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，但其使用受到连续使用后发生的严重副作用的限制。其原因尚不清楚，但在左旋多巴治疗期间，组织左旋多巴大大超过了正常存在的几乎检测不到的水平，因此左旋多巴的过载失调了儿茶酚胺系统。我们的假设提出，感测高水平的L-多巴和DA作为底物的酶，如L-芳香族氨基酸脱羧酶（LAAD）、多巴胺（DA）-β羟化酶（DBH）和儿茶酚-O-甲基转移酶（COMT），以及催化用于L-多巴和DA代谢的辅因子S-腺苷甲硫氨酸合成的甲硫氨酸腺苷转移酶（MAT）被诱导。COMT和MAT的诱导将增加L-多巴和DA的代谢，并将产生干扰甲基代谢物。DBH的诱导将产生异位去甲肾上腺素（NE），其可稀释DA在黑质纹状体通路中的功效。诱导的LAAD会加速左旋多巴对DA的催化作用，引起DA峰。DA反过来又会引起LAAD的反馈抑制，产生可能有助于引起开关效应的DA脉动供应。"我们的假设基于初步结果，表明左旋多巴诱导COMT和MAT，这些酶反过来代谢左旋多巴和DA。左旋多巴也诱导大脑LAAD。DA的甲基代谢产物3-甲氧基酪胺（3-MT）和3，4-二甲基苯乙胺（DIMPEA）分别降低和增加运动活动和DA受体结合，并且在注射L-多巴的PD大鼠模型和L-多巴治疗的PD患者中出现高水平的3-O-甲基多巴（3-OMD）。3-OMD降低了左旋多巴的疗效和DA的转换。研究还发现左旋多巴治疗PD患者的心律失常是由NE升高引起的。  具体目的是：（1）进一步研究L-多巴对COMT、MAT、LAAD和DBH的诱导作用。（#2）确定LAAD的诱导是否引起DA浪涌，并且DA反过来抑制LAAD，从而引起可能与开关效应相关的DA的脉动供应。（#3）定位黑质纹状体神经元中的DBH诱导和NE产生，并确定NE是否与DA从纹状体组织共同释放。（#4）评估3-O-甲基多巴，3-MT和DIMPEA的行为和受体效应，以了解它们是否有助于左旋多巴的副作用。"这些研究将集中在基底神经节的变化。正在研究的生物化学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，该项目的前景是找到在L-多巴的有益作用不受影响时靶向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.