An Organ-Specific Metabolite Annotation Approach for Ambient Mass Spectrometry Imaging Reveals Spatial Metabolic Alterations of a Whole Mouse Body

Abstract

Rapid and accurate metabolite annotation in mass spectrometry imaging (MSI) can improve the efficiency of spatially resolved metabolomics studies and accelerate the discovery of reliable in situ disease biomarkers. To date, metabolite annotation tools in MSI generally utilize isotopic patterns, but high-throughput fragmentation-based identification and biological and technical factors that influence structure elucidation are active challenges. Here, we proposed an organ-specific, metabolite-database-driven approach to facilitate efficient and accurate MSI metabolite annotation. Using data-dependent acquisition (DDA) in liquid chromatography coupled with tandem mass spectrometry (LC−MS/MS) to generate high-coverage product ions, we identified 1620 unique metabolites from eight mouse organs (brain, liver, kidney, heart, spleen, lung, muscle, and pancreas) and serum. Following the evaluation of the adduct form difference of metabolite ions between LC−MS and airflow-assisted desorption electrospray ionization (AFADESI)-MSI and deciphering organ-specific metabolites, we constructed a metabolite database for MSI consisting of 27,407 adduct ions. An automated annotation tool, MSIannotator, was then created to conduct metabolite annotation in the MSI dataset with high efficiency and confidence. We applied this approach to profile the spatially resolved landscape of the whole mouse body and discovered that metabolites were distributed across the body in an organ-specific manner, which even spanned different mouse strains. Furthermore, the spatial metabolic alteration in diabetic mice was delineated across different organs, exhibiting that differentially expressed metabolites were mainly located in the liver, brain, and kidney, and the alanine, aspartate, and glutamate metabolism pathway was simultaneously altered in these three organs. This approach not only enables robust metabolite annotation and visualization on a body-wide level but also provides a valuable database resource for underlying organ-specific metabolic mechanisms.

Time of acquisition and high spatial resolution mass spectrometry imaging

“…MSI has also been used to image entire neonatal mouse specimens, 16,17 which are much larger than a routine MSI sample. Though this is an exaggerated example, Figure 3 illustrates how small pixel size (e.g., 10 μm or 0.01 mm) would render this unfeasible.…”

Advanced mass spectrometric and spectroscopic methods coupled with machine learning for in vitro diagnosis

“…Copyright 2019, American Chemical Society. (C) LC–MS/MS Information‐Integrated Organ‐Specific Metabolite Annotation Workflow for DESI–MSI 110 . Copyright 2022, American Chemical Society.…”

“…They revealed organ metabolism remains highly specific (Figure 4C). 110 Yan et al. combined DESI–MSI and immunofluorescence to realize cell‐type‐specific and in situ metabolic profiling in tissue samples.…”

“…(C) LC-MS/MS Information-Integrated Organ-Specific Metabolite Annotation Workflow for DESI-MSI. 110 Copyright 2022, American Chemical Society. (D) DESI-MSI combined with PLS-DA for cell-type-specific and in situ metabolic profiling.…”

Evaluation of Quantitative Platforms for Single Target Mass Spectrometry Imaging

“…Mass spectrometry imaging (MSI) has pushed the boundary of pharmaceutical studies by allowing for ever more precise understanding of the distribution of drugs [ 1 , 2 ], metabolites [ 3 , 4 ], and endogenous products [ 5 , 6 ] within tissue sections. Advancements in MSI technology have improved both the sensitivity and resolution with sensitivity routinely approaching 1 microgram of analyte (for m / z ~300–800) per gram of tissue [ 7 , 8 ], and resolution reaching 5 μm on commercial platforms [ 9 , 10 ].…”