The Capacity of Red Blood Cells to Reduce Nitrite Determines Nitric Oxide Generation under Hypoxic Conditions
The Capacity of Red Blood Cells to Reduce Nitrite Determines Nitric Oxide Generation under Hypoxic Conditions
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DOI：
10.1371/journal.pone.0101626
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发表时间：
2014-07-09
期刊：
影响因子：
3.7
通讯作者：
Kuypers, Frans A.
中科院分区：
文献类型：
--
作者：
Fens, Marcel H.;Larkin, Sandra K.;Kuypers, Frans A.
一氧化氮(NO)是血管张力的关键调节因子。内皮型一氧化氮合酶(ENOS)在常氧条件下负责NO的生成。然而，在低氧条件下，eNOS是不活跃的，红细胞(RBC)提供了一条替代亚硝酸盐生成NO的途径，以调节缺氧的血管扩张。虽然血红蛋白的亚硝酸还原酶活性已为人们所熟知，但对于具有生理浓度的完整红细胞产生NO的情况却知之甚少。我们的目标是开发和应用一种新的方法来深入了解RBC在低氧条件下将亚硝酸盐转化为NO的能力。我们建立了一个新的实验装置来评估不同条件下亚硝酸盐的摄取和NO从红细胞释放到气相中的情况。NO的测量结果与临床公认的呼出NO的测量结果相似。亚硝酸盐摄取迅速，在低氧条件下，经过最初的滞后期，红细胞释放的NO在时间上是恒定的。氧的存在显著减少了NO的释放，而抑制eNOS和黄嘌呤氧化还原酶(XOR)并不影响NO的释放。在低氧条件下，pH降低会增加NO的释放。低温降低了NO的释放，而高温增加了NO的释放。与成人血红蛋白相比，胎儿血红蛋白没有改变NO的释放，而镰刀状红细胞显示出释放NO的能力增强。在所有条件下，RBC对亚硝酸盐的摄取都是相似的。这项研究表明，在低氧条件下，红细胞对亚硝酸盐的吸收很快，NO持续释放到气相中的时间较长。红细胞环境的变化，如pH、温度或血红蛋白类型，都会影响NO的释放。
Nitric oxide (NO) is a key regulator of vascular tone. Endothelial nitric oxide synthase (eNOS) is responsible for NO generation under normoxic conditions. Under hypoxia however, eNOS is inactive and red blood cells (RBC) provide an alternative NO generation pathway from nitrite to regulate hypoxic vasodilation. While nitrite reductase activity of hemoglobin is well acknowledged, little is known about generation of NO by intact RBC with physiological hemoglobin concentrations. We aimed to develop and apply a new approach to provide insights in the ability of RBC to convert nitrite into NO under hypoxic conditions. We established a novel experimental setup to evaluate nitrite uptake and the release of NO from RBC into the gas-phase under different conditions. NO measurements were similar to well-established clinical measurements of exhaled NO. Nitrite uptake was rapid, and after an initial lag phase NO release from RBC was constant in time under hypoxic conditions. The presence of oxygen greatly reduced NO release, whereas inhibition of eNOS and xanthine oxidoreductase (XOR) did not affect NO release. A decreased pH increased NO release under hypoxic conditions. Hypothermia lowered NO release, while hyperthermia increased NO release. Whereas fetal hemoglobin did not alter NO release compared to adult hemoglobin, sickle RBC showed an increased ability to release NO. Under all conditions nitrite uptake by RBC was similar. This study shows that nitrite uptake into RBC is rapid and release of NO into the gas-phase continues for prolonged periods of time under hypoxic conditions. Changes in the RBC environment such as pH, temperature or hemoglobin type, affect NO release.