Progenitor cells in vascular disease

Challenges and opportunities in the islet transplantation microenvironment: a comprehensive summary of inflammatory cytokine, immune cells, and vascular endothelial cells

It is now understood that islet transplantation serves as a β-cell replacement therapy for type 1 diabetes. Many factors impact the survival of transplanted islets, especially those related to the microenvironment. This review explored microenvironmental components, including vascular endothelial cells, inflammatory cytokines, and immune cells, and their profound effects on post-islet transplantation survival rates. Furthermore, it revealed therapeutic strategies aimed at targeting these elements. Current evidence suggests that vascular endothelial cells are pivotal in facilitating vascularization and nutrient supply and establishing a new microcirculation network for transplanted islets. Consequently, preserving the functionality of vascular endothelial cells emerges as a crucial strategy to enhance the survival of islet transplantation. Release of cytokines will lead to activation of immune cells and production and release of further cytokines. While immune cells hold undeniable significance in regulating immune responses, their activation can result in rejection reactions. Thus, establishing immunological tolerance within the recipient's body is essential for sustaining graft functionality. Indeed, future research endeavors should be directed toward developing precise strategies for modulating the microenvironment to achieve higher survival rates and more sustained transplantation outcomes. While acknowledging certain limitations inherent to this review, it provides valuable insights that can guide further exploration in the field of islet transplantation. In conclusion, the microenvironment plays a paramount role in islet transplantation. Importantly, we discuss novel perspectives that could lead to broader clinical applications and improved patient outcomes in islet transplantation.

Impaired LEF1 Activation Accelerates iPSC-Derived Keratinocytes Differentiation in Hutchinson-Gilford Progeria Syndrome

Hutchinson–Gilford progeria syndrome (HGPS) is a detrimental premature aging disease caused by a point mutation in the human LMNA gene. This mutation results in the abnormal accumulation of a truncated pre-lamin A protein called progerin. Among the drastically accelerated signs of aging in HGPS patients, severe skin phenotypes such as alopecia and sclerotic skins always develop with the disease progression. Here, we studied the HGPS molecular mechanisms focusing on early skin development by differentiating patient-derived induced pluripotent stem cells (iPSCs) to a keratinocyte lineage. Interestingly, HGPS iPSCs showed an accelerated commitment to the keratinocyte lineage than the normal control. To study potential signaling pathways that accelerated skin development in HGPS, we investigated the WNT pathway components during HGPS iPSCs-keratinocytes induction. Surprisingly, despite the unaffected β-catenin activity, the expression of a critical WNT transcription factor LEF1 was diminished from an early stage in HGPS iPSCs-keratinocytes differentiation. A chromatin immunoprecipitation (ChIP) experiment further revealed strong bindings of LEF1 to the early-stage epithelial developmental markers K8 and K18 and that the LEF1 silencing by siRNA down-regulates the K8/K18 transcription. During the iPSCs-keratinocytes differentiation, correction of HGPS mutation by Adenine base editing (ABE), while in a partial level, rescued the phenotypes for accelerated keratinocyte lineage-commitment. ABE also reduced the cell death in HGPS iPSCs-derived keratinocytes. These findings brought new insight into the molecular basis and therapeutic application for the skin abnormalities in HGPS.

Exposure to Fine Particulate Matter Air Pollution Alters mRNA and miRNA Expression in Bone Marrow-Derived Endothelial Progenitor Cells from Mice

Exposure to fine particulate matter (PM2.5) air pollution is associated with quantitative deficits of circulating endothelial progenitor cells (EPCs) in humans. Related exposures of mice to concentrated ambient PM2.5 (CAP) likewise reduces levels of circulating EPCs and induces defects in their proliferation and angiogenic potential as well. These changes in EPC number or function are predictive of larger cardiovascular dysfunction. To identify global, PM2.5-dependent mRNA and miRNA expression changes that may contribute to these defects, we performed a transcriptomic analysis of cells isolated from exposed mice. Compared with control samples, we identified 122 upregulated genes and 44 downregulated genes in EPCs derived from CAP-exposed animals. Functions most impacted by these gene expression changes included regulation of cell movement, cell and tissue development, and cellular assembly and organization. With respect to miRNA changes, we found that 55 were upregulated while 53 were downregulated in EPCs from CAP-exposed mice. The top functions impacted by these miRNA changes included cell movement, cell death and survival, cellular development, and cell growth and proliferation. A subset of these mRNA and miRNA changes were confirmed by qRT-PCR, including some reciprocal relationships. These results suggest that PM2.5-induced changes in gene expression may contribute to EPC dysfunction and that such changes may contribute to the adverse cardiovascular outcomes of air pollution exposure.

Vascular smooth muscle remodeling in health and disease

In blood vessels, vascular smooth muscle cells (VSMCs) generally exist in two major phenotypes: contractile and non-contractile (synthetic). The contractile phenotype is predominant and includes quiescent or differentiated VSMCs, which function as the regulators of blood vessel diameter and blood flow. According to some literature in the field, contractile VSMCs do not switch to the non-contractile phenotype due to the activation of specific transcription factors that are considered as guardians of the contractile phenotype. However, a vast amount of the literature uses the terms remodeling and phenotype switching of contractile VSMCs interchangeably based mainly on studies dealing with atherosclerosis. The use of the terms remodeling and switching to describe changes in phenotype based on morphological criteria can be confusing. The term remodeling was first used to describe morphological changes in the heart and was soon used to describe phenotype changes of contractile VSMCs based on morphological criteria. The latter were introduced in early studies, and new molecular criteria were later added, including changes in gene expression, which could be irreversible. In this review, we will discuss the different views concerning remodeling and possible switching of contractile VSMCs to a non-contractile phenotype. We conclude that only remodeling of contractile VSMCs may take place upon vascular injury and disease.

Mediterranean Diet and Endothelial Function: A Review of its Effects at Different Vascular Bed Levels

The Mediterranean diet has recently been the focus of considerable attention as a palatable model of a healthy diet. Its influence on many cardiovascular risk factors, combined with its proven effect in reducing the risk of cardiovascular events in primary prevention, has boosted scientific interest in this age-old nutritional model. Many of the underlying mechanisms behind its health-giving effects have been revealed, from the modulation of the microbiota to the function of high-density lipoproteins (HDL), and it seems to deliver its health benefits mainly by regulating several key mechanisms of atherosclerosis. In this review, we will review the evidence for its regulation of endothelial function, a key element in the early and late stages of atherosclerosis. In addition, we will assess studies which evaluate its effects on the functioning of different arterial territory vessels (mainly the microvascular, peripheral and central vascular beds), focusing mainly on the capillary, brachial and carotid arteries. Finally, we will evaluate the molecular mechanisms which may be involved.

Endothelial Progenitor Cells as a Marker of Vascular Damage But not a Predictor in Acute Microangiopathy-Associated Stroke

Background: The aim of the study was to assess the number of endothelial progenitor cells (EPCs) in patients with acute stroke due to cerebral microangiopathy and evaluate whether there is a relationship between their number and clinical status, radiological findings, risk factors, selected biochemical parameters, and prognosis, both in ischemic and hemorrhagic stroke. Methods: In total, 66 patients with lacunar ischemic stroke, 38 patients with typical location hemorrhagic stroke, and 22 subjects from the control group without acute cerebrovascular incidents were included in the prospective observational study. The number of EPCs was determined in serum on the first and eighth day after stroke onset using flow cytometry and identified with the immune-phenotype classification determinant (CD)45−, CD34+, CD133+. Results: We demonstrated a significantly higher number of EPCs on the first day of stroke compared to the control group (med. 17.75 cells/µL (0–488 cells/µL) vs. 5.24 cells/µL (0–95 cells/µL); p = 0.0006). We did not find a relationship between the number of EPCs in the acute phase of stroke and the biochemical parameters, vascular risk factors, or clinical condition. In females, the higher number of EPCs on the first day of stroke is related to a favorable functional outcome on the eighth day after the stroke onset compared to males (p = 0.0355). We found that a higher volume of the hemorrhagic focus on the first day was correlated with a lower number of EPCs on the first day (correlation coefficient (R) = −0.3378, p = 0.0471), and a higher number of EPCs on the first day of the hemorrhagic stroke was correlated with a lower degree of regression of the hemorrhagic focus (R = −0.3896, p = 0.0367). Conclusion: The study showed that endothelial progenitor cells are an early marker in acute microangiopathy-associated stroke regardless of etiology and may affect the radiological findings in hemorrhagic stroke. Nevertheless, their prognostic value remains doubtful in stroke patients.

Development of a Coaxial 3D Printing Platform for Biofabrication of Implantable Islet-Containing Constructs

Over the last two decades, pancreatic islet transplantations have become a promising treatment for Type I diabetes. However, although providing a consistent and sustained exogenous insulin supply, there are a number of limitations hindering the widespread application of this approach. These include the lack of sufficient vasculature and allogeneic immune attacks after transplantation, which both contribute to poor cell survival rates. Here, these issues are addressed using a biofabrication approach. An alginate/gelatin-based bioink formulation is optimized for islet and islet-related cell encapsulation and 3D printing. In addition, a custom-designed coaxial printer is developed for 3D printing of multicellular islet-containing constructs. In this work, the ability to fabricate 3D constructs with precise control over the distribution of multiple cell types is demonstrated. In addition, it is shown that the viability of pancreatic islets is well maintained after the 3D printing process. Taken together, these results represent the first step toward an improved vehicle for islet transplantation and a potential novel strategy to treat Type I diabetes.

Tryptase promotes breast cancer angiogenesis through PAR-2 mediated endothelial progenitor cell activation

Mast cells have been demonstrated to accumulate around and within solid tumors of numerous types, and express a number of pro-angiogenic compounds, including tryptase. They may serve an early role in angiogenesis within developing tumors. In the present study, the role and mechanism of tryptase in the activation of endothelial progenitor cells (EPCs) in breast cancer angiogenesis were evaluated. Human umbilical cord blood EPCs were isolated and cultured. MB-MDA-231 breast cancer cells were then pretreated with tryptase, and the conditioned medium was collected. The effects of tryptase on the migratory and angiogenesis abilities of EPCs were determined using wound-healing and tube formation assays, respectively. The effect of tryptase on the proliferation of EPCs was detected using a Cell Counting Kit-8 assay. Alterations in proteinase activated receptor (PAR)-2, phosphorylated (p)-protein kinase B (AKT), p-extracellular signal-regulated kinase (p-ERK) and vascular endothelial growth factor receptor (VEGFR)-2 expression were analyzed, in tryptase or conditioned medium-treated EPCs, by western blot analysis and reverse transcription-quantitative polymerase chain reaction. It was confirmed that the EPCs expressed PAR-2; and that tryptase treatment promoted the migration and tube formation of EPCs. Treatment with a PAR-2 agonist had a similar effect to tryptase, whereas treatment with a tryptase inhibitor, APC366, or a PAR-2 inhibitor, SAM 11, inhibited the effect of tryptase treatment. Tryptase and PAR-2 agonists did not affect the rate of EPC proliferation. MB-MDA-231 cells also expressed PAR-2. Treatment with tryptase or conditioned medium increased the expression of PAR-2, p-AKT, p-ERK and VEGFR-2 in EPCs. In conclusion, tryptase activated EPCs via PAR-2-mediated AKT and ERK signaling pathway activation, thereby enhancing angiogenesis in breast cancer.

Mobilization of endothelial progenitor cell in patients with acute ischemic stroke

Endothelial progenitor cells (EPCs) have important effect in tissue repair in ischemic organs. The present study was conducted to demonstrate the mobilization of EPCs and its possible mechanism after acute ischemic stroke (AIS). A total of 148 individuals were examined, including 106 patients with ischemic stroke and 42 healthy controls. Seventy-one patients with imaging-confirmed AIS were examined at days 1, 7, 14, and 21 after stroke onset. Circulating EPCs were quantified by flow cytometry using CD133 and KDR surface markers. Serum stromal cell-derived factor-1 (SDF-1) concentrations were determined by enzyme-linked immunosorbent assay. Patients with AIS had significantly lower EPC level than that in the controls (0.022 ± 0.013 vs 0.051 ± 0.020; p < 0.01). This difference did not remain significant after adjusting for risk factors at multivariate analysis. Blood pressure, triglyceride, low-density lipoprotein (LDL), and fasting blood sugar were inversely correlated with EPC levels (p < 0.01). Systolic blood pressure and LDL remained independent predictors of baseline EPC levels. The number of circulating EPCs increased on day 7 after AIS, reached a peak on day 14, and decreased on day 21. The concentration of SDF-1 had similar changes. The increment of EPCs was correlated with the infarct volume (r = 0.708; p = 0.006) and SDF-1 concentration on day 14 (r = 0.714; p < 0.001). Baseline EPC level in patients with AIS reflects the cumulative vascular endothelial damage. EPCs could be mobilized into peripheral circulation in response to stroke stress. This mobilization was associated with the increased expression of SDF-1.

Kinetics of circulating endothelial progenitor cells in patients undergoing carotid artery surgery

Aim

Endothelial progenitor cells (EPCs) are primitive cells found in the bone marrow and peripheral blood (PB). In particular, the potential of EPCs to differentiate into mature endothelial cells remains of high interest for clinical applications such as bio-functionalized patches for autologous seeding after implantation. The objective of this study was to determine EPCs’ kinetics in patients undergoing carotid artery thromboendarterectomy (CTEA) and patch angioplasty.

Methods

Twenty CTEA patients were included (15 male, mean age 76 years). PB samples were taken at 1 day preoperatively, and at 1, 3, and 5 days postoperatively. Flow cytometric analysis was performed for CD34, CD133, KDR, and CD45. Expression of KDR, SDF-1α, and G-CSF was analyzed by means of enzyme-linked immunosorbent assay.

Results

Fluorescence-activated cell sorting analysis revealed 0.031%±0.016% (% of PB mononuclear cells) KDR+ cells and 0.052%±0.022% CD45−/CD34+/CD133+ cells, preoperatively. A 33% decrease of CD45−/CD34+/CD133+ cells was observed at day 1 after surgery. However, a relative number (compared to initial preoperative values) of CD45−/CD34+/CD133+ cells was found on day 3 (82%) and on day 5 (94%) postoperatively. More profound upregulated levels of CD45−CD34+/CD133+ cells were observed for diabetic (+47% compared to nondiabetic) and male (+38% compared to female) patients. No significant postoperative time-dependent differences were found in numbers of KDR+ cells and the concentrations of the cytokines KDR and G-CSF. However, the SDF-1α levels decreased significantly on day 1 postoperatively but returned to preoperative levels by day 3.

Conclusion

CTEA results in short-term downregulation of circulating EPCs and SDF-1α levels. Rapid return to baseline levels might indicate participation of EPCs in repair mechanisms following vascular injury.

Endothelial progenitor cells as a biological marker of peripheral artery disease

The role of endothelial progenitor cells (EPCs) in peripheral artery disease (PAD) remains unclear. We hypothesized that EPC mobilization and function play a central role in the development of endothelial dysfunction and directly influence the degree of atherosclerotic burden in peripheral artery vessels. The number of circulating EPCs, defined as CD34(+)/KDR(+) cells, were assessed by flow cytometry in 91 subjects classified according to a predefined sample size of 31 non-diabetic PAD patients, 30 diabetic PAD patients, and 30 healthy volunteers. Both PAD groups had undergone endovascular treatment in the past. As a functional parameter, EPC colony-forming units were determined ex vivo. Apart from a broad laboratory analysis, a series of clinical measures using the ankle-brachial index (ABI), flow-mediated dilatation (FMD) and carotid intima-media thickness (cIMT) were investigated. A significant reduction of EPC counts and proliferation indices in both PAD groups compared to healthy subjects were observed. Low EPC number and pathological findings in the clinical assessment were strongly correlated to the group allocation. Multivariate statistical analysis revealed these findings to be independent predictors of disease appearance. Linear regression analysis showed the ABI to be a predictor of circulating EPC number (p=0.02). Moreover, the functionality of EPCs was correlated by linear regression (p=0.017) to cIMT. The influence of diabetes mellitus on EPCs in our study has to be considered marginal in already disease-affected patients. This study demonstrated that EPCs could predict the prevalence and severity of symptomatic PAD, with ABI as the determinant of the state of EPC populations in disease-affected groups.

Loss of endothelial-ARNT in adult mice contributes to dampened circulating proangiogenic cells and delayed wound healing

The recruitment and homing of circulating bone marrow-derived cells include endothelial progenitor cells (EPCs) that are critical to neovascularization and tissue regeneration of various vascular pathologies. We report here that conditional inactivation of hypoxia-inducible factor's (HIF) transcriptional activity in the endothelium of adult mice (Arnt(ΔiEC) mice) results in a disturbance of infiltrating cells, a hallmark of neoangiogenesis, during the early phases of wound healing. Cutaneous biopsy punches show distinct migration of CD31(+) cells into wounds of control mice by 36 hours. However, a significant decline in numbers of infiltrating cells with immature vascular markers, as well as decreased transcript levels of genes associated with their expression and recruitment, were identified in wounds of Arnt(ΔiEC) mice. Matrigel plug assays further confirmed neoangiogenic deficiencies alongside a reduction in numbers of proangiogenic progenitor cells from bone marrow and peripheral blood samples of recombinant vascular endothelial growth factor-treated Arnt(ΔiEC) mice. In addition to HIF's autocrine requirements in endothelial cells, our data implicate that extrinsic microenvironmental cues provided by endothelial HIF are pivotal for early migration of proangiogenic cells, including those involved in wound healing.

N-Acetylcysteine Ameliorates Experimental Autoimmune Myocarditis in Rats via Nitric Oxide

BACKGROUND

Oxidative stress may play an important role in the development of myocarditis. We investigated the effects of N-acetylcysteine (NAC), a potent antioxidant, on experimental autoimmune myocarditis (EAM) in rats.

METHODS AND RESULTS

A rat model of porcine myosin-induced EAM was used. After the immunization with myosin, NAC (20 mg/kg/d) or saline was injected intraperitoneally on days 1 to 21. Additional myosin-immunized rats treated with NAC were orally given 25 mg/kg/d of N(G)-nitro-l-arginine methylester (l-NAME), an inhibitor of nitric oxide (NO) synthase, and N(G)-nitro-d-arginine methylester (d-NAME), an inactive enantiomer. The NAC treatment improved cardiac pathology associated with reduced superoxide production. In the EAM rats treated with NAC associated with oral l-NAME, but not with oral d-NAME, the severity of myocarditis was not reduced. Expression of intercellular adhesion molecule 1 was reduced by NAC treatment. Myocardial c-kit(+) cells were demonstrated only in the NAC-treated group. Hemodynamic study showed that the increased left ventricular mass produced by myocardial inflammation tended to be reduced by NAC treatment.

CONCLUSION

Treatment with NAC ameliorated myocardial injury via NO system in a rat model of myocarditis.

Scaffolds for tissue engineering of cardiac valves

Tissue engineered heart valves offer a promising alternative for the replacement of diseased heart valves avoiding the limitations faced with currently available bioprosthetic and mechanical heart valves. In the paradigm of tissue engineering, a three-dimensional platform - the so-called scaffold - is essential for cell proliferation, growth and differentiation, as well as the ultimate generation of a functional tissue. A foundation for success in heart valve tissue engineering is a recapitulation of the complex design and diverse mechanical properties of a native valve. This article reviews technological details of the scaffolds that have been applied to date in heart valve tissue engineering research.

Regulation of smooth muscle cells in development and vascular disease: current therapeutic strategies

Vascular smooth muscle cells (SMCs) exhibit extensive phenotypic diversity and rapid growth during embryonic development, but maintain a quiescent, differentiated state in adult. The pathogenesis of vascular proliferative diseases involves the proliferation and migration of medial vascular SMCs into the vessel intima, possibly reinstating their embryonic gene expression programs. Multiple mitogenic stimuli induce vascular SMC proliferation through cell cycle progression. Therapeutic strategies targeting cell cycle progression and mitogenic stimuli have been developed and evaluated in animal models of atherosclerosis and vascular injury, and several clinical studies. Recent discoveries on the recruitment of vascular progenitor cells to the sites of vascular injury suggest new therapeutic potentials of progenitor cell-based therapies to accelerate re-endothelialization and prevent engraftment of SMC-lineage progenitor cells. Owing to the complex and multifactorial nature of SMC regulation, combinatorial antiproliferative approaches are likely to be used in the future in order to achieve maximal efficacy and reduce toxicity.

The β-cell/EC axis: how do islet cells talk to each other?

Within the pancreatic islet, the β-cell represents the ultimate biosensor. Its central function is to accurately sense glucose levels in the blood and consequently release appropriate amounts of insulin. As the only cell type capable of insulin production, the β-cell must balance this crucial workload with self-preservation and, when required, regeneration. Evidence suggests that the β-cell has an important ally in intraislet endothelial cells (ECs). As well as providing a conduit for delivery of the primary input stimulus (glucose) and dissemination of its most important effector (insulin), intraislet blood vessels deliver oxygen to these dense clusters of metabolically active cells. Furthermore, it appears that ECs directly impact insulin gene expression and secretion and β-cell survival. This review discusses the molecules and pathways involved in the crosstalk between β-cells and intraislet ECs. The evidence supporting the intraislet EC as an important partner for β-cell function is examined to highlight the relevance of this axis in the context of type 1 and type 2 diabetes. Recent work that has established the potential of ECs or their progenitors to enhance the re-establishment of glycemic control following pancreatic islet transplantation in animal models is discussed.

Endothelial progenitor cells enhance islet engraftment, influence β-cell function, and modulate islet connexin 36 expression

The success of pancreatic islet transplantation is limited by delayed engraftment and suboptimal function in the longer term. Endothelial progenitor cells (EPCs) represent a potential cellular therapy that may improve the engraftment of transplanted pancreatic islets. In addition, EPCs may directly affect the function of pancreatic β-cells. The objective of this study was to examine the ability of EPCs to enhance pancreatic islet transplantation in a murine syngeneic marginal mass transplant model and to examine the mechanisms through which this occurs. We found that cotransplanted EPCs improved the cure rate and initial glycemic control of transplanted islets. Gene expression data indicate that EPCs, or their soluble products, modulate the expression of the β-cell surface molecule connexin 36 and affect glucose-stimulated insulin release in vitro. In conclusion, EPCs are a promising candidate for improving outcomes in islet transplantation, and their mechanisms of action warrant further study.

Alternative conduits for microvascular anastomoses

Thrombotic events in vascular substitutes are the main cause of obliteration of most microvascular prostheses and subsequent failure of microvascular anastomoses. The development of new biomaterials for vascular replacement aims to obtain an ideal graft for microvascular surgery. Completely bioresorbable vascular prostheses with the capacity to induce regeneration and growth of a new vascular segment seem to overcome the limitations of contemporary artificial prostheses, mostly made of artificial materials and lacking the capacity to grow and be remodeled. Autologous vessels are currently the most used material for small-diameter arterial replacement. Immune acceptance is a major advantage offered by this technique, but the time required is a limitation in emergency surgery. The need for a prosthetic graft that would have the same properties as a small-diameter conduit has led investigators to pursue many avenues in vascular biology. This article details the development of microvascular synthetic prostheses, clarifying the current status and the future aims.

Microvascular repair: post-angiogenesis vascular dynamics

Vascular compromise and the accompanying perfusion deficits cause or complicate a large array of disease conditions and treatment failures. This has prompted the exploration of therapeutic strategies to repair or regenerate vasculatures, thereby establishing more competent microcirculatory beds. Growing evidence indicates that an increase in vessel numbers within a tissue does not necessarily promote an increase in tissue perfusion. Effective regeneration of a microcirculation entails the integration of new stable microvessel segments into the network via neovascularization. Beginning with angiogenesis, neovascularization entails an integrated series of vascular activities leading to the formation of a new mature microcirculation, and includes vascular guidance and inosculation, vessel maturation, pruning, AV specification, network patterning, structural adaptation, intussusception, and microvascular stabilization. While the generation of new vessel segments is necessary to expand a network, without the concomitant neovessel remodeling and adaptation processes intrinsic to microvascular network formation, these additional vessel segments give rise to a dysfunctional microcirculation. While many of the mechanisms regulating angiogenesis have been detailed, a thorough understanding of the mechanisms driving post-angiogenesis activities specific to neovascularization has yet to be fully realized, but is necessary to develop effective therapeutic strategies for repairing compromised microcirculations as a means to treat disease.

Cellular therapies for the treatment of non-union: the past, present and future

Non-union fracture is a pathological condition having some impairment of the cellular part of the repair: a reduction of MSC and of the osteoblastic activation. Non union is therefore a good indication for cell-based therapies using stem cells. We described the rational of this treatment and described the technique of autologous bone marrow concentrate implantation that was until now used. With the development of stem cell research and regenerative medicine, we believed that therapy based on cytotherapy has great potential. In this review, clinical applications of cytotherapy are summarized and analyzed. Current problems and future challenges are discussed.

Endothelial progenitor cells: current issues on characterization and challenging clinical applications

Since their discovery about a decade ago, endothelial precursor cells (EPC) have been subjected to intensive investigation. The vision to stimulate respectively suppress a key player of vasculogenesis opened a plethora of clinical applications. However, as research opened deeper insights into EPC biology, the enthusiasm of the pioneer era has been damped in favour of a more critical view. Recent research is focused on three major questions: The fact that the number of EPC in peripheral blood is exceedingly low has consistently raised suspicion whether these cells can plausibly have an impact on physiological or pathophysiological processes. Secondly, whereas the key role of EPC in tumourigenesis has been strongly emphasized by various groups in the past, recent publications are challenging this hypothesis. Thirdly, the lack of consensus on EPC-defining markers and standardized protocols for their detection have repeatedly led to difficulties concerning comparability between papers. In this current review, an overview on recent findings on EPC biology is given, their challenging clinical implications are discussed and the perplexity underlying the current controversial debate is illustrated.

Monocyte chemoattractant protein-1/CCR2 axis promotes vein graft neointimal hyperplasia through its signaling in graft-extrinsic cell populations

OBJECTIVE

To evaluate direct versus indirect monocyte chemoattractant protein (MCP)-1/CCR2 signaling and to identify the cellular producers and effectors for MCP-1 during neointimal hyperplasia (NIH) development in vein grafts.

METHODS AND RESULTS

Genomic analysis revealed an overrepresentation of 13 inflammatory pathways in wild-type vein grafts compared with CCR2 knockout vein grafts. Further investigation with various vein graft-host combinations of MCP-1- and CCR2-deficient mice was used to modify the genotype of cells both inside (graft-intrinsic group) and outside (graft-extrinsic group) the vein wall. CCR2 deficiency inhibited NIH only when present in cells extrinsic to the graft wall, and MCP-1 deficiency required its effectiveness in cells both intrinsic and extrinsic to the graft wall to suppress NIH. Deletion of either MCP-1 or CCR2 was equally effective in inhibiting NIH. CCR2 deficiency in the predominant neointimal cell population had no impact on NIH. Direct MCP-1 stimulation of primary neointimal smooth muscle cells had minimal influence on cell proliferation and matrix turnover, confirming an indirect mechanism of action.

CONCLUSIONS

MCP-1/CCR2 axis accelerates NIH via its signaling in graft-extrinsic cells, particularly circulating inflammatory cells, with cells both intrinsic and extrinsic to the graft wall being critical MCP-1 producers. These findings underscore the importance of systemic treatment for anti-MCP-1/CCR2 therapies.

In vitro labeling of endothelial progenitor cells isolated from peripheral blood with superparamagnetic iron oxide nanoparticles

The transplantation of endothelial progenitor cells (EPCs) provides a novel method for the treatment of human tumors or vascular diseases. Magnetic resonance imaging (MRI) has proven to be effective in tracking transplanted stem cells by labeling the cells with superparamagnetic iron oxide (SPIO) nanoparticles. The SPIO has been used to label and track the EPCs; however, the effect of SPIO upon EPCs remains unclear on a cellular level. In the present study, EPCs were labeled with home-synthesized SPIO nanoparticles in vitro and the biological characteristics of the labeled EPCs were evaluated. The EPCs were isolated from the peripheral blood of New Zealand rabbits and cultured in fibronectin-coated culture flasks. The EPCs were labeled with home-synthesized SPIO nanoparticles at a final iron concentration of 20 µg/ml. Labeled EPCs were confirmed with transmission electron microscopy and Prussian blue staining. The quantity of iron/cell was detected by atomic absorption spectrometry. The membranous antigens of EPCs were detected by cytofluorimetric analysis. Cell viability and proliferative capability between the labeled and unlabeled EPCs were compared. The rabbit EPCs were effectively labeled and the labeling efficiency was approximately 95%. The SPIO nanoparticles were localized in the endosomal vesicles of the EPCs, which were confirmed by transmission electron microscopy. No significant differences were found in cell viability and proliferative capability between labeled and unlabeled EPCs (P>0.05). In conclusion, rabbit peripheral blood EPCs were effectively labeled by home-synthesized SPIO nanoparticles, without influencing their main biological characteristics.

Biological characteristics of foam cell formation in smooth muscle cells derived from bone marrow stem cells

Bone marrow mesenchymal stem cells (BMSC) can differentiate into diverse cell types, including adipogenic, osteogenic, chondrogenic and myogenic lineages. There are lots of BMSC accumulated in atherosclerosis vessels and differentiate into VSMC. However, it is unclear whether VSMC originated from BMSC (BMSC-SMC) could remodel the vessel in new tunica intima or promote the pathogenesis of atherosclerosis. In this study, BMSC were differentiated into VSMC in response to the transforming growth factor β (TGF-β) and shown to express a number of VSMC markers, such as α-smooth muscle actin (α-SMA) and smooth muscle myosin heavy chain1 (SM-MHC1). BMSC-SMC became foam cells after treatment with 80 mg/L ox-LDL for 72 hours. Ox-LDL could upregulate scavenger receptor class A (SR-A) but downregulate the ATP-binding cassette transporter A1 (ABCA1) and caveolin-1 protein expression, suggesting that modulating relative protein activity contributes to smooth muscle foam cell formation in BMSC-SMC. Furthermore, we found that BMSC-SMC have some biological characteristics that are similar to VSMC, such as the ability of proliferation and secretion of extracellular matrix, but, at the same time, retain some biological characteristics of BMSC, such as a high level of migration. These results suggest that BMSC-SMC could be induced to foam cells and be involved in the development of atherosclerosis.

Calcitonin gene-related peptide released from endothelial progenitor cells inhibits the proliferation of rat vascular smooth muscle cells induced by angiotensin II

We have recently demonstrated that endothelial progenitor cells (EPCs) inhibit AngII-induced proliferation of vascular smooth muscle cells (VSMCs) by inactivating MAPKs and NF-κB signaling pathway and reducing expression of oncogene c-myc and c-fos. The inhibitory effect of EPCs on VSMCs is associated with paracrine mechanism. However, the potential mechanism of EPCs on the regulation of AngII-induced proliferation of VSMCs was unknown. Calcitonin gene-related peptide (CGRP) could inhibit AngII-induced proliferation and transformation of VSMCs. However, it has not been known whether CGRP released from EPCs is a potential regulator in regulation of AngII-induced proliferation of VSMCs. Early endothelial progenitor cell-conditioned medium(E-EPC-CM) was pre-incubated with functional blocking antibodies against CGRP for 1 h or VSMCs was preteated with CGRP(837)(CGRP receptor antagonist) for 1 h before VSMCs were pretreated with CM for 30 min. DNA synthesis ability, total protein levels, cell survival, signal transduction, and expressions of c-myc and c-fos of VSMCs induced by AngII (10(-6)mol/l) were detected to assess the role of CGRP in AngII-induced proliferation of VSMCs. E-EPC-CM could significantly inhibit AngII-induced DNA synthesis ability, total protein levels, cell survival, phosphorylation of ERK, JNK, p38, p65, and expressions of c-myc and c-fos compared with the control group(P < 0.05). However, Pretreatment with anti-CGRP antibody and CGRP(837) could significantly weaken the inhibitory effect of E-EPC-CM on proliferation of VSMCs induced by AngII (P < 0.05). EPCs exert anti-proliferative effects on VSMCs mediated by the release of CGRP.

Osteo-progenitors in vascular calcification: a circulating cell theory

Vascular calcification has been associated with the incidence of cardiovascular events and thus there has been interest in better understanding its pathogenesis. Early theories considered vascular calcification to be a passive process which occurred as a non-specific response to tissue injury or necrosis. More recent theories propose vascular calcification results from loss of molecular inhibitors or via an active cell mediated process. The origin of the cells responsible for vascular calcification is controversial and may vary in different sites and patients. Calcification has been reported as result of apoptosis or death of vascular smooth muscle cells for example. One novel source of cells controlling vascular calcification is from the bone marrow. A circulating immature bone marrow derived population has been identified and a small subset of this bone marrow population has been reported to possess bone forming properties in vitro and hence termed osteo-progenitors. This article reviews evidence supporting the contribution of these naive bone marrow derived circulating osteo-progenitor cells in vascular calcification.

Endothelial progenitor cells in sudden sensorineural hearing loss

CONCLUSIONS

Endothelial progenitor cells (EPCs) are a unique subtype of circulating cells with properties similar to those of embryonal angioblasts. They have the potential to proliferate and to differentiate into mature endothelial cells. EPCs are reduced in patients with vascular risk factors due to a decreased mobilization, an increased consumption at the site of damage or a reduced half-life. The results of this study confirm the existence of an endothelial dysfunction in patients with sudden sensorineural hearing loss (SSHL) and support the vascular involvement in the pathogenesis of the disease.

OBJECTIVE

The aim of this study was to evaluate the concentration of EPCs in patients affected by SSHL.

METHODS

Twenty-one patients affected by SSHL were evaluated. The number of EPCs was analyzed by flow cytometry analysis of peripheral blood CD34+KDR+CD133+ cells.

RESULTS

Circulating levels of EPCs were significantly lower in SSHL patients compared with controls. In particular, CD34+KDR+ cells and CD34+CD133+KDR+ cells were significantly reduced (p < 0.05).

Mediterranean diet reduces endothelial damage and improves the regenerative capacity of endothelium

BACKGROUND

Endothelial dysfunction is a fundamental step in the atherosclerotic disease process. Activation or injury of the endothelium leads to a variety of inflammatory disorders, including the release of microparticles. Endothelial progenitor cells may contribute to the maintenance of the endothelium by replacing injured mature endothelial cells.

OBJECTIVE

We studied the influence of dietary fat on the release of endothelial microparticles (EMPs) and endothelial progenitor cells (EPCs) in elderly subjects.

DESIGN

Twenty healthy, elderly subjects (10 men and 10 women) consumed 3 diets following a randomized crossover design, each for 4 wk: a saturated fatty acid diet; a low-fat, high-carbohydrate diet; and a Mediterranean diet (MedDiet) enriched in monounsaturated fatty acids. We investigated total microparticles, EMPs from activated endothelial cells (activated EMPs), EMPs from apoptotic endothelial cells (apoptotic EMPs), EPCs, oxidative stress variables, and ischemic reactive hyperemia (IRH).

RESULTS

The MedDiet led to lower total microparticle, activated EMP, and apoptotic EMP concentrations and higher EPC numbers than did the other diets (P < 0.001). We detected lower superoxide dismutase activity (P < 0.001), a higher plasma β-carotene concentration (P < 0.001), and lower urinary isoprostane and plasma nitrotyrosine concentrations after consumption of the MedDiet than after consumption of the other 2 diets (P < 0.05). Furthermore, the occurrence of IRH was higher after consumption of the MedDiet than after consumption of the other 2 diets (P < 0.05).

CONCLUSION

Consumption of the MedDiet induces a reduction in endothelial damage and dysfunction, which is associated with an improvement in the regenerative capacity of the endothelium, in comparison with 2 other diets.

In vivo serial MR imaging evaluates neointimal hyperplasia inhibited by intravenously transfused endothelial progenitor cells in carotid artery injured mice

PURPOSE

to study the feasibility of in vivo MR imaging in evaluation of endothelial progenitor cells (EPCs) on the progress of neointimal hyperplasia after carotid artery injury in mice.

METHODS

fifteen Kunming mice were injured in left carotid artery by removal of endothelium with a flexible wire 7 days after splenectomy. EPCs were collected by in vitro culture of spleen-derived mouse mononuclear cells (MNCs) in endothelial basal medium. After artery injury, the mice received EPCs (n= 6), phosphate buffered solution (PBS) (n= 6), and DiI-Ac-LDL labeled EPCs (n= 3) intravenously. In vivo serial MR imaging were performed at different time points after artery injury, and vessel-wall thickness and vessel-wall area at injury site were measured on MR imaging.

RESULTS

transfused Dil-Ac-LDL-labeled EPCs were found at the injury site by histopathological analyses. Vessel wall of injured artery was observed and quantitatively analyzed with MR imaging. Vessel-wall thickness was .487 ± .122 mm in the non-EPCs transfusion group and .294 ± .051 mm in the EPCs transfusion group 15 days after artery injury (P= .005). While vessel-wall area was .860 ± .182 mm(2) in the non-EPCs transfusion group and .468 ± .141 mm(2) in the EPCs transfusion group 15 days after artery injury (P= .002). Therefore, the neointimal hyperplasia of injured artery in the EPCs transfusion group was lesser than that in the non-EPCs transfusion group.

CONCLUSION

neointimal hyperplasia can be reduced by intravenous transfusion of EPCs and analyzed on in vivo MR imaging after vascular injury.

Vascular stem cells: a new concept in the pathogenesis of atherosclerosis and interventions for coronary heart disease

Vascular stem cells are undifferentiated, oligopotent progenitor cells that are capable of giving rise to mature, functional cells in the vascular wall. Several types of vascular progenitor cells have been identified and characterized from embryonic and adult tissues, including progenitors with the potential to differentiate into endothelial and smooth muscle cells. The progenitors for endothelial and smooth muscle cells reside in atherosclerotic or restenotic lesions and circulate in the bloodstream. These stem cells may malfunction under the influence of the risk factors for atherosclerosis, as well as by medical interventions. The biological activities of these stem cells contribute to the regeneration, repair and remodeling of arterial walls injured by atherosclerosis. Hypercholesterolemia, inflammation, mechanical stress and genetic defects may interact in regulating the vascular stem cell response to atherogenic stimulation. Stem cell production, potency, growth and differentiation may decline as people age. Clarifying the cellular and molecular pathways that govern stem cell growth, differentiation and apoptosis should help clinical scientists to understand the pathogenesis of atherosclerosis and to develop novel therapeutic strategies for coronary heart disease. Recent clinical trials demonstrate encouraging outcomes of stem cell therapies.

Magnetic labeling, imaging and manipulation of endothelial progenitor cells using iron oxide nanoparticles

Endothelial progenitor cells (EPCs), originating from bone marrow, play a significant role in the repair of ischemic tissue and injured blood vessels. They are also involved in tumor angiogenesis. The therapeutic potential of EPCs for regenerative medicine and cancer treatment calls for new methods for monitoring and controlling cell migration. This review focuses on promising magnetic methods based on the internalization of magnetic nanoparticles by EPCs. We first describe the cellular uptake of iron oxide nanoparticles depending on their surface properties. We thus review the use of MRI for the detection of labeled cells and for noninvasive follow-up of EPCs homing in sites of endothelium regeneration. Finally, we show that remotely applied magnetic forces may enable intracellular manipulation and may optimize cell-delivery strategies for localizing cell therapy to target sites.

Osteocalcin positive mononuclear cells are associated with the severity of aortic calcification

OBJECTIVE

To assess the association of circulating bone marrow-derived osteo-progenitors with vascular calcification in mouse models and patients with peripheral artery disease.

METHODS

We estimated the percentage of circulating mononuclear cells expressing osteocalcin in 2 mouse models of aortic calcification developed in osteoprotegerin-deficient mice (OPG(-/-)) using flow cytometry. Aortic calcification was assessed in mice principally by a bioassay of harvested aortas. In patients with peripheral artery disease osteocalcin-positive cells (estimated by flow cytometry) were related to aortic calcification volume assessed from computed tomography.

RESULTS

The amount of extractable aortic calcium was increased in both mouse models used in comparison to controls. The percentage of circulating mononuclear cells expressing osteocalcin was correlated to the amount of extractable aortic calcium in male (r=0.525, p=0.02) and female OPG(-/-) (r=0.564, p=0.02) mice and also in animals in which calcification was accelerated using calcitriol (r=0.64, p=0.01). Patients with more severe aortic calcification had a greater percentage of circulating OCN(+) MNCs (median 4.07%, IQR 3.76-4.39, n=12) than those with less severe aortic calcification (median 3.10%, IQR 2.32-3.60, n=11, p=0.05).

CONCLUSIONS

This study demonstrates that aortic calcification can be robustly quantified in 2 mouse models. In these models and patients with peripheral artery disease circulating osteocalcin positive mononuclear cells are associated with the severity of aortic calcification.

Expression profiles of nestin in vascular smooth muscle cells in vivo and in vitro

Nestin is an intermediate filament protein expressed in neural and mesenchymal stem cells. Here, we investigated the expression of nestin in vascular smooth muscle cells (VSMCs) in vivo and in vitro. In the developing arteries, medial VSMCs were found to express nestin; its expression was prominent in embryos but was down-regulated after birth (3-6 weeks) in a region-dependent manner; its expression was abolished in the adult. Thus, the expression of nestin is specific to developing VSMCs. In primary VMSC cultures, nestin expression was induced by serum, but was independent of cell-cycle progression. Signaling analyses revealed that the serum-induced nestin expression depended on the extracellular signal-regulated kinase (ERK) and protein kinase B (PKB)(Akt) pathways, via the platelet derived growth factor (PDGF) and epidermal growth factor (EGF) receptors. Nestin expression was closely related to the up-regulation and activation of Sp1 and Sp3. Among major serum growth factors and cytokines, PDGF-BB was the most potent inducer of nestin expression. Nestin was also up-regulated in arteries undergoing vascular remodeling following balloon injury. Its expression was particularly strong in the cells lining the lumen of the neointima, suggesting a possible correlation between nestin expression and the progression of vascular remodeling.

Age-dependent mobilization of circulating endothelial progenitor cells in infants and young children undergoing cardiac surgery with cardiopulmonary bypass

This study was designed to find the effects of age on circulating endothelial progenitor cells (EPCs) and their mobilization in infants and young children following surgical correction of congenital heart defects. In 60 consecutive infants and young children (1month to 3years old) undergoing repair of atrial/ventricular septal defect, the numbers of EPCs and plasma levels of IL-6, -8, -10, TNF-alpha, VEGF and G-CSF were determined preoperatively, at the end of cardiopulmonary bypass (CPB), as well as 6, 12, 24, 48, 72 and 96h following surgery. Preoperative EPCs were reduced with increased age, similar to changes in plasma VEGF and G-CSF levels. Rapid mobilizations of EPCs and plasma VEGF, G-CSF were induced by cardiac surgery with CPB in all infants and young children, and the increased volumes of EPCs, VEGF and G-CSF decreased with age decreasing. The increased volumes of IL-6, -8, -10 and TNF-alpha were similar in different age groups. However, mobilization of EPCs, plasma VEGF and G-CSF were limited in infants <6months old, which did not correlate with change in inflammatory IL activation. Preoperative EPCs and plasma levels of VEGF and G-CSF were reduced with increasing age in infants and young children. Although a significant increase in EPCs and release of cytochemokines were observed in infants undergoing CPB, the mobilization of EPCs of the infants <6months old are limited.

Validation of Endothelial Progenitor Cells in Human Umbilical Veins and the Isolated Endothelial Cells

To detect endothelial progenitor cells in human umbilical veins and isolated endothelial cells, the authors examined protein and mRNA expression levels of cell surface markers for endothelial progenitor cells in human umbilical veins before and after trypsin treatment and at different passages of the isolated endothelial cells. CD133(+) (2.14 +/- 0.57 per mm) and KDR(+) (35.74 +/- 8.28 per mm) cells were observed in the intima of umbilical veins. The amounts of CD133(+), KDR(+), CD34(+), and CD105(+) cells decreased in the intima after trypsin treatment, whereas the percent of CD133(+) and KDR(+)cells in the media did not change significantly. Moreover, similar protein and mRNA expression levels of CD133 and KDR were detected in the umbilical veins before and after trypsin treatment. In the isolated cells from umbilical veins, the percent of CD133(+) and CD34(+) cells in P1 was 3.43% +/- 3.85%, which was higher than those in P3 (0.17% +/- 0.21%, p = 0.005) and P6 (0.14% +/- 0.18%, p = .001). The mRNA expression levels of CD133 and CD105 were down-regulated in later passages compared to those in P1, whereas the expression level of KDR was up-regulated in late passages. Thus it is suggested that endothelial progenitor cells reside in the distinct zone (e.g., initma and media) of human umbilical veins, and retain the capacity of differentiation to endothelial cells in vitro.

Differentiation patterning of vascular smooth muscle cells (VSMC) in atherosclerosis

To investigate the involvement of transdifferentiation and dedifferentiation phenomena inside atherosclerotic plaques, we analyzed the differentiation status of vascular smooth muscle cells (VSMC) in vitro and in vivo. Forty normal autoptic and 20 atherosclerotic carotid endarterectomy specimens as well as 20 specimens of infrarenal and suprarenal aortae were analyzed for the expression of cytokeratins 7 and 18 and beta-catenin as markers (epithelial transdifferentiation) as well as CD31 and CD34 (embryonic dedifferentiation) by conventional and double fluorescence immunohistochemistry and reverse transcription polymerase chain reaction. Looking at these markers, additional cell culture experiments with human aortic (HA)-VSMC were done under stimulation with IL-1beta, IL-6, and TNF-alpha. Cytokeratins and beta-catenin were expressed significantly higher in atherosclerotic than in normal carotids primarily localized in VSMC of the shoulder/cap region of atherosclerotic lesions. Additionally, heterogeneous cellular coexpression of CD31 and/or CD34 was observed in subregions of progressive atherosclerotic lesions by VSMC. The expression of those differentiation markers by stimulated HA-VSMC showed a time and cytokine dependency in vitro. Our findings show that (1) VSMC of progressive atheromas have the ability of differentiation, (2) that transdifferentiation and dedifferentiation phenomena are topographically diverse localized in the subregions of advanced atherosclerotic lesions, and (3) are influenced by inflammatory cytokines like IL-1beta, IL-6, and TNF-alpha.

Polymorphonuclear blood leukocytes and restenosis after intracoronary implantation of drug-eluting stents

Peripheral blood contents of osteonectin-positive progenitor cells and polymorphonuclear granulocytes were examined by flow cytometry in 38 patients after myocardial revascularisation with drug-eluting stents. Repeat coronary angiography performed 6-12 months after stent implantation revealed in-stent restenosis in 15 patients and its absence in 23 patients. The plasma levels of osteonectin-positive progenitor cells, neutrophils, and basophils did not differ in patients with and without restenosis. Eosinophil blood levels in patients with and without restenosis were 262+/-68 and 124+/-67 cells/microL (mean+/-SD, p<0.001), respectively. Only one of 19 patients (5%) with eosinophil content lower than the distribution median for the entire group developed restenosis, whereas in the group with eosinophil contents higher than the median (n=19) restenosis occurred in 14 patients (74%, p<0.001). Our findings suggest that the frequency of restenoses after stenting is related to high peripheral blood eosinophil content.

Vascular progenitor cells and translational research: the role of endothelial and smooth muscle progenitor cells in endogenous arterial remodelling in the adult

There has been much recent research into the therapeutic use of stem and progenitor cells for various diseases. Alongside this, there has also been considerable interest in the normal roles that endogenous precursor cells may play in both physiological and pathological settings. In the present review, we focus on two types of progenitor cell which are of potential relevance to vascular homoeostasis, namely the EPC (endothelial progenitor cell) and the smooth muscle progenitor cell. We discuss evidence for their existence and sources in adults, and the various techniques currently used to identify these cells. We examine data obtained from studies using different methods of progenitor identification and relate these to each other, in order to provide a framework in which to interpret the literature in this area. We review evidence for the influence of these vascular progenitor cells upon vascular function and the development and progression of atherosclerosis.

Cell therapy of hip osteonecrosis with autologous bone marrow grafting

BACKGROUND

One of the reasons for bone remodeling leading to an insufficient creeping substitution after osteonecrosis in the femoral head may be the small number of progenitor cells in the proximal femur and the trochanteric region. Because of this lack of progenitor cells, treatment modalities should stimulate and guide bone remodeling to sufficient creeping substitution to preserve the integrity of the femoral head. Core decompression with bone graft is used frequently in the treatment of osteonecrosis of the femoral head. In the current series, grafting was done with autologous bone marrow obtained from the iliac crest of patients operated on for early stages of osteonecrosis of the hip before collapse with the hypothesis that before stage of subchondral collapse, increasing the number of progenitor cells in the proximal femur will stimulate bone remodeling and creeping substitution and thereby improve functional outcome.

MATERIALS AND METHODS

Between 1990 and 2000, 342 patients (534 hips) with avascular osteonecrosis at early stages (Stages I and II) were treated with core decompression and autologous bone marrow grafting obtained from the iliac crest of patients operated on for osteonecrosis of the hip. The percentage of hips affected by osteonecrosis in this series of 534 hips was 19% in patients taking corticosteroids, 28% in patients with excessive alcohol intake, and 31% in patients with sickle cell disease. The mean age of the patients at the time of decompression and autologous bone marrow grafting was 39 years (range: 16-61 years). The aspirated marrow was reduced in volume by concentration and injected into the femoral head after core decompression with a small trocar. To measure the number of progenitor cells transplanted, the fibroblast colony forming unit was used as an indicator of the stroma cell activity.

RESULTS

Patients were followed up from 8 to 18 years. The outcome was determined by the changes in the Harris hip score, progression in radiographic stages, change in volume determined by digitizing area of the necrosis on the different cuts obtained on MRI, and by the need for hip replacement. Total hip replacement was necessary in 94 hips (evolution to collapse) among the 534 hips operated before collapse (Stages I and II). Sixty-nine hips with stage I osteonecrosis of the femoral head at the time of surgery demonstrated total resolution of osteonecrosis based on preoperative and postoperative MRI studies; these hips did not show any changes on plain radiographs. Before treatment, these 69 osteonecrosis had only a marginal band like pattern as abnormal signal and a volume less than 20 cubic centimeters. The intralesional area had kept a normal signal as regards the signal of the femoral head outside the osteonecrosis area. For the 371 other hips without collapse at the most recent follow up (average 12 years), the mean preoperative volume of the osteonecrosis was 26 cm(3) (minimum 12, maximum 30 cm(3)). The mean volume of the abnormal signal measured on MRI at the most recent follow up (mean 12 years) was 12 cm(3). The abnormal signal persisting as a sequelae was seen on T1 images as an intralesional area of low intensity signal with a disappearance of the marginal band like pattern.

CONCLUSION

According to our experience, best indication for the procedure is symptomatic hips with osteonecrosis without collapse. In some patients who had Steinberg stage III osteonecrosis (subchondral lucency, no collapse) successful outcomes (no further surgery) has been obtained between 5 to 10 years. Therefore in selected patients, even more advanced disease can be considered for core decompression. Patients who had the greater number of progenitor cells transplanted in their hips had better outcomes.

Inhibited atherosclerotic plaque formation by local administration of magnetically labeled endothelial progenitor cells (EPCs) in a rabbit model

PURPOSE

To investigate whether atherosclerosis can be prevented by magnetically labeled endothelial progenitor cells (EPCs) in rabbits.

MATERIALS AND METHODS

EPCs derived from rabbit periphery blood were labeled with a superparamagnetic iron oxide (SPIO) agent Fe(2)O(3)-poly-L-lysine (Fe(2)O(3)-PLL). Rabbit atherosclerosis was induced by high-cholesterol-diet following balloon injury via catheterization of right common carotid artery (RCCA). Fe(2)O(3)-PLL labeled EPCs (2 x 10(6)) and media were allowed to interact with the RCCA for 25 min in EPC-treated rabbits (n=14) and control rabbits (n=7) animals respectively. MRI was performed with a 1.5T-magnet to measure RCCA signal intensity (SI) and caliber at week 1, 2, 3, 6, 12, and 15 with animals euthanized in groups for histopathology.

RESULTS

In EPC-treated rabbits, T(2)(*)-weighted MRI showed SI loss in RCCA at week 1 and 2 followed by normalization after week 3. MRI outcomes corresponded well to findings of Prussian blue staining. MRI at week 6, 12 and 15 showed little stenosis of RCCA in EPC-treated rabbits, but moderate to severe stenoses in control rabbits. Histology at week 15 revealed significantly thinner RCCA wall (277.62 microm vs. 382.95 microm, P=0.026), greater internal diameter (913.33 microm vs. 789.64 microm, P=0.037) and smaller plaque (398.60mm(2) vs. 597.70 mm(2), P=0.047) in EPC-treated rabbits relative to control rabbits.

CONCLUSION

Atherosclerosis at RCCA was inhibited by SPIO-labeled EPCs, which was depicted with a clinical MRI scanner over 2 weeks after cell administration, suggesting that EPCs may play a role in restoration of endothelial injury and prevention of atherosclerosis.

Thrombin bound to a fibrin clot confers angiogenic and haemostatic properties on endothelial progenitor cells

Recent data suggest that endothelial progenitor cells (EPCs) are involved in recanalizing venous thrombi. We examined the impact of a fibrin network, and particularly of adsorbed thrombin, on EPCs derived from cord blood CD34(+) cells. Fibrin networks generated in microplates by adding CaCl(2) to platelet-depleted plasma retained adsorbed thrombin at the average concentration of 4.2 nM per well. EPCs expressed high levels of endothelial cell protein C receptor and thrombomodulin, allowing the generation of activated protein C on the fibrin matrix in the presence of exogenous human protein C. The fibrin matrix induced significant EPC proliferation and, when placed in the lower chamber of a Boyden device, strongly enhanced EPC migration. These effects were partly inhibited by hirudin by 41% and 66%, respectively), which suggests that fibrin-adsorbed thrombin interacts with EPCs via the thrombin receptor PAR-1. Finally, spontaneous lysis of the fibrin network, studied by measuring D-dimer release into the supernatant, was inhibited by EPCs but not by control mononuclear cells. Such an effect was associated with a 10-fold increase in plasminogen activator inhibitor-1 (PAI-1) secretion by EPCs cultivated in fibrin matrix. Overall, our data show that EPCs, in addition to their angiogenic potential, have both anticoagulant and antifibrinolytic properties. Thrombin may modulate these properties and contribute to thrombus recanalization by EPCs.

Platelets modulate atherogenesis and progression of atherosclerotic plaques via interaction with progenitor and dendritic cells

Platelets not only play a role in the late complications of atherosclerosis, but are also essential in its initiation, interacting with endothelial cells and leukocytes. Platelet adhesion to injured or atherosclerotic vessels is critical for the initiation of atherosclerotic lesion formation in vivo. Increasing evidence has recently highlighted the role of progenitor cells in inflammation, atherogenesis, and atheroprogression. Recruitment of progenitor and dendritic cells to sites of vascular injury is poorly understood so far. Both human progenitor and dendritic cells significantly adhere to platelets, indicating that platelets adherent to collagen or to endothelial cells can serve as a bridging mechanism directing circulating progenitor and dendritic cells to sites of impaired vasculature. Moreover, platelets regulate differentiation of progenitor cells to endothelial cells or macrophages and foam cells and modulate essential functions of dendritic cells, including their activation, differentiation and apoptosis in vitro. This review describes recent findings on platelet interaction with progenitor cells or dendritic cells and discusses potential consequences of this interaction in atherosclerosis.