Localized and analyte-specific normalization for imaging-MALDI-MS - towards quantitative imaging of lipids in tissue

成像 MALDI-MS 的局部和分析物特异性标准化 - 实现组织中脂质的定量成像

• 批准号: 400912714
• 负责人: Privatdozent Dr. Jens Soltwisch
• 金额: --
• 依托单位: Forschungsabteilung Biomedizinische Massenspektrometrie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/400912714?language=en
• 关键词: Localized; analyte; specific; normalization; imaging

MALDI-MSI has in recent years become a heavily used technique in imaging mass spectrometry with dedicated platforms now readily available. For the analysis of tissue samples, (phospho-)lipids are often the analyte of choice. Next to a high abundance and preferable ionization efficiencies, their vital role in the metabolism makes them a prime target of biomedical research. To unveil the role of a specific lipid species in the context of a specific tissue, it is important to correctly depict its distribution within the sample. In order to do so, a molecular identity has to be assigned to the determined m/z-value and the respective signal intensities have to be translated to quantities of material for each pixel. While sophisticated hard- and software solutions allow for the identification of lipid signals based on accurate mass, quantification in MALDI-MSI remains a difficult task. This is due to a number of factors inherent to sample preparation and the MALDI-process itself, that greatly influence ion yields in MALDI and that may vary for different regions. This greatly hampers a straightforward conversion of signal intensity to the underlying amount of material across the tissue. One important phenomenon in this regards is the ion suppression effect that arises from the competition for charge between different analytes during the MALDI-process. Especially apparent in the analysis of complex mixtures the presence of an easily ionizable analyte can significantly decrease the signal intensity of a second compound that is less susceptible for ionization. On top of that, physical and chemical properties of the tissue, but also the choice of matrix and preparation method influence the extraction of analyte into the applied matrix layer and therefore also the resulting signal intensity. The proposed project will thoroughly investigate and characterize both the ion suppression effect as well as the extraction of analyte from tissue under MALDI-MSI conditions. For that lipid extracts of specific tissue regions will be produced and quantitatively characterized with ESI-MS. This way, signal intensities in MALDI-MSI can be directly compared to the underlying amounts of substance. In a second approach, artificial tissue with well-defined lipid content can be constructed and examined. These highly simplified samples allow for the systematic and quantitative analysis of the ion suppression effect between different lipid classes. Building on the broad basis of collected data we will develop individualized normalization strategies. These will include the use of external non-endogenous lipid standards suitable to normalize for ion suppression effects as well as location and analyte specific correction factors accounting for the extraction from the tissue. As a result we hope to deliver a robust and practical method that enables the direct translation of MALDI-MSI data to the visualization of relative amounts of material within the analyzed tissue.

近年来，MALDI-MSI 已成为成像质谱分析中广泛使用的技术，专用平台现已可用。对于组织样品的分析，（磷酸）脂质通常是首选分析物。除了高丰度和更好的电离效率之外，它们在新陈代谢中的重要作用使它们成为生物医学研究的主要目标。为了揭示特定脂质种类在特定组织中的作用，正确描述其在样品中的分布非常重要。为此，必须将分子身份分配给确定的 m/z 值，并且必须将相应的信号强度转换为每个像素的材料数量。 虽然复杂的硬件和软件解决方案允许基于精确质量识别脂质信号，但 MALDI-MSI 中的定量仍然是一项艰巨的任务。这是由于样品制备和 MALDI 过程本身固有的许多因素造成的，这些因素极大地影响了 MALDI 中的离子产率，并且不同地区的离子产率可能有所不同。这极大地阻碍了信号强度直接转换为组织中的基本物质量。这方面的一个重要现象是 MALDI 过程中不同分析物之间电荷竞争产生的离子抑制效应。在复杂混合物的分析中尤其明显的是，容易电离的分析物的存在可以显着降低不易电离的第二种化合物的信号强度。最重要的是，组织的物理和化学特性以及基质的选择和制备方法都会影响分析物提取到所应用的基质层中，因此也会影响所得的信号强度。拟议的项目将彻底研究和表征离子抑制效应以及 MALDI-MSI 条件下从组织中提取分析物。为此，将生产特定组织区域的脂质提取物并使用 ESI-MS 进行定量表征。这样，MALDI-MSI 中的信号强度可以直接与基础物质的量进行比较。在第二种方法中，可以构建并检查具有明确脂质含量的人造组织。这些高度简化的样品可以对不同脂质类别之间的离子抑制效应进行系统和定量分析。在收集的数据的广泛基础上，我们将制定个性化的标准化策略。这些将包括使用适合离子抑制效应标准化的外部非内源性脂质标准品，以及考虑从组织中提取的位置和分析物特定校正因子。因此，我们希望提供一种稳健且实用的方法，能够将 MALDI-MSI 数据直接转换为分析组织内材料相对量的可视化。