Inhibition of N-methyl-D-aspartate receptors increases paraoxon-induced apoptosis in cultured neurons.
Organophosphorus (OP) compounds, used as insecticides and chemical warfare agents, are potent neurotoxins. We examined the neurotoxic effect of paraoxon (O,O-diethyl O-p-nitrophenyl phosphate), an organophosphate compound, and the role of NMDA receptors as a mechanism of action in cultured cerebellar granule cells. Paraoxon is neurotoxic to cultured rat cerebellar granule cells in a time- and concentration-dependent manner. Cerebellar granule cells are less sensitive to the neurotoxic effects of paraoxon on day in vitro (DIV) 4 than neurons treated on DIV 8. Surprisingly, the N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801, enhances paraoxon-mediated neurotoxicity suggesting that NMDA receptors may play a protective role. Pretreatment with a subtoxic concentration of N-methyl-D-aspartate (NMDA) [100 microM] protects about 40% of the vulnerable neurons that would otherwise die from paraoxon-induced neurotoxicity. Moreover, addition of a neuroprotective concentration of NMDA 3 h after treatment with paraoxon provides the same level of protection. Because paraoxon-mediated neuronal cell death is time-dependent, we hypothesized that apoptosis may be involved. Paraoxon increases apoptosis about 10-fold compared to basal levels. The broad-spectrum caspase inhibitor (Boc-D-FMK) and the caspase-9-specific inhibitor (Z-LEHD-FMK) protect against paraoxon-mediated apoptosis, paraoxon-stimulated caspase-3 activity and neuronal cell death. MK-801 increases, whereas NMDA blocks paraoxon-induced apoptosis and paraoxon-stimulated caspase-3 activity. These results suggest that activation of NMDA receptors protect neurons against paraoxon-induced neurotoxicity by blocking apoptosis initiated by paraoxon.
Wu
Xuan
X
Department of Neurology, Uniformed Services University of the Health Sciences, Building A, Room 1036, 4301 Jones Bridge Road, Bethesda, MD 20814, USA.
Tian
Feng
F
Okagaki
Peter
P
Marini
Ann M
AM
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects*; D001593:Benzyl Compounds / Q000494:pharmacology; D002038:Bungarotoxins / Q000494:pharmacology; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002525:Cerebellar Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018679:Cholinergic Agonists / Q000494:pharmacology; D018680:Cholinergic Antagonists / Q000494:pharmacology; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010261:Paraoxon / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013997:Time Factors
D000590:Amino Acid Chloromethyl Ketones; D001593:Benzyl Compounds; C476029:Boc-D-FMK; D002038:Bungarotoxins; D061945:Caspase Inhibitors; D018679:Cholinergic Agonists; D018680:Cholinergic Antagonists; D002800:Cholinesterase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D006845:Hydrocarbons, Fluorinated; D016194:Receptors, N-Methyl-D-Aspartate; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D010261:Paraoxon