Role of Tyrosine in MDMA Toxicity

酪氨酸在 MDMA 毒性中的作用

• 批准号: 7579929
• 负责人: Bryan K Yamamoto
• 金额: $ 24.7万
• 依托单位: UNIVERSITY OF TOLEDO HEALTH SCI CAMPUS
• 依托单位国家: 美国
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-03-10 至 2011-02-28
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7579929
• 关键词: Address; Affect; Amino Acids; Amphetamine Abuse; Aromatic-L-Amino-Acid Decarboxylases; Brain; Carboxy-Lyases; Cell Survival; Cells; Data; Dependency; Detection; Dopamine; Dyes; Environment; Fever; Fluorescamine; Hippocampus (Brain); Hydrogen Peroxide; Incubated; Individual; Induced Hyperthermia; Lactate Dehydrogenase; Lipid Peroxidation; Measures; Mediating; Mediator of activation protein; Membrane Potentials; Microdialysis; Mitochondria; Modeling; Nerve Degeneration; Neurons; Neutral Amino Acids; Oxidative Stress; Presynaptic Terminals; Process; Proxy; Quinones; Reactive Oxygen Species; Relative (related person); Research Personnel; Role; Serotonin; System; Temperature; Testing; Toxic effect; Tyramine; Tyrosine; analog; base; dopaminergic neuron; ecstasy; extracellular; in vivo; mitochondrial membrane; neurotoxicity; novel; novel strategies; oxidation; oxidative damage; research study

DESCRIPTION (provided by applicant): The widely abused amphetamine analogue, 3 4-methylenedioxymethamphetamine (MDMA, Ecstasy) selectively damages the axon terminals of 5-HT neurons in the brain. Several lines of evidence suggest that dopamine (DA) contributes to this toxicity. Although DA clearly produces oxidative by-products such as reactive oxygen species and quinones, it remains unclear as to how DA-derived oxidative species produce selective damage to 5HT terminals, a hallmark of MDMA-induced neurotoxicity. More specifically, the mechanism as to how DA accumulates within 5-HT terminals to produce its selective damage is unknown. The overaraching hypothesis of the current proposal is that L- tyrosine, the amino acid precursor of DA, contributes to the neurodegenerative process. This hypothesis is based on our recent preliminary data indicating a 5-fold increase in the extracellular concentration of tyrosine measured in vivo after MDMA. Unlike DA, tyrosine is actively transported from the periphery and into the brain and neurons. While tyrosine is the natural precursor for DA synthesis within DA neurons, high concentrations of tyrosine in 5HT neurons may have deleterious consequences. The hypothetical framework of this proposal is that the oxidative environment produced by MDMA and hyperthermia in 5-HT neurons causes the non-enzymatic oxidation of tyrosine to the DA precursor, DOPA. Aromatic amino acid decarboxylase (AADC), within the 5-HT terminal then would decarboxylate DOPA to DA, leading to an accumulation of DA and consequently, DA-derived reactive oxygen species and oxidative damage within 5HT terminals. This hypothesized role of tyrosine as a mediator of MDMA-induced toxicity is a novel mechanism that effectively synthesizes current existing hypotheses and to some extent, discrepant observations and apparent caveats into a cohesive, theoretical and testable framework. The Specific Aims are (1) to demonstrate the non-enzymatic oxidation of tyrosine to DOPA and DA within 5HT neurons, (2) to characterize the contributions of L-tyrosine and tyramine to MDMA and hyperthermia-induced oxidative stress and (3) to assess subsequent neuronal damage. The use of cultured RN46A 5HT cells is a novel approach that is uniquely suited to address the hypothesized mechanism of MDMA-induced damage. These experiments will directly measure the individual and relative effects of MDMA, tyrosine, hyperthermia, and the formation of intracellular dopamine on oxidative processes within 5-HT neurons and how these variables affect cell viability. The testing of this model in conjunction with in vivo microdialysis studies, provides a unique and powerful approach to address enigmatic issues previously related to MDMA-induced neurodegeneration of 5HT systems

描述（由申请人提供）：广泛滥用的苯丙胺类似物，3-4-亚甲二氧基甲基苯丙胺（MDMA，摇头丸）选择性损害大脑中 5-HT 神经元的轴突末端。多项证据表明多巴胺 (DA) 会导致这种毒性。尽管 DA 明显产生氧化副产物，如活性氧和醌，但 DA 衍生的氧化物质如何对 5HT 末端（MDMA 诱导的神经毒性的标志）产生选择性损伤仍不清楚。更具体地说，DA 如何在 5-HT 末端积累并产生选择性损伤的机制尚不清楚。当前提议的首要假设是，L-酪氨酸（DA 的氨基酸前体）有助于神经退行性过程。这一假设基于我们最近的初步数据，该数据表明在服用 MDMA 后体内测得的细胞外酪氨酸浓度增加了 5 倍。与 DA 不同，酪氨酸从外周主动转运至大脑和神经元。虽然酪氨酸是 DA 神经元内 DA 合成的天然前体，但 5HT 神经元中高浓度的酪氨酸可能会产生有害后果。该提议的假设框架是 MDMA 和 5-HT 神经元中的高温产生的氧化环境导致酪氨酸非酶氧化为 DA 前体 DOPA。 5-HT 末端内的芳香族氨基酸脱羧酶 (AADC) 会将 DOPA 脱羧为 DA，导致 DA 积累，从而导致 DA 衍生的活性氧和 5HT 末端内的氧化损伤。酪氨酸作为 MDMA 诱导毒性介质的假设作用是一种新机制，它有效地将当前现有的假设以及在某种程度上的差异观察和明显的警告综合到一个有凝聚力的、理论的和可测试的框架中。 具体目标是 (1) 证明 5HT 神经元内酪氨酸非酶促氧化为 DOPA 和 DA，(2) 表征 L-酪氨酸和酪胺对 MDMA 和热疗诱导的氧化应激的贡献，以及 (3) 评估随后的神经元损伤。使用培养的 RN46A 5HT 细胞是一种新方法，特别适合解决 MDMA 诱导损伤的假设机制。这些实验将直接测量 MDMA、酪氨酸、高温和细胞内多巴胺的形成对 5-HT 神经元内氧化过程的个体和相对影响，以及这些变量如何影响细胞活力。该模型的测试与体内微透析研究相结合，提供了一种独特而强大的方法来解决先前与 MDMA 诱导的 5HT 系统神经变性相关的神秘问题