EPR Imaging of Brain O2 in Drug Abuse

描述(申请人提供)：分子氧在大脑生理控制中发挥中心作用，如果没有其他原因，O2是酶的最终电子受体，这些酶对重要的神经递质：多巴胺、5-羟色胺和去甲肾上腺素的生物合成至关重要。因此，氧气水平的变化直接影响体内平衡。令人惊讶的是，鉴于O2在脑生理学中的重要性，还没有实现对大脑中O2的定量以及因滥用药物(如甲基苯丙胺)而导致的变化的不同成像模式。分子氧是顺磁性的，拓宽了其他顺磁性物种的EPR谱线，如氮氧化物。这些化合物的EPR谱线宽度的测量变化被用来估计均相溶液中的O2浓度。随着具有成像能力的低频EPR光谱和适当的自旋探针的发展，在活体、现场和实时可靠地估计局部O2浓度是可行的。发展微创EPR成像以定量大脑中的O2的一个障碍是将O2敏感的探针传输到这个器官的困难。在这里，我们建议合成氧敏感的自旋探针，例如氮氧化物，它可以传递到大脑并分布在整个脑组织，可以用来定位和定量这个组织中的氧。在一系列初步研究的基础上，我们证明了氮氧化物通过小鼠血脑屏障进入大脑的可行性。目前的提案将重点放在甲基苯丙胺的原则证明上，甲基苯丙胺是一种日益滥用的兴奋剂，也导致不安全性行为的增加。众所周知，甲基苯丙胺长期给药会导致神经毒性，这种毒性涉及自由基和O2还原物种。6-9因此，这笔赠款的目标是开发氮氧化物和EPR作为一种成像手段，以绘制和定量小鼠大脑中的O2，并研究甲基苯丙胺对其中O2水平的影响，从而为研究其作用机制和神经毒性提供一种补充方法。为了实现这笔赠款的目标，将解决三个具体目标。1.合成专门设计的氮氧化物，使其能够穿过血脑屏障进入大脑。2.确定针对特定目标#1合成的化合物的药代动力学和药效学特征，确定氮氧基环上的哪些结构特征促进高浓度进入大脑，足以通过低频EPR波谱成像和定量O2。3.利用特定目标#1和#2的优化参数，获得甲基苯丙胺急性处理后小鼠脑内PO2分布的变化。分子氧在脑生理控制中发挥核心作用，因为它对重要神经递质：多巴胺、5-羟色胺和去甲肾上腺素的生物合成至关重要。这笔赠款旨在开发EPR成像，作为研究滥用药物对大脑氧气使用的影响的工具，这可能对了解药物滥用人类的大脑功能障碍至关重要。

DESCRIPTION (provided by applicant): Molecular oxygen plays a central role in the control of brain physiology, if for no other reason than O2 is the terminal electron acceptor for enzymes that are crucial to the biosynthesis of the important neurotransmitters: dopamine, serotonin and norepinephrine. And, thus changes in O2 levels directly impact homeostasis. Surprisingly, given the significance of O2 in brain physiology, the quantitation of O2 in the brain and changes thereof as the result of drug abuse, such as methamphetamine, with different imaging modalities has not been achieved. Molecular oxygen, being paramagnetic, broadens the EPR spectral lines of other paramagnetic species, such as nitroxides. Measured changes in EPR spectral line width of these compounds have been used to estimate O2 concentrations in homogenous solutions. With development of low-frequency EPR spectroscopy with imaging capability and the appropriate spin probes; it is feasible to reliably estimate local O2 concentrations in vivo, in situ and in real time. An obstacle in the development of minimally invasive EPR imaging to quantitate O2 in the brain is the difficulty of transporting O2-sensitive probes to this organ. Herein, we propose to synthesize O2-sensitive spin probes, e.g., nitroxides, that can be delivered to the brain and distributed throughout, which can be used to map and quantitate O2 in this tissue. Based on a series of pilot studies, we demonstrated the feasibility of transporting a nitroxide across a mouse blood-brain barrier and into the brain. The current proposal will focus on a proof-of-principle with methamphetamine, an increasingly abused stimulant that is also leading to an increase in unsafe sexual practices. Methamphetamine is known to lead to neurotoxicity on chronic administration, and that the toxicity involves free radicals and O2 reduction species.6-9 Thus, the Objective of this grant is to develop nitroxides and EPR as an imaging modality to map and quantitate O2 in mouse brain and to study the effects methamphetamine has on O2 levels therein, thereby allowing a complimentary method of studying its mechanism of action and neurotoxicity. To accomplish the Objective of this grant, three Specific Aims will be addressed. 1. Synthesize nitroxides specifically designed that will allow their transport across the blood-brain barrier into the brain. 2. Determine the pharmacokinetic and pharmacodynamic profiles of compounds synthesized in Specific Aim #1, determining what structural features on the nitroxyl ring promote high concentrations into brain, sufficient to image and quantitate O2 by low-frequency EPR spectroscopy. 3. Obtain changes in pO2 distribution in mouse brain acutely treated with methamphetamine, using the optimized parameters from Specific Aim #1 and #2. Molecular oxygen plays a central role in the control of brain physiology, as it crucial to the biosynthesis of the important neurotransmitters: dopamine, serotonin and norepinephrine. This grant is designed to develop EPR imaging as a tool to study the effects of drugs of abuse on brain oxygen use, which may be critical to understanding brain dysfunction in drug abusing humans.