EPR Imaging of Brain O2 in Drug Abuse

描述（由申请人提供）：分子氧在脑生理控制中起着核心作用，如果没有其他原因，O2是酶的终端电子受体，对重要神经递质的生物合成至关重要：多巴胺，血清素和去甲肾上腺素。因此，氧气水平的变化直接影响体内平衡。令人惊讶的是，考虑到氧在脑生理学中的重要性，用不同的成像方式来定量大脑中的氧及其作为药物滥用（如甲基苯丙胺）的变化还没有实现。分子氧具有顺磁性，使其他顺磁性物质（如氮氧化物）的EPR谱线变宽。这些化合物的EPR谱线宽度的测量变化已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光谱和合适的自旋探针的发展；在体内、原位和实时可靠地估计局部O2浓度是可行的。发展微创EPR成像以定量脑内O2的一个障碍是难以将O2敏感探针运送到该器官。在此，我们建议合成对O2敏感的自旋探针，例如氮氧化物，可以传递到大脑并分布在整个组织中，可用于绘制和定量该组织中的O2。基于一系列的初步研究，我们证明了将一种氮氧化物通过小鼠血脑屏障进入大脑的可行性。目前的提案将侧重于对甲基苯丙胺的原理验证，甲基苯丙胺是一种日益滥用的兴奋剂，也导致不安全的性行为增加。已知甲基苯丙胺长期服用可导致神经毒性，毒性涉及自由基和氧还原物质。6-9因此，这项资助的目的是开发氮氧化物和EPR作为一种成像方式来绘制和定量小鼠大脑中的氧气，并研究甲基苯丙胺对其中的氧气水平的影响，从而为研究其作用机制和神经毒性提供一种补充方法。为达成此奖助金的目标，将会有三个具体目标。1. 合成特别设计的氮氧化物，使它们能够通过血脑屏障进入大脑。2. 确定在Specific Aim #1中合成的化合物的药代动力学和药效学特征，确定硝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光谱成像和定量O2。3. 使用Specific Aim #1和#2的优化参数，获得甲基苯丙胺急性处理小鼠脑中pO2分布的变化。分子氧在控制大脑生理方面起着核心作用，因为它对重要神经递质的生物合成至关重要：多巴胺、血清素和去甲肾上腺素。这项拨款旨在发展EPR成像，作为研究滥用药物对脑氧使用影响的工具，这可能对了解滥用药物的人的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.