Andrea Cerrato, Aldo Laganà, Anna Laura Capriotti

Department of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185, Rome, Italy, and Biostructures and Biosystems National Institute (INBB), Viale delle Medaglie d'Oro, 305, 00136, Rome, Italy

Lipidomics, once considered a branch of metabolomics, has nowadays gained its proper analytical approaches that differ significantly from routinary methods for metabolomics. Shotgun mass spectrometry (MS) and liquid chromatography coupled to MS are the foremost techniques for lipidomics either in a targeted or untargeted fashion. The recent trends in lipidomics generally follow two interconnected paths: (i) aiming at a more straightforward and automatized lipid identification and (ii) widening the structural information that can be obtained by MS-based lipidomics. As such, data processing and identification by software programs are toughened by a large number of adducts and several isomeric mass overlaps, that occur any time different lipid species generate adducts with the same sum composition [1]. A buffer modification workflow approach that takes advantage of the physicochemical and ionization properties of phosphocholine-containing lipids was proposed for their MS-based identification [2]. Moreover, despite being the foremost technique for lipidomics, high-resolution MS is not sufficient for elucidating the lipid structures, especially when it comes to the regiochemistry of carbon-carbon double bonds1, which play a major role in the properties of cell membranes. Over the years, several approaches have been proposed in combination with HRMS for elucidating the regiochemistry of double bonds, including unconventional fragmentation techniques and derivatization before MS analysis [1]. Paternò-Büchi (PB) reactions of fatty acids with ketones have been successfully proposed for pinpointing double bonds in fatty acids, as PB-derivatized lipids generate diagnostic product ions under CID fragmentation in positive ion mode [1]. Our research group has proposed an alternative to the PB reaction for negative ion mode analysis based on an aza-Paternò-Büchi (aPB) reaction of lipids with 6-azauracil, that allowed enhancing the ionization based on its functional groups [4]. Among other possible approaches, the emerging inverse electron-demand Diels–Alder reactions with tetrazines stand out for their unmatchable kinetics and have found several applications in basic biology, protein imaging, and therapeutics [3]. Recently, we presented the first proof of concept of a catalyst-free click IEDDA reaction to pinpoint carbon-carbon double bonds in free and conjugated fatty acids in untargeted MS-based lipidomics.

Keywords: high-resolution mass spectrometry, isomeric mass overlaps, bio-orthogonal reactions, lipidomics

References

1. Rustam Y. H., Reid G. E., Analytical Chemistry, 90 (2018), pag. 347-397. DOI: 10.1021/acs.analchem.7b04836

2. Cerrato A., Aita S. E., et al., Analytical Chemistry, 93 (2021), pag. 15042-15048. DOI: 10.1021/acs.analchem.1c02944 

3. Cerrato A., Capriotti A. L., et al., Analytical Chemistry, 94 (2022), pag. 13117-13125. DOI: 10.1021/acs.analchem.2c02549

4. Cerrato A., Cavaliere C., et al., Analytical Chemistry, 96 (2024), pag. 10817-10826. DOI: 10.1021/acs.analchem.4c02146