Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) visualizes the distribution of phospho- and glycolipids in tissue sections. However, C=C double-bond (db) positional isomers generally cannot be distinguished. Now an on-tissue Paternò-Büchi (PB) derivatization procedure that exploits benzaldehyde as a MALDI-MSI-compatible reagent is introduced. Laser-induced postionization (MALDI-2) was used to boost the yields of protonated PB products. Collision-induced dissociation of these species generated characteristic ion pairs, indicative of C=C position, for numerous singly and polyunsaturated phospholipids and glycosphingolipids in mouse brain tissue. Several db-positional isomers of phosphatidylcholine and phosphatidylserine species were expressed with highly differential levels in the white and gray matter areas of cerebellum. Our PB-MALDI-MS/MS procedure could help to better understand the physiological role of these db-positional isomers.
Visualizing the differential
distribution of carbon–carbon
double bond (CC db) positional isomers of unsaturated phospholipids
(PL) in tissue sections by use of refined matrix-assisted laser desorption
ionization mass spectrometry imaging (MALDI MSI) technologies offers
a high promise to deeper understand PL metabolism and isomer-specific
functions in health and disease. Here we introduce an on-tissue ozonization
protocol that enables a particular straightforward derivatization
of unsaturated lipids in tissue sections. Collision-induced dissociation
(CID) of MALDI-generated ozonide ions (with yields in the several
ten percent range) produced the Criegee fragment ion pairs, which
are indicative of CC db position(s). We used our technique
for visualizing the differential distribution of Δ9 and Δ11
isomers of phosphatidylcholines in mouse brain and in human colon
samples with the desorption laser spot size 15 μm, emphasizing
the potential of the technique to expose local isomer-specific metabolism
of PLs.
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