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Akinyemi AJ, Miah MR, Ijomone OM, Tsatsakis A, Soares FAA, Tinkov AA, Skalny AV, Venkataramani V, Aschner M. Lead (Pb) exposure induces dopaminergic neurotoxicity in Caenorhabditis elegans: Involvement of the dopamine transporter. Toxicol Rep 2019; 6:833-840. [PMID: 31463204 PMCID: PMC6709386 DOI: 10.1016/j.toxrep.2019.08.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 07/29/2019] [Accepted: 08/02/2019] [Indexed: 12/12/2022] Open
Abstract
Lead (Pb) is an environmental neurotoxicant, and has been implicated in several neurological disorders of dopaminergic dysfunction; however, the molecular mechanism of its toxicity has yet to be fully understood. This study investigated the effect of Pb exposure on dopaminergic neurodegeneration and function, as well as expression level of several dopaminergic signaling genes in wild type (N2) and protein kinase C (pkc) mutant Caenorhabditis elegans. Both N2 and pkc mutant worms were exposed to Pb2+ for 1 h. Thereafter, dopaminergic (DAergic) neurodegeneration, behavior and gene expression levels were assessed. The results revealed that Pb2+ treatment affects dopaminergic cell morphology and structure in worms expressing green fluorescent protein (GFP) under a DAergic cell specific promoter. Also, there was a significant impairment in dopaminergic neuronal function as tested by basal slowing response (BSR) in wild-type, N2 worms, but no effect was observed in pkc mutant worms. Furthermore, Pb2+ exposure increased dat-1 gene expression level when compared with N2 worms, but no alteration was observed in the pkc mutant strains. LC–MS analysis revealed a significant decrease in dopamine content in worms treated with Pb2+ when compared with controls. In summary, our results revealed that Pb2+ exposure induced dopaminergic dysfunction in C. elegans by altering dat-1 gene levels, but pkc mutants showed significant resistance to Pb2+ toxicity. We conclude that PKC activation is directly involved in the neurotoxicity of Pb.
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Affiliation(s)
- Ayodele Jacob Akinyemi
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States
| | - Mahfuzur R Miah
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States
| | - Omamuyovwi M Ijomone
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States.,Department of Anatomy, School of Health and Health Technology, Federal University of Technology Akure (FUTA), Nigeria
| | - Aristidis Tsatsakis
- Laboratory of Toxicology and Forensic Sciences, Medical School, University of Crete, Heraklion, Greece
| | - Félix Alexandre Antunes Soares
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States.,Universidade Federal de Santa Maria, Centro de Ciências Naturais e Exatas, Departamento de Bioquímica e Biologia Molecular, Santa Maria, RS, Brazil
| | | | - Anatoly V Skalny
- Peoples' Friendship University of Russia (RUDN University), Moscow, Russian Federation.,I. M. Sechenov First Moscow State Medical University, Moscow, Russia
| | - Vivek Venkataramani
- Department of Hematology and Medical Oncology, University Medical Center Göttingen (UMG), Göttingen, Germany.,Institute of Pathology, University Medical Center Göttingen (UMG), Göttingen, Germany
| | - Michael Aschner
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States
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Ngueta G, Verner MA, Fiocco AJ, Lupien S, Plusquellec P. Blood lead levels and hypothalamic-pituitary-adrenal function in middle-aged individuals. ENVIRONMENTAL RESEARCH 2018; 160:554-561. [PMID: 29102031 DOI: 10.1016/j.envres.2017.10.032] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 09/10/2017] [Accepted: 10/19/2017] [Indexed: 06/07/2023]
Abstract
Experimental and epidemiological studies suggested that exposure to lead (Pb) may influence the hypothalamic-pituitary-adrenal (HPA) axis. However, previous studies have yielded mixed results. We evaluated changes in basal salivary cortisol levels and acute cortisol responsivity to psychological stress in relation with blood Pb levels (BPb), in Caucasian individuals 50-67 years of age. Data were collected through the Study of Genetics, Stress and Cognitive Development (2004-2006). Diurnal basal and stress-reactive salivary cortisol levels were collected and BPb levels were determined using inductively coupled plasma mass spectroscopy. A total of 65 participants were included in the current study. General linear mixed models were used to assess the association between BPb level and change in cortisol secretion over time, for diurnal basal pattern and stress-reactive pattern, respectively. The geometric mean BPb was 2.70μg/dL (± 1.44) and two exposure groups were created based on the median value of 2.48µg/dL. No difference in geometric mean of salivary cortisol (µg/dL) at awakening was observed between High and Low BPb groups (0.23 (± 0.11) vs 0.20 (± 0.11), p = 0.36). The overall pattern of change in both diurnal basal (from the awakening to bedtime) and reactive salivary cortisol (during the stress induction protocol) did not differ between groups. In these middle-aged and older adults, we concluded that Pb exposure, within the range observed in the current study, was associated with neither diurnal nor stress-reactive cortisol secretion. Further investigation with larger datasets are needed to confirm our observations.
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Affiliation(s)
- Gérard Ngueta
- Department of Occupational and Environmental Health, Université de Montréal, Montreal, Canada; Université de Montréal Public Health Research Institute, Montreal, Canada.
| | - Marc-André Verner
- Department of Occupational and Environmental Health, Université de Montréal, Montreal, Canada; Université de Montréal Public Health Research Institute, Montreal, Canada
| | | | - Sonia Lupien
- Center for Studies on Human Stress, Montreal Mental Health University Institute, Montreal, Canada; Department of Psychiatry, Université de Montréal, Montreal, Canada
| | - Pierrich Plusquellec
- Center for Studies on Human Stress, Montreal Mental Health University Institute, Montreal, Canada; School of Psychoeducation, Université de Montréal, Montreal, Canada.
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Kasten-Jolly J, Heo Y, Lawrence DA. Central nervous system cytokine gene expression: modulation by lead. J Biochem Mol Toxicol 2011; 25:41-54. [PMID: 21322097 DOI: 10.1002/jbt.20358] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The environmental heavy metal toxicant, lead (Pb) has been shown to be more harmful to the central nervous system (CNS) of children than to adults, given that Pb exposure affects the neural system during development. Because growth factors and cytokines play very important roles in development of the CNS, we have examined the impact of Pb exposure on the expression of cytokines during CNS development. Cytokine expression was studied in post-natal-day 21 (pnd21) mice by microarray, real-time RT-PCR, Luminex, and ELISA methodologies. BALB/c mouse pups were exposed to Pb through the dam's drinking water (0.1 mM Pb acetate), from gestation-day 8 (gd8) to pnd21. Two cytokines, interleukin-6 (IL-6) and transforming growth factor-β1 (TGF-β1), displayed significantly changed transcript levels in the presence of Pb. IL-6 and TGF-β1 both have signal transduction cascades that can cooperatively turn on the gene for the astrocyte marker glial-fibrillary acidic protein (GFAP). Microarray results indicated that Pb exposure significantly increased expression of GFAP. Pb also modulated IL-6, TGF-β1, and IL-18 protein expression in select brain regions. The deleterious effects of Pb on learning and long-term memory are posited to result from excessive astrocyte growth and/or activation with concomitant interference with neural connections. Differential neural expression of cytokines in brain regions needs to be further investigated to mechanistically associate Pb and neuroinflammation with behavioral and cognitive changes.
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Affiliation(s)
- Jane Kasten-Jolly
- Laboratory of Clinical and Experimental Endocrinology and Immunology, Wadsworth Center, 120 New Scotland Avenue, Albany, NY 12208, USA
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Zhong Z, Zhang C, Rizak JD, Cui Y, Xu S, Che Y. Chronic prenatal lead exposure impairs long-term memory in day old chicks. Neurosci Lett 2010; 476:23-6. [DOI: 10.1016/j.neulet.2010.03.074] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2009] [Revised: 03/27/2010] [Accepted: 03/29/2010] [Indexed: 10/19/2022]
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Sanders T, Liu Y, Buchner V, Tchounwou PB. Neurotoxic effects and biomarkers of lead exposure: a review. REVIEWS ON ENVIRONMENTAL HEALTH 2009; 24:15-45. [PMID: 19476290 PMCID: PMC2858639 DOI: 10.1515/reveh.2009.24.1.15] [Citation(s) in RCA: 486] [Impact Index Per Article: 32.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Lead, a systemic toxicant affecting virtually every organ system, primarily affects the central nervous system, particularly the developing brain. Consequently, children are at a greater risk than adults of suffering from the neurotoxic effects of lead. To date, no safe lead-exposure threshold has been identified. The ability of lead to pass through the blood-brain barrier is due in large part to its ability to substitute for calcium ions. Within the brain, lead-induced damage in the prefrontal cerebral cortex, hippocampus, and cerebellum can lead to a variety of neurologic disorders. At the molecular level, lead interferes with the regulatory action of calcium on cell functions and disrupts many intracellular biological activities. Experimental studies have also shown that lead exposure may have genotoxic effects, especially in the brain, bone marrow, liver, and lung cells. Knowledge of the neurotoxicology of lead has advanced in recent decades due to new information on its toxic mechanisms and cellular specificity. This paper presents an overview, updated to January 2009, of the neurotoxic effects of lead with regard to children, adults, and experimental animals at both cellular and molecular levels, and discusses the biomarkers of lead exposure that are useful for risk assessment in the field of environmental health.
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Affiliation(s)
- Talia Sanders
- Molecular Toxicology Research Laboratory, NIH RCMI - Center for Environmental Health, College of Science, Engineering, and Technology, Jackson State University, Jackson, MS, USA
| | - Yiming Liu
- Molecular Toxicology Research Laboratory, NIH RCMI - Center for Environmental Health, College of Science, Engineering, and Technology, Jackson State University, Jackson, MS, USA
| | | | - Paul B. Tchounwou
- Molecular Toxicology Research Laboratory, NIH RCMI - Center for Environmental Health, College of Science, Engineering, and Technology, Jackson State University, Jackson, MS, USA
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Aykin-Burns N, Ercal N. Effects of selenocystine on lead-exposed Chinese hamster ovary (CHO) and PC-12 cells. Toxicol Appl Pharmacol 2006; 214:136-43. [PMID: 16442139 DOI: 10.1016/j.taap.2005.12.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2005] [Revised: 12/05/2005] [Accepted: 12/06/2005] [Indexed: 11/29/2022]
Abstract
Lead is a pervasive environmental toxin that affects multiple organ systems, including the nervous, renal, reproductive, and hematological systems. Even though it is probably the most studied toxic metal, some of the symptoms of lead toxicity still cannot be explained by known molecular mechanisms. Therefore, lead-induced oxidative stress has recently started to gain attention. This in vitro study confirms the existence of oxidative stress due to lead exposure. Administration of lead acetate (PbA) to cultures of Chinese hamster ovary cells (CHO) had a concentration-dependent inhibitory effect on colony formation and cell proliferation. This inhibition was eliminated by 5 microM selenocystine (SeCys). In order to evaluate the nature of SeCys's effect, we measured glutathione (GSH), its oxidized form glutathione disulfide (GSSG), malondialdehyde (MDA), catalase, and GSH peroxidase (GPx) activities in lead-exposed CHO cells both in the presence and absence of SeCys. Increases in MDA, catalase, and GPx activities were observed in cultures that received only PbA, but supplementation with SeCys returned these measures to pretreatment levels. The ratio of GSH to GSSG increased in lead-exposed cells incubated in SeCys-enhanced media but declined in cultures treated with PbA only. In order to determine whether SeCys also reverses lead-induced neurotoxicity, a neuronal cell line, PC-12 cells, was used. Lead's inhibition on neurite formation was significantly eliminated by SeCys in PC-12 cells. Our results suggest that SeCys can confer protection against lead-induced toxicity in CHO cells and neurotoxicity in PC-12 cells.
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Affiliation(s)
- Nukhet Aykin-Burns
- Department of Chemistry, University of Missouri-Rolla, 1870 Miner Circle, 142 Schrenk Hall, Rolla, MO 65409, USA
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7
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Davidovics Z, DiCicco-Bloom E. Moderate lead exposure elicits neurotrophic effects in cerebral cortical precursor cells in culture. J Neurosci Res 2005; 80:817-25. [PMID: 15884012 DOI: 10.1002/jnr.20539] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Lead (Pb) persists as an environmental toxicant despite aggressive environmental and occupational regulation. Neurotoxicological effects of acute Pb poisoning range from subtle cognitive deficits, to clumsiness and ataxia, to coma and seizures. In adult neurotoxicity, reductions of blood Pb levels are often associated with reversal of clinical signs. In children, however, the effects are more likely to endure, with even low levels of chronic Pb exposure correlating with decreasing IQ. These persistent effects likely result from neurodevelopmental insults, such as altered cell survival or maturation, although the mechanisms have not been fully defined. In the present study we define the effects of moderate-level Pb exposure on mammalian neurogenesis using a well-characterized cortical precursor model. Gestational day 14.5 rat cerebral cortical precursor cells were cultured in defined media and cell number, precursor proliferation, apoptosis, and neuritic process outgrowth were assessed following exposure to a range of Pb acetate concentrations. Surprisingly, whereas a concentration of 30 microg/ml Pb acetate was acutely toxic to neurons, concentrations between 1 and 10 microg/ml Pb acetate (approximately 3 microM and 30 microM Pb, respectively) increased cell number: 10 times as many cells exposed to 10 microg/ml Pb were present on day 4 as compared to control. The increase in cell number was not a result of increased proliferation, however, as DNA synthesis did not increase. Rather, Pb exposure maintained the survival of cortical precursors, as the progressive apoptosis occurring under control conditions was markedly reduced by the metal. Additionally, neuritic process initiation and outgrowth increased in a concentration-dependent manner, with processes four times as abundant on day 1 and twice as long on day 2. These results suggest that brief exposure to lead during neurogenesis directly affects cell survival and process development, potentially altering cortical arrangement. Consequently, alterations in neural circuitry may underlie some of the neurological effects of Pb exposure during brain development.
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Affiliation(s)
- Zev Davidovics
- Department of Neuroscience and Cell Biology, UMDNJ-Robert Wood Johnson Medical School, Piscataway, 08854, USA
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Toscano CD, McGlothan JL, Guilarte TR. Lead exposure alters cyclic-AMP response element binding protein phosphorylation and binding activity in the developing rat brain. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2003; 145:219-28. [PMID: 14604762 DOI: 10.1016/j.devbrainres.2003.08.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We examined the effect of lead (Pb(2+)) exposure during development on cyclic-AMP response element binding protein (CREB) expression and phosphorylation in cortical and hippocampal nuclear extracts at postnatal (PN) days 7, 14, 21 and 50. We also examined the binding of CREB family proteins to the cyclic-AMP response element (CRE) using a novel filter-binding assay that provides a quantitative measure of binding kinetics. In the hippocampus and cerebral cortex of control rats, CREB and phospho-CREB (pCREB; serine-133) expression is highest at PN7 and decreases steadily until PN50. Developmental Pb(2+) exposure does not affect total CREB levels but decreases pCREB levels at PN14 and PN50 in the cortex and at PN50 in the hippocampus. Using the filter-binding assay, we measured a 30% decrease in B(max) and 38% decrease in the Kd of CREB family proteins for the CRE in PN50 hippocampal nuclear fractions prepared from Pb(2+)-exposed rats. A similar, but nonsignificant, trend is observed in the cortex of PN50 lead-exposed rats. In addition, a 70% increase in the B(max) was observed in the cortex of PN14 lead-exposed rats without a significant change in the Kd. These disruptions in pCREB expression and binding activity of CREB family members during the ontogeny of the rat brain begin to decipher intracellular mechanisms of Pb(2+) neurotoxicity.
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Affiliation(s)
- Christopher D Toscano
- Department of Environmental Health Sciences, The Johns Hopkins University, Bloomberg School of Public Health, 615 North Wolfe Street, Room W2001, Baltimore, MD 21205, USA
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Yang JH, Derr-Yellin EC, Kodavanti PRS. Alterations in brain protein kinase C isoforms following developmental exposure to a polychlorinated biphenyl mixture. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2003; 111:123-35. [PMID: 12654512 DOI: 10.1016/s0169-328x(02)00697-6] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
PCBs have been shown to alter several neurochemical end-points and are implicated in the etiology of some neurological diseases. Recent in vivo studies from our laboratory indicated that developmental exposure to a commercial PCB mixture, Aroclor 1254, caused perturbations in calcium homeostasis and changes in protein kinase C (PKC) activities in rat brain. However, it is not known which molecular substances are targets for PCB-induced developmental neurotoxicity. Since the PKC signaling pathway has been implicated in the modulation of motor behavior as well as learning and memory, and the roles of PKC are subspecies specific, the present study attempted to analyze the effects on selected PKC isozymes in the cerebellum and the hippocampus following developmental exposure (gestational day 6 through postnatal day 21) to a PCB mixture, Aroclor 1254. The results indicated that the developmental exposure to PCBs caused significant hypothyroxinemia and age-dependent alterations in the translocation of PKC isozymes; the effects were greatly significant at postnatal day (PND) 14. Immunoblot analysis of PKC-alpha (alpha) from both cerebellum and hippocampus revealed that developmental exposure to Aroclor 1254 caused a significant decrease in cytosolic fraction and an increase in particulate fraction. There was no significant difference between these two brain regions on the level of fractional changes. However, the ratio between the fractions (particulate/cytosol) from cerebellum only was increased in a dose-dependent manner. Analysis of PKC-gamma (gamma) in cerebellum on PND14 showed a decrease in cytosolic fraction in both dose groups and an increase in particulate fraction at high dose (6 mg/kg) only. The ratio between the two fractions was increased in a dose-dependent manner. In the hippocampus, there was a significant decrease in PKC-gamma in cytosolic fraction of the high-dose group and a significant increase in particulate fraction of the low-dose group. But, the ratio between the fractions showed a significant increase (2.6-fold increase in high dose on PND14). Analysis of PKC-epsilon (epsilon) in cerebellum showed a significant decrease in cytosolic fraction at PND14, while particulate PKand an increase in ratio between fractions at 6 mg/kg on PND14. The results from this study indicate that the patterns of subcellular distributions of PKC isoforms following a developmental PCB exposure were PKC isozyme- and developmental stage-specific. Considering the significant role of PKC signaling in motor behavior, learning and memory, it is suggested that altered subcellular distribution of PKC isoforms at critical periods of brain development may be a possible mechanism of PCB-induced neurotoxic effects and that PKC-alpha, gamma, and epsilon may be among the target molecules implicated with PCB-induced neurological impairments during developmental exposure. It is believed that this is the first report successfully identifying PKC isoforms responding to PCBs during developmental exposure.
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Affiliation(s)
- Jae-Ho Yang
- National Academy of Sciences, National Research Council, Washington, DC, USA
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Shahak H, Slotkin TA, Yanai J. Alterations in PKCgamma in the mouse hippocampus after prenatal exposure to heroin: a link from cell signaling to behavioral outcome. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2003; 140:117-25. [PMID: 12524182 DOI: 10.1016/s0165-3806(02)00607-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Administration of heroin to pregnant mice evokes neurochemical and behavioral deficits consequent to disruption of septohippocampal cholinergic innervation, notably involving desensitization of the ability of cholinergic receptors to activate PKC activity. The present study further evaluates whether desensitization occurs specifically for the PKCgamma isoform, the behaviorally relevant subtype, as compared to PKCalpha. Mice were exposed transplacentally to heroin on gestational days (GD) 9-18 via s.c. maternal injections (10 mg/kg per day). In young adulthood (50 days old), control offspring showed an increase in hippocampal cell membrane PKCgamma after incubation with the muscarinic cholinergic receptor agonist, carbachol, indicative of translocation from the cytosol. Prenatal exposure to heroin eliminated this response, whereas basal PKCgamma levels were unchanged. In contrast, PKCalpha, which is not related to heroin-induced behavioral deficits, did not show a loss of response. The present findings strongly point to abnormalities in the responsiveness of PKCgamma as a mechanism underlying the neurobehavioral teratogenicity of heroin.
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Affiliation(s)
- Halit Shahak
- The Ross Laboratory for Studies in Neural Birth Defects, Department of Anatomy and Cell Biology, The Hebrew University-Hadassah Medical School, P.O. Box 12272, 91120 Jerusalem, Israel
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Olivi L, Sisk J, Bressler J. The involvement of lipid activators of protein kinase C in the induction of ZIF268 in PC12 cells exposed to lead. Neurochem Res 2003; 28:65-71. [PMID: 12587664 DOI: 10.1023/a:1021696011920] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Lead (Pb) induces the expression of immediate early genes (IEG) in PC12 cells by a mechanism that involves protein kinase C (PKC). To define the mechanisms, the involvement of two commonly observed lipid activators of PKC, diacylglycerols, and phosphatidylinositols, were examined. A dose-dependent increase in the expression of the IEG zif268 was observed in PC12 cells exposed to Pb. The PKC inhibitor Ro-31-8220 blocked the induction. An increase in levels of diacylglycerols was observed in PC12 cells exposed to Pb, but the increase was inhibited by Ro-31-8220. The phosphatidylinositol 3-kinase inhibitor Wortmannin, but not the inhibitor LY 294002, blocked the induction zif268 in Pb-exposed cells. Small increases in phosphatidylinositol 3-kinase activity were observed after exposure to Pb. In summary, diacylglycerols are elevated in PC12 cells exposed to Pb by a mechanism that requires PKC. It is possible that diacylglycerols contribute to the induction of zif268 by Pb by sustaining PKC activation.
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Affiliation(s)
- Luisa Olivi
- Kennedy Krieger Research Institute, Baltimore, Maryland 21205, USA
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Cremin JD, Smith DR. In vitro vs in vivo Pb effects on brain protein kinase C activity. ENVIRONMENTAL RESEARCH 2002; 90:191-199. [PMID: 12477464 DOI: 10.1016/s0013-9351(02)00007-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Alteration of normal protein kinase C (PKC) function by environmental Pb exposure during neurodevelopment is hypothesized to be an important mechanism of toxicity underlying neurologic impairment. Previous studies have reported widely varying effects of Pb on PKC, possibly in part because of differences in in vitro and in vivo models used in those studies. Therefore, we tested the hypothesis that, with comparable tissue Pb levels, the effects of in vitro Pb exposure on brain PKC are the same as the effects caused by in vivo Pb exposure of intact animals. For chronic in vivo Pb exposure, female Long-Evans rats were exposed to Pb or vehicle from postnatal days 1 to 34-36 (n=10/treatment). For in vitro Pb exposure, homogenate of the frontal cortex region was exposed directly to Pb in an amount comparable to that accumulated in brain during chronic in vivo Pb exposure. Brain Pb levels were measured using ultraclean techniques and inductively coupled plasma mass spectrometry. PKC activity was subsequently determined in cytosolic and membrane subcellular fractions in the frontal cortex, hippocampus, and remaining brain regions. Results indicate that brain Pb levels following in vivo Pb exposure were increased approximately 20-fold above those of nonexposed animals (vehicle group [Pb] approximately 130ng Pb/g dry wt.). However, in vivo Pb exposure did not measurably alter brain PKC activity in the regions tested. In contrast, in vitro Pb exposure significantly increased PKC activity by approximately 20% in the frontal cortex homogenate membrane subcellular fraction. These results indicate that Pb added in vitro caused more dramatic effects than those produced by a comparable amount of Pb in the tissue from in vivo exposure. While the mechanisms underlying these outcomes are not clear, they suggest that in vitro models might not accurately reflect effects of chronic low-level in vivo Pb exposure.
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Affiliation(s)
- John D Cremin
- Department of Environmental Toxicology, University of California, Santa Cruz, CA 95064, USA
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Kim KA, Chakraborti T, Goldstein G, Johnston M, Bressler J. Exposure to lead elevates induction of zif268 and Arc mRNA in rats after electroconvulsive shock: the involvement of protein kinase C. J Neurosci Res 2002; 69:268-77. [PMID: 12111808 DOI: 10.1002/jnr.10296] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Exposure to lead is well known to impair cognitive function in young children. Because of the importance of gene regulation for neurodevelopment, we examined the effect of lead on the induction of the mRNA of the immediate early genes zif268 and Arc. The time course for the induction of zif268 mRNA and Arc mRNA by electroconvulsant shock (ECS) was altered in the area of the dentate gyrus of the hippocampus in rats exposed to lead from postnatal days (PND) 1 to 28. Other areas of the hippocampus were not affected by lead. The effects on the induction of zif268 mRNA were observed at blood lead levels as low as 12 microg/dl. No change in the induction of zif268 mRNA was observed in the hippocampus of rats exposed to lead from PND 28 to PND 56. Because of the possible involvement of protein kinase C (PKC) in the effect of lead, activation of different isoforms of PKC was investigated. An increase in the amount of PKC epsilon and PKC gamma was observed at 60 min after ECS in the membrane fraction from hippocampus, indicating activation of these isoforms. The amount of PKC epsilon in membranes was higher in rats exposed to lead than in rats not exposed to lead after ECS. Taken together, the data suggest that lead may disturb regulation of specific immediate early genes by activating PKC epsilon.
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Affiliation(s)
- Kyung-Ah Kim
- Department of Environmental Health Sciences, School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA
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Nihei MK, Guilarte TR. Molecular changes in glutamatergic synapses induced by Pb2+: association with deficits of LTP and spatial learning. Neurotoxicology 2001; 22:635-43. [PMID: 11770885 DOI: 10.1016/s0161-813x(01)00035-3] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
What are the molecular bases for the neurotoxicity that occurs after developmental exposure to low levels of Pb2+, and are these effects persistent and detrimental in adults? Our inability to understand specific mechanisms behind Pb2+ neurotoxicity has long been one of many problem areas of this preventable childhood disease. The sensitivity of the developing brain to Pb2+-induced neurotoxicity is an outcome of the many unique characteristics that comprise the developing central nervous system. The developing brain can be exposed to significant concentrations of Pb2+ during vulnerable periods of development such as synapse formation, gene and protein expression, and other diverse molecular changes associated with these processes. Recently, changes in NMDA receptor subunits were identified in animals that showed cognitive deficits induced by exposure to Pb2+. This molecular association is important because it provides new evidence in the characterization of developmental Pb2+ neurotoxicity that supports physiological findings of impairments in synaptic plasticity and behavior. This review updates information from molecular studies that can be directly associated with impairments of behavior and synaptic plasticity, and outlines the functional consequences of molecular differences in Pb2+-exposed animals that illuminate potential mechanisms of Pb2+-induced neurotoxicity.
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Affiliation(s)
- M K Nihei
- Department of Environmental Health Sciences, The Johns Hopkins University School of Hygiene and Public Health, Baltimore, MD 21205, USA
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Ramesh GT, Jadhav AL. Levels of protein kinase C and nitric oxide synthase activity in rats exposed to sub chronic low level lead. Mol Cell Biochem 2001; 223:27-33. [PMID: 11681719 DOI: 10.1023/a:1017549003114] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The intracellular regulation of protein kinase C (PKC) and nitric oxide synthase (NOS) in relation to the accumulation of lead (Pb2+) in various brain regions following low-level lead exposure (50 ppm) for 90 days in rats was investigated. PKC and NOS are important enzymes in mediating cellular transduction mechanisms and in the regulation of neuronal plasticity. Rats exposed to Pb2+ resulted in blood Pb2+ levels similar to those observed in children affected due to Pb2+ exposure. Further, we examined whether Pb2+ accumulation changed the intracellular signaling mechanisms in different brain regions. Results of these experiments indicate that significant region specific Pb2+ accumulation is associated with down regulation of PKC. The down regulation of PKC increased the activity of NOS following Pb2+ exposure. Thus, the change in PKC activity in respect to Pb2+ accumulation increased NOS activity. These results suggest that neuronal toxicity during Pb2+ exposure is linked to the modulation of PKC followed by NOS activation.
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Affiliation(s)
- G T Ramesh
- College of Pharmacy & Health Sciences, Texas Southern University, Houston 77004, USA
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Costa LG, Guizzetti M, Lu H, Bordi F, Vitalone A, Tita B, Palmery M, Valeri P, Silvestrini B. Intracellular signal transduction pathways as targets for neurotoxicants. Toxicology 2001; 160:19-26. [PMID: 11246120 DOI: 10.1016/s0300-483x(00)00435-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The multiple cascades of signal transduction pathways that lead from receptors on the cell membrane to the nucleus, thus translating extracellular signals into changes in gene expression, may represent important targets for neurotoxic compounds. Among the biochemical steps and pathways that have been investigated are the metabolism of cyclic nucleotides, the formation of nitric oxide, the metabolism of membrane phospholipids, the activation of a multitude of protein kinases and the induction of transcription factors. This brief review will focus on the interactions of three known neurotoxicants, lead, ethanol and polychlorinated biphenyls, with signal transduction pathways, particularly the family of protein kinase C isozymes, and discusses how such effects may be involved in their neurotoxicity.
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Affiliation(s)
- L G Costa
- Department of Environmental Health, University of Washington, 4225 Roosevelt #100, Seattle, WA 98105, USA.
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Nihei MK, McGlothan JL, Toscano CD, Guilarte TR. Low level Pb(2+) exposure affects hippocampal protein kinase C gamma gene and protein expression in rats. Neurosci Lett 2001; 298:212-6. [PMID: 11165444 DOI: 10.1016/s0304-3940(00)01741-9] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We examined the effect of chronic exposure to lead (Pb(2+)) on protein kinase C (PKC) in 50-day-old rat hippocampus. Cytosolic and membrane fractions of hippocampus from Pb(2+)-exposed rats showed reduced expression of PKC gamma protein. In contrast, a significant elevation of PKC gamma mRNA was observed in pyramidal and dentate granule cell layers. Protein expression of alpha, beta I, beta II and epsilon isoenzymes were unchanged in Pb(2+)-exposed rats, as was [(3)H]phorbol 12,13 dibutyrate (PDBu) binding in tissue slices. Differences were not observed in Ca(2+)-dependent or -independent PKC activity, or in PKC-specific back-phosphorylation of hippocampal homogenates from Pb(2+)-exposed rats. Reduced subcellular levels of PKC gamma in Pb(2+)-exposed rats suggest that signal transduction in the hippocampus may be selectively altered and may be important in manifesting Pb(2+)-induced impairments of synaptic plasticity, learning and memory.
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Affiliation(s)
- M K Nihei
- Department of Environmental Health Sciences, The Johns Hopkins University, School of Hygiene and Public Health, 615 North Wolfe Street, Room W2001, Baltimore, MD 21205, USA
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Yun SW, Gärtner U, Arendt T, Hoyer S. Increase in vulnerability of middle-aged rat brain to lead by cerebral energy depletion. Brain Res Bull 2000; 52:371-8. [PMID: 10922516 DOI: 10.1016/s0361-9230(00)00274-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The neurotoxic effects of low-level lead (Pb) during senescence are increasing interests of importance. We investigated the effects of low-level Pb on the brain in a normal condition and a pathophysiological condition of energy shortage that is commonly found in age-related neurological diseases. Middle-aged rats (15 months old) were exposed to 200 mg/l Pb acetate in drinking water for 2 months and thereafter received bilateral intracerebroventricular injections of streptozotocin (STZ). After 1 month's additional exposure to the same level of Pb solution as before the rats were sacrificed. Blood and brain Pb levels were measured by graphite furnace atomic absorption spectrophotometry. Energy-rich phosphate levels in the brain were determined by high-performance liquid chromatography equipped with a UV detector. Astroglial activation and glucose-regulated protein (GRP)94 expression were examined immunohistochemically. Exposure to Pb increased the blood Pb level to 10.8 microg/dl and the brain Pb level to 0.052 microg/g. But a significant additional increase in the brain Pb level, to 0.101 microg/g, became obvious in rats treated with Pb + STZ. Both Pb and STZ induced perturbation in brain energy metabolism, but no further alteration in energy metabolite levels was found in rats treated with Pb + STZ. Astroglial activation and GRP94-positive astrocytes and neurons were found only in the brains of Pb + STZ-treated rats. These results suggest that exposure to low-level Pb can perturb brain energy metabolism and the brain becomes more vulnerable to Pb when it is under energy stress.
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Affiliation(s)
- S W Yun
- Department of Pathochemistry and General Neurochemistry, University of Heidelberg, Heidelberg, Germany
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Hussain RJ, Parsons PJ, Carpenter DO. Effects of lead on long-term potentiation in hippocampal CA3 vary with age. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2000; 121:243-52. [PMID: 10876039 DOI: 10.1016/s0165-3806(00)00051-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The effects of lead on long-term potentiation (LTP) in the hippocampal area CA3 were different in 30-day (P30) and 60-day-old (P60) rats upon either acute perfusion of lead to the isolated brain slice from controls or when recorded from slices from rats after chronic developmental exposure to lead. Lead caused a significant inhibition of LTP in 30-day CA3, and a significant potentiation in 60-day CA3 with either exposure paradigm. Consistent with the effects on LTP, lead inhibits phorbol ester-induced synaptic potentiation in 30-day rats and enhances phorbol ester-induced potentiation in 60-day rats. Protein kinase C (PKC) has been implicated in actions of lead but previous investigations have reported either a stimulation or a blockade of PKC by lead. Our results are consistent with the hypothesis that the effects of lead on LTP are mediated via an action on PKC, which varies with age.
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Affiliation(s)
- R J Hussain
- Department of Environmental Health and Toxicology, School of Public Health, University at Albany, One University Place, B242, Rensselaer, NY 12144, USA
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Yun S, Lannert H, Hoyer S. Chronic exposure to low-level lead impairs learning ability during aging and energy metabolism in aged rat brain. Arch Gerontol Geriatr 2000; 30:199-213. [PMID: 10867164 DOI: 10.1016/s0167-4943(00)00054-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The neurotoxic effect of chronic exposure to low-level lead (Pb) with advancing age is becoming an important social issue of public health. To examine the effects of low-level Pb treatment on behavior, cognition and brain energy metabolism in aging, we administered 200 ppm Pb acetate to adult (10-month-old) male Wistar rats for 12.5 months. After 12.5 months' exposure, the mean Pb levels in blood and brain had increased to 17.5 µg/dl and 0.07 µg/g, respectively, and the rats showed impaired learning and memory functions in a holeboard spatial memory test. No significant difference was found between experimental and control groups in locomotor activity and passive avoidance tests. By HPLC analysis of energy-rich phosphate concentrations, mild abnormalities were found in parietotemporal cortex and hippocampus, but only the 4.4% decrease of ATP in the parietotemporal cortex was statistically significant. These results suggest that chronic exposure to Pb during aging stage may selectively impair learning and memory functions and may cause slight cerebral energy impairment.
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Affiliation(s)
- S Yun
- Department of Pathochemistry and General Neurochemistry, University of Heidelberg, Im Neuenheimer Feld 220/221, D-69120, Heidelberg, Germany
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