Formation and Metabolism of Salsolinol Enantiomers

1-甲基-4-苯基-1，2，3，6-四氢吡啶（1-Methyl-4-phenyl-1，2，3，6-tetrahydropyridine，MPTP）是一种外源性（人工合成的）神经毒素， 人类、非人类灵长类动物和大鼠的帕金森症。猪毛菜醇（6，7-二羟基-1-甲基-1，2，3，4 - 四氢异喹啉，Sal）是MPTP样神经毒素。它的一些I相代谢物，例如N-甲基- （R）-Sal，已经显示靶向和损伤特别是多巴胺能黑质纹状体神经元，诱导 帕金森症。不幸的是，Sal可以在体内由多巴胺（a）的缩合形成。 大脑中的神经递质）和乙醛（酒精的代谢物）。有趣的是，两人 N-甲基-水杨酸的对映异构体表现出不同的神经毒理学性质。N-甲基-（R）-水杨酸诱导 帕金森症大鼠，但N-甲基-（S）-Sal没有。然而，在体内的立体化学方面， 这些神经毒性对映异构体的形成和代谢仍然是未知的。为 例如，关于生理液体中Sal的立体特异性存在的文献数据是 前后矛盾本研究的目的是确定的生物合成和代谢途径， Sal对映异构体。为此，开发适当的分析方法， 需要同时定量Sal及其I相代谢物的对映体。我们 提出建立基于毛细管HPLC /串联质谱的手性分析方法 光谱仪用于此目的。分析方法确定后，将进行研究 结果：1）测定大鼠内源性水杨酸及其代谢产物的对映体组成 脑和生理液体; 2）使用以下方法研究Sal在大鼠脑中的体内形成： 在对大鼠施用13 C标记的乙醛和甘草酸后进行微透析; 3） 使用13 C标记的Sal或N-甲基-Sal的Sal和N-甲基-Sal的I相代谢物 对映异构体（例如[1，m-13 C2]-猪毛菜醇）;和4）评估对映异构体Sal的神经毒性 PC-12中的主要I相代谢产物包括N-甲基水杨醛和N-甲基-4-羟基水杨醛 和SH-SY 5 Y细胞。这一假说是，神经毒性更强的（R）-对映体的外消旋化 内源性Sal及其代谢产物的释放是导致健康人解毒的主要途径。 神经系统本文采用改进的手性分析方法， 体内微透析和稳定同位素标记技术，研究将作出重大贡献 与我们对这些神经毒素的体内形成和代谢的了解相比， 在某些神经退行性疾病如帕金森病的发病机制中，从这些 研究，也将取得重大进展，了解立体化学方面的 一般神经毒性。

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is an exogenous (synthetic) neurotoxin inducing Parkinsonism in humans, non-human primates, and rats. Salsolinol (6,7-dihydroxy-1-methyl-1, 2, 3, 4 -tetrahydroisoquinoline, Sal) is an MPTP-like neurotoxin. Some of its phase I metabolites, e.g. N-methyl- (R)-Sal, have been shown to target and injure particularly dopaminergic nigrostriatal neurons inducing Parkinsonism. Unfortunately, Sal can be formed in vivo from the condensation of dopamine (a neurotransmitter in the brain) and acetaldehyde (a metabolite of alcohol). Very interestingly, the two enantiomers of N-methyl-Sal exhibit distinct neurotoxicological properties. N-methyl-(R)-Sal induces Parkinsonism in rats, but N-methyl-(S)-Sal does not. However, the stereochemical aspects of in-vivo formation and metabolism of these neurotoxic enantiomers remain largely unknown. For example, literature data on the stereospecific occurrence of Sal in physiological fluids are inconsistent. The goal of this research is to identify the biosynthetic and metabolic pathways of Sal enantiomers. To this end, the development of suitable analytical methodology for simultaneous quantification of the enantiomers of Sal and its phase I metabolites is needed. We are proposing to develop a chiral analytical method based on capillary HPLC /tandem mass spectrometry for this purpose. After the analytical methodology is in place, studies will be carried out: 1) to determine the enantiomeric compositions of endogenous Sal and its metabolites in rat brain and physiological fluids; 2) to investigate in vivo formation of Sal in rat brain using microdialysis after administering 13C labeled acetaldehyde and pyruvic acid to rats; 3) to profile the phase I metabolites of Sal and N-methyl-Sal using 13C labeled Sal or N-methyl-Sal enantiomers (e.g. [1 ,m-13C2]-salsolinol); and 4) to assess the neurotoxicity of enantiomeric Sal and its major phase I metabolites including N-methyl-Sal and N-methyl-4-hydroxyl-Sal in PC-12 and SH-SY5Y cells. The hypothesis is that racemization of the more neurotoxic (R)-enantiomers of endogenous Sal and its metabolites is a major pathway leading to detoxification in a healthy nervous system. By using the improved methodology for chiral analysis in combination with in vivo microdialysis and stable isotope labeling techniques, the research will contribute significantly to our knowledge of in vivo formation and metabolism of these neurotoxins involved in the pathogenesis of certain neurodegenerative disorders such as Parkinson's disease. From these studies, significant gains will also be made in understanding the stereochemical aspects of neurotoxicity in general.