Vascular endothelial growth factor stimulates angiogenesis without improving collateral blood flow following hindlimb ischemia in rabbits

Enhanced notch signaling modulates unproductive revascularization in response to nitric oxide-angiopoietin signaling in a mouse model of peripheral ischemia

INTRODUCTION

Arteriolargenesis can be induced by concomitant stimulation of nitric Oxide (NO)-Angiopoietin receptor (Tie)-Vascular Endothelial Growth Factor (VEGF) signaling in the rat mesentery angiogenesis assay. We hypothesized that the same combination of exogenously added growth factors would also have a positive impact on arteriolargenesis and, consequently, the recovery of blood flow in a model of unilateral hindlimb ischemia.

RESULTS AND METHODS

NO-Tie mice had faster blood flow recovery compared to control mice, as assessed by laser speckle imaging. There was no change in capillary density within the ischemic muscles, but arteriole density was higher in NO-Tie mice. Given the previously documented beneficial effect of VEGF signaling, we tested whether NO-Tie-VEGF mice would show further improvement. Surprisingly, these mice recovered no differently from control, arteriole density was similar and capillary density was lower. Dll4 is a driver of arterial specification, so we hypothesized that Notch1 expression would be involved in arteriolargenesis. There was a significant upregulation of Notch1 transcripts in NO-Tie-VEGF compared with NO-Tie mice. Using soluble Dll4 (sDll4), we stimulated Notch signaling in the ischemic muscles of mice. NO-Tie-sDll4 mice had significantly increased capillary and arteriole densities, but impaired blood flow recovery.

CONCLUSION

These results suggest that Dll4 activation early on in revascularization can lead to unproductive angiogenesis and arteriolargenesis, despite increased vascular densities. These results suggest spatial and temporal balance of growth factors needs to be perfected for ideal functional and anatomical revascularisation.

Challenges in Translating from Bench to Bed-Side: Pro-Angiogenic Peptides for Ischemia Treatment

We describe progress and obstacles in the development of novel peptide-hydrogel therapeutics for unmet medical needs in ischemia treatment, focusing on the development and translation of therapies specifically in peripheral artery disease (PAD). Ischemia is a potentially life-threatening complication in PAD, which affects a significant percentage of the elderly population. While studies on inducing angiogenesis to treat PAD were started two decades ago, early results from animal models as well as clinical trials have not yet been translated into clinical practice. We examine some of the challenges encountered during such translation. We further note the need for sustained angiogenic effect involving whole growth factor, gene therapy and synthetic growth factor strategies. Finally, we discuss the need for tissue depots for de novo formation of microvasculature. These scaffolds can act as templates for neovasculature development to improve circulation and healing at the preferred anatomical location.

Pro-Angiogenic Effects of Low Dose Ethoxidine in a Murine Model of Ischemic Hindlimb: Correlation between Ethoxidine Levels and Increased Activation of the Nitric Oxide Pathway

Ethoxidine, a benzo[c]phenanthridine derivative, has been identified as a potent inhibitor of topoisomerase I in cancer cell lines. Our group has reported paradoxical properties of ethoxidine in cellular processes leading to angiogenesis on endothelial cells. Because low concentration ethoxidine is able to favor angiogenesis, the present study aimed to investigate the ability of 10^-9 M ethoxidine to modulate neovascularization in a model of mouse hindlimb ischemia. After inducing unilateral hindlimb ischemia, mice were treated for 21 days with glucose 5% or with ethoxidine, to reach plasma concentrations equivalent to 10^-9 M. Laser Doppler analysis showed that recovery of blood flow was 1.5 fold higher in ethoxidine-treated mice in comparison with control mice. Furthermore, CD31 staining and angiographic studies confirmed an increase of vascular density in ethoxidine-treated mice. This ethoxidine-induced recovery was associated with an increase of NO production through an enhancement of eNOS phosphorylation on its activator site in skeletal muscle from ischemic hindlimb. Moreover, real-time RT-PCR and western blots have highlighted that ethoxidine has pro-angiogenic properties by inducing a significant enhancement in vegf transcripts and VEGF expression, respectively. These findings suggest that ethoxidine could contribute to favor neovascularization after an ischemic injury by promoting the NO pathway and VEGF expression.

Effects of Topical Icing on Inflammation, Angiogenesis, Revascularization, and Myofiber Regeneration in Skeletal Muscle Following Contusion Injury

Contusion injuries in skeletal muscle commonly occur in contact sport and vehicular and industrial workplace accidents. Icing has traditionally been used to treat such injuries under the premise that it alleviates pain, reduces tissue metabolism, and modifies vascular responses to decrease swelling. Previous research has examined the effects of icing on inflammation and microcirculatory dynamics following muscle injury. However, whether icing influences angiogenesis, collateral vessel growth, or myofiber regeneration remains unknown. We compared the effects of icing vs. a sham treatment on the presence of neutrophils and macrophages; expression of CD34, von Willebrands factor (vWF), vascular endothelial growth factor (VEGF), and nestin; vessel volume; capillary density; and myofiber regeneration in skeletal after muscle contusion injury in rats. Muscle tissue was collected 1, 3, 7, and 28 d after injury. Compared with uninjured rats, muscles in rats that sustained the contusion injury exhibited major necrosis, inflammation, and increased expression of CD34, vWF, VEGF, and nestin. Compared with the sham treatment, icing attenuated and/or delayed neutrophil and macrophage infiltration; the expression of vWF, VEGF, and nestin; and the change in vessel volume within muscle in the first 7 d after injury (P < 0.05). By contrast, icing did not influence capillary density in muscle 28 d after injury (P = 0.59). The percentage of immature myofibers relative to the total number of fibers was greater in the icing group than in the sham group 28 d after injury (P = 0.026), but myofiber cross-sectional area did not differ between groups after 7 d (P = 0.35) and 28 d (P = 0.30). In conclusion, although icing disrupted inflammation and some aspects of angiogenesis/revascularization, these effects did not result in substantial differences in capillary density or muscle growth.

Collateral Growth in the Peripheral Circulation: A Review

Arterial occlusive diseases are a major cause of morbidity and death in the United States. The enlargement of pre-existing vessels, which bypass the site of arterial occlusion, provide a natural way for the body to compensate for such obstructions. Individuals differ in their capacity to develop collateral vessels. In recent years much attention has been focused upon therapy to promote collateral development, primarily using individual growth factors. Such studies have had mixed results. Persistent controversies exist regarding the initiating stimuli, the processes involved in enlargement, the specific vessels that should be targeted, and the most appropriate terminology. Consequently, it is now recognized that more research is needed to extend our knowledge of the complex process of collateral growth. This basic science review addresses five questions essential in understanding current problems in collateral growth research and the development of therapeutic interventions.

Blockage of Src by Specific siRNA as a Novel Therapeutic Strategy to Prevent Destructive Repair in Steroid-Associated Osteonecrosis in Rabbits

Vascular hyperpermeability and highly upregulated bone resorption in the destructive repair progress of steroid-associated osteonecrosis (SAON) are associated with a high expression of VEGF and high Src activity (Src is encoded by the cellular sarcoma [c-src] gene). This study was designed to prove our hypothesis that blocking the VEGF-Src signaling pathway by specific Src siRNA is able to prevent destructive repair in a SAON rabbit model. Destructive repair in SAON was induced in rabbits. At 2, 4, and 6 weeks after SAON induction, VEGF, anti-VEGF, Src siRNA, Src siRNA+VEGF, control siRNA, and saline were introduced via intramedullary injection into proximal femora for each group, respectively. Vascularization and permeability were quantified by dynamic contrast-enhanced (DCE) MRI. At week 6 after SAON induction, proximal femurs were dissected for micro-computed tomography (μCT)-based trabecular architecture with finite element analysis (FEA), μCT-based angiography, and histological analysis. Histological evaluation revealed that VEGF enhanced destructive repair, whereas anti-VEGF prevented destructive repair and Src siRNA and Src siRNA+VEGF prevented destructive repair and enhanced reparative osteogenesis. Findings of angiography and histomorphometry were consistent with those determined by DCE MRI. Src siRNA inhibited VEGF-mediated vascular hyperpermeability but preserved VEGF-induced neovascularization. Bone resorption was enhanced in the VEGF group and inhibited in the anti-VEGF, Src siRNA, Src siRNA+VEGF groups as determined by both 3D μCT and 2D histomorphometry. FEA showed higher estimated failure load in the Src siRNA and Src siRNA+VEGF groups when compared to the vehicle control group. Blockage of VEGF-Src signaling pathway by specific Src siRNA was able to prevent steroid-associated destructive repair while improving reconstructive repair in SAON, which might become a novel therapeutic strategy.

Role of copper in regression of cardiac hypertrophy

Pressure overload causes an accumulation of homocysteine in the heart, which is accompanied by copper depletion through the formation of copper-homocysteine complexes and the excretion of the complexes. Copper supplementation recovers cytochrome c oxidase (CCO) activity and promotes myocardial angiogenesis, along with the regression of cardiac hypertrophy and the recovery of cardiac contractile function. Increased copper availability is responsible for the recovery of CCO activity. Copper promoted expression of angiogenesis factors including vascular endothelial growth factor (VEGF) in endothelial cells is responsible for angiogenesis. VEGF receptor-2 (VEGFR-2) is critical for hypertrophic growth of cardiomyocytes and VEGFR-1 is essential for the regression of cardiomyocyte hypertrophy. Copper, through promoting VEGF production and suppressing VEGFR-2, switches the VEGF signaling pathway from VEGFR-2-dependent to VEGFR-1-dependent, leading to the regression of cardiomyocyte hypertrophy. Copper is also required for hypoxia-inducible factor-1 (HIF-1) transcriptional activity, acting on the interaction between HIF-1 and the hypoxia responsible element and the formation of HIF-1 transcriptional complex by inhibiting the factor inhibiting HIF-1. Therefore, therapeutic targets for copper supplementation-induced regression of cardiac hypertrophy include: (1) the recovery of copper availability for CCO and other critical cellular events; (2) the activation of HIF-1 transcriptional complex leading to the promotion of angiogenesis in the endothelial cells by VEGF and other factors; (3) the activation of VEGFR-1-dependent regression signaling pathway in the cardiomyocytes; and (4) the inhibition of VEGFR-2 through post-translational regulation in the hypertrophic cardiomyocytes. Future studies should focus on target-specific delivery of copper for the development of clinical application.

SDF-1 fused to a fractalkine stalk and a GPI anchor enables functional neovascularization

The facilitated recruitment of vascular progenitor cells (VPCs) to ischemic areas might be a therapeutic target for neovascularization and repair. However, efficient and directed attraction of VPCs remains a major challenge in clinical application. To enhance VPC homing, we developed a fusion protein (S1FG), based on the biology of stroma-derived factor-1/CXCL12 and the mucin backbone taken from fractalkine/CXCL12. A GPI-anchor was included to link the fusion-protein to the cell surface. HUVECs transfected with S1FG were capable of increasing firm adhesion of CXCR4+-mononuclear cells (THP-1) under shear stress conditions in vitro. In an in vivo rabbit model of chronic hind limb ischemia, local S1FG application enhanced the recruitment of adoptively transferred embryonic EPCs (eEPCs) to the ischemic muscles 2.5-fold. S1FG combined with eEPC(low) (2 × 10(6)) yielded similar capillary growth as eEPC(high) (5 × 10(6)) alone. Compared to controls, collateral formation was increased in the S1FG eEPC(low) group, but not the eEPC(high) group without S1FG, whereas perfusion was found enhanced in both groups. In addition, S1FG also increased collateral formation and flow when combined with AMD3100 treatment, to increase circulating levels of endogenous VPC. These data demonstrate that the fusion protein S1FG is capable of enhancing the recruitment of exogenously applied or endogenously mobilized progenitor cells to sites of injury. Recombinant versions of S1FG applied via catheters in combination with progenitor cell mobilization may be useful in the treatment of chronic ischemic syndromes requiring improved perfusion.

Cotransfection of vascular endothelial growth factor-A and platelet-derived growth factor-B via recombinant adeno-associated virus resolves chronic ischemic malperfusion role of vessel maturation

OBJECTIVES

We set out to investigate the ability of cardiotropic adeno-associated viral vector (AAV2.9 = recombinant adeno-associated virus [rAAV]) to induce prolonged expression of vascular endothelial growth factor (VEGF)-A and platelet-derived growth factor (PDGF)-B in a rabbit hindlimb ischemia model and a pig model of hibernating myocardium.

BACKGROUND

Gene therapy to induce angiogenesis and arteriogenesis has produced mixed results. However, long-acting viruses, such as rAAV, as well as combined induction of angiogenesis and vessel maturation might extend the therapeutic potential.

METHODS

In rabbits, 0.5 x 10(11) particles rAAV.VEGF-A with or without 1 x 10(12) particles rAAV.PDGF-B were retroinfused at day 7 after femoral artery excision. At days 7 and 35, collateral counts and perfusion were determined, each value given as the day 35/day 7 ratio. Capillary-to-muscle fiber ratio was determined at day 35. In pigs, implantation of a reduction stent graft into the circumflex artery led to complete occlusion at day 28. At this time point, retroinfusion of rAAV.VEGF-A (1 x 10(13) particles), rAAV.VEGF-A/PDGF-B (2 x 10(12) and 4 x 10(12) particles, respectively) or mock transfection was performed. Ejection fraction and left ventricular end-diastolic pressure were assessed at days 28 and 56.

RESULTS

In rabbits, rAAV.VEGF-A strongly induced angiogenesis (capillary-to-muscle fiber ratio; 1.67 +/- 0.09 vs. 1.32 +/- 0.11 in rAAV.LacZ-treated limbs, p < 0.05), but not collateral growth (125 +/- 7% vs. 106 +/- 7%, p = NS) or perfusion (136 +/- 12% vs. 107 +/- 9%, p = NS). With VEGF-A/PDGF-B cotransfection, collateral growth increased to 146 +/- 9%, perfusion to 163 +/- 8% of the respective day 7 value (p < 0.05). In the pig model, retroinfusion of rAAV.VEGF-A/PDGF-B increased regional myocardial blood flow reserve from 101 +/- 4% (rAAV.Mock) to 129 +/- 8% (p < 0.05), based on collateral growth (3.2 +/- 0.3 in rAAV.Mock vs. 9.0 +/- 0.4 in rAAV.VEGF-A/PDGF-B, p < 0.05), whereas rAAV.VEGF-A did not alter flow reserve (112 +/- 7%) or collateral count (5.2 +/- 0.7). rAAV.VEGF-A/PDGF-B improved ejection fraction (55 +/- 5% vs. 34 +/- 3% in rAAV.Mock, p < 0.05) unlike rAAV.VEGF-A (37 +/- 2%).

CONCLUSIONS

Retroinfusion of rAAV.VEGF-A alone induces angiogenesis, but fails to enhance collateralization and perfusion, unless PDGF-B is cotransfected. In addition to neovascularization, rAAV.VEGF-A/PDGF-B improves regional and global myocardial function in hibernating myocardium.

Immunohistochemical study of the growth factors, aFGF, bFGF, PDGF-AB, VEGF-A and its receptor (Flk-1) during arteriogenesis

Growth factors are viewed as main arteriogenic stimulators for collateral vessel growth. However, the information about their native expression and distribution in collateral vessels is still limited. This study was designed to profile expression of acidic and basic FGF, platelet-derived growth factor (PDGF-AB) and vascular endothelial growth factor (VEGF-A) and its receptor, fetal liver kinase-1 (Flk-1) during arteriogenesis by confocal immunofluorescence in both dog ameroid constrictor model and rabbit arteriovenous shunt model of arteriogenesis. We found that: (1) in normal arteries (NA) in dog heart, aFGF, bFGF, and PDGF-AB all were mainly expressed in endothelial cells (EC) and media smooth muscle cells (SMC), but the expression of aFGF was very weak, with those of the other two being moderate; (2) in collateral arteries (CAs), aFGF, bFGF, and PDGF-AB all were significantly upregulated (P < 0.05); they were present in all the layers of the vascular wall and were 2.1, 1.7, and 1.9 times higher than that in NA, respectively; and (3) in NA in rabbit hind limb, VEGF-A was absent, Flk-1 was only weakly present in endothelial cells, but in one week CAs VEGF-A and Flk-1 were significantly increased in both shunt and ligation sides; this was more evident in the shunt-side CAs, 2.3, and 2 times higher than that in the ligation side, respectively. In conclusion, our data demonstrate for the first time that growth factors, aFGF, bFGF, and PDGF-AB are significantly upregulated in collateral vessels in dog heart, and enhanced VEGF-A and its receptor, Flk-1, are associated with rapid and lasting increased shear stress. These findings suggest that endogenous production of growth factors could be an important factor promoting collateral vessel growth.

Marvels, mysteries, and misconceptions of vascular compensation to peripheral artery occlusion

Peripheral arterial disease is a major health problem and there is a significant need to develop therapies to prevent its progression to claudication and critical limb ischemia. Promising results in rodent models of arterial occlusion have generally failed to predict clinical success and led to questions of their relevance. While sub-optimal models may have contributed to the lack of progress, we suggest that advancement has also been hindered by misconceptions of the human capacity for compensation and the specific vessels which are of primary importance. We present and summarize new and existing data from humans, Ossabaw miniature pigs, and rodents which provide compelling evidence that natural compensation to occlusion of a major artery (i) may completely restore perfusion, (ii) occurs in specific pre-existing small arteries, rather than the distal vasculature, via mechanisms involving flow-mediated dilation and remodeling (iii) is impaired by cardiovascular risk factors which suppress the flow-mediated mechanisms and (iv) can be restored by reversal of endothelial dysfunction. We propose that restoration of the capacity for flow-mediated dilation and remodeling in small arteries represents a largely unexplored potential therapeutic opportunity to enhance compensation for major arterial occlusion and prevent the progression to critical limb ischemia in the peripheral circulation.

Sustained release of sphingosine 1-phosphate for therapeutic arteriogenesis and bone tissue engineering

Sphingosine 1-phosphate (S1P) is a bioactive phospholipid that impacts migration, proliferation, and survival in diverse cell types, including endothelial cells, smooth muscle cells, and osteoblast-like cells. In this study, we investigated the effects of sustained release of S1P on microvascular remodeling and associated bone defect healing in vivo. The murine dorsal skinfold window chamber model was used to evaluate the structural remodeling response of the microvasculature. Our results demonstrated that 1:400 (w/w) loading and subsequent sustained release of S1P from poly(lactic-co-glycolic acid) (PLAGA) significantly enhanced lumenal diameter expansion of arterioles and venules after 3 and 7 days. Incorporation of 5-bromo-2-deoxyuridine (BrdU) at day 7 revealed significant increases in mural cell proliferation in response to S1P delivery. Additionally, three-dimensional (3D) scaffolds loaded with S1P (1:400) were implanted into critical-size rat calvarial defects, and healing of bony defects was assessed by radiograph X-ray, microcomputed tomography (muCT), and histology. Sustained release of S1P significantly increased the formation of new bone after 2 and 6 weeks of healing and histological results suggest increased numbers of blood vessels in the defect site. Taken together, these experiments support the use of S1P delivery for promoting microvessel diameter expansion and improving the healing outcomes of tissue-engineered therapies.

Treatment with Autologous Bone Marrow Mononuclear Cells in Patients with Critical Lower Limb Ischaemia. A Pilot Study

Background and Aims:

Treatment with autologous, bone marrow mononuclear stem cells has shown effects in patients with chronic limb ischaemia in one randomized clinical study. The aim of the study was to test the potential effect of stem cell treatment in a strict defined group of patients with stable critical limb ischaemia (CLI). Design: A prospective, combined-centre pilot study.

Material:

Eight patients with CLI of the lower extremities, and without any other treatment options.

Methods:

Bone marrow cells were harvested from the patient's iliac crest and, after separation, injected into the calf muscles of the affected leg. Outcome was evaluated by digital subtraction angiography (DSA), visual analogue scale (VAS) and several non-invasive circulatory physiological tests.

Results:

There were no complications from the procedures. Two patients were amputated two months after cell injection. Five patients reported pain relief after four months. Five patients could be evaluated at eight months. According to VAS and physiological tests, they were all either stable or showed improvement.

Conclusion:

This method seems to be a safe option for treating patients with CLI. Inclusion of patients took a long time, mainly because many patients with CLI are offered endovascular treatment in our institution. While symptomatic improvement was found in individual patients, larger trials are required to investigate efficacy. This will probably require multi-centre participation.

Stimulation of collateral artery growth: a potential treatment for peripheral artery disease

In the course of peripheral artery occlusive disease, blood flow to peripheral tissue progressively decreases in a substantial portion of patients, leading to insufficient oxygenation and to the occurrence of claudication or critical limb ischemia. Arteriogenesis (collateral artery growth) is a powerful natural mechanism by which large conductance vessels develop that circumvent sites of obstruction. Promising experimental data on both hypoxia-driven angiogenesis as well as monocyte-orchestrated arteriogenesis have raised high hopes for clinical application. Both endothelial growth factors to stimulate angiogenesis (i.e., capillary growth) and monocyte-attracting or -activating substances to stimulate arteriogenesis, have been proposed as potential new therapeutic agents. However, transferring the promising experimental results into clinical practice has been more cumbersome than initially anticipated. Some recent clinical studies are now focusing more specifically on the stimulation of arteriogenesis. This review will critically evaluate the results of preclinical and clinical investigations on the stimulation of vascular growth, focusing specifically on the peripheral circulation.

Expression of Vascular Endothelial Growth Factor Receptor-2 in the Muscle Flap with Ischemic Injury in Rats

BACKGROUND

Ischemia of muscle flaps is a significant problem in reconstructive surgery. Administration of either recombinant vascular endothelium growth factor (VEGF) protein or gene transfers has been conducted to improve the survival of ischemic tissue. These biophysiological functions of VEGF are mediated through its receptor. In this study the changes of expression in VEGF receptor mRNA in muscle flaps with acute ischemia were examined in a rat gracilis muscle flap model.

MATERIALS AND METHODS

Twenty-four Sprague Dawley rats were used. The ischemia of the flap was induced by clamping its vascular pedicle. At 3-, 6-, and 18-h intervals, the flaps were biopsied for histology and examination of VEGFR-2 mRNA gene expression. The muscle flap without ischemia was used as the control.

RESULTS

The results showed that the VEGFR-2 mRNA level was significantly increased 3 h after ischemia was induced and then attenuated to the baseline at 6 and 18 h ischemia.

CONCLUSIONS

This study delineated the changes in expression of VEGFR-2 receptor in muscle flap in several postischemic intervals and provided a timeframe for the clinical application of VEGF.

Microenvironmental VEGF distribution is critical for stable and functional vessel growth in ischemia

The critical role of vascular endothelial growth factor (VEGF) expression levels in developmental angiogenesis is well established. Nonetheless, the effects of different local (microenvironmental) VEGF concentrations in ischemia have not been studied in the adult organism, and VEGF delivery to patients has been disappointing. Here, we demonstrate the existence of both lower and upper threshold levels of microenvironmental VEGF concentrations for the induction of therapeutic vessel growth in ischemia. In the ischemic hind limb, implantation of myoblasts transduced to express VEGF164 at different levels per cell increased blood flow only moderately, and vascular leakage and aberrant preangiomatous vessels were always induced. When the same total dose was uniformly distributed by implanting a monoclonal population derived from a single VEGF-expressing myoblast, blood flow was fully restored to nonischemic levels, collateral growth was induced, and ischemic damage was prevented. Hemangiomas were avoided and only normal, pericyte-covered vessels were induced persisting over 15 mo. Surprisingly, clones uniformly expressing either lower or higher VEGF levels failed to provide any functional benefit. A biphasic effect of VEGF dose on vessel number and diameter was found. Blood flow was only improved if vessels were increased both in size and in number. Microenvironmental VEGF concentrations determine efficacy and safety in a therapeutic setting.

Autoperipheral blood mononuclear cell transplantation improved giant ulcers due to chronic arteriosclerosis obliterans

We report the case of a 74-year-old man with Fontaine stage IV chronic arteriosclerosis obliterans who had been suffering from inveterate giant skin ulcers on the dorsum and heel of the right foot. As conventional medical treatments had not improved these ulcers and surgical treatment was considered unfeasible, amputation of the right lower limb below the knee appeared to represent the only option. The patient was admitted to Tottori University Hospital to attempt a new angiogenic therapy using auto-mononuclear cell transplantation to avoid amputation. On admission, neither right ankle blood pressure nor transcutaneous partial pressure of oxygen at the right toe were detectable. The patient had a history of multiple cerebral infarctions, and collection of mononuclear cells from bone marrow was considered too difficult, so collection of peripheral blood mononuclear cells was selected. Transcutaneous partial pressure of oxygen and skin temperature in the treated limb started to improve from 2 weeks after implantation. Ulcer size was recognizably reduced by 1 month after treatment. Partial auto-skin implantation on the right heel was performed 2 months after treatment, and the giant skin ulcer was finally completely covered. No adverse effects were noted during follow-up lasting 1 year. These results suggest that peripheral blood mononuclear cell implantation may offer a suitable alternative rescue therapy for patients with critical limb ischemia whose general condition is not good.

CD151 promotes neovascularization and improves blood perfusion in a rat hind-limb ischemia model

PURPOSE

To evaluate the efficiency of recombinant adeno-associated virus (rAAV)-mediated CD151 gene delivery in promoting neovascularization and improving blood perfusion in the skeletal muscle of the rat hind-limb ischemia model.

METHODS

CD151 was constructed into the rAAV vector. Twelve Wistar rats were randomly divided into 2 groups of 6 rats each and then intramuscularly injected with rAAV-CD151 or rAAV-GFP, respectively, in one hind limb. Two weeks after gene delivery, the femoral arteries in the treated limbs were excised to establish the model of hind-limb ischemia. Expression of the transgene product CD151 was confirmed by Western blot and the reverse transcription polymerase chain reaction. The skin temperature, angiographic score, and capillary density of the hind limb were measured to assess blood perfusion and neovascularization 6 weeks after transfection.

RESULTS

Compared to the group transfected with GFP, the CD151 group showed a 63% higher angiographic score (p<0.05) and an 18% increase in capillary density (p<0.05). In addition, the mean skin temperature of the AAV-CD151-transfected hind limbs was equivalent to the level of the contralateral nonischemic limb, whereas the limb temperature in the GFP-transfected rats was significantly lower than the nonischemic control. The expression of CD151 in the ischemic hind limb injected with rAAV-CD151 was significantly higher than limbs injected with rAAV-GFP. The CD151 mRNA and protein expression was persistently observed in the injected muscle for at least 6 weeks after injection, while no human CD151 mRNA could be detected in remote organs or rAAV-GFP-injected muscles.

CONCLUSIONS

This study demonstrates that the rAAV-mediated CD151 gene transfer into rat skeletal muscles is efficient, stable, and has no ectopic expression. Moreover, rAAV-mediated CD151 gene transfer stimulates neovascularization, especially arteriogenesis, and thereby improves blood perfusion in a rat hind-limb ischemia model. These findings suggest that CD151 could be a new target for neovascularization therapy in ischemic disease, and rAAV-mediated CD151 gene transfer may be useful for treatment of ischemic disease.

Angiogenesis is confined to the transient period of VEGF expression that follows adenoviral gene delivery to ischemic muscle

Therapeutic angiogenesis involves the introduction of exogenous growth factor proteins and genes into ischemic tissues to augment endogenous factors and promote new vessel growth. Positive results from studies in animal models of peripheral arterial disease (PAD) and coronary artery disease over the past decade have supported the implementation of clinical trials testing vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) proteins and genes. Although several clinical trials reported positive results, others have been disappointing and results of a recent Phase II trial of VEGF delivered by adenovirus (the RAVE trial) were negative. It has been suggested that the duration of gene expression following delivery by adenovirus may be insufficient to produce stable vessels. Here we present direct evidence in support of this using the rabbit ischemic hindlimb model injected with adenovirus encoding VEGF165. Immunohistology indicated an activation of endothelial cell cycling and proliferation 2-3 days after VEGF delivery that coincided closely with transient VEGF expression. Ki-67-positive endothelial nuclei were evident at high levels in capillaries and large vessels in muscles from treated animals. Angiography indicated increased density of both large and small vessels in Ad-VEGF-treated muscle at 1 week, but no significant differences thereafter. The early burst of endothelial proliferation was accompanied by increased nuclear fragmentation and condensation in VEGF-treated muscles, suggesting coincident apoptosis. No further endothelial cell proliferation took place after 1 week although there was still evidence of apoptosis. The results suggest that angiogenesis is confined to the short period of VEGF expression produced by adenovirus and early gains in collateralization rapidly regress to control levels when VEGF production ceases.

Catecholamines augment collateral vessel growth and angiogenesis in hindlimb ischemia

Catecholamine stimulation of α1-adrenoceptors exerts growth factor-like activity, mediated by generation of reactive oxygen species, on arterial smooth muscle cells and adventitial fibroblasts and contributes to hypertrophy and hyperplasia in models of vascular injury and disease. Adrenergic trophic activity also contributes to flow-mediated positive arterial remodeling by augmenting proliferation and leukocyte accumulation. To further examine this concept, we studied whether catecholamines contribute to collateral growth and angiogenesis in hindlimb insufficiency. Support for this hypothesis includes the above-mentioned studies, evidence that ischemia augments norepinephrine release from sympathetic nerves, and proposed involvement of reactive oxygen species in angiogenesis and collateral growth. Mice deficient in catecholamine synthesis [by gene deletion of dopamine β-hydroxylase (DBH−/−)] were studied. At 3 wk after femoral artery ligation, increases in adductor muscle perfusion were similar in DBH−/− and wild-type mice, whereas recovery of plantar perfusion and calf microsphere flow were attenuated, although not significantly. Preexisting collaterals in adductor of wild-type mice showed increases in lumen diameter (60%) and medial and adventitial thickness (57 and 119%, P < 0.05 here and below). Lumen diameter increased similarly in DBH−/− mice (52%); however, increases in medial and adventitial thicknesses were reduced (30 and 65%). Leukocyte accumulation in the adventitia/periadventitia of collaterals was 39% less in DBH−/− mice. Increased density of α-smooth muscle actin-positive vessels in wild-type adductor (45%) was inhibited in DBH−/− mice (2%). Although both groups experienced similar atrophy in the gastrocnemius (∼22%), the increase in capillary-to-muscle fiber ratio in wild-type mice (21%) was inhibited in DBH−/− mice (7%). These data suggest that catecholamines may contribute to collateral growth and angiogenesis in tissue ischemia.

Gene therapy with adenovirus-mediated VEGF enhances skin flap prefabrication

We investigated the feasibility in rats of enhancing skin-flap prefabrication with subdermal injections of adenovirus-encoding vascular endothelial growth factor (Ad-VEGF). The left saphenous vascular pedicle was used as a source for vascular induction. A peninsular abdominal flap (8 x 8 cm) was elevated as distally based, keeping the epigastric vessels intact on both sides. After the vascular pedicle was tacked underneath the abdominal flap, 34 rats were randomly divided into three groups according to treatment protocol. The implantation site around the pedicle was injected with Ad-VEGF in group I (n = 10), with adenovirus-encoding green fluorescent protein (Ad-GFP) in control group I (n = 14), and with saline in control group II (n = 10). All injections were given subdermally at four points around the implanted vessel by an individual blinded to the treatment protocol. The peninsular flap was sutured in its place, and 4 weeks later, an abdominal island flap based solely on the implanted vessels was elevated. The prefabricated island flap was sutured back, and flap viability was evaluated on day 7. Skin specimens were stained with hematoxylin and eosin for histological evaluation. In two rats from each group, microangiography was performed to visualize the vascularity of the prefabricated flaps. There was a significant increase in survival of prefabricated flaps in the Ad-VEGF group compared to the control groups: Ad-VEGF, 88.9 +/- 6.1% vs. Ad-GFP, 65.6 +/- 9.4% (P < 0.05) and saline, 56.0 +/- 3.4% (P < 0.05). Sections from four prefabricated flaps treated with Ad-GFP revealed multiple sites of shiny deposits of green fluorescent protein around the area of local administration 1 day and 3 weeks after gene therapy. Histological examination done under high-power magnification (x400) with a light microscope revealed increased vascularity and mild inflammation surrounding the implanted vessel in all groups. However, we were unable to demonstrate any significant quantitative difference with respect to vascularity and inflammatory infiltrates in prefabricated flaps treated with Ad-VEGF compared with controls. Microangiographic studies showed increased vascularity around the implanted pedicle, which was similar in all groups. However, vascularization was distributed in a larger area in the prefabricated flaps treated with Ad-VEGF. In this study, the authors demonstrated that adenovirus-mediated VEGF gene therapy increased the survival of prefabricated flaps, suggesting that it may allow prefabrication of larger flaps and have the potential to reduce the time required for flap maturation.

VEGF165 and angiopoietin-1 decreased myocardium infarct size through phosphatidylinositol-3 kinase and Bcl-2 pathways

Angiogenic growth factors, vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang1) could decrease myocardial infarct size, which was assumed to be related with newly formed capillaries. We doubted that these capillaries could do this solely and the potential protective mechanisms of VEGF and Ang1 on myocardium need to be evaluated. Three types of adenoviruses encoding human VEGF(165) (Ad-VEGF(165)), human angiopoietin-1 (Ad-Ang1) and green fluorescent protein (Ad-GFP, as a parallel control) were constructed. Experiments were taken both in vitro and in vivo. As in vitro, the antiapoptosis effect of VEGF(165), Ang1 and VEGF(165)+Ang1 on cardiac myoblasts was observed, which seemed to be related with the activation of phosphatidylinositol-3 kinase and Bcl-2 pathways. As in vivo, adenoviruses were intramyocardially injected immediately after the ligation of the left anterior descending coronay arteries in rats. The results showed positive effect of VEGF(165), Ang1 and VEGF(165)+Ang1 on decreasing the myocardial infarct size at the 7th day. Myocardial PI-3K activity and Bcl-2 expression were elevated relatively at the 3rd day. The protective effect of VEGF(165) and Ang1 on the myocardium may broaden their functional research and contribute to their clinical use in the future.

Adenoviral gene transfer with soluble vascular endothelial growth factor receptors impairs angiogenesis and perfusion in a murine model of hindlimb ischemia

BACKGROUND

The purpose of the current study was to examine the contribution of endogenous vascular endothelial growth factor (VEGF) to ischemia-induced angiogenesis and perfusion.

METHODS AND RESULTS

C57BL/6J mice (n=28) were subjected to unilateral hindlimb ischemia after intravenous injection of recombinant adenoviruses (10(9) plaque-forming units) encoding the ligand-binding ectodomain of VEGF receptor 1 (VEGFR1/Ad Flt1), VEGF receptor 2 (VEGFR2/Ad Flk1-Fc), a control murine IgG2alpha Fc fragment (Ad Fc), or vehicle (phosphate-buffered saline). Hindlimb perfusion was assessed by both laser Doppler and fluorescent microsphere injection 10 days after surgery. The role of endogenous VEGF in ischemia-induced angiogenesis and arteriogenesis was measured by capillary density and microangiography, respectively. Adenoviral gene transfer with soluble VEGFRs significantly attenuated hindlimb perfusion as assessed by laser Doppler and microsphere analysis (P<0.05). Furthermore, soluble VEGFRs significantly reduced ischemia-induced angiogenesis and collateral growth and inhibited histological recovery of muscle tissue. Adverse events consistent with ongoing vascular insufficiency such as limb necrosis or gangrene were observed only in animals expressing soluble VEGFRs and not in control animals.

CONCLUSIONS

Systemic, soluble receptor-mediated VEGF inhibition indicates an essential role for endogenous VEGF during postischemic angiogenesis and hindlimb perfusion.

Quantitative microcomputed tomography analysis of collateral vessel development after ischemic injury

Transgenic mouse models are increasingly being used to investigate the functions of specific growth factors or matrix proteins to design therapeutic strategies for controlling blood vessel growth. However, the available methodologies for evaluating angiogenesis and arteriogenesis in these models are limited by animal size, user subjectivity, the power to visualize the three-dimensional vessel networks, or the capability to employ a vigorous quantitative analysis. In this study, we employed contrast-enhanced microcomputed tomography imaging to assess collateral development after induction of hindlimb ischemia in the mouse. The morphological parameters vessel volume, connectivity, number, thickness, thickness distribution, separation, and degree of anisotropy were evaluated in control and surgery limbs 0, 3, and 14 days postsurgery. Results indicate that the vascular volume of the surgically manipulated limb was reconstituted as early as 3 days after femoral artery excision through development of a series of highly connected, small caliber, closely spaced, and isotropically oriented collateral vessels. Parametric analyses were completed to assess the sensitivity of the calculated morphological parameters to variations in image binarization threshold and voxel size. Images taken at the 36-μm voxel size were found to be optimal for evaluating collateral vessel formation, whereas 8- to 16-μm voxel sizes were needed to resolve smaller vascular structures. This study demonstrates the utility of microcomputed tomography as a robust method for quantitative, three-dimensional analysis of blood vessel networks. Whereas these initial efforts focused on the mouse hindlimb ischemia model, the developed techniques may be applied to a variety of model systems to investigate mechanisms of angiogenesis and arteriogenesis.

Tyrosine phosphatase inhibition augments collateral blood flow in a rat model of peripheral vascular disease

During embryonic development, the growth of blood vessels requires the coordinated activation of endothelial receptor tyrosine kinases (RTKs) such as vascular endothelial growth factor receptor-2 (VEGFR-2) and Tie-2. Similarly, in adulthood, activation of endothelial RTKs has been shown to enhance development of the collateral circulation and improve blood flow to ischemic tissues. Recent evidence suggests that RTK activation is negatively regulated by protein tyrosine phosphatases (PTPs). In this study, we used the nonselective PTP inhibitor bis(maltolato)oxovanadium IV (BMOV) to test the potential efficacy of PTP inhibition as a means to enhance endothelial RTK activation and improve collateral blood flow. In cultured endothelial cells, pretreatment with BMOV augmented VEGFR-2 and Tie-2 tyrosine phosphorylation and enhanced VEGF- and angiopoietin-1-mediated cell survival. In rat aortic ring explants, BMOV enhanced vessel sprouting, a process that can be influenced by both VEGFR-2 and Tie-2 activation. Moreover, 2 wk of BMOV treatment in a rat model of peripheral vascular disease enhanced collateral blood flow similarly to VEGF, and after 4 wk, BMOV was superior to VEGF. Taken together, these studies provide evidence that PTPs are important regulators of endothelial RTK activation and for the first time demonstrate the potential utility of phosphatase inhibition as a means to promote collateral development and enhance collateral blood flow to ischemic tissue.