Newcomer T A, Rosenberg P A, Aizenman E
Department of Neurobiology, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA.
J Neurosci. 1995 Apr;15(4):3172-7. doi: 10.1523/JNEUROSCI.15-04-03172.1995.
The quinone derivative of 2,4,5-trihydroxyphenylalanine (TOPA) is a selective non-NMDA agonist and excitotoxin. While 3,4-dihydroxyphenylalanine (DOPA)-containing physiological solutions have been shown to generate TOPA and TOPA quinone (TOPA compounds), there have been no previous reports demonstrating the formation of this toxin in biological preparations. Here, using a pheochromocytoma catecholaminergic clonal cell line (PC12), we have identified TOPA compounds as by-products of catecholamine synthesis. PC12 cells incubated for 45 min with 30 microM tyrosine as a catecholamine precursor produced 1.0 +/- 0.2 pmol/10(6) cells of total TOPA compounds. The formation of these compounds could be enhanced nearly twofold when the cells were stimulated with 56 mM KCl. Moreover, the addition of a DOPA decarboxylase inhibitor (30 microM NSD-1015) increased the formation of TOPA compounds in both the unstimulated and stimulated conditions to a maximum of 5.5 +/- 0.7 pmol/10(6) cells after a 45 min incubation. A time-course analysis revealed that DOPA production above baseline levels coincided with the detectable generation of TOPA compounds. Finally, we observed an inhibition of TOPA compounds formation by 100 microM reduced glutathione, suggesting that these catecholamine products are formed from the extracellular autoxidation of DOPA. We propose that TOPA quinone may be an underestimated component of catecholamine toxicity that could be partly responsible for the demise of neurons in several neurodegenerative disorders, including 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.
2,4,5-三羟基苯丙氨酸（TOPA）的醌衍生物是一种选择性非N-甲基-D-天冬氨酸（NMDA）激动剂和兴奋性毒素。虽然含3,4-二羟基苯丙氨酸（DOPA）的生理溶液已被证明可生成TOPA和TOPA醌（TOPA化合物），但此前尚无报告表明在生物制剂中会形成这种毒素。在此，我们使用嗜铬细胞瘤儿茶酚胺能克隆细胞系（PC12），鉴定出TOPA化合物是儿茶酚胺合成的副产物。用30微摩尔酪氨酸作为儿茶酚胺前体培养45分钟的PC12细胞，产生了1.0±0.2皮摩尔/10⁶个细胞的总TOPA化合物。当用56毫摩尔氯化钾刺激细胞时，这些化合物的形成可增加近两倍。此外，添加DOPA脱羧酶抑制剂（30微摩尔NSD-1015）可使在未刺激和刺激条件下TOPA化合物的形成在培养45分钟后增加至最大5.5±0.7皮摩尔/10⁶个细胞。时间进程分析显示，高于基线水平的DOPA产生与可检测到的TOPA化合物生成同时发生。最后，我们观察到100微摩尔还原型谷胱甘肽可抑制TOPA化合物的形成，这表明这些儿茶酚胺产物是由DOPA的细胞外自氧化形成的。我们提出，TOPA醌可能是儿茶酚胺毒性中一个被低估的成分，可能部分导致包括帕金森病和亨廷顿病在内的几种神经退行性疾病中神经元死亡。此外，TOPA醌可能代表了第一种在大脑中可能合成的已确定的选择性非NMDA激动剂。
