Lipidomics, i.e., the study of the pathways and networks involved in the lipid metabolism within a living system, is an interesting field of study due to the diversity of fatty acid building blocks. The complete lipid profile, or “lipidome”, of a system can be studied, for example, using chromatography, mass spectrometry, and bioinformatics approaches. Unsaturated fatty acid isomers are responsible for much of the lipidome’s possible diversity. However, the isomers of unsaturated fatty acids can be difficult to distinguish using existing analytical approaches based on mass spectrometry.

Stephen J. Blanksby, Queensland University of Technology, Brisbane, Australia, and colleagues have developed a new approach to complete fatty acid profiling, combining fatty acid analysis via LC–OzID–MS/MS (liquid chromatography–ozone-induced dissociation–tandem mass spectrometry) with a custom-designed software for automated data analysis. The team calls the approach, which is particularly well-suited to finding the positions and configurations of C=C bonds, “ozone-enabled fatty acid discovery”, or OzFAD.

First, lipids are extracted from a sample, hydrolyzed, and derivatized with a charged group. Then they are separated by liquid chromatography and subjected to electrospray ionization (ESI) and OzID before being analyzed using mass spectrometry. Software is used to select possible target compounds at the different retention times, and the resulting raw target list is refined by resampling. The collected data was used to search for product ions arising from ozone-induced dissociation at all possible double bond positions, employing automated filtering. The prepared target list is used to guide the search for precursor and product signals at different retention times.

The work led to the discovery of a large number of newly described, naturally occurring unsaturated fatty acids. For example, the team found new omega-3 polyunsaturated fatty acids in a pooled sample of vernix caseosa (a biomaterial found on the skin of newborn babies) and sciadonic acid (pictured) in human blood plasma. The researchers also detected several non-methylene interrupted fatty acids in human prostate and breast cancer cell lines. They state that lipids from human blood plasma, vernix caseosa, and cancer cells contain a significantly larger number of unsaturated fatty acids than previously reported.

• Ozone-enabled fatty acid discovery reveals unexpected diversity in the human lipidome,
  Jan Philipp Menzel, Reuben S. E. Young, Aurélie H. Benfield, Julia S. Scott, Puttandon Wongsomboon, Lukáš Cudlman, Josef Cvačka, Lisa M. Butler, Sónia T. Henriques, Berwyck L. J. Poad, Stephen J. Blanksby,
  Nat. Commun. 2023.
  https://doi.org/10.1038/s41467-023-39617-9