Effect of MALDI Matrices on Lipid Analyses of Biological Tissues Using MALDI-2 Post-Ionization Mass Spectrometry

Abstract

<p>Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) allows for highly multiplexed, untargeted detection of many hundreds of analytes from tissue. Recently, laser post-ionization (MALDI-2) has been developed for increased ion yield and sensitivity for lipid IMS. However, the dependence of MALDI-2 performance on the various lipid classes is largely unknown. To understand the effect of the applied matrix on MALDI-2 analysis of lipids, samples including an equimolar lipid standard mixture, various tissue homogenates, and intact rat kidney tissue sections were analyzed using the following matrices: α-cyano-4-hydroxycinnamic acid (CHCA), 2’,5’-dihydroxyacetophenone (DHA), 2’,5’-dihydroxybenzoic acid (DHB), and norharmane (NOR). Lipid signal enhancement of protonated species using MALDI-2 technology varied based on the matrix used. Although signal improvements were observed for all matrices, the most dramatic effects using MALDI-2 were observed using NOR and DHB. For lipid standards analyzed by MALDI-2, NOR provided the broadest coverage, enabling the detection of all 13 protonated standards, including non-polar lipids, whereas DHB gave less coverage but gave the highest signal increase for those lipids recorded. With respect to tissue homogenates and rat kidney tissue, mass spectra were compared and showed that the number and intensity of neutral lipids tentatively identified with MALDI-2 using NOR increased significantly (e.g. 5-fold intensity increase for triacylglycerol). In the cases of DHB with MALDI-2, the number of protonated lipids identified from tissue homogenates doubled with 152 on average compared to 76 with MALDI alone. High spatial resolution imaging (~20 µm) of rat kidney tissue showed similar results using DHB with 125 lipids tentatively identified from MALDI-2 spectra versus just 72 using standard MALDI. From the four matrices tested, NOR provided the greatest increase in sensitivity for neutral lipids (triacylglycerol, diacylglycerol, monoacylglycerol, cholesterol ester) and DHB provided the highest overall number of lipids detected using MALDI-2 technology. </p>

Spatial Metabolomics and Lipidomics Reveal the Mechanisms of the Enhanced Growth of Breast Cancer Cell Spheroids Exposed to Triclosan

“…However, MALDI demonstrated an enhanced ability to detect PC species (e.g., PC (32:2)) compared to MALDI-2 (Figure B and Table S6). These results were consistent with several previous reports showing that MALDI-2 was able to increase the intensities for various lipid classes except for PC. , …”

“…Besides, the selection of the matrix may affect the results for detecting compounds by using MALDI-2. For instance, MG(18:1) and CE (18:1) could not be detected in both MALDI-2 and MALDI using the DHB matrix . However, using the norharmane matrix, these two compounds could be detected in MALDI-2 but not in MALDI …”

Analysis of carbohydrates and glycoconjugates by matrix‐assisted laser desorption/ionization mass spectrometry: An update for 2019–2020

“…The effect of different matrices on MALDI-2 signals from lipids has been studied using CHCA, 2,5dihydroxyacetophenone (DHAP, 12), DHB and norharmane (McMillen, Fincher, et al, 2020). Improvements in signal strength ([M + H] + ions) were observed for all matrices with the most dramatic effects from norharmane (53) and DHB.…”

Enhancement of Lipid Signals in Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry with Ammonium Fluoride as a Matrix Additive

“…One of the challenges in mass spectrometry is the lack of uniformity in the ionization efficiency of macromolecules . Ionization efficiency is dependent on a variety of factors and differs drastically not only between different macromolecules but also between molecules of the same class, such as lipids. , Many advances have been made to increase the specificity and sensitivity of lipid species detected in MSI, such as improvements in instrumentation, , adding washing steps during sample processing, , matrix composition, , and introducing additives in matrix application. ,, Of particular interest to this work are matrix additives as they represent a simple means to increase lipid sensitivity without the added complexity of extensive protocol modifications and can be applied to existing in-house instrumentation.…”