Brunelli R, Mei G, Krasnowska E K, Pierucci F, Zichella L, Ursini F, Parasassi T
I and II Clinica Ostetrica e Ginecologica, Universitá di Roma La Sapienza, Viale del Policlinico 155, 00185 Roma, Italy.
Biochemistry. 2000 Nov 14;39(45):13897-903. doi: 10.1021/bi000341p.
Among different proposed mechanisms to account for the protection exerted by estrogens against cardiovascular diseases, the antioxidant effect has attracted considerable attention. We confirmed that 17-beta-estradiol (E2), when added to human LDL at a 6:1 ratio to apoB-100, markedly delays the phase of massive LDL lipid peroxidation induced by Cu(2+). We also observed an increased oxidative resistance of E2-treated LDL by monitoring the early phase of oxidative degradation on the basis of increased LDL surface polarity by the generalized polarization of the lipophilic fluorescent probe 2-(dimethylamino)-6-lauroylnaphthalene (Laurdan). A scavenging of free radicals by E2 is ruled out since, consistent with its structure, its rate constant for the reduction of peroxy radicals is extremely low, i.e., 0.02% of that of vitamin E. Tryptophan fluorescence lifetime and circular dichroism measurements revealed that (i) apoB-100 undergoes a conformational modification and a progressive loss of secondary structure during lipid peroxidation; (ii) E2 increases apoB-100 secondary structure and modifies its conformation; and (iii) the apoB-100 conformational change induced by E2 makes this protein resistant to modifications brought about by lipid peroxidation. We propose that E2, by affecting apoB-100 secondary structure and conformation, modifies the interaction of this protein with the outer layer of the LDL particle thus increasing its overall oxidative resistance.
在为雌激素对心血管疾病的保护作用所提出的不同机制中，抗氧化作用引起了相当大的关注。我们证实，当以6:1的比例将17-β-雌二醇（E2）添加到与人载脂蛋白B-100（apoB-100）结合的人低密度脂蛋白（LDL）中时，能显著延迟由铜离子（Cu(2+)）诱导的大量LDL脂质过氧化阶段。我们还通过监测基于亲脂性荧光探针2-（二甲基氨基）-6-月桂酰萘（Laurdan）的广义极化作用导致的LDL表面极性增加所引起的氧化降解早期阶段，观察到经E2处理的LDL的抗氧化性增强。由于E2的结构，其还原过氧自由基的速率常数极低，即仅为维生素E的0.02%，因此可以排除E2对自由基的清除作用。色氨酸荧光寿命和圆二色性测量结果表明：（i）在脂质过氧化过程中，apoB-100会发生构象修饰和二级结构的逐渐丧失；（ii）E2会增加apoB-100的二级结构并改变其构象；（iii）E2诱导的apoB-100构象变化使该蛋白质对脂质过氧化带来的修饰具有抗性。我们提出，E2通过影响apoB-100的二级结构和构象，改变了该蛋白质与LDL颗粒外层的相互作用，从而提高了其整体抗氧化性。
