From Whole-body Sections Down to Cellular Level, Multiscale Imaging of Phospholipids by MALDI Mass Spectrometry

Abstract

Significant progress in instrumentation and sample preparation approaches have recently expanded the potential of MALDI imaging mass spectrometry to the analysis of phospholipids and other endogenous metabolites naturally occurring in tissue specimens. Here we explore some of the requirements necessary for the successful analysis and imaging of phospholipids from thin tissue sections of various dimensions by MALDI time-of-flight mass spectrometry. We address methodology issues relative to the imaging of whole-body sections such as those cut from model laboratory animals, sections of intermediate dimensions typically prepared from individual organs, as well as the requirements for imaging areas of interests from these sections at a cellular scale spatial resolution. We also review existing limitations of MALDI imaging MS technology relative to compound identification. Finally, we conclude with a perspective on important issues relative to data exploitation and management that need to be solved to maximize biological understanding of the tissue specimen investigated. Molecular & Cellular Proteomics 10: 10.1074/mcp.O110.004259, 1-11, 2011.Since its introduction in the late 90s (1), MALDI imaging mass spectrometry (MS) technology has witnessed a phenomenal expansion. Initially introduced for the mapping of intact proteins from fresh frozen tissue sections (2), imaging MS is now routinely applied to a wide range of different compounds including peptides, proteins, lipids, metabolites, and xenobiotics (3-7). Numerous compound-specific sample preparation protocols and analytical strategies have been developed. These include tissue sectioning and handling (8 -14), automated matrix deposition approaches and data acquisition strategies (15-21), and the emergence of in situ tissue chemistries (22)(23)(24)(25). Originally performed on sections cut from fresh frozen tissue specimens, methodologies incorporating an in situ enzymatic digestion step prior to matrix application have been optimized to access the proteome locked in formalin-fixed paraffin-embedded tissue biopsies (25)(26)(27)(28)(29). The possibility to use tissues preserved using non-cross-linking approaches has also been demonstrated (30 -32). These methodologies are of high importance for the study of numerous diseases because they potentially allow the retrospective analysis for biomarker validation and discovery of the millions of tissue biopsies currently stored worldwide in tissue banks and repositories.In the past decade, instrumentation for imaging MS has also greatly evolved. Whereas the first MS images were collected with time-of-flight instruments (TOF) capable of repetition rates of a few hertz, modern systems are today capable of acquiring data in the kilohertz range and above with improved sensitivity, mass resolving power, and accuracy, significantly reducing acquisition time and improving image quality (33, 34). Beyond time-of-flight analyzers, other MALDIbased instruments have been used such as ion traps (35-37), Qq TOF instruments (38 -40), and ...

Development of Laser Desorption Imaging Mass Spectrometry Methods to Investigate the Molecular Composition of Latent Fingermarks

“…Solvent-free matrix deposition on fingermarks was carried out in a sublimation apparatus (Chemglass Life Science, Vineland, NJ, USA) as previously described [30]. The temperature and the time of sublimation were optimized for each matrix to ensure the best coverage and MALDI efficiency (number of signals detected and signal to noise).…”

“…Recently, matrix sublimation was demonstrated to be a powerful approach for very homogeneous matrix deposition that allows for the detection and IMS of small molecules and proteins with high sensitivity and high spatial resolution [30][31][32]. In the first approach proposed herein, we provide an alternative to the Bdry-wet^method using sublimation for homogeneous matrix deposition followed by automated solvent spray deposition.…”

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