Correlation between Entothelial Microparticle Binding to Monocytes and Monocyte Nitric Oxide Production in Prothrombotic and Inflammatory Disorders

Introduction: Endothelial microparticle binding to monocytes has been shown to induce monocyte activation in vitro. In this study, we examined the correlations between EMP binding to monocytes and monocyte levels of nitric oxide (NO), as a marker of monocyte activation in different clinical conditions. Methods: We studied 186 subjects with acute venous thromboembolism (n=25), atrial fibrillation (n=48), metabolic syndrome (n=37), congestive heart failure (n=44), and normal controls (n=32). Using flow cytometry, we measured monocyte levels of NO by flow cytometry after loading monocytes with the membrane permeable NO-selective fluorescent indicator DAF-DA. Two different populations of EMP-monocyte conjugates were also measured. EMP62E+-monocyte and EMP54+-monocyte conjugates were measured based on the detection of E-selectin (CD62E) or CD54, respectively, coexpressed with CD45 in monocytes. Results: Pearson correlation coefficients between monocyte NO levels and EMP-monocyte conjugates are shown in the Table. A highly significant correlation was found between EMP62E+-monocyte conjugates and monocyte NO levels in patients with congestive heart failure (r=0.43; p=0.003). In contrast, EMP54+-monocyte conjugates strongly correlated with monocyte NO in patients with venous thromboembolism (r=0.58; p=0.009) and metabolic syndrome (r=0.49; p=0.002). No correlation was found between these conjugates and monocyte NO levels in atrial fibrillation or normal controls. Conclusions: The binding of different species of EMP to monocytes correlates with monocyte NO levels in clinical states such as congestive heart failure, metabolic syndrome, and venous thromboembolism. However, this correlation was not found in atrial fibrillation or normal controls. Our findings support the concept that the binding of different species of EMP exert different biological effects and/or reflect different biologic processes in specific disease states. Further research is needed to determine whether the binding of EMP species to monocytes regulates nitric oxide production by monocytes and whether monocytes themselves regulate the binding of different species of EMP in different disease states. Correlation between Monocyte NO levels and EMP-Monocyte Conjugates in different conditions. EMP54+-Monocyte Conjugates EMP62E+-Monocyte Conjugates Pearson r p value Pearson r p value Metabolic Syndrome 0.49 0.002 0.13 0.54 Venous Thromboembolism 0.51 0.009 0.12 0.57 Congestive Heart Failure 0.22 0.14 0.43 0.003 Atrial Fibrillation 0.22 0.14 0.17 0.24 Normal Controls 0.03 0.85 0.27 0.13