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Azevedo LF, Karpova N, Rocha BA, Barbosa Junior F, Gobe GC, Hornos Carneiro MF. Evidence on Neurotoxicity after Intrauterine and Childhood Exposure to Organomercurials. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2023; 20:1070. [PMID: 36673825 PMCID: PMC9858833 DOI: 10.3390/ijerph20021070] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Revised: 01/03/2023] [Accepted: 01/04/2023] [Indexed: 06/17/2023]
Abstract
Although the molecular mechanisms underlying methylmercury toxicity are not entirely understood, the observed neurotoxicity in early-life is attributed to the covalent binding of methylmercury to sulfhydryl (thiol) groups of proteins and other molecules being able to affect protein post-translational modifications from numerous molecular pathways, such as glutamate signaling, heat-shock chaperones and the antioxidant glutaredoxin/glutathione system. However, for other organomercurials such as ethylmercury or thimerosal, there is not much information available. Therefore, this review critically discusses current knowledge about organomercurials neurotoxicity-both methylmercury and ethylmercury-following intrauterine and childhood exposure, as well as the prospects and future needs for research in this area. Contrasting with the amount of epidemiological evidence available for methylmercury, there are only a few in vivo studies reporting neurotoxic outcomes and mechanisms of toxicity for ethylmercury or thimerosal. There is also a lack of studies on mechanistic approaches to better investigate the pathways involved in the potential neurotoxicity caused by both organomercurials. More impactful follow-up studies, especially following intrauterine and childhood exposure to ethylmercury, are necessary. Childhood vaccination is critically important for controlling infectious diseases; however, the safety of mercury-containing thimerosal and, notably, its effectiveness as preservative in vaccines are still under debate regarding its potential dose-response effects to the central nervous system.
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Affiliation(s)
- Lara Ferreira Azevedo
- Department of Clinical Analyses, Toxicology and Food Sciences, School of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, Ribeirão Preto 14040-903, SP, Brazil
| | - Nina Karpova
- Department of Clinical Analyses, Toxicology and Food Sciences, School of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, Ribeirão Preto 14040-903, SP, Brazil
| | - Bruno Alves Rocha
- Department of Clinical Analyses, Toxicology and Food Sciences, School of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, Ribeirão Preto 14040-903, SP, Brazil
| | - Fernando Barbosa Junior
- Department of Clinical Analyses, Toxicology and Food Sciences, School of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, Ribeirão Preto 14040-903, SP, Brazil
| | - Glenda Carolyn Gobe
- Kidney Disease Research Group, School of Medicine, Translational Research Institute, University of Queensland, 37 Kent Street, Woolloongabba, QLD 4102, Australia
| | - Maria Fernanda Hornos Carneiro
- Department of Pharmacy, Faculty of Chemistry and Pharmacy, Pontificia Universidad Católica de Chile, Santiago 7820436, Chile
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Methylmercury promotes oxidative stress and autophagy in rat cerebral cortex: Involvement of PI3K/AKT/mTOR or AMPK/TSC2/mTOR pathways and attenuation by N-acetyl-L-cysteine. Neurotoxicol Teratol 2023; 95:107137. [PMID: 36403891 DOI: 10.1016/j.ntt.2022.107137] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2022] [Revised: 11/13/2022] [Accepted: 11/13/2022] [Indexed: 11/19/2022]
Abstract
Methylmercury (MeHg) is a potent neurotoxicant that could induce oxidative stress and autophagy. However, the underlying mechanisms through which MeHg affects the central nervous system have not been fully elucidated, and little has been known of the interaction between oxidative stress and autophagy. Therefore, rats were administrated with different MeHg concentrations to evaluate the neurotoxic effects and autophagy in cerebral cortex. Moreover, we have investigated the neuroprotective role of N-acetyl-L-cysteine (NAC) against MeHg-induced neurotoxicity in order to estimate the regulation effects of oxidative stress on autophagy. A total of 64 rats, 40 of which were randomly divided into control and MeHg-treated (4, 8 and 12 μ mol/kg) groups. The remaining 24 rats were divided into control, NAC control (1 mmol/kg), 12 μ mol/kg MeHg, and NAC pretreatment. Administration of 12 μ mol/kg MeHg significantly increased behavioral and pathological abnormalities, and autophagy levels. In addition, the oxidative stress levels increased, together with abnormal expression of autophagy-related molecules. Pretreatment with NAC significantly prevented MeHg-induced oxidative stress and PI3K/AKT/mTOR or AMPK/TSC2/mTOR-mediated autophagy. In conclusion, the present study suggested that oxidative stress can regulate autophagy through PI3K/AKT/mTOR or AMPK/TSC2/mTOR pathways. This study provides a theoretical basis for the study and treatment of MeHg-induced neurotoxicity.
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Sousa AH, Pereira JPG, Malaquias AC, Sagica FDES, de Oliveira EHC. Intracellular accumulation and DNA damage caused by methylmercury in glial cells. J Biochem Mol Toxicol 2022; 36:e23170. [PMID: 35822649 DOI: 10.1002/jbt.23170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2021] [Revised: 05/14/2022] [Accepted: 07/01/2022] [Indexed: 11/10/2022]
Abstract
Mercury is widely used in industrial and extractive processes, and the improper disposal of waste or products containing this metal produces a significant impact on ecosystems, causing adverse effects on living organisms, including humans. Exposure to methylmercury, a highly toxic organic compound, causes important neurological and developmental impairments. Recently, the genotoxicity of mercurial compounds has gained prominence as one of the possible mechanisms associated with the neurological effects of mercury, mostly by disturbing the mitotic spindle and causing chromosome loss. In this sense, it is important to investigate if these compounds can also cause direct damage to DNA, such as single and double-strand breaks. Thus, the aim of this study was to investigate the cytotoxic and genotoxic potential of methylmercury in cell lines derived from neurons (B103) and glia (C6), exposed to methylmercury (MeHg) for 24 h, by analyzing cell viability, metabolic activity, and damage to DNA and chromosomes. We found that in comparison to the neuronal cell line, glial cells showed higher tolerance to MeHg, and therefore a higher LC50 and consequent higher intracellular accumulation of Hg, which led to the occurrence of several genotoxic effects, as evidenced by the presence of micronuclei, bridges, sprouts, and chromosomal aberrations.
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Affiliation(s)
- Aline H Sousa
- Programa de Pós Graduação em Epidemiologia e vigilância em Saúde, Instituto Evandro Chagas, Ananindeua, Pará, Brazil.,Seção de Bacteriologia, Instituto Evandro Chagas, Ananindeua, Pará, Brazil
| | - João P G Pereira
- Programa de Pós Graduação em Epidemiologia e vigilância em Saúde, Instituto Evandro Chagas, Ananindeua, Pará, Brazil.,Seção de Meio Ambiente, Instituto Evandro Chagas, Ananindeua, Pará, Brazil
| | - Allan C Malaquias
- Faculdade de Medicina, Universidade Federal do Pará, Campus de Altamira, Pará, Brazil
| | | | - Edivaldo H C de Oliveira
- Seção de Meio Ambiente, Instituto Evandro Chagas, Ananindeua, Pará, Brazil.,Faculdade de Ciências Naturais, ICEN, Universidade Federal do Pará, Belém, Pará, Brazil
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Wildner G, Loreto JS, de Almeida P, Claro MT, Ferreira SA, Barbosa NV. Short exposure to ethyl and methylmercury prompts similar toxic responses in Drosophila melanogaster. Comp Biochem Physiol C Toxicol Pharmacol 2022; 252:109216. [PMID: 34710619 DOI: 10.1016/j.cbpc.2021.109216] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 10/07/2021] [Accepted: 10/14/2021] [Indexed: 12/30/2022]
Abstract
Methylmercury (MeHg) and ethylmercury (EtHg) are important mercury organic forms in terms of human poisoning. Since the comparative effects of compounds are mainly in vitro, this study was designed to investigate the toxicities induced by MeHg and EtHg in an in vivo study using adult Drosophila melanogaster (D. melanogaster). Firstly, we performed a survival curve, where the flies were fed on a medium containing MeHg and EtHg at concentrations ranging from 2.5 to 200 μM, until the end of their lifespan. After that, the concentrations 25 and 200 μM of MeHg and EtHg were chosen to be tested in a short exposure for 5 days. The analysis of survival by Kaplan-Meier plot revealed that all concentrations of MeHg and EtHg reduced significantly the lifespan of the flies. Short exposure to both concentrations of MeHg and EtHg impaired the ability of flies in the climbing assay and induced lipid peroxidation. Only the flies exposed to the highest concentration had viability loss, thiol depletion, and increased reactive species (RS) and Hg levels in the whole body. Our findings indicate that MeHg and EtHg exhibit similar toxic effects in vivo, and that oxidative stress is a phenomenon behind the toxicity of both mercurials. The data obtained also reinforce the use of D. melanogaster as a useful organism for basic toxicological research.
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Affiliation(s)
- Guilherme Wildner
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Avenida Roraima, 1000, 97105-900 Santa Maria, RS, Brazil
| | - Julia Sepel Loreto
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Avenida Roraima, 1000, 97105-900 Santa Maria, RS, Brazil
| | - Pamela de Almeida
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Avenida Roraima, 1000, 97105-900 Santa Maria, RS, Brazil
| | - Mariana Torri Claro
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Avenida Roraima, 1000, 97105-900 Santa Maria, RS, Brazil
| | - Sabrina Antunes Ferreira
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Avenida Roraima, 1000, 97105-900 Santa Maria, RS, Brazil
| | - Nilda Vargas Barbosa
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Avenida Roraima, 1000, 97105-900 Santa Maria, RS, Brazil.
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Yuan L, Shi X, Tang BZ, Wang WX. Real-time in vitro monitoring of the subcellular toxicity of inorganic Hg and methylmercury in zebrafish cells. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2021; 236:105859. [PMID: 34004410 DOI: 10.1016/j.aquatox.2021.105859] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2020] [Revised: 04/19/2021] [Accepted: 05/01/2021] [Indexed: 06/12/2023]
Abstract
Mercury (Hg) is a prominent environmental contaminant and can cause various subcellular effects. Elucidating the different subcellular toxicities of inorganic Hg (Hg2+) and methylmercury (MeHg) is critical for understanding their overall cytotoxicity. In this study, we employed aggregation-induced emission (AIE) probes to investigate the toxicity of Hg at the subcellular level using an aquatic embryonic zebrafish fibroblast cell line ZF4 as a model. The dynamic monitoring of lysosomal pH and the mapping of pH distribution during Hg2+ or MeHg exposure were successfully realized for the first time. We found that both Hg2+ and MeHg decreased the mean lysosomal pH, but with contrasting effects and mechanisms. Hg2+ had a greater impact on lysosomal pH than MeHg at a similar intracellular concentration. In addition, Hg2+ in comparison to MeHg exposure led to an increased number of lysosomes, probably because of their different effects on autophagy. We further showed that MeHg (200 nM) exposure had an inverse effect on mitochondrial respiratory function. A high dose (1000 nM) of Hg2+ increased the amount of intracellular lipid droplets by 13%, indicating that lipid droplets may potentially play a role in Hg2+detoxification. Our study suggested that, compared with other parameters, lysosome pH was most sensitive to Hg2+ and MeHg. Therefore, lysosomal pH can be used as a potential biomarker to assess the cellular toxicity of Hg in vitro.
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Affiliation(s)
- Liuliang Yuan
- Division of Life Science, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong, China; School of Energy and Environment and State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong, China
| | - Xiujuan Shi
- Department of Chemistry, Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, HKUST, Clear Water Bay, Kowloon, Hong Kong, China
| | - Ben Zhong Tang
- Department of Chemistry, Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, HKUST, Clear Water Bay, Kowloon, Hong Kong, China
| | - Wen-Xiong Wang
- School of Energy and Environment and State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong, China; Research Centre for the Oceans and Human Health, City University of Hong Kong Shenzhen Research Institute, Shenzhen518057, China.
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Environmentally relevant developmental methylmercury exposures alter neuronal differentiation in a human-induced pluripotent stem cell model. Food Chem Toxicol 2021; 152:112178. [PMID: 33831500 DOI: 10.1016/j.fct.2021.112178] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Revised: 03/15/2021] [Accepted: 03/30/2021] [Indexed: 12/14/2022]
Abstract
Developmental methylmercury (MeHg) exposure selectively targets the cerebral and cerebellar cortices, as seen by disruption of cytoarchitecture and glutamatergic (GLUergic) neuron hypoplasia. To begin to understand the mechanisms of this loss of GLUergic neurons, we aimed to develop a model of developmental MeHg neurotoxicity in human-induced pluripotent stem cells differentiating into cortical GLUergic neurons. Three dosing paradigms at 0.1 μM and 1.0 μM MeHg, which span different stages of neurodevelopment and reflect toxicologically relevant accumulation levels seen in human studies and mammalian models, were established. With these exposure paradigms, no changes were seen in commonly studied endpoints of MeHg toxicity, including viability, proliferation, and glutathione levels. However, MeHg exposure induced changes in mitochondrial respiration and glycolysis and in markers of neuronal differentiation. Our novel data suggests that GLUergic neuron hypoplasia seen with MeHg toxicity may be due to the partial inhibition of neuronal differentiation, given the increased expression of the early dorsal forebrain marker FOXG1 and corresponding decrease in expression on neuronal markers MAP2 and DCX and the deep layer cortical neuronal marker TBR1. Future studies should examine the persistent and latent functional effects of this MeHg-induced disruption of neuronal differentiation as well as transcriptomic and metabolomic alterations that may mediate MeHg toxicity.
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Tinant G, Neefs I, Das K, Rees JF, Larondelle Y, Debier C. Methylmercury displays pro-adipogenic properties in rainbow trout preadipocytes. CHEMOSPHERE 2021; 263:127917. [PMID: 33297014 DOI: 10.1016/j.chemosphere.2020.127917] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2020] [Revised: 07/27/2020] [Accepted: 08/03/2020] [Indexed: 06/12/2023]
Abstract
Methylmercury (MeHg) is a ubiquitous contaminant largely found in aquatic environments, especially in species at high trophic level such as salmonids. The aim of this study was to evaluate the effects of MeHg on adipocyte differentiation and lipid metabolism in rainbow trout. Primary cultured preadipocytes were exposed to increasing concentrations of MeHg during six days with or without a hormonal cocktail. Main results showed a dose-dependent intracellular accumulation of neutral lipids with a preferential uptake of n-3 polyunsaturated fatty acids. Interestingly, this accumulation occurred after a fairly low uptake of MeHg by preadipocytes and was maintained after the cellular exposure to MeHg. In membrane phospholipids, arachidonic acid (20:4 n-6) was released in a dose-dependent manner. At the transcriptional level, the expression of several adipocyte-specific genes (perilipin 2 and apolipoprotein Eb) as well as lipid-related genes (fatty acid synthase and fatty acid binding protein 11a) was up-regulated in preadipocytes exposed to MeHg. These results highlight for the first time the disrupting effect of MeHg in trout adipocyte metabolism, providing new insights regarding the role of environmental pollutants in adipose tissue dysfunction and related pathologies.
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Affiliation(s)
- Gilles Tinant
- Louvain Institute of Biomolecular Science and Technology (LIBST), Université catholique de Louvain, Croix Du Sud 4-5/L7.07.03, 1348, Louvain-la-Neuve, Belgium.
| | - Ineke Neefs
- Louvain Institute of Biomolecular Science and Technology (LIBST), Université catholique de Louvain, Croix Du Sud 4-5/L7.07.03, 1348, Louvain-la-Neuve, Belgium
| | - Krishna Das
- Laboratory of Oceanology, Université de Liège, 11 Allée Du 6 Août, B6C, 4000, Liège, Belgium
| | - Jean-François Rees
- Louvain Institute of Biomolecular Science and Technology (LIBST), Université catholique de Louvain, Croix Du Sud 4-5/L7.07.03, 1348, Louvain-la-Neuve, Belgium
| | - Yvan Larondelle
- Louvain Institute of Biomolecular Science and Technology (LIBST), Université catholique de Louvain, Croix Du Sud 4-5/L7.07.03, 1348, Louvain-la-Neuve, Belgium
| | - Cathy Debier
- Louvain Institute of Biomolecular Science and Technology (LIBST), Université catholique de Louvain, Croix Du Sud 4-5/L7.07.03, 1348, Louvain-la-Neuve, Belgium.
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Gaudet HM, Christensen E, Conn B, Morrow S, Cressey L, Benoit J. Methylmercury promotes breast cancer cell proliferation. Toxicol Rep 2018; 5:579-584. [PMID: 29868453 PMCID: PMC5984200 DOI: 10.1016/j.toxrep.2018.05.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Revised: 05/02/2018] [Accepted: 05/13/2018] [Indexed: 10/26/2022] Open
Abstract
CONTEXT Metalloestrogens are small ionic metals that activate the estrogen receptor (ER). Studies have shown that when metalloestrogens bind to the ER, there is an increase in transcription and expression of estrogen-regulated genes, which induces proliferation of estrogen-dependent breast cancer. Methylmercury (MeHg), a metalloestrogen, is present in the environment and is toxic at moderate to high concentrations. However, at lower concentrations MeHg may promote the proliferation of ER-positive breast cancers and protect cells against pro-apoptotic signals. OBJECTIVE To investigate the effects of MeHg treatment on breast cancer cells in vitro. MATERIALS AND METHODS MCF7 breast cancer cells were treated with concentrations of MeHg ranging from 1 nM to 100 mM. Hg analysis was used to quantify intracellular mercury concentrations. Cell proliferation and apoptosis were determined by cell counting and Annexin-V staining, respectively. RESULTS We defined a protocol that maximizes cellular exposure to mercury. Treatment of human ER-positive breast cancer cells with 1 nM MeHg promoted proliferation, while treatment with a concentration of 100 nM induced apoptosis. DISCUSSION AND CONCLUSIONS Clarifying the effects of MeHg on breast cancer will improve our understanding of how environmental toxins affect tumor progression and may lead to the development of future therapeutic strategies.
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Inflammatory response following in vitro exposure to methylmercury with and without n-3 long chain polyunsaturated fatty acids in peripheral blood mononuclear cells from systemic lupus erythematosus patients compared to healthy controls. Toxicol In Vitro 2018; 52:272-278. [PMID: 29778720 DOI: 10.1016/j.tiv.2018.05.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Revised: 05/10/2018] [Accepted: 05/15/2018] [Indexed: 01/29/2023]
Abstract
Methylmercury (MeHg) is a proposed environmental stimulus in systemic lupus erythematosus (SLE). Humans are primarily exposed to MeHg through fish consumption. Fish are also important sources of n-3 long chain polyunsaturated fatty acids (n-3 LCPUFA). This in vitro study investigated the inflammatory response of isolated peripheral blood mononuclear cells (PBMCs), when exposed to either MeHg alone or with added n-3 LCPUFA, from SLE patients (N = 12) compared to healthy sex matched controls (N = 12). The PBMCs were isolated and exposed to 200 nM of MeHg for 24 h with or without pre-exposure to eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) at a concentration of 100 μM each. Supernatants were analyzed for the inflammatory markers. Following exposure to MeHg, mean TNF-α concentrations were significantly higher in SLE patients (2226.01 ± 348.98pg/ml) compared to controls (701.40 ± 680.65 pg/ml) (P = .008). Pre-exposure of cells with MeHg and EPA resulted in a significantly higher concentration of IL-8 in supernatants from SLE patients (2137.83 ± 1559.01 pg/ml) compared to that of the controls (879.26 ± 979.49 pg/ml) (P = .030). EPA and DHA attenuated the pro-inflammatory inducing effects of MeHg in SLE and control cells. In summary, exposure to MeHg stimulated a higher TNF-α response in SLE patients compared with healthy controls; nevertheless the presence of n-3 LCPUFA reduced the overall inflammatory response, albeit to a lesser degree in SLE patients.
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Maniero MÁ, Guerrero-Gimenez ME, Fanelli MA, Wuilloud RG. Inorganic mercury in mammary cells: viability, metal uptake but efflux? Biometals 2017; 31:69-80. [DOI: 10.1007/s10534-017-0068-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Accepted: 11/20/2017] [Indexed: 11/28/2022]
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Bjørklund G, Dadar M, Mutter J, Aaseth J. The toxicology of mercury: Current research and emerging trends. ENVIRONMENTAL RESEARCH 2017; 159:545-554. [PMID: 28889024 DOI: 10.1016/j.envres.2017.08.051] [Citation(s) in RCA: 240] [Impact Index Per Article: 34.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Revised: 08/27/2017] [Accepted: 08/30/2017] [Indexed: 05/16/2023]
Abstract
Mercury (Hg) is a persistent bio-accumulative toxic metal with unique physicochemical properties of public health concern since their natural and anthropogenic diffusions still induce high risk to human and environmental health. The goal of this review was to analyze scientific literature evaluating the role of global concerns over Hg exposure due to human exposure to ingestion of contaminated seafood (methyl-Hg) as well as elemental Hg levels of dental amalgam fillings (metallic Hg), vaccines (ethyl-Hg) and contaminated water and air (Hg chloride). Mercury has been recognized as a neurotoxicant as well as immunotoxic and designated by the World Health Organization as one of the ten most dangerous chemicals to public health. It has been shown that the half-life of inorganic Hg in human brains is several years to several decades. Mercury occurs in the environment under different chemical forms as elemental Hg (metallic), inorganic and organic Hg. Despite the raising understanding of the Hg toxicokinetics, there is still fully justified to further explore the emerging theories about its bioavailability and adverse effects in humans. In this review, we describe current research and emerging trends in Hg toxicity with the purpose of providing up-to-date information for a better understanding of the kinetics of this metal, presenting comprehensive knowledge on published data analyzing its metabolism, interaction with other metals, distribution, internal doses and targets, and reservoir organs.
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Affiliation(s)
- Geir Bjørklund
- Council for Nutritional and Environmental Medicine, Toften 24, 8610 Mo i Rana, Norway.
| | - Maryam Dadar
- Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran
| | | | - Jan Aaseth
- Innlandet Hospital Trust and Inland Norway University of Applied Sciences, Elverum, Norway
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Methylmercury Uptake into BeWo Cells Depends on LAT2-4F2hc, a System L Amino Acid Transporter. Int J Mol Sci 2017; 18:ijms18081730. [PMID: 28786956 PMCID: PMC5578120 DOI: 10.3390/ijms18081730] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Revised: 07/28/2017] [Accepted: 08/01/2017] [Indexed: 12/24/2022] Open
Abstract
The organic mercury compound methylmercury (MeHg) is able to target the fetal brain. However, the uptake of the toxicant into placental cells is incompletely understood. MeHg strongly binds to thiol-S containing molecules such as cysteine. This MeHg-l-cysteine exhibits some structural similarity to methionine. System L plays a crucial role in placental transport of essential amino acids such as leucine and methionine and thus has been assumed to also transport MeHg-l-cysteine across the placenta. The uptake of methylmercury and tritiated leucine and methionine into the choriocarcinoma cell line BeWo was examined using transwell assay and small interfering (si)RNA mediated gene knockdown. Upon the downregulation of large neutral amino acids transporter (LAT)2 and 4F2 cell-surface antigen heavy chain (4F2hc), respectively, the levels of [3H]leucine in BeWo cells are significantly reduced compared to controls treated with non-targeting siRNA (p < 0.05). The uptake of [3H]methionine was reduced upon LAT2 down-regulation as well as methylmercury uptake after 4F2hc silencing (p < 0.05, respectively). These findings suggest an important role of system L in the placental uptake of the metal. Comparing the cellular accumulation of mercury, leucine, and methionine, it can be assumed that (1) MeHg is transported through system L amino acid transporters and (2) system L is responsible for the uptake of amino acids and MeHg primarily at the apical membrane of the trophoblast. The findings together can explain why mercury in contrast to other heavy metals such as lead or cadmium is efficiently transported to fetal blood.
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Lohren H, Bornhorst J, Fitkau R, Pohl G, Galla HJ, Schwerdtle T. Effects on and transfer across the blood-brain barrier in vitro-Comparison of organic and inorganic mercury species. BMC Pharmacol Toxicol 2016; 17:63. [PMID: 27978854 PMCID: PMC5159962 DOI: 10.1186/s40360-016-0106-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Accepted: 11/19/2016] [Indexed: 01/22/2023] Open
Abstract
Background Transport of methylmercury (MeHg) across the blood-brain barrier towards the brain side is well discussed in literature, while ethylmercury (EtHg) and inorganic mercury are not adequately characterized regarding their entry into the brain. Studies investigating a possible efflux out of the brain are not described to our knowledge. Methods This study compares, for the first time, effects of organic methylmercury chloride (MeHgCl), EtHg-containing thiomersal and inorganic Hg chloride (HgCl2) on as well as their transfer across a primary porcine in vitro model of the blood-brain barrier. Results With respect to the barrier integrity, the barrier model exhibited a much higher sensitivity towards HgCl2 following basolateral incubation (brain-facing side) as compared to apical application (blood-facing side). These HgCl2 induced effects on the barrier integrity after brain side incubation are comparable to that of the organic species, although MeHgCl and thiomersal exerted much higher cytotoxic effects in the barrier building cells. Hg transfer rates following exposure to organic species in both directions argue for diffusion as transfer mechanism. Inorganic Hg application surprisingly resulted in a Hg transfer out of the brain-facing compartment. Conclusions In case of MeHgCl and thiomersal incubation, mercury crossed the barrier in both directions, with a slight accumulation in the basolateral, brain-facing compartment, after simultaneous incubation in both compartments. For HgCl2, our data provide first evidence that the blood-brain barrier transfers mercury out of the brain.
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Affiliation(s)
- Hanna Lohren
- Department of Food Chemistry, Institute of Nutritional Science, Univeristy of Potsdam, Potsdam, Germany
| | - Julia Bornhorst
- Department of Food Chemistry, Institute of Nutritional Science, Univeristy of Potsdam, Potsdam, Germany
| | - Romy Fitkau
- Department of Food Chemistry, Institute of Nutritional Science, Univeristy of Potsdam, Potsdam, Germany
| | - Gabriele Pohl
- Department of Food Chemistry, Institute of Nutritional Science, Univeristy of Potsdam, Potsdam, Germany
| | | | - Tanja Schwerdtle
- Department of Food Chemistry, Institute of Nutritional Science, Univeristy of Potsdam, Potsdam, Germany.
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Ferain A, Bonnineau C, Neefs I, Rees JF, Larondelle Y, Schamphelaere KACD, Debier C. The fatty acid profile of rainbow trout liver cells modulates their tolerance to methylmercury and cadmium. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2016; 177:171-181. [PMID: 27288598 DOI: 10.1016/j.aquatox.2016.05.023] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Revised: 05/12/2016] [Accepted: 05/22/2016] [Indexed: 06/06/2023]
Abstract
The polyunsaturated fatty acid (PUFA) composition of fish tissues, which generally reflects that of the diet, affects various cellular properties such as membrane structure and fluidity, energy metabolism and susceptibility to oxidative stress. Since these cellular parameters can play an important role in the cellular response to organic and inorganic pollutants, a variation of the PUFA supply might modify the toxicity induced by such xenobiotics. In this work, we investigated whether the cellular fatty acid profile has an impact on the in vitro cell sensitivity to two environmental pollutants: methylmercury and cadmium. Firstly, the fatty acid composition of the rainbow trout liver cell line RTL-W1 was modified by enriching the growth medium with either alpha-linolenic acid (ALA, 18:3n-3), eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3), linoleic acid (LA, 18:2n-6), arachidonic acid (AA, 20:4n-6) or docosapentaenoic acid (DPA, 22:5n-6). These modified cells and their control (no PUFA enrichment) were then challenged for 24h with increasing concentrations of methylmercury or cadmium. We observed that (i) the phospholipid composition of the RTL-W1 cells was profoundly modulated by changing the PUFA content of the growth medium: major modifications were a high incorporation of the supplemented PUFA in the cellular phospholipids, the appearance of direct elongation and desaturation metabolites in the cellular phospholipids as well as a change in the gross phospholipid composition (PUFA and monounsaturated fatty acid (MUFA) levels and n-3/n-6 ratio); (ii) ALA, EPA and DPA enrichment significantly protected the RTL-W1 cells against both methylmercury and cadmium; (iv) DHA enrichment significantly protected the cells against cadmium but not methylmercury; (v) AA and LA enrichment had no impact on the cell tolerance to both methylmercury and cadmium; (vi) the abundance of 20:3n-6, a metabolite of the n-6 biotransformation pathway, in phospholipids was negatively correlated to the cell tolerance to both methylmercury and cadmium. Overall, our results highlighted the importance of the fatty acid supply on the tolerance of fish liver cells to methylmercury and cadmium.
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Affiliation(s)
- Aline Ferain
- Institute of Life Sciences, Université catholique de Louvain, Place Croix du Sud 2/L7.05.08, B-1348 Louvain-la-Neuve, Belgium.
| | - Chloé Bonnineau
- Institute of Life Sciences, Université catholique de Louvain, Place Croix du Sud 2/L7.05.08, B-1348 Louvain-la-Neuve, Belgium; Irstea, UR MALY, Centre de Lyon-Villeurbanne, rue de la Doua 5/32108, F-69616 Villeurbanne, France
| | - Ineke Neefs
- Institute of Life Sciences, Université catholique de Louvain, Place Croix du Sud 2/L7.05.08, B-1348 Louvain-la-Neuve, Belgium
| | - Jean François Rees
- Institute of Life Sciences, Université catholique de Louvain, Place Croix du Sud 2/L7.05.08, B-1348 Louvain-la-Neuve, Belgium
| | - Yvan Larondelle
- Institute of Life Sciences, Université catholique de Louvain, Place Croix du Sud 2/L7.05.08, B-1348 Louvain-la-Neuve, Belgium
| | - Karel A C De Schamphelaere
- Laboratory of Environmental Toxicology and Aquatic Ecology, Environmental Toxicology Unit, Ghent University, J. Plateaustraat 22, B-9000 Ghent, Belgium
| | - Cathy Debier
- Institute of Life Sciences, Université catholique de Louvain, Place Croix du Sud 2/L7.05.08, B-1348 Louvain-la-Neuve, Belgium
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Mechanisms involved in the transport of mercuric ions in target tissues. Arch Toxicol 2016; 91:63-81. [PMID: 27422290 DOI: 10.1007/s00204-016-1803-y] [Citation(s) in RCA: 108] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 07/07/2016] [Indexed: 01/16/2023]
Abstract
Mercury exists in the environment in various forms, all of which pose a risk to human health. Despite guidelines regulating the industrial release of mercury into the environment, humans continue to be exposed regularly to various forms of this metal via inhalation or ingestion. Following exposure, mercuric ions are taken up by and accumulate in numerous organs, including brain, intestine, kidney, liver, and placenta. In order to understand the toxicological effects of exposure to mercury, a thorough understanding of the mechanisms that facilitate entry of mercuric ions into target cells must first be obtained. A number of mechanisms for the transport of mercuric ions into target cells and organs have been proposed in recent years. However, the ability of these mechanisms to transport mercuric ions and the regulatory features of these carriers have not been characterized completely. The purpose of this review is to summarize the current findings related to the mechanisms that may be involved in the transport of inorganic and organic forms of mercury in target tissues and organs. This review will describe mechanisms known to be involved in the transport of mercury and will also propose additional mechanisms that may potentially be involved in the transport of mercuric ions into target cells.
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Evans RD, Hickie B, Rouvinen-Watt K, Wang W. Partitioning and kinetics of methylmercury among organs in captive mink (Neovison vison): A stable isotope tracer study. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2016; 42:163-169. [PMID: 26855415 DOI: 10.1016/j.etap.2016.01.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 01/08/2016] [Accepted: 01/09/2016] [Indexed: 06/05/2023]
Abstract
Despite the importance of methylmercury (MeHg) as a neurotoxin, we have relatively few good data on partitioning and kinetics of MeHg among organs, particularly across the blood-brain barrier, for mammals that consume large quantities of fish. The objective of this study was to determine the partition coefficients between blood and brain, liver and kidney and fur for MeHg under steady-state conditions and to measure the half-lives for MeHg in these organs. Captive mink (Neovison vison) were fed a diet enriched with two stable isotopes of Hg, Me(199)Hg and Me(201)Hg for a period of 60 days. After a period of 10 days the diet was changed to contain only Me(201)Hg so that, between days 10 and 60, we were able to measure both uptake and elimination rates from blood, brain, liver kidney and fur. Liver and kidney response was very rapid, closely following changes in blood concentrations but there was a small lag time between peak blood concentrations and peak brain concentrations. Half-lives for MeHg were 15.4, 10.2 and 13.4 days for brain, liver and kidney, respectively. There was no measurable conversion of the MeHg to inorganic Hg (IHg) in the brain over the 60 day period, unlike in liver and kidney.
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Affiliation(s)
- R Douglas Evans
- School of the Environment, Trent University, Peterborough, ON K9L 0G2, Canada; Water Quality Centre, Trent University, Peterborough, ON K9L 0G2, Canada.
| | - Brendan Hickie
- School of the Environment, Trent University, Peterborough, ON K9L 0G2, Canada
| | | | - Wei Wang
- School of the Environment, Trent University, Peterborough, ON K9L 0G2, Canada
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Ayyathan DM, Chandrasekaran R, Thiagarajan K. Neuroprotective effect of Tagara, an Ayurvedic drug against methyl mercury induced oxidative stress using rat brain mitochondrial fractions. Altern Ther Health Med 2015; 15:268. [PMID: 26264039 PMCID: PMC4533944 DOI: 10.1186/s12906-015-0793-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Accepted: 07/22/2015] [Indexed: 11/10/2022]
Abstract
BACKGROUND Methyl mercury (MeHg), an important environmental toxicant is implicated in neurological disorders such as Hunter-Russell syndrome and Autism. Therefore, the present work is in search of new drugs that can alleviate MeHg toxicity. In this connection, Tagara, an ayurvedic drug is used for assessing its neuro protective effect against MeHg toxicity. METHODS In the present study, we assessed the phytochemical contents of Tagara by colorimetric and HPLC analyses. The neuroprotective effect of Tagara on MeHg induced neurotoxicity was measured in terms of viability by MTT assay and oxidative stress in terms of catalase activity, glutathione and thiobarbituric acid reactive substance levels. Further, the chelating effect of Tagara towards MeHg was performed to identify the molecular mechanism. Statistical analysis was done by statistical package for social sciences (SPSS) version 16.0. RESULTS The results demonstrated that Tagara contains significant amounts of phenols and flavonoids. Also, HPLC analysis of Tagara revealed the presence of essential oils such as hydroxyvalerenic and valerenic acids. Our results demonstrated that exposure of rat brain mitochondrial fractions to MeHg resulted in a dose dependent death in MTT assay and IC50 value was found to be 10 μM. However, a 250 μg dose of Tagara effectively prevented MeHg induced mitochondrial damage. The oxidative stress caused by MeHg results in elevated levels of reactive oxygen species as evidenced by elevated TBARS (Thiobarbituric acid-reactive substances) levels and diminished catalase enzyme activity and glutathione content. However, Tagara at 250 μg concentration offsets these alterations caused by MeHg. Further, Tagara also diminished GSH oxidation caused by MeHg, confirming its chelating effect, one of the molecular mechanisms that triggers protection against oxidative damage. CONCLUSION Our results revealed that MeHg induced toxicity is predominantly mediated through oxidative stress mechanism and the propensity of Tagara to abolish such reactions. Hence, we propose that Tagara with a source of potential neuroprotectants may be a useful approach to alleviate MeHg associated neurotoxicity.
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Vázquez M, Vélez D, Devesa V. Participation of b0,+and B0,+systems in the transport of mercury bound to cysteine in intestinal cells. Toxicol Res (Camb) 2015. [DOI: 10.1039/c4tx00205a] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The main source of exposure to mercury (Hg) as divalent inorganic Hg [Hg(ii)] and methylmercury (CH3Hg) is the diet, in which complexes with the amino acid cysteine (Hg–Cys) may be found.
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Affiliation(s)
- M. Vázquez
- Instituto de Agroquímica y Tecnología de Alimentos (IATA-CSIC)
- Avenida Agustín Escardino 7
- Valencia
- Spain
| | - D. Vélez
- Instituto de Agroquímica y Tecnología de Alimentos (IATA-CSIC)
- Avenida Agustín Escardino 7
- Valencia
- Spain
| | - V. Devesa
- Instituto de Agroquímica y Tecnología de Alimentos (IATA-CSIC)
- Avenida Agustín Escardino 7
- Valencia
- Spain
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Vázquez M, Vélez D, Devesa V. In vitro characterization of the intestinal absorption of methylmercury using a Caco-2 cell model. Chem Res Toxicol 2014; 27:254-64. [PMID: 24397474 DOI: 10.1021/tx4003758] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Methylmercury (CH3Hg) is one of the forms of mercury found in food, particularly in seafood. Exposure to CH3Hg is associated with neurotoxic effects during development. In addition, methylmercury has been classified by the International Agency for Research on Cancer as a possible human carcinogen. Although the diet is known to be the main source of exposure, few studies have characterized the mechanisms involved in the absorption of this contaminant. The present study examines the absorption process using the Caco-2 cell line as a model of the intestinal epithelium. The results indicate that transport across the intestinal cell monolayer in an absorptive direction occurs mainly through passive transcellular diffusion. This mechanism coexists with carrier-mediated transcellular transport, which has an active component. The participation of H(+)- and Na(+)-dependent transport was observed. Inhibition tests point to the possible participation of amino acid transporters (B(0,+) system, L system, and/or y(+)L system) and organic anion transporters (OATs). Our study suggests the participation in CH3Hg absorption of transporters that have already been identified as being responsible for the transport of this species in other systems, although further studies are needed to confirm their participation in intestinal absorption. It should be noted that CH3Hg experiences important cellular acumulation (48-78%). Considering the toxic nature of this contaminant, this fact could affect intestinal epithelium function.
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Affiliation(s)
- Marta Vázquez
- Instituto de Agroquímica y Tecnología de Alimentos (IATA-CSIC) , Avenida Agustín Escardino 7, 46980 Paterna, Valencia, Spain
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Intestinal transport of methylmercury and inorganic mercury in various models of Caco-2 and HT29-MTX cells. Toxicology 2013; 311:147-53. [PMID: 23793072 DOI: 10.1016/j.tox.2013.06.002] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Revised: 06/07/2013] [Accepted: 06/12/2013] [Indexed: 12/29/2022]
Abstract
Food is the main pathway of exposure to mercury for most of the population. In food, mercury is generally present as inorganic mercury [Hg(II)] or methylmercury [MeHg]. Both chemical forms have some degree of toxicity, especially MeHg, which is considered a powerful neurotoxicant during development and is classified as a possible human carcinogen. Since the main exposure pathway is oral, gastrointestinal absorption is a decisive step in the process by which mercury reaches the systemic circulation. However, there are few studies that characterize this absorption process. The present work evaluates transport and cellular retention of Hg(II) and MeHg, using various models of the intestinal epithelium (Caco-2 monocultures and Caco-2/HT29-MTX co-cultures in various proportions). Additionally, a study was made of the influence of the mucus secreted by HT29-MTX cells and of substances normally present in the gastrointestinal tract (l-cysteine, bile salts and food components) on mercury transport and accumulation. The results show that incorporation of HT29-MTX reduces the permeability coefficient of Hg(II) and MeHg. This decrease coincides with an increase in cellular accumulation, since mercury is retained in the layer of mucus secreted by HT29-MTX cells [Hg(II): 40%; MeHg: 70%]. The presence of l-cysteine, bile salts and food matrix components increases the percentage of both species that is not absorbed. It is noteworthy that in all the conditions assayed the intracellular accumulation of mercury was very high (37-77%). This study shows the importance of the cell model and assay conditions for an in vitro evaluation of intestinal transport of mercury species.
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21
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Zimmermann LT, Santos DB, Naime AA, Leal RB, Dórea JG, Barbosa F, Aschner M, Rocha JBT, Farina M. Comparative study on methyl- and ethylmercury-induced toxicity in C6 glioma cells and the potential role of LAT-1 in mediating mercurial-thiol complexes uptake. Neurotoxicology 2013; 38:1-8. [PMID: 23727015 DOI: 10.1016/j.neuro.2013.05.015] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Revised: 05/17/2013] [Accepted: 05/21/2013] [Indexed: 11/30/2022]
Abstract
Various forms of mercury possess different rates of absorption, metabolism and excretion, and consequently, toxicity. Methylmercury (MeHg) is a highly neurotoxic organic mercurial. Human exposure is mostly due to ingestion of contaminated fish. Ethylmercury (EtHg), another organic mercury compound, has received significant toxicological attention due to its presence in thimerosal-containing vaccines. This study was designed to compare the toxicities induced by MeHg and EtHg, as well as by their complexes with cysteine (MeHg-S-Cys and EtHg-S-Cys) in the C6 rat glioma cell line. MeHg and EtHg caused significant (p<0.0001) decreases in cellular viability when cells were treated during 30min with each mercurial following by a washing period of 24h (EC50 values of 4.83 and 5.05μM, respectively). Significant cytotoxicity (p<0.0001) was also observed when cells were treated under the same conditions with MeHg-S-Cys and EtHg-S-Cys, but the respective EC50 values were significantly increased (11.2 and 9.37μM). l-Methionine, a substrate for the l-type neutral amino acid carrier transport (LAT) system, significantly protected against the toxicities induced by both complexes (MeHg-S-Cys and EtHg-S-Cys). However, no protective effects of l-methionine were observed against MeHg and EtHg toxicities. Corroborating these findings, l-methionine significantly decreased mercurial uptake when cells were exposed to MeHg-S-Cys (p=0.028) and EtHg-S-Cys (p=0.023), but not to MeHg and EtHg. These results indicate that the uptake of MeHg-S-Cys and EtHg-S-Cys into C6 cells is mediated, at least in part, through the LAT system, but MeHg and EtHg enter C6 cells by mechanisms other than LAT system.
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Affiliation(s)
- Luciana T Zimmermann
- Departamento de Bioquímica, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina, Brazil.
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22
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Mori N, Yamamoto M, Tsukada E, Yokooji T, Matsumura N, Sasaki M, Murakami T. Comparison of in vivo with in vitro pharmacokinetics of mercury between methylmercury chloride and methylmercury cysteine using rats and Caco2 cells. ARCHIVES OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY 2012; 63:628-36. [PMID: 22932937 DOI: 10.1007/s00244-012-9800-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Accepted: 08/06/2012] [Indexed: 05/26/2023]
Abstract
The in vivo and in vitro pharmacokinetics of mercury (Hg) were compared between methylmercury chloride (MeHg·Cl) and methylmercury cysteine (MeHg-Cys) using rats and Caco2 cells because humans can be exposed to MeHg compounds through dietary fish. The in vivo pharmacokinetics of Hg immediately after the digestion of MeHg compounds are still obscure. In Caco2 cells, membrane uptake and subcellular distribution of MeHg compounds were examined. When rats received it intravenously, MeHg·Cl showed 20-fold greater plasma and 2-fold greater blood concentrations of Hg than MeHg-Cys, indicating that their pharmacokinetic properties are different. One hour later, however, Hg concentrations in plasma and blood became virtually identical between MeHg·Cl and MeHg-Cys, although blood Hg concentrations were >100-fold greater than those in plasma. When administered into the closed rat's jejunum loop, MeHg·Cl and MeHg-Cys were rapidly and efficiently taken up by intestinal membranes, and Hg was retained in intestinal membranes for a relatively long time. When administered orally, no difference was observed in plasma and blood Hg concentrations between MeHg·Cl and MeHg-Cys: plasma and blood Hg concentrations increased gradually and reached steady levels at 8 h after administration. In Caco2 cells, uptake of MeHg-Cys was significantly suppressed by L-leucine, although this was not seen with MeHg·Cl. In Caco2 cells, 81 % of Hg was recovered from cytosol fractions and 13 % of Hg from nuclear fractions (including debris) after a 2-h incubation with MeHg-Cys. In conclusion, the mechanism of membrane uptake and volume of distribution in the initial distribution phase were clearly different between MeHg·Cl and MeHg-Cys. However, such pharmacokinetic differences between them disappeared 1 h after intravenous and after oral routes of administration, possibly due to the metabolism in the body.
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Affiliation(s)
- Nobuhiro Mori
- Laboratory of Biopharmaceutics and Pharmacokinetics, Faculty of Pharmaceutical Sciences, Hiroshima International University, Hiro-koshingai, Kure, Hiroshima, Japan
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23
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Pochini L, Peta V, Indiveri C. Inhibition of the OCTN2 carnitine transporter by HgCl2and methylmercury in the proteoliposome experimental model: insights in the mechanism of toxicity. Toxicol Mech Methods 2012; 23:68-76. [DOI: 10.3109/15376516.2012.719166] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Syversen T, Kaur P. The toxicology of mercury and its compounds. J Trace Elem Med Biol 2012; 26:215-26. [PMID: 22658719 DOI: 10.1016/j.jtemb.2012.02.004] [Citation(s) in RCA: 231] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2012] [Accepted: 02/07/2012] [Indexed: 12/27/2022]
Abstract
A concentrated review on the toxicology of inorganic mercury together with an extensive review on the neurotoxicology of methylmercury is presented. The challenges of using inorganic mercury in dental amalgam are reviewed both regarding the occupational exposure and the possible health problems for the dental patients. The two remaining "mysteries" of methylmercury neurotoxicology are also being reviewed; the cellular selectivity and the delayed onset of symptoms. The relevant literature on these aspects has been discussed and some suggestions towards explaining these observations have been presented.
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Affiliation(s)
- Tore Syversen
- Norwegian University of Science and Technology, Department of Neuroscience, Trondheim, Norway.
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25
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Krey A, Kwan M, Chan HM. Mercury speciation in brain tissue of polar bears (Ursus maritimus) from the Canadian Arctic. ENVIRONMENTAL RESEARCH 2012; 114:24-30. [PMID: 22406289 DOI: 10.1016/j.envres.2012.01.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2011] [Revised: 01/03/2012] [Accepted: 01/31/2012] [Indexed: 05/31/2023]
Abstract
Methylmercury (MeHg) is a neurotoxicant that has been found at elevated concentrations in the Arctic ecosystem. Little is known about its internal dose in wildlife such as polar bears. We measured concentrations of mercury (Hg) in three different brain regions (cerebellum, frontal lobe and brain stem) of 24 polar bears collected from the Nunavik, Canada between 2000 and 2003. Speciation of Hg was measured by High Performance Liquid Chromatography coupled to Inductively Coupled Plasma Mass Spectroscopy (HPLC-ICP-MS). Concentrations of mean total Hg in brain tissue were up to 625 times lower (0.28 ± 0.07 mg kg(-1) dry weight (dw) in frontal lobe, 0.23 ± 0.07 mg kg(-1) dw in cerebellum and 0.12 ± 0.0 3mg kg(-1) dw in brain stem) than the mean total Hg concentration previously reported in polar bear liver collected from Eastern Baffin Island. Methylmercury (MeHg) accounted for 100% of the Hg found in all three brain regions analyzed. These results suggest that polar bear might reduce the toxic effects of Hg by limiting the uptake into the brain and/or decrease the rate of demethylation so that Hg can be excreted from the brain more easily. The toxicokinetics and the blood-brain-barrier mechanisms of polar bears are still unknown and further research is required.
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Affiliation(s)
- Anke Krey
- Natural Resources and Environmental Studies, University of Northern British Columbia, Prince George, BC, Canada
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26
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Acosta-Saavedra LC, Moreno ME, Rodríguez-Kessler T, Luna A, Arias-Salvatierra D, Gómez R, Calderon-Aranda ES. Environmental exposure to lead and mercury in Mexican children: a real health problem. Toxicol Mech Methods 2011; 21:656-66. [PMID: 21981766 DOI: 10.3109/15376516.2011.620997] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Exposure to lead (Pb) and mercury (Hg) remains a world public health problem, particularly for young children in developing countries. In Mexico, the main sources of exposure to Pb and Hg are wastes from human activities that increase the natural sources of these metals. Pb and Hg are highly toxic during development and maturation periods of the central nervous system (CNS); these effects are associated with the risk for neurodegenerative diseases. Mexico has numerous exposure sources to Pb and Hg; nevertheless, information on exposure in children is limited, particularly for Hg. Therefore, we conducted a review of the studies performed in children exposed to Pb and Hg. Data presented support that an important proportion of Mexican children have Pb levels above values associated with dangerous effects. On the other hand, studies on Hg-exposure are scarce, so we need more studies to estimate the magnitude of the problem and to determine exposure levels in Mexican children. Available data support the urgent need for coordinated actions among researchers, and health and environmental government authorities to implement education and nutritional campaigns, as well as to decrease exposure and effects of Pb and Hg. In addition, there must be a priority for the implementation of educational campaigns directed to the general population, but with emphasis in parents, education staff and health care providers to decrease both the risk of exposure of children to Pb and Hg and the effects of the exposure to these metals.
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Yoshida E, Toyama T, Shinkai Y, Sawa T, Akaike T, Kumagai Y. Detoxification of Methylmercury by Hydrogen Sulfide-Producing Enzyme in Mammalian Cells. Chem Res Toxicol 2011; 24:1633-5. [DOI: 10.1021/tx200394g] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Eiko Yoshida
- Doctoral Program in Biomedical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan
| | - Takashi Toyama
- Doctoral Program in Biomedical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan
- Japan Society for the Promotion of Science, 1-8 Chiyoda-ku, Tokyo 102-8472, Japan
| | - Yasuhiro Shinkai
- Doctoral Program in Biomedical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan
| | - Tomohiro Sawa
- Department of Microbiology, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto 860-8556, Japan
| | - Takaaki Akaike
- Department of Microbiology, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto 860-8556, Japan
| | - Yoshito Kumagai
- Doctoral Program in Biomedical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan
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Garrecht M, Austin DW. The plausibility of a role for mercury in the etiology of autism: a cellular perspective. TOXICOLOGICAL AND ENVIRONMENTAL CHEMISTRY 2011; 93:1251-1273. [PMID: 22163375 PMCID: PMC3173748 DOI: 10.1080/02772248.2011.580588] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2011] [Accepted: 04/10/2011] [Indexed: 05/23/2023]
Abstract
Autism is defined by a behavioral set of stereotypic and repetitious behavioral patterns in combination with social and communication deficits. There is emerging evidence supporting the hypothesis that autism may result from a combination of genetic susceptibility and exposure to environmental toxins at critical moments in development. Mercury (Hg) is recognized as a ubiquitous environmental neurotoxin and there is mounting evidence linking it to neurodevelopmental disorders, including autism. Of course, the evidence is not derived from experimental trials with humans but rather from methods focusing on biomarkers of Hg damage, measurements of Hg exposure, epidemiological data, and animal studies. For ethical reasons, controlled Hg exposure in humans will never be conducted. Therefore, to properly evaluate the Hg-autism etiological hypothesis, it is essential to first establish the biological plausibility of the hypothesis. This review examines the plausibility of Hg as the primary etiological agent driving the cellular mechanisms by which Hg-induced neurotoxicity may result in the physiological attributes of autism. Key areas of focus include: (1) route and cellular mechanisms of Hg exposure in autism; (2) current research and examples of possible genetic variables that are linked to both Hg sensitivity and autism; (3) the role Hg may play as an environmental toxin fueling the oxidative stress found in autism; (4) role of mitochondrial dysfunction; and (5) possible role of Hg in abnormal neuroexcitory and excitotoxity that may play a role in the immune dysregulation found in autism. Future research directions that would assist in addressing the gaps in our knowledge are proposed.
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Affiliation(s)
- Matthew Garrecht
- Swinburne Autism Bio-Research Initiative, Faculty of Life and Social Sciences, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
| | - David W. Austin
- Swinburne Autism Bio-Research Initiative, Faculty of Life and Social Sciences, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
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Roos DH, Puntel RL, Lugokenski TH, Ineu RP, Bohrer D, Burger ME, Franco JL, Farina M, Aschner M, Rocha JBT, de Vargas Barbosa NB. Complex methylmercury-cysteine alters mercury accumulation in different tissues of mice. Basic Clin Pharmacol Toxicol 2011; 107:789-92. [PMID: 20486922 DOI: 10.1111/j.1742-7843.2010.00577.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Methylmercury (MeHg) can cause deleterious effects in vertebrate tissues, particularly in the central nervous system. MeHg interacts with sulfhydryl groups from low and high molecular weight thiols in the blood, which can facilitate MeHg uptake into different tissues. The purpose of this study was to examine the effect of MeHg-Cysteine (MeHg-Cys) complex administration on Hg-uptake in cerebral areas (cortex and cerebellum), liver and kidney of adult mice. Animals were divided into four groups: control (1 mL/kg distilled water), MeHg (2 mg/kg), Cys (2 mg/kg) and MeHg-Cys complex (0.8 molar ratio). Mice received one intraperitoneal injection per day for 60 consecutive days. Treatment with MeHg significantly increased mercury concentrations in all tissues analysed when compared with the control group. The accumulation of mercury in brain and in liver was further increased in animals that received MeHg-Cys complex when compared with the MeHg alone group. However, renal Hg decreased in MeHg-Cys treated mice, when compared with the group treated only with MeHg. In summary, the transport of MeHg-Cys complex was tissue-specific, and we observed an increase in its uptake by liver and brain as well as a decrease in kidney.
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Affiliation(s)
- Daniel Henrique Roos
- Departamento de Química, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, Santa Maria, Brazil
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Ni M, Li X, Yin Z, Sidoryk-Węgrzynowicz M, Jiang H, Farina M, Rocha JBT, Syversen T, Aschner M. Comparative study on the response of rat primary astrocytes and microglia to methylmercury toxicity. Glia 2011; 59:810-20. [PMID: 21351162 DOI: 10.1002/glia.21153] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Accepted: 01/11/2011] [Indexed: 12/16/2022]
Abstract
As the two major glial cell types in the brain, astrocytes and microglia play pivotal but different roles in maintaining optimal brain function. Although both cell types have been implicated as major targets of methylmercury (MeHg), their sensitivities and adaptive responses to this metal can vary given their distinctive properties and physiological functions. This study was carried out to compare the responses of astrocytes and microglia following MeHg treatment, specifically addressing the effects of MeHg on cell viability, reactive oxygen species (ROS) generation and glutathione (GSH) levels, as well as mercury (Hg) uptake and the expression of NF-E2-related factor 2 (Nrf2). Results showed that microglia are more sensitive to MeHg than astrocytes, a finding that is consistent with their higher Hg uptake and lower basal GSH levels. Microglia also demonstrated higher ROS generation compared with astrocytes. Nrf2 and its downstream genes were upregulated in both cell types, but with different kinetics (much faster in microglia). In summary, microglia and astrocytes each exhibit a distinct sensitivity to MeHg, resulting in their differential temporal adaptive responses. These unique sensitivities appear to be dependent on the cellular thiol status of the particular cell type.
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Affiliation(s)
- Mingwei Ni
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
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31
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Oppedisano F, Galluccio M, Indiveri C. Inactivation by Hg2+ and methylmercury of the glutamine/amino acid transporter (ASCT2) reconstituted in liposomes: Prediction of the involvement of a CXXC motif by homology modelling. Biochem Pharmacol 2010; 80:1266-73. [PMID: 20599776 DOI: 10.1016/j.bcp.2010.06.032] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2010] [Revised: 06/19/2010] [Accepted: 06/21/2010] [Indexed: 10/19/2022]
Abstract
The effect of HgCl(2), methylmercury and mersalyl on the glutamine/amino acid (ASCT2) transporter reconstituted in liposomes has been studied. Mercuric compounds externally added to the proteoliposomes, inhibited the glutamine/glutamine antiport catalyzed by the reconstituted transporter. Similar effects were observed by pre-treating the proteoliposomes with the mercurials and then removing unreacted compounds before the transport assay. The inhibition was reversed by DTE, cysteine and N-acetyl-cysteine but not by S-carboxymethyl-cysteine. The data demonstrated that the inhibition was due to covalent reaction of mercuric compounds with Cys residue(s) of the transporter. The IC(50) of the transporter for HgCl(2), methylmercury and mersalyl, were 1.4+/-0.10, 2.4+/-0.16 or 3.1+/-0.19 microM, respectively. Kinetic studies of the inhibition showed that the reagents behaved as non-competitive inhibitor. The presence of glutamine or Na(+) during the incubation of the mercuric compounds with the proteoliposomes did not exerted any protective effect on the inhibition. None of the compounds was transported by the reconstituted transporter. A metal binding motif CXXC has been predicted as possible site of interaction of the mercuric compounds with the transporter on the basis of the homology structural model of ASCT2 obtained using the glutamate transporter homologue from Pyrococcus horikoshii as template.
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Affiliation(s)
- Francesca Oppedisano
- Department of Cell Biology, University of Calabria, Via P.Bucci 4c, 87036 Arcavacata di Rende, Italy
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Gundacker C, Gencik M, Hengstschläger M. The relevance of the individual genetic background for the toxicokinetics of two significant neurodevelopmental toxicants: mercury and lead. Mutat Res 2010; 705:130-140. [PMID: 20601101 DOI: 10.1016/j.mrrev.2010.06.003] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2010] [Revised: 06/07/2010] [Accepted: 06/10/2010] [Indexed: 11/25/2022]
Abstract
The heavy metals mercury and lead are well-known and significant developmental neurotoxicants. This review summarizes the genetic factors that modify their toxicokinetics. Understanding toxicokinetics (uptake, biotransformation, distribution, and elimination processes) is a key precondition to understanding the individual health risks associated with exposure. We selected candidate susceptibility genes when evidence was available for (1) genes/proteins playing a significant role in mercury and lead toxicokinetics, (2) gene expression/protein activity being induced by these metals, and (3) mercury and lead toxicokinetics being affected by gene knockout/knockdown or (4) by functional gene polymorphisms. The genetic background is far better known for mercury than for lead toxicokinetics. Involved are genes encoding L-type amino acid transporters, organic anion transporters, glutathione (GSH)-related enzymes, metallothioneins, and transporters of the ABC family. Certain gene variants can influence mercury toxicokinetics, potentially explaining part of the variable susceptibility to mercury toxicity. Delta-aminolevulinic acid dehydratase (ALAD), vitamin D receptor (VDR) and hemochromatosis (HFE) gene variants are the only well-established susceptibility markers of lead toxicity in humans. Many gaps remain in our knowledge about the functional genomics of this issue. This calls for studies to detect functional gene polymorphisms related to mercury- and lead-associated disease phenotypes, to demonstrate the impact of functional polymorphisms and gene knockout/knockdown in relation to toxicity, to confirm the in vivo relevance of genetic variation, and to examine gene-gene interactions on the respective toxicokinetics. Another crucial aspect is knowledge on the maternal-fetal genetic background, which modulates fetal exposure to these neurotoxicants. To completely define the genetically susceptible risk groups, research is also needed on the genes/proteins involved in the toxicodynamics, i.e., in the mechanisms causing adverse effects in the brain. Studies relating the toxicogenetics to neurodevelopmental disorders are lacking (mercury) or very scarce (lead). Thus, the extent of variability in susceptibility to heavy metal-associated neurological outcomes is poorly characterized.
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Affiliation(s)
- Claudia Gundacker
- Institute of Medical Genetics, Medical University of Vienna, Währinger Strasse 10, A-1090 Vienna, Austria.
| | - Martin Gencik
- Praxis fur Humangenetik, Brünnlbadgasse 15, A-1090 Vienna, Austria
| | - Markus Hengstschläger
- Institute of Medical Genetics, Medical University of Vienna, Währinger Strasse 10, A-1090 Vienna, Austria
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Dynamic accumulation and redistribution of methylmercury in the lens of developing zebrafish embryos and larvae. J Biol Inorg Chem 2010; 15:1137-45. [DOI: 10.1007/s00775-010-0674-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2010] [Accepted: 05/06/2010] [Indexed: 12/13/2022]
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Ceccatelli S, Daré E, Moors M. Methylmercury-induced neurotoxicity and apoptosis. Chem Biol Interact 2010; 188:301-8. [PMID: 20399200 DOI: 10.1016/j.cbi.2010.04.007] [Citation(s) in RCA: 215] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2010] [Revised: 04/06/2010] [Accepted: 04/08/2010] [Indexed: 12/24/2022]
Abstract
Methylmercury is a widely distributed environmental toxicant with detrimental effects on the developing and adult nervous system. Due to its accumulation in the food chain, chronic exposure to methylmercury via consumption of fish and sea mammals is still a major concern for human health, especially developmental exposure that may lead to neurological alterations, including cognitive and motor dysfunctions. Mercury-induced neurotoxicity and the identification of the underlying mechanisms has been a main focus of research in the neurotoxicology field. Three major mechanisms have been identified as critical in methylmercury-induced cell damage including (i) disruption of calcium homeostasis, (ii) induction of oxidative stress via overproduction of reactive oxygen species or reduction of antioxidative defenses and (iii) interactions with sulfhydryl groups. In vivo and in vitro studies have provided solid evidence for the occurrence of neural cell death, as well as cytoarchitectural alterations in the nervous system after exposure to methylmercury. Signaling cascades leading to cell death induced by methylmercury involve the release of mitochondrial factors, such as cytochrome c and AIF with subsequent caspase-dependent or -independent apoptosis, respectively; induction of calcium-dependent proteases calpains; interaction with lysosomes leading to release of cathepsins. Interestingly, several pathways can be activated in parallel, depending on the cell type. In this paper, we provide an overview of recent findings on methylmercury-induced neurotoxicity and cell death pathways that have been described in neural and endocrine cell systems.
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Affiliation(s)
- Sandra Ceccatelli
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.
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