Adapted MS/MSALL Shotgun Lipidomics Approach for Analysis of Cardiolipin Molecular Species

Cardiolipin (Ptd₂ Gro) is a complex, doubly charged phospholipid located in the inner mitochondrial membrane where it plays an essential role in regulating bioenergetics. Abnormalities in Ptd₂ Gro content or composition have been associated with mitochondrial dysfunction in a variety of disease states. Here, we report the development of an adapted high-resolution data-independent acquisition (DIA) MS/MS^ALL shotgun lipidomic method to enhance the accuracy and reproducibility of Ptd₂ Gro molecular species quantitation from biological samples. Utilizing the doubly charged molecular ions and the isotopic pattern with negative mode electrospray ionization mass spectrometry (ESI-MS) using an adapted MS/MS^ALL approach, we profiled more than 150 individual Ptd₂ Gro species, including monolysocardiolipin (MLPtd₂ Gro). The method described in this study demonstrated high reproducibility, sensitivity, and throughput with a wide dynamic range. This high-resolution MS/MS^ALL shotgun lipidomics approach could be extended to screening aberrations of Ptd₂ Gro metabolism involved in mitochondrial dysfunction in various pathological conditions and diseases.

Monoacylglycerol Analysis Using MS/MS(ALL) Quadruple Time of Flight Mass Spectrometry

Monoacylglycerols (MAGs) are structural and bioactive metabolites critical for biological function. Development of facile tools for measuring MAG are essential to understand its role in different diseases and various pathways. A data-independent acquisition method, MS/MS(ALL), using electrospray ionization (ESI) coupled quadrupole time of flight mass spectrometry (MS), was utilized for the structural identification and quantitative analysis of individual MAG molecular species. Compared with other acylglycerols, diacylglycerols (DAG) and triacylglycerols (TAG), MAG characteristically presented as a dominant protonated ion, [M + H]⁺, and under low collision energy as fatty acid-like fragments due to the neutral loss of the glycerol head group. At low concentrations (<10 pmol/µL), where lipid-lipid interactions are rare, there was a strong linear correlation between ion abundance and MAG concentration. Moreover, using the MS/MS(ALL) method the major MAG species from human plasma and mouse brown and white adipose tissues were quantified in less than 6 min. Collectively, these results demonstrate that MS/MS(ALL) analysis of MAG is an enabling strategy for the direct identification and quantitative analysis of low level MAG species from biological samples with high throughput and sensitivity.

Lipid Profiling of In Vitro Cell Models of Adipogenic Differentiation: Relationships With Mouse Adipose Tissues

Our objective was to characterize lipid profiles in cell models of adipocyte differentiation in comparison to mouse adipose tissues in vivo. A novel lipid extraction strategy was combined with global lipid profiling using direct infusion and sequential precursor ion fragmentation, termed MS/MS(ALL) . Perirenal and inguinal white adipose tissue and interscapular brown adipose tissues from adult C57BL/6J mice were analyzed. 3T3-L1 preadipocytes, ear mesenchymal progenitor cells, and brown adipose-derived BAT-C1 cells were also characterized. Over 3000 unique lipid species were quantified. Principal component analysis showed that perirenal versus inguinal white adipose tissues varied in lipid composition of triacyl- and diacylglycerols, sphingomyelins, glycerophospholipids and, notably, cardiolipin CL 72:3. In contrast, hexosylceramides and sphingomyelins distinguished brown from white adipose. Adipocyte differentiation models showed broad differences in lipid composition among themselves, upon adipogenic differentiation, and with adipose tissues. Palmitoyl triacylglycerides predominate in 3T3-L1 differentiation models, whereas cardiolipin CL 72:1 and SM 45:4 were abundant in brown adipose-derived cell differentiation models, respectively. MS/MS(ALL) data suggest new lipid biomarkers for tissue-specific lipid contributions to adipogenesis, thus providing a foundation for using in vitro models of adipogenesis to reflect potential changes in adipose tissues in vivo. J. Cell. Biochem. 117: 2182-2193, 2016. © 2016 Wiley Periodicals, Inc.

Comparative Lipidomics of Caenorhabditis elegans Metabolic Disease Models by SWATH Non-Targeted Tandem Mass Spectrometry

Tandem mass spectrometry (MS/MS) with Sequential Window Acquisition of all Theoretical (SWATH) mass spectra generates a comprehensive archive of lipid species within an extract for retrospective, quantitative MS/MS analysis. Here we apply this new technology in Caenorhabditis elegans (C. elegans) to identify potential lipid mediators and pathways. The DAF-1 type I TGF-β and DAF-2 insulin receptors transmit endocrine signals that couple metabolic status to fertility and lifespan. Mutations in daf-1 and daf-2 reduce prostaglandin-endoperoxide synthase (i.e., Cox)-independent prostaglandin synthesis, increase triacylglyceride storage, and alter transcription of numerous lipid metabolism genes. However, the extent to which DAF-1 and DAF-2 signaling modulate lipid metabolism and the underlying mechanisms are not well understood. MS/MS^ALL with SWATH analysis across the groups identified significant changes in numerous lipids, including specific triacylglycerols, diacylglycerols, and phosphatidylinositols. Examples are provided, using retrospective neutral loss and precursor ion scans as well as MS/MS spectra, to help identify annotated lipids and search libraries for lipids of interest. As proof of principle, we used comparative lipidomics to investigate the prostaglandin metabolism pathway. SWATH data support an unanticipated model: Cox-independent prostaglandin synthesis may involve lysophosphatidylcholine and other lyso glycerophospholipids. This study showcases the power of comprehensive, retrospectively searchable lipid archives as a systems approach for biological discovery in genetic animal models.