Logan Steele
Muscle wasting, or the loss of muscle tissue, is a common problem for people with cancer. This condition is called cancer cachexia and is associated with serious clinical consequences such as physical impairment, poor quality of life, reduced tolerance to treatments, and shorter survival. The mechanisms underlying cancer-related muscle wasting are not yet fully understood, but a prominent role is played by increased muscle protein degradation, impaired muscle protein synthesis, and defective myogenesis. Research is ongoing to better understand and treat this condition, with some potential therapeutic targets and promising drugs already identified.
| Characteristics | Values |
|---|---|
| Name | Cancer cachexia, Muscle wasting |
| Occurrence | 80% of people with cancer |
| Mortality rate | 30% |
| Causes | Reduced nutrient intake, metabolic abnormalities, cytokines, hormones, tumour-derived humoral factors, increased muscle protein degradation, impaired muscle protein synthesis, defective myogenesis, mitochondrial dysfunction, insulin resistance, inflammation |
| Treatment | Appetite stimulants, medicines, soft diets, adding calories, tube feeding, exercise, multimodal therapy, IL-6 inhibitor drugs |
| Prevention | Early recognition and treatment of nutritional and metabolic alterations |
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What You'll Learn
Cancer cachexia
Muscle wasting, or the loss of muscle tissue, is a common problem for people with cancer. The loss of contractile strength and function associated with muscle wasting and the onset of chronic fatigue may result in reduced physical activity, which can further exacerbate muscle loss. Cachexia is associated with an increased mortality rate and is thought to directly cause up to 30% of cancer deaths, often due to heart or respiratory failure related to muscle loss.
The molecular mechanisms underlying cancer-related muscle wasting have not been fully elucidated. Available evidence suggests that a prominent role is played by increased muscle protein degradation, although impaired muscle protein synthesis and defective myogenesis may also contribute. In addition, alterations in energy metabolism involving mitochondrial dysfunction have been implicated in the wasting process. The prevalence of muscle loss has been reported as between 20% and 70%, depending on the type of tumour and the criteria used for assessment.
Research groups have identified a possible mechanism for how cancer cells may be sending messages to muscle cells, resulting in cancer-related muscle wasting. Cachexia may result from reduced nutrient intake and/or availability (secondary to anorexia, malabsorption or mechanical obstruction) and metabolic abnormalities, triggered by a complex network of cytokines, hormones, and other tumour- and host-derived humoral factors.
Currently, there are no effective treatments for cachexia. However, researchers have launched clinical trials to test exercise and nutrition-based treatments, as well as drugs that target the inhibition of catabolism. At least one drug has been shown to help people with cancer cachexia maintain lean muscle mass, which is critical for daily functioning and the ability to tolerate cancer treatments.
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Muscle protein degradation
Muscle wasting, or the loss of muscle tissue, is a common problem for people with cancer. This condition is called cancer cachexia and it negatively impacts patients' prognosis and quality of life. Cachexia may result from reduced nutrient intake and/or metabolic abnormalities triggered by a complex network of cytokines, hormones, and other factors.
Muscle wasting is associated with serious clinical consequences such as physical impairment, poor quality of life, reduced tolerance to treatments, and shorter survival. While the precise mechanisms of muscle wasting are not fully understood, increased muscle protein degradation is believed to play a prominent role. In addition, impaired muscle protein synthesis and defective myogenesis may also contribute.
Muscle protein breakdown (MPB) is an important metabolic component of muscle remodelling, adaptation to training, and increasing muscle mass. Degradation of muscle proteins occurs through the integration of three main systems: autophagy and the calpain and ubiquitin-proteasome systems. These systems are intricately linked and regulated in a complex manner. The ubiquitin-proteasome system (UPS), in particular, is recognised as a major intracellular protein degradation system that plays an essential role in protein degradation during muscle atrophy.
UPS-mediated protein quality control is known to be impaired in aging and diseases. Exercise is a well-known non-pharmacological approach to promote muscle protein turnover rates and has been studied extensively in the context of muscle hypertrophy. However, there are still gaps in the understanding of how muscle protein degradation is regulated at the molecular level, especially in the context of cancer-induced muscle wasting.
Recent studies have provided new insights into the cellular mechanisms of muscle wasting, suggesting that cancer progression leads to a decrease in skeletal muscle ribosomes, which are responsible for protein synthesis. This reduction in ribosomes may explain the loss of muscle mass observed in cancer patients. By understanding the underlying mechanisms of muscle wasting, researchers can develop effective therapeutic strategies to improve patient outcomes and quality of life.
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Insulin resistance
Muscle wasting, or the loss of muscle tissue, is a common problem for people with cancer. Cancer cachexia, a multifactorial condition that negatively impacts a patient's prognosis and quality of life, is a severe and disabling clinical condition that frequently accompanies the development of many types of cancer. Cachexia may result from reduced nutrient intake and/or metabolic abnormalities triggered by a complex network of cytokines, hormones, and other factors.
In insulin-sensitive states, the binding of insulin to its receptor increases PI3K activity, which in turn increases the phosphorylation of Akt. This cascade results in decreased proteolytic activity. However, in insulin-resistant states, PI3K activity is decreased, leading to reduced phosphorylation of Akt. Lower levels of pAkt release the inhibition of FoxO and caspase-3, resulting in increased proteolytic activity.
The infusion of physiologically relevant doses of insulin can decrease skeletal muscle protein degradation without affecting blood glucose levels or protein synthesis. Higher doses of insulin, however, only decrease blood glucose levels without further effect on protein degradation. Thus, insulin has the potential to regulate skeletal muscle mass within a limited range of concentrations, primarily through alterations in protein degradation.
While the precise mechanisms of muscle wasting in cancer are not yet fully understood, the presence of insulin resistance in cancer patients warrants significant attention. Further investigation of the role of insulin resistance in cancer cachexia is needed to improve the treatment and prevention of this syndrome.
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Cytokines and inflammation
Cancer cachexia is a wasting syndrome that occurs in up to 80% of people with advanced cancer. It is characterised by a pronounced systemic muscle wasting and weakness, including the loss of fat mass. Cachexia is one of the main causes of cancer-related deaths, yet there are still no approved drugs for its treatment.
Cancer cachexia is associated with a systemic inflammatory response, which is linked to weight and muscle loss and poorer outcomes in patients with cancer. Tumours secrete pro-inflammatory mediators for growth, defence against cell death, and promotion of metastasis. As the tumour grows, it may activate an uncontrolled increase in pro-inflammatory cytokines, which in turn initiates cancer-related muscle wasting.
Inflammation influences both the levels and behaviour of cytokines, which have ripple effects throughout the body. This can cause skeletal muscle to wither (sarcopenia) and reduce the desire to eat (anorexia), further robbing the body of the fuel it needs.
The presence of inflammatory cytokines can affect skeletal muscle through several direct mechanisms, relying on the activation of the corresponding receptor expressed by the muscle. This results in the inhibition of muscle protein synthesis (MPS), elevation of catabolic activity through the ubiquitin-proteasomal system (UPS) and autophagy, and impairment of myogenesis.
In addition, systemic inflammatory mediators indirectly contribute to muscle wasting through dysregulation of tissue and organ systems. For example, the cytokine Interleukin-6 (IL-6) is a central player in a cycle of tumour growth and cachexia through cross-talk among tumours, fat and muscle. Another cytokine, GDF15, binds to a protein called GFRAL, which is produced by neurons in a part of the brain involved in appetite control. Treatments targeting GDF15 and GFRAL are currently being tested in clinical trials as cachexia treatments.
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Exercise as a treatment
Muscle wasting, or the loss of muscle tissue, is a common problem for people with cancer. It is a severe and disabling clinical condition that frequently accompanies the development of many types of cancer. The precise mechanisms of muscle wasting have long eluded doctors and scientists, but recent studies have provided new insights.
Exercise has been proposed as a potential therapy for cancer-induced muscle wasting, also known as cancer cachexia. Cancer cachexia is a progressive disorder characterised by body weight, fat, and muscle loss. It is associated with metabolic disruptions, inflammation, hypogonadism, and physical inactivity, which can negatively impact muscle mass and function. Exercise is known for its anti-inflammatory effects and its ability to stimulate anabolic signalling. It has the potential to improve the muscle's sensitivity to anabolic stimuli, reduce wasting through protein synthesis modulation, and downregulate proteolytic factors.
While there is no current recommendation for exercise in the management of cachexia, research suggests that exercise may play a beneficial role in cancer-induced muscle wasting. Experimental studies have shown that treadmill exercise training can attenuate the initiation and progression of cancer cachexia in mice. Both endurance and resistance exercises can modulate the inflammatory response in tumour-bearing rats. Voluntary wheel running has been found to prevent cachexia, increase survival, and alleviate muscle wasting in mice undergoing chemotherapy.
In humans, exercise programs during cancer treatment can be challenging to implement due to factors such as chronic fatigue, anemia, cardiac dysfunction, and other comorbidities. However, evidence suggests that physical exercise may have positive effects on cancer patients during and after active treatment. Both aerobic and resistance exercises, or a combination of both, may contribute to improving muscle strength in cancer patients. Resistance exercise, in particular, appears to have a favourable impact on muscle mass, although more evidence is needed to confirm this.
The role of exercise in managing muscle loss in cancer is still being explored, and ongoing clinical trials are investigating the use of personalised exercise programs in combination with nutritional support and/or anti-inflammatory interventions. These multimodal therapy approaches are likely to be more effective in targeting muscle loss. However, it is important to note that the response to exercise in individuals with cancer-induced muscle wasting may differ from that of healthy individuals. The complexity and intensity of exercise interventions required to promote skeletal muscle hypertrophy can be challenging for some cancer patients to achieve.
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Frequently asked questions
Muscle wasting, or the loss of muscle tissue, is a common problem for people with cancer. It is associated with serious clinical consequences such as physical impairment, poor quality of life, reduced tolerance to treatments, and shorter survival.
The precise mechanisms of muscle wasting in cancer patients are not yet fully understood. However, it is believed to be caused by a combination of factors, including increased muscle protein degradation, impaired muscle protein synthesis, defective myogenesis, and alterations in energy metabolism involving mitochondrial dysfunction. Research suggests that cancer progression leads to a decrease in skeletal muscle ribosomes, which are responsible for protein synthesis, resulting in muscle wasting.
Muscle wasting is a prevalent issue in cancer patients, with an estimated 80% of people with cancer experiencing significant muscle wasting. The prevalence of muscle loss varies depending on the type and stage of cancer, ranging from 16% in early-stage breast cancer to 40.3% in hepatocellular carcinoma patients.
