Phospholipids play an important role in the lipid bilayers of living organisms, acting as a structural barrier for cellular and subcellular protection, being fundamental component for the proper functioning of other membrane components, such as proteins, receptors and ion channels. In addition, phospholipids contribute to the storage of a number of lipid mediators, which are involved in important cellular functional activities, such as the immune response, neural cell homeostasis, neuroinflammation, and oxidative stress. Therefore, alterations in phospholipid metabolism are associated with numerous diseases, including Alzheimer's disease (AD). For the study of phospholipids, the combined use of different modalities of mass spectrometry, such as direct infusion mass spectrometry (shotgun metabolomics), and reversed phase ultra-high performance liquid chromatography (RP-UPLC) with molecular mass spectrometry detection, have been tested. However, due to the complexity of these samples, selective detection methods for phosphorous, based on liquid chromatography with phosphorous-tagged detection by ICP-MS have been checked, which allows phospholipids quantification without the use of structurally matched standards.
The abnormal metabolism of lipids and phospholipids in brain is reflected in peripheral serum, who’s most important results are the following: 1) Lysophospholipids, decreased levels of different species of lysophosphatidylcholines (LPC), lysophosphatidylethanolamine (LPE) and lysoplasmenylcholine (LPPC), were detected in serum; 2) Phosphatidylcholine (PC). It has been observed the decreases of polyunsaturated fatty acid (PUFA) and a correlative increase of saturated fatty acids (SFA); 3) Phosphatidylethanolamine (PE), which have a content of PUFAs higher that PC, it has been observed a decrease of these polyunsaturated fatty acids in serum of AD patients, possibly as a consequence of oxidative stress. 4) Plasmalogens, major constituents of neural membrane forming part of myelin sheath, being also involved in other metabolic functions.  It has been observed deficiency of plasmenylethanolamine  (PPE), which constitutes up to 70% of total plasmalogens in serum that has been traditionally associated with AD development and progress.