Thomas S R, Neuzil J, Stocker R
Biochemistry Group, Heart Research Institute, Camperdown, Sydney, NSW, Australia.
Arterioscler Thromb Vasc Biol. 1996 May;16(5):687-96. doi: 10.1161/01.atv.16.5.687.
There is considerable interest in the ability of antioxidant supplementation, in particular with vitamin E, to attenuate LDL oxidation, a process implicated in atherogenesis. Since vitamin E can also promote LDL lipid peroxidation, we investigated the effects of supplementation with vitamin E alone or in combination with coenzyme Q on the early stages of the oxidation of isolated LDL. Isolated LDL was obtained from healthy subjects before and after in vitro enrichment with vitamin E (D-alpha-tocopherol, alpha-TOH) or dietary supplementation with D-alpha-TOH (1 g/d) and/or coenzyme Q (100 mg/d). LDL oxidation initiation was assessed by measurement of the consumption of alpha-TOH and cholesteryl esters containing polyunsaturated fatty acids and the accumulation of cholesteryl ester hydroperoxides during incubation of LDL in the transition metal-containing Ham's F-10 medium in the absence and presence of human monocyte-derived macrophages (MDMs). Native LDL contained 8.5 +/- 2 molecules of alpha-TOH and 0.5 to 0.8 molecules of ubiquinol-10 (CoQ10H2, the reduced form of coenzyme Q) per lipoprotein particle. Incubation of this LDL in Ham's F-10 medium resulted in a time-dependent loss of alpha-TOH with concomitant stoichiometric conversion of the major cholesteryl esters to their respective hydroperoxides. MDMs enhanced this process. LDL lipid peroxidation occurred via a radical chain reaction in the presence of alpha-TOH, and the rate of this oxidation decreased on alpha-TOH depletion. In vitro enrichment of LDL with alpha-TOH resulted in an LDL particle containing sixfold to sevenfold more alpha-TOH, and such enriched LDL was more readily oxidized in the absence and presence of MDMs compared with native LDL. In vivo alpha-TOH-deficient LDL, isolated from a patient with familial isolated vitamin E deficiency, was highly resistant to Ham's F-10-initiated oxidation, whereas dietary supplementation with vitamin E restored the oxidizability of the patient's LDL. Oral supplementation of healthy individuals for 5 days with either alpha-TOH or coenzyme Q increased the LDL levels of alpha-TOH and CoQ10H2 by two to three or three to four times, respectively. alpha-TOH-supplemented LDL was significantly more prone to oxidation, whereas CoQ10H2-enriched LDL was more resistant to oxidation initiation by Ham's F-10 medium than native LDL. Cosupplementation with both alpha-TOH and coenzyme Q resulted in LDL with increased levels of alpha-TOH and CoQ10H2, and such LDL was markedly more resistant to initiation of oxidation than native or alpha-TOH-enriched LDL. These results demonstrate that oral supplementation with alpha-TOH alone results in LDL that is more prone to oxidation initiation, whereas cosupplementation with coenzyme Q not only prevents this prooxidant activity of vitamin E but also provides the lipoprotein with increased resistance to oxidation.
抗氧化剂补充剂，特别是维生素E，减轻低密度脂蛋白（LDL）氧化的能力引起了人们相当大的兴趣，LDL氧化是一个与动脉粥样硬化形成有关的过程。由于维生素E也能促进LDL脂质过氧化，我们研究了单独补充维生素E或与辅酶Q联合补充对分离的LDL氧化早期阶段的影响。分离的LDL取自健康受试者，在体外使用维生素E（D-α-生育酚，α-TOH）富集前后，以及进行D-α-TOH（1 g/d）和/或辅酶Q（100 mg/d）膳食补充后。通过测量α-TOH和含有多不饱和脂肪酸的胆固醇酯的消耗以及在含过渡金属的Ham's F-10培养基中，在不存在和存在人单核细胞衍生巨噬细胞（MDM）的情况下LDL孵育期间胆固醇酯氢过氧化物的积累，评估LDL氧化起始情况。天然LDL每个脂蛋白颗粒含有8.5±2个α-TOH分子和0.5至0.8个泛醇-10（CoQ10H2，辅酶Q的还原形式）分子。将这种LDL在Ham's F-10培养基中孵育导致α-TOH随时间依赖性损失，同时主要胆固醇酯化学计量转化为各自的氢过氧化物。MDM增强了这一过程。在α-TOH存在下，LDL脂质过氧化通过自由基链反应发生，并且这种氧化速率在α-TOH耗尽时降低。用α-TOH对LDL进行体外富集导致LDL颗粒含有的α-TOH比原来多六至七倍，与天然LDL相比，这种富集的LDL在不存在和存在MDM的情况下都更容易被氧化。从家族性单纯维生素E缺乏症患者分离出的体内α-TOH缺乏的LDL对Ham's F-10引发的氧化具有高度抗性，而维生素E膳食补充恢复了患者LDL的氧化能力。健康个体口服α-TOH或辅酶Q 5天分别使LDL中的α-TOH和CoQ10H2水平增加两至三倍或三至四倍。补充α-TOH的LDL明显更易于氧化，而富含CoQ10H2的LDL比天然LDL对Ham's F-10培养基引发的氧化更具抗性。同时补充α-TOH和辅酶Q导致LDL中α-TOH和CoQ10H2水平增加，并且这种LDL对氧化起始的抗性明显高于天然或富含α-TOH的LDL。这些结果表明，单独口服补充α-TOH会导致LDL更易于氧化起始，而同时补充辅酶Q不仅可防止维生素E的这种促氧化活性，还能使脂蛋白对氧化的抗性增加。
