1,6-Diphenyl-1,3,5-hexatriene (DPH) as a Novel Matrix for MALDI MS Imaging of Fatty Acids, Phospholipids, and Sulfatides in Brain Tissues

Abstract

1,6-Diphenyl-1,3,5-hexatriene (DPH) is a commonly used fluorescence probe for studying cell membrane-lipids due to its affinity toward the acyl chains in the phospholipid bilayers. In this work, we investigated its use in matrix-assisted laser desorption/ionization (MALDI) as a new matrix for mass spectrometry imaging (MSI) of mouse and rat brain tissue. DPH exhibits very minimal matrix-induced background signals for the analysis of small molecules (below m/z of 1000). In the negative ion mode, DPH permits the highly sensitive detection of small fatty acids (m/z 200-350) as well as a variety of large lipids up to m/z of 1000, including lyso-phospholipid, phosphatidic acid (PA), phosphoethanolamine (PE), phosphatidylserine (PS), phosphatidylglycerol (PG), phosphatidylinositol (PI), and sulfatides (ST). The analytes were mostly detected as the deprotonated ion [M - H]. Our results also demonstrate that sublimated DPH is stable for at least 24 h under the vacuum of our MALDI mass spectrometer. The ability to apply DPH via sublimation coupled with its low volatility allows us to perform tissue imaging of the above analytes at high spatial resolution. The degree of lipid fragmentation was determined experimentally at varying laser intensities. The results illustrated that the use of relatively low laser energy is important to minimize the artificially generated fatty acid signals. On the other hand, the lipid fragmentation obtained at higher laser energies provided tandem MS information useful for lipid structure elucidation.

Recent Developments of Useful MALDI Matrices for the Mass Spectrometric Characterization of Lipids

“…Since FFA are of significant interest, there are quite often suggestions of new and promising matrix compounds. One auspicious new matrix for the MALDI-based analysis of FFA, investigated by Ibrahim and coworkers, is 1,6-diphenyl-1,3,5-hexatriene (DPH) [37], due to its negligible background signals under low laser fluences. In this context, the combination of DPH and elevated laser fluences allow the investigation of the fatty acyl composition of lipids, since this condition leads to the cleavage of the fatty acyl residues.…”

“…It is important to note that 1,5-DAN may be applied by either spraying or sublimation, at which the latter usually gives a more homogeneous matrix coating [123]. Other matrices, namely, N -phenyl-2-naphthylamine [148] and the fluorescence probe DPH (1,6-diphenyl-1,3,5-hexatriene) [37] have been described to represent suitable matrices to unravel lipid localization by MALDI imaging.…”

Recent advances in mass spectrometry imaging for multiomics application in neurology

“…For MALDI‐MSI, the identification of matrices that cover a wider chemical scope is another factor that has been developed and optimized to improve the sensitivity of existing platforms and increase the application of MSI to even wide areas of neurological research (Cerruti, Benabdellah, Laprevote, Touboul, & Brunelle, ; Chan et al, ; Fulop et al, ; Ibrahim, Jurcic, Wang, Whitehead, & Yeung, ; Jackson et al, ; Liu et al, ; Shanta et al, , ; Shariatgorji et al, ; Wang et al, ; Wang, Han, Yang, Pan, & Borchers, ; Yang & Caprioli, , ; Zhou et al, ). Previously, we demonstrated that MSI technique was capable of a spatial tissue mapping of ceramide structures in gangliosides that could not be distinguished using established histologic tools (Chan et al, ).…”

“…MSI has been widely used in mapping lipids in mouse brain tissues, including fatty acids (Hirahara et al, ; Ibrahim et al, ; Lerner et al, ; Wu, Comi, Li, Rubakhin, & Sweedler, ; Zhou et al, ), ceramides (Barbacci et al, ; Muller et al, ; Nielsen et al, ; Woods et al, ), cardiolipins (Amoscato et al, ; Sparvero et al, ), phospholipids (Angel, Spraggins, Baldwin, & Caprioli, ; Guo et al, ; Hama et al, ; Hankin et al, ; Jadoul et al, ; Janfelt et al, ; Koizumi et al, ; Landgraf et al, ; Matsumoto et al, , ; Miyawaki et al, ; Shanta et al, ; Smith et al, ; Sparvero et al, ; Sugiura et al, ; Wang et al, ; Wang, Wang, & Han, ; Whitehead et al, ; Zaima et al, ), and sphingolipids (Caughlin et al, , ; Caughlin, Park, Yeung, Cechetto, & Whitehead, ; Chan et al, ; Dufresne et al, ; Ermini et al, ; Goto‐Inoue et al, ; Jackson et al, , ; Jones et al, ; Meriaux, Franck, Wisztorski, Salzet, & Fournier, ; Sugiura, Shimma, Konishi, Yamada, & Setou, ; Weishaupt, Caughlin, Yeung, & Whitehead, ; Whitehead et al, ). Gangliosides, amphipathic molecules composed of a ceramide lipid anchor linked to an oligosaccharide, are sialic acid‐containing glycosphingolipids and play numerous important roles in neuronal functions.…”

Silver spray deposition for AgLDI imaging MS of cholesterol and other olefins on thin tissue sections

“…Matrix‐assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) is a powerful analytical technique that can provide insight into the distribution of biomolecules within thin tissue sections . Originally introduced for proteomic studies, this technology is now widely adopted for lipidomic studies thanks to the discovery of novel matrices and sample preparation approaches . Beyond traditional organic matrices, metal matrices have also been studied to determine their ability to aid with the desorption ionization of specific biomolecules for MS and IMS studies .…”