Enhancement of protein sensitivity for MALDI imaging mass spectrometry after chemical treatment of tissue sections

Abstract

MALDI imaging mass spectrometry (IMS) has become a valuable tool for the investigation of the content and distribution of molecular species in tissue specimens. Numerous methodological improvements have been made to optimize tissue section preparation and matrix deposition protocols, as well as MS data acquisition and processing. In particular for proteomic analyses, washing the tissue sections before matrix deposition has proven useful to improve spectral qualities by increasing ion yields and the number of signals observed. We systematically explore here the effects of several solvent combinations for washing tissue sections. To minimize experimental variability, all of the measurements were performed on serial sections cut from a single mouse liver tissue block. Several other key steps of the process such as matrix deposition and MS data acquisition and processing have also been automated or standardized. To assess efficacy, after each washing procedure the total ion current and number of peaks were counted from the resulting protein profiles. These results were correlated to on-tissue measurements obtained for lipids. Using similar approaches, several selected washing procedures were also tested for their ability to extend the lifetime as well as revive previously cut tissue sections. The effects of these washes on automated matrix deposition and crystallization behavior as well as their ability to preserve tissue histology were also studied. Finally, in a full-scale IMS study, these washing procedures were tested on a human renal cell carcinoma

Imaging of Phospholipids in Formalin Fixed Rat Brain Sections by Matrix Assisted Laser Desorption/Ionization Mass Spectrometry

“…M atrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) was introduced in 1997 [1] and has been widely presented as a powerful method for imaging large [2][3][4][5][6][7][8][9][10][11][12][13][14] and small molecules [15][16][17][18][19][20][21][22][23][24] in tissue. The technique has been applied to a diverse range of applications but there has been particular interest in evaluating opportunities in disease state profiling.…”

MALDI imaging and profiling MS of higher mass proteins from tissue

“…It has previously been shown that washing the tissue sections with organic solvents such as chloroform and EtOH before matrix deposition increases the number and intensities of protein signals up to 20 kDa [27][28][29]. To test if the increased high mass sensitivity and charge capacity of the high mass HM1 detector may benefit imaging MS of higher mass proteins, mouse brain tissue sections were washed with chloroform and ethanol, prepared with a matrix solution of 20 mg/mL SA in AcN:0.1% TFA (7:3, vol/vol), and then analyzed using an AutoFlex III MALDI-ToF equipped with an MCP and a HM1 detector.…”

Application of Probe Electrospray Ionization Mass Spectrometry (PESI-MS) to Clinical Diagnosis: Solvent Effect on Lipid Analysis

“…In these studies, alcohol was employed to remove salts, lipids, and any other component that would interfere with spectral analyses of biological specimens [18,19]. Additionally, Seeley et al also reported that alcohol-based washes, in particular isopropanol, are the most effective for protein analysis in a MALDI imaging as they effectively remove lipids from biological specimens [20]. Therefore, using alcohols seemed to be one of the ideal choices for better extraction of molecules, especially lipids that are major constituents of cell membranes.…”