Thermal injury in rats alters glucose utilization by skin, wound, and small intestine, but not by skeletal muscle

Effect of Collagen Hydrolysate and Fish Oil on High-Sensitivity C-Reactive Protein and Glucose Homeostasis in Patients with severe Burn; a Randomized Clinical Trial

Introduction:

Collagen and omega-3 fatty acids (FAs) are suggested to have anti-inflammatory, anti-oxidant, and insulin-sensitizing properties. The aim of this study was to investigate the effect of collagen hydrolysate and omega-3 FAs on inflammation and insulin resistance in patients with major burns.

Methods:

In this double-blind randomized clinical trial, 66 patients with 20-45% burns were assigned to either of the three groups of collagen (40 gr/d), collagen (40 gr/d) plus fish oil (10 ml/d), or control. High-sensitivity C-reactive protein (hs-CRP), fasting blood glucose (FBG) and insulin concentrations, and homeostatic model assessment for insulin resistance (HOMA-IR) were assessed at baseline, as well as end of weeks two and three.

Results:

Based on post-hoc analyses, hs-CRP levels were significantly lower in the collagen (p=0.026) and collagen+omega-3 (p=0.044) groups compared to the control group, at week three. However, pre- to post- (week three) changes of hs-CRP were significantly higher only in the collagen+omega-3 group compared to the control group (173.2 vs. 103.7 mg/l, p=0.024). After three weeks of the intervention, insulin (11.3 and 11.9 vs. 22.8 µIU/ml) and HOMA-IR (2.9 and 2.8 vs. 7.9) values seemed to be clinically, but not statistically, lower in both intervention groups compared to the control group. Pre- to post- (week three) values of FBG decreased significantly in the collagen (p=0.002) and collagen+omega-3 (p=0.036) groups. Insulin (p=0.008) and HOMA-IR (p=0.001) decreased significantly only in the collagen+omega-3 group at week three compared to the baseline.

Conclusions:

Supplementation with collagen hydrolysate and omega-3 FAs can improve hs-CRP concentration and probably insulin resistance in patients with severe burns. Omega-3 FAs had additional effects on modulating inflammation. Larger clinical trials are needed to confirm the current findings especially in terms of glucose homeostasis.

Review: Insulin resistance and mitochondrial dysfunction following severe burn injury

The insulin signaling pathway plays a pivotal role in glucose metabolism and metabolic homeostasis. Disruption of this pathway is commonly seen in critical illness such as following severe burn injuries where homeostatic control is lost, leading to "insulin resistance" with poor blood glucose control. The aberrant signaling pathways involved in insulin resistance following burn injury include increases in hyperglycemic stress hormones, pro-inflammatory cytokines and free radical production. Leakage of mitochondrial sequestered self-antigens and signaling between mitochondria and endoplasmic reticulum also contribute to insulin resistance. Greater understanding of molecular processes involved in burn-related insulin resistance could potentially lead to the development of novel therapeutic approaches to improve patient management.

Metabolic and Endocrine Considerations After Burn Injury

Severe burn injury is followed by a profound hypermetabolic response that persists up to 2 years after injury. It is mediated by up to 50-fold elevations in plasma catecholamines, cortisol, and glucagon that lead to whole-body catabolism, elevated resting energy expenditures, and multiorgan dysfunction. Modulation of the response by early excision and grafting of burn wounds, thermoregulation, control of infection, early and continuous enteral nutrition, and pharmacologic treatments aimed at mitigating physiologic derangements have markedly decreased morbidity.

Combination of radiation and burn injury alters [¹⁸F] 2-fluoro-2-deoxy-D-glucose uptake in mice

Radiation exposure and burn injury have both been shown to alter glucose utilization in vivo. The present study was designed to study the effect of burn injury combined with radiation exposure on glucose metabolism in mice using [¹⁸F] 2-fluoro-2-deoxy-D-glucose (¹⁸FDG). Groups of male mice weighing approximately 30 g were studied. Group 1 was irradiated with a ¹³⁷Cs source (9 Gy). Group 2 received full thickness burn injury on 25% TBSA followed by resuscitation with saline (2 ml, IP). Group 3 received radiation followed 10 minutes later by burn injury. Group 4 were sham-treated controls. After treatment, the mice were fasted for 23 hours and then injected (IV) with 50 μCi of ¹⁸FDG. One hour postinjection, the mice were sacrificed, and biodistribution was measured. Positive blood cultures were observed in all groups of animals compared to the shams. Increased mortality was observed after 6 days in the burn plus radiated group as compared to the other groups. Radiation and burn treatments separately or in combination produced major changes in ¹⁸FDG uptake by many tissues. In the heart, brown adipose tissue, and spleen, radiation plus burn produced a much greater increase (P < .0001) in ¹⁸FDG accumulation than either treatment separately. All three treatments produced moderate decreases in ¹⁸FDG accumulation (P < .01) in the brain and gonads. Burn injury, but not irradiation, increased ¹⁸FDG accumulation in skeletal muscle; however, the combination of burn plus radiation decreased ¹⁸FDG accumulation in skeletal muscle. This model may be useful for understanding the effects of burns plus irradiation injury on glucose metabolism and in developing treatments for victims of injuries produced by the combination of burn plus irradiation.

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.

SILAM for quantitative proteomics of liver Akt1/PKBα after burn injury

Akt1/protein kinase Bα (Akt1/PKBα) is a downstream mediator of the insulin signaling system. In this study we explored mechanism(s) for its role in burn injury. Akt1/PKBα in liver extracts from mice with burn injury fed with (²H₇)-L-Leu was immunoprecipitated and isolated with SDS-PAGE. Two tryptic peptides, one in the kinase loop and a control peptide just outside of the loop were sequenced via nano-LC interfaced with quadruple time-of-flight tandem mass spectrometry (Q-TOF tandem MS). Their relative isotopologue abundances were determined by stable isotope labeling by amino acids in mammalians (SILAM). Relative quantifications based on paired heavy/light peptides were obtained in 3 steps. The first step included homogenization of mixtures of equal amounts of tissue from burned and sham-treated animals (i.e., isotope dilution) and acquisition of uncorrected data based on parent monoisotopic MS ion ratios. The second step included determination of isotopic enrichment of the kinase from burned mice on Day 7 and the third step enrichment correction of partially labeled heavy and light monoisotopic MS ion ratios for relative quantification of bioactivity (loop peptide) and expression level (control peptide). Protein synthesis and enrichment after injury were found to be dependent on tissue and turnover of individual proteins. Three heavy and light monoisotopic ion ratios for albumin peptides from burned mice indicated ~55% enrichment and ~16.7-fold downregulation. In contract, serum amyloid P had ~66% enrichment and was significantly upregulated. Akt1/PKBα had ~56% enrichment and kinase level in response to the burn injury was upregulated compared with the control peptide. However, kinase bioactivity, represented by the Cys²⁹⁶ peptide, was significantly reduced. Overall, we demonstrated that i) quantitative proteomics can be performed without completely labeled mice; ii) measurement of enrichment of acyl-tRNAs is unnecessary and iii) Cys²⁹⁶ plays an important role in kinase activity after burn injury.

Nutrition in burns: Galveston contributions

Aggressive nutrition support is recommended following severe burn injury. Initially, such injury results in a prolonged and persistent hypermetabolic response mediated by a 10- to 20-fold elevation in plasma catecholamines, cortisol, and inflammatory mediators. This response leads to twice-normal metabolic rates, whole-body catabolism, muscle wasting, and severe cachexia. Thus, it is relevant to review the literature on nutrition in burns to adjust/update treatment. Failure to meet the increased substrate requirements may result in impaired wound healing, multiorgan dysfunction, increased susceptibility to infection, and death. Therefore, aggressive nutrition support is essential to ensure adequate burn care, attenuate the hypermetabolic response, optimize wound healing, minimize devastating catabolism, and reduce morbidity and mortality. Here, the authors provide nutrition recommendations gained from prospective trials, retrospective analyses, and expert opinions based on the authors' practices in Galveston, Texas, and Vienna, Austria.

The hypermetabolic response to burn injury and interventions to modify this response

Severe burn injury is followed by a profound hypermetabolic response that persists up to 24 months after injury. It is mediated by up to 50-fold elevations in plasma catecholamines, cortisol, and inflammatory cells that lead to whole-body catabolism, elevated resting energy expenditures, and multiorgan dysfunction. All of these metabolic and physiologic derangements prevent full rehabilitation and acclimatization of burn survivors back into society. Modulation of the response by early excision and grafting of burn wounds, thermoregulation, early and continuous enteral feeding with high-protein high-carbohydrate feedings, and pharmacologic treatments have markedly decreased morbidity.

Metabolic implications of severe burn injuries and their management: a systematic review of the literature

BACKGROUND

Severe burn patients are some of the most challenging critically ill patients, with an extreme state of physiologic stress and an overwhelming systemic metabolic response. A major component of severe burn injury is a hypermetabolic state associated with protein losses and a significant reduction of lean body mass. The second prominent component is hyperglycemia. Reversal of the hypermetabolic response by manipulating the patient's physiologic and biochemical environment through the administration of specific nutrients, growth factors, or other agents, often in pharmacologic doses, is emerging as an essential component of the state of the art in severe burn management. The present review aims at summarizing the new treatment modalities established to reduce the catabolic burden of severe burn injuries, for which there is some evidence-based support.

METHODS

A systematic review of the literature was conducted. Search tools included Elsevier ScienceDirect, EMBASE.com, Medline (OVID), MedlinePlus, and PubMed. Topics searched were Nutrition and Burns, Metabolic Response and Burns, Hypermetabolism and Burns, Hyperglycemia and Burns, and several more specific topics when indicated. With a focus on the most recently published articles, abstracts were reviewed and, when found relevant, were included as references. Full text articles, whenever available, were retrieved.

RESULTS

Many issues remain unanswered. Unfortunately, the present state of our knowledge does not allow the formulation of clear-cut guidelines. Only general trends can be outlined, and these will certainly have some practical applications but above all will dictate future research in the field.

Isolated Perfusion of a Tubed Superficial Epigastric Flap in a Rodent Model

BACKGROUND

Isolated perfusion models can yield important data regarding metabolism of the skin. An effective model must remain stable during perfusion but respond appropriately to metabolic and vascular stimuli. We describe the design and characterization of a tubed superficial epigastric isolated perfusion flap.

MATERIALS AND METHODS

Tubed superficial epigastric flaps were created in 20 male Sprague Dawley rats. Forty-eight hours later the femoral vessels were cannulated and the flaps were perfused using a Krebs-Heinseleit buffer containing albumin for a period of 2 h. In five of the flaps norepinephrine and acetylcholine were added sequentially to the perfusate to determine vascular reactivity. In a further four flaps insulin (20 U/liter) and iodoacetate (5 mM) were added to the perfusate to confirm that the flap was metabolically active and reactive. Venous outflow was collected at regular intervals and analyzed for electrolytes, lactate, and glucose content. Vascularity and skin perfusion were characterized using barium microangiography and methylene blue dye injection.

RESULTS

This flap model was found to be stable in terms of arterial pressure, electrolyte levels, and lactate production over the perfusion period. Norepinephrine caused a sharp increase in vascular resistance, which was reversed by administration of acetylcholine. Lactate production increased appropriately with the addition of insulin to the perfusate with a rapid decline following addition of the glycolysis inhibitor iodoacetate. There was no leakage of perfusate or significant swelling of the flap during the perfusion.

CONCLUSIONS

The tubed superficial epigastric artery flap makes an effective model for isolated perfusion studies of the skin with a wide range of experimental applications.

C3a levels and occurrence of subdermal vascular thrombosis are age-related in deep second-degree burn wounds

BACKGROUND

After second-degree burns, thrombosis of the subdermal vascular plexus may occur, necessitating epifascial necrectomy instead of tangential excision to ensure split skin graft healing. Until now, no parameter has been obtained to explain this phenomenon.

METHODS

Thirty-four patients with deep second-degree burn wounds were divided into 2 groups. In group 1, patients' age was < 60 years, in group 2, > 60 years. In each patient, 2 microdialysis catheters were introduced into subdermal tissue of deep second-degree thermal wounds immediately after admission. Another 2 catheters were introduced in control tissue. We measured biochemical parameters (lactate, glycerol and glucose) and complement 3a (C3a) until surgery was performed. The surgically removed tissue was examined histologically.

RESULTS

In thermal wounds of both groups, glucose levels fell, but lactate and glycerol levels rose compared to healthy tissue. Within the first 24 hours after trauma, C3a levels were significant higher in both groups, compared with controls (P < .01). After 24 hours the levels in group 1 had fallen to nonsignificant values, while in group 2 these levels remained high until surgery was performed (P < .001). We found significantly more thrombotic blood vessels in deep dermal tissue of group 2 (P < .005). Abbreviated burn severity index score was comparable in both groups.

CONCLUSIONS

C3a is continuously elevated in deep second-degree burned wounds in patients > 60 years. This finding may be related to the occurrence of significantly more thrombotic blood vessels in deep dermal tissue of elderly patients. Microdialysis therapy is a useful tool to measure metabolic and immunologic parameters in thermally damaged tissue.

Quantitative effects of thermal injury and insulin on the metabolism of the skeletal muscle using the perfused rat hindquarter preparation

Injury from a severe burn or trauma can propel the body into a hypermetabolic state that can lead to the significant erosion of lean muscle mass. Investigations describing this process have been somewhat limited due to the lack of adequate experimental models. Here we report the use of a perfused rat hindquarter preparation to study the consequences of a moderate burn injury (approximately 20% total body surface area), with or without the addition of exogenous insulin (12.5 mU/mL), on the fluxes of major metabolites across the isolated skeletal muscle. The metabolic flux data was further analyzed using metabolic flux analysis (MFA), which allows for the estimation of the impact of these conditions on the intracellular muscle metabolism. Results indicate that this model is able to capture the increased rate of proteolysis, glutamine formation, and the negative nitrogen balance associated with the burn-induced hypermetabolic state. The inclusion of exogenous insulin resulted in significant changes in several fluxes, including an increase in the metabolism of glucose and the flux through the pentose phosphate pathway, as well as a reduction in the metabolism of glutamine, alanine, and leucine. However, insulin administration did not affect the nitrogen balance or the rate of proteolysis in the muscle, as has been suggested using other techniques. The use of the perfused hindquarter model coupled with MFA is a physiologically relevant and experimentally flexible platform for the exploration of skeletal muscle metabolism under catabolic conditions, and it will be useful in quantifying the specific metabolic consequences of other therapeutic advances.

Skin Metabolism in Transdermal Therapeutic Systems

Skin has at least two barriers with protective functions: the stratum corneum physical barrier and a biochemical barrier in the epidermis and dermis. Numerous chemical and physical enhancers exist for transdermal therapeutic systems; some cause irritation, and possibly influence enzyme deactivation. Knowledge of enzymatic skin reactions is important for developing safe and efficacious transdermal systems for treatment not only of skin diseases but also for systemic application. This paper overviews the effects of (a) chemical enhancers and additives, (b) drug structure, and (c) physical enhancement on skin metabolism.

Support of the metabolic response to burn injury

Severe burn causes metabolic disturbances that can last for a year after injury; persistent and profound catabolism hampers rehabilitative efforts and delays the meaningful return of individuals to society. The simplest, effective anabolic strategies for severe burn injuries are: early excision and grafting of the wound; prompt treatment of sepsis; maintenance of environmental temperature at 30-32 degrees C; continuous feeding of a high carbohydrate, high protein diet, preferably by the enteral route; and early institution of vigorous and aerobic resistive exercise programmes. To further keep erosion of lean body mass to a minimum, administration of anabolic agents, recombinant human growth hormone, insulin, oxandrolone, or anticatabolic drugs such as propranolol are alternative approaches. Exogenous continuous low-dose insulin infusion, beta blockade with propranolol, and use of the synthetic testosterone analogue oxandrolone are the most cost effective and least toxic pharmacological treatments to date.

Does the oxidative/glycolytic ratio determine proliferation or death in immune recognition?

Here we discuss the possibility that the way cells utilize fuel(s) for energy confers the properties that can be recognized by the immune system and, reciprocally, that recognition by the immune system can alter the balance of the cell's energy metabolism. We propose that immune recognition, of somatic cells via MHC can alter the their energy metabolism and induce a metabolic shift. We demonstrate the reciprocal relationship that inducing a shift in metabolism toward glycolysis by supplying glucose and insulin results in the upregulation of immunologically recognizable molecules such as cell surface Fas. Thus, immune recognition can induce metabolic deviation. Metabolic deviation can result in altered immune recognition and ultimately in cell proliferation, cell differentiation, or cell death.

A rabbit model for metabolic studies after burn injury

BACKGROUND

A rabbit burn model was developed and characterized, which will allow conduct of repeated, noninvasive and more sophisticated in vivo metabolic studies to explore the pathophysiology of burn injury, owing to its larger blood volume and tissue mass than the rat.

MATERIALS AND METHODS

A 20% body surface, full thickness burn was applied to the backs of six anesthetized rabbits by immersion into a boiling-water bath for 10 s, followed by resuscitation with saline. Resting energy expenditure (REE) was measured daily in pre- and postburn periods. Whole body protein kinetics were evaluated using L-[1(-13)C]leucine tracer, on the preburn and the third postburn day. Fasting plasma glucose was also measured.

RESULTS

A significant elevation of REE began on the second postburn day and reached 34 +/- 8% above the preburn level (P < 0.05, paired t test) on the third postburn day. The fasting plasma leucine flux and oxidation were significantly elevated from their preburn levels (both P < 0.05), indicating an accelerated proteolysis and a more negative body protein balance (P < 0.05); however, the rate of whole body protein synthesis did not differ significantly pre- and postburn injury. Fasting plasma glucose also increased (P < 0.001). on the third postburn day. The burn scar remained intact during the study, without any sign of infection.

CONCLUSIONS

The metabolic changes observed in this animal model can be attributed to burn injury per se and they mimic those for flow phase in burn patients. This rabbit burn model should be suitable for exploring mechanistic aspects of the burn-induced changes in metabolism and nutrient balance.

Abnormalities in glucose metabolism and their relevance to nutrition support in the critically ill

This review covers the recent advances that have been made in understanding the abnormalities of glucose metabolism found in critically ill patients. The alterations in the pathways of glucose production and utilization and the hormones and cytokines responsible for these are described. Therapies that have the potential to alter abnormal glucose metabolism and improve nutritional status are discussed.

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.