Gaut Joseph P, Belaaouaj Abderrazzaq, Byun Jaeman, Roberts L Jackson, Maeda Nobuyo, Frei Balz, Heinecke Jay W
Department of Surgery, Washington University, St. Louis, MO 63110, USA.
Free Radic Biol Med. 2006 May 1;40(9):1494-501. doi: 10.1016/j.freeradbiomed.2005.12.013. Epub 2006 Jan 6.
The observation that antioxidant vitamins fail to confer protective benefits in large, well-designed randomized clinical trials has led many to question the role of oxidative stress in the pathogenesis of disease. However, there is little evidence that proposed antioxidants actually scavenge reactive intermediates in vivo. Ascorbate reacts rapidly with oxidants produced by activated neutrophils in vitro, and neutrophils markedly increase their oxidant production when mice are infected intraperitoneally with the gram-negative bacterium Klebsiella pneumoniae. To explore the antioxidant properties of ascorbate in vivo, we therefore used K. pneumoniae infection as a model of oxidative stress. When mice deficient in L-gulono-gamma-lactone oxidase (Gulo(-/-)), the rate-limiting enzyme in ascorbate synthesis, were depleted of ascorbate and infected with K. pneumoniae, they were three times as likely as ascorbate-replete Gulo(-/-)mice to die from infection. Mass spectrometric analysis of peritoneal lavage fluid revealed a marked increase in the levels of oxidized amino acids and of F2-isoprostanes (sensitive and specific markers of lipid oxidation) in infected animals. Surprisingly, there were no significant differences in the levels of the oxidation products in the ascorbate-deficient and -replete Gulo(-/-)mice. Our observations suggest that ascorbate plays a previously unappreciated role in host defense mechanisms against invading pathogens but that the vitamin does not protect amino acids and lipids from oxidative damage during acute inflammation. To examine the oxidation hypothesis of disease, optimal antioxidant regimens that block oxidative reactions in animals and humans need to be identified.
在大型、设计良好的随机临床试验中，抗氧化维生素未能带来保护作用，这一观察结果使许多人质疑氧化应激在疾病发病机制中的作用。然而，几乎没有证据表明所提出的抗氧化剂能在体内清除反应性中间体。在体外，抗坏血酸与活化的中性粒细胞产生的氧化剂迅速反应，当小鼠经腹腔感染革兰氏阴性菌肺炎克雷伯菌时，中性粒细胞的氧化剂生成会显著增加。因此，为了探究抗坏血酸在体内的抗氧化特性，我们将肺炎克雷伯菌感染用作氧化应激模型。当缺乏L-古洛糖酸-γ-内酯氧化酶（Gulo(-/-)）（抗坏血酸合成中的限速酶）的小鼠体内抗坏血酸耗尽并感染肺炎克雷伯菌时，它们死于感染的可能性是抗坏血酸充足的Gulo(-/-)小鼠的三倍。对腹腔灌洗液的质谱分析显示，感染动物体内氧化氨基酸和F2-异前列腺素（脂质氧化的敏感且特异标志物）的水平显著升高。令人惊讶的是，抗坏血酸缺乏和充足的Gulo(-/-)小鼠体内氧化产物的水平没有显著差异。我们的观察结果表明，抗坏血酸在宿主抵御入侵病原体的防御机制中发挥着此前未被认识到的作用，但在急性炎症期间，这种维生素并不能保护氨基酸和脂质免受氧化损伤。为了检验疾病的氧化假说，需要确定能在动物和人类中阻断氧化反应的最佳抗氧化方案。
