Title : Bioanalytical methodologies for the study of phospholipids in Alzheimer disease
Abstract:
Phospholipids play an important role in living organisms’ lipid bilayers, acting as a structural barrier for cellular and subcellular protection, being a fundamental component for the correct function of membrane proteins, receptors and ion channels. In addition, phospholipids also act as storage depot of a complex meshwork of lipid mediators, such as eicosanoids, lysophospholipids, platelet activating factors or diacylglycerides, which exert a diverse array of effects on cellular functional activities, including neural cell homeostasis, immune responsiveness, oxidative stress, and neuroinflammation. Therefore, defects in phospholipids metabolism are related to numerous diseases, such as Alzheimer disease (AD)[1]. Thereby, although major hallmarks of AD are the formation of senile plaques and neurofibrillary tangles, the changes in phospholipids could be used as biomarkers in AD, using non-invasive samples such as human serum.
In this study, shotgun metabolomics of serum samples was performed by direct infusion mass spectrometry (DIMS) for the screening of phospholipids involved in neurodegenerative processes associated with AD. Furthermore, a targeted analytical approach focused on phospholipids was optimized, using reversed phase ultra-high performance liquid chromatography (RP-UPLC) and detection by molecular mass spectrometry. However, the high complexity of samples requires selective detection methods based on phosphorous-tagging by the coupling of LC with ICP-MS [2], enabling phospholipids quantification without the use of structurally matched standards. This combination of different mass spectrometry-based metabolomics strategies allows to deep insight into the dyshomeostasis of phospholipids in AD.
This abnormal metabolism results in important biochemical changes in brain, which are reflected in peripheral serum, who’s most important results are the following: 1) Lysophospholipids. Decreased levels of different species of lysophosphatidylcholine (LPC), and similar trend for lysophosphatidylethanolamine (LPE) and lysoplasmenylcholine (LPPC), which reflects the alteration of metabolism of choline-containing compounds, along with other families such as ethanolamine and plasmenylcholine, in serum; 2) Phosphatidylcholine (PC). It has been observed the decreases of polyunsaturated fatty acid (PUFA) in the molecular moiety of PCs and the correlative increase of saturated fatty acids (SFA). This change in fatty acid composition of membrane lipids affects their biophysical properties (fluidity, permeability and charge) contributing to membrane damage in AD pathogenesis. 3) Phosphatidylethanolamine (PE). PEs are an important family of brain phospholipids with a content of PUFAs higher that PC, having been observed a decrease of these polyunsaturated fatty acids in serum of AD patients, possibly as a consequence of oxidative stress. 4) Plasmalogens, which are 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.
[1] González-Domínguez R, García-Barrera T, Gómez-Ariza JL. Combination of metabolomic and phospholipid-profiling approaches for the study of Alzheimer's disease. J. Proteomics 2014; 104: 37-47.
[2] Kovačevič M, Leber R, Kohlwein SD, Goessler W. Application of inductively coupled plasma mass spectrometry to phospholipid analysis. J Anal At Spectrom 2004; 19:80–4.
What will audience learn from your presentation?
- The study demonstrates the great possibilities of the combined use of molecular and atomic mass spectrometry in metabolomics.
- The application of these methodologies to serum samples reflects the systemic nature of Alzheimer's disease and the interest in using early warning biomarkers based on non-invasive samples.
- Diagnostic tests can be designed based on several families of metabolites, such as lysophospholipids, phosphatidylcholines, phosphatidylethanolamines and plasmalogens.
