NITROXIDES AS PROTECTORS AGAINST OXIDATIVE STRESS

氮氧化物作为氧化应激的保护剂

• 批准号: 6290749
• 负责人: JAMES B MITCHELL
• 金额: --
• 依托单位: DIVISION OF CLINICAL SCIENCES - NCI
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6290749
• 关键词: Rodentias; analog; chemical structure function; cytotoxicity; drug screening /evaluation; electron spin resonance spectroscopy; free radical scavengers; hydrogen peroxide; ionizing radiation; laboratory mouse; neoplastic cell; nitrogen oxides; oxidation reduction reaction; oxidative stress; oxidizing agents; radiation protection; radioprotective agents; superoxide dismutase; superoxides; tissue /cell culture

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. We have completed an in vitro study to identify the most efficient nitroxide for protection purposes. Over 110 nitroxides were evaluated in a structure activity relationship study. We have identified 6 nitroxides that afford significantly more radioprotection than tempol (the first nitroxide shown to have radioprotective properties) and have also identified 3 analogs that radiosensitize aerobic cells. These agents will be evaluated and compared with tempol in vivo. Large quantities of several of the six protective nitroxides are being synthesized for further study of these newly discovered protectors. We have recently shown that heme proteins exposed to oxidants form highly toxic ferryl moieties and that nitroxides detoxify these toxic species and confer enhanced catalase-like activity to heme species. Reasoning in an analogous fashion we are investigating the affects of nitroxides as modulators of nitric oxide synthase because intermediates within the enzyme which depend on heme redox chemistry may be altered in the presence of nitroxides. We are also investigating in in vivo models, the activity of nitroxides appended to macromolecules such as albumin. Since these agents readily penetrate cell membranes, they may be of use in other areas of medical research such as ischemia/reperfusion injury studies, prevention of cataracts, inflammatory processes and aging. Nitroxides (such as tempol) which have been used as electron paramagnetic resonance (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. Different nitroxides analogues that do not influence blood pressure when administered to animals have been positively identified as radioprotectors thus eliminating the hemodynamic concerns of tempol administration. Recent studies 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 EPR imaging studies in one tumor-bearing animal model has shown more rapid reduction of nitroxides in tumor compared to normal tissue. We are presently seeking to identify and define cellular and physiological factors responsible for this differential effect using our newly constructed functional EPR imaging instrumentation for small animals. 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 are presently studying G6PD status in tumor versus normal tissue. Using nitroxide spin probes, the functional EPR imaging system will also enable us to map out oxygen levels in tissue as well as study various redox parameters of tissue.Studies are presently underway evaluating the radioprotective properties of tempol applied topically to the rectum of rats. Since the rectum is a major normal tissue damaged during radiotherapy for patients with prostate and/or cervix cancer, we will consider using tempol clinically to protect the rectum should our pre-clinical studies prove positive. Our present studies are directed on nitroxide delivery methods to rectal tissue to optimize nitroxide concentration.Preliminary studies have indicated that long term administration of tempol (in the food or drinking water) to p53 knockout mice extends their life span. p53 knockout mice die several months after birth due to rapid tumor induction. Tempol administration extended the life span of these animals ~35-70%. The mechanism of this effect is unknown and is presently a major focus. Lastly, since these agents 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. It has recently been shown that tempol administration after induced ischemia of rat brain markedly reduced the infarct volume associated with ischemia/reperfusion.

已被用作EPR自旋标记物的氮氧化物（如tempol）已显示出超氧化物歧化酶（SOD）活性，并且是保护细胞免受各种氧化应激（包括过氧化氢、超氧化物、有机氢过氧化物、氧化还原循环化疗药物和电离辐射）的非常有效的试剂。我们已经证明，Tempol保护细胞在体外和小鼠对电离辐射。因此，氮氧化物代表了一类新的辐射防护剂，其可广泛用于保护人类免受辐射。重要的是，我们已经表明tempol不保护啮齿动物肿瘤组织;我们认为其机制涉及正常组织与肿瘤组织的差异代谢还原特性。在荷瘤动物模型中的体内电子顺磁共振成像研究显示，与正常组织相比，肿瘤中的氮氧化物减少更快。我们已经完成了一项体外研究，以确定最有效的氮氧化物保护的目的。在结构活性关系研究中评价了110多种氮氧自由基。我们已经确定了6个氮氧化物，提供显着更多的辐射保护比tempol（第一个氮氧化物显示具有辐射防护性能），还确定了3个类似物，辐射敏化需氧细胞。这些药物将在体内进行评估和比较tempol。六种保护性氮氧自由基中的几种正被大量合成，以进一步研究这些新发现的保护剂。我们最近表明，血红素蛋白暴露于氧化剂形成高毒性的铁基部分和氮氧化物解毒这些有毒的物种，并赋予增强的过氧化氢酶样活性血红素物种。以类似的方式推理，我们正在研究氮氧化物作为一氧化氮合酶调节剂的影响，因为在氮氧化物存在下，依赖于血红素氧化还原化学的酶内的中间体可能会改变。我们也在研究在体内模型中，附加到大分子如白蛋白的氮氧自由基的活性。由于这些试剂容易穿透细胞膜，它们可用于医学研究的其他领域，如缺血/再灌注损伤研究，预防白内障，炎症过程和衰老。已被用作电子顺磁共振（EPR）自旋标记物的氮氧化物（如tempol）已显示出超氧化物歧化酶（SOD）活性，并且是保护细胞免受各种氧化应激（包括过氧化氢、超氧化物、有机氢过氧化物、氧化还原循环化疗药物和电离辐射）的非常有效的试剂。我们已经证明，tempol保护细胞在体外和小鼠对电离辐射。不同的氮氧化物类似物，不影响血压时，给药动物已被确定为积极的辐射防护，从而消除了血液动力学的问题tempol管理。最近的研究表明，tempol不保护啮齿动物肿瘤组织，我们认为其机制涉及正常组织与肿瘤组织的差异代谢还原特性。在一个荷瘤动物模型中的体内EPR成像研究显示，与正常组织相比，肿瘤中的氮氧化物减少更快。我们目前正在寻求识别和定义的细胞和生理因素负责这种差异的影响，使用我们新构建的功能EPR成像仪器的小动物。最近的研究表明，葡萄糖6磷酸脱氢酶（G6 PD）缺陷的细胞减少氮氧化物的羟胺比对照细胞慢得多，这表明在氮氧化物还原的重要生化途径的作用。我们目前正在研究肿瘤与正常组织中的G6 PD状态。使用氮氧自旋探针，功能性EPR成像系统也将使我们能够绘制出组织中的氧水平，以及研究组织的各种氧化还原参数。由于直肠是前列腺癌和/或宫颈癌患者在放疗期间受损的主要正常组织，如果我们的临床前研究证明是阳性的，我们将考虑在临床上使用tempol来保护直肠。我们目前的研究是针对氮氧化物的直肠组织的递送方法，以优化nitroxideconcentration.Preliminary研究表明，长期给予tempol（在食物或饮用水）p53基因敲除小鼠延长其寿命。p53基因敲除小鼠在出生后几个月由于快速的肿瘤诱导而死亡。Tempol给药延长了这些动物的寿命约35- 70%。这种效应的机制尚不清楚，目前是一个主要焦点。最后，由于这些药剂容易穿透细胞膜并且是有效的抗氧化剂，因此它们可用于医学研究的其他领域，例如缺血/再灌注损伤研究、预防白内障、炎症过程和衰老。最近的研究表明，在诱导大鼠脑缺血后给予tempol可显著减少与缺血/再灌注相关的梗死体积。