untargeted lipidomics

untargeted lipidomics • Lipids are the main components of biological membranes. They are not only a major form of energy storage in living cells, but also well- known cell signaling mediators. • The lipidome is composed of eight major categories, more than 80 major classes, 300 sub-classes, and thousands of lipid species with various concentrations. Lipidomics is the systematical study of all lipid molecules (>30,000 individual species) within a biological system, tissue, fluid or cell. To understand cellular physiology and pathophysiology well, comprehensive identification and precise quantification of lipids is crucial in lipidomics research. • Untargeted lipidomics makes it possible to analyze hundreds to thousands of individual lipid species simultaneously, which is valuable to evaluate an individual’s health status. Differences in lipid profiles have been reported in investigations of cancer, diabetes, Alzheimer’s disease and cardiovascular disease. Such amounts of detailed lipid profiles are available to assess medical risks, monitor and optimize patient treatments and are the basis for the concept of precision medicine. Applications of untargeted lipidomics include agro science, biomarkers, Alzheimer's, atherosclerosis, cardiovascular, cancer, diabetes and obesity disease research, clinical diagnostics, drug discovery and systems biology.

• Though lipid is a major part of the metabolome, the insolubility of many lipids in aqueous solutions makes it is necessary to use different methods from that for more water-soluble components of the metabolome. Mass spectrometry (MS) is the dominant platform in lipidomics, while nuclear magnetic resonance (NMR) has been used wildely in metabolomic studies. Gas chromatography (GC)–MS was a major tool for lipid profiling studies in the past. However, this technology has been replaced by the interfacing of desorption ionization techniques of atmospheric pressure ionization (API) and matrix-assisted laser desorption/ionization (MALDI) with MS. API, usually electro- spray ionization (ESI), is often linked to a liquid chromatography (LC) system for separation prior to MS analysis. MALDI is mostly performed under vacuum and is not usually linked to LC separation, while MALDI can be performed from thin-layer chromatography (TLC) plates. MALDI –MS imaging (MSI) is becoming a more and more adopted technology in lipidomics, which can provide spatial information to lipid classes in tissues. Through measurement of the mass-to-charge ratio (m/z) of ionized species, MS gives molecular weight information. Many modern MS instruments can offer mass accuracy at a level of 0.001–0.002 m/z, which allows m/z searches against the Lipid Maps database of compounds or identify ionized molecules through various commercial or open-source software. Tandem mass spectrometry (MS/MS) or multistage fragmentation (MSn) experiments can give structural information.