We developed a sample preparation procedure which renders significant parts of the endogenous peptidome as well as metabolome accessible for MSI on FFPE tissue sections. Analogous to immunohistochemistry (IHC), this MSI-based method was designated mass spectrometry histochemistry (MSHC). Together with expert hardware engineers, software developers, (bio)informaticians, as well as (histo)pathologists and research institute scientists, we are currently optimizing MSHC.
Aim is to make MSHC sufficiently sensitive, robust, and 'user-friendly', so that the vast archives of clinically well-documented human FFPE materials piled up in biobanks all over the planet can be easily mined. This way a MSHC Atlas of the FFPE Human Body (Healthy and Diseased) is being compiled, complementing classical histology atlases for use in pathological applications, including translational disease biomarker discovery. Obviously, our Human FFPE MSHC Atlas is intended to be integrated with current complementary initiatives, including Human Protein Atlas, and Human BioMolecular Atlas Program.
Human FFPE tissues are procured directly from biobanks, in compliance with ethical and GDPR regulations. A wide variety of healthy and cancerous tissues of different organs are included in this study, as well as neuronal tissues producing well-known neuropeptides. Neurohypohysiarian nonapeptides oxytocin and vasopressin serve as 'positive controls' for human endogenous peptide MSHC. An automated sprayer (HTX TM) is employed for consistent MALDI matrix (DHB) application on 5 micron deparaffinated histological sections. FTMS data are acquired with an LTQ Orbitrap Velos (ThermoFisher) equipped with an atmospheric pressure MALDI source (AP MALDI UHR, MassTech). The AP MALDI slide adaptor had to be modified to accommodate regular histology glasses. FTMS data (*.raw and corresponding *.xml files) are directly analyzed with Mozaic QR (Spectroswiss), without the need for conversion to imzml.
MSHC of human FFPE tissues allows routine imaging at 20 micron lateral resolution of peptides as well as metabolites with high mass accuracy (<1-2 ppm). Multi-Gbyte data (recorded in full profile acquisition mode) from sections of nonapeptide peptide synthesizing hypothalamic neurosecretory perikarya demonstrate that MSHC qualifies as another single cell 'omics' technology. Large MSHC data sets from human carcinoids show unique disease specific metabolite distributions, indicating that MSHC based patient stratification is already feasible today.