Muscle atrophy in cachexia: can dietary protein tip the balance?

Evolving concepts on perioperative nutrition of sarcopenic cancer patients

The recent recognition of the association of sarcopenia with an increased risk of complications after a surgical procedure calls for rethinking the proper approach of the perioperative care in cancer patients. Sarcopenia is broadly considered in literature according to three different definitions: loss of muscle mass, loss of muscle mass plus reduced muscle function and myosteatosis. The aim of this short review on this issue is to define the excess of risk by type of primary and of surgical procedure, depending on the definition of sarcopenia, to speculate on this association (casual versus causal) and to examine the current therapeutical approaches. The analysis of the data shows that sarcopenia, defined as loss of muscle mass plus reduced muscle function, has the higher predictive power for the occurrence of postoperative complications than the two other definitions, and any definition of sarcopenia works better than the usual indexes or scores of surgical risk. Our analysis supports the concept that: a) sarcopenia is frequently associated with inflammation, but inflammation cannot be considered the only or the absolute cause for sarcopenia, b) sarcopenia is not a simple marker of risk but can have a direct role in the increase of risk. Data on perioperative care of sarcopenic cancer patients are scanty but a correct approach cannot rely on nutritional support alone but on a combined approach of optimized nutrition and exercise, hopefully associated with an anti-inflammatory treatment. This strategy should be applied proactively in keeping with the recent recommendations of the American Society of Clinical Oncology for the medical treatment of advanced cancer patients even if a clear demonstration of effectiveness is still lacking.

Guideline for the Management of Diabetes Mellitus in the Elderly in China (2024 Edition)

With the deepening of aging in China, the prevalence of diabetes in older people has increased noticeably, and standardized diabetes management is critical for improving clinical outcomes of diabetes in older people. In 2021, the National Center of Gerontology, Chinese Society of Geriatrics, and Diabetes Professional Committee of Chinese Aging Well Association organized experts to write the first guideline for diabetes diagnosis and treatment in older people in China, the Guideline for the Management of Diabetes Mellitus in the Elderly in China (2021 Edition). The guideline emphasizes that older patients with diabetes are a highly heterogeneous group requiring comprehensive assessment and stratified and individualized management strategies. The guideline proposes simple treatments and de-intensified treatment strategies for older patients with diabetes. This edition of the guideline provides clinicians with practical and operable clinical guidance, thus greatly contributing to the comprehensive and full-cycle standardized management of older patients with diabetes in China and promoting the extensive development of clinical and basic research on diabetes in older people and related fields. In the past 3 years, evidence-based medicine for older patients with diabetes and related fields has further advanced, and new treatment concepts, drugs, and technologies have been developed. The guideline editorial committee promptly updated the first edition of the guideline and compiled the Guideline for the Management of Diabetes Mellitus in the Elderly in China (2024 Edition). More precise management paths for older patients with diabetes are proposed, for achieving continued standardization of the management of older Chinese patients with diabetes and improving their clinical outcomes.

High-protein home parenteral nutrition in malnourished oncology patients: a systematic literature review

INTRODUCTION

Up to 83% of oncology patients are affected by cancer-related malnutrition, depending on tumour location and patient age. Parenteral nutrition can be used to manage malnutrition, but there is no clear consensus as to the optimal protein dosage. The objective of this systematic literature review (SLR) was to identify studies on malnourished oncology patients receiving home parenteral nutrition (HPN) where protein or amino acid delivery was reported in g/kg bodyweight/day, and to compare outcomes between patients receiving low (< 1 g/kg bodyweight/day), standard (1-1.5 g/kg/day), and high-protein doses (> 1.5 g/kg/day).

METHODS

Literature searches were performed on 5th October 2021 in Embase, MEDLINE, and five Cochrane Library and Centre for Reviews and Dissemination databases. Searches were complemented by hand-searching of conference proceedings, a clinical trial registry, and bibliographic reference lists of included studies and relevant SLRs/meta-analyses.

RESULTS

Nineteen publications were included; sixteen investigated standard protein, two reported low protein, and one included both, but none assessed high-protein doses. Only one randomised controlled trial (RCT) was identified; all other studies were observational studies. The only study to compare two protein doses reported significantly greater weight gain in patients receiving 1.15 g/kg/day than those receiving 0.77 g/kg/day.

CONCLUSION

At present, there is insufficient evidence to determine the optimal protein dosage for malnourished oncology patients receiving HPN. Data from non-HPN studies and critically ill patients indicate that high-protein interventions are associated with increased overall survival and quality of life; further studies are needed to establish whether the same applies in malnourished oncology patients.

The metabolite butyrate produced by gut microbiota inhibits cachexia-associated skeletal muscle atrophy by regulating intestinal barrier function and macrophage polarization

OBJECTIVE

Cachexia, marked by muscle atrophy, poses substantial challenges for prevention and treatment. This study delves into the unclear role of butyrate, a gut microbiota metabolite, in cachexia by examining gut microbiota and short-chain fatty acid (SCFA) profiles in human and mouse fecal samples.

METHODS

We analyzed cachexia-associated gut microbiota and SCFA profiles using 16S rRNA sequencing and metabolomic techniques. Mouse cachexia models were developed with C26 cells, and LPS was used to induce muscle cell atrophy in C2C12 cells. We evaluated butyrate's in vivo effects on intestinal health, muscle preservation, inflammation, and macrophage activity. In vitro studies focused on butyrate's influence on macrophage polarization and the subsequent effects on muscle cells.

RESULTS

Both cachexia patients and mice exhibited gut microbiota imbalances, irregular butyrate concentrations, and a decline in butyrate-producing bacteria. In vivo tests showed that butyrate counteract cachexia-induced muscle atrophy by adjusting the Akt/mTOR/Foxo3a and Fbox32/Trim63 pathways. These butyrate also bolstered intestinal barrier integrity, minimized endotoxin migration, and mitigated oxidative stress. Furthermore, butyrate curtailed inflammation and macrophage penetration in muscles. In vitro experimental results demonstrate that butyrate inhibit macrophage polarization towards the M1 phenotype and promote polarization towards the M2 phenotype. Both M1 and M2 macrophages influence the aforementioned pathways and oxidative stress, participating in the regulation of muscle cell atrophy.

CONCLUSION

Our study delineates the intricate interplay between gut microbiota dysbiosis, butyrate fluctuations, and cachexia progression. Butyrate not only reinforces the intestinal barrier but also orchestrates macrophage polarization, mitigating muscle atrophy and averting cachexia-induced muscle deterioration. Concurrently, the M1 and M2 macrophages play pivotal roles in modulating skeletal muscle cell atrophy. This highlights the potential of utilizing the gut-derived metabolite butyrate as a promising therapeutic approach for addressing cachexia-related issues.

Cancer cachexia: molecular mechanisms and treatment strategies

Muscle wasting is a consequence of physiological changes or a pathology characterized by increased catabolic activity that leads to progressive loss of skeletal muscle mass and strength. Numerous diseases, including cancer, organ failure, infection, and aging-associated diseases, are associated with muscle wasting. Cancer cachexia is a multifactorial syndrome characterized by loss of skeletal muscle mass, with or without the loss of fat mass, resulting in functional impairment and reduced quality of life. It is caused by the upregulation of systemic inflammation and catabolic stimuli, leading to inhibition of protein synthesis and enhancement of muscle catabolism. Here, we summarize the complex molecular networks that regulate muscle mass and function. Moreover, we describe complex multi-organ roles in cancer cachexia. Although cachexia is one of the main causes of cancer-related deaths, there are still no approved drugs for cancer cachexia. Thus, we compiled recent ongoing pre-clinical and clinical trials and further discussed potential therapeutic approaches for cancer cachexia.

Metabolic Remodeling in Skeletal Muscle Atrophy as a Therapeutic Target

Skeletal muscle is a highly responsive tissue, able to remodel its size and metabolism in response to external demand. Muscle fibers can vary from fast glycolytic to slow oxidative, and their frequency in a specific muscle is tightly regulated by fiber maturation, innervation, or external causes. Atrophic conditions, including aging, amyotrophic lateral sclerosis, and cancer-induced cachexia, differ in the causative factors and molecular signaling leading to muscle wasting; nevertheless, all of these conditions are characterized by metabolic remodeling, which contributes to the pathological progression of muscle atrophy. Here, we discuss how changes in muscle metabolism can be used as a therapeutic target and review the evidence in support of nutritional interventions and/or physical exercise as tools for counteracting muscle wasting in atrophic conditions.

High protein diet improves the overall survival in older adults with advanced gastrointestinal cancer

BACKGROUND

High protein diet (HDP) promotes improvement of lean body mass in elderly without cancer; but the impact of high protein intake on muscle strength and mortality in cancer patients remains to be elucidated. This study evaluates the association between HPD on handgrip strength (HGS) and survival in older adults outpatients with advanced gastrointestinal cancer.

METHODS

Ninety-one patients with advanced gastrointestinal cancer (>65% tumor stage III-IV) undergoing radiotherapy, chemotherapy or surgery were enrolled. Upon first oncological visit, tumor stage was assessed by a physician. Then, a nutritionist or a dietitian measured the body mass index (BMI), HGS by means of a dynamometer, and dietary food intake by using 24h food recall. Patients were stratified in HPD (i.e, ≥1.5 g/kg/d) or low protein diet (LPD: <1.5 g/kg/d). Kaplan-Meier curve was used to assess the survival since the cancer diagnosis.

RESULTS

HPD was reported by approximately 30% of patients. Protein intake was significantly higher in HPD vs LPD patients (2.2 ± 0.8 vs. 0.8 ± 0.4 g/kg/d, respectively; p < 0.0001). No significant association was found between HPD and HGS, even after adjustment for physical activity, alcohol intake, smoking, sex, age, tumor stage, oncologic treatment and BMI (OR: 0.97 [95%CI: 0.88-1.08], p = 0.64), or for energy intake kcal/kg/day, leucine g/d and lipids g/d (OR: 0.93 [95%CI: 0.85-1.03, p = 0.19]. In addition, HPD group showed higher overall survival than LPD group (HPD: 14.7 vs. LPD: 7.3 months, p = 0.04).

CONCLUSION

HPD is not associated with better muscle function as measured by HGS, but with overall survival in older adults outpatients with advanced gastrointestinal cancer. HPD may represent a strategy to mitigate the cancer-induced mortality and should be further explored.

Nutrition interventions to treat low muscle mass in cancer

Many patients with cancer experience poor nutritional status, which detrimentally impacts clinical outcomes. Poor nutritional status in cancer is primarily manifested by severe muscle mass (MM) depletion, which may occur at any stage (from curative to palliative) and often co-exists with obesity. The objective of this article was to discuss gaps and opportunities related to the role of nutrition in preventing and reversing low MM in cancer. It also provides a narrative review of relevant nutritional interventions for patients capable of oral intake. The impact of nutrition interventions to prevent/treat low MM in cancer is not well understood, potentially due to the limited number of studies and of clinically viable, accurate body composition assessment tools. Additionally, the type of study designs, inclusion criteria, length of intervention, and choice of nutritional strategies have not been optimal, likely underestimating the anabolic potential of nutrition interventions. Nutrition studies are also often of short duration, and interventions that adapt to the metabolic and behavioural changes during the clinical journey are needed. We discuss energy requirements (25-30 kcal/kg/day) and interventions of protein (1.0-1.5 g/kg/day), branched-chain amino acids (leucine: 2-4 g/day), β-hydroxy β-methylbutyrate (3 g/day), glutamine (0.3 g/kg/day), carnitine (4-6 g/day), creatine (5 g/day), fish oil/eicosapentanoic acid (2.0-2.2 g/day EPA and 1.5 g/day DHA), vitamin/minerals (e.g. vitamin D: 600-800 international units per day), and multimodal approaches (nutrition, exercise, and pharmaceutical) to countermeasure low MM in cancer. Although the evidence is variable by modality type, interventions were generally not specifically studied in the context of cancer. Understanding patients' nutritional requirements could lead to targeted prescriptions to prevent or attenuate low MM in cancer, with the overall aim of minimizing muscle loss during anti-cancer therapy and maximizing muscle anabolism during recovery. It is anticipated that this will, in turn, improve overall health and prognostication including tolerance to treatment and survival. However, oncology-specific interventions with more robust study designs are needed to facilitate these goals.

Treatment of Diabetes in Older Adults: An Endocrine Society* Clinical Practice Guideline

OBJECTIVE

The objective is to formulate clinical practice guidelines for the treatment of diabetes in older adults.

CONCLUSIONS

Diabetes, particularly type 2, is becoming more prevalent in the general population, especially in individuals over the age of 65 years. The underlying pathophysiology of the disease in these patients is exacerbated by the direct effects of aging on metabolic regulation. Similarly, aging effects interact with diabetes to accelerate the progression of many common diabetes complications. Each section in this guideline covers all aspects of the etiology and available evidence, primarily from controlled trials, on therapeutic options and outcomes in this population. The goal is to give guidance to practicing health care providers that will benefit patients with diabetes (both type 1 and type 2), paying particular attention to avoiding unnecessary and/or harmful adverse effects.

Cachexia and advanced dementia

Cachexia is a complex metabolic process that is associated with several end-stage organ diseases. It is known to be also associated with advanced dementia, although the pathophysiologic mechanisms are still largely unknown. The present narrative review is aimed at presenting recent insights concerning the pathophysiology of weight loss and wasting syndrome in dementia, the putative mechanisms involved in the dysregulation of energy balance, and the interplay among the chronic clinical conditions of sarcopenia, malnutrition, and frailty in the elderly. We discuss the clinical implications of these new insights, with particular attention to the challenging question of nutritional needs in advanced dementia and the utility of tube feeding in order to optimize the management of end-stage dementia.

Multiple optic gland signaling pathways implicated in octopus maternal behaviors and death

Post-reproductive life in the female octopus is characterized by an extreme pattern of maternal care: the mother cares for her clutch of eggs without feeding until her death. These maternal behaviors are eradicated if the optic glands, the octopus analog of the vertebrate pituitary gland, are removed from brooding females. Despite the optic gland's importance in regulating maternal behavior, the molecular features underlying optic gland function are unknown. Here, we identify major signaling systems of the Octopus bimaculoides optic gland. Through behavioral analyses and transcriptome sequencing, we report that the optic gland undergoes remarkable molecular changes that coincide with transitions between behavioral stages. These include the dramatic upregulation and downregulation of catecholamine, steroid, insulin and feeding peptide pathways. Transcriptome analyses in other tissues demonstrate that these molecular changes are not generalized markers of senescence, but instead, specific features of the optic glands. Our study expands the classic optic gland-pituitary gland analogy and more specifically, it indicates that, rather than a single 'self-destruct' hormone, the maternal optic glands employ multiple pathways as systemic hormonal signals of behavioral regulation.

Nutrition Support for Critically Ill Patients With Cancer

Oncology patients often experience the classic signs of malnutrition-weight loss as well as fat and muscle wasting, which have been associated with poor tolerance to treatment and increased morbidity and mortality. Nutrition status may be an important factor in determining tolerance to treatment and outcomes associated with it. Thus, identification of those with preexisting malnutrition or who are at risk for developing malnutrition is crucial not only at time of cancer diagnosis but also throughout the treatment course so that nutrition interventions may be implemented to prevent development or worsening of malnutrition in this high-risk population. These patients often have extremely complicated hospital courses due to the aggressive nature of the disease and treatment, leading to intensive care unit admission and periods of critical illness. Critical illness is associated with catabolism, extreme stress on the body, and a state of systemic inflammation. During critical illness, it is important to provide adequate nutrition to prevent further break down of lean muscle mass and oxidative cellular injury and to regulate favorable immune responses. The purpose of this review is to discuss the importance of nutrition screening and assessment for the critically ill patient with cancer; to appropriately identify those at risk for, or who have developed, malnutrition; and to provide appropriate interventions to optimize nutrition status. This review also discusses the complications and difficulties associated with feeding this patient population and offers nutrition support recommendations.

Differentiating Sarcopenia and Cachexia Among Patients With Cancer

Patients with cancer are at an increased risk for muscle loss via 2 distinct mechanisms: sarcopenia, defined as the age-associated decrease in muscle mass related to changes in muscle synthesis signaling pathways, and/or cachexia, defined as cytokine-mediated degradation of muscle and adipose depots. Both wasting disorders are prevalent; among patients with cancer, 15%-50% are sarcopenic and 25%-80% are cachectic. Muscle mass may be difficult to quantify in overweight/obese individuals. Often, overweight/obese patients with cancer are assumed to be normally nourished when in fact severe muscle depletion may be present. No universally accepted treatment exists for preventing or reversing sarcopenia or cachexia in patients with cancer. Current treatment options are limited to nutrition therapy and exercise, which may lead to difficulties in adherence during cancer treatment. Future treatments may provide pharmaceutical therapy that targets muscle degradation and synthesis pathways. There is a need to determine a multimodal treatment plan for muscle depletion to improve quality of life, survival, and therapy complications in patients with cancer.

Effects of oral meal feeding on whole body protein breakdown and protein synthesis in cachectic pancreatic cancer patients

BACKGROUND

Pancreatic cancer is often accompanied by cachexia, a syndrome of severe weight loss and muscle wasting. A suboptimal response to nutritional support may further aggravate cachexia, yet the influence of nutrition on protein kinetics in cachectic patients is poorly understood.

METHODS

Eight cachectic pancreatic cancer patients and seven control patients received a primed continuous intravenous infusion of l-[ring-(2)H5]phenylalanine and l-[3,3-(2)H2]tyrosine for 8 h and ingested sips of water with l-[1-(13)C]phenylalanine every 30 min. After 4 h, oral feeding was started. Whole body protein breakdown, protein synthesis, and net protein balance were calculated. Results are given as median with interquartile range.

RESULTS

Baseline protein breakdown and protein synthesis were higher in cachectic patients compared with the controls (breakdown: 67.1 (48.1-79.6) vs. 45.8 (42.6-46.3) µmol/kg lean body mass/h, P = 0.049; and synthesis: 63.0 (44.3-75.6) vs. 41.8 (37.6-42.5) µmol/kg lean body mass/h, P = 0.021). During feeding, protein breakdown decreased significantly to 45.5 (26.9-51.1) µmol/kg lean body mass/h (P = 0.012) in the cachexia group and to 33.7 (17.4-37.1) µmol/kg lean body mass/h (P = 0.018) in the control group. Protein synthesis was not affected by feeding in cachectic patients: 58.4 (46.5-76.1) µmol/kg lean body mass/h, but was stimulated in controls: 47.9 (41.8-56.7) µmol/kg lean body mass/h (P = 0.018). Both groups showed a comparable positive net protein balance during feeding: cachexia: 19.7 (13.1-23.7) and control: 16.3 (13.6-25.4) µmol/kg lean body mass/h (P = 0.908).

CONCLUSION

Cachectic pancreatic cancer patients have a higher basal protein turnover. Both cachectic patients and controls show a comparable protein anabolism during feeding, albeit through a different pattern of protein kinetics. In cachectic patients, this is primarily related to reduced protein breakdown, whereas in controls, both protein breakdown and protein synthesis alterations are involved.

An official American Thoracic Society/European Respiratory Society statement: update on limb muscle dysfunction in chronic obstructive pulmonary disease

BACKGROUND

Limb muscle dysfunction is prevalent in chronic obstructive pulmonary disease (COPD) and it has important clinical implications, such as reduced exercise tolerance, quality of life, and even survival. Since the previous American Thoracic Society/European Respiratory Society (ATS/ERS) statement on limb muscle dysfunction, important progress has been made on the characterization of this problem and on our understanding of its pathophysiology and clinical implications.

PURPOSE

The purpose of this document is to update the 1999 ATS/ERS statement on limb muscle dysfunction in COPD.

METHODS

An interdisciplinary committee of experts from the ATS and ERS Pulmonary Rehabilitation and Clinical Problems assemblies determined that the scope of this document should be limited to limb muscles. Committee members conducted focused reviews of the literature on several topics. A librarian also performed a literature search. An ATS methodologist provided advice to the committee, ensuring that the methodological approach was consistent with ATS standards.

RESULTS

We identified important advances in our understanding of the extent and nature of the structural alterations in limb muscles in patients with COPD. Since the last update, landmark studies were published on the mechanisms of development of limb muscle dysfunction in COPD and on the treatment of this condition. We now have a better understanding of the clinical implications of limb muscle dysfunction. Although exercise training is the most potent intervention to address this condition, other therapies, such as neuromuscular electrical stimulation, are emerging. Assessment of limb muscle function can identify patients who are at increased risk of poor clinical outcomes, such as exercise intolerance and premature mortality.

CONCLUSIONS

Limb muscle dysfunction is a key systemic consequence of COPD. However, there are still important gaps in our knowledge about the mechanisms of development of this problem. Strategies for early detection and specific treatments for this condition are also needed.

Early body weight loss during concurrent chemo-radiotherapy for non-small cell lung cancer

BACKGROUND AND PURPOSE

Radiation-esophagitis and weight loss are frequently observed toxicities in patients treated with concurrent chemo-radiotherapy (CT-RT) for non-small cell lung cancer (NSCLC) and might be related. The purpose was to investigate whether weight loss already starts early after initiation of CT-RT and precedes radiation-esophagitis.

MATERIALS AND METHODS

In a retrospective cohort, weight and esophagitis grade ≥2 were assessed during the first weeks of (CT-)RT in patients treated with concurrent (n = 102) or sequential (n = 92) therapy. In a prospective validation study, data on body weight, esophagitis grade ≥2, nutritional intake and muscle strength were obtained before, during and following CT-RT.

RESULTS

In the retrospective cohort, early weight loss was observed in concurrently treated patients (p = 0.002), independent of esophagitis ≥ grade 2. Early weight loss was also observed in the prospective cohort (p = 0.003) and was not accompanied by decreases in nutritional intake. In addition lower limb muscle strength rapidly declined (p = 0.042). In the later weeks of treatment, further body weight loss occurred (p < 0.001) despite increased nutritional supplementation and body weight was only partly recovered after 4 weeks post CT-RT (p = 0.003).

CONCLUSIONS

Weight loss during concurrent CT-RT for NSCLC starts early and prior to onset of esophagitis, requiring timely and intense nutritional rehabilitation.

Sarcopenia, cachexia and aging: diagnosis, mechanisms and therapeutic options - a mini-review

By the year 2050, individuals over the age of 65 years will comprise 20% of the US population. Loss of muscle mass and strength is common in this age group and it is associated with increased dependence, frailty and mortality. Sarcopenia, defined as the loss of muscle mass and function associated with aging, and cachexia, defined as weight loss due to an underlying illness, are muscle wasting disorders of particular relevance in the aging population, but they go largely unrecognized. In this review we highlight the common pathophysiological mechanisms underlying muscle loss in sarcopenia and cachexia, the factors unique to each condition and means of diagnosing and differentiating them clinically. Therapeutic options including exercise, nutritional therapy, androgens and growth hormone as well as their practical limitations are discussed. We also shed light on newer agents being developed as potential therapeutic options for wasting diseases.

MTOR signaling and ubiquitin-proteosome gene expression in the preservation of fat free mass following high protein, calorie restricted weight loss

Caloric restriction is one of the most efficient ways to promote weight loss and is known to activate protective metabolic pathways. Frequently reported with weight loss is the undesirable consequence of fat free (lean muscle) mass loss. Weight loss diets with increased dietary protein intake are popular and may provide additional benefits through preservation of fat free mass compared to a standard protein, high carbohydrate diet. However, the precise mechanism by which a high protein diet may mitigate dietary weight loss induced reductions in fat free mass has not been fully elucidated. Maintenance of fat free mass is dependent upon nutrient stimulation of protein synthesis via the mTOR complex, although during caloric restriction a decrease (atrophy) in skeletal muscle may be driven by a homeostatic shift favouring protein catabolism. This review evaluates the relationship between the macronutrient composition of calorie restricted diets and weight loss using metabolic indicators. Specifically we evaluate the effect of increased dietary protein intake and caloric restricted diets on gene expression in skeletal muscle, particularly focusing on biosynthesis, degradation and the expression of genes in the ubiquitin-proteosome (UPP) and mTOR signaling pathways, including MuRF-1, MAFbx/atrogin-1, mTORC1, and S6K1.

Muscle function in COPD: a complex interplay

The skeletal muscles play an essential role in life, providing the mechanical basis for respiration and movement. Skeletal muscle dysfunction is prevalent in all stages of chronic obstructive pulmonary disease (COPD), and significantly influences symptoms, functional capacity, health related quality of life, health resource usage and even mortality. Furthermore, in contrast to the lungs, the skeletal muscles are potentially remedial with existing therapy, namely exercise-training. This review summarizes clinical and laboratory observations of the respiratory and peripheral skeletal muscles (in particular the diaphragm and quadriceps), and current understanding of the underlying etiological processes. As further progress is made in the elucidation of the molecular mechanisms of skeletal muscle dysfunction, new pharmacological therapies are likely to emerge to treat this important extra-pulmonary manifestation of COPD.

Protein and Amino Acid Supplementation Does Not Alter Proteolytic Gene Expression following Immobilization

Objective. To determine if supplementation of protein and amino acids (PAA) decreases skeletal muscle expression of atrophy-related genes, muscle mass, and strength during immobilization in humans. Methods. Twenty males wore a lower-limb immobilization boot for 28 days and consumed either a PAA supplement (28 g protein) or carbohydrate placebo (28 g maltodextrose), while consuming their normal daily diet. Testing sessions included dietary analysis, lower-leg girth and body composition measurements, strength testing, and gastrocnemius muscle biopsies. Muscle was analyzed for mRNA expression of markers in the ubiquitin and calpain systems, myostatin, TNF-α, and NF-κB. Results. All genes of interest increased over time (P < .05), but there was no difference between groups. Lower-leg girth decreased over time (P = 0.02); however, there were no significant changes in body composition or strength. Conclusion. Short-term lower-limb disuse, despite the absence of significant muscle atrophy, is associated with increases in skeletal muscle gene expression of several proteolysis-related genes. These changes do not appear to be altered by oral PAA supplementation.