Quantification of circulating endothelial progenitor cells: A methodological comparison of six flow cytometric approaches

Effects of high-intensity interval training on vascular function in patients with cardiovascular disease: a systematic review and meta-analysis

Background: Exercise training improves endothelial function in patients with cardiovascular disease (CVD). However, the influence of training variables remains unclear. The aim of this study was to evaluate the effect of high-intensity interval training (HIIT), compared to moderate intensity training (MIT) and other exercise modalities (i.e., resistance and combined exercise), on endothelial function, assessed by arterial flow-mediated dilation (FMD) or endothelial progenitor cells (EPCs), in patients with CVD. Secondly, we investigated the influence of other training variables (i.e., HIIT protocol). Methods: The PICOS strategy was used to identify randomised and non-randomised studies comparing the effect of HIIT and other exercise modalities (e.g., MIT) on endothelial function in patients with CVD. Electronic searches were carried out in Pubmed, Embase, and Web of Science up to November 2022. The TESTEX scale was used to evaluate the methodological quality of the included studies. Random-effects models of between-group mean difference (MD) were estimated. A positive MD indicated an effect in favour of HIIT. Heterogeneity analyses were performed by the chi-square test and I 2 index. Subgroup analyses evaluated the influence of potential moderator variables. Results: Fourteen studies (13; 92.9% randomised) were included. Most of the studies trained 3 days a week for 12 weeks and performed long HIIT. No statistically significant differences were found between HIIT and MIT for improving brachial FMD in patients with coronary artery disease (CAD) and heart failure with reduced ejection fraction (HFrEF) (8 studies; MD+ = 0.91% [95% confidence interval (CI) = -0.06, 1.88]). However, subgroup analyses showed that long HIIT (i.e., > 1 min) is better than MIT for enhancing FMD (5 studies; MD+ = 1.46% [95% CI = 0.35, 2.57]), while no differences were found between short HIIT (i.e., ≤ 1 min) and MIT (3 studies; MD+ = -0.41% [95% CI = -1.64, 0.82]). Insufficient data prevented pooled analysis for EPCs, and individual studies failed to find statistically significant differences (p > .050) between HIIT and other exercise modalities in increasing EPCs. Discussion: Poor methodological quality could limit the precision of the current results and increase the inconsistency. Long HIIT is superior to MIT for improving FMD in patients with CAD or HFrEF. Future studies comparing HIIT to other exercise modalities, as well as the effect on EPCs and in HF with preserved ejection fraction are required. Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/#myprospero, identifier CRD42022358156.

Exercise Training Effects on Circulating Endothelial and Progenitor Cells in Heart Failure

Heart failure (HF) is a major public health issue worldwide with increased prevalence and a high number of hospitalizations. Patients with chronic HF and either reduced ejection fraction (HFrEF) or mildly reduced ejection fraction (HFmrEF) present vascular endothelial dysfunction and significantly decreased circulating levels of endothelial progenitor cells (EPCs). EPCs are bone marrow-derived cells involved in endothelium regeneration, homeostasis, and neovascularization. One of the unsolved issues in the field of EPCs is the lack of an established method of identification. The most widely approved method is the use of monoclonal antibodies and fluorescence-activated cell sorting (FACS) analysis via flow cytometry. The most frequently used markers are CD34, VEGFR-2, CD45, CD31, CD144, and CD146. Exercise training has demonstrated beneficial effects on EPCs by increasing their number in peripheral circulation and improving their functional capacities in patients with HFrEF or HFmrEF. There are two potential mechanisms of EPCs mobilization: shear stress and the hypoxic/ischemic stimulus. The combination of both leads to the release of EPCs in circulation promoting their repairment properties on the vascular endothelium barrier. EPCs are important therapeutic targets and one of the most promising fields in heart failure and, therefore, individualized exercise training programs should be developed in rehabilitation centers.

The impact of different forms of exercise on circulating endothelial progenitor cells in cardiovascular and metabolic disease

Circulating endothelial progenitor cells (EPCs) contribute to vascular repair and their monitoring could have prognostic clinical value. Exercise is often prescribed for the management of cardiometabolic diseases, however, it is not fully understood how it regulates EPCs.

OBJECTIVES

to systematically examine the acute and chronic effects of different exercise modalities on circulating EPCs in patients with cardiovascular and metabolic disease.

METHODS

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

RESULTS

six electronic databases and reference lists of eligible studies were searched to April 2021. Thirty-six trials met the inclusion criteria including 1731 participants. Acute trials: in chronic heart failure (CHF), EPC mobilisation was acutely increased after high intensity interval or moderate intensity continuous exercise training, while findings were inconclusive after a cardiopulmonary cycling exercise test. Maximal exercise tests acutely increased EPCs in ischaemic or revascularized coronary artery disease (CAD) patients. In peripheral arterial disease (PAD), EPC levels increased up to 24 h post-exercise. In patients with compromised metabolic health, EPC mobilisation was blunted after a single exercise session. Chronic trials: in CHF and acute coronary syndrome, moderate intensity continuous protocols, with or without resistance exercise or calisthenics, increased EPCs irrespective of EPC identification phenotype. Findings were equivocal in CAD regardless of exercise mode, while in severe PAD disease EPCs increased. High intensity interval training increased EPCs in hypertensive metabolic syndrome and heart failure reduced ejection fraction.

CONCLUSION

the clinical condition and exercise modality influence the degree of EPC mobilisation and magnitude of EPC increases in the long term.

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.

The impact of different forms of exercise on circulating endothelial progenitor cells in cardiovascular and metabolic disease

Circulating endothelial progenitor cells (EPCs) contribute to vascular repair and their monitoring could have prognostic clinical value. Exercise is often prescribed for the management of cardiometabolic diseases, however, it is not fully understood how it regulates EPCs.

OBJECTIVES

to systematically examine the acute and chronic effects of different exercise modalities on circulating EPCs in patients with cardiovascular and metabolic disease.

METHODS

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

RESULTS

six electronic databases and reference lists of eligible studies were searched to April 2021. Thirty-six trials met the inclusion criteria including 1731 participants. Acute trials: in chronic heart failure (CHF), EPC mobilisation was acutely increased after high intensity interval or moderate intensity continuous exercise training, while findings were inconclusive after a cardiopulmonary cycling exercise test. Maximal exercise tests acutely increased EPCs in ischaemic or revascularized coronary artery disease (CAD) patients. In peripheral arterial disease (PAD), EPC levels increased up to 24 h post-exercise. In patients with compromised metabolic health, EPC mobilisation was blunted after a single exercise session. Chronic trials: in CHF and acute coronary syndrome, moderate intensity continuous protocols, with or without resistance exercise or calisthenics, increased EPCs irrespective of EPC identification phenotype. Findings were equivocal in CAD regardless of exercise mode, while in severe PAD disease EPCs increased. High intensity interval training increased EPCs in hypertensive metabolic syndrome and heart failure reduced ejection fraction.

CONCLUSION

the clinical condition and exercise modality influence the degree of EPC mobilisation and magnitude of EPC increases in the long term.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (third edition)

The third edition of Flow Cytometry Guidelines provides the key aspects to consider when performing flow cytometry experiments and includes comprehensive sections describing phenotypes and functional assays of all major human and murine immune cell subsets. Notably, the Guidelines contain helpful tables highlighting phenotypes and key differences between human and murine cells. Another useful feature of this edition is the flow cytometry analysis of clinical samples with examples of flow cytometry applications in the context of autoimmune diseases, cancers as well as acute and chronic infectious diseases. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid. All sections are written and peer-reviewed by leading flow cytometry experts and immunologists, making this edition an essential and state-of-the-art handbook for basic and clinical researchers.

The acute and long-term effects of a cardiac rehabilitation program on endothelial progenitor cells in chronic heart failure patients: Comparing two different exercise training protocols

Background

Vascular endothelial dysfunction is an underlying pathophysiological feature of chronic heart failure (CHF). Endothelial progenitor cells (EPCs) are also impaired. The purpose of the study was to assess the effect of a cardiac rehabilitation (CR) program on the increase of EPCs at rest and on the acute response after maximal exercise in patients with CHF and investigate whether there were differences between two exercise training protocols and patients of NYHA II and III classes.

Methods

Forty-four patients with stable CHF enrolled in a 36-session CR program and were randomized in one training protocol; either high-intensity interval training (HIIT) or HIIT combined with muscle strength (COM). All patients underwent maximum cardiopulmonary exercise testing (CPET) before and after the CR program and venous blood was drawn before and after each CPET. Five endothelial cellular populations, expressed as cells/10⁶ enucleated cells, were quantified by flow cytometry.

Results

An increase in all endothelial cellular populations at rest was observed after the CR program (p < 0.01). The acute response after maximum exercise increased in 4 out of 5 endothelial cellular populations after rehabilitation. Although there was increase in EPCs at rest and the acute response after rehabilitation in each exercise training group and each NYHA class, there were no differences between HIIT and COM groups or NYHA II and NYHA III classes (p > 0.05).

Conclusions

A 36-session CR program increases the acute response after maximum CPET and stimulates the long-term mobilization of EPCs at rest in patients with CHF. These benefits seem to be similar between HIIT and COM exercise training protocols and between patients of different functional classes.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

Determination of Circulating Endothelial Cells and Endothelial Progenitor Cells Using Multicolor Flow Cytometry in Patients with Thrombophilia

BACKGROUND/AIMS

Endothelial progenitor cells (EPCs) and circulating endothelial cells (CECs) have been described as markers of endothelial damage and dysfunction in several diseases, including deep venous thrombosis. Their role in patients with known thrombophilia has not yet been evaluated. Both EPCs and CECs represent extremely rare cell populations. Therefore, it is essential to use standardized methods for their identification and quantification.

METHODS

In this study, we used multicolor flow cytometry to analyze the number of EPCs and CECs in patients with thrombophilia with or without a history of thrombosis. Patients with hematological malignancies after high-dose chemotherapy and patients with acute myocardial infarction were used as positive controls.

RESULTS

EPC and CEC immunophenotypes were determined as CD45dim/-CD34+CD146+CD133+ and CD45dim/-CD34+CD146+CD133-, respectively. Increased levels of endothelial cells were observed in positive control groups. No significant changes in the number of EPCs or CECs were detected in patients with thrombophilia compared to healthy controls.

CONCLUSION

Our optimized multicolor flow cytometry method allows unambiguous identification and quantification of endothelial cells in the peripheral blood. Our results support previous studies showing that elevated levels of CECs could serve as an indicator of endothelial injury or dysfunction. Normal levels of CECs or EPCs were found in patients with thrombophilia.

Optimized multiparametric flow cytometric analysis of circulating endothelial cells and their subpopulations in peripheral blood of patients with solid tumors: a technical analysis

Background

Circulating endothelial cells (CECs) and their subpopulations could be potential novel biomarkers for various malignancies. However, reliable enumerable methods are warranted to further improve their clinical utility. This study aimed to optimize a flow cytometric method (FCM) assay for CECs and subpopulations in peripheral blood for patients with solid cancers.

Patients and methods

An FCM assay was used to detect and identify CECs. A panel of 60 blood samples, including 44 metastatic cancer patients and 16 healthy controls, were used in this study. Some key issues of CEC enumeration, including sample material and anticoagulant selection, optimal titration of antibodies, lysis/wash procedures of blood sample preparation, conditions of sample storage, sufficient cell events to enhance the signal, fluorescence-minus-one controls instead of isotype controls to reduce background noise, optimal selection of cell surface markers, and evaluating the reproducibility of our method, were integrated and investigated. Wilcoxon and Mann–Whitney U tests were used to determine statistically significant differences.

Results

In this validation study, we refined a five-color FCM method to detect CECs and their subpopulations in peripheral blood of patients with solid tumors. Several key technical issues regarding preanalytical elements, FCM data acquisition, and analysis were addressed. Furthermore, we clinically validated the utility of our method. The baseline levels of mature CECs, endothelial progenitor cells, and activated CECs were higher in cancer patients than healthy subjects (P<0.01). However, there was no significant difference in resting CEC levels between healthy subjects and cancer patients (P=0.193).

Conclusion

We integrated and comprehensively addressed significant technical issues found in previously published assays and validated the reproducibility and sensitivity of our proposed method. Future work is required to explore the potential of our optimized method in clinical oncologic applications.

Circulating endothelial cells and their subsets: novel biomarkers for cancer

Angiogenesis contributes to the growth of solid tumors. Antiangiogenic agents are widely used in various cancers and considerable efforts have been made in the development of novel biomarkers that can predict the outcome of an anticancer treatment. Of those, circulating endothelial cells (CECs) and their subsets constitute a surrogate tool for monitoring disease activity. However, owing to the lack of standardization on the phenotypes and detection of CECs and their subsets, results have always been inconsistent and uninterpretable. In this review, we focus on the biological characteristics in terms of physiology, phenotypes and detection of CECs along with their subsets; review the current scenario of CEC enumeration as a surrogate biomarker in clinical oncology; and explore their future potential applications.

Preservation and enumeration of endothelial progenitor and endothelial cells from peripheral blood for clinical trials

AIMS

Endothelial progenitor cells (EPCs) are markers of vascular repair. Increased numbers of circulating endothelial cells (ECs) are associated with endothelial damage.

MATERIALS & METHODS

We enumerated EPC-EC by using Enrichment kit with addition of anti-human CD146-PE/Cy7 from peripheral blood mononuclear cell (PBMC) isolated either by red blood cell (RBC) lysing solution or by Ficoll centrifugation, and from fresh and preserved samples. PBMCs were quantified by flow cytometry.

RESULTS

RBC lysis yielded higher percentage of PBMC (p = 0.0242) and higher numbers of PBMC/ml (p = 0.0039) than Ficoll. Absolute numbers of CD34(+)CD133(+)VEGFR2(+) and CD146(+)CD34(+)VEGFR2(+) were higher (p = 0.0117 for both), when isolated by RBC lysis than by Ficoll, when no difference in other subsets was found. Cryopreservation at -160°C and -80°C and short-term preservation at room temperature decreased EPC-EC.

CONCLUSIONS

Our data support use of fresh samples and isolation of PBMC from human blood by RBC lysis for enumeration of EPC and EC.

Absolute circulating pericyte progenitor cell counts in mice by flow cytometry: comparison of 2 single-platform technologies

BACKGROUND

Accumulating evidence indicates that circulating pericyte progenitor cells (CPPCs) may be angiogenic biomarkers in cancer and diabetes. Their validity as biomarkers depends on the accuracy of techniques used for enumeration. In this report, absolute CPPC counts were performed by 2 single-platform technologies. The reliability of the 2 methods, including retest reliability and intraobserver and interobserver variability, was assessed according to the intraclass correlation coefficient (ICC). The linear correlation and agreement among both methods were assessed, and the stability of CPPC numbers in blood samples was analyzed.

METHODS

The blood samples were obtained from ICR mice. The samples were processed through a no-lyse, 1-wash procedure, and Syto16+CD45-CD31-CD140b+ CPPCs were analyzed by exclusion of dead cells and by fluorescence-minus-one control. CPPCs were enumerated by 2 methods: bead-based 123count eBeads count (eBioscience) and direct volume-based Accuri C6 Flow Cytometer count (BD). The cells were measured immediately and after storage of blood samples for 24 and 48 hours.

RESULTS

There were excellent retest correlations and intraobserver and interobserver agreement in both methods. The 2 methods showed a high linear correlation (R2 = 0.923) and with a high level of agreement (0.986). It was demonstrated that CPPCs are unstable in blood samples.

CONCLUSIONS

In this study, 2 reproducible protocols for CPPC quantification were established. These protocols should facilitate future studies to further define the role of CPPCs as cellular biomarkers.

The real face of endothelial progenitor cells - Circulating angiogenic cells as endothelial prognostic marker?

Endothelial progenitor cells (EPCs) have been extensively studied for almost 19 years now and were considered as a potential marker for endothelial regeneration ability. On the other hand, circulating endothelial cells (CEC) were studied as biomarker for endothelial injury. Yet, in the literature, there is also huge incoherency in regards to terminology and protocols used. This results in misleading conclusions on the role of so called "EPCs", especially in the clinical field. The discrepancies are mainly due to strong phenotypic overlap between EPCs and circulating angiogenic cells (CAC), therefore changes in "EPC" terminology have been suggested. Other factors leading to inconsistent results are varied definitions of the studied populations and the lack of universal data reporting, which could strongly affect data interpretation. The current review is focused on controversies concerning the use of "EPCs"/CAC and CEC as putative endothelial diagnostic markers.

An Integrated Platform for Isolation, Processing, and Mass Spectrometry-based Proteomic Profiling of Rare Cells in Whole Blood

Isolation and molecular characterization of rare cells (e.g. circulating tumor and stem cells) within biological fluids and tissues has significant potential in clinical diagnostics and personalized medicine. The present work describes an integrated platform of sample procurement, preparation, and analysis for deep proteomic profiling of rare cells in blood. Microfluidic magnetophoretic isolation of target cells spiked into 1 ml of blood at the level of 1000-2000 cells/ml, followed by focused acoustics-assisted sample preparation has been coupled with one-dimensional PLOT-LC-MS methodology. The resulting zeptomole detection sensitivity enabled identification of ∼4000 proteins with injection of the equivalent of only 100-200 cells per analysis. The characterization of rare cells in limited volumes of physiological fluids is shown by the isolation and quantitative proteomic profiling of first MCF-7 cells spiked into whole blood as a model system and then two CD133+ endothelial progenitor and hematopoietic cells in whole blood from volunteers.

Endothelial dysfunction in acute brain injury and the development of cerebral ischemia

Cerebral ischemia (CeI) is a major complicating event after acute brain injury (ABI) in which endothelial dysfunction is a key player. This study evaluates cellular markers of endothelial function and in vivo reactive hyperemia in patients with ABI and their relationship to the development of cerebral ischemia. We studied cellular markers of endothelial dysfunction and the peripheral reactive hyperemia index (RHI) in 26 patients with ABI at admission and after 6 and 12 days, and compared these with those of healthy volunteers (n = 15). CeI was determined clinically or by computer tomography. In patients with ABI, RHI at admission was significantly reduced compared with healthy subjects (P = 0.003), coinciding with a decrease in circulating endothelial progenitor cells (EPC; P = 0.002). The RHI recovered in eight patients without development of CeI, but failed to fully recover by day 12 in three of four patients who developed CeI. Despite recovery of the RHI within 12 days in these patients (P = 0.003), EPC count remained significantly lower after 12 days in patients with ABI (P = 0.022). CD31(+) T cells and endothelial microparticles were not different between controls and patients. No differences were noted in cellular markers of endothelial dysfunction in patients developing CeI and those not. In conclusion, patients with ABI exhibit impaired microvascular endothelial function measured as RHI and a decreased circulating level of EPC.

Fundamentals and application of magnetic particles in cell isolation and enrichment: a review

Magnetic sorting using magnetic beads has become a routine methodology for the separation of key cell populations from biological suspensions. Due to the inherent ability of magnets to provide forces at a distance, magnetic cell manipulation is now a standardized process step in numerous processes in tissue engineering, medicine, and in fundamental biological research. Herein we review the current status of magnetic particles to enable isolation and separation of cells, with a strong focus on the fundamental governing physical phenomena, properties and syntheses of magnetic particles and on current applications of magnet-based cell separation in laboratory and clinical settings. We highlight the contribution of cell separation to biomedical research and medicine and detail modern cell-separation methods (both magnetic and non-magnetic). In addition to a review of the current state-of-the-art in magnet-based cell sorting, we discuss current challenges and available opportunities for further research, development and commercialization of magnetic particle-based cell-separation systems.

Circulating endothelial cells and progenitors as prognostic factors during autoimmune thrombotic thrombocytopenic purpura: results of a prospective multicenter French study

BACKGROUND

Autoimmune thrombotic thrombocytopenic purpura (AI-TTP) is characterized by an excess of circulating ultralarge von Willebrand factor (VWF) caused by anti-ADAMTS-13 autoantibodies. Animal studies, however, have shown that endothelial cell activation may also be an important trigger of AI-TTP.

OBJECTIVES

To prospectively study circulating biomarkers of endothelial lesion and activation, such as circulating endothelial cells (CECs), soluble P-selectin (sP-selectin), or VWF, and of endothelial repair, such as circulating progenitor cells (CPCs) and endothelial progenitor cells (EPCs), in AI-TTP, in relation to disease severity and prognosis.

RESULTS

Twenty-two patients were included in this study. CEC (P < 0.01), VWF (P < 0.05) and sP-selectin (P < 0.01) levels were significantly increased during crisis, and returned to baseline levels during remission. Both CEC (P < 0.05) and sP-selectin (P < 0.05) levels were significantly higher in patients who died or developed neurologic sequelae. CPC levels were substantially increased during the acute phase of the disease (P < 0.001), and returned to baseline levels during remission. Among CPCs, EPC levels were also increased during crisis (P < 0.05) and significantly decreased during remission. Patients who received < 16 plasma exchanges (PEs) had significantly higher EPC counts (P < 0.05) than those who needed more numerous PEs to obtain remission, suggesting that initial EPC counts may be associated with faster endothelial repair.

CONCLUSION

The profile of circulating endothelial markers shows massive endothelial activation and repair/remodeling during AI-TTP, and suggests that CECs and EPCs may be promising prognostic biomarkers of the disease.

The endothelium, a protagonist in the pathophysiology of critical illness: focus on cellular markers

The endotheliumis key in the pathophysiology of numerous diseases as a result of its precarious function in the regulation of tissue homeostasis. Therefore, its clinical evaluation providing diagnostic and prognostic markers, as well as its role as a therapeutic target, is the focus of intense research in patientswith severe illnesses. In the critically ill with sepsis and acute brain injury, the endothelium has a cardinal function in the development of organ failure and secondary ischemia, respectively. Cellular markers of endothelial function such as endothelial progenitor cells (EPC) and endothelialmicroparticles (EMP) are gaining interest as biomarkers due to their accessibility, although the lack of standardization of EPC and EMP detection remains a drawback for their routine clinical use. In this paper we will review data available on EPC, as a general marker of endothelial repair, and EMP as an equivalent of damage in critical illnesses, in particular sepsis and acute brain injury. Their determination has resulted in new insights into endothelial dysfunction in the critically ill. It remains speculative whether their determination might guide therapy in these devastating acute disorders in the near future.

Improving cardiovascular outcomes in rheumatic diseases: therapeutic potential of circulating endothelial progenitor cells

Patients with Rheumatoid Arthritis (RA) and Systemic Lupus Erythematosus (SLE) have a significantly increased risk of cardiovascular disease (CVD). The reason for this is unclear but may be due, at least in part, to the failure of endothelial repair mechanisms. Over the last 15 years there has been much interest in the mechanisms of endothelial renewal and its potential as a therapy for CVD. In the circulation there are two distinct populations of cells; myeloid angiogenic cells (MACs) which augment repair by the paracrine secretion of angiogenic factors, and outgrowth endothelial cells (OECs) which are true endothelial progenitor cells (EPCs) and promote vasculogenesis by differentiating into mature endothelium. There are marked abnormalities in the number and function of these cells in patients with RA and SLE. Inflammatory cytokines including interferon-alpha (IFNα) and tumour-necrosis factor alpha (TNFα) both impair MAC and OEC function ex vivo and may therefore contribute to the CVD risk in these patients. Whilst administration of mononuclear cells, MACs and other progenitors has improved cardiovascular outcomes in the acute setting, this is not a viable option in chronic disease. The pharmacological manipulation of MAC/OEC function in vivo however has the potential to significantly improve endothelial repair and thus reduce CVD in this high risk population.

Tumor vascularity in prostate cancer: an update on circulating endothelial cells and platelets as noninvasive biomarkers

In order to individually tailor prostate cancer (PCa) treatment, clinicians need better tools to predict prognosis and treatment response. Given the relationship between angiogenesis and cancer progression, circulating endothelial cells (CECs) and their progenitors have logically been proposed as potential biomarkers. The utility of their baseline levels and kinetics has been investigated for years. However, owing to a lack of standardization and validation of CEC and circulating endothelial progenitors enumeration protocols, results have been inconsistent in prostate and other cancers. Similarly, platelets play a significant part in cancer progression, yet the role of platelet-related biomarkers in PCa is unclear. While there have been a number of theoretically interesting platelet-related markers proposed, limited research has been conducted in PCa patients. Currently, CECs and platelets do not have a clear role as biomarkers in routine PCa care. Given the theoretical merits of these cells, prospective trials are warranted.

Cryopreservation and Enumeration of Human Endothelial Progenitor and Endothelial Cells for Clinical Trials

BACKGROUND

Endothelial progenitor cells (EPC) are markers of endothelial injury and may serve as a surrogate marker for vascular repair in interventional clinical trials. Objectives of this study were to modify a method of isolation of peripheral blood mononuclear cells (PBMC) and enumeration of EPC and mature endothelial cells (EC) from peripheral blood and to evaluate influence of cryopreservation on viability of PBMC and on numbers of EPC and EC.

PATIENTS/METHODS

EPC and EC were analyzed in healthy volunteers in freshly isolated PBMC collected in CPT (cell preparation tubes) and in PBMC cryopreserved with: 1) Gibco Recovery™ Cell Culture Freezing Medium, 2) custom freezing medium. Viability of PBMC was tested using DAPI. EPC were gated for CD45- CD34+CD133+/-VEGFR2+/- and EC were gated for CD45-CD146+CD34+/-VEGFR2+/-.

RESULTS

Cryopreservation for 7 days at -80°C decreased viable PBMC from 94 ± 0.5% (fresh) to 84 ± 4% (the custom medium) and to 69 ± 8% (Gibco medium), while cryopreservation at -65°C decreased viability to 60 ± 6% (p<0.001, the custom medium) and 49 ± 5% (p<0.001, Gibco medium). In fresh samples early EPC (CD45- CD34+CD133+VEGFR2+) were enumerated as 0.2 ± 0.06%, late EPC(CD45-CD146+CD34+VEGFR2+) as 0.6 ± 0.1% and mature EC (CD45-CD146+CD34-VEGFR2+) as 0.8 ± 0.3%of live PBMC. Cryopreservation with Gibco and the custom freezing medium at -80°C for 7 days decreased numbers EPC and EC, however, this decrease was not statistically significant.

CONCLUSIONS

Our data indicate that cryopreservation at -80°C for 7 days decreases, although not significantly, viability of PBMC and numbers of subsets of EC and EPC. This method may provide an optimized approach to isolation and short-term cryopreservation of subsets of EPC and of mature EC suitable for multicenter trials.

Human endothelial progenitor cells

Human endothelial progenitor cells (EPCs) have been generally defined as circulating cells that express a variety of cell surface markers similar to those expressed by vascular endothelial cells, adhere to endothelium at sites of hypoxia/ischemia, and participate in new vessel formation. Although no specific marker for an EPC has been identified, a panel of markers has been consistently used as a surrogate marker for cells displaying the vascular regenerative properties of the putative EPC. However, it is now clear that a host of hematopoietic and vascular endothelial subsets display the same panel of antigens and can only be discriminated by an extensive gene expression analysis or use of a variety of functional assays that are not often applied. This article reviews our current understanding of the many cell subsets that constitute the term EPC and provides a concluding perspective as to the various roles played by these circulating or resident cells in vessel repair and regeneration in human subjects.

Assessment of endothelial dysfunction in childhood obesity and clinical use

The association of obesity with noncommunicable diseases, such as cardiovascular complications and diabetes, is considered a major threat to the management of health care worldwide. Epidemiological findings show that childhood obesity is rapidly rising in Western society, as well as in developing countries. This pandemic is not without consequences and can affect the risk of future cardiovascular disease in these children. Childhood obesity is associated with endothelial dysfunction, the first yet still reversible step towards atherosclerosis. Advanced research techniques have added further insight on how childhood obesity and associated comorbidities lead to endothelial dysfunction. Techniques used to measure endothelial function were further brought to perfection, and novel biomarkers, including endothelial progenitor cells, were discovered. The aim of this paper is to provide a critical overview on both in vivo as well as in vitro markers for endothelial integrity. Additionally, an in-depth description of the mechanisms that disrupt the delicate balance between endothelial damage and repair will be given. Finally, the effects of lifestyle interventions and pharmacotherapy on endothelial dysfunction will be reviewed.

Comparative analysis of circulating endothelial progenitor cells in age-related macular degeneration patients using automated rare cell analysis (ARCA) and fluorescence activated cell sorting (FACS)

Background

Patients with age-related macular degeneration (ARMD) begin with non-neovascular (NNV) phenotypes usually associated with good vision. Approximately 20% of NNV-ARMD patients will convert to vision debilitating neovascular (NV) ARMD, but precise timing of this event is unknown. Developing a clinical test predicting impending conversion to NV-ARMD is necessary to prevent vision loss. Endothelial progenitor cells (EPCs), defined as CD34⁺VEGR2⁺ using traditional fluorescence activated cell sorting (FACS), are rare cell populations known to be elevated in patients with NV-ARMD compared to NNV-ARMD. FACS has high inter-observer variability and subjectivity when measuring rare cell populations precluding development into a diagnostic test. We hypothesized that automated rare cell analysis (ARCA), a validated and FDA-approved technology for reproducible rare cell identification, can enumerate EPCs in ARMD patients more reliably. This pilot study serves as the first step in developing methods for reproducibly predicting ARMD phenotype conversion.

Methods

We obtained peripheral venous blood samples in 23 subjects with NNV-ARMD or treatment naïve NV-ARMD. Strict criteria were used to exclude subjects with known angiogenic diseases to minimize confounding results. Blood samples were analyzed in masked fashion in two separate laboratories. EPCs were independently enumerated using ARCA and FACS within 24 hours of blood sample collection, and p<0.2 was considered indicative of a trend for this proof of concept study, while statistical significance was established at 0.05.

Results

We measured levels of CD34⁺VEGFR2⁺ EPCs suggestive of a trend with higher values in patients with NV compared to NNV-ARMD (p = 0.17) using ARCA. Interestingly, CD34⁺VEGR2⁺ EPC analysis using FACS did not produce similar results (p = 0.94).

Conclusions

CD34⁺VEGR2⁺ may have predictive value for EPC enumeration in future ARCA studies. EPC measurements in a small sample size were suggestive of a trend in ARMD using ARCA but not FACS. ARCA could be a helpful tool for developing a predictive test for ARMD phenotype conversion.

Plerixafor plus granulocyte colony-stimulating factor improves the mobilization of hematopoietic stem cells in patients with non-Hodgkin lymphoma and low circulating peripheral blood CD34+ cells

Many institutions have adopted algorithms based on preapheresis circulating CD34+ cell counts to optimize the use of plerixafor. However, a circulating peripheral blood CD34+ cell threshold that predicts mobilization failure has not been defined. The superiority of plerixafor + granulocyte colony-stimulating factor (G-CSF) over placebo + G-CSF for hematopoietic stem cell mobilization and collection was shown for patients with non-Hodgkin lymphoma in a phase III, prospective, randomized, controlled study. The question remains as to which patients may benefit most from the use of plerixafor. In this post hoc retrospective analysis, mobilization outcomes were compared between the 2 treatment arms in patients stratified by peripheral blood CD34+ cell count (<5, 5 to 9, 10 to 14, 15 to 19, or ≥20 cells/μL) obtained before study treatment and apheresis. Compared with placebo plus G-CSF, plerixafor plus G-CSF significantly increased the peripheral blood CD34+ cells/μL over prior day levels in all 5 stratified groups. The probability of subsequent transplantation without a rescue mobilization was far greater in the plerixafor-treated patients for the lowest initial (day 4) peripheral blood CD34+ cells/μL groups (<5, 5 to 9, or 10 to 14). Engraftment and durability were the same for the 2 treatment groups for all strata, but the effect in the lower strata could be altered by the addition of cells from rescue mobilizations. These findings may provide insight into the optimal use of plerixafor in all patients undergoing stem cell mobilization.

A flow cytometric protocol for enumeration of endothelial progenitor cells and monocyte subsets in human blood

BACKGROUND

Accumulating evidence intensively advises circulating endothelial progenitor cells (EPCs) and monocyte subsets as surrogate cellular biomarkers in cardiovascular and cancer disease. However, a general standard on their quantification is still elusive, thus precluding a routine monitoring and comparative interpretation of clinical studies.

OBJECTIVE

We intend to develop an advanced and express flow cytometric protocol for proper ex vivo quantification of monocyte subsets and EPCs in human blood.

METHODS

We employ now lyse/no-wash procedure and bead-based determination of absolute cell counts. We use three-color antibody panels at appropriate compensation. Analysis of rare events and low antigen expression in the EPC experiment is strengthening by sequential gating with exclusion of dead cells, as well as by matching high-intensity fluorochromes to low-density markers and by implementing the fluorescence-minus-one control.

RESULTS

Analysis of peripheral blood of ten healthy donors revealed median (IQR) value of 1.88 (1.35-2.85) viable CD45(dim)CD34)VEGFR2+ EPCs per microliter. Analysis of monocytes revealed 329.5 (264.5-374.8), 16.0 (8.0-22.2) and 26.5 (19.8-36.3) cells per microliter for classical CD14++(high))CD16⁻, intermediate CD14++CD16+(mid) and non-classical CD14+(low))CD16++ monocytes.

CONCLUSION

Our current protocol provides quantitative information under a simple gating logic while using commonly accepted fluorochromes. This assay is therefore highly adapted for routine use.

Endothelial progenitor cells in cardiovascular disease and chronic inflammation: from biomarker to therapeutic agent

The discovery of endothelial progenitor cells in the 1990s challenged the paradigm of angiogenesis by showing that cells derived from hematopoietic stem cells are capable of forming new blood vessels even in the absence of a pre-existing vessel network, a process termed vasculogenesis. Since then, the majority of studies in the field have found a strong association between circulating endothelial progenitor cells and cardiovascular risk. Several studies have also reported that inflammation influences the mobilization and differentiation of endothelial progenitor cells. In this review, we discuss the emerging role of endothelial progenitor cells as biomarkers of cardiovascular disease as well as the interplay between inflammation and endothelial progenitor cell biology. We will also review the challenges in the field of endothelial progenitor cell-based therapy.

Endothelial progenitors as tools to study vascular disease

Endothelial progenitor cells (EPCs) have great clinical value because they can be used as diagnostic biomarkers and as a cellular therapy for promoting vascular repair of ischaemic tissues. However, EPCs also have an additional research value in vascular disease modelling to interrogate human disease mechanisms. The term EPC is used to describe a diverse variety of cells, and we have identified a specific EPC subtype called outgrowth endothelial cell (OEC) as the best candidate for vascular disease modelling because of its high-proliferative potential and unambiguous endothelial commitment. OECs are isolated from human blood and can be exposed to pathologic conditions (forward approach) or be isolated from patients (reverse approach) in order to study vascular human disease. The use of OECs for modelling vascular disease will contribute greatly to improving our understanding of endothelial pathogenesis, which will potentially lead to the discovery of novel therapeutic strategies for vascular diseases.

Clinically relevant microfluidic magnetophoretic isolation of rare-cell populations for diagnostic and therapeutic monitoring applications

Cells of biomedical interest are, despite their functional significance, often present in very small numbers. Therefore the analysis and isolation of previously inaccessible rare cells, such as peripheral hematopoietic stem cells, endothelial progenitor cells, or circulating tumor cells, require efficient, sensitive, and specific procedures that do not compromise the viability of the cells. The current study builds on previous work on a rationally designed microfluidic magnetophoretic cell separation platform capable of throughputs of 240 μL min(-1). Proof-of-concept was first conducted using MCF-7 (1-1000 total cells) as the target rare cell spiked into high concentrations of Raji B-lymphocyte nontarget cells (~10(6) total cells). These experiments lead to the establishment of a magnet-based separation for the isolation of 50 MCF-7 cells directly from whole blood. Results show an efficiency of collection greater than 85%, with a purity of over 90%. Next, resident endothelial progenitor cells and hematopoietic stem cells are directly isolated from whole human blood in a rapid and efficient fashion (>96%). Both cell populations could be simultaneously isolated and, via immunofluorescent staining, individually identified and enumerated. Overall, the presented device illustrates a viable separation platform for high purity, efficient, and rapid collection of rare cell populations directly from whole blood samples.

Design and validation of an endothelial progenitor cell capture chip and its application in patients with pulmonary arterial hypertension

The number of circulating endothelial progenitor cells (EPCs) inversely correlates with cardiovascular risk and clinical outcome, and thus has been proposed as a valuable biomarker for risk assessment, disease progression, and response to therapy. However, current strategies for isolation of these rare cells are limited to complex, laborious approaches. The goal of this study was the design and validation of a disposable microfluidic platform capable of selectively capturing and enumerating EPCs directly from human whole blood in healthy and diseased subjects, eliminating sample preprocessing. We then applied the "EPC capture chip" clinically and determined EPC numbers in blood from patients with pulmonary arterial hypertension (PAH). Blood was collected in tubes and injected into polymeric microfluidic chips containing microcolumns pre-coated with anti-CD34 antibody. Captured cells were immunofluorescently stained for the expression of stem and endothelial antigens, identified and counted. The EPC capture chip was validated with conventional flow cytometry counts (r = 0.83). The inter- and intra-day reliability of the microfluidic devices was confirmed at different time points in triplicates over 1-5 months. In a cohort of 43 patients with three forms of PAH (idiopathic/heritable, drug-induced, and connective tissue disease), EPC numbers are ≈50% lower in PAH subjects vs. matched controls and inversely related to two potential disease modifiers: body mass index and postmenopausal status. The EPC capture chip (5 × 30 × 0.05 mm(3)) requires only 200 μL of human blood and has the strong potential to serve as a rapid bedside test for the screening and monitoring of patients with PAH and other proliferative cardiovascular, pulmonary, malignant, and neurodegenerative diseases.

From bench to bedside: what physicians need to know about endothelial progenitor cells

Since the discovery of endothelial progenitor cells in 1997, the scientific world has seen their ups and downs. There has been much discussion about the detection methods of endothelial progenitor cells and their diagnostic and predictive value. A lack of standardized methods to define endothelial progenitor cells has led to a number of nomenclatures and measuring methods that are difficult for clinicians to oversee. Therefore, only specialized hematologists and cardiologists were aware of their existence. Now it is time for a change: Most of the controversies have been eliminated by elaborate studies. This review aims to give an overview to the clinically working physician about the measurement, diagnostic potential, predictive value, and therapeutic potential of endothelial progenitor cells.

Proteomics: a reality-check for putative stem cells

The concept of using stem cells for cardiovascular repair holds great potential, but uncertainties in preclinical experiments must be addressed before their therapeutic application. Contemporary proteomic techniques can help to characterize cell preparations more thoroughly and identify some of the potential causes that may lead to a high failure rate in clinical trials. The first part of this review discusses the broader application of proteomics to stem cell research by providing an overview of the main proteomic technologies and how they might help the translation of stem cell therapy. The second part focuses on the controversy about endothelial progenitor cells (EPCs) and raises cautionary flags for marker assignment and assessment of cell purity. A proteomics-led approach in early outgrowth EPCs has already raised the awareness that markers used to define their endothelial potential may arise from an uptake of platelet proteins. A platelet microparticle-related transfer of endothelial characteristics to mononuclear cells can result in a misinterpretation of the assay. The necessity to perform counterstaining for platelet markers in this setting is not fully appreciated. Similarly, the presence of platelets and platelet microparticles is not taken into consideration when functional improvements are directly attributed to EPCs, whereas saline solutions or plain medium serve as controls. Thus, proteomics shed new light on the caveats of a common stem cell assay in cardiovascular research, which might explain some of the inconsistencies in the field.

Optimization of a highly standardized carboxyfluorescein succinimidyl ester flow cytometry panel and gating strategy design using discriminative information measure evaluation

The design of a panel to identify target cell subsets in flow cytometry can be difficult when specific markers unique to each cell subset do not exist, and a combination of parameters must be used to identify target cells of interest and exclude irrelevant events. Thus, the ability to objectively measure the contribution of a parameter or group of parameters toward target cell identification independent of any gating strategy could be very helpful for both panel design and gating strategy design. In this article, we propose a discriminative information measure evaluation (DIME) based on statistical mixture modeling; DIME is a numerical measure of the contribution of different parameters towards discriminating a target cell subset from all the others derived from the fitted posterior distribution of a Gaussian mixture model. Informally, DIME measures the "usefulness" of each parameter for identifying a target cell subset. We show how DIME provides an objective basis for inclusion or exclusion of specific parameters in a panel, and how ranked sets of such parameters can be used to optimize gating strategies. An illustrative example of the application of DIME to streamline the gating strategy for a highly standardized carboxyfluorescein succinimidyl ester (CFSE) assay is described.

Vascular stem cells and ischaemic retinopathies

Retinal ischaemic disorders such as diabetic retinopathy and retinal vein occlusion are common. The hypoxia-related stimuli from oxygen-deprived neural and glial networks can drive expression of growth factors and cytokines which induce leakage from the surviving vasculature and/or pre-retinal and papillary neovascularisation. If left untreated, retinal vascular stasis, hypoxia or ischaemia can lead to macular oedema or fibro-vascular scar formation which are associated with severe visual impairment, and even blindness. Current therapies for ischaemic retinopathies include laser photocoagulation, injection of corticosteroids or VEGF-antibodies and vitreoretinal surgery, however they carry significant side effects. As an alternative approach, we propose that if reparative intra-retinal angiogenesis can be harnessed at the appropriate stage, ischaemia could be contained or reversed. This review provides evidence that reperfusion of ischaemic retina and suppression of sight-threatening sequelae is possible in both experimental and clinical settings. In particular, there is emphasis on the clinical potential for endothelial progenitor cells (EPCs) to promote vascular repair and reversal of ischaemic injury in various tissues including retina. Gathering evidence from an extensive published literature, we outline the molecular and phenotypic nature of EPCs, how they are altered in disease and provide a rationale for harnessing the vascular reparative properties of various cell sub-types. When some of the remaining questions surrounding the clinical use of EPCs are addressed, they may provide an exciting new therapeutic option for treating ischaemic retinopathies.

Endothelial cells (EC) and endothelial precursor cells (EPC) kinetics in hematological patients undergoing chemotherapy or autologous stem cell transplantation (ASCT)

Our objective was to study the kinetics of circulating endothelial cells (EC) and endothelial precursor cells (EPC) in hematological patients during chemotherapy and autologous stem cell transplantion (ASCT). Eighteen newly diagnosed patients and 17 patients undergoing ASCT were studied and compared to healthy controls. ECs were evaluated as CD146+CD31+Lin- cells, while EPCs were evaluated as CD34+CD133+Lin-, or CD34+VEGFR2+Lin- cells, or CFU-En colony forming units. Numbers of these cells were evaluated before and after treatment, and, in patients treated with ASCT, during mobilization of hematopoietic progenitors. Both newly diagnosed patients and patients before ASCT had significantly higher number of CD146+CD31+Lin- cells and significantly lower number of CFU-En colonies than healthy controls. These parameters did not return to normal for at least 3 months after chemotherapy or ASCT. Numbers of CFU-En did not correlate either with numbers of CD34+CD133+Lin- cells or with numbers of CD34+VEGFR2+Lin- cells but they did correlate with numbers of CD4+ lymphocytes and NK cells. In conclusion, we have found that hematological patients have higher number of EC and lower numbers of CFU-En than healthy controls and that these parameters do not return to normal after short-term follow-up. Furthermore, our observations support emerging data that CFU-En represent cell population different from flowcytometrically defined EC and endothelial precursors and that their development requires cooperation of monocytes and CD4+ lymphocytes. However, cells forming CFU-En express endothelial surface markers and can contribute to proper endothelial function by NO production.

RIA reamings and hip aspirate: a comparative evaluation of osteoprogenitor and endothelial progenitor cells

Autologous bone grafting represents the gold standard modality to treat atrophic non-unions by virtue of its osteoinductive and osteoconductive properties. The common harvest site is the iliac crest, but there are major concerns due to limited volume and considerable donor site morbidity. Alternative autologous bone graft can be harvested from the femoral bone cavity using a newly developed 'Reamer Irrigator Aspirator' (RIA). Osseous aspirated particles can be recovered with a filter and used as auto-graft. The purpose of this study was to compare the concentration and differentiation potential of mesenchymal stem cells (MSC) and endothelial progenitor cells (EPC) harvested with the RIA technique or from the iliac crest, respectively. RIA aspirate was collected from 26 patients undergoing intramedullary nailing of femur fractures. Iliac crest aspirate was collected from 38 patients undergoing bone graft transplantation. Concentration of MSC and EPC were assessed by means of the MSC colony assay, EPC culture assay and flowcytometry (CD34, CD133, VEGF-R2), respectively. Osteogenic differentiation of MSC's was measured by von Kossa staining. Patients in both groups did not significantly differ regarding their age, gender or pre-existing health conditions. In comparison to aspirates obtained from iliac crest the RIA aspirates from the femur contained a significantly higher percentage of CD34+ progenitor cells, a significantly higher concentration of MSC and a significantly higher concentration of early EPC. The percentage of late EPC did not differ between both sites. Moreover, the capability of MSC for calcium deposition was significantly enhanced in MSC obtained with RIA. Our results show that RIA aspirate is a rich source for different types of autologous progenitor cells, which can be used to accelerate healing of bone and other musculoskeletal tissues.

Endothelial progenitor cells in mixed cryoglobulinemia

OBJECTIVE

Endothelial progenitor cells (EPC) are a rare population of circulating cells involved in vascular homeostasis. Our aim was to analyze EPC in patients with mixed cryoglobulinemia (MC).

METHODS

EPC were evaluated by cytometry according to guidelines of the International Society for Hematotherapy and Graft Engineering in 17 patients with MC and 36 controls.

RESULTS

Numbers of EPC were significantly increased in MC compared to controls and correlated with cryocrit, but not with clinical manifestations of the disease.

CONCLUSION

The high number of EPC might indicate an intact vascular repair ability. Alternatively, EPC might be defective in homing ability and their increase may represent the attempt to restore vascular integrity.

Molecular analysis of endothelial progenitor cell (EPC) subtypes reveals two distinct cell populations with different identities

Background

The term endothelial progenitor cells (EPCs) is currently used to refer to cell populations which are quite dissimilar in terms of biological properties. This study provides a detailed molecular fingerprint for two EPC subtypes: early EPCs (eEPCs) and outgrowth endothelial cells (OECs).

Methods

Human blood-derived eEPCs and OECs were characterised by using genome-wide transcriptional profiling, 2D protein electrophoresis, and electron microscopy. Comparative analysis at the transcript and protein level included monocytes and mature endothelial cells as reference cell types.

Results

Our data show that eEPCs and OECs have strikingly different gene expression signatures. Many highly expressed transcripts in eEPCs are haematopoietic specific (RUNX1, WAS, LYN) with links to immunity and inflammation (TLRs, CD14, HLAs), whereas many transcripts involved in vascular development and angiogenesis-related signalling pathways (Tie2, eNOS, Ephrins) are highly expressed in OECs. Comparative analysis with monocytes and mature endothelial cells clusters eEPCs with monocytes, while OECs segment with endothelial cells. Similarly, proteomic analysis revealed that 90% of spots identified by 2-D gel analysis are common between OECs and endothelial cells while eEPCs share 77% with monocytes. In line with the expression pattern of caveolins and cadherins identified by microarray analysis, ultrastructural evaluation highlighted the presence of caveolae and adherens junctions only in OECs.

Conclusions

This study provides evidence that eEPCs are haematopoietic cells with a molecular phenotype linked to monocytes; whereas OECs exhibit commitment to the endothelial lineage. These findings indicate that OECs might be an attractive cell candidate for inducing therapeutic angiogenesis, while eEPC should be used with caution because of their monocytic nature.

Quantification of circulating endothelial progenitor cells in human peripheral blood: establishing a reliable flow cytometry protocol

OBJECTIVES

Accurate enumeration of circulating endothelial progenitor cells (CEP) is essential for their potential application as biomarkers of angiogenesis. In this study different stem cell markers (CD34, CD133) and endothelial cell antigens (KDR/VEGFR-2, CD31) in different flow cytometric protocols were assessed for the purpose of CEP quantification.

METHODS

Blood samples from 19 healthy volunteers and 16 patients with different cancer types were analyzed by means of flow cytometry. Mononuclear cell gating was compared to additional gating on CD45-negative cells. CD34+/KDR+ and CD31+/CD133+ cells were analyzed in a direct immunolabeling approach. CEP were measured at different time points in individual patients and after storage of blood samples for 24h and 48h, respectively.

RESULTS

In contrast to previous studies, measurement of CD34+/KDR+ cells was an unreliable method for CEP enumeration, regardless of the applied gating strategy. However, detection of CD31+/CD133+ cells in a combined mononuclear cell and CD45-negative gating approach provided a reproducible method for CEP quantification. In individual blood donors, the CEP numbers were stable over time. For the first time, it was demonstrated that CEP are unstable in extracorporeal blood samples.

CONCLUSION

In this study, a reproducible protocol for CEP quantification was established. This protocol should facilitate future studies with the goal to further define the role of CEP as angiogenic biomarkers.

Exercise acutely reverses dysfunction of circulating angiogenic cells in chronic heart failure

AIMS

Recruitment of endothelial progenitor cells (EPCs) and enhanced activity of circulating angiogenic cells (CACs) might explain the benefits of exercise training in reversing endothelial dysfunction in chronic heart failure (CHF) patients. We studied baseline EPC numbers and CAC function and the effect of a single exercise bout.

METHODS AND RESULTS

Forty-one CHF patients (mild, n = 22; severe, n = 19) and 13 healthy subjects were included. Migratory activity of CACs was evaluated in vitro and circulating CD34+ and CD34+/KDR+ (EPC) cells were quantified by flow cytometry before and after cardiopulmonary exercise testing (CPET). Circulating stromal cell-derived factor-1alpha (SDF-1alpha) and vascular endothelial growth factor (VEGF) concentrations were measured. Both CAC migration as well as CD34+ cell numbers were significantly reduced in CHF, whereas CD34+/KDR+ cells were not different from controls. Endothelial dysfunction was related to impaired CAC migration (r = 0.318, P = 0.023). Cardiopulmonary exercise testing improved CAC migration in severe (+52%, P < 0.005) and mild CHF (+31%, P < 0.005), restoring it to levels similar to controls. Following CPET, SDF-1alpha increased in healthy controls and mild CHF (P < 0.005). Vascular endothelial growth factor, CD34+, and CD34+/KDR+ cell numbers remained unchanged.

CONCLUSION

The present findings reveal a potent stimulus of acute exercise to reverse CAC dysfunction in CHF patients with endothelial dysfunction.

An optimized flow cytometry protocol for analysis of angiogenic monocytes and endothelial progenitor cells in peripheral blood

Circulating adult CD34(+)VEGFR2(+) endothelial progenitor cells (EPCs) have been shown to differentiate into endothelial cells, thus contributing to vascular homeostasis. Furthermore, a subset of circulating CD14(+) monocytes coexpresses CD16 together with the angiopoietin receptor Tie2 and has been functionally implicated in tumor angiogenesis. However, clinically applicable protocols for flow cytometric quantification of EPCs and Tie2(+) monocytes in peripheral blood and a consensus on reference values remain elusive. The number of Tie2(+)CD14(+)CD16(mid) angiogenic monocytes and CD34(+)VEGFR2(+)CD45(low/-) EPCs was assessed in the peripheral venous blood of patients with stable coronary artery disease by three-color flow cytometry using specific monoclonal antibodies conjugated to PerCP, PE, PE-Cy7, APC, and APC-Cy7. Scatter multigating with exclusion of dead cells was performed to dissect complex mononuclear cell populations. This analysis was further refined by matching bright fluorochromes (PE-Cy7, PE, APC) with dimly expressed markers (CD34, VEGFR2, Tie2), by automatic compensation for minimizing fluorescence spillover and by using fluorescence-minus-one (FMO) controls to determine positive/negative boundaries. Presuming a Gaussian distribution, we obtained average values (mean +/- SD) of 1.45 +/- 1.29% for Tie2(+)CD14(+)CD16(mid) monocytes (n = 11, range: 0.12-3.64%) and 0.019 +/- 0.013% for CD34(+)VEGFR2(+)CD45(low/-) EPCs (n = 17, range: 0.003-0.042%). The intra- and inter-assay variability was 1.6% and 4.5%, respectively. We have optimized a fast and sensitive assay for the flow cytometric quantification of circulating angiogenic monocytes and EPCs in cardiovascular medicine. This protocol may represent a basis for standardized analysis and monitoring of these cell subsets to define their normal range and prognostic/diagnostic value in clinical use.

Evidence of dysfunction of endothelial progenitors in pulmonary arterial hypertension

RATIONALE

Severe pulmonary arterial hypertension (PAH) is characterized by the formation of plexiform lesions and concentric intimal fibrosis in small pulmonary arteries. The origin of cells contributing to these vascular lesions is uncertain. Endogenous endothelial progenitor cells are potential contributors to this process.

OBJECTIVES

To determine whether progenitors are involved in the pathobiology of PAH.

METHODS

We performed immunohistochemistry to determine the expression of progenitor cell markers (CD133 and c-Kit) and the major homing signal pathway stromal cell-derived factor-1 and its chemokine receptor (CXCR4) in lung tissue from patients with idiopathic PAH, familial PAH, and PAH associated with congenital heart disease. Two separate flow cytometric methods were employed to determine peripheral blood circulating numbers of angiogenic progenitors. Late-outgrowth progenitor cells were expanded ex vivo from the peripheral blood of patients with mutations in the gene encoding bone morphogenetic protein receptor type II (BMPRII), and functional assays of migration, proliferation, and angiogenesis were undertaken. measurements and main results: There was a striking up-regulation of progenitor cell markers in remodeled arteries from all patients with PAH, specifically in plexiform lesions. These lesions also displayed increased stromal cell-derived factor-1 expression. Circulating angiogenic progenitor numbers in patients with PAH were increased compared with control subjects and functional studies of late-outgrowth progenitor cells from patients with PAH with BMPRII mutations revealed a hyperproliferative phenotype with impaired ability to form vascular networks.

CONCLUSIONS

These findings provide evidence of the involvement of progenitor cells in the vascular remodeling associated with PAH. Dysfunction of circulating progenitors in PAH may contribute to this process.