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Fujimura M, Unoki T. BDNF specifically expressed in hippocampal neurons is involved in methylmercury neurotoxicity resistance. ENVIRONMENTAL TOXICOLOGY 2024; 39:3149-3159. [PMID: 38323385 DOI: 10.1002/tox.24174] [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: 12/03/2023] [Revised: 01/10/2024] [Accepted: 01/17/2024] [Indexed: 02/08/2024]
Abstract
Methylmercury (MeHg) causes selective neuronal damage to cerebrocortical neurons (CCNs) in the central nervous system, but not to hippocampal neurons (HiNs), which are highly vulnerable to neurodegenerative diseases. In our previous study using cultured rat neurons, we performed a comprehensive gene expression analysis and found that the brain-derived neurotrophic factor (BDNF), a neurotrophin (NT), was specifically expressed in HiNs. Therefore, to elucidate the causal factors of MeHg toxicity resistance in HiNs, we conducted a comparative study of the protein expression and function of several NTs, including BDNF, using CCNs showing vulnerability to MeHg toxicity and HiNs showing resistance. BDNF was specifically expressed in HiNs, whereas nerve growth factor was barely detectable in either neuron type. In addition, other NTs, NT3 and NT4/5, were expressed in small but nearly equal amounts in both neuron types. Furthermore, among the various pathways involved in MeHg neurotoxicity, the p44/42 MAPK pathway was specifically activated in HiNs, even without MeHg treatment. siRNAs were used to reduce NTs in both neuron types. Only a specific reduction in BDNF attenuated the resistance to MeHg toxicity and p44/42 MAPK activation in HiNs. In addition, the external addition of BDNF and NT4/5, which act on the same tyrosine receptor kinase (Trk), TrkB, suppressed MeHg neurotoxicity in both neuron types. These results suggest that BDNF, expressed specifically in HiNs, is involved in the resistance to MeHg neurotoxicity via TrkB. Additionally, the activation of the p44/42 MAPK pathway may contribute to the inhibitory effect of BDNF on MeHg neurotoxicity.
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Affiliation(s)
- Masatake Fujimura
- Department of Basic Medical Science, National Institute for Minamata Disease, Kumamoto, Japan
| | - Takamitsu Unoki
- Department of Basic Medical Science, National Institute for Minamata Disease, Kumamoto, Japan
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Fujimura M. Gabapentin improves neuropathic pain in Minamata disease model rats. Environ Health Prev Med 2024; 29:31. [PMID: 38825526 PMCID: PMC11157338 DOI: 10.1265/ehpm.24-00035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2024] [Accepted: 05/02/2024] [Indexed: 06/04/2024] Open
Abstract
BACKGROUND Methylmercury (MeHg), the causative agent of Minamata disease, damages the cranial nervous system and causes specific sensory disturbances, especially hypoesthesia, in the extremities. However, recent reports demonstrate that patients with chronic Minamata disease conversely develop neuropathic pain in the lower extremities. Studies on our established Minamata disease model rats showed that MeHg-mediated neurodegeneration might induce neuropathic pain by over time through inducing rewiring with neuronal activation in the somatosensory cortex via microglial activation in the spinal dorsal horn. METHODS In this study, the effects of gabapentin, a potentially effective treatment for neuropathic pain, was evaluated using this Minamata disease model rats. To further elucidate the mechanism of its medicinal effects, histochemical and biochemical analyses of the nervous system of Minamata disease model rats were conducted. RESULTS Gabapentin treatment restored the reduction in the pain threshold caused by MeHg exposure in rats. Histochemical and biochemical analyses revealed that gabapentin showed no effect on MeHg-induced neurodegeneration in entire nervous system and microglial activation in the spinal dorsal horn. However, it was shown that gabapentin may reduce excessive synaptogenesis through its antagonist action on the alpha2-delta-1 subunit of calcium channels in the somatosensory cortex. CONCLUSIONS These results indicate that gabapentin may alleviated neuropathic pain in MeHg poisoning, as typified by Minamata disease, by reversibly modulation synaptic rewiring in the somatosensory cortex.
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Affiliation(s)
- Masatake Fujimura
- Department of Basic Medical Sciences, National Institute for Minamata Disease, Minamata, Japan
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Fujimura M. Fasudil, a ROCK inhibitor, prevents neuropathic pain in Minamata disease model rats. Toxicol Lett 2022; 371:38-45. [PMID: 36244566 DOI: 10.1016/j.toxlet.2022.10.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Revised: 09/24/2022] [Accepted: 10/11/2022] [Indexed: 02/13/2023]
Abstract
Methylmercury (MeHg), an environmental toxicant, is known to cause sensory impairment by inducing neurodegeneration of sensory nervous systems. However, in recent years, it has been revealed that neuropathic pain occurs in the chronic phase of MeHg poisoning, that is, in current Minamata disease patients. Our recent study using Minamata disease model rats demonstrated that MeHg-mediated neurodegeneration in the sensory nervous system may induce inflammatory microglia production in the dorsal horn of the spinal cord and subsequent somatosensory cortical rewiring, leading to neuropathic pain. We hypothesized that inhibition of the Rho-associated coiled coil-forming protein kinase (ROCK) pathway could prevent MeHg-induced neuropathic pain because the ROCK pathway is known to be involved in inducing the production of inflammatory microglia. Here, we showed for the first time that Fasudil, a ROCK inhibitor, can prevent neuropathic pain in Minamata disease model rats. In this model, Fasudil significantly suppressed nerve injury-induced inflammatory microglia production in the dorsal horn of the spinal cord and prevented subsequent somatosensory cortical rewiring. These results suggest that the ROCK pathway is involved in the onset and development of neuropathic pain in the chronic phase of Minamata disease, and that its inhibition is effective in pain prevention.
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Affiliation(s)
- Masatake Fujimura
- Department of Basic Medical Sciences, National Institute for Minamata Disease, 4058-18 Hama, Minamata, Kumamoto 867-0008, Japan.
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Fujimura M, Usuki F, Nakamura A. Methylmercury induces hyperalgesia/allodynia through spinal cord dorsal horn neuronal activation and subsequent somatosensory cortical circuit formation in rats. Arch Toxicol 2021; 95:2151-2162. [PMID: 33847776 DOI: 10.1007/s00204-021-03047-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Accepted: 04/01/2021] [Indexed: 12/30/2022]
Abstract
Methylmercury (MeHg) is known to cause serious neurological deficits in humans. In this study, we investigated the occurrence of MeHg-mediated neuropathic pain and identified the underlying pathophysiological mechanism in a rat model of MeHg exposure. Rats were exposed to MeHg (20 ppm in drinking water) for 3 weeks. Neurological damage was observed in the primary afferent neuronal system, including the dorsal root nerve and the dorsal column of the spinal cord. The MeHg-exposed rats showed hyperalgesia/allodynia, compared to controls, as evidenced by a significant decrease in the threshold of mechanical pain evaluated using an algometer with calibrated forceps. Immunohistochemistry revealed the accumulation of activated microglia in the dorsal root nerve, dorsal column, and dorsal horn of the spinal cord. Western blot analyses of the dorsal part of the spinal cord demonstrated an increase in inflammotoxic and inflammatory cytokines and a neuronal activation related protein, phospho-CRE bunding protein (CREB). The results suggest that dorsal horn neuronal activation was mediated by inflammatory factors excreted by accumulated microglia. Furthermore, analyses of the cerebral cortex demonstrated increased expression of phospho-CREB and thrombospondin-1, which is known to be an important factor for excitatory synapse formation, specifically in the somatosensory cortical area. In addition, the expression of pre- and post-synaptic markers was increased in this cortex area. These results suggested that the new cortical circuit was wired specifically in the somatosensory cortex. In conclusion, MeHg-mediated dorsal horn neuronal activation with inflammatory microglia might induce somatosensory cortical rewiring, leading to hyperalgesia/allodynia.
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Affiliation(s)
- Masatake Fujimura
- Department of Basic Medical Sciences, National Institute for Minamata Disease, Kumamoto, Japan.
| | - Fusako Usuki
- Division of Neuroimmunology, Joint Research Center for Human Retrovirus Infection, Kagoshima University, Kagoshima, Japan
| | - Atsushi Nakamura
- Department of Clinical Medicine, National Institute for Minamata Disease, Kumamoto, Japan
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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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Martins AC, Ke T, Bowman AB, Aschner M. New insights on mechanisms underlying methylmercury-induced and manganese-induced neurotoxicity. CURRENT OPINION IN TOXICOLOGY 2021; 25:30-35. [PMID: 33898886 PMCID: PMC8061890 DOI: 10.1016/j.cotox.2021.03.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Toxic and essential elements are widely distributed in the Earth's crust and individuals may be exposed to several of them. Indeed, exposure to toxic elements such as mercury (Hg) can be a potential health risk factor of health, mainly by ingestion of fish containing methylmercury (MeHg). On the other hand, essential elements such as manganese (Mn) play an important role in physiological process in human body. However, Mn overexposure may cause toxic effects. In this respect, the neurotoxic effects of MeHg and Mn on the developing brain are well recognized. Therefore, in this critical review, we address the effects of MeHg and Mn on cell signaling pathways which may contribute to molecular mechanisms involved in MeHg- and Mn-induced neurotoxicity.
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Affiliation(s)
- Airton C Martins
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY, USA
| | - Tao Ke
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY, USA
| | - Aaron B Bowman
- School of Health Sciences, Purdue University, West Lafayette, IN, USA
| | - Michael Aschner
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY, USA
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Shinoda Y, Yamada Y, Yoshida E, Takahashi T, Tsuneoka Y, Eto K, Kaji T, Fujiwara Y. Hypoalgesia and recovery in methylmercury-exposed rats. J Toxicol Sci 2021; 46:303-309. [PMID: 34078837 DOI: 10.2131/jts.46.303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Methylmercury (MeHg), the causal substrate in Minamata disease, can lead to severe and chronic neurological disorders. The main symptom of Minamata disease is sensory impairment in the four extremities; however, the sensitivity of individual sensory modalities to MeHg has not been investigated extensively. In the present study, we performed stimulus-response behavioral experiments in MeHg-exposed rats to compare the sensitivities to pain, heat, cold, and mechanical sensations. MeHg (6.7 mg/kg/day) was orally administered to 9-week-old Wistar rats for 5 days and discontinued for 2 days, then administered daily for another 5 days. The four behavioral experiments were performed daily on each rat from the beginning of MeHg treatment for 68 days. The pain sensation decreased significantly from day 11 onwards, but recovered to control levels on day 48. Other sensory modalities were not affected by MeHg exposure. These findings suggest that the pain sensation is the sensory modality most susceptive to MeHg toxicity and that this sensitivity is reversible following discontinuation of the exposure.
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Affiliation(s)
- Yo Shinoda
- Department of Environmental Health, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences
| | - Yuta Yamada
- Department of Environmental Health, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences
| | - Eiko Yoshida
- Department of Environmental Health, Faculty of Pharmaceutical Sciences, Tokyo University of Science
| | - Tsutomu Takahashi
- Department of Environmental Health, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences
| | - Yayoi Tsuneoka
- Department of Environmental Health, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences
| | - Komyo Eto
- Health and Nursing Facilities for the Aged, Jushindai, Shinwakai
| | - Toshiyuki Kaji
- Department of Environmental Health, Faculty of Pharmaceutical Sciences, Tokyo University of Science
| | - Yasuyuki Fujiwara
- Department of Environmental Health, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences
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