Anticytokine treatment prevents the increase in the activity of ATP-ubiquitin- and Ca(2+)-dependent proteolytic systems in the muscle of tumour-bearing rats

Pathogenesis of Sarcopenia in Chronic Kidney Disease-The Role of Inflammation, Metabolic Dysregulation, Gut Dysbiosis, and microRNA

Chronic kidney disease (CKD) is a progressive disorder associated with a decline in kidney function. Consequently, patients with advanced stages of CKD require renal replacement therapies, such as dialysis and kidney transplantation. Various conditions lead to the development of CKD, including diabetes mellitus, hypertension, and glomerulonephritis, among others. The disease is associated with metabolic and hormonal dysregulation, including uraemia and hyperparathyroidism, as well as with low-grade systemic inflammation. Altered homeostasis increases the risk of developing severe comorbidities, such as cardiovascular diseases or sarcopenia, which increase mortality. Sarcopenia is defined as a progressive decline in muscle mass and function. However, the precise mechanisms that link CKD and the development of sarcopenia are poorly understood. Knowledge about these linking mechanisms might lead to the introduction of precise treatment strategies that could prevent muscle wasting. This review discusses inflammatory mediators, metabolic and hormonal dysregulation, gut microbiota dysbiosis, and non-coding RNA alterations that could link CKD and sarcopenia.

Evidence for reciprocal network interactions between injured hearts and cancer

Heart failure (HF) and cancer are responsible for 50% of all deaths in middle-aged people. These diseases are tightly linked, which is supported by recent epidemiological studies and case control studies, demonstrating that HF patients have a higher risk to develop cancer such as lung and breast cancer. For HF patients, a one-size-fits-all clinical management strategy is not effective and patient management represents a major economical and clinical burden. Anti-cancer treatments-mediated cardiotoxicity, leading to HF have been extensively studied. However, recent studies showed that even before the initiation of cancer therapy, cancer patients presented impairments in the cardiovascular functions and exercise capacity. Thus, the optimal cardioprotective and surveillance strategies should be applied to cancer patients with pre-existing HF. Recently, preclinical studies addressed the hypothesis that there is bilateral interaction between cardiac injury and cancer development. Understanding of molecular mechanisms of HF-cancer interaction can define the profiles of bilateral signaling networks, and identify the disease-specific biomarkers and possibly therapeutic targets. Here we discuss the shared pathological events, and some treatments of cancer- and HF-mediated risk incidence. Finally, we address the evidences on bilateral connection between cardiac injury (HF and early cardiac remodeling) and cancer through secreted factors (secretoms).

Breakdown of Filamentous Myofibrils by the UPS-Step by Step

Protein degradation maintains cellular integrity by regulating virtually all biological processes, whereas impaired proteolysis perturbs protein quality control, and often leads to human disease. Two major proteolytic systems are responsible for protein breakdown in all cells: autophagy, which facilitates the loss of organelles, protein aggregates, and cell surface proteins; and the ubiquitin-proteasome system (UPS), which promotes degradation of mainly soluble proteins. Recent findings indicate that more complex protein structures, such as filamentous assemblies, which are not accessible to the catalytic core of the proteasome in vitro, can be efficiently degraded by this proteolytic machinery in systemic catabolic states in vivo. Mechanisms that loosen the filamentous structure seem to be activated first, hence increasing the accessibility of protein constituents to the UPS. In this review, we will discuss the mechanisms underlying the disassembly and loss of the intricate insoluble filamentous myofibrils, which are responsible for muscle contraction, and whose degradation by the UPS causes weakness and disability in aging and disease. Several lines of evidence indicate that myofibril breakdown occurs in a strictly ordered and controlled manner, and the function of AAA-ATPases is crucial for their disassembly and loss.

The Redox Balance: A Target for Interventions Against Muscle Wasting in Cancer Cachexia?

Significance: The management of cancer patients is frequently complicated by the occurrence of a complex syndrome known as cachexia. It is mainly characterized by muscle wasting, a condition that associates with enhanced protein breakdown and with negative energy balance. While the mechanisms underlying cachexia have been only partially elucidated, understanding the pathogenesis of muscle wasting in cancer hosts is mandatory to design new targeted therapeutic strategies. Indeed, most of cancer patients will experience cachexia during the course of their disease, and about 25% of cancer-related deaths are due to this syndrome, rather than to the tumor itself. Recent Advances: Compelling evidence suggests that an altered redox homeostasis likely contributes to cancer-induced muscle protein depletion, directly or indirectly activating the intracellular degradative pathways. In addition, oxidative stress impinges on both mitochondrial number and function; the other way round, altered mitochondria lead to enhanced redox imbalance, creating a vicious loop that eventually results in negative energy metabolism. Critical Issues: The present review focuses on the possibility that pharmacological and nonpharmacological strategies able to restore a physiologic redox balance could be useful components of treatment schedules aimed at counteracting cancer-induced muscle wasting. Future Directions: Exercise and the use of exercise mimetic drugs represent the most promising approaches capable of reinforcing the muscle antioxidant defenses of cancer patients. The results from ongoing and new clinical trials are needed to validate the preclinical studies and provide effective therapies for cancer cachexia. Antioxid. Redox Signal. 33, 542-558.

Breast cancer-released exosomes trigger cancer-associated cachexia to promote tumor progression

Cancer-secreted exosomes are emerging mediators of cancer-associated cachexia. Here, we show that miR-155 secreted by breast cancer cells is a potent role on the catabolism of adipocytes and muscle cells through targeting the PPARγ. After cocultivated with mature adipocytes or C2C12, tumour cells exhibit an aggressive phenotype via inducing epithelial-mesenchymal transition while breast cancer-derived exosomes increased catabolism and release the metabolites in adipocytes and muscle cells. In adipocytes, cancer cell-secreted miR-155 promotes beige/brown differentiation and remodel metabolism in resident adipocytes by downregulating the PPARγ expression, but does not significantly affect biological conversion in C2C12. Likewise, propranolol ameliorates tumour exosomes-associated cachectic wasting through upregulating the PPARγ expression. In summary, we have demonstrated that the transfer of miR-155 from exosomes acts as an oncogenic signal reprograming systemic energy metabolism and leading to cancer-associated cachexia in breast cancer.

The Skeletal Muscle as an Active Player Against Cancer Cachexia

The management of cancer patients is frequently complicated by the occurrence of cachexia. This is a complex syndrome that markedly impacts on quality of life as well as on tolerance and response to anticancer treatments. Loss of body weight, wasting of both adipose tissue and skeletal muscle and reduced survival rates are among the main features of cachexia. Skeletal muscle wasting has been shown to depend, mainly at least, on the induction of protein degradation rates above physiological levels. Such hypercatabolic pattern is driven by overactivation of different intracellular proteolytic systems, among which those dependent on ubiquitin-proteasome and autophagy. Selective rather than bulk degradation of altered proteins and organelles was also proposed to occur. Within the picture described above, the muscle is frequently considered a sort of by-stander tissue where external stimuli, directly or indirectly, can poise protein metabolism toward a catabolic setting. By contrast, several observations suggest that the muscle reacts to the wasting drive imposed by cancer growth by activating different compensatory strategies that include anabolic capacity, the activation of autophagy and myogenesis. Even if muscle response is eventually ill-fated, its occurrence supports the idea that in the presence of appropriate treatments the development of cancer-induced wasting might not be an ineluctable event in tumor hosts.

Modulating Metabolism to Improve Cancer-Induced Muscle Wasting

Muscle wasting is one of the main features of cancer cachexia, a multifactorial syndrome frequently occurring in oncologic patients. The onset of cachexia is associated with reduced tolerance and response to antineoplastic treatments, eventually leading to clinical conditions that are not compatible with survival. Among the mechanisms underlying cachexia, protein and energy dysmetabolism play a major role. In this regard, several potential treatments have been proposed, mainly on the basis of promising results obtained in preclinical models. However, at present, no treatment yet reached validation to be used in the clinical practice, although several drugs are currently tested in clinical trials for their ability to improve muscle metabolism in cancer patients. Along this line, the results obtained in both experimental and clinical studies clearly show that cachexia can be effectively approached by a multidirectional strategy targeting nutrition, inflammation, catabolism, and inactivity at the same time. In the present study, approaches aimed to modulate muscle metabolism in cachexia will be reviewed.

Chemotherapy-related cachexia is associated with mitochondrial depletion and the activation of ERK1/2 and p38 MAPKs

Cachexia affects the majority of cancer patients, with currently no effective treatments. Cachexia is defined by increased fatigue and loss of muscle function resulting from muscle and fat depletion. Previous studies suggest that chemotherapy may contribute to cachexia, although the causes responsible for this association are not clear. The purpose of this study was to investigate the mechanism(s) associated with chemotherapy-related effects on body composition and muscle function. Normal mice were administered chemotherapy regimens used for the treatment of colorectal cancer, such as Folfox (5-FU, leucovorin, oxaliplatin) or Folfiri (5-FU, leucovorin, irinotecan) for 5 weeks. The animals that received chemotherapy exhibited concurrent loss of muscle mass and muscle weakness. Consistently with previous findings, muscle wasting was associated with up-regulation of ERK1/2 and p38 MAPKs. No changes in ubiquitin-dependent proteolysis or in the expression of TGFβ-family members were detected. Further, marked decreases in mitochondrial content, associated with abnormalities at the sarcomeric level and with increase in the number of glycolytic fibers were observed in the muscle of mice receiving chemotherapy. Finally, ACVR2B/Fc or PD98059 prevented Folfiri-associated ERK1/2 activation and myofiber atrophy in C2C12 cultures. Our findings demonstrate that chemotherapy promotes MAPK-dependent muscle atrophy as well as mitochondrial depletion and alterations of the sarcomeric units. Therefore, these findings suggest that chemotherapy potentially plays a causative role in the occurrence of muscle loss and weakness. Moreover, the present observations provide a strong rationale for testing ACVR2B/Fc or MEK1 inhibitors in combination with anticancer drugs as novel strategies aimed at preventing chemotherapy-associated muscle atrophy.

Interference with Ca2+-Dependent Proteolysis Does Not Alter the Course of Muscle Wasting in Experimental Cancer Cachexia

Protein hypercatabolism significantly contributes to the onset and progression of muscle wasting in cancer cachexia. In this regard, a major role is played by the ATP-ubiquitin-proteasome-dependent pathway and by autophagy. However, little is known about the relevance of the Ca²⁺-dependent proteolytic system. Since previous results suggested that this pathway is activated in the skeletal muscle of tumor hosts, the present study was aimed to investigate whether inhibition of Ca²⁺-dependent proteases (calpains) may improve cancer-induced muscle wasting. Two experimental models of cancer cachexia were used, namely the AH-130 Yoshida hepatoma and the C26 colon carcinoma. The Ca²⁺-dependent proteolytic system was inhibited by treating the animals with dantrolene or by overexpressing in the muscle calpastatin, the physiologic inhibitor of Ca²⁺-dependent proteases. The results confirm that calpain-1 is overexpressed and calpastatin is reduced in the muscle of rats implanted with the AH-130 hepatoma, and show for the first time that the Ca²⁺-dependent proteolytic system is overactivated also in the C26-bearing mice. Yet, administration of dantrolene, an inhibitor of the Ca²⁺-dependent proteases, did not modify tumor-induced body weight loss and muscle wasting in the AH-130 hosts. Dantrolene was also unable to reduce the enhancement of protein degradation rates occurring in rats bearing the AH-130 hepatoma. Similarly, overexpression of calpastatin in the tibialis muscle of the C26 hosts did not improve muscle wasting at all. These observations suggest that inhibiting a single proteolytic system is not a good strategy to contrast cancer-induced muscle wasting. In this regard, a more general and integrated approach aimed at targeting the catabolic stimuli rather than the proteolytic activity of a single pathway would likely be the most appropriate therapeutic intervention.

Effect of the specific proteasome inhibitor bortezomib on cancer-related muscle wasting

BACKGROUND

Muscle wasting, a prominent feature of cancer cachexia, is mainly caused by sustained protein hypercatabolism. The enhanced muscle protein degradation rates rely on the activity of different proteolytic systems, although the Adenosine triphosphate (ATP)-ubiquitin-proteasome-dependent pathway and autophagy have been shown to play a pivotal role. Bortezomib is a potent reversible and selective proteasome and NF-κB inhibitor approved for the clinical use, which has been shown to be effective in preventing muscle wasting in different catabolic conditions. The aim of the present study has been to investigate whether pharmacological inhibition of proteasome by bortezomib may prevent skeletal muscle wasting in experimental cancer cachexia.

METHODS

Cancer cachexia was induced in rats by intraperitoneal injection of Yoshida AH-130 ascites hepatoma cells and in mice by subcutaneous inoculation of C26 carcinoma cells. Animals were then further randomized to receive bortezomib. The AH-130 hosts were weighted and sacrificed under anaesthesia, on Days 3, 4, 5, and 7 after tumour inoculation, while C26-bearing mice were weighted and sacrificed under anaesthesia 12 days after tumour transplantation. NF-κB and proteasome activation, MuRF1 and atrogin-1 mRNA expression and beclin-1 protein levels were evaluated in the gastrocnemius of controls and AH-130 hosts.

RESULTS

Bortezomib administration in the AH-130 hosts, although able to reduce proteasome and NF-κB DNA-binding activity in the skeletal muscle on Day 7 after tumour transplantation, did not prevent body weight loss and muscle wasting. In addition, bortezomib exerted a transient toxicity, as evidenced by the reduced food intake and by the increase in NF-κB DNA-binding activity in the AH-130 hosts 3 days after tumour transplantation. Beclin-1 protein levels were increased by bortezomib treatment in Day 3 controls but were unchanged on both Days 3 and 7 in the AH-130 hosts, suggesting that an early compensatory induction of autophagy may exist in healthy but not in tumour-bearing animals. Regarding C26-bearing mice, bortezomib did not prevent as well body and muscle weight loss 12 days after tumour implantation.

CONCLUSIONS

The results obtained suggest that proteasome inhibition by bortezomib is not able to prevent muscle wasting in experimental cancer cachexia. Further studies are needed to address the issue whether a different dosage of bortezomib alone or in combination with other drugs modulating different molecular pathways may effectively prevent muscle wasting during cancer cachexia.

Molecular pathways leading to loss of skeletal muscle mass in cancer cachexia--can findings from animal models be translated to humans?

Background

Cachexia is a multi-factorial, systemic syndrome that especially affects patients with cancer of the gastrointestinal tract, and leads to reduced treatment response, survival and quality of life. The most important clinical feature of cachexia is the excessive wasting of skeletal muscle mass. Currently, an effective treatment is still lacking and the search for therapeutic targets continues. Even though a substantial number of animal studies have contributed to a better understanding of the underlying mechanisms of the loss of skeletal muscle mass, subsequent clinical trials of potential new drugs have not yet yielded any effective treatment for cancer cachexia. Therefore, we questioned to which degree findings from animal studies can be translated to humans in clinical practice and research.

Discussion

A substantial amount of animal studies on the molecular mechanisms of muscle wasting in cancer cachexia has been conducted in recent years. This extensive review of the literature showed that most of their observations could not be consistently reproduced in studies on human skeletal muscle samples. However, studies on human material are scarce and limited in patient numbers and homogeneity. Therefore, their results have to be interpreted critically.

Summary

More research is needed on human tissue samples to clarify the signaling pathways that lead to skeletal muscle loss, and to confirm pre-selected drug targets from animal models in clinical trials. In addition, improved diagnostic tools and standardized clinical criteria for cancer cachexia are needed to conduct standardized, randomized controlled trials of potential drug candidates in the future.

Whey-hydrolyzed peptide-enriched immunomodulating diet prevents progression of liver cirrhosis in rats

OBJECTIVE

Liver fibrosis and subsequent cirrhosis is a major cause of death worldwide, but few effective antifibrotic therapies are reported. Whey-hydrolyzed peptide (WHP), a major peptide component of bovine milk, exerts anti-inflammatory effects in experimental models. A WHP-enriched diet is widely used for immunomodulating diets (IMD) in clinical fields. However, the effects of WHP on liver fibrosis remain unknown. The aim of this study was to investigate the antifibrotic effects of WHP in a rat cirrhosis model.

METHODS

Progressive liver fibrosis was induced by repeated intraperitoneal administration of dimethylnitrosamine (DMN) for 3 wk. Rats were fed either a WHP-enriched IMD (WHP group) or a control enteral diet (control group). The degree of liver fibrosis was compared between groups. Hepatocyte-protective effects were examined using hepatocytes isolated from rats fed a WHP diet. Reactive oxygen species and glutathione in liver tissue were investigated in the DMN cirrhosis model.

RESULTS

Macroscopic and microscopic progression of liver fibrosis was remarkably suppressed in the WHP group. Elevated serum levels of liver enzymes and hyaluronic acid, and liver tissue hydroxyproline content were significantly attenuated in the WHP group. Necrotic hepatocyte rates with DMN challenge, isolated from rats fed a WHP-enriched IMD, were significantly lower. In the DMN cirrhosis model, reactive oxygen species were significantly lower, and glutathione was significantly higher in the WHP group's whole liver tissue.

CONCLUSION

A WHP-enriched IMD effectively prevented progression of DMN-induced liver fibrosis in rats via a direct hepatocyte-protective effect and an antioxidant effect through glutathione synthesis.

Autophagic-lysosomal pathway is the main proteolytic system modified in the skeletal muscle of esophageal cancer patients

BACKGROUND

In cancer cachexia, muscle depletion is related to morbidity and mortality. Muscle-wasting mechanisms in cancer patients are not fully understood.

OBJECTIVE

We investigated the involvement of the proteolytic systems (proteasome, autophagic-lysosomal, calpain, and caspase) in muscle wasting during cancer cachexia.

DESIGN

Esophageal cancer patients [n = 14; mean ± SD age: 64.1 ± 6.6 y] and weight-stable control patients undergoing reflux surgery (n = 8; age: 57.5 ± 5.8 y) were included. Enzymatic activities were measured in the vastus lateralis and diaphragm. Protein expressions were also measured in the vastus lateralis of control (n = 7) and cancer (n = 8) patients.

RESULTS

Proteasome, calpain, and caspase 3 activities in the vastus lateralis and diaphragm muscles did not differ between the 2 groups. Cathepsin B and L activities were 90% (± SD) [2.4 ± 0.2 compared with 1.3 ± 0.2 pmol 7-amido-4-methylcoumarin (AMC) · μg protein⁻¹ · min⁻¹; P < 0.001] and 115% (5.3 ± 0.4 compared with 2.5 ± 0.3 pmol AMC · μg protein⁻¹ · min⁻¹; P < 0.001) greater, respectively, in the vastus lateralis of cancer patients than in that of control subjects. We observed (in conjunction with increased lysosomal protease activities) higher microtubule-associated protein 1 light chain 3B-II/I ratios (0.14 ± 0.08 compared with 0.04 ± 0.04) and cathepsin B and L expressions in the vastus lateralis of cancer patients than in that of control subjects (P < 0.05). Protein expression of p62 in the vastus lateralis did not differ between the 2 groups.

CONCLUSIONS

The autophagic-lysosomal pathway in the skeletal muscle of cancer patients was modified, whereas other proteolytic systems were unchanged. These findings suggest involvement of the autophagic-lysosomal proteolytic system during cancer cachexia development in humans.

Motor protein function in skeletal abdominal muscle of cachectic cancer patients

Cachexia presents with ongoing muscle wasting, altering quality of life in cancer patients. Cachexia is a limiting prognostic factor for patient survival and health care costs. Although animal models and human trials have shown mechanisms of motorprotein proteolysis, not much is known about intrinsic changes of muscle functionality in cancer patients suffering from muscle cachexia, and deeper insights into cachexia pathology in humans are needed. To address this question, rectus abdominis muscle samples were collected from several surgical control, non-cachectic and cachectic cancer patients and processed for skinned fibre biomechanics, molecular in vitro motility assays, myosin isoform protein compositions and quantitative ubiquitin polymer protein analysis. In pre-cachectic and cachectic cancer patient samples, maximum force was significantly compromised compared with controls, but showed an unexpected increase in myofibrillar Ca²⁺ sensitivity consistent with a shift from slow to fast myosin isoform expression seen in SDS-PAGE analysis and in vitro motility assays. Force deficit was specific for ‘cancer’, but not linked to presence of cachexia. Interestingly, quantitative ubiquitin immunoassays revealed no major changes in static ubiquitin polymer protein profiles, whether cachexia was present or not and were shown to mirror profiles in control patients. Our study on muscle function in cachectic patients shows that abdominal wall skeletal muscle in cancer cachexia shows signs of weakness that can be partially attributed to intrinsic changes to contractile motorprotein function. On protein levels, static ubiquitin polymeric distributions were unaltered, pointing towards evenly up-regulated ubiquitin protein turnover with respect to ubiquitin conjugation, proteasome degradation and de-ubiquitination.

Cancer cachexia: impact, mechanisms and emerging treatments

Many forms of cancer present with a complex metabolic profile characterised by loss of lean body mass known as cancer cachexia. The physical impact of cachexia contributes to decreased patient quality of life, treatment success and survival due to gross alterations in protein metabolism, increased oxidative stress and systemic inflammation. The psychological impact also contributes to decreased quality of life for both patients and their families. Combination therapies that target multiple pathways, such as eicosapentaenoic acid administered in combination with exercise, appetite stimulants, antioxidants or anti-inflammatories, have potential in the treatment of this complex syndrome and require further development.

Autophagic degradation contributes to muscle wasting in cancer cachexia

Muscle protein wasting in cancer cachexia is a critical problem. The underlying mechanisms are still unclear, although the ubiquitin-proteasome system has been involved in the degradation of bulk myofibrillar proteins. The present work has been aimed to investigate whether autophagic degradation also plays a role in the onset of muscle depletion in cancer-bearing animals and in glucocorticoid-induced atrophy and sarcopenia of aging. The results show that autophagy is induced in muscle in three different models of cancer cachexia and in glucocorticoid-treated mice. In contrast, autophagic degradation in the muscle of sarcopenic animals is impaired but can be reactivated by calorie restriction. These results further demonstrate that different mechanisms are involved in pathologic muscle wasting and that autophagy, either excessive or defective, contributes to the complicated network that leads to muscle atrophy. In this regard, particularly intriguing is the observation that in cancer hosts and tumor necrosis factor α-treated C2C12 myotubes, insulin can only partially blunt autophagy induction. This finding suggests that autophagy is triggered through mechanisms that cannot be circumvented by using classic upstream modulators, prompting us to identify more effective approaches to target this proteolytic system.

The regulation of skeletal muscle protein turnover during the progression of cancer cachexia in the Apc(Min/+) mouse

Muscle wasting that occurs with cancer cachexia is caused by an imbalance in the rates of muscle protein synthesis and degradation. The Apc(Min/+) mouse is a model of colorectal cancer that develops cachexia that is dependent on circulating IL-6. However, the IL-6 regulation of muscle protein turnover during the initiation and progression of cachexia in the Apc(Min/+) mouse is not known. Cachexia progression was studied in Apc(Min/+) mice that were either weight stable (WS) or had initial (≤5%), intermediate (6-19%), or extreme (≥20%) body weight loss. The initiation of cachexia reduced %MPS 19% and a further ∼50% with additional weight loss. Muscle IGF-1 mRNA expression and mTOR targets were suppressed with the progression of body weight loss, while muscle AMPK phosphorylation (Thr 172), AMPK activity, and raptor phosphorylation (Ser 792) were not increased with the initiation of weight loss, but were induced as cachexia progressed. ATP dependent protein degradation increased during the initiation and progression of cachexia. However, ATP independent protein degradation was not increased until cachexia had progressed beyond the initial phase. IL-6 receptor antibody administration prevented body weight loss and suppressed muscle protein degradation, without any effect on muscle %MPS or IGF-1 associated signaling. In summary, the %MPS reduction during the initiation of cachexia is associated with IGF-1/mTOR signaling repression, while muscle AMPK activation and activation of ATP independent protein degradation occur later in the progression of cachexia. IL-6 receptor antibody treatment blocked cachexia progression through the suppression of muscle protein degradation, while not rescuing the suppression of muscle protein synthesis. Attenuation of IL-6 signaling was effective in blocking the progression of cachexia, but not sufficient to reverse the process.

The "parallel pathway": a novel nutritional and metabolic approach to cancer patients

Cancer-associated malnutrition results from a deadly combination of anorexia, which leads to reduced food intake, and derangements of host metabolism inducing body weight loss, and hindering its reversal with nutrient supplementation. Cancer patients often experience both anorexia and weight loss, contributing to the onset of the clinical feature named as anorexia-cachexia syndrome. This condition has a negative impact upon patients' nutritional status. The pathogenesis of the anorexia-cachexia syndrome is multifactorial, and is related to: tumour-derived factors, host-derived factors inducing metabolic derangements, and side effects of anticancer therapies. In addition, the lack of awareness of cancer patients' nutritional issues and status by many oncologists, frequently results in progressive weight loss going undiagnosed until it becomes severe. The critical involvement of host inflammatory response in the development of weight loss, and, in particular, lean body mass depletion, limits the response to the provision of standard nutrition support. A novel nutritional and metabolic approach, named "parallel pathway", has been devised that may help maintain or improve nutritional status, and prevent or delay the onset of cancer cachexia. Such an approach may improve tolerance to aggressive anticancer therapies, and ameliorate the functional capacity and quality of life even in advanced disease stages. The "parallel pathway" implies a multiprofessional and multimodal approach aimed at ensuring early, appropriate and continuous nutritional and metabolic support to cancer patients in any phase of their cancer journey.

Are tumoral factors responsible for host tissue wasting in cancer cachexia?

Both cytokines and tumor factors have been implicated in tissue loss in cancer cachexia. Loss of adipose tissue is most likely due to the tumor (and host) factor zinc-alpha2-glycoprotein because of its direct lipolytic effect, ability to sensitize adipocytes to lipolytic stimuli and increased expression in cachexia. TNF-alpha and the tumor factor proteolysis-inducing factor are the major contenders for skeletal muscle atrophy; both increase protein degradation through the ubiquitin-proteasome pathway and depress protein synthesis through phosphorylation of eukaryotic initiation factor 2 alpha. However, while most studies report proteolysis-inducing factor levels to correlate with the appearance of cachexia, there is some disagreement regarding a correlation between serum levels of TNF-alpha and weight loss. Furthermore, only antagonists to proteolysis inducing factor prevent muscle loss in cancer patients, suggesting that tumor factors are the most important.

Therapeutic potential of proteasome inhibition in Duchenne and Becker muscular dystrophies

Duchenne muscular dystrophy (DMD) and its milder allelic variant, Becker muscular dystrophy (BMD), result from mutations of the dystrophin gene and lead to progressive muscle deterioration. Enhanced activation of proteasomal degradation underlies critical steps in the pathogenesis of the DMD/BMD dystrophic process. Previously, we demonstrated that treatment with the proteasome inhibitor MG-132 rescues the cell membrane localization of dystrophin and the dystrophin glycoprotein complex in mdx mice, a natural genetic mouse model of DMD. The current work aims to thoroughly define the therapeutic potential in dystrophinopathies of Velcade, a drug that selectively blocks the ubiquitin-proteasome pathway. Velcade is particularly intriguing since it has been approved for the treatment of multiple myeloma. Therefore, its side effects in humans have been explored. Velcade effects were analyzed through two independent methodological approaches. First, we administered the drug systemically in mdx mice over a 2-week period. In this system, Velcade restores the membrane expression of dystrophin and dystrophin glycoprotein complex members and improves the dystrophic phenotype. In a second approach, we treated with the compound explants from muscle biopsies of DMD or BMD patients. We show that the inhibition of the proteasome pathway up-regulates dystrophin, alpha-sarcoglycan, and beta-dystroglycan protein levels in explants from BMD patients, whereas it increases the proteins of the dystrophin glycoprotein complex in DMD cases.

The effects of pentoxifylline on skeletal muscle contractility and neuromuscular transmission during hypoxia

OBJECTIVES

The objective of this study was to investigate the effects of pentoxifylline (PTX), a drug that is mainly used for indications related to tissue hypoxia, on hypoxia-induced inhibition of skeletal muscle contractility and neuromuscular transmission in mice. We hypothesized that chronic PTX treatment alters skeletal muscle contractility and hypoxia-induced dysfunction.

MATERIALS AND METHODS

Mice were treated with 50 mg/kg PTX or saline intraperitoneally for a week. Following ether anesthesia, diaphragm muscles were removed; isometric muscle contractions and action potentials were recorded. Time to reach neuromuscular blockade and the rate of recovery of muscle contractility were assessed during hypoxia and re-oxygenation.

RESULTS

The PTX group displayed 90% greater twitch amplitudes (P < 0.01). Hypoxia depressed twitch contractions and caused neuromuscular blockade in both groups. However, neuromuscular blockade occurred earlier in PTX-treated animals (P < 0.05). Muscle contractures developed during hypoxia were more pronounced in the PTX group (P < 0.05). Re-oxygenation reduced contracture and indirect muscle contractions resumed. The rate of recovery of contractions was faster (P < 0.05) and the amplitude of contractions was greater (P < 0.01) in the PTX group. PTX treatment increased amplitude (P < 0.05) and shortened action potential (P < 0.05) without altering resting membrane potential, excitation threshold, and neurotransmitter release.

CONCLUSION

Chronic PTX treatment increases diaphragm contractility, but amplifies hypoxia-induced contractile dysfunction in mice. These results may implicate important clinical consequences for clinical usage of PTX in hypoxia-related conditions.

Anti-TNF treatment reduces rat skeletal muscle wasting in monocrotaline-induced cardiac cachexia

The aim was to explore efficacy of tumor necrosis factor (TNF) inhibitors in attenuating increases in anorexia and ubiquitin proteasome pathway transcripts in cardiac cachexia, a potentially lethal condition that responds poorly to current treatments. Cardiac cachexia was rapidly induced with monocrotaline in Sprague-Dawley rats. Either soluble TNF receptor-1 or the general inhibitor of TNF production, pentoxifylline, was given to diminish TNF action on the first indication of cachexia. Animals were anesthetized with a ketamine-xylazine-acepromazine cocktail, and then skeletal muscles were removed for subsequent measurements including ubiquitin proteasome pathway transcripts and Western blots. Both soluble TNF receptor-1 and pentoxifylline attenuated losses in both body and skeletal muscle masses and also reduced increases in selected ubiquitin proteasome pathway transcripts. The action of soluble TNF receptor-1 was partly through reversal of reduced food consumption, while the effects of pentoxifylline were independent of food intake. Here we demonstrate, for the first time, that attenuation of anorexia by soluble TNF receptor-1 treatment in monocrotaline-induced cardiac cachexia is responsible for attenuating increases in some ubiquitin proteasome pathway transcripts as well as preserving body mass and attenuating loss of skeletal muscle mass.

Cardiac cachexia: a systematic overview

Cardiac cachexia as a terminal stage of chronic heart failure carries a poor prognosis. The definition of this clinical syndrome has been a matter of debate in recent years. This review describes the ongoing discussion about this issue and the complex pathophysiology of cardiac cachexia and chronic heart failure with particular focus on immunological, metabolic, and hormonal aspects at the intracellular and extracellular level. These include regulators such as neuropeptide Y, leptin, melanocortins, ghrelin, growth hormone, and insulin. The regulation of feeding is discussed as are nutritional aspects in the treatment of the disease. The mechanisms of wasting in different body compartments are described. Moreover, we discuss several therapeutic approaches. These include appetite stimulants like megestrol acetate, medroxyprogesterone acetate, and cannabinoids. Other drug classes of interest comprise angiotensin-converting enzyme inhibitors, beta-blockers, anabolic steroids, beta-adrenergic agonists, anti-inflammatory substances, statins, thalidomide, proteasome inhibitors, and pentoxifylline.

Positive and negative modulation of peptidases by pro-inflammatory cytokines

The capacity of pro-inflammatory cytokines to modulate proteolysis was analyzed by liquid chromatography using human fibroblasts as cell model and enzyme source, and the immunodominant epitope gp100(280-288) (YLEPGPVTA) as substrate. The measurements made after fibroblast pre-incubation with either IL-1, TNF, or IL-6 plus its soluble receptors have been compared with those made with un-stimulated fibroblasts. The results obtained suggest an uneven association of cytokine treatment with substrate degradation, and with a prevailingly positive - but also negative - association with release of smaller peptides and free amino acids. Data obtained by separately measuring these two groups of by-products indicate that, after IL-1 cell pre-treatment, the velocity of formation of both groups of by-products increased, resulting in a net increase of substrate degradation. After TNF and IL-6 pre-treatment, the increase of one group was compensated by a decrease of the other group; specifically, the compensation was only partial for TNF, and overall substrate hydrolysis increased. In the case of IL-6, the increase of free amino acids was almost exactly compensated by a reduction of peptidic by-products, resulting in a negligible increase of substrate hydrolysis. In addition, the existence of reaction time-related modifications in the apparent velocity of substrate degradation and formation of by-products, allows hypothesizing different effects of cytokines on the enzymes degrading the substrate with different time constants. Taken together, these data can be interpreted as indicating different, positive and negative, effects of the three cytokines on the individual enzymes expressed by fibroblasts and capable of degrading peptidic substrates.

The biological mechanisms of cancer-related skeletal muscle wasting: the role of progressive resistance exercise

Cancer results in perturbations in skeletal muscle protein metabolism leading to muscle wasting. Although severe wasting is seen primarily in persons with advanced malignancies, a number of cancer patients show some degree of wasting at presentation. Although cancer-related skeletal muscle wasting is attributable, in part, to decreased muscle protein synthesis, its primary cause appears to be increased muscle protein degradation. Although several proteolytic systems may be involved, compelling evidence suggests that the major system responsible for skeletal muscle protein degradation in cancer is the ATP-dependent ubiquitin- proteasome system. Other contributing factors include proinflammatory cytokines and the tumor-released proteolysis-inducing factor. Decreased physical activity and decreased nutritional intake may also play a role. Cancer-related skeletal muscle wasting is clinically significant because of its profound effects on functional outcomes and quality of life. Nevertheless, no specific interventions have proved to be effective in preventing or reversing the problem. Interventions such as nutritional supplementation and appetite stimulants are only partially helpful. A nonpharmacologic intervention that may attenuate cancer-related skeletal muscle wasting is progressive resistance exercise training (PRT). PRT is a potent stimulus of growth in muscle mass and strength. PRT may attenuate cancer-related skeletal muscle wasting by downregulating the activity of proinflammatory cytokines and by increasing the phosphorylation of intramuscular amino acid-signaling molecules. This article discusses several cancer-related skeletal muscle wasting mechanisms and proposes how PRT might attenuate muscle wasting by counteracting some of these mechanisms.

Calpain activity and muscle wasting in sepsis

Muscle wasting in sepsis reflects activation of multiple proteolytic mechanisms, including lyosomal and ubiquitin-proteasome-dependent protein breakdown. Recent studies suggest that activation of the calpain system also plays an important role in sepsis-induced muscle wasting. Perhaps the most important consequence of calpain activation in skeletal muscle during sepsis is disruption of the sarcomere, allowing for the release of myofilaments (including actin and myosin) that are subsequently ubiquitinated and degraded by the 26S proteasome. Other important consequences of calpain activation that may contribute to muscle wasting during sepsis include degradation of certain transcription factors and nuclear cofactors, activation of the 26S proteasome, and inhibition of Akt activity, allowing for downstream activation of Foxo transcription factors and GSK-3beta. The role of calpain activation in sepsis-induced muscle wasting suggests that the calpain system may be a therapeutic target in the prevention and treatment of muscle wasting during sepsis. Furthermore, because calpain activation may also be involved in muscle wasting caused by other conditions, including different muscular dystrophies and cancer, calpain inhibitors may be beneficial not only in the treatment of sepsis-induced muscle wasting but in other conditions causing muscle atrophy as well.

Muscle wasting and interleukin-6-induced atrogin-I expression in the cachectic Apc ( Min/+ ) mouse

Interleukin-6 (IL-6) is necessary for cachexia in Apc ( Min/+ ) mice, but the mechanisms inducing this myofiber wasting have not been established. The purpose of this study was to examine gastrocnemius muscle wasting in the Apc ( Min/+ ) mouse and to determine IL-6 regulated mechanisms contributing to muscle loss. Gastrocnemius type IIB mean fiber cross-sectional area (CSA) from Apc ( Min/+ ) mice decreased 32% between 13 and 22 weeks of age. Apc ( Min/+ ) mice lacking IL-6 did not have type IIB fiber atrophy, while overexpression of circulating IL-6 exacerbated the loss of type IIB fiber CSA in Apc ( Min/+ ) mice. Muscle Atrogin-I mRNA expression was induced at least ninefold at 18 and 22 weeks of age compared to 13-week-old mice. Atrogin-I gene expression was also induced by overexpression of circulating IL-6. These data suggest that high circulating IL-6 levels induce type IIB fiber CSA loss in Apc ( Min/+ ) mice, and circulating IL-6 is sufficient to regulate Atrogin-I gene expression in cachectic mice.

The cytokine basis of cachexia and its treatment: are they ready for prime time?

Cachexia is a hypercatabolic condition that is often associated with the terminal stages of many diseases, in which the patient's resting metabolic rate is high and loss of muscle and fat tissue mass occur at an alarming rate. The patient also usually has concurrent anorexia, amplifying the wasting syndrome that is cachexia. The greater the extent of cachexia (regardless of underlying disease), the worse the prognosis. Efforts to treat cachexia over the years have fallen short of satisfactorily reversing the wasting syndrome. This article reviews the pathophysiology of cachexia, enumerating the different pro-inflammatory cytokines that contribute to the syndrome and attempting to illustrate their interwoven pathways. We also review the different treatments that have been explored, as well as the recent literature addressing the use of anti-cytokine therapy to treat cachexia.

Muscle myostatin signalling is enhanced in experimental cancer cachexia

BACKGROUND/AIMS

Myostatin belongs to the transforming growth factor-beta superfamily and negatively regulates skeletal muscle mass. Its deletion induces muscle overgrowth, while, on the contrary, its overexpression or systemic administration cause muscle atrophy. The present study was aimed at investigating whether muscle depletion as occurring in an experimental model of cancer cachexia, the rat bearing the Yoshida AH-130 hepatoma, is associated with modulations of myostatin signalling and whether the cytokine tumour necrosis factor-alpha may be relevant in this regard.

MATERIALS AND METHODS

Protein levels of myostatin, follistatin (myostatin endogenous inhibitor) and the activin receptor type IIB have been evaluated in the gastrocnemius of tumour-bearing rats by Western blotting. Circulating myostatin and follistatin in tumour hosts were evaluated by immunoprecipitation, while the DNA-binding activity of the SMAD transcription factors was determined by electrophoretic-mobility shift assay.

RESULTS

In day 4 tumour hosts muscle myostatin levels were comparable to controls, yet follistatin was reduced, and SMAD DNA-binding activity was enhanced. At day 7, both myostatin and follistatin increased in tumour bearers, while SMAD DNA-binding activity was unchanged. To investigate whether tumour necrosis factor-alpha contributed to induce such changes, rats were administered pentoxifylline, an inhibitor of tumour necrosis factor-alpha synthesis that partially corrects muscle depletion in tumour-bearing rats. The drug reduced both myostatin expression and SMAD DNA-binding activity in day 4 tumour hosts and up-regulated follistatin at day 7.

CONCLUSIONS

These observations suggest that myostatin pathway should be regarded as a potential therapeutic target in cancer cachexia.

Novel treatments for cancer cachexia

Cancer cachexia is a debilitating and life-threatening syndrome characterised by anorexia, body weight loss, loss of adipose tissue and skeletal muscle, and accounts for > or = 20% of deaths in neoplastic patients. Cancer cachexia significantly impairs quality of life and response to antineoplastic therapies, increasing the morbidity and mortality of cancer patients. Muscle wasting is the most important phenotypic feature of cancer cachexia and the principle cause of function impairment, fatigue and respiratory complications, and is mainly related to a hyperactivation of muscle proteolytic pathways. Existing therapeutic strategies have proven to be only partially effective. In the last decade, the correction of anorexia, the inhibition of catabolic processes and the stimulation of anabolic pathways in muscle has been attempted pharmacologically, giving encouraging results in animal models and through preliminary clinical trials.

Cyclic adenosine monophosphate-phosphodiesterase inhibitors reduce skeletal muscle protein catabolism in septic rats

We have previously shown that catecholamines exert an inhibitory effect on muscle protein degradation through a pathway involving the cyclic adenosine monophosphate (cAMP) cascade in normal rats. In the present work, we investigated in vivo and in vitro effects of cAMP-phosphodiesterase inhibitors on protein metabolism in skeletal muscle from rats submitted to a model of acute sepsis. The in vivo muscle protein metabolism was evaluated indirectly by measurements of the tyrosine interstitial concentration using microdialysis. Muscle blood flow (MBF) was monitored by ethanol perfusion technique. Sepsis was induced by cecal ligation and puncture and resulted in lactate acidosis, hypotension, and reduction in MBF (-30%; P < 0.05). Three-hour septic rats showed an increase in muscle interstitial tyrosine concentration (approximately 150%), in arterial plasma tyrosine levels (approximately 50%), and in interstitial-arterial tyrosine concentration difference (approximately 200%; P < 0.05). Pentoxifylline (50 mg/kg of body weight, i.v.) infusion during 1 h after cecal ligation and puncture prevented the tumor necrosis factor alpha increase and significantly reduced by 50% (P < 0.05) the interstitial-arterial tyrosine difference concentration. In situ perfusion with isobutylmethylxanthine (IBMX; 10(-3) M) reduced by 40% (P < 0.05) the muscle interstitial tyrosine in both sham-operated and septic rats. Neither pentoxifylline nor IBMX altered MBF. The addition of IBMX (10(-3) M) to the incubation medium increased (P < 0.05) muscle cAMP levels and reduced proteolysis in both groups. The in vitro addition of H89, a protein kinase A inhibitor, completely blocked the antiproteolytic effect of IBMX. The data show that activation of cAMP-dependent pathways and protein kinase A reduces muscle protein catabolism during basal and septic state.

Modulations of the calcineurin/NF-AT pathway in skeletal muscle atrophy

Calcineurin has been proposed to regulate skeletal muscle hypertrophy, while its relevance to the pathogenesis of muscle atrophy is unknown. The present study was aimed to investigate if perturbations of the calcineurin pathway may be involved in causing skeletal muscle atrophy in two different experimental conditions: cancer cachexia (rats bearing the AH-130 hepatoma), and hyperglycemia (rats treated with streptozotocin). Calcineurin expression in the gastrocnemius was comparable between tumor hosts and controls. By contrast, besides unchanged calcineurin mRNA levels, those of protein were lower in diabetic animals than in controls. The DNA-binding activity of the transcription factors NF-AT and MEF-2 was analysed as an indirect measure of calcineurin activity in vivo. The nuclear translocation of both factors was similar in tumor hosts and controls. Consistently with the reduced calcineurin protein levels, NF-AT DNA-binding activity significantly decreased in the gastrocnemius of diabetic rats compared to controls. Finally, muscle wasting correction afforded in the AH-130 hosts by pentoxifylline or interleukin-15 was not paralleled by changes of calcineurin mRNA levels, while treatment of diabetic animals with dehydroepiandrosterone partially prevented calcineurin down-regulation. These results suggest that modulations of calcineurin activity may be involved in the pathogenesis of muscle wasting in diabetes though not in cancer cachexia.

Energy homeostasis and cachexia in chronic kidney disease

Loss of protein stores, presenting as clinical wasting, is reported to have a prevalence of 30-60% and is an important risk factor for mortality in chronic kidney disease (CKD) patients. There is debate as to whether the clinical wasting in CKD patients represents malnutrition or cachexia. Malnutrition results from inadequate intake of nutrients, despite a good appetite, and manifests as weight loss associated with adaptive metabolic responses such as decreased basic metabolic rate and preservation of lean body mass at the expense of fat mass. Furthermore, the abnormalities in malnutrition can usually be overcome simply by supplying more food or altering the composition of the diet. In contrast, cachexia is characterized by maladaptive responses such as anorexia, elevated basic metabolic rate, wasting of lean body tissue, and underutilization of fat tissue for energy. Diet supplementation and intradialytic parenteral nutrition have not been successful in reversing cachexia in CKD. The etiology of cachexia in CKD is complex and multifactorial. Two major factors causing muscle wasting in uremia are acidosis and decreased insulin responses. Inflammation secondary to cytokines may also play a significant role. The hypoalbuminemia of CKD patients is principally associated with inflammation and not changes in food intake. There is also recent evidence that hypothalamic neuropeptides may be important in the downstream signaling of cytokines in the pathogenesis of cachexia in CKD. Elevated circulating levels of cytokines, such as leptin, may be an important cause of uremia-associated cachexia via signaling through the central melanocortin system. Further research into the molecular pathways leading to cachexia may lead to novel therapeutic therapy for this devastating and potentially fatal complication of CKD.

Cancer cachexia: it's time for more clinical trials

Cancer cachexia (CC) is a multifactorial paraneoplastic syndrome characterized by anorexia, body weight loss, loss of adipose tissue and skeletal muscle, accounting for at least 20% of deaths in neoplastic patients. CC significantly impairs quality of life and response to anti-neoplastic therapies, increasing morbidity and mortality of cancer patients. Muscle wasting is the most important phenotypic feature of CC and the principal cause of function impairment, fatigue and respiratory complications, mainly related to a hyperactivation of muscle proteolytic pathways. Most current therapeutic strategies to counteract CC have proven to be only partially effective. In the last decade, the correction of anorexia, the inhibition of catabolic processes and the stimulation of anabolic pathways in muscle have been attempted pharmacologically with encouraging results in animal models and through preliminary clinical trials. However, data in the clinical setting are still scanty and non definitive. It is time to start prospective, randomized, controlled trials to evaluate which drugs are effective in counteracting the loss of lean of muscle mass and in improving nutritional status and quality of life in patients affected by cancer-related cachexia.

Inflammatory factors in age-related muscle wasting

PURPOSE OF REVIEW

This review focuses on recent evidence pointing to the importance of inflammatory factors in the onset and progression of age-related muscle wasting, also known as sarcopenia, and discusses critical areas of uncertainty within the literature that require further development in order to identify novel therapeutics.

RECENT FINDINGS

The research performed in recent years has only strengthened the evidence that inflammatory factors are important in the progression of a catabolic state in muscle wasting. Interactions among various inflammatory cytokines and anabolic factors have been observed, with the balance skewed in favor of catabolism in sarcopenia. Adiposity appears to play an important role in the inflammatory process and possibly the onset of sarcopenia. Inflammatory factors are likely to play an important role in the increased activity of the ubiquitin proteasome, which we argue should be a primary target for the development of molecular therapeutics.

SUMMARY

Future research will need to delve into the molecular interactions that link inflammatory factors and the imbalance between muscle anabolism and catabolism that develops with aging. Identification of specific pathways of importance to sarcopenia will have relevance to a wide range of wasting disorders.

IGF-1 is downregulated in experimental cancer cachexia

Cancer cachexia is characterized by skeletal muscle wasting that is mainly supported by hypercatabolism. Muscle atrophy has been suggested to depend on impaired IGF-1 signal transduction pathway. The present study has been aimed at investigating the IGF-1 system in rats bearing the AH-130 hepatoma, a well-characterized model of cachexia. IGF-1 mRNA expression in the gastrocnemius of tumor hosts progressively decreases to ∼50% of controls. By contrast, both IGF-1 receptor and insulin receptor mRNA levels increase in day 7 AH-130 hosts. IGF-1 and insulin circulating levels, as well as IGF-1 expression in the liver, are reduced. Muscle wasting in the AH-130 bearers is associated with hyperactivation of the ubiquitin-proteasome system. Consistently, the mRNA levels of ubiquitin and of the ubiquitin ligases atrogin-1 and MuRF1 are significantly increased in the gastrocnemius of day 7 AH-130 hosts. Exogenous IGF-1 administered to tumor bearers does not prevent cachexia. IGF-1 mRNA levels also have been evaluated in the gastrocnemius of AH-130 hosts treated with pentoxifylline, an inhibitor of TNF-α synthesis, alone or combined with formoterol, a β2-adrenergic agonist. Both treatments partially correct muscle atrophy without modifying IGF-1 and atrogin-1 mRNA levels, whereas MuRF1 hyperexpression is reduced by the combination of pentoxifylline with formoterol. These results demonstrate for the first time that the IGF-1 system is downregulated in cancer cachexia, although the underlying mechanism remains unknown. Moreover, no simple relation linking IGF-1 and/or atrogin-1 mRNA levels and muscle atrophy could be observed in these experimental conditions. Further studies are thus needed to clarify both issues.

Effects of tumor necrosis factor-alpha on the 26S proteasome and 19S regulator in skeletal muscle of severely scalded mice

The negative nitrogen balance after burns is an important factor in the rehabilitation and treatment of burn injury. It is known that the 26s protesome system plays a key role in the protein breakdown of skeletal muscle in some pathological situations, including burns, although the mechanism of which remains poorly understood. The present study surveyed the effect of tumor necrosis factor-alpha (TNF-alpha) on the 26S proteasome sysytem after burn injury, which is thought to be principally responsible for the proteolysis. The means of immuno-precipitation-deduction and enzyme-linked immunosorbent assay were used to test the change of activities and contents of 26S proteasome and 19S regulator in skeletal muscle of mice inflicted with 30% TBSA third-degree burns. The genes expression of 19S regulator's subunits Psmc2, Psmc5, Psmd1, and Psmd2 were examined by the use of reverse-transcription polymerase chain reaction. The results showed that TNF-alpha and burn can markedly increased the activities and contents of 26S proteasome and 19S regulator in mice skeletal muscle. In addition, the expression levels of the 19S regulator's subunits also were remarkably increased. The monoclonal antibody to TNF-alpha obviously can diminish the increment of the activities and contents of 26S proteasome and 19S regulator as much as the expression levels of the 19S regulator's subunits. The results suggested that TNF-alpha can activate the 26S proteasome system in skeletal muscle, thus enhancing the degradation of protein, which is associated with the development of negative nitrogen balance after scald.

The AP-1/CJUN signaling cascade is involved in muscle differentiation: Implications in muscle wasting during cancer cachexia

The aim of the present study was to investigate a possible role of the AP-1 signaling cascade in the process of wasting associated with cancer cachexia at the level of skeletal muscle. The injection of virus containing the TAM67 protein (a blocker of the AP-1 protein) to the gastrocnemius muscle of tumour-bearing rats resulted in a significant recovery of the muscle mass (which is dramatically reduced as a result of tumour burden), therefore suggesting that AP-1 is certainly involved in the signaling associated with muscle protein accretion. In conclusion, the gene therapy approach presented here clearly suggests an important role for AP-1 in muscle signaling during catabolic states.

Skeletal muscle apoptosis is not increased in gastric cancer patients with mild–moderate weight loss

Numerous experimental and clinical studies have shown that skeletal muscle apoptotis may increase in wasting conditions and suggest that apoptosis might contribute to the loss of lean body mass. Data in cancer patients are still lacking. The present study aimed at verifying whether apoptosis was enhanced in the skeletal muscle of 16 patients with gastric cancer with respect to controls. A biopsy specimen was obtained from the rectus abdominis muscle. The occurrence of apoptosis in muscle biopsies was determined morphologically by the fluorescent transferase-mediated dUTP nick end labeling assay and by immunohistochemistry for caspase-3 and caspase-1. Mean weight loss was 6+/-2% in cancer patients and 0.5+/-0.1% in controls (p<0.0001). Serum albumin levels (g/dL) were 3.7+/-0.3 in cancer patients and 4.1+/-0.2 in controls (p<0.05). The percentage of apoptotic myonuclei was similar in cancer patients and in controls (1.5+/-0.3 versus 1.4+/-0.2, respectively; p=ns), in gastric cancer patients with mild (1.6+/-0.4) or moderate-severe weight loss (1.4+/-0.5) (p=ns), and in the different stages of disease (stages I-II: 1.5+/-0.7; stage III: 1.3+/-0.4; stage IV: 1.6+/-0.3; p=ns). By immunohistochemistry, caspase-1 and caspase-3 positive fibers were absent in controls and in neoplastic patients. Poly-ADP-ribosyl polymerase, a typical caspase-3 substrate whose processing is indicative of caspase-3 activation, was not cleaved in muscle biopsies of cancer patients. These data suggest that skeletal muscle apoptosis is not increased in neoplastic patients with mild-moderate weight loss and argue against the hypotheses that caspase-3 activation might be an essential step of myofibrillar proteolysis in cancer-related muscle wasting.

Myostatin induces cachexia by activating the ubiquitin proteolytic system through an NF-κB-independent, FoxO1-dependent mechanism

Myostatin, a transforming growth factor-beta (TGF-beta) super-family member, has been well characterized as a negative regulator of muscle growth and development. Myostatin has been implicated in several forms of muscle wasting including the severe cachexia observed as a result of conditions such as AIDS and liver cirrhosis. Here we show that Myostatin induces cachexia by a mechanism independent of NF-kappaB. Myostatin treatment resulted in a reduction in both myotube number and size in vitro, as well as a loss in body mass in vivo. Furthermore, the expression of the myogenic genes myoD and pax3 was reduced, while NF-kappaB (the p65 subunit) localization and expression remained unchanged. In addition, promoter analysis has confirmed Myostatin inhibition of myoD and pax3. An increase in the expression of genes involved in ubiquitin-mediated proteolysis is observed during many forms of muscle wasting. Hence we analyzed the effect of Myostatin treatment on proteolytic gene expression. The ubiquitin associated genes atrogin-1, MuRF-1, and E214k were upregulated following Myostatin treatment. We analyzed how Myostatin may be signaling to induce cachexia. Myostatin signaling reversed the IGF-1/PI3K/AKT hypertrophy pathway by inhibiting AKT phosphorylation thereby increasing the levels of active FoxO1, allowing for increased expression of atrophy-related genes. Therefore, our results suggest that Myostatin induces cachexia through an NF-kappaB-independent mechanism. Furthermore, increased Myostatin levels appear to antagonize hypertrophy signaling through regulation of the AKT-FoxO1 pathway.

Ca(2+)-dependent proteolysis in muscle wasting

Skeletal muscle wasting is a prominent feature of cachexia, a complex systemic syndrome that frequently complicates chronic diseases such as inflammatory and autoimmune disorders, cancer and AIDS. Muscle wasting may also develop as a manifestation of primary or neurogenic muscular disorders. It is now generally accepted that muscle depletion mainly arises from increased protein catabolism. The ubiquitin-proteasome system is believed to be the major proteolytic machinery in charge of such protein breakdown, yet there is evidence suggesting that Ca(2+)-dependent system, lysosomes and, in some conditions at least, even caspases are involved as well. The role of Ca(2+)-dependent proteolysis in skeletal muscle wasting is reviewed in the present paper. This system relies on the activity of calpains, a family of Ca(2+)-dependent cysteine proteases, whose regulation is complex and not completely elucidated. Modulations of Ca(2+)-dependent proteolysis have been associated with muscle protein depletion in various pathological contexts and particularly with muscle dystrophies. Calpains can only perform a limited proteolysis of their substrates, however they may play a critical role in initiating the breakdown of myofibrillar protein, by releasing molecules that become suitable for further degradation by proteasomes. Some evidence would also support a role for lysosomes and caspases in muscle wasting. Thus it cannot be excluded that different intracellular proteolytic systems may coordinately concur in shifting muscle protein turnover towards excess catabolism. Many different signals have been proposed as potentially involved in triggering the enhanced protein breakdown that underlies muscle wasting. How they are transduced to initiate the hypercatabolic response and to activate the proteolytic pathways remains largely unknown, however.

Prevention and treatment of cancer cachexia: new insights into an old problem

Cancer cachexia (CC) is a multifactorial paraneoplastic syndrome characterized by anorexia, body weight loss, loss of adipose tissue and skeletal muscle, accounting for at least 20% of deaths in neoplastic patients. CC significantly impairs quality of life and response to anti-neoplastic therapies, increasing morbidity and mortality of cancer patients. Muscle wasting is the most important phenotypic feature of CC and the principal cause of function impairment, fatigue and respiratory complications, mainly related to a hyperactivation of muscle proteolytic pathways. Most therapeutic strategies to CC have proven to be only partially effective . The inhibition of catabolic processes in muscle has been attempted pharmacologically with encouraging results in animal models. However, data in the clinical setting are still scanty and contradictory. Stimulation of muscle anabolism could represent a promising and valid therapeutic alternative for cancer-related muscle wasting. This goal may be currently achieved with the conventional, short-acting and adverse side effect-rich anabolic steroids. Insulin-like growth factor-1 (IGF-1) plays a critical role in muscle homeostasis, hypertrophy and regeneration. IGF-1 overexpression at the muscular level by gene therapy reverses muscle hypotrophy secondary to catabolic conditions and induces muscle hypertrophy increasing muscle mass and strength. This allows the speculation that this approach could also prove effective in modulating cancer-induced muscle wasting, while avoiding the potentially hazardous side effects of systemic IGF-1 administration. The present review will focus on the potential biochemical and molecular targets of CC therapy, and will define the rationale for a novel, gene therapy-based approach.

Molecular pathways leading to cancer cachexia

Loss of body weight in cancer patients strongly influences morbidity and mortality. Recent studies have suggested that both tumor and host factors play a major role in tissue catabolism in cachexia, leading to upregulation of degradative pathways in both skeletal muscle and adipose tissue.

Is bortezomib, a proteasome inhibitor, effective in treating cancer-associated weight loss? Preliminary results from the North Central Cancer Treatment Group

BACKGROUND

Weight loss predicts a poor prognosis for cancer patients, and previous studies have implicated the ubiquitin-proteasome pathway as a major mediator of cancer-associated weight loss. The recent emergence of bortezomib, a proteasome inhibitor, now allows testing on whether proteasome inhibition is effective therapy for cancer-associated weight loss.

METHODS

This study represents a subanalysis from two prior antineoplastic trials in patients with adenocarcinoma of the pancreas. The first included 46 patients with metastatic pancreatic cancer who were treated with single-agent bortezomib (intravenous doses of 1.5 or 1.3 mg/m2 on days 1, 4, 8, and 11 of a 21-day cycle). The second included 42 patients with pancreatic cancer treated with single-agent octreotide (200 or 500 microg subcutaneously three times a day). The FACT-C questionnaire provided appetite and related data for bortezomib-treated patients. Serial weight data were available from both trials. Such data from the octreotide trial were utilized for comparative purposes because the latter holds no track record in treating cancer-associated weight loss.

RESULTS

Bortezomib- and octreotide-treated patients were roughly comparable at baseline, and neither agent demonstrated notable antineoplastic effects. FACT-C data suggested stable appetite, but high patient dropout rates invite caution in interpretation. For example, in response to "I have a good appetite," mean scores for bortezomib-treated patients were 45 at baseline (n=42), 45 at the end of cycle 1 (n=26), and 44 at the end of cycle 2 (n=9). In contrast, weight data appeared more straightforward to interpret: direct comparisons of mean change in weight from baseline between bortezomib- and octreotide-treated patients showed no significant differences between groups.

CONCLUSIONS

These preliminary results suggest that bortezomib shows negligible favorable effects on cancer-associated weight loss in patients with metastatic pancreatic cancer. We conclude that further study of bortezomib specifically in this setting and for this indication is not warranted.

Conjugated linoleic acid preserves gastrocnemius muscle mass in mice bearing the colon-26 adenocarcinoma

Cancer cachexia is a syndrome of weight loss, muscle wasting, fatigue, and anorexia that occurs in patients with advanced or recurrent solid tumor disease. Tumor necrosis factor-alpha (TNFalpha) and prostaglandin E2 (PGE2) have been implicated in the biology of cachexia and serve as possible targets for treatment of this condition. Conjugated linoleic acid (CLA) is a polyunsaturated fatty acid that alters the synthesis of PGE2 and reduces the negative effects of TNF on body weight of healthy mice. We hypothesized that a diet supplemented with .5% CLA might reduce muscle wasting in mice bearing the colon-26 adenocarcinoma, an animal model of cancer cachexia. CLA preserved gastrocnemius muscle mass and reduced TNF receptors in muscle of tumor-bearing mice. These data suggest that CLA may preserve muscle mass by reducing the catabolic effects of TNF on skeletal muscle.