Endothelial colony forming units: are they a reliable marker of endothelial progenitor cell numbers?

Responses of Endothelial Progenitor Cells to Chronic and Acute Physical Activity in Healthy Individuals

Endothelial progenitor cells (EPCs) are circulating cells of various origins that possess the capacity for renewing and regenerating the endothelial lining of blood vessels. During physical activity, in response to factors such as hypoxia, changes in osmotic pressure, and mechanical forces, endothelial cells undergo intense physiological stress that results in endothelial damage. Circulating EPCs participate in blood vessel repair and vascular healing mainly through paracrine signalling. Furthermore, physical activity may play an important role in mobilising this important cell population. In this narrative review, we summarise the current knowledge on the biology of EPCs, including their characteristics, assessment, and mobilisation in response to both chronic and acute physical activity in healthy individuals.

The impact of different forms of exercise on endothelial progenitor cells in healthy populations

Circulating endothelial progenitor cells (EPCs) contribute to vascular healing and neovascularisation, while exercise is an effective means to mobilise EPCs into the circulation.

OBJECTIVES

to systematically examine the acute and chronic effects of different forms of exercise on circulating EPCs in healthy populations.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were followed.

RESULTS

thirty-one articles met the inclusion criteria including 747 participants aged 19 to 76 years. All included trials used flow cytometry for identification of circulating EPCs. Eight and five different EPC phenotypes were identified in the acute and chronic trials, respectively. In the acute trials, moderate intensity continuous (MICON), maximal, prolonged endurance, resistance and high intensity interval training (HIIT) exercise protocols were utilised. Prolonged endurance and resistance exercise had the most profound effect on circulating EPCs followed by maximal exercise. In the chronic trials, MICON exercise, HIIT, HIIT compared to MICON and MICON compared to exergame (exercise modality based on an interactive video game) were identified. MICON exercise had a positive effect on circulating EPCs in older sedentary individuals which was accompanied by improvements in endothelial function and arterial stiffness. Long-stage HIIT (4 min bouts) appears to be an effective means and superior than MICON exercise in mobilising circulating EPCs. In conclusion, both in acute and chronic trials the degree of exercise-induced EPC mobilisation depends upon the exercise regime applied. In future, more research is warranted to examine the dose-response relationship of different exercise forms on circulating EPCs using standardised methodology and EPC phenotype.

CD34+CD133+CD309+ circulating angiogenic cell level is reduced but positively related to hydroxychloroquine use in SLE patients-a case-control study and meta-regression analysis

OBJECTIVES

To identify and quantify the level of CD34+CD133+CD309+ circulating angiogenic cells (CAC) and explore factors associated with the level of CAC in patients with SLE.

METHODS

The peripheral blood mononuclear cells of consecutive SLE patients and demographically matched healthy controls (HC) were extracted and identified, enumerated and compared for CAC levels by multi-colour flow cytometry based on the EULAR Scleroderma Trials and Research (EUSTAR) recommendation. Meta-analyses were performed by combining the current and previous case-control studies, aiming to increase the statistical power to discern the difference in CAC level between SLE patients and HC. Mixed-model meta-regression was conducted to explore potential demographic and clinical factors that were associated with CAC level.

RESULTS

A lower level of CAC was found in 29 SLE patients compared with 24 HC [mean (s.d.) 10.76 (13.9) vs 24.58 (25.4) cells/ml, P = 0.015]. Random-effects meta-analyses of the current and six previously published case-control studies involving 401 SLE patients and 228 HC revealed a lower CAC level compared with HC (standardized mean difference = -2.439, P = 0.001). Meta-regression analysis demonstrated that HCQ use was associated with a more discrepant CAC level between both groups (P = 0.01115).

CONCLUSION

SLE patients had a significantly lower CD34+CD133+CD309+ CAC level than HC, and HCQ use was associated with a more discrepant CAC level between SLE patients and HC. This study triggers further observational, interventional and mechanistic studies to address the beneficial impact of HCQ on the functionality of CAC in SLE patients.

Intrinsic Vascular Repair by Endothelial Progenitor Cells in Acute Coronary Syndromes: an Update Overview

Bone marrow-derived endothelial progenitor cells (EPCs) play a key role in the maintenance of endothelial homeostasis and endothelial repair at areas of vascular damage. The quantification of EPCs in peripheral blood by flow cytometry is a strategy to assess this reparative capacity. The number of circulating EPCs is inversely correlated with the number of cardiovascular risk factors and to the occurrence of cardiovascular events. Therefore, monitoring EPCs levels may provide an accurate assessment of susceptibility to cardiovascular injury, greatly improving risk stratification of patients with high cardiovascular risk, such as those with an acute myocardial infarction. However, there are many issues in the field of EPC identification and quantification that remain unsolved. In fact, there have been conflicting protocols used to the phenotypic identification of EPCs and there is still no consensual immunophenotypical profile that corresponds exactly to EPCs. In this paper we aim to give an overview on EPCs-mediated vascular repair with special focus on acute coronary syndromes and to discuss the different phenotypic profiles that have been used to identify and quantify circulating EPCs in several clinical studies. Finally, we will synthesize evidence on the prognostic role of EPCs in patients with high cardiovascular risk.

Significance of endothelial progenitor cells (EPC) for tumorigenesis of head and neck squamous cell carcinoma (HNSCC): possible marker of tumor progression and neovascularization?

OBJECTIVES

Angiogenesis and neovascularisation plays a crucial role for tumorigenesis and tumor progression in head and neck squamous cell carcinoma (HNSCC). The aim of our study was to investigate the neovascularization capacity by endothelial progenitor cells (EPC) in tumor patient as a possible predictor for tumor progression and tumor stage.

MATERIALS AND METHODS

Therefore, we investigated the cell number and biologic activity by cell migration and colony-forming ability of EPC. Cells were isolated from the peripheral venous blood of 79 patients who suffer HNSCC in different stages of disease. Thirty-three healthy individuals served as the control group.

RESULTS

Significantly increased biological activities were reflected by expression of the migration rate (1027 ± 1510) in comparison to the control group (632 ± 269) and the clonal potency measured by colony-forming unit (CFU) (tumor patients (19.7 ± 12.3) vs. control group (10.84 ± 4.8)). To determine whether or not EPC number can be used as a valid prognostic marker for clinical outcome of tumor patients, we furthermore compared a "high EPC-number-subgroup" (HI) with a "low EPC-number-subgroup" (LO) in a Kaplan-Meier survival curve. The HI-subgroup shows herein clearly a worse outcome.

CONCLUSIONS

Our findings indicate a possible pathway for EPC to play a critical role in the vasculogenesis and consequently in the progression of HNSCC.

CLINICAL RELEVANCE

Our findings could serve as possible predictors for the neovascularisation potential in HNSCC tumor patients.

Vascular Dysfunction in Patients With Young β-Thalassemia

We aimed to study the endothelial dysfunction among children and adolescents with transfusion-dependent β-thalassemia using von Willebrand factor antigen (VWF:Ag) and flow cytometric analysis of circulating CD144+ endothelial microparticles (EMPs) and endothelial progenitor cells (CD34+VEGFR2+) and assess their relation to iron overload, erythropoietin and chelation therapy as well as echocardiographic parameters and carotid intima–media thickness. The VWF:Ag, EMPs, and CD34+VEGFR2+ cells were significantly higher among patients with β-thalassemia than controls ( P < .001). The type of chelation and patients’ compliance did not influence the results. No significant correlations were found between the studied vascular markers. Patients with evident heart disease had higher VWF: Ag, EMPs, and CD34+VEGFR2+ cells than those without. Carotid intima–media thickness was increased among patients but not correlated with vascular markers. We suggest that procoagulant EMPs and VWF: Ag are involved in cardiovascular complications in patients with young β-thalassemia. CD34+VEGFR2+ cells were further increased in response to tissue injury contributing to reendothelialization and neovascularization.

Alterations of circulating bone marrow-derived VEGFR-2+ progenitor cells in isolated limb perfusion with or without rhTNF-α

BACKGROUND

Circulating endothelial progenitor cells (cEPCs) as recruited to the angiogenic vascular system of malignant tumors have been proposed as a biomarker in malignancies. The effect of antitumor chemotherapy on cEPCs is not fully understood. We examined the level of cEPCs, vascular endothelial growth factor (VEGF), and angiopoietin-2 in the blood of sarcoma and melanoma patients before and after isolated limb perfusion (ILP) with or without recombinant human tumor necrosis factor-α (rhTNF-α).

METHODS

Twenty-two patients, 11 each with soft tissue sarcoma or recurrent melanoma of the limb, were recruited. ILP was performed with rhTNF-α/melphalan (TNF) or melphalan only (no TNF). Fifteen healthy volunteers served as control subjects. Blood was sampled before and up to 6 weeks after ILP. Peripheral blood mononuclear cells were isolated by density gradient centrifugation, and annexin V-negative cells were characterized as cEPCs by triple staining for CD133(+), CD34, and VEGFR-2(+).

RESULTS

Before treatment, cEPC numbers were significantly increased in sarcoma (0.179 ± 0.190 %) and melanoma patients (0.110 ± 0.073 %) versus healthy controls (0.025 ± 0.018 %; P < 0.01), but did not differ significantly between sarcoma and melanoma patients. cEPC decreased significantly after ILP in patients with no TNF compared to pretreatment values (P < 0.05) and were significantly lower at 4 h, 48 h, and 1 week compared to ILP with TNF (P < 0.05). Values 6 weeks after ILP were significantly lower than before ILP in both investigated groups (P < 0.01).

CONCLUSIONS

ILP with TNF results in activation of bone marrow-derived EPCs compared to ILP without TNF. Alteration of cEPCs and angiopoietin-2 by rhTNF-α might account for the cytotoxicity and hemorrhagic effects on tumor vessels during limb perfusion procedures.

Circulating CD133(+)VEGFR2 (+) and CD34 (+)VEGFR2 (+) cells and arterial function in patients with beta-thalassaemia major

Arterial dysfunction has been documented in patients with beta-thalassaemia major. This study aimed to determine the quantity and proliferative capacity of circulating CD133(+)VEGFR2(+) and CD34(+)VEGFR2(+) cells in patients with beta-thalassaemia major and those after haematopoietic stem cell transplantation (HSCT), and their relationships with arterial function. Brachial arterial flow-mediated dilation (FMD), carotid arterial stiffness, the quantity of these circulating cells and their number of colony-forming units (CFUs) were determined in 17 transfusion-dependent thalassaemia patients, 14 patients after HSCT and 11 controls. Compared with controls, both patient groups had significantly lower FMD and greater arterial stiffness. Despite having increased CD133(+)VEGFR2(+) and CD34(+)VEGFR2(+) cells, transfusion-dependent patients had significantly reduced CFUs compared with controls (p = 0.002). There was a trend of increasing CFUs across the three groups with decreasing iron load (p = 0.011). The CFUs correlated with brachial FMD (p = 0.029) and arterial stiffness (p = 0.02), but not with serum ferritin level. Multiple linear regression showed that CFU was a significant determinant of FMD (p = 0.043) and arterial stiffness (p = 0.02) after adjustment of age, sex, body mass index, blood pressure and serum ferritin level. In conclusion, arterial dysfunction found in patients with beta-thalassaemia major before and after HSCT may be related to impaired proliferation of CD133(+)VEGFR2(+) and CD34(+)VEGFR2(+) cells.

Immunophenotypic characterization of human monocyte subsets: possible implications for cardiovascular disease pathophysiology

OBJECTIVES

Monocytes include several subsets with different and sometimes divergent roles in immunity, atherogenesis and reparative processes.

OBJECTIVES

We aimed to perform detailed immunophenotypic and functional characterization of human monocyte subsets.

PATIENTS/METHODS

Analysis of surface markers of blood and bone marrow monocyte subsets and functional characterization of blood monocyte subsets in healthy volunteers was performed using flow cytometry.

RESULTS

In the present study, we show the presence of three subsets which could be unequivocally distinguished by surface expression of CD14, CD16 and CCR2 as CD14(+)CD16(-)CCR2(+) (Mon1), CD14(+)CD16(+)CCR2(+) (Mon2) and CD14(low)CD16(+)CCR2(-) (Mon3) subsets. In comparison with the classic Mon1, the Mon2 subset had the highest expression of Tie2, CXCR4, CD163, CD115, receptors to inter-cellular adhesion molecule-1 (ICAM-1), vascular endothelial growth factor (VEGF), and the highest surface levels of apolipoprotein B and ferritin. In contrast, Mon3 had maximal expression of VCAM-1 receptors and CD204. The Mon2 and Mon3 subsets had significantly lower activity of the NFκB pathway than Mon1. Mon1 and Mon2 had similar phagocytic activity, which was significantly higher compared with Mon3. All three subsets were present in bone marrow, although the relative proportion of Mon2 in bone marrow was about 2.5-fold higher compared with that seen in blood. Significant differences in cytokine production in response to endotoxin stimulation were observed between the three monocyte subsets.

CONCLUSION

Given their immunophenotypic similarity, the newly characterized Mon2 population may represent the previously reported pluripotent progenitor/pro-angiogenic monocytes.

CXCR2-Dependent Endothelial Progenitor Cell Mobilization in Pancreatic Cancer Growth

Neovascularization is essential for tumor growth. We have previously reported that the chemokine receptor CXCR2 is an important regulator in tumor angiogenesis. Here we report that the mobilization of bone marrow (BM)-derived endothelial progenitor cells (EPCs) is impaired in CXCR2 knockout mice harboring pancreatic cancers. The circulating levels of EPCs (positive for CD34, CD117, CD133, or CD146) are decreased in the bone marrow and/or blood of tumor-bearing CXCR2 knockout mice. CXCR2 gene knockout reduced BM-derived EPC proliferation, differentiation, and vasculogenesis in vitro. EPCs double positive for CD34 and CD133 increased tumor angiogenesis and pancreatic cancer growth in vivo. In addition, CD133(+) and CD146(+) EPCs in human pancreatic cancer are increased compared with normal pancreas tissue. These findings indicate a role of BM-derived EPC in pancreatic cancer growth and provide a cellular mechanism for CXCR2 mediated tumor neovascularization.

Decreased level and defective function of circulating endothelial progenitor cells in children with moyamoya disease

Circulating endothelial progenitor cells (EPCs) play an important role in physiological and pathological neovascularization and may be involved in attenuating ischemic diseases. This study aimed to characterize circulating EPCs in moyamoya disease (MMD), one of the most common pediatric cerebrovascular diseases. Twenty-eight children with MMD prior to any surgical treatment and 12 healthy volunteers were recruited. Peripheral blood mononuclear cells (PBMNCs) were isolated and cultured in endothelial cell growth medium. Temporal change of phenotype of cells was analyzed on days 0 and 7. The formation of EPC clusters was evaluated on day 7. The CD34(+), CD133(+), and KDR(+) cells, and the number of EPC clusters was significantly reduced in children with MMD. In controls, CD34(+) cells were significantly decreased on day 7 compared with day 0, but in MMD they were only slightly decreased. The change in KDR(+) cells on day 7 compared with day 0 was the reverse of that for CD34(+) cells. Functional assay of EPC demonstrated less tube formation and increased senescent-like phenotype in children with MMD. Analysis of the circulating EPCs of MMD children reveals decreased level and defective function. This study suggests that circulating EPCs may be associated with MMD pathogenesis.

Increased levels of circulating endothelial progenitor cells in patients with Moyamoya disease

BACKGROUND AND PURPOSE

Chronic cerebral ischemia leads to higher risk for strokes attributable to insufficient collateralization, resulting from inadequate capacity for arteriogenesis and angiogenesis. Patients with Moyamoya disease (MMD) have similar transient ischemic attack frequencies compared to patients with chronic cerebral ischemia with other etiologies, but a strong capacity for arteriogenesis and angiogenesis. The mechanisms involved in the upregulation of the arteriogenesis and angiogenesis in MMD still remain unknown. In the present study we investigated if circulating endothelial progenitor cells are increasingly mobilized during MMD.

METHODS

Twenty MMD patients, 8 patients with atherosclerotic cerebrovascular disease, and 15 healthy individuals were included in this study. Peripheral blood mononuclear cells were isolated by Ficoll density gradient centrifugation and circulating endothelial progenitor cells were characterized by triple staining using antibodies against CD133, CD34, and vascular endothelial growth factor receptor-2. Serum concentrations of vascular endothelial growth factor and granulocyte-macrophage colony-stimulating factor were determined by enzyme-linked immunosorbent assay.

RESULTS

In MMD patients the number of circulating endothelial progenitor cells was significantly higher than in atherosclerotic cerebrovascular disease patients (P<0.002) and healthy controls (P<0.0001). Serum vascular endothelial growth factor concentrations in MMD patients and in atherosclerotic cerebrovascular disease patients were significantly higher compared to those in healthy controls (P<0.0001). Similar findings were observed for granulocyte-macrophage colony-stimulating factor. An inverse correlation between circulating endothelial progenitor cell numbers and serum levels of vascular endothelial growth factor (r=-0.53; P<0,02) was found in the MMD group.

CONCLUSIONS

Our results show increased circulating endothelial progenitor cell numbers in MMD, which may play a role in the increased arteriogenesis and angiogenesis in MMD. Moreover, our results suggest that increased circulating endothelial progenitor cell mobilization in MMD may not be entirely mediated by vascular endothelial growth factor or granulocyte-macrophage colony-stimulating factor.

Endothelial progenitor cell number and colony-forming capacity in overweight and obese adults

OBJECTIVE

To investigate whether adiposity influences endothelial progenitor cell (EPC) number and colony-forming capacity.

DESIGN

Cross-sectional study of normal weight, overweight and obese adult humans.

PARTICIPANTS

Sixty-seven sedentary adults (aged 45-65 years): 25 normal weight (body mass index (BMI) <or=25 kg/m(2); 12 males/13 females); 18 overweight (BMI=25-29.9 kg/m(2); 12 males/6 females); and 24 obese (BMI >or=30 kg/m(2); 18 males/6 females). All participants were non-smokers and free of overt cardiometabolic disease.

MEASUREMENTS

Peripheral blood samples were collected and circulating EPC number was assessed by flow cytometry. Putative EPCs were defined as CD45(-)/CD34(+)/VEGFR-2(+)/CD133(+) or CD45(-)/CD34(+) cells. EPC colony-forming capacity was measured in vitro using a colony-forming unit (CFU) assay.

RESULTS

Number of circulating putative EPCs (either CD45(-)/CD34(+)/VEGFR-2(+)/CD133(+) or CD45(-)/CD34(+) cells) was lower (P<0.05) in obese (0.0007+/-0.0001%; 0.050+/-0.006%) compared with overweight (0.0016+/-0.0004%; 0.089+/-0.019%) and normal weight (0.0015+/-0.0003%; 0.082+/-0.008%) adults. There were no differences in EPC number between the overweight and normal weight groups. EPC colony formation was significantly less in the obese (6+/-1) and overweight (4+/-1) compared with normal weight (9+/-2) adults.

CONCLUSION

These results indicate that: (1) the number of circulating EPCs is lower in obese compared with overweight and normal weight adults; and (2) EPC colony-forming capacity is blunted in overweight and obese adults compared with normal weight adults. Impairments in EPC number and function may contribute to adiposity-related cardiovascular risk.

Normal levels and function of endothelial progenitor cells in patients with psoriatic arthritis

Endothelial progenitor cells (EPCs) are a population of bone marrow derived cells which have been attributed with the ability to migrate into areas of tissue ischemia and to posses reparative qualities. EPCs have been shown to be decreased in level and function in various inflammatory disorders. Psoriasis and psoriatic arthritis are associated with an increase in cardiovascular morbidity. The aim of the study was to investigate the number of EPCs among patients suffering from psoriasis and psoriatic arthritis. Patients suffering from active psoriasis and psoriatic arthritis were recruited as well as healthy controls. Disease activity was assessed with the DAS-28, BASDAI and PASI scores. Peripheral blood mononuclear cells were isolated and EPC numbers evaluated by FACS analysis using the CD34/133 and CD34/KDR. No significant difference was found between numbers of EPCs between healthy controls, patients with psoriasis and psoriatic arthritis. A significant correlation was found between levels of VGEF and the BASDAI score. The results of the current study do not support a significant role for EPCs in the pathogenesis of psoriasis and psoriatic arthritis.

Technical notes on endothelial progenitor cells: ways to escape from the knowledge plateau

In the last 10 years an increasing interest has been devoted to the study of endothelial progenitor cells (EPCs), a subtype of immature cells involved in endothelial repair and neoangiogenesis. EPCs have been discovered as a novel integrated part of the cardiovascular system, which plays a comprehensive role in tissue homeostasis. Consistently, alterations and/or reduction of the circulating EPC pool have been associated with different manifestations of cardiovascular disorders and atherosclerosis. This is why, the extent of the EPC pool is now considered a mirror of vascular health, while EPC reduction has become a surrogate biomarker of cardiovascular risk and of the ongoing vascular damage. Unfortunately, the methods used to study EPCs still lack standardization, and this is significantly decelerating progress in the field. In this review, we focus on some aspects related to the two methods used to assess circulating EPCs: flow cytometry and cell culture. We uncover the many traps hidden in the choice of the right protocol, and suggest the best solutions on the basis of evidence and background theories.