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Dórea JG. Neurotoxic effects of combined exposures to aluminum and mercury in early life (infancy). ENVIRONMENTAL RESEARCH 2020; 188:109734. [PMID: 32544722 DOI: 10.1016/j.envres.2020.109734] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 05/22/2020] [Accepted: 05/23/2020] [Indexed: 06/11/2023]
Abstract
Aluminum and mercury are environmentally ubiquitous. Individually they are both neurotoxic elements with shared neuro-pathogenic pathways: oxidative stress, altered neurotransmission, and disruption of the neuroendocrine and immune systems. In the infant, Al and Hg differ in type of exposure, absorption, distribution (brain access), and metabolism. In environmentally associated exposure (breast milk and infant formulas) their co-occurrences fluctuate randomly, but in Thimerosal-containing vaccines (TCVs) they occur combined in a proprietary ratio; in these cases, low-doses of Thimerosal-ethylmercury (EtHg) and adjuvant-Al present the most widespread binary mixture in less developed countries. Although experimental studies at low doses of the binary Hg and Al mixture are rare, when studied individually they have been shown to affect neurological outcomes negatively. In invitro systems, comparative neurotoxicity between Al and Hg varies in relation to the measured parameters but seems less for Al than for Hg. While neurotoxicity of environmental Hg (mainly fish methyl-Hg, MeHg) is associated with neurobehavioral outcomes in children, environmental Al is not associated, except in certain clinical conditions. Therefore, the issues of their neurotoxic effects (singly or combined) are discussed. In the infant (up to six months) the organic-Hg and Al body burdens from a full TCV schedule are estimated to reach levels higher than that originating from breastfeeding or from high aluminum soy-based formulas. Despite worldwide exposure to both Al and Hg (inorganic Hg, MeHg, and Thimerosal/EtHg), our knowledge on this combined exposure is insufficient to predict their combined neurotoxic effects (and with other co-occurring neurotoxicants).
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Affiliation(s)
- José G Dórea
- Universidade de Brasília, Brasília, 70919-970, DF, Brazil.
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2
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Ramos A, Dos Santos MM, de Macedo GT, Wildner G, Prestes AS, Masuda CA, Dalla Corte CL, Teixeira da Rocha JB, Barbosa NV. Methyl and Ethylmercury elicit oxidative stress and unbalance the antioxidant system in Saccharomyces cerevisiae. Chem Biol Interact 2020; 315:108867. [PMID: 31672467 DOI: 10.1016/j.cbi.2019.108867] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 10/07/2019] [Accepted: 10/21/2019] [Indexed: 11/19/2022]
Abstract
Methylmercury (MeHg) and Ethylmercury (EtHg) are toxic to the central nervous system. Human exposure to MeHg and EtHg results mainly from the consumption of contaminated fish and thimerosal-containing vaccines, respectively. The mechanisms underlying the toxicity of MeHg and EtHg are still elusive. Here, we compared the toxic effects of MeHg and EtHg in Saccharomyces cerevisiae (S. cerevisiae) emphasizing the involvement of oxidative stress and the identification of molecular targets from antioxidant pathways. Wild type and mutant strains with deleted genes for antioxidant defenses, namely: γ-glutamylcysteine synthetase, glutathione peroxidase, catalase, superoxide dismutase, mitochondrial peroxiredoxin, cytoplasmic thioredoxin, and redox transcription factor Yap1 were used to identify potential pathways and proteins from cell redox system targeted by MeHg and EtHg. MeHg and EtHg inhibited cell growth, decreased membrane integrity, and increased the granularity and production of reactive species (RS) in wild type yeast. The mutants were predominantly less tolerant of mercurial than wild type yeast. But, as the wild strain, mutants exhibited higher tolerance to MeHg than EtHg. Our results indicate the involvement of oxidative stress in the cytotoxicity of MeHg and EtHg and reinforce S. cerevisiae as a suitable model to explore the mechanisms of action of electrophilic toxicants.
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Affiliation(s)
- Angelica Ramos
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil
| | - Matheus M Dos Santos
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil
| | - Gabriel T de Macedo
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil
| | - Guilherme Wildner
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil
| | - Alessandro S Prestes
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil
| | - Claudio A Masuda
- Instituto de Bioquímica Médica Leopoldo De Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil
| | | | | | - Nilda V Barbosa
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil.
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Dórea JG. Multiple low-level exposures: Hg interactions with co-occurring neurotoxic substances in early life. Biochim Biophys Acta Gen Subj 2018; 1863:129243. [PMID: 30385391 DOI: 10.1016/j.bbagen.2018.10.015] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2018] [Revised: 10/01/2018] [Accepted: 10/19/2018] [Indexed: 12/11/2022]
Abstract
All chemical forms of Hg can affect neurodevelopment; however, low levels of organic Hg (methylmercury-MeHg and ethylmercury-EtHg in Thimerosal-containing vaccines, hereafter 'TCV') exposures during early life (pregnancy and lactation) co-occur with other environmental neurotoxic substances. These neurotoxicants may act in parallel, synergistically, or antagonistically to Hg. Nevertheless, the risks of neurotoxicity associated with multiple neuro-toxicants depend on type, time, combinations of exposure, and environmental and/or genetic-associated factors. Neurological developmental disorders, delays in cognition and behavioral outcomes associated with multiple exposures (which include Hg) may show transient or lasting outcomes depending on constitutional and/or environmental factors that can interact to neutralize, aggravate or attenuate these effects; often these studies are challenging to interpret. During pregnancy and lactation, fish-MeHg exposure is frequently confounded with the opposing effects of neuroactive nutrients (in fish) that lead to positive, negative, or no effects on neurobehavioral tests. In infancy, exposures to acute binary mixtures (TCV- EtHg and Al-adjuvants in infant immunizations) are associated with increased risks of tics and other developmental disorders. Despite the certitude that promulgates single environmental neurotoxicants, empirical comparisons of combined exposures indicate that Hg-related outcome is uneven. Hg in combination with other neurotoxic mixtures may elevate risks of neurotoxicity, but these risks arise in circumstances that are not yet predictable. Therefore, to achieve the goals of the Minamata treaty and to safeguard the health of children, low levels of mercury exposure (in any chemical form) needs to be further reduced whether the source is environmental (air- and food-borne) or iatrogenic (pediatric TCVs).
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Affiliation(s)
- José G Dórea
- Universidade de Brasília, Brasília 70919-970, DF, Brazil..
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Dórea JG. Low-dose Thimerosal (ethyl-mercury) is still used in infants` vaccines: Should we be concerned with this form of exposure? J Trace Elem Med Biol 2018; 49:134-139. [PMID: 29895363 DOI: 10.1016/j.jtemb.2018.05.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2018] [Accepted: 05/16/2018] [Indexed: 12/25/2022]
Abstract
In developing countries, Thimerosal-containing vaccines (TCV) are the main causes of organic Hg exposure for newborns, neonates, and infants immunized with TCV. This article addresses early-life exposure to this unique organic mercury compound (ethylmercury-EtHg) and the risks of its exposure. English language studies pertaining to Thimerosal/EtHg toxicity and exposure during early life were searched in PubMed; and, those publications judged to be relevant to the topic of this review were selected. The risk from the neurotoxic effects of pre- and post-natal Hg exposures depend, in part, on aggravating or attenuating environmental and/or genetic-associated factors. Health authorities in charge of controlling infectious disease dismiss the toxicology of mercury (immunological and subtle neurological effects as insignificant) related to low-dose Thimerosal. The review addresses the evidence that brings into question the safety of Thimerosal that is still present in vaccines given to pregnant women, infants, and children in developing countries, and recognizes the ethical imperative to extend the use of Thimerosal-free vaccines to developing countries, not just developed countries.
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Affiliation(s)
- José G Dórea
- Health Sciences, Universidade de Brasília, Brasília, 70919-970, DF, Brazil.
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The Putative Role of Environmental Mercury in the Pathogenesis and Pathophysiology of Autism Spectrum Disorders and Subtypes. Mol Neurobiol 2017; 55:4834-4856. [DOI: 10.1007/s12035-017-0692-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2017] [Accepted: 07/13/2017] [Indexed: 01/28/2023]
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Dórea JG. Low-dose Thimerosal in pediatric vaccines: Adverse effects in perspective. ENVIRONMENTAL RESEARCH 2017; 152:280-293. [PMID: 27816865 DOI: 10.1016/j.envres.2016.10.028] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Revised: 10/26/2016] [Accepted: 10/27/2016] [Indexed: 06/06/2023]
Abstract
Vaccines are prophylactics used as the first line of intervention to prevent, control and eradicate infectious diseases. Young children (before the age of six months) are the demographic group most exposed to recommended/mandatory vaccines preserved with Thimerosal and its metabolite ethylmercury (EtHg). Particularly in the less-developed countries, newborns, neonates, and young children are exposed to EtHg because it is still in several of their pediatric vaccines and mothers are often immunized with Thimerosal-containing vaccines (TCVs) during pregnancy. While the immunogenic component of the product has undergone more rigorous testing, Thimerosal, known to have neurotoxic effects even at low doses, has not been scrutinized for the limit of tolerance alone or in combination with adjuvant-Al during immaturity or developmental periods (pregnant women, newborns, infants, and young children). Scientific evidence has shown the potential hazards of Thimerosal in experiments that modeled vaccine-EtHg concentrations. Observational population studies have revealed uncertainties related to neurological effects. However, consistently, they showed a link of EtHg with risk of certain neurodevelopment disorders, such as tic disorder, while clearly revealing the benefits of removing Thimerosal from children's vaccines (associated with immunological reactions) in developed countries. So far, only rich countries have benefited from withdrawing the risk of exposing young children to EtHg. Regarding Thimerosal administered to the very young, we have sufficient studies that characterize a state of uncertainty: the collective evidence strongly suggests that Thimerosal exposure is associated with adverse neurodevelopmental outcomes. It is claimed that the continued use of Thimerosal in the less-developed countries is due to the cost to change to another preservative, such as 2-phenoxyethanol. However, the estimated cost increase per child in the first year of life is lower than estimated lifetime cost of caring for a child with a neurodevelopmental disorder, such tic disorder. The evidence indicates that Thimerosal-free vaccine options should be made available in developing countries.
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Affiliation(s)
- José G Dórea
- Professor Emeritus, Faculty of Health Sciences, Universidade de Brasilia, 70919-970 Brasilia, DF, Brazil.
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Heavy Metals and Human Health: Mechanistic Insight into Toxicity and Counter Defense System of Antioxidants. Int J Mol Sci 2015; 16:29592-630. [PMID: 26690422 PMCID: PMC4691126 DOI: 10.3390/ijms161226183] [Citation(s) in RCA: 502] [Impact Index Per Article: 55.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 12/01/2015] [Accepted: 12/03/2015] [Indexed: 02/07/2023] Open
Abstract
Heavy metals, which have widespread environmental distribution and originate from natural and anthropogenic sources, are common environmental pollutants. In recent decades, their contamination has increased dramatically because of continuous discharge in sewage and untreated industrial effluents. Because they are non-degradable, they persist in the environment; accordingly, they have received a great deal of attention owing to their potential health and environmental risks. Although the toxic effects of metals depend on the forms and routes of exposure, interruptions of intracellular homeostasis include damage to lipids, proteins, enzymes and DNA via the production of free radicals. Following exposure to heavy metals, their metabolism and subsequent excretion from the body depends on the presence of antioxidants (glutathione, α-tocopherol, ascorbate, etc.) associated with the quenching of free radicals by suspending the activity of enzymes (catalase, peroxidase, and superoxide dismutase). Therefore, this review was written to provide a deep understanding of the mechanisms involved in eliciting their toxicity in order to highlight the necessity for development of strategies to decrease exposure to these metals, as well as to identify substances that contribute significantly to overcome their hazardous effects within the body of living organisms.
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Dórea JG. The neurological effects of prenatal and postnatal exposure to mercury need to include ethylmercury. CHEMOSPHERE 2015; 139:667-668. [PMID: 25001312 DOI: 10.1016/j.chemosphere.2014.06.045] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2014] [Accepted: 06/14/2014] [Indexed: 06/03/2023]
Affiliation(s)
- José G Dórea
- Faculty of Health Sciences, Universidade de Brasília, C.P. 04322, 70919-970 Brasília, DF, Brazil.
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Geier DA, King PG, Hooker BS, Dórea JG, Kern JK, Sykes LK, Geier MR. Thimerosal: Clinical, epidemiologic and biochemical studies. Clin Chim Acta 2015; 444:212-20. [DOI: 10.1016/j.cca.2015.02.030] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 02/06/2015] [Accepted: 02/14/2015] [Indexed: 10/24/2022]
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Dórea JG. Exposure to mercury and aluminum in early life: developmental vulnerability as a modifying factor in neurologic and immunologic effects. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2015; 12:1295-313. [PMID: 25625408 PMCID: PMC4344667 DOI: 10.3390/ijerph120201295] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Accepted: 01/20/2015] [Indexed: 01/15/2023]
Abstract
Currently, ethylmercury (EtHg) and adjuvant-Al are the dominating interventional exposures encountered by fetuses, newborns, and infants due to immunization with Thimerosal-containing vaccines (TCVs). Despite their long use as active agents of medicines and fungicides, the safety levels of these substances have never been determined, either for animals or for adult humans—much less for fetuses, newborns, infants, and children. I reviewed the literature for papers reporting on outcomes associated with (a) multiple exposures and metabolism of EtHg and Al during early life; (b) physiological and metabolic characteristics of newborns, neonates, and infants relevant to xenobiotic exposure and effects; (c) neurobehavioral, immunological, and inflammatory reactions to Thimerosal and Al-adjuvants resulting from TCV exposure in infancy. Immunological and neurobehavioral effects of Thimerosal-EtHg and Al-adjuvants are not extraordinary; rather, these effects are easily detected in high and low income countries, with co-exposure to methylmercury (MeHg) or other neurotoxicants. Rigorous and replicable studies (in different animal species) have shown evidence of EtHg and Al toxicities. More research attention has been given to EtHg and findings have showed a solid link with neurotoxic effects in humans; however, the potential synergic effect of both toxic agents has not been properly studied. Therefore, early life exposure to both EtHg and Al deserves due consideration.
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Affiliation(s)
- José G Dórea
- Department of Nutrition, Faculty of Health Sciences, Universidade de Brasilia, 70919-970 DF Brasilia, Brazil.
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Kalkbrenner AE, Schmidt RJ, Penlesky AC. Environmental chemical exposures and autism spectrum disorders: a review of the epidemiological evidence. Curr Probl Pediatr Adolesc Health Care 2014; 44:277-318. [PMID: 25199954 PMCID: PMC4855851 DOI: 10.1016/j.cppeds.2014.06.001] [Citation(s) in RCA: 183] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2014] [Revised: 06/09/2014] [Accepted: 06/12/2014] [Indexed: 12/11/2022]
Abstract
In the past decade, the number of epidemiological publications addressing environmental chemical exposures and autism has grown tremendously. These studies are important because it is now understood that environmental factors play a larger role in causing autism than previously thought and because they address modifiable risk factors that may open up avenues for the primary prevention of the disability associated with autism. In this review, we covered studies of autism and estimates of exposure to tobacco, air pollutants, volatile organic compounds and solvents, metals (from air, occupation, diet, dental amalgams, and thimerosal-containing vaccines), pesticides, and organic endocrine-disrupting compounds such as flame retardants, non-stick chemicals, phthalates, and bisphenol A. We included studies that had individual-level data on autism, exposure measures pertaining to pregnancy or the 1st year of life, valid comparison groups, control for confounders, and adequate sample sizes. Despite the inherent error in the measurement of many of these environmental exposures, which is likely to attenuate observed associations, some environmental exposures showed associations with autism, especially traffic-related air pollutants, some metals, and several pesticides, with suggestive trends for some volatile organic compounds (e.g., methylene chloride, trichloroethylene, and styrene) and phthalates. Whether any of these play a causal role requires further study. Given the limited scope of these publications, other environmental chemicals cannot be ruled out, but have not yet been adequately studied. Future research that addresses these and additional environmental chemicals, including their most common routes of exposures, with accurate exposure measurement pertaining to several developmental windows, is essential to guide efforts for the prevention of the neurodevelopmental damage that manifests in autism symptoms.
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Affiliation(s)
- Amy E Kalkbrenner
- Zilber School of Public Health, University of Wisconsin-Milwaukee, Milwaukee, WI
| | - Rebecca J Schmidt
- Department of Public Health Sciences, University of California Davis School of Medicine, Davis, CA; Medical Investigation of Neurodevelopmental Disorders (MIND) Institute, University of California Davis, Sacramento, CA
| | - Annie C Penlesky
- Zilber School of Public Health, University of Wisconsin-Milwaukee, Milwaukee, WI
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The Role of Heavy Metal Pollution in Neurobehavioral Disorders: a Focus on Autism. REVIEW JOURNAL OF AUTISM AND DEVELOPMENTAL DISORDERS 2014. [DOI: 10.1007/s40489-014-0028-3] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Raymond LJ, Deth RC, Ralston NVC. Potential Role of Selenoenzymes and Antioxidant Metabolism in relation to Autism Etiology and Pathology. AUTISM RESEARCH AND TREATMENT 2014; 2014:164938. [PMID: 24734177 PMCID: PMC3966422 DOI: 10.1155/2014/164938] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Revised: 01/07/2014] [Accepted: 01/27/2014] [Indexed: 11/17/2022]
Abstract
Autism and autism spectrum disorders (ASDs) are behaviorally defined, but the biochemical pathogenesis of the underlying disease process remains uncharacterized. Studies indicate that antioxidant status is diminished in autistic subjects, suggesting its pathology is associated with augmented production of oxidative species and/or compromised antioxidant metabolism. This suggests ASD may result from defects in the metabolism of cellular antioxidants which maintain intracellular redox status by quenching reactive oxygen species (ROS). Selenium-dependent enzymes (selenoenzymes) are important in maintaining intercellular reducing conditions, particularly in the brain. Selenoenzymes are a family of ~25 genetically unique proteins, several of which have roles in preventing and reversing oxidative damage in brain and endocrine tissues. Since the brain's high rate of oxygen consumption is accompanied by high ROS production, selenoenzyme activities are particularly important in this tissue. Because selenoenzymes can be irreversibly inhibited by many electrophiles, exposure to these organic and inorganic agents can diminish selenoenzyme-dependent antioxidant functions. This can impair brain development, particularly via the adverse influence of oxidative stress on epigenetic regulation. Here we review the physiological roles of selenoproteins in relation to potential biochemical mechanisms of ASD etiology and pathology.
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Affiliation(s)
- Laura J. Raymond
- Energy & Environmental Research Center, University of North Dakota, 15 North 23rd Street, Stop 9018, Grand Forks, ND 58202, USA
| | - Richard C. Deth
- Department of Pharmaceutical Sciences, Northeastern University, Boston, MA 02115, USA
| | - Nicholas V. C. Ralston
- Energy & Environmental Research Center, University of North Dakota, 15 North 23rd Street, Stop 9018, Grand Forks, ND 58202, USA
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Dórea JG, Marques RC, Abreu L. Milestone achievement and neurodevelopment of rural Amazonian toddlers (12 to 24 months) with different methylmercury and ethylmercury exposure. JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH. PART A 2014; 77:1-13. [PMID: 24555642 DOI: 10.1080/15287394.2014.861335] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Neurological outcomes (Gesell development schedules [GDS]), age of walking, and age of talking were studied in 299 toddlers (12 to 24 mo) in relation to environmental (fish consumption and tin mining) exposure. Exposure to fish methylmercury (MeHg) consumption and iatrogenic ethylmercury (EtHg) in Thimerosal-containing vaccines (TCV) was quantified in toddlers from two rural villages (n = 91, Itapuã; n = 218, Bom Futuro) respectively populated by fishers and cassiterite miners. Median total hair Hg (HHg) concentrations of infants from Itapuã (3.5 μg/g) were significantly higher than those of infants from Bom Futuro (2.2 μg/g). Median EtHg exposure from TCV was also significantly higher in toddlers from Itapuã (137.5 μg) than in those from Bom Futuro (112.5 μg). There were no significant differences between groups for any of the Gesell schedules; however, there were proportionally more compromised toddlers (GDS < 70) in Itapuã than Bom Futuro. Median age of talking was not statistically different but median age of walking was significantly higher in Bom Futuro. In toddlers from both villages, of fishers and miners, HHg concentrations were significantly correlated with family fish consumption. A logistic regression model was applied to all infants after classification into two groups: above or below the median Gesell schedules. Overall, there was no distinctive pattern of neurodevelopment associated with either HHg or EtHg exposure; however, nutritional status was significantly associated with GDS. In conclusion, milestone achievement was delayed in toddlers from tin-ore mining communities. Despite significantly higher exposure to both forms of organic Hg (MeHg from maternal fish consumption, and EtHg from TCV) in toddlers from the fishing village, significant differences were seen only among the proportions of most severely affected toddlers (GDS < 70).
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Affiliation(s)
- José G Dórea
- a Department of Nutrition , Universidade de Brasília , Brasília , Brazil
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Kern JK, Haley BE, Geier DA, Sykes LK, King PG, Geier MR. Thimerosal exposure and the role of sulfation chemistry and thiol availability in autism. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2013; 10:3771-800. [PMID: 23965928 PMCID: PMC3774468 DOI: 10.3390/ijerph10083771] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Revised: 07/10/2013] [Accepted: 07/11/2013] [Indexed: 01/22/2023]
Abstract
Autism spectrum disorder (ASD) is a neurological disorder in which a significant number of the children experience a developmental regression characterized by a loss of previously acquired skills and abilities. Typically reported are losses of verbal, nonverbal, and social abilities. Several recent studies suggest that children diagnosed with an ASD have abnormal sulfation chemistry, limited thiol availability, and decreased glutathione (GSH) reserve capacity, resulting in a compromised oxidation/reduction (redox) and detoxification capacity. Research indicates that the availability of thiols, particularly GSH, can influence the effects of thimerosal (TM) and other mercury (Hg) compounds. TM is an organomercurial compound (49.55% Hg by weight) that has been, and continues to be, used as a preservative in many childhood vaccines, particularly in developing countries. Thiol-modulating mechanisms affecting the cytotoxicity of TM have been identified. Importantly, the emergence of ASD symptoms post-6 months of age temporally follows the administration of many childhood vaccines. The purpose of the present critical review is provide mechanistic insight regarding how limited thiol availability, abnormal sulfation chemistry, and decreased GSH reserve capacity in children with an ASD could make them more susceptible to the toxic effects of TM routinely administered as part of mandated childhood immunization schedules.
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Affiliation(s)
- Janet K. Kern
- Institute of Chronic Illnesses, Inc., Silver Spring, MD 20905, USA; E-Mails: (D.A.G.); (M.R.G.)
| | - Boyd E. Haley
- Department of Chemistry, University of Kentucky, Lexington, KY 40506, USA; E-Mail:
| | - David A. Geier
- Institute of Chronic Illnesses, Inc., Silver Spring, MD 20905, USA; E-Mails: (D.A.G.); (M.R.G.)
| | - Lisa K. Sykes
- CoMeD, Inc., Silver Spring, MD 20905, USA; E-Mails: (L.K.S.); (P.G.K.)
| | - Paul G. King
- CoMeD, Inc., Silver Spring, MD 20905, USA; E-Mails: (L.K.S.); (P.G.K.)
| | - Mark R. Geier
- Institute of Chronic Illnesses, Inc., Silver Spring, MD 20905, USA; E-Mails: (D.A.G.); (M.R.G.)
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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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Vaccine adverse events reported during the first ten years (1998-2008) after introduction in the state of Rondonia, Brazil. BIOMED RESEARCH INTERNATIONAL 2013; 2013:853083. [PMID: 23509790 PMCID: PMC3586457 DOI: 10.1155/2013/853083] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/02/2012] [Revised: 01/07/2013] [Accepted: 01/11/2013] [Indexed: 02/01/2023]
Abstract
Despite good safety records, vaccines given to young children can cause adverse events. We investigated the reported adverse events following immunization (AEFI) of vaccines given to children of less than seven years of age during the first ten years (1998 to 2008) in the state of Rondonia, Brazil. We worked with the events related to BCG (Bacillus Calmett-Guérin), HB (hepatitis B), DTwP/Hib (diphtheria-tetanus-pertussis+Hemophillus influenza b), DTP (diphtheria-tetanus-pertussis), MMR (mumps, measles, rubella), and YF (yellow fever) vaccines because they were part of the recommended scheme. The number of doses of vaccines given was 3,231,567 with an average of AEFI of 57.2/year during the studied period. DTwP/Hib was responsible for 298 (57.8%), DTP 114 (22.9%), HB 31 (6%), MMR 28 (5.4%), BCG 24 (4.7%), and YF 20 (3.9%) of the reported AEFI. The combination of the AEFI for DTwP/Hib vaccines showed the highest number of systemic (61.4%) and local events (33.8%). Young children (≤1-year old) were more susceptible to AEFI occurring in the 6 hours (54.2%) following vaccine uptake. This study suggests significant differences in reactogenicity of vaccines and that despite limitations of the AEFI Brazilian registry system we cannot ignore underreporting and should use the system to expand our understanding of adverse events and effects.
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Dórea JG, Farina M, Rocha JBT. Toxicity of ethylmercury (and Thimerosal): a comparison with methylmercury. J Appl Toxicol 2013; 33:700-11. [PMID: 23401210 DOI: 10.1002/jat.2855] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Revised: 12/10/2012] [Accepted: 12/11/2012] [Indexed: 12/18/2022]
Abstract
Ethylmercury (etHg) is derived from the metabolism of thimerosal (o-carboxyphenyl-thio-ethyl-sodium salt), which is the most widely used form of organic mercury. Because of its application as a vaccine preservative, almost every human and animal (domestic and farmed) that has been immunized with thimerosal-containing vaccines has been exposed to etHg. Although methylmercury (meHg) is considered a hazardous substance that is to be avoided even at small levels when consumed in foods such as seafood and rice (in Asia), the World Health Organization considers small doses of thimerosal safe regardless of multiple/repetitive exposures to vaccines that are predominantly taken during pregnancy or infancy. We have reviewed in vitro and in vivo studies that compare the toxicological parameters among etHg and other forms of mercury (predominantly meHg) to assess their relative toxicities and potential to cause cumulative insults. In vitro studies comparing etHg with meHg demonstrate equivalent measured outcomes for cardiovascular, neural and immune cells. However, under in vivo conditions, evidence indicates a distinct toxicokinetic profile between meHg and etHg, favoring a shorter blood half-life, attendant compartment distribution and the elimination of etHg compared with meHg. EtHg's toxicity profile is different from that of meHg, leading to different exposure and toxicity risks. Therefore, in real-life scenarios, a simultaneous exposure to both etHg and meHg might result in enhanced neurotoxic effects in developing mammals. However, our knowledge on this subject is still incomplete, and studies are required to address the predictability of the additive or synergic toxicological effects of etHg and meHg (or other neurotoxicants).
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Affiliation(s)
- José G Dórea
- Department of Nutrition, Faculty of Health Sciences, Universidade de Brasilia, 70919-970, Brasilia, DF, Brazil.
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Dórea JG. Re: "prenatal exposure to mercury and infant neurodevelopment in a multicenter cohort in Spain: study of potential modifiers". Am J Epidemiol 2012; 176:1194-5; author reply 1195-6. [PMID: 23161896 DOI: 10.1093/aje/kws386] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Mrozek-Budzyn D, Majewska R, Kieltyka A, Augustyniak M. Neonatal exposure to Thimerosal from vaccines and child development in the first 3years of life. Neurotoxicol Teratol 2012; 34:592-7. [DOI: 10.1016/j.ntt.2012.10.001] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2011] [Revised: 10/03/2012] [Accepted: 10/05/2012] [Indexed: 11/27/2022]
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Mercury disposition in suckling rats: comparative assessment following parenteral exposure to thiomersal and mercuric chloride. J Biomed Biotechnol 2012; 2012:256965. [PMID: 22899883 PMCID: PMC3412121 DOI: 10.1155/2012/256965] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Accepted: 05/25/2012] [Indexed: 01/31/2023] Open
Abstract
Due to the facts that thiomersal-containing vaccine is still in use in many developing countries, and all forms of mercury have recognised neurotoxic, nephrotoxic, and other toxic effects, studies on disposition of ethylmercury and other mercury forms are still justified, especially at young age. Our investigation aimed at comparing mercury distribution and rate of excretion in the early period of life following exposure to either thiomersal (TM) or mercuric chloride (HgCl₂) in suckling rats. Three experimental groups were studied: control, TM, and HgCl₂, with 12 to18 pups in each. Both forms of mercury were administered subcutaneously in equimolar quantities (0.81 μmol/kg b.w.) three times during the suckling period (on the days of birth 7, 9, and 11) to mimic the vaccination regimen in infants. After the last administration of TM or HgCl₂, total mercury retention and excretion was assessed during following six days. In TM-exposed group mercury retention was higher in the brain, enteral excretion was similar, and urinary excretion was much lower compared to HgCl₂-exposed sucklings. More research is still needed to elucidate all aspects of toxicokinetics and most harmful neurotoxic potential of various forms of mercury, especially in the earliest period of life.
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Multiple toxic heavy metals and neonatal neurobehavior in China require considering co-exposure to Thimerosal-ethylmercury and adjuvant-aluminum. Neurotoxicol Teratol 2012; 34:219. [DOI: 10.1016/j.ntt.2011.09.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Lee BE, Ha EH. Response to commentary "Co-exposure and confounders during neurodevelopment: we need them in the bigger picture of secondhand smoke exposure during pregnancy". ENVIRONMENTAL RESEARCH 2012; 112:235. [PMID: 22018923 DOI: 10.1016/j.envres.2011.09.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2011] [Accepted: 09/14/2011] [Indexed: 05/31/2023]
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Dórea JG. Co-exposure and confounders during neurodevelopment: we need them in the bigger picture of secondhand smoke exposure during pregnancy. ENVIRONMENTAL RESEARCH 2011; 111:1332-1333. [PMID: 21996059 DOI: 10.1016/j.envres.2011.09.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Accepted: 09/14/2011] [Indexed: 05/31/2023]
Affiliation(s)
- José G Dórea
- C.P. 04322, Faculty of Health Sciences, Universidade de Brasilia, 70919-970 Brasilia, DF, Brazil.
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Barile JP, Kuperminc GP, Weintraub ES, Mink JW, Thompson WW. Thimerosal exposure in early life and neuropsychological outcomes 7-10 years later. J Pediatr Psychol 2011; 37:106-18. [PMID: 21785120 DOI: 10.1093/jpepsy/jsr048] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
OBJECTIVE The authors used a public use data set to investigate associations between the receipt of thimerosal-containing vaccines and immune globulins early in life and neuropsychological outcomes assessed at 7-10 years. METHODS The data were originally created by evaluating 1,047 children ages 7-10 years and their biological mothers. This study developed seven latent neuropsychological factors and regressed them on a comprehensive set of covariates and thimerosal exposure variables. RESULTS The authors found no statistically significant associations between thimerosal exposure from vaccines early in life and six of the seven latent constructs. There was a small, but statistically significant association between early thimerosal exposure and the presence of tics in boys. CONCLUSIONS This finding should be interpreted with caution due to limitations in the measurement of tics and the limited biological plausibility regarding a causal relationship.
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Affiliation(s)
- John P Barile
- Department of Psychology, Georgia State University, USA.
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Dórea JG, Bezerra VLVA, Fajon V, Horvat M. Speciation of methyl- and ethyl-mercury in hair of breastfed infants acutely exposed to thimerosal-containing vaccines. Clin Chim Acta 2011; 412:1563-6. [PMID: 21575620 DOI: 10.1016/j.cca.2011.05.003] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2011] [Revised: 05/02/2011] [Accepted: 05/02/2011] [Indexed: 01/13/2023]
Abstract
BACKGROUND Different chemical forms of mercury occur naturally in human milk. The most controversial aspect of early post-natal exposure to organic mercury is ethylmercury (EtHg) in thimerosal-containing vaccines (TCV) still being used in many countries. Thus exclusively breastfed infants can be exposed to both, fish derived methylmercury (MeHg) in maternal diets and to EtHg from TCV. The aim of the study is to evaluate a new analytical method for ethyl and methyl mercury in hair samples of breastfed infants who had received the recommended schedule of TCV. METHODS The hair of infants (<12 months) that had been exposed to TCV (Hepatitis B and DTaP) was analysed. A method coupling isothermal gas chromatography with cold-vapor atomic fluorescence spectrometry was used for MeHg which can also speciate EtHg in biological matrices. RESULTS In 20 samples of infants' hair, all but two samples showed variable amounts of MeHg (10.3 to 668 ng/g), while precise and reliable concentrations of EtHg (3.7 to 65.0 ng/g) were found in 15 of the 20 samples. A statistically significant inverse association (r=-05572; p=0.0384) was found between hair-EtHg concentrations and the time elapsed after the last TCV shot. CONCLUSIONS The analytical method proved sensitive enough to quantify EtHg in babies' hair after acute exposure to thimerosal in vaccine shots. Provided that the mass of hair was above 10mg, organic-mercury exposure during early life can be speciated, and quantified in babies' first hair, thus opening opportunities for clinical and forensic studies.
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Affiliation(s)
- José G Dórea
- Department of Environmental Sciences, Jožef Stefan Institute, Ljubljana, Slovenia.
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Dórea JG. Integrating Experimental (In Vitro and In Vivo) Neurotoxicity Studies of Low-dose Thimerosal Relevant to Vaccines. Neurochem Res 2011; 36:927-38. [DOI: 10.1007/s11064-011-0427-0] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/12/2011] [Indexed: 12/01/2022]
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Research into mercury exposure and health education in subsistence fish-eating communities of the Amazon basin: potential effects on public health policy. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2010; 7:3467-77. [PMID: 20948936 PMCID: PMC2954557 DOI: 10.3390/ijerph7093467] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 08/02/2010] [Revised: 08/30/2010] [Accepted: 09/10/2010] [Indexed: 01/17/2023]
Abstract
The neurotoxic effects of fish-methylmercury (meHg) consumed regularly are considered hazardous to fetuses and newborn infants; as a result fish consumption advisories are an important asset to control meHg exposure in affluent societies. These concerns are now part of health promotion programs for Amazon subsistence villagers. While urban dwellers in affluent societies can choose an alternative nutritious diet, traditional and subsistence communities are caught up in controversial issues and lifestyle changes with unintended health consequences. Traditional fish-eating populations of industrialized and non-industrialized regions may be exposed to different neurotoxic substances: man-made pollutants and environmentally occurring meHg. Additionally, in non-industrialized countries, pregnant women and infants are still being immunized with thimerosal-containing vaccines (TCVs) which degrade to ethylmercury (etHg). Therefore, the complexity involving fish-meHg associated with wild-fish choices and Hg exposure derived from TCVs is difficult to disentangle and evaluate: are villagers able to distinguish exposure to differently hazardous chemical forms of Hg (inorganic, fish-meHg, and injected etHg)? Is it possible that instead of helping to prevent a plausible (unperceived) fish-meHg associated neurocognitive delay we may inadvertently arouse panic surrounding Hg exposure and disrupt subsistence fish-eating habits (necessary for survival) and life-saving vaccination programs (required by public health authorities)? These questions characterize the incompleteness of information related on the various chemical forms of Hg exposure and the need to convey messages that do not disrupt nutritional balance and disease prevention policies directed at Amazonian subsistence communities.
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