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Crofton KM, Zoeller RT. Mode of Action: Neurotoxicity Induced by Thyroid Hormone Disruption During Development—Hearing Loss Resulting From Exposure to PHAHs. Crit Rev Toxicol 2008; 35:757-69. [PMID: 16417043 DOI: 10.1080/10408440591007304] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
An increasing incorporation of mode of action (MOA) information into risk assessments has led to examination of animal MOAs to determine relevance to humans. We examined a specific MOA for developmental neurotoxicity using the MOA/Human Relevance Framework (Meek et al., 2003). The postulated MOA of ototoxicity in rats involves early postnatal exposure to polychlorinated biphenyls (PCBs) via lactation, an upregulation of hepatic uridine diphosphoglucuronyltransferases (UGTs), and subsequent hypothyroxinemia during a critical period of cochlear development, with the ultimate neurotoxic consequence of hearing loss. This review concludes with high confidence in the animal MOA and medium confidence for the interspecies concordance for the key events in the MOA. Possible interspecies differences in toxicodynamic factors moderate confidence in some key events. In addition, there is a question of whether ambient human exposures are large enough to cause human fetal hypothyroxinemia to the degree needed to cause hearing loss. Data gaps identified by this analysis include a need to characterize the induciblity of human fetal UGTs and the comparative sensitivity of UGT induction by xenobiotics in rats and humans. Research on these areas of uncertainty will increase confidence that this MOA for PCBs is not likely to not occur in humans, assuming normal conditions of limited ambient exposure.
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Affiliation(s)
- Kevin M Crofton
- US Environmental Protection Agency, Research Triangle Park, North Carolina 27711, USA.
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Zoeller RT, Tyl RW, Tan SW. Current and Potential Rodent Screens and Tests for Thyroid Toxicants. Crit Rev Toxicol 2008; 37:55-95. [PMID: 17364705 DOI: 10.1080/10408440601123461] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
This article reviews current rodent screens and tests to detect thyroid toxicants. Many points of disruption for thyroid toxicants are outlined and include: (a) changes in serum hormone level; (b) thyroperoxidase inhibitors; (c) the perchlorate discharge test; (d) inhibitors of iodide uptake; (e) effects on iodothyronine deiodinases; (f) effects on thyroid hormone action; and (g) role of binding proteins (e.g., rodent transthyretin). The major thyroid endpoints currently utilized in existing in vivo assay protocols of the Organization for Economic Cooperation and Development (OECD), Japanese researchers, and U.S. Environmental Protection Agency (EPA) include thyroid gland weight, histopathology, circulating thyroid hormone measurements, and circulating thyroid-stimulating hormone (TSH). These endpoints can be added into the existing in vivo assays for reproduction, development, and neurodevelopment that are outlined in this chapter. Strategic endpoints for possible addition to existing protocols to detect effects on developmental and adult thyroid endpoints are discussed. Many of these endpoints for detecting thyroid system disruption require development and additional research before they can be considered in existing assays. Examples of these endpoints under development include computer-assisted morphometry of the brain and evaluation of treatment-related changes in gene expression, thyrotropin-releasing hormone (TRH) and TSH challenge tests, and tests to evaluate thyroid hormone (TH)-dependent developmental events, especially in the rodent brain (e.g., measures of cerebellar and cortical proliferation, differentiation, migration, apoptosis, planimetric measures and gene expression, and oligodendrocyte differentiation). Finally, TH-responsive genes and proteins as well as enzyme activities are being explored. Existing in vitro tests are also reviewed, for example, thyroid hormone (TH) metabolism, receptor binding, and receptor activation assays, and their restrictions are described. The in vivo assays are currently the most appropriate for understanding the potential effects of a thyroid toxicant on the thyroid system. The benefits and potential limitations of the current in vivo assays are listed, and a discussion of the rodent thyroid system in the context of human health is touched upon. Finally, the importance of understanding the relationship between timing of exposure, duration of dose, and time of acquisition of the endpoints in interpreting the results of the in vivo assays is emphasized.
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Affiliation(s)
- R Thomas Zoeller
- Biology Department, Morrill Science Center, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, USA.
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Mortensen AS, Kortner TM, Arukwe A. Thyroid hormone-dependent gene expression as a biomarker of short-term 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) exposure in European common frog (Rana temporaria) tadpoles. Biomarkers 2008; 11:524-37. [PMID: 17056472 DOI: 10.1080/13547500600806717] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The effects on thyroid hormone-dependent gene biomarker responses of the persistent organochlorine pesticide metabolite 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) were investigated after exposure of 4-week-old European common frog (Rana temporaria) (stage 36) tadpoles to two (0.001 and 0.01 ppm) DDE concentrations. Total body weight, total length, and tail length and width increased after 3-day exposure to DDE. Expression patterns of genes encoding for growth hormone, thyroid-stimulating hormone (TSHbeta) and thyroid hormone receptor (TRalpha and TRbeta) isoforms were evaluated in the head, body and tail regions using a validated real-time polymerase chain reaction (PCR) method. The mRNA expression of growth hormone in the body, and TSHbeta in the head showed significant DDE concentration-dependent decreases. While DDE caused variable effects on TRalpha mRNA steady-state, the expression of TRbeta was significantly decreased in the tail by DDE in a concentration-specific manner. The effect of DDE exposure on TRbeta mRNA expression showed a negative correlation with tail length and width during the exposure period. The unique pattern of a DDE-induced decrease of tail TRbeta expression probably reflects the significant role of this thyroid hormone receptor isoform in tail re-absorption and overall metamorphosis in anuran species. Therefore, the present study shows that the evaluation of thyroid hormone-dependent genes may represent quantitative biomarkers of acute exposure to organochlorine pesticides in anuran species during critical developmental periods such as metamorphosis. Given the widespread environmental levels of DDT and its metabolites, these pollutants will remain a subject of concern and their effects on anuran species should be studied in more detail.
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Affiliation(s)
- A S Mortensen
- Department of Biology, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
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Miyazaki W, Iwasaki T, Takeshita A, Tohyama C, Koibuchi N. Identification of the functional domain of thyroid hormone receptor responsible for polychlorinated biphenyl-mediated suppression of its action in vitro. ENVIRONMENTAL HEALTH PERSPECTIVES 2008; 116:1231-6. [PMID: 18795168 PMCID: PMC2535627 DOI: 10.1289/ehp.11176] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2007] [Accepted: 05/13/2008] [Indexed: 05/03/2023]
Abstract
BACKGROUND Polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins, and poly-chlorinated dibenzofurans adversely affect the health of humans and various animals. Such effects might be partially exerted through the thyroid hormone (TH) system. We previously reported that one of the hydroxylated PCB congeners suppresses TH receptor (TR)-mediated transcription by dissociating TR from the TH response element (TRE). However, the binding site of PCB within TR has not yet been identified. OBJECTIVES We aimed to identify the functional TR domain responsible for the PCB-mediated suppression of TR action by comparing the magnitude of suppression using several representative PCB/dioxin congeners. MATERIALS AND METHODS We generated chimeric receptors by combining TR and glucocorticoid receptor (GR) and determined receptor-mediated transcription using transient transfection-based reporter gene assays, and TR-TRE binding using electrophoretic mobility shift assays. RESULTS Although several PCB congeners, including the hydroxylated forms, suppressed TR-mediated transcription to various degrees, 2,3,7,8-tetrachlorodibenzo-p-dioxin did not alter TR action, but 2,3,4,7,8-pentachlorodibenzofuran weakly suppressed it. The magnitude of suppression correlated with that of TR-TRE dissociation. The suppression by PCB congeners was evident from experiments using chimeric receptors containing a TR DNA-binding domain (DBD) but not a GR-DBD. CONCLUSIONS Several nondioxin-like PCB congeners and hydroxylated PCB compounds suppress TR action by dissociating TR from TRE through interaction with TR-DBD.
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Affiliation(s)
- Wataru Miyazaki
- Department of Integrative Physiology, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Toshiharu Iwasaki
- Department of Integrative Physiology, Gunma University Graduate School of Medicine, Maebashi, Japan
- Address correspondence to T. Iwasaki, Department of Integrative Physiology, Division of Biological Regulation, Gunma University Graduate School of Medicine, Maebashi, Gunma 371-8511, Japan. Telephone: 81-27-220-7923. Fax: 81-27-220-7926. E-mail:
| | - Akira Takeshita
- Endocrine Center, Toranomon Hospital and Okinaka Memorial Institute for Medical Research, Tokyo, Japan
| | - Chiharu Tohyama
- Laboratory of Environmental Health Sciences, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, University of Tokyo, Tokyo, Japan
| | - Noriyuki Koibuchi
- Department of Integrative Physiology, Gunma University Graduate School of Medicine, Maebashi, Japan
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55
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Bansal R, Zoeller RT. Polychlorinated biphenyls (Aroclor 1254) do not uniformly produce agonist actions on thyroid hormone responses in the developing rat brain. Endocrinology 2008; 149:4001-8. [PMID: 18420739 PMCID: PMC2488245 DOI: 10.1210/en.2007-1774] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Thyroid hormone (TH) is essential for normal brain development, and polychlorinated biphenyls (PCBs) are known to interfere with TH action in the developing brain. Thus, it is possible that the observed neurotoxic effects of PCB exposure in experimental animals and humans are mediated in part by their ability to interfere with TH signaling. PCBs may interfere with TH signaling by reducing circulating levels of TH, acting as TH receptor analogs, or both. If PCBs act primarily by reducing serum TH levels, then their effects should mimic those of low TH. In contrast, if PCBs act primarily as TH agonists in the developing brain, then they should mimic the effect of T(4) in hypothyroid animals. We used a two-factor design to test these predictions. Both hypothyroidism (Htx) and/or PCB treatment reduced serum free and total T(4) on postnatal d 15. However, only Htx increased pituitary TSHbeta expression. RC3/neurogranin expression was decreased by Htx and increased by PCB treatment. In contrast, Purkinje cell protein-2 expression was reduced in hypothyroid animals and restored by PCB treatment. Finally, PCB treatment partially ameliorated the effect of Htx on the thickness of the external granule layer of the cerebellum. These studies demonstrate clearly that PCB exposure does not mimic the effect of low TH on several important TH-sensitive measures in the developing brain. However, neither did PCBs mimic T(4) in hypothyroid animals on all end points measured. Thus, PCBs exert a complex action on TH signaling in the developing brain.
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Affiliation(s)
- Ruby Bansal
- Department of Biology, University of Massachusetts, Amherst, Massachusetts 01003, USA
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56
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Sun H, Shen OX, Xu XL, Song L, Wang XR. Carbaryl, 1-naphthol and 2-naphthol inhibit the beta-1 thyroid hormone receptor-mediated transcription in vitro. Toxicology 2008; 249:238-42. [PMID: 18584933 DOI: 10.1016/j.tox.2008.05.008] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2008] [Revised: 05/13/2008] [Accepted: 05/14/2008] [Indexed: 11/30/2022]
Abstract
Effects of pesticides on the function of thyroid have attracted lots of attention because thyroid hormones (THs) play a major role in mammalian brain development. In order to screen for compounds that acted on the thyroid hormone receptor (TR) signaling pathway, we transiently transfected the vector pGal4-L-TRbeta1 (Gal4 DBD fused to hTRbeta1 LBD) and Gal4-responsive luciferase reporter pUAS-tk-Luc into HepG2 cell, developing a reporter gene assay which showed good response to triiodothyronine (T3) and thyroxine (T4) with the median effective concentration (EC(50)) of 0.46 and 25.53 nM, respectively. Bisphenol A exhibited weak anti-thyroid hormone activity with median inhibitory concentration (IC(50)) value of 6.45 x 10(-5)M. The assay showed acceptable repeatability to T3 with intra coefficient of variability (CV) of 5.9% and inter CV of 11.7%. Carbaryl, 1-naphthol (1-NAP) and 2-naphthol (2-NAP) were tested for their agonist and antagonist activities. As a result, we found that all the three related chemicals possessed TR antagonist activity and none of them showed the agonist activity. These results further indicated that TR might be the targets of industrial chemicals. And this assay provided a useful tool for investigating the effects of environment chemicals on thyoid function.
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Affiliation(s)
- Hong Sun
- Key Laboratory of Reproductive Medicine, Institute of Toxicology, Nanjing Medical University, Nanjing, China
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57
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Pessah IN, Seegal RF, Lein PJ, LaSalle J, Yee BK, Van De Water J, Berman RF. Immunologic and neurodevelopmental susceptibilities of autism. Neurotoxicology 2008; 29:532-45. [PMID: 18394707 PMCID: PMC2475601 DOI: 10.1016/j.neuro.2008.02.006] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2008] [Revised: 02/14/2008] [Accepted: 02/14/2008] [Indexed: 02/02/2023]
Abstract
Symposium 5 focused on research approaches that are aimed at understanding common patterns of immunological and neurological dysfunction contributing to neurodevelopmental disorders such as autism and ADHD. The session focused on genetic, epigenetic, and environmental factors that might act in concert to influence autism risk, severity and co-morbidities, and immunological and neurobiological targets as etiologic contributors. The immune system of children at risk of autism may be therefore especially susceptible to psychological stressors, exposure to chemical triggers, and infectious agents. Identifying early biomarkers of risk provides tangible approaches toward designing studies in animals and humans that yield a better understanding of environmental risk factors, and can help identify rational intervention strategies to mitigate these risks.
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Affiliation(s)
- Isaac N Pessah
- School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
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58
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Gauger KJ, Giera S, Sharlin DS, Bansal R, Iannacone E, Zoeller RT. Polychlorinated biphenyls 105 and 118 form thyroid hormone receptor agonists after cytochrome P4501A1 activation in rat pituitary GH3 cells. ENVIRONMENTAL HEALTH PERSPECTIVES 2007; 115:1623-30. [PMID: 18007995 PMCID: PMC2072832 DOI: 10.1289/ehp.10328] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2007] [Accepted: 08/15/2007] [Indexed: 05/17/2023]
Abstract
BACKGROUND Polychlorinated biphenyls (PCBs) may interfere with thyroid hormone (TH) signaling by reducing TH levels in blood, by exerting direct effects on TH receptors (TRs), or both. OBJECTIVE Our objective was to identify individual PCBs that directly affect TH signaling by acting on the TR. METHODS We administered a mixture of six PCB congeners based on their ortho substitution pattern, including PCBs 77 and 126 (non-ortho), PCBs 105 and 118 (mono-ortho), and PCBs 138 and 153 (di-ortho), to pregnant Sprague-Dawley rats from gestational days (G) 6 to 16. This mixture, or various combinations of the components, was also evaluated in a transient transfection system using GH3 cells. RESULTS The mixture reduced serum TH levels in pregnant rats on G16 but simultaneously up-regulated the expression of malic enzyme in liver. It also functioned as a TR agonist in vitro; however, none of the individual PCB congeners comprising this mixture were active in this system. Using the aryl hydrocarbon receptor (AhR) antagonist alpha-naphthoflavone, and the cytochrome P450 (CYP)1A1 antagonist ellipticine, we show that the effect of the mixture on the thyroid hormone response element required AhR and CYP1A1. CONCLUSIONS We propose that PCB 126 induces CYP1A1 through the AhR in GH3 cells, and that CYP1A1 activates PCB 105 and/or 118 to a form a compound that acts as a TR agonist. These data suggest that some tissues may be especially vulnerable to PCBs interfering directly with TH signaling due to their capacity to express CYP1A1 in response to coplanar PCBs (or other dioxin-like molecules) if sufficient mono-ortho PCBs are present.
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Affiliation(s)
- Kelly J. Gauger
- Molecular and Cellular Biology Program, University of Massachusetts Amherst, Massachusetts, USA
- Pioneer Valley Life Science Institute, Baystate Medical Center, Spingfield, Massachusetts, USA
| | - Stefanie Giera
- Molecular and Cellular Biology Program, University of Massachusetts Amherst, Massachusetts, USA
- Institute of Pharmacology and Toxicology, Department of Toxicology, University of Tübingen, Tübingen, Germany
| | - David S. Sharlin
- Molecular and Cellular Biology Program, University of Massachusetts Amherst, Massachusetts, USA
| | - Ruby Bansal
- Department of Biology, Morrill Science Center, University of Massachusetts, Amherst, Massachusetts, USA
| | - Eric Iannacone
- Molecular and Cellular Biology Program, University of Massachusetts Amherst, Massachusetts, USA
- Fairleigh Dickinson University, Madison, New Jersey, USA
| | - R. Thomas Zoeller
- Molecular and Cellular Biology Program, University of Massachusetts Amherst, Massachusetts, USA
- Department of Biology, Morrill Science Center, University of Massachusetts, Amherst, Massachusetts, USA
- Address correspondence to R.T. Zoeller, Biology Department, University of Massachusetts, 611 North Pleasant St., Amherst, MA 01003 USA. Telephone: (413) 545-2088. Fax: (413) 545-3243. E-mail:
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Otake T, Yoshinaga J, Enomoto T, Matsuda M, Wakimoto T, Ikegami M, Suzuki E, Naruse H, Yamanaka T, Shibuya N, Yasumizu T, Kato N. Thyroid hormone status of newborns in relation to in utero exposure to PCBs and hydroxylated PCB metabolites. ENVIRONMENTAL RESEARCH 2007; 105:240-6. [PMID: 17490634 DOI: 10.1016/j.envres.2007.03.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2006] [Revised: 03/02/2007] [Accepted: 03/27/2007] [Indexed: 05/15/2023]
Abstract
The associations between in utero exposure to polychlorinated biphenyls (PCBs) or hydroxylated PCB metabolites (OH-PCBs), and free thyroxin (fT4) or thyroid-stimulating hormone (TSH) status in the newborn were investigated as a pilot study of a large-scale epidemiologic study on in utero PCB or OH-PCB exposure and thyroid function of the newborns. Umbilical cord tissue was used as the media for the biological monitoring of PCBs/OH-PCBs exposure in utero. For the measurement of fT4 and TSH, a heel-prick blood sample spotted on filter paper, which is called Guthrie card, is collected from each neonate at day 4-6 postpartum for this study when the mass screening sampling was performed. We showed that the concentration of total OH-PCBs and one of the OH-PCB congeners (OH-PCB 187) was related significantly to higher fT4 level of newborns. On the other hand, the concentration of total PCBs and PCB congeners (PCB 118, 138, 153, and 180) showed no relationship with fT4 and TSH level of the newborns. The results obtained in this pilot study indicated the possibility that in utero OH-PCBs exposure affects thyroid hormone status of newborns.
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Affiliation(s)
- Takamitsu Otake
- Department of Environmental Studies, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8563, Japan
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60
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Lein PJ, Yang D, Bachstetter AD, Tilson HA, Harry GJ, Mervis RF, Kodavanti PRS. Ontogenetic alterations in molecular and structural correlates of dendritic growth after developmental exposure to polychlorinated biphenyls. ENVIRONMENTAL HEALTH PERSPECTIVES 2007; 115:556-63. [PMID: 17450224 PMCID: PMC1852648 DOI: 10.1289/ehp.9773] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2006] [Accepted: 01/16/2007] [Indexed: 05/03/2023]
Abstract
OBJECTIVE Perinatal exposure to polychlorinated biphenyls (PCBs) is associated with decreased IQ scores, impaired learning and memory, psychomotor difficulties, and attentional deficits in children. It is postulated that these neuropsychological deficits reflect altered patterns of neuronal connectivity. To test this hypothesis, we examined the effects of developmental PCB exposure on dendritic growth. METHODS Rat dams were gavaged from gestational day 6 through postnatal day (PND) 21 with vehicle (corn oil) or the commercial PCB mixture Aroclor 1254 (6 mg/kg/day). Dendritic growth and molecular markers were examined in pups during development. RESULTS Golgi analyses of CA1 hippocampal pyramidal neurons and cerebellar Purkinje cells indicated that developmental exposure to PCBs caused a pronounced age-related increase in dendritic growth. Thus, even though dendritic lengths were significantly attenuated in PCB-treated animals at PND22, the rate of growth was accelerated at later ages such that by PND60, dendritic growth was comparable to or even exceeded that observed in vehicle controls. Quantitative reverse transcriptase polymerase chain reaction analyses demonstrated that from PND4 through PND21, PCBs generally increased expression of both spinophilin and RC3/neurogranin mRNA in the hippocampus, cerebellum, and cortex with the most significant increases observed in the cortex. CONCLUSIONS This study demonstrates that developmental PCB exposure alters the ontogenetic profile of dendritogenesis in critical brain regions, supporting the hypothesis that disruption of neuronal connectivity contributes to neuropsychological deficits seen in exposed children.
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Affiliation(s)
- Pamela J. Lein
- Center for Research on Occupational and Environmental Toxicology, Oregon Health & Science University, Portland, Oregon, USA
| | - Dongren Yang
- Center for Research on Occupational and Environmental Toxicology, Oregon Health & Science University, Portland, Oregon, USA
| | - Adam D. Bachstetter
- Neurostructural Research Labs, Tampa, Florida, USA
- Center of Excellence for Aging and Brain Repair and Department of Neurosurgery, University of South Florida College of Medicine, Tampa, Florida, USA
| | - Hugh A. Tilson
- Cellular and Molecular Toxicology Branch, Neurotoxicology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| | - G. Jean Harry
- National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina, USA
| | - Ronald F. Mervis
- Neurostructural Research Labs, Tampa, Florida, USA
- Center of Excellence for Aging and Brain Repair and Department of Neurosurgery, University of South Florida College of Medicine, Tampa, Florida, USA
| | - Prasada Rao S. Kodavanti
- Cellular and Molecular Toxicology Branch, Neurotoxicology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
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Tabuchi M, Veldhoen N, Dangerfield N, Jeffries S, Helbing CC, Ross PS. PCB-related alteration of thyroid hormones and thyroid hormone receptor gene expression in free-ranging harbor seals (Phoca vitulina). ENVIRONMENTAL HEALTH PERSPECTIVES 2006; 114:1024-31. [PMID: 16835054 PMCID: PMC1513321 DOI: 10.1289/ehp.8661] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Persistent organic pollutants are environmental contaminants that, because of their lipophilic properties and long half-lives, bioaccumulate within aquatic food webs and often reach high concentrations in marine mammals, such as harbor seals (Phoca vitulina). Exposure to these contaminants has been associated with developmental abnormalities, immunotoxicity, and reproductive impairment in marine mammals and other high-trophic-level wildlife, mediated via a disruption of endocrine processes. The highly conserved thyroid hormones (THs) represent one vulnerable endocrine end point that is critical for metabolism, growth, and development in vertebrates. We characterized the relationship between contaminants and specific TH receptor (TR) gene expression in skin/blubber biopsy samples, as well as serum THs, from free-ranging harbor seal pups (n = 39) in British Columbia, Canada, and Washington State, USA. We observed a contaminant-related increase in blubber TR-alpha gene expression [total polychlorinated biphenyls (capital sigmaPCBs); r = 0.679; p < 0.001] and a concomitant decrease in circulating total thyroxine concentrations (capital sigmaPCBs; r = -0.711; p < 0.001) . Consistent with results observed in carefully controlled laboratory and captive feeding studies, our findings suggest that the TH system in harbor seals is highly sensitive to disruption by environmental contaminants. Such a disruption not only may lead to adverse effects on growth and development but also could have important ramifications for lipid metabolism and energetics in marine mammals.
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Affiliation(s)
- Maki Tabuchi
- Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, British Columbia, Canada
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Koibuchi N, Iwasaki T. Regulation of brain development by thyroid hormone and its modulation by environmental chemicals. Endocr J 2006; 53:295-303. [PMID: 16702774 DOI: 10.1507/endocrj.kr-69] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Affiliation(s)
- Noriyuki Koibuchi
- Department of Integrative Physiology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
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63
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Koibuchi N. Thyroid hormone action in developing brain and its modulation by polyhalogenated aromatic hydrocarbons. ACTA ACUST UNITED AC 2006. [DOI: 10.1016/j.ics.2005.11.068] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Sharlin DS, Bansal R, Zoeller RT. Polychlorinated biphenyls exert selective effects on cellular composition of white matter in a manner inconsistent with thyroid hormone insufficiency. Endocrinology 2006; 147:846-58. [PMID: 16282356 DOI: 10.1210/en.2005-0778] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Developmental exposure to polychlorinated biphenyls (PCBs) is associated with a variety of cognitive deficits in humans, and recent evidence implicates white matter development as a potential target of PCBs. Because PCBs are suspected of interfering with thyroid hormone (TH) signaling in the developing brain, and because TH is important in oligodendrocyte development, we tested the hypothesis that PCB exposure affects the development of white matter tracts by disrupting TH signaling. Pregnant Sprague Dawley rats were exposed to the PCB mixture Aroclor 1254 (5 mg/kg), with or without cotreatment of goitrogens from gestational d 7 until postnatal d 15. Treatment effects on white matter development were determined by separately measuring the cellular density and proportion of myelin-associated glycoprotein (MAG)-positive, O4-positive, and glial fibrillary acidic protein (GFAP)-positive cells in the genu of the corpus callosum (CC) and in the anterior commissure (AC). Hypothyroidism decreased the total cell density of the CC and AC as measured by 4',6-diamidino-2-phenylindole dihydrochloride (DAPI) staining and produced a disproportionate decrease in MAG-positive oligodendrocyte density with a simultaneous increase in GFAP-positive astrocyte density. These data indicate that hypothyroidism reduces cellular density of CC and AC and fosters astrocyte development at the expense of oligodendrocyte density. In contrast, PCB exposure significantly reduced total cell density but did not disproportionately alter MAG-positive oligodendrocyte density or change the ratio of MAG-positive oligodendrocytes to GFAP-positive astrocytes. Thus, PCB exposure mimicked some, but not all, of the effects of hypothyroidism on white matter composition.
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Affiliation(s)
- David S Sharlin
- Molecular and Cellular Biology Program, University of Massachusetts-Amherst, Morrill Science Center, 01003, USA
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66
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Opinion of the Scientific Panel on contaminants in the food chain [CONTAM] related to the presence of non dioxin-like polychlorinated biphenyls (PCB) in feed and food. EFSA J 2005. [DOI: 10.2903/j.efsa.2005.284] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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Sugawara N, Nakai K, Nakamura T, Ohba T, Suzuki K, Kameo S, Satoh C, Satoh H. Developmental and neurobehavioral effects of perinatal exposure to polychlorinated biphenyls in mice. Arch Toxicol 2005; 80:286-92. [PMID: 16244857 DOI: 10.1007/s00204-005-0042-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2005] [Accepted: 09/28/2005] [Indexed: 10/25/2022]
Abstract
Because behavioral deficits associated with gestational exposure to polychlorinated biphenyls (PCBs) have been a concern, we studied the developmental and neurobehavioral effects of perinatal exposure to Aroclor 1254 (A1254), a commercial mixture of PCBs, in mice. The PCB mixture (A1254; 0, 6, 18, and 54 mg/kg body weight) was administered to pregnant mice (C57BL/6Cr) every 3 days by gavage from gestational day (GD) 6 to postnatal day (PND) 20. Compared with the control, treatment with A1254 did not alter the maternal body weight during the gestation and lactation periods. The body weight of the offspring did not differ among treatments. To assess the effects on offspring following such exposure, physical and neurobehavioral development (i.e., pinna detachment, hair growth, eye opening, incisor eruption, grasp reflex, righting reflex, walking, negative geotaxis, and cliff avoidance) was observed before weaning. At PND 7, poor adult-like responses in negative geotaxis were observed in all exposed groups. When the offspring were at 8-week old, the PCB-treated (18 mg/kg body weight) mice showed a decreased walking speed in the open-field test, and a prolonged time to reach the platform in the water maze test. Spontaneous locomotion activity was not affected by PCB exposure at 9 weeks . These results showed that perinatal exposure to PCBs produces several behavioral alterations in mice. Although dose-dependent changes were not observed, the neurobehavioral effects such as a decreased walking speed in the open-field test and a prolonged time to reach the platform in the water maze test remained in adulthood after the seeming recovery from the transient delay in development before weaning.
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Affiliation(s)
- Norio Sugawara
- Department of Environmental Health Sciences, Tohoku University Graduate School of Medicine, 2-1 Seiryomachi, Aoba-ku, Sendai, 980-8575, Japan.
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68
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Takser L, Mergler D, Baldwin M, de Grosbois S, Smargiassi A, Lafond J. Thyroid hormones in pregnancy in relation to environmental exposure to organochlorine compounds and mercury. ENVIRONMENTAL HEALTH PERSPECTIVES 2005; 113:1039-45. [PMID: 16079076 PMCID: PMC1280346 DOI: 10.1289/ehp.7685] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Polychlorinated biphenyls (PCBs), chlorinated pesticides, and mercury are global environmental contaminants that can disrupt the endocrine system in animals and humans. However, there is little evidence that they can interfere with endocrine status in pregnant women and neonates at low levels of exposure. The aim of this study was to examine thyroid hormone levels during pregnancy and in cord blood in relation to blood concentrations of organochlorine compounds (OCs) and Hg in healthy women recruited during pregnancy. We found a significant negative correlation between maternal total triiodothyronine levels and three non-coplanar congeners (PCB-138, PCB-153, and PCB-180), three pesticides (p,p -DDE, cis-nanochlor, and hexachlorobenzene), and inorganic Hg independently, without any other changes in thyroid status. No significant relationships were observed between OCs and cord serum thyroid hormones. Cord serum free thyroxin was negatively correlated with inorganic Hg. These results suggest that at even low levels of exposure, persistent environmental contaminants can interfere with thyroid status during pregnancy.
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Affiliation(s)
- Larissa Takser
- Laboratoire de Physiologie Materno-foetale, Université du Quebec à Montréal, Montréal, Quebec, Canada
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69
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Fritsche E, Cline JE, Nguyen NH, Scanlan TS, Abel J. Polychlorinated biphenyls disturb differentiation of normal human neural progenitor cells: clue for involvement of thyroid hormone receptors. ENVIRONMENTAL HEALTH PERSPECTIVES 2005; 113:871-6. [PMID: 16002375 PMCID: PMC1257648 DOI: 10.1289/ehp.7793] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Polychlorinated biphenyls (PCBs) are ubiquitous environmental chemicals that accumulate in adipose tissues over the food chain. Epidemiologic studies have indicated that PCBs influence brain development. Children who are exposed to PCBs during development suffer from neuropsychologic deficits such as a lower full-scale IQ (intelligence quotient), reduced visual recognition memory, and attention and motor deficits. The mechanisms leading to these effects are not fully understood. It has been speculated that PCBs may affect brain development by interfering with thyroid hormone (TH) signaling. Because most of the data are from animal studies, we established a model using primary normal human neural progenitor (NHNP) cells to determine if PCBs interfere with TH-dependent neural differentiation. NHNP cells differentiate into neurons, astrocytes, and oligodendrocytes in culture, and they express a variety of drug metabolism enzymes and nuclear receptors. Like triiodothyronine (T3), treatment with the mono-ortho-substituted PCB-118 (2,3',4,4 ,5-pentachlorobiphenyl; 0.01-1 microM) leads to a dose-dependent increase of oligodendrocyte formation. This effect was congener specific, because the coplanar PCB-126 (3,3',4,4 ,5-pentachlorobiphenyl) had no effect. Similar to the T3 response, the PCB-mediated effect on oligodendrocyte formation was blocked by retinoic acid and the thyroid hormone receptor antagonist NH-3. These results suggest that PCB-118 mimics T3 action via the TH pathway.
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Affiliation(s)
- Ellen Fritsche
- Group of Toxicology, Institut für umweltmedizinische Forschung gGmbH an der Heinrich-Heine Universität, Düsseldorf, Germany.
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70
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Builee TL, Hatherill JR. The role of polyhalogenated aromatic hydrocarbons on thyroid hormone disruption and cognitive function: a review. Drug Chem Toxicol 2005; 27:405-24. [PMID: 15573475 DOI: 10.1081/dct-200039780] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Thyroid hormones (TH) are essential to normal brain development, influencing behavior and cognitive function in both adult and children. It is suggested that conditions found in TH abnormalities such as hypothyroidism, hyperthyroidism and generalized resistance to thyroid hormone (GRTH) share symptomatic behavioral impulses found in cases of attention deficit hyperactivity disorder (ADHD) and other cognitive disorders. Disrupters of TH are various and prevalent in the environment. This paper reviews the mechanisms of TH disruption caused by the general class of polyhalogenated aromatic hydrocarbons (PHAH)'s acting as thyroid disrupters (TD). PHAHs influence the hypothalamus-pituitary-thyroid (HPT) axis, as mimicry agents affecting synthesis and secretion of TH. Exposure to PHAH induces liver microsomal enzymes UDP-glucuronosyltransferase (UGT) resulting in accelerated clearance of TH. PHAHs can compromise function of transport and receptor binding proteins such as transthyretin and aryl hydrocarbon receptors (Ahr). Glucose metabolism and catecholamine synthesis are disrupted in the brain by the presence of PHAH. Further, PHAH can alter brain growth and development by perturbing cytoskeletal formation, thereby affecting neuronal migration, elongation and branching. The complex relationships between PHAH and cognitive function are examined in regard to the disruption of T4 regulation in the hypothalamus-pituitary-thyroid axis, blood, brain, neurons, liver and pre and postnatal development.
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Affiliation(s)
- T L Builee
- Environmental Studies Program, University of California at Santa Barbara, Santa Barbara, California 93106-4160, USA
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71
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Zoeller RT, Bansal R, Parris C. Bisphenol-A, an environmental contaminant that acts as a thyroid hormone receptor antagonist in vitro, increases serum thyroxine, and alters RC3/neurogranin expression in the developing rat brain. Endocrinology 2005; 146:607-12. [PMID: 15498886 DOI: 10.1210/en.2004-1018] [Citation(s) in RCA: 322] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Considering the importance of thyroid hormone (TH) in brain development, it is of potential concern that a wide variety of environmental chemicals can interfere with thyroid function or, perhaps of greater concern, with TH action at its receptor (TR). Recently bisphenol-A (BPA, 4,4' isopropylidenediphenol) was reported to bind to the rat TR and act as an antagonist in vitro. BPA is a high production volume chemical, with more than 800 million kg of BPA produced annually in the United States alone. It is detectable in serum of pregnant women and cord serum taken at birth; is 5-fold higher in amniotic fluid at 15-18 wk gestation, compared with maternal serum; and was found in concentrations of up to 100 ng/g in placenta. Thus, the human population is widely exposed to BPA and it appears to accumulate in the fetus. We now report that dietary exposure to BPA of Sprague Dawley rats during pregnancy and lactation causes an increase in serum total T4 in pups on postnatal d 15, but serum TSH was not different from controls. The expression of the TH-responsive gene RC3/neurogranin, measured by in situ hybridization, was significantly up-regulated by BPA in the dentate gyrus. These findings suggest that BPA acts as a TH antagonist on the beta-TR, which mediates the negative feedback effect of TH on the pituitary gland, but that BPA is less effective at antagonizing TH on the alpha-TR, leaving TRalpha-mediated events to respond to elevated T4.
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Affiliation(s)
- R Thomas Zoeller
- Biology Department, Morrill Science Center, University of Massachusetts, Amherst, Massachusetts 01003, USA.
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72
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Gauger KJ, Kato Y, Haraguchi K, Lehmler HJ, Robertson LW, Bansal R, Zoeller RT. Polychlorinated biphenyls (PCBs) exert thyroid hormone-like effects in the fetal rat brain but do not bind to thyroid hormone receptors. ENVIRONMENTAL HEALTH PERSPECTIVES 2004; 112:516-23. [PMID: 15064154 PMCID: PMC1241914 DOI: 10.1289/ehp.6672] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants routinely found in human and animal tissues. Developmental exposure to PCBs is associated with neuropsychologic deficits, which may be related to effects on thyroid hormone (TH) signaling in the developing brain. However, PCBs may interfere with TH signaling solely by reducing circulating levels of TH, or they may exert direct effects on TH receptors (TRs). Therefore, we tested whether maternal exposure to a commercial PCB mixture, Aroclor 1254 (A1254), exerts effects in the fetal brain by one or both of these mechanisms. Dams were dosed daily with 0, 1, or 4 mg/kg A1254 from gestational day 6 (GD6) until they were sacrificed on GD16. A1254 significantly reduced circulating levels of triiodothyronine (T3) and thyroxine (T4) in pregnant rats but increased the expression of several TH-responsive genes in the fetal cortex, including neuroendocrine-specific protein A (NSP-A), RC3/neurogranin, and Oct-1. These findings are consistent with a direct action of PCBs on TRs. However, we did not identify parent PCB congeners or metabolites that bound to rat TRs isolated from hepatic nuclei. These findings indicate that PCBs can interfere with TH signaling in the fetal brain by direct actions on the fetus rather than by producing maternal hypothyroidism.
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Affiliation(s)
- Kelly J Gauger
- Biology Department, Molecular and Cellular Biology Program, Morrill Science Center, University of Massachusetts, Amherst, MA 01003, USA
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73
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Koibuchi N, Jingu H, Iwasaki T, Chin WW. Current perspectives on the role of thyroid hormone in growth and development of cerebellum. THE CEREBELLUM 2004; 2:279-89. [PMID: 14964687 DOI: 10.1080/14734220310011920] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The thyroid hormone (TH) is essential for growth and development of brain, including the cerebellum. Deficiency of TH during the perinatal period results in abnormal cerebellar development, which is well documented in rodent animal models. TH exerts its major effect by binding to the nuclear TH receptor (TR), a ligand-regulated transcription factor. Although TR is highly expressed in many brain regions, including the cerebellum, TH-target genes that likely play critical roles in brain development have not yet been fully clarified. At present, however, expression of many cerebellar genes is known to be altered by perinatal hypothyroidism. Interestingly, after the critical period of TH action (first 2 weeks of postnatal life in rodent cerebellum), the activities of many genes that are altered by perinatal hypothyroidism return to the same levels as those of euthyroid animal despite morphological alterations. Several prominent candidate genes that may play key roles in TH-mediated cerebellar development are discussed in this review. On the other hand, TR-mediated transcription may be modulated by various substances. The nuclear hormone receptor superfamily contains more than 40 transcriptional factors and, most of these receptors are present in the brain. Possible interactions between TR and such transcription factors are also discussed. Further, several additional issues that need to be clarified are discussed. One such issue is the discrepancy of phenotypes among TR-knockout and perinatal hypothyroid mice. Recent studies have provided several important clues to address this issue. Another current area that needs attention is the effect of endocrine disruptors on brain development. Since the molecular structures of TH and several endocrine disrupting chemicals are similar, the effect of such chemicals on brain may be exerted at least in part through the TH system. Recent studies have shown the possible interaction between TR and such chemicals. Overall, this review provides current findings regarding molecular mechanisms on TH action in cerebellar development.
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Affiliation(s)
- Noriyuki Koibuchi
- Department of Integrative Physiology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
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74
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Bogazzi F, Raggi F, Ultimieri F, Russo D, Campomori A, McKinney JD, Pinchera A, Bartalena L, Martino E. Effects of a mixture of polychlorinated biphenyls (Aroclor 1254) on the transcriptional activity of thyroid hormone receptor. J Endocrinol Invest 2003; 26:972-8. [PMID: 14759069 DOI: 10.1007/bf03348194] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Polychlorinated biphenyls (PCBs) are environmental contaminants which may affect thyroid function. PCBs may reduce serum thyroid hormone (TH) concentrations by either displacing T4 from TH transport proteins or increasing its hepatic metabolism. The reduced serum T4 causes neurological and growth defects in animals exposed to PCBs during the perinatal period, which can partially be reverted by T4 administration. In addition to a hypothyroid-like syndrome, a direct action of PCBs on TH-sensitive genes has been postulated. In the present study the effects of Aroclor 1254 (ARO), a mixture of PCBs, on transcription of TH-dependent genes were investigated. A reporter plasmid containing the TH-responsive element (TRE) of malic enzyme (ME) gene was used in transient transfections to assess the responsiveness to ARO. ARO (10 microM) reduced the CAT activity by about 50% and competed with T3 to reduce the induction of transcription. Cotransfection of TH receptor (TR) and a wild type TRE was required to reveal ARO inhibitiry effect, which was abolished by a mock reaction not containing TR or by a mutated TRE. ARO reduced the 125I-T3 binding to TR by 30%, but did not affect the interaction of TR with a 32P-labeled TRE in gel shift assay. ARO is likely to produce a conformational change in in vitro translated TR, leading to its increased proteolysis by trypsin. These results demonstrate that ARO interacts with TR, thereby affecting the transcription of TH-sensitive genes, and provide a molecular basis to further explain the complex effects of PCBs on TH disruption.
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Affiliation(s)
- F Bogazzi
- Department of Endocrinology and Metabolism, University of Pisa, Pisa, Italy.
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75
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Jelaso AM, Lehigh-Shirey E, Predenkiewicz A, Means J, Ide CF. Aroclor 1254 alters morphology, survival, and gene expression in Xenopus laevis tadpoles. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2002; 40:24-35. [PMID: 12211073 DOI: 10.1002/em.10089] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
PCBs are persistent environmental contaminants that cause a variety of adverse health effects in wildlife and humans. This article describes the use of signature gene expression patterns that link increased PCB exposure with progressive, adverse biological effects. Developing Xenopus laevis tadpoles of two age classes were exposed to the PCB mixture Aroclor 1254 for 2 days. Real-time PCR was used to quantitate mRNA expression for 11 physiologically relevant, potential bioindicator genes. Younger tadpoles (5 days postfertilization) were resistant to Aroclor 1254 and showed few changes in gross morphology, swimming behavior, survival, or gene expression. Older tadpoles (11 days postfertilization) were more susceptible to Aroclor 1254. Exposure to 25 and 50 ppm Aroclor 1254 caused alterations in gross morphology and swimming behavior and statistically significant decreases in survival. These tadpoles showed statistically significant decreases in gene expression for 9 out of the 11 genes measured. Tadpoles exposed to 10 ppm showed incipient health changes but had gene expression profiles similar to the tadpoles treated with higher doses of Aroclor 1254. Tadpoles exposed to 1 ppm did not exhibit any observable adverse health effects, yet statistically significant decreases in gene expression occurred in these tadpoles (4 out of 11 genes). After prolonged exposure, tadpoles exposed to 1 and 10 ppm Aroclor 1254 exhibited health effects similar to those exposed to higher concentrations. Therefore, changes in expression of specific genes may serve not only as molecular bioindicators of Aroclor 1254 exposure but also as predictors of impending adverse health effects.
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Affiliation(s)
- Anna M Jelaso
- Environmental Institute, Western Michigan University, Kalamazoo 49008, USA.
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76
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Abstract
The term "endocrine disrupting chemicals" is commonly used to describe environmental agents that alter the endocrine system. Laboratories working in this emerging field-environmental endocrine research-have looked at chemicals that mimic or block endogenous vertebrate steroid hormones by interacting with the hormone's receptor. Environmental chemicals known to do this do so most often with receptors derived from the steroid/thyroid/retinoid gene family. They include ubiquitous and persistent organochlorines, as well as plasticizers, pharmaceuticals, and natural hormones. These chemicals function as estrogens, antiestrogens, and antiandrogens but have few, if any, structural similarities. Therefore, receptor-based or functional assays have the best chance of detecting putative biological activity of environmental chemicals. Three nuclear estrogen receptor forms-alpha, beta, and gamma-as well as multiple membrane forms and a possible mitochondrial form have been reported, suggesting a previously unknown diversity of signaling pathways available to estrogenic chemicals. Examples of environmental or ambient estrogenization occur in laboratory experiments, zoo animals, domestic animals, wildlife, and humans. Environmentally estrogenized phenotypes may differ depending upon the time of exposure-i.e., whether the exposure occurred at a developmental (organizational and irreversible) or postdevelopmental (activational and reversible) stage. The term "estrogen" must be defined in each case, since steroidal estrogens differ among themselves and from synthetic or plant-derived chemicals. An "estrogen-like function" seems to be an evolutionarily ancient signal that has been retained in a number of chemicals, some of which are vertebrate hormones. Signaling, required for symbiosis between plants and bacteria, may be viewed, therefore, as an early example of hormone cross-talk. Developmental feminization at the structural or functional level is an emerging theme in species exposed, during embryonic or fetal life, to estrogenic compounds. Human experience as well as studies in experimental animals with the potent estrogen diethylstilbestrol provide informative models. Advances in the molecular genetics of sex differentiation in vertebrates facilitate mechanistic understanding. Experiments addressing the concept of gene imprinting or induction of epigenetic memory by estrogen or other hormones suggest a link to persistent, heritable phenotypic changes seen after developmental estrogenization, independent of mutagenesis. Environmental endocrine science provides a new context in which to examine the informational content of ecosystem-wide communication networks. As common features come to light, this research may allow us to predict environmentally induced alterations in internal signaling systems of vertebrates and some invertebrates and eventually to explicate environmental contributions to human reproductive and developmental health.
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Affiliation(s)
- J A McLachlan
- Department of Pharmacology, Tulane University Health Sciences Center, Environmental Endocrinology Laboratory, Center for Bioenvironmental Research, Tulane and Xavier Universities, New Orleans, Louisiana 70112-2699, USA.
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77
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Faroon OM, Keith S, Jones D, de Rosa C. Effects of polychlorinated biphenyls on development and reproduction. Toxicol Ind Health 2001; 17:63-93. [PMID: 12117298 DOI: 10.1191/0748233701th097oa] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article, which constitutes the release of an important section of the Toxicological Profile for Polychlorinated Biphenyls (ATSDR 2000) into the scientific literature, focuses on the developmental and reproductive effects of this group of synthetic organic chemicals (PCBs) in humans and animals. Information on other health effects, toxicokinetics, mechanisms of toxicity, biomarkers, interactions, chemical and physical properties, potential for human exposure, and regulations and advisories is detailed in the profile. Interested readers are encouraged to consult the original toxicological profile for more information. Profiles can be requested from ATSDR's Information Center by telephone (1-888-42-ATSDR [1-888-422-8737] or E-mail: (atsdric@cdc.gov).
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Affiliation(s)
- O M Faroon
- Agency for Toxic Substances and Disease Registry, US Department of Health and Human Services, Atlanta, Georgia 30333, USA.
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78
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Dorman DC, Allen SL, Byczkowski JZ, Claudio L, Fisher JE, Fisher JW, Harry GJ, Li AA, Makris SL, Padilla S, Sultatos LG, Mileson BE. Methods to identify and characterize developmental neurotoxicity for human health risk assessment. III: pharmacokinetic and pharmacodynamic considerations. ENVIRONMENTAL HEALTH PERSPECTIVES 2001; 109 Suppl 1:101-11. [PMID: 11250810 PMCID: PMC1240547 DOI: 10.1289/ehp.01109s1101] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
We review pharmacokinetic and pharmacodynamic factors that should be considered in the design and interpretation of developmental neurotoxicity studies. Toxicologic effects on the developing nervous system depend on the delivered dose, exposure duration, and developmental stage at which exposure occurred. Several pharmacokinetic processes (absorption, distribution, metabolism, and excretion) govern chemical disposition within the dam and the nervous system of the offspring. In addition, unique physical features such as the presence or absence of a placental barrier and the gradual development of the blood--brain barrier influence chemical disposition and thus modulate developmental neurotoxicity. Neonatal exposure may depend on maternal pharmacokinetic processes and transfer of the xenobiotic through the milk, although direct exposure may occur through other routes (e.g., inhalation). Measurement of the xenobiotic in milk and evaluation of biomarkers of exposure or effect following exposure can confirm or characterize neonatal exposure. Physiologically based pharmacokinetic and pharmacodynamic models that incorporate these and other determinants can estimate tissue dose and biologic response following in utero or neonatal exposure. These models can characterize dose--response relationships and improve extrapolation of results from animal studies to humans. In addition, pharmacologic data allow an experimenter to determine whether exposure to the test chemical is adequate, whether exposure occurs during critical periods of nervous system development, whether route and duration of exposure are appropriate, and whether developmental neurotoxicity can be differentiated from direct actions of the xenobiotic.
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Affiliation(s)
- D C Dorman
- Chemical Industry Institute of Toxicology, Research Triangle Park, North Carolina, USA
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