Correlative mass spectrometry imaging, applying time‐of‐flight secondary ion mass spectrometry and atmospheric pressure matrix‐assisted laser desorption/ionization to a single tissue section

Abstract

RationaleMass spectrometry imaging (MSI) is a powerful tool for mapping the surface of a sample. Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) and atmospheric pressure matrix‐assisted laser desorption/ionization (AP‐MALDI) offer complementary capabilities. Here, we present a workflow to apply both techniques to a single tissue section and combine the resulting data for the example of human colon cancer tissue.MethodsFollowing cryo‐sectioning, images were acquired using the high spatial resolution (1 μm pixel size) provided by TOF‐SIMS. The same section was then coated with a para‐nitroaniline matrix and images were acquired using AP‐MALDI coupled to an Orbitrap mass spectrometer, offering high mass resolution, high mass accuracy and tandem mass spectrometry (MS/MS) capabilities. Datasets provided by both mass spectrometers were converted into the open and vendor‐independent imzML file format and processed with the open‐source software MSiReader.ResultsThe TOF‐SIMS and AP‐MALDI mass spectra show strong signals of fatty acids, cholesterol, phosphatidylcholine and sphingomyelin. We showed a high correlation between the fatty acid ions detected with TOF‐SIMS in negative ion mode and the phosphatidylcholine ions detected with AP‐MALDI in positive ion mode using a similar setting for visualization. Histological staining on the same section allowed the identification of the anatomical structures and their correlation with the ion images.ConclusionsThis multimodal approach using two MSI platforms shows an excellent complementarity for the localization and identification of lipids. The spatial resolution of both systems is at or close to cellular dimensions, and thus spatial correlation can only be obtained if the same tissue section is analyzed sequentially. Data processing based on imzML allows a real correlation of the imaging datasets provided by these two technologies and opens the way for a more complete molecular view of the anatomical structures of biological tissues.

Mammalian sphingoid bases: Biophysical, physiological and pathological properties

“…It has the advantage of being a versatile technique with submicron three-dimensional spatial resolution and represents a good alternative to the use of more invasive methodologies that use fluorescently tagged lipid molecules [278,279]. Moreover, advances in mass spectrometry imaging might be a promising strategy to address membrane lipid composition and lipid trafficking in intact cells [280][281][282].…”

Mass Spectrometry Imaging: A Review of Emerging Advancements and Future Insights

“…Then, matrix was applied to the same tissue section and AP-MALDI was used to identify lipids at high mass accuracy and also to perform on-tissue MS/MS. 195 Additionally, the same ionization mechanisms can be used for multimodal systems for analyzing different molecular species. For example, MALDI-MSI can be used to analyze both N-glycans and proteins using sequential analysis of the PNGaseF enzyme to release glycans followed by application of trypsin to analyze proteins from the same tissue section using FFPE tissues.…”

MALDI Imaging for Proteomic Painting of Heterogeneous Tissue Structures

“…[8] In principle, MALDI imaging can be based upon detection of peptides, [9,10] proteins, [11] carbohydrates, [12] and fatty acids. [13] Particular attention was given to MALDI imaging for cancer typing, [14] determination of cancer heterogeneity, [15] tumor margins, [16] and identification of drug and metabolites in cancer tissue. [17] Tumor heterogeneity will attract special interest in the next years since biological behavior of a tumor strongly depends on the most poorly differentiated area of the respective tumor.…”

“…In the past, introduction into clinical routine was prevented by low acquisition time of spectra, absence of adequate biostatistical software, and low level of standardization . In principle, MALDI imaging can be based upon detection of peptides, proteins, carbohydrates, and fatty acids . Particular attention was given to MALDI imaging for cancer typing, determination of cancer heterogeneity, tumor margins, and identification of drug and metabolites in cancer tissue .…”