The correlation of in vivo burn scar contraction with the level of α-smooth muscle actin expression

Perifascial areolar tissue graft promotes angiogenesis and wound healing in an exposed ischemic component rabbit model

Multiple studies have reported the use of perifascial areolar tissue (PAT) grafts to treat wounds involving exposed ischemic tissues, avascular structures, and defective membrane structures. Our objective was to assess the quantitative effects of PAT grafts and their suitability for wounds with ischemic tissue exposure and to qualitatively determine the factors through which PAT promotes wound healing and repair. We conducted histological, immunohistochemical, and mass spectrometric analyses of the PAT grafts. PAT grafts contain numerous CD34+ progenitor/stem cells, extracellular matrix, growth factors, and cytokines that promote wound healing and angiogenesis. Furthermore, we established a male rabbit model to compare the efficacy of PAT grafting with that of an occlusive dressing treatment (control) for wounds with cartilage exposure. PAT grafts could cover ischemic components with granulation tissue and promote angiogenesis. Macroscopic and histological observations of the PAT graft on postoperative day seven revealed capillaries bridging the ischemic tissue (vascular bridging). Additionally, the PAT graft suppressed wound contraction and alpha smooth muscle actin (αSMA) levels and promoted epithelialization. These findings suggested that PAT can serve as a platform to enhance wound healing and promote angiogenesis. This is the first study to quantify the therapeutic efficacy of PAT grafts, revealing their high value for the treatment of wounds involving exposed ischemic structures. The effectiveness of PAT grafts can be attributed to two primary factors: vascular bridging and the provision of three essential elements (progenitor/stem cells, extracellular matrix molecules, and growth factors/cytokines). Moreover, PAT grafts may be used as transplant materials to mitigate excessive wound contraction and the development of hypertrophic scarring.

Establishment and validation of a nomogram to predict the neck contracture after skin grafting in burn patients: A multicentre cohort study

Cervical burn contracture is one of the burn contractures with the highest incidence and severity, and there is no effective method to predict the risk of neck contracture. This study aimed to investigate the effect of combined cervicothoracic skin grafting on the risk of neck contracture in burn patients and to develop a nomogram to predict the risk of neck contracture after skin grafting in burn patients. Data from 212 patients with burns who underwent neck skin grafting were collected from three hospitals, and the patients were randomly divided into training and validation sets. Independent predictors were identified through univariate and multivariate logistic regression analyses and incorporated into a prognostic nomogram. Its performance was assessed using the receiver operating characteristic area under the curve, calibration curve, and decision curve analysis. Burn depth, combined cervicothoracic skin grafting, graft thickness, and neck graft size were significantly associated with neck contractures. In the training cohort, the nomogram had an area under the curve of 0.894. The calibration curve and decision curve analysis indicated good clinical applicability of the nomogram. The results were tested using a validation dataset. Combined cervicothoracic skin grafting is an independent risk factor for neck contracture. Our nomogram demonstrated excellent performance in predicting neck contracture risk.

Epidemiology and Predictors for Cervical Burn Scar Contractures: A Multicenter Cohort Study

Cervical burn scar contracture (BSC) affects many important neck functions and the patients' quality of life. However, it remains unclear which patients have a higher risk of neck BSCs. This study aimed to describe the epidemiology and identify the independent risks of cervical BSC formation and severity. Clinical and demographic data of 106 patients with burn scars were retrospectively collated and analyzed from 3 different Chinese hospitals between December 2016 and December 2020. Both univariate and multivariate logistic regression analyses were performed to identify the independent risks for BSC formation and severity at 12 months postburn. Lateral flexion was the most common plane of motion (POM) limited by contractures (29.4%), whereas the POM most commonly limited by severe contractures was the extension (24.6%). Most patients with contractures had those in 3 to 4 POMs (72.1%). Neck skin grafting was an independent risk factor for BSC formation, and cervical and cervicothoracic skin grafting were independent risk factors for BSC severity. These results may help to identify high-risk patients with contractures in the early stages of burns to carry out individualized early prevention and treatment.

Functional molecule-mediated assembled copper nanozymes for diabetic wound healing

BACKGROUND

The complex hyperglycemic, hypoxic, and reactive oxygen species microenvironment of diabetic wound leads to vascular defects and bacterial growth and current treatment options are relatively limited by their poor efficacy.

RESULTS

Herein, a functional molecule-mediated copper ions co-assembled strategy was constructed for collaborative treatment of diabetic wounds. Firstly, a functional small molecule 2,5-dimercaptoterephthalic acid (DCA) which has symmetrical carboxyl and sulfhydryl structure, was selected for the first time to assisted co-assembly of copper ions to produce multifunctional nanozymes (Cu-DCA NZs). Secondly, the Cu-DCA NZs have excellent multicatalytic activity, and photothermal response under 808 nm irradiation. In vitro and in vivo experiments showed that it not only could efficiently inhibit bacterial growth though photothermal therapy, but also could catalyze the conversion of intracellular hydrogen peroxide to oxygen which relieves wound hypoxia and improving inflammatory accumulation. More importantly, the slow release of copper ions could accelerate cellular proliferation, migration and angiogenesis, synergistically promote the healing of diabetic wound furtherly.

CONCLUSIONS

The above results indicate that this multifunctional nanozymes Cu-DCA NZs may be a potential nanotherapeutic strategy for diabetic wound healing.

Model to Inhibit Contraction in Third-Degree Burns Employing Split-Thickness Skin Graft and Administered Bone Marrow-Derived Stem Cells

Third-degree burns typically result in pronounced scarring and contraction in superficial and deep tissues. Established techniques such as debridement and grafting provide benefit in the acute phase of burn therapy, nevertheless, scar and contraction remain a challenge in deep burns management. Our ambition is to evaluate the effectiveness of novel cell-based therapies, which can be implemented into the standard of care debridement and grafting procedures. Twenty-seven third-degree burn wounds were created on the dorsal area of Red Duroc pig. After 72 h, burns are surgically debrided using a Weck knife. Split-thickness skin grafts (STSGs) were then taken after debridement and placed on burn scars combined with bone marrow stem cells (BM-MSCs). Biopsy samples were taken on days 17, 21, and 45 posttreatment for evaluation. Histological analysis revealed that untreated control scars at 17 days are more raised than burns treated with STSGs alone and/or STSGs with BM-MSCs. Wounds treated with skin grafts plus BM-MSCs appeared thinner and longer, indicative of reduced contraction. qPCR revealed some elevation of α-SMA expression at day 21 and Collagen Iα2 in cells derived from wounds treated with skin grafts alone compared to wounds treated with STSGs + BM-MSCs. We observed a reduction level of TGFβ-1 expression at days 17, 21, and 45 in cells derived from wounds treated compared to controls. These results, where the combined use of stem cells and skin grafts stimulate healing and reduce contraction following third-degree burn injury, have a potential as a novel therapy in the clinic.

Copper-rich multifunctional Prussian blue nanozymes for infected wound healing

The healing process of infected wounds was limited by bacterial infection, excessive reactive oxygen species (ROS) accumulation, and tissue hypoxia. In order to alleviate the above situations, herein, a copper-rich multifunctional ultra-small Prussian blue nanozymes (HPP@Cu NZs) was constructed for infected wound synergistic treatment. Firstly, hyaluronic acid was modified by branched polyethyleneimine which could form a complex with copper ions, to construct copper-rich Prussian blue nanozymes. Secondly, the HPP@Cu NZs have a uniform ultra-small nano size and excellent photothermal response performance, exhibition of multifunctional enzymatic activity and anti-inflammatory properties. Finally, the slow release of copper ions in the HPP@Cu NZs could effectively promote the formation of new blood vessels, thus giving it multifunctional properties. In vitro and in vivo experiments showed that it not only could effectively inhibit and kill bacteria under 808 nm near-infrared laser but also could remove excessive ROS, regulate oxygen levels, and anti-inflammation. More importantly, the release of copper ions could synergistically promote the healing of infected wounds as well as good biocompatibility. Overall, our studies provide a multifunctional strategy for infected wounds with synergistic treatment based on carrier construction.

Comparative Transcriptome Analysis of Superficial and Deep Partial-Thickness Burn Wounds in Yorkshire vs Red Duroc Pigs

Hypertrophic scars are a common negative outcome of deep partial-thickness burn wounds resulting in increased dermal thickness, wound area contracture, and inflammation of the affected area. The red Duroc and Yorkshire porcine breeds are common large animal models for studying dermal wounds due to their structural similarities to human skin; however, the porcine transcriptomic profiles of dermal burn wounds and healing process are not well known. In response, a longitudinal transcriptomic comparative study was conducted comparing red Duroc and Yorkshire superficial and DPT burn wounds to their respective control uninjured tissue. Using next-generation RNA-sequencing, total RNAs were isolated from burn wound tissue harvested at 0, 3, 7, 15, 30, and 60 days post-burn and mRNA-seq and gene expression read counts were generated. Significant differentially expressed genes relative to uninjured tissue were defined and active biological processes were determined using gene set enrichment analyses. Additionally, collagen deposition, α-SMA protein concentration, epidermal and dermal thickness measurements, and wound area changes in response to burn injury were characterized. Overall, the red Duroc pigs, in response to both burn wound types, elicited a more robust and prolonged inflammatory immune response, fibroblast migration and proliferation as well as heightened levels of extracellular matrix modulation relative to respective burn types in the Yorkshire pigs. Collectively, the red Duroc deep partial-thickness burn wounds produce a greater degree of hypertrohic scar like response compared to Yorkshire DPT burn wounds. These findings will facilitate future porcine burn studies down-selecting treatment targets and determining effects of novel therapeutic strategies.

Dramatic Effect of Botulinum Toxin Type A on Hypertrophic Scar: A Promising Therapeutic Drug and Its Mechanism Through the SP-NK1R Pathway in Cutaneous Neurogenic Inflammation

Background

Hypertrophic scar formation may be related to cutaneous neurogenic inflammation (CNI) through the substance P-neurokinin 1 receptor (SP-NK1R) signaling pathway. As a widely used drug in aesthetic clinical work, botulinum toxin type A (BTX-A) has a therapeutic effect on scars, but the actual mechanism remains unclear. This study aimed to clarify the potential mechanism by which BTX-A inhibits CNI in hypertrophic scars both in vitro and in vivo.

Methods

Tissue samples were obtained from surgical excisions. Immunohistological analysis was used to locate SP in human hypertrophic scars and normal skin. RT-PCR and western blot analysis were used to evaluate the expression of collagens after SP/BTX-A treatment. A rabbit ear scar model was used to explore the in vivo effect of BTX-A on scar treatment.

Results

SP and NK-1R were overexpressed in hypertrophic scars compared to normal skin tissues. Collagen secretion of hypertrophic scar-derived fibroblasts increased with increasing doses of SP. However, BTX-A may downregulate collagen expression through SP-NK1R pathway with or without the presence of SP inducing agent capsaicin. Meanwhile, SP inhibited the expression of NK-1R, and this inhibition was blocked by pretreatment with BTX-A. In vivo, intralesional BTX-A injection can also reduce the volume of scars and inhibit collagen secretion. Capsaicin may cause more severe scar manifestations, while the therapeutic effect of BTX-A remains.

Conclusion

Our research confirms that CNI stimulates fibroblasts during scar formation, while BTX-A can reduce collagen secretion by inhibiting the SP-NK1R signaling pathway, thus identifying a novel therapeutic target for this benign solid skin tumor.

Rhamnolipids from non-pathogenic Acinetobacter calcoaceticus: Bioreactor-scale production, characterization and wound healing potency

Rhamnolipids are predominantly produced from the opportunistic pathogen Pseudomonas aeruginosa, which restricts their scaled-up production and biomedical applications. Moreover, the wound healing property of rhamnolipids is mainly focused on either mono- or di-rhamnolipid congeners, which are obtained after extensive and costly purification procedures. Here, crude rhamnolipids from non-pathogenic Acinetobacter calcoaceticus BU-03 have been prepared and characterized and their wound healing potency evaluated in vitro and in vivo. Rhamnolipid extract was produced in a bioreactor by batch fermentation at a concentration of 12.7 ± 1.4 g/L. Characterization of the extract by Fourier Transform Infrared spectroscopy and mass spectrometry revealed characteristic rhamnolipid peaks. Rha-C10-C10 and Rha-Rha-C10-C10 appeared as the predominant congeners along with minor quantities of six more congeners. The rhamnolipid extract obtained from A. calcoaceticus had no toxicity against mouse fibroblast L929 cells and accelerated their migration. Transforming growth factor beta 1 (TGF-β1) has been shown to promote fibroblast migration by activating Smad3. It was found that the rhamnolipid extract enhanced Smad3 phosphorylation in L929 cells. In vivo studies showed that it promoted wound healing in mice with excisional wounds. The protein levels of TGF-β1 and alpha smooth muscle actin (α-SMA), a highly contractile protein, were significantly increased by 2.56- and 1.51-fold, respectively, in extract-treated compared with vehicle control-treated wounds, indicating that the activation of TGF-β1 signaling is possibly involved in the wound healing effect. These results suggest that a rhamnolipid extract obtained from A. calcoaceticus has potential as a wound healing material for topical application in cutaneous wound treatment.

Gelatin Loaded Titanium Dioxide and Silver Oxide Nanoparticles: Implication for Skin Tissue Regeneration

Treatment of burn wounds has many requirements to ensure wound closure with healthy tissue, increased vascularization, guarantee edema resolution, and control bacterial infection. We propose that titanium oxide (TiO₂) nanoparticles (NPs) will be more efficient than silver dioxide (Ag₂O) in the treatment of burn wounds. Herein, gelatin loaded NPs (GLT-NPs) were evaluated for their efficacy to regenerate second-degree burn wound in rabbit skin. TEM results revealed that the average particle sizes were ⁓ 7.5 and 17 nm for Ag₂O and TiO₂ NPs, respectively. The results of the in vivo application of GLT-NPs on burn wound in the rabbit revealed that both Ag₂O and TiO₂ NPs were efficient than the control none treated (CTRL) and GLT group. In terms of the healing rate, the GLT-TiO₂ did not show any significant difference than GLT-Ag₂O (99.57% vs. 99.85%, p = 0.2). Meanwhile, the healing rate was significantly higher in both NPs' treated groups than CTRL (94.16%, p < 0.01) and GLT group (95.07%, p < 0.05). Also, the histological analysis using H&E staining showed re-epithelization, less edema, and enhanced vascularization in both GLT-NPs than CTRL and GLT groups. Furthermore, immunohistochemical analysis of TGF-β1 and α-SMA revealed significantly a higher expression in both GLT-NPs groups than CTRL and GLT groups at weeks 1 and 2 (p < 0.05). Interestingly, TGF-β1 and α-SMA were substantially higher in GLT- TiO₂ than GLT-Ag₂O at weeks 1 and 2 (p < 0.05), but the expression was not significant at week 3. In conclusion, GLT-NPs showed higher regenerative capacity and enhanced the healing quality after burn wound compared to CTRL and GLT. Graphical abstract.

Corilagin alleviates hypertrophic scars via inhibiting the transforming growth factor (TGF)-β/Smad signal pathway

AIMS

Exploring the effects of corilagin on hypertrophic scar (HS) and its underlying mechanisms.

MAIN METHODS

Human HS-derived fibroblasts (HSFs) were isolated and treated with corilagin. To investigate the effects of corilagin on HSFs, quantitative real time polymerase chain reaction (qRT-PCR), western blotting, wound healing, and immunofluorescence assays were performed. These effects were confirmed in a rabbit ear scar model by histological and immunohistochemical studies. Lastly, western blot assay was performed to detect the protein levels of several components of the transforming growth factor (TGF)-β/Smad signaling pathway, as well as the protein levels of matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs).

KEY FINDINGS

Corilagin showed multiple effects on HSFs, including does-dependent inhibition of collagen production, cell proliferation, and migration, besides suppression of the activation of HSFs. Moreover, corilagin suppressed HS formation and collagen deposition in a rabbit ear scar model. Corilagin also inhibited fibroblast proliferation and α-smooth muscle actin (α-SMA) expression in vivo. Finally, western blot analysis revealed that corilagin downregulated the protein levels of TGF-β1 and TGF-β receptor type I (TGFβRI), thus lowering the level of p-smad2/3, also affected the protein levels of MMPs and TIMP1.

SIGNIFICANCE

Corilagin could be a potential agent for HS treatment through the inhibition of extracellular matrix (ECM) deposition and multiple functions of fibroblasts.

A novel human ex vivo skin model to study early local responses to burn injuries

Burn injuries initiate numerous processes such as heat shock response, inflammation and tissue regeneration. Reliable burn models are needed to elucidate the exact sequence of local events to be able to better predict when local inflammation triggers systemic inflammatory processes. In contrast to other ex vivo skin culture approaches, we used fresh abdominal skin explants to introduce contact burn injuries. Histological and ultrastructural analyses confirmed a partial-thickness burn pathology. Gene expression patterns and cytokine production profiles of key mediators of the local inflammation, heat shock response, and tissue regeneration were analyzed for 24 h after burn injury. We found significantly increased expression of factors involved in tissue regeneration and inflammation soon after burn injury. To investigate purely inflammation-mediated reactions we injected lipopolysaccharide into the dermis. In comparison to burn injury, lipopolysaccharide injection initiated an inflammatory response while expression patterns of heat shock and tissue regeneration genes were unaffected for the duration of the experiment. This novel ex vivo human skin model is suitable to study the local, early responses to skin injuries such as burns while maintaining an intact overall tissue structure and it gives valuable insights into local mechanisms at the very beginning of the wound healing process after burn injuries.

Angiotensin-Converting Enzyme Inhibitor, Captopril, Improves Scar Healing in Hypertensive Rats

Pathological cutaneous scars, with aberrant extracellular matrix accumulation, have multiple origins. Antihypertensive medications, such as calcium channel blockers, have been used to treat pathological scars. However, a relationship between angiotensin-converting enzyme (ACE) inhibitors, pathological scars, and blood pressure (BP) has never been reported. Here, we aimed to compare the differences in scar development and the effects of the administration of systemic ACE inhibitor on scar tissue in a normotensive rat, the Wistar Kyoto rat (WKY), a hypertensive rat, and the spontaneously hypertensive rat (SHR). Using an 8-mm punch, we created two full-thickness skin defects in a total of 32 rats (16 WKY and 16 SHR) to obtain a total of 64 wounds. We established control WKY (n = 16), captopril-treated WKY (n = 16), control SHR (n = 16), and captopril-treated SHR (n = 16) groups and started captopril (100 mg/g per day) treatment on day 21 in the appropriate groups. The BP of all groups was measured at 0, 3, and 5 weeks. The scar area was measured by histopathological examination, and scarring was expressed in terms of scar area and fibroblast and capillary counts. The expression of heat shock protein (HSP) 47, type I and III collagens, alpha-smooth muscle actin (α-SMA), Ki67, and vascular endothelial growth factor (VEGF) was investigated using immunohistochemistry. The scar area and fibroblast count were significantly higher in control SHR than in control WKY. The scar area, fibroblast count, and capillary count were significantly smaller in captopril-treated SHR than in control SHR. Immunostaining for α-SMA, Ki67, and VEGF also showed a noticeable decrease in scarring in the treated SHR compared with that in control SHR. Thus, BP affects scar development in a rat model, and an ACE inhibitor is more effective at reducing scars in hypertensive rats than in normotensive rats.

Nanoparticle-functionalized dressings for the treatment of third-degree skin burns - histopathological and immunohistochemical study

Skin burns are one of the most common injuries associated with increased morbidity and mortality, especially in the children and the elderlies. Severe burns, especially, result in a systemic immune and inflammatory response, which may reflect in multiple organ insufficiency, and a fast and effective local restorative process is essential for functionality recovering, as well as for interrupting the generalized systemic response. We have aimed here to assess the effect of different wound dressings in what it regards the morphology and clinical restoration after a skin burn. On a rat animal model, we have evaluated the macroscopic and histopathological features of controlled third degree skin burns in control animals versus treatments with local dressings of silver sulfadiazine (SDA) cream, simple gel (G), gel + silver nanoparticles (AgNPs) (G+NPS), gel + exosomes (G+EXO) and gel + AgNPs + exosomes (Gel+NPS+EXO), at 14 days and, respectively, 21 days after the lesion. Tissue fragments were harvested and processed for histopathology and immunohistochemistry. Immunofluorescence was utilized to evaluate the maturity of underlaying granulation tissue based on double stainings for smooth muscle actin (SMA) and cluster of differentiation 31 (CD31). Our study showed variability in what it regards the vessel density and immunoexpression of SMA between the treatments, and image analysis revealed that most SMA reduction and blood vessel density reduction in the maturing granulation tissue occurred for the G+NPS and G+NPS+EXO treatments. A complete re-epithelization was also observed for the G+NPS+EXO treatment. Overall, our results show that improved topic treatments promote faster re-epithelization and reparation of the dermis after skin burn lesions, providing thus an avenue for new treatments that aim both local recuperation and systemic infection prevention.

A highly simulated scar model developed by grafting human thin split-thickness skin on back of nude mouse: The remodeling process, histological characteristics of scars

A predictive scar animal model is needed in order to study the mechanism and assess the therapies before its use in humans. However, due to the differences in wound healing patterns and regeneration ability, none of the existing models can fully simulate the characteristics of human scar. The aim of this study was to build a model that recapitulated the developing process and outcomes of human hypertrophic scar (HS). Nude mice were grafted with thin split-thickness human skins. The dynamic changes and final outcomes of the grafts were investigated. The results showed that human skin grafts survived and underwent progressive scarring remodeling in morphology and histology. Scar related markers (α-SMA, CD34, Collage I, TGF-β1) were positive in immunohistology. Protein expressions in TGF-β1/Smad2/3 pathway were increased in accordance with HS during the development process by western blotting. It was finally proved that scar reconstructed by this model matches a real-world human HS. This is a stable, easy to reproduce model for studying the scar formation process and its properties.

Reabilitação motora orofacial em queimaduras em cabeça e pescoço: uma revisão sistemática de literatura

RESUMO Objetivos Investigar estudos sobre o tratamento das queimaduras em cabeça e pescoço, nas diversas áreas da saúde envolvidas na assistência a queimados (médica, enfermagem, fonoaudiologia, fisioterapia e terapia ocupacional), avaliando a eficácia das técnicas empregadas, principalmente no que se refere à reabilitação da funcionalidade da musculatura em cabeça e pescoço. Estratégia de pesquisa Os artigos foram selecionados por meio da base de dados PubMed, utilizando os descritores “burn and face and speech-language pathology”, “burn and face and speech language”, “burn and face and rehabilitation”, “burn and face and myofunctional rehabilitation”, “burn and face and myofunctional therapy”, “nonsurgical and scar and management”, “burn and face and nonsurgical” e “burn and face and scar and management”. Critérios de seleção Foram incluídos artigos que investigaram os tratamentos das queimaduras em cabeça e pescoço, associados à reabilitação da funcionalidade da musculatura em cabeça e pescoço, utilizando exercícios musculares e/ou terapias manuais. Resultados A maioria dos tratamentos descritos apresentou efeitos benéficos para pacientes com queimaduras. Foi observada grande variabilidade da metodologia adotada para a aplicação e verificação dos efeitos dos tratamentos. Conclusão Apesar do crescente número de pesquisas, ainda não existe consenso quanto à melhor técnica terapêutica e ao real benefício de cada uma delas. Existe uma grande diversidade nos protocolos de tratamento, sendo que um número pequeno de estudos de tratamento visa a funcionalidade do sistema miofuncional orofacial. A maioria dos estudos tem, como foco, atividades motoras isoladas, que visam à mobilidade mandibular.

Early cessation of pressure garment therapy results in scar contraction and thickening

Pressure garment therapy is often prescribed to improve scar properties following full-thickness burn injuries. Pressure garment therapy is generally recommended for long periods of time following injury (1-2 years), though it is plagued by extremely low patient compliance. The goal of this study was to examine the effects of early cessation of pressure garment therapy on scar properties. Full-thickness burn injuries were created along the dorsum of red Duroc pigs. The burn eschar was excised and wound sites autografted with split-thickness skin. Scars were treated with pressure garments within 1 week of injury and pressure was maintained for either 29 weeks (continuous pressure) or for 17 weeks followed by cessation of pressure for an additional 12 weeks (pressure released); scars receiving no treatment served as controls. Scars that underwent pressure garment therapy were significantly smoother and less contracted with decreased scar height compared to control scars at 17 weeks. These benefits were maintained in the continuous pressure group until week 29. In the pressure released group, grafts significantly contracted and became more raised, harder and rougher after the therapy was discontinued. Pressure cessation also resulted in large changes in collagen fiber orientation and increases in collagen fiber thickness. The results suggest that pressure garment therapy effectively improves scar properties following severe burn injury; however, early cessation of the therapy results in substantial loss of these improvements.

Effect of skin graft thickness on scar development in a porcine burn model

Animal models provide a way to investigate scar therapies in a controlled environment. It is necessary to produce uniform, reproducible scars with high anatomic and biologic similarity to human scars to better evaluate the efficacy of treatment strategies and to develop new treatments. In this study, scar development and maturation were assessed in a porcine full-thickness burn model with immediate excision and split-thickness autograft coverage. Red Duroc pigs were treated with split-thickness autografts of varying thickness: 0.026in. ("thin") or 0.058in. ("thick"). Additionally, the thin skin grafts were meshed and expanded at 1:1.5 or 1:4 to evaluate the role of skin expansion in scar formation. Overall, the burn-excise-autograft model resulted in thick, raised scars. Treatment with thick split-thickness skin grafts resulted in less contraction and reduced scarring as well as improved biomechanics. Thin skin autograft expansion at a 1:4 ratio tended to result in scars that contracted more with increased scar height compared to the 1:1.5 expansion ratio. All treatment groups showed Matrix Metalloproteinase 2 (MMP2) and Transforming Growth Factor β1 (TGF-β1) expression that increased over time and peaked 4 weeks after grafting. Burns treated with thick split-thickness grafts showed decreased expression of pro-inflammatory genes 1 week after grafting, including insulin-like growth factor 1 (IGF-1) and TGF-β1, compared to wounds treated with thin split-thickness grafts. Overall, the burn-excise-autograft model using split-thickness autograft meshed and expanded to 1:1.5 or 1:4, resulted in thick, raised scars similar in appearance and structure to human hypertrophic scars. This model can be used in future studies to study burn treatment outcomes and new therapies.

Delivery of Allogeneic Adipose Stem Cells in Polyethylene Glycol-Fibrin Hydrogels as an Adjunct to Meshed Autografts After Sharp Debridement of Deep Partial Thickness Burns

Harvesting of autografts results in donor site morbidities and is limited in scenarios such as large total body surface area burns. In these instances, coverage is increased by meshing grafts at the expense of delayed biologic closure. Moreover, graft meshing increases the likelihood of contraction and hypertrophic scarring, limits range of motion, and worsens cosmesis. Many tissue engineering technologies have touted the promise of adipose‐derived stem cells (ASCs) for burn wounds. The primary objective of the current study was to determine feasibility and efficacy of in situ ASC delivery via PEGylated fibrin (FPEG) hydrogels as adjuncts to meshed split thickness skin grafts in a porcine model. Deep partial thickness burns were created on the dorsum of anesthetized Yorkshire pigs, and subsequently debrided on post‐burn day 4. After debridement, wounds were treated with: split thickness skin grafts (STSG); meshed STSG (mSTSG); and mSTSG + FPEG with increasing doses of ASCs. We show that FPEG hydrogels can be delivered in situ to prevent the contraction seen after meshing of STSG. Moreover, ASCs delivered in FPEG dose‐dependently increase blood vessel size which significantly correlates with CD31 protein levels. The current study reports a dual‐action adjunct therapy to autografting administered in situ, wherein FPEG acts as both scaffolding to prevent contraction, and as a delivery vehicle for ASCs to accelerate angiogenesis. This strategy may be used to incorporate other biologics for generating tissue engineered products aimed at improving wound healing and minimizing donor sites or scarring. stemcellstranslationalmedicine2018;7:360–372

Dermis, acellular dermal matrix, and fibroblasts from different layers of pig skin exhibit different profibrotic characteristics: evidence from in vivo study

To explore the profibrotic characteristics of the autografted dermis, acellular dermal matrix, and dermal fibroblasts from superficial/deep layers of pig skin, 93 wounds were established on the dorsa of 7 pigs. 72 wounds autografted with the superficial/deep dermis and acellular dermal matrix served as the superficial/deep dermis and acellular dermal matrix group, respectively, and were sampled at 2, 4, and 8 weeks post-wounding. 21 wounds autografted with/without superficial/deep dermal fibroblasts served as the superficial/deep dermal fibroblast group and the control group, respectively, and were sampled at 2 weeks post-wounding. The hematoxylin and eosin staining showed that the wounded skin thicknesses in the deep dermis group (superficial acellular dermal matrix group) were significantly greater than those in the superficial dermis group (deep acellular dermal matrix group) at each time point, the thickness of the cutting plane in the deep dermal fibroblast group was significantly greater than that in the superficial dermal fibroblast group and the control group. The western blots showed that the α-smooth muscle actin expression in the deep dermis group (superficial acellular dermal matrix group) was significantly greater than that in the superficial dermis group (deep acellular dermal matrix group) at each time point. In summary, the deep dermis and dermal fibroblasts exhibited more profibrotic characteristics than the superficial ones, on the contrary, the deep acellular dermal matrix exhibited less profibrotic characteristics than the superficial one.

Naringenin attenuates fibroblast activation and inflammatory response in a mechanical stretch-induced hypertrophic scar mouse model

The pathogenesis and therapy of hypertrophic scars (HS) have not yet been established. The aim of the present study was to investigate the potential effect of naringenin on HS and its underlying mechanisms. The mouse model of HS was prepared by a mechanical stretch device and then treated with naringenin at various concentrations. Histological studies were performed to evaluate scar hypertrophy by hematoxylin and eosin, as well as Masson's trichrome staining. The activation of HS fibroblasts was determined based on reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR), western blotting and immunohistochemical staining. Following observing the retention of inflammation cells by immunohistochemistry, the cytokines, including tumor necrosis factor (TNF)‑α, interleukin (IL)‑1β, IL‑6 and transforming growth factor (TGF)‑β1, mRNA and protein levels were quantitated by RT‑qPCR, ELISA and western blotting methods. As a result, naringenin significantly inhibited the formation of HS in a concentration‑dependent manner. In addition, naringenin inhibited fibroblast activation and inflammatory cell recruitment. In addition, mRNA and protein expression levels of TNF‑α, IL‑1β, IL‑6 and TGF‑β1 were downregulated following naringenin treatment. The current study highlighted a new pharmacological activity of naringenin on HS. The mechanism of action of naringenin was associated with the inhibition of fibroblast activation and local inflammation. These results suggested that naringenin may serve as a novel agent for treatment of HS.

Honokiol Alleviates Hypertrophic Scar by Targeting Transforming Growth Factor-β/Smad2/3 Signaling Pathway

Hypertrophic scar (HPS) presents as excessive extracellular matrix deposition and abnormal function of fibroblasts. However, there is no single satisfactory method to prevent HPS formation so far. Here, we found that honokiol (HKL), a natural compound isolated from Magnolia tree, had an inhibitory effect on HPS both in vitro and in vivo. Firstly, HKL could dose-dependently down-regulate the mRNA and protein levels of type I collagen, type III collagen, and α-smooth muscle actin (α-SMA) in hypertrophic scar-derived fibroblasts (HSFs). Secondly, HKL suppressed the proliferation, migration abilities of HSFs and inhibited HSFs activation to myofibroblasts, but had no effect on cell apoptosis. Besides, the in vivo rabbit ear scar model further affirmed the inhibitory effects of HKL on collagen deposition, proliferating cell nuclear antigen and α-SMA. Finally, Western blot results showed that HKL reduced the phosphorylation status of Smad2/3, as well as affected the protein levels of matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinase1. Taken together, this study demonstrated that HKL alleviated HPS by suppressing fibrosis-related molecules and inhibiting HSFs proliferation, migration as well as activation to myofibroblasts via Smad-dependent pathway. Therefore, HKL could be used as a potential agent for treating HPS and other fibrotic diseases.

A mathematical model for the simulation of the contraction of burns

A continuum hypothesis-based model is developed for the simulation of the contraction of burns in order to gain new insights into which elements of the healing response might have a substantial influence on this process. Tissue is modeled as a neo-Hookean solid. Furthermore, (myo)fibroblasts, collagen molecules, and a generic signaling molecule are selected as model components. An overview of the custom-made numerical algorithm is presented. Subsequently, good agreement is demonstrated with respect to variability in the evolution of the surface area of burns over time between the outcomes of computer simulations and measurements obtained in an experimental study. In the model this variability is caused by varying the values for some of its parameters simultaneously. A factorial design combined with a regression analysis are used to quantify the individual contributions of these parameter value variations to the dispersion in the surface area of healing burns. The analysis shows that almost all variability in the surface area can be explained by variability in the value for the myofibroblast apoptosis rate and, to a lesser extent, the value for the collagen molecule secretion rate. This suggests that most of the variability in the evolution of the surface area of burns over time in the experimental study might be attributed to variability in these two rates. Finally, a probabilistic analysis is used in order to investigate in more detail the effect of variability in the values for the two rates on the healing process. Results of this analysis are presented and discussed.

Growth factor pathways in hypertrophic scars: Molecular pathogenesis and therapeutic implications

Hypertrophic scars represent the most common complication of skin injury and are caused by excessive cutaneous wound healing characterized by hypervascularity and pathological deposition of extracellular matrix (ECM) components. To date, the optimal and specific treatment methods for hypertrophic scars have not been available in the clinic. Current paradigm has established fibroblasts and myofibroblasts as pivotal effector cells in the pathophysiology of wound healing. Their biological properties including origin, proliferation, migration, contraction and ECM regulation have profound impacts on the progression and regression of hypertrophic scars. These complex processes are executed and modulated by a signaling network involving a number of growth factors and cytokines. Of particular importance is transforming growth factor-β, platelet-derived growth factor, connective tissue growth factor, epidermal growth factor, and vascular endothelial growth factor. This review article briefly describes the biological functions of fibroblasts and myofibroblasts during hypertrophic scars, and thereafter examines the up-to-date molecular knowledge on the roles of key growth factor pathways in the pathophysiology of hypertrophic scars. Importantly, the therapeutic implications and future challenges of these molecular discoveries are critically discussed in the hope of advancing therapeutic approaches to limit pathological scar formation.

Antecedent thermal injury worsens split-thickness skin graft quality: A clinically relevant porcine model of full-thickness burn, excision and grafting

Current standard of care for full-thickness burn is excision followed by autologous split-thickness skin graft placement. Skin grafts are also frequently used to cover surgical wounds not amenable to linear closure. While all grafts have potential to contract, clinical observation suggests that antecedent thermal injury worsens contraction and impairs functional and aesthetic outcomes. This study evaluates the impact of antecedent full-thickness burn on split-thickness skin graft scar outcomes and the potential mediating factors. Full-thickness contact burns (100°C, 30s) were created on the backs of anesthetized female Yorkshire Pigs. After seven days, burn eschar was tangentially excised and covered with 12/1000th inch (300μm) split-thickness skin graft. For comparison, unburned wounds were created by sharp excision to fat before graft application. From 7 to 120days post-grafting, planimetric measurements, digital imaging and biopsies for histology, immunohistochemistry and gene expression were obtained. At 120days post-grafting, the Observer Scar Assessment Scale, colorimetry, contour analysis and optical graft height assessments were performed. Twenty-nine porcine wounds were analyzed. All measured metrics of clinical skin quality were significantly worse (p<0.05) in burn injured wounds. Histological analysis supported objective clinical findings with marked scar-like collagen proliferation within the dermis, increased vascular density, and prolonged and increased cellular infiltration. Observed differences in contracture also correlated with earlier and more prominent myofibroblast differentiation as demonstrated by α-SMA staining. Antecedent thermal injury worsens split-thickness skin graft quality, likely by multiple mechanisms including burn-related inflammation, microscopically inadequate excision, and dysregulation of tissue remodeling. A valid, reliable, clinically relevant model of full-thickness burn, excision and skin replacement therapy has been demonstrated. Future research to enhance quality of skin replacement therapies should be directed toward modulation of inflammation and assessments for complete excision.

Myofibroblasts contribute to but are not necessary for wound contraction

Wound contraction facilitates tissue repair. The correct balance between too little contraction, which leads to non-healing wounds, and too much contraction, which leads to contractures, is important for optimal healing. Thus, understanding which cells cause wound contraction is necessary to optimize repair. Wound contraction is hypothesized to develop from myofibroblast (cells which express alpha-smooth muscle actin; ACTA2) contractility, while the role of fibroblast contractility is unknown. In this study, we utilized ACTA2 null mice to determine what role fibroblasts play in wound contraction. Human scar contractures were immunostained for ACTA2, beta-cytoplasmic actin (ACTB), and gamma-cytoplasmic actin (ACTG1). Full-thickness cutaneous wounds were created on dorsum of ACTA2(+/+) mice and strain-matching ACTA2(+/-) and ACTA2(-/-) mice. Wound contraction was quantified. Tissue was harvested for histologic, immunohistochemical and protein analysis. Compared with surrounding unwounded skin, human scar tissue showed increased expression of ACTA2, ACTB, and ACTG1. ACTA2 was focally expressed in clusters. ACTB and ACTG1 were widely, highly expressed throughout scar tissue. Wound contraction was significantly retarded in ACTA2(-/-) mice, as compared to ACTA2(+/+) controls. Control mice had increased epithelialization, cell proliferation, and neovascularization. ACTA2(-/-) mice had lower levels of apoptosis, and fewer total numbers of cells. Smaller amount of collagen deposition and immature collagen organization in ACTA2(-/-) mice demonstrate that wounds were more immature. These data demonstrate that myofibroblasts contribute to but are not necessary for wound contraction. Mechanisms by which fibroblasts promote wound contraction may include activation of contractile signaling pathways, which promote interaction between non-muscle myosin II and ACTB and ACTG1.

Autologous Graft Thickness Affects Scar Contraction and Quality in a Porcine Excisional Wound Model

BACKGROUND

Texture, color, and durability are important characteristics to consider for skin replacement in conspicuous and/or mobile regions of the body such as the face, neck, and hands. Although autograft thickness is a known determinant of skin quality, few studies have correlated the subjective and objective characters of skin graft healing with their associated morphologic and cellular profiles. Defining these relationships may help guide development and evaluation of future skin replacement strategies.

METHODS

Six-centimeter-diameter full-thickness wounds were created on the back of female Yorkshire pigs and covered by autografts of variable thicknesses. Skin quality was assessed on day 120 using an observer scar assessment score and objective determinations for scar contraction, erythema, pigmentation, and surface irregularities. Histological, histochemical, and immunohistochemical assessments were performed.

RESULTS

Thick grafts demonstrated lower observer scar assessment score (better quality) and decreased erythema, pigmentation, and surface irregularities. Histologically, thin grafts resulted in scar-like collagen proliferation while thick grafts preserves the dermal architecture. Increased vascularity and prolonged and increased cellular infiltration were observed among thin grafts. In addition, thin grafts contained predominately dense collagen fibers, whereas thick grafts had loosely arranged collagen. α-Smooth muscle actin staining for myofibroblasts was observed earlier and persisted longer among thinner grafts.

CONCLUSIONS

Graft thickness is an important determinant of skin quality. High-quality skin replacements are associated with preserved collagen architecture, decreased neovascularization, and decreased inflammatory cellular infiltration. This model, using autologous skin as a metric of quality, may give a more informative analysis of emerging skin replacement strategies.

Loureirin B inhibits fibroblast proliferation and extracellular matrix deposition in hypertrophic scar via TGF-β/Smad pathway

The ethanolic extract of Resina Draconis (RDEE) has been reported beneficial to normal wound healing yielding more regularly arranged collagen fibres. Loureirin B, a major component in RDEE, has been supposed to be effective on the prevention and treatment of pathological scars. To investigate the therapeutic effects of loureirin B on hypertrophic scar (HS), fibroblasts from human HS and normal skin (NS) were isolated. Results showed that loureirin B dose-dependently downregulated both mRNA and protein levels of type I collagen (ColI), type III collagen (ColIII) and α-smooth muscle actin (α-SMA) in HS fibroblasts. Loureirin B also suppressed fibroblast proliferative activity and redistributed cell cycle, but did not affect cell apoptosis. In vivo rabbit ear scar model, loureirin B significantly improved the arrangement and deposition of collagen fibres, decreased protein levels of ColI, ColIII and α-SMA and suppressed myofibroblast differentiation and scar proliferative activity. In NS fibroblasts, loureirin B effectively inhibited TGF-β1-induced upregulation of ColI, ColIII and α-SMA levels, myofibroblast differentiation and the activation of Smad2 and Smad3. Loureirin B also affected mRNA levels of major MMPs and TIMPs in TGF-β1-stimulated fibroblasts. Taken together, this study demonstrates that loureirin B could downregulate the expression of fibrosis-related molecules by regulating MMPs and TIMPs levels, inhibit scar fibroblast proliferation and suppress TGF-β1-induced fibrosis, during which TGF-β1/Smad2/3 pathway is likely involved. These findings suggest that loureirin B is a potential therapeutic compound for HS treatment.

Topical application of ALK5 inhibitor A-83-01 reduces burn wound contraction in rats by suppressing myofibroblast population

Burn scar contracture that follows the healing of deep dermal burns causes severe deformation and functional impairment. However, its current therapeutic interventions are limited with unsatisfactory outcomes. When we treated deep second-degree burns in rat skin with activin-like kinase 5 (ALK5) inhibitor A-83-01, it reduced wound contraction and enhanced the area of re-epithelialization so that the overall time for wound closing was not altered. In addition, it reduced myofibroblast population in the dermis of burn scar with a diminished deposition of its biomarker proteins such as α-SMA and collagen. Treatment of rat dermal fibroblast with A-83-01 inhibited transforming growth factor-β1 (TGF-β1)-dependent induction of α-SMA and collagen type I. Taken together, these results suggest that topical application of ALK5 inhibitor A-83-01 could be effective in preventing the contraction of burn wound without delaying the wound closure by virtue of its inhibitory activity against the TGF-β-induced increase of myofibroblast population.

Increased CCT-eta expression is a marker of latent and active disease and a modulator of fibroblast contractility in Dupuytren's contracture

Dupuytren's contracture (DC) is a fibroproliferative disorder of unknown etiology characterized by a scar-like contracture that develops in the palm and/or digits. We have previously reported that the eta subunit of the chaperonin containing T-complex polypeptide (CCT-eta) is increased in fibrotic wound healing, and is essential for the accumulation of α-smooth muscle actin (α-SMA) in fibroblasts. The purpose of this study was to determine if CCT-eta is similarly implicated in the aberrant fibrosis seen in DC and to investigate the role of CCT-eta in the behavior of myo/fibroblasts in DC. Fibroblasts were obtained from DC-affected palmar fascia, from adjacent phenotypically normal palmar fascia in the same DC patients (PF), and from non-DC palmar fascial tissues in patients undergoing carpal tunnel (CT) release. Inherent contractility in these three populations was examined using fibroblast-populated collagen lattices (FPCLs) and by cell traction force microscopy. Expression of CCT-eta and α-SMA protein was determined by Western blot. The effect of CCT-eta inhibition on the contractility of DC cells was determined by deploying an siRNA versus CCT-eta. DC cells were significantly more contractile than both matching palmar fascial (PF) cells and CT cells in both assays, with PF cells demonstrating an intermediate contractility in the FPCL assay. Whereas α-SMA protein was significantly increased only in DC cells compared to PF and CT cells, CCT-eta protein was significantly increased in both PF and DC cells compared to CT cells. siRNA-mediated depletion of CCT-eta inhibited the accumulation of both CCT-eta and α-SMA protein in DC cells, and also significantly decreased the contractility of treated DC cells. These observations suggest that increased expression of CCT-eta appears to be a marker for latent and active disease in these patients and to be essential for the increased contractility exhibited by these fibroblasts.

Strategies Demonstrating Efficacy in Reducing Wound Contraction In Vivo

SIGNIFICANCE

Scarring continues to present a significant clinical problem. Wound contraction leads to scarring and is mediated by myofibroblasts and contractile forces across the wound bed. Contracture formation can have a significant impact on the quality of life of the patient, particularly where function and appearance are affected.

RECENT ADVANCES

Novel tissue-engineered matrices, cell-based therapies, and medicinal therapeutics have shown significant reduction in wound contraction in in-vivo models, particularly at early time points. These have been accompanied in many cases by reduced numbers of myofibroblasts, and in some by increased angiogenesis and improved neodermal architecture.

CRITICAL ISSUES

There are no animal models that replicate all aspects of wound healing as seen in patients. Therefore, information obtained from in vivo studies should be assessed critically. Additional studies, in particular those that seek to elucidate the mechanisms by which novel therapies reduce contraction, are needed to gain sufficient confidence to move into clinical testing.

FUTURE DIRECTIONS

The use of knockout mouse models in particular has generated significant advances in knowledge of the mechanisms behind myofibroblast conversion and other factors involved in generating tension across the wound. Medicinal therapeutics and tissue-engineering approaches that seek to disrupt/alter these pathways hold much promise for future development and translation to clinical practice.

Alternatives for animal wound model systems

In this chapter a review of animal model systems already being utilized to study normal and pathologic wound healing is provided. We also go into details on alternatives for animal wound model systems. The case is made for limitations in the various approaches. We also discuss the benefits/limitations of in vitro/ex vivo systems bringing everything up to date with our current work on developing a cell-based reporter system for diabetic wound healing.

Epithelial-mesenchymal transition, TGF-β, and osteopontin in wound healing and tissue remodeling after injury

Epithelial-mesenchymal transition (EMT) is a process essential to wound healing and tissue remodeling after a thermal burn or other injury. EMT is characterized by phenotypic changes in epithelial cells that render them apolar, with decreased cell-cell adhesions, increased motility, and changes in cytoskeletal architecture similar to mesenchymal stem cells. With regard to healing a thermal burn wound, many facets of wound healing necessitate cells to undergo these phenotypic changes; two will be described in the following review. The first is the differentiation of epithelial cells into myofibroblasts that rebuild the extracellular matrix and facilitate wound contraction. The second is reepithelialization by keratinocytes. The primary cytokine signal identified in the literature that triggers EMT is transforming growth factor (TGF)-β. In addition to its vital role in the induction of EMT, TGF-β has many other roles in the wound healing process. The following review will provide evidence that EMT is a central event in wound healing. It will also show the importance of a regulated amount of TGF-β for proper wound healing. Finally, osteopontin will be briefly discussed with its relation to wound healing and its connections to EMT and TGF-β.