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Nakamura R, Iwai T, Takanezawa Y, Shirahata T, Konishi N, Ohshiro Y, Uraguchi S, Tanabe M, Kobayashi Y, Sakamoto K, Nakahara T, Yamamoto M, Kiyono M. Oleanolic acid-3-glucoside, a synthetic oleanane-type saponin, ameliorates methylmercury-induced dysfunction of synaptic transmission in mice. Toxicology 2024; 506:153867. [PMID: 38906242 DOI: 10.1016/j.tox.2024.153867] [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: 04/11/2024] [Revised: 06/07/2024] [Accepted: 06/17/2024] [Indexed: 06/23/2024]
Abstract
Methylmercury (MeHg) is widely distributed in nature and is known to cause neurotoxic effects. This study aimed to examine the anti-MeHg activity of oleanolic acid-3-glucoside (OA3Glu), a synthetic oleanane-type saponin derivative, by evaluating its effects on motor function, pathology, and electrophysiological properties in a mouse model of MeHg poisoning. Mice were orally administered 2 or 4 mg·kg-1·d-1 MeHg with or without 100 µg·kg-1·d-1 OA3Glu 5x/week for four weeks. Motor function was evaluated using beam-walking and dynamic weight-bearing (DWB) tests. High-dose MeHg exposure significantly increased the frequency of stepping off the hind leg while crossing the beam in the beam-walking test, and increased weight on forelegs when moving freely in the DWB test. OA3Glu treatment alleviated motor abnormality caused by high-dose MeHg exposure in both motor function tests. Additionally, OA3Glu treatment reduced the number of contracted Purkinje cells frequently observed in the cerebellum of MeHg-treated groups, although cerebrum histology was similar in all experimental groups. The synaptic potential amplitude in the cerebellum decreased as MeHg exposure increased, which was restored by OA3Glu treatment. Even in the cerebrum, where the effects of MeHg were not observed, the amplitude of the field potential was suppressed with increasing MeHg exposure but was restored with OA3Glu treatment. Taken together, the study findings suggest that OA3Glu improves neurotransmission and movement disorders associated with MeHg exposure via protection of Purkinje cells in the cerebellum while ameliorating pre/post-synaptic deficits in the cerebral cortex in which no changes were observed at the tissue level, potentially providing a treatment to mitigate MeHg toxicity.
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Affiliation(s)
- Ryosuke Nakamura
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Takashi Iwai
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Yasukazu Takanezawa
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Tatsuya Shirahata
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Naruki Konishi
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Yuka Ohshiro
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Shimpei Uraguchi
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Mitsuo Tanabe
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Yoshinori Kobayashi
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Kenji Sakamoto
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan; Faculty of Pharma-Sciences, Teikyo University, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan
| | - Tsutomu Nakahara
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Megumi Yamamoto
- Department of Environment and Public Health, National Institute for Minamata Disease, 4058-18, Hama, Minamata, Kumamoto 867-0008, Japan
| | - Masako Kiyono
- School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan.
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Reardon AJF, Karathra J, Ribbenstedt A, Benskin JP, MacDonald AM, Kinniburgh DW, Hamilton TJ, Fouad K, Martin JW. Neurodevelopmental and Metabolomic Responses from Prenatal Coexposure to Perfluorooctanesulfonate (PFOS) and Methylmercury (MeHg) in Sprague-Dawley Rats. Chem Res Toxicol 2019; 32:1656-1669. [PMID: 31340646 DOI: 10.1021/acs.chemrestox.9b00192] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Methylmercury (MeHg) and perfluorooctanesulfonate (PFOS) are major contaminants of human blood that are both common in dietary fish, thereby raising questions about their combined impact on human development. Here, pregnant Sprague-Dawley rats ingested a daily dose, from gestational day 1 through to weaning, of either 1 mg/kg bw PFOS (PFOS-only), 1 mg/kg MeHg (MeHg-only), a mixture of 0.1 mg/kg PFOS and 1 mg/kg MeHg (Low-Mix), or of 1 mg/kg of PFOS and 1 mg/kg MeHg (High-Mix). Newborns were monitored for physical milestones and reflexive developmental responses, and in juveniles the spontaneous activity, anxiety, memory, and cognition were assessed. Targeted metabolomics of 199 analytes was applied to sectioned brain regions of juvenile offspring. Newborns in the High-Mix group had decreased weight gain as well as delayed reflexes and innate behavioral responses compared to controls and individual chemical groups indicating a toxicological interaction on early development. In juveniles, cumulative mixture effects increased in a dose-dependent manner in tests of anxiety-like behavior. However, other developmental test results suggested antagonism, as PFOS-only and MeHg-only juveniles had increased hyperactivity and thigmotaxic behavior, respectively, but fewer effects in Low-Mix and High-Mix groups. Consistent with these behavioral observations, a pattern of antagonism was also observed in neurochemicals measured in rat cortex, as PFOS-only and MeHg-only juveniles had altered concentrations of metabolites (e.g., lipids, amino acids, and biogenic amines), while no changes were evident in the combined exposures. The cortical metabolites altered in PFOS-only and MeHg-only exposed groups are involved in inhibitory and excitatory neurotransmission. These proof-of-principle findings at relatively high doses indicate the potential for toxicological interaction between PFOS and MeHg, with developmental-stage specific effects. Future mixture studies at lower doses are warranted, and prospective human birth cohorts should consider possible confounding effects from PFOS and mercury exposure on neurodevelopment.
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Affiliation(s)
- Anthony J F Reardon
- Department of Laboratory Medicine and Pathology , University of Alberta , Edmonton , Alberta T6G 2G3 , Canada
| | - Jacqueline Karathra
- Department of Laboratory Medicine and Pathology , University of Alberta , Edmonton , Alberta T6G 2G3 , Canada
| | - Anton Ribbenstedt
- Department of Environmental Science and Analytical Chemistry (ACES) , Stockholm University , Stockholm SE-11418 , Sweden
| | - Jonathan P Benskin
- Department of Environmental Science and Analytical Chemistry (ACES) , Stockholm University , Stockholm SE-11418 , Sweden
| | - Amy M MacDonald
- Alberta Centre for Toxicology , University of Calgary , Calgary , Alberta T2N 1N4 , Canada
| | - David W Kinniburgh
- Alberta Centre for Toxicology , University of Calgary , Calgary , Alberta T2N 1N4 , Canada
| | - Trevor J Hamilton
- Department of Psychology , MacEwan University , Edmonton , Alberta T5J 4S2 , Canada
| | - Karim Fouad
- Department of Physical Therapy , University of Alberta , Edmonton , Alberta T6G 2G4 , Canada
| | - Jonathan W Martin
- Department of Laboratory Medicine and Pathology , University of Alberta , Edmonton , Alberta T6G 2G3 , Canada.,Department of Environmental Science and Analytical Chemistry (ACES) , Stockholm University , Stockholm SE-11418 , Sweden
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Newland MC, Reed MN, Rasmussen E. A hypothesis about how early developmental methylmercury exposure disrupts behavior in adulthood. Behav Processes 2015; 114:41-51. [PMID: 25795099 DOI: 10.1016/j.beproc.2015.03.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Accepted: 03/10/2015] [Indexed: 10/23/2022]
Abstract
Events that disrupt the early development of the nervous system have lifelong, irreversible behavioral consequences. The environmental contaminant, methylmercury (MeHg), impairs neural development with effects that are manifested well into adulthood and even into aging. Noting the sensitivity of the developing brain to MeHg, the current review advances an argument that one outcome of early MeHg exposure is a distortion in the processing of reinforcing consequences that results in impaired choice, poor inhibition of prepotent responding, and perseveration on discrimination reversals (in the absence of alteration of extradimensional shifts). Neurochemical correlates include increased sensitivity to dopamine agonists and decreased sensitivity to gamma-aminobutyric acid (GABA) agonists. This leads to a hypothesis that the prefrontal cortex or dopamine neurotransmission is especially sensitive to even subtle gestational MeHg exposure and suggests that public health assessments of MeHg based on intellectual performance may underestimate the impact of MeHg in public health. Finally, those interested in modeling neural development may benefit from MeHg as an experimental model.
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Affiliation(s)
| | - Miranda N Reed
- Department of Psychology, Center for Neuroscience and Center for Basic and Translational Stroke Research, West Virginia University, Morgantown 26506, WV, USA
| | - Erin Rasmussen
- Department of Psychology, Idaho State University, Pocatello, ID 83209, USA
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Liu Q, Wu C, Cai H, Hu N, Zhou J, Wang P. Cell-based biosensors and their application in biomedicine. Chem Rev 2014; 114:6423-61. [PMID: 24905074 DOI: 10.1021/cr2003129] [Citation(s) in RCA: 185] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Qingjun Liu
- Biosensor National Special Laboratory, Key Laboratory of Biomedical Engineering of the Ministry of Education, Department of Biomedical Engineering, Zhejiang University , Hangzhou 310027, China
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Low level prenatal exposure to methylmercury disrupts neuronal migration in the developing rat cerebral cortex. Toxicology 2012; 304:57-68. [PMID: 23220560 DOI: 10.1016/j.tox.2012.11.019] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Revised: 11/11/2012] [Accepted: 11/15/2012] [Indexed: 11/22/2022]
Abstract
We determined the effects of low-level prenatal MeHg exposure on neuronal migration in the developing rat cerebral cortex using in utero electroporation. We used offspring rats born to dams that had been exposed to saline or various doses of MeHg (0.01 mg/kg/day, 0.1 mg/kg/day, and 1 mg/kg/day) from gestational day (GD) 11-21. Immunohistochemical examination of the brains of the offspring was conducted on postnatal day (PND) 0, PND3, and PND7. Our results showed that prenatal exposure to low levels of MeHg (0.1 mg/kg/day or 1 mg/kg/day) during the critical stage in neuronal migration resulted in migration defects of the cerebrocortical neurons in offspring rats. Importantly, our data revealed that the abnormal neuronal distribution induced by MeHg was not caused by altered proliferation of neural progenitor cells (NPCs), induction of apoptosis of NPCs and/or newborn neurons, abnormal differentiation of NPCs, and the morphological changes of radial glial scaffold, indicating that the defective neuronal positioning triggered by exposure to low-dose of MeHg is due to the impacts of MeHg on the process of neuronal migration itself. Moreover, we demonstrated that in utero exposure to low-level MeHg suppresses the expression of Rac1, Cdc42, and RhoA, which play key roles in the migration of cerebrocortical neurons during the early stage of brain development, suggesting that the MeHg-induced migratory disturbance of cerebrocortical neurons is likely associated with the Rho GTPases signal pathway. In conclusion, our results provide a novel perspective on clarifying the mechanisms underlying the impairment of neuronal migration induced by MeHg.
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Yuan Y. Methylmercury: a potential environmental risk factor contributing to epileptogenesis. Neurotoxicology 2012; 33:119-26. [PMID: 22206970 PMCID: PMC3285480 DOI: 10.1016/j.neuro.2011.12.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2011] [Revised: 12/12/2011] [Accepted: 12/14/2011] [Indexed: 12/29/2022]
Abstract
Epilepsy or seizure disorder is one of the most common neurological diseases in humans. Although genetic mutations in ion channels and receptors and some other risk factors such as brain injury are linked to epileptogenesis, the underlying cause for the majority of epilepsy cases remains unknown. Gene-environment interactions are thought to play a critical role in the etiology of epilepsy. Exposure to environmental chemicals is an important risk factor. Methylmercury (MeHg) is a prominent environmental neurotoxicant, which targets primarily the central nervous system (CNS). Patients or animals with acute or chronic MeHg poisoning often display epileptic seizures or show increased susceptibility to seizures, suggesting that MeHg exposure may be associated with epileptogenesis. This mini-review highlights the effects of MeHg exposure, especially developmental exposure, on the susceptibility of humans and animals to seizures, and discusses the potential role of low level MeHg exposure in epileptogenesis. This review also proposes that a preferential effect of MeHg on the inhibitory GABAergic system, leading to disinhibition of excitatory glutamatergic function, may be one of the potential mechanisms underlying MeHg-induced changes in seizure susceptibility.
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Affiliation(s)
- Yukun Yuan
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824, USA.
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