Fukuzawa K, Matsuura K, Tokumura A, Suzuki A, Terao J
Faculty of Pharmaceutical Sciences, Tokushima University, Japan.
Free Radic Biol Med. 1997;22(5):923-30. doi: 10.1016/s0891-5849(96)00485-6.
Scavenging of singlet oxygen (1O2) by alpha-tocopherol (alpha-Toc) was investigated in liposomes. 1O2 was generated by photoirradiation in the presence of two photosensitizers, water-soluble methylene blue (MB) and lipid-soluble 12-(1-pyrene)dodecanoic acid (PDA). The rates of oxidation of alpha-Toc differed depending on the photosensitizing dye and the membrane charge: in the MB-system, alpha-Toc was oxidized fast in negatively charged dimyristoylphosphatidylcholine (DMPC) liposomes containing dicetylphosphate (DCP) and slowly in neutrally charged DMPC liposomes and positively charged DMPC liposomes containing stearylamine (SA), but in the PDA-system, the oxidation rate was independent of the membrane charge. The charge-dependent difference in the MB-system would be due to the site of 1O2 generation depending on the charge-dependent distribution of MB, because positively charged MB increased the zeta-potential of DCP-DMPC liposomes by its interaction with DCP at the membrane surface, but changed the zeta-potentials of DMPC and SA-DMPC liposomes less because of its location in the bulk water phase. The oxidation rate of alpha-Toc in liposomes was different from that in EtOH solution: in the MB system, the oxidation rate was faster in EtOH solution than in DMPC or SA-DMPC liposomes but the same as that in DCP-DMPC liposomes. However, in the PDA system, the oxidation rate was slower in EtOH solution than in DMPC liposomes with or without a charge. Membrane fluidity changed the rate of alpha-Toc oxidation in liposomes, the rate being higher in the liquid crystalline phase than the gel phase, as judged by the higher rate in DMPC liposomes than in dipalmitoylphosphatidylcholine (DPPC) liposomes at 30 degrees C. The rate constants of alpha-Toc for scavenging, the chemical reaction and physical quenching of 1O2 were determined in membranes using DCP-DMPC liposomes labeled with 1,3-diphenyl-isobenzofuran (DPBF), which traps 1O2. These constants differed in the two photosensitizing systems, being higher in the MB-system than in the PDA-system, and were lower than those in EtOH solution.
在脂质体中研究了α-生育酚（α-Toc）对单线态氧（1O2）的清除作用。在两种光敏剂——水溶性亚甲蓝（MB）和脂溶性12-(1-芘)十二烷酸（PDA）存在的情况下，通过光照射产生1O2。α-Toc的氧化速率因光敏染料和膜电荷的不同而有所差异：在MB体系中，α-Toc在含有磷酸二鲸蜡酯（DCP）的带负电荷的二肉豆蔻酰磷脂酰胆碱（DMPC）脂质体中快速氧化，在中性电荷的DMPC脂质体和含有硬脂胺（SA）的带正电荷的DMPC脂质体中氧化缓慢，但在PDA体系中，氧化速率与膜电荷无关。MB体系中电荷依赖性差异可能是由于1O2的产生位点取决于MB的电荷依赖性分布，因为带正电荷的MB通过与膜表面的DCP相互作用增加了DCP-DMPC脂质体的ζ电位，但由于其位于本体水相中，对DMPC和SA-DMPC脂质体的ζ电位影响较小。α-Toc在脂质体中的氧化速率与在乙醇溶液中的不同：在MB体系中，乙醇溶液中的氧化速率比在DMPC或SA-DMPC脂质体中快，但与在DCP-DMPC脂质体中的相同。然而，在PDA体系中，乙醇溶液中的氧化速率比带电荷或不带电荷的DMPC脂质体中慢。膜流动性改变了脂质体中α-Toc的氧化速率，如在30℃下DMPC脂质体中的速率高于二棕榈酰磷脂酰胆碱（DPPC）脂质体，表明液晶相比凝胶相的氧化速率更高。使用标记有捕获1O2的1,3-二苯基异苯并呋喃（DPBF）的DCP-DMPC脂质体在膜中测定了α-Toc清除、化学反应和物理猝灭1O2的速率常数。这些常数在两种光敏体系中不同，在MB体系中高于PDA体系，且低于乙醇溶液中的常数。
