Detection of Localized Hepatocellular Amino Acid Kinetics by using Mass Spectrometry Imaging of Stable Isotopes

Abstract

Mass spectrometry imaging (MSI) simultaneously detects and identifies the spatial distribution of numerous molecules throughout tissues. Currently, MSI is limited to providing a static and ex vivo snapshot of highly dynamic systems in which molecules are constantly synthesized and consumed. Herein, we demonstrate an innovative MSI methodology to study dynamic molecular changes of amino acids within biological tissues by measuring the dilution and conversion of stable isotopes in a mouse model. We evaluate the method specifically on hepatocellular metabolism of the essential amino acid l‐phenylalanine, associated with liver diseases. Crucially, the method reveals the localized dynamics of l‐phenylalanine metabolism, including its in vivo hydroxylation to l‐tyrosine and co‐localization with other liver metabolites in a time course of samples from different animals. This method thus enables the dynamics of localized biochemical synthesis to be studied directly from biological tissues.

Following spatial Aβ aggregation dynamics in evolving Alzheimer’s disease pathology by imaging stable isotope labeling kinetics

“…While NanoSIMS imaging provides outstanding data on nanoscopic isotope enrichment, one challenge of the technique is the limited molecular information retrievable, permitting analysis of intact peptides and proteins. This is something that can be achieved with matrix-assisted laser desorption/ionization MS-based IMS (MALDI-IMS), which has been successfully demonstrated for monitoring spatial enrichment and metabolization of intraperitoneally injected, stable isotope-labeled drug candidates (26) or intranasally instilled and intraperitoneally injected stable isotope-labeled phospholipids (27). Most importantly, MALDI-IMS allows for comprehensive, chemically specific A peptide imaging of A pathology in AD mouse models (10,28) and in postmortem human AD brain tissue (29,30).…”

On‐tissue chemical derivatization reagents for matrix‐assisted laser desorption/ionization mass spectrometry imaging

“…The results showed quantities of free amino acids higher in the metastatic regions than parenchymal regions of tumorbearing livers. The authors thus suggested that metabolic remodeling Arts et al 20 also performed OTCD using TAHS reagent to enable a sensitive detection of many free amino acids and their labeled analogues. They presented a novel method based on stable isotope labeling to study dynamic molecular changes of amino acids within tissues.…”

“…The authors thus suggested that metabolic remodeling of the host tissue may be caused by the development of metastases. Arts et al 20 also performed OTCD using TAHS reagent to enable a sensitive detection of many free amino acids and their labeled analogues. They presented a novel method based on stable isotope labeling to study dynamic molecular changes of amino acids within tissues.…”

Mass spectrometry imaging of phosphatidylcholine metabolism in lungs administered with therapeutic surfactants and isotopic tracers

“…Such approaches have been more widely applied using secondary ion mass spectrometry (SIMS), but due to the extensive fragmentation observed by SIMS whereby often only elemental or diatomic fragments are observed (e.g., Nano SIMS), it is difficult to study the metabolism of individual lipid species 18,19 . Recently several groups have coupled isotope labelling with MALDI 20 or with desorption electrospray ionisation (DESI) 21 , both of which enable detection of intact lipid species. These studies utilised heavy water labelling of mice to study region-specific lipid synthesis in breast cancer and mouse brain tissue, respectively.…”