Adaptation of the ubiquitin-proteasome proteolytic pathway in cancer cachexia

Muscle alterations in the development and progression of cancer-induced muscle atrophy: a review

Cancer cachexia-cancer-associated body weight and muscle loss-is a significant predictor of mortality and morbidity in cancer patients across a variety of cancer types. However, despite the negative prognosis associated with cachexia onset, there are no clinical therapies approved to treat or prevent cachexia. This lack of treatment may be partially due to the relative dearth of literature on mechanisms occurring within the muscle before the onset of muscle wasting. Therefore, the purpose of this review is to compile the current scientific literature on mechanisms contributing to the development and progression of cancer cachexia, including protein turnover, inflammatory signaling, and mitochondrial dysfunction. We define "development" as changes in cell function occurring before the onset of cachexia and "progression" as alterations to cell function that coincide with the exacerbation of muscle wasting. Overall, the current literature suggests that multiple aspects of cellular function, such as protein turnover, inflammatory signaling, and mitochondrial quality, are altered before the onset of muscle loss during cancer cachexia and clearly highlights the need to study more thoroughly the developmental stages of cachexia. The studying of these early aberrations will allow for the development of effective therapeutics to prevent the onset of cachexia and improve health outcomes in cancer patients.

mTOR and Tumor Cachexia

Cancer cachexia affects most patients with advanced forms of cancers. It is mainly characterized by weight loss, due to muscle and adipose mass depletion. As cachexia is associated with increased morbidity and mortality in cancer patients, identifying the underlying mechanisms leading to cachexia is essential in order to design novel therapeutic strategies. The mechanistic target of rapamycin (mTOR) is a major intracellular signalling intermediary that participates in cell growth by upregulating anabolic processes such as protein and lipid synthesis. Accordingly, emerging evidence suggests that mTOR and mTOR inhibitors influence cancer cachexia. Here, we review the role of mTOR in cellular processes involved in cancer cachexia and highlight the studies supporting the contribution of mTOR in 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.

Cancer cachexia update in head and neck cancer: Pathophysiology and treatment

The pathophysiology of cancer cachexia remains complex. A comprehensive literature search was performed up to April 2013 using PubMed, the Cochrane Library, Cumulative Index to Nursing and Allied Health Literature, and the Google search engine. In this review, we focus on the different mediators of impaired anabolism and upregulated catabolism that alter the skeletal muscle homeostasis resulting in the wasting of cancer cachexia. We present recent evidence of targeted treatment modalities from clinical trials along with their potential mechanisms of action. We also report on the most current evidence from randomized clinical trials using multimodal treatments in patients with cancer cachexia, but also the evidence from head and neck cancer-specific trials. A more complete understanding of the pathophysiology of the syndrome may lead to more effective targeted therapies and improved outcomes for patients.

Effects of celecoxib and ibuprofen on metabolic disorders induced by Walker-256 tumor in rats

The contribution of anti-inflammatory property of celecoxib in the improvement of metabolic disorders in cancer is unknown. The purpose of this study was to compare the effects of celecoxib and ibuprofen, non-steroidal anti-inflammatory drugs (NSAIDs), on several metabolic changes observed in Walker-256 tumor-bearing rats. The effects of these NSAIDs on the tumor growth were also assessed. Celecoxib or ibuprofen (both at 25 mg/Kg) was administered orally for 12 days, beginning on the day the rats were inoculated with Walker-256 tumor cells. Celecoxib treatment prevented the losses in body mass and mass of retroperitoneal adipose tissue, gastrocnemius, and extensor digitorum longus muscles in tumor-bearing rats. Celecoxib also prevented the rise in blood levels of triacylglycerol, urea, and lactate, the inhibition of peripheral response to insulin and hepatic glycolysis, and tended to attenuate the decrease in the food intake, but had no effect on the reduction of glycemia induced by the tumor. In addition, celecoxib treatment increased the number of Walker-256 cells with signs of apoptosis and the tumor necrosis area and prevented the tumor growth. In contrast, ibuprofen treatment had no effect on metabolic parameters affected by the Walker-256 tumor or tumor growth. It can be concluded that celecoxib, unlike ibuprofen, ameliorated several metabolic changes in rats with Walker-256 tumor due to its anti-tumor effect and not its anti-inflammatory property.

Synthesis and activity of proteasome inhibitors

Among its various catalytic activities, "chymotrypsin-like" activity of proteasome, a large multicatalytic proteinase complex has emerged as the focus of drug discovery efforts in cancer therapy. Herein, we report results from our investigation on a series of peptidomimetic inhibitors.

Nuclear transcription factor κ B activation and protein turnover adaptations in skeletal muscle of patients with progressive stages of lung cancer cachexia

BACKGROUND

Experimental models of cancer cachexia have indicated that systemic inflammation induces muscle-protein breakdown and wasting via muscular nuclear transcription factor κB (NF-κB) activation. This process may limit the efficacy of nutritional intervention.

OBJECTIVES

We assessed muscle NF-κB activity and protein turnover signaling in progressive stages of clinical lung cancer cachexia and assessed whether circulating factors can induce muscular NF-κB activity.

DESIGN

Patients with lung cancer precachexia (n = 10) and cachexia (n = 16) were cross-sectionally compared with 22 healthy control subjects. mRNA transcripts of muscle proteolytic (ubiquitin proteasome system and autophagy lysosomal pathway) and myogenic markers and protein expression of PI3K/Akt, myostatin, and autophagy signaling were measured. A multiplex analysis showed the systemic inflammatory status, whereas plasma exposure to stable NF-κB-luciferase-reporter muscle cells revealed NF-κB inducibility.

RESULTS

Compared with healthy control subjects, cachectic patients had reduced (appendicular) muscle mass (-10%), muscle fiber atrophy (-27%), and decreased quadriceps strength (-31%). Subtle alterations in the muscle morphology were also detectable in precachectic patients, without changes in body composition. Despite increased Akt phosphorylation, downstream phosphosubstrates glycogen synthase kinase 3β, mammalian target of rapamycin, and Forkhead box protein were unaltered. The expression of autophagy effectors B cell lymphoma 2/adenovirus E1B 19-kDa protein-interacting protein 3 and microtubule-associated proteins 1A/1B light chain 3B gradually increased from precachectic to cachectic patients, without differences in E3 ubiquitin ligases. Systemic and local inflammation was evident in cachexia and intermediate in precachexia, but the plasma of both patients groups caused ex vivo muscle NF-κB activation.

CONCLUSIONS

In lung cancer, muscular NF-κB activity is induced by factors contained within the circulation. Autophagy may contribute to increased muscle proteolysis in lung cancer cachexia, whereas the absence of downstream changes in phosphosubstrates despite increased Akt phosphorylation suggests impaired anabolic signaling that may require targeted nutritional intervention.

Protein damage, repair and proteolysis

Proteins are continuously affected by various intrinsic and extrinsic factors. Damaged proteins influence several intracellular pathways and result in different disorders and diseases. Aggregation of damaged proteins depends on the balance between their generation and their reversal or elimination by protein repair systems and degradation, respectively. With regard to protein repair, only few repair mechanisms have been evidenced including the reduction of methionine sulfoxide residues by the methionine sulfoxide reductases, the conversion of isoaspartyl residues to L-aspartate by L-isoaspartate methyl transferase and deglycation by phosphorylation of protein-bound fructosamine by fructosamine-3-kinase. Protein degradation is orchestrated by two major proteolytic systems, namely the lysosome and the proteasome. Alteration of the function for both systems has been involved in all aspects of cellular metabolic networks linked to either normal or pathological processes. Given the importance of protein repair and degradation, great effort has recently been made regarding the modulation of these systems in various physiological conditions such as aging, as well as in diseases. Genetic modulation has produced promising results in the area of protein repair enzymes but there are not yet any identified potent inhibitors, and, to our knowledge, only one activating compound has been reported so far. In contrast, different drugs as well as natural compounds that interfere with proteolysis have been identified and/or developed resulting in homeostatic maintenance and/or the delay of disease progression.

Prophylactic effects of swimming exercise on autophagy-induced muscle atrophy in diabetic rats

Diabetes decreases skeletal muscle mass and induces atrophy. However, the mechanisms by which hyperglycemia and insulin deficiency modify muscle mass are not well defined. In this study, we evaluated the effects of swimming exercise on muscle mass and intracellular protein degradation in diabetic rats, and proposed that autophagy inhibition induced by swimming exercise serves as a hypercatabolic mechanism in the skeletal muscles of diabetic rats, supporting a notion that swimming exercise could efficiently reverse the reduced skeletal muscle mass caused by diabetes. Adult male Sprague-Dawley rats were injected intraperitoneally with streptozotocin (60 mg/kg body weight) to induce diabetes and then submitted to 1 hr per day of forced swimming exercise, 5 days per week for 4 weeks. We conducted an intraperitoneal glucose tolerance test on the animals and measured body weight, skeletal muscle mass, and protein degradation and examined the level of autophagy in the isolated extensor digitorum longus, plantaris, and soleus muscles. Body weight and muscle tissue mass were higher in the exercising diabetic rats than in control diabetic rats that remained sedentary. Compared to control rats, exercising diabetic rats had lower blood glucose levels, increased intracellular contractile protein expression, and decreased autophagic protein expression. We conclude that swimming exercise improves muscle mass in diabetes-induced skeletal muscle atrophy, suggesting the activation of autophagy in diabetes contributes to muscle atrophy through hypercatabolic metabolism and that aerobic exercise, by suppressing autophagy, may modify or reverse skeletal muscle wasting in diabetic patients.

Serendipity in discovery of proteasome inhibitors

Among its various catalytic activities, the 'chymotrypsin-like' activity of the proteasome, a large multicatalytic proteinase complex has emerged as the focus of drug discovery efforts in cancer therapy. Herein, a series of first generation (2S, 3R)-2-amino-3-hydroxybutyric acid derived proteasome inhibitors that were discovered serendipitously en route to original goal of generating a series of sterically constrained oxazoline derivatives has been reported.

Proteasome inhibitors for cancer therapy

Proteasome, a large multicatalytic proteinase complex that plays an important role in processing of proteins, has been shown to possess multiple catalytic activities. Among its various activities, the 'chymotrypsin-like' activity of proteasome has emerged as the focus of drug discovery efforts in cancer therapy. Herein we report chiral boronate derived novel, potent, selective and cell-permeable peptidomimetic inhibitors 6 and 7 that displayed activity against various rodent and human tumor cell lines (in vitro).

The prognostic impact of circulating proteasome concentrations in patients with epithelial ovarian cancer

BACKGROUND

Intracellularly, the ubiquitin-proteasome system participates in crucial functions such as cell cycling, differentiation, proliferation, gene transcription, and apoptosis. However, in malignancies including ovarian cancer increased extracellular concentrations of circulating 20S proteasomes (c-proteasomes) have been detected in blood. We tested the hypothesis that the c-proteasome plasma concentration is a biomarker associated with the clinical course of ovarian cancer patients.

METHODS

20S-proteasome venous plasma concentration was measured by ELISA in patients presenting with ovarian cancer before (n=120) and after (n=68) primary treatment, and in healthy volunteers (n=55). The median follow-up time was 19 months. To assess the relation of proteasome expression with c-proteasome concentration, tumor specimens from 27 patients were immunohistochemically stained for 20S proteasome using an antibody directed against the core subunits of the catalytic domain of the 20S proteasome.

RESULTS

Median c-proteasome concentration was higher (p<0.0001) in untreated ovarian cancer patients (457.5 ng/ml, range: 200-12540 ng/ml) than in healthy controls 290 ng/ml, range: 140-425 ng/ml). Following completion of primary treatment, the median c-proteasome concentration increased (p=0.003) relative to baseline (595 ng/ml, range: 200-20000 ng/ml) and concentrations positively correlated (p=0.031) with residual disease left at primary surgery. Patients with post-treatment c-proteasome concentrations exceeding the cohort's median showed a diminished survival (p=0.045). We found no correlation between c-proteasome concentration and strength of proteasomal staining in tumor specimens.

CONCLUSIONS

Circulating proteasome concentrations correlate with residual tumor mass and might be a prognostic variable in ovarian cancer following primary therapy.

Diagnostic value and prognostic significance of plasmatic proteasome level in patients with melanoma

Plasmatic proteasome (p-proteasome) also called circulating proteasome has recently been described as a tumor marker. We investigated the diagnostic and prognostic accuracies of p-proteasome levels in a melanoma population classified according to the American Joint Committee on Cancer staging system. Using an ELISA test, we measured p-proteasome levels in 90 patients and 40 controls between March 2003 and March 2008. The subunit composition of p-proteasomes was determined in metastatic melanoma by proteomic analysis. The mean p-proteasome levels were correlated with stages (P < 0.0001; r(S) = 0.664). They were significantly higher in patients with stage IV and stage III with lymph node metastasis (9187 ± 1294 and 5091 ± 454 ng/ml, respectively) compared to controls (2535 ± 187 ng/ml; P < 0.001), to stage I/II (2864 ± 166 ng/ml; P < 0.001) and to stage III after curative lymphadenectomy (2859 ± 271 ng/ml; P < 0.001). The diagnostic accuracy of p-proteasome was evaluated by receiver operating characteristic analysis. With a cut-off of 4300 ng/ml, diagnostic specificity and sensitivity of p-proteasome for regional or visceral metastases were respectively 96.3% and 72.2%. In univariate analysis, high p-proteasome levels (>4300 ng/ml) were significantly correlated with an increased risk of progression [hazard ratio (HR) = 7.34; 95% CI 3.54-15.21, P < 0.0001] and a risk of death (HR = 5.92; 95% CI 2.84-12.33, P < 0.0001). In multivariate analysis, high p-proteasome levels were correlated with a poorer clinical outcome in the subgroup analysis limited to patients with disease stages I, II and III. Proteomic analysis confirmed the presence of all proteasome and immunoproteasome subunits. Taken together, these results indicate that p-proteasomes are a new marker for metastatic dissemination in patients with melanoma.

Molecular events and signalling pathways involved in skeletal muscle disuse-induced atrophy and the impact of countermeasures

Disuse-induced skeletal muscle atrophy occurs following chronic periods of inactivity such as those involving prolonged bed rest, trauma and microgravity environments. Deconditioning of skeletal muscle is mainly characterized by a loss of muscle mass, decreased fibre cross-sectional area, reduced force, increased fatigability, increased insulin resistance and transitions in fibre types. A description of the role of specific transcriptional mechanisms contributing to muscle atrophy by altering gene expression during muscle disuse has recently emerged and focused primarily on short period of inactivity. A better understanding of the transduction pathways involved in activation of proteolytic and apoptotic pathways continues to represent a major objective, together with the study of potential cross-talks in these cellular events. In parallel, evaluation of the impact of countermeasures at the cellular and molecular levels in short- and long-term disuse experimentations or microgravity environments should undoubtedly and synergistically increase our basic knowledge in attempts to identify new physical, pharmacological and nutritional targets to counteract muscle atrophy. These investigations are important as skeletal muscle atrophy remains an important neuromuscular challenge with impact in clinical and social settings affecting a variety of conditions such as those seen in aging, cancer cachexia, muscle pathologies and long-term space exploration.

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.

Muscle wasting in diabetic and in tumor-bearing rats: role of oxidative stress

Cachexia is a debilitating syndrome characterized by body weight loss, muscle wasting, and anemia. Muscle wasting results from an altered balance between protein synthesis and degradation rates. Reactive oxygen species are indicated as crucial players in the onset of muscle protein hypercatabolism by upregulating elements of the ubiquitin-proteasome pathway. The present study has been aimed at evaluating comparatively the involvement of oxidative stress in the pathogenesis of skeletal muscle wasting in two different experimental models: rats rendered hyperglycemic by treatment with streptozotocin and rats bearing the Yoshida AH-130 ascites hepatoma. For this purpose, both tumor bearers and diabetic animals have been treated with dehydroepiandrosterone (DHEA), a multifunctional steroid endowed with multitargeted antioxidant properties. We show that diabetic rats and AH-130 rats share several features, hypoinsulinemia, occurrence of oxidative stress, and positive response to DHEA administration, although the extent of the effects of DHEA largely differs between diabetic animals and tumor-bearing rats. The hypercatabolism, evaluated in terms of proteasome activity and expression of atrogin-1 and MuRF1, is activated in AH-130 rats, whereas it is lacking in streptozotocin-treated rats. Moreover, we demonstrate that the role of oxidative stress can interfere with muscle wasting through different mechanisms, not necessarily involving NF-kappaB activation. In conclusion, the present results show that, although skeletal muscle wasting occurs in both diabetic rats and tumor-host rats, the underlying mechanisms are different. Moreover, despite oxidative stress being detectable in both experimental models, its contribution to muscle wasting is not comparable.

Cancer-Associated Cachexia and Underlying Biological Mechanisms

Cancer metastases (spread to distant organs from the primary tumor site) signify systemic, progressive, and essentially incurable malignant disease. Anorexia and wasting develop continuously throughout the course of incurable cancer. Overall, in Westernized countries nearly exactly half of current cancer diagnoses end in cure and the other half end in death; thus, cancer-associated cachexia has a high prevalence. The pathophysiology of cancer-associated cachexia has two principal components: a failure of food intake and a systemic hypermetabolism/hypercatabolism syndrome. The superimposed metabolic changes result in a rate of depletion of physiological reserves of energy and protein that is greater than would be expected based on the prevailing level of food intake. These features indicate a need for nutritional support, metabolic management, and a clear appreciation of the context of life-limiting illness.

Intracellular signaling during skeletal muscle atrophy

A variety of conditions lead to skeletal muscle atrophy including muscle inactivity or disuse, multiple disease states (i.e., cachexia), fasting, and age-associated atrophy (sarcopenia). Given the impact on mobility in the latter conditions, inactivity could contribute in a secondary manner to muscle atrophy. Because different events initiate atrophy in these different conditions, it seems that the regulation of protein loss may be unique in each case. In fact differences exist between the regulation of the various atrophy conditions, especially sarcopenia, as evidenced in part by comparisons of transcriptional profiles as well as by the unique triggering molecules found in each case. By contrast, recent studies have shown that many of the intracellular signaling molecules and target genes are similar, particularly among the atrophies related to inactivity and cachexia. This review focuses on the most recent findings related to intracellular signaling during muscle atrophy. Key findings are discussed that relate to signaling involving muscle ubiquitin ligases, the IGF/PI3K/Akt pathway, FOXO activity, caspase-3 activity, and NF-kappaB signaling, and an attempt is made to construct a unifying picture of how these data can be connected to better understand atrophy. Once more detailed cellular mechanisms of the atrophy process are understood, more specific interventions can be designed for the attenuation of protein loss.

Common symptoms in advanced cancer

The key points of this article are anorexia and cachexia are: A major cause of cancer deaths. Several drugs are available to treat anorexia and cachexia. Dyspnea in cancer usually is caused by several factors. Treatment consists of reversing underlying causes, empiric bronchodilators, cortico-steroids--and in the terminally ill patients-opioids, benzodiazepines,and chlorpromazine. Delirium is associated with advanced cancer. Empiric treatment with neuroleptics while evaluating for reversible causes is a reasonable approach to management. Nausea and vomiting are caused by extra-abdominal factors (drugs,electrolyte abnormalities, central nervous system metastases) or intra-abdominal factors (gastroparesis, ileus, gastric outlet obstruction, bowel obstruction). The pattern of nausea and vomiting differs depending upon whether the cause is extra- or intra-abdominal. Reversible causes should be sought and empiric metoclopramide or haloperidol should be initiated. Fatigue may be caused by anemia, depression, endocrine abnormalities,or electrolyte disturbances that should be treated before using empiric methylphenidate. Constipation should be treated with laxatives and stool softeners. Both should start with the first opioid dose.

Indomethacin preserves muscle mass and reduces levels of E3 ligases and TNF receptor type 1 in the gastrocnemius muscle of tumor-bearing mice

Tumor-induced skeletal muscle wasting involves tumor necrosis factor (TNF) and the ubiquitin-proteasome pathway of muscle protein degradation. In this study, growth of the colon-26 adenocarcinoma in mice was associated with diminished gastrocnemius muscle mass and increased muscle levels of actin, ubiquitin-conjugated proteins, free ubiquitin, E3 ubiquitin ligases, and the type 1 TNF receptor (TNFR1). Indomethacin at 1 or 5 mg/kg/day reduced tumor growth and muscle levels of TNFR1. However, only the 5 mg dose of indomethacin reduced muscle wasting and muscle levels of the E3 ligases and actin. These data suggest that the beneficial effects of indomethacin in the treatment of tumor-induced skeletal muscle wasting may involve inhibition of TNF- and ubiquitin-mediated pathways of muscle protein degradation. These data also demonstrate that E3 ligases, which are involved in disuse atrophy, also are associated with tumor-induced skeletal muscle wasting.

Induction of proteasome expression in skeletal muscle is attenuated by inhibitors of NF-kappaB activation

The potential for inhibitors of nuclear factor-κB (NF-κB) activation to act as inhibitors of muscle protein degradation in cancer cachexia has been evaluated both in vitro and in vivo. Activation of NF-κB is important in the induction of proteasome expression and protein degradation by the tumour factor, proteolysis-inducing factor (PIF), since the cell permeable NF-κB inhibitor SN50 (18 μM) attenuated the expression of 20S proteasome α-subunits, two subunits of the 19S regulator MSS1 and p42, and the ubiquitin-conjugating enzyme, E2_14k, as well as the decrease in myosin expression in murine myotubes. To assess the potential therapeutic benefit of NF-κB inhibitors on muscle atrophy in cancer cachexia, two potential inhibitors were employed; curcumin (50 μM) and resveratrol (30 μM). Both agents completely attenuated total protein degradation in murine myotubes at all concentrations of PIF, and attenuated the PIF-induced increase in expression of the ubiquitin–proteasome proteolytic pathway, as determined by the ‘chymotrypsin-like’ enzyme activity, proteasome subunits and E2_14k. However, curcumin (150 and 300 mg kg⁻¹) was ineffective in preventing weight loss and muscle protein degradation in mice bearing the MAC16 tumour, whereas resveratrol (1 mg kg⁻¹) significantly attenuated weight loss and protein degradation in skeletal muscle, and produced a significant reduction in NF-κB DNA-binding activity. The inactivity of curcumin was probably due to a low bioavailability. These results suggest that agents which inhibit nuclear translocation of NF-κB may prove useful for the treatment of muscle wasting in cancer cachexia.

Regulation of Protein Catabolism by Muscle-Specific and Cytokine-Inducible Ubiquitin Ligase E3α-II during Cancer Cachexia

The progressive depletion of skeletal muscle is a hallmark of many types of advanced cancer and frequently is associated with debility, morbidity, and mortality. Muscle wasting is primarily mediated by the activation of the ubiquitin-proteasome system, which is responsible for degrading the bulk of intracellular proteins. E3 ubiquitin ligases control polyubiquitination, a rate-limiting step in the ubiquitin-proteasome system, but their direct involvement in muscle protein catabolism in cancer remains obscure. Here, we report the full-length cloning of E3alpha-II, a novel "N-end rule" ubiquitin ligase, and its functional involvement in cancer cachexia. E3alpha-II is highly enriched in skeletal muscle, and its expression is regulated by proinflammatory cytokines. In two different animal models of cancer cachexia, E3alpha-II was significantly induced at the onset and during the progression of muscle wasting. The E3alpha-II activation in skeletal muscle was accompanied by a sharp increase in protein ubiquitination, which could be blocked by arginine methylester, an E3alpha-selective inhibitor. Treatment of myotubes with tumor necrosis factor alpha or interleukin 6 elicited marked increases in E3alpha-II but not E3alpha-I expression and ubiquitin conjugation activity in parallel. E3alpha-II transfection markedly accelerated ubiquitin conjugation to endogenous cellular proteins in muscle cultures. These findings show that E3alpha-II plays an important role in muscle protein catabolism during cancer cachexia and suggest that E3alpha-II is a potential therapeutic target for muscle wasting.

Focal dysfunction of the proteasome: a pathogenic factor in a mouse model of amyotrophic lateral sclerosis

Mutations in the Cu/Zn-superoxide dismutase (SOD-1) gene are responsible for a familial form of amyotrophic lateral sclerosis (fALS). The present study demonstrated impaired proteasomal function in the lumbar spinal cord of transgenic mice expressing human SOD-1 with the ALS-causing mutation G93A (SOD-1(G93A)) compared to non-transgenic littermates (LM) and SOD-1(WT) transgenic mice. Chymotrypsin-like activity was decreased as early as 45 days of age. By 75 days, chymotrypsin-, trypsin-, and caspase-like activities of the proteasome were impaired, at about 50% of control activity in lumbar spinal cord, but unchanged in thoracic spinal cord and liver. Both total and specific activities of the proteasome were reduced to a similar extent, indicating that a change in proteasome function, rather than a decrease in proteasome levels, had occurred. Similar decreases of total and specific activities of the proteasome were observed in NIH 3T3 cell lines expressing fALS mutants SOD-1(G93A) and SOD-1(G41S), but not in SOD-1(WT) controls. Although overall levels of proteasome were maintained in spinal cord of SOD-1(G93A) transgenic mice, the level of 20S proteasome was substantially reduced in lumbar spinal motor neurons relative to the surrounding neuropil. It is concluded that impairment of the proteasome is an early event and contributes to ALS pathogenesis.

Indomethacin and ibuprofen preserve gastrocnemius muscle mass in mice bearing the colon-26 adenocarcinoma

Skeletal muscle wasting is a prominent feature of cancer cachexia and involves decreased muscle protein synthesis and increased activity of the ubiquitin-proteasome pathway of protein degradation. We report that both indomethacin and ibuprofen improved body weight and weight of the gastrocnemius muscle in tumor-bearing mice. Ibuprofen increased the soluble protein content of the muscle without affecting muscle levels of phosphorylated p70 S6 kinase, a ribosomal kinase involved in protein synthesis. Paradoxically, indomethacin increased levels of ubiquitin-conjugated proteins. Further study is needed to understand the mechanism of action by which indomethacin and ibuprofen preserve body weight and muscle mass in the tumor-bearing mice. The data suggest that ibuprofen may have beneficial effects in the treatment of cancer cachexia.

Mechanisms of skeletal muscle depletion in wasting syndromes: role of ATP-ubiquitin-dependent proteolysis

PURPOSE OF REVIEW

Muscle protein wasting frequently complicates patient outcome in several chronic pathologies. The underlying mechanisms remain largely obscure, although studies on experimental models have clarified that a complex interplay of different factors such as nutrient supply, classical hormones, cytokines and other less well defined factors likely concur in causing muscle depletion. The aim of the present review is to highlight some crucial points in the interpretation of the data available about the contribution of the different proteolytic systems, with particular reference to the ubiquitin-proteasome system, in the onset of muscle protein wasting in disease states.

RECENT FINDINGS

Much effort has been directed to understanding the role of different signals, transduction pathways, and proteolytic mechanisms in the acceleration of muscle protein catabolism. Several reports propose that ATP-ubiquitin-dependent proteolysis plays a critical role in the enhancement of muscle protein catabolism observed in different pathological states. Other papers, however, suggest that the lysosomal or the calcium-dependent proteolytic pathways or both may be involved. Finally, the studies have been extended to evaluate the possibility of interfering pharmacologically with the onset of muscle protein hypercatabolism.

SUMMARY

As the present overview points out, several questions still remain unanswered in the issue of muscle wasting. While many different signals that have the potential to enforce the acceleration of muscle protein breakdown have been identified, it is largely unknown how they are transduced and converge into the hypercatabolic response and how the proteolytic pathways involved are activated. The concept seems to emerge that there may be a coordinated action of different proteolytic pathways in setting up muscle protein turnover towards excess catabolism.

Adverse and beneficial functions of proteolytic enzymes in skeletal muscle. An overview

Proteolytic enzymes (proteases) comprise a family of enzymes which hydrolyse protein or peptide substrates in the generalised process of intracellular protein degradation, a process essential for the normal functioning of all cells. Proteases may also have a wide range of additional functions, including metabolic control of physiologically active oligopeptides or precursor protein forms, antigen presentation/recognition by the major histocompatibility complex in the cellular immune response, as well as in digestion, blood clotting, complement activation, etc. In this article, the nomenclature and classification of proteolytic enzymes in skeletal muscle, and their role in normal muscle physiological processes have been reviewed, including exercise, muscle development and ageing. Although proteases play an important role in normal muscle functioning, in pathological situations the enzymes may themselves be regarded as 'toxic agents' in terms of their damaging effects on muscle tissue. Muscle damage resulting from inappropriate activity of proteolytic enzymes in muscle wasting associated with muscular dystrophies, denervation atrophy, inflammatory myopathies, cancer, sepsis, diabetes and alcoholism have been reviewed. In addition, evidence that the adverse effects of drugs known to induce muscle wasting, such as corticosteroids, (or beneficial effects of growth promoting drugs) may be mediated via proteolytic enzymes is also reviewed.

Update on anorexia and cachexia

Declining physical, emotional, and social function as a result of anorexia and cachexia are considerable contributors to discomfort for cancer patients and their families, and they impair the patient's ability to express optimal physical and psychosocial potential as long as possible. This decline no longer has to be accepted as an indispensable sequel to advanced cancer, just as pain is no longer considered to be unavoidable. A routine screening for anorexia and cachexia and associated symptoms is necessary, as is a careful, comprehensive assessment, because the condition is not always obvious. Decisions about anorexia and cachexia treatment are guided by prioritizing the different, concurrent physical, psychosocial, and existential problems and by considering the natural course of the cancer and the effects of antineoplastic therapies. Reversible causes for anorexia and cachexia need to be identified and treated, if appropriate. Nutritional interventions are often indicated; patients with a predominant starvation component and without inflammation may profit the most. New pharmacologic therapies for primary anorexia and cachexia syndrome are expected to enter clinical practice soon; however, until then, treatment with corticosteroids, progestins, or prokinetics may be indicated for some patients. To understand a multicausal syndrome, multimodal and interdisciplinary therapy is required. Specialist palliative care services can be helpful to provide, hand-in-hand with the disease specialists [172], assessment and management of psychophysical symptoms and sociospiritual needs of patients during the course of the illness and at the end of life [173]. Research efforts aim to better characterize subgroups of patients suffering from secondary causes of anorexia and cachexia and to elucidate the mechanisms involved in the primary anorexia and cachexia syndrome. Increasingly individualized treatments are expected with combination treatments that involve different mechanisms including nutrition.

Hypercatabolism and hypermetabolism in wasting states

The year 2001/2002 has been marked by a number of exciting new results for our understanding of anabolic and catabolic mediators and their participation in wasting states, as reflected by the contents of this section. It becomes ever more apparent that a clear understanding of how to shut off hypercatabolic and hypermetabolic processes is needed to underpin effective strategies for wasting syndromes. A particularly interesting development in the control of degradative processes in skeletal muscle is the discovery of several muscle-specific ubiquitin ligases. These enzymes, which confer specificity to the degradation of myofibrillar proteins and are situated in a pathway of proteolysis common to a variety of wasting states, may prove to be a valuable point of intervention in muscle atrophy. In the clinical arena, studies on non-small cell lung cancer patients as well as broader patient populations with solid tumours provide more evidence for a high incidence of hypermetabolism as well as low energy intake. The best therapies currently available for the cancer cachexia/anorexia syndrome have numerous limitations and tend mainly to attenuate losses rather than to promote a net gain of weight or lean body mass. Sustained hypermetabolism over the long course of disease progression constitutes an important contributor to negative energy balance, and its presence is likely to be a limiting factor to the success of current treatment approaches.

Torbafylline (HWA 448) inhibits enhanced skeletal muscle ubiquitin-proteasome-dependent proteolysis in cancer and septic rats

The development of new pharmacological approaches for preventing muscle wasting in cancer is an important goal because cachectic patients display a reduced response to chemotherapy and radiotherapy. Xanthine derivatives such as pentoxifylline inhibit tumour necrosis factor-alpha (TNF) production, which has been implicated in the signalling of muscle wasting. However, the effect of pentoxifylline has been inconclusive in clinical trials. We report here the first direct evidence that daily injections of torbafylline (also known as HWA 448), another xanthine derivative, had no effect by itself on muscle proteolysis in control healthy rats. In cancer rats, the drug blocked the lipopolysaccharide-induced hyperproduction of TNF and prevented muscle wasting. In these animals HWA 448 suppressed the enhanced proteasome-dependent proteolysis, which is sensitive to the proteasome inhibitor MG132, and the accumulation of high-molecular-mass ubiquitin (Ub) conjugates in the myofibrillar fraction. The drug also normalized the enhanced muscle expression of Ub, which prevails in the atrophying muscles from cancer rats. In contrast, HWA 448 did not reduce the increased expression of either the 14 kDa Ub conjugating enzyme E2 or the ATPase and non-ATPase subunits of the 19 S regulatory complex of the 26 S proteasome, including the non-ATPase subunit S5a, which recognizes polyUb degradation signals. Finally, the drug also prevented muscle wasting in septic rats (which exhibit increased TNF production), and was much more potent than pentoxifylline or other xanthine derivatives. Taken together, the data indicate that HWA 448 is a powerful inhibitor of muscle wasting that blocks enhanced Ub-proteasome-dependent proteolysis in situations where TNF production rises, including cancer and sepsis.

Management of muscle wasting in cancer-associated cachexia: understanding gained from experimental studies

BACKGROUND

Cancer-associated cachexia is a syndrome of progressive wasting of body energy (adipose) and protein (skeletal muscle) reserves. Cachexia occurs in a majority of advanced cancer patients. Extensive loss of muscle mass is one factor likely to be associated with fatigue in cancer patients.

METHODS

Research with animal models of cancer-associated cachexia that have focused on the processes of muscle protein synthesis and degradation are reviewed in this article. Modulation of the production or action of anabolic and catabolic factors known to regulate muscle protein synthesis and degradation have been employed to identify causal factors in muscle wasting.

RESULTS

Impaired muscle protein synthesis and activation of catabolism participate in cancer-associated muscle atrophy. The relative roles of multiple factors, including a low level of physical activity, poor nutritional status, and secretion of catabolic mediators of host or tumor origin, are discussed herein. A diversity of putative mediators has been identified, and a number of common themes are beginning to emerge.

CONCLUSIONS

Multiple distinct catabolic profiles exist in animal models of cancer-associated muscle wasting. The presence of these catabolic phenotypes in cancer patients must be determined, and the application of successful treatments will depend on our ability to determine which categories of patients experience the greatest benefit.

Elongated conformers of charge states +11 to +15 of bovine ubiquitin studied using ESI-FAIMS-MS

Recent advancements in high-field asymmetric waveform ion mobility spectrometry (FAIMS) have led to significant improvements in the application of this technology to the study of protein conformers. Compared with previous work, the maximum value of the separation voltage (i.e., the dispersion voltage) has increased, thereby enabling multiple, elongated conformers of individual charge states of bovine ubiquitin to be separated in the gas phase (e.g., four conformers of each of the +11 and +12 charge states were separated). The use of a carrier gas mixture of 40% nitrogen and 60% helium changed the separation selectivity compared with pure nitrogen and enhanced the signal intensity, especially for the +14 and +15 charge states (the latter was not detected in a nitrogen carrier gas). Conformer cross sections were determined using the FAIMS/energy-loss method and found to be similar within a given charge state. The cross sections for conformers of charge states +13, + 14, and +15 plateau at about 2000 A2 suggesting that the structure of bovine ubiquitin is essentially unfolded after the addition of the 13th proton.

Cancer-induced fatigue and skeletal muscle wasting: the role of exercise

Fatigue is the most frequently reported symptom by cancer patients. Many of these patients perceive fatigue as the most distressing symptom associated with their illness because it imposes limitations on their physical activity level. Skeletal muscle wasting, which occurs as part of cancer cachexia, is one of the mechanisms that contribute to fatigue. Cancer-induced skeletal muscle wasting may occur despite normal food intake and is not prevented by nutritional supplementation. Evidence suggests that endurance exercise ameliorates cancer-related fatigue. There is no compelling evidence to support that exercise-induced reduction in fatigue is related to preservation of muscle mass. Resistance exercise attenuates muscle wasting associated with a variety of catabolic conditions. However, its effects on cancer-induced muscle wasting have not been adequately studied. This article describes the physiological mechanisms implicated in the induction of cancer-related muscle wasting, summarizes findings from endurance and resistance exercise studies in relation to fatigue and muscle wasting during cancer and selected clinical conditions, and proposes directions for future research.

Amino acid regulation of gene expression

The impact of nutrients on gene expression in mammals has become an important area of research. Nevertheless, the current understanding of the amino acid-dependent control of gene expression is limited. Because amino acids have multiple and important functions, their homoeostasis has to be finely maintained. However, amino-acidaemia can be affected by certain nutritional conditions or various forms of stress. It follows that mammals have to adjust several of their physiological functions involved in the adaptation to amino acid availability by regulating the expression of numerous genes. The aim of the present review is to examine the role of amino acids in regulating mammalian gene expression and protein turnover. It has been reported that some genes involved in the control of growth or amino acid metabolism are regulated by amino acid availability. For instance, limitation of several amino acids greatly increases the expression of the genes encoding insulin-like growth factor binding protein-1, CHOP (C/EBP homologous protein, where C/EBP is CCAAT/enhancer binding protein) and asparagine synthetase. Elevated mRNA levels result from both an increase in the rate of transcription and an increase in mRNA stability. Several observations suggest that the amino acid regulation of gene expression observed in mammalian cells and the general control process described in yeast share common features. Moreover, amino acid response elements have been characterized in the promoters of the CHOP and asparagine synthetase genes. Taken together, the results discussed in the present review demonstrate that amino acids, by themselves, can, in concert with hormones, play an important role in the control of gene expression.

Regulation of skeletal-muscle-protein turnover in cancer-associated cachexia

Cancer is frequently associated with anorexia, weight loss, negative nitrogen balance, and skeletal-muscle wasting. Depletion of skeletal-muscle mass is critical to overall survival of the patient, can prolong rehabilitation to normal function after recovery, and decreases quality of life in a palliative-care setting. The biochemical and physiologic bases of cancer-associated muscle wasting have been most fully investigated in animal models. These studies provide evidence for suppressed protein synthesis and activated proteolysis in cancer-associated muscle wasting and indicate a need for both anabolic and anticatabolic therapies. Several humoral factors of host or tumor origin are implicated in altered muscle-protein metabolism, including cytokines, metabolites of arachidonic acid, and a proteolysis-inducing glycoprotein; their interrelationships are less well characterized. Several catabolic mediators may share common downstream mechanisms because they ultimately activate the ATP-, ubiquitin-, and proteasome-dependent intracellular proteolytic system. Although important gaps in our current understanding remain, data available from animal studies can be used as a basis to develop relevant studies in human subjects.

Manipulation of the ubiquitin-proteasome pathway in cachexia: pentoxifylline suppresses the activation of 20S and 26S proteasomes in muscles from tumor-bearing rats

The development of pharmacological approaches for preventing the loss of muscle proteins would be extremely valuable for cachectic patients. For example, severe wasting in cancer patients correlates with a reduced efficacy of chemotherapy and radiotherapy. Pentoxifylline (PTX) is a very inexpensive xanthine derivative, which is widely used in humans as a haemorheological agent, and inhibits tumor necrosis factor transcription. We have shown here that a daily administration of PTX prevents muscle atrophy and suppresses increased protein breakdown in Yoshida sarcoma-bearing rats by inhibiting the activation of a nonlysosomal, Ca(2+)-independent proteolytic pathway. PTX blocked the ubiquitin pathway, apparently by suppressing the enhanced expression of ubiquitin, the 14-kDa ubiquitin conjugating enzyme E2, and the C2 20S proteasome subunit in muscle from cancer rats. The 19S complex and 11S regulator associate with the 20S proteasome and regulate its peptidase activities. The mRNA levels for the ATPase subunit MSS1 of the 19S complex increased in cancer cachexia, in contrast with mRNAs of other regulatory subunits. This adaptation was suppressed by PTX, suggesting that the drug inhibited the activation of the 26S proteasome. This is the first demonstration of a pharmacological manipulation of the ubiquitin-proteasome pathway in cachexia with a drug which is well tolerated in humans. Overall, the data suggest that PTX can prevent muscle wasting in situations where tumor necrosis factor production rises, including cancer, sepsis, AIDS and trauma.