Polychlorinated biphenyls as hormonally active structural analogues

Theoretical Studies on the Quantitative Structure-Toxicity Relationship of Polychlorinated Biphenyl Congeners Reveal High Affinity Binding to Multiple Human Nuclear Receptors

Polychlorinated biphenyls (PCBs) are organic chemicals consisting of a biphenyl structure substituted with one to ten chlorine atoms, with 209 congeners depending on the number and position of the chlorine atoms. PCBs are widely known to be endocrine-disrupting chemicals (EDCs) and have been found to be involved in several diseases/disorders. This study takes various molecular descriptors of these PCBs (e.g., molecular weight) and toxicity endpoints as molecular activities, investigating the possibility of correlations via the quantitative structure-toxicity relationship (QSTR). This study then focuses on molecular docking and dynamics to investigate the docking behavior of the strongest-binding PCBs to nuclear receptors and compares these to the docking behavior of their natural ligands. Nuclear receptors are a family of transcription factors activated by steroid hormones, and they have been investigated to consider the impact of PCBs on humans in this context. It has been observed that the docking affinity of PCBs is comparable to that of the natural ligands, but they are inferior in terms of stability and interacting forces, as shown by the RMSD and total energy values. However, it is noted that most nuclear receptors respond to PCBs similarly to how they respond to their natural ligands-as shown in the RMSF plots-the most similar of which are seen in the ER, THR-β, and RAR-α. However, this study is performed purely in silico and will need experimental verification for validation.

Endocrine disruptors and endometriosis

Endometriosis is a hormone-dependent inflammatory gynecological disease of reproductive-age women. It is clinically and pathologically characterized by the presence of functional endometrium as heterogeneous lesions outside the uterine cavity. The two major symptoms are chronic pelvic pain and infertility, which profoundly affect women's reproductive health and quality of life. This significant individual and public health concerns underscore the importance of understanding the pathogenesis of endometriosis. The environmental endocrine-disrupting chemicals (EDCs) are exogenous agents that interfere with the synthesis, secretion, transport, signaling, or metabolism of hormones responsible for homeostasis, reproduction, and developmental processes. Endometriosis has been potentially linked to exposure to EDCs. In this review, based on the robust literature search, we have selected four endocrine disruptors (i) polychlorinated biphenyls (PCB)s (ii) dioxins (TCDD) (iii) bisphenol A (BPA) and its analogs and (iv) phthalates to elucidate their critical role in the etiopathogenesis of endometriosis. The epidemiological and experimental data discussed in this review indicate that these four EDCs activate multiple intracellular signaling pathways associated with proinflammation, estrogen, progesterone, prostaglandins, cell survival, apoptosis, migration, invasion, and growth of endometriosis. The available information strongly indicates that environmental exposure to EDCs such as PCBs, dioxins, BPA, and phthalates individually or collectively contribute to the pathophysiology of endometriosis. Further understanding of the molecular mechanisms of how these EDCs establish endometriosis and therapeutic strategies to mitigate the effects of these EDCs in the pathogenesis of endometriosis are timely needed. Moreover, understanding the interactive roles of these EDCs in the pathogenesis of endometriosis will help regulate the exposure to these EDCs in reproductive age women.

Dietary Exposure to Polychlorinated Biphenyls and Dioxins and Its Relationship to Telomere Length in Subjects Older Than 55 Years from the SUN Project

Exposure to persistent organic pollutants (POPs) may influence telomere length (TL), which is considered as a marker of biological age associated with the risk of chronic disease. We hypothesized that dietary exposure to polychlorinated biphenyls (PCBs) and dioxins could affect TL. Our aim was to evaluate the association of dietary exposure to PCBs and dioxins with TL. In this cross-sectional study of 886 subjects older than 55 y (mean age: 67.7; standard deviation (SD): 6.1; 27% women) from the “Seguimiento Universidad de Navarra” (SUN) project. TL was determined by real-time quantitative polymerase chain reaction and dietary PCBs and dioxins exposure was collected using a validated 136-item Food Frequency Questionnaire. Multivariable linear regression models were used to control for potential confounding factors. Shorter TL was associated with dietary total PCBs (SD of T/S ratio/(ng/day) = −0.30 × 10⁻⁷; 95% CI, −0.55 × 10⁻⁷ to −0.06 × 10⁻⁷), dioxin-like PCBs (DL-PCBs) (SD of T/S ratio/(pg WHO TEQ (Toxic Equivalents)/day) = −6.17 × 10⁻⁷; 95% CI, −11.30 × 10⁻⁷ to −1.03 × 10⁻⁷), and total TEQ exposure (SD of T/S ratio/(pg WHO TEQ/day) = −5.02 × 10⁻⁷; 95% CI, −9.44 × 10⁻⁷ to −0.61 × 10⁻⁷), but not with dioxins (SD of T/S ratio/(pg WHO TEQ/day) = −13.90 × 10⁻⁷; 95% CI, −37.70 × 10⁻⁷ to 9.79 × 10⁻⁷). In this sample of middle-aged and older Spanish adults, dietary exposure to total PCBs and DL-PCBs alone and together with dioxins was associated with shorter TL. Further longitudinal studies, preferably with POPs measured in biological samples, are needed to confirm this finding.

Atresia of ovarian follicles in fishes, and implications and uses in aquaculture and fisheries

Atresia of ovarian follicles, that is the degenerative process of germ cells and their associated somatic cells, is a complex process involving apoptosis, autophagy and heterophagy. Follicular atresia is a normal component of fish oogenesis and it is observed throughout the ovarian cycle, although it is more frequent in regressing ovaries during the postspawning period. An increased occurrence of follicular atresia above physiological rates reduces fish fecundity and even causes reproductive failure in both wild and captive-reared fish stocks, and hence, this phenomenon has a wide range of implications in applied sciences such as fisheries and aquaculture. The present article reviews the available literature on both basic and applied traits of oocyte loss by atresia, including its morpho-physiological aspects and factors that cause a supraphysiological increase of follicular atresia. Finally, the review presents the use of early follicular atresia identification in the selection process of induced spawning in aquaculture and the implications of follicular atresia in fisheries management.

Investigating Acute and Subchronic Effects of Neonicotinoids on Northwestern Salamander Larvae

This research investigated the adverse effects of neonicotinoids on the Northwestern salamander (Ambystoma gracile; NWS) after acute and subchronic exposures during early aquatic life stages via whole organism (i.e., growth, development) and molecular (i.e., gene expression) level endpoints. In a 96-h exposure, NWS larvae were exposed to four imidacloprid concentrations (250, 750, 2250, 6750 µg/L) and a water control treatment, and no effects on survival, body weight, snout-vent length (SVL), and total body length were observed. However, a significant 1.70- and 2.33-fold decrease in thyroid receptor β (TRβ) mRNA expression levels were detected in the larvae exposed to 750 and 2250 µg/L imidacloprid, respectively, compared with the larvae in the water control. In subsequent subchronic experiments, NWS larvae were exposed for 35 days to imidacloprid alone and an equal part mixture of neonicotinoids (imidacloprid, clothianidin, and thiamethoxam (ICT)) at three concentrations (10, 100 and 1000 µg total neonicotinoids/L) and a water control. In these experiments, there were no effects on larval survival, body weight, SVL, and total body length. However, advanced development of larvae in the 100 µg/L imidacloprid treatment was observed compared with the control after 35-day imidacloprid exposure, providing some evidence of disruption of the thyroid endocrine axis at an environmentally relevant concentration. Ultimately, there is a paucity of studies conducted examining the sensitivity of salamanders to pollutants; thus, this study reports novel findings that will contribute to understanding the sensitivity of a Caudate amphibian model to a common environmental pollutant.

A Global, Cross-System Meta-Analysis of Polychlorinated Biphenyl Biomagnification

Studies evaluating the mechanisms underpinning the biomagnification of polychlorinated biphenyls (PCBs), a globally prevalent group of regulated persistent organic pollutants, commonly couple chemical and stable isotope analyses to identify bioaccumulation pathways. Due to analytical costs constraining the scope, sample size, and range of congeners analyzed, and variation in methodologies preventing cross-study syntheses, how PCBs biomagnify at food web, regional, and global scales remains uncertain. To overcome these constraints, we compiled diet (stable isotopes) data and lipid-normalized concentrations of sum total PCB (PCB_ST), seven indicator PCB congeners, and their sum (PCB_∑7). Our analyses revealed that the number of congeners analyzed, region, and class most strongly predicted PCB_ST, while similarly, region, class, and feeding location best predicted PCB_∑7 and all seven congeners. We also discovered that PCB_ST, PCB_∑7, and the seven indicator congeners all occur in higher concentrations in freshwater than marine ecosystems but are more likely to biomagnify in the latter. Moreover, although the seven congeners vary in their propensity to biomagnify, their trophic magnification factors are all generally greater in the Atlantic than the Pacific. Thus, novel insights regarding PCB biomagnification across taxonomic, food webs, regional, and global scales can be gleaned by leveraging existing data to overcome analytical constraints.

Halogen Bonding Interactions of Polychlorinated Biphenyls and the Potential for Thyroid Disruption

Polychlorinated biphenyl (PCB) flame retardants are persistent pollutants and inhibit neurodevelopment, particularly in the early stages of life. Halogen bonding (XB) to the iodothyronine deiodinases (Dio) that modulate thyroid hormones (THs) is a potential mechanism for endocrine disruption. Cl⋅⋅⋅Se XB interactions of PCBs with SeMe- , a small model of the Dio active site selenocysteine, are compared with previous results on polybrominated diphenylethers (PBDEs) and THs using density functional theory. PCBs generally display weaker XB interactions compared to PBDEs and THs, consistent with the dependence of XB strength on the size of the halogen (I>Br>Cl). PCBs also do not meet a proposed energy threshold for substrates to undergo dehalogenation, suggesting they may behave as competitive inhibitors of Dio in addition to other mechanisms of endocrine disruption. XB interactions in PCBs are position-dependent, with ortho interactions slightly more favorable than meta and para interactions, suggesting that PCBs may have a greater effect on certain classes of Dio. Flexibility of PCBs around the biphenyl C-C bond is limited by ortho substitutions relative to the biphenyl linkage, which may contribute to the ability to inhibit Dio and other TH-related proteins.

A Halogen Bonding Perspective on Iodothyronine Deiodinase Activity

Iodothyronine deiodinases (Dios) are involved in the regioselective removal of iodine from thyroid hormones (THs). Deiodination is essential to maintain TH homeostasis, and disruption can have detrimental effects. Halogen bonding (XB) to the selenium of the selenocysteine (Sec) residue in the Dio active site has been proposed to contribute to the mechanism for iodine removal. Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) are known disruptors of various pathways of the endocrine system. Experimental evidence shows PBDEs and their hydroxylated metabolites (OH-BDEs) can inhibit Dio, while data regarding PCB inhibition are limited. These xenobiotics could inhibit Dio activity by competitively binding to the active site Sec through XB to prevent deiodination. XB interactions calculated using density functional theory (DFT) of THs, PBDEs, and PCBs to a methyl selenolate (MeSe⁻) arrange XB strengths in the order THs > PBDEs > PCBs in agreement with known XB trends. THs have the lowest energy C–X*-type unoccupied orbitals and overlap with the Se lp donor leads to high donor-acceptor energies and the greatest activation of the C–X bond. The higher energy C–Br* and C–Cl* orbitals similarly result in weaker donor-acceptor complexes and less activation of the C–X bond. Comparison of the I···Se interactions for the TH group suggest that a threshold XB strength may be required for dehalogenation. Only highly brominated PBDEs have binding energies in the same range as THs, suggesting that these compounds may inhibit Dio and undergo debromination. While these small models provide insight on the I···Se XB interaction itself, interactions with other active site residues are governed by regioselective preferences observed in Dios.

Endocrine disrupting chemicals: exposure, effects on human health, mechanism of action, models for testing and strategies for prevention

Endocrine Disrupting Chemicals (EDCs) are a global problem for environmental and human health. They are defined as "an exogenous chemical, or mixture of chemicals, that can interfere with any aspect of hormone action". It is estimated that there are about 1000 chemicals with endocrine-acting properties. EDCs comprise pesticides, fungicides, industrial chemicals, plasticizers, nonylphenols, metals, pharmaceutical agents and phytoestrogens. Human exposure to EDCs mainly occurs by ingestion and to some extent by inhalation and dermal uptake. Most EDCs are lipophilic and bioaccumulate in the adipose tissue, thus they have a very long half-life in the body. It is difficult to assess the full impact of human exposure to EDCs because adverse effects develop latently and manifest at later ages, and in some people do not present. Timing of exposure is of importance. Developing fetus and neonates are the most vulnerable to endocrine disruption. EDCs may interfere with synthesis, action and metabolism of sex steroid hormones that in turn cause developmental and fertility problems, infertility and hormone-sensitive cancers in women and men. Some EDCs exert obesogenic effects that result in disturbance in energy homeostasis. Interference with hypothalamo-pituitary-thyroid and adrenal axes has also been reported. In this review, potential EDCs, their effects and mechanisms of action, epidemiological studies to analyze their effects on human health, bio-detection and chemical identification methods, difficulties in extrapolating experimental findings and studying endocrine disruptors in humans and recommendations for endocrinologists, individuals and policy makers will be discussed in view of the relevant literature.

Prenatal exposure to Polychlorinated Biphenyls and body fatness in girls

Polychlorinated biphenyls (PCBs) are synthetic, organochlorine compounds previously used in industrial processes. Although banned in 1980's across Europe, these chemicals persist in the environment and are associated with adverse health outcomes in children. We investigated the association between in utero concentrations of PCBs and girls' body fatness. Concentrations of various PCB congeners (PCB 118, PCB 138, PCB 153, PCB 170, and PCB 180) were measured in maternal serum samples collected in the early 1990's. Body fatness was measured in the daughters at 9 y of age using body mass index (BMI) and dual-energy x-ray absorptiometry (DXA) for percent body fat. Using multivariable linear regression, we explored associations between prenatal PCB congener concentrations and body fatness outcomes. Among 339 mother-daughter dyads, the median and interquartile range (IQR) for PCB congeners ranged between 15.0 ng g^-1 (11.0-20.8) for PCB 118 to 64.6 ng g^-1 (48.6-86.3) for PCB 153. Among daughters, the median was 27.5% (21.7-34.6) for percent body fat, 39.6% (36.4-43.5) for percent trunk fat, 4.9 kg m^-2 (3.5-7.0) for fat mass index and 18.1 kg m^-2 (16.3-20.6) for body mass index. Multivariable-adjusted regression analyses showed little or no association between prenatal PCB concentrations with daughters' body fatness measures. Prenatal concentrations of PCB congeners were not strongly associated with measures of body fatness in girls.

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.

Thyroid-disrupting chemicals and brain development: an update

This review covers recent findings on the main categories of thyroid hormone-disrupting chemicals and their effects on brain development. We draw mostly on epidemiological and experimental data published in the last decade. For each chemical class considered, we deal with not only the thyroid hormone-disrupting effects but also briefly mention the main mechanisms by which the same chemicals could modify estrogen and/or androgen signalling, thereby exacerbating adverse effects on endocrine-dependent developmental programmes. Further, we emphasize recent data showing how maternal thyroid hormone signalling during early pregnancy affects not only offspring IQ, but also neurodevelopmental disease risk. These recent findings add to established knowledge on the crucial importance of iodine and thyroid hormone for optimal brain development. We propose that prenatal exposure to mixtures of thyroid hormone-disrupting chemicals provides a plausible biological mechanism contributing to current increases in the incidence of neurodevelopmental disease and IQ loss.

Effects of in ovo exposure to 3,3',4,4'-tetrachlorobiphenyl (PCB 77) on heart development in tree swallow (Tachycineta bicolor)

Tree swallow (Tachycineta bicolor) eggs from 2 uncontaminated sites, the Patuxent Research Refuge (Laurel, MD, USA) and the Cobleskill Reservoir (Cobleskill, NY, USA) were dosed with polychlorinated biphenyl (PCB) 77 to evaluate effects on the developing cardiovascular system. To ensure embryonic viability, treatments were administered into the air cell at embryonic day 2.5 including: untreated (control), vehicle (filtered sterilized fatty acid mixture), 100 ng/g and 1000 ng/g egg. Eggs were dosed in the field with 0.2 μL/egg, returned to the nest, collected at embryonic day 13, hatched in the laboratory, and necropsied. The PCB 77-treated hatchlings were compared with uninjected, vehicle-injected, and environmentally exposed hatchlings collected from a PCB-contaminated Upper Hudson River (NY, USA) site. The PCB 77-treated embryos showed no effects on hatching success or hatchling mortality, heart index, or morphological measures of 4 distinct heart layers (heart width, length, septal thickness, total and ventricular cavity area) compared with controls. Hatchlings that had received PCB 77 exhibited increased incidence of a cardiomyopathy and absence of the ventricular heart wall compact layer (Chi square test; p < 0.001); environmentally exposed embryos showed no apparent effects. The compact layer is essential in development and overall heart function for ventricular cardiomyocyte proliferation and normal heart contraction. The finding that in ovo exposure to PCB 77 resulted in distinct cardiomyopathy has implications for long-term individual fitness. Environ Toxicol Chem 2018;37:116-125. © 2017 SETAC.

Triclocarban and Triclosan Inhibit Human Aromatase via Different Mechanisms

Human aromatase (CYP19A1) is an important enzyme, which produces estrogen from androgen for maintaining the female reproductive function and pregnancy. Triclocarban and triclosan are antimicrobial chemicals added to personal care, household, and industrial products. They could be endocrine disruptors and may disrupt human CYP19A1 activity. In the present study, we investigated the effects of triclocarban and triclosan on estradiol production and human CYP19A1 activity in JEG-3 cells. Triclocarban and triclosan reduced estradiol production in JEG-3 cells. Triclocarban and triclosan inhibited human CYP19A1 with IC₅₀ values of 15.81 and 6.26 μM, respectively. Triclosan competitively inhibited CYP19A1, while triclocarban noncompetitively inhibited this enzyme. Docking study showed that triclosan bound to the steroid-binding pocket of CYP19A1, while triclocarban was off this target, suggesting a different mechanism. In conclusion, triclocarban and triclosan are inhibitors of human CYP19A1.

Ziram inhibits aromatase activity in human placenta and JEG-3 cell line

Placenta produces progesterone and estradiol for maintaining pregnancy. Two critical enzymes are responsible for their production: 3β-hydroxysteroid dehydrogenase 1 (HSD3B1) that catalyzes the formation of progesterone from pregnenolone and aromatase that catalyzes the production of estradiol from testosterone. Fungicide ziram may disrupt the placental steroid production. In the present study, we investigated the effects of ziram on steroid formation in human placental cell line JEG-3 cells and on HSD3B1 and aromatase in the human placenta. Ziram did not inhibit progesterone production in JEG-3 cells and HSD3B1 activity at 100μM. Ziram was a potent aromatase inhibitor with the half maximal inhibitory concentration (IC₅₀) value of 333.8nM. When testosterone was used to determine the mode of action, ziram was found to be a competitive inhibitor. Docking study showed that ziram binds to the testosterone binding pocket of the aromatase. In conclusion, ziram is a potent inhibitor of human aromatase.

Perinatal exposure to organohalogen pollutants decreases vasopressin content and its mRNA expression in magnocellular neuroendocrine cells activated by osmotic stress in adult rats

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are environmental pollutants that produce neurotoxicity and neuroendocrine disruption. They affect the vasopressinergic system but their disruptive mechanisms are not well understood. Our group reported that rats perinatally exposed to Aroclor-1254 (A1254) and DE-71 (commercial mixtures of PCBs and PBDEs) decrease somatodendritic vasopressin (AVP) release while increasing plasma AVP responses to osmotic activation, potentially emptying AVP reserves required for body-water balance. The aim of this research was to evaluate the effects of perinatal exposure to A1254 or DE-71 (30mgkg/day) on AVP transcription and protein content in the paraventricular and supraoptic hypothalamic nuclei, of male and female rats, by in situ hybridization and immunohistochemistry. cFOS mRNA expression was evaluated in order to determine neuroendocrine cells activation due to osmotic stimulation. Animal groups were: vehicle (control); exposed to either A1254 or DE-71; both, control and exposed, subjected to osmotic challenge. The results confirmed a physiological increase in AVP-immunoreactivity (AVP-IR) and gene expression in response to osmotic challenge as reported elsewhere. In contrast, the exposed groups did not show this response to osmotic activation, they showed significant reduction in AVP-IR neurons, and AVP mRNA expression as compared to the hyperosmotic controls. cFOS mRNA expression increased in A1254 dehydrated groups, suggesting that the AVP-IR decrease was not due to a lack of the response to the osmotic activation. Therefore, A1254 may interfere with the activation of AVP mRNA transcript levels and protein, causing a central dysfunction of vasopressinergic system.

PCDD/F and dioxin-like PCB minimization: A 13-year experimental study along the flue gas cleaning system of a secondary aluminium refining plant

A 13-years study shows that a careful design of the flue gas cleaning system of a full scale secondary aluminium refining plant results in a minimized and very stable emission of Polychlorinated Dibenzo-p-Dioxins (PCDD), Polychlorinated Dibenzo Furans (PCDF) and dioxin-like Polychlorinated Biphenyls (PCB). The value of equivalent toxicity of PCDD/F in the emission was definitely of an order of magnitude less than the regulation limit. In the initial flue gas cleaning system, the PCB mean fingerprint after the slow cooling of the flue gas was typical of de novo synthesis. Instead, in the presence of quenching, there was evidence that the fast cooling of flue gas prevented the PCB de novo synthesis. In fact, the PCB profile was similar to that in the air collected from the aspiration hoods for the quenching. The gas-phase and solid-phase partitioning of PCBs, before and after the fabric filters, highlights the predominant role of the vapor phase with respect to the total removal efficiency. The polycyclic aromatic hydrocarbons breakdown could be an additional de novo formation pathway even in industrial plants.

Secular Trend of Age at Menarche in Chinese Adolescents Born From 1973 to 2004

OBJECTIVES

To estimate secular trend and factors influencing the age at menarche for Chinese girls born from 1973 to 2004.

METHODS

Data were collected from the China Health and Nutrition Survey, a prospective open cohort and an ongoing nationwide health and nutrition survey, consisting of 3199 apparently healthy Chinese girls aged 6 to 18 years at entry from 1991 to 2011. Average age at menarche and its 95% confidence interval were estimated by weighted means of Kaplan-Meier survival analysis. Cox proportional hazard models were applied to identify the independent predictive factors of age at menarche.

RESULTS

The age at menarche declined from 14.25 in Chinese girls born before 1976 to 12.60 in girls born after 2000, with an estimated decline of 0.51 years per decade (P < .001). The downward trend of age at menarche for rural girls was greater than for urban girls (0.62 vs 0.35 years per decade; P < .001). Girls living in urban areas, living in central areas, with high BMI, and with high-energy diets had a high risk of early menarche, whereas girls living on the east coast who had high-carbohydrate diets had a low risk of early menarche.

CONCLUSIONS

The authors of this study found a continuous downward secular trend of age at menarche for Chinese girls in both urban and rural areas born from 1973 to 2004. Among all variables, urban residency, BMI, and energy intake are negatively associated with age at menarche, whereas carbohydrate intake is positively associated with age at menarche.

Exposure to modern, widespread environmental endocrine disrupting chemicals and their effect on the reproductive potential of women: an overview of current epidemiological evidence

Growing evidence indicates that exposure to widespread, environmental contaminants called endocrine disruptors (EDCs) negatively affects animal and human reproductive health and has been linked to several diseases including infertility. This review aims to evaluate the impact of environmental exposure to endocrine disrupting chemicals [phthalates, parabens, triclosan, bisphenol A (BPA), organochlorine (PCBs) and perfluorinated (PFCs) compounds] on the reproductive potential among women, by reviewing most recently published literature. Epidemiological studies focusing on EDCs exposure and reproductive potential among women for the last 16 years were identified by a search of the PUBMED, MEDLINE, EBSCO and TOXNET literature databases. The results of the presented studies show that exposure to EDCs impacts the reproductive potential in women, measured by ovarian reserve and by assisted reproductive technology outcomes. Exposure to environmental endocrine disrupting chemicals decrease: (i) oestradiol levels (BPA); (ii) anti-Müllerian hormone concentrations (PCBs); (iii) antral follicle count (BPA, parabens, phthalates); (iv) oocyte quality (BPA, triclosan, phthalates, PCBs); (v) fertilization rate (PFCs, PCBs); (vi) implantation (BPA, phthalates, PCBs); (vii) embryo quality (triclosan, PCBs, BPA); (viii) rate of clinical pregnancy and live births (parabens, phthalates). The studies were mostly well-designed and used prospective cohorts with the exposure assessment based on the biomarker of exposure. Considering the suggested health effects, more epidemiological data is urgently needed to confirm the presented findings.

Secular trends in the timing of skeletal maturation as assessed by the cervical vertebrae maturation method

Objective

To investigate the presence of secular trends in skeletal maturation of girls and boys as assessed by the use of cervical vertebrae bones.

Materials and methods

The study compared two main groups: the first included data collected from the Denver growth study (1930s to 1960s) and the second included data collected from recent pretreatment records (1980s to 2010s) of patients from the orthodontic clinic of a North American University. The records from the two groups were all for Caucasian subjects. The sample for each group included 78 lateral cephalographs for girls and the same number for boys. The age of the subjects ranged from 7 to 18 years. Cervical vertebrae maturation (CVM) stages were directly assessed from the radiographs according to the method described by Hassel and Farman in which six CVM stages were designated from cervical vertebrae 2, 3, and 4.

Results

The mean age of girls from the Denver growth study and girls from the university clinic in each of the six CVM stages was not different at P ≤0.05. However, the mean age of boys from the two groups was not different only in stage 3 (P = 0.139) and stage 4 (P = 0.211).

Conclusions

The results showed no evidence to indicate a tendency for earlier skeletal maturation of girls or boys. Boys in the university group started their skeletal maturation later than boys in the Denver group and completed their maturation earlier. Gender was a significant factor affecting skeletal maturation stages in both Denver and university groups.

Polychlorinated biphenyls target Notch/Dll and VEGF R2 in the mouse placenta and human trophoblast cell lines for their anti-angiogenic effects

The intrauterine environment is particularly vulnerable to environmental exposures. We previously established a mouse model that provided evidence for pregnancy complications and placental anti-angiogenesis in response to Aroclor 1254 (A-1254), a mixture of polychlorinated biphenyls (PCBs). Importantly, these effects were observed in IL-10^-/-, but not wild type, mice, suggesting that IL-10 deficiency predisposes to pregnancy disruptive effects of environmental toxicants. However, the mechanisms by which PCBs cause anti-angiogenic effects are unclear. Here, we evaluated PCB-mediated anti-angiogenic effects by diverse but complementary approaches, including HUVEC-mediated trophoblast invasion in nude mice, in vitro three-dimensional capillary tube formation involving HUVEC and/or HTR8 trophoblasts, and aortic ring endothelial cell outgrowth/sprouting. Taken together, our data suggest that PCBs act as potent anti-angiogenic agents. Importantly, we show that treatment of pregnant IL-10^-/- mice with A-1254 resulted in placental activation of the Notch/Delta-like ligand (Dll) pathway, a master regulator of cell-cell interaction and vascular patterning. Similar results were obtained with HUVEC and HTR8 trophoblasts. Rescue of A-1254-induced disruption of HUVEC-based tube formation by γ-secretase inhibitor L1790 confirmed the critical role of the Notch/Dll pathway. Our data suggest that PCBs impart pregnancy disruptive functions by activating the Notch/Dll pathway and by inducing anti-angiogenic effects at the maternal-fetal interface.

Obesity, Persistent Organic Pollutants and Related Health Problems

The present review aims to delve into persistent organic pollutants (POPs) , as xenobiotics, in correlation to human health. POPs exhibit a group of common characteristics, including lipophilicity, persistence to decomposition and bioaccumulation in tissues. POPs have been thoroughly studied by former researchers, as they offer a particular interest in the elucidation of metabolic, endocrine and immune perturbation caused by their synergy with intracellular mechanisms. Herein particular focus is attributed to the relationship of POPs with obesity provocation. Obesity nowadays receives epidemic dimensions, as its prevalence elevates in an exponential degree. POPs-induced obesity rotates around interfering in metabolic and endocrinal procedures and interacting with peroxisome-proliferator and retinoic receptors. Moreover, polymorphisms in CYP gene families exert a negative result, as they incapacitate detoxification of POPs. Obesity could be deemed as a multidimensional condition, as various factors interact to lead to an obesogenic result. Therefore, concomitant disorders may occur, from mild to lethal, and get intensified due to POPs exposure. POPs exact function mechanisms remain rather enigmatic, thus further investigation should be prospectively performed, for a more lucid picture of this issue, and, consequently for the establishment of alternative solutions.

Effects of dietary oxidized tyrosine products on insulin secretion via the thyroid hormone T3-regulated TRβ1–Akt–mTOR pathway in the pancreas

Oxidized tyrosine products (OTPs) have been detected in commercial foods with high protein content.

Exposure to PBB-153 and Digit Ratio

The ratio between the second and fourth digits is a sexually dimorphic measure, established in utero and linked to prenatal sex steroid levels. An association was found between prenatal levels of Polybrominated Biphenyls, a synthetic chemical suspected to disrupt the endocrine system function, and the digit ratio in adult women.

Effects of PCB 126 and PCB 153 on secretion of steroid hormones and mRNA expression of steroidogenic genes (STAR, HSD3B, CYP19A1) and estrogen receptors (ERα, ERβ) in prehierarchical chicken ovarian follicles

The objective of this study was to assess the in vitro effects of dioxin-like PCB 126 and non-dioxin-like PCB 153 on basal and ovine LH (oLH)-stimulated testosterone (T) and estradiol (E2) secretion and expression of steroidogenic genes (STAR, HSD3B and CYP19A1) and estrogen receptors α (ERα) and β (ERβ) in white (WF) and yellowish (YF) prehierarchical follicles of the hen ovary. Steroid concentrations in a medium and gene expression in follicles following 6h of exposition were determined by RIA and real-time qPCR, respectively. Both PCBs increased basal and oLH-stimulated T secretion by the WF follicles. PCB 126 reduced basal E2 secretion by the WF follicles. PCB 153 elevated but PCB 126 reduced oLH-stimulated E2 secretion by the prehierarchical follicles. PCB 126 increased basal STAR and HSD3B and reduced CYP19A1 mRNA expression in these follicles. PCB 153 increased basal expression of STAR and HSD3B in YF follicles, but diminished HSD3B mRNA levels in the WF. The studied PCBs had an opposite effect on basal and oLH-stimulated CYP19A1 mRNA expression in prehierarchical follicles. Both PCBs modulated basal and inhibited oLH-stimulated ERα and ERβ gene expression in the prehierarchical follicles. In conclusion, data of the current study demonstrate the congener-specific effects of PCBs on sex steroid secretion by prehierarchical follicles of the chicken ovary, which are at least partly related to STAR, HSD3B and CYP19A1 gene expression. It is suggested that PCBs, by influencing follicular steroidogenesis and expression of estrogen receptors, may impair development and selection of yellowish follicles to the preovulatory hierarchy.

Development of yeast reporter assays for the enhanced detection of environmental ligands of thyroid hormone receptors α and β from Xenopus tropicalis

Thyroid hormones (THs) are involved in the regulation of metabolic homeostasis during the development and differentiation of vertebrates, particularly amphibian metamorphosis, which is entirely controlled by internal TH levels. Some artificial chemicals have been shown to exhibit TH-disrupting activities. In order to detect TH disruptors for amphibians, we herein developed a reporter assay using yeast strains expressing the thyroid hormone receptors (TRs) α and β together with the transcriptional coactivator SRC-1, all of which were derived from the frog Xenopus tropicalis (XT). These yeast strains responded to endogenous THs (T₂, T₃, and T₄) in a dose-dependent manner. They detected the TR ligand activities of some artificial chemicals suspected to exhibit TH-disrupting activities, as well as TR ligand activity in river water collected downstream of sewage plant discharges, which may have originated from human excrement. Moreover, the responses of XT TR strains to these endogenous and artificial ligands were stronger than those of yeast strains for human TRα and β assays, which had previously been established in our laboratory. These results indicate that the yeast reporter assay system for XT TRα and β is valuable for assessing TR ligand activities in environmental samples that may be particularly potent in amphibians.

Exposure to polychlorinated biphenyls and the thyroid gland - examining and discussing possible longitudinal health effects in humans

BACKGROUND

Many previous studies have dealt with the effect of polychlorinated biphenyls (PCBs) on the thyroid gland, but their findings are inconsistent. One problem of these studies has been their use of cross-sectional designs.

OBJECTIVES

The aim of the current study is to investigate longitudinal effects of PCBs on the thyroid gland, focusing on: morphological changes in thyroid tissue (i.e. thyroid volume), changes in thyroid hormones and in thyroid antibodies.

METHODS

A total of 122 individuals (Mage=44.7) were examined over a period of four years (t(1) until t(4)). Medical history was collected via interviews, an ultrasound examination was performed and blood samples were taken to determine plasma PCB levels, thyroid stimulating hormone (TSH), free triiodthyronine (fT3), free thyroxine (fT4), thyroid peroxidase antibodies (TPOab), thyreoglobulin antibodies (TGab) and thyroid-stimulating hormone receptor antibodies (TSHRab). Rank correlation coefficients and mixed effect models were performed controlling for age and total lipids.

RESULTS

There were negative correlations between higher chlorinated biphenyls and fT3, cross-sectionally as well as longitudinally. We also found an interaction effect of higher-chlorinated PCBs over time for fT4 as well as TSHRab. In case of high exposure, a decrease in fT4 and an increase in TSHRab level were found over time. In regards to the other variables, our findings yielded no clear results in the examined time period.

CONCLUSION

This is the first study to shows a PCB-related effect on fT3, fT4 and TSHRab over a four year period. The data also suggest that morphological and antibody findings remain inconsistent and do not allow for unambiguous interpretation.

Divergent Effects of Dioxin- or Non-Dioxin-Like Polychlorinated Biphenyls on the Apoptosis of Primary Cell Culture from the Mouse Pituitary Gland

Polychlorinated biphenyls (PCBs) can disrupt the endocrine function, promote neoplasms and regulate apoptosis in some tissues; however, it is unknown whether PCBs can affect the apoptosis of pituitary cells. The study evaluated the effect of PCBs on the apoptosis of normal pituitary cells and the underlying mechanisms. Primary cell cultures obtained from mouse pituitary glands were exposed to Aroclor 1254 or selected dioxin-like (PCB 77, PCB 126) or non-dioxin-like (PCB 153, PCB 180) congeners. Apoptosis was evaluated by Annexin V staining, DNA fragmentation, and TUNEL assay. Both the expression and activity of caspases were analyzed. Selective thyroid hormone receptor (TR) or aryl-hydrocarbon receptor (AhR) or CYP1A1 antagonist were used to explore the mechanisms underlying PCBs action. Our results showed that Aroclor 1254 induced the apoptosis of pituitary cells as well as the final caspase-3 level and activity through the extrinsic pathway, as shown by the increased caspase-8 level and activity. On the other hand, the intrinsic pathway evaluated by measuring caspase-9 expression was silent. The selected non-dioxin-like congeners either increased (PCB 180) or reduced (PCB 153) pituitary cell apoptosis, affecting the extrinsic pathway (PCB 180), or both the extrinsic and intrinsic pathways (PCB 153), respectively. In contrast, the dioxin-like congeners (PCB 77 and PCB 126) did not affect apoptosis. The anti-apoptotic phenotype of PCB 153 was counteracted by a TR or a CYP1A1 antagonist, whereas the pro-apoptotic effect of PCB 180 was counteracted by an AhR antagonist. The induced apoptosis of Aroclor 1254 or PCB 180 was associated with a reduction of cell proliferation, whereas the decreased apoptosis due to PCB 153 increased cell proliferation by 30%. In conclusion, our data suggest that non-dioxin-like PCBs may modulate apoptosis and the proliferation rate of pituitary cells that have either pro- or anti-apoptotic effects depending on the specific congeners. However, the impact of PCBs on the process of pituitary tumorigenesis remains to be elucidated.

Retinoid-xenobiotic interactions: the Ying and the Yang

The literature provides compelling evidence pointing to tight metabolic interactions between retinoids and xenobiotics. These are extensive and important for understanding xenobiotic actions in the body. Within the body, retinoids affect xenobiotic metabolism and actions and conversely, xenobiotics affect retinoid metabolism and actions. This article summarizes data that establish the importance of retinoid-dependent metabolic pathways for sustaining the body's responses to xenobiotic exposure, including the roles of all-trans- and 9-cis-retinoic acid for protecting mammals from harmful xenobiotic effects and for ensuring xenobiotic elimination from the body. This review will also consider molecular mechanisms underlying xenobiotic toxicity focusing on how this may contribute to retinoid deficiency and disruption of normal retinoid homeostasis. Special attention is paid to xenobiotic molecular targets (nuclear receptors, regulatory proteins, enzymes, and transporters) which affect retinoid metabolism and signaling.

Effects of currently used pesticides and their mixtures on the function of thyroid hormone and aryl hydrocarbon receptor in cell culture

Evidence suggest that exposure to pesticides can interfere with the endocrine system by multiple mechanisms. The endocrine disrupting potential of currently used pesticides in Denmark was analyzed as single compounds and in an equimolar mixture of 5 selected pesticides. The pesticides were previously analyzed for effects on the function of estrogen and androgen receptors, the aromatase enzyme and steroidogenesis in vitro. In this study, the effect on thyroid hormone (TH) function and aryl hydrocarbon receptor (AhR) transactivity was assessed using GH3 cell proliferation assay (T-screen) and AhR responsive luciferase reporter gene bioassay, respectively. Thirteen pesticides were analyzed as follows: 2-methyl-4-chlorophenoxyacetic acid, terbuthylazine, iodosulfuron-methyl-sodium, mesosulfuron-methyl, metsulfuron-methyl, chlormequat chloride, bitertanol, propiconazole, prothioconazole, mancozeb and its metabolite ethylene thiourea, cypermethrin, tau-fluvalinate, and malathion (currently banned in DK). In the T-screen, prothioconazole, malathion, tau-fluvalinate, cypermethrin, terbuthylazine and mancozeb significantly stimulated and bitertanol and propiconazole slightly reduced the GH3 cell proliferation. In the presence of triiodothyronine (T3), prothioconazole, tau-fluvalinate, propiconazole, cypermethrin and bitertanol significantly antagonized the T3-induced GH3 cell proliferation. Eleven of the tested pesticides agonized the AhR function, and bitertanol and prothioconazole inhibited the basal AhR activity. Bitertanol, propiconazole, prothioconazole and cypermethrin antagonized the TCDD-induced AhR transactivation at the highest tested concentration. The 5-component mixture had inducing effect but the combined effect could not be predicted due to the presence of bitertanol eliciting inhibitory effect. Upon removal of bitertanol from the mixture, the remaining four pesticides acted additively. In conclusion, our data suggest that pesticides currently used in Denmark can interfere with TH signaling and AhR function in vitro and might have the potential to cause endocrine disruption.

Environmental Polychlorinated Biphenyl Exposure and Breast Cancer Risk: A Meta-Analysis of Observational Studies

BACKGROUND

Association between polychlorinated biphenyl (PCB) exposure and breast cancer risk has been widely studied, but the results remain controversial. We performed a meta-analysis to evaluate the evidences from observational studies on PCB exposure and breast cancer risk.

METHODS

Relevant studies with data on internal PCB dose were identified from PubMed, EMBASE, CBM and CNKI databases through November 2014. Multivariable-adjusted odds ratio (OR) with 95% confidence intervals (CIs) were applied to assess the association between PCB exposure and breast cancer risk. Heterogeneity test, sensitivity analysis, subgroup analysis and publication bias test were also performed. To further explore the association between specific groups of PCB congeners and breast cancer, we examined the PCB congeners classified, according to their structural, biological and pharmacokinetics properties, as group I (potentially estrogenic), group II (potentially anti-estrogenic and immunotoxic, dioxin-like), and group III (phenobarbital, CYP1A and CYP2B inducers, biologically persistent).

RESULTS

Of 660 studies screened, 25 studies which met criteria were selected, involving a total of 12866 participants (6088 cases and 6778 controls) from eight countries. The results showed that the risk of breast cancer was associated with group II (OR = 1.23, 95% CI: 1.08-1.40) and group III (OR = 1.25, 95% CI: 1.09-1.43) PCBs, but not with group I (OR = 1.10, 95%CI: 0.97-1.24) PCBs or total PCB exposure (OR = 1.09, 95%CI: 0.97-1.22).

CONCLUSIONS

Our meta-analysis based on the selected studies found group II and group III PCB exposure might contribute to the risk of breast cancer. More studies in developing countries with higher PCB levels are needed, as well as studies to explore the relationships between mixtures of organochlorine compounds and breast cancer risk.

The effect of the aquatic contaminants bisphenol-A and PCB-95 on the zebrafish lateral line

Environmental toxicants such as bisphenol-A (BPA) and polychlorinated biphenyls (PCBs) are prevalent in our water supply, soil, and many food products and can profoundly affect the central nervous system. Both BPA and PCBs can disrupt endocrine signaling, which is important for auditory development and function, but the effect of these toxicants on the auditory periphery is not understood. In this study we investigated the effect of PCB-95 and BPA on lateral line development, function, and regeneration in larval zebrafish. The lateral line is a system of mechanosensory hair cells on the exterior of the fish that are homologous to the hair cells located in the mammalian inner ear. We found that PCB-95 had no effect on lateral line development or hair cell survival. BPA also did not affect lateral line development, but instead had a significant effect on both hair cell survival and regeneration. BPA-induced hair cell loss is both dose- and time-dependent, with concentrations of 1 μM or higher killing lateral line hair cells during a 24h exposure period. Pharmacologic manipulation experiments suggest that BPA kills hair cells via activation of oxidative stress pathways, similar to prior reports of BPA toxicity in other tissues. We also observed that hair cells killed with neomycin, a known ototoxin, failed to regenerate normally when BPA was present, suggesting that BPA in aquatic environments could impede innate regenerative responses in fishes. Collectively, these data demonstrate that BPA can have detrimental effects on sensory systems, both in aquatic life and perhaps in terrestrial organisms, including humans.

Aroclor 1254 inhibits the chemiluminescence response of peritoneal cavity cells from sharpsnout sea bream (Diplodus puntazzo)

Chronic exposure to polychlorinated biphenyls (PCBs) affect the immune system of fish and could lead to a decreased disease resistance. The effects of Aroclor 1254, PCB mixtures, on the Diplodus puntazzo innate immunity were examined by assaying the zymosan stimulated chemiluminescence response (CL) of peritoneal cavity cells (PCCs) at various times (1, 24, 48 h and 1-4 weeks) from intraperitoneal injection of the xenobiotic (1 mg kg(-1) body weight). Controls were performed by assaying cells from medium-treated fish. Since the kinetic of the chemiluminescence response showed the highest peak at 25 min after the zymosan stimulation of the cells, the values found at that time were considered. The CL enhancement observed at 1 h after the treatment with xenobiotic was followed by a decreased response at 24 h and appeared to be lower at 1-4 weeks when compared to the CL response of the control, suggesting a protracted effect of PCBs on the peritoneal cavity. Since PCCs incubated in vitro for 1 h with 0.05 and 0.1 μg ml(-1) Aroclor showed an enhanced CL, the effect of the xenobiotic could be exerted on the cell responsiveness to zymosan. It is known that fish CL response of PCCs can be imputed to phagocyte (macrophages and neutrophils) activation, these cells and their responsiveness to zymosan can be used in immunotoxicology assay to monitor the fish health in polluted environment.

Tetrabromobisphenol A disrupts vertebrate development via thyroid hormone signaling pathway in a developmental stage-dependent manner

Data concerning effects of tetrabromobisphenol A (TBBPA) on thyroid hormone (TH)-dependent vertebrate development have been limited, although TBBPA has been demonstrated in vitro to disrupt the TH signaling pathway at the transcriptional level. In this study, we investigated the effects of TBBPA on T3-induced and spontaneous Xenopus laevis metamorphosis, which share many similarities with TH-dependent development in higher vertebrates. In a 6-day T3-induced metamorphosis assay using premetamorphic tadpoles, 10-1000 nM TBBPA exhibited inhibitory effects on T3-induced expression of TH-response genes and morphological changes in a concentration-dependent manner, with a weak stimulatory action on tadpole development and TH-response gene expression in the absence of T3 induction. In a spontaneous metamorphosis assay, we further found that TBBPA promoted tadpole development from stage 51 to 56 (pre- and prometamorphic stages) but inhibited metamorphic development from stage 57 to 66 (metamorphic climax). These results strongly show that TBBPA, even at low concentrations, disrupts TH-dependent development in a developmental stage-dependent manner, i.e., TBBPA exhibits an antagonistic activity at the developmental stages when animals have high endogenous TH levels, whereas it acts as an agonist at the developmental stages when animals have low endogenous TH levels. Our study highlights the adverse influences of TBBPA on TH-dependent development in vertebrates.

Current concepts in neuroendocrine disruption

In the last few years, it has become clear that a wide variety of environmental contaminants have specific effects on neuroendocrine systems in fish, amphibians, birds and mammals. While it is beyond the scope of this review to provide a comprehensive examination of all of these neuroendocrine disruptors, we will focus on select representative examples. Organochlorine pesticides bioaccumulate in neuroendocrine areas of the brain that directly regulate GnRH neurons, thereby altering the expression of genes downstream of GnRH signaling. Organochlorine pesticides can also agonize or antagonize hormone receptors, adversely affecting crosstalk between neurotransmitter systems. The impacts of polychlorinated biphenyls are varied and in many cases subtle. This is particularly true for neuroedocrine and behavioral effects of exposure. These effects impact sexual differentiation of the hypothalamic-pituitary-gonadal axis, and other neuroendocrine systems regulating the thyroid, metabolic, and stress axes and their physiological responses. Weakly estrogenic and anti-androgenic pollutants such as bisphenol A, phthalates, phytochemicals, and the fungicide vinclozolin can lead to severe and widespread neuroendocrine disruptions in discrete brain regions, including the hippocampus, amygdala, and hypothalamus, resulting in behavioral changes in a wide range of species. Behavioral features that have been shown to be affected by one or more these chemicals include cognitive deficits, heightened anxiety or anxiety-like, sociosexual, locomotor, and appetitive behaviors. Neuroactive pharmaceuticals are now widely detected in aquatic environments and water supplies through the release of wastewater treatment plant effluents. The antidepressant fluoxetine is one such pharmaceutical neuroendocrine disruptor. Fluoxetine is a selective serotonin reuptake inhibitor that can affect multiple neuroendocrine pathways and behavioral circuits, including disruptive effects on reproduction and feeding in fish. There is growing evidence for the association between environmental contaminant exposures and diseases with strong neuroendocrine components, for example decreased fecundity, neurodegeneration, and cardiac disease. It is critical to consider the timing of exposures of neuroendocrine disruptors because embryonic stages of central nervous system development are exquisitely sensitive to adverse effects. There is also evidence for epigenetic and transgenerational neuroendocrine disrupting effects of some pollutants. We must now consider the impacts of neuroendocrine disruptors on reproduction, development, growth and behaviors, and the population consequences for evolutionary change in an increasingly contaminated world. This review examines the evidence to date that various so-called neuroendocrine disruptors can induce such effects often at environmentally-relevant concentrations.

Association between dietary intakes of PCBs and the risk of obesity: the SUN project

BACKGROUND

Polychlorinated biphenyls (PCB) are persistent organic pollutants (POP) that are consumed because of their bioaccumulation through the food chain. Recent studies have suggested the implication of POPs in the development of metabolic diseases such as type 2 diabetes and obesity. However, this relationship is not entirely consistent, and has not been investigated in longitudinal studies. The purpose of this study was to prospectively examine the association between dietary intake of PCBs and the incidence of obesity in the Seguimiento Universidad de Navarra (SUN) Project.

METHODS

Our study included 12 313 participants without obesity at baseline, who were followed-up for a median of 8.1 years. Dietary intakes of PCBs, expressed as WHO toxic equivalents, were assessed at baseline through a 136-item semiquantitative food-frequency questionnaire. The published concentration levels of PCBs measured in samples of food consumed in Spain were used to estimate intakes. Multivariable Cox regression models were fitted to estimate HRs and 95% CI for incident obesity.

RESULTS

During follow-up, we observed 621 incident cases of obesity. After adjustment for total energy intake and additional adjustment for potential confounders, participants in the fifth quintile of PCBs intake were at higher risk of becoming obese (adjusted HR: 1.58; (95% CI 1.21 to 2.06)) compared to those in the first quintile. The linear trend test was statistically significant (p<0.001).

CONCLUSIONS

Dietary intake of PCBs as estimated using a food frequency questionnaire was associated with a higher incidence of obesity. Nevertheless, further longitudinal studies are needed to confirm our results.

Polychlorinated biphenyls impair dibutyryl cAMP-induced astrocytic differentiation in rat C6 glial cell line

In the central nervous system, alteration of glial cell differentiation can affect brain functions. Polychlorinated biphenyls (PCBs) are persistent environmental chemical contaminants that exert neurotoxic effects in glial and neuronal cells. We examined the effects of a commercial mixture of PCBs, Aroclor1254 (A1254) on astrocytic differentiation of glial cells, using the rat C6 cell line as in vitro model. The exposure for 24 h to sub-toxic concentrations of A1254 (3 or 9 μM) impaired dibutyryl cAMP-induced astrocytic differentiation as showed by the decrease of glial fibrillary acidic protein (GFAP) protein levels and inhibition in change of cell morphology toward an astrocytic phenotype. The A1254 inhibition was restored by the addition of a protein kinase C (PKC) inhibitor, bisindolylmaleimide (bis), therefore indicating that PCBs disturbed the cAMP-induced astrocytic differentiation of C6 cells via the PKC pathway. The phosphorylation of signal transducer and activator of transcription 3 (STAT3) is essential for cAMP-induced transcription of GFAP promoter in C6 cells. Our results indicated that the exposure to A1254 (3 or 9 μM) for 24 h suppressed cAMP-induced STAT3 phosphorylation. Moreover, A1254 reduced cAMP-dependent phosphorylation of STAT3 requires inhibition of PKC activity. Together, our results suggest that PCBs induce perturbation in cAMP/PKA and PKC signaling pathway during astrocytic differentiation of glial cells.