The Bright Future of Peptidomics

HistoSnap: A Novel Software Tool to Extract m/z-Specific Images from Large MSHC Datasets

We describe an informatics tool for comfortable browsing through highly complex, multi-gigabyte mass spectrometry histochemistry (MSHC) datasets, via clever ion-specific image extraction.The package is developed particularly for the untargeted localization/discovery of biomolecules such as endogenous (neuro)secretory peptides on histological sections of biobanked formaldehyde-fixed paraffin-embedded (FFPE) samples straight from tissue banks.Atmospheric pressure-MALDI-Orbitrap MSHC data of sections through human pituitary adenomas in which two well-known human neuropeptides are detected are used as an example to demonstrate the key features of the novel software, named HistoSnap.

Spatially Resolved Neuropeptide Characterization from Neuropathological Formalin-Fixed, Paraffin-Embedded Tissue Sections by a Combination of Imaging MALDI FT-ICR Mass Spectrometry Histochemistry and Liquid Extraction Surface Analysis-Trapped Ion Mobility Spectrometry-Tandem Mass Spectrometry

To make the vast collections of well-documented human clinical samples archived in biobanks accessible for mass spectrometry imaging (MSI), recent developments have focused on the label-free top-down MS analysis of neuropeptides in sections of formalin-fixed, paraffin-embedded (FFPE) tissues. In analogy to immunohistochemistry (IHC), this variant of MSI has been designated MSHC (mass spectrometry histochemistry). Besides the detection and localization of neuropeptide and other biomolecular MS signals in these FFPE samples, there is great interest in their molecular identification and full characterization. We here used matrix assisted laser desorption ionization (MALDI) MSI employing ultrahigh-resolution FT-ICR MS on 2,5-dihydroxybenzoic acid (DHB) coated five-micron sections of human FFPE pituitary to demonstrate clear isotope patterns and elemental composition assignment of neuropeptides (with ∼1 ppm mass accuracy). Besides tandem MS fragmentation pattern analysis to deduce or confirm amino acid sequence information (Arg-vasopressin for the case presented here), there is a need for orthogonal primary structure characterization of the peptide-like MS signals of biomolecules desorbed directly off FFPE tissue sections. In the present work, we performed liquid extraction surface analysis (LESA) extractions on consecutive (uncoated) tissue slices. This enables the successful characterization by ion mobility MS of vasopressin present in FFPE material. Differences in sequence coverage are discussed on the basis of the mobility selected collision induced dissociation (CID), electron capture dissociation (ECD), and UV photodissociation (UVPD) MS/MS. Using Arg-vasopressin as model case (a peptide with a disulfide bridged ring structure), we illustrate the use of LESA in combination with a reduction agent for effective sequencing using mobility selected CID, ECD, and UVPD MS/MS.