Animal models of wound repair: Are they cutting it?

Antimicrobial endotoxin-neutralizing peptides promote keratinocyte migration via P2X7 receptor activation and accelerate wound healing in vivo

BACKGROUND AND PURPOSE

Wound healing is a complex process that is essential to provide skin homeostasis. Infection with pathogenic bacteria such as Staphylococcus aureus can lead to chronic wounds, which are challenging to heal. Previously, we demonstrated that the antimicrobial endotoxin-neutralizing peptide Pep19-2.5 promotes artificial wound closure in keratinocytes. Here, we investigated the mechanism of peptide-induced cell migration and if Pep19-2.5 accelerates wound closure in vivo.

EXPERIMENTAL APPROACH

Cell migration was examined in HaCaT keratinocytes and P2X7 receptor-overexpressing HEK293 cells using the wound healing scratch assay. The protein expression of phosphorylated ERK1/2, ATP release, calcium influx and mitochondrial ROS were analysed to characterize Pep19-2.5-mediated signalling. For in vivo studies, female BALB/c mice were wounded and infected with methicillin-resistant S. aureus (MRSA) or left non-infected and treated topically with Pep19-2.5 twice daily for 6 days.

KEY RESULTS

Specific P2X7 receptor antagonists inhibited Pep19-2.5-induced cell migration and ERK1/2 phosphorylation in keratinocytes and P2X7 receptor-transfected HEK293 cells. ATP release was not increased by Pep19-2.5; however, ATP was required for cell migration. Pep19-2.5 increased cytosolic calcium and mitochondrial ROS, which were involved in peptide-induced migration and ERK1/2 phosphorylation. In both non-infected and MRSA-infected wounds, the wound diameter was reduced already at day 2 post-wounding in the Pep19-2.5-treated groups compared to vehicle, and remained decreased until day 6.

CONCLUSIONS AND IMPLICATIONS

Our data suggest the potential application of Pep19-2.5 in the treatment of non-infected and S. aureus-infected wounds and provide insights into the mechanism involved in Pep19-2.5-induced wound healing.

Review: Multimodal bioactive material approaches for wound healing

Wound healing is a highly complex process of tissue repair that relies on the synergistic effect of a number of different cells, cytokines, enzymes, and growth factors. A deregulation in this process can lead to the formation of a non-healing chronic ulcer. Current treatment options, such as collagen wound dressings, are unable to meet the demand set by the wound environment. Therefore, a multifaceted bioactive dressing is needed to elicit a targeted affect. Wound healing strategies seek to develop a targeted effect through the delivery of a bioactive molecule to the wound by a hydrogel or a polymeric scaffold. This review examines current biomaterial and small molecule-based approaches that seek to develop a bioactive material for targeted wound therapy and accepted wound healing models for testing material efficacy.

Collagen Fibers in the Healing Process of Rat Achilles Tendon Rupture Using Different Times of Ultrasound Therapy

Objective: The aim of this study was to evaluate the organization of collagen fibers in the healing process of rat Achilles tendon rupture using different times of ultrasound therapy (TUS). Approach: Forty Wistar rats were selected. Among these, 32 were submitted to total tenotomy of the calcaneous tendon and divided into 5 groups: control group (CG, n = 8), without tenotomy or any treatment; tenotomy group (n = 8), with tenotomy and without treatment; TUS groups-TUS3 (n = 8), TUS4 (n = 8), and TUS5 (n = 8)-submitted to tenotomy and treated with TUS for 3, 4, and 5 min per effective radiating area (ERA), respectively. The animals were sacrificed on the 12th postoperative day. The tendons were surgically removed for analysis of the collagen fiber organization using the birefringence technique (OR, optical retardation). Results: The collagen fibers exhibited better aggregation and organization in the UST3, TUS4, and TUS5 groups compared with CG (p < 0.05). The TUS5 group had better response rates in intergroup comparison. Innovation: The dose response of therapeutic TUS is influenced by many variables. The scientific evidence to support the dosimetry is insufficient. The application time is an important variable to be considered in TUS. In this study, the longer the application time, the better for organization and aggregation of collagen fibers in the rat tendon. Conclusion: TUS applied for 5 min per ERA presented higher dose response to the organization of collagen fibers in the healing process of rat Achilles tendon rupture.

Nanopharmaceuticals for wound healing - Lost in translation?

Today, many of the newly developed pharmaceuticals and medical devices take advantage of nanotechnology and with a rising incidence of chronic diseases such as diabetes and cardiovascular disease, the number of patients afflicted globally with non-healing wounds is growing. This has created a requirement for improved therapies and wound care. However, converting the strategies applied in early research into new products is still challenging. Many of them fail to comply with the market requirements. This review discusses the legal and scientific challenges in the design of nanomedicines for wound healing. Are they lost in translation or is there a new generation of therapeutics in the pipeline?

Antimicrobial Peptides and Their Therapeutic Potential for Bacterial Skin Infections and Wounds

Alarming data about increasing resistance to conventional antibiotics are reported, while at the same time the development of new antibiotics is stagnating. Skin and soft tissue infections (SSTIs) are mainly caused by the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) which belong to the most recalcitrant bacteria and are resistant to almost all common antibiotics. S. aureus and P. aeruginosa are the most frequent pathogens isolated from chronic wounds and increasing resistance to topical antibiotics has become a major issue. Therefore, new treatment options are urgently needed. In recent years, research focused on the development of synthetic antimicrobial peptides (AMPs) with lower toxicity and improved activity compared to their endogenous counterparts. AMPs appear to be promising therapeutic options for the treatment of SSTIs and wounds as they show a broad spectrum of antimicrobial activity, low resistance rates and display pivotal immunomodulatory as well as wound healing promoting activities such as induction of cell migration and proliferation and angiogenesis. In this review, we evaluate the potential of AMPs for the treatment of bacterial SSTIs and wounds and provide an overview of the mechanisms of actions of AMPs that contribute to combat skin infections and to improve wound healing. Bacteria growing in biofilms are more resistant to conventional antibiotics than their planktonic counterparts due to limited biofilm penetration and distinct metabolic and physiological functions, and often result in chronification of infections and wounds. Thus, we further discuss the feasibility of AMPs as anti-biofilm agents. Finally, we highlight perspectives for future therapies and which issues remain to bring AMPs successfully to the market.

The earthworm Dendrobaena veneta (Annelida): A new experimental-organism for photobiomodulation and wound healing

Photobiomodulation (PBM) is a manipulation of cellular behavior using non-ablative low intensity light sources. This manipulation triggers a cascade of metabolic effects and physiological changes resulting in improved tissue repair, of benefit in the treatment of tissue injury, degenerative or autoimmune diseases. PBM has witnessed an exponential increase in both clinical instrument technology and applications. It is therefore of benefit to find reliable experimental models to test the burgeoning laser technology for medical applications. In our work, we proposed the earthworm Dendrobaena veneta for the study of nonablative laser-light effects on wound healing. In our preliminary work, D. veneta has been shown to be positively affected by PBM. New tests using D. veneta were set up to evaluate the effectiveness of a chosen 808 nm-64 J/cm²–1W-CW laser therapy using the AB2799 hand-piece with flat-top bean profile, on the wound healing process of the earthworm. Effective outcome was assimilated through examining the macroscopic, histological, and molecular changes on the irradiated posterior-segment of excised-earthworms with respect to controls. Three successive treatments, one every 24 hours, were concluded as sufficient to promote the wound healing, by effects on muscular and blood vessel contraction, decrement of bacteria load, reduction of inflammatory processes and tissue degeneration. D. veneta was demonstrated to be a reliable experimental organism that meets well the 3Rs principles and the National Science Foundation statement. Through their genetic and evolutionary peculiarity, comparable to those of scientifically accredited models, D. veneta allows the effect of laser therapies by multidisciplinary methods, at various degree of complexity and costs to be investigated.

Comparative Degradomics of Porcine and Human Wound Exudates Unravels Biomarker Candidates for Assessment of Wound Healing Progression in Trauma Patients

Impaired cutaneous wound healing is a major complication in elderly people and patients suffering from diabetes, the rate of which is rising in industrialized countries. Heterogeneity of clinical manifestations hampers effective molecular diagnostics and decisions for appropriate therapeutic regimens. Using a customized positional quantitative proteomics workflow, we have established a time-resolved proteome and N-terminome resource from wound exudates in a clinically relevant pig wound model that we exploited as a robust template to interpret a heterogeneous dataset from patients undergoing the same wound treatment. With zyxin, IQGA1, and HtrA1, this analysis and validation by targeted proteomics identified differential abundances and proteolytic processing of proteins of epidermal and dermal origin as prospective biomarker candidates for assessment of critical turning points in wound progression. Thus, we show the possibility of using a fine-tuned animal wound model to bridge the translational gap as a prerequisite for future extended clinical studies with large cohorts of individuals affected by healing impairments. Data are available via ProteomeXchange with identifier PXD006674.

Effect of High- and Low-Frequency Transcutaneous Electrical Nerve Stimulation on Angiogenesis and Myofibroblast Proliferation in Acute Excisional Wounds in Rat Skin

OBJECTIVE

This study evaluated the effects of high- (HF) and low-frequency (LF) transcutaneous electrical nerve stimulation on angiogenesis and myofibroblast proliferation in acute excisional wounds in rat skin.

DESIGN

This was an experimental controlled and randomized study.

PARTICIPANTS

An excisional wound was made on the back of 90 adult male EPM1-Wistar rats using an 8-mm punch.

INTERVENTIONS

The animals were randomly assigned to the HF group (80 Hz), LF group (5 Hz), or control group. Transcutaneous electrical nerve stimulation (pulse duration, 200 microseconds; current amplitude, 15 mA) was delivered (session length, 60 minutes) on 3 consecutive days.

MEAN OUTCOME MEASURE

Immunohistochemistry was performed on postoperative days 3, 7, and 14 for counting blood vessels and myofibroblasts.

MEAN OUTCOME RESULTS

The LF group had significantly more blood vessels than the HF group on day 3 (P = .004). The HF group had significantly less blood vessels than did the control group on days 7 (P = .002) and 14 (P = .034) and less myofibroblasts than did both the LF and control groups on day 3 (P = .004) and less than did the control group on day 7 (P = .001).

CONCLUSION

There seems to be a benefit to the use of LF transcutaneous electrical nerve stimulation in the healing of acute excisional wounds, but further studies are warranted.

Microscopy Based Methods for the Assessment of Epithelial Cell Migration During In Vitro Wound Healing

Cell migration is a mandatory aspect for wound healing. Creating artificial wounds on research animal models often results in costly and complicated experimental procedures, while potentially lacking in precision. In vitro culture of epithelial cell lines provides a suitable platform for researching the cell migratory behavior in wound healing and the impact of treatments on these cells. The physiology of epithelial cells is often studied in non-confluent conditions; however, this approach may not resemble natural wound healing conditions. Disrupting the epithelium integrity by mechanical means generates a realistic model, but may impede the application of molecular techniques. Consequently, microscopy based techniques are optimal for studying epithelial cell migration in vitro. Here we detail two specific methods, the artificial wound scratch assay and the artificial migration front assay, that can obtain quantitative and qualitative data, respectively, on the migratory performance of epithelial cells.

Effect of high- and low- frequency transcutaneous electrical nerve stimulation (TENS) on angiogenesis and wound contraction in acute excisional wounds in rat skin

Abstract Introduction: Transcutaneous electrical nerve stimulation (TENS) can alter the local temperature, increase skin blood flow and induce the release of vasodilator neuropeptides and growth factors. These changes may be related to the effects of TENS on the tissue repair process. Objective: To assess the effect of high- and low-frequency TENS on angiogenesis and the contraction of acute excisional wounds in rat skin. Methods: Fifty-four young adult male EPM1-Wistar rats were used in the study. An excisional wound was performed on the back of each animal using an 8mm punch. The animals were randomly assigned to three groups: the High-frequency Group (HG: 80 Hz), Low-frequency Group (LG: 5 Hz), and Sham Group (SG: TENS turned off). TENS was delivered on three days consecutives. Pulse duration and current intensity were 200 µs and 15 mA. The length of each TENS session was 60 minutes. Microscopic and macroscopic assessments were performed on 3, 7 and 14 postoperative (PO) days. Hematoxylin-eosin staining was utilized to quantify the neoformed blood vessels. Photographs were taken to determine the percentage of wound contraction. After assessment, the animals were painlessly sacrificed. Results: There were increases in angiogenesis in the HG on the 3 PO day, and in the LG on the 14 PO day. No significant differences in wound contraction were found between the groups on the different PO days. Conclusion: High frequency TENS improved angiogenesis, and neither frequency of TENS had any influence on the contraction of acute excisional wounds in rat skin.

Strategies for Optimizing the Soft Tissue Seal around Osseointegrated Implants

Percutaneous and permucosal devices such as catheters, infusion pumps, orthopedic, and dental implants are commonly used in medical treatments. However, these useful devices breach the soft tissue barrier that protects the body from the outer environment, and thus increase bacterial infections resulting in morbidity and mortality. Such associated infections can be prevented if these devices are effectively integrated with the surrounding soft tissue, and thus creating a strong seal from the surrounding environment. However, so far, there are no percutaneous/permucosal medical devices able to prevent infection by achieving strong integration at the soft tissue-device interface. This review gives an insight into the current status of research into soft tissue-implant interface and the challenges associated with these interfaces. Biological soft/hard tissue interfaces may provide insights toward engineering better soft tissue interfaces around percutaneous devices. In this review, focus is put on the history and current findings as well as recent progress of the strategies aiming to develop a strong soft tissue seal around osseointegrated implants, such as orthopedic and dental implants.

The effect of color type on early wound healing in farmed mink (Neovison vison)

BACKGROUND

Individual differences of mink, including color type, are speculated to affect the course of wound healing, thereby impacting wound assessment and management on the farms, as well as the assessment of wounds in forensic cases. In this study, we examined the effect of color type on early wound healing in farmed mink. Full thickness excisional wounds (2 × 2 cm) were made on the back in 18 mink of the color types Brown, Silverblue and Blue Iris. Gross and microscopic pathology of the wounds was evaluated 2 days post-wounding together with degree of wound size reduction, presence of bacteria and blood analyses.

RESULTS

Pathological examination on day 2 showed the greatest mean wound size reduction in Brown mink (11.0%) followed by Blue Iris (7.9%) and Silverblue (1.6%). Bacteria were cultured from all wounds, and predominantly Staphylococcus species were recovered in mixed or pure culture. Histopathology from day 2 wounds showed a scab overlying necrotic wound edges, which were separated from underlying vital tissue by a demarcation zone rich in polymorphonuclear leukocytes. Fibroblasts and plump endothelial cells were more numerous in the deeper tissues. Complete blood count parameters were within normal ranges in most cases, however, the mink showed mildly to markedly decreased hematocrit and six mink of the color types Silverblue and Blue Iris showed moderately elevated numbers of circulating segmented neutrophils on day 2. There was a marked increase in concentration of serum amyloid A from day 0 to day 2 in all color types.

CONCLUSIONS

We have described differences in early wound healing between mink of the color types Brown, Silverblue and Blue Iris by use of an experimental wound model in farmed mink. The most pronounced difference pertained to the degree of wound size reduction which was greatest in Brown mink, followed by Blue Iris and Silverblue, respectively.

The efficacy of probiotics as pharmacological treatment of cutaneous wounds: Meta-analysis of animal studies

The aim of the current meta-analysis of animal studies was to evaluate the efficacy of probiotics as pharmacological treatment of cutaneous wounds. A systematic electronic literature search was conducted and in total six animal studies which undertake twelve experiments met our inclusion criteria. We used the percentage (%) of wound area at the end of the first week after initial wounding to evaluate the efficacy of the probiotic treatment. The heterogeneity was estimated as statistically significant (p<0.0001) and therefore the meta-analysis was performed with the random-effect model. Based on the estimated Hedges' g (Hedges, 1982), the administration of probiotics was associated with acceleration of the wound contraction (g=-2.55; 95%CI=-3.59, -1.50; p<0.0001). The meta-regression analysis showed that the moderator sterile kefir extract has the greater effect on the overall estimated efficacy of probiotic treatment (g=-5.6983; p=0.0442) with bacteria probiotic therapies (70% kefir gel, L. brevis, L. fermentum, L. plantarum, L. reuteri) following (g=-2.3814; p=0.0003). For bacteria dose moderator, the results showed that increase in bacterial dose corresponds to increase of the estimated overall effect size (g=-10.2056; p=0.0053). The linear regression test of funnel plot asymmetry showed absence of publication bias. In conclusion, the results indicate that probiotics administration is an effective pharmacological treatment of cutaneous wounds. However, due to the heterogeneity among studies, further research is required.

Biomaterials and Nanotherapeutics for Enhancing Skin Wound Healing

Wound healing is an intricate process that requires complex coordination between many cell types and an appropriate extracellular microenvironment. Chronic wounds often suffer from high protease activity, persistent infection, excess inflammation, and hypoxia. While there has been intense investigation to find new methods to improve cutaneous wound care, the management of chronic wounds, burns, and skin wound infection remain challenging clinical problems. Ideally, advanced wound dressings can provide enhanced healing and bridge the gaps in the healing processes that prevent chronic wounds from healing. These technologies have great potential for improving outcomes in patients with poorly healing wounds but face significant barriers in addressing the heterogeneity and clinical complexity of chronic or severe wounds. Active wound dressings aim to enhance the natural healing process and work to counter many aspects that plague poorly healing wounds, including excessive inflammation, ischemia, scarring, and wound infection. This review paper discusses recent advances in the development of biomaterials and nanoparticle therapeutics to enhance wound healing. In particular, this review focuses on the novel cutaneous wound treatments that have undergone significant preclinical development or are currently used in clinical practice.

The refined biomimetic NeuroDigm GEL™ model of neuropathic pain in a mature rat

Background: Many humans suffering with chronic neuropathic pain have no objective evidence of an etiological lesion or disease. Frequently their persistent pain occurs after the healing of a soft tissue injury. Based on clinical observations over time, our hypothesis was that after an injury in mammals the process of tissue repair could cause chronic neural pain. Our objectives were to create the delayed onset of neuropathic pain in rats with minimal nerve trauma using a physiologic hydrogel, and characterize the rats' responses to known analgesics and a targeted biologic. Methods: In mature male Sprague Dawley rats (age 9.5 months) a percutaneous implant of tissue-derived hydrogel was placed in the musculofascial tunnel of the distal tibial nerve. Subcutaneous morphine (3 mg/kg), celecoxib (10 mg/kg), gabapentin (25 mg/kg) and duloxetine (10 mg/kg) were each screened in the model three times each over 5 months after pain behaviors developed. Sham and control groups were used in all screenings. A pilot study followed in which recombinant human erythropoietin (200 units) was injected by the GEL™ neural procedure site. Results: The GEL group gradually developed mechanical hypersensitivity lasting months. Morphine, initially effective, had less analgesia over time. Celecoxib produced no analgesia, while gabapentin and duloxetine at low doses demonstrated profound analgesia at all times tested. The injected erythropoietin markedly decreased bilateral pain behavior that had been present for over 4 months, p ≤ 0.001. Histology of the GEL group tibial nerve revealed a site of focal neural remodeling, with neural regeneration, as found in nerve biopsies of patients with neuropathic pain. Conclusion: The refined NeuroDigm GEL™ model induces a neural response resulting in robust neuropathic pain behavior. The analgesic responses in this model reflect known responses of humans with neuropathic pain. The targeted recombinant human erythropoietin at the ectopic neural lesion appears to alleviate the persistent pain behavior in the GEL™ model rodents.

The refined biomimetic NeuroDigm GEL™ Model of neuropathic pain in the mature rat

Background:Many humans suffering with chronic pain have no clinical evidence of a lesion or disease. They are managed with a morass of drugs and invasive procedures. Opiates usually become less effective over time. In many, their persistent pain occurs after the healing of a soft tissue injury. Current animal models of neuropathic pain typically create direct neural damage with open surgeries using ligatures, neurectomies, chemicals or other forms of deliberate trauma. However, we have observed clinically that after an injury in humans, the naturally occurring process of tissue repair can cause chronic neural pain.Methods:We demonstrate how the refined biomimetic NeuroDigm GEL™ Model, in the mature male rat, gradually induces neuropathic pain behavior with a nonsurgical percutaneous implant of tissue-derived hydrogel in the musculo-fascial tunnel of the distal tibial nerve. Morphine, Celecoxib, Gabapentin and Duloxetine were each screened in the model three times each over 5 months after pain behaviors developed. A pilot study followed in which recombinant human erythropoietin was applied to the GEL neural procedure site.Results:The GEL Model gradually developed neuropathic pain behavior lasting months. Morphine, initially effective, had less analgesia over time. Celecoxib produced no analgesia, while gabapentin and duloxetine at low doses had profound analgesia at all times tested. The injected erythropoietin markedly decreased bilateral pain behavior that had been present for over 4 months. Histology revealed a site of focal neural remodeling, with neural regeneration, as in human biopsies.Conclusion:The refined NeuroDigm GEL™ Model induces localized neural remodeling resulting in robust neuropathic pain behavior. The analgesics responses in this model reflect known responses of humans with neuropathic pain. The targeted recombinant human erythropoietin appears to heal the ectopic focal neural site, as demonstrated by the extinguishing of neuropathic pain behavior present for over 4 months.

A Novel Proliposomal Ropivacaine Oil: Pharmacokinetic-Pharmacodynamic Studies After Subcutaneous Administration in Pigs

BACKGROUND

Liposomal local anesthetics are limited by a short liposomal shelf-life, even when under refrigeration. We describe a novel proliposomal ropivacaine that produces liposomes in situ, only after exposure to aqueous media.

METHODS

In vitro: Nanoparticles were assessed (particle size distribution analyzer, cryo-transmission electron microscopy) at baseline and after exposure to saline/plasma.

TOXICITY

In porcine wound healing study (n = 12), healing was assessed by photography, clinical assessment, and histology. Pharmacodynamics: Seventeen young piglets were randomly assigned to plain 0.5% ropivacaine (n = 5), proliposomal 4% ropivacaine (n = 6), or sham (n = 6). Tactile threshold was assessed using von Frey filaments applied to the surgical wound; the nonoperated skin was used as a control. Tactile threshold over time was determined using area under the curve (AUC) and assessed by 1-way analysis of variance.

PHARMACOKINETICS

8 young piglets were randomly assigned to plain 0.5% (25 mg, n = 4) or proliposomal 4% (200 mg, n = 4) ropivacaine. Plasma ropivacaine was assessed by high-performance liquid chromatography at baseline and at intervals over 36 hours. Paired ropivacaine concentration (from wound exudate and plasma) was obtained at 96 hours. Data were analyzed using noncompartmental and compartmental models.

RESULTS

In vitro: On exposure to saline and plasma, the study drug was transformed from a homogenous oil to an emulsion containing liposomes of approximately 1.4-μm diameter; this effect was dilution dependent and stable over time.

TOXICITY

All wounds healed well; no effect of drug group was observed. Pharmacodynamics: Plain and proliposomal ropivacaine provided sensory anesthesia for approximately 6 and 30 hours, respectively. There was an approximately 7-fold increase in the AUC of anesthesia for proliposomal ropivacaine compared with plain ropivacaine (mean difference, 1010; 95% confidence interval [CI], 625-1396 g·h/mm; P < 0.0001).

PHARMACOKINETICS

There was no difference in Cmax (2.31 ± 0.74 vs 2.32 ± 0.46 mg/L), despite an approximately 8-fold difference in dose. However, proliposomal ropivacaine was associated with a marked prolongation of Tmax (6.50 ± 6.35 vs 0.5 ± 0.0 hours), terminal half-life (16.07 ± 5.38 vs 3.46 ± 0.88 hours; P = 0.0036), and ropivacaine-time AUC (47.72 ± 7.16 vs 6.36 ± 2.07 h·mg/L; P < 0.0001), when compared with plain ropivacaine. The proliposomal formulation provided an approximately 250-fold higher ropivacaine concentration in the surgical wound (mean difference, 3783 ng/mL; 95% CI, 1708-5858; P = 0.001) and an approximately 25-fold higher wound:plasma ropivacaine concentration ratio (mean difference, 126; 95% CI 38-213; P = 0.011).

CONCLUSIONS

Proliposomal ropivacaine exerted prolonged anesthesia with delayed elimination, typical for liposomal drugs. The advantage of this novel proliposomal ropivacaine is its ease of preparation and its extended shelf-stability (>2 years) at room temperature.

Laser-Generated Shockwaves as a Treatment to Reduce Bacterial Load and Disrupt Biofilm

OBJECTIVE

The goal of this paper is to demonstrate and evaluate the potential efficacy of laser-generated shockwave (LGS) therapy on biofilm infected tissue.

METHODS

To demonstrate proof of concept, Staphylococcus epidermidis was allowed to proliferate on ex vivo pigskin, until mature biofilm formation was achieved, and then subjected to LGS. Bacterial load between control and treated samples was compared using the swab technique and colony counting. Scanning electron microscopy (SEM) was then used to visualize the biofilm growth and resulting reduction in biofilm coverage from treatment. Images were false colored to improve contrast of biofilm, and percent biofilm coverage was computed, along with biofilm cluster size.

RESULTS

LGS reduced bacterial load by 69% (p = 0.008). Imaging showed biofilm coverage reduced by 52% and significantly reduced average cluster size (p 0.001).

CONCLUSION

LGS therapy reduced the burden of bacterial biofilm on ex vivo pigskin and can be visualized using SEM imaging.

SIGNIFICANCE

LGS therapy is a new treatment for infected wounds, allowing rapid disruption of biofilm to 1) remove bacteria and 2) increase susceptibility of remaining biofilm to topical antibiotics. This can lead to improved wound healing times, reduced patient morbidity, and decreased healthcare costs.

Oestrogen promotes healing in a bacterial LPS model of delayed cutaneous wound repair

Wound infection is a major clinical problem, yet understanding of bacterial host interactions in the skin remains limited. Microbe-derived molecules, known as pathogen-associated molecular patterns, are recognised in barrier tissues by pattern-recognition receptors. In particular, the pathogen-associated molecular pattern, lipopolysaccharide (LPS), a component of microbial cell walls and a specific ligand for Toll-like receptor 4, has been widely used to mimic systemic and local infection across a range of tissues. Here we administered LPS derived from Klebsiella pneumoniae, a species of bacteria that is emerging as a wound-associated pathogen, to full-thickness cutaneous wounds in C57/BL6 mice. Early in healing, LPS-treated wounds displayed increased local apoptosis and reduced proliferation. Subsequent healing progression was delayed with reduced re-epithelialisation, increased proliferation, a heightened inflammatory response and perturbed wound matrix deposition. Our group and others have previously demonstrated the beneficial effects of 17β-estradiol treatment across a range of preclinical wound models. Here we asked whether oestrogen would effectively promote healing in our LPS bacterial infection model. Intriguingly, co-treatment with 17β-estradiol was able to promote re-epithelialisation, dampen inflammation and induce collagen deposition in our LPS-delayed healing model. Collectively, these studies validate K. pneumoniae-derived LPS treatment as a simple yet effective model of bacterial wound infection, while providing the first indication that oestrogen could promote cutaneous healing in the presence of infection, further strengthening the case for its therapeutic use.

Measurements in wound healing with observations on the effects of topical agents on full thickness dermal incised wounds

INTRODUCTION

A multitude of topical wound treatments are used today. Although it is well established that the micro-environment of healing wounds can be altered to improve healing, it is difficult to measure the subtle differences in outcome where therapies are compared.

METHOD

We compared wound healing properties between four different topical agents in surgically incised wounds in a pig model. The four topical agents, 5% Povidone-Iodine cream, 1% Silver-Sulphadiazine, 2% Mupirocin, and 1% Silver-Sulphadiazine plus 1mg/100g recombinant-human epithelial growth factor (EGF) were randomly assigned to four test animals each. Test agents were compared to each other and to untreated controls. We investigated existing and new methodologies of measurement of wound healing: clinical and histological visual scoring systems, immuno-histochemistry, and computerized image analysis of the wounds on days 3, 7, and 28.

RESULTS

All agents were found to have improved healing rates with better cellular architecture. Healing was faster, histological appearance resembled normal architecture sooner, clinical appearance improved, mitotic activity was stimulated and more collagen was deposited in comparison to the wounds with no agents. EGF-treated wounds showed an increased rate of epithelisation, but the rate of healing did not correlate well with evaluation of cosmetic outcome.

CONCLUSION

Topical agents improve all aspects of wound healing. The addition of a human recombinant EGF to Silver-Sulphadiazine increases epithelial growth and amounts of collagen in the regenerating wounds at day 7.

Systemic effects of oral tolerance reduce the cutaneous scarring

BACKGROUND

Immunological tolerance refer to the inhibition of specific immune responsiveness and the ingestion of proteins previous to immunization is a reliable method to induce (oral) tolerance. Parenteral exposure to tolerated antigens, in adjuvant, trigger indirect and systemic effects that inhibits concomitant immune responses to other unrelated antigens and also decrease unrelated inflammatory responses. Interesting, intraperitoneal (i.p.) exposure to orally-tolerated proteins soon before an incisional linear skin wound improves the healing by primary intention in mice. An important clinical and surgical objective is to identify strategies to improve wound healing and reduce scarring.

OBJECTIVE

To evaluate whether i.p. injection of an orally-tolerated protein improves wound healing by secondary intention and reduce scarring of full-thickness excisional skin injury.

METHODS

C57Bl/6 mice were turned tolerant to ovalbumin (OVA) by drinking a solution containing OVA; seven days later, they received an i.p. injection of OVA plus Al(OH)3 adjuvant immediately before two full-thickness excisional skin wounds, under anesthesia. The wound healing process was evaluated macro and microscopically after H&E, toluidine blue and Gomori's Trichrome staining. The presence of granulocytes, macrophages, miofibroblasts, fibronectin, collagen I and collagen III was investigated by immunofluorescence and the levels of cytokines by flow cytometry or ELISA. Mice not tolerant to OVA were included as controls.

RESULTS

The i.p. injection of OVA+Al(OH)3 in mice orally tolerant to OVA reduced the subsequent inflammatory response in the wound bed and the cutaneous scarring. There was a change in the pattern of collagen deposition making it more similar to the pattern observed in intact skin. In tolerant mice, mast cells and granulocytes (Ly-6C/G+), were reduced, while lymphocytes (CD3+) were increased in the wound bed. Time course analysis of Th1/Th2/Th17 cytokines and growth factors showed slightly differences between tolerant and control groups.

CONCLUSION

Parenteral injection of an orally-tolerated protein has systemic consequences that impair the inflammatory response triggered by skin injury and reduce the cutaneous scarring.

Making maxillary barbels with a proximal-distal gradient of Wnt signals in matrix-bound mesenchymal cells

The evolution of specific appendages is made possible by the ontogenetic deployment of general cell signaling pathways. Many fishes, amphibians and reptiles have unique skin appendages known as barbels, which are poorly understood at the cellular and molecular level. In this study, we examine the cell arrangements, cell division patterns, and gene expression profiles associated with the zebrafish maxillary barbel, or ZMB. The earliest cellular organization of the ZMB is an internal whorl of mesenchymal cells in the dermis of the maxilla; there is no epithelial placode, nor any axially-elongated epithelial cells as expected of an apical ectodermal ridge (AER). As the ZMB develops, cells in S-phase are at first distributed randomly throughout the appendage, gradually transitioning to a proliferative population concentrated at the distal end. By observing ZMB ontogenetic stages in a Wnt-responsive transgenic reporter line, TCFsiam, we identified a strongly fluorescent mesenchymal cell layer within these developing appendages. Using an in vitro explant culture technique on developing barbel tissues, we co-localized the fluorescent label in these cells with the mitotic marker EdU. Surprisingly, the labeled cells showed little proliferation, indicating a slow-cycling subpopulation. Transmission electron microscopy of the ZMB located these cells in a single, circumferential layer within the barbel's matrix core. Morphologically, these cells resemble fibroblasts or osteoblasts; in addition to their matrix-bound location, they are identified by their pancake-shaped nuclei, abundant rough endoplasmic reticulum, and cytoplasmic extensions into the surrounding extracellular matrix. Taken together, these features define a novel mesenchymal cell population in zebrafish, the "TCF(+) core cells." A working model of barbel development is proposed, in which these minimally mitotic mesodermal cells produce collagenous matrix in response to ectodermally-derived Wnt signals deployed in a proximal-distal gradient along the appendage. This documents a novel mechanism of vertebrate appendage outgrowth. Similar genetic signals and cell behaviors may be responsible for the independent and repeated evolution of barbel structures in other fish species.

Triterpenes with healing activity: A systematic review

The purpose of this review was to systematically evaluate the literature on the efficacy of triterpenes for wound healing. We searched for original studies in the Medline, SCIDIRECT and LILACS databases published from 1910 to 2013. For each study, the title, abstract and full article were evaluated by two reviewers. We identified 2181 studies; however, after application of the inclusion and exclusion criteria, only 12 studies were subjected to further review. In surgical wounds, the triterpenes induced a reduction in time to closure, and this effect was reported in virtually all wound types. Triterpenes also modulate the production of ROS in the wound microenvironment, accelerating the process of tissue repair. Triterpenes may also induce cell migration, cell proliferation and collagen deposition. Although the pharmacological effects of triterpenes are well characterized, little is known about their effects in cells involved in healing, such as keratinocytes and fibroblasts. In addition, the lack of studies on the risks associated with the therapeutic use of triterpenes is worrisome. Our study reveals that triterpenes seem to favor wound healing; however, toxicological studies with these compounds are required. Taken together, these findings show that the triterpenes are a class of molecules with significant promise that leads for the development of new drugs to treat skin injury.

Ultrasonic Stimulation of Mouse Skin Reverses the Healing Delays in Diabetes and Aging by Activation of Rac1

Chronic skin-healing defects are one of the leading challenges to lifelong well-being, affecting 2-5% of populations. Chronic wound formation is linked to age and diabetes and frequently leads to major limb amputation. Here we identify a strategy to reverse fibroblast senescence and improve healing rates. In healthy skin, fibronectin activates Rac1 in fibroblasts, causing migration into the wound bed, and driving wound contraction. We discover that mechanical stimulation of the skin with ultrasound can overturn healing defects by activating a calcium/CamKinaseII/Tiam1/Rac1 pathway that substitutes for fibronectin-dependent signaling and promotes fibroblast migration. Treatment of diabetic and aged mice recruits fibroblasts to the wound bed and reduces healing times by 30%, restoring healing rates to those observed in young, healthy animals. Ultrasound treatment is equally effective in rescuing the healing defects of animals lacking fibronectin receptors, and can be blocked by pharmacological inhibition of the CamKinaseII pathway. Finally, we discover that the migration defects of fibroblasts from human venous leg ulcer patients can be reversed by ultrasound, demonstrating that the approach is applicable to human chronic samples. By demonstrating that this alternative Rac1 pathway can substitute for that normally operating in the skin, we identify future opportunities for management of chronic wounds.

Demonstration of the rat ischemic skin wound model

The propensity for chronic wounds in humans increases with ageing, disease conditions such as diabetes and impaired cardiovascular function, and unrelieved pressure due to immobility. Animal models have been developed that attempt to mimic these conditions for the purpose of furthering our understanding of the complexity of chronic wounds. The model described herein is a rat ischemic skin flap model that permits a prolonged reduction of blood flow resulting in wounds that become ischemic and resemble a chronic wound phenotype (reduced vascularization, increased inflammation and delayed wound closure). It consists of a bipedicled dorsal flap with 2 ischemic wounds placed centrally and 2 non-ischemic wounds lateral to the flap as controls. A novel addition to this ischemic skin flap model is the placement of a silicone sheet beneath the flap that functions as a barrier and a splint to prevent revascularization and reduce contraction as the wounds heal. Despite the debate of using rats for wound healing studies due to their quite distinct anatomic and physiologic differences compared to humans (i.e., the presence of a panniculus carnosus muscle, short life-span, increased number of hair follicles, and their ability to heal infected wounds) the modifications employed in this model make it a valuable alternative to previously developed ischemic skin flap models.

Advances in drug delivery systems (DDSs) to release growth factors for wound healing and skin regeneration

Current advances in novel drug delivery systems (DDSs) to release growth factors (GFs) represent a great opportunity to develop new therapies or enhance the effectiveness of available medical treatments. These advances are particularly relevant to the field of regenerative medicine, challenging healthcare issues such as wound healing and skin repair. To this end, biocompatible biomaterials have been extensively studied to improve in vivo integration of DDSs, to enhance the bioactivity of the released drugs and to deliver bioactive molecules in a localised and controlled manner. Thus, this review presents an overview of DDSs to release GFs for skin regeneration, particularly emphasising on (i) polymeric micro and nanospheres, (ii) lipid nanoparticles, (iii) nanofibrous structures, (iv) hydrogels and (v) scaffolds. In addition, this review summarises the current animal models available for studying wound healing and the clinical trials and marketed medications based on GF administration indicated for chronic wound treatment.

FROM THE CLINICAL EDITOR

Chronic wounds currently pose a significant burden worldwide. With advances in science, novel drug delivery systems have been developed for growth factors delivery. In this comprehensive review, the authors highlighted current drug delivery systems for the enhancement of wound healing and their use in clinical settings.

The immunology of the porcine skin and its value as a model for human skin

The porcine skin has striking similarities to the human skin in terms of general structure, thickness, hair follicle content, pigmentation, collagen and lipid composition. This has been the basis for numerous studies using the pig as a model for wound healing, transdermal delivery, dermal toxicology, radiation and UVB effects. Considering that the skin also represents an immune organ of utmost importance for health, immune cells present in the skin of the pig will be reviewed. The focus of this review is on dendritic cells, which play a central role in the skin immune system as they serve as sentinels in the skin, which offers a large surface area exposed to the environment. Based on a literature review and original data we propose a classification of porcine dendritic cell subsets in the skin corresponding to the subsets described in the human skin. The equivalent of the human CD141(+) DC subset is CD1a(-)CD4(-)CD172a(-)CADM1(high), that of the CD1c(+) subset is CD1a(+)CD4(-)CD172a(+)CADM1(+/low), and porcine plasmacytoid dendritic cells are CD1a(-)CD4(+)CD172a(+)CADM1(-). CD209 and CD14 could represent markers of inflammatory monocyte-derived cells, either dendritic cells or macrophages. Future studies for example using transriptomic analysis of sorted populations are required to confirm the identity of these cells.

Growth and remodelling for profound circular wounds in skin

Wound healing studies both in vitro and in vivo have received a lot of attention recently. In vivo wound healing is a multi-step process involving physiological factors such as fibrinogen forming the clot, the infiltrated inflammatory cells, the recruited fibroblasts and the differentiated myofibroblasts as well as deposited collagens. All these actors play their roles at different times, aided by a cascade of morphogenetic agents and the result for the repair is approximatively successful but the imperfection is remained for large scars with fibrosis. Here, we want to study wound healing from the viewpoint of skin biomechanics, integrating the particular layered geometry of the skin, and the role of the neighbouring wound epidermis. After 2 days post-injury, it migrates towards the wound centre to cover the hole, the migration being coupled to proliferation at the wound border. Such a process is dominated by the skin properties which varies with ages, locations, pathologies, radiations, etc. It is also controlled by passive (actin, collagen) and active (myo-fibroblasts) fibres. We explore a growth model in finite elasticity of a bilayer surrounding a circular wound, only the interior one being proliferative and contractile. We discuss the occurrence of an irregular wound geometry generated by stresses and show quantitatively that it results from the combined effects of the stiffness, the size of the wound, eventually weakened by actin cables. Comparison of our findings is made with known observations or experiments in vivo.

A systematic review of the wound-healing effects of monoterpenes and iridoid derivatives

The search for more effective and lower cost therapeutic approaches for wound healing remains a challenge for modern medicine. In the search for new therapeutic options, plants and their metabolites are a great source of novel biomolecules. Among their constituents, the monoterpenes represent 90% of essential oils, and have a variety of structures with several activities such as antimicrobial, anti-inflammatory, antioxidant and wound healing. Based on that, and also due to the lack of reviews concerning the wound-healing activity of monoterpenes, we performed this systematic review-which provides an overview of their characteristics and mechanisms of action. In this search, the terms "terpenes", "monoterpenes", "wound healing" and "wound closure techniques" were used to retrieve articles published in LILACS, PUBMED and EMBASE until May 2013. Seven papers were found concerning the potential wound healing effect of five compouds (three monoterpenes and two iridoid derivatives) in preclinical studies. Among the products used for wound care, the films were the most studied pharmaceutical form. Monoterpenes are a class of compounds of great diversity of biological activities and therapeutic potential. The data reviewed here suggest that monoterpenes, although poorly studied in this context, are promising compounds for the treatment of chronic wound conditions.

Late failure of a split-thickness skin graft in the setting of homozygous factor V Leiden mutation: a case report and correlative animal model from the Wound Etiology and Healing (WE-HEAL) study

We present the case of a 53-year-old Caucasian male smoker with remote history of left lower extremity deep venous thrombosis (DVT) and a strong family history of thrombosis, who presented to the Center for Wound Healing at MedStar Georgetown University Hospital with spontaneous left leg ulceration. Prothrombotic evaluation showed homozygosity for the factor V Leiden (FVL) mutation. Therapeutic anticoagulation was commenced with warfarin (Coumadin®) and the patient underwent successful debridement and Apligraf® followed by split-thickness skin graft (STSG) of two wounds. He had an uneventful postoperative course and on the 27th postoperative day the grafts were 95% intact. However, by postoperative day 41 there was 10% graft loss, and over the subsequent 2 weeks both grafts necrosed. On further questioning, it transpired that the patient had discontinued his warfarin on postoperative day 37 because he thought that it was no longer necessary. The patient is enrolled in the Wound Etiology and Healing (WE-HEAL) study, and at the time of the original graft, residual skin fragments from the STSG were transplanted onto a nude mouse for development of an animal model of wound healing. The mouse graft was successful and was harvested at postoperative day 87 for pathological examination. We review the mechanisms by which prothrombotic states, particularly FVL mutation, can contribute to skin graft failure and delayed wound healing. This case highlights the importance of considering prothrombotic conditions in patients with spontaneous leg ulcerations and the impact of therapeutic anticoagulation on healing. It further allows us to demonstrate the efficacy of the animal model in which residual fragments of STSG tissue are utilised for transplant onto nude mice for manipulation in the laboratory.

Mast cell activity in the healing wound: more than meets the eye?

Mast cells (MCs) are an important part of the innate immune system and are abundant in barrier organs such as the skin. They are known primarily for initiating allergic reactions, but many other biological functions have now been described for these cells. Studies have indicated that during wound repair, MCs enhance acute inflammation, stimulate reepithelialization and angiogenesis, and promote scarring. MCs have also been linked to abnormal healing, with high numbers of MCs observed in chronic wounds, hypertrophic scars and keloids. Although MCs have gained attention in the wound healing field, several unique features of MCs have yet to be examined in the context of cutaneous repair. These include the ability of MCs to: (i) produce anti-inflammatory mediators; (ii) release mediators without degranulating; and (iii) change their phenotype. Recent findings highlight the complexity of MCs and suggest that more information is needed to understand their complete range of activities during repair.

Reduced Il17a expression distinguishes a Ly6c(lo)MHCII(hi) macrophage population promoting wound healing

Macrophages are the main components of inflammation during skin wound healing. They are critical in wound closure and in excessive inflammation, resulting in defective healing observed in chronic wounds. Given the heterogeneity of macrophage phenotypes and functions, we here hypothesized that different subpopulations of macrophages would have different and sometimes opposing effects on wound healing. Using multimarker flow cytometry and RNA expression array analyses on macrophage subpopulations from wound granulation tissue, we identified a Ly6c(lo)MHCII(hi) "noninflammatory" subset that increased both in absolute number and proportion during normal wound healing and was missing in Ob/Ob and MYD88-/- models of delayed healing. We also identified IL17 as the main cytokine distinguishing this population from proinflammatory macrophages and demonstrated that inhibition of IL17 by blocking Ab or in IL17A-/- mice accelerated normal and delayed healing. These findings dissect the complexity of the role and activity of the macrophages during wound inflammation and may contribute to the development of therapeutic approaches to restore healing in chronic wounds.