Heparin-independent mitogenicity in an endothelial and smooth muscle cell chimeric growth factor (S130K-HBGAM)

Heparin-Modified Collagen Gels for Controlled Release of Pleiotrophin: Potential for Vascular Applications

A fast re-endothelialization, along with the inhibition of neointima hyperplasia, are crucial to reduce the failure of vascular bypass grafts. Implants modifications with molecules capable of speeding up the re-endothelialization process have been proposed over the last years. However, clinical trials of angiogenic factor delivery have been mostly disappointing, underscoring the need to investigate a wider array of angiogenic factors. In this work, a drug release system based on a type I collagen hydrogel has been proposed for the controlled release of Pleiotrophin (PTN), a cytokine known for its pro-angiogenetic effects. Heparin, in virtue of its ability to sequester, protect and release growth factors, has been used to better control the release of PTN. Performances of the PTN drug delivery system on endothelial (ECs) and smooth muscle cells (SMCs) have been investigated. Structural characterization (mechanical tests and immunofluorescent analyses of the collagen fibers) was performed on the gels to assess if heparin caused changes in their mechanical behavior. The release of PTN from the different gel formulations has been analyzed using a PTN-specific ELISA assay. Cell viability was evaluated with the Alamar Blue Cell Viability Assay on cells directly seeded on the gels (direct test) and on cells incubated with supernatant, containing the released PTN, obtained from the gels (indirect test). The effects of the different gels on the migration of both ECs and SMCs have been evaluated using a Transwell migration assay. Hemocompatibility of the gel has been assessed with a clotting/hemolysis test. Structural analyses showed that heparin did not change the structural behavior of the collagen gels. ELISA quantification demonstrated that heparin induced a constant release of PTN over time compared to other conditions. Both direct and indirect viability assays showed an increase in ECs viability while no effects were noted on SMCs. Cell migration results evidenced that the heparin/PTN-modified gels significantly increased ECs migration and decreased the SMCs one. Finally, heparin significantly increased the hemocompatibility of the collagen gels. In conclusion, the PTN-heparin-modified collagen here proposed can represent an added value for vascular medicine, able to ameliorate the biological performance, and integration of vascular grafts.

Pleiotrophin: Analysis of the endothelialisation potential

PURPOSE

Endothelialisation of vascular substitutes, in fact, remains one of the most unsolved problems in cardiovascular diseases treatment. Stromal Derived Factor 1 (SDF-1) has been largely investigated as an endothelialisation promoter and Pleiotrophin is a promising alternative. Although it has been known to exert beneficial effects on different cell types, its potential as an inducer of proliferation and migration of endothelial cells was not investigated. Therefore, this work is aimed to compare the effects of Pleiotrophin on proliferation and migration of endothelial cells with respect to SDF-1.

MATERIALS/METHODS

Endothelial cell line EA.hy926 was treated with Pleiotrophin (50 ng/ml) or SDF-1 (50 ng/ml). Cell viability was evaluated by MTT assay and migration assays were performed in Transwell chambers. Wound healing potential was evaluated by scratch wound assay. CXCR4, RPTP β/ζ, PCNA and Rac1 expression was detected by Western Blot.

RESULTS

Interestingly, Pleiotrophin significantly increased the viability of the treated endothelial cells with respects to SDF-1. The migratory ability of the endothelial cells was also improved in the presence of Pleiotrophin with reference to the SDF-1 treatment. Moreover, Western Blot analysis showed how the treatment with Pleiotrophin can induce an increase in the expression of RPTP β/ζ, PCNA and Rac1 compared to SDF-1.

CONCLUSION

Due to the significant effects exerted on viability, migration and repair ability of endothelial cells compared to SDF-1, Pleiotrophin can be considered as an interesting molecule to promote re-endothelialisation.

Heparin reduces overcirculation-induced pulmonary artery remodeling through p38 MAPK in piglet

BACKGROUND

Artery remodeling is the principal change of pulmonary artery hypertension. Heparin has been shown to inhibit vascular smooth muscle cell proliferation. We hypothesized that heparin may modulate vascular remodeling in pulmonary artery hypertension, and explored the mechanism.

METHODS

A localized overcirculation-induced artery remodeling was created in piglets by anastomosing the left lower lobe pulmonary artery (LLLPA) to the thoracic aortic artery. Piglets were treated with heparin or saline for 4 weeks. Hemodynamic data were collected, and histology of the lung was assessed. We investigated the expressions of several candidate genes in lung and further observed the involvement of P38 mitogen-activated protein kinases (MAPK). The effects of heparin on the growth of cultured pulmonary arterial vascular smooth muscle cell and P38 MAPK expression were further determined under various conditions.

RESULTS

Four weeks after the shunt setup, overcirculation caused significant LLLPA remodeling, pressure increase, and pulmonary vascular resistance increase, and LLLPA flow reduction compared with that immediately after the shunt setup. Heparin reduced the LLLPA remodeling, pressure, and pulmonary vascular resistance, and increased the LLLPA flow compared with that not heparin treated. Shunt and heparin treatment did not change the piglet's systemic hemodynamics. Shunt increased the expression of P38 MAPK and heparin decreased its expression in the shunted LLLPA. Both heparin and P38 MAPK inhibitor suppressed VSMC growth and P38 MAPK expression in the cultured VSMC, but they did not present additive effects when the two treatments were combined.

CONCLUSIONS

Heparin reduces overcirculation-induced pulmonary artery remodeling through a P38 MAPK-dependent pathway.

Angiogenic endothelial cell invasion into fibrin is stimulated by proliferating smooth muscle cells

These studies aimed to determine the effect of smooth muscle cells (SMCs) on angiogenic behavior of endothelial cells (ECs) within fibrin hydrogels, an extracellular matrix (ECM) commonly used in tissue engineering. We developed a 3-D, fibrin-based co-culture assay of angiogenesis consisting of aggregates of SMCs with ECs seeded onto the aggregates' surface. Using digital fluorescence micrography, EC matrix invasion was quantified by average length of sprouts (ALS) and density of sprout formation (DSF). We demonstrated that ECs and SMCs co-invade into the ECM in close proximity to one another. ECs that were co-cultured with SMCs demonstrated increased invasion compared to ECs that were cultured alone at all time points. At Day 19, the ALS of ECs in co-culture was 327+/-58μm versus 70+/-11μm of ECs cultured alone (p=.01). The DSF of co-cultured ECs was also significantly greater than that of ECs cultured alone (p=.007 on Day 19). This appeared to be a function of both increased EC invasion as well as improved persistence of EC sprout networks. At 7days, ECs in co-culture with proliferation-inhibited SMCs previously treated with Mitomycin-C (MMC) demonstrated significantly attenuated sprouting compared to ECs co-cultured with SMCs that were untreated with MMC (82+/-14μm versus 205+/-32μm; p<.05). In assays in which multiple co-culture aggregates were cultured within a single hydrogel, we observed directional invasion of sprouts preferentially towards the other aggregates within the hydrogel. In co-culture assays without early EC/SMC contact, the ALS of ECs cultured in the presence of SMCs was significantly greater than those cultured in the absence of SMCs by Day 3 (320+/-21μm versus 187+/-16μm; p<.005). We conclude that SMCs augment EC matrix invasion into 3-D fibrin hydrogels, at least in part resulting from SMC proliferative and invasive activities. Directed invasion between co-culture aggregates and augmented angiogenesis in the absence of early contact suggests a paracrine mechanism for the observed results.

Synthesis of multilayered alginate microcapsules for the sustained release of fibroblast growth factor-1

Alginate microcapsules coated with a permselective poly-L-ornithine (PLO) membrane have been investigated for the encapsulation and transplantation of islets as a treatment for type 1 diabetes. The therapeutic potential of this approach could be improved through local stimulation of microvascular networks to meet mass transport demands of the encapsulated cells. Fibroblast growth factor-1 (FGF-1) is a potent angiogenic factor with optimal effect occurring when it is delivered in a sustained manner. In this article, a technique is described for the generation of multilayered alginate microcapsules with an outer alginate layer that can be used for the delivery of FGF-1. The influence of alginate concentration and composition (high mannuronic acid (M) or guluronic acid (G) content) on outer layer size and stability, protein encapsulation efficiency, and release kinetics was investigated. The technique results in a stable outer layer of alginate with a mean thickness between 113 and 164 μm, increasing with alginate concentration and G-content. The outer layer was able to encapsulate and release FGF-1 for up to 30 days, with 1.25% of high G alginate displaying the most sustained release. The released FGF-1 retained its biologic activity in the presence of heparin, and the addition of the outer layer did not alter the permselectivity of the PLO coat. This technique could be used to generate encapsulation systems that deliver proteins to stimulate local neovascularization around encapsulated islets.

FRNK overexpression limits the depth and frequency of vascular smooth muscle cell invasion in a three-dimensional fibrin matrix

Pathological vascular smooth muscle cell (VSMC) behavior after vascular interventions such as angioplasty or bypass is initiated within the 3D environment of the vessel media. Here VSMCs proliferate, invade the surrounding matrix, migrate adluminally, and deposit substantial amounts of matrix, leading to myointimal hyperplasia and decreased blood flow to critical organs and tissue. Since focal adhesion kinase (FAK) mediates many of the VSMC responses to these pathologic events, it provides a reasonable pharmacologic target to limit this invasive VSMC behavior and to better understand the cellular pathophysiology of this disease. Here we quantified the effectiveness of disabling FAK in VSMCs with its dominant-negative inhibitor, FAK-related nonkinase (FRNK), in a clinically relevant 3D assay. We found that FRNK overexpression decreased VSMC invasion (both the length and frequency) in this matrix. These effects were demonstrated in the presence and absence of chemical mitotic inhibition, suggesting that FAK's effect on cellular matrix invasion, migration, and proliferation utilize separate and/or redundant signaling cascades. Mechanistically, FAK inhibition decreased its localization to focal adhesions which led to a significant decrease in FAK autophosphorylation and the phosphorylation of the serine/threonine kinase, AKT. Together these findings suggest that disruption of FAK signaling may provide a pharmaceutical tool that limits pathological VSMC cell behavior.

Characterization of the chemotactic and mitogenic response of SMCs to PDGF-BB and FGF-2 in fibrin hydrogels

The delivery of growth factors to cellularize biocompatible scaffolds like fibrin is a commonly used strategy in tissue engineering. We characterized smooth muscle cells (SMC) proliferation and chemotaxis in response to PDGF-BB and FGF-2, alone and in combination, in 2D culture and in 3D fibrin hydrogels. While both growth factors induced an equipotent mitogenic response in 2D culture, only FGF-2 was significantly mitogenic for SMCs in 3D culture. Only PDGF-BB was significantly chemotactic in a modified Boyden chamber assay. In a 3D assay of matrix invasion, both growth factors induced an invasive response into the fibrin hydrogel in both proliferating and nonproliferating, mitomycin C (MMC) treated cells. The invasive response was less attenuated by the inhibition of proliferation in PDGF-BB stimulated cells compared with FGF-2 stimulated cells. We conclude that SMCs cultured in fibrin hydrogels have a more robust chemotactic response to PDGF-BB compared with FGF-2, and that the response to FGF-2 is more dependent on cell proliferation. Delivery of both growth factors together potentiates the chemotactic, but not mitogenic response to either growth factor alone.

Local delivery of a collagen-binding FGF-1 chimera to smooth muscle cells in collagen scaffolds for vascular tissue engineering

We investigated the delivery of R136K-CBD (a collagen-binding mutant chimera of fibroblast growth factor-1) with a type I collagen scaffold as the delivery vehicle to smooth muscle cells (SMCs) for vascular tissue engineering. The binding affinity of R136K-CBD to 3-D collagen scaffolds was investigated both in the presence and absence of cells and/or salts. 2-D and 3-D visualization of delivery of R136K-CBD into SMCs were accomplished by combined fluorescent and reflection confocal microscopy. The mitogenic effect of collagen-immobilized R136K-CBD on SMCs in 3-D collagen was studied by Cyquant assay at different time intervals. In the group devoid of salt and cells, no detectable release of R136K-CBD into overlying culture media was found, compared with burst-and-continuous release of R136K and FGF-1 over a 14-day period in all other groups. The release rate of R136K-CBD was 1.7 and 1.6-fold less than R-136K and FGF-1 when media was supplemented with 2m salt (P<0.0001), and 2.6 and 2.5-fold less in cell-populated collagen hydrogels (P<0.0001), respectively. R136K-CBD showed essentially uniform binding to collagen and its distribution was dependent on that of the collagen scaffold. Internalization of R136K-CBD into SMCs was documented by confocal microscopy. 3-D local delivery of collagen-immobilized R136K-CBD increased the proliferation of SMCs in the collagen matrix to significantly greater levels and for a significantly greater duration than R136K or FGF-1, with 2.0 and 2.1-fold more mitogenicity than R136K and FGF-1 respectively (P<0.0001) at day 7. The results suggest that our collagen-binding fusion protein is an effective strategy for growth factor delivery for vascular tissue engineering.

Chimeric vitronectin:insulin-like growth factor proteins enhance cell growth and migration through co-activation of receptors

Complexes comprised of IGF-I, IGF-binding proteins and the ECM protein vitronectin (VN) stimulate cell migration and growth and can replace the requirement for serum for the ex vivo expansion of cells, as well as promote wound healing in vivo. Moreover, the activity of the complexes is dependent on co-activation of the IGF-I receptor and VN-binding integrins. In view of this we sought to develop chimeric proteins able to recapitulate the action of the multiprotein complex within a single molecular species. We report here the production of two recombinant chimeric proteins, incorporating domains of VN linked to IGF-I, which mimic the functions of the complex. Further, the activity of the chimeric proteins is dependent on co-activation of the IGF-I- and VN-binding cell surface receptors. Clearly the use of chimeras that mimic the activity of growth factor:ECM complexes, such as these, offer manufacturing advantages that ultimately will facilitate translation to cost-effective therapies.

Growing a living blood vessel: insights for the second hundred years

Cardiovascular disease continues to be the leading cause of death worldwide, and the prevalence of cardiovascular disease has reached epidemic proportions worldwide. Not surprisingly this has led to an increasing number of vascular procedures annually. Unfortunately, the success of these procedures over time continues to limit their long-term effects. Biomedical engineering approaches to improve upon current prosthetic grafts, developing new prosthetic grafts, and creating tissue engineered blood vessels for clinical application offer hope of improving the durability of vascular interventions and improving patients' treatment for cardiovascular disease.

Improving endothelial healing with novel chimeric mitogens

BACKGROUND

Chimeric proteins may be used to direct cell-specific activity. Heparin-binding growth-associated molecule (HBGAM) binds to cell receptors that are relatively more robust on endothelial cells, and it may confer endothelial cell selectivity to potent angiogens such as fibroblast growth factor-1 (FGF-1).

METHODS

By ligating fibroblast growth factor or its potent mutant, S130K, to HBGAM, we tested their effect on re-endothelialization after angioplasty injury by using a canine model.

RESULTS

Both HBGAM/S130K- and HBGAM/FGF-1-treated arteries had increased neointimal mitotic index and re-endothelialization rates at 30 days compared with control arteries without inducing a significant increase in the neointimal thickness or the ratio of neointimal to medial thickness between treatment and control groups.

CONCLUSION

HBGAM/S130K and HBGAM/FGF-1 facilitates endothelial healing without myointimal thickening after canine carotid artery balloon angioplasty injury. Application of these growth factors in fibrin glue may improve endothelialization clinically after angioplasty or endarterectomy.

Sustained low levels of fibroblast growth factor-1 promote persistent microvascular network formation

BACKGROUND

Therapeutic neovascularization using high growth factor concentrations may lead to transient vessel formation and abnormal microvascular structure. The goal of this study was to quantify temporal and concentration effects of fibroblast growth factor-1 (FGF-1) on the persistence and morphology of microvascular networks.

METHODS

Endothelial cells were incubated in suspension culture forming aggregates that were embedded in fibrin glue (FG) and stimulated with varying concentrations of FGF-1 with of heparin. Capillary networks formed were quantified for 21 days.

RESULTS

High FGF-1 concentrations resulted in rapid and intense sprout formation, with excessive branching. At later times, these vessels regressed, with cellular debris in former vessel locations. At later times, the 1-ng/mL group surpassed the high concentration groups with continuous sprout growth and complete FG vascularization by 23 days.

CONCLUSION

Sustained low levels of FGF-1 maintained a persistent microvascular network response, whereas higher levels resulted in abnormal phenotype followed by vessel regression.

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.