L-DOPA OVERLOAD: MECHANISMS FOR THE SIDE EFFECTS.

描述（由申请人提供）：左旋多巴是多巴胺（DA）的前体，是治疗帕金森病（PD）症状最有效的药物，但持续使用后会出现严重的副作用，限制了其使用。原因尚不清楚，但在左旋多巴治疗期间，组织中的左旋多巴大大超过了正常存在的几乎无法检测到的水平，因此左旋多巴过量会对儿茶酚胺系统产生失调。我们的假设提出，感应高水平左旋多巴和DA作为底物的酶，如L-芳香氨基酸脱羧酶（LAAD）、多巴胺(DA)- β羟化酶（DBH）和儿茶酚- o -甲基转移酶（COMT），以及催化合成辅助因子s -腺苷蛋氨酸的蛋氨酸腺苷转移酶（MAT），用于左旋多巴和DA的代谢。COMT和MAT的诱导会增加左旋多巴和DA的代谢，并产生干扰性的甲基代谢物。DBH的诱导会产生异位去甲肾上腺素（NE），可能会稀释DA在黑质纹状体通路中的作用。诱导的LAAD会加速左旋多巴对DA的催化作用，导致DA激增。DA反过来又会引起LAAD的反馈抑制，产生脉冲式的DA供应，这可能有助于引起开关效应。“我们的假设基于左旋多巴诱导COMT和MAT的初步结果，这两种酶反过来代谢左旋多巴和DA。左旋多巴也能诱导脑LAAD。DA的甲基代谢物3-甲氧基酪胺（3- mt）和3,4-二甲氧基苯基乙胺（DIMPEA）分别降低和增加了左旋多巴注射的PD大鼠模型和左旋多巴治疗的PD患者的运动活性和DA受体结合和3- o -甲基多巴（3- OMD）的高水平。3- OMD降低左旋多巴的疗效和DA的周转。研究还发现左旋多巴治疗的PD患者心律失常是由NE升高引起的。具体目的是：(1)进一步研究左旋多巴对COMT、MAT、LAAD和DBH的诱导作用。(2)确定LAAD的诱导是否会导致DA浪涌，而DA反过来抑制LAAD，导致可能与开关效应有关的DA脉动供应。（# 3）在黑质纹状体神经元中定位DBH诱导和NE的产生，并确定NE是否与纹状体组织中的DA共同释放。评估3- o -甲基多巴、3-MT和DIMPEA的行为和受体效应，以了解它们是否会导致左旋多巴的副作用。“研究将集中在基底神经节的变化上。正在研究的生化途径是药物作用的关键，其结果可以很容易地转化为治疗，因此，该项目的前景是在左旋多巴的有益作用不会受到损害的情况下，找到针对特定酶和代谢途径的药物。

DESCRIPTION (provided by applicant):  L-dopa, the precursor of dopamine (DA), is the most effective drug used for treating the symptoms of Parkinson's disease (PD), but its use is limited by serious side effects that occur after continuous use. The causes are unknown, but during L-dopa treatments tissue L-dopa greatly exceeds the barely detectable levels that normally exist, therefore the overload of L-dopa dys-regulates the catecholamine system. Our hypothesis proposes that enzymes that sense the high levels of L-dopa and DA as substrates, such as L- aromatic amino acid decarboxylase (LAAD), dopamine (DA)-beta hydroxylase (DBH) and catechol-O- methyltransferase (COMT), as well as methionine adenosyltransferase (MAT) that catalyses the synthesis of the cofactor, S-adenosylmethionine, for the metabolism of L-dopa and DA, are induced. The induction of COMT and MAT will increase the metabolism of L-dopa and DA and will generate interfering methyl metabolites. The induction of DBH will produce ectopic norepinephrine (NE) that may dilute the efficacy of DA in the nigrostriatal pathway. The induced LAAD will accelerate the catalysis of L-dopa to DA, causing DA surge. DA in turn will cause feedback inhibition of LAAD, generating a pulsatile supply of DA that may help to cause the on-off effects. "We base our hypothesis on preliminary results showing that L-dopa induced COMT and MAT, enzymes that, in turn, metabolize L-dopa and DA. L-dopa also induced brain LAAD. The methyl metabolites of DA, 3-methoxytyramine (3-MT) and 3,4-dimethoxyl-phenylethylamine (DIMPEA), respectively, decreased and increased motor activities and DA receptor binding and 3-O-methyldopa (3- OMD) occurred in high levels in rat models of PD injected with L-dopa and in L-dopa-treated PD patients. 3- OMD decreased the efficacy of L-dopa and the turnover of DA. Studies also found that cardiac arrhythmia in L-dopa-treated PD patients was caused by increased NE.  The specific aims are: (# 1) To further study the induction of COMT, MAT as well as LAAD and DBH by L-dopa. (# 2) Determine if the induction of LAAD causes DA surges and that DA in turn counter inhibits LAAD causing a pulsatile supply of DA that may be related to the on-off effects. (# 3) Localize DBH induction and NE production in nigrostriatal neurons and determine if NE is co-released with DA from striatal tissues. (#4) Evaluate the behavioral and receptor effects of 3-O-methyldopa, 3-MT and DIMPEA, to know if they contribute to the side effects of L-dopa. "The studies will focus on changes in the basal ganglia. The biochemical pathways being studied are at the crux of drug actions and the results can be readily translated into therapy, so, the outlook for the project is to find agents that will target specific enzymes and metabolic pathways at times when the beneficial effects of L-dopa will not be compromised.