Garner B, Witting P K, Waldeck A R, Christison J K, Raftery M, Stocker R
Biochemistry, The Heart Research Institute, Sydney New South Wales 2050, Australia.
J Biol Chem. 1998 Mar 13;273(11):6080-7. doi: 10.1074/jbc.273.11.6080.
The lipids of high density lipoproteins (HDL) are initially oxidized in preference to those in low density lipoprotein when human plasma is exposed to aqueous peroxyl radicals. In this work we report on the relative susceptibility of HDL protein and lipid to oxidation and on the role HDL's alpha-tocopherol (alpha-TOH) plays in modulating protein oxidation. Exposure of isolated HDL to either low fluxes of aqueous peroxyl radicals, Cu2+ ions, or soybean lipoxygenase resulted in the oxidation of apoAI and apoAII during the earliest stages of the reaction, i.e. after consumption of ubiquinol-10 and in the presence of alpha-TOH. Hydro(pero)xides of cholesteryl esters and phospholipids initially accumulated together with specific oxidized forms of apoAI and apoAII, separated by high pressure liquid chromatography. The specific oxidized forms of apoAI were 16 and 32 mass units heavier than those of the native apolipoproteins and contained 1 and 2 methionine sulfoxide residues per protein, respectively. The third methionine residue in apoAI, as well as Trp residues, remained unoxidized during the earliest stages of HDL oxidation examined. Exposure of isolated apoAI to peroxyl radicals, Cu2+, or soybean lipoxygenase resulted in nonspecific (for peroxyl radicals) or no discernible protein oxidation (Cu2+ and soybean lipoxygenase). This indicated that the formation of the specific oxidized forms of apoAI observed with native HDL was not the result of direct reaction of these oxidants with the apolipoprotein. In vitro and in vivo enrichment of HDL with alpha-TOH resulted in a dose-dependent increase in the extent of peroxyl radical-induced formation of HDL cholesteryl ester hydroperoxides (r = 0.96) and cholesteryl ester hydroxides (r = 0. 92), as well as the loss of apoAI (r = 0.96) and apoAII (r = 0.94). alpha-TOH enrichment also enhanced HDL lipid and protein oxidation induced by Cu2+ or soybean lipoxygenase. These results indicate that the earliest stages of HDL oxidation are accompanied by the oxidation of specific methionine residues in apoAI and apoAII and that in the absence of co-antioxidants, alpha-TOH can promote this process.
当人血浆暴露于水相过氧自由基时，高密度脂蛋白（HDL）的脂质优先于低密度脂蛋白的脂质被氧化。在这项工作中，我们报告了HDL蛋白质和脂质对氧化的相对敏感性，以及HDL的α-生育酚（α-TOH）在调节蛋白质氧化中所起的作用。将分离的HDL暴露于低通量的水相过氧自由基、Cu2+离子或大豆脂氧合酶中，在反应的最早阶段，即在泛醇-10消耗后且存在α-TOH的情况下，会导致载脂蛋白AI（apoAI）和载脂蛋白AII（apoAII）氧化。胆固醇酯和磷脂的氢过氧化物最初与apoAI和apoAII的特定氧化形式一起积累，通过高压液相色谱分离。apoAI的特定氧化形式比天然载脂蛋白重16和32质量单位，每个蛋白质分别含有1和2个甲硫氨酸亚砜残基。在检测的HDL氧化的最早阶段，apoAI中的第三个甲硫氨酸残基以及色氨酸残基仍未被氧化。将分离的apoAI暴露于过氧自由基、Cu2+或大豆脂氧合酶中，会导致非特异性（对于过氧自由基）或无明显的蛋白质氧化（Cu2+和大豆脂氧合酶）。这表明用天然HDL观察到的apoAI特定氧化形式的形成不是这些氧化剂与载脂蛋白直接反应的结果。在体外和体内用α-TOH富集HDL导致过氧自由基诱导的HDL胆固醇酯氢过氧化物（r = 0.96）和胆固醇酯氢氧化物（r = 0.92）形成程度呈剂量依赖性增加，以及apoAI（r = 0.96）和apoAII（r = 0.94）的损失。α-TOH富集还增强了由Cu2+或大豆脂氧合酶诱导的HDL脂质和蛋白质氧化。这些结果表明，HDL氧化的最早阶段伴随着apoAI和apoAII中特定甲硫氨酸残基的氧化，并且在没有协同抗氧化剂的情况下，α-TOH可以促进这一过程。
