Tri-modal MALDI-MS Imaging: new frontiers in diagnostics

Introduction: Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) is a unique technology that enables the in-situ detection of a broad range of biomolecules, including lipids, N-glycans, and proteins. In particular, combining multilevel molecular data can potentially improve the detection of novel disease signatures and lead to the improved stratification of patients. Here, we present a workflow that highlights the feasibility to detect lipids, N-glycans, and proteins from the same formalin-fixed paraffin embedded (FFPE) tissue section. Methods: For each section of FFPE clinical specimens, MALDI-MSI was performed in three modalities using a Bruker rapifleXTM MALDI TissuetyperTM. First of all, lipids were analysed within the m/z 500 to 1200 range. Subsequently, N-glycans, that were cleaved following digestion with PNGase-F, were analysed within the m/z 1000 to 3000 range. Finally, proteolytic peptides, obtained following digestion with trypsin, were analysed within the m/z 700 to 3000 range. All image acquisitions were performed using a laser beam scan of 44μm and a raster setting of 50 μm in both x and y co-ordinates. Results: Initially, we detected a limited number of lipids within FFPE tissue sections, as expected, whose lateral distribution was in accordance with the morphological structures present within the tissue. Furthermore, we noticed that lateral diffusion of the N-glycans and tryptic peptides in the subsequent analysis was limited, despite the numerous tissue washes and matrix applications. Finally, comparing the spatial distribution of key signals detected at these multi-molecular levels, complementary information could be obtained and regions of tissue with altered molecular profiles could be highlighted. Conclusions: The tri-modal approach presented here would be the first of its kind to consecutively detect lipids, N-Glycans and tryptic peptides in a single FFPE tissue. In conclusion, the workflow described here may be useful for a deeper understanding of complex diseases, where both lipids and proteins pathways are involved, and for assisting the pathologist in the diagnosis and stratification of patients, that may be not possible when considering a single group of analytes.