Stromal progenitor cell therapy corrects the wound-healing defect in the ischemic rabbit ear model of chronic wound repair

Chronic wounds create a formidable clinical problem resulting in considerable morbidity and healthcare expenditure. The etiology for wound healing impairment appears to be multifactorial; however, ischemia is a common factor in most types of chronic wounds. Ideal therapy for such wounds would be to correct deficiencies in growth factors and matrix components and provide cellular precursors required for timely wound closure. We hypothesized that stromal progenitor cell (SPC) therapy could correct the ischemic wound-healing defect through both direct and indirect mechanisms. To test this hypothesis, we used the ischemic rabbit ear model of chronic wound healing. We found that treatment of the wounds with SPCs was able to reverse the ischemic wound-healing impairment, with improved granulation tissue formation and reepithelialization compared with vehicle or bone marrow mononuclear cell controls. In vitro, SPCs were found to produce factors involved in angiogenesis and reepithelialization, and extracellular matrix components, providing evidence for both direct and indirect mechanisms for the observed correction of the healing impairment in these wounds. Treatment of ischemic wounds with SPCs can dramatically improve wound healing and provides a rationale for further studies focused on SPCs as a potential cellular therapy in impaired wound healing.     

Wound bed preparation: a systematic approach to wound management

The healing process in acute wounds has been extensively studied and the knowledge derived from these studies has often been extrapolated to the care of chronic wounds, on the assumption that nonhealing chronic wounds were simply aberrations of the normal tissue repair process. However, this approach is less than satisfactory, as the chronic wound healing process differs in many important respects from that seen in acute wounds. In chronic wounds, the orderly sequence of events seen in acute wounds becomes disrupted or “stuck” at one or more of the different stages of wound healing. For the normal repair process to resume, the barrier to healing must be identified and removed through application of the correct techniques. It is important, therefore, to understand the molecular events that are involved in the wound healing process in order to select the most appropriate intervention. Wound bed preparation is the management of a wound in order to accelerate endogenous healing or to facilitate the effectiveness of other therapeutic measures. Experts in wound management consider that wound bed preparation is an important concept with significant potential as an educational tool in wound management. This article was developed after a meeting of wound healing experts in June 2002 and is intended to provide an overview of the current status, role, and key elements of wound bed preparation. Readers will be able to examine the following issues; ? the current status of wound bed preparation; ? an analysis of the acute and chronic wound environments; ? how wound healing can take place in these environments; ? the role of wound bed preparation in the clinic; ? the clinical and cellular components of the wound bed preparation concept; ? a detailed analysis of the components of wound bed preparation. (WOUND REP REG 2003;11:1–28)     

Response to tissue injury

Cutaneous injury, whether by laser, chemical, or scalpel, results in scar formation. The normal response to such an insult occurs in the middle of a continuum of wound repair processes. On one end of the continuum are the overhealed responses (i.e., keloids). On the opposite end are tissue regeneration and scarless healing as seen in fetal wounds. This article reviews the molecular biology and mechanisms leading to these various clinical phenotypes and discusses future potential modalities that may replicate the scarless wound healing mechanism in adults.     

Wound bed preparation: a systematic approach to wound management

The healing process in acute wounds has been extensively studied and the knowledge derived from these studies has often been extrapolated to the care of chronic wounds, on the assumption that nonhealing chronic wounds were simply aberrations of the normal tissue repair process. However, this approach is less than satisfactory, as the chronic wound healing process differs in many important respects from that seen in acute wounds. In chronic wounds, the orderly sequence of events seen in acute wounds becomes disrupted or "stuck" at one or more of the different stages of wound healing. For the normal repair process to resume, the barrier to healing must be identified and removed through application of the correct techniques. It is important, therefore, to understand the molecular events that are involved in the wound healing process in order to select the most appropriate intervention. Wound bed preparation is the management of a wound in order to accelerate endogenous healing or to facilitate the effectiveness of other therapeutic measures. Experts in wound management consider that wound bed preparation is an important concept with significant potential as an educational tool in wound management.
This article was developed after a meeting of wound healing experts in June 2002 and is intended to provide an overview of the current status, role, and key elements of wound bed preparation. Readers will be able to examine the following issues;
• the current status of wound bed preparation;
• an analysis of the acute and chronic wound environments;
• how wound healing can take place in these environments;
• the role of wound bed preparation in the clinic;
• the clinical and cellular components of the wound bed preparation concept;
• a detailed analysis of the components of wound bed preparation.
(WOUND REP REG 2003;11:1–28)     

Cellular events and biomarkers of wound healing

Researchers have identified several of the cellular events associated with wound healing. Platelets, neutrophils, macrophages, and fibroblasts primarily contribute to the process. They release cytokines including interleukins (ILs) and TNF-α, and growth factors, of which platelet-derived growth factor (PDGF) is perhaps the most important. The cytokines and growth factors manipulate the inflammatory phase of healing. Cytokines are chemotactic for white cells and fibroblasts, while the growth factors initiate fibroblast and keratinocyte proliferation. Inflammation is followed by the proliferation of fibroblasts, which lay down the extracellular matrix. Simultaneously, various white cells and other connective tissue cells release both the matrix metalloproteinases (MMPs) and the tissue inhibitors of these metalloproteinases (TIMPs). MMPs remove damaged structural proteins such as collagen, while the fibroblasts lay down fresh extracellular matrix proteins. Fluid collected from acute, healing wounds contains growth factors, and stimulates fibroblast proliferation, but fluid collected from chronic, nonhealing wounds does not. Fibroblasts from chronic wounds do not respond to chronic wound fluid, probably because the fibroblasts of these wounds have lost the receptors that respond to cytokines and growth factors. Nonhealing wounds contain high levels of IL1, IL6, and MMPs, and an abnormally high MMP/TIMP ratio. Clinical examination of wounds inconsistently predicts which wounds will heal when procedures like secondary closure are planned. Surgeons therefore hope that these chemicals can be used as biomarkers of wounds which have impaired ability to heal. There is also evidence that the application of growth factors like PDGF will help the healing of chronic, nonhealing wounds.KEY WORDS: Cytokines, growth factors, matrix metalloproteinases, platelet-derived growth factor, wound healingIn the last 30 or so years, researchers have identified several of the cellular and biochemical events associated with wound healing. The process is becoming clearer, with the understanding of the cells and chemicals that help wounds to heal, and of those that inhibit healing. Investigators are trying to analyze the chemicals in chronic wounds in order to determine their condition and fitness for closure. A major advance is the clinical application of some of these chemicals to improve outcomes in wound healing.In this paper we look at the biology of normal and abnormal healing, see if wounds analysis can predict poor healing, and review some literature on the clinical applications of this knowledge.     

Naturally occurring growth factors in porcine wounds treated with autologous keratinocytes in a liquid environment

A step toward an improved understanding of the complex mechanisms of growth factor interactions may lie in the detection of endogenous growth factors during normal wound healing. The findings of this study on standardized full thickness wounds in swine, provide direct evidence that growth factors were present in the wound fluid in the picogram range (highest concentrations ranging from 1273 pg/ml for transforming growth factor-beta (TGFβ) to 85.6 pg/ml for platelet-derived growth factor-AB (PDGF-AB ) during healing. The presence of transplanted autologous keratinocyte suspensions and cultured epithelial sheet graft had no significant effect upon the observed growth factor levels, although transplanted keratinocyte cell suspensions (KCS) and cultured epidermal autografts (CEA) did accelerate healing in comparison to control wounds in our model (KCS treated wounds healed in 13.2±0.9 days, CEA in 13.7 days±0.8 and control wounds in 14.7 days±0.3). The variable occurrence of growth factors during normal wound healing may suggest possible mechanisms of growth factor interaction which could have an impact on the future design of their therapeutic use. Received: 28 September 1998 / Accepted: 16 November 1998     

Aberrant wound healing in the horse: Naturally occurring conditions reminiscent of those observed in man

Impaired wound healing represents an enormous clinical and financial problem for companion animals and humans alike. Unfortunately, most models used to study healing rely on rodents, which have significant differences in the healing and scarring process and rarely develop complications. In order to better simulate impaired healing, the model should strive to reproduce the natural processes of healing and delayed healing. Wounds on the limbs of horses display similarities to wounds in humans in their epithelialization/contraction ratio, genetic influence as well as dysregulated cytokine profile and the spontaneous development of fibroproliferative disorders. Veterinarians have access to advanced wound therapies that are often identical to those provided to human patients. Wound research in large animals has resulted in new wound models as well as a better understanding of the physiology, immunology, and local environmental impact on both normal and aberrant wound healing. One such model reproduces the naturally occurring fibroproliferative disorder of horses known as exuberant granulation tissue. Comparisons between the normally healing and impaired wounds provide insight into the repair process and can facilitate product development. A better understanding of the wound healing physiopathology based on clinically accurate animal models should lead to the development of novel therapies thereby improving outcomes in both human and veterinary patients.     

Bioengineered alternative tissues and hyperbaric oxygen in lower extremity wound healing

With the advent and clinical application of recombinant chemical and cellular mediators of wound healing and a better understanding of the importance of serial debridement, most foot wounds can be healed with little morbidity. Despite these advances, there remains the recalcitrant wound for which more heroic efforts seem warranted. For these patients, advanced wound healing technologies, orthobiologics, and bioengineered alternative tissues may tilt the scales in the direction of definitive wound closure.     

A new concept of a multidisciplinary wound healing center and a national expert function of wound healing.

HYPOTHESIS: An independent, multidisciplinary wound healing center in an accepted national expert function of wound healing is the optimal way to improve prophylaxis and treatment of patients with problem wounds. DESIGN: A clinical perspective analysis. SETTING: An independent, multidisciplinary wound healing center focusing on all types of problem wounds, organized as a university hospital department, and integrated in an expert function in the national health care organization of Denmark. PATIENTS AND METHODS: Patients with all types of problem wounds referred to and treated in the center during the first years of its existence provided a model for a new multidisciplinary structure for treatment of wound patients in the health care system. RESULTS: During the first 3 years of the fully functioning wound healing center, a total of 23 802 patient consultations were performed in the outpatient clinic, and 1014 patients with problem wounds were hospitalized in the inpatient ward. The surgical concept of the center has resulted in improved healing rates in patients with leg ulcers and decreased rates of major amputations. The outpatient function has resulted in a decrease in the number of patients transported in beds to the center. This structure provides better opportunities for basic and clinical research as well as for establishing expert education for all types of health care personnel. The center's structure has been the background for establishing an expert function in wound healing, allowing the wound healing area area to be fully integrated in the Danish National Health Care System. Overall, the concept and structure of the center have enhanced the knowledge and understanding of wound problems and increased the status of wound healing and patient care. CONCLUSIONS: Establishing multidisciplinary centers integrated into an accepted national expert function of wound healing is an optimal way to improve the clinical outcome of prophylaxis and treatment of all types of problem wounds. This model, with minor adjustments, may be applicable for both industrialized and developing countries.     

Macrophages: A review of their role in wound healing and their therapeutic use

Macrophages are mononuclear phagocytes established during embryogenesis and derived from the yolk sac or the fetal liver but also recruited from the blood and bone marrow under proliferative inflammatory conditions (such as tissue repair). Most importantly, they take on distinct phenotypes and functions crucial to healing upon localization in the wound. The objective of this review is to summarize recent findings in regard to the cellular mechanisms of macrophages and chronic wounds. Advances in the potential use of macrophage therapy have arisen based, in part, on the fact that early recruitment of macrophages is critical to wound healing. Higher quality evidence is needed to support the use of macrophage therapy for chronic wound types, as is a better understanding of the signaling related to macrophage polarization, activation of macrophages, and their effect of mechanisms of repair. An evaluation of the currently available research on mechanism of action may lead to a better understanding of the signaling processes of the many macrophage phenotypes, as well as their roles and outcomes in wound healing, which could then guide the development and eventual widespread use of macrophage therapies.     

Real-time analysis of the kinetics of angiogenesis and vascular permeability in an animal model of wound healing

The use of engineered tissue for the treatment of a variety of acute to chronic wounds has become a clinical standard, and a better understanding of the cellular mechanisms of re-vascularization and barrier integrity could enhance clinical outcomes. Here, we focus on the characterization of the re-vascularization of acellular grafts such as Integra™ in an animal model to better understand the physiological properties of blood vessels growing in the collagen–glycosaminoglycan matrix vs. wound margins. While Integra™ has been extensively studied in pre-clinical models, the re-modeling mechanisms of the capillary bed under these matrices are not well understood. Therefore, our first objective was to quantify the kinetics of re-vascularization. The second objective was to assess changes in vascular permeability (VP) of the wound bed compared to normal adjacent skin. The third objective was to establish a non-invasive and quantitative assay for the measurement of VP to facilitate the rapid and reproducible characterization of vascular integrity. Using an excisional wound model in mice, we characterize the appearance, growth, and maturation of blood vessels in an Integra™ graft over 28 days after surgery. Initial appearance of blood vessels in the graft was observed at 7 days, with angiogenesis peaking between 7 and 14 days. The onset of VP coincided with the increase in re-vascularization of the wound bed and there was a sustained elevation of VP that declined to baseline by 28 days. We propose a non-invasive strategy to assess VP of the wound capillary bed will facilitate a better understanding of the cell and molecular basis of angiogenesis in wound healing.     

The general case for redox control of wound repair

The orthodox view has been that reactive oxygen species are primarily damaging to cells. There is general agreement that while high (3%) doses of H(2)O(2) may serve as a clinical disinfectant, its overall effect on healing is not positive. Current work shows that at very low concentrations, reactive oxygen species may regulate cellular signaling pathways by redox-dependent mechanisms. Recent discoveries show that almost all cells of the wound microenvironment contain specialized enzymes that utilize O(2) to generate reactive oxygen species. Numerous aspects of wound healing are subject to redox control. An understanding of how endogenous reactive oxygen species are generated in wound-related cells may influence the healing process and could result in new redox-based therapeutic strategies. Current results with growth factor therapy of wounds have not met clinical expectations. Many of these growth factors, such as platelet-derived growth factor, rely on reactive oxygen species for functioning. Redox-based strategies may serve as effective adjuncts to jump-start healing of chronic wounds. The understanding of wound-site redox biology is also likely to provide novel insights into the fundamental mechanisms that would help to optimize conditions for oxygen therapy. While a window of therapeutic opportunity seems to exist under conditions of low concentrations of reactive oxygen species, high levels may complicate regeneration and remodeling of nascent tissue.     

Physiologie und Pathophysiologie der Heilung von Defektwunden

Understanding wound healing involves more than simply stating that there are the three phases of inflammation, proliferation and maturation. Wound healing is a complex series of actions, reactions and interactions among cells and mediators in a sequential and simultaneously ongoing temporal process within a spatial frame. At first this article will attempt to provide a concise summary of the events, cellular components and main influential mediators of wound healing over time. Secondly, the pathophysiology of chronic non-healing wounds is described where an imbalance of stimulating and inhibiting factors causes failure of healing. The most relevant extrinsic and intrinsic determinants are described and related to the cellular and molecular level of disturbed wound healing. A basic understanding of wound healing is a prerequisite for any prophylactic or therapeutic maneuver to maintain or re-establish wound equilibrium to give a satisfactory healing trajectory.     

Early wound healing exhibits cytokine surge without evidence of hypoxia

OBJECTIVE: To ascertain the spatial and temporal relation of wound hypoxia to the cell types involved, expression of selected angiogenic cytokines, the proliferative status of cells in the wound site, and angiogenesis. SUMMARY BACKGROUND DATA: Hypoxia is considered to drive the angiogenic response by upregulating angiogenic cytokines observed during wound healing. But this correlation has not been shown on a cell-to-cell basis in vivo because of limitations in measuring tissue PO2 at the cellular level. METHODS: Using punch biopsy wounds in rats as a wound healing model, the distributions of vascular endothelial growth factor, transforming growth factor-beta, tumor necrosis factor-alpha, and pimonidazole adducts (as a hypoxia marker) were followed immunohistochemically during the healing process. RESULTS: Hypoxia was absent on day 1 after wounding, even though angiogenesis and maximal expression of cytokines were observed in the wounds. Hypoxia peaked in the granulation tissue stage at day 4 and correlated with increased cellularity and cellular proliferation. Hypoxia started to decrease after day 4 and was limited to the remnant blood vessels and epithelial layer in the scar tissue. CONCLUSIONS: Induction of angiogenic cytokines early during wound healing may be due to triggering mechanisms other than hypoxia. Alternatively, the unique pattern of development and decline of cellular hypoxia as wound cellularity and proliferation regress suggest its involvement in initiating vascular regression during the later stages of healing.     

The science of wound bed preparation

The concept of wound bed preparation (WBP) heralded a new era in terms of how we treat wounds. It emphasized the difference between acute and chronic wounds, and it cemented the idea that the processes involved in the healing of acute wounds do not apply completely to the healing of chronic wounds. The arbitrary division of the normal healing process into the phases of hemostasis, inflammation, proliferation, and maturation addresses the events in acute wound healing. We have realized that the impediments to healing in chronic wounds lead to a failure to progress through these phases and are independent factors that make the chronic wound a much more complex condition. A major advance in resolving or addressing the chronic wound has been the concept of WBP. WBP allows us to address the problems of wound healing individually-the presence of necrotic tissue, hypoxia, high bacterial burden, corrupt matrix, and senescent cells within the wound bed. In WBP we can optimize our therapeutic agents to accelerate endogenous healing or to increase the effectiveness of advanced therapies.     

基因治疗与皮肤创面愈合

皮肤创面愈合过程是一个多因素参与的复杂过程,慢性、难愈创面严重影响了人们的生活质量.重组生长因子已经在临床用于改善创面愈合,但由于半衰期短、生物利用度低等原因,使得其临床疗效欠佳.近年来,随着基因工程技术的不断发展,基因治疗已经成为改善创面愈合的一种新的治疗方法.本文就目前基因治疗方法的优缺点、治疗性基因选择和正在进行的临床试验等方面进行了综述.     

神经生长因子加速猪深Ⅱ度烧伤创面愈合的实验

目的 探讨神经生长因子(nerve growth factors，NGF)对猪烧伤创面愈合的影响。方法 小白家猪6只，用控温控压仪在其背部制成24个直径为2．5cm的深Ⅱ度创面，随机分为4组，每6个创面为1组，即等渗盐水对照组，NGF1、2．5、5μg／ml治疗组。治疗后3、5、9d进行组织学检查、羟脯氨酸测定、细胞DNA周期分析及各组创面愈合时间比较。结果 治疗组上皮增生活跃且上皮化较对照组提前；治疗组创面组织羟脯氨酸含量，均有一个先下降后升高的过程，尤其在第5天，与对照组相比明显下降；细胞DNA周期分析表明，治疗组在S期细胞数较对照组均有明显增多；创面愈合时间较对照组提前。结论 局部应用NGF能促进烧伤深Ⅱ度创面愈合。     

Non‐animal models of wound healing in cutaneous repair: In silico,in vitro,ex vivo,and in vivo models of wounds and scars in human skin

Tissue repair models are essential to explore the pathogenesis of wound healing and scar formation, identify new drug targets/biomarkers and to test new therapeutics. However, no animal model is an exact replicate of the clinical situation in man as in addition to differences in the healing of animal skin; the response to novel therapeutics can be variable when compared to human skin. The aim of this review is to evaluate currently available non‐animal wound repair models in human skin, including: in silico, in vitro, ex vivo, and in vivo. The appropriate use of these models is extremely relevant to wound‐healing research as it enables improved understanding of the basic mechanisms present in the wound healing cascade and aid in discovering better means to regulate them for enhanced healing or prevention of abnormal scarring. The advantage of in silico models is that they can be used as a first in virtue screening tool to predict the effect of a drug/stimulus on cells/tissues and help plan experimental research/clinical trial studies but remain theoretical until validated. In vitro models allow direct quantitative examination of an effect on specific cell types alone without incorporating other tissue‐matrix components, which limits their utility. Ex vivo models enable immediate and short‐term evaluation of a particular effect on cells and its surrounding tissue components compared with in vivo models that provide direct analysis of a stimulus in the living human subject before/during/after exposure to a stimulus. Despite clear advantages, there remains a lack of standardisation in design, evaluation and follow‐up, for acute/chronic wounds and scars in all models. In conclusion, ideal models of wound healing research are desirable and should mimic not only the structure but also the cellular and molecular interactions, of wound types in human skin. Future models may also include organ/skin‐on‐a‐chip with potential application in wound healing research.     

Mucosal wound healing: the roles of age and sex

HYPOTHESIS: It remains unclear whether aging delays wound healing, as past human studies have not adequately controlled for confounding factors such as morbidity and medications. Furthermore, although dermal wounds heal more quickly in women than in men, clinical observations suggest that the opposite may be true for mucosal healing. We assessed age and sex differences in mucosal wound healing, and we hypothesized that aging delays healing and sex modulates healing independent of age. DESIGN AND SETTING: Clinical experimental study performed from June 2000 to August 2003 involving younger and older adult volunteers from the general community. PARTICIPANTS: Two hundred twelve male and female volunteers aged 18 to 35 years (n = 119) or 50 to 88 years (n = 93). INTERVENTION: Standardized 3.5-mm circular wounds were placed on the oral hard palates of volunteers. MAIN OUTCOME MEASURE: Wound videographs were taken daily for 7 days after wounding to assess wound closure. RESULTS: Wounds healed significantly more slowly in older adults compared with younger adults (P<.001) regardless of sex. This remained true even when individuals receiving medication and/or having a coexisting medical condition were excluded. Mucosal wounds healed more slowly in women than in men (P = .008) regardless of age. These effects were independent of demographic factors such as ethnicity, alcohol or nicotine use, or body mass index. CONCLUSIONS: Wound closure in older individuals was clearly delayed even when eliminating potential age-related confounds, indicating that aging does slow wound healing. Wound closure in women was also delayed, suggesting that wound healing is modulated by different mechanisms depending on tissue type. These findings may help target patients with increased surgical risks and greater need for postsurgical care.