Shorthand notation for lipid structures derived from mass spectrometry

TLDR

Mass spectrometry of lipids lacks a standardized, practical annotation, particularly for low‑resolution instruments that cannot distinguish fatty acid chains or bond types. The authors propose a shorthand notation that extends LIPID MAPS nomenclature to include detailed structural information, such as stereochemistry, that is not automatically provided by MS. They developed rules based on LIPID MAPS terminology to annotate lipid species, covering glycerophospholipids, fatty acids, glycerolipids, sphingolipids, and sterols, thereby filling the missing structural gaps. The resulting shorthand nomenclature offers a standard method for reporting lipid species from mass spectrometry and for building lipid databases.

Abstract

There is a need for a standardized, practical annotation for structures of lipid species derived from mass spectrometric approaches; i.e., for high-throughput data obtained from instruments operating in either high- or low-resolution modes. This proposal is based on common, officially accepted terms and builds upon the LIPID MAPS terminology. It aims to add defined levels of information below the LIPID MAPS nomenclature, as detailed chemical structures, including stereochemistry, are usually not automatically provided by mass spectrometric analysis. To this end, rules for lipid species annotation were developed that reflect the structural information derived from the analysis. For example, commonly used head group-specific analysis of glycerophospholipids (GP) by low-resolution instruments is neither capable of differentiating the fatty acids linked to the glycerol backbone nor able to define their bond type (ester, alkyl-, or alk-1-enyl-ether). This and other missing structural information is covered by the proposed shorthand notation presented here. Beyond GPs, we provide shorthand notation for fatty acids/acyls (FA), glycerolipids (GL), sphingolipids (SP), and sterols (ST). In summary, this defined shorthand nomenclature provides a standard methodology for reporting lipid species from mass spectrometric analysis and for constructing databases.