Tandem Mass Spectrometry Imaging Enables High Definition for Mapping Lipids in Tissues

Abstract

Mass spectrometry imaging (MSI) of lipids in biological tissues is useful for correlating molecular distribution with pathological results, which could provide useful information for both biological research and disease diagnosis. It is well understood that the lipidome could not be clearly deciphered without tandem mass spectrometry analysis, but this is challenging to achieve in MSI due to the limitation in sample amount at each image spot. Here we develop a multiplexed MS2 imaging (MS2I) method that can provide MS2 images for 10 lipid species or more for each sampling spot, providing spatial structural lipidomic information. Coupling with on‐tissue photochemical derivatization, imaging of 20 phospholipid C=C location isomers is also realized, showing enhanced molecular images with high definition in structure for mouse brain and human liver cancer tissue sections. Spatially mapped t‐distributed stochastic neighbor embedding has also been adopted to visualize the tumor margin with enhancement by structural lipidomic information.

Revealing Structure and Localization of Steroid Regioisomers through Predictive Fragmentation Patterns in Mass Spectrometry Imaging

“…Despite the excitement of simultaneously visualizing multiple steroids in brain tissue, each m / z may contain multiple isobars and isomers that are unresolved, even with high-resolution mass measurements. Isobaric and isomeric endogenous species have been previously mapped in tissue by combining MSI with MS 2 , MS 3 , or MS 4 . ,,− Here, we demonstrate imaging of steroids with isomeric precision by their distinctive CRF pattern using silver-doped PA nano-DESI and report their distributions in mouse brain tissue (Figure j–t). The similar distribution of the precursor and DPI for estradiol and pregnanolone suggests that this isomer is the major analyte in the mass channel (Figure k–l and n–o).…”

Next Generation of Mass Spectrometry Imaging: from Micrometer to Subcellular Resolution

“…At present, it has become one of the key technologies for biological MSI analysis. MALDI has shown significant advantages in the detection of molecular ions almost without fragment ions, especially lipids or proteins in biological samples. − The applications of organic matrices play an important role in it, including α-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB), et al Abundance matrices of small organic molecules have been proposed in recent years and molecule detection in biological samples is to a great extent dependent on the choice of a proper matrix . The matrix selection and disposition have been detailly summarized in the updated review of recent advances and will not be elaborated on here.…”

“…This problem is mitigated by time-of-flight secondary ion mass spectroscopy (ToF-SIMS) technology, but the spatial resolution is also sacrificed, making its optimal value about 1 μm. − Based on the laser beam desorption/ionization source, different MSI methodologies displayed multiscale spatial resolution. For example, matrix-assisted laser desorption ionization MSI (MALDI-MSI) has a strong application in mapping the oocyte or tissue with imaging resolutions ranging from a few micrometers to dozens of micrometer. − Recently developed MALDI-2 imaging technology, combined with the transmission laser ablation method, amazingly raised the spatial resolution to ∼600 nm . This submicrometer level of spatial resolution has also been verified for single-cell research.…”

MS3 Imaging Enables the Simultaneous Analysis of Phospholipid C═C and sn-Position Isomers in Tissues

“…The strategy of chemical derivatization-coupled MS/MS bypasses the reaction required inside the mass analyzer. On-tissue or online derivatization was explored by a PB reaction, − epoxidation, and singlet-oxygen reaction for MSI applications. These methods improve the sensitivity for detection of phospholipids and CC location isomers; however, due to a lack of capability to identify the chain composition, these methods cannot allocate CC locations onto the fatty acyl chain (e.g., PC 16:0_18:1­( n -9) or PC 16:0/18:1).…”