Clinical Applications of Nitrite and Nitrate

正常志愿者输注亚硝酸盐和实验动物吸入一氧化氮的结果表明，一氧化氮可以作为一种激素进行运输，因此有可能成为一种药理制剂（即药物）。然而，NO在镰状细胞患者中相对较小的血管效应可能是由于循环血红蛋白的存在，这有助于这种和其他慢性和急性溶血性综合征的病理生理学，特别是我们发现在老年患者中严重且高频率的肺动脉高压并发症。我们还发现，no生物活性破坏似乎发生在组织中，其程度远远大于血管床。我们也很幸运能够使用重症医学系的犬类设备，在缺氧的狗身上测试吸入的亚硝酸盐和硝酸盐离子，看看以这种方式给予NO生物活性是否在治疗上是可能的。我们测试硝酸盐，因为有证据表明肺组织中有一定水平的酶，如黄嘌呤氧化还原酶，它可以将硝酸盐离子还原为亚硝酸盐和NO。我们发现吸入亚硝酸盐对肺部和全身参数的强烈影响，正如其他动物模型所报道的那样，但硝酸盐的影响只是间歇性的。这些结果刚刚发表。然而，我们也发现，饮食中硝酸盐和亚硝酸盐的限制大大降低了这些离子的水平（比血液或肝脏中的含量要高，比许多基因操作要高），这些离子返回到饮食中会导致快速积累，在某些情况下甚至会“超调”水平。

The results of nitrite infusions in normal volunteers and NO inhalation in experimental animals suggest that NO can be transported as a hormone and thus has the potential to be a pharmacological agent (i.e., a drug). Howeve, the relatively small vascular effects of NO in our sickle cell patients is likely due to the presence of circulating hemoglobin and that this contributes to the pathophysiology of this and other chronic and acute hemolytic syndromes, especially the pulmonary hypertension complications which we have found to be severe and of high frequency in older patients. We also find that NO-bioactivity destruction appears to occur in tissues to a much greater extent than in the vascular bed. We have also been fortunate in being able to use the Critical Care Medicine Department canine facility and test inhaled nitrite and nitrate ions in hypoxic dogs to see if administering NO bioactivity in this way would be therapeutically possible. We tested nitrate as there is evidence that pulmonary tissue has some levels of enzymes, such as xanthine oxido-reductase that can reduce nitrate ions to nitrite and NO. We have found strong effects of nitrite inhalation on both pulmonary and systemic parameters, as has been reported for other animal models, but the effects of nitrate are only seen intermittently. These results have just been published. However, we also find that dietary limitations of nitrate and nitrite lower these levels greatly (more than in blood or liver and more than many genetic manipulations) and that return of these ions to the diet results in rapid accumulation and, indeed, in some cases an "overshoot" of the levels. 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 eventually in human subjects. They have sent us samples from various animal ingestion studies and we are using our highly sensitive and accurate chemi-luminescence 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.) Early human studies have examined the effects of ascorbic acid on dietary nitrate and nitrite absorption. Our collaborators in Bangkok have administered low levels of nitrite to thalassemia patients and we have worked with them to show that VASP phosphorylation is affected, as a parameter for measuring platelet inhibition (as described in DK 025104). Most encouraging, we have established a robust collaboration with a muscle physiology group in Exeter, UK and we have been measuring the levels of nitrate at rest and with exercise in the human tissues and have confirmed that our animal results obtain for human subjects, including the high levels of nitrate in muscle and its decrease with robust exercise. We believe that muscle levels of nitrate must be considered in dietary interventions, for pharmacological effects or for affecting performance. These results have also been recently published. Two new projects have very recently been initiated. First, we are studying the mechanism of nitroglycerine reduction as our recent work has suggested the possibility of new pathways, including reduction by salivary bacteria, that might enhance the clinical utility of this classic agent. Second, we began by measuring nitrate and nitrite levels in whole rodent eyes as a beginning of measuring these levels in various compartments of the eye in larger animal models and perhaps in human samples. Our later results in porcine studies very importantly suggest that the lacrimal glands pump nitrate ions from blood into the tears where several processes could convert it to nitrite and/or NO for adsorption into the eye. We believe that this process contributes to the normal function of the retina and eye and may be useful as therapy of conditions such as glaucoma and macular degeneration. Clinical studies with the Department of Ophthalmology at MedStar are now being planned.