Putative endothelial progenitor cells are associated with flow-mediated dilation in refractory hypertensives

Background. Hypertension has been related to endothelial dysfunction. Patients with refractory hypertension ( RH) have a reduced number of endothelial progenitor cells (EPCs). Aim. To evaluate if blood EPC levels relate to endothelium-dependent vasodilation (ED-VD) in RH. Methods. We analyzed 29 RH confirmed by 24-h ambulatory blood pressure monitoring and assessed complete clinical and laboratory evaluation. EPCs were isolated from peripheral mononuclear cells (MNC) by flow cytometry. ED-VD was determined measuring flow-mediated dilation (FMD) by venous occlusion plethysmography. Results. Circulating EPCs/10(5) MNC (median [Q1-Q3]): 23.0 [4.5-53.8]. FMD (median [Q1-Q3]): 211.7 [79.5-365.8]%. Significant correlations with log-FMD: EPCs (r=0.469; p=0.018) and homocysteine (r=-0.414; p=0.045). There was no collinearity between EPCs and homocysteine. FMD did not correlate with age, gender, office BP, 24-h systolic blood pressure or 24-h diastolic blood pressure, laboratory parameters, C-reactive-protein, left ventricular-mass index, dyslipidaemia, smoking habit and statin or angiotensin system blockers treatment. Multiple linear regression analysis showed that after age-adjustment, EPC (p=0.027) and homocysteine (p=0.004) were the only variables that predicted FMD (R=0.740). After dividing patients according to EPC number, patients in the lower tertile showed a significantly reduced FMD compared with those in the group of the two upper tertiles of EPC: log-FMD (mean +/- SD): 4.7 +/- 0.9 vs 5.6 +/- 0.8, respectively (p=0.031). Conclusions. ED-VD independently correlates with circulating EPCs in RH. Homocysteine is also an independent predictor of lower FMD in such patients.