Patel R P, Svistunenko D, Wilson M T, Darley-Usmar V M
Department of Biological and Chemical Sciences (Central Campus), University of Essex, Colchester, U.K.
Biochem J. 1997 Mar 1;322 ( Pt 2)(Pt 2):425-33. doi: 10.1042/bj3220425.
The Cu(II)-promoted oxidation of lipids is a lipid hydroperoxide (LOOH)-dependent process that has been used routinely to assess the oxidizability of low-density lipoprotein (LDL) in human subjects. Metal-dependent redox reactions, including those mediated by copper, have been implicated in the pathogenesis ofatherosclerosis. Despite its widespread use and possible biological significance, key elements of the mechanism are not clear. For example, although it is evident that copper acts as a catalyst, which implies a redox cycle between the Cu(II) and Cu(I) redox states, the reductants remain uncertain. In LDL these could include alpha-tocopherol, amino acid residues on the protein and LOOH. However, both alpha-tocopherol and amino acid residues are probably consumed before the most rapid phase of lipid peroxidation occurs, suggesting that another reductant must be donating electrons to Cu(II), the most likely candidate being LOOH. This role has been disputed, since LDLs nominally devoid of LOOH are still capable of reducing Cu(II) to Cu(I) and thermodynamic calculations for this reaction are not favourable. Direct investigation of the role of LOOH as reductant has not been reported and in the present study, using simple lipid systems and LDL, we have re-examined this issue using the Cu(I) chelator bathocuproine. We have shown that Cu(II) may promote lipid peroxidation in liposomes, which do not contain either protein or alpha-tocopherol, and that this is associated with reduction to Cu(I). The data also indicate that an equilibrium between free Cu(II) and LOOH exists, which only in the presence of an oxidizable substrate, i.e. unsaturated fatty acids, is shifted towards formation of Cu(I) and lipid-derived peroxyl radicals. We propose that reduction of Cu(II) by LOOH is a necessary component in sustaining the propagation of lipid peroxidation and that the formation of peroxyl radicals and their products in a lipid environment is sufficient to overcome thermodynamic barriers to the reaction.
铜（II）促进的脂质氧化是一个依赖脂质氢过氧化物（LOOH）的过程，该过程已被常规用于评估人类受试者中低密度脂蛋白（LDL）的氧化能力。包括铜介导的反应在内的金属依赖性氧化还原反应与动脉粥样硬化的发病机制有关。尽管其被广泛使用且可能具有生物学意义，但其机制的关键要素尚不清楚。例如，虽然很明显铜起催化剂的作用，这意味着在Cu（II）和Cu（I）氧化还原状态之间存在一个氧化还原循环，但还原剂仍不确定。在LDL中，这些还原剂可能包括α-生育酚、蛋白质上的氨基酸残基和LOOH。然而，在脂质过氧化最快速的阶段发生之前，α-生育酚和氨基酸残基可能都已被消耗，这表明一定有另一种还原剂在向Cu（II）提供电子，最有可能的候选者是LOOH。这一作用一直存在争议，因为名义上不含LOOH的LDL仍然能够将Cu（II）还原为Cu（I），并且该反应的热力学计算结果并不乐观。尚未有关于直接研究LOOH作为还原剂作用的报道，在本研究中，我们使用简单的脂质系统和LDL，通过Cu（I）螯合剂bathocuproine重新审视了这个问题。我们已经表明，Cu（II）可以促进不含蛋白质或α-生育酚的脂质体中的脂质过氧化，并且这与还原为Cu（I）有关。数据还表明，游离Cu（II）和LOOH之间存在平衡，只有在存在可氧化底物即不饱和脂肪酸的情况下，该平衡才会向形成Cu（I）和脂质衍生的过氧自由基的方向移动。我们提出，LOOH还原Cu（II）是维持脂质过氧化传播的必要组成部分，并且在脂质环境中过氧自由基及其产物的形成足以克服该反应的热力学障碍。
