Muscle protein catabolism after severe burn: effects of IGF-1/IGFBP-3 treatment

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.

IGF-I/IGFBP-3 ameliorates alterations in protein synthesis, eIF4E availability, and myostatin in alcohol-fed rats

Chronic alcohol consumption decreases the concentration of the anabolic hormone IGF-I, and this change is associated with impaired muscle protein synthesis. The present study evaluated the ability of IGF-I complexed with IGF-binding protein (IGFBP)-3 to modulate the alcohol-induced inhibition of muscle protein synthesis in gastrocnemius. After 16 wk on an alcohol-containing diet, either the IGF-I/IGFBP-3 binary complex (BC) or saline was injected two times daily for three consecutive days. After the final injection of BC (3 h), plasma IGF-I concentrations were elevated in alcohol-fed rats to values not different from those of similarly treated control animals. Alcohol feeding decreased the basal rate of muscle protein synthesis by limiting translational efficiency. BC treatment of alcohol-fed rats increased protein synthesis back to basal control values, but the rate remained lower than that of BC-injected control rats. The BC partially reversed the alcohol-induced decrease in the binding of eukaryotic initiation factor (eIF)4E with eIF4G. This change was associated with reversal of the alcohol-induced dephosphorylation of eIF4G but was independent of changes in the phosphorylation of either 4E-BP1 or eIF4E. However, BC reversed the alcohol-induced increase in IGFBP-1 and muscle myostatin, known negative regulators of IGF-I action and muscle mass. Hence, exogenous IGF-I, administered as part of a BC to increase its circulating half-life, can in part reverse the decreased protein synthesis observed in muscle from chronic alcohol-fed rats by stimulating selected components of translation initiation. The data support the role of IGF-I as a mediator of chronic alcohol myopathy in rats.

Control of the Size of the Human Muscle Mass

This review is divided into two parts, the first dealing with the cell and molecular biology of muscle in terms of growth and wasting and the second being an account of current knowledge of physiological mechanisms involved in the alteration of size of the human muscle mass. Wherever possible, attempts have been made to interrelate the information in each part and to provide the most likely explanation for phenomena that are currently only partially understood. The review should be of interest to cell and molecular biologists who know little of human muscle physiology and to physicians, physiotherapists, and kinesiologists who may be familiar with the gross behavior of human muscle but wish to understand more about the underlying mechanisms of change.

Insulin-like growth factor (IGF)-I/IGF-binding protein-3 complex: therapeutic efficacy and mechanism of protection against type 1 diabetes

IGF-I regulates islet beta-cell growth, survival, and metabolism and protects against type 1 diabetes (T1D). However, the therapeutic efficacy of free IGF-I may be limited by its biological half-life in vivo. We investigated whether prolongation of its half-life as an IGF-I/IGF binding protein (IGFBP)-3 complex affords increased protection against T1D and whether this occurs by influencing T cell function and/or islet beta-cell growth and survival. Administration of IGF-I either alone or as an IGF-I/IGFBP-3 complex reduced the severity of insulitis and delayed the onset of T1D in nonobese diabetic mice, but IGF-I/IGFBP-3 was significantly more effective. Protection from T1D elicited by IGF-I/IGFBP-3 was mediated by up-regulated CCL4 and down-regulated CCL3 gene expression in pancreatic draining lymph nodes, activation of the phosphatidylinositol 3-kinase and Akt/protein kinase B signaling pathway of beta-cells, reduced beta-cell apoptosis, and stimulation of beta-cell replication. Reduced beta-cell apoptosis resulted from elevated Bcl-2 and Bcl-X(L) activity and diminished caspase-9 activity, indicating a novel role for a mitochondrial-dependent pathway of beta-cell death. Thus, IGF-I/IGFBP-3 affords more efficient protection from insulitis, beta-cell destruction, and T1D than IGF-I, and this complex may represent an efficacious therapeutic treatment for the prevention of T1D.

Effects of insulin-like growth factor-1/binding protein-3 complex on muscle atrophy in rats

Muscle atrophy and wasting is a serious problem that occurs in patients with prolonged debilitating illness, burn injury, spinal injury, as well as with space flight. Current treatment for such atrophy, which often relies on nutritional supplementation and physical therapy, is of limited value in preventing the muscle wasting that occurs. Considerable recent attention has focused on the use of anabolic growth factors such as insulin-like growth factor (IGF-1) in preventing muscle atrophy during limb disuse or with various catabolic conditions. However, potential side effects such as hypoglycemia appear to be limiting factors in the usefulness of IGF-1 for clinical treatment of muscle wasting conditions. The formulation of IGF-1 used in this study (IGF-1/BP3) is already bound to its endogenous-binding protein (BP3) and, as a result, has a greater specificity of action and significantly less hypoglycemic effect. Using a rat model of hind limb suspension (HLS) for 10 days, we induced marked muscle atrophy that was accompanied by enhanced muscle proteolysis and reduced muscle protein content. When HLS rats were treated with IGF-1/BP3 (50 mg/kg, b.i.d.), they retained greater body and muscle mass. Muscle protein degradation was significantly reduced and muscle protein content was preserved. The rate of protein synthesis, although somewhat reduced in HLS muscle, was not significantly elevated by IGF-1/BP3 treatment. Volume density of HLS-treated muscles were increased compared to untreated HLS rats and the actual number of fibers per area of muscle was likewise increased. The results of the current study suggest that IGF-1/BP3 might be useful for inhibiting muscle proteolysis in catabolic conditions and thus preserving muscle protein content and mass.

Improved net protein balance, lean mass, and gene expression changes with oxandrolone treatment in the severely burned

OBJECTIVE

To determine the effects of the anabolic agent oxandrolone on muscle protein and gene expression in severely burned children.

SUMMARY BACKGROUND DATA

The authors previously showed that oxandrolone increased net muscle protein synthesis in emaciated burned patients receiving delayed treatment for severe burns. They hypothesized that similar effects would be seen in those treated early after burn.

METHODS

Thirty-two severely burned children were enrolled in a prospective randomized trial. Subjects underwent studies to assess leg protein net balance 5 days after the first excision and grafting procedure. Immediately after these studies, treatment with placebo (n = 18) or 0.1 mg/kg oxandrolone (n = 14) twice a day was started. One week after this, another net balance study was performed in each subject. Body weights and total body potassium counting were used to determine body compositional changes. Muscle biopsies were taken 1 week after treatment in oxandrolone subjects to examine gene expression changes with gene array (12,600 genes).

RESULTS

Protein net balance did not change in the placebo group, while oxandrolone-treated subjects had a significant improvement. Body weights and fat free mass significantly decreased in the placebo group, while no changes were found in the oxandrolone-treated subjects. Expression changes were seen in 14 genes in the oxandrolone group compared to placebo. Some of these included myosin light chain (+2.7-fold change), tubulin (+2.3), calmodulin (-2.3), and protein phosphatase I inhibitor (-2.8).

CONCLUSIONS

Oxandrolone improves protein net balance and lean mass in the severely burned. These changes are associated with increased gene expression for functional muscle proteins.

Effects of early excision and aggressive enteral feeding on hypermetabolism, catabolism, and sepsis after severe burn

BACKGROUND

Severe burn induces a systemic hypermetabolic response, which includes increased energy expenditure, protein catabolism, and diminished immunity. We hypothesized that early burn excision and aggressive enteral feeding diminish hypermetabolism.

METHODS

Forty-six burned children were enrolled into a cohort analytic study. Cohorts were segregated according to time from burn to transfer to our institution for excision, grafting, and nutritional support. No subject had undergone wound excision or continuous nutritional support before transfer. Resting energy expenditure, skeletal muscle protein kinetics, the degree of bacterial colonization from quantitative cultures, and the incidence of burn sepsis were measured as outcome variables.

RESULTS

Early, aggressive treatment did not decrease energy expenditure; however, it did markedly attenuate muscle protein catabolism when compared with delay in aggressive treatment. Wound colonization and sepsis were diminished in the early treatment group as well.

CONCLUSION

Early excision and concurrent aggressive feeding attenuate muscle catabolism and improve infectious outcomes after burn.

Current pharmacotherapy for the treatment of severe burns

The pharmacotherapy of burn care has evolved from the first topical antibiotics instituted > 30 years ago. These have helped greatly to reduce the incidence of burn wound sepsis, but a better understanding of the principles of burn care has resulted in earlier burn wound excision and complete coverage with autograft, cadaver skin, synthetic dressings, and amnion. This has markedly reduced septic complications and ameliorated the hypermetabolic response to burn injury. The hypermetabolic response, which is mediated by hugely increased levels of circulating catecholamines, prostaglandins, glucagon and cortisol, causes profound skeletal muscle catabolism, immune deficiency, peripheral lipolysis, reduced bone mineralisation, reduced linear growth, and increased energy expenditure. Supportive therapy and pharmacological manipulation, acutely and during rehabilitation, with growth hormone, insulin and related proteins, oxandrolone and propranolol can ameliorate the hypermetabolic response, improving survival and long-term outcome. Despite judicious use of topical and systemic antibiotics, opportunistic nosocomial bacterial resistance threatens to annul the improved survival of patients with severe burns. Patterns of emerging resistance encountered in burn units need to be considered, in light of a decreasing antibiotic armamentarium. A holistic approach to pharmacotherapy of severely burned patients including current practice in antimicrobial control, analgesia, sedation, and anxiety management is required. Current therapy of frequently encountered problems, such as post-burn pruritus, prophylaxis of deep venous thrombosis and peptic ulceration, and pharmacological manipulation of inhalation injury in the burned patient is described. Current pharmacotherapy to ameliorate psychosocial problems associated with burns such as acute stress disorder, depression and post traumatic stress disorder are discussed. Better analgesics, newer antibiotics and immune stimulating drugs are required to reduce mortality and morbidity in large burns.

In vivo rabbit hindquarter model for assessment of regional burn hypermetabolism

Severe burn injury evokes hypermetabolism and muscle wasting, despite nominally adequate nutrition. Although there is much information on whole organism and isolated tissue metabolism after burn injury, data examining regional burn hypermetabolism in vivo are lacking. Using surgically implanted (general anesthesia) regional vascular catheters and primed constant infusion of l-[1-(13)C]phenylalanine tracer, we have determined in vivo burn-induced alterations in rabbit hindquarter protein and energy metabolism. Burn injury evokes increased whole body resting energy expenditure and phenylalanine turnover, accompanied by significantly increased hindquarter proteolysis, creating a negative protein balance in burned rabbit hindquarter. Hindquarter oxygen consumption showed an increase after burn injury, but it did not reach statistical significance. Burn-induced changes in hindquarter protein turnover account for approximately one-third of the whole animal hypermetabolism. This model offers a system for regional manipulation of postburn hypermetabolism.

Improved contractile function of the mdx dystrophic mouse diaphragm muscle after insulin-like growth factor-I administration

Limited knowledge exists regarding the efficacy of insulin-like growth factor I (IGF-I) administration as a therapeutic intervention for muscular dystrophies, although findings from other muscle pathology models suggest clinical potential. The diaphragm muscles of mdx mice (a model for Duchenne muscular dystrophy) were examined after 8 weeks of IGF-I administration (1 mg/kg s.c.) to test the hypothesis that IGF-I would improve the functional properties of dystrophic skeletal muscles. Force per cross-sectional area was approximately 49% greater in the muscles of treated mdx mice (149.6 +/- 9.6 kN/m(2)) compared with untreated mice (100.1 +/- 4.6 kN/m(2), P < 0.05), and maintenance of force over repeated maximal contraction was enhanced approximately 30% in muscles of treated mice (P < 0.05). Diaphragm muscles from treated mice comprised fibers with approximately 36% elevated activity of the oxidative enzyme succinate dehydrogenase, and approximately 23% reduction in the proportion of fast IId/x muscle fibers with concomitant increase in the proportion of type IIa fibers compared with untreated mice (P < 0.05). The data demonstrate that IGF-I administration can enhance the fatigue resistance of respiratory muscles in an animal model of dystrophin deficiency, in conjunction with enhancing energenic enzyme activity. As respiratory function is a mortality predictor in Duchenne muscular dystrophy patients, further evaluation of IGF-I intervention is recommended.

Recombinant human growth hormone modulates the hepatic acute-phase response and P-selectin in burned rats

The purpose of this study was to determine the effect of recombinant human growth hormone (rhGH) on serum constitutive proteins, cytokines, P-selectin, and insulin-like growth factor (IGF-1) in the thermally injured rats.Sprague-Dawley rats (64 males) were given 30% total body surface area full thickness scald burn. They were randomly divided to receive either 2.5mg/kg per day im rhGH or saline (control). Rats were sacrified on postburn days 1, 2, 5, and 7, and serum constitutive proteins, cytokines, P-selectin, and IGF-1 levels were measured.Serum IGF-1 levels were increased on days 2, 5, or 7 after burn in rhGH-treated rats compared with controls (P<0.001, <0.01 and <0.001, respectively). Serum transferrin and albumin levels were increased on days 7 after burn in rhGH-treated rats compared with controls (P<0.05). The cytokines increased after thermal injury. The rhGH decreased serum levels of tumor necrosis factor-alpha on postburn days 1 compared with controls (P<0.001). Serum levels of interleukin-1 were decreased on days 1 and 2 after burn in rhGH treated rats compared with controls (P<0.001, <0.01, respectively). Rats receiving rhGH showed significantly increased P-selectin levels at 5 and 7 postburn days compared with controls (P<0.001). Our data indicate that rhGH, given after thermal injury, increased albumin, transferrin, IGF-1, and P-selectin levels and decreased serum tumor necrosis factor-alpha and interleukin-1 levels.

Catabolic response to stress and potential benefits of nutrition support

The catabolic response to sepsis, severe injury, and burn is characterized by whole-body protein loss, mainly reflecting increased breakdown of muscle proteins, in particular myofibrillar proteins. Glucocorticoids and various proinflammatory cytokines are important regulators of muscle proteolysis in stressed patients. There is evidence that breakdown of proteins by the ubiquitin-proteasome pathway plays an important role in muscle cachexia, although other mechanisms may participate, such as calcium- and calpain-dependent release of myofilaments from the sarcomere. Three types of treatments have been used to reduce or prevent the catabolic response to injury and sepsis: 1). nutritional, 2). hormonal, and 3). pharmacologic. With regard to nutrition support, it is generally believed that enteral feeding is superior to parenteral feeding and that early feeding is better than late feeding. Although "immune-enhancing" enteral nutrition has been shown in several recent studies to improve outcome in critically ill patients, the specific effects of these treatments on the catabolic response in muscle are not known. In addition to nutrition support, various hormones, including insulin, growth hormone, and insulin-like growth factor-1, may blunt the catabolic response in patients with stress. Experimental studies have indicated that other treatments may become available in the future, including cytokine antibodies, calcium antagonists, and induction of heat shock response. Methods to prevent or reduce the catabolic response to stress are important considering the significant clinical consequences of muscle cachexia.

Age-dependency of insulin-like growth factors, insulin-like growth factor-binding proteins, and acid labile subunit in plasma and wounds of surgical patients

Wound problems are common in the elderly. We hypothesized that age-related decrements in blood levels of components of the insulin-like growth factor (IGF) system are reflected in the wound environment. In this prospective, observational study IGF-I, IGF-II, IGF-binding protein-2, IGF-binding protein-3, and acid labile subunit were measured by immunoassays in the wound fluid and plasma of young (23.5 +/- 3.3 years) and elderly (78.9 +/- 6.2 years) patients before and daily for 4 days after elective surgery. IGFs, IGFBP-3, and acid labile subunit in plasma were significantly lower in the elderly group (p < 0.0001). The decrements of these proteins in plasma were reflected in corresponding decrements of 25-70% in the wound fluid of elderly patients (p < 0.0001). Additionally, bioavailability of IGF-I was less in the aged. The IGF parameters in the wound displayed a constant ratio with those of blood, suggesting that blood contributes a major share of the IGF that enters the wound during the initial phase of healing. The current data adds to accumulating evidence that a decline in the IGF system in aged patients contributes to the healing deficits observed in the elderly.

Modulation of types I and II acute phase reactants with insulin-like growth factor-1/binding protein-3 complex in severely burned children

OBJECTIVE

To determine whether 0.5 mg/kg insulin-like growth factor (IGF)-1/binding protein (IGFBP)-3, given intravenously, effectively alters the acute phase response in severely burned children.

DESIGN

Longitudinal trial with each patient serving as their own control.

SETTING

University-affiliated pediatric bum center.

PATIENTS

Nine children, 15 yrs of age or less, with burns covering >40% of the total body surface area.

INTERVENTIONS

Standard burn care with early burn wound excision and grafting. Blood sampled at defined time points before and after operative procedures.

MEASUREMENTS AND RESULTS

Determination of types I and II acute phase reactant proteins, constitutive serum proteins, serum cytokines, serum IGF-1, IGFBP-3, and growth hormone levels. Treatment with IGF-1/BP-3 attenuated increases in type I (complement 3, alpha1-acidglycoprotein) and type II (haptoglobin, alpha1-antitrypsin) acute phase proteins. Further, IGF-1/BP-3 increased constitutive serum protein levels (prealbumin, retinol binding protein, transferrin) and decreased serum IL-6 levels.

CONCLUSIONS

Low-dose IGF-1/BP-3 effectively attenuated the type I and type II hepatic acute phase response, increased serum levels of constitutive proteins, and modulated the hypermetabolic response.

Reversal of catabolism by beta-blockade after severe burns

BACKGROUND

The catecholamine-mediated hypermetabolic response to severe burns causes increased energy expenditure and muscle-protein catabolism. We hypothesized that blockade of beta-adrenergic stimulation with propranolol would decrease resting energy expenditure and muscle catabolism in patients with severe burns.

METHODS

Twenty-five children with acute and severe burns (more than 40 percent of total body-surface area) were studied in a randomized trial. Thirteen received oral propranolol for at least two weeks, and 12 served as untreated controls. The dose of propranolol was adjusted to decrease the resting heart rate by 20 percent from each patient's base-line value. Resting energy expenditure and skeletal-muscle protein kinetics were measured before and after two weeks of beta-blockade (or no therapy, in controls). Body composition was measured serially throughout hospitalization.

RESULTS

Patients in the control group and the propranolol group were similar with respect to age, weight, percentage of total body-surface area burned, percentage of body-surface area with third-degree burns, and length of time from injury to metabolic study. Beta-blockade decreased the heart rates and resting energy expenditure in the propranolol group, both as compared with the base-line values (P<0.001 and P=0.01, respectively) and as compared with the values in the control group (P=0.03 and P=0.001, respectively). The net muscle-protein balance increased by 82 percent over base-line values in the propranolol group (P=0.002), whereas it decreased by 27 percent in the control group (P not significant). The fat-free mass, as measured by whole-body potassium scanning, did not change substantially in the propranolol group, whereas it decreased by a mean (+/-SE) of 9+/-2 percent in the control group (P=0.003).

CONCLUSIONS

In children with burns, treatment with propranolol during hospitalization attenuates hypermetabolism and reverses muscle-protein catabolism.

Testosterone administration in severe burns ameliorates muscle catabolism

OBJECTIVE

To assess the effects of testosterone administration on muscle protein metabolism after severe burn injury. We hypothesized that restoration of blood testosterone concentrations would restore an important anabolic stimulus to skeletal muscle, and would further increase the anabolic response of muscle to amino acid supplementation.

DESIGN

Pre- and postintervention trial conducted between September 1997 and July 1999.

SETTING

Burn intensive care unit.

PATIENTS

Six severely burned male patients (>70% total body surface area).

INTERVENTION

Testosterone enanthate, 200 mg/wk (intramuscularly), for 2 wks.

MEASUREMENTS AND MAIN RESULTS

Muscle protein synthesis, breakdown, and amino acid kinetics were determined. After a basal period in each study, we subsequently investigated the response to acute amino acid supplementation during enteral feeding. Total testosterone increased significantly from baseline to the low normal range after 1 wk, and to upper normal range after two injections (p <.001). Protein synthesis was unchanged, however, protein synthetic efficiency increased 2-fold (p <.01). Protein breakdown decreased almost 2-fold after testosterone enanthate (p <.05), resulting in an improvement in net amino acid balance to a value that was approximately zero (p <.0001). Amino acid supplementation at either time point provided no additional effects.

CONCLUSIONS

Restoration of blood testosterone can ameliorate the muscle catabolism of severe burn injury with normal feedings.

Liposomal IGF-1 gene transfer modulates pro- and anti-inflammatory cytokine mRNA expression in the burn wound

The use of systemic IGF-1 has been shown to attenuate the postburn hypermetabolic response and improve burn wound healing. Local IGF-1 gene therapy, however, promotes re-epithelialization in the burn wound without the side-effects associated with systemic delivery. We tested the hypothesis that these beneficial effects are due to changes in local cytokine production. Adult male Sprague-Dawley rats received a 40% total body surface area full-thickness scald burn and randomly received a subcutaneous injection at the burn wound margin of saline or cationic liposomes containing a IGF-1 cDNA construct. Animals were killed at 1, 4, 7 and 10 days after burn trauma. Skin biopsies at the wound border were harvested for total RNA extraction. Cytokine mRNA expression was determined using a multi-probe RNase protection assay. Data are presented as means +/- s.e.m. Statistical analysis used the unpaired t-test or Mann-Whitney test where appropriate. Significance was accepted at P < 0.05. Treatment of the burn wound with liposomal IGF-1-cDNA transfer decreased IL-1beta mRNA levels on day 10 after burn trauma from five-fold burn-induced increases compared with sham-treated rats, to near the control values present in unburned skin samples. Similarly, there was an eight-fold increase in TNF-alpha mRNA expression on postburn day 10 that was abrogated by IGF-1 gene therapy. Local IGF-1 gene transfer attenuates the mRNA expression of the inflammatory cytokines IL-1beta and TNF-alpha in the burn wound. This change may improve burn wound healing by decreasing prolonged local inflammation.

Skeletal muscle apoptosis after burns is associated with activation of proapoptotic signals

Critical illness is associated with muscle wasting and muscle weakness. Using burn injury as a model of local and systemic inflammatory response, we tested the hypothesis that thermal injury causes apoptosis in muscle. After a 40% body surface area burn to rats, abdominal muscles beneath the burn and limb muscles distant from the burn were examined for apoptosis at varying times after burn. Ladder assay, ELISA, and histological methods showed evidence of apoptosis in the abdominal muscles within 4-12 h with peak changes occurring at 3-7 days. Maximal apoptosis was also evident at distant limb muscles at 3-7 days. Investigation of proapoptotic pathways indicated mitochondrial membrane potential to be altered by 1 h after burn. Starting at 15 min after burn, cytochrome c was released from the mitochondria into the cytosol, followed by increased activity of caspase-3, starting at 6 h after burn. These studies suggest that mitochondria and caspase-mediated apoptotic pathways may be an additional mechanism of muscle weight loss in burns and may be potential therapeutic targets for prevention of muscle wasting.

IGF-I/IGFBP-3 binary complex modulates sepsis-induced inhibition of protein synthesis in skeletal muscle

The present study evaluated the ability of insulin-like growth factor I (IGF-I) complexed with IGF binding protein-3 (IGFBP-3) to modulate the sepsis-induced inhibition of protein synthesis in gastrocnemius. Beginning 16 h after the induction of sepsis, either the binary complex or saline was injected twice daily via a tail vein, with measurements made 3 and 5 days later. By day 3, sepsis had reduced plasma IGF-I concentrations approximately 50% in saline-treated rats. Administration of the binary complex provided exogenous IGF-I to compensate for the sepsis-induced diminished plasma IGF-I. Sepsis decreased rates of protein synthesis in gastrocnemius relative to controls by limiting translational efficiency. Treatment of septic rats with the binary complex for 5 days attenuated the sepsis-induced inhibition of protein synthesis and restored translational efficiency to control values. Assessment of potential mechanisms regulating translational efficiency showed that neither the sepsis-induced change in gastrocnemius content of eukaryotic initiation factor 2B (eIF2B), the amount of eIF4E associated with 4E binding protein-1 (4E-BP1), nor the phosphorylation state of 4E-BP1 or eIF4E were altered by the binary complex. Overall, the results are consistent with the hypothesis that decreases in plasma IGF-I are partially responsible for enhanced muscle catabolism during sepsis.

Determinants of skeletal muscle catabolism after severe burn

OBJECTIVE

To determine which patient factors affect the degree of catabolism after severe burn.

SUMMARY BACKGROUND DATA

Catabolism is associated with severe burn and leads to erosion of lean mass, impaired wound healing, and delayed rehabilitation.

METHODS

From 1996 to 1999, 151 stable-isotope protein kinetic studies were performed in 102 pediatric and 21 adult subjects burned over 20-99. 5% of their total body surface area (TBSA). Patient demographics, burn characteristics, and hospital course variables were correlated with the net balance of skeletal muscle protein synthesis and breakdown across the leg. Data were analyzed sequentially and cumulatively through univariate and cross-sectional multiple regression.

RESULTS

Increasing age, weight, and delay in definitive surgical treatment predict increased catabolism (P < .05). Body surface area burned increased catabolism until 40% TBSA was reached; catabolism did not consistently increase thereafter. Resting energy expenditure and sepsis were also strong predictors of net protein catabolism. Among factors that did not significantly correlate were burn type, pneumonia, wound contamination, and time after burn. From these results, the authors also infer that gross muscle mass correlates independently with protein wasting after burn.

CONCLUSIONS

Heavier, more muscular subjects, and subjects whose definitive surgical treatment is delayed are at the greatest risk for excess catabolism after burn. Sepsis and excessive hypermetabolism are also associated with protein catabolism.

Metabolic derangements in sepsis and septic shock

This article examines the spectrum of metabolic alterations in sepsis and septic shock. The clinical manifestations, neuroendocrine control, and bioenergetics of the "ebb" and "flow" phases of sepsis are reviewed. Characteristic alterations in carbohydrate, fat, and protein metabolism induced by sepsis are outlined. Finally, the implications of these metabolic alterations for the nutritional support of patients with sepsis are discussed.

Insulin-like growth factor I in combination with insulin-like growth factor binding protein 3 affects the hepatic acute phase response and hepatic morphology in thermally injured rats

OBJECTIVE

To modulate the hepatic acute phase response after a thermal injury by the administration of insulin-like growth factor I (IGF-I) in combination with its principal binding protein 3 (IGFBP-3).

SUMMARY BACKGROUND DATA

The hepatic acute phase response is a cascade of events initiated to restore homeostasis after trauma; however, a prolonged response contributes to multiorgan failure, hypermetabolism, complications, and death. Although IGF-1 has been shown to improve cell recovery and play a major role in liver regeneration, its effect on the hepatic acute phase response is not known.

METHODS

Sprague-Dawley rats (56 males) received a 60% total body surface area third-degree scald burn and were randomly divided to receive either rhIGF-I/BP-3 (10 mg/kg/day given subcutaneously) or saline (control). Rats were killed on postburn days 1, 2, 5, and 7 and serum glucose, electrolytes, acute phase reactant proteins, tumor necrosis factor alpha, interleukin 1 beta, interleukin 6, and rat and human serum IGF-I and IGFBP-3 were measured. Hepatic protein concentrations, hepatocyte proliferation, and hepatocyte apoptosis were determined.

RESULTS

No hypoglycemia or electrolyte imbalance could be shown in rats receiving the growth factor complex compared with saline. rhIGF-I/BP-3 increased serum protein on postburn days 2 and 7, albumin on days 5 and 7, and transferrin on days 1, 5, and 7, and decreased haptoglobin and alpha1-acid glycoprotein on postburn days 5 and 7 compared with controls. IGF-I/ BP-3 had no effect on type II acute phase proteins. Rats receiving IGF-I/BP-3 had lower serum levels of interleukin 1 beta and tumor necrosis factor alpha on the first day after burn compared with controls, whereas serum levels of interleukin 6 did not change. rhIGF-I/BP-3 significantly increased total liver protein content on postburn days 1, 2, 5, and 7 compared with controls. IGF-I/BP-3 increased hepatocyte proliferation and decreased hepatocyte apoptosis versus controls.

CONCLUSION

In combination with its principal binding protein, rhIGF-I decreases the proinflammatory cytokines interleukin 1 beta and tumor necrosis factor alpha, followed by a decrease in type I acute phase proteins. IGF-I/BP-3 had no effect on interleukin 6 and type II acute phase proteins. Decreases in acute phase protein and proinflammatory cytokine synthesis were associated with increases in constitutive hepatic proteins, total liver protein content, and hepatocyte proliferation. IGF-I/BP-3 attenuates the hypermetabolic response after thermal injury and may improve the clinical outcome.

Use of Growth Hormone and Insulin-like Growth Factor 1 for Treatment of Tissue Wasting in Catabolic Conditions

Trauma, surgery, burn injury, sepsis, prolonged bed rest, cancer, and AIDS are examples of catabolic states that can lead to a significant loss of lean body tissues and skeletal muscle. The physiologic stresses associated with these catabolic conditions can impair immune function, alter drug response, and delay the recovery process. Although enhanced nutritional supplementation is a mainstay for treating tissue wasting in these conditions, it is of limited effectiveness in reversing skeletal muscle protein loss or enhancing anabolism in lean body tissues. The use of anabolic hormones such as Growth Hormone (GH) or Insulin-Like Growth Factor 1 (IGF-1) to limit lean body wasting and preserve muscle mass in these conditions has been widely investigated. This article was designed to give pharmacists and patient care professionals an overview of recent literature involving anabolic hormone treatment of tissue wasting. The use of these agents in the clinical setting may undergo significant expansion in the near future.

Anabolic effects of insulin-like growth factor in combination with insulin-like growth factor binding protein-3 in severely burned adults

BACKGROUND

The purpose of this study was to determine the anabolic effects of recombinant human insulin-like growth factor-I (rhIGF-1) complexed with its principal binding protein IGF-1 binding protein-3 (IGFBP-3) in severely burned adults.

METHODS

Ten burned adults were studied consecutively after receiving saline (pretreatment), then rhIGF-1/IGFBP-3 (treatment) for 5 days. Doses were 1, 2, and 4 mg/kg per day. Glucose, electrolytes, hormones, and leg muscle protein metabolism were determined. Nine other studies were performed on similarly injured adults at comparable times to the treatment studies to control for time effects.

RESULTS

Serum IGF-1 and IGFBP-3 levels increased with all doses, but no incremental increases were found. Leg protein balance improved with rhIGF-1/IGFBP-3, which was associated with an increase in muscle protein fractional synthetic rate. These effects were independent of time. All patients were euglycemic without electrolyte imbalances.

CONCLUSION

Net protein synthesis in the isolated leg of severely burned adults improved with rhIGF-1/IGFBP-3 without development of glucose abnormalities.

Current status of anabolic hormone administration in human burn injury

Survival after massive burns has increased due to advances in critical care and wound closure techniques. Because of the ravages of hypermetabolism that is so prevalent in these patients, survivors are left with significant lean body mass losses that correspond to decreased strength with which to begin the rehabilitation phase. Efforts to decrease lean body mass catabolism by environmental regulation, early wound closure, and sufficient caloric provision modify the hypermetabolic response to an extent; however, further manipulations are required to optimize recovery fully. Pharmacologic intervention with hormone agonists and antagonists holds this promise. This article reviews some of the current investigations in this area and points out the future work that needs to be done to elucidate the field of anabolic hormones after severe injury.

Nutrition in the intensive care unit

Nutritional support has become a routine part of the care of the critically ill patient. It is an adjunctive therapy, the main goal of which is to attenuate the development of malnutrition, yet the effectiveness of nutritional support is often thwarted by an underlying hostile metabolic milieu. This requires that these metabolic changes be taken into consideration when designing nutritional regimens for such patients. There is also a need to conduct large, multi-center studies to acquire more knowledge of the cost-benefit and cost effectiveness of nutritional support in the critically ill.