Circulating endothelial progenitor cells are reduced in hemodialysis patients

Associations Between Inflammatory and Bone Turnover Markers and Mortality in Hemodialysis Patients

Background/Objectives: Chronic kidney disease-mineral and bone disorder (CKD-MBD) and systemic inflammation contribute to mortality in hemodialysis (HD) patients. The primary aim of this study was to determine whether specific CKD-MBD markers and inflammatory biomarkers are associated with increased mortality risk in HD patients. Methods: We conducted a retrospective cohort study on 63 stage 5D CKD patients undergoing maintenance HD. Serum intact parathyroid hormone (iPTH), soluble Klotho, calcium, phosphorus, 25(OH)D (25-hydroxyvitamin D), transforming growth factor-beta (TGF-β), vascular endothelial growth factor (VEGF), C-reactive protein (CRP), and interleukin-6 (IL-6) were analyzed. A Cox regression analysis assessed mortality predictors, and linear regression analysis evaluated CKD-MBD-inflammation correlations. Results: Lower iPTH (<329.3 pg/mL) levels were the only significant mortality predictor (p = 0.042). Other CKD-MBD markers (calcium, phosphorus, 25(OH)D, VEGF, TGF-β) did not impact survival. Soluble Klotho correlated positively with IL-6 (r = 0.57, p < 0.001), suggesting a compensatory inflammatory response. Conclusions: Our findings demonstrate that low iPTH levels and advanced age are independent predictors of mortality in hemodialysis patients. The positive association between soluble Klotho and IL-6 suggests a potential compensatory inflammatory response. These results highlight the need for further research to clarify underlying mechanisms and to explore novel therapeutic strategies.

Prognostic Factors After Bone Marrow-Derived Mononuclear Cell Implantation in No-Option Chronic Limb-Threatening Ischemia Patients with Atherosclerotic Lower Extremity Artery Disease

Previous studies have reported the efficacy and safety of therapeutic angiogenesis through bone marrow-derived mononuclear cell (BM-MNC) implantation in patients with no-option chronic limb-threatening ischemia (CLTI) from atherosclerotic lower extremity artery disease (LEAD). However, uncertain clinical prognostic factors impact treatment outcomes. This study aimed to elucidate the long-term outcomes of patients with atherosclerotic LEAD-derived no-option CLTI after BM-MNC implantation and to identify prognostic factors.In this retrospective, single-center, observational study, the primary endpoints included the long-term prognosis of BM-MNC implantation and factors influencing 1-year outcomes. A total of 92 limbs in 84 patients were analyzed in the final cohort (mean age: 67 years; male, 65%). The 5- and 10-year overall survival rates were 50.0% and 31.0%, respectively, while the 5- and 10-year amputation-free survival rates were 37.6% and 23.3%, respectively. Multivariate logistic analysis linked all-cause mortality to age ≥ 70 years, hemodialysis, smoking, and a controlling nutrition status score ≥ 5. Major amputation or mortality was associated with male sex, hemodialysis, and C-reactive protein levels ≥ 3.0 mg/dL. No adverse events were associated with therapeutic angiogenesis.These findings endorse the feasibility and safety of BM-MNC implantation for patients with no-option CLTI due to atherosclerotic LEAD. Moreover, the study highlights the significance of several prognostic factors, including advanced age, hemodialysis, smoking, and inflammatory markers, in influencing the long-term outcomes of this treatment.

Effects of calcitriol on peripheral endothelial progenitor cells and renal renovation in rats with chronic renal failure

BACKGROUND

The role of calcitriol (1,25-dihydroxyvitamin D₃ or 1,25-(OH)₂D₃) in physiological processes, such as anti-fibrosis, anti-inflammation, and immunoregulation is known; however, its role in the remodeling of the glomerular capillary endothelium in rats with chronic renal failure (CRF) remains unclear.

METHODS

Here, we analyzed the role/number of endothelial progenitor cells (EPCs), renal function, and pathological alterations in rats with CRF, and compared the results before and after supplementation with calcitriol in vivo.

RESULTS

Amongst the three experimental groups (sham group, CRF group, and calcitriol-treated group (0.03 μg/kg/d), we observed substantially elevated cell adhesion and vasculogenesis in vivo in the calcitriol-treated group. Additionally, lower levels of serum creatinine (Scr) and blood urea nitrogen (BUN) was recorded in the calcitriol-treated group than the CRF group (p > 0.05). Calcitriol treatment also resulted in an improvement in renal pathological injury.

CONCLUSIONS

Thus, calcitriol could ameliorate the damage of glomerular arterial structural and renal tubules vascular network integrity, maybe through regulating the number and function of EPCs in the peripheral blood of CRF rats. Treatment with it may improve outcomes in patients with renal insufficiency or combined cardiac insufficiency. Calcitriol could ameliorate CRF-induced renal pathological injury and renal dysfunction by remodeling of the glomerular capillary endothelium, thus, improving the function of glomerular endothelial cells.

Circulating Progenitor Cells in Patients With Coronary Artery Disease and Renal Insufficiency

Patients with coronary artery disease and renal insufficiency (RI) (estimated glomerular filtration rate <60 ml/min/1.73 m²) are at an increased risk of cardiovascular events. The contribution of regenerative capacity, measured as circulating progenitor cell (CPC) counts, to this increased risk is unclear. CPCs were enumerated as cluster of differentiation (CD) 45^med+ mononuclear cells expressing CD34+, CD133+, CXCR4+ (chemokine [C-X-C motif] receptor 4), and VEGF2R+ (vascular endothelial growth factor receptor 2) epitopes in 1,281 subjects with coronary artery disease (35% with RI). Patients with RI and low (<median) hematopoietic CPCs (CD34+, CD34+/CD133+, and CD34+/CXCR4+) were at an increased risk of cardiovascular death or myocardial infarction events (hazard ratios: 1.75 to 1.80) during 3.5-year follow-up, while those with RI and high CPCs (>median) were at a similar risk as those without RI.

Dysregulation of Vascular Endothelial Progenitor Cells Lung-Homing in Subjects with COPD

Chronic obstructive pulmonary disease (COPD) is characterized by fixed airflow limitation and progressive decline of lung function and punctuated by occasional exacerbations. The disease pathogenesis may involve activation of the bone marrow stimulating mobilization and lung-homing of progenitor cells. We investigated the hypothesis that lower circulating numbers of vascular endothelial progenitor cells (VEPCs) are a consequence of increased lung-sequestration in COPD. Nonatopic, current or ex-smokers with diagnosed COPD and nonatopic, nonsmoking normal controls were enrolled. Blood and induced sputum extracted primitive hemopoietic progenitors (HPCs) and VEPC were enumerated by flow cytometry. Migration and adhesive responses to fibronectin were assessed. In sputum, VEPC numbers were significantly greater in COPD compared to normal controls. In blood, VEPCs were significantly lower in COPD versus normal controls. There were no differences in HPC levels between the two groups in either compartment. Functionally, there was a greater migrational responsiveness of progenitors from COPD subjects to stromal cell-derived factor-1alpha (SDF-1α) compared to normal controls. This was associated with greater numbers of CXCR4⁺ progenitors in sputum from COPD. Increased migrational responsiveness of progenitor cells may promote lung-homing of VEPC in COPD which may disrupt maintenance and repair of the airways and contribute to COPD disease pathogenesis.

Endothelial Progenitor Cells Predict Long-Term Mortality in Hemodialysis Patients

BACKGROUND

The endothelial progenitor cells (EPCs) dysfunction is a critical event in the initiation of atherosclerotic plaque development and the level of circulating EPCs can be considered a biomarker of cardiovascular events. The level and functional change in EPCs has been investigated in hemodialysis patients, but the effect of absolute number of EPCs on risk of death has not yet been explored. We hypothesized that the number of EPCs predicted death from cardiovascular and all-cause mortality in hemodialysis patients.

METHODS

We evaluate the association between endothelial progenitor cells and clinical outcome in 154 patients on maintenance hemodialysis. The blood sample was drawn at the time of patient enrollment and EPCs were identified by flow cytometry using triple staining for CD34/CD133/KDR.

RESULTS

The median duration of follow-up was 4.19 years. There were 79 (51.3%) deaths during the follow-up period, 41 of whom died due to a confirmed cardiovascular cause. The cumulative survival was greater in the high-EPC group than the low-EPC group for all-cause and cardiovascular mortality. Decreased EPCs levels were associated with a significant increase in the risk of cardiovascular and all-cause mortality after adjusting for age, gender, current smokers, diabetes mellitus, and hypertension.

CONCLUSIONS

The level of circulating EPCs independently predicts the clinical outcome in patients on maintenance hemodialysis. Thus, the EPCs levels may be a useful predictive tool for evaluating the risk of death in maintenance hemodialysis patients.

Challenges and opportunities for stem cell therapy in patients with chronic kidney disease

Chronic kidney disease (CKD) is a global health care burden affecting billions of individuals worldwide. The kidney has limited regenerative capacity from chronic insults, and for the most common causes of CKD, no effective treatment exists to prevent progression to end-stage kidney failure. Therefore, novel interventions, such as regenerative cell-based therapies, need to be developed for CKD. Given the risk of allosensitization, autologous transplantation of cells to boost regenerative potential is preferred. Therefore, verification of cell function and vitality in CKD patients is imperative. Two cell types have been most commonly applied in regenerative medicine. Endothelial progenitor cells contribute to neovasculogenesis primarily through paracrine angiogenic activity and partly by differentiation into mature endothelial cells in situ. Mesenchymal stem cells also exert paracrine effects, including proangiogenic, anti-inflammatory, and antifibrotic activity. However, in CKD, multiple factors may contribute to reduced cell function, including older age, coexisting cardiovascular disease, diabetes, chronic inflammatory states, and uremia, which may limit the effectiveness of an autologous cell-based therapy approach. This Review highlights current knowledge on stem and progenitor cell function and vitality, aspects of the uremic milieu that may serve as a barrier to therapy, and novel methods to improve stem cell function for potential transplantation.

Uremic Toxicity of Advanced Glycation End Products in CKD

Advanced glycation end products (AGEs), a heterogeneous group of compounds formed by nonenzymatic glycation reactions between reducing sugars and amino acids, lipids, or DNA, are formed not only in the presence of hyperglycemia, but also in diseases associated with high levels of oxidative stress, such as CKD. In chronic renal failure, higher circulating AGE levels result from increased formation and decreased renal clearance. Interactions between AGEs and their receptors, including advanced glycation end product-specific receptor (RAGE), trigger various intracellular events, such as oxidative stress and inflammation, leading to cardiovascular complications. Although patients with CKD have a higher burden of cardiovascular disease, the relationship between AGEs and cardiovascular disease in patients with CKD is not fully characterized. In this paper, we review the various deleterious effects of AGEs in CKD that lead to cardiovascular complications and the role of these AGEs in diabetic nephropathy. We also discuss potential pharmacologic approaches to circumvent these deleterious effects by reducing exogenous and endogenous sources of AGEs, increasing the breakdown of existing AGEs, or inhibiting AGE-induced inflammation. Finally, we speculate on preventive and therapeutic strategies that focus on the AGE-RAGE axis to prevent vascular complications in patients with CKD.

Functional characterization of late outgrowth endothelial progenitor cells in patients with end-stage renal failure

Renal transplantation is potentially curative in renal failure, but long-term efficacy is limited by untreatable chronic rejection. Endothelial damage contributes to chronic rejection and is potentially repairable by circulating endothelial progenitor cells (EPC). The frequency and function of EPC are variably influenced by end-stage renal failure (ESRF). Here, we isolated and functionally characterized the late outgrowth EPC (LO-EPC) from ESRF patients to investigate their potential for endothelial repair. Patients with ESRF generated more LO-EPC colonies than healthy controls and had higher plasma levels of IL-1rα, IL-16, IL-6, MIF, VEGF, Prolactin, and PLGF. Patients' LO-EPC displayed normal endothelial cell morphology, increased secretion of PLGF, MCP-1, and IL-1β, and normal network formation in vitro and in vivo. They demonstrated decreased adhesion to extracellular matrix. Integrin gene profiles and protein expression were comparable in patients and healthy volunteers. In some patients, mesenchymal stem cells (MSC) were co-isolated and could be differentiated into adipocytes and osteocytes in vitro. This is the first study to characterize LO-EPC from patients with ESRF. Their behavior in vitro reflects the presence of elevated trophic factors; their ability to proliferate in vitro and angiogenic function makes them candidates for prevention of chronic rejection. Their impaired adhesion and the presence of MSC are areas for potential therapeutic intervention.

P-cresol, but not p-cresylsulphate, disrupts endothelial progenitor cell function in vitro

BACKGROUND

Patients afflicted with chronic kidney disease (CKD) typically suffer from cardiovascular disease (CVD) which is a leading cause of patient mortality. It has been demonstrated that two distinct physiological events contribute to this disease state. These include the abundance of abnormally high levels of protein-bound uraemic toxins as well as functionally aberrant endothelial progenitor cells (EPCs). Specifically, it has been demonstrated that the uraemic toxin p-cresol (pC; 4-methylphenol) inhibits EPC proliferation and tube formation in previous in vitro studies. More recently, however, it has been demonstrated that circulating pC is actually conjugated and that p-cresylsulphate (pCS) is its main metabolite. Therefore, within the context of this study, we examined the in vitro effects of pC and pCS treatment on cultured human EPCs.

METHODS

Late-outgrowth EPCs were treated with physiological concentrations of pC or pCS (10, 40, 80, and 160 or 10, 40, 80, 160 and 320 µg/mL for up to 72 h, respectively) in the presence of 4% human serum albumin (HSA). Cell proliferation was determined using WST-1 assay, while migration and tube formation assays were used to evaluate EPC function in vitro. Cell cycle analyses were also performed to determine the effects of pC and pCS on cell cycle status.

RESULTS

With regard to EPC proliferation, data demonstrate that pC in the presence or absence of HSA had an IC50 of 80.1 and 100.8 µg/mL 72 h post-treatment, respectively, while pCS-treated groups did not impair EPC proliferation. Similarly, pC-treated groups showed limited vessel formation and migration compared with controls and no detrimental effects were seen with pCS treatment. Lastly, pC treatment of EPCs caused cells to accumulate in the G2/M phase of the cell cycle with accompanied down-regulation of cyclin B1 and phosphorylated CDK1. pCS had no effect on cell cycle parameters.

CONCLUSIONS

Our data demonstrate that pC and pCS have different effects on EPC function. Since there is a dearth of data that have focused on the toxicity of pCS, further research should be performed to determine the exact biological toxicity of pCS on the cardiovascular system.

The effects of low-dose nepsilon-(carboxymethyl)lysine (CML) and nepsilon-(carboxyethyl)lysine (CEL), two main glycation free adducts considered as potential uremic toxins, on endothelial progenitor cell function

Background

Patients with chronic kidney disease (CKD) are at high risk of cardiovascular disease (CVD). Endothelial progenitor cell (EPCs) dysfunction plays a key role in this pathogenesis. Uremic retention toxins have been reported to be in associated with EPC dysfunction. Advanced glycation end-products (AGEs) free adducts, including Nepsilon-(carboxymethyl)lysine (CML) and Nepsilon-(carboxyethyl)lysine (CEL), are formed by physiological proteolysis of AGEs and released into plasma for urinary excretion. They are retained in CKD patients and are considered to be potential uremic toxins. Though AGEs have been demonstrated to impair EPC function in various ways, the effect of AGE free adducts on EPC function has not been studied. Thus, we examined the role of CML and CEL in the regulation of growth-factor-dependent function in cultured human EPCs and the mechanisms by which they may affect EPC function.

Methods

Late outgrowth EPCs were incubated with different concentrations of CML or CEL for up to 72 hours. Cell proliferation was determined using WST-1 and BrdU assays. Cell apoptosis was tested with annexin V staining. Migration and tube formation assays were used to evaluate EPC function.

Results

Though CML and CEL were determined to have anti-proliferative effects on EPCs, cells treated with concentrations of CML and CEL in the range found in CKD patients had no observable impairment on migration or tube formation. CML and CEL did not induce EPC apoptosis. The reduced growth response was accompanied by significantly less phosphorylation of mitogen-activated protein kinases (MAPKs).

Conclusions

Our study revealed that CML and CEL at uremic concentrations have low biological toxicity when separately tested. The biologic effects of AGE free adducts on the cardiovascular system merit further study.

Association of circulating endothelial progenitor cells (CD14+-EPC) with renal function in patients with coronary artery disease

BACKGROUND

The relationships between the endothelial progenitor cells (EPCs)-CD34(+) and CD14(+) and coronary artery disease (CAD) were reported and the association of CD34(+) cells with renal function was studied previously. Another kind EPC-CD14(+) cell and its association with renal function in patients with CAD have not been reported yet. Our aim was to assess CD14(+) cell counts versus renal function in CAD.

METHODS AND RESULTS

We studied 242 patients with severe angiographic CAD and 30 healthy control participants. The CD14(+) cells were enumerated by flow cytometry. With lowering glomerular filtration rate (GFR), CD14(+) cell numbers (percentage of lymphocytes, median and interquartile range) decreased: 0.04 (0.03-0.06), 0.03 (0.02-0.05), 0.02 (0.01-0.03) for estimated glomerular filtration rate (eGFR) ≥90, 60 to 89, and 30 to 89 mL/min per 1.73 m(2), respectively (P < .001 for trend). The CD14(+) cell counts correlated with eGFR (r = .27, P = .03). By multivariate liner regression analysis, the difference remains significant (P = .02).

CONCLUSIONS

The CD14(+) cell depletion is associated with renal dysfunction in CAD.

Sonic hedgehog-modified human CD34+ cells preserve cardiac function after acute myocardial infarction

RATIONALE

Ischemic cardiovascular disease represents one of the largest epidemics currently facing the aging population. Current literature has illustrated the efficacy of autologous, stem cell therapies as novel strategies for treating these disorders. The CD34+ hematopoetic stem cell has shown significant promise in addressing myocardial ischemia by promoting angiogenesis that helps preserve the functionality of ischemic myocardium. Unfortunately, both viability and angiogenic quality of autologous CD34+ cells decline with advanced age and diminished cardiovascular health.

OBJECTIVE

To offset age- and health-related angiogenic declines in CD34+ cells, we explored whether the therapeutic efficacy of human CD34+ cells could be enhanced by augmenting their secretion of the known angiogenic factor, sonic hedgehog (Shh).

METHODS AND RESULTS

When injected into the border zone of mice after acute myocardial infarction, Shh-modified CD34+ cells (CD34(Shh)) protected against ventricular dilation and cardiac functional declines associated with acute myocardial infarction. Treatment with CD34(Shh) also reduced infarct size and increased border zone capillary density compared with unmodified CD34 cells or cells transfected with the empty vector. CD34(Shh) primarily store and secrete Shh protein in exosomes and this storage process appears to be cell-type specific. In vitro analysis of exosomes derived from CD34(Shh) revealed that (1) exosomes transfer Shh protein to other cell types, and (2) exosomal transfer of functional Shh elicits induction of the canonical Shh signaling pathway in recipient cells.

CONCLUSIONS

Exosome-mediated delivery of Shh to ischemic myocardium represents a major mechanism explaining the observed preservation of cardiac function in mice treated with CD34(Shh) cells.

Vascular incompetence in dialysis patients--protein-bound uremic toxins and endothelial dysfunction

Patients with chronic kidney disease (CKD) have a much higher risk of cardiovascular diseases than the general population. Endothelial dysfunction, which participates in accelerated atherosclerosis, is a hallmark of CKD. Patients with CKD display impaired endothelium-dependent vasodilatation, elevated soluble biomarkers of endothelial dysfunction, and increased oxidative stress. They also present an imbalance between circulating endothelial populations reflecting endothelial injury (endothelial microparticles and circulating endothelial cells) and repair (endothelial progenitor cells). Endothelial damage induced by a uremic environment suggests an involvement of uremia-specific factors. Several uremic toxins, mostly protein-bound, have been shown to have specific endothelial toxicity: ADMA, homocysteine, AGEs, and more recently, p-cresyl sulfate and indoxyl sulfate. These toxins, all poorly removed by hemodialysis therapies, share mechanisms of endothelial toxicity: they promote pro-oxidant and pro-inflammatory response and inhibit endothelial repair. This article (i) reviews the evidence for endothelial dysfunction in CKD, (ii) specifies the involvement of protein-bound uremic toxins in this dysfunction, and (iii) discusses therapeutic strategies for lowering uremic toxin concentrations or for countering the effects of uremic toxins on the endothelium.

Effect of darbepoetin alfa on endothelial progenitor cells and vascular reactivity in chronic kidney disease

Endothelial progenitor cells (EPCs) are thought to be important for maintaining normal vascular function. We conducted a prospective study evaluating the effect of the erythropoiesis-stimulating agent darbepoetin alfa on EPCs and vascular function in patients with chronic kidney disease (CKD), with or without diabetes. Thirty subjects with CKD (20 subjects with type II diabetes mellitus and 10 without diabetes mellitus) received weekly subcutaneous administration of darbepoetin alfa for 4 weeks. EPCs were measured at baseline and 2 and 4 weeks after drug administration. Vascular function was measured with brachial ultrasound and cell activity was measured with a cell proliferation assay. Cells expressing CD133, CD34, CD146 and CD146/31 were significantly elevated (all p < 0.05), flow-mediated vasodilatation increased 2.1%, 95% CI: (0.4%, 3.8%) and colony-forming units increased twofold, 95% CI: (1.7, 2.3) after 4 weeks of treatment with darbepoetin alfa. Subjects with diabetes exhibited an increase in a subset of EPCs (CD133( +) and 34(+), p < 0.01 and p = 0.06, respectively), vasodilatation and proliferation. In conclusion, the administration of darbepoetin alfa for 4 weeks increased a subset of EPCs, improved endothelial function and increased cell proliferation, including those with diabetes, which is consistent with a favorable improvement in vascular health.

Mechanism by which chronic kidney disease causes cardiovascular disease and the measures to manage this phenomenon

In Japan, the number of chronic kidney disease (CKD) patients is thought to be 13,300,000, next in size after those with hypertension and diabetes. Although the number of patients with CKD seems large, it does not mean that all these patients require special treatment. Among them, nephrologists should pay special attention to patients with glomerular filtration rate below 50 mL/min/1.73 m(2) and progressive deterioration of renal function. Treatment of these CKD patients by a limited number of specialists is simply impossible; hence, it is essential to request treatment from physicians who are involved in general internal medicine and primary care. It is well known that not only does CKD cause end-stage renal failure, it also causes the onset of cardiovascular diseases (CVD) such as cardiac infarction and cerebral stroke; however, the question is how much significance does CKD have as a risk factor for CVD. It is understandable that hypertension and CVD are often complications of CKD; however, in addition to what is conventionally mentioned, there are three or four mechanisms that we would like to emphasize, and discuss herein. Among them, we would like to stress the role of klotho genes with special reference to the generation of CVD in CKD patients. When patients develop CKD, it is therefore necessary to remove as far as possible any factors that could represent a risk for CVD. Moreover, by taking appropriate measures against clinical conditions that often complicate CKD, such as hypertension, renal anemia, hyperuricemia, and hyperlipidaemia, the development of CVD can be prevented.

Regenerative medicine of the kidney

End stage renal disease is a major health problem in this country and worldwide. Although dialysis and kidney transplantation are currently used to treat this condition, kidney regeneration resulting in complete healing would be a desirable alternative. In this review we focus our attention on current therapeutic approaches used clinically to delay the onset of kidney failure. In addition we describe novel approaches, like Tissue Engineering, Stem cell Applications, Gene Therapy, and Renal Replacement Therapy that may one day be possible alternative therapies for patients with the hope of delaying kidney failure or even stopping the progression of renal disease.

Association between circulating endothelial progenitor cells and hs-CRP in patients with diabetes

Aim

Endothelial progenitor cells (EPCs) play a critical role in maintaining endothelial function and might affect the progression of vascular disease. This study investigated the relationship between circulating EPCs and high-sensitivity C-reactive protein (hs-CRP) in patients with diabetes.

Methods

Our study population comprised 190 consecutive patients, with and without diabetes. To obtain EPC numbers, CD34+ and CD133+ cells in peripheral blood were counted by flow cytometry.

Results

Significantly higher hs-CRP levels were observed in patients with diabetes than in those without diabetes. However, the number of EPCs was significantly lower in diabetic patients and in patients with high hs-CRP levels. Patients with diabetes and high hs-CRP levels showed a marked decrease in the number of EPCs compared with non-diabetic patients with low hs-CRP levels.

Conclusion

These results suggest that inflammation leads to decreased circulating EPCs in patients with diabetes, which might be related to the pathogenesis of diabetic vascular disease.

Endothelial-regenerating cells: an expanding universe

Atherosclerosis is the most common cause for cardiovascular diseases and is based on endothelial dysfunction. A growing body of evidence suggests the contribution of bone marrow-derived endothelial progenitor cells, monocytic cells, and mature endothelial cells to vessel formation and endothelial rejuvenation. To this day, various subsets of these endothelial-regenerating cells have been identified according to cellular origin, phenotype, and properties in vivo and in vitro. However, the definition and biology, especially of endothelial progenitor cells, is complex and under heavy debate. In this review, we focus on current definitions of endothelial progenitor cells, highlight the clinical relevance of endothelial-regenerating cells, and provide new insights into cell-cell interactions involved in endothelial cell rejuvenation.

Endothelial progenitor cells and endothelial vesicles - what is the significance for patients with chronic kidney disease?

Endothelial progenitor cells are cells derived from the bone marrow that circulate in the bloodstream and can exhibit phenotypic characteristics of endothelial cells. They are thought to be involved in postnatal vasculogenesis and to potentially help repair injured endothelium. Circulating endothelial cells are mature endothelial cells in the circulation, and endothelial vesicles or microparticles are thought to be derived from the membranes of endothelial cells as a result of injury or activation. Recent research has focused on using these markers of endothelial injury and repair to assess the state of endothelial health. These efforts have been hampered by lack of uniformity in methodology and terminology. Recent developments in flow cytometry techniques have allowed better characterization and definition of these cells. We review the common techniques used to identify and isolate these cells, clinical studies in patients with chronic kidney disease (CKD) where they serve as markers of endothelial health and predictors of outcome, and possible mechanisms of progenitor cell dysfunction in CKD.

Levels of circulating endothelial progenitor cells are related to uremic toxins and vascular injury in hemodialysis patients

BACKGROUND

Patients suffering from chronic kidney diseases (CKD) exhibit cardiovascular diseases and profound endothelial dysfunction. CKD patients have reduced numbers of endothelial progenitor cells, but little is known about the factors influencing these numbers.

OBJECTIVES

Among these factors, we hypothesized that uremic toxins and vascular injury affect endothelial progenitor cells.

PATIENTS/METHODS

Thirty-eight hemodialysis patients were investigated and compared with 21 healthy controls. CD34+CD133+ immature progenitors, CD34+KDR+ endothelial progenitors cells (EPC) and myeloid EPC (mEPC) were counted in peripheral blood. Levels of uremic toxins beta(2)-microglobulin, indole-3 acetic acid, indoxylsulfate, p-cresylsulfate and homocysteine were measured. Vascular injury was assessed in hemodialysis (HD) patients by measuring aortic pulse wave velocity and plasma levels of endothelial microparticles. In vitro experiments were performed to study the effect of uremic toxins on apoptosis of progenitor cells.

RESULTS AND CONCLUSIONS

CD34+CD133+ immature progenitor cell number was negatively correlated with the levels of uremic toxins beta(2)-microglobulin and indole-3 acetic acid. In vitro, indole-3 acetic acid induced apoptosis of CD133+ cells. These data indicate uremic toxins have a deleterious role on progenitor cells, early in the differentiation process. Moreover, mEPC number was positively correlated with markers of vascular injury-pulse wave velocity and endothelial microparticle levels. This suggests that vascular lesions could stimulate progenitor cell mobilization, even in a context of reduced EPC induced by CKD. In conclusion, uremic toxins and vascular injury appear to affect endothelial progenitor cell biology in CKD.

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).

Hypertension induced by erythropoietin has a correlation with truncated erythropoietin receptor mRNA in endothelial progenitor cells of hemodialysis patients

Endothelial nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) contribute to erythropoietin (EPO)-induced hypertension, a major adverse reaction associated with EPO therapy. To investigate the mechanism of EPO-induced hypertension, we examined circulating endothelial progenitor cells (EPCs) taken from 56 hemodialysis (HD) patients. Among these EPCs (which reflect the condition of the endothelium), we looked for EPO receptor (EPOR) mRNAs. A truncated form of EPOR acts as a dominant negative regulator of EPO signaling, leading to hypertension. We found that the ratio of truncated EPOR mRNA in EPCs has a correlation with EPO-induced increase in blood pressure (r = 0.36, P = 0.02). The ratio of truncated to total EPOR mRNA in EPCs had an inverse correlation with EPO-induced cGMP production in vitro (r = -0.31, P = 0.02). A similar correlation was observed in cultured human endothelial cells after transfection of the full-length or truncated forms of EPOR (r = -0.92, P < 0.001). It follows, therefore, that evaluation of EPOR isoform mRNA in EPCs can predict EPO-induced hypertension. The termination of the EPO signal by truncated EPORs may decrease NO/cGMP production after EPO exposure, thereby raising blood pressure.

Molecular evaluation of circulating endothelial progenitor cells in children undergoing hemodialysis and after kidney transplantation

Increased risk of cardiovascular disease in end-stage renal disease (ESRD) has been explained by accelerated atherosclerosis and impaired angiogenesis, in which endothelial progenitor cells (EPC) may play key roles. Circulating cells with endothelial progenitor phenotype have not been evaluated in children with ESRD. Using a quantitative reverse transcriptase polymerase chain reaction (RT-PCR) approach, we measured endothelial-specific and progenitor-associated genes VE-cadherin (VE-C), CD146, CD31, tyrosine-protein kinase receptor (Tie-2), Flk1, CD133, and growth factors promoting EPC function, vascular endothelial growth factor (VEGF), erythropoietin (EPO), and stromal cell-derived factor-1 (SDF-1) in the blood of pediatric patients undergoing hemodialysis and after transplantation. Patients' metabolic parameters were correlated with EPC marker gene levels. Compared with controls, circulating VE-cadherin, CD146, Flk1, VEGF, and EPO RNA levels were decreased in ESRD and normalized in transplanted patients. Levels of VE-cadherin, which were the most significantly reduced in ESRD (p = 0.001) inversely correlated in all of the patient population with serum urea and creatinine concentration, whereas among the ESRD group showed an inverse correlation with diastolic blood pressure (BP), interventricular septum thickness (IVST), and left ventricular mass index. Pediatric ESRD patients may have lower angiogenic potential and increased cardiovascular morbidity, because of decreased expression of circulating endothelial cell specific transcripts. Prospective studies are required to link this expression pattern and its restoration in transplanted patients to cardiovascular outcome.

Low circulating CD34+ cell count is associated with poor prognosis in chronic hemodialysis patients

Circulating CD34-positive (CD34(+)) cells, a population that includes endothelial progenitor cells, are believed to contribute to vascular homeostasis. Here we determine the prognostic value of CD34(+) cell measurements in 216 chronic hemodialysis patients. A total of 43 cardiovascular events and 13 deaths occurred over an average 23 months follow-up in this cohort. A cutoff number for circulating CD34(+) cells was determined by receiver operating characteristic curve analysis to maximize the power of the CD34(+) cell count in predicting future cardiovascular events. Based on this, 93 patients were categorized as having low and 123 patients as having high numbers of CD34(+) cells, determined by flow cytometry at the time of enrollment. Both cumulative cardiovascular event-free survival and all-cause survival were significantly less in the group of patients with low numbers of CD34(+) cells. By multivariate analyses, a low level of circulating CD34(+) cells was an independent and significant predictor for both cardiovascular events and all-cause mortality. Our study shows that a reduced number of circulating CD34(+) cells is significantly associated with vascular risks and all-cause mortality in patients on chronic hemodialysis. These cells may be a useful biomarker.

Changes in angiogenesis-related factors in serum following autologous bone marrow cell implantation for severe limb ischemia

OBJECTIVE

Bone marrow mononuclear cell (BM-MNC) implantation (BMI) for critical severe limb ischemia especially for Buerger's disease shows excellent clinical results but the mechanism of this treatment is still unknown. In this study, we investigated the changes in serum levels of angiogenesis-related factors after BMI treatment.

RESEARCH DESIGN/METHODS

Twelve patients whose BMI treatments were clinically very effective was selected out of ninteen cases, nine patients had Buerger's disease, two patients had arteriosclerosis obliterans and one had systemic sclerosis. Venous bood from femoral vein or brachial vein of the recipient limbs of these patients.

RESULTS

Adrenomedulin (AM), soluble vascular cell adhesion molecule-1 (sVCAM-1), and C-reactive protein (CRP) serum levels 24 h after BMI treatment were significantly increased compared with those before BMI treatment (p < 0.05). Vascular endothelial growth factor (VEGF) serum levels after BMI treatment significantly increased between 1 week and 3 months after BMI treatment (p < 0.05). Nitric oxide (NO) serum levels after BMI treatment increased significantly 2 weeks after BMI treatment (p < 0.05). There was no correlation between the numbers of implanted cells and serum levels of measured angiogenesis-related factors that were significantly increased after BMI treatment.

CONCLUSION

It was concluded that the mechanism underlying BMI treatment consists of early and late phases. The early phase involves the direct action by implanted cells, and the late phase involves indirect paracrine action. In addition, it was considered that BMI treatment is effective when we implant a sufficient level of bone marrow (600 ml) to treat severe limb ischemia.

Perioperative iloprost and endothelial progenitor cells in uremic patients with severe limb ischemia undergoing peripheral revascularization

The incidence of severe limb ischemia (SLI) is high among haemodialysis (HD) patients. Limb rescue rate after surgical revascularization is relatively poor compared with patients with normal renal function. Prostanoids are an interesting category as adjuvants to revascularization. New vessel growth develops not exclusively by proliferation of endothelial cells in vascular extremities but also by cells mobilized from the bone marrow (HSC), transformed into endothelial progenitor cells (EPC) contributing to both re-endothelialization and neovascularization. Basal number of HSC and EPC is significantly reduced in HD patients and correlated with a subsequent defective neovascularization. The aim of this study was to evaluate the effects of perioperative treatment with iloprost in uremic patients with acute ischemia of lower limbs, undergoing surgical revascularization, on endothelial progenitor cells, hypothesizing a possible biological mechanism induced by the prostanoids. A search was also made for vascular remodeling processes through the analysis of the concentrations of soluble adhesion molecules (i-CAM, v-CAM, e-selectin), biochemical markers of endothelial activation. Thirty HD patients with SLI undergoing peripheral revascularization were enrolled (15 were treated with iloprost and 15 with a placebo). Iloprost was administered as an intra-arterial bolus of 3000 ng over 1 to 3 min immediately after revascularization and in the same affected artery. Serum samples were taken before revascularization (T0), at 6 (T6) and 24 h (T24) after infusion to measure sICAM-1, sE-selectin, and sVCAM-1, and for quantification of HSC and EPC. Progenitors were identified by specific surface markers CD34+, CD133+ and VEGFR2+. Count was conducted using PROCOUNT performed in a TRUCOUNT tube and with a FACSort flow cytometer. Before revascularization, all patients showed a decreased number of HSC and EPC. After 6 h, HSC augmented significantly compared with T0 in both groups. The iloprost group attained a significant increase compared with the placebo group. HSC levels reduced drastically at T24. EPC augmented significantly compared with basal level after 24 h. In the iloprost group, the increase was considerable compared with the placebo group. A close negative correlation, assessed by Pearson coefficient (r), was found between HSC and EPC at T24 in the iloprost group (R = 0.82 P < 0.01). Adhesion molecules had increased levels at T6 and T24 in both groups. Moreover, a close positive correlation, assessed by Pearson coefficient, was found between EPC and adhesion molecules in both groups but the iloprost group maintained a better statistical association. Revascularization stimulated HSC and EPC release from bone marrow but at a different time: HSC increased suddenly at 6 h and diminished to a minimal amount at T24, conversely, EPC increased significantly only at T24. Iloprost treatment was able to amplify this mechanism validating recent findings (North TE et al., [31]). Adhesion molecules as markers of endothelial activation and vascular development confirmed this tendency.

Emerging biomarkers for evaluating cardiovascular risk in the chronic kidney disease patient: how do new pieces fit into the uremic puzzle?

Premature cardiovascular disease (CVD), including stroke, peripheral vascular disease, sudden death, coronary artery disease, and congestive heart failure, is a notorious problem in patients with chronic kidney disease (CKD). Because the presence of CVD is independently associated with kidney function decline, it appears that the relationship between CKD and CVD is reciprocal or bidirectional, and that it is this association that leads to the vicious circle contributing to premature death. As randomized, placebo-controlled trials have so far been disappointing and unable to show a survival benefit of various treatment strategies, such a lipid-lowering, increased dialysis dose and normalization of hemoglobin, the risk factor profile seems to be different in CKD compared with the general population. Indeed, seemingly paradoxical associations between traditional risk factors and cardiovascular outcome in patients with advanced CKD have complicated our efforts to identify the real cardiovascular culprits. This review focuses on the many new pieces that need to be fit into the complicated puzzle of uremic vascular disease, including persistent inflammation, endothelial dysfunction, oxidative stress, and vascular ossification. Each of these is not only highly prevalent in CKD but also more strongly linked to CVD in these patients than in the general population. However, a causal relationship between these new markers and CVD in CKD patients remains to be established. Finally, two novel disciplines, proteomics and epigenetics, will be discussed, because these tools may be helpful in the understanding of the discussed vascular risk factors.

Spatiotemporal control over growth factor signaling for therapeutic neovascularization

Many of the qualitative roles of growth factors involved in neovascularization have been delineated, but it is unclear yet from an engineering perspective how to use these factors as therapies. We propose that an approach that integrates quantitative spatiotemporal measurements of growth factor signaling using 3-D in vitro and in vivo models, mathematic modeling of factor tissue distribution, and new delivery technologies may provide an opportunity to engineer neovascularization on demand.

The unique character of cardiovascular disease in chronic kidney disease and its implications for treatment with lipid-lowering drugs

Although the risk for cardiovascular disease (CVD) is high in individuals with chronic kidney disease (CKD), there are very limited data to guide the use of lipid-lowering drugs (LLDs) in this population because the major trials of LLDs in the general population have included very few individuals with CKD. The pathophysiologic and epidemiologic differences of CVD in the CKD population suggest that the study findings derived in the general population may not be directly applicable to those with CKD, and the few trials that have been directed at patients with kidney disease have not shown clear clinical benefits of LLDs. The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) Work Group has provided consensus-based guidelines for managing dyslipidemias in individuals with CKD and after renal transplantation. Since the publication of these statements, further data have emerged and multiple studies are ongoing to define better the role of LLDs in patients with CKD. In this article, the data that are pertinent to the CKD population are reviewed, and updated recommendations for use of LLD in the CKD population are provided.

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

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

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

Effects of haemodialysis on circulating endothelial progenitor cell count

During haemodialysis (HD) the endothelium is the first organ to sense and to be impaired by mechanical and immunological stimuli. We hypothesized that a single HD session induces mobilization of endothelial progenitor cells (EPCs) and that cardiovascular risk factors may influence this process. We quantified EPCs at different maturational stages (CD34+, CD133+/VEGFR2+) in blood samples from 30 patients, during HD and on the interdialytic day, and in 10 healthy volunteers. Samples were drawn at the start of HD, 1, 2 and 3 h after, at the end of HD and at 24 h on the interdialytic day. Patients were divided into two groups based on a recent risk scoring system (SCORE project): low-risk (LR) and high-risk groups (HR). HD patients showed a significantly reduced basal number of EPCs with respect to healthy volunteers. In contrast, we observed increasing EPCs during HD whereas they diminished on the interdialytic day. The EPC number was directly correlated with HD time progression. The EPC number during HD was increased in the HR group with respect to the LR group. We had a direct correlation between risk score and number of EPCs. Cardiovascular risk factors influenced the mobilization of stem cells from the bone marrow. This feature could be the direct consequence of an augmented request of stem cells to respond to the most important endothelial impairment but could also show a defective capacity of EPCs to home in and repair the sites of vascular injury.

Working hypothesis to redefine endothelial progenitor cells

Since 1997, postnatal vasculogenesis has been purported to be an important mechanism for neoangiogenesis via bone marrow (BM)-derived circulating endothelial progenitor cells (EPCs). Based on this paradigm, EPCs have been extensively studied as biomarkers to assess severity of cardiovascular disease and as a cell-based therapy for several human cardiovascular disorders. In the majority of studies to date, EPCs were identified and enumerated by two primary methodologies; EPCs were obtained and quantified following in vitro cell culture, or EPCs were identified and enumerated by flow cytometry. Both methods have proven controversial. This review will attempt to outline the definition of EPCs from some of the most widely cited published reports in an effort to provide a framework for understanding subsequent studies in this rapidly evolving field. We will focus this review on studies that used cell culture techniques to define EPCs.

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

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

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

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

Circulating endothelial progenitor cells predict coronary artery disease severity

BACKGROUND

Circulating endothelial progenitor cells (EPCs) may play an important role in the body's defense against atherosclerosis. Previous studies have shown an association between EPC numbers and the presence of traditional coronary artery disease (CAD) risk factors. The relationship between EPC numbers and the severity of atherosclerosis is, however, not known.

METHODS

EPC counts were measured by quantitative cell culture in 122 patients undergoing diagnostic cardiac catheterization. The association between patients' EPC count and the presence of multivessel CAD and traditional cardiac risk factors was assessed using logistic regression analysis.

RESULTS

The median age of the study population was 58 years; 37% had multivessel CAD, 29% had diabetes, and 14% had myocardial infarction this admission. EPC counts did not vary significantly with most established cardiac risk factors but were lower in diabetics versus nondiabetics and trended toward lower numbers in older patients. EPC count was the second strongest predictor of multivessel CAD, after patient age. Patients with multivessel disease had significantly lower EPC counts than those without (median, 3 vs 13; P < .0088). For every 10 colony forming unit increase in EPCs, a patient's likelihood for multivessel CAD declined by 20% (P < .001).

CONCLUSION

This study demonstrates an inverse relationship between circulating EPCs and CAD severity, independent of traditional risk factors. If confirmed in ongoing studies, this may represent an important new diagnostic and therapeutic target for coronary disease treatment.

Endothelial Progenitor Cells in Chronic Renal Insufficiency

There is growing evidence for a role of endothelial progenitor cells (EPCs) in the repair of damaged endothelium. It remains unclear which cell populations are most useful for clinical trials. Administration of drugs increasing EPC numbers and/or improving functional properties seems attractive. Further basic research is necessary to understand the mechanisms of mobilization, differentiation and homing of EPC in general and in particular under uremic conditions. Nephrologists should search for strategies to ameliorate EPC dysfunction of uremia. In this way it might be possible to test whether improved EPC biology is associated with decreased cardiovascular mortality in uremic humans. In any such studies the difficulties are going to be related to the complex procedures for EPC isolation, the testing of their identity and differentiation and their propagation before use.

Subtotal nephrectomy impairs ischemia-induced angiogenesis and hindlimb re-perfusion in rats

Kidney disease is associated with increased cardiovascular morbidity, but underlying mechanisms are poorly understood. We tested the hypothesis that chronic renal insufficiency impairs angioadaptation in a rat model of hindlimb ischemia. Twenty male Sprague-Dawley rats (8 weeks old) underwent subtotal nephrectomy (5/6SNX) or sham surgery (each n=10). Ten weeks later, unilateral hindlimb ischemia was induced in all animals. Hindlimb perfusion was assessed by laser Doppler perfusion imaging and fluorescent microsphere injection studies 2 weeks after surgery. Ischemia-induced angiogenesis was measured by analyzing capillary density using CD31 immunofluorescence. Expression of vascular endothelial growth factor (VEGF), its receptors (VEGFRs) and inducible as well as endothelial nitric oxide (NO) synthase was measured by real-time reverse transcription-polymerase chain reaction. Laser Doppler hindpaw perfusion was significantly reduced in 5/6SNX compared to sham-operated animals. Impaired hindlimb re-perfusion in 5/6SNX vs control rats was confirmed by fluorescent microsphere injection studies (relative perfusion of ischemic vs non-ischemic limb: 68.9+/-6.4 vs 92.4+/-3.6%, P=0.005). Ischemic skeletal muscle neovascularization increased to a greater extent in sham-operated compared to 5/6SNX rats (69+/-8 vs 29+/-7%, P<0.05). VEGF and VEGFR-1/2 mRNA expression increased in ischemic hindlimbs of control rats, whereas no change or a decrease was observed in 5/6SNX. In contrast, inducible and endothelial NO synthase expression did not significantly differ between sham and 5/6SNX rats. Chronic renal insufficiency impairs angiogenesis and limb perfusion in a rat hindlimb ischemia model. Impaired angioadaptation may contribute to the poor prognosis of patients with renal failure suffering from peripheral arterial disease.

Endothelial progenitor cells: diagnostic and therapeutic considerations

Endothelial progenitor cells (EPCs) may be defined as adherent cells derived from peripheral blood- or bone marrow-derived mononuclear cells demonstrating acLDL uptake and isolectin-binding capacity. The number of circulating EPCs inversely correlates with the number of cardiovascular risk factors and is reduced in cardiovascular disease. This measurement may therefore serves as a surrogate marker for cardiovascular disease risk. EPC numbers can be modified by various means. However, the effectiveness of risk-factor modification on EPC number and function is currently unknown. Furthermore, EPCs may be used as a potential therapy for a variety of vascular disease states including ischaemia, restenosis and pulmonary hypertension. This review provides an update on multiple factors that affect EPC number as well as highlighting the potential use of EPCs as a novel marker of vascular dysfunction. Furthermore, potential gene- and/or EPC-based approaches to a number of vascular disease states are explored.

Therapeutic angiogenesis by bone marrow implantation for critical hand ischemia in patients with peripheral arterial disease: a pilot study

OBJECTIVE

Implantation of bone marrow mononuclear cells (BM-MNCs), including endothelial progenitor cells, into ischemic lower limbs has been shown to improve symptoms in patients with peripheral arterial diseases (PAD). This study investigated whether BM-MNC implantation (BMI) is also effective for the ischemic hands of these patients.

METHODS

Seven PAD patients with hand ischemia were enrolled: six patients had thromboangiitis obliterans and one had collagen disease. All seven had symptoms involving either resting pain or non-healing ischemic ulcers of the hand. Approximately 600 mL of MNCs were separated from BM and concentrated to a final volume of 40-50 mL, which were injected into ischemic hands. Ischemic status was evaluated by measuring the digital/brachial pressure index (DBI), visual analog pain scale, and the healing of ulcers before and 6 months after BMI.

RESULTS

The mean number of implanted MNCs, CD34-positive cells, and CD34,133-positive cells was 3.67 +/- 0.53 x 10(9), 4.94 +/- 2.45 x 10(7), and 2.52 +/- 1.57 x 10(7), respectively. Mean DBI in those patients was 0.15 +/- 0.30 before BMI and significantly increased to 0.67 +/- 0.19 at 6 months after BMI (p = 0.004). All patients also showed improvement of pain scale and ischemic ulcers. There was no significant correlation between the number of implanted cells and improvement in the degree of DBI or the pain scale.

CONCLUSION

Autologous BMI could be a promising and safe method of therapeutic angiogenesis for critical hand ischemia in PAD patients.

Circulating endothelial cells and endothelial progenitor cells: two sides of the same coin, or two different coins?

Circulating endothelial cells (CECs) and endothelial progenitor cells (EPCs) are two populations of recently discovered endothelioid cells present in the blood. The former are thought to arise from the intima, the latter from the bone marrow. However, it is becoming clear that these are not in fact homogenous populations (e.g. differing degrees of apoptosis, necrosis and viability, differing expression of monocyte markers) but do in fact represent more than one species of endothelioid cell. Thus whilst originally defined by different criteria (e.g. CD146 by immunobeads, CD34 by flow cytometry) and the perception of independence, there is also growing evidence of some degree of commonality, i.e. some cells co-expressing CD146 and CD34. Furthermore, relationships between these two cells types and, for example, plasma and physiological indicators of vascular damage, and the risk factors for atherosclerosis, suggest a potential role for these cells in the pathophysiology of this disease, possibly as markers. The current document reviews this evidence, presenting a view of some degree of shared ancestry that may have implications for pathophysiology and cell biology.