Clinical Applications of Nitrite

正如之前在本报告和相关的NO年度报告（DK 025093-18）中所总结的那样，在过去的二十年里，我们与我们的直接和国际合作者一起，展示了哺乳动物和人体中NO形成的主要新途径，即，亚硝酸根离子还原形成NO。这补充了各种NOS酶的活性，特别是在缺氧条件下。因此，我们专注于亚硝酸盐管理的生理和药理作用，以及硝酸盐摄入（这是由唾液细菌转化为亚硝酸盐）和这些氮氧化物在组织和哺乳动物体内的通量。 正如相关报告所总结的，各种生理途径，如脑血流量、红细胞储存、血小板反应性和血液凝固，都受到这些化合物水平的极大影响。 DK 025093系列报告中总结的最新工作表明，某些哺乳动物组织也可以将硝酸根离子还原为亚硝酸根，然后还原为NO。因此，我们必须确定在食品和药物中摄入这些化合物的实用性和安全性，并研究各种因素如何影响其从饮食中的吸收。 我们还希望测量它们在各种生物液体（如血液和尿液）以及环境中的水平。 几年来，我们一直在与里斯本的一个小组合作，开发基于电极的水和其他环境流体中亚硝酸盐的测定方法;鉴于亚硝酸盐在血液和其他生物液体中的重要性，我们现在将这项工作重新定向到更微观的尺度，使得对动物和人类样品的测量可能是可行的，并且最近公布了一个微观的细节，电极，其可以允许在生理相关浓度下进行这种测定。 在动物和人中的硝酸盐-亚硝酸盐-NO代谢的详细代谢研究需要示踪剂研究，这可以使用无毒的重同位素。 我们在纽卡斯尔的合作者正在开发在动物身上做这件事的方案，然后可能在人类身上做。他们从各种动物摄入研究中向我们发送了样本，我们正在使用我们高度灵敏和准确的化学发光方法来定量这些血液样本中的硝酸盐和亚硝酸盐水平。(One他们的工作人员访问了我们的实验室几个星期，学习如何进行这些测定。我们在巴西圣保罗的合作者在NO药理学方面有丰富的经验，我们正在与他们合作研究各种高血压动物模型，希望最终进行临床研究。我们的第一个结果，最近发表的，表明管理的抗氧化剂Tempol与肾血管高血压啮齿动物改善血管反应亚硝酸盐，但抗高血压反应不受影响。最后，我们与英国埃克塞特的肌肉生理学小组建立了合作关系，我们预计-一旦所有许可生效-测量人体组织中休息和运动时的硝酸盐水平，以查看我们的动物结果是否适用于人类受试者。 我们还参加了NIH主办的关于口服硝酸盐和亚硝酸盐在食品和药物中的效用和安全性的讨论。 这些讨论最近发表，并提出了增加硝酸盐和亚硝酸盐水平的许多可能的健康益处，特别是通过口服，并建议进行新的研究，看看以前假设的这种摄入的有害影响是否真的有效。

As was summarized previously in this and the related NO annual report (DK 025093-18) over the last two decades we have, with our immediate and international collaborators, shown a major new route for NO formation in the mammalian and human bodies, i.e., the reduction of nitrite ions to form NO. This complements, especially under hypoxic conditions, the activity of the various NOS enzymes. As a result we have focused on physiological and pharmacological effects of nitrite administration, as well as nitrate ingestion (which is converted to nitrite by salivary bacteria) and the fluxes in these nitrogen oxides in tissues and in the mammalian body. As summarized in the related report, various physiological pathways such as brain blood flow, red cell storage, platelet reactivity and blood clotting are very much influenced by the levels of these compounds. Recent work summarized in the DK 025093 series of reports suggest that some mammalian tissues can also reduce nitrate ions to nitrite and then NO. It is thus essential that we establish the utility and safety of ingestion of these compounds in foods and medicines and to examine how various factors affect their absorption from the diet. We also wish to measure their levels in various biological fluids, such as blood and urine, as well as in the environment. For some years we have been working with a group in Lisbon to develop electrode-based assays for nitrite in water and other environmental fluids; in view of the importance of nitrite in blood and other biological fluids we have now redirected this work to a more micro scale so that measurements on animal and human samples may be feasible and have recently published details of a micro-electode which may allow such assays at physiologically relevant concentrations. Detailed metabolic studies of nitrate-nitrite-NO metabolism in animals and people require tracer studies which may be approached using non-toxic heavy isotopes. Our collaborators in Newcastle are developing protocols to do this in animals and then perhaps in human subjects. The have sent us samples from various animal ingestion studies and we are using our highly sensitive and accurate chemi-luminesence methods to quantity nitrate and nitrite levels in these blood samples. (One of their staff visited our laboratory for several weeks to learn how to do these assays.) Our collaborators in Sao Paulo, Brazil have much experience in pharmacology of NO and we are working with them on various animal models of hypertension with the hope of eventual clinical studies. Our first results, recently published, show that administration of an anti-oxidant Tempol to rodents with reno-vascular hypertension improved the vascular responses to nitrite but that the anti-hypertensive responses were not affected. Lastly we have established a collaboration with a muscle physiology group in Exeter, UK and we anticipate -once all permissions are effected -measuring the levels of nitrate at rest and with exercise - in the human tissues to see if our animal results obtain for human subjects. We have also participated in an NIH-sponsored discussion of the utility and safety of orally administered nitrate and nitrite in food and as medications. These deliberations were recently published and suggest many possible health benefits of increasing nitrate and nitrite levels, especially by oral administration, and suggest new studies to see if previously postulated harmful effects of such ingestion were really valid.