The selective serotonergic neurotoxicity of 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) depends on their systemic metabolism. We have recently shown that inhibition of brain endothelial cell γ-glutamyl transpeptidase (γ-GT) potentiates the neurotoxicity of both MDMA and MDA, indicating that metabolites that are substrates for this enzyme contribute to the neurotoxicity. Consistent with this view, glutathione (GSH) and N -acetylcysteine conjugates of α-methyl dopamine (α-MeDA) are selective neurotoxicants. However, neurotoxic metabolites of MDMA or MDA have yet to be identified in brain. Using in vivo microdialysis coupled to liquid chromatography-tandem mass spectroscopy and a high-performance liquid chromatography-coulometric electrode array system, we now show that GSH and N -acetylcysteine conjugates of N -methyl-α-MeDA are present in the striatum of rats administered MDMA by subcutaneous injection. Moreover, inhibition of γ-GT with acivicin increases the concentration of GSH and N -acetylcysteine conjugates of N -methyl-α-MeDA in brain dialysate, and there is a direct correlation between the concentrations of metabolites in dialysate and the extent of neurotoxicity, measured by decreases in serotonin (5-HT) and 5-hydroxyindole acetic (5-HIAA) levels. Importantly, the effects of acivicin are independent of MDMA-induced hyperthermia, since acivicin-mediated potentiation of MDMA neurotoxicity occurs in the context of acivicin-mediated decreases in body temperature. Finally, we have synthesized 5-( N -acetylcystein- S -yl)- N -methyl-α-MeDA and established that it is a relatively potent serotonergic neurotoxicant. Together, the data support the contention that MDMA-mediated serotonergic neurotoxicity is mediated by the systemic formation of GSH and N -acetylcysteine conjugates of N -methyl-α-MeDA (and α-MeDA). The mechanisms by which such metabolites access the brain and produce selective serotonergic neurotoxicity remain to be determined.
3,4-亚甲二氧基苯
丙胺(
MDA)和3,4-亚甲二氧基甲基苯
丙胺(M
DMA,摇头丸)的选择性
血清素能神经毒性取决于它们的全身代谢。我们最近的研究表明,抑制脑内皮细胞的γ-谷
氨酰转肽酶(
γ-GT)会增强M
DMA和
MDA的神经毒性,这表明作为该酶底物的代谢物会导致神经毒性。与这一观点一致,
谷胱甘肽(GSH)和α-
甲基多巴胺(α-Me
DA)的N-乙酰半胱
氨酸共轭物是选择性神经毒剂。然而,尚未在大脑中发现亚甲二氧基甲基苯
丙胺或
MDA 的神经毒性代谢物。通过使用体内微透析法、
液相色谱-串联质谱法和高效
液相色谱-库仑计电极阵列系统,我们发现在皮下注射 M
DMA 的大鼠纹状体中存在 GSH 和 N - 乙酰半胱
氨酸共轭物 N - 甲基-α-Me
DA。此外,用
阿西维辛抑制
γ-GT会增加脑透析液中GSH和N-甲基-α-Me
DA的N-乙酰半胱
氨酸共轭物的浓度,而且透析液中代谢物的浓度与神经毒性程度直接相关,神经毒性程度通过
血清素(5-HT)和
5-羟基吲哚乙酸(5-H
IAA)
水平的下降来衡量。重要的是,
阿西维辛的作用与M
DMA诱导的高热无关,因为
阿西维辛介导的M
DMA神经毒性增效是在
阿西维辛介导的体温下降的背景下发生的。最后,我们合成了 5-( N -acetylcystein- S -yl)- N -methyl-α-Me
DA 并确定它是一种相对强效的
血清素能神经毒剂。总之,这些数据支持以下论点,即亚甲二氧基甲基苯
丙胺介导的
血清素能神经毒性是由 N -甲基-α-Me
DA(和 α-Me
DA)的 GSH 和 N -乙酰半胱
氨酸共轭物的全身性形成介导的。这些代谢物进入大脑并产生选择性
血清素能神经毒性的机制仍有待确定。