Abstract 10537: A Comparison of Endothelial Nitric Oxide Synthase(eNOS)-Based Platelet Subpopulation Ratios and Platelet VEGF Content Within Covid-19

Abstract

Background: Nitric oxide (NO) regulates both thrombosis and vascular leakage, two of the major complications of severe Covid19. Platelet-derived NO inhibits adhesion/aggregation and within microvascular endothelial cells NO-signalling mediates vascular endothelial growth factor (VEGF/VPF)-induced permeability. Recently, we identified novel platelet subpopulations with a differential ability to produce NO and the presence/absence of endothelial nitric oxide synthase (eNOS). We showed that eNOS-negative (eNOS neg ) platelets initiate adhesion and aggregation, while eNOS-positive (eNOS pos ) platelets limit aggregate growth. As inflammatory cytokines are known to counter-regulate eNOS and VEGF expression, we hypothesized that the ratio of eNOS-negative to -positive platelets may be increased in COVID-19 patients along with their VEGF content. Aims: To determine the eNOS-positive to -negative platelet ratio and platelet VEGF levels within the blood of hospitalized COVID-19 patients. Methods: Platelets were isolated from age- and sex-matched COVID-19 patients (ICU and non-ICU) and COVID-negative healthy controls. Isolated platelets were intracellularly stained for eNOS, VEGF, and for surface CD62P and analyzed using flow cytometry. A multiplex assay was used to measure plasma cytokines. Results: The percentage of eNOS neg platelets within the blood of COVID-19 patients (ICU and non-ICU) was higher than that within healthy controls and their levels correlated with disease severity (81.2±2.8% ICU vs. 66.0 ±3.1% non-ICU vs. 6.1± 1.3% controls, P -value < 0.0001). Accordingly, the percentage of eNOS pos platelets in COVID-19 patients was lower compared to controls, while the platelet VEGF content and surface CD62P of COVID-19 patients in ICU was higher than that of healthy controls. Further, COVID-19 patients demonstrated higher TNFα, IL-6, and IL-1β plasma concentrations than controls. Conclusion: Preliminary data suggests that eNOS-negative to -positive platelet ratios and VEGF content increase with COVID-19 severity, potentially predisposing patients to thrombosis and enhanced vascular permeability upon platelet activation. These platelet changes may be due to the actions of inflammatory cytokines on megakaryocytes.