Haptoglobin 2 variant and endothelial glycocalyx shedding in sepsis-induced ARDS

点击翻译按钮获取中文摘要

ABSTRACT Sepsis-induced acute respiratory distress syndrome (ARDS) is a leading cause of acute respiratory failure in critical illness. Morbidity and mortality are high and there are no proven pharmacologic therapies other than antimicrobials. Sepsis-associated ARDS is characterized by pathologic degradation of the pulmonary endothelial glycocalyx—a glycosaminoglycan-enriched endovascular layer necessary for pulmonary vascular homeostasis. There is a vital need to identify early triggers of endothelial glycocalyx degradation in sepsis, both to enhance our understanding of pathophysiology, and critically, to identify new therapeutic targets for prevention and early treatment of sepsis-induced ARDS. Our published and preliminary data suggest that (1) cell-free hemoglobin (CFH) is released into the circulation in sepsis and contributes to oxidant-mediated organ dysfunction and death; (2) CFH can directly injure the lung endothelial glycocalyx, causing degradation and shedding; (3) haptoglobin, an endogenous scavenger for cell-free hemoglobin that limits its ability to cause oxidative injury has a common genetic variant, HP-2, that increases the risk of ARDS in both humans and mice with sepsis; and (4) patients and mice with sepsis and the HP-2 variant have increased degradation of the endothelial glycocalyx and evidence of increased oxidative stress. The studies in this proposal will build on these preliminary findings to characterize the mechanisms by which CFH-mediated endothelial glycocalyx degradation is modified by the HP-2 genotype. Our primary goal is to translate these findings to new targeted therapies that will be tested in our novel isolated human lung model as preparation for rapid translation to targeted clinical trials in sepsis. In Aim 1, we will use state-of-the-art mass spectrometry analyses of circulating glycosaminoglycan fragments to determine the extent and signature of endothelial glycocalyx shedding in patients with the HP-2 variant, study the association with ARDS and determine downstream mechanisms of endothelial injury. In Aim 2 we will use genetically manipulated mouse models to determine the contribution of heparanase and oxidative injury to glycocalyx degradation in mice with the HP-2 genotype. In Aim 3, we will test the therapeutic potential of targeting oxidant mediated injury in the HP-2 genotype to preserve the endothelial glycocalyx in the isolated perfused human lung as a translational bridge to future patient studies. The studies proposed in these aims have the potential for major and sustained scientific impact. Since HP-2 is the most common allele of the HP gene and over 40% of people of European or African ancestry are homozygous for this allele, targeting patients with the HP2 genotype with therapies to prevent endothelial glycocalyx degradation is a new approach that could have a major impact on clinical outcomes.