Erythropoietin regulates endothelial progenitor cells

Mesenchymal stem cell therapy for chronic renal failure

IMPORTANCE OF THE FIELD

Chronic kidney disease (CKD) has become a worldwide public health problem. Renal transplantation is the treatment of choice for end-stage renal disease, but is limited by a small number of organ donors and the immune barrier. To overcome these problems, new therapeutic strategies for tissue repair have recently emerged.

AREAS COVERED IN THIS REVIEW

We discuss the therapeutic potential of mesenchymal stem cells (MSCs) in kidney injury and examine the latest reports providing evidence supporting MSC efficacy in the treatment of chronic renal failure (CRF).

WHAT THE READER WILL GAIN

MSCs improve histological and functional outcomes in various CRF model systems. Paracrine effects rather than transdifferentiation might result in the prevention of progressive renal failure. In addition, MSCs can reprogram kidney cell differentiation, and modulate neo-kidney transplantation in CRF.

TAKE HOME MESSAGE

Although many practical problems remain to be addressed, treatment with MSCs will enter the mainstream of CRF treatment.

Preventing negative effects of smoking on microarterial anastomosis

Although microsurgery has rapid expanded, problems related to microarterial anastomosis continue. Cigarette smoking is one of the major risks for anastomosis by increasing platelet adhesion, and its effects on endothelial cells. Aim of this article is to study the negative effects of cigarettes on microarterial anastomosis line, and to investigate the protective effects of recombinant human erythropoietin (rHuEPO).Ninety-six Sprague-Dawley male rats were divided into 3 groups: group 1 was the control. Rats in groups 2 and 3 were exposed to cigarette smoke starting 21 days prior to surgery for 3 times a day. In group 3, additional 150 IU/kg rHuEPO was given via subcutaneously every 48 hours after microvascular anastomosis, femoral arterial samples, and blood samples were taken for assessment at 1st, 3rd, 5th, and 7th day. Intimae/media ratios were calculated for morphologic analyses.On morphologic analysis of femoral arteries there were statistically significant differences for all 3 groups at 1st, 3rd, 5th, and 7th days (P < 0, 05). The group that made differences was group 2, according to one-way analysis of variance within 3 groups in all days.Smoking decreases endothelial cells healing and causes more thromboses. rHuEPO can prevent these negative effects of smoking.

Bone marrow and circulating stem/progenitor cells for regenerative cardiovascular therapy

Cardiovascular disease is the leading cause of death and disability in the Western world. In addition to the advancement of current therapeutic approaches to reduce the associated morbidity and mortality, regenerative medicine and cell-based therapy have been areas of continuous investigation. Circulating and bone-marrow-derived stem or endothelial progenitor cells are an attractive source for regenerative therapy in the cardiovascular field. In this review, we highlight the advantages and limitations of this approach with a focus on key observations from animal studies and clinical trials.

Relationship of microparticles to progenitor cells as a measure of vascular health in a diabetic population

OBJECTIVE

Quantitative measures are needed to identify diabetic patients at higher risk for CV events. Cell-derived microparticles (MPs) are submicron membrane vesicles released from activated cells that are indicative of cell damage. Progenitor cells (PCs) including proangiogenic cells (PACs), often termed endothelial progenitor cells (EPCs), are mediators of reparative capacity. We examined whether the relationship of MPs to PCs/PACs could be used as an improved and clinically feasible index of vascular pathology.

METHODS AND RESULTS

Plasma samples were collected from patients with early-stage (ES, Diagnosis < 1 year) and long-term (LT, Diagnosis > 5 years,) Type 2 diabetes and compared with age related healthy subjects (H). PC and MP subtypes were measured by a combination of flow cytometry and ELISA-based methods. The ratio of procoagulant MPs/CD34(+) PCs proved a valuable index to distinguish between subject groups (P = 0.01). This index of compromised vascular function was highest in the LT group despite intensive statin therapy and was more informative than a range of soluble protein biomarkers.

CONCLUSIONS

This is the first report of a relationship between MPs and PCs in Type 2 diabetes. This ratio may provide a quantitative and clinically feasible measurement of vascular dysfunction and cardiovascular risk in patients with diabetes. © 2010 International Clinical Cytometry Society.

Erythropoietin 2nd cerebral protection after acute injuries: a double-edged sword?

Over the past 15 years, a large body of evidence has revealed that the cytokine erythropoietin exhibits non-erythropoietic functions, especially tissue-protective effects. The discovery of EPO and its receptors in the central nervous system and the evidence that EPO is made locally in response to injury as a protective factor in the brain have raised the possibility that recombinant human EPO (rhEPO) could be administered as a cytoprotective agent after acute brain injuries. This review highlights the potential applications of rhEPO as a neuroprotectant in experimental and clinical settings such as ischemia, traumatic brain injury, and subarachnoid and intracerebral hemorrhage. In preclinical studies, EPO prevented apoptosis, inflammation, and oxidative stress induced by injury and exhibited strong neuroprotective and neurorestorative properties. EPO stimulates vascular repair by facilitating endothelial progenitor cell migration into the brain and neovascularisation, and it promotes neurogenesis. In humans, small clinical trials have shown promising results but large prospective randomized studies failed to demonstrate a benefit of EPO for brain protection and showed unwanted side effects, especially thrombotic complications. Recently, regions have been identified within the EPO molecule that mediate tissue protection, allowing the development of non-erythropoietic EPO variants for neuroprotection conceptually devoid of side effects. The efficacy and the safety profile of these new compounds are still to be demonstrated to obtain, in patients, the benefits observed in experimental studies.

Endothelial progenitor cells and cardiovascular events in patients with chronic kidney disease--a prospective follow-up study

Background

Endothelial progenitor cells (EPCs) mediate vascular repair and regeneration. Their number in peripheral blood is related to cardiovascular events in individuals with normal renal function.

Methods

We evaluated the association between functionally active EPCs (cell culture) and traditional cardiovascular risk factors in 265 patients with chronic kidney disease stage V receiving hemodialysis therapy. Thereafter, we prospectively assessed cardiovascular events, e.g. myocardial infarction, percutaneous transluminal coronary angioplasty (including stenting), aorto-coronary bypass, stroke and angiographically verified stenosis of peripheral arteries, and cardiovascular death in this cohort.

Results

In our patients EPCs were related only to age (r = 0.154; p = 0.01). During a median follow-up period of 36 months 109 (41%) patients experienced a cardiovascular event. In a multiple Cox regression analysis, we identified EPCs (p = 0.03) and patient age (p = 0.01) as the only independent variables associated with incident cardiovascular events. Moreover, a total of 70 patients died during follow-up, 45 of those due to cardiovascular causes. Log rank test confirmed statistical significance for EPCs concerning incident cardiovascular events (p = 0.02).

Conclusions

We found a significant association between the number of functionally active EPCs and cardiovascular events in patients with chronic kidney disease. Thus, defective vascular repair and regeneration may be responsible, at least in part, for the enormous cardiovascular morbidity in this population.

Potential manipulation of endothelial progenitor cells in diabetes and its complications

Diabetes mellitus increases cardiovascular risk through its negative impact on vascular endothelium. Although glucotoxicity and lipotoxicity account for endothelial cell damage, endothelial repair is also affected by diabetes. Endothelial progenitor cells (EPCs) are involved in the maintenance of endothelial homoeostasis and in the process of new vessel formation. For these reasons, EPCs are thought to have a protective impact within the cardiovascular system. In addition, EPCs appear to modulate the functioning of other organs, providing neurotropic signals and promoting repair of the glomerular endothelium. The exact mechanisms by which EPCs provide cardiovascular protection are unknown and the definition of EPCs is not standardized. Notwithstanding these limitations, the literature consistently indicates that EPCs are altered in type 1 and type 2 diabetes and in virtually all diabetic complications. Moreover, experimental models suggest that EPC-based therapies might help prevent or reverse the features of end-organ complications. This identifies EPCs as having a novel pathogenic role in diabetes and being a potential therapeutic target. Several ways of favourably modulating EPCs have been identified, including lifestyle intervention, commonly used medications and cell-based approaches. Herein, we provide a comprehensive overview of EPC pathophysiology and the potential for EPC modulation in diabetes.

Mechanism of endothelial dysfunction in chronic kidney disease

Endothelium is the largest organ in the body strategically located between the wall of blood vessels and the blood stream. The human body contains approximately 10(13) endothelial cells weighing approximately 1kg, and covering a surface area of 4000 to 7000m(2) equivalent to the soccer playground. Hypertension and shear stress, inflammation, diabetes-associated factors such as advanced glycated end products, and uremic toxins are some of the prevalent risk factors of endothelial dysfunction in chronic kidney disease. In renal failure endothelial dysfunction and atherosclerosis are almost universal, as well as cardiovascular complications. Endothelial cell damage or injury is invariably associated with such clinical conditions as thrombosis, hypertension, renal failure and atherosclerosis and may be also responsible for accelerated atherosclerosis in patients with chronic renal failure. Traditional risk factor cannot explain the high prevalence and incidence of cardiovascular disease in chronic kidney disease, therefore other non-traditional risk factors such as endothelial dysfunction, oxidative stress or insulin resistance have increasingly been studied. In this review paper mechanism of endothelial dysfunction, including the role of nitric oxide pathway, adipocytokines and hemodialysis-induced endothelial dysfunction is discussed.

Effects of granulocyte-colony-stimulating factor on progenitor cell mobilization and heart perfusion and function in normal mice

BACKGROUND AIMS

Mobilization of stem cells and progenitor cells from the bone marrow (BM) into the peripheral blood (PB) by granulocyte-colony-stimulating factor (G-CSF) is being investigated for cardiac regeneration in ischemic heart disease. However, hematopoietic (HPC), mesenchymal (MPC) and endothelial (EPC) progenitor mobilization have not been optimized and the effect of G-CSF on myocardial perfusion and cardiac function in a normal heart has never been studied.

METHODS

Normal mice were injected daily for 1-10 days with subcutaneous recombinant human G-CSF. PB and BM were evaluated for HPC and EPC by flow cytometry and HPC and MPC by hematopoietic (CFU-GM) and mesenchymal (CFU-F) colony assays. Echocardiography, microSPECT imaging, cardiac catheterization and immunohistochemistry were performed in mice treated for 10 days.

RESULTS

HPC and CFU-GM in PB peaked after 2 days, CFU-F after 4 days and EPC after 3 days. Thereafter, while HPC temporally decreased before showing a second peak, EPC remained detectable only at low levels. In BM, hematopoietic stem cells (HSC) and CFU-GM did not increase much overall but peaked twice on days 2 and 7. EPC (peak on day 7) production increased in the BM, but CFU-F formation declined considerably after day 2. G-CSF enhanced myocardial perfusion and vascularization but impaired hemodynamic performance of the heart through apparently increased ventricular wall rigidity.

CONCLUSIONS

G-CSF induces the mobilization of HPC, EPC and CFU-F progenitors in PB according to very different patterns, and has a significant impact on perfusion and function of the normal heart.

Enhanced progenitor cell recruitment and endothelial repair after selective endothelial injury of the mouse kidney

Primary and/or secondary injury of the renal microvascular endothelium is a common finding in various renal diseases. Besides well-known endothelial repair mechanisms, including endothelial cell (EC) proliferation and migration, homing of extrinsic cells such as endothelial progenitor cells (EPC) and hematopoietic stem cells (HSC) has been shown in various organs and may contribute to microvascular repair. However, these mechanisms have so far not been studied after selective microvascular injury in the kidney. The present study investigated the time course of EPC and HSC stimulation and homing following induction of selective EC injury in the mouse kidney along with various angiogenic factors potentially involved in EC repair and progenitor cell stimulation. Erythropoietin was used to stimulate progenitor cells in a therapeutic approach. We found that selective EC injury leads to a marked stimulation of EPCs, HSCs, and various angiogenic factors to orchestrate microvascular repair. Angiogenic factors started to increase as early as 30 min after disease induction. Progenitor cells could be first detected in the circulation and the spleen before they selectively homed to the diseased kidney. Injection of a high dose of erythropoietin 2 h after disease induction markedly attenuated vascular injury through nonhemodynamic mechanisms, possibly involving vascular endothelial growth factor release.

Sonic hedgehog is a critical mediator of erythropoietin-induced cardiac protection in mice

Erythropoietin reportedly has beneficial effects on the heart after myocardial infarction, but the underlying mechanisms of these effects are unknown. We here demonstrate that sonic hedgehog is a critical mediator of erythropoietin-induced cardioprotection in mice. Treatment of mice with erythropoietin inhibited left ventricular remodeling and improved cardiac function after myocardial infarction, independent of erythropoiesis and the mobilization of bone marrow-derived cells. Erythropoietin prevented cardiomyocyte apoptosis and increased the number of capillaries and mature vessels in infarcted hearts by upregulating the expression of angiogenic cytokines such as VEGF and angiopoietin-1 in cardiomyocytes. Erythropoietin also increased the expression of sonic hedgehog in cardiomyocytes, and inhibition of sonic hedgehog signaling suppressed the erythropoietin-induced increase in angiogenic cytokine expression. Furthermore, the beneficial effects of erythropoietin on infarcted hearts were abolished by cardiomyocyte-specific deletion of sonic hedgehog. These results suggest that erythropoietin protects the heart after myocardial infarction by inducing angiogenesis through sonic hedgehog signaling.

HDL cholesterol is a strong determinant of endothelial progenitor cells in hypercholesterolemic subjects

Endothelial progenitor cells (EPC) can repair the endothelial layer and are considered a component of the cardiovascular system. EPC number and function may change under pathological conditions, including cardiovascular risk factors. The study was carried out to investigate circulating EPC number, in vitro function and relationship with LDL-C, HDL-C and endothelium-dependent vasodilatation in hypercholesterolemic subjects. Forty-one male and 39 female subjects, age>35 and<45, LDL cholesterol plasma level>130 mg/dl with normal (> or =50 mg/dl females and> or =40 mg/dl males) or low HDL-C, absence of any concomitant disorders and/or drug treatment, at their first diagnosis of hypercholesterolemia, were consecutively recruited in the Outpatient Service of the Medical Pathophysiology Department of Rome Sapienza University. In high LDL-C patients, circulating EPC number was decreased and EPC capability to migrate was impaired as well. This pattern was far less evident in the normal HDL-C subgroup. The endothelium-dependent vasodilatation (EDV) was significantly decreased according to the HDL-C decrease in male but not in female subjects. Univariate analysis showed a direct correlation between EPC number and EDV, and the association persisted after adjustment for sex, age and HDL-C, which were all significantly correlated to EDV, which may suggest a protective role of EPC on endothelium in vivo. Our study documented that, in hypercholesterolemic subjects, HDL-C is a strong determinant of EPC number and function, and EPC number decrease is an independent risk factor for endothelial dysfunction.

Regulation of bone marrow-derived vascular progenitor cell mobilization and maintenance

Cell therapy is a promising option for treating ischemic diseases and heart failure. Bone marrow-derived vasculogenic cells, including progenitor cells and proangiogenic cells, have been shown to augment the functional recovery after ischemia. However, cardiovascular diseases affect the functional activity of the endogenous progenitor cell pools. The local microenvironment, also termed the stem cell niche, provides essential cues that maintain stem and progenitor cell functions and direct cell fate decisions in the bone marrow. A disturbed niche might lead to cell dysfunction (eg, by exhaustion). In addition, the niche controls mobilization of the cells into the circulation. This review will discuss the impact of cardiovascular disease on stem cell niches and summarize strategies targeting the niche for mobilization of vasculogenic cells.

Dysfunctional endothelial progenitor cells in chronic kidney disease

Putative endothelial progenitor cells play a role in organ regeneration, and their incompetence may be important in the development of chronic kidney disease. The mechanisms of this incompetence are broad and range from poor mobilization, viability, and engraftment to impaired differentiation into mature endothelial cells. By contrasting the role of endothelial progenitor cells in tissue regeneration with their developing incompetence in chronic kidney disease, we emphasize the importance of designing rational pharmacologic strategies to tackle such incompetence in the broader search for therapies to attenuate chronic disease.

Is there a role for erythropoietin in cardiovascular disease?

IMPORTANCE OF THE FIELD

Despite the advances in the cardiovascular field, cardiovascular diseases remain an important health problem with a high mortality rate. Novel therapeutic attempts that target myocardial ischemia and heart failure offer attractive adjuncts and/or alternatives to commonly employed regimens. The development of novel laboratory technologies over the last decade has led to substantial progress in bringing new therapies to the bedside.

AREAS COVERED IN THIS REVIEW

Current experimental and clinical trials in the use of erythropoietin (EPO) in cardiovascular diseases are reviewed.

WHAT THE READER WILL GAIN

This review will widen knowledge of the therapeutic potential of EPO's non-erythropoietic beneficial effects in a clinical cardiovascular setting.

TAKE HOME MESSAGE

Results from preclinical trials regarding the non-erythropoietic effects of erythropoietin are really encouraging. Further clinical studies are warranted to define the beneficial role of EPO in the clinical setting of coronary artery disease, heart failure and peripheral artery disease.

Induction of nitric oxide by erythropoietin is mediated by the β common receptor and requires interaction with VEGF receptor 2

Vascular endothelial growth factor (VEGF) and erythropoietin (EPO) have profound effects on the endothelium and endothelial progenitor cells (EPCs), which originate from the bone marrow and differentiate into endothelial cells. Both EPO and VEGF have demonstrated an ability to increase the number and performance properties of EPCs. EPC behavior is highly dependent on nitric oxide (NO), and both VEGF and EPO can stimulate intracellular NO. EPO can bind to the homodimeric EPO receptor (EPO-R) and the heterodimeric receptor, EPO-R and the common β receptor (βC-R). Although VEGF has several receptors, VEGF-R2 appears most critical to EPC function. We demonstrate that EPO induction of NO is dependent on the βC-R and VEGF-R2, that VEGF induction of NO is dependent on the expression of the βC-R, and that the βC-R and VEGF-R2 interact. This is the first definitive functional and structural evidence of an interaction between the 2 receptors and has implications for the side effects of EPO.

Cardiovascular effects of erythropoietin an update

Erythropoietin (EPO) is a therapeutic product of recombinant DNA technology and it has been in clinical use as stimulator of erythropoiesis over the last two decades. Identification of EPO and its receptor (EPOR) in the cardiovascular system expanded understanding of physiological and pathophysiological role of EPO. In experimental models of cardiovascular and cerebrovascular disorders, EPO exerts protection either by preventing apoptosis of cardiac myocytes, smooth muscle cells, and endothelial cells, or by increasing endothelial production of nitric oxide. In addition, EPO stimulates mobilization of progenitor cells from bone marrow thereby accelerating repair of injured endothelium and neovascularization. A novel signal transduction pathway involving EPOR--β-common heteroreceptor is postulated to enhance EPO-mediated tissue protection. A better understanding of the role of β-common receptor signaling as well as development of novel analogs of EPO with enhanced nonhematopoietic protective effects may expand clinical application of EPO in prevention and treatment of cardiovascular and cerebrovascular disorders.

A regenerative strategy for heart failure in hypoplastic left heart syndrome: intracoronary administration of autologous bone marrow-derived progenitor cells

Novel surgical strategies have dramatically improved the initial outcome of newborns with hypoplastic left heart syndrome. However, the single systemic right ventricle remains a major challenge, with limited effectiveness of pharmacologic therapy. The present case documents that the intracoronary administration of autologous bone marrow-derived progenitor cells is technically feasible in a critically ill infant with hypoplastic left heart syndrome and severe heart failure after a hybrid comprehensive stage II procedure. Cell therapy might represent an option before heart transplantation in children with single ventricle physiology presenting with severe heart failure.

Endothelial-vasoprotective effects of high-density lipoprotein are impaired in patients with type 2 diabetes mellitus but are improved after extended-release niacin therapy

BACKGROUND

High-density lipoprotein (HDL)-raising therapies are currently under intense evaluation, but the effects of HDL may be highly heterogeneous. We therefore compared the endothelial effects of HDL from healthy subjects and from patients with type 2 diabetes mellitus and low HDL (meeting the criteria for metabolic syndrome), who are frequently considered for HDL-raising therapies. Moreover, in diabetic patients, we examined the impact of extended-release (ER) niacin therapy on the endothelial effects of HDL.

METHODS AND RESULTS

HDL was isolated from healthy subjects (n=10) and patients with type 2 diabetes (n=33) by sequential ultracentrifugation. Effects of HDL on endothelial nitric oxide and superoxide production were characterized by electron spin resonance spectroscopy analysis. Effects of HDL on endothelium-dependent vasodilation and early endothelial progenitor cell-mediated endothelial repair were examined. Patients with diabetes were randomized to a 3-month therapy with ER niacin (1500 mg/d) or placebo, and endothelial effects of HDL were characterized. HDL from healthy subjects stimulated endothelial nitric oxide production, reduced endothelial oxidant stress, and improved endothelium-dependent vasodilation and early endothelial progenitor cell-mediated endothelial repair. In contrast, these beneficial endothelial effects of HDL were not observed in HDL from diabetic patients, which suggests markedly impaired endothelial-protective properties of HDL. ER niacin therapy improved the capacity of HDL to stimulate endothelial nitric oxide, to reduce superoxide production, and to promote endothelial progenitor cell-mediated endothelial repair. Further measurements suggested increased lipid oxidation of HDL in diabetic patients, and a reduction after ER niacin therapy.

CONCLUSIONS

HDL from patients with type 2 diabetes mellitus and metabolic syndrome has substantially impaired endothelial-protective effects compared with HDL from healthy subjects. ER niacin therapy not only increases HDL plasma levels but markedly improves endothelial-protective functions of HDL in these patients, which is potentially more important.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov. Identifier: NCT00346970.

Effects of recombinant human erythropoietin on platelet activation in acute myocardial infarction: results of a double-blind, placebo-controlled, randomized trial

BACKGROUND

Erythropoietin mitigates myocardial damage and improves ventricular performance after experimental ischemic injury. This study assessed safety and efficacy markers relevant to the biological activity of recombinant human erythropoietin (rHuEpo) in patients with acute myocardial infarction (MI).

METHODS

We conducted a prospective, placebo-controlled, randomized, double-blind trial to determine the effects of intravenous rHuEpo (200 U/kg daily for 3 consecutive days) on measures of platelet and endothelial cell activation, soluble Fas ligand, and peripheral blood mononuclear cell (PBMC) expression of angiogenesis signaling proteins in 44 subjects with acute MI treated with aspirin and clopidogrel after successful percutaneous coronary intervention.

RESULTS

Recombinant human erythropoietin did not alter bleeding time, platelet function assay closure time, von Willebrand factor levels, soluble P-selectin, or soluble Fas ligand levels when compared with placebo. By contrast, rHuEpo significantly increased expression of erythropoietin receptor, vascular endothelial growth factor receptor Flt-1, and phosphorylated phosphatidylinositol 3-kinase in PBMCs when compared with placebo (all Ps < .05).

CONCLUSIONS

In acute MI patients treated with aspirin and clopidogrel, short-term administration of rHuEpo did not alter markers of platelet and endothelial cell activation associated with thrombosis, yet did increase expression of angiogenesis signaling proteins in PBMCs when compared with placebo. These data provide preliminary evidence of safety and biologic activity of rHuEpo at this dosing and support continued enrollment in ongoing efficacy trials.

Relationship of erythropoietin, fetal hemoglobin, and hydroxyurea treatment to tricuspid regurgitation velocity in children with sickle cell disease

Hydroxyurea and higher hemoglobin F improve the clinical course and survival in sickle cell disease, but their roles in protecting from pulmonary hypertension are not clear. We studied 399 children and adolescents with sickle cell disease at steady state; 38% were being treated with hydroxyurea. Patients on hydroxyurea had higher hemoglobin concentration and lower values for a hemolytic component derived from 4 markers of hemolysis (P < or = .002) but no difference in tricuspid regurgitation velocity compared with those not receiving hydroxyurea; they also had higher hemoglobin F (P < .001) and erythropoietin (P = .012) levels. Hemoglobin F correlated positively with erythropoietin even after adjustment for hemoglobin concentration (P < .001). Greater hemoglobin F and erythropoietin each independently predicted higher regurgitation velocity in addition to the hemolytic component (P < or = .023). In conclusion, increase in hemoglobin F in sickle cell disease may be associated with relatively lower tissue oxygen delivery as reflected in higher erythropoietin concentration. Greater levels of erythropoietin or hemoglobin F were independently associated with higher tricuspid regurgitation velocity after adjustment for degree of hemolysis, suggesting an independent relationship of hypoxia with higher systolic pulmonary artery pressure. The hemolysis-lowering and hemoglobin F-augmenting effects of hydroxyurea may exert countervailing influences on pulmonary blood pressure in sickle cell disease.

Role of endothelial progenitor cells in diabetes mellitus

Endothelial progenitor cells (EPCs) are bone marrow-derived cells involved in endothelial healing and angiogenesis. EPCs are considered an integrated component of the cardiovascular system, which promotes vascular health. Derangement of EPC biology in diabetes has been hailed as a novel concept in the pathogenesis of micro- and macro-vascular complications. Additionally, EPCs are considered to be disease biomarkers, as they provide an index of cardiovascular risk. The mechanisms leading to EPC dysfunction in diabetes may include defective mobilization from bone marrow to peripheral blood and reduced half-life. Hyperglycemia is considered the major determinant of microvascular complications, while other mechanisms concur to increase the risk of cardiovascular disease in diabetic patients. EPCs may represent a novel pathophysiological connection to understand development and progression of diabetic complications.

Combined intermittent hypoxia and surface muscle electrostimulation as a method to increase peripheral blood progenitor cell concentration

Background

Our goal was to determine whether short-term intermittent hypoxia exposure, at a level well tolerated by healthy humans and previously shown by our group to increase EPO and erythropoiesis, could mobilize hematopoietic stem cells (HSC) and increase their presence in peripheral circulation.

Methods

Four healthy male subjects were subjected to three different protocols: one with only a hypoxic stimulus (OH), another with a hypoxic stimulus plus muscle electrostimulation (HME) and the third with only muscle electrostimulation (OME). Intermittent hypobaric hypoxia exposure consisted of only three sessions of three hours at barometric pressure 540 hPa (equivalent to an altitude of 5000 m) for three consecutive days, whereas muscular electrostimulation was performed in two separate periods of 25 min in each session. Blood samples were obtained from an antecubital vein on three consecutive days immediately before the experiment and 24 h, 48 h, 4 days and 7 days after the last day of hypoxic exposure.

Results

There was a clear increase in the number of circulating CD34+ cells after combined hypobaric hypoxia and muscular electrostimulation. This response was not observed after the isolated application of the same stimuli.

Conclusion

Our results open a new application field for hypobaric systems as a way to increase efficiency in peripheral HSC collection.

B-type natriuretic peptide enhances vasculogenesis by promoting number and functional properties of early endothelial progenitor cells

OBJECTIVE

To test the hypothesis that B-type natriuretic peptide (BNP) acts as a potent vasculogenic agent by enhancing the number, proliferation, adhesion, and migration of endothelial progenitor cells (EPCs).

BACKGROUND

BNP is a neurohormonal peptide that predicts outcome and used for treatment in chronic heart failure patients. It has been shown to promote angiogenesis in experimental animals. EPCs have been demonstrated to contribute to postnatal angiogenesis and vasculogenesis.

METHODS

The number of EPC colony forming units (CFU) and levels of N-terminal ProBNP were assayed in patients with severe, yet controlled, New York Heart Association (NYHA) II-IV heart failure. The in vitro effects of BNP on early EPC-CFU numbers, proliferation, migration, adhesive, and vascular tube formation capacities were studied using human and murine systems. The effects of in vivo BNP administration on Sca-1/Flk-1 progenitors and on vasculogenesis in the hindlimb ischemia model were then assayed in wild-type mice.

RESULTS

A significant correlation was found between circulating N-terminal ProBNP levels and EPC-CFU numbers. We observed a dose-dependent effect of BNP on the numbers of CFU and proliferation capacity of human EPCs as well as on their adhesive, migratory, and tube formation properties, in vitro. Systemic BNP administration to mice led to a significant increase in bone marrow Sca-1/Flk-1 EPCs and improvement in blood flow and capillary density in the ischemic limbs of mice.

CONCLUSIONS

BNP promotes vessel growth by increasing the number of endothelial progenitors and enhancing their functional properties. These provasculogenic properties of BNP could account for some of its beneficial effects in chronic heart failure patients and may be harnessed for the purpose of improving collateral formation in ischemic subjects.

The role of hypoxia in 2-butoxyethanol-induced hemangiosarcoma

To understand the molecular mechanisms underlying compound-induced hemangiosarcomas in mice, and therefore, their human relevance, a systems biology approach was undertaken using transcriptomics and Causal Network Modeling from mice treated with 2-butoxyethanol (2-BE). 2-BE is a hemolytic agent that induces hemangiosarcomas in mice. We hypothesized that the hemolysis induced by 2-BE would result in local tissue hypoxia, a well-documented trigger for endothelial cell proliferation leading to hemangiosarcoma. Gene expression data from bone marrow (BM), liver, and spleen of mice exposed to a single dose (4 h) or seven daily doses of 2-BE were used to develop a mechanistic model of hemangiosarcoma. The resulting mechanistic model confirms previous work proposing that 2-BE induces macrophage activation and inflammation in the liver. In addition, the model supports local tissue hypoxia in the liver and spleen, coupled with increased erythropoeitin signaling and erythropoiesis in the spleen and BM, and suppression of mechanisms that contribute to genomic stability, events that could be contributing factors to hemangiosarcoma formation. Finally, an immunohistochemistry method (Hypoxyprobe) demonstrated that tissue hypoxia was present in the spleen and BM. Together, the results of this study identify molecular mechanisms that initiate hemangiosarcoma, a key step in understanding safety concerns that can impact drug decision processes, and identified hypoxia as a possible contributing factor for 2-BE-induced hemangiosarcoma in mice.

NADPH oxidase Nox2 is required for hypoxia-induced mobilization of endothelial progenitor cells

RATIONALE

Endothelial progenitor cells (EPCs, defined as sca-1(+)flk-1(+)lin(-) mononuclear blood cells) contribute to vascular repair. The role of hypoxia and reactive oxygen species (ROS) in mobilization and function of these cells is incompletely understood.

OBJECTIVE

We studied the contribution of the NADPH oxidase Nox2, an important vascular source of ROS in this context.

METHODS AND RESULTS

Hypoxia (10% oxygen) induced the mobilization of EPCs in wild-type (WT) and Nox1 but not in Nox2 knockout (Nox2(y/-)) mice. As erythropoietin (EPO) is known to induce EPC mobilization, we focused on this hormone. EPO induced the mobilization of EPCs in WT and Nox1(y/-) but not Nox2(y/-) animals. Transplantation of bone marrow from Nox2(y/-) mice into WT-mice blocked mobilization in response to hypoxia and EPO, whereas transplantation of WT bone marrow into Nox2(y/-) mice restored mobilization. Reendothelialization of the injured mouse carotid artery was enhanced by hypoxia as well as by EPO, and this effect was not observed in Nox2(y/-) mice or after transplantation of Nox2(y/-) bone marrow. In cultured EPCs from WT but not Nox2(y/-) mice, EPO induced ROS production, migration, and proliferation. EPO signaling involves the STAT5 transcription factor. EPO-induced STAT5-dependent reporter gene expression was absent in Nox2-deficient cells. siRNA against the redox-sensitive phosphatase SHP-2 restored EPO-mediated STAT5 induction and inhibition of SHP-2 restored EPO-induced migration in Nox2-deficient cells

CONCLUSIONS

We conclude that Nox2-derived ROS inactivate SHP-2 and thereby facilitate EPO signaling in EPCs to promote hypoxia-induced mobilization and vascular repair by these cells.

Significance of immune cell function monitoring in renal transplantation after Thymoglobulin induction therapy

Monitoring of immune status in transplant recipients is essential for predicting the risk of rejection or infection. In this study, we assessed the significance of immune cell function in 76 renal allograft recipients after Thymoglobulin induction and initiation of maintenance immunosuppression. Using the Immuknow (Cylex Inc) assay, the amount of adenosine triphosphate (ATP) produced by CD4+ cells in response to phytohemagglutinin (PHA) was measured in patients whole blood. In parallel, the frequency and phenotype of CD4+ T cells were determined by flow cytometry. The Immuknow assay yielded paradoxically high ATP values during the first 3 months post-transplantation, despite very low CD4+ T cell counts. High ATP values were caused by peripheral blood myeloid cells, did not predict rejection, and occurred primarily in transplant recipients who received darbepoietin (p = 0.017). CD4+ T cells displayed predominantly an activated/memory phenotype and comprised a subpopulation of CD25+FOXP3+ cells. Over the first 5 months post-transplantation, mean ATP activity gradually decreased, whereas CD4+ T cell counts slowly increased. Low ATP values were predictive of infection (p = 0.002). Thus Immuknow results need to be interpreted with caution in patients receiving Thymoglobulin induction therapy. Although low ATP levels identify patients at increased risk for infection, high ATP values fail to correlate with rejection and do not justify increased immunosuppression.

Sustained release of erythropoietin using biodegradable gelatin hydrogel microspheres persistently improves lower leg ischemia

OBJECTIVES

We hypothesized that erythropoietin (EPO)-immersed gelatin hydrogel microspheres (GHM) injected into ischemic legs might continuously release a small amount of EPO to locally stimulate angiogenesis without unfavorable systemic effects.

BACKGROUND

EPO is a potent angiogenic factor, but its use for relieving ischemic organs is limited because of the untoward systemic erythrogenic effect and its short half-life in plasma.

METHODS

The right femoral arteries of BALB/c mice were ligated. Recombinant human EPO (5,000 IU/kg)-immersed GHM was injected into the right hind limb muscles (n = 12); the control groups included a saline-injected group (n = 12), an EPO-injected group (n = 8), and an empty GHM-injected group (n = 8).

RESULTS

Eight weeks later, improvement of blood perfusion to the ischemic limb was significantly augmented in the EPO-GHM group compared with any of the control groups. There was no increase in the hemoglobin level, nor was there any increase in endothelial progenitor cells. However, capillary and arteriolar densities were significantly increased in this group. Although the treatment did not affect the levels of vascular endothelial growth factor or interleukin-1 beta, it up-regulated the EPO receptor and matrix metalloproteinase-2 and activated the downstream signaling of Akt and also endothelial nitric oxide synthase in ischemic limbs, which might have been associated with the evident angiogenic and arteriogenic effects in the present system.

CONCLUSIONS

The present drug delivery system is suggested to have potential as a novel noninvasive therapy for ischemic peripheral artery disease.

Endothelial Progenitor Cells and Their Potential Clinical Applications in Peripheral Arterial Disease

Endothelial progenitor cells (EPCs) were originally thought to be present only during embryonic development. New evidence suggests that they can persist into adult life, circulate in the peripheral blood and may play an important part in endothelial repair and replacement of dysfunctional endothelium. They may also play a role in the formation of new blood vessels (angiogenesis, vasculogenesis, and arteriogenesis) in ischemic tissues. In addition, EPCs have the potential to endothelialize small-diameter prosthetic vascular bypass grafts and generate a nonthrombogenic surface, thereby increasing the patency rate of these grafts. EPCs may also be used in the clinical assessment of risk of vascular disease. In this review, the authors discuss the potential use of EPCs in the management of peripheral arterial disease (PAD).

Intracardiac injection of erythropoietin induces stem cell recruitment and improves cardiac functions in a rat myocardial infarction model

Erythropoietin (EPO) protects the myocardium from ischaemic injury and promotes beneficial remodelling. We assessed the therapeutic efficacy of intracardiac EPO injection and EPO-mediated stem cell homing in a rat myocardial infarction (MI) model. Following MI, EPO (3000 U/kg) or saline was delivered by intracardiac injection. Compared to myocardial infarction control group (MIC), EPO significantly improved left ventricular function (n =11-14, P < 0.05) and decreased right ventricular wall stress (n = 8, P < 0.05) assessed by pressure-volume loops after 6 weeks. MI-EPO hearts exhibited smaller infarction size (20.1 +/- 1.1% versus 27.8 +/- 1.2%; n = 6-8, P < 0.001) and greater capillary density (338.5 +/- 14.7 versus 259.8 +/- 9.2 vessels per mm2; n = 6-8, P < 0.001) than MIC hearts. Direct EPO injection reduced post-MI myocardial apoptosis by approximately 41% (0.27 +/- 0.03% versus 0.42 +/- 0.03%; n = 6, P= 0.005). The chemoattractant SDF-1 was up-regulated significantly assessed by quantitative realtime PCR and immunohistology. c-Kit(+) and CD34(+) stem cells were significantly more numerous in MI-EPO than in MIC at 24 hrs in peripheral blood (n = 7, P < 0.05) and 48 hrs in the infarcted hearts (n = 6, P < 0.001). Further, the mRNAs of Akt, eNOS and EPO receptor were significantly enhanced in MI-EPO hearts (n = 7, P < 0.05). Intracardiac EPO injection restores myocardial functions following MI, which may attribute to the improved early recruitment of c-Kit(+) and CD34(+) stem cells via the enhanced expression of chemoattractant SDF-1.

The scope of coronary heart disease in patients with chronic kidney disease

Chronic kidney disease (CKD) affects approximately 13% of the U.S. population and is associated with increased risk of cardiovascular complications. Once renal replacement therapy became available, it became apparent that the mode of death of patients with advanced CKD was more likely than not related to cardiovascular compromise. Further observation revealed that such compromise was related to myocardial disease (related to hypertension, stiff vessels, coronary heart disease, or uremic toxins). Early on, the excess of cardiovascular events was attributed to accelerated atherosclerosis, inadequate control of blood pressure, lipids, or inflammatory cytokines, or perhaps poor glycemia control. In more recent times, outcome research has given us further information that relates even lesser degrees of renal compromise to an excess of cardiovascular events in the general population and in those with already present atherosclerotic disease. As renal function deteriorates, certain physiologic changes occur (perhaps due to hemodynamic, inflammatory, or metabolic changes) that decrease oxygen-carrying capacity of the blood by virtue of anemia, make blood vessels stiffer by altering collagen or through medial calcinosis, raise the blood pressure, increase shearing stresses, or alter the constituents of atherosclerotic plaque or the balance of thrombogenesis and thrombolysis. At further levels of renal dysfunction, tangible metabolic perturbations are recognized as requiring specific therapy to reduce complications (such as for anemia and hyperparathyroidism), although outcome research to support some of our current guidelines is sorely lacking. Understanding the process by which renal dysfunction alters the prognosis of cardiac disease might lead to further methods of treatment. This review will outline the relationship of CKD to coronary heart disease with respect to the current understanding of the traditional and nontraditional risk factors, the role of various imaging modalities, and the impact of coronary revascularization on outcome.

Estradiol-induced, endothelial progenitor cell-mediated neovascularization in male mice with hind-limb ischemia

We investigated whether administration of estradiol to male mice augments mobilization of bone marrow-derived endothelial progenitor cells (EPC) and incorporation into foci of neovascularization after hind-limb ischemia, thereby contributing to blood flow restoration. Mice were randomized and implanted with placebo pellets or pellets containing low-dose estradiol (0.39 mg) or high-dose estradiol (1.7 mg). Hind-limb ischemia was induced by unilateral resection of the left femoral artery 1 week after pellet implantation, then EPC mobilization and functional recovery was evaluated. EPC recruitment was assessed in mice transplanted with bone marrow from transgenic donors expressing beta-galactosidase driven by the Tie-2 promoter. EPC culture assay performed 2 weeks after pellet implantation revealed a significantly greater (p<0.05) number of circulating EPCs in the high-dose estradiol group than in the low-dose estradiol and placebo groups. At 3 and 4 weeks after induction of hind-limb ischemia, perfusion was significantly greater (p<0.05) in high-dose estradiol mice than in mice implanted with the low-dose estradiol or placebo pellets. At 1 and 4 weeks after hind-limb ischemia surgery, more bone marrow-derived EPCs, identified as beta-galactosidase-positive cells, were observed in ischemic regions from high-dose estradiol animals than in low-dose (p<0.05) or placebo groups (p<0.05). These results indicate that estradiol dose-dependently increases the levels of EPCs in peripheral blood in male animals, improves the recovery of blood flow, and decreases limb necrosis after hind-limb ischemia, and that this enhancement occurs, in part, through augmentation of EPC mobilization and greater incorporation of bone marrow-derived EPCs into foci of neovascularization.

Erythropoietin and renoprotection

In the haematopoietic system, the principal function of erythropoietin (EPO) is the regulation of RBC production. Consequently, following the cloning of the EPO gene, recombinant human EPO (rHuEPO) forms have been widely used for treatment of anaemia in chronic kidney disease and chemotherapy-induced anaemia in cancer patients. However, a steadily growing body of evidence indicates that the therapeutic benefits of rHuEPO could be far beyond the correction of anaemia. Several articles have been recently published on the tissue-protective, nonhaematological effects of rHuEPO that prevent ischaemia-induced tissue damage in several organs including the kidney.In this review, we focus on nonhaematological effects of rHuEPO in various experimental settings of acute and chronic kidney injury. Because this tissue-protective action of rHuEPO is not the result of correction of anaemia-related tissue hypoxia, we will also discuss potential molecular pathways involved. Finally, we will review the current literature on clinical studies with rHuEPO or analogous substances and progression of chronic kidney disease, and propose possible clinical renoprotective strategies.

Endothelial progenitor cells and their potential clinical implication in cardiovascular disorders

Risk factors associated with cardiovascular diseases reduce the availability of endothelial progenitor cells (EPC) by affecting their mobilization and integration into injured vascular sites. The existence of a bone marrow reservoir of EPC has attracted interest, especially as target for therapeutic intervention in different pathological settings. Among the cardiovascular risk factors, hypertension has been shown to be a strongest predictor of EPC migratory impairment. However, at present, data concerning EPC biology are still limited. In this article we provide an overview of data relevant to their potential clinical implications in cardiovascular disorders. In addition, the recent advances in understanding the role of EPC in the pathophysiology of hypertension are discussed.

Endothelial progenitor cell dysfunction in patients with progressive chronic kidney disease

Endothelial progenitor cells (EPC) contribute to repair and maintenance of the vascular system, but in patients with chronic kidney disease (CKD), the number and function of EPC may be affected by kidney dysfunction. We assessed numbers and the angiogenic function of EPC from patients with CKD in relation to disease progression. In a cross-sectional, prospective study, 50 patients with varying degrees of CKD, including 20 patients undergoing dialysis and 10 healthy controls, were included. Mononuclear cells were isolated, and circulating EPC were quantified by flow cytometry based on expression of CD14 and CD34. EPC were cultured on fibronectin-coated supramolecular films of oligocaprolactone under angiogenic conditions to determine their angiogenic capacity and future use in regenerative medicine. CKD patients had normal numbers of circulating CD14+ EPC but reduced numbers of circulating CD34+ EPC. Furthermore, EPC from patients with CKD displayed functional impairments, i.e., hampered adherence, reduced endothelial outgrowth potential, and reduced antithrombogenic function. These impairments were already observed at stage 1 CKD and became more apparent when CKD progressed. Dialysis treatment only partially ameliorated EPC impairments in patients with CKD. In conclusion, EPC number and function decrease with advancing CKD, which may hamper physiological vascular repair and can add to the increased risk for cardiovascular diseases observed in CKD patients.

Review article: endothelial progenitor cells in renal disease

This brief overview is intended to provide basic information about endothelial progenitors, their definition and consensus markers used for their detection, describe the pathways of their mobilization and homing and highlight the mechanisms and manifestations of their incompetence that occurs in some chronic kidney diseases. Discussion is geared towards the potential role of endothelial progenitor cells in organ regeneration, in particular, in kidney regeneration. The concept we attempted to promote attributes to the incompetence of endothelial progenitor cells in failed regeneration and ensuing progression of chronic kidney disease. This field of inquiry remains insufficiently explored, especially in renal diseases. Promising areas for future exploration are emphasized.