Burn-induced Hypermetabolism Research Articles

HOUSING TEMPERATURE ALTERS BURN INDUCED HYPERMETABOLISM IN MICE.

Mice used in biomedical research are typically housed at ambient temperatures (22-24 °C) below thermoneutrality (26-31 °C). This chronic cold stress triggers a hypermetabolic response that may limit the utility of mice in modeling hypermetabolism in response to burns. To evaluate the effect of housing temperature on burn-induced hypermetabolism, mice were randomly assigned to receive sham, small, or large scald burns. Mice recovered for 21 days in metabolic phenotyping cages at 24 °C or 30 °C. Regardless of sex or sham/burn treatment, mice housed at 24 °C had greater total energy expenditure (TEE, P < 0.001), which was largely attributable to greater basal energy expenditure (BEE) when compared to mice housed at 30 °C (P < 0.001). Thermoneutral housing (30 °C) altered adipose tissue mass in a sex-dependent manner. Compared to sham and small burn groups, large burns resulted in greater water vapor loss, regardless of housing temperature (P < 0.01). Compared to sham, large burns resulted in greater BEE and TEE in mice housed at 24 °C, however, this hypermetabolic response to large burns was blunted in female mice housed at 30 °C, and absent in male mice housed at 30 °C. Locomotion was significantly reduced in mice with large burns compared to sham and small burn groups, irrespective of sex or housing temperature (P < 0.05). Housing at 30 °C revealed sexual dimorphism in terms of the impact of burns on body mass and composition, where males with large burns displayed marked cachexia, whereas females did not. Collectively, this study demonstrates a sex-dependent role for housing temperature in influencing energetics and body composition in a rodent model of burn trauma.

BURNS INDUCE ALTERATIONS IN THE ACYL PROTEOME OF MICE AND HUMANS.

Hypermetabolic reprogramming triggered by thermal injury causes substantial morbidity and mortality. Despite the therapeutic potential of targeting this response, the underlying mechanisms remain poorly understood. Interestingly, protein S-acylation is a reversible posttranslational modification induced by metabolic alterations via DHHC acyltransferases. While this modification aids in the regulation of cellular functions, deregulated S-acylation contributes to various diseases by altering protein structure, stability, and localization. However, whether and how S-acylation may impact morbidity and mortality during postburn hypermetabolism is unknown. In this study, we discovered that alterations in the acyl proteome play a key role in mediating adverse outcomes that occur after burn injury. Using a murine model, we show that burn injury induces profound changes in the expression of various DHHC isoforms in metabolic organs central to regulating postburn hypermetabolism, the adipose tissue, and liver. This was accompanied by increased levels of S-acylated proteins in several pathways involved in mediating the adverse hypermetabolic response, including ER stress, lipolysis, and browning. In fact, similar results were also observed in adipose tissue from severely burned patients, as reflected by increased S-acylation of ERK1/2, eIF2a, ATGL, FGF21, and UCP1 relative to nonburn controls. Importantly, pharmacologically targeting this posttranslational modification using a nonselective DHHC inhibitor effectively attenuated burn-induced ER stress, lipolysis, and browning induction in an ex vivo explant model. Together, these findings suggest that S-acylation may facilitate the protein activation profile that drives burn-induced hypermetabolism and that targeting it could potentially be an effective strategy to restore metabolic function and improve outcomes after injury.

Subcutaneous white adipose tissue independently regulates burn-induced hypermetabolism via immune-adipose crosstalk

Severe burns induce a chronic hypermetabolic state that persists well past wound closure, indicating that additional internal mechanisms must be involved. Adipose tissue is suggested to be a central regulator in perpetuating hypermetabolism, although this has not been directly tested. Here, we show that thermogenic adipose tissues are activated in parallel to increases in hypermetabolism independent of cold stress. Using an adipose tissue transplantation model, we discover that burn-derived subcutaneous white adipose tissue alone is sufficient to invoke a hypermetabolic response in a healthy recipient mouse. Concomitantly, transplantation of healthy adipose tissue alleviates metabolic dysfunction in a burn recipient. We further show that the nicotinic acetylcholine receptor signaling pathway may mediate an immune-adipose crosstalk to regulate adipose tissue remodeling post-injury. Targeting this pathway could lead to innovative therapeutic interventions to counteract hypermetabolic pathologies.

288 Propranolol Use in Adult Burn Patients: Results from a Multi-center Safety and Efficacy Trial

Abstract Introduction The hypermetabolic response induced by a large burn is associated with increased cardiac work, total body wasting, and impaired physical function, leading to delays in psychosocial recovery and reintegration into society, and persistence of chronic conditions. Modulation of this response could reduce long-term burn morbidity. Catecholamines drive burn-induced hypermetabolism, therefore clinicians have employed the non-selective beta-adrenergic receptor blocker propranolol to reduce cardiac stress and the hypermetabolic response. Here, in a masked, placebo-controlled study, we investigated the safety and efficacy of the administration of propranolol to adult burn patients during the acute hospitalization period. Methods Adults with large burns (n=157, mean 38 ± 15% TBSA) were enrolled at 13 participating centers. Subjects were randomized to receive placebo (n=75) or propranolol (n=82) with data collected for 72 and 79 subjects, respectively. Propranolol administration was initiated with an oral dose of 0.2 mg/kg dose and adjusted to decrease mean heart rate by 20%. The primary endpoint was effect on cardiac rate pressure product (CRPP), while the secondary endpoints included infections and survival. Adverse events were also tracked. Assessments were conducted between the time of consent and discharge, with a long-term follow-up visit occurring approximately 5 months post-burn on average. Results CRPP was significantly reduced with propranolol during the acute hospitalization period (p&amp;lt; 0.0001, Fig 1). The initial dose of propranolol adequately reduced heart rate in most patients. Infections were not different between cohorts. Cardiac complications (atrial arrhythmias, ventricular arrhythmias, cardiac arrest) occurred at similar rates for each group, as did additional complications (abdominal compartment syndrome, deep vein thromboses, pneumothorax, pulmonary embolus). Mortality was similar for both the placebo and propranolol cohorts. Post-discharge heart rates and blood pressures were similar in both groups at approximately 5 months following injury. Conclusions This study demonstrates that the short-term administration of propranolol to adults with large burns decreases CRPP without increasing complications, infections, or mortality. Furthermore, a safe dosing strategy was identified. This strategy may be effective for reducing acute cardiac stress and hypermetabolism. Future studies should focus on the effects of propranolol administration for longer periods, determining the effects on additional endpoints like the hypermetabolic response, pathologic scarring, long-term cardiac dysfunction, whether smaller burns benefit from the administration of propranolol.

The Effect of Lipolysis Inhibitor Acipimox on Brown Adipose Tissue Bioenergetics and Uncoupling Protein Abundance in Severely Burned Rats

IntroductionUncoupling protein 1 (UCP1) activation in brown adipose tissue (BAT) contributes to the hypermetabolic stress response to burn trauma. Strategies that target BAT UCP1 could be beneficial in controlling burn‐induced hypermetabolism. Acipimox, an inhibitor of adipose tissue lipolysis, has been shown to be effective at blunting burn‐induced lipolysis and expression of UCP1 protein in rodent white adipose tissue. The impact of acipimox on BAT bioenergetics and uncoupling protein abundance is currently unknown. We hypothesized that acipimox would blunt burn‐induced UCP‐1 dependent respiration and UCP‐1 protein levels in BAT.MethodsSixty‐four male Sprague‐Dawley rats received a 60% TBSA scald burn (n=32) or sham procedure (n=32) and were subsequently randomized to receive either acipimox (n=16/group; 50 mg/kg/day i.p.) or vehicle (n=16/group) daily for 7d. BAT was harvested from the interscapular fat pad on day 7 after burn and mitochondrial respiratory function assessed by high‐resolution respirometry. GDP‐sensitive respiration was assayed as a direct measure of UCP1 function. UCP1 and adenine nucleotide translocator (ANT2) protein levels were determined by western blot.ResultsUCP1‐dependent and UCP1‐independent uncoupled respiration in BAT was reduced at 7d after severe burn, independent of treatment (injury effect, P&lt;0.01). Post‐burn, UCP1‐dependent respiration accounted for 65% of total uncoupled respiration compared to 59% in sham rats (injury effect, P&lt;0.05), independent of treatment. Acipimox appeared to exert a lowering effect on UCP1‐dependent respiration (treatment effect, P=0.07) but not on UCP1‐independent respiration. Neither burn nor treatment with acipimox had a significant effect on UCP1 protein levels. Protein levels of ANT2, a carrier protein involved in fatty acid‐induced uncoupling, were greater in response to acipimox (treatment effect, P&lt;0.05).ConclusionBAT UCP1 function than UCP1 protein content is greater in severely burned rats. Acipimox appears to reduce UCP1‐dependent respiration, independent of UCP1 protein levels. The effect of acipimox on BAT ANT2 protein content may partly explain the absence of an effect on UCP1‐independent respiration, but this warrants further investigation.The protocol was approved by the University of Texas Medical Branch IACUC.

Burn-induced hypermetabolism and skeletal muscle dysfunction.

Critical illnesses, including sepsis, cancer cachexia, and burn injury, invoke a milieu of systemic metabolic and inflammatory derangements that ultimately results in increased energy expenditure leading to fat and lean mass catabolism. Burn injuries present a unique clinical challenge given the magnitude and duration of the hypermetabolic response compared with other forms of critical illness, which drastically increase the risk of morbidity and mortality. Skeletal muscle metabolism is particularly altered as a consequence of burn-induced hypermetabolism, as it primarily provides a main source of fuel in support of wound healing. Interestingly, muscle catabolism is sustained long after the wound has healed, indicating that additional mechanisms beyond wound healing are involved. In this review, we discuss the distinctive pathophysiological response to burn injury with a focus on skeletal muscle function and metabolism. We first examine the diverse consequences on skeletal muscle dysfunction between thermal, electrical, and chemical burns. We then provide a comprehensive overview of the known mechanisms underlying skeletal muscle dysfunction that may be attributed to hypermetabolism. Finally, we review the most promising current treatment options to mitigate muscle catabolism, and by extension improve morbidity and mortality, and end with future directions that have the potential to significantly improve patient care.

Stress response induced by burn injury and its regulation strategy

Severe burns trigger the stress response, cause different degrees of damage to the body, and participate in the occurrence and development of immune dysfunction and hypermetabolism after burn. Rational application of analgesic and sedative drugs is the major method of inhibiting the severe burn-induced stress response, which can alleviate the organ damages and reduce the incidence of burn sepsis. Furthermore, integrated approaches including wound management, infection control, nutritional support, and gastrointestinal tract protection, as well as sleep management, etc., collectively contribute to the alleviation of stress response after burn injury. To further improve the success rate of severe burn treatment, it is essential to study the changes of various stresses, endocrine hormones and immune patterns in patients with severe burn, to explore the mechanism and regulation of burn-induced hypermetabolism, and to reach a consensus on sedation and analgesia strategy, the management of stress response and hypermetabolism after severe burns.

Effect of celecoxib in treatment of burn-induced hypermetabolism.

Background: Cyclooxygenase-2 (COX-2) catalyzes the rate-limiting step of prostanoid biosynthesis. Under pathologic conditions, COX-2 activity can produce reactive oxygen species and toxic prostaglandin metabolites that exacerbate injury and metabolic disturbance. The present study was performed to investigate the effect of Celecoxib (the inhibitor of COX-2) treatment on lipolysis in burn mice.Methods: One hundred male BALB/c mice were randomly divided into sham group, burn group, celecoxib group, and burn with celecoxib group (25 mice in each group). Thirty percent total body surface area (TBSA) full-thickness injury was made for mice to mimic burn injuries. Volume of oxygen uptake (VO2), volume of carbon dioxide output (VCO2), respiratory exchange ratio (RER), energy expenditure (EE), COX-2 and uncoupled protein-1 (UCP-1) expression in brown adipose tissue (BAT) were measured for different groups.Results: Adipose tissue (AT) activation was associated with the augmentation of mitochondria biogenesis, and UCP-1 expression in isolated iBAT mitochondria. In addition, VO2, VCO2, EE, COX-2, and UCP-1 expression were significantly higher in burn group than in burn with celecoxib group (P<0.05).Conclusion: BAT plays important roles in burn injury-induced hypermetabolism through its morphological changes and elevating the expression of UCP-1. Celecoxib could improve lipolysis after burn injury.

SAT-006 Dihydrotestosterone (DHT) Enhances Major Burn Injury Wound Healing by Regulating the Inflammatory Response in Mice

Androgen analogy (Oxandrolone) have been reported to better maintain lean body mass, with improved hypermetabolic responses and shortened healing time for major burn injured patients. This is contradictory to that androgens inhibit local wound repair in men and male mice. The aim of this study therefore is to identify the role of pure androgen dihydrotesterone (DHT) in complex major burn injury, in particularly whether androgen targets local healing process or systemic burn induced hypermetabolism. A DHT silastic tube was subcutaneously implanted to male Balb/c mice prior to surgery as the treatment group. A 2 X 2 cm2 full thickness contact burn wound was created on the dorsal skin of wild type littermates (control) or DHT treated mice. Wound healing rate and body weight changes were measured and compared between treatment and non-treatment group. The serum level of inflammatory cytokine/chemokine was measured using a Multiplex Immunoassay System. Spleen immune cells enumeration was analysis by flow cytometry. Inflammation, re-epithelialization, cell proliferation and collagen deposition was analysed using histology, immunohistochemistry and RT-PCR. In the present study, we found DHT treatment better maintained the body weight in mice and significantly promoted wound healing over 14 days, whereas DHT treatment had no effect on burn-induced hypermetabolism. In control group, major burn injury triggered an acute systematic inflammation response, resulting in significant increased weight of spleen, excess infiltration of nucleated erythroid cells in red pulps of spleen and a significant increase in number of splenic monocytes over 21 days. DHT treatment shortened the systemic inflammation response, evidenced via reduced splenic weight and the number of monocytes in spleen and circulation at day 14 and 21. This finding is further confirmed by less infiltration of macrophages in wound area at day 14 and 21 compared to control group. Taken together, our results suggesting the DHT treatment significantly improve wound healing by accelerated turnover of inflammation response but not through the metabolism. Further studies are necessary to define the exact mechanisms and DHT treatment could be a new therapeutic approach to improve the survivability of major burn injured patient.

Burn Trauma Acutely Increases the Respiratory Capacity and Function of Liver Mitochondria.

A complete understanding of the role of the liver in burn-induced hypermetabolism is lacking. We investigated the acute effect of severe burn trauma on liver mitochondrial respiratory capacity and coupling control as well as the signaling events underlying these alterations. Male BALB/c mice (8-12 weeks) received full-thickness scald burns on ∼30% of the body surface. Liver tissue was harvested 24 h postinjury. Mitochondrial respiration was determined by high-resolution respirometry. Citrate synthase activity was determined as a proxy of mitochondrial density. Male Sprague-Dawley rats received full-thickness scald burns to ∼60% of the body surface. Serum was collected 24 h postinjury. HepG2 cells were cultured with serum-enriched media from either sham- or burn-treated rats. Protein levels were analyzed via western blot. Mass-specific (P = 0.01) and mitochondrial-specific (P = 0.01) respiration coupled to ATP production significantly increased in the liver after burn. The respiratory control ratio for ADP (P = 0.04) and the mitochondrial flux control ratio (P = 0.03) were elevated in the liver of burned animals. Complex III and Complex IV protein abundance in the liver increased after burn by 17% and 14%, respectively. Exposure of HepG2 cells to serum from burned rats increased the pAMPKα:AMPKα ratio (P < 0.001) and levels of SIRT1 (P = 0.01), Nrf2 (P < 0.001), and PGC1α (P = 0.02). Severe burn trauma augments respiratory capacity and function of liver mitochondria, adaptations that augment ATP production. This response may be mediated by systemic factors that activate signaling proteins responsible for regulating cellular energy metabolism and mitochondrial biogenesis.

Effects of a caspase and a calpain inhibitor on resting energy expenditures in normal and hypermetabolic rats: a pilot study.

Several diseases induce hypermetabolism, which is characterized by increases in resting energy expenditures (REE) and whole body protein loss. Exaggerated protein degradation is thought to be the driving force underlying this response. The effects of caspase and calpain inhibitors on REE in physiological and hypermetabolic conditions, however, are unknown. Thus, we studied whether MDL28170 (calpain inhibitor) or z-VAD-fmk (caspase inhibitor) affect REE under physiological conditions and during hypermetabolism post-burn. Rats were treated five times weekly and observed for 6 weeks. Treatment was started 2 h (early) or 48 h (late) after burn. In normal rats, MDL28170 transiently increased REE to 130 % of normal during week 2-4. z-VAD-fmk reduced REE by 20-25 % throughout the observation period. Within 14 days after burns, REE increased to 130+/-5 %. Whereas MDL28170/early treatment did not affect REE, MDL28170/late transiently increased REE to 180+/-10 % of normal by week 4 post-burn. In contrast, with z-VAD-fmk/early REE remained between 90-110 % of normal post-burn. z-VAD-fmk/late did not affect burn-induced increases in REE. These data suggest that caspase cascades contribute to the development of hypermetabolism and that burn-induced hypermetabolism can be pharmacologically modulated. Our data point towards caspase cascades as possible therapeutic targets to attenuate hypermetabolism after burns, and possibly in other catabolic disease processes.

Proteasome Inhibition After Burn Injury.

The objective of this study was to assess the effects of proteasome inhibition on the development of burn-induced hypermetabolism. Rats underwent 30-40% total BSA scald burn or sham injury. The proteasome inhibitor bortezomib (0.1 mg/kg) or vehicle (n = 10) was administered i.p. 3× weekly starting at 2 hours (early bortezomib, n = 20) or 48 hours (late-bortezomib, n = 13) postburn. Body weights were determined weekly. Resting energy expenditures (REE) were measured at days 0 (baseline), 7, 14, 21, and 42 postburn. At day 42, blood and pectoral muscle were harvested. Routine blood chemistry parameters were analyzed. Proteasome content, proteasome peptidase activities, and ubiquitin-protein conjugates were measured in muscle extracts. As compared with sham-vehicle-treated animals, specific proteasome activities were increased after burn and vehicle treatment. Bortezomib treatment inhibited proteasome activities and increased ubiquitin-protein conjugates after sham and burn injury. Bortezomib treatment did not affect REE after sham procedure. REE significantly increased by 47% within 7 days and remained elevated until day 42 after burn and vehicle treatment. After early-bortezomib treatment, burn-induced increases in REE were delayed and significantly reduced by 42% at day 42, as compared with vehicle treatment. With late-bortezomib treatment, burn-induced increases in REE were also delayed but not attenuated at day 42. Mortality was 20% with vehicle, 65% (median survival time: 1.875 days) with early-bortezomib and 25% with late-bortezomib treatment after burns (P < .05 early-bortezomib vs vehicle and late-bortezomib). Proteasome inhibition delays development of burn-induced hypermetabolism. Although proteasome inhibition early after burn injury reduces the hypermetabolic response, it significantly increases early burn-associated mortality.

Burn Induces Browning of the Subcutaneous White Adipose Tissue in Mice and Humans.

SUMMARYBurn is accompanied by long-lasting immunometabolic alterations referred to as hypermetabolism that are characterized by a considerable increase in resting energy expenditure and substantial whole-body catabolism. In burned patients, the length and magnitude of the hypermetabolic state is the highest of all patients and associated with profoundly increased morbidity and mortality. Unfortunately, the mechanisms involved in hypermetabolism are essentially unknown. We hypothesized that the adipose tissue plays a central role for the induction and persistence of hypermetabolism post-burn injury. Here, we show that burn induces a switch in the phenotype of the subcutaneous fat from white to beige, with associated characteristics such as increased mitochondrial mass and UCP1 expression. Our results further demonstrate the significant role of catecholamines and interleukin-6 in this process. We conclude that subcutaneous fat remodeling and browning represent an underlying mechanism that explains the elevated energy expenditure in burn-induced hypermetabolism.

Influence of inhalation injury on energy expenditure in severely burned children

ObjectiveDetermine the effect of inhalation injury on burn-induced hypermetabolism in children. DesignProspective study comparing hypermetabolism (i.e., resting energy expenditure and oxygen consumption) in burned children with and without inhalation injury during acute hospitalization. SettingSingle pediatric burn center. PatientsEighty-six children (1–18 years) with ≥40% total body surface area burns were stratified to two groups: no inhalation injury and inhalation injury. InterventionsNone. Main measurements and resultsInhalation injury was diagnosed based on bronchoscopic evaluation. At admission, PaO2:FiO2 ratios (an index of respiratory distress) were significantly higher in patients with no inhalation injury than in patients with inhalation injury. No differences were detected in resting energy expenditure or percent of the predicted basal metabolic rate between groups. Additionally, oxygen consumption did not significantly differ between groups. ConclusionsInhalation injury does not augment the burn-induced hypermetabolic stress response in children, as reflected by resting energy expenditure and oxygen consumption.

Leukocyte Infiltration and Activation of the NLRP3 Inflammasome in White Adipose Tissue Following Thermal Injury*

Severe thermal injury is associated with extreme and prolonged inflammatory and hypermetabolic responses, resulting in significant catabolism that delays recovery or even leads to multiple organ failure and death. Burned patients exhibit many symptoms of stress-induced diabetes, including hyperglycemia, hyperinsulinemia, and hyperlipidemia. Recently, the nucleotide-binding domain, leucine-rich family (NLR), pyrin-containing 3 (NLRP3) inflammasome has received much attention as the sensor of endogenous "danger signals" and mediator of "sterile inflammation" in type II diabetes. Therefore, we investigated whether the NLRP3 inflammasome is activated in the adipose tissue of burned patients, as we hypothesize that, similar to the scenario observed in chronic diabetes, the cytokines produced by the inflammasome mediate insulin resistance and metabolic dysfunction. Prospective cohort study. Ross Tilley Burn Centre & Sunnybrook Research Institute. We enrolled 76 patients with burn sizes ranging from 1% to 70% total body surface area. All severely burned patients exhibited burn-induced insulin resistance and hyperglycemia. None. We examined the adipose tissue of control and burned patients and found, via flow cytometry and gene expression studies, increased infiltration of leukocytes-especially macrophages-and evidence of inflammasome priming and activation. Furthermore, we observed increased levels of interleukin-1β in the plasma of burned patients when compared to controls. In summary, our study is the first to show activation of the inflammasome in burned humans, and our results provide impetus for further investigation of the role of the inflammasome in burn-induced hypermetabolism and, potentially, developing novel therapies targeting this protein complex for the treatment of stress-induced diabetes.

Activities of nonlysosomal proteolytic systems in skeletal and cardiac muscle during burn-induced hypermetabolism.

The aim of this study was to assess the activity of nonlysosomal proteolytic systems in skeletal and cardiac muscle during burn-induced hypermetabolism (BHM) in rats. Rats underwent 30% TBSA scald burn or sham injury and were observed for up to 42 days. Body weights and resting energy expenditures were determined weekly. Skeletal (soleus/pectoral) muscle and hearts were harvested on days 0 (=control), 7, 14, 21, and 42 after burn. Calpain, caspase-1, caspase-3/7, caspase-6, caspase-8, caspase-9, and proteasome peptidase activities were measured in tissue extracts. Hypermetabolism developed within 3 weeks after burns, as documented by increased resting energy expenditures and decreased body weights on postburn days 21 to 42 (P < 0.05 vs control). Calpain activities did not show significant alterations. Pan caspase activities increased by time and were significantly increased in skeletal and cardiac muscle extracts during hypermetabolism. Although increases in caspase-1, caspase-8, and caspase-9 activities were predominantly responsible for elevated pan caspase activities in skeletal muscle, increases in caspase-6 activities dominated in the heart. Proteasome peptidase activities in skeletal muscle extracts were not significantly altered. Proteasome peptidase activities in heart extracts increased time dependently and were significantly increased during BHM. Activation of caspase cascades during BHM constitutes a uniform response in skeletal and cardiac muscle and may contribute to enhanced metabolic protein turnover. Activation of myocardial proteasome activities may reflect persistent cardiac stress. Further exploration of caspase cascades and the proteasome as therapeutic targets to influence long-term consequences of BHM appears justified.

Thermal Injury Activates the eEF2K‐Dependent eEF2 Pathway in Pediatric Patients

Burn induces a hypermetabolic state characterized by alterations in protein metabolism, which is associated with increased morbidity and mortality. Eukaryotic elongation factor 2 (eEF2) plays a crucial role in regulating protein synthesis in many diseases, but whether it participates in burn-induced hypermetabolism is unclear. The aim of this study was to determine the expression of eEF2 and the upstream eEF2-inactivating kinase, eEF2K, in severely burned pediatric patients. Eight pediatric patients (> 40% total body surface area) and 3 nonburned pediatric volunteers were enrolled. Muscle and skin biopsies were collected at early (0-10 days postburn [dpb]), middle (11-49 dpb), and late (50-365 dpb) time points. Resting energy expenditure (REE), body composition, and muscle protein fractional synthesis rate (FSR) were measured. Proteins were extracted and analyzed by Western blotting. To further investigate the protein synthesis pathway, microarray data from muscle and skin were examined from 22 nonburned and 20 burned children. Burn patients exhibited a profound hypermetabolic response, as seen by a significant increase in REE (P < .05) and loss of lean body mass without altered muscle FSR, indicating a shift to catabolism after thermal injury. In muscle, the phosphorylation of eEF2K-dependent eEF2 was down regulated early and middle postburn. Similar changes in eEF2K and eEF2 levels occurred in skin at the early time point. Total amounts of eEF2 and eEF2K were not altered. Burn induces prolonged activation of eEF2K and eEF2. Alterations in these mediators may contribute to profound hypermetabolism in severely burned patients.

Mediation of burn-induced hypermetabolism by CRF receptor-2 activity

Hypermetabolism and anorexia are significant problems associated with major burn trauma. Recent studies have implicated hypothalamic peptides and receptors of the corticotropin releasing factor (CRF) family as putative mediators of burn-induced hypermetabolism. Increased neuronal activity at the CRF type 2 receptor (CRF R-2) appeared particularly involved in the expression of elevated resting energy expenditure (REE) following major burn trauma. In the present study we continued these investigations of CRF R-2 mediation of burn-induced hypermetabolism, demonstrating that 3rd ventricle injection of CRF R-2 antisense oligodeoxynucleotide (ODN) normalized REE in burned rats. Similar treatments with CRF or CRF R-1 antisense ODNs had no significant effect in burned rats. In addition, 3rd ventricle injection of the selective CRF R-2 antagonist, antisauvagine-30, also reduced REE significantly in burned rats, while similar treatment with the selective CRF R-1 antagonist, antalarmin, was without effect. To determine which endogenous peptide was altered following burn we measured hypothalamic levels of urocortin (UCN) and CRF 15 days after burn injury, finding UCN was significantly elevated by nearly 3-fold, while CRF level tended to be decreased. We also assessed hypothalamic mRNA peptide and receptor expression by real-time PCR 7, 14, and 21 days post-burn, observing decreased CRF expression 7 and 21 days post-burn, decreased UCN-2 expression 7 days post-burn, and no significant alteration in UCN-1 at any time point. However, CRF R-2 mRNA was elevated at each post-burn time point. These results continue to suggest that increased neuronal activity is integrally involved in the mediation of burn-induced hypermetabolism, and that one of the UCN peptides may be the endogenous ligand affecting this receptor.

Reduction of Burn-Induced Hypermetabolism Following Treatment with Corticotropin Releasing Factor Receptor 2 Antisense Oligonucleotide

Reduction of Burn-Induced Hypermetabolism Following Treatment with Corticotropin Releasing Factor Receptor 2 Antisense Oligonucleotide

Possible role of CRF peptides in burn-induced hypermetabolism

Hypermetabolism and anorexia are significant problems associated with major burn trauma. Recent studies have shown that hypothalamic corticotropin releasing factor (CRF) elevates metabolic rate, while neuropeptide Y (NPY) reduces it. CRF also elicits anorexia, while NPY stimulates feeding. We hypothesized that elevation of CRF and decrease of NPY may be mediators of these negative effects of burn trauma. Therefore, we assessed concentrations of CRF and NPY in hypothalamus of burned rats one, three, and twenty-one days after a 30% body surface area, full-thickness, open flame burn. In addition we determined whether a biochemical lesion of CRF receptors using 3rd ventricle injections of a saporin–CRF conjugated peptide would decrease resting energy expenditure (REE). We found a three-day period of anorexia, with REE significantly increasing three days after the burn trauma. Concentrations of NPY were increased in the PVN-containing dorsomedial region of the hypothalamus 1 and 3 days after burn trauma, but were increased further in the day 1 pair-fed rats suggesting this change was a consequence of the anorexia. Levels of CRF were decreased in the ventromedial region of the hypothalamus in day 1 and day 3 burned and PF rats. Treatment with the saporin–CRF conjugate normalized REE and reduced CRF receptor-2 density in the hypothalamus of burned rats, and blocked CRF-induced hypermetabolism in sham-burned rats. Although these results suggest a role of CRF receptors in mediating burn-induced hypermetabolism, CRF itself may not be the principle ligand, as suggested by the significant elevation of hypothalamic urocortin 15 days after burn injury.