PURPOSE: Endothelial microparticles (EMP) are small membrane vesicles released by activated or apoptotic endothelial cells. Recent studies indicate that different species of EMP reflect different biologic processes and exert different biologic functions. Furthermore, some species bind and activate leukocytes. The purpose of our study was to examine different phenotypic species of circulating EMP and EMP-leukocyte (EMP-L) conjugates among patients with acute coronary syndromes (ACS).
METHODS: We studied 40 patients with ACS and compared them to 22 healthy controls. Using flow cytometry, we measured EMP identified by E-selectin (EMP62E), CD51 (EMP51) and CD54 (EMP54). Free EMP levels are expressed in counts/μL). EMP62E- and EMP54-leukocyte conjugates were measured by the detection of E-selectin (CD62E) or CD54, respectively, co-expressed with CD45 in leukocytes and are expressed as fluorescence intensity units (FLIU).
RESULTS: Compared to controls, patients with ACS had significantly higher levels of free EMP51 (332 vs. 119 counts/μL; p=0.02) but similar levels of EMP54 and EMP62E. However, patients with ACS had significantly higher levels of EMP54-monocyte (1.99 vs. 1.19 FLIU; p<0.001), EMP54-neutrophil (2.00 vs. 1.46; p=0.003) and EMP54-lymphocyte (1.26 vs. 1.21; p=0.02)conjugates. Patients with ACS also demonstrated significantly elevated levels of CD62E-lymphocyte (1.20 vs.1.14 FLIU; p=0.02)and EMP62E-monocyte (1.85 vs. 1.32; p<0.0001) conjugates.
CONCLUSION: Increased binding of EMP to leukocytes occurs in ACS, which may promote thrombosis and inflammation through its known effects on leukocyte activation and tissue-factor activity. Increased binding to leukocytes also results in normal levels of the free form of some EMP species. Analysis of free EMP is therefore limited and concomitant assessment of EMP-L conjugates is important.
CLINICAL IMPLICATIONS: Binding of EMP to leukocytes may represent a risk marker as well as a novel therapeutic target in ACS.
DISCLOSURE: Julio Chirinos, None.