Endothelial Nitric Oxide Synthase Inhibition Does Not Alter Endothelial Progenitor Cell Colony Forming Capacity or Migratory Activity

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Abstract
Endothelial nitric oxide synthase (eNOS) activity has been shown to play a pivotal role in the mobilization of endothelial progenitor cells (EPCs) into the circulation from bone marrow. Indeed, in eNOS-deficient mice, exercise-induced EPC mobilization is severely diminished. We determined ex vivo whether circulating EPC colony-forming capacity and migratory activity are influenced by eNOS activity. Peripheral-blood mononuclear cells were isolated from 20 healthy adults and preplated for 2 days, and nonadherent cells were further cultured for 7 days in the presence and absence of NG-nitro-L-arginine methyl ester (L-NAME, 300 μM, an eNOS antagonist) to determine EPC colony-forming units. Migratory activity of EPCs, cultured with and without L-NAME (300 μM) was determined by utilizing a modified Boyden chamber. The number of EPC colony-forming units was not significantly different when cultured in the absence or presence of L-NAME (21 ± 5 vs 18 ± 5). Moreover, eNOS inhibition did not alter EPC migratory activity; mean fluorescence was similar in samples cultured with (983 ± 126 RFUs) and without (962 ± 105 RFUs) L-NAME. These in vitro results suggest that, in contrast to EPC mobilization from the bone marrow, eNOS does not exert a modulatory influence on the functional capacity of circulating EPCs to either form colonies or migrate.