Adenoviral-mediated overexpression of platelet-derived growth factor-B corrects ischemic impaired wound healing

Recombinant adenovirus-p21 attenuates proliferative responses associated with excessive scarring

Excessive cutaneous scarring is an important clinical disorder resulting in adverse tissue growth and function as well as undesirable cosmetic appearance. p21WAF-1/Cip-1 is a cyclin-dependent kinase inhibitor that blocks cell cycle progression and inhibits cell proliferation. We used a recombinant adenovirus containing the human p21WAF-1/Cip-1 cDNA (rAd-p21) to evaluate proliferative responses in skin models. In vitro dose-response studies using primary human dermal fibroblasts resulted in a dose-dependent expression of p21WAF-1/Cip-1 protein and a 3- to 80-fold reduction in cell proliferation as measured by 5-bromodeoxyuridine incorporation. Further, rAd-p21 reduced type I procollagen production when compared to control virus. A rat polyvinyl alcohol sponge model was used to determine rAd-p21 effects on granulation tissue formation in vivo. Sponges pretreated with a granulation tissue stimulator, rAd-PDGF-B and subsequently rAd-p21 on a second injection, showed a p21WAF-1/Cip-1 specific dose-dependent decrease in percent granulation fill as the rAd-p21 dose increased (p < 0.001). Immunohistochemistry identified human p21WAF-1/Cip-1 expression in sponges treated with rAd-p21 5 days postinjection. Additionally, 5-bromodeoxyuridine and Ki67 staining in sponges treated with rAd-p21 showed a significant decrease in proliferation when compared to rAd-platelet-derived growth factor-B alone or vehicle control groups (p < 0.01). These data support the utility of p21WAF-1/Cip-1 in targeting hyperproliferative disorders of the skin.

Glutathione enhances fibroblast collagen contraction and protects keratinocytes from apoptosis in hyperglycaemic culture

BACKGROUND

Cutaneous wound healing is relatively slow in patients with diabetes.

OBJECTIVES

To test the hypothesis that this defect in healing of wounds in patients with diabetes results from dysfunction of skin fibroblasts and epidermal keratinocytes and that this dysfunction is related to disrupted intracellular glutathione (GSH) homeostasis.

METHODS

We investigated the effects of esterified GSH on the contraction of fibroblasts in a fibroblast-populated collagen lattice and on keratinocyte apoptosis.

RESULTS

High glucose medium (hyperglycaemia) reduced the contraction ability of fibroblasts (P < 0.05). The normalization of glucose medium concentrations for hyperglycaemic fibroblasts did not restore the contraction capacity. The percentage of apoptotic keratinocytes was statistically higher in hyperglycaemic cells (P < 0.05). GSH media concentrations ranging from 0.1 to 100 micromol L(-1) restored the ability of hyperglycaemic fibroblasts to contract the gels in a concentration-dependent manner. Primary human keratinocytes grown in hyperglycaemic medium were more susceptible to apoptosis, and treatment with esterified GSH rescued the keratinocytes from apoptosis.

CONCLUSIONS

These data suggest that intracellular GSH can normalize skin cell functions disrupted by in vitro cell growth under hyperglycaemic conditions.

Gene therapy in the treatment of lower extremity wounds

This article presents a brief overview of the etiology of chronic wounds of the lower extremities and their current medical and surgical treatment. Gene therapy as a potential tool for treating therapeutically challenging wounds is described in terms of the vectors employed in gene transfer, as well as the strategies used to promote wound healing. Results from animal model studies, as well as clinical trials, are presented.

Gene transfer in tissue repair: status, challenges and future directions

Wound repair involves a complex interaction of various cell types, extracellular matrix molecules and soluble mediators. Details on signals controlling wound cell activities are beginning to emerge. In recent years this knowledge has been applied to a number of therapeutic strategies in soft tissue repair. Key challenges include re-adjusting the adult repair process in order to augment diseased healing processes, and providing the basis for a regenerative rather than a reparative wound environment. In particular, the local delivery of pluripotent growth factor molecules to the injured tissue has been intensively investigated over the past decade. Limited success of clinical trials indicates that an important aspect of the growth factor wound-healing paradigm is the effective delivery of these polypeptides to the wound site. A molecular genetic approach in which genetically modified cells synthesise and deliver the desired growth factor in a time-regulated manner is a powerful means to overcome the limitations associated with the (topical) application of recombinant growth factor proteins. This article summarises repair mechanisms and their failure, and gives an overview of techniques and studies applied to gene transfer in tissue repair. It also provides perspectives on potential targets for gene transfer technology.

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.

Gene therapy with adenoviral plasmids or naked DNA of vascular endothelial growth factor and platelet-derived growth factor accelerates healing of duodenal ulcer in rats

After we demonstrated that daily intragastric administration of angiogenic growth factors like basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), or vascular endothelial growth factor (VEGF) accelerated the healing of chronic duodenal ulcers in rats, we hypothesized that a single dose of gene therapy related to these growth factors may be enough to accelerate the healing of duodenal ulcers through enhancement of synthesis of endogenous angiogenic growth factors. Thus, we compared the effects of intraduodenal or intravenous adenoviral vectors and naked DNA transducing the genes for either VEGF or PDGF in experimental duodenal ulcers induced by cysteamine in rats. Sprague-Dawley female rats with confirmed duodenal ulcers were randomly divided into control and treatment groups. The controls received either intraduodenal injection of buffer or the beta-galactosidase-transducing adenoviral vector. Rats treated with a single or double dose of adenoviral vector or naked DNA of VEGF or PDGF had significantly smaller ulcers than the controls. Histologic analysis demonstrated that reepithelized granulation tissue with prominent angiogenesis replaced the ulcers. Western blotting, immunohistochemistry, and enzyme-linked immunosorbent assay of duodenal mucosa confirmed that the expression of VEGF or PDGF proteins was enhanced by the transgenes, whereas beta-galactosidase staining in multiple organs identified that the transgenes, especially after local administration were only localized in the duodenum, stomach, and jejunum. These results suggest that gene therapy with either VEGF or PDGF may be a rapid approach to achieve duodenal ulcer healing.

Synthetic Biocompatible Cyclodextrin-Based Constructs for Local Gene Delivery to Improve Cutaneous Wound Healing

The localized, sustained delivery of growth factors for wound healing therapy is actively being explored by gene transfer to the wound site. Biocompatible matrices such as bovine collagen have demonstrated usefulness in sustaining gene therapy vectors that express growth factors in local sites for tissue repair. Here, new synthetic biocompatible materials are prepared and shown to deliver a protein to cultured cells via the use of an adenoviral delivery vector. The synthetic construct consists of a linear, beta-cyclodextrin-containing polymer and an adamantane-based cross-linking polymer. When the two polymers are combined, they create an extended network by the formation of inclusion complexes between the cyclodextrins and adamantanes. The properties of the network are altered by controlling the polymer molecular weights and the number of adamantanes on the cross-linking polymer, and these modifications and others such as replacement of the beta-cyclodextrin (host) and adamantane (guest) with other cyclodextrins (hosts such as alpha, gamma, and substituted members) and inclusion complex forming molecules (guests) provide the ability to rationally design network characteristics. Fibroblasts exposed to these synthetic constructs show proliferation rates and migration patterns similar to those obtained with collagen. Gene delivery (green fluorescent protein) to fibroblasts via the inclusion of adenoviral vectors in the synthetic construct is equivalent to levels observed with collagen. These in vitro results suggest that the synthetic constructs are suitable for in vivo tissue repair applications.

Adenoviral mediated gene transfer of PDGF-B enhances wound healing in type I and type II diabetic wounds

We have shown that the genetically diabetic mouse (C57BLKS/J-m+/+Lepr(db)) has a wound healing and neovascularization deficit associated with an inability to recruit endothelial precursor cells (EPCs) to the wound. This may account for a fundamental mechanism in impaired diabetic wound healing. We hypothesized that the adenoviral mediated overexpression of platelet-derived growth factor-B (PDGF-B) would enhance wound healing, improve neovascularization, and recruit EPCs to the epithelial wound in three diabetic mouse models. Eight-mm full-thickness flank wounds were made in db/db, nonobese NOD/Ltj, streptozotocin, and C57BLKS/J mice. Wounds were treated with either 1 x 10(8) PFU Ad-PDGF-B or Ad LacZ or phosphate buffered saline solution. Wounds harvested at seven days were analyzed for epithelial gap, blood vessel density, granulation tissue area, and EPCs per high powered field. All three diabetic models have a significant wound healing and neovascularization defect compared to C57BLKS/J controls. Adenoviral-PDGF-B treatment significantly enhanced epithelial gap closure in db/db, streptozotocin, and nonobese NOD/Ltj mice as compared to diabetic phosphate buffered saline solution or Ad LacZ controls. A similar increase in the formation of granulation tissue and vessel density was also observed. All three models had reduced levels of GATA-2 positive EPCs in the wound bed that was corrected by the adenoviral mediated gene transfer of PDGF. EPC recruitment was positively correlated with neovascularization and wound healing. Three different diabetic models have a wound healing impairment and a decreased ability to recruit EPCs. The vulnerary effect of adenoviral mediated gene therapy with PDGF-B significantly enhanced wound healing and neovascularization in diabetic wounds. The PDGF-B mediated augmentation of EPC recruitment to the wound bed may be a fundamental mechanism of these results.

Cytokines and wound healing: the role of cytokine and anticytokine therapy in the repair response

Wound healing is an integrated and complex process involving a large number of regulatory molecules, including proinflammatory cytokines and growth factors, and an orchestrated tissue response. Dysregulation in cytokine or growth factor expression dramatically alters the normal wound healing process, and blocking the inappropriate production of specific proinflammatory cytokines or supplementing the milieu with increased quantities of growth factors has demonstrated the central role played by these mediators. Both protein-based and DNA-based (gene transfer) therapies are currently under clinical development as tools to improve the healing process. Although there has been some success with these approaches in both experimental models and in patients, only through a better understanding of the complexity and diversity of the wound healing process, as well as an improved comprehension of the time-dependent and concentration-dependent responses to individual proinflammatory cytokines or growth factors, will further development in the therapeutic treatment of healing wounds be attained.

Impact of aging on gene expression in a rat model of ischemic cutaneous wound healing

BACKGROUND

Tissue ischemia and aging are independent features associated with the healing impairment of cutaneous wounds. However, the pathophysiology of these processes as they relate to impaired-healing wounds is poorly understood.

MATERIALS AND METHODS

A single full-thickness biopsy wound was made on both ears of young (3-6 month) and aged (>24 month) Fisher rats. One ear was rendered ischemic by transection of the vasculature at the ear base, while the other ear served as an internal nonischemic control. Wounds were harvested from 3 to 7 days and were evaluated histologically for either granulation tissue formation and epithelialization. Total RNA from wounds harvested at postoperative day 7 was probed using a nylon-based cDNA array to assess global genetic expression alterations.

RESULTS

Healing in the rat ear model is impaired by both ischemia and advanced age as measured by granulation tissue formation and wound epithelialization. Granulation tissue formation was affected to a greater degree by ischemia than age (-58% versus -21%, respectively) while epithelialization displayed an opposite response (-17% versus -53%, respectively). Global analysis of gene expression suggests that ischemia engenders a marked increase in genes displaying altered expression in aged animals compared to young animals. Importantly, all possible alterations in gene expression are found in samples from aged ischemic wounds, indicating that gene regulation is not simply depressed by advanced age.

CONCLUSIONS

Wound epithelialization appears to be affected to a greater degree by advanced age than by ischemia. The results demonstrate the distinctive phenotype presented by the clinically relevant combination of age and ischemia in an in vivo model of cutaneous wound healing.

Platelet-derived growth factor gene delivery stimulates ex vivo gingival repair

Destruction of tooth support due to the chronic inflammatory disease periodontitis is a major cause of tooth loss. There are limitations with available treatment options to tissue engineer soft tissue periodontal defects. The exogenous application of growth factors (GFs) such as platelet-derived growth factor (PDGF) has shown promise to enhance oral and periodontal tissue regeneration. However, the topical administration of GFs has not led to clinically significant improvements in tissue regeneration because of problems in maintaining therapeutic protein levels at the defect site. The utilization of PDGF gene transfer may circumvent many of the limitations with protein delivery to soft tissue wounds. The objective of this study was to test the effect of PDGF-A and PDGF-B gene transfer to human gingival fibroblasts (HGFs) on ex vivo repair in three-dimensional collagen lattices. HGFs were transduced with adenovirus encoding PDGF-A and PDGF-B genes. Defect fill of bilayer collagen gels was measured by image analysis of cell repopulation into the gingival defects. The modulation of gene expression at the defect site and periphery was measured by RT-PCR during a 10-day time course after gene delivery. The results demonstrated that PDGF-B gene transfer stimulated potent (>4-fold) increases in cell repopulation and defect fill above that of PDGF-A and corresponding controls. PDGF-A and PDGF-B gene expression was maintained for at least 10 days. PDGF gene transfer upregulated the expression of phosphatidylinosital 3-kinase and integrin alpha5 subunit at 5 days after adenovirus transduction. These results suggest that PDGF gene transfer has potential for periodontal soft tissue-engineering applications.

Growth factors and chronic wound healing: past, present, and future

Growth substances (cytokines and growth factors) are soluble signaling proteins affecting the process of normal wound healing. Cytokines govern the inflammatory phase that clears cellular and extracellular matrix debris. Wound repair is controlled by growth factors (platelet-derived growth factor [PDGF], keratinocyte growth factor, and transforming growth factor beta). Endogenous growth factors communicate across the dermal-epidermal interface. PDGF is important for most phases of wound healing. Becaplermin (PDGF-BB), the only growth factor approved by the Food and Drug Administration, requires daily application for neuropathic wound healing. Gene therapy is under development for more efficient growth factor delivery; a single application will induce constitutive growth factor expression for weeks. Based on dramatic preclinical animal studies, a phase 1 clinical trial planned on a PDGF genetic construct appears promising.

Accelerated diabetic wound healing using cultured dermal fibroblasts retrovirally transduced with the platelet-derived growth factor B gene

The treatment of diabetic wounds is a considerable clinical challenge. In this study, mouse dermal fibroblasts retrovirally transduced with the human platelet-derived growth factor B (PDGF-B) gene were used to treat diabetic mouse wounds. The PDGF-B gene was obtained from human umbilical vein endothelial cells, cloned into retroviral vectors, and introduced into diabetic mouse C57B1/ks-db/db dermal fibroblasts. In vitro results demonstrated production of PDGF-B protein by these transduced cells at steady-state levels of 1000 ng PDGF-B/10(6) cells/24 hours, and expression of PDGF-B mRNA. These cells were seeded onto polyglycolic acid scaffold matrices and used to treat diabetic mouse 20-mm x 20-mm full-thickness excisional dorsal skin wounds. Measurement of the residual epithelial gap at 21 days showed significantly accelerated healing (P < 0.05) of wounds treated with PDGF-transduced cells (epithelial gap 10.46 +/- 1.20 mm) compared with untreated wounds (14.66 +/- 0.591 mm), wounds treated with polyglycolic acid alone (14.80 +/- 0.575 mm), or wounds treated with negative control LNCX-transduced cells (13.76 +/- 0.831 mm). Immunohistochemical staining showed intense staining for PDGF in wounds treated with PDGF-B-transduced cells. This study demonstrates the promising potential for gene therapy in diabetic wound healing.

Gene therapy in wound healing

Gene therapy is a new and emerging technology that has been catalyzed by the progress of the Human Genome Project. It employs the process of manipulating genes to achieve a clinically beneficial alteration in gene product. Wound healing lends itself to the application of gene therapy by virtue of the vast array of proteins involved in its complex cascade. This article provides an overview of the background to gene therapy and describes current techniques in use as applied to wound healing. The authors show the potential role that many candidate genes may offer in the future for optimizing wound healing through gene therapy.

Platelet derived growth factor (PDGF) responsive epidermis formed from human keratinocytes transduced with the PDGF beta receptor gene

Platelet-derived growth factor is a major proliferative and migratory stimulus for connective tissue cells during the initiation of skin repair processes. In response to injury, locally produced platelet-derived growth factor is secreted by a diversity of cutaneous cell types whereas target activity is confined to cells of mesenchymal origin, e.g. dermal fibroblasts and smooth muscle cells. Although epidermal cells contribute to cutaneous platelet-derived growth factor activity by their ample capacity to secrete platelet-derived growth factor ligand, normal epidermal keratinocytes are not known to express any member of the platelet-derived growth factor receptor family. In order to study if epidermis may be genetically transformed to a platelet-derived growth factor sensitive compartment we aimed to introduce the gene encoding human platelet-derived growth factor receptor beta (PDGF beta R) into epidermal keratinocytes using a retrovirus-derived vector. Successful gene transfer to primary cells was confirmed by immunofluorescence staining, southern blotting, and ligand-induced receptor autophosphorylation. By culturing a mixture of PDGF beta R-transduced and unmodified keratinocytes at the air-liquid interface on devitalized dermis, we were able to establish a multilayered epithelium showing histologic similarities to that evolved from native keratinocytes or keratinocytes transduced with the reporter gene encoding enhanced green fluorescent protein. Receptor-modified epidermal tissue cultured for 6 days and examined by immunofluorescence microscopy was shown to contain PDGF beta R-expressing keratinocytes distributed in all layers of living epidermis. By continued tissue culture in serum-containing medium, the epidermis became increasingly cornified although receptor-positive cells were still observed within the viable basal compartment. Stimulation of PDGF beta R-transduced epidermis with recombinant platelet-derived growth factor BB had a mitogenic effect as reflected by an increased frequency of Ki-67 positive keratinocytes. The study demonstrates that transgene expression of human PDGF beta R can be achieved in epidermal keratinocytes by retroviral transduction, and that ligand activation of such gene-modified skin equivalent enhances cell proliferation. In perspective, viral PDGF beta R gene transfer to keratinocytes may be a useful approach in studies of receptor tyrosine kinase mediated skin repair and epithelialization.

Cellular, biochemical, and clinical aspects of wound healing

BACKGROUND

The response to tissue injury requires the symphonious interaction of immune cells, keratinocytes, fibroblasts, and endothelial cells, which unite to regenerate the damaged epithelium. Recent insights have elucidated the cellular and molecular mechanisms required for wound healing and have raised the prospect of novel therapeutic targets.

METHODS

Review of the pertinent literature.

RESULTS

The initial inflammatory response leads to the influx of macrophages and neutrophils, which release cytokines, growth factors, and nitric oxide, and induce nearby keratinocytes to migrate across the wounded epithelium. This process, known as re-epithelialization, requires integrin-mediated activation of Rho-GTPases. The subsequent influx of fibroblasts and endothelial cells results in the production of tissue stroma and formation of new blood vessels, which lead to the generation of functional tissue. Importantly, disease states associated with impaired or excessive wound healing can be attributed to defects in these responses, providing a rationale for the use of evidence-based biological therapies.

CONCLUSION

The elucidation of the cellular and biochemical response to wound healing is essential for an understanding to the treatment of clinical conditions during which impaired healing is encountered.

Stroma formation and angiogenesis by overexpression of growth factors, cytokines, and proteolytic enzymes in human skin grafted to SCID mice

Reorganization of skin during wound healing, inflammatory disorders, or cancer growth is the result of expression changes of multiple genes associated with tissue morphogenesis. We wanted to identify proteins involved in skin remodeling and select those that may be targeted for agonistic or antagonist therapeutic approaches in various disease processes. Full-thickness human skin was grafted to severe combined immunodeficient mice and injected intradermally with 38 different adenoviral vectors inserted with 37 different genes coding for growth factors, cytokines, proteolytic enzymes and their inhibitors, adhesion receptors, oncogenes, and tumor suppressor genes. Responses were characterized for infiltration of inflammatory cells, vascular density, matrix formation, fibroblast-like cell proliferation, and epidermal hyperplasia. Of the 17 growth factor vectors, 16 induced histological changes in human skin. Members of the VEGF and angiopoietin families induced neovascularization. PDGFs and TGF-betas stimulated connective tissue formation, and the chemokines IL-8 and MCP-1 attracted inflammatory neutrophils and monocytes, respectively. The serine protease uPA induced a vascular response similar to that of VEGF. Vectors with adhesion receptors, oncogenes and tumor suppressor genes had, with few exceptions, little effects on skin architecture. The overall results suggest that adenoviral vectors can effectively remodel the architecture of human skin for studies in morphogenesis, inflammatory skin disorders, wound healing, and cancer development.

Gene therapy for tissue regeneration

Tissue repair and regeneration are the normal biological responses of many different tissues in the body to injury. During the healing process, profound changes occur in cell composition and extracellular matrix (ECM) formation. Fibroblasts and equivalent reparative cells migrate to the wounded area and subsequently proliferate. These cells and reparative cells from the surrounding tissue are responsible for the rapid repair which results in tissue regeneration. Growth factors, one of which is transforming growth factor-beta (TGF-beta), stimulate fibroblasts and smooth muscle cells to proliferate and synthesize ECM proteins. This process of early repair provides a rapid way to restore new tissue and mechanical integrity. This early tissue repair process is normally followed by involution, which requires the production and activation of proteases, tissue maturation and remodeling, reorganization and finally regeneration. Alternately, failure to replace the critical components of the ECM, including elastin and basement membrane, results in abnormal regeneration of the epithelial cell layer. Although remodeling should occur during healing, provisional repair may be followed by excessive synthesis and deposition of collagen, which results in irreversible fibrosis and scarring. This excessive fibrosis which occurs in aberrant healing is at least in part mediated by persistent TGF-beta. Because of the central role of collagen in the wound healing process, the pharmacological control of collagen synthesis has been of paramount importance as a possible way to abrogate aberrant healing and prevent irreversible fibrosis. Fibrosis is an abnormal response to tissue injury.

Growth factors in the treatment of diabetic foot ulcers

BACKGROUND

Chronic foot ulceration is a major source of morbidity in diabetic patients. Despite traditional comprehensive wound management, including vascular reconstruction, there remains a cohort of patients with non-responding wounds, often resulting in amputation. These wounds may benefit from molecular manipulation of growth factors to enhance the microcirculation.

METHODS

A review of the current literature was performed using Pubmed, with secondary references obtained from key articles.

RESULTS AND CONCLUSION

There has been a generally disappointing clinical outcome from growth factor trials, although topical platelet-derived growth factor has shown significant benefit and should be considered in non-healing, well perfused ulcers after failure of conventional wound care. The modulatory role of the extracellular matrix in the cellular response to growth factors and data from regenerative-type fetal wound healing are further areas of interest. The chemical induction of microvessel formation may become a future therapeutic option.

Sense oligonucleotide competition for gene promoter binding and activation

Considerable evidence has ensued on the importance of growth factors during regeneration both for cell replication and for stimulation of reparative cells to synthesize and secrete extracellular matrix components. During the healing process if the growth factor concentration is too high because of over-expression, abnormal wound healing and tissue fibrosis will occur. The growth factor concentration at the wound site may be controlled by gene therapy and the titration of gene dosage. However, if there is a narrow window between the beneficial effects and adverse effects of gene therapy, oligonucleotide approaches may be used concurrently with gene therapy to control growth factor concentration(s) at the wound site. Antisense oligos offer a method to control the concentration of growth factors at the level of translation. A novel method using sense oligos to the proalpha1 (I) collagen gene to inhibit gene transcription and collagen synthesis has recently been reported. The exogenous modified oligodeoxynucleotide competes with the cis-element (i.e. the transforming growth factor-beta (TGF-beta) element) in the distal 5'-flanking region of the proalpha1 (I) collagen gene for the trans-acting factor (i.e. the TGF-beta activator protein complex), thereby down regulating promoter activity of the proalpha1 (I) collagen gene and inhibiting type I collagen synthesis. The oligonucleotide approaches, both antisense and sense therapies, may be used to regulate over-expression of growth factors and thereby either eliminate or lessen the potential adverse effects of gene therapy.

Adenovirus-mediated VEGF(165) gene transfer enhances wound healing by promoting angiogenesis in CD1 diabetic mice

It has been previously shown that vascular endothelial growth factor (VEGF) plays a central role in promoting angiogenesis during wound repair and that healing-impaired diabetic mice show decreased VEGF expression levels. In order to investigate the potential benefits of gene therapy with growth factors on wound repair, a replication-deficient recombinant adenovirus vector carrying the human VEGF(165) gene (AdCMV.VEGF(165)) was topically applied on excisional wounds of streptozotocin-induced diabetic mice. Treatment with AdCMV.VEGF(165) significantly accelerated wound closure when compared with AdCMV.LacZ-treated, as well as saline-treated control mice, by promoting angiogenesis at the site of injury. Our findings suggest that AdCMV.VEGF(165) may be regarded as a therapeutic tool for the treatment of diabetic ulcers.

Gene therapy--its potential in surgery

Advances in techniques have resulted in practical applications for gene therapy, which is becoming applicable for the treatment of human disease. This review outlines the advantages and disadvantages of the techniques available. Examples of research efforts in the treatment of diseases of relevance to the surgeon (cardiovascular diseases, cancer, wound healing, fracture repair, and in organ transplantation) are presented.

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.

Enhanced adenoviral-vector mediated gene transfer using human albumin solder

BACKGROUND AND OBJECTIVE

Laser tissue welding with human albumin solder (HAS) has been used as an alternative method of wound closure. Adenoviral vectors have been used to introduce various cytokine genes into wounds to accelerate wound closure. In the present study, we were interested in the effect of HAS on adenoviral vector transfer of the beta-galactosidase (beta-gal) gene in vitro and in vivo.

STUDY DESIGN/MATERIALS AND METHODS

3T3 fibroblasts were used to study the effect of HAS on beta-gal gene transfer in vitro. The presence of beta-gal was determined by Western blot, and its activity by a colorimetric assay. A punch biopsy model of wound healing in pigs was used for in vivo experiments.

RESULTS

HAS increased the efficiency of adenoviral-mediated beta-gal transduction and stabilized the adenovirus at room temperature. HAS protected adenovirus from inactivation by laser, both in vitro and in vivo.

CONCLUSIONS

HAS may stabilize adenoviral vectors to deliver cytokine genes in future wound healing experiments.

Adenovirus-mediated ex vivo gene transfer of human vascular endothelial growth factor in a rabbit laryngotracheal reconstruction model

Free autologous cartilage, which is used in laryngotracheal reconstruction (LTR), may undergo progressive necrosis as a result of delayed revascularization. Angiogenic growth factors, such as vascular endothelial growth factor (VEGF), promote angiogenesis in the ischemic environment. We studied the effect of ex vivo gene transfer of VEGF121 on cartilage angiogenesis and graft survival in a rabbit model of LTR. Sixty rabbits underwent LTR with auricular cartilage. The grafts were treated at 1 x 10(9) plaque-forming units with 1) VEGF121 (n = 20), 2) LacZ reporter gene (n = 20), or 3) saline solution (n = 20). Graft neovascularization and survival were histologically assayed at 1 and 10 weeks. Angiogenesis was enhanced at both 1 and 10 weeks after treatment with VEGF121 as compared to controls (p < .001). No statistical improvement in graft survival was evident after treatment with VEGF121. Ex vivo gene transfer to cartilage may be a promising gene therapy strategy to enhance revascularization--and, potentially, cartilage survival--under the proper conditions.

Gene therapy in plastic surgery

Recent developments in gene therapy have shown promise in the treatment of soft-tissue repair, bone formation, nerve regeneration, and cranial suture development. This special topic article reviews commonly used methods of gene therapy and discusses their various advantages and disadvantages. In addition, an overview of new developments in gene therapy as they relate to plastic surgery is provided.

Gene transfer therapy in vascular diseases

Somatic gene therapy of vascular diseases is a promising new field in modern medicine. Recent advancements in gene transfer technology have greatly evolved our understanding of the pathophysiologic role of candidate disease genes. With this knowledge, the expression of selective gene products provides the means to test the therapeutic use of gene therapy in a multitude of medical conditions. In addition, with the completion of genome sequencing programs, gene transfer can be used also to study the biologic function of novel genes in vivo. Novel genes are delivered to targeted tissue via several different vehicles. These vectors include adenoviruses, retroviruses, plasmids, plasmid/liposomes, and oligonucleotides. However, each one of these vectors has inherent limitations. Further investigations into developing delivery systems that not only allow for efficient, targeted gene transfer, but also are stable and nonimmunogenic, will optimize the clinical application of gene therapy in vascular diseases. This review further discusses the available mode of gene delivery and examines six major areas in vascular gene therapy, namely prevention of restenosis, thrombosis, hypertension, atherosclerosis, peripheral vascular disease in congestive heart failure, and ischemia. Although we highlight some of the recent advances in the use of gene therapy in treating vascular disease discovered primarily during the past two years, many excellent studies published during that period are not included in this review due to space limitations. The following is a selective review of practical uses of gene transfer therapy in vascular diseases. This review primarily covers work performed in the last 2 years. For earlier work, the reader may refer to several excellent review articles. For instance, Belalcazer et al. (6) reviewed general aspects of somatic gene therapy and the different vehicles used for the delivery of therapeutic genes. Gene therapy in restenosis and stimulation of angiogenesis in the cardiac muscle are discussed in reviews by several investigators (13,26,57,74,83). In another review, Meyerson et al. (43) discuss advances in gene therapy for vascular proliferative disorders and chronic peripheral and cardiac ischemia.

Expression of the oxygen-regulated protein ORP150 accelerates wound healing by modulating intracellular VEGF transport

Expression of angiogenic factors such as VEGF under conditions of hypoxia or other kinds of cell stress contributes to neovascularization during wound healing. The inducible endoplasmic reticulum chaperone oxygen-regulated protein 150 (ORP150) is expressed in human wounds along with VEGF. Colocalization of these two molecules was observed in macrophages in the neovasculature, suggesting a role of ORP150 in the promotion of angiogenesis. Local administration of ORP150 sense adenovirus to wounds of diabetic mice, a treatment that efficiently targeted this gene product to the macrophages of wound beds, increased VEGF antigen in wounds and accelerated repair and neovascularization. In cultured human macrophages, inhibition of ORP150 expression caused retention of VEGF antigen within the endoplasmic reticulum (ER), while overexpression of ORP150 promoted the secretion of VEGF into hypoxic culture supernatants. Taken together, these data suggest an important role for ORP150 in the setting of impaired wound repair and identify a key, inducible chaperone-like molecule in the ER. This novel facet of the angiogenic response may be amenable to therapeutic manipulation.

Lysine: Is it worth more?

Lysine, an essential cationic amino acid, has a positively charged R group. The structure of lysine is given as (H(3)N(+)-)CH(-COO(-))-CH(2)-CH(2)-CH(2)-CH(2)-N(+)H(3).While the anabolic role(s) of the molecule has been in focus for quite a few decades now, its biological properties, e.g. role in cellular proliferation in vitro (both anchorage dependent and anchorage independent) and in vivo, its ability to induce strong inflammatory and immune responses - both humoral and cell mediated, its role in augmented healing of all types of wounds in animal models as well as in human subjects (both acute and chronic), as well as its role in inducing extensive angiogenic responses, have never received reasonable attention so far. In the current brief and indicative review (rather than exhaustive reviews of each area), we intend to bring these biological properties of the molecule to focus while discussing a few other interesting aspects - lysine as a food preservative as well as its possible role(s) in immune therapy. While the areas look extremely divergent, we propose a common denominator in the form of a possible molecular mechanism of action of the molecule in all these diverse situations.

Matrix immobilization enhances the tissue repair activity of growth factor gene therapy vectors

Although growth factor proteins display potent tissue repair activities, difficulty in sustaining localized therapeutic concentrations limits their therapeutic activity. We reasoned that enhanced histogenesis might be achieved by combining growth factor genes with biocompatible matrices capable of immobilizing vectors at delivery sites. When delivered to subcutaneously implanted sponges, a platelet-derived growth factor B-encoding adenovirus (AdPDGF-B) formulated in a collagen matrix enhanced granulation tissue deposition 3- to 4-fold (p < or = 0.0002), whereas vectors encoding fibroblast growth factor 2 or vascular endothelial growth factor promoted primarily angiogenic responses. By day 8 posttreatment of ischemic excisional wounds, collagen-formulated AdPDGF-B enhanced granulation tissue and epithelial areas up to 13- and 6-fold (p < 0.009), respectively, and wound closure up to 2-fold (p < 0.05). At longer times, complete healing without excessive scar formation was achieved. Collagen matrices were shown to retain both vector and transgene products within delivery sites, enabling the transduction and stimulation of infiltrating repair cells. Quantitative PCR and RT-PCR demonstrated both vector DNA and transgene mRNA within wound beds as late as 28 days posttreatment. By contrast, aqueous formulations allowed vector seepage from application sites, leading to PDGF-induced hyperplasia in surrounding tissues but not wound beds. Finally, repeated applications of PDGF-BB protein were required for neotissue induction approaching equivalence to a single application of collagen-immobilized AdPDGF-B, confirming the utility of this gene transfer approach. Overall, these studies demonstrate that immobilizing matrices enable the controlled delivery and activity of tissue promoting genes for the effective regeneration of injured tissues.

Involvement of platelet-derived growth factor in disease: development of specific antagonists

Platelet-derived growth factor (PDGF) is a family of dimeric isoforms that stimulates, e.g., growth, chemotaxis and cell shape changes of various connective tissue cell types and certain other cells. The cellular effects of PDGF isoforms are exerted through binding to two structurally related tyrosine kinase receptors. Ligand binding induces receptor dimerization and autophosphorylation. This enables a number of SH2 domain containing signal transduction molecules to bind to the receptors, thereby initiating various signaling pathways. PDGF isoforms have important roles during the embryonic development, particularly in the formation of connective tissue in various organs. In the adult, PDGF stimulates wound healing. Overactivity of PDGF has been implicated in certain disorders, including fibrotic conditions, atherosclerosis, and malignancies. Different kinds of PDGF antagonists are currently being developed and evaluated in different animal disease models, as well as in clinical trials.

Particle-mediated gene therapy of wounds

Gene therapy is becoming a reality, and it is a particularly attractive approach for wound healing, because the wound site is often exposed, the treatment and condition should be transient, and gene products such as growth factors and cytokines suffer from problems with bioavailability and stability. Among the techniques for gene delivery to the wound site, particle-mediated bombardment with a device called the gene gun has become an important developmental tool. This instrument has been used in numerous examples of wound gene therapy with growth factors or their receptors in the last decade. Among the advantages of particle-mediated bombardment are ease and speed of preparation of the delivery vehicle, the stability of the DNA preparation, the absence of (viral) antigens, the ability to target the projectiles to different tissue depths and areas, and the rapid shedding of both particles and DNA if they are targeted to the epidermis. Clinical application of the technology remains limited by the relatively low efficiency of the method, the potential tissue damage created by impact of the particles, and the coverage area. The gene gun can also be used to facilitate the discovery and validation of gene products as wound healing agents.

Comparison and evaluation of gene therapy and epigenetic approaches for wound healing

During the past decade considerable evidence has mounted concerning the importance of growth factors in the wound healing process both for cell replication and for stimulating reparative cells to synthesize and secrete extracellular matrix components. During normal wound healing the growth factor concentration has to be maintained at a certain level. If the growth factor concentration is too low, normal healing fails to occur. Whereas if the growth factor concentration is too high due to either over-expression of the growth factor or too much growth factor being applied to the wound, aberrant wound healing will occur. One approach for controlling the amount of growth factor at the wound site during normal healing is through gene therapy and the titration of gene dosage. However if a narrow window exists between the beneficial therapeutic effect and toxic effects with increasing gene dosage, an agent may be necessary to give in combination with gene therapy to regulate the over-expression of growth factor. In addition to genetic approaches to regulate wound healing, epigenetic approaches also exist. Antisense oligodeoxynucleotides have been shown to regulate wound repair in certain model systems and to determine the protein(s) necessary for normal wound healing. A novel approach to regulate the activity of collagen genes, thereby affecting fibrosis, is to use a sense oligodeoxynucleotide having the same sequence of the cis element which regulates the promoter activity of a particular collagen gene. This exogenous oligodeoxynucleotide will compete with the cis element in the collagen gene for the trans-acting factor which regulates promoter activity. These epigenetic approaches afford the opportunity to regulate over-expression of growth factor and therefore preclude the potential toxic effects of gene therapy. Both genetic and epigenetic approaches for regulating the wound healing process, either normal or aberrant wound healing, have certain advantages and disadvantages which are discussed in the present article.

Adenoviral-mediated gene transfer in wound healing

The application of gene transfer strategies to wound healing is not an obvious use of this technology until one considers the important role of cytokines and growth factors in the normal wound healing response. Several gene transfer strategies have been proposed, from in vitro retroviral-mediated gene transfer with autologous transplantation, to in vivo plasmid based gene transfer as retroviral gene transfer. The limitations of these approaches have been efficiency of gene transfer, transgene expression and biologic response. Adenoviral-mediated gene transfer in wound healing is a relatively new application of this vector. The advantage of the adenovirus as a gene transfer vector lies in its ability to transduce nondividing cells of all types at very high efficiency without integration into the host cell's genome. The disadvantage of adenovirus as a vector is the relatively short duration of transgene expression and the inflammatory response it elicits. In the setting of wound healing brief duration of high levels of transgene may be all that is necessary to favorably influence wound healing. Secondly, as wound healing is fundamentally an inflammatory response, the inflammation elicited by the adenovirus may not be detrimental as long as the transgene is a growth factor with significant vulnerary effects such as platelet-derived growth factor-B. This review summarizes the current state of adenoviral-mediated gene transfer in experimental models of impaired wound healing which have laid the groundwork for proposed phase I clinical trials of adenoviral-mediated gene transfer of platelet-derived growth factor-B in chronic venous leg ulcers and chronic nonhealing diabetic foot ulcers. Adenoviral-mediated gene transfer is a useful tool in the study of the role of specific cytokines and growth factors in normal and impaired wound healing. Adenoviral-mediated gene transfer may hold significant promise for clinical application as a means of efficient growth factor delivery in correcting impaired wound healing.

Clinical protocol: Phase I trial to evaluate the safety of H5.020CMV.PDGF-B for the treatment of a diabetic insensate foot ulcer

Most patients with chronic wounds fail to heal in a reasonable period of time. Despite considerable advances in elucidating the molecular basis of wound repair, attempts at developing new therapies have been disappointing. In fact, in the few studies where cytokine growth factors have been efficacious, their effect has been dramatically less than would have been predicted from animal studies. We hypothesize that platelet-derived growth factor-BB, a growth factor associated with wound healing, when produced in large quantities within the wound bed due to adenovirus mediated gene overexpression by the cells of the wound bed will dramatically enhance wound healing. Simply stated, we plan to insure the delivery of the growth factor by using gene therapy techniques so that cells locally involved in the wound healing process will temporarily increase their production of platelet-derived growth factor-BB. We present the first step in the series of human investigations to test this hypothesis which is a phase I clinical trial. Our proposed study is designed to assess local and systemic toxicity, and the feasibility of using the maximum tolerated dose of H5.020CMV.PDGF-b associated with in vivo platelet-derived growth factor-BB gene transduction via an intraulcer injection of H5.020CMV.PDGF-b in patients with a diabetic insensate foot ulcer.

Gene therapy in wound repair and regeneration

The potential use of gene therapy to treat human disease increases with the development of various physical, chemical, and biological methods to deliver genes to mammalian cells, and with our rapidly expanding knowledge of the human genome. One area of therapeutic interest for gene therapy is the treatment of wound healing disorders. Most recently, recombinant human growth factor therapy has been examined as a means to treat problem wounds. However, this approach suffers from the difficulty in providing an accurate dose of growth factor and the expense of the recombinant proteins. Delivery of a gene that could be expressed within the wound is an attractive alternative to application of the protein. This review discusses several methods that have been used to deliver genes encoding growth factor proteins into wounds and the advantages/disadvantages of each approach. Novel methods to regulate the expression of the transgene are also presented, highlighting the ability of these unique vector systems to adjust gene dose as the wound heals. We expect that gene therapy will become a significant treatment modality for those wound healing pathologies refractory to other wound management approaches in the years ahead.

Transcriptional targeting of adenoviral gene delivery into migrating wound keratinocytes using FiRE, a growth factor-inducible regulatory element

Impaired cutaneous wound healing is a common complication in diabetes, ischemia and venous insufficiency of lower extremities, and in long-term treatment with corticosteroids or other immunosuppressive agents. In development of gene therapy for wound repair, expression of therapeutic transgenes should be precisely targeted and controlled. Here, we describe a recombinant adenovirus RAdFiRE-EGFP, in which a growth factor inducible element (FiRE) of the murine syndecan-1 gene controls the expression of enhanced green fluorescent protein (EGFP) reporter gene. Treatment of RAdFiRE-EGFP-transduced murine epidermal keratinocytes in culture with FiRE-activating growth factor markedly enhanced the expression of EGFP. In ex vivo organ culture of wounded murine skin transduced with RAdFiRE-EGFP, the EGFP expression was specifically detected in wound margin keratinocytes, but not in intact skin. Activity of EGFP was first detected 2 days after a single application of RAdFiRE-EGFP and persisted up to 10 days. Similarly, FiRE-driven EGFP expression was detected specifically in epidermal keratinocytes in the edge of incisional wounds in murine skin transduced with RAdFiRE-EGFP. In contrast, adenovirus-mediated lacZ expression driven by CMV promoter was detected scattered in epidermal, dermal and subcutaneous layers in ex vivo and in vivo wounds, as well as in intact skin. These data demonstrate the feasibility of FiRE as a tool for transcriptional targeting of adenovirus-mediated transgene expression to cutaneous wound edge keratinocytes.

Collagen-embedded platelet-derived growth factor DNA plasmid promotes wound healing in a dermal ulcer model

BACKGROUND

Gene therapy has shown limited efficacy for treating congenital diseases, partly due to temporary gene expression and host immune responses. Such results suggest that gene therapy is ideal for chronic wound treatment where limited duration of target gene expression is required. This study tested the wound healing effects of topically applied platelet-derived growth factor (PDGF)-A or -B chain DNA plasmids embedded within a collagen lattice.

MATERIALS AND METHODS

Four 6-mm dermal ulcer wounds were created in the ears of young adult New Zealand White rabbits made ischemic by division of the central and rostral arteries. Wounds were treated with lyophilized collagen containing PDGF-B DNA (1.0-3.0 mg), PDGF-A DNA (1.0 mg), irrelevant DNA (1.0 mg), or collagen alone. Wounds were dressed and harvested after 10 days for measurement of granulation tissue formation, epithelialization, and wound closure. Results were evaluated with a paired two-tailed Student t test, with P values < 0.05 considered significant.

RESULTS

PDGF-B DNA increased new granulation tissue (NGT) formation up to 52% and epithelialization 34% compared with controls. Wound closure was increased up to threefold. At 1.0 mg DNA, PDGF-A and PDGF-B stimulated similar responses. No difference in NGT or epithelialization was seen between control groups.

CONCLUSIONS

PDGF DNA gene therapy is effective at accelerating wound healing in ischemic dermal ulcers and provides a viable alternative to peptide growth factor therapy.

FGF2-Targeted adenovirus encoding platelet-derived growth factor-B enhances de novo tissue formation

Gene therapy has yet to achieve reproducible clinical efficacy, due to inadequate gene delivery, inadequate gene expression, or dose-limiting toxicity. We have developed a gene therapy technology for tissue repair and regeneration that employs a structural matrix for DNA delivery. The matrix holds the DNA vector at the treatment site and provides a scaffolding for in-growth and accumulation of repair cells and efficient DNA transfection. We now report, for the first time, matrix-mediated delivery of targeted DNA vectors for soft tissue repair. A collagen matrix was used to deliver an adenoviral vector encoding platelet-derived growth factor-B (AdPDGF-B), resulting in efficient transgene expression in vitro and in vivo. Increases in the overall levels of expression and in the relative amounts of secreted PDGF-BB were achieved when AdPDGF-B was conjugated to fibroblast growth factor (FGF2) such that the virus was targeted for cellular uptake via FGF receptors. Matrix-mediated delivery of AdPDGF-B enhanced wound healing responses in vivo, and FGF2 targeting generated effects comparable to nontargeted vectors at significantly lower doses. Therefore, matrix-mediated delivery in combination with FGF2 targeting overcomes some of the safety and efficacy limitations of current gene therapy strategies and is an attractive therapeutic approach for tissue repair and regeneration.

Genetic modification of cultured skin substitutes by transduction of human keratinocytes and fibroblasts with platelet-derived growth factor-A

Gene therapy promises the potential for improved treatment of cutaneous wounds. This study evaluated whether genetically modified cultured skin substitutes can act as vehicles for gene therapy in an athymic mouse model of wound healing. Human keratinocytes and fibroblasts were genetically engineered by retroviral transduction to overexpress human platelet-derived growth factor-A chain. Three types of skin substitutes were prepared from collagen-glycosaminoglycan substrates populated with fibroblasts and keratinocytes: HF-/HK-, containing both unmodified fibroblasts and keratinocytes; HF-/HK+, containing unmodified fibroblasts and modified keratinocytes; and HF+/HK-, containing modified fibroblasts and unmodified keratinocytes. Skin substitutes were cultured for two weeks before grafting to full-thickness wounds on athymic mice. The modified skin substitutes secreted significantly elevated levels of platelet-derived growth factor throughout the culture period. Expression of retroviral platelet-derived growth factor-A mRNA was maintained after grafting to mice, and was detected in all HF-/HK+ grafts and one HF+/HK- graft at two weeks after surgery. Although no differences were seen between control and modified grafts, the results suggest that genetically modified cultured skin substitutes can be a feasible mechanism for cutaneous gene therapy. The cultured skin model used for these studies has advantages over other skin analogs containing only epidermal cells; because it contains both fibroblasts and keratinocytes, it therefore offers greater opportunities for genetic modification and potential modulation of wound healing.