dizocilpine-maleate and methylmercuric-chloride

Methylmercury (MeHg), a known neurotoxin, has been reported to alter glutamate homeostasis in the neuronal environment resulting in excitotoxicity. This study was conducted to investigate whether, and if so, under what conditions, that low dose MeHg would enhance the toxicity of glutamate and to what extent that blockade of NMDA receptors would alter MeHg and glutamate's toxicity in cultured neuroblastoma cells. Neuroblastoma cells (SH-SY5Y) were used in a cell culture model to study effects of MeHg, glutamate (glu), a calcium chelator (BAPTA-AM), and a noncompetitive NMDA antagonist, MK-801 on cell growth, cell survival, and phosphorylation of tau protein, as a measure of cellular events associated with tauopathies. Exposure of cells to a combination of MeHg (50 nM) and glutamate (1 mM) resulted in both a greater decrease in cell viability as well as a greater induction in tau phosphorylation, as compared to exposures with MeHg and glutamate alone. MK-801, an NMDA receptor antagonist, and the intracellular calcium chelator, BAPTA-AM, both significantly inhibited tau hyperphosphorylation and protected cells from the effects of combination exposures to glutamate and MeHg. These results may indicate that exposure to even nontoxic levels of MeHg may prime neuronal cells to be more susceptible to neuronal injury from excitotoxicants such as glutamate and thus may increase the likelihood of neurological disease states. In conclusion, low-dose MeHg-induced toxicity may be related to an increase in the cellular response to glutamate and that NMDA receptor antagonists may provide a potential treatment for MeHg-associated neurological diseases.

Topics: Calcium; Cell Line, Tumor; Cell Survival; Chelating Agents; Dizocilpine Maleate; Egtazic Acid; Glutamic Acid; Humans; Methylmercury Compounds; Neuroblastoma; Phosphorylation; Receptors, N-Methyl-D-Aspartate; tau Proteins

Overexposure to methylmercury (MeHg) has been known to induce neurotoxicity. The objective of this study is to explore mechanisms that contribute to MeHg-induced nerve cell apoptosis focusing on the alteration of intracellular Ca(2+) homeostasis and expression of N-methyl-D-aspartate receptors (NMDARs) subunits in rat cerebral cortex and whether MK801, a non-competitive NMDAR antagonist, could attenuate MeHg-induced neurotoxicity. Fifty rats were randomly divided into five groups of 10 animals in each group: control group, MK801 control group, MeHg-treated group (4 and 12 μmol/kg) and MK801 pre-treated group. Administration of MeHg at a dose of 12 μmol/kg for 4 weeks significantly increased in intracellular [Ca(2+)](i) and total Hg levels and that enhanced neurocyte apoptosis rate in cerebral cortex. In addition, the inhibitory effect of MeHg on Na(+)-K(+)-ATPase and Ca(2+)-ATPases might be one of the reasons that cause a significant increase of [Ca(2+)](i) in neurocyte. Over activated by increased cytosolic Ca(2+) loading, calpains degraded NMDAR subunits leading ultimately to nerve cell damage. However, pretreatment with MK801 at a dose of 0.3 μmol/kg could prevent Ca(2+) homeostasis dysregulation and alleviate the neurocyte apoptosis. In conclusion, the neuroprotective effects of MK801 appeared to be mediated not only via its NMDA receptor binding properties but also by maintaining intracellular calcium homeostasis.

Topics: Animals; Apoptosis; Calcium; Calcium-Transporting ATPases; Calpain; Cerebral Cortex; Cytoplasm; Dizocilpine Maleate; Homeostasis; Methylmercury Compounds; Neurons; Neuroprotective Agents; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Sodium-Potassium-Exchanging ATPase; Transcription, Genetic

Methylmercury (MeHg) is one of the ubiquitous environmental toxicants, which can induce oxidative stress and an indirect excitotoxicity caused by altered glutamate (Glu) metabolism. However, little is known of the interaction between oxidative stress and Glu metabolism play in MeHg poisoning rats. We have investigated the neuroprotective role of MK-801, a non-competitive N-methyl-d-aspartate receptors (NMDAR) antagonist, against MeHg-induced neurotoxicity. Fifty rats were randomly divided into five groups of 10 animals in each group: control group, MK-801 control group, MeHg-treated group (4 and 12 μmol/kg) and MK-801 pre-treated group. Administration of MeHg at a dose of 12 μmol/kg for four weeks significantly increased in ROS and total Hg levels and that caused lipid, protein and DNA peroxidative damage in cerebral cortex. In addition, MeHg also reduced nonenzymic (reduced glutathione, GSH) and enzymic (glutathione peroxidase, GPx and superoxide dismutase, SOD) antioxidants and enhanced neurocyte apoptosis rate in cerebral cortex. MeHg-induced ROS production appears to inhibit the activity of the glutamine synthetase (GS), leading to Glu metabolism dysfunction. Pretreatment with MK-801 at a dose of 0.3 μmol/kg prevented the alterations of the activities of PAG and GS and oxidative stress. In addition, pretreatment with MK-801 significantly alleviated the neurocyte apoptosis rate and histopathological damage. In conclusion, the results suggested ROS formation resulting from MeHg- and Glu-induced oxidative stress contributed to neuronal injury. MK-801 possesses the ability to attenuate MeHg-induced neurotoxicity in the cerebral cortex through mechanisms involving its NMDA receptor binding properties and antioxidation.

Topics: Animals; Apoptosis; Cerebral Cortex; Dizocilpine Maleate; Dose-Response Relationship, Drug; Environmental Pollutants; Female; Glutamic Acid; Male; Mercury Poisoning, Nervous System; Methylmercury Compounds; Neuroprotective Agents; Oxidative Stress; Rats; Rats, Wistar; Reactive Oxygen Species

The neurotoxic effects of methylmercury on cerebral neuron cultures derived from neonatal mouse were studied. Exposure of cerebral neurons to methylmercury chloride resulted in significant cell damage and death in a time-dependent manner in cerebral neuron cultures. The methylmercury neurotoxicity was blocked by oxygen radical scavengers such as glutathione, catalase, selenium, and cysteine. Antagonists of the N-methyl-D-aspartate (NMDA) receptor, including MK-801 (a non-competitive NMDA antagonist), D-2-amino-5-phosphonovaleric acid (APV) (a competitive NMDA antagonist), and 7-chlorokynurenic acid (an antagonist at the glycine site associated with the NMDA receptor), similarly blocked methylmercury-induced neurotoxicity in cerebral neuron cultures. These results indicate that both oxygen radicals and excitotixic amino acids are involved in the methylmercury-induced neurotoxicity of cerebral neuron cultures.

Topics: Animals; Antioxidants; Catalase; Cells, Cultured; Cerebral Cortex; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glutathione; Kynurenic Acid; Methylmercury Compounds; Mice; Neurons; Receptors, N-Methyl-D-Aspartate