Transplantation of ex vivo expanded endothelial progenitor cells for therapeutic neovascularization

Systemic inhibition of tumour angiogenesis by endothelial cell-based gene therapy

Angiogenesis and post-natal vasculogenesis are two processes involved in the formation of new vessels, and both are essential for tumour growth and metastases. We isolated endothelial cells from human blood mononuclear cells by selective culture. These blood outgrowth cells expressed endothelial cell markers and responded correctly to functional assays. To evaluate the potential of blood outgrowth endothelial cells (BOECs) to construct functional vessels in vivo, NOD-SCID mice were implanted with Lewis lung carcinoma cells subcutaneously (s.c.). Blood outgrowth endothelial cells were then injected through the tail vein. Initial distribution of these cells occurred throughout the lung, liver, spleen, and tumour vessels, but they were only found in the spleen, liver, and tumour tissue 48 h after injection. By day 24, they were mainly found in the tumour vasculature. Tumour vessel counts were also increased in mice receiving BOEC injections as compared to saline injections. We engineered BOECs to deliver an angiogenic inhibitor directly to tumour endothelium by transducing them with the gene for human endostatin. These cells maintained an endothelial phenotype and decreased tumour vascularisation and tumour volume in mice. We conclude that BOECs have the potential for tumour-specific delivery of cancer gene therapy.

Absence of a relationship between immunophenotypic and colony enumeration analysis of endothelial progenitor cells in clinical haematopoietic cell sources

BACKGROUND

The discovery of adult endothelial progenitor cells (EPC) offers potential for vascular regenerative therapies. The expression of CD34 and VEGFR2 by EPC indicates a close relationship with haematopoietic progenitor cells (HPC), and HPC-rich sources have been used to treat cardiac and limb ischaemias with apparent clinical benefit. However, the laboratory characterisation of the vasculogenic capability of potential or actual therapeutic cell autograft sources is uncertain since the description of EPC remains elusive. Various definitions of EPC based on phenotype and more recently on colony formation (CFU-EPC) have been proposed.

METHODS

We determined EPC as defined by proposed phenotype definitions (flow cytometry) and by CFU-EPC in HPC-rich sources: bone marrow (BM); cord blood (CB); and G-CSF-mobilised peripheral blood (mPB), and in HPC-poor normal peripheral blood (nPB).

RESULTS

As expected, the highest numbers of cells expressing the HPC markers CD34 or CD133 were found in mPB and least in nPB. The proportions of CD34+ cells co-expressing CD133 is of the order mPB>CB>BM approximately nPB. CD34+ cells co-expressing VEGFR2 were also most frequent in mPB. In contrast, CFU-EPC were virtually absent in mPB and were most readily detected in nPB, the source lowest in HPC.

CONCLUSION

HPC sources differ in their content of putative EPC. Normal peripheral blood, poor in HPC and in HPC-related phenotypically defined EPC, is the richest source of CFU-EPC, suggesting no direct relationship between the proposed EPC immunophenotypes and CFU-EPC potential. It is not apparent whether either of these EPC measurements, or any, is an appropriate indicator of the therapeutic vasculogenic potential of autologous HSC sources.

Interferon-alpha promotes abnormal vasculogenesis in lupus: a potential pathway for premature atherosclerosis

Individuals with systemic lupus erythematosus (SLE) have a striking increase in premature atherosclerosis of unclear etiology. Accelerated endothelial cell apoptosis occurs in SLE and correlates with endothelial dysfunction. Endothelial progenitor cells (EPCs) and myelomonocytic circulating angiogenic cells (CACs) are crucial in blood vessel repair after vascular damage, and decreased levels or abnormal function of EPCs/CACs are established atherosclerosis risk factors. We investigated if vascular repair is impaired in SLE. We report that SLE patients display abnormal phenotype and function of EPCs/CACs. These abnormalities are characterized by significant decreases in the number of circulating EPCs (310 +/- 50 EPCs/mL of blood in SLE versus 639 +/- 102 in controls) and significant impairments in the capacity of EPCs/CACs to differentiate into mature ECs and synthesize adequate levels of the proangiogenic molecules vascular endothelial growth factor (VEGF) and hepatic growth factor (HGF). These abnormalities are triggered by interferon-alpha (IFN-alpha), which induces EPC and CAC apoptosis and skews myeloid cells toward nonangiogenic phenotypes. Lupus EPCs/CACs have increased IFN-alpha expression and their supernatants promote higher induction of IFN-inducible genes. Importantly, neutralization of IFN pathways restores a normal EPC/CAC phenotype in lupus. SLE is characterized by an imbalance between endothelial cell damage and repair triggered by type I IFNs, which might promote accelerated atherosclerosis.

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

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

Peripheral infusion of rat bone marrow derived endothelial progenitor cells leads to homing in acute lung injury

BACKGROUND

Bone marrow-derived progenitors for both epithelial and endothelial cells have been observed in the lung. Besides mature endothelial cells (EC) that compose the adult vasculature, endothelial progenitor cells (EPC) are supposed to be released from the bone marrow into the peripheral blood after stimulation by distinct inflammatory injuries. Homing of ex vivo generated bone marrow-derived EPC into the injured lung has not been investigated so far. We therefore tested the hypothesis whether homing of EPC in damaged lung tissue occurs after intravenous administration.

METHODS

Ex vivo generated, characterized and cultivated rat bone marrow-derived EPC were investigated for proliferation and vasculogenic properties in vitro. EPC were tested for their homing in a left-sided rat lung transplant model mimicking a severe acute lung injury. EPC were transplanted into the host animal by peripheral administration into the femoral vein (10(6) cells). Rats were sacrificed 1, 4 or 9 days after lung transplantation and homing of EPC was evaluated by fluorescence microscopy. EPC were tested further for their involvement in vasculogenesis processes occurring in subcutaneously applied Matrigel in transplanted animals.

RESULTS

We demonstrate the integration of intravenously injected EPC into the tissue of the transplanted left lung suffering from acute lung injury. EPC were localized in vessel walls as well as in destructed lung tissue. Virtually no cells were found in the right lung or in other organs. However, few EPC were found in subcutaneous Matrigel in transplanted rats.

CONCLUSION

Transplanted EPC may play an important role in reestablishing the endothelial integrity in vessels after severe injury or at inflammatory sites and might further contribute to vascular repair or wound healing processes in severely damaged tissue. Therapeutic applications of EPC transplantation may ensue.

Human fetal aorta contains vascular progenitor cells capable of inducing vasculogenesis, angiogenesis, and myogenesis in vitro and in a murine model of peripheral ischemia

Vasculogenesis, the formation of blood vessels in embryonic or fetal tissue mediated by immature vascular cells (ie, angioblasts), is poorly understood. We report the identification of a population of vascular progenitor cells (hVPCs) in the human fetal aorta composed of undifferentiated mesenchymal cells that coexpress endothelial and myogenic markers. Under culture conditions that promoted cell differentiation, hVPCs gave rise to a mixed population of mature endothelial and mural cells when progenitor cells were stimulated with vascular endothelial growth factor-A or platelet-derived growth factor-betabeta. hVPCs grew as nonadherent cells and, when embedded in a three-dimensional collagen gel, reorganized into cohesive cellular cords that resembled mature vascular structures. hVPC-conditioned medium contained angiogenic substances (vascular endothelial growth factor-A and angiopoietin-2) and strongly stimulated the proliferation of endothelial cells. We also demonstrate the therapeutic efficacy of a small number of hVPCs transplanted into ischemic limb muscle of immunodeficient mice. hVPCs markedly improved neovascularization and inhibited the loss of endogenous endothelial cells and myocytes, thus ameliorating the clinical outcome from ischemia. We conclude that fetal aorta represents an important source for the investigation of the phenotypic and functional features of human vascular progenitor cells.

Neovascularization and cardiomyocytes regeneration in acute myocardial infarction after bone marrow stromal cell transplantation: Comparison of infarct-relative and noninfarct-relative arterial approaches in swine

BACKGROUND

Adult bone marrow stromal cells could differentiate into myogenic endothelial progenitor cells and has been investigated for the potential value in regeneration. Recently, it has been reported that bone marrow cells (BMCs) are able to repair the infracted myocardium by intracoronary transplantation via infarct-related artery in humans. Unfortunately, we cannot open the infarcted artery by traditional reperfusion therapies in some patients. We investigate the hypothesis that BMCs transplantation might get the same effect via noninfarct-relative artery. This alternative approach may have potential application in clinical practice.

METHODS

A swine myocardial infarction model was established by distal left anterior descending artery ligation. Bone marrow stromal cells isolated, culture-expanded and labeled with bromodeoxyuridine (BrdU) were used as donor cells. Four weeks after coronary artery ligation, either a graft of 5x10(6) donor cells (n=12) or culture medium (n=6) was infused into infarcted area via infarct-relative artery (left coronary artery, n=6) and noninfarct-relative artery (right coronary artery, n=6). Heart function was evaluated by gate cardiac perfusion imaging before the transplantation and 4 weeks after transplantation. The donor cell localization and differentiation were identified by immunohistochemical staining for BrdU and beta-myosin heavy chain (beta-MHC) and angiogenesis was assessed by immunohistochemical staining for alpha-smooth muscle actin (alpha-SMA) and Factor VIII.

RESULTS

Gate cardiac perfusion imaging demonstrated that the cardiac function was significantly improved after the stromal cell transplantation via both infarct-relative and noninfarct-relative coronary arteries compared with control group (45.03+/-2.71 and 47.78+/-2.64 vs 30.36+/-2.76, P<0.05). Four weeks after transplantation, BrdU and beta-MHC positive cells were detected within the infarct area. Vessel densities in infarct area and infarct border area were increased significantly in both transplantation groups compared to the control group (98.68+/-5.32 and 87.49+/-6.04 vs 48.46+/-4.88, P<0.05).

CONCLUSIONS

Transplantation of bone marrow stromal cell via both infarct-relative and noninfarct-relative coronary arteries improved heart function in the myocardial infarction animals by stimulating cardiomyocyte regeneration and angiogenesis.

Cardiac hypertrophy: mechanisms and therapeutic opportunities

Cardiac hypertrophy and heart failure are major causes of morbidity and mortality in Western societies. Many factors have been implicated in cardiac remodeling, including alterations in gene expression in myocytes, cardiomyocytes apoptosis, cytokines and growth factors that influence cardiac dynamics, and deficits in energy metabolism as well as alterations in cardiac extracellular matrix composition. Many therapeutic means have been shown to prevent or reverse cardiac hypertrophy. New concepts for characterizing the pathophysiology of cardiac hypertrophy have been drawn from various aspects, including medical therapy and gene therapy, or use of stem cells for tissue regeneration. In this review, we focus on various types of cardiac hypertrophy, defining the causes of hypertrophy, describing available animal models of hypertrophy, discussing the mechanisms for development of hypertrophy and its transition to heart failure, and presenting the potential use of novel promising therapeutic strategies derived from new advances in basic scientific research.

PSGL-1-mediated activation of EphB4 increases the proangiogenic potential of endothelial progenitor cells

Endothelial progenitor cell (EPC) transplantation has beneficial effects for therapeutic neovascularization; however, only a small proportion of injected cells home to the lesion and incorporate into the neocapillaries. Consequently, this type of cell therapy requires substantial improvement to be of clinical value. Erythropoietin-producing human hepatocellular carcinoma (Eph) receptors and their ephrin ligands are key regulators of vascular development. We postulated that activation of the EphB4/ephrin-B2 system may enhance EPC proangiogenic potential. In this report, we demonstrate in a nude mouse model of hind limb ischemia that EphB4 activation with an ephrin-B2-Fc chimeric protein increases the angiogenic potential of human EPCs. This effect was abolished by EphB4 siRNA, confirming that it is mediated by EphB4. EphB4 activation enhanced P selectin glycoprotein ligand-1 (PSGL-1) expression and EPC adhesion. Inhibition of PSGL-1 by siRNA reversed the proangiogenic and adhesive effects of EphB4 activation. Moreover, neutralizing antibodies to E selectin and P selectin blocked ephrin-B2-Fc-stimulated EPC adhesion properties. Thus, activation of EphB4 enhances EPC proangiogenic capacity through induction of PSGL-1 expression and adhesion to E selectin and P selectin. Therefore, activation of EphB4 is an innovative and potentially valuable therapeutic strategy for improving the recruitment of EPCs to sites of neovascularization and thereby the efficiency of cell-based proangiogenic therapy.

A promising technique for transplantation of bone marrow-derived endothelial progenitor cells into rat heart

OBJECTIVE

To investigate the feasibility of intracoronary application of endothelial progenitor cells and the subsequent distribution within the heart.

METHODS

Endothelial progenitors cells (EPCs) cultured from rat bone marrow were identified by double-positive staining with Dil-Ac-LDL and BS1-lectin. Twenty-four hours before cell transplantation, EPCs were labeled with 5-bromo-2'-deoxyuridine (BrdU). Cells (5 x 10(5) in 250-microl medium) were injected into healthy rats, either as intracoronary application (n=11) or as intramyocardial injection (n = 6). At 15 min or 3 days posttransplantation, hearts as well as other organs (lung, liver, kidney, and spleen) were collected and processed for subsequent BrdU immunohistochemistry. The number of BrdU-positive cells per tissue area was counted.

RESULTS

Compared to intramyocardial injection, intracoronary administration resulted in more than twice as much positive cells in the heart (P < .05), with no local differences within the heart. Whereas after 15 min, EPCs were equally distributed in all examined organs (except for the spleen), cells that were still present after 3 days, approximately 10%, were selectively restricted to the heart.

CONCLUSIONS

Our data indicate that the intracoronary application provides a promising technique for EPC transplantation in the rat heart.

Endothelial progenitor cells as therapeutic vectors in cardiovascular disorders: from experimental models to human trials

Cell-based therapy approaches for the restoration of blood flow in ischemic organs has recently received growing interest. A considerable number of reports have documented the presence of circulating, bone marrow-derived endothelial progenitor cells (EPC) in adult peripheral blood. These putative cells are thought to participate in postnatal growth of new blood vessels. Mounting evidence from animal studies point to potential therapeutic applications of EPCs in the treatment of a wide range of cardiovascular (CV) disorders, while preliminary results from the pilot clinical trials still remain equivocal. Here, we review the experimental data that has accumulated so far from animal and clinical studies regarding the potential importance of EPCs. In addition, we discuss the potential hurdles as well as future options of EPC-based therapy.

Endothelial progenitor cells for postnatal vasculogenesis

Bone marrow-derived endothelial progenitor cells (EPCs) are present in the systemic circulation, are augmented in response to certain cytokines and/or tissue ischemia, and are home to--as well as incorporate into--sites of neovascularization. On the basis of these aspects, EPCs have attractive potential therapeutic applications for cardiovascular ischemic diseases as a novel cell-based strategy, mainly via a vasculogenesis mechanism. This review provides an update of the biology of EPCs, as well as highlighting the potential use of these cells for therapeutic regeneration.

Decreased endothelial progenitor cells in umbilical cord blood in severe preeclampsia

BACKGROUND/AIMS

We compared the numbers of endothelial progenitor cells (EPCs) in umbilical cord blood in severe preeclampsia and normal pregnancy, along with the cord blood plasma levels of free VEGF and sVEGFR-1.

METHODS

Umbilical cord blood EPC counts in severe preeclampsia (n = 15) and gestationally matched normal pregnant women (n = 30) were retrospectively analyzed. Cord plasma free VEGF and sVEGFR-1 levels were measured by enzyme immunoassay.

RESULTS

Significantly higher systolic blood pressure, lower birth weight, and higher rate of small for gestational age were noted in the severe preeclampsia group. Circulating EPCs in cord blood and umbilical cord plasma free VEGF were significantly decreased in severe preeclampsia compared to the control group (p = 0.009 and 0.04, respectively).

CONCLUSION

In severe preeclampsia, cord blood EPCs were reduced markedly and this was accompanied by a significant decrease in cord plasma free VEGF which is known to play a role in EPC mobilization.

Comparison of intracardiac cell transplantation: autologous skeletal myoblasts versus bone marrow cells

An increasing number of patients living with cardiovascular disease (CVD) and still unacceptably high mortality created an urgent need to effectively treat and prevent disease-related events. Within the past 5 years, skeletal myoblasts (SKMBs) and bone marrow (or blood)-derived mononuclear cells (BMNCs) have demonstrated preclinical efficacy in reducing ischemia and salvaging already injured myocardium, and in preventing left ventricular (LV) remodeling, respectively. These findings have been translated into clinical trials, so far totaling over 200 patients for SKMBs and over 800 patients for BMNCs. These safety/feasibility and early phase II studies showed promising but somewhat conflicting symptomatic and functional improvements, and some safety concerns have arisen. However, the patient population, cell type, dose, time and mode of delivery, and outcome measures differed, making comparisons problematic. In addition, the mechanisms through which cells engraft and deliver their beneficial effects remain to be fully elucidated. It is now time to critically evaluate progress made and challenges encountered in order to select not only the most suitable cells for cardiac repair but also to define appropriate patient populations and outcome measures. Reiterations between bench and bedside will increase the likelihood of cell therapy success, reduce the time to development of combined of drug- and cell-based disease management algorithms, and offer these therapies to patients to achieve a greater reduction of symptoms and allow for a sustained improvement of quality of life.

Cell therapy and gene therapy using endothelial progenitor cells for vascular regeneration

The isolation of endothelial progenitor cells (EPCs) derived from adult bone marrow (BM) was an epoch-making event for the recognition of "neovessel formation" occurring as physiological and pathological responses in adults. The finding that EPCs home to sites of neovascularization and differentiate into endothelial cells (ECs) in situ is consistent with "vasculogenesis," a critical paradigm well described for embryonic neovascularization, but proposed recently in adults, in which a reservoir of stem or progenitor cells contributes to vascular organogenesis. EPCs have also been considered as therapeutic agents to supply the potent origin of neovascularization under pathological conditions. Considering the regenerative implications, gene modification of stem cells has advantages over conventional gene therapy. Ex vivo gene transfection of stem cells may avoid administration of vectors and vehicles into the recipient organism. Stem cells isolated from adults may exhibit age-related, genetic, or acquired disease-related impairment of their regenerative ability. Transcriptional or enzymatic gene modification may constitute an effective means to maintain, enhance, or inhibit EPCs' capacity to proliferate or differentiate. This chapter provides an update of EPC biology as well as EPCs' potential use for therapeutic regeneration.

Prevention of diabetic microangiopathy by prophylactic transplant of mobilized peripheral blood mononuclear cells

AIM

To investigate whether the prophylactic local delivery of mobilized peripheral blood mononuclear cells (M-PBMNC) could prevent peripheral microangiopathy in diabetic nude mice.

METHODS

Diabetic nude mice were induced with intraperitoneal injections of streptozotocin. With the time course of diabetes, we detected the capillary and arteriole density of mice adductor muscles by immunohistopathy. In situ apoptosis was detected by using TdT-mediated dUTP nick end labeling (TUNEL) methods. M-PBMNC were labeled and locally delivered to the adductor muscles. Mononuclear cells were also isolated and cultured in vitro for the detection and counting of endothelial progenitor cells(EPC).

RESULTS

Rarefication of capillaries and arterioles, enhanced apoptosis in adductor muscles, and reduced circulating EPC in diabetic nude mice. Prophylactic local delivery of M-PBMNC halted the progression of microvascular rarefaction in hind-limb skeletal muscles by inhibiting apoptosis. We detected the survival, migration and incorporation of transplanted M-PBMNC into the murine vasculature in vivo. In addition, more EPC were available from M-PBMNC than non-mobilized cells.

CONCLUSION

These results suggested that the prophylactic local delivery of M-PBMNC may represent a novel approach for the treatment of microvascular complications in diabetics.

Circulating Endothelial Progenitor Cells, C-Reactive Protein and Severity of Coronary Stenosis in Chinese Patients with Coronary Artery Disease

We sought to investigate whether numbers and activity of circulating endothelial progenitor cells (EPCs) correlate with severity of coronary stenosis as well as cardiovascular risk factors in patients with stable coronary artery disease (CAD). Number of circulating EPCs was analyzed in 104 consecutive patients with proven or clinically suspected CAD. Adhesive and migratory activity was also determined. The number of EPCs was lower in patients with a single diseased coronary artery (Group II, n=35, p<0.05 vs. Group I) or multiple diseased arteries (Group III, n=25, p<0.01 vs. Group I, p<0.05 vs. Group II) compared to those with normal coronary arteries (Group I, n=44). The number of EPCs was also related with angiographic Gensini score (r=-0.355, p=0.006). In addition, concentrations of C-reactive protein (CRP) were elevated in patients with CAD, and positively correlated with Gensini score (r=0.476, p=0.001). As for the risk factors, the number of EPCs was also inversely correlated with age (p=0.001), high sensitivity-CRP (p=0.012), hypertension (p=0.042) and family history of CAD (p=0.043). Most importantly, the migratory capacity of EPCs was compromised in patients with CAD, and inversely correlated with the angiographic Gensini score (r=-0.315, p=0.021). EPCs isolated from patients with CAD also showed an impaired adhesive activity (p<0.05). In conclusion, in patients with stable CAD, reduction in the number and impairment in the function of circulating EPCs were correlated with the severity of coronary stenosis. CRP may play an important role in reducing the number of EPCs and accelerating atherosclerosis. Given the important role of EPCs in neovascularization of ischemic tissue, a decrease in the number and activity of EPCs may contribute to the impaired vascularization in patients with CAD.

Bone marrow-derived cells: the influence of aging and cellular senescence

During the course of an entire lifespan, tissue repair and regeneration is made possible by the presence of adult stem cells. Stem cell expansion, maintenance, and differentiation must be tightly controlled to assure longevity. Hematopoietic stem cells (HSC) are greatly solicited given the daily high blood cell turnover. Moreover, several bone marrow-derived cells including HSC, mesenchymal stromal cells (MSC), and endothelial progenitor cells (EPC) also significantly contribute to peripheral tissue repair and regeneration, including tumor formation. Therefore, factors influencing bone marrow-derived cell proliferation and functions are likely to have a broad impact. Aging has been identified as one of these factors. One hypothesis is that aging directly affects stem cells as a consequence of exhaustive proliferation. Alternatively, it is also possible that aging indirectly affects stem cells by acting on their microenvironment. Cellular senescence is believed to have evolved as a tumor suppressor mechanism capable of arresting growth to reduce risk of malignancy. In opposition to apoptosis, senescent cells accumulate in tissues. Recent evidence suggests their accumulation contributes to the phenotype of aging. Senescence can be activated by both telomere-dependent and telomere-independent pathways. Genetic alteration, genome-wide DNA damage, and oxidative stress are inducers of senescence and have recently been identified as occurring in bone marrow-derived cells. Below is a review of the link between cellular senescence, aging, and bone marrow-derived cells, and the possible consequences aging may have on bone marrow trans plantation procedures and emerging marrow-derived cell-based therapies.

Contribution of endothelial progenitors and proangiogenic hematopoietic cells to vascularization of tumor and ischemic tissue

PURPOSE OF REVIEW

During the last several years, a substantial amount of evidence from animal as well as human studies has advanced our knowledge of how bone marrow derived cells contribute to neoangiogenesis. In the light of recent findings, we may have to redefine our thinking of endothelial cells as well as of perivascular mural cells.

RECENT FINDINGS

Inflammatory hematopoietic cells, such as macrophages, have been shown to promote neoangiogenesis during tumor growth and wound healing. Dendritic cells, B lymphocytes, monocytes, and other immune cells have also been found to be recruited to neoangiogenic niches and to support neovessel formation. These findings have led to the concept that subsets of hematopoietic cells comprise proangiogenic cells that drive adult revascularization processes. While evidence of the importance of endothelial progenitor cells in adult vasculogenesis increased further, the role of these comobilized hematopoietic cells has been intensely studied in the last few years.

SUMMARY

Angiogenic factors promote mobilization of vascular endothelial growth factor receptor 1-positive hematopoietic cells through matrix metalloproteinase-9 mediated release of soluble kit-ligand and recruit these proangiogenic cells to areas of hypoxia, where perivascular mural cells present stromal-derived factor 1 (CXCL-12) as an important retention signal. The same factors are possibly involved in mobilization of vascular endothelial growth factor receptor 2-positive endothelial precursors that may participate in neovessel formation. The complete characterization of mechanisms, mediators and signaling pathways involved in these processes will provide novel targets for both anti and proangiogenic therapeutic strategies.

Tissue distribution of endothelial cells in vivo following intravenous injection

OBJECTIVE

Recent studies have suggested that endothelial cells derived from circulating endothelial progenitors can be used as carriers for cell-based therapy. However, the in vivo homing properties of mature endothelial cells are still unclear. In this paper, we studied the kinetics and specificity of endothelial homing to sites of angiogenesis.

METHODS

The kinetics of the distribution of endothelial cells in mice following intravenous injection of 3H-thymidine-labeled microvascular endothelial cells were examined. To detect the homing of viable and apoptotic endothelial cells, GFP-labeled microvascular endothelial cells were injected intravenously in immunodeficient mice.

RESULTS

We observed that endothelial cells injected intravenously transit rapidly through the lungs, but do not home specifically to any organ. We did not observe specific accumulation of endothelial cells in subcutaneously implanted tumors following intravenous injection. Rare GFP-labeled endothelial cells were observed in the proximity of tumor blood vessels. However, similar findings were seen when GFP-labeled apoptotic endothelial cells were injected intravenously.

CONCLUSION

These findings suggest that integration of mature endothelial cells to the vasculature is a rare event and that engulfment of apoptotic bodies, independent of nuclear fusion, may be misinterpreted as cell plasticity, and care should be taken in the interpretation of such findings.

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.

Isolation of an adult blood-derived progenitor cell population capable of differentiation into angiogenic, myocardial and neural lineages

Blood-derived adult stem cells were previously considered impractical for therapeutic use because of their small numbers. This report describes the isolation of a novel human cell population derived from the peripheral blood, termed synergetic cell population (SCP), and defined by the expression of CD31Bright, CD34+, CD45-/Dim and CD34Bright, but not lineage-specific features. The SCP was capable of differentiating into a variety of cell lineages upon exposure to defined culture conditions. The resulting cells exhibited morphological, immunocytochemical and functional characteristics of angiogenic, neural or myocardial lineages. Angiogenic cell precursors (ACPs) expressed CD34, CD133, KDR, Tie-2, CD144, von Willebrand factor, CD31Bright, concomitant binding of Ulex-Lectin and uptake of acetylated low density lipoprotein (Ac-LDL), secreted interleukin-8, vascular endothelial growth factor and angiogenin and formed tube-like structures in vitro. The majority of CD31Bright ACP cells demonstrated Ac-LDL uptake. Neural cell precursors (NCPs) expressed the neuronal markers Nestin, betaIII-Tubulin, and Neu-N, the glial markers GFAP and O4, and responded to neurotransmitter stimulation. Myocardial cell precursors (MCPs) expressed Desmin, cardiac Troponin and Connexin 43. In conclusion, the simple and rapid method of SCP generation and the resulting considerable quantities of lineage-specific precursor cells makes it a potential source of autologous treatment for a variety of diseases.

Enhancement of Viability of Fat Grafts in Nude Mice by Endothelial Progenitor Cells

BACKGROUND

A recent discovery showed that endothelial progenitor cells (EPCs) could augment collateral vessel growth to ischemic tissues.

OBJECTIVE

The objective was to demonstrate the effects of EPCs on the vasculogenesis and survival of free transplanted fat tissues in nude mice.

METHODS

EPCs from human donors were cultured in vitro for 7 days. Human fat tissues were injected subcutaneously into the scalps of 20 6-week-old nude male mice. EPCs stained with CM-DiI were mixed with the transplanted fat tissues and injected into the mice. EBM-2 medium was used as control group. The animals were euthanized 15 weeks after the procedure. Graft volume were measured, and histologic evaluation was performed. The central part of fat tissues was histologically evaluated 15 weeks after the fat injection.

RESULTS

The survival volume of the experimental group was significantly greater than that of the control group (p< .05). Less cyst formation and fibrosis was obtained in the experimental group. Histologic evaluation of the central part of fat tissues 15 weeks after the fat injection showed that capillary densities increased markedly in the experimental group mice.

CONCLUSION

The results indicate that EPCs have the ability to enhance the survival and the quality of the transplanted fat tissues.

The discovery of endothelial progenitor cells. An historical review

Although the earliest sites of hematopoietic cell and endothelial cell differentiation in the yolk sac blood islands were identified about 100 years ago, cells with hemangioblast properties have not yet been identified in vivo. Endothelial cells differentiate from angioblasts in the embryo and from endothelial progenitor cells, mesoangioblasts and multipotent adult progenitor cells in the adult bone marrow. Endothelial progenitor cells (EPC) were initially described by Asahara et al. [Asahara T, Murohara T, Sullivan A, et al. Isolation of putative progenitor endothelial cells for angiogenesis. Science 1997;275:964-7.], and the past few years have seen a rapid expansion of our knowledge of EPC biology. Prior to the discovery of this cell type, new vessel formation was believed to occur to proliferation of existing endothelial cells. These findings have overturned the previous dogma that vasculogenesis can only occur during embryogenesis. Questions persist regarding their functional characteristics, as well as the precise panel of cell surface markers that define this cell population.

Recombinant human granulocyte-colony-stimulating factor-mobilized and apheresis-collected endothelial progenitor cells: a novel blood cell component for therapeutic vasculogenesis

BACKGROUND

Endothelial progenitor cells (EPCs) have been identified among hematopoietic tissue-derived progenitor cells that are mobilized into the peripheral blood (PB) as a result of tissue injury. It therefore seems likely that circulating EPCs have therapeutic potential by aiding in the neovascularization of ischemic tissue. This study provides clinical data on the availability of circulating EPCs at steady state and after recombinant human granulocyte-colony-stimulating factor (rHuG-CSF) mobilization and their collection by leukapheresis.

STUDY DESIGN AND METHODS

Eight healthy donors underwent rHuG-CSF treatment over 4 days, followed by leukapheresis. Blood samples taken before rHuG-CSF treatment and before apheresis as well as apheresis-collected samples were analyzed by flow cytometry and by real time reverse transcription-polymerase chain reaction for cells expressing EPC-specific surface markers and tissue markers, respectively, and for EPC colony-forming cells.

RESULTS

The median PB concentration of CD34+133+ vascular endothelial growth factor receptor-2 (VEGFR-2)-+ EPCs increased 8-fold from steady state to mobilized, and the concentration of CD34+133-VEGFR-2+ EPCs increased by 10-fold. This mobilization pattern was similar to that of hematopoietic CD34+, CD133+, and CD34+117+ progenitor cells. The increase in the median circulating colony-forming unit EPC concentration was 10-fold over baseline. The median absolute number of CD34+133+VEGFR-2+ cells collected by large-volume leukapheresis was 0.8 x 10(6) per kg of body weight. In addition, a small subset of immature CD133+34- cells coexpressing VEGFR-2 was identified in mobilized PB and in the apheresis collection. EPC-specific cells contained in the apheresis product were also identified as expressing mRNA for the CD31 antigen, Tie-2, and VEGFR-2.

CONCLUSION

Circulating EPCs represent a novel blood cell component that can be collected by apheresis in large quantities and can be used clinically, either unmanipulated or EPC-selected, for therapeutic vasculogenesis.

Cellular cardiomyoplasty by catheter-based infusion of stem cells in clinical settings

Myocardial infarction is the leading cause of congestive heart failure and death in the industrialized world. However, the intrinsic repair mechanism of the heart is inadequate. Current therapy is limited in preventing ventricular remodeling, but can not regenerate the lost cardiomyocytes. Recent interests have been focused on cellular cardiomyoplasty which is an outside intervention to support the reparative process in the heart through transplantation of stem/progenitor cells or cardiac cells. Cellular cardiomyoplasty with stem cells is a possible option to reverse the adverse hemodynamic and neurohormonal imbalance after myocardial infarction. Experimental studies and clinical trials suggest that cellular cardiomyoplasty may benefit tissue perfusion and contractile performance of the injured heart. Although the mechanisms are still intensively debated, cellular cardiomyoplasty with stem cells has already been introduced into the clinical settings. However, it is an important challenge how stem cells are delivered to targeted area. In early studies on animals, intramyocardial injection of stem cells after thoracotomy is the predominant transplantation route which is not suitable for most patients in clinical settings. Then the catheter-based infusion of stem cells is clinically introduced and rapidly developed in patients because of the safety, convenience and mini-invasion. We mainly review the progress in catheter-based transplantation with stem cells in order to fully understand the application of various intervention-based approaches to stem cells transplantation in clinical settings.

Myeloid cell trafficking and tumor angiogenesis

Tumor growth and metastasis depend on neovascularization, the growth of new blood vessels. Recent findings have revealed that tumor neovascularization is regulated in part by monocytes, which are myeloid lineage cells from the bone marrow. Tumors exhibit significant monocyte infiltrates, which are actively recruited to the tumor microenvironment. Upon tumor infiltration, monocytes can participate in tumor neovascularization. Monocytes can either differentiate into macrophages, which express proangiogenic growth factors, or into endothelial-like cells, which may directly participate in neovascularization. Preliminary studies in animals suggest that modulation of bone marrow-derived cell trafficking into tumors will provide a useful new approach in cancer therapy.

Regenerative medicine for cardiovascular disorders-new milestones: adult stem cells

Cardiovascular disorders are the leading causes of mortality and morbidity in the developed world. Cell-based modalities have received considerable scientific attention over the last decade for their potential use in this clinical arena. This review was intended as a brief overview on the subject of therapeutic potential of adult stem cells in cardiovascular medicine with basic science findings and the current status of clinical applications. The historical perspective and basic concepts are reviewed and a description of current applications and potential adverse effects in cardiovascular medicine is given. Future improvements on cell-based therapies will likely provide remarkable improvement in survival and quality of life for millions of patients with cardiovascular disorders.

Transcoronary transplantation of progenitor cells after myocardial infarction

BACKGROUND

Pilot studies suggest that intracoronary transplantation of progenitor cells derived from bone marrow (BMC) or circulating blood (CPC) may improve left ventricular function after acute myocardial infarction. The effects of cell transplantation in patients with healed myocardial infarction are unknown.

METHODS

After an initial pilot trial involving 17 patients, we randomly assigned, in a controlled crossover study, 75 patients with stable ischemic heart disease who had had a myocardial infarction at least 3 months previously to receive either no cell infusion (23 patients) or infusion of CPC (24 patients) or BMC (28 patients) into the patent coronary artery supplying the most dyskinetic left ventricular area. The patients in the control group were subsequently randomly assigned to receive CPC or BMC, and the patients who initially received BMC or CPC crossed over to receive CPC or BMC, respectively, at 3 months' follow-up.

RESULTS

The absolute change in left ventricular ejection fraction was significantly greater among patients receiving BMC (+2.9 percentage points) than among those receiving CPC (-0.4 percentage point, P=0.003) or no infusion (-1.2 percentage points, P<0.001). The increase in global cardiac function was related to significantly enhanced regional contractility in the area targeted by intracoronary infusion of BMC. The crossover phase of the study revealed that intracoronary infusion of BMC was associated with a significant increase in global and regional left ventricular function, regardless of whether patients crossed over from control to BMC or from CPC to BMC.

CONCLUSIONS

Intracoronary infusion of progenitor cells is safe and feasible in patients with healed myocardial infarction. Transplantation of BMC is associated with moderate but significant improvement in the left ventricular ejection fraction after 3 months.

Myoseverin Is a Potential Angiogenesis Inhibitor by Inhibiting Endothelial Cell Function and Endothelial Progenitor Cell Differentiation

Myoseverin, a new microtubule-binding molecule, acts reversibly on myoblast proliferation without the cytotoxic effects displayed by nonpurine-based microtubule-disrupting molecules, like taxol, vinblastine, nocodazole, and the colchicines. In this study, we examined the effects of myoseverin on in vitro function of endothelial cells and endothelial progenitor cell differentiation in order to explore the possibility for the application of myoseverin as a reversible antiangiogenic agent. Myoseverin potently inhibited proliferation of human umbilical vein endothelial cells (HUVECs) in a dose-dependent manner with an IC50 of approximately 8 microM. When myoseverin was removed after treatment for 3 days, all the cells pretreated at a concentration range of 2.5-80 microM resumed the cell growth. It also inhibited VEGF-induced HUVEC migration dose dependently. When mononuclear cells (MNCs) isolated from human cord blood were cultured on fibronectin-coated plates for 7 days, myoseverin decreased the number of adherent cells in a dose-dependent manner with IC50 of approximately 9 microM. It also suppressed the development of ac-LDL uptake ability as well as the expression of endothelial lineage markers, KDR, CD31, and vWF. Finally, it inhibited formation of HUVECs or ex vivo cultivated EPCs into capillary-like structure on Matri-gel and in vivo angiogenesis on the chick chorioallantoic membrane. Therefore, these results suggest that myoseverin can be effectively used for the inhibition of new vessel growth by inhibiting endothelial cell function and differentiation of progenitor cells.

Stem cell biology for vascular regeneration

The isolation of endothelial progenitor cells (EPCs) derived from bone marrow (BM) was one epoch-making event for the recognition of neovessel formation in adults occurring as physiological and pathological responses. The finding that EPCs home to sites of neovascularization and differentiate into endothelial cells (ECs) in situ is consistent with vasculogenesis, a critical paradigm that has been well described for embryonic neovascularization, but proposed recently in adults in which a reservoir of stem or progenitor cells contribute to vascular organogenesis. EPCs have also been considered as therapeutic agents to supply the potent origin of neovascularization under pathological conditions. This chapter highlights an update of EPC biology as well as its potential use for therapeutic regeneration.

Normalization of coronary blood flow in the infarct-related artery after intracoronary progenitor cell therapy: intracoronary Doppler substudy of the TOPCARE-AMI trial

BACKGROUND

Coronary microvascular dysfunction contributes to infarct extension and poor prognosis after an acute myocardial infarction (AMI). Recently, progenitor cell application has been demonstrated to improve neovascularization and myocardial function after experimental myocardial infarction. Therefore, we investigate coronary blood flow regulation in patients after AMI treated with intracoronary progenitor cell therapy.

METHODS AND RESULTS

In the TOPCARE-AMI trial, patients received either bone marrow-derived or circulating progenitor cells into the infarct-related artery 3-7 days after AMI. The present substudy investigates in 40 patients coronary blood flow regulation at the time of progenitor cell therapy and at 4-month follow-up by i.c. Doppler in the infarct artery as well as a reference vessel. At the initial measurement, coronary flow reserve (CFR) was reduced in the infarct artery compared to the reference vessel (median 2.5 vs. 3.4, p<0.001). At 4-month follow-up, intracoronary progenitor cell therapy was associated with a normalization of CFR in the infarct artery (median 3.9 vs. reference vessel 3.8, p=0.15). CFR also improved in the reference vessel, but mechanisms were different: reference vessel increase in CFR was secondary to an increased basal vascular resistance, probably due to reduced need for hypercontractility. In contrast, in the infarct artery, adenosine-induced minimal vascular resistance profoundly decreased, indicating an increased maximal coronary vascular conductance capacity. In addition, in a non-randomized matched control group (n=8), minimal vascular resistance in the infarct artery was significantly elevated compared to progenitor cell treated patients 4 months after AMI (p=0.012).

CONCLUSIONS

Intracoronary progenitor cell therapy after AMI is associated with complete restoration of coronary flow reserve due to a substantial improvement of maximal coronary vascular conductance capacity. The clinical importance of improved microcirculation by progenitor cell therapy in patients after AMI has to be established in further randomized trials.

The origin and in vivo significance of murine and human culture-expanded endothelial progenitor cells

In adults highly purified populations of early hematopoietic progenitors or cells derived from ex vivo expanded unmobilized human peripheral blood mononuclear cells contribute to new blood vessel formation. However, the source of these culture-expanded endothelial progenitor cells (CE-EPCs) remains controversial. We demonstrate that ex vivo expansion of unmobilized human peripheral blood generated CE-EPCs with similar numbers, kinetics, and antigen expression profile as compared to plating unfractionated CD34(+)/lin(-)-enriched bone marrow mononuclear cells. Both CE-EPC populations uniformly co-expressed myeloid and endothelial markers, suggesting that peripheral blood progenitor enumeration does not correlate with the numbers of early outgrowth CE-EPCs. Using purified myeloid subpopulations obtained from mice harboring the lacZ transgene driven by an endothelial-specific promoter, we showed that the immature myeloid lineage marker CD31(+) cells generated CE-EPCs with fourfold greater frequency than mature myeloid populations. Biphenotypic cells co-expressing myeloid/endothelial antigens were not detected in circulating human or murine peripheral blood or bone marrow but were associated with murine tumors. Unlike CE-EPCs, CD14(+) leukocytes admixed within tumors did not generate vWF-positive blood vessels during a similarly defined period of tumor growth, but some leukocytes up-regulated the endothelial marker VE-cadherin. Taken together, the data suggest that the local neovascular microenvironment may facilitate vasculogenesis by promoting endothelial differentiation and that CE-EPCs may accelerate such vasculo-genesis.

The effects of HMG-CoA reductase inhibitor on vascular progenitor cells

Circulating bone marrow-derived vascular progenitor cells contribute to angiogenesis, atherosclerosis, and the response to vascular injury. These vascular progenitor cells consist of two cell groups, endothelial progenitor cells (EPCs) and smooth muscle progenitor cells (SMPCs). Although HMG-CoA reductase inhibitors (statins) have been reported to inhibit atherosclerosis partially by increased EPCs, the effects of statins on SMPCs are unclear. Therefore, we investigated the relationship between EPCs and SMPCs and whether pravastatin has atheroprotective effects on SMPCs. Peripheral mononuclear cells (MNCs) were isolated and cultured on fibronectin-coated dishes in SMPC medium. MNCs were stained with acetylated low density lipoprotein and lectin, or alpha-smooth muscle actin, and cell numbers were counted. mRNA expression and vascular endothelial growth factor (VEGF) protein synthesis of MNCs were evaluated. Pravastatin significantly increased the number of EPC and decreased the number of SMPC. mRNA expression of VEGF, endothelial nitric oxide synthase, VEGF receptor-2 (KDR), and Akt were up-regulated, and VEGF secretion was increased by pravastatin. The present study demonstrated that pravastatin has promotive effects on the differentiation from MNCs to EPC cells, while inhibitory effects to SMPC cells. Our findings suggest a previously unreported mechanism of the effect of statin therapy on vascular progenitor cells.

Circulating Endothelial Progenitor Cells During Normal Pregnancy and Pre-Eclampsia

PROBLEM

Endothelial progenitor cell (EPC), which mediates neovascularization of uterine endometrium may be involved in the neovascularization in the utero-placental circulation. We evaluated whether EPC proliferation in pre-eclampsia (PE) differed from that in normal pregnancy.

METHOD OF STUDY

EPC number in peripheral blood (20 non-pregnancy, 36 normal pregnancy, 10 PE) was measured using flow cytometry. Peripheral blood mononuclear cell was cultured for 7 days and EPC proliferation was assessed based on detection of the uptake of acetylated low-density lipoprotein and lectin. Furthermore, the proliferative activity induced by angiotensin II (Ang II) and tumor necrosis factor-alpha (TNF-alpha) was measured by BrdU assay.

RESULTS

EPC number in peripheral blood did not differ significantly between PE and normal pregnancy; however, EPC proliferation was significantly increased in PE. Furthermore, Ang II and TNF-alpha induced the proliferation of EPC derived from patients with PE.

CONCLUSIONS

In PE, some factors including Ang II and TNF-alpha stimulated EPC proliferation; however, the impairment of EPC mobilization into systemic circulation by serum factors may contribute to insufficient regeneration of EC in disturbed utero-placental circulation of PE.

High-density lipoprotein cholesterol regulates endothelial progenitor cells by increasing eNOS and preventing apoptosis

OBJECTIVE

Endothelial progenitor cells (EPCs) are implicated as an important marker of endothelial function and cardiovascular risk. In the present study, we examined whether high-density lipoprotein (HDL) cholesterol plays a role in the peripheral EPC levels and its underlying mechanisms in the HDL cholesterol-induced elevation of EPCs.

METHODS

For the clinical study, vascular risk factors and blood markers were measured and EPC colony forming units were counted after 7 days of culture. For the in vitro study, after 7 days of culture, EPCs were incubated in the presence or absence of HDL for 24h followed by measurements of eNOS and pro-MMP-9 expression and caspase-3 activity.

RESULTS

EPC colony levels significantly correlated with HDL levels (P=0.017). HDL treatment significantly increased eNOS protein expression in EPCs (P<0.001) while it significantly decreased pro-MMP-9 levels at the concentration of 50 microg/mL (P=0.002). Homocysteine treatment significantly increased caspase-3 activity whereas HDL significantly decreased it as compared to the homocysteine-only treated group.

INTERPRETATION

The data demonstrate that EPC colony levels are significantly lower in individuals with low HDL and that HDL increases eNOS and decreases pro-MMP-9 in EPCs. HDL also prevents EPC apoptosis through inhibition of caspase-3 activity suggesting a possible mechanism for its positive effects on circulating EPC numbers.

Adipose tissue-derived stromal cells as a novel option for regenerative cell therapy

Adult stem cells hold great promise for use in tissue repair and regeneration, and the delivery of autologous progenitor cells into ischemic tissue is emerging as a novel therapeutic option. We and others have recently demonstrated the potential impact of adipose tissue-derived stromal cells (ADSC) on regenerative cell therapy for ischemic diseases. The main benefit of ADSC is that they can be easily harvested from patients by a simple, minimally invasive method and also easily cultured. Cultured ADSC can be induced to differentiate into not only adipocytes, but also bone, neurons or endothelial cells in certain conditions. Interestingly, they secrete a number of angiogenesis-related cytokines, such as vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF), which might be suitable for regenerative cell therapy for ischemic diseases. In the ischemic mouse hindlimb, the angiogenic score was improved in the ADSC-treated group. Moreover, recent reports demonstrated that these ADSC can also be induced to differentiate into cardiac myocytes. These adipose tissue-derived cells have potential in angiogenic cell therapy for ischemic disease, and might be applied for regenerative cell therapy instead of bone marrow cells in the near future.

Stem cell use in a patient with an ischemic foot ulcer: a case study

Stem cell research has been discussed in both the political and popular arenas lately. Some types of stem cell research are controversial; however, not all stem cell research involves harvesting cells from an embryo or an aborted fetus. Another type of stem cell, the adult stem cell, resides within tissues and organs of the body and is responsible for repair after injury. Recent interest has focused on using adult stem cells isolated from a patient's bone marrow to stimulate the development of new blood vessels (a process called angiogenesis) in patients with peripheral vascular disease. These specialized stem cells are referred to as endothelial progenitor cells (EPCs). In laboratory and clinical studies it has been shown that these EPCs are involved in arterial repair and remodeling, as well as angiogenesis. The following case presentation will show how a patient with an ischemic toe ulcer and rest pain, who had no options for conventional revascularization, benefited from the injection of stem cells into her calf muscle. The process of angiogenesis using EPCs will be examined discussing the screening criteria and possible adverse events. The patient's history and progress throughout the recovery period will be reviewed.

Identification of the adult human hemangioblast

Recent studies show that human CD133(+) (previously known as AC133(+)) cells from mobilized peripheral blood consist of stem cells with either hematopoietic or endothelial potential. To test whether this population also contains individual precursors with both capacities, the defining characteristics of the elusive adult hemangioblast, we developed a culture system that allows single-cell analyses of differentiation. In the presence of vascular endothelial growth factor (VEGF), stem cell growth factor (SCGF), and FLT-3 ligand, CD133(+)-enriched cells were first expanded and the amplified cells were transduced with a vector encoding an enhanced green fluorescent protein (EGFP) marker gene. Single EGFP(+) cells were then cocultured with corresponding non-transduced cells from the same experiment, yielding 50-100 marked cells in 8% of the wells after 2 weeks. The resultant cells were divided and differentiated with either granulocyte colony-stimulating factor (G-CSF) or with SCGF and VEGF. These culture conditions resulted in the formation of neutrophil or endothelial cells, respectively, as identified morphologically and by phenotypic staining. Dual differentiation of EGFP(+) cells could be observed in one-quarter of clones from single-seeded cells, suggesting that 2% of EGFP(+) cells were in fact human hemangioblasts. These cells could be expanded for at least 28 days without losing this dual capacity. Hence, this culture system may be of clinical relevance in the development of cellular therapies for disorders involving hematopoiesis and the vascular system. In addition, our results provide important information related to the development of the vasculature and the potential role of hemangioblasts in vasculogenesis in adult humans.

Human adipose tissue-derived mesenchymal stem cells improve postnatal neovascularization in a mouse model of hindlimb ischemia

BACKGROUND/AIM

It has been reported that adipose tissue contain progenitor cells with angiogenic potential and that therapy based on adipose tissue-derived progenitor cells administration may constitute a promising cell therapy in patients with ischemic disease. In this study we evaluated the effect of culture-expanded mesenchymal stem cells (MSC) derived from adipose tissue on neovascularization and blood flow in an animal model of limb ischemia in immunodeficient mice.

METHODS

MSC were cultured from human adipose tissue by collagenase digestion. Hindlimb ischemia was created by ligating the proximal femoral artery of male nude mice. Human adipose tissue stromal cells (hADSC) were transplanted one day or 7 days after ligation.

RESULTS

During culture expansion of hADSC CD34 expression was downregulated. The laser Doppler perfusion index was significantly higher in the CD34(-), Flk-1(-), CD31(-) ADSC-transplanted group than in the control group, even when cells were transplanted 7 days after hindlimb ischemia. Histological examination showed that hADSC transplantation recovered muscle injury and increased vascular density, compared with the control group. The effect of hADSC was correlated with the number of transplanted cells, but not with the ratio of CD34 expression. In vitro, hADSC can form vessel-like structure and express von Willibrand Factor. Conditioned media from hADSC increased proliferation and inhibited apoptotic cell death in of human aortic endothelial cells.

CONCLUSION

This study showed that hADSC can be an ideal source for therapeutic angiogenesis in ischemic disease.

Labelling of human mesenchymal stem cells with indium-111 for SPECT imaging: effect on cell proliferation and differentiation

PURPOSE

Stem cell therapy seems to be a new treatment option within cardiac diseases to improve myocardial perfusion and function. However, the delivery and traceability of the cells represent a problem. Radioactive labelling with 111In could be a method for tracking mesenchymal stem cells (MSCs). However, 111In could influence the viability and differentiation capacity of MSCs, which would limit its use. Therefore, the aim of this study was to evaluate the influence of 111In labelling in doses relevant for SPECT imaging in humans on the viability and differentiation capacity of human MSCs.

METHODS AND RESULTS

Human MSCs isolated from bone marrow were incubated with 111In-tropolone (15-800 Bq/cell). The labelling efficiency was approximately 25% with 30 Bq/cell 111In. The MSC doubling time was 1.04+/-0.1 days and was not influenced by 111In within the range 15-260 Bq/cell. Using 30 Bq 111In/cell it was possible to label MSCs to a level relevant for clinical scintigraphic use. With this dose, 111In had no effect on characteristic surface and intracellular markers of cultured MSCs analysed both by flow cytometry and by real-time polymerase chain reaction. Further, the labelled MSCs differentiated towards endothelial cells and formed vascular structures.

CONCLUSION

It is possible to label human MSCs with 111In for scintigraphic tracking of stem cells delivered to the heart in clinical trials without affecting the viability and differentiation capacity of the MSCs. This creates an important tool for the control of stem cell delivery and dose response in clinical cardiovascular trials.

Angiogenic cell therapy for hepatic fibrosis

Progression of liver fibrosis has been linked with injuries associated with hypoxia and neovascularization. Neovascularization consists of angiogenesis and vasculogenesis, representing formation of blood vessels by differentiation of endothelial progenitor cells (EPCs). We investigated antifibrogenic and regenerative effects of EPC transplantation in chronic liver injury. Rat EPCs were isolated from bone marrow cells and examined in vitro for lineage markers. Recipient rats were injected intraperitoneally with dimethylnitrosamine (DMN) three times weekly for 4 weeks, plus EPC transplantation once weekly for 4 weeks. Transplanted rats showed suppression of liver fibrogenesis. Expression of growth factors promoting liver regeneration such as hepatocyte growth factor (HGF), transforming growth factor (TGF)-alpha, epidermal growth factor (EGF), and vascular endothelial growth factor (VEGF) was increased in transplanted rats, together with hepatocyte proliferation. Normal liver function parameters such as transaminase, total bilirubin, total protein, and albumin were maintained in transplanted rats. EPC transplantation is effective not only for preventing liver fibrosis but also for promoting regeneration in chronically damaged livers. Also, recently it has been reported that green fluorescent protein-positive bone marrow cells contribute to the liver tissue repair of fibrosis model rats. EPC transplantation might become an alternative if further preclinical investigation finds it to be effective in severely cirrhotic livers.

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.

G-CSF and AMD3100 mobilize monocytes into the blood that stimulate angiogenesis in vivo through a paracrine mechanism

There is compelling evidence that circulating angiogenic cells exist that are able to home to sites of vascular injury and stimulate angiogenesis. However, the number of angiogenic cells in the blood is low, limiting their delivery to sites of ischemia. Treatment with certain cytokines may mobilize angiogenic cells into the blood, potentially circumventing this limitation. Herein, we show that treatment with granulocyte colony-stimulating factor (G-CSF) or AMD3100, a novel CXCR4 antagonist, significantly stimulated angiogenesis in a murine model of acute hindlimb ischemia. The kinetics of angiogenic-cell mobilization by these agents appears to be distinct, with more rapid revascularization observed in AMD3100-treated mice. Combination treatment with G-CSF and AMD3100 resulted in the earliest and most complete recovery in blood flow to the ischemic hindlimb. Adoptive transfer of mobilized blood mononuclear cells, while potently stimulating angiogenesis, did not result in the significant incorporation of donor cells into the neoendothelium. Cell-fractionation studies showed that it is the monocyte population in the blood that mediates angiogenesis in this model. Collectively, these data suggest that monocytes mobilized into the blood by G-CSF or AMD3100 stimulate angiogenesis at sites of ischemia through a paracrine mechanism.

One-year follow-up of transcoronary sinus administration of autologous bone marrow in patients with chronic refractory angina

PURPOSE

Based on our preclinic studies with autologous unfractionated bone marrow (AUBM) via coronary sinus with transitory occlusion, a clinic study in patients with chronic refractory angina was designed. The objectives were to evaluate tolerance of the procedure, safety, and feasibility with 1 year follow-up.

METHODS AND MATERIALS

Clinical study with inclusion and exclusion criteria defined by an Independent Clinical Committee was carried out. Fifteen patients underwent transcoronary sinus administration with a 15-min occlusion of freshly aspirated and filtered AUBM (60-120 ml). Feasibility was evaluated with Seattle Angina Questionnaire (SAQ), Canadian Cardiovascular Society (CCS) angina classification, perfusion dipyridamole, and coronary angiography.

RESULTS

There were no changes in the tolerance parameters. There were no deaths or myocardial infarction during the follow-up. Three patients were readmitted into the hospital. During the follow-up, one patient was diagnosed with cancer of the lung. Improvement of 30% in the quality of life was evaluated by SAQ. The CCS angina classification showed that the mean angina class was 3.0+/-0.53 at baseline, which improved to 1.6+/-0.63 at 1 year (P<.001). Perfusion imaging (core lab) showed improvement in 12 of 15 patients, with a mean improvement of 40.9% at rest (22 vs. 13) (P<.01) and 45.3% at stress (26.5 vs. 14.5) (P<.05). Coronary angiography showed more collateral vessels in 10 of 15 patients.

CONCLUSIONS

We can conclude that AUBM via coronary sinus is feasible in patients with chronic refractory angina after 1 year follow-up, and it appears to be safe.

Effects of rapamycin on number activity and eNOS of endothelial progenitor cells from peripheral blood

The aim of this investigation is to determine whether rapamycin treatment has any effect on endothelial progenitor cells (EPCs). Total mononuclear cells (MNCs) were isolated from peripheral blood by Ficoll density gradient centrifugation, and then the cells were plated on fibronectin-coated culture dishes. After 7 days in culture, attached cells were stimulated with rapamycin (in a series of final concentrations: 0.1, 1.0, 2.0 and 5.0 g/ml) for 6, 12, 24 and 48 h. EPCs were characterized as adherent cells, double positive for DiLDL uptake and lectin binding by direct fluorescence staining. EPC proliferation and migration were determined using the MTT assay and a modified version of the Boyden chamber assay, respectively. An EPC adhesion assay was performed by replating the cells on fibronectin-coated dishes; adherent cells were then counted. Tube formation activity was assayed by using a tube formation assay kit and endothelial nitric oxide synthase (eNOS) was assayed by Western blot analysis. Incubation of isolated human MNCs with rapamycin decreased the number of EPCs present; rapamycin also decreased EPCs proliferative, migratory, adhesive, tube formation capacity and eNOS production in a concentration- and time-dependent manner. Rapamycin was found to decrease the number, proliferative, migratory, adhesive and tube formation capacities of the EPCs, and also was found to decreases eNOS in the EPCs.

Vascular protection in brain ischemia

Vascular damage occurring after cerebral ischemia may lead to a worse outcome in patients with ischemic stroke, as it facilitates edema formation and hemorrhagic transformation. There are several phases in the development of vascular injury (acute, subacute and chronic) and different mediators act in each one. Therapeutic options to avoid vascular injury must be focused on acting in each phase. However, even though experimental studies have demonstrated the benefit of therapeutic interventions both in the acute and chronic phases of cerebral ischemia, only the chronic phase offers a therapeutic window sufficiently wide enough to provide vascular protection in clinical practice. Several drugs including erythropoietin and HMG-CoA reductase inhibitors (statins), antihypertensive (angiotensin modulators), antibiotics (minocycline) and antihyperglycemic drugs (thiazolidinediones) have been proved to provide vascular protection in patients with ischemic stroke. Anti-inflammatory, antioxidant, and antiapoptotic actions are responsible for the vascular protective effect related to these drugs.

Basic fibroblast growth factor and granulocyte colony-stimulating factor enhance mucosal surface expansion after adult small bowel transplantation without vascular reconstruction in rats

AIM

We showed previously that adult small bowel could be transplanted successfully in rats without vascular reconstruction by removing the graft serosa. In this study, we assessed if granulocyte colony-stimulating factor (G-CSF) or basic fibroblast growth factor (bFGF) could improve graft survival in the same rat model.

METHOD

A 10-mm-long adult small bowel graft from an adult 12-week-old Lewis rat was transplanted into a pouch created in the omentum of a 5-week-old Lewis rat (syngeneic bowel transplantation [SBTx], n = 49). Graft serosa was removed just before SBTx in the serosectomy group (n = 29) and left intact in the nonserosectomy group (n = 20). Each group was divided into 3 subgroups (sG): sG-1 had no G-CSF or bFGF; sG-2 had daily subcutaneous injections of G-CSF; and sG-3 had continuous infusion of bFGF around the graft in the omentum. All grafts were harvested 14 days after SBTx and studied histologically. A mucosal surface expansion score (MSES) was used where 0 = no mucosa on the graft, 1 = mucosa on one fourth of the graft, 2 = mucosa on one half of the graft, 3 = mucosa on three fourths of the graft, and 4 = mucosa on the whole graft. The density of CD34-positive capillaries per 1000 nuclei was also measured.

RESULTS

Serosectomy group MSES were significantly higher than nonserosectomy group MSES indicating that grafts survived (P < .0001). CD34-positive capillaries in serosectomy group subgroups for mucosa were 103.9 +/- 34.2, 130.2 +/- 52.0, and 132.3 +/- 37.7, respectively; for muscle, 74.4 +/- 38.0, 86.2 +/- 32.9, and 82.4 +/- 30.3, respectively; and for omentum, 73.8 +/- 30.1, 151.3 +/- 60.3, and 140.0 +/- 49.0, respectively. Mucosal surface expansion score and overall CD34-positive capillaries for sG-2 and sG-3 were significantly higher than for sG-1 (both, P < .05).

CONCLUSION

Our results suggest that G-CSF and bFGF enhance angiogenesis and mucosal surface expansion.

Effects of aspirin on number, activity and inducible nitric oxide synthase of endothelial progenitor cells from peripheral blood

AIM

To investigate whether aspirin has an influence on endothelial progenitor cells (EPC).

METHODS

Total mononuclear cells (MNC) were isolated from peripheral blood by Ficoll density gradient centrifugation, then cells were plated on fibronectin-coated culture dishes. After 7 d of culture, attached cells were stimulated with aspirin (to achieve final concentrations of 1, 2, 5, and 10 mmol/L) for 3, 6, 12, and 24 h. EPC were characterized as adherent cells that were double positive for 1,1-dioctadecyl-3,3,3,3-tetramethylindocarbocyanine low density lipoprotein (DiLDL) uptake and lectin binding by direct fluorescent staining. EPC proliferation and migration were assayed using a 3-(4,5-dimethyl-2 thiazoyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay and a modified Boyden chamber assay, respectively. An EPC adhesion assay was performed by replating the EPC on fibronectin-coated dishes, and then adherent cells were counted. In vitro vasculogenesis activity was assayed by using an in vitro vasculogenesis kit. Inducible nitric oxide synthase (iNOS) was assayed by Western blotting.

RESULTS

Incubation of isolated human MNC with aspirin decreased the number of EPC. Aspirin also decreased the proliferative, migratory, adhesive, and in vitro vasculogenesis capacity of EPC, and also their iNOS levels in a concentration- and time-dependent manner.

CONCLUSION

Aspirin decreases (1) the number of EPC; (2) the proliferative, migratory, adhesive and in vitro vasculogenesis capacities of EPC; and (3) iNOS levels in EPC.