Novel Neuroprotection by Caffeine in Parkinson's Disease

描述(摘自申请者摘要)：最新流行病学研究 已经强烈地将咖啡和其他咖啡因的消费联系在一起 饮料可显著降低患帕金森氏症的风险 (PD)，增加了咖啡因保护神经的可能性。许多中枢神经系统效应 咖啡因的作用归因于它对A2a亚型的拮抗作用 腺苷受体(A2AR)。我们最近发现咖啡因和 氯苯乙酰咖啡因(一种更特异的A2A拮抗剂)以及基因 A2AR的失活对小鼠的MPTP神经毒性都有保护作用。 此外，我们还观察到，A2AR阻断或A2A缺乏可以减少 体内有毒的MPTP代谢产物MPP+的水平。以融合为基础 根据流行病学和分子数据，我们假设咖啡因可以减弱 神经毒素通过一种新的方式诱导多巴胺能神经元变性 一种依赖于2a的机制。我们建议(回应PA 99-054) 咖啡因诱导的神经保护及其机制的系统表征 在PD的MPTP模型中使用互补的药理学和遗传学 A2AR失活的方法。特定目标1将调查以下因素的影响 咖啡因对MPTP神经毒性的影响 多巴胺能黑质纹状体神经元(即多巴胺能神经元)功能障碍 黑质的损失，以及多巴胺含量的减少和 纹状体中的重摄取部位)。咖啡因的效力和时间进程 对MPTP诱导的黑质纹状体损害的保护将是 已经成立了。特定目标2将确定咖啡因的初始机制 在减弱MPTP毒性方面的作用。的药理学考量 咖啡因作为神经保护候选介体的已知分子靶点 将通过比较A1的特定抑制剂的效果来进行研究 血管内皮细胞受体、A2受体、GABAA受体与磷酸二酯酶活性 MPTP模型。将寻求更明确的A2AR参与演示 通过比较咖啡因对野生型和A2AR基因敲除小鼠的影响。 特指目标3将探索A2AR介导的两种看似合理的机制 咖啡因的神经保护作用。我们将研究MPTP在体内的代谢和 体外单胺氧化酶活性追求改变的可能性 神经毒素代谢有助于咖啡因的神经保护作用。 最后，根据A2AR阻断降低纹状体谷氨酸和 多巴胺释放，我们将评估咖啡因和A2AR失活的能力 降低这些神经递质的潜在毒性细胞外水平 用MPTP在体内诱导。这些实验加在一起将建立一种新的 A2AR失活在PD MPTP模型中的神经保护作用 咖啡因可能降低帕金森病发病风险的潜在机制。 随着特异性A2a受体拮抗剂现已被引入帕金森病临床 对它们的急性运动益处进行试验，了解它们对 帕金森病潜在的神经退行性变过程可能具有相当大的治疗性， 以及流行病学的意义。

DESCRIPTION (Adapted from Applicant's Abstract): Recent epidemiological studies have strongly linked the common consumption of coffee and other caffeinated beverages to a significantly reduced risk of developing Parkinson's disease (PD), raising the possibility of neuroprotection by caffeine. Many CNS effects of caffeine have been attributed to its antagonistic actions on the A2A subtype of adenosine receptor (A2AR). We have recently found that caffeine and chlorostyryl-caffeine (a more specific A2A antagonist) as well as genetic inactivation of the A2AR all protect against MPTP neurotoxicity in mice. Furthermore, we have observed that A2AR blockade or A2A deficiency can reduce the levels of the toxic MPTP metabolite, MPP+ in vivo. Based on the convergence of epidemiological and molecular data, we hypothesize that caffeine attenuates neurotoxin-induced dopaminergic neuron degeneration through a novel A2A-dependent mechanism. We propose (in response to PA 99-054) to systematically characterize caffeine-induced neuroprotection and its mechanism in the MPTP model of PD using complementary pharmacological and genetic approaches to A2AR inactivation. Specific Aim 1 will investigate the effects of caffeine on MPTP-induced neurotoxicity by analyzing the death as well as dysfunction of dopaminergic nigrostriatal neurons (i.e., dopaminergic neuron loss in the substantia nigra, as well as depletion of dopamine content and re-uptake sites in the striatum). Caffeine's potency and time course of protection against these MPTP-induced nigrostriatal lesions will be established. Specific Aim 2 will determine caffeine's initial mechanism of action in the attenuation of MPTP toxicity. Pharmacological consideration of caffeine's known molecular targets as candidate mediators of neuroprotection will be pursued by comparing the effects of specific inhibitors of A1 receptors, A2 receptors, GABAA receptors and phosphodiesterase activity in the MPTP model. A more definitive demonstration of A2AR involvement will be pursued by comparing the effects of caffeine in wild-type and A2AR knockout mice. Specific Aim 3 will explore two plausible mechanisms of A2AR-mediated neuroprotection by caffeine. We will examine MPTP metabolism in vivo and monoamine oxidase activity in vitro to pursue the possibility that altered neurotoxin metabolism contributes to the neuroprotective effects of caffeine. Lastly, based on evidence that A2AR blockade reduces striatal glutamate and dopamine release, we will assess the ability of caffeine and A2AR inactivation to reduce the potentially toxic extracellular levels of these neurotransmitters induced by MPTP in vivo. Together these experiments stand to establish a novel neuroprotective role for A2AR inactivation in the MPTP model of PD, as well as a potential mechanism by which caffeine may reduce the risk of developing PD. As specific A2A receptor antagonists are now being introduced in PD clinical trials for their acute motor benefits, an understanding of their effects on the underlying neurodegenerative process in PD may be of considerable therapeutic, as well as epidemiological, significance.