Stocker R, Bowry V W, Frei B
Heart Research Institute, Sydney, New South Wales, Australia.
Proc Natl Acad Sci U S A. 1991 Mar 1;88(5):1646-50. doi: 10.1073/pnas.88.5.1646.
The temporal disappearance of natural antioxidants associated with human low density lipoprotein (LDL) in relation to the appearance of various classes of lipid hydroperoxides was investigated under three types of oxidizing conditions. Freshly isolated LDL from plasma of healthy subjects was free of detectable amounts of lipid hydroperoxides as measured by HPLC postcolumn chemiluminescence detection. Exposure of such LDL to a mild, constant flux of aqueous peroxyl radicals led to rapid and complete oxidation of ubiquinol-10, followed by slower partial depletion of lycopene, beta-carotene, and alpha-tocopherol. After an initial lag period of complete inhibition of detectable lipid peroxidation, formation of hydroperoxides of cholesterol esters, triglycerides, and phospholipids was observed. The onset of detectable lipid peroxidation corresponded closely with the completion of ubiquinol-10 consumption. However, small amounts of ascorbate, present as a contaminant in the LDL preparation, rather than ubiquinol-10 itself were responsible for the initial lag period. Thus, complete consumption of ubiquinol-10 was preceded by that of ascorbate, and exposure of ascorbate-free LDL to aqueous peroxyl radicals resulted in immediate formation of detectable amounts of lipid hydroperoxides. The rate of radical-mediated formation of lipid hydroperoxides in ascorbate-free LDL was low as long as ubiquinol-10 was present, but increased rapidly after its consumption, even though more than 80% and 95% of endogenous carotenoids and alpha-tocopherol, respectively, were still present. Qualitatively similar results were obtained when peroxyl radicals were generated within LDL or when the lipoprotein was exposed to oxidants produced by activated human polymorphonuclear leukocytes. LDL oxidation was reduced significantly by supplementing the lipoprotein preparation with physiological amounts of either ascorbate or ubiquinol-10. Our data show that ubiquinol-10 is much more efficient in inhibiting LDL oxidation than either lycopene, beta-carotene, or alpha-tocopherol.
在三种氧化条件下，研究了与人类低密度脂蛋白（LDL）相关的天然抗氧化剂的暂时消失与各类脂质氢过氧化物出现之间的关系。通过HPLC柱后化学发光检测法测定，从健康受试者血浆中新鲜分离的LDL不含可检测量的脂质氢过氧化物。将此类LDL暴露于温和、恒定通量的水性过氧自由基中，导致泛醇-10迅速完全氧化，随后番茄红素、β-胡萝卜素和α-生育酚缓慢部分消耗。在可检测的脂质过氧化完全抑制的初始滞后期后，观察到胆固醇酯、甘油三酯和磷脂的氢过氧化物形成。可检测脂质过氧化的开始与泛醇-10消耗的完成密切对应。然而，LDL制剂中作为污染物存在的少量抗坏血酸而非泛醇-10本身导致了初始滞后期。因此，抗坏血酸在泛醇-10完全消耗之前就已耗尽，将不含抗坏血酸的LDL暴露于水性过氧自由基中会导致立即形成可检测量的脂质氢过氧化物。在不含抗坏血酸的LDL中，只要存在泛醇-10，自由基介导的脂质氢过氧化物形成速率就很低，但在其消耗后迅速增加，尽管分别仍有超过80%和95%的内源性类胡萝卜素和α-生育酚存在。当在LDL内产生过氧自由基或脂蛋白暴露于活化的人类多形核白细胞产生的氧化剂时，获得了定性相似的结果。通过向脂蛋白制剂中补充生理量的抗坏血酸或泛醇-10，LDL氧化显著降低。我们的数据表明，泛醇-10在抑制LDL氧化方面比番茄红素、β-胡萝卜素或α-生育酚更有效。
