1-o-hexadecyl-2-arachidonyl-sn-glycero-3-phosphocholine and 2-2--azobis(2-amidinopropane)

Plasmenyl phospholipids are a structurally unique class of lipids that contain a vinyl ether substituent at the sn-1 position of the glycerol backbone, imparting unique susceptibility to oxidative reactions that may take place at the cell membrane lipid bilayer. Several studies have supported the hypothesis 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 oxidation of arachidonate-containing plasmalogen-glycerophosphocholine (GPC) was studied using electrospray tandem mass spectrometry after exposure to the free radical initiator 2, 2'-azobis(2-amidinopropane)hydrochloride (AAPH). Various oxidized GPC products involving the sn-1 position alone (1-formyl-2-arachidonyl 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 observed and structurally identified. The results of these experiments suggest that oxidation of plasmenyl phospholipids esterified with polyunsaturated fatty acid groups at sn-2 likely undergo unique and specific free radical oxidation at the 1'-alkenyl position as well as oxidation of the double bond closest to the ester moiety at sn-2.

Topics: Amidines; Arachidonic Acids; Free Radicals; Glycerylphosphorylcholine; Lipid Peroxidation; Mass Spectrometry; Phospholipid Ethers; Plasmalogens

alpha-Tocopherol was reacted with the phosphatidylcholines (PCs), 1-palmitoyl-2-linoleoyl-3-sn-PC (PLPC), 1-palmitoyl-2-linolenoyl-3-sn-PC, 1-palmitoyl-2-arachidonoyl-3-sn-PC (PAPC) and 1-stearoyl-2-arachidonoyl-3-sn-PC, in the presence of the free radical initiator, 2,2'-azobis (2,4-dimethylvaleronitrile), at 37 degrees C. The addition products of alpha-tocopherol with the PC peroxyl radicals were isolated and identified as 8a-(PC-dioxy)-alpha-tocopherones, in which the peroxyl radicals derived from each PC molecule attacked the 8a-position of the alpha-tocopheroxyl radical. The antioxidative efficiency of alpha-tocopherol against the peroxidation of PLPC and PAPC in liposomes was assessed by the formation of the reaction products of alpha-tocopherol. When alpha-tocopherol was oxidized in the presence of the water-soluble free radical initiator, 2,2'-azobis (2-amidinopropane) dihydrochloride, epoxy-alpha-tocopherylquinones were mainly produced together with 8a-(PC-dioxy)-alpha-tocopherones and alpha-tocopherylquinone. The yield of alpha-tocopherylquinone was increased by treating each sample with dilute acid which indicates the presence of tocopherone precursors other than the 8a-(PC-dioxy)-alpha-tocopherones. The same products were also detected from iron-dependent peroxidation, although the yields were very low.

Topics: Amidines; Free Radicals; Lipid Peroxidation; Liposomes; Oxidants; Phosphatidylcholines; Phospholipid Ethers; Vitamin E