Stone D M, Hanson G R, Gibb J W
Department of Pharmacology and Toxicology, University of Utah, Salt Lake City 84112.
J Neurochem. 1989 Aug;53(2):572-81. doi: 10.1111/j.1471-4159.1989.tb07372.x.
The activity of tryptophan hydroxylase (EC 1.14.16.4) from rat brain was significantly decreased 1 h following a single systemic injection of 3,4-methylenedioxymethamphetamine (MDMA) when assessed ex vivo by radioenzymatic assay or in vivo by the quantitation of 5-hydroxytryptophan accumulation following central L-aromatic amino acid decarboxylase inhibition. Recovery of enzymatic activity in vivo, which occurred within 24 h of low-dose MDMA treatment, appeared not to involve synthesis of new enzyme protein, because the return of enzymatic activity was not prevented by prior cycloheximide. Acutely MDMA-depressed cortical tryptophan hydroxylase activity could be completely restored in vitro by a prolonged (20-24 h) anaerobic incubation in the presence of dithiothreitol and Fe2+ at 25 degrees C; partial reconstitution occurred when 2-mercapto-ethanol was substituted for dithiothreitol. Cortical tryptophan hydroxylase acutely inactivated by methamphetamine or p-chloroamphetamine could be similarly reactivated. MDMA-inactivated cortical tryptophan hydroxylase derived from rats killed later than 3 days after drug treatment could not be significantly reactivated under the conditions described above, indicating the development of irreversible enzymatic damage. Kinetic analysis of enzyme reactivation revealed an approximate doubling of enzyme Vmax with no change in enzyme affinity for either substrate, tryptophan, or pterin cofactor. These studies suggest that MDMA and its congeners inactivate central tryptophan hydroxylase by inducing oxidation of key enzyme sulfhydryl groups. The reactivation capacity of drug-inactivated enzyme at various times after MDMA treatment may provide a means of assessing the development of MDMA-induced neurotoxicity.
通过放射性酶法体外评估或通过抑制中枢L-芳香族氨基酸脱羧酶后定量5-羟色氨酸积累体内评估发现，单次全身注射3,4-亚甲基二氧甲基苯丙胺（摇头丸）1小时后，大鼠脑内色氨酸羟化酶（EC 1.14.16.4）的活性显著降低。低剂量摇头丸治疗后24小时内体内酶活性的恢复似乎不涉及新酶蛋白的合成，因为酶活性的恢复并未被预先使用的环己酰亚胺所阻止。急性摇头丸抑制的皮质色氨酸羟化酶活性在体外可通过在25℃下于二硫苏糖醇和Fe2+存在下延长（20 - 24小时）厌氧孵育而完全恢复；当用2-巯基乙醇替代二硫苏糖醇时会发生部分重构。被甲基苯丙胺或对氯苯丙胺急性灭活的皮质色氨酸羟化酶可类似地被重新激活。药物治疗后3天以上处死的大鼠来源的摇头丸灭活的皮质色氨酸羟化酶在上述条件下不能被显著重新激活，表明发生了不可逆的酶损伤。酶重新激活的动力学分析显示酶Vmax大约增加一倍，而酶对底物色氨酸或蝶呤辅因子的亲和力没有变化。这些研究表明，摇头丸及其同系物通过诱导关键酶巯基的氧化来使中枢色氨酸羟化酶失活。摇头丸治疗后不同时间药物灭活酶的重新激活能力可能提供一种评估摇头丸诱导的神经毒性发展的方法。
