Department of Ophthalmology and the Graduate School of Biomedical Sciences, University of Texas Southwestern Medical Center, Dallas, TX, USA.
Steroids. 2010 Oct;75(10):726-33. doi: 10.1016/j.steroids.2010.04.011. Epub 2010 May 12.
Very long chain cholesteryl esters (CE) are a major group of lipids found in meibomian gland secretions (MGS, also called meibum). MGS are produced by the meibomian glands of human and animal eyelids. They are a critical part of the tear film which covers the exposed ocular surface and serves various physiological roles. The composition of CE of MGS is complex, and still remains poorly understood. Here, a liquid chromatography-ion trap mass spectrometry (LC-MS) procedure developed to analyze CE is described, and a detailed composition of human meibomian CE is reported. MGS were collected from donors, analyzed without any modifications by LC-MS in positive and negative ion modes (PIM and NIM), and quantified using lipid standards where available. CE comprised about 30% of human meibum by mass. More than 40 individual CE species were found and characterized. In PIM, CE were observed as spontaneously in-source generated product ions m/z 369. The signals of the proton adducts of intact CE (M+H)(+) were of very low intensity. In NIM, all tested CE spontaneously fragmented in-source producing signals of their respective FA. By combining the LC and MS information, the most abundant CE were found to be based on FA ranging from C(16) to at least C(32) in the following order C(26:0)>C(25:0)>C(24:0)>C(27:0)>C(24:1)=C(18:1)=C(20:0)>other CE. We conclude that the FA composition of CE can be successfully established in LC-MS experiments conducted in NIM. Meibomian CE have a large presence of both saturated and unsaturated FA with an average molar ratio of 4 to 1, respectively.
非常长链胆甾醇酯 (CE) 是睑板腺分泌物 (MGS，也称为睑脂) 中存在的主要脂质组分之一。MGS 由人类和动物眼睑的睑板腺产生。它们是覆盖暴露的眼表面的泪膜的重要组成部分，具有多种生理作用。MGS 中的 CE 组成复杂，目前仍知之甚少。这里，描述了一种开发用于分析 CE 的液相色谱-离子阱质谱 (LC-MS) 程序，并报告了人睑板 CE 的详细组成。从供体中收集 MGS，在正离子模式 (PIM) 和负离子模式 (NIM) 下通过 LC-MS 进行无需任何修饰的分析，并在有脂质标准品的情况下进行定量。CE 占人睑脂质量的约 30%。发现并表征了超过 40 种不同的 CE 物质。在 PIM 中，CE 作为自发的源内产生的产物离子 m/z 369 被观察到。完整 CE 的质子加合物 (M+H)(+) 的信号强度非常低。在 NIM 中，所有测试的 CE 都在源内自发断裂，产生各自 FA 的信号。通过结合 LC 和 MS 信息，发现最丰富的 CE 基于 FA，范围从 C(16) 到至少 C(32)，顺序为 C(26:0)>C(25:0)>C(24:0)>C(27:0)>C(24:1)=C(18:1)=C(20:0)>其他 CE。我们得出结论，在 NIM 中进行的 LC-MS 实验中可以成功建立 CE 的 FA 组成。睑板腺 CE 含有大量的饱和和不饱和 FA，其平均摩尔比分别为 4:1。
