Investigation of oxidized lipids with (patho)physiological relevance using mass spectrometric methods and their improved detection using MS imaging

脂质是细胞膜的基本组成部分，在所有组织中浓度相对较高。炎症过程中自由基的过量产生，即活性氧或氮（ROS或RNS），可以氧化性地改变特别是不饱和磷脂（PL）。氧化脂质及其衍生物在心血管疾病、糖尿病、动脉粥样硬化和肿瘤的发展中起着重要作用。由于缺乏合适的检测方法，氧化PL的检测，特别是组织中空间分辨的检测是一个很大的挑战。这些氧化产物的分析是困难的，因为两个原因：首先，一些氧化产物，如氢过氧化物，在这里应用的MALDI-MS（基质辅助激光解吸和电离质谱）条件下很难检测到，因为它们在（UV）激光照射下被耗尽。此外，一些氧化产物，如链缩短的醛与生物源化合物，如蛋白质或磷脂酰乙醇胺发生反应，并且无法以其原始分子量检测到。另一个问题是，只有少数氧化脂质是商业上可用的，这些（瞬态）产品需要在内部生成。因此，在本项目中，脂质氧化产物的质谱检测，特别是MALDI质谱，将被研究和改进。最初，氧化PL是通过不同的方法从市售PL中生成的。通过使用新的基质物质和对现有基质物质进行化学修饰，调整MALDI条件，使其能够检测各种不稳定的PL氧化产物。接下来，这些条件被转移到生物样本（精浆，血浆）中，我们已经知道这些生物样本容易发生脂质氧化。最后，使用成像质谱（MSI）在选定的组织切片（健康和炎症肝组织）上检测氧化PL。这项工作将与来自曼海姆（MSI）和亚琛（小鼠肝组织）的小组合作进行。除了评估天然组织外，这些组织还将加入一定量的氧化PL，以确定该方法的可实现检测限。这应该回答一个问题，哪些参数需要通过MALDI MSI“微调”来监测炎症过程并避免伪像。从方法学和医学的角度来看，预期的结果具有很高的科学和社会经济价值。MSI提供了特定的化学信息，可以对（炎症）疾病的进展和预后做出结论。组织组成的可靠信息（几乎是实时的）将有助于推进肿瘤手术。

Lipids are essential components of cellular membranes, which are present in comparatively high concentrations in all tissues. The excessive generation of radicals, i.e. reactive oxygen or nitrogen species (ROS or RNS) during inflammatory processes, can oxidatively alter particularly unsaturated phospholipids (PL). Oxidized lipids and products derived thereof play an important role during the development of cardiovascular diseases, diabetes, atherosclerosis and tumors. The detection of oxidized PL, particularly spatially resolved in tissues, is a big challenge due to the lack of suitable detection methods. Analytics of these oxidation products is difficult because of two reasons: first, some oxidation products, such as hydroperoxides are hardly detectable under conditions of the here applied MALDI-MS (matrix-assisted laser desorption and ionization mass spectrometry), because they are depleted under (UV) laser irradiation. Furthermore, some oxidation products, such as chain-shortened aldehydes react with biogenic compounds, like proteins or phosphatidylethanolamines and are not detected with their original molecular weight. Another problem is that only a few oxidized lipids are commercially available and these (transient) products need to be generated in-house. Thus, the detectability of lipid oxidation products by mass spectrometry – particularly MALDI MS – is to be investigated and improved during this project. Initially, oxidized PL are being generated from commercially available PL by different methods. By using new matrix substances and chemically modifying established ones, MALDI conditions shall be adjusted to enable the detection of all kinds of labile PL oxidation products. Next, these conditions are being transferred to biological samples (seminal plasma, blood plasma) from which it is already known that these are prone to lipid oxidation. Finally, oxidized PL are being detected on selected tissue slices (healthy and inflamed liver tissue) using imaging MS (MSI). This work will be performed in cooperation with groups from Mannheim (MSI) and Aachen (mouse liver tissue). Beside the evaluation of the native tissues, these tissues will also be spiked with defined amounts of oxidized PL in order to determine the achievable detection limits of the method. This should answer the question, which parameters need to be "fine tuned" to monitor inflammation processes by MALDI MSI and to avoid artifacts. The expected results are of high scientific and socio-economic value from the methodological as well as from the medical point of view. MSI gives specific chemical information, that allows conclusions about the progression and the prognosis of (inflammatory) diseases. Reliable information on the tissue composition (in almost real time) would help to advance tumor surgery.