Cellular and mitochondrial changes in glutamate-induced HT4 neuronal cell death

Elevated levels of extracellular glutamate are neurotoxic. The cytotoxic pr operty of extracellular glutamate is known to mediate two primary mechanism s, excitotoxicity and excitotoxicity-independent processes. The excitotoxic ity-independent pathway was investigated in the current study in a mouse hi ppocampal-derived HT4 cell line. Exposure of HT4 cells to glutamate for 12h induced loss of cell viability preceded by rapid loss of intracellular red uced glutathione followed by accumulation of intracellular reactive oxygen species, elevation of intracellular Ca2+, progressive loss of mitochondrial membrane potential swelling and loss of mitochondrial outer membrane integ rity. Glutamate-induced loss of DNA integrity has been detected. The antiox idants or-tocopherol and trolox, mitochondrial calcium uniporter inhibitor Ruthenium Red and protein synthesis inhibitor cycloheximide all showed prot ection against glutamate-induced toxicity. None of the protective agents ex cept for or-tocopherol controlled the glutamate-induced reactive oxygen spe cies build-up. However, these cell death regulators prevented the glutamate -induced mitochondrial damage and regulated glutamate-induced increase in i ntracellular Ca2+. Carbonyl cyanide p-trifluoro-merhoxyphenyl-hydrazone. a mitochondrial uncoupler, partially protected against glutamate-induced cell death and mitochondrial damage, while the mitochondrial ribosomal inhibito r chloramphenicol and extracellular Ca2+ chelator ethylene glycol-bis(beta- aminoethyl ether)-N,N,N',N'-tetraacetic acid did not protect the cells agai nst glutamate treatment. The results of this study demonstrated that mitochondrial dysfunction was a key event in the excitotoxicity-independent component of neuronal cell dea th. Reactive oxygen species accumulation and glutathione depletion were pro minent in glutamate-treated cells; however, these events were not direct me diators of cell death. (C) 2000 IBRO. Published by Elsevier Science Ltd.