Hepatic Metabolism and Susceptibility to Ecstasy Toxicity

描述（由申请人提供）：一些不良反应与使用3,4-（¿）-亚甲基二氧基甲基苯丙胺（MDMA；摇头丸，XTC， E）有关，其中最令人担忧的是对血清素能神经递质系统的长期毒性。因此，使用和滥用摇头丸有可能造成重大的公共卫生问题。MDMA的神经毒性作用依赖于给药途径和频率。在外周给药后，直接向大脑注射MDMA或MDA都不能再现神经毒性，这表明母体安非他明不太可能是神经毒性作用的唯一原因。我们（和其他人）已经提出肝脏衍生的MDMA和MDA代谢物介导神经毒性。我们假设MDA和MDMA的数量较少，但活性的肝脏代谢物有助于它们的神经毒性，其中一类代谢物来自n -甲基-？-methyldopamine (N-methyl - ?-MeDA)和？-MeDA，然后用谷胱甘肽（GSH）清除邻醌。此外，由于碳原子a到胺基代表一个立体中心，MDMA可以存在于两种不同的三维镜像结构，或对映体：(R)-MDMA和(S)-MDMA。事实上，对映体的药理学特征不同，它们的相对神经毒性也不同。因此，在动物模型中，(S)-MDMA似乎是5 -羟色胺能神经元退化的主要因素。由于MDMA的所有主要肝脏代谢物都保留了立体中心，因此所有代谢物都以一对非对映异构体的形式存在（谷胱甘肽也含有一个手性中心）。因此，MDMA的神经毒性不仅依赖于肝脏代谢，而且我们假设具有(S)-构型的代谢物将比相应的(R)-非对映异构体更有效。由于代谢是神经毒性表达的必要条件，因此MDMA I期（P450）和II期（COMT）代谢的差异将是个体对MDMA神经毒性易感性的重要决定因素。在人类中，负责MDMA代谢的I期（CYP2D6）和II期（COMT）酶是多态性的，表现出显著的个体间差异。由于导致MDMA诱导的神经毒性易感性的个体差异的因素尚不清楚，并且由于神经毒性依赖于代谢，我们假设MDMA的I期和II期代谢的差异调节了个体对神经毒性的易感性。本应用程序中提出的研究旨在测试这些总体假设，并检查这些代谢物进入大脑的途径。因此，我们将测试以下假设：MDMA代谢物的神经毒性具有定向选择性（Specific Aim #1）；对神经毒性的易感性由I期和II期肝脏代谢调节（Specific Aim #2）；由于神经毒性需要将水溶性代谢物摄取到大脑中，因此毒性也受大脑摄取和大脑输出过程（III期代谢）之间的平衡调节（Specific Aim #3）。总之，关于MDMA相对于其神经毒性的药效学和毒代动力学知之甚少，也不知道导致个体间易感性的因素，本应用旨在解决我们知识中的这些缺陷。公共卫生相关性：使用和滥用3,4-（¿）-亚甲基二氧基甲基苯丙胺（MDMA；摇头丸，XTC， E）会产生若干不良影响，其中最令人担忧的是对大脑中被称为血清素能神经元的特殊细胞的长期损害。因此，使用和滥用摇头丸有可能造成重大的公共卫生问题。特别是，神经毒性的发展需要MDMA由肝脏代谢为随后进入大脑的代谢物。因为负责MDMA代谢和大脑对代谢物摄取的蛋白质在不同的个体之间差异很大，所以了解这些不同过程对MDMA神经毒性的相对贡献将有助于我们识别那些可能更容易受到MDMA副作用影响的个体（或者类似药物）。

DESCRIPTION (provided by applicant): Several adverse effects are associated with the use of 3,4-(¿)-methylenedioxymethamphetamine (MDMA; Ecstasy, XTC, E), the most worrisome of which is long-term toxicity to the serotonergic neurotransmitter system. MDMA use and abuse therefore has the potential to give rise to a major public health problem. The neurotoxic effects of MDMA are dependent on the route and frequency of drug administration. Direct injection of either MDMA or MDA into the brain fails to reproduce the neurotoxicity following peripheral administration, indicating that the parent amphetamines are unlikely to be solely responsible for the neurotoxic effect. We (and others) have proposed that liver-derived metabolites of MDMA and MDA mediate the neurotoxicity. We hypothesize that quantitatively minor, yet reactive hepatic metabolites of MDA and MDMA contribute to their neurotoxicity, and that one such class of metabolites arise from the oxidation of N-methyl-?-methyldopamine (N-methyl-?-MeDA) and ?-MeDA, followed by scavenging of the ortho-quinones with glutathione (GSH). Moreover, because the carbon atom a to the amine group represents a stereogenic center, MDMA can exist in two different three-dimensional mirror-image structures, or enantiomers: (R)-MDMA and (S)-MDMA. Indeed, the pharmacological profiles of the enantiomers differ, as does their relative neurotoxicity. Thus, in animal models, (S)-MDMA appears to be the major contributor to the degeneration of serotonergic neurons. Because all the principal hepatic metabolites of MDMA retain the stereogenic center, it follows that all of the metabolites exist as a pair of diastereoisomers (GSH also contains a chiral center). Therefore, not only is the neurotoxicity of MDMA dependent upon hepatic metabolism, but we hypothesize that metabolites possessing the (S)-configuration will be more potent than the corresponding (R)-diastereoisomers. Because metabolism is necessary for the expression of neurotoxicity, differences in the Phase I (P450) and Phase II (COMT) metabolism of MDMA will be important determinants of individual susceptibility to the neurotoxicity of MDMA. In humans, the phase I (CYP2D6) and phase II (COMT) enzymes responsible for MDMA metabolism are polymorphic, exhibiting significant inter-individual differences. Since the factors that contribute to the inter-individual variability in susceptibility to MDMA induced neurotoxicity are not known, and since neurotoxicity is dependent upon metabolism, we hypothesize that differences in the phase I and phase II metabolism of MDMA modulate individual susceptibility to neurotoxicity. Studies proposed in this application are designed to test these overall hypotheses and to examine the pathways by which such metabolites gain access to the brain. We will therefore test the hypotheses that the neurotoxicity of MDMA metabolites is stereoselective (Specific Aim #1), that susceptibility to neurotoxicity is modulated by both Phase I and Phase II hepatic metabolism (Specific Aim #2) and that because neurotoxicity requires the uptake of water soluble metabolites into brain, toxicity is also regulated by the balance between brain uptake and brain export processes (Phase III metabolism) (Specific Aim #3). In summary, little is known about the pharmacodynamics and toxicokinetics of MDMA relative to its neurotoxicity, nor of the factors that contribute to inter-individual susceptibility, and this application is designed to address these deficits in our knowledge. PUBLIC HEALTH RELEVANCE: Several adverse effects are associated with the use and abuse of 3,4-(¿)-methylenedioxymethamphetamine (MDMA; Ecstasy, XTC, E), the most worrisome of which is long-term damage to specialized cells within the brain, known as serotonergic neurons. MDMA use and abuse therefore has the potential to give rise to a major public health problem. In particular, the development of neurotoxicity requires metabolism of MDMA by the liver into a metabolite that subsequently enters the brain. Because the proteins responsible for both the metabolism of MDMA and the brain uptake of the metabolites vary considerably between different individuals, knowledge of the relative contribution of these different processes to the neurotoxicity of MDMA will assist in our ability to identify those individuals who may be more susceptible to the adverse effects of MDMA (and perhaps to similar drugs).