Mouse Model of Burn Wound and Infection: Thermal (Hot Air) Lesion-Induced Immunosuppression

New burn model for developing consistent second- and third-degree burn injuries in rats

OBJECTIVE

This study's aim was: (1) introduce the digital drying oven as a reproducible, controllable, and accurate heating device for burn model creation. (2) Define the heating temperature appropriate for developing consistent second and third-degree burn injuries in rats.

RESULTS

Burns appeared deeper with more distinct borders in groups (B) and (C) than in group (A). The stainless-steel rod at 100 ºC created burn injuries of the second degree, evidenced by the sloughing of the epidermis and necrosis in the epithelium and upper part of the dermis. Heating at 150 and 200 ºC created third-degree burn injuries, where necrosis involved the epidermis and dermis and extended to the subcutaneous fat and muscles. The depth of the burn wound in the group (B) (371.2 ± 41.3 μm) and (C) (385.2 ± 38.0 μm) was significantly deeper compared with the group (A) (178 ± 46.6 μm) (P < 0.001). The digital drying oven is a reliable, reproducible, and controllable heating device for creating burn models. The stainless-steel rod (63 g and 8 mm) heated at 100 and 150 ºC with a contact time of 30 s is adequate for creating consistent second and third-degree burn injuries in rats, respectively.

Characterization of heterogeneous skin constructs for full thickness skin regeneration in murine wound models

An autologous heterogeneous skin construct (AHSC) has been developed and used clinically as an alternative to traditional skin grafting techniques for treatment of cutaneous defects. AHSC is manufactured from a small piece of healthy skin in a manner that preserves endogenous regenerative cellular populations. To date however, specific cellular and non-cellular contributions of AHSC to the epidermal and dermal layers of closed wounds have not been well characterized given limited clinical opportunity for graft biopsy following wound closure. To address this limitation, a three-part mouse full-thickness excisional wound model was developed for histologic and macroscopic graft tracing. First, fluorescent mouse-derived AHSC (mHSC) was allografted onto non-fluorescent recipient mice to enable macroscopic and histologic time course evaluation of wound closure. Next, mHSC-derived from haired pigmented mice was allografted onto gender- and major histocompatibility complex (MHC)-mismatched athymic nude mouse recipients. Resulting grafts were distinguished from recipient murine skin via immunohistochemistry. Finally, human-derived AHSC (hHSC) was xenografted onto athymic nude mice to evaluate engraftment and hHSC contribution to wound closure. Experiments demonstrated that mHSC and hHSC facilitated wound closure through production of viable, proliferative cellular material and promoted full-thickness skin regeneration, including hair follicles and glands in dermal compartments. This combined macroscopic and histologic approach to tracing AHSC-treated wounds from engraftment to closure enabled robust profiling of regenerated architecture and further understanding of processes underlying AHSC mechanism of action. These models may be applied to a variety of wound care investigations, including those requiring longitudinal assessments of healing and targeted identification of donor and recipient tissue contributions.

Lactoferricin inspired peptide AMC-109 augments the effect of ciprofloxacin against Pseudomonas aeruginosa biofilm in chronic murine wounds

OBJECTIVES

The pathophysiology of chronic wounds is characterized by prolonged inflammation, low mitogenic-activity, high protease-/low inhibitor-activity, microbiota changes and biofilm formation, in combination with the etiology of the original insult. One strategy to promote healing is to terminate the parasitism-like-relationship between the biofilm-growing-pathogen and the host response. The antimicrobial peptide AMC-109 is a potential treatment with low resistance-potential and broad-spectrum coverage with rapid bactericidal effect. Our purpose was to investigate if adjunctive AMC-109 could augment the ciprofloxacin effect in a chronic Pseudomonas aeruginosa wound model.

METHODS

Third-degree-burns were inflicted on 33BALB/c mice. P.Aeruginosa embedded in seaweed alginate was injected under the eschar to mimic a biofilm. Mice were randomized to receive AMC-109, combined AMC-109 and ciprofloxacin, ciprofloxacin or placebo for 5 days followed by sample collection.

RESULTS

Lower bacterial load was seen in the double treated group when compared to both monotherapy groups (AMC-109, p=0.008 and ciprofloxacin, p=0.03). To evaluate the innate host response, quantification of cytokines and growth factors were performed. The pro-inflammatory response was dampened in the double-treated mice, compared to the mono-ciprofloxacin-treated group (p=0.0009). A lower mobilization of neutrophils from the bone marrow was indicated by reduced granulocyte-colony-stimulating factor in all treatment groups compared to the placebo group. Improved tissue-remodeling was indicated by the highest level of tissue inhibitor of metalloproteases and low metalloprotease level in the double-treated group.

CONCLUSIONS

AMC-109 revealed adjunctive anti-pseudomonas abilities augmenting the antimicrobial effect of ciprofloxacin in this wound model. The study indicates a potential role for AMC-109 in treating chronic wounds with complicating biofilm infections.

Animal models in vaccinology: state of the art and future perspectives for an animal-free approach

Vaccine discovery and development is mainly driven by studies on immunogenicity and safety based on the appropriate animal models. In this review we will describe the importance of animal models in vaccinology, from research and development to pre-licensure and post-licensure commitments with particular emphasis on the advantages and limitations of each animal species. Finally, we will describe the most modern technologies, the new in vitro and ex vivo models and the new advances in the field which may drive into a new era of 'animal free' vaccinology.

A Next-Generation Sequencing of Plasma Exosome-Derived microRNAs and Target Gene Analysis with a Microarray Database of Thermally Injured Skins: Identification of Blood-to-Tissue Interactions at Early Burn Stage

BACKGROUND

Plasma exosome-derived microRNA (miRNA) profiles following thermal injury and their relationship with gene expression derangements in burned skin remain unexplored. This study focused on the identification of key miRNA-mRNA axes in potential blood-to-tissue interactions at early burn stage.

METHODS

Plasma exosomes were obtained from 6 severe burn patients 4-7 days post injury and 6 healthy volunteers. Next-generation sequencing (NGS) of exosomal small RNAs presented the differentially expressed miRNAs (DEMs). Target genes of the DEMs were predicted in the mirDIP database. Dataset GSE8056 was enrolled to acquire differentially expressed genes (DEGs) in burned skin compared to normal skin. Overlap between the DEGs and target genes of the DEMs were focus genes. The protein-protein interaction (PPI) network and enrichment analyses of the focus genes demonstrated hub genes and suggested underlying mechanisms and pathways. The hub genes and upstream DEMs were selected to construct key miRNA-mRNA axes.

RESULTS

The NGS of plasma exosome-derived small RNAs identified 85 DEMs (14 downregulated miRNAs and 71 upregulated miRNAs) with 12,901 predicted target genes. Dataset GSE8056 exhibited 1861 DEGs in partial-thickness burned skins 4-7 days postburn. The overlap between DEGs and target genes of DEMs displayed 1058 focus genes. The top 9 hub genes (CDK1, CCNB1, CCNA2, BUB1B, PLK1, KIF11, AURKA, NUSAP1 and CDCA8) in the PPI network of the focus genes pointed to 16 upstream miRNAs in DEMs, including 4 downregulated miRNAs (hsa-miR-6848-3p, has-miR-4684-3p, has-miR-4786-5p and has-miR-365a-5p) and 12 upregulated miRNAs (hsa-miR-6751-3p, hsa-miR-718, hsa-miR-4754, hsa-miR-6754-3p, hsa-miR-4739, hsa-miR-6739-5p, hsa-miR-6884-3p, hsa-miR-1224-3p, hsa-miR-6878-3p, hsa-miR-6795-3p, hsa-miR-550a-3p, and hsa-miR-550b-3p). A key miRNA-mRNA network in potential blood-to-tissue interactions at early burn stage was therefore constructed.

CONCLUSION

An NGS and bioinformatic analysis in the study identified key miRNA-mRNA axes in potential blood-to-tissue interactions at early burn stage, suggesting plasma exosome-derived miRNAs may impact on the alteration patterns of gene expressions in a burn wound.

Evaluation of Pseudomonas aeruginosa pathogenesis and therapeutics in military-relevant animal infection models

Modern combat-related injuries are often associated with acute polytrauma. As a consequence of severe combat-related injuries, a dysregulated immune response results in serious infectious complications. The gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that often causes life-threatening bloodstream, lung, bone, urinary tract, and wound infections following combat-related injuries. The rise in the number of multidrug-resistant P. aeruginosa strains has elevated its importance to civilian clinicians and military medicine. Development of novel therapeutics and treatment options for P. aeruginosa infections is urgently needed. During the process of drug discovery and therapeutic testing, in vivo testing in animal models is a critical step in the bench-to-bedside approach, and required for Food and Drug Administration approval. Here, we review current and past literature with a focus on combat injury-relevant animal models often used to understand infection development, the interplay between P. aeruginosa and the host, and evaluation of novel treatments. Specifically, this review focuses on the following animal infection models: wound, burn, bone, lung, urinary tract, foreign body, and sepsis.

Recent Advances in Experimental Burn Models

Experimental burn models are essential tools for simulating human burn injuries and exploring the consequences of burns or new treatment strategies. Unlike clinical studies, experimental models allow a direct comparison of different aspects of burns under controlled conditions and thereby provide relevant information on the molecular mechanisms of tissue damage and wound healing, as well as potential therapeutic targets. While most comparative burn studies are performed in animal models, a few human or humanized models have been successfully employed to study local events at the injury site. However, the consensus between animal and human studies regarding the cellular and molecular nature of systemic inflammatory response syndrome (SIRS), scarring, and neovascularization is limited. The many interspecies differences prohibit the outcomes of animal model studies from being fully translated into the human system. Thus, the development of more targeted, individualized treatments for burn injuries remains a major challenge in this field. This review focuses on the latest progress in experimental burn models achieved since 2016, and summarizes the outcomes regarding potential methodological improvements, assessments of molecular responses to injury, and therapeutic advances.

Adjunctive S100A8/A9 Immunomodulation Hinders Ciprofloxacin Resistance in Pseudomonas aeruginosa in a Murine Biofilm Wound Model

Objective

Pseudomonas aeruginosa is known to contribute to the pathogenesis of chronic wounds by biofilm-establishment with increased tolerance to host response and antibiotics. The neutrophil-factor S100A8/A9 has a promising adjuvant effect when combined with ciprofloxacin, measured by quantitative bacteriology, and increased anti- and lowered pro-inflammatory proteins. We speculated whether a S100A8/A9 supplement could prevent ciprofloxacin resistance in infected wounds.

Method

Full-thickness 2.9cm²-necrosis was inflicted on 32 mice. On day 4, P.aeruginosa in seaweed alginate was injected sub-eschar to mimic a mono-pathogenic biofilm. Mice were randomized to receive ciprofloxacin and S100A8/A9 (n=14), ciprofloxacin (n=12) or saline (n=6). Half of the mice in each group were euthanized day 6 and the remaining day 10 post-infection. Mice were treated until sacrifice. Primary endpoint was the appearance of ciprofloxacin resistant P.aeruginosa. The study was further evaluated by genetic characterization of resistance, means of quantitative bacteriology, wound-size and cytokine-production.

Results

Three mice receiving ciprofloxacin monotherapy developed resistance after 14 days. None of the mice receiving combination therapy changed resistance pattern. Sequencing of fluoroquinolone-resistance determining regions in the ciprofloxacin resistant isolates identified two high-resistant strains mutated in gyrA C248T (MIC>32µg/ml) and a gyr B mutation was found in the sample with low level resistance (MIC=3µg/ml). Bacterial densities in wounds were lower in the dual treated group compared to the placebo group on both termination days.

Conclusion

This study supports the ciprofloxacin augmenting effect and indicates a protective effect in terms of hindered ciprofloxacin resistance of adjuvant S100A8/A9 in P.aeruginosa biofilm infected chronic wounds.

Lignin-Incorporated Nanogel Serving As an Antioxidant Biomaterial for Wound Healing

Oxidative phosphorylation is an important biological process in the body to produce energy, during which oxygen free radicals are generated as byproduct. Excessive oxygen free radicals cause cell death and reduce the rate of tissue regeneration and healing in a wound. Lignin is a natural antioxidant derived from plants, but its biomedical application is restricted because of the uncertain biocompatibility. In this work, we developed a lignin-incorporated nanogel and explored its application for wound healing. Lignin was extracted from coconut husks and determined to have strong antioxidant activity (IC₅₀ = 25.7 ppm). Various amounts of lignin were incorporated into thermoresponsive nanogels, which were produced from polyurethane copolymers of polyethylene glycol (PEG), polypropylene glycol (PPG), and polydimethylsiloxane (PDMS). It was shown that the addition of lignin had minimal effects on the gelation and rheological properties of the nanogel but slightly increased the critical micelle concentration (CMC) of poly(PEG/PPG/PDMS urethane) copolymer from 3.38 × 10^-4 g mL^-1 to 4.61 × 10^-4 g mL^-1. The lignin-incorporated nanogels did not display detectable cytotoxicity. The lignin-incorporated nanogel possessed antioxidant activity, as it reduced the active oxygen level, protecting the LO2 cells from apoptosis caused by oxidative stress. More importantly, in vivo studies demonstrated that the lignin-incorporated nanogels accelerated the healing of burn wounds in mice as proved by the increased expression of Ki67, one marker of cell proliferation. The present work demonstrates that lignin-incorporated nanogel could serve as an antioxidant wound-dressing material and facilitate the wound healing.

Active neutrophil responses counteract Candida albicans burn wound infection of ex vivo human skin explants

Burn wounds are highly susceptible sites for colonization and infection by bacteria and fungi. Large wound surface, impaired local immunity, and broad-spectrum antibiotic therapy support growth of opportunistic fungi such as Candida albicans, which may lead to invasive candidiasis. Currently, it remains unknown whether depressed host defenses or fungal virulence drive the progression of burn wound candidiasis. Here we established an ex vivo burn wound model, where wounds were inflicted by applying preheated soldering iron to human skin explants, resulting in highly reproducible deep second-degree burn wounds. Eschar removal by debridement allowed for deeper C. albicans penetration into the burned tissue associated with prominent filamentation. Active migration of resident tissue neutrophils towards the damaged tissue and release of pro-inflammatory cytokine IL-1β accompanied the burn. The neutrophil recruitment was further increased upon supplementation of the model with fresh immune cells. Wound area and depth decreased over time, indicating healing of the damaged tissue. Importantly, prominent neutrophil presence at the infected site correlated to the limited penetration of C. albicans into the burned tissue. Altogether, we established a reproducible burn wound model of candidiasis using ex vivo human skin explants, where immune responses actively control the progression of infection and promote tissue healing.

An Invertebrate Burn Wound Model That Recapitulates the Hallmarks of Burn Trauma and Infection Seen in Mammalian Models

The primary reason for skin graft failure and the mortality of burn wound patients, particularly those in burn intensive care centers, is bacterial infection. Several animal models exist to study burn wound pathogens. The most commonly used model is the mouse, which can be used to study virulence determinants and pathogenicity of a wide range of clinically relevant burn wound pathogens. However, animal models of burn wound pathogenicity are governed by strict ethical guidelines and hindered by high levels of animal suffering and the high level of training that is required to achieve consistent reproducible results. In this study, we describe for the first time an invertebrate model of burn trauma and concomitant wound infection. We demonstrate that this model recapitulates many of the hallmarks of burn trauma and wound infection seen in mammalian models and in human patients. We outline how this model can be used to discriminate between high and low pathogenicity strains of two of the most common burn wound colonizers Pseudomonas aeruginosa and Staphylococcus aureus, and multi-drug resistant Acinetobacter baumannii. This model is less ethically challenging than traditional vertebrate burn wound models and has the capacity to enable experiments such as high throughput screening of both anti-infective compounds and genetic mutant libraries.

Laryngotracheal Reconstruction in the Pediatric Burn Patient: Surgical Techniques and Decision Making

The management of laryngotracheal stenosis (LTS) in the pediatric burn patient is complex and requires a multidisciplinary approach. The mainstay of treatment for LTS is laryngotracheal reconstruction (LTR), however, limited reports of burn-specific LTR techniques exist. Here, we provide insight into the initial airway evaluation, surgical decision making, anesthetic challenges, and incision modifications based on our experience in treating patients with this pathology. The initial airway evaluation can be complicated by microstomia, trismus, and neck contractures-the authors recommend treatment of these complications prior to initial airway evaluation to optimize safety. The surgical decision making regarding pursuing single-stage LTR, double-stage LTR, and 1.5-stage LTR can be challenging-the authors recommend 1.5-stage LTR when possible due to the extra safety of rescue tracheostomy and the decreased risk of granuloma, which is especially important in pro-inflammatory burn physiology. Anesthetic challenges include obtaining intravenous access, securing the airway, and intravenous induction-the authors recommend peripherally inserted central catheter when appropriate, utilizing information from the initial airway evaluation to secure the airway, and avoidance of succinylcholine upon induction. Neck and chest incisions are often within the TBSA covered by the burn injury-the authors recommend modifying typical incisions to cover unaffected skin whenever possible in order to limit infection and prevent wound healing complications. Pediatric LTR in the burn patient is challenging, but can be safe when the surgeon is thoughtful in their decision making.

Current status and future outlook of nano-based systems for burn wound management

Wound healing process is a natural and intricate response of the body to its injuries and includes a well-orchestrated sequence of biochemical and cellular phenomena to restore the integrity of skin and injured tissues. Complex nature and associated complications of burn wounds lead to an incomplete and prolonged recovery of these types of wounds. Among different materials and systems which have been used in treating the wounds, nanotechnology driven therapeutic systems showed a great opportunity to improvement and enhancement of the healing process of different type of wounds. The aim of this study is to provide an overview of the recent studies about the various nanotechnology-based management of burn wounds and the future outlook of these systems in this area. Laboratory and animal models for assessing the efficacy of these systems in burn wound management also discussed.

Developing a Simple Burn Model in Rats of Different Ages

This article describes a simple and safe model of partial and full thickness burn injury in rats of different ages, which will be essential in our future burn research to explore the age-related mechanism of wound repair and new therapies for burn injuries. A self-made metal column, which was heated in a boiling water bath, was applied for different time periods to the lower back of rats of different ages in burn creation. Wounds were observed visibly at different time points postburn. Biopsies were obtained and examined at 72-hour postburn to determine the depth of burns. The contact durations producing the desired depth of injury in the rat model under constant temperature and pressure were: 3 seconds (deep second degree) and 5 seconds (third degree) in 1-month-old rats; 3 seconds (superficial second degree), 5 seconds (deep second degree), and 7-9 seconds (third degree) in 2-month-old rats; 3-5 seconds (superficial second degree), 7-9 seconds (deep second degree), and 11-13 seconds (third degree) in 12- and 18-month-old rats. This reliable and reproducible experimental model produces consistent burn injuries in rats of different ages by regulating the contact durations, which will help us to understand the underlying pathophysiology of burn injuries and develop novel therapeutic modalities for burn patients of different ages.

Non-Propellant Foams of Green Nano-Silver and Sulfadiazine: Development and In Vivo Evaluation for Burn Wounds

PURPOSE

A non-propellant based foam (NPF) system was developed incorporating the antibiotics, pectin capped green nano-silver and sulfadiazine (SD) for the topical treatment of burn wounds as a convenient alternative to the existing therapies.

METHODS

NPF were prepared using various surfactants and oils forming a nanoemulsion. Anti-microbial studies by resazurin microtitre assay, ex vivo diffusion, in vivo skin permeation and deposition studies, and acute irritation studies were carried out. NPF was applied onto secondary thermal wounds manifested on mice models followed by macroscopic and histological examinations.

RESULTS

NPF had an average globule size of <75 nm. The viscosity was ~10 cP indicating the feasibility of expulsion from the container upon actuation. With no skin irritation, the foams showed a higher skin deposition of SD. A high contraction and an evident regeneration of the skin tissue upon treatment with NPF indicated a good recovery from the thermal injury was apparent from the histology studies.

CONCLUSION

NPF represents an alternative topical formulation that can be employed as a safe and effective treatment modality for superficial second degree (partial thickness) burn wounds. With a minimal requirement of mechanical force, the no-touch application of NPF makes it suitable for sensitive and irritant skin surfaces.

Immunomodulatory properties of cimetidine: Its therapeutic potentials for treatment of immune-related diseases

Histamine exerts potent modulatory impacts on the cells of innate- [including neutrophils, monocytes, macrophages, dendritic cells (DCs), natural killer (NK) cells and NKT cells] and adaptive immunity (such as Th1-, Th2-, Th17-, regulatory T-, CD8⁺ cytotoxic T cells, and B cells) through binding to histamine receptor 2 (H2R). Cimetidine, as an H2R antagonist, reverses the histamine-mediated immunosuppression, as it has powerful stimulatory effects on the effector functions of neutrophils, monocytes, macrophages, DCs, NK cells, NKT cells, Th1-, Th2-, Th17-, and CD8⁺ cytotoxic T cells. However, cimetidine reduces the regulatory/suppressor T cell-mediated immunosuppression. Experimentally, cimetidine potentiate some immunologic activities in vitro and in vivo. The therapeutic potentials of cimetidine as an immunomodulatory agent were also investigated in a number of human diseases (such as cancers, viral warts, allergic disorders, burn, and bone resorption) and vaccination. This review aimed to provide a concise summary regarding the impacts of cimetidine on the immune system and highlight the cellular mechanisms of action and the immunomodulatory effects of this drug in various diseases to give novel insights regarding the therapeutic potentials of this drug for treatment of immune-related disorders. The review encourages more investigations to consider the immunomodulatory characteristic of cimetidine for managing of immune-related disorders.