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

Rabbit Endothelial Progenitor Cells Derived From Peripheral Blood and Bone Marrow: An Ultrastructural Comparative Study

The present study was designed to compare the ultrastructure of early endothelial progenitor cells (EPCs) derived from rabbit peripheral blood (PB-EPCs) and bone marrow (BM-EPCs). After the cells had been isolated and cultivated up to passage 3, microphotographs obtained from transmission electron microscope were evaluated from qualitative and quantitative (unbiased stereological approaches) points of view. Our results revealed that both cell populations displayed almost identical ultrastructural characteristics represented by abundant cellular organelles dispersed in the cytoplasm. Moreover, the presence of very occasionally occurring mature endothelial-specific Weibel–Palade bodies (WPBs) confirmed their endothelial lineage origin. The more advanced stage of their differentiation was also demonstrated by the relatively low nucleus/cytoplasm (N/C) ratios (0.41 ± 0.19 in PB-EPCs; 0.37 ± 0.25 in BM-EPCs). Between PB-EPCs and BM-EPCs, no differences in proportions of cells occupied by nucleus (28.13 ± 8.97 versus 25.10 ± 11.48%), mitochondria (3.71 ± 1.33 versus 4.23 ± 1.00%), and lipid droplets (0.65 ± 1.01 versus 0.36 ± 0.40%), as well as in estimations of the organelles surface densities were found. The data provide the first quantitative evaluation of the organelles of interest in PB-EPCs and BM-EPCs, and they can serve as a research framework for understanding cellular function.

Ultrasound and Magnetic Responsive Drug Delivery Systems for Cardiovascular Application

With the increasing insight into molecular mechanisms of cardiovascular disease, a promising solution involves directly delivering genes, cells, and chemicals to the infarcted myocardium or impaired endothelium. However, the limited delivery efficiency after administration fails to reach the therapeutic dose and the adverse off-target effect even causes serious safety concerns. Controlled drug release via external stimuli seems to be a promising method to overcome the drawbacks of conventional drug delivery systems (DDSs). Microbubbles and magnetic nanoparticles responding to ultrasound and magnetic fields respectively have been developed as an important component of novel DDSs. In particular, several attempts have also been made for the design and fabrication of dual-responsive DDS. This review presents the recent advances in the ultrasound and magnetic fields responsive DDSs in cardiovascular application, followed by their current problems and future reformation.

Molecular Profiling and Gene Banking of Rabbit EPCs Derived from Two Biological Sources

Endothelial progenitor cells (EPCs) have been broadly studied for several years due to their outstanding regenerative potential. Moreover, these cells might be a valuable source of genetic information for the preservation of endangered animal species. However, a controversy regarding their characterization still exists. The aim of this study was to isolate and compare the rabbit peripheral blood- and bone marrow-derived EPCs with human umbilical vein endothelial cells (HUVECs) in terms of their phenotype and morphology that could be affected by the passage number or cryopreservation as well as to assess their possible neuro-differentiation potential. Briefly, cells were isolated and cultured under standard endothelial conditions until passage 3. The morphological changes during the culture were monitored and each passage was analyzed for the typical phenotype using flow cytometry, quantitative real–time polymerase chain reaction (qPCR) and novel digital droplet PCR (ddPCR), and compared to HUVECs. The neurogenic differentiation was induced using a commercial kit. Rabbit cells were also cryopreserved for at least 3 months and then analyzed after thawing. According to the obtained results, both rabbit EPCs exhibit a spindle-shaped morphology and high proliferation rate. The both cell lines possess same stable phenotype: CD14⁻CD29⁺CD31⁻CD34⁻CD44⁺CD45⁻CD49f⁺CD73⁺CD90⁺CD105⁺CD133⁻CD146⁻CD166⁺VE-cadherin⁺VEGFR-2⁺SSEA-4⁺MSCA-1⁻vWF⁺eNOS⁺AcLDL⁺ALDH⁺vimentin⁺desmin⁺α-SMA⁺, slightly different from HUVECs. Moreover, both induced rabbit EPCs exhibit neuron-like morphological changes and expression of neuronal markers ENO2 and MAP2. In addition, cryopreserved rabbit cells maintained high viability (>85%) and endothelial phenotype after thawing. In conclusion, our findings suggest that cells expanded from the rabbit peripheral blood and bone marrow are of the endothelial origin with a stable marker expression and interesting proliferation and differentiation capacity.

Treatment of atherosclerosis through transplantation of endothelial progenitor cells overexpressing dimethylarginine dimethylaminohydrolase (DDAH) in rabbits

BACKGROUND

Endothelial dysfunction is a key event in the development of vascular diseases, including atherosclerosis. Endothelial progenitor cells (EPCs) play an important role in vascular repair. Decreased dimethylarginine dimethylaminohydrolase (DDAH) activity is observed in several pathological conditions, and it is associated with an increased risk of vascular disease. We hypothesized that bone marrow-derived EPCs and combination therapy with DDAH2-EPCs could reduce plaque size and ameliorate endothelial dysfunction in an atherosclerosis rabbit model.

METHOD

Four groups of rabbits (n = 8 per group) were subjected to a hyperlipidemic diet for a month. After establishing the atherosclerosis model, rabbits received 4 × 10⁶ EPC, EPCs expressing DDAH2, through femoral vein injection, or saline (the control group with basic food and the untreated group). One month after transplantation, plaque thickness, endothelial function, oxidative stress, and inflammatory mRNAs, DDAH, and eNOS function were assessed.

RESULTS

DDAH2-EPCs transplantation (p < 0.05) and EPCs transplantation (p < 0.05) were both associated with a reduction in plaque size compared to the control saline injection. The antiproliferative and antiatherogenic effects of EPCs were further enhanced by the overexpression of DDAH2 (p < 0.05, DDAH2-EPCs vs. EPCs). Furthermore, DDAH2-EPCs transplantation significantly increased endothelium integrity compared to the EPCs transplantation.

CONCLUSION

Transplantation of EPCs overexpressing DDAH2 may enhance the repair of injured endothelium by reducing inflammation and restoring endothelial function. Therefore, pCMV6-mediated DDAH2 gene-transfected EPCs are a potentially valuable tool for the treatment of atherosclerosis.

MRI tracing of ultrasmall superparamagnetic iron oxide nanoparticle‑labeled endothelial progenitor cells for repairing atherosclerotic vessels in rabbits

Endothelial progenitor cells (EPCs) have been discovered to be relevant to the prognosis of cardiovascular diseases. Previous research has demonstrated that EPCs serve vital roles in the occurrence and development of atherosclerosis. Significant improvements have been made in MRI technology and in the experimental use of EPCs for therapeutic angiogenesis and vascular repair. Nevertheless, the migratory, adhesive, proliferative and angiogenic properties of EPCs remain unknown. The aims of the present study were to investigate the potential of using non-invasive monitoring with ultrasmall superparamagnetic iron oxide nanoparticle (USPION)-labeled endothelial progenitor cells (EPCs) after transplantation, and to assess the treatment outcomes in an atherosclerotic rabbit model. EPCs derived from rabbit peripheral blood samples were labeled with USPION-poly-l-lysine (USPION-PLL). The morphology, proliferation, adhesive ability and labeling efficiency of the EPCs were determined by optical and electron microscopy. Moreover, biological activity was assessed by flow cytometry. In addition, T2-weighted image fast spin-echo MRI was used to detect cell labeling. USPION content in the labeled EPCs was determined by Prussian blue staining and scanning electron microscopy. Rabbit atherosclerosis model was established using a high-fat diet. USPION-labeled EPCs were transplanted into rabbits, and in vivo MRI was performed 1 and 7 days after transplantation. It was found that EPCs cultured on Matrigel formed capillary-like structures, and expressed the surface markers CD133, CD31, CD34 and vascular endothelial growth factor receptor 2 (VEGFR2). The optimal USPION concentration was 32 µg/ml, as determined by adhesion and proliferation assays. It was identified that USPION-PLL nanoparticles were 10–20 nm in diameter. Histopathological analysis results indicated that 1 day after transplantation of the labeled EPCs, blue-stained granules were observed in the intima of vascular lesions in rabbit models after Prussian blue staining. Therefore, the present results suggest that USPION-labeled EPCs may play a role in repairing endothelial injury and preventing atherosclerosis in vivo.

Shear stress: An essential driver of endothelial progenitor cells

The blood flow through vessels produces a tangential, or shear, stress sensed by their innermost layer (i.e., endothelium) and representing a major hemodynamic force. In humans, endothelial repair and blood vessel formation are mainly performed by circulating endothelial progenitor cells (EPCs) characterized by a considerable expression of vascular endothelial growth factor receptor 2 (VEGFR2), CD34, and CD133, pronounced tube formation activity in vitro, and strong reendothelialization or neovascularization capacity in vivo. EPCs have been proposed as a promising agent to induce reendothelialization of injured arteries, neovascularization of ischemic tissues, and endothelialization or vascularization of bioartificial constructs. A number of preconditioning approaches have been suggested to improve the regenerative potential of EPCs, including the use of biophysical stimuli such as shear stress. However, in spite of well-defined influence of shear stress on mature endothelial cells (ECs), articles summarizing how it affects EPCs are lacking. Here we discuss the impact of shear stress on homing, paracrine effects, and differentiation of EPCs. Unidirectional laminar shear stress significantly promotes homing of circulating EPCs to endothelial injury sites, induces anti-thrombotic and anti-atherosclerotic phenotype of EPCs, increases their capability to form capillary-like tubes in vitro, and enhances differentiation of EPCs into mature ECs in a dose-dependent manner. These effects are mediated by VEGFR2, Tie2, Notch, and β1/3 integrin signaling and can be abrogated by means of complementary siRNA/shRNA or selective pharmacological inhibitors of the respective proteins. Although the testing of sheared EPCs for vascular tissue engineering or regenerative medicine applications is still an unaccomplished task, favorable effects of unidirectional laminar shear stress on EPCs suggest its usefulness for their preconditioning.

The Effect of Granulocyte Colony-Stimulating Factor on the Progression of Atherosclerosis in Animal Models: A Meta-Analysis

Background

Atherosclerosis is a common inflammatory disease. Stem cell and endothelial progenitor cell treatments can improve cardiac function after myocardial infarction. Granulocyte colony-stimulating factor (G-CSF) is a mobilisation agent, mobilising stem cells from the bone marrow to circulation in the blood. G-CSF may constitute a treatment of atherosclerosis. We have conducted meta-analysis to evaluate the current evidence for the effect of G-CSF on the progression of atherosclerosis in animal models and to provide reference for preclinical experiments and future human clinical trials of atherosclerosis treatment.

Methods

We searched several databases and conducted a meta-analysis across seven articles using a random-effect model. All statistical analyses were performed using Review Manager Version 5.2 and Stata 12.0.

Results

We found that G-CSF therapy was associated with reduced atherosclerotic lesion area (weighted mean difference (WMD): 7.29%; 95% confidence interval (CI): 2.06-12.52%; P = 0.006). No significant differences in total serum cholesterol (P = 0.54) and triglyceride levels (P = 0.95) were noted in G-CSF treatment groups compared with controls. Multivariable metaregression analysis revealed that the animal type (rabbit, P = 0.022) and frequency of G-CSF administration (>20, P = 0.007) impacted the atherosclerotic lesion area changes.

Conclusion

The meta-analysis suggested that G-CSF treatment might inhibit the progression of atherosclerosis in animal models.

Vascular aging: Molecular mechanisms and potential treatments for vascular rejuvenation

Aging is the main risk factor contributing to vascular dysfunction and the progression of vascular diseases. In this review, we discuss the causes and mechanisms of vascular aging at the tissue and cellular level. We focus on Endothelial Cell (EC) and Smooth Muscle Cell (SMC) aging due to their critical role in mediating the defective vascular phenotype. We elaborate on two categories that contribute to cellular dysfunction: cell extrinsic and intrinsic factors. Extrinsic factors reflect systemic or environmental changes which alter EC and SMC homeostasis compromising vascular function. Intrinsic factors induce EC and SMC transformation resulting in cellular senescence. Replenishing or rejuvenating the aged/dysfunctional vascular cells is critical to the effective repair of the vasculature. As such, this review also elaborates on recent findings which indicate that stem cell and gene therapies may restore the impaired vascular cell function, reverse vascular aging, and prolong lifespan.

Stem cell therapy for abrogating stroke-induced neuroinflammation and relevant secondary cell death mechanisms

Ischemic stroke is a leading cause of death worldwide. A key secondary cell death mechanism mediating neurological damage following the initial episode of ischemic stroke is the upregulation of endogenous neuroinflammatory processes to levels that destroy hypoxic tissue local to the area of insult, induce apoptosis, and initiate a feedback loop of inflammatory cascades that can expand the region of damage. Stem cell therapy has emerged as an experimental treatment for stroke, and accumulating evidence supports the therapeutic efficacy of stem cells to abrogate stroke-induced inflammation. In this review, we investigate clinically relevant stem cell types, such as hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), endothelial progenitor cells (EPCs), very small embryonic-like stem cells (VSELs), neural stem cells (NSCs), extraembryonic stem cells, adipose tissue-derived stem cells, breast milk-derived stem cells, menstrual blood-derived stem cells, dental tissue-derived stem cells, induced pluripotent stem cells (iPSCs), teratocarcinoma-derived Ntera2/D1 neuron-like cells (NT2N), c-mycER(TAM) modified NSCs (CTX0E03), and notch-transfected mesenchymal stromal cells (SB623), comparing their potential efficacy to sequester stroke-induced neuroinflammation and their feasibility as translational clinical cell sources. To this end, we highlight that MSCs, with a proven track record of safety and efficacy as a transplantable cell for hematologic diseases, stand as an attractive cell type that confers superior anti-inflammatory effects in stroke both in vitro and in vivo. That stem cells can mount a robust anti-inflammatory action against stroke complements the regenerative processes of cell replacement and neurotrophic factor secretion conventionally ascribed to cell-based therapy in neurological disorders.

Beneficial Effects of Reconstituted High-Density Lipoprotein (rHDL) on Circulating CD34+ Cells in Patients after an Acute Coronary Syndrome

Background

High-density lipoproteins (HDL) favorably affect endothelial progenitor cells (EPC). Circulating progenitor cell level and function are impaired in patients with acute coronary syndrome (ACS). This study investigates the short-term effects of reconstituted HDL (rHDL) on circulating progenitor cells in patients with ACS.

Methods and Findings

The study population consisted of 33 patients with recent ACS: 20 patients from the ERASE trial (randomized to receive 4 weekly intravenous infusions of CSL-111 40 mg/kg or placebo) and 13 additional patients recruited as controls using the same enrolment criteria. Blood was collected from 16 rHDL (CSL-111)-treated patients and 17 controls at baseline and at 6–7 weeks (i.e. 2–3 weeks after the fourth infusion of CSL-111 in ERASE). CD34⁺ and CD34⁺/kinase insert domain receptor (KDR⁺) progenitor cell counts were analyzed by flow cytometry. We found preserved CD34⁺ cell counts in CSL-111-treated subjects at follow-up (change of 1.6%), while the number of CD34⁺ cells was reduced (-32.9%) in controls (p = 0.017 between groups). The level of circulating SDF-1 (stromal cell-derived factor-1), a chemokine involved in progenitor cell recruitment, increased significantly (change of 21.5%) in controls, while it remained unchanged in CSL-111-treated patients (p = 0.031 between groups). In vitro exposure to CSL-111 of early EPC isolated from healthy volunteers significantly increased CD34⁺ cells, reduced early EPC apoptosis and enhanced their migration capacity towards SDF-1.

Conclusions

The relative increase in circulating CD34⁺ cells and the low SDF-1 levels observed following rHDL infusions in ACS patients point towards a role of rHDL in cardiovascular repair mechanisms.

Circulating angiogenic cell function is inhibited by cortisol in vitro and associated with psychological stress and cortisol in vivo

Psychological stress and glucocorticoids are associated with heightened cardiovascular disease risk. We investigated whether stress or cortisol would be associated with reduced circulating angiogenic cell (CAC) function, an index of impaired vascular repair. We hypothesized that minority-race individuals who experience threat in interracial interactions would exhibit reduced CAC function, and that this link might be explained by cortisol. To test this experimentally, we recruited 106 African American participants for a laboratory interracial interaction task, in which they received socially evaluative feedback from Caucasian confederates. On a separate day, a subset of 32 participants (mean age=26years, 47% female) enrolled in a separate biological substudy and provided blood samples for CAC isolation and salivary samples to quantify the morning peak in cortisol (the cortisol awakening response, CAR). CAC function was quantified using cell culture assays of migration to vascular endothelial growth factor (VEGF) and secretion of VEGF into the culture medium. Heightened threat in response to an interracial interaction and trait anxiety in vivo were both associated with poorer CAC migratory function in vitro. Further, threat and poorer sustained attention during the interracial interaction were associated with a higher CAR, which in turn, was related to lower CAC sensitivity to glucocorticoids. In vitro, higher doses of cortisol impaired CAC migratory function and VEGF protein secretion. The glucocorticoid receptor antagonist RU486 reversed this functional impairment. These data identify a novel, neuroendocrine pathway by which psychological stress may reduce CAC function, with potential implications for cardiovascular health.

Preclinical models of atherosclerosis. The future of Hybrid PET/MR technology for the early detection of vulnerable plaque

Cardiovascular diseases are the leading cause of death in developed countries. The aetiology is currently multifactorial, thus making them very difficult to prevent. Preclinical models of atherothrombotic diseases, including vulnerable plaque-associated complications, are now providing significant insights into pathologies like atherosclerosis, and in combination with the most recent advances in new non-invasive imaging technologies, they have become essential tools to evaluate new therapeutic strategies, with which can forecast and prevent plaque rupture. Positron emission tomography (PET)/computed tomography imaging is currently used for plaque visualisation in clinical and pre-clinical cardiovascular research, albeit with significant limitations. However, the combination of PET and magnetic resonance imaging (MRI) technologies is still the best option available today, as combined PET/MRI scans provide simultaneous data acquisition together with high quality anatomical information, sensitivity and lower radiation exposure for the patient. The coming years may represent a new era for the implementation of PET/MRI in clinical practice, but first, clinically efficient attenuation correction algorithms and research towards multimodal reagents and safety issues should be validated at the preclinical level.

Impact of lysophosphatidylcholine on survival and function of UEA-1(+)acLDL (+) endothelial progenitor cells in patients with coronary artery disease

Lysophosphatidylcholine (LPC) generated from oxidized low-density lipoprotein by lipoprotein-associated phospholipase A2 plays a key role in plaque inflammation and vulnerability. Endothelial progenitor cells (EPCs) can repair injured endothelium and exert anti-inflammatory effects of vulnerable plaque. We study the impact and mechanisms of LPC on UEA-1 and acLDL binding EPCs (UEA-1(+)acLDL(+) EPCs). UEA-1(+)acLDL(+) EPCs from coronary artery disease (CAD) patients were cultured and exposed to LPC at different concentrations and different timepoints. We determined the significant concentration (40 μM). UEA-1(+)acLDL(+) EPCs were preincubated for 30 min with pravastatin (20 μM) with LY249002, a specific inhibitor of the Akt signaling pathway, and exposed for 24 h to LPC 40 μM. The survival, migration, adhesion, and proliferation of UEA-1(+)acLDL(+) EPCs were assessed. To examine the mechanisms of LPC toxicity and pravastatin effects, phosphorylated Akt and endothelial nitric oxide synthase (eNOS) levels and the ratio of Bcl-2/Bax protein expression were assessed. LPC induced apoptosis and impaired migration and adhesion of UEA-1(+)acLDL(+) EPCs significantly. The detrimental effects of LPC were attenuated by pravastatin. However, when UEA-1(+)acLDL(+) EPCs were pretreated with pravastatin and LY249002, a specific inhibitor of the Akt signaling pathway, simultaneously, the beneficial effects of pravastatin were abolished. Furthermore, LPC suppressed Akt and eNOS phosphorylation and increased Bcl-2/Bax expression. The effects of LPC on Akt/eNOS and Bcl-2/Bax activity were reversed by pravastatin. In conclusion, LPC inhibited UEA-1(+)acLDL(+) EPCs survival and impaired its functions, and these were attributable to inhibition of the Akt/eNOS and Bcl-2/Bax pathway. Pravastatin reversed the detrimental action of LPC. These findings suggest that LPC inhibition can be a possible strategy for CAD through EPC revitalization.

Superparamagnetic iron oxide based nanoprobes for imaging and theranostics

The need to target, deliver and subsequently evaluate the efficacy of therapeutics in the treatment of a disease has provided added impetus in developing novel and highly efficient contrast agents. Superparamagnetic iron oxide nanoparticles (SPIONs) have offered tremendous potential in designing advanced magnetic resonance imaging (MRI) diagnostic agents, due to their unique physicochemical properties. There has been tremendous effort devoted in the recent past in developing synthetic methodologies through which their size, hydrodynamic radii, chemical composition and morphologies could be tailored at the nanoscale. This enables one to fine tune their magnetic behavior, and thus their MRI response. While novel synthetic strategies are being assembled for directing SPIONs to the diseased site as well as imparting them stealth and biocompatibility, it is also essential to evaluate their biological toxicological profiles. This review highlights recent advances that have been made in the synthesis of SPIONs, subsequent functionalization with desired entities, and a discussion on their use as MRI contrast agents in cardiovascular research.

Intracoronary infusion of mononuclear bone marrow-derived stem cells is associated with a lower plaque burden after four years

AIM

To assess the long-term effects of intracoronary stem cell (SC) infusion following acute myocardial infarction (AMI) on the local atherosclerotic process at the site of infusion after four years of follow-up.

METHODS

We evaluated 18 post-AMI patients. Group 1 consisted of nine patients given an intracoronary injection of autologous mononuclear SC, and group 2 consisted of nine patients given a placebo injection. The plaque count, plaque burden (PB) and coronary calcium score (CCS) were assessed using multislice 64 CT angiography of the coronary tree four years after SC injection.

RESULTS

The total PB and CCS along the entire coronary segment distal to the site of infusion were significantly lower in the SC group (PB-702 mm(3) vs. 1.465 mm(3), p=0.0006; CCS-295 vs. 796, p＜ 0.0001).The mean PB per coronary artery was 112.12 mm(3)±16.82 mm(3) for the treated arteries vs. 189.56 mm(3)±20.98 mm(3) for the untreated arteries (p＜0.0001), while the mean CCS was 53.12±16.4 vs. 106.43±10.86 (p＜0.0001). In the SC group, there were significant differences in the mean PB (87.75 mm(3) vs. 112.12 mm(2), p= 0.005) and mean CCS (36.87 vs. 53.12, p=0.04) between the coronary segment infused with SC and the entire coronary artery.

CONCLUSIONS

Multislice CT angiography of atheromatous plaques in the coronary tree four years after SC infusion in post-AMI patients indicates a significantly lower atheromatous plaque burden, as demonstrated by a lower plaque volume and lower CCS at the site of stem cell infusion compared with other coronary territories.

Silica-coated superparamagnetic iron oxide nanoparticles targeting of EPCs in ischemic brain injury

Intravenous transplantation of endothelial progenitor cells (EPCs) reduced ischemic brain injury. However, less cell homing to damaged sites limited its functions. In present study, we labeled EPCs with silica-coated superparamagnetic iron oxide nanoparticles (SiO4@SPIONs) and applied exterior magnetic field to guide SiO4@SPIONs-labeled EPCs (SiO4@SPIONs-EPCs) to the ischemic hemisphere of the brain. We optimized SiO4@SPIONs labeling dose, which did not affect proliferation, migration and tube formation of EPCs in vitro. SiO4@SPIONs-EPCs homing was greatly increased in ischemic hemisphere with magnetic field treatment in mice underwent transient middle cerebral artery occlusion (tMCAO). Injection of SiO4@SPIONs-EPCs and followed by magnetic field treatment showed improved neurobehavioral outcomes, reduced brain atrophic volume, increased microvessel density and VEGF expression in the ischemic perifocal region compared to groups without magnetic field treatment (p < 0.05). Our results demonstrated that exterior magnetic field could guide SiO4@SPIONs-EPCs to ischemic region and enhance therapeutic effect, suggesting that magnetic-guided SiO4@SPIONs-EPCs delivery is a promising approach in cerebral ischemic therapy.

Reduced number and impaired function of circulating endothelial progenitor cells in patients with abdominal aortic aneurysm

AIM

Circulating endothelial progenitor cells (EPCs) are associated with coronary artery disease (CAD) and predict its outcome. Although the pathophysiology of abdominal aortic aneurysm (AAA) is different, it shares some risk factors with CAD. Therefore, the correlation between EPCs and AAA was investigated.

METHODS AND RESULTS

Seventy-eight subjects (age 77.2 ± 7.8 years) with suspected AAA were prospectively enrolled. Cut-off values (men, 3.5-5.5 cm; women, 3-5 cm) were used to define normal aorta, small AAA, and large AAA on thoraco-abdominal computer tomography. Endothelial function was measured by flow-mediated vasodilation (FMD). Flow cytometry and colony-forming units (CFUs) were used to evaluate circulating EPC numbers. Circulating EPCs were defined as mononuclear cells with low CD45 staining and double-positive staining for KDR, CD34, or CD133. Late out-growth EPCs were cultured from six patients with large AAAs and six age- and sex-matched controls to evaluate proliferation, adhesion, migration, tube formation, and senescence. FMD was significantly lower with large (5.26% ± 3.11%) and small AAAs (6.31% ± 3.66%) than in controls (8.88% ± 4.83%, P=0.008). Both CFUs (normal 38.39 ± 12.99, small AAA 21.22 ± 7.14, large AAA 6.98 ± 1.97; P=0.026) and circulating EPCs (CD34(+)/KDR(+) and CD133(+)/KDR(+)) were significantly fewer in AAA patients than in controls. On multivariate analysis, CFUs and circulating EPCs (CD34(+)/KDR(+)) were independently, inversely correlated to AAA diameter. Proliferation, adhesion, migration, tube formation, and senescence of late EPCs were significantly impaired in AAA patients.

CONCLUSION

The number and function of EPCs were impaired in AAA patients, suggesting their potential role in AAA.

Long-term MRI tracking of dual-labeled adipose-derived stem cells homing into mouse carotid artery injury

Background

Stem cell therapy has shown great promise for regenerative repair of injured or diseased tissues. Adipose-derived stem cells (ADSCs) have become increasingly attractive candidates for cellular therapy. Magnetic resonance imaging has been proven to be effective in tracking magnetic-labeled cells and evaluating their clinical relevance after cell transplantation. This study investigated the feasibility of imaging green fluorescent protein-expressing ADSCs (GFP-ADSCs) labeled with superparamagnetic iron oxide particles, and tracked them in vivo with noninvasive magnetic resonance imaging after cell transplantation in a model of mouse carotid artery injury.

Methods

GFP-ADSCs were isolated from the adipose tissues of GFP mice and labeled with superparamagnetic iron oxide particles. Intracellular stability, proliferation, and viability of the labeled cells were evaluated in vitro. Next, the cells were transplanted into a mouse carotid artery injury model. Clinical 3 T magnetic resonance imaging was performed immediately before and 1, 3, 7, 14, 21, and 30 days after cell transplantation. Prussian blue staining and histological analysis were performed 7 and 30 days after transplantation.

Results

GFP-ADSCs were found to be efficiently labeled with superparamagnetic iron oxide particles, with no effect on viability and proliferation. Homing of the labeled cells into the injured carotid artery tissue could be monitored by magnetic resonance imaging.

Conclusion

Magnetically labeled ADSCs with expression of GFP can home into sites of vascular injury, and may provide new insights into understanding of cell-based therapy for cardiovascular lesions.

Effects of Iron Oxide Nanoparticle Labeling on Human Endothelial Cells

Iron oxide nanoparticles (INOPS) are a potential contrast agent for magnetic resonance (MR) tracking of transplanted endothelial cells. The objective of this study was to examine the effect of INOPS labeling on endothelial cells. The mixture of INOPS and poly-l-lysine (PLL) was used to label human endothelial cells. Labeling efficiency was examined by Prussian blue staining, transmission electron microscopy, and atomic absorption spectrometry. The effect of iron oxide concentration on cell viability and proliferation were determined. The correlation of reactive oxygen species (ROS) and apoptosis was also examined. In vitro MRI scanning was carried out using a 1.5T MR system. INOPS-PLL could be readily taken up by endothelial cells and subsequently induce MRI signal intensity changes. However, higher labeling concentration (>50 μg/ml) and longer incubation (48 h) can affect cell viability and proliferation. Mitochondrial damage, apoptosis, and autolysosmes were observed under high INOPS-PLL concentrations, which were correlated to ROS production. INOPS-PLL nanoparticles can be used to label transplanted endothelial cells. However, high concentration of INOPS can impair cell viability, possibly through ROS-mediated apoptosis and autophagy.

Five-year results of intracoronary infusion of the mobilized peripheral blood stem cells by granulocyte colony-stimulating factor in patients with myocardial infarction

AIM

To evaluate the long-term effects of peripheral blood stem cell therapy in myocardial infarction (MI) patients.

METHODS AND RESULTS

A total of 163 patients with MI who were successfully revascularized with drug-eluting stents were enrolled and randomly assigned to four groups: acute MI (AMI) cell infusion, AMI control, old MI (OMI) cell infusion, and OMI control. We compared 5 years' clinical outcomes between the cell infusion group (57 and 22 patients with AMI and OMI, respectively) and the control (60 and 24 patients with AMI and OMI, respectively). In the time-sequence comparison from baseline to 6 and 24 months follow-up after AMI, left ventricular ejection fraction (LVEF) by cardiac magnetic resonance imaging was significantly improved in the cell infusion group (n = 57), but not in the control group (n = 60). In the between-group comparison, the difference in improvement of LVEF for 2 years after AMI did not reach statistical significance between cell infusion and control groups. Intriguingly, the major adverse cardiac events for 5 years were significantly reduced in the cell infusion group (n = 79) compared with the control (n = 84; composite of cardiac death, non-fatal MI, hospitalization for heart failure and angina, and target vessel revascularization; 22.8 vs. 39.3%, P = 0.015).

CONCLUSIONS

Peripheral blood stem cell therapy has potential to improve long-term cardiovascular outcomes in MI patients.

Endothelial progenitor cells in atherosclerosis

Endothelial progenitor cells (EPCs) are involved in the maintenance of endothelial homoeostasis and in the process of new vessel formation. Experimental and clinical studies have shown that atherosclerosis is associated with reduced numbers and dysfunction of EPCs; and that medications alone are able to partially reverse the impairment of EPCs in patients with atherosclerosis. Therefore, novel EPC-based therapies may provide enhancement in restoring EPCs' population and improvement of vascular function. Here, for a better understanding of the molecular mechanisms underlying EPC impairment in atherosclerosis, we provide a comprehensive overview on EPC characteristics, phenotypes, and the signaling pathways underlying EPC impairment in atherosclerosis.

Superparamagnetic iron oxide (SPIO) labeling efficiency and subsequent MRI tracking of native cell populations pertinent to pulmonary heart valve tissue engineering studies

The intimal and medial linings of the pulmonary artery consist largely of vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs), respectively. The migration of these cell types to a potential tissue-engineered pulmonary valve (TEPV) implant process is therefore of interest in understanding the valve remodeling process. Visualization and cell tracking by MRI, which employs hypointense contrast achievable through the use of superparamagnetic iron oxide (SPIO) microparticles to label cells, provides a method in which this can be studied. We investigated the SPIO labeling efficiency of human VECs and VSMCs, and used two- and three-dimensional gradient echo sequences to track the migration of these cells in agar gel constructs. Protamine sulfate (4.5 µg/mL) was used to enhance SPIO uptake and was found to have no influence on cell viability or proliferation. MRI experiments were initially performed using a 9.4-T scanner. The results demonstrated that the spatial positions of hypointense spots were relatively unchanged over 12 days. Subsequent MR experiments performed at 7 T demonstrated that three-dimensional imaging provided the best spatial resolution to assess cell fate. R(2)* maps were bright in SPIO cell-encapsulated gels in comparison with unlabeled counterparts. Signal voids were ruled out as hypointense regions owing to the smooth exponential decay of T(2)* in these voxels. As a next step, we intend to use the SPIO cell labeling and MR protocols established in this study to assess whether hemodynamic stresses will alter the vascular cell migratory patterns. These studies will shed light on the mechanisms of vascular remodeling after TEPV implantation.

Development of molecular imaging and nanomedicine in China

The rapid progress of molecular imaging (MI) and the application of nanotechnology in medicine have the potential to advance the foundations of diagnosis, treatment, and prevention of diseases. Although MI and biomedical nanotechnology are still in a formative phase in China, much has been achieved over the last decade. This article provides a commentary on the development and current status of nanomedicine in China, with a selective focus on Chinese nanoparticle synthesis technology, the development of imaging equipment, and the preclinical application of novel MI probes.

An experimental study on MR imaging of atherosclerotic plaque with SPIO marked endothelial cells in a rabbit model

PURPOSE

To investigate how to label macrophages in atherosclerotic plaques with superparamagnetic iron oxide (SPIO) nanoparticles and trace SPIO with MR imaging.

MATERIALS AND METHODS

Atherosclerotic lesions of a rabbit model were induced by a combination of high-fat and high-cholesterol diet and subsequent endothelial abrasion of the abdominal aorta. SPIO particles were pretreated with poly-L-lysine. SPIO nanoparticles and SPIO-labeled human endothelial cells (ECV-304) were IV injected into model animals, respectively. The MRI scans and histopathological examination were performed 12 h and 24 h after the injection. The imaging and histopathological data were analyzed.

RESULTS

Prussian blue staining of the vessel specimens indicated that SPIO particles were not found in the atheroma but in the Kupffer's cells of the liver after SPIO injection. However, the accumulation of SPIO particles in the atheroma was confirmed in animals received SPIO-labeled endothelial cell transplantation. The best quality MR scan sequences of rabbit abdominal aorta were T(2) WI fat suppression, T(1) WI, and DIR series, on which of MR image had a higher quality. Signal loss of the original incrassate plaque in the vessel wall on T(2) WI was found in 6 of 10 animals received SPIO-labeled endothelial cell transplantation.

CONCLUSION

SPIO-labeled endothelial cells were superior to SPIO for MR imaging of atherosclerotic plaques.

In vivo serial MR imaging of magnetically labeled endothelial progenitor cells homing to the endothelium injured artery in mice

BACKGROUND

Emerging evidence of histopathological analyses suggests that endothelial progenitor cells (EPCs) play an important role in vascular diseases. Neointimal hyperplasia can be reduced by intravenous transfusion of EPCs after vascular injury in mice. Therefore, it would be advantageous to develop an in vivo technique that can explore the temporal and spatial migration of EPCs homing to the damaged endothelium noninvasively.

METHODOLOGY/PRINCIPAL FINDINGS

The left carotid common artery (LCCA) was injured by removal of endothelium with a flexible wire in Kunming mice. EPCs were collected by in vitro culture of spleen-derived mouse mononuclear cells (MNCs). EPCs labeling was carried out in vitro using Fe₂O₃-poly-L-lysine (Fe₂O₃-PLL). In vivo serial MR imaging was performed to follow-up the injured artery at different time points after intravenous transfusion of EPCs. Vessel wall areas of injured artery were computed on T₂WI. Larger MR signal voids of vessel wall on T₂WI was revealed in all 6 mice of the labeled EPC transfusion group 15 days after LCCA injury, and it was found only in 1 mouse in the unlabeled EPC transfusion group (p = 0.015). Quantitative analyses of vessel wall areas on T₂WI showed that the vessel wall areas of labeled EPC transfusion group were less than those of unlabeled EPC transfusion group and control group fifteen days after artery injury (p<0.05). Histopathological analyses confirmed accumulation and distribution of transfused EPCs at the injury site of LCCA.

CONCLUSIONS/SIGNIFICANCE

These data indicate that MR imaging might be used as an in vivo method for the tracking of EPCs homing to the endothelium injured artery.

Cell-based therapies for diabetic complications

In recent years, accumulating experimental evidence supports the notion that diabetic patients may greatly benefit from cell-based therapies, which include the use of adult stem and/or progenitor cells. In particular, mesenchymal stem cells and the circulating pool of endothelial progenitor cells have so far been the most studied populations of cells proposed for the treatment of vascular complications affecting diabetic patients. We review the evidence supporting their use in this setting, the therapeutic benefits that these cells have shown so far as well as the challenges that cell-based therapies in diabetic complications put out.

Efficient nano iron particle-labeling and noninvasive MR imaging of mouse bone marrow-derived endothelial progenitor cells

In this study, we sought to label mouse bone marrow-derived endothelial progenitor cells (EPCs) with Resovist^® in vitro and to image them using 7.0 Tesla (T) magnetic resonance imaging (MRI). Mouse bone marrow-derived EPCs were cultured in endothelial basal medium with endothelial growth supplement. They were then characterized by immunocytochemistry, flow cytometry, and fluorescence quantitative polymerase chain reaction. Their functions were evaluated by measuring their uptake of 1,1-dioctadecyl-3,3,3,3-tetramethylindocarbocyanine-labeled acetylated low-density lipoprotein (Dil-Ac-LDL), binding of fluorine isothiocyanate (FITC)-labeled Ulex europaeus agglutinin (UEA), and formation of capillary-like networks. EPCs were labeled with superparamagnetic iron oxide (SPIO) and their proliferation was then assessed in a water-soluble tetrazolium (WST-8)-based cell proliferation assay. Spin echo sequence (multislice, multiecho [MSME]) and gradient echo sequence (2D-FLASH) were used to detect differences in the numbers of labeled cells by 7.0 T MRI. The results showed that the cultured cells were of “cobblestone”-like shape and positive for CD133, CD34, CD31, von Willebrand factor, kinase domain receptor, and CD45, but negative for F4/80. They could take up Dil-Ac-LDL, bind FITC-UEA, and form capillary-like networks on Matrigel in vitro. Prussian-blue staining demonstrated that the cells were efficiently labeled with SPIO. The single-cell T2* effect was more obvious in the 2D-FLASH sequence than in the MSME sequence. Further, there were almost no adverse effects on cell vitality and proliferation. In conclusion, mouse bone marrow-derived EPCs can be efficiently labeled with SPIO and imaged with 7.0-T MRI. They may thus be traced by MRI following transplantation for blood vessel disorders and cancer treatment.

Endothelial progenitor cells: novel biomarker and promising cell therapy for cardiovascular disease

Bone-marrow-derived EPCs (endothelial progenitor cells) play an integral role in the regulation and protection of the endothelium, as well as new vessel formation. Peripheral circulating EPC number and function are robust biomarkers of vascular risk for a multitude of diseases, particularly CVD (cardiovascular disease). Importantly, using EPCs as a biomarker is independent of both traditional and non-traditional risk factors (e.g. hypertension, hypercholesterolaemia and C-reactive protein), with infused ex vivo-expanded EPCs showing potential for improved endothelial function and either reducing the risk of events or enhancing recovery from ischaemia. However, as the number of existing cardiovascular risk factors is variable between patients, simple EPC counts do not adequately describe vascular disease risk in all clinical conditions and, as such, the risk of CVD remains. It is likely that this limitation is attributable to variation in the definition of EPCs, as well as a difference in the interaction between EPCs and other cells involved in vascular control such as pericytes, smooth muscle cells and macrophages. For EPCs to be used regularly in clinical practice, agreement on definitions of EPC subtypes is needed, and recognition that function of EPCs (rather than number) may be a better marker of vascular risk in certain CVD risk states. The present review focuses on the identification of measures to improve individual risk stratification and, further, to potentially individualize patient care to address specific EPC functional abnormalities. Herein, we describe that future therapeutic use of EPCs will probably rely on a combination of strategies, including optimization of the function of adjunct cell types to prime tissues for the effect of EPCs.

Role of endothelial progenitor cells in the beneficial effects of physical exercise on atherosclerosis and coronary artery disease

In clinical trials as well as in several animal experiments it is evident that physical exercise is a powerful tool to positively influence the development and/or progression of atherosclerosis and coronary artery disease (CAD). The main target of physical exercise seems to be the maintenance of an intact endothelial cell layer. Since the discovery that endothelial progenitor cells (EPCs) are present in the circulation and the knowledge that exercise, either as a single exercise bout or an exercise training program, have the potency to mobilize EPCs from the bone marrow, the contribution of the EPCs for the preservation or repair of the endothelial cell layer is still under debate. Either the EPCs differentiate into mature endothelial cells, or they stimulate via a paracrine mechanism mature endothelial cells to proliferate. It is still unclear, if the exercise-induced mobilization of EPCs is casually related to the improvement of endothelial function. This review will discuss the role of endothelial progenitor cells in the beneficial effects of physical exercise on atherosclerosis and coronary artery disease.

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.

The promise of cell-based therapies for diabetic complications: challenges and solutions

The discovery of endothelial progenitor cells (EPCs) in human peripheral blood advanced the field of cell-based therapeutics for many pathological conditions. Despite the lack of agreement about the existence and characteristics of EPCs, autologous EPC populations represent a novel treatment option for complications requiring therapeutic revascularization and vascular repair. Patients with diabetic complications represent a population of patients that may benefit from cellular therapy yet their broadly dysfunctional cells may limit the feasibility of this approach. Diabetic EPCs have decreased migratory prowess and reduced proliferative capacity and an altered cytokine/growth factor secretory profile that can accelerate deleterious repair mechanisms rather than support proper vascular repair. Furthermore, the diabetic environment poses additional challenges for the autologous transplantation of cells. The present review is focused on correcting diabetic EPC dysfunction and the challenges involved in the application of cell-based therapies for treatment of diabetic vascular complications. In addition, ex vivo and in vivo functional manipulation(s) of EPCs to overcome these hurdles are discussed.

Endothelial progenitor cells--an evolving story

The first description of endothelial progenitor cells (EPC) in 1997 led rapidly to substantial changes in our understanding of angiogenesis, and within 5 years to the first clinical studies in humans using bone marrow derived EPC to enhance coronary neovascularisation and cardiac function after myocardial ischemia. However, to improve the success of this therapy a clearer understanding of the biology of EPC is needed. This article summarises recent data indicating that most EPC are not, in fact, endothelial progenitors but can be better described as angiogenic monocytes, and explores the implications this has for their future therapeutic use.

Vascular effects of a low-carbohydrate high-protein diet

The cardiovascular complications of obesity have prompted interest in dietary interventions to reduce weight, including low-carbohydrate diets that are generally high in protein and fat. However, little is known about the long-term effects of these diets on vascular health. We examined the cardiovascular effects of a low-carbohydrate, high-protein diet (LCHP) in the ApoE(-/-) mouse model of atherosclerosis and in a model of ischemia-induced neovascularization. Mice on a LCHP were compared with mice maintained on either the standard chow diet (SC) or the Western diet (WD) which contains comparable fat and cholesterol to the LCHP. LCHP-fed mice developed more aortic atherosclerosis and had an impaired ability to generate new vessels in response to tissue ischemia. These changes were not explained by alterations in serum cholesterol, inflammatory mediators or infiltrates, or oxidative stress. The LCHP diet substantially reduced the number of bone marrow and peripheral blood endothelial progenitor cells (EPCs), a marker of vascular regenerative capacity. EPCs from mice on a LCHP diet also manifest lower levels of activated (phosphorylated) Akt, a serine-threonine kinase important in EPC mobilization, proliferation, and survival. Taken together, these data demonstrate that in animal models LCHP diets have adverse vascular effects not reflected in serum markers and that nonlipid macronutrients can modulate vascular progenitor cells and pathophysiology.

Promoting mechanisms of vascular health: circulating progenitor cells, angiogenesis, and reverse cholesterol transport

To understand and promote vascular health, we must reduce the aggression to the vessel wall and enhance the physiologic mechanisms leading to restoration of vessel wall function. Three main defense mechanisms are responsible for maintaining cardiovascular homeostasis: the regenerative production of endothelial progenitor cells, vessel wall angiogenesis, and macrophage-mediated reverse cholesterol transport. Endothelial progenitor cells can restore vessel wall function and reduce atherosclerosis. In patients with risk factors, high levels of circulating progenitor cells increase event-free survival from cardiovascular events. Mobilization of progenitor cells includes physical and pharmacological approaches, of which exercise and statin therapy have great potential. Angiogenesis is a pivotal defense mechanism to counteract hypoxia and is needed for plaque regression. However, neovessels are susceptible for intraplaque hemorrhage, particularly in diabetes mellitus. In these patients, the haptoglobin 2-2 genotype is the more affected, and may benefit from an antioxidant approach. Finally, the reverse cholesterol transport system is the main mechanism for plaque regression. In addition to high-density lipoprotein cholesterol, apolipoprotein A-I therapies and the promotion of cholesterol efflux from macrophages by the ABCA1 and ABCG1 transporter systems hold great promise and may be available for therapeutic application in the near future.