The role of growth factors in wound healing

Adjuncts to preparing wounds for closure: hyperbaric oxygen, growth factors, skin substitutes, negative pressure wound therapy (vacuum-assisted closure)

Achieving closure in a chronic wound requires provision of adequate oxygen delivery to the tissue, adequate protein and other nutritional factors, a moist environment, an appropriate inflammatory milieu, dèbridement, and correction of contributing medical diagnoses. In some patients, these conditions are achieved easily, whereas in others, greater effort is required. Adjunctive treatments, including HBO2, growth factors, skin substitutes, and negative-pressure wound therapy (e.g., V.A.C.) can provide the proper conditions for healing in appropriately selected patients.

Different preparation methods to obtain platelet components as a source of growth factors for local application

BACKGROUND

Autologous platelet components were recently used as part of tissue-engineering strategies in oral and maxillofacial surgery. Various preparation methods were investigated to define standardized blood bank components and to collect data on the growth factor content of human platelets before and after storage.

STUDY DESIGN AND METHODS

Apheresis platelets (AP), buffy coat-derived platelets (BCP), platelets prepared by tube method (TP), and highly concentrated samples prepared from AP and from BCP were evaluated for standard quality criteria of platelet components and for their concentration of transforming growth factor (TGF)-ss1, platelet-derived growth factor (PDGF)-AB, and PDGF-BB. AP were stored for 5 days. On Days 3 and 5, these components and freshly prepared, highly concentrated samples were evaluated for the same measures.

RESULTS

Platelet concentration in TP was lower than that in the other groups (p<0.05). However, the concentrations of PDGF-AB, PDGF-BB, and TGF-ss1 were comparable in the three groups. TP showed higher spontaneous CD62 expression than did AP and BCP. The three preparation procedures resulted in significantly different WBC contamination, with the highest levels in TP. For the whole series of measurements, there was a strong correlation between growth factor levels and platelet concentration (p<0.05), which was due to the face that the growth factor content of concentrated platelet samples was tenfold that of AP, BCP, and TP. In TP, the WBC concentration was correlated with PDGF levels (p<0.05). After 5-day storage, the mean levels of PDGF-AB, PDGF-BB, and TGF-ss1 were 57.1, 43.0, and 72.0 percent of the initial values in AP. Overall, multiple regression analysis revealed the following factors influencing the measured growth factor concentrations: platelet concentration, baseline CD62 expression, lactate production, and WBC contamination.

CONCLUSION

Various methods enable the preparation of platelet components and of highly concentrated components for local use according to standard blood banking criteria. The obtained components differ, particularly in their WBC content and in vitro platelet activation. These findings are relevant for planning and evaluating further studies of locally usable autologous platelet components.

Blockade of receptor for advanced glycation end-products restores effective wound healing in diabetic mice

Receptor for advanced glycation end-products (RAGE), and two of its ligands, AGE and EN-RAGEs (members of the S100/calgranulin family of pro-inflammatory cytokines), display enhanced expression in slowly resolving full-thickness excisional wounds developed in genetically diabetic db+/db+ mice. We tested the concept that blockade of RAGE, using soluble(s) RAGE, the extracellular ligand-binding domain of the receptor, would enhance wound closure in these animals. Administration of sRAGE accelerated the development of appropriately limited inflammatory cell infiltration and activation in wound foci. In parallel with accelerated wound closure at later times, blockade of RAGE suppressed levels of cytokines; tumor necrosis factor-alpha; interleukin-6; and matrix metalloproteinases-2, -3, and -9. In addition, generation of thick, well-vascularized granulation tissue was enhanced, in parallel with increased levels of platelet-derived growth factor-B and vascular endothelial growth factor. These findings identify a central role for RAGE in disordered wound healing associated with diabetes, and suggest that blockade of this receptor might represent a targeted strategy to restore effective wound repair in this disorder.

[Integra, a new surgical alternative for the treatment of massive burns. Clinical evaluation of acute and reconstructive surgery: 39 cases]

Early excision and prompt coverage in severely burned patients are the best way to lessen morbidity and improve survival. Repair of full-thickness burns requires replacement of both dermal and epidermal components of skin and treatment with split thickness autografts replaces both of them. But healthy skin is not sufficient in extensive burns. Alternative to split thickness skin grafts have been studied by several groups including epidermis, dermis or a complete replacement comprising epidermis and dermis. Because of the difficulties in homografts supplying, a new way was use to replace the dermis. In 1981, Yannas and Burke were the first to develop such a matrix. Intégra is available in France since 1997 and was used in our service for the treatment of both acute and reconstructive surgery for burned patients. Twenty patients were treated for acute surgery. Nineteen patients were treated for reconstructive surgery of burn scar contractures. Fifty-one grafts of Intégra were performed. Long-term final results seem to show that Intégra improve cosmetical and functional results and is a new surgical alternative for the treatment of burns in the acute phase as well as in late surgery of deformities.

Specific growth factors and the healing of chronic wounds

Part II of this two-part review focuses on the function of specific growth factors in wound healing and considers the results of clinical trials of their use in chronic wounds.

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.

A dynamic regulator: the role of growth factors in tissue repair

Growth factors have the potential to improve wound healing during the three main phases of wound repair. This review, the first in a two-part series, explains how they do this.

The future of nutrition and wound healing

Nutrition is vital to all bodily processes. During wound healing, it is essential that nutrients are available as they form the building blocks for tissue repair. Nutrition may therefore affect healing due to an overall deficiency of intake, either due to non-availability or due to inability of the patient to absorb sufficiently to meet their requirements. Alternatively, deficiencies of specific nutrients may also inhibit healing and on the converse some additives, not normally present in large quantity in the diet, may have beneficial effects. This review considers the nutritional factors affecting wound healing and some developments that may alter the future of therapy.

Role of platelet-derived growth factor as an adjunct to surgery in the management of pressure ulcers

Management options for pressure ulcers include local wound care, surgical repair, and, more recently, topical application of platelet-derived growth factor (PDGF). PDGF is a glycoprotein that is mitogenic for mesenchymal cells and has been studied extensively for applicability in promoting the healing of chronic human wounds. Using data obtained from a multicenter clinical trial for the treatment of full-thickness pressure ulcers, a subset analysis was performed to investigate the outcome of salvage surgery for pressure ulcers, after incomplete closure occurred with the topical use of either recombinant human PDGF-BB (rhPDGF-BB) or placebo gel. At the University of Michigan Wound Care Center, subset data from a randomized, double-blind, placebo-controlled, parallel group clinical trial were reviewed to compare the effects of three concentrations of rhPDGF-BB on full-thickness pressure ulcers of the trunk with those of the placebo. Twenty-eight patients were enrolled and 27 completed the trial. An intent-to-treat analysis was used to evaluate data. If the ulcer did not heal by the end of the 16-week trial period, the surgeon, still blinded to the treatment group, offered salvage surgical repair of the pressure ulcer. Eleven patients underwent salvage surgical repair using myocutaneous flaps, primary closure, or skin grafts. Of three patients who received placebo followed by surgery, none progressed to full healing within 1 year. Of 12 patients in the treatment group who received rhPDGF-BB and salvage surgery, 11 (92 percent) ultimately healed the ulcers within 1 year after the start of the clinical trial. These findings suggest that treatment with rhPDGF-BB before surgery enhances the ability to achieve a closed wound over surgery alone. It must yet be determined to what degree rhPDGF-BB contributed to the excellent results seen in the rhPDGF-BB/surgery group. It is possible that rhPDGF-BB "primes" the local wound milieu to make it more responsive to complete closure following surgical treatment.

Leukemia inhibitory factor gene improves skin allograft survival in the mouse model

BACKGROUND

Leukemia inhibitory factor (LIF) is a widely expressed cytokine involved in both local and systemic immune response. Furthermore, it has been implicated in various immunological processes including thymic T cell maturation and embryo implantation. We investigated implication of various modalities in the application of prolonged and viable allograft to the wound, using cytokines and growth factors.

MATERIALS

BALB/c and B6D2F1 strains of mice were used either as a skin graft donor or host. LIF cDNA inserted in plasmid vector or the vector alone was injected intradermally in graft skin and observed up to 21 days. LIF, LIF-receptor, gp130, as well as type 1 and 2 T helper cytokine expressions were investigated by reverse transcription polymerasse chain reaction, in situ hybridization, and histological studies.

RESULTS

LIF cDNA-treated groups showed significantly improved graft survival compared to the vector-treated control in 21 days postoperatively for grafting from B6D2F1 to BALB/c and BALB/c to B6D2F1. LIF and LIF receptor mRNA expressions were observed 24 hr and 21 days posttransplantation. The gp130 expression was only observed in LIF-treated B6D2F1 to BALB/c allografting on day 21 posttransplantation. LIF transcripts were strongly present in the epidermal, dermal, and subdermal tissues as determined by an in situ hybridization of LIF-treated grafting.

CONCLUSIONS

These results suggest that LIF cDNA treatment is an effective and beneficial adjuvant for the skin allograft survival. Improved skin allograft modulation by cytokine gene transfer is a potentially promising therapy for temporary large skin coverage.

Growth factors regulate expression of mineral associated genes in cementoblasts

BACKGROUND

Knowledge of the responsiveness of cells within the periodontal region to specific bioactive agents is important for improving regenerative therapies. The aim of this study was to determine the effect of specific growth factors, insulin-like growth factor-I (IGF-I), platelet-derived growth factor-BB (PDGF-BB), and transforming growth factor-beta (TGF-beta) on cementoblasts in vitro and ex vivo.

METHODS

Osteocalcin (OC) promoter driven SV40 transgenic mice were used to obtain immortalized cementoblasts. Growth factor effects on DNA synthesis were assayed by [3H]-thymidine incorporation. Northern analysis was used to determine the effects of growth factors on gene expression profile. Effects of growth factors on cementoblast induced biomineralization were determined in vitro (von Kossa stain) and ex vivo (re-implantation of cells in immunodeficient (SCID) mice).

RESULTS

All growth factors stimulated DNA synthesis compared to control. Twenty-four hour exposure of cells to PDGF-BB or TGF-beta resulted in a decrease in bone sialoprotein (BSP) and osteocalcin (OCN) mRNAs while PDGF-BB also increased osteopontin (OPN) mRNA. Cells exposed to IGF-I for 24 hours exhibited decreased transcripts for OCN and OPN with an upregulation of BSP mRNA noted at 72 hours. In vitro mineralization was inhibited by continuous application of PDGF-BB or TGF-beta, while cells exposed to these factors prior to implantation into SCID mice still promoted biomineralization.

CONCLUSIONS

These data indicate IGF-I, PDGF-BB, and TGF-beta influence mitogenesis, phenotypic gene expression profile, and biomineralization potential of cementoblasts suggesting that such factors alone or in combination with other agents may provide trigger factors required for regenerating periodontal tissues.

Initiating the inflammatory phase of incisional healing prior to tissue injury

BACKGROUND

The time required for incisional healing accounts for the majority of postoperative pain and convalescence. Impaired healing prolongs the process further. If a method for accelerating acute incisional wound healing could be developed, patients would benefit from decreased wound failure and an earlier return to their premorbid condition.

MATERIALS AND METHODS

In a rat dermal model, cytokine or vehicle infiltration prior to incision was performed using a single dose or four daily doses preincision. Planned incision sites were primed with the proinflammatory cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) or platelet-derived growth factor BB (PDGF-BB) in an effort to activate the inflammatory phase of healing prior to wounding. At the time of incision closure, one half of the incisions were treated with transforming growth factor beta(2) (TGF-beta(2)). Incisional sites were biopsied and stained with hematoxylin and eosin and immunohistochemistry for inflammatory cells and fibroblast populations and breaking strength was measured.

RESULTS

Priming skin with GM-CSF or PDGF-BB mimicked the early inflammatory phase of wound healing. Macrophage staining (EB1) and fibroblast staining (vimentin) were significantly increased prior to incision. Inflammatory priming as well as priming coupled with TGF-beta(2) at the time of the incision closure synergistically improved breaking strength.

CONCLUSION

This study demonstrates that sequential therapy consisting of priming of tissue with an inflammatory cytokine followed by application of a proliferative cytokine at the time of incision closure nearly doubles the breaking strength of an acute wound. By manipulating the inflammatory and early proliferative phases of wound healing with tissue growth factors, it may be possible to accelerate acute wound repair and shift the wound healing trajectory to the left.

Current challenges in wound care management: an overview

This article provides an overview of the latest theories and technology in compression therapy, and the use of growth factors and skin substitutes. Compression therapy is a major factor in the treatment of venous leg ulcers and is widely used and readily available on the Drug Tariff. Skin substitute and growth factors provide a new technological approach to wound healing with hope for the future management of both acute and chronic wounds. While new technologies are an exciting prospect for the future of wound management, there can be no substitute for good wound care. In the interest of optimum wound management and patient care, health professionals have a duty to find ways to improve patients' quality of life.

Occlusion following laser resurfacing promotes reepithelialization and wound healing

One of the critical parameters that has not been examined carefully following laser skin resurfacing is the effect of eschar on the wound healing process. Because occlusive dressings minimize the occurrence of eschar, the present study was undertaken to evaluate the effect of occlusion following laser resurfacing. It is clear that CO2 lasers promote epidermal cell loss and variable amounts of dermal injury. To characterize the wound repair process after laser treatment, biopsy specimens were obtained 2 to 4 days after treatment. Specimens from 15 patients were examined; the preauricular biopsy specimens were paired such that one specimen was from skin that had been occluded and the other specimen (from the same patient) was from skin treated without occlusion. Skin specimens were examined by indirect immunofluorescence using antibodies to specific epidermal and dermal antigens. The results indicate that the keratinocytes that repopulate the epidermis migrate from the hair follicles and express keratin 17, an intermediate filament protein expressed in keratinocytes during the early stages of wound healing. The migration of keratin 17-expressing cells begins 48 hours following laser resurfacing in skin treated with occlusion, whereas cell migration from the follicles of skin treated without occlusion is delayed. In summary, occlusion promotes enhanced cell migration and diminished eschar formation, resulting in more rapid healing.

Recombinant human platelet-derived growth factor-BB (becaplermin) for healing chronic lower extremity diabetic ulcers: an open-label clinical evaluation of efficacy

Topically applied recombinant human platelet-derived growth factor-BB (becaplermin) is a new pharmacologically active therapy for chronic, neuropathic, lower extremity diabetic ulcers. In previous studies, becaplermin gel was administered once daily but dressings were changed twice daily. In the present study of 134 patients with diabetes mellitus and full thickness lower extremity ulcers, dressings were changed only once per day, simplifying the treatment regimen. Efficacy criteria included the percentage of patients achieving complete healing within the 20-week treatment period, the time to achieve complete healing, the rate of ulcer recurrence during the 6-month period following healing, and treatment compliance. Complete healing of ulcers was achieved in 57. 5% of patients, with a mean time to closure of 63 days and a recurrence rate of 21% at 6 months. Of the potential factors affecting ulcer healing, only drug compliance (p < 0.001), dressing compliance (p < 0.01), the presence of infection (p < 0.01), baseline ulcer area (p < 0.05), and baseline total wound evaluation score (p < 0.05) were significantly associated with healing. Results of this study further confirm the efficacy and safety of becaplermin gel for the treatment of lower extremity diabetic ulcers.

Epidermal growth factor and keratinocyte growth factor differentially regulate epidermal migration, growth, and differentiation

Various growth factors such as epidermal growth factor and keratinocyte growth factor have been reported to promote wound closure and epidermal regeneration. In the present study epidermis reconstructed on de-epidermized dermis was used to investigate the effects of epidermal growth factor and keratinocyte growth factor on keratinocyte proliferation, migration and differentiation. Our results show that epidermal growth factor supplemented cultures share many of the features which are observed during regeneration of wounded epidermis: a thickening of the entire epidermis, an enhanced rate of proliferation and migration, and an increase in keratin 6, keratin 16, skin-derived antileukoproteinase, involucrin and transglutaminase 1 expression. The increase in transglutaminase 1 protein is accompanied by an increase in the amount of active transglutaminase 1 enzyme. Surprisingly no increase in keratin 17 is observed. Prolonging the culture period for more than two weeks results in rapid senescence and aging of the cultures. In contrast, keratinocyte growth factor supplemented cultures have a tissue architecture that is similar to healthy native epidermis and remains unchanged for at least 4 weeks of air-exposure. The rate of proliferation and the expression of keratins 6, 16 and 17, skin-derived antileukoproteinase, involucrin and transglutaminase 1 is similar to that found in healthy epidermis and furthermore keratinocyte migration does not occur. When the culture medium is supplemented with a combination of keratinocyte growth factor and a low concentration of epidermal growth factor, skin-derived antileukoproteinase, involucrin and keratins 6, 16 and 17 expression is similar to that found in cultures supplemented with keratinocyte growth factor alone and in healthy epidermis. Only high transglutaminase 1 expression remains similar to that observed in cultures supplemented with epidermal growth factor alone. Our results show that the regulation of keratinocyte growth, migration and differentiation depends on the availability of these growth factors. Epidermal growth factor may play a dominant early role in wound healing by stimulating keratinocyte proliferation and migration while keratinocyte growth factor may play a role later in the repair process by stabilizing epidermal turnover and barrier function.

Potential role of growth factors and extracellular matrix in wound healing after laryngotracheal reconstruction

Laryngotracheal reconstruction (LTR) has been used for more than 20 years to treat infants and children with subglottic stenosis. Results after pediatric LTR have been satisfactory; however, approximately 10% of children have recurrent airway narrowing after LTR. The purpose of our study was to determine whether a correlation existed between specific growth factors and extracellular matrix in patients with adequate wound healing capability as compared with patients with poor wound healing capability. Histologic sections from 27 patients who underwent LTR were cut, and immunohistochemical staining was performed for transforming growth factor-beta, platelet-derived growth factor, fibronectin, tenascin, transforming growth factor-alpha, and vascular endothelial growth factor. Results showed that patients with adequate wound healing capability had a positive correlation with vasculature fibronectin, vasculature tenascin, and stromal fibronectin. Patients with poor wound healing capability had a positive correlation with stromal vascular endothelial growth factor.

Arnebin-1 accelerates normal and hydrocortisone-induced impaired wound healing

Wound healing involves inflammation, cell proliferation, matrix deposition, and tissue remodeling. Interaction of different cells, extracellular matrix proteins, and their receptors are mediated by cytokines and growth factors during wound healing. In this study, we have evaluated the effect of arnebin-1, a natural product isolated from Arnebia nobilis, on normal and impaired wound healing in cutaneous punch wound model. Arnebin-1 was applied topically daily on wounds of hydrocortisone-treated or untreated animals. Arnebin-1 significantly accelerated healing of wounds with or without hydrocortisone treatment as revealed by a reduction in the wound width and gap length compared with controls. Arnebin-1 treatment promoted the cell proliferation, migration, and vessel formation to form a thick granulation tissue and re-epithelialization of the wounds. An increase in the synthesis of collagen, fibronectin and transforming growth factor-beta1 was seen in arnebin-1-treated wounds compared with the untreated control. As transforming growth factor-beta1 is known to enhance wound healing, and associated with the wound healing defect in hydrocortisone-treated wounds, the enhanced expression of transforming growth factor-beta1 at both translational and transcriptional level by arnebin-1 may be responsible for the enhancement of wound healing during normal and impaired wound repair. These studies suggest that arnebin-1 could be developed as a potent therapeutic agent for wound healing in steroid-impaired wounds.

Healing of chronic leg ulcers in diabetic necrobiosis lipoidica with local granulocyte-macrophage colony stimulating factor treatment

Two young insulin-dependent diabetic patients suffering from chronic nonhealing leg ulcers of necrobiosis lipoidica diabeticorum were treated by applying topically recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) on the ulcer repetitively during 10 weeks. Evaluation of ulcer size was assessed with clinical examinations at 1-week or 2-week intervals. Topical GM-CSF healed the ulcers of both patients in 10 weeks. Decrease in the size of the ulcers was already evident after the first topical applications. During follow-up, the ulcers have remained healed for more than 3 years. This excellent treatment result suggests that topically applied GM-CSF may be a valuable drug for chronic, nonhealing ulcers in patients with diabetes.

Cytokines and anti-cytokine therapy: clinical potential for treatment of feline disease

Cytokines are soluble proteins produced by nucleated cells throughout the body. They have wide ranging effects on cell growth and differentiation, mediating immune responses, haemopoiesis and tissue repair. Advances in recombinant DNA technology have led to a vast increase in knowledge of their biological properties and subsequently their use in human clinical trials. The use of human cytokines in feline medicine has been of limited success as the action of cytokines is often species restricted or their activity may be neutralized due to antibody formation. Recently, however, many feline cytokines have been cloned which raises the possibility of their future use in the management and prevention of feline disease. Ultimately, they may find widespread clinical uses including the treatment of cancer, cytopenias and viral infections and as vaccine adjuvants.

The microvascular composition of the healing wound compared at skin sites with nutritive versus arteriovenous perfusion

Background. In the rat, there is a significantly greater blood flow response to wounding at the back, a site perfused mainly by small capillaries, than at the paw, which has a much higher density of arterioles and venules. Materials and methods. We characterized the microvascular composition of wounds at the two skin sites in 11 Wistar Kyoto rats using a quantitative imaging program. Blood flow was compared using laser Doppler technology. Results. Prior to wounding, skin blood flow was much greater at the paw (7.1 +/- 0.5 ml 100 g tissue-1 min-1) than at the back (2.1 +/- 0.1 ml 100 g tissue-1 min-1, P < 0.01) at baseline. Seven days after wounding, blood flow both at the center (8.3 +/- 1.4 ml 100 g tissue-1 min-1) and at the perimeter of the back wound (4.1 +/- 0.5 ml 100 g tissue-1 min-1) had increased substantially. In contrast, skin blood flow at the perimeter of the paw wound had increased moderately (12. 7 +/- 2.0 ml 100 g tissue-1 min-1), but there was no change at the center of the wound (6.9 +/- 0.9 ml 100 g tissue-1 min-1). There were three times more microvessels per mm2 at the paw site (39.3 +/- 3.6) than at the back (13.1 +/- 1.5) prior to wounding. The wound granulation tissue was very vascular; the numerical density of vessels was identical at back (166 +/- 9) and at paw (154 +/- 6). Despite the marked increase in blood flow at the perimeter of the back wound, there was no difference in the microvascular density (15. 2 +/- 1.4) compared to baseline, nor was there a difference at the paw perimeter (39.4 +/- 3.6) compared to baseline. Conclusions. This study demonstrates that the microvascular constitutions of granulation tissues at the paw and back are identical. Thus, the rise in flow at the back wound and reduction in flow at the paw wound are entirely consistent with similar microvascular compositions of these two sites. Yet, there is increased flow at the back wound perimeter where there is no significant change in microvascular constitution compared to unwounded skin. Therefore, a microvascular structure no different from that prior to wounding functions very differently after wounding. Clearly vasoregulatory factors impact on the wound to modify flow through the microvascular network.

Signal transduction in wound pharmacology

Growth factors such as TGF-beta, PDGF and FGF are thought to play important roles in wound healing. However, their biological activity and signal transduction during wound repair remain poorly understood. Growth factors are often ligands for receptor tyrosine kinase and receptor serine/threonine kinases. With recent advances in signal transduction by receptor kinases, we are beginning to understand the underlying mechanism of how growth factors may regulate cutaneous wound repair. In this paper, we will describe the pharmacological effects of growth factors on wound healing, and discuss the potential underlying signaling mechanisms. Thus, we hope to provide the basis for designing more specific therapeutics for wound healing in the near future.

Clinical efficacy of becaplermin (rhPDGF-BB) gel. Becaplermin Gel Studies Group

The results of four multicenter, randomized, placebo-controlled, parallel group studies of the efficacy of becaplermin gel are reviewed here. The four studies included a total of 922 patients, all of whom received a standardized regimen of good ulcer care. Patients were randomized to receive placebo gel, 30 or 100 microg/g becaplermin gel, or good ulcer care alone. In Studies 1 and 2, the incidence of complete healing was significantly higher in patients receiving becaplermin gel (30 microg/g, Study 1; 100 microg/g, Study 2) compared with that in patients receiving placebo gel. In Study 3, which was not powered for statistical analysis, the incidence of complete healing in patients treated with 100 microg/g becaplermin gel was approximately twice that of patients treated with good ulcer care alone. In Study 4, there was no significant difference in the incidence of complete healing in patients treated with becaplermin gel versus good ulcer care alone.

Effects of chronic wound fluid on the structure and biological activity of becaplermin (rhPDGF-BB) and becaplermin gel

In this study, the effects of chronic wound fluid on the structure and biological activity of becaplermin (recombinant human platelet-derived growth factor-BB [rhPDGF-BB]) were evaluated. Wound fluid was collected from 12 subjects with diabetic ulcers or pressure ulcers. Wound fluid +/- becaplermin was added to cell cultures before- and after incubation for 12 hours at 37 degrees C or after 12 hours' topical treatment. Biological activity, concentration, and immunogenicity were determined by [3H]thymidine incorporation into quiescent human foreskin fibroblasts, enzyme-linked immunosorbent assay (ELISA), and Western blot analysis, respectively. No PDGF-BB or mitogenic activity was detected in chronic wound fluid alone. Mitogenic activity was present in post-treatment samples from becaplermin-treated subjects but not placebo-treated subjects. Exposure to chronic wound fluid for 12 hours did not alter the amount, banding pattern, or mitogenic activity of becaplermin. Biologically active becaplermin remains in wound fluid 12 hours after topical application of becaplermin gel.

Physiology and healing dynamics of chronic cutaneous wounds

In the last few decades, a great deal of progress has been made in understanding the cellular and biochemical interplay that comprises the normal wound healing response. This response is a complex process involving intricate interactions among a variety of different cell types, structural proteins, growth factors, and proteinases. The normal wound repair process consists of three phases--inflammation, proliferation, and remodeling--that occur in a predictable sequence and comprise a series of cellular and biochemical events. A review of the biochemical and physiologic processes that regulate wound healing and the cascade of cellular events that gives rise to the healing process is presented here.

Semiquantitative reverse transcription-polymerase chain reaction analysis of mRNA for growth factors and growth factor receptors from normal and healing rabbit medial collateral ligament tissue

Growth factors and their receptors play an essential role in the development, maturation, and response to injury of all tissues. A number of studies have explored the possibility of improving ligament healing with exogenous growth factors. However, limited data is available regarding the endogenous growth factor network in ligaments on which any exogenous growth factors must impact. The purpose of this study was to assess the endogenous growth factor network with molecular techniques. By the sensitive reverse transcription-polymerase chain reaction technique, transcripts for a number of growth factors and receptors were detected with RNA isolated from normal and healing rabbit medial collateral ligament tissues. These include transforming growth factor-beta1, insulin-like growth factors I and II, basic fibroblast growth factor, endothelin-1, and the receptors for insulin and insulin-like growth factor II. Semiquantitative reverse transcription-polymerase chain reaction analysis of RNA from normal and scar tissues from the medial collateral ligament revealed that the levels of several transcripts were elevated in the scar tissue. It was not possible to confirm biological activity because of the hypocellularity of the tissues; however, the results obtained indicate that the reverse transcription-polymerase chain reaction approach to defining the endogenous growth factor-receptor phenotype is feasible, and further definition should contribute to the development of rational approaches to exogenous therapy to improve healing.

Towards a molecular definition of keratinocyte activation after acute injury to stratified epithelia

While in recent years we have come to increasingly appreciate the multifaceted role of skin, probably none of these novel contributions is as vital as its barrier function, inferred centuries ago. In human skin this function is fulfilled nearly entirely by the epidermis, a thin stratified squamous epithelium made up primarily of keratinocytes and located at the skin surface. Disruption of the integrity of epidermis triggers a homeostatic response involving blood-derived elements and resident skin cell types that is designed to rapidly restore a functional epithelial lining over the wound site. This article is focused on the process of recruitment of keratinocytes from intact skin tissue at the proximal wound edges to participate in re-epithelialization.