Molecular Probes in Tandem Electrospray Ionization Mass Spectrometry: Application to Tracing Chemical Changes of Specific Phospholipid Molecular Species

Abstract

New ionization and detection techniques in mass spectrometry have been successfully applied for efficient analyses of complex biological systems. It is, however, still difficult to trace structural changes of a specific molecular species in such systems. In the present study, a molecular probe strategy in combination with tandem electrospray ionization mass spectrometry has been examined using synthetic deuterium-labeled phosphatidylcholine hydroperoxide (PC-OOH/D3) and ethyl-labeled phosphatidylcholine having docosahexaenoic acid side chain (DHA-PC/Et). Administration of a mixture of PC-OOH/D3 and DHA-PC/Et to human blood and human skin surface, followed by extraction and analysis with collision-induced tandem electrospray ionization mass spectrometry demonstrated that metabolites of both molecular probes can be detected simultaneously with strict selectivity. The present method is also found to be useful in tracing chemical changes of the unstable docosahexaenoyl group on the surface of processed fish. The activity of phospholipase A2 can also be assessed using a phospholipid molecular probe with a linoleoyl and a deuteriomethyl group via selective detection of the lyso-phospholipid product by mass spectrometry. The advantage of the present method is that no chromatographic separation is required and analysis can be performed under strictly the same condition for different molecular probes, affording multiple data by one experiment. The present strategy may be useful for tracing time-dependent phenomena in dynamic phospholipid biochemistry, and can be widely used for any biological and food systems.

Formation of Aldehydic Phosphatidylcholines during the Anaerobic Decomposition of a Phosphatidylcholine Bearing the 9-Hydroperoxide of Linoleic Acid

“…This is speculated to partly involve rearrangement of dimeric radical 27 to 31 , followed by expulsion of a hydroperoxyl radical (HOO ∙ ) from the latter to form peroxide-linked dimer 32 . Similar expulsion of the HOO ∙ may have been involved in the recently reported conversion of PC-13-LA-OOH (a PC bearing 13-LA-OOH 1 ) to an octadecatrienoyl-PC on human skin [ 34 ]. Cleavage of the O-O bond in peroxide 32 affords an alkoxy radical whose further cyclization and reaction with a peroxyl radical may lead to formation of epoxyalkoxyl radical 33 , whose β -scission affords 11-oxo-9-undecenoyl-PC 34 ( m/z 704) and an oxiranyl radical.…”