Passivation of metallic stents after arterial gene transfer of phVEGF165 inhibits thrombus formation and intimal thickening

Intra-arterial injection of mesenchymal stem cells to accelerate neointima formation after endovascular stenting in a rabbit model

OBJECTIVE

Delayed neointima formation over a neurovascular stent is associated with thrombotic complications that can lead to stroke. The purpose of this study was to evaluate whether an intra-arterial injection of mesenchymal stem cells (MSCs) after stent placement leads to improved neointima and reduced thrombus formation over the device.

METHODS

Solitaire stents were placed into the aortas of rabbits that were divided into MSC and control groups. The MSC group received an intra-arterial injection of MSCs through the same microcatheter used for stent deployment. Optical coherence tomography (OCT) was used to evaluate and compare neointima and thrombus formation in a blinded fashion. Explanted specimens were also imaged with scanning electron microscopy (SEM) and evaluated by observers blinded to group allocation using an endothelialization scoring system.

RESULTS

The 3-day MSC group was similar to the 7-day controls in terms of stent strut coverage ratio and maximum neointimal thickness, but these values were significantly higher than the 3-day control group based on a hierarchical mixed-effects linear regression analysis. SEM revealed a significantly higher endothelialization score for the MSC group compared with controls at the same time point. There was no difference in thrombus formation between any of the groups.

CONCLUSIONS

The intra-arterial injection of MSCs after endovascular stenting accelerated early neointima formation but had no effect on thrombus formation in this study. Larger studies are required to verify these findings and determine the durability and mechanism of this effect.

Development of In Vitro Endothelialised Stents - Review

Endovascular treatment is prevalent as a primary treatment for coronary and peripheral arterial diseases. Although the introduction of drug-eluting stents (DES) dramatically reduced the risk of in-stent restenosis, stent thrombosis persists as an issue. Notwithstanding improvements in newer generation DES, they are yet to address the urgent clinical need to abolish the late stent complications that result from in-stent restenosis and are associated with late thrombus formation. These often lead to acute coronary syndromes with high mortality in coronary artery disease and acute limb ischemia with a high risk of limb amputation in peripheral arterial disease. Recently, a significant amount of research has focused on alternative solutions to improve stent biocompatibility by using tissue engineering. There are two types of tissue engineering endothelialisation methods: in vitro and in vivo. To date, commercially available in vivo endothelialised stents have failed to demonstrate antithrombotic or anti-stenosis efficacy in clinical trials. In contrast, the in vitro endothelialisation methods exhibit the advantage of monitoring cell type and growth prior to implantation, enabling better quality control. The present review discusses tissue-engineered candidate stents constructed by distinct in vitro endothelialisation approaches, with a particular focus on fabrication processes, including cell source selection, stent material composition, stent surface modifications, efficacy and safety evidence from in vitro and in vivo studies, and future directions.

Mechanical and physio-biological properties of peptide-coated stent for re-endothelialization

Background

The aim of this study was to characterize the mechanical and physio-biological properties of peptide-coated stent (PCS) compared to commercialized drug-eluting stents (DESs).

Methods

WKYMVm (Trp-Lys-Tyr-Met-Val-D-Met), a stimulating peptide for homing endothelial colony-forming cell was specially synthesized and coated to bare metal stent (BMS) by dopamine-derived coordinated bond. Biological effects of PCS were investigated by endothelial cell proliferation assay and pre-clinical animal study. And mechanical properties were examined by various experiment.

Results

The peptide was well-coated to BMS and was maintained and delivered to 21 and 7 days in vitro and in vivo, respectively. Moreover, the proliferation of endothelial cell in PCS group was increased (approximately 36.4 ± 5.77%) in PCS group at 7 day of culture compare to BMS. Although, the radial force of PCS was moderated among study group. The flexibility of PCS was (0.49 ± 0.082 N) was greatest among study group. PCS did not show the outstanding performance in recoil and foreshortening test (3.1 ± 0.22% and 2.1 ± 0.06%, respectively), which was the reasonable result under the guide line of FDA (less than 7.0%). The nominal pressure (3.0 mm in a diameter) of PCS established by compliance analysis was 9 atm. The changing of PCS diameter by expansion was similar to other DESs, which is less than 10 atm of pressure for the nominal pressure.

Conclusions

These results suggest that the PCS is not inferior to commercialized DES. In addition, since the PCS was fabricated as polymer–free process, secondary coating with polymer-based immunosuppressive drugs such as –limus derivatives may possible.

Time Course of Reendothelialization with Polyzene-F Nanocoated Cobra PzF™ Coronary Stent on Rabbit Iliac Arteries

PURPOSE

Evaluation of reendothelialization with a new thin struts cobalt chromium alloy stent coated with a nano-layer of Polyzene™-F (PzF) in a rabbit iliac artery model.

METHODS

Fifteen stented external rabbit iliac arteries were harvested at Day 7 for electron microscopy analysis following Cobra PzF stents implantation to assess reendothelialization and compare to historical data. Ten additional rabbits were used to assess time course of reendothelialization at 3 and 5 days.

RESULTS

At Day 7, almost complete coverage of endothelial cells was observed with a coverage of 99.54 ± 0.25% of the stented area. No thrombus area was noted. At Day 3, more than half of examined pieces was reendothelialized and reached 78.30 ± 3.7% at Day 5 (p < .01 between each group). All stents were well expanded against the arterial wall and no struts were mal-apposed.

CONCLUSIONS

Reendothelialization was rapid and complete at Day 7. This is the fastest reendothelization process after stenting in this model. No stent occlusion was observed.

Deficiency of MAPK-activated protein kinase 2 (MK2) prevents adverse remodelling and promotes endothelial healing after arterial injury

Maladaptive remodelling of the arterial wall after mechanical injury (e. g. angioplasty) is characterised by inflammation, neointima formation and media hypertrophy, resulting in narrowing of the affected artery. Moreover, mechanical injury of the arterial wall causes loss of the vessel protecting endothelial cell monolayer. Mitogen-activated protein kinase (MAPK)-activated protein kinase 2 (MK2), a major downstream target of p38 MAPK, regulates inflammation, cell migration and proliferation, essential processes for vascular remodelling and reendothelialisation. Therefore, we investigated the role of MK2 in remodelling and reendothelialisation after arterial injury in genetically modified mice in vivo. Hypercholesterolaemic low-densitylipoprotein- receptor-deficient mice (ldlr-/- ) were subjected to wire injury of the common carotid artery. MK2-deficiency (ldlr-/-/mk2-/- ) nearly completely prevented neointima formation, media hypertrophy, and lumen loss after injury. This was accompanied by reduced proliferation and migration of MK2-deficient smooth muscle cells. In addition, MK2-deficiency severely reduced monocyte adhesion to the arterial wall (day 3 after injury, intravital microscopy), which may be attributed to reduced expression of the chemokine ligands CCL2 and CCL5. In line, MK2-deficiency significantly reduced the content of monocytes, neutrophiles and lymphocytes of the arterial wall (day 7 after injury, flow cytometry). In conclusion, in a model of endothelial injury (electric injury), MK2-deficiency strongly increased proliferation of endothelial cells and improved reendothelialisation of the arterial wall after injury. Deficiency of MK2 prevents adverse remodelling and promotes endothelial healing of the arterial wall after injury, suggesting that MK2-inhibition is a very attractive intervention to prevent restenosis after percutaneous therapeutic angioplasty.

The impact of vascular endothelial growth factor +405 C/G polymorphism on long-term outcome and severity of coronary artery disease

BACKGROUND

The association between genetic variations of vascular endothelial growth factor (VEGF) gene and the risk for atherosclerosis has been hypothesized. We aimed to assess the relationship between rs2010963 (+405 C/G) polymorphism and presence, severity, and outcome of coronary artery disease (CAD) in an Iranian cohort.

METHODS

Genotyping of VEGF rs2010963 polymorphism was performed on 520 individuals, comprising 347 patients with documented coronary artery disease based on angiography report and 173 individuals with normal coronary arteries, using the TaqMan real-time PCR method. In final, 484 subjects were followed up over a 5-year period for cardiovascular-related outcomes.

RESULTS

C allele of VEGF rs2010963 polymorphism was related to increase risk for CAD and also slightly to 5-year cardiovascular mortality. The 5-year survival in C and G allele subgroups were 92.3% and 94.3% in CAD group and 95.7% and 98.0% in non-CAD group, respectively.

CONCLUSIONS

Vascular endothelial growth factor rs2010963 polymorphism may be associated with the presence of CAD and its long-term survival, but not with its severity. To the best of our knowledge, this is the first report of genetic association between rs2010963 SNP and CAD-related death. It can be thus suggested that rs2010963 VEGF gene can be considered as a genetic risk predictor for CAD and its outcomes.

Rescuing Impaired Re-endothelialization of Drug-Eluting Stents Using the Hepatocyte Growth Factor

BACKGROUND

Current commercially available drug-eluting stents (DESs) are criticized for the problem of stent thrombosis by induced impaired re-endothelialization (RE). The solving of this challenge could be boosted by endothelial progenitor cells (EPCs). The purpose of this study was to examine the effects of hepatocyte growth factor (HGF) on this process.

METHODS

The abundance and functional capacity of circulating EPC was analyzed by a fluorescence-activated cell sorter and western blot. The in vivo effect of HGF on DES patency, RE, and neointimal formation was investigated in a hypercholesterolemic rabbit model.

RESULTS

After 7 days of HGF administration, the number of CD34+/CD133+ progenitor cells had increased significantly. HGF also significantly inhibited the onset of senescence of EPC due to a decrease in protein expression of p53 and p21. In the in vivo study, HGF-treated DES had a higher patency rate than the control group (11/12 vs. 6/12, P = 0.032). Moreover, the HGF-treated group exhibited better RE (control group: 69.5 ± 12.9%, HGF group: 88.8 ± 8.4%, P = 0.006), but significantly smaller areas of neointima (control group: 0.68 ± 0.15 mm², HGF group: 0.45 ± 0.18 mm², P = 0.02).

CONCLUSION

HGF efficiently ameliorates the vascular response to stent implantation, and has an important redeeming influence on the deleterious endothelial effects of DES.

Bio-functionalization of biomedical metals

Bio-functionalization means to endow biomaterials with bio-functions so as to make the materials or devices more suitable for biomedical applications. Traditionally, because of the excellent mechanical properties, the biomedical metals have been widely used in clinic. However, the utilized functions are basically supporting or fixation especially for the implantable devices. Nowadays, some new functions, including bioactivity, anti-tumor, anti-microbial, and so on, are introduced to biomedical metals. To realize those bio-functions on the metallic biomedical materials, surface modification is the most commonly used method. Surface modification, including physical and chemical methods, is an effective way to alter the surface morphology and composition of biomaterials. It can endow the biomedical metals with new surface properties while still retain the good mechanical properties of the bulk material. Having analyzed the ways of realizing the bio-functionalization, this article briefly summarized the bio-functionalization concepts of six hot spots in this field. They are bioactivity, bony tissue inducing, anti-microbial, anti-tumor, anticoagulation, and drug loading functions.

The metamorphosis of vascular stents: passive structures to smart devices

The role of nanotechnology enabled techniques in the evolution of vascular stents.

Association of Egr3 genetic polymorphisms and coronary artery disease in the Uygur and Han of China

Background

Endothelial cell activation and dysfunction are the foundation of atherosclerosis, including coronary artery disease (CAD). Endothelial cell activation is mediated by the level of gene transcription. Early growth response 3 (Egr3) is a critical determinant of vascular endothelial growth factor (VEGF) signalling in activated endothelial cells. If endothelial cells are excessively activated, it may lead to vasculopathic diseases, such as pathologic angiogenesis, inflammation, and atherosclerosis. The aim of the present study was to assess the association between the Egr3 gene polymorphisms and CAD.

Methods

Two independent case–control studies that involved the Han group (409 CAD patients and 351 control subjects) and the Uygur group (299 CAD patients and 303 control subjects) analysed the relationship between Egr3 SNPs (rs1996147 and rs1008949) and CAD. Genotyping was undertaken using the TaqMan SNP genotyping assay.

Results

The entire Uygur group and the males in the Uygur group showed a higher frequency of the A allele (rs1996147) in CAD patients than in the control subjects (P = 0.003 and P = 0.005, respectively). Additionally, the distribution of the recessive model of rs1996147 (AA vs GG + AG) for the total sample and the males was significantly different between CAD patients and control participants (P = 0.002 and P = 0.003, respectively), and the difference remained statistically significant following multivariate adjustment (Total: OR = 1.705; 95% CI: 1.166-2.494, P = 0.006; males: OR = 1.908, 95% CI: 1.189-3.062, P = 0.007). However, for Uygur females, we did not observe a difference in the allele frequency or genotypic distribution of rs1996147 between CAD patients and control participants. Similarly, the distribution of the rs1996147 allele frequency or genotypes showed no significant difference between patients with CAD and control participants in the Han group. The distribution of rs1008949 genotypes, dominant model, recessive model, and allele frequency did not show a significant difference between patients with CAD and the control subjects in the Han and Uygur groups.

Conclusion

rs1996147 may be a novel polymorphism of the Egr3 gene associated with CAD in males of the Chinese Uygur population.

Angiotensin converting enzyme insertion/deletion (I/D) (rs4646994) and Vegf polymorphism (+405G/C; rs2010963) in type II diabetic patients: Association with the risk of coronary artery disease

HYPOTHESIS

Little is known about the concomitant presence of the angiotensin-converting enzyme (ACE) (rs4646994) D allele and vascular endothelial growth factor(VEGF) (+405G/C; rs2010963) G allele on the susceptibility of coronary artery disease (CAD). Here we examined the hypothesis that ACE-D and VEGF-G alleles act synergistically to increase the severity of CAD in patients with type II diabetes mellitus (T2DM).

MATERIALS AND METHODS

The VEGF (rs2010963) and ACE (rs4646994) genotypes were detected by polymerase chain reaction - restriction fragment length polymorphism (PCR-RFLP) and PCR, respectively in 510 T2DM patients undergoing their first coronary angiography. Diabetic patients were classified as T2DM patients with and without CAD (control).

RESULTS

The crude odds ratio (OR) for the presence of CAD in ID+DD and D allele carriers were 1.98 (p=0.01) and 1.55 (p=0.001), respectively. Also, adjusted ORs in the presence of normolipidemia and the absence of history of hypertension for the risk of CAD in the either ACE(rs4646994) D allele or VGEF(rs2010963)-G alleles were 2.08 (p=0.004) and 1.75 (p=0.024), respectively. In addition, the concomitant presence of the ACE-D and VEGF-G alleles increased the risk of CAD 2.25-fold (p=0.043).

CONCLUSION

Our results indicated that ACE(rs4646994)-D allele alone and in the presence of VEGF(rs2010963)-G allele can be an important independent risk factor for susceptibility of CAD in T2DM patients even after correcting for conventional risk factors in a population of Iran.

Surface projections of titanium substrates increase antithrombotic endothelial function in response to shear stress

Despite the therapeutic benefits of both mechanical circulatory assist devices and nitinol stents with titanium (Ti) outer surfaces, problems remain with thrombosis at the blood-contacting surface. Covering these surfaces with a layer of endothelium would mimic the native lining of the cardiovascular system, potentially decreasing thrombotic complications. Since surface topography is known to affect the phenotype of a seeded cell layer and since stents and ventricular assist devices exhibit surface protrusions, we tested the hypothesis that endothelial cells (ECs) have altered function on Ti surfaces with protrusions of 1.25, 3, and 5 μm height, compared with smooth Ti surfaces. ECs and nuclei were more aligned and ECs were more elongated on all patterned surfaces. Cell area was reduced on the 3 and 5 μm features. Expression of eNOS and COX2 was not altered by patterned surfaces, but expression of KLF-2 was higher on 1.25 and 5 μm features. Nitric oxide production following exposure to flow was higher on the 5 μm features. These results show that some antithrombogenic functions of ECs are significantly enhanced for ECs cultured on surface protrusions, and no functions are diminished, informing the future design of implant surfaces for endothelialization.

Therapeutic angiogenesis for myocardial ischemia revisited: basic biological concepts and focus on latest clinical trials

Therapeutic angiogenesis is based on the premise that the development of new blood vessels can be augmented by exogenous administration of the appropriate growth factors. Over the last years, successful preclinical studies and promising results of early clinical trials have created great excitement about the potential of therapeutic angiogenesis for patients with advanced ischemic heart disease. The authors provide an overview of the biology of angiogenesis, the basic characteristics of angiogenic factors, and the different routes of their delivery. They discuss experimental studies in animal models of myocardial ischemia and outline available clinical studies on therapeutic angiogenesis for myocardial ischemia. Related safety issues are also addressed followed by a critical perspective about the future of proangiogenic therapies for ischemic cardiovascular disorders. Despite the established proof of concept and reasonable safety, however, results of the latest trials on therapeutic angiogenesis for myocardial ischemia have provided inconsistent results and the definite means of inducing clinically useful therapeutic angiogenesis remain elusive. More studies are required to gain further insights into the biology of angiogenesis and address pharmacological limitations of current approaches of angiogenic therapy. The authors hope and envisage that in the not-too-distant future, these investigative efforts will lead to important new strategies for treatment of myocardial ischemic syndromes. Means of non-invasive individualized pharmacological therapeutic neovascularization may be the next major advance in the treatment of ischaemic heart disease.

Rebuilding the damaged heart: the potential of cytokines and growth factors in the treatment of ischemic heart disease

Cytokine therapy promises to provide a noninvasive treatment option for ischemic heart disease. Cytokines are thought to influence angiogenesis directly via effects on endothelial cells or indirectly through progenitor cell-based mechanisms or by activating the expression of other angiogenic agents. Several cytokines mobilize progenitor cells from the bone marrow or are involved in the homing of mobilized cells to ischemic tissue. The recruited cells contribute to myocardial regeneration both as a structural component of the regenerating tissue and by secreting angiogenic or antiapoptotic factors, including cytokines. To date, randomized, controlled clinical trials have not reproduced the efficacy observed in pre-clinical and small-scale clinical investigations. Nevertheless, the list of promising cytokines continues to grow, and combinations of cytokines, with or without concurrent progenitor cell therapy, warrant further investigation.

Human aortic endothelial cell response to 316L stainless steel material microstructure

The role of metal microstructure (e.g. grain sizes) in modulating cell adherence behavior is not well understood. This study investigates the effect of varying grain sizes of 316L stainless steel (SS) on the attachment and spreading of human aortic endothelial cells (HAECs). Four different grain size samples; from 16 to 66 microm (ASTM 9.0-4.9) were sectioned from sheets. Grain structure was revealed by polishing and etching with glycergia. Contact angle measurement was done to assess the hydrophilicity of the specimens. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the roughness and surface chemistry of the specimens. Cells were seeded on mechanically polished and chemically etched specimens followed by identification of activated focal adhesion sites using fluorescently tagged anti-pFAK (phosphorylated focal adhesion kinase). The 16 microm grain size etched specimens had significantly (P < 0.01) higher number of cells attached per cm(2) than other specimens, which may be attributed to the greater grain boundary area and associated higher surface free energy. This study shows that the underlying material microstructure may influence the HAEC behavior and may have important implications in endothelialization.

Promoting Vascular Regeneration as an Alternative to Conventional Angioplasty-Based Intervention

Technologies in interventional Cardiology have evolved from balloon to mechanical ablation, atherectomy, stenting, and brachytherapy to current drug eluting interventional strategies. New challenges are to develop techniques that not only prevent restenosis, but also promote vascular and endothelial healing after (balloon) injury. Endothelial healing approaches range from preventing endothelial injury to restoring endothelial function and reendothelialization by pharmacotherapy and cell therapy. These novel healing strategies warrant further exploration as they may represent an alternative to drug-eluting stent approaches.

Vascular endothelial growth factor genetic variability and coronary artery disease in Brazilian population

Atherosclerosis results from a complex interaction between environment and genetic risk factors. The gene encoding vascular endothelial growth factor (VEGF) is associated with differential protein expression and has been investigated in coronary artery disease (CAD) studies. Based on this, we aimed at determining if patients with CAD are affected by polymorphisms (-2 578, -1 154, and 936) in the VEGF gene, and also if these polymorphisms are associated with the number of diseased vessels and degree of arterial obstruction. The case group was formed by 175 Caucasian patients with angiographically confirmed CAD, and the control group involved 108 Caucasian patients with normal coronary angiograms. Polymerase chain reaction (PCR) was used for genotyping. Allele frequencies for VEGF -2 578A, -1 154A, and 936T were 0.46, 0.38, and 0.14 in cases and 0.49, 0.30, and 0.13 in control subjects. Allele and genotype distribution did not significantly differ between groups. A higher frequency of the VEGF -2 578AA genotype was observed in the group with three vessel disease (P = 0.008). No association between the VEGF -2 578, -1 154, and 936 polymorphisms and degree of arterial obstruction was observed. The frequency of carriers of two copies of the haplotype AG (-2 578/-1 154) were higher in the group with three-vessel disease (P = 0.05). In summary, our report shows that the VEGF -2 578 polymorphism has an influence on CAD severity, possibly because of a reduced VEGF expression, suggesting a protective effect of VEGF in atherosclerosis.

Update on drug-eluting stents for prevention of restenosis

Despite the success of coronary stent implantations in the last decade, in-stent restenosis due to neointimal hyperplasia remains a problem to overcome. Neointimal hyperplasia is a vascular response to stent injury and mainly consists of proliferation of smooth muscle cells and deposition of extracellular matrix. Recently, local drug delivery has been advocated as a potential strategy to prevent in-stent restenosis. Unprecedented results have been obtained in early clinical studies on sirolimus-eluting and paclitaxel-eluting stents. Trials using various pharmaceutical coatings on different coronary stents are ongoing. More types of drug-eluting stents are expected on the market in the near future. Meanwhile, the evaluation of drug-eluting stents is entering the second phase in which the safety and efficacy in more complex lesion subsets and different clinical presentations are being investigated. Results including cost-benefit analyses are expected to have a tremendous impact on the practice of interventional cardiology in the next decade.

Delivery of large biopharmaceuticals from cardiovascular stents: a review

This review focuses on new and emerging large-molecule bioactive agents delivered from stent surfaces in drug-eluting stents (DESs) to inhibit vascular restenosis in the context of interventional cardiology. New therapeutic agents representing proteins, nucleic acids (small interfering RNAs and large DNA plasmids), viral delivery vectors, and even engineered cell therapies require specific delivery designs distinct from traditional smaller-molecule approaches on DESs. While small molecules are currently the clinical standard for coronary stenting, extension of the DESs to other lesion types, peripheral vasculature, and nonvasculature therapies will seek to deliver an increasingly sophisticated armada of drug types. This review describes many of the larger-molecule and biopharmaceutical approaches reported recently for stent-based delivery with the challenges associated with formulating and delivering these drug classes compared to the current small-molecule drugs. It also includes perspectives on possible future applications that may improve safety and efficacy and facilitate diversification of the DESs to other clinical applications.

Matrices and scaffolds for drug delivery in vascular tissue engineering

The purpose of this review is to give an overview of strategies using natural and artificial substrates to present active biomolecules in the development of vascular structures. Two primary topics are discussed. The first is the replacement and augmentation of arteries using vascular grafts or stents. Second is the recruitment of microvasculature secondary to an ischemic event or for the purpose of developing perfused, large-volume tissue-engineered constructs. Significant overlap exists among these topics. The focus is therefore on specific drug delivery strategies with discussion of a number of emerging themes. Where applicable, results from clinical trials have been included. Early work in the field includes covalent and nonspecific immobilization of growth factors, while more recent work emphasizes biologically inspired control over localization and temporal presentation. Novel strategies for matrix-mediated release can deliver multiple growth factors and/or cells in a manner that mimics tissue development and healing. Challenges that remain within this field center on controlling reciprocal interactions among the three fundamental tissue engineering components of scaffolds, cells and signals.

Atherosclerosis and the protective role played by different proteins in apolipoprotein E-deficient mice

The aim of the present study was to analyze the early events in atherogenesis and the role of pro- or anti-atherosclerotic proteins in the development of atherosclerotic lesions. We used apolipoprotein E-deficient (E(0)) mice that spontaneously develop hypercholesterolemia and atherosclerotic lesions in the aorta in a time-dependent manner. Aortas of mice aged 6, 8, 10 and 12 weeks were examined to determine histopathological changes. In mice aged 8-12 weeks, developing atherosclerotic lesions were present in different regions of the aortas. These lesions protruded into the lumen of the vessel and showed lipid deposits, lipid-filled macrophages and extensive accumulation of collagen and elastic fibers throughout the entire arterial wall. A parallel immunohistochemical study included analysis of three proteins known to be involved in atherosclerosis, i.e. inducible nitric oxide synthase (iNOS, NOS2), vascular endothelial growth factor (VEGF) and matrix metalloproteinase-2 (MMP2). Increased immunolabelling of iNOS and VEGF accompanied atherosclerosis development in E(0) mice aged 8, 10 and 12 weeks. On the contrary, immunolabelling for MMP2 was negative in E(0) mice aged 10 and 12 weeks. Our results indicate morphological alterations in the Tunica intima and Tunica media of atherosclerotic aortas and possible protective roles for iNOS and VEGF proteins against atherosclerosis development. These data may be relevant for developing therapeutic strategies for atherosclerosis development.

Gene therapy for restenosis: biological solution to a biological problem

Coronary artery disease remains a significant health threat afflicting millions of individuals worldwide. Despite the development of a variety of technologies and catheter based interventions, post-procedure restenosis is still a significant concern. Gene therapy has emerged as a promising approach aimed at modification of cellular processes that give rise to restenosis. When juxtaposed alongside the failure of traditional pharmacotherapeutics to eliminate restenosis, gene therapy has engendered great expectations for cubing coronary restenosis. In this review we have discussed an overview of gene therapy approaches that hve been utilized to reduce restenosis in preclinical and clinical studies, current status of anti-restenosis gene therapy and perspectives on its future application. For brevity, we have limited our discussion on anti-restenosis gene therapy to the introduction of a nucleic acid to the cell, tissue, organ or organism in order to give rise to the expression of a protein, the function of which will confer therapeutic effect. For the purpose of this review, we have focused ou discussion on two relevant anti-restenosis strategies, anti-proliferative and pro-endothelialization.

Ischemic tissue repair by autologous bone marrow-derived stem cells: scientific basis and preclinical data

The success of therapies targeting acute myocardial ischemia and the aging of the population due to improved general medical care has resulted in an increasing population of patients with chronic myocardial ischemia and congestive heart failure who remain symptomatic despite having exhausted the currently available therapeutic options. In this chapter we review the scientific underpinnings of autologous bone marrow-derived cell therapy and the early clinical experience that has fuelled interest in this approach.

Adventitial VEGF165 gene transfer prevents lumen loss through induction of positive arterial remodeling after PTCA in porcine coronary arteries

Negative arterial remodeling still plays an important role in the pathogenesis of coronary restenosis even in the era of interventional stenting (e.g. arterial narrowing occurs proximal and distal of a stented segment). Previous studies suggest that increased angiogenesis and inhibited regression of injury-induced adventitial microvessels prevents negative remodeling. We have examined the effect of local vascular endothelial growth factor (VEGF(165)) gene transfer on adventitial microvessel angiogenesis/regression and arterial remodeling after coronary angioplasty. Twenty pigs underwent angioplasty, each one in two major coronary arteries, followed by plasmid liposome gene transfer with either VEGF(165) or control gene LacZ (50 microg DNA with 50 microg of Lipofectine) into the (peri)adventitial space using a needle injection catheter. Arteries were examined at days 1, 7, 14, and 28. Local delivery of VEGF(165) gene into the outer compartments of balloon-injured porcine coronary arteries reduced lumen area loss due to distinct positive remodeling (arterial enlargement). Prevention of adventitial microvessel regression, enhanced adventitial elastin accumulation, reduced adventitial myofibroblast numbers, and a pronounced adventitial inflammatory response considered as a part of arterial healing seem to be the main VEGF-mediated mechanisms indicating the therapeutic potential of VEGF for restenosis prevention.

Effects on blood compatibility in vitro by combining a direct P2Y12 receptor inhibitor and heparin coating of stents

The effect of the direct platelet P2Y12 receptor inhibitor, AR-C69931MX, on activation of blood induced by stents with and without heparin coating was investigated using a whole blood Chandler loop model in vitro. Stents were deployed in Chandler loops. Fresh human blood with heparin and AR-C69931MX was rotated for 1 h at 37 degrees C and used for measurements of platelets, microparticles, thrombin-antithrombin complex (TAT), fibrinogen binding to platelets, P-selectin expression by platelets, CD11b, Prothrombin Fragment F1+2, FXIa-AT, FXIIa-AT, C3a, sC5b-9 and stent score. In the first experiment there were four study groups with unmodified stents: 1a, no AR-C69931MX; 1b, 250 nmol/L; 1c, 750 nmol/L; 1d, 2250 nmol/L of AR-C69931MX. In the second experiment the concentration of AR-C69931MX was 500 nmol/L: 2a; tubings without stent; 2b; tubings with heparin-coated stent; 2c; tubings with unmodified stents. Heparin-coated stents were used in the third experiment: 3a; no AR-C69931MX; 3b; 500 nmol/L of AR-C69931MX. In the first experiment there were significant differences in all parameters analysed except for C3a, and stent score when the group with no AR-C69931MX was compared to all the groups with AR-C69931MX. In the second experiment there were significant differences in platelet count, TAT, FXIa-AT, FXIIa-AT and stent score when unmodified stents were compared to loops with no stents and partly to loops with heparin-coated stents. In the third experiment there was a significant reduction in generation of TAT, stent score and better preservation of platelet number by combining the platelet inhibitor and heparin-coated stents as compared to heparin-coated stents alone. The conclusion is that the direct P2Y12 receptor inhibitor AR-C69931MX reduced the different aspects of activation of blood induced by both unmodified and heparin-coated stents.

Effects of local gene transfer of VEGF on neointima formation after balloon injury in hypercholesterolemic rabbits

Enhancement of the generation of nitric oxide (NO) and vascular endothelial growth factor (VEGF) are suggested to prevent restenosis after angioplasty. Accordingly, we tested whether the local delivery of L-arginine (L-Arg), a substrate for NO generation and the VEGF gene, alone or in combination, can influence neointima formation in hypercholesterolemic rabbits. Balloon injury of the iliac arteries was performed in 24 New Zealand White rabbits fed a 1% cholesterol diet for 3 weeks followed by a local infusion of: (1) pSG5VEGF165 plasmid alone (1000 microg); (2) pSG5VEGF165 (1000 microg) with L-Arg (800mg); (3) L-Arg (800mg) alone; and (4) L-Arg (800 mg) with naked pSVbeta-gal plasmid (1000 microg). The animals were kept on the hypercholesterolemic diets for a further 28 days, when vessels were taken for morphometric analysis and immunocytochemistry. Endogenous rabbit VEGF concentration in the plasma increased significantly at 7 days after injury (17.06 +/- 1.57 vs 23.01 +/- 1.9 pg/ml; p < 0.02) and remained elevated for up to 28 days (28.46 +/- 5.24; p < 0.01). Injured arteries exhibited strong immunocytochemical staining for rabbit VEGF. Rabbits that received a VEGF gene transfer revealed more prominent neointima formation, whereas treatment with L-Arg was associated with significantly less intimal thickness (p < 0.05). Local transfer of the VEGF gene does not inhibit neointima formation in hypercholesterolemic rabbits. Our results suggest that VEGF gene therapy applied locally in atherosclerotic arteries may not be beneficial.

Proliferation of endothelial cell on polytetrafluoroethylene vascular graft materials carried VEGF gene plasmid

OBJECTIVE

To investigate whether vascular endothelial growth factor (VEGF) gene plasmid carried by polytetrafluoroethylene (PTFE) vascular graft materials could transfect endothelial cells (ECs) and promote their growth.

METHODS

PTFE vascular graft materials carried with pCDI-hVEGF(121), pCDI or pEGFP were incubated in Tris-buffer solution and the values of optical density of 260 nm at different time were plotted, then the DNA controlled release curve was made. ECs derived from human umbilical vein were seeded on the pCDI-hVEGF(121)/pCDI/pEGFP-PTFE materials or tissue culture plates, ECs numbers were counted and VEGF protein concentrations at different time were measured by enzyme-linked immunoadsorbent assay method. Green fluorescent protein (GFP) expression in ECs on pEGFP-PTFE materials was examined with fluorescence microscopy.

RESULTS

The controlled release curve showed that the gene released from PTFE materials was rapid within 8 h, then slowed down and that the gene released continuously even after 72 h. At 24, 72 and 120 h, ECs number and proliferation rate of pCDI-hVEGF(121)-PTFE materials were higher than those of pCDI or pEGFP-PTFE materials (P<0.05). VEGF protein concentration of pCDI-hVEGF(121)-PTFE materials was higher than that of pCDI or pEGFP-PTFE materials at 6, 24, 72 and 120 h (P<0.01). GFP expression in ECs on the pEGFP-PTFE materials could be detected by fluorescence microscopy.

CONCLUSION

PTFE graft can be used as a carrier of VEGF gene plasmid, VEGF gene carried by PTFE can transfect ECs and promote ECs growth.

Efficient transduction and seeding of human endothelial cells onto metallic stents using bicistronic pseudo-typed retroviral vectors encoding vascular endothelial growth factor

BACKGROUND

Stents seeded with genetically modified endothelial cells (EC) may provide an attractive therapeutic modality for treating vascular diseases by combining the mechanical properties of the metallic stent with the biologic activity of native or genetically engineered ECs. The clinical feasibility of implanting seeded stents depends on the ability to achieve adequate stent coverage within a clinically applicable time frame. We tested the hypothesis that this goal could be achieved by seeding stents with human ECs overexpressing vascular endothelial growth factor (VEGF) and by using an efficient gene transfer system.

METHODS AND RESULTS

Efficiency of gene transfer to human ECs using an amphotropic retroviral vector and a gibbon ape leukemia virus (GALV) pseudo-typed retroviral vector was examined and compared. For assessment of transduction rates, LacZ-encoding vectors were used and beta-galactosidase activity was determined 48 h after gene transfer. The transduction rate of primary human ECs using the amphotropic retroviral vector encoding the LacZ gene was low (2.9+/-2% of cells). Under the same conditions, the GALV pseudo-typed vector encoding LacZ transduced 94+/-2% of cells (P<.001). To test the effect of VEGF gene transfer on stent coverage, we transduced ECs using a bicistronic GALV pseudo-typed retroviral vector encoding either GFP alone or both VEGF and GFP. Since all transduced cells expressed GFP, stent coverage by ECs could be assessed by fluorescent inverted microscopy, which demonstrated that stent coverage by ECs overexpressing VEGF was more rapid and effective than coverage by ECs overexpressing GFP. Progressively increasing quantities of VEGF protein were detected in the conditioned medium of stents seeded with endothelia cells expressing VEGF 2, 3, and 5 days after seeding.

CONCLUSIONS

High-rate gene transfer to human primary ECs was observed 48 h after transduction with GALV pseudo-typed retroviral vectors, eliminating the need for the time-consuming process of cell selection. Seeding with ECs overexpressing VEGF improved stent coverage and was associated with continuing secretion of the protein. The findings provide support for the feasibility of implanting genetically engineered biologically active cellular-coated stents.

Histological postmortem study of an internal carotid artery aneurysm treated with the Neuroform stent

OBJECTIVE

Endovascular treatment of wide-necked and fusiform aneurysms has been advanced by the introduction of the flexible intracranial Neuroform stent (Boston Scientific/Target, Fremont, CA). It is recognized that these deployed intracranial stents are thrombogenic until endothelialization of the stent presumably takes place. We report here the first postmortem histological analysis of a patient with an internal carotid artery aneurysm treated with the Neuroform stent.

METHODS

A 51-year-old man had a right-sided supraclinoid internal carotid artery aneurysm. After discussions, he underwent elective stenting (Neuroform stent; 4.5 x 20 mm) across the neck of the aneurysm without complications. Repeat angiography at the 3-month follow-up examination revealed a decrease in size of the aneurysm. Attempted coiling at that time was unsuccessful. The patient died 1 month later of a left-sided intracranial hemorrhage (122 d after stent deployment), and, according to his wishes, his brain was donated for scientific study. On receipt, the right cavernous internal carotid artery was removed and sent for histological evaluation (Boston Scientific Laboratories, Fremont, CA).

RESULTS

The parent artery demonstrated mild intimal thickening proximal to the stent. The stent itself was noted to be abutting the internal elastic lamina with moderate intimal hyperplasia, but this was not noted to cause significant stenosis. The aneurysm was filled with fibrocellular tissue in the periphery, which extended along the neck. However, the midportion of the neck was void of any fibrocellular tissue, with thrombus-like material noted inside the aneurysm.

CONCLUSION

Cadaveric histological evaluation of the implanted Neuroform stent 4 months after stenting showed complete endothelialization of the stent and well as significant de novo fibroelastic tissue formation along the neck of the aneurysm. Longer follow-up studies are needed to evaluate the dynamics and delayed effects of endothelialization of the Neuroform stent.

VEGF polymorphisms and severity of atherosclerosis

INTRODUCTION

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor, and neovascularisation has been shown to be important in atherosclerotic plaque development. There is some disagreement as to whether VEGF acts as a pro-atherosclerotic or anti-atherosclerotic factor. In the present study we have sought to clarify this by determining genotypes and haplotypes for three reportedly functional VEGF SNPs in a large series of well documented coronary atherosclerosis patients.

METHODS

VEGF -2578, -1154, and -634 single nucleotide polymorphisms were genotyped in 984 subjects from the Southampton Atherosclerosis Study, using the 5' nuclease assay for allelic discrimination (TaqMan).

RESULTS

VEGF -2578 genotypes showed a significantly different distribution in patients without myocardial infarction when stratified according to number of diseased arteries. VEGF -2578 was also associated with mean number of stenotic segments in the same patient group. The AA genotype was a risk factor and CC was protective. These associations were significant before and after adjustment for classic risk factors, and were reflected in associations between VEGF haplotypes and the number of diseased arteries and stenotic segments. As VEGF -2578 CC has been provisionally shown to be associated with higher VEGF expression than the AA genotype, these results are consistent with a protective effect for VEGF in atherosclerosis development. Some changes in VEGF -1154 genotype frequencies were also detected, but no significant associations were detected for any one particular genotype.

CONCLUSIONS

This study provides preliminary evidence that VEGF polymorphism is associated with development of atherosclerosis, possibly via regulation of VEGF expression, supporting a protective effect for VEGF in atherosclerosis. These results require replication in an independent study group, combined with study of additional candidate polymorphisms in the VEGF gene.

Adventitial Microvessel Formation After Coronary Stenting and the Effects of SU11218, a Tyrosine Kinase Inhibitor

OBJECTIVES

The aim of this study was to delineate the temporal profile of adventitial microvessel (Ad-MV) formation after stenting, its relationship to arterial wall hypoxia, and the effects of a tyrosine kinase inhibitor (TKI), SU11218, on Ad-MV and in-stent intimal hyperplasia (IH).

BACKGROUND

Adventitial microvessels have been reported after arterial injury; however, the underlying stimulus for this response and its relationship to IH is unknown.

METHODS

Coronary stenting was performed in 40 pigs randomized to SU11218 (n = 20) or placebo (n = 20). Vessel wall hypoxia was assessed by pimonidazole adducts and hypoxia-inducible factor (HIF)-1 alpha expression. Adventitial microvessels were quantified by three-dimensional microscopic computed tomography (3D micro CT). Intimal hyperplasia was measured by intravascular ultrasound (IVUS), 3D micro CT, and morphometry. The effects of SU11218 were assessed in vitro on smooth muscle cell (SMC) and endothelial cell (EC) functions and in vivo on Ad-MV and IH.

RESULTS

Hypoxia was evident in the vessel wall at 48 h and persisted for four weeks. Adventitial microvessels increased significantly at one week (24 +/- 7 microvessels/segment) and four weeks (23 +/- 7 microvessels/segment) compared with uninjured arteries (16 +/- 2 microvessels/segment; p < 0.001) and correlated with IH (r = 0.77, p < 0.001). The TKI SU11218 inhibited platelet-derived growth factor receptor-beta phosphorylation, EC and SMC DNA synthesis, and migration in a dose-dependent manner in vitro and significantly inhibited Ad-MV (16 +/- 5 vs. 23 +/- 7 microvessels/segment in placebo, p < 0.001) and produced approximately 80% reduction in IH (0.52 +/- 0.51 mm2 vs. 2.47 +/- 1.66 mm2 in placebo, p < 0.001) at four weeks in vivo.

CONCLUSIONS

Arterial stenting causes arterial wall hypoxia followed by Ad-MV formation. The TKI SU11218 inhibits both Ad-MV formation and IH and represents a promising therapeutic agent to prevent in-stent restenosis.

Drug-Eluting Coronary Stents

The introduction and widespread use of coronary stents have been the most important advancement in the percutaneous treatment of coronary artery disease since the introduction of balloon angioplasty. Coronary artery stents reduce the rate of angiographic and clinical restenosis compared to balloon angioplasty. This angiographic restenosis was further reduced with the introduction of drug-eluting stents and hence further reduction in the frequency of major adverse cardiac events. Herein we present a comprehensive and up-to-date review about the use of drug-eluting stents in the treatment of coronary artery disease.

Influence of various cell-detachment solutions on endothelial cells after catheter abrasion for prosthesis colonization prior to implantation

We (1) evaluated the effectiveness of different media on the detachment of endothelial cells (ECs) from a catheter brush (Cragg thrombolytic catheter system) that was previously used for endothelial cell abrasion in 10 cm human umbilical vein (HUV) segments; (2) tested the practicability of endovascular catheter brush abrasion followed by EC detachment from the catheter brush, in vitro culture of harvested ECs, and finally endothelialization of a prosthesis; and (3) analyzed the defect created by the catheter brush in HUV segments after endovascular catheter abrasion. Best results in detachment of ECs from the catheter brush were obtained with a mixture of phosphate-buffered saline + 1% human albumin. EC vitality was time-dependent in the collected HUV segments postdelivery. Harvested EC viability decreased from (26.28 +/- 5.76)% (0-3 h postdelivery) to (17.29 +/- 4.56)% (after 4-8 h). ECs were easily cultured ex vivo within 2-3 weeks; seeded on nitinol stents, they grew to confluency and formed a monolayer on the stent surface (determined by scanning electron microscopy - SEM). Histological and SEM analysis of HUV segments that had undergone previous catheter brush abrasion revealed slight disruption of the intima but intact subintimal layers. Our findings indicate an advantageous method of capturing and culturing primary ECs for gene therapy or for the analysis and diagnosis of certain blood vessel diseases, especially in cases in which endovascular intervention is performed anyway. Moreover, and of high relevance to the biomaterial field, theoretically the procedure could be used to endothelialze a prosthesis ex vivo for implantation into the patient from whom the ECs were harvested, to reduce the inherent thrombogenicity of the prosthesis.

Hypoxic regulation of VEGF, HIF-1(alpha) in coronary collaterals development

BACKGROUND

The interindividual variability for the development of collaterals in coronary artery disease is dependent on the hypoxic induction level of VEGF. To determine whether the hypoxic induction of VEGF is controlled by the transcription of HIF-1 (alpha), the VEGF and HIF-1 (alpha) m-RNA levels were correlated to hypoxia in monocytes harvested from patients with coronary artery disease.

METHODS

The collateral scoring system used was modified from the TIMI system. The mononuclear cell layer of the patients' blood was cultured in hypoxia (1% O2, 5% CO2, 94%N2) and normoxia (5% CO2, 95% room air) for 17 hours. The VEGF and HIF-1 (alpha) mRNA levels were measured using a RT-PCR technique. We calculated the fold inductionsof VEGF, HIF-1 (alpha) mRNA with hypoxia by dividing the hypoxic and the normoxic values.

RESULTS

We found significantly higher hypoxic inductions of VEGF m-RNA in patients with collaterals compared to patients with no collaterals. However, there was no differencein the hypoxic inductions of HIF-1 (alpha) between the two groups (VEGF m-RNA mean fold inductions 3.71 +/- 3.30 versus 1.65 +/- 0.62, p=0.012, HIF-1(alpha) mRNA 1.42 +/- 0.58 versus 1.20 +/- 0.39, p=0.165).

CONCLUSIONS

We concluded that the interindividual variability in the hypoxic inductions of VEGF m-RNA in monocytes in patients is not controlled by the transcriptional levels of HIF-1 (alpha) with hypoxia. These findings suggest that a mechanism such as the post-transcriptional modification of HIF-1(alpha) is involved in the hypoxic inductions of VEGF.

Serum hepatocyte growth factor levels predict long-term clinical outcome after percutaneous coronary revascularization

AIMS

To evaluate, in patients referred for elective percutaneous coronary revascularization (PCR) without heparin pre-treatment, the relationship between baseline serum levels of the angiogenic growth factors, vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF), and clinical outcome.

METHODS AND RESULTS

In 488 consecutive patients undergoing elective coronary angioplasty, hsC-reactive protein, HGF, and VEGF levels were measured before heparin administration. The primary endpoint, a composite of death and myocardial infarction, occurred in 44 patients at a median follow-up of 14.9 months. At baseline, VEGF levels were related to C-reactive protein levels and inversely related to age; HGF levels were related to C-reactive protein levels, diabetes, and recent clinical instability. In the univariate analysis, HGF had a significant positive relationship (P=0.003) with the primary endpoint. A similar trend was observed for VEGF (P=0.11). The only three variables significantly associated with the primary endpoint in the multivariable Cox model were HGF (P=0.004), C-reactive protein (P=0.007), and diabetes (P=0.04).

CONCLUSION

Our results demonstrate that in patients, without heparin pre-treatment, referred for PCR, a high serum level of HGF is an independent predictor of clinical events during follow-up and is correlated with other surrogate measures of the activity of atherosclerosis.

Poly(N-isopropylacrylamide) copolymer films as vehicles for the sustained delivery of proteins to vascular endothelial cells

The aim of this study was to establish the capacity of thermoresponsive poly(N-isopropylacrylamide) copolymer films to deliver bioactive concentrations of vascular endothelial growth factor (VEGF165) to human aortic endothelial cells (HAEC) over an extended time period. Films were prepared using a 50:50 (w/w) mixture of non-crosslinkable and crosslinkable copolymers of the following monomer compositions (w/w): 85:15, N-isopropylacrylamide (NiPAAm):N-tert-butylacrylamide (NtBAAm); and 85:13:2 NiPAAm:NtBAAm:acrylamidobenzophenone (ABzPh, crosslinking agent), respectively. After crosslinking by UV irradiation, the ability of films to incorporate a fluorescently labeled carrier protein (FITC-labeled BSA, 1 mg loaded per film), at 4 degrees C, was first established. Incorporation into the matrix was confirmed by the observation that increasing film thickness from 5 to 10 microm increased release from collapsed films at 37 degrees C (1.76 +/- 0.15 and 10.98 +/- 3.38 microg/mL, respectively, at 24 h postloading) and that this difference was maintained at 5 days postloading (1.81 +/- 0.25 and 13.8 +/- 2.3 microg/mL, respectively). Incorporation was also confirmed by visualization using confocal microscopy. When 10-microm films were loaded with a BSA solution (1 mg/mL) containing VEGF165 (3 microg/mL), sustained release of VEGF165 was observed (10.75 +/- 3.11 ng at 24 h; a total of 31.32 +/- 8.50 ng over 7 days). Furthermore, eluted VEGF165 increased HAEC proliferation by 18.2% over control. The absence of cytotoxic species in medium released from the copolymer films was confirmed by the lack of effect of medium (incubated with copolymer films for 3 days) on HAEC viability. In conclusion this study has shown that NiPAAm:NtBAAm copolymers can be loaded with a therapeutic protein and can deliver bioactive concentrations to human vascular endothelial cells over an extended time period.

Improved blood compatibility of a stent graft by combining heparin coating and abciximab

The aim of this study was to assess the combined effect of heparin coating of a stent graft and administration of abciximab, on platelet and coagulation activity in vitro.

METHODS

Stent grafts with an expanded polytetrafluoroethylene (ePTFE) membrane interfoliated between two stents were deployed in tubings to form Chandler loops. Fresh human blood with a low concentration of heparin and various doses of abciximab was rotated for 1 h, then collected and used for measurements of platelets, thrombin-antithrombin complex (TAT), CD11b, complement and contact activation of coagulation. In the first set of experiments, all stent grafts were heparin coated. There were three study groups: Group 1a (no abciximab, n=5); Group1b (abciximab in a concentration of 3.3 microg/ml, n=5); Group 1c (abciximab in a concentration of 8.3 microg/ml, n=5). In the second set of experiments, the concentration of abciximab was 3.3 microg/ml. There were three study groups: Group 2a (untreated stent grafts, n=4); Group 2b (heparin-coated stent grafts, n=4); Group 2c (heparin-coated PVC tubings with no stent grafts, n=4).

RESULTS

In the first set of experiments, there was a significant reduction in platelet count in Group 1c compared to Group 1a and Group 1b. There was a significant reduction in TAT in Group 1b and Group 1c as compared to Group 1a. In the second set of experiments, TAT was reduced in Group 2b and Group 2c compared to Group 2a. Contact activation was lowered in Group 1b and Group 1c as compared to Group 1a for both FXIa-AT (0.088 and 0.088 vs. 0.115) and FXIIa-AT (0.12 and 0.12 vs. 0.19).

CONCLUSION

Heparin coating of a stent graft was shown to improve blood compatibility and this was further enhanced by addition of abciximab.

Intratumoural administration of dendritic cells: hostile environment and help by gene therapy

Like paratroopers in special operations, dendritic cells (DCs) can be deployed behind the enemy borders of malignant tissue to ignite an antitumour immune response. 'Cross-priming T cell responses' is the code name for their mission, which consists of taking up antigen from transformed cells or their debris, migrating to lymphoid tissue ferrying the antigenic cargo, and meeting specific T cells. This must be accomplished in such an immunogenic manner that specific T lymphocytes would mount a robust enough response as to fully reject the malignancy. To improve their immunostimulating activity, local gene therapy can be very beneficial, either by transfecting DCs with genes enhancing their performance, or by preparing tumour tissue with pro-inflammatory mediators. In addition, endogenous DCs from the tumour host can be attracted into the malignant tissue following transfection of certain chemokine genes into tumour cells. On their side, tumour stroma and malignant cells set up a hostile immunosuppressive environment for artificially released or attracted DCs. This milieu is usually rich in transforming growth factor-beta, vascular endothelial growth factor, and IL-10, -6 and -8, among other substances that diminish DC performance. Several molecular strategies are being devised to interfere with the immunosuppressive actions of these substances and to further enhance the level of anticancer immunity achieved after artificial release of DCs intratumourally.