CLINICAL RESEARCH
Age-dependent depression in circulating endothelial progenitor cells inpatients undergoing coronary artery bypass grafting
Robert J. Scheubel, MD* ,*,
Holger Zorn*,
Rolf-Edgar Silber, MD*,
Oliver Kuss, PhD ,
Henning Morawietz, PhD ,
Juergen Holtz, MD and
Andreas Simm, PhD*
* Department of Cardiothoracic Surgery, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
Institute of Epidemiology, Biostatistics, and Informatics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
Institute of Pathophysiology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
Department of Vascular Endothelium and Microcirculation, University of Technology, Dresden, Germany
* Reprint requests and correspondence: Dr. Robert J. Scheubel, Klinik für Herz- und Thoraxchirurgie, Martin-Luther-Universitaet Halle-Wittenberg, Ernst-Grube-Str. 40, D-06097 Halle (Saale), Germany.
robert.scheubel{at}medizin.uni-halle.de
 |
Abstract
|
|---|
OBJECTIVES: The effect of patient age on circulating endothelial progenitor cells (EPCs) and their mobilization during coronary artery bypass grafting (CABG) was assessed.
BACKGROUND: The EPCs are able to contribute to reparative neovascularization after tissue ischemia. In experimental models, reparative neovascularization is impaired in senescent animals, but the role of EPCs in this impairment, especially in humans, is unknown.
METHODS: In 50 consecutive patients (43 to 80 years old) with stable coronary artery disease undergoing CABG, the numbers of EPCs and the plasma levels of interleukin (IL)-6, IL-8, IL-10, and IL-18, as well as vascular endothelial growth factor (VEGF) and placental growth factor, were determined preoperatively, after coming off bypass, and 6, 12, 24, and 72 h postoperatively.
RESULTS: Preoperative values of EPCs were lowered with increasing age, similar to the lowering of plasma VEGF levels. These age-associated decreases could not be explained by differences in atherosclerotic risk factors or cardiac function. Bypass surgery induced a rapid mobilization in EPCs, IL-6, IL-8, IL-10, and VEGF, with a peak 6 h postoperatively. Persistently lower levels of EPCs and VEGF throughout the observation period were observed in patients >69 years old, which could not be explained by differences in the operative procedure or inflammatory IL activation.
CONCLUSIONS: Despite a significant increase in EPCs and release of cytochemokines during CABG, age is a major limiting factor for mobilization of EPCs. Further studies are necessary to improve the strategies for mobilization, ex vivo expansion, and re-transplantation of EPCs in aging patients.
|
Abbreviations and Acronyms
| | APC | = allophycocyanin | | CABG | = coronary artery bypass grafting | | CAD | = coronary artery disease | | CPB | = cardiopulmonary bypass | | EC | = endothelial cell | | EPC | = endothelial progenitor cell | | KDR | = kinase insert domain containing receptor | | IL | = interleukin | | PlGF | = placental growth factor | | PTCA | = percutaneous transluminal coronary angioplasty | | VEGF | = vascular endothelial growth factor |
|
Coronary artery bypass grafting (CABG) or percutaneous transluminal coronary angioplasty (PTCA) is used to reconstitute flow into post-stenotic, chronically underperfused myocardium. This post-stenotic myocardium consists of connective tissue scars, dying cardiomyocytes, and hypo- active or chronically hibernating myocardium with microvascular disturbances due to microthrombi and decreased capillary density (1). When bulk flow is successfully reconstituted by CABG or PTCA, the gradual recovery of microcirculation is considered as decisive for the recovery of mechanical function of surviving post-stenotic myocardium (2).
Traditionally, neovascularization of disturbed microcirculation was considered to result exclusively from the proliferation, migration, and remodeling of fully differentiated endothelial cells (ECs) derived from pre-existing blood vessels (3). Recently, however, it was demonstrated that circulating, bone marrow-derived endothelial progenitor cells (EPCs) may home to sites of postnatal neovascularization and differentiate into ECs in situ (4), which is called "vasculogenesis" (5). Vascular trauma, as it occurs during surgical procedures, or inflammation leads to a cascade of events that result in the chemoattraction of inflammatory cells or other cell types to the site of injury (6). These blood-borne cells produce pro-angiogenic factors that, in turn, attract other cell types such as circulating EPCs (7). Systemic inflammatory responses have been described after cardiac surgery with cardiopulmonary bypass (CPB) (8). Contact of the blood components with the artificial surface of the extracorporeal circuit, ischemia-reperfusion injury, endotoxemia, and operative trauma are possible causes for this phenomenon (8). Trauma has been considered as the critical stimulus for the mobilization of EPCs and pro-angiogenic vascular endothelial growth factor (VEGF) during CABG (9). It has been speculated that this mobilization may contribute to the revascularization of injured tissue (9), which would be of great clinical relevance for a successful outcome of CABG.
Presently, there is a strong trend to perform CABG in patients of advanced age (10). However, experimental data indicate impaired neoangiogenesis in ischemic tissues and impaired re-endothelialization of vascular lesions as a function of advanced age (11–13). The mechanisms for this age-dependent impairment of vascular repair are largely unknown. Therefore, we analyzed the influence of age on CABG-induced mobilization of EPCs and cytochemokines with angiogenesis-modulating potential in a cohort of consecutive patients with stable coronary artery disease (CAD) scheduled for elective CABG. Probably, several types of endothelial precursor or progenitor cells have angiogenic potential after homing into traumatic tissue (14–18). Therefore, we used two phenotypic markers (CD34 [19] and AC133 or CD133 [20]), which are expressed in all EPC types, but in the case of AC133, not in differentiated ECs (15,17,21). This was done to exclude from our analysis any mature or dying ECs with doubtful angiogenic capacity, potentially released from damaged vessels in old patients.
In this analysis, we demonstrate that the preoperative number of circulating EPCs in patients with stable CAD is reduced with increasing age, together with decreased plasma VEGF levels. During CABG, mobilization of circulating EPCs could be detected in all patients, but this mobilization remained on a persistently lower level in the older patient group, suggesting that the responsiveness for mobilization of EPCs is impaired with age. Optimized strategies for ex vivo expansion of those cells might be especially required in the elderly, if transplantation of these cells into post-stenotic tissue will develop as a future co-therapy to existing interventions of revascularization.
|
Methods
|
|---|
After approval by the local ethics committee of the University of Halle-Wittenberg, 50 consecutive patients with angiographically documented one-, two-, or three-vessel CAD gave written, informed consent and were enrolled in this prospective study. The patient characteristics are summarized in Table 1. Exclusion criteria were as follows: re-operation for CABG; children; pregnancy; coumarin anticoagulant treatment; coagulopathy; liver dysfunction; nephropathy with dialysis; medication with immune-modulating agents such as steroids and anti-inflammatory agents; any history or signs of infectious disease before surgery; re-animation or revision after CABG; and implantation of an intra-aortic balloon pump or ventricular assist device. All patients underwent nonemergent CABG and received the same intravenous anesthesia, consisting of sufentanil (Sufenta, Janssen-Cilag, Neuss, Germany), propofol (Disoprivan, AstraZeneca, Wedel, Germany), and midazolam (Dormicum, Roche, Grenzach-Wyhlen, Germany) under a standardized protocol. The CPB circuit consisted of roller pumps (Stoeckert, München, Germany), a membrane oxygenator (CML Duo, Cobe, Arvada, Colorado), a hard-shell venous reservoir (Cobe), and a 43-µm arterial filter (Cobe Sentry). Full-dose heparin (350 U/kg; Liquemin N 25000, Hoffmann-La Roche, Grenzach-Wyhlen, Germany) was applied before cannulation of the ascending aorta and right atrium for installation of CPB. Aprotinin (Trasylol, Bayer, Leverkusen, Germany) was given at dosage of 3 x 106 U to all patients. Induction of heart arrest was performed by the use of cold crystalloid cardioplegia (Bretschneider-HTK, Köhler, Alsbach, Germany), intermittent cold blood cardioplegia, or intermittent normothermic blood cardioplegia. After coming off bypass, the patient was given protamine (Protamin ICN 1000 I.E./ml, ICN, Frankfurt/Main, Germany) to neutralize the heparin dosage to 100%.
The blood samples were taken in heparinized tubes at six time points for each patient as follows: sample 1, 10 min before induction of anesthesia; sample 2, after coming off bypass; sample 3, in the intensive care unit 6 h after surgery; sample 4, in the ICU 12 h after surgery; sample 5, 24 h after surgery; and sample 6, 72 h after surgery. All blood samples were evaluated by flow cytometry within 24 h or immediately spun at 1,000 g for 15 min. The plasma was separated and frozen at –20°C.
Flow cytometric analysis.
A volume of 100 µl peripheral blood was incubated for 15 min with 2 ml of 1x ammonium chloride lysing solution (Becton Dickinson, Heidelberg, Germany). After centrifugation at 500 g, the cells were resuspended in 100 µl buffer (containing 45 ml RPMI-1640 cell culture medium, 5 ml bovine calf serum, and 500 µl 3% NaN3) and incubated for 30 min in the dark with fluorescein isothiocyanate-labeled monoclonal antibodies against human CD34 (Becton Dickinson) and allophycocyanin (APC)-labeled monoclonal antibodies against human AC133 (Miltenyi Biotec, Bergisch Gladbach, Germany). Isotype-identical antibodies served as controls (Becton Dickinson). After incubation, cells were washed with 2 ml washing solution (Becton Dickinson), centrifuged at 500 g for 5 min, and resuspended in 500 µl washing solution (Becton Dickinson). Before each analysis, 7-amino-actinomycin-D was added as a viability stain. Each analysis included 100,000 events within the lymphocyte gate. Thus, we obtained the number of EPCs per 100,000 lymphocytes (EPC/lymphocytes) and, after adjustment for the number of leukocytes in peripheral blood and the fraction of lymphocytes/leukocytes, the number of EPCs per 100 µl blood (EPC/blood). Representative examples of these flow cytometric analyses are shown in Figures 1a to 1f.
View larger version (34K):
[in this window]
[in a new window]
|
Figure 1 Representative dot blot flow cytometric analysis of the mobilized endothelial progenitor cells/lymphocytes, quantifying the number of CD34+ and AC133+ cells in the older (>69 years) and younger patients (<62 years) preoperatively (c, d) and 6 h after surgery (e, f), together with isotype control of older (a) and younger patients (b). APC = allophycocyanin; FITC = fluorescein isothiocyanate.
|
|
Functional characterization of CD34+ and AC133+ progenitor cells.
The endothelial differentiation potential of these progenitor cells was assessed by analyzing the expression of EC-specific markers after incubation for three days in an endothelial growth medium (EGM-2, BioWhittaker, Verviers, Belgium) on fibronectin-coated culture dishes (Becton Dickinson). Human CD34+ cells were isolated from "buffy coats" of donor blood via immunomagnetic CD34 microbead extraction (Miltenyi Biotec), according to the manufacturer's instructions, and analyzed by flow cytometry for AC133-APC (Miltenyi Biotec), AcLDLDiI binding (Paesel & Lorei, Hanau, Germany), vascular/endothelial-cadherin-phycoerythrin (Santa Cruz, Heidelberg, Germany), and kinase insert domain containing receptor (KDR) (ReliaTech, Braunschweig, Germany), visualized using APC-conjugated rat anti-mouse monoclonal antibody (Becton Dickinson). Viable double-positive CD34/AC133 cells had a mean fluorescence due to AcLDL binding of 30.0 relative units (rU), which increased to 100.2 rU after 3 days of differentiation in EGM-2, a mean fluorescence of VE-cadherin of 3.7, which increased to 32.7 rU, and a mean florescence of KDR of 65.4 rU, which increased to 457.3 rU. This differentiation potential of CD34+/AC133+ progenitor cells toward an endothelial phenotype, documented representatively, justifies their denomination as EPCs. However, the functional characterization of CD34+/AC133+ cells was not performed in all investigated samples of patients. As the true differentiation of CD34+/AC133+ cells toward an endothelial phenotype can be proved only in vivo, our investigation was an analysis of CD34+/AC133+ progenitor cells, which should have the potential to differentiate toward an endothelial phenotype.
Plasma VEGF, placental growth factor (PlGF), interleukin (IL)-6, IL-8, IL-10, and IL-18 levels.
Quantitative determination of the cytokine plasma levels of patients was performed in duplicate by a highly sensitive enzyme-linked immunosorbent assay (R&D Systems, Wiesbaden, Germany), according to the manufacturer's instructions. Samples were analyzed in a FLUOstar OPTIMA (BMG, Offenburg, Germany).
Statistical analysis.
For statistical analysis, standard methods were used, as indicated in the figure legends and tables—for example, Pearson's correlation coefficient (Fig. 2) (see Results section), repeated measures analysis of variance (ANOVA) models (Figs. 3, 4, and 5), ordinary ANOVA models (Fig. 5), linear regression (Table 2) (see Results section), and t tests (Table 1). Pairwise comparisons were Bonferroni-adjusted to avoid spurious significances. Calculations were performed by SAS version 8e (SAS Institute Inc., Cary, North Carolina).
View larger version (17K):
[in this window]
[in a new window]
|
Figure 2 Age-dependent decrease of preoperative endothelial progenitor cells (EPC) values (a, b) and plasma vascular endothelial growth factor (VEGF) level (c) in patients undergoing coronary artery bypass graft surgery. The Pearson correlation coefficient and p values of the corresponding significance test of the respective values are indicated.
|
|
View larger version (27K):
[in this window]
[in a new window]
|
Figure 3 Mobilization of endothelial progenitor cells (EPC) and leukocytes by coronary artery bypass graft surgery. Reported significances (*p < 0.05, **p < 0.01, ***p < 0.001) were calculated by Bonferroni-adjusted pairwise comparisons with the preoperative level within a repeated measurement analysis of variance model for the respective parameter at five different time points. CPB = cardiopulmonary bypass.
|
|
View larger version (20K):
[in this window]
[in a new window]
|
Figure 4 Induction of cytochemokines by coronary artery bypass graft surgery. Reported significances (*p < 0.05, **p < 0.01, ***p < 0.001) were calculated by Bonferroni-adjusted pairwise comparisons with the preoperative level within a repeated measurement analysis of variance model for the respective parameter at three different time points. IL = interleukin; PlGF = placental growth factor; VEGF = vascular endothelial growth factor.
|
|
View larger version (17K):
[in this window]
[in a new window]
|
Figure 5 Age dependency of endothelial progenitor cells (EPCs)/lymphocytes (a), EPCs/blood (b), and vascular endothelial growth factor (VEGF) (c) after coronary artery bypass graft surgery. The global age effects (EPCs/lymphocytes: p < 0.01; EPCs/blood: p < 0.01; VEGF: p < 0.05) between the two age groups <62 and >69 years were assessed within a repeated measures analysis of variance model also adjusting for time. Reported significances (*p < 0.05) for VEGF between the two age groups <62 and >69 years at the time points preoperatively and 6 h postoperatively were calculated by separate (for each time point) analysis of variance models. The three comparisons between the age groups at each time point were Bonferroni-adjusted. Circles = <62 years; squares = 62 to 69 years; triangles = >69 years.
|
|
|
Results
|
|---|
Patients.
The characteristics of the 50 consecutive patients with elective CABG (median age 65 years, range 43 to 80 years) are presented in Table 1, together with basal circulating EPC values and plasma cytochemokine levels. The patients were classified into three age groups: <62, 62 to 69, and >69 years old. In patients of advanced age, the number of circulating EPCs/lymphocytes, as well as EPCs/blood, and VEGF plasma levels were significantly reduced. These values showed a negative correlation with age (Figs. 2a to 2c). Furthermore, there was an age-independent correlation of VEGF with EPCs/lymphocytes (p = 0.002) and with EPCs/blood (p = 0.001). Basal EPC values did not correlate with other risk factors (Table 2), with the cumulative number of risk factors, or with any other plasma cytochemokine level. The association between age and EPC values persisted even after adjustment for risk factors in a linear regression model (Table 2).
Mobilization of EPCs and induction of cytochemokines by CABG.
After CPB, there was a biphasic response of EPC values (Fig. 3). The first phase consisted of an increase in EPCs/lymphocytes, 1.5-fold at the end of CPB and 2-fold 6 h later, relative to the preoperative baseline value, respectively (Fig. 3a). Concomitantly, we observed a two-fold increase in leukocytosis (Fig. 3b) and a progressive decline in the fraction of lymphocytes/leukocytes (Fig. 3c). These alterations resulted in a two-fold increase in circulating EPCs/blood at the end of CPB, which returned to basal levels 6 h later (Fig. 3d). The EPCs/lymphocytes transiently returned to or below preoperative levels one day after surgery (Fig. 3a), whereas the fraction of lymphocytes/leukocytes and circulating EPCs/blood declined below baseline levels (Figs. 3c and 3d). The second phase of increase in EPCs/lymphocytes occurred three days later (Fig. 3a), whereas the leukocytosis remained elevated throughout this period (Fig. 3b).
An apparently similar biphasic response could be observed for plasma levels of VEGF and IL-10 (Fig. 4a). After a first increase 6 h postoperatively (2.6-fold for VEGF and 10.7-fold for IL-10), both plasma levels declined transiently after one day, but the second phase of increase after 3 days did not reach the level of significance relative to the previous values (Fig. 4a). The pro-inflammatory cytokines IL-6 and IL-8 showed a monophasic response, a 50-fold increase for IL-6, and a 10-fold increase for IL-8 after 6 h (Fig. 4b). In addition, the increase of IL-6 after 6 h correlated significantly with the time on CPB (p = 0.009). For PlGF and IL-18, postoperative plasma levels did not change significantly relative to preoperative values (Fig. 4c).
In the first phase of the surgery-induced increase in EPC values, the increase in EPCs/lymphocytes showed a negative age dependency (r = –0.307, p = 0.03). However, the increase in neither EPCs/blood nor EPCs/lymphocytes correlated with any other risk factor, New York Heart Association classification, or operative data. Furthermore, there was no positive correlation of the increases in EPC values with any of the operation-induced increases in plasma cytochemokines.
In the three age groups, the biphasic response of EPCs/lymphocytes and EPCs/blood was similar, but this response remained at significantly higher levels in the younger group compared with the older patients throughout the observation period (Figs. 5a and 5b). In plasma VEGF, the oldest patient group had a retarded response, with significantly lower values 6 h after the end of CPB, compared with younger patients, and significantly lower values throughout the observation period (Fig. 5c).
|
Discussion
|
|---|
This study demonstrates that the basal number of circulating EPCs in patients with stable CAD is decreased with increasing age. Furthermore, plasma VEGF levels are reduced with increasing age. This age-associated decrease could not be explained by higher prevalences of other risk factors, such as male gender, diabetes mellitus, hypertension, or hyperlipoproteinemia at older ages (Table 2), nor by any differences in left ventricular function or New York Heart Association classes. The operative trauma of complex cardiac surgery with CPB induced a mobilization in EPCs/lymphocytes and EPCs/blood in all patients, but this mobilization remained on a persistently lower level in the older patient group, which could not be explained by any differences in the operative procedure (time on CPB, cross-clamping time, or number of grafts) or in the operation-induced increase in cytochemokines with a reported potency for modulation of angiogenesis (IL-6, IL-8, and IL-10).
To the best of our knowledge, similar age-associated losses in the number of circulating endothelial-related progenitor cells in patients undergoing CABG have not been reported so far. In 45 male subjects without a history of cardiovascular disease, the Framingham risk score and impairment of endothelium-mediated, flow-dependent brachial artery dilation were strong predictors of depressed numbers in circulating progenitor cells with colony-forming capacity (22). In a mixed group of healthy probands and CAD patients, Vasa et al. (23) reported age-associated losses in circulating cells positive for CD34+ and KDR+, which may include progenitor cells and mobilized ECs (21). In their cohort, smoking was a strong predictor of lowered values in CD34+/KDR+ cells, independent of age (23). In our patients, self-reported smoking status, which is notoriously unreliable before cardiac surgery, could not be verified by interrogations of spouses or relatives. This may explain why we could not detect an effect of smoking on circulating EPCs.
The reasons for the age-associated losses in circulating EPCs remain unknown at present. In our study, there was an age-independent correlation of circulating EPCs with plasma VEGF levels. Circulating or transplanted EPCs contribute to post-ischemic neovascularization in animal experiments (4,7,24,25) and patients (26,27), and angiogenic factors like VEGF and PlGF are involved in this neovascularization (28–31). In animals, advanced age is associated with attenuated post-ischemic neovascularization and attenuated local induction of VEGF (12,13,32). Similarly, arterial re-endothelialization after vascular trauma is attenuated in old animals in which trauma-induced local VEGF expression is lower and local VEGF supplementation rescues vascular healing (11). Experimental elevation of plasma VEGF in mice by inoculation with adenoviral vectors induced rapid mobilization of endothelial precursor cells (9). Therefore, it is tempting to propose that lowered VEGF levels in our elderly patients are the reason for lowered circulating EPCs. However, this causality remains to be proven for basal steady-state levels, and the cause of depressed circulating VEGF levels in elderly patients remains unknown. In experimental studies, hypoxia-inducible factor-1 stabilization by hypoxia, which mediates hypoxic VEGF expression, is attenuated in cells from old animals (12). This might be relevant for the attenuated and retarded CABG-induced activation of plasma VEGF in older patients (Fig. 5). However, this may be less relevant for the age-associated lowering in basal VEGF levels before surgery.
Local and systemic inflammation by vascular trauma is considered an important contributor of post-ischemic neovascularization (33). In our patients, the operative trauma resulted in a substantial mobilization of cytochemokines with angiogenesis-modulating potential (28,31,34–37), except for IL-18 and PlGF (Fig. 4). These observations are in agreement with previous reports (38–40). Although none of these activated factors could be directly correlated with the individual increase in EPCs during and after the operation in our patients, it is reasonable to assume that the complex spectrum of inflammatory activation is contributing to the mobilization of surgery-induced EPCs. Similar conclusions have been derived from observations on transient mobilization of KDR+/AC133+ cells in patients after burns or CABG (9). The kinetics of mobilization in that study differed somewhat from our observations, but the two studies are not directly comparable owing to differences in progenitor cell analysis (9). It is remarkable that the substantial inflammatory activation during surgery in our study could not abolish age-associated differences in EPC levels.
The decline in the fraction of lymphocytes/leukocytes after CPB down to one-quarter that of the baseline value at 12 h after CPB (Fig. 3c) most likely reflects substantial homing of lymphocytes into tissues in response to the systemic inflammatory activation induced by CPB. Homing must also contribute to the decline of circulating EPCs/blood during this time (Fig. 3d). Therefore, circulating EPC levels underestimate the amount of EPC mobilization. However, quantification of lymphocyte or EPC homing could not be obtained in our patients.
Application of different populations of EPCs or other mononuclear bone marrow cells improves postischemic organ function and microcirculation in animals and patients (16,24–27,41,42). However, it is not clear whether the surgery-induced mobilization of EPCs is sufficient for such a contribution. Furthermore, it is unclear whether the EPCs in elderly patients have the same angiogenic potential compared with those of younger patients. The EPCs collected from the circulation can be amplified in vitro (24,26). The co-application of amplified EPCs, together with native artery recanalization or bypass grafting, probably will develop as a therapeutic option in the future. The experimental data (12,13,32) suggest that such co-therapy is especially desirable in elderly patients. Our data suggest that mobilization of such cells for therapeutic application might be more difficult with an increasing age of patients.
Conclusions.
Application of EPCs might expand the tools for therapeutic revascularization and regeneration. However, this potential future strategy seems to be aggravated in aging patients because of lowered numbers of EPCs and lowered VEGF plasma levels. The inflammatory activation by complex CABG does not offset this age-associated lowering. Therefore, further studies are required for a better understanding of optimized strategies for recruitment, ex vivo expansion, and retransplantation strategies involving EPCs in aging patients.
|
Acknowledgments
|
|---|
The authors express their appreciation for the cooperation of the patients and staff of the Clinic for Cardiothoracic Surgery in Halle (Saale), Germany. They also thank S. Kahrstedt, M. Stiller, and R. Busath for their excellent technical assistance.
|
Footnotes
|
|---|
This work was supported by grants from the German Bundesministerium für Bildung und Forschung, or BMBF (NBL 3, FKZ 3/6) and the Deutsche Forschungsgemeinschaft (SFB 598/B1, A5).
|
References
|
|---|
1. Heusch G, Schulz R. Hibernating myocardium: a review. J Mol Cell Cardiol. 1996;28:2359–2372[CrossRef][Medline]
2. Heusch G, Schulz R. The biology of myocardial hibernation. Trends Cardiovasc Med. 2000;10:108–114[CrossRef][Medline]
3. Folkman J, Shing Y. Angiogenesis. J Biol Chem. 1992;267:10931–10934[Free Full Text]
4. Asahara T, Masuda H, Takahashi T, et al. Bone marrow origin of endothelial progenitor cells responsible for postnatal vasculogenesis in physiological and pathological neovascularization. Circ Res. 1999;85:221–228[Abstract/Free Full Text]
5. Risau W, Flamme I. Vasculogenesis. Annu Rev Cell Dev Biol. 1995;11:73–91[CrossRef][Medline]
6. Nissen NN, Polverini PJ, Koch AE, Volin MV, Gamelli RL, DiPietro LA. Vascular endothelial growth factor mediates angiogenic activity during the proliferative phase of wound healing. Am J Pathol. 1998;152:1445–1452[Abstract]
7. Takahashi T, Kalka C, Masuda H, et al. Ischemia- and cytokine-induced mobilization of bone marrow-derived endothelial progenitor cells for neovascularization. Nat Med. 1999;5:434–438[CrossRef][Medline]
8. Paparella D, Yau TM, Young E. Cardiopulmonary bypass induced inflammation: pathophysiology and treatment: an update. Eur J Cardiothorac Surg. 2002;21:232–244[Abstract/Free Full Text]
9. Gill M, Dias S, Hattori K, et al. Vascular trauma induces rapid but transient mobilization of VEGFR2(+)/AC133(+) endothelial precursor cells. Circ Res. 2001;88:167–174[Abstract/Free Full Text]
10. Graham MM, Ghali WA, Faris PD, Galbraith PD, Norris CM, Knudtson ML. Survival after coronary revascularization in the elderly. Circulation. 2002;105:2378–2384[Abstract/Free Full Text]
11. Gennaro G, Menard C, Michaud SE, Rivard A. Age-dependent impairment of reendothelialization after arterial injury: role of vascular endothelial growth factor. Circulation. 2003;107:230–233[Abstract/Free Full Text]
12. Rivard A, Berthou-Soulie L, Principe N, et al. Age-dependent defect in vascular endothelial growth factor expression is associated with reduced hypoxia-inducible factor 1 activity. J Biol Chem. 2000;275:29643–29647[Abstract/Free Full Text]
13. Rivard A, Fabre JE, Silver M, et al. Age-dependent impairment of angiogenesis. Circulation. 1999;99:111–120[Abstract/Free Full Text]
14. Quirici N, Soligo D, Caneva L, Servida F, Bossolasco P, Deliliers GL. Differentiation and expansion of endothelial cells from human bone marrow CD133(+) cells. Br J Haematol. 2001;115:186–194[CrossRef][Medline]
15. Peichev M, Naiyer AJ, Pereira D, et al. Expression of VEGFR-2 and AC133 by circulating human CD34(+) cells identifies a population of functional endothelial precursors. Blood. 2000;95:952–958[Abstract/Free Full Text]
16. Kawamoto A, Tkebuchava T, Yamaguchi J, et al. Intramyocardial transplantation of autologous endothelial progenitor cells for therapeutic neovascularization of myocardial ischemia. Circulation. 2003;107:461–468[Abstract/Free Full Text]
17. Asahara T, Murohara T, Sullivan A, et al. Isolation of putative progenitor endothelial cells for angiogenesis. Science. 1997;275:964–967[Abstract/Free Full Text]
18. Rafii S. Circulating endothelial precursors: mystery, reality, and promise. J Clin Invest. 2000;105:17–19[Medline]
19. Nadali G, de Wynter EA, Testa NG. CD34 cell separation: from basic research to clinical applications. Int J Clin Lab Res. 1995;25:121–127[Medline]
20. Bhatia M. AC133 expression in human stem cells. Leukemia. 2001;15:1685–1688[Medline]
21. Walter DH, Dimmeler S. Endothelial progenitor cells: regulation and contribution to adult neovascularization. Herz. 2002;27:579–588[CrossRef][Medline]
22. Hill JM, Zalos G, Halcox JP, et al. Circulating endothelial progenitor cells, vascular function, and cardiovascular risk. N Engl J Med. 2003;348:593–600[Abstract/Free Full Text]
23. Vasa M, Fichtlscherer S, Aicher A, et al. Number and migratory activity of circulating endothelial progenitor cells inversely correlate with risk factors for coronary artery disease. Circ Res. 2001;89:E1–E7[Medline]
24. Kalka C, Masuda H, Takahashi T, et al. Transplantation of ex vivo expanded endothelial progenitor cells for therapeutic neovascularization. Proc Natl Acad Sci USA. 2000;97:3422–3427[Abstract/Free Full Text]
25. Kocher AA, Schuster MD, Szabolcs MJ, et al. Neovascularization of ischemic myocardium by human bone-marrow-derived angioblasts prevents cardiomyocyte apoptosis, reduces remodeling and improves cardiac function. Nat Med. 2001;7:430–436[CrossRef][Medline]
26. Assmus B, Schachinger V, Teupe C, et al. Transplantation of Progenitor Cells and Regeneration Enhancement in Acute Myocardial Infarction (TOPCARE-AMI). Circulation. 2002;106:3009–3017[Abstract/Free Full Text]
27. Strauer BE, Brehm M, Zeus T, et al. Repair of infarcted myocardium by autologous intracoronary mononuclear bone marrow cell transplantation in humans. Circulation. 2002;106:1913–1918[Abstract/Free Full Text]
28. Carmeliet P, Moons L, Luttun A, et al. Synergism between vascular endothelial growth factor and placental growth factor contributes to angiogenesis and plasma extravasation in pathological conditions. Nat Med. 2001;7:575–583[CrossRef][Medline]
29. Hattori K, Dias S, Heissig B, et al. Vascular endothelial growth factor and angiopoietin-1 stimulate postnatal hematopoiesis by recruitment of vasculogenic and hematopoietic stem cells. J Exp Med. 2001;193:1005–1014[Abstract/Free Full Text]
30. Hattori K, Heissig B, Wu Y, et al. Placental growth factor reconstitutes hematopoiesis by recruiting VEGFR1(+) stem cells from bone-marrow microenvironment. Nat Med. 2002;8:841–849[CrossRef][Medline]
31. Luttun A, Tjwa M, Moons L, et al. Revascularization of ischemic tissues by PlGF treatment, and inhibition of tumor angiogenesis, arthritis and atherosclerosis by anti-Flt1. Nat Med. 2002;8:831–840[CrossRef][Medline]
32. Edelberg JM, Tang L, Hattori K, Lyden D, Rafii S. Young adult bone marrow-derived endothelial precursor cells restore aging-impaired cardiac angiogenic function. Circ Res. 2002;90:E89–E93
33. Frangogiannis NG, Smith CW, Entman ML. The inflammatory response in myocardial infarction. Cardiovasc Res. 2002;53:31–47[Abstract/Free Full Text]
34. Wei LH, Kuo ML, Chen CA, et al. Interleukin-6 in cervical cancer: The relationship with vascular endothelial growth factor. Gynecol Oncol. 2001;82:49–56[CrossRef][Medline]
35. Ferrara N. Vascular endothelial growth factor and the regulation of angiogenesis. Recent Prog Horm Res. 2000;55:15–35[Medline]
36. Garcia-Hernandez ML, Hernandez-Pando R, Gariglio P, Berumen J. Interleukin-10 promotes B16-melanoma growth by inhibition of macrophage functions and induction of tumor and vascular cell proliferation. Immunology. 2002;105:231–243[CrossRef][Medline]
37. Park CC, Morel JC, Amin MA, Connors MA, Harlow LA, Koch AE. Evidence of IL-18 as a novel angiogenic mediator. J Immunol. 2001;167:1644–1653[Abstract/Free Full Text]
38. Diegeler A, Doll N, Rauch T, et al. Humoral immune response during coronary artery bypass grafting: a comparison of limited approach, ‘off-pump’ technique, and conventional cardiopulmonary bypass. Circulation. 2000;102(Suppl III):III95–III100
39. Franke A, Lante W, Fackeldey V, et al. Proinflammatory and antiinflammatory cytokines after cardiac operation: different cellular sources at different times. (withdiscussion)Ann Thorac Surg. 2002;74:363–371[Abstract/Free Full Text]
40. Wan S, LeClerc JL, Vincent JL. Cytokine responses to cardiopulmonary bypass: lessons learned from cardiac transplantation. Ann Thorac Surg. 1997;63:269–276[Abstract/Free Full Text]
41. Orlic D, Kajstura J, Chimenti S, et al. Bone marrow cells regenerate infarcted myocardium. Nature. 2001;410:701–705[CrossRef][Medline]
42. Kawamoto A, Gwon HC, Iwaguro H, et al. Therapeutic potential of ex vivo expanded endothelial progenitor cells for myocardial ischemia. Circulation. 2001;103:634–637[Abstract/Free Full Text]
This article has been cited by other articles:
|
|
|
|
 
O. Dotsenko and M. Jahangiri
Endogenous stem cells in patients undergoing coronary artery bypass graft surgery
Eur. J. Cardiothorac. Surg.,
September 1, 2009;
36(3):
563 - 571.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S.-H. Wang, S.-J. Lin, Y.-H. Chen, F.-Y. Lin, J.-C. Shih, C.-C. Wu, H.-L. Wu, and Y.-L. Chen
Late Outgrowth Endothelial Cells Derived From Wharton Jelly in Human Umbilical Cord Reduce Neointimal Formation After Vascular Injury: Involvement of Pigment Epithelium-Derived Factor
Arterioscler Thromb Vasc Biol,
June 1, 2009;
29(6):
816 - 822.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. M. Leone, M. Valgimigli, M. B. Giannico, V. Zaccone, M. Perfetti, D. D'Amario, A. G. Rebuzzi, and F. Crea
From bone marrow to the arterial wall: the ongoing tale of endothelial progenitor cells
Eur. Heart J.,
April 2, 2009;
30(8):
890 - 899.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S H Schirmer, F C van Nooijen, J J Piek, and N van Royen
Stimulation of collateral artery growth: travelling further down the road to clinical application
Heart,
February 1, 2009;
95(3):
191 - 197.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. M. Smadja, P. Gaussem, L. Mauge, D. Israel-Biet, F. Dignat-George, S. Peyrard, G. Agnoletti, P. R. Vouhe, D. Bonnet, and M. Levy
Circulating Endothelial Cells: A New Candidate Biomarker of Irreversible Pulmonary Hypertension Secondary to Congenital Heart Disease
Circulation,
January 27, 2009;
119(3):
374 - 381.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. R. Seals, C. A. DeSouza, A. J. Donato, and H. Tanaka
Habitual exercise and arterial aging
J Appl Physiol,
October 1, 2008;
105(4):
1323 - 1332.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. J. Weiss, J. K. Kolls, L. A. Ortiz, A. Panoskaltsis-Mortari, and D. J. Prockop
Stem Cells and Cell Therapies in Lung Biology and Lung Diseases
Proceedings of the ATS,
July 15, 2008;
5(5):
637 - 667.
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Dimmeler and A. Leri
Aging and Disease as Modifiers of Efficacy of Cell Therapy
Circ. Res.,
June 6, 2008;
102(11):
1319 - 1330.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. J. Povsic and P. J. Goldschmidt-Clermont
Review: Endothelial progenitor cells: markers of vascular reparative capacity
Therapeutic Advances in Cardiovascular Disease,
June 1, 2008;
2(3):
199 - 213.
[Abstract]
[PDF]
|
|
|
|
|
|
|
M. Thill, N. V. Strunnikova, M. J. Berna, N. Gordiyenko, K. Schmid, S. W. Cousins, D. J. S. Thompson, and K. G. Csaky
Late Outgrowth Endothelial Progenitor Cells in Patients with Age-Related Macular Degeneration
Invest. Ophthalmol. Vis. Sci.,
June 1, 2008;
49(6):
2696 - 2708.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Tongers and D. W. Losordo
Frontiers in Nephrology: The Evolving Therapeutic Applications of Endothelial Progenitor Cells
J. Am. Soc. Nephrol.,
November 1, 2007;
18(11):
2843 - 2852.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C.-D. Kan, S.-H. Li, R. D. Weisel, S. Zhang, and R.-K. Li
Recipient Age Determines the Cardiac Functional Improvement Achieved by Skeletal Myoblast Transplantation
J. Am. Coll. Cardiol.,
September 11, 2007;
50(11):
1086 - 1092.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
V. L.T. Ballard and J. M. Edelberg
Stem Cells and the Regeneration of the Aging Cardiovascular System
Circ. Res.,
April 27, 2007;
100(8):
1116 - 1127.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. L. Hoetzer, G. P. Van Guilder, H. M. Irmiger, R. S. Keith, B. L. Stauffer, and C. A. DeSouza
Aging, exercise, and endothelial progenitor cell clonogenic and migratory capacity in men
J Appl Physiol,
March 1, 2007;
102(3):
847 - 852.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. K. Trousdale, S. V. Pollak, J. Klein, L. Lobel, Y. Funahashi, N. Feirt, and J. W. Lustbader
Single-Chain Bifunctional Vascular Endothelial Growth Factor (VEGF)-Follicle-Stimulating Hormone (FSH)-C-Terminal Peptide (CTP) Is Superior to the Combination Therapy of Recombinant VEGF plus FSH-CTP in Stimulating Angiogenesis during Ovarian Folliculogenesis
Endocrinology,
March 1, 2007;
148(3):
1296 - 1305.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
E. Shantsila, T. Watson, and G. Y.H. Lip
Endothelial Progenitor Cells in Cardiovascular Disorders
J. Am. Coll. Cardiol.,
February 20, 2007;
49(7):
741 - 752.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. Thum, S. Hoeber, S. Froese, I. Klink, D. O. Stichtenoth, P. Galuppo, M. Jakob, D. Tsikas, S. D. Anker, P. A. Poole-Wilson, et al.
Age-Dependent Impairment of Endothelial Progenitor Cells Is Corrected by Growth Hormone Mediated Increase of Insulin-Like Growth Factor-1
Circ. Res.,
February 16, 2007;
100(3):
434 - 443.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
N. Roberts, Q. Xiao, G. Weir, Q. Xu, and M. Jahangiri
Endothelial Progenitor Cells are Mobilized After Cardiac Surgery
Ann. Thorac. Surg.,
February 1, 2007;
83(2):
598 - 605.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Mieno, M. Boodhwani, R. T. Clements, B. Ramlawi, N. R. Sodha, J. Li, and F. W. Sellke
Aging is associated with an impaired coronary microvascular response to vascular endothelial growth factor in patients
J. Thorac. Cardiovasc. Surg.,
December 1, 2006;
132(6):
1348 - 1355.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. G. Shaffer, S. Greene, A. Arshi, G. Supple, A. Bantly, J. S Moores, M. S Parmacek, and E. R Mohler III
Effect of acute exercise on endothelial progenitor cells in patients with peripheral arterial disease
Vascular Medicine,
November 1, 2006;
11(4):
219 - 226.
[Abstract]
[PDF]
|
|
|
|
|
|
|
J. Leor and M. Marber
Endothelial Progenitors: A New Tower of Babel?
J. Am. Coll. Cardiol.,
October 17, 2006;
48(8):
1588 - 1590.
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. P. Fadini, S. V. de Kreutzenberg, A. Coracina, I. Baesso, C. Agostini, A. Tiengo, and A. Avogaro
Circulating CD34+ cells, metabolic syndrome, and cardiovascular risk
Eur. Heart J.,
September 2, 2006;
27(18):
2247 - 2255.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Mieno, B. Ramlawi, M. Boodhwani, R. T. Clements, K. Minamimura, T. Maki, S.-H. Xu, C. Bianchi, J. Li, and F. W. Sellke
Role of Stromal-Derived Factor-1{alpha} in the Induction of Circulating CD34+CXCR4+ Progenitor Cells After Cardiac Surgery.
Circulation,
July 4, 2006;
114(1 Suppl):
186 - 192.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
E. Zengin, F. Chalajour, U. M. Gehling, W. D. Ito, H. Treede, H. Lauke, J. Weil, H. Reichenspurner, N. Kilic, and S. Ergun
Vascular wall resident progenitor cells: a source for postnatal vasculogenesis
Development,
April 15, 2006;
133(8):
1543 - 1551.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. Galasso, S. Schiekofer, K. Sato, R. Shibata, D. E. Handy, N. Ouchi, J. A. Leopold, J. Loscalzo, and K. Walsh
Impaired Angiogenesis in Glutathione Peroxidase-1-Deficient Mice Is Associated With Endothelial Progenitor Cell Dysfunction
Circ. Res.,
February 3, 2006;
98(2):
254 - 261.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Susen, K. Sautiere, F. Mouquet, F. Cuilleret, A. Chmait, E. P. McFadden, B. Hennache, F. Richard, P. de Groote, J.-M. Lablanche, et al.
Serum hepatocyte growth factor levels predict long-term clinical outcome after percutaneous coronary revascularization
Eur. Heart J.,
November 2, 2005;
26(22):
2387 - 2395.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. M. Hill, M. A. Syed, A. E. Arai, T. M. Powell, J. D. Paul, G. Zalos, E. J. Read, H. M. Khuu, S. F. Leitman, M. Horne, et al.
Outcomes and Risks of Granulocyte Colony-Stimulating Factor in Patients With Coronary Artery Disease
J. Am. Coll. Cardiol.,
November 1, 2005;
46(9):
1643 - 1648.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. Thum, D. Tsikas, S. Stein, M. Schultheiss, M. Eigenthaler, S. D. Anker, P. A. Poole-Wilson, G. Ertl, and J. Bauersachs
Suppression of Endothelial Progenitor Cells in Human Coronary Artery Disease by the Endogenous Nitric Oxide Synthase Inhibitor Asymmetric Dimethylarginine
J. Am. Coll. Cardiol.,
November 1, 2005;
46(9):
1693 - 1701.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. Zhang, S. Fazel, H. Tian, D. A. G. Mickle, R. D. Weisel, T. Fujii, and R.-K. Li
Increasing donor age adversely impacts beneficial effects of bone marrow but not smooth muscle myocardial cell therapy
Am J Physiol Heart Circ Physiol,
November 1, 2005;
289(5):
H2089 - H2096.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Ruel, E. J. Suuronen, J. Song, V. Kapila, D. Gunning, G. Waghray, F. D. Rubens, and T. G. Mesana
Effects of off-pump versus on-pump coronary artery bypass grafting on function and viability of circulating endothelial progenitor cells
J. Thorac. Cardiovasc. Surg.,
September 1, 2005;
130(3):
633 - 639.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
B.-O. Kim, H. Tian, K. Prasongsukarn, J. Wu, D. Angoulvant, S. Wnendt, A. Muhs, D. Spitkovsky, and R.-K. Li
Cell Transplantation Improves Ventricular Function After a Myocardial Infarction: A Preclinical Study of Human Unrestricted Somatic Stem Cells in a Porcine Model
Circulation,
August 30, 2005;
112(9_suppl):
I-96 - I-104.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Massa, V. Rosti, I. Ramajoli, R. Campanelli, A. Pecci, G. Viarengo, V. Meli, M. Marchetti, R. Hoffman, and G. Barosi
Circulating CD34+, CD133+, and Vascular Endothelial Growth Factor Receptor 2-Positive Endothelial Progenitor Cells in Myelofibrosis With Myeloid Metaplasia
J. Clin. Oncol.,
August 20, 2005;
23(24):
5688 - 5695.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
V. J. Dzau, M. Gnecchi, A. S. Pachori, F. Morello, and L. G. Melo
Therapeutic Potential of Endothelial Progenitor Cells in Cardiovascular Diseases
Hypertension,
July 1, 2005;
46(1):
7 - 18.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. Schmidt-Lucke, L. Rossig, S. Fichtlscherer, M. Vasa, M. Britten, U. Kamper, S. Dimmeler, and A. M. Zeiher
Reduced Number of Circulating Endothelial Progenitor Cells Predicts Future Cardiovascular Events: Proof of Concept for the Clinical Importance of Endogenous Vascular Repair
Circulation,
June 7, 2005;
111(22):
2981 - 2987.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. Heiss, S. Keymel, U. Niesler, J. Ziemann, M. Kelm, and C. Kalka
Impaired Progenitor Cell Activity in Age-Related Endothelial Dysfunction
J. Am. Coll. Cardiol.,
May 3, 2005;
45(9):
1441 - 1448.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. P. Brandes, I. Fleming, and R. Busse
Endothelial aging
Cardiovasc Res,
May 1, 2005;
66(2):
286 - 294.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Simons
Angiogenesis: Where Do We Stand Now?
Circulation,
March 29, 2005;
111(12):
1556 - 1566.
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. C. Sane
The endothelial life insurance plan
Blood,
November 1, 2004;
104(9):
2615 - 2616.
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. C. Capogrossi
Cardiac Stem Cells Fail With Aging: A New Mechanism for the Age-Dependent Decline in Cardiac Function
Circ. Res.,
March 5, 2004;
94(4):
411 - 413.
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. J. Reed and J. M. Edelberg
Impaired Angiogenesis in the Aged
Sci. Aging Knowl. Environ.,
February 18, 2004;
2004(7):
pe7 - 7.
[Abstract]
[Full Text]
|
|
|
|
Top
Abstract
Methods