salicylates and 1-(4-methoxyphenyl)pyridinium

MPTP is a neurotoxin thought to damage dopaminergic neurons through free radical formation. MPTP is metabolized in the brain to MPP(+), which is taken up into dopaminergic neurons via the dopamine transporter and assumed to impair mitochondrial function. We used striatal synaptosomes and telencephalic mitochondria to further investigate MPP(+) mechanism of action. For comparison, the respiratory toxins FCCP, a cyanide analog that uncouples mitochondrial ATP production, and rotenone, a NADH dehydrogenase inhibitor, were also tested. FCCP, MPP(+) and rotenone caused a rapid but stable decrease in [3H]dopamine (DA) uptake by striatal synaptosomes. Two free radical scavengers, the salen-manganese complex EUK-134, and the spin trap s-PBN, did not prevent MPP(+)-induced decrease in DA uptake. However, addition of ATP during synaptosome preparation resulted in partial recovery of MPP(+)-induced [3H]DA uptake decrease. Generation of oxygen free radicals by treatment of telencephalic mitochondria with MPP(+), FCCP, or rotenone, was evaluated by measuring DCF fluorescence, while light emission by the luciferin-luciferase complex was used to determine ATP levels. MPP(+), unlike rotenone, did not produce oxygen free radicals, but rather blocked ATP production in mitochondria, as did FCCP and rotenone. Taken together, these results suggest that MPP(+) toxicity, at least during its initial stages, is primarily due to a decrease in ATP synthesis by mitochondria and not to free radical formation.

Topics: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; Adenosine Triphosphate; Animals; Antioxidants; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; Cyclic N-Oxides; Dopamine; Dopamine Agents; Dopamine Uptake Inhibitors; Free Radicals; In Vitro Techniques; Male; Mazindol; Mitochondria; Neostriatum; Nitrogen Oxides; Organometallic Compounds; Pyridinium Compounds; Rats; Rats, Sprague-Dawley; Rotenone; Salicylates; Subcellular Fractions; Synaptosomes; Uncoupling Agents

Increased formation of hydroxyl free radicals (.OH) reflected by .OH adduct of salicylate in brain dialysate was demonstrated during the sustained (more than 2 hours) dopamine overflow elicited by 75 nmol of 1-methyl-4-phenyldihydropyridine (MPDP+) and 1-methyl-4-phenylpyridinium (MPP+) in the rat striatum. Owing to its weak dopamine releasing action, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) did not significantly increase the .OH formation. This data suggests that sustained elevation of dopamine in the extracellular fluid elicited by MPTP analogues can be auto-oxidized, which in turn leads (possibly by indirect mechanisms) to the formation of cytotoxic .OH free radicals near the nigrostriatal terminals.

Topics: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; Animals; Corpus Striatum; Dialysis; Dopamine; Free Radicals; Hydroxides; Hydroxyl Radical; Male; Nerve Endings; Perfusion; Pyridinium Compounds; Rats; Rats, Sprague-Dawley; Salicylates; Salicylic Acid; Substantia Nigra