dizocilpine-maleate and Teratocarcinoma

Copper, a transition metal with essential biological functions, exerts neurotoxic effects when present in excess. The aim of the present study was to better elucidate cellular and molecular mechanisms of CuSO4 toxicity in differentiated P19 neurons. Exposure to 0.5 mM CuSO4 for 24 h provoked moderate decrease in viability, accompanied with barely increased generation of reactive oxygen species (ROS) and caspase-3/7 activity. Glutathione (GSH) and ATP contents were depleted, lactate dehydrogenase inactivated, and glyceraldehyde-3-phosphate dehydrogenase overexpressed. In severely damaged neurons exposed to only two times higher concentration, classical caspase-dependent apoptosis was triggered as evidenced by marked caspase-3/7 activation and chromatin condensation. Multifold increase in ROS, together with very pronounced ATP and GSH loss, strongly suggests impairment of redox homeostasis. At higher copper concentration protease calpains were also activated, and neuronal injury was prevented in the presence of calpain inhibitor leupeptin through the mechanism that affects caspase activation. MK-801 and nifedipine, inhibitors of calcium entry, and H-89 and UO126, inhibitors of PKA and ERK signaling respectively, exacerbated neuronal death only in severely damaged neurons, while ROS-scavenger quercetin and calcium chelator BAPTA attenuated toxicity only at lower concentration. In a dose-dependent manner copper also provoked transcriptional changes of genes involved in intracellular signaling and induction of apoptosis (p53, c-fos, Bcl-2 and Bax). The obtained results emphasize differences in triggered neuronal-death processes in a very narrow range of concentrations and give further insight into the molecular mechanisms of copper toxicity with the potential to improve current therapeutic approaches in curing copper-related neurodegenerative diseases.

Topics: Adenosine Triphosphate; Animals; Apoptosis; Apoptosis Regulatory Proteins; Calpain; Caspases; Cell Line, Tumor; Chelating Agents; Chromatin; Copper Sulfate; Dizocilpine Maleate; Gene Expression Regulation; Glutathione; Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating); Leupeptins; Mice; Neoplasm Proteins; Neurons; Nifedipine; Oxidation-Reduction; Oxidative Stress; Protease Inhibitors; Protein Kinase Inhibitors; Reactive Oxygen Species; RNA, Messenger; Signal Transduction; Teratocarcinoma

Postmitotic neurons were generated from the human NT-2 teratocarcinoma cell line in a novel rapid differentiation procedure. These neurons were used to establish an in vitro assay system that allows the investigation of hypoxic/ischaemic cell damage and the development of neuroprotective strategies. In experiments of simulated ischaemia, the neurons were subjected to anoxia and hypoglycaemia. The viability of NT-2 neuronal cells was significantly reduced by anoxia especially in the presence of glutamate, reflecting the cellular vulnerability to excitotoxic conditions. The addition of the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 reduced glutamate-induced neuronal damage. Calcium imaging showed that NT-2 neurons increased cytosolic calcium levels in response to stimulation with glutamate or NMDA, an effect that was abolished in calcium free medium and at low pH values. The NMDA receptor antagonists MK-801, AP 5 and ketamine reduced the NMDA-induced response, suggesting the presence of functional NMDA receptors in the human neuronal cells. The mitochondrial potential of neurons was estimated using the fluorescent dye rhodamine 123 (R123). The fluorescence imaging experiments indicated an energetic collapse of mitochondrial functions during anoxia, suggesting that the human NT-2 neurons can be used to investigate subcellular processes during the excitotoxic cascade.

Topics: Aging; Calcimycin; Calcium; Cell Death; Cell Line, Tumor; Cell Survival; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Fluorescein; Glutamic Acid; Humans; Hypoxia; Ionophores; Mitochondria; N-Methylaspartate; Neurons; Teratocarcinoma; Time Factors

The excitotoxic response of NT2-N cells, a clonal line of human teratocarcinoma cells that are terminally differentiated into neuron-like cells, was examined using several endpoints. A 15 min exposure to glutamate produced a dose-dependent toxicity with a maximal cell loss of 80-90% in 6 week old cells. The rapidly triggered excitotoxicity induced by glutamate was blocked by NMDA selective antagonists, was calcium dependent and pH sensitive and could be mimicked by NMDA but not by non-NMDA agonists, AMPA, kainate or quisqualate. The non-NMDA agonists however caused toxicity on prolonged exposure. The NMDA receptor modulators glycine and spermidine enhanced glutamate-mediated toxicity whereas ifenprodil potently and completely inhibited toxicity suggesting that the toxic response is mediated by the NR1/NR2B combination of NMDA subunits. These cells can be rescued from death up to 1 hr after removal of glutamate by NMDA receptor blockade, removal of extracellular Ca2+ or lowering of pH. The extent of rescue is directly related to the time elapsed before intervention. Blockage of NMDA receptor activity for 1 hr immediately after removal of glutamate is both necessary and sufficient for complete rescue. Glutamate-mediated toxicity was not prevented by nitric oxide synthase inhibitors nor was nitric oxide synthase detected in NT2-N cells indicating that nitric oxide is not required for glutamate-mediated excitotoxicity. In summary, NT2-N cells exhibit a robust excitotoxic response and represent a novel model system in which to study the molecular basis of excitotoxic cell death.

Topics: 2-Amino-5-phosphonovalerate; Cell Death; Cellular Senescence; Dizocilpine Maleate; Glutamic Acid; Humans; Neurons; Neurotoxins; Nitric Oxide; Receptors, N-Methyl-D-Aspartate; Teratocarcinoma; Tumor Cells, Cultured