The effect of major thermal injury on plasma ketone body levels

Cardiometabolic disease risk markers are increased following burn injury in children

Introduction

Burn injury in children causes prolonged systemic effects on physiology and metabolism leading to increased morbidity and mortality, yet much remains undefined regarding the metabolic trajectory towards specific health outcomes.

Methods

A multi-platform strategy was implemented to evaluate the long-term immuno-metabolic consequences of burn injury combining metabolite, lipoprotein, and cytokine panels. Plasma samples from 36 children aged 4-8 years were collected 3 years after a burn injury together with 21 samples from non-injured age and sex matched controls. Three different ¹H Nuclear Magnetic Resonance spectroscopic experiments were applied to capture information on plasma low molecular weight metabolites, lipoproteins, and α-1-acid glycoprotein.

Results

Burn injury was characterized by underlying signatures of hyperglycaemia, hypermetabolism and inflammation, suggesting disruption of multiple pathways relating to glycolysis, tricarboxylic acid cycle, amino acid metabolism and the urea cycle. In addition, very low-density lipoprotein sub-components were significantly reduced in participants with burn injury whereas small-dense low density lipoprotein particles were significantly elevated in the burn injured patient plasma compared to uninjured controls, potentially indicative of modified cardiometabolic risk after a burn. Weighted-node Metabolite Correlation Network Analysis was restricted to the significantly differential features (q <0.05) between the children with and without burn injury and demonstrated a striking disparity in the number of statistical correlations between cytokines, lipoproteins, and small molecular metabolites in the injured groups, with increased correlations between these groups.

Discussion

These findings suggest a 'metabolic memory' of burn defined by a signature of interlinked and perturbed immune and metabolic function. Burn injury is associated with a series of adverse metabolic changes that persist chronically and are independent of burn severity and this study demonstrates increased risk of cardiovascular disease in the long-term. These findings highlight a crucial need for improved longer term monitoring of cardiometabolic health in a vulnerable population of children that have undergone burn injury.

1H-NMR Metabolomics Identifies Significant Changes in Metabolism over Time in a Porcine Model of Severe Burn and Smoke Inhalation

Burn injury initiates a hypermetabolic response leading to muscle catabolism and organ dysfunction but has not been well-characterized by high-throughput metabolomics. We examined changes in metabolism over the first 72 h post-burn using proton nuclear magnetic resonance (1H-NMR) spectroscopy and serum from a porcine model of severe burn injury. We sought to quantify the changes in metabolism that occur over time in response to severe burn and smoke inhalation in this preliminary study. Fifteen pigs received 40% total body surface area (TBSA) burns with additional pine bark smoke inhalation. Arterial blood was drawn at baseline (pre-burn) and every 24 h until 72 h post-injury or death. The aqueous portion of each serum sample was analyzed using 1H-NMR spectroscopy and metabolite concentrations were used for principal component analysis (PCA). Thirty-eight metabolites were quantified in 39 samples. Of these, 31 showed significant concentration changes over time (p < 0.05). PCA revealed clustering of samples by time point on a 2D scores plot. The first 48 h post-burn were characterized by high concentrations of histamine, alanine, phenylalanine, and tyrosine. Later timepoints were characterized by rising concentrations of 2-hydroxybutyrate, 3-hydroxybutyrate, acetoacetate, and isovalerate. No significant differences in metabolism related to mortality were observed. Our work highlights the accumulation of organic acids resulting from fatty acid catabolism and oxidative stress. Further studies will be required to relate accumulation of the four organic carboxylates identified in this analysis to outcomes from burn injury.

Oxidation of D(-)3-hydroxybutyrate administered to rats with extensive burns

Although the suppressive effect of 3-hydroxybutyrate (3-OHB) on post-traumatic protein catabolism in traumatized patients is well documented, the oxidation of exogenously administered 3-OHB during catabolic stress has not been investigated. The present study was designed to evaluate, using radioactive isotopes, total body oxidation in rats with and without burn stress to which 3-OHB had been exogenously administered, in comparison with total body oxidation in such rats that had received glucose. The rats were divided into four groups, based on whether or not a 30% full-thickness burn was inflicted, and the type of infusate they received after the burn, namely, 3-OHB or glucose. The total exhaled CO2 was collected for 6h after the infusion was commenced, and 14CO2 was assayed in a liquid scintillation spectrometer. Oxidation of the infusate was calculated from the percentage of exhaled 14CO2 derived from the infused substrates. The plasma concentration of 3-OHB was significantly increased after the infusion in both the burned and non-burned rats. The total exhaled 14CO2 from the rats infused with glucose decreased from 48.2 +/- 2.4% to 40.8 +/- 3.7% (means +/- SD, P < 0.001) after thermal injury. However, the total exhaled 14CO2 from the rats infused with 3-OHB appeared sooner, and there was no difference in the total expired 14CO2 derived from 3-OHB between the burned and non-burned rats, at 68.1 +/- 2.7% vs 66.4 +/- 3.4%, respectively. These findings suggest that even under conditions of burn stress, 3-OHB can be oxidized normally if the plasma concentration of 3-OHB is elevated by exogenous administration.

Nutritional support of the burned patient

Burn patients develop a number of physiologic alterations among which is a markedly increased metabolic rate. Other metabolic changes include an increased rate of glucose production and utilization, a decreased rate of lipid metabolism, and an increased rate of both protein catabolism and anabolism. These alterations can effect other physiologic parameters, including immune function. They necessitate administration of large quantities of calories and protein to achieve positive nitrogen balance. The physiologic derangements leading to the hypermetabolism and the methods for supplying the nutritional needs are discussed in this review.

Nutrition for adult burn patients: a review

Adequate nutritional support is an important aspect of burn therapy. To accomplish this goal, nutrition assessment must be conducted, with particular attention given to the determination of energy and macronutrient needs. Providing these nutrients by the enteral route is recommended.

The effect of glucose administration on carbohydrate metabolism after head injury

The role of intravenous infusion of glucose in limiting ketogenesis and the effect of glucose on cerebral metabolism following severe head injury were studied in 21 comatose patients. The patients were randomly assigned to alimentation with or without glucose. Systemic protein wasting, arterial concentrations of energy substrates, and cerebral metabolism of these energy substrates were monitored for 5 days postinjury. Both groups were in negative nitrogen balance, and had wasting of systemic proteins despite substantial protein intake. Blood and cerebrospinal fluid (CSF) glucose concentrations were highest on Day 1, but remained higher than normal fasting levels on all days of study, even in the patients who received no exogenous glucose. Although there were no differences in blood or CSF glucose concentrations in the two groups of patients, the glucose group had higher plasma insulin levels, with a mean +/- standard deviation of 14.8 +/- 7.3 microU/ml compared to 10.3 +/- 4.2 microU/ml in the saline group. The blood concentrations of beta-hydroxybutyrate, acetoacetate, pyruvate, glycerol, and the free fatty acids were higher in the saline group than in the glucose group. Cerebral oxygen consumption was similar in the two groups, while the cerebral metabolism of glucose and of the ketone bodies was dependent on whether glucose was administered. In the glucose group, glucose was the only energy substrate utilized by the brain. In the saline group, the ketone bodies beta-hydroxybutyrate and acetoacetate replaced glucose to the extent of 16% of the brain's total energy production. Cerebral lactate production and CSF lactate concentration were lower in the saline group. These studies suggest that administration of glucose during the early recovery period of severe head injury is a major cause of suppressed ketogenesis, and may increase production of lactic acid by the traumatized brain by limiting the availability of nonglycolytic energy substrates.

Amino acid metabolism in thermal burns

Burn injury induces time-dependent variations in plasma amino acids, ie, an initial hyperaminoacidemia reflecting proteolysis in the wound areas, a decrease in gluconeogenic amino acids a consequence of excessive utilization in the liver, and a progressive return to normal. There is also a durable hyperphenylalaninemia, reflecting increased protein turnover and specific alterations of sulfur amino acids. In burned rats, the same general pattern is observed, except that glycine rather than alanine and glutamine exhibits the largest variations. Improvements in nutritional support with regard to the amino acid composition of diets are envisaged.

Medium-chain triglyceride-based fat emulsions: an alternative energy supply in stress and sepsis

Medium-chain triglycerides (MCTs) and medium-chain fatty acids (MCFAs) have special physicochemical properties such as small molecular weight, small interfacial tension against water, and for the fatty acids, solubility in biological fluids. As a result the metabolic pathways followed by these fats in an organism are different and simpler, or identical but more rapid, than those followed by long-chain triglycerides (LCTs) and long-chain fatty acids (LCFAs). Consequently the MCTs have found numerous applications in oral or enteral nutrition and, more recently, in parenteral nutrition. The infusion of conventional fat emulsions in stress and sepsis is still controversial. A main question is whether an MCT supply can be beneficial for these patients. In this review, we will discuss different aspects of modified lipid and protein metabolism: exchanges between exogenous fat particles and lipoproteins; exogenous fat clearance, storage, and oxidation; reticuloendothelial system function; nitrogen balance; and hepatic function. For each of these perturbations, the MCT/LCT and structured lipid emulsions are theoretically capable to provide an appropriate solution. The efficiency of these emulsions has been demonstrated experimentally on animal models of stress and sepsis. However, the value of MCT-based fat emulsions for these pathological states has still to be ascertained by clinical studies.

Carnitine supplementation vs. medium-chain triglycerides in postburn nutritional support

The effect of dietary supplementation of carnitine on protein metabolism was studied in a burned guinea-pig model. Animals bearing a 30 per cent total body surface area burn were enterally infused with three isocaloric and isonitrogenous diets via gastrostomy feeding tubes for 14 days. Two diets contained safflower oil (long-chain triglycerides, LCT) and another diet contained medium-chain triglycerides (MCT) as their lipid sources (30 per cent of total calories as lipid). L-Carnitine was added to one of the two diets containing safflower oil. There were no significant differences in nitrogen balance, urinary excretion, serum albumin or transferrin among the three groups. However, the use of MCT in place of LCT appeared to increase liver weight and liver nitrogen. In this model, carnitine supplementation did not enhance the nitrogensparing effect of fat following burn injury.

Free fatty acid turnover and lipolysis in septic mechanically ventilated cancer-bearing humans

Loss of body fat and lean body mass are features of critical illness, and anabolism is difficult to achieve despite parenteral nutrition. Resting energy expenditure (REE), free fatty acid turnover (FFT) and glycerol turnover (glyTO) were measured in septic, mechanically ventilated cancer-bearing patients, both fasting and immediately following or during a glucose infusion providing 87% of REE. No patient was in septic shock nor required pressor support. In the fasting state, REE was greatly elevated compared with basal energy expenditure calculated using the Harris-Benedict equations. Fasting FFT (14.2 +/- 0.9 mumol/kg/min) and glyTO (4.7 +/- 0.5 mumol/kg/min) were elevated compared with normal humans. Fasting respiratory quotient (RQ) was 0.68 +/- 0.02 and did not rise significantly with glucose. Fat appears to be the preferred calorie source in septic, cancer-bearing humans even in the presence of glucose. As similar, but less pronounced, changes have been seen in septic and injured humans without cancer, it is likely that these changes are not cancer-specific.

Nutritional considerations for the burned patient

The metabolic response to injury is one of marked catabolic hormonal predominance resulting in hypermetabolism and protein wasting. Energy expenditure increases with increasing severity of injury, but reaches a maximum of twice resting energy expenditure when 50 per cent TBSA is burned. We agree with the nutritional recommendations of the group at the Boston Shriner's Burn Institute and the Massachusetts General Hospital. These include providing calories at twice the resting energy expenditure, as predicted by the Harris-Benedict equations, for patients with greater than 30 per cent BSAB; protein is provided at 2.5 gm per kg per day based on ideal body weight. It is important to recognize that these are optimal goals, but their attainment must be governed by safety considerations for the patient. It is probably safe to supplement intake with a multivitamin and vitamin C, as well as zinc, but our understanding of micronutrient therapy for stressed patients is rudimentary.

Arterio-venous differences in amino acids, glucose, lactate and fatty acids in burn patients; effect of ornithine alpha-ketoglutarate

The study concerns two groups of seven burn patients matched for age, weight and total burn surface. Both groups received conventional enteral nutrition, while one was given a 10 g/day alpha-ketoglutarate ornithine (OKG) supplement. Femoral venous and arterial blood was taken from day 2 to day 13 post-burn in order to determine levels of amino acids, nonesterified fatty acids (NEFA), glucose and lactate. In the control group large negative arterio-venous differences (DeltaA-V) were observed in amino acid and lactate levels whereas they were significantly lower with regard to Hyp, Gly, Lys and Ala in the OKG-treated group. DeltaA-V was near zero for glucose and NEFA in both groups. These results support the view that OKG-therapy limits the output of amino acids in the leg and that glucose and NEFA do not constitute the main fuel in muscle.