Analysis of oxidized glycerophosphocholine lipids using electrospray ionization mass spectrometry and microderivatization techniques

Oxidized low-density lipoprotein (LDL) is thought to play an important role in atherogenesis and cardiovascular disease in humans. Oxidized LDL is a c omplex mixture of many oxidized species, including numerous oxidized glycer ophospholipids. Electrospray ionization and tandem mass spectrometry as wel l as microchemical derivatization of high-performance liquid chromatographi cally purified fractions derived from oxidized LDL were investigated as mea ns to determine the structure of individual components present in oxidized LDL. One major oxidized phosphocholine lipid had an [M + H](+) ion at m/z 6 50. Derivatization to the trimethylsilyl ether and methoxime caused shifts in mass which, along with negative ion collision-induced dissociation mass spectra, were consistent with the presence of three species, 1-palmitoyl-2- (9-oxononanoyl)glycerophosphocholine and two isomeric 1-octadecanoyl-2-(hyd roxyheptenoyl)glycerophosphocholines. These species were chemically synthes ized. Trimethylsilylation of free hydroxyl groups increased the mass of the phospholipid acyl chains containing hydroxyl groups by 72 u. Conversion of carbonyl groups to the methoxylamine derivative increased the mass by 29 u . Ozonolysis of those products which contained double bonds proved to be a facile technique to determine the position and number of double bonds prese nt. The use of these techniques was illustrated in the structural character ization of one major component (m/z 650, positive ions) in oxidized LDL as 1-octadecanoyl-2-(7-hydroxy-hepta-5-enoyl)glycerophosphocholine. A possible mechanism for the formation of this unique chain-shortened glycerophosphol ipid is proposed. Copyright (C) 2000 John Wiley & Sons, Ltd.