Deep Lipidomics and Molecular Imaging of Unsaturated Lipid Isomers: A Universal Strategy Initiated by mCPBA Epoxidation

Abstract

Cellular lipidome is highly regulated through lipogenesis, rendering diverse double-bond positional isomers (C=C isomer) of a given unsaturated lipid species. In recent years, there are increasing reports indicating the physiological roles of C=C isomer compositions associated with diseases, while the biochemistry has not been fully understood due to the challenge in characterizing lipid isomers inherent to conventional mass spectrometry-based lipidomics. To address this challenge, we reported a universal, user-friendly, derivatization-based strategy, MELDI (mCPBA Epoxidation for Lipid Double-bond Identification), which enables both large-scale identification and spatial mapping of biological C=C isomers using commercial mass spectrometers without any instrument modification. With the developed liquid-chromatography mass spectrometry (LC-MS) lipidomics workflow, we elucidated more than 100 isomers among mono-and poly-unsaturated fatty acids and glycerophospholipids in both human serum, where novel isomers of low abundance were unambiguously quantified for the first time. The capability of MELDI-LC-MS in lipidome analysis was further demonstrated using the differentiated 3T3-L1 adipocytes, providing an insight into the cellular lipid reprogramming upon stearoyl-coenzyme A desaturase 1 (SCD1) inhibition. Finally, we highlighted the versatility of MELDI coupled with mass spectrometry imaging to spatially resolve cancer-associated alteration of lipid isomers in a metastatic mouse tissue section. Our results suggested that MELDI will contribute to current lipidomics pipelines with a deeper level of structural information, allowing us to investigate underlying lipid biochemistry.

On‐Demand Electrochemical Epoxidation in Nano‐Electrospray Ionization Mass Spectrometry to Locate Carbon–Carbon Double Bonds

“…Additionally,w eo bserved the presence of byproduct peaks at m/z 800.5788 and 816.5733 (+ 14 Da and + O + 14 Da) in relatively low intensities (2-10 %) accompanying the formation of lipid epoxides (see Figure S5). Unlike other epoxidation methods such as those driven by plasma [14] or the m-CPBAr eagent [15] that require ac ertain reaction time or need to be performed off-line,t he electroepoxidation of lipids can be switched on and off simply by changing the voltage,where the lipid solution in the nanoESI emitter was intact and reusable for other aims.T he ion chronograms of protonated lipid, mono-epoxide,a nd diepoxide are shown in Figure 3b,w here the onset of electroepoxidation is seen to respond rapidly and reproducibly to the voltage change.…”

Imaging Isomers on a Biological Surface: A Review

“…69) Subsequently, CID can be used for fragmentation, which will generate a diagnostic pair of fragments of 16 Da apart. 69,70) Feng et al performed this reaction by mixing mCPBA in dichloromethane with yeast extract for direct infusion ESI-MS/MS analysis. 69) Kuo et al performed in situ epoxidation by spraying tiny droplets of an mCPBA solution onto tissue sections before DESI-MSI analysis.…”

“…69) Kuo et al performed in situ epoxidation by spraying tiny droplets of an mCPBA solution onto tissue sections before DESI-MSI analysis. 70) Intensity ratios of diagnostic ions were used to create a fractional distribution image of epoxy-fatty acid 18 : 1, showing an enriched level of the ∆11 isomer in the tumor region. e summed distribution of the lipid phosphatidylglycerol (PG) 18 : 1_16 : 0 was unable to distinguish this region.…”

Multifunctional Reactive MALDI Matrix Enabling High-Lateral Resolution Dual Polarity MSI and Lipid C=C Position-Resolved MS2I

“…ultraviolet (UV) photodissociation mass spectrometry, [14][15][16][17] radical-directed dissociation, 18,19 ozone-induced dissociation (OzID), 20 infrared (IR) action spectroscopy of ultra-cold ions, 21 have been reported. In-solution functionalization via epoxidation 22,23 or photochemical Paternò-Büchi (PB) functionalization prior ESI is also capable to identify lipid DB positions. [24][25][26][27][28] The latter functionalization scheme, pioneered by Ma and Xia, 29 has been used by numerous groups to assign DB positions in direct infusion and LC-MS workflows.…”