Applications of stable isotopes in MALDI imaging: current approaches and an eye on the future

Abstract

Matrix-assisted laser desorption/ionisation-imaging mass spectrometry (MALDI-IMS) is now an established imaging modality with particular utility in the study of biological, biomedical and pathological processes. In the first instance, the use of stable isotopically labelled (SIL) compounds in MALDI-IMS has addressed technical barriers to increase the accuracy and versatility of this technique. This has undoubtedly enhanced our ability to interpret the two-dimensional ion intensity distributions produced from biological tissue sections. Furthermore, studies using delivery of SIL compounds to live tissues have begun to decipher cell, tissue and inter-tissue metabolism while maintaining spatial resolution. Here, we review both the technical and biological applications of SIL compounds in MALDI-IMS, before using the uptake and metabolism of glucose in bovine ocular lens tissue to illustrate the current limitations of SIL compound use in MALDI-IMS. Finally, we highlight recent instrumentation advances that may further enhance our ability to use SIL compounds in MALDI-IMS to understand biological and pathological processes.

Methodology Establishment and Application of VITEK Mass Spectrometry to Detect Carbapenemase-Producing Klebsiella pneumoniae

“…According to the second strategy, microbiologists try to identify antimicrobial-resistant bacteria by exploring how they grow in an antibiotic environment. Some studies distinguish the sensitive bacteria from specific antibiotic resistance by the differences in their growth process through the culture of pathogenic bacteria on isotope-labeled medium (Sparbier et al, 2013;Grey et al, 2021). However, the special medium limitations, background peak interference, and other factors have influenced the development of this method in clinical microbiology laboratories.…”

Image to insight: exploring natural products through mass spectrometry imaging

“…Interested readers are kindly referred to other reports. 80,81 Depending on the labelling regime, organisms can be labelled uniformly or non-uniformly with different degrees of enrichment. In “global SIL” approaches, stable isotopes are introduced into biological systems via main nutrient sources in order to completely label all endogenously produced metabolites; 82 while in “tracer-based SIL”, a labelled compound (namely tracer) is administrated to the organism as a metabolic substrate.…”

Local metabolism in preclinical disease models studied with mass spectrometry imaging

“…Of note, conventional MSI typically captures a static snapshot of a highly dynamic metabolic system at a single time-point within a given tissue sample [81], hence suffering from sampling bias and the limitation of tracing dynamic metabolic changes over time. In this context, stable isotopic labeling, offers the opportunity to study the dynamics of metabolic fluxes [220], since the incorporation of isotopes (commonly 13 C, 2 H, and 15 N) into target metabolites, amino acids, small peptides or water [221] produces shifted mass signals, including the labeled precursor and the products of its metabolic conversion, which can be detected by MS-based technologies [220]. Combining targeted MSI, stable isotope labeling with the use of animal models can therefore reveal spatially resolved dynamics of targeted molecule synthesis and turn over occurring in tissue samples [81].…”

“…Moreover, slight delocalizations can be observed at a higher spatial resolution, such as 25 μm [491]. Thus, the chosen derivatization method should be compatible with the scale of achievable MSI spatial resolution and type of embedding [221]. Furthermore, the development of effective matrices for MALDI but with reduced matrix background, as well as better derivatization strategies that are less time-consuming and compatible with high spatial resolution MSI are highly required.…”

“…While MALDI-MSI dramatically increases the specificity of metabolites detection [221], it is, due to its invasiveness, limited to providing a single and static snapshot of highly dynamic systems in which molecules are constantly synthesized and consumed [81]. Using stable isotope labeling of compounds such as lipids [123,494], amino acids [490,491,495] and glucose [496,497] in MALDI-MSI combined with longitudinal animal studies allows tracing metabolic processes in which the labeled molecules are involved in a time-resolved manner.…”