Yeh George C, Henderson Jeffrey P, Byun Jaeman, André d'Avignon D, Heinecke Jay W
Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA.
Arch Biochem Biophys. 2003 Oct 1;418(1):1-12. doi: 10.1016/s0003-9861(03)00256-x.
Reactive nitrogen and oxygen species are implicated in the damage of ischemic tissue that is reperfused. One important pathway may involve xanthine oxidase. Xanthine oxidase uses xanthine, a product of ATP degradation in ischemic tissue, to produce superoxide and hydrogen peroxide. Superoxide reacts rapidly with nitric oxide to form peroxynitrite, a powerful oxidant. Another potential source of reactive nitrogen species is the myeloperoxidase-hydrogen peroxide-nitrite system of activated phagocytes. We demonstrate that peroxynitrite and myeloperoxidase nitrate xanthine in vitro. Through 13C NMR spectroscopy, UV/visible spectroscopy, and mass spectrometry, the major product was identified as 8-nitroxanthine. Xanthine nitration by peroxynitrite was optimal at neutral pH and was markedly stimulated by physiological concentrations of bicarbonate. Xanthine nitration by myeloperoxidase required hydrogen peroxide and nitrite. However, it was independent of chloride ion and little affected by scavengers of hypochlorous acid, suggesting that the reactive agent is a nitrogen dioxide-like species. 8-Nitroxanthine was generated by a low, steady flux of peroxynitrite, and also by the myeloperoxidase-hydrogen peroxide-nitrite system of activated human neutrophils, suggesting that the reactions may be physiologically relevant. 8-Nitroxanthine may exert biological effects because it markedly increased the production of superoxide by the xanthine oxidase-xanthine system. Our observations suggest a mechanism for the enhanced formation of superoxide in reperfused tissue, which might increase the production of peroxynitrite and 8-nitroxanthine. Generation of 8-nitroxanthine by peroxynitrite and myeloperoxidase could represent a positive feedback mechanism that enhances further the production of both reactive oxygen and nitrogen species in ischemic tissue that is reperfused.
活性氮和氧物质与再灌注的缺血组织损伤有关。一条重要途径可能涉及黄嘌呤氧化酶。黄嘌呤氧化酶利用缺血组织中ATP降解产物黄嘌呤来生成超氧化物和过氧化氢。超氧化物与一氧化氮迅速反应形成过氧亚硝酸盐，一种强氧化剂。活性氮物质的另一个潜在来源是活化吞噬细胞的髓过氧化物酶-过氧化氢-亚硝酸盐系统。我们证明过氧亚硝酸盐和髓过氧化物酶在体外可使黄嘌呤硝化。通过13C核磁共振光谱、紫外/可见光谱和质谱分析，主要产物被鉴定为8-硝基黄嘌呤。过氧亚硝酸盐对黄嘌呤的硝化在中性pH时最佳，并受到生理浓度碳酸氢盐的显著刺激。髓过氧化物酶对黄嘌呤的硝化需要过氧化氢和亚硝酸盐。然而，它不依赖于氯离子，且几乎不受次氯酸清除剂的影响，这表明反应性试剂是一种类似二氧化氮的物质。低水平、稳定的过氧亚硝酸盐通量以及活化的人中性粒细胞的髓过氧化物酶-过氧化氢-亚硝酸盐系统均可生成8-硝基黄嘌呤，这表明这些反应可能具有生理相关性。8-硝基黄嘌呤可能发挥生物学作用，因为它显著增加了黄嘌呤氧化酶-黄嘌呤系统中超氧化物的产生。我们的观察结果提示了再灌注组织中超氧化物生成增加的一种机制，这可能会增加过氧亚硝酸盐和8-硝基黄嘌呤的产生。过氧亚硝酸盐和髓过氧化物酶生成8-硝基黄嘌呤可能代表一种正反馈机制，进一步增强再灌注缺血组织中活性氧和氮物质的产生。
