Plasmid gene delivery to human keratinocytes through a fibrin-mediated transfection system

Physical and mechanical cues affecting biomaterial-mediated plasmid DNA delivery: insights into non-viral delivery systems

BACKGROUND

Whilst traditional strategies to increase transfection efficiency of non-viral systems aimed at modifying the vector or the polyplexes/lipoplexes, biomaterial-mediated gene delivery has recently sparked increased interest. This review aims at discussing biomaterial properties and unravelling underlying mechanisms of action, for biomaterial-mediated gene delivery. DNA internalisation and cytoplasmic transport are initially discussed. DNA immobilisation, encapsulation and surface-mediated gene delivery (SMD), the role of extracellular matrix (ECM) and topographical cues, biomaterial stiffness and mechanical stimulation are finally outlined.

MAIN TEXT

Endocytic pathways and mechanisms to escape the lysosomal network are highly variable. They depend on cell and DNA complex types but can be diverted using appropriate biomaterials. 3D scaffolds are generally fabricated via DNA immobilisation or encapsulation. Degradation rate and interaction with the vector affect temporal patterns of DNA release and transgene expression. In SMD, DNA is instead coated on 2D surfaces. SMD allows the incorporation of topographical cues, which, by inducing cytoskeletal re-arrangements, modulate DNA endocytosis. Incorporation of ECM mimetics allows cell type-specific transfection, whereas in spite of discordances in terms of optimal loading regimens, it is recognised that mechanical loading facilitates gene transfection. Finally, stiffer 2D substrates enhance DNA internalisation, whereas in 3D scaffolds, the role of stiffness is still dubious.

CONCLUSION

Although it is recognised that biomaterials allow the creation of tailored non-viral gene delivery systems, there still are many outstanding questions. A better characterisation of endocytic pathways would allow the diversion of cell adhesion processes and cytoskeletal dynamics, in order to increase cellular transfection. Further research on optimal biomaterial mechanical properties, cell ligand density and loading regimens is limited by the fact that such parameters influence a plethora of other different processes (e.g. cellular adhesion, spreading, migration, infiltration, and proliferation, DNA diffusion and release) which may in turn modulate gene delivery. Only a better understanding of these processes may allow the creation of novel robust engineered systems, potentially opening up a whole new area of biomaterial-guided gene delivery for non-viral systems.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Fibrin-based delivery strategies for acute and chronic wound healing

Fibrin, a natural hydrogel, is the end product of the physiological blood coagulation cascade and naturally involved in wound healing. Beyond its role in hemostasis, it acts as a local reservoir for growth factors and as a provisional matrix for invading cells that drive the regenerative process. Its unique intrinsic features do not only promote wound healing directly via modulation of cell behavior but it can also be fine-tuned to evolve into a delivery system for sustained release of therapeutic biomolecules, cells and gene vectors. To further augment tissue regeneration potential, current strategies exploit and modify the chemical and physical characteristics of fibrin to employ combined incorporation of several factors and their timed release. In this work we show advanced therapeutic approaches employing fibrin matrices in wound healing and cover the many possibilities fibrin offers to the field of regenerative medicine.

Sustained-released mixture of vascular endothelial growth factor 165 and fibrin glue strengthens healing of ileal anastomoses in a rabbit model with intraperitoneal infection

Purpose

To investigate the effects of a sustained-released mixture of vascular endothelial growth factor 165 (VEGF165) and fibrin glue (FG) local administration on postoperative rabbit ileal anastomoses.

Methods

One hundred twenty-eight male and female New Zealand white rabbits underwent intraperitoneal infection subsequent ileal anastomosis surgery were divided randomly into 4 groups, including 32 animals in each, applied with saline solution, FG, rhVEGF165 and a mixture of rhVEGF165 with FG (VEGF + FG) on the anastomoses, respectively. The incidences of anastomotic leakage were observed. Histopathological examination for inflammatory infiltration, fibroblast proliferation, and capillary vascular proliferation were performed. Then, bursting pressure and hydroxyproline concentrations were assessed in anastomoses sits on postoperative days 3, 5, 7, and 14.

Results

Rabbits in VEGF + FG group had the lowest incidence of leakage (P < 0.05). Histological evaluations revealed that granulation tissue was formed on days 5 after anastomosis; fibroblast proliferation and capillary vascular proliferation were significantly increased on days 7 and 14 in VEGF + FG group. Furthermore, there was a statistically significant difference in the mean bursting pressures between VEGF + FG group and other groups on days 7 and 14 (P < 0.05), and rabbits in VEGF + FG group exhibited a higher concentration than VEGF group (P < 0.05) and FG group (P < 0.05) on day 14.

Conclusion

Administration of VEGF165 mixed with FG to ileal anastomosis accelerates wound healing and enhances the anastomosis by increased angiogenesis.

Fibrin matrices: The versatile therapeutic delivery systems

Fibrin sealants, that have been employed for over a century by surgeons to stop post surgery bleeding, are finding novel applications in the controlled delivery of antibiotics and several other therapeutics. Fibrinogen can be easily purified from blood plasma and converted by thrombolysis to fibrin that undergoes spontaneous aggregation to form insoluble clot. During the gelling, fibrin can be formulated into films, clots, threads, microbeads, nanoconstructs and nanoparticles. Whole plasma clots in the form of beads and microparticles can also be prepared by activating endogenous thrombin, for possible drug delivery. Fibrin formulations offer remarkable scope for controlling the porosity as well as in vivo degradability and hence the release of the associated therapeutics. Binding/covalent-linking of therapeutics to the fibrin matrix, crosslinking of the matrix with bifunctional reagents and coentrapment of protease inhibitors have been successful in regulating both in vitro and in vivo release of the therapeutics. The release rates can also be remarkably lowered by preentrapment of therapeutics in insoluble particles like liposomes or by anchoring them to the matrix via molecules that bind them as well as fibrin.

The role of gene therapy in regenerative surgery: updated insights

BACKGROUND

In the past two decades, regenerative surgeons have focused increasing attention on the potential of gene therapy for treatment of local disorders and injuries. Gene transfer techniques may provide an effective local and short-term induction of growth factors without the limits of other topical therapies. In 2002, Tepper and Mehrara accurately reviewed the topic: given the substantial advancement of research on this issue, an updated review is provided.

METHODS

Literature indexed in the National Center for Biotechnology Information database (PubMed) has been reviewed using variable combinations of keywords ("gene therapy," "regenerative medicine," "tissue regeneration," and "gene medicine"). Articles investigating the association between gene therapies and local pathologic conditions have been considered. Attention has been focused on articles published after 2002. Further literature has been obtained by analysis of references listed in reviewed articles.

RESULTS

Gene therapy approaches have been successfully adopted in preclinical models for treatment of a large variety of local diseases affecting almost every type of tissue. Experiences in abnormalities involving skin (e.g., chronic wounds, burn injuries, pathologic scars), bone, cartilage, endothelia, and nerves have been reviewed. In addition, the supporting role of gene therapies to other tissue-engineering approaches has been discussed. Despite initial reports, clinical evidence has been provided only for treatment of diabetic ulcers, rheumatoid arthritis, and osteoarthritis.

CONCLUSIONS

Translation of gene therapy strategies into human clinical trials is still a lengthy, difficult, and expensive process. Even so, cutting-edge gene therapy-based strategies in reconstructive procedures could soon set valuable milestones for development of efficient treatments in a growing number of local diseases and injuries.

In vitro and in vivo epidermal growth factor gene therapy for diabetic ulcers with electrospun fibrous meshes

Human epidermal growth factor (hEGF) gene therapy was achieved with an electrospun nanofibrous mesh with matrix metalloproteinase (MMP) responsiveness to control release of plasmid human epidermal growth factor (phEGF) in diabetic ulcers. For MMP responsiveness, linear poly(ethyleneimine) (LPEI) was immobilized on the surface of the nanofiber via an MMP-cleavable linker. phEGF was electrostatically incorporated into LPEI-immobilized nanofibrous meshes with various charge ratios and phEGF incorporation efficiency was increased with increasing charge ratios. The release of both phEGF and LPEI was significantly increased in the presence of MMP-2 due to the enzymatic digestion of the MMP-cleavable linkage between the matrix and LPEI. Human dermal fibroblasts with the released fraction showed a higher expression level of hEGF compared to naked phEGF or phEGF/LPEI complexes. Diabetic wounds treated with phEGF-incorporated nanofibrous meshes showed high hEGF expression level and accelerated wound recovery rates without wound contractions for 14days. Neocollagen and cytokeratin accumulation were significantly increased as well as the expression of the keratinocyte-specific markers at the re-epithelized tissue treated with phEGF nanofibrous meshes, which clearly indicates that EGF gene was transfected to dermal cells and this consequently assisted wound recovery without phenotypic changes of the re-epithelized tissues. Thus, phEGF-incorporated nanofibrous mesh is expected to accelerate the wound-healing process as well as reduce wound contraction during recovery from diabetic ulcers.

Tissue engineering and regenerative medicine -where do we stand?

Tissue Engineering (TE) in the context of Regenerative Medicine (RM) has been hailed for many years as one of the most important topics in medicine in the twenty-first century. While the first clinically relevant TE efforts were mainly concerned with the generation of bioengineered skin substitutes, subsequently TE applications have been continuously extended to a wide variety of tissues and organs. The advent of either embryonic or mesenchymal adult stem-cell technology has fostered many of the efforts to combine this promising tool with TE approaches and has merged the field into the term Regenerative Medicine. As a typical example in translational medicine, the discovery of a new type of cells called Telocytes that have been described in many organs and have been detected by electron microscopy opens another gate to RM. Besides cell-therapy strategies, the application of gene therapy combined with TE has been investigated to generate tissues and organs. The vascularization of constructs plays a crucial role besides the matrix and cell substitutes. Therefore, novel in vivo models of vascularization have evolved allowing axial vascularization with subsequent transplantation of constructs. This article is intended to give an overview over some of the most recent developments and possible applications in RM through the perspective of TE achievements and cellular research. The synthesis of TE with innovative methods of molecular biology and stem-cell technology appears to be very promising.

Vascularization of the dermal support enhances wound re-epithelialization by in situ delivery of epidermal keratinocytes

Despite significant advances in management of severe wounds such as burns and chronic ulcers, autologous split-thickness skin grafts are still the gold standard of care. The main problems with this approach include pain and discomfort associated with harvesting autologous tissue, limited availability of donor sites, and the need for multiple surgeries. Although tissue engineering has great potential to provide alternative approaches for tissue regeneration, several problems have hampered progress in translating technological advances to clinical reality. Specifically, engineering of skin substitutes requires long culture times and delayed vascularization after implantation compromises graft survival. To address these issues we developed a novel two-prong strategy for tissue regeneration in vivo: (1) vascularization of acellular dermal scaffolds by infiltration of angiogenic factors; and (2) generation of stratified epidermis by in situ delivery of epidermal keratinocytes onto the prevascularized dermal support. Using athymic mouse as a model system, we found that incorporation of angiogenic factors within acellular human dermis enhanced the density and diameter of infiltrating host blood vessels. Increased vascularization correlated with enhanced proliferation and stratification of the neoepidermis originating from the fibrin-keratinocyte cell suspension. This strategy promoted tissue regeneration in vivo with no need for engineering skin substitutes; therefore, it may be useful for treatment of major wounds when skin donor sites are scarce and rapid wound coverage is required.

Fibrin as a delivery system for therapeutic drugs and biomolecules

Fibrin is a natural biopolymer involved in the coagulation cascade. It acts as a reservoir for growth factors, cells, and enzymes during wound healing and provides a scaffold for the synthesis of extracellular matrix. Thus, the use of fibrin has expanded in recent years from traditional use as a sealant for surgical applications, to a tissue engineering scaffold capable of providing nature's cues for tissue regeneration. This paper reviews the advantageous biological aspects of fibrin, the history of the scaffold material, and its present role in the delivery of drugs, growth factors, cells, and gene vectors. Examples are given of studies where the structure and form of the scaffold have been manipulated for optimal release of the therapeutic agent, optimal cellular activity, and investigation into stem cell differentiation. It is evident from the body of literature presented that the benefits of fibrin are being exploited for a vast range of tissue engineering applications and that fibrin remains a key scaffold material for the delivery of drugs and biomolecules.

Fibrin-lipoplex system for controlled topical delivery of multiple genes

Nonviral gene delivery via natural biomacromolecules show great promise as controlled release systems while avoiding the associated drawbacks with viral gene delivery such as immunogenicity and safety issues. Here, a fibrin-lipoplex system for topical delivery of multiple genes is described. In vitro release analysis showed efficient retention of the lipoplexes in the fibrin scaffold. The biomolecular interaction between fibrinogen and liposomes was investigated qualitatively using surface plasmon resonance. The strong binding between the lipoplexes and the fibrinogen component of the scaffold was observed and that could explain the in vitro release profile observed in our studies. Both in vitro and in vivo transfection studies using multiple reporter genes were performed to establish the bioactivity of released lipoplexes. The ability of the lipoplexes to transfect fibroblasts in vitro was shown to be maintained even after extended periods of encapsulation within the scaffold. Furthermore, in a rabbit ear ulcer model, the fibrin-lipoplex system was shown to have significantly higher transfection efficiency for two reporter genes at day 7 when compared to lipoplexes alone, suggesting that this fibrin-lipoplex system is suitable for extended release of lipoplexes for topical gene delivery applications.

Fibrin scaffold promotes adenoviral gene transfer and controlled vector delivery

Gene therapy using adenoviral vectors in tissue regeneration is hindered by a short duration of transgene expression. It is hypothesized that a fibrin scaffold will enhance delivery of the adenovirus to a wound site, precluding the need for high repeated doses. It was aimed to analyze whether fibrin could deliver a low single dose of viral vector to a wound site, without compromising transfection efficiency. Fibrin scaffold containing adenovirus encoding beta-galactosidase, fibrin alone, adenovirus alone, and no treatment groups were applied to a rabbit ear ulcer model. beta-Galactosidase transgene expression was measured at 7 and 14 days. Transgene expression was enhanced in the fibrin containing adenovirus group at 7 days. By 14 days, there was low expression and no difference between groups. Stereological methods assessing wound healing aimed to determine whether the adenovirus capsid elicited an unfavorable inflammatory response and whether fibrin's beneficial properties were altered by addition of adenovirus. The fibrin adenovirus group showed a wound-healing response similar to fibrin alone, showing maximum cellularity and angiogenesis at 7 days. By 14 days, cellularity and angiogenesis subsided, and this effect was not inhibited by the presence of adenovirus. Adenovirus alone did not cause an unfavorable inflammatory response. It is concluded the fibrin aids in the delivery of a low-dose viral vector, thereby avoiding a chronic inflammatory response, and allowing superior transfection than viral vector alone. This has wide-ranging implications on the use of viral vectors in tissue engineering.

Cell-controlled and spatially arrayed gene delivery from fibrin hydrogels

We investigated fibrin-mediated gene transfer by embedding pDNA within the hydrogel during polymerization and using two modes of gene transfection with cells placed either on the surface (2D transfection) or within the hydrogel (3D transfection). Using this model, we found that cell transfection depended strongly on the local cell-pDNA microenvironment as defined by the 2D vs. 3D context, target cell type and density, as well as fibrinogen and pDNA concentrations. When cells were embedded within the fibrin matrix lipofectamine-induced cell death decreased significantly, especially at low target cell density. Addition of fibrinolytic inhibitors decreased gene transfer in a dose-dependent manner, suggesting that fibrin degradation may be necessary for efficient gene transfer. We also provided proof-of-concept that fibrin-mediated gene transfer can be used for spatially localized gene delivery, which is required in cell-transfection microarrays. When lipoplex-containing hydrogels were spotted in an array format gene transfer was strictly confined to pDNA-containing fibrin spots with no cross-contamination between neighboring sites. Collectively, our data suggest that fibrin may be used as a biomaterial to deliver genes in an efficient, cell-controlled and spatially localized manner for potential applications in vitro or in vivo.

Fibrin hydrogels for non-viral vector delivery in vitro

Fibrin based hydrogels have been employed in vitro as a scaffold to promote tissue formation and investigate underlying molecular mechanisms. These hydrogels support a variety of cellular processes, and are being developed to enhance the presentation of biological cues, or to tailor the biological cues for specific tissues. The presentation of these cues could alternatively be enhanced through gene delivery, which can be employed to induce the expression of tissue inductive factors in the local environment. This report investigates gene delivery within fibrin hydrogels for two in vitro models of tissue growth: i) cell encapsulation within and ii) cell seeding onto the hydrogel. Naked plasmid and lipoplexes can be efficiently entrapped within the hydrogel, and after 1 day in solution more than 70% of the entrapped DNA is retained within the gel, with a sustained release observed for at least 19 days. Encapsulated lipoplexes did not aggregate and retain their original size. Transgene expression in vitro by delivery of lipoplexes was a function of the fibrinogen and DNA concentration. For encapsulated cells, all cells had intracellular plasmid and transgene expression persisted for at least 10 days, with maximal levels achieved at day 1. For cell infiltration, expression levels were less than those observed for encapsulation, and expression increased throughout the culture period. The increasing expression levels suggest that lipoplexes retain their activity after encapsulation; however, interactions between fibrin and the lipoplexes likely limit internalization. The inclusion of non-viral vectors into fibrin-based hydrogels can be employed to induce transgene expression of encapsulated and infiltrating cells, and may be employed with in vitro models of tissue growth to augment the intrinsic bioactivity of fibrin.

A fibrin glue composition as carrier for nucleic acid vectors

PURPOSE

Gene delivery from biomaterials has become an important tool in tissue engineering. The purpose of this study was to generate a gene vector-doted fibrin glue as a versatile injectable implant to be used in gene therapy supported tissue regeneration.

METHODS

Copolymer-protected polyethylenimine(PEI)-DNA vectors (COPROGs), naked DNA and PEI-DNA were formulated with the fibrinogen component of the fibrin glue TISSUCOL and lyophilized. Clotting parameters upon rehydration and thrombin addition were measured, vector release from fibrin clots was determined. Structural characterizations were carried out by electron microscopy. Reporter and growth factor gene delivery to primary keratinocytes and chondrocytes in vitro was examined. Finally,chondrocyte colonized clots were tested for their potency in cartilage regeneration in a osteochondral defect model.

RESULTS

The optimized glue is based on the fibrinogen component of TISSUCOL, a fibrin glue widely used in the clinics, co-lyophilized with copolymer-protected polyethylenimine(PEI)- DNA vectors (COPROGs). This material, when rehydrated, forms vector-containing clots in situ upon thrombin addition and is suitable to mediate growth factor gene delivery to primary keratinocytes and primary chondrocytes admixed before clotting. Unprotected PEI-DNA in the same setup was comparatively unsuitable for clot formation while naked DNA was ineffective in transfection. Naked DNA was released rapidly from fibrin clots (>70% within the first seven days) in contrast to COPROGs which remained tightly immobilized over extended periods of time (0.29% release per day). Electron microscopy of chondrocytecolonized COPROG-clots revealed avid endocytotic vector uptake. In situ BMP-2 gene transfection and subsequent expression in chondrocytes grown in COPROG clots resulted in the upregulation of alkaline phosphatase expression and increased extracellular matrix formation in vitro. COPROG-fibrinogen preparations with admixed autologous chondrocytes when clotted in situ in osteochondral defects in the patellar grooves of rabbit femura gave rise to luciferase reporter gene expression detectable for two weeks (n=3 animals per group). However, no significant improvement in cartilage formation in osteochondral defects filled with autologous chondrocytes in BMP-2-COPROG clots was achieved in comparison to controls (n=8 animals per group).

CONCLUSIONS

COPROGs co-lyophilized with fibrinogen are a simple basis for an injectable fibrin gluebased gene-activated matrix. The preparation can be used is complete analogy to fibrin glue preparations that are used in the clinics. However, further improvements in transgene expression levels and persistence are required to yield cartilage regeneration in the osteochondral defect model chosen in this study.

Fibrin-embedded administration of VEGF plasmid enhances skin flap survival

The aim of the present study was to experimentally evaluate whether topical fibrin-mediated administration of a vascular endothelial growth factor (VEGF)-A plasmid to the wound bed can protect skin flaps from necrosis. A plasmid expression vector containing the VEGF-A cDNA was constructed. The plasmid was then administered to the wound bed of rat abdominal skin flaps in a fibrin sealant. The percentage of viable, ischemic and necrotic tissue was assessed postoperatively as a baseline and after 3 and 7 days using digital surface area morphometry. Laser Doppler imaging of the flaps and VEGF-A Western blot analysis of flap tissue were performed to assess angiogenesis and VEGF-A tissue levels. Flaps treated with VEGF plasmids in the presence of uptake enhancing Lipofectamine transfection reagent increased flap survival 7 days postoperatively significantly associated with markedly elevated tissue perfusion and enhanced tissue VEGF-A protein expression. Our results indicate that topical fibrin-mediated administration of a VEGF-A plasmid may serve as an alternative to previous strategies in treating ischemic skin flaps. The suggested therapeutic approach is easily applicable and inexpensive in preparation. Thus, this protocol may also enhance wound healing in posttrauma skin lacerations or in skin grafts.

Gene transfer strategies in tissue engineering

Aiming for regeneration of severed or lost parts of the body, the combined application of gene therapy and tissue engineering has received much attention by regenerative medicine. Techniques of molecular biology can enhance the regenerative potential of a biomaterial by co-delivery of therapeutic genes, and several different strategies have been used to achieve that goal. Possibilities for application are many-fold and have been investigated to regenerate tissues such as skin, cartilage, bone, nerve, liver, pancreas and blood vessels. This review discusses advantages and problems encountered with the different gene delivery strategies as far as they relate to tissue engineering, analyses the positive aspects of polymeric gene delivery from matrices and discusses advances and future challenges of gene transfer strategies in selected tissues.

Strategies to enhance transductional efficiency of adenoviral-based gene transfer to primary human fibroblasts and keratinocytes as a platform in dermal wounds

Genetically modified keratinocytes and fibroblasts are suitable for delivery of therapeutic genes capable of modifying the wound healing process. However, efficient gene delivery is a prerequisite for successful gene therapy of wounds. Whereas adenoviral vectors (Ads) exhibit superior levels of in vivo gene transfer, their transductional efficiency to cells resident within wounds may nonetheless be suboptimal, due to deficiency of the primary adenovirus receptor, coxsackie-adenovirus receptor (CAR). We explored CAR-independent transduction to fibroblasts and keratinocytes using a panel of CAR-independent fiber-modified Ads to determine enhancement of infectivity. These fiber-modified adenoviral vectors included Ad 3 knob (Ad5/3), canine Ad serotype 2 knob (Ad5CAV-2), RGD (Ad5.RGD), polylysine (Ad5.pK7), or both RGD and polylysine (Ad5.RGD.pK7). To evaluate whether transduction efficiencies of the fiber-modified adenoviral vectors correlated with the expression of their putative receptors on keratinocytes and fibroblasts, we analyzed the mRNA levels of CAR, alpha upsilon integrin, syndecan-1, and glypican-1 using quantitative polymerase chain reaction. Analysis of luciferase and green fluorescent protein transgene expression showed superior transduction efficiency of Ad5.pK7 in keratinocytes and Ad5.RGD.pK7 in fibroblasts. mRNA expression of alpha upsilon integrin, syndecan-1 and glypican-1 was significantly higher in primary fibroblasts than CAR. In keratinocytes, syndecan-1 expression was significantly higher than all the other receptors tested. Significant infectivity enhancement was achieved in keratinocytes and fibroblasts using fiber-modified adenoviral vectors. These strategies to enhance infectivity may help to achieve higher clinical efficacy of wound gene therapy.

Effect of adenoviral mediated overexpression of fibromodulin on human dermal fibroblasts and scar formation in full-thickness incisional wounds

Fibromodulin, a member of the small leucine-rich proteoglycan family, has been recently suggested as a biologically significant mediator of fetal scarless repair. To assess the role of fibromodulin in the tissue remodeling, we constructed an adenoviral vector expressing human fibromodulin cDNA. We evaluated the effect of adenovirus-mediated overexpression of fibromodulin in vitro on transforming growth factors and metalloproteinases in fibroblasts and in vivo on full-thickness incisional wounds in a rabbit model. In vitro, we found that Ad-Fibromodulin induced a decrease of expression of TGF-beta(1) and TGF-beta(2) precursor proteins, but an increase in expression of TGF-beta(3) precursor protein and TGF-beta type II receptor. In addition, fibromodulin overexpression resulted in decreased MMP-1 and MMP-3 protein secretion but increased MMP-2, TIMP-1, and TIMP-2 secretion, whereas MMP-9 and MMP-13 were not influenced by fibromodulin overexpression. In vivo evaluation by histopathology and tensile strength demonstrated that Ad-Fibromodulin administration could ameliorate wound healing in incisional wounds. In conclusion, although the mechanism of scar formation in adult wounds remains incompletely understood, we found that fibromodulin overexpression improves wound healing in vivo, suggesting that fibromodulin may be a key mediator in reduced scarring.

Tissue engineering of injectable muscle: three-dimensional myoblast-fibrin injection in the syngeneic rat animal model

BACKGROUND

Surgical treatment of skeletal muscle loss resulting from trauma, tumor ablation, or inborn tissue defects is hampered by the scarcity of functional substitute tissue. By using techniques of tissue engineering, reconstitution of skeletal muscle defects might become a more viable option. However, it is necessary to develop an adequate, practical method for delivering myoblasts within a three-dimensional scaffold in vivo. The aim of this study was to create and evaluate a novel method for the transfer of myoblasts with clinically approved components within a three-dimensional matrix.

METHODS

The authors injected expanded primary male myoblasts into muscle defects in female syngeneic rats using a two-way syringe (Duploject) within a three-dimensional fibrin matrix. Detection and evaluation were performed using Y chromosome in situ hybridization, antidesmin immunostaining, and hematoxylin and eosin staining. To identify possible differences by means of integration, the injected myoblasts were compared with 7 days of precultivated constructs.

RESULTS

Injected myoblasts showed increasing integration into host muscle fibers in a time-dependent manner, exclusively at the injection site. Antidesmin staining revealed a conserved myogenic phenotype of transplanted cells. The fibrin matrix resolved over a period of 12 weeks, with no indication of an inflammatory reaction. No significant difference in the number of detected Y chromosome-positive nuclei was found between the two transplantation groups.

CONCLUSIONS

The presented technique of myoblast-fibrin injection indicates a clinical potential for reconstruction of skeletal muscle defects in vivo using a ready-to-use device in combination with tissue-engineering methods.

Gene-modified tissue-engineered skin: the next generation of skin substitutes

Tissue engineering combines the principles of cell biology, engineering and materials science to develop three-dimensional tissues to replace or restore tissue function. Tissue engineered skin is one of most advanced tissue constructs, yet it lacks several important functions including those provided by hair follicles, sebaceous glands, sweat glands and dendritic cells. Although the complexity of skin may be difficult to recapitulate entirely, new or improved functions can be provided by genetic modification of the cells that make up the tissues. Gene therapy can also be used in wound healing to promote tissue regeneration or prevent healing abnormalities such as formation of scars and keloids. Finally, gene-enhanced skin substitutes have great potential as cell-based devices to deliver therapeutics locally or systemically. Although significant progress has been made in the development of gene transfer technologies, several challenges have to be met before clinical application of genetically modified skin tissue. Engineering challenges include methods for improved efficiency and targeted gene delivery; efficient gene transfer to the stem cells that constantly regenerate the dynamic epidermal tissue; and development of novel biomaterials for controlled gene delivery. In addition, advances in regulatable vectors to achieve spatially and temporally controlled gene expression by physiological or exogenous signals may facilitate pharmacological administration of therapeutics through genetically engineered skin. Gene modified skin substitutes are also employed as biological models to understand tissue development or disease progression in a realistic three-dimensional context. In summary, gene therapy has the potential to generate the next generation of skin substitutes with enhanced capacity for treatment of burns, chronic wounds and even systemic diseases.

Gene technology and tissue engineering

The interest in gene therapy to treat human diseases has increased with the advances in recombinant DNA technology and the improved physical, chemical and biological methods of delivering genes to mammalian cells. Areas of therapeutic interest for gene therapy relevant for tissue engineering are, for example, in the treatment of wounds, skin diseases, nerve, bone, and muscle diseases. The transfer of a gene into a cell can lead to the addition or modification of a function and may be an attractive alternative to the pharmacological use of proteins. The complementation of defective functions could also be an effective treatment for inherited skin diseases with a gene defect. The two major challenges facing gene technology in tissue engineering are the problem of identifying appropriate genes that are effective in tissue repair, and the reliable expression of the therapeutic gene at clinically beneficial levels. This review discusses principles and methods of delivering genes encoding growth factors into cells, together with their respective advantages and disadvantages.

Optimization of a fibrin scaffold for sustained release of an adenoviral gene vector

One of the major limitations of adenovirus as an efficient gene delivery vehicle is its transient nature of transgene expression. At present, no biodegradable release system exists that permits the sustained release of gene delivery. This study aimed to optimize a biodegradable fibrin scaffold for sustained adenoviral mediated gene delivery. Scaffold formulations were fabricated incorporating an adenoviral vector encoding beta-galactosidase, and each scaffold was incubated in elution fluid. The level of transfection of cells was measured to assess virus diffusion from each scaffold at different time periods. Results showed that viral particles were present in the elution fluid and had the ability to transfect cells at different time points. Depending on the scaffold formulation, variable rates of diffusion were seen. Analysis of scaffold microarchitecture using stereo pairs showed that variable pore depth is seen in different fibrin scaffold concentration, which may be a determining factor in the diffusion rate. It was concluded that sustained release of the adenovirus could be attained up to 192 h at the optimal concentration of 60 mg/mL fibrinogen and 4 IU thrombin.

Stimulation of chondrocytes in vitro by gene transfer with plasmids coding for epidermal growth factor (hEGF) and basic fibroblast growth factor (bFGF)

Human epidermal growth factor (hEGF) and basic fibroblast growth factor (bFGF) influence critical characteristics of chondrocytes. The effects on metabolism and differentiation were evaluated following transfection using specific plasmids coding for both cytokines. Chondrocytes were isolated from femoral head cartilage of patients undergoing a hip arthroplasty for femoral neck fracture. Following collagenase-digestion, cells were cultured in monolayers, and cell proliferation, glucosaminoglycan-production and collagen type II expression were monitored 10 days after isolation. Addition of recombinant hEGF and bFGF resulted in a significant increase in cell proliferation and glucosaminoglycan production. Chondrocytes were transfected with vectors coding for either hEGF or bFGF and the production of these proteins was measured in supernatants by ELISA. Expression kinetics showed different patterns: hEGF was detectable 2.5 days following transfection and peaked at day 5.5, whereas bFGF-production reached its maximum 1.5 days after transfection, declining thereafter. Chondrocytes endogenously produced significant amounts of bFGF within 5 days following isolation. Proliferation of hEGF-transfected cells increased up to 81%; bFGF-transfection caused an increase up to 76%. Similarly, glucosaminoglycan-production was enhanced up to 120% by hEGF-transfection and 37% by bFGF transfection, respectively. Collagen type II production decreased following transfection with both plasmids. Temporary in vitro gene transfer of the growth factors hEGF and bFGF provides a method to stimulate chondrocyte proliferation and induces signs of dedifferentiation, which would limit a reasonable clinical application.

Inductive tissue engineering with protein and DNA-releasing scaffolds

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

Tissue engineering of cultured skin substitutes

Skin replacement has been a challenging task for surgeons ever since the introduction of skin grafts by Reverdin in 1871. Recently, skin grafting has evolved from the initial autograft and allograft preparations to biosynthetic and tissue-engineered living skin replacements. This has been fostered by the dramatically improved survival rates of major burns where the availability of autologous normal skin for grafting has become one of the limiting factors. The ideal properties of a temporary and a permanent skin substitute have been well defined. Tissue-engineered skin replacements: cultured autologous keratinocyte grafts, cultured allogeneic keratinocyte grafts, autologous/allogeneic composites, acellular biological matrices, and cellular matrices including such biological substances as fibrin sealant and various types of collagen, hyaluronic acid etc. have opened new horizons to deal with such massive skin loss. In extensive burns it has been shown that skin substitution with cultured grafts can be a life-saving measure where few alternatives exist. Future research will aim to create skin substitutes with cultured epidermis that under appropriate circumstances may provide a wound cover that could be just as durable and esthetically acceptable as conventional split-thickness skin grafts. Genetic manipulation may in addition enhance the performance of such cultured skin substitutes. If cell science, molecular biology, genetic engineering, material science and clinical expertise join their efforts to develop optimized cell culture techniques and synthetic or biological matrices then further technical advances might well lead to the production of almost skin like new tissue-engineered human skin products resembling natural human skin.

Enhanced neovasculature formation in ischemic myocardium following delivery of pleiotrophin plasmid in a biopolymer

Coronary heart disease is currently the leading killer in the western world. Therapeutic angiogenic agents are currently being examined for treatment of this disease. We have recently demonstrated the effective use of Pleiotrophin (PTN) as a therapeutic agent for treatment of ischemic myocardium. We have also shown that injection of the biopolymer fibrin glue preserves left ventricular geometry and prevents a deterioration of cardiac function following myocardial infarction. Due to the low transfection efficiency of naked plasmid injections, we examined the use of PTN plasmid and the biopolymer as a gene-activated matrix in the myocardium. In this study, we demonstrate that delivery of PTN plasmid in fibrin glue increases neovasculature formation compared to injection of the naked plasmid in saline.

Gene transfer to epidermal stem cells: implications for tissue engineering

The skin is an attractive target for gene therapy because it is easily accessible and shows great potential as an ectopic site for protein delivery in vivo. Genetically modified epidermal cells can be used to engineer three-dimensional skin substitutes, which when transplanted can act as in vivo 'bioreactors' for delivery of therapeutic proteins locally or systemically. Although some gene transfer technologies have the potential to afford permanent genetic modification, differentiation and eventual loss of genetically modified cells from the epidermis results in temporary transgene expression. Therefore, to achieve stable long-term gene expression, it is critical to deliver genes to epidermal stem cells, which possess unlimited growth potential and self-renewal capacity. This review discusses the recent advances in epidermal stem cell isolation, gene transfer and engineering of skin substitutes. Recent efforts that employ gene therapy and tissue engineering for the treatment of genetic diseases, chronic wounds and systemic disorders, such as leptin deficiency or diabetes, are reviewed. Finally, the use of gene-modified tissue-engineered skin as a biological model for understanding tissue development, wound healing and epithelial carcinogenesis is also discussed.

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.

Fibrin Glue Alone and Skeletal Myoblasts in a Fibrin Scaffold Preserve Cardiac Function after Myocardial Infarction

Current efforts in cardiac tissue engineering center around the use of scaffolds that deliver cells to the epicardial surface. In this study, we examined the effects of fibrin glue as an injectable scaffold and wall support in ischemic myocardium. The left coronary artery of rats was occluded for 17 min, followed by reperfusion. Echocardiography was performed 8 days after infarction. One to 2 days later, either 0.5% bovine serum albumin (BSA) in phosphate-buffered saline, fibrin glue alone, skeletal myoblasts alone, or skeletal myoblasts in fibrin glue were injected into the ischemic left ventricle. Echocardiography was again performed 5 weeks after injection. The animals were then sacrificed and the hearts were fresh frozen and sectioned for histology and immunohistochemistry. Both the fractional shortening (FS) and infarct wall thickness of the BSA group decreased significantly after 5 weeks (p = 0.0005 and 0.02, respectively). In contrast, both measurements for the fibrin glue group, cells group, and cells in fibrin glue group did not change significantly (FS: p = 0.18, 0.89, and 0.19, respectively; wall thickness: p = 0.40, 0.44, 0.43, respectively). Fibrin glue is capable of preserving infarct wall thickness and cardiac function after a myocardial infarction in rats and may be useful as a biomaterial scaffold for myocardial cell transplantation.

A Novel Role of Fibrin in Epidermal Healing: Plasminogen-Mediated Migration and Selective Detachment of Differentiated Keratinocytes

Recent studies have shown that fibrin promotes epidermal regeneration in vitro and maintains the stem cell population after transplantation of keratinocytes in vivo. As epidermal keratinocytes do not express integrin alpha(v)beta3, the receptor for fibrin and fibrinogen, the mechanism through which fibrin affects epidermal cells remains elusive. To investigate the role of fibrin in epidermal wound healing, we developed an in vitro model in which fibrin was added to the top of wounded keratinocyte monolayers grown on collagen. With this matrix topology, keratinocytes migrate between the collagen on their basal side and fibrin on their apical side mimicking migration of the epidermis in vivo. Using this model, we found that fibrin promoted keratinocyte migration in low and high calcium concentrations by exposing the cells to plasminogen. The migration rate depended strongly on the concentration of fibrinogen and the rate of plasmin-mediated fibrin degradation. Surprisingly, fibrin and fibrinogen caused significant detachment of keratinocytes which was prevented by the addition of calcium. Further examination using flow cytometry revealed that the detached cells were larger, more granular, and had very low levels of beta1 integrin, which are all signs of differentiated keratinocytes. Our results suggest a novel dual role of fibrin in epidermal healing. First, fibrin promotes keratinocyte migration indirectly by exposing plasminogen to migrating cells, and second, fibrin selectively disrupts adhesion of differentiated keratinocytes. Our data are novel and may have important implications in understanding wound healing and in the use of fibrin as a biomaterial for protein and gene delivery.

Cutaneous gene transfer for skin and systemic diseases

Recent progress in molecular genetics has illuminated the basis for a wide variety of inherited and acquired diseases. Gene therapy offers an attractive therapeutic approach capitalizing upon these new mechanistic insights. The skin is a uniquely attractive tissue site for development of new genetic therapeutic approaches both for its accessibility as well as for the large number of diseases that are amenable in principle to cutaneous gene transfer. Amongst these opportunities are primary monogenic skin diseases, chronic wounds and systemic disorders characterized by low or absent levels of circulating polypeptides. For cutaneous gene therapy to be effective, however, significant progress is required in a number of domains. Recent advances in vector design, administration, immune modulation, and regulation of gene expression have brought the field much nearer to clinical utility.