Polychlorinated biphenyls, organochlorine pesticides and neurodevelopment

Endocrine disrupting chemical mixture exposure and risk of papillary thyroid cancer in U.S. military personnel: A nested case-control study

Single-pollutant methods to evaluate associations between endocrine disrupting chemicals (EDCs) and thyroid cancer risk may not reflect realistic human exposures. Therefore, we evaluated associations between exposure to a mixture of 18 EDCs, including polychlorinated biphenyls (PCBs), brominated flame retardants, and organochlorine pesticides, and risk of papillary thyroid cancer (PTC), the most common thyroid cancer histological subtype. We conducted a nested case-control study among U.S. military servicemembers of 652 histologically-confirmed PTC cases diagnosed between 2000 and 2013 and 652 controls, matched on birth year, sex, race/ethnicity, military component (active duty/reserve), and serum sample timing. We estimated mixture odds ratios (OR), 95% confidence intervals (95% CI), and standard errors (SE) for associations between pre-diagnostic serum EDC mixture concentrations, overall PTC risk, and risk of histological subtypes of PTC (classical, follicular), adjusted for body mass index and military branch, using quantile g-computation. Additionally, we identified relative contributions of individual mixture components to PTC risk, represented by positive and negative weights (w). A one-quartile increase in the serum mixture concentration was associated with a non-statistically significant increase in overall PTC risk (OR = 1.19; 95% CI = 0.91, 1.56; SE = 0.14). Stratified by histological subtype and race (White, Black), a one-quartile increase in the mixture was associated with increased classical PTC risk among those of White race (OR = 1.59; 95% CI = 1.06, 2.40; SE = 0.21), but not of Black race (OR = 0.95; 95% CI = 0.34, 2.68; SE = 0.53). PCBs 180, 199, and 118 had the greatest positive weights driving this association among those of White race (w = 0.312, 0.255, and 0.119, respectively). Findings suggest that exposure to an EDC mixture may be associated with increased classical PTC risk. These findings warrant further investigation in other study populations to better understand PTC risk by histological subtype and race.

The Body, the Brain, the Environment, and Parkinson's Disease

The brain- and body-first models of Lewy body disorders predict that aggregated alpha-synuclein pathology usually begins in either the olfactory system or the enteric nervous system. In both scenarios the pathology seems to arise in structures that are closely connected to the outside world. Environmental toxicants, including certain pesticides, industrial chemicals, and air pollution are therefore plausible trigger mechanisms for Parkinson's disease and dementia with Lewy bodies. Here, we propose that toxicants inhaled through the nose can lead to pathological changes in alpha-synuclein in the olfactory system that subsequently spread and give rise to a brain-first subtype of Lewy body disease. Similarly, ingested toxicants can pass through the gut and cause alpha-synuclein pathology that then extends via parasympathetic and sympathetic pathways to ultimately produce a body-first subtype. The resulting spread can be tracked by the development of symptoms, clinical assessments, in vivo imaging, and ultimately pathological examination. The integration of environmental exposures into the brain-first and body-first models generates testable hypotheses, including on the prevalence of the clinical conditions, their future incidence, imaging patterns, and pathological signatures. The proposed link, though, has limitations and leaves many questions unanswered, such as the role of the skin, the influence of the microbiome, and the effects of ongoing exposures. Despite these limitations, the interaction of exogenous factors with the nose and the gut may explain many of the mysteries of Parkinson's disease and open the door toward the ultimate goal -prevention.

The influence of environmental factors on premature ovarian insufficiency and ovarian aging

Premature ovarian insufficiency and ovarian aging are complex conditions that affect women's reproductive health and overall well-being. They are both characterized by hypergonadotropic hypogonadism and infertility, and together affect about 1 in 100 women by the age of 40. This review explores the influence of environmental factors on the development and progression of premature ovarian insufficiency and ovarian aging. When referring to environmental factors, we include a wide range of external agents and conditions, including chemicals, socioeconomic factors and lifestyle choices. Through a review of the literature, we attempt to highlight the link between environmental factors and ovarian health. We examine the impact of endocrine-disrupting chemicals, such as bisphenol A and phthalates, on ovarian function and investigate the mechanisms by which these chemicals can disrupt hormone signaling pathways, leading to alterations in ovarian reserve, oocyte quality, and folliculogenesis. Moreover, we explore lifestyle factors like obesity, stress, smoking and alcohol in relation to their effects on ovarian aging. Epigenetic changes may play a crucial role in the prevalence of premature ovarian insufficiency. Understanding the impact of environmental factors on premature ovarian insufficiency and ovarian aging is very important in public and clinical health contexts. By identifying risk factors, healthcare providers can develop targeted and strategic prevention and intervention plans. Furthermore, this knowledge can promote reproductive health and minimize exposure to harmful environmental agents.

Insights into Organochlorine Pesticides Exposure in the Development of Cardiovascular Diseases: A Systematic Review

Many human diseases such as cancer, neurological diseases, autism and diabetes are associated with exposure to pesticides, especially organochlorine pesticides. However, pesticide exposure is also associated with cardiovascular disease (CVD) as the leading cause of death worldwide. In this systematic review, results on the link between organochlorine pesticide pollution and CVD were collected from databases (Medline (PubMed), Scopus and Science Direct) in May 2022 from studies published between 2010 and 2022. A total of 24 articles were selected for this systematic review. Sixteen articles were extracted by reviewers using a standardized form that included cross-sectional, cohort, and ecological studies that reported exposure to organochlorine pesticides in association with increased CVD risk. In addition, eight articles covering molecular mechanisms organochlorine pesticides and polychlorinated biphenyls (PCBs) on cardiovascular effects were retrieved for detailed evaluation. Based on the findings of the study, it seems elevated circulating levels of organochlorine pesticides and PCBs increase the risk of coronary heart disease, especially in early life exposure to these pesticides and especially in men. Changes in the regulatory function of peroxisome proliferator-activated γ receptor (PPARγ), reduction of paroxonase activity (PON1), epigenetic changes of histone through induction of reactive oxygen species, vascular endothelial inflammation with miR-expression 126 and miR-31, increased collagen synthesis enzymes in the extracellular matrix and left ventricular hypertrophy (LVH) and fibrosis are mechanisms by which PCBs increase the risk of CVD. According to this systematic review, organochlorine pesticide exposure is associated with increased risk of CVD and CVD mortality through the atherogenic and inflammatory molecular mechanism involving fatty acid and glucose metabolism.

Origin, dietary exposure, and toxicity of endocrine-disrupting food chemical contaminants: A comprehensive review

Endocrine-disrupting chemicals (EDCs) are a growing public health concern worldwide. Consumption of foodstuffs is currently thought to be one of the principal exposure routes to EDCs. However, alternative ways of human exposure are through inhalation of chemicals and dermal contact. These compounds in food products such as canned food, bottled water, dairy products, fish, meat, egg, and vegetables are a ubiquitous concern to the general population. Therefore, understanding EDCs' properties, such as origin, exposure, toxicological impact, and legal aspects are vital to control their release to the environment and food. The present paper provides an overview of the EDCs and their possible disrupting impact on the endocrine system and other organs.

Comprehensive understanding of electrochemical treatment systems combined with biological processes for wastewater remediation

The presence of toxic pollutants in wastewater discharge can affect the environment negatively due to presence of the organic and inorganic contaminants. The application of the electrochemical process in wastewater treatment is promising, specifically in treating these harmful pollutants from the aquatic environment. This review focused on recent applications of the electrochemical process for the remediation of such harmful pollutants from aquatic environments. Furthermore, the process conditions that affect the electrochemical process performance are evaluated, and the appropriate treatment processes are suggested according to the presence of organic and inorganic contaminants. Electrocoagulation, electrooxidation, and electro-Fenton applications in wastewater have shown effective performance with high removal rates. The disadvantages of these processes are the formation of toxic intermediate metabolites, high energy consumption, and sludge generation. To overcome such disadvantages combined ecotechnologies can be applied in large-scale wastewater pollutants removal. The combination of electrochemical and biological treatment has gained importance, increased removal performance remarkably, and decreased operational costs. The critical discussion with depth information in this review could be beneficial for wastewater treatment plant operators throughout the world.

Associations of Prenatal Chemical and Nonchemical Stressors with Early-Adulthood Anxiety and Depressive Symptoms

BACKGROUND

Prenatal exposure to environmental chemicals may increase risk of childhood internalizing problems, but few studies have explored the potential for longer-term consequences of such exposures.

OBJECTIVE

We evaluated associations between prenatal organochlorine and metal levels and early adulthood internalizing symptoms, considering whether sociodemographic/nonchemical stressors modified these associations.

METHODS

Participants were 209 young adults, born (1993-1998) to mothers residing in or near New Bedford, Massachusetts. As part of the early-adult assessment, self-reported anxiety (7-item Generalized Anxiety Disorder scale) and depressive (8-item Patient Health Questionnaire) symptoms (≥10: elevated symptoms) were ascertained. We previously analyzed levels of cord serum organochlorines [hexachlorobenzene, dichlorodiphenyldichloroethylene (p,p'-DDE), polychlorinated biphenyls (ΣPCB4: sum of congeners 118, 138, 153, 180)] and whole blood lead shortly after participants' birth, and levels of cord whole blood manganese from archived samples at the time of the adolescent study visit. We used modified Poisson regression models and quantile g-computation, adjusting for sociodemographics, and explored whether biological sex, race/ethnicity (proxy for unmeasured consequences of racism), prenatal social disadvantage (assessed when participants were neonates), and quality of the home environment (assessed during adolescence) modified these associations.

RESULTS

Participants were (mean±standard deviation) 22.1±1.5 y old, 76% Non-Hispanic White, and 67% female. Prenatal hexachlorobenzene, p,p'-DDE, and lead exposures were moderately associated with increased risk of elevated anxiety symptoms. There were strata-specific associations for prenatal social disadvantage and quality of home environment such that adverse associations of p,p'-DDE and lead and the overall mixture with anxiety and depressive symptoms were largely only evident in those with lower nonchemical stress [e.g., risk ratio and 95% confidence interval (CI) per doubling p,p'-DDE for anxiety: 1.54 (95% CI: 1.20, 1.99) in high-quality home environments and 0.77 (95% CI: 0.51, 1.16) in low-quality home environments]. Associations between prenatal hexachlorobenzene and p,p'-DDE and anxiety symptoms were stronger for underrepresented racial/ethnic group participants vs. Non-Hispanic Whites. We found minimal evidence for sex-specific effects, and no consistent associations with manganese or ΣPCB4.

DISCUSSION

Prenatal organochlorine pesticides and lead exposure possibly increases risk of internalizing problems, particular anxiety symptoms, in young adults. Varying risk was observed by sociodemographic/nonchemical stressor strata, demonstrating the importance of considering interactions between chemical and other stressors. https://doi.org/10.1289/EHP11171.

Maternal serum persistent organic pollutant exposure and offspring diagnosed ADHD in a national birth cohort

BACKGROUND

Evidence implicates environmental factors in attention-deficit/hyperactivity disorder (ADHD) risk. Prenatal exposures to polychlorinated biphenyls (PCBs) and the pesticide metabolite p,p'-dichlorodiphenyl dichloroethylene (DDE) have been linked to lower cognitive ability, increased impulsivity, and attention related deficits in the offspring. However, information on the relationship of these exposures to the risk of clinically diagnosed ADHD is limited.

OBJECTIVES

To determine whether prenatal maternal levels of PCBs or DDE are associated with ADHD diagnosis in the offspring.

METHODS

The investigation was conducted in the Finnish Prenatal Study of ADHD (FIPS-ADHD), a case-control study nested in a national birth cohort. Cases were born in 1998 or 1999 and diagnosed with ADHD (ICD-9 314x or ICD-10 F90. x) according to the national Care Register for Health Care. Each case was individually matched to a control on sex, date, and place of birth. PCB congeners (PCB 74, 99, 118, 138, 153, 156, 170, 180, 183, 187) and DDE were quantified from archived prenatal maternal sera from 359 matched case-control pairs using gas chromatography - high triple quadrupole mass spectrometry. Maternal total PCBs were quantified as the sum of concentrations of the measured congeners. Associations with ADHD were examined using conditional logistic regression.

RESULTS

Maternal PCB or DDE levels greater than the 75th percentiles of the control distributions showed no evidence of association with offspring ADHD (PCBs: adjusted odds ratio (aOR) = 1.01, 95% CI = 0.63, 1.60), p = 0.98; DDE: aOR = 1.13, 95% CI = 0.71, 1.81; p = 0.60). Maternal levels of either pollutant dichotomized at the 90th percentile or considered as a continuous variable also did not show evidence for association with offspring ADHD diagnosis.

DISCUSSION

This study did not find evidence for association of maternal prenatal levels of PCBs or DDE with clinical diagnosis of offspring ADHD; however, this does not rule out the possibility of an impact on subclinical phenotypes.

Assessment of Polychlorinated Biphenyls and Their Hydroxylated Metabolites in Postmortem Human Brain Samples: Age and Brain Region Differences

Exposure to polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (OH-PCBs) has been implicated in neurodevelopmental disorders. However, the distribution of PCBs and OH-PCBs in the human brain has not been characterized. This study investigated the age-, sex-, and brain region-specific distribution of all 209 PCBs using gaschromatography-tandem mass spectrometry (GC-MS/MS) in neonatal (N = 7) and adult (N = 7) postmortem brain samples. OH-PCB analyses were performed by GC-MS/MS (as methylated derivatives) and, in a subset of samples, by nontarget liquid chromatography high-resolution mass spectrometry (Nt-LCMS). Fourteen higher chlorinated PCB congeners were observed with a detection frequency >50%. Six lower chlorinated PCBs were detected with a detection frequency >10%. Higher chlorinated PCBs were observed with higher levels in samples from adult versus younger donors. PCB congener profiles from adult donors showed more similarities across brain regions and donors than younger donors. We also assess the potential neurotoxicity of the PCB residues in the human brain with neurotoxic equivalency (NEQ) approaches. The median ΣNEQs, calculated for the PCB homologues, were 40-fold higher in older versus younger donors. Importantly, lower chlorinated PCBs made considerable contributions to the neurotoxic potential of PCB residues in some donors. OH-PCBs were identified for the first time in a small number of human brain samples by GC-MS/MS and Nt-LCMS analyses, and all contained four or fewer chlorine.

Prenatal exposure to a mixture of organochlorines and metals and internalizing symptoms in childhood and adolescence

BACKGROUND

Although prenatal chemical exposures influence neurobehavior, joint exposures are not well explored as risk factors for internalizing disorders through adolescence.

OBJECTIVE

To evaluate associations of prenatal organochlorine and metal exposures, considered individually and as a mixture, with mid-childhood and adolescent internalizing symptoms.

METHODS

Participants were 468 children from a prospective cohort recruited at birth (1993-1998) in New Bedford, Massachusetts. Organochlorines (hexachlorobenzene, p,p'-dichlorodiphenyl dichloroethylene, polychlorinated biphenyls) and metals (lead, manganese) were analyzed in cord blood. Internalizing symptoms (anxiety, depressive, somatic) were assessed via multiple informants on the Conners' Rating Scale (CRS) at 8-years and Behavior Assessment System for Children, Second Edition (BASC-2) at 15-years; higher T-scores indicate greater symptoms. Overall and sex-specific covariate-adjusted associations were evaluated using Bayesian Kernel Machine Regression (BKMR) and five-chemical linear regression models.

RESULTS

The cohort was socioeconomically diverse (35% household income <$20,000; 55% maternal ≤ high school education at birth). Most chemical concentrations were consistent with background levels [e.g., median (range) cord blood lead: 1.1 (0-9.4) μg/dL]. BKMR suggested linear associations and no interactions between chemicals. The overall mixture was positively associated with Conners' Parent Rating Scale (CPRS) and BASC-2 Self Report of Personality (SRP) anxiety and depressive symptoms, and negatively with somatic symptoms. Prenatal lead was positively associated with adolescent anxiety symptoms [1.56 (95% CI: 0.50, 2.61) BASC-2 SRP Anxiety score increase per doubling lead]. For CRPS and BASC-2 SRP, a doubling of cord blood manganese was positively associated with internalizing symptoms for girls [e.g., 3.26 (95% CI: 0.27, 6.25) BASC-2 SRP Depression score increase], but not boys. Organochlorine exposures were not adversely associated with internalizing symptoms.

DISCUSSION

Low-level prenatal lead exposure was positively associated with adolescent anxiety symptoms, and prenatal manganese exposure was positively associated with internalizing symptoms for girls from mid-childhood through adolescence. In utero neurotoxicant metal exposures may contribute to the emergence of anxiety and depression.

Prenatal exposure to pesticide residues in the diet in association with child autism-related traits: Results from the EARLI study

Prior work has suggested associations between prenatal exposure to several classes of pesticides and child autism spectrum disorder (ASD). We examined a previously developed pesticide residue burden score (PRBS) and intake of high pesticide residue foods in association with ASD-related traits. Participants were drawn from the Early Autism Risk Longitudinal Investigation (EARLI) (n = 256), a cohort following mothers who previously had a child with ASD through a subsequent pregnancy and that child's development. ASD-related traits were captured according to total Social Responsiveness Scale (SRS) scores at age 3 (mean raw total SRS score = 35.8). Dietary intake was assessed through a food frequency questionnaire collected during pregnancy. We also incorporated organic intake and fatty foods in modified versions of the PRBS. Associations between high-residue fruit and vegetable intake, the overall PRBS and modified versions of it, and SRS scores were assessed using multivariable linear regression. Overall, we did not observe associations between pesticide residues in foods and ASD-related outcomes, and modified versions of the PRBS yielded similar findings. However, reductions in ASD-related traits were observed with higher overall fruit and vegetable intake (adjusted estimates for Q4 vs. Q1: β -12.76, 95%CI -27.8, 2.3). Thus, findings from this high familial probability cohort did not suggest relationships between pesticide residues in the diet according to the PRBS and ASD-related traits. Beneficial effects of fruit and vegetable intake may influence these relationships. Future work should consider fruit and vegetable intake in association with ASD-related outcomes. LAY SUMMARY: Diet is the main source of exposure to most pesticides in use today. In this study, we examined the relationship between pesticide exposure from residues in the diet during pregnancy and child autism-related traits. We found that these pesticide residues from the diet were not related to child autism-related outcomes at age three. However, higher prenatal fruit and vegetable intake was associated with reductions in child autism-related traits.

Associations of prenatal exposure to mixtures of organochlorine pesticides and smoking and drinking behaviors in adolescence

It is important to identify the factors that influence the prevalence of disinhibitory behaviors, as tobacco and alcohol use in adolescence is a strong predictor of continued use and substance abuse into adulthood. Organochlorine pesticides (OCPs) are persistent organic pollutants that pose a potential risk to the developing fetus and offspring long-term health. We examined associations between prenatal exposure OCPs and their metabolites (i.e., p,p'-DDT, p,p'-DDE, o,p'-DDT, oxychlordane, and hexachlorobenzene (HCB)), both as a mixture and single compounds, and alcohol consumption and smoking at adolescence in a sample (n = 554) from the Child Health and Development Studies prospective birth cohort. Bayesian Kernel Machine Regression demonstrated a trend of higher risk of alcohol use and smoking with higher quartile mixture levels. Single-component analysis showed increased odds of smoking and drinking with increases in lipid-adjusted p,p'-DDE serum levels (aOR = 2.06, 95% CI 0.99-4.31, p = 0.05, per natural log unit increase). We found significant effect modification in these associations by sex with higher p,p'-DDT serum levels (aOR = 0.26, 95% CI 0.09-0.076, p = 0.01, per natural log unit increase) was associated with lower odds of smoking and drinking in female adolescents, while higher p,p'-DDE serum levels (aOR = 2.98, 95% CI 1.04-8.51, p = 0.04, per natural log unit increase) was associated with higher odds of the outcomes. Results of the mutually adjusted model were not significant for male adolescents. Further research to understand reasons for these sex-differences are warranted.

An 'Omics Approach to Unraveling the Paradoxical Effect of Diet on Perfluorooctanesulfonic Acid (PFOS) and Perfluorononanoic Acid (PFNA)-Induced Hepatic Steatosis

Perfluoroalkyl substances (PFAS) are a family of toxicants universally detected in human serum and known to cause dyslipidemia in animals and humans. Hepatic steatosis, which is defined as lipid deposition in the liver, is known to be a consequence of poor diet. Similarly, PFAS are known to induce hepatic steatosis in animals on a low-fat chow. This study explored diet-PFAS interactions in the liver and their potential to modulate hepatic steatosis. Male C57BL/6J mice were fed with either a low-fat diet (10% kcal from fat, LFD) or a moderately high-fat diet (45% kcal from fat, HFD) with or without perfluorooctanesulfonic acid (3 ppm, PFOS) or perfluorononanoic acid (3 ppm, PFNA) in feed for 12 weeks. Livers were excised for histology and quantification of PFAS and lipids. The PFOS and PFNA coadministration with HFD reduced the hepatic accumulation of lipid and PFAS relative to the LFD treatment groups. Furthermore, transcriptomic analysis revealed that PFAS administration in the presence of an HFD significantly reduces expression of known hepatic PFAS uptake transporters, organic anion transporter proteins. Transcriptomics and proteomics further revealed several pathways related to lipid metabolism, synthesis, transport, and storage that were modulated by PFAS exposure and further impacted by the presence of dietary fat. Both dietary fat content and the chemical functional head group exerted significant influence on hepatic PFAS accumulation and the resulting biochemical signature, suggesting that diet and structure should be considered in the design and interpretation of research on PFAS induced hepatic steatosis.

Maternal exposure to a human based mixture of persistent organic pollutants (POPs) affect gene expression related to brain function in mice offspring hippocampus

Male and female mice pups were exposed to a low and high dose of a human relevant mixture of persistent organic pollutants (POPs) during pregnancy and lactation. Most compounds detected in the dams were found in offspring brains. The mice offspring exhibited changed expression of hippocampal genes involved in cognitive function (Adora2a, Auts2, Crlf1, Chrnb2, Gdnf, Gnal, Kcnh3), neuroinflammation (Cd47, Il1a), circadian rhythm (Per1, Clock), redox signalling (Hmox2) and aryl hydrocarbon receptor activation (Cyp1b1). A few genes were differentially expressed in males versus females. Mostly, similar patterns of gene expression changes were observed between the low and high dose groups. Effects on learning and memory function measured in the Barnes maze (not moving, escape latency) were found in the high dose group when combined with moderate stress exposure (air flow from a fan). Mediation analysis indicated adaptation to the effects of exposure since gene expression compensated for learning disabilities (escape latency, walking distance and time spent not moving in the maze). Additionally, random forest analysis indicated that Kcnh3, Gnal, and Crlf1 were the most important genes for escape latency, while Hip1, Gnal and the low exposure level were the most important explanatory factors for passive behaviour (not moving). Altogether, this study showed transfer of POPs to the offspring brains after maternal exposure, modulating the expression level of genes involved in brain function.

Gut Microbiome Critically Impacts PCB-induced Changes in Metabolic Fingerprints and the Hepatic Transcriptome in Mice

Polychlorinated biphenyls (PCBs) are ubiquitously detected and have been linked to metabolic diseases. Gut microbiome is recognized as a critical regulator of disease susceptibility; however, little is known how PCBs and gut microbiome interact to modulate hepatic xenobiotic and intermediary metabolism. We hypothesized the gut microbiome regulates PCB-mediated changes in the metabolic fingerprints and hepatic transcriptome. Ninety-day-old female conventional and germ-free mice were orally exposed to the Fox River Mixture (synthetic PCB mixture, 6 or 30 mg/kg) or corn oil (vehicle control, 10 ml/kg), once daily for 3 consecutive days. RNA-seq was conducted in liver, and endogenous metabolites were measured in liver and serum by LC-MS. Prototypical target genes of aryl hydrocarbon receptor, pregnane X receptor, and constitutive androstane receptor were more readily upregulated by PCBs in conventional conditions, indicating PCBs, to the hepatic transcriptome, act partly through the gut microbiome. In a gut microbiome-dependent manner, xenobiotic, and steroid metabolism pathways were upregulated, whereas response to misfolded proteins-related pathways was downregulated by PCBs. At the high PCB dose, NADP, and arginine appear to interact with drug-metabolizing enzymes (ie, Cyp1-3 family), which are highly correlated with Ruminiclostridium and Roseburia, providing a novel explanation of gut-liver interaction from PCB-exposure. Utilizing the Library of Integrated Network-based Cellular Signatures L1000 database, therapeutics targeting anti-inflammatory and endoplasmic reticulum stress pathways are predicted to be remedies that can mitigate PCB toxicity. Our findings demonstrate that habitation of the gut microbiota drives PCB-mediated hepatic responses. Our study adds knowledge of physiological response differences from PCB exposure and considerations for further investigations for gut microbiome-dependent therapeutics.

Persistent organic pollutants at the synapse: Shared phenotypes and converging mechanisms of developmental neurotoxicity

The developing nervous system is sensitive to environmental and physiological perturbations in part due to its protracted period of prenatal and postnatal development. Epidemiological and experimental studies link developmental exposures to persistent organic pollutants (POPs) including polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, polybrominated diphenyl ethers, and benzo(a)pyrene to increased risk for neurodevelopmental disorders in children. Mechanistic studies reveal that many of the complex cellular processes that occur during sensitive periods of rapid brain development are cellular targets for developmental neurotoxicants. One area of research interest has focused on synapse formation and plasticity, processes that involve the growth and retraction of dendrites and dendritic spines. For each chemical discussed in this review, we summarize the morphological and electrophysiological data that provide evidence that developmental POP exposure produces long-lasting effects on dendritic morphology, spine formation, glutamatergic and GABAergic signaling systems, and synaptic transmission. We also discuss shared intracellular mechanisms, with a focus on calcium and thyroid hormone homeostasis, by which these chemicals act to modify synapses. We conclude our review highlighting research gaps that merit consideration when characterizing synaptic pathology elicited by chemical exposure. These gaps include low-dose and nonmonotonic dose-response effects, the temporal relationship between dendritic growth, spine formation, and synaptic activity, excitation-inhibition balance, hormonal effects, and the need for more studies in females to identify sex differences. By identifying converging pathological mechanisms elicited by POP exposure at the synapse, we can define future research directions that will advance our understanding of these chemicals on synapse structure and function.

Polychlorinated Biphenyls (PCBs): Risk Factors for Autism Spectrum Disorder?

Autism spectrum disorder (ASD) includes a group of multifactorial neurodevelopmental disorders defined clinically by core deficits in social reciprocity and communication, restrictive interests and repetitive behaviors. ASD affects one in 54 children in the United States, one in 89 children in Europe, and one in 277 children in Asia, with an estimated worldwide prevalence of 1-2%. While there is increasing consensus that ASD results from complex gene x environment interactions, the identity of specific environmental risk factors and the mechanisms by which environmental and genetic factors interact to determine individual risk remain critical gaps in our understanding of ASD etiology. Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that have been linked to altered neurodevelopment in humans. Preclinical studies demonstrate that PCBs modulate signaling pathways implicated in ASD and phenocopy the effects of ASD risk genes on critical morphometric determinants of neuronal connectivity, such as dendritic arborization. Here, we review human and experimental evidence identifying PCBs as potential risk factors for ASD and discuss the potential for PCBs to influence not only core symptoms of ASD, but also comorbidities commonly associated with ASD, via effects on the central and peripheral nervous systems, and/or peripheral target tissues, using bladder dysfunction as an example. We also discuss critical data gaps in the literature implicating PCBs as ASD risk factors. Unlike genetic factors, which are currently irreversible, environmental factors are modifiable risks. Therefore, data confirming PCBs as risk factors for ASD may suggest rational approaches for the primary prevention of ASD in genetically susceptible individuals.

A framework for assessing the impact of chemical exposures on neurodevelopment in ECHO: Opportunities and challenges

The Environmental influences on Child Health Outcomes (ECHO) Program is a research initiative funded by the National Institutes of Health that capitalizes on existing cohort studies to investigate the impact of early life environmental factors on child health and development from infancy through adolescence. In the initial stage of the program, extant data from 70 existing cohort studies are being uploaded to a database that will be publicly available to researchers. This new database will represent an unprecedented opportunity for researchers to combine data across existing cohorts to address associations between prenatal chemical exposures and child neurodevelopment. Data elements collected by ECHO cohorts were determined via a series of surveys administered by the ECHO Data Analysis Center. The most common chemical classes quantified in multiple cohorts include organophosphate pesticides, polychlorinated biphenyls, polybrominated diphenyl ethers, environmental phenols (including bisphenol A), phthalates, and metals. For each of these chemicals, at least four ECHO cohorts also collected behavioral data during infancy/early childhood using the Child Behavior Checklist. For these chemicals and this neurodevelopmental assessment (as an example), existing data from multiple ECHO cohorts could be pooled to address research questions requiring larger sample sizes than previously available. In addition to summarizing the data that will be available, the article also describes some of the challenges inherent in combining existing data across cohorts, as well as the gaps that could be filled by the additional data collection in the ECHO Program going forward.

Enzymatic assays for the assessment of toxic effects of halogenated organic contaminants in water and food. A review

Halogenated organic compounds are a particular group of contaminants consisting of a large number of substances, and of great concern due to their persistence in the environment, potential for bioaccumulation and toxicity. Some of these compounds have been classified as persistent organic pollutants (POPs) under The Stockholm Convention and many toxicity assessments have been conducted on them previously. In this work we provide an overview of enzymatic assays used in these studies to establish toxic effects and dose-response relationships. Studies in vivo and in vitro have been considered with a particular emphasis on the impact of halogenated compounds on the activity of relevant enzymes to the humans and the environment. Most information available in the literature focuses on chlorinated compounds, but brominated and fluorinated molecules are also the target of increasing numbers of studies. The enzymes identified can be classified as enzymes: i) the activities of which are affected by the presence of halogenated organic compounds, and ii) those involved in their metabolisation/detoxification resulting in increased activities. In both cases the halogen substituent seems to have an important role in the effects observed. Finally, the use of these enzymes in biosensing tools for monitoring of halogenated compounds is described.

Embryonic Exposure to 2,2',3,5',6-pentachlorobiphenyl (PCB-95) Causes Developmental Malformations in Zebrafish

2,2',3,5',6-Pentachlorobiphenyl (PCB-95) is an environmental neurotoxicant. There is accumulated evidence that some neurotoxic effects of PCB-95 are caused by increased spontaneous Ca²⁺ oscillations in neurons resulting from modifying ryanodine receptors (RyR) in calcium-releasing channels. However, there are large gaps in explaining brain and other developmental malformations on embryonic PCB-95 exposure. In the present study, we address those deficiencies by studying the toxic effects of PCB-95 using zebrafish as an ontogenetic model. To characterize these effects, zebrafish embryos with intact chorions were exposed to 4 different concentrations of PCB-95 (0.25, 0.5, 0.75, and 1 ppm) for 3 consecutive days. The controls were maintained in 0.5 × E2 medium or egg water and in 0.1% (v/v) dimethyl sulfoxide (DMSO)/0.5 × E2 medium or egg water. PCB-95-treated groups showed dose-dependent decreases in survival and hatching rates, with increased rates of developmental malformations when compared to controls. These include morphological malformations, brain cell necrosis, and smaller eye sizes at 5 d post fertilization. These data suggest potential mechanisms underlying the abnormal behavior observed in a visual stimulus assay. The present study provides insight into PCB-95-induced developmental toxicity and supports the use of the zebrafish model in understanding the effects of PCB-95 exposure. Environ Toxicol Chem 2019;39:162-170. © 2019 SETAC.

Prenatal Exposure to Endocrine-disrupting Chemicals in Relation to Autism Spectrum Disorder and Intellectual Disability

BACKGROUND

Exposure to endocrine disruptors is unavoidable. Many such compounds are suspected to impact neurologic development of children, but most studies conducted have considered effects of individual chemicals in isolation. Because exposures co-occur, it is important to consider their health impacts in a single regression framework.

METHODS

We applied Bayesian statistical tools (including shared mean and mixture priors for 25 unique chemicals) to study independent associations of endocrine disruptor biomarkers with autism spectrum disorder (ASD) (n = 491) and intellectual disability (n = 155), compared with 373 general population controls, in the Early Markers for Autism study. We measured biomarkers in maternal serum collected and stored from midpregnancy and considered them individually or as a class (i.e., summed polychlorinated biphenyls). We adjusted all models for original matching factors (child sex and month and year of birth), maternal age, maternal race/ethnicity, parity, and maternal education at the time samples were collected. We estimated the change in the odds of ASD or intellectual disability per 1 SD increase in the z-score of measured biomarker concentration for each chemical.

RESULTS

Odds of ASD and intellectual disability did not change with increasing concentration for any specific endocrine disruptor. The effect estimates for each chemical were centered on or near an odds ratio of 1.00 in both models where we applied a shared mean or a mixture prior.

CONCLUSION

Our mixtures analyses do not suggest an independent relationship with ASD or intellectual disability with any of the 25 chemicals examined together in this mixtures analysis.

Adverse effects of hexaclorobenzene exposure in children and adolescents

BACKGROUND

Hexachlorobenzene (HCB: C₆Cl₆) is a persistent, bioaccumulative chemical formerly used worldwide in pesticide mixtures but also produced as a by-product in the chemical and metallurgical industry. Despite current international restrictions in the use and production of HCB, the majority of the general population still show detectable levels of HCB, which raises concerns on the potential health implications of the exposure.

OBJECTIVE

To compile and synthesize the available scientific evidence regarding the adverse effects of exposure to HCB in children and adolescents.

METHODS

A review of the literature focused on the adverse effects of HCB exposure in children. Eligible studies were systematically screened from searches in Medline, Scopus and Ebsco-host databases. A total of 62 studies were finally included.

RESULTS AND DISCUSSION

In our search we found evidences of potential health effects linked to HCB exposure at different levels (e.g. neurotoxic, nephrotoxic, immunotoxic, hepatotoxic and toxicogenomic), although the conclusions are still contradictory. Further prospective research is needed, considering the special vulnerability of children and adolescent population as well as the ubiquity of the exposure.

Gut microbiome: An intermediary to neurotoxicity

There is growing recognition that the gut microbiome is an important regulator for neurological functions. This review provides a summary on the role of gut microbiota in various neurological disorders including neurotoxicity induced by environmental stressors such as drugs, environmental contaminants, and dietary factors. We propose that the gut microbiome remotely senses and regulates CNS signaling through the following mechanisms: 1) intestinal bacteria-mediated biotransformation of neurotoxicants that alters the neuro-reactivity of the parent compounds; 2) altered production of neuro-reactive microbial metabolites following exposure to certain environmental stressors; 3) bi-directional communication within the gut-brain axis to alter the intestinal barrier integrity; and 4) regulation of mucosal immune function. Distinct microbial metabolites may enter systemic circulation and epigenetically reprogram the expression of host genes in the CNS, regulating neuroinflammation, cell survival, or cell death. We will also review the current tools for the study of the gut-brain axis and provide some suggestions to move this field forward in the future.

Neuroimaging signatures of brain plasticity in adults with prenatal exposure to polychlorinated biphenyls: Altered functional connectivity on functional MRI

Prenatal exposure to polychlorinated biphenyls (PCBs), persistent organic pollutants in food chains and environment, exerts negative effects on children's cognitive function. To study the long-term effects, we examined cognitive functions in the male children of women with substantial PCB exposure in Taiwan during 1978-1979 and investigated neural basis of cognitive function changes through structural magnetic resonance imaging (MRI) and functional MRI (fMRI), which included resting-state and task-activated fMRI with two paradigms: a 2-back task and a picture rotation task. Ten men aged 30.0 ± 3.7 years with prenatal exposure to PCBs and 11 unexposed controls aged 28.1 ± 3.1 years participated. Both groups had similar cognitive phenotypes and behavioral results. Structural MRI analysis results showed that the PCB group had increased cortical thickness over the right inferior parietal lobule. In the resting-state study, the PCB group showed alterations in the default mode network. During the tasks, the PCB group showed decreased task-induced deactivation signals in cognition-associated brain areas during the 2-back task but enhanced deactivations during the picture rotation task. This study demonstrated altered structural MRI as well as resting and task-related fMRI in men with prenatal PCB exposure, suggesting altered brain plasticity and compensatory neuropsychological performance.

A review of environmental and health effects of organochlorine pesticide residues in Africa

Organochlorine pesticides (OCPs) are generally categorized as chlorinated cyclodienes, chlorodiphenylethanes, chlorinated benzenes and cyclohexanes. The presence of OCP residues in foodstuffs, water, soil, sediments, blood serum and air has generated a surge of global interest. This is due to their severe environmental and health ill-effects. OCPs are characteristically described as persistent and bio-accumulating substances prone to long-range transportation. The aim of this present study is to assess the environmental and health risks associated with OCP residues. Published works on OCPs in surface water, sediments and fish samples were reviewed. Possible non-carcinogenic (Hazard Quotient, HQ and Hazard Index, HI) and carcinogenic (Cancer Risk, CR) health effects of OCPs were assessed in fish samples. High concentrations of OCP residues were determined in environmental samples from African countries. The non-carcinogenic health assessment of OCPs in most fish samples from Nigeria revealed HI values greater than 1.0 establishing their adverse effects. The CR data of OCPs in fish samples also showed values higher than the permissible standard of 1.0 × 10^-4 indicating possible development of cancer through fish consumption.

Sex-Dependent Effects of 2,2',3,5',6-Pentachlorobiphenyl on Dendritic Arborization of Primary Mouse Neurons

Early life exposures to environmental contaminants are implicated in the pathogenesis of many neurodevelopmental disorders (NDDs). These disorders often display sex biases, but whether environmental neurotoxicants act in a sex-dependent manner to modify neurodevelopment is largely unknown. Since altered dendritic morphology is associated with many NDDs, we tested the hypothesis that male and female primary mouse neurons are differentially susceptible to the dendrite-promoting activity of 2,2',3,5',6-pentachlorobiphenyl (PCB 95). Hippocampal and cortical neuron-glia co-cultures were exposed to vehicle (0.1% dimethylsulfoxide) or PCB 95 (100 fM-1 μM) from day in vitro 7-9. As determined by Sholl analysis, PCB 95-enhanced dendritic growth in female but not male hippocampal and cortical neurons. In contrast, both male and female neurons responded to bicuculline with increased dendritic complexity. Detailed morphometric analyses confirmed that PCB 95 effects on the number and length of primary and nonprimary dendrites varied depending on sex, brain region and PCB concentration, and that female neurons responded more consistently with increased dendritic growth and at lower concentrations of PCB 95 than their male counterparts. Exposure to PCB 95 did not alter cell viability or the ratio of neurons to glia in cultures of either sex. These results demonstrate that cultured female mouse hippocampal and cortical neurons are more sensitive than male neurons to the dendrite-promoting activity of PCB 95, and suggest that mechanisms underlying PCB 95-induced dendritic growth are sex-dependent. These data highlight the importance of sex in neuronal responses to environmental neurotoxicants.

Toxicokinetics of Chiral PCB 136 and Its Hydroxylated Metabolites in Mice with a Liver-Specific Deletion of Cytochrome P450 Reductase

Exposure to polychlorinated biphenyls (PCBs) has been implicated in adverse human health effects, including developmental neurotoxicity. Several neurotoxic PCBs are chiral and undergo atropisomeric enrichment in vivo due to atropselective metabolism by cytochrome P450 enzymes. Here we study how the liver-specific deletion of the cytochrome P450 reductase ( cpr) gene alters the toxicokinetics of 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136) in mice. Male and female mice with a liver-specific deletion of cpr (KO) and congenic wild-type (WT) mice were exposed to a single oral dose of racemic PCB 136 (6.63 mg/kg). Levels and chiral signatures of PCB 136 and its hydroxylated metabolites were determined 1-48 h after PCB exposure in whole blood. Blood levels of PCB 136 were typically higher in M-WT compared to F-WT mice. At the later time points, F-KO mice had significantly higher PCB 136 levels than F-WT mice. 2,2',3',4,6,6'-Hexachlorobiphenyl-3-ol (3-150), 2,2',3,3',6,6'-hexachlorobiphenyl-4-ol (4-136), 2,2',3,3',6,6'-hexachlorobiphenyl-5-ol (5-136), and 4,5-dihydroxy-2,2',3,3',6,6'-hexachlorobiphenyl (4,5-136) were detected in blood, with 5-136 and 4-136 being major metabolites. At later time points, the sum of HO-PCB (∑HO-PCB) levels exceeded PCB 136 levels in the blood; however, higher ∑HO-PCB than PCB 136 levels were observed later in KO than WT mice. PCB 136 and its major metabolites displayed atropisomeric enrichment in a manner that depended on the time point, sex, and genotype. Toxicokinetic analysis revealed sex and genotype-dependent differences in toxicokinetic parameters for PCB 136 atropisomers and its metabolites. The results suggest that mice with a liver-specific deletion of the cpr gene can potentially be used to assess how an altered metabolism of neurotoxic PCB congeners affects neurotoxic outcomes following exposure of the offspring to PCBs via the maternal diet.

Assessing the Relation between Plasma PCB Concentrations and Elevated Autistic Behaviours using Bayesian Predictive Odds Ratios

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by impaired social communication and repetitive or stereotypic behaviours. In utero exposure to environmental chemicals, such as polychlorinated biphenyls (PCBs), may play a role in the etiology of ASD. We examined the relation between plasma PCB concentrations measured during pregnancy and autistic behaviours in a subset of children aged 3⁻4 years old in the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, a pregnancy and birth cohort of 546 mother-infant pairs from Canada (enrolled: 2008⁻2011). We quantified the concentrations of 6 PCB congeners that were detected in >40% of plasma samples collected during the 1st trimester. At age 3⁻4 years, caregivers completed the Social Responsiveness Scale-2 (SRS), a valid and reliable measure of children's reciprocal social and repetitive behaviours and restricted interests. We examined SRS scores as both a continuous and binary outcome, and we calculated Bayesian predictive odds ratios for more autistic behaviours based on a latent variable model for SRS scores >60. We found no evidence of an association between plasma PCB concentrations and autistic behaviour. However, we found small and imprecise increases in the mean SRS score and odds of more autistic behaviour for the highest category of plasma PCB concentrations compared with the lowest category; for instance, an average increase of 1.4 (95%PCI: -0.4, 3.2) in the mean SRS (exposure contrast highest versus lowest PCB category) for PCB138 translated to an odds ratio of 1.8 (95%PCI: 1.0, 2.9). Our findings illustrate the importance of measuring associations between PCBs and autistic behaviour on both continuous and binary scales.

Association of Maternal Insecticide Levels With Autism in Offspring From a National Birth Cohort

OBJECTIVE

Autism is a complex neurodevelopmental disorder with a largely unknown etiology. To date, few studies have investigated prenatal exposure to toxins and risk of autism by using maternal biomarkers of exposure. Persistent organic pollutants are lipophilic halogenated organic compounds and include the insecticide dichlorodiphenyltrichloroethane (DDT), as well as its metabolite p,p'-dichlorodiphenyl dichloroethylene (p,p'-DDE), and polychlorinated biphenyls (PCBs). The objective of this study was to test whether elevated maternal levels of persistent organic pollutants are associated with autism among offspring.

METHOD

The investigation was derived from the Finnish Prenatal Study of Autism, a national birth cohort study based on a nested case-control design. Cases of autism among children born between 1987 and 2005 were ascertained by national registry linkages. In cases of childhood autism and matched control subjects (778 matched case-control pairs), maternal serum specimens from early pregnancy were assayed for levels of p,p'-DDE and total levels of PCBs.

RESULTS

The odds of autism among offspring were significantly increased with maternal p,p'-DDE levels that were in the highest 75th percentile, with adjustment for maternal age, parity, and history of psychiatric disorders (odds ratio=1.32, 95% CI=1.02, 1.71). The odds of autism with intellectual disability were increased by greater than twofold with maternal p,p'-DDE levels above this threshold (odds ratio=2.21, 95% CI=1.32, 3.69). There was no association between total levels of maternal PCBs and autism.

CONCLUSIONS

These findings provide the first biomarker-based evidence that maternal exposure to insecticides is associated with autism among offspring. Although further research is necessary to replicate this finding, this study has implications for the prevention of autism and may provide a better understanding of its pathogenesis.

PCB 95 promotes dendritic growth in primary rat hippocampal neurons via mTOR-dependent mechanisms

Polychlorinated biphenyls (PCBs), and in particular non-dioxin-like (NDL) congeners, continue to pose a significant risk to the developing nervous system. PCB 95, a prevalent NDL congener in the human chemosphere, promotes dendritic growth in rodent primary neurons by activating calcium-dependent transcriptional mechanisms that normally function to link activity to dendritic growth. Activity-dependent dendritic growth is also mediated by calcium-dependent translational mechanisms involving mechanistic target of rapamycin (mTOR), suggesting that the dendrite-promoting activity of PCB 95 may also involve mTOR signaling. Here, we test this hypothesis using primary neuron-glia co-cultures derived from the hippocampi of postnatal day 0 Sprague Dawley rats. PCB 95 (1 nM) activated mTOR in hippocampal cultures as evidenced by increased phosphorylation of mTOR at ser2448. Pharmacologic inhibition of mTOR signaling using rapamycin (20 nM), FK506 (5 nM), or 4EGI-1 (1 µM), and siRNA knockdown of mTOR, or the mTOR complex binding proteins, raptor or rictor, blocked PCB 95-induced dendritic growth. These data identify mTOR activation as a novel molecular mechanism contributing to the effects of PCB 95 on dendritic arborization. In light of clinical data linking gain-of-function mutations in mTOR signaling to neurodevelopmental disorders, our findings suggest that mTOR signaling may represent a convergence point for gene by environment interactions that confer risk for adverse neurodevelopmental outcomes.

Polychlorinated biphenyls (PCBs) as sentinels for the elucidation of Arctic environmental change processes: a comprehensive review combined with ArcRisk project results

Polychlorinated biphenyls (PCBs) can be used as chemical sentinels for the assessment of anthropogenic influences on Arctic environmental change. We present an overview of studies on PCBs in the Arctic and combine these with the findings from ArcRisk-a major European Union-funded project aimed at examining the effects of climate change on the transport of contaminants to and their behaviour of in the Arctic-to provide a case study on the behaviour and impact of PCBs over time in the Arctic. PCBs in the Arctic have shown declining trends in the environment over the last few decades. Atmospheric long-range transport from secondary and primary sources is the major input of PCBs to the Arctic region. Modelling of the atmospheric PCB composition and behaviour showed some increases in environmental concentrations in a warmer Arctic, but the general decline in PCB levels is still the most prominent feature. 'Within-Arctic' processing of PCBs will be affected by climate change-related processes such as changing wet deposition. These in turn will influence biological exposure and uptake of PCBs. The pan-Arctic rivers draining large Arctic/sub-Arctic catchments provide a significant source of PCBs to the Arctic Ocean, although changes in hydrology/sediment transport combined with a changing marine environment remain areas of uncertainty with regard to PCB fate. Indirect effects of climate change on human exposure, such as a changing diet will influence and possibly reduce PCB exposure for indigenous peoples. Body burdens of PCBs have declined since the 1980s and are predicted to decline further.

Editor's Highlight: Congener-Specific Disposition of Chiral Polychlorinated Biphenyls in Lactating Mice and Their Offspring: Implications for PCB Developmental Neurotoxicity

Chiral polychlorinated biphenyl (PCB) congeners have been implicated by laboratory and epidemiological studies in PCB developmental neurotoxicity. These congeners are metabolized by cytochrome P450 (P450) enzymes to potentially neurotoxic hydroxylated metabolites (OH-PCBs). The present study explores the enantioselective disposition and toxicity of 2 environmentally relevant, neurotoxic PCB congeners and their OH-PCB metabolites in lactating mice and their offspring following dietary exposure of the dam. Female C57BL/6N mice (8-weeks old) were fed daily, beginning 2 weeks prior to conception and continuing throughout gestation and lactation, with 3.1 µmol/kg bw/d of racemic 2,2',3,5',6-pentachlorobiphenyl (PCB 95) or 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136) in peanut butter; controls received vehicle (peanut oil) in peanut butter. PCB 95 levels were higher than PCB 136 levels in both dams and pups, consistent with the more rapid metabolism of PCB 136 compared with PCB 95. In pups and dams, both congeners were enriched for the enantiomer eluting second on enantioselective gas chromatography columns. OH-PCB profiles in lactating mice and their offspring were complex and varied according to congener, tissue and age. Developmental exposure to PCB 95 versus PCB 136 differentially affected the expression of P450 enzymes as well as neural plasticity (arc and ppp1r9b) and thyroid hormone-responsive genes (nrgn and mbp). The results suggest that the enantioselective metabolism of PCBs to OH-PCBs may influence neurotoxic outcomes following developmental exposures, a hypothesis that warrants further investigation.

Transcriptomic profiling of mTOR and ryanodine receptor signaling molecules in developing zebrafish in the absence and presence of PCB 95

The mechanistic target of rapamycin (mTOR) and ryanodine receptor (RyR) signaling pathways regulate fundamental processes of neurodevelopment, and genetic mutations within these pathways have been linked to neurodevelopmental disorders. While previous studies have established that these signaling molecules are expressed in developing zebrafish, a detailed characterization of the ontogenetic profile of these signaling molecules is lacking. Thus, we evaluated the spatiotemporal expression of key transcripts in mTOR and RyR signaling pathways in wildtype zebrafish at 24, 72 and 120 hours post fertilization (hpf). We further determined whether transcriptional profiles of a subset of genes in both pathways were altered by exposure to PCB 95 (2,2′,3,5′,6-pentachlorobiphenyl), a pervasive environmental contaminant known to cause developmental neurotoxicity in mammalian systems via RyR-dependent mechanisms. Quantitative PCR revealed that transcription generally increased across development. Genes in the signaling pathway upstream of the mTORC1 complex, and the RyR-paralogs, ryr2a and ryr3, were robustly upregulated, and in situ hybridization of ryr3 coincided with a transcriptional shift from muscle to neuronal tissue after 24 hpf. Static waterborne exposure to PCB 95 beginning at 6 hpf significantly altered transcription of genes in both pathways. These changes were concentration- and time-dependent, and included downregulation of rptor, a member of the mTORC1 complex, at both 72 and 120 hpf, and increased transcript levels of the RyR paralog ryr2b and downstream target of RyR signaling, Wingless-type 2ba (wnt2ba) at 72 hpf. The detailed transcriptomic profiling of key genes within these two signaling pathways provides a baseline for identifying other environmental factors that modify normal spatiotemporal expression patterns of mTOR and RyR signaling pathways in the developing zebrafish, as illustrated here for PCB 95.

Pesticides

There is growing evidence about the influence of chemical exposures on specific molecular systems and mechanisms involved in cognitive and mental function. Evidence is also emerging about the negative impact of these chemical exposures on mental health, including depression, suicide, and other risks. Despite the growing appreciation of these factors, however, little attention has been paid to the ethical and social implications of their interactions. Drawing on recent work that argues for an environmental neuroethics approach that explicitly brings together ethics, environment, and conditions of the central nervous system, this article focuses on these critical issues for pesticides specifically.

Polychlorinated biphenyl and polybrominated diphenyl ether profiles in serum from cattle, sheep, and goats across California

It has been previously been shown by our lab and others that persistent organic pollutants, such as polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), are contaminants in milk produced for human consumption. To further this research we determined the concentration of 21 PCB and 14 PBDE congeners in livestock serum, mainly bovine, across California. Congeners were extracted from serum using solid phase extraction (SPE), cleaned up by silica cartridge and quantified using gas chromatography-triple quadruple mass spectrometry. We detected significant differences among species and the production class of cattle (beef or dairy). The sum of all 21 PCB congeners (ΣPCBs) in caprine and ovine sera had a mean value of 9.26 and 9.13 ng/mL, respectively, compared to 3.98 ng/mL in bovine sera. The mean value for the sum of all 14 PBDE congeners (ΣPBDEs) in caprine and ovine sera was 2.82 and 2.39 ng/mL, respectively, compared to 0.91 ng/mL in bovine sera. Mean ΣPCBs in dairy cattle was 5.92 ng/mL compared to 2.70 ng/mL in beef cattle. Mean ΣPBDEs in dairy cattle was 1.33 ng/mL compared to 0.70 ng/mL in beef cattle. There were no regional differences in the ΣPCBs or ΣPBDEs in cattle distributed across California. These results highlight the fact that livestock are still being exposed to these pollutants yet little is known about where this exposure may be coming from.

Detection of 3,3'-Dichlorobiphenyl in Human Maternal Plasma and Its Effects on Axonal and Dendritic Growth in Primary Rat Neurons

3,3'-Dichlorobiphenyl (PCB 11), a byproduct of pigment production, is increasingly detected in environmental samples. While more highly chlorinated PCB congeners are known developmental neurotoxicants, nothing is known about the potential developmental neurotoxicity of PCB 11. To address this critical data gap, we measured PCB 11 levels in human maternal plasma and quantified the effects of PCB 11 and its major metabolites on morphometric parameters of neuronal connectivity in cultured primary neurons. Mass spectrometry analyses of plasma from 241 pregnant women enrolled in the MARBLES study (University of California, Davis) detected PCB 11 in all samples at concentrations ranging from 0.005 to 1.717 ng/ml. Morphometric analyses of primary neuron-glia co-cultures dissociated from the neocortices or hippocampi of neonatal Sprague Dawley rats exposed to vehicle or concentrations ranging from 1 attamolar (aM) to 1 micromolar (µM) of PCB 11, OH-PCB 11, or PCB 11 sulfate indicated that PCB 11 and both metabolites significantly increased axonal and dendritic growth in cortical and hippocampal pyramidal neurons. PCB 11 significantly altered neuronal morphogenesis at concentrations as low as 1 femtomolar (fM), which is ∼0.22 ng/ml. These data suggest the potential for the developing human brain to be exposed to PCB 11, and demonstrate that environmentally relevant levels of PCB 11 alter axonal and dendritic growth in neuronal cell types critically involved in cognitive and higher-order behaviors. These findings identify PCB 11 as a potential environmental risk factor for adverse neurodevelopmental outcomes in humans.

Pesticides, polychlorinated biphenyls and polycyclic aromatic hydrocarbons in cerebrospinal fluid of amyotrophic lateral sclerosis patients: a case-control study

Neurotoxic chemicals including several pesticides have been suggested to play a role in the etiology of amyotrophic lateral sclerosis (ALS). We investigated the relation between organochlorine pesticides and their metabolites (OCPs), polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in the etiology of sporadic ALS, determining for the first time their levels in cerebrospinal fluid as indicator of antecedent exposure. We recruited 38 ALS patients and 38 controls referred to an Italian clinical center for ALS care, who underwent a lumbar puncture for diagnostic purposes between 1994-2013, and had 1mL of cerebrospinal fluid available for the determination of OCPs, PCBs and PAHs. Many chemicals were undetectable in both case and control CSF samples, and we found little evidence of any increased disease risk according to higher levels of exposure. Among males >60 years, we found a slight but statistically very unstable increased ALS risk with higher levels of the congener PCB 28 and the OCP metabolite p,p'-DDE. Overall, these results do not suggest an involvement of the neurotoxic chemicals investigated in this study in disease etiology, although small numbers limited the precision of our results.

Independent Maternal and Fetal Genetic Effects on Midgestational Circulating Levels of Environmental Pollutants

Maternal exposure to environmental pollutants could affect fetal brain development and increase autism spectrum disorder (ASD) risk in conjunction with differential genetic susceptibility. Organohalogen congeners measured in maternal midpregnancy blood samples have recently shown significant, but negative associations with offspring ASD outcome. We report the first large-scale maternal and fetal genetic study of the midpregnancy serum levels of a set of 21 organohalogens in a subset of 790 genotyped women and 764 children collected in California by the Early Markers for Autism (EMA) Project. Levels of PCB (polychlorinated biphenyl) and PBDE (polybrominated diphenyl ether) congeners showed high maternal and fetal estimated SNP-based heritability (h²_g) accounting for 39–99% of the total variance. Genome-wide association analyses identified significant maternal loci for p,p′-DDE (P = 7.8 × 10⁻¹¹) in the CYP2B6 gene and for BDE-28 (P = 3.2 × 10⁻⁸) near the SH3GL2 gene, both involved in xenobiotic and lipid metabolism. Fetal genetic loci contributed to the levels of BDE-100 (P = 4.6 × 10⁻⁸) and PCB187 (P = 2.8 × 10⁻⁸), near the potential metabolic genes LOXHD1 and PTPRD, previously implicated in neurodevelopment. Negative associations were observed for BDE-100, BDE153, and the sum of PBDEs with ASD, partly explained by genome-wide additive genetic effects that predicted PBDE levels. Our results support genetic control of midgestational biomarkers for environmental exposures by nonoverlapping maternal and fetal genetic determinants, suggesting that future studies of environmental risk factors should take genetic variation into consideration. The independent influence of fetal genetics supports previous hypotheses that fetal genotypes expressed in placenta can influence maternal physiology and the transplacental transfer of organohalogens.

Polychlorinated Biphenyl and Organochlorine Pesticide Concentrations in Maternal Mid-Pregnancy Serum Samples: Association with Autism Spectrum Disorder and Intellectual Disability

BACKGROUND

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) are neurodevelopmental toxicants, but few studies have examined associations with autism spectrum disorder (ASD).

OBJECTIVES

We aimed to determine whether prenatal exposure to PCBs and OCPs influences offspring risk of ASD and intellectual disability without autism (ID).

METHODS

We conducted a population-based case-control study among Southern California births, including children with ASD (n = 545) meeting Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV-TR) criteria and ID (n = 181), as well as general population (GP) controls (n = 418). Concentrations of 11 PCB congeners and 2 OCPs measured in banked second-trimester serum samples were compared between the diagnostic groups. Logistic regression was used to calculate crude and adjusted odds ratios (AOR) for associations with ASD, and separately for ID, compared with GP controls, by quartiles of analyte concentrations in primary analyses.

RESULTS

Geometric mean levels of several PCB congeners were higher in the ASD group than in the ID and GP groups. ASD risk was elevated for a number of PCB congeners, particularly for the highest vs. lowest quartile of PCB138/158 (AOR = 1.79; 95% CI: 1.10, 2.71) and PCB153 (AOR = 1.82; 95% CI: 1.10, 3.02), and for highest deciles of other congeners in secondary analyses. PCB138/158 was also associated with increased ID (AOR = 2.41; 95% CI: 1.18, 4.91), though no trend was suggested. OCPs were not associated with increased risk of ASD in primary analyses, whereas nonmonotonic increases in risk of ID were found with p,p´-DDE.

CONCLUSIONS

Our results suggest higher levels of some organochlorine compounds during pregnancy are associated with ASD and ID. Citation: Lyall K, Croen LA, Sjödin A, Yoshida CK, Zerbo O, Kharrazi M, Windham GC. 2017. Polychlorinated biphenyl and organochlorine pesticide concentrations in maternal mid-pregnancy serum samples: association with autism spectrum disorder and intellectual disability. Environ Health Perspect 125:474-480; http://dx.doi.org/10.1289/EHP277.

Review of reviews on exposures to synthetic organic chemicals and children's neurodevelopment: Methodological and interpretation challenges

Environmental epidemiology data are becoming increasingly important in public health decision making, which commonly incorporates a systematic review of multiple studies. This review addresses two fundamental questions: What is the quality of available reviews on associations between exposure to synthetic organic chemicals and neurodevelopmental outcomes? What is the value (e.g., quality and consistency) of the underlying literature? Published reviews on associations between synthetic organic environmental chemical exposures and neurodevelopmental outcomes in children were systematically evaluated. Seventy-four relevant reviews were identified, and these were evaluated with respect to four methodological characteristics: (1) systematic inclusion/exclusion criteria and reproducible methods for search and retrieval of studies; (2) structured evaluation of underlying data quality; (3) systematic assessment of consistency across specific exposure-outcome associations; and (4) evaluation of reporting/publication bias. None of the 74 reviews fully met the criteria for all four methodological characteristics. Only four reviews met two criteria, and six reviews fulfilled only one criterion. Perhaps more importantly, the higher quality reviews were not able to meet all of the criteria owing to the shortcomings of underlying studies, which lacked comparability in terms of specific research question of interest, overall design, exposure assessment, outcome ascertainment, and analytic methods. Thus, even the most thoughtful and rigorous review may be of limited value if the underlying literature includes investigations that address different hypotheses and are beset by methodological inconsistencies and limitations. Issues identified in this review of reviews illustrate considerable challenges that are facing assessments of epidemiological evidence.

Prenatal exposure to persistent organic pollutants in association with offspring neuropsychological development at 4years of age: The Rhea mother-child cohort, Crete, Greece

BACKGROUND

Persistent Organic Pollutants (POPs) are highly-resistant compounds to environmental degradation and due to fat solubility they bioaccumulate through the food chain. As they cross the placenta, in utero exposure to POPs could disrupt child neurodevelopment as they are considered to be neurotoxic.

AIMS

We examined whether in utero exposure to levels of different POPs is associated with offspring cognitive and behavioral outcomes at 4years of age in a mother-child cohort in Crete, Greece (Rhea study).

METHODS

We included 689 mother-child pairs. Concentrations of several polychlorinated biphenyls (PCBs) and other organochlorine compounds (dichlorodiphenyl dichloroethene [DDE], hexachlorobenzene [HCB]) were determined in maternal serum collected in the first trimester of pregnancy by triple quadrupole mass spectrometry. Neurodevelopment at 4years was assessed by means of the McCarthy Scales of Children's Abilities. Behavioral difficulties were assessed by Strengths and Difficulties Questionnaire and Attention Deficit Hyperactivity Disorder Test. Linear regression analyses were used to estimate the associations between the exposures and outcomes of interest after adjustment for potential confounders.

RESULTS

Children with "high" HCB concentrations (≥90th percentile) in maternal serum, demonstrated decreased scores in perceptual performance (adjusted β=-6.07; 95% CI: -10.17, -1.97), general cognitive (adjusted β=-4.97; 95% CI: -8.99, -0.96), executive function (adjusted β=-6.24; 95% CI: -10.36, -2.11) and working memory (adjusted β=-4.71; 95% CI: -9.05, -0.36) scales at 4years of age. High exposure to PCBs (≥90th percentile) during pregnancy was associated with a 4.62 points reduction in working memory score at 4years of age (95% CI: -9.10, -0.14). Prenatal exposure to DDE, HCB and PCBs was not associated with child behavioral difficulties.

CONCLUSIONS

The findings suggest that prenatal exposure to HCB and PCBs may contribute to reduced cognitive development at preschool age. Our results raise the possibility that exposure to HCB may play a more important role in child cognition than previously considered.

DNA methylation: a mechanism linking environmental chemical exposures to risk of autism spectrum disorders?

There is now compelling evidence that gene by environment interactions are important in the etiology of autism spectrum disorders (ASDs). However, the mechanisms by which environmental factors interact with genetic susceptibilities to confer individual risk for ASD remain a significant knowledge gap in the field. The epigenome, and in particular DNA methylation, is a critical gene expression regulatory mechanism in normal and pathogenic brain development. DNA methylation can be influenced by environmental factors such as diet, hormones, stress, drugs, or exposure to environmental chemicals, suggesting that environmental factors may contribute to adverse neurodevelopmental outcomes of relevance to ASD via effects on DNA methylation in the developing brain. In this review, we describe epidemiological and experimental evidence implicating altered DNA methylation as a potential mechanism by which environmental chemicals confer risk for ASD, using polychlorinated biphenyls (PCBs), lead, and bisphenol A (BPA) as examples. Understanding how environmental chemical exposures influence DNA methylation and how these epigenetic changes modulate the risk and/or severity of ASD will not only provide mechanistic insight regarding gene-environment interactions of relevance to ASD but may also suggest potential intervention strategies for these and potentially other neurodevelopmental disorders.

Chiral polychlorinated biphenyls: absorption, metabolism and excretion--a review

Seventy eight out of the 209 possible polychlorinated biphenyl (PCB) congeners are chiral, 19 of which exist under ambient conditions as stable rotational isomers that are non-superimposable mirror images of each other. These congeners (C-PCBs) represent up to 6 % by weight of technical PCB mixtures and undergo considerable atropisomeric enrichment in wildlife, laboratory animals, and humans. The objective of this review is to summarize our current knowledge of the processes involved in the absorption, metabolism, and excretion of C-PCBs and their metabolites in laboratory animals and humans. C-PCBs are absorbed and excreted by passive diffusion, a process that, like other physicochemical processes, is inherently not atropselective. In mammals, metabolism by cytochrome P450 (P450) enzymes represents a major route of elimination for many C-PCBs. In vitro studies demonstrate that C-PCBs with a 2,3,6-trichlorosubstitution pattern in one phenyl ring are readily oxidized to hydroxylated PCB metabolites (HO-PCBs) by P450 enzymes, such as rat CYP2B1, human CYP2B6, and dog CYP2B11. The oxidation of C-PCBs is atropselective, thus resulting in a species- and congener-dependent atropisomeric enrichment of C-PCBs and their metabolites. This atropisomeric enrichment of C-PCBs and their metabolites likely plays a poorly understood role in the atropselective toxicity of C-PCBs and, therefore, warrants further investigation.

Decrease in prosaposin in spermatozoon is associated with polychlorinated biphenyl exposure

Polychlorinated biphenyls (PCBs) are a class of ubiquitous persistent organic pollutants and they have been associated with declining male fertility. In the present study, we aimed to determine the responsiveness of prosaposin (Psap) expression to PCB exposure. Male C57 mice were exposed to PCB mixture (Aroclor 1254) of environmental related doses by oral gavage. After exposure for 50 days, the expression of Psap was significantly decreased by PCB exposure in epididymides and epydidymal spermatozoa, but not in testis. The Psap abundance in sperm was decreased in a dose-dependent manner. Benchmark dose modeling revealed the 95% lower confidence limit on the benchmark dose (BMDL) and Benchmark Dose (BMD) for Psap reduction were 1.25 and 8.89 μg/kg Aroclor 1254, and for sperm motility reduction were 11.85 and 61.9 μg/kg Aroclor 1254. The depressed Psap level also showed a significant correlation (P<0.01, r=-0.531) with PCB accumulation in liver. In men with detectable PCB exposure in semen, Psap expression in sperm was significantly decreased whereas the semen parameters were unaffected. Linear regression showed that a negative association between total PCB level in seminal plasma and Psap level in ejaculated spermatozoa (P<0.05, r=-0.396). In conclusion, our data suggested that the abundance of Psap in sperm sample may be a sensitive endpoint to predict PCB exposure.

Persistent organic pollutants measured in maternal serum and offspring neurodevelopmental outcomes--a prospective study with long-term follow-up

Fetal exposure to persistent organic pollutants (POPs) has been linked to adverse neurodevelopment, but few studies have had follow-up beyond childhood. The purpose of this study was to examine the association of maternal serum concentrations of two perfluoroalkyl acids (perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS)), polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethylene (p,p'-DDE) and hexachlorobenzene (HCB) with offspring behavioural and affective disorders and scholastic achievement in a prebirth cohort study with 20 years of follow up. Between 1988 and 1989 pregnant women (n=965) were recruited for the prebirth Danish Fetal Origins 1988 (DaFO88) Cohort in Aarhus, Denmark. Perfluoroalkyl acids, PCBs, p,p'-DDE, and HCB were quantified in serum from week 30 of gestation (n=876 for perfluoroalkyl acids/872 for PCBs, p,p'-DDE, HCB). Offspring were followed up through national registries until 2011. We evaluated associations between maternal serum concentrations of these POPs and offspring neurodevelopmental outcomes, defined as: first admission diagnosis or prescription of medication until age >20 for (1) ADHD; (2) depression; and (3) scholastic achievement defined as mean grade on a standardized written examination given in the 9th grade (final exams of compulsory school in Denmark). Maternal concentrations of organochlorine substances and perfluoroalkyl acids were higher than present day levels. During the follow-up period there were 27 (3.1%) cases of ADHD and 104 (11.9%) cases of depression; the mean scholastic achievement was 6.7 (SD 2.3). Overall we found no association for maternal levels of any of the measured pollutants with offspring behavioural and affective disorders or with scholastic achievement. Our analyses based on biomarkers from a cohort of over 800 pregnant women with long-term close to complete follow-up through national registries showed little evidence of a programming effect of PFOA, PFOS, PCBs, p,p'-DDE, and HCB in relation to clinically and functionally relevant offspring neurodevelopmental outcomes.

Polymorphism in Cytochrome P450 2D6, Glutathione S-Transferases Pi 1 Genes, and Organochlorine Pesticides in Alzheimer Disease: A Case-Control Study in North Indian Population

OBJECTIVES

It has been assumed that the association between Alzheimer disease (AD) and pesticides may be stronger among genetically susceptible individuals. The aim of the study was to examine the genetic polymorphism in cytochrome P450 2D6 (CYP2D6) and glutathione S-transferases pi 1 (GSTP1) with respect to organochlorine pesticides (OCPs) and metals in AD.

METHODS

This study included 100 patients with AD and 100 age-matched controls. The genetic polymorphisms were analyzed by restriction fragment length polymorphism. The OCPs and serum metal levels were determined using gas chromatography and an autoanalyzer, respectively.

RESULTS

We found a statistically significant association between AD and high levels of β-hexachlorocyclohexane (β-HCH; odds ratio [OR] = 2.064, 95% confidence intervals [95% CIs] = 1.373-3.102, dieldrin [OR = 2.086, 95% CI = 1.224-3.555], and copper [OR = 1.038, 95% CI = 1.012-1.064). The significant low level of magnesium (OR = 0.151, 95% CI = 0.047-0.489) even appears to have a protective role against AD. The GSTP1*B (P = .009) and GSTP1*C (P = .011) allelic variants were associated with increase in AD risk.

CONCLUSION

This study demonstrates that the GSTP1*B and *C allelic variants may be considered a candidate gene for AD. It can be suggested that although CYP2D6*4 polymorphism is not a risk of AD, the CYP2D6*4 and GSTP1 polymorphism may interact with β-HCH, dieldrin, and copper to influence the risk of AD.

Potential effects of environmental chemical contamination in congenital heart disease

There is compelling evidence that prenatal exposures to environmental xenobiotics adversely affect human development and childhood. Among all birth defects, congenital heart disease (CHD) is the most prevalent of all congenital malformations and remains the leading cause of death. It has been estimated that in most cases the causes of heart defects remain unknown, while a growing number of studies have indicated the potential role of environmental agents as risk factors in CHD occurrence. In particular, maternal exposure to chemicals during the first trimester of pregnancy represents the most critical window of exposure for CHD. Specific classes of xenobiotics (e.g. organochlorine pesticides, organic solvents, air pollutants) have been identified as potential risk factors for CHD. Nonetheless, the knowledge gained is currently still incomplete as a consequence of the frequent heterogeneity of the methods applied and the difficulty in estimating the net effect of environmental pollution on the pregnant mother. The presence of multiple sources of pollution, both indoor and outdoor, together with individual lifestyle factors, may represent a further confounding element for association with the disease. A future new approach for research should probably focus on individual measurements of professional, domestic, and urban exposure to physical and chemical pollutants in order to accurately retrace the environmental exposure of parents of affected offspring during the pre-conceptional and pregnancy periods.

The environmental neurotoxicant PCB 95 promotes synaptogenesis via ryanodine receptor-dependent miR132 upregulation

Non-dioxin-like (NDL) polychlorinated biphenyls (PCBs) are widespread environmental contaminants linked to neuropsychological dysfunction in children. NDL PCBs increase spontaneous Ca(2+) oscillations in neurons by stabilizing ryanodine receptor (RyR) calcium release channels in the open configuration, which results in CREB-dependent dendritic outgrowth. In this study, we address the question of whether activation of CREB by NDL PCBs also triggers dendritic spine formation. Nanomolar concentrations of PCB 95, a NDL congener with potent RyR activity, significantly increased spine density and the frequency of miniature EPSCs in primary dissociated rat hippocampal cultures coincident with upregulation of miR132. Inhibition of RyR, CREB, or miR132 as well as expression of a mutant p250GAP cDNA construct that is not suppressed by miR132 blocked PCB 95 effects on spines and miniature EPSCs. PCB 95 also induced spine formation via RyR- and miR132-dependent mechanisms in hippocampal slice cultures. These data demonstrate a novel mechanism of PCB developmental neurotoxicity whereby RyR sensitization modulates spine formation and synaptogenesis via CREB-mediated miR132 upregulation, which in turn suppresses the translation of p250GAP, a negative regulator of synaptogenesis. In light of recent evidence implicating miR132 dysregulation in Rett syndrome and schizophrenia, these findings identify NDL PCBs as potential environmental risk factors for neurodevelopmental disorders.