magnetic fields (MF) is increasing due to applications like electronic article surveillance systems and induction heating cooking hobs. However, limited data is available on their possible health effects. The present study assessed behavioral and histopathological consequences of exposing mice to 7.5 kHz MF at 12 or 120 μT for 5 weeks. No effects were observed on body weight, spontaneous activity, motor coordination, level of anxiety or aggression. In the Morris swim task, mice in the 120 μT group showed less steep learning curve than the other groups, but did not differ from controls in their search bias in the probe test. The passive avoidance task indicated a clear impairment of memory over 48 h in the 120 μT group. No effects on astroglial activation or neurogenesis were observed in the hippocampus. The mRNA expression of brain-derived neurotrophic factor did not change but expression of the proinflammatory cytokine tumor necrosis factor alpha mRNA was significantly increased in the 120 μT group. These findings suggest that 7.5 kHz MF exposure may lead to mild learning and memory impairment, possibly through an inflammatory reaction in the hippocampus.

The MATEX cohort - a Finnish population register birth cohort to study health effects of prenatal exposures

Background

The prevalence of chronic diseases, such as immune, neurobehavioral, and metabolic disorders has increased in recent decades. According to the concept of Developmental Origin of Health and Disease (DOHaD), developmental factors associated with environmental exposures and maternal lifestyle choices may partly explain the observed increase. Register-based epidemiology is a prime tool to investigate the effects of prenatal exposures over the whole life course.

Our aim is to establish a Finnish register-based birth cohort, which can be used to investigate various (prenatal) exposures and their effects during the whole life course with first analyses focusing on maternal smoking and air pollution. In this paper we (i) review previous studies to identify knowledge gaps and overlaps available for cross-validation, (ii) lay out the MATEX study plan for register linkages, and (iii) analyse the study power of the baseline MATEX cohort for selected endpoints identified from the international literature.

Methods/design

The MATEX cohort is a fully register-based cohort identified from the Finnish Medical Birth Register (MBR) (1987–2015). Information from the MBR will be linked with other Finnish health registers and the population register to link the cohort with air quality data. Epidemiological analyses will be conducted for maternal smoking and air pollution and a range of health endpoints.

Discussion

The MATEX cohort consists of 1.75 million mother-child pairs with a maximum follow up time of 29 years. This makes the cohort big enough to reach sufficient statistical power to investigate rare outcomes, such as birth anomalies, childhood cancers, and sudden infant death syndrome (SIDS). The linkage between different registers allows for an extension of the scope of the cohort and a follow up from the prenatal period to decades later in life.

Electronic supplementary material

The online version of this article (10.1186/s12889-017-4881-8) contains supplementary material, which is available to authorized users.

Skeletal and dental effects on rats following in utero/lactational exposure to the non-dioxin-like polychlorinated biphenyl PCB 180

Polychlorinated biphenyls (PCBs) are a large class of persistent organic pollutants that are potentially harmful to human and wildlife health. Although a small number of dioxin-like (DL) PCBs are well characterized, the majority of PCBs have non-dioxin-like (NDL) modes of action and biological effects that are less understood. We conducted a dose-response study of the skeletal and dental effects of in utero/lactational exposure to 2,2',3,4,4',5,5'-heptachlorobiphenyl (PCB 180), a NDL PCB congener that is abundantly present in the environment and foods, including mother’s milk. In a sample of 35- and 84-day-old male and female offspring from pregnant rats exposed to different doses of PCB 180 (0, 10, 30, 100, 300, and 1000 mg/kg bw), we measured the three-dimensional (3D) coordinates of 27 landmarks on the craniofacial skeleton with a Microscribe G2X system, the buccolingual width of all molars with digital sliding calipers, and a variety of tibial parameters with peripheral quantitative computed tomography (pQCT) and a biomechanical testing apparatus. The landmark coordinates were analyzed for variation in size, shape, and fluctuating asymmetry (FA) using MorphoJ software, showing no effects on cranial size, on FA in females only (i.e., decreased asymmetry), and on shape in both sexes (i.e., decreased facial length and shift in the palatal suture). In the maxillary teeth, females in the highest dose group showed a significant decrease of 0.1 mm (p = 0.033) of the second molar only, whereas males in most dose groups showed average increases of 0.1 mm (p = 0.006–0.044) in all three molars. In the mandibular teeth, the only significant response to PCB 180 exposure was the average increase of 0.1 mm (p = 0.001–0.025) in the third molars of males only. Males also shower greater sensitivity in postcranial effects of increased tibial length and decreased cortical bone mass density, although only females showed significant effects on tibial bone area and thickness. These results demonstrate marked sex differences in effects of PCB 180, which can be attributed to differences in their underlying biological mechanisms of toxicity. Furthermore, although tooth and bone development are targets of both DL and NDL compounds, this study shows that there are marked differences in their mechanisms and effects.

Effects of intermediate frequency magnetic fields on male fertility indicators in mice

Human exposure to intermediate frequency (IF) fields is increasing due to new applications such as electronic article surveillance systems, wireless power transfer and induction heating cookers. However, limited data is available on effects of IF magnetic fields (MF) on male fertility function. This study was conducted to assess possible effects on fertility indicators from exposure to IF MF. Male C57BL/6J mice were exposed continuously for 5 weeks to 7.5kHz MF at 12 and 120μT. Sperm cells from cauda epididymis were analysed for motility, total sperm counts, and head abnormalities. Motile sperm cells were classified as progressive or non-progressive. Testicular spermatid heads were counted as well. The body weight development and reproductive tissue weights were not affected. No exposure-related differences were observed in sperm counts or sperm head abnormalities. Proportion of non-motile cells was significantly decreased in the 120µT group, and a corresponding increase was seen in the percentage of motile cells (significant in non-progressive motile cells). In conclusion, no adverse effects on fertility indicators were observed. Increased sperm motility is an interesting finding that needs to be confirmed in further studies.

TCDD-induced mitochondrial superoxide production does not lead to mitochondrial degeneration or genomic instability in human SH-SY5Y neuroblastoma cells

Several genotoxic and non-genotoxic agents have been reported to cause delayed genetic damage in the progeny of the exposed cells. Such induced genomic instability (IGI) may be a driving force in carcinogenesis, and it is thus highly important to understand the cellular events accompanying it. The aim of this study was to investigate whether 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) affects mitochondrial integrity and can consequently induce genomic instability. Mitochondrial integrity was evaluated by measuring mitochondrial superoxide production, mitochondrial membrane potential, and mitochondrial activity. Micronucleus formation was used to assess immediate genetic damage and IGI. The assays were performed either immediately, 8 or 15d after the exposure. Mitochondrial superoxide production was increased by TCDD immediately after the exposure. No consistent effects on mitochondrial integrity were observed at later time points, although slightly decreased mitochondrial membrane potential at 8d and increased mitochondrial superoxide potential production at 15 after exposure were observed in the TCDD-exposed cells. TCDD did not cause immediate genetic damage, and significant IGI was not observed. In conclusion, the present results suggest that immediate TCDD-induced increase in mitochondrial superoxide level does not lead to persistent loss of mitochondrial integrity or IGI in human SH-SY5Y neuroblastoma cells.

Synergistic proinflammatory interactions of microbial toxins and structural components characteristic to moisture-damaged buildings

Indoor exposure to microbes and their structural and metabolic compounds is notoriously complex. To study proinflammatory interactions between the multiple microbial agents, macrophages derived from human THP-1 monocytic cells were exposed to several concentrations of microbial toxins alone (emodin, enniatin B, physcion, sterigmatocystin, valinomycin) and in combination with microbial structural components (bacterial lipopolysaccharide [LPS] or fungal β-glucan). While the expression of proinflammatory cytokines TNFα and IL-1β to single toxins alone was modest, low-dose co-exposure with structural components increased the responses of emodin, enniatin B, and valinomycin synergistically, both at the mRNA and protein level, as measured by RT-qPCR and ELISA, respectively. Co-exposure of toxins and β-glucan resulted in consistent synergistically increased expression of several inflammation-related genes, while some of the responses with LPS were also inhibitory. Co-exposure of toxins with either β-glucan or LPS induced also mitochondrial damage and autophagocytosis. The results demonstrate that microbial toxins together with bacterial and fungal structural components characteristic to moisture-damaged buildings can have drastic synergistic proinflammatory interactions at low exposure levels.

Maternal Smoking and the Risk of Cancer in Early Life - A Meta-Analysis

BACKGROUND

In spite of the well-known harmful effects on the fetus, many women continue smoking during pregnancy. Smoking as an important source of toxic chemicals may contribute to the developmental origin of diseases.

OBJECTIVES

The aim of this work was to pursue the possible association between maternal smoking and cancer in early life. Specifically, we wanted to identify the associated early life cancer types, and to quantify the associations.

METHODS

In a systematic literature search 825 articles were identified in PubMed and Web of Science, and 55 more through the reference lists. Of these 62 fulfilled the criteria for inclusion in meta-analyses. Using Mantel-Haenszel or DerSimonian and Laird method, depending on heterogeneity of the studies, pooled estimates and 95% confidence intervals for eight cancer types were calculated.

RESULTS

Smoking during pregnancy was associated with an increased risk for for brain and central nervous system tumors (OR = 1.09; 95% CI = 1.02-1.17). Although the risk for lymphoma was also associated (OR = 1.21; 95% CI = 1.05-1.34), it did not hold up in subgroup analyses. Leukemia was not found to be associated with maternal smoking. Five other cancer types (bone, soft tissue, renal, hepatic, and germ cell cancer) were also examined, but the number of studies was too limited to exclude the possibility of maternal smoking as a risk factor for cancer in offspring.

CONCLUSIONS

According to our meta-analyses, maternal smoking is associated with nervous system cancers, but not with leukemia in early life. Confirming or rejecting associations of maternal smoking with lymphoma and the five other cancer types requires further studies.

Biomonitoring of selected persistent organic pollutants (PCDD/Fs, PCBs and PBDEs) in Finnish and Russian terrestrial and aquatic animal species

BACKGROUND

The Finnish and Russian animal species (semi-domesticated reindeer, Finnish wild moose, Baltic grey seal and Baltic herring) samples were biomonitored in terrestrial and aquatic environments for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs) and polybrominated diphenylethers (PBDEs).

RESULTS

Grey seal (Halichoerus grypus) was clearly the most contaminated species. The mean PBDE concentration in grey seal was 115 ng/g fat, and the highest WHO-PCDD/F-PCB-TEQ (toxic equivalent set by WHO) was 327 pg/g fat. In Finnish, reindeer WHO-PCDD/F-TEQ varied from 0.92 pg/g fat in muscle to 90.8 pg/g fat in liver. WHO-PCDD/F-TEQ in moose liver samples was in the range of 0.7-4.26 pg/g fat, and WHO-PCB-TEQ in the range of 0.42-3.34 pg/g fat. Overall moose had clearly lower PCDD/F and DL-PCB concentrations in their liver than reindeer.

CONCLUSIONS

Terrestrial animals generally had low POP concentrations, but in reindeer liver dioxin levels were quite high. All Finnish and Russian reindeer liver samples exceeded the EU maximum level [8] for PCDD/Fs (10 pg/g fat), which is currently set for bovine animals.

Persistent organic pollutants and non-alcoholic fatty liver disease in morbidly obese patients: a cohort study

BACKGROUND

In animal experiments persistent organic pollutants (POPs) cause hepatosteatosis. In epidemiological studies POPs have positive associations with serum markers of nonalcoholic fatty liver disease (NAFLD) and together with obesity synergistic association with insulin resistance. Because insulin resistance and obesity are critical in NAFLD pathogenesis, we investigated the association of serum pollutant levels with liver histology and alanine aminotransferase (ALT) in morbidly obese.

METHODS

Liver biopsies were from 161 participants of the Kuopio Obesity Surgery Study (KOBS) who underwent bariatric surgery 2005-2011. Liver histology was categorized as normal, steatosis and non-alcoholic steatohepatitis (NASH). Liver phenotype at baseline and ALT at baseline and 12 months post-surgery were correlated to serum POP concentrations at respective time points. As lipophilic POPs concentrate to smaller fat volume during weight loss, serum levels before and 12 months after bariatric surgery were compared.

RESULTS

Baseline serum concentration of PCB-118, β-HCH and several PFAAs had an inverse association with lobular inflammation possibly due to changes in bile acid metabolism. ALT had negative associations with many POPs at baseline that turned positive at 12 months after major clinical improvements. There was an interaction between some POPs and sex at 12 months, and in stratified data positive associations were observed mainly in females but not in males.

CONCLUSIONS

We found a negative association between serum concentrations of PCB-118, β-HCH and several PFAAs with lobular inflammation at baseline. Positive POPs-ATL associations at 12 months among women suggest that increased POP concentrations may decrease the degree of liver recovery.

Temporal trends in the levels of polychlorinated dioxins, -furans, -biphenyls and polybrominated diethyl ethers in bank voles in Northern Finland

Dioxin-like chemicals and brominated flame retardants are ubiquitous in the environment, despite the introduction of international prohibitions and restrictions. These chemicals do not remain in the vicinity of their source, instead they can be transported over long distances, in fact even to pristine areas in the northern latitudes. However, there have been rather few time series experiments monitoring the trends in the levels of chlorinated and brominated forms of these chemicals in the environment. In this study, the concentrations of polychlorinated dibenzo-p-dioxins and -furans (PCDDs/Fs), polychlorinated biphenyls (PCBs) and polybrominated diethyl ethers (PBDEs) were measured in the liver and muscle of bank voles (Myodes glareolus) caught in a remote area in Finnish Lapland during 1986-2007. Five time points were selected: years 1986, 1992, 1998, 2003 and 2007. The levels of PCDDs/Fs and PCBs declined from 1986 until 2003 in both females and males, but tended to increase again in 2007. The peak levels of the most abundant PBDE congeners (PBDEs 47, 99, 100 and 153) were measured in 1998 and 2003. These results reveal that the levels of dioxin-like chemicals remain high also in rural areas in Lapland, whereas the concentrations of brominated flame retardants decreased and follow the current restriction prohibitions.

Hydroxyl metabolite of PCB 180 induces DNA damage signaling and enhances the DNA damaging effect of benzo[a]pyrene

Non-dioxin-like (NDL) polychlorinated biphenyls (PCBs) and their hydroxyl metabolites (OH-PCBs) are ubiquitous environmental contaminants in human tissues and blood. The toxicological impact of these metabolites is poorly understood. In this study rats were exposed to ultrapure PCB180 (10-1000mg/kgbw) for 28days and induction of genotoxic stress in liver was investigated. DNA damage signaling proteins (pChk1Ser317 and γH2AXSer319) were increased dose dependently in female rats. This increase was paralleled by increasing levels of the metabolite 3'-OH-PCB180. pChk1 was the most sensitive marker. In in vitro studies HepG2 cells were exposed to 1μM of PCB180 and 3'-OH-PCB180 or the positive control benzo[a]pyrene (BaP, 5μM). 3'-OH-PCB180, but not PCB180, induced CYP1A1 mRNA and γH2AX. CYP1A1 mRNA induction was seen at 1h, and γH2AX at 3h. The anti-oxidant N-Acetyl-l-Cysteine (NAC) completely prevented, and 17β-estradiol amplified the γH2AX induction by 3'-OH-PCB180. As 3'-OH-PCB180 induced CYP1A1, a major BaP-metabolizing and activating enzyme, interactions between 3'-OH-PCB180 and BaP was also studied. The metabolite amplified the DNA damage signaling response to BaP. In conclusion, metabolism of PCB180 to its hydroxyl metabolite and the subsequent induction of CYP1A1 seem important for DNA damage induced by PCB180 in vivo. Amplification of the response with estradiol may explain why DNA damage was only seen in female rats.

Craniofacial form is altered by chronic adult exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in Han/Wistar and Long-Evans rats with different aryl hydrocarbon receptor (AhR) structures

Mammalian bone has shown a variety of responses to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure in experimental and wildlife studies. Although many responses have been well characterized in the postcranial skeleton, dioxin-induced effects on the cranium are largely unknown. In this study, we investigated the effects of chronic adult exposure to TCDD on cranial size and shape in dioxin-resistant Han/Wistar (H/W) and dioxin-sensitive Long–Evans (L–E) rat strains. Three-dimensional landmark configurations for the face, vault, and base of the cranium were recorded and analyzed using geometric morphometrics (GM) and dose–response modeling. The strongest effects were shown by L–E and H/W rats with daily exposures of 100 and 1000 ng TCDD/kg bw/day, respectively, resulting in significant reductions in centroid size (CS) in all three cranial modules for both strains except for the vault in H/W rats. Consistent with previous evidence of intraspecific variation in TCDD resistance, the benchmark doses (CEDs) for cranial size reduction in L–E rats were roughly 10-fold lower than those for H/W rats. For both strains, the face showed the greatest size reduction from the highest doses of TCDD (i.e., 3.6 and 6.3% decreases in H/W and L–E rats, respectively), most likely related to dose-dependent reductions in limb bone size and body weight gain. However, intrinsic morphological differences between strains were also observed: although the control groups of H/W and L–E rats had vaults and bases of comparable size, the face was 6.4% larger in L–E rats. Thus, although H/W rats possess an altered aryl hydrocarbon receptor (AhR) that appears to mediate and provides some resistance to TCDD exposure, their smaller reductions in facial size may also relate to strain-specific patterns of cranial development and growth. Future research will be aimed at understanding how ontogenetic factors may modulate toxic effects of prenatal and lactational exposure on the mammalian skeleton.

Role of microRNAs and DNA Methyltransferases in Transmitting Induced Genomic Instability between Cell Generations

There is limited understanding of how radiation or chemicals induce genomic instability, and how the instability is epigenetically transmitted to the progeny of exposed cells or organisms. Here, we measured the expression of microRNAs (miRNAs) and DNA methyltransferases (DNMTs) in murine embryonal fibroblasts exposed to ionizing radiation or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which were previously shown to induce genomic instability in this cell line. Cadmium was used as a reference agent that does not induce genomic instability in our experimental model. Measurements at 8 and 15 days after exposure did not identify any such persistent changes that could be considered as signals transmitting genomic instability to the progeny of exposed cells. However, measurements at 2 days after exposure revealed findings that may reflect initial stages of genomic instability. Changes that were common to TCDD and two doses of radiation (but not to cadmium) included five candidate signature miRNAs and general up-regulation of miRNA expression. Expression of DNMT3a, DNMT3b, and DNMT2 was suppressed by cadmium but not by TCDD or radiation, consistently with the hypothesis that sufficient expression of DNMTs is necessary in the initial phase of induced genomic instability.

Toxicological profile of ultrapure 2,2',3,4,4',5,5'-heptachlorbiphenyl (PCB 180) in adult rats

PCB 180 is a persistent non-dioxin-like polychlorinated biphenyl (NDL-PCB) abundantly present in food and the environment. Risk characterization of NDL-PCBs is confounded by the presence of highly potent dioxin-like impurities. We used ultrapure PCB 180 to characterize its toxicity profile in a 28-day repeat dose toxicity study in young adult rats extended to cover endocrine and behavioral effects. Using a loading dose/maintenance dose regimen, groups of 5 males and 5 females were given total doses of 0, 3, 10, 30, 100, 300, 1000 or 1700 mg PCB 180/kg body weight by gavage. Dose-responses were analyzed using benchmark dose modeling based on dose and adipose tissue PCB concentrations. Body weight gain was retarded at 1700 mg/kg during loading dosing, but recovered thereafter. The most sensitive endpoint of toxicity that was used for risk characterization was altered open field behavior in females; i.e. increased activity and distance moved in the inner zone of an open field suggesting altered emotional responses to unfamiliar environment and impaired behavioral inhibition. Other dose-dependent changes included decreased serum thyroid hormones with associated histopathological changes, altered tissue retinoid levels, decreased hematocrit and hemoglobin, decreased follicle stimulating hormone and luteinizing hormone levels in males and increased expression of DNA damage markers in liver of females. Dose-dependent hypertrophy of zona fasciculata cells was observed in adrenals suggesting activation of cortex. There were gender differences in sensitivity and toxicity profiles were partly different in males and females. PCB 180 adipose tissue concentrations were clearly above the general human population levels, but close to the levels in highly exposed populations. The results demonstrate a distinct toxicological profile of PCB 180 with lack of dioxin-like properties required for assignment of WHO toxic equivalency factor. However, PCB 180 shares several toxicological targets with dioxin-like compounds emphasizing the potential for interactions.

Dose- and time-dependent changes of micronucleus frequency and gene expression in the progeny of irradiated cells: two components in radiation-induced genomic instability?

Murine embryonic C3H/10T½ fibroblasts were exposed to X-rays at doses of 0.2, 0.5, 1, 2 or 5 Gy. To follow the development of radiation-induced genomic instability (RIGI), the frequency of micronuclei was measured with flow cytometry at 2 days after exposure and in the progeny of the irradiated cells at 8 and 15 days after exposure. Gene expression was measured at the same points in time by PCR arrays profiling the expression of 84 cancer-relevant genes. The micronucleus results showed a gradual decrease in the slope of the dose-response curve between days 2 and 15. The data were consistent with a model assuming two components in RIGI. The first component is characterized by dose-dependent increase in micronuclei. It may persist more than ten cell generations depending on dose, but eventually disappears. The second component is more persistent and independent of dose above a threshold higher than 0.2 Gy. Gene expression analysis 2 days after irradiation at 5 Gy showed consistent changes in genes that typically respond to DNA damage. However, the consistency of changes decreased with time, suggesting that non-specificity and increased heterogeneity of gene expression are characteristic to the second, more persistent component of RIGI.

Gestational and lactational exposure to the polychlorinated biphenyl mixture Aroclor 1254 modulates retinoid homeostasis in rat offspring

Polychlorinated biphenyls (PCBs) induce a broad spectrum of biochemical and toxic effects in mammals including alterations of the vital retinoid (vitamin A) system. The aim of this study was to characterize alterations of tissue retinoid levels in rat offspring and their dams following gestational and lactational exposure to the PCB mixture Aroclor 1254 (A1254) and to assess the interrelationship of these changes with other established sensitive biochemical and toxicological endpoints. Sprague-Dawley rat dams were exposed orally to 0 or 15 mg/kg body weight/day of A1254 from gestational day 1 to postnatal day (PND) 23. Livers, kidneys and serum were collected from the offspring on PNDs 35, 77 and 350. Tissue and serum retinoid levels, hepatic cytochrome P450 (CYP) enzymes and serum thyroid hormones were analyzed. A multivariate regression between A1254 treatment, hepatic retinoid levels, hepatic CYP enzymes activities, thyroid hormone levels and body/liver weights was performed using an orthogonal partial least-squares (PLS) analysis. The contribution of dioxin-like (DL) components of A1254 to the observed effects was also estimated using the toxic equivalency (TEQ) concept. In both male and female offspring short-term alterations in tissue retinoid levels occurred at PND35, i.e. decreased levels of hepatic retinol and retinoic acid (RA) metabolite 9-cis-4-oxo-13,14-dihydro-RA with concurrent increases in hepatic and renal all-trans-RA levels. Long-term changes consisted of decreased hepatic retinyl palmitate and increased renal retinol levels that were apparent until PND350. Retinoid system alterations were associated with altered CYP enzyme activities and serum thyroid hormone levels as well as body and liver weights in both offspring and dams. The estimated DL activity was within an order of magnitude of the theoretical TEQ for different endpoints, indicating significant involvement of DL congeners in the observed effects. This study shows that tissue retinoid levels are affected both short- and long-term by developmental A1254 exposure and are associated with alterations of other established endpoints of toxicological concern.

Persistent organic pollutant levels in semi-domesticated reindeer (Rangifer tarandus tarandus L.), feed, lichen, blood, milk, placenta, foetus and calf

A study concerning persistent organic pollutants in Finnish semi-domesticated reindeer was conducted in northern Finland. The aim of this study was to explore POP presence in different tissues of reindeer. In addition, it was studied how POPs are transported from food concentrates and lichen to reindeer hind tissues and further to the placenta, foetus, milk and calf. Concentrations of 17 polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs), 37 polychlorinated biphenyls (PCBs) (including 12 dioxin-like PCBs), and 15 polybrominated diphenyl ethers (PBDEs) were analysed. In most of the reindeer muscle tissue samples PCBs were clearly dominating compounds (on average 58% of the total WHO-TEQ). The total WHO-TEQ was higher in the muscle tissue of reindeer calves than in their corresponding hinds (on average 1.7 pg/g fat vs. 1.1 pg/g fat, respectively). The total WHO-TEQ concentrations were higher in the muscle and liver tissues of reindeer hinds than in their blood or placentas. The foetuses had clearly lower WHO-TEQ concentrations than their corresponding hinds. The contribution of WHO-PCDD/F-TEQ to the total WHO-TEQ was somewhat higher in the liver than in the muscle tissue. The reindeer hind-calf pair, which had gone through the lichen diet, had on average higher WHO-PCDD/F- and PCB-TEQ concentrations in their tissues than the hind-calf-pair that had gone through the reindeer food concentrate diet. WHO-PCB-TEQs in the reindeer foetuses were equal with the concentrations of placentas. The reindeer foetuses contained generally more PBDEs than their corresponding hinds and placentas. This may indicate effective transport of these compounds through the placenta of reindeer.

Dopamine-dependent behavior in adult rats after perinatal exposure to purity-controlled polychlorinated biphenyl congeners (PCB52 and PCB180)

Since knowledge about toxic effects of non-dioxinlike (NDL) PCBs is fragmentary, regulatory panels have concluded that risk assessment of these congeners is hampered or impossible. As the dopaminergic system is one of the main targets in PCB-related neurotoxic effects after developmental exposure, we selected catalepsy induced by the dopamine receptor blocker haloperidol to characterize effects of the NDL congeners PCB52 and PCB180 in adult offspring from exposed rat dams. Rat dams were treated with PCB congeners by gavage using six dose levels (total doses: PCB52 - 0, 30, 100, 300, 1000 or 3000 mg/kg body wt.; PCB180 - 0, 10, 30, 100, 300, or 1000 mg/kg body wt.) to allow benchmark dose analysis of the results. Testing of adult offspring (starting at 180 days of age) for catalepsy induced by injection with haloperidol revealed slightly prolonged latencies to movement onset in female offspring exposed to PCB52. Exposure to PCB180 resulted in more pronounced effects, with generally reduced latencies in male offspring. These results indicate reduced dopaminergic activity after PCB52 exposure, whereas the outcome for PCB180 may be related to increased extracellular dopamine as reported in the literature.Benchmark dose analyses revealed that both PCB congeners exerted effects mainly at moderate exposure levels. Together, these results underline the importance of effects on the dopaminergic system as indicated by studies in human females after occupational PCB exposure.

In utero and lactational exposure to a mixture of environmental contaminants detected in Canadian Arctic human populations alters retinoid levels in rat offspring with low margins of exposure

Arctic inhabitants are highly exposed to persistent organic pollutants (POP), which may produce adverse health effects. This study characterized alterations in tissue retinoid (vitamin A) levels in rat offspring and their dams following in utero and lactational exposure to the Northern Contaminant Mixture (NCM), a mixture of 27 contaminants including polychlorinated biphenyls (PCB), organochlorine (OC) pesticides, and methylmercury (MeHg), present in maternal blood of the Canadian Arctic Inuit population. Further, effect levels for retinoid system alterations and other endpoints were compared to the Arctic Inuit population exposure and their interrelationships were assessed. Sprague-Dawley rat dams were dosed with NCM from gestational day 1 to postnatal day (PND) 23. Livers, kidneys and serum were obtained from offspring on PND35, PND77, and PND350 and their dams on PND30 for analysis of tissue retinoid levels, hepatic cytochrome P-450 (CYP) enzymes, and serum thyroid hormones. Benchmark doses were established for all endpoints, and a partial least-squares regression analysis was performed for NCM treatment, hepatic retinoid levels, CYP enzyme induction, and thyroid hormone levels, as well as body and liver weights. Hepatic retinoid levels were sensitive endpoints, with the most pronounced effects at PND35 though still apparent at PND350. The effects on tissue retinoid levels and changes in CYP enzyme activities, body and liver weights, and thyroid hormone levels were associated and likely driven by dioxin-like compounds in the mixture. Low margins of exposure were observed for all retinoid endpoints at PND35. These findings are important for health risk assessment of Canadian Arctic populations and further support the use of retinoid system analyses in testing of endocrine-system-modulating compounds.

New insights to the role of aryl hydrocarbon receptor in bone phenotype and in dioxin-induced modulation of bone microarchitecture and material properties

Bone is a target for high affinity aryl hydrocarbon receptor (AHR) ligands, such as dioxins. Although bone morphology, mineral density and strength are sensitive endpoints of dioxin toxicity, less is known about effects on bone microarchitecture and material properties. This study characterizes TCDD-induced modulations of bone tissue, and the role of AHR in dioxin-induced bone toxicity and for normal bone phenotype. Six AHR-knockout (Ahr(-/-)) and wild-type (Ahr(+/+)) mice of both genders were exposed to TCDD weekly for 10 weeks, at a total dose of 200μg/kgbw. Bones were examined with micro-computed tomography, nanoindentation and biomechanical testing. Serum levels of bone remodeling markers were analyzed, and the expression of genes related to osteogenic differentiation was profiled using PCR array. In Ahr(+/+) mice, TCDD-exposure resulted in harder bone matrix, thinner and more porous cortical bone, and a more compact trabecular bone compartment. Bone remodeling markers and altered expression of a number of osteogenesis related genes indicated imbalanced bone remodeling. Untreated Ahr(-/-) mice displayed a slightly modified bone phenotype as compared with untreated Ahr(+/+) mice, while TCDD exposure caused only a few changes in bones of Ahr(-/-) mice. Part of the effects of both TCDD-exposure and AHR-deficiency were gender dependent. In conclusion, exposure of adult mice to TCDD resulted in harder bone matrix, thinner cortical bone, mechanically weaker bones and most notably, increased trabecular bone volume fraction in Ahr(+/+) mice. AHR is involved in bone development of a normal bone phenotype, and is crucial for manifestation of TCDD-induced bone alterations.

Synergistic effects of tributyltin and 2,3,7,8-tetrachlorodibenzo-p-dioxin on differentiating osteoblasts and osteoclasts

The purpose of this study was to examine the effects of the persistent and accumulative environmental pollutants tributyltin (TBT) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) individually and in combination on differentiating bone cells. TBT and TCDD are chemically distinct compounds with different mechanisms of toxicity, but they typically have the same sources of exposure and both have been shown to affect bone development at low exposure levels. Bone marrow stem cells were isolated from femurs and tibias of C57BL/6J mice, differentiated in culture into osteoblasts or osteoclasts and exposed to 0.1-10nM TBT, 0.01-1nM TCDD or 10nM TBT+ 1nM TCDD. In osteoblasts, the combined exposure to TBT and TCDD significantly decreased the mRNA expression of alkaline phosphatase and osteocalcin more than TBT or TCDD alone. PCR array showed different gene expression profiles for TBT and TCDD individually, and the combination evoked several additional alterations in gene expression. Expression of aryl hydrocarbon receptor repressor (AHRR) was increased by TCDD as expected, but simultaneous exposure to TBT prevented the increase thus potentially strengthening AHR-mediated effects of TCDD. The number of osteoclasts was reduced by TCDD alone and in combination with TBT, but TBT alone had no effect. However, the total area of resorbed bone was remarkably lower after combined exposure than after TBT or TCDD alone. In conclusion, very low concentrations of TBT and TCDD have synergistic deleterious effects on bone formation and additive effects on bone resorption.

Dioxin induces genomic instability in mouse embryonic fibroblasts

Ionizing radiation and certain other exposures have been shown to induce genomic instability (GI), i.e., delayed genetic damage observed many cell generations later in the progeny of the exposed cells. The aim of this study was to investigate induction of GI by a nongenotoxic carcinogen, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Mouse embryonic fibroblasts (C3H10T1/2) were exposed to 1, 10 or 100 nM TCDD for 2 days. Micronuclei (MN) and expression of selected cancer-related genes were assayed both immediately and at a delayed point in time (8 days). For comparison, similar experiments were done with cadmium, a known genotoxic agent. TCDD treatment induced an elevated frequency of MN at 8 days, but not directly after the exposure. TCDD-induced alterations in gene expression were also mostly delayed, with more changes observed at 8 days than at 2 days. Exposure to cadmium produced an opposite pattern of responses, with pronounced effects immediately after exposure but no increase in MN and few gene expression changes at 8 days. Although all responses to TCDD alone were delayed, menadione-induced DNA damage (measured by the Comet assay), was found to be increased directly after a 2-day TCDD exposure, indicating that the stability of the genome was compromised already at this time point. The results suggested a flat dose-response relationship consistent with dose-response data reported for radiation-induced GI. These findings indicate that TCDD, although not directly genotoxic, induces GI, which is associated with impaired DNA damage response.

Significant interspecies differences in induction profiles of hepatic CYP enzymes by TCDD in bank and field voles

The gene expression and induction of cytochrome P450 (CYP)-enzymes following 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) peroral administration was studied in the livers of two wild vole species--the bank vole (Myodes glareolus) and the field vole (Microtus agrestis). The dioxin-sensitive C57BL/6 mouse was used as a reference. Doses of 0.05, 0.5, 5.0, and 50 µg/kg were applied to ascertain a dose-response relationship, and the dose of 50 µg/kg was applied to the study time course for up to 96 h. The cytochrome P450 1A1 (CYP1A1) mRNA expression showed an expected dose-dependent increase equally in both vole species. Bank voles expressed notably higher CYP2A mRNA levels as compared with field voles. Both species exhibited dose-dependent increases in putative CYP1A-, CYP2B-, and CYP2A-associated activities as measured by fluorometric assays for ethoxyresorufin-O-deethylase (EROD), penthoxyresorufin-O-depenthylase (PROD), and 7-ethoxycoumarin-O-deethylase (ECOD), respectively. Putative CYP2A-associated coumarin-7-hydroxylase (COH) activity showed a slight increase at the two highest doses of TCDD in field voles but not in bank voles, and their basal COH activity was only one-fourth or less of that in field voles. Overall, however, bank voles tended to exhibit higher CYP-associated enzyme activities measured at the two largest doses of TCDD than field voles. A western blot analysis of aryl hydrocarbon receptor (AhR) revealed that the two vole species had differential band patterns, suggesting dissimilar structures for their AhRs.

Associations between congenital cryptorchidism in newborn boys and levels of dioxins and PCBs in placenta

In animal studies, exposure to dioxins has been associated with disrupted development of the male reproductive system, including testicular maldescent. Some polychlorinated biphenyls (PCBs) have also dioxin-like effects. In addition, one previous case-control study has reported an association between congenital cryptorchidism and colostrum PCB levels. We performed a case-control study to evaluate whether congenital cryptorchidism in boys was associated with increased levels of dioxins or PCBs in placenta reflecting foetal exposure. In addition, associations between placenta levels of these chemicals and reproductive hormone levels in boys at 3 months were studied. Placentas were collected in a Danish-Finnish joint prospective cohort study on cryptorchidism (1997-2001). The boys were examined for cryptorchidism at birth and at 3 months. Altogether, 280 placentas [112 Finnish (56 cases, 56 controls) and 168 Danish (39 cases, 129 controls)] were analysed for 17 toxic polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and 37 PCBs (including 12 dioxin-like PCBs). Infant serum samples taken at 3 months were analysed for reproductive hormones. No significant differences between cases and controls were observed in either country in dioxin WHO-TEq levels (median 9.78 vs. 8.47 pg/g fat, respectively, in Finland, and 11.75 vs. 10.88 pg/g fat in Denmark) or PCB WHO-TEq levels (median 2.12 vs. 2.15 pg/g fat in Finland, 2.34 vs. 2.10 pg/g fat in Denmark) or total-TEq levels (median 11.66 vs. 10.58 pg/g fat in Finland, 13.94 vs. 13.00 pg/g fat in Denmark). Placenta WHO-TEq levels of dioxins were not associated with infant reproductive hormone levels at 3 months. In Finland, PCB WHO-TEq levels in placenta associated positively with infant LH levels. WHO-TEq levels of dioxins and PCBs and total-TEq levels were higher in Danish than Finnish samples. In conclusion, no association between placenta levels of dioxins or PCBs and congenital cryptorchidism was found. Significant country differences in chemical levels were observed.

Retinoic acid drives aryl hydrocarbon receptor expression and is instrumental to dioxin-induced toxicity during palate development

BACKGROUND

Palate development depends on complex events and is very sensitive to disruption. Accordingly, clefts are the most common congenital malformations worldwide, and a connection is proposed with fetal exposure to toxic factors or environmental contaminants, such as dioxins. There is increasing evidence that dioxin interferes with all-trans-retinoic acid (atRA), a hormone-like signal derived from vitamin A, which plays an essential role during embryonic development. Although similarities have been described between dioxin-induced toxicity and the outcome of altered atRA signaling during palate development, their relationship needs to be clarified.

OBJECTIVES

We used a genetic approach to understand the interaction between atRA and dioxin and to identify the cell type targeted by dioxin toxicity during secondary palate formation in mice.

METHODS

We analyzed the phenotype of mouse embryos harboring an atRA-sensitive reporter transgene or bearing null mutations for atRA-synthesizing enzymes (RALDH) or atRA receptors (RAR) and maternally exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at gestation day 10.5.

RESULTS

We found that an intact atRA signal was required to enable TCDD to induce cleft palate. This mandatory atRA signal was generated through the activity of RALDH3 in the nasal epithelium and was transduced by RARγ (RARG) in the nasal mesenchyme, where it notably controlled aryl hydrocarbon receptor (Ahr) transcript levels. TCDD also did not alter the developmental pattern of atRA signaling during palate formation.

CONCLUSIONS

TCDD-induced alteration of secondary palate development in the mouse appears to depend on atRA signaling, which controls AHR expression. This mechanism is likely conserved throughout vertebrate evolution and may therefore be relevant in humans.