Inhibition of glutamate-induced mitochondrial depolarization by tamoxifen in cultured neurons.
In central neurons, glutamate receptor activation causes massive calcium influx and induces a mitochondrial depolarization, which is partially blocked by cyclosporin A, suggesting a possible activation of the mitochondrial permeability transition pore (PTP) as a mechanism. It has been recently reported that tamoxifen (an antiestrogen chemotherapeutic agent) blocks the PTP in isolated liver mitochondria, similar to cyclosporin A. In this study, we tested whether tamoxifen inhibits the mitochondrial depolarization induced by glutamate receptor activation in intact cultured neurons loaded with the fluorescent dye 5,5',6,6'-tetrachloro-1,1',3, 3'-tetraethylbenzimidazolylcarbocyanine iodide. This dye reports disruptions in mitochondrial membrane potential, which can be caused by PTP activation. We found that glutamate (100 microM for 10 min) causes a robust mitochondrial depolarization that is partially inhibited by tamoxifen. The maximum inhibitory concentration of tamoxifen was 0.3 microM, with concentrations higher and lower than 0.3 microM being less effective. However, although tamoxifen (0.3 microM) blocked glutamate-induced mitochondrial depolarization, it did not inhibit glutamate-induced neuronal death, in contrast to the PTP inhibitor cyclosporin A. A relatively high concentration of tamoxifen (100 microM) caused mitochondrial depolarization itself and was neurotoxic. These data suggest that tamoxifen may be an inhibitor of the PTP in intact neurons. However, the lack of specificity of most PTP inhibitors, and the difficulty in measuring PTP in intact cells, preclude definite conclusions about the role of PTP in excitotoxic injury.
Hoyt
K R
KR
Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA. hoyt.31@osu.edu
McLaughlin
B A
BA
Higgins
D S
DS
Reynolds
I J
IJ
D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology* / Q000633:toxicity; D001562:Benzimidazoles; D002232:Carbocyanines; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D003576:Electron Transport Complex IV / Q000378:metabolism; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology* / Q000633:toxicity; D005456:Fluorescent Dyes; D018698:Glutamic Acid / Q000494:pharmacology*; D006651:Histocytochemistry; D008297:Male; D008314:Malonates / Q000633:toxicity; D008564:Membrane Potentials / Q000187:drug effects; D008566:Membranes / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects*; D017072:Neostriatum / Q000166:cytology / Q000187:drug effects; D009474:Neurons / Q000187:drug effects* / Q000648:ultrastructure; D010539:Permeability / Q000187:drug effects; D016548:Prosencephalon / Q000166:cytology / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013629:Tamoxifen / Q000494:pharmacology* / Q000633:toxicity
D018931:Antineoplastic Agents, Hormonal; D001562:Benzimidazoles; D002232:Carbocyanines; D018691:Excitatory Amino Acid Antagonists; D005456:Fluorescent Dyes; D008314:Malonates; D013629:Tamoxifen; C068624:5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolocarbocyanine; D018698:Glutamic Acid; D003576:Electron Transport Complex IV