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Chen J, Chen W, Zhang J, Zhao H, Cui J, Wu J, Shi A. Dual effects of endogenous formaldehyde on the organism and drugs for its removal. J Appl Toxicol 2024; 44:798-817. [PMID: 37766419 DOI: 10.1002/jat.4546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Revised: 08/25/2023] [Accepted: 09/04/2023] [Indexed: 09/29/2023]
Abstract
Endogenous formaldehyde (FA) is produced in the human body via various mechanisms to preserve healthy energy metabolism and safeguard the organism. However, endogenous FA can have several negative effects on the body through epigenetic alterations, including cancer growth promotion; neuronal, hippocampal and endothelial damages; atherosclerosis acceleration; haemopoietic stem cell destruction and haemopoietic cell production reduction. Certain medications with antioxidant effects, such as glutathione, vitamin E, resveratrol, alpha lipoic acid and polyphenols, lessen the detrimental effects of endogenous FA by reducing oxidative stress, directly scavenging endogenous FA or promoting its degradation. This study offers fresh perspectives for managing illnesses associated with endogenous FA exposure.
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Affiliation(s)
- Jiaxin Chen
- Yunnan Key Laboratory of Integrated Traditional Chinese and Western Medicine for Chronic Disease in Prevention and Treatment, Yunnan University of Chinese Medicine, Kunming, China
- Key Laboratory of Microcosmic Syndrome Differentiation, Yunnan University of Chinese Medicine, Kunming, China
| | - Wenhui Chen
- Yunnan Key Laboratory of Integrated Traditional Chinese and Western Medicine for Chronic Disease in Prevention and Treatment, Yunnan University of Chinese Medicine, Kunming, China
- Key Laboratory of Microcosmic Syndrome Differentiation, Yunnan University of Chinese Medicine, Kunming, China
| | - Jinjia Zhang
- Yunnan Key Laboratory of Integrated Traditional Chinese and Western Medicine for Chronic Disease in Prevention and Treatment, Yunnan University of Chinese Medicine, Kunming, China
- Key Laboratory of Microcosmic Syndrome Differentiation, Yunnan University of Chinese Medicine, Kunming, China
| | - Huanhuan Zhao
- Yunnan Key Laboratory of Integrated Traditional Chinese and Western Medicine for Chronic Disease in Prevention and Treatment, Yunnan University of Chinese Medicine, Kunming, China
- Key Laboratory of Microcosmic Syndrome Differentiation, Yunnan University of Chinese Medicine, Kunming, China
| | - Ji Cui
- Yunnan Key Laboratory of Integrated Traditional Chinese and Western Medicine for Chronic Disease in Prevention and Treatment, Yunnan University of Chinese Medicine, Kunming, China
- Key Laboratory of Microcosmic Syndrome Differentiation, Yunnan University of Chinese Medicine, Kunming, China
| | - Junzi Wu
- Yunnan Key Laboratory of Integrated Traditional Chinese and Western Medicine for Chronic Disease in Prevention and Treatment, Yunnan University of Chinese Medicine, Kunming, China
- Key Laboratory of Microcosmic Syndrome Differentiation, Yunnan University of Chinese Medicine, Kunming, China
- Department of Basic Medical, Yunnan University of Chinese Medicine, Kunming, China
| | - Anhua Shi
- Yunnan Key Laboratory of Integrated Traditional Chinese and Western Medicine for Chronic Disease in Prevention and Treatment, Yunnan University of Chinese Medicine, Kunming, China
- Key Laboratory of Microcosmic Syndrome Differentiation, Yunnan University of Chinese Medicine, Kunming, China
- Department of Basic Medical, Yunnan University of Chinese Medicine, Kunming, China
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2
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Li S, Li Z, Wu M, Zhou Y, Tang W, Zhong H. Mercury transformations in algae, plants, and animals: The occurrence, mechanisms, and gaps. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 911:168690. [PMID: 38000748 DOI: 10.1016/j.scitotenv.2023.168690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 11/16/2023] [Accepted: 11/16/2023] [Indexed: 11/26/2023]
Abstract
Mercury (Hg) is a global pollutant showing potent toxicity to living organisms. The transformations of Hg are critical to global Hg cycling and Hg exposure risks, considering Hg mobilities and toxicities vary depending on Hg speciation. Though currently well understood in ambient environments, Hg transformations are inadequately explored in non-microbial organisms. The primary drivers of in vivo Hg transformations are far from clear, and the impacts of these processes on global Hg cycling and Hg associated health risks are not well understood. This hinders a comprehensive understanding of global Hg cycling and the effective mitigation of Hg exposure risks. Here, we focused on Hg transformations in non-microbial organisms, particularly algae, plants, and animals. The process of Hg oxidation/reduction and methylation/demethylation in organisms were reviewed since these processes are the key transformations between the dominant Hg species, i.e., elemental Hg (Hg0), divalent inorganic Hg (IHgII), and methylmercury (MeHg). By summarizing the current knowledge of Hg transformations in organisms, we proposed the potential yet overlooked drivers of these processes, along with potential challenges that hinder a full understanding of in vivo Hg transformations. Knowledge summarized in this review would help achieve a comprehensive understanding of the fate and toxicity of Hg in organisms, providing a basis for predicting Hg cycles and mitigating human exposure.
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Affiliation(s)
- Shouying Li
- School of the Environment, Nanjing University, State Key Laboratory of Pollution Control and Resource Reuse, Nanjing 210023, China
| | - Zhuoran Li
- School of the Environment, Nanjing University, State Key Laboratory of Pollution Control and Resource Reuse, Nanjing 210023, China
| | - Mengjie Wu
- School of the Environment, Nanjing University, State Key Laboratory of Pollution Control and Resource Reuse, Nanjing 210023, China
| | - Yang Zhou
- School of the Environment, Nanjing University, State Key Laboratory of Pollution Control and Resource Reuse, Nanjing 210023, China
| | - Wenli Tang
- School of the Environment, Nanjing University, State Key Laboratory of Pollution Control and Resource Reuse, Nanjing 210023, China.
| | - Huan Zhong
- School of the Environment, Nanjing University, State Key Laboratory of Pollution Control and Resource Reuse, Nanjing 210023, China.
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Barkay T, Gu B. Demethylation─The Other Side of the Mercury Methylation Coin: A Critical Review. ACS ENVIRONMENTAL AU 2022; 2:77-97. [PMID: 37101582 PMCID: PMC10114901 DOI: 10.1021/acsenvironau.1c00022] [Citation(s) in RCA: 38] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The public and environmental health consequences of mercury (Hg) methylation have drawn much attention and considerable research to Hg methylation processes and their dynamics in diverse environments and under a multitude of conditions. However, the net methylmercury (MeHg) concentration that accumulates in the environment is equally determined by the rate of MeHg degradation, a complex process mediated by a variety of biotic and abiotic mechanisms, about which our knowledge is limited. Here we review the current knowledge on MeHg degradation and its potential pathways and mechanisms. We describe detoxification by resistant microorganisms that employ the Hg resistance (mer) system to reductively break the carbon-mercury (C-Hg) bond producing methane (CH4) and inorganic mercuric Hg(II), which is then reduced by the mercuric reductase to elemental Hg(0). Very recent research has begun to elucidate a mechanism for the long-recognized mer-independent oxidative demethylation, likely involving some strains of anaerobic bacteria as well as aerobic methane-oxidizing bacteria, i.e., methanotrophs. In addition, photochemical and chemical demethylation processes are described, including the roles of dissolved organic matter (DOM) and free radicals as well as dark abiotic demethylation in the natural environment about which little is currently known. We focus on mechanisms and processes of demethylation and highlight the uncertainties and known effects of environmental factors leading to MeHg degradation. Finally, we suggest future research directions to further elucidate the chemical and biochemical mechanisms of biotic and abiotic demethylation and their significance in controlling net MeHg production in natural ecosystems.
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Affiliation(s)
- Tamar Barkay
- Department of Biochemistry and Microbiology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, New Jersey 08901, United States
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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4
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Kou Y, Zhao H, Cui D, Han H, Tong Z. Formaldehyde toxicity in age-related neurological dementia. Ageing Res Rev 2022; 73:101512. [PMID: 34798299 DOI: 10.1016/j.arr.2021.101512] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 11/02/2021] [Accepted: 11/08/2021] [Indexed: 02/02/2023]
Abstract
The primordial small gaseous molecules, such as: NO, CO, H2S and formaldehyde (FA) are present in the brains. Whether FA as well as the other molecules participates in brain functions is unclear. Recently, its pathophysiological functions have been investigated. Notably, under physiological conditions, learning activity induces a transient generation of hippocampal FA, which promotes memory formation by enhancing N-methyl-D-aspartate (NMDA)-currents. However, ageing leads to FA accumulation in brain for the dysregulation of FA metabolism; and excessive FA directly impairs memory by inhibiting NMDA-receptor. Especially, in Alzheimer's disease (AD), amyloid-beta (Aβ) accelerates FA accumulation by inactivating alcohol dehydrogenase-5; in turn, FA promotes Aβ oligomerization, fibrillation and tau hyperphosphorylation. Hence, there is a vicious circle encompassing Aβ assembly and FA generation. Even worse, FA induces Aβ deposition in the extracellular space (ECS), which blocks the medicines (dissolved in the interstitial fluid) flowing into the damaged neurons in the deep cortex. However, phototherapy destroys Aβ deposits in the ECS and restores ISF flow. Coenzyme Q10, which scavenges FA, was shown to ameliorate Aβ-induced AD pathological phenotypes, thus suggesting a causative relation between FA toxicity and AD. These findings suggest that the combination of these two methods is a promising strategy for treating AD.
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Xu J, Jin X, Ye Z, Wang D, Zhao H, Tong Z. Opposite Roles of Co-enzyme Q10 and Formaldehyde in Neurodegenerative Diseases. Am J Alzheimers Dis Other Demen 2022; 37:15333175221143274. [PMID: 36455136 PMCID: PMC10624093 DOI: 10.1177/15333175221143274] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
Most of neurodegenerative diseases (NDD) have no cure. The common etiology of neurodegenerations is unclear. Air pollutant-gaseous formaldehyde is notoriously known to induce demyelination and cognitive impairments. Unexpectedly, an amount of formaldehyde has been detected in the brains. Multiple factors can induce the generation and accumulation of endogenous formaldehyde. Excessive formaldehyde can induce oxidative stress to generate H2O2; in turn, H2O2 promote formaldehyde production. Clinical investigations have shown that an abnormal high level of formaldehyde but low level of coenzyme Q10 (coQ10) was observed in patients with NDD. Further studies have proven that excessive formaldehyde directly inactivates coQ10, reduces the ATP generation, enhances oxidative stress, initiates inflammation storm, induces demyelination; subsequently, it results in neurodegeneration. Although the low water solubility of coQ10 limits its clinical application, nanomicellar water-soluble coQ10 exhibits positive therapeutical effects. Hence, nanopackage of coQ10 may be a promising strategy for treating NDD.
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Affiliation(s)
- Jinan Xu
- Institute of Ningbo, Wenzhou Medical University, Wenzhou, China
- Key Laboratory of Alzheimer’s Disease of Zhejiang Province, Institute of Aging, Oujiang Laboratory, School of Mental Health, Wenzhou Medical University, Wenzhou, China
| | - Xingjiang Jin
- Key Laboratory of Alzheimer’s Disease of Zhejiang Province, Institute of Aging, Oujiang Laboratory, School of Mental Health, Wenzhou Medical University, Wenzhou, China
| | - Zuting Ye
- Key Laboratory of Alzheimer’s Disease of Zhejiang Province, Institute of Aging, Oujiang Laboratory, School of Mental Health, Wenzhou Medical University, Wenzhou, China
| | - Dandan Wang
- Key Laboratory of Alzheimer’s Disease of Zhejiang Province, Institute of Aging, Oujiang Laboratory, School of Mental Health, Wenzhou Medical University, Wenzhou, China
| | - Hang Zhao
- Key Laboratory of Alzheimer’s Disease of Zhejiang Province, Institute of Aging, Oujiang Laboratory, School of Mental Health, Wenzhou Medical University, Wenzhou, China
| | - Zhiqian Tong
- Institute of Ningbo, Wenzhou Medical University, Wenzhou, China
- Key Laboratory of Alzheimer’s Disease of Zhejiang Province, Institute of Aging, Oujiang Laboratory, School of Mental Health, Wenzhou Medical University, Wenzhou, China
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Zhao H, Huang X, Tong Z. Formaldehyde-Crosslinked Nontoxic Aβ Monomers to Form Toxic Aβ Dimers and Aggregates: Pathogenicity and Therapeutic Perspectives. ChemMedChem 2021; 16:3376-3390. [PMID: 34396700 DOI: 10.1002/cmdc.202100428] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 08/14/2021] [Indexed: 01/02/2023]
Abstract
Alzheimer's disease (AD) is characterized by the presence of senile plaques in the brain. However, medicines targeting amyloid-beta (Aβ) have not achieved the expected clinical effects. This review focuses on the formation mechanism of the Aβ dimer (the basic unit of oligomers and fibrils) and its tremendous potential as a drug target. Recently, age-associated formaldehyde and Aβ-derived formaldehyde have been found to crosslink the nontoxic Aβ monomer to form the toxic dimers, oligomers and fibrils. Particularly, Aβ-induced formaldehyde accumulation and formaldehyde-promoted Aβ aggregation form a vicious cycle. Subsequently, formaldehyde initiates Aβ toxicity in both the early-and late-onset AD. These facts also explain why AD drugs targeting only Aβ do not have the desired therapeutic effects. Development of the nanoparticle-based medicines targeting both formaldehyde and Aβ dimer is a promising strategy for improving the drug efficacy by penetrating blood-brain barrier and extracellular space into the cortical neurons in AD patients.
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Affiliation(s)
- Hang Zhao
- Institute of Aging, Key Laboratory of Alzheimer's Disease of Zhejiang Province, School of Mental Health, Wenzhou Medical University, Wenzhou, 325035, China
| | - Xuerong Huang
- Wenzhou Medical University Affiliated Hospital 3, Department of Neurology, Wenzhou, 325200, China
| | - Zhiqian Tong
- Institute of Aging, Key Laboratory of Alzheimer's Disease of Zhejiang Province, School of Mental Health, Wenzhou Medical University, Wenzhou, 325035, China
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Novo JP, Martins B, Raposo RS, Pereira FC, Oriá RB, Malva JO, Fontes-Ribeiro C. Cellular and Molecular Mechanisms Mediating Methylmercury Neurotoxicity and Neuroinflammation. Int J Mol Sci 2021; 22:ijms22063101. [PMID: 33803585 PMCID: PMC8003103 DOI: 10.3390/ijms22063101] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2021] [Revised: 03/06/2021] [Accepted: 03/15/2021] [Indexed: 02/06/2023] Open
Abstract
Methylmercury (MeHg) toxicity is a major environmental concern. In the aquatic reservoir, MeHg bioaccumulates along the food chain until it is consumed by riverine populations. There has been much interest in the neurotoxicity of MeHg due to recent environmental disasters. Studies have also addressed the implications of long-term MeHg exposure for humans. The central nervous system is particularly susceptible to the deleterious effects of MeHg, as evidenced by clinical symptoms and histopathological changes in poisoned humans. In vitro and in vivo studies have been crucial in deciphering the molecular mechanisms underlying MeHg-induced neurotoxicity. A collection of cellular and molecular alterations including cytokine release, oxidative stress, mitochondrial dysfunction, Ca2+ and glutamate dyshomeostasis, and cell death mechanisms are important consequences of brain cells exposure to MeHg. The purpose of this review is to organize an overview of the mercury cycle and MeHg poisoning events and to summarize data from cellular, animal, and human studies focusing on MeHg effects in neurons and glial cells. This review proposes an up-to-date compendium that will serve as a starting point for further studies and a consultation reference of published studies.
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Affiliation(s)
- João P. Novo
- Institute for Clinical and Biomedical Research (iCBR), Center for Innovative Biomedicine and Biotechnology (CIBB), and Institute of Pharmacology and Experimental Therapeutics, Faculty of Medicine, University of Coimbra, 3000-548 Coimbra, Portugal; (J.P.N.); (B.M.); (R.S.R.); (F.C.P.)
| | - Beatriz Martins
- Institute for Clinical and Biomedical Research (iCBR), Center for Innovative Biomedicine and Biotechnology (CIBB), and Institute of Pharmacology and Experimental Therapeutics, Faculty of Medicine, University of Coimbra, 3000-548 Coimbra, Portugal; (J.P.N.); (B.M.); (R.S.R.); (F.C.P.)
| | - Ramon S. Raposo
- Institute for Clinical and Biomedical Research (iCBR), Center for Innovative Biomedicine and Biotechnology (CIBB), and Institute of Pharmacology and Experimental Therapeutics, Faculty of Medicine, University of Coimbra, 3000-548 Coimbra, Portugal; (J.P.N.); (B.M.); (R.S.R.); (F.C.P.)
- Experimental Biology Core, University of Fortaleza, Health Sciences, Fortaleza 60110-001, Brazil
| | - Frederico C. Pereira
- Institute for Clinical and Biomedical Research (iCBR), Center for Innovative Biomedicine and Biotechnology (CIBB), and Institute of Pharmacology and Experimental Therapeutics, Faculty of Medicine, University of Coimbra, 3000-548 Coimbra, Portugal; (J.P.N.); (B.M.); (R.S.R.); (F.C.P.)
| | - Reinaldo B. Oriá
- Laboratory of Tissue Healing, Ontogeny and Nutrition, Department of Morphology and Institute of Biomedicine, School of Medicine, Federal University of Ceará, Fortaleza 60430-270, Brazil;
| | - João O. Malva
- Institute for Clinical and Biomedical Research (iCBR), Center for Innovative Biomedicine and Biotechnology (CIBB), and Institute of Pharmacology and Experimental Therapeutics, Faculty of Medicine, University of Coimbra, 3000-548 Coimbra, Portugal; (J.P.N.); (B.M.); (R.S.R.); (F.C.P.)
- Correspondence: (J.O.M.); (C.F.-R.)
| | - Carlos Fontes-Ribeiro
- Institute for Clinical and Biomedical Research (iCBR), Center for Innovative Biomedicine and Biotechnology (CIBB), and Institute of Pharmacology and Experimental Therapeutics, Faculty of Medicine, University of Coimbra, 3000-548 Coimbra, Portugal; (J.P.N.); (B.M.); (R.S.R.); (F.C.P.)
- Correspondence: (J.O.M.); (C.F.-R.)
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8
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Farzan SF, Howe CG, Chen Y, Gilbert-Diamond D, Korrick S, Jackson BP, Weinstein AR, Karagas MR. Prenatal and postnatal mercury exposure and blood pressure in childhood. ENVIRONMENT INTERNATIONAL 2021; 146:106201. [PMID: 33129000 PMCID: PMC7775884 DOI: 10.1016/j.envint.2020.106201] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Revised: 09/29/2020] [Accepted: 10/08/2020] [Indexed: 05/25/2023]
Abstract
Elevated blood pressure in childhood is an important risk factor for hypertension in adulthood. Environmental exposures have been associated with elevated blood pressure over the life course and exposure to mercury (Hg) has been linked to cardiovascular effects in adults. As subclinical vascular changes begin early in life, Hg may play a role in altered blood pressure in children. However, the evidence linking early life Hg exposure to altered blood pressure in childhood has been largely inconsistent. In the ongoing New Hampshire Birth Cohort Study, we investigated prenatal and childhood Hg exposure at multiple time points and associations with blood pressure measurements in 395 young children (mean age 5.5 years, SD 0.4). Hg exposure was measured in children's toenail clippings at age 3 and in urine at age 5-6 years, as well as in maternal toenail samples collected at ∼28 weeks gestation and 6 weeks postpartum, the latter two samples reflecting early prenatal and mid-gestation exposures, respectively. Five measurements of systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) were averaged for each child using a standardized technique. In covariate-adjusted linear regression analyses, we observed that a 0.1 μg/g increase in child toenail Hg at age 3 or a 0.1 μg/L urine Hg at age 5-6 were individually associated with greater DBP (toenail β: 0.53 mmHg; 95% CI: -0.02, 1.07; urine β: 0.48 mmHg; 95% CI: 0.10, 0.86) and MAP (toenail β: 0.67 mmHg; 95% CI: 0.002, 1.33; urine β: 0.55 mmHg; 95% CI: 0.10, 1.01). Neither early prenatal nor mid-gestation Hg exposure, as measured by maternal toenails, were related to any changes to child BP. Simultaneous inclusion of both child urine Hg and child toenail Hg in models suggested a potentially stronger relationship of urine Hg at age 5-6 with DBP and MAP, as compared to toenail Hg at age 3. Our findings suggest that Hg exposure during childhood is associated with alterations in BP. Childhood may be an important window of opportunity to reduce the impacts of Hg exposure on children's blood pressure, and in turn, long-term health.
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Affiliation(s)
- Shohreh F Farzan
- Department of Preventive Medicine, Keck School of Medicine of University of Southern California, Los Angeles, CA, USA.
| | - Caitlin G Howe
- Department of Preventive Medicine, Keck School of Medicine of University of Southern California, Los Angeles, CA, USA; Department of Epidemiology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA
| | - Yu Chen
- Department of Population Health, New York University School of Medicine, New York, NY, USA
| | - Diane Gilbert-Diamond
- Department of Epidemiology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA; Children's Environmental Health & Disease Prevention Research Center at Dartmouth, Hanover, NH, USA
| | - Susan Korrick
- Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA, USA; Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA
| | - Brian P Jackson
- Department of Earth Sciences, Dartmouth College, Hanover, NH, USA
| | - Adam R Weinstein
- Department of Medical Education and Pediatrics, Geisel School of Medicine, Hanover, NH, USA
| | - Margaret R Karagas
- Department of Epidemiology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA; Children's Environmental Health & Disease Prevention Research Center at Dartmouth, Hanover, NH, USA
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Takanezawa Y, Nakamura R, Matsuda H, Yagi T, Egawa Z, Sone Y, Uraguchi S, Adachi T, Kiyono M. Intracellular Demethylation of Methylmercury to Inorganic Mercury by Organomercurial Lyase (MerB) Strengthens Cytotoxicity. Toxicol Sci 2019; 170:438-451. [DOI: 10.1093/toxsci/kfz094] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Abstract
Some methylmercury (MeHg) is converted to inorganic mercury (Hg2+) after incorporation into human and animal tissues, where it can remain for a long time. To determine the overall toxicity of MeHg in tissues, studies should evaluate low concentrations of Hg2+. Although demethylation is involved, the participating enzymes or underlying mechanisms are unknown; in addition, the low cell membrane permeability of Hg2+ makes these analyses challenging. We established model cell lines to assess toxicities of low concentrations of Hg2+ using bacterial organomercury lyase (MerB). We engineered MerB-expressing HEK293 and HeLa cell lines that catalyze MeHg demethylation. These cells were significantly more sensitive to MeHg exposure compared to the parental cells. MeHg treatment remarkably induced metallothioneins (MTs) and hemeoxygenase-1 (HMOX-1) mRNAs and modest expression of superoxide dismutase 1, whereas catalase and glutathione peroxidase 1 mRNAs were not up-regulated. merB knockdown using small interfering RNA supported the induction of MT and HMOX-1 mRNA by MerB enzymatic activity. Pretreatment with Trolox, a water-soluble vitamin E analog, did not inhibit MeHg-induced elevation of MT-Ix and HMOX-1 mRNAs in MerB-expressing cells, suggesting that Hg2+ works independently of reactive oxygen species generation. Similar results were obtained in cells expressing MerB, suggesting that high MTs and HMOX-1 induction and cytotoxicity are common cellular responses to low intracellular Hg2+ concentrations. This is the first study to establish cell lines that demethylate intracellular MeHg to Hg2+ using bacterial MerB for overcoming the low membrane permeability of Hg2+ and exploring the intracellular responses and toxicities of low Hg2+ concentrations.
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Affiliation(s)
- Yasukazu Takanezawa
- Department of Public Health, School of Pharmacy, Kitasato University, Minato-ku, Tokyo 108-8641
| | - Ryosuke Nakamura
- Department of Public Health, School of Pharmacy, Kitasato University, Minato-ku, Tokyo 108-8641
| | - Haruki Matsuda
- Department of Public Health, School of Pharmacy, Kitasato University, Minato-ku, Tokyo 108-8641
| | - Tomomi Yagi
- Department of Public Health, School of Pharmacy, Kitasato University, Minato-ku, Tokyo 108-8641
| | - Zen Egawa
- Department of Public Health, School of Pharmacy, Kitasato University, Minato-ku, Tokyo 108-8641
| | - Yuka Sone
- Department of Public Health, School of Pharmacy, Kitasato University, Minato-ku, Tokyo 108-8641
| | - Shimpei Uraguchi
- Department of Public Health, School of Pharmacy, Kitasato University, Minato-ku, Tokyo 108-8641
| | - Tatsumi Adachi
- Faculty of Pharmacy, Chiba Institute of Science, Choshi, Chiba 288-0025, Japan
| | - Masako Kiyono
- Department of Public Health, School of Pharmacy, Kitasato University, Minato-ku, Tokyo 108-8641
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