Molecular mechanisms of human thyrocyte dysfunction induced by low concentrations of polychlorinated biphenyl 118 through the Akt/FoxO3a/NIS pathway

Endocrine-disrupting chemicals and autoimmune diseases

Endocrine-disrupting chemicals (EDCs) widely exist in people's production and life which have great potential to damage human and animal health. Over the past few decades, growing attention has been paid to the impact of EDCs on human health, as well as immune system. So far, researchers have proved that EDCs (such as bisphenol A (BPA), phthalate, tetrachlorodibenzodioxin (TCDD), etc.) affect human immune function and promotes the occurrence and development of autoimmune diseases (ADs). Therefore, in order to better understand how EDCs affect ADs, we summarized the current knowledge about the impact of EDCs on ADs, and elaborated the potential mechanism of the impact of EDCs on ADs in this review.

Role of FOXO3a Transcription Factor in the Regulation of Liver Oxidative Injury

Oxidative stress has been identified as a key mechanism in liver damage caused by various chemicals. The transcription factor FOXO3a has emerged as a critical regulator of redox imbalance. Multiple post-translational changes and epigenetic processes closely regulate the activity of FOXO3a, resulting in synergistic or competing impacts on its subcellular localization, stability, protein-protein interactions, DNA binding affinity, and transcriptional programs. Depending on the chemical nature and subcellular context, the oxidative-stress-mediated activation of FOXO3a can induce multiple transcriptional programs that play crucial roles in oxidative injury to the liver by chemicals. Here, we mainly review the role of FOXO3a in coordinating programs of genes that are essential for cellular homeostasis, with an emphasis on exploring the regulatory mechanisms and potential application of FOXO3a as a therapeutic target to prevent and treat liver oxidative injury.

Protective effects of curcumin against thyroid hormone imbalance after gas explosion-induced traumatic brain injury via activation of the hypothalamic-pituitary-thyroid axis in male rats

Gas explosion (GE)-induced traumatic brain injury (TBI) can affect thyroid hormone (TH) homeostasis in miners. This study evaluated the effects of hepatic transthyretin and hypothalamic-pituitary-thyroid (HPT) axis on thyroids and explored the protective effect and mechanism of curcumin on GE-induced TBI. Thirty rats were randomly divided into three groups (10 per group): first group (control group)-rats received GE treatment once; second group (GE group)-rats received GE treatment (200 m from the source of the explosion once); third group (GE + Cur group)-rats received curcumin (Cur) by lavage at a dose of 100 mg/kg/day once every other day for 7 days after receiving GE. After GE, the pathological changes were analyzed by hemotoxylin and eosin staining, and the levels of serum reactive oxygen species (ROS), urine iodine (UI), THs, nuclear factor-kappa B (NF-κB), superoxide dismutase (SOD), glutathione peroxidase (Gpx), and malondialdehyde (MDA) were analyzed using ELISA. Expression of proteins in the HPT axis of rats was examined by immunohistochemistry and Western blotting. We found that GE could induce pathologic changes in rat thyroid and liver. Serum levels of THs, NF-κB and serum redox state became unbalanced in rats after GE. GE could inhibit the biosynthesis and biotransformation of THs by affecting key HPT axis proteins. Additionally, GE reduced the level of hepatic transthyretin. Serum THs levels and thyroid sections were almost recovered to normal after curcumin treatment. The aforementioned key HPT axis proteins in the curcumin group showed opposite expression trends. In summary, GE affected THs balance while curcumin can protect against these injury effects by affecting TH biosynthesis, biotransformation, and transport, and inducing oxidative stress and inflammatory responses.

Network Toxicology Guided Mechanism Study on the Association between Thyroid Function and Exposures to Polychlorinated Biphenyls Mixture

Polychlorinated biphenyls (PCBs) are persistent and highly toxic pollutants, which can accumulate in organisms and produce toxic effects, especially damaging the function of thyroid hormones. So far, the molecular mechanism of PCBs mixture and their metabolites interfering with thyroid hormones has not been studied thoroughly except for individual compounds. In this study, PubMed, Web of Science, and STITCH databases were used to search PCBs and their corresponding target proteins. The intersection of PCBs and thyroid hormone dysfunction target proteins was obtained from GeneCards. The “compounds-targets-pathways” network was constructed by Cytoscape software. And KEGG and Go analyses were performed for key targets. Finally, molecular docking was used to verify the binding effect. Four major active components, five key targets, and 10 kernel pathways were successfully screened by constructing the network. Functional enrichment analysis showed that the interference was mediated by cancer, proteoglycans, PI3K-Akt, thyroid hormone, and FoxO signaling pathways. The molecular docking results showed that the binding energies were less than -5 kcal·mol-1. PCBs and their metabolites may act on the key targets of MAPK3, MAPK1, RXRA, PIK3R1, and TP53. The toxic effect of sulfated and methyl sulfone PCBs is greater. The method of screening targets based on the simultaneous action of multiple PCBs can provide a reference for other research. The targets were not found in previous metabolite toxicity studies. It also provides a bridge for the toxic effects and experimental research of PCBs and their metabolites in the future.

GLIS3 mediated by the Rap1/PI3K/AKT signal pathway facilitates real-ambient PM2.5 exposure disturbed thyroid hormone homeostasis regulation

Exposure to fine particulate matter (PM_2.5) could damage multiple organs and systems. Recent epidemiological studies have shown that PM_2.5 can disrupt dynamic balance of thyroid hormone (TH). However, the underlying mechanism by which PM_2.5 interferes with TH remains unclear. This study evaluated the role of Gli-similar3 (GLIS3) in the effect of PM_2.5 on TH synthesis in mice using a real-ambient exposure system, in Shijiazhuang City, Hebei Province. The PM_2.5exposure group (PM) and filtered air group (FA) were placed in the exposure device for four and eight weeks. The results showed that the PM_2.5 exposure altered the structure of the thyroid gland. Moreover, after PM_2.5 exposure for eight weeks, the exposure level of free thyroxine (FT4) increased and the expression level of thyroid stimulating hormone (TSH) decreased in serum of mice. In addition, PM_2.5 exposure significantly increased the expression of proteins related to thyroid hormone synthesis, such as sodium iodide transporter (NIS), thyroid peroxidase (TPO) and thyroglobulin (TG). Next, we found that GLIS3 and thyroid transcription factor Paired box 8 (PAX8) also increased after PM_2.5 exposure. In order to further explore the potential molecular mechanism, we carried out transcriptome sequencing. KEGG analysis of the top 10 pathways revealed that the Ras-associated protein 1 (Rap1) signaling pathway could activate transcription factors and is related to thyroid cell survival. Additionally, PM_2.5 exposure significantly increased the protein levels of Rap1 and its active form (Rap1 +GTP). We speculate that the active state of Rap1 is believed to be involved in activating the expression of transcription factor GLIS3. In conclusion, PM_2.5 exposure induces histological changes in the thyroid gland and thyroid dysfunction in mice. The exposure activates GLIS3 through the Rap1/PI3K/AKT pathway to promote the expression of proteins related to thyroid hormone synthesis, leading to increased dysregulating TH homeostasis.

PM2.5 disrupts thyroid hormone homeostasis through activation of the hypothalamic-pituitary-thyroid (HPT) axis and induction of hepatic transthyretin in female rats 2.5

Fine particulate matter (PM_2.5), a ubiquitous environmental pollutant, has been indicated to affect thyroid hormone (TH) homeostasis in women, but the detailed mechanism behind this effect remains unclear. The objective of this study was to evaluate the roles of the hypothalamic-pituitary-thyroid (HPT) axis and hepatic transthyretin in the thyroid-disrupting effects of PM_2.5. Sprague Dawley rats were treated with PM_2.5 (0, 15 and 30 mg/kg) by passive pulmonary inhalation for 49 days; and recovery experimental group rats were dosed with PM_2.5 (30 mg/kg) for 35 days, and no treatment was done during the subsequent 14 days. PM_2.5 was handled twice a day by passive pulmonary inhalation throughout the study. After treatment, pathological changes were analyzed by performing haemotoxylin and eosin staining, measuring levels of THs and urine iodine (UI) in serum, plasma, and urine samples using enzyme-linked immunoabsorbent assay, and expression of proteins in the hypothalamus, pituitary, thyroid, and liver tissues of rats were analyzed by immunohistochemistry and Western blotting. The levels of oxidative stress factors, such as reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (Gpx), and nuclear factor-kappa B (NF-κB) in female rats' plasma were also evaluated by ELISA. The results of these analyses revealed that PM_2.5 treatment induced pathologic changes in rat thyroid and liver characterized by increased follicular cavity size and decreased amounts of follicular epithelial cells and fat vacuoles, respectively. Serum levels of triiodothyronine, thyroxine, and thyroid stimulating hormone were significantly decreased, plasma NF-κB level was increased and plasma redox state was unbalanced (enhanced ROS, MDA and Gpx levels; reduced SOD activities) in female rats treated with PM_2.5 (P < 0.05). PM_2.5 treatment suppressed the biosynthesis and biotransformation of THs by increasing sodium iodide symporter, thyroid transcription factor 1, thyroid transcription factor 2, and paired box 8 protein expression levels (P < 0.05). Additionally, thyroid stimulating hormone receptor and thyroid peroxidase levels were significantly decreased (P < 0.05). Both thyrotropin releasing hormone receptor and thyroid stimulating hormone beta levels were enhanced (P < 0.05). Moreover, transport of THs was inhibited due to reduced protein expression of hepatic transthyretin upon treatment with PM_2.5. In summary, PM_2.5 treatment could perturb TH homeostasis by affecting TH biosynthesis, biotransformation, and transport, affecting TH receptor levels, and inducing oxidative stress and inflammatory responses. Activation of the HPT axis and altered hepatic transthyretin levels therefore appear to play a crucial role in PM_2.5-induced thyroid dysfunction.

2,3',4,4',5-Pentachlorobiphenyl Induced Thyrocyte Autophagy by Promoting Calcium Influx via Store-Operated Ca2+ Entry

PCB118, a 2,3',4,4',5-pentachlorobiphenyl, has been shown to destroy thyroidal ultrastructure and induce thyrocyte autophagy. Previously, we reported that PCB118 promoted autophagosome formation in vivo and in vitro, but more details remain to be revealed. To explore the underlying mechanism by which PCB118 regulates thyrocyte autophagy, Fischer rat thyroid cell line-5 (FRTL-5) cells were exposed to different doses of PCB118 at 0, 0.25, 2.5, and 25 nM for 0-48 h. Western blot analysis of autophagy-related proteins P62, BECLIN1, and LC3 demonstrated that PCB118 induced autophagy formation in dose- and time-dependent manner. Moreover, laser scanning confocal microscopy and flow cytometry showed PCB118 treatment led to time- and dose-dependent increase in intracellular calcium concentration ([Ca2+]i). Additionally, PCB118 promoted store-operated Ca2+ entry (SOCE) channel followed by significant increase of ORAI1 and STIM1 protein levels. On the other hand, PCB118 induced thyroidal autophagy via class III β-tubulin (TUBB3)/death-associated protein kinase 2 (DAPK2)/myosin regulatory light chain (MRLC)/autophagy-related 9A (ATG9A) pathway in FRTL-5 cells. Pretreatment with SOCE inhibitor SKF96365 reduced cytosolic Ca2+, ORAI1, STIM1, and BECLIN1 levels as well as LC3 II/LC3 I ratio, while increased P62 expression. SKF96365 also inhibited TUBB3/DAPK2/MRLC/ATG9A pathway in FRTL-5 cells treated by PCB118. Our results provide evidence that PCB118 may induce thyroidal autophagy through TUBB3-related signaling pathway, and these effects are likely to be regulated by calcium influx via SOCE channel.

SCREENED: A Multistage Model of Thyroid Gland Function for Screening Endocrine-Disrupting Chemicals in a Biologically Sex-Specific Manner

Endocrine disruptors (EDs) are chemicals that contribute to health problems by interfering with the physiological production and target effects of hormones, with proven impacts on a number of endocrine systems including the thyroid gland. Exposure to EDs has also been associated with impairment of the reproductive system and incidence in occurrence of obesity, type 2 diabetes, and cardiovascular diseases during ageing. SCREENED aims at developing in vitro assays based on rodent and human thyroid cells organized in three different three-dimensional (3D) constructs. Due to different levels of anatomical complexity, each of these constructs has the potential to increasingly mimic the structure and function of the native thyroid gland, ultimately achieving relevant features of its 3D organization including: 1) a 3D organoid based on stem cell-derived thyrocytes, 2) a 3D organoid based on a decellularized thyroid lobe stromal matrix repopulated with stem cell-derived thyrocytes, and 3) a bioprinted organoid based on stem cell-derived thyrocytes able to mimic the spatial and geometrical features of a native thyroid gland. These 3D constructs will be hosted in a modular microbioreactor equipped with innovative sensing technology and enabling precise control of cell culture conditions. New superparamagnetic biocompatible and biomimetic particles will be used to produce "magnetic cells" to support precise spatiotemporal homing of the cells in the 3D decellularized and bioprinted constructs. Finally, these 3D constructs will be used to screen the effect of EDs on the thyroid function in a unique biological sex-specific manner. Their performance will be assessed individually, in comparison with each other, and against in vivo studies. The resulting 3D assays are expected to yield responses to low doses of different EDs, with sensitivity and specificity higher than that of classical 2D in vitro assays and animal models. Supporting the "Adverse Outcome Pathway" concept, proteogenomic analysis and biological computational modelling of the underlying mode of action of the tested EDs will be pursued to gain a mechanistic understanding of the chain of events from exposure to adverse toxic effects on thyroid function. For future uptake, SCREENED will engage discussion with relevant stakeholder groups, including regulatory bodies and industry, to ensure that the assays will fit with purposes of ED safety assessment. In this project review, we will briefly discuss the current state of the art in cellular assays of EDs and how our project aims at further advancing the field of cellular assays for EDs interfering with the thyroid gland.

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.

2,3',4,4',5-Pentachlorobiphenyl induced autophagy of the thyrocytes via DAPK2/PKD/VPS34 pathway

2,3',4,4',5-Pentachlorobiphenyl (PCB118) has been shown to cause thyroidal ultrastructure lesions, but the underlying mechanism remains elusive. This study aimed to elucidate the mechanism by which PCB118 induces the abnormalities of the thyrocytes. Wistar rats were injected intraperitoneally with PCB118 (0, 10, 100 and 1000 μg/kg/d) for 13 weeks, and FRTL-5 cells were treated with PCB118 (0, 0.25, 2.5 and 25 nM). Transmission electron microscopy showed typical autophagosomes in the thyroid of PCB118-treated rats. Immunofluorescence staining showed dose-dependent increase of autophagy in FRTL-5 cells exposed to PCB118. In vivo and vitro studies found that Tubulin beta 3 class III (Tubb3) mRNA and protein levels decreased significantly, while Death-associated protein kinase 2 (DAPK2) increased after PCB118 exposure, and the binding between Tubb3 and DAPK2 was enhanced by PCB118 in a dose-dependent manner. Moreover, PCB118 resulted in the upregulation of Protein kinase D (PKD) and downregulation of Phosphatidylinositol 3-kinase (VPS34) in mRNA levels, and the activation of PKD and VPS34 phosphorylation. Additionally, Tubb3 small interfering RNA (siTubb3) suppressed DAPK2 protein expression and PKD phosphorylation in FRTL-5 cells, while VPS34 phosphorylation was inhibited by siPKD. Furthermore, DAPK2, PKD and VPS34 were upregulated by Tubb3 overexpression following PCB118 exposure. Our results demonstrate that low concentrations of PCB118 could promote thyroid autophagy formation and cause the abnormalities in thyroidal ultrastructure, and these effects are likely to be mediated by DAPK2/PKD/VPS34 dependent pathway.

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

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

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.

The thyroid gland and thyroid hormones in sheepshead minnow (Cyprinodon variegatus) during early development and metamorphosis

The sheepshead minnow is widely used in ecotoxicological studies that only recently have begun to focus on disruption of the thyroid axis by xenobiotics and endocrine disrupting compounds. However, reference levels of the thyroid prohormone thyroxine (T4) and biologically active hormone 3,5,3'-triiodothyronine (T3) and their developmental patterns are unknown. This study set out to describe the ontogeny and morphology of the thyroid gland in sheepshead minnow, and to correlate these with whole-body concentrations of thyroid hormones during early development and metamorphosis. Eggs were collected by natural spawning in our laboratory. T4 and T3 were extracted from embryos, larvae and juveniles and an enzyme-linked immunoassay was used to measure whole-body hormone levels. Length and body mass, hatching success, gross morphology, thyroid hormone levels and histology were measured. The onset of metamorphosis at 12-day post-hatching coincided with surges in whole-body T4 and T3 concentrations. Thyroid follicles were first observed in pre-metamorphic larvae at hatching and were detected exclusively in the subpharyngeal region, surrounding the ventral aorta. Follicle size and thyrocyte epithelial cell heights varied during development, indicating fluctuations in thyroid hormone synthesis activity. The increase in the whole-body T3/T4 ratio was indicative of an increase in outer ring deiodination activity. This study establishes a baseline for thyroid hormones in sheepshead minnows, which will be useful for the understanding of thyroid hormone functions and in future studies of thyroid toxicants in this species.

The fetal ovary exhibits temporal sensitivity to a 'real-life' mixture of environmental chemicals

The development of fetal ovarian follicles is a critical determinant of adult female reproductive competence. Prolonged exposure to environmental chemicals (ECs) can perturb this process with detrimental consequences for offspring. Here we report on the exposure of pregnant ewes to an environmental mixture of ECs derived from pastures fertilized with sewage sludge (biosolids): a common global agricultural practice. Exposure of pregnant ewes to ECs over 80 day periods during early, mid or late gestation reduced the proportion of healthy early stage fetal follicles comprising the ovarian reserve. Mid and late gestation EC exposures had the most marked effects, disturbing maternal and fetal liver chemical profiles, masculinising fetal anogenital distance and greatly increasing the number of altered fetal ovarian genes and proteins. In conclusion, differential temporal sensitivity of the fetus and its ovaries to EC mixtures has implications for adult ovarian function following adverse exposures during pregnancy.

Toxic chemicals and thyroid function: hard facts and lateral thinking

Increasing quantities of evidence-based data incriminate a large number of environmental pollutants for toxic effects on the thyroid. Among the many chemical contaminants, halogenated organochlorines and pesticides variably affect the hypothalamic-pituitary-thyroid axis and disrupt thyroid function. PCBs and their metabolites and PBDEs bind to thyroid transport proteins, such as transthyretin, displace thyroxine, and disrupt thyroid function. Meanwhile, at the molecular level, PCB congeners may activate phosphorylation of Akt, p-Akt, and forkhead box O3a (FoxO3a) protein resulting in inhibition of the natrium/iodide symporter. Given therefore the growing concern developing around these multiple toxic chemicals today invading numerous environments and their long-term deleterious effects not only on the thyroid but also on general health, we strongly advocate their strict regulation and, moreover, their gradual reduction. A good degree of "lateral thinking", we feel, will lead to a use of chemicals that will enhance life while concurrently carefully protecting the environment.

2,3',4,4',5-Pentachlorobiphenyl Induces Inflammatory Responses in the Thyroid Through JNK and Aryl Hydrocarbon Receptor-Mediated Pathway

Polychlorinated biphenyls (PCBs) are durable and widely distributed environmental contaminants that can compromise the normal functions of multiple organs and systems; one important mechanism is the induction of inflammatory disorders. In this study, we explored the influences of 2,3',4,4',5-pentachlorobiphenyl (PCB118) on inflammatory responses and its underlying mechanisms in the thyroid. Wistar rats were administered PCB118 intraperitoneally at 0, 10, 100, and 1000 μg/kg/d, 5 days a week for 13 weeks; rat thyroid FRTL-5 cells were treated with PCB118 (0, 0.25, 2.5, and 25 nM) for indicated time. Results revealed that PCB118 promoted the generation of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and intercellular adhesion molecule-1 (ICAM-1) in a time- and dose-related manner and decreased sodium/iodide symporter (NIS) protein expression. Moreover, stimulation with PCB118 resulted in the upregulation of the aryl hydrocarbon receptor (AhR)-responsive gene cytochrome P450 1A1 in FRTL-5 cells; whereas pretreatment with the AhR inhibitor α-naphthoflavone or AhR small interfering RNA (siRNA) suppressed AhR, CYP1A1, IL-6, and ICAM-1 and restored NIS expression. In vivo and in vitro studies also suggested that the c-Jun N-terminal kinase (JNK) pathway was activated on PCB118 exposure, and the experiments using siRNA for JNK partially blocked PCB118-induced upregulation of IL-6 and ICAM-1 and downregulation of NIS. Altogether, PCB118 stimulates production of IL-6, TNF-α, and ICAM-1 in the thyroid through AhR and JNK activations and subsequently interferes with NIS expression, resulting in the disruption of thyroid structure and function.