MSI MALDI-MS for Direct Lipid Profiling of Intact Tissues

Abstract

Matrix-Assisted Laser Desorption/Ionization coupled with Mass Spectrometry (MALDI-MS) has become the method of choice for mass spectrometry based imaging (MSI) of lipids directly from tissue sections.[1] Molecular ion identification and localization with a 20-sensitivity can be achieved over a wide mass range (typically, 400-2 kDa).Current challenges are in the sample preparation method and matrix deposition to improve analysis reproducibility. For MALDI experiments, matrix choice is strongly dependent on the chemical class of interest. Lipids account for up to 50% of the dried weight of brain tissue sections compared to other chemical classes and are vital brain function regulators. Lipidomic analysis of brain tissues has significantly increased in relation to better understanding the role of lipids in the development of debilitating neurodege Our work focuses on the applications of MALDI-MS for direct lipid mapping in model systems as a function of a biological question (e.g., disease vs. non disease, low vs. high fatty acid diet, etc.). Comparison between positive and negative MS mode shows that molecular ion emission can be directly correlated to the surface concentration, the ionization probability and lipid classification. Two distinct lipid distributions were observed and can be attributed to the difference in the charge carriers (lipid head groups) for the different lipid classes.References:

APCI(+)FT-ICR MS Analysis of Hydrocarbons Using Isooctane as Ionizing Reagent - A Comparison with HTGC-FID, GC×GC-MS and NMR

“…All mass spectra were externally calibrated using L-arginine (200-2000 m/z), then internally recalibrated using the most abundant homologous alkylated compounds in each sample. [17][18][19][20][21][22] The tandem mass spectrometry (MS 2 ) experiments were performed on a quadrupole coupled to an FT-ICR mass spectrometer, Q-FT-ICR MS. APCI(+)MS/MS experiments were performed using collision energies of 15-30% for the ions of m/z 561, 589, 603, 645, 673, and 701, and 0-30% for the two PAH commercial standards (ions of m/z 229 and 301). 23 The resolving power (m/∆m 50% from 420,000 to 530,000, where m corresponds to m/z 400 and ∆m 50% is the full peak width at half-maximum peak height) and mass accuracy lower than 1-3 ppm provided the unambiguous molecular formula assignments for all singly charged molecular ions.…”

“…Generally, this behavior provides evidence that PAHs are not a significant portion of the paraffins standards. 22,23 From the APCI(+)MS/MS spectra, DBE versus CN plots were constructed for ions of m/z 701, 645, 561, 673, 589, and 603 (standard P4, Figures 4a-4f), corresponding to the HC[H] class. For the ions of DBE = 0 (m/z 701 and 645), the produced fragments showed a continuous distribution of CNs ranging from C 18 to C 43 with DBE = 0 for n-paraffin molecules (Figures 4a-4b).…”