MRI contrast for molecular and cellular imaging of the brain

用于大脑分子和细胞成像的 MRI 对比

• 批准号: 8557065
• 负责人: Alan Koretsky
• 金额: $ 269.07万
• 依托单位: NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8557065
• 关键词: Adult; Affect; Animals; Binding; Biological Assay; Biological Process; Blood - brain barrier anatomy; Brain; Calcium; Calcium Channel; Cell physiology; Cells; Clinical; Complex; Contrast Media; Cytoplasmic Granules; Detection; Development; Disease; Effectiveness; Endocytosis; Endosomes; Enzymes; Exposure to; Gene Expression; Generations; Goals; Gold; Hour; Human; Image; Imaging Techniques; Immune; Immunologic Surveillance; In Vitro; Inflammation; Injection of therapeutic agent; Interneurons; Ions; Iron; Isotopes; Label; Lead; Life; Ligands; Location; Lysosomes; Magnetic Resonance Imaging; Manganese; Measures; Metals; Microfabrication; Modeling; Molecular; Monitor; Neurons; Odors; Particle Size; Peripheral; Phase; Polymers; Population; Positron-Emission Tomography; Pre-Clinical Model; Process; Property; Rattus; Relaxation; Reporter; Reporting; Resolution; Rodent; Shapes; Silicon Dioxide; Solutions; Structure; Synapses; T-Lymphocyte; Techniques; Time; Tissues; Transferrin; Translating; Transplantation; Virus Diseases; Work; base; biomaterial compatibility; cell motility; deprivation; in vivo; interest; iron oxide; manganese chloride; migration; molecular imaging; molecular/cellular imaging; nanoparticle; nanosized; nerve stem cell; neuron development; novel; olfactory bulb; particle; receptor; response; sensor; subventricular zone; success; voltage

There is rapidly increasing interest in developing molecular imaging approaches that enable traditional radiological imaging techniques to obtain a wide range of information about molecular and cellular processes that occur in normal and diseased tissue. A range of information is considered important such as the ability to monitor cell migration, the development of reporters that enable imaging of gene expression, the development of robust strategies to image receptors, and the development of environmentally sensitive agents that can be used to detect the presence of specific enzymes or monitor changes in ion status. The long term goals of this work are to develop strategies that enable MRI contrast that is sensitive to a wide range of molecular and cellular processes. This work builds on over 15 years of work where we have demonstrated the first MRI strategy for detecting gene expression, the first MRI approach for monitoring a surrogate of calcium influx, the first MRI approach for performing neuronal track tracing, and the first MRI approach for monitoring the migration of single cells in vivo. These all represented initial reports by any radiological imaging technique which enabled these processes to be measured. These techniques are finding widespread application to imaging pre-clinical models of a broad range of diseases. Over the past year we have made progress in all of the specific aims. Aim 1: Develop iron oxide based contrast for labeling and imaging the migration of endogenous neural stem cells. Over the past few years we have demonstrated the unique advantages of micron sized iron oxide particles for MRI of specific cells. Single cells can be detected and indeed, single particles within single cells can be detected. The main paradigm for MRI of cell migration is to label cells ex vivo and monitor migration after transplantation into an animal. These studies have traditionally required very efficient labeling using nano sized particles. The ability to detect a single particle enables inefficient labeling strategies. In particular, over the past few years we have demonstrated that injection of particles into the ventricles of the rat brain enables particles to be taken up by neural precursors in the subventricular zone and MRI can monitor the migration of cells to the oflactory bulb. Over the past year we have completed a study to determine if daily exposure to odor for two weeks affects the migration of these new cells. The only significant effect was an increase in number of new neurons in the mitral cell layer of the olfactory bulb. These cells have been shown to be simular to granule layer interneurons. We have begun to monitor the response to odor deprivation using naris occlusion. In addition, we are measuring the migratory rates of cells to determine if these rates are ever modulated. We are extending our ability to image the migration of single cells through the entire brain to study immune brain interactions in a model of virus infection. This work has required working out effective strategies to label T cells, a population of cell that has been very difficult to label. This offers the unique potential to follow the low level peripheral immune surveillance that occurs in the normal adult brain as well as any changes due to inflammation or degeneration. Aim 2: Apply microfabrication techniques to manufacture unique metal structures that may be valuable for MRI contrast. Iron oxide particles commonly used for MRI are very potent contrast agents enabling detection of single mciron sized particles. However, due to bulk phase manufacture of particles they are not very uniform and they do not contain very high content of metal. A solution to this problem is to use modern microfabrication techniques to manufacture metal based, micron sized contrast agents. To begin this work we have explored a variety of approachs to microfabrication oof MRI contrast agents. Over the past few years we have shown that double dougnut and cylinder structures offer unique advantages for distinguishing particles. Microfabriaction of simple iron discs lead to 10 times more potent contrast than presently available particles. Over the past year wein order to translate this work to tracking cells we have developed strategies to effectively gold coat the particles enbaling stability and biocompatibility in living cells. Furthermore, we have demonstrated that we can accurately locate these microfabricated particles to accuracy abotu a facotr of two higher than than the pixel resolution enabling very high determination of the location. This will enable tracking of particles or cell loaded particles to higher resolution than is available from standard MRI. Finally, we have explored new shapes that give interesting MRI properties. Aim 3: Develop novel delivery mechanisms to extend the applicability of manganese enhanced MRI. Over the past ten years we have demonstrated the remarkable utility of the manganese ion for MRI contrast. Manganese ion enters cells on ligand or voltage gated calcium channels and so can be used as an MRI agent to monitor calcium influx. Once inside of neurons, manganese will move in an anterograde direction and cross functional synapses enabling neuronal networks to be imaged with MRI. Finally, manganese given systemically gives cytoarchitectural information about the rodent brain. These successes have us interested in broadening the ways in which manganese ion can be delivered to cells. Over the past couple of years we have made transferrin-manganese complexes. When bound to transferrin manganese is a poor MRI contrast agent. However, when transferrin is taken up by cells it can release manganese which is then trapped intracellularly. Thus, transferrin manganese is an agent that monitors the successful endocytosis of the transferrin by its receptor. We have demonstrated the same effects with MnOxide based nanoparticles. At pH 7 MnO is insoluble and a very weak contrast agent. At low pH, as found in endosomes/lysosomes these particles dissolve greatly increasing MRI relaxation effects. We have completed studies that show that a silica coat on these particles delays dissolution for up to four hours both in vitro and in vivo. Particles injected into the brain had slower rates of contrast development and neuronal tracing then did injection of MnCl2. This opens the possibility of making coatings that can be enzymatically degraded enabling specific in vivo assay of these enzymes. We have demonstrated another approach to makin Mn nanoparticles using block co-polymer synthesis. The first generation of these agents have very high relaxivities and the relaxivity can be modulated. Finally, we have begun to explore ways to translate the advantages of Manganese enhanced MRI to human use one makes use of manganese postiron emitting isotopes that will enable PET to obtain similar information that can be obtained with manganese enhanced MRI. Aim 4: Develop strategies that enable cellular processes to alter the relaxivity of MRI contrast agents. In specific aim 3 we demonstrated a way in which a normal biological process (endocytosis of transferrin-Mn or MnO particles) can alter the effectiveness of an MRI contrast agent. It would be very exciting to find ways in which this can occur which are sensitive to other biological processes. To this end we have begun to explore ways in which the microfabricated particles produced under Aim 2 can be modulated. Over the past year we have confirmed that the microfabricated particles can be made into a pH sensor . The strategy used is generalizable to sense many other processes. The block co-polymer agents offer many possibilities for making environmentally sensitive MRI agents and these will be explored over the next year.

人们对开发分子成像方法的兴趣迅速增加，这些方法使传统的放射成像技术能够获得有关正常和患病组织中发生的分子和细胞过程的广泛信息。 一系列信息被认为是重要的，例如监测细胞迁移的能力、能够对基因表达成像的报告基因的开发、对受体成像的稳健策略的开发以及可用于检测特定酶的存在或监测离子状态变化的环境敏感剂的开发。 这项工作的长期目标是开发策略，使 MRI 对比对广泛的分子和细胞过程敏感。 这项工作建立在超过 15 年的工作基础上，其中我们展示了第一个用于检测基因表达的 MRI 策略、第一个用于监测钙流入替代物的 MRI 方法、第一个用于执行神经元轨迹追踪的 MRI 方法，以及第一个用于监测体内单细胞迁移的 MRI 方法。 这些都代表了任何能够测量这些过程的放射成像技术的初步报告。 这些技术广泛应用于多种疾病的临床前模型成像。 过去一年，我们在所有具体目标上都取得了进展。 目标 1：开发基于氧化铁的造影剂，用于标记内源性神经干细胞的迁移并对其进行成像。 在过去的几年中，我们已经展示了微米级氧化铁颗粒用于特定细胞 MRI 的独特优势。 可以检测单个细胞，并且实际上可以检测单个细胞内的单个颗粒。 细胞迁移 MRI 的主要范例是离体标记细胞并监测移植到动物体内后的迁移。 传统上，这些研究需要使用纳米尺寸的颗粒进行非常有效的标记。 检测单个粒子的能力使得标记策略效率低下。特别是，在过去的几年里，我们已经证明，将粒子注射到大鼠脑室中可以使粒子被脑室下区的神经前体细胞吸收，并且 MRI 可以监测细胞向泌乳球的迁移。在过去的一年里，我们完成了一项研究，以确定连续两周每天接触气味是否会影响这些新细胞的迁移。唯一显着的效果是嗅球二尖瓣细胞层中新神经元数量的增加。 这些细胞已被证明与颗粒层中间神经元相似。我们已经开始使用鼻孔阻塞来监测对气味剥夺的反应。 此外，我们正在测量细胞的迁移速率，以确定这些速率是否受到调节。 我们正在扩展我们对单个细胞在整个大脑中的迁移进行成像的能力，以研究病毒感染模型中的免疫脑相互作用。 这项工作需要制定有效的策略来标记 T 细胞，这是一种非常难以标记的细胞群。 这为跟踪正常成人大脑中发生的低水平外周免疫监视以及由于炎症或退化引起的任何变化提供了独特的潜力。 目标 2：应用微加工技术来制造可能对 MRI 对比有价值的独特金属结构。 常用于 MRI 的氧化铁颗粒是非常有效的造影剂，能够检测单个微米大小的颗粒。 然而，由于颗粒的本体相制造，它们不是很均匀，并且它们不包含很高含量的金属。 该问题的解决方案是使用现代微加工技术来制造基于金属的微米级造影剂。 为了开始这项工作，我们探索了多种 MRI 造影剂微加工方法。在过去的几年中，我们已经证明双环形和圆柱结构为区分颗粒提供了独特的优势。 简单铁盘的微加工可产生比现有颗粒强 10 倍的对比度。 在过去的一年里，为了将这项工作转化为跟踪细胞，我们制定了有效地对颗粒进行金涂层的策略，以保证活细胞的稳定性和生物相容性。此外，我们已经证明，我们可以准确地定位这些微加工颗粒，其精度比像素分辨率高出大约两倍，从而能够非常高地确定位置。 这将使粒子或细胞负载粒子的跟踪达到比标准 MRI 更高的分辨率。 最后，我们探索了能够提供有趣的 MRI 特性的新形状。 目标 3：开发新的传递机制以扩展锰增强 MRI 的适用性。 在过去的十年中，我们已经证明了锰离子在 MRI 对比方面的显着效用。 锰离子通过配体或电压门控钙通道进入细胞，因此可用作 MRI 试剂来监测钙流入。 一旦进入神经元内部，锰将沿顺行方向移动并跨功能突触，使神经元网络能够通过 MRI 进行成像。 最后，系统地给予锰可以提供有关啮齿动物大脑的细胞结构信息。 这些成功使我们对拓宽将锰离子输送到细胞的方式感兴趣。在过去的几年里，我们已经制备了转铁蛋白-锰复合物。 当与转铁蛋白结合时，锰是一种较差的 MRI 造影剂。 然而，当转铁蛋白被细胞吸收时，它可以释放锰，然后将其捕获在细胞内。 因此，转铁蛋白锰是一种通过其受体监测转铁蛋白成功内吞作用的试剂。 我们已经证明了基于氧化锰的纳米颗粒具有相同的效果。 pH 值为 7 时，MnO 不溶，是一种非常弱的造影剂。 在低 pH 值下，正如在内体/溶酶体中发现的那样，这些颗粒会溶解，大大增加 MRI 松弛效果。 我们完成的研究表明，这些颗粒上的二氧化硅涂层可在体外和体内延迟溶解长达四个小时。 与注射 MnCl2 相比，注射到大脑中的粒子的对比显影和神经元追踪速度较慢。这开启了制造可被酶降解的涂层的可能性，从而能够对这些酶进行特定的体内测定。 我们已经展示了另一种使用嵌段共聚物合成来制造锰纳米粒子的方法。第一代这些试剂具有非常高的弛豫率并且弛豫率可以调节。 最后，我们已经开始探索如何将锰增强 MRI 的优势转化为人类使用，即利用锰后铁发射同位素，使 PET 能够获得与锰增强 MRI 可以获得的类似信息。 目标 4：制定策略，使细胞过程能够改变 MRI 造影剂的弛豫度。 在具体目标 3 中，我们展示了一种正常生物过程（转铁蛋白-Mn 或 MnO 颗粒的内吞作用）可以改变 MRI 造影剂有效性的方法。 找到对其他生物过程敏感的实现这种情况的方法将是非常令人兴奋的。 为此，我们已经开始探索对 Aim 2 下产生的微加工粒子进行调制的方法。 在过去的一年里，我们已经证实微加工颗粒可以制成pH传感器。所使用的策略可推广到感知许多其他过程。 嵌段共聚物试剂为制造环境敏感的 MRI 试剂提供了多种可能性，这些将在明年进行探索。