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.

Construction and characterization of a thrombin-resistant designer FGF-based collagen binding domain angiogen.

Humans demonstrate limited spontaneous endothelialization of prosthetic bypass grafts. However the local application of growth factors to prosthetic grafts or to injured blood vessels can provide an immediate effect on endothelialization. Novel chimeric proteins combining potent angiogens with extracellular matrix binding domains may localize to exposed matrices and provide sustained activity to promote endothelial regeneration after vascular interventions. We have ligated a thrombin-resistant mutant of fibroblast growth factor (FGF)-1 (R136K) with a collagen binding domain (CBD) in order to direct this growth factor to sites of exposed vascular collagen or selected bioengineered scaffolds. While FGF-1 and R136K are readily attracted to a variety of matrix proteins, R136K-CBD demonstrated selective and avid binding to collagen approximately 4x that of FGF-1 or R136K alone (P<0.05). The molecular stability of R136K-CBD was superior to FGF-1 and R136K. Its chemotactic activity was superior to R136K and FGF-1 (11+/-1% vs. 6+/-2% and 4+/-1%; P<0.01). Its angiogenic activity was similar to R136K and significantly greater than control by day 2 (P<0.01). After day 3, FGF-1-treated endothelial cell's (EC) sprouts had regressed back to levels insignificant compared to the control group (P=0.17), while both R136K and R136K-CBD continued to demonstrate greater sprout lengthening as compared to control (P<0.0002). The mitogenic activity of all growth factors was greater than control groups (20% PBS); in all comparisons (P<0.0001). This dual functioning angiogen provides proof of concept for the application of designer angiogens to matrix binding proteins to intelligently promote endothelial regeneration of selected matrices.

High-dose gamma irradiation for soft tissue allografts: High margin of safety with biomechanical integrity.

Screening and processing methods currently in place have made the risk of bacterial and viral infections from allograft tissues extremely low. However, the development of a terminal sterilization method that does not adversely affect tissue function would provide an added safety to tissues for transplantation. We assessed whether high-dose gamma irradiation could be used as an effective terminal sterilization method for allografts without impairing the preimplantation mechanical integrity of the tissues. Semitendinosus tendons were pretreated with a radioprotectant solution and then irradiated to 50 kGy under well-defined conditions that included a tight dose range and maintained low temperatures. Maximum force, strain, stress, modulus, and strain energy density for tendons irradiated to 50 kGy were compared to nonirradiated control tendons and tendons irradiated to 18 kGy by a commercial tissue bank using their existing method. The preimplantation biomechanical properties of the 50-kGy group compared favorably to the nonirradiated and 18 kGy groups. A study to evaluate the postimplantation mechanical and biological performance of grafts irradiated to 50 kGy is ongoing. Pathogen inactivation was also quantified following 50 kGy of irradiation, with > or =4.5 logs of Sindbis virus and 4.9 logs of parvovirus kill achieved. Analysis of Clostridium sordellii inactivation kinetics indicated that a 16 log10 reduction is predicted with 50 kGy of irradiation. A high dose of gamma irradiation using the described conditions can reduce infectious risks associated with soft tissue allografts while maintaining the preimplantation biomechanical performance of the tissues.

Effective use of optimized, high-dose (50 kGy) gamma irradiation for pathogen inactivation of human bone allografts.

The safety of tissue allografts has come under increased scrutiny due to recent reports of allograft-associated bacterial and viral infections in tissue recipients. We report that 50 kGy of gamma irradiation, nearly three times the dose currently used, is an effective pathogen inactivation method when used under optimized conditions that minimize damage to the tissue. Cancellous bone dowels treated with a radioprotectant solution and 50 kGy of optimized irradiation had an ultimate compressive strength and modulus of elasticity equal to conventionally irradiated (18 kGy) and non-irradiated control bone grafts. We subjected bone dowels treated with this pathogen inactivation method to an in vitro cytotoxicity test using three different mammalian cell lines and concluded that the treated grafts were not cytotoxic. The log reduction of nine pathogens spiked into radioprotectant-treated bone irradiated to 50 kGy was also tested. We achieved 4.9 logs of inactivation of a model virus for HIV and hepatitis C and 5 logs inactivation of a model virus for human parvovirus B-19. Complete inactivation (6.0-9.2 logs) of seven clinically relevant microorganisms was demonstrated. The results show that a combination of radioprotectants and optimized, high-dose gamma irradiation is a viable method for producing safer cancellous bone grafts that have the mechanical strength of existing grafts.

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

BACKGROUND: Through site-directed mutagenesis we have created a favorable fibroblast growth factor-1 (FGF-1) mutant (S130K) and linked it to a heparin-binding growth-associated molecule (HBGAM) to form the chimera S130K-HBGAM creating a heparin-independent, endothelial cell (EC)-specific mitogen. METHODS: The proliferative responses of primary canine carotid artery smooth muscle cells (SMC) and jugular vein EC to FGF-1, S130K, or S130K-HBGAM, with and without heparin (5 U/mL), was quantitated by measuring tritiated thymidine uptake over 24 hours and expressing the results as percent of positive control (20% fetal bovine serum [FBS]) for group comparison. RESULTS: Unlike FGF-1, both S130K and S130K-HBGAM are heparin-independent mitogens for EC and SMC. S130K-HBGAM was equivalent to FGF-1 with heparin at 6 nmol/L. S130K-HBGAM did not demonstrate relative EC specificity in this assay. CONCLUSIONS: At higher concentrations, S130K-HBGAM is a potent, heparin-independent EC and SMC mitogen. Co-culture assays and in vivo delivery models may demonstrate EC specificity not identified in this single cell type proliferation assay.

Functional integrity of intravenous immunoglobulin following irradiation with a virucidal dose of gamma radiation.

Although intravenous immunoglobulins (IVIG) and other plasma therapeutics have had a relatively good safety record, improved methods for viral clearance are constantly being evaluated and incorporated into new manufacturing processes. Gamma irradiation has been used routinely to assure sterility of healthcare products and medical devices, but it has not been applied successfully as a viral inactivation method for biologics. We examine whether virucidal doses of gamma irradiation (50 kGy) can be delivered to a manufacturing intermediate form of IVIG, a fractionated plasma paste, with negligible effect on structural and functional integrity of purified IgG product. Immunoglobulins from paste were examined for radiation-induced damage by SDS-PAGE and ELISAs utilizing viral antigens specific for rubella, CMV and mumps. Fc domain integrity was assessed by immunoblotting, quantitatively comparing the binding of irradiated and non-irradiated materials to cell surface Fcgamma receptors, and by employing quantitative RT-PCR to study the kinetics of accumulation of mRNA for the immune modulatory cytokines IL-1alpha, IL-1beta, IL-4, IL-8, IFNgamma, and TNFalpha. The results demonstrate that Fab and Fc domains of IVIG remain essentially intact and functional after gamma irradiation to virucidal doses, suggesting that this method could be used to enhance the safety of IVIG products.

Controlled gamma-irradiation mediated pathogen inactivation of human urokinase preparations with significant recovery of enzymatic activity.

Human sources of urokinase have led to the contamination of in-process lots of commercially available material with human pathogens. Effective pathogen inactivation of urokinase preparations can be achieved through the use of gamma-irradiation. Additionally, the presence of a free radical scavenger (ascorbate) and the control of temperature have resulted in maintenance of the enzymatic activity of urokinase without a significant effect on the pathogen inactivation properties of gamma-irradiation. In this study we have optimized the conditions during gamma-irradiation to achieve inactivation of porcine parvovirus by 5 logs and vaccinia virus to levels below the limits of detection, while maintaining 92% of urokinase activity. Product specific optimization of gamma-irradiation has the potential to provide effective pathogen inactivation while maintaining substantial functional activity for many therapeutic proteins.

R136K fibroblast growth factor-1 mutant induces heparin-independent migration of endothelial cells through fibrin glue.

OBJECTIVES: R136K is a mutation of fibroblast growth factor-1 (FGF-1) in which arginine replaces lysine at the primary thrombin cleavage site. This may be important in vivo in inducing endothelial cell (EC) migration and coverage of arterial injury sites by allowing R136K to be used in a fibrin glue delivery system, without thrombin-induced degradation, in the absence of heparin. The objectives of this study were to determine whether R136K, with and without heparin, can induce migration of EC and smooth muscle cells (SMC) through fibrin glue, and to compare these results with those of wild-type FGF-1; and to determine the resistance of R136K to thrombin-induced degradation versus FGF-1. METHODS: The dose-response migration through fibrin glue induced by wild-type FGF-1 and the R136K mutant in the presence and absence of heparin was tested with EC and SMC. Migration was tested with 50, 100, and 200 ng/mL of both FGF-1 and R136K, either with or without 5 U/mL of heparin. Migration of EC was also assessed after growth inhibition with mitomycin C. A novel modified Boyden chamber-type migration assay using fibrin glue on the upper surface of the chamber filter was used to test migration. The fluorescent marker calcein was used to identify those cells that had migrated through the fibrin glue and were embedded in the filter. Molecular degradation by thrombin was assessed with sodium dodecylsulfate polyacrylamide gel electrophoresis. RESULTS: For EC, R136K in the absence of heparin induced significantly more migration than did FGF-1 at 50 (P <.002), 100 (P <.0001), and 200 (P <.0001) ng/mL. In the presence of heparin, a chemotactic response of EC to cytokine was seen at all doses, with no significant difference between FGF-1 and R136K. A dose-dependent difference was noted in this group between the 100 and 200 ng/mL concentrations of cytokine (for FGF-1, P <.0001; for R136K, P <.0001). SMC showed no difference in migration with FGF-1, R136K, or negative control at any dose in the presence or absence of heparin. Gel electrophoresis demonstrated that R136K was more resistant to thrombin degradation than was FGF-1. CONCLUSION: Site-directed mutagenesis of FGF-1 to R136K enables induction of heparin-independent migration of EC through fibrin glue at an optimal concentration of 100 ng/mL. Neither FGF-1 nor R136K elicits SMC migration through fibrin glue. The ability of R136K to induce EC migration through fibrin glue in the absence of heparin may prove useful in vivo by inducing EC migration and coverage of arterial injury sites, thus potentially reducing thrombogenicity and intimal hyperplasia.

Effective use of gamma irradiation for pathogen inactivation of monoclonal antibody preparations.

Gamma irradiation has been used for decades as an effective method of pathogen inactivation of relatively inert materials. Until recently, its application to biologicals has resulted in unacceptable losses in functional activity. In this report we demonstrate that the damaging secondary effects of gamma irradiation can be controlled while maintaining the pathogen inactivation properties due to damage by primary effects. Control is achieved by a combination of protection from free radical damage to a monoclonal antibody through the use of the antioxidant ascorbate and by freeze-drying to minimize the potential for generating free radicals. The data demonstrate a synergy of these two approaches that results in quantitative recovery of functional activity while maintaining the ability to inactivate greater than 5 logs of porcine parvovirus infectivity.

Integrin clustering induces kinectin accumulation.

Integrin receptors mediate the formation of adhesion complexes and play important roles in signal transduction from the extracellular matrix. Integrin-based adhesion complexes (IAC) contain proteins that link integrins to the cytoskeleton and recruit signaling molecules, including vinculin, paxillin, focal adhesion kinase, talin and alpha-actinin. In this study, we describe a approximately 160 kDa protein that is markedly enriched at IAC induced by clustering integrins with fibronectin-coated beads. Protein sequence analysis reveals that this approximately 160 kDa protein is kinectin. Kinectin is an integral membrane protein found in endoplasmic reticulum, and it serves as a receptor for the motor protein kinesin. Fibronectin-induced IAC sequestered over half of the total cellular content of kinectin within 20 minutes. In addition, two other ER-resident proteins, RAP [low-density lipoprotein receptor-related protein (LRP) receptor-associated protein] and calreticulin, were found to be clustered at IAC, whereas kinesin was not. Our results identify a novel class of constituents of IAC.