Nitroxides as Protectors Against Oxidative Stress

已被用作EPR自旋标记的氮氧化物(如temol)已被证明具有超氧化物歧化酶(SOD)活性，并在保护细胞免受包括过氧化氢、超氧化物、有机过氧化氢、氧化还原循环化疗药物和电离辐射在内的各种氧化应激的影响方面非常有效。我们已经证明了Tempoll对体外细胞和小鼠的电离辐射都有保护作用。因此，氮氧化物代表了一种新的辐射防护剂，可能在保护人类免受辐射方面具有广泛的用途。重要的是，我们已经证明tempoll不能保护啮齿动物的肿瘤组织；我们认为其机制涉及正常组织和肿瘤组织的不同代谢还原特性。体内荷瘤动物模型的电子顺磁共振成像研究表明，与正常组织相比，肿瘤中氮氧化物的减少更快。最近的研究表明，葡萄糖6-磷酸脱氢酶(G6PD)缺陷的细胞将氮氧化物还原为羟胺的速度比对照细胞慢得多，这表明这一重要的生化途径在氮氧化物还原过程中发挥了作用。我们最近还表明，细胞内谷胱甘肽水平是组织中氮氧化物减少的主要决定因素。这些研究将使我们能够最好地确定氮氧化物作为正常组织潜在选择性辐射防护剂的适当给药途径。我们最近还发现，氮氧化物可以对抗雌激素代谢产物的细胞毒性和致突变性。这些研究将扩大到探索它们对体内肿瘤模型的影响。最后，初步研究表明，长期(在食物或饮用水中)给p53基因敲除小鼠服用tempoll可以延长它们的寿命。此外，在对照组小鼠中，我们观察到长期服用temol可显著减轻体重，我们最近发现，这与骨骼肌中线粒体解偶联蛋白2的表达增加有关。由于氮氧化物很容易穿透细胞膜，是有效的抗氧化剂，它们可能在医学研究的其他领域中使用，如缺血/再灌注损伤研究、预防白内障、炎症过程和衰老。

Nitroxides (such as tempol) which have been used as EPR spin labels have been shown to exhibit superoxide dismutase (SOD) activity and are quite effective agents in protecting cells against a wide variety of oxidative stresses including hydrogen peroxide, superoxide, organic hydroperoxides, redox-cycling chemotherapy drugs, and ionizing radiation. We have demonstrated that Tempol protects both cells in vitro and mice against ionizing radiation. Thus, the nitroxides represent a new class of radiation protectors that may have widespread use in protecting humans against radiation. Importantly, we have shown that tempol does not protect rodent tumor tissue; the mechanism of which we believe involves differential metabolic reduction properties of normal versus tumor tissue. In vivo electron paramagnetic resonance imaging studies in a tumor-bearing animal model has shown more rapid reduction of nitroxides in tumor compared to normal tissue. Recent studies have shown that cells deficient in glucose 6 phosphate dehydrogenase (G6PD) reduce the nitroxide to the hydroxylamine much slower than control cells suggesting a role for this important biochemical pathway in nitroxide reduction. We have also recently shown that intracellular glutathione levels are a major determinant of nitroxide reduction in tissues. These studies will enable us to best determine the appropriate routes of administration for nitroxides as potentially selective radioprotectors of normal tissues. We have also recently shown that nitroxides protect against the cytotoxicity and mutagenicity of estrogen metabolites. These studies will be expanded to explore their impact to in vivo tumor models. Lastly, preliminary studies have indicated that long-term administration of tempol (in the food or drinking water) to p53 knockout mice extends their life span. Additionally in control mice we have observed that long-term administration of tempol results in dramatic weight reduction, which we have recently correlated, with increased expression of mitochondrial uncoupling protein 2 in skeletal muscle. Since nitroxides readily penetrate cell membranes and are potent antioxidants, they may be of use in other areas of medical research such as ischemia/reperfusion injury studies, prevention of cataracts, inflammatory processes, and aging.