Hemoglobin-Mediated Oxidation of Low-Density Lipoprotein (oxLDL) Contributes to Lung Microvascular Endothelial Dysfunction Via Lectin-Like Oxidized LDL Receptor 1 (LOX-1)
Authors: Meegan Jamie , Douglas Joel , Riedmann Kyle , Ware Lorraine , Bastarache Julie 
Published: May 2024

Introduction: Lung microvascular endothelial barrier disruption is a critical feature of acute lung injury during several pathologies, including sepsis. 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. However, the precise signaling mechanisms involved in CFH-mediated lung microvascular barrier dysfunction are incompletely understood. One potential mechanism by which CFH might disrupt the microvascular endothelial barrier is through its known ability to oxidize lipids and lipoproteins, including low-density lipoprotein (LDL). Oxidized LDL (oxLDL) is a known endothelial barrier disruptor, primarily signaling through scavenger receptors such as lectin-like oxidized LDL receptor 1 (LOX-1). We hypothesized that CFH-mediated oxidation of LDL exacerbates lung microvascular endothelial barrier dysfunction via LOX-1. Methods: For experimental studies, LDL was oxidized by combining LDL with CFH in a test tube overnight at 37°C and oxidation of LDL was quantified by TBARS assay. In primary human lung microvascular endothelial cells (HLMVEC), barrier dysfunction was assessed with expert permeability testing (XPerT) assay. HLMVEC were stimulated with vehicle control (PBS), LDL (0.05 mg/mL), CFH (0.5 mg/mL), or LDL oxidized by CFH (LDL+CFH) with or without one-hour pre-treatment of hemoglobin scavenger haptoglobin (1:1) or LOX-1 inhibitor BI-0115 (Boehringer Ingelheim, 10 μM). Cleaved caspase-3 (CST 9661, 1:500) was assessed with immunofluorescence microscopy. To test whether CFH and oxLDL are associated in clinical sepsis, circulating levels of CFH and oxLDL were measured in 60 sepsis patients via ELISA. Results: Oxidation of LDL by CFH (p=0.0006 by TBARS) exacerbated HLMVEC barrier dysfunction (p<0.0001 by XPerT) but was partially prevented by scavenging CFH with haptoglobin (p<0.0001 by XPerT) or blocking LOX-1 receptor (p<0.0001 by XPerT). Oxidation of LDL by CFH stimulation of HLMVEC also increased caspase-3 activation (p<0.0001 by immunofluorescence of cleaved caspase-3). In sepsis patients, circulating oxLDL levels correlated with CFH (r=0.4, p=0.002). Conclusions: Oxidation of LDL by CFH contributes to lung microvascular endothelial injury via LOX-1 receptor and activation of caspase-3; targeting this pathway may hold therapeutic potential to treat pathologies in which CFH is elevated, including sepsis-induced acute lung injury/ARDS. Funding: Parker B. Francis Fellowship (JEM); NIH K99HL166865 (JEM), R01HL158906 (LBW), R01HL164937 (LBW), R21GM144915 (LBW, JAB), R35HL150783 (JAB), RF1AG075341 (JAB). This is the full abstract presented at the American Physiology Summit 2024 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.