Oxidative and non-oxidative mechanisms of neuronal cell death and apoptosis by L-3,4-dihydroxyphenylalanine (L-DOPA) and dopamine.
1. The present study was designed to evaluate the nature of intervening agents in L-DOPA- and dopamine-induced neurotoxicity in Neuro-2A cells. 2. In the absence of cells and in conditions of light protection, at 37 degrees C, L-DOPA or dopamine (1 mM) in culture medium degraded spontaneously in a time-dependent manner, this being prevented by ascorbic acid (200 microM) and other antioxidants, namely glutathione (1 mM), N-acetyl-L-cysteine (1 mM), sodium metabisulphite (200 microM), but not N-ter-butyl-alpha-phenylnitrone (1 mM) and deferoxamine (100 microM). 3. The viability of Neuro-2A cells declined following treatment with L-DOPA or dopamine in a concentration- and time-dependent manner. The decrease in cell viability by L-DOPA (10+/-4% of control) or dopamine (15+/-4% of control) was markedly attenuated by antioxidants (ascorbic acid, glutathione, N-acetyl-L-cysteine and sodium metabisulphite). Autoxidation of L-DOPA or dopamine was accompanied by the formation of H(2)O(2) in a time-dependent manner, this being completely prevented by ascorbic acid at 24 h or markedly reduced at 48 h. 4. Protective effects of 100 U ml(-1) catalase (40+/-1% of control) against L-DOPA-induced cell death were lower than those conferred by 200 microM ascorbic acid (70+/-3% of control). Catalase-induced protection (59+/-5% of control) against dopamine-induced cell death was similar to that conferred by 200 microM ascorbic acid (57+/-4% of control). L-DOPA-induced neuronal cell death was also accompanied by increases in caspase-3 activity, this being insensitive to ascorbic acid. Dopamine-induced increase in caspase-3 activity occurred only when autoxidation of the amine was prevented by ascorbic acid. 5. It is suggested that in addition to generation of H(2)O(2) and quinone formation, L-DOPA- and dopamine-induced cell death may result from induction of apoptosis, as evidenced by increases in caspase-3 activity. Dopamine per se induces apoptosis by a mechanism independent of oxidative stress, as evidenced by the fact that increases in caspase-3 activity occurred only when autoxidation of the amine was prevented.
Pedrosa
R
R
Institute of Pharmacology and Therapeutics, Faculty of Medicine, 4200 Porto, Portugal.
Soares-da-Silva
P
P
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D004298:Dopamine / Q000633:toxicity*; D007980:Levodopa / Q000633:toxicity*; D051379:Mice; D009474:Neurons / Q000166:cytology* / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects* / Q000502:physiology; D014407:Tumor Cells, Cultured
D000975:Antioxidants; D007980:Levodopa; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; D004298:Dopamine