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

Implications of xenobiotic-response element(s) and aryl hydrocarbon receptor in health and diseases

The effect of air pollution on public health is severely detrimental. In humans; the physiological response against pollutants is mainly elicited via the activation of aryl hydrocarbon receptor (AhR). It acts as a prime sensor of xenobiotic chemicals, also functioning as a transcription factor regulating a variety of gene expressions. Along with AhR, another pivotal element of the pollution stress pathway is Xenobiotic Response Elements (XREs). XRE, as studied are some conserved sequences in the DNA, responsible for the physiological response against pollutants. XRE is present at the upstream of the inducible target genes of AhR and it regulates the function of the AhR. XRE(s) are highly conserved in species as it has only eight specific sequences found so far in humans, mice, and rats. Inhalation of toxicants like dioxins, gaseous industrial effluents, and smoke from burning fuel and tobacco leads to predominant damage to the lungs. However, scientists are exploring the involvement of AhR in chronic diseases for example chronic obstructive pulmonary disease (COPD) and also other lethal diseases like lung cancer. In this review, we summarise what is known at this time about the roles played by the XRE and AhR in our molecular systems that have a defined control in the normal maintenance of homeostasis as well as dysfunctions.

Sex Dependent Action of Aroclor 1254 on Basal and sGnRHa-Stimulated Secretion of LH from the Pituitary Cells of Common Carp, Cyprinus carpio L

Polychlorinated biphenyls (PCBs) affect the hypothalamic-pituitary-gonadal axis in many vertebrates, changing the hormonal regulation of reproduction. To identify one of the possible sites of action of PCBs on gonadotropin release in common carp, the direct effects of Aroclor 1254 on luteinizing hormone (LH) secretion from dispersed pituitary cells were investigated. Pituitary cells were obtained from sexually mature male and female common carp (Cyprinus carpio L.) at the time of natural spawning. The cells were incubated with different concentrations of Aroclor 1254 (5, 10, 50 and 100 ng mL–1 medium) and/or salmon gonadotropin-releasing hormone analogue (sGnRHa) at a concentration of 10−8 M. LH levels were measured in the cultured medium by the ELISA method after 10 hours of cell incubation. Incubation of male pituitary cells in the presence of tested concentrations of Aroclor did not change the basal LH secretion to the media. In the female pituitary cell incubations Aroclor (5, 10 and 100 ng mL–1 medium) caused a significant increase in LH concentrations in comparison to control incubations. In the case of sGnRHastimulated LH secretion in incubations of cells of both sexes, all the concentrations of Aroclor significantly stimulated LH release and potentiated stimulatory effects of sGnRH analogue. These results indicate that endocrine disrupters, such as Aroclor 1254, may affect reproduction in fish, acting also directly on gonadotrophs at the level of the pituitary gland, changing LH secretion.

Endocrine-disrupting chemicals and their effects on puberty

Sexual maturation in humans is characterized by a unique individual variability. Pubertal onset is a highly heritable polygenic trait but it is also affected by environmental factors such as obesity or endocrine disrupting chemicals. The last 30 years have been marked by a constant secular trend toward earlier age at onset of puberty in girls and boys around the world. More recent data, although more disputed, suggest an increased incidence in idiopathic central precocious puberty. Such trends point to a role for environmental factors in pubertal changes. Animal data suggest that the GnRH-neuronal network is highly sensitive to endocrine disruption during development. This review focuses on the most recent data regarding secular trend in pubertal timing as well as potential new epigenetic mechanisms explaining the developmental and transgenerational effects of endocrine disrupting chemicals on pubertal timing.

PCB153 reduces apoptosis in primary cultures of murine pituitary cells through the activation of NF-κB mediated by PI3K/Akt

Polychlorinated biphenyls (PCBs) are persistent pollutants involved in human tumorigenesis. PCB153 is a ubiquitous non-dioxin-like PCB with proliferative and anti-apoptotic effects. To explore the impact of PCB153 in the survival of pituitary cells, we exposed murine pituitary primary cells to PCB153 10 μM for 24 h. Apoptosis was assessed by RT-qPCR, Western-blot, immunoprecipitation, caspase activity, and immunofluorescence. We found that PCB153 decreased pituitary apoptosis through both the extrinsic and intrinsic pathways. PCB153 reduced the level of the pro-apoptotic protein p38-MAPK. Otherwise, PCB153 activated PI3K/Akt and Erk1/2 pathways and enhanced the expression and nuclear translocation of NF-κB. Cotreatments with specific inhibitors revealed that only PI3K/Akt changed the caspase-3 expression and NF-κB activation induced by PCB153. Also, PCB153 decreased the expression of the pro-apoptotic and pro-senescent cyclins p53 and p21. In summary, exposure to PCB153 leads to a downregulation of apoptosis in the pituitary driven by a PI3K/Akt-mediated activation of NF-κB.

The influence of polyphenols on metabolic disorders caused by compounds released from plastics - Review

Persistent organic pollutants (POPs) released from plastics into water, soil and air are significant environmental and health problem. Continuous exposure of humans to these substances results not only from the slow biodegradation of plastics but also from their ubiquitous use as industrial materials and everyday products. Exposure to POPs may lead to neurodegenerative disorders, induce inflammation, hepatotoxicity, nephrotoxicity, insulin resistance, allergies, metabolic diseases, and carcinogenesis. This has spurred an increasing intense search for natural compounds with protective effects against the harmful components of plastics. In this paper, we discuss the current state of knowledge concerning the protective functions of polyphenols against the toxic effects of POPs: acrylonitrile, polychlorinated biphenyls, dioxins, phthalates and bisphenol A. We review in detail papers from the last two decades, analyzing POPs in terms of their sources of exposure and demonstrate how polyphenols may be used to counteract the harmful environmental effects of POPs. The protective effect of polyphenols results from their impact on the level and activity of the components of the antioxidant system, enzymes involved in the elimination of xenobiotics, and as a consequence - on the level of reactive oxygen species (ROS). Polyphenols present in daily diet may play a protective role against the harmful effects of POPs derived from plastics, and this interaction is related, among others, to the antioxidant properties of these compounds. To our knowledge, this is the first extensive review of in vitro and in vivo studies concerning the molecular mechanisms of interactions between selected environmental toxins and polyphenols.

Identification of Sex-Specific Transcriptome Responses to Polychlorinated Biphenyls (PCBs)

PCBs are classified as xenoestrogens and carcinogens and their health risks may be sex-specific. To identify potential sex-specific responses to PCB-exposure we established gene expression profiles in a population study subdivided into females and males. Gene expression profiles were determined in a study population consisting of 512 subjects from the EnviroGenomarkers project, 217 subjects who developed lymphoma and 295 controls were selected in later life. We ran linear mixed models in order to find associations between gene expression and exposure to PCBs, while correcting for confounders, in particular distribution of white blood cells (WBC), as well as random effects. The analysis was subdivided according to sex and development of lymphoma in later life. The changes in gene expression as a result of exposure to the six studied PCB congeners were sex- and WBC type specific. The relatively large number of genes that are significantly associated with PCB-exposure in the female subpopulation already indicates different biological response mechanisms to PCBs between the two sexes. The interaction analysis between different PCBs and WBCs provides only a small overlap between sexes. In males, cancer-related pathways and in females immune system-related pathways are identified in association with PCBs and WBCs. Future lymphoma cases and controls for both sexes show different responses to the interaction of PCBs with WBCs, suggesting a role of the immune system in PCB-related cancer development.

A combination of ternary classification models and reporter gene assays for the comprehensive thyroid hormone disruption profiles of 209 polychlorinated biphenyls

Computational toxicology is widely applied to screen tens and thousands of potential environmental endocrine disruptors (EDCs) for its great efficiency and rapid evaluation in recent years. Polychlorinated biphenyls (PCBs) with 209 congeners have not been comprehensively tested for their ability to interact with the thyroid receptor (TR), which is one of the most extensively studied targets related to the effects of EDCs. In this study, we aimed to determine the thyroid-disrupting mechanisms of 209 PCBs through the combination of a novel computational ternary classification model and luciferase reporter gene assay. The reporter gene assay was performed to examine the hormone activities of 22 PCBs via TR to classify their profiles as agonistic, antagonistic or inactive. Thus, six agonists, eleven antagonists and seven inactive chemicals against TR were identified in in vitro assays. Then, six relevant variables, including molecular structural descriptors and molecular docking scores, were selected for describing compounds. Machine learning methods (i.e., linear discriminant analysis (LDA) and support vector machines (SVM)) were used to build classification models. The optimal model was obtained by using SVM, with an accuracy of 88.24% in the training set, 80.0% in the test set and 75.0% in 10-fold cross-validation. The remaining 187 PCB congeners' hormone activities were predicted using the obtained models. Out of these PCBs, the SVM model predicted 38 agonists and 81 antagonists. The findings revealed that higher chlorinated PCBs tended to have TR-antagonistic activities, whereas lower chlorinated PCBs were agonists. This study provided a reference for further exploring PCBs' thyroid effect.

MicroRNA-150-5p affects cell proliferation, apoptosis, and EMT by regulation of the BRAFV600E mutation in papillary thyroid cancer cells

Papillary thyroid cancer (PTC) is the most common endocrine malignancy. Studies have confirmed an association between microRNA (miRNA) and the BRAF^V600E mutation in various cellular biological processes of PTC. This study aimed to clarify the potential relationship between miR-150-5p and the BRAF^V600E mutation in PTC. Human PTC cell lines B-CPAP and TPC-1 were transfected with the miR-150-5p mimic, an inhibitor, and the corresponding controls. Then, cell proliferation, viability, and apoptosis were detected by bromodeoxyuridine, trypan blue exclusion, and flow cytometry assays. The expressions of the main factors of cell cycle, epithelial mesenchymal transition (EMT), and DNA mismatch repair were examined by Western blot analysis and a real-time quantitative polymerase chain reaction. Additionally, pc-BRAF^V600E was transfected into B-CPAP and TPC-1 cells to determine the relationship between miR-150-5p and BRAF^V600E . In addition, the methyl ethyl ketone (MEK)/extracellular signal-regulated kinase (ERK) signal pathway was examined using Western blot analysis. Overexpression of miR-150-5p promoted cell proliferation and viability, inhibited apoptosis, and upregulated cell cycle factor expressions at 50 passages of B-CPAP and TPC-1 cells after transfection. Overexpression of miR-150-5p led to an obvious decrease in E-cadherin expression, but enhanced N-cadherin, Slug and Vimentin, ZEB1, and Snail expression. Moreover, overexpression of miR-150-5p markedly suppressed POLD3, MSH2, and MSH3 expression. Furthermore, BRAF^V600E overexpression increased the expression level of miR-150-5p in TPC cells, and overexpression of telomerase reverse transcriptase further enhanced the promoting effect of BRAF^V600E on miR-150-5p expression in B-CPAP and TPC-1 cells. Finally, BRAF^V600E overexpression activated the MEK/ERK signal pathway in B-CPAP and TPC-1 cells. These data indicated that miR-150-5p promoted cell proliferation, suppressed apoptosis, and accelerated the EMT process by regulation of the BRAF^V600E mutation. Our findings will help elucidate the pathogenesis of PTC and identify biomarkers.

Enantioselective Toxicity in Adult Zebrafish ( Danio rerio) Induced by Chiral PCB91 through Multiple Pathways

This study aimed to further investigate the toxic mechanism of chiral polychlorinated biphenyl (PCB) 91 in adult zebrafish ( Danio rerio) exposed to racemic (rac-), (+)-, or (-)-PCB91 for 63 days. The enantioselective mortalities of adult zebrafish exposed to rac-/(+)-/(-)-PCB91 were 95.86, 50.08, and 81.50%, respectively. Tubular necrosis and cellular hypertrophy occurred in the kidneys of (-)-PCB91-treated groups, whereas demyelination and immune cell infiltration occurred in brains of the rac-, (+)-, and (-)-PCB91-treated groups. Additionally, exposure to chiral PCB91 enantioselectively induced neurotoxicity, apoptosis, and inflammation in brain tissues owing to perturbations of gene expression, protein content and sphingolipid levels. The high mortality after rac-/(+)-PCB91 exposure might be due to toxic effects on brain tissue, while the high mortality after (-)-PCB91 exposure might be due to toxic effects on kidney as well as brain tissues. Thus, our findings offer an important reference for elucidating the enantioselective toxicological mechanism of chiral PCBs in aquatic organisms.

Acromegaly, genetic variants of the aryl hydrocarbon receptor pathway and environmental burden

Increasing evidence suggests that environmental contaminants can exert endocrine disruptors activities and that pollution exposition can have a role in tumorigenic processes. Several environmental pollutants have been shown to affect pituitary cells biology and function. The aryl hydrocarbon receptor (AHR) pathway is involved in xenobiotics' metabolism and in tumorigenesis. A deregulation of the AHR pathway could have a role in pituitary tumours' pathophysiology, especially in the GH secreting ones. AHR-interacting protein (AIP) is one of the key partners of AHR and is implicated in pituitary tumours' pathogenesis. Moreover, an increased prevalence of acromegaly has been reported in a highly polluted area of the province of Messina (Sicily, Italy). Nevertheless, at present, few data are available about the potential role of environmental factors in the pathogenesis and clinical expression of GH secreting pituitary tumours. This review is aimed at discussing the evidences on the potential links among environmental pollutants, the AHR pathway and the pathophysiology of GH-secreting pituitary adenomas.

Effects of environmental pollutants on signaling pathways in rat pituitary GH3 adenoma cells

An increased rate of acromegaly was reported in industrialized areas, suggesting an involvement of environmental pollutants in the pathogenesis and behavior of GH-secreting pituitary adenomas. Based on these premises, the aim of the study was to evaluate the effects of some widely diffused pollutants (i.e. benzene, BZ; bis(2-ethylhexyl) phthalate, DEHP and polychlorinated biphenyls, PCB) on growth hormone secretion, the somatostatin and estrogenic pathways, viability and proliferation of rat GH-producing pituitary adenoma (GH3) cells. All the pollutants induced a statistically significant increase in GH secretion and interfered with cell signaling. They all modulated the expression of SSTR2 and ZAC1, involved in the somatostatin signaling, and the expression of the transcription factor FOXA1, involved in the estrogen receptor signaling. Moreover, all the pollutants increased the expression of the CYP1A1, suggesting AHR pathway activation. None of the pollutants impacted on cell proliferation or viability. Present data demonstrate that exposure to different pollutants, used at in vivo relevant concentrations, plays an important role in the behavior of GH3 pituitary adenoma cells, by increasing GH secretion and modulating several cellular signaling pathways. These observations support a possible influence of different pollutants in vivo on the GH-adenoma aggressiveness and biological behavior.

The Complex Biology of the Aryl Hydrocarbon Receptor and Its Role in the Pituitary Gland

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor best known for its ability to mediate the effects of environmental toxins such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or dioxin), polycyclic aromatic hydrocarbons (PAHs), benzene, and polychlorinated biphenyls (PCBs) through the initiation of transcription of a number of metabolically active enzymes. Therefore, the AHR has been studied mostly in the context of xenobiotic signaling. However, several studies have shown that the AHR is constitutively active and plays an important role in general cell physiology, independently of its activity as a xenobiotic receptor and in the absence of exogenous ligands. Within the pituitary, activation of the AHR by environmental toxins has been implicated in disruption of gonadal development and fertility. Studies carried out predominantly in mouse models have revealed the detrimental influence of several environmental toxins on specific cell lineages of the pituitary tissue mediated by activation of AHR and its downstream effectors. Activation of AHR during fetal development adversely affected pituitary development while adult models exposed to AHR ligands demonstrated varying degrees of pituitary dysfunction. Such dysfunction may arise as a result of direct effects on pituitary cells or indirect effects on the hypothalamic-pituitary-gonadal axis. This review offers in-depth analysis of all aspects of AHR biology, with a particular focus on its role and activity within the adenohypophysis and specifically in pituitary tumorigenesis. A novel mechanism by which the AHR may play a direct role in pituitary cell proliferation and tumor formation is postulated. This review therefore attempts to cover all aspects of the AHR's role in the pituitary tissue, from fetal development to adult physiology and the pathophysiology underlying endocrine disruption and pituitary tumorigenesis.

Role of AhR in positive regulation of cell proliferation and survival

The aryl hydrocarbon receptor (AhR) is an important nuclear transcription factor that is best known for mediating toxic responses by adjusting numbers of metabolism-related enzymes, including CYP1A1 and CYP1B1. Previous findings have revealed that, in addition to negatively regulating cell proliferation and survival, AhR may also positively regulate these pathways. Here, we review these findings and summarize distinct mechanisms by which AhR promotes cell proliferation and survival, including modulation of receptor expression, growth factor signalling and apoptosis, regulating the cell cycle and promoting cytokine expression. This review will aid better understanding the role of AhR in positive regulation of cell proliferation and survival.