Adult 'endothelial progenitor cells'. Renewing vasculature

SARS-CoV-2 and endothelial cell interaction in COVID-19: molecular perspectives

SARS-CoV-2 is the agent responsible for the coronavirus disease (COVID-19), which has been declared a pandemic by the World Health Organization. The clinical evolution of COVID-19 ranges from asymptomatic infection to death. Older people and patients with underlying medical conditions, particularly diabetes, cardiovascular and chronic respiratory diseases are more susceptible to develop severe forms of COVID-19. Significant endothelial damage has been reported in COVID-19 and growing evidence supports the key pathophysiological role of this alteration in the onset and the progression of the disease. In particular, the impaired vascular homeostasis secondary to the structural and functional damage of the endothelium and its main component, the endothelial cells, contributes to the systemic proinflammatory state and the multiorgan involvement observed in COVID-19 patients. This review summarizes the current evidence supporting the proposition that the endothelium is a key target of SARS-CoV-2, with a focus on the molecular mechanisms involved in the interaction between SARS-CoV-2 and endothelial cells.

A new method of culturing rat bone marrow endothelial progenitor cells in vitro

Background

Endothelial progenitor cells (EPCs) play an important role in the re-endothelialization of ischemic cerebrovascular disease. However, the current acquisition method has some deficiencies. This study aimed to design a new and practical method for obtaining EPCs.

Methods

Bone marrow was obtained autologously from the right tibia of living rats. Briefly, the right tibia bone was carefully exposed and two holes (1 mm in diameter) were made in the tuberosity and lower one-third of the tibia, respectively. A PE-50 catheter and syringe (5 mL) were inserted through the holes to aspirate the bone marrow. Bone marrow mononuclear cells (BMMCs) were isolated by density-gradient centrifugation with Ficoll and counted. Adherent cell culture continued for 2 weeks, and the medium was replaced every 3 days.

Results

During the first days of culture, adherent cells formed a monolayer, consisting predominantly of small-sized cells. Single large cells with endothelial morphology were observed. On day 4, the nonadherent cells were removed, and the adherent cells were left for further culture. On day 6-7, a proliferating population of round cells formed clusters in the culture chamber, and morphological analysis revealed a homogeneous population of colony-forming units (CFUs). Large, flat cells with endothelial morphology sprouted from the CFUs, which had nearly disappeared by day 14 of culture. The adherent cells were positive for CD133 and vascular endothelial growth factor receptor 2 (VEGFR2), internalized acetylated low-density lipoprotein, and bound ulex europaeus-agglutinin-I, but were negative for CD45, which correlated with the endothelial morphology and ability to form capillaries of EPCs.

Conclusions

Our results are direct evidence that mononuclear cells (MCS) from living rat bone marrow can be used to culture EPCs in vitro under certain culture conditions, providing a new method for the further study of autologous EPC transplantation.

Endothelial progenitor cells as the target for cardiovascular disease prediction, personalized prevention, and treatments: progressing beyond the state-of-the-art

Stimulated by the leading mortalities of cardiovascular diseases (CVDs), various types of cardiovascular biomaterials have been widely investigated in the past few decades. Although great therapeutic effects can be achieved by bare metal stents (BMS) and drug-eluting stents (DES) within months or years, the long-term complications such as late thrombosis and restenosis have limited their further applications. It is well accepted that rapid endothelialization is a promising approach to eliminate these complications. Convincing evidence has shown that endothelial progenitor cells (EPCs) could be mobilized into the damaged vascular sites systemically and achieve endothelial repair in situ, which significantly contributes to the re-endothelialization process. Therefore, how to effectively capture EPCs via specific molecules immobilized on biomaterials is an important point to achieve rapid endothelialization. Further, in the context of predictive, preventive, personalized medicine (PPPM), the abnormal number alteration of EPCs in circulating blood and certain inflammation responses can also serve as important indicators for predicting and preventing early cardiovascular disease. In this contribution, we mainly focused on the following sections: the definition and classification of EPCs, the mechanisms of EPCs in treating CVDs, the potential diagnostic role of EPCs in predicting CVDs, as well as the main strategies for cardiovascular biomaterials to capture EPCs.

Co-immobilization of CD133 antibodies, vascular endothelial growth factors, and REDV peptide promotes capture, proliferation, and differentiation of endothelial progenitor cells

Capture of endothelial progenitor cells (EPCs) in situ has been considered as a promising strategy for the rapid endothelialization and long-term patency of artificial blood vessels and implant devices. In this study, a CD133⁺ EPC capture surface was fabricated by grafting CD133 antibody (a more specific EPC surface marker than CD34) and Arg-Glu-Asp-Val (REDV) peptideon the methacrylate-grafted hyaluronic acid (MA-HA) and heparin-hybridized (MA-HA&Heparin) resisting layer. Vascular endothelial growth factor (VEGF) was further conjugated to the immobilized heparin. This engineered surface showed good hemocompatibility and significantly higher ability of capturing CD133⁺ EPCs from human peripheral blood mononuclear cells (PBMCs) and obviously upregulated the expression of endothelial cell (EC) marker genes of EPCs such as VEGF receptor 2 (VEGFR2), CD31, VE-cadherin, and von Willebrand factor (vWF), facilitating the differentiation of EPCs into ECs. The dramatically enhanced EPC proliferation on this surface was dependent on the integrin-VEGFR synergistic signaling, as ERK1/2 phosphorylation was only significantly enhanced on the REDV and VEGF co-immobilized surface. This study highlights a new surface coating strategy for blood-contact materials based on the specific EPC capturing and rapid endothelialization. STATEMENT OF SIGNIFICANCE: Capture of endothelial progenitor cells (EPCs) in situ is a promising strategy for the rapid endothelialization and long-term patency of artificial blood vessels and scaffolds. More specific capture of EPCs by targeting CD133 rather than CD34 can better reduce the risk of inflammation and restenosis. On the other hand, an appropriate microenvironment for EPC proliferation is equally important for endothelialization, which is rarely considered by the existing EPC capture strategies. In this study, the capture ratio of EPCs was significantly increased by simultaneously grafting CD133 antibody and VEGF on a MA-HA and heparin-hybridized antifouling layer. Further, proliferation of EPCs after capture was significantly promoted by grafting VEGF and REDV peptide through the integrin-VEGFR synergistic signaling. This study highlights a new strategy for the surface coating of blood-contact materials based on specific EPC capture and rapid endothelialization.

High levels of endothelial progenitor cells and circulating endothelial cells in patients with Behçet's disease and their relationship to disease activity

BACKGROUND

Behçet's disease is a multisystemic vasculitis, associated with vascular endothelial dysfunction. Currently, the prognosis is unpredictable, because there is still no valid laboratory marker indicating the disease activity in Behçet's disease. Endothelial progenitor cells and circulating endothelial cells are newly introduced hematological markers which are presumed to take part in the pathogenesis of vasculitis.

OBJECTIVES

To evaluate the levels of endothelial progenitor cells and subtypes and circulating endothelial cells in patients with Behçet's disease and to describe their relationship with the disease activity.

METHODS

A total of 45 patients with Behçet's disease and 28 healthy controls were included in the study. Endothelial progenitor cells (CD34+CD133+KDR+ as early endothelial progenitor cells and CD34+KDR+ as late endothelial progenitor cells), and circulating endothelial cells (CD34+CD133+) were measured by flow cytometry.

RESULTS

The mean plasma level of endothelial progenitor cells and circulating endothelial cells, vascular endothelial growth factor, matrix metalloproteinase-9, C-reactive protein, and erythrocyte sedimentation rate were significantly higher in patients with Behçet's disease. All of these parameters except circulating endothelial cells were also found to be higher in patients with active disease than in patients with inactive disease. Early endothelial progenitor cells showed significant correlations with C-reactive protein and circulating endothelial cells.

STUDY LIMITATIONS

The cross-sectional nature of the study and patient characteristics such as being under treatment, which can affect endothelial progenitor cells numbers.

CONCLUSION

The increase in endothelial progenitor cells may play an essential role in the repair of endothelial injury in Behçet's disease, especially in the active period of the disease. Thus, endothelial progenitor cells can indicate the disease activity. In addition, endothelial progenitor cells and circulating endothelial cells can be used as endothelial repair and injury markers for Behçet's disease, respectively.

Morphological and Molecular Analysis of In Vitro Tubular Structures from Bovine Yolk Sac-Derived MSCs

The yolk sac is an extraembryonic membrane, of saccular form, connected to the ventral region of the embryo. It is the main source of nutrition for the embryo during the period when the placenta is not fully formed. The aim of this study was to generate tubular structures using mesenchymal stem cells from the bovine yolk sac (bYS-MSCs) and determine if these structures can be a model for in vitro vasculogenesis. The evaluation of this tissue by histochemistry revealed a strong marking of collagen fibers and PAS technique negativity. In transmission electron microscopy, cytoplasmic organelles with large nuclei were observed. The vessel formation assay on a Matrigel substrate showed that the mesenchymal cells of the yolk sac without growth factors (VEGF) are capable of forming branches, sprouting cells, and tubular structures similar to capillary blood. These tubular structures were xenotransplanted subcutaneously into the mesentery of BALB/c/nude mice; after 45 days, vascularized tissue and extensions of blood vessels around the tubular structures could be observed. Real-time PCR (qPCR) demonstrated an expression of the VEGF gene in different gestational age groups. No difference in distribution or expression was detected among groups. Our results suggest that the spontaneous formation of tubules from the yolk sac can be an experimental model to elucidate initial organogenesis and the possible formation of blood capillaries from in vitro mesenchymal cells and possible route of organoid production.

Improved Neo-Endothelialization of Small Diameter ePTFE Grafts with Titanium Coating

Background

Patency of small synthetic bypass grafts is inferior compared to autologous grafts for revascularization procedures. Titanium coating of foreign surfaces has shown to decrease thrombogenicity, enhance biocompatibility and promote adhesion of endothelial cells. The aim of this study was to test the effect of titanium coating of small diameter ePTFE grafts on short term patency, neo-endothelialization and neointimal proliferation.

Methods

Bilateral carotid graft interposition was performed in 5 pigs with uncoated (n=5) and titanium-coated (n=5) ePTFE grafts (internal diameter=4 mm, length=5 cm), thus each pig served as its own control. At the end of the study (30 ± 3 days), patency and stenosis severity was assessed by carotid angiography. Animals were sacrificed and grafts were excised for histology and scanning electron microscopy. Morphometry of histologic sections was carried out to determine neointimal proliferation and percentage of neo-endothelial coverage.

Results

Patency rate was 80% for uncoated and titanium-coated grafts. Quantitative angiography did not show any significant difference in lumen size between two groups. Morphometry revealed a significantly higher cellular coverage with CD 31 positive endothelial cells for titanium-coated (84 ± 19%) than uncoated grafts (48 ± 26%, p<0.001). There was a non significant trend (p=0.112) towards increased neointimal proliferation in titanium-coated (94 ± 61 μm2/μm) compared to uncoated grafts (60 ± 57 μm2/μm).

Conclusions

Patency rate in uncoated and titanium-coated ePTFE grafts is similar at one month. However, titanium coated grafts show a significant improvement in neo-endothelialization compared to uncoated grafts.

N-Acetylated Proline-Glycine-Proline Accelerates Cutaneous Wound Healing and Neovascularization by Human Endothelial Progenitor Cells

Human endothelial progenitor cells (hEPCs) are promising therapeutic resources for wound repair through stimulating neovascularization. However, the hEPCs-based cell therapy has been hampered by poor engraftment of transplanted cells. In this study, we explored the effects of N-acetylated Proline-Glycine-Proline (Ac-PGP), a degradation product of collagen, on hEPC-mediated cutaneous wound healing and neovascularization. Treatment of hEPCs with Ac-PGP increased migration, proliferation, and tube-forming activity of hEPCs in vitro. Knockdown of CXCR2 expression in hEPCs abrogated the stimulatory effects of Ac-PGP on migration and tube formation. In a cutaneous wound healing model of rats and mice, topical application of Ac-PGP accelerated cutaneous wound healing with promotion of neovascularization. The positive effects of Ac-PGP on wound healing and neovascularization were blocked in CXCR2 knockout mice. In nude mice, the individual application of Ac-PGP treatment or hEPC injection accelerated wound healing by increasing neovascularization. Moreover, the combination of Ac-PGP treatment and hEPC injection further stimulated wound healing and neovascularization. Topical administration of Ac-PGP onto wound bed stimulated migration and engraftment of transplanted hEPCs into cutaneous dermal wounds. Therefore, these results suggest novel applications of Ac-PGP in promoting wound healing and augmenting the therapeutic efficacy of hEPCs.

Novel peptides for small-caliber graft functionalization selected by a phage display of endothelial-positive/platelet-negative combined selection

A new protocol to identify peptides with EPCs high affinity and at the same time the ability to suppress the interaction with platelets was presented.

In-vivo quantification of the revascularization of a human acellular dermis seeded with EPCs and MSCs in co-culture with fibroblasts and pericytes in the dorsal chamber model in pre-irradiated tissue

INTRODUCTION

Transplantation of a cell-seeded graft may improve wound healing after radiotherapy. However, the survival of the seeded cells depends on a rapid vascularization of the graft. Co-culturing of adult stem cells may be a promising strategy to accelerate the vessel formation inside the graft. Thus, we compared the in vivo angiogenic potency of mesenchymal stem cells (MSC) and endothelial progenitor cells (EPC) using dorsal skinfold chambers and intravital microscopy.

MATERIALS AND METHODS

Cells were isolated from rat bone marrow and adipose tissue and characterized by immunostaining and flow cytometry. Forty-eight rats received a dorsal skinfold chamber and were divided into 2 main groups, irradiated and non-irradiated. Each of these 2 groups were further subdivided into 4 groups: unseeded matrices, matrices + fibroblasts + pericytes, matrices + fibroblasts + pericytes + MSCs and matrices + fibroblasts + pericytes + EPCs. Vessel densities were quantified semi-automatically using FIJI.

RESULTS

Fibroblasts + pericytes - seeded matrices showed a significantly higher vascular density in all groups with an exception of non-irradiated rats at day 12 compared to unseeded matrices. Co-seeding of MSCs increased vessel densities in both, irradiated and non-irradiated groups. Co-seeding with EPCs did not result in an increase of vascularization in none of the groups.

DISCUSSION

We demonstrated that the pre-radiation treatment led to a significant decreased vascularization of the implanted grafts. The augmentation of the matrices with fibroblasts and pericytes in co-culture increased the vascularization compared to the non-seeded matrices. A further significant enhancement of vessel ingrowth into the matrices could be achieved by the co-seeding with MSCs in both, irradiated and non-irradiated groups.

Scaffolds and Cell-Based Tissue Engineering for Blood Vessel Therapy

The increasing morbidity of cardiovascular diseases in modern society has made it crucial to develop a small-caliber blood vessel. In the absence of appropriate autologous vascular grafts, an alternative prosthesis must be constructed for cardiovascular disease patients. The aim of this article is to describe the advances in making cell-seeded cardiovascular prostheses. It also discusses the combinations of types of scaffolds and cells, especially autologous stem cells, which are suitable for application in tissue-engineered vessels with the favorable properties of mechanical strength, antithrombogenicity, biocompliance, anti-inflammation, fatigue resistance and long-term durability. This article highlights the advancements in cellular tissue-engineered vessels in recent years.

Diabetic wound healing in a MMP9-/- mouse model

Reduced mobilization of endothelial progenitor cells (EPCs) from the bone marrow (BM) and impaired EPC recruitment into the wound represent a fundamental deficiency in the chronic ulcers. However, mechanistic understanding of the role of BM-derived EPCs in cutaneous wound neovascularization and healing remains incomplete, which impedes development of EPC-based wound healing therapies. The objective of this study was to determine the role of EPCs in wound neovascularization and healing both under normal conditions and using single deficiency (EPC) or double-deficiency (EPC + diabetes) models of wound healing. MMP9 knockout (MMP9 KO) mouse model was utilized, where impaired EPC mobilization can be rescued by stem cell factor (SCF). The hypotheses were: (1) MMP9 KO mice exhibit impaired wound neovascularization and healing, which are further exacerbated with diabetes; (2) these impairments can be rescued by SCF administration. Full-thickness excisional wounds with silicone splints to minimize contraction were created on MMP9 KO mice with/without streptozotocin-induced diabetes in the presence or absence of tail-vein injected SCF. Wound morphology, vascularization, inflammation, and EPC mobilization and recruitment were quantified at day 7 postwounding. Results demonstrate no difference in wound closure and granulation tissue area between any groups. MMP9 deficiency significantly impairs wound neovascularization, increases inflammation, decreases collagen deposition, and decreases peripheral blood EPC (pb-EPC) counts when compared with wild-type (WT). Diabetes further increases inflammation, but does not cause further impairment in vascularization, as compared with MMP9 KO group. SCF improves neovascularization and increases EPCs to WT levels (both nondiabetic and diabetic MMP9 KO groups), while exacerbating inflammation in all groups. SCF rescues EPC-deficiency and impaired wound neovascularization in both diabetic and nondiabetic MMP9 KO mice. Overall, the results demonstrate that BM-derived EPCs play a significant role during wound neovascularization and that the SCF-based therapy with controlled inflammation could be a viable approach to enhance healing in chronic diabetic wounds.

Circulating endothelial progenitor cells in periodontitis

BACKGROUND

Several biologically plausible mechanisms have been proposed to mediate the association between periodontitis and atherosclerotic vascular disease (AVD), including adverse effects on vascular endothelial function. Circulating endothelial progenitor cells (cEPCs) are known to contribute to vascular repair, but limited data are available regarding the relationship between cEPC levels and periodontitis. The aims of this cross-sectional study are to investigate the levels of hemangioblastic and monocytic cEPCs in patients with periodontitis and periodontally healthy controls and to associate cEPC levels with the extent and severity of periodontitis.

METHODS

A total of 112 individuals (56 patients with periodontitis and 56 periodontally healthy controls, aged 26 to 65 years; mean age: 43 years) were enrolled. All participants underwent a full-mouth periodontal examination and provided a blood sample. Hemangioblastic cEPCs were assessed using flow cytometry, and monocytic cEPCs were identified using immunohistochemistry in cultured peripheral blood mononuclear cells. cEPC levels were analyzed in the entire sample, as well as in a subset of 50 pairs of patients with periodontitis/periodontally healthy controls, matched with respect to age, sex, and menstrual cycle.

RESULTS

Levels of hemangioblastic cEPCs were approximately 2.3-fold higher in patients with periodontitis than periodontally healthy controls, after adjustments for age, sex, physical activity, systolic blood pressure, and body mass index (P = 0.001). A non-significant trend for higher levels of monocytic cEPCs in periodontitis was also observed. The levels of hemangioblastic cEPCs were positively associated with the extent of bleeding on probing, probing depth, and clinical attachment loss. Hemangioblastic and monocytic cEPC levels were not correlated (Spearman correlation coefficient 0.03, P = 0.77), suggesting that they represent independent populations of progenitor cells.

CONCLUSION

These findings further support the notion that oral infections have extraoral effects and document that periodontitis is associated with a mobilization of EPCs from the bone marrow, apparently in response to systemic inflammation and endothelial injury.

Endothelial Progenitor Cell Fraction Contained in Bone Marrow-Derived Mesenchymal Stem Cell Populations Impairs Osteogenic Differentiation

In bone tissue engineering (TE) endothelial cell-osteoblast cocultures are known to induce synergies of cell differentiation and activity. Bone marrow mononucleated cells (BMCs) are a rich source of mesenchymal stem cells (MSCs) able to develop an osteogenic phenotype. Endothelial progenitor cells (EPCs) are also present within BMC. In this study we investigate the effect of EPCs present in the BMC population on MSCs osteogenic differentiation. Human BMCs were isolated and separated into two populations. The MSC population was selected through plastic adhesion capacity. EPCs (CD34⁺ and CD133⁺) were removed from the BMC population and the resulting population was named depleted MSCs. Both populations were cultured over 28 days in osteogenic medium (Dex⁺) or medium containing platelet lysate (PL). MSC population grew faster than depleted MSCs in both media, and PL containing medium accelerated the proliferation for both populations. Cell differentiation was much higher in Dex⁺ medium in both cases. Real-time RT-PCR revealed upregulation of osteogenic marker genes in depleted MSCs. Higher values of ALP activity and matrix mineralization analyses confirmed these results. Our study advocates that absence of EPCs in the MSC population enables higher osteogenic gene expression and matrix mineralization and therefore may lead to advanced bone neoformation necessary for TE constructs.

Circulating endothelial cells are increased in chronic myeloid leukemia blast crisis

We measured circulating endothelial precursor cells (EPCs), activated circulating endothelial cells (aCECs), and mature circulating endothelial cells (mCECs) using four-color multiparametric flow cytometry in the peripheral blood of 84 chronic myeloid leukemia (CML) patients and 65 healthy controls; and vascular endothelial growth factor (VEGF) by quantitative real-time PCR in 50 CML patients and 32 healthy controls. Because of an increase in mCECs, the median percentage of CECs in CML blast crisis (0.0146%) was significantly higher than in healthy subjects (0.0059%, P<0.01) and in the accelerated phase (0.0059%, P=0.01). There were no significant differences in the percentages of CECs in chronic- or active-phase patients and healthy subjects (P>0.05). In addition, VEGF gene expression was significantly higher in all phases of CML: 0.245 in blast crisis, 0.320 in the active phase, and 0.330 in chronic phase patients than it was in healthy subjects (0.145). In conclusion, CML in blast crisis had increased levels of CECs and VEGF gene expression, which may serve as markers of disease progression and may become targets for the management of CML.

The Role of Stem Cells in Wound Angiogenesis

Significance: Revascularization plays a critical role in wound healing and is regulated by a complex milieu of growth factors and cytokines. Deficiencies in revascularization contribute to the development of chronic nonhealing wounds. Recent Advances: Stem-cell-based therapy provides a novel strategy to enhance angiogenesis and improve wound healing. With bioethical concerns associated with embryonic stem cells, focus has shifted to different populations of vascular precursors, isolated from adult somatic tissue. Three main populations have been identified: endothelial progenitor cells, mesenchymal stem cells, and induced-pluripotent stem cells. These populations demonstrate great promise to positively influence neovascularization and wound repair. Critical Issues: Further studies to more definitively define each population are necessary to efficiently translate stem-cell-based therapeutic angiogenesis to the bedside. Better understanding of the physiologic pathways of how stem cells contribute to angiogenesis in normal tissue repair will help identify targets for successful therapeutic angiogenesis. Future Directions: Active studies in both animal models and clinical trials are being conducted to develop effective delivery routes, including dosing, route, and timing. Stem-cell-based therapy holds significant potential as a strategy for therapeutic angiogenesis in the care of patients with chronic nonhealing wounds.

[Assessment of endothelial function in autoimmune diseases]

Numerous autoimmune-inflammatory rheumatic diseases have been associated with accelerated atherosclerosis or other types of vasculopathy leading to an increase in cardiovascular disease incidence. In addition to traditional cardiovascular risk factors, endothelial dysfunction is an important early event in the pathogenesis of atherosclerosis, contributing to plaque initiation and progression. Endothelial dysfunction is characterized by a shift of the actions of the endothelium toward reduced vasodilation, a proinflammatory and a proadhesive state, and prothrombic properties. Therefore, assessment of endothelial dysfunction targets this vascular phenotype using several biological markers as indicators of endothelial dysfunction. Measurements of soluble adhesion molecules (ICAM-1, VCAM-1, E-selectin), pro-thrombotic factors (thrombomodulin, von Willebrand factor, plasminogen activator inhibitor-1) and inflammatory cytokines are most often performed. Regarding the functional assessment of the endothelium, the flow-mediated dilatation of conduit arteries is a non-invasive method widely used in pathophysiological and interventional studies. In this review, we will briefly review the most relevant information upon endothelial dysfunction mechanisms and explorations. We will summarize the similarities and differences in the biological and functional assessments of the endothelium in different autoimmune diseases.

Obstructive sleep apnea and endothelial progenitor cells

BACKGROUND

Obstructive sleep apnea (OSA) occurs in 4% of middle-aged men and 2% of middle-aged women in the general population, and the prevalence is even higher in specific patient groups. OSA is an independent risk factor for a variety of cardiovascular diseases. Endothelial injury could be the pivotal determinant in the development of cardiovascular pathology in OSA. Endothelial damage ultimately represents a dynamic balance between the magnitude of injury and the capacity for repair. Bone marrow-derived endothelial progenitor cells (EPCs) within adult peripheral blood present a possible means of vascular maintenance that could home to sites of injury and restore endothelial integrity and normal function.

METHODS

We summarized pathogenetic mechanisms of OSA and searched for available studies on numbers and functions of EPCs in patients with OSA to explore the potential links between the numbers and functions of EPCs and OSA. In particular, we tried to elucidate the molecular mechanisms of the effects of OSA on EPCs.

CONCLUSION

Intermittent hypoxia cycles and sleep fragmentation are major pathophysiologic characters of OSA. Intermittent hypoxia acts as a trigger of oxidative stress, systemic inflammation, and sympathetic activation. Sleep fragmentation is associated with a burst of sympathetic activation and systemic inflammation. In most studies, a reduction in circulating EPCs has emerged. The possible mechanisms underlying the decrease in the number or function of EPCs include prolonged inflammation response, oxidative stress, increased sympathetic activation, physiological adaptive responses of tissue to hypoxia, reduced EPC mobilization, EPC apoptosis, and functional impairment in untreated OSA. Continuous positive airway pressure (CPAP) therapy for OSA affects the mobilization, apoptosis, and function of EPCs through preventing intermittent hypoxia episodes, improving sleep quality, and reducing systemic inflammation, oxidative stress levels, and sympathetic overactivation. To improve CPAP adherence, the medical staff should pay attention to making the titration trial a comfortable first CPAP experience for the patients; for example, using the most appropriate ventilators or proper humidification. It is also important to give the patients education and support about CPAP use in the follow-up, especially in the early stage of the treatment.

The Role of Endothelial Progenitor Cells in Postnatal Vasculogenesis: Implications for Therapeutic Neovascularization and Wound Healing

SIGNIFICANCE

Postnatal vasculogenesis mediated via endothelial progenitor cells (EPCs) contributes to re-endothelialization and augments neovascularization after ischemia and tissue injury, providing a novel therapeutic application. However, controversy exists with respect to the origin, identification, and contributions of the EPCs to neovascularization, necessitating further study.

RECENT ADVANCES

Bone marrow (BM) or circulating cells expressing cd133/vascular endothelial growth factor receptor 2 include those with endothelial progenitor capacity. Increasing evidence suggests that there are additional BM-derived (myeloid; mesenchymal cells) and non-BM-derived (peripheral and cord-blood; tissue-resident) cell populations which also give rise to endothelial cells (ECs) and contribute to re-endothelialization and growth factor release after ischemia and tissue injury. Currently, EPCs are being used as diagnostic markers for the assessment of cardiovascular and tumor risk/progression. Techniques aimed at enhancing ex vivo expansion and the therapeutic potential of these cells are being optimized.

CRITICAL ISSUES

Mobilization and EPC-mediated neovascularization are critically regulated. Stimulatory (growth factors, statins, and exercise) or inhibitory factors (obesity, diabetes, and other cardiovascular diseases) modulate EPC numbers and function. Recruitment and incorporation of EPCs require a coordinated sequence of signaling events, including adhesion, migration (by integrins), and chemoattraction. Finally, EPCs differentiate into ECs and/or secrete angiogenic growth factors. These cells are highly plastic, and depending on the microenvironment and presence of other cells, EPCs transdifferentiate and/or undergo cell fusion and become cells of a different lineage. Therefore, in vitro culture conditions should be optimized to mimic the in vivo milieu to fully characterize the biological function and contribution of EPCs to postnatal vasculogenesis.

FUTURE DIRECTIONS

Advances in characterization of the EPC biology and enhancement of EPC functions are required. In addition, innovative tissue-engineered carrier matrices that permit embedding of EPCs and provide optimal conditions for EPC survival and endothelial outgrowth will further contribute to EPC-mediated therapeutic applications in wound healing and ischemia repair.

Endothelial progenitor cells in the pathogenesis of idiopathic pulmonary fibrosis: an evolving concept

Background

Idiopathic pulmonary fibrosis (IPF) has been associated with abnormal vascular remodeling. Bone marrow derived endothelial progenitor cells (EPCs) are considered to possess lung tissue repair and vascular remodeling properties.

Objectives

The study aimed to assess early EPCs levels and EPCs endogenous vascular endothelial growth factor (VEGF) expression in IPF. In order to examine alterations in the mobilization of EPCs from the bone marrow we measured plasma VEGF.

Main Results

Twenty-three patients with IPF and fifteen healthy subjects were included. The number of early EPCs colonies was markedly reduced in IPF patients vs controls (6.00±6.49 vs 49.68±16.73, respectively, p<0.001). EPCs were further decreased in patients presenting systolic pulmonary arterial pressure (sPAP)≥35 mmHg. The number of colonies per well correlated negatively with P_(A-a)O₂ (r =  −0.750, p<0.001). Additionally, VEGF mRNA levels were significantly increased in IPF patients. There were no differences observed in VEGF plasma levels in IPF patients when compared to controls.

Conclusions

The current data suggest that inadequate levels of early EPCs may potentially contribute to suppressed repair and recovery of the damaged pulmonary endothelium and thereby may drive the sequence of events in profibrogenic direction. Increased VEGFmRNA levels in the clinical context of IPF may represent a compensatory mechanism to overcome reduced EPCs levels.

Pattern formation during vasculogenesis

Vasculogenesis, the assembly of the first vascular network, is an intriguing developmental process that yields the first functional organ system of the embryo. In addition to being a fundamental part of embryonic development, vasculogenic processes also have medical importance. To explain the organizational principles behind vascular patterning, we must understand how morphogenesis of tissue level structures can be controlled through cell behavior patterns that, in turn, are determined by biochemical signal transduction processes. Mathematical analyses and computer simulations can help conceptualize how to bridge organizational levels and thus help in evaluating hypotheses regarding the formation of vascular networks. Here, we discuss the ideas that have been proposed to explain the formation of the first vascular pattern: cell motility guided by extracellular matrix alignment (contact guidance), chemotaxis guided by paracrine and autocrine morphogens, and sprouting guided by cell-cell contacts.

Vascular Network Formation in Expanding versus Static Tissues: Embryos and Tumors

In this perspectives article, we review scientific literature regarding de novo formation of vascular networks within tissues undergoing a significant degree of motion. Next, we contrast dynamic pattern formation in embryos to the vascularization of relatively static tissues, such as the retina. We argue that formation of primary polygonal vascular networks is an emergent process, which is regulated by biophysical mechanisms. Dynamic empirical data, derived from quail embryos, show that vascular beds readily form within a moving extracellular matrix (ECM) microenvironment-which we analogize to the de novo vascularization of small rapidly growing tumors. Our perspective is that the biophysical rules, which govern cell motion during vasculogenesis, may hold important clues to understanding how the first vessels form in certain malignancies.

Therapeutic angiogenesis in patients with severe limb ischemia by transplantation of a combination stem cell product

OBJECTIVE

Angiogenesis involves the interplay of endothelial progenitor cells, pericytes, growth factors, and cellular matrix components. The use of mesenchymal stem cells, which are closely related to pericytes and produce diverse angiogenic growth factors and matrix molecules, seems to be a promising therapeutic modality. We postulate that the use of a combination cell product (mesenchymal stem cells in conjunction with a source of endothelial progenitor cells) is safe and efficient and may optimize the clinical results obtained with the use of endothelial progenitor cells alone. This study assessed whether the intramuscular infusion of a combination cell product represents a viable, effective, and lasting therapeutic modality to improve perfusion in severely ischemic limbs.

METHODS

Patients with limb ischemia (n=26) received an intramuscular (gastrocnemius) infusion of the combination cell product in the most ischemic leg and a placebo product in the (less ischemic) contralateral leg. Clinical follow-up (months 0.5, 1, 2, and 4 postinfusion) included evaluation of pain-free walking time, ankle-brachial index, perfusion scintigraphy, and quality of life survey.

RESULTS

No adverse events occurred after infusion. Efficacy assessment indicated that after cell infusion there was a significant improvement in walking time and ankle-brachial index. In addition, technetium-99m-tetrofosmin scintigraphy demonstrated a significant increase of perfusion in the treated limbs compared with the respective control legs.

CONCLUSIONS

This phase II clinical trial shows that the use of a combination cell therapy is safe and effective in increasing blood flow in the ischemic legs of patients with limb ischemia.

Potential therapeutic effect of bone marrow-derived mesenchymal stem cells in acute pancreatitis

Acute pancreatitis is an inflammatory disease with dropsical, hemorrhagic or even necrotic conditions of the pancreas caused by several factors. It has significant morbidity and mortality, but no specific therapy is available so far. Bone marrow-derived mesenchymal stem cells (BMSCs) have multiple differentiation potential. They can not only differentiate to form endoderm and ectoblast cells, but also participate in tissue regeneration, repair and anti-inflammation. Recent studies have demonstrated that BMSCs have potential therapeutical effect in acute pancreatitis. BMSCs can migrate to injury tissue, multiply, be transformed to pancreatic stem cells and then participate in the process of regeneration. They also renovate vascular endothelium to improve blood circulation, adjust and control the cytokines to decrease inflammation, and regulate immunization. Here we review the recent advances in understanding the role of BMSCs in the treatment of acute pancreatitis.

Distribution of exogenous endothelial progenitor cells in a rat model of hepatoma and their impact on liver cancer formation

AIM: To investigate the role of endothelial progenitor cells (EPCs) in the formation of liver cancer and to explore the possibility of using EPCs as a delivery vehicle for the treatment of liver cancer.

METHODS: Isolated and cultured EPCs were labeled with DAPI in vitro. Sprague-Dawley rats were divided into three groups: control group, model group, and EPC group. The model group and EPC group were intraperitoneally injected with diethylnitrosamine (DEN) to induce liver cancer, while the control group was injected with saline. Rats of the EPC group were further divided into three subgroups and intravenously injected with 1 mL of low (1 × 10⁵/150 μL), medium (2 × 10⁵/150 μL), and high (4 × 10⁵/150 μL) concentrations of EPCs-DAPI suspension, respectively, while the control group and model group were injected with equal volume of saline. At weeks 4, 6 and 8, rats were killed to take liver tissue samples to detect the expression of EPCs markers CD34, CD133, and KDR, and serum samples to measure the levels of ALT, AST, and AFP. EPCs-DAPI-positive area (PA) was quantified using the Imagepro plus image analysis software.

RESULTS: Positive expression of cell surface markers CD34, CD133, and KDR could be detected on cultured cells after 7 days of culture. Serum ALT, AST, and AFP differed significantly between the low-concentration EPC group and model group at week 4, between the medium-concentration EPC group and model group at week 6, and between the high-concentration EPC group and model group at week 8 (all P < 0.01). Positive DAPI was detected in all the EPC groups, and the positive rate of DAPI was dependent on the concentration of injected EPCs and injection duration. PA was significantly different among rats injected with different concentrations of EPCs at all time points (all P < 0.05), but showed no significant differences among rats injected with the same concentration of EPCs at different time points (all P > 0.05).

CONCLUSION: EPCs affect liver function in the rat model of liver cancer in a concentration- and time-dependent manner. EPCs in the liver can promote the formation of liver cancer. EPCs have a tropism to liver cancer in vivo.

Cellular players in angiogenesis during the course of systemic sclerosis

Vascular endothelial injury in Systemic Sclerosis (SSc) leads to pathological changes in the blood vessels that adversely impact the physiology of many organs, resulting in chronic tissue ischemia. The response to hypoxia induces complex cellular and molecular mechanisms in the attempt to recover endothelial cell function and tissue perfusion. The progressive losses of capillaries on one hand, and the vascular remodeling of arteriolar vessels on the other, result in insufficient blood flow, causing severe and chronic hypoxia. Hypoxia is a major stimulus of angiogenesis, leading to the expression of pro-angiogenic molecules, mainly of Vascular Endothelial Growth Factor (VEGF), which triggers the angiogenic process. Nevertheless, in SSc patients there is no evidence of adaptive angiogenesis. Failure of the angiogenic process in SSc largely depends on alteration in the balance between pro- and anti-angiogenic factors, as well as on functional alterations of the cellular players involved in the angiogenic and vasculogenic program. A decreased urokinase plasminogen activator (uPA) dependent invasion, proliferation, and capillary morphogenesis, was showed in SSc endothelial cells (EC). Although hematopoietic endothelial progenitor cells (EPC) count in the peripheral blood of SSc patients is still a matter of controversy, alterations in mobilization process, an excessive immune-mediated EPC destruction in the peripheral circulation or in the bone marrow, a progressive depletion of EPCs following homing to ischemic tissues under persistent peripheral vascular injury, an intrinsic functional impairment could lead to poor vasculogenesis. Human mesenchymal stem cells represent an alternative source of endothelial progenitor cells and it has been observed that their angiogenic potential is reduced in SSc. Targeting autologous stem and progenitor cells could be an ideal tool to counteract and repair dysfunctional angiogenesis.

Platelet released growth factors boost expansion of bone marrow derived CD34(+) and CD133(+) endothelial progenitor cells for autologous grafting

Stem cell based autologous grafting has recently gained mayor interest in various surgical fields for the treatment of extensive tissue defects. CD34(+) and CD133(+) cells that can be isolated from the pool of bone marrow mononuclear cells (BMC) are capable of differentiating into mature endothelial cells in vivo. These endothelial progenitor cells (EPC) are believed to represent a major portion of the angiogenic regenerative cells that are released from bone marrow when tissue injury has occurred. In recent years tissue engineers increasingly looked at the process of vessel neoformation because of its major importance for successful cell grafting to replace damaged tissue. Up to now one of the greatest problems preventing a clinical application is the large scale of expansion that is required for such purpose. We established a method to effectively enhance the expansion of CD34(+) and CD133(+) cells by the use of platelet-released growth factors (PRGF) as a media supplement. PRGF were prepared from thrombocyte concentrates and used as a media supplement to iscove's modified dulbecco's media (IMDM). EPC were immunomagnetically separated from human bone morrow monocyte cells and cultured in IMDM + 10% fetal calf serum (FCS), IMDM + 5%, FCS + 5% PRGF and IMDM + 10% PRGF. We clearly demonstrate a statistically significant higher and faster cell proliferation rate at 7, 14, 21, and 28 days of culture when both PRGF and FCS were added to the medium as opposed to 10% FCS or 10% PRGF alone. The addition of 10% PRGF to IMDM in the absence of FCS leads to a growth arrest from day 14 on. In histochemical, immunocytochemical, and gene-expression analysis we showed that angiogenic and precursor markers of CD34(+) and CD133(+) cells are maintained during long-term culture. In summary, we established a protocol to boost the expansion of CD34(+) and CD133(+) cells. Thereby we provide a technical step towards the clinical application of autologous stem cell transplantation.

Vascular disease and stem cell therapies

INTRODUCTION AND BACKGROUND

Peripheral vascular disease is the leading cause of limb ischemia (LI). LI is manifested by claudication, ischemic rest pain, ulcers or gangrene. It is the result of peripheral arterial disease due to atherosclerosis. Over the last decade, several centers around the world have initiated clinical trials utilizing stem cells as a treatment for this disease.

SOURCES OF DATA

Published medical literature, clinical trials announced in clinical trials.gov and TCA cellular therapy experience.

AREAS OF AGREEMENT

There is general agreement that stem cells are useful for LI.

AREAS OF CONTROVERSY

These arise from the type of cells, dose, route of administration and methods to evaluate efficacy.

GROWING POINTS

Growing evidence suggests that bone marrow derived-mesenchymal stem cells are as good as or superior to mononuclear cells, and a combination of both cell types may be even better.

AREAS TIMELY FOR DEVELOPING RESEARCH

Based on current trials and publications, several promising biological products could become part of the therapeutic arsenal for LI. This may include combinations of more than one type of adult/induced pluripotent stem cells/embryonic stem cells, use of stem cells with growth factors or extracellular matrix molecules.

Comparative analysis of the predictive power of different endothelial progenitor cell phenotypes on cardiovascular outcome

AIM

To compare the predictive power of different endothelial progenitor cell (EPC) phenotypic markers for future cardiovascular events.

METHODS

Peripheral blood was collected from 76 consecutive patients with acute coronary syndromes (ACS) who underwent percutaneous coronary intervention in our institute. The various EPC phenotypes of peripheral blood mononuclear cells were CD34+CD133+, CD34+KDR+, and CD 133+KDR+. The outcome endpoint included cardiovascular mortality, recurrent ACS, and hospitalization for decompensated heart failure during a 24-mo follow-up period.

RESULTS

CD34+CD133+ cells (P = 0.034), but not CD34+KDR+ (P = 0.35) or CD 133+KDR+ cells (P = 0.19), were found to predict recurrent ACS. We found no correlation between EPCs measured by any of the three phenotypic combinations of accepted CD markers and the total combination of these separate outcomes.

CONCLUSION

The EPC CD34+CD133+ phenotype, but not the CD34+KDR+ or the CD 133+KDR+ phenotypes, is predictive of future adverse cardiovascular outcomes.

Combination Stem Cell Therapy for the Treatment of Severe Limb Ischemia: Safety and Efficacy Analysis

The infusion of a source of endothelial progenitors (EPCs) to limb ischemia (LB) patients has been used to increase angiogenesis. Because the formation of new blood vessels involves, in addition to EPCs, other cells and angiogenic regulators, we postulate that a combination cell therapy including EPCs and mesenchymal stem cells (a source of pericytes progenitors and angiogenic regulators) may represent a preferential stimuli for the development of blood vessels. In this phase I clinical trial, patients with LI were infused with a cell product consisting of autologous bone marrow-derived mononuclear and mesenchymal stem cells. After 10 2 months of follow-up, efficacy assessment demonstrated improvements in walking time, ankle brachial pressure, and quality of life. Concomitantly, angiographic and 99mTc-TF perfusion scintigraphy scores confirmed increased perfusion in the treated limbs. These results show that the use of a combination cell therapy is safe, feasible, and appears effective in patients with LI.

Safety and efficacy of therapeutic angiogenesis as a novel treatment in patients with critical limb ischemia

BACKGROUND

In some patients with critical limb ischemia (CLI) the possibility of revascularizing treatment does not exist. In this case therapeutic angiogenesis (TA) using autologous endothelial progenitor cell (EPC) transplantation could be an alternative. The objective of our study was to evaluate the safety and efficacy of TA using EPC.

METHODS

Twenty-eight patients with CLI who were not candidates for surgical or endovascular revascularization were included in a prospective study. To mobilize EPCs from the bone marrow, granulocyte colony-stimulating growth factor was injected subcutaneously at doses of 5 microg/kg/day for 5 days. Apheresis was performed, obtaining 50 mL of blood with a high rate of EPCs (CD34(+) and CD133(+) cells were counted). EPCs were implanted in the ischemic limb by intramuscular injections. Primary end points were the safety and feasibility of the procedure and limb salvage rate for amputation at 12 months. Other variables studied were improvement in rest pain, healing of ulcers, ankle-brachial pressure index (ABI), and digital plethysmography. All procedures were done pretreatment and every 3 months for a year on average. Postransplantation arteriography was done in selected cases.

RESULTS

No adverse effects were observed. Mean follow-up was 14 months. Before treatment, mean basal ABI was 0.35+/-0.2 and at 18 months postimplantation, 0.72+/-0.51 (p=0.009). There was a mean decrease of five points in pain scale: basal 8.7+/-1, after TA 3.8+/-2.9 (p=0.01). Seven patients required major amputation. Kaplan-Meier analysis revealed a limb salvage rate of 74.4% after 1 year.

CONCLUSION

Implantation of EPCs in CLI is a safe alternative, improves tissue perfusion, and obtains high amputation-free rates. Nevertheless, this is a small cohort and results should be tested with long randomized trials.

Angiogenic factor-enriched platelet-rich plasma enhances in vivo bone formation around alloplastic graft material

PURPOSE

Although most researchers agree that platelet-rich plasma (PRP) is a good source of autogenous growth factors, its effect on bone regeneration is still controversial. The purpose of this study was to evaluate whether increasing angiogenic factors in the human PRP to enhance new bone formation through rapid angiogenesis.

MATERIAL AND METHODS

In vitro, the human platelets were activated with application of shear stress, 20 µg/ml collagen, 2 mM CaCl(2) and 10U thrombin/1 × 10(9) platelets. Level of vascular endothelial growth factor (VEGF) and platelet microparticle (PMP) in the activated platelets were checked. In the animal study, human angiogenic factors-enriched PRP was tested in 28 athymic rat's cranial critical bone defects with β-TCP. Angiogenesis and osteogenesis were evaluated by laser Doppler perfusion imaging, histology, dual energy X-ray densinometry, and micro-computed tomography.

RESULTS

In vitro, this human angiogenic factors-enriched PRP resulted in better cellular proliferation and osteogenic differentiation. In vivo, increasing angiogenic potential of the PRP showed significantly higher blood perfusion around the defect and enhanced new bone formation around acellular bone graft material.

CONCLUSION

Angiogenic factor-enriched PRP leads to faster and more extensive new bone formation in the critical size bone defect. The results implicate that rapid angiogenesis in the initial healing period by PRP could be supposed as a way to overcome short term effect of the rapid angiogenesis.

Characterization of umbilical cord blood-derived late outgrowth endothelial progenitor cells exposed to laminar shear stress

Endothelial progenitor cells isolated from umbilical cord blood (CB-EPCs) represent a promising source of endothelial cells for synthetic vascular grafts and tissue-engineered blood vessels since they are readily attainable, can be easily isolated, and possess a high proliferation potential. The objective of this study was to compare the functional behavior of late outgrowth CB-EPCs with human aortic endothelial cells (HAECs). CB-EPCs and HAECs were cultured on either smooth muscle cells in a coculture model of a tissue-engineered blood vessels or fibronectin adsorbed to Teflon-AF-coated glass slides. Late outgrowth CB-EPCs expressed endothelial cell-specific markers and were negative for the monocytic marker CD14. CB-EPCs have higher proliferation rates than HAECs, but are slightly smaller in size. CB-EPCs remained adherent under supraphysiological shear stresses, oriented and elongated in the direction of flow, and expressed similar numbers of alpha(5)beta(1) and alpha(v)beta(3) integrins and antithrombotic genes compared to HAECs. There were some differences in mRNA levels of E-selectin and vascular cell adhesion molecule 1 between CB-EPCs and HAECs; however, protein levels were similar on the two cell types, and CB-EPCs did not support adhesion of monocytes in the absence of tumor necrosis factor-alpha stimulation. Although CB-EPCs expressed significantly less endothelial nitric oxide synthase protein after exposure to flow than HAECs, nitric oxide levels induced by flow were not significantly different. These results suggest that late outgrowth CB-EPCs are functionally similar to HAECs under flow conditions and are a promising cell source for cardiovascular therapies.

Stem cell-like human endothelial progenitors show enhanced colony-forming capacity after brief sevoflurane exposure: preconditioning of angiogenic cells by volatile anesthetics

BACKGROUND

Endothelial progenitor cells play a pivotal role in tissue repair, and thus are used for cell replacement therapies in "regenerative medicine." We tested whether the anesthetic sevoflurane would modulate growth or mobilization of these angiogenic cells.

METHODS

In an in vitro model, mononuclear cells isolated from peripheral blood of healthy donors were preconditioned with sevoflurane (3 times 30 min at 2 vol% interspersed by 30 min of air). Colony-forming units were determined after 9 days in culture and compared with time-matched untreated control. Using magnetic cell sorting, CD133+/CD34+ endothelial progenitors were enriched from human umbilical cord blood, and vascular endothelial growth factor (VEGF), VEGFR2 (KDR), granulocyte colony-stimulating factor (G-CSF), STAT3, c-kit, and CXCR4 expressions were determined in sevoflurane-treated and untreated cells by real-time reverse transcriptase polymerase chain reaction. In a volunteer study with crossover design, we tested whether sevoflurane inhalation (<1 vol% end-tidal concentration) would mobilize endothelial progenitor cells from the bone marrow niche into the circulation using flow cytometry of peripheral blood samples. VEGF and G-CSF plasma levels were also measured.

RESULTS

In vitro sevoflurane exposure of mononuclear cells enhanced colony-forming capacity and increased VEGF mRNA levels in CD133+/CD34+ cord blood cells (P = 0.017). Sevoflurane inhalation in healthy volunteers did not alter the number of CD133+/CD34+ or KDR+/CD34+ endothelial progenitors in the circulation, but increased the number of colony-forming units (P = 0.034), whereas VEGF and G-CSF plasma levels remained unchanged.

CONCLUSIONS

Sevoflurane preconditioning promotes growth and proliferation of stem cell-like human endothelial progenitors. Hence, it may be used to promote perioperative vascular healing and to support cell replacement therapies.

[Novel therapies of non-revascularizing peripheral arterial occlusive disease: therapeutic angiogenesis]

Critical limb ischemia is the end stage of peripheral arterial occlusive disease, with a deep impact in patient's quality of life. In some patients, there is no revascularizing treatment options, that determines major limb amputation in a high percentage of patients, not only for uncontrolled limb pain but also for complications of the trophic lesions. In the last years, several studies have shown the possibility to increase the perfusion in the ischemic tissue, by recombinant proteins, gene therapy or cellular therapy, all of them known as therapeutic angiogenesis. Several good results have been published but the way of treatment, doses and possible adverse effects still lack definitive conclusions. Randomized comparative studies should be carried out to determine the best treatment option.

Endothelial progenitor cells and their potential therapeutic applications

Endothelial progenitor cells (EPCs) are derived from the bone marrow (BM) and peripheral blood (PB), contributing to tissue repair in various pathological conditions via the formation of new blood vessels, that is, neovascularization. EPCs can be mobilized into the circulation in response to growth factors and cytokines released following stimuli such as vascular trauma, wounding and cancer. EPCs are involved in vasculogenesis during embryogenesis, but are now recognized to have a significant bearing upon disease outcome through their contribution to neovascularization in a variety of pathological states in adulthood. EPCs exist in very small numbers, especially in circulating blood in adults where they only account for 0.01% of all cells. We discuss the contribution and potential therapeutic applications of EPCs in disease, also noting the prognostic value of PB EPC numbers, especially in heart disease and cancer.

GM-CSF accelerates proliferation of endothelial progenitor cells from murine bone marrow mononuclear cells in vitro

OBJECTIVE

To test whether the GM-CSF accelerates the proliferation of bone marrow endothelial progenitor cells (BM EPCs).

METHODS

BM EPCs were induced by endothelial cell conditioned medium (EC-CM). The effect of different concentrations of GM-CSF on the proliferation of BM EPCs was evaluated by the formation of EC-cols, MTT assay, and cell cycle assay. The single progenitor cell growth curves were quantified.

RESULTS

The data indicated that GM-CSF accelerated the proliferation of BM EPCs both in colony numbers and colony size. MTT confirmed the effect of GM-CSF on accelerating the proliferation of BM EPCs. The single colony experiments showed that EC-cols expressed different proliferation capacity, suggesting that the EC-cols with different proliferation potentials might have been derived from different levels of immature progenitors. The cell cycle assay showed that the rate of cells entering into S phase was 9.3% in the group treated with GM-CSF and 2.1% in the controls. Furthermore, these cells displayed the specific endothelial cell markers and formed capillary-like structures.

CONCLUSIONS

GM-CSF accelerates proliferation of BM EPCs. The potential beneficial of GM-CSF in the application of treating vascular ischemic patients is promising.

Prostate-specific membrane antigen expression in regeneration and repair

Prostate-specific membrane antigen is a type II transmembrane glycoprotein, expressed in benign and neoplastic prostatic tissue as well as endothelial cells of neovasculature from a variety of tumors. The expression of prostate-specific membrane antigen in nonneoplastic neovasculature has not been well studied. Therefore, we studied nonneoplastic reparative and regenerative human tissues, as well as preneoplastic tissue, to determine the presence of prostate-specific membrane antigen-expressing neovasculature. Formalin-fixed paraffin-embedded tissue from keloids, granulation tissue from heart valves and pleura, proliferative and secretory endometrium, and Barrett's mucosa with and without dysplasia were stained for the expression of prostate-specific membrane antigen (3E6). Vessels of proliferative, mid-secretory, and late secretory endometrium were consistently strongly positive for prostate-specific membrane antigen expression in all ten cases of each type (100%). Vessels associated with granulation tissue from pleural peels and heart valves were positive in 10 of 12 cases (83%) and 7 of 10 cases (70%), respectively. Keloids had prostate-specific membrane antigen-expressing endothelial cells in 6 of 15 cases (40%). Prostate-specific membrane antigen was not expressed by vessels associated with Barrett's mucosa with low-grade dysplasia (12 foci), high-grade dysplasia (24 foci), or no dysplasia (18 foci). A variety of nonneoplastic neovasculature expresses prostate-specific membrane antigen, including vessels in proliferative endometrium, granulation tissue, and some scars. This is the first study showing that prostate-specific membrane antigen is expressed in neovasculature from physiologic regenerative and reparative conditions. The folate hydrolase activity of prostate-specific membrane antigen may facilitate vasculogenesis and angiogenesis by increasing local availability of folic acid. These findings will enhance our overall understanding of blood vessel development and will enable us to better understand the effects of anti-prostate-specific membrane antigen therapies, which are already being explored in clinical trials.

A polysaccharide isolated from the brown seaweed Sargassum stenophyllum exerts antivasculogenic effects evidenced by modified morphogenesis

A polysaccharide (Sarg) extracted from the brown marine alga Sargassum stenophyllum was studied for its antivasculogenic effects in both in vivo and in vitro assays, as well as for its capacity to modify embryonic morphogenetic processes endogenously regulated by bFGF, a well-known angiogenic stimulator. The antivasculogenic activity of Sarg (6-1500 microg/implant) was evaluated in a chick yolk sac membrane assay and the embryonic morphogenesis was measured as the percentage cephalic length. Sarg alone (96-1500 microg/implant) and co-administered with hydrocortisone (HC; 156 microg/implant) decreased the vitelline vessel number by 23-100% and 54-100% respectively. The polysaccharide potentiated the antivasculogenic effect of HC (42% inhibition). Basic fibroblast growth factor-stimulated vasculogenesis (141% of vessels as compared to control) was partially reversed by Sarg. The treatment with Sarg also decreased the percentage cephalic length of 3.5- and 4-day chick embryos (as cultured in vivo and in vitro, respectively), uncoupled from any impairment in the body shape or embryotoxic effect. Due to polyanionic characteristics of Sarg, which are similar to those seen in the heparin molecule, we suggest that this polysaccharide should modulate the activity of heparin-binding vascular growth factors (such as bFGF, which also acts as a morphogen) mimetically interfering with heparan sulfate proteoglycans during microvessel formation.