Use of mechanistic data in the IARC evaluations of the carcinogenicity of polychlorinated biphenyls and related compounds

Complex roles for sulfation in the toxicities of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are persistent organic toxicants derived from legacy pollution sources and their formation as inadvertent byproducts of some current manufacturing processes. Metabolism of PCBs is often a critical component in their toxicity, and relevant metabolic pathways usually include their initial oxidation to form hydroxylated polychlorinated biphenyls (OH-PCBs). Subsequent sulfation of OH-PCBs was originally thought to be primarily a means of detoxication; however, there is strong evidence that it may also contribute to toxicities associated with PCBs and OH-PCBs. These contributions include either the direct interaction of PCB sulfates with receptors or their serving as a localized precursor for OH-PCBs. The formation of PCB sulfates is catalyzed by cytosolic sulfotransferases, and, when transported into the serum, these metabolites may be retained, taken up by other tissues, and subjected to hydrolysis catalyzed by intracellular sulfatase(s) to regenerate OH-PCBs. Dynamic cycling between PCB sulfates and OH-PCBs may lead to further metabolic activation of the resulting OH-PCBs. Ultimate toxic endpoints of such processes may include endocrine disruption, neurotoxicities, and many others that are associated with exposures to PCBs and OH-PCBs. This review highlights the current understanding of the complex roles that PCB sulfates can have in the toxicities of PCBs and OH-PCBs and research on the varied mechanisms that control these roles.

Ten years after: findings from the medical surveillance program on Health Effects in High-Level Exposure to PCB (HELPcB)

After the detection of high environmental and occupational exposure to polychlorinated biphenyls (PCBs) in a German recycling company for transformers and capacitors in 2010, the multidisciplinary medical surveillance program "HELPcB" (Health Effects in High-Level Exposure to PCB) was established for former PCB-exposed workers of the company, their family members, employees of surrounding companies, and area residents to investigate potential adverse health effects by PCB exposure in a longitudinal study approach with up to seven examination time points between 2010 and 2019. More than 300 individuals were enrolled into the program. Assessments particularly included plasma and urine concentrations of PCB congeners and their metabolites, clinical laboratory parameters, Comet assay, analysis of telomere length, neuropsychological examinations, psychological screening, abdominal and thyroid ultrasound examination. This review summarizes the main results of the studies conducted in the HELPcB program yielding relevant new data on potential adverse effects of PCB exposure in humans and potential mechanisms that underlie these effects. Even larger studies in PCB-exposed individuals are warranted to confirm the results of this program and to further establish causality between PCB exposure and clinical effects in humans.

Cisplatin-based combination therapy for cancer

Cisplatin, that is, cis-diamminedichloroplatinum is a coordinate compound that is mainly preferred as prior treatment against several solid tumors and malignancies like ovaries, head and neck, testicular, and lung cancers because of its anticancer activity. Cisplatin binds at the N7 position of purine and forms adducts, leading to altered activity of DNA that triggers apoptosis. DNA damage is followed by several signaling pathways like induced oxidative stress, upregulated p53, mitogen-activated protein kinase (MAPK), and Jun N-terminal kinases (JNK) or Akt pathways along with induced apoptosis. Additionally, cisplatin treatment comes with few disadvantages such as toxic effects, that is, hepatotoxicity, cardiotoxicity, neurotoxicity, etc., and drug resistance. Furthermore, to overcome cisplatin resistance and toxicological effects, combination drug therapy has been considered. The aim of the review is to focus on the molecular mechanism of action of cisplatin and combination drug therapy to reduce the side effects in cancer therapy.

Evaluation of genotoxicity and cytotoxicity of inhabitants of Vila Rural Água Viva, Brazil, exposed to agrochemicals using the micronucleus buccal cytome assay

The aim of this study was to carry out a pilot investigation, using a buccal micronucleus cytome assay, with the population of Vila Rural Água Viva (Francisco Beltrão, Paraná, Brazil), environmentally exposed to agrochemicals. The data shows statistically differences between the control group (not exposed) and the population of Vila Rural regarding the cytotoxicity and mutagenicity. There was no significant change between the average relative frequencies of these data whether divided between smokers and non-smokers, or practitioners of physical activities or not. It was also observed that age or time of exposure to agrochemicals did not show a linear relationship with the average relative frequencies of cytotoxicity and mutagenicity data. The work shows the presence of 2,4-D herbicide in water sample of community, then it is hoped that the results will assist in guiding the dangers to health and the environment from exposure to agrochemicals.

OUP accepted manuscript

Exposure to environmental toxicants during preconception has been shown to affect offspring health and epigenetic mechanisms such as DNA methylation are hypothesized to be involved in adverse outcomes. However, studies addressing the effects of exposure to environmental toxicants during preconception on epigenetic changes in gametes are limited. The objective of this study is to determine the effect of preconceptional exposure to a dioxin-like polychlorinated biphenyl (3,3',4,4',5-pentachlorobiphenyl [PCB126]) on DNA methylation and gene expression in testis. Adult zebrafish were exposed to 3 and 10 nM PCB126 for 24 h and testis tissue was sampled at 7 days postexposure for histology, DNA methylation, and gene expression profiling. Reduced representation bisulfite sequencing revealed 37 and 92 differentially methylated regions (DMRs) in response to 3 and 10 nM PCB126 exposures, respectively. Among them, 19 DMRs were found to be common between both PCB126 treatment groups. Gene ontology (GO) analysis of DMRs revealed that enrichment of terms such as RNA processing, iron-sulfur cluster assembly, and gluconeogenesis. Gene expression profiling showed differential expression of 40 and 1621 genes in response to 3 and 10 nM PCB126 exposures, respectively. GO analysis of differentially expressed genes revealed enrichment of terms related to xenobiotic metabolism, oxidative stress, and immune function. There is no overlap in the GO terms or individual genes between DNA methylation and RNA sequencing results, but functionally many of the altered pathways have been shown to cause spermatogenic defects.

In-situ fabrication of a chlorine-functionalized covalent organic framework coating for solid-phase microextraction of polychlorinated biphenyls in surface water

The functionalization of covalent organic frameworks (COFs) identifies significant potential for developing selective coating materials for solid-phase microextraction (SPME). Herein, a chlorine-functionalized covalent organic framework (CF-COF) was in-situ synthesized by employing triformylphloroglucinol (Tp) and 2,5-dichloro-1,4-phenylenediamine (2,5-DCA) as monomers on an amino-functionalized stainless steel wire. The obtained CF-COF coated fiber exhibited a higher enrichment capacity for polychlorinated biphenyls (PCBs) than commercial fibers and non-chlorinated COF fiber, owing to a more hydrophobic surface, size-matching effect, a large number of micropores and the π-π stacking interactions between COF coating and analytes. As a practical application, the CF-COF coated fiber was applied to the headspace extraction of 17 PCBs prior to their quantification by GC/MS. The established analytical method offered a good linearity in the range of 0.1-1000 ng L^-1, low detection limits of 0.0015-0.0088 ng L^-1, and satisfactory enhancement factors (EFs) of 699-4281. The repeatability for single fiber and the fiber-to-fiber reproducibility was lower than 9.26% and 9.33%, respectively. The proposed method was verified to be sensitive, selective, and applicable for the analysis of ultra-trace PCBs in environmental surface water samples with the recoveries ranged from 78.7% to 124.0%.

Key Characteristics of Cardiovascular Toxicants

BACKGROUND

The concept of chemical agents having properties that confer potential hazard called key characteristics (KCs) was first developed to identify carcinogenic hazards. Identification of KCs of cardiovascular (CV) toxicants could facilitate the systematic assessment of CV hazards and understanding of assay and data gaps associated with current approaches.

OBJECTIVES

We sought to develop a consensus-based synthesis of scientific evidence on the KCs of chemical and nonchemical agents known to cause CV toxicity along with methods to measure them.

METHODS

An expert working group was convened to discuss mechanisms associated with CV toxicity.

RESULTS

The group identified 12 KCs of CV toxicants, defined as exogenous agents that adversely interfere with function of the CV system. The KCs were organized into those primarily affecting cardiac tissue (numbers 1-4 below), the vascular system (5-7), or both (8-12), as follows: 1) impairs regulation of cardiac excitability, 2) impairs cardiac contractility and relaxation, 3) induces cardiomyocyte injury and death, 4) induces proliferation of valve stroma, 5) impacts endothelial and vascular function, 6) alters hemostasis, 7) causes dyslipidemia, 8) impairs mitochondrial function, 9) modifies autonomic nervous system activity, 10) induces oxidative stress, 11) causes inflammation, and 12) alters hormone signaling.

DISCUSSION

These 12 KCs can be used to help identify pharmaceuticals and environmental pollutants as CV toxicants, as well as to better understand the mechanistic underpinnings of their toxicity. For example, evidence exists that fine particulate matter [PM ≤2.5μm in aerodynamic diameter (PM2.5)] air pollution, arsenic, anthracycline drugs, and other exogenous chemicals possess one or more of the described KCs. In conclusion, the KCs could be used to identify potential CV toxicants and to define a set of test methods to evaluate CV toxicity in a more comprehensive and standardized manner than current approaches. https://doi.org/10.1289/EHP9321.

Different co-culture models reveal the pivotal role of TBBPA-promoted M2 macrophage polarization in the deterioration of endometrial cancer

Tetrabromobisphenol A (TBBPA), an emerging organic pollutant widely detected in human samples, has a positive correlation with the development of endometrial cancer (EC), but its underlying mechanisms have not yet been fully elucidated. Tumor-associated macrophages (TAM), one of the most vital components in tumor microenvironment (TME), play regulatory roles in the progression of EC. Consequently, this study mainly focuses on the macrophage polarization in TME to unveil the influence of TBBPA on the progression of EC and involved mechanisms. Primarily, low doses of TBBPA treatment up-regulated M2-like phenotype biomarkers in macrophage. The data from in vitro co-culture models suggested TBBPA-driven M2 macrophage polarization was responsible for the EC deterioration. Results from in vivo study further confirmed the malignant proliferation of EC promoted by TBBPA. Mechanistically, TBBPA-mediated miR-19a bound to the 3'-UTR regions of SOCS1, resulting in down-regulation of SOCS1 followed by the phosphorylation of JAK and STAT6. The present study not only revealed for the first time the molecular mechanism of TBBPA-induced EC's deterioration based on macrophage polarization, but also established co-culture models, thus providing a further evaluation method for the exploration of environmental pollutants-induced tumor effects from the role of TME.

A Congener-specific and Mixture Analysis of Plasma Polychlorinated Biphenyl Levels and Incident Breast Cancer

BACKGROUND

Polychlorinated biphenyls (PCBs), a diverse class of chemicals, are hypothesized mammary carcinogens. We examined plasma levels of 17 PCBs as individual congeners and as a mixture in association with breast cancer using a novel approach based on quantile g-computation.

METHODS

This study included 845 White and 562 Black women who participated in the population-based, case-control Carolina Breast Cancer Study Phase I. Cases (n = 748) were women with a first diagnosis of histologically confirmed, invasive breast cancer residing in 24 counties in central and eastern North Carolina; controls (n = 659) were women without breast cancer from the same counties. PCBs were measured in plasma samples obtained during the study interview. We estimated associations [covariate-adjusted odds ratios (ORs) and 95% confidence intervals (CIs)] between individual PCB congeners and breast cancer using multivariable logistic regression. We assessed PCB mixtures using quantile g-computation and examined effect measure modification by race.

RESULTS

Comparing highest and lowest tertiles of PCBs resulted in ORs of 1.3 (95% CI = 0.95, 1.8) for congener 74, 1.4 (95% CI = 1.0, 1.9) for 99, 1.3 (95% CI = 0.91, 1.8) for 194, and 1.2 (95% CI = 0.90, 1.7) for 201. Among all women, we estimated a joint effect of the PCB mixture with an OR of 1.3 (95% CI = 0.98, 1.6) per tertile change. In race-stratified analyses, associations for tertiles of PCB mixtures were stronger among Black women (OR = 1.5; 95% CI = 1.0, 2.3) than among White women (OR = 1.1; 95% CI = 0.81, 1.6).

CONCLUSION

Our results are consistent with the hypothesis that exposure to PCB mixtures increase the risk of breast cancer, but studies of populations with different exposure profiles are needed.

Effect of exposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs) on mitochondrial DNA (mtDNA) copy number in rats

Mitochondria are intracellular organelles responsible for biological oxidation and energy production. These organelles are susceptible to damage from oxidative stress and compensate for damage by increasing the number of copies of their own genome, mitochondrial DNA (mtDNA). Cancer and environmental exposure to some pollutants have also been associated with altered mtDNA copy number. Since exposures to polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have been shown to increase oxidative stress, we hypothesize that mtDNA copy number will be altered with exposure to these compounds. mtDNA copy number was measured in DNA from archived frozen liver and lung specimens from the National Toxicology Program (NTP) study of female Harlan Sprague Dawley rats exposed to TCDD (3, 10, or 100 ng/kg/day), dioxin-like (DL) PCB 126 (10, 100, or 1000 ng/kg/day), non-DL PCB 153 (10, 100, or 1000 μg/kg/day), and PCB 126 + PCB 153 (10 ng/kg/day + 10 μg/kg/day, 100 ng/kg/day + 100 μg/kg/day, or 1000 ng/kg/day + 1000 μg/kg/day, respectively) for 13 and 52 weeks. An increase in mtDNA copy number was observed in the liver and lung of rats exposed to TCDD and the lung of rats exposed to the mixture of PCB 126 and PCB 153. A statistically significant positive dose-dependent trend was also observed in the lung of rats exposed to PCB 126 and a mixture of PCB 153 and PCB 126, although in neither case was the control copy number significantly exceeded at any dose level. These exposures produced a range of pathological responses in these organs in the two-year NTP studies. Conversely, there was a significant decrease or no change in mtDNA copy number in the liver and lung of rats exposed to non-DL PCB 153. This is consistent with a general lack of PCB 153 mediated liver or lung injury in the NTP study, with the exception of liver hypertrophy. Together, the results suggest that an increase in mtDNA copy number may serve as a sensitive, early biomarker of mitochondrial injury and oxidative stress that contributes to the development of the toxicity of dioxin-like compounds.

Lycopene ameliorates the effect of Aroclor 1254 on morphology, proliferation, and angiogenesis of the thyroid gland in rat

Aroclor 1254 is a mixture of polychlorinated biphenyls that are reported to disrupt thyroid hormone homeostasis, yet little is known on its effect on thyroid gland microarchitecture. Lycopene is a commonly used potent antioxidant. This study is a biochemical, histological, and immunohistochemical assessment of the effect of Aroclor 1254 on the morphology, proliferation, and angiogenesis of the thyroid gland in rat and to evaluate the possible ameliorating role of lycopene. Twenty-four adult male albino rats were divided into 4 groups; Control, lycopene-treated (4 mg/kg/day orally for 30 days), Aroclor 1254-treated (2 mg/kg/day intraperitoneally for 30 days), and lycopene & Aroclor 1254-treated group. Serum thyroid hormones, thyroid-stimulating hormone (TSH), and tissue malondialdehyde (MDA) were quantified. Thyroid specimens were processed for histological staining with hematoxylin and eosin, periodic acid-Schiff, and Mallory's trichrome stains as well as immunohistochemical staining for detection of calcitonin, Ki67, and VEGF. In this study, Aroclor 1254-treated animals recorded a significant decline in both serum T3 and T4 coupled with a significant elevation in both TSH and tissue MDA. Histological sections showed small irregular follicles with the formation of hyperplastic and micro follicles. Some follicular and parafollicular cells depicted nuclear and cytoplasmic alterations associating with scanty or absent colloid in addition to signs of inflammation and fibrosis. A significant upregulation in the immunohistochemical expression of calcitonin, Ki67, and VEGF was recorded. Lycopene co-treatment successfully reinstated the values of most studied parameters and retrieved a near-control thyroid morphology. In conclusion, Aroclor 1254 impacted the thyroid hormone homeostasis, morphology, proliferation, and angiogenesis of the thyroid gland in rat, while lycopene efficiently ameliorated these adverse effects.

Establishment of a CoMFA Model Based on the Combined Activity of Bioconcentration, Long-Range Transport, and Highest Infrared Signal Intensity and Molecular Design of Environmentally Friendly PBB Derivatives

In the current study, a comparative molecular field analysis (CoMFA) model with the combined activity of polybrominated biphenyls (PBBs) bioconcentration, long-range transport, and the highest infrared signal intensity (weight ratio of 5:4:1) was constructed based on the threshold method and was further evaluated and analyzed. PBB-153 derivatives with improved combined activity values of bioconcentration, long-range transport, and the highest infrared signals intensity were designed based on contour maps of the CoMFA model. The environmental stability and functionality of the derivatives were also evaluated. The constructed model showed good prediction ability, fitting ability, stability, and external prediction ability. The contribution rates of electrostatic and steric fields to the combined activity of PBBs were 53.4% and 46.6%, respectively. Four PBB-153 derivatives with significantly improved bioconcentration, long-range transport and the highest infrared signal intensity (the combined activity value of these three parameters decreased) were screened with good environmental stability and functionality. Results validated the accuracy and reliability, and ability of the generated model to realize the simultaneous modification of the three activities of the target molecule. The binding ability of the designed derivatives to food chain biodegradation enzymes increased, thereby verifying the improvement in the bioconcentration. The half-lives of the derivatives in air and their ability to be absorbed by the plants significantly improved compared to the target molecule, further showing that the long-range transport of derivatives was reduced. In addition, the introduction of the –NO group caused the N =O stretching vibration of the derivatives to increase the infrared signal intensity. The present model provides a theoretical design method for the molecular modification of environmentally friendly PBBs.

Endocrine Disrupting Chemicals and Thyroid Cancer: An Overview

Endocrine disruptive chemicals (EDC) are known to alter thyroid function and have been associated with increased risk of certain cancers. The present study aims to provide a comprehensive overview of available studies on the association between EDC exposure and thyroid cancer. Relevant studies were identified via a literature search in the National Library of Medicine and National Institutes of Health PubMed as well as a review of reference lists of all retrieved articles and of previously published relevant reviews. Overall, the current literature suggests that exposure to certain congeners of flame retardants, polychlorinated biphenyls (PCBs), and phthalates as well as certain pesticides may potentially be associated with an increased risk of thyroid cancer. However, future research is urgently needed to evaluate the different EDCs and their potential carcinogenic effect on the thyroid gland in humans as most EDCs have been studied sporadically and results are not consistent.

Metabolic activation and toxicological evaluation of polychlorinated biphenyls in Drosophila melanogaster

Degradation of polychlorinated biphenyls (PCBs) is initiated by cytochrome P450 (CYP) enzymes and includes PCB oxidation to OH-metabolites, which often display a higher toxicity than their parental compounds. In search of an animal model reflecting PCB metabolism and toxicity, we tested Drosophila melanogaster, a well-known model system for genetics and human disease. Feeding Drosophila with lower chlorinated (LC) PCB congeners 28, 52 or 101 resulted in the detection of a human-like pattern of respective OH-metabolites in fly lysates. Feeding flies high PCB 28 concentrations caused lethality. Thus we silenced selected CYPs via RNA interference and analyzed the effect on PCB 28-derived metabolite formation by assaying 3-OH-2',4,4'-trichlorobiphenyl (3-OHCB 28) and 3'-OH-4',4,6'-trichlorobiphenyl (3'-OHCB 28) in fly lysates. We identified several drosophila CYPs (dCYPs) whose knockdown reduced PCB 28-derived OH-metabolites and suppressed PCB 28 induced lethality including dCYP1A2. Following in vitro analysis using a liver-like CYP-cocktail, containing human orthologues of dCYP1A2, we confirm human CYP1A2 as a PCB 28 metabolizing enzyme. PCB 28-induced mortality in flies was accompanied by locomotor impairment, a common phenotype of neurodegenerative disorders. Along this line, we show PCB 28-initiated caspase activation in differentiated fly neurons. This suggested the loss of neurons through apoptosis. Our findings in flies are congruent with observation in human exposed to high PCB levels. In plasma samples of PCB exposed humans, levels of the neurofilament light chain increase after LC-PCB exposure, indicating neuronal damage. In summary our findings demonstrate parallels between Drosophila and the human systems with respect to CYP mediated metabolism and PCB mediated neurotoxicity.

TBBPA stimulated cell migration of endometrial cancer via the contribution of NOX-generated ROS in lieu of energy metabolism

Due to the extensive applications and deleterious effects of Tetrabromobisphenol A (TBBPA), the health risk and possible mechanisms have been a topic of concern. However, the knowledge on carcinogenic risk of TBBPA and corresponding mechanisms remains scarce. In this study, endometrial cancer cells were exposed to low doses of TBBPA and its main derivatives including TBBPA bis (2,3-dibromopropyl ether) (TBBPA-BDBPE) and TBBPA bis (2-hydroxyethyl ether) (TBBPA-BHEE). The data from wound healing and transwell assays demonstrated that TBBPA treatment exhibited the strongest enhanced effect on cell migration among other tested treatments. Of note, the process of invasion rather than epithelial-mesenchymal transition (EMT) was accompanied by the occurrence of migration elevated by TBBPA. Furthermore, the levels of several metabolite indicators were measured to assess the underlying mechanisms involved in TBBPA-induced cell migration. The findings suggested that NADPH oxidase (NOX)-driven ROS instead of energy metabolism was sensitive to TBBPA stimulation. In addition, molecular docking supported a link between TBBPA ligand and NOX receptor. Accordingly, this study has provided new insights for TBBPA-induced carcinogenic effects and may arise peoples' vigilance to environmental pollution of brominated flame retardant.

Carcinogenic and teratogenic status of human population and polychlorinated biphenyls contaminations of soils and biota (European pied flycatcher) in a Perm (Western Ural, Russia)

Polychlorinated biphenyls (PCBs) are included in the persistent organic pollutants designated by the Stockholm Convention and are hazardous compounds both for the environment and public health. The aim of this study was to determine the level of environmental pollution of PCBs in the Perm, in soil and biota (European pied flycatcher), and to analyze whether its presence was the cause of cancer and congenital malformations in the population. Soils in the study area had PCB concentrations of 101.87 µg/kg in the Industrialniy District and 27.81 µg/kg in the Leninskiy District of the Perm in 2005. The chemical composition of the individual PCBs and PCB groups were the same in the soils of both regions. The blood of nestlings of the European pied flycatcher raised in the Industrialniy District contained 9.61 ng PCB/ml, while those in the Leninskiy District had 5.64 ng PCB/ml in 2005. A linear correlation was established between the PCB contamination of soils and PCB contamination of pied flycatcher nestling's blood, and inverse linear correlation was established between the content of PCB in the blood of nestlings and the success of breeding of the pied flycatcher in Perm. An epidemiological analysis revealed a high incidence of cancer among the human population of the Industrialniy and Leninskiy districts (371.7 and 376.85 cases per 100,000 population, mean for the 2003-2018, respectively), which exceeded the figure for the whole of Perm (350.77 cases per 100,000 population, mean for the 2003-2018). The incidence rate of congenital malformations in Perm for the study period was 48.51 per 1000 human births. However, a decrease in the concentration of PCBs in soil and biota over a 15-year period (2005-2019) to the less than the detection limit did not lead to a decrease in the incidence of these diseases. Probably, PCB contamination was not the main cause of oncological diseases and congenital malformations in the population of the study area.

Mortality in Yusho patients exposed to polychlorinated biphenyls and polychlorinated dibenzofurans: a 50-year retrospective cohort study

BACKGROUND

In 1968, the Yusho incident resulted in accidental exposure to polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), and related compounds in Japan. This study updated the risk of mortality in Yusho patients.

METHODS

We obtained updated cohort data for all Yusho patients for the period 1968-2017. We calculated standardized mortality ratios (SMRs) for all-cause and cause-specific mortality over a 50-year follow-up period compared with the general population in Japan.

RESULTS

A total of 1664 Yusho patients with 63,566 person-years of follow up were included in the analysis. Among males, excess mortality was observed for all cancers (SMR: 1.22, 95% confidence interval [CI]: 1.02 to 1.45) and lung cancer (SMR: 1.59, 95% CI: 1.12 to 2.19). Among females, increased mortality was observed for liver cancer (SMR: 2.05, 95% CI: 1.02 to 3.67). No significant increase was seen in non-cancer-related mortality compared with the general population.

CONCLUSIONS

Carcinogenic risk in humans after exposure to PCBs and PCDFs remains higher among Yusho patients. Our findings suggest the importance of care engagement and optimum management to deal with the burden of Yusho disease.

Telomeres as targets for the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs) in rats

Telomere length (TL) can be affected by various factors, including age and oxidative stress. Changes in TL have been associated with chronic disease, including a higher risk for several types of cancer. Environmental exposure of humans to PCBs and dioxins has been associated with longer or shorter leukocyte TL. Relative telomere length (RTL) may serve as a biomarker associated with neoplastic and/or non-neoplastic responses observed with chronic exposures to TCDD and PCBs. RTL was measured in DNA isolated from archived frozen liver and lung tissues from the National Toxicology Program (NTP) studies conducted in female Harlan Sprague Dawley rats exposed for 13, 30, and 52 weeks to TCDD, dioxin-like (DL) PCB 126, non-DL PCB 153, and a mixture of PCB 126 and PCB 153. RTL was assessed by quantitative polymerase chain reaction (qPCR). Consistent with literature, decreased liver and lung RTL was seen with aging. Relative to time-matched vehicle controls, RTL was increased in both the liver and lung tissues of rats exposed to TCDD, PCB 126, PCB 153, and the mixture of PCB 126 and PCB 153, which is consistent with most epidemiological studies that found PCB exposures were associated with increased leukocyte RTL. Increased RTL was observed at doses and/or time points where little to no pathology was observed. In addition to serving as a biomarker of exposure to these compounds in rats and humans, increases in RTL may be an early indicator of neoplastic and non-neoplastic responses that occur following chronic exposure to TCDD and PCBs.

Sustainable strategy for municipal solid waste disposal in Hong Kong: current practices and future perspectives

Hong Kong (HK) is confronted by increasing problems of solid waste disposal, as it is an overpopulated city with limited land resources. Currently, solid waste disposal mainly relies on three landfills located in the New Territories. However, the current waste treatment facilities and policies cannot appropriately control and manage increments of solid waste. The primary reason is the increased amount of municipal solid waste (MSW) caused by the growth of the population and the economy, with food waste accounting for the largest proportion of MSW in HK. The secondary reason is that the capacity of existing landfills will be exhausted in the near future as the level of waste generated continues to grow. To deal with these problems, in this paper, we propose five approaches with the aim of identifying the most sustainable strategy for efficient solid waste disposal in HK: a food waste recycling program; an MSW charging scheme; the implementation of incineration plants (i.e., waste to energy); black soldier fly bioconversion and a waste trading scheme; and black soldier fly bioconversion and a hybrid anaerobic digestion system. This is followed by a detailed demonstration of each approach, particularly focusing on the benefits, limitations, and implementation of each in the case of HK. The results of this study may shed light on how to effectively and sustainably manage the increasing amount of solid waste in HK.

Cardiovascular Effects of Polychlorinated Biphenyls and Their Major Metabolites

BACKGROUND

Xenobiotic metabolism is complex, and accounting for bioactivation and detoxification processes of chemicals remains among the most challenging aspects for decision making with in vitro new approach methods data.

OBJECTIVES

Considering the physiological relevance of human organotypic culture models and their utility for high-throughput screening, we hypothesized that multidimensional chemical-biological profiling of chemicals and their major metabolites is a sensible alternative for the toxicological characterization of parent molecules vs. metabolites in vitro.

METHODS

In this study, we tested 25 polychlorinated biphenyls (PCBs) [PCB 3, 11, 52, 126, 136, and 153 and their relevant metabolites (hydroxylated, methoxylated, sulfated, and quinone)] in concentration-response (10 nM-100μM) for effects in human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs) and endothelial cells (ECs) (iPSC-derived and HUVECs). Functional phenotypic end points included effects on beating parameters and intracellular Ca2+ flux in CMs and inhibition of tubulogenesis in ECs. High-content imaging was used to evaluate cytotoxicity, mitochondrial integrity, and oxidative stress.

RESULTS

Data integration of a total of 19 physicochemical descriptors and 36 in vitro phenotypes revealed that chlorination status and metabolite class are strong predictors of the in vitro cardiovascular effects of PCBs. Oxidation of PCBs, especially to di-hydroxylated and quinone metabolites, was associated with the most pronounced effects, whereas sulfation and methoxylation of PCBs resulted in diminished bioactivity.

DISCUSSION

Risk characterization analysis showed that although in vitro derived effective concentrations exceeded the levels measured in the general population, risks cannot be ruled out due to the potential for population variability in susceptibility and the need to fill data gaps using read-across approaches. This study demonstrated a strategy for how in vitro data can be used to characterize human health risks from PCBs and their metabolites. https://doi.org/10.1289/EHP7030.

Plasma levels of polychlorinated biphenyls (PCBs) and breast cancer mortality: The Carolina Breast Cancer Study

BACKGROUND

It is unknown whether carcinogenic and endocrine disrupting polychlorinated biphenyls (PCBs) influence mortality following breast cancer. We examined plasma levels of 17 PCB congeners in association with mortality among women with breast cancer.

METHODS

Participants included 456 white and 292 black women in North Carolina who were diagnosed with primary invasive breast cancer from 1993 to 1996, and who had PCB and lipid measurements from blood samples obtained an average of 4.1 months after diagnosis. Over a median follow-up of 20.6 years, there were 392 deaths (210 from breast cancer). We used Cox regression to estimate covariate-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for all-cause and breast cancer-specific 5-year mortality, and 20-year mortality (conditional on 5-year survival) in association with tertiles and continuous ln-transformed lipid-adjusted PCB levels.

RESULTS

The highest (vs. lowest) tertiles of PCB74, PCB99, and PCB118 were associated with 5-year breast cancer-specific mortality HRs of 1.46 (95%CI = 0.86-2.47), 1.57 (95%CI = 0.90-2.73), and 1.86 (95%CI = 1.07-3.23), respectively. Additionally, one-ln unit increases in PCB74, PCB99, PCB118, and total PCBs were each associated with 33-40% increases in 5-year breast cancer-specific mortality rates. The PCBs were not, however, associated with longer-term breast cancer-specific mortality. For all-cause mortality, one-ln unit increases in PCB118, PCB146, PCB153, PCB182, PCB187, and total PCBs were associated with 20-37% increases in 20-year all-cause mortality rates among women who survived at least 5 years.

CONCLUSION

PCBs may increase the risk of short-term breast cancer-specific mortality and long-term all-cause mortality among women with breast cancer.

Cardiovascular and cancer mortality in relation to dietary polychlorinated biphenyls and marine polyunsaturated fatty acids: a nutritional-toxicological aspect of fish consumption

BACKGROUND

Co-exposure to environmental contaminants present in fish could mitigate the beneficial effects of fish consumption and possibly explain the lack of association observed for mortality in some geographical regions.

OBJECTIVE

To assess the independent associations of dietary exposure to polychlorinated biphenyls (PCBs) and long-chain omega-3 fish fatty acids intake with cardiovascular and cancer mortality.

METHODS

We used the prospective population-based Swedish Mammography Cohort and the Cohort of Swedish Men comprising 32 952 women and 36 545 men, free from cancer, cardiovascular disease and diabetes at baseline in 1998. Validated estimates of dietary PCBs and long-chain omega-3 fish fatty acids [i.e. eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] intake were obtained via a food frequency questionnaire at baseline. Information on death was ascertained through register linkage.

RESULTS

During a mean follow-up of 15.5 years, we ascertained 16 776 deaths. We observed for cardiovascular mortality, comparing extreme quintiles in multivariable models mutually adjusted for PCBs and EPA-DHA, dose-dependent associations for dietary PCB exposure, hazard ratio (HR) 1.31 (CI 95%: 1.08 to 1.57; P-trend 0.005) and for dietary EPA-DHA intake, HR 0.79 (CI 95%: 0.66 to 0.95; P-trend 0.041). For cancer mortality, no clear associations were discerned.

CONCLUSION

The beneficial effect of fish consumption on the cardiovascular system seems compromised by co-exposure to PCBs - one likely explanation for the inconsistent associations observed between fish consumption and mortality.

Adolescent exposure to environmental level of PCBs (Aroclor 1254) induces non-alcoholic fatty liver disease in male mice

Polychlorinated biphenyls (PCBs) are persistent organic pollutants found in various environmental media, and there is growing evidence that PCBs may contribute to the pathogenesis of non-alcoholic fatty liver disease (NAFLD). The purposes of this study were to investigate whether environmental level of Aroclor 1254 (a commercial mixture of PCBs) exposure to adolescent male mice could induce the development of NAFLD and the mechanisms involved. Twenty-one-day-old male C57BL/6 mice were exposed to Aroclor 1254 (0.5-500 μg/kg body weight) by oral gavage once every third day for 60 days. The results showed that exposure to Aroclor 1254 increased body weight and decreased the liver-somatic index in a dose-dependent manner. Aroclor 1254 administration increased lipid accumulation in the liver and induced the mRNA expression of genes associated with lipogenesis, including acetyl-CoA carboxylase 1 (Acc1), acetyl-CoA carboxylase 2 (Acc2) and fatty acid synthase (Fasn). Moreover, Aroclor 1254 decreased peroxisome proliferator-activated receptor alpha (PPARα) signaling and lipid oxidation. In addition, we found that Aroclor 1254 administration induced oxidative stress in mouse liver and elevated the protein level of cyclooxygenase 2 (COX-2), an inflammatory molecule, possibly via the endoplasmic reticulum (ER) stress inositol-requiring enzyme 1α-X-box-binding protein-1 (IRE1α-XBP1) pathway, but not the nuclear factor-κB (NF-κB) pathway. In summary, adolescent exposure to environmental level of PCBs stimulated oxidative stress, ER stress and the inflammatory response and caused NAFLD in male mice. This work provides new insight into the idea that adolescent exposure to environmental level of PCBs might induce the development of NAFLD under the regulation of ER stress in males.

Serum Levels of Commonly Detected Persistent Organic Pollutants and Per- and Polyfluoroalkyl Substances (PFASs) and Mammographic Density in Postmenopausal Women

There are little epidemiological data on the impact of persistent organic pollutants (POPs) and endocrine disruptors on mammographic density (MD), a strong predictor of breast cancer. We assessed MD in 116 non-Hispanic white post-menopausal women for whom serum concentrations of 23 commonly detected chemicals including 3 polybrominated diphenyl ethers (PBDEs), 8 per- and polyfluoroalkyl substances (PFASs), and 12 polychlorinated biphenyls (PCBs) had been measured. Linear regression analyses adjusting for potential confounders were used to examine the associations between the levels of the chemical compounds, modeled as continuous and dichotomized (above/below median) variables, and square-root-transformed MD. None of the associations were statistically significant after correcting for multiple testing. Prior to correction for multiple testing, all chemicals with un-corrected p-values < 0.05 had regression coefficients less than zero, suggesting inverse associations between increased levels and MD, if any. The smallest p-value was observed for PCB-153 (regression coefficient for above-median vs. below-median levels: −0.87, un-corrected p = 0.008). Neither parity nor body mass index modified the associations. Our results do not support an association between higher MD and serum levels of PBDEs, PCBs, or PFASs commonly detected in postmenopausal women.

Species-Specific Characteristics Influence Contaminant Accumulation Trajectories and Signatures Across Ontogeny in Three Pelagic Shark Species

Factors influencing organic contaminant accumulation in sharks, especially across ontogeny, are not well-known. Contaminant concentrations were measured in three species of sharks (Blue, Shortfin Mako, and Common Thresher) across a range of size classes (neonatal to adult) that vary in their ecological and physiological characteristics. Empirical data was compared to a theoretical framework that predicted the shape of lifetime accumulation curves. We found that a one-size-fits-all accumulation model was not appropriate as species-specific characteristics had a significant effect on contaminant accumulation trajectories. Maternal offloading likely has an important effect on determining neonatal shark contaminant starting points, and trophic ecology and physiology may interact to affect the shape of species' contaminant accumulation curves. Makos were found to have the highest accumulation potential and Blues the lowest, with Threshers being intermediate in accumulation potential. Changes in species' ecology and/or physiology were also reflected in contaminant signature changes over ontogeny. If contaminant concentrations are to be used as a proxy for risk, species-specific characteristics need to be taken into account when estimating contaminant exposure and its potential negative effects on shark health and human consumption safety.

PCB Emissions from Paint Colorants

Polychlorinated biphenyls (PCBs) are known human carcinogens that are byproducts of pigment manufacturing and found in colorants used to tint consumer paints sold in the United States and elsewhere. PCBs have the potential to be emitted from paint containing these pigments. To quantify the gas-phase emissions of ∑PCBs, we used polyurethane foam (PUF) to capture emissions from freshly applied colorants. Some PCB emissions were detected on the PUF after 1 day. After 6 weeks, all PCBs found in the colorant were also found on the PUF. Even the fully chlorinated PCB209 was emitted from green colorant. Mono- and dichlorinated PCBs were released from the colorant at a faster rate than the higher chlorinated congeners. By the end of the experiment, all the lower chlorinated congeners were absent from the colorant while more than 75% of the higher chlorinated congeners remained in the sample. The rate of PCB emissions from paint colorants is a function of the surface/air equilibrium coefficient, and the presence of water accelerates the emissions. Although concentrations of PCBs in colorants are less than 285 ng g^-1, PCB emissions from colorants in paint can cause environmentally relevant concentrations of ≥500 pg m^-3 within hours of painting a room.

Pre-diagnostic serum concentrations of organochlorines and risk of acute myeloid leukemia: A nested case-control study in the Norwegian Janus Serum Bank Cohort

BACKGROUND

Epidemiologic studies suggest an increased risk of leukemia among individuals occupationally exposed to some organochlorine (OC) compounds. Associations between serum OC pesticide and polychlorinated biphenyl (PCB) levels and risk of acute myeloid leukemia (AML), the most common subtype of acute leukemia in adult populations, have not been evaluated prospectively in the general population.

OBJECTIVE

We evaluated the risk of AML in relation to pre-diagnostic serum levels of OC pesticides and PCBs in a case-control study nested within the Janus Serum Bank Cohort.

METHODS

Janus is a large population-based cohort containing biologic samples collected beginning in the early 1970s from ~318,000 individuals in Norway. Serum levels of 11 OC pesticides or their metabolites and 34 PCB congeners were measured in 56 AML cases and 288 controls. Conditional logistic regression was conducted to evaluate associations between lipid-adjusted serum OC levels and risk of AML.

RESULTS

Higher serum levels of total chlordane/heptachlor metabolites were associated with AML risk (3rd vs. 1st tertile odds ratio (OR) = 2.26, 95% confidence interval (CI) = 0.91-5.63; p_trend = 0.11). Significant exposure-response associations were observed for levels of heptachlor epoxide (3rd vs. 1st tertile OR = 2.85, 95% CI = 1.05-7.73; p_trend = 0.02) and dieldrin (3rd vs. 1st tertile OR = 2.71, 95% CI = 1.07-6.83; p_trend = 0.03). No significant exposure-response associations with AML risk were observed for total DDT or individual isomers and derivatives. Higher serum levels of p,p'-DDT showed a non-significant increase in risk, but the exposure-response became attenuated when co-adjusting for heptachlor epoxide or dieldrin levels. Serum PCB levels were not significantly associated with AML risk.

CONCLUSIONS

Our data suggest that higher serum levels of dieldrin and metabolites derived from chlordane/heptachlor are associated with risk of AML in the general Norwegian population, based on samples collected on average ~17 years before diagnosis. Further research in populations with historically high or recent exposure to DDT is warranted to assess the association with AML risk with body burden of specific DDT isomers and derivatives.

Telomerase gene expression bioassays indicate metabolic activation of genotoxic lower chlorinated polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are ubiquitously occurring pollutants with different chemical and toxicological properties. In this study we evaluated blood plasma samples of two PCB-exposed cohorts for their ability to alter telomerase (hTERT) gene expression. Blood plasma from PCB-exposed individuals inhibited hTERT expression depending solely on the concentration of lower chlorinated PCBs, with the lowest observed adverse effect level (LOAEL) at a plasma concentration between 0.5 and 2 µg/L of LC PCBs. Individual OH-metabolites derived from the WHO indicator congeners PCB 28 and PCB 101 mimicked these effects on hTERT expression in vitro with high toxicity, including DNA damage. However, by the combination of different OH-metabolites, the bio effective PCB concentration was reduced and the respective effects on hTERT expression could be increased. At a concentration which showed no toxic activity in MTT assay, hTERT inhibition reflected the interference of OH-PCBs with the mitochondrial respiratory chain, which could lead to the production of reactive oxygen species (ROS). As individual OH-metabolites already showed a much stronger inhibition of hTERT gene expression at a lower concentration than their parental compounds, the hTERT gene expression bioassay described in this study seems to indicate metabolic activation of LC PCBs rather than the mere effect of LC PCBs on their own. In summary, this study provides dose-response linkages between effects of lower chlorinated PCBs and their concentrations in human plasma.

A nested case-control study of polychlorinated biphenyls, organochlorine pesticides, and thyroid cancer in the Janus Serum Bank cohort

BACKGROUND

Polychlorinated biphenyls (PCBs) and organochlorine pesticides have been associated with altered thyroid hormone levels in humans, but their relationship with thyroid cancer is unknown.

METHODS

We conducted a nested case-control study of thyroid cancer in the Norwegian Janus Serum Bank cohort using pre-diagnostic blood samples from 1972 to 1985. Incident thyroid cancer (n = 108) was ascertained through 2008. Controls were matched 2:1 by age, date of blood draw, gender, and county. We used gas chromatography/mass spectrometry to quantify 36 PCB congeners and metabolites of pesticides DDT, chlordane, hexachlorocyclohexane, and hexachlorobenzene. PCBs and pesticide metabolites were evaluated individually and summed by degree of chlorination and parent compound, respectively. Odds ratios (OR) and 95% confidence intervals (CI) were computed using conditional logistic regression per specified increase in lipid-adjusted concentration. We additionally stratified analyses by birth cohort (1923-1932, 1933-1942, 1943-1957).

RESULTS

Increasing concentration of DDT metabolites (OR_{per 1000 ng/g} = 0.80, 95%CI = 0.66-0.98) was inversely associated with thyroid cancer. Associations for PCBs were null or in inverse direction. We observed interactions for total PCBs, moderately-chlorinated PCBs, and chlordane metabolites with birth cohort (p ≤ 0.04). Among participants born 1943-1957, total PCBs (OR_{per 100 ng/g} = 1.25, 95%CI = 1.00-1.56), moderately-chlorinated PCBs (OR_{per 100 ng/g} = 1.31, 95%CI = 1.01-1.70), and chlordane metabolites (OR_{per 10 ng/g} = 1.78, 95%CI = 1.09-2.93) were positively associated with thyroid cancer. For individuals born before 1943, associations were generally null or in the inverse direction.

CONCLUSIONS

Emissions of PCBs and OC pesticides varied over time. Different risk patterns by birth cohort suggest the potential importance of timing of exposure in thyroid cancer risk. Further evaluation of these associations is warranted.

Hyperpigmentation and higher incidence of cutaneous malignancies in moderate-high PCB- and dioxin exposed individuals

Polychlorinated biphenyls (PCB) are well known persistent and toxic environmental pollutants. Our aim was to identify effects of moderate-high exposure to dioxin-like (dl) and non-dioxin-like (ndl)-PCBs on the skin in order to provide more insight in the pathophysiological effects of these compounds. We performed a dermatological examination on 92 former workers from a transformer recycling company with known elevated serum PCB and/or dioxin (polychlorinated dibenzo-p-dioxin/polychlorinated dibenzo-p-furan (PCDD/F)) levels. In addition, we performed a skin cancer screening over a period of seven years (2010-2016) on resp. 268, 271, 210, 149, 92, 129 and 79 participants. We found a higher incidence of acne and malignancies of the skin (malignant melanoma, basal cell carcinoma and mycosis fungoides) in the workers compared to normal population. The probability of having hyperpigmentation on the skin was statistically significantly higher in workers with higher sumPCBs- (OR:1.09(1.12-2.17)), dioxin-like (dl)-PCBs- (OR:1.56(1.12-2.17)) and dioxin (PCDD/Fs) (OR:1.09(1.02-1.16)) levels. Age was a confounding factor in this model. Formation of hyperpigmentation could be an indicator for (moderate-high) exposure to toxic compounds like PCBs. The higher incidence of cutaneous malignancies found in the workers might be associated with PCB- and dioxin exposure, warranting further investigation on larger cohorts.

PCB126 Inhibits the Activation of AMPK-CREB Signal Transduction Required for Energy Sensing in Liver

3,3',4,4',5-pentachlorobiphenyl (PCB126), a dioxin-like PCB, elicits toxicity through a wide array of noncarcinogenic effects, including metabolic syndrome, wasting, and nonalcoholic fatty-liver disease. Previously, we reported decreases in the transcription of several enzymes involved in gluconeogenesis, before the early onset of lipid accumulation. Hence, this study was aimed at understanding the impact of resultant decreases gluconeogenic enzymes on growth, weight, and metabolism in the liver, upon extended exposure. Male Sprague Dawley rats (75-100 g), fed a defined AIN-93G diet, were injected (ip) with single dose of soy oil (5 ml/kg body weight; n = 14) or PCB126 (5 µmol/kg; n = 15), 28 days, prior euthanasia. A subset of rats from each group were fasted for 12 h (vehicle [n = 6] and PCB126 [n = 4]). Rats only showed significant weight loss between days 14 and 28 (p < .05) and some mortality (p = .0413). As in our previous studies, the expression levels of enzymes involved in gluconeogenesis (Pepck-c, G6Pase, Sds, Pc, and Ldh-A) and glycogenolysis (Pygl) were strongly downregulated. The decreased expression of these enzymes in PCB126-treated rats after a 12 h fast decreased hepatic glucose production from glycogen and gluconeogenic substrates, exacerbating the hypoglycemia. Additionally, PCB126 caused hepatic steatosis and decreased the expression of the transcription factor Pparα and its targets, necessary for fatty-acid oxidation. The observed metabolic disruption across multiple branches of fasting metabolism resulted from inhibition in the activation of enzyme AMPK and transcription factor CREB signaling, necessary for "sensing" energy-deprivation and the induction of enzymes that respond to the PCB126 triggered fuel crisis in liver.

Sources and toxicities of phenolic polychlorinated biphenyls (OH-PCBs)

Polychlorinated biphenyls (PCBs), a group of 209 congeners that differ in the number and position of chlorines on the biphenyl ring, are anthropogenic chemicals that belong to the persistent organic pollutants (POPs). For many years, PCBs have been a topic of interest because of their biomagnification in the food chain and their environmental persistence. PCBs with fewer chlorine atoms, however, are less persistent and more susceptible to metabolic attack, giving rise to chemicals characterized by the addition of one or more hydroxyl groups to the chlorinated biphenyl skeleton, collectively known as hydroxylated PCBs (OH-PCBs). In animals and plants, this biotransformation of PCBs to OH-PCBs is primarily carried out by cytochrome P-450-dependent monooxygenases. One of the reasons for infrequent detection of lower chlorinated PCBs in serum and other biological matrices is their shorter half-lives, and their metabolic transformation, resulting in OH-PCBs or their conjugates, such as sulfates and glucuronides, or macromolecule adducts. Recent biomonitoring studies have reported the presence of OH-PCBs in human serum. The occurrence of OH-PCBs, the size of this group (there are 837 mono-hydroxyl PCBs alone), and their wide spectra of physical characteristics (pKa's and log P's ranging over 5 to 6 orders of magnitude) give rise to a multiplicity of biological effects. Among those are bioactivation to electrophilic metabolites that can form covalent adducts with DNA and other macromolecules, interference with hormonal signaling, inhibition of enzymes that regulate cellular concentrations of active hormones, and interference with the transport of hormones. This new information creates an urgent need for a new perspective on these often overlooked metabolites.

Emissions of Tetrachlorobiphenyls (PCBs 47, 51, and 68) from Polymer Resin on Kitchen Cabinets as a Non-Aroclor Source to Residential Air

Both Aroclor and non-Aroclor sources of airborne polychlorinated biphenyls (PCBs) were found in residential homes. We deployed passive air samplers at 16 residences and found PCB-47, PCB-51, and PCB-68 to account for up to 50% of measured indoor ΣPCBs (2700 pg m-3). Although PCB-47 and PCB-51 are neurotoxins present in Aroclor mixtures (<2.5 and <0.3 wt %, respectively), we found them at much higher levels than expected for any Aroclor source. PCB-68 is not present in Aroclor mixtures. Another non-Aroclor congener, PCB-11, a byproduct of pigment manufacturing, was found inside and outside of every household and was frequently the predominate congener. We conducted direct measurements of surface emissions and identified finished cabinetry to be a major source of PCB-47, PCB-51, and PCB-68. We hypothesize that these congeners are inadvertent byproducts of polymer sealant manufacturing and produced from the decomposition of 2,4-dichlorobenzoyl peroxide used as an initiator in free-radical polymerization of polyester resins. The presence of these three compounds in polymer products, such as silicone, has been widely noted, but to our knowledge they have never been shown to be a significant environmental source of PCBs.

Enantioselectivity of 2,2',3,5',6-Pentachlorobiphenyl (PCB 95) Atropisomers toward Ryanodine Receptors (RyRs) and Their Influences on Hippocampal Neuronal Networks

Nineteen ortho-substituted PCBs are chiral and found enantioselectively enriched in ecosystems. Their differential actions on biological targets are not understood. PCB 95 (2,2',3,5',6-pentachlorobiphenyl), a chiral PCB of current environmental relevance, is among the most potent toward modifying ryanodine receptors (RyR) function and Ca²⁺ signaling. PCB 95 enantiomers are separated and assigned aR- and aS-PCB 95 using three chiral-column HPLC and circular dichroism spectroscopy. Studies of RyR1-enriched microsomes show aR-PCB 95 with >4× greater potency (EC₅₀ = 0.20 ± 0.05 μM), ∼ 1.3× higher efficacy (B_max = 3.74 ± 0.07 μM) in [³H]Ryanodine-binding and >3× greater rates (R = 7.72 ± 0.31 nmol/sec/mg) of Ca²⁺ efflux compared with aS-PCB 95, whereas racemate has intermediate activity. aR-PCB 95 has modest selectivity for RyR2, and lower potency than racemate toward the RyR isoform mixture in brain membranes. Chronic exposure of hippocampal neuronal networks to nanomolar PCB 95 during a critical developmental period shows divergent influences on synchronous Ca²⁺ oscillation (SCO): rac-PCB 95 increasing and aR-PCB 95 decreasing SCO frequency at 50 nM, although the latter's effects are nonmonotonic at higher concentration. aS-PCB95 shows the greatest influence on inhibiting responses to 20 Hz electrical pulse trains. Considering persistence of PCB 95 in the environment, stereoselectivity toward RyRs and developing neuronal networks may clarify health risks associated with enantioisomeric enrichment of PCBs.

Serum polychlorinated biphenyls and leukocyte telomere length in a highly-exposed population: The Anniston Community Health Survey

BACKGROUND

Serum polychlorinated biphenyls (PCBs) have previously been associated with longer leukocyte telomere length (LTL) in most, but not all, of the few previous studies. PCBs were produced in Anniston, Alabama from 1929 to 1971 and participants of the Anniston Community Health Survey (ACHS) were highly exposed.

OBJECTIVES

We evaluated serum levels of 35 PCBs and relative telomere length in 559 ACHS participants.

METHODS

Relative LTL was measured in DNA extracted from blood clots. We assessed PCBs individually, grouped by chlorination, and summed PCBs. We used linear regression to assess the association between each PCB metric while adjusting for pertinent covariates.

RESULTS

Serum PCBs were associated with longer LTL among white participants and the oldest age group of black participants. Among white participants, compared with those in the first quartile of sum PCBs those in the third quartile of sum PCBs had 8.09% longer relative LTL (95% CI: 1.99; 14.55) and those in the fourth had 7.58% longer relative LTL (95%CI: -0.01; 15.76) (p-quadratic=0.05). Among African American participants, serum PCBs were associated with longer relative LTL among those over age 64 only. Tests for interaction were not statistically significant.

CONCLUSIONS

We observed a non-linear positive association between serum PCBs and LTL among white participants. Serum PCBs were associated with longer LTL in the oldest age group of African Americans. This association may provide insight into the cancers previously associated with exposure to PCBs, melanoma and non-Hodgkin lymphoma, which have been associated with long LTL in previous studies.

Polychlorinated biphenyls and its potential role in endometriosis

With the progress of global industrialization and environmental deterioration, the relationship between human health and the living environment has become an increasing focus of attention. Polychlorinated biphenyls (PCBs, including dioxin-like polychlorinated biphenyls and non-dioxin-like polychlorinated biphenyls), as part of the organic chlorine contaminants, have been suspected as playing a role in the etiopathogenesis of endometriosis. Several population-based studies have proposed that exposure to PCBs may increase the risk of developing endometriosis, while some epidemiological studies have failed to find any association between PCBs and endometriosis. The purpose of this review is to discuss the potential pathophysiological relationship between endometriosis and PCBs with a focus on both dioxin-like polychlorinated biphenyls and non-dioxin-like polychlorinated biphenyls.

Zero-valent iron particles for PCB degradation and an evaluation of their effects on bacteria, plants, and soil organisms

Two types of nano-scale zero-valent iron (nZVI-B prepared by borohydride reduction and nZVI-T produced by thermal reduction of iron oxide nanoparticles in H₂) and a micro-scale ZVI (mZVI) were compared for PCB degradation efficiency in water and soil. In addition, the ecotoxicity of nZVI-B and nZVI-T particles in treated water and soil was evaluated on bacteria, plants, earthworms, and ostracods. All types of nZVI and mZVI were highly efficient in degradation of PCBs in water, but had little degradation effect on PCBs in soil. Although nZVI-B had a significant negative impact on the organisms tested, treatment with nZVI-T showed no negative effect, probably due to surface passivation through controlled oxidation of the nanoparticles.

How well can carcinogenicity be predicted by high throughput "characteristics of carcinogens" mechanistic data?

IARC has begun using ToxCast/Tox21 data in efforts to represent key characteristics of carcinogens to organize and weigh mechanistic evidence in cancer hazard determinations and this implicit inference approach also is being considered by USEPA. To determine how well ToxCast/Tox21 data can explicitly predict cancer hazard, this approach was evaluated with statistical analyses and machine learning prediction algorithms. Substances USEPA previously classified as having cancer hazard potential were designated as positives and substances not posing a carcinogenic hazard were designated as negatives. Then ToxCast/Tox21 data were analyzed both with and without adjusting for the cytotoxicity burst effect commonly observed in such assays. Using the same assignments as IARC of ToxCast/Tox21 assays to the seven key characteristics of carcinogens, the ability to predict cancer hazard for each key characteristic, alone or in combination, was found to be no better than chance. Hence, we have little scientific confidence in IARC's inference models derived from current ToxCast/Tox21 assays for key characteristics to predict cancer. This finding supports the need for a more rigorous mode-of-action pathway-based framework to organize, evaluate, and integrate mechanistic evidence with animal toxicity, epidemiological investigations, and knowledge of exposure and dosimetry to evaluate potential carcinogenic hazards and risks to humans.

Do polychlorinated biphenyls cause cancer? A systematic review and meta-analysis of epidemiological studies on risk of cutaneous melanoma and non-Hodgkin lymphoma

In 2015 a IARC Working Group upgraded the classification of PCBs to Group 1 "Carcinogenic to humans", also on the basis of evidence from epidemiological studies showing an excess risk for melanoma. Increased risks for non-Hodgkin lymphoma (NHL) and breast cancer were also reported though the evidence was limited. However, some recent reviews of studies on PCB exposure and risk of cancer provided discrepant findings. Therefore, we re-evaluated the association between exposure to PCBs and risk of melanoma and NHL by a systematic review and meta-analysis. We retrieved 11 independent cohort studies on occupationally exposed workers. About half of them showed increased standardized mortality or incidence ratios (SMRs or SIRs) for melanoma and none for NHL. The pooled SMRs were 1.32 (95% CI: 1.05-1.64) for melanoma and 0.94 (0.73-1.23) for NHL. Among population-based cohort and case-control studies with individual measures of PCB exposure, one only study was carried out on PCB exposure and melanoma, showing an odds ratio (OR) of 6.0 (2.0-18.2) for the highest compared to lowest quartile of PCB distribution. 13 cohort and case-control studies evaluated the association between NHL and PCB concentration in blood or subcutaneous fat, with summary OR = 1.5 (1.1-1.7) for the highest vs lowest quantile of PCB distribution. However, two cohort studies on people intoxicated by rice oil containing PCBs found no excess of deaths for skin cancer and inconsistent results for NHL. In conclusion, these findings do not provide a strong evidence that PCB exposure can increase the risk of melanoma and NHL in humans.

Glyphosate toxicity and carcinogenicity: a review of the scientific basis of the European Union assessment and its differences with IARC

Glyphosate is the most widely used herbicide worldwide. It is a broad spectrum herbicide and its agricultural uses increased considerably after the development of glyphosate-resistant genetically modified (GM) varieties. Since glyphosate was introduced in 1974, all regulatory assessments have established that glyphosate has low hazard potential to mammals, however, the International Agency for Research on Cancer (IARC) concluded in March 2015 that it is probably carcinogenic. The IARC conclusion was not confirmed by the EU assessment or the recent joint WHO/FAO evaluation, both using additional evidence. Glyphosate is not the first topic of disagreement between IARC and regulatory evaluations, but has received greater attention. This review presents the scientific basis of the glyphosate health assessment conducted within the European Union (EU) renewal process, and explains the differences in the carcinogenicity assessment with IARC. Use of different data sets, particularly on long-term toxicity/carcinogenicity in rodents, could partially explain the divergent views; but methodological differences in the evaluation of the available evidence have been identified. The EU assessment did not identify a carcinogenicity hazard, revised the toxicological profile proposing new toxicological reference values, and conducted a risk assessment for some representatives uses. Two complementary exposure assessments, human-biomonitoring and food-residues-monitoring, suggests that actual exposure levels are below these reference values and do not represent a public concern.

Use of high-throughput in vitro toxicity screening data in cancer hazard evaluations by IARC Monograph Working Groups

Evidence regarding carcinogenic mechanisms serves a critical role in International Agency for Research on Cancer (IARC) Monograph evaluations. Three recent IARC Working Groups pioneered inclusion of the US Environmental Protection Agency (EPA) ToxCast program high-throughput screening (HTS) data to supplement other mechanistic evidence. In Monograph V110, HTS profiles were compared between perfluorooctanoic acid (PFOA) and prototypical activators across multiple nuclear receptors. For Monograph V112-113, HTS assays were mapped to 10 key characteristics of carcinogens identified by an IARC expert group, and systematically considered as an additional mechanistic data stream. Both individual assay results and ToxPi-based rankings informed mechanistic evaluations. Activation of multiple nuclear receptors in HTS assays showed that PFOA targets not only peroxisome proliferator activated receptors, but also other receptors. ToxCast assays substantially covered 5 of 10 key characteristics, corroborating literature evidence of "induces oxidative stress" and "alters cell proliferation, cell death or nutrient supply" and filling gaps for "modulates receptor-mediated effects." Thus, ToxCast HTS data were useful both in evaluating specific mechanistic hypotheses and in contributing to the overall evaluation of mechanistic evidence. However, additional HTS assays are needed to provide more comprehensive coverage of the 10 key characteristics of carcinogens that form the basis of current IARC mechanistic evaluations.

Graphene Oxide Nanoprisms for Sensitive Detection of Environmentally Important Aromatic Compounds with SERS

Recent advances in graphene-based sensors have shown that heavily oxidized (GO) and reduced graphene oxide (rGO) are attractive materials for environmental sensing due to their unique chemical and physical properties. We describe here the fabrication of nanostructured GO assemblies with Ag nanoprisms for improved detection with surface enhanced Raman scattering (SERS). Specifically, 100-μm-sized, periodic-nanoprism-array domains were fabricated on top of the GO layers by GO-assisted lithography (GOAL). The atomically thin GO underlayers are shown to attract cyclic aromatic molecules to the surface, likely via π-π stacking interactions. The close proximity of the analyte to GO and nanoprism (NP) tips effectively suppresses fluorescent background and affords a plausible tertiary enhancement of photon emissions via an electron charge transfer (CT) process. The adsorption of analyte to rGO-NP leads to the appearance and/or shift of several Raman bands, which provided a means to gain molecular insights into the graphene-enhanced scattering process. The analytical merits were characterized with model compound Rhodamine 6G, where the detection limit could reach subnanomolar concentrations. The nanoprism GO substrates also prove effective for SERS multiplex measurement of several legacy aromatic pollutants. Three tetrachlorobiphenyl isomers could be identified from a mixture using their autonomous nonoverlapping molecular fingerprints, and the substrate offers remarkable trace detection of 2,2',3,3'-tetrachlorobiphenyl (PCB-77).

Concentrations of environmental organic contaminants in meat and meat products and human dietary exposure: A review

Meat and meat products is one of the most relevant food groups in an important number of human diets. Recently, the IARC, based on results of a number of epidemiological studies, classified the consumptions of red meat and processed meat as "probably carcinogenic to humans" and as "carcinogenic to humans", respectively. It was suggested that the substances responsible of the potential carcinogenicity would be mainly generated during meat processing, such as curing and smoking, or when meat is heated at high temperatures. However, the exposure to environmental pollutants through meat consumption was not discussed. The purpose of the present paper was to review recent studies reporting the concentrations of PCDD/Fs, DL-PCBs and PAHs in meat and meat products, as well as the human exposure to these pollutants through the diet. It is concluded that the health risks derived from exposure to carcinogenic environmental contaminants must be considered in the context of each specific diet, which besides meat and meat products, includes other foodstuffs containing also chemical pollutants, some of them with carcinogenic potential. Anyhow, meat and meat products are not the main food group responsible of the dietary exposure to carcinogenic (or probably carcinogenic) environmental organic pollutants.

Induction of micronuclei and cell cycle arrest by some tri- and tetrachlorobiphenyls in mammalian cells deficient in xenobiotic-metabolizing enzymes

Polychlorinated biphenyls (PCBs) are persistent organic pollutants with continued public health concerns. The lower chlorinated biphenyls are supposed to be mutagenic following metabolic activation. However, in a preliminary study, we recently observed induction of micronuclei by several PCBs in a subclone of Chinese hamster V79 cell line, V79-Mz, which is deficient in xenobiotic-metabolizing enzyme activities. In this study, metabolism-free genotoxicity of PCBs was investigated, using 10 tri- and tetrachlorobiphenyls, in V79, V79-Mz, and human hepatoma (HepG2) cell lines. Among the four tetrachlorobiphenyls, 2,4,4',5- and 2,3'4,4'-tetrachlorobiphenyl-both having a noncoplanar configuration-induced micronuclei in V79-Mz cells, while their coplanar analogs 3,4,4',5- and 3,3',4,4'-tetrachlorobiphenyl were inactive. Furthermore, 2,3,3'- (PCB 20) and 2,3,4'-trichlorobiphenyl (PCB 22) started to induce micronuclei in V79-Mz cells at 10 μM and higher concentrations, demonstrating more potent effects than observed with 2,2',3-, 2,2',4-, 2,2',5, and 2,4,4'-trichlorobiphenyl. As representative compounds, PCB 20 and 22 induced micronuclei in relatively high concentrations in HepG2 cells (p53-proficient), though they did not induce Hprt gene mutations in V79-Mz cells. PCB 20 and 22 increased mitotic index and induced cell cycle arrest at the G2/M phase, with effects more potent in V79-Mz than in V79 cells. This study suggests that 2,3,4'- and 2,3,3'-substituted PCBs are micronuclei inducers and G2/M arresters among a number of trichlorobiphenyls in mammalian cell lines, though with potency lower than that observed recently in V79-derived cells expressing human CYP2E1. Similarly, some noncoplanar tetrachlorobiphenyls possess metabolism-independent chromosome-damaging potentials. Environ. Mol. Mutagen. 58:199-208, 2017. © 2017 Wiley Periodicals, Inc.

Alterations in geometry, biomechanics, and mineral composition of juvenile rat femur induced by nonplanar PCB-155 and/or planar PCB-169

Exposure to widespread lipophilic and bioaccumulative polychlorinated biphenyls (PCBs) induces diverse biochemical and toxicological responses in various organs, including the bone. The aim of this study was to evaluate the changes in growth rate, geometry, serum, and bone biochemical parameters and biomechanics of juvenile rat femur induced by lactational exposure to nonplanar PCB-155 and planar PCB-169 individually and in combination. Fifteen lactating Wistar rats were divided into four groups (PCB-169, PCB-155, PCB-155+169, and control), and PCBs were administered intraperitoneally at different time points after delivery. Femurs from 22-day-old offspring were analyzed by microCT, three-point bending test and inductively coupled plasma-mass spectrometry (ICP-MS) to obtain data on bone geometry, biomechanics and mineral composition. The serum levels of calcium, phosphate and alkaline phosphatase were also determined. Lactational exposure to planar PCB-169 resulted in shorter and thinner femurs, reduced endosteal and periosteal perimeters, smaller total cross-sectional and medullary areas, and lowered serum bone marker levels and calcium levels in the bone, while femur mechanical properties were not significantly altered. The changes observed in the combination exposure (PCB-155+169) group were similar to those observed in the PCB-169 group but were less pronounced. In summary, our results demonstrate that alterations in lactationally exposed offspring were primarily induced by planar PCB-169. The milder outcome in the combined group suggested that the PCB-169-mediated toxic effects on the bone might be reduced by a nonplanar PCB-155 congener. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1135-1146, 2017.

miR-21 is involved in skeletal deficiencies of zebrafish embryos exposed to polychlorinated biphenyls

Polychlorinated biphenyl (PCB) exposure increases the incidence and severity of skeletal diseases, but little is known about the mechanisms that mediate this relationship. We exposed zebrafish embryos to PCB₁₂₅₄ and assessed the changes in bone morphology protein receptor II (BMPRII), which is involved in bone formation and embryonic development, miRNA-21, for which BMPRII is a known target, and calcium metabolism. PCB₁₂₅₄ upregulated the expression of miR-21 and suppressed BMPRII expression. The inhibition of miR-21 reversed the downregulation of BMPRII and alleviated the PCB₁₂₅₄-induced loss of calcium. These findings suggest new biomarkers of developmental defects of the skeleton caused by PCBs.

PCB126-Induced Disruption in Gluconeogenesis and Fatty Acid Oxidation Precedes Fatty Liver in Male Rats

3,3',4,4',5-Pentachlorobiphenyl (PCB126), a dioxin-like polychlorinated biphenyl (PCB) and a potent aryl hydrocarbon receptor (AhR) agonist, is implicated in the disruption of both carbohydrate and lipid metabolism which ultimately leads to wasting disorders, metabolic disease, and nonalcoholic fatty liver disease. However, the mechanisms are unclear. Because liver is the target organ for PCB toxicity and responsible for metabolic homeostasis, we hypothesized that early disruption of glucose and lipid homeostasis contributes to later manifestations such as hepatic steatosis. To test this hypothesis, groups of male Sprague Dawley rats, fed on AIN-93G diet, were injected (intraperitoneal.) with a single bolus of PCB126 (5 µmol/kg) at various time intervals between 9 h and 12 days prior to euthanasia. An early decrease in serum glucose and a gradual decrease in serum triglycerides were observed over time. Liver lipid accumulation was most severe at 6 and 12 days of exposure. Transcript levels of cytosolic phosphoenol-pyruvate carboxykinase (Pepck-c/Pck1) and glucose transporter (Glut2/Slc2a2) involved in gluconeogenesis and hepatic glucose transport were time-dependently downregulated between 9 h and 12 days of PCB126 exposure. Additionally, transcript levels of Pparα, and its targets acyl-CoA oxidase (Acox1) and hydroxy-3-methylglutaryl-CoA synthase 2 (Hmgcs2), were also downregulated, indicating changes in peroxisomal fatty acid oxidation and ketogenesis. In a separate animal study, we found that the measured changes in the transcript levels of Pepck-c, Glut2, Pparα, Acox1, and Hmgcs2 were also dose dependent. Furthermore, PCB126-induced effects on Pepck-c were demonstrated to be AhR dependent in rat H4IIE hepatocytes. These results indicate that PCB126-induced wasting and steatosis are preceded initially by (1) decreased serum glucose caused by decreased hepatic glucose production, followed by (2) decreased peroxisomal fatty acid oxidation.