Analysis of Complex Lipidomes

ANDREAS UPHOFF, MARTIN HERMANSSON, PERTTU HAIMI, and PENTTI SOMERHARJU  

Institute of Biomedicine, Department of Biochemistry, University of Helsinki, 00014 Helsinki, Finlarul 

Recent developments in mass spectrometry, particularly the introduction of the ESI method, have paved way to functional lipidomics, i.e., the use of detailed lipid profile of cell or tissues to unravel biological phenomena and the mechanisms underlying various metabolic perturbations or diseases. 

At present, ESI-MS allows quantitative analysis of hundreds of phospholipid species present in a sample. Two different approaches are commonly used. The 

The other, LC-MS, approach makes use of on-line preseparation of the lipids before MS analysis. This method allows analysis of species for which no specific scan modes exist. Also, many isobaric species, not readily resolved by MS/MS, can be analyzed. Finally, this method, particularly when employing multiple reaction monitoring (MRM), provides the highest sensitivity of detection of many minor lipid classes as the suppression effects are minimized. 

---

M. Hermansson, A. Uphoff, R. Kakela, P. Somerhaqu, Automated quantitative analysis of complex lipidomes by LC-MS, Anal. Chem., 77 (2005) 2166. 

Hermansson M, et al. Automated quantitative analysis of complex lipidomes by liquid... 

The exact structural and spatial characterization of the lipids is still very limited, particularly in routine determination of lipids. As an example, routine determination of snl/sn2 acyl positions in PLs is not possible, nor is the determination of positions of double bonds or acyl chain branching. Such information would be important to understand the data in the biochemical context (e.g., affinity for specific lipid enzymes). While promising efforts are under way, it may still take time before the emerging tools for lipid structural elucidation are introduced in routine lipidomic analyses. Big advances have also been made over the past years in the developments of methods for surface analysis of lipids. These approaches will be crucial for in-depth elucidation of the spatial complexity of cellular and subcellular lipidomes. 

Rainville, P.D., Stumpf, C.L., Shockcor, J.P., Plumb, R.S. and Nicholson, J.K. (2007) Novel application of reversed-phase UPLC-oaTOF-MS for bpid analysis in complex biological mixtures A new tool for lipidomics. J. Proteome Res. 6, 552-558. 

Masoodi, M., Eiden, M., Kouhnan, A., Spaner, D. and Volmer, DA. (2010) Comprehensive lipidomics analysis of bioactive lipids in complex regulatory networks. Anal. Chem. 82, 8176-8185. 

Recent methodological developments in MS have made quantitative analysis of the complex lipidomes of mammalian cells and tissues feasible for the first time. Phospholipids can already be analyzed in a routine manner and the analysis of most other lipid classes should be possible as soon as some issues regarding quantification, particularly the availability of suitable standards, have been resolved. A detailed analysis of lipidomes is expected to provide a powerful tool for the diagnosis and understanding of the mechanism of various lipid-related diseases and disorders, including atherosclerosis and type 2 diabetes. This, however, will require integration of the lipidomics data with those of genomics, proteomics, and other omics, which may not be trivial. 

Through global lipidomics, each distinct lipid species present in a cell s lip-idome can be identified. A shotgun lipidomics approach, which uses an ESI-intrasource separation of Upids from a complex extract, multidimensional mass spectrometry, and computer-assisted array analysis, is described. 

---