Stolze K, Udilova N, Nohl H
Institute of Pharmacology and Toxicology, Veterinary University of Vienna, Austria.
Acta Biochim Pol. 2000;47(4):923-30.
Unsaturated lipids are rapidly oxidized to toxic products such as lipid hydroperoxides, especially when transition metals such as iron or copper are present. In a Fenton-type reaction Fe2+ converts lipid hydroperoxides to the very short-lived lipid alkoxyl radicals. The reaction was started upon the addition of Fe2+ to an aqueous linoleic acid hydroperoxide (LOOH) emulsion and the spin trap in the absence of oxygen. Even when high concentrations of spin traps were added to the incubation mixture, only secondary radical adducts were detected, probably due to the rapid re-arrangement of the primary alkoxyl radicals. With the commercially available nitroso spin trap MNP we observed a slightly immobilized ESR spectrum with only one hydrogen splitting, indicating the trapping of a methinyl fragment of a lipid radical. With DMPO or 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO) adducts were detected with carbon-centered lipid radical, with acyl radical, and with the hydroxyl radical. We also synthesized lipophilic derivatives of the spin trap DEPMPO in order to detect lipid radical species generated in the lipid phase. With all spin traps studied a lipid-derived carbon-centered radical was obtained in the anaerobic incubation system Fe2+/LOOH indicating the trapping of a lipid radical, possibly generated as a secondary reaction product of the primary lipid alkoxyl radical formed. Under aerobic conditions an SOD-insensitive oxygen-centered radical adduct was formed with DEPMPO and its lipophilic derivatives. The observed ESR parameters were similar to those of alkoxyl radical adducts, which were independently synthesized in model experiments using Fe3+-catalyzed nucleophilic addition of methanol or t-butanol to the respective spin trap.
不饱和脂质会迅速氧化为脂质氢过氧化物等有毒产物，尤其是在存在铁或铜等过渡金属的情况下。在芬顿型反应中，Fe2+将脂质氢过氧化物转化为寿命极短的脂质烷氧基自由基。该反应是在无氧条件下，向亚油酸氢过氧化物（LOOH）水乳液和自旋捕获剂中加入Fe2+后启动的。即使向孵育混合物中加入高浓度的自旋捕获剂，也仅检测到次级自由基加合物，这可能是由于初级烷氧基自由基的快速重排所致。使用市售的亚硝基自旋捕获剂MNP，我们观察到一个仅有一个氢分裂的略微固定的电子顺磁共振谱，表明捕获了脂质自由基的次甲基片段。使用DMPO或5-二乙氧基磷酰基-5-甲基-1-吡咯啉N-氧化物（DEPMPO）时，检测到了以碳为中心的脂质自由基、酰基自由基和羟基自由基的加合物。我们还合成了自旋捕获剂DEPMPO的亲脂性衍生物，以检测在脂质相中产生的脂质自由基物种。在厌氧孵育系统Fe2+/LOOH中，使用所有研究的自旋捕获剂都获得了一个源自脂质的以碳为中心的自由基，这表明捕获了一个脂质自由基，它可能是初级脂质烷氧基自由基形成的次级反应产物。在有氧条件下，DEPMPO及其亲脂性衍生物形成了一种对超氧化物歧化酶不敏感的以氧为中心的自由基加合物。观察到的电子顺磁共振参数与烷氧基自由基加合物的相似，后者是在模型实验中通过Fe3+催化甲醇或叔丁醇与相应自旋捕获剂的亲核加成独立合成的。
