The Wound Healing Process

Prolonged clinical and histologic effects from CO2 laser resurfacing of atrophic acne scars

BACKGROUND

The recent development of high-energy pulsed CO2 lasers that minimize thermal injury to uninvolved adjacent structures has revolutionized the manner in which atrophic facial scars are recontoured. Significant improvement of atrophic scars with laser resurfacing has clearly been demonstrated; however, the exact timing for assessment of skin for further treatment has varied due to the unknown amount of time needed after laser scar resurfacing to effect maximal collagen formation and remodeling.

OBJECTIVE

The aim of this study was to determine the immediate and long-term (12-18 months) histologic and clinical effects of atrophic acne scars after CO2 laser resurfacing in order to provide physician guidelines for postoperative clinical assessment for retreatment.

METHODS

Sixty patients (50 women, 10 men, mean age 38 years, skin types I-V) with moderate to severe atrophic facial scars were evaluated. Nineteen patients received regional cheek treatment and 41 patients received full-face resurfacing with a high-energy pulsed CO2 laser. Independent clinical assessments of treated scars were performed at 1, 6, 12, and 18 months and blinded histologic analyses were made of skin biopsies immediately prior to and after laser resurfacing, and at 1, 6, 12, and 18 months postoperatively in six patients.

RESULTS

Significant immediate and prolonged clinical improvement in skin tone, texture, and appearance of CO2 laser-irradiated scars was seen in all patients. Average clinical improvement scores were 2.22 (69%) at 1 month, 2.1 (67%) at 6 months, 2.37 (73%) at 12 months, and 2.5 (75%) at 18 months. Continued collagenesis and subsequent dermal remodeling were observed on histologic examination of biopsied tissue up to 18 months after surgery.

CONCLUSION

Continued clinical improvement was observed as long as 18 months after CO2 laser resurfacing of atrophic scars, with an 11% increase in improvement observed between 6 and 18 months postoperatively. We propose that a longer postoperative interval (12-18 months) prior to assessment for re-treatment be advocated in order to permit optimal tissue recovery and an opportunity for collagen remodeling.

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.

Multiple Roles for IL-12 in a Model of Acute Septic Peritonitis

The present study addressed the role of IL-12 in a murine model of septic peritonitis, induced by cecal ligation and puncture (CLP). Although CLP surgery induced IL-12 production at 6 and 24 h after surgery, IL-12 immunoneutralization was clearly deleterious in this model: 54% of CLP mice receiving preimmune serum survived, whereas mice administered IL-12 antisera prior to CLP experienced a 25% survival rate. IL-12 immunoneutralization not only led to increased mortality, but also appeared to promote a shift away from IL-12 and IFN-γ, in favor of IL-10. This cytokine shift corresponded to changes in bacterial load, as CLP mice receiving IL-12 antiserum yielded more CFUs from the peritoneal cavity at 24 h after CLP. To address the role of bacterial infection in IL-12 antiserum-induced mortality following CLP, antibiotics were administered for 4 days after surgery. Despite regular antibiotic administration, IL-12 immunoneutralization still reduced survival in CLP mice. Furthermore, histology of the ceca revealed that mice administered IL-12 antisera failed to show typical organization of the damaged cecum wall. Accordingly, Gram staining revealed bacteria within peritoneal fluids from these mice, while peritoneal fluids from CLP mice that received preimmune serum and antibiotics were free of bacteria. Altogether, these data suggested multiple important roles for IL-12 in the evolution of murine septic peritonitis.

Opportunities for mupirocin calcium cream in the emergency department

Mupirocin calcium cream is a newly reformulated topical antibiotic with a bactericidal spectrum specific for the pathogens that frequently cause secondary infections in superficial wounds. Both the calcium cream and ointment formulations have demonstrated efficacy in the treatment of secondarily infected traumatic lesions and dermatoses, including eczema, burns, wounds, bites, and ulcers. Mupirocin has a low risk of systemic and topical complications. To date, antimicrobial resistance is rare among target pathogens. The use of mupirocin to treat secondary wound infection has a profile of high efficacy and does not impair the normal healing in traumatized skin.

Expression of heat shock proteins in mouse skin during wound healing

Wound healing conditions generate a stressful environment for the cells involved in the regeneration process and are therefore postulated to influence the expression of heat shock proteins (Hsps). We have examined the expression of four Hsps (Hsp27, Hsp60, Hsp70 and Hsp90) and a keratin (keratin 6) by immunohistochemistry during cutaneous wound repair from Day 1 to Day 21 after wounding in the mouse. Hsps were constitutively expressed in normal mouse epidermis and their patterns of expression were modified during the healing process. The changes were not directly linked to the time course of the healing process but rather were dependent on the location of cells in the regenerating epidermis. In the thickened epidermis, Hsp60 was induced in basal and low suprabasal cells, Hsp70 showed a reduced expression, and Hsp90 and Hsp27 preserved a suprabasal pattern with an induction in basal and low suprabasal cells. All Hsps had a uniform pattern of expression in the migrating epithelial tongue. These observations suggest that the expression of Hsps in the neoepidermis is related to the proliferation, the migration, and the differentiation states of keratinocytes within the wound.

Strongly enhanced serum levels of vascular endothelial growth factor (VEGF) after polytrauma and burn

Angiogenesis is a key component of the repair mechanisms triggered by tissue injury. Vascular endothelial growth factor (VEGF) is an important mediator of angiogenesis, as it acts directly and specifically on endothelial cells. VEGF produced locally in regenerating tissue may spill over into the systemic circulation, and measuring levels of circulating VEGF may allow monitoring of angiogenesis. To determine whether circulating VEGF is increased after severe injury, we measured concentrations of VEGF in serial serum samples of 23 mechanical burn patients, 55 patients with multiple trauma and 56 healthy normal controls, using a newly established ELISA assay. In burn patients, serum VEGF was increased on day 1 (369.4 +/- 88.0 pg/ml) and on day 3 (452.0 +/- 65.3 pg/ml), reached highest levels on day 14 (1809.5 +/- 239.7 pg/ml) and was still elevated on day 21 post-burn (1339.8 +/- 208.7 pg/ml) (mean +/- SEM, p < 0.01), when compared with healthy controls (82.2 +/- 10.8 pg/ml (mean +/- SEM)). Likewise, in trauma patients, serum VEGF showed a trend towards elevated values on the day of admission (186.9 +/- 43.9 pg/ml) and on day 3 after injury (193.2 +/- 62.1 pg/ml). Thereafter, serum VEGF increased further (day 7,507.0 +/- 114.7 pg/ml), peaked on day 14 (742.4 +/- 151.8 pg/ml) and was still elevated on day 21 after injury (693.1 +/- 218.6 pg/ml (mean +/- SEM, p < 0.01)). No significant correlation was observed between peak serum VEGF and initial severity of mechanical (Injury Severity Score) or burn injury (percentage of body surface burned). However, in both burn and trauma patients, the subgroup of patients with uncomplicated healing showed significantly higher increases of serum VEGF than the subgroup who developed severe complications during the post-traumatic course, such as sepsis, adult respiratory distress syndrome or multiple organ failure (p < 0.05). Thus, markedly enhanced levels of serum VEGF are present one to three weeks after trauma or burn injury. Further, occurrence of severe complications during the post-traumatic period is associated with lesser increases of serum VEGF.

Thymosin α1 Stimulates Endothelial Cell Migration, Angiogenesis, and Wound Healing

In wound healing, lymphoid cells release soluble factors that attract fibroblasts and macrophages, initiating repair, endothelial cell migration, angiogenesis, and matrix production. We analyzed the effect of thymosin α1 (Tα1) on endothelial cell migration, angiogenesis, and wound healing. Tα1, a 28 amino acid peptide initially isolated from the thymus, enhanced the morphologic differentiation of endothelial cells and was a potent chemoattractant for endothelial cells and monocytes in vitro. In vivo, Tα1 stimulated angiogenesis in a subcutaneous model. When given either topically or i.p., it accelerated wound healing in a punch model, demonstrating that Tα1 promotes angiogenesis and wound healing.

Hyperbaric oxygen therapy for deep second degree burns: an experimental study in the guinea pig

Most previous animal studies reporting improved epithelialisation and healing of burn wounds under hyperbaric oxygen (HBO) did not include the conventional treatment with topical antibiotics as part of the protocol, and did not compare the effectiveness of HBO therapy with that of normobaric 100% oxygen (NO). The purpose of our study was to compare the results of combined treatment with HBO + silver sulfadiazine (SS) and those of treatment with NO + SS or SS alone. Deep second degree burns were produced on the depilated backs of 54 guinea pigs using a validated burn protocol. The animals were assigned to three treatment groups: HBO + SS, NO + SS, and SS. Dressings were changed daily. HBO was administered at 2 atmospheres absolute (ATA) for 90 min BID, and NO for 90 min BID. The parameters compared among the groups were laser Doppler flowmetry, and burn wound contracture and re-epithelialisation data derived from computerised planimetry of photographs of the wound. No differences in laser Doppler flowmetry results or the magnitude of contracture were found between the groups. Significantly increased re-epithelialisation was observed under NO + SS starting 10 days after the burn (P = 0.02, ANOVA). This significance stems from the difference between the HBO + SS and NO + SS groups (Tukey test). These data indicate that excessively high levels of tissue PO2 might compromise burn healing, and explain our results. A further study comparing combined treatment using a milder HBO protocol + SS and NO + SS is indicated in the search for the optimal HBO regimen.

Inhibition of fibroblast collagen synthesis and proliferation by levamisole and 5-fluorouracil

Experimental studies indicate that anastomotic healing in the intestine is compromised by the immediate postoperative administration of 5-fluorouracil and levamisole. Since fibroblast functions are crucial to healing, we investigated the effects of (combinations of) both drugs on proliferation and collagen synthesis of rat skin fibroblasts in vitro. Proliferation was measured in actively dividing cells by cellular [3H]thymidine uptake and collagen synthesis in non-dividing cells by [3H]proline incorporation into collagenase-digestible protein. 5-Fluorouracil strongly and significantly (P < 0.05) reduced DNA synthesis and collagen synthesis at concentrations of 1 microM or more. The latter effect was not specific for collagen since total protein production was affected similarly. Both effects depended on the duration of exposure to the drugs. Levamisole also inhibited fibroblast proliferation dose-dependently, but less effectively than 5-fluorouracil: 50% inhibition was observed at approximately 0.1 mM. Collagen synthesis was unaffected by levamisole. If levamisole was added together with a low (0.1 microM) concentration of 5-fluorouracil, which in itself did not decrease thymidine incorporation, levamisole's antiproliferative effects became apparent at concentrations as low as 1 microM. A similar effect, but at a much higher concentration (1 mM) was noted on fibroblast collagen synthesis. These results indicate that levamisole potentiates 5-fluorouracil effects in fibroblast cultures and that direct effects of these drugs, alone or in combination, on fibroblast proliferation and collagen synthesis may be responsible for their negative influence on wound repair.

Activated macrophages and the blood-brain barrier: inflammation after CNS injury leads to increases in putative inhibitory molecules

The cellular responses to spinal cord or brain injury include the production of molecules that modulate wound healing. This study examined the upregulation of chondroitin sulfate proteoglycans, a family of molecules present in the wound healing matrix that may inhibit axon regeneration in the central nervous system (CNS) after trauma. We have demonstrated increases in these putative inhibitory molecules in brain and spinal cord injury models, and we observed a close correlation between the tissue distribution of their upregulation and the presence of inflammation and a compromised blood-brain barrier. We determined that the presence of degenerating and dying axons injured by direct trauma does not provide a sufficient signal to induce the increases in proteoglycans observed after injury. Activated macrophages, their products, or other serum components that cross a compromised blood-brain barrier may provide a stimulus for changes in extracellular matrix molecules after CNS injury. While gliosis is associated with increased levels of proteoglycans, not all reactive astrocytes are associated with augmented amounts of these extracellular matrix molecules, which suggests a heterogeneity among glial cells that exhibit a reactive phenotype. Chondroitin sulfate also demarcates developing cavities of secondary necrosis, implicating these types of boundary molecules in the protective response of the CNS to trauma.

Tie2 expression and phosphorylation in angiogenic and quiescent adult tissues

Angiogenesis, the process of new vessels sprouting from the existing vasculature, is a critical process during early development. However, angiogenesis rarely occurs in the adult, except in response to cyclic hormonal stimulation in the ovary and uterus, in response to injury, and in response to pathological conditions such as tumorigenesis and diabetes mellitus. Tie2 (also known as Tek) is a novel endothelium-specific receptor tyrosine kinase, which has been demonstrated to be essential for the development of the embryonic vasculature; Tie2 knockout mice die by embryonic day 10.5 with specific defects in the formation of microvessels. Tie2 is downregulated later in embryogenesis, and its function in the adult has been relatively unexplored. To gain insight into the potential functions of Tie2 in the adult vasculature, Tie2 expression was examined in adult tissues undergoing angiogenesis and in quiescent tissues. Tie2 expression was localized by immunohistochemistry to the endothelium of neovessels in rat tissues undergoing angiogenesis during hormonally stimulated follicular maturation and uterine development and in healing skin wounds. Immunoprecipitation and RNase protection assay demonstrated upregulation of Tie2 protein and mRNA in rat and mouse skin wounds, respectively. Moreover, Tie2 immunoprecipitated from skin wounds was tyrosine-phosphorylated, indicating active downstream signaling. Surprisingly, Tie2 was also expressed in the entire spectrum of the quiescent vasculature (arteries, veins, and capillaries) in a wide range of adult tissues, and Tie2 immunoprecipitated from quiescent adult tissues was also tyrosine-phosphorylated. Together, these results suggest a dual function for Tie2 in adult tissues involving both angiogenesis and vascular maintenance.

The ontogeny of canine small intestinal submucosa regenerated bladder

PURPOSE

Small intestinal submucosa has previously been shown to promote regeneration of transitional epithelium, smooth muscle and peripheral nerves in rat and dog bladders. The origin of these regenerated components is presently unknown. This study attempts to define the origin of vascular, smooth muscle and peripheral nerve regeneration.

MATERIALS AND METHODS

A total of 22 adult male dogs weighing 25 to 30 kg. underwent partial cystectomy and immediate augmentation with a small intestinal submucosa patch graft. The small intestinal submucosa graft-native bladder interface was marked with permanent marking sutures for future reference. Small intestinal submucosa regenerated bladders were harvested at 2, 3, 4, 6, 8 and 10 weeks after augmentation. The tissue was then studied with routine histology and immunohistochemistry using factor VIII, smooth muscle specific actin (1A4) and neurofilament staining.

RESULTS

Results demonstrated that epithelialization of the graft surface was complete by 3 to 4 weeks with normal transitional histology. In the early periods neovascularization was prominent throughout the entire graft, as shown by factor VIII staining. Later more mature vessels were noted. Early in muscle formation sheets of elongated spindle cells extended into the graft from the incised native bladder at both surgical margins and ran parallel to the mucosal surface. At 4 weeks this spindle cell proliferation completely traversed the graft. Trichrome stained sections of the 4-week-old grafts showed no evidence of muscle differentiation and the spindle cells appeared to be fibroblasts. However, these cells stained positive for smooth muscle specific actin (1A4), indicating myogenic potential. Between weeks 4 and 6 the spindle cells became more haphazardly arranged and were separated by loose interstitium. By weeks 8 to 10 there was distinct smooth muscle bundle formation within these areas of proliferating myocytes. Neural regeneration appeared to coincide with smooth muscle development. Early neurofilament positive cells were noted predominantly at the graft-native bladder interface. At 4 weeks neurofilament positive cells were present throughout the graft and by 10 weeks nerve trunks composed of several nerve fibers were identified in association with newly formed smooth muscle bundles.

CONCLUSIONS

Small intestinal submucosa serves as a platform for bladder regeneration. Neovascularization smooth muscle and neural regeneration appear to occur through pannus ingrowth from the graft-native bladder interface. Smooth muscle regeneration seems to begin with the maturation of myofibroblasts, which migrate into the graft as early as 2 weeks after augmentation, and it progresses to the formation of distinct smooth muscle bundles by 10 weeks.

Scar wars: implications of fetal wound healing for the pediatric burn patient

Scar formation and fibrosis often cause devastating disabilities in children suffering severe burn injury. In contrast to the child, the fetus has the ability to heal skin injury without scar formation, and instead with regeneration of epithelial and mesenchymal tissues and restoration of normal skin architecture. In this paper we review those unique features of the fetus and fetal wound healing that may contribute to the scarless repair process. It is hoped that an understanding of these remarkable reparative capabilities may lead to the development of new wound healing therapies that reduce or prevent scar formation and fibrosis in the management of children with burns.

Laser resurfacing of atrophic scars

Many patients seek treatment for the disfigurement caused by obvious variations in skin texture secondary to atrophic scarring. Many different procedures, including dermabrasion, chemical peels, punch grafting, and augmentation with filling materials, have been implemented for the treatment of atrophic scars. With the advent of high-energy, pulsed and scanned CO2 laser technology, precisely controlled, layer-by-layer tissue vaporization may be achieved with minimal thermal damage to adjacent skin. Atrophic scars resulting from acne, surgery, or trauma respond more favorably to laser resurfacing than to other, more conventional forms of treatment when proper techniques are employed.

Split-thickness skin grafting for lower extremity ulcerations

BACKGROUND

Leg ulcers are often refractory to conservative treatment, often mandating the use of skin grafting.

OBJECTIVES

This review article discusses skin grafts, with special emphasis on split-thickness grafts for lower extremity ulcerations.

METHODS

Historical background, proposed mechanisms of action, biology of skin grafts, techniques for skin grafting, and results after grafting are discussed separately.

RESULTS

Skin grafting has been performed for centuries. However, how skin grafts work, whether solely as tissue replacement or, additionally, as a stimulus for healing, is still not fully known. After placement, the grafted skin proceeds through a series of phases by which nutrients are supplied and neovascularization occurs. Adherence to the ulcer bed through interactions between the graft and the ulcer bed appear critical. When meshed split-thickness skin grafts are properly performed, success rates from 50% to 75% have been reported for refractory venous ulcers.

CONCLUSIONS

Better understanding of the biologic and clinical aspects of skin grafting should lead to improved patient care.

LEARNING OBJECTIVES

After studying this article, participant should be able: 1. To understand the various types of skin grafts. 2. To learn the potential mechanisms of action of how skin grafts work. 3. To appreciate the benefit of skin grafts for lower extremity ulcerations.

Enhanced biosynthesis of extracellular matrix proteins and TGF-beta 1 by polyinosinic-polycytidylic acid during cutaneous wound healing in vivo

In our previous study, we have shown that polyinosinic-polycytidylic acid (poly I:C), a double-stranded RNA, and a potent inducer of interferon, enhanced the wound healing in rats and mice. Increased levels of laminin and collagen, and greater influx of dermal fibroblasts were observed in poly I:C-treated wounds as compared to untreated wounds (Bhartiya et al., 1992, J. Cell. Physiol., 150:312-319). In this study, we have explored the mechanism of enhanced wound healing by poly I:C in rats. Poly I:C (1 mg/kg) in phosphate buffered saline was injected intraperitoneally 18 h prior to wound healing, and the animals were sacrificed on day 3 postwounding. Immunofluorescence studies showed increased expression of adhesion molecules that includes ICAM-1 (intercellular adhesion molecule-1;CD54) and VCAM-1 (vascular cell adhesion molecule; CD 106) in poly I:C-treated wounds as compared to untreated control. Poly I:C treatment resulted in an increase in the mRNA levels of collagen type 1 (alpha), collagen III, laminin B1, and transforming growth factor-beta 1(TGF-beta 1) in wounds compared to untreated wounds as demonstrated by in situ hybridization and PCR analysis. These studies suggests that poly I:C upregulates the biosynthesis of adhesion molecules, extracellular matrix proteins (ECM), and TGF-beta 1 in the wound bed. Adhesion molecules and ECM play a major role in wound healing, and TGF-beta 1 has been known to be a potent wound healer. Therefore, the increased expression of these molecules may play a role in the enhanced healing by poly I:C observed in rats.

Evaluation of angiogenic inhibitors with an in vivo quantitative angiogenesis method using agarose microencapsulation and mouse hemoglobin enzyme-linked immunosorbent assay

In the present work, using a previously reported in vivo quantitative tumor-angiogenesis model, we attempted to ascertain whether this animal model is suitable for practical use in monitoring inhibitors of tumor angiogenesis. Mouse sarcoma-180 cells, human A431 cells or rat C6 cells microencapsulated in agarose beads were implanted s.c. into C57BL/6 mice. The level of blood vessel induction at the agarose pellet site was evaluated using mouse hemoglobin enzyme-linked immunosorbent assay on day 10 after implantation. Hydrocortisone, tetrahydro-S, medroxyprogesterone acetate, pentosan polysulfate and suramin inhibited blood vessel growth in our in vivo tumor-angiogenesis assay system, and heparin enhanced the antiangiogenic effects of hydrocortisone and tetrahydro-S. These results are almost entirely consistent with those observed in common assay systems, and suggest that this method may be useful for the identification and quantitative evaluation of inhibitors of tumor angiogenesis.

Selective enhancement by tumor necrosis factor-alpha of vascular permeability of new blood vessels induced with agarose hydrogel-entrapped Meth-A fibrosarcoma cells

We have previously developed a simple and quantitative method for assessment of in vivo tumor cell-induced angiogenesis by means of microencapsulation of tumor cells in agarose hydrogel and mouse hemoglobin ELISA (mHb-ELISA). In this article, we report that the new blood vessels induced with agarose-encapsulated tumor cells have the same sensitivity to tumor necrosis factor-alpha (TNF-alpha) as the original solid-tumor vessels. Agarose beads (average diameter = 200 microns), in which Meth-A fibrosarcoma cells were microencapsulated, were subcutaneously implanted in non-syngeneic ddY mice. Ten days later, extensive angiogenesis was observed on the implanted sites of Meth-A agarose heads, whereas no new blood vessels were induced with cell-free agarose heads. The vascular permeability of the new blood vessels induced with agarose-microencapsulated Meth-A cells was selectively and significantly enhanced by the i.v. injection of TNF-alpha, and it reached the maximum level at 2 h after the injection of TNF-alpha. At 4 h after the injection of TNF-alpha, the vascular permeability was reduced to the basal level. This permeability profile in Meth-A agarose beads in ddY mice is very similar to that in Meth-A solid tumor in syngeneic BALB/c mice. On the other hand, TNF-alpha-treatment did not affect the vascular permeability of other normal tissues or inflammatory tissue in ddY mice. These results strongly suggest that the new blood vessels induced with agarose-microencapsulated tumor cells have the specific characteristics of tumor vessels. Our in vivo angiogenesis assay system should be useful not only to screen anti-angiogenetic agents, but also to elucidate the mechanism of tumor angiogenesis.

A mathematical model for fibro-proliferative wound healing disorders

The normal process of dermal wound healing fails in some cases, due to fibro-proliferative disorders such as keloid and hypertrophic scars. These types of abnormal healing may be regarded as pathologically excessive responses to wounding in terms of fibroblastic cell profiles and their inflammatory growth-factor mediators. Biologically, these conditions are poorly understood and current medical treatments are thus unreliable. In this paper, the authors apply an existing deterministic mathematical model for fibroplasia and wound contraction in adult mammalian dermis (Olsen et al., J. theor. Biol. 177, 113-128, 1995) to investigate key clinical problems concerning these healing disorders. A caricature model is proposed which retains the fundamental cellular and chemical components of the full model, in order to analyse the spatiotemporal dynamics of the initiation, progression, cessation and regression of fibro-contractive diseases in relation to normal healing. This model accounts for fibroblastic cell migration, proliferation and death and growth-factor diffusion, production by cells and tissue removal/decay. Explicit results are obtained in terms of the model processes and parameters. The rate of cellular production of the chemical is shown to be critical to the development of a stable pathological state. Further, cessation and/or regression of the disease depend on appropriate spatiotemporally varying forms for this production rate, which can be understood in terms of the bistability of the normal dermal and pathological steady states-a central property of the model, which is evident from stability and bifurcation analyses. The work predicts novel, biologically realistic and testable pathogenic and control mechanisms, the understanding of which will lead toward more effective strategies for clinical therapy of fibro-proliferative disorders.

Enhanced modulation of keratinocyte motility by transforming growth factor-alpha (TGF-alpha) relative to epidermal growth factor (EGF)

Epidermal growth factor (EGF) and transforming growth factor (TGF)-alpha are high-affinity polypeptide ligands for the EGF receptor, which mediates their biologic activities. In this study, we directly compared the actions of both ligands in promoting keratinocyte motility. We found that normal and tumorigenic human keratinocytes responded to activation of the EGF receptor by either EGF or TGF-alpha; however, the two ligands did not elicit identical responses with regard to cell locomotion. TGF-alpha was more effective than EGF at promoting colony dispersion (cell scattering), in vitro wound closure, and single-cell migration as assessed by phagokinetic track analysis. In contrast, EGF and TGF-alpha evoked identical profiles for DNA synthesis with regard to concentration dependence and magnitude of response in normal keratinocytes and in a squamous cell carcinoma line. The overall pattern of tyrosine phosphorylation of intracellular substrates was similar when cells were stimulated with either growth factor; however, a limited number of differences in the kinetics or magnitude of protein phosphorylation were detected in subcellular fractions. These findings demonstrate that two growth factors implicated in promoting mitogenesis and locomotion may elicit divergent responses with regard to one biologic activity while retaining similar responses for other activities. This suggests that ligand-mediated mitogenic responses may not be tightly coupled to motogenic activity and further illustrates the multifunctional roles of polypeptide growth factors.

Topical hydrogen peroxide treatment of ischemic ulcers in the guinea pig: blood recruitment in multiple skin sites

BACKGROUND

Oxygen deficit is a key factor associated with delayed healing of ischemic wounds in human beings. Topical oxygen-releasing compounds such as hydrogen peroxide or tetrachlorodecaoxide have been suggested as therapy for ischemic tissue.

OBJECTIVE

Our purpose was to monitor the effect of hydrogen peroxide cream on the process of ischemic ulcer healing with a model for ischemic ulcers in the guinea pig.

METHODS

Measurement of vascular perfusion with a laser Doppler velocimeter and gross observations of percentage of nonnecrotic wound surface were made on ischemic wounds in guinea pigs after treatment with either a hydrogen peroxide cream or a placebo cream.

RESULTS

Visual evaluations of the percentage of nonnecrotic wound surface showed no statistically significant differences among the treatments. In contrast, vascular perfusion measurements resulted in statistically significant differences. Blood flow was significantly higher up to day 15 in ulcers treated with 2% hydrogen peroxide cream than in those treated with placebo cream. Vascular perfusion was significantly higher in ulcers treated with 3.5% hydrogen peroxide cream than in ulcers treated with either 1.5% hydrogen peroxide cream or placebo. Adjacent control sites in guinea pigs whose ulcers were treated with hydrogen peroxide cream showed increased vascular perfusion compared with corresponding sites in animals whose ulcers were treated with placebo. Even distant flank control sites of ulcers treated with 3.5% hydrogen peroxide cream showed increased vascular perfusion.

CONCLUSION

Treatment of ischemia-induced ulcers with hydrogen peroxide cream enhanced cutaneous blood recruitment not only to ulcers and adjacent sites, but also to distant sites.

Split-thickness skin grafting of leg ulcers. The University of Miami Department of Dermatology's experience (1990-1993)

BACKGROUND

Skin grafting for large and recalcitrant lower extremity ulcers is a commonly used therapy. However, the success rate for grafts performed by dermatologists is largely unknown.

OBJECTIVE

To analyze our experience with meshed split-thickness skin grafts for leg ulcers.

METHODS

We retrospectively analyzed all hospitalized dermatology patients who underwent meshed split-thickness skin grafting for lower extremity ulceration due to a variety of causes performed by the Department of Dermatology at the University of Miami over a 3-year period (1990-1993).

RESULTS

Twenty-nine patients with 36 ulcers were grafted. Greater than 90% of ulcers had initial graft take. At long-term follow-up, 52% of ulcers were healed, 26% were partially healed, and 22% recurred.

CONCLUSION

We conclude that meshed split-thickness skin grafting is a safe and effective therapy for recalcitrant lower extremity ulcers.

Pre versus post-operative radiotherapy of resectable squamous cell carcinoma of the head and neck

The literature on pre-operative radiotherapy (RT) vs. post-operative RT in patients with advanced, resectable squamous cell carcinoma of the head and neck is reviewed and the theoretical arguments for and against the two different modalities discussed. It was possible to identify eleven reports published during the last four decades (1965-91) evaluating different aspects of pre- vs. post-operative RT given at comparable dose levels. Two reports were of prospective, randomised clinical studies and nine of retrospective comparisons. Together, the eleven studies comprised 1,358 patients (326 in prospective studies). The bulk of the evidence clearly suggests post-operative loco-regional control to be superior to pre-operative RT. However, this seems to be offset by the subsequent development of distant metastases or metachronous tumours.