The Effect of Perinatal TCDD Exposure on Caries Susceptibility in Rats

Assessment of Selected Morphological, Physical and Chemical Parameters of the Teeth of the Offspring of Female Rats Exposed to 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), Taking into Account the Protective Role of Selected Antioxidants-Preliminary Study

The studies conducted so far indicate a negative effect of dioxins on the structure of the alveolar bone and teeth, especially in the developmental period in rats. The research aimed to analyze the indirect effect of dioxins contained in the body of female rats on the structure of the dental organ in their offspring in the neonatal period and to determine the possibility of reducing potential dioxin disorders of the structure of hard tissues in the offspring of intoxicated mothers by simultaneous administration of vitamin E or acetylsalicylic acid (ASA). Another goal of the research was to determine the level of magnesium, calcium and phosphorus contained in bone tissue as indicators of the mineralization process of hard tissues in rats, in the case of using 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and acetylsalicylic acid or α-tocopherol. The experiment was carried out on eight female rats of the Buffalo strain divided into four groups. From the offspring of eight females, the mandibles were removed from the mandibular joints, and then, after the removal of soft tissues, they were prepared for individual tests. Selected morphological, chemical and physical parameters of the teeth of the offspring of female rats from the experimental groups were analyzed. The analysis showed the effect of vitamin E and ASA on the content of Mg, Ca and P. In combination with TCDD, vitamin E and ASA, they positively inhibit the inflammatory process, preventing the leaching of Ca and Mg from the bones. ASA counteracted this phenomenon much more effectively than vitamin E. Detailed analysis of the tooth morphology showed that the molars' crowns exhibit shape disturbances under the influence of TCDD. Individual nodules in teeth T1, T2, T3 did not fuse, and the roots showed signs of hypertrophy. The study confirmed the negative effect of TCDD on tooth development. Teeth arising early in development are the most sensitive to the disorders, while the later ones are less exposed to the toxic effects of TCDD transmitted by the mother.

Effects of Acute 2,3,7,8-Tetrachlorodibenzo-p-Dioxin Exposure on the Circulating and Cecal Metabolome Profile

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a polyhalogenated planar hydrocarbon belonging to a group of highly toxic and persistent environmental contaminants known as "dioxins". TCDD is an animal teratogen and carcinogen that is well characterized for causing immunosuppression through activation of aryl hydrocarbon receptor (AHR). In this study, we investigated the effect of exposure of mice to an acute dose of TCDD on the metabolic profile within the serum and cecal contents to better define the effects of TCDD on host physiology. Our findings demonstrated that within the circulating metabolome following acute TCDD exposure, there was significant dysregulation in the metabolism of bioactive lipids, amino acids, and carbohydrates when compared with the vehicle (VEH)-treated mice. These widespread changes in metabolite abundance were identified to regulate host immunity via modulating nuclear factor-kappa B (NF-κB) and extracellular signal-regulated protein kinase (ERK1/2) activity and work as biomarkers for a variety of organ injuries and dysfunctions that follow TCDD exposure. Within the cecal content of mice exposed to TCDD, we were able to detect changes in inflammatory markers that regulate NF-κB, markers of injury-related inflammation, and changes in lysine degradation, nicotinamide metabolism, and butanoate metabolism, which collectively suggested an immediate suppression of broad-scale metabolic processes in the gastrointestinal tract. Collectively, these results demonstrate that acute TCDD exposure results in immediate irregularities in the circulating and intestinal metabolome, which likely contribute to TCDD toxicity and can be used as biomarkers for the early detection of individual exposure.

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

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

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.

Dioxin risk assessment: mechanisms of action and possible toxicity in human health

Dioxin-like compounds (DLCs) have been classified by the World Health Organization (WHO) as one of the most persistent toxic chemical substances in the environment, and they are associated with several occupational activities and industrial accidents around the world. Since the end of the 1970s, these toxic chemicals have been banned because of their human toxicity potential, long half-life, wide dispersion, and they bioaccumulate in the food web. This review serves as a primer for environmental health professionals to provide guidance on short-term risk assessment of dioxin and to identify key findings for health and exposure assessment based on policies of different agencies. It also presents possible health effects of dioxins, mechanisms of action, toxic equivalency factors (TEFs), and dose-response characterization. Key studies related to toxicity values of dioxin-like compounds and their possible human health risk were identified through PubMed and supplemented with relevant studies characterized by reviewing the reference lists in the review articles and primary literature. Existing data decreases the scope of analyses and models in relevant studies to a manageable size by focusing on the set of important studies related to the perspective of developing toxicity values of DLCs.

Integrated ecological risk assessment of dioxin compounds

Current ecological risk assessment (ERA) schemes focus mainly on bioaccumulation and toxicity of pollutants in individual organisms. Ecological models are tools mainly used to assess ecological risks of pollutants to ecosystems, communities, and populations. Their main advantage is the relatively direct integration of the species sensitivity to organic pollutants, the fate and mechanism of action in the environment of toxicants, and life-history features of the individual organism of concern. To promote scientific consensus on ERA schemes, this review is intended to provide a guideline on short-term ERA involving dioxin chemicals and to identify key findings for exposure assessment based on policies of different agencies. It also presents possible adverse effects of dioxins on ecosystems, toxicity equivalence methodology, environmental fate and transport modeling, and development of stressor-response profiles for dioxin-like chemicals.

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.

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.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure on bone material properties

Dioxins are known to decrease bone strength, architecture and density. However, their detailed effects on bone material properties are unknown. Here we used nanoindentation methods to characterize the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on nanomechanical behaviour of bone matrix. Pregnant rats were treated with a single intragastric dose of TCDD (1 microg/kg) or vehicle on gestational day 11. Tibias of female offspring were sampled on postnatal day (PND) 35 or 70, scanned at mid-diaphysis with pQCT, and evaluated by three-point bending and nanoindentation. TCDD treatment decreased bone mineralization (p<0.05), tibial length (p<0.01), cross-sectional geometry (p<0.05) and bending strength (p<0.05). Controls showed normal maturation pattern between PND 35 and 70 with decreased plasticity by 5.3% and increased dynamic hardness, storage and complex moduli by 26%, 13% and 12% respectively (p<0.05), while similar maturation was not observed in TCDD-exposed pups. In conclusion, for the first time, we demonstrate retardation of bone matrix maturation process in TCDD-exposed animals. In addition, the study confirms that developmental TCDD exposure has adverse effects on bone size, strength and mineralization. The current results in conjunction with macromechanical behaviour suggest that reduced bone strength caused by TCDD is more associated with the mineralization and altered geometry of bones than with changes at the bone matrix level.

Dental caries in Faroese children exposed to polychlorinated biphenyls

The effects of exposure to polychlorinated biphenyls (PCBs) on dental caries of first permanent molars in children in the Faroe Islands, where the population is exposed to PCBs in their traditional diet, were evaluated. This study was part of a cohort study aimed at determining developmental risks resulting from the consumption of contaminated seafood. One hundred and fourteen children from a birth cohort of 182 mother-child pairs, aged 9-10 years, were examined. Caries scoring was performed according to WHO criteria; cavitated and noncavitated lesions were included. Exposure assessment was based on the PCB concentrations in maternal milk samples. Data from the project data set provided information on various confounding factors. Mean maternal milk PCB concentration was 2205 (range 70-11,150)ng/g lipids. The number of carious surfaces of first permanent molars correlated with milk PCB concentration (r=0.26, p=0.01). In multivariate linear regression analysis, PCB exposure was significantly related to caries susceptibility. The findings support an association between children's PCB exposure and caries prevalence.

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

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

Developmental dental toxicity of dioxin and related compounds--a review

Non-halogenated polycyclic aromatic hydrocarbons (PAHs) and halogenated aromatic hydrocarbons such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs, or dioxins), and polychlorinated biphenyls (PCBs) are wide-spread environmental pollutants that have unequivocal adverse effects on different species, including humans. Accidental exposure of children to high amounts of PCDD/Fs has been found to be associated with developmental enamel defects and missing permanent teeth. An association between dioxin exposure via mother's milk and developmental mineralisation defects in permanent first molars was also found in otherwise healthy Finnish children born in the late 1980s but not in those born in the late 1990s. Results of experimental animal studies in vivo and in vitro are compatible with findings in human teeth. In addition to the dose, dental effects of the most toxic dioxin congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), essentially depend on the stage of tooth development at the time of exposure. Accordingly, TCDD arrests early rat and mouse molar tooth development and in more advanced teeth it interferes with mineralisation of enamel and dentine and arrests root development. Expression of the specific dioxin receptor (AhR) in dental cells at TCDD-sensitive stages of tooth development suggests that the dental, like other developmental effects of TCDD, are mediated by the AhR. Early effects also depend on the epidermal growth factor receptor and involve enhanced apoptosis. The lowest TCDD dose (30ng/kg) causing adverse dental effects in rats has been estimated to result in maternal tissue levels approaching the high end of human background range and human milk PCDD/F levels that were associated with enamel defects in children. However, because of the uniform and clear decline in background dioxin and PCB levels in mother's milk during the last twenty years, dioxins are currently likely to be of small or no account as regards developmental dental defects in children. Even so, this is not the case after heavy exposure and little is known about the possible synergistic effects of these toxicants with other chemicals interfering with tooth development.