CLASSIC IL-6 SIGNALING IS ASSOCIATED WITH POOR OUTCOMES IN BURN PATIENTS

ABSTRACT

Background: Interleukin (IL)-6 is a multifunctional cytokine with both a proinflammatory and anti-inflammatory role. In many studies, IL-6 increases rapidly after burn injury and is associated with poor outcomes. However, there are two aspects to IL-6; it can signal via its soluble IL-6 receptor (sIL-6R), which is referred to as trans-signaling and is regarded as the proinflammatory pathway. The role of sIL-6R postburn injury has yet to be explored in its entirety. We hypothesized that patients with a lower ratio of IL-6 to sIL-6R would have worse outcomes. Methods: Patients admitted to our burn center within 7 days of injury were included in this study. Patients were divided into two groups based on IL-6 and sIL-6R levels measured within the first 7 days postburn injury. Patients were in the high ratio group if their IL-6/sIL-6R ratio was ≥0.185. Clinical outcomes included organ biomarkers, morbidities, and hospital length of stay. Groups were compared using Student's t test, Mann-Whitney U , and Fisher's exact test as appropriate; a P value of <0.05 was considered statistically significant. Results: We studied 86 patients with a median age of 50 years (36-66 years) and a median total body surface area burn of 18% (10-31). There were 40 patients categorized with a low IL-6/sIL-6R ratio and 46 patients with a high IL-6/sIL-6R ratio. Patients in the high IL-6/sIL-6R ratio group had a significantly greater total body surface area burn ( P < 0.001) and a significantly greater proportion of patients with inhalation injury ( P = 0.001). Levels of IL-6 were significantly higher in patients with a high IL-6/sIL-6R ratio ( P < 0.0001). However, levels of sIL-6R were not significantly different among the low and high groups ( P = 0.965). Mortality was significantly greater in the high IL-6/sIL-6R ratio group (3% vs. 26%; P = 0.002). Conclusions: Interestingly, patients with a higher ratio of IL-6/sIL-6R had significantly greater mortality. Using sIL-6R as a marker for the proinflammatory immune response, we expected patients with a lower IL-6/sIL-6R ratio to have poor outcomes, typically associated with a hyperinflammatory or exaggerated immune response. However, the absolute value of sIL-6R did not differ. This suggests that classical signaling of IL-6 via its membrane-bound receptor, with an anti-inflammatory function, is important.

Skin Tissue Engineering Advances in Burns: A Brief Introduction to the Past, the Present, and the Future Potential

Burn injuries are a severe form of skin damage with a significant risk of scarring and systemic sequelae. Approximately 11 million individuals worldwide suffer burn injuries annually, with 180,000 people dying due to their injuries. Wound healing is considered the main determinant for the survival of severe burns and remains a challenge. The surgical treatment of burn wounds entails debridement of necrotic tissue, and the wound is covered with autologous skin substitutes taken from healthy donor areas. Autologous skin transplantation is still considered to be the gold standard for wound repair. However, autologous skin grafts are not always possible, especially in cases with extensive burns and limited donor sites. Allografts from human cadaver skin and xenografts from pig skin may be used in these situations to cover the wounds temporarily. Alternatively, dermal analogs are used until permanent coverage with autologous skin grafts or artificial skins can be achieved, requiring staged procedures to prolong the healing times with the associated risks of local and systemic infection. Over the last few decades, the wound healing process through tissue-engineered skin substitutes has significantly enhanced as the advances in intensive care ensuring early survival have led to the need to repair large skin defects. The focus has shifted from survival to the quality of survival, necessitating accelerated wound repair. This special volume of JBCR is dedicated to the discoveries, developments, and applications leading the reader into the past, present, and future perspectives of skin tissue engineering in burn injuries.

Lipolysis-derived linoleic acid drives beige fat progenitor cell proliferation

De novo beige adipocyte biogenesis involves the proliferation of progenitor cells in white adipose tissue (WAT); however, what regulates this process remains unclear. Here, we report that in mouse models but also in human tissues, WAT lipolysis-derived linoleic acid triggers beige progenitor cell proliferation following cold acclimation, β3-adrenoceptor activation, and burn injury. A subset of adipocyte progenitors, as marked by cell surface markers PDGFRα or Sca1 and CD81, harbored cristae-rich mitochondria and actively imported linoleic acid via a fatty acid transporter CD36. Linoleic acid not only was oxidized as fuel in the mitochondria but also was utilized for the synthesis of arachidonic acid-derived signaling entities such as prostaglandin D2. Oral supplementation of linoleic acid was sufficient to stimulate beige progenitor cell proliferation, even under thermoneutral conditions, in a CD36-dependent manner. Together, this study provides mechanistic insights into how diverse pathophysiological stimuli, such as cold and burn injury, promote de novo beige fat biogenesis.

A Randomized Trial of Enteral Glutamine for Treatment of Burn Injuries

BACKGROUND

Glutamine is thought to have beneficial effects on the metabolic and stress response to severe injury. Clinical trials involving patients with burns and other critically ill patients have shown conflicting results regarding the benefits and risks of glutamine supplementation.

METHODS

In a double-blind, randomized, placebo-controlled trial, we assigned patients with deep second- or third-degree burns (affecting ≥10% to ≥20% of total body-surface area, depending on age) within 72 hours after hospital admission to receive 0.5 g per kilogram of body weight per day of enterally delivered glutamine or placebo. Trial agents were given every 4 hours through a feeding tube or three or four times a day by mouth until 7 days after the last skin grafting procedure, discharge from the acute care unit, or 3 months after admission, whichever came first. The primary outcome was the time to discharge alive from the hospital, with data censored at 90 days. We calculated subdistribution hazard ratios for discharge alive, which took into account death as a competing risk.

RESULTS

A total of 1209 patients with severe burns (mean burn size, 33% of total body-surface area) underwent randomization, and 1200 were included in the analysis (596 patients in the glutamine group and 604 in the placebo group). The median time to discharge alive from the hospital was 40 days (interquartile range, 24 to 87) in the glutamine group and 38 days (interquartile range, 22 to 75) in the placebo group (subdistribution hazard ratio for discharge alive, 0.91; 95% confidence interval [CI], 0.80 to 1.04; P = 0.17). Mortality at 6 months was 17.2% in the glutamine group and 16.2% in the placebo group (hazard ratio for death, 1.06; 95% CI, 0.80 to 1.41). No substantial between-group differences in serious adverse events were observed.

CONCLUSIONS

In patients with severe burns, supplemental glutamine did not reduce the time to discharge alive from the hospital. (Funded by the U.S. Department of Defense and the Canadian Institutes of Health Research; RE-ENERGIZE ClinicalTrials.gov number, NCT00985205.).

Outbreak of Carbapenemase-Producing Enterobacteriaceae in a Regional Burn Center

Antimicrobial resistance is an increasing problem in hospitals worldwide; however, the prevalence of carbapenemase-producing Enterobacteriaceae (CPE) in our region is low. Burn patients are vulnerable to infection because of the loss of the protective skin barrier, thus burn centers prioritize infection prevention and control (IP&C). This report describes a CPE outbreak in a regional burn center. In a period of 2.5 months, four nosocomial cases of CPE were identified, three containing the Klebsiella pneumoniae carbapenemase (KPC) gene and one Verona integrin-encoded metallo-β-lactamase (VIM) gene. The first two cases were identified while there was no CPE patient source on the unit. CPE KPC gene was then isolated in sink drains of three rooms. In addition to rigorous IP&C practices already in place, we implemented additional outbreak measures including restricting admissions to patients with complex burns or burns ≥10% TBSA, admitting patients to other in-patient units, and not permitting elective admissions. We began cohorting patients using nursing team separation for CPE-positive and -negative patients and geographical separation on the unit. Despite aggressive IP&C measures already in place, hospital-acquired CPE colonization/infection occurred. Given that CPE contaminated sinks of the same enzyme were identified, we believe hospital sink drains may the source. This highlights the importance of sink design and engineering solutions to prevent the formation of biofilm and reduce splashing. CPE infections are associated with poor outcomes in patients and significant health system costs due to a longer length of stay and additional institutional resources.

EVALUATING SEPSIS CRITERIA IN DETECTING ALTERATIONS IN CLINICAL, METABOLIC, AND INFLAMMATORY PARAMETERS IN BURN PATIENTS

ABSTRACT

Sepsis has become the leading cause of death in burn patients. Furthermore, sepsis and septic complications result in significant morbidities and longer hospitalization, which has profound impacts on the healthcare system. Despite this, sepsis in burn patients is surprisingly poorly understood and characterized. This retrospective, single-institution cohort study aimed to increase our understanding of the septic response after burns. We hypothesized that different sepsis definitions will results in distinctive septic trajectories and biochemical patterns after injury. Sepsis was defined by our burn center-specific prospective definition, the American Burn Association criteria, Sepsis-3 criteria, and the Mann-Salinas criteria. Applying these definitions, we compared clinical, metabolic, and inflammatory markers in septic and nonseptic burn patients. We found that the Sepsis-3 criteria are the most reliable screening tool used before clinical diagnoses for detecting sepsis trajectories and biochemical patterns. Moreover, we characterized distinct temporal alterations in biomarkers during the pre- and post-septic periods in burn patients, which may be incorporated into future sepsis definitions to improve the accuracy of a sepsis diagnosis in burn patients.

Aging Impairs the Cellular Interplay between Myeloid Cells and Mesenchymal Cells during Skin Healing in Mice

Impaired wound healing is a major issue in the elderly population and is associated with substantial health and economic burden, which is exponentially increasing with the growing aging population. While the underlying pathobiology of disturbed skin healing by aging is linked to several genetic and epigenetic factors, little is known about the cell-cell interaction during the wound healing process in aged individuals, particularly the mesenchymal stem cell (MSCs)-macrophages axis. In this study, by using a thermal injury animal model in which we compared the wound healing process of adult and young mice, we found that the insufficient pool of MSCs in adult animals are deficient in migrating to the wound bed and instead are restricted to the wound edge. We identified a deficiency of a CD90-positive MSC subpopulation in the wounds of adult animals, which is positively correlated with the number of F4/80+ macrophages. In vitro, we found that CD90+ cells preferentially adhere to the myeloid cells forming doublet cells. Thus, our findings highlight that in adult mice subjected to a thermal injury, impaired wound healing is likely mediated by a disturbed cellular interplay between myeloid cells and mesenchymal cells.

563 Fire safety in homeless encampments

Introduction

It is well known that people experiencing homelessness are at a greater risk for burn injury. Our burn centre saw an increase in admissions of homeless individuals during the pandemic. Typically, we partner with our hospital’s communications staff to share burn prevention public service announcements. But our usual method of broadcasting information through media like newspapers, blog posts, Facebook, or Instagram was not necessarily going to reach people sleeping rough. This report describes the development of a partnership between a burn centre, outreach workers, and people with lived experience of homelessness to improve fire safety in encampments.

Methods

Our goal was to create a Fire Safety Manual and hold Fire Safety Training Sessions. We conducted surveys that asked encampment residents questions like, “What do you use fires for?” “What fire hazards do you see at encampments?” and “How do you think fires could best be prevented?”. We used the results of this survey to guide the training manual and held workshops to engage encampment residents and incorporate feedback into the manual.

Results

The manual uses harm reductions strategies and focuses on real-life situations encountered by folks living outdoors—the manual outlines how to safely start a fire and what to do if a fire occurs. The reality is that people are trying to survive freezing winters while sleeping outside; this means that some safety standards are not possible, and the guide had to reflect that. For example, we practiced fire escape plans during training sessions and had to think about obstacles like tents with only one way out. A solution was to keep a utility knife inside and outside the tent in case one had to cut through to escape or free someone. An encampment resident suggested hiding the knives so they would not be used as weapons. We purchased fire extinguishers, fire blankets, and first aid kits that we distributed during training.

Conclusions

Education is critical to prevent burn injuries. Burn centre staff may be experts on burn prevention, but we are not experts on surviving outside. We have to be accountable to this community. This means listening, building trust, and partnering with people living outdoors. People who did training sessions were empowered to start fire brigades in their encampments. Crucial concepts are to meet people where they are and always to include people with lived experience: “Nothing about us without us.”

43 Mapping the Hypermetabolic Response in Burn Patients

Introduction

Hypermetabolism, characterized by drastic increases in whole-body catabolism and resting energy expenditure (REE), is a hallmark response to a severe burn injury. This is believed to be driven in part by alterations in adipose tissue metabolism. We proposed to define the hypermetabolic response in adipose tissue from burn patients and create a roadmap of markers indicative of hypermetabolism to improve prognosis. We hypothesized that catabolic markers, such as uncoupling protein-1 (Ucp1) and growth differentiation factor-15 (Gdf15), would positively correlate with increasing days post-burn and REE.

Methods

Adult burn patients (n=65) admitted to our burn center between 2011—2019 were included in this study. Subcutaneous white adipose tissues (sWAT) from the site of injury (n=85) and plasma were collected from severely burned patients ( ³20% total body surface area). Gene expression and circulating cytokine levels were measured by RT-qPCR and multiplex assays, respectively.

Results

We found a significant correlation between increasing Ucp1 gene expression and days post-burn (p< 0.0001). Moreover, when samples were stratified into acute (1-3 days post-burn), moderate (4-9 days post-burn), and long-term ( >10 days post-burn) timepoints, a significant increase in Ucp1 gene expression was detected only in adipose tissues from long-term time points in comparison to non-burned control tissues (p< 0.01). However, we found that REE remained stagnant throughout hospital stay after a burn injury in our patient cohort. Thus, we did not detect a significant correlation between Ucp1 gene expression and REE. Further, while Gdf15 expression was most pronounced, albeit statistically insignificant, during the moderate timepoints, we did not detect any significant differences when correlated with days post-burn. Additionally, we determined that circulating levels of IL-6, IL-10, and monocyte chemoattractant protein-1 (MCP-1) were greatly elevated within the first seven days post-burn and gradually decreased over time, while vascular endothelial growth factor (VEGF) concentrations followed a similar pattern to Ucp1 gene expression.

Conclusions

While Gdf15 expression may not accurately reflect catabolism in the adipose tissues of burn patients, Ucp1 gene expression may be used as a marker indicating a peak hypermetabolic period after ten days post-burn. This may also be reflected by circulating concentrations of VEGF. Moreover, IL-6, IL-10 and MCP-1 may be used as early determinants before the onset of hypermetabolism.

16 Association of Frailty and Comorbidities with Burn Outcomes: A Multicenter Study

Introduction

Previous work has demonstrated the association of increased frailty and mortality in burn patients, but the impact of specific co-morbidities and frailty on burn patients’ short term outcomes has not been explored. The purpose of this study was to determine the relationship of frailty and patient comorbidities on in-hospital mortality and length of stay (LOS).

Methods

A retrospective chart review of all acutely injured burn patients admitted from January 2016 - December 2017 at 3 US ABA verified burn centers was conducted. Demographics and all comorbidities included in the burn database were collected. The modified frailty index-11 score (MFI) was calculated for each patient. Descriptive statistics, univariate and multivariate analysis were completed to determine the relationship between frailty and comorbidities with mortality, LOS, and LOS/% Total Body Surface Area (%TBSA).

Results

1615 patients were included. Mean age was 45.9 + 17.7 years and 1145 (70.9%) were male. Mean %TBSA was 9.6%+14.2% and mean MFI was 0.43 + 0.74. The mean LOS was 12.3 days + 21.1. A total of 1542 (95.5%) patients survived to discharge. The most common co-morbidities present on admission were: smoking (336, 22.7%), hypertension (HTN, 313, 19.4%), drug dependence (247, 15.3), diabetes (DM, 175, 10.8%), alcoholism (171,10.6%), major psychiatric illness (MPI, 169,10.5%), heart failure (CHF, 23, 1.4%), obesity (7, 4.3%), and respiratory disease (RD, 136, 8.4%). Multivariate logistic regression revealed that RD (OR 3.6, 95%CI 1.4-9.4), age (OR 1.1, 95%CI 1.06-1.1), and %TBSA (OR 1.1, 95%CI 1.1-1.17) were independently predictive of mortality. Multiple linear regression demonstrated patients without alcoholism (β -3.9 95% CI -5.7- -2.1), MPI (β -3.8 95% CI -4.9- -3.0), drug dependence (β -3.9 95% CI -5.7- -2.1), and DM (β -2.0 95% CI -5.7- -2.8) had shorter LOS. Though MFI, heart failure, DM, MPI, alcoholism, and HTN, were all significant for LOS/%TBSA in univariate analysis, they were NOT significant in the multivariate linear regression model.

Conclusions

MFI does not independently contribute to mortality or LOS when accounting for other patient co-morbidities. Respiratory disease on admission is associated with mortality, and major psychiatric illness and drug dependence increase LOS. This information will be used to develop interventions for these groups in order to improve mortality, and decrease LOS.

48 Metformin Rescues the Aging-induced Failure of Post-burn White Adipose Browning

Introduction

Severe burns are responsible for an estimated 300,000 deaths per year worldwide. While modern burn care has markedly improved survival for pediatric and adult patients, this is sadly not the case for one population: the elderly. Despite being the fastest-growing demographic in North America, burn patients over the age of 60 years have the highest mortality and morbidity rates. Recent evidence suggests that progressive aging induces several structural and functional alterations which impair the capacity of older trauma patients to adequately respond to stress. Indeed, it was discovered that reduced survival in elderly burn patients is associated with the failure to initiate the browning of white adipose tissue (WAT) —a hallmark of the systemic response to injury commonly observed in adults. Interestingly, the widely used hypoglycemic drug metformin has been found to protect against aging-induced metabolic decline in various pathological conditions. Thus, we investigated the anti-aging effects of metformin on the metabolic deterioration of post-burn WAT responses in elderly patients and mice after injury.

Methods

Human WAT was obtained from elderly patients admitted to our burn center. Elderly (75-week) mice received a full-thickness scald burn and/or daily intraperitoneal injections of metformin (100 mg/kg) for 7 days. The inguinal WAT was harvested for histological analyses. Mitochondrial respiration was measured via Seahorse XF96. Gene and protein expression was assessed via RT-PCR and western blot, respectively.

Results

Post-burn metformin treatment restores the thermogenic activation of WAT in elderly patients and mice, reflected by the increased expression of key browning markers, UCP-1 and PGC-1α (p< 0.05). This was accompanied by higher mitochondrial respiration, improved lipolysis (p< 0.05) and increased fat wasting (p< 0.01) relative to control counterparts. The anti-aging effects of metformin appeared to be mediated by AMPK, which consequently increased [NAD⁺] (p< 0.01), thereby promoting activation of the longevity-specific enzyme Sirt-1 (p< 0.05).

Conclusions

Here, we show that post-burn metformin treatment effectively rejuvenates adaptive metabolic responses in elderly WAT by targeting key longevity pathways which rescue the age-dependent loss of being back to youthful levels. Our findings support the potential of anti-aging modalities to improve care and outcomes in elderly burned patients.

551 Age Does Not Predict Admission Culture Positivity

Introduction

Burn patients are susceptible to wound infections, urinary tract infections, pneumonia, and bloodstream infections. With rising rates of community colonization with multidrug-resistant organisms (MDRO), the colonization of wounds with commensal organisms is more concerning than ever, which is particularly true in patients with recent hospital admissions, advanced age, or institutional living situations. The purpose of this study was to examine if age was a factor in obtaining admission cultures and if older patients were more likely to have positive cultures.

Methods

A retrospective chart review was conducted involving burn patients admitted at three ABA verified burn centers from January 2016 - December 2017. Data collected included demographics, burn injury, and cultures obtained within 24 hours of admission. Patients were divided into 10-year age increments from 20 to ≥ 80 years old. Data analysis was conducted using Chi-square, Fisher Exact, and Kruskal-Wallis tests.

Results

A total of 1615 patients (mean age 45.9± 17.7 years, 1145 males (70.9%), mean burn size (TBSA) 9.6± 14.2%) were analyzed. Admission cultures obtained were: 656 (40.6%) wound cultures, 196 (12.1%) urine cultures, 139 (8.6%) blood cultures, and 1445 (89.5%) Methicillin-Resistant Staphylococcus Aureus (MRSA) screen. In all age groups, there were no significant differences between patients who had wound cultures (p = 0.97), blood cultures (p = 0.39), or MRSA screening (p = 0.9). As patients aged, they were more likely to have urine cultures obtained (p=0.01); - 23% of patients >80 years old had urine cultures ordered at admission compared to 8.6-16.9% of younger patients. Positive results by age group: wound cultures (p= 0.09), urine cultures (p= 0.16), blood cultures (0.10), MRSA screen (p=0.98). In looking at increased exposure to MDROs prior to admission by age groups, patients in the 61–70year (8.33%), 71–80-year (5.68%), and >80-year (6.67%) age groups were more likely to have a recent (within 30 days) hospitalization (p = 0.02), but there was no significant difference in pre-hospital institutionalization (i.e., prison, skilled nursing facility) by age group (p = 0.06). With a recent hospitalization, MRSA screening was more likely to be positive (11.3% vs. 4.9%, p = 0.05).

Conclusions

All burn patients are susceptible to infections. Urine cultures were more likely to be obtained in older burn injured patients who are 80 years of age or older. There was no significant difference in culture positivity by age. Apart from MRSA screen positivity, there was no increased risk of urine, wound, or blood culture positivity with recent hospitalization or institutionalization. The utility of screening all patients for MDROs on admission should be considered for patients 20 years of age and older.

120 The Association of Admission Cultures with Burn Outcomes

Introduction

Burn patients are susceptible to infections. It is thought that burn wounds are initially sterile and become colonized by commensal and environmental microorganisms. Many burn centers have protocols to routinely screen patients for infection on admission. The ability of culture results to predict outcomes in burn patients has not been examined. In this study, we aim to examine the relationship between admission cultures and burn outcomes. We hypothesize that patients who have positive cultures on admission will have increased mortality and length of stay (LOS).

Methods

A retrospective chart review was conducted using electronic medical records for all adult patients admitted to three ABA verified burn centers from January 2016 -December 2017. Data collected included patient demographics, burn injury, burn outcomes, and cultures obtained within the first 24 hours of admission. Data analysis was conducted using Chi-square, Fisher Exact, Spearman Correlation, Wilcoxon 2-sample, and Kruskal-Wallis tests.

Results

A total of 1615 patients (mean age 45.87±17.65 years, 1145 males [70.9%]) were analyzed. Mean total body surface area burn (TBSA) was 9.6±14.2% and 10% had inhalation injuries. In this study population, the median LOS was 7 days (Interquartile range [IQR] = 12) and 72 patients (4.5%) expired. Older patients (p &lt; .0001), those with higher scores on the 11-factor modified frailty index (mFI-11) (p &lt; 0.0001), a higher TBSA (p&lt; .0.0001) and inhalation injury (p &lt; 0.0001) had a higher mortality rate. In examining the effect of admission cultures on mortality, there was no significant difference in mortality based on wound culture (p 0.14), Clostridium difficile (C. diff) (p 0.25), or urine culture (p=0.79) results. Patients with positive Methicillin-Resistant Staphylococcus Aureus (MRSA) screening (p 0.04) and those with positive blood cultures (p 0.01) were more likely to die from their injuries. Older patients (r= 0.14, p &lt; 0.0001), those with a larger TBSA (r=0.49, p &lt; 0.0001), and a higher MFI-11 score (r=0.12, p &lt; 0.0001) had and increased LOS.. There was no association between LOS and positive wound cultures (p 0.08), or blood cultures (p 0.49) upon admission. Patients with positive MRSA results (p 0.003) and urine cultures (p 0.01) upon admission had a longer LOS while those with positive C. diff results had a shorter LOS (p 0.01).

Conclusions

Mortality is associated with standard predictors of outcomes (age, burn size, inhalation injuries, frailty scores) and positive MRSA screens and blood cultures. Patients with larger burns (define larger burn-maybe use the degree scale), a positive MRSA and negative C. diff had a longer LOS. Based on these results, cultures should be considered in all patients upon admission to the hospital as they are predictive of burn outcomes.

Large animal models of thermal injury

Burn injury results in a triad of inter-related adaptive responses: a systemic inflammatory response, a stress response, and a consequent hypermetabolic state which supports the former two. These pathological responses extend beyond the site of injury to affect distant organs and influence long-term outcomes in the patient. Animal models have proven valuable in advancing our understanding of mechanisms underlying the multifactorial manifestations of burn injury. While rodent models have been unprecedented in providing insights into signaling pathways, metabolic responses, protein turnover, cellular and molecular changes; small animal models do not replicate hypermetabolism, hyperinflammation, and wound healing after a burn injury as seen in humans. Herein, we provide a concise review of preferred large animal models utilized to understand burn pathophysiology based on organ systems and associated dysfunction. Additionally, we present a detailed protocol of contact burn injury in the Yorkshire pig model with a focus on preoperative care, anesthesia, analgesia, wound excision and grafting, dressing application, and frequency of dressing changes.

NLRP3 knockout enhances immune infiltration and inflammatory responses and improves survival in a burn sepsis model

Although sepsis in burn patients is a major contributor to mortality, treatments are not always effective and underlying mechanisms have yet to be completely elucidated. NLRP3 inflammasome orchestrates burn-induced, inflammatory-driven pathophysiologic processes. Here, we determined the mechanism of NLRP3 inflammasome activation on bacterial clearance and mortality in burn sepsis. We obtained tissue and blood from 30 wild-type and 30 Nlrp3^-/- mice. Mice were subjected to a two-hit model of 25-30% TBSA scald burn followed by Pseudomonas aeruginosa wound infection 72 hours after injury. We also obtained tissue from 34 adult burn patients (≥18 years of age) with early (0-11 days post-burn) and later (≥12 days post-burn) surgical time-points and ten healthy controls. Murine studies indicated that Nlrp3^-/- had 30% improved survival and bacterial clearance at the site of injury and is systemically relative to burn sepsis wild type. Greater macrophage and neutrophil infiltration occurred acutely after infection (12 hours) to the site of injury and adipose tissue. This was followed by increased macrophage and neutrophil infiltration to lymphoid organs and liver beyond the acute phase (24 and 72 hours). Interestingly, Nlrp3 ablation increased acute systemic inflammation (IL-6, TNF-α, IL-1β). Septic burn patients had persistently increased adipose NLRP3 by-product expression beyond the acute phase that was more pronounced in late-onset sepsis. Our findings suggest that Nlrp3 genetic ablation enhanced acute tissue-specific inflammatory responsiveness. Likely, this occurs by paradoxically increasing acute immune infiltration and inflammation with a non-persistent response. Clinically, persistent NLRP3-mediated inflammation occurs in septic versus normal burn patients and potentially detrimentally impacts patient outcomes.

Thermal Stress Induces Long-Term Remodeling of Adipose Tissue and Is Associated with Systemic Dysfunction

ABSTRACT

Severe burns are characterized by the magnitude and duration of the hypermetabolic response thereafter, and demarcated by the loss of lean body mass and catabolism of fat stores. The aim of the present study was to delineate the temporal and location-specific physiological changes to adipose depots and downstream consequences post-burn in a murine model of thermal injury. C57BL/6 mice were subjected to a 30% total body surface area burn and body mass, food intake, and tissue mass were monitored for various time points up until 60 days postinjury. Mitochondrial respirometry was performed using a Seahorse XF96 analyzer. Lipolytic markers and browning markers were analyzed via Western blotting and histology. A severe burn results in a futile cycle of lipolysis and white adipose tissue (WAT) browning, the sequelae of which include fat catabolism, hepatomegaly, and loss of body mass despite increased food intake. A dynamic remodeling of epididymal WAT was observed with acute and chronic increases in lipolysis. Moreover, we demonstrate that pathological browning of inguinal WAT persists up to 60 days post-burn, highlighting the magnitude of the β-adrenergic response to thermal injury. Our data suggests that adipose depots have a heterogeneous response to burns and that therapeutic interventions targeting these physiological changes can improve outcomes. These data may also have implications for treating catabolic conditions such as cancer cachexia as well as developing treatments for obesity and type II diabetes.

CNS-Spleen Axis - a Close Interplay in Mediating Inflammatory Responses in Burn Patients and a Key to Novel Burn Therapeutics

Severe burn-induced inflammation and subsequent hypermetabolic response can lead to profound infection and sepsis, resulting in multiple organ failure and high mortality risk in patients. This represents an extremely challenging issue for clinicians as sepsis is the leading cause of mortality in burn patients. Since hyperinflammation and immune dysfunction are a result of an immune imbalance, restoring these conditions seem to have promising benefits for burn patients. A key network that modulates the immune balance is the central nervous system (CNS)-spleen axis, which coordinates multiple signaling pathways, including sympathetic and parasympathetic pathways. Modulating inflammation is a key strategy that researchers use to understand neuroimmunomodulation in other hyperinflammatory disease models and modulating the CNS-spleen axis has led to improved clinical outcomes in patients. As the immune balance is paramount for recovery in burn-induced sepsis and patients with hyperinflammatory conditions, it appears that severe burn injuries substantially alter this CNS-spleen axis. Therefore, it is essential to address and discuss the potential therapeutic techniques that target the CNS-spleen axis that aim to restore homeostasis in burn patients. To understand this in detail, we have conducted a systematic review to explore the role of the CNS-spleen axis and its impact on immunomodulation concerning the burn-induced hypermetabolic response and associated sepsis complications. Furthermore, this thorough review explores the role of the spleen, CNS-spleen axis in the ebb and flow phases following a severe burn, how this axis induces metabolic factors and immune dysfunction, and therapeutic techniques and chemical interventions that restore the immune balance via neuroimmunomodulation.

Stem Cell Therapy for Burns: Story so Far

Burn injuries affect approximately 11 million people annually, with fatalities amounting up to 180,000. Burn injuries constitute a global health issue associated with high morbidity and mortality. Recent years have seen advancements in regenerative medicine for burn wound healing encompassing stem cells and stem cell-derived products such as exosomes and conditioned media with promising results compared to current treatment approaches. Sources of stem cells used for treatment vary ranging from hair follicle stem cells, embryonic stem cells, umbilical cord stem cells, to mesenchymal stem cells, such as adipose-derived mesenchymal stem cells, bone marrow-derived mesenchymal stem cells, and even stem cells harvested from discarded burn tissue. Stem cells utilize various pathways for wound healing, such as PI3/AKT pathway, WNT-β catenin pathway, TGF-β pathway, Notch and Hedgehog signaling pathway. Due to the paracrine signaling mechanism of stem cells, exosomes and conditioned media derived from stem cells have also been utilized in burn wound therapy. As exosomes and conditioned media are cell-free therapy and contain various biomolecules that facilitate wound healing, they are gaining popularity as an alternative treatment strategy with significant improvement in outcomes. The treatment is provided either as direct injections or embedded in a natural/artificial scaffold. This paper reviews in detail the different sources of stem cells, stem cell-derived products, their efficacy in burn wound repair, associated signaling pathways and modes of delivery for wound healing.

Adipose browning response to burn trauma is impaired with aging

BACKGROUND

The incidence of burn injuries in older patients is dramatically increasing as the population of older people grows. Despite the increased demand for elderly burn care, the mechanisms that mediate increased morbidity and mortality in older trauma patients are unknown. We recently showed that a burn injury invokes white adipose tissue browning that leads to a substantially increased hypermetabolic response associated with poor outcomes. Therefore, the aim of this study was to determine the effect of age on the metabolic adipose response of browning after a burn injury.

METHOD

One hundred and seventy patients with burn injury admitted to the Ross Tilley Burn Centre were prospectively enrolled and grouped by age as older (≥50 years) and young (≤35 years). Adipose tissue and sera were collected and analyzed for browning markers and metabolic state via histology, gene expression, and resting energy expenditure assays.

RESULTS

We found that older patients with burn injury lacked the adipose browning response, as they showed significant reductions in uncoupling protein 1 (UCP1) expression. This failure of the browning response was associated with reduced whole-body metabolism and decreased survival in older patients with burn injury. Mechanistically, we found that the adipose of both aged patients after burn trauma and aged mice after a burn showed impairments in macrophage infiltration and IL-6, key immunological regulators of the browning process after a severe trauma.

CONCLUSION

Targeting pathways that activate the browning response represents a potential therapeutic approach to improve outcomes after burn trauma for elderly patients.

FUNDING

NIH (R01-GM087285-01), Canadian Institutes of Health Research (grant no. 123336), and Canada Foundation for Innovation Leaders Opportunity Fund (no. 25407).

Low-protein diet accelerates wound healing in mice post-acute injury

BACKGROUND

Wound healing processes are influenced by macronutrient intake (protein, carbohydrate and fat). The most favourable diet for cutaneous wound healing is not known, although high-protein diets are currently favoured clinically. This experimental study investigates the optimal macronutrient balance for cutaneous wound healing using a mouse model and the Geometric Framework, a nutrient modelling method, capable of analyzing the individual and interactive effects of a wide spectrum of macronutrient intake.

METHODS

Two adjacent and identical full-thickness skin excisions (1 cm2) were surgically created on the dorsal area of male C57BL/6 mice. Mice were then allocated to one of 12 high-energy diets that varied in protein, carbohydrate and fat content. In select diets, wound healing processes, cytokine expression, energy expenditure, body composition, muscle and fat reserves were assessed.

RESULTS

Using the Geometric Framework, we show that a low-protein intake, coupled with a balanced intake of carbohydrate and fat is optimal for wound healing. Mice fed a low-protein diet progressed quickly through wound healing stages with favourable wound inflammatory cytokine expression and significantly accelerated collagen production. These local processes were associated with an increased early systemic inflammatory response and a higher overall energy expenditure, related to metabolic changes occurring in key macronutrient reserves in lean body mass and fat depots.

CONCLUSIONS

The results suggest that a low-protein diet may have a greater potential to accelerate wound healing than the current clinically used high-protein diets.

Admission creatinine is associated with poor outcomes in burn patients

INTRODUCTION

Renal failure is the most common organ failure in severely burned patients. However, defining acute kidney injury and renal failure is very challenging. This study was designed to determine the relationship between a biomarker commonly measured on admission, serum creatinine, and outcomes in burn patients.

METHODS

We conducted a retrospective cohort study of adult patients (≥ 18 years) with a burn ≥ 5% total body surface area (TBSA) and a serum creatinine level measured within the first 72 h after injury. Patients were admitted over an 11-year period and divided into two groups based on creatinine levels measured within the first 72 h after injury. Patients were categorized in the high creatinine group if they had a measured creatinine ≥107 μmol/L (≥1.21 mg/dL); this value was chosen as the threshold for creatinine based on our institution's reference range. Clinical outcomes included morbidities, hospital length of stay, and mortality. Multivariable logistic regression was used to model the association between high admission creatinine and each outcome, adjusting for patient and injury characteristics.

RESULTS

We studied 923 patients, mean age 47 ± 18 years and median 13% (IQR 8-24) TBSA burned. There were 718 patients categorized with low admission creatinine and 205 patients with high admission creatinine. After adjustment for patient and injury characteristics, high admission creatinine was associated with a significantly higher rate of sepsis (OR 3.44; 95% CI 2.11-5.59), pneumonia (OR 4.56; 95% CI 1.8-11.53), and mortality (OR 3.59; 95% CI 1.91-6.75).

CONCLUSIONS

Elevated creatinine on admission is associated with an increased risk of morbidity and mortality. We suggest that admission creatinine can be used as a "red flag" to identify patients at a higher risk for poor outcomes.

Comparison of clinical outcomes of lower extremity burns in diabetic and non-diabetic patients: a retrospective analysis

Diabetes mellitus is an increasingly prevalent chronic disease that leads to long-term health consequences. Some long-term clinical sequelae of diabetes include coronary artery disease, peripheral vascular disease, peripheral neuropathy, and impaired wound healing. These can increase hospital stay and complications such as wound infections and amputations among patients with lower extremity burns. A retrospective analysis was performed of all isolated lower extremity burns from a single tertiary burn care centre from 2006-2017. Patients were stratified by diabetic status and the incidence of lower extremity amputations was the primary outcome. Multivariable regression was used to model the association between diabetes and amputations, adjusting for patient and injury characteristics. A total of 198 patients were identified as meeting inclusion criteria, 160 were non-diabetic and 38 were diabetic. Age was significantly different between non-diabetic and diabetic patients; mean age was 46 ± 18 years versus 62 ± 17 years (p<0.0001). Length of stay was also significantly different, median length of stay was 11 (IQR 7-15) versus 18 (IQR 12-24) (p<0.001), with diabetic patients staying longer. There was a significantly greater proportion of diabetic patients that had an amputation (control 4% versus diabetic 29%; p<0.0001). After adjustment for patient and injury characteristics, there was a significant association between diabetes and amputation (p=0.002). Among patients with isolated lower extremity burns, those with a pre-existing condition of diabetes had a longer hospitalization and increased amputations, despite similar size of burn. Diabetes is an important risk factor to acknowledge in patients with these injuries to optimize care.

Interleukin-6 blockade, a potential adjunct therapy for post-burn hypermetabolism

Severe burns remain a leading cause of death and disability worldwide. Despite advances in patient care, the excessive and uncontrolled hypermetabolic stress response induced by this trauma inevitably affects every organ system causing substantial morbidity and mortality. Recent evidence suggests interleukin-6 (IL-6) is a major culprit underlying post-burn hypermetabolism. Indeed, genetic deletion of IL-6 alleviates various complications associated with poor clinical outcomes including the adverse remodeling of adipose tissue, cachexia and hepatic steatosis. Thus, pharmacological blockade of IL-6 may be a more favorable treatment option to fully restore metabolic function after injury. To test this, we investigated the safety and effectiveness of blocking IL-6 for post-burn hypermetabolism using a validated anti-IL-6 monoclonal antibody (mAb) in our experimental murine model. Here, we show daily anti-IL-6 mAb administration protects against burn-induced weight loss (P < .0001) without any adverse effect on mortality. At the organ level, post-burn treatment with the IL-6 blocker suppressed the thermogenic activation of adipose tissue (P < .01) and its associated wasting (P < .05). The reduction of browning-induced lipolysis (P < .0001) indirectly decreased hepatic lipotoxicity (P < .01) which improved liver dysfunction (P < .05). Importantly, the beneficial effects of this anti-IL-6 agent extended to the skin, reflected by the decrease in excessive collagen deposition (P < .001) and genes involved in pathologic fibrosis and scarring (P < .05). Together, our results indicate that post-burn IL-6 blockade leads to significant improvements in systemic hypermetabolism by inhibiting pathological alterations in key immunometabolic organs. These findings support the therapeutic potential of anti-IL-6 interventions to improve care, quality of life, and survival in burned patients.

Oxandrolone in the Treatment of Burn Injuries: A Systematic Review and Meta-analysis

Severe burns induce a profound hypermetabolic response, leading to a prolonged state of catabolism associated with organ dysfunction and delay of wound healing. Oxandrolone, a synthetic testosterone analog, may alleviate the hypermetabolic catabolic state thereby decreasing associated morbidity. However, current literature has reported mixed outcomes on complications following Oxandrolone use, specifically liver and lung function. We conducted an updated systematic review and meta-analysis studying the effects of Oxandrolone on mortality, length of hospital stay, progressive liver dysfunction, and nine secondary outcomes. We searched Pubmed, EMBASE, Web of Science, CINAHL, and Cochrane Databases of Systematic Reviews and Randomized Controlled Trials. Thirty-one randomized control trials and observational studies were included. Basic science and animal studies were excluded. Only studies comparing Oxandrolone to standard of care, or placebo, were included. Oxandrolone did not affect rates of mortality (relative risk [RR]: 0.72; 95% confidence interval [CI]: 0.47 to 1.08; P = .11) or progressive liver dysfunction (RR: 1.04; 95% CI: 0.59 to 1.85; P = .88), but did decrease length of stay in hospital. Oxandrolone significantly increased weight regain, bone mineral density, percent lean body mass, and decreased wound healing time for donor graft sites. Oxandrolone did not change the incidence of transient liver dysfunction or mechanical ventilation requirements. There is evidence to suggest that Oxandrolone is a beneficial adjunct to the acute care of burn patients; shortening hospital stays and improving several growth and wound healing parameters. It does not appear that Oxandrolone increases the risk of progressive or transient liver injury, although monitoring liver enzymes is recommended.