Besting Vitamin E: Sidechain Substitution is Key to the Reactivity of Naphthyridinol Antioxidants in Lipid Bilayers
Besting Vitamin E: Sidechain Substitution is Key to the Reactivity of Naphthyridinol Antioxidants in Lipid Bilayers
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DOI：
10.1021/ja309153x
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发表时间：
2013-01-30
影响因子：
15
通讯作者：
Pratt, Derek A.
中科院分区：
文献类型：
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作者：
Li, Bo;Harjani, Jitendra R.;Pratt, Derek A.
合成了一系列具有不同侧链取代的α-生育酚（α-TOH，右）的萘啶醇类似物，以确定这些有效抗氧化剂的亲脂性的系统性变化如何影响其在脂质双层中的自由基捕获活性、通过水溶性还原剂的再生性以及与人生育酚转运蛋白（TTP）的结合。使用最近开发的高通量测定法在磷脂酰胆碱单层脂质体中测定萘啶醇的活性，该测定法采用在氧化后经历荧光增强的α-TOH（H2 B-PMHC）的硼二吡咯亚甲基缀合物。萘啶醇提供了一个剂量依赖性的保护H2 B-PMHC与前所未有的过氧自由基捕获活性的脂质双层。虽然侧链长度和/或支化对其表观反应性没有影响，但它显著影响反应化学计量，其中更多的亲脂性化合物捕获两个过氧自由基，而更多的亲水性化合物捕获显著少于一个。有人建议，亲脂性较低的化合物在水相中迅速自氧化，更亲脂性的化合物的双层保护它们免受自氧化的优先分区。还使用H2 B-PMHC在脂质体中研究了亲脂性萘啶醇与水溶性还原剂的协同性，并且当与α-TOH相比时，显示抗坏血酸盐、N-乙酰半胱氨酸和尿酸盐中的每一种的上级再生性。与人TTP（生育酚的生物利用度的关键决定因素）的结合测定揭示，萘啶醇可以是蛋白质的非常好的配体。事实上，具有八个或更多个碳的侧链的萘二醇对TTP的亲和力与α-TOH相似，并且在一种情况下比α-TOH好α倍。
A series of naphthyridinol analogs of alpha-tocopherol (alpha-TOH, right) with varying sidechain substitution was synthesized to determine how systematic changes in the lipophilicity of these potent antioxidants impact their radical-trapping activities in lipid bilayers, regenerability by water-soluble reductants, and binding to human tocopherol transport protein (TTP). The activities of the naphthyridinols were assayed in phosphatidylcholine unilamellar liposomes using a recently developed high-throughput assay that employs a boron dipyrromethene conjugate of alpha-TOH (H2B-PMHC) that undergoes fluorescence enhancement upon oxidation. The naphthyridinols afforded a dose-dependent protection of H2B-PMHC consistent with unprecedented peroxyl radical-trapping activity in lipid bilayers. While sidechain length and/or branching had no effect on their apparent reactivity, it dramatically impacted reaction stoichiometry, with more lipophilic compounds trapping two peroxyl radicals and more hydrophilic compounds trapping significantly less than one. It is suggested that the less lipophilic compounds autoxidize rapidly in the aqueous phase and that preferential partitioning of the more lipophilic compounds to the bilayer protects them from autoxidation. The cooperativity of a lipophilic naphthyridinol with water-soluble reducing agents was also studied in liposomes using H2B-PMHC and revealed superior regenerability by each of ascorbate, N-acetylcysteine, and urate when compared to alpha-TOH. Binding assays with human TTP, a key determinant of the bioavailability of the tocopherols, reveal that the naphthyiridinols can be very good ligands for the protein. In fact, naphthyridinols with sidechains of eight or more carbons had affinities for TTP which were similar to, and in one case alpha-fold better than, alpha-TOH.