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

Burns: an update on current pharmacotherapy

INTRODUCTION

The worldwide occurrence of burn injuries remains high despite efforts to reduce injury incidence through public awareness campaigns and improvements in living conditions. In 2004, almost 11 million people experienced burns severe enough to warrant medical treatment. Advances over the past several decades in aggressive resuscitation, nutrition, excision and grafting have reduced morbidity and mortality. Incorporation of pharmacotherapeutics into treatment regimens may further reduce complications of severe burn injuries.

AREAS COVERED

Severe burn injuries, as well as other forms of stress and trauma, trigger a hypermetabolic response that, if left untreated, impedes recovery. In the past two decades, use of anabolic agents, β-adrenergic receptor antagonists and anti-hyperglycemic agents has successfully counteracted post-burn morbidities including catabolism, the catecholamine-mediated response and insulin resistance. Here, the authors review the most up-to-date information on currently used pharmacotherapies in the treatment of these sequelae of severe burns and the insights that have expanded the understanding of the pathophysiology of severe burns.

EXPERT OPINION

Existing drugs offer promising advances in the care of burn injuries. Continued gains in the understanding of the molecular mechanisms driving the hypermetabolic response will enable the application of additional existing drugs to be broadened to further attenuate the hypermetabolic response.

17β-Estradiol reappropriates mass lost to the hypermetabolic state in thermally injured rats

BACKGROUND

The hypermetabolic response to severe thermal injury is unlike any physiologic response seen in medicine. While some parallels can be drawn to shock and sepsis states, this response is typified by its intensity and duration. Our group has been interested in the myriad effects of estrogens after injury, specifically the ability of estrogens to reduce inflammatory responses. Given this, and the known link between severe inflammation and the hypermetabolic response, we examined the effects of a single dose of 17β estradiol administered after a severe thermal injury in rats.

METHODS

Twelve male Sprague-Dawley rats were subject to either a sham burn or a 40% total body surface area burn, followed by fluid resuscitation. Burned animals were divided into a vehicle and treatment group, with injections given 15 min after the injury. Animals were monitored for a period of 45 d, with markers of hypermetabolism (weight, fecal output, food intake, and serum insulin and glucose) measured daily.

RESULTS

We identified a significant difference in daily measured weights between the burned groups. We observed a sparing of body mass during the acute phase lasting 2 wk after the injury and an improved recovery phase during the remainder of the study. Glucose and insulin levels during the first week of the study did not differ between the treatment groups.

CONCLUSION

Estrogen may have a role in preserving body mass after severe thermal injury. Further studies are required to determine if this spared body mass composition.

Multifaceted role of insulin-like growth factors and mammalian target of rapamycin in skeletal muscle

This review describes the current literature on the interaction between insulin-like growth factors, endocrine hormones, and branched-chain amino acids on muscle physiology in healthy young individuals and during select pathologic conditions. Emphasis is placed on the mechanism by which physical and hormonal signals are transduced at the cellular level to either grow or atrophy skeletal muscle. The key role of the mammalian target of rapamycin and its ability to respond to hypertrophic and atrophic signals informs our understanding how a combination of physical, nutritional, and pharmacologic therapies may be used in tandem to prevent or ameliorate reductions in muscle mass.

Role of Growth Hormone Deficiency and Treatment in Chronic Kidney Disease

Malnutrition and inflammation are strong predictors of mortality in advanced kidney disease, especially in patients on renal replacement therapy. The complex relationship between kidney disease, uremia, and malnutrition significantly contributes to the increased morbidity and mortality in this patient population potentially through a relative deficiency in growth hormone (GH). With an approximate 26 million Americans currently affected by some stage of chronic kidney disease and a predicted 750,000 people to be on dialysis by 2020, there is a need to develop innovative strategies aimed at reducing the high mortality seen in dialysis patients. We will review evidence on one such intervention with infusion of recombinant GH to improve the nutritional and inflammatory state, thereby expecting to improve the mortality and morbidity in this patient population.

Long-term persistance of the pathophysiologic response to severe burn injury

Background

Main contributors to adverse outcomes in severely burned pediatric patients are profound and complex metabolic changes in response to the initial injury. It is currently unknown how long these conditions persist beyond the acute phase post-injury. The aim of the present study was to examine the persistence of abnormalities of various clinical parameters commonly utilized to assess the degree hypermetabolic and inflammatory alterations in severely burned children for up to three years post-burn to identify patient specific therapeutic needs and interventions.

Methodology/Principal Findings

Patients: Nine-hundred seventy-seven severely burned pediatric patients with burns over 30% of the total body surface admitted to our institution between 1998 and 2008 were enrolled in this study and compared to a cohort non-burned, non-injured children. Demographics and clinical outcomes, hypermetabolism, body composition, organ function, inflammatory and acute phase responses were determined at admission and subsequent regular intervals for up to 36 months post-burn. Statistical analysis was performed using One-way ANOVA, Student's t-test with Bonferroni correction where appropriate with significance accepted at p<0.05. Resting energy expenditure, body composition, metabolic markers, cardiac and organ function clearly demonstrated that burn caused profound alterations for up to three years post-burn demonstrating marked and prolonged hypermetabolism, p<0.05. Along with increased hypermetabolism, significant elevation of cortisol, catecholamines, cytokines, and acute phase proteins indicate that burn patients are in a hyperinflammatory state for up to three years post-burn p<0.05.

Conclusions

Severe burn injury leads to a much more profound and prolonged hypermetabolic and hyperinflammatory response than previously shown. Given the tremendous adverse events associated with the hypermetabolic and hyperinflamamtory responses, we now identified treatment needs for severely burned patients for a much more prolonged time.

What, how, and how much should patients with burns be fed?

The hypermetabolic response to severe burn injury is characterized by hyperdynamic circulation and profound metabolic, physiologic, catabolic, and immune system derangements. Failure to satisfy overwhelming energy and protein requirements after, and during, severe burn injury results in multiorgan dysfunction, increased susceptibility to infection, and death. Attenuation of the hypermetabolic response by various pharmacologic modalities is emerging as an essential component of the management of patients with severe burn injury. This review focuses on the more recent advances in therapeutic strategies to attenuate the hypermetabolic response and its postburn-associated insulin resistance.

Activation of the dopamine 1 and dopamine 5 receptors increase skeletal muscle mass and force production under non-atrophying and atrophying conditions

BACKGROUND

Control of skeletal muscle mass and force production is a complex physiological process involving numerous regulatory systems. Agents that increase skeletal muscle cAMP levels have been shown to modulate skeletal muscle mass and force production. The dopamine 1 receptor and its closely related homolog, the dopamine 5 receptor, are G-protein coupled receptors that are expressed in skeletal muscle and increase cAMP levels when activated. Thus we hypothesize that activation of the dopamine 1 and/or 5 receptor will increase skeletal muscle cAMP levels thereby modulating skeletal muscle mass and force production.

METHODS

We treated isolated mouse tibialis anterior (TA) and medial gastrocnemius (MG) muscles in tissue bath with the selective dopamine 1 receptor and dopamine 5 receptor agonist SKF 81297 to determine if activation of skeletal muscle dopamine 1 and dopamine 5 receptors will increase cAMP. We dosed wild-type mice, dopamine 1 receptor knockout mice and dopamine 5 receptor knockout mice undergoing casting-induced disuse atrophy with SKF 81297 to determine if activation of the dopamine 1 and dopamine 5 receptors results in hypertrophy of non-atrophying skeletal muscle and preservation of atrophying skeletal muscle mass and force production.

RESULTS

In tissue bath, isolated mouse TA and MG muscles responded to SKF 81297 treatment with increased cAMP levels. Treating wild-type mice with SKF 81297 reduced casting-induced TA and MG muscle mass loss in addition to increasing the mass of non-atrophying TA and MG muscles. In dopamine 1 receptor knockout mice, extensor digitorum longus (EDL) and soleus muscle mass and force was not preserved during casting with SKF 81297 treatment, in contrast to significant preservation of casted wild-type mouse EDL and soleus mass and EDL force with SKF 81297 treatment. Dosing dopamine 5 receptor knockout mice with SKF 81297 did not significantly preserve EDL and soleus muscle mass and force although wild-type mouse EDL mass and force was significantly preserved SKF 81297 treatment.

CONCLUSIONS

These data demonstrate for the first time that treatment with a dopamine 1/5 receptor agonist results in (1) significant preservation of EDL, TA, MG and soleus muscle mass and EDL muscle force production during periods of atrophy and (2) hypertrophy of TA and MG muscle. These effects appear to be mainly mediated by both the dopamine 1 and dopamine 5 receptors.

Mycobacterium ulcerans infections cause progressive muscle atrophy and dysfunction, and mycolactone impairs satellite cell proliferation

Clinical observations from Buruli ulcer (BU) patients in West Africa suggest that severe Mycobacterium ulcerans infections can cause skeletal muscle contracture and atrophy leading to significant impairment in function. In the present study, male mice C57BL/6 were subcutaneously injected with M. ulcerans in proximity to the right biceps muscle, avoiding direct physical contact between the infectious agent and the skeletal muscle. The histological, morphological, and functional properties of the muscles were assessed at different times after the injection. On day 42 postinjection, the isometric tetanic force and the cross-sectional area of the myofibers were reduced by 31% and 29%, respectively, in the proximate-infected muscles relative to the control muscles. The necrotic areas of the proximate-infected muscles had spread to 7% of the total area by day 42 postinjection. However, the number of central nucleated fibers and myogenic regulatory factors (MyoD and myogenin) remained stable and low. Furthermore, Pax-7 expression did not increase significantly in mycolactone-injected muscles, indicating that the satellite cell proliferation is abrogated by the toxin. In addition, the fibrotic area increased progressively during the infection. Lastly, muscle-specific RING finger protein 1 (MuRF-1) and atrogin-1/muscle atrophy F-box protein (atrogin-1/MAFbx), two muscle-specific E3 ubiquitin ligases, were upregulated in the presence of M. ulcerans. These findings confirmed that skeletal muscle is affected in our model of subcutaneous infection with M. ulcerans and that a better understanding of muscle contractures and weakness is essential to develop a therapy to minimize loss of function and promote the autonomy of BU patients.

Can we protect the gut in critical illness? The role of growth factors and other novel approaches

The intestine plays a central role in the pathophysiology of critical illness and is frequently called the "motor" of the systemic inflammatory response. Perturbations to the intestinal barrier can lead to distant organ damage and multiple organ failure. Therefore, identifying ways to preserve intestinal integrity may be of paramount importance. Growth factors and other peptides have emerged as potential tools for modulation of intestinal inflammation and repair due to their roles in cellular proliferation, differentiation, migration, and survival. This review examines the involvement of growth factors and other peptides in intestinal epithelial repair during critical illness and their potential use as therapeutic targets.

Systemic IGF-I administration attenuates the inhibitory effect of chronic arthritis on gastrocnemius mass and decreases atrogin-1 and IGFBP-3

Adjuvant arthritis is an animal model of rheumatoid arthritis that decreases liver and circulating IGF-I as well as skeletal muscle mass. The aim of this work was to elucidate whether IGF-I administration was able to prevent the effect of arthritis on body weight and on two skeletal muscles, gastrocnemius and soleus. On day 4 after adjuvant injection, control and arthritic rats were treated with IGF-I (100 microg/kg s.c.) two times a day, until day 15 when all rats were killed. Arthritis decreased body weight gain and gastrocnemius weight. In arthritic rats, IGF-I treatment increased body weight gain and gastrocnemius weight, without modifying food intake or the external signs of arthritis. Arthritis increased atrogin-1 and muscle ring finger 1 (MuRF1) gene expression in the gastrocnemius and to a lesser extent in the soleus muscle. IGF-I attenuated the arthritis-induced increase in atrogin-1 and MuRF1 expression in the gastrocnemius, whereas it did not modify the expression of these genes in the soleus muscle. Arthritis also increased IGF-binding protein (IGBP)-3 and IGFBP-5 gene expression in gastrocnemius and soleus, whereas IGF-I administration decreased IGFBP-3, but not IGFBP-5, gene expression in both muscles. In both groups of arthritic rats and in control rats treated with IGF-I, proliferating cell nuclear antigen and myogenic differentiation proteins were increased in the gastrocnemius. These data suggest that the inhibitory effect of chronic arthritis on skeletal muscle is higher in fast glycolytic than in slow oxidative muscle and that IGF-I administration attenuates this effect and decreases atrogin-1 and IGFBP-3 gene expression.

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.

A pharmacokinetic and dosing study of intravenous insulin-like growth factor-I and IGF-binding protein-3 complex to preterm infants

In preterm infants, low levels of insulin like growth factor 1 (IGF-I) have been associated with impaired growth and retinopathy of prematurity. Our objective was to study safety and pharmacokinetics of i.v. administered rhIGF-I with its binding protein 3 (rhIGFBP-3) to preterm infants. At 3 d chronological age, an i.v. 3 h infusion of rhIGF-I/rhIGFBP-3 was administered followed by serial measurements of IGF-I and IGFBP-3. Infants were evaluated for physiologic safety measurements. The individual dose of rhIGF-I ranged from 1 to 12 microg/kg. The study was conducted at Queen Silvia Children's Hospital, Gothenburg, Sweden, between January and November 2007. Five patients (3 F) with mean (range) post menstrual age 27 wk (26-29) and birth weight 1022 g (810-1310) participated. IGF-I and IGFBP-3 levels before infusion were median (range) 18 (12-28) and 771 (651-1047) ng/mL, respectively. Immediately after study drug infusion, serum IGF-I and IGFBP-3 levels were 38 (25-59) and 838 (754-1182) ng/mL, respectively. Median (range) half-life for IGF-I and IGFBP-3 was 0.79 (0.59-1.42) and 0.87 (0.85-0.94) hours, respectively. Blood glucose, insulin, sodium, potassium, and physiologic safety measures were within normal ranges. The rhIGF-I/rhIGFBP-3 equimolar proportion was effective in increasing serum IGF-I levels and administration under these study conditions was safe and well tolerated.

The hepatic response to thermal injury: is the liver important for postburn outcomes?

Thermal injury produces a profound hypermetabolic and hypercatabolic stress response characterized by increased endogenous glucose production via gluconeogenesis and glycogenolysis, lipolysis, and proteolysis. The liver is the central body organ involved in these metabolic responses. It is suggested that the liver, with its metabolic, inflammatory, immune, and acute phase functions, plays a pivotal role in patient survival and recovery by modulating multiple pathways following thermal injury. Studies have evaluated the role and function of the liver during the postburn response and showed that liver integrity and function are essential for survival, and that hepatic acute phase proteins are strong predictors for postburn survival. This review discusses these studies and delineates the pivotal role of the liver in patients following severe thermal injury.

Ghrelin inhibits skeletal muscle protein breakdown in rats with thermal injury through normalizing elevated expression of E3 ubiquitin ligases MuRF1 and MAFbx

We previously determined that ghrelin synthesis was downregulated after burn injury and that exogenous ghrelin retained its ability both to stimulate food intake and to restore plasma growth hormone levels in burned rats. These observations and the finding that anabolic hormones can attenuate skeletal muscle catabolism led us to investigate whether ghrelin could attenuate burn-induced skeletal muscle protein breakdown in rats. These studies were performed in young rats (50-60 g) 24 h after approximately 30% total body surface area burn injury. Burn injury increased total and myofibrillar protein breakdown in extensor digitorum longus (EDL) muscles assessed by in vitro tyrosine and 3-methyl-histidine release, respectively. Continuous 24-h administration of ghrelin (0.2 mg.kg(-1).h(-1)) significantly inhibited both total and myofibrillar protein breakdown in burned rats. Ghrelin significantly attenuated burn-induced changes in mRNA expression of IGFBP-1 and IGFBP-3 in liver. In EDL, ghrelin attenuated the increases in mRNA expression of the binding proteins, but had no significant effect on reduced expression of IGF-I. Ghrelin markedly reduced the elevated mRNA expression of TNF-alpha and IL-6 in EDL muscle that occurred after burn. Moreover, ghrelin normalized plasma glucocorticoid levels, which were elevated after burn. Expression of the muscle-specific ubiquitin-ligating enzyme (E3) ubiquitin ligases MuRF1 and MAFbx were markedly elevated in both EDL and gastrocnemius and were normalized by ghrelin. These results suggest that ghrelin is a powerful anticatabolic compound that reduces skeletal muscle protein breakdown through attenuating multiple burn-induced abnormalities.

Curcumin and muscle wasting: a new role for an old drug?

Sepsis, severe injury, and cancer are associated with loss of muscle mass. Muscle wasting in these conditions is mainly caused by increased proteolysis, at least in part regulated by nuclear factor-kappaB. Despite recent progress in the understanding of mediators and mechanisms involved in muscle wasting, effective and universally accepted treatments by which muscle atrophy can be prevented or reversed are still lacking. We review recent evidence suggesting that curcumin (diferuloylmethane), a component of the spice turmeric, may prevent loss of muscle mass during sepsis and endotoxemia and may stimulate muscle regeneration after traumatic injury. Curcumin has been part of the traditional Asian medicine for centuries, mainly because of its anti-inflammatory properties. Studies suggest that inhibition of nuclear factor-kappaB is one of the mechanisms by which curcumin exerts its ant-inflammatory effects. Curcumin is easily accessible, inexpensive, and non-toxic even at high doses, and may therefore offer an important treatment modality in muscle wasting and injury. It should be noted, however, that the muscle-sparing effects of curcumin are not universally accepted, and more studies are therefore needed to further test the role of curcumin in the prevention and treatment of muscle wasting.

Insulin resistance postburn: underlying mechanisms and current therapeutic strategies

The profound hypermetabolic response to burn injury is associated with insulin resistance and hyperglycemia, significantly contributing to the incidence of morbidity and mortality in this patient population. These responses are present in all trauma, surgical, or critically ill patients, but the severity, length, and magnitude is unique for burn patients. Although advances in therapeutic strategies to attenuate the postburn hypermetabolic response have significantly improved the clinical outcome of these patients during the past years, therapeutic approaches to overcome stress-induced hyperglycemia have remained challenging. Intensive insulin therapy has been shown to significantly reduce morbidity and mortality in critically ill patients. High incidence of hypoglycemic events and difficult blood glucose titrations have led to investigation of alternative strategies, including the use of metformin, a biguanide, or fenofibrate, a peroxisome proliferator-activated receptor (PPAR)-gamma agonist. Nevertheless, weaknesses and potential side affects of these drugs reinforces the need for better understanding of the molecular mechanisms underlying insulin resistance postburn that may lead to novel therapeutic strategies further improving the prognosis of these patients. This review aims to discuss the mechanisms underlying insulin resistance induced hyperglycemia postburn and outlines current therapeutic strategies that are being used to modulate hyperglycemia after thermal trauma.

[Hyperglycemia in the critically ill: meaning and treatment]

Hyperglycemia is commun in critically ill patients without previously known diabetes. Hyperglycemia occurring in these patients is mainly a consequence of stress associated to complex glucose metabolism abnormalities which have deleterious effects on tissues and vascular function. Several epidemiologic and intervention studies had established that hyperglycemia is related to morbidity and mortality. Maintenance of normoglycemia with intensive insulin therapy seems to decrease morbidity and mortalities in severe acute illnesses. However the benefit of most of these intervention trials remain controversial mainly in stroke, myocardial infarction and severe sepsis. Moreover strict normoglycemia required to obtain an optimal benefit increases the risk of hypoglycaemia which may be particularly harmful in patients in critical state.

Nutritional and Pharmacological Modulation of the Metabolic Response of Severely Burned Patients: Review of the Literature (Part II)*

Severe burn patients are some of the most challenging critically ill patients, with an extreme state of physiological stress and an overwhelming systemic metabolic response. Increased energy expenditure to cope with this insult necessitates mobilization of large amounts of substrate from fat stores and active muscle for repair and fuel, leading to catabolism. The hypermetabolic response can last for as long as nine months to one year after injury and is associated with impaired wound healing, increased infection risks, erosion of lean body mass, hampered rehabilitation, and delayed reintegration of burn survivors into society. Reversal of the hypermetabolic response by manipulating the patient's physiological and biochemical environment through the administration of specific nutrients, growth factors, or other agents, often in pharmacological doses, is emerging as an essential component of the state of the art in severe burn management. Early enteral nutritional support, control of hyperglycaemia, blockade of catecholamine response, and use of anabolic steroids have all been proposed to attenuate hypermetabolism or to blunt catabolism associated with severe burn injury. The present study is a literature review of the proposed nutritional and metabolic therapeutic measures in order to determine evidence-based best practice. Unfortunately, the present state of our knowledge does not allow the formulation of clear-cut guidelines. Only general trends can be outlined which will certainly have some practical applications but above all will dictate future research in the field.

Pathophysiologic response to severe burn injury

OBJECTIVE

To improve clinical outcome and to determine new treatment options, we studied the pathophysiologic response postburn in a large prospective, single center, clinical trial.

SUMMARY BACKGROUND DATA

A severe burn injury leads to marked hypermetabolism and catabolism, which are associated with morbidity and mortality. The underlying pathophysiology and the correlations between humoral changes and organ function have not been well delineated.

METHODS

Two hundred forty-two severely burned pediatric patients [>30% total body surface area (TBSA)], who received no anabolic drugs, were enrolled in this study. Demographics, clinical data, serum hormones, serum cytokine expression profile, organ function, hypermetabolism, muscle protein synthesis, incidence of wound infection sepsis, and body composition were obtained throughout acute hospital course.

RESULTS

Average age was 8 +/- 0.2 years, and average burn size was 56 +/- 1% TBSA with 43 +/- 1% third-degree TBSA. All patients were markedly hypermetabolic throughout acute hospital stay and had significant muscle protein loss as demonstrated by a negative muscle protein net balance (-0.05% +/- 0.007 nmol/100 mL leg/min) and loss of lean body mass (LBM) (-4.1% +/- 1.9%); P < 0.05. Patients lost 3% +/- 1% of their bone mineral content (BMC) and 2 +/- 1% of their bone mineral density (BMD). Serum proteome analysis demonstrated profound alterations immediately postburn, which remained abnormal throughout acute hospital stay; P < 0.05. Cardiac function was compromised immediately after burn and remained abnormal up to discharge; P < 0.05. Insulin resistance appeared during the first week postburn and persisted until discharge. Patients were hyperinflammatory with marked changes in IL-8, MCP-1, and IL-6, which were associated with 2.5 +/- 0.2 infections and 17% sepsis.

CONCLUSIONS

In this large prospective clinical trial, we delineated the complexity of the postburn pathophysiologic response and conclude that the postburn response is profound, occurring in a timely manner, with derangements that are greater and more protracted than previously thought.

Mecasermin rinfabate: rhIGF-I/rhIGFBP-3 complex: iPLEX

BACKGROUND

Mecasermin rinfabate (iPLEX), comprising rhIGF-I complexed to rhIGFBP-3, was developed in an attempt to prolong the half-life of IGF-I and potentially reduce side effects. It is administered as a once-daily subcutaneous injection. Treatment with rhIGF-I has been explored in a number of growth and endocrine disorders.

OBJECTIVE

To review the published literature regarding the pharmacokinetics, safety profile and clinical efficacy of Mecasermin rinfabate.

METHODS

A comprehensive search via the NCBI PubMed portal was performed using the search terms rhIGF-I/rhIGFBP-3 complex, iPLEX and Somatokine.

RESULTS

The effects of Mecasermin rinfabate have been explored in a number of clinical situations including diabetes, severe insulin resistance, osteopaenia, burns and growth hormone insensitivity syndrome, with outcomes similar to those of rhIGF-I alone.

CONCLUSIONS

The biological effects of Mecasermin rinfabate are largely similar to those previously reported with rhIGF-I. There are little published data pertaining to pharmacokinetic properties in human subjects, and the side effect profile appears similar to that of rhIGF-I alone.

Regulation of muscle mass by growth hormone and IGF-I

Growth hormone (GH) is widely used as a performance-enhancing drug. One of its best-characterized effects is increasing levels of circulating insulin-like growth factor I (IGF-I), which is primarily of hepatic origin. It also induces synthesis of IGF-I in most non-hepatic tissues. The effects of GH in promoting postnatal body growth are IGF-I dependent, but IGF-I-independent functions are beginning to be elucidated. Although benefits of GH administration have been reported for those who suffer from GH deficiency, there is currently very little evidence to support an anabolic role for supraphysiological levels of systemic GH or IGF-I in skeletal muscle of healthy individuals. There may be other performance-enhancing effects of GH. In contrast, the hypertrophic effects of muscle-specific IGF-I infusion are well documented in animal models and muscle cell culture systems. Studies examining the molecular responses to hypertrophic stimuli in animals and humans frequently cite upregulation of IGF-I messenger RNA or immunoreactivity. The circulatory/systemic (endocrine) and local (autocrine/paracrine) effects of GH and IGF-I may have distinct effects on muscle mass regulation.

Gender differences in pediatric burn patients: does it make a difference?

OBJECTIVE

There is evidence that females have a better outcome in intensive care units (ICUs) when compared with males. The aim of the present study was to compare hospital course and physiologic markers between severely burned pediatric females and males.

SUMMARY BACKGROUND DATA

One-hundred eighty-nine children sustaining a >or=40% total body surface area burn were divided into females (n = 76) and males (n = 113).

METHODS

: Patient demographics, clinical parameters, and mortality were noted. Muscle protein synthesis was determined by stable isotope technique. Resting energy expenditure (REE) was measured by indirect calorimetry and body composition by dual x-ray absorptiometry. Serum hormones, proteins, and cytokines were determined. Cardiac function and liver size were determined by repeated ultrasound measurements.

RESULTS

There were no significant differences between females and males for mortality, demographics, burn size, nutritional intake, or concomitant injuries. ICU stay was in females: 29+/-3 days whereas the stay in males was 38+/-3 days, P < 0.05. Females had a significant attenuated loss in muscle protein net balance (females: -0.028+/-0.001% vs. males: -0.05+/-0.007%) and an increase in lean body mass (Delta females: 5+/-4% vs. Delta males: -1+/-3%), P < 0.05. Percent-predicted REE was significantly decreased in females compared with males, P < 0.05. Systemic inflammatory markers and stress hormone levels were significantly decreased in females, P < 0.05. Cardiac and liver dysfunction were significantly attenuated in females compared with males, P < 0.05.

CONCLUSIONS

Female burned patients exert an attenuated inflammatory and hypermetabolic response compared with males. This decrease is reflected in improved muscle protein net balance and preservation of lean body mass, which are associated with shortened hospital stay.

Urinary cortisol and catecholamine excretion after burn injury in children

INTRODUCTION

A severe burn causes increased levels of urine cortisol and catecholamines. However, little is known about the magnitude of this increase or how and when the levels return to normal. The purpose of this study was to determine in a large clinical prospective trial the acute and long-term pattern of urine cortisol and catecholamine expression in severely burned children.

METHODS

Pediatric patients with burns greater than 40% total body surface area (TBSA), admitted to our unit over a 6-yr period, were included into the study. Clinical data including length of stay, number of operations, and duration and number of infections were determined. Patients had regular 24-h urine collections during their acute admission and reconstructive periods. Urine collections were analyzed for cortisol, epinephrine, and norepinephrine. Each urine cortisol was compared with age-adjusted reference ranges. Ninety-five percent confidence intervals and ANOVA analysis were used where appropriate.

RESULTS

Two hundred twelve patients were included in the study (75 females and 137 males), with a mean +/- sem TBSA of 58 +/- 1% (third-degree 45 +/- 2%) and mean age of 9 +/- 0.4 yr. Urinary cortisol levels were significantly increased (3- to 5-fold) up to 100 d after the burn and then approached normal levels (P < 0.05). The rise in urine cortisol was significantly higher in male than female patients (P < 0.05). Early hypercortisolemia was associated with increased duration of severe infection (P < 0.05). Persistent hypercortisolemia was associated with increases in both infection rates and duration of severe infection (P < 0.05). Urinary catecholamines showed a significant increase at 11-20 d after the burn (P < 0.05). Urinary norepinephrine levels were significantly increased up to 20 d and then returned to normal (P < 0.05).

CONCLUSIONS

Urinary levels of cortisol, epinephrine, and norepinephrine are significantly increased after a major burn. Early hypercortisolemia is associated with increased duration of severe infection. Persistent hypercortisolemia is associated with increases in both infection rates and duration of severe infection.

Burn size determines the inflammatory and hypermetabolic response

Background

Increased burn size leads to increased mortality of burned patients. Whether mortality is due to inflammation, hypermetabolism or other pathophysiologic contributing factors is not entirely determined. The purpose of the present study was to determine in a large prospective clinical trial whether different burn sizes are associated with differences in inflammation, body composition, protein synthesis, or organ function.

Methods

Pediatric burned patients were divided into four burn size groups: <40% total body surface area (TBSA) burn, 40–59% TBSA burn, 60–79% TBSA burn, and >80% TBSA burn. Demographic and clinical data, hypermetabolism, the inflammatory response, body composition, the muscle protein net balance, serum and urine hormones and proteins, and cardiac function and changes in liver size were determined.

Results

One hundred and eighty-nine pediatric patients of similar age and gender distribution were included in the study (<40% TBSA burn, n = 43; 40–59% TBSA burn, n = 79; 60–79% TBSA burn, n = 46; >80% TBSA burn, n = 21). Patients with larger burns had more operations, a greater incidence of infections and sepsis, and higher mortality rates compared with the other groups (P < 0.05). The percentage predicted resting energy expenditure was highest in the >80% TBSA group, followed by the 60–79% TBSA burn group (P < 0.05). Children with >80% burns lost the most body weight, lean body mass, muscle protein and bone mineral content (P < 0.05). The urine cortisol concentration was highest in the 80–99% and 60–79% TBSA burn groups, associated with significant myocardial depression and increased change in liver size (P < 0.05). The cytokine profile showed distinct differences in expression of IL-8, TNF, IL-6, IL-12p70, monocyte chemoattractant protein-1 and granulocyte–macrophage colony-stimulating factor (P < 0.05).

Conclusion

Morbidity and mortality in burned patients is burn size dependent, starts at a 60% TBSA burn and is due to an increased hypermetabolic and inflammatory reaction, along with impaired cardiac function.

Efficacy and safety of mecasermin rinfabate

There has been interest in using recombinant human (rh) insulin-like growth factor (IGF)-I (rhIGF-I) to treat short stature, either alone or in combination with its binding protein (insulin-like growth factor binding protein [IGFBP]-3). IGF-I has been shown to increase growth velocity in children with IGF deficiency, either as a result of growth hormone insensitivity syndrome (GHIS) or IGF gene deletion. However, there have been adverse events, particularly hypoglycaemia, reported with administration of unbound rhIGF-I. In addition, the serum half-life of unbound rhIGF-I is shorter when administered to patients with GHIS, who have low serum concentrations of its binding proteins IGFBP-3 and acid-labile subunit (ALS), than when administered to normal volunteers or to the patient with an IGF-I gene deletion (who had normal levels of IGFBP-3). iPlex (mecasermin rinfabate), an equimolar mixture of IGF-I and its binding protein IGFBP-3, was developed to prolong the half-life and to counteract acute adverse events (particularly hypoglycaemia) associated with administration of IGF-I. Although there are no published data on the efficacy of mecasermin rinfabate in treating growth disorders, it does appear that mecasermin rinfabate has a longer half-life in patients with GHIS than unbound IGF-I, and fewer reports of adverse events (including hypoglycaemia) when administered to patients with diabetes.

Restoration of hormonal action and muscle protein

This review focuses on the effects of restoring hormonal levels and/or influence on muscle protein metabolism in the stressed state. We have highlighted our clinical experience in the administration of anabolic and anticatabolic agents in stressed clinical populations, primarily adult and pediatric burn injury, as well as patients undergoing elective hip arthroplasty. Our previous experience entails the administration of anabolic hormones, such as testosterone and its derivatives, growth hormone, insulin-like growth factor-1 combined with its binding protein 3, and insulin. Current efforts focus on the administration of anticatabolic agents to reduce the effects of hypercortisolemia. Muscle protein metabolism was determined by stable isotope methodology. Our results indicate that normalization of anabolic hormone concentrations or amelioration of hormonal resistance restores the effects of feeding on skeletal muscle protein metabolism. Anabolic hormone administration results in a more favorable muscle protein balance in severely burned patients. Amelioration of hypercortisolemia in the stressed state leads to an improvement in protein kinetics. To summarize, alterations in hormonal influence that accompany stress states favor the loss of muscle protein. Restoration or normalization of hormonal influence improves muscle protein kinetics and ameliorates the loss of muscle nitrogen. To restore hormonal influence, clinicians should consider reestablishing anabolic stimuli and reducing catabolic stimuli.

GSK-3beta activity is increased in skeletal muscle after burn injury in rats

Previous reports suggest that burn-induced muscle proteolysis can be inhibited by treatment with GSK-3beta inhibitors, suggesting that burn injury may be associated with increased GSK-3beta activity. The influence of burn injury on muscle GSK-3beta activity, however, is not known. We determined the effect of a 30% total body surface full-thickness burn injury in rats on muscle GSK-3beta activity by measuring GSK-3beta activity and tissue levels of serine 9 phosphorylated GSK-3beta, p(Ser9)-GSK-3beta, by Western blot analysis and immunohistochemistry. Because burn-induced muscle wasting is, at least in part, mediated by glucocorticoids, we used dexamethasone-treated cultured muscle cells in which GSK-3beta expression was reduced with small interfering RNA (siRNA) to further assess the role of GSK-3beta in muscle atrophy. Burn injury resulted in a seven-fold increase in GSK-3beta activity in skeletal muscle. This effect of burn was accompanied by reduced tissue levels of p(Ser9)-GSK-3beta, suggesting that burn injury stimulates GSK-3beta in skeletal muscle secondary to inhibited phosphorylation of the enzyme. In addition, burn injury resulted in inhibited phosphorylation and activation of Akt, an upstream regulatory mechanism of GSK-3beta activity. Reducing the expression of GSK-3beta in cultured muscle cells with siRNA inhibited dexamethasone-induced protein degradation by approximately 50%. The results suggest that burn injury stimulates GSK-3beta activity in skeletal muscle and that GSK-3beta may, at least in part, regulate glucocorticoid-mediated muscle wasting.

Metabolic response to injury and role of anabolic hormones

PURPOSE OF REVIEW

To provide a short review of the literature describing the hypermetabolic response to injury and potential treatments. Associated findings include changes in inflammatory mediators and secreted hormones.

RECENT FINDINGS

Treatments should be aimed at decreasing the response and potentially the use of anabolic agents. Of note, recent interest in the hyperglycemic response to injury and insulin treatment will be highlighted.

SUMMARY

The current metabolic care of the burned patient including nutrition is now being unfolded. It is relatively clear that anabolic treatment should be considered in all those with severe injury. Timing of the treatment, however, is still a topic of discussion.

The use of anabolic agents in catabolic states

OBJECTIVE

We plan to review the current problem of lean mass erosion in catabolic states, caused by injury and critical illness. This protein loss is driven by the hormonal imbalance and excess inflammation referred to as the "stress response to injury." We then plan to provide the current concepts on the use of available anabolic agents to attenuate the excess catabolism.

DATA SOURCE

The available published literature on the pathogenesis of acute catabolic states and the use of anabolic and anticatabolic agents, their indications, mechanism of action, and potential complications was reviewed.

DATA EXTRACTION

The current understanding and experience of the available anabolic and anticatabolic agents as well as the rationale for the use of each anabolic agent are described.

CONCLUSION

We conclude that the preservation of lean body mass (body protein) is extremely important in the management of critical care populations, as lean mass loss leads to severe morbidity and increased mortality. Essentially, all of the available anabolic agents stimulate protein synthesis and decrease protein breakdown, but all have different mechanisms of action. Adequate nutrition, especially protein intake, is essential for any anabolism to occur. Combined anabolic therapy also appears to be advantageous. Although controlling the inflammatory response would also be of major benefit in further controlling protein loss, effective and safe anti-inflammatory agents have not yet become clinically available for this purpose.

Predictive value of circulating insulin-like growth factor I levels in ischemic stroke outcome

CONTEXT

Cerebrovascular disease is highly prevalent in the general population, frequently leading to permanent invalidity and reduced quality of life. IGF-I is recognized as an important neuroprotective factor against cerebral hypoxic insult.

OBJECTIVE

The objective of the study was to evaluate pituitary function, in particular GH-IGF-I axis, in adult patients receiving rehabilitation after an ischemic stroke.

SUBJECTS AND METHODS

We studied 42 patients (12 females; age range, 50-88 yr) during rehabilitation after stroke, evaluating the relationship between the GH-IGF-I axis and the severity (National Institutes of Health stroke scale) and outcome [Rancho Los Amigos Scale of Cognitive Functioning (LCFS); Functional Independence Measure (FIM); modified Ranking Scale] from stroke.

RESULTS

GH deficiency was demonstrated in five patients (11.9%). Peak GH after GHRH + arginine test and IGF-I levels did not correlate with severity of stroke. IGF-I was positively correlated with LCFS (r = 0.305, P < 0.05) and the difference between FIM on admission and at discharge from rehabilitation (DeltaFIM; r = 0.361, P < 0.02). Outcome indexes (LCFS, FIM at discharge, DeltaFIM) and occurrence of favorable outcome (modified Ranking Scale 0-1) were significantly (P < 0.05) higher in patients with IGF-I levels 161.8 mug/dl or greater (50th percentile of the patient distribution). LH-FSH deficiency (three cases), ACTH deficiency (one case), and hyperprolactinemia (two cases) were detected. One patient had primary hypogonadism, and six males had low testosterone with normal LH and FSH levels. By multivariate analysis, IGF-I level was the main significant predictor of DeltaFIM and LCFS.

CONCLUSIONS

Ischemic stroke may be associated with pituitary dysfunction, particularly GH and gonadotropin deficiencies. The higher IGF-I levels observed in patients with better outcome suggest a possible neuroprotective role of IGF-I. Circulating IGF-I may predict functional performance during rehabilitation and ischemic stroke outcome.

The influence of age and gender on resting energy expenditure in severely burned children

INTRODUCTION

Recent evidence suggests that female severely burned children have higher endogenous anabolic hormone levels and a shorter ICU stay compared with males. The purpose of this study was to analyze the influence of age and gender on resting energy expenditure (REE) in severely burned children from acute hospitalization through 12 months postburn.

METHODS

A total of 100 pediatric patients with > 40% total body surface area (TBSA) burn were enrolled in a prospective study and followed by indirect calorimetry measurements. The REE was expressed as actual REE kcal/d, percent of predicted REE, and REE/ body mass index (BMI). Statistical analysis was performed by Student t test and one-way ANOVA for repeated measures. Significance was accepted at P < 0.05.

RESULTS

The measured REE was significantly higher in males versus females at all time points (P < 0.05). The percent of predicted REE was significantly higher in males versus females during the acute hospitalization, at discharge, 6 and 9 months postburn (P < 0.05). The REE/BMI showed a significant difference between males and females at the acute and discharge time period (P < 0.05). In children 3 to 9.9 years of age, the measured REE and the percent of predicted REE were significantly higher in males versus females during the acute study, at discharge and 6 months postburn (P < 0.05). The measured REE at discharge, 9 and 12 months postburn for children >10 years of age was significantly higher in males compared with females (P < 0.05).

CONCLUSION

Data show that female children exert a decreased hypermetabolic response compared with male children, which may improve burn outcomes in females.

Effects of long-term continuous use of immune-enhancing enteral formula on nutritional and immunologic status in non-surgical patients

OBJECTIVE

Although the perioperative use of immune-enhancing enteral formula (IEEF) effectively reduces the rate of infectious complications, whether chronic use of IEEF is beneficial is unknown. A prospective randomized clinical trial was performed to examine the safety and effectiveness of long-term IEEF on nutritional and immunologic status in non-surgical patients receiving total enteral nutrition through the gastrostomy access route.

METHODS

A total of 30 patients were randomly assigned to two groups in which they received total enteral nutrition, an IEEF (n = 15) or a regular polymeric enteral formula (control group; n = 15) for 12 wk. Nutritional and immunologic variables were periodically examined.

RESULTS

Serum concentrations of insulin-like growth factor-I increased significantly for the IEEF group throughout the study. Although serum concentrations of dihomo-gamma-linoleic acid decreased significantly in the IEEF group, serum concentrations of eicosapentaenoic acid and docosahexaenoic acid increased significantly, as did concentrations of serum arginine and ornithine. The CD4/CD8 ratio and natural killer cell activity also increased for the IEEF group, but the differences were not significant. The B-cell fraction increased and the T-cell fraction of peripheral lymphocytes decreased for the IEEF group. Neither infectious nor non-infectious complications occurred during the study period in either group, except for a significant increase in serum urea nitrogen and uric acid concentrations for the IEEF group.

CONCLUSION

Long-term use of IEEF is safe in non-surgical patients and results in a significant increase in serum insulin-like growth factor-I concentrations in association with increased humoral immunity.

Resting energy expenditure in severely burned children: Analysis of agreement between indirect calorimetry and prediction equations using the Bland–Altman method

INTRODUCTION

Knowledge of a child's resting energy expenditure (REE) is essential in optimizing nutritional support for severely burned children. The provision of adequate nutritional support is vital in order to avoid the consequences of malnutrition or overfeeding. Nutritional requirements for severely burned children are often based on equations for estimates of REE. The accuracy of the predictive equations of REE has been questioned and many authors have advocated the measurement of REE. This study tests the hypothesis that estimates of REE vary significantly from measured REE (MREE) in a population of severely burned children, and are not accurate for determining nutritional requirements.

METHODS

In 91 severely burned children aged between 3 and 18 years, REE was measured by indirect calorimetry (MREE) at the height of the hypermetabolic response and compared with predicted equations (PREE) from the Food and Agriculture/World Health Organization/United Nations University (FAO/WHO/UNU), Schofield-HW and Harris-Benedict. Agreement between indirect calorimetry and predicted equations was assessed following the Bland-Altman method.

RESULTS

In the entire cohort group, predicted REE from all three equations were significantly lower compared to MREE (p<0.05). There was poor agreement between the MREE and predicted using all three equations. The Schofield-HW equation showed the lowest mean MREE-PREE difference: 635+/-526 kcal/day (limits of agreement -608 and 1878 kcal/day; 95% confidence interval for the bias 525-745 kcal/day). Additionally, all three equations under predicted REE and were not significantly different from one another (p=0.98).

CONCLUSIONS

Until more accurate predicted equations are developed, we recommend indirect calorimetry measurements for determining resting energy expenditure in severely burned children.

Post burn muscle wasting and the effects of treatments

Severe burns are typically followed by a hypermetabolic response that lasts for at least 9-12 months post-injury. The endocrine status is also markedly altered with an initial and then sustained increase in proinflammatory 'stress' hormones such as cortisol and other glucocorticoids, and catecholamines including epinephrine and norepinephrine by the adrenal medulla and cortex. These hormones exert catabolic effects leading to muscle wasting, the intensity of which depends upon the percentage of total body surface area (TBSA) involved, as well as the time elapsed since initial injury. Pharmacological and non-pharmacological strategies may be used to reverse the catabolic effect of thermal injury. Non-pharmacological strategies include early excision and wound closure of burn wound, aggressive treatment of sepsis, elevation of the environmental temperature to thermal neutrality (31.5+/-0.7 degrees C), high carbohydrate, high protein continuous enteral feeding and early institution of resistive exercise programs. Pharmacological modulators of the post-burn hypermetabolic response may be achieved through the administration of recombinant human growth hormone, low dose insulin infusion, use of the synthetic testosterone analogue, oxandrolone and beta blockade with propranolol. This paper aims to review the current understanding of post-burn muscle proteolysis and the effects of clinical and pharmacological strategies currently being studied to reverse it curb these debilitating sequelae of severe burns.

The pharmacologic modulation of the hypermetabolic response to burns

Patients with burns less than 40% TBSA do not have catabolism unless sepsis develops. Those with burns more than 40% TBSA always experience catabolism, which causes metabolic derangements that persist for at least 1 year after the injury in most body tissues. The accomplishments of the past decade have placed us in the midst of an exciting paradigm shift from what used to be a primary concern (ie, mortality) to areas that are more likely to enhance the quality of life of burn survivors. Modulating postburn hypermetabolism for the burned patient is of overwhelming importance in both the immediate care stage and the rehabilitative stage. Postburn hypermetabolism cannot be completely reversed but may be manipulated by nonpharmacologic and pharmacologic means. Early burn wound excision and complete wound closure, prevention of sepsis, the maintenance of thermal neutrality for the patient by elevation of the ambient temperature, and graded resistance exercises during convalescence are simple, highly effective primary treatment goals. Although the initial burn injury and sepsis-related complications principally determine the extent of the metabolic response in burn victims, obligatory activity, background- and procedural-related pain, and anxiety also greatly increase metabolic rates. Judicious maximal narcotic support, appropriate sedation, and supportive psychotherapy are mandatory if their effects are to be minimized. Several anabolic and anticatabolic agents are available for use during immediate care and rehabilitation. Exogenous, continuous low-dose insulin infusion, beta-blockade with propranolol, and the use of the synthetic testosterone analogue oxandrolone are the most cost-effective and least toxic therapies to date. These greatly assist therapeutic minimization of the loss of lean body mass and linear growth delay and are effective in burned patients with and without sepsis. Adverse effects, cost benefits, and the ease of administration and monitoring must be examined when considering the possibility of their use.

Metabolic and hormonal changes of severely burned children receiving long-term oxandrolone treatment

OBJECTIVE

When given to children for 1 year after a severe burn, oxandrolone significantly improves lean body mass, bone mineral content, and muscle strength. The beneficial effects of oxandrolone on height and weight were observed 1 year after treatment was discontinued. To study the efficacy of oxandrolone in severely burned children for 12 months after burn and 12 months after the drug was discontinued.

SUMMARY BACKGROUND DATA

Oxandrolone attenuates body catabolism during the acute phase after burn. It is unclear whether oxandrolone would have any beneficial effects during long-term treatment or if there were any effects after the drug was stopped.

METHODS

Sixty-one children with 40% total body surface area burns were enrolled in this study. Patients were randomized into those to receive oxandrolone (n = 30) or placebo (n = 31) for the first 12 months. Treatment was discontinued after 12 months, and the patients were studied without the drug for the following 12 months. At discharge and 6, 12, 18, and 24 months after burn, height, weight, body composition, resting energy expenditure, muscle strength, and serum human growth hormone, insulin-like growth factor-I (IGF-1), IGF binding protein-3, insulin, cortisol, parathyroid hormone, tri-iodothyronine uptake (T3 uptake), and free thyroxine index (FTI) were measured. Statistical analysis used Tukey multiple comparison test. Significance was accepted at P < 0.05.

RESULTS

Oxandrolone improved lean body mass, bone mineral content and muscle strength compared with controls during treatment, P < 0.05. Serum IGF-1, T3 uptake, and FTI were significantly higher during drug treatment compared with controls, P < 0.05. Significant increases in height and weight with oxandrolone were observed after the end of treatment.

CONCLUSIONS

Oxandrolone improved body composition and strength in severely burned children during the 12 months of treatment. Its effect on height and weight continued after treatment was discontinued.

Myopathies in critical illness: characterization and nutritional aspects

Myopathies related to critical illness have received increasing recognition over the past decade and are common in patients even after a brief period in the intensive care unit. Recent studies have revealed that myopathies in the critically ill may in fact be more prevalent than neuropathies and that morbidity and mortality may be greater. Protein catabolism, an increase in urinary nitrogen loss, and muscle wasting are observed in critical illness myopathy. Muscle biopsies in critically ill patients demonstrate low glutamine levels, low protein/DNA levels, and high concentrations of extracellular water. The increased flux of glutamine in muscle in these patients is thought to be insufficient to meet the body's requirement for glutamine, and thus in critical illness this amino acid may be classified as "conditionally essential." Three subtypes of critical illness myopathy have been described that are often grouped together as acute quadriplegic myopathy: thick-filament myopathy, critical illness myopathy, and necrotizing myopathy. These can be differentiated based on clinical features and muscle biopsy. Treatments for critical illness myopathies range from primary prevention, i.e., avoiding myopathy-inducing drugs, to novel nutritional therapies, such as glutamine and glutathione supplementation. One should be particularly vigilant for the development of myopathies in critically ill alcoholic patients, who may have a chronic alcoholic myopathy at baseline. In the past decade, advances have been made in characterizing and identifying patients with myopathies due to critical illness. However, additional studies must be performed in order to develop appropriate therapies for this potentially devastating disorder.

Pharmacodynamic considerations with recombinant human insulin-like growth factor-I in children

AIM

To report effects of weight-based recombinant human insulin-like growth factor-I (rhIGF-I) on IGF axis parameters in children with hyperinsulinism.

METHODS

Open label trial with subcutaneous rhIGF-I (40 microg/kg/dose). Patients studied were children (1 month to 11 years) with diffuse hyperinsulinism (n = 7). Serial serum IGF and insulin-like growth factor binding protein (IGFBP) concentrations were measured by RIA and analyzed by linear Pearson regression.

RESULTS

Following the initial rhIGF-I dose, total insulin-like growth factor-I (IGF-I) rose by 56% at 30 min (p < 0.01) and 85% at 120 min (p < 0.02). Serum IGF-II, IGFBP-2, and IGFBP-3 levels did not change. Peak serum IGF-I levels within 12 h of the initial rhIGF-I dose were 167-700 mg/ml. The variable peak IGF-I response is attributable in part to IGFBP-3 differences across this pediatric age range. Models of rhIGF-I dosing based upon body surface area (BSA) or initial IGFBP-3 resulted in predictable peak serum IGF-I levels (r = 0.78; p < 0.03). Recalculating rhIGF-I dosing based upon the BSA . IGFBP-3 product correlated closely with peak IGF-I level (r = 0.85; p < 0.007).

CONCLUSIONS

Weight-based IGF-I dosing in this cohort resulted in variable IGF-I levels. Considering BSA and serum IGFBP-3 concentration in children is appropriate for subcutaneous IGF-I administration. A combination of these values may yield predictable individualization of rhIGF-I dosing.

Insulin-like growth factor-I treatment of growth disorders, diabetes mellitus and insulin resistance

Insulin-like growth factor I (IGF-I) has many potential therapeutic uses because of its varied effects--growth promotion, insulin-like influence on glucose metabolism, and neuroprotection resulting from cell-proliferative and antiapoptotic properties--but they have not been investigated systematically in clinical situations. The growth-promoting effect of recombinant human IGF-I (rhIGF-I) in the extensively studied growth hormone insensitivity syndrome (GHIS; Laron syndrome) signifies an endocrine role for the GH-IGF system. The metabolism of (adult) patients with severe insulin resistance is improved by rhIGF-I, which--together with insulin therapy--also improves metabolic control in type 1 and 2 diabetes. Further studies on IGF-I metabolic effects and growing understanding of the IGF-I-IGF-binding protein system could open new therapeutic avenues.

Effects of growth hormone on anthropometric measurements and cardiac function in children with thermal injury

Severe burn injuries are associated with growth delays a persistent hypermetabolic response and severe muscle catabolism and wasting. Growth hormone (GH), a potent anabolic agent and salutary modulator of post-traumatic metabolic responses has been shown to decrease muscle wasting, improve net protein synthesis and attenuate growth delays in burned children. In non-burned populations, GH has recently been shown to be of benefit in enhancing cardiac performance and improving cardiac contractility and efficiency. Yet, whether administration of GH will induce similar improvements in cardiac function in severely burned children is presently unknown. We therefore, investigated whether the administration of GH initiated upon hospital discharge (95% healed) and continued for 1-year post-burn would improve resting cardiac function in burned children. Severely burned children were randomized to receive either saline placebo (n = 37) or 0.05 mg/kg per day of GH (n = 39) from discharge until 12-month post-burn. Outcome variables included height, weight, lean body mass, resting energy expenditure, cardiac index, stroke-volume index, heart rate and left ventricular ejection fraction.

RESULTS

height, weight, lean body mass and ejection fraction showed a significant increase with GH. Our results indicate that severely burned children treated with long-term GH show a significant improvement in left ventricular ejection fraction.

Activation of the vasoactive intestinal peptide 2 receptor modulates normal and atrophying skeletal muscle mass and force

Of the two known vasoactive intestinal peptide receptors (VPAC1R and VPAC2R), the VPAC2R is expressed in skeletal muscle. To evaluate the function of the VPAC2R in the physiological control of skeletal muscle mass, we utilized the VPAC1R selective agonist [K15,R16,L27]VIP(1-7) GRF(8-27)-NH2 and the VPAC2R selective agonist Ro-25-1553 to treat mice and rats undergoing either nerve damage-, corticosteroid-, or disuse-induced skeletal muscle atrophy. These analyses demonstrated that activation of VPAC2R, but not VPAC1R, reduced the loss of skeletal muscle mass and force during conditions of skeletal muscle atrophy resulting from corticosteroid administration, denervation, casting-induced disuse, increased skeletal muscle mass, and force of nonatrophying muscles. These studies indicate that VPAC2R agonists may have utility for the treatment of skeletal muscle-wasting diseases.

Hypovitaminosis D in acutely injured pediatric burn patients

PROBLEM

The prevalence of vitamin D insufficiency, its etiology, and associated sequelae among acutely injured burn patients is unknown.

OBJECTIVE

This study assessed vitamin D and endocrine status, as well as the effect of anabolic agents, in pediatric patients who had sustained burns in excess of 25% total body surface area (TBSA).

SUBJECTS

Sixty-nine patients with a mean TBSA burn of 50.6+/-2.2% (range 27% to 94%) and full thickness injury of 41.3+/-3.0% (range 0% to 94%) were studied. Subjects ranged in age from 0.6 to 18 years (mean, 5.8+/-0.6 years). Main outcome measures Blood samples were obtained for serum 25-hydroxyvitamin D (D25), 1,25-dihydroxyvitamin D (D1,25), albumin, cortisol, triiodothyronine (T3), tetraiodothyronine (T(4)), thyroid stimulating hormone (TSH), and parathormone (PTH).

RESULTS

Two hundred eighty morning blood samples of D25 and D1,25 demonstrated that 45% and 26.2% were low and 8.9% and 11% were very low, respectively. At least one low D25 or D1,25 level occurred in 62.3% of all subjects. Very low levels were noted in 23.2% of all patients. There was an increased incidence of hyperparathyroidism in patients with very low serum D25. Vitamin D25 and D1,25 levels were lower in subjects with larger burns or inhalation injury, as well as those treated with thyroxine or oxandrolone. Serum albumin, cortisol, T(4), and TSH were not correlated with concentration of vitamin D.

CONCLUSIONS

Demonstration of a high incidence of low serum vitamin D indicates vitamin D status may be significantly compromised in burned children. It is unclear why vitamin D deficiency exists in this population. The most effective way to improve vitamin D status remains elusive at this time.