Role of Xanthine Oxidase in Heme-induced Vascular Dysfunction

项目总结/摘要 溶血或红细胞破裂导致的血管损伤是一个重要的临床问题 与许多溶血性病理学相关，包括镰状细胞病（SCD）、败血症和医源性 心肺转流手术、心室辅助装置和瓣膜置换术中的问题。在溶血过程中， 红细胞释放血红蛋白，随后释放血红素，导致血液中的氧化环境。 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 据报道与许多溶血性疾病有关。血红素水平升高 在溶血病理生物学中，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连接小鼠模型血管内血红素损伤过度扩增， 循环XO水平（>20倍）。这一点很重要，因为数十年来文献中的偏见表明这一水平 XO在循环中的放大被认为是有害的。与这一长期存在的教条相反，我们的新 数据表明XO在血红素过载期间反而承担保护作用。初步研究证明了抑制作用 在血红素超载期间，XO与非布司他联合使用会降低存活率，加速器官损伤， 与对照组相比，炎症反应。与此一致，来自SCD患者和小鼠的血浆 SCD模型显示循环XO升高。重要的是，生物化学研究发现了一种新的 XO的功能：通过产生H2 O2和随后螯合血红素衍生的游离铁来“分裂”血红素 以保护内皮免受明显的血红素损伤。因此，我们假设， 当血液结合蛋白饱和时，肝XO被释放到循环中，结合到内皮上，并呈现血管内皮细胞。 在血红素过载和SCD相关血红素危机期间的保护作用，由于其降解血红素的能力， 随后通过产生尿酸螯合游离铁。我们将使用三个具体目标来检验这一假设： 目的1：确定XO是否在血管内血红素过载期间介导保护作用。目标2：确定XO是否有助于 “血红素裂解”和随后的经由XO衍生的尿酸的铁螯合。目的3：调查是否升高 SCD中XO可预防血红素诱导的血管闭塞危象。填补这一知识空白可能会发现新的 解决血管内溶血相关的血管功能障碍的策略，一般来说，和SCD，具体来说。

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.