Growth factors as wound healing agents

Wound healing can no longer be considered a generic term: it is the summation of a complex series of processes beginning with coagulation and ending in remodelling. This review, therefore, summarizes the past year's advances in growth factor research according to the roles of the individual growth factors in the specific processes of the wound healing scheme.     

Immunohistochemical localization of growth factors in fetal wound healing

Fetal wound healing occurs rapidly, in a regenerative fashion, and without scar formation, by contrast with adult wound healing, where tissue repair results in scar formation which limits tissue function and growth. The extracellular matrix deposited in fetal wounds contains essentially the same structural components as that in the adult wound but there are distinct differences in the spatial and temporal distribution of these components. In particular the organization of collagen in the healed fetal wound is indistinguishable from the normal surrounding tissue. Rapidity of healing, lack of an inflammatory response, and an absence of neovascularization also distinguish fetal from adult wound healing. The mechanisms controlling these differing processes are undefined but growth factors may play a critical role. The distribution of growth factors in healing fetal wounds is unknown. We have studied, by immunohistochemistry, the localization of platelet-derived growth factor (PDGF), transforming growth factor beta (TGF beta), and basic fibroblast growth factor (bFGF), in fetal, neonatal, and adult mouse lip wounds. TGF beta and bFGF were present in neonatal and adult wounds, but were not detected in the fetal wounds, while PDGF was present in fetal, neonatal, and adult wounds. This pattern correlates with the known effects in vitro of these factors, the absence of an inflammatory response and neovascularization in the fetal wound, and the patterns of collagen deposition in both fetal and adult wounds. The results suggest that it may be possible to manipulate the adult wound to produce more fetal-like, scarless, wound healing.     

Stress and wound healing.

An experiment was performed to compare the effects of stressors--cold, heat and noise--on primary wound activity (i.e., wound closure in the first 24 h after wound infliction) and on rate of healing in mice. A significant correlation was found between reduced primary wound activity and a faster rate of healing. Conversely, a correlation was found between relatively greater primary wound activity and a slower rate of healing. A possible explanation of this correlation is a compensatory mechanism inherent to the skin healing process. This mechanism is visualized as (1) stress exposure affecting the skin by (a) causing it to become thinner and tauter and (b) causing it to have less elastic recoil; therefore, (2) when a square wound is produced in stressed skin, (a) the wound does not recoil readily or gapes soon after cutting and (b) a longer wound perimeter results. Because there is evidence that rate of healing is governed by cells on the wound perimeter, the greater the perimeter, the greater the number of cells that will undergo rapid mitosis and the faster will be the rate of healing. Therefore, stressed skin will heal at a faster rate, compensating for the loss of elasticity and cellular depletion caused by stress. This study is of interest to anthropology because it deals with dynamic adaptation, trying to grasp the meaning of the elusive endocrine interface between environmental stimulation and a measurable physical entity like healing. This work may have revealed a functional complex that is common to the healing of all mammalian skin, whereby retarding effects of stress on the healing process are obviated.     

Growth factors in ulcer healing: lessons from recent studies.

Growth factors such as epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF) and more recently vascular endothelial growth factor (VEGF) have been used extensively to heal experimental gastric, duodenal and colonic ulcers in animal models. Encouraging results have been reported in clinical trials with EGF and bFGF. Since our laboratory has been involved with the initial ulcer healing studies with bFGF, PDGF and VEGF, we summarize here the major lessons from these studies and from literature data. These conclusions relate to the role of: 1) gastrointestinal (GI) secretion; 2) epithelial versus vascular components of the healing; 3) efficacy in the upper and lower GI tract; 4) quality of ulcer healing; as well as 5) the endogenous origin; and 6) molar potency of growth factors. Namely, among these growth factors only EGF inhibits gastric acid and stimulates duodenal bicarbonate secretion, while chronic administration of bFGF slightly enhances gastric secretion and PDGF has no effect demonstrating that potent ulcer healing can be achieved without influencing acid base and mucus secretion. This might be related to the fact that these growth factors stimulate with varying potency virtually all the cellular elements needed for ulcer healing, e.g., epithelial cell proliferation and migration by EGF > bFGF > PDGF, fibroblast proliferation by bFGF > PDGF and angiogenesis by VEGF > bFGF > PDGF > EGF. Conceptually, the most interesting results were obtained recently with VEGF which is virtually specific for angiogenesis, illustrating that stimulation of vascular factors is sufficient for ulcer healing because epithelial cells apparently spontaneously proliferate and migrate over a dense granulation tissue to complete the healing process. Since these growth factors directly stimulate the cell components of ulcer healing, it is probably not surprising that they are active in both upper and lower GI tract lesions, produce good quality of ulcer healing in comparison with spontaneously healed duodenal ulcers which are hypovascular and muscle regeneration is not part of natural healing. Contrary to other antiulcer drugs, these growth factors are endogenously derived and play a role in the natural history of ulcer healing, and since these relatively large peptides (18-45 kDa) are active in ng quantities, their molar potency is 2-7 million times superior to cimetidine-like drugs. Thus growth factors are endogenously derived very potent antiulcer drugs which act independently of GI secretion, are active in upper and lower GI lesions, and since they stimulate virtually all the cells of the healing process, they produce an excellent quality of ulcer healing.     

Fibroblast-matrix interactions in wound healing and fibrosis.

The regulation of matrix deposition is a key event in many physiological and pathological situations. It involves the activity of mediators in autocrine and paracrine fashions and the contact of cells with the surrounding extracellular matrix as well. The tightly regulated balance of both mechanisms guarantees rapid and adaptive cellular responses to meet changes in the biological requirements of the environment. Disturbances lead to wound healing defects or the development of fibrosis. The molecular mechanisms for these regulatory events are only partially understood, but involve the activity of integrins and a structural continuum of extracellular matrix-receptor-cytoskeleton-nucleus for transfer of information and the regulation of activated genes.     

Wet wound healing

Wound treatment in a flexible transparent chamber attached to the perimeter of the wound and containing a liquid has been extensively tested in preclinical experiments in pigs and found to offer several advantages. It protects the wound; the liquid medium or saline in the chamber provides in vivo tissue culture-like conditions; and antibiotics, analgesics, and various molecules can be delivered to the wound through the chamber. The wound chamber causes no injury to the wound itself or to the surrounding intact skin. Topical delivery of, for instance, antibiotics can provide very high concentrations at the wound site and with a favorable direction of the concentration gradient. A series of 28 wounds in 20 patients were treated with a wound chamber containing saline and antibiotics. Most patients had significant comorbidity and had not responded to conservative or surgical management with débridement and delayed primary closure or skin grafts. Six wounds had foreign bodies present; four of these were joint prostheses. Seven patients were on corticosteroids for rheumatoid arthritis, lupus, or chronic obstructive pulmonary disease, and four patients had diabetes. Most patients were treated with the wound chamber in preparation for a delayed skin graft or flap procedure, but one was treated with a wound chamber until the wound healed. Twenty-five of the wounds (89 percent) healed, and five wounds (18 percent) required additional conservative management after the initial chamber treatment and grafting procedure. Of the three wounds that did not heal, one healed after additional chamber treatment, one had a skin graft that did not take, and one required reamputation at a higher level. Antibiotic delivery was less than one intravenous dose daily, which avoided the potential for systemic absorption to toxic levels. Antibiotics such as vancomycin and gentamicin could be used in concentrations of up to 10,000 times the minimal inhibitory concentration. Forty-eight hours after application, 20 percent or more of the original antibiotic concentration was present in the wound chamber fluid. In conclusion, the wound chamber provides a safe, powerful tool in the treatment of difficult infected wounds.     

Growth factors and extracellular matrix proteins during wound healing promoted with frozen cultured sheets of human epidermal keratinocytes

In a murine model of full-thickness wounds, healing is stimulated by the application of human frozen cultured epidermal sheets. With immunofluorescence techniques, we studied, during this process, the spatial and temporal pattern of expression of: transforming growth factor-alpha (TGF-alpha); transforming growth factor-beta (TGF-beta) isoforms 1, 2, and 3; platelet-derived growth factor (PDGF); and the extracellular matrix proteins fibronectin, collagen IV, and tenascin. The growth factors, with the exception of PDGF, were found to be located in the frozen cultured sheet of keratinocytes before and after its application to the wound, whereas collagen IV and tenascin were deposited in the connective tissue under the frozen cultures. None of these factors were detected in control wound beds. Monoclonal antibodies against collagen IV and tenascin showed that both were of murine origin. We propose that the frozen cultures of human keratinocytes promote faster reepithelialization through the release of growth factors such as TGF-alpha which directly enhance migration and proliferation of murine keratinocytes, and through the stimulation of murine subepithelial cells, by TGF-beta, to secrete basement membrane proteins such as collagen IV, laminin, and tenascin, which provide a provisional substrate that improves migration of the murine epidermal cells.     

Redox signals in wound healing

Physical trauma represents one of the most primitive challenges that threatened survival. Healing a problem wound requires a multi-faceted comprehensive approach. First and foremost, the wound environment will have to be made receptive to therapies. Second, the appropriate therapeutic regimen needs to be identified and provided while managing systemic limitations that could secondarily limit the healing response. Unfortunately, most current solutions seem to aim at designing therapeutic regimen with little or no consideration of the specific details of the wound environment and systemic limitations. One factor that is centrally important in making the wound environment receptive is correction of wound hypoxia. Recent work have identified that oxygen is not only required to disinfect wounds and fuel healing but that oxygen-dependent redox-sensitive signaling processes represent an integral component of the healing cascade. Over a decade ago, it was proposed that in biological systems oxidants are not necessarily always the triggers for oxidative damage and that oxidants such as H(2)O(2) could actually serve as signaling messengers and drive several aspects of cellular signaling. Today, that concept is much more developed and mature. Evidence supporting the role of oxidants such as H(2)O(2) as signaling messenger is compelling. A complete understanding of the continuum between the classical and emergent roles of oxygen requires a thorough consideration of current concepts in redox biology. The objective of this review is to describe our current understanding of how redox-sensitive processes may drive dermal tissue repair.     

Ixodid tick salivary gland products target host wound healing growth factors

For successful blood-feeding, ticks must confront the host immune system comprising many cells and signaling molecules, mainly cytokines and growth factors. These factors bind to specific receptors on the cell membranes, thereby initiating a signaling cascade that leads to distinct cellular activities. Ticks are able to manipulate host immune responses via molecules secreted from their salivary glands. Saliva of ixodid ticks contains factors binding important cytokines and their subgroup, chemokines. Here we demonstrate that constituents of tick salivary gland extract (SGE) also appear to bind growth factors: transforming growth factor beta (TGF-β1), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF-2), and hepatocyte growth factor (HGF), depending on tick species. SGE derived from Amblyommavariegatum reacted with TGF-β1, PDGF, FGF-2 and HGF; Dermacentorreticulatus and Rhipicephalusappendiculatus with TGF-β1, FGF-2 and HGF; and Ixodes ricinus and Ixodesscapularis with PDGF. SGE from the species targeting PDGF (A. variegatum and I. ricinus) also inhibited cell proliferation in vitro and induced a change in morphology of different cell lines. These effects correlated with disruption of the actin cytoskeleton. Such effects were not observed with SGE of the two species that did not target PDGF. Targeting of wound healing growth factors appears to be yet another strategy ixodid ticks adopt for suppression of inflammation and successful haematophagy.     

Fibronectin and wound healing

I have tried to briefly review the evidence (summarized in Table II) indicating that fibronectin is important in cutaneous wound healing. Fibronectin appears to be an important factor throughout this process. It promotes the spreading of platelets at the site of injury, the adhesion and migration of neutrophils, monocytes, fibroblasts, and endothelial cells into the wound region, and the migration of epidermal cells through the granulation tissue. At the level of matrix synthesis, fibronectin appears to be involved both in the organization of the granulation tissue and basement membrane. In terms of tissue remodeling, fibronectin functions as a nonimmune opsonin for phagocytosis of debris by fibroblasts, keratinocytes, and under some circumstances, macrophages. Fibronectin also enhances the phagocytosis of immune-opsonized particles by monocytes, but whether this includes phagocytosis of bacteria remains to be determined. In general, phagocytosis of bacteria has not appeared to involve fibronectin. On the contrary, the presence of fibronectin in the wound bed may promote bacterial attachment and infection. Because of the ease of experimental manipulations, wound healing experiments have been carried out on skin more frequently than other tissues. As a result, the possible role of fibronectin has not been investigated thoroughly in the repair of internal organs and tissues. Nevertheless, it seems reasonable to speculate that fibronectin plays a central role in all wound healing situations. Finally, the wound healing problems of patients with severe factor XIII deficiencies may occur because of their inability to incorporate fibronectin into blood clots.     

瘦素与创伤愈合

瘦素作为一种多靶器官、多功能的生长因子,它在机体中具有广泛的生理作用。瘦素可能是一种新的促创伤愈合因子,它参与了创伤愈合进程的调节,腹膜内注射瘦素或局部涂抹瘦素加速了动物伤口愈合的速度。本文主要综述了近年来瘦素促进伤口愈合作用的研究现状,并从瘦素在伤口愈合过程中对上皮再生、胶原合成、血管生成、炎症反应等几方面的作用,探讨了瘦素通过调控其它促创伤愈合因子的生成及活性来发挥促伤口愈合作用的机制与途径。     

巨噬细胞与创伤愈合

巨噬细胞是创伤愈合过程中一系列复杂反应中的关键环节,它调节成纤维细胞和血管内皮细胞的生物学活性,在创伤愈合过程中占有不可替代的作用。加强巨噬细胞功能和应用细胞因匀能有效地促进创伤愈合。     

Host defense peptides in wound healing

Host defense peptides are effector molecules of the innate immune system. They show broad antimicrobial action against gram-positive and -negative bacteria, and they likely play a key role in activating and mediating the innate as well as adaptive immune response in infection and inflammation. These features make them of high interest for wound healing research. Non-healing and infected wounds are a major problem in patient care and health care spending. Increasing infection rates, growing bacterial resistance to common antibiotics, and the lack of effective therapeutic options for the treatment of problematic wounds emphasize the need for new approaches in therapy and pathophysiologic understanding. This review focuses on the current knowledge of host defense peptides affecting wound healing and infection. We discuss the current data and highlight the potential future developments in this field of research.