New Findings Shed Light on Formation and Analysis of Doubly Charged Lipid-Metal Ion Complexes

Phospholipids play a vital role in the composition of eukaryotic cell membranes, and changes in their structure can signify metabolic variations or disease states. A recent study led by Sven Heiles and published in the Journal of the American Society for Mass Spectrometry explores the formation and tandem mass spectrometry of doubly charged lipid-metal ion complexes, offering new insights into the analysis of phospholipid structures and relative quantification of isomers (1).

Eicosapentaenoic acid (EPA) fish oil omega-3 fatty acid, molecul | Image Credit: © molekuul.be - stock.adobe.com

The researchers observed that various classes of phospholipids form doubly charged lipid-metal ion complexes during electrospray ionization (ESI). By utilizing water-free methanol and introducing divalent metal salts into the ESI spray solutions, the team achieved abundant doubly charged lipid-metal ion complexes, surpassing the abundance of protonated compounds by up to 70 times.

Through higher-energy collisional dissociation and collision-induced dissociation, the researchers were able to generate a diverse range of fragment ions specific to different lipid classes. These fragment ions provided valuable information for assigning lipid classes, identifying fatty acid moieties, distinguishing isomers of branched chain fatty acids, and performing relative quantification in positive-ion mode.

One notable application of this analytical approach is the differentiation of fatty acid branching-site isomers in phospholipid mixtures, allowing for the identification of specific isomeric compounds. The researchers demonstrated the capability of the method to pinpoint branching sites in saturated fatty acids within both free fatty acids and glycerophospholipids.

The ability to analyze doubly charged lipid-metal ion complexes provides a valuable tool for the characterization and relative quantification of phospholipid structures, particularly when routine tandem mass spectrometry or liquid chromatography methods without authentic standards face challenges. This advancement in lipid analysis has significant implications for the study of metabolic states, disease markers, and lipid variations associated with distinct organisms.

The work conducted by Sven Heiles and the team at Leibniz-Institut für Analytische Wissenschaften and the University of Duisburg-Essen sheds light on the formation and analysis of doubly charged lipid-metal ion complexes, paving the way for enhanced understanding and investigation of phospholipid structures in various biological systems. The findings contribute to the advancement of mass spectrometry techniques and offer promising avenues for future research in lipidomics and related fields.

Reference

(1) Hormann, F-L.; Sommer, S.; Heiles, S. Formation and Tandem Mass Spectrometry of Doubly Charged Lipid-Metal Ion Complexes. J. Am. Soc. Mass Spectrom. 2023. DOI: https://doi.org/10.1021/jasms.3c00126