Cell-free hemoglobin-mediated oxidation of low-density lipoprotein (oxLDL) contributes to lung microvascular endothelial dysfunction during sepsis

Introduction: Disruption of the microvascular endothelial barrier is a critical pathological feature of sepsis-induced acute lung injury. Plasma cell-free hemoglobin (CFH) is elevated in approximately 80% of patients with sepsis and is independently associated with development of acute respiratory distress syndrome (ARDS) and mortality. Oxidized CFH (ferric, 3+) can oxidize low-density lipoprotein (oxLDL), which signals through its major endothelial receptor, the lectin-like oxidized LDL receptor 1 (LOX-1), to cause endothelial dysfunction through several pro-inflammatory pathways including activation of mitogen-activated protein kinases (MAPKs). However, little is known regarding whether LOX-1 receptor signaling leads to microvascular endothelial hyperpermeability or acute lung injury, especially in the context of sepsis. We hypothesized that oxidation of LDL by CFH contributes to lung microvascular endothelial barrier dysfunction and worse outcomes during sepsis through LOX-1 and downstream p38 MAPK. Methods: To test whether generation of oxLDL by CFH is associated with endothelial injury in clinical sepsis, circulating levels of CFH, oxLDL, and vascular injury marker sVE-cadherin were measured in 24 sepsis patients via ELISA and tested for association with development of ARDS. LDL was oxidized by combining LDL with CFH in a test tube overnight at 37°C and oxLDL was quantified by TBARS assay. In primary human lung microvascular endothelial cells (HLMVEC) transendothelial electrical resistance (TER), a measure of barrier dysfunction, was assessed by Electric Cell-substrate Impedance Sensing (ECIS). LOX-1 receptor was blocked using BI-0115 (Boehringer Ingelheim, 20 μM) and p38 MAPK was inhibited using NiPp (100 μM). Results: In sepsis patients, plasma oxLDL levels correlated with CFH (r=0.686, p=0.016) and sVE-cadherin (r=0.603, p=0.012), and tended to be higher in those who developed ARDS (38 U/L [IQR 27, 45] vs. 27 U/L [IQR 19, 35], p=0.1). Oxidation of LDL by CFH exacerbated HLMVEC barrier dysfunction compared to control, LDL, or CFH. Barrier dysfunction induced by CFH or oxLDL was attenuated by blocking the LOX-1 receptor or p38 MAPK. Conclusions: Increased plasma CFH and oxLDL are associated with vascular injury during clinical sepsis; one mechanism by which CFH may cause vascular hyperpermeability and sepsis-mediated lung injury is through oxidation of LDL which can drive signaling through the endothelial LOX-1 receptor and activation of p38 MAPK. NIH R35HL150783, R21GM144915, R01HL158906, R01HL164937, T32HL094296; Parker B. Francis Fellowship This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.