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Fujimura M.,National Institute for Minamata Disease | Cheng J.,Shanghai JiaoTong University | Zhao W.,Shanghai JiaoTong University
Brain Research | Year: 2012

Methylmercury (MeHg) is an environmental pollutant that is toxic to the developing central nervous system (CNS) in children, even at low exposure levels. Perinatal exposure to MeHg is known to induce neurological symptoms with neuropathological changes in the CNS. However, the relationship between the neurological symptoms and neuropathological changes induced in offspring as a result of exposure to low-dose MeHg is not well defined. In the present study, neurobehavioral analyses revealed that exposure to a low level of MeHg (5 ppm in drinking water) during developmental caused a significant deficit in the motor coordination of rats in the rotating rod test. In contrast, general neuropathological findings, including neuronal cell death and the subsequent nerve inflammation, were not observed in the region of the cerebellum responsible for regulating motor coordination. Surprisingly, the expression of synaptophysin (SPP), a marker protein for synaptic formation, significantly decreased in cerebellar granule cells. These results showed that perinatal exposure to low-dose MeHg causes neurobehavioral impairment without general neuropathological changes in rats. We demonstrated for the first time that exposure to low-dose MeHg during development induces the dysfunction of motor coordination due to changes of synaptic homeostasis in cerebellar granule cells. © 2012 Elsevier B.V.

Fujimura M.,National Institute for Minamata Disease | Yamashita A.,Yokohama City University
Scientific Reports | Year: 2013

We demonstrate that methylmercury (MeHg)-susceptible cells preconditioned with an inhibitor of endoplasmic reticulum (ER) Ca2+-ATPase, thapsigargin, showed resistance to MeHg cytotoxicity through favorable stress responses, which included phosphorylation of eukaryotic initiation factor 2 alpha (Eif2α), accumulation of activating transcription factor 4 (Atf4), upregulation of stress-related proteins, and activation of extracellular signal regulated kinase pathway. In addition, ER stress preconditioning induced suppression of nonsense-mediated mRNA decay (NMD) mainly through the phospho-Eif2α-mediated general suppression of translation initiation and possible combined effects of decreased several NMD components expression. Atf4 accumulation was not mediated by NMD inhibition but translation inhibition of its upstream open reading frame (uORF) and translation facilitation of its protein-coding ORF by the phospho-Eif2α. These results suggested that ER stress plays an important role in MeHg cytotoxicity and that the modulation of ER stress has therapeutic potential to attenuate MeHg cytotoxicity, the underlying mechanism being the induction of integrated stress responses.

Yanagisawa R.,Japan National Institute of Environmental Studies | Koike E.,Japan National Institute of Environmental Studies | Win-Shwe T.-T.,Japan National Institute of Environmental Studies | Yamamoto M.,National Institute for Minamata Disease | Takano H.,Kyoto University
Environmental Health Perspectives | Year: 2014

Background: Hexabromocyclododecane (HBCD) is an additive flame retardant used in the textile industry and in polystyrene foam manufacturing. Because of its lipophilicity and persistency, HBCD accumulates in adipose tissue and thus has the potential of causing metabolic disorders through disruption of lipid and glucose homeostasis. However, the association between HBCD and obesity remains unclear. Objectives: We investigated whether exposure to HBCD contributes to initiation and progression of obesity and related metabolic dysfunction in mice fed a normal diet (ND) or a high-fat diet (HFD). Methods: Male C57BL/6J mice were fed a HFD (62.2 kcal% fat) or a ND and treated orally with HBCD (0, 1.75, 35, or 700 μg/kg body weight) weekly from 6 to 20 weeks of age. We examined body weight, liver weight, blood biochemistry, histopathological changes, and gene expression profiles in the liver and adipose tissue. Results: In HFD-fed mice, body and liver weight were markedly increased in mice treated with the high (700 μg/kg) and medium (35 μg/kg) doses of HBCD compared with vehicle. This effect was more prominent in the high-dose group. These increases were paralleled by increases in random blood glucose and insulin levels and enhancement of microvesicular steatosis and macrophage accumulation in adipose tissue. HBCD-treated HFD-fed mice also had increased mRNA levels of Pparg (peroxisome proliferator-activated receptor-γ) in the liver and decreased mRNA levels of Glut4 (glucose transporter 4) in adipose tissue compared with vehicle-treated HFD-fed mice. Conclusions: Our findings suggest that HBCD may contribute to enhancement of diet-induced body weight gain and metabolic dysfunction through disruption of lipid and glucose homeostasis, resulting in accelerated progression of obesity.

Grandjean P.,University of Southern Denmark | Grandjean P.,Harvard University | Satoh H.,Tohoku University | Murata K.,Akita University | Eto K.,National Institute for Minamata Disease
Environmental Health Perspectives | Year: 2010

Background: The scientific discoveries of health risks resulting from methylmercury exposure began in 1865 describing ataxia, dysarthria, constriction of visual fields, impaired hearing, and sensory disturbance as symptoms of fatal methylmercury poisoning.Objective: Our aim was to examine how knowledge and consensus on methylmercury toxicity have developed in order to identify problems of wider concern in research.Data sources and extraction: We tracked key publications that reflected new insights into human methylmercury toxicity. From this evidence, we identified possible caveats of potential significance for environmental health research in general. Synthesis: At first, methylmercury research was impaired by inappropriate attention to narrow case definitions and uncertain chemical speciation. It also ignored the link between ecotoxicity and human toxicity. As a result, serious delays affected the recognition of methylmercury as a cause of serious human poisonings in Minamata, Japan. Developmental neurotoxicity was first reported in 1952, but despite accumulating evidence, the vulnerability of the developing nervous system was not taken into account in risk assessment internationally until approximately 50 years later. Imprecision in exposure assessment and other forms of uncertainty tended to cause an underestimation of methylmercury toxicity and repeatedly led to calls for more research rather than prevention.Conclusions: Coupled with legal and political rigidity that demanded convincing documentation before considering prevention and compensation, types of uncertainty that are common in environmental research delayed the scientific consensus and were used as an excuse for deferring corrective action. Symptoms of methylmercury toxicity, such as tunnel vision, forgetfulness, and lack of coordination, also seemed to affect environmental health research and its interpretation.

Voegborlo R.B.,Kwame Nkrumah University Of Science And Technology | Matsuyama A.,National Institute for Minamata Disease | Adimado A.A.,Kwame Nkrumah University Of Science And Technology | Akagi H.,International Mercury Laboratory
Food Chemistry | Year: 2011

Concentrations of methylmercury (MeHg) residues were determined in different marine and freshwater fishes from Ghana. Samples were treated with ethanolic potassium hydroxide in water bath at 100°C for 1h. After neutralising with HCl and washing with hexane, MeHg was extracted with dithizone in toluene, cleaned up and determined by gas chromatography with electron capture detection (GC-ECD). The method was sensitive with good precision, detection limit of 0.0005μgg-1 (0.5μgkg-1) and provided good separation for organomercury compounds. The validity of the method was established using dogfish muscle certified reference material, DORM-2. The method was applied to different fish species. Concentration of MeHg in the edible muscle tissue of the tested fish ranged from 0.009 to 0.107μgg-1 wet weight. The concentrations of MeHg in the fish samples obtained do not however, constitute any significant mercury exposure to the general population through consumption of the tested fish species. © 2010 Elsevier Ltd.

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