The delivery of angiogenic factors to the heart by microsphere therapy

MMP-sensitive PEG hydrogel modified with RGD promotes bFGF, VEGF and EPC-mediated angiogenesis

Traumatic soft tissue defects such as bedsores, chronic skin ulcers, limb necrosis, osteonecrosis and other ischemic orthopedic diseases are the most clinically intractable and common problems in orthopedics due to unsatisfactory conventional treatments. The present study designed poly(ethylene glycol; PEG) hydrogels with covalently binded arginylglycylaspartic acid (RGD). Endothelial progenitor cells (EPCs) were encapsulated in the modified hydrogel along with vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). Results demonstrated that the modified hydrogel displayed good mechanical properties appropriate for a sustained release carrier. RGD modification significantly promoted EPC biocompatibility. VEGF and bFGF encapsulation enhanced the adhesion of EPCs, promoted the production of extracellular matrix and facilitated EPC proliferation. In addition, bFGF and VEGF induced angiogenesis. The combination of growth factors and EPCs in the hydrogel displayed a strong synergy to improve biocompatibility. The present results provided a potential novel treatment approach for soft tissue defects such as bone exposure, chronic skin ulcers, bedsores, limb necrosis, osteonecrosis and other ischemic diseases.

VEGF165Amicrosphere therapy for myocardial infarction suppresses acute cytokine release and increases microvascular density but does not improve cardiac function

Angiogenesis induced by growth factor-releasing microspheres can be an off-the-shelf and immediate alternative to stem cell therapy for acute myocardial infarction (AMI), independent of stem cell yield and comorbidity-induced dysfunction. Reliable and prolonged local delivery of intact proteins such as VEGF is, however, notoriously difficult. Our objective was to create a platform for local angiogenesis in human-sized hearts, using polyethylene-glycol/polybutylene-terephthalate (PEG-PBT) microsphere-based VEGF165Adelivery. PEG-PBT microspheres were biocompatible, distribution was size dependent, and a regimen of 10 × 10615-μm microspheres at 0.5 × 106/min did not induce cardiac necrosis. Efficacy, studied in a porcine model of AMI with reperfusion rather than chronic ischemia used for most reported VEGF studies, shows that microspheres were retained for at least 35 days. Acute VEGF165Arelease attenuated early cytokine release upon reperfusion and produced a dose-dependent increase in microvascular density at 5 wk following AMI. However, it did not improve major variables for global cardiac function, left ventricular dimensions, infarct size, or scar composition (collagen and myocyte content). Taken together, controlled VEGF165Adelivery is safe, attenuates early cytokine release, and leads to a dose-dependent increase in microvascular density in the infarct zone but does not translate into changes in global or regional cardiac function and scar composition.

Tetanus toxoid-pulsed monocyte vaccination for augmentation of collateral vessel growth

Background

The pathogenesis of collateral growth (arteriogenesis) has been linked to both the innate and adaptive immune systems. While therapeutic approaches for the augmentation of arteriogenesis have focused on innate immunity, exploiting both innate and adaptive immune responses has not been examined. We hypothesized that tetanus toxoid (tt) immunization of mice followed by transplantation of monocytes (Mo) exposed ex vivo to tt augments arteriogenesis after ligation of the hind limb.

Methods and Results

Mo were generated from nonimmunized BALB/c mice, exposed ex vivo to tt for 24 hours and intravenously injected (ttMo, 2.5×10⁶) into the tail veins of tt‐immunized syngeneic mice whose hind limbs had been ligated 24 hours prior to transplantation. Laser Doppler perfusion imaging was applied, and a perfusion index (PI) was calculated (ratio ligated/unligated). Twenty‐one days after ligation, the arteriogenesis of untreated BALB/c mice was limited (PI=0.49±0.09). Hind limb function was impaired in 80% of animals. Injection of non‐engineered Mo insignificantly increased the PI to 0.56±0.07. However, ttMo transplantation resulted in a strong increase of the PI to 0.82±0.08 (n=7; P<0.001), with no (0%) detectable functional impairment. ttMo injected into nonimmunized mice had no effect. The strong arteriogenic response of ttMo transplantation into immunized mice was prevented when mice had been depleted of T‐helper cells by CD4‐antibody pretreatment (PI=0.50±0.08; n=17; P<0.001), supporting the hypothesis that transplanted cells interact with recipient lymphocytes.

Conclusions

Transplantation of ttMo into pre‐immunized mice strongly promotes arteriogenesis. This therapeutic approach is feasible and highly attractive for the alleviation of morbidity associated with vascular occlusive disease.

Cell-responsive hydrogel for encapsulation of vascular cells

The in vitro potential of a synthetic matrix metalloproteinase (MMP)-responsive poly(ethylene glycol) (PEG)-based hydrogel as a bioactive co-encapsulation system for vascular cells and a small bioactive peptide, thymosin beta4 (Tbeta4), was examined. We show that the physical incorporation of Tbeta4 in this bioactive matrix creates a three-dimensional (3D) environment conducive for human umbilical vein endothelial cell (HUVEC) adhesion, survival, migration and organization. Gels with entrapped Tbeta4 increased the survival of HUVEC compared to gels without Tbeta4, and significantly up-regulated the endothelial genes vascular endothelial-cadherin and angiopoietin-2, whereas von Willebrand factor was significantly down-regulated. Incorporation of Tbeta4 significantly increased MMP-2 and MMP-9 secretion of encapsulated HUVEC. The gel acts as a controlled Tbeta4-release system, as MMP-2 and MMP-9 enzymes trigger the release. In addition, Tbeta4 facilitated HUVEC attachment and induced vascular-like network formation upon the PEG-hydrogels. These MMP-responsive PEG-hydrogels may thus serve as controlled co-encapsulation system of vascular cells and bioactive factors for in situ regeneration of ischemic tissues.

Collateral circulation: past and present

Following an arterial occlusion outward remodeling of pre-existent inter-connecting arterioles occurs by proliferation of vascular smooth muscle and endothelial cells. This is initiated by deformation of the endothelial cells through increased pulsatile fluid shear stress (FSS) caused by the steep pressure gradient between the high pre-occlusive and the very low post-occlusive pressure regions that are interconnected by collateral vessels. Shear stress leads to the activation and expression of all NOS isoforms and NO production, followed by endothelial VEGF secretion, which induces MCP-1 synthesis in endothelium and in the smooth muscle of the media. This leads to attraction and activation of monocytes and T-cells into the adventitial space (peripheral collateral vessels) or attachment of these cells to the endothelium (coronary collaterals). Mononuclear cells produce proteases and growth factors to digest the extra-cellular scaffold and allow motility and provide space for the new cells. They also produce NO from iNOS, which is essential for arteriogenesis. The bulk of new tissue production is carried by the smooth muscles of the media, which transform their phenotype from a contractile into a synthetic and proliferative one. Important roles are played by actin binding proteins like ABRA, cofilin, and thymosin beta 4 which determine actin polymerization and maturation. Integrins and connexins are markedly up-regulated. A key role in this concerted action which leads to a 2-to-20 fold increase in vascular diameter, depending on species size (mouse versus human) are the transcription factors AP-1, egr-1, carp, ets, by the Rho pathway and by the Mitogen Activated Kinases ERK-1 and -2. In spite of the enormous increase in tissue mass (up to 50-fold) the degree of functional restoration of blood flow capacity is incomplete and ends at 30% of maximal conductance (coronary) and 40% in the vascular periphery. The process of arteriogenesis can be drastically stimulated by increases in FSS (arterio-venous fistulas) and can be completely blocked by inhibition of NO production, by pharmacological blockade of VEGF-A and by the inhibition of the Rho-pathway. Pharmacological stimulation of arteriogenesis, important for the treatment of arterial occlusive diseases, seems feasible with NO donors.

Improving cell engraftment with tissue engineering

Cardiac cell therapy has not yet resulted in long-term clinical benefits or major recovery of myocardial function in humans. To date, most of the cardiac effects of cell-based therapy are believed to be mediated by a local angiogenic response rather than by the formation of neosyncytial contractile units such as had initially been hoped for. Therefore, repopulation of the ischemic or infarcted heart with progenitor cells that have vasculogenic potential may be an important mechanism to improve contractile function, both in the presence of viable and nonviable myocardium. This constitutes a focus within scientific reach; however, the low engraftment and viability of progenitor cells after transplantation necessitate the exploration of novel delivery techniques. Because biomaterials have the capacity to improve cell retention, survival, and differentiation, tissue engineering is now being explored as an approach to support cell-based therapies and enhance their efficacy. In this article, we address current progress made in tissue engineering to support cell therapy for the heart, and summarize our work in the development of biomaterials toward improving cell delivery and vascularization of ischemic tissue.

Del-1 gene transfer induces cerebral angiogenesis in mice

Developmental endothelial locus-1 (Del-1) is a novel angiomatrix protein that has been shown to stimulate a potent angiogenic response and promote functional recovery in hind-limb and cardiac ischemia in animal models; however, its impact on cerebral angiogenesis is unknown. In this study, we investigated whether Del-1 overexpression via gene transfer induces cerebral angiogenesis in a murine model, and examined Del-1 expression after ischemic stroke. Cerebral Del-1 overexpression was achieved with AAV (adeno-associated virus) transduction system via stereotactic injection. Control mice were injected with AAV-lacZ. Del-1 gene transduction led to a significant induction of cerebral angiogenesis compared to AAV-lacZ treatment at 4 weeks after gene transfer (Del-1: 97+/-7 vs lacZ: 64+/-28, vessels/field, p<0.05). Mice transduced with AAV-Del-1 showed significantly elevated vascular densities for up to 6 weeks after gene delivery. In addition, double immunofluorescent staining showed co-localization of endothelial cell marker CD31 with BrdU (specific marker for proliferating cells), indicating that Del-1 promoted endogenous endothelial cell proliferation and angiogenesis. Our immunohistochemical staining also showed that Del-1 expression was markedly up-regulated in the peri-infarct area at 3 days after permanent focal cerebral ischemia compared to the sham-operated non-ischemic control. Our data suggest that Del-1 may participate in modulating cerebral angiogenesis, and that gene transfer of Del-1 may provide a novel and potent means for stimulating cerebral angiogenesis.

Neovascularization of ischemic myocardium by newly isolated tannins prevents cardiomyocyte apoptosis and improves cardiac function

During remodeling progress post myocardial infarction, the contribution of neoangiogenesis to the infarct-bed capillary is insufficient to support the greater demands of the hypertrophied but viable myocardium resulting in further ischemic injury to the viable cardiomyocytes at risk. Here we reported the bio-assay-guided identification and isolation of angiogenic tannins (angio-T) from Geum japonicum that induced rapid revascularization of infarcted myocardium and promoted survival potential of the viable cardiomyocytes at risk after myocardial infarction. Our results demonstrated that angio-T displayed potent dual effects on up-regulating expression of angiogenic factors, which would contribute to the early revascularization and protection of the cardiomyocytes against further ischemic injury, and inducing antiapoptotic protein expression, which inhibited apoptotic death of cardiomyocytes in the infarcted hearts and limited infarct size. Echocardiographic studies demonstrated that angio-T-induced therapeutic effects on acute infarcted myocardium were accompanied by significant functional improvement by 2 days after infarction. This improvement was sustained for 14 days. These therapeutic properties of angio-T to induce early reconstitution of a blood supply network, prevent apoptotic death of cardiomyocytes at risk, and improve heart function post infarction appear entirely novel and may provide a new dimension for therapeutic angiogenesis medicine for the treatment of ischemic heart diseases.

Neovascularization of ischemic myocardium by newly isolated tannins prevents cardiomyocyte apoptosis and improves cardiac function

During remodeling progress post myocardial infarction, the contribution of neoangiogenesis to the infarct-bed capillary is insufficient to support the greater demands of the hypertrophied but viable myocardium resulting in further ischemic injury to the viable cardiomyocytes at risk. Here we reported the bio-assay-guided identification and isolation of angiogenic tannins (angio-T) from Geum japonicum that induced rapid revascularization of infarcted myocardium and promoted survival potential of the viable cardiomyocytes at risk after myocardial infarction. Our results demonstrated that angio-T displayed potent dual effects on up-regulating expression of angiogenic factors, which would contribute to the early revascularization and protection of the cardiomyocytes against further ischemic injury, and inducing antiapoptotic protein expression, which inhibited apoptotic death of cardiomyocytes in the infarcted hearts and limited infarct size. Echocardiographic studies demonstrated that angio-T-induced therapeutic effects on acute infarcted myocardium were accompanied by significant functional improvement by 2 days after infarction. This improvement was sustained for 14 days. These therapeutic properties of angio-T to induce early reconstitution of a blood supply network, prevent apoptotic death of cardiomyocytes at risk, and improve heart function post infarction appear entirely novel and may provide a new dimension for therapeutic angiogenesis medicine for the treatment of ischemic heart diseases.

Repair of Infarcted Myocardium by an Extract of Geum japonicum with Dual Effects on Angiogenesis and Myogenesis

Background: It has become apparent recently that cardiac myocytes can divide after myocardial infarction, a circumstance that challenges the orthodox view that myocytes may be terminally differentiated. Replacement of the necrosed heart tissue by newly regenerated functional myocardium is a therapeutic ideal, but attempts to reconstitute functional myocardia and coronary vessels have been less successful.

Methods: We isolated a fraction containing 5 compounds from the Chinese herb Geum japonicum, which stimulates the processes of angiogenesis and cardiomyogenesis. We investigated these dual properties in both ex vivo and in vivo systems.

Results: We observed that this bioactive fraction displayed favorable dual actions on early angiogenesis and cardiomyogenesis in acute myocardial infarction in an animal model. Our results demonstrated that application of this bioactive fraction showed pronounced effects on limiting infarct size by 35%–45%, stimulating early development of new blood vessels in 24 h, and regenerating myocardium, replacing ∼49% of the total infarction volume after 2 weeks. Echocardiographic studies demonstrated marked improvement of left ventricular function within 2 days after infarction, and the improvement was sustained for &gt;1 month.

Conclusions: The properties of this bioactive fraction appear to be entirely novel and represent a new approach for the treatment of ischemic heart disease.

Cardiovascular gene delivery: The good road is awaiting

Atherosclerotic cardiovascular disease is a leading cause of death worldwide. Despite recent improvements in medical, operative, and endovascular treatments, the number of interventions performed annually continues to increase. Unfortunately, the durability of these interventions is limited acutely by thrombotic complications and later by myointimal hyperplasia followed by progression of atherosclerotic disease over time. Despite improving medical management of patients with atherosclerotic disease, these complications appear to be persisting. Cardiovascular gene therapy has the potential to make significant clinical inroads to limit these complications. This article will review the technical aspects of cardiovascular gene therapy; its application for promoting a functional endothelium, smooth muscle cell growth inhibition, therapeutic angiogenesis, tissue engineered vascular conduits, and discuss the current status of various applicable clinical trials.

Three catheter-based strategies for cardiac delivery of therapeutic gelatin microspheres

Gelatin hydrogel microspheres (GHMs) have been reported as novel non-viral vectors for gene or protein delivery (GHM therapy). However, the components of an effective catheter-based delivery strategy for GHM therapy are unknown. We evaluated the effectiveness of three catheter-based strategies for cardiac GHM therapy: (1) antegrade injection (AI) via coronary arteries; (2) retrograde injection (RI) via coronary veins; and (3) direct myocardial injection (DI) via the coronary sinus. AI distributed microspheres homogeneously throughout the target area with 73+/-11% retention. RI scattered microspheres non-homogenously with 22+/-8% retention. DI distributed microspheres in the needle-advanced area with 47+/-14% retention. However, despite high efficiency, AI did not show biological effects of inducing angiogenesis from basic fibroblast growth factor bound to GHMs. Furthermore, focal micro-infarctions, owing to micro-embolism of aggregated GHMs into small coronary arterioles, were detected in the AI group. Conversely, only RI and DI groups displayed increased coronary flow reserve. DI groups also demonstrated increased capillary density. These results suggest that RI and DI are effective for cardiac GHM therapy, while AI appears inappropriate owing to the risk of focal infarctions.

Localized Angiogenesis Induced by Human Vascular Endothelial Growth Factor-Activated PLGA Sponge

The objective of this study was to assess the in vitro release kinetics and the in vivo angiogenic effect of human vascular endothelial growth factor (VEGF)-activated poly(DL-lactide-co-glycolide) (PLGA) sponge. The highly porous sponges (each 3 x 4 x 4 mm(3)) were activated by soaking in a VEGF solution (2.5 or 5.0 microg) and then freeze-drying. In vitro release in PBS was investigated by a competitive enzyme immunoassay for up to 3 weeks. The burst-type initial release within the first 3 days followed a more controlled one lasting for >2 weeks. The angiogenic potential of the VEGF sponge was evaluated by subcutaneous implantation into the epigastric groin fascia of Wistar rats. Histomorphometry and SEM confirmed the formation of new capillaries infiltrating the sponge pores starting from the first week and the drastic anostomosis at weeks 2 and 3. However, the rats implanted with control sponges or receiving VEGF injection exhibited much lower or no angiogenic response, respectively. TEM revealed the neo-vessels had a single endothelial layer surrounded by the matrix inoculated with the rat circulation. The results indicate that VEGF-activated PLGA sponge can be considered as a tool to establish neovascularized subcutaneous transplantation sites for tissue-engineering applications.

Gelatin Hydrogel Microspheres Enable Pinpoint Delivery of Basic Fibroblast Growth Factor for the Development of Functional Collateral Vessels

Background— Various growth factors promote collateral vessel development and are regarded as promising for the treatment of vascular occlusive diseases. However, an efficacious delivery system for them has yet to be established. We devised a strategy to augment functional collateral vessels by using acidic gelatin hydrogel microspheres (AGHMs) incorporating basic fibroblast growth factor (bFGF). The aim of the present study was to investigate the hypothesis that by intra-arterial (IA) administration of bFGF-impregnated AGHMs, bFGF could be delivered from AGHMs trapped in distal small-diameter vessels and thereby induce functional collateral vessels with an assured blood supply through the process of arteriogenesis.

Methods and Results— Various sizes of AGHMs (3 mg) incorporating 125 I-labeled bFGF were injected into the left internal iliac artery of a rabbit model of hindlimb ischemia. Less than 50% of radioactivity accumulated in the ischemic hindlimb after injection of AGHMs that were 10 μm in diameter, whereas ≈80% of radioactivity was counted in the ischemic limb after administration of 29- or 59-μm-diameter AGHMs. Calf blood pressure ratio and the ratio of regional blood flow of the bilateral hindlimbs immediately before and after IA administration of 29-μm–diameter AGHMs showed no significant change. Then we evaluated the function of the developed collateral vessels 28 days after IA administration of bFGF-impregnated, 29-μm-diameter AGHMs. IA administration of bFGF-impregnated AGHMs induced marked collateral vessel improvement compared with IA administration of phosphate buffered saline–treated AGHMs and intramuscular administration of bFGF-impregnated AGHMs.

Conclusions— IA administration of bFGF-impregnated, 29-μm-diameter AGHMs strongly induced functional collateral vessels without worsening ischemia, indicating the possible therapeutic usefulness of this approach.

Testing clinical therapeutic angiogenesis using basic fibroblast growth factor (FGF-2)

Therapeutic angiogenesis represents an attempt to relieve inadequate blood flow by the directed growth and proliferation of blood vessels. Neovascularization is a complex process involving multiple growth factors, receptors, extracellular matrix glycoproteins, intracellular and extracellular signaling pathways, and local and bone-marrow-derived constituent cells, all responding to a symphonic arrangement of temporal and spatial cues. In cardiovascular disease, patients with refractory angina and lower extremity intermittent claudication seem most amenable to early tests of therapeutic angiogenesis. Monotherapy with the recombinant protein basic fibroblast growth factor (FGF-2) has been tested in six human trials. These have shown provisional safety, and two have provided 'proof of concept' for the strategy of therapeutic angiogenesis. One large randomized phase II trial failed to show significant efficacy in coronary artery disease. Another showed significant efficacy in peripheral artery disease, although the magnitude of benefit was disappointing at the dose tested. This overview details the suitable clinical trial design and further steps toward the clinical development of FGF-2.

Denatured collagen as support for a FGF-2 delivery system: physicochemical characterizations and in vitro release kinetics and bioactivity

Collagen-based materials have scaffold properties to support bioactive molecules such as growth factor (GF). Gelatin, a denatured collagen, may have also some potential to interact with GF. An alternative process to denature collagen using trifluoroacetic acid (TFA) was investigated. Physicochemical characterization (XPS, DSC, isoelectric point, water uptake) of TFA-denatured collagen was comparable to regular gelatin, except a significant hydrophilicity and a pH sensitivity. FGF-2 was mixed with either regular gelatin or TFA-denatured collagen, then incorporated to a collagen sponge. Autoradiography revealed a relatively homogenous distribution of radiolabeled FGF-2 within the sponge. In vitro release kinetic of radiolabeled FGF-2 was investigated as well as the bioactivity of FGF-2 towards endothelial cell growth. The mixture was also sorbed to hydrogels made of ethylene vinyl acetate co-polymer and poly(2-hydroxyethyl methacrylate), and to cell culture insert membranes as control. Release of FGF-2 from collagen was progressive in the presence of TFA-denatured collagen, and cell growth was stimulated (significant peak at 8 and 10 days) by TFA-denatured collagen and FGF-2 eluted particularly from collagen sponges. Whereas control hydrogels, and those with regular gelatin showed a early stimulation of cell growth (1-5 days). Thus, the combination of both FGF-2 and an acid-denatured collagen in collagen sponges allows to sustain in vitro endothelial cell activity.

Biopolymeric delivery matrices for angiogenic growth factors

The development of new therapeutic approaches that aim to help the body exert its natural mechanisms for vascularized tissue growth (therapeutic angiogenesis) has become one of the most active areas of tissue engineering. Through basic research, several growth factor families and cytokines that are capable to induce physiological blood vessel formation have been identified. Indeed, preclinical and clinical investigations have indicated that therapeutic administration of angiogenic factors, such as the prototypic vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF), to sites of ischemia in the heart or the limb can improve regional blood flow. For new and lasting tissue vascularization, prolonged tissue exposure to these factors could be critical. Furthermore, as shown for VEGF, dosage must be tightly controlled, as excess amounts of VEGF can cause severe vascular leakage and hypotension. This review emphasizes natural and synthetic polymer matrices with respect to their development as vehicles for local and controlled delivery of angiogenic proteins, such as VEGF and bFGF, and their clinical applicability. In the dawn of experimental vascular engineering, new biomaterial schemes for clinical growth factor administration that take better account of biological principles of angiogenic growth factor function and the cell biological basis necessary to produce functional vasculature are evolving. Alongside their base function as protective embedment for angiogenic growth factors, these new classes of bioactive polymers are engineered with additional functionalities that better preserve growth factor activity and more closely mimic the in vivo release mechanisms and profiles of angiogenic growth factors from the extracellular matrix (ECM). Consequently, the preparation of both natural or completely synthetic materials with biological characteristics of the ECM has become central to many tissue engineering approaches that aim to deliver growth factors in a therapeutically efficient mode. Another promising venue to improve angiogenic performance is presented by biomaterials that allow sequential delivery of growth factors with complementary roles in blood vessel initiation and stabilization.

In vivo electroporation enhances plasmid-based gene transfer of basic fibroblast growth factor for the treatment of ischemic limb

BACKGROUND

Angiogenic therapy for ischemic tissues using angiogenic growth factors has been reported on an experimental and a clinical level. Electroporation enhances the efficiency of plasmid-based gene transfer in a variety of tissues. The purpose of this study was to evaluate the angiogenic effects of plasmid-based gene transfer using basic fibroblast growth factor (bFGF) in combination with electroporation.

MATERIALS AND METHODS

The transfection efficiency of in vivo electroporation in rabbit skeletal muscles was evaluated using pCAccluc+ encoding luciferase. To evaluate the angiogenic effects of bFGF gene in ischemic limb, we constructed a plasmid, pCAcchbFGFcs23, containing human bFGF cDNA fused with the secretory signal sequence of interleukin (IL)-2. Then, 500 microg of pCAcchbFGFcs23 or pCAZ3 (control plasmid) was injected into the ischemic thigh muscles in a rabbit model of hind limb ischemia with in vivo electroporation (bFGF-E(+) group and LacZ-E(+) group). Other sets of animals were injected with pCAcchbFGFcs23 (bFGF-E(-) group) or pCAZ3 (LacZ-E(-) group) without electroporation. Then 28 days later, calf blood pressure ratio, angiographic score, in vivo blood flow, and capillary density in the ischemic limb were measured.

RESULTS

Gene transfer efficiency increased markedly with the increase in voltage up to 100 V. Regarding angiogenic responses, calf blood pressure ratio, in vivo blood flow, and capillary density only in the bFGF-E(+) group were significantly higher than those in LacZ-E(-) group. Angiographic scores in the bFGF-E(+) and bFGF-E(-) groups were significantly higher than that in the LacZ-E(-) group.

CONCLUSION

These data suggest that in vivo electroporation enhances bFGF gene transfer for the treatment of ischemic limb muscles.

Transplantation of monocytes: a novel strategy for in vivo augmentation of collateral vessel growth

Therapeutic augmentation of collateral vessel growth (arteriogenesis) is of particular clinical interest. Because monocytes localize to areas of collateral growth and create a highly arteriogenic environment through secretion of multiple growth factors, we tested the hypothesis that monocyte "homing" can therapeutically be exploited. We have used a rabbit model of arteriogenesis to investigate the therapeutic potential of transplanted rabbit monocytes that were either ex vivo stimulated or adenovirally transduced to express a transgene encoding an arteriogenic growth factor. The monocytes were intravenously injected 24 hr or 7 days after ligation of the animal's right femoral artery. Seven days after transplantation collateral flow was determined with a doppler flow probe and collateral vessels were quantified angiographically. Whereas transplantation of allogeneic cells (same species) resulted in a strong promotion of arteriogenesis, most likely through induction of local inflammation and recruitment of recipient monocytes, transplantation of autologous cells (same animal) was not able to significantly augment collateralization. However, when autologous monocytes were used as vehicles to deliver granulocyte macrophage-colony stimulating factor as therapeutic transgene, collateralization was strongly augmented. Their localization to the site of collateral development posttransplantation was demonstrated by ex vivo transduction with beta-galactosidase. Because isolation of monocytes is clinically widely available their ex vivo engineering and transplantation represents an intriguing new strategy for therapeutic arteriogenesis.

Cell‐demanded release of VEGF from synthetic, biointeractive cell‐ingrowth matrices for vascularized tissue growth

Local, controlled induction of angiogenesis remains a challenge that limits tissue engineering approaches to replace or restore diseased tissues. We present a new class of bioactive synthetic hydrogel matrices based on poly(ethylene glycol) (PEG) and synthetic peptides that exploits the activity of vascular endothelial growth factor (VEGF) alongside the base matrix functionality for cellular ingrowth, that is, induction of cell adhesion by pendant RGD-containing peptides and provision of cell-mediated remodeling by cross-linking matrix metalloproteinase substrate peptides. By using a Michael-type addition reaction, we incorporated variants of VEGF121 and VEGF165 covalently within the matrix, available for cells as they invade and locally remodel the material. The functionality of the matrix-conjugated VEGF was preserved and was critical for in vitro endothelial cell survival and migration within the matrix environment. Consistent with a scheme of locally restricted availability of VEGF, grafting of these VEGF-modified hydrogel matrices atop the chick chorioallontoic membrane evoked strong new blood vessel formation precisely at the area of graft-membrane contact. When implanted subcutaneously in rats, these VEGF-containing matrices were completely remodeled into native, vascularized tissue. This type of synthetic, biointeractive matrix with integrated angiogenic growth factor activity, presented and released only upon local cellular demand, could become highly useful in a number of clinical healing applications of local therapeutic angiogenesis.

Factors regulating arteriogenesis

Growth of collateral vessels is potentially able to preserve structure and a variable degree of function in subtended tissues in the presence of arterial occlusions. The process of transformation of a small arteriole into much larger conductance artery is called arteriogenesis. Small arterioles that interconnect side branches proximal from the arterial occlusion with distal ones experience increased fluid shear stress because of the increased blood flow velocity attributable to the pressure gradient along the bridging collaterals. This activates the endothelium and leads to monocyte adhesion and infiltration with the subsequent production of growth factors and proteases. Preexistent arterioles are essential. Their presence is genetically determined. Arteriogenesis is not organ- or species-specific; coronary or peripheral collateral vessels develop following the same design principles in mice, rats, rabbits, or dogs. In contrast to angiogenesis, arteriogenesis is not dependent on the presence of hypoxia/ischemia.

Gene transfer as a tool to induce therapeutic vascular growth

Therapeutic induction of vascular growth may provide a treatment option for those patients with myocardial or peripheral ischemia who are not suited to conventional revascularization therapies. Some lymphatic vascular disorders may also be amenable to this therapy. However, clear evidence of efficacy must be obtained from phase 2 and 3 clinical trials before these new treatments can be entered into clinical practice. Apart from the clinical applications, gene transfer aimed at stimulating or blocking vascular growth with various growth factors, cytokines, transcription factors and receptors or their antagonists is useful for analyzing the effects of those molecules on the vasculature, especially when gene targeting results in lethality or when large animal models are required.

A novel method for removing residual acetone from gelatin microspheres

PURPOSE

To develop a method for removing residual acetone from gelatin microspheres.

METHODS

Free-flowing gelatin microspheres were either heated under vacuum or subjected to a stream of humidified air in a specially designed apparatus for removal of the residual acetone. To understand the removal mechanism, hygroscopic and thermal properties of the microspheres were examined.

RESULTS

Heating the gelatin microspheres under vacuum did not reduce the acetone level below 2%, but the use of humidified air under fluidizing condition reduced the residual acetone in gelatin microspheres by an additional two orders of magnitude. The rate of acetone removal was a strong function of the relative humidity (RH) of the air stream; higher RH accelerated acetone removal. Other variables influencing the acetone removal rate are the mean particle diameter and the linear velocity of the humidified air. Under high relative humidities, significant amounts of moisture were absorbed into gelatin microspheres, reducing their glass transition temperature below 25 degrees C.

CONCLUSION

The residual acetone in gelatin microspheres can be efficiently removed when exposed to air of high RH. Mechanisms of water-dependent acetone removal are proposed.

Role of monocytes and macrophages in adult angiogenesis: a light at the tunnel's end

In spite of sustained efforts, there are still gaps in our understanding of angiogenesis as it takes place in vivo. Older observations and a number of recent developments strongly involve the blood mononuclear cell population, collectively known as monocytes (MC), in the normal and pathological adult angiogenesis. An emerging paradigm should eventually incorporate the established biochemical cross talk between MC and their descendents, tissular macrophages (Mph), and the endothelial cells (EC); additionally, it should account for both the intercellular cooperation at the morphological level and the phenotypic overlap between the two cell populations. This focused review puts together the pieces of this puzzle in such a way as to suggest an alternative angiogenic model applicable to adult animals, and particularly to pathological conditions. A working hypothesis is put forward, which is centered on the preformation of capillary lumen as a "tunnel" drilled by penetrating MC/Mph. The tunnels may be colonized in a later stage by sprouts, circulating progenitor endothelial cells (CPEC) or transdifferentiated EC. Thus, MC/Mph are suggested to be included among the targets of therapeutic manipulation of angiogenesis.

Prospects for microtechnology and nanotechnology in bioengineering of replacement microvessels

CONTEXT

Due to its anticipated curative potential, therapeutic angiogenesis recently became a major preoccupation for the biomedical research community. Most of the related work reported to date employs either biochemical or genetic tools.

OBJECTIVE

To identify opportunities for application of the current developments in microtechnology and nanotechnology to the field of therapeutic angiogenesis.

DATA SOURCES

Survey of recent English-language literature on microvascular tissue engineering in the context of therapeutic angiogenesis. We include our results regarding the role played by microtopographical cues in the progression of angiogenesis, such as those produced during processing of the extracellular matrix by chronic inflammatory cells.

CONCLUSION

While notable accomplishments have been identified in the field of tissue engineering of larger vessels, reports on purposeful assembly of microvascular structures with the ability to be transferred in vivo by implantation are still scarce. Under these circumstances, we suggest the development of a new class of implantable biomedical microdevices, that is, "angiogenesis assist devices" (or "angiochips"), and we indicate some of their conceivable applications.

Transfection by polyethyleneimine-coated microspheres

Polyethyleneimine (PEI) can be used as a DNA delivery mechanism in cell culture and in vivo. Cells can be transfected by using surface-bound PEI, as well as by PEI/DNA microparticles. In the present experiments we extended these observations by preparing microspheres with covalently attached PEI. Blends of poly(epsilon-CBZ-L-lysine) mixed with poly(D,L-lactic-co-glycolic acid) were formed into microspheres using a double-emulsification/solvent evaporation procedure. CBZ (carbobenzoxy) groups on the surface of microspheres were removed by Li(0) /liquid ammonia reduction. Surface amino groups were used for covalent attachment of PEI and other molecules. Silica microspheres with bonded-phase PEI were also used. Microspheres were mixed with plasmid DNA encoding green fluorescent protein and added to cultured cells. PEI-coated microspheres transfected cultured Caco cells and MH-S alveolar macrophages. Expression of the transfected DNA increased over several days. MH-S cells phagocytosed PEI-coated silica microspheres, which were shown to reside in an acidic subcellular compartment. This was demonstrated by conjugating a pH-sensitive fluorescent dye (seminaphthofluorescein, SNAFL) to the microsphere surface. Transfection of MH-S cells was increased when plasmid DNA was complexed with histone on the surface of the microspheres.

CONCLUSION

PEI-coated microspheres have potential as a DNA delivery device with advantages of the unique properties of PEI and ease of surface chemical modification.

Extensive in vivo angiogenesis following controlled release of human vascular endothelial cell growth factor: implications for tissue engineering and wound healing

Vascular endothelial cell growth factor (VEGF) has strong stimulating effects on vascularization. Though very potent, VEGF is rapidly degraded due to its short half-life and when administrated by uncontrolled and nonspecific methods; however, its systemic administration in large doses can cause harmful side effects. Controlled release technology would allow delivering desired levels of bioactive VEGF within extended periods and permit examination of the in vivo effects of the compound in a broader way. The objective of this study was to determine the in vitro release behavior of VEGF from calcium alginate microspheres and the potency of this controlled release system in promoting localized neovascularization at the subcutaneous site of the rat model. In vitro release of human VEGF165 (2 and 4 microg/cm3 microsphere) was studied for 3 weeks under static conditions at 25 degrees C, and daily hormone release was measured using a competitive enzyme immunoassay. Following an uncontrolled release within the first 4 days, a quite constant zero-order VEGF release of 50 to 90 and 70 to 120 ng/day was achieved from 2 and 4 microg/cm3 polymer loaded microspheres respectively. In vivo angiogenesis was studied for a period of 8 weeks and evaluated using immunoperoidase staining and histopathological measurements. In vivo studies with rats (n = 24) showed a considerable level of capillary network formation at the epigastric groin fascia of VEGF microsphere-implanted rats starting from the first week. The most extensive neovascularization was observed in the group with 3 week postimplanted 4 microg VEGF containing microspheres; this level of vascularization was quite similar after 8 weeks. While the control group showed no evidence of angiogenesis, the difference in VEGF-induced neovascularization is statistically significant (p < 0.03). Immunostaining of the specimens showed a strong relationship between the release of human VEGF and neovascularization. The controlled VEGF release system described here promotes vigorous angiogenesis and has applicability for tissue engineering and wound healing studies.

Adenovirus-mediated ex vivo gene transfer of basic fibroblast growth factor promotes collateral development in a rabbit model of hind limb ischemia

Adenovirus-mediated ex vivo gene transfer of basic fibroblast growth factor (bFGF), a new strategy for the treatment of chronic vascular occlusive disease, was examined in a rabbit model of hind limb ischemia. The left femoral artery was completely excised to induce an ischemic state in the hind limb of male rabbits. Simultaneously, a skin section was resected from the wound, and host fibroblasts were cultured. The cultured fibroblasts were infected with adenovirus vector containing modified human bFGF cDNA with the secretory signal sequence (AxCAMAssbFGF) or LacZ cDNA (AxCALacZ). At 21 days after femoral artery excision, the gene-transduced fibroblasts were administered through the left internal iliac artery. The fibroblasts significantly accumulated in the ischemic hind limb, and the AxCAMAssbFGF-treated cells secreted bFGF for less than 14 days without elevation of systemic bFGF level. At 28 days after cell administration, calf blood pressure ratio, angiographic score, capillary density of muscle tissue and blood flow of the left internal iliac artery were determined, and animals with AxCAMAssbFGF-treated cells showed significantly greater development of collateral vessels, as compared with those with AxCALacZ-treated cells. These findings suggest that adenovirus-mediated ex vivo gene transfer of bFGF was effective for improvement of chronic limb ischemia.

The future of human gene therapy

Human gene therapy (HGT) is defined as the transfer of nucleic acids (DNA) to somatic cells of a patient which results in a therapeutic effect, by either correcting genetic defects or by overexpressing proteins that are therapeutically useful. In the past, both the professional and the lay community had high (sometimes unreasonably high) expectations from HGT because of the early promise of treating or preventing diseases effectively and safely by this new technology. Although the theoretical advantages of HGT are undisputable, so far HGT has not delivered the promised results: convincing clinical efficacy could not be demonstrated yet in most of the trials conducted so far, while safety concerns were raised recently as the consequence of the "Gelsinger Case" in Philadelphia. This situation resulted from the by now well-recognized disparity between theory and practice. In other words, the existing technologies could not meet the practical needs of clinically successful HGT so far. However, over the past years, significant progress was made in various enabling technologies, in the molecular understanding of diseases and the manufacturing of vectors. HGT is a complex process, involving multiple steps in the human body (delivery to organs, tissue targeting, cellular trafficking, regulation of gene expression level and duration, biological activity of therapeutic protein, safety of the vector and gene product, to name just a few) most of which are not completely understood. The prerequisite of successful HGT include therapeutically suitable genes (with a proven role in pathophysiology of the disease), appropriate gene delivery systems (e.g., viral and non-viral vectors), proof of principle of efficacy and safety in appropriate preclinical models and suitable manufacturing and analytical processes to provide well-defined HGT products for clinical investigations. The most promising areas for gene therapy today are hemophilias, for monogenic diseases, and cardiovascular diseases (more specifically, therapeutic angiogenesis for myocardial ischemia and peripheral vascular disease, restenosis, stent stenosis and bypass graft failure) among multigenic diseases. This is based on the relative ease of access of blood vessels for HGT, and also because existing gene delivery technologies may be sufficient to achieve effective and safe therapeutic benefits for some of these indications (transient gene expression in some but not all affected cells is required to achieve a therapeutic effect at relatively low [safe] dose of vectors). For other diseases (including cancer) further developments in gene delivery vectors and gene expression systems will be required. It is important to note, that there will not be a "universal vector" and each clinical indication may require a specific set of technical hurdles to overcome. These will include modification of viral vectors (to reduce immunogenicity, change tropism and increase cloning capacity), engineering of non-viral vectors by mimicking the beneficial properties of viruses, cell-based gene delivery technologies, and development of innovative gene expression regulation systems. The technical advances together with the ever increasing knowledge and experience in the field will undoubtedly lead to the realization of the full potential of HGT in the future.

Development of poly-(D,L-lactide--coglycolide) microsphere formulations containing recombinant human vascular endothelial growth factor to promote local angiogenesis

Although preclinical animal studies have demonstrated the utility of recombinant human vascular endothelial growth factor (rhVEGF) in promoting neovascularization in regions of ischemia, rhVEGF systemic administration did not provide clinical benefit to patients in recent placebo-controlled Phase II clinical trials. The amount of rhVEGF localized in the ischemic region after systemic administration is minimal and does not persist for more than 1 day. A greater persistence of rhVEGF at the region of ischemia may provide an increased angiogenesis with the eventual formation of patent blood vessels to restore nourishment to the tissues. We sought to develop a formulation of rhVEGF in poly(D,L-lactide--co-glycolide) (PLG) microspheres that would provide a continuous local delivery of intact protein. A stable formulation of rhVEGF for encapsulation contained a small amount of a stabilizing sugar, trehalose. Addition of excess trehalose increased the rate of release from the PLG. In addition, PLG with free acid end groups appeared to retard the initial release of rhVEGF by associating with it through ionic interactions at the positively charged heparin binding domain. rhVEGF was released continuously for 21 days with a very low (less than 10%) initial burst. The released rhVEGF aggregated and hydrolyzed over time and lost heparin affinity but not receptor affinity. The compression molding of rhVEGF PLG microspheres into disks yielded formulations with a low initial release and a lag of 10 days followed by complete release. The PLG microsphere formulations were assessed in the corneal implant model of angiogenesis and generated a dose-dependent angiogenic response. These formulations were also administered intravitreally and subretinally, generating local neovascularization comparable to the human disease states, vitroretinopathy and age-related macular degeneration, respectively. The rhVEGF PLG formulations may increase local angiogenesis without systemic side effects and may also be useful in the development of ocular disease models.

Therapeutic angiogenesis for ischemic heart disease

The de-novo formation of vessels (angiogenesis) and the remodelling of preexisting collateral vessels (arteriogenesis) are processes that occur naturally in ischemic heart disease. Promoting these processes by administration of various substances or other physical stimuli (therapeutic angiogenesis) may provide a future strategy for the treatment of ischemic vascular diseases. Mechanisms of angiogenesis and arteriogenesis, as well as trials of therapeutic angiogenesis in animal models and humans are reviewed.

Isolation and cultivation of Ca2+ tolerant cardiomyocytes from the adult rat: improvements and applications

1. Primary cultures of cardiomyocytes provide a valuable tool for the study of the pharmacological and toxicological properties of drugs and chemicals, but for several technical reasons cardiomyocytes from adult animals are not routinely used in long-term culture. Because of significant advances in cardiovascular research, tissue engineering and cell transplantation, the need to isolate primary cells from adult animal and/or human tissue is likely to increase in the future. 2. The most common protocols for the isolation and cultivation of cardiomyocytes have been reviewed and the various approaches have been compared. The recent advances in cell culture techniques and the use of the cytoprotective agent, e.g. 2,3-butanedione monoxime greatly increases cell yield and cell viability of isolated and cultured cardiomyocytes. New concepts emerge that enabled an assessment of cellular differentiation in cultured cardiomyocytes and certain specific nuclear transcription factors may play a pivotal role in this process.

A new model of chronic cardiac ischemia in rabbits

Chronic cardiac ischemia has mainly been studied in large species such as pigs or dogs. Little research has been performed using small species such as rabbits. In the present study, 1-3 wk after implantation of a novel device (ameroid) on the circumflex coronary artery of New Zealand White rabbits, vessel patency was evaluated by coronary angiography, corrosion cast, and radiolabeled microspheres. Coronary angiograms showed, after 21 days, either total occlusion or severe stenosis in seven of eight arteries, which was confirmed by corrosion casts. The ameroid group had less blood flow in the epicardial (-62%) and endocardial (-54%) layers of the ischemic area compared with sham-operated rabbits (P < 0.05). Blood flow increased in the ischemic area compared with day 0 during acute occlusion, suggesting that progressive coronary occlusion initiated the growth of de novo collateral vessels. Thus we have developed a new model of chronic cardiac ischemia in rabbits with documented progressive coronary stenosis and occlusion that is suitable to test various therapeutic angiogenesis strategies.

Cardiovascular gene therapy

Vascular gene transfer potentially offers new treatments for cardiovascular diseases. It can be used to overexpress therapeutically important proteins and correct genetic defects, and to test experimentally the effects of various genes in a local vascular compartment. Vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) gene transfers have improved blood flow and collateral development in ischaemic limb and myocardium. Promising therapeutic effects have been obtained in animal models of restenosis or vein-graft thickening with the transfer of genes coding for VEGF, nitric-oxide synthase, thymidine kinase, retinoblastoma, growth arrest homoeobox, tissue inhibitor of metalloproteinases, cyclin or cyclin-dependent kinase inhibitors, fas ligand and hirudin, and antisense oligonucleotides against transcription factors or cell-cycle regulatory proteins. First experiences of VEGF gene transfer and decoy oligonucleotides in human beings have been reported. However, further developments in gene-transfer vectors, gene-delivery techniques and identification of effective treatment genes will be required before the full therapeutic potential of gene therapy in cardiovascular disease can be assessed.

Integration of endothelial cells in multicellular spheroids prevents apoptosis and induces differentiation

Single endothelial cells (EC) seeded in suspension culture rapidly undergo apoptosis. Addition of survival factors, such as VEGF and FGF-2, does not prevent apoptosis of suspended EC. However, when cells are allowed to establish cell-cell contacts, they become responsive to the activities of survival factors. These observations have led to the development of a three-dimensional spheroid model of EC differentiation. EC spheroids remodel over time to establish a differentiated surface layer of EC and a center of unorganized EC that subsequently undergo apoptosis. Surface EC become quiescent, establish firm cell-cell contacts, and can be induced to express differentiation antigens (e.g., induction of CD34 expression by VEGF). In contrast, the unorganized center spheroid cells undergo apoptosis if they are not rescued by survival factors. The responsiveness to the survival factor activities of VEGF and FGF-2 was not dependent on cell shape changes since it was retained after cytochalasin D treatment. Taken together, these findings characterize survival factor requirements of unorganized EC and indicate that polarized surface EC differentiate to become independent of exogenous survival factors. Furthermore, they demonstrate that spheroid cell culture systems are useful not just for the study of tumor cells and embryonic stem cells but also for the analysis of differentiated functions of nontransformed cells.

Regulating angiogenesis: a new therapeutic strategy

Angiogenesis is the proliferation of endothelial and smooth muscle cells to form new blood vessels. Largely muted after adolescence, angiogenesis may be reignited by cancerous cells. Neoangiogenesis plays a primary role in tumor growth and metastases. Antiangiogenic therapy to limit and even reverse the growth of tumors are under investigation and showing promise. A derivative of fumagillin, TNP 470, is the first angiogenesis inhibitor to be given to humans. Surprisingly, several potent inhibitors are derived from tumors themselves. Researchers nowc recognize that stimulation of angiogenesis may have a place in the treatment of cardiovascular disease. Reestablishing blood flow to ischemic tissue through angiogenesis may provide a biologic "bypass" for patients with ischemic heart disease. The same applies to the treatment of peripheral vascular disease.