|Representative structures of oxidized cardiolipin species produced by singlet oxygen, as seen by HPLC-MS/MS spectral data.
The phospholipid cardiolipin predominantly is found in the mitochondrial inner membrane, in association with the components of the electron transport chain. Because electron transport generates a large amount of reactive oxygen species, the proximity of the fatty acid chains of CL to the various ETC complexes make it a likely target of oxidative damage. Oxidized CL products, therefore, could serve as biomarkers for the presence of ROS. However, characterization of oxidized CL is highly challenging as major CL species have four unsaturated acyl chains, whereas other phospholipids usually only have one. In this study, the researchers exposed CL to either singlet oxygen (1O2), the radical initiator AAPH (2,2’-azobis(2-methylpropionamidine) dihydrochloride) or room air and characterized the resulting oxidized CL species using reversed-phase ion-pair high pressure liquid chromatography tandem mass spectrometry. With this combined approach, they could detect the distinctive fragment ions associated with specific oxidized species of similar mass and thus fully distinguish major and minor CL species. The results showed that monohydroperoxides and bismonohydroperoxides were generated under all three conditions, whereas dihydroperoxides were produced only by 1O2. This suggests that singlet-oxygen mediated damage has a chemotype distinct from radical-mediated damage, offering more insight into the mechanisms of oxidative stress.
Cardiolipin: Characterization of Distinct Oxidized Molecular Species
Junhwan Kim, Paul E. Minkler, Robert G. Salomon, Vernon E. Anderson and Charles L. Hoppel
J. Lipid Res., published online Sept. 20, 2010