Mass Spectrometry Imaging with Isomeric Resolution Enabled by Ozone‐Induced Dissociation

Abstract

Mass spectrometry imaging (MSI) enables the spatial distributions of molecules possessing different mass‐to‐charge ratios to be mapped within complex environments revealing regional changes at the molecular level. Even at high mass resolving power, however, these images often reflect the summed distribution of multiple isomeric molecules, each potentially possessing a unique distribution coinciding with distinct biological function(s) and metabolic origin. Herein, this chemical ambiguity is addressed through an innovative combination of ozone‐induced dissociation reactions with MSI, enabling the differential imaging of isomeric lipid molecules directly from biological tissues. For the first time, we demonstrate both double bond‐ and sn‐positional isomeric lipids exhibit distinct spatial locations within tissue. This MSI approach enables researchers to unravel local lipid molecular complexity based on both exact elemental composition and isomeric structure directly from tissues.

Imaging Isomers on a Biological Surface: A Review

“…sodium acetate has been found to be bene cial for the OzID, as the sodiated lipids have a higher yield of ozonolysis products compared to the protonated or potassiated lipids. 39,57,61) is is consistent among various publications, indicating that sodium has a faster reaction rate and suggesting the participation of the charge carrier, perhaps via chelation of the double bond, in the mechanism of the reaction. 56,58) It has also been found that the trans isomer reacts faster than the cis isomer.…”

A lipidomic workflow capable of resolving sn- and CC location isomers of phosphatidylcholines

“…Notably, the same pair of sn-isomers was found to distribute distinctly in the tumor region relative to surrounding tissue in a mouse brain section, as recently revealed by OzID MALDI-imaging 31 and DESI-UVPD- imaging. 33,45 Our data clearly suggest that PC 16:0_18:1 may contain four structural isomers from combinations of two snisomers and two C]C location isomers of the C18:1. Quantitative comparison of each individual isomer, however, is challenging for the current workow because C]C isomeric ratios of the sn-2 fatty acyl chain cannot be measured independently.…”

“…Several recent MS imaging studies clearly demonstrated that lipid isomers, including fatty acyl compositional isomers, sn-, and C]C location isomers, were distributed heterogeneously in tissue sections or among different types of tissues, likely carrying distinct functions. [31][32][33]45 In an earlier study, we reported that changes of C]C location isomers were more sensitive to pathological conditions than lipid prole changes. 19 In this study, we were interested to test if changes of PC snisomers would differentiate lipidomes of diseased and healthy states, which may be potentially used as markers in biomedical and clinical studies.…”

“…27,28 All these developments greatly expand the toolbox for lipid analysis; more importantly, they not only provide rst-time analysis of lipidomes at the isomer level 11,19,[28][29][30] but also demonstrate the link between altered isomer compositions with disease quantitatively and spatially. [31][32][33][34] Radical-directed fragmentation has attracted increasing attention in MS/MS method development due to its unique capabilities in differentiating structural isomers of biomolecules, which otherwise cannot be obtained from chargedirected fragmentations typically seen from CID. 35,36 A common approach to induce radical-directed fragmentation from even-electron precursor ions, the most common ionic form derived from electrospray ionization (ESI), is to initiate homolytic cleavage of a covalent bond within the ion.…”

Reshaping Lipid Biochemistry by Pushing Barriers in Structural Lipidomics

“…Isomer‐resolved MALDI‐MSI has also been reported using OzID . This work provided the first example of the differentiation of both db‐ and sn ‐isomers during MSI.…”