Small-caliber vascular grafts based on a piezoelectric nanocomposite elastomer: Mechanical properties and biocompatibility.

The development of small-caliber grafts still represents a challenge in the field of vascular prostheses. Among other factors, the mechanical properties mismatch between natural vessels and artificial devices limits the efficacy of state-of-the-art materials. In this paper, a novel nanocomposite graft with an internal diameter of 6 mm is proposed. The device is obtained through spray deposition using a semi-interpenetrating polymeric network combining poly(ether)urethane and polydimethilsyloxane. The inclusion of BaTiO3 nanoparticles endows the scaffold with piezoelectric properties, which may be exploited in the future to trigger beneficial biological effects. Graft characterization demonstrated a good nanoparticle dispersion and an overall porosity that was not influenced by the presence of nanoparticles. Graft mechanical properties resembled (or even ameliorated) the ones of natural vessels: both doped and non-doped samples showed a Young's modulus of ∼700 kPa in the radial direction and ∼900 kPa in the longitudinal direction, an ultimate tensile strength of ∼1 MPa, a strain to failure of ∼700%, a suture retention force of ∼1.7 N and a flexural rigidity of ∼2.5 × 10-5 N m2. The two grafts differed in terms of burst strength that resulted ∼800 kPa for the control non-doped samples and ∼1100 kPa for the doped ones. The graft doped with BaTiO3 nanoparticles showed a d33 coefficient of 1.91 pm/V, almost double than the non-doped control. The device resulted highly stable, with a mass loss smaller than 2% over 3 months and an excellent biocompatibility.

Endothelial progenitor cell secretome delivered by novel polymeric nanoparticles in ischemic hindlimb.

Endothelial progenitor cells (EPCs) contribute to ischemic tissue repair by paracrine secretion up-regulated by hypoxia. In this study we use novel nanoparticles (NPs) as carriers for a controlled release of EPC secretome (CM) to improve their angiogenic properties. The in vivo effect in ischemic hindlimb rat model was evaluated, comparing hypoxic EPC-CM-NPs with hypoxic EPC-CM alone. A proteomic characterization of hypoxic CM and the in vitro effect on endothelial cells (HUVECs) were also performed. Up to 647 protein, 17 of which with angiogenic properties, were upregulated by hypoxia. Moreover, hypoxic EPC-CM significantly promoted capillary-like structures on Matrigel. A significant increase of blood perfusion in ischemic limbs at 2 weeks with EPC-CM-loaded NPs as compared to both EPC-CM and control and a significant increase of capillary formation were observed. The use of EPC-CM-NPs significantly improved neoangiogenesis in vivo, underlining the advantages of controlled release in regenerative medicine.

Oligonucleotide biofunctionalization enhances endothelial progenitor cell adhesion on cobalt/chromium stents.

As the endothelium still represents the ideal surface for cardiovascular devices, different endothelialization strategies have been attempted for biocompatibility and nonthrombogenicity enhancement. Since endothelial progenitor cells (EPCs) could accelerate endothelialization, preventing thrombosis and restenosis, the aim of this study was to use oligonucleotides (ONs) to biofunctionalize stents for EPC binding. In order to optimize the functionalization procedure before its application to cobalt-chromium (Co/Cr) stents, discs of the same material were preliminarily used. Surface aminosilanization was assessed by infrared spectroscopy and scanning electron microscopy. A fluorescent endothelial-specific ON was immobilized on aminosilanized surfaces and its presence was visualized by confocal microscopy. Fluorescent ON binding to porcine blood EPCs was assessed by flow cytometry. Viability assay was performed on EPCs cultured on unmodified, nontargeting ON or specific ON-coated discs; fluorescent staining of nuclei and F-actin was then performed on EPCs cultured on unmodified or specific ON-coated discs and stents. Disc biofunctionalization significantly increased EPC viability as compared to both unmodified and nontargeting ON-coated surfaces; cell adhesion was also significantly increased. Stents were successfully functionalized with the specific ON, and EPC binding was confirmed by confocal microscopy. In conclusion, stent biofunctionalization for EPC binding was successfully achieved in vitro, suggesting its use to obtain in vivo endothelialization, exploiting the natural regenerative potential of the human body.

Effect of aging on metabolic pathways in endothelial progenitor cells.

Age represents a significant risk factor for the onset and progression of cardiovascular disease, with the increase in life expectancy in developed countries going in parallel with increased incidence of such pathologies. Treatment strategies alternative or additive to pharmacological treatments are needed. The relationship between aging and progenitor cell-mediated repair is of great interest. Endothelial progenitor cells (EPC) mediate repair mechanisms for endothelial regeneration and maintenance, but they are subject to age-associated changes affecting negatively their number and/or function. Aim of this review is to examine the impact of age on EPC-mediated vascular repair, with a focus on the metabolic pathways involved and on the therapeutic targets with potential for attenuating this effect.

Effect of platelet lysate on human cells involved in different phases of wound healing.

BACKGROUND: Platelets are rich in mediators able to positively affect cell activity in wound healing. Aim of this study was to characterize the effect of different concentrations of human pooled allogeneic platelet lysate on human cells involved in the different phases of wound healing (inflammatory phase, angiogenesis, extracellular matrix secretion and epithelialization). METHODOLOGY/PRINCIPAL FINDINGS: Platelet lysate effect was studied on endothelial cells, monocytes, fibroblasts and keratinocytes, in terms of viability and proliferation, migration, angiogenesis, tissue repair pathway activation (ERK1/2) and inflammatory response evaluation (NFκB). Results were compared both with basal medium and with a positive control containing serum and growth factors. Platelet lysate induced viability and proliferation at the highest concentrations tested (10% and 20% v/v). Whereas both platelet lysate concentrations increased cell migration, only 20% platelet lysate was able to significantly promote angiogenic activity (p<0.05 vs. control), comparably to the positive control. Both platelet lysate concentrations activated important inflammatory pathways such as ERK1/2 and NFκB with the same early kinetics, whereas the effect was different for later time-points. CONCLUSION/SIGNIFICANCE: These data suggest the possibility of using allogeneic platelet lysate as both an alternative to growth factors commonly used for cell culture and as a tool for clinical regenerative application for wound healing.

Significant endothelin release in patients treated with foam sclerotherapy.

BACKGROUND: Foam sclerotherapy has been proven to be a safe and effective treatment for superficial venous insufficiency, but transient visual and neurologic disturbances continue to be reported. These side effects have been theorized to be related to the presence of air or gases in the sclerosing foam that results in "bubble" migration into the cerebral circulation. We present a differing hypothesis that significant amounts of endothelin are released from the treated veins, amounts capable of causing these complications. MATERIAL AND METHODS: We tested the release of endothelin 1 (ET-1) in 12 rats after sclerotherapy with sodium tetradecyl sulfate (STS) in liquid and foam preparations. In 11 human subjects, we measured ET-1 in systemic circulation and in a draining vein after foam sclerotherapy with polidocanol. RESULTS: Rats treated with STS showed a significant increase in ET-1 levels 1 and 5 minutes after foam sclerotherapy. Patients treated with foam sclerotherapy showed a marked increase in ET-1 levels that correlated significantly with local ET-1 levels. CONCLUSIONS: Evidence of ET-1 release represents a plausible relationship explaining neurologic and visual disturbances reported after sclerotherapy.

Differential effects of fondaparinux and bemiparin on angiogenic and vasculogenesis-like processes.

INTRODUCTION: Conventional therapy for venous thromboembolism or acute coronary syndrome involves the administration of glycoanticoagulants (heparins) or oligosaccharides (fondaparinux). We evaluated the effects of such drugs on angiogenesis and vasculogenesis-like models. MATERIALS AND METHODS: Human umbilical vein endothelial cells or human endothelial progenitor cells were treated with bemiparin, fondaparinux or unfractionated heparin, at concentrations reflecting the doses used in clinical practice. After 24h, cell viability, proliferation, tubule formation and angiogenic molecular mechanisms, such as activation of the serine/threonine kinase AKT, were assessed. In vivo angiogenesis was studied using a Matrigel sponge assay in mice. RESULTS: Bemiparin gave a significant decrease of in vitro angiogenesis as shown by the reduction of endothelial cell tubule network, while both fondaparinux and unfractionated heparin did not show any significant effect. In assays of Matrigel sponge invasion in mice, unfractionated heparin was able to stimulate angiogenesis and, conversely, bemiparin inhibited angiogenesis. Furthermore, both bemiparin and fondaparinux caused a significant reduction in an in vitro vasculogenesis-like model, as demonstrated by the decrease of tubule network after co-seeding of endothelial progenitor cells and human umbilical vein endothelial cells. In addition, unfractionated heparin but not bemiparin was able to increase AKT phosphorylation. CONCLUSIONS: In in vitro experiments, bemiparin was the only drug to show an anti-angiogenic and vasculogenic-like effect, unfractionated heparin showed only a trend to increase in angiogenesis assay and fondaparinux affected only the vasculogenesis-like model. Notably, the in vivo experiments corroborated these data. Such results are important for the choice of a patient-tailored therapy.

Fibrin as a scaffold for cardiac tissue engineering.

Fibrin is a natural biopolymer with many interesting properties, such as biocompatibility, bioresorbability, ease of processing, ability to be tailored to modify the conditions of polymerization, and potential for incorporation of both cells and cell mediators. Moreover, the fibrin network has a nanometric fibrous structure, mimicking extracellular matrix, and it can also be used in autologous applications. Therefore, fibrin has found many applications in tissue engineering, combined with cells, growth factors, or drugs. Because a major limitation of cardiac cell therapy is low cell engraftment, the use of biodegradable scaffolds for specific homing and in situ cell retention is desirable. Thus, fibrin-based injectable cardiac tissue engineering may enhance cell therapy efficacy. Fibrin-based biomaterials can also be used for engineering heart valves or cardiac patches. The aim of this review is to show cardiac bioengineering uses of fibrin, both as a cell delivery vehicle and as an implantable biomaterial.

Circulating endothelial progenitor cells and large artery structure and function in young subjects with uncomplicated type 1 diabetes.

BACKGROUND: Carotid intima-media thickness (IMT), indices of large artery stiffness and measures of endothelium function may be used as markers of early atherosclerosis in type 1 diabetes mellitus (T1DM). The aim of the present study was to compare the indices of large artery structure and function as well as endothelial function and regenerating capacity between adolescents with T1DM and healthy control of similar age. In addition, the associations of different vascular measures with endothelial progenitor cells (EPCs), glyco-metabolic control and serum levels of advanced glycation endproducts (AGEs), soluble receptors for AGEs (sRAGE) and adiponectin were evaluated. METHODS: Sixteen uncomplicated young T1DM patients (mean age 18 ± 2 years, history of disease 11 ± 5 years, HbA1c 7.7 ± 1.1%) and 26 controls (mean age 19 ± 2 years) were studied. A radiofrequency-based ultrasound system (Esaote MyLab 70) was used to measure carotid IMT and wave speed (WS, index of local stiffness), applanation tonometry (PulsePen) was applied to obtain central pulse pressure (PP) and augmentation index (AIx), and carotid-femoral pulse wave velocity (PWV, Complior) was used as index of aortic stiffness. Peripheral endothelium-dependent vasodilation was determined as reactive hyperemia index (RHI, EndoPAT). Circulating EPCs, glycometabolic profile, AGEs (autofluorescence method), sRAGE and adiponectin were also measured. RESULTS: After adjusting for age, sex and blood pressure, T1DM adolescents had significantly higher carotid IMT (456 ± 7 vs. 395 ± 63 µm, p < 0.005), carotid WS (p < 0.005), PWV (p = 0.01), AIx (p < 0.0001) and central PP (p < 0.01) and lower EPCs (p = 0.02) as compared to controls. RHI was reduced only in diabetic patients with HbA1c ≥7.5% (p < 0.05). In the overall population, EPCs were an independent determinant of carotid IMT (together with adiponectin), while fasting plasma glucose was an independent determinant of carotid WS, AIx and central PP. CONCLUSIONS: Our findings suggest that young subjects with relatively long-lasting T1DM have a generalized preclinical involvement of large artery structure and function, as well as a blunted endothelium regenerating capacity. Hyperglycemia and suboptimal chronic glycemic control seem to deteriorate the functional arterial characteristics, such as large arteries stiffness, wave reflection and peripheral endothelium-dependent vasodilation, whereas an impaired endothelium regenerating capacity and adiponectin levels seem to influence arterial structure.

Endothelial progenitor cells in prehypertension.

Blood pressure within prehypertensive levels confers higher cardiovascular risk. As prehypertension is also an intermediate stage for full hypertension, a precocious intervention with lifestyle changes or drugs is therefore appealing. Endothelial injury and dysfunction are thought to contribute to cardiovascular risk in prehypertension. Endothelial progenitor cell impairment has been linked to endothelial dysfunction, atherosclerotic disease progression and cardiovascular events. A potential mechanism contributing to the heightened cardiovascular risk in prehypertension may be linked to abnormalities in endothelial progenitor cell number and/or function. Aim of this review is to be up to date about the recent work on the correlation between endothelial progenitor cells and prehypertension and the possible prevention, treatment, and control of this pathology. The effect of an approach based on dietary intervention on both blood pressure and endothelial progenitor cells will be also shown.

Smoking and endothelial progenitor cells: a revision of literature.

Accumulating evidence indicates that circulating endothelial progenitor cells (EPCs) derived from bone marrow contribute to reendothelialization of injuried vessels as well as neo-vascularization of ischemic lesions in either a direct or an indirect way. Moreover, the number and/or the functional activity of EPCs are inversely correlated with risk factors for cardiovascular disease. Among the different risk factors, cigarette smoking is a major cause of reducing the numbers and function of circulating EPCs. This review is a revision of recent literature on EPC alteration associated with smoking. In particular, we show the recent observation on the effects of active and second hand smoke (SHS) exposure on EPC number and functional activity. This review also considers the effects of nicotine and other smoke compounds on EPC number and activity, in in vitro and in vivo models.

Oxidative stress in response to high glucose levels in endothelial cells and in endothelial progenitor cells: evidence for differential glutathione peroxidase-1 expression.

Endothelial cells and endothelial progenitor cells (EPCs) play a key role in the pathogenesis of vascular disease. Both cell types are affected by the oxidative stress but their susceptibility may be different. This study aimed to investigate the antioxidative enzymes activated in EPCs after high constant glucose exposure as compared to endothelial cells (HUVECs). Both cells were incubated in the presence of normal (5mM) and high constant (25mM) d-glucose, as well as l-glucose as osmotic control for 48 and 96h. After a 48-hour exposure to high d-glucose, cell viability was significantly decreased both in EPCs and HUVECs as compared with normal d-glucose (p<0.01). However, after 96h there was no difference between EPCs grown on normal or high d-glucose, while HUVEC viability was affected by high d-glucose at 96h too (p<0.001). High d-glucose exposure induced a significant increase in reactive oxygen species (ROS) production in both cell types at 48h; however, after 96h, a significant decrease in ROS production (p<0.01) and a parallel marked increase in glutathione peroxidase type 1 (GPx-1) expression (p<0.01) and activity (p<0.01) were observed in EPCs compared to HUVECs. These data suggest that EPCs have a well-adaptive response to oxidative stress induced by constant and sustained high glucose exposure. This resistance to high glucose levels might be due to increased expression and activity of glutathione peroxidase allowing better cell survival.

Inflammatory markers and cardiac function in acute coronary syndrome: difference in ST-segment elevation myocardial infarction (STEMI) and in non-STEMI models.

PURPOSE: No studies have been addressed to the differences in inflammation kinetics between ST-segment elevation myocardial infarction (STEMI) and non-ST-segment elevation myocardial infarction (NSTEMI). PATIENTS AND METHODS: Forty consecutive patients with acute coronary syndrome (ACS) (n=23 STEMI, age=61.7+/-10.3 years; n=17 NSTEMI, age=65.6+/-11.3 years) were enrolled within 12h after symptoms. All patients received therapy according to the current Guidelines. Blood samples were collected at admission (t0), on days 7 (t1) and 30 (t2) to evaluate CD40 ligand (CD40L), transforming growth factor (TGF)-beta, interleukin (IL)-6, tumor necrosis factor (TNF)-alpha and its receptors TNFRI and TNFRII, high sensitivity C-reactive protein (hs-CRP), serum amyloid A (SAA) and white blood cells (WBC). Echocardiographic parameters were also evaluated. RESULTS: STEMI patients, at admission, had significantly higher median values of hs-CRP (p<0.001), WBC (p<0.01), ferritin (p<0.0005) and IL-6 (p<0.05) than NSTEMI. On the contrary, NSTEMI patients had lower median levels of every inflammatory marker except for CD40L (p<0.05) that was significantly higher. Moreover, three out of four deceased patients presented levels of CD40L higher than the median. At admission, STEMI showed a reduced ejection fraction (EF, p<0.01) and increased wall motion score index (WMSI, p<0.001) and end-diastolic volume (EDV, p<0.05) vs NSTEMI. An inverse correlation between admission values of inflammatory markers (SAA and WBC) and cardiac function was observed (p<0.05). Moreover, the necrosis marker troponin I was positively correlated with both WMSI (p<0.05) and hs-CRP (p<0.05). Regarding the inflammation kinetics, a difference was observed in the two groups only for WBC (p<0.05) and SAA (p<0.05). SAA showed higher values in STEMI at t0 and t1. In both groups, TGF-beta had an increase at t1 and t2 with respect to admission, while IL-6 had a decreasing trend. The total incidence of major adverse clinical events (MACE) was 22.5% at t2, with a mortality rate of 10%. CONCLUSION: These observations suggest a differential inflammatory pattern in STEMI and NSTEMI patients. The absence of significant correlations between inflammatory indexes and myocardial infarction in NSTEMI supports the hypothesis that a different pattern of inflammation occurs in these patients. CD40L may have an important role as a marker for risk stratification in patients with ACS.

Human peripheral blood endothelial progenitor cells synthesize and express functionally active tissue factor.

INTRODUCTION: Endothelial progenitor cells are circulating cells able to home to sites of vascular damage and to contribute to the revascularization of ischemic areas. We evaluated whether endothelial progenitor cells synthesize tissue factor, a procoagulant protein also involved in angiogenesis. MATERIALS AND METHODS: Endothelial progenitor cells were obtained from the peripheral blood mononuclear fraction of normal donors and cultured in endothelial medium supplemented with specific growth factors. The procoagulant activity expressed by cells disrupted by freeze-thaw cycles was assessed by a one stage clotting assay. Tissue factor mRNA expression was evaluated by RT-PCR. RESULTS: Endothelial progenitor cells do not express procoagulant activity in baseline conditions. However, lipopolysaccharide induces the expression of procoagulant activity. The effect is dose-dependent and reaches statistical significance at 100 ng/mL lipopolysaccharide. Inhibition with an anti-tissue factor antibody and amplification of cDNA with primers based on the tissue factor sequence confirm the identity of this activity with tissue factor. The kinetics of tissue factor expression by endothelial progenitor cells is identical to that of human umbilical vein endothelial cells showing maximal activity within 4 hours, and then decreasing; in contrast, tissue factor expression by mononuclear cells lasts for longer times. Both 5,6-dichloro-beta D-ribofuranosyl-benzimidazole and cycloheximide prevented the expression of procoagulant activity. Stimulation of endothelial progenitor cells with tumor necrosis factor-alpha did not elicit any detectable procoagulant activity. CONCLUSIONS: Endothelial progenitor cells can be stimulated by lipopolysaccharide to synthesize tissue factor. This protein might be involved in thrombotic phenomena and might contribute to endothelial progenitor cells related neovascularization.

The prostacyclin analogue iloprost increases circulating endothelial progenitor cells in patients with critical limb ischemia.

Patients with critical limb ischemia (CLI) have low levels of endothelial progenitor cells (EPC). Iloprost has been demonstrated to stimulate vascular endothelial growth factor (VEGF) and promote angiogenesis. We investigated the effects of iloprost on EPC levels in vivo in CLI patients. Twenty-three patients with stage III and IV CLI were treated with iloprost for four weeks, improving clinical and instrumental parameters. Mononuclear cells isolated from peripheral blood were cultured to obtain "early" EPC, evaluated counting adherent cells with double positivity for acetylated low-density lipoprotein uptake and Ulex Europaeus lectin at flow cytometry. These cells also co-expressed the monocyte markers CD14 and CD45. Iloprost increased EPC number in the whole patient population: pre-treatment median: 13,812/ml; range: 1,263-83,648/ml; post-treatment median: 23,739/ml; range: 3,385-99,251/ml; p = 0.035, irrespective of age, sex, disease stage or atherosclerosis risk factors. In conclusion, iloprost increases EPC number in peripheral blood in vivo. Such an effect may have therapeutic relevance.

Polymorphic analysis of the matrix metalloproteinase-9 gene and susceptibility to sporadic abdominal aortic aneurysm.

Abdominal aortic aneurysm (AAA) has a multifactorial aetiology and the importance of genetic components is getting increasing interest. Alteration in the structure of the vascular extracellular matrix has been described in AAA. Matrix metalloproteinases (MMPs) degrade extracellular matrix proteins which alter the vessel wall stability. We evaluated two different polymorphisms, a CA repeat and a cytosine to thymidine transition in the promoter sequence of MMP-9 gene for frequency in 146 patients with AAA. We compared the results with those of 156 healthy subjects. No difference was found in the allelic distribution of either polymorphisms. We therefore found no evidence that MMP-9 is a marker of susceptibility for AAA.

Endothelial progenitor cells induction by short-term stimulation with phytohaemagglutinin of mononuclear cells.

BACKGROUND: The identification of circulating endothelial progenitors cells (EPCs) in the adult has forced to reconsider how new blood vessels grow in physiological and pathological conditions. Neovascularization during adult life has long been attributed to angiogenesis only. However, recent studies have revealed that peripheral blood EPCs may be recruited and incorporated into sites of active neovascularization. PURPOSE: To verify that EPCs are induced from peripheral blood mononuclear cells (PBMCs) and bone marrow derived mononuclear cells (BMMCs) upon short-term stimulation with phytohaemoagglutinin (PHA), a potent T-cell mitogen. METHODS: PBMCs and BMMCs were isolated from healthy donors. Freshly isolated or depleted of adherent cells (one day and three days of adherence) mononuclear cells (MCs) were cultured in RPMI, 10% FBS, containing PHA (10 microl/10(6) cells) for 24 h. After stimulation with PHA, clusters of adherent cells were further propagated in M199 containing L-glutammine, Hepes, 20% FBS, heparin, antibiotics and bovine retina extract for 1 and 2 weeks. PBMCs and BMMCs cultured without PHA stimulation served as controls. FACS of EPCs was performed on attached cells after 7 and 14 days of culture. RESULTS AND CONCLUSION: After stimulation of MCs with PHA for 24 h, many cells clusters were observed and around these clusters some adherent EC-like cells were observed. These cells were ovoid but a very little of these were elongated in morphology, however their number and size gradually increased during culture. However a longer time was needed for obtaining EPCs from MCs harvested after adherence. Thus this indicates that short-term signals provided by PHA must be sufficient for MCs to express the ligands necessary for the induction of EPCs but signals from monocytes/macrophages are important for a more rapid differentiation.