Circulating endothelial progenitor cell levels and function in patients who experienced late coronary stent thrombosis

AIMS: The pathogenesis of late coronary stent thrombosis may be related to impaired arterial healing. Endothelial progenitor cells (EPCs) have been shown to play an important role in repair and re-endothelialization following vascular injury. We hypothesized that patients who develop late stent thrombosis may have reduced or dysfunctional EPCs, and aimed to compare EPC level and function in patients who experienced stent thrombosis vs. matched controls. METHODS AND RESULTS: Patients who developed late (> 30 days) stent thrombosis within the past 3 years were compared with matched patients who underwent stenting and did not develop stent thrombosis. All patients had blood samples taken ≥ 3 months from the stent thrombosis or index procedure. The proportion of peripheral mononuclear cells (PMNCs) expressing vascular endothelial growth factor receptor 2 (VEGFR-2), CD133, and CD34 was evaluated by flow cytometry. Endothelial progenitor cell colony forming units (CFUs) were grown from PMNCs, characterized and counted following 7 days of culture. The two groups (n = 30 each) were well-matched (93.3% men, mean age 60-62 years, 33.3% diabetes, 73-80% DESs). The proportion of cells co-expressing VEGFR-2, CD133, and CD34 was lower in the stent thrombosis group compared with the control [VEGFR-2(+)CD133(+): 0.18% (0.03-0.41%) vs. 0.47% (0.16-0.66%), P = 0.01; VEGFR-2(+)CD34(+): 0.32% (0.22-0.70%) vs. 0.66% (0.24-1.1%), P = 0.03]. The number of EPC CFUs was also lower in the stent thrombosis group [3.9% (3.2-5.5%) vs. 8.3% (6.5-13.4%) colonies/well, respectively, P < 0.0001]. CONCLUSION: Patients who suffered late coronary stent thrombosis appear to have reduced levels of circulating EPCs and impaired functional properties of the cells. These findings require validation by further studies, but may contribute to understanding the pathogenesis of late stent thrombosis.