Metal Oxide Laser Ionization Mass Spectrometry Imaging of Fatty Acids and Their Double Bond Positional Isomers

Abstract

We present a novel combination of a metal oxide laser ionization mass spectrometry imaging (MOLI MSI) technique with off-line lipid derivatization by ozone for the detection of fatty acids (FA) and their carbon−carbon double bond (CC) positional isomers in biological tissues. MOLI MSI experiments were realized with CeO 2 and TiO 2 nanopowders using a vacuum matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometer in the negative mode. The catalytic properties of these metal oxides allow FA cleavage from phospholipids under UV laser irradiation. At the same time, fragile ozonides produced at the sites of unsaturation decomposed, yielding four diagnostic ions specific for the CC positions. Advantageously, two MOLI MSI runs from a single tissue sprayed with the metal oxide suspension were performed. The first run prior to ozone derivatization revealed the distribution of FAs, while the second run after the reaction with ozone offered additional information about FA CC isomers. The developed procedure was demonstrated on MSI of a normal mouse brain and human colorectal cancer tissues uncovering the differential distribution of FAs down to the isomer level. Compared to the histological analysis, MOLI MSI showed the distinct distribution of specific FAs in different functional parts of the brain and in healthy and cancer tissues pointing toward its biological relevance. The developed technique can be directly adopted by laboratories with MALDI TOF analyzers and help in the understanding of the local FA metabolism in tissues.

Temporally and spatially resolved molecular profiling in fingerprint analysis using indium vanadate nanosheets-assisted laser desorption ionization mass spectrometry

“…In the last decades, multifarious nanomaterials (e.g. porous silicon [ 8 , 9 ], carbon-based materials [ 10 – 12 ], metal oxides [ 13 – 16 ], metal-organic frameworks [ 17 , 18 ], and metal nanomaterials [ 19 , 20 ]) several techniques have been developed for the fabrication of SALDI nano-matrices. The efficacy of these nano-matrices has been extensively demonstrated in several applications of SALDI-MS. For instance, Pleskunov et al reported niobium nanoparticles based SALDI-MS method for multiple phospholipids analysis on mouse brain tissue [ 21 ].…”

A Five-Year Update on Matrix Compounds for MALDI-MS Analysis of Lipids

“…Other approaches make use of ozonolysis [ 22 , 24 ] or the Paternò-Büchi reaction [ 25 ]. CeO 2 and TiO 2 nanopowders, in combination with ozonolysis, are also known to enable the scission of double bonds under conditions of UV irradiation [ 26 ]. Some oxidation products of FFA (such as chain-shortened aldehydes, for instance, nonanal) can hardly be detected by MALDI-MS because they are lost in the vacuum.…”

Establishing carbon–carbon double bond position and configuration in unsaturated fatty acids by gas-phase infrared spectroscopy

“…4,10 The challenge of FA identication is further confounded by the identical electron ionization mass spectra of isomeric FAMEs. 11,12 Utilization of 3-pyridylcarbinol esters 11,13 and other derivatization [14][15][16][17][18][19][20][21] or ion activation 22,23 strategies can instead yield diagnostic mass spectral fragments for DB position assignment in FAs. However, apart from rare exceptions, [24][25][26][27][28] these tandem MS approaches are agnostic to DB geometry.…”