Novel Neuroprotection by Caffeine in Parkinson's Disease

描述（改编自申请人摘要）：最近的流行病学研究 咖啡和其他含咖啡因的饮料的共同消费 显著降低患帕金森病的风险 (PD)，提高了咖啡因神经保护的可能性。许多CNS影响 咖啡因对A2 A亚型的拮抗作用 腺苷受体（A2 AR）。我们最近发现咖啡因和 氯苯乙烯-咖啡因（一种更特异的A2 A拮抗剂）以及遗传 A2 AR的失活都保护小鼠免受MPTP神经毒性。 此外，我们已经观察到A2 AR阻断或A2 A缺乏可以减少 体内毒性MPTP代谢物MPP+的水平。基于收敛性 流行病学和分子数据，我们假设咖啡因减弱 神经毒素诱导的多巴胺能神经元变性通过一种新的 A2 A依赖机制。我们建议（响应PA 99-054）： 系统研究咖啡因神经保护作用及其机制 在PD的MPTP模型中，使用互补的药理学和遗传学 A2 AR失活的方法。具体目标1将研究以下因素的影响： 咖啡因对MPTP诱导的神经毒性的影响 多巴胺能黑质纹状体神经元的功能障碍（即，多巴胺能神经元 黑质的损失，以及多巴胺含量的消耗， 纹状体中的再摄取位点）。咖啡因的效力和时间过程 对这些MPTP诱导的黑质纹状体病变的保护将是 确立了习具体目标2将确定咖啡因的初始机制， 在MPTP毒性衰减中的作用。药理学考虑 咖啡因作为神经保护候选介质的已知分子靶点 将通过比较A1的特异性抑制剂的作用来进行 受体，A2受体，GABAA受体和磷酸二酯酶活性， MPTP模型将对A2 AR的参与进行更明确的演示 通过比较咖啡因在野生型和A2 AR敲除小鼠中的作用。 具体目标3将探讨A2 AR介导的两种可能的机制。 咖啡因的神经保护作用我们将在体内研究MPTP代谢， 单胺氧化酶活性在体外追求的可能性，改变 神经毒素代谢有助于咖啡因的神经保护作用。 最后，基于A2 AR阻断可减少纹状体谷氨酸和 多巴胺释放，我们将评估咖啡因和A2 AR失活的能力， 以降低这些神经递质的潜在毒性细胞外水平 MPTP在体内诱导。这些实验共同建立了一种新的 在PD的MPTP模型中A2 AR失活的神经保护作用，以及 咖啡因可能降低患PD风险的潜在机制。 由于特异性A2 A受体拮抗剂现在被引入PD临床 他们的急性运动的好处，了解他们的影响， PD中潜在的神经变性过程可能具有相当大的治疗作用， 以及流行病学的重要性。

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.