Noguchi N, Gotoh N, Niki E
Department of Reaction Chemistry, Faculty of Engineering, University of Tokyo, Japan.
Biochim Biophys Acta. 1993 Jul 1;1168(3):348-57.
Although the oxidation of low density lipoprotein (LDL) has been studied extensively, its dynamics have received much less attention. The present study was carried out aiming to elucidate the rates and products of the oxidation of LDL induced by free radicals generated in three different ways by hydrophilic and lipophilic azo radical initiators and copper. The oxidations were followed by measuring the formation of lipid oxidation products, the uptake of oxygen, consumption of vitamin E, and the fragmentation and acquisition of negative charge by apolipoprotein B within a single oxidation reaction. LDL was oxidized by a free radical chain mechanism independent of the manner of initiating free radical generation to give phosphatidylcholine hydroperoxide (PCOOH) and cholesteryl ester hydroperoxide (CEOOH) as major primary products. When the radicals were generated within the LDL compartment, CEOOH was formed almost exclusively and quantitatively at the initial stage. The kinetic chain length for the oxidation of cholesteryl ester was larger than that for phosphatidylcholine in the presence and absence of vitamin E even when the radicals were generated initially in the aqueous phase. PCOOH and CEOOH accumulated with increasing extent of oxidation, but then decreased at the later stage of oxidation. The decrease in hydroperoxides was more significant in copper-induced oxidations. The thiobarbituric acid reactive substances also increased with time, but they accounted for less than 10% of total oxygen uptake. Oxidative modification of apo B was also observed. The modification of apo B, that is, fragmentation and increase in negative charge correlated well with the oxidation of lipids independent of the manner of chain initiation. It was also suggested that some radicals formed in the aqueous phase attacked apo B directly. These results suggest the importance of chain propagation in the oxidative modification of LDL and also the lipophilic, chain-breaking antioxidants within LDL in its inhibition.
尽管对低密度脂蛋白（LDL）的氧化已进行了广泛研究，但其动力学受到的关注要少得多。本研究旨在阐明由亲水性和亲脂性偶氮自由基引发剂及铜以三种不同方式产生的自由基所诱导的LDL氧化速率和产物。通过在单一氧化反应中测量脂质氧化产物的形成、氧气摄取、维生素E消耗以及载脂蛋白B的碎片化和负电荷获得情况来跟踪氧化过程。LDL通过自由基链式机制被氧化，与引发自由基产生的方式无关，主要初级产物为磷脂酰胆碱氢过氧化物（PCOOH）和胆固醇酯氢过氧化物（CEOOH）。当自由基在LDL区室中产生时，CEOOH几乎在初始阶段就完全定量形成。在有和没有维生素E的情况下，胆固醇酯氧化的动力学链长都大于磷脂酰胆碱氧化的动力学链长，即使自由基最初在水相中产生也是如此。PCOOH和CEOOH随着氧化程度的增加而积累，但在氧化后期又会减少。在铜诱导的氧化中，氢过氧化物的减少更为显著。硫代巴比妥酸反应性物质也随时间增加，但它们占总氧气摄取量的不到10%。还观察到载脂蛋白B的氧化修饰。载脂蛋白B的修饰，即碎片化和负电荷增加，与脂质氧化密切相关，与链引发方式无关。还表明在水相中形成的一些自由基直接攻击载脂蛋白B。这些结果表明链传播在LDL氧化修饰中的重要性，以及LDL内亲脂性链断裂抗氧化剂在其抑制中的重要性。
