Development of TEFs for PCB congeners by using an alternative biomarker--thyroid hormone levels

Effects of dioxin exposure on reproductive and thyroid hormone levels and male sexual function in airbase military workers in Vietnam

Dioxins are endocrine disruptors that may disturb male sexual and reproductive function. Studies on human populations are limited, and their results are controversial. This study evaluated the impact of dioxin exposure on reproductive and thyroid hormone levels and sexual function in men. A total of 140 men working in four military airbases (three bases were formerly contaminated with dioxin by the herbicide spraying campaign in the Vietnam War) were recruited to measure the serum dioxin levels. Four reproductive hormones (testosterone, follicle-stimulating hormone, luteinizing hormone (LH), and prolactin) and three thyroid hormones (free triiodothyronine (FT3), free thyroxin (FT4), and thyroid stimulating hormone) were measured. Male sexual function endpoints including sexual drive, erection, ejaculation, problems, and overall satisfaction were assessed by the Brief Male Sexual Function Inventory. The percentage of subjects with low testosterone and LH levels was 19.6% and 16.7%, respectively. Dioxins, especially 2,3,7,8-tetrachlorodibenzo-P-dioxin and toxic equivalent concentrations of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans, were inversely associated with testosterone and prolactin levels, but positively associated with FT3 and FT4, and showed adverse relationships with sexual function, such as sexual drive, problems, and overall satisfaction. Our results suggested that exposure to dioxin disrupts the homeostasis of reproductive and thyroid hormones leading to adverse effects on male sexual function.

An introduction to the sources, fate, occurrence and effects of endocrine disrupting chemicals released into the environment

Many classes of compounds are known or suspected to disrupt the endocrine system of vertebrate and invertebrate organisms. This review of the sources and fate of selected endocrine disrupting chemicals (EDCs) in the environment includes classes of compounds that are "legacy" contaminants, as well as contaminants of emerging concern. EDCs included for discussion are organochlorine compounds, halogenated aromatic hydrocarbons, brominated flame retardants, per- and polyfluoroalkyl substances, alkylphenols, phthalates, bisphenol A and analogues, pharmaceuticals, drugs of abuse and steroid hormones, personal care products, and organotins. An exhaustive survey of the fate of these contaminants in all environmental media (e.g., air, water, soil, biota, foods and beverages) is beyond the scope of this review, so the priority is to highlight the fate of EDCs in environmental media for which there is a clear link between exposure and endocrine effects in humans or in biota from other taxa. Where appropriate, linkages are also made between the fate of EDCs and regulatory limits such as environmental quality guidelines for water and sediments and total daily intake values for humans.

Temporal-spatial survey of PAHs and PCBs in the Atlantic Iberian northwest coastline, and evaluation of their sources and risks for both humans and aquatic organisms

Herein, sixteen priority sixteen priority polycyclic aromatic hydrocarbons (PAHs) and seven polychlorinated biphenyls (PCBs), considered seawater quality indicators, were quantified in four beaches of the Iberian (Portuguese) northwest coastline, including one ornithological reserve. These seashores are close to an important industrial region and a harbour. Water samples were extracted for PAHs and PCBs in their aqueous phase (DAP) and suspended particulate matter (SPM) and analysed by GC-MS/MS. Annual average concentrations reached ∼8 ng/L (DAP) and ∼100 ng/g dw (SPM) for PAHs and ∼3 ng/L (DAP) and ∼19 ng/g dw (SPM) for PCBs. PAHs and PCBs had fluctuations suggestive of seasonality. The possible origins of PAHs point to pyrogenic (forest fires) and petrogenic activities linked to maritime transports. The source(s) of PCBs appear to be related with leaks from waste sorting centres located in the vicinity of the sampling sites, together with the burning of contaminated materials. Toxic equivalents (TEQs) suggested a low carcinogenic potential for PAHs in seawater samples (∼0.3 ng/L and ∼4 ng/g dw, for DAP and SPM). Evaluation of risk coefficients for Σ16 PAHs revealed "Low-risk" of both matrices in all sampling areas. PCBs thyroid toxicity equivalents (TEQs-TH), suggested a low impact on biota (∼7.0E-05 ng/L and ∼5.2E-04 ng/g dw, for DAP and SPM). However, in vivo acute assays with Artemia salina exposed to environmental concentrations of PAHs, PCBs, and mixtures, confirmed the theoretical approach, showing that this coastline is not "Risk-free". This fact calls for further toxicological approaches to fully understand the risks posed by these compounds locally.

Comparative Lethality of In ovo Exposure to PCB 126, PCB 77, and 2 Environmentally Relevant PCB Mixtures in Japanese Quail (Coturnix japonica)

The Japanese quail (Coturnix japonica) egg bioassay was used to directly compare the toxicity of 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 3,3',4,4'-tetrachlorobiphenyl (PCB 77), and 2 environmentally relevant polychlorinated biphenyl (PCB) mixtures over specified dose ranges relative to vehicle and uninjected controls. Measures included lethality and deformities. Results showed clear dose-response relationships for PCB 126 and the 2 PCB mixtures by logistic analysis of covariance using a varying threshold model because there was a low but significant slope for mortality of vehicle controls over incubation. No dose-dependent increase in mortality was observed with PCB 77 treatment. Mortality increased above baseline for PCB 126 and the 2 mixtures after embryonic day 7 (ED07) to a stable slope from ED10. Median lethal doses and thresholds for response differed for PCB 126 and the 2 PCB mixtures, with the mixtures having lower initial toxicity and all showing progressively greater toxicity over the course of development. Further, the lethality of the PCB mixtures appeared to involve both aryl hydrocarbon receptor (AhR) and non-AhR mechanisms. Incidence of deformities was unrelated to treatments. In summary, complex mixtures of PCBs were lethal in a dose-related manner, with sublethal effects from exposure to PCB 77. Environ Toxicol Chem 2019;38:2637-2650. © 2019 SETAC.

Comparative Analyses of the 12 Most Abundant PCB Congeners Detected in Human Maternal Serum for Activity at the Thyroid Hormone Receptor and Ryanodine Receptor

Polychlorinated biphenyls (PCBs) pose significant risk to the developing human brain; however, mechanisms of PCB developmental neurotoxicity (DNT) remain controversial. Two widely posited mechanisms are tested here using PCBs identified in pregnant women in the MARBLES cohort who are at increased risk for having a child with a neurodevelopmental disorder (NDD). As determined by gas chromatography-triple quadruple mass spectrometry, the mean PCB level in maternal serum was 2.22 ng/mL. The 12 most abundant PCBs were tested singly and as a mixture mimicking the congener profile in maternal serum for activity at the thyroid hormone receptor (THR) and ryanodine receptor (RyR). Neither the mixture nor the individual congeners (2 fM to 2 μM) exhibited agonistic or antagonistic activity in a THR reporter cell line. However, as determined by equilibrium binding of [3H]ryanodine to RyR1-enriched microsomes, the mixture and the individual congeners (50 nM to 50 μM) increased RyR activity by 2.4-19.2-fold. 4-Hydroxy (OH) and 4-sulfate metabolites of PCBs 11 and 52 had no TH activity; but 4-OH PCB 52 had higher potency than the parent congener toward RyR. These data support evidence implicating RyRs as targets in environmentally triggered NDDs and suggest that PCB effects on the THR are not a predominant mechanism driving PCB DNT. These findings provide scientific rationale regarding a point of departure for quantitative risk assessment of PCB DNT, and identify in vitro assays for screening other environmental pollutants for DNT potential.

Embryonic effects of an environmentally relevant PCB mixture in the domestic chicken

Studies were conducted to develop methods to assess the effects of a complex mixture of polychlorinated biphenyls (PCBs) in the domestic chicken (Gallus domesticus). Treatments were administered by egg injection to compare embryonic effects of an environmentally relevant PCB congener mixture in the domestic chicken over a range of doses. Chicken eggs were injected with the PCB mixture with a profile similar to that found in avian eggs collected on the upper Hudson River, New York, USA, at doses that spanned 0 to 98 μg/g egg. Eggs were hatched in the laboratory to ascertain hatching success. In the domestic chicken, the median lethal dose was 0.3 μg/g. These data demonstrate adverse effects of an environmentally relevant PCB mixture and provide the basis for further work using in vitro and other models to characterize the potential risk to avian populations. Environ Toxicol Chem 2018;37:2513-2522. © 2018 SETAC.

Overview of Cadmium Thyroid Disrupting Effects and Mechanisms

Humans are exposed to a significant number of chemicals that are suspected to produce disturbances in hormone homeostasis. Hence, in recent decades, there has been a growing interest in endocrine disruptive chemicals. One of the alleged thyroid disrupting substances is cadmium (Cd), a ubiquitous toxic metal shown to act as a thyroid disruptor and carcinogen in both animals and humans. Multiple PubMed searches with core keywords were performed to identify and evaluate appropriate studies which revealed literature suggesting evidence for the link between exposure to Cd and histological and metabolic changes in the thyroid gland. Furthermore, Cd influence on thyroid homeostasis at the peripheral level has also been hypothesized. Both in vivo and in vitro studies revealed that a Cd exposure at environmentally relevant concentrations results in biphasic Cd dose-thyroid response relationships. Development of thyroid tumors following exposure to Cd has been studied mainly using in vitro methodologies. In the thyroid, Cd has been shown to activate or stimulate the activity of various factors, leading to increased cell proliferation and a reduction in normal apoptotic activity. Evidence establishing the association between Cd and thyroid disruption remains ambiguous, with further studies needed to elucidate the issue and improve our understanding of Cd-mediated effects on the thyroid gland.

Mechanisms of Action Point Towards Combined PBDE/NDL-PCB Risk Assessment

At present, human risk assessment of the structurally similar non-dioxin-like (NDL) PCBs and polybrominated diphenylethers (PBDEs) is done independently for both groups of compounds. There are however obvious similarities between NDL-PCBs and PBDEs with regard to modulation of the intracellular calcium homeostasis (basal calcium levels, voltage-gated calcium channels, calcium uptake, ryanodine receptor) and thyroid hormone (TH) homeostasis (TH levels and transport). which are mechanisms of action related to neurobehavioral effects (spontaneous activity, habituation and learning ability). There also similarities in agonistic interactions with the hepatic nuclear receptors PXR and CAR. Several effects on developmental (reproductive) processes have also been observed, but results were more dispersed and insufficient to compare both groups of compounds. The available mechanistic information is sufficient to warrant a dose addition model for NDL-PCBs and PBDEs, including their hydroxylated metabolites.Although many of the observed effects are similar from a qualitative point of view for both groups, congener or tissue specific differences have also been found. As this is a source of uncertainty in the combined hazard and risk assessment of these compounds, molecular entities involved in the observed mechanisms and adverse outcomes associated with these compounds need to be identified. The systematical generation of (quantitative) structure-activity information for NDL-PCBs and PBDEs on these targets (including potential non-additive effects) will allow a more realistic risk estimation associated with combined exposure to both groups of compounds during early life. Additional validation studies are needed to quantify these uncertainties for risk assessment of NDL-PCBs and PBDEs.

Uptake of radiolabeled 3,3',4,4'-tetrachlorobiphenyl into Japanese quail egg compartments and embryo following air cell and albumen injection

The avian embryo is an excellent model for testing adverse developmental effects of environmental chemicals as well as uptake and movement of xenobiotics within the egg compartments. Before incubation at embryonic day 0, ¹⁴ C 3,3',4,4'-tetrachlorobiphenyl (¹⁴ C PCB 77) was injected into Japanese quail eggs either onto the air cell or into the albumen. All egg components were collected on embryonic day 1, 5, or 10, and concentrations of ¹⁴ C PCB 77 were measured in various egg components (shell, membrane, yolk, albumen, and embryo). The results showed measurable ¹⁴ C PCB 77 in all egg components, with changing concentrations in each egg component over the course of embryonic development. Specifically, concentrations in the shell content decreased between embryonic days 1 and 10, increased in albumen from embryonic days 1 to 5 and then decreased at embryonic day 10, and increased in both yolk and embryo from embryonic days 1 to 10. Vehicle and injection site both influenced ¹⁴ C PCB 77 allantoic fluid concentrations, with little effect on other egg components except for the inner shell membrane. The fatty acid vehicle injected into the albumen yielded the highest ¹⁴ C PCB 77 recovery. These findings demonstrate dynamic movement of toxicants throughout the egg components during avian embryonic development and a steady increase of relatively low levels of ¹⁴ C PCB 77 in the embryo compared with the yolk, albumen, and shell, suggesting that embryonic uptake (i.e., exposure) mirrors utilization of egg components for nutrition and growth during development. Environ Toxicol Chem 2018;37:126-135. © 2017 SETAC.

Transcriptional profiling and biological pathway analysis of human equivalence PCB exposure in vitro: indicator of disease and disorder development in humans

BACKGROUND AND AIMS

Our earlier gene-expression studies with a Slovak PCBs-exposed population have revealed possible disease and disorder development in accordance with epidemiological studies. The present investigation aimed to develop an in vitro model system that can provide an indication of disrupted biological pathways associated with developing future diseases, well in advance of the clinical manifestations that may take years to appear in the actual human exposure scenario.

METHODS

We used human Primary Blood Mononuclear Cells (PBMC) and exposed them to a mixture of human equivalence levels of PCBs (PCB-118, -138, -153, -170, -180) as found in the PCBs-exposed Slovak population. The microarray studies of global gene expression were conducted on the Affymetrix platform using Human Genome U133 Plus 2.0 Array along with Ingenuity Pathway Analysis (IPA) to associate the affected genes with their mechanistic pathways. High-throughput qRT-PCR Taqman Low Density Array (TLDA) was done to further validate the selected 6 differentially expressed genes of our interest, viz., ARNT, CYP2D6, LEPR, LRP12, RRAD, TP53, with a small population validation sample (n=71).

RESULTS

Overall, we revealed a discreet gene expression profile in the experimental model that resembled the diseases and disorders observed in PCBs-exposed population studies. The disease pathways included endocrine system disorders, genetic disorders, metabolic diseases, developmental disorders, and cancers, strongly consistent with the evidence from epidemiological studies.

INTERPRETATION

These gene finger prints could lead to the identification of populations and subgroups at high risk for disease, and can pose as early disease biomarkers well ahead of time, before the actual disease becomes visible.

The effect of chitosan on the concentration of 17β-estradiol and free triiodothyronine in mice exposed to polychlorinated biphenyls (PCBs)

The aim of this work was to examine (i) how the applied PCB mixture influences the level of 17β-estradiol (E2) and free triiodothyronine (FT3) in the blood plasma of mice (C57/BL/6J) and (ii) whether supplementation with chitosan would protect against the observed changes in the examined plasma hormone concentrations. In the study we used a mixture of indicator PCBs (CB no. 28, 52, 101, 118, 138, 153, 180) and our results showed their anti-estrogenic effects. Exposure to the mixture resulted in a significant decrease (P < 0.05) in plasma concentration of E2 relative to the control, and chitosan administration did not prevent the decrease. To the contrary, E2 concentration in the blood plasma of the mice which received both the PCB mixture and chitosan was lower compared to those which did not receive chitosan. Exposure to the PCBs also resulted in a decrease in FT3 concentration in the treatedgroup, although it was not as pronounced as for E2 and was prevented with dietary supplementation with chitosan, with the observed FT3 level in the chitosan-treated group similar to the control. In summary, supplementation with chitosan can only to a certain extent minimize the negative effects of exposure to PCBs.

Cloning of three 2,3-dihydroxybiphenyl-1,2-dioxygenase genes from Achromobacter sp. BP3 and the analysis of their roles in the biodegradation of biphenyl

Three 2,3-dihydroxybiphenyl 1,2-dioxygenase genes (designated as bphC1, bphC2 and bphC3) were cloned from a biphenyl-degrading strain Achromobacter sp. BP3. The amino acid sequence of BphC1 and BphC3 had high similarity (>99%) with the reported BphCs, while BphC2 showed relatively low identity (29.51-50.17%) with the reported BphCs, which indicated that bphC2 might be a novel gene. The bphC1, bphC2 and bphC3 genes were expressed in Escherichia coli BL21 and the products were homogenously purified. BphC1, BphC2 and BphC3 displayed maximum activity at 30°C, 30°C and 40°C, respectively. Their optimal catalysis pH was 8.0, 9.0 and 9.0, respectively. BphC1 and BphC2 had higher substrate affinity and catalytic efficiency on 2,3-dihydroxybiphenyl, while BphC3 exhibited these features on aromatic monocyclic substrates. The bphC1 gene was only induced by biphenyl and bphC3 was induced by both biphenyl and toluene, while bphC2 was constitutively expressed in strain BP3. These results suggested that BphC1 and BphC3 played a role in the upstream and downstream metabolic pathways of biphenyl, respectively. However, BphC2 might play a supplementary role and contribute more to the upstream than to the downstream pathway.

Relative effect potency estimates of dioxin-like activity for dioxins, furans, and dioxin-like PCBs in adults based on two thyroid outcomes

BACKGROUND

Toxic equivalency factors (TEFs) are an important component in the risk assessment of dioxin-like human exposures. At present, this concept is based mainly on in vivo animal experiments using oral dosage. Consequently, the current human TEFs derived from mammalian experiments are applicable only for exposure situations in which oral ingestion occurs. Nevertheless, these "intake" TEFs are commonly-but incorrectly-used by regulatory authorities to calculate "systemic" toxic equivalents (TEQs) based on human blood and tissue concentrations, which are used as biomarkers for either exposure or effect.

OBJECTIVES

We sought to determine relative effect potencies (REPs) for systemic human concentrations of dioxin-like mixture components using thyroid volume or serum free thyroxine (FT4) concentration as the outcomes of interest.

METHODS

We used a benchmark concentration and a regression-based approach to compare the strength of association between each dioxin-like compound and the thyroid end points in 320 adults residing in an organochlorine-polluted area of eastern Slovakia.

RESULTS

REPs calculated from thyroid volume and FT4 were similar. The regression coefficient (β)-derived REP data from thyroid volume and FT4 level were correlated with the World Health Organization (WHO) TEF values (Spearman r = 0.69, p = 0.01 and r = 0.62, p = 0.03, respectively). The calculated REPs were mostly within the minimum and maximum values for in vivo REPs derived by other investigators.

CONCLUSIONS

Our REPs calculated from thyroid end points realistically reflect human exposure scenarios because they are based on chronic, low-dose human exposures and on biomarkers reflecting body burden. Compared with previous results, our REPs suggest higher sensitivity to the effects of dioxin-like compounds.

Maternal serum persistent organic pollutants in the Finnish Prenatal Study of Autism: A pilot study

Recent research emphasizes the contribution of environmental as well as genetic factors to the etiology of autism but studies testing associations between chemical exposures and autism have been limited. Prenatal exposure to persistent organic pollutants (POPs) has previously been associated with decrements in cognitive and developmental performance. We conducted a pilot study in the Finnish Prenatal Study of Autism (FiPS-A). Seventy-five cases with autism and 75 controls matched on sex, birth year, urbanization and maternal age were sampled from first-born children in the Finnish Maternity Cohort, which includes over 1million births. The study sample included births occurring from 1991 to 2000. Subjects were followed up for autism through 2007. DDT, DDE, PCB-118, PCB-138, PCB-153, PCB-156, PCB-170, PCB-180, hexachlorobenzene, and BDE-47 were measured in archived maternal serum samples taken during pregnancy using gas chromatography-high resolution mass spectrometry. Correlations between pollutant measures were assessed and mechanistically-related weighting schemes for summarizing PCB levels were compared. Case and control differences were assessed using graphical and statistical methods. All analytes, with the exception of DDT and BDE-47, were detected above the limit of quantification in all samples. The correlation between levels of individual PCB congeners and weighted summary measures was high (0.71-1.00). Paired t-tests revealed no significant differences between cases and controls for log-transformed mean values of any analyte; however, in an adjusted model the odds ratios for autism were 1.91 (p=0.29) and 1.79 (p=0.36) respectively, for subjects with total PCBs and DDE above the 90th percentile of control values. Levels of prenatal PCB exposure in FIPS-A were similar to the levels which previously correlated with poorer neurodevelopmental measures in other populations. Further study in a larger sample will be required to fully determine whether exposure to high POP levels is associated with autism diagnosis in the population.

Upstream adverse effects in risk assessment: a model of polychlorinated biphenyls, thyroid hormone disruption and neurological outcomes in humans

BACKGROUND

Increasing data on early biological changes from chemical exposures requires new interpretation tools to support decision-making.

OBJECTIVES

To test the possibility of applying a quantitative approach using human data linking chemical exposures and upstream biological perturbations to overt downstream outcomes.

METHODS

Using polychlorinated biphenyl (PCB) exposures and maternal thyroid hormone (TH) perturbations as a case study, we model three relationships: (1) prenatal PCB exposures and TH changes, using free T(4) (FT(4)); (2) prenatal TH and childhood neurodevelopmental outcomes; and (3) prenatal PCB exposures and childhood neurodevelopmental outcomes (IQ). We surveyed the epidemiological literature; extracted relevant quantitative data; and developed models for each relationship, applying meta-analysis where appropriate.

RESULTS

For relationship 1, a meta-analysis of 3 studies gives a coefficient of -0.27 pg/mL FT(4) per ln(sum of PCBs) (95% confidence interval [CI] -0.82 to 0.27). For relationship 2, regression coefficients from three studies of maternal FT(4) levels and cognitive scores ranged between 0.99 IQ points/(pg/mL FT(4)) (95% CI -0.31 to 2.2) and 7.6 points/(pg/mL FT(4)) (95% CI 1.2 to 16.3). For relationship 3, a meta-analysis of five studies produces a coefficient of -1.98 IQ points (95% CI -4.46 to 0.50) per unit increase in ln(sum of PCBs). Combining relationships 1 and 2 yields an estimate of -2.0 to -0.27 points of IQ per unit increase in ln(sum of PCBs).

CONCLUSIONS

Combining analysis of chemical exposures and early biological perturbations (PCBs and FT(4)) with analysis of early biological perturbations and downstream overt effects (FT(4) and IQ) yields estimates within the range of studies of exposures and overt effects (PCBs and IQ). This is an example approach using upstream biological perturbations for effect prediction.

Individual polychlorinated biphenyl (PCB) congeners produce tissue- and gene-specific effects on thyroid hormone signaling during development

Polychlorinated biphenyls (PCB) are industrial chemicals linked to developmental deficits that may be caused in part by disrupting thyroid hormone (TH) action by either reducing serum TH or interacting directly with the TH receptor (TR). Individual PCB congeners can activate the TR in vitro when the metabolic enzyme cytochrome P4501A1 (CYP1A1) is induced, suggesting that specific PCB metabolites act as TR agonists. To test this hypothesis in vivo, we compared two combinations of PCB congeners that either activate the TR (PCB 105 and 118) or not (PCB 138 and 153) in the presence or absence of a PCB congener (PCB 126) that induces CYP1A1 in vitro. Aroclor 1254 was used as a positive control, and a group treated with propylthiouracil was included to characterize the effects of low serum TH. We monitored the effects on TH signaling in several peripheral tissues by measuring the mRNA expression of well-known TH-response genes in these tissues. Aroclor 1254 and its component PCB 105/118/126 reduced total T(4) to the same extent as that of propylthiouracil but increased the expression of some TH target genes in liver. This effect was strongly correlated with CYP1A1 expression supporting the hypothesis that metabolism is necessary. Effects were gene and tissue specific, indicating that tissue-specific metabolism is an important component of PCB disruption of TH action and that PCB metabolites interact in complex ways with the TR. These are essential mechanisms to consider when evaluating the health risks of contaminant exposures, for both PCB and other polycyclic compounds known to interact with nuclear hormone receptors.