Investigation of Zinc Neurochemistry by Optical Sensing and MRI

描述（由申请人提供）：本研究的长期目标是设计用于结合、可视化和定量神经生物系统中移动锌的分子传感器。大脑海马神经元突触前囊泡中的内源性锌储存在生理刺激下释放，在学习和记忆中发挥不完全确定的作用。类似的移动锌储存存在于嗅球（OB）处理气味信息，通过更直接的信号传导途径从鼻子传递。脑内不受控制的Zn2+释放与癫痫、缺血或钝性头部创伤后的损伤有关。为了研究这些神经化学现象，需要Zn2+响应传感器来跟踪生理和病理刺激下被动员离子的时空分布。传感器的设计、合成、评价和优化是本研究项目的主要内容。每个传感器最多有三个模块。最低限度，将有锌结合和锌报告单位。结合模块通常包括具有可变Zn2+亲和力的多齿配体，在神经元组织中对Zn2+的选择性优于竞争离子，以及快速，可逆的协调，以监测ms时间尺度上的生物变化。锌报告模块将是荧光或磷光，用于光学成像（OI）实验，或能够改变水弛豫速率，用于磁共振成像（MRI）研究。荧光报告包括山蒽酮和单壁碳纳米管衍生物。磷光传感器是基于环金属化铱（III）配合物。MRI结构利用锰（III）卟啉。采用附加可选的第三个模块将基于光致发光的锌传感器定位到程序化的细胞靶标上，以研究生理或病理刺激后信号转导通路中特定位点的Zn2+动力学。一个相关的目标是制备锌选择性，快速螯合剂，用于结合研究移动Zn2+的生物学功能。锌传感器和螯合剂的热力学、动力学、光物理和理论研究将指导合成方向的改进，以优化其应用价值。具体应用包括通过OI评估关于移动锌在海马苔藓纤维突触和OB肾小球神经传递中的作用的假设，以及在生理和病理条件下海马移动锌活性的MRI可视化。这个项目与公共卫生有关，因为它将提供一种方法来检验关于流动Zn2+在大脑中的功能的理论，并通过这种方法来评估锌水平不受控制与神经退行性疾病（如阿尔茨海默氏症）和更急性的毒性脑病之间的假设关联。所设计的化学也将促进工具的开发，以测量发生在其他组织（如前列腺和胰腺）中的移动锌储存，在这些组织中，对移动Zn2+的定量有可能早期发现涉及这些器官的疾病。

DESCRIPTION (provided by applicant): The long-term goal of this research is to devise molecular sensors for binding, visualizing, and quantifying mobile zinc in neurobiological systems. Endogenous stores of zinc in presynaptic vesicles of hippocampal neurons in the brain are released upon physiological stimulation to perform an incompletely defined role in learning and memory. Similar mobile zinc stores present in the olfactory bulb (OB) process odorant information trans- mitted from the nose in a more direct signaling pathway. Uncontrolled Zn2+ release in the brain is associated with damage following seizure, ischemia, or blunt head trauma. In order to study these neurochemical phenomena, Zn2+ responsive sensors are required that can track the spatial and temporal distribution of the mobilized ion in response to physiological and pathological stimuli. The design, synthesis, evaluation, and optimization of the sensors constitute the major components of this research project. Each sensor will have up to three modules. Minimally, there will be zinc-binding and zinc-reporting units. The binding modules typically comprise multidentate ligands with variable Zn2+ affinity, selectivity for Zn2+ over competing ions in neuronal tissue, and fast, reversible coordination to monitor biological changes on the ms time scale. The zinc-reporting module will be either fluorescent or phosphorescent, for use in optical imaging (OI) experiments, or capable of altering water relaxation rates, for use in magnetic resonance imaging (MRI) studies. Fluorescent reporters include xanthenone and single-walled carbon nanotube derivatives. Phosphorescent sensors are based on cyclometalated iridium(III) complexes. MRI constructs utilize manganese(III) porphyrins. Strategies are adopted for attaching an optional third module to localize photoluminescence-based zinc sensors to programmed cellular targets to investigate Zn2+ dynamics at specific sites in a signal transduction pathway following physiological or pathological stimulation. An associated objective is to prepare zinc-selective, rapid chelating agents to be used in conjunction with investigations of the biological functions of mobile Zn2+. Thermodynamic, kinetic, photophysical, and theoretical studies of the zinc sensors and chelators will guide synthetic directions for making improvements to optimize their utility in applications. Specific applications include the evaluation by OI of hypotheses concerning the roles of mobile zinc in neurotransmission at mossy fiber synapses in the hippocampus and at glomeruli in the OB and the visualization by MRI of mobile zinc activity in the hippocampus under physiological and pathological conditions. This project is relevant to public health, for it will provide the means to test theories about the functions of mobile Zn2+ in the brain as well as the means by which to assess the postulated association of uncontrolled zinc levels with neurodegenerative diseases, such as Alzheimer's, and with more acute toxic encephalopathies. The chemistry devised will also facilitate the development of tools to measure mobile zinc stores that occur in other tissues such as the prostate and pancreas, where quantitation of mobile Zn2+ has the potential for early detection of diseases involving these organs.