Ricki Y. Fram

Insulin sensitivity and mitochondrial function are improved in children with burn injury during a randomized controlled trial of fenofibrate.

Objective:To determine some of the mechanisms involved in insulin resistance immediately following burn trauma, and to determine the efficacy of PPAR-α agonism for alleviating insulin resistance in this population. Summary Background Data:Hyperglycemia following trauma, especially burns, is well documented. However, the underlying insulin resistance is not well understood, and there are limited treatment options. Methods:Twenty-one children 4 to 16 years of age with >40% total body surface area burns were enrolled in a double-blind, prospective, placebo-controlled randomized trial. Whole body and liver insulin sensitivity were assessed with a hyperinsulinemic-euglycemic clamp, and insulin signaling and mitochondrial function were measured in muscle biopsies taken before and after ∼2 weeks of either placebo (PLA) or 5 mg/kg of PPAR-α agonist fenofibrate (FEN) treatment, within 3 weeks of injury. Results:The change in average daily glucose concentrations was significant between groups after treatment (146 ± 9 vs. 161 ± 9 mg/dL PLA and 158 ± 7 vs. 145 ± 4 FEN; pretreatment vs. posttreatment; P = 0.004). Insulin-stimulated glucose uptake increased significantly in FEN (4.3 ± 0.6 vs. 4.5 ± 0.7 PLA and 5.2 ± 0.5 vs. 7.6 ± 0.6 mg/kg per minute FEN; pretreatment vs. posttreatment; P = 0.003). Insulin trended to suppress hepatic glucose release following fenofibrate treatment (P = 0.06). Maximal mitochondrial ATP production from pyruvate increased significantly after fenofibrate (P = 0.001) and was accompanied by maintained levels of cytochrome C oxidase and citrate synthase activity levels. Tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 in response to insulin increased significantly following fenofibrate treatment (P = 0.04 for both). Conclusions:Fenofibrate treatment started within 1 week postburn and continued for 2 weeks significantly decreased plasma glucose concentrations by improving insulin sensitivity, insulin signaling, and mitochondrial glucose oxidation. Fenofibrate may be a potential new therapeutic option for treating insulin resistance following severe burn injury.

PPAR-α agonism improves whole body and muscle mitochondrial fat oxidation, but does not alter intracellular fat concentrations in burn trauma children in a randomized controlled trial

BackgroundInsulin resistance is often associated with increased levels of intracellular triglycerides, diacylglycerol and decreased fat β-oxidation. It was unknown if this relationship was present in patients with acute insulin resistance induced by trauma.MethodsA double blind placebo controlled trial was conducted in 18 children with severe burn injury. Metabolic studies to assess whole body palmitate oxidation and insulin sensitivity, muscle biopsies for mitochondrial palmitate oxidation, diacylglycerol, fatty acyl Co-A and fatty acyl carnitine concentrations, and magnetic resonance spectroscopy for muscle and liver triglycerides were compared before and after two weeks of placebo or PPAR-α agonist treatment.ResultsInsulin sensitivity and basal whole body palmitate oxidation as measured with an isotope tracer increased significantly (P = 0.003 and P = 0.004, respectively) after PPAR-α agonist treatment compared to placebo. Mitochondrial palmitate oxidation rates in muscle samples increased significantly after PPAR-α treatment (P = 0.002). However, the concentrations of muscle triglyceride, diacylglycerol, fatty acyl CoA, fatty acyl carnitine, and liver triglycerides did not change with either treatment. PKC-θ activation during hyper-insulinemia decreased significantly following PPAR-α treatment.ConclusionPPAR-α agonist treatment increases palmitate oxidation and decreases PKC activity along with reduced insulin sensitivity in acute trauma, However, a direct link between these responses cannot be attributed to alterations in intracellular lipid concentrations.

Human mitochondrial oxidative capacity is acutely impaired after burn trauma.

BACKGROUND Mitochondrial proteins and genes are damaged after burn injury in animals and are assessed in human burn patients in this study. METHODS The rates of maximal muscle mitochondrial oxidative capacity (adenosine triphosphate production) and uncoupled oxidation (heat production) for both palmitate and pyruvate were measured in muscle biopsies from 40 children sustaining burns on more than 40% of their body surface area and from 13 healthy children controls. RESULTS Maximal mitochondrial oxidation of pyruvate and palmitate were reduced in burn patients compared with controls (4.0 +/- .2:1.9 +/- .1 micromol O2/citrate synthase activity/mg protein/min pyruvate; control:burn; P < .001 and 3.0 +/- .1: .9 +/- .03 micromol O2/citrate synthase activity/mg protein/min palmityl CoA; control:burn; P = .003). Uncoupled oxidation was the same between groups. CONCLUSIONS The maximal coupled mitochondrial oxidative capacity is severely impaired after burn injury, although there are no alterations in the rate of uncoupled oxidative capacity. It may be that the ratio of these indicates that a larger portion of energy production in trauma patients is wasted through uncoupling, rather than used for healing.

Glucan phosphate potentiates endotoxin-induced interferon-γ expression in immunocompetent mice, but attenuates induction of endotoxin tolerance

Glucan phosphate has been shown to enhance antimicrobial immunity in a variety of experimental models. However, the mechanisms by which glucans enhance resistance to infection remain largely unknown. Interferon-gamma (IFN-gamma) is a key regulator of both innate and acquired immunity. Suppression of IFN-gamma production is a prominent feature of the altered immune response that follows major trauma or sepsis. The present studies were designed to determine the effect of glucan phosphate on IFN-gamma expression in normal mice and endotoxin [lipopolysaccharide (LPS)]-tolerant mice. The model of LPS tolerance was used because it results in patterns of cytokine expression similar to those commonly observed following severe trauma or sepsis. Glucan treatment potentiated LPS-induced IFN-gamma expression in control mice. The induction of LPS tolerance resulted in marked suppression of LPS-induced IFN-gamma production. However, co-administration of glucan with LPS, during the tolerance induction phase, attenuated the LPS-tolerant response. Interleukin-12 (IL-12) and IL-18 are important mediators of LPS-induced IFN-gamma production. LPS-induced IL-12 p40 mRNA expression was increased in the spleens of glucan-treated mice compared with controls. Induction of LPS tolerance caused marked suppression of IL-12 production, a response that was attenuated by glucan treatment. IL-18 was constitutively expressed in both control and LPS-tolerant mice, and LPS-induced serum levels of IL-18 were increased in mice treated with glucan. T cells isolated from glucan-treated mice exhibited increased IFN-gamma expression in response to IL-12 and IL-18, as well as increased expression of the IL-12 and IL-18 receptors. The ability of glucan to potentiate IFN-gamma expression in control mice provides a potential mechanism by which glucan enhances antimicrobial immunity. The ability of glucan to attenuate suppressed IFN-gamma expression in LPS-tolerant mice denotes its potential benefit for the treatment of trauma and sepsis-induced immunosuppression.

Intensive insulin therapy improves insulin sensitivity and mitochondrial function in severely burned children.

Objective:To institute intensive insulin therapy protocol in an acute pediatric burn unit and study the mechanisms underlying its benefits. Design:Prospective, randomized study. Setting:An acute pediatric burn unit in a tertiary teaching hospital. Patients:Children, 4-18 yrs old, with total body surface area burned ≥40% and who arrived within 1 wk after injury were enrolled in the study. Interventions:Patients were randomized to one of two groups. Intensive insulin therapy maintained blood glucose levels between 80 and 110 mg/dL. Conventional insulin therapy maintained blood glucose ≤215 mg/dL. Measurements and Main Results:Twenty patients were included in the data analysis consisting of resting energy expenditure, whole body and liver insulin sensitivity, and skeletal muscle mitochondrial function. Studies were performed at 7 days postburn (pretreatment) and at 21 days postburn (posttreatment). Resting energy expenditure significantly increased posttreatment (1476 ± 124 to 1925 ± 291 kcal/m2·day; p = .02) in conventional insulin therapy as compared with a decline in intensive insulin therapy. Glucose infusion rate was identical between groups before treatment (6.0 ± 0.8 conventional insulin therapy vs. 6.8 ± 0.9 mg/kg·min intensive insulin therapy; p = .5). Intensive insulin therapy displayed a significantly higher glucose clamp infusion rate posttreatment (9.1 ± 1.3 intensive insulin therapy versus 4.8 ± 0.6 mg/kg·min conventional insulin therapy, p = .005). Suppression of hepatic glucose release was significantly greater in the intensive insulin therapy after treatment compared with conventional insulin therapy (5.0 ± 0.9 vs. 2.5 ± 0.6 mg/kg·min; intensive insulin therapy vs. conventional insulin therapy; p = .03). States 3 and 4 mitochondrial oxidation of palmitate significantly improved in intensive insulin therapy (0.9 ± 0.1 to 1.7 ± 0.1 &mgr;m O2/CS/mg protein/min for state 3, p = .004; and 0.7 ± 0.1 to 1.3 ± 0.1 &mgr;m O2/CS/mg protein/min for state 4, p < .002), whereas conventional insulin therapy remained at the same level of activity (0.9 ± 0.1 to 0.8 ± 0.1.&mgr;m O2/CS/mg protein/min for state 3, p = .4; 0.6 ± 0.03 to 0.7 ± 0.1 &mgr;m O2/CS/mg protein/min, p = .6). Conclusion:Controlling blood glucose levels ≤120 mg/dL using an intensive insulin therapy protocol improves insulin sensitivity and mitochondrial oxidative capacity while decreasing resting energy expenditure in severely burned children.

Insulin resistance, secretion and breakdown are increased 9 months following severe burn injury

Insulin resistance in the acute burn period has been well described, however, it is unknown if alterations in glucose metabolism persist beyond discharge from the acute injury. To measure the duration of insulin resistance following recovery from the acute burn injury, we performed a prospective cross-sectional study with a standard 2-h oral glucose tolerance test in 46 severely burned children at 6, 9 or 12 months following initial injury. Glucose uptake and insulin secretion were assessed following the glucose load. Results were compared to those previously published in healthy children. At 6 months after burn, the 2-h glucose concentration was significantly (P<0.001) greater than controls, and the area under the curve (AUC) of glucose was significantly higher compared to 12 months and to healthy children (P=0.027 and P<0.001, respectively). The 9-month AUC glucose was higher than controls (P<0.01). The 6-month 2-h insulin was significantly higher than controls, as was the AUC of insulin in all time points post-burn. The AUC of C-peptide was significantly greater at 6 months after injury compared to 9 and 12 months (P<0.01 for both). Increased 2h and AUC glucose and insulin indicate that glucose metabolism is still affected at 6 and 9 months after injury, and coincides with previously documented defects in bone and muscle metabolism at these time points. Insulin breakdown is also still increased in this population. Further study of this population is warranted to determine if specific treatment is needed.

Impaired glucose tolerance in pediatric burn patients at discharge from the acute hospital stay.

Hyperglycemia, secondary to the hypermetabolic stress response, is a common occurrence after thermal injury. This stress response has been documented to persist up to 9 months postburn. The purpose of this study was to measure insulin sensitivity in severely burned children before discharge when wounds are 95% healed. Twenty-four children, aged 4 to 17 years, with burns ≥40% TBSA underwent a 2-hour oral glucose tolerance test before discharge from the acute pediatric burn unit. Plasma glucose and insulin levels as well as the Homeostasis Model Assessment for Insulin Resistance (HOMAIR) were compared with published oral glucose tolerance test data from healthy, nonburned children. There was a significant difference between severely burned children and nonburned, healthy children with respect to the HOMAIR. Severely burned children had a HOMAIR of 3.53 ± 1.62 compared with the value in nonburned, healthy children of 1.28 ± 0.16 (P < .05). Insulin resistance secondary to the hypermetabolic stress response persists in severely burned children when burn wounds are at least 95% healed. The results of this study warrant future investigations into therapeutic options for the burned child during the rehabilitative phase of their care after injury.

Insulin Sensitivity is Related to Fat Oxidation and Protein Kinase C Activity in Children With Acute Burn Injury

Impaired fatty acid oxidation occurs with type 2 diabetes and is associated with accumulations of intracellular lipids, which may increase diacylglycerol (DAG), stimulate protein kinase C activity, and inactivate insulin signaling. Glucose and fat metabolism are altered in burn patients, but have never been related to intracellular lipids or insulin signaling. Thirty children sustaining >40% total body surface area burns were studied acutely with glucose and palmitate tracer infusions and a hyper-insulinemic euglycemic clamp. Muscle triglyceride, DAG, fatty acyl CoA, and insulin signaling were measured. Liver and muscle triglyceride levels were measured with magnetic resonance spectroscopy. Muscle samples from healthy children were controls for DAG concentrations. Insulin sensitivity was reduced and correlated with whole body palmitate &bgr;-oxidation (P = .004). Muscle insulin signaling was not stimulated by hyper-insulinemia. Tissue triglyceride concentrations and activated protein kinase C-&bgr; were elevated, whereas the concentration of DAG was similar to the controls. Free fatty acid profiles of muscle triglyceride did not match DAG. Insulin resistance following burn injury is accompanied by decreased insulin signaling and increased protein kinase C-&bgr; activation. The best metabolic predictor of insulin resistance in burned patients was palmitate oxidation.

INFLUENCE OF INHALATION INJURY ON ENERGY EXPENDITURE IN SEVERELY BURNED CHILDREN

OBJECTIVE Determine the effect of inhalation injury on burn-induced hypermetabolism in children. DESIGN Prospective study comparing hypermetabolism (i.e., resting energy expenditure and oxygen consumption) in burned children with and without inhalation injury during acute hospitalization. SETTING Single pediatric burn center. PATIENTS Eighty-six children (1-18 years) with ≥40% total body surface area burns were stratified to two groups: no inhalation injury and inhalation injury. INTERVENTIONS None. MAIN MEASUREMENTS AND RESULTS Inhalation 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. CONCLUSIONS Inhalation injury does not augment the burn-induced hypermetabolic stress response in children, as reflected by resting energy expenditure and oxygen consumption.