Structural characterization of oxidized phospholipid products derived fromarachidonate-containing plasmenyl glycerophosphocholine

Plasmenyl phospholipids are a structurally unique class of lipids that cont ain a vinyl ether substituent at the sn-1 position of the glycerol backbone , imparting unique susceptibility to oxidative reactions that may take plac e at the cell membrane lipid bilayer. Several studies have supported the hy pothesis that plasmalogens may be antioxidant molecules that protect cells from oxidative stress. Because the molecular mechanism for the antioxidant properties of plasmenyl phospholipids is not fully understood, the oxidatio n of arachidonate-containing plasmalogen-glycerophosphocholine (GPC) was st udied using electrospray tandem mass spectrometry after exposure to the fre e radical initiator 2,2'-azobis(2-amidinopropane)hydrochloride (AAPH). Vari ous oxidized GPC products involving the sn-1 position alone (1-formyl-2-ara chidonyl lipids and lysophospholipid), oxidation products involving the sn- 2 position alone (chain-shortened omega-aldehyde radyl substituents at sn-2 ) as well as products oxidized both at the sn-1 and sn-2 positions were obs erved and structurally identified. The results of these experiments suggest that oxidation of plasmenyl phospholipids esterified with polpunsaturated fatty acid groups at sn-2 likely undergo unique and specific free radical o xidation at the 1'-alkenyl position as well as oxidation of the double bond closest to the ester moiety at sm-2.