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

The Role of Exercise in Cancer-Related Sarcopenia and Sarcopenic Obesity

One of the most common adverse effects of cancer and its therapeutic strategies is sarcopenia, a condition which is characterised by excess muscle wasting and muscle strength loss due to the disrupted muscle homeostasis. Moreover, cancer-related sarcopenia may be combined with the increased deposition of fat mass, a syndrome called cancer-associated sarcopenic obesity. Both clinical conditions have significant clinical importance and can predict disease progression and survival. A growing body of evidence supports the claim that physical exercise is a safe and effective complementary therapy for oncology patients which can limit the cancer- and its treatment-related muscle catabolism and promote the maintenance of muscle mass. Moreover, even after the onset of sarcopenia, exercise interventions can counterbalance the muscle mass loss and improve the clinical appearance and quality of life of cancer patients. The aim of this narrative review was to describe the various pathophysiological mechanisms, such as protein synthesis, mitochondrial function, inflammatory response, and the hypothalamic-pituitary-adrenal axis, which are regulated by exercise and contribute to the management of sarcopenia and sarcopenic obesity. Moreover, myokines, factors produced by and released from exercising muscles, are being discussed as they appear to play an important role in mediating the beneficial effects of exercise against sarcopenia.

Females display relatively preserved muscle quality compared with males during the onset and early stages of C26-induced cancer cachexia

Cancer cachexia is clinically defined by involuntary weight loss >5% in <6 mo, primarily affecting skeletal muscle. Here, we aimed to identify sex differences in the onset of colorectal cancer cachexia with specific consideration to skeletal muscle contractile and metabolic functions. Eight-weeks old BALB/c mice (69 males, 59 females) received subcutaneous C26 allografts or PBS vehicle. Tumors were developed for 10-, 15-, 20-, or 25 days. Muscles and organs were collected, in vivo muscle contractility, protein synthesis rate, mitochondrial function, and protein turnover markers were assessed. One-way ANOVA within sex and trend analysis between sexes were performed, P < 0.05. Gastrocnemius and tibialis anterior (TA) muscles became atrophic in male mice at 25 days, whereas female mice exhibited no significant differences in muscle weights at endpoints despite presenting hallmarks of cancer cachexia (fat loss, hepatosplenomegaly). We observed lowered muscle contractility and protein synthesis concomitantly to muscle mass decay in males, with higher proteolytic markers in muscles of both sexes. mRNA of Opa1 was lower in TA, whereas Bnip3 was higher in gastrocnemius after 25 days in male mice, with no significant effect in female mice. Our data suggest relative protections to skeletal muscle in females compared with males despite other canonical signs of cancer cachexia and increased protein degradation markers; suggesting we should place onus upon nonmuscle tissues during early stages of cancer cachexia in females. We noted potential protective mechanisms relating to skeletal muscle contractile and mitochondrial functions. Our findings underline possible heterogeneity in onset of cancer cachexia between biological sexes, suggesting the need for sex-specific approaches to treat cancer cachexia.NEW & NOTEWORTHY Our study demonstrates biological-sex differences in phenotypic characteristics of cancer cachexia between male and female mice, whereby females display many common characteristics of cachexia (gonadal fat loss and hepatosplenomegaly), protein synthesis markers alterations, and common catabolic markers in skeletal muscle despite relatively preserved muscle mass in early-stage cachexia compared with males. Mechanisms of cancer cachexia appear to differ between sexes. Data suggest need to place onus of early cancer cachexia detection and treatment on nonmuscle tissues in females.

The time-course of cancer cachexia onset reveals biphasic transcriptional disruptions in female skeletal muscle distinct from males

BACKGROUND

Cancer-cachexia (CC) is a debilitating condition affecting up to 80% of cancer patients and contributing to 40% of cancer-related deaths. While evidence suggests biological sex differences in the development of CC, assessments of the female transcriptome in CC are lacking, and direct comparisons between sexes are scarce. This study aimed to define the time course of Lewis lung carcinoma (LLC)-induced CC in females using transcriptomics, while directly comparing biological sex differences.

RESULTS

We found the global gene expression of the gastrocnemius muscle of female mice revealed biphasic transcriptomic alterations, with one at 1 week following tumor allograft and another during the later stages of cachexia development. The early phase was associated with the upregulation of extracellular-matrix pathways, while the later phase was characterized by the downregulation of oxidative phosphorylation, electron transport chain, and TCA cycle. When DEGs were compared to a known list of mitochondrial genes (MitoCarta), ~ 47% of these genes were differently expressed in females exhibiting global cachexia, suggesting transcriptional changes to mitochondrial gene expression happens concomitantly to functional impairments previously published. In contrast, the JAK-STAT pathway was upregulated in both the early and late stages of CC. Additionally, we observed a consistent downregulation of Type-II Interferon signaling genes in females, which was associated with protection in skeletal muscle atrophy despite systemic cachexia. Upregulation of Interferon signaling was noted in the gastrocnemius muscle of cachectic and atrophic male mice. Comparison of female tumor-bearing mice with males revealed ~ 70% of DEGs were distinct between sexes in cachectic animals, demonstrating dimorphic mechanisms of CC.

CONCLUSION

Our findings suggest biphasic disruptions in the transcriptome of female LLC tumor-bearing mice: an early phase associated with ECM remodeling and a late phase, accompanied by the onset of systemic cachexia, affecting overall muscle energy metabolism. Notably, ~ 2/3 of DEGs in CC are biologically sex-specific, providing evidence of dimorphic mechanisms of cachexia between sexes. Downregulation of Type-II Interferon signaling genes appears specific to CC development in females, suggesting a new biological sex-specific marker of CC not reliant on the loss of muscle mass, that might represent a protective mechanism against muscle loss in CC in female mice.

Blocking muscle wasting via deletion of the muscle-specific E3 ligase MuRF1 impedes pancreatic tumor growth

Cancer-induced muscle wasting reduces quality of life, complicates or precludes cancer treatments, and predicts early mortality. Herein, we investigate the requirement of the muscle-specific E3 ubiquitin ligase, MuRF1, for muscle wasting induced by pancreatic cancer. Murine pancreatic cancer (KPC) cells, or saline, were injected into the pancreas of WT and MuRF1^-/- mice, and tissues analyzed throughout tumor progression. KPC tumors induces progressive wasting of skeletal muscle and systemic metabolic reprogramming in WT mice, but not MuRF1^-/- mice. KPC tumors from MuRF1^-/- mice also grow slower, and show an accumulation of metabolites normally depleted by rapidly growing tumors. Mechanistically, MuRF1 is necessary for the KPC-induced increases in cytoskeletal and muscle contractile protein ubiquitination, and the depression of proteins that support protein synthesis. Together, these data demonstrate that MuRF1 is required for KPC-induced skeletal muscle wasting, whose deletion reprograms the systemic and tumor metabolome and delays tumor growth.

Blocking muscle wasting via deletion of the muscle-specific E3 ubiquitin ligase MuRF1 impedes pancreatic tumor growth

Cancer-induced muscle wasting reduces quality of life, complicates or precludes cancer treatments, and predicts early mortality. Herein, we investigated the requirement of the muscle-specific E3 ubiquitin ligase, MuRF1, for muscle wasting induced by pancreatic cancer. Murine pancreatic cancer (KPC) cells, or saline, were injected into the pancreas of WT and MuRF1-/- mice, and tissues analyzed throughout tumor progression. KPC tumors induced progressive wasting of skeletal muscle and systemic metabolic reprogramming in WT mice, but not MuRF1-/- mice. KPC tumors from MuRF1-/- mice also grew slower, and showed an accumulation of metabolites normally depleted by rapidly growing tumors. Mechanistically, MuRF1 was necessary for the KPC-induced increases in cytoskeletal and muscle contractile protein ubiquitination, and the depression of proteins that support protein synthesis. Together, these data demonstrate that MuRF1 is required for KPC-induced skeletal muscle wasting, whose deletion reprograms the systemic and tumor metabolome and delays tumor growth.

Dose-response relationship of resistance training for muscle morphology and strength in elderly cancer patients: A meta-analysis

Objective

To systematically evaluate the effects of resistance training (RT) on muscle strength and muscle hypertrophy in elderly cancer patients, and to provide dose-response relationships of RT variables that could improve muscle strength and morphology in elderly cancer patients.

Method

The Review Manager 5.3 was applied to analyze the 12 literatures (616 participants) through random or fixed effects model and global effect size to examine upper limb strength, lower extremity strength, and muscle hypertrophy. Sub-group analysis was made on five variables: the total number of repeated training times/week, load intensity, exercise frequency/week, exercise duration and gender. This study also examines the heterogeneity and publication bias.

Results

Twelve literatures (616 participants, 60-80 years) were included in meta-analysis. RT significantly increased the upper limb muscular strength (SMD = 0.51, 95% CI: 0.10-0.93; Z = 2.41; p = 0.02) and lower extremity strength (SMD = 0.48, 95% CI: 0.28-0.67; Z = 4.82; p < 0.00001), but had no significant effect on muscle morphology(SMD = 0.21, 95% CI: 0.01-0.42; Z = 1.88; p = 0.06). In subgroup analysis for lower extremity muscle strength in elderly male cancer patients, it was found that male intensity of 70-90%1RM, volume of 400-500 times per week, frequencies of 3 times per week, and session of 12-24 weeks, revealed the greatest effect. Funnel plot of the three studies shows that the results were reliable, and no publication bias was found.

Conclusion

RT had medium effects on improving muscle strength in elderly cancer patients, but it is not effective in improving muscle hypertrophy. In addition, when RT is performed, different training protocols can have an effect on the growth of muscle strength. Therefore, a lower extremity training protocol with a training intensity of 70-90% 1RM, a total of 400-500 repetitions per week, 3 times per week, and an exercise session of 12-24 weeks is most effective in improving lower extremity strength in elderly male cancer patients.

LP07 and LLC preclinical models of lung cancer induce divergent anabolic deficits and expression of pro-inflammatory effectors of muscle wasting

Preclinical models have been instrumental to elucidate the mechanisms underlying muscle wasting in lung cancer (LC). We investigated anabolic deficits and the expression of proinflammatory effectors of muscle wasting in the LP07 and Lewis lung carcinoma (LLC) tumor models. Tumor growth resulted in significant weakness in LP07 but not in LLC mice despite similar reductions in gastrocnemius muscle mass in both models. The LP07 tumors caused a reduction in ribosomal (r)RNA and a decrease in rRNA gene (rDNA) transcription elongation, whereas no changes in ribosomal capacity were evident in LLC tumor-bearing mice. Expression of RNA Polymerase I (Pol I) elongation-associated subunits Polr2f, PAF53, and Znrd1 mRNAs was significantly elevated in the LP07 model, whereas Pol I elongation-related factors FACT and Spt4/5 mRNAs were elevated in the LLC mice. Reductions in RPS6 and 4E-BP1 phosphorylation were similar in both models but were independent of mTOR phosphorylation in LP07 mice. Muscle inflammation was also tumor-specific, IL-6 and TNF-α mRNA increased with LLC tumors, and upregulation of NLRP3 mRNA was independent of tumor type. In summary, although both models caused muscle wasting, only the LP07 model displayed muscle weakness with reductions in ribosomal capacity. Intracellular signaling diverged at the mTOR level with similar reductions in RPS6 and 4E-BP1 phosphorylation regardless of tumor type. The increase in proinflammatory factors was more pronounced in the LLC model. Our results demonstrate novel divergent anabolic deficits and expression of proinflammatory effectors of muscle wasting in the LP07 and LLC preclinical models of lung cancer.NEW & NOTEWORTHY We provide novel data demonstrating significant divergence in anabolic deficits and the expression of proinflammatory effectors of muscle wasting consequent to different lung-derived tumors.

Creatinine-cystatin C ratio and mortality in cancer patients: a retrospective cohort study

BACKGROUND

Muscle wasting is prevalent in cancer patients, and early recognition of this phenomenon is important for risk stratification. Recent studies have suggested that the creatinine-cystatin C ratio may correlate with muscle mass in several patient populations. The association between creatinine-cystatin C ratio and survival was assessed in cancer patients.

METHODS

A total of 3060 patients who were evaluated for serum creatinine and cystatin C levels at the time of cancer diagnosis were included. The primary outcome was 6-month mortality. The 1-year mortality, and length of intensive care unit (ICU) and hospital stay were also evaluated.

RESULTS

The mean age was 61.6 ± 13.5 years, and 1409 patients (46.0%) were female. The median creatinine and cystatin C levels were 0.9 (interquartile range [IQR], 0.6-1.3) mg/dL and 1.0 (IQR, 0.8-1.5) mg/L, respectively, with a creatinine-cystatin C ratio range of 0.12-12.54. In the Cox proportional hazards analysis, an increase in the creatinine-cystatin C ratio was associated with a significant decrease in the 6-month mortality (per 1 creatinine-cystatin C ratio, hazard ratio [HR] 0.35; 95% confidence interval [CI], 0.28-0.44). When stratified into quartiles, the risk of 6-month mortality was significantly lower in the highest quartile (HR 0.30; 95% CI, 0.24-0.37) than in the lowest quartile. Analysis of 1-year mortality outcomes revealed similar findings. These associations were independent of confounding factors. The highest quartile was also associated with shorter lengths of ICU and hospital stay (both P < 0.001).

CONCLUSIONS

The creatinine-cystatin C ratio at the time of cancer diagnosis significantly associates with survival and hospitalization in cancer patients.

Exercise Counteracts the Deleterious Effects of Cancer Cachexia

Simple Summary

This review provides an overview of the effects of exercise training on the major mechanisms related to cancer cachexia (CC). The review also discusses how cancer comorbidities can influence the ability of patients/animals with cancer to perform exercise training and what precautions should be taken when they exercise. The contribution of other factors, such as exercise modality and biological sex, to exercise effectiveness in ameliorating CC are also elaborated in the final sections. We provide meticulous evidence for how advantageous exercise training can be in patients/animals with CC at molecular and cellular levels. Finally, we emphasise what factors should be considered to optimise and personalise an exercise training program in CC.

Abstract

Cancer cachexia (CC) is a multifactorial syndrome characterised by unintentional loss of body weight and muscle mass in patients with cancer. The major hallmarks associated with CC development and progression include imbalanced protein turnover, inflammatory signalling, mitochondrial dysfunction and satellite cell dysregulation. So far, there is no effective treatment to counteract muscle wasting in patients with CC. Exercise training has been proposed as a potential therapeutic approach for CC. This review provides an overview of the effects of exercise training in CC-related mechanisms as well as how factors such as cancer comorbidities, exercise modality and biological sex can influence exercise effectiveness in CC. Evidence in mice and humans suggests exercise training combats all of the hallmarks of CC. Several exercise modalities induce beneficial adaptations in patients/animals with CC, but concurrent resistance and endurance training is considered the optimal type of exercise. In the case of cancer patients presenting comorbidities, exercise training should be performed only under specific guidelines and precautions to avoid adverse effects. Observational comparison of studies in CC using different biological sex shows exercise-induced adaptations are similar between male and female patients/animals with cancer, but further studies are needed to confirm this.

Exercise in People With Cancer: A Spotlight on Energy Regulation and Cachexia

Exercise is increasingly becoming a standard of cancer care, with well-documented benefits for patients including improved mental wellbeing and reduced treatment-related side effects. However, important gaps in knowledge remain about how to optimise exercise prescription for people with cancer. Importantly, it remains unclear how exercise affects the progression of cancer cachexia (a wasting disease stemming from energy imbalance, and a common manifestation of advanced malignant disease), particularly once the condition has already developed. It was recently suggested that the anti-tumour effect of exercise might come from improved energetic capacity. Here, we highlight the possible effect of exercise on energetic capacity and energy regulation in the context of cancer, and how this might affect the progression of cancer cachexia. We suggest that due to the additional energy demand caused by the tumour and associated systemic inflammation, overreaching may occur more easily in people with cancer. Importantly, this could result in impaired anti-tumour immunity and/or the exacerbation of cancer cachexia. This highlights the importance of individualised exercise programs for people with cancer, with special consideration for the regulation of energy balance, ongoing monitoring and possible nutritional supplementation to support the increased energy demand caused by exercise.

Individual Differences in Chemosensory Perception Amongst Cancer Patients Undergoing Chemotherapy: A Narrative Review

Chemotherapy is an aggressive form of treatment for cancer and its toxicity directly affects the eating behavior of many patients, usually by adversely affecting their sense of smell and/or taste. These sensory alterations often lead to serious nutritional deficiencies that can jeopardize the patient's recovery, and even continue to affect their lives once treatment has terminated. Importantly, however, not all patients suffer from such alterations to their chemical senses; and those who do, do not necessarily describe the side effects in quite the same way, nor suffer from them with equal intensity. The origin of these individual differences between cancer patients undergoing chemotherapy treatment has not, as yet, been studied in detail. This review is therefore designed to encourage future research that can help to address the perceptual/sensory problems (and the consequent malnutrition) identified amongst this group of patients in a more customized/personalized manner. In particular, by providing an overview of the possible causes of these large individual differences that have been reported in the literature. For this reason, in addition to the narrative bibliographic review, several possible strategies that could help to improve the chemosensory perception of food are proposed.

Mitochondrial aberrations during the progression of disuse atrophy differentially affect male and female mice

BACKGROUND

Disuse decreases muscle size and is predictive of mortality across multiple pathologies. Detriments to mitochondrial function are hypothesized to underlie disuse-induced muscle atrophy. Little data exist on early mechanisms contributing to onset of these pathologies, nor is it known how they differ between sexes. The purpose of this study was to examine differential and conserved responses to mitochondrial quality control in male and female mice during the development and progression of disuse-induced atrophy.

METHODS

One hundred C57BL/6J mice (50 male and 50 female) were hindlimb unloaded to induce disuse atrophy for 0 (con), 24, 48, 72, or 168 h. At designated time-points, extensor digitorum longus, gastrocnemius, and soleus muscles were collected for analysis of mitochondrial quality control markers.

RESULTS

One hundred sixty-eight hours of disuse resulted in ~25% lower oxidative muscle fibre CSA in both male (P = 0.003) and female (P = 0.02) mice without any differences due to disuse in glycolytic fibres. In male mice, 48 h of unloading was sufficient to result in ~67% greater mitochondrial oxidative stress as assessed by the reporter gene pMitoTimer compared with 0 h (P = 0.002), this mitochondrial stress preceded detectable muscle loss. However in female mice, mitochondrial oxidative stress did not occur until 168 h of disuse (~40% greater mitochondrial oxidative stress in 168 h compared with 0 h of disuse, P < 0.0001). Blunted oxidative stress in female mice appeared to coincide with greater inductions of autophagy and mitophagy in female mice (~3-fold greater BNIP3 and ~6-fold greater LC3II/I ratio P < 0.0001 and P = 0.038 respectively). Male mice overall had greater reactive oxygen species (ROS) production compared with female mice. Female mice had a greater induction of ROS within 24 h of disuse (~4-fold greater compared with 0 h, P < 0.0001); whereas male mice did not have greater ROS production until 168 h of disuse (~2-fold greater, P < 0.0001). Although all muscle types exhibited some alterations to mitochondrial quality control, such as increased markers of mitophagy and fission, the soleus muscle in both male and female mice exhibited consistent alterations to various markers of mitochondrial quality. Markers of mitochondrial translation were approximately 30-50% lower within 24 h of unloading in both male and female soleus muscle (P value ranges: <0.0001-0.03).

CONCLUSIONS

Disuse negatively affects mitochondria differentially between sexes during development of muscle wasting. Acutely, female mice may forgo muscle mass to maintain mitochondrial quality compared with male mice. These differences may contribute to divergent clinical manifestations of atrophy.

Identification and Elucidation of the Protective isomiRs in Lung Cancer Patient Prognosis

MicroRNAs (miRNAs) are approximately 20–22 nucleotides in length, which are well known to participate in the post-transcriptional modification. The mature miRNAs were observed to be varied on 5′ or 3′ that raise another term—the isoforms of mature miRNAs (isomiRs), which have been proven not the artifacts and discussed widely recently. In our research, we focused on studying the 5′ isomiRs in lung adenocarcinoma (LUAD) in The Cancer Genome Atlas (TCGA). We characterized 75 isomiRs significantly associated with better prognosis and 43 isomiRs with poor prognosis. The 75 protective isomiRs can successfully distinguish tumors from normal samples and are expressed differently between patients of early and late stages. We also found that most of the protective isomiRs tend to be with downstream shift and upregulated compared with those with upstream shift, implying that a possible selection occurs during cancer development. Among these protective isomiRs, we observed a highly positive and significant correlation, as well as in harmful isomiRs, suggesting cooperation within the group. However, between protective and harmful, there is no such a concordance but conversely more negative correlation, suggesting the possible antagonistic effect between protective and harmful isomiRs. We also identified that two isomiRs miR-181a-3p|-3 and miR-181a-3p|2, respectively, belong to the harmful and protective groups, suggesting a bidirectional regulation of their originated archetype—miR-181a-3p. Additionally, we found that the protective isomiRs of miR-21-5p, which is an oncomiR, may be evolved as the tumor suppressors through producing isomiRs to hinder metastasis. In summary, these results displayed the characteristics of the protective isomiRs and their potential for developing the treatment of lung cancer.

The oestrous cycle and skeletal muscle atrophy: Investigations in rodent models of muscle loss

NEW FINDINGS

What is the central question of this study? Is the oestrous cycle affected during disuse atrophies and, if so, how are oestrous cycle changes related to musculoskeletal outcomes? What is the main finding and its importance? Rodent oestrous cycles were altered during disuse atrophy, which was correlated with musculoskeletal outcomes. However, the oestrous cycle did not appear to be changed by Lewis lung carcinoma, which resulted in no differences in muscle size in comparison to healthy control animals. These findings suggest a relationship between the oestrous cycle and muscle size during atrophic pathologies.

ABSTRACT

Recent efforts have focused on improving our understanding of female muscle physiology during exposure to muscle atrophic stimuli. A key feature of female rodent physiology is the oestrous cycle. However, it is not known how such stimuli interact with the oestrous cycle to influence muscle health. In this study, we investigated the impact of muscle atrophic stimuli on the oestrous cycle and how these alterations are correlated with musculoskeletal outcomes. A series of experiments were performed in female rodents, including hindlimb unloading (HU), HU followed by 24 h of reloading, HU combined with dexamethasone treatment, and Lewis lung carcinoma. The oestrous cycle phase was assessed throughout each intervention and correlated with musculoskeletal outcomes. Seven or 14 days of HU increased the duration in dioestrus or metoestrus (D/M; low hormones) and was negatively correlated with gastrocnemius mass. Time spent in D/M was also negatively correlated with changes in grip strength and bone density after HU, and with muscle recovery 24 h after the cessation of HU. The addition of dexamethasone strengthened these relationships between time in D/M and reduced musculoskeletal outcomes. However, in animals with Lewis lung carcinoma, oestrous cyclicity did not differ from that of control animals, and time spent in D/M was not correlated with either gastrocnemius mass or tumour burden. In vitro experiments suggested that enhanced protein synthesis induced by estrogen might protect against muscle atrophy. In conclusion, muscle atrophic insults are correlated with changes in the oestrous cycle, which are associated with deterioration in musculoskeletal outcomes. The magnitude of oestrous cycle alterations depends on the atrophic stimuli.

Reduced rDNA transcription diminishes skeletal muscle ribosomal capacity and protein synthesis in cancer cachexia

Muscle wasting in cancer is associated with deficits in protein synthesis, yet, the mechanisms underlying this anabolic impairment remain poorly understood. The capacity for protein synthesis is mainly determined by the abundance of muscle ribosomes, which is in turn regulated by transcription of the ribosomal (r)RNA genes (rDNA). In this study, we investigated whether muscle loss in a preclinical model of ovarian cancer is associated with a reduction in ribosomal capacity and was a consequence of impaired rDNA transcription. Tumor bearing resulted in a significant loss in gastrocnemius muscle weight and protein synthesis capacity, and was consistent with a significant reduction in rDNA transcription and ribosomal capacity. Despite the induction of the ribophagy receptor NUFIP1 mRNA and the loss of NUFIP1 protein, in vitro studies revealed that while inhibition of autophagy rescued NUFIP1, it did not prevent the loss of rRNA. Electrophoretic analysis of rRNA fragmentation from both in vivo and in vitro models showed no evidence of endonucleolytic cleavage, suggesting that rRNA degradation may not play a major role in modulating muscle ribosome abundance. Our results indicate that in this model of ovarian cancer-induced cachexia, the ability of skeletal muscle to synthesize protein is compromised by a reduction in rDNA transcription and consequently a lower ribosomal capacity. Thus, impaired ribosomal production appears to play a key role in the anabolic deficits associated with muscle wasting in cancer cachexia.

Cancer cachexia: molecular mechanism and pharmacological management

Cancer cachexia often occurs in malignant tumors and is a multifactorial and complex symptom characterized by wasting of skeletal muscle and adipose tissue, resulting in weight loss, poor life quality and shorter survival. The pathogenic mechanism of cancer cachexia is complex, involving a variety of molecular substrates and signal pathways. Advancements in understanding the molecular mechanisms of cancer cachexia have provided a platform for the development of new targeted therapies. Although recent outcomes of early-phase trials have showed that several drugs presented an ideal curative effect, monotherapy cannot be entirely satisfactory in the treatment of cachexia-associated symptoms due to its complex and multifactorial pathogenesis. Therefore, the lack of definitive therapeutic strategies for cancer cachexia emphasizes the need to develop a better understanding of the underlying mechanisms. Increasing evidences show that the progression of cachexia is associated with metabolic alternations, which mainly include excessive energy expenditure, increased proteolysis and mitochondrial dysfunction. In this review, we provided an overview of the key mechanisms of cancer cachexia, with a major focus on muscle atrophy, adipose tissue wasting, anorexia and fatigue and updated the latest progress of pharmacological management of cancer cachexia, thereby further advancing the interventions that can counteract cancer cachexia.

Development and progression of cancer cachexia: Perspectives from bench to bedside

Cancer cachexia (CC) is a devastating syndrome characterized by weight loss, reduced fat mass and muscle mass that affects approximately 80% of cancer patients and is responsible for 22%–30% of cancer-associated deaths. Understanding underlying mechanisms for the development of CC are crucial to advance therapies to treat CC and improve cancer outcomes. CC is a multi-organ syndrome that results in extensive skeletal muscle and adipose tissue wasting; however, CC can impair other organs such as the liver, heart, brain, and bone as well. A considerable amount of CC research focuses on changes that occur within the muscle, but cancer-related impairments in other organ systems are understudied. Furthermore, metabolic changes in organ systems other than muscle may contribute to CC. Therefore, the purpose of this review is to address degenerative mechanisms which occur during CC from a whole-body perspective. Outlining the information known about metabolic changes that occur in response to cancer is necessary to develop and enhance therapies to treat CC. As much of the current evidences in CC are from pre-clinical models we should note the majority of the data reviewed here are from pre-clinical models.

Sex Differences in Cancer Cachexia

PURPOSE OF REVIEW

Cachexia, a feature of cancer and other chronic diseases, is marked by progressive weight loss and skeletal muscle wasting. This review aims to highlight the sex differences in manifestations of cancer cachexia in patients, rodent models, and our current understanding of the potential mechanisms accounting for these differences.

RECENT FINDINGS

Male cancer patients generally have higher prevalence of cachexia, greater weight loss or muscle wasting, and worse outcomes compared with female cancer patients. Knowledge is increasing about sex differences in muscle fiber type and function, mitochondrial metabolism, global gene expression and signaling pathways, and regulatory mechanisms at the levels of sex chromosomes vs. sex hormones; however, it is largely undetermined how such sex differences directly affect the susceptibility to stressors leading to muscle wasting in cancer cachexia. Few studies have investigated basic mechanisms underlying sex differences in cancer cachexia. A better understanding of sex differences would improve cachexia treatment in both sexes.

Myokines in treatment-naïve patients with cancer-associated cachexia

Cancer-associated cachexia is a complex metabolic syndrome characterized by weight loss and systemic inflammation. Muscle loss and fatty infiltration into muscle are associated with poor prognosis in cancer patients. Skeletal muscle secretes myokines, factors with autocrine, paracrine and/or endocrine action, which may be modified by or play a role in cachexia. This study examined myokine content in the plasma, skeletal muscle and tumor homogenates from treatment-naïve patients with gastric or colorectal stages I-IV cancer with cachexia (CC, N = 62), or not (weight stable cancer, WSC, N = 32). Myostatin, interleukin (IL) 15, follistatin-like protein 1 (FSTL-1), fatty acid binding protein 3 (FABP3), irisin and brain-derived neurotrophic factor (BDNF) protein content in samples was measured with Multiplex technology; body composition and muscle lipid infiltration were evaluated in computed tomography, and quantification of triacylglycerol (TAG) in the skeletal muscle. Cachectic patients presented lower muscle FSTL-1 expression (p = 0.047), higher FABP3 plasma content (p = 0.0301) and higher tumor tissue expression of FABP3 (p = 0.0182), IL-15 (p = 0.007) and irisin (p = 0.0110), compared to WSC. Neither muscle TAG content, nor muscle attenuation were different between weight stable and cachectic patients. Lumbar adipose tissue (AT) index, visceral AT index and subcutaneous AT index were lower in CC (p = 0.0149, p = 0.0455 and p = 0.0087, respectively), who also presented lower muscularity in the cohort (69.2% of patients; p = 0.0301), compared to WSC. The results indicate the myokine profile in skeletal muscle, plasma and tumor is impacted by cachexia. These findings show that myokines eventually affecting muscle wasting may not solely derive from the muscle itself (as the tumor also may contribute to the systemic scenario), and put forward new perspectives on cachexia treatment targeting myokines and associated receptors and pathways.

Marked Increased Production of Acute Phase Reactants by Skeletal Muscle during Cancer Cachexia

Simple Summary

Muscle wasting during cancer is recognized as an independent predictor of mortality. The aim of this study was to characterize the changes in the muscle secretome associated with cancer cachexia to gain a better understanding of the mechanisms involved and to identify secreted proteins which may reflect this wasting process. Our study demonstrated that skeletal muscle is a source of several acute phase reactants during cancer cachexia that may hold the key to a cachexia-specific signature. Future work will have to determine whether some of these acute phase reactants contribute to and/or reflect the muscle atrophy caused by cancer, therefore representing potential therapeutic targets and/or biomarkers of cancer cachexia.

Abstract

Loss of skeletal muscle mass in cancer cachexia is recognized as a predictor of mortality. This study aimed to characterize the changes in the muscle secretome associated with cancer cachexia to gain a better understanding of the mechanisms involved and to identify secreted proteins which may reflect this wasting process. The changes in the muscle proteome of the C26 model were investigated by label-free proteomic analysis followed by a bioinformatic analysis in order to identify potentially secreted proteins. Multiple reaction monitoring and Western blotting were used to verify the presence of candidate proteins in the circulation. Our results revealed a marked increased muscular production of several acute phase reactants (APR: Haptoglobin, Serine protease inhibitor A3N, Complement C3, Serum amyloid A-1 protein) which are released in the circulation during C26 cancer cachexia. This was confirmed in other models of cancer cachexia as well as in cancer patients. Glucocorticoids and proinflammatory cytokines are responsible for an increased production of APR by muscle cells. Finally, their muscular expressions are strongly positively correlated with body weight loss as well as the muscular induction of atrogens. Our study demonstrates therefore a marked increased production of APR by the muscle in cancer cachexia.

Mitochondrial Function and Protein Turnover in the Diaphragm are Altered in LLC Tumor Model of Cancer Cachexia

It is established that cancer cachexia causes limb muscle atrophy and is strongly associated with morbidity and mortality; less is known about how the development of cachexia impacts the diaphragm. The purpose of this study was to investigate cellular signaling mechanisms related to mitochondrial function, reactive oxygen species (ROS) production, and protein synthesis during the development of cancer cachexia. C57BL/J6 mice developed Lewis Lung Carcinoma for either 0 weeks (Control), 1 week, 2 weeks, 3 weeks, or 4 weeks. At designated time points, diaphragms were harvested and analyzed. Mitochondrial respiratory control ratio was ~50% lower in experimental groups, which was significant by 2 weeks of cancer development, with no difference in mitochondrial content markers COXIV or VDAC. Compared to the controls, ROS was 4-fold elevated in 2-week animals but then was not different at later time points. Only one antioxidant protein, GPX3, was altered by cancer development (~70% lower in experimental groups). Protein synthesis, measured by a fractional synthesis rate, appeared to become progressively lower with the cancer duration, but the mean difference was not significant. The development and progression of cancer cachexia induces marked alterations to mitochondrial function and ROS production in the diaphragm and may contribute to increased cachexia-associated morbidity and mortality.