Role of Xanthine Oxidase in Heme-induced Vascular Dysfunction

项目摘要/摘要 溶血或红细胞破裂引起的血管损伤是一个重要的临床问题。 与多种溶血病理有关，包括镰状细胞病(SCD)、脓毒症和医源性 体外循环手术、心脏辅助装置和瓣膜置换术中的问题。在溶血期间， 红细胞释放血红蛋白，然后释放出血红素，导致体内的氧化环境。 血管内空间。有趣的是，循环中黄嘌呤氧化酶(XO)水平的显著升高也是 据报道与多种溶血性疾病有关。虽然血红素水平升高是很好的 以溶血病理生物学为特征，血红素和XO活性增加之间的关系尚不清楚。 在这里，我们提供了新的数据，将血管内血红素损伤的小鼠模型与血管内血红素的过度放大联系起来。 循环XO水平(&gt；20倍)。这一点很重要，因为文献中长达数十年的偏见表明这一水平 循环中的XO放大被认为是有害的。与这个由来已久的教条相反，我们的新 数据表明，在血红素超载期间，XO反而起到了保护作用。初步研究显示抑制作用 在血红素超载期间使用非布索他汀的XO会降低存活率，加速器官损伤，并升高 炎症反应与对照组比较。与此一致的是，SCD患者和一只小鼠的血浆 SCD模型显示了循环XO中的高度。重要的是，生化研究发现了一种新的 对XO的作用：通过产生H_2O_2和随后的血红素衍生的游离铁的螯合来“裂解”血红素 通过尿酸，以保护内皮免受明显的血红素损伤。因此，我们假设如下 血凝蛋白饱和时，肝脏XO被释放到循环中，与内皮结合，并呈现一种血管- 在血红素超载和SCD相关的血红素危机中的保护作用，这是由于它能够降解血红素和 随后，通过产生尿酸来螯合游离铁。我们将使用三个具体目标来验证这一假设： 目的1：确定XO是否在血管内血红素超负荷时起到保护作用。目标2：确定XO是否有助于 “血红素裂解”和随后通过XO衍生的尿酸的铁络合。目标3：调查是否升高 SCD中的XO对血红素诱导的血管闭塞危机具有保护作用。填补这一知识空白可能会发现新的 一般情况下，与血管内溶血相关的血管功能障碍的解决策略，以及特殊情况下的SCD。

PROJECT SUMMARY/ABSTRACT Vascular injury resulting from hemolysis or ruptured red blood cells is an important clinical issue associated with numerous hemolytic pathologies including sickle cell disease (SCD), sepsis and iatrogenic issues in cardiopulmonary bypass surgery, ventricular assist devices and valve replacement. During hemolysis, red cells release hemoglobin that subsequently discharges heme leading to an oxidative milieu in the intravascular space. Interestingly, substantial elevation in circulating levels of xanthine oxidase (XO) is also reported to be associated with numerous hemolytic diseases. While elevated levels of heme are well characterized in hemolysis pathobiology, the relationship between heme and increased XO activity is unclear. Here, we provide new data connecting a murine model of intravascular heme injury to excessive amplification in circulating XO levels (>20-fold). This is important as decades-long bias in the literature would suggest this level of XO amplification in the circulation to be considered deleterious. Contrary to this long-standing dogma, our new data suggest XO instead assumes a protective role during heme overload. Pilot studies demonstrate inhibition of XO with febuxostat during heme overload decreases survival, accelerates organ damage, and elevates inflammatory responses compared to controls. Consistent with this, plasma from both SCD patients and a murine model of SCD demonstrate elevation in circulating XO. Importantly, biochemical studies have identified a novel function for XO: the “splitting” of heme via H2O2 production and subsequent chelation of heme-derived free iron via uric acid in order to protect the endothelium from overt heme damage. As such, we hypothesize that following hemopexin saturation, hepatic XO is released to the circulation, binds to endothelium, and assumes a vaso- protective role during heme overload and SCD-associated heme crisis due to its ability to degrade heme and subsequently chelate free iron by producing uric acid. We will test this hypothesis using three specific aims: Aim 1: Define if XO mediates protection during intravascular heme overload. Aim 2: Determine if XO facilitates “heme splitting” and subsequent iron chelation via XO-derived uric acid. Aim 3: Investigate whether elevated XO in SCD protects against heme-induced vaso-occlusive crisis. Filling this knowledge gap may uncover new strategies to address the vascular dysfunction allied to intravascular hemolysis, in general, and SCD, in specific.