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Mechanisms of oxidative stress in methylmercury-induced neurodevelopmental toxicity. Neurotoxicology 2021; 85:33-46. [PMID: 33964343 DOI: 10.1016/j.neuro.2021.05.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 05/02/2021] [Accepted: 05/03/2021] [Indexed: 12/15/2022]
Abstract
Methylmercury (MeHg) is a long-lasting organic environmental pollutant that poses a great threat to human health. Ingestion of seafood containing MeHg is the most important way by which it comes into contact with human body, where the central nervous system (CNS) is the primary target of MeHg toxicity. During periods of pre-plus postnatal, in particular, the brain of offspring is vulnerable to specific developmental insults that result in abnormal neurobehavioral development, even without symptoms in mothers. While many studies on neurotoxic effects of MeHg on the developing brain have been conducted, the mechanisms of oxidative stress in MeHg-induced neurodevelopmental toxicity is less clear. Hitherto, no single process can explain the many effects observed in MeHg-induced neurodevelopmental toxicity. This review summarizes the possible mechanisms of oxidative stress in MeHg-induced neurodevelopmental toxicity, highlighting modulation of Nrf2/Keap1/Notch1, PI3K/AKT, and PKC/MAPK molecular pathways as well as some preventive drugs, and thus contributes to the discovery of endogenous and exogenous molecules that can counteract MeHg-induced neurodevelopmental toxicity.
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Varian-Ramos CW, Whitney M, Rice GW, Cristol DA. Form of Dietary Methylmercury does not Affect Total Mercury Accumulation in the Tissues of Zebra Finch. BULLETIN OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY 2017; 99:1-8. [PMID: 28497383 DOI: 10.1007/s00128-017-2104-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Accepted: 05/03/2017] [Indexed: 06/07/2023]
Abstract
Exposure to mercury in humans, other mammals, and birds is primarily dietary, with mercury in the methylated form and bound to cysteine in the tissues of prey items. Yet dosing studies are generally carried out using methylmercury chloride. Here we tested whether the accumulation of total mercury in zebra finch blood, egg, muscle, liver, kidney or brain differed depending on whether dietary mercury was complexed with chloride or cysteine. We found no effect of form of mercury on tissue accumulation. Some previous studies have found lower accumulation of mercury in tissues of animals fed complexed mercury. Much remains to be understood about what happens to ingested mercury once it enters the intestines, but our results suggest that dietary studies using methylmercury chloride in birds will produce similar tissue accumulation levels to those using methylmercury cysteine.
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Affiliation(s)
- Claire W Varian-Ramos
- Institute for Integrative Bird Behavior Studies, Biology Department, College of William and Mary, P.O. Box 8795, Williamsburg, VA, 23187, USA.
- Biology Department, Colorado State University - Pueblo, 2200 Bonforte Blvd., Pueblo, CO, 81011, USA.
| | - Margaret Whitney
- Institute for Integrative Bird Behavior Studies, Biology Department, College of William and Mary, P.O. Box 8795, Williamsburg, VA, 23187, USA
| | - Gary W Rice
- Chemistry Department, College of William and Mary, P.O. Box 8795, Williamsburg, VA, 23187, USA
| | - Daniel A Cristol
- Institute for Integrative Bird Behavior Studies, Biology Department, College of William and Mary, P.O. Box 8795, Williamsburg, VA, 23187, USA
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Risher JF, Tucker P. Alkyl Mercury-Induced Toxicity: Multiple Mechanisms of Action. REVIEWS OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY 2017; 240:105-149. [PMID: 27161558 PMCID: PMC10508330 DOI: 10.1007/398_2016_1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
There are a number of mechanisms by which alkylmercury compounds cause toxic action in the body. Collectively, published studies reveal that there are some similarities between the mechanisms of the toxic action of the mono-alkyl mercury compounds methylmercury (MeHg) and ethylmercury (EtHg). This paper represents a summary of some of the studies regarding these mechanisms of action in order to facilitate the understanding of the many varied effects of alkylmercurials in the human body. The similarities in mechanisms of toxicity for MeHg and EtHg are presented and compared. The difference in manifested toxicity of MeHg and EtHg are likely the result of the differences in exposure, metabolism, and elimination from the body, rather than differences in mechanisms of action between the two.
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Affiliation(s)
- John F Risher
- Division of Toxicology and Human Health Sciences, Agency for Toxic Substances and Disease Registry, 1600 Clifton Road (MS F-58), Atlanta, GA, 30333, USA.
| | - Pamela Tucker
- Division of Toxicology and Human Health Sciences, Agency for Toxic Substances and Disease Registry, 1600 Clifton Road (MS F-58), Atlanta, GA, 30333, USA
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Sahin D, Erdolu CO, Karadenizli S, Kara A, Bayrak G, Beyaz S, Demir B, Ates N. Effects of gestational and lactational exposure to low dose mercury chloride (HgCl2) on behaviour, learning and hearing thresholds in WAG/Rij rats. EXCLI JOURNAL 2016; 15:391-402. [PMID: 27540351 PMCID: PMC4983802 DOI: 10.17179/excli2016-315] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Accepted: 06/05/2016] [Indexed: 01/18/2023]
Abstract
We investigated the effects of inorganic mercury exposure during gestational/lactational periods on the behaviour, learning and hearing functions in a total of 32, 5-week-old and 5-month-old WAG/Rij rats (equally divided into 4 groups as 5-week and 5-month control mercury exposure groups). We evaluated the rats in terms of locomotor activity (LA), the Morris-water-maze (MWM) test and the passive avoidance (PA) test to quantify learning and memory performance; we used distortion product otoacoustic emission (DPOAE) tests to evaluate hearing ability. There were no significant differences between the 5-week-old rat groups in LA, and we detected a significant difference (p < 0.05) in the HgCl2-treated group in PA, MWM and DPOAE tests compared with the control group. The HgCl2-treated 5-week-old group exhibited worse emotional memory performance in PA, worse spatial learning and memory performances in MWM. There were no significant differences between the groups of 5-month-old rats in LA, MWM or PA. However, the DPOAE tests worsened in the mid- and high-frequency hearing thresholds. The HgCl2-treated 5-month-old group exhibited the most hearing loss of all groups. Our results convey that mercury exposure in young rats may worsen learning and memory performances as well as hearing at high-frequency levels. While there was no statistically significant difference in the behavior and learning tests in adult rats, the DPOAE test produced poorer results. Early detection of effects of mercury exposure provides medicals team with an opportunity to determinate treatment regimens and mitigate ototoxicity. DPOAE test can be used in clinical and experimental research investigating heavy metal ototoxicity.
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Affiliation(s)
- Deniz Sahin
- Kocaeli University / Medical Faculty, Physiology, Kocaeli, Turkey
| | | | | | - Ahmet Kara
- Sakarya University Training and Research Hospital, Otorhinolaryngology Department, Sakarya,Turkey
| | - Gunce Bayrak
- Kocaeli University / Medical Faculty, Kocaeli, Turkey
| | - Sumeyye Beyaz
- Kocaeli University / Medical Faculty, Kocaeli, Turkey
| | - Buse Demir
- Kocaeli University / Medical Faculty, Kocaeli, Turkey
| | - Nurbay Ates
- Kocaeli University / Medical Faculty, Physiology, Kocaeli, Turkey
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Adedara IA, Rosemberg DB, Souza DO, Kamdem JP, Farombi EO, Aschner M, Rocha JBT. Biochemical and behavioral deficits in the lobster cockroach Nauphoeta cinerea model of methylmercury exposure. Toxicol Res (Camb) 2015. [DOI: 10.1039/c4tx00231h] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Methylmercury (MeHg) is well-known for its neurodevelopmental effects both in animals and in humans.
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Affiliation(s)
- Isaac A. Adedara
- Departamento de Bioquímica e Biologia Molecular
- CCNE
- Universidade Federal de Santa Maria
- 97105-900 Santa Maria
- Brazil
| | - Denis B. Rosemberg
- Departamento de Bioquímica e Biologia Molecular
- CCNE
- Universidade Federal de Santa Maria
- 97105-900 Santa Maria
- Brazil
| | - Diogo O. Souza
- Departamento de Bioquímica
- Instituto de Ciências Básicas da Saúde
- Universidade Federal do Rio Grande do Sul
- 90035-003 Porto Alegre
- Brazil
| | - Jean P. Kamdem
- Departamento de Bioquímica e Biologia Molecular
- CCNE
- Universidade Federal de Santa Maria
- 97105-900 Santa Maria
- Brazil
| | - Ebenezer O. Farombi
- Drug Metabolism and Toxicology Research Laboratories
- Department of Biochemistry
- College of Medicine
- University of Ibadan
- Ibadan
| | - Michael Aschner
- Department of Molecular Pharmacology
- Albert Einstein College of Medicine Forchheimer 209
- Bronx
- USA
| | - Joao B. T. Rocha
- Departamento de Bioquímica e Biologia Molecular
- CCNE
- Universidade Federal de Santa Maria
- 97105-900 Santa Maria
- Brazil
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Martinez-Finley EJ, Caito S, Slaughter JC, Aschner M. The Role of skn-1 in methylmercury-induced latent dopaminergic neurodegeneration. Neurochem Res 2013; 38:2650-60. [PMID: 24194349 DOI: 10.1007/s11064-013-1183-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2013] [Revised: 09/09/2013] [Accepted: 10/17/2013] [Indexed: 02/07/2023]
Abstract
Mercury (Hg) is a persistent environmental bioaccumulative metal, with developmental exposure to methylmercury (MeHg) resulting in long-term health effects. We examined the impact of early-life exposure to MeHg and knockdown of skn-1 on dopaminergic (DAergic) neurodegeneration in the nematode Caenorhabditis elegans. SKN-1, a the major stress-activated cytoprotective transcription factors, promotes the transcription of enzymes that scavenge free radicals, synthesizes glutathione and catalyzes reactions that increase xenobiotic excretion. Deletions or mutations in this gene suppress stress resistance. Thus, we hypothesized that the extent of MeHg's toxicity is dependent on intact skn-1 response; therefore skn-1 knockout (KO) worms would show heightened sensitivity to MeHg-induced toxicity compared to wildtype worms. In this study we identified the impact of early-life MeHg exposure on Hg content, stress reactivity and DAergic neurodegeneration in wildtype, and skn-1KO C. elegans. Hg content, measured by Inductively Coupled Plasma Mass Spectrometry, showed no strain-dependent differences. Reactive oxygen species generation was dramatically increased in skn-1KO compared to wildtype worms. Structural integrity of DAergic neurons was microscopically assessed by visualization of fluorescently-labeled neurons, and revealed loss of neurons in skn-1KO and MeHg exposed worms compared to wildtype controls. Dopamine levels detected by High-performance liquid chromatography, were decreased in response to MeHg exposure and decreased in skn-1KO worms, and functional behavioral assays showed similar findings. Combined, these studies suggest that knockdown of skn-1 in the nematode increases DAergic sensitivity to MeHg exposure following a period of latency.
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Affiliation(s)
- Ebany J Martinez-Finley
- Division of Pediatric Toxicology and Clinical Pharmacology, Vanderbilt University Medical Center, 11425 MRB IV, 2215-B Garland Ave., Nashville, TN, 37232-0414, USA
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Kong HK, Wong MH, Chan HM, Lo SCL. Chronic exposure of adult rats to low doses of methylmercury induced a state of metabolic deficit in the somatosensory cortex. J Proteome Res 2013; 12:5233-45. [PMID: 23984759 DOI: 10.1021/pr400356v] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Because of the ever-increasing bioaccumulation of methylmercury (MeHg) in the marine food chain, human consumers are exposed to low doses of MeHg continually through seafood consumption. Epidemiological studies strongly suggest that chronic prenatal exposure to nanomolar of MeHg has immense negative impacts on neurological development in neonates. However, effects of chronic exposure to low doses (CELDs) of MeHg in adult brains on a molecular level are unknown. The current study aims to investigate the molecular effects of CELD of MeHg on adult somatosensory cortex in a rat model using proteomic techniques. Young adult rats were fed with a low dose of MeHg (40 μg/kg body weight/day) for a maximum of 12 weeks. Whole proteome expression of the somatosensory cortex (S1 area) of normal rats and those with CELD to MeHg were compared. Levels of MeHg, total calcium, adenosine triphosphate (ATP), and pyruvate were also measured. Comparative proteomic studies of the somatosensory cortexes revealed that 94 proteins involved in the various metabolic processes (including carbohydrate metabolism, generation of precursors for essential metabolites, energy, proteins, cellular components for morphogenesis, and neurotransmission) were down-regulated. Consequently, levels of important end products of active metabolism including ATP, pyruvate, and total calcium were also found to be significantly reduced concomitantly. Our results showed that CELD of MeHg induced a state of metabolic deficit in the somatosensory cortex of adult rats.
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Affiliation(s)
- Hang-Kin Kong
- Food Safety and Technology Research Centre, The Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University , Room Y810, Lee Shau Kee Building (Block Y), Hung Hom, Hong Kong, China
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Selderslaghs IWT, Hooyberghs J, Blust R, Witters HE. Assessment of the developmental neurotoxicity of compounds by measuring locomotor activity in zebrafish embryos and larvae. Neurotoxicol Teratol 2013; 37:44-56. [PMID: 23357511 DOI: 10.1016/j.ntt.2013.01.003] [Citation(s) in RCA: 91] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2012] [Revised: 01/17/2013] [Accepted: 01/17/2013] [Indexed: 12/27/2022]
Abstract
The developmental neurotoxic potential of the majority of environmental chemicals and drugs is currently undetermined. Specific in vivo studies provide useful data for hazard assessment but are not amenable to screen thousands of untested compounds. In this study, methods which use zebrafish embryos, eleutheroembryos and larvae as model organisms, were proposed as alternatives for developmental neurotoxicity (DNT) testing. The evaluation of spontaneous tail coilings in zebrafish embryos aged 24-26 hours post fertilization (hpf) and the swimming activity of eleutheroembryos at 120 and larvae at 144 hpf, i.e. parameters for locomotor activity, were investigated as potential endpoints for DNT testing, according to available standard protocols. The overall performance and predictive value of these methods was then examined by testing a training set of 10 compounds, including known developmental neurotoxicants and compounds not considered to be neurotoxic. The classification of the selected compounds as either neurotoxic or non-neurotoxic, based on the effects observed in zebrafish embryos and larvae, was compared to available mammalian data and an overall concordance of 90% was achieved. Furthermore, the specificity of the selected endpoints for DNT was evaluated as well as the potential similarities between zebrafish and mammals with regard to mechanisms of action for the selected compounds. Although further studies, including the screening of a large testing set of compounds are required, we suggest that the proposed methods with zebrafish embryos and larvae might be valuable alternatives for animal testing for the screening and prioritization of compounds for DNT.
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Affiliation(s)
- Ingrid W T Selderslaghs
- VITO NV, Flemish Institute for Technological Research, Environmental Risk and Health, Boeretang 200, Mol, Belgium.
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Piersma AH, Hernandez LG, van Benthem J, Muller JJA, van Leeuwen FR, Vermeire TG, van Raaij MTM. Reproductive toxicants have a threshold of adversity. Crit Rev Toxicol 2011; 41:545-54. [DOI: 10.3109/10408444.2011.554794] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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Wu C. Overview of developmental and reproductive toxicity research in China: history, funding mechanisms, and frontiers of the research. BIRTH DEFECTS RESEARCH. PART B, DEVELOPMENTAL AND REPRODUCTIVE TOXICOLOGY 2010; 89:9-17. [PMID: 20135688 DOI: 10.1002/bdrb.20231] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Reproductive and developmental toxicology (DART) is the discipline that deals with adverse effects on male and female resulting from exposures to harmful chemical and physical agents. DART research in China boasted a long history, but presently has fallen behind the western world in education and research. The funding mechanisms for DART research in China were similar to that for other toxicological disciplines, and the funding has come from research grants and fellowships provided by national, ministerial, and provincial institutions. Finally, the frontiers of DART research in China could be summarized as follows: (1) use of model animals such as the zebrafish and roundworm, and use of cutting-edge techniques such as stem cell culture, as well as transgenic, metabonomic, and virtual screening to study the mechanisms of developmental toxicity for some important toxicants in China; (2) use of model animals and other lower-level sentinel organisms to evaluate and monitor the developmental toxicogical risk of environmental chemicals or pollutants; (3) epidemiological studies of some important reproductive hazards; (4) in-depth studying of the reproductive and developmental toxicity of some important environmental chemicals; and (5) evaluation and study of the reproductive and developmental toxicity of traditional Chinese medicines.
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Affiliation(s)
- Chunqi Wu
- National Beijing Center for Drug Safety Evaluation and Research, Beijing Institute of Toxicology and Pharmacology, PR China.
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Effects of postnatal exposure to methylmercury on spatial learning and memory and brain NMDA receptor mRNA expression in rats. Toxicol Lett 2009; 188:230-5. [PMID: 19409459 DOI: 10.1016/j.toxlet.2009.04.021] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2008] [Revised: 04/08/2009] [Accepted: 04/20/2009] [Indexed: 12/21/2022]
Abstract
The extreme vulnerability of developing nervous system to methylmercury (MeHg) is well documented. Still unclear is the consequence of different postnatal period exposure to MeHg. We investigated the critical postnatal phase when MeHg induced neurotoxicity in rats and the underlying mechanism. Rats were given 5mg/(kg day) methylmercury chloride (MMC) orally on postnatal day (PND) 7, PND14, PND28, and PND60 for consecutive 7 days. A control group was treated with 0.9% sodium chloride solution 5 ml/(kg day) instead. On PND69, spatial learning and memory was evaluated by Morris water maze test. Behavior deficits were found in MMC-treated rats of PND7 and PND14 groups (p<0.01). N-methyl-D-aspartate (NMDA) receptor 2 subunits mRNA expressions were evaluated 3 days after the last administration. In hippocampus, the mRNA expression of NR2A and NR2B decreased, but the NR2C expression increased in PND14 group following MMC-treatment (p<0.01). In cerebral cortex, mRNA expression of NR2A decreased, with NR2C expression elevating in PND14 group following MMC-treatment (p<0.05). These observations suggest that the postnatal exposure to MeHg during PND7-20 could cause neurobehavioral deficits which extend to adulthood. Furthermore, the abnormal expression of NMDAR 2 subunits might associate with the impairment.
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