Erythropoietin regulates endothelial progenitor cells

Endothelial progenitor cells, late stent thrombosis and delayed re-endothelialisation

A decade ago, the description of a primitive novel cell type capable of differentiating into cells expressing a mature endothelial cell -phenotype and their capacity to incorporate into regions of active angiogenesis, witnessed the emergence of endothelial progenitor cell (EPC) biology1. The development and maturation of this new concept in vascular biology has resulted in numerous studies describing the role of EPCs in a myriad of disease states where abnormalities of the vasculature have been implicated. Thus, from pre-eclampsia to pulmonary hypertension, erythropoietin administration to erectile dysfunction and cancer to coronary disease the discovery of EPCs has added greatly to the understanding of basic pathophysiology. However, it is in the study of coronary artery -disease where this paradigm shift has had greatest impact, not only regarding basic disease mechanisms, but in the rapid translation of these findings into a clinical context. The purpose of this review is to outline the current understanding of the EPC phenotypes and their relationship with risk factors for coronary disease. In addition, the potential problems of EPC dysfunction and its impact on percutaneous intervention will be appraised together with both pharmacological and stent based strategies to augment EPC -number and function.

Potential roles of erythropoietin in the management of anaemia and other complications diabetes

Erythropoietin (EPO) is a haematopoietic cytokine, mainly generated in the renal cortex, and its secretion and action is impaired in chronic kidney disease (CKD). Early renal damage in diabetes mellitus (DM) is usually not detected because diabetes-induced nephron hypertrophy maintains glomerular filtration rate (GFR) and an elevated plasma creatinine concentration is a relatively late manifestation of diabetic nephropathy. However, anaemia occurs more frequently in subjects with DM when compared with those with non-DM renal disease. While reduced production and a blunted response to EPO occurs in DM with early renal damage, other factors including chronic inflammation, autonomic neuropathy and iron deficiency are also important. Although recombinant human erythropoietin (rhEPO) has been an effective therapeutic agent in CKD anaemia, it appears to be more effective in patients with DM, even in earlier stages. Nevertheless, patients with DM are also more likely to be iron deficient, a barrier to effective rhEPO therapy. The effect of treatment on the reliability of haemoglobin A(1c) as an index of glycaemic control must be remembered. It is proposed that anaemia and its causes must be important components of care in subjects with early diabetic renal damage.

Heart disease and erythropoietin

An additional target for reducing infarct size, namely, attenuation of apoptosis, has recently emerged. Erythropoietin (Epo) exhibits properties that may attenuate this process and enhance neovascularization, thereby preserving jeopardized myocardium. Potentially adverse effects of Epo, including hypertension, thrombosis and possible exacerbation of occult neoplasms can likely be averted with analogues such as carbamylated and asialo Epo, which are devoid of erythropoietic effects, yet retain tissue-protective characteristics. With a single, but adequate dose of Epo administered early after the onset of acute myocardial infarction, coupled with therapy to induce reperfusion, tissue protection conferred by Epo and its analogues may facilitate the preservation of myocardium subjected to ischemic insults, thereby improving prognosis.

Vascular endothelial damage and repair in antineutrophil cytoplasmic antibody-associated vasculitis

OBJECTIVE

Antineutrophil cytoplasmic antibody-associated vasculitis (AAV) is characterized by necrotizing vessel wall inflammation, paralleled by the detachment of endothelial cells. The repair of such endothelial defects is crucial for the maintenance of regular structure and function of the injured vessels. Bone marrow-derived endothelial progenitor cells (EPCs) are thought to play a pivotal role in the regeneration of damaged endothelium. The aim of this study was to investigate whether EPCs are involved in vascular repair in AAV.

METHODS

We assessed disease activity, CD34+ hematopoietic progenitor cells (HPCs) using flow cytometry, EPCs using an in vitro assay, and circulating endothelial cells (CECs) by immunomagnetic isolation from the peripheral blood of 31 patients with active AAV at 1, 3, and 6 months after the initiation of immunosuppressive therapy.

RESULTS

In patients with untreated active disease, HPC and EPC numbers were comparable with those in healthy control subjects (n = 64). With the induction of remission, the number of HPCs and EPCs increased significantly, from a median of 1.5 cells/microl (range 0.0-7.0) to a median of 3.2 cells/microl (range 0.76-9.2) (P < 0.001) and from a median of 261 cells/high-power field (range 171-643) to a median of 470 cells/high-power field (range 168-996) (P < 0.021), respectively. In contrast, the initially elevated number of CECs decreased significantly (P < 0.001). We observed no correlation between the number of HPCs or EPCs and the leukocyte count, the thrombocyte count, or kidney function.

CONCLUSION

In patients with AAV, the numbers of circulating CD34+ HPCs and EPCs increased significantly after the institution of immunosuppressive therapy and disease remission. This finding points to a role of circulating CD34+ HPCs and EPCs in endothelial repair in vasculitis. Targeted stimulation of these cells might represent a new possibility of improving vascular healing in AAV.

Erythropoietin, progenitors, and repair

The erythropoietin-erythropoietin-receptor (EPO-EPO-R) system has recently been identified as an important cellular survival pathway. Its presence has also been demonstrated in the kidney and identified as a therapeutic target to prevent loss of renal function. Part of the protective effects may be related to the action of erythropoietin on endothelial function and expansion of endothelial progenitor cells. This paper reviews current evidence for involvement of these mechanisms in EPO-mediated renoprotection.

Role of erythropoietin in the brain

Multi-tissue erythropoietin receptor (EPO-R) expression provides for erythropoietin (EPO) activity beyond its known regulation of red blood cell production. This review highlights the role of EPO and EPO-R in brain development and neuroprotection. EPO-R brain expression includes neural progenitor cells (NPC), neurons, glial cells and endothelial cells. EPO is produced in brain in a hypoxia sensitive manner, stimulates NPC proliferation and differentiation, and neuron survival, and contributes to ischemic preconditioning. Mice lacking EPO or EPO-R exhibit increased neural cell apoptosis during development before embryonic death due to severe anemia. EPO administration provides neural protection in animal models of brain ischemia and trauma, reducing the extent of injury and damage. Intrinsic EPO production in brain and EPO stimulation of endothelial cells contribute to neuroprotection and these are of particular importance since only low levels of EPO appear to cross the blood-brain barrier when administered at high dose intravenously. The therapeutic potential of EPO for brain ischemia/trauma and neurodegenerative diseases has shown promise in early clinical trial and awaits further validation.

A New Role of Thrombopoietin Enhancing ex Vivo Expansion of Endothelial Precursor Cells Derived from AC133-positive Cells

We previously reported that CD31(bright) cells, which were sorted from cultured AC133(+) cells of adult peripheral blood cells, differentiated more efficiently into endothelial cells than CD31(+) cells or CD31(-) cells, suggesting that CD31(bright) cells may be endothelial precursor cells. In this study, we found that CD31(bright) cells have a strong ability to release cytokines. The mixture of vascular endothelial growth factor (VEGF), thrombopoietin (TPO), and stem cell factor stimulated ex vivo expansion of the total cell number from cultured AC133(+) cells of adult peripheral blood cells and cord blood cells, resulting in incrementation of the adhesion cells, in which endothelial nitric oxide synthase and kinase insert domain-containing receptor were positive. Moreover, the mixture of VEGF and TPO increased the CD31(bright) cell population when compared with VEGF alone or the mixture of VEGF and stem cell factor. These data suggest that TPO is an important growth factor that can promote endothelial precursor cells expansion ex vivo.

Neuroplasticity and cellular therapy in cerebral infarction

Stroke is the second to third most common cause of death in adults, and more than a third of people who survive a stroke will have severe disability. Therapeutic options currently centre on fibrinolytic treatment, but its limitations restrict use to a small proportion of patients. Although a wide range of neuroprotective substances has been effective in experimental models, they have repeatedly failed in clinical trials because of toxicity or loss of effectiveness. Recent strategies based on neuroplasticity and cellular therapy have shown significant efficacy in improving functional recovery in experimental models, although further study is still necessary to clarify how the brain responds to ischaemic damage and is able to reorganize itself in the long term. Although steps must still be taken to ensure the safety and feasibility of treatments based on neuroplasticity and cellular therapy, neurorepair strategies provide promising future therapeutic options for stroke.

Repeated Low-dose of Erythropoietin is Associated with Improved Left Ventricular Function in Rat Acute Myocardial Infarction Model

OBJECTIVE

To evaluate the potential protective affects of Epo on left ventricular (LV) function and remodeling after acute myocardial infarction (MI).

METHODS

Epo was injected into the peritoneum of male Wistar rats (250 g) during 6 weeks post induction of MI. Rats were divided into five groups: MI treated with single high dose (MT1, 5,000 U/kg, n=10), single high dose (5,000 U/kg) and repeated high doses (MTHi, 1,000 U/kg twice a week; n=8), or single high dose (5,000 U/kg) and repeated low doses (MTLo, 750 U/kg once a week, n=10), MI non-treated (MNT, n=10), sham (S, n=5). Echocardiography was performed 3.6+/-1.5 days and 43.7+/-2.3 days post MI. Collagen deposition and infarct size were measured on histological sections using computerized image analysis. Apoptosis was assessed by ApopTag staining.

RESULTS

Baseline fractional shortening (FS) was similar between groups. Six weeks after MI the FS of MTLo (26.9%) was significantly higher compared to MNT (17.8%), MT1 (19.5%) and MTH (22.3%) (p=0.01). However, remodeling indices (end diastolic and end systolic areas, LV circumference) did not improve in the Epo groups, and even worsened in the MTHi group. There was significantly less collagen staining in non-infarct areas in MT1 and MTHi groups compared to MNT and MTLo (0.38+/-0.3%, 0.49+/-0.34%, vs 0.89+/-0.41%, 0.95+/-0.33%, respectively, p<0.001). The number of ApopTag positive nucleus was significantly higher in the MNT group compared to the MT1, MTHi, MTLo groups (14.4+/-8, 7.6+/-4, 5.8+/-7, 4.8+/-5, respectively, p=0.01 for trend).

CONCLUSION

Repeated low doses of Epo after MI improved LV function, but the role of Epo on remodeling is not clear. It did not reduce left ventricular indices, but reduces fibrosis and apoptosis. High Epo doses reduced LV function and aggravated remodeling.

Erythropoietin and treatment of non-anemic conditions--cardiovascular protection

The well-established physiological function of erythropoietin (EPO) is the induction of erythropoiesis. A growing body of evidence indicates that EPO has tissue-protective effects and prevents tissue damage during ischemia and inflammation. Tissue protection after ischemia and injury has been found in the brain, heart, and kidney. It has been speculated that EPO has anti-apoptotic effects in cardiovascular cells. These novel effects of EPO seem to be independent of its erythropoietic activity. Unclear is the role of the known EPO receptor or whether other signaling pathways are involved; a novel EPO receptor might be involved in tissue protection by this hormone. This review article summarizes present knowledge of cardiovascular and renal protective effects of EPO and discusses possible underlying mechanisms.

Endothelial progenitor cells and cerebrovascular diseases

Identifying factors that may increase the risk of stroke and assessing if treatment of such conditions may lower that risk are important in the management of cerebrovascular disease. Tobacco smoking, poor diet, hypertension and hyperlipidemia remain the major risk factors, and treatment of these conditions has been shown to significantly reduce stroke. In recent years, research has shown that stem cells from a variety of sources can be used as a tool to study and prevent the events that lead to stroke. In this regard, a population of adult stem cells, called endothelial progenitor cells (EPCs), have been identified in peripheral blood and may play an important role in tissue vascularization and endothelium homeostasis in the adult. Most of the studies on EPCs have been carried out on patients with cardiovascular diseases; however, there is emerging evidence which suggests that the introduction or mobilization of EPCs can restore tissue vascularization even after cerebrovascular diseases (CVD), such as ischemic stroke or intracerebral haemorrhage. In this review, we discuss the present level of knowledge about the characteristics of EPCs, their possible therapeutic role in CVD and how they could alter clinical practice in the future.

Darbepoetin alfa protects the rat heart against infarction: dose-response, phase of action, and mechanisms

Erythropoietin is known to stimulate red cell production and has recently been shown to protect the heart against injury from ischemia/reperfusion. However, it is unknown whether darbepoetin alfa (Dpa), a long-acting analog of erythropoietin, can play a protective role against myocardial infarction. We assessed the potential protective role of Dpa in an in vivo rat model of myocardial ischemia/reperfusion and the underlying mechanisms. We found that a single intravenous Dpa treatment immediately before 30 minutes of regional ischemia reduced myocardial necrosis following 120 minutes of reperfusion in a dose-dependent manner. Optimal protection with Dpa against myocardial infarction was manifest at a dose of 2.5 microg/kg. Dpa conferred cardioprotection when administered after the onset of ischemia and at the start of reperfusion. Dpa (2.5 microg/kg) also reduced infarct size and Troponin I leakage 24 hours after reperfusion. Inhibition of p42/44 MAPK (PD98059), p38 MAPK (SB203580), mitochondrial ATP-dependent potassium (KATP) channels (5-HD), sarcolemmal KATP channels (HMR 1098), but not phosphatidylinositol-3 (PI3) kinase/Akt (Wortmannin and LY 294002) abolished Dpa-induced cardioprotection. Dpa confers immediate and sustained cardioprotection in rats, suggesting a potential therapeutic role of this long-acting erythropoietin analog for the treatment of acute myocardial infarction.

Granulocyte colony-stimulating factor has a negative effect on stroke outcome in a murine model

The administration of CD34-positive cells after stroke has been shown to have a beneficial effect on functional recovery by accelerating angiogenesis and neurogenesis in rodent models. Granulocyte colony-stimulating factor (G-CSF) is known to mobilize CD34-positive cells from bone marrow and has displayed neuroprotective properties after transient ischemic stress. This led us to investigate the effects of G-CSF administration after stroke in mouse. We utilized permanent ligation of the M1 distal portion of the left middle cerebral artery to develop a reproducible focal cerebral ischemia model in CB-17 mice. Animals treated with G-CSF displayed cortical atrophy and impaired behavioral function compared with controls. The negative effect of G-CSF on outcome was associated with G-CSF induction of an exaggerated inflammatory response, based on infiltration of the peri-infarction area with CD11b-positive and F4/80-positive cells. Although clinical trials with G-CSF have been started for the treatment of myocardial and limb ischemia, our results indicate that caution should be exercised in applying these results to cerebral ischemia.

Oxidant stress impairs in vivo reendothelialization capacity of endothelial progenitor cells from patients with type 2 diabetes mellitus: restoration by the peroxisome proliferator-activated receptor-gamma agonist rosiglitazone

BACKGROUND

Endothelial progenitor cells (EPCs) are thought to contribute to endothelial recovery after arterial injury. We therefore compared in vivo reendothelialization capacity of EPCs derived from patients with diabetes mellitus and healthy subjects. Moreover, we examined the effect of treatment with the peroxisome proliferator-activated receptor-gamma agonist rosiglitazone on oxidant stress, nitric oxide (NO) bioavailability, and the in vivo reendothelialization capacity of EPCs from diabetic individuals.

METHODS AND RESULTS

In vivo reendothelialization capacity of EPCs from diabetic patients (n=30) and healthy subjects (n=10) was examined in a nude mouse carotid injury model. Superoxide and NO production of EPCs was determined by electron spin resonance spectroscopy. Thirty patients with diabetes mellitus were randomized to 2 weeks of rosiglitazone (4 mg BID p.o.) or placebo treatment. In vivo reendothelialization capacity of EPCs derived from diabetic subjects was severely reduced compared with EPCs from healthy subjects (reendothelialized area: 8+/-3% versus 37+/-10%; P<0.001). EPCs from diabetic individuals had a substantially increased superoxide production and impaired NO bioavailability. Small-interfering RNA silencing of NAD(P)H oxidase subunit p47(phox) reduced superoxide production and restored NO bioavailability and in vivo reendothelialization capacity of EPCs from diabetic patients. Importantly, rosiglitazone therapy normalized NAD(P)H oxidase activity, restored NO bioavailability, and improved in vivo reendothelialization capacity of EPCs from diabetic patients (reendothelialized area: placebo versus rosiglitazone, 8+/-1% versus 38+/-5%; P<0.001).

CONCLUSIONS

In vivo reendothelialization capacity of EPCs derived from individuals with diabetes mellitus is severely impaired at least partially as a result of increased NAD(P)H oxidase-dependent superoxide production and subsequently reduced NO bioavailability. Rosiglitazone therapy reduces NAD(P)H oxidase activity and improves reendothelialization capacity of EPCs from diabetic individuals, representing a potential novel mechanism whereby peroxisome proliferator-activated receptor-gamma agonism promotes vascular repair.

Erythropoietin blockade inhibits the induction of tumor angiogenesis and progression

Background

The induction of tumor angiogenesis, a pathologic process critical for tumor progression, is mediated by multiple regulatory factors released by tumor and host cells. We investigated the role of the hematopoietic cytokine erythropoietin as an angiogenic factor that modulates tumor progression.

Methodology/Principal Findings

Fluorescently-labeled rodent mammary carcinoma cells were injected into dorsal skin-fold window chambers in mice, an angiogenesis model that allows direct, non-invasive, serial visualization and real-time assessment of tumor cells and neovascularization simultaneously using intravital microscopy and computerized image analysis during the initial stages of tumorigenesis. Erythropoietin or its antagonist proteins were co-injected with tumor cells into window chambers. In vivo growth of cells engineered to stably express a constitutively active erythropoietin receptor EPOR-R129C or the erythropoietin antagonist R103A-EPO were analyzed in window chambers and in the mammary fat pads of athymic nude mice. Co-injection of erythropoietin with tumor cells or expression of EPOR-R129C in tumor cells significantly stimulated tumor neovascularization and growth in window chambers. Co-injection of erythropoietin antagonist proteins (soluble EPOR or anti-EPO antibody) with tumor cells or stable expression of antagonist R103A-EPO protein secreted from tumor cells inhibited angiogenesis and impaired tumor growth. In orthotopic tumor xenograft studies, EPOR-R129C expression significantly promoted tumor growth associated with increased expression of Ki67 proliferation antigen, enhanced microvessel density, decreased tumor hypoxia, and increased phosphorylation of extracellular-regulated kinases ERK1/2. R103A-EPO antagonist expression in mammary carcinoma cells was associated with near-complete disruption of primary tumor formation in the mammary fat pad.

Conclusions/Significance

These data indicate that erythropoietin is an important angiogenic factor that regulates the induction of tumor cell-induced neovascularization and growth during the initial stages of tumorigenesis. The suppression of tumor angiogenesis and progression by erythropoietin blockade suggests that erythropoietin may constitute a potential target for the therapeutic modulation of angiogenesis in cancer.

Erythropoietin improves cardiac function through endothelial progenitor cell and vascular endothelial growth factor mediated neovascularization

AIMS

Erythropoietin (EPO) improves cardiac function and induces neovascularization in chronic heart failure (CHF), although the exact mechanism has not been elucidated. We studied the effects of EPO on homing and incorporation of endothelial progenitor cells (EPC) into the myocardial microvasculature and myocardial expression of angiogenic factors.

METHODS AND RESULTS

CHF was induced in rats by coronary artery ligation resulting in myocardial infarction (MI) after bone marrow had been replaced by human placental alkaline phosphatase (hPAP) transgenic cells. We studied the effects of darbepoetin alfa treatment (EPO, 40 microg/kg, every 3 weeks, starting 3 weeks after MI) on longitudinal changes in left ventricular (LV) function, circulating EPC, myocardial histology, and expression of vascular endothelial growth factor (VEGF) determined 9 weeks after MI. EPO prevented LV-dilatation and improved cardiac function (all P < 0.05), which was associated with 42% increased capillary growth (P < 0.01). EPO-induced mobilization of EPC from the bone marrow (P < 0.01), which resulted in a three-fold increased homing of EPC into the cardiac microvasculature. The percentage of the endothelium that consisted of bone marrow derived cells was significantly increased (3.9 +/- 0.5 vs. 11.4 +/- 1%, P < 0.001) comprising 30% of the newly formed capillaries. In addition, EPO treatment resulted in a 4.5-fold increased myocardial expression of VEGF, which correlated strongly with neovascularization (r = 0.67; P < 0.001). VEGF was equally expressed by endothelial cells of myocardial and bone marrow origin.

CONCLUSION

EPO-induced neovascularization in post-MI heart failure is mediated through a combination of EPC recruitment from the bone marrow and increased myocardial expression of VEGF.

Cell Therapy in Kidney Disease: Cautious Optimism … But Optimism Nonetheless

The recently discovered therapeutic potential of stem or progenitor cells has initiated development of novel treatments in a number of diseases—treatments that could not only improve patients’ quality of life, but also halt or even prevent disease progression. Hypertension; fluctuations in glycemia, electrolytes, nutrient levels, and circulating volume; and frequent infections and the associated inflammation all greatly impair the endothelium in patients undergoing peritoneal dialysis. As our understanding of the regulatory function of the endothelium advances, focus is increasingly being placed on endothelial repair in acute and chronic renal failure and after renal transplantation. The potential of progenitor cells to repair damaged endothelium and to reduce inflammation in patients with renal failure remains unexamined; however, a successful cell therapy could reduce morbidity and mortality in kidney disease.

Important contributions have been made in identifying progenitor cell populations in the kidney, and further investigations into the relationships of these cells with the pathophysiology of the disease are underway. As the kidney disease field prepares for the first human trials of progenitor cell therapies, we deemed it important to review representative original research, and to share our perspectives and lessons learned from clinical trials of progenitor cell–based therapies that have commenced in patients with cardiovascular disease.

Retinal and choroidal microangiopathies: therapeutic opportunities

Pathological angiogenesis in the retina and underlying choroid is a major cause of visual impairment in all age groups. The last decade has seen an explosion in the clinical availability of antiangiogenic compounds. Emphasis has been placed on inhibitors of the VEGF signaling pathway and considerable success has been achieved with aptamers and antibodies that bind VEGF. However, regression of neovascularization is rarely permanent and the regrowth of new vessels, often within a few months, requires multiple applications of drug. A number of antiangiogenic factors such as IGFBP3, SDF-1 blockers, PEDF, gamma-secretase, Delta-like ligand 4, and integrin antagonists have been identified, which act either indirectly on the VEGF system or independent of it. The importance of other candidates such as HIF-1alpha and protein kinase CK2, which act as "master" regulators of angiogenesis, offer realistic alternative targets for pharmacological intervention. The concept of combination therapy is rapidly gaining interest in the eye field and co-administration of two angiogenic agents (e.g., a CK2 inhibitor with a somatostatin analog, octreotide) are often significantly more effective at inhibiting retinal angiogenesis than either drug alone. The following review will discuss the current therapies available for aberrant ocular angiogenesis, consider new candidate targets for development of antiangiogenic compounds and emphasize the importance of combinatorial pharmacological agents in the treatment of such a dynamic cellular event as angiogenesis.

Erythropoietin-induced neurovascular protection, angiogenesis, and cerebral blood flow restoration after focal ischemia in mice

Restoration of local blood supply in the post-ischemic brain plays a critical role in tissue repair and functional recovery. The present investigation explored beneficial effects of recombinant human erythropoietin (rhEPO) on vascular endothelial cell survival, angiogenesis, and restoration of local cerebral blood flow (LCBF) after permanent focal cerebral ischemia in adult mice. Saline or rhEPO (5,000 U/kg, intraperitoneal) was administered 30 mins before ischemia and once daily after ischemic stroke. Immunohistochemistry showed an enhancing effect of rhEPO on expression of EPO receptor (EPOR) of endothelial cells in the penumbra region 3 to 21 days after the ischemic insult. The treatment with rhEPO decreased ischemia-induced cell death and infarct volume 3 days after stroke. Specifically, rhEPO reduced the number of terminal deoxynucleotidyl transferase biotin-dUPT nick end labeling- and caspase-3-positive endothelial cells in the penumbra region. Colocalization of the vessel marker glucose transporter-1 (Glut-1) and cell proliferation marker 5-bromo-2'-deoxyuridine indicated enhanced angiogenic activity in rhEPO-treated mice 7 to 21 days after stroke. Western blot showed upregulation of the expression of angiogenic factors Tie-2, Angiopoietin-2, and vascular endothelial growth factor in rhEPO-treated animals. Local cerebral blood flow was measured by laser scanning imaging 3 to 21 days after stroke. At 14 days, LCBF in the penumbra was recovered to preischemia levels in rhEPO-treated mice but not in control mice. Our data suggest that rhEPO treatment upregulates the EPOR level in vascular endothelial cells, confers neurovascular protection, and enhances angiogenesis. We further show a promoting effect of rhEPO on LCBF recovery in the ischemic brain. These rhEPO-induced effects may contribute to therapeutic benefits in the treatment of ischemic stroke.

Biologic properties of endothelial progenitor cells and their potential for cell therapy

Recent studies indicate that portions of ischemic and tumor neovasculature are derived by neovasculogenesis, whereby bone marrow (BM)-derived circulating endothelial progenitor cells (EPCs) home to sites of regenerative or malignant growth and contribute to blood vessel formation. Recent data from animal models suggest that a variety of cell types, including unfractionated BM mononuclear cells and those obtained by ex vivo expansion of human peripheral blood or enriched progenitors, can function as EPCs to promote tissue vasculogenesis, regeneration, and repair when introduced in vivo. The promising preclinical results have led to several human clinical trials using BM as a potential source of EPCs in cardiac repair as well as ongoing basic research on using EPCs in tissue engineering or as cell therapy to target tumor growth.

Estrogen induces endothelial progenitor cells proliferation and migration by estrogen receptors and PI3K-dependent pathways

Estrogen induces endothelial progenitor cells (EPCs) migration and proliferation, which may serve as a potential target for coronary artery disease, but the mechanisms are unclear. We hypothesized that estrogen receptors (ERs) and phosphatidylinositol 3-kinase (PI3K) signaling pathway, which represent particularly important roles of action for estrogen, may contribute to estrogen-induced EPCs migration and proliferation. Bone marrow mononuclear cells (MNCs) were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with growth factors as previously described. A total of 87.32+/-5.13% of adherent cells showed uptake of acetylated low-density lipoprotein and lectin binding. Immunostaining and fluorescence activated cell sorting confirmed the endothelial progenitor phenotype. RT-PCR, immunocytochemistry staining and Western blot demonstrated expression of ERs. Exposure to 17beta-estradiol significantly improved EPCs migration and proliferation. Those effects were blocked by pretreatment with the pharmacological PI3K blockers LY294002 (1 h, 10 micromol/L) and ICI-182780 (1 h, 10 micromol/L), a specific estrogen receptor antagonist, which show involvement of estrogen receptors and PI3K pathway. These results suggest that estrogen induces EPCs migration and proliferation via ERs and PI3K pathway which provided a novel insight and treatment strategy of vascular biology.

Early haemoglobin-independent increase of plasma erythropoietin levels in patients with acute myocardial infarction

AIMS

We studied plasma erythropoietin (EPO) levels and their relation with CD34(+)VEGFR-2(+) (mature and progenitor endothelial cells) and CD34(+) CD133(+)VEGFR-2(+), or CD34(+) CD117(+)VEGFR-2(+) (early/immature endothelial progenitors) cells in patients with acute myocardial infarction (AMI).

METHODS AND RESULTS

Fifty AMI patients undergoing percutaneous coronary intervention (PCI) within 6 h of symptom onset were enrolled. EPO, measured by ELISA, and cell subsets, by cytofluorimetric analysis, were evaluated before PCI, 24 h and 7 days afterwards. Forty-five healthy subjects (CTRLs) were studied. Plasma EPO levels were higher in AMI patients at admission, 24 h, and 7 days (P = 0.04, P = 0.0001, P = 0.001, respectively) than in CTRLs. No correlation was evidenced between EPO and haemoglobin (Hb) or haematocrit at admission or 24 h after AMI. Differently, both Hb and haematocrit inversely correlated with EPO at day 7 (P = 0.0016, P = 0.029, respectively). Plasma EPO levels correlated with CD34(+)CD133(+)VEGFR-2(+) cells at day 7 (P = 0.03).

CONCLUSION

AMI patients have increased plasma EPO levels until day 7. In the early phase, plasma EPO levels are Hb-independent; at day 7, an Hb-modulated increase of EPO correlates with the percentage of CD34(+)CD133(+)VEGFR-2(+) cells.

Erythropoietin, a hypoxia-regulated factor, elicits a pro-angiogenic program in human mesenchymal stem cells

OBJECTIVE

The ability of erythropoietin (EPO) to elicit a pro-angiogenic effect on human mesenchymal stem cells (hMSC) was tested. hMSC are currently under study as therapeutic delivery agents that target tumor vessels. Hypoxia favors the differentiation of hMSC towards a pro-angiogenic program. However, the classical angiogenic factors, vascular endothelial growth factor and basic fibroblast growth factor, are not fully capable of restoring this effect. The hypoxia-regulated factor, EPO, induces angiogenesis in endothelial cells. Here, EPO's pro-angiogenic effect on hMSC was analyzed.

METHODS

hMSC were tested for EPO receptor expression by western blot, immunofluorescence, and flow cytometry assays. Downstream receptor signaling components JAK and STAT were measured by standard assays. Pro-angiogenesis effects mediated by EPO treatment of hMSC were measured by proliferation, cytokine, or pro-angiogenesis factor secretion, metalloprotease activation, migration, invasion, wound healing, and tubule formation assays.

RESULTS

hMSC express the cognate EPO receptor and are capable of promoting angiogenesis following EPO treatment in all the angiogenesis assays tested. EPO-treated hMSC proliferate and secrete pro-angiogenesis factors more readily than untreated hMSC. EPO leads to increased hMSC chemotaxis, migration, and activation of matrix metalloprotease-2. This treatment causes greater recruitment of vessels as measured in an in vivo angiogenesis assay.

CONCLUSION

EPO is capable of eliciting a pro-angiogenesis program in hMSC that instigates secretion of angiogenic factors and the subsequent recruitment of endothelium. This study defines a novel mechanism for tumor cell recruitment of blood vessels that is important to consider in the design of stem cell-based therapies.

Endothelial-like Vascular Progenitor Cells (VPCs) from Allogeneic and Autologous Donors: Mobilization Features Distinct from Hematopoietic Progenitors

Endothelial-like progenitor cells circulate in the peripheral blood (PB) and can be enumerated using cell culture-based progenitor assays. These circulating vascular progenitor cells (VPCs) are implicated in new vessel formation and regenerative potential in several animal and human models of tissue injury. Given the emerging role of VPCs in regenerative processes and the limited information on the availability of such progenitor cells, we sought to determine baseline circulating VPC levels in healthy allogeneic donors and autologous hematopoietic transplant patients. VPC numbers were also measured in peripheral blood stem cell (PBSC) grafts from both graft types. Immunohistochemistry revealed that VPC clusters obtained under our culture conditions were CD45(+) and acquired endothelial features (CD31 and vascular endothelial-cadherin) in vitro upon angiogenic stimulation and gradually lost monocytic surface markers (CD14). Before PBSC mobilization, VPCs levels varied substantially in healthy donors and were markedly lower in patients with hematologic malignancies compared with healthy allogeneic donors with 27 +/- 15 versus 99 +/- 21 VPCs/mL (mean +/- SEM), respectively (P = .001). In patients undergoing stem cell mobilization, VPCs in the PB increased from 7 +/- 2 on day 0 to 51 +/- 9 by day 7 of mobilization (P = .05), representing a median fold increase of 8.9 (range, 3.0-29.8). Although autologous transplant patients underwent more intensive mobilization, VPCs were higher in allogeneic (7.2 +/- 1.4 x 10(3)/kg) than in autologous (2.6 +/- 1.5 x 10(3)/kg) mobilized PB grafts (P = .045). To identify predictors of VPC content, graft VPCs were compared with levels of CD34(+) cells, total colony forming unit (CFU), or granulocyte-macrophage colony forming unit (GM-CFU). None of these hematopoietic progenitors correlated with VPC numbers in PBSC grafts (P = NS). However, PB monocyte levels were highly correlated with circulating VPC levels (r = 0.71, P < .0001). Thus, our analysis identified significant variability in VPCs at baseline and in PBSC grafts from healthy donors. Nevertheless, these donors remain a better source of VPCs than do autologous transplant patients. Importantly, VPC mobilization occurs independently of hematopoietic mobilization. In view of the potential role of VPCs in recovery from transplant-related tissue injury, angiogenic mobilization strategies that complement hematopoietic mobilization will need to be specifically designed.

Endothelial progenitor cells in cardiovascular disorders

The important role of the vascular endothelium in cardiovascular health is increasingly recognized. However, mature endothelial cells possess limited regenerative capacity. There is therefore much interest in circulating endothelial progenitor cells (EPCs) among the scientific community, especially into their purported role in maintenance of endothelial integrity and function, as well as postnatal neovascularization. It has been suggested that these cells might not only be responsible for the continuous recovery of the endothelium after injury/damage, but also might take part in angiogenesis, giving the hope of new treatment opportunities. Indeed, there is accumulating evidence showing reduced availability and impaired EPC function in the presence of both cardiovascular disease and associated comorbid risk factors. Thus, many studies into the potential for use of EPCs in the clinical setting are being undertaken. The goal of this review article is to provide an overview of data relevant to the clinical role of EPCs and perspectives for treatment of cardiovascular disorders.

Human recombinant erythropoietin protects the striated muscle microcirculation of the dorsal skinfold from postischemic injury in mice

Erythropoietin (EPO) has been proposed as a novel cytoprotectant in ischemia-reperfusion (I/R) injury of the brain, heart, and kidney. However, whether EPO exerts its protection by prevention of postischemic microcirculatory deterioration is unknown. We have investigated the effect of EPO on I/R-induced microcirculatory dysfunctions. We used the mouse dorsal skinfold chamber preparation to study nutritive microcirculation and leukocyte-endothelial cell interaction in striated muscle of the dorsal skinfold by in vivo fluorescence microscopy before 3 h of ischemia and during 5 days of reperfusion. Animals were pretreated with EPO (5,000 U/kg body wt) 1 or 24 h before ischemia. Vehicle-treated I/R-injured animals served as controls. Additional animals underwent sham operation only or were pretreated with EPO but not subjected to I/R. I/R significantly (P < 0.05) reduced functional capillary density, increased microvascular permeability, and enhanced venular leukocyte-endothelial cell interaction during early reperfusion. These findings were associated with pronounced (P < 0.05) arteriolar constriction and diminution of blood flow during late reperfusion. Pretreatment with EPO induced EPO receptor and endothelial nitric oxide synthase expression at 6 h of reperfusion (P < 0.05). In parallel, EPO significantly (P < 0.05) reduced capillary perfusion failure and microvascular hyperpermeability during early reperfusion and arteriolar constriction and flow during late reperfusion. EPO pretreatment substantially (P < 0.05) diminished I/R-induced leukocytic inflammation by reducing the number of rolling and firmly adhering leukocytes in postcapillary venules. EPO applied 1 h before ischemia induced angiogenic budding and sprouting at 1 and 3 days of reperfusion and formation of new capillary networks at 5 days of reperfusion. Thus our study demonstrates for the first time that EPO effectively attenuates I/R injury by preserving nutritive perfusion, reducing leukocytic inflammation, and inducing new vessel formation.

Endothelial progenitor cells: a new target for the prevention of cardiovascular diseases

Endothelial progenitor cells (EPCs) are circulating precursor cells that have been implicated recently in vascular and cardiac regeneration. There is an ongoing discussion on the immunocytological definition of EPCs, based on various surface markers, and currently different cell types are included in the term 'EPC'. This review summarizes the mechanisms that influence function, survival, mobilization and differentiation of EPCs. Furthermore, there are several reports on the clinical use of EPCs for the treatment of cardiovascular diseases. We have focused specifically on the influence of physical activity on EPC function.

Important role of erythropoietin receptor to promote VEGF expression and angiogenesis in peripheral ischemia in mice

We have recently demonstrated that endogenous erythropoietin (Epo)/Epo receptor (EpoR) system plays an important protective role in hypoxia-induced pulmonary hypertension. However, it remains to be examined whether vascular EpoR system contributes to angiogenesis in response to ischemia. We examined angiogenesis in EpoR(-/-)-rescued mice that lack EpoR in most organs including cardiovascular system except erythroid-lineage cells. Two weeks after femoral artery ligation, blood flow recovery, activation of VEGF/VEGF receptor system, and mobilization of endothelial progenitor cells were all impaired in EpoR(-/-)-rescued mice as compared with wild-type (WT) mice. Bone marrow (BM) transplantation with WT-BM cells in EpoR(-/-)-rescued mice partially but significantly improved blood flow recovery after hindlimb ischemia. The extent of VEGF upregulation and the number of BM-derived cells in ischemic tissue were significantly less in EpoR(-/-)-rescued mice compared with WT mice even after BM reconstitution with WT-BM cells. Similarly, the recovery of blood flow was significantly impaired in recipient EpoR(-/-)-rescued mice that had been transplanted with WT-BM or EpoR(-/-)-rescued-BM as compared with recipient WT mice. Furthermore, the Matrigel implantation assay and aortic ring assay showed that microvessel growth in vitro was significantly reduced in EpoR(-/-)-rescued mice as compared with WT mice. These results indicate that vascular EpoR system also plays an important role in angiogenesis in response to hindlimb ischemia through upregulation of VEGF/VEGF receptor system, both directly by enhancing neovascularization and indirectly by recruiting endothelial progenitor cells and BM-derived proangiogenic cells.

Functional and Pharmacokinetic Outcomes after a Single Intravenous Infusion of Recombinant Human Erythropoietin in Patients with Malignant Extradural Spinal Cord Compression

AIMS

To determine the cerebrospinal fluid concentrations and the functional and pain outcomes after a single intravenous infusion of erythropoietin at the start of a standard radiotherapy and steroid protocol.

MATERIALS AND METHODS

Ten paraparetic patients with malignant extradural spinal cord compression who were eligible for radiotherapy, lumbar puncture and intravenous epoetin alpha were enrolled. The patients received epoetin alpha 1500 IU/kg intravenously over 30 min followed by a standardised dexamethasone and radiotherapy protocol. A lumbar puncture and venipuncture were carried out 24-30 h after the epoetin alpha infusion. The patients were followed closely at defined intervals.

RESULTS

Erythropoietin was detectable in the cerebrospinal fluid in all eight patients sampled (median 92.5 mIU/ml, range 17.8-214.0 mIU/ml). Before treatment, eight patients were non-ambulatory and two patients were ambulatory with assistance. After treatment, eight (80%, 95% confidence interval [CI] 44-97%) improved at least one functional class and recovered or maintained ambulation. Five of seven patients (71%; 95% CI 29-96%) with objective sensory deficits and one of seven (14%; 95% CI 0-58%) catheter-dependent patients recovered. Overall, 78% (95% CI 40-97%) had a pain response.

CONCLUSIONS

After an intravenous infusion of epoetin alpha, radiotherapy and steroids, high concentrations of erythropoietin were detectable in the cerebrospinal fluid. Patients with malignant extradural spinal cord compression showed encouraging improvements in neurological function and pain.

Erythropoietin after a century of research: younger than ever

In the light of the enthusiasm regarding the use of recombinant human erythropoietin (Epo) and its analogues for treatment of the anaemias of chronic renal failure and malignancies it is worth remembering that today's success has been based on a century of laborious research. The concept of the humoral regulation of haematopoiesis was first formulated in 1906. The term 'erythropoietin' for the erythropoiesis-stimulating hormone was introduced in 1948. Native human Epo was isolated in 1977 and its gene cloned in 1985. During the last 15 yr, major progress has been made in identifying the molecules controlling Epo gene expression, primarily the hypoxia-inducible transcription factors (HIF) that are regulated by specific O2 and oxoglutarate requiring Fe2+-containing dioxygenases. With respect to the action of Epo, its dimeric receptor (Epo-R) has been characterised and shown to signal through protein kinases, anti-apoptotic proteins and transcription factors. The demonstration of Epo-R in non-haematopoietic tissues indicates that Epo is a pleiotropic viability and growth factor. The neuroprotective and cardioprotective potentials of Epo are reviewed with a focus on clinical research. In addition, studies utilising the Epo derivatives with prolonged half-life, peptidic and non-peptidic Epo mimetics, orally active drugs stimulating endogenous Epo production and Epo gene transfer are reviewed.

End-stage renal disease causes an imbalance between endothelial and smooth muscle progenitor cells

Patients with end-stage renal disease (ESRD) on hemodialysis have an increased risk of cardiovascular disease (CVD). Circulating endothelial progenitor cells (EPC) contribute to vascular regeneration and repair, thereby protecting against CVD. However, circulating smooth muscle progenitor cells (SPC) may contribute to adverse vascular remodeling. We hypothesized that an imbalance occurs between EPC and SPC in ESRD patients and sampled progenitor cells from 45 ESRD patients receiving regular treatment. Our study is the first to show reduced numbers of CD34+KDR+ hematopoietic stem cell (HSC)-derived EPC (type I EPC). Furthermore, monocyte-derived EPC cultured from mononuclear cells (type II EPC) were reduced in number and had a reduced capacity to stimulate endothelial cell angiogenesis. In contrast, SPC outgrowth was unaffected. In vitro incubation with uremic serum impaired type II EPC outgrowth from healthy donor mononuclear cells and did not influence SPC outgrowth. The hemodialysis procedure itself induced HSC apoptosis and caused an acute depletion of circulating EPC. Taken together, the decreased number and impaired function of EPC are compatible with impaired endogenous vascular repair in hemodialysis patients, whereas the unaffected SPC numbers suggest that the potential of progenitor cells to contribute to adverse remodeling is retained. This EPC-SPC imbalance may contribute to the acceleration of CVD in ESRD patients and could offer novel therapeutic targets.

Organ protection by hypoxia and hypoxia-inducible factors

Since the first description of a protective effect of hypoxic preconditioning in the heart, the principle of reducing tissue injury in response to ischemia by prior exposure to hypoxia was confirmed in a number of cells and organs. However, despite impressive preclinical results, hypoxic preconditioning has so far failed to reach clinical application. Nevertheless, it remains of significant interest to induce genes that are normally activated during hypoxia and ischemia as part of an endogenous escape mechanism prior to or during the early phase of an ischemic insult. This approach has recently been greatly facilitated by the identification of hypoxia-inducible factors (HIFs), transcription factors that operate as a master switch in the cellular response to hypoxia. Far more than 100 target genes are regulated by HIF, including genes such as erythropoietin and hemoxygenase-1, which have been shown to be tissue-protective. The identification of small molecule inhibitors of the oxygen-sensing HIF-prolyl hydroxlases now offers the possibility to mimic the hypoxic response by pharmacological stabilization of HIF in order to achieve organ protection. Oxygen-independent activation of HIF is therefore a promising therapeutic strategy for the prevention of organ injury and failure.

Delayed erythropoietin therapy reduces post-MI cardiac remodeling only at a dose that mobilizes endothelial progenitor cells

We examined the cardiac effects of chronic erythropoietin (EPO) therapy initiated 7 days after myocardial infarction (MI) in rats. A single high dose of EPO has been shown to reduce infarct size by preventing apoptosis when injected immediately after myocardial ischemia. The proangiogenic potential of EPO has also been reported, but the effects of chronic treatment with standard doses after MI are unknown. In this study, rats underwent coronary occlusion followed by reperfusion or a sham procedure. Infarcted rats were assigned to one of three treatment groups: 1) 0.75 μg/kg darbepoetin (MI+darb 0.75, n = 12); 2) 1.5 μg/kg darbepoetin (MI+darb 1.5, n = 12); 3) vehicle (MI+PBS, n = 16), once a week from day 7 postsurgery. Sham rats received the vehicle alone ( n = 10). After 8 wk of treatment, the animals underwent echocardiography, left ventricular pressure-volume measurements, and peripheral blood endothelial progenitor cell (EPC) counting. MI size and capillary density in the border zone and the area at risk (AAR) were measured postmortem. The AAR was similar in the three MI groups. Compared with MI+PBS, the MI+darb 1.5 group showed a reduction in the MI-to-AAR ratio (20.8% vs. 38.7%; P < 0.05), as well as significantly reduced left ventricle dilatation and improved cardiac function. This reduction in post-MI remodeling was accompanied by increased capillary density ( P < 0.05) and by a higher number of EPC ( P < 0.05). Both darbepoetin doses increased the hematocrit, whereas MI+darb 0.75 did not increase EPC numbers or capillary density and had no functional effect. We found that chronic EPO treatment reduces MI size and improves cardiac function only at a dose that induces EPC mobilization in blood and that increases capillary density in the infarct border zone.

Expression and function of erythropoietin receptors in tumors

Safety concerns surrounding the use of recombinant human erythropoietin (Epo) to treat anemia in cancer patients were raised after 2 recent clinical studies reported a worse survival outcome in patients who received epoetin alpha or epoetin beta compared with patients who received placebo. Although those findings contrasted with previous clinical studies, which demonstrated no difference in survival for cancer patients who received erythropoiesis-stimulating agents (ESAs), some investigators have suggested a potential role for ESAs in promoting tumor growth through 1) stimulation of Epo receptors (EpoR) expressed in tumors, 2) stimulation and formation of tumor vessels, and/or 3) enhanced tumor oxygenation. The first and second hypotheses appeared to be supported by some EpoR expression and ESA in vitro studies. However, these conclusions have been challenged because of poor specificity of EpoR-detection methodologies, conflicting data from different groups, and the lack of correlation between in vitro data and in vivo findings in animal tumor models. For this report, the authors reviewed the biology of EpoR in erythropoiesis and compared and contrasted the reported findings on the role of ESAs and EpoR in tumors.

Progenitor cells for cardiac repair

Repair of diseased or injured myocardium by cell-based therapies is likely to require a multi-pronged approach. New myocytes will need to be generated, integrated with existing myocardial tissue, and perfused with a newly acquired vascular system. There are many potential avenues to achieve this goal, and optimizing repair is likely to require a synthetic therapeutic approach. In this review, we discuss several issues to be considered in cell-based cardiac repair, some progress which has been made toward this goal, and future directions.

EPO: renoprotection beyond anemia correction

Until recently the major physiological function of erythropoietin (EPO) was thought to be the induction of erythropoiesis. However, a growing body of evidence indicates that EPO has tissue-protective properties and prevents ischemia induced tissue damage in several organs including the kidney. A pivotal intracellular pathway mediating the beneficial effects of EPO is the activation of Akt, i.e. serine/threonine protein kinase B. As a result, Akt phosphorylates the proapoptotic factor Bad, which in turn causes inhibition of programmed cell death (apoptosis). In the present article we review data on the non-hematological effects of recombinant human EPO (rHuEPO) in different experimental settings of acute and chronic kidney injury, and discuss clinical renoprotective strategies with rHuEPO or analogues substances that are not related to anemia correction.

Protective Effects of Erythropoietin in Cardiac Ischemia

Erythropoietin (EPO) is a hypoxia-induced hormone produced in the kidneys that stimulates hematopoiesis in the bone marrow. However, recent studies have also shown important nonhematopoietic effects of EPO. A functional EPO receptor is found in the cardiovascular system, including endothelial cells and cardiomyocytes. In animal studies, treatment with EPO during ischemia/reperfusion in the heart has been shown to limit the infarct size and the extent of apoptosis. In the longer term, EPO may promote ischemia-induced neovascularization, either by stimulating endothelial cells in situ or by mobilizing endothelial progenitor cells from bone marrow. The effects of EPO in the ischemic heart support the concept of EPO as a pleiotropic, tissue-protective agent for other organs expressing the EPO receptor. We recently performed a first randomized clinical study showing the safety and feasibility of EPO administration in patients with acute myocardial infarction. Future clinical studies are warranted to translate the beneficial effects of EPO from basic experiments to cardiac patients.

Kidney transplantation substantially improves endothelial progenitor cell dysfunction in patients with end-stage renal disease

Endothelial progenitor cells (EPC) are involved in endothelial repair and maintenance. Dysfunction of EPC may contribute to accelerated arteriosclerosis in chronic kidney disease. Kidney transplantation (KTx) improves both survival and endothelial function of dialysis patients. In a prospective study, we tested to which extent KTx changes EPC biology. We studied number and function (migratory activity, adhesion to extracellular matrix proteins and to mature endothelial cells [EC]) of EPC in 20 patients during dialysis and 3, 6, 9 and 12 months after KTx. Twenty-two healthy volunteers served as matched controls. Circulating precursor populations were measured by flow cytometric analysis. Cytokines relevant for EPC mobilization were monitored. Compared to the dialysis state, KTx increased the migration of EPC to approximately 2-fold. Adhesion to fibronectin and to collagen type IV was significantly increased after KTx. An improved adhesion rate of EPC to mature EC was observed. The number of EPC decreased. The amount of precursor populations showed no difference compared to the pretransplant state. Our study shows an improved function of EPC after KTx. This finding indicates an improved potential for endothelial repair which in turn may contribute to enhanced endothelial function and reduced cardiovascular morbidity after KTx.

Potential role of endothelial progenitor cells in the pathophysiology of heart failure: clinical implications and perspectives

Endothelial dysfunction is thought to play a major role in the development and clinical complications of heart failure. Endothelial progenitor cells (EPCs) have been shown to provide an endogenous repair mechanism to counteract detrimental risk factor-induced effects and replace dysfunctional endothelium. The number and in vitro function of EPCs is altered in patients with heart failure, as a result of its pathophysiological mechanisms. EPCs could represent a substitutional marker to guide preventive or therapeutic interventions in this disease. Enhancing the number and functional capacity of EPCs with targeted interventions may elicit functional improvement in individuals with heart failure. However, the exact role of EPCs in heart failure and their potential therapeutic implications still remain to be elucidated.

Serum vascular endothelial growth factor in cyanotic congenital heart disease functionally contributes to endothelial cell kinetics in vitro

BACKGROUND

Remarkable amounts of neovascularization develop in patients with cyanotic congenital heart disease who have low pulmonary blood flow and systemic cyanosis, but the factors functionally responsible for angiogenesis in cyanotic congenital heart disease have not been determined.

METHODS AND RESULTS

To investigate the functional angiogenic molecules in serum from these patients, serum angiogenic activity was studied in 21 patients (systemic oxygen saturation: 82+/-1.9%) and in 17 healthy controls. Patient serum was more active in stimulating the tube formation of human umbilical vein endothelial cells (HUVECs) into capillary-like structures than control serum (150% vs 104% of internal control; p<0.001). This increased serum angiogenic activity normalized after total cardiac repair (p<0.001). The migration activity of HUVECs was also accelerated in patient serum (p=0.007). To identify the molecules in patient serum affecting tube formation of HUVECs, we examined the effects of an inhibitor or a neutralizing antibody against various angiogenic molecules on in vitro angiogenesis. Both the soluble vascular endothelial growth factor (VEGF) receptor 1 and the VEGF receptor 2 tyrosine kinase inhibitor SU5416 reduced the basal serum angiogenic activity of patients and this was reversed by a supplement of recombinant human VEGF.

CONCLUSION

Our results indicate that serum VEGF functionally contributes to vascular endothelial cell kinetics in patients with cyanotic congenital heart disease.