Bone Marrow-derived Progenitor Cells Research Articles

Stem Cell Recruitment After Injury: Lessons for Regenerative Medicine

Tissue repair and regeneration are thought to involve resident cell proliferation as well as the selective recruitment of circulating stem and progenitor cell populations through complex signaling cascades. Many of these recruited cells originate from the bone marrow, and specific subpopulations of bone marrow cells have been isolated and used to augment adult tissue regeneration in preclinical models. Clinical studies of cell-based therapies have reported mixed results, however, and a variety of approaches to enhance the regenerative capacity of stem cell therapies are being developed based on emerging insights into the mechanisms of progenitor cell biology and recruitment following injury. This article discusses the function and mechanisms of recruitment of important bone marrow-derived stem and progenitor cell populations following injury, as well as the emerging therapeutic applications targeting these cells.

The Role of Bone Marrow-derived Progenitor Cells in the Systemic Response to Radiation-induced Lung Damage

The Role of Bone Marrow-derived Progenitor Cells in the Systemic Response to Radiation-induced Lung Damage

High Level of Circulating Endothelial Progenitor Cells Positively Correlates with Serum Vascular Endothelial Growth Factor in Patients with Renal Cell Carcinoma

Although accumulated evidence indicates that circulating endothelial progenitor cells contribute to tumor neovascularization, to our knowledge the level of these cells and its correlation with serum vascular endothelial growth factor in patients with renal cell carcinoma have not been studied. We measured this level and investigated its clinical significance in patients with renal cell carcinoma. The level of circulating endothelial progenitor cells (percent of total peripheral blood mononuclear cells) was quantified by assaying the CD45(-)CD34(+)vascular endothelial growth factor receptor 2(+) cell phenotype in 53 patients with renal cell carcinoma, 33 with benign renal tumors and 40 healthy controls. Serum vascular endothelial growth factor was quantified. The mean circulating endothelial progenitor cell level in patients with renal cell carcinoma was 0.281%, significantly higher than in patients with benign renal tumors and healthy controls (0.073% and 0.076%, respectively, each p <0.001). Patients with stage III-IV renal cell carcinoma had a statistically higher level of these cells than those with stage I-II (0.339% vs 0.243%, p <0.001). The mean level in patients with renal cell carcinoma greater than 7 cm was 0.331%, significantly higher than in those with tumors 4 or less and 4 to 7 cm (0.225% and 0.231%, respectively, each p <0.001). Mean serum vascular endothelial growth factor in patients with renal cell carcinoma was higher than in patients with benign renal tumors and healthy controls (315.5 vs 34.6 and 26.9 pg/ml, respectively, each p <0.001). The preoperative circulating endothelial progenitor cell level positively correlated with serum vascular endothelial growth factor in patients with renal cell carcinoma (r = 0.710, p <0.001). Levels of these cells and of vascular endothelial growth factor significantly decreased postoperatively compared to preoperatively (0.081% vs 0.297% and 31.69 vs 310.70 pg/ml, respectively, each p <0.001). A high circulating endothelial progenitor cell level was found in patients with renal cell carcinoma, which positively correlated with serum vascular endothelial growth factor. Results support the potential use of circulating endothelial progenitor cells as a novel biomarker for renal cell carcinoma.

Diabetes and aging: a different phenotypic commitment of circulating and resident stem cells?

Atherosclerosis is a vascular disease largely attributed to chronic vascular injury, and its clinical manifestations appear more frequently in aged subjects. Accumulation of vascular smooth muscle cells in the tunica intima plays a major role in the pathogenesis of atherosclerosis. Arterial smooth muscle cells are heterogeneous even in the normal vessel wall and display more marked different phenotypes in pathological conditions. Smooth muscle cells in atherosclerotic plaques display a de-differentiated or ‘‘synthetic’’ phenotype compared to a ‘‘contractile’’ phenotype in the normal media. Aorta stiffens with age and other cardiovascular risk factors. In particular, diabetes-induced activation of the renin–angiotensin system increases the expression of angiotensin II, further increasing aortic calcification and stiffness. Thus, alterations of aortic and carotid walls in patients with diabetes were traditionally considered a sort of ‘‘accelerated aging.’’ In the last years, the contribution of stem cells to atherosclerosis has been highlighted. Bone marrow and peripheral blood-derived endothelial and vascular smooth muscle cell resident progenitors both contribute to vascular remodeling during atherogenetic process and aging [1]. Both circulating and resident progenitor cells have been evocated to contribute to the response of the adult arterial wall to damage. Chronic treatment with bone marrow-derived progenitor cells from young non-atherosclerotic ApoE/ mice prevents atherosclerosis progression in ApoE/ recipients despite persistent hypercholesterolemia, whereas bone marrow-derived progenitor cells from older ApoE/ mice with atherosclerosis were much less effective [2]. These findings suggest that the progressive bone marrow-derived progenitor cells deficit may contribute to the development of atherosclerosis. Nevertheless, atherosclerotic lesions are characterized from the increase of stem cell markerexpressing cells, and macroscopically normal aortas from human and rat aged donors show an increased number of VEGFR-1 and c-kit cells in the thickened intima [3]. Also, diabetes alters the function of circulating progenitor cells. Depletion of bone marrow-derived angiogenic cell populations may further promote atherogenesis and aortic calcification in patients with diabetes mellitus [4]. In multivariable analyses, the increase in colony-forming units from endothelial progenitor cells was associated with the decrease in coronary artery and abdominal aortic calcification [5]. These changes were not associated with changes in CD34 expression, suggesting that a decreased angiogenic potential contributes to the development of human atherosclerosis. Moreover, decreasing colonyforming capacity associated with the progressive increase of calcification scores [5]. Recently, it has been reported that diabetes mellitus patients had significantly higher expression of osteocalcin and bone alkaline phosphatase on circulating VEGFR-2/CD34 progenitor cells than control subjects [6]. Moreover, cultured VEGFR-2/CD34 cells from diabetes mellitus patients formed structures highly suggestive of calcified nodules, strongly suggesting that circulating progenitor cells from diabetic patients show a drift toward a pro-calcific phenotype that may be driven by inflammatory signals in response to injury [6], similarly to that observed in non-vascular tissues [7]. Monocyte– macrophage recruitment is a crucial step for a correct angiogenesis, and this mechanism is mainly mediated by VEGFR-1, that favors the increase of vessel lumen, vessel Communicated by Massimo Federici.

DBA-Lectin Reactivity Defines Mouse Uterine Natural Killer Cell Subsets with Biased Gene Expression1

Endometrial decidualization, a process essential for blastocyst implantation in species with hemochorial placentation, is accompanied by an enormous but transient influx of natural killer (NK) cells. Mouse uterine NK (uNK) cell subsets have been defined by diameter and cytoplasmic granule number, reflecting stage of maturity, and by histochemical reactivity with Periodic Acid Schiff (PAS) reagent with or without co-reactivity with Dolichos biflorus agglutinin (DBA) lectin. We asked whether DBA- and DBA+ mouse uNK cells were equivalent using quantitative RT-PCR analyses of flow-separated, midpregnancy (Gestation Day [gd] 10) cells and immunohistochemistry. CD3E (CD3)-IL2RB (CD122)+DBA cells were identified as the dominant Ifng transcript source. Skewed IFNG production by uNK cell subsets was confirmed by analysis of uNK cells from eYFP-tagged IFNG-reporter mice. In contrast, CD3E-IL2RB+DBA+ uNK cells expressed genes compatible with significantly greater potential for IL22 synthesis, angiogenesis, and participation in regulation mediated by the renin-angiotensin system (RAS). CD3E-IL2RB+DBA+ cells were further divided into VEGFA+ and VEGFA- subsets. CD3E-IL2RB+DBA+ uNK cells but not CD3E-IL2RB+DBA- uNK cells arose from circulating, bone marrow-derived progenitor cells by gd6. These findings indicate the heterogeneous nature of mouse uNK cells and suggest that studies using only DBA+ uNK cells will give biased data that does not fully represent the uNK cell population.

Well MET: Exosomes promote metastasis through transfer of MET from melanoma to bone marrow progenitors

Well <scp>MET</scp>: Exosomes promote metastasis through transfer of <scp>MET</scp> from melanoma to bone marrow progenitors

Injected matrix stimulates myogenesis and regeneration of mouse skeletal muscle after ischaemic injury

Biomaterial-guided regeneration represents a novel approach for the treatment of myopathies. Revascularisation and the intramuscular extracellular matrix are important factors in stimulating myogenesis and regenerating muscle damaged by ischaemia. In this study, we used an injectable collagen matrix, enhanced with sialyl LewisX (sLeX), to guide skeletal muscle differentiation and regeneration. The elastic properties of collagen and sLeX-collagen matrices were similar to those of skeletal muscle, and culture of pluripotent mESCs on the matrices promoted their differentiation into myocyte-like cells expressing Pax3, MHC3, myogenin and Myf5. The regenerative properties of matrices were evaluated in ischaemic mouse hind-limbs. Treatment with the sLeX-matrix augmented the production of myogenic-mediated factors insulin-like growth factor (IGF)-1, and IGF binding protein-2 and -5 after 3 days. This was followed by muscle regeneration, including a greater number of regenerating myofibres and increased transcription of Six1, M-cadherin, myogenin and Myf5 after 10 days. Simultaneously, the sLeX-matrix promoted increased mobilisation and engraftment of bone marrow-derived progenitor cells, the development of larger arterioles and the restoration of tissue perfusion. Both matrix treatments tended to reduce maximal forces of ischaemic solei muscles, but sLeX-matrix lessened this loss of force and also prevented muscle fatigue. Only sLeX-matrix treatment improved mobility of mice on a treadmill. Together, these results suggest a novel approach for regenerative myogenesis, whereby treatment only with a matrix, which possesses an inherent ability to guide myogenic differentiation of pluripotent stem cells, can enhance the endogenous vascular and myogenic regeneration of skeletal muscle, thus holding promise for future clinical use.

Involvement of Bone Marrow-Derived Vascular Progenitor Cells in Neovascularization During Formation of the Corpus Luteum in Mice1

Neovascularization is necessary for formation of the corpus luteum (CL) and includes angiogenesis and vasculogenesis. Vasculogenesis is the formation of new blood vessels by bone marrow-derived endothelial progenitor cells. Here we investigated whether vasculogenesis occurs in neovascularization during CL formation. Mice transplanted with bone marrow from transgenic mice expressing green fluorescent protein (GFP) were injected with equine chorionic gonadotropin and human chorionic gonadotropin (hCG) to induce ovulation and subsequent CL formation. Immunohistochemistry was performed on the ovaries obtained before hCG injection and at 6, 12, and 24 h after hCG injection using antibodies for CD34 or CD31 (an endothelial cell marker), platelet-derived growth factor receptor beta (PDGFR-beta, a pericyte marker), F4/80 (a macrophage marker), and GFP (a bone marrow-derived cell marker). Cells immunostained for CD34, PDGFR-beta, F4/80, and GFP were present in the theca cell layer of the preovulatory follicle before hCG injection. Each of these cell types invaded the granulosa cell layer after hCG injection, and a number of them were observed in the CL 24 h after hCG injection. Fluorescence-based immunohistochemistry or double immunohistochemical staining revealed that a few CD34/CD31-positive cells and PDGFR-beta-positive cells were also positive for GFP in the preovulatory follicle and CL, and that many of the GFP-positive cells recruited to the CL during CL formation were F4/80-positive macrophages. In conclusion, bone marrow-derived vascular progenitor cells and macrophages contribute to neovascularization during CL formation.

Systemic Preconditioning by a Prolyl Hydroxylase Inhibitor Promotes Prevention of Skin Flap Necrosis via HIF-1-Induced Bone Marrow-Derived Cells

BackgroundLocal skin flaps often present with flap necrosis caused by critical disruption of the blood supply. Although animal studies demonstrate enhanced angiogenesis in ischemic tissue, no strategy for clinical application of this phenomenon has yet been defined. Hypoxia-inducible factor 1 (HIF-1) plays a pivotal role in ischemic vascular responses, and its expression is induced by the prolyl hydroxylase inhibitor dimethyloxalylglycine (DMOG). We assessed whether preoperative stabilization of HIF-1 by systemic introduction of DMOG improves skin flap survival.Methods and ResultsMice with ischemic skin flaps on the dorsum were treated intraperitoneally with DMOG 48 hr prior to surgery. The surviving area with neovascularization of the ischemic flaps was significantly greater in the DMOG-treated mice. Significantly fewer apoptotic cells were present in the ischemic flaps of DMOG-treated mice. Interestingly, marked increases in circulating endothelial progenitor cells (EPCs) and bone marrow proliferative progenitor cells were observed within 48 hr after DMOG treatment. Furthermore, heterozygous HIF-1α-deficient mice exhibited smaller surviving flap areas, fewer circulating EPCs, and larger numbers of apoptotic cells than did wild-type mice, while DMOG pretreatment of the mutant mice completely restored these parameters. Finally, reconstitution of wild-type mice with the heterozygous deficient bone marrow cells significantly decreased skin flap survival.ConclusionWe demonstrated that transient activation of the HIF signaling pathway by a single systemic DMOG treatment upregulates not only anti-apoptotic pathways but also enhances neovascularization with concomitant increase in the numbers of bone marrow-derived progenitor cells.

TGF-β1-induced LPP expression dependant on Rho kinase during differentiation and migration of bone marrow-derived smooth muscle progenitor cells

Lipoma preferred partner (LPP) has been identified as a protein which is highly selective for smooth muscle progenitor cells (SMPCs) and regulates differentiation and migration of SMPCs, but mechanisms of LPP expression are not elucidated clearly. The aim of the present study was to discuss the mechanisms by which LPP expression is regulated in the differentiation and migration of SMPCs induced by TGF-β1. It was found that TGF-β1 could significantly increase the expression of LPP, smooth muscle α-actin, smooth muscle myosin heavy chain (SM-MHC), and smoothelin in SMPCs. Moreover, inactivation of Rho kinase (ROK) with ROK inhibitors significantly inhibited LPP mRNA expression in TGF-β1-treated SMPCs and mouse aortic smooth muscle cells (MAoSMCs). At the same time, LPP silencing with short interfering RNA significantly decreased SMPCs migration. In conclusion, LPP appears to be a ROK-dependant SMPCs differentiation marker that plays a role in regulating SMPCs migration.

Endogenous Stem Cell Therapy Enhances Fat Graft Survival

Lipoaspirate centrifugation creates graded density of adipose tissue. High-density fat contains more vasculogenic cytokines and progenitor cells and has greater graft survival than low-density fat. The authors hypothesize that accelerating the bone marrow-derived progenitor cell response to injected low-density fat will improve its graft survival. Male 8-week-old FVB mice (n=60) were grafted with either high-density (n=20) or low-density (n=40) human lipoaspirate. Half of the mice receiving low-density fat (n=20) were treated with a stem cell mobilizer for 14 days. Grafted fat was harvested at 2 and 10 weeks for analysis. Low-density fat, low-density fat plus daily AMD3100, and high-density fat had 26±3.0, 61.2±7.5, and 49.6±3.5 percent graft survival, respectively, at 2 weeks (low-density fat versus low-density fat plus daily AMD3100 and low-density fat versus high-density fat, both p<0.01). Similar results were observed 10 weeks after grafting. Mice receiving low-density fat plus daily AMD3100 had significantly more vasculogenic progenitor cells per cubic centimeter of peripheral blood (p<0.01) and more new blood vessels (p<0.01). Both low-density fat plus daily AMD3100 and high-density fat contained more stromal-derived factor-1α and vascular endothelial growth factor mRNA/protein. Endogenous progenitor cell mobilization enhances low-density fat neovascularization, increases vasculogenic cytokine expression, and improves graft survival to a level equal to that of high-density fat grafts.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Platelets and Platelet Interaction with Progenitor Cells in Vascular Homeostasis and Inflammation

Platelet adhesion on vascular wall is the first step following vascular injury. Differential platelet secretion supports angiogenesis and vascular homeostasis. Progenitor cells are pluripotent cells responsible for tissue regeneration and wound healing. Upon ischemia bone marrow-derived progenitor cells are mobilized into peripheral circulation and domiciliate into peripheral organ vasculature and either give birth to a series of cardiovascular cells, including endothelial cells, macrophages, smooth muscle cells, or support in a paracrinic way the angiogenic capacity of local tissue cells. Mobilization, chemotaxis, adhesion, differentiation and interaction with vascular cells are essential steps of progenitor cell-mediated tissue repair. This review summarizes the recent advances in our understanding of platelet function with focus on interaction with progenitor cells and its role in cardiovascular homeostasis. Moreover, the role of platelet microparticles in progenitor cell function is separately addressed. Understanding the mechanisms of platelet interaction with progenitor cells provides us with new insights in the mechanisms of vascular homeostasis and possible new therapeutical targets supporting vascular repair.

IL-34 is a tissue-restricted ligand of CSF1R required for the development of Langerhans cells and microglia

The differentiation of bone marrow-derived progenitor cells into monocytes, tissue macrophages and some dendritic cell (DC) subtypes requires the growth factor CSF1 and its receptor, CSF1R. Langerhans cells (LCs) and microglia develop from embryonic myeloid precursor cells that populate the epidermis and central nervous system (CNS) before birth. Notably, LCs and microglia are present in CSF1-deficient mice but absent from CSF1R-deficient mice. Here we investigated whether an alternative CSF1R ligand, interleukin 34 (IL-34), is responsible for this discrepancy. Through the use of IL-34-deficient (Il34(LacZ/LacZ)) reporter mice, we found that keratinocytes and neurons were the main sources of IL-34. Il34(LacZ/LacZ) mice selectively lacked LCs and microglia and responded poorly to skin antigens and viral infection of the CNS. Thus, IL-34 specifically directs the differentiation of myeloid cells in the skin epidermis and CNS.

Fibrocytes in health and disease

Fibrocytes, a group of bone marrow-derived mesenchymal progenitor cells, were first described in 1994 as fibroblast-like, peripheral blood cells that migrate to regions of tissue injury. These cells are unique in their expression of extracellular matrix proteins concomitantly with markers of hematopoietic and monocyte lineage. The involvement of fibrocytes and the specific role they play in the process of wound repair has been a focus of study since their initial description. Fibrocytes contribute to the healing repertoire via several mechanisms; they produce a combination of cytokines, chemokines, and growth factors to create a milieu favorable for repair to occur; they serve as antigen presenting cells (APCs); they contribute to wound closure; and, they promote angiogenesis. Furthermore, regulatory pathways involving serum amyloid P, leukocyte-specific protein 1, and adenosine A2A receptors have emphasized the significant role that fibrocytes have in wound healing and fibrosis. The therapeutic targeting of fibrocytes holds promise for the augmentation of wound repair and the treatment of different fibrosing disorders.

Protein Kinase G-I Deficiency Induces Pulmonary Hypertension through Rho A/Rho Kinase Activation

Protein kinase G (PKG) plays an important role in the regulation of vascular smooth cell contractility and is a critical mediator of nitric oxide signaling, which regulates cardiovascular homeostasis. PKG-I-knockout (Prkg1(-/-)) mice exhibit impaired nitric oxide/cGMP-dependent vasorelaxation and systemic hypertension. However, it remains unknown whether PKG-I deficiency induces pulmonary hypertension. In this study, we characterized the hypertensive pulmonary phenotypes in Prkg1(-/-) mice and delineated the underlying molecular basis. We observed a significant increase in right ventricular systolic pressure in Prkg1(-/-) mice in the absence of systemic hypertension and left-sided heart dysfunction. In addition, we observed marked muscularization of distal pulmonary vessels in Prkg1(-/-) mice. Microangiography revealed impaired integrity of the pulmonary vasculature in Prkg1(-/-) mice. Mechanistically, PKG-I-mediated phosphorylation of Rho A Ser188 was markedly decreased, and the resultant Rho A activation was significantly increased in Prkg1(-/-) lung tissues, which resulted in Rho kinase activation. The i.t. administration of fasudil, a Rho kinase inhibitor, reversed the hypertensive pulmonary phenotype in Prkg1(-/-) mice. Taken together, these data show that PKG-I deficiency induces pulmonary hypertension through Rho A/Rho kinase activation-mediated vasoconstriction and pulmonary vascular remodeling.

Activation of alternative pathways of angiogenesis and involvement of stem cells following anti-angiogenesis treatment in glioma.

Malignant gliomas are hypervascular tumors that are highly resistant to all the currently available multimodal treatments. Therefore, anti-angiogenic therapies targeting VEGF or VEGF receptors (VEGFRs) were designed and thought to be an effective tool for controlling the growth of malignant gliomas. However, recent results of early clinical trials using humanized monoclonal antibodies against VEGF (Bevacizumab), as well as small-molecule tyrosine kinase inhibitors that target different VEGF receptors (VEGFRs) (Vatalanib, Vandetanib, Sunitinib, Sorafenib, etc) alone or in combination with other therapeutic agents demonstrated differing outcomes, with the majority of reports indicating that glioma developed resistance to the employed anti-angiogenic treatments. It has been noted that continued anti-angiogenic therapy targeting only the VEGF-VEGFR system might affect pro-angiogenic factors other than VEGF, such as basic fibroblast growth factor (bFGF), stromal derived factor 1 (SDF-1) and Tie-2. These factors may in turn stimulate angiogenesis by mobilizing bone marrow derived precursor cells, such as endothelial progenitor cells (EPCs), which are known to promote angiogenesis and vasculogenesis. In this short review, the current antiangiogenic treatments, possible mechanisms of activation of alternative pathways of angiogenesis, and possible involvement of bone marrow derived progenitor cells in the failure of anti-angiogenic treatments are discussed.

Abstract 31: In Vivo Targeting of Inflammation Associated Myeloid-Related Protein 8/14 via Gadolinium Immunonanoparticles

Background: Myeloid-related protein 8/14 complex (Mrp-8/14) is a highly expressed extracellularly secreted protein, implicated in atherosclerosis. In this study, we evaluated the feasibility of targeting Mrp in-vivo through synthetic immuno-nanoprobes. Methods and Results: Anti-Mrp-14 and nonspecific IgG-conjugated gadolinium nanoprobes (aMrp-NP and IgG-NP respectively) were synthesized and characterized. Apolipoprotein E deficient (ApoE-/-) or ApoE-/-/Mrp14-/-(DKO) animals were fed a high-fat diet for 20 weeks followed by assessment of in-vivo pharmacokinetics and vascular targeting via magnetic resonance imaging (MRI). Bone marrow-derived myeloid progenitor cells were isolated from both ApoE -/- and DKO mice and differentiated to macrophages (BMDM). BMDM were treated with LPS, with or without Mrp8, Mrp14, or Mrp8/14 and conditioned media (CM) was collected and used for in-vitro studies. Mrp-activated cells secreted significant amounts of pro-inflammatory cytokines which was abolished by pretreatment with aMrp-NP. We show in vitro that aMrp-NP binds endothelial cells previously treated with CM containing Mrp8/14. MRI following intravenous delivery of aMrp-NP revealed prolonged and substantial delineation of plaque in ApoE -/- but not DKO animals with favorable pharmacokinetics (Figure 1). Flow-cytometric analysis of aortic digesta revealed aMrp-NP presence in Ly-6G+, CD11b+, CD11c+ and CD31+ cells in ApoE -/- but not in DKO animals. Conclusion: Targeted imaging with aMrp-NP demonstrates enhancement of plaque with binding to inflammatory cells and reduction in inflammation. This strategy has promise as a theranostic approach for atherosclerosis

Bone Marrow Microenvironment: A Newly Recognized Target for Diabetes- Induced Cellular Damage

Diabetes mellitus is considered a cardiovascular disease owing to its prevalent association with cardiovascular morbidity and mortality. Cardiovascular events are not only more frequent but also complicated with more severe outcomes in diabetic patients as compared with non-diabetic patients. One mechanism accounting for this difference consists of the impairment of the regenerative cellular machinery, which contributes to tissue healing. Recent evidence indicates the contribution of resident progenitor cells in post-ischemic tissue remodeling. In addition, a wide spectrum of cells from distant sources, including the bone marrow, is attracted and home to the healing tissue. Diabetes affects the process of mobilization and recruitment as well as intrinsic functional properties of bone marrow-derived progenitor cells. This review highlights current evidence for diabetes-induced damage of bone marrow hematopoietic progenitor cells in the endosteal and vascular niches.

Relationship Among Endothelial Response to Hyperemia, Bone Marrow-Derived Progenitor Cells, and Parathyroid Hormone in Renal Transplantation

Endothelial dysfunction may contribute to modulate cardiovascular complications in renal transplant recipients (RTRs), and a relationship between endothelial dysfunction and parathyroid hormone (PTH) levels in RTRs has been demonstrated. We evaluated the relationship between endothelial response to hyperemia and circulating progenitor cells (CPCs) and endothelial progenitor cells (EPCs) PTH, and genetic parameters in RTRs. In 120 RTRs and in healthy subjects without (n=107, group A) and with cardiovascular risk factors (n=109, group B), we evaluated endothelial response to hyperemia through digital tonometry (peripheral arterial tonometry) detected by reactive hyperemia index (RHI) and EPCs and CPCs by flow cytometry. In RTRs, RHI median value was lower than in group A (P=0.05). EPC number was significantly lower in RTRs than in groups A and B (P<0.0001), whereas PTH median value was significantly higher (P<0.0001). In RTRs, RHI values were significantly lower according to the presence of three or more risk factors (P=0.04) and positively correlated with EPCs (P=0.04) but not with PTH (P=0.2). In patients who underwent dialysis for more than 5 years, lower RHI values (P=0.08), EPC number (P=0.5), and higher PTH concentrations (P=0.09) than in patients with less than 1 year dialysis time were observed. No relationship between eNOS gene -786T>C, 894G>T, and 4a/4b polymorphisms and RHI, EPC, and CPC number was found. This study shows an altered endothelial response, associated with reduced EPCs, and increased PTH in RTRs; the evaluation of endothelial status in RTRs may contribute to better assess the risk profile of these patients.