Erythropoietin is a potent physiologic stimulus for endothelial progenitor cell mobilization

The role of obesity and its bioclinical correlates in the progression of chronic kidney disease

In spite of a progressive fall in the incidence of traditional risk factors of cardiovascular morbidity (cigarette smoking, high blood pressure, and hyperlipidemia), there is an upward trend in the prevalence of obesity and chronic kidney disease (CKD). Furthermore, there is a strong correlation between body mass indices and the relative risk of progression of CKD. The close biophysiological interaction between obesity and CKD is evident by a similar occurrence of comorbidities including insulin resistance, hyperlipidermia, endothelial dysfunction, and sleep disorders. Truncal obesity is a primary component of metabolic syndrome; unlike peripheral fat, the visceral adipocytes are more resistant to insulin. In addition, lipolysis results in a release of free fatty acid and TG, whereas hypertriglycedemia is potentiated by uremic activation of fatty acid synthase. Hypertriglycedemia and low HDL cholesterol increase the relative risk of progression of CKD. Furthermore, endothelial inflammation and premature atherosclerosis are promoted by hyperhomocysteinemia and oxidation of LDL, both of which are commonly observed in CKD and obesity. Predominance of oxidative stress in both obesity and azotemia stimulate synthesis of angiotensin II, which in turn increases TGF-B and plasminogen activator inhibitor-1, thereby propagating glomerular fibrosis. Furthermore, local synthesis of angiotensinogen by adipocytes, leptin activation of sympathetic nervous system, and hyperinsulinemia contribute to the development of hypertension in obesity and CKD. In addition, increased renal tubular expression of Na-K-ATPase and a blunted response to natiuretic hormones in obesity promote salt and water retention. Glomerular hyperfiltration from systemic volume load and hypertension results in mesangial cellular proliferation and progressive renal fibrosis. In addition, maternal nutritional deprivation increases the incidence of obesity, hypertension, and diabetes in adulthood. Reduced fetal protein synthesis contributes to oxidative glomerular injury and impairment of renal morphogenesis. Thus, kidneys are poorly equipped to handle physiologic stress that may result from the rapid body growth and programmed metabolic dysfunction later in life. Finally, in order to minimize morbidity of obesity-related kidney disease, preventive strategy must include optimal maternal health care, promotion of healthy nutrition and routine physical exercise, and early detection of CKD.

Stem cells for repair of the heart

PURPOSE OF REVIEW

Stem cell therapy for treatment of cardiac disease has shown therapeutic potential.

RECENT FINDINGS

A number of stem and progenitor populations have been identified for potential use in cardiac repair. Each possesses a unique potency that justifies consideration for use. Autologous, unfractionated bone marrow cells or skeletal myoblasts were used in early clinical trails to evaluate reparative effects on recent or record infarcts. In each case, evidence of limited improvement in cardiac function was obtained. Myoblast grafts were unexpectedly correlated with arrhythmias, thereby identifying a safety issue. The small number of patients and the lack of randomized control groups preclude conclusions regarding efficacy. Randomized controlled, intermediate-sized, double-blind clinical trials must be undertaken to this end.

SUMMARY

Cellular therapy may be useful in the treatment of cardiac disease in adults. Appropriate adaptations to meet unique requirements for treatment of pediatric cardiovascular disease may be required. Bone marrow and skeletal myoblasts do not promote true tissue regeneration in spite of observed functional improvement. Trials using cells possessing true potential for (trans)differentiation may elucidate the potential and value of this therapy as a reparative modality. Development of optimal strategies for targeted delivery consistent with pathobiology is of exception clinical relevance.

Therapeutic angiogenesis by ex vivo expanded erythroid progenitor cells

Recent reports have demonstrated that erythroid progenitor cells contain and secrete various angiogenic cytokines. Here, the impact of erythroid colony-forming cell (ECFC) implantation on therapeutic angiogenesis was investigated in murine models of hindlimb ischemia. During the in vitro differentiation, vascular endothelial growth factor (VEGF) secretion by ECFCs was observed from day 3 (burst-forming unit erythroid cells) to day 10 (erythroblasts). ECFCs from day 5 to day 7 (colony-forming unit erythroid cells) showed the highest VEGF productivity, and day 6 ECFCs were used for the experiments. ECFCs contained larger amounts of VEGF and fibroblast growth factor-2 (FGF-2) than peripheral blood mononuclear cells (PBMNCs). In tubule formation assays with human umbilical vein endothelial cells, ECFCs stimulated 1.5-fold more capillary growth than PBMNCs, and this effect was suppressed by antibodies against VEGF and FGF-2. Using an immunodeficient hindlimb ischemia model and laser-Doppler imaging, we evaluated the limb salvage rate and blood perfusion after intramuscular implantation of ECFCs. ECFC implantation increased both the salvage rate (38% vs. 0%, P < 0.05) and the blood perfusion (82.8% vs. 65.6%, P < 0.01). In addition, ECFCs implantation also significantly increased capillaries with recruitment of vascular smooth muscle cells and the capillary density was 1.6-fold higher than in the control group. Continuous production of human VEGF from ECFCs in the skeletal muscle was confirmed at least 7 days after the implantation. Implantation of ECFCs promoted angiogenesis in ischemic limbs by supplying angiogenic cytokines (VEGF and FGF-2), suggesting a possible novel strategy for therapeutic angiogenesis.

Biology of bone marrow-derived endothelial cell precursors

Over the past decade, the old idea that the bone marrow contains endothelial cell precursors has become an area of renewed interest. While some still believe that there are no endothelial precursors in the blood, even among those who do, there is no consensus as to what they are or what they do. In this review, we describe the problems in identifying endothelial cells and conclude that expression of endothelial nitric oxide synthase may be the most reliable antigenic indicator of the phenotype. The evidence for two different classes of endothelial precursors is also presented. We suggest that, though there is no single endothelial cell precursor, we may be able to use these phenotypic variations to our advantage in better understanding their biology. We also discuss how a variety of genetic, epigenetic, and methodological differences can account for the seemingly contradictory findings on the physiological relevance of bone marrow-derived precursors in normal vascular maintenance and in response to injury. Data on the impact of tumor type and location on the contribution of bone marrow-derived cells to the tumor vasculature are also presented. These data provide hope that we may ultimately be able to predict those tumors in which bone marrow-derived cells will have a significant contribution and design therapies accordingly. Finally, factors that regulate bone marrow cell recruitment to and function in the endothelium are beginning to be identified, and several of these, including stromal derived factor 1, monocyte chemoattractant factor-1, and vascular endothelial growth factor are discussed.

Endothelial progenitor cells: biology and therapeutic potential in hypertension

PURPOSE OF REVIEW

In this review, we summarize some of the recent advances in our understanding of the biology of endothelial progenitor cells, and discuss the potential relevance of these progenitor cells for endothelial function and associated microvascular abnormalities that can form the structural basis of essential hypertension.

RECENT FINDINGS

Both in experimental models of hypertension and in patients with hypertension, the function of endothelial progenitor cells is impaired. Also, some antihypertensive drugs that have been associated with reversal of endothelial function and microvascular rarefaction appear to correct endothelial progenitor cell dysfunction.

SUMMARY

While information on endothelial progenitor biology is still limited in patients with hypertension in comparison with, for example, patients with coronary artery disease, it is a topic that warrants the attention of researchers in the hypertension field, as it may have important implications for the development of organ damage, and potentially could be linked to the pathogenesis of hypertension itself.

Tissue engineering of vascular conduits

BACKGROUND

Autologous conduits are not available in up to 40 per cent of patients with arteriopathy who require coronary or lower limb revascularization, and access sites for renal dialysis may eventually become exhausted. Synthetic prostheses achieve a poor patency rate in small-calibre anastomoses. This review examines how vascular tissue engineering may be used to address these issues.

METHODS

A Medline search was performed, using the keywords "vascular tissue engineering", "small diameter vascular conduit", "vascular cell biology", "biomechanics", "cell seeding" and "graft endothelialization". Key references were hand-searched for relevant papers.

RESULTS AND CONCLUSION

In vitro and in vivo approaches are currently being used for guided cell repopulation of both biological and synthetic scaffolds. The major clinical problem has been extended culture time (approximately 6 weeks), which precludes their use in the acute setting. However, recent advances have led not only to improved patency rates for prostheses, but also to a potential reduction in culture time. In addition, increased mobilization of endothelial progenitor cells in the presence of ischaemic tissue may increase the autologous cell yield for scaffold reseeding with further reduction in culture time.

Essential role of ICAM-1/CD18 in mediating EPC recruitment, angiogenesis, and repair to the infarcted myocardium

Bone marrow-derived endothelial progenitor cells (EPCs) have the ability to migrate to ischemic organs. However, the signals that mediate trafficking and recruitment of these cells are not well understood. Using a functional genomics strategy, we determined the genes that were upregulated in the ischemic myocardium and might be involved in EPC recruitment. Among them, CD18 and its ligand ICAM-1 are particularly intriguing because CD18 and its heterodimer binding chains CD11a and CD11b were correspondingly expressed in ex vivo-expanded EPCs isolated from rat and murine bone marrows. To further verify the functional role of CD18 in mediating EPC recruitment and repair to the infarcted myocardium, we used neutralizing antibody to block CD18. Blockade of CD18 in EPCs significantly inhibited their attachment capacity in vitro and reduced their recruitment to the ischemic myocardium in vivo by 95%. Moreover, mice receiving EPCs that were treated with control isotype IgG exhibited significantly increased capillary density in the infarct border zone, reduced cardiac dilatation, ventricular wall thinning, and fibrosis when compared with myocardial infarction mice receiving PBS and CD18 blockade reversed the EPC-mediated improvements to the infarcted heart. Thus, our results suggest an essential role of CD18 in mediating EPC recruitment and the subsequent functional effects on the infarcted heart.

Erythropoietin Enhances Neovascularization of Ischemic Myocardium and Improves Left Ventricular Dysfunction After Myocardial Infarction in Dogs

OBJECTIVES

We investigated the effects of erythropoietin (EPO) on neovascularization and cardiac function after myocardial infarction (MI).

BACKGROUND

Erythropoietin exerts antiapoptotic effects and mobilizes endothelial progenitor cells (EPCs).

METHODS

We intravenously administered EPO (1,000 IU/kg) immediately [EPO(0) group], 6 h [EPO(6h) group], or 1 week [EPO(1wk) group] after the permanent ligation of the coronary artery in dogs. Control animals received saline immediately after the ligation.

RESULTS

The infarct size 6 h after MI was significantly smaller in the EPO(0) group than in the control group (61.5 +/- 6.0% vs. 22.9 +/- 2.2%). One week after MI, the circulating CD34-positive mononuclear cell numbers in both the EPO(0) and the EPO(6h) groups were significantly higher than in the control group. In the ischemic region, the capillary density and myocardial blood flow 4 weeks after MI was significantly higher in both the EPO(0) and the EPO(6h) groups than in the control group. Four weeks after MI, left ventricular (LV) ejection fraction in the EPO(6h) (48.6 +/- 1.9%) group was significantly higher than that in either the control (41.9 +/- 0.9%) or the EPO(1wk) (42.6 +/- 1.2%) group but significantly lower than that in the EPO(0) group (56.1 +/- 2.3%). The LV end-diastolic pressure 4 weeks after MI in both the EPO(0) and the EPO(6h) groups was significantly lower than either the control or the EPO(1wk) group. Hematologic parameters did not differ among the groups.

CONCLUSIONS

In addition to its acute infarct size-limiting effect, EPO enhances neovascularization, likely via EPC mobilization, and improves cardiac dysfunction in the chronic phase, although it has time-window limitations.

Endothelial progenitor cells: from bench to bedside

Strong evidence suggests that bone marrow-derived cells play a role in physiological and pathological blood vessel growth in the adult, both by augmenting angiogenesis through the secretion of angiogenic growth factors and by providing a rich source of progenitor cells that can differentiate into mature vascular endothelial cells. This is a true paradigm shift, since adult neovascularization processes were thought to be limited to angiogenesis. The cells that are critical to postnatal blood vessel growth – endothelial progenitor cells – may be analogous to the embryonic angioblast, in that they can circulate, proliferate and participate in the development of vascular networks by differentiating in situ, probably via the formation of cell clusters into mature endothelial cells. Therefore, initial reports have seen analogs to the process of vasculogenesis in the embryo, where the de novo synthesis of vessels occurs through the formation of blood island-like clusters, which subsequently connect and eventually form systemic vasculature. Recent work implicates precursors of endothelial cells in such processes as myocardial ischemia and infarction, limb ischemia, wound healing, atherosclerosis, endogenous endothelial repair and tumor vascularization. These new insights into the vascular biology of endothelial regeneration and repair led to the development of new cell therapeutic strategies to enhance adult neovascularization and re-endothelialization in ischemic cardiovascular diseases.

Angiogenic murine endothelial progenitor cells are derived from a myeloid bone marrow fraction and can be identified by endothelial NO synthase expression

OBJECTIVE

Endothelial progenitor cells (EPCs) contribute to postnatal neovascularization and are therefore of great interest for autologous cell therapies to treat ischemic vascular disease. However, the origin and functional properties of these EPCs are still in debate.

METHODS AND RESULTS

Here, ex vivo expanded murine EPCs were characterized in terms of phenotype, lineage potential, differentiation from bone marrow (BM) precursors, and their functional properties using endothelial NO synthase (eNOS)-green fluorescent protein transgenic mice. Despite high phenotypic overlap with macrophages and dendritic cells, EPCs displayed unique eNOS expression, endothelial lineage potential in colony assays, and angiogenic characteristics, but also immunologic properties such as interleukin-12p70 production and low levels of T-cell stimulation. The majority of EPCs developed from an immature, CD31(+)Ly6C+ myeloid progenitor fraction in the BM. Addition of myeloid growth factors such as macrophage-colony-stimulating factor (M-CSF) and granulocyte/macrophage (GM)-CSF stimulated the expansion of spleen-derived EPCs but not BM-derived EPCs.

CONCLUSIONS

The close relationship between EPCs and other myeloid lineages may add to the complexity of using them in cell therapy. Our mouse model could be a highly useful tool to characterize EPCs functionally and phenotypically, to explore the origin and optimize the isolation of EPC fractions for therapeutic neovascularization.

Sestamibi single photon emission computed tomography immediately after primary percutaneous coronary intervention identifies patients at risk for large infarcts

BACKGROUND

Primary percutaneous coronary intervention (PCI) for ST-elevation myocardial infarction results in TIMI 3 flow in most patients. However, despite TIMI 3 flow, some patients do not achieve adequate tissue perfusion and have large infarctions. Techniques that, in the acute setting, could identify these patients at increased risk would potentially enable specific interventions to enhance perfusion. The object of the present study was to test whether corrected TIMI frame count (CTFC), myocardial blush grade (MBG), ST-segment resolution, and myocardial perfusion imaging (MPI) can identify those patients who, despite successful treatment with primary PCI for ST-elevation myocardial infarction, are at risk for large infarcts.

METHODS

In 61 patients with TIMI 3 flow after primary PCI, CTFC, MBG, ST-segment resolution, and quantitative MPI by technetium Tc 99m sestamibi single photon emission computed tomography were estimated immediately after primary PCI. Infarct size was assessed by peak lactate dehydrogenase (LDH) and by MPI after 3 months.

RESULTS

Infarct size by MPI was 12% (4, 23), and peak LDH was 1410 U/L (870, 2220); these measures correlated (rho = 0.80, P < .001). The acute perfusion defect predicted infarct size using either method (MPI rho = 0.88, P < .001; LDH rho = 0.77, P < .001); ST-segment residual correlated weakly to infarct size, whereas CTFC and MBG did not. In multivariate analysis, the acute perfusion defect was the only significant predictor of infarct size.

CONCLUSION

Myocardial perfusion imaging performed immediately after successful PCI can identify patients at increased risk for large infarcts due to impaired tissue perfusion. Acute MPI might serve as a tool for early identification of patients, who, despite epicardial TIMI 3 flow, have inadequate tissue level perfusion.

Bone marrow mononuclear cells are recruited to the sites of VEGF-induced neovascularization but are not incorporated into the newly formed vessels

Vascular endothelial growth factor (VEGF) is a key regulator of blood vessel formation during both vasculogenesis and angiogenesis. The prolonged expression of VEGF in the normoperfused skeletal muscles of adult rodents after gene transfer using AAV vectors induces the formation of a large set of new capillaries and small arteries. Notably, this process is accompanied by the massive infiltration by mononuclear cells. This observation raises the possibility that these cells might represent circulating progenitors that are eventually incorporated in the newly formed vessels. Here we explore this possibility by exploiting 4 different experimental models based on (a) the transplantation of male bone marrow into female recipients; (b) the transplantation of Tie2-GFP transgenic bone marrow; (c) the transplantation of bone marrow in the presence of erythropoietin (EPO), a mobilizer of endothelial progenitor cells (EPCs); and (d) the reimplantation of ex vivo–expanded EPCs. In all 4 models, VEGF acted as a powerful attractor of bone marrow–derived mononuclear cells, bearing different myeloid and endothelial markers proper of the EPCs to the sites of neovascularization. In no case, however, were the attracted cells incorporated in the newly formed vasculature. These observations indicate that new blood vessel formation induced by VEGF occurs through bona fide sprouting angiogenesis; the contribution of the infiltrating bone marrow–derived cells to this process still remains enigmatic.

Cytokine-mediated deployment of SDF-1 induces revascularization through recruitment of CXCR4+ hemangiocytes

The mechanisms through which hematopoietic cytokines accelerate revascularization are unknown. Here, we show that the magnitude of cytokine-mediated release of SDF-1 from platelets and the recruitment of nonendothelial CXCR4+ VEGFR1+ hematopoietic progenitors, 'hemangiocytes,' constitute the major determinant of revascularization. Soluble Kit-ligand (sKitL), thrombopoietin (TPO, encoded by Thpo) and, to a lesser extent, erythropoietin (EPO) and granulocyte-macrophage colony-stimulating factor (GM-CSF) induced the release of SDF-1 from platelets, enhancing neovascularization through mobilization of CXCR4+ VEGFR1+ hemangiocytes. Although revascularization of ischemic hindlimbs was partially diminished in mice deficient in both GM-CSF and G-CSF (Csf2-/- Csf3-/-), profound impairment in neovascularization was detected in sKitL-deficient Mmp9-/- as well as thrombocytopenic Thpo-/- and TPO receptor-deficient (Mpl-/-) mice. SDF-1-mediated mobilization and incorporation of hemangiocytes into ischemic limbs were impaired in Thpo-/-, Mpl-/- and Mmp9-/- mice. Transplantation of CXCR4+ VEGFR1+ hemangiocytes into Mmp9-/- mice restored revascularization, whereas inhibition of CXCR4 abrogated cytokine- and VEGF-A-mediated mobilization of CXCR4+ VEGFR1+ cells and suppressed angiogenesis. In conclusion, hematopoietic cytokines, through graded deployment of SDF-1 from platelets, support mobilization and recruitment of CXCR4+ VEGFR1+ hemangiocytes, whereas VEGFR1 is essential for their angiogenic competency for augmenting revascularization. Delivery of SDF-1 may be effective in restoring angiogenesis in individuals with vasculopathies.

Erythropoietin-mobilized endothelial progenitors enhance reendothelialization via Akt-endothelial nitric oxide synthase activation and prevent neointimal hyperplasia

We investigated whether the mobilization of endothelial progenitor cells (EPCs) by exogenous erythropoietin (Epo) promotes the repair of injured endothelium. Recombinant human Epo was injected (1000 IU/kg for the initial 3 days) after wire injury of the femoral artery of mice. Neointimal formation was inhibited by Epo to 48% of the control (P<0.05) in an NO-dependent manner. Epo induced a 1.4-fold increase in reendothelialized area of day 14 denuded vessels, 55% of which was derived from bone marrow (BM) cells. Epo increased the circulating Sca-1(+)/Flk-1(+) EPCs (2.0-fold, P<0.05) with endothelial properties NO dependently. BM replacement by GFP- or beta-galactosidase-overexpressing cells showed that Epo stimulated both differentiation of BM-derived EPCs and proliferation of resident ECs. BM-derived ECs increased 2.2- to 2.7-fold (P<0.05) in the Epo-induced neoendothelium, where the expression of Epo receptor was upregulated. Epo induced Akt/eNOS phosphorylation and NO synthesis on EPCs and exerted an antiapoptotic action on wire-injured arteries. In conclusion, Epo treatment inhibits the neointimal hyperplasia after arterial injury in an NO-dependent manner by acting on the injured vessels and mobilizing EPCs to the neo-endothelium.

Circulating progenitor cells are reduced in patients with severe lung disease

Patients with chronic severe lung disease are prone to develop pulmonary vascular remodeling, possibly through pulmonary endothelial dysfunction. Circulating endothelial progenitor cells (EPCs) are involved in maintenance of endothelial homeostasis. The aim of this study was to assess whether obstructive and restrictive lung diseases are associated with modification of EPC number in peripheral blood. The study was cross-sectional and involved patients with obstructive (n = 15) and restrictive (n = 15) lung disease on oxygen therapy and 15 control subjects. Circulating EPCs were defined by the surface expression of CD34, CD133, and kinase-insert domain receptor. Results from spirometric tests, blood gas analyses, and blood cell counts have been related to EPC numbers. Patients with chronic hypoxia and severe lung disease showed lower levels of all progenitors than do control subjects. A consensual further reduction of EPC was found in restrictive patients in comparison with obstructive patients. Among restrictive patients, EPC reduction was related to reduced lung volumes and impaired alveolo-arterial diffusion, whereas progenitor cell levels were directly related to erythrocyte number. Considering obstructive patients, significant correlations were found between progenitor cell levels and bronchial obstruction and between progenitor cell levels and arterial oxygen tension. These findings demonstrate a reduction of EPCs in patients with chronic lung disease and long-lasting hypoxia. This alteration was more evident in restrictive patients and correlated to disease severity. Depletion of circulating EPCs may be involved in altered endothelial homeostasis of pulmonary circulation in these disorders.

Association between higher cumulative doses of recombinant erythropoietin and risk for retinopathy of prematurity

BACKGROUND

Retinopathy of prematurity is a complication of premature birth that varies in its severity. The incidence and severity of retinopathy of prematurity at our perinatal center in a regional referral hospital changed substantially during 1995 to 1998 and presented us with an opportunity to examine whether there was a protective effect on risk of retinopathy associated with exposure to recombinant erythropoietin.

METHODS

We undertook a retrospective cohort study. From January 1995 through December 1998, charts of infants weighing<1500 g, who were 30 weeks' gestation or less, and who were admitted and survived to the first eye examination at 6 weeks were reviewed. Primary and secondary risk factors were recorded from the first 6 weeks of life. Of the eligible infants, 327 of 390 (84%) had complete records and retinal examinations. The probability for progression of retinopathy was estimated by logistic regression multivariate analysis using the continuation-ratio model.

RESULTS

The overall incidence of retinopathy of prematurity was 36%. Recombinant erythropoietin exposure, as total 6-week dose, was independently associated with an increased risk for progression of retinopathy, OR=1.27 per 500 units/kg (95%CI=1.04, 1.55, P=0.02). Postnatal day of recombinant erythropoietin initiation also was associated with retinopathy risk but did not reach conventional statistical significance, OR=1.07 (CI=1.00, 1.14, P=0.07).

CONCLUSIONS

These findings identify an association between cumulative recombinant erythropoietin exposure, used to reduce blood transfusions in premature infants, and an increased risk for retinopathy of prematurity. The nonhematopoietic properties of erythropoietin may account for the above findings, however further evaluation with confirmation is required.

Clinical and therapeutical implications of EPC biology in atherosclerosis

Bone marrow-derived circulating endothelial progenitor cells have been successfully used to enhance angiogenesis after tissue ischemia. The role of endothelial progenitor cells in endothelial cell homeostasis and their putative role in atherogenesis have been recently investigated. Cardiovascular risk factors negatively influence endothelial progenitor cell number and function while vasculoprotection e.g. by statins, estrogens and physical activity may be partly mediated by progenitor cells. Endogenous mobilization or injection of ex-vivo generated endothelial progenitor cells is associated with an enhanced reendothelialization, an improvement of endothelial function and reduced atherosclerotic burden. In contrast, endothelial progenitor cells may promote plaque angiogenesis in animal models and may negatively influence plaque development and stability. However, in humans with coronary atherosclerotic disease, endothelial progenitor cells are a novel risk predictor for cardiovascular mortality and morbidity. In this review we focus on the role of circulating endothelial progenitor cells in endothelial cell repair mechanisms at the vascular wall and their potentially protective and therapeutic role in atherosclerotic disease.

Important role of endogenous erythropoietin system in recruitment of endothelial progenitor cells in hypoxia-induced pulmonary hypertension in mice

BACKGROUND

Recent studies have suggested that endogenous erythropoietin (Epo) plays an important role in the mobilization of bone marrow-derived endothelial progenitor cells (EPCs). However, it remains to be elucidated whether the Epo system exerts protective effects on pulmonary hypertension (PH), a fatal disorder encountered in cardiovascular medicine.

METHODS AND RESULTS

A mouse model of hypoxia-induced PH was used for study. We evaluated right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary vascular remodeling in mice lacking the Epo receptor (EpoR) in nonerythroid lineages (EpoR(-/-) rescued mice) after 3 weeks of exposure to hypoxia. Those mice lack EpoR in the cardiovascular system but not in the hematopoietic system. The development of PH and pulmonary vascular remodeling were accelerated in EpoR(-/-) rescued mice compared with wild-type mice. The mobilization of EPCs and their recruitment to the pulmonary endothelium were significantly impaired in EpoR(-/-) rescued mice. By contrast, reconstitution of the bone marrow with wild-type bone marrow cells ameliorated PH in the EpoR(-/-) rescued mice. Hypoxia enhanced the expression of EpoR on pulmonary endothelial cells in wild-type but not EpoR(-/-) rescued mice. Finally, hypoxia activated endothelial nitric oxide synthase in the lungs in wild-type mice but not in EpoR(-/-) rescued mice.

CONCLUSIONS

These results indicate that the endogenous Epo/EpoR system plays an important role in the recruitment of EPCs and prevents the development of PH during chronic hypoxia in mice in vivo, suggesting the therapeutic importance of the system for the treatment of PH.

Realizing the cardiac stem cell promise: a case for trophism

Recent advances in stem cell biology have given rise the new field of cardiac regenerative medicine. Specifically, the development of cardiac stem cell science now offers the promise of novel cardiovascular therapies based on a dynamic body of basic and translational research. Importantly, the potential wide-spread clinical application of this technology will require that therapies be optimized for individuals with potential impairments in cardiac stem cell function. To this end, the previous experience of hematopoietic stem cell therapies can provide important guidance in the development and maturation of the young cardiac stem cell field. Parallel to the impact that exogenous growth factors have made in the field of hematopoietic therapies, the discovery and potential application of the factor(s) that govern cardiac regeneration may speed the progression of cardiac stem cell technology into an assessable and potent clinical therapy.

Angiogenesis and endothelial cell repair in renal disease and allograft rejection

This review discusses the concept that the turnover and replacement of endothelial cells is a major mechanism in the maintenance of vascular integrity within the kidney. CD133+CD34+KDR+ endothelial cell progenitor cells emigrate from the bone marrow and differentiate into CD34+KDR+ expressing cells, which are present in high numbers within the circulation. These progenitor cells are available for recruitment into normal or inflamed tissues to facilitate endothelial cell repair. In several forms of renal disease, proinflammatory insults mediate oxidative stress, senescence, and sloughing of endothelial cells. A lack of growth factors or an inefficient recruitment of endothelial cell progenitors results in hypoxic tissue injury and accelerates the process of chronic renal failure. Augmentation of vascular repair by the provision of growth factors such as vascular endothelial growth factor or by the transfer of progenitor cells directly into the kidney can be protective and prevent ongoing interstitial damage. In allografts, persistent injury results in excessive turnover of graft vascular endothelial cells. Moreover, chronic damage elicits a response that is associated with the recruitment of both leukocytes and endothelial cell progenitors, facilitating an overlapping process of inflammation and angiogenesis. Because the angiogenesis reaction itself is proinflammatory, this process becomes self-sustaining. Collectively, these data indicate that angiogenesis and endothelial cell turnover are important in renal inflammatory processes and allograft rejection. Manipulation of the response may have therapeutic implications to protect against injury and chronic disease processes.

Dynamics of mobilization and homing of endothelial progenitor cells after acute renal ischemia: modulation by ischemic preconditioning

Endothelial progenitor cells (EPCs) have been shown to participate in tissue repair under diverse physiological and pathological conditions. It is unknown whether EPCs are mobilized in response to acute renal injury. The aim of this study was to characterize EPC mobilization and homing in the course of acute renal ischemia. Mice were subjected to unilateral renal artery clamping (UC) for 25 min. At 10 min, 3, 6, 24 h, and 7 days after UC, the pool of circulating and splenic CD34+/Flk-1+ cells within the monocytic population was detected by flow cytometry. For ischemic preconditioning (IPC), the first UC was performed 7 days before the repeated ischemic episode. For EPC detection in the kidney, cryosections were stained for c-Kit+/Tie-2+ cells. The number of circulating EPCs was not significantly affected at any time after UC compared with sham-operated or control mice. IPC did not significantly change the circulating pool of EPCs. Splenectomy performed before UC resulted in a surge of circulating EPCs. Accordingly, splenic EPCs were significantly increased after UC at 3 and 6 h, but not at later times. EPC homing to the spleen was absent in IPC animals. Immunohistochemical analysis of the kidneys showed a sixfold increase in the number of c-Kit+/Tie-2+ cells localized in the medullopapillary region in mice by day 7 after ischemia. Enriched population of c-Kit+/Tie-2+ cells from the medullopapillary parenchyma of Tie-2green fluorescent protein chimeric mice subjected to IPC was isolated and transplanted to wild-type mice with acute renal ischemia. This procedure resulted in the improvement of renal function in recipients. In conclusion, 1) renal ischemia rapidly (within 3-6 h) mobilizes EPCs, which transiently home to the spleen, acting as a temporary reservoir of mobilized EPCs; 2) the late phase of IPC is associated with the mobilization of the splenic pool and accumulation of EPCs in the renal medullopapillary region; and 3) transplantation of EPC-enriched cells from the medullopapillary parenchyma afforded partial renoprotection after renal ischemia, suggesting the role of the recruited EPCs in the functional rescue.

Influence of Cardiovascular Risk Factors on Endothelial Progenitor Cells

The ideal way to prevent and cure atherosclerosis and the subsequent end organ damage is to restore and rejuvenate the dysfunctional vasculature and the damaged organs. Various studies have underlined the important role of bone marrow-derived endothelial progenitor cells (EPCs) in vasculogenesis and angiogenesis of ischemic tissue, but only a few studies have concentrated on the role of EPCs in the prevention and therapy of atherosclerosis. Extended endothelial cell damage by cardiovascular risk factors can result in endothelial cell apoptosis with loss of the integrity of the endothelium. The consequences are an increased vascular permeability of the endothelium followed by facilitated migration of monocytes and vascular smooth muscle cell proliferation, resulting in the premature manifestation of an atherosclerotic lesion. A growing body of evidence suggests that circulating EPCs play an important role in endothelial cell regeneration. Systemic transfusion or intrinsic mobilization of EPCs enhances the restoration of the endothelium after focal endothelial denudation, resulting in a diminished neointima formation. In mice with atherosclerotic lesions, bone-marrow-derived stem cells are able to reduce atherosclerotic plaque size. However, various studies have demonstrated that in humans, cardiovascular risk factors impair number and function of EPCs, potentially restricting the therapeutic potential of progenitor cells. The current review focuses on the role of cardiovascular risk factors on endothelial cell apoptosis and EPCs with its pathophysiological consequences for atherogenesis and a regenerative therapy approach and will highlight the role of EPCs as a marker for cardiovascular mortality and morbidity.

Comparative Analysis of Methods for Assessment of Circulating Endothelial Progenitor Cells

The number and properties of endothelial progenitor cells (EPC) in disease states is of considerable interest due to the importance attributed to this distinct cell population. However, there has been no study comparing each of the methods employed in the same sampled individuals. Herein, we performed an analysis of several methods used for circulating EPC assessment and correlated them with humoral factors known to influence their numbers. Thirty-eight individuals (mean age of 34 +/- 9 years) were tested. Peripheral blood mononuclear cells were obtained and stained for FACS analysis with antibodies to CD34, CD45, CD133, and KDR and the remaining cells grown under endothelial cell conditions for assessment of colony-forming unit (CFU) numbers and adhesive properties. Levels of circulating vascular endothelial growth factor (VEGF), erythropoietin (EPO), and C-reactive protein (CRP) were determined and correlated with each of the EPC markers. CFU numbers did not correlate with CD34/KDR or CD34/CD133/KDR and negatively correlated with CD34/ CD133 numbers. CD34/KDR numbers correlated with CD34/CD133/KDR, but not with CD34/ CD133. Only CD34/KDR and CD34/CD133/KDR correlated with VEGF serum levels. The number of EPC adhering to fibronectin and endothelial cells correlated with CFU numbers and not with either of the EPC membrane markers. Current methods for quantitatively assessing numbers of circulating EPC are not correlated. VEGF serum levels are associated only with CD34/KDR and CD34/ CD133/KDR, whereas CFU numbers correlate with EPC functional properties. These findings may suggest that CD34/KDR is more appropriate for the definition of circulating EPC, whereas CFU numbers are more likely to reflect their ability to proliferate.

Endothelial Progenitor Cells in Kidney Transplant Recipients

BACKGROUND

Lower concentrations of endothelial progenitor cells (EPCs) may be associated with increased cardiovascular risk. EPC counts and their correlates have not yet been studied in kidney transplant recipients (KTR).

METHODS

We cross-sectionally studied EPC counts in 105 middle-aged KTR (mean estimated glomerular filtration rate 45.2 ml/min/1.73 m; range: 5.4 to 117.5). Using univariate and multivariate linear regression assuming a gamma distribution of the outcome, we examined the associations between counts of cultured EPCs and traditional cardiovascular disease risk factors (hypertension, diabetes, hyperlipidemia, smoking), kidney function, and immunosuppressive agents, amongst others.

RESULTS

The median count of cultured EPCs was 34 cells per high-power field (interquartile range: 19 to 64), comparable to healthy individuals. From multivariate analyses, we found independent inverse associations between counts of cultured EPCs and body mass index, mean arterial pressure, and history of cardiovascular disease. Statin use was associated with greater EPC counts, whereas patients receiving azathioprine or angiotensin II receptor treatment had lower EPC counts (all P<0.01).

CONCLUSIONS

This study suggests negative associations in KTR between EPC counts and body mass index, and blood pressure, whereas statin use was associated with greater EPC counts. These findings raise the hypothesis whether EPCs are responsible, at least in part, for the well established associations between these factors and cardiovascular outcomes in KTR.

Stem cells and progenitor cells in renal disease

Stem cells and progenitor cells are necessary for repair and regeneration of injured renal tissue. Infiltrating or resident stem cells can contribute to the replacement of lost or damaged tissue. However, the regulation of circulating progenitor cells is not well understood. We have analyzed the effects of erythropoietin on circulating progenitor cells and found that low levels of erythropoietin induce mobilization and differentiation of endothelial progenitor cells. In an animal model of 5/6 nephrectomy we could demonstrate that erythropoietin ameliorates tissue injury. Full regeneration of renal tissue demands the existence of stem cells and an adequate local "milieu," a so-called stem cell niche. We have previously described a stem cell niche in the kidneys of the dogfish, Squalus acanthus. Further analysis revealed that in the regenerating zone of the shark kidney, stem cells exist that can be induced by loss of renal tissue to form new glomeruli. Such animal models improve our understanding of stem cell behavior in the kidney and may eventually contribute to novel therapies.

No Age-Related Change in Circulating Endothelial Progenitor Cells in Healthy Subjects

Endothelial progenitor cells were isolated from peripheral blood obtained from 32 healthy volunteers without cardiovascular risk factors who ranged in age from 20 to 61 years (mean [+/- SD] age, 34.1 +/- 9.6 years). The fractions of CD34(+) endothelial progenitor cells expressing kinase insert domain receptor-1, CD62E, or CD31 were analyzed with flow cytometry. Correlation analysis demonstrated that there was no significant correlation between subject age and the fraction of circulating CD34(+) mononuclear cells expressing kinase insert domain receptor-1 (P = 0.324; r = -0.180). Similarly, there was no significant correlation between subject age and the fraction of circulating CD34(+) mononuclear cells expressing CD62E (P = 0.496; r = -0.125) or the fraction of circulating CD34(+) mononuclear cells expressing CD31 (P = 0.245; r = -0.212). In conclusion, the experimental results showed that there was no age-related change in the basal level of circulating endothelial progenitor cells in healthy subjects without cardiovascular risk factors.

Hyperhomocysteinemia inhibits post-injury reendothelialization in mice

OBJECTIVE

Hyperhomocysteinemia (HHcy) is a risk factor for cardiovascular disease and has been reported to inhibit endothelial cell (EC) growth. Notwithstanding, precisely how HHcy regulates EC growth in vivo remains unknown. In this study, we established a mouse model of endothelial injury and reendothelialization and examined the role and mechanism of HHcy in endothelial repair.

METHODS AND RESULTS

A mouse model of carotid artery air-dry endothelium denudation and reendothelialization was established and used to evaluate post-injury endothelial repair in mice with the gene deletion of cystathionine-beta-synthase (CBS). Moderate and severe HHcy were induced in CBS+/+ and CBS-/+ mice through a high-methionine diet. Post-injury reendothelialization, which correlated with increased post-injury neointima formation, was impaired in severe HHcy mice. To elucidate the underlying mechanism, we examined circulating endothelial progenitor cells (EPC) in HHcy mice and studied the effect of homocysteine (Hcy) on proliferation, migration, and adhesion of human umbilical vein endothelial cells (HUVEC). The peripheral EPC population was not significantly altered in HHcy mice. Hcy had a profound inhibitory effect on EC proliferation and migration at physiologically relevant concentrations and inhibited EC adhesion at concentrations of 200 microM and higher.

CONCLUSION

We have established a convenient and accurate mouse model of carotid injury in which the reendothelialization process can be precisely quantified. In addition, we have observed impaired reendothelialization and increased neointimal formation in severe HHcy mice. The capacity of Hcy to inhibit proliferation and migration of EC may be responsible for impaired reendothelialization and contribute to arteriosclerosis in HHcy.

Imbalance between detached circulating endothelial cells and endothelial progenitor cells in chronic kidney disease

BACKGROUND

Patients with chronic kidney disease (CKD) display endothelial dysfunction and are at a high risk for atherosclerotic cardiovascular disease (CVD). Recent studies suggest that circulating detached endothelial cells (CECs) and stimulated endothelial progenitor cells (EPCs) from the bone marrow may reflect endothelial damage.

METHODS

We correlated the levels of CECs expressing the endothelial cell inflammation marker (MICA+ cells) and EPCs (Tie-2+ or VEGFR-2+ cells) in a population of 19 (55 +/- 3 years; 42% males) patients with advanced CKD (median glomerular filtration rate 8 ml/min). In addition, the levels of CD-31+ cells were investigated. Twenty healthy age- (49 +/- 2 years) and gender- (50% men) matched subjects served as controls.

RESULTS

CECs expressing MICA were increased (7.6 +/- 2.7 vs. 1.6 +/- 0.3%; p < 0.05) in CKD patients, however EPCs expressing Tie-2 or VEGFR-2 were significantly decreased (0.16 +/- 0.07 vs. 0.53 +/- 0.15%; p < 0.05, and 0.42 +/- 0.10 vs. 2.80 +/- 0.72%; p < 0.01, respectively) as compared to controls. Furthermore, we also found that the levels of CD-31+ cells were significantly elevated (22.8 +/- 4.2 vs. 9.4 +/- 0.8%; p < 0.01) in CKD patients. Patients on angiotensin-converting enzyme (ACE) inhibitors tended (p = 0.06) to have higher levels of VEGFR-2+ cells (0.57 +/- 0.14 vs. 0.16 +/- 0.11%).

CONCLUSION

Our results suggest that there is a marked imbalance between the CEC and EPC numbers in patients with CKD. Further research is needed to evaluate the independent role of inflammatory endothelial markers as well as the effects of ACE inhibitors on mobilization of EPCs in patients with advanced CKD.

Cytokine-based treatment of accidentally irradiated victims and new approaches

A major goal of medical management of acute radiation syndrome following accidental exposures to ionizing radiation (IR) is to mitigate the risks of infection and hemorrhage related to the period of bone marrow aplasia. This can be achieved by stimulating the proliferation and differentiation of residual hematopoietic stem and progenitor cells (HSPC) related to either their intrinsic radioresistance or the heterogeneity of dose distribution. This is the rationale for treatment with hematopoietic growth factors. In fact, apoptosis has recently been shown to play a major role in the death of the continuum of more or less radiosensitive HSPC, soon after irradiation. Therefore, administration of antiapoptotic cytokine combinations such as stem cell factor, Flt-3 ligand, thrombopoietin, and interleukin-3 (4F), may be important for multilineage recovery, particularly when these factors are administered early. Moreover, acute exposure to high doses of IR induces sequential, deleterious effects responsible for a delayed multiple organ dysfunction syndrome. These considerations strongly suggest that therapeutics could include tissue-specific cytokines, such as keratinocyte growth factor, and pleiotropic agents, such as erythropoietin, in addition to hematopoietic growth factors to ensure tissue damage repair and mitigate the inflammatory processes. Noncytokine drugs have also been proposed as an alternative to treat hematopoietic or nonhematopoietic radiation effects. To develop more effective treatments for radiation injuries, basic research is required, particularly to improve understanding of stem cell needs within their environment. In the context of radiological terrorism and radiation accidents, new growth promoting molecules need to be approved and available cytokines stockpiled.

Mechanisms of Disease: cell death in acute renal failure and emerging evidence for a protective role of erythropoietin

Acute renal failure--characterized by a sudden loss of the ability of the kidneys to excrete nitrogenous waste, and to maintain electrolyte homeostasis and fluid balance--is a frequently encountered clinical problem, particularly in the intensive care unit. Unfortunately, advances in supportive interventions have done little to reduce the high mortality associated with this condition. Might erythropoietin (EPO) have utility as a therapeutic agent in acute renal failure? This hormone mediates anti-apoptotic effects in the bone marrow, facilitating maturation and differentiation of erythroid progenitors. New evidence indicates that EPO also exerts anti-apoptotic effects in the brain, heart and vasculature, which can limit the degree of organ damage. Here, we review the emerging biological role of EPO in the kidney and the pathophysiology of ischemia-reperfusion injury in an attempt to understand the therapeutic potential of EPO in acute renal failure.

Diabetic nephropathy and anaemia

Anaemia is a frequent complication of diabetic nephropathy. It has only recently been recognised that in diabetic patients anaemia is seen not only in preterminal renal failure, but also frequently in patients with only minor derangement of renal function. At any level of glomerular filtration rate (GFR) anaemia is more frequent and severe in diabetic compared to nondiabetic patients. A major cause of anaemia is an inappropriate response of erythropoietin to anaemia. Additional factors are iron deficiency and iatrogenic factors, e.g. ACE inhibitor treatment. When serum creatinine is still normal, the erythropoietin concentration is predictive of more rapid loss of glomerular function. When serum creatinine is elevated, the haemoglobin values are predictive of the rate of progression. It is currently under investigation whether reversal of anaemia attenuates the rate of progression. Because most of the late complications of diabetes (retinopathy, neuropathy, heart disease, peripheral arterial disease) involve ischaemic tissue damage, it would be intuitively plausible that treatment with human recombinant erythropoietin should be beneficial, but definite evidence for this hypothesis is currently not available.

Anaemia and the heart

Anaemia is common in patients with congestive heart failure (CHF). Its prevalence increases with disease severity as a consequence of renal insufficiency, cytokine production, blood loss, iron deficiency, malnutrition and/or plasma volume overload. Anaemia can contribute to worsening of CHF. There is a nonlinear relationship (U-shaped curve) between haemoglobin and survival. Prevalence of anaemia among elderly people with acute myocardial infarction is high and is associated with more frequent in-hospital events, including death. Anaemia is also associated with higher in-hospital mortality rate after coronary bypass surgery and with all-cause and cardiac mortality after percutaneous coronary interventions. Patients with anaemia and cardiovascular disease have a higher mortality rate after cardiac/noncardiac surgery as compared to those with anaemia but without cardiovascular disease or those with cardiovascular disease but without anaemia. However, not all authors confirmed these findings. Therefore, multicentre trials to clarify this issue are urgently needed. Pleiotropic effects of recombinant human erythropoietin include reduction of myocardial and cerebral infarct size without an increase in haematocrit, neovascularization as well as mobilization of endothelial progenitor cells.

Anaemia after renal transplantation

Anaemia is a frequent complication among long-term renal transplant recipients. A prevalence of approximately 40% has been reported in several studies. If renal function declines to stage 5 kidney disease, the prevalence of anaemia in kidney transplants is even higher. A positive correlation between haemoglobin concentration and creatinine clearance has been reported, which is a function of endogenous erythropoietin production by the functioning graft. Inflammation related to a retained kidney graft may cause hypo-responsiveness to erythropoietic agents once kidney transplant recipients return to dialysis. Furthermore, the use of azathioprine, mycophenolate mofetil and sirolimus may be associated with post-transplant anaemia. Along with erythropoietin deficiency, depletion of iron stores is one of the major reasons for anaemia in the kidney transplant population. The proportion of hypochromic red blood cells appears to be a useful parameter to measure iron supply and utilization as well as to estimate mortality risks in kidney transplant recipients. While anaemia is an important cardiovascular risk-factor after transplantation, our data suggest that anaemia is not associated with mortality and graft loss. Nevertheless, inadequate attention is paid so far to the management of anaemia after renal transplantation. A promising future aspect for risk reduction of cardiovascular disease includes the effect of erythropoietic agents on endothelial progenitor cells.

Angiogenesis in the human heart: gene and cell therapy

The concept of therapeutic angiogenesis -- stimulation of new vessels growth to restore blood supply to ischemic tissue has been studied in a number of clinical trials in patients with advanced coronary and peripheral arterial disease. This review discusses the main biological processes underlying new vessel growth and addresses applications of growth factor and cell therapy based on the stimulation of angiogenesis. While still very young and controversial, cell therapy has an enormous potential that is yet to be explored. Multiple questions remain unanswered including the choice of the best cell type, patient selection and the mechanism of action. Nevertheless, much should be expected in this area in the next decade with the likely emergence of new therapies for treatment of ischemic diseases.

Role of erythropoietin in anemia after heart transplantation

BACKGROUND

Anemia after heart transplantation is common; however, there are scant data on etiology and treatment. This study evaluates type of anemia and the effects of erythropoietin therapy.

METHODS

In 37 anemic heart transplant recipients (31 male/59.1+/-10.3 years/hemoglobin <12.0 g/dl), complete anemia work-up was performed including erythropoietin determination. For three months, 12 anemic patients with renal failure (9 male/64.1+/-13.6 years) were treated with 1-3x4000 IU of epoietin beta/week; treatment endpoints were hemoglobin levels and quality of life as determined by questionnaire.

RESULTS

In 31 patients no other cause of anemia than renal insufficiency (mean creatinine 1.9+/-0.9 mg/dl, mean calculated GFR 50.8+/-21.5 ml/min, no hemodialysis) was found; in 93.5% of these patients with renal insufficiency, measured erythropoietin levels were markedly lower than predicted [Beguin Y, Clemons GK, Pootrakul P, Fillet G. Quantitative assessment of erythropoiesis and functional classification of anemia based on measurements of serum transferrin receptor and erythropoietin. Blood 1993; 81(4):1067-1076.]. There was an inverse correlation of hemoglobin levels with serum creatinine/creatinine clearance and a strong trend for inverse correlation of erythropoietin levels. All 12 patients treated with erythropoietin showed a significant increase in hemoglobin levels after three months returning to pre-treatment values within 3 months of cessation of therapy (before study 10.8+/-1.1 g/dl, end of study 14.1+/-1.7 g/dl, three months after end of study 11.6+/-2.1 g/dl; p<0.005). Quality of life was significantly improved in eight patients (75%).

CONCLUSIONS

Anemia after heart transplantation is associated with moderate renal failure and low erythropoietin levels in most patients. Erythropoietin therapy resulted in increased hemoglobin levels in all and improved quality of life in 75% of patients. Erythropoietin may be a superior marker of functional renal impairment after heart transplantation; its therapeutic substitution allows effective anemia management and improves quality of life.

Tissue engineering of angiogenesis with autologous endothelial progenitor cells

Adult bone marrow and peripheral blood contain small subsets of mononuclear cells that can be differentiated into endothelial-like cells in vitro. Experimental and clinical transplantation of such cell isolates--often referred to as endothelial stem/progenitor cells--into ischaemic or infarcted areas shows their incorporation into sites of new vessel growth along with improvement of regional blood flow. Emerging evidence suggests that these beneficial effects on vascular growth can be attributed to the paracrine activation of resident endothelial cells, rather than their integration into new endothelium. Autologous endothelial progenitor cells can also substitute for native vessel-derived endothelial cells in tissue-engineered vascular autografts.

Nocturnal hemodialysis is associated with restoration of impaired endothelial progenitor cell biology in end-stage renal disease

Cardiovascular disease is the principal cause of death in end-stage renal disease (ESRD) patients. Endothelial progenitor cells (EPCs) play a critical role in vascular repair, and improving EPC biology represents a novel therapeutic target. Three groups of age- and gender-matched patients were studied: 1) 10 healthy control, 2) 12 conventional hemodialysis (CHD) patients, and 3) 10 nocturnal hemodialysis (NHD) patients. EPC number and migratory function were assessed. Left ventricular mass index (LVMI) was derived, and correlations between EPC biology, uremic clearance, and LVMI were made. Compared with controls, EPC number and function were markedly impaired in CHD patients [(3.48 ± 1.2 vs. 0.86 ± 0.20%/50,000 cells, P < 0.05) and (18.8 ± 2.64 vs. 3.75 ± 0.34 cells/high-power field, P < 0.05), respectively]. In contrast, EPC number and function were normal in NHD patients [(3.48 ± 1.17 vs. 3.83 ± 0.77%/50,000 cells) and (18.8 ± 2.6 vs. 22.2 ± 2.4 cells/high-power field), respectively]. Among ESRD patients, EPC number and function inversely correlated with predialysis urea concentration ( r = −0.40; r = −0.57), LVMI ( r = −0.41; −0.46) and systolic BP ( r = −0.58; r = −0.44). We demonstrate that NHD is associated with restoration of abnormal EPC biology in ESRD. Given the increasing importance of EPCs in the repair and restoration of cardiovascular function, these data have important clinical implications for vascular risk in ESRD patients.

Cardioprotection by Recombinant Human Erythropoietin Following Acute Experimental Myocardial Infarction: Dose Response and Therapeutic Window

BACKGROUND

Recombinant human erythropoietin (rhEPO) protects tissue from ischemic damage, but translation of this finding into useful guidelines with respect to human trials for myocardial infarction (MI) requires a determination of the minimum effective rhEPO dose and the therapeutic window following MI.

METHOD AND RESULTS

Serial echocardiography revealed that during four weeks following MI, induced by a permanent coronary ligation in rats, the LV end-diastolic and end-systolic volumes in untreated rats expanded from 0.35 +/- 0.01 and 0.14 +/- 0.01 ml to 0.84 +/- 0.04 and 0.61 +/- 0.06 ml, respectively, and ejection fraction (EF) reduced by 50%. A single i.v. injection of rhEPO immediately following MI in a dose of 150 IU/kg was as effective as 3,000 IU/kg in causing a 2-fold reduction of the number of apoptotic nuclei in the AAR 24-h later, a 2-fold reduction of the MI size measured 4 weeks later, attenuation of progressive LV dilatation and fall in EF. A 3000 IU/kg dose had similar therapeutic effects when delayed by 4, 8, or 12 h following MI, but was not effective after a 24-h delay. A single dose of 150 IU/kg was effective within 4 h post-MI, but was without effect if administered after an 8-h delay.

CONCLUSION

Cell death, final MI size, myocardial remodeling and functional decline are significantly reduced in rats by a single injection of rhEPO in a dose as low as 150 IU/kg if administered during the first 4 h after the ischemic event. Higher doses extend the therapeutic window up to 12 h.

Erythropoietin and myocardial protection: what's new?

Erythropoietin (EPO), the principal hematopoietic cytokine produced by the kidney and the liver in fetuses, regulates mammalian erythropoiesis and exhibits diverse cellular effects in non-hematopoietic tissues. The introduction of recombinant human EPO (rhEPO) has marked a significant advance in the management of anemia associated with chronic renal failure. At the same time, experimental studies have unveiled its potential cardioprotective actions. As with other preconditioning agents, administration of exogenous rhEPO can confer myocardial protection against ischemia-reperfusion injury, in terms of reduction in cellular apoptosis and necrosis as well as improvement in myocardial functional recovery. The purpose of this study is to review current information regarding the various protocols used to investigate the effects of rhEPO administration as well as its cardioprotective properties. We also address the potential mechanisms underlying the protective effects of EPO. A better understanding of these mechanisms is essential for the development of clinical applications and the design of novel therapeutical strategies.

Pleiotropic renal actions of erythropoietin

CONTEXT

Erythropoietin (EPO), which is used clinically as recombinant human EPO (rHuEPO) for anaemia associated with end-stage renal failure and cancer chemotherapy, also has pleiotropic properties. Although EPO and its receptor are primary mediators of the normal physiological response to hypoxia, rHuEPO can provide impressive protection against acute ischaemic injury in several organs and tissues. The longer-acting hyperglycosylated derivative of EPO, darbepoetin-alpha, is also used for anaemia and has pleiotropic properties. However, the ability of EPO or its analogues to act directly to reduce the severity of renal injury associated with chronic renal failure is not known.

STARTING POINT

Ferdinand Bahlmann and colleagues (Circulation 2004; 110: 1006-12) investigated whether low-dose subcutaneous darbepoetin-alpha could protect against renal dysfunction and injury in rats with induced chronic renal failure. Given once weekly, the drug improved renal function and reduced histological evidence of renal injury. Treated rats also had greater weight gain than controls, with no change in systemic blood pressure. The drug did not increase packed-cell volume and it improved survival. WHERE NEXT?: Although the pleiotropic actions of rHuEPO can ameliorate ischaemic and nephrotoxic acute renal failure, Bahlmann's work is the first evidence that darbepoetin-alpha reduces the renal dysfunction and injury of chronic renal failure. Thus rHuEPO and its analogues might have a use in patients with different types of renal failure. These pleiotropic actions, seen at lower doses, must be separated from the haemopoietic properties that occur at clinical doses and which, at the highest doses, might lead to unwanted effects. Novel analogues of EPO are devoid of haemopoietic activity but still possess protective properties. Their ability to reduce renal injury and dysfunction awaits investigation.

History of Cardiovascular Disease Is Associated With Endothelial Progenitor Cells in Peritoneal Dialysis Patients

BACKGROUND

It is unknown whether traditional cardiovascular disease risk factors influence the number of endothelial progenitor cells (EPCs) and whether numbers of EPCs correlate with endothelial function in patients with end-stage renal disease.

METHODS

In a cross-sectional study of 38 peritoneal dialysis patients, we examined numbers of circulating CD34+/KDR+/CD133+ cells, CD34+ hematopoietic stem cells, and EPCs cultured from peripheral blood. We also assessed conventional cardiovascular disease risk factors, such as history of vascular disease, diabetes, hypercholesterolemia, hypertension, and smoking. We determined endothelial function by measurement of endothelium-dependent and endothelium-independent reactivity of forearm resistance arteries by using strain-gauge plethysmography.

RESULTS

Numbers of EPCs cultured from peripheral blood and forearm blood flow reactivity did not differ between erythropoietin-treated peritoneal dialysis patients and healthy individuals. A history of vascular disease was associated with number of cultured EPCs, but other cardiovascular disease risk factors showed no association. Furthermore, there was no association of endothelial-dependent and endothelial-independent forearm blood flow reactivity with EPCs in peritoneal dialysis patients.

CONCLUSION

In this first study of EPCs in peritoneal dialysis patients, we found an association between history of vascular disease and EPCs, but no association of EPCs with endothelial function or other cardiovascular disease risk factors.

Detection of circulating endothelial cells and endothelial progenitor cells by flow cytometry

The finding of angiogenic and vasculogenic cells in the peripheral circulation may have profound effects on the course of a variety of diseases ranging from cancer to cardiovascular disease. These cells are ascribed to be endothelial in nature and are generally referred to as circulating endothelial cells if mature or as endothelial progenitor cells if immature. Different approaches have been used to detect these cells, including in vitro culture, magnetic bead isolation, and flow cytometry. We review flow cytometric methods for the detection and enumeration of these cells and provide technical suggestions to promote the accurate enumeration of circulating endothelial cells and endothelial progenitor cells.

Vascular progenitor cells: origin and mechanisms of mobilization, differentiation, integration, and vasculogenesis

The recent discovery of progenitor cells in peripheral blood that can differentiate into endothelial or vascular smooth muscle cells has led to the re-evaluation of many traditionally held beliefs about vascular biology. Most notably, concepts of vascular regeneration and repair, previously considered limited to the proliferation of existing differentiated cells within vascular tissue, have been expanded to include the potential for postnatal vasculogenesis. These cells have since been identified in the bone marrow, heart, skeletal muscle, and other peripheral tissues, including the vasculature itself. The significance of these cells lies not only in developing our understanding of normal vascular biology, but also in the insights they may provide into vascular diseases such as atherosclerosis. In addition, a potential role in therapeutics has already been explored in early clinical trials in humans. The mechanisms underlying the mobilization, target tissue integration, differentiation, and the observed therapeutic benefits of these cells are now being elucidated. It is these mechanisms, and the current understanding of the lineage of these cells, that constitutes the focus of this review.