Cardiolipins (CLs) are an important, regulated lipid class both in prokaryotic and eukaryotic cells, yet they remain largely unexplored by matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) in tissues. To date, no in-depth optimization studies of label-free visualization of CLs in complex biological samples have been reported. Here we report a streamlined modification to our previously reported MALDI-MSI method for detection of endogenous CLs in prokaryotic and eukaryotic cells based on preparation with norharmane (NRM) matrix. Notably, the use of NRM matrix permitted sensitive detection (4.7 pg/mm2) of spotted CL synthetic standards. By contrast, four other MALDI matrices commonly used for lipid analysis failed to generate CL ions. Using this NRM-based method, endogenous CLs were detected from two types of complex biological samples: dried bacterial arrays and mouse tissue sections. In both cases, using NRM resulted in a better signal/noise for CL ions than the other matrices. Furthermore, inclusion of a washing step improved CL detection from tissue and this combined tissue preparation method (washing and NRM matrix) was used to profile normal mouse lung. Mouse lung yielded 26 unique CLs that were mapped and identified. Consistent with previous findings, CLs containing polyunsaturated fatty acids (PUFAs) were found in abundance in the airway and vascular features of the lung. This work represents a comprehensive investigation of detection conditions for CL using MALDI-MSI in complex biological samples that resulted in a streamlined method that enables future studies of the biological role(s) of CL in tissue.

中文翻译：

---

通过 MALDI-MSI 使用 Norharmane 矩阵简化原核和真核样品中心磷脂的分析。

心磷脂 (CLs) 是原核细胞和真核细胞中一种重要的、受调控的脂质类别，但它们在组织中的基质辅助激光解吸/电离质谱成像 (MALDI-MSI) 在很大程度上仍未被探索。迄今为止，还没有关于复杂生物样品中 CL 的无标记可视化的深入优化研究的报道。在这里，我们报告了对我们之前报道的 MALDI-MSI 方法的简化修改，该方法基于使用去甲胺 (NRM) 基质的制备来检测原核和真核细胞中的内源性 CL。值得注意的是，NRM 基质的使用允许对斑点 CL 合成标准进行灵敏检测 (4.7 pg/mm2)。相比之下，常用于脂质分析的其他四种 MALDI 基质未能产生 CL 离子。使用这种基于 NRM 的方法，从两种类型的复杂生物样品中检测到内源性 CL：干细菌阵列和小鼠组织切片。在这两种情况下，与其他基质相比，使用 NRM 会导致 CL 离子的信号/噪声更好。此外，包含洗涤步骤改进了组织中的 CL 检测，这种组合的组织制备方法（洗涤和 NRM 基质）用于分析正常小鼠肺。小鼠肺产生了 26 个独特的 CLs，这些 CLs 被映射和识别。与之前的发现一致，在肺的气道和血管特征中发现了大量含有多不饱和脂肪酸 (PUFA) 的 CL。