Interleukin 1 and tumor necrosis factor do not regulate protein balance in skeletal muscle

α7 Nicotinic Acetylcholine Receptor Agonists Regulate Inflammation and Growth Hormone Resistance in Sepsis

ABSTRACT

During sepsis the normal induction of circulating insulin-like growth factor-I (IGF-I) by growth hormone (GH) action on liver is attenuated, a phenomenon called hepatic GH resistance. Hepatic GH resistance can be caused by cytokine-mediated activation of the NF-κB pathway which interferes with normal GH-signaling. The afferent and efferent fibers of the vagus nerve are integral to the cholinergic anti-inflammatory pathway (CAP) which attenuates hepatic TNFα production by activating the α7 nicotinic acetylcholine receptor (α7nAChR). We examined the effects of selective afferent vagotomy (SAV) and α7nAChR activation on sepsis-induced mortality, hepatic and systemic inflammation, the GH/IGF system and hepatic GH resistance using Sprague Dawley (SD) rats, C57BL/6 wild type (WT) mice, and α7nAChR knockout (KO) mice. Capsaicin was used to perform SAV and GTS-21 (α7nAChR agonist) was used to activate the α7nAChR. Sepsis-induced mortality, hepatic NF-κB activation, and plasma cytokine levels were increased in SAV rats and reduced in GTS-21-treated mice. The effects of sepsis on the GH/IGF-I system plasma IGF-I, IGF binding protein-1 (IGFBP-1), hepatic IGF-I, IGFBP-1, and GH receptor (GHR) mRNA and rhGH-responsiveness in mice were improved by GTS-21. Collectively these results confirm the protective effects of the anti-inflammatory CAP and α7nAChR activation in sepsis. They also provide evidence the CAP and α7nAChR activation could be used to attenuate hepatic GH resistance and anabolic failure in sepsis.

New insights on the regulation of cancer cachexia by N-3 polyunsaturated fatty acids

Cancer cachexia is a multifactorial syndrome that develops during malignant tumor growth. Changes in plasma levels of several hormones and inflammatory factors result in an intense catabolic state, decreased activity of anabolic pathways, anorexia, and marked weight loss, leading to cachexia development and/or accentuation. Inflammatory mediators appear to be related to the control of a highly regulated process of muscle protein degradation that accelerates the process of cachexia. Several mediators have been postulated to participate in this process, including TNF-α, myostatin, and activated protein degradation pathways. Some interventional therapies have been proposed, including nutritional (dietary, omega-3 fatty acid supplementation), hormonal (insulin), pharmacological (clenbuterol), and nonpharmacological (physical exercise) therapies. Omega-3 (n-3) polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid, are recognized for their anti-inflammatory properties and have been used in therapeutic approaches to treat or attenuate cancer cachexia. In this review, we discuss recent findings on cellular and molecular mechanisms involved in inflammation in the cancer cachexia syndrome and the effectiveness of n-3 PUFAs to attenuate or prevent cancer cachexia.

Oleate Prevents Palmitate-Induced Atrophy via Modulation of Mitochondrial ROS Production in Skeletal Myotubes

Accumulation of saturated fatty acids contributes to lipotoxicity-related insulin resistance and atrophy in skeletal muscle. Conversely, unsaturated fatty acids like docosahexaenoic acid were proven to preserve muscle mass. However, it is not known if the most common unsaturated oleate will protect skeletal myotubes against palmitate-mediated atrophy, and its specific mechanism remains to be elucidated. Therefore, we investigated the effects of oleate on atrophy-related factors in palmitate-conditioned myotubes. Exposure of myotubes to palmitate, but not to oleate, led to an induction of fragmented nuclei, myotube loss, atrophy, and mitochondrial superoxide in a dose-dependent manner. Treatment of oleate to myotubes attenuated production of palmitate-induced mitochondrial superoxide in a dose-dependent manner. The treatment of oleate or MitoTEMPO to palmitate-conditioned myotubes led to inhibition of palmitate-induced mRNA expression of proinflammatory (TNF-α and IL6), mitochondrial fission (Drp1 and Fis1), and atrophy markers (myostatin and atrogin1). In accordance with the gene expression data, our immunocytochemistry experiment demonstrated that oleate and MitoTEMPO prevented or attenuated palmitate-mediated myotube shrinkage. These results provide a mechanism indicating that oleate prevents palmitate-mediated atrophy via at least partial modulation of mitochondrial superoxide production.

Dexmedetomidine ameliorates muscle wasting and attenuates the alteration of hypothalamic neuropeptides and inflammation in endotoxemic rats

Dexmedetomidine is generally used for sedaton in critically ill, it could shorten duration of mechanical ventilation, ICU stay and lower basic metabolism. However, the exact mechanism of these positive effects remains unkown. Here we investigated the hypothesis that dexmedetomidine could ameliorate muscle wasting in endotoxemic rats and whether it was related to hypothalamic neuropeptides alteration and inflammation. Fourty-eight adult male Sprague–Dawley rats were intraperitoneally injected with lipopolysaccharide (LPS) (5 mg/kg) or saline, followed by 50 μg/kg dexmedetomidine or saline administration via the femoral vein catheter (infusion at 5 μg·kg^-1·hr^-1). Twenty-four hours after injection, hypothalamus tissues and skeletal muscle were obtained. Muscle wasting was measured by the mRNA expression of two E3 ubiquitin ligases, muscle atrophy F-box (MAFbx) and muscle ring finger 1 (MuRF-1) as well as 3-methylhistidine (3-MH) and tyrosine release. Hypothalamic inflammatory markers and neuropeptides expression were also detected in all four groups. Results showed that LPS administration led to significant increase in hypothalamic inflammation together with muscle wasting. Increased hypothalamic neuropeptides, proopiomelanocortin (POMC), cocaine and amphetamine-related transcript (CART) and neuropeptides Y (NPY) and decreased agouti-related protein (AgRP) were also observed. Meanwhile dexmedetomidine administration ameliorated muscle wasting, hypothalamic inflammation and modulated the alteration of neuropeptides, POMC, CART and AgRP, in endotoxemic rats. In conclusion, dexmedetomidine could alleviate muscle wasting in endotoxemic rats, and it could also attenuate the alteration of hypothalamic neuropeptides and reduce hypothalamic inflammation.

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.

Endotoxemia-induced muscle wasting is associated with the change of hypothalamic neuropeptides in rats

In critical patients, sepsis-induced muscle wasting is considered to be an important contributor to complications and mortality. Previous work mainly focuses on the peripheral molecular mechanism of muscle degradation, however little evidence exists for the role of central nervous system in the process. In the present study, we, for the first time, characterized the relationship between muscle wasting and central neuropeptide changes in a septic model. Thirty-six adult male Sprague-Dawley rats were intraperitoneally injected with lipopolysaccharide (LPS) or saline. Twelve, 24 and 48 hrs after injection, skeletal muscle and hypothalamus tissues were harvested. Muscle wasting was measured by the mRNA expression of two E3 ubiquitin ligases, muscle ring finger 1 (MuRF-1) and muscle atrophy F-box (MAFbx), as well as 3-methyl-histidine (3-MH) and tyrosine release. Hypothalamic neuropeptides and inflammatory marker expressions were also measured in three time points. LPS injection caused an increase expression of MuRF-1 and MAFbx, and a significant higher release of 3-MH and tyrosine. Hypothalamic neuropeptides, proopiomelanocortin (POMC), cocaine- and amphetamine-regulated transcript (CART), agouti-related protein (AgRP) and neuropeptide Y (NPY) presented a dynamic change after LPS injection. Also, hypothalamic inflammatory markers, interleukin-1 β (IL-1β) and tumor necrosis factor α (TNF-α) increased substantially after LPS administration. Importantly, the expressions of POMC, AgRP and CART were well correlated with muscle atrophy gene, MuRF-1 expression. These findings suggest hypothalamic peptides and inflammation may participate in the sepsis-induced muscle wasting, but the exact mechanism needs further study.

Characterization of GLPG0492, a selective androgen receptor modulator, in a mouse model of hindlimb immobilization

Background

Muscle wasting is a hallmark of many chronic conditions but also of aging and results in a progressive functional decline leading ultimately to disability. Androgens, such as testosterone were proposed as therapy to counteract muscle atrophy. However, this treatment is associated with potential cardiovascular and prostate cancer risks and therefore not acceptable for long-term treatment. Selective Androgen receptor modulators (SARM) are androgen receptor ligands that induce muscle anabolism while having reduced effects in reproductive tissues. Therefore, they represent an alternative to testosterone therapy. Our objective was to demonstrate the activity of SARM molecule (GLPG0492) on a immobilization muscle atrophy mouse model as compared to testosterone propionate (TP) and to identify putative biomarkers in the plasma compartment that might be related to muscle function and potentially translated into the clinical space.

Methods

GLPG0492, a non-steroidal SARM, was evaluated and compared to TP in a mouse model of hindlimb immobilization.

Results

GLPG0492 treatment partially prevents immobilization-induced muscle atrophy with a trend to promote muscle fiber hypertrophy in a dose-dependent manner. Interestingly, GLPG0492 was found as efficacious as TP at reducing muscle loss while sparing reproductive tissues. Furthermore, gene expression studies performed on tibialis samples revealed that both GLPG0492 and TP were slowing down muscle loss by negatively interfering with major signaling pathways controlling muscle mass homeostasis. Finally, metabolomic profiling experiments using ¹H-NMR led to the identification of a plasma GLPG0492 signature linked to the modulation of cellular bioenergetic processes.

Conclusions

Taken together, these results unveil the potential of GLPG0492, a non-steroidal SARM, as treatment for, at least, musculo-skeletal atrophy consecutive to coma, paralysis, or limb immobilization.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-291) contains supplementary material, which is available to authorized users.

Response to nutritional support and therapeutic approaches of amino acid and protein metabolism in surgical patients

The response to critical illness involves alterations in all aspects of metabolic control, favoring catabolism of body protein. In particular, body protein loss occurring as a result of the alteration of protein metabolism has been reported to be inversely correlated with the survival of critically ill patients. Despite the availability of various therapeutic modalities aiming to prevent loss of the body protein pool, such as total parenteral nutrition, enteral nutrition designed to provide excessive calories as a form of energy substrate, and protein itself, the loss of body protein cannot be prevented by any of these. Loss of the boyd protein store occurs as a consequence of the alteration of the intermediate metabolism that works for the production of energy substrate. This alteration of substrate metabolism may be linked to the alteration of protein metabolism. However, no specific factors regulating amino acid and protein metabolism have been identified. Thus, further investigations evaluating amino acid and protein metabolism are required to obtain better understanding of metabolic regulation in the body, which may lead to the development of novel and more effective therapeutic modalities for nutrition in the future.

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.

Cytokines in muscle damage

Multiple cellular and molecular processes are rapidly activated following skeletal muscle damage to restore normal muscle structure and function. These processes typically involve an inflammatory response and potentially the consequent occurrence of secondary damage before their resolution and the completion of muscle repair or regeneration. The overall outcome of the inflammatory process is potentially divergent, with the induction of prolonged inflammation and further muscle damage, or its active termination and the promotion of muscle repair and regeneration. The final, detrimental, or beneficial effect of the inflammatory response on muscle repair is influenced by specific interactions between inflammatory and muscle cell-derived cytokines that act as positive and/or negative regulators to coordinate local and systemic inflammatory-related events and modulate muscle repair process. A crucial balance between proinflammatory and anti-inflammatory cytokines appears to attenuate an excessive inflammatory reaction, prevent the development of muscle fibrosis, and adequately promote the regenerative process. In this review, we address the interactive cytokine responses following muscle damage, in the context of induction and progression, or resolution of muscle inflammation and the promotion of muscle repair.

The proteasome inhibitor MG132 reduces immobilization-induced skeletal muscle atrophy in mice

Background

Skeletal muscle atrophy is a serious concern for the rehabilitation of patients afflicted by prolonged limb restriction. This debilitating condition is associated with a marked activation of NFκB activity. The ubiquitin-proteasome pathway degrades the NFκB inhibitor IκBα, enabling NFκB to translocate to the nucleus and bind to the target genes that promote muscle atrophy. Although several studies showed that proteasome inhibitors are efficient to reduce atrophy, no studies have demonstrated the ability of these inhibitors to preserve muscle function under catabolic condition.

Methods

We recently developed a new hindlimb immobilization procedure that induces significant skeletal muscle atrophy and used it to show that an inflammatory process characterized by the up-regulation of TNFα, a known activator of the canonical NFκB pathway, is associated with the atrophy. Here, we used this model to investigate the effect of in vivo proteasome inhibition on the muscle integrity by histological approach. TNFα, IL-1, IL-6, MuRF-1 and Atrogin/MAFbx mRNA level were determined by qPCR. Also, a functional measurement of locomotors activity was performed to determine if the treatment can shorten the rehabilitation period following immobilization.

Results

In the present study, we showed that the proteasome inhibitor MG132 significantly inhibited IκBα degradation thus preventing NFκB activation in vitro. MG132 preserved muscle and myofiber cross-sectional area by downregulating the muscle-specific ubiquitin ligases atrogin-1/MAFbx and MuRF-1 mRNA in vivo. This effect resulted in a diminished rehabilitation period.

Conclusion

These finding demonstrate that proteasome inhibitors show potential for the development of pharmacological therapies to prevent muscle atrophy and thus favor muscle rehabilitation.

Hypothalamic regulation of muscle metabolism

PURPOSE OF REVIEW

The interest in obesity research has produced a large body of data describing the impact of neuronal signaling in the hypothalamus and brainstem on metabolic regulation in the periphery. Studies have historically focused on central regulation of metabolism in adipose and hepatic tissue. Recent studies highlight an important role for these same central regulatory centers in the control of muscle metabolism. This review will focus on these new studies, and will highlight the implications of these new data for the study of muscle catabolism in disease states.

RECENT FINDINGS

The balance of anabolism and catabolism in muscle requires activation of the hypothalamic-pituitary-adrenal axis as well as changes in energy-dependent signaling pathways in the muscle. It is now apparent that the sympathetic nervous system conveys much of this information between key metabolism-regulating nuclei in the hypothalamus and skeletal muscle.

SUMMARY

Peripheral signals conveying information regarding the metabolic status of the animal appear to alter the function of metabolic centers in the brain that in turn regulate energy partitioning in muscle via a sympathetic relay. Our understanding of how this system is regulated in normal physiological states and in obesity is providing important clues for understanding muscle catabolism in disease.

Activation of caspase-3 in the skeletal muscle during haemodialysis

BACKGROUND AND OBJECTIVE

Muscle atrophy in end-stage renal disease (ESRD) may be due to the activation of apoptotic and proteolytic pathways. We hypothesized that activation of caspase-3 in the skeletal muscle mediates apoptosis and proteolysis during haemodialysis (HD).

MATERIALS AND METHODS

Eight ESRD patients were studied before (pre-HD) and during HD and the findings were compared with those from six healthy volunteers. Protein kinetics was determined by primed constant infusion of L-(ring (13)C(6) ) Phenylalanine.

RESULTS

Caspase-3 activity in the skeletal muscle was higher in ESRD patients pre-HD than in controls (24966·0 ± 4023·9 vs. 15293·3 ± 2120·0 units, P<0·01) and increased further during HD (end-HD) (37666·6 ± 4208·3 units) (P<0·001). Actin fragments (14 kDa) generated by caspase-3 mediated cleavage of actomyosin was higher in the skeletal muscle pre-HD (68%) and during HD (164%) compared with controls. The abundance of ubiquitinized carboxy-terminal actin fragment was also significantly increased during HD. Skeletal muscle biopsies obtained at the end of HD exhibited augmented apoptosis, which was higher than that observed in pre-HD and control samples (P<0·001). IL-6 content in the soluble fraction of the muscle skeletal muscle was increased significantly during HD. Protein kinetic studies showed that catabolism was higher in ESRD patients during HD compared with pre-HD and control subjects. Muscle protein catabolism was positively associated with caspase-3 activity and skeletal muscle IL-6 content.

CONCLUSION

Muscle atrophy in ESRD may be due to IL-6 induced activation of caspase-3 resulting in apoptosis as well as muscle proteolysis during HD.

Enhanced inflammation with high carbohydrate intake during recovery from eccentric exercise

Inflammation associated with adipose tissue is modulated by macronutrient availability. For example, glucose increases inflammation in obese but not lean individuals. Little is known about how macronutrient intake influences inflammation associated with muscle. The aim of this study was to determine the impact of macronutrient intake differences during recovery from eccentric exercise on the inflammatory response. The study was a cross-over design in which young men and women (n = 12) completed high and low carbohydrate (CHO) conditions. Both conditions consisted of six sets of ten maximal high-force eccentric contractions of the elbow flexors and extensors followed by a controlled diet for the first 8 h post-exercise. Glucose, insulin, tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, and C-reactive protein were measured from blood samples pre-exercise, 1.5, 4, 8, and 24 h post-exercise. Perceived muscle soreness, strength loss, and serum CK activity were measured through 120 h post-exercise. Perceived soreness was elevated (P < 0.001) at all time points post-exercise in both conditions and was higher (P < 0.05) in the high compared to the low CHO condition. IL-1beta increased (P = 0.05) 24 h post-exercise in the high compared to the low CHO condition. There was a trend (P = 0.06) for IL-6 to be elevated in the high compared to the low CHO condition. We conclude that inflammation induced by high-force eccentric exercise in skeletal muscle is greater when a high CHO compared to a low CHO diet is consumed during recovery.

Effect of fish oil supplementation for two generations on changes of lymphocyte function induced by Walker 256 cancer cachexia in rats

Fish oil supplementation has been shown to improve the cachectic state of tumor-bearing animals and humans. Our previous study showed that fish oil supplementation (1 g per kg body weight per day) for 2 generations had anticancer and anticachetic effects in Walker 256 tumor-bearing rats as demonstrated by reduced tumor growth and body weight loss and increased food intake and survival. In this study, the effect of fish oil supplementation for 2 generations on membrane integrity, proliferation capacity, and CD4/CD8 ratio of lymphocytes isolated from mesenteric lymph nodes, spleen, and thymus of Walker 256 tumor-bearing animals was investigated. We also determined fish oil effect on plasma concentration and ex vivo production of cytokines [tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), interleukin-4 (IL-4), IL-6, and IL-10]. Lymphocytes from thymus of tumor-bearing rats presented lower viability, but this change was abolished by fish oil supplementation. Tumor growth increased proliferation of lymphocytes from all lymphoid organs, and fish oil supplementation abolished this effect. Ex vivo production of TNF-alpha and IL-6 was reduced in supplemented animals, but IL-4 and IL-10 secretion was stimulated in both nontumor and tumor-bearing rats. IL-10 and IFN-gamma plasma levels was also decreased in supplemented animals. These results suggest that the anticachetic effects of fish oil supplementation for a long period of time (2 generations) in Walker 256 tumor-bearing rats may be associated to a decrease in lymphocyte function as demonstrated by reduced viability, proliferation capacity, and cytokine production.

Phase II nonrandomized study of the efficacy and safety of COX-2 inhibitor celecoxib on patients with cancer cachexia

Chronic inflammation is one of the main features of cancer cachexia. Experimental and clinical studies showed that cyclooxygenase-2 inhibitors, such as celecoxib, may be beneficial in counteracting major symptoms of this devastating syndrome. We carried out a prospective phase II clinical trial to test the safety and effectiveness of an intervention with the COX-2 inhibitor celecoxib (300 mg/day for 4 months) on key variables of cachexia (lean body mass, resting energy expenditure, serum levels of proinflammatory cytokines, and fatigue) in patients with advanced cancer at different sites. A sample of 24 patients was enrolled from January to December 2008 and all were deemed assessable. A significant increase of lean body mass and a significant decrease of TNF-alpha were observed. Moreover, an improvement of grip strength, quality of life, performance status, and Glasgow prognostic score was shown. There were no grade 3/4 toxicities. Patient compliance was very good; no patient had to reduce the celecoxib dosage nor interrupt treatment. Our results showed that the COX-2 selective inhibitor celecoxib is an effective single agent for the treatment of cancer cachexia. Although the treatment of cancer cachexia, a multifactorial syndrome, is more likely to yield success with a multitargeted approach; in the present study, we were able to show that a treatment, such as celecoxib, addressing a single target, albeit very important as chronic inflammation, could have positive effects. Therefore, phase III clinical trials are warranted to test the efficacy and safety of celecoxib.

A novel hindlimb immobilization procedure for studying skeletal muscle atrophy and recovery in mouse

Skeletal muscle atrophy is a serious concern for patients afflicted by limb restriction due to surgery (e.g., arthrodesis), several articular pathologies (e.g., arthralgia), or simply following cast immobilization. To study the molecular events involved in this immobilization-induced debilitating condition, a convenient mouse model for atrophy is lacking. Here we provide a new immobilization procedure exploiting the normal flexion of the mouse hindlimb using a surgical staple to fix the ventral part of the foot to the distal part of the calf. Histological analysis revealed that our approach induced significant skeletal muscle atrophy by reducing the myofiber size of the tibialis anterior (TA) muscle by 36% compared with the untreated contralateral TA within a few days postimmobilization. Two molecular markers for atrophy, atrogin-1/muscle atrophy F-box (atrogin-1/MAFbx) and muscle ring finger 1 (MuRF-1) mRNAs, were significantly upregulated by 1.9- and 5.9-fold, respectively. Interestingly, our model also revealed the presence of an early inflammatory process during atrophy, characterized by the mRNA upregulation of TNF-α, IL-1, and IL-6 (1.9-, 2.4-, and 3.4-fold, respectively) simultaneously with the upregulation of the common leukocyte marker CD45 (6.1-fold). Moreover, muscle rapidly recovered on remobilization, an event associated with significantly increased levels of uncoupling protein-3 and peroxisome proliferator-activated receptor γ coactivator-1α mRNA, key components of prooxidative muscle metabolism. This model offers unexpected new insights into the molecular events involved in immobilization atrophy.

Attenuation of depression of muscle protein synthesis induced by lipopolysaccharide, tumor necrosis factor, and angiotensin II by beta-hydroxy-beta-methylbutyrate

beta-Hydroxy-beta-methylbutyrate (HMB; 50 microM) has been shown to attenuate the depression in protein synthesis in murine myotubes in response to lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha) with or without interferon-gamma (IFN-gamma), and angiotensin II (ANG II). The mechanism for the depression of protein synthesis by all three agents was the same and was attributed to activation of double-stranded RNA-dependent protein kinase (PKR) with the subsequent phosphorylation of eukaryotic initiation factor 2 (eIF2) on the alpha-subunit as well as increased phosphorylation of the elongation factor (eEF2). Myotubes expressing a catalytically inactive PKR variant, PKRDelta6, showed no depression of protein synthesis in response to either LPS or TNF-alpha, confirming the importance of PKR in this process. There was no effect of any of the agents on phosphorylation of mammalian target of rapamycin (mTOR) or initiation factor 4E-binding protein (4E-BP1), and thus no change in the amount of eIF4E bound to 4E-BP1 or the concentration of the active eIF4E.eIF4G complex. HMB attenuated phosphorylation of eEF2, possibly by increasing phosphorylation of mTOR, and also attenuated phosphorylation of eIF2alpha by preventing activation of PKR. These results suggest that HMB may be effective in attenuating muscle atrophy in a range of catabolic conditions.

NF-kappaB signaling in skeletal muscle: prospects for intervention in muscle diseases

Muscle remodeling is an important physiological process that promotes adaptive changes in cytoarchitecture and protein composition after exercise, aging, or disease conditions. Numerous transcription factors have been reported to regulate skeletal muscle homeostasis. NF-κB is a major pleiotropic transcription factor modulating immune, inflammatory, cell survival, and proliferating responses; however, its role in muscle development, physiology, and disease has just started to be elucidated. The current review article aims to summarize the literature on the role of NF-κB signaling in skeletal muscle pathophysiology, investigated over the last years using in vitro and more recently in vivo systems. Understanding the exact role of NF-κB in muscle cells will allow better therapeutic manipulations in the setting of human muscle diseases.

Interleukin-6 expression after infectious bronchitis virus infection in chickens

Viral infections in chickens pose a major health threat to the poultry industry. Infectious bronchitis virus (IBV) usually causes respiratory disease; however, the disease severity is influenced by the genotype of the chicken and the IBV strain involved. Nephropathogenic strains of IBV, such as the Australian T strain, can cause high mortalities due to kidney failure characterized by mononuclear cell infiltration and inflammation. In a previous study, a line of specific pathogen-free chickens, the S-line, was shown to be susceptible to high mortalities from IBV infection. The cause of these high mortalities is unknown but it is suspected that differential cytokine expression may play a role. With this in mind, we decided to study the role of the proinflammatory cytokine interleukin (IL)-6 during infection to determine its contribution to nephritis and influence on disease susceptibility. To investigate this, we infected the susceptible S-line and the more disease-resilient HWL line with the T strain of IBV and measured their cytokine response levels. In both lines of birds, IL-6 mRNA levels were elevated in the kidneys at 4 d postinfection. However, in S-line chickens, these levels were 20 times higher than those in the HWL chickens. In addition, S-line birds also showed three times higher serum IL-6 levels than HWL birds after IBV infection. These findings suggest that IL-6 may play a role in IBV-induced nephritis and may open an avenue to develop alternative strategies, such as the use of antiinflammatory cytokines, to overcome the nephropathogenic effects of IBV.

The Inhibitory Effects of Interleukin‐1 on Growth Hormone Action During Catabolic Illness

Growth hormone (GH) induces the expression of the anabolic genes responsible for growth, metabolism, and differentiation. Normally, GH stimulates the synthesis of circulating insulin-like growth factor-I (IGF-I) by liver, which upregulates protein synthesis in many tissues. The development of GH resistance during catabolic illness or inflammation contributes to loss of body protein, resulting in multiple complications that prolong recovery and cause death. In septic patients, increased levels of proinflammatory cytokines and GH resistance are commonly observed together. Numerous studies have provided evidence that the inhibitory effects of cytokines on skeletal muscle protein synthesis during sepsis and inflammation are mediated indirectly by changes in the GH/IGF-I system. Interleukin (IL)-1, a member of the family of proinflammatory cytokines, interacts with most cell types and is an important mediator of the inflammatory response. Infusion of a specific IL-1 receptor antagonist (IL-1Ra) ameliorates protein catabolism and GH resistance during systemic infection. This suggests that IL-1 is an important mediator of GH resistance during systemic infection or inflammation. Consequently, a better understanding of the interaction between GH, IL-1, and the regulation of protein metabolism is of great importance for the care of the patient.

Interleukin-1 inhibits the induction of insulin-like growth factor-I by growth hormone in CWSV-1 hepatocytes

Sepsis results in hepatic "growth hormone (GH) resistance" with reductions in plasma IGF-I despite a two- to fourfold increase in circulating GH. In this study, we examine the effects of IL-1 on GH receptor (GHR) expression, GH signaling (via the JAK/STAT and MAPK pathways), and the induction of gene expression [IGF-I mRNA and serine protease inhibitor (Spi) 2.1] by GH in CWSV-1 hepatocytes. Incubation of cells with IL-1beta (10 ng/ml, 24 h) had no effect on the relative abundance of GHR or signaling proteins JAK2, STAT5b, and ERK1/2 in cell lysates. Baseline phosphorylation of GHR, JAK2, STAT5b, and ERK1/2 was minimal. After GH stimulation, tyrosine phosphorylation of GHR, JAK2, STAT5b, and ERK1/2 increased 2- to 10-fold. However, neither the time course nor the magnitude of GHR, JAK2, and ERK1/2 phosphorylation by GH were significantly altered by IL-1. The GH-induced translocation of STAT5b to the nucleus was not prevented by IL-1. Although phosphorylated STAT5 in nuclear extracts from GH + IL-1 cells was decreased by 24% (vs. controls) 15 min after GH stimulation, this did not result in reduced STAT5-DNA binding activity. Pretreatment with IL-1 did not significantly decrease IGF-I mRNA stability. We conclude that IL-1 only minimally affects the time course of JAK2/STAT5 and MAPK signaling by GH. Therefore, an inhibitory effect of IL-1 on IGF-I and Spi 2.1 mRNA synthesis by GH represents the most likely mechanism for IL-1-mediated GH resistance.

IKKbeta/NF-kappaB activation causes severe muscle wasting in mice

Muscle wasting accompanies aging and pathological conditions ranging from cancer, cachexia, and diabetes to denervation and immobilization. We show that activation of NF-kappaB, through muscle-specific transgenic expression of activated IkappaB kinase beta (MIKK), causes profound muscle wasting that resembles clinical cachexia. In contrast, no overt phenotype was seen upon muscle-specific inhibition of NF-kappaB through expression of IkappaBalpha superrepressor (MISR). Muscle loss was due to accelerated protein breakdown through ubiquitin-dependent proteolysis. Expression of the E3 ligase MuRF1, a mediator of muscle atrophy, was increased in MIKK mice. Pharmacological or genetic inhibition of the IKKbeta/NF-kappaB/MuRF1 pathway reversed muscle atrophy. Denervation- and tumor-induced muscle loss were substantially reduced and survival rates improved by NF-kappaB inhibition in MISR mice, consistent with a critical role for NF-kappaB in the pathology of muscle wasting and establishing it as an important clinical target for the treatment of muscle atrophy.

Cancer cachexia is regulated by selective targeting of skeletal muscle gene products

Cachexia is a syndrome characterized by wasting of skeletal muscle and contributes to nearly one-third of all cancer deaths. Cytokines and tumor factors mediate wasting by suppressing muscle gene products, but exactly which products are targeted by these cachectic factors is not well understood. Because of their functional relevance to muscle architecture, such targets are presumed to represent myofibrillar proteins, but whether these proteins are regulated in a general or a selective manner is also unclear. Here we demonstrate, using in vitro and in vivo models of muscle wasting, that cachectic factors are remarkably selective in targeting myosin heavy chain. In myotubes and mouse muscles, TNF-alpha plus IFN-gamma strongly reduced myosin expression through an RNA-dependent mechanism. Likewise, colon-26 tumors in mice caused the selective reduction of this myofibrillar protein, and this reduction correlated with wasting. Under these conditions, however, loss of myosin was associated with the ubiquitin-dependent proteasome pathway, which suggests that mechanisms used to regulate the expression of muscle proteins may be cachectic factor specific. These results shed new light on cancer cachexia by revealing that wasting does not result from a general downregulation of muscle proteins but rather is highly selective as to which proteins are targeted during the wasting state.

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.

Evaluation of the mechanism of vascular endothelial growth factor improvement of ischemic flap survival in rats

This study evaluated the effects of exogenous vascular endothelial growth factor (VEGF) on the regulation of cytokines in a rat dorsal ischemic skin flap model. Exogenous VEGF (1 microg/ml) was injected subdermally into the flaps of 12 rats before the flaps were sutured back in place. Another 12 rats with flaps received saline injections, as a control group. Biopsy specimens were obtained from the flaps treated with VEGF or saline solution, at positions 2.5, 5.5, and 8.5 cm from the distal edge of the flaps, at 12 hours (n = 6 for each group) and 24 hours (n = 6 for each group) after suturing of the flaps. Expression of cytokine, growth factor, and inducible nitric oxide synthase was measured. The results demonstrated that expression of tumor necrosis factor-alpha and nitric oxide synthase in the distal part of the VEGF-treated flaps was significantly decreased, compared with the control values, at 12 and 24 hours postoperatively. It was concluded that administration of exogenous VEGF could protect flaps from ischemia-reperfusion injury through the regulation of proinflammatory cytokines and the inhibition of cytotoxic nitric oxide production.

Capsaicin-sensitive nerves regulate the metabolic response to abdominal sepsis

BACKGROUND

Both the systemic release of inflammatory mediators and activation of the neuroendocrine axis by sensory afferent nerves (SANs) have been implicated as initiators of the metabolic response to infection. In this study, we investigate the role of SANs as mediators of protein catabolism and the insulin-like growth factor (IGF) axis during abdominal sepsis using capsaicin (Cap) to selectively destroy nociceptive sensory axons.

METHODS

Four groups of male Sprague-Dawley rats were studied: Control, Control+Cap, Sepsis, and Sepsis+Cap. Rats were injected with Cap (75 mg/kg) on day 1 and (50 mg/kg) on day 2 to destroy SANs. Time-matched control and septic rats were pair-fed and injected with vehicle on the same schedule. Controls underwent sham laparotomy, while septic rats had a fecal-agar pellet inoculated with Escherichia coli and Bacteroides fragilis implanted in the peritoneal cavity. Blood and tissues were harvested 5 days after the induction of sepsis. Plasma IGF-I, IGFBP-1, and -3 were measured by radioimmunoassay and Western blot analysis. IGF-I, acid-labile subunit (ALS), IGFBP-1 and -3 mRNA levels were determined by Northern blot analysis.

RESULTS

Mortality was 40% in septic rats vs 0% in the sepsis+Cap group. Capsaicin had no effect on muscle mass, protein content, or the IGF system in control rats. However, sepsis-induced reductions in gastrocnemius mass (25%) and protein content (35%) were ameliorated by capsaicin. The sepsis-induced decrease in hepatic IGF-I mRNA and circulating IGF-I (26%), as well as the 4-fold increase in plasma IGFBP-1 and hepatic IGFBP-1 mRNA were prevented by capsaicin.

CONCLUSIONS

Capsaicin-sensitive nerves mediate mortality, the catabolism of skeletal muscle, and selected elements of the IGF system during abdominal sepsis. The results suggest an important role for nociceptive SANs and the neuroendocrine system in mediating the host response to abdominal infection.

Tumor necrosis factor-regulated biphasic activation of NF-kappa B is required for cytokine-induced loss of skeletal muscle gene products

NF-kappaB activation is classically defined as a transient response initiated by the degradation of IkappaB inhibitor proteins leading to nuclear import of NF-kappaB and culminating with the resynthesis of IkappaBalpha and subsequent inactivation of the transcription factor. Although this type of regulation is considered the paradigm for NF-kappaB activation, other regulatory profiles are known to exist. By far the most common of these is chronic or persistent activation of NF-kappaB. In comparison, regulation of NF-kappaB in a biphasic manner represents a profile that is scarcely documented and whose biological significance remains poorly understood. Here we show using differentiated skeletal muscle cells, that tumor necrosis factor (TNF) induces NF-kappaB activation in a biphasic manner. Unlike the first transient phase, which is terminated within 1 h of cytokine addition, the second phase persists for an additional 24-36 h. Biphasic activation is mediated at both the levels of NF-kappaB DNA binding and transactivation function, and both phases are dependent on the IKK/26 S proteasome pathway. We find that regulation of the first transient phase is mediated by the degradation and subsequent resynthesis of IkappaBalpha, as well as by a TNF-induced expression of A20. Second phase activity correlates with persistent down-regulation of both IkappaBalpha and IkappaBbeta proteins, derived from a continuous TNF signal. Finally, we demonstrate that inhibition of NF-kappaB prior to initiation of the second phase of activity inhibits cytokine-mediated loss of muscle proteins. We propose that the biphasic activation of NF-kappaB in response to TNF may play a key regulatory role in skeletal muscle wasting associated with cachexia.

Interferon gamma modulates trauma-induced muscle wasting and immune dysfunction

OBJECTIVE

To test the effect of burn injury in mice congenitally deficient in interferon gamma (IFN-gamma) and as well as in wild-type animals treated with IFN-gamma neutralizing antibody.

SUMMARY BACKGROUND DATA

The mechanisms underlying muscle wasting following burn trauma are incompletely characterized, although the hypercatabolic state is a consequence of increased proteasomal degradation. Concurrently, burn injury results in an immunocompromised state, and subsequent infections are the leading cause of morbidity and mortality in these patients. IFN-gamma, best conceptualized as a macrophage activating protein, modulates a variety of biologic pathways potentially relevant to muscle wasting and immune dysfunction.

METHODS

Mice received either a 20% total body surface area burn or a control sham treatment. At days 1, 2, and 7 following treatment, skeletal muscle, peripheral blood, and spleen were harvested from both groups. Protein synthesis and degradation rates were measured. Lymphocyte subpopulation expression of major histocompatibility complex I (MHC I) molecules was assessed by flow cytometry, and proliferation capacity was measured using mixed lymphocyte reaction.

RESULTS

IFN-gamma is critically involved in burn-induced weight loss; moreover, absence of IFN-gamma virtually abolished skeletal muscle hypercatabolism following burn injury. Lymphocyte proliferation and MHC I expression in the setting of burn trauma are also normalized in the absence of IFN-gamma. Both antigen presentation and proliferation functions are independently affected.

CONCLUSIONS

IFN-gamma plays a fundamental role in mediating the hypercatabolic state of multiple cell types following burn trauma.

Tumor necrosis factor mediates hepatic growth hormone resistance during sepsis

During sepsis, growth hormone (GH) resistance contributes to the catabolism of muscle protein. To determine the role of tumor necrosis factor (TNF) as a mediator of GH resistance, we examined the effects of a TNF antagonist [TNF-binding protein (TNFbp)] on the GH/insulin-like growth factor (IGF) I system during abdominal sepsis. To investigate potential mechanisms, the effects of TNF on the IGF-I response to GH and GH signaling were examined in cultured rat hepatocytes (CWSV-1). Three groups of rats were studied: Control, Sepsis, and Sepsis + TNFbp. Liver, gastrocnemius, and plasma were collected on day 5. In gastrocnemius, neither sepsis nor TNFbp altered the abundance of IGF-I mRNA. However, septic rats demonstrated an increase in circulating GH and a reduction in plasma IGF-I concentrations that was ameliorated by pretreatment with TNFbp. Liver from septic rats demonstrated a 50% reduction in GH receptor (GHR) and IGF-I mRNA on day 5 that was attenuated by TNFbp. However, the abundance of GHR protein was not different in liver from Control, Sepsis, or Sepsis + TNFbp rats. Consequently, a decreased amount of hepatic GHR does not explain the GH-resistant septic state. In CWSV-1 hepatocytes, TNF-alpha had no effect on GHR protein level but inhibited the induction of IGF-I mRNA by GH. Nuclear protein from TNF-treated hepatocytes demonstrated similar levels of phosphorylated signal transducer and activator of transcription-5 (STAT5) and DNA binding relative to controls 5 min after GH treatment. However, both of these parameters were decreased (vs. control) in TNF-treated cells 60 min after GH treatment. Collectively, these results suggest that TNF mediates hepatic GH resistance during sepsis by inhibiting the duration of signaling via the janus kinase-2/STAT5 pathway.

Cachexia in rheumatoid arthritis

Rheumatoid arthritis is a debilitating, chronic, systemic, autoimmune disease of unknown etiology that causes destruction of joint cartilage and bone. It generally occurs between the fourth and sixth decades of life, and affects two to three times more women than men. It is characterized by joint stiffness, pain, and swelling, and is accompanied by a loss of body cell mass. This loss of cell mass, known as rheumatoid cachexia, predominates in skeletal muscle, but also occurs in the viscera and immune system. Thus, rheumatoid cachexia leads to muscle weakness and a loss of functional capacity, and is believed to accelerate morbidity and mortality in rheumatoid arthritis. Currently there is no established mechanism for rheumatoid cachexia, but it is accompanied by elevated resting energy expenditure, accelerated whole-body protein catabolism, and excess production of the inflammatory cytokines, tumor necrosis factor-alpha and interleukin-1beta. Tumor necrosis factor-alpha is probably the central mediator of muscle wasting in rheumatoid arthritis, and is known to act synergistically with interleukin-1beta to promote cachexia. In general, tumor necrosis factor-alpha and interleukin-1beta are thought to alter the balance between protein degradation and protein synthesis in rheumatoid arthritis to cause muscle wasting. The precise mechanism by which they do this is not known. Reduced peripheral insulin action and low habitual physical activity are important consequences of rheumatoid arthritis, and have also been implicated as mediators of rheumatoid cachexia. Insulin inhibits muscle protein degradation. Consequently, reduced peripheral insulin action in rheumatoid arthritis is thought to be permissive to cytokine-driven muscle loss. The cause of reduced peripheral insulin action in rheumatoid arthritis is not known, but tumor necrosis factor-alpha has been shown to interfere with insulin receptor signaling and is probably an important contributor. Low habitual physical activity has consistently been observed in rheumatoid arthritis and is an important consequence of, and contributor to, muscle wasting. In addition, low physical activity predisposes to fat gain and is believed to precipitate a negative reinforcing cycle of muscle loss, reduced physical function, and fat gain in rheumatoid arthritis, which leads to 'cachectic obesity'. To date, there is no standard treatment for rheumatoid cachexia. However, physical exercise is currently believed to be the most important and clinically relevant countermeasure against rheumatoid cachexia. In general, a combination of skeletal muscle strength training and aerobic exercise is recommended, but must be prescribed with the patient's disease status, overall health, and safety in mind. Future studies should investigate the safety, efficacy, and required dose of anti-cytokine therapy for the treatment of rheumatoid cachexia. In this review, we outline the current definition of rheumatoid cachexia, and discuss the etiology, pathogenesis, and treatment of rheumatoid cachexia.

Lethal weight loss: the focus shifts to signal transduction

A hallmark of life-threatening disease in vertebrates is cachexia, a syndrome of weight loss with progressive erosion of body protein. Tumor necrosis factor (TNF) and other endogenously derived factors are sufficient to mediate the pathophysiology of cachexia in vivo, but the downstream signaling pathways have remained a mystery until recently. Tracey describes the involvement of the stress-activated protein kinase p38 and the transcriptional regulators nuclear factor kappa B and peroxisome proliferator-activated receptor gamma coactivator-1 in causing alterations in myocytes and skeletal muscle physiology. Furthermore, soluble factors including TNF and proteolysis-inducing factor may enhance protein degradation through the ubiquitin-proteosome pathway.

TNF-alpha impairs heart and skeletal muscle protein synthesis by altering translation initiation

This study examined potential mechanisms contributing to the inhibition of protein synthesis in skeletal muscle and heart after administration of tumor necrosis factor (TNF)-alpha. Rats had vascular catheters implanted, and TNF-alpha was infused continuously for 24 h. TNF-alpha decreased in vivo-determined rates of global protein synthesis in gastrocnemius (39%) and heart (25%). The TNF-alpha-induced decrease in protein synthesis in the gastrocnemius involved a reduction in the synthesis of both myofibrillar and sarcoplasmic proteins. To identify potential mechanisms responsible for regulating mRNA translation, we examined several eukaryotic initiation factors (eIFs) and elongation factors (eEFs). TNF-alpha decreased the activity of eIF-2B in muscle (39%) but not in heart. This diminished activity was not caused by a reduction in the content of eIF-2B epsilon or the content and phosphorylation state of eIF-2 alpha. Skeletal muscle and heart from TNF-alpha-treated rats demonstrated 1) an increased binding of the translation repressor 4E-binding protein-1 (4E-BP1) with eIF-4E, 2) a decreased amount of eIF-4E associated with eIF-4G, and 3) a decreased content of the hyperphosphorylated gamma-form of 4E-BP1. In contrast, the infusion of TNF-alpha did not alter the content of eEF-1 alpha or eEF-2, or the phosphorylation state of eEF-2. In summary, these data suggest that TNF-alpha impairs skeletal muscle and heart protein synthesis, at least in part, by decreasing mRNA translational efficiency resulting from an impairment in translation initiation associated with alterations in eIF-4E availability.

Managing cancer-related anorexia/cachexia

Cancer-related anorexia/cachexia (CAC) is a complex phenomenon in which metabolic abnormalities, proinflammatory cytokines produced by the host immune system, circulating tumour-derived catabolic factors, decreased food intake, and probably additional unknown factors, all play different roles. This review examines the mechanisms of CAC and its management. All the potential modalities of intervention from nutritional to pharmacological approaches are included with a clear distinction between unproven, investigational and well established treatments. Among the latter, the progestogens are currently considered the most effective and safest drugs for the management of CAC. Agents currently under investigation for CAC include thalidomide, pentoxifylline and melatonin, which most probably act on cytokine release, and clenbuterol, which acts on muscle mass and to antagonise protein wasting. Our personal experience with the synthetic progestogens megestrol and medroxyprogesterone supports their use as first-line agents. In addition, our work on the potential role of antioxidant agents in counteracting the oxidative stress, which appears to be involved in CAC, shows them to be promising agents when used in combination chemotherapy regimens either alone or with other 'biologics'. There is an ongoing need for quality of life questionnaires which specifically address the most significant symptoms present in patients with CAC.

Effects of dietary supplementation with Yucca schidigera Roezl ex Ortgies and its saponin and non-saponin fractions on rat metabolism

Yucca schidigera Roezl ex Ortgies, family Lillaceae, was fractionated with butan-1-ol to yield a butanol extractable fraction (BE; saponin fraction) and a non-butanol fraction (NBE; non-saponin fraction). Four groups of eight male rats were allowed ad libitum access to diets supplemented with water (control) or 200 mg x kg(-1) total Y. schidigera (TOT) or 200 mg x kg(-1) of each of the fractions (NBE or BE). The effects of dietary supplementation with the fractions and their interactions in TOT were analyzed according to the factorial experimental design by two-way analysis of variance. All three supplementation groups displayed significantly reduced serum urea levels (P < 0.05). The TOT and NBE fractions were found to significantly increase serum insulin levels (P < 0.01) in the absence of any fluctuations in serum glucose levels. Urea cycle enzyme activities, namely, arginase (EC 3.5.3.1) and argininosuccinate lyase (EC 4.3.2.1), were significantly decreased (P < 0.05) in vivo, although no effect was observed in vitro. Both fractions displayed effects, indicating that the active constituents are present in both fractions.

NF-kappaB-induced loss of MyoD messenger RNA: possible role in muscle decay and cachexia

MyoD regulates skeletal muscle differentiation (SMD) and is essential for repair of damaged tissue. The transcription factor nuclear factor kappa B (NF-kappaB) is activated by the cytokine tumor necrosis factor (TNF), a mediator of skeletal muscle wasting in cachexia. Here, the role of NF-kappaB in cytokine-induced muscle degeneration was explored. In differentiating C2C12 myocytes, TNF-induced activation of NF-kappaB inhibited SMD by suppressing MyoD mRNA at the posttranscriptional level. In contrast, in differentiated myotubes, TNF plus interferon-gamma (IFN-gamma) signaling was required for NF-kappaB-dependent down-regulation of MyoD and dysfunction of skeletal myofibers. MyoD mRNA was also down-regulated by TNF and IFN-gamma expression in mouse muscle in vivo. These data elucidate a possible mechanism that may underlie the skeletal muscle decay in cachexia.

Exercise and the immune system: regulation, integration, and adaptation

Stress-induced immunological reactions to exercise have stimulated much research into stress immunology and neuroimmunology. It is suggested that exercise can be employed as a model of temporary immunosuppression that occurs after severe physical stress. The exercise-stress model can be easily manipulated experimentally and allows for the study of interactions between the nervous, the endocrine, and the immune systems. This review focuses on mechanisms underlying exercise-induced immune changes such as neuroendocrinological factors including catecholamines, growth hormone, cortisol, beta-endorphin, and sex steroids. The contribution of a metabolic link between skeletal muscles and the lymphoid system is also reviewed. The mechanisms of exercise-associated muscle damage and the initiation of the inflammatory cytokine cascade are discussed. Given that exercise modulates the immune system in healthy individuals, considerations of the clinical ramifications of exercise in the prevention of diseases for which the immune system has a role is of importance. Accordingly, drawing on the experimental, clinical, and epidemiological literature, we address the interactions between exercise and infectious diseases as well as exercise and neoplasia within the context of both aging and nutrition.

Results of a dose-intense phase 1 study of a combination chemotherapy regimen with cisplatin and epidoxorubicin including medroxyprogesterone acetate and recombinant interleukin-2 in patients with inoperable primary lung cancer

Based on the role of cytokines in the pathogenesis of cancer-related anorexia-cachexia and the ability of progestins, such as medroxyprogesterone acetate, to reduce cytokine production and relieve cancer-related anorexia-cachexia symptoms, the authors designed an open, dose-finding phase I study of a combined chemotherapy regimen (cisplatin [CDDP], epidoxorubicin [EPI]), including recombinant interleukin-2 (IL-2) and medroxyprogesterone acetate for patients with stage IIIB to IV inoperable primary lung cancer. The end points were clinical response and toxicity with definition of dose-limiting toxicity and maximal tolerable dose; relief of cancer-related anorexia-cachexia symptoms; the assessment of patient serum levels of IL-1beta, IL-6, tumor-necrosing factor-alpha (TNF-alpha), and soluble IL-2 receptor (sIL-2R). From March to October 1997, 16 patients (M:F ratio, 14:2; mean age, 60.5 years; age range, 41 to 74 years) were enrolled. All patients were evaluable for toxicity and 14 of them for response. The patients were assigned to increasing dose levels of drugs according to a dose-escalation schedule. The weekly schedule consisted of a combination of CDDP given intravenously on day 1, EPI given intravenously on day 1, 1 g/day medroxyprogesterone acetate given orally on days 1 to 7, and recombinant IL-2 1.8 MIU administered subcutaneously on days 2 to 7 plus 300 microg granulocyte-colony stimulating factor support given subcutaneously on days 2 to 5. Administration of medroxyprogesterone acetate began 1 week before the first cycle. Dose escalation of the drugs was as follows: 30 mg x m2 x week(-1) CDDP and 25 mg x m2 x week(-1) EPI (first level, two patients); 30 mg x m2 x week(-1) CDDP and 33 mg x m2 x week(-1) EPI (second level, 2 patients); 40 mg x m2 x week(-1) CDDP and 33 mg x m2 x week(-1) EPI (third level, 6 patients); and 40 mg x m2 x week(-1) CDDP and 40 mg x m2 x week(-1) EPI (fourth level, 6 patients). Six cycles were planned for each patient. The actual dose intensity delivered was more than 80% of the projected dose intensity of all drugs. After six cycles, clinical response (according to World Health Organization criteria), toxicity (according to World Health Organization criteria), Eastern Cooperative Oncology Group (ECOG) performance status, body weight, appetite, and serum levels of cytokines were evaluated. After six cycles, 9 of 14 patients (64.3%) had partial response, 3 of 14 (21.4%) had stable disease, and 2 of 14 (14.3%) had progressive disease, and the objective response rate was 64.3%. ECOG performance status and body weight did not change significantly after treatment, whereas appetite showed an increase that was of borderline statistical significance. Toxicity was acceptable and only hematologic. Dose-limiting toxicity was established at the fourth dose level; consequently, maximal tolerable dose was assessed at the third dose level. Before treatment, the serum levels of IL-1beta, IL-6, and TNF-alpha were significantly greater in the patients than in healthy persons. The comparison between pretreatment and posttreatment serum values of IL-1beta, IL-6, TNF-alpha, and sIL-2R did not reveal significant differences in the patients. Similar results were obtained when the patients were considered as responders (partial response) or non-responders (stable or progressive disease) to therapy. Only IL-6 serum levels were increased (p = 0.014) after treatment.

Effect of Pseudomonas infection on weight loss, lung mechanics, and cytokines in mice

Poor growth, Pseudomonas aeruginosa endobronchitis, pulmonary inflammation, and decline of lung function are hallmarks of cystic fibrosis (CF), yet the relationship between these features is poorly understood. Because animal models of chronic bronchopulmonary infection with P. aeruginosa used to study pulmonary inflammation in CF have also been associated with weight loss, we sought to determine whether this weight loss was due to the inflammatory process and/or to changes in lung function. P. aeruginosa-laden agarose beads were instilled into the lungs of mice. Weight loss was greatest 3 d after Pseudomonas infection. Infected mice had a rapid though transient rise in absolute neutrophil counts, mTNF-alpha, mIL-1beta, mIL-6, mip-2, and KC in bronchoalveolar lavage fluid. There was no difference in lung resistance or lung compliance measured by body plethysmography between infected and control mice. Weight loss did correlate with the concentration of proinflammatory cytokine levels 3 d after inoculation of mice with Pseudomonas, and body composition analysis revealed loss of skeletal muscle mass. These results suggest that weight loss in P. aeruginosa-infected mice was associated with the inflammatory process and not with altered pulmonary responsiveness. These findings may provide insights into the cause of cachexia and weight loss seen in patients with CF.

Gram-negative bacterial sepsis and the sepsis syndrome

Gram-negative sepsis syndrome is an increasingly common complication in medical and surgical patients. The molecular and cellular mechanisms underlying this dreaded complication are yielding to investigation. These studies have led to a multiplicity of targets for novel therapies. Despite highly promising results in many animal studies, clinical studies have been disappointing.

TNF-binding protein ameliorates inhibition of skeletal muscle protein synthesis during sepsis

We examined the effects of TNF-binding protein (TNFBP) on regulatory mechanisms of muscle protein synthesis during sepsis in four groups of rats: Control; Control+TNFBP; Septic; and Septic+TNFBP. Saline (1. 0 ml) or TNFBP (1 mg/kg, 1.0 ml) was injected daily starting 4 h before the induction of sepsis. The effect of TNFBP on gastrocnemius weight, protein content, and the rate of protein synthesis was examined 5 days later. Sepsis reduced the rate of protein synthesis by 35% relative to controls by depressing translational efficiency. Decreases in protein synthesis were accompanied by similar reductions in protein content and muscle weight. Treatment of septic animals with TNFBP for 5 days prevented the sepsis-induced inhibition of protein synthesis and restored translational efficiency to control values. TNFBP treatment of Control rats for 5 days was without effect on muscle protein content or protein synthesis. We also assessed potential mechanisms regulating translational efficiency. The phosphorylation state of p70(S6) kinase was not altered by sepsis. Sepsis reduced the gastrocnemius content of eukaryotic initiation factor 2Bepsilon (eIF2Bepsilon), but not eIF2alpha. The decrease in eIF2Bepsilon content was prevented by treatment of septic rats with TNFBP. TNFBP ameliorates the sepsis-induced changes in protein metabolism in gastrocnemius, indicating a role for TNF in the septic process. The data suggest that TNF may impair muscle protein synthesis by reducing expression of specific initiation factors during sepsis.

Mouse extensor digitorum longus muscle preparation as a tool in nutrition research: a quantitative comparison to in vivo and cell culture experiments

Incubated restrained and unrestrained extensor digitorum longus (EDL) muscles from adult non-growing mice were evaluated as a tool in non-steady state nutrition experiments. Energy state was determined by nucleotide determinations in muscles. Protein synthesis was estimated by the amount of L-[U-14C]phenylalanine incorporated into proteins, and protein balance was measured by tyrosine release from muscle proteins. Confluent cultured L6 rat muscle cells served as a reference system in steady state without hypoxia being sensitive to growth factors and regulatory peptides at physiologic concentrations. Irrespective of medium composition, incubated EDL muscles remained in negative protein balance, being unrelated to the resting tension of the incubated muscles. Energy-rich phosphates were not restored to normal levels during incubation, but protein synthesis was not attenuated by the decline in energy state. Fractional protein synthesis (0.05-0.15%/h) remained constant for up to 6 h of EDL incubation, and was comparable to protein synthesis in cultured confluent non-proliferating myocytes (0.20-0.30%/h) and to mixed leg muscles measured in vivo (0.10-0.20%/h). Protein synthesis in incubated EDL muscles reflected alterations in muscle peptide formation in vivo following either oral provision of food or parenteral injection of insulin. EDL muscles were sensitive to in vitro exposure to both insulin (60-125 microU/mL) and insulin-like growth factor 1 (IGF-1) (1000 ng/mL). The sensitivity to insulin seemed to be modified by the nutritional state (starved/fed) of the animals before sacrifice. Protein synthesis in EDL muscles was less responsive to serum-containing growth factors (IGF-1, epidermal growth factor [EGF], platelet-derived growth factor [PDGF]) compared to confluent L6 muscle cells, which probably reflected different receptor expression. Our results demonstrate that protein metabolism in incubated unrestrained mouse EDL muscles reflects in vivo protein metabolism.