MALDI imaging mass spectrometry and analysis of endogenous peptides

Abstract

In recent years, MALDI imaging mass spectrometry (MALDI-IMS) has developed as a promising tool to investigate the spatial distribution of biomolecules in intact tissue specimens. Ion densities of various molecules can be displayed as heat maps while preserving anatomical structures. In this short review, an overview of different biomolecules that can be analyzed by MALDI-IMS is given. Many reviews have covered imaging of lipids, small metabolites, whole proteins and enzymatically digested proteins in the past. However, little is known about imaging of endogenous peptides, for example, in the rat brain, and this will therefore be highlighted in this review. Furthermore, sample preparation of frozen or formalin-fixed, paraffin-embedded (FFPE) tissue is crucial for imaging experiments. Therefore, some aspects of sample preparation will be addressed, including washing and desalting, the choice of MALDI matrix and its deposition. Apart from mapping endogenous peptides, their reliable identification in situ still remains challenging and will be discussed as well.

Peptidomics for the discovery and characterization of neuropeptides and hormones

“…Neuroendocrine tissue and select types of neuronal populations often contain high local concentrations of neuropeptides and thus are suitable for direct analysis either by matrix-assisted laser desorption/ionization (MALDI) MS profiling [33] or MALDI MS imaging (MSI) with minimal sample manipulation [34–38]. Mass spectrometers with standard or interchangeable MALDI ion sources usually have MS/MS capabilities, which allow automatic or manual sequencing of peptides in solid tissue samples [39, 40].…”

“…Mass spectrometers with standard or interchangeable MALDI ion sources usually have MS/MS capabilities, which allow automatic or manual sequencing of peptides in solid tissue samples [39, 40]. MALDI MSI has an added benefit of being capable of mapping peptides to specific loci within the tissue section [34, 38]. Combined with in situ or immunohistological analyses of selected neuropeptides, direct MS measurements reveal neuropeptide distribution patterns in organs or tissues of interest [27].…”

Ecological venomics: How genomics, transcriptomics and proteomics can shed new light on the ecology and evolution of venom

“…in-situ mass spectrometry, in the form of Imaging Mass Spectrometry (IMS), may circumvent this problem; IMS provides a unique opportunity to provide information about the arrangement of proteins and small molecules in the tissue, highlighting spatial specificity of molecules that will be lost otherwise in tissue extraction (for reviews see [153,154] without the need for sequence data. However, the quantitative data available with these methods is of low resolution, and cannot distinguish between individual proteins with similar activities (although 2D zymography may come very close to it).…”

Biomarker Characterization by MALDI–TOF/MS

“…To date, MALDI-based IMS has been used in a wide range of applications: different cell types in a tissue growing were well defined by IMS [151][152][153][154][155][156][157][158][159][160], drug metabolic processes in mice were studied by IMS of whole body dissections of mice [162], and the accumulation of tainted chemical compounds in specific organs such as melamine in kidney was proven by IMS [163]. More applications about MALDI-based IMS can be found in several reviews [164][165][166][167][168][169][170][171].…”