One-step lipid extraction for plasma lipidomics analysis by liquid chromatography mass spectrometry

In the past decade, various lipidomics methodologies have been developed using mass spectrometry based analytical technologies, enabling wide coverage lipid detection in a quantitative manner. Hence, lipidomics has become a widely-accepted approach for biomarker discovery and mechanism elucidation in both medical and biology research fields; however, there are still technical challenges. In this study, focusing on the sample preparation procedure, a single step deproteinization by a water-soluble organic solvent, such as methanol (MeOH), ethanol (EtOH), isopropanol (IPA) or acetonitrile (ACN), was evaluated and proved to be satisfactory for lipidomics analysis. Moreover, during this investigation ACN deproteinization was revealed to not be an effective method for lipid extraction because lipid decomposition was observed during the protein precipitation process through lipase activation, potentially due to the insufficient protein denaturation. Therefore, excluding ACN, protein precipitation by alcohol was evaluated as the lipid extraction reagent. Moreover, adding the MTBE-MeOH (mMM) method, one of the major liquid-liquid extraction methods for shotgun lipidomics, these four approaches were compared. Lipids were extracted from mouse plasma by these four methods and used for exhaustive lipid profiling by liquid chromatography mass spectrometry (LC/MS) analysis. Comparison of these four methods revealed that alcohol based protein precipitation was a useful sample preparation procedure for LC/MS based lipidomics analysis. Whereas MeOH extraction was appropriate for hydrophilic lipid species, IPA was effective for hydrophobic lipids such as triacylglycerols (TG). In practice, EtOH extraction is thought to be the best approach to cover wide range of lipid species using a simple preparation procedure.