TOPA QUINONE, A KAINATE-LIKE AGONIST AND EXCITOTOXIN, IS GENERATED BYA CATECHOLAMINERGIC CELL-LINE

The quinone derivative of 2,4,5-trihydroxyphenylalanine (TOPA) is a se lective non-NMDA agonist and excitotoxin. While 3,4-dihydroxyphenylala nine (DOPA)-containing physiological solutions have been shown to gene rate TOPA and TOPA quinone (TOPA compounds), there have been no previo us reports demonstrating the formation of this toxin in biological pre parations, Here, using a pheochromocytoma catecholaminergic clonal cel l line (PC12), we have identified TOPA compounds as by-products of cat echolamine synthesis, PC12 cells incubated for 45 min with 30 mu M tyr osine as a catecholamine precursor produced 1.0 +/- 0.2 pmol/10(6) cel ls of total TOPA compounds, The formation of these compounds could be enhanced nearly twofold when the cells were stimulated with 56 mM KCI, Moreover, the addition of a DOPA decarboxylase inhibitor (30 mu M NSD -1015) increased the formation of TOPA compounds in both the unstimula ted and stimulated conditions to a maximum of 5.5 +/- 0.7 pmol/10(6) c ells after a 45 min incubation, A time-course analysis revealed that D OPA production above baseline levels coincided with the detectable gen eration of TOPA compounds, Finally, we observed an inhibition of TOPA compounds formation by 100 mu M reduced glutathione, suggesting that t hese catecholamine products are formed from the extracellular autoxida tion of DOPA, We propose that TOPA quinone may be an underestimated co mponent of catecholamine toxicity that could be partly responsible for the demise of neurons in several neurodegenerative disorders, includi ng Parkinson's and Huntington's disease, In addition, TOPA quinone may represent the first identified selective non-NMDA agonist that may be synthesized in the brain.