What's new in burns and metabolism

Early expression of IL-10, IL-12, ARG1, and NOS2 genes in peripheral blood mononuclear cells synergistically correlate with patient outcome after burn injury

BACKGROUND

No methods exist to rapidly and accurately quantify the immune insult created by burn injuries. The development of a rapid, noninvasive clinical biomarker assay that evaluates a burn patient's underlying immune dysfunction and predicts clinical outcomes could transform burn care. We aimed to determine a set of peripheral biomarkers that correlates with clinical outcomes of burn patients.

METHODS

This prospective observational study enrolled two patient cohorts within a single burn center into an institutionally approved institutional review board study. Blood draws were performed <48 hours after injury. Initial unbiased immune gene expression analysis compared 23 burn patients and 6 healthy controls using multiplex immune gene expression analysis of RNA from peripheral blood mononuclear cells. We then performed confirmatory outcomes analysis in 109 burn patients and 19 healthy controls using a targeted rapid quantitative polymerase chain reaction. Findings were validated and modeled associations with clinical outcomes using a regression model.

RESULTS

A total of 149 genes with a significant difference in expression from burn patients compared with controls were identified. Pathway analysis identified pathways related to interleukin (IL)-10 and inducible nitric oxide synthase signaling to have significant z scores. quantitative polymerase chain reaction analysis of IL-10, IL-12, arginase 1 (ARG1), and inducible nitric oxide synthase demonstrated that burn injury was associated with increased expression of ARG1 and IL-10, and decreased expression of nitric oxide synthase 2 (NOS2) and IL-12. Burn severity, acute lung injury, development of infection, failure of skin autograft, and mortality significantly correlated with expression of one or more of these genes. Ratios of IL-10/IL-12, ARG1/NOS2, and (ARG1-IL-10)/(NOS2-IL-12) transcript levels further improved the correlation with outcomes. Using a multivariate regression model, adjusting for patient confounders demonstrated that (ARG1-IL-10)/(NOS2-IL-12) significantly correlated with burn severity and development of acute lung injury.

CONCLUSION

We present a means to predict patient outcomes early after burn injury using peripheral blood, allowing early identification of underlying immune dysfunction.

LEVEL OF EVIDENCE

Prognostic/Epidemiological; Level II.

Burn Injury Induces Proinflammatory Plasma Extracellular Vesicles That Associate with Length of Hospital Stay in Women: CRP and SAA1 as Potential Prognostic Indicators

Severe burn injury is a devastating form of trauma that results in persistent immune dysfunction with associated morbidity and mortality. The underlying drivers of this immune dysfunction remain elusive, and there are no prognostic markers to identify at-risk patients. Extracellular vesicles (EVs) are emerging as drivers of immune dysfunction as well as biomarkers. We investigated if EVs after burn injury promote macrophage activation and assessed if EV contents can predict length of hospital stay. EVs isolated early from mice that received a 20% total body surface area (TBSA) burn promoted proinflammatory responses in cultured splenic macrophages. Unbiased LC-MS/MS proteomic analysis of early EVs (<72 h post-injury) from mice and humans showed some similarities including enrichment of acute phase response proteins such as CRP and SAA1. Semi-unbiased assessment of early human burn patient EVs found alterations consistent with increased proinflammatory signaling and loss of inhibition of CRP expression. In a sample of 50 patients with large burn injury, EV SAA1 and CRP were correlated with TBSA injury in both sexes and were correlated with length of hospital stay in women. These findings suggest that EVs are drivers of immune responses after burn injury and their content may predict hospital course.

Plasma extracellular vesicles released after severe burn injury modulate macrophage phenotype and function

Extracellular vesicles (EVs) have emerged as key regulators of immune function across multiple diseases. Severe burn injury is a devastating trauma with significant immune dysfunction that results in an ∼12% mortality rate due to sepsis-induced organ failure, pneumonia, and other infections. Severe burn causes a biphasic immune response: an early (0-72 h) hyper-inflammatory state, with release of damage-associated molecular pattern molecules, such as high-mobility group protein 1 (HMGB1), and proinflammatory cytokines (e.g., IL-1β), followed by an immunosuppressive state (1-2+ wk post injury), associated with increased susceptibility to life-threatening infections. We have reported that early after severe burn injury HMGB1 and IL-1β are enriched in plasma EVs. Here we tested the impact of EVs isolated after burn injury on phenotypic and functional consequences in vivo and in vitro using adoptive transfers of EV. EVs isolated early from mice that underwent a 20% total body surface area burn injury (burn EVs) caused similar hallmark cytokine responses in naïve mice to those seen in burned mice. Burn EVs transferred to RAW264.7 macrophages caused similar functional (i.e., cytokine secretion) and immune gene expression changes seen with their associated phase of post-burn immune dysfunction. Burn EVs isolated early (24 h) induced MCP-1, IL-12p70, and IFNγ, whereas EVs isolated later blunted RAW proinflammatory responses to bacterial endotoxin (LPS). We also describe significantly increased HMGB1 cargo in burn EVs purified days 1 to 7 after injury. Thus, burn EVs cause immune outcomes in naïve mice and macrophages similar to findings after severe burn injury, suggesting EVs promote post-burn immune dysfunction.

Determination of lymphocytes surface markers in patients with thermal burns and the influence of burn size on mononuclear cell subsets

Background: Thermal burn injuries impair the host defence system. Hence, in the present study, we aimed at investigating the changes in the number and phenotype of peripheral blood lymphocyte populations (T, B, and natural killer cells) and their subpopulations in patients with thermal burns and determining the relationships with different sizes of total body surface area (TBSA). Methods: Blood samples from 67 patients, admitted to Motahary Burn Center in Tehran, with burns from 30% to more than 70% TBSA were collected on Days 3 and 7 postburn. Lymphocytes and their subpopulations were identified by monoclonal antibodies. The cells were analyzed using flow cytometry. The results were compared with healthy controls. Results: In this study, 3 and 7 days after burn injury, the percentages of CD3+, CD4+ and CD8+ lymphocyte significantly decreased, CD4+/CD8+ ratios were below the normal range, and CD19+ (B cells) significantly increased. No significant difference was obtained in the mean percentage of CD16+ (NK cells) between Days 3 and 7 postburn. Patients with burns of 30% TBSA or greater (>70%) had a significant reduction in CD3+, CD4+ and CD8+ ( T cells) numbers up to 7 days compared with 3 days after burn injury. Patients with 30% to >70 % TBSA burn failed to show any significant changes in CD4+/CD8+ ratio as well as CD16+ (NK cells) 3 to 7 days after burn. In patients with burns more than 30% to>70% TBSA, CD19+ (B cells) number changes were found to be complicated after 3 and 7 days. Conclusion: The results of this study suggest that alterations of immune cell surface markers and TBSA% can reflect postburn lymphocyte activation.

Direct detection of blood nitric oxide reveals a burn-dependent decrease of nitric oxide in response to Pseudomonas aeruginosa infection

PURPOSE

Burn is associated with severe immune dysfunction, including an anti-inflammatory state that occurs late after burn. While increased nitric oxide (NO) production is associated with severe infection and sepsis, the effect of burn trauma on these levels during a non-lethal infection remains unknown. We hypothesized that in a mouse model, (1) NO levels would be increased after infection without trauma and (2) burn would lead to decreased NO production even during infection.

METHODS

Mice were infected via intra-tracheal inoculation with Pseudomonas aeruginosa 14 d following a 20% total body surface area contact burn. At 48h following infection, blood was drawn to quantify NO concentrations using a microfluidic electrochemical sensor.

SIGNIFICANT FINDINGS

In uninjured mice, infection caused a significant increase in blood NO levels. Increases in NO occurred in a dose-dependent response to the bacterial inoculum. Following burn, an identical infection did not elicit increases in NO.

CONCLUSIONS

While increases in NO are expected over the course of an infection without prior trauma, burn and subsequent immune suppression decreases NO levels even in the presence of infection.

The role of hydrogen sulfide in burns

Hydrogen sulfide is a novel gasotransmitter that has been shown to play a major role in regulating vascular tone. However, the role of hydrogen sulfide in inflammation, sepsis and burns has only recently been studied. In animal studies, hydrogen sulfide has been shown to play a role in both promoting and inhibiting inflammation. Understanding the role of H2S in sepsis and shock is particularly important due to the high mortality associated with both conditions. In animal sepsis models, hydrogen sulfide appears to increase survival. Severe burns are associated with an inflammatory response that causes increased permeability and edema. Currently, there are few studies that have examined the exact role of hydrogen sulfide in burns. However, the role of hydrogen sulfide in inflammation enables us to hypothesize its role in burns. This review highlights the role of hydrogen sulfide in the mechanisms of action underlying inflammation, wound healing and sepsis as well as examining the potential role of hydrogen sulfide in burns. The authors of this article hope that this review will stimulate research to discover the exact role of this fascinating molecule in burns.

5-HT2a receptor antagonism reduces burn-induced macromolecular efflux in rats

BACKGROUND

Major thermal injuries lead to a systemic inflammatory response with systemic capillary leakage and multiple organ dysfunction. This systemic inflammatory response is induced by a variety of immunmodulative molecules including TNFα and serotonin. Unspecific serotonin antagonism leads to reduced macromolecular efflux in rat mesenteries after burn plasma transfer. The aim of the present study was to evaluate the effect of specific 5-HT2a antagonism on early burn edema.

METHODS

Donor rats (DR) underwent thermal injury (100 °C water, 30% BSA, 12 s) for positive controls. For negative controls, DR underwent sham burn (37 °C water, 30% BSA, 12 s). DR plasma (harvested 4 h post-trauma) was transferred to healthy individuals for positive controls. Study rats received burn plasma (BP) and a Bolus injection of Ketanserin (Ket) (1 mg kg(-1) body weight). Negative controls underwent sham burn plasma infusion. Intravital microscopy was performed in mesenteric venules (0/60/120 min). Edema was assessed by FITC-albumin extravasation. Additionally, leukocyte rolling and sticking (cells mm(-2)) as well as microhemodynamic parameters were assessed.

RESULTS

Significant systemic capillary leakage was observed after BP transfer at 120 min and additional administration of Ket attenuated the postburn edema to sham burn levels. Ket also leads to significantly decreased leukocyte-endothelial interactions when compared to positive controls.

CONCLUSION

5-HT2a antagonism reduces plasma extravasation after burn plasma transfer in healthy individuals. The influence of leukocyte-endothelial interactions on postburn edema remains unclear.

Comparison of skin effects of immediate treatment modalities in experimentally induced hydrofluoric acid skin burns

Hydrofluoric acid (HF) burns cause immediate damage and painful long-term sequellae. Traditionally, chelating agents have been used as the initial treatment for such burns. We have introduced epidermal growth factor (EGF) into an HF model to compare EGF with Ca(2+) and Mg(2+) treatments; 40 Sprague Dawley rats were divided into five groups. Each rat suffered a 6 × 4 cm(2) burn induced by 40% HF. Group 1 had no treatment, group 2 had saline injected beneath the burn, group 3 received magnesium sulphate injections, group 4 received calcium gluconate and group 5 received EGF. Specimens were evaluated via planimetry and biopsy at intervals of 4, 8, 24 and 72 hours. Fluid losses were significantly less in the Mg(2+) and EGF groups. The EGF group had the smallest burn area, least oedema, least polymorphonuclear granulocyte (PMN) infiltration, most angiogenesis and highest fibroblast proliferation of any group (P < 0·005). EGF limited HF damage morphologically and histologically more effectively than Ca(2+) or Mg(2+). This finding indicates that HF treatment via growth factors may be an improvement over chelation therapy.

Myosin light chain kinase signaling in endothelial barrier dysfunction

Microvascular barrier dysfunction is a serious problem that occurs in many inflammatory conditions, including sepsis, trauma, ischemia-reperfusion injury, cardiovascular disease, and diabetes. Barrier dysfunction permits extravasation of serum components into the surrounding tissue, leading to edema formation and organ failure. The basis for microvascular barrier dysfunction is hyperpermeability at endothelial cell-cell junctions. Endothelial hyperpermeability is increased by actomyosin contractile activity in response to phosphorylation of myosin light chain by myosin light chain kinase (MLCK). MLCK-dependent endothelial hyperpermeability occurs in response to inflammatory mediators (e.g., activated neutrophils, thrombin, histamine, tumor necrosis factor alpha, etc.), through multiple cell signaling pathways and signaling molecules (e.g., Ca(++) , protein kinase C, Src kinase, nitric oxide synthase, etc.). Other signaling molecules protect against MLCK-dependent hyperpermeability (e.g., sphingosine-1-phosphate or cAMP). In addition, individual MLCK isoforms play specific roles in endothelial barrier dysfunction, suggesting that isoform-specific inhibitors could be useful for treating inflammatory disorders and preventing multiple organ failure. Because endothelial barrier dysfunction depends upon signaling through MLCK in many instances, MLCK-dependent signaling comprises multiple potential therapeutic targets for preventing edema formation and multiple organ failure. The following review is a discussion of MLCK-dependent mechanisms and cell signaling events that mediate endothelial hyperpermeability.

Erythropoietin in the prevention of experimental burn progression

Background

Damage control is essential in first aid of burn lesions. The aim of the present study was to investigate whether systemic erythropoietin (EPO) administration could prevent secondary burn progression in an experimental model.

Methods

The burn comb model creates four rectangular burn surfaces intercalated by three unburned zones prone to progression. Twenty-one Wistar rats were randomized to a control group or to receive intraperitoneal EPO (500 units per kg) once a day for 5 days starting 45 min (EPO45min) or 6 h (EPO6h) after burn injury. Histological analyses assessing burn depth, inflammation and neoangiogenesis, planimetric evaluation of burn progression, and laser Doppler flowmetry to assess perfusion were performed after 1, 4 and 7 days. Final scarring time and contracture rate were assessed once a week.

Results

Burn progression was decreased significantly with EPO45min but not EPO6h; progression of burn depth stopped in the intermediate dermis (mean(s.e.m.) burn depth score 3·3(0·6) for EPO45min versus 4·7(0·3) and 5·0(0·0) for EPO6h and control respectively on day 7; P = 0·026) and the surface extension was significantly reduced (45(8), 65(4) and 78(4) respectively on day 7; P = 0·017). This was paralleled by faster re-establishment of perfusion with EPO45min (114(5) per cent on day 4 versus 85(6) and 91(3) per cent for EPO6h and control respectively; P = 0·096). The reduction in progression resulted in a decreased healing time (7·3(0·7) weeks for EPO45min versus 11·5(1·0) and 10·8(0·5) weeks for EPO6h and control; P = 0·020) and contracture rate (P = 0·024).

Conclusion

Early EPO prevented burn progression, mainly by improved vascular perfusion.

Development of Metabolic Indicators of Burn Injury: Very Low Density Lipoprotein (VLDL) and Acetoacetate Are Highly Correlated to Severity of Burn Injury in Rats

Hypermetabolism is a significant sequela to severe trauma such as burns, as well as critical illnesses such as cancer. It persists in parallel to, or beyond, the original pathology for many months as an often-fatal comorbidity. Currently, diagnosis is based solely on clinical observations of increased energy expenditure, severe muscle wasting and progressive organ dysfunction. In order to identify the minimum number of necessary variables, and to develop a rat model of burn injury-induced hypermetabolism, we utilized data mining approaches to identify the metabolic variables that strongly correlate to the severity of injury. A clustering-based algorithm was introduced into a regression model of the extent of burn injury. As a result, a neural network model which employs VLDL and acetoacetate levels was demonstrated to predict the extent of burn injury with 88% accuracy in the rat model. The physiological importance of the identified variables in the context of hypermetabolism, and necessary steps in extension of this preliminary model to a clinically utilizable index of severity of burn injury are outlined.

High-dose vitamin C treatment reduces capillary leakage after burn plasma transfer in rats

Oxidative stress after burn injuries leads to systemic capillary leakage and leukocyte activation. This study evaluates whether antioxidative treatment with high-dose vitamin C leads to burn edema reduction and prevention of leukocyte activation after burn plasma transfer. Donor rats underwent a burn (n = 7; 100 degrees C water, 12 seconds, 30% body surface area) or sham burn (37 degrees C water; n = 2) procedure and were killed after 4 hours for plasma harvest. This plasma was administered to study rats (continuous infusion). Rats were randomized to four groups (n = 8 each; burn plasma alone [BP]; burn plasma/vitamin C-bolus 66 mg/kg and maintenance dose 33 mg/kg/hr [VC66]; burn plasma/vitamin C-bolus 33 mg/kg and maintenance dose 17.5 mg/kg/hr [VC33]; and sham burn plasma [SB]). Intravital fluorescence microscopy in the mesentery was performed at 0, 60, and 120 minutes for microhemodynamic parameters, leukocyte adherence, and fluorescein isothiocyanate-albumin extravasation. No differences were observed in microhemodynamics at any time. Burn plasma induced capillary leakage, which was significantly higher compared with sham burn controls (P < .001). VC66 treatment reduced microvascular barrier dysfunction to sham burn levels, whereas VC33 had no significant effect. Leukocyte sticking increased after burn plasma infusion, which was not found for sham burn. Vitamin C treatment did not influence leukocyte activation (P > .05). Burn plasma transfer leads to systemic capillary leakage. High-dose vitamin C treatment (bolus 66 mg/kg and maintenance dose 33 mg/kg/hr) reduces endothelial damage to sham burn levels, whereas half the dose is inefficient. Leukocyte activation is not influenced by antioxidative treatment. Therefore, capillary leakage seems to be independent from leukocyte-endothelial interactions after burn plasma transfer. High-dose vitamin C should be considered for parenteral treatment in every burn patient.

Myosin light chain kinase in microvascular endothelial barrier function

Microvascular barrier dysfunction is implicated in the initiation and progression of inflammation, posttraumatic complications, sepsis, ischaemia-reperfusion injury, atherosclerosis, and diabetes. Under physiological conditions, a precise equilibrium between endothelial cell-cell adhesion and actin-myosin-based centripetal tension tightly controls the semi-permeability of microvascular barriers. Myosin light chain kinase (MLCK) plays an important role in maintaining the equilibrium by phosphorylating myosin light chain (MLC), thereby inducing actomyosin contractility and weakening endothelial cell-cell adhesion. MLCK is activated by numerous physiological factors and inflammatory or angiogenic mediators, causing vascular hyperpermeability. In this review, we discuss experimental evidence supporting the crucial role of MLCK in the hyperpermeability response to key cell signalling events during inflammation. At the cellular level, in vitro studies of cultured endothelial monolayers treated with MLCK inhibitors or transfected with specific inhibiting peptides have demonstrated that induction of endothelial MLCK activity is necessary for hyperpermeability. Ex vivo studies of live microvessels, enabled by development of the isolated, perfused venule method, support the importance of MLCK in endothelial permeability regulation in an environment that more closely resembles in vivo tissues. Finally, the role of MLCK in vascular hyperpermeability has been confirmed with in vivo studies of animal disease models and the use of transgenic MLCK210 knockout mice. These approaches provide a more complete view of the role of MLCK in vascular barrier dysfunction.

Role of hydrogen sulfide in severe burn injury-induced inflammation in mice

Endogenous hydrogen sulfide (H(2)S) is naturally synthesized in many types of mammalian cells from L-cysteine in the reactions catalyzed by cystathionine-β-synthase and cystathionine-γ-lyase (CSE). H(2)S has been demonstrated to play a proinflammatory role in various animal models of hindpaw edema, acute pancreatitis, lipopolysaccharide-induced endotoxemia and cecal ligation, and puncture-induced sepsis. Full-thickness burns that exceed 25% of the total body surface area (TBSA) produce a profound systemic inflammatory reaction characterized by leukocyte activation and plasma leakage in the microvasculature of tissues and organs remote from the wound. The aim of this study was to investigate the effect of local burn injury on induced distant organ endogenous H(2)S release and expression of CSE. Male BALB/c mice were subjected to 30% TBSA full-thickness burn and treated with saline (administered intraperitoneally [i.p.]); DL-propargylglycine (PAG, 50 mg/kg i.p.), which is a CSE inhibitor; or sodium hydrosulfide (NaHS, 10 mg/kg i.p.), which is an H(2)S donor. PAG was administered either 1 h before or 1 h after the burn injury, whereas NaHS was given at the same time as the burn injury. Measurements of liver myeloperoxidase (MPO) activities, liver H(2)S-synthesizing activity, plasma H(2)S level and liver and lung CSE mRNA expression and histological examination of tissues were performed after burn injury. Burn injury significantly increased the plasma H(2)S level and liver H(2)S synthesis 8 h after burn compared with the sham group. Burn injury also resulted in a significant upregulation of CSE mRNA in liver and lung. Prophylactic as well as therapeutic administration of PAG significantly reduced burn-associated systemic inflammation, as evidenced by MPO activity and histological changes in liver and lung. Injection of NaHS significantly aggravated burn-associated systemic inflammation. Therefore, our findings show for the first time the role of H(2)S in contributing to inflammatory damage after burn injury.

Endothelial contractile cytoskeleton and microvascular permeability

Microvascular barrier dysfunction represents a significant problem in clinical conditions associated with trauma, burn, sepsis, acute respiratory distress syndrome, ischemia-reperfusion injury, and diabetic retinopathy. An important cellular mechanism underlying microvascular leakage is the generation of contractile force from the endothelial cytoskeleton, which counteracts cell-cell and cell-matrix adhesions leading to paracellular hyperpermeability. In this review, we present recent experimental evidence supporting the critical role of MLCK-activated, RhoA/ROCK-regulated contractile cytoskeleton in endothelial permeability response to inflammatory and thrombotic stimuli arising from thermal injury, activated neutrophils, vascular endothelial growth factor, and fibrinogen degradation products. Further understanding the molecular basis of microvascular barrier structure and function would contribute to the development of novel therapeutic targets for treating circulatory disorders and vascular injury.

Toll-like receptor 4 contributes to microvascular inflammation and barrier dysfunction in thermal injury

Systemic and microvascular inflammation plays a key role in the development of multiple organ failure after infection, sepsis, and traumatic injury. Toll-like receptors (TLRs) regulate host responses to pathogens and sterile, injury-associated inflammatory responses. We investigated whether TLR-4 contributes to microvascular dysfunction during thermal injury in vivo in anesthetized wild-type or TLR-4 (-/-) mice receiving either a 25% total body surface area full-thickness scald burn or sham treatment on the dorsal skin. Using intravital microscopy, we assessed the hemodynamics and leukocyte dynamics in the mesenteric microvasculature as representative of the splanchnic microcirculation at a site remote from the burn wound. The transvascular flux of fluorescein isothiocyanate-albumin across mesenteric venules was measured as an indicator of microvascular permeability. Furthermore, cultured microvascular endothelial cell models were used to evaluate the endothelial-specific mechanisms involved in TLR-4-mediated barrier dysfunction. The results showed significantly elevated microvascular permeability in wild-type mice after burn, whereas this response was markedly attenuated in TLR-4 (-/-) mice. Burn injury also increased leukocyte adhesion in mesenteric venules of wild-type mice, and a blunted leukocyte response was seen in the TLR-4 mice. Treatment of endothelial cell monolayers with burn plasma induced a rapid reduction in the transendothelial electrical resistance measured by electric cell-substrate impedance sensing, indicative of endothelial cell-cell adhesive barrier dysfunction. Reducing expression of TLR-4 with siRNA treatment attenuated this response. Taken together, these data indicate that TLR-4 plays an important role in microvascular leakage and leukocyte adhesion under the inflammatory condition associated with nonseptic thermal injury.

Toll-like receptor 2 and 4 ligation results in complex altered cytokine profiles early and late after burn injury

BACKGROUND

Toll-like receptors (TLR) 2 and TLR4 expressed on innate immune cells are important mediators of the immune response to pathogens. In this study, we hypothesized that burn injury results in altered cytokine secretion profiles after TLR2 or TLR4 ligation that is associated with altered TLR expression on innate immune cells.

METHODS

Female C56BL/6 mice were subjected to 20% full thickness burn or sham injury. Three or 14 days after injury whole splenocytes or purified splenic macrophages were cultured with TLR2 ligand peptidoglycan or TLR4 ligand lipopolysaccharide. Supernatants were assayed for TNF-alpha, MCP-1, IL-6 and IL-10. Cell death was assessed using flow cytometry. Innate CD11b F4/80 macrophages were sorted 14 days after burn injury and TLR2 and 4 expression was determined by quantitative reverse-transcriptase polymerase chain reaction and flow cytometry.

RESULTS

Burn injury results in a steady accumulation in the periphery of CD11bF4/80 macrophages. Macrophages purified early after burn injury upregulated TLR2 and 4, followed by a decrease of TLR2 and TLR4 expression late after burn injury. TLR2 and TLR4 ligation of an equivalent number of purified macrophages 3 days after burn injury revealed no significant differences in cytokine secretion compared with sham. Stimulation 14 days after burn injury revealed a significant reduction in tumor necrosis factor-alpha secretion by macrophages compared with sham mice. In contrast, interleukin-10 was significantly increased (mean, approximately 1.8-fold) late after burn injury after either TLR2 or TLR4 stimulation. Interleukin-6 and monocyte chemotactic protein-1 secretion was unchanged from sham levels. In contrast, whole splenocyte stimulation resulted in increased cytokine 3 days and 14 days after burn injury. This effect is likely caused by the accumulation of TLR macrophages, which are resistant to TLR-induced cell death.

CONCLUSIONS

Cytokine secretion profiles after TLR2 and TLR4 ligation after burn injury are altered in a manner not clearly reflective of an anti-inflammatory or proinflammatory state and are associated with unique changes in the macrophage population. TLR2 and TLR4 ligation have complex and varied roles in mediating the immune response to burn injury.

Nutrition in burns: Need for an aggressive dynamic approach

INTRODUCTION

Extensive burns elicit a pronounced metabolic response causing physiological derangements leading to the hyper-metabolic state. The hyper-metabolic response is accompanied by severe catabolism and a loss of lean body mass and also by a progressive decline of host defenses that impairs the immunological response.

AIMS

A study was conducted in our hospital to assess various aspects of nutritional management of burns considering the ground realities of general hospital. The main aim of the study was to assess the use of early naso-gastric tube insertion, charting out daily calorie intake and to appropriately decrease the deficit with use of low cost feeds taking in to consideration the local dietary habits.

MATERIALS AND METHODS

A total 138 cases were studied prospectively during April 2003 to March 2005, which were compared with 206 controls taken retrospectively from April 2000 to March 2003. The cases and controls were compared regarding the mortality rate, average days of stay and number of procedure done after dividing them in to various categories (%Burns) using the Z-test and student t-test.

DISCUSSION AND CONCLUSION

The use of early naso-gastric tube insertion, charting out daily calorie intake and using low cost feeds consistent with local dietary habits lead to a significant decrease in average number of days and the number of procedures in 20-39% TBSA burns; and caused the significant decrease in mortality, average number of days and the number of procedure in 40-59%TBSA burns.

Increased Toll-like receptor 4 expression on T cells may be a mechanism for enhanced T cell response late after burn injury

BACKGROUND

Burn injury is associated with a dynamic T cell response. We have previously reported an enhanced functional T cell response 14 days after burn injury. Toll-like receptors (TLR), primarily expressed on innate immune cells, have recently been identified on certain T cell subsets, including activated and memory T cells. Our hypothesis is that increased TLR4 expression on memory T cells may be a mechanism for enhanced T cell response 14 days after burn injury.

METHODS

Splenocytes from wild-type C57Bl/6 mice were harvested 14 days after a 20% total body surface area (TBSA) scald burn or sham injury. Splenocytes ex vivo were surface stained either with monoclonal anti-CD3, anti-CD4, anti-CD8, or anti-CD44 antibodies or a two-step biotin-TLR4 monoclonal antibody-streptavidin-FITC surface stain and results analyzed by flow cytometry.

RESULTS

TLR4 expression is successfully detected on CD4 and CD8 T cells. TLR4 expression is significantly (p < 0.05) increased on CD4 T cells and CD8 T cells 14 days after burn injury. There is a significant (p < 0.05) increase in CD44 (memory) CD4 and CD44 (memory) CD8 T cells 14 days after burn injury and this is associated with a significant (p < 0.05) increase of TLR4 expression in both T cell populations.

CONCLUSIONS

This study demonstrates for the first time the potential role of TLR4 expression on memory T cells generated late after burn injury. Although further analysis is required, these data reiterate the importance of adaptive immunity and the complexity of the immune response to burn injury.

Burn wound infections

Burns are one of the most common and devastating forms of trauma. Patients with serious thermal injury require immediate specialized care in order to minimize morbidity and mortality. Significant thermal injuries induce a state of immunosuppression that predisposes burn patients to infectious complications. A current summary of the classifications of burn wound infections, including their diagnosis, treatment, and prevention, is given. Early excision of the eschar has substantially decreased the incidence of invasive burn wound infection and secondary sepsis, but most deaths in severely burn-injured patients are still due to burn wound sepsis or complications due to inhalation injury. Burn patients are also at risk for developing sepsis secondary to pneumonia, catheter-related infections, and suppurative thrombophlebitis. The introduction of silver-impregnated devices (e.g., central lines and Foley urinary catheters) may reduce the incidence of nosocomial infections due to prolonged placement of these devices. Improved outcomes for severely burned patients have been attributed to medical advances in fluid resuscitation, nutritional support, pulmonary and burn wound care, and infection control practices.

Lymphopenia-Induced Homeostatic Proliferation of CD8+T Cells Is a Mechanism for Effective Allogeneic Skin Graft Rejection following Burn Injury

Burn patients are immunocompromised yet paradoxically are able to effectively reject allogeneic skin grafts. Failure to close a massive burn wound leads to sepsis and multiple system organ failure. Immune suppression early (3 days) after burn injury is associated with glucocorticoid-mediated T cell apoptosis and anti-inflammatory cytokine responses. Using a mouse model of burn injury, we show CD8+ T cell hyperresponsiveness late (14 days) after burn injury. This is associated with a CD8+ T cell pro- and anti-inflammatory cytokine secretion profile, peripheral lymphopenia, and accumulation of a rapidly cycling, hyperresponsive memory-like CD8+CD44+ IL-7R- T cells which do not require costimulation for effective Ag response. Adoptive transfer of allospecific CD8+ T cells purified 14 days postburn results in enhanced allogeneic skin graft rejection in unburned recipient mice. Chemical blockade of glucocorticoid-induced lymphocyte apoptosis early after burn injury abolishes both the late homeostatic accumulation of CD8+ memory-like T cells and the associated enhanced proinflammatory CD8+ T cell response, but not the late enhanced CD8+ anti-inflammatory response. These data suggest a mechanism for the dynamic CD8+ T cell response following injury involving an interaction between activation, apoptosis, and cellular regeneration with broad clinical implications for allogeneic skin grafting and sepsis.

Burn wound infections

Burns are one of the most common and devastating forms of trauma. Patients with serious thermal injury require immediate specialized care in order to minimize morbidity and mortality. Significant thermal injuries induce a state of immunosuppression that predisposes burn patients to infectious complications. A current summary of the classifications of burn wound infections, including their diagnosis, treatment, and prevention, is given. Early excision of the eschar has substantially decreased the incidence of invasive burn wound infection and secondary sepsis, but most deaths in severely burn-injured patients are still due to burn wound sepsis or complications due to inhalation injury. Burn patients are also at risk for developing sepsis secondary to pneumonia, catheter-related infections, and suppurative thrombophlebitis. The introduction of silver-impregnated devices (e.g., central lines and Foley urinary catheters) may reduce the incidence of nosocomial infections due to prolonged placement of these devices. Improved outcomes for severely burned patients have been attributed to medical advances in fluid resuscitation, nutritional support, pulmonary and burn wound care, and infection control practices.

PKC-dependent, burn-induced adherens junction reorganization and barrier dysfunction in pulmonary microvascular endothelial cells

Rat lung microvascular endothelial cell monolayers were exposed to donor plasma from burned rats (25% total body surface area) at 1:3 dilution for 30 min. Immunofluorescence analysis revealed that concomitant with gap formation alterations were seen in the adherens junction (AJ) proteins beta-catenin and vascular endothelial-cadherin. Both of these components were shown to exist in a smooth, uniform arrangement at the cell periphery in untreated cells. However, upon exposure to burn plasma, this uniformity was lost, and the AJ proteins showed a disrupted, zipper-like pattern at the cells' edge. In addition, these proteins were absent from areas of gap formation between the cells, and an increase in punctate staining throughout the cells suggests they were internalized in response to burn plasma. Measurements of both transendothelial electrical resistance and FITC-albumin flux across the cell monolayer were used to assess barrier integrity. Our study found that exposure to burn plasma rapidly caused the electrical resistance across confluent monolayers to decrease and albumin flux to increase, phenomena associated with barrier dysfunction. Furthermore, all the above responses to burn plasma were attenuated when cells were pretreated with the PKC inhibitor bisindolylmaleimide, suggesting that PKC is required for burn-induced pulmonary endothelial dysfunction.

The effects of transforming growth factor-beta neutralization on postburn humoral immunity

BACKGROUND

Burn injury induces immunosuppression, which is associated with an increased susceptibility to infection. Our laboratory has demonstrated that burn injury also impairs humoral immunity. We reported that burn injury enhanced expression of transforming growth factor-beta (TGF-beta) mRNA and that exogenous TGF-beta further impaired humoral immunity. The objective of this study was to clarify the role of TGF-beta on humoral immunity after burn injury with a neutralizing experiment.

METHODS

Twelve BALB/c mice were randomly divided into two groups: sham and burn. Anesthetized mice received a 20% full-thickness burn or sham injury. The murine splenocytes containing 1.5 x 10 cells/mL were cultured with 2.5 microg/mL of lipopolysaccharide with or without 0.5 ng/mL of TGF-beta or 1 microg/mL of anti-TGF-beta neutralizing antibody, if necessary. Concentrations of immunoglobulin (Ig) M in the cell culture supernatant were determined by enzyme-linked immunosorbent assay and the number of IgM-secreting cells in the culture was measured by enzyme-linked immunospot assay.

RESULTS

After 2-day culture, neutralization of TGF-beta dramatically restored IgM synthesis after burn injury. After 5-day culture, however, it restored IgM concentration but failed to restore a number of IgM-secreting cells.

CONCLUSION

This neutralizing experiment demonstrated that TGF-beta is one of the inhibitors of IgM synthesis after burn injury. However, neutralization of TGF-beta was not enough to completely restore humoral immunity after burn injury. Investigation of the mechanism of impaired IgM synthesis after burn injury should be continued.

Myosin light chain phosphorylation and pulmonary endothelial cell hyperpermeability in burns

Major cutaneous burns result in not only localized tissue damage but broad systemic inflammation causing organ system damage distal to the burn site. It is well recognized that many problems result from the release of inflammatory mediators that target vascular endothelial cells, causing organ dysfunction. The pulmonary microvessels are particularly susceptible to functional abnormalities as a direct consequence of exposure to burn-induced inflammatory mediators. Traditional therapeutic intervention is quite often ineffective in treating burn patients suffering from systemic problems. A possible explanation for this ineffectiveness may be that because so many mediators are released, supposedly activating numerous signaling cascades that interact with each other, targeting of upstream factors in these cascades on an individual basis becomes futile. Therefore, if an end-point effector responsible for endothelial dysfunction following burn injury could be identified, it may present a target for intervention. In this study, we identified phosphorylation of myosin light chain (MLC) as a required element of burn plasma-induced hyperpermeability across rat lung microvascular endothelial cell monolayers. In addition, pharmacological inhibition of myosin light chain kinase (MLCK) and Rho kinase as well as transfection of MLCK-inhibiting peptide blocked actin stress fiber formation and MLC phosphorylation in response to burn plasma. The results suggest that blocking MLC phosphorylation may provide therapeutic intervention in burn patients with the goal of alleviating systemic inflammation-induced endothelial dysfunction.

Myosin light chain kinase-dependent microvascular hyperpermeability in thermal injury

Although the critical role of systemic inflammatory edema in the development of multiple organ failure in patients with massive burns has been fully recognized, the precise mechanisms responsible for the accumulation of blood fluid and proteins in tissues remote from the burn wound are poorly understood. The aim of this study was to test the hypothesis that circulating factors released during thermal injury cause microvascular leakage by triggering endothelial cell contraction and barrier dysfunction. A third-degree scald burn was induced in rats on the dorsal skin covering 25% total body surface area. The microcirculation and transvascular flux of albumin were observed in the rat mesentery using intravital fluorescence microscopy. The direct effect of circulating factors on microvascular barrier function was assessed by measuring the apparent permeability coefficient of albumin in isolated rat mesenteric venules during perfusion of plasma freshly withdrawn from burned rats. The in vivo study showed that the transvenular flux of albumin was significantly increased over a 6-h period with a maximal response seen at 3 h postburn. Importantly, perfusion of noninjured venules with burn plasma induced a time-dependent increase in albumin permeability. Pharmacological inhibition of protein kinase C, Src tyrosine kinases, or mast cell activation did not significantly affect the hyperpermeability response; however, blockage of myosin light chain phosphorylation with the myosin light chain kinase inhibitor ML-7 greatly attenuated the burn-induced increase in venular permeability in a dose-related pattern. The results support a role for endogenous circulating factors in microvascular leakage during burns. Myosin light chain phosphorylation-dependent endothelial contractile response may serve as an end-point effector leading to microvascular barrier dysfunction.

Nutritional support for the burn-injured patient

The nutritional needs of the bum-injured patient are exaggerated and change constantly with the patient's stage of convalescence. Nurses working closely with other members of the health care team, specifically the nutritional specialist, can positively affect the patient's survival by optimizing the nutritional assessment,delivering enteral feedings that meet established goals,minimizing the negative consequences of hyperglycemia, and minimizing unnecessary energy expenditures by the patient. Adequate nutritional is required for wound healing, immunocompetence, and, ultimately,patient survival.

Disaster preparation and management for the intensive care unit

The purpose of this report is to provide information regarding preparation for disaster management from the perspective of ICU physicians. Both a framework toward ICU preparation for disaster management and a guide to the relevant literature are presented. Our objective is to show that the understanding of disaster preparedness on multiple levels, including government, hospital, ICU, and clinician, may lead to optimal management in a disaster.

Interferon gamma modulates trauma-induced muscle wasting and immune dysfunction

OBJECTIVE

To test the effect of burn injury in mice congenitally deficient in interferon gamma (IFN-gamma) and as well as in wild-type animals treated with IFN-gamma neutralizing antibody.

SUMMARY BACKGROUND DATA

The mechanisms underlying muscle wasting following burn trauma are incompletely characterized, although the hypercatabolic state is a consequence of increased proteasomal degradation. Concurrently, burn injury results in an immunocompromised state, and subsequent infections are the leading cause of morbidity and mortality in these patients. IFN-gamma, best conceptualized as a macrophage activating protein, modulates a variety of biologic pathways potentially relevant to muscle wasting and immune dysfunction.

METHODS

Mice received either a 20% total body surface area burn or a control sham treatment. At days 1, 2, and 7 following treatment, skeletal muscle, peripheral blood, and spleen were harvested from both groups. Protein synthesis and degradation rates were measured. Lymphocyte subpopulation expression of major histocompatibility complex I (MHC I) molecules was assessed by flow cytometry, and proliferation capacity was measured using mixed lymphocyte reaction.

RESULTS

IFN-gamma is critically involved in burn-induced weight loss; moreover, absence of IFN-gamma virtually abolished skeletal muscle hypercatabolism following burn injury. Lymphocyte proliferation and MHC I expression in the setting of burn trauma are also normalized in the absence of IFN-gamma. Both antigen presentation and proliferation functions are independently affected.

CONCLUSIONS

IFN-gamma plays a fundamental role in mediating the hypercatabolic state of multiple cell types following burn trauma.