Brain Tissue Studied Using Mass Spectrometry Imaging

In a new study published in Analytical Chemistry, a group of scientists tested a new means of analyzing lipids in brain tissue using mass spectrometry imaging (MSI) (1).

MSI has led to great advances in how scientists comprehend lipid metabolism and spatial distribution in tissues and cells. However, few MSI studies quantitively approach lipid imaging, and those that have only focus on one lipid class at a time.

In this study, the scientists instead used a multiclass internal standard (IS) mixture, which was sprayed over the tissue surface with concentrations reflecting those of endogenous lipids. This allowed for quantitative MSI (Q-MSI) of 13 lipid classes and subclasses, representing nearly 200 sum-composition lipid species. This was done with MALDI (negative ion mode) and MALDI-2 (positive ion mode), as well as pixel-wise normalization of each lipid species, like approaches that are used in shotgun lipidomics. The Q-MSI approach covered 3 orders of magnitude in a dynamic range (with lipid concentrations reported in pmol/mm2), revealing subtle distribution compared to data without normalization. The method’s robustness was evaluated by repeating experiments in two laboratories using timsTOF and Orbitrap mass spectrometers with a ~4-fold difference in mass resolution power.

Overall, there was a strong correlation in the Q-MSI results between the two approaches. Outliers were rationalized by either isobaric interferences or one instrument being more sensitive towards a particular lipid species. According to the scientists, “These data provided insight into how the mass resolving power can affect Q-MSI data” (1). This approach can enable future large-scale Q-MSI studies across lipid classes and subclasses, revealing how absolute lipid concentrations can vary throughout and between biological tissues.

Reference

1. Vandenbosch, M.; Mutuku, S. M.; Mantas, M. J. Q.; Patterson, N. H.; Hallmark, T.; Claesen, M.; Heeren, R. M. A.; Hatcher, N. G.; Verbeeck, N.; Ekroos, K.; Ellis, S. R. Toward Omics-Scale Quantitative Mass Spectrometry Imaging of Lipids in Brain Tissue Using a Multiclass Internal Standard Mixture. Anal. Chem. 2023. DOI: https://doi.org/10.1021/acs.analchem.3c02724