Angiogenic synergism, vascular stability and improvement of hind-limb ischemia by a combination of PDGF-BB and FGF-2

A Novel Approach to Therapeutic Angiogenesis for Patients With Critical Limb Ischemia by Sustained Release of Basic Fibroblast Growth Factor Using Biodegradable Gelatin Hydrogel An Initial Report of the Phase I-IIa Study

BACKGROUND

Limb ischemia remains a challenge. To overcome shortcomings or limitations of gene therapy or cell transplantation, a sustained release system of basic fibroblast growth factor (bFGF) using biodegradable gelatin hydrogel has been developed.

METHODS AND RESULTS

A phase I-IIa study was performed, in which 7 patients had critical limb ischemia. They were intramuscularly injected with 200 microg of bFGF-incorporated gelatin hydrogel microspheres into the gastrocnemius of the ischemic limb. End-points were safety and feasibility of treatment after 4 and 24 weeks. One patient was excluded from the study for social reasons, but only after symptomatic improvements. In the evaluation of the other 6 patients, significant improvements were observed in the distance walked in 6 min (295+/-42 m vs 491+/-85 m for pretreatment vs after 24 weeks, p=0.023) and in transcutaneous oxygen pressure (53.5+/-5.2 mmHg vs 65.5+/-4.0 mmHg, p=0.03). The rest pain scale also improved (3.5+/-0.2 vs 1.0+/-0.6, p=0.022). The ankle-brachial pressure index improved at 4 weeks but not at 24 weeks. Among 5 patients who had a non-healing foot ulcer, the ulcer was completely healed in 3 patients, reduced in 1, and there was no change in 1 patient at 24 weeks. The blood levels of bFGF were undetected or within the normal level in all patients.

CONCLUSIONS

The sustained release of bFGF from gelatin hydrogel might be simple, safe, and effective to achieve therapeutic angiogenesis because it did not need genetic materials or collection of implanted cells, and because it did not have any general effects, which was supported by there being no elevation of the bFGF serum level.

Therapeutic Targets of Multiple Angiogenic Factors for the Treatment of Cancer and Metastasis

Like any growing healthy tissues, tumors build up their blood vessels by three mechanisms: angiogenesis, vasculogenesis, and intersucception. Vascular endothelial growth factor-A (VEGF-A) is one of the key factors responsible for stimulation and maintenance of the disorganized, leaky, and torturous tumor vasculature. In addition to VEGF-A, tumors produce multiple other factors to stimulate blood vessel growth. These include members in the platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), VEGF-C, insulin-like growth factor (IGF), angiopoietin (Ang), and hepatocyte growth factor (HGF) families. Recent studies show that these angiogenic factors can also promote lymphangiogenesis and potentially lymphatic metastasis. Understanding the roles of individual and combined angiogenic factors in promoting tumor angiogenesis is crucial for defining therapeutic targets and antiangiogenic drug development for the treatment of cancer.

Vascular Wall Maturation and Prolonged Angiogenic Effect by Endothelial-Specific Platelet-Derived Growth Factor Expression

BACKGROUND

The implementation of angiogenic gene therapy at clinics is hindered by the transience of the therapeutic effect. Recruiting vascular wall smooth muscle cells, a process termed 'maturation', can stabilize newly formed vessels.

OBJECTIVE

To induce angiogenesis followed by vessel maturation in a murine ischemic limb model by endothelial cell-specific promoter regulated expression of vascular endothelial growth factor (VEGF) and platelet-derived growth factor-BB (PDGF-BB).

METHODS

We constructed adenoviral vectors containing angiogenic factors VEGF and PDGF-B regulated by a modified preproendothelin-1 (PPE-1-3x) promoter and investigated their angiogenic effect in a murine ischemic limb model.

RESULTS

VEGF gene therapy increased perfusion and the vessel density in the limb shortly after expression with PPE-1-3x promoter or cytomegalovirus (CMV) promoter vectors, but only PPE-1-3xVEGF treatment exhibited a sustained effect. Expression of PDGF-B by PPE-1-3x promoter resulted in morphological maturation of the vasculature and further increased the perfusion, while nonspecific expression of PDGF-B with CMV promoter had no therapeutic effect. Regulation of dual therapy with VEGF and PDGF-B by PPE-1-3x promoter resulted in an early-onset, sustained angiogenic effect accompanied by vessel maturation.

CONCLUSIONS

Systemic gene therapy with the angiogenic factors VEGF and PDGF-B under angiogenic- endothelial cell-specific regulation was effective in inducing functionally and morphologically mature vasculature.

Therapeutic angiogenesis using novel vascular endothelial growth factor-E/human placental growth factor chimera genes

BACKGROUND

Vascular endothelial growth factor-A (VEGF-A) promotes angiogenesis but causes adverse side effects such as edema or tissue inflammation. VEGF-E, found in the genome of the Orf virus, specifically binds to VEGF receptor-2 and shows mitotic activity on endothelial cells. Recently, we created two forms of VEGF-E and human placental growth factor (PlGF) chimera genes (VEGF-E chimera #9 and VEGF-E chimera #33), which are humanized genes with VEGF-E function but showing less antigenicity.

METHODS AND RESULTS

We examined potential proangiogenic activities of these chimera genes. Four types of expression plasmids (pCDNA3.1-LacZ, phVEGF-A, pVEGF-Echimera#9, and pVEGF-Echimera#33) were administered in a rat model of hindlimb ischemia. Either pVEGF-Echimera#9, pVEGF-Echimera#33, or phVEGF-A significantly increased the ratio of ischemic/normal hindlimb blood-flow compared with the control pCDNA3.1-LacZ treated group (by 1.5-fold, 1.5-fold, and 1.4-fold, respectively, P<0.05). Histochemical staining by alkaline phosphatase also revealed that either pVEGF-Echimera#9, pVEGF-Echimera#33, or phVEGF-A increased the capillary density compared with the pCDNA3.1-LacZ treated group (1.4-fold, 1.5-fold, and 1.5-fold, respectively, P<0.05). Furthermore, immunostaining for anti-ED1 revealed that fewer macrophages had infiltrated in both pVEGF-Echimera#9 and pVEGF-Echimera#33 groups compared with the phVEGF-A group (P<0.05).

CONCLUSIONS

Novel VEGF-E/human PlGF chimera genes, pVEGF-Echimera#9, and pVEGF-Echimera#33 significantly stimulated angiogenesis in response to tissue ischemia to an almost identical extent to that induced by phVEGF-A with fewer tissue inflammation responses.

Application of bFGF and BDNF to Improve Angiogenesis and Cardiac Function

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a survival factor for endothelial cells and expresses in the ischemic myocytes. The purpose of this study was to assess whether the simultaneous application of basic fibroblast growth factor (bFGF) and BDNF incorporating gelatin hydrogels improves angiogenesis and cardiac function in ischemic myocardium compared with bFGF applied alone.

MATERIALS AND METHODS

Direct intramyocardial injection of 100 microg of bFGF plus 25 microg of BDNF, 100 microg of bFGF, or saline were performed in canine infarct model. Colored microspheres were injected to assess the regional myocardial blood flow. Cardiac function was evaluated by cine magnetic resonance imaging (MRI). Immunohistochemical staining and enzyme linked immunosorbent assay (ELISA) were used to observe the localization and expression of bFGF and BDNF protein, and myocardial microvessel density was assessed by von Willebrand factor staining.

RESULTS

Left ventricular ejection fraction (LVEF) was higher in bFGF plus BDNF group than in saline or bFGF group. Blood flow of the peri-infarct region was increased by bFGF plus BDNF treatment. The distribution of bFGF and BDNF-positive cardiomyocytes was similar in three groups. The expression of bFGF and BDNF protein and microvessel density in bFGF plus BDNF group was higher than in the other two groups.

CONCLUSIONS

This study indicates that the sustained dual release of bFGF and BDNF incorporating gelatin hydrogels can improve angiogenesis and left ventricular function in the ischemic myocardium compared with bFGF applied alone. bFGF plus BDNF administration may be a promising therapeutic strategy for the treatment of ischemic myocardium.

Principles and therapeutic implications of angiogenesis, vasculogenesis and arteriogenesis

The vasculature is the first organ to arise during development. Blood vessels run through virtually every organ in the body (except the avascular cornea and the cartilage), assuring metabolic homeostasis by supplying oxygen and nutrients and removing waste products. Not surprisingly therefore, vessels are critical for organ growth in the embryo and for repair of wounded tissue in the adult. Notably, however, an imbalance in angiogenesis (the growth of blood vessels) contributes to the pathogenesis of numerous malignant, inflammatory, ischaemic, infectious and immune disorders. During the last two decades, an explosive interest in angiogenesis research has generated the necessary insights to develop the first clinically approved anti-angiogenic agents for cancer and blindness. This novel treatment is likely to change the face of medicine in the next decade, as over 500 million people worldwide are estimated to benefit from pro- or anti-angiogenesis treatment. In this following chapter, we discuss general key angiogenic mechanisms in health and disease, and highlight recent developments and perspectives of anti-angiogenic therapeutic strategies.

Preclinical activity of ABT-869, a multitargeted receptor tyrosine kinase inhibitor

ABT-869 is a structurally novel, receptor tyrosine kinase (RTK) inhibitor that is a potent inhibitor of members of the vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptor families (e.g., KDR IC50 = 4 nmol/L) but has much less activity (IC50s > 1 micromol/L) against unrelated RTKs, soluble tyrosine kinases, or serine/threonine kinases. The inhibition profile of ABT-869 is evident in cellular assays of RTK phosphorylation (IC50 = 2, 4, and 7 nmol/L for PDGFR-beta, KDR, and CSF-1R, respectively) and VEGF-stimulated proliferation (IC50 = 0.2 nmol/L for human endothelial cells). ABT-869 is not a general antiproliferative agent because, in most cancer cells, >1,000-fold higher concentrations of ABT-869 are required for inhibition of proliferation. However, ABT-869 exhibits potent antiproliferative and apoptotic effects on cancer cells whose proliferation is dependent on mutant kinases, such as FLT3. In vivo ABT-869 is effective orally in the mechanism-based murine models of VEGF-induced uterine edema (ED50 = 0.5 mg/kg) and corneal angiogenesis (>50% inhibition, 15 mg/kg). In tumor growth studies, ABT-869 exhibits efficacy in human fibrosarcoma and breast, colon, and small cell lung carcinoma xenograft models (ED50 = 1.5-5 mg/kg, twice daily) and is also effective (>50% inhibition) in orthotopic breast and glioma models. Reduction in tumor size and tumor regression was observed in epidermoid carcinoma and leukemia xenograft models, respectively. In combination, ABT-869 produced at least additive effects when given with cytotoxic therapies. Based on pharmacokinetic analysis from tumor growth studies, efficacy correlated more strongly with time over a threshold value (cellular KDR IC50 corrected for plasma protein binding = 0.08 microg/mL, >or=7 hours) than with plasma area under the curve or Cmax. These results support clinical assessment of ABT-869 as a therapeutic agent for cancer.

Heparin binding nanostructures to promote growth of blood vessels

Controlling new blood vessel formation is of interest in regenerative medicine and cancer treatment. Heparin, a biopolymer that binds to angiogenic growth factors, was used to nucleate the self-assembly of nanostructures from designed peptide amphiphile molecules. This process yields rigid nanofibers that display heparin chains to orient proteins for cell signaling. In vivo, the nanostructures stimulated extensive new blood vessel formation using nanogram amounts of growth-factor proteins that by themselves did not induce any detectable angiogenesis.

Abdominal Aortic Aneurysm Rupture Is Associated With Increased Medial Neovascularization and Overexpression of Proangiogenic Cytokines

Objective— Matrix metalloproteinase (MMP) activity has been linked to abdominal aortic aneurysm (AAA) rupture. Medial neovascularization (MNV), a histopathologic characteristic of AAAs, involves proteolytic degradation of extracellular matrix by MMPs to facilitate endothelial cell migration. The role of MNV in aneurysm rupture is unknown. This study investigated whether MNV is increased in aneurysm rupture.

Methods and Results— Biopsy samples from aneurysm rupture edge were compared with control biopsy samples from aneurysm wall at the level of rupture and from anterior sac in 12 ruptured AAAs. Further controls were obtained from anterior sac of 10 nonruptured AAAs. MNV, microvessel diameter, maturity index, and inflammatory infiltrate were quantified using morphometric analyses following immunohistochemistry. Expression of proangiogenic mediators was quantified using quantitative real-time-polymerase chain reaction. Compared with anterior sac and aneurysm wall at level of rupture, MNV was increased ( P <0.001) in rupture edge biopsy samples and consisted of smaller diameter ( P <0.001) and more immature microvessels ( P <0.001). mRNA expression of α v -integrin, vascular endothelial growth factor, vascular endothelial-cadherin, monocyte chemoattractant protein-1, and vimentin was increased ( P <0.05) in rupture edge biopsy samples.

Conclusions— This study demonstrated increased medial neovascularization and overexpression of proangiogenic cytokines at aneurysm rupture edge. Further investigations into whether this angiogenic response was a causative factor of aneurysm rupture are needed.

Endothelial progenitor cells transfected with PDGF: cellular and molecular targets for prevention of diabetic microangiopathy

Microvascular insufficiency represents a major cause of end-organ failure among diabetics. Prevention at early stage of disease is therefore necessary and is a focus of current investigations. Progression of diabetes is complicated by endothelial cell apoptosis as well as occlusion of arteriole and capillary leading to microvascular rarefaction. This favors the formation of non-healing limb ulcers and limits the benefit of revascularization. Recent study indicated that reduction of platelet derived growth factor (PDGF) expression was indeed critical, in causing functional and morphological vascular changes, namely the dissociation of pericytes from the capillaries in muscles. Diabetic microangiopathy is a result of pericytes dissociation from reduced PDGF as well as vessel rarefaction from reduced number of endothelial progenitor cells (EPCs) and EPC dysfunction. Since blood vessels develop through the assembly of these two principal cell types--endothelial cells and pericytes/smooth muscle cells, prevention of diabetic microangiopathy requires interventions targeting at both cell types in a complementary and synergistic manner. An improved recruitment of EPCs will help repair of injured endothelium while molecular targeting with PDGF will enhance pericytes recruitment. EPCs modified with PDGF therefore hold promise as the next generation of agents for prevention of microangiopathy.

Improved angiogenic response in pig heart following ischaemic injury using human skeletal myoblast simultaneously expressing VEGF165 and angiopoietin-1

OBJECTIVE

To achieve angiogenic interaction between VEGF(165) and angiopoietin-1 (Ang-1) using a novel adenoviral bicistronic vector (Ad-Bic) encoding the two factors and delivered ex vivo using sex-mismatched human skeletal myoblasts.

METHODS AND RESULTS

A myocardial infarction model was developed in 29 female pigs; randomised into four groups: DMEM (group-1, n=6); Adenovirus null (Ad-null) vector-myoblast (group-2, n=5); Ad-Ang-1 myoblast (group 3, n=7) and Ad-Bic-myoblast (group-4, n=11). Three weeks later, 5 ml DMEM without myoblasts or containing 3 x 10(8) myoblasts carrying lac-z gene and transduced with Ad-null, Ad-Ang-1 or Ad-Bic were injected intra-myocardially in and around the infarct. 2D-echocardiography and fluorescent microsphere studies 6- and 12-weeks post-treatment revealed significantly improved cardiac performance and regional blood flow in groups 3 and 4. Histological studies and Y-chromosome analysis revealed extensive survival of lac-z positive myoblasts staining positive for human proteins in the pig heart. ELISA, immunostaining and RT-PCR revealed that Ad-Bic transduced myoblasts concomitantly but transiently expressed hVEGF(165) and Ang-1 both in vitro and in vivo. Double fluorescent immunostaining of the tissue sections for vWFactor-III and smooth muscle actin showed significantly higher vascular density of mature blood vessels per low power microscopic field in groups 3 and 4 at 6- and 12-weeks.

CONCLUSION

Our combined approach led to enhanced angiogenesis with a greater percentage of functionally mature blood vessels in a porcine heart.

Current state and perspective on medical treatment of critical leg ischemia: gene and cell therapy

Critical limb ischemia (CLI) is a severe disease associated with a high risk of amputation and mortality. In patients who cannot be revascularized, several medical options have been tested, including the use of prostanoids, spinal cord stimulation, and lumbar sympathectomy. None of these treatments has demonstrated a benefit on the amputation rates after 6 months of follow-up; these treatments cannot therefore be recommended for CLI treatment in patients for whom surgery is not an option. In this setting, gene therapy and cell therapy to stimulate angiogenesis have been tested mainly in phase I and II clinical trials and are reviewed in this article. These studies demonstrated the short-term safety and feasibility of these new approaches, but larger randomized studies remain necessary to demonstrate their clinical benefits and longterm safety.

Analysis of aromatase and 17beta-hydroxysteroid dehydrogenase type 2 messenger ribonucleic acid expression in deep endometriosis and eutopic endometrium using laser capture microdissection

OBJECTIVE

To investigate mRNA expression of aromatase and 17beta-hydroxysteroid dehydrogenase type 2 (17betaHSD2) in epithelial and stromal cells from eutopic and ectopic endometrium of patients with deep endometriosis.

DESIGN

Prospective study.

SETTING

University hospital.

PATIENT(S)

Patients with deep endometriosis and fertile women with macroscopically normal pelvic cavities.

INTERVENTION(S)

During surgery, 30 endometrial and 16 endometriotic samples were obtained from 30 patients with deep endometriosis. Control endometrial samples were obtained from 24 fertile women with macroscopically normal pelvic cavities who underwent laparoscopic tubal ligation or reversal of tubal sterilization. Epithelial cells and stromal cells from endometrial or endometriotic tissues were microdissected using laser capture microdissection.

MAIN OUTCOME MEASURE(S)

Expression levels of aromatase and 17betaHSD2 mRNA in microdissected epithelial and stromal cells were determined using quantitative real-time reverse transcriptase polymerase chain reaction.

RESULT(S)

Aromatase mRNA expression was significantly higher in epithelial cells than in stromal cells in both eutopic and ectopic endometrium obtained from endometriosis patients. In the ectopic endometrium of 8 patients (8/16, 50%), 17betaHSD2 expression was not detected in either epithelial or stromal cells. In eutopic endometrium from endometriosis patients, 17betaHSD2 expression in epithelial cells was significantly increased during the early, middle, and late secretory phases compared with the late proliferative phase, whereas no significant cyclical difference was detected in control endometrium.

CONCLUSION(S)

Local estrogen concentration may be much higher in epithelial cells than in stromal cells in deep endometriotic tissue.

Hepatocyte growth factor is a lymphangiogenic factor with an indirect mechanism of action

Hepatocyte growth factor (HGF) has previously been reported to act as a hemangiogenic factor, as well as a mitogenic factor for a variety of tumor cells. Here, we demonstrate that HGF is a lymphangiogenic factor, which may contribute to lymphatic metastasis when overexpressed in tumors. In a mouse corneal lymphangiogenesis model, implantation of HGF induces sprouting and growth of new lymphatic vessel expressing the lymphatic vessel endothelial specific marker hyaluronan receptor-1 (Lyve-1). Unlike blood vessels, the Lyve-1-positive structures consist of blunt-ended vessels of large diameters that generally lack expression of CD31. The growth of HGF-induced lymphatic vessels can be partially blocked by a soluble VEGFR-3, suggesting that HGF may stimulate lymphatic vessel growth through an indirect mechanism. Consistent with this finding, the HGF receptor (c-Met) is only localized on corneal blood vessels but is absent on lymphatic vessels in a mouse corneal assay. In a transgenic mouse model that expresses HGF under the control of the whey acidic protein (WAP) gene promoter, transgenic females develop tumors in the mammary glands after several pregnancies. Interestingly, dilated Lyve-1-positive lymphatic vessels accumulate in the peritumoral area and occasionally penetrate into the tumor tissue. Our findings indicate that HGF may play a critical role in lymphangiogenesis and potentially contribute to lymphatic metastasis.

A review of new developments in tissue engineering therapy for periodontitis

This article focuses on recent advances in the regeneration of periodontium using tissue engineering and examines new technologies that will lead to further advances in periodontal therapy. The various advantages and drawbacks of protein-based, cell-based, and genetic-engineering approaches are evaluated. The debate between those who aim to regenerate periodontal tissues and researchers who have focused on the reconstitution of structural elements of the teeth is examined. The isolation of human dental stem cells from deciduous and adult wisdom teeth might hold the key to allowing the replacement of teeth and the regeneration of supporting tissue. The combination of scientific research, following on from advances in other fields, with clinical research in dentistry could yield a solution to the debilitating and widespread problem of periodontitis.

Combined Sustained Delivery of Basic Fibroblast Growth Factor and Administration of Granulocyte Colony-Stimulating Factor:Synergistic Effect on Angiogenesis in Mouse Ischemic Limbs

PURPOSE

To investigate whether the efficacy of a single angiogenic therapy (sustained delivery of basic fibroblast growth factor [bFGF] or administration of granulocyte colony-stimulating factor [G-CSF]) can be enhanced further by combining the therapies.

METHODS

One day after surgical induction of hind-limb ischemia, groups of 6 mice were randomized to receive either no treatment, sustained delivery (SD) of bFGF, endothelial progenitor cell (EPC) mobilization with G-CSF administration, or a combination of bFGF SD + G-CSF administration.

RESULTS

G-CSF administration increased significantly (p < 0.05) the number of EPC lineages (CD34 + /AC133 + cells) in both peripheral blood and bone marrow compared to no G-CSF administration. The bFGF SD and G-CSF administration individually increased the capillary and arteriole densities significantly versus no treatment (capillary density: 659 +/- 48/mm2 and 385 +/- 59/mm2, respectively, versus 280 +/- 28/mm2; p < 0.05; arteriole density: 34 +/- 9/mm2 and 41 +/- 6/mm2, respectively, versus 15 +/- 2/mm2; p<0.05). Importantly, bFGF SD + G-CSF further increased the capillary and arteriole densities compared to either strategy alone (capillary density: 786 +/- 40/mm2 versus 659 +/- 48/mm2 and 385 +/- 59/mm2, respectively, p < 0.05; arteriole density: 55 +/- 10/mm2 versus 34 +/- 9/mm2 and 41 +/- 6/mm2, respectively, p < 0.05).

CONCLUSION

This study demonstrates that the combined therapy of sustained bFGF delivery and G-CSF administration potentiates the angiogenic efficacy of either single therapy in mouse hind-limb ischemia models.

Delivery of sphingosine 1-phosphate from poly(ethylene glycol) hydrogels

While protein growth factors promote therapeutic angiogenesis, delivery of lipid factors such as sphingosine 1-phosphate (S1P) may provide better stabilization of newly formed vessels. We developed a biomaterial for the controlled delivery of S1P, a bioactive lipid released from activated platelets. Multiarm poly(ethylene glycol)-vinyl sulfone was cross-linked with albumin, a lipid-transporting protein, to form hydrogels. The rate of S1P release from the materials followed Fickian kinetics and was dependent upon the presence of lipid carriers in the release solution. Delivery of S1P from RGD-modified hydrogels increased the cell migration speed of endothelial cells growing on the materials. The materials also induced angiogenesis in the chorioallantoic membrane assay. Our data demonstrate that the storage and release of lipid factors provides a new route for the induction of angiogenesis by artificial materials.

MEK hyperphosphorylation coincides with cell cycle shut down of cultured smooth muscle cells

Smooth muscle cells (SMCs) form the backbone of arteries and their proliferation hallmarks collateral vessel growth, a process termed arteriogenesis, as well as pathogenic responses such as restenosis. Since signaling pathways in SMCs are the main targets for therapeutic interventions, we aimed to determine how and to what extent the activation of the ubiquitous MEK-ERK signaling pathway correlates with important in vivo phenomena such as dedifferentiation, nuclear activation and proliferation of SMCs. Specificity of this pathway was monitored using MEK inhibitors UO126 and PD98059 in platelet derived growth factor-AB (PDGF-AB)- and fibroblast growth factor-2 (FGF-2)-stimulated SMCs. PDGF-AB induced a rapid MEK activation followed by phosphorylation of the MEK substrates ERK1/2 while FGF-2 showed a less pronounced and delayed activation. Both growth factors triggered a marked phosphorylation of c-Myc and expression of Egr1. Pretreatment with MEK inhibitors suppressed the activation of the ERK cascade, abolished the down-regulation of desmin and led to cell cycle arrest. However, the reversibility of p27Kip1 down-regulation by UO126 was mainly observed after PDGF-AB stimulation, indicating MEK independent p27Kip1 down-regulation by FGF-2. Surprisingly, treatment of SMCs with UO126 or PD98059 increased the level of MEK phosphorylation in a dose dependent manner at serine residues 217/221 in the presence as well as in the absence of both growth factors. Our results strongly imply that depending on the environmental context phosphorylation of serines 217/221 serves as an "on" as well as an "off " switch.

Increased endogenous angiogenic response and hypoxia-inducible factor-1alpha in human critical limb ischemia

OBJECTIVE

The potent physiologic endogenous angiogenic response to ischemic stimuli is often suboptimal, and therefore, a better understanding of the basic mechanisms is essential for the use in therapeutic angiogenesis. Hypoxia-inducible factor-1 (HIF-1) is a major transcription factor that promotes ischemia-driven angiogenesis and is induced when the HIF-1alpha subunit is upregulated. However, little is known about the endogenous angiogenic response and the role of HIF-1alpha in human critical limb ischemia (CLI). We aimed to investigate the extent of the angiogenic response and the expression of HIF-1alpha in the lower limbs of CLI patients.

METHOD

Skeletal muscle biopsy specimens were obtained from the lower limbs of 12 patients with CLI and 12 patients without limb ischemia (controls), with ethical committee approval. Microvessel density (MVD) was determined by using endothelial marker anti-CD31, and HIF-1alpha expressions were determined by immunohistochemistry. MVD was measured as the median number of microvessels in x200 magnification fields. Five random fields per section and three sections per biopsy specimen were analyzed. Enzyme-linked immunoabsorbent assay and Western blotting were used to quantify the HIF-1alpha levels. Colocalization between cell-specific antigens was investigated by double immunofluorescence labelling by using confocal microscopy. Statistical analyses were performed with the Mann-Whitney U test.

RESULTS

The CLI group have significantly higher MVD, with an increase of 2.7-fold compared with the controls (P < 0.001). HIF-1alpha expression was significantly increased in CLI muscles (P < 0.001) and was localized to vascular endothelial cells.

CONCLUSIONS

Our findings suggest that the endogenous angiogenic response occurs in CLI. The increased HIF-1alpha level and colocalization to vascular endothelial cells suggest that HIF-1alpha plays a role in the physiologic endogenous angiogenic response in CLI. Therefore, augmentation of the HIF-1alpha pathway may be an important aspect in therapeutic angiogenesis.

Magnetic resonance angiography of collateral vessel growth in a rabbit femoral artery ligation model

Collateral vessel growth was visualized in a rabbit femoral artery ligation model by serial contrast-enhanced magnetic resonance angiography (MRA) at 1.5 T in comparison with X-ray angiography (XRA). XRA and MRA were performed directly after femoral artery ligation (day 0+) and after 7 and 21 days. XRA (in-plane resolution, 0.3x0.3 mm) was performed with arterial catheterization for fast injection of iodinated contrast agent just proximal to the aortic bifurcation. MRA (in-plane, 0.6x0.6 mm) was performed at 1.5 T with a five-element phased-array coil and slow injection of gadolinium-based MR contrast agent into an ear vein. Collateral vessel scores on two-dimensional XRA projections and on three-dimensional digitally subtracted rotational MRA maximum intensity projections were obtained by two observers and compared. Collateral vessel counts and minimal detectable vessel diameters for MRA and XRA were combined in a computational flow model to interpret differences in spatial detection limits between imaging modalities in terms of flow. Collateral vessel scores were significantly higher in the ligated limb at day 7 (P < 0.05) and more so at day 21 (P < 0.001), in comparison with day 0+ or in the non-ligated control limb on both XRA and MRA. Significantly more (smaller) vessels were visualized with XRA than with MRA, particularly on day 21 (P < 0.05). Inter-observer agreement was high for both XRA (kappa = 0.82) and MRA (kappa = 0.78). The flow model showed that collateral vessels with diameters > 0.3 mm scored by XRA as well as MRA represent nearly 100% of the total blood flow, whereas smaller (0.1-0.3 mm diameter) vessels that can only be detected with XRA contribute little to the blood flow. Serial contrast-enhanced MRA can non-invasively visualize sub-millimeter collateral vessels that represent nearly 100% of the restored blood flow, in a femoral artery ligation model.

VEGF-A and FGF-2 synergistically promote neoangiogenesis through enhancement of endogenous PDGF-B-PDGFRbeta signaling

Combined stimulation with VEGF-A, FGF-2, or PDGF-BB has emerged as a potent strategy for therapeutic angiogenesis, although the mechanisms underlying the synergism of these factors are not well understood. In the present study, we investigated the mechanism of synergism between VEGF-A and FGF-2 by using Matrigel plug assay in vivo and embryonic stem cell (ESC)-derived VEGF receptor 2 (VEGFR2)-positive cells in vitro. Experiments in vitro revealed that, in addition to having direct mitogenic effects, these molecules enhance intercellular PDGF-B signaling in a cell-type specific manner: VEGF-A enhances endothelial PDGF-B expression, whereas FGF-2 enhances mural PDGF receptor beta (PDGFRbeta) expression. Co-stimulation with VEGF-A and FGF-2 caused significant mural cell recruitment in vitro and formation of functional neovasculature in vivo, compared with single-agent stimulation. These effects were abrogated not only by anti-PDGFRbeta neutralizing antibody, but also by exogenous PDGF-BB, which could overwhelm the endogenous PDGF-BB distribution. These findings indicated the importance of preservation of the periendothelial PDGF-BB gradient. Thus, we demonstrated that the directional enhancement of endogenous PDGF-B-PDGFRbeta signaling is indispensable for the synergistic effect of VEGF-A and FGF-2 on neoangiogenesis in adults. The findings provide insights into the mechanisms underlying the effects of co-stimulation by growth factors, which could lead to rational design of therapeutic angiogenic strategies.

Diabetic Microangiopathy in Ischemic Limb Is a Disease of Disturbance of the Platelet-Derived Growth Factor-BB/Protein Kinase C Axis but Not of Impaired Expression of Angiogenic Factors

Diabetic foot is caused by microangiopathy and is suggested to be a result of impaired angiogenesis. Using a severe hindlimb ischemia model of streptozotocin-induced diabetic mice (STZ-DM), we show that diabetic foot is a disease solely of the disturbance of platelet-derived growth factor B-chain homodimer (PDGF-BB) expression but not responses of angiogenic factors. STZ-DM mice frequently lost their hindlimbs after induced ischemia, whereas non-DM mice did not. Screening of angiogenesis-related factors revealed that only the expression of PDGF-BB was impaired in the STZ-DM mice on baseline, as well as over a time course after limb ischemia. Supplementation of the PDGF-B gene resulted in the prevention of autoamputation, and, furthermore, a protein kinase C (PKC) inhibitor restored the PDGF-BB expression and also resulted in complete rescue of the limbs of the STZ-DM mice. Inhibition of overproduction of advanced-glycation end product resulted in dephosphorylation of PKC-α and restored expression of PDGF-BB irrespective of blood sugar and HbA1c, indicating that advanced-glycation end product is an essential regulator for PKC/PDGF-BB in diabetic state. These findings are clear evidence indicating that diabetic vascular complications are caused by impairment of the PKC/PDGF-B axis, but not by the impaired expression of angiogenic factors, and possibly imply the molecular target of diabetic foot.

Arteriogenic gene therapy in patients with unreconstructable critical limb ischemia: a randomized, placebo-controlled clinical trial of adenovirus 5-delivered fibroblast growth factor-4

The objectives of this study were to assess the safety and potential clinical efficacy of adenovirus-delivered fibroblast growth factor-4 (Ad5FGF-4) by intramuscular injection into patients with critical limb ischemia (CLI). This study was a double-blind, randomized, placebo-controlled study with escalating dose groups of 2.87 x 10(8) to 2.87 x 10(10) viral particles. Thirteen patients with CLI were randomized to receive active drug (n = 10) or placebo (n = 3). Safety evaluations and efficacy parameters (ankle-brachial index, digital subtraction angiograms, magnetic resonance imaging, and scintigraphy) were performed at baseline and for 12 weeks after treatment. Injections of Ad5FGF-4 were generally well tolerated and considered safe. Transfection efficacy at these concentrations may have been limited or local. The small sample size did not allow any firm conclusions regarding clinical efficacy but a trend toward more and slightly larger blood vessels was observed in the angiograms. It is concluded that intramuscular injection of Ad5FGF-4 into CLI patients seemed safe, but transfection efficacy was limited at the assessed doses. Conclusions regarding clinical efficacy are impossible to draw from this small patient cohort.

Exogenous Basic Fibroblast Growth Factor Increases Collateral Blood Flow in Female Rats With Femoral Artery Occlusion

The goal of this study was to determine if extended duration of FGF-2 infusion would further expand collateral blood flow (BF) in female rats with bilateral femoral artery occlusion; rats were infused with either FGF-2 or placebo intra-arterially for 14, 28, and 42 days. Blood flows were measured with isotope labeled microspheres. Blood pressure and heart rate were similar between the treatment groups by ANOVA. In Placebo groups; baseline collateral dependent blood flows to the calf muscle were 11 mL/min/100 g to 17 mL/min/100 g at 4 hours after femoral artery occlusion, calf muscle blood flow increased to 39 +/- 4.2, 49 +/- 4.2, and 48 +/- 3.3 mL/min/100 g following 16, 30, and 44 days femoral artery occlusion respectively. In FGF-2-treated groups, calf muscle blood flows were further increased by 36%, 57%, and 35% over the corresponding time point of Placebo groups (P < 0.001). Exogenous FGF-2 infusion for 28 days showed higher collateral dependent blood flows than the FGF-2 14 days infused group (P < 0.001). Extended duration of exogenous FGF-2 delivery up to 42 days failed to further expand the collateral blood flow. This implies a self-limiting mechanism that might govern the collateral vascular remodeling induced by FGF-2. Our results indicate that female rats can obtain similar extent collateral blood flow expansion as that found in the male rats.

Bone challenges for the hand surgeon: from basic bone biology to future clinical applications

Bone is a complex tissue composed of a calcified extracellular matrix with specialized cells that produce, maintain, and resorb the bone. Bone also has a rich vascular and neural supply. Bone has a great capability of regeneration, healing, and remodelling that is influenced by external factors, such as stress forces, and internal regulators that include hormones, vitamins, and growth factors. These factors dictate bone biology, and variations result in pathophysiologic conditions that have clinical implications in hand surgery. Solutions to the challenges in hand surgery rely on a thorough understanding of the biology of bone.

Heterodimerization of FGF-receptor 1 and PDGF-receptor-alpha: a novel mechanism underlying the inhibitory effect of PDGF-BB on FGF-2 in human cells

Previous evidence has shown that platelet-derived growth factor-BB (PDGF-BB) and fibroblast growth factor-2 (FGF-2) directly interact with high affinity, leading to potent reciprocal inhibitory effects on bovine endothelial cells and rat vascular smooth muscle cells. In this study, we report that PDGF-BB inhibits a series of FGF-2-induced events, such as proliferation of human umbilical vein endothelial cells (HUVECs), FGF-2 cellular internalization, phosphorylation of intracellular signaling factors including p38, rac1/cdc42, MKK4, and MKK3/6, and phosphorylation of FGF-receptor 1 (FGF-R1). PDGF-receptor-alpha (PDGF-Ralpha) was found to mediate PDGF-BB inhibitory effects because its neutralization fully restored FGF-2 mitogenic activity and internalization. Additional biochemical analyses, coimmunoprecipitation experiments, and FRET analysis showed that FGF-R1 and PDGF-Ralpha directly interact in vitro and in vivo and that this interaction is somehow increased in the presence of the corresponding ligands FGF-2 and PDGF-BB. These results suggest that FGF-R1/PDGF-Ralpha heterodimerization may represent a novel endogenous mechanism to modulate the action of these receptors and their ligands and to control endothelial cell function.

Inductive tissue engineering with protein and DNA-releasing scaffolds

Cellular differentiation, organization, proliferation and apoptosis are determined by a combination of an intrinsic genetic program, matrix/substrate interactions, and extracellular cues received from the local microenvironment. These molecular cues come in the form of soluble (e.g. cytokines) and insoluble (e.g. ECM proteins) factors, as well as signals from surrounding cells that can promote specific cellular processes leading to tissue formation or regeneration. Recent developments in the field of tissue engineering have employed biomaterials to present these cues, providing powerful tools to investigate the cellular processes involved in tissue development, or to devise therapeutic strategies based on cell replacement or tissue regeneration. These inductive scaffolds utilize natural and/or synthetic biomaterials fabricated into three-dimensional structures. This review summarizes the use of scaffolds in the dual role of structural support for cell growth and vehicle for controlled release of tissue inductive factors, or DNA encoding for these factors. The confluence of molecular and cell biology, materials science and engineering provides the tools to create controllable microenvironments that mimic natural developmental processes and direct tissue formation for experimental and therapeutic applications.

The Role of Therapeutic Angiogenesis in Tissue Repair and Regeneration

PURPOSE

To provide the physician and registered professional nurse with an understanding of angiogenesis and an overview of therapeutic angiogenesis modalities used to manage wounds and other tissue repair situations.

TARGET AUDIENCE

This continuing education activity is intended for physicians and nurses with an interest in learning more about angiogenesis and therapeutic angiogenesis modalities to manage wounds and other tissue repair situations.

OBJECTIVES

After reading the article and taking the test, the participant should be able to:

Arteriolization of capillaries and FGF-2 upregulation in skeletal muscles of patients with chronic peripheral arterial disease

OBJECTIVE

Microvascular changes in ischemic skeletal muscle are described derived from patients with long-lasting peripheral arterial disease (PAD).

METHODS

Skeletal muscles from the lower limb of 17 patients (obtained after amputation) with chronic PAD and 4 asymptomatic controls (obtained from biopsies after bypass surgery) were evaluated by electron microscopy and immunohistochemistry.

RESULTS

The capillaries in skeletal muscles of PAD patients were surrounded by a more than 1 microm-thick coat, which was positively stained for basement membrane pericapillary coat collagen type IV. Thickness of the coat correlated with presence of PAD (p < .0001), and less strongly with diabetes mellitus (p = .023) and age of patients (p = .019). The majority of the capillaries in skeletal muscles of PAD patients (71.1 +/- 15.3%) were covered with cells positive for smooth muscle cell actin (sma) as compared to samples from asymptomatic controls (22.8% +/- 9.6%; p < .0001) suggesting advanced arteriolization. Semiquantitative analysis revealed that patients with PAD demonstrate a higher expression of FGF-2 in capillary endothelial cells (67.8 +/- 17.5%) as compared to controls (10.2 +/- 8.4%; p < .0001), whereas VEGF immunoreactivity was only occasionally present in extravascular cells.

CONCLUSION

Thickened collagen type IV-positive basement membranes in combination with a significant increase in sma-coverage indicate arteriolization of capillaries characteristic for chronic PAD, what may be related to high FGF-2 expression in capillary endothelial cells.

Critical role of microenvironmental factors in angiogenesis

Therapeutic angiogenesis, which entails the induction of new blood vessels by the delivery of angiogenic growth factors, is a highly attractive approach to the treatment of ischemic diseases. However, it is becoming increasingly clear that this is not easily achieved, as the effects of angiogenic growth factors can differ markedly depending on the timing of their expression, on the shape of the concentration gradients they form in vivo, and the inter-actions between endothelial cells and pericytes they induce. In fact, the same dose of vascular endothelial growth factor can induce stable, nonleaky, pericyte-covered normal capillaries or aberrant vascular structures that develop into hemangiomas. This difference in outcome can be due solely to the spatial characteristics of the delivery method. If delivery allows a homogeneous spatial distribution of VEGF in the microenvironment around each producing cell, angiogenesis can be therapeutic, whereas if the total dose is the average of diverse spatial levels, aberrant angiogenesis cannot be avoided. To achieve therapeutic angiogenesis, a means of regulating the microenvironmental levels of angiogenic factors will be critical to the generation of effective new treatment strategies.

Custom design of the cardiac microenvironment with biomaterials

Many strategies for repairing injured myocardium are under active investigation, with some early encouraging results. These strategies include cell therapies, despite little evidence of long-term survival of exogenous cells, and gene or protein therapies, often with incomplete control of locally-delivered dose of the factor. We propose that, ultimately, successful repair and regeneration strategies will require quantitative control of the myocardial microenvironment. This precision control can be engineered through designed biomaterials that provide quantitative adhesion, growth, or migration signals. Quantitative timed release of factors can be regulated by chemical design to direct cellular differentiation pathways such as angiogenesis and vascular maturation. Smart biomaterials respond to the local environment, such as protease activity or mechanical forces, with controlled release or activation. Most of these new biomaterials provide much greater flexibility for regenerating tissues ex vivo, but emerging technologies like self-assembling nanofibers can now establish intramyocardial cellular microenvironments by injection. This may allow percutaneous cardiac regeneration and repair approaches, or injectable-tissue engineering. Finally, materials can be made to multifunction by providing sequential signals with custom design of differential release kinetics for individual factors. Thus, new rationally-designed biomaterials no longer simply coexist with tissues, but can provide precision bioactive control of the microenvironment that may be required for cardiac regeneration and repair.

A novel adenoviral gutless vector encoding sphingosine kinase promotes arteriogenesis and improves perfusion in a rabbit hindlimb ischemia model

OBJECTIVES

We previously demonstrated that sphingosine kinase (SPK) increases the level of extracellular sphingosine-1-phosphate and promotes neovascularization in a mouse matrigel model. In this study, we tested the hypothesis that SPK gene transfer using a novel adenoviral 'gutless' vector (AGV) can enhance arteriogenesis in a rabbit hindlimb ischemia model.

METHODS

Thirty-five male New Zealand white rabbits were randomized to the AGV-SPK group (n=13), AGV-null group (n=13), and control group (n=9). On day 10, after the induction of unilateral hindlimb ischemia, gene vectors or buffer were introduced and the effect examined on day 30, using calf blood pressure, quantitative angiographic analysis, and histology.

RESULTS

Calf systolic blood pressure ratios of the ischemic limb to the normal limb on day 30 were 0.77+/-0.13 in control groups, including the AGV-null group, and 0.91+/-0.14 in the AGV-SPK group (P<0.05). Angiographic vessel counts were significantly increased (8.0+/-2.1 at baseline and 11.8+/-3.2 on day 30, P<0.001) in the AGV-SPK group. Histologic analysis showed that microscopic total vessel counts on day 30 were 3.5+/-1.8/field in the control and AGV-null group and 5.4+/-1.0/field in the AGV-SPK group. Arterioles (AGV-SPK; 3.0+/-0.8 versus control and AGV-null; 2.1+/-1.1, P<0.05) were significantly increased in the AGV-SPK group.

CONCLUSIONS

This study shows that SPK promotes arteriogenesis, as evidenced by the maximal improvement in the blood pressure restoration and collateral vessel counts. SPK may be an important angiogenic target to improve perfusion in ischemic tissues.

Bradycardia Stimulates Vascular Growth During Gradual Coronary Occlusion

OBJECTIVE

In cultured endothelium, stretch induces release of growth factors that contribute to angiogenesis. We tested the hypothesis that bradycardia, which prolongs ventricular diastolic filling time and volume, promotes collateral vessel growth.

METHODS AND RESULTS

An ameroid occluder was placed on coronary arteries of dogs with normal heart rates (AM) or bradycardia (55 bpm; AM+BC). A third group had normal heart rates and no ameroid (control [CON]). Four weeks after occluder placement, myocardial blood flow at rest and maximal vasodilation (adenosine) at equivalent heart rates and vascular morphometry of hearts were measured. In AM dogs, conductance (myocardial flow/diastolic pressure) of collateral-dependent myocardium was similar to collateral-independent myocardium during rest but increased to only one third of CON during maximal vasodilation. In contrast, in AM+BC dogs, conductance was similar in collateral-dependent and -independent regions during maximal vasodilation. Arteriolar length density in collateral-dependent myocardium was 80% greater in AM+BC than AM dogs. Capillary length density in collateral-dependent region of AM dogs was lower than CON but normal in AM+BC dogs. The angiopoietin receptor Tie-2 increased in collateral-dependent regions of AM and AM+BC groups, whereas vascular endothelial growth factor increased in collateral-dependent and -independent regions only in AM+BC dogs.

CONCLUSIONS

Chronic bradycardia during gradual coronary artery occlusion facilitates angiogenesis/arteriogenesis in collateral-dependent myocardium and preserves maximal perfusion.

Induction of tumor arrest and differentiation with prolonged survival by intermittent hypoxia in a mouse model of acute myeloid leukemia

We showed previously that mild real hypoxia and hypoxia-mimetic agents induced in vitro cell differentiation of acute myeloid leukemia (AML). We here investigate the in vivo effects of intermittent hypoxia on syngenic grafts of leukemic blasts in a PML-RARalpha transgenic mouse model of AML. For intermittent hypoxia, leukemic mice were housed in a hypoxia chamber equivalent to an altitude of 6000 m for 18 hours every consecutive day. The results show that intermittent hypoxia significantly prolongs the survival of the leukemic mice that received transplants, although it fails to cure the disease. By histologic and cytologic analyses, intermittent hypoxia is shown to inhibit the infiltration of leukemic blasts in peripheral blood, bone marrow, spleen, and liver without apoptosis induction. More intriguingly, intermittent hypoxia also induces leukemic cells to undergo differentiation with progressive increase of hypoxia-inducible factor-1alpha protein, as evidenced by morphologic criteria of maturating myeloid cells and increased expression of mouse myeloid cell differentiation-related antigens Gr-1 and Mac-1. Taken together, this study represents the first attempt to characterize the in vivo effects of hypoxia on an AML mouse model. Additional investigations may uncover ways to mimic the differentiative effects of hypoxia in a manner that will benefit human patients with AML.

Opinion: emerging mechanisms of tumour lymphangiogenesis and lymphatic metastasis

Malignant tumours can spread to lymph nodes through lymphatic vessels. Recent studies show that tumours produce a range of growth factors that directly or indirectly stimulate lymphatic vessel growth (lymphangiogenesis) and lymphatic metastasis. These findings indicate that tumour lymphangiogenesis, similar to haemangiogenesis, is a complex process that is regulated by multiple growth factors. Understanding the underlying mechanisms by which tumours induce lymphangiogenesis might provide important information for the therapeutic intervention of metastatic spread.

In Vitro Functional Assessment of Human Skeletal Myoblasts After Transduction With Adenoviral Bicistronic Vector Carrying Human VEGF165 and Angiopoietin-1

OBJECTIVES

We report in vitro functional assessment of human skeletal myoblasts with adenoviral bicistronic vector carrying human vascular endothelial growth factor-165 (hVEGF165) and angiopoietin-1 (Ang-1).

METHODS

Myoblasts were assessed for their purity by desmin expression. A replication incompetent adenoviral bicistronic vector (Ad-Bic) carrying both hVEGF165 and Ang-1 was used for transduction of myoblasts. Transduction efficiency was assessed by dual fluorescent immunostaining of the transduced myoblasts. Expression efficiency was analyzed by enzyme linked immunosorbent assay (ELISA), Western blot and reverse transcription polymerase chain reaction (RT-PCR). The biological activity of the secreted human VEGF165 and Ang-1 was determined by human umbilical vein endothelial cells (HUVEC) proliferation assay, Thymidine [H3] incorporation assay and capillary-like structure formation.

RESULTS

The myoblasts preparation was >98% pure. Fluorescent immunostaining showed >95% transduction efficiency. The transduced myoblasts secreted VEGF(165) for up to 30 days after transduction, with peak level (32 +/- 4 ng/ml) at day 8 after transduction as revealed by VEGF ELISA. Western blot further confirmed that both angiogenic factors were actively secreted by transduced myoblasts. The molecular weight was 42 kD for hVEGF165 and 70 kD for Ang-1 respectively. The expression of hVEGF165 and Ang-1 was significantly reduced at day-30 after transduction as seen by RT-PCR. The conditioned medium from bicistronic vector transduced myoblasts stimulated HUVEC to proliferate much faster than other conditioned media (>1.5 folds). Thymidine incorporation assay further confirmed this finding. Matrigel experiment suggested that HUVEC under the condition of both growth factors formed significantly more capillary-like structure.

CONCLUSIONS

The bicistronic vector transduced myoblasts provides a novel strategy for therapeutic angiomyogenesis for cardiac repair.

Platelet-derived growth factor (PDGF) and glial tumorigenesis

Platelet-derived growth factor (PDGF) has long been implicated in cancer and is known to be involved in many biological processes. In Central Nervous System (CNS) neoplasms, particularly gliomas, PDGF is often over-expressed. However, what role PDGF plays in tumor progression remains to be fully described. A wide range of work from in vitro studies to mouse models have implicated the PDGF pathway in various processes including proliferation, cellular migration, development, and angiogenesis. Being a secreted factor, PDGF not only has autocrine effects on producing cells but also has potential for paracrine effects on other tumor cells and the tumor microenvironment. The development of small molecules that inhibit the PDGF receptor and various subsequent signaling components promises to introduce new approaches to the treatment of gliomas.

Platelet-derived growth factor (PDGF-BB) and brain-derived neurotrophic factor (BDNF) induce striatal neurogenesis in adult rats with 6-hydroxydopamine lesions

The effects of i.c.v. infused platelet-derived growth factor and brain-derived neurotrophic factor on cell genesis, as assessed with bromodeoxyuridine (BrdU) incorporation, were studied in adult rats with unilateral 6-hydroxydopamine lesions. Both growth factors increased the numbers of newly formed cells in the striatum and substantia nigra to an equal extent following 10 days of treatment. At 3 weeks after termination of growth factor treatment, immunostaining of BrdU-labeled cells with the neuronal marker NeuN revealed a significant increase in newly generated neurons in the striatum. In correspondence, many doublecortin-labeled neuroblasts were also observed in the denervated striatum following growth factor treatment. Further evaluation suggested that a subset of these new neurons expresses the early marker for striatal neurons Pbx. However, no BrdU-positive cells were co-labeled with DARPP-32, a protein expressed by mature striatal projection neurons. Both in the striatum and in the substantia nigra there were no indications of any newly born cells differentiating into dopaminergic neurons following growth factor treatment, such that BrdU-labeled cells never co-expressed tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. In conclusion, our results suggest that administration of these growth factors is capable of recruiting new neurons into the striatum of hemiparkinsonian rats.

Repair of infarcted myocardium mediated by transplanted bone marrow-derived CD34+ stem cells in a nonhuman primate model

Rodent and human clinical studies have shown that transplantation of bone marrow stem cells to the ischemic myocardium results in improved cardiac function. In this study, cynomolgus monkey acute myocardial infarction was generated by ligating the left anterior descending artery, and autologous CD34(+) cells were transplanted to the peri-ischemic zone. To track the in vivo fate of transplanted cells, CD34(+) cells were genetically marked with green fluorescent protein (GFP) using a lentivirus vector before transplantation (marking efficiency, 41% on average). The group receiving cells (n = 4) demonstrated improved regional blood flow and cardiac function compared with the saline-treated group (n =4) at 2 weeks after transplant. However, very few transplanted cell-derived, GFP-positive cells were found incorporated into the vascular structure, and GFP-positive cardiomyocytes were not detected in the repaired tissue. On the other hand, cultured CD34(+) cells were found to secrete vascular endothelial growth factor (VEGF), and the in vivo regional VEGF levels showed a significant increase after the transplantation. These results suggest that the improvement is not the result of generation of transplanted cell-derived endothelial cells or cardiomyocytes; and raise the possibility that angiogenic cytokines secreted from transplanted cells potentiate angiogenic activity of endogenous cells.

START Trial: a pilot study on STimulation of ARTeriogenesis using subcutaneous application of granulocyte-macrophage colony-stimulating factor as a new treatment for peripheral vascular disease

BACKGROUND

Granulocyte-macrophage colony-stimulating factor (GM-CSF) was recently shown to increase collateral flow index in patients with coronary artery disease. Experimental models showed beneficial effects of GM-CSF on collateral artery growth in the peripheral circulation. Thus, in the present study, we evaluated the effects of GM-CSF in patients with peripheral artery disease.

METHODS AND RESULTS

A double-blinded, randomized, placebo-controlled study was performed in 40 patients with moderate or severe intermittent claudication. Patients were treated with placebo or subcutaneously applied GM-CSF (10 microg/kg) for a period of 14 days (total of 7 injections). GM-CSF treatment led to a strong increase in total white blood cell count and C-reactive protein. Monocyte fraction initially increased but thereafter decreased significantly as compared with baseline. Both the placebo group and the treatment group showed a significant increase in walking distance at day 14 (placebo: 127+/-67 versus 184+/-87 meters, P=0.03, GM-CSF: 126+/-66 versus 189+/-141 meters, P=0.04) and at day 90. Change in walking time, the primary end point of the study, was not different between groups. No change in ankle-brachial index was found on GM-CSF treatment at day 14 or at day 90. Laser Doppler flowmetry measurements showed a significant decrease in microcirculatory flow reserve in the control group (P=0.03) and no change in the GM-CSF group.

CONCLUSIONS

The present study does not support the use of GM-CSF for treatment of patients with moderate or severe intermittent claudication. Issues that need to be addressed are dosing, the selection of patients, and potential differences between GM-CSF effects in the coronary and the peripheral circulation.

Therapeutic neovascularization: contributions from bioengineering

A number of pathological entities and surgical interventions could benefit from therapeutic stimulation of new blood vessel formation. Although strategies designed for promoting neovascularization have shown promise in preclinical models, translation to human application has met with limited success when angiogenesis is used as the single therapeutic mechanism. While clinical protocols continue to be optimized, a number of exciting new approaches are being developed. Bioengineering has played an important role in the progress of many of these innovative new strategies. In this review, we present a general outline of therapeutic neovascularization, with an emphasis on investigations using engineering principles to address this vexing clinical problem. In addition, we identify some limitations and suggest areas for future research.

Adenoviral-mediated delivery of early growth response factor-1 gene increases tissue perfusion in a murine model of hindlimb ischemia

To test the hypothesis that overexpression of early growth response factor-1 (Egr-1) contributes to the revascularization of ischemic limbs, a constitutively active form of Egr-1 (Egr-1*) was made and evaluated in vitro and in vivo. Analyses of the transduced myocytes revealed significant upregulation of bFGF, PDGF-A, PDGF-B, IGF-II, and TGF-beta1. A coculture assay of the paracrine effects indicated that Ad-Egr-1* promoted proliferation and migration of endothelial cells. When Ad-Egr-1* was injected into the tibialis anterior muscle of mice, followed by explant culture in growth factor-reduced Matrigel, many capillary-like structures were observed in the Egr-1* group compared with minimal sprouting from the LacZ group, suggesting an angiogenic potential of Egr-1*. Next we evaluated Ad-Egr-1* in a murine model of hindlimb ischemia. Compared with slow revascularization in the control PBS or LacZ group, a rapid increase in tissue perfusion was observed in the Egr-1* group and the difference in flux ratio was statistically significant at day 7. In the injected muscle, expression of Egr-1*, upregulation of its target genes, and increased number of vessels staining positive for smooth muscle alpha-actin were observed. These results suggest that Egr-1 plays an important role in vascular recovery after occlusion and could be a potential target for therapeutic angiogenesis.

Stromal stem cells and platelet-rich plasma improve bone allograft integration

Early vascular invasion is a key factor in bone allograft incorporation. It may reduce the complications related to slow and incomplete bone integration. Bone-marrow-derived stromal stem cells associated with platelet-rich plasma are potent angiogenic inducers proven to release vascular endothelial growth factor. Our goal was to test whether the combination of stromal stem cells and platelet-rich plasma is able to increase massive allograft integration in a large animal model with sacrifice at 4 months. A critical defect was made in the mid-diaphysis of the metatarsal bone of 10 sheep; the study group received an allograft plus stromal stem cells, platelet-rich plasma, and collagen (six animals) and the control group received only the allograft (four animals). Investigation was done with radiographs, mechanical tests and histomorphometric analysis, including new vascularization. Results showed substantial new bone formation in the allograft of the study group. Bone formation is correlated with better vascular invasion and remodeling of the graft in the study group. These results confirm the key role played by stromal stem cells and platelet-rich plasma in bone repair. Further studies are needed to better define the role stromal stem cells play when implanted alone.

Nerve growth factor activates aorta endothelial cells causing PI3K/Akt- and ERK-dependent migration

Nerve growth factor (NGF) is a well-known neurotrophin. We determined whether NGF can activate endothelial cell migration and signalling that underlie angiogenic processes. We showed that aorta endothelial cells express mRNA for both the receptor tyrosine kinase TrkA and the p75 neurotrophin receptor (p75NTR) that associates with TrkA when signalling occurs. Pig aortic endothelial cells migrated when exposed to an NGF gradient, due to the simultaneous activation of the phosphatidylinositol 3-kinase and extracellular signal-regulated kinase signalling pathways. Furthermore, morphological changes were found in migrating cells: they appear with elongated structures with a smaller cell volume than control cells. Our data show that NGF is an activator of endothelial cells and suggest that NGF plays a role in mediating angiogenesis.

Anti-tumor necrosis factor-{alpha} therapies attenuate adaptive arteriogenesis in the rabbit

The specific antagonists of tumor necrosis factor-alpha (TNF-alpha), infliximab and etanercept, are established therapeutic agents for inflammatory diseases such as rheumatoid arthritis and Crohn's disease. Although the importance of TNF-alpha in chronic inflammatory diseases is well established, little is known about its implications in the cardiovascular system. Because proliferation of arteriolar connections toward functional collateral arteries (arteriogenesis) is an inflammatory-like process, we tested in vivo the hypothesis that infliximab and etanercept have antiarteriogenic actions. Sixty-three New Zealand White rabbits underwent femoral artery occlusion and received infliximab, etanercept, or vehicle according to clinical dosage regimes. After 1 wk, collateral conductance, assessed with fluorescent microspheres, revealed significant inhibition of arteriogenesis (collateral conductance): 52.4 (SD 8.1), 35.2 (SD 7.7), and 33.3 (SD 10.1) ml x min(-1) x 100 mmHg(-1) with PBS, infliximab, and etanercept, respectively (P < 0.001). High-resolution angiography showed no significant differences in number of collateral arteries, but immunohistochemical analysis demonstrated a decrease in mean collateral diameter, proliferation of vascular smooth muscle cells, and reduction of leukocyte accumulation around collateral arteries in treated groups. Infliximab and etanercept bound to infiltrating leukocytes, which are important mediators of arteriogenesis. Infliximab induced monocyte apoptosis, and neither substance affected monocyte expression of the adhesion molecule Mac-1. We demonstrated that TNF-alpha serves as a pivotal modulator of arteriogenesis, which is attenuated by treatment with TNF-alpha inhibitors. Reduction of collateral conductance is most likely due to inhibition of perivascular leukocyte infiltration and subsequent lower vascular smooth muscle cell proliferation. This is the first report showing a negative influence of TNF-alpha inhibitors on collateral artery growth.

Neurotrophins promote revascularization by local recruitment of TrkB+ endothelial cells and systemic mobilization of hematopoietic progenitors

The neurotrophin brain-derived neurotrophic factor (BDNF) is required for the maintenance of cardiac vessel wall stability during embryonic development through direct angiogenic actions on endothelial cells expressing the tropomysin receptor kinase B (TrkB). However, the role of BDNF and a related neurotrophin ligand, neurotrophin-4 (NT-4), in the regulation of revascularization of the adult tissues is unknown. To study the potential angiogenic capacity of BDNF in mediating the neovascularization of ischemic and non-ischemic adult mouse tissues, we utilized a hindlimb ischemia and a subcutaneous Matrigel model. Recruitment of endothelial cells and promotion of channel formation within the Matrigel plug by BDNF and NT-4 was comparable to that induced by VEGF-A. The introduction of BDNF into non-ischemic ears or ischemic limbs induced neoangiogenesis, with a 2-fold increase in the capillary density. Remarkably, treatment with BDNF progressively increased blood flow in the ischemic limb over 21 days, similar to treatment with VEGF-A. The mechanism by which BDNF enhances capillary formation is mediated in part through local activation of the TrkB receptor and also by recruitment of Sca-1+CD11b+ pro-angiogenic hematopoietic cells. BDNF induces a potent direct chemokinetic action on subsets of marrow-derived Sca-1+ hematopoietic cells co-expressing TrkB. These studies suggest that local regional delivery of BDNF may provide a novel mechanism for inducing neoangiogenesis through both direct actions on local TrkB-expressing endothelial cells in skeletal muscle and recruitment of specific subsets of TrkB+ bone marrow-derived hematopoietic cells to provide peri-endothelial support for the newly formed vessels.

Neurotrophins promote revascularization by local recruitment of TrkB+ endothelial cells and systemic mobilization of hematopoietic progenitors

The neurotrophin brain-derived neurotrophic factor (BDNF) is required for the maintenance of cardiac vessel wall stability during embryonic development through direct angiogenic actions on endothelial cells expressing the tropomysin receptor kinase B (TrkB). However, the role of BDNF and a related neurotrophin ligand, neurotrophin-4 (NT-4), in the regulation of revascularization of the adult tissues is unknown. To study the potential angiogenic capacity of BDNF in mediating the neovascularization of ischemic and non-ischemic adult mouse tissues, we utilized a hindlimb ischemia and a subcutaneous Matrigel model. Recruitment of endothelial cells and promotion of channel formation within the Matrigel plug by BDNF and NT-4 was comparable to that induced by VEGF-A. The introduction of BDNF into non-ischemic ears or ischemic limbs induced neoangiogenesis, with a 2-fold increase in the capillary density. Remarkably, treatment with BDNF progressively increased blood flow in the ischemic limb over 21 days, similar to treatment with VEGF-A. The mechanism by which BDNF enhances capillary formation is mediated in part through local activation of the TrkB receptor and also by recruitment of Sca-1+CD11b+ pro-angiogenic hematopoietic cells. BDNF induces a potent direct chemokinetic action on subsets of marrow-derived Sca-1+ hematopoietic cells co-expressing TrkB. These studies suggest that local regional delivery of BDNF may provide a novel mechanism for inducing neoangiogenesis through both direct actions on local TrkB-expressing endothelial cells in skeletal muscle and recruitment of specific subsets of TrkB+ bone marrow-derived hematopoietic cells to provide peri-endothelial support for the newly formed vessels.