Mechanism of lipid peroxidation of liposomes by cold atmospheric pressure plasma jet irradiation.

Liposome lipid peroxidation induced by cold atmospheric pressure plasma jet (CAPPJ) irradiation was investigated. The formation of thiobarbituric acid reactive substances (TBARS), an indicator of lipid peroxidation final products, as a function of irradiation was observed. Lipid radicals, peroxidation reaction intermediates generated by CAPPJ irradiation, were confirmed by increased NBD-pen fluorescence intensity. Additionally, lipid peroxidation products, liposomal phosphatidylcholine (PC) isomers, were analyzed by LC-MS/MS. Products specific to singlet oxygen (¹O₂) oxidation, 16:0/10-hydroperoxy-8E,12Z-octadecanoic acid (10-8E,12Z-HpODE) PC and 16:0/12-9E,13E-HpODE PC, were not detected, but radical oxidation specific products 16:0/13-9E,11E-HpODE PC and 16:0/9-10E,12E-HpODE PC were. This suggests that during CAPPJ irradiation, radicals, rather than ¹O₂, are the primary reactive species of lipid peroxidation. This is also supported by the β-carotene quenching of ¹O₂ not suppressing TBARS and lipid radical generation. Also, neither TBARS formation nor lipid radical generation were suppressed by SOD, indicating that the superoxide radical (O₂ ^•-) is not responsible for the lipid peroxidation reaction. As the CAPPJ irradiation of water produces large quantities of hydroxyl radical (^•OH) and ^•OH scavengers decreased the amount of TBARS produced by CAPPJ irradiation, it is highly plausible that ^•OH is the primary species involved in CAPPJ-induced liposome lipid peroxidation.