Is there a circulating proteolysis-inducing factor during sepsis?

The Sick and the Weak: Neuropathies/Myopathies in the Critically Ill

Critical illness polyneuropathies (CIP) and myopathies (CIM) are common complications of critical illness. Several weakness syndromes are summarized under the term intensive care unit-acquired weakness (ICUAW). We propose a classification of different ICUAW forms (CIM, CIP, sepsis-induced, steroid-denervation myopathy) and pathophysiological mechanisms from clinical and animal model data. Triggers include sepsis, mechanical ventilation, muscle unloading, steroid treatment, or denervation. Some ICUAW forms require stringent diagnostic features; CIM is marked by membrane hypoexcitability, severe atrophy, preferential myosin loss, ultrastructural alterations, and inadequate autophagy activation while myopathies in pure sepsis do not reproduce marked myosin loss. Reduced membrane excitability results from depolarization and ion channel dysfunction. Mitochondrial dysfunction contributes to energy-dependent processes. Ubiquitin proteasome and calpain activation trigger muscle proteolysis and atrophy while protein synthesis is impaired. Myosin loss is more pronounced than actin loss in CIM. Protein quality control is altered by inadequate autophagy. Ca(2+) dysregulation is present through altered Ca(2+) homeostasis. We highlight clinical hallmarks, trigger factors, and potential mechanisms from human studies and animal models that allow separation of risk factors that may trigger distinct mechanisms contributing to weakness. During critical illness, altered inflammatory (cytokines) and metabolic pathways deteriorate muscle function. ICUAW prevention/treatment is limited, e.g., tight glycemic control, delaying nutrition, and early mobilization. Future challenges include identification of primary/secondary events during the time course of critical illness, the interplay between membrane excitability, bioenergetic failure and differential proteolysis, and finding new therapeutic targets by help of tailored animal models.

Tumour necrosis factor (TNF) and interleukin-1 (IL-1) induce muscle proteolysis through different mechanisms

The purpose of this study was to test the hypothesis that muscle proteolysis induced by TNF or IL-1 is mediated by glucocorticoids. Rats were treated with 300 mug kg(-1) of recombinant human preparations of IL-1alpha (rIL-1alpha) or TNFalpha (rTNFalpha) divided into three equal intraperitoneal doses given over 16 h. Two hours before each cytokine injection, rats were given 5 mg kg(-1) of the glucocorticoid receptor blocker mifepristone RU 38486, by gavage or were gavaged with the vehicle. Eighteen hours after the first cytokine injection, total and myofibrillar protein breakdown rates were determined in incubated extensor digitorum longus muscles as release of tyrosine and 3-methylhistidine, respectively. Total and myofibrillar proteolytic rates were increased following injection of rIL-1alpha or rTNFalpha. Proteolysis induced by rIL-1alpha was not altered by treatment with RU 38486. In contrast, the glucocorticoid receptor blocker inhibited the proteolytic effect of rTNFalpha. The results suggest that the proteolytic effect of TNF is mediated by glucocorticoids and that IL-1 induces muscle proteolysis through a glucocorticoid independent pathway.

The roles of insulin and hyperglycemia in sepsis pathogenesis

Hyperglycemia is a risk marker of morbidity and mortality in acute critical illness, and insulin therapy seems to be beneficial in this patient group. Whether this is true for a population of sepsis patients, as such, has not been investigated in clinical trials, but evidence from in vitro studies and experimental sepsis suggests that this may be the case. The endocrinology of septic patients is characterized by a shift in the balance between insulin and its counter-regulatory hormones favoring the latter. This leads to prominent metabolic derangements composed of high release and low use of glucose, amino acids, and free fatty acids (FFA), resulting in increased blood levels of these substrates. Circulating, proinflammatory mediators further enhance this state of global catabolism. Increased levels of glucose and FFA have distinct effects on inflammatory signaling leading to additional release of proinflammatory mediators and endothelial and neutrophil dysfunction. Insulin has the inherent capability to counteract the metabolic changes observed in septic patients. Concomitantly, insulin therapy may act as a modulator of inflammatory pathways inhibiting the unspecific, inflammatory activation caused by metabolic substrates. Given these properties, insulin could conceivably be serving a dual purpose for the benefit of septic patients.

Mechanisms of host wasting induced by administration of cytokines in rats

This study determined the effects of chronic administration of the two principal proximate cytokines, interleukin-1 (IL-1) and tumor necrosis factor (TNF), on host wasting in rats. The effects were compared with those observed in a matched pair-fed group to distinguish the contribution from anorexia. Both TNF and IL-1 produced weight loss, net nitrogen loss, and skeletal muscle catabolism and increased liver weight. Such effects were independent from and additive to those resulting from semistarvation. However, under equivalent nutritional conditions, TNF infusion led to a greater effect on muscle protein catabolism and liver weight and caused liver protein anabolism, whereas only the group receiving IL-1 had altered glucose metabolism in the postabsorptive state. Tachyphylaxis was seen in the response of food intake over time after administration of IL-1. These actions define the two principal mechanisms for the development of protein calorie malnutrition that occur because of cytokine action, anorexia producing semistarvation and an increased net protein catabolic rate reducing anabolic efficiency.

Metabolic changes in rats during a continuous infusion of recombinant interleukin-1

The effects of recombinant interleukin-1 (IL-1), given as a continuous infusion for 6 days, on host responses were determined in rats. The development of fever, change in food intake and body weight, and key components of the acute-phase response in energy and protein metabolism were assessed. The effects of IL-1 were compared with those observed in a matched pair-fed group (semistarved), to distinguish the contribution from anorexia, and in a group that received IL-1 for 4 h acutely. IL-1 significantly increased core temperature, plasma levels of IL-6, and acute-phase protein production and decreased food intake and the circulating zinc level. The catabolic effects of IL-1 on nitrogen loss and muscle protein breakdown were independent of, and additive to those from malnutrition. The changes in energy expenditure, cumulative urinary nitrogen, and hydroxyproline excretion in the chronic IL-1 group were increased over semistarved animals. Finally, changes in muscle protein kinetics were only seen with chronic IL-1 infusion, and the changes in acute-phase protein were greater.

Cytokine control of nutrition and metabolism in critical illness

During the last two decades, major advances in technology and in our fundamental understanding of the biologic aspects of sepsis and cancer cachexia have dramatically affected the therapeutic strategies available to the surgeon to care for critically ill patients. It is clear, however, that cytokines affect whole body nutrition and metabolism and are responsible for many of the clinically observed nutritional effects of injury, infection, and cancer, including fever, hypermetabolism, anorexia, protein catabolism, cachexia, and altered fat, glucose, and trace mineral metabolism. These metabolic and nutritional effects of cytokines are influenced by the nutritional status of the host, which is generally altered during the course of the critical illness. In the future, the use of specialized diets and the use of selective cytokine blockade are likely to be important components of the overall care of the catabolic patient.

Reduced muscle protein breakdown in septic rats following treatment with interleukin-1 receptor antagonist

1. The role of interleukin-1 (IL-1) in sepsis-induced muscle proteolysis was assessed by treating septic rats with recombinant IL-1 receptor antagonist (rIL-1ra). 2. In initial experiments, we tested the effectiveness of IL-1ra in preventing muscle proteolysis induced by administration of IL-1. 3. When normal rats were treated with rIL-1 alpha (three intraperitoneal doses of 100 micrograms/kg body weight each over 16 hr), total and myofibrillar muscle protein breakdown rates, measured as release of tyrosine and 3-methylhistidine, respectively, by incubated extensor digitorum longus muscles, were significantly increased. 4. This metabolic response to IL-1 alpha was completely abolished by rIL-1ra, administered as three intraperitoneal doses of 3 mg/kg body weight each over 16 hr. 5. In subsequent experiments, sepsis was induced in rats by cecal ligation and puncture (CLP); non-septic rats were sham-operated. 6. Treatment of septic rats over 16 hr with a total dose of 25 mg/kg body weight of rIL-1ra reduced, but did not normalize, the increased muscle protein breakdown rates seen during sepsis. 7. When the dose of rIL-1ra was more than doubled and given as a constant infusion at a rate of 4.2 mg/kg body weight/hr for 16 hr, the increased rate of muscle proteolysis in septic rats was normalized. 8. The present study offers the first direct evidence that IL-1 is involved in the regulation of muscle proteolysis during sepsis.

Effects of flurbiprofen on recombinant human IL-1 alpha-induced fever and associated clinical, haematological and blood biochemical changes in the dwarf goat

Flurbiprofen, a potent NSAID, was given as an intravenous infusion (1 mg/kg) to dwarf goats. After drug administration, no significant changes were observed in heart rate and rumen motility, whereas rectal temperature increased slightly; mean plasma glucose and creatinine concentrations gradually increased during the observation period. Plasma iron concentration and the number of circulating lymphocytes were significantly lower after flurbiprofen infusion. Intravenous injection of recombinant human interleukin-1 alpha (r. HuIL-1 alpha: 0.5 microgram/kg) caused shivering, fever, inhibition of rumen contractions, tachycardia, hypoferraemia, hypozincaemia, hyperglycaemia followed by hypoglycaemia, changes in plasma urea and creatinine values, lymphopaenia and neutropaenia followed by neutrophilic leukocytosis. Pretreatment with flurbiprofen partly antagonized the febrile reactions to r.HuIL-1 alpha. The r.HuIL-1 alpha-induced tachycardia and inhibition of rumen contractions were only delayed. The drug prevented the initial hyperglycaemia but did not abolish the secondary hypoglycaemia. Furthermore, flurbiprofen delayed the decline in plasma zinc and iron concentrations, whereas plasma creatinine values were significantly lower. Finally, after drug pretreatment the changes in circulating neutrophils were more pronounced. These data demonstrate that most of the haematological, blood biochemical, and clinical effects of r.HuIL-1 alpha cannot be blocked by flurbiprofen, suggesting that an increased synthesis of prostaglandins is not involved in these r.HuIL-1 alpha-induced effects.

In vivo administration of interleukin-1 alpha induces muscle proteolysis in normal and adrenalectomized rats

The effect on muscle protein turnover of recombinant interleukin-1 alpha (rIL-1 alpha), 300 micrograms/kg body weight (BW) administered intraperitoneally (IP) in three divided doses over 18 hours, was studied in rats. Protein synthesis rate was determined by measuring incorporation of 14C-phenylalanine into protein, and total and myofibrillar protein breakdown rates were determined by measuring release of tyrosine and 3-methylhistidine, respectively, in incubated extensor digitorum longus muscles. To assess the role of glucocorticoids in rIL-1 alpha-related metabolic alterations, plasma levels of corticosterone following rIL-1 alpha injection and the effect of rIL-1 alpha on muscle protein breakdown in adrenalectomized and sham-adrenalectomized rats were determined. Total and myofibrillar protein breakdown rates were increased by 45% and 167%, respectively, following treatment of normal rats with rIL-1 alpha; muscle protein synthesis was not altered by the cytokine. Plasma corticosterone levels were markedly elevated following rIL-1 alpha injection, with a maximal level occurring at 30 minutes. However, administration of rIL-1 alpha resulted in increased total and myofibrillar protein breakdown rates in both adrenalectomized and sham-adrenalectomized rats. The results suggest that increased muscle proteolysis following administration of rIL-1 alpha is independent of glucocorticoids.

Effect of indomethacin on postoperative protein metabolism after gastrectomy under total parenteral nutrition

A randomized trial was undertaken to evaluate the effects of postoperative indomethacin (IDM) administration on protein metabolism in 20 patients who underwent an uncomplicated distal gastrectomy and were placed on post-operative total parenteral nutrition (TPN). Ten patients (the IDM group) received 50 mg of IDM every 8 h after operation up to postoperative day (POD) 4 while the other ten patients (the control group) received neither IDM nor any other non-steroidal anti-inflammatory drug, postoperatively. Though the requirement for postoperative plasma transfusion was significantly greater in the IDM group, the albumin level on POD 1 was significantly lower in this group than in the control group. The postoperative changes of C-reactive protein, retinol binding protein, and pre-albumin between the two groups showed no difference. Moreover, the urinary 3-methylhistidine excretion, N-balance, and plasma aminogram on POD 4 also demonstrated no difference. We thus concluded that post-operative IDM administration after elective surgery has no additional anti-catabolic effect on the presence of TPN.

Muscle protein breakdown during endotoxemia in rats and after treatment with interleukin-1 receptor antagonist (IL-1ra)

The purpose of this study was to examine the effect of endotoxemia on muscle protein degradation and to test the hypothesis that muscle proteolysis during endotoxemia is regulated by interleukin-1 (IL-1). Both total and myofibrillar protein breakdown rates in incubated extensor digitorum longus muscles were increased after the subcutaneous injection of 0.1 or 1.0 mg/kg endotoxin in rats. The endotoxin-induced increase in muscle protein breakdown was blunted by IL-1 receptor antagonist, administered intraperitoneally at a total dose of 45 or 105 mg/kg. Results suggest that endotoxemia in rats gives rise to sepsislike changes in muscle protein breakdown. Increased muscle protein breakdown during endotoxemia may be regulated, at least in part, by IL-1.

The effect of interleukin-1 alpha and the glucocorticoid receptor blocker RU 38486 on total and myofibrillar protein breakdown in skeletal muscle

The purpose of the present study was to test the hypothesis that muscle proteolysis induced by interleukin-1 alpha (IL-1 alpha) is mediated by glucocorticoids. Male Sprague-Dawley rats, weighing 40-60 g, were treated with recombinant IL-1 alpha (rIL-1 alpha), 300 micrograms/kg in three divided intraperitoneal doses over 16 hr, or corresponding control injections. Groups of rats received the glucocorticoid receptor blocker RU 38486 by gavage (15 mg/kg in three divided doses over 16 hr) or were subjected to sham-gavage. In other experiments we tested the effectiveness of the same dose of RU 38486 to block muscle proteolysis in rats treated with corticosterone (200 mg/kg in two divided doses over 16 hr). Total and myofibrillar protein breakdown rates in incubated extensor digitorum longus muscles were determined by measuring release of tyrosine and 3-methylhistidine, respectively. Administration of rIL-1 alpha increased total and myofibrillar protein breakdown by 49 and 134%, respectively. This effect of the cytokine was not affected by RU 38486. The same dose of RU 38486, however, completely blocked the increase in total and myofibrillar protein breakdown induced by corticosterone. The results suggest that muscle proteolysis induced by the administration of rIL-1 alpha is not mediated by glucocorticoids.

Cytokines and glucocorticoids in the regulation of the "hepato-skeletal muscle axis" in sepsis

Sepsis results in muscle catabolism and peripheral release of amino acids with a concomitant uptake of amino acids in liver and acute-phase protein synthesis. In addition, there appears to be a cytokine-induced process that blocks muscle amino acid uptake in sepsis, further diverting amino acids from the periphery to the liver. In this article, evidence that cytokines and glucocorticoids play an important role in the regulation of hepatic and muscle protein metabolism during sepsis is presented.