Combined Elemental and Biomolecular Mass Spectrometry Imaging for Probing the Inventory of Tissue at a Micrometer Scale

Abstract

Several complementary mass spectrometric imaging techniques allow mapping of various analytes within biological tissue sections. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) quantitatively detects elements and isotopes with very high sensitivity and a particularly high dynamical range. Matrix-assisted laser desorption/ionization ion mobility mass spectrometry (MALDI-IM-MS) allows a pixel-by-pixel classification and identification of biomolecules.In order to dispose of the healthy hemisphere as an internal calibrant in addition to routinely used external standards, adjacent brain sections of mice with a unilateral 6-OHDA lesion of the medial forebrain bundle were chosen as exemplary samples. We demonstrate a comprehensive way of data acquisition and analysis by coregistering mass spectrometric data on photomicrographs as common reference space and thus providing trimodal spatial information. Registering subsequent planar element maps yielded continuous 3-dimensional data sets. Furthermore, we introduce a correction of MSI data for variable slice thickness applicable to all MSI techniques. In the present case, we observed increased concentrations of iron, manganese, and copper in the lesioned substantia nigra while monounsaturated lipid levels were decreased in the identical region of interest. Our techniques provide new insights into the intricate spatial relationship of morphology and chemistry within tissue.

Ambient Molecular Analysis of Biological Tissue Using Low-Energy, Femtosecond Laser Vaporization and Nanospray Postionization Mass Spectrometry

“…These features were identified as phospholipids, i.e., phosphatidylcholine (PC) and phosphatidylethanolamine (PE), and listed in Table S-3 in the Supplementary Material. The peak detected at m/z 760.6 corresponds to PC(34:1) and has been observed previously for the analysis of mouse brain section by MALDI [47][48][49], SIMS [45], and LAESI [12]. The low abundance features in the mass region m/z <700 are likely fragments of lipids or metabolites.…”

“…Peaks were labeled and confirmed by comparing the blank-subtracted spectra with the nanospray blank spectra. Features identified from plant sample were assigned by searching in the METLIN database [37] All the assignments were further confirmed by comparing with literature data [12,33,[39][40][41][42][43][44][45][46][47][48][49][50].…”

Laser ablation ICP-MS for quantitative biomedical applications

“…MALDI-MS or ESI-MS) [2,98,99]. It is worth highlighting, however, that combining LA-ICP-MS and protein fingerprinting methods ("integrated speciation" by heteroatom-tagged proteomics) helps to overcome some of the current limitations of the approaches more commonly used in proteomics.…”

Mass Spectrometry Imaging of Biomolecular Information

“…Atmospheric pressure (ambient) ionization methods have increasingly been developed and used, as recently reviewed 8 . Laser ablation inductively coupled plasma mass spectrometry imaging (LA-ICP MSI), as an elemental detector technique, has been used for marker-based detection of biomolecules 9 . It is not covered in this review, in order to keep the focus on direct molecular detection principles.…”