Design and Testing of an Experimental Steam-Induced Burn Model in Rats

Current understanding of thermo(dys)regulation in severe burn injury and the pathophysiological influence of hypermetabolism, adrenergic stress and hypothalamic regulation—a systematic review

Background

In this systematic review, we summarize the aetiology as well as the current knowledge regarding thermo(dys)regulation and hypothermia after severe burn trauma and aim to present key concepts of pathophysiology and treatment options. Severe burn injuries with >20% total body surface area (TBSA) affected commonly leave the patient requiring several surgical procedures, prolonged hospital stays and cause substantial changes to body composition and metabolism in the acute and long-term phase. Particularly in severely burned patients, the loss of intact skin and the dysregulation of peripheral and central thermoregulatory processes may lead to substantial complications.

Methods

A systematic and protocol-based search for suitable publications was conducted following the PRISMA guidelines. Articles were screened and included if deemed eligible. This encompasses animal-based in vivo studies as well as clinical studies examining the control-loops of thermoregulation and metabolic stability within burn patients

Results

Both experimental animal studies and clinical studies examining thermoregulation and metabolic functions within burn patients have produced a general understanding of core concepts which are, nonetheless, lacking in detail. We describe the wide range of pathophysiological alterations observed after severe burn trauma and highlight the association between thermoregulation and hypermetabolism as well as the interactions between nearly all organ systems. Lastly, the current clinical standards of mitigating the negative effects of thermodysregulation and hypothermia are summarized, as a comprehensive understanding and implementation of the key concepts is critical for patient survival and long-term well-being.

Conclusions

The available in vivo animal models have provided many insights into the interwoven pathophysiology of severe burn injury, especially concerning thermoregulation. We offer an outlook on concepts of altered central thermoregulation from non-burn research as potential areas of future research interest and aim to provide an overview of the clinical implications of temperature management in burn patients.

Experimental models for controlled burn injuries in rats: a systematic analysis of original methods and burn devices

AIM

Despite a wide variety of models found in literature, choosing the right one can be difficult as many of them are lacking precise methodology. This study aims to analyze and compare original burn models in terms of burn device and technique, parameters, and wound depth assessment.

METHODS

A systematic search was performed according to PRISMA guidelines on studies describing original experimental burn models in rats. The adapted PICO formula and ARRIVE checklist were followed for inclusion and assessment of quality of studies. Characteristics of animals, burn technique, burn parameters and method of histological confirmation of burn depth were recorded.

RESULTS

Twenty-seven studies were included in the final analysis. Most studies used direct contact with skin for burn infliction (n=20). The rat's dorsum was the most common site (n=18). Ten studies used manually controlled burn devices, while ten designed automatic burn devices with control over temperature (n=10), exposure time (n=5), and pressure (n=5). Most studies (n=7) used a single biopsy taken from the center of the wound to confirm burn depth immediately after burn infliction.

CONCLUSION

From the wide variety of burn models in current literature, our study provides an overview of the most relevant experimental burn models in rats aiding researchers to understand what needs to be addressed when designing their burn protocol. Models cannot be compared as burn parameters variate significantly. Assessment of burn depth should be done in a standardized, sequential fashion in future burn studies to increase reproducibility.

Challenges with Wound Infection Models in Drug Development

Wound research is an evolving science trying to unfold the complex untold mechanisms behind the wound healing cascade. In particular, interest is growing regarding the role of microorganisms in both acute and chronic wound healing. Microbial burden plays an important role in the persistence of chronic wounds, ultimately resulting in delayed wound healing. It is therefore important for clinicians to understand the evolution of infection science and its various etiologies. Therefore, to understand the role of bacterial biofilm in chronic wound pathogenesis, various in vitro and in vivo models are required to investigate biofilms in wound-like settings. Infection models should be refined comprising an important signet of biofilms. These models are eminent for translational research to obtain data for designing an improved wound care formulation. However, all the existing models possess limitations and do not fit properly in the model frame for developing wound care agents. Among various impediments, one of the major drawbacks of such models is that the wound they possess does not mimic the wound a human develops. Therefore, a novel wound infection model is required which can imitate the human wounds. This review article mainly discusses various in vitro and in vivo models showing microbial colonization, their advantages and challenges. Apart from these models, there are also present ex vivo wound infection models, but this review mainly focused on various in vitro and in vivo models available for studying wound infection in controlled conditions. This information might be useful in designing an ideal wound infection model for developing an effective wound healing formulation.

Healing Effects of Human Amniotic Membrane and Burned Wool on the Second-degree Burn in Rats

Background:

This study aimed to compare sheep burnt wool and human amniotic membrane (AM) on second-degree burn wound healing in rats.

Materials and Methods:

Seventy-two adult male rats of Sprague Dawley underwent general anesthesia, and a deep second-degree burn was created on their skin by a hot iron plate. Afterward, human AM, silver sulfadiazine ointment (SSD), and sheep burned wool were used on wound area for burn treatment. On days 7, 14, and 21 of the experiment, the rats were sacrificed, and histopathological assessments were done.

Results:

Human AM, in comparison with other groups, significantly (P<0.05) showed better improvement in all pathologic variables. Burned wool showed significant improvement compared to the control group on day 7 in the angiogenesis, on day 14 in granulation tissue formation and epithelial formation, and on day 21 in new epithelial formation (P<0.05). Burned wool compared with SSD ointment in granulation tissue formation improved significantly (P<0.05) on days 7 and 14. Also, SSD ointment in comparison with the control group significantly improved (P<0.05) granulation tissue formation and macrophage on day 7.

Conclusion:

Human AM has a significant effect on the treatment of second-degree burn. Burned wool has a better effect on wound healing than SSD ointment and negative control group without treatment in terms of granulation tissue and epithelium formation.

Effects of Fibroblast Growth Factor 2 on Burn Injury and Repair Process: Analysis Using a Refined Mouse Model

Background

Burn injury is one of the most debilitating traumas, which induces multiple organ dysfunctions, resulting in high levels of morbidity and mortality. Fibroblast growth factor 2 (FGF2) has been applied to burn injury, whose precise mechanisms underlying facilitating the healing have not been fully understood. Although various animal models have been developed in pigs, rabbits, rats, and mice, no mouse model that creates burns consistent in their extent and depth have not been developed. Here, we developed a mouse burn model, and investigated details of the burn process, and elucidated the mechanisms of FGF2 effects.

Methods

A device with an 8-mm metal probe and a temperature controller was developed, which controls the temperature of the probe. Using the device, 1 or 2 of full-thickness burn injuries were generated on the back under catagen/telogen of 6-month-old C57BL/6 male mice. After 24 hours, FGF2 or phosphate-buffered saline was injected into the injured region, and at days 3, 5, and 7, histological and immunohistochemical analysis was performed to observe the injury and repair process.

Results

The device constantly generated a mouse full-thickness burn injury. The repair was initiated on the bottom of the burn as well as the margin. Local treatment with FGF2 displayed higher levels of immunostaining for both CD31+ and alpha-smooth muscle actin.

Conclusions

The device we developed is useful to generate a mouse burn injury model. FGF2 facilitates tissue repair with an increased number of both CD31+ and αSMA+ cells.

Effect of Hydrogen Sulfide on the Mitogen-Activated Protein Kinase Signaling Pathway in Cultured Skin Macrophages of Burned Rats

BACKGROUND

This study aims to investigate the effect of hydrogen sulfide on the mitogen-activated protein kinases signaling pathway in in vitro cultured skin macrophages of burned rats.

MATERIALS AND METHODS

Thirteen healthy Sprague-Dawley rats were divided into five groups: normal control group, burned control group, sodium hydrogen sulfide group, glibenclamide group, and sodium hydrogen sulfide + glibenclamide group. The burned rats were made into a deep II° 5% total body surface area flame burn injury model. The skin basement macrophages were separated from the skin of normal rats and the wound skin of burned rats and cultured. At 1, 6, and 12 h after intervention, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 protein levels were detected by Western blot, and ERK, p38, and JNK messenger RNA (mRNA) levels were detected by reverse transcription polymerase chain reaction.

RESULTS

Differences in ERK, p38, and JNK mRNA and protein levels between the normal control group and burned control group were statistically significant (P < 0.05). At the same time point, the ERK, p38, and JNK mRNA and protein levels in the NaSH group were different from those in other groups, and the differences were statistically significant (P < 0.05).

CONCLUSIONS

Hydrogen sulfide has a regulatory effect on ERK, JNK, and p38 in the mitogen-activated protein kinases signaling pathway in macrophages of burned rats.

Evaluation of wound healing potential of pomegranate (Punica granatum) whole fruit extract on skin burn wound in rats (Rattus norvegicus)

Objective:

This research was conducted to study the wound healing process of whole fruit pomegranate extract (punica granatum) standardized with 40% ellagic acid ointment for deep second-degree burn wound of skin in the rat (Rattus norvegicus).

Materials and Methods:

Powder of standardized pomegranate extract (SPE) with 40% ellagic acid was processed to become ointments. Twenty-five male rats, weighed 150–180 gm at 3 months of age, were randomly divided into five groups. After anesthetized, stainless circle plate with 1 cm of diameter in 85°C was contacted firmly toward right gluteal of rat skins for 5 sec in order to create deep second-degree burn wound. Control groups consist of (T0) cream base and (T1) 1% silver sulfadiazine. Treatment groups consist of (T2) 2.5% SPE, (T3) 5% SPE, and (T4) 10% SPE. Histopathological preparation used hematoxylin-eosin stained skin samples. Histological observations were performed using the optics microscope against collagen, the number of polymorphonuclear cell (PMN) infiltration, the degree of angiogenesis, and re-epithelization. The results were statistically compared between groups.

Results:

Microscopic observation on the wound healing process on the collagen, PMN infiltration, angiogenesis, and re-epithelization showed that topical administration of 10% SPE in burns gives the best result. This is characterized by a high density of collagen with a good arrangement, which is accompanied by a complete and mature epithelium, low number of inflammatory cells, and angiogenesis. This may be caused by the compounds in the pomegranate extract, which have the antioxidant, anti-inflammatory, and anti-bacterial effects.

Conclusion:

This study reveals that 10% SPE accelerates the healing of deep second-degree burn wound. Thus, pomegranate standardized with 40% ellagic acid is a promising herb for the healing of burn wound of skin.

Enoxaparin pretreatment effect on local and systemic inflammation biomarkers in the animal burn model

Low-molecular weight heparins (LMWH) are anticoagulants that have shown anti-inflammatory activity in several experimental models. Hot water burn inflammatory model accurately simulates human clinical situations allowing its use for nociception test and evaluation of anti-inflammatory drugs. The present study aims to evaluate the enoxaparin pretreatment on local and systemic inflammation biomarkers in the animal burn model. Inflammation was induced by submersing the rat left hind paw in water at 60^o C for 60 s. C-reactive protein (CRP) and thrombin-antithrombin complex (TAT) were estimated by immunosorbent assay, fibrinogen (Fg) by the gravimetric method and paw oedema by orthogonal digital photography. Highest values of paw oedema, CRP and TAT were observed at 4 h post-burn while Fg peak occurs at 12 h post-burn; enoxaparin pretreatment decreased oedema (- 32.1%), and concentration of TAT (- 66.7%), PCR (- 37.9%) and Fg (- 8%). This study shows that enoxaparin has local and systemic anti-inflammatory effects and should be considered as a potential adjuvant drug for the treatment of burns.