@article{loziuk_meier_johnson_ghashghaei_muddiman_2016, title={TransOmic analysis of forebrain sections in Sp2 conditional knockout embryonic mice using IR-MALDESI imaging of lipids and LC-MS/MS label-free proteomics}, volume={408}, ISSN={1618-2642 1618-2650}, url={http://dx.doi.org/10.1007/s00216-016-9421-3}, DOI={10.1007/s00216-016-9421-3}, abstractNote={Quantitative methods for detection of biological molecules are needed more than ever before in the emerging age of "omics" and "big data." Here, we provide an integrated approach for systematic analysis of the "lipidome" in tissue. To test our approach in a biological context, we utilized brain tissue selectively deficient for the transcription factor Specificity Protein 2 (Sp2). Conditional deletion of Sp2 in the mouse cerebral cortex results in developmental deficiencies including disruption of lipid metabolism. Silver (Ag) cationization was implemented for infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) to enhance the ion abundances for olefinic lipids, as these have been linked to regulation by Sp2. Combining Ag-doped and conventional IR-MALDESI imaging, this approach was extended to IR-MALDESI imaging of embryonic mouse brains. Further, our imaging technique was combined with bottom-up shotgun proteomic LC-MS/MS analysis and western blot for comparing Sp2 conditional knockout (Sp2-cKO) and wild-type (WT) cortices of tissue sections. This provided an integrated omics dataset which revealed many specific changes to fundamental cellular processes and biosynthetic pathways. In particular, step-specific altered abundances of nucleotides, lipids, and associated proteins were observed in the cerebral cortices of Sp2-cKO embryos.}, number={13}, journal={Analytical and Bioanalytical Chemistry}, publisher={Springer Science and Business Media LLC}, author={Loziuk, Philip and Meier, Florian and Johnson, Caroline and Ghashghaei, H. Troy and Muddiman, David C.}, year={2016}, month={Mar}, pages={3453–3474} }
 @article{meier_garrard_muddiman_2014, title={Silver dopants for targeted and untargeted direct analysis of unsaturated lipids via infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI)}, volume={28}, ISSN={["1097-0231"]}, DOI={10.1002/rcm.7041}, abstractNote={RATIONALEUnsaturated lipids play a crucial role in cellular processes as signaling factors, membrane building blocks or energy storage molecules. However, adequate mass spectrometry imaging of this diverse group of molecules remains challenging. In this study we implemented silver cationization for direct analysis by infrared matrix‐assisted laser desorption electrospray ionization (IR‐MALDESI) to enhance the ion abundances for olefinic lipids and facilitate peak assignment.METHODSTrace amounts of silver nitrate were doped into the electrospray solvent of an IR‐MALDESI imaging source coupled to an Orbitrap mass analyzer. Calcifediol was examined as a model compound to demonstrate the effect of silver dopants on sensitivity and assay robustness. Dried human serum spots were subsequently analyzed to compare Ag‐doped solvents with previously described solvent compositions. Mass differences as well as ion abundance ratio filters were employed to interpret results based on the characteristic isotopic pattern of silver.RESULTSOlefinic lipids were readily observed as silver adducts in IR‐MALDESI analyses. Silver cationization decreased the limit of detection for calcifediol by at least one order of magnitude and was not affected in complex biological matrices. The ion abundance ratio and mass difference of [M + 107Ag+]+ and [M + 109Ag+]+ were successfully applied to facilitate the spectral assignment of silver adducts. Overall, silver cationization increased the analyte coverage in human serum by 43% compared with a standard IR‐MALDESI approach.CONCLUSIONSSilver cationization has been shown to enhance IR‐MALDESI sensitivity and selectivity for unsaturated lipids, even when applied to complex samples. Increased compound coverage, enhanced robustness as well as the developed tools for peak assignment and mapping of isotopic patterns will clearly benefit future mass spectrometry imaging studies. Copyright © 2014 John Wiley & Sons, Ltd.}, number={22}, journal={RAPID COMMUNICATIONS IN MASS SPECTROMETRY}, author={Meier, Florian and Garrard, Kenneth P. and Muddiman, David C.}, year={2014}, month={Nov}, pages={2461–2470} }