Inverse relationship between the apoptotic rate and the time elapsed from thermal injuries in deep partial thickness burns

Clostridium Collagenase Impact on Zone of Stasis Stabilization and Transition to Healthy Tissue in Burns

Clostridium collagenase has provided superior clinical results in achieving digestion of immediate and accumulating devitalized collagen tissue. Recent studies suggest that debridement via Clostridium collagenase modulates a cellular response to foster an anti-inflammatory microenvironment milieu, allowing for a more coordinated healing response. In an effort to better understand its role in burn wounds, we evaluated Clostridium collagenase’s ability to effectively minimize burn progression using the classic burn comb model in pigs. Following burn injury, wounds were treated with Clostridium collagenase or control vehicle daily and biopsied at various time points. Biopsies were evaluated for factors associated with progressing necrosis as well as inflammatory response associated with treatment. Data presented herein showed that Clostridium collagenase treatment prevented destruction of dermal collagen. Additionally, treatment with collagenase reduced necrosis (HMGB1) and apoptosis (CC3a) early in burn injuries, allowing for increased infiltration of cells and protecting tissue from conversion. Furthermore, early epidermal separation and epidermal loss with a clearly defined basement membrane was observed in the treated wounds. We also show that collagenase treatment provided an early and improved inflammatory response followed by faster resolution in neutrophils. In assessing the inflammatory response, collagenase-treated wounds exhibited significantly greater neutrophil influx at day 1, with macrophage recruitment throughout days 2 and 4. In further evaluation, macrophage polarization to MHC II and vascular network maintenance were significantly increased in collagenase-treated wounds, indicative of a pro-resolving macrophage environment. Taken together, these data validate the impact of clostridial collagenases in the pathophysiology of burn wounds and that they complement patient outcomes in the clinical scenario.

Connexin 43 upregulation in burns promotes burn conversion through spread of apoptotic death signals

BACKGROUND

Burn wounds continue to worsen after initial injury in a process known as burn conversion, which lasts about 3-5 days. It causes burn wounds to enlarge and deepen, leading to greater morbidity. Apoptosis is one of the factors contributing to the conversion of the zone of stasis into the zone of coagulation. Suppression of apoptosis has been associated with reducing burn conversion. Connexin 43 (Cx43) gap junctions facilitate the spread of apoptotic signals from dying cells to healthy neighbouring cells in injured tissues through the bystander effect.

OBJECTIVES

The study is to understand the role of Cx43 in burn conversion.

METHODS

In our study, 15 burn tissue samples were arranged into three groups as early (beginning of burn conversion), intermediate (extensive burn conversion) and late (established burn conversion) burns.

RESULTS

We found a striking increase in the amount of Cx43 protein expressed in the dermal fibroblasts (identified with heat shock protein 47 (HSP47) staining) in the zone of stasis in early and intermediate burns. These dermal fibroblasts also express high levels of cleaved-Caspase 3 indicating on-going apoptosis.

CONCLUSIONS

Our findings suggest that elevation of Cx43 may play an active role in burn conversion spreading apoptosis in the early and intermediate burn wound.

Grafting of mesenchymal stem cell-seeded small intestinal submucosa to repair the deep partial-thickness burns

PURPOSE

Regenerative medicine provides many treatments for burn wounds, of which cell-seeded substitutes are encouraging for large and deep burns. To assess the feasibility of mesenchymal stem cell (MSC)-seeded small intestinal submucosa (SIS) to repair the deep partial-thickness burns, a rat study was performed.

MATERIALS & METHODS

The burn model was created by contacting the dorsal surface directly with boiled water for 10 seconds. MSCs at passage 3 were seeded on the SIS before implantation. Three days after burn injury, the grafts were implanted onto the burn area. At 3, 7, 14 and 21 days post implantation, gross observation and histological assessments were performed.

RESULTS

SIS alone and MSC-seeded SIS were able to accelerate the burn wound closure by enhancing granulation tissue formation, increasing wound maturity, improving revascularization, and inducing the proliferation of neo-epidermal cells. Additionally, MSC-seeded SIS was much more effective than SIS alone for the repair of deep partial-thickness burns.

CONCLUSION

Both SIS and MSC-seeded SIS were able to repair the large and deep burn wounds and the loaded MSCs possessed positive effects to accelerate the wound closure in a rat model.

Spatiotemporal progression of cell death in the zone of ischemia surrounding burns

Burns are dynamic injuries, characterized by progressive death of surrounding tissue over time. Although central to an understanding of burn injury progression, the spatiotemporal degrees and rates of cellular necrosis and apoptosis in the zone of ischemia surrounding burns are not well characterized. Using a validated porcine hot comb model, we probed periburn tissue at 1, 4, and 24 hours after injury for high-mobility group box 1 as a marker of necrosis and activated cleaved caspase-3 as a marker of apoptosis, followed by spatiotemporal morphometric analysis. We found that necrosis was the most prominent mechanism of cell death in burn injury progression, with significant progression between 1 and 4 hours postburn. Apoptosis appeared not to play a role in early burn injury progression but was observed in cells at the interface of necrotic and viable tissue at 24 hours postburn. Our findings imply that intervention within the first 4 hours following injury is likely necessary to limit burn injury progression. Additionally, based on high-mobility group box 1 staining patterns, we define distinct early, intermediate, and late pathological signs of cell necrosis that may facilitate delineation of causal mechanistic relationships of burn injury progression in vivo.

The year in burns 2008

For 2008, approximately 1200 original burn research articles were published in scientific journals using the English language. This article reviews those with the most impact on burn treatment according to the Editor of one of the major journals (Burns). As in the previous year's review, articles were divided into the following topic areas: epidemiology, wound characterisation, critical care physiology, inhalation injury, infection, metabolism and nutrition, psychological considerations, pain management, rehabilitation, and burn reconstruction. Each selected article is mentioned briefly with editorial comment.

Apoptosis is differentially regulated by burn severity and dermal location

BACKGROUND

The cellular processes that contribute to cell death in burns are poorly understood. This study evaluated the distribution and extent of apoptosis in an established rat model of acute dermal burn injury.

MATERIALS AND METHODS

A branding iron (100 degrees C) was applied to the depilated dorsum of seven rats, creating burn contact times of 1-8, 10, 12, and 14 s. Biopsies were collected and immunohistochemistry performed for apoptosis and cell injury/necrosis by detection of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and high-mobility group box 1 (HMGB1), respectively. The slides were scored by evaluating staining in superficial, middle, and deep dermal fields. Within these, basal keratinocytes of the epidermis, mesenchymal cells, adnexal epithelia, and vasculature wall cells were morphometrically analyzed for stain detection of selected markers.

RESULTS

TUNEL staining had an inverse relationship with contact time in most fields except in deep dermal mesenchymal cells where it was increased. HMGB1 nuclear staining was significantly decreased with progressive contact time consistent with transition to cell injury/necrosis.

CONCLUSIONS

This study is the first to demonstrate that apoptosis rate is dependent on dermal location, cell type, and severity of thermal injury. Furthermore, this work suggests that for most dermal locations increased thermal injury corresponds with decreased apoptosis and increased cell injury/necrosis. Together, these findings indicate that many parameters can regulate apoptosis in burn wounds, and these results will be critical to understanding burn pathogenesis and assessing future therapies.