Decreased cerebral glucose utilization in rats during the ebb phase of thermal injury

The impact of burn injury on the central nervous system

Burn injuries can be devastating, with life-long impacts including an increased risk of hospitalization for a wide range of secondary morbidities. One area that remains not fully understood is the impact of burn trauma on the central nervous system (CNS). This review will outline the current findings on the physiological impact that burns have on the CNS and how this may contribute to the development of neural comorbidities including mental health conditions. This review highlights the damaging effects caused by burn injuries on the CNS, characterized by changes to metabolism, molecular damage to cells and their organelles, and disturbance to sensory, motor and cognitive functions in the CNS. This damage is likely initiated by the inflammatory response that accompanies burn injury, and it is often long-lasting. Treatments used to relieve the symptoms of damage to the CNS due to burn injury often target inflammatory pathways. However, there are non-invasive treatments for burn patients that target the functional and cognitive damage caused by the burn, including transcranial magnetic stimulation and virtual reality. Future research should focus on understanding the mechanisms that underpin the impact of a burn injury on the CNS, burn severity thresholds required to inflict damage to the CNS, and acute and long-term therapies to ameliorate deleterious CNS changes after a burn.

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.

Single hind limb burn injury to mice alters nuclear factor-κB expression and [¹⁸F] 2-fluoro-2-deoxy-D-glucose uptake

Burn trauma to the extremities can produce marked systemic effects in mice. Burn injury to the dorsal surface of mice is also associated with changes in glucose metabolism ([18F] 2-fluoro-2-deoxy-D-glucose [18FDG] uptake) by brown adipose tissue (BAT) and nuclear factor (NF)-κB activity in several tissues including skeletal muscle. This study examined the effect of a single hind limb burn in mice on 18FDG uptake by NF-κB activity in vivo, and blood flow was determined by laser Doppler techniques. Male NF-κB luciferase reporter mice (28-30 g) were anesthetized, both legs were shaven, and the right leg was subjected to scald injury by immersion in 90°C water for 5 seconds. Sham-treated animals were used as controls. Each burned and sham mouse was resuscitated with saline (2 mL, i.p.). The individual animals were placed in wire bottom cages with no food and free access to water. After 24 hours, the animals were imaged with laser Doppler for measuring blood flow in the hind limb. The animals were then unanesthetized with 50 μCi of FDG or luciferin (1.0 mg, i.v.) via tail vein. Five minutes after luciferin injection, NF-κB mice were studied by bioluminescence imaging with a charge-coupled device camera. One hour after 18FDG injection, the animals were killed with carbon dioxide overdose, and 18FDG biodistribution was measured. Tissues were also analyzed for NF-κB luciferase activity. The scalding procedure used here produced a full-thickness burn injury to the leg with sharp margins. 18FDG uptake by the burned leg was lower than that in the contralateral limb. Similarly, luciferase activity and blood flow in the burned leg were lower than those in the contralateral leg. 18FDG uptake by BAT and heart increased, whereas that by brain decreased. In conclusion, the present study suggests that burn injury to a single leg decreased FDG uptake by skeletal muscle but increased 18FDG uptake by BAT. The injury to the leg reduced NF-κB expression compared with the contralateral leg and the uninjured skeletal muscle of the sham but activated NF-κB expression in a number of other organs. These findings are consistent with the hypothesis that burn trauma to the extremities can produce marked systemic effects, including activation of NF-κB expression and activation of 18FDG uptake by BAT.

Resolvin D2 restores neutrophil directionality and improves survival after burns

Following severe burns and trauma injuries, the changes of neutrophil migratory phenotype are a double-edged sword. Activated neutrophils migrate into injured tissues and help contain microbial infections, but they can also enter normal tissues and damage vital organs. Depleting the neutrophils from circulation protects vital organs against neutrophil-induced damage but leaves the body exposed to infectious complications. Here we show that restoring normal neutrophil migratory phenotype in rats with burn injuries correlates with improved survival in a classical double-injury model of sequential burn and septic insults. We uncovered that the directionality of neutrophils from burned rats can be restored both in vitro by 1 nM resolvin D2 (RvD2) and in vivo by RvD2 for 7 d, 25 ng/kg body mass (8-10 ng/rat). Restoring neutrophil directionality dramatically increases survival after a second septic insult at d 9 postburn. Survival of RvD2-treated animals increases from 0 to 100% after lipopolysaccharide injection and is extended by 1 wk after cecal ligation. Survival does not significantly increase when the restoration of neutrophil directionality is incomplete, following shorter regimens of RvD2. We conclude that restoring neutrophil directionality using RvD2 could have prophylactic value and delay lethal complications after burn injuries.

Brown adipose tissue and its modulation by a mitochondria-targeted peptide in rat burn injury-induced hypermetabolism

Hypermetabolism is a prominent feature of burn injury, and altered mitochondria function is presumed to contribute to this state. Recently, brown adipose tissue (BAT) was found to be present not only in rodents but also in humans, and its activity is associated with resting metabolic rate. In this report, we elucidate the relationship between burn injury-induced hypermetabolism and BAT activity and the possible role of the mitochondria-targeted peptide SS31 in attenuating burn injury-induced hypermetabolism by using a rat burn injury model. We demonstrate that burn injury induces morphological changes in interscapular BAT (iBAT). Burn injury was associated with iBAT activation, and this effect was positively correlated with increased energy expenditure. BAT activation was associated with augmentation of mitochondria biogenesis, and UCP1 expression in the isolated iBAT mitochondria. In addition, the mitochondria-targeted peptide SS31 attenuated burn injury-induced hypermetabolism, which was accompanied by suppression of UCP1 expression in isolated mitochondria. Our results suggest that BAT plays an important role in burn injury-induced hypermetabolism through its morphological changes and expression of UCP1.

Previous burn injury predisposes mice to lipopolysaccharide-induced changes in glucose metabolism

In mice, it has been demonstrated that at 7 days after burn injury, injection of lipopolysaccharide (LPS) is more lethal than the same dose at 1 day after injury. In the present study, we examined the effect of LPS injection to mice burned 7 days previously on glucose metabolism ([(18)F] 2-fluoro-2-deoxy-D-glucose [(18)FDG] uptake) in vivo. CD-1 male mice (25-28 g, Charles River Breeding Laboratories, Wilmington, MA) were anesthetized, backs shaven, and subjected to dorsal full thickness burn on 25% TBSA. Sham-treated animals were used as controls. Six days after burn injury, all mice were fasted overnight. One half of the burned and sham controls were subsequently injected IP with LPS (10 mg/kg; Escherichia coli). The remaining animals were injected with saline IP. Two hours later, all mice were injected IV with 50 μCi of (18)F FDG. One hour later, the animals were euthanized, and biodistribution was measured. Tissues were weighed, and radioactivity was measured with a well-type γ counter. Results were expressed as %dose/g tissue, mean ± SEM. The combination of burn 7 days previously and LPS significantly increased mortality compared to animals with burn alone, LPS alone, or sham controls. Burn injury 7 days previously caused a significant decrease in (18)FDG uptake by the brain compared to sham controls. The combination of LPS and burn injury 7 days previously produced a significant increase in (18)FDG uptake by brown adipose tissue and heart compared with either treatment separately. LPS produced a significant increase in (18)FDG uptake by lung, spleen, and gastrointestinal tract of the sham animals, changes that were different in mice burned 7 days previously and injected with LPS. The present results suggest that burn injury 7 days previously predisposes mice to alterations in (18)FDG uptake produced by LPS. These changes may relate, in part, to the increased lethality of LPS injection in previously burned mice.

Estrogen treatment following severe burn injury reduces brain inflammation and apoptotic signaling

Background

Patients with severe burn injury experience a rapid elevation in multiple circulating pro-inflammatory cytokines, with the levels correlating with both injury severity and outcome. Accumulations of these cytokines in animal models have been observed in remote organs, however data are lacking regarding early brain cytokine levels following burn injury, and the effects of estradiol on these levels. Using an experimental animal model, we studied the acute effects of a full-thickness third degree burn on brain levels of TNF-α, IL-1β, and IL-6 and the protective effects of acute estrogen treatment on these levels. Additionally, the acute administration of estrogen on regulation of inflammatory and apoptotic events in the brain following severe burn injury were studied through measuring the levels of phospho-ERK, phospho-Akt, active caspase-3, and PARP cleavage in the placebo and estrogen treated groups.

Methods

In this study, 149 adult Sprague-Dawley male rats received 3rd degree 40% total body surface area (TBSA) burns. Fifteen minutes following burn injury, the animals received a subcutaneous injection of either placebo (n = 72) or 17 beta-estradiol (n = 72). Brains were harvested at 0.5, 1, 2, 4, 6, 8, 12, 18, and 24 hours after injury from the control (n = 5), placebo (n = 8/time point), and estrogen treated animals (n = 8/time point). The brain cytokine levels were measured using the ELISA method. In addition, we assessed the levels of phosphorylated-ERK, phosphorylated-Akt, active caspase-3, and the levels of cleaved PARP at the 24 hour time-point using Western blot analysis.

Results

In burned rats, 17 beta-estradiol significantly decreased the levels of brain tissue TNF-α (~25%), IL-1β (~60%), and IL-6 (~90%) when compared to the placebo group. In addition, we determined that in the estrogen-treated rats there was an increase in the levels of phospho-ERK (p < 0.01) and Akt (p < 0.05) at the 24 hour time-point, and that 17 beta-estradiol blocked the activation of caspase-3 (p < 0.01) and subsequent cleavage of PARP (p < 0.05).

Conclusion

Following severe burn injury, estrogens decrease both brain inflammation and the activation of apoptosis, represented by an increase in the levels of phospho-Akt and inhibition of caspase-3 activation and PARP cleavage. Results from these studies will help further our understanding of how estrogens protect the brain following burn injury, and may provide a novel, safe, and effective clinical treatment to combat remote secondary burn injury in the brain and to preserve cognition.

Burn-related metabolic and signaling changes in rat brain

Postburn alterations in the morphology and metabolism of brain tissue have been previously reported. It was demonstrated in our previous study that thermal injury decreased glucose usage in rat brain during the ebb phase. The cellular and molecular signaling events that trigger the pathophysiologic alterations, however, have not yet been characterized. In the present report, the authors have examined the effect of burn injury on mitogen-activated protein kinases (MAPKs) activities and insulin signaling in the brain tissue. Rats were subjected to 50% total body surface area full thickness scald injury. Brain samples were collected at 6 hours after injury. Tissue lysates were analyzed for MAPKs activities, insulin receptor substrate (IRS)-1 expression, and Akt activity which were determined by western blot and immunoprecipitation. Burn injury stimulated the stress-responsive components, SAPK/JNK, p38 MAP kinase and p44/42 MAP kinase, and increased IRS-1 expression and Akt activity. There was no change, however, on the phosphorylation of Ser307 of IRS-1 in brain tissue. The present data is consistent with the hypothesis that activation of the three major MAPKs pathways appears to be events involved in the mechanisms of burn injury induced insulin resistance and encephalopathy. Changes in signal transduction pathways in the brain after burn injury provide the underlying molecular mechanism of neurologic abnormalities (burn encephalopathy) that occur in burn patients.

Postmortem effect of pentobarbital anesthetic on survival of adult cortical neurons in primary culture

We determined whether pentobarbital anesthetic is required to culture postmortem adult rat neurons. Pentobarbital treatment resulted in two-fold increases in neuron survival in culture after 2 and 4 h postmortem compared to non-anesthetic controls, but was not as effective as simple postmortem treatment on ice and therefore not essential.

Neutrophil metabolic activity but not neutrophil sequestration reflects the development of pancreatitis-associated lung injury

OBJECTIVE

Activated neutrophils are presumed to injure pulmonary endothelium by releasing oxygen radicals, proteases, and proinflammatory cytokines. Standard counting methods do not distinguish between leukocytosis, neutrophil sequestration, and activation. We used leukocyte uptake of the glucose analog [18F]fluorodeoxyglucose (18FDG), which indicates postmigrational neutrophil activity, to identify and quantify the relationship between acute respiratory distress syndrome and neutrophil activation in experimental pancreatitis in rats.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Mild and severe pancreatitis models in the rat. INTERVENTIONS Pulmonary (with muscle as control) leukocyte accumulation was assessed by uptake of technetium-99m-labeled chemotactic peptide (fMLFK) and confirmed by measurement of myeloperoxidase activity. Neutrophil activity was assessed by 18FDG uptake. Tissue-to-blood ratios for fMLFK, 18FDG, and leukocytes were calculated to control for background. Neutrophils were counted in histologic sections of saline-perfused lungs. Bronchoalveolar lavage fluid was assessed for neutrophil migration and autoradiographed for intracellular 18FDG localization.

MEASUREMENTS AND MAIN RESULTS

Lung myeloperoxidase activity, 18FDG, and peripheral white blood cells all significantly increased in both mild and severe pancreatitis, but lung fMLFK only increased in severe pancreatitis. After correction for blood background, only 18FDG in lung (but not muscle) was significantly increased in pancreatitis (severe > mild > normal, p<.001). Histologic analysis showed significant increase in extravascular (migrated) neutrophils only in severe pancreatitis. Autoradiography of bronchoalveolar lavage fluid confirmed the 18FDG within intra-alveolar neutrophils.

CONCLUSIONS

In this pancreatitis model of acute respiratory distress syndrome, there was nonspecific and noninjurious increase of neutrophils in the lung, attributable in part to background leukocytosis and to intravascular sequestration. However, 18FDG uptake uniquely showed that interstitial and intra-alveolar neutrophil migration and activation occurred in severe but not in mild pancreatitis, consistent with clinical correlations between acute respiratory distress syndrome and severity of underlying systemic disease. 18FDG uptake, which is also accessible by positron emission tomography scanning, better quantitates the contribution of activated neutrophils to tissue injury than other measurements of neutrophil accumulation or sequestration.

Epidural analgesia reduces the release of amino acids from peripheral tissues in the ebb phase of the metabolic response to major upper abdominal surgery

The purpose of this prospective cohort study was to compare metabolic effects of epidural or patient controlled analgesia (PCA) in patients undergoing major upper abdominal surgery. Seventeen patients undergoing major upper abdominal surgery were included: 10 received perioperative epidural analgesia (Group I) and the remainder received morphine via a PCA device for postoperative analgesia (Group II). A number of measures compared between one day preoperatively (day 1) and day 2 postoperatively included femoral arterial and venous blood concentrations of glucose, lactate, pyruvate and amino acids. In addition, the relevant flux values were measured from the products of the respective arteriovenous substrate concentration differences and calf blood flow. The efflux of lactate from peripheral tissues was greater in Group II than in Group I (P < 0.01): glucose and pyruvate efflux did not differ between groups. There was no difference between groups in mean individual and total flux of amino acids on day-1. However increased efflux between day-1 and day 2 was found for alanine, valine, isoleucine, leucine, phenylalanine, lysine, arginine in both groups, and for serine, glycine, tyrosine and histidine in Group II (P < 0.05). The efflux of glycine, methionine, amino benzoic acid, alanine, and lysine was less in Group I than Group II on day 2 (P < 0.05). There was a significant difference in the total amino acid flux on day 2 (Group I = -1.2 mumol. (100 ml tissue)-1.min-1 cf Group II = -2.5 mumol. (100 ml tissue)-1.min-1; P = 0.04). In conclusion, perioperative epidural analgesia was associated with a reduced postoperative amino acid efflux two days following major upper abdominal surgery.

Insulin resistance in burns and trauma

Thermal injury in animal models clearly alters glucose metabolism. Insulin resistance results, with the wound in the skin receiving increased glucose, presumably to be used for wound healing and fighting invasion by foreign organisms. Using the whole-body imaging capacities of PET, it may now be possible to explore in greater detail the mechanism(s) responsible for the skeletal muscle wasting that is associated with burn and trauma patients, and possibly to develop strategies to prevent muscle atrophy without interfering with wound healing.