Full-Thickness Thermal Injury Delays Wound Closure in a Murine Model

An in silico modeling approach to understanding the dynamics of the post-burn immune response

Introduction

Burns are characterized by a massive and prolonged acute inflammation, which persists for up to months after the initial trauma. Due to the complexity of the inflammatory process, Predicting the dynamics of wound healing process can be challenging for burn injuries. The aim of this study was to develop simulation models for the post-burn immune response based on (pre)clinical data.

Methods

The simulation domain was separated into blood and tissue compartments. Each of these compartments contained solutes and cell agents. Solutes comprise pro-inflammatory cytokines, anti-inflammatory cytokines and inflammation triggering factors. The solutes diffuse around the domain based on their concentration profiles. The cells include mast cells, neutrophils, and macrophages, and were modeled as independent agents. The cells are motile and exhibit chemotaxis based on concentrations gradients of the solutes. In addition, the cells secrete various solutes that in turn alter the dynamics and responses of the burn wound system.

Results

We developed an Glazier-Graner-Hogeweg method-based model (GGH) to capture the complexities associated with the dynamics of inflammation after burn injuries, including changes in cell counts and cytokine levels. Through simulations from day 0 - 4 post-burn, we successfully identified key factors influencing the acute inflammatory response, i.e., the initial number of endothelial cells, the chemotaxis threshold, and the level of chemoattractants.

Conclusion

Our findings highlight the pivotal role of the initial endothelial cell count as a key parameter for intensity of inflammation and progression of acute inflammation, 0 - 4 days post-burn.

Cassia Angustifolia Primed ASCs Accelerate Burn Wound Healing by Modulation of Inflammatory Response

BACKGROUND

Thermal traumas impose a huge burden on healthcare systems. This merits the need for advanced but cost-effective remedies with clinical prospects. In this context, we prepared a regenerative 3D-construct comprising of Cassia angustifolia extract (SM) primed adipose-derived stem cells (ASCs) laden amniotic membrane for faster burn wound repair.

METHODS

ASCs were preconditioned with SM (30 µg/ml for 24 h), and subsequently exposed to in-vitro thermal injury (51 °C,10 min). In-vivo thermal injury was induced by placing pre-heated copper-disc (2 cm diameter) on dorsum of the Wistar rats. ASCs (2.0 × 105) pre-treated with SM (SM-ASCs), cultured on stromal side of amniotic membrane (AM) were transplanted in rat heat-injury model. Non-transplanted heat-injured rats and non-heat-injured rats were kept as controls.

RESULTS

The significantly upregulated expression of IGF1, SDF1A, TGFβ1, VEGF, GSS, GSR, IL4, BCL2 genes and downregulation of BAX, IL6, TNFα, and NFkB1 in SM-ASCs in in-vitro and in-vivo settings confirmed its potential in promoting cell-proliferation, migration, angiogenesis, antioxidant, cell-survival, anti-inflammatory, and wound healing activity. Moreover, SM-ASCs induced early wound closure, better architecture, normal epidermal thickness, orderly-arranged collagen fibers, and well-developed skin appendages in healed rat-skin transplanted with AM+SM-ASCs, additionally confirmed by increased expression of structural genes (Krt1, Krt8, Krt19, Desmin, Vimentin, α-Sma) in comparison to untreated-ASCs laden-AM transplanted in heat injured rats.

CONCLUSION

SM priming effectively enabled ASCs to counter thermal injury by significantly enhancing cell survival and reducing inflammation upon transplantation. This study provides bases for development of effective combinational therapies (natural scaffold, medicine, and stem cells) with clinical prospects for treating burn wounds.

Multifunctional effects of wound dressing based on chitosan-coordinated argentum with resistant bacterial penetration

Third-degree scald, causing serious tissue destruction with continuous pain, easily leads to microbial infections and delayed wound healing. Therefore, a multifunctional treatment is attractive for seriously damaged tissue. Herein, carboxymethyl chitosan-coordinated argentum (Ag-CMC) was synthesized via a complexation method, and then the Ag⁺ release, antibacterial activity, biocompatibility, pain relief and wound healing properties of Ag-CMC were investigated in vitro and in vivo. The results revealed that Ag⁺ had interacted with carboxymethyl chitosan, containing approximately 1.2% of silver. The Ag-CMC (50-200 μg/mL) with Ag⁺ sustained release exhibited significant antibacterial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, drug-resistant E. coli, PA, MRSA and good biocompatibility with L929 cells. Furthermore, antibacterial and wound healing experiments demonstrated that Ag-CMC achieved an effective contraction rate of 90% after 28 days by accelerating re-epithelialization, regulating inflammation response, relieving pain and infections. Therefore, Ag-CMC is a safe multifunctional treatment for wound healing and infections.

IGF-1-Expressing Placenta-Derived Mesenchymal Stem Cells Promote Scalding Wound Healing

BACKGROUND

Stem cell-based regenerative therapy is a novel approach to severe damaged skin. Perinatal tissues such as placenta are considered as promising alternatives. The present study aimed to investigate the effect of insulin-like growth factor-1 (IGF-1)-expressing placenta-derived mesenchymal stem cells (hPMSCs) on healing of burn wounds.

MATERIALS AND METHODS

hPMSCs were isolated from human placenta, and IGF-1 was transducted into hPMSCs via lentivirus. Flow cytometry and MTT assay were performed to assess cell apoptosis and viability, respectively. Immunostaining of CK19 and ki67 was for evaluating epithelial differentiation ability and cell proliferation. For in vivo studies, we established a mouse model of scalding and performed local administration of IGF-1-expressing hPMSCs via subcutaneous injection. Wound histology was analyzed with H&E staining. The expression of fibrogenic cytokines was detected by western blot. The production of pro-inflammatory factors was measured by ELISA.

RESULTS

Overexpression of IGF-1 promoted cell proliferation and epithelial differentiation of hPMSCs in vitro and in vivo. Mice with burn injury displayed increased wound contraction and healing rates following treatment with IGF-1-expressing hPMSCs. There was less inflammatory infiltration and reduced collagen disposition in the presence of IGF-1 at the wound site. Administration of IGF-1-expressing hPMSCs suppressed inflammation by decreasing the levels of pro-inflammatory cytokines including tumor necrosis factor-α, interleukin-1β, and interleukin-6. Besides, IGF-1 increased VEGF expression, and decreased TGF-β1, collagen I and collagen III expressions in vivo.

CONCLUSIONS

IGF-1-expressing PMSCs promotes cell proliferation and epithelial differentiation, inhibits inflammation and collagen deposition, and thus contributes to wound healing.

Quality of coding within clinical datasets: A case-study using burn-related hospitalizations

The quality of clinical data held in administrative databases is crucial for appropriate funding of health care services. As Diagnosis-Related Groups (DRGs) continue to play an important role in hospital payment mechanisms, proper coding of diagnoses and procedures is of most concern. This study used an administrative, nationwide Portuguese inpatient database to characterize and assess coding patterns in burn-related hospitalization data, with a special focus on identifying suspected miscoding practices that could be affecting APR-DRG (All-Patient Refined Diagnosis-Related Groups) classification. Using coded clinical data of 4,182 burn-related admissions occurred between 2011 and 2015, we compared APR-DRG and Severity of Illness (SOI) frequencies between hospitals with a burn unit in Portugal. The frequencies of individual diagnosis and procedure codes among episodes grouped within the same APR-DRG were also compared. Hospitals with a burn unit in Portugal differed significantly in the frequencies of APR-DRGs 842 and 844. Proper coding of extensive third-degree burns might be related with the observed discrepant frequencies of APR-DRGs across the evaluated hospitals. Facilities also differed significantly concerning the proportions of SOI levels in certain APR-DRGs. Significant differences in reporting certain comorbidities and common hospital procedures, especially non-operating room procedures, might have influenced the observed discrepancies in SOI levels. Moreover, there seems to be a lack of standard in coding debridement procedures among the evaluated hospitals. Overall, we found some suspected coding patterns that could potentially be associated with miscoding practices impacting APR-DRG classification. Those findings could not only be relevant for planning future audit processes and improving medical coding practices, but also for discussing quality and desirable features of burn-related clinical data, keeping in mind their use for other purposes beyond DRG grouping, namely clinical and health care services research, as well as health care management.

Short time insulin treatment post burn improves elastic-collagen rearrangement and reepithelization

Extensive burn may cause acute resistance to insulin, which accentuates hypermetabolism, impairs glucose metabolism, immune dysfunction and risks of sepsis. To minimize these effects, insulin is used as a treatment. The purpose was to analyze the collagen-elastic arrangement effects of insulin on the burned skin. Wistar rats were assigned in groups: control (C); control with insulin (C + I); scald burn injury (SBI); and SBI with insulin (SBI+ I). SBI were submitted to 45% total body surface area burn and the insulin-treated groups received insulin (5 UI/Kg/day) for 4 or 14 days (d). Insulin levels, glucose tolerance test and HOMA index were determined. The skin sections were analyzed for histophatological and morphoquantitative data. Histopathological findings showed increased reepithelization of SBI+ I and formation of a new muscle layer after 14 days. In the collagen-elastic arrangement, insulin for 4 days increased the volume fraction (Vv) of thin collagen and elastic fibers. After 14 days, independently of injury, insulin decreased the elastic fibers. Insulin was able to reverse damages in the collagen-elastic rearrangement and stimulate reepithelization after 4 days. Untreated scald-burned animals showed higher Vv of thick collagen after 4 days, while those treated had a higher Vv of thin collagen. The Vv of elastic fibers was increased in SBI+ I for 4 days. In conclusion, insulin treatment was able to stimulate reepithelization. It also reversed the damages to the collagen-elastic arrangement in the scald-burned group, improving the organization of thin collagen and increasing the Vv of elastic fibers in the injured group treated with insulin for a short time, that is, for 4 days.

The Cutaneous Inflammatory Response to Thermal Burn Injury in a Murine Model

Many burn interventions aim to target the inflammatory response as a means of enhancing healing or limiting hypertrophic scarring. Murine models of human burns have been developed, but the inflammatory response to injury in these models has not been well defined. The aim of this study was to profile inflammatory cell populations and gene expression relative to healing and scarring in a murine model of thermal burns. Cutaneous injuries were created on the dorsal region of C57Bl/6 mice using a heated metal rod. Animals were euthanized at selected time points over ten weeks, with the lesions evaluated using macroscopic measurements, histology, immunofluorescent histochemistry and quantitative PCR. The burn method generated a reproducible, partial-thickness injury that healed within two weeks through both contraction and re-epithelialization, in a manner similar to human burns. The injury caused an immediate increase in pro-inflammatory cytokine and chemokine expression, coinciding with an influx of neutrophils, and the disappearance of Langerhans cells and mast cells. This preceded an influx of dendritic cells and macrophages, a quarter of which displayed an inflammatory (M1) phenotype, with both populations peaking at closure. As with human burns, the residual scar increased in size, epidermal and dermal thickness, and mast cell numbers over 10 weeks, but abnormal collagen I-collagen III ratios, fibre organization and macrophage populations resolved 3–4 weeks after closure. Characterisation of the inflammatory response in this promising murine burn model will assist future studies of burn complications and aid in the preclinical testing of new anti-inflammatory and anti-scarring therapies.

Standardization of deep partial-thickness scald burns in C57BL/6 mice

Mouse burn models are used to understand the wound healing process and having a reproducible model is important. The different protocols used by researchers can lead to differences in depth of partial-thickness burn wounds. Additionally, standardizing a protocol for mouse burns in the laboratory for one strain may result in substantially different results in other strains. In our current study we describe the model development of a deep partial-thickness burn in C57BL/6 mice using hot water scalding as the source of thermal injury. As part of our model development we designed a template with specifications to allow for even contact of bare mouse skin (2×3 cm) with hot water while protecting the rest of the mouse. Burn depth was evaluated with H&E, Masson's trichrome, and TUNEL staining. Final results were validated with pathology analysis. A water temperature of 54°C with a scalding time of 20 seconds produced consistent deep partial-thickness burns with available equipment described. Other than temperature and time, factors such as template materials and cooling steps after the burn could affect the uniformity of the burns. These findings are useful to burn research by providing some key parameters essential for researchers to simplify the development of their own mouse burn models.

Platelet and coagulation function before and after burn and smoke inhalation injury in sheep

BACKGROUND

Smoke inhalation and burn injury remain a major source of morbidity and mortality. There is known dysregulation of hemostasis in burn patients, but either hypercoagulation or hypocoagulation states are reported. Sheep are an established animal model for studying burn pathology and provide robust data on hemostatic function at baseline and after injury.

METHODS

After an IACUC-approved protocol, 15 sheep were anesthetized and subjected to a 40% full thickness burn with smoke inhalation. Blood was sampled at baseline, 1 day postinjury (early effects) and days 2, 3, and 4 (late effects) after injury. Assays at each timepoint assessed: hemostatic function by thromboelastography (TEG), platelet counts and function by flow cytometry and aggregometry, coagulation protein levels, and free hemoglobin. Data were analyzed by the Wilcoxon paired test (nonparametric) with significance set at less than 0.05.

RESULTS

By 24 hours postinjury, platelet counts had dropped, whereas the percent activated platelets increased. Absolute platelet functional response to the agonist adenosine diphosphate (ADP) decreased, whereas response to collagen showed no significant difference. On a per platelet basis, ADP response was unchanged, whereas the collagen response was elevated. Prothrombin time and activated partial thromboplastin time were prolonged. TEG parameters decreased significantly from baseline. Fibrinogen and factor V were trending up; coagulation proteins ATIII, factors IX and X were decreased.Late effects were followed in six animals. At day 4, platelet counts remained depressed compared with baseline with a nadir at day 2; responses to agonist on a per platelet basis remained the same for ADP and stayed elevated for collagen. Platelets continued to have elevated activation levels. Fibrinogen and factor V remained significantly elevated, whereas TEG parameters and prothrombin time, factors IX and X returned to near baseline levels.

CONCLUSION

Coagulation parameters and hemostasis are dysregulated in sheep after smoke inhalation and burn. By 24 hours, sheep were hypocoagulable and subsequently became hypercoagulable by day 4. These results suggest a three-stage coagulopathy in burn injuries with a known early consumptive hypercoagulable state which is followed by a relatively hypocoagulable state with increased bleeding risk and then a return to a relatively unknown hypercoagulability with increased susceptibility to thrombotic disorders.

Downregulation of let-7b promotes COL1A1 and COL1A2 expression in dermis and skin fibroblasts during heat wound repair

MicroRNAs (miRs), a class of non‑coding RNAs 18‑25 nucleotides in length, generally serve suppressive role in the regulation of gene expression via directly binding to the 3'‑untranslated region (UTR) of their target mRNA. Previous studies have identified several miRs to be involved in thermal injury repair. However, the role of miR let‑7b during the recovery of thermal injury, in addition to the underlying mechanisms, has not previously been studied. In the present study, the expression of let‑7b was observed to be significantly increased in skin tissue shortly following thermal injury, however, gradually reduced during the recovery of thermal injury. Notably, similar findings were observed in heat‑denatured skin fibroblasts. Furthermore, collagen, type I, alpha 1 (COL1A1) and collagen, type I, alpha 2 (COL1A2), which are associated with the synthesis of type I collagen, were identified as two targets of let‑7b in skin fibroblasts. The overexpression of let‑7b was observed to upregulate the protein expression levels of COL1A1 and COL1A2, while knockdown of let‑7b reduced the levels of COL1A1 and COL1A2 in skin fibroblasts. Furthermore, COL1A1 and COL1A2 were significantly downregulated shortly following thermal injury, while gradually upregulated during healing, in heat‑damaged skin tissue and skin fibroblasts, with the expression profiles opposite to that of let‑7b. Taken together, this suggests that the downregulation of let‑7b in heat‑damaged dermis promotes the synthesis of type I collagen and thus aids in burn wound repair.