Lipidomics technologies

Ekroos, K., ed. (2013) Lipidomics Technologies and Applications. John Wiley Sons, Weiheim, Germany... 

Han, X., Jiang, X. (2009) A review of lipidomic technologies applicable to sphin-golipidomics and their relevant applications. Eur. J. Lipid Sci. Technol. Ill, 39-52. 

Recent advances of mass spectrometry and chromatography, and their hyphenated technologies in lipidomics analyses have been reviewed by Li and coworkers [38]. Soft ionization techniques such hquid secondary ion mass spectrometry (LSI-MS) [39] and FAB [40] allowed the mass spectrometric analyses of polar thermally labile molecules of masses up to a few thousand daltons. Later, MALDI [41] and electrospray ionization (ESI) [42] permitted the direct analysis of native biomolecules within the megadalton masses without derivatization. 

Taki, T. 2013. Bio-recognition and functional lipidomics by glycosphingolipid transfer technology, Proc. Jpn. Acad. Ser. B Phys. Biol Scl, 89 302-320. 

MALDI-MS is generally performed at (complex) lipids mixtures, although post-LC-column fractionation systems have been developed as well. Additionally, MALDI-MS imaging of TLC plates is useful technology in Upid analysis [219]. The application of MALDI-MS in lipid analysis and lipidomics has been extensively reviewed [193, 194, 220, 221]. The most widely applied matrices in lipid analysis are DHB and 2,6-dihydroxyacetophenone (DHAP). Unlike in ESI-MS, MALDI-MS provides positive-ion response for all phospholipid classes. Individual components may be observed as [M+H]+, [M+Na], [M+K]+, or adduct ions with additional HWa - or H+/K+-exchange, thus significantly complicating the interpretation and (relative) quantification of individual components in... 

The term lipidome first appeared in the literature in 2001 [25]. In 2002, Ril-fors and Lindblom [54] coined the term functional lipidomics as the study of the role played by membrane lipids. In 2003, the field bloomed with different definitions [41, 55], demonstrations of technologies [41, 56], and biological applications [41, 57, 58]. Han and Gross first defined the field of lipidomics through integrating the specific chemical properties inherent in lipid species with a comprehensive mass spectrometric approach [41]. Since then, all areas of the field have been greatly accelerated. 

In addition to this enabling advance for direct tissue lipid analysis, the significance of IM-MS in lipidomics is numerous. First, separation of isomers, isobars, and con-formers is rendered possible with the addition of IM cells to mass spectrometers [97], which allows identification of novel lipid classes and species in a high-throughput manner. Moreover, analysis of chiral isomers could be achieved by the introduction of chiral reagents into an ion-mobility cell as demonstrated in other studies [98]. Finally, the duty cycle of IM-MS is short relative to LC separations and can thus be coupled to such techniques to form 3D modalities such as LC-IM-MS [102]. A recent review paper [103], which extensively discusses the principles of IM-MS technology and its applications for lipidomics, should be consulted for the readers who are interested in this area of research. 

In this chapter, the lipidomics approaches developed based on the electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) technologies (see Chapter 2) are described. Although matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has played many important roles in lipidomics and is also discussed in the chapter, it is no doubt that the majority of the platforms for lipidomics analysis currently used are based on ESI-MS in conjunction with MS/MS analyses. 

At the current stage, MDMS is decomposed into multiple 2D MS for ease of use and displayed by varying only one variable at a time while keeping the others fixed under experimental conditions. It is anticipated that advanced computational technology can eventually facilitate the direct use of 3D MS or MDMS and provide a new level of information directly obtainable from the MS analysis in the next generation of computational MDMS-based shotgun lipidomics. 

The LC-MS approach is currently the most popular approach for lipid analysis [55-57], although it may not be the best choice for global lipid analysis (i.e., lipidomics). The rationale behind the LC-MS approaches is to maximally exploit the LC separation technology with the most sensitive detection power of MS currently available. Three major factors are generally considered for successful development of LC-MS methodology in lipidomics, as well as understanding the principles of those developments. 

Although many systematic indices (e.g.. Lipid MAPS, Chemical Entries of Biological Interest (ChEBI), lUPAC International Chemical Identifiers (InChl), simplified molecular-input line entry system (SMILES)) were developed to list the chemical compounds, these indices (identifiers) can only be meaningful if the compound is totally identified. However, in practice, lipidomics analysis in many cases can only provide partial identification of lipid molecular structures at the current development of technology. Moreover, different lipidomics approaches provide different levels of stmctural identification of lipid species. Therefore, how to clearly express and report the information about the levels of identification for the structures of lipid species (which can be derived fi om MS analysis) is not only helpful for the readers but also important for bioinformatics and data communication. To this end, the analysis by shotgun lipidomics could be used as a typical example to explain these levels. Similar phenomena also exist in the analysis of lipid species employing LC-MS-based approaches. 

Many modern technologies (including MS, nuclear magnetic resonance spectroscopy, fluorescence spectroscopy, chromatography, and microfluidic devices) have been used in lipidomics for quantification of lipid species in biological systems [1], Clearly, ESI-MS has evolved to be one of the most popular and powerful technologies for quantitative analyses of individual lipid species [2-5]. 

Although several technologies have been used in lipidomics to identify, quantify, and understand the structure and function of lipids in biological systems, it is clear that the progress of lipidomics has been accelerated by the development of modern mass spectrometry (e.g., electrospray ionization (ESI) and matrix-assisted laser desorption/ionization). Mass spectrometric analysis of lipids plays a key role in the discipline. Therefore, this book is focused on the mass spectrometry of lipids that has occurred in these years. Other technologies for analysis of lipids, particularly those with chromatography, can be found in the book entitled Lipid Analysis Isolation, Separation, Identification and Lipidomic Analysis written by Drs William W. Christie and Xianlin Han. Readers who are interested in classical techniques and applications of mass spectrometry for analysis of lipids should refer to Dr Robert C. Murphy s book entitled Mass Spectrometry of Lipids. 

This chapter has discussed the applications of MALDI and ESI techniques for lipid analyses for both structural characterization and quantitation. In particular, the methodologies that are currently available for quantitation of individual lipid molecular species based on both ESI/MS and MALDI/MS are discussed in some detail. The limitations associated with each method and the potential concerns related to accurate quantitation of lipids have also been addressed. Overall, ESI/MS is the principal modality for global lipid identification and quantitation at the present time MALDI/MS can be selected as a primary screening technique before conducting large-scale lipid analyses and future technological developments may contribute to its enhanced usage. Therefore, a combination of both techniques will dramatically accelerate the development of lipidomics. 

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