Whiteman M, Ketsawatsakul U, Halliwell B
Department of Biochemistry, Faculty of Medicine, National University of Singapore, Singapore.
Ann N Y Acad Sci. 2002 May;962:242-59. doi: 10.1111/j.1749-6632.2002.tb04072.x.
Peroxynitrite is implicated in numerous human diseases. Hence, there is considerable interest in potential therapeutic peroxynitrite scavengers. It has been claimed that uric acid is a powerful peroxynitrite scavenger. We previously observed that uric acid is a powerful inhibitor of tyrosine nitration induced by peroxynitrite, but fails to prevent alpha(1)-antiproteinase (alpha(1)-AP) inactivation induced by peroxynitrite. However, the reactivity of peroxynitrite is significantly modified by bicarbonate and this has not been considered in evaluating the scavenging activity of uric acid and other endogenous antioxidant compounds. In the presence of bicarbonate (25 mM), the ability of uric acid, ascorbate, Trolox, and GSH to inhibit peroxynitrite-mediated tyrosine and guanine nitration is decreased. Protection against peroxynitrite-mediated alpha(1)-AP inactivation is also decreased by ascorbate, Trolox, and GSH, but it is enhanced by uric acid. Bicarbonate also inhibits the ability of these compounds to prevent peroxynitrite-mediated ABTS radical cation formation. However, the abilities of these antioxidants to prevent peroxynitrite-mediated bleaching of pyrogallol red are enhanced by bicarbonate. These results show that physiologic concentrations of bicarbonate substantially modify the ability of uric acid to prevent peroxynitrite-mediated reactions. This study highlights the need to use several different assays in the presence of physiologically relevant concentrations of bicarbonate when assessing compounds for peroxynitrite scavenging, in order to avoid misleading results.
过氧亚硝酸盐与多种人类疾病有关。因此，人们对潜在的治疗性过氧亚硝酸盐清除剂有相当大的兴趣。据称尿酸是一种强大的过氧亚硝酸盐清除剂。我们之前观察到尿酸是过氧亚硝酸盐诱导的酪氨酸硝化的强力抑制剂，但不能阻止过氧亚硝酸盐诱导的α1抗蛋白酶（α1-AP）失活。然而，碳酸氢盐会显著改变过氧亚硝酸盐的反应性，而在评估尿酸和其他内源性抗氧化化合物的清除活性时并未考虑这一点。在存在碳酸氢盐（25 mM）的情况下，尿酸、抗坏血酸、Trolox和谷胱甘肽抑制过氧亚硝酸盐介导的酪氨酸和鸟嘌呤硝化的能力降低。抗坏血酸、Trolox和谷胱甘肽对过氧亚硝酸盐介导的α1-AP失活的保护作用也降低，但尿酸可增强这种保护作用。碳酸氢盐还抑制这些化合物阻止过氧亚硝酸盐介导的ABTS自由基阳离子形成的能力。然而，碳酸氢盐可增强这些抗氧化剂阻止过氧亚硝酸盐介导的邻苯三酚红褪色的能力。这些结果表明，生理浓度的碳酸氢盐会显著改变尿酸预防过氧亚硝酸盐介导反应的能力。这项研究强调，在评估用于过氧亚硝酸盐清除的化合物时，需要在生理相关浓度的碳酸氢盐存在下使用几种不同的测定方法，以避免产生误导性结果。
