Muscle wasting: an overview of recent developments in basic research

Association of muscle wasting with mortality risk among adults: A systematic review and meta-analysis of prospective studies

The relationship between muscle wasting and mortality risk in the general population remains unclear. Our study was conducted to examine and quantify the associations between muscle wasting and all-cause and cause-specific mortality risks. PubMed, Web of Science and Cochrane Library were searched until 22 March 2023 for main data sources and references of retrieved relevant articles. Prospective studies investigating the associations of muscle wasting with risks of all-cause and cause-specific mortality in the general population were eligible. A random-effect model was used to calculate the pooled relative risk (RR) and 95% confidence intervals (CIs) for the lowest versus normal categories of muscle mass. Subgroup analyses and meta-regression were performed to investigate the potential sources of heterogeneities among studies. Dose-response analyses were conducted to evaluate the relationship between muscle mass and mortality risk. Forty-nine prospective studies were included in the meta-analysis. A total of 61 055 deaths were ascertained among 878 349 participants during the 2.5- to 32-year follow-up. Muscle wasting was associated with higher mortality risks of all causes (RR = 1.36, 95% CI, 1.28 to 1.44, I²  = 94.9%, 49 studies), cardiovascular disease (CVD) (RR = 1.29, 95% CI, 1.05 to 1.58, I²  = 88.1%, 8 studies), cancer (RR = 1.14, 95% CI, 1.02 to 1.27, I²  = 38.7%, 3 studies) and respiratory disease (RR = 1.36, 95% CI, 1.11 to 1.67, I²  = 62.8%, 3 studies). Subgroup analyses revealed that muscle wasting, regardless of muscle strength, was significantly associated with a higher all-cause mortality risk. Meta-regression showed that risks of muscle wasting-related all-cause mortality (P = 0.06) and CVD mortality (P = 0.09) were lower in studies with longer follow-ups. An approximately inverse linear dose-response relationship was observed between mid-arm muscle circumference and all-cause mortality risk (P < 0.01 for non-linearity). Muscle wasting was associated with higher mortality risks of all causes, CVD, cancer and respiratory disease in the general population. Early detection and treatment for muscle wasting might be crucial for reducing mortality risk and promoting healthy longevity.

Low Intensity Respiratory Muscle Training in COVID-19 Patients after Invasive Mechanical Ventilation: A Retrospective Case-Series Study

Worldwide, healthcare systems had to respond to an exponential increase in COVID-19 patients with a noteworthy increment in intensive care units (ICU) admissions and invasive mechanical ventilation (IMV). The aim was to determine low intensity respiratory muscle training (RMT) effects in COVID-19 patients upon medical discharge and after an ICU stay with IMV. A retrospective case-series study was performed. Forty COVID-19 patients were enrolled and divided into twenty participants who received IMV during ICU stay (IMV group) and 20 participants who did not receive IMV nor an ICU stay (non-IMV group). Maximal expiratory pressure (PEmax), maximal inspiratory pressure (PImax), COPD assessment test (CAT) and Medical Research Council (MRC) dyspnea scale were collected at baseline and after 12 weeks of low intensity RMT. A greater MRC dyspnea score and lower PImax were shown at baseline in the IMV group versus the non-IMV group (p < 0.01). RMT effects on the total sample improved all outcome measurements (p < 0.05; d = 0.38−0.98). Intragroup comparisons after RMT improved PImax, CAT and MRC scores in the IMV group (p = 0.001; d = 0.94−1.09), but not for PImax in the non-IMV group (p > 0.05). Between-groups comparison after RMT only showed MRC dyspnea improvements (p = 0.020; d = 0.74) in the IMV group versus non-IMV group. Furthermore, PImax decrease was only predicted by the IMV presence (R2 = 0.378). Low intensity RMT may improve respiratory muscle strength, health related quality of life and dyspnea in COVID-19 patients. Especially, low intensity RMT could improve dyspnea level and maybe PImax in COVID-19 patients who received IMV in ICU.

Medidas antropométricas versus grosor de masa muscular como predictores de mortalidad en la unidad de cuidado intensivo

Introducción. En Colombia, la tasa de mortalidad en la Unidad de Cuidados Intensivos es cercana al 32 %, por lo anterior, se han estudiado múltiples predictores de mortalidad que identifiquen de manera precoz una evolución inadecuada. La masa muscular corresponde a cerca del 50 % del peso corporal y cumple importantes funciones metabólicas, como la generación de energía y la homeostasis de la glucosa. Se ha informado la disminución de hasta el 1,6 % de la masa muscular por día en pacientes críticos, factor relacionado con la mortalidad. Métodos. Se realizó un estudio de cohorte prospectiva entre enero de 2020 y diciembre de 2021, con una muestra no probabilística a conveniencia, incluyendo a los pacientes que ingresaron a las diferentes Unidad de Cuidados Intensivos del Hospital Universitario Hernando Moncaleano Perdomo, en quienes se realizó un registro periódico de las medidas antropométricas y del grosor del musculo cuádriceps. Resultados. Se incluyeron 82 pacientes, encontrando como variables asociadas a la mortalidad la edad, el número de días de hospitalización, el índice de masa corporal y el delta del musculo cuádriceps. Una medida del grosor del musculo cuádriceps al ingreso menor de 2,5 cm, se asoció con alto riesgo de muerte y una disminución de más de 1,72 cm durante el control ecográfico se relacionó con mal pronóstico. Conclusiones. Aunque estas variables se eligieron en función de su asociación con mortalidad, nuestros resultados emplean importantes características, como la medición del grosor muscular y su delta durante la estancia en la unidad de cuidados intensivos, lo que indica un mayor consumo de las reservas fisiológicas, asociándose a mayor riesgo de complicaciones y mortalidad.

Mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force

The hypoxia-inducible nuclear-encoded mitochondrial protein NADH dehydrogenase (ubiquinone) 1 alpha subcomplex, 4-like 2 (NDUFA4L2) has been demonstrated to decrease oxidative phosphorylation and production of reactive oxygen species in neonatal cardiomyocytes, brain tissue and hypoxic domains of cancer cells. Prolonged local hypoxia can negatively affect skeletal muscle size and tissue oxidative capacity. Although skeletal muscle is a mitochondrial rich, oxygen sensitive tissue, the role of NDUFA4L2 in skeletal muscle has not previously been investigated. Here we ectopically expressed NDUFA4L2 in mouse skeletal muscles using adenovirus-mediated expression and in vivo electroporation. Moreover, femoral artery ligation (FAL) was used as a model of peripheral vascular disease to induce hind limb ischemia and muscle damage. Ectopic NDUFA4L2 expression resulted in reduced mitochondrial respiration and reactive oxygen species followed by lowered AMP, ADP, ATP, and NAD⁺ levels without affecting the overall protein content of the mitochondrial electron transport chain. Furthermore, ectopically expressed NDUFA4L2 caused a ~20% reduction in muscle mass that resulted in weaker muscles. The loss of muscle mass was associated with increased gene expression of atrogenes MurF1 and Mul1, and apoptotic genes caspase 3 and Bax. Finally, we showed that NDUFA4L2 was induced by FAL and that the Ndufa4l2 mRNA expression correlated with the reduced capacity of the muscle to generate force after the ischemic insult. These results show, for the first time, that mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force. Specifically, induced NDUFA4L2 reduces mitochondrial activity leading to lower levels of important intramuscular metabolites, including adenine nucleotides and NAD⁺ , which are hallmarks of mitochondrial dysfunction and hence shows that dysfunctional mitochondrial activity may drive muscle wasting.

Alaska backcountry expeditionary hunting promotes rapid improvements in metabolic biomarkers in healthy males and females

We have previously reported negative energy balance and health benefits during an Alaska backcountry expeditionary hunting (ABEH) immersion in two males. The purpose of our present study was to increase the number of participants, include females, and evaluate macronutrient intake and serum lipids. Four men (age: 46 ± 6 year, BMI: 26 ± 1 kg/m2 ) and three women (age: 46 ± 11 year, BMI: 25 ± 3 kg/m2 ) were recruited. Doubly labeled water methodology and dietary recall were utilized to assess energy expenditure and energy intake, respectively. Data were collected during pre- and post-ABEH visits. Body composition was measured using dual-energy x-ray absorptiometry and the cross-sectional area of skeletal muscle in the upper leg (XT), and intrahepatic lipid (IHL) was determined using magnetic resonance imaging and/or spectroscopy (MRI/MRS). Blood parameters were measured by LabCorp. Paired T-tests were used for statistical analysis. Data are reported as mean ± SD and considered significant at p < 0.05. Total energy intake was 7.7 ± 3.4 MJ/day and total energy expenditure was 17.4 ± 2.6 MJ/day, resulting in a negative energy balance of -9.7 ± 3.4 MJ/day. Protein intake(grams)/body weight(kilograms)/day was 1.0 ± 0.4. There were reductions in body weight (Δ-1.5 ± 0.7 kg), BMI (Δ-0.3 ± 0.2 kg/m2 ), fat mass (Δ-1.7 ± 0.9 kg), and IHL (Δ-0.3 ± 0.3% water peak). There were no changes in lean tissue mass (Δ0.6 ± 1.4 kg) or XT (Δ-1.3 ± 3.3 cm2 ). There were significant reductions in total cholesterol (Δ-44 ± 35 mg/dl), LDL-cholesterol (Δ-25 ± 14 mg/dl), VLDL-cholesterol (Δ-7 ± 7 mg/dl), and triglycerides (Δ-35 ± 33 mg/dl). The ABEH immersion resulted in considerable negative energy balance and provided comprehensive benefits in metabolic health without any reduction in skeletal muscle.

The Role of Cullin-RING Ligases in Striated Muscle Development, Function, and Disease

The well-orchestrated turnover of proteins in cross-striated muscles is one of the fundamental processes required for muscle cell function and survival. Dysfunction of the intricate protein degradation machinery is often associated with development of cardiac and skeletal muscle myopathies. Most muscle proteins are degraded by the ubiquitin-proteasome system (UPS). The UPS involves a number of enzymes, including E3-ligases, which tightly control which protein substrates are marked for degradation by the proteasome. Recent data reveal that E3-ligases of the cullin family play more diverse and crucial roles in cross striated muscles than previously anticipated. This review highlights some of the findings on the multifaceted functions of cullin-RING E3-ligases, their substrate adapters, muscle protein substrates, and regulatory proteins, such as the Cop9 signalosome, for the development of cross striated muscles, and their roles in the etiology of myopathies.

Inorganic Arsenic Exposure Decreases Muscle Mass and Enhances Denervation-Induced Muscle Atrophy in Mice

Arsenic is a toxic metalloid. Infants with a low birth-weight have been observed in areas with high-level arsenic in drinking water ranging from 463 to 1025 μg/L. A distal muscular atrophy side effect has been observed in acute promyelocytic leukemia patients treated with arsenic trioxide (As₂O₃) for therapy. The potential of As₂O₃ on muscle atrophy remains to be clarified. In this study, the myoatrophic effect of arsenic was evaluated in normal mice and sciatic nerve denervated mice exposed with or without As₂O₃ (0.05 and 0.5 ppm) in drinking water for 4 weeks. We found that both 0.05 and 0.5 ppm As₂O₃ increased the fasting plasma glucose level; but only 0.5 ppm arsenic exposure significantly decreased muscle mass, muscle endurance, and cross-sectional area of muscle fibers, and increased muscle Atrogin-1 protein expression in the normal mice. Both 0.05 and 0.5 ppm As₂O₃ also significantly enhanced the inhibitory effects on muscle endurance, muscle mass, and cross-sectional area of muscle fibers, and increased the effect on muscle Atrogin-1 protein expression in the denervated mice. These in vivo results suggest that inorganic arsenic at doses relevant to humans may possess myoatrophic potential.

Exposure of low-concentration arsenic induces myotube atrophy by inhibiting an Akt signaling pathway

Arsenic, a widely distributed toxic metalloid, has been found to be associated with the low-birth-weight infants and the impairment of muscle regenerative capacity in areas with high levels of arsenic in drinking water. The distal muscular atrophy is one of side effects of arsenic trioxide (As₂O₃) for acute promyelocytic leukemia therapy. We hypothesized that arsenic may be a potential risk factor for skeletal muscle atrophy. Here, we investigated the action and molecular mechanism of low-dose arsenic on the induction of skeletal muscle atrophy in a skeletal muscle cell model. The differentiated C2C12 myotubes were treated with As₂O₃ (0.25-1 μM) for 48 h without apparent effects on cell viability. The signaling molecules for myotube atrophy were assessed. Submicromolar-concentration As₂O₃ dose-dependently triggered C2C12 myotube atrophy and increased the protein expressions of atrogenes Atrogin1 and MuRF1 and inhibited the upstream phosphorylated proteins Akt and FoxO1, while As₂O₃ dose-dependently increased AMPK phosphorylation in myotubes. Akt activator SC79 could significantly reverse the As₂O₃-induced myotube atrophy. These results suggest that arsenic is capable of inducing myotube atrophy by inhibiting an Akt signaling pathway.

Nilotinib impairs skeletal myogenesis by increasing myoblast proliferation

Background

Tyrosine kinase inhibitors (TKIs) are effective therapies with demonstrated antineoplastic activity. Nilotinib is a second-generation FDA-approved TKI designed to overcome Imatinib resistance and intolerance in patients with chronic myelogenous leukemia (CML). Interestingly, TKIs have also been shown to be an efficient treatment for several non-malignant disorders such fibrotic diseases, including those affecting skeletal muscles.

Methods

We investigated the role of Nilotinib on skeletal myogenesis using the well-established C2C12 myoblast cell line. We evaluated the impact of Nilotinib during the time course of skeletal myogenesis. We compared the effect of Nilotinib with the well-known p38 MAPK inhibitor SB203580. MEK1/2 UO126 and PI3K/AKT LY294002 inhibitors were used to identify the signaling pathways involved in Nilotinib-related effects on myoblast. Adult primary myoblasts were also used to corroborate the inhibition of myoblasts fusion and myotube-nuclei positioning by Nilotinib.

Results

We found that Nilotinib inhibited myogenic differentiation, reducing the number of myogenin-positive myoblasts and decreasing myogenin and MyoD expression. Furthermore, Nilotinib-mediated anti-myogenic effects impair myotube formation, myosin heavy chain expression, and compromise myotube-nuclei positioning. In addition, we found that p38 MAPK is a new off-target protein of Nilotinib, which causes inhibition of p38 phosphorylation in a similar manner as the well-characterized p38 inhibitor SB203580. Nilotinib induces the activation of ERK1/2 and AKT on myoblasts but not in myotubes. We also found that Nilotinib stimulates myoblast proliferation, a process dependent on ERK1/2 and AKT activation.

Conclusions

Our findings suggest that Nilotinib may have important negative effects on muscle homeostasis, inhibiting myogenic differentiation but stimulating myoblasts proliferation. Additionally, we found that Nilotinib stimulates the activation of ERK1/2 and AKT. On the other hand, we suggest that p38 MAPK is a new off-target of Nilotinib. Thus, there is a necessity for future studies to investigate the long-term effects of TKIs on skeletal muscle homeostasis, along with potential detrimental effects in cell differentiation and proliferation in patients receiving TKI therapies.

Electronic supplementary material

The online version of this article (10.1186/s13395-018-0150-5) contains supplementary material, which is available to authorized users.

Iron limitation promotes the atrophy of skeletal myocytes, whereas iron supplementation prevents this process in the hypoxic conditions

There is clinical evidence that patients with heart failure and concomitant iron deficiency have increased skeletal muscle fatigability and impaired exercise tolerance. It was expected that a skeletal muscle cell line subjected to different degrees of iron availability and/or concomitant hypoxia would demonstrate changes in cell morphology and in the expression of atrophy markers. L6G8C5 rat skeletal myocytes were cultured in normoxia or hypoxia at optimal, reduced or increased iron concentrations. Experiments were performed to evaluate the iron content in cells, cell morphology, and the expression of muscle specific atrophy markers [Atrogin1 and muscle-specific RING-finger 1 (MuRF1)], a gene associated with the atrophy/hypertrophy balance [mothers against decapentaplegic homolog 4 (SMAD4)] and a muscle class-III intermediate filament protein (Desmin) at the mRNA and protein level. Hypoxic treatment caused, as compared to normoxic conditions, an increase in the expression of Atrogin-1 (P<0.001). Iron-deficient cells exhibited morphological abnormalities and demonstrated a significant increase in the expression of Atrogin-1 (P<0.05) and MuRF1 (P<0.05) both in normoxia and hypoxia, which indicated activation of the ubiquitin proteasome pathway associated with protein degradation during muscle atrophy. Depleted iron in cell culture combined with hypoxia also induced a decrease in SMAD4 expression (P<0.001) suggesting modifications leading to atrophy. In contrast, cells cultured in a medium enriched with iron during hypoxia exhibited inverse changes in the expression of atrophy markers (both P<0.05). Desmin was upregulated in cells subjected to both iron depletion and iron excess in normoxia and hypoxia (all P<0.05), but the greatest augmentation of mRNA expression occurred when iron depletion was combined with hypoxia. Notably, in hypoxia, an increased expression of Atrogin-1 and MuRF1 was associated with an increased expression of transferrin receptor 1, reflecting intracellular iron demand (R=0.76, P<0.01; R=0.86, P<0.01). Hypoxia and iron deficiency when combined exhibited the most detrimental impact on skeletal myocytes, especially in the context of muscle atrophy markers. Conversely, iron supplementation in in vitro conditions acted in a protective manner on these cells.

Integrative analysis of methylomic and transcriptomic data in fetal sheep muscle tissues in response to maternal diet during pregnancy

BACKGROUND

Numerous studies have established a link between maternal diet and the physiological and metabolic phenotypes of their offspring. In previous studies in sheep, we demonstrated that different maternal diets altered the transcriptome of fetal tissues. However, the mechanisms underlying transcriptomic changes are poorly understood. DNA methylation is an epigenetic mark regulating transcription and is largely influenced by dietary components of the one-carbon cycle that generate the methyl group donor, SAM. Therefore, in the present study, we tested whether different maternal diets during pregnancy would alter the DNA methylation and gene expression patterns in fetal tissues.

RESULTS

Pregnant ewes were randomly divided into two groups which received either hay or corn diet from mid-gestation (day 67 ± 5) until day 131 ± 1 when fetuses were collected by necropsy. A total of 1516 fetal longissimus dorsi (LD) tissues were used for DNA methylation analysis and gene expression profiling. Whole genome DNA methylation using methyl-binding domain enrichment analysis revealed 60 differentially methylated regions (DMRs) between hay and corn fetuses with 39 DMRs more highly methylated in the hay fetuses vs. 21 DMRs more highly methylated in the corn fetuses. Three DMRs (LPAR3, PLIN5-PLIN4, and the differential methylation of a novel lincRNA) were validated using bisulfite sequencing. These DMRs were associated with differential gene expression. Additionally, significant DNA methylation differences were found at the single CpG level. Integrative methylome and transcriptome analysis revealed an association between gene expression and inter-/intragenic methylated regions. Furthermore, intragenic DMRs were found to be associated with expression of neighboring genes.

CONCLUSIONS

The findings of this study imply that maternal diet from mid- to late-gestation can shape the epigenome and the transcriptome of fetal tissues, and putatively affect phenotypes of the lambs.

The mitochondrial metabolic reprogramming agent trimetazidine as an 'exercise mimetic' in cachectic C26-bearing mice

BACKGROUND

Cancer cachexia is characterized by muscle depletion and exercise intolerance caused by an imbalance between protein synthesis and degradation and by impaired myogenesis. Myofibre metabolic efficiency is crucial so as to assure optimal muscle function. Some drugs are able to reprogram cell metabolism and, in some cases, to enhance metabolic efficiency. Based on these premises, we chose to investigate the ability of the metabolic modulator trimetazidine (TMZ) to counteract skeletal muscle dysfunctions and wasting occurring in cancer cachexia.

METHODS

For this purpose, we used mice bearing the C26 colon carcinoma as a model of cancer cachexia. Mice received 5 mg/kg TMZ (i.p.) once a day for 12 consecutive days. A forelimb grip strength test was performed and tibialis anterior, and gastrocnemius muscles were excised for analysis. Ex vivo measurement of skeletal muscle contractile properties was also performed.

RESULTS

Our data showed that TMZ induces some effects typically achieved through exercise, among which is grip strength increase, an enhanced fast-to slow myofibre phenotype shift, reduced glycaemia, PGC1α up-regulation, oxidative metabolism, and mitochondrial biogenesis. TMZ also partially restores the myofibre cross-sectional area in C26-bearing mice, while modulation of autophagy and apoptosis were excluded as mediators of TMZ effects.

CONCLUSIONS

In conclusion, our data show that TMZ acts like an 'exercise mimetic' and is able to enhance some mechanisms of adaptation to stress in cancer cachexia. This makes the modulation of the metabolism, and in particular TMZ, a suitable candidate for a therapeutic rehabilitative protocol design, particularly considering that TMZ has already been approved for clinical use.

Exercise and Transversus Abdominis Muscle Atrophy after 60-d Bed Rest

PURPOSE

This study aimed to investigate atrophy in the deep abdominal muscles, spinal extensors, and the effect of high-load resistive exercise with and without whole-body vibration after 60 d of strict bed rest.

METHODS

Twenty-four subjects underwent 60 d of head-down tilt bed rest and performed either resistive vibration exercise (RVE), resistive exercise only (RE), or no exercise control (2nd Berlin BedRest Study). The thickness of the transversus abdominis, internal oblique, and erector spinae muscles and the area of the multifidus muscle were measured bilaterally via real-time ultrasound. Intention-to-treat analysis was implemented, and P values were adjusted by the false discovery rate method.

RESULTS

At the end of the bed rest, transversus abdominis thickness was reduced by 18.3% in the inactive group (P = 0.00011) with no significant change in the RVE (-4.0%; P = 0.014 vs control) or RE (-5.0%; P = 0.10 vs control) groups. In the inactive subjects, internal oblique thickness reduced by 10.6% (P = 0.0025) and by 7% (P > 0.05) in each of the training groups. The lengthening of the lumbar spine was greatest on day 1 (+7.4%, P = 0.004) and day 2 (+6.3%, P = 0.004; day 54: +4.1%, P = 0.023). A 4.7% reduction of multifidus area was observed on day 1 of bed rest (P = 0.0049) and a 4.2% reduction of erector spinae thickness was observed on day 2 (P = 0.0011). Extensor atrophy and spinal lengthening was not affected by exercise. No significant difference was seen between RVE and RE.

CONCLUSION

Bed rest leads to atrophy of the transversus abdominis and internal oblique muscles. The exercise program, which implemented lower-limb and back extension exercises against shoulder restraints, was able to reduce atrophy seen in transversus abdominis in bed rest.

Cardiac muscle wasting in individuals with cancer cachexia

Aims

Cachexia is a severe complication of cancer that adversely affects the course of the disease and is associated with high rates of mortality. Patients with cancer manifest symptoms, such as fatigue, shortness of breath, and impaired exercise tolerance, which are clinical signs of chronic heart failure. The aim of this study was to evaluate cardiac muscle wasting in cancer individuals.

Methods and results

We retrospectively analysed 177 individuals who died of cancer, including 58 lung, 60 pancreatic, and 59 gastrointestinal (GI) cancers, and 42 cancer‐free controls who died of other, non‐cardiovascular reasons. Cancer cachexia (CC) was defined based on clinical and/or pathological diagnosis, body mass index (BMI) <20.0 kg/m² and/or oedema‐free body weight loss of 5.0% during the previous year or less. The pathology reports were analysed for BMI, heart weight (HW), and left and right ventricular wall thicknesses (LVWT and RVWT, respectively). The analysis of clinical data included recording of biochemical parameters and medication data of study patients. CC was detected in 54 (30.5%) subjects. Individuals with CC had a significantly lower HW than non‐cachectic subjects (363.1 ± 86.2 vs. 447.0 ± 128.9 g, P < 0.001) and control group (412.9 ± 75.8 g, P < 0.05). BMI correlated with HW in cases with GI cancer (r = 0.44, P < 0.001), lung cancer (r = 0.53, P < 0.0001), and pancreatic cancer (r = 0.39, P < 0.01).

Conclusions

Body weight loss in individuals with lung, pancreatic, and GI cancers is accompanied by a decrease in HW. In patients with CC who receive cancer treatment, screening for cardiac muscle wasting may have clinical importance.

Relationship between skeletal muscle mass and cardiac function during exercise in community-dwelling older adults

Aims

This study aimed to investigate the relationship between skeletal muscle mass and cardiac functional parameters in older adults during cardiopulmonary exercise testing (CPET).

Methods and results

Sixty‐three Japanese community‐dwelling older adults were enrolled (20 men and 43 women; mean age 80 years, range 65–97 years). Cardiac functional parameters during exercise were assessed using CPET. Skeletal muscle mass index (SMI) was calculated by dividing the appendicular lean mass (measured using dual‐energy X‐ray absorptiometry) by height in metres squared. Subjects were divided into two groups: men with SMI ≥ 7.0 kg/m² and women with SMI ≥ 5.4 kg/m² (non‐sarcopenic group); or men with SMI < 7.0 kg/m² and women with SMI < 5.4 kg/m² (sarcopenic group). There were significant positive correlations between SMI and peak oxygen uptake (VO₂) (r = 0.631, P < 0.001), and between SMI and peak VO₂/heart rate (HR) (r = 0.683, P < 0.001). However, only peak VO₂/HR significantly differed between groups in both sexes. Multiple linear regression analyses with peak VO₂/HR as a dependent variable showed that SMI was the only independent determinant after adjusting for potential confounders. After 4 month follow‐up of 47 participants, there was still a significant positive correlation between SMI and peak VO₂/HR (r = 0.567, P < 0.001), and between percent change of SMI and percent change of peak VO₂/HR (r = 0.305, P < 0.05).

Conclusions

Peak VO₂/HR, an index of stroke volume at peak exercise, was associated with SMI. This indicates that skeletal muscle mass might affect cardiac function during exercise.

Sarcopenia, cachexia, and muscle performance in heart failure: Review update 2016

Cachexia in the context of heart failure (HF) has been termed cardiac cachexia, and represents a progressive involuntary weight loss. Cachexia is mainly the result of an imbalance in the homeostasis of muscle protein synthesis and degradation due to a lower activity of protein synthesis pathways and an over-activation of protein degradation. In addition, muscle wasting leads to of impaired functional capacity, even after adjusting for clinical relevant variables in patients with HF. However, there is no sufficient therapeutic strategy in muscle wasting in HF patients and very few studies in animal models. Exercise training represents a promising intervention that can prevent or even reverse the process of muscle wasting, and worsening the muscle function and performance in HF with muscle wasting and cachexia. The pathological mechanisms and effective therapeutic approach of cardiac cachexia remain uncertain, because of the difficulty to establish animal cardiac cachexia models, thus novel animal models are warranted. Furthermore, the use of improved animal models will lead to a better understanding of the pathways that modulate muscle wasting and therapeutics of muscle wasting of cardiac cachexia.

Nutrition, frailty, and sarcopenia

Frailty and sarcopenia are important concepts in the quest to prevent physical dependence, as geriatrics are shifting towards identifications of early stages of disability. Definitions of both sarcopenia and frailty are still developing, and both concepts clearly overlap in their physical aspects. Malnutrition (both undernutrition and obesity) plays a key role in the pathogenesis of frailty and sarcopenia. The quality of the diet along the lifespan has a close relation with the incidence of both entities, and nutritional interventions may be able to reduce the incidence or revert either of them. This brief review explores the role of energy and protein intake and other key nutrients on muscle function. Nutrition may be a key element of multimodal interventions for frailty and sarcopenia. The results of the "Sarcopenia and Physical fRailty IN older people: multi-componenT Treatment strategies" (SPRINTT) trial will offer key insights on the effect of such interventions in frail, sarcopenic older individuals.

The effect of exercise hypertrophy and disuse atrophy on muscle contractile properties: a mechanomyographic analysis

PURPOSE

To determine whether mechanomyographic (MMG) determined contractile properties of the biceps brachii change during exercise-induced hypertrophy and subsequent disuse atrophy.

METHODS

Healthy subjects (mean ± SD, 23.7 ± 2.6 years, BMI 21.8 ± 2.4, n = 19) performed unilateral biceps curls (9 sets × 12 repetitions, 5 sessions per week) for 8 weeks (hypertrophic phase) before ceasing exercise (atrophic phase) for the following 8 weeks (non-dominant limb; treatment, dominant limb; control). MMG measures of muscle contractile properties (contraction time; T _c, maximum displacement; D _max, contraction velocity; V _c), electromyographic (EMG) measures of muscle fatigue (median power frequency; MPF), strength measures (maximum voluntary contraction; MVC) and measures of muscle thickness (ultrasound) were obtained.

RESULTS

Two-way repeated measures ANOVA showed significant differences (P < 0.05) between treatment and control limbs. During the hypertrophic phase treatment MVC initially declined (weeks 1-3), due to fatigue (decline in MPF), followed by improvement against control during weeks 6-8. Between weeks 5 and 8 treatment, muscle thickness was greater than control, reflecting gross hypertrophy. MMG variables Dmax (weeks 2, 7) and Vc (weeks 7, 8) declined. During the atrophic phase, MVC (weeks 9-12) and muscle thickness (weeks 9, 10) initially remained high before declining to control levels, reflecting gross atrophy. MMG variables D _max (weeks 9, 14) and V _c (weeks 9, 14, 15) also declined during the atrophic phase. No change in T _c was found throughout the hypertrophic or atrophic phases.

CONCLUSIONS

MMG detects changes in contractile properties during stages of exercise-induced hypertrophy and disuse atrophy suggesting its applicability as a clinical tool in musculoskeletal rehabilitation.

Dysfunction of respiratory muscles in critically ill patients on the intensive care unit

Muscular weakness and muscle wasting may often be observed in critically ill patients on intensive care units (ICUs) and may present as failure to wean from mechanical ventilation. Importantly, mounting data demonstrate that mechanical ventilation itself may induce progressive dysfunction of the main respiratory muscle, i.e. the diaphragm. The respective condition was termed 'ventilator-induced diaphragmatic dysfunction' (VIDD) and should be distinguished from peripheral muscular weakness as observed in 'ICU-acquired weakness (ICU-AW)'. Interestingly, VIDD and ICU-AW may often be observed in critically ill patients with, e.g. severe sepsis or septic shock, and recent data demonstrate that the pathophysiology of these conditions may overlap. VIDD may mainly be characterized on a histopathological level as disuse muscular atrophy, and data demonstrate increased proteolysis and decreased protein synthesis as important underlying pathomechanisms. However, atrophy alone does not explain the observed loss of muscular force. When, e.g. isolated muscle strips are examined and force is normalized for cross-sectional fibre area, the loss is disproportionally larger than would be expected by atrophy alone. Nevertheless, although the exact molecular pathways for the induction of proteolytic systems remain incompletely understood, data now suggest that VIDD may also be triggered by mechanisms including decreased diaphragmatic blood flow or increased oxidative stress. Here we provide a concise review on the available literature on respiratory muscle weakness and VIDD in the critically ill. Potential underlying pathomechanisms will be discussed before the background of current diagnostic options. Furthermore, we will elucidate and speculate on potential novel future therapeutic avenues.

Cardiac cachexia: hic et nunc

Cardiac cachexia (CC) is the clinical entity at the end of the chronic natural course of heart failure (HF). Despite the efforts, even the most recent definition of cardiac cachexia has been challenged, more precisely, the addition of new criteria on top of obligatory weight loss. The pathophysiology of CC is complex and multifactorial. A better understanding of pathophysiological pathways in body wasting will contribute to establish potentially novel treatment strategies. The complex biochemical network related with CC and HF pathophysiology underlines that a single biomarker cannot reflect all of the features of the disease. Biomarkers that could pick up the changes in body composition before they convey into clinical manifestations of CC would be of great importance. The development of preventive and therapeutic strategies against cachexia, sarcopenia, and wasting disorders is perceived as an urgent need by healthcare professionals. The treatment of body wasting remains an unresolved challenge to this day. As CC is a multifactorial disorder, it is unlikely that any single agent will be completely effective in treating this condition. Among all investigated therapeutic strategies, aerobic exercise training in HF patients is the most proved to counteract skeletal muscle wasting and is recommended by treatment guidelines for HF.

Evaluation of C-terminal Agrin Fragment as a marker of muscle wasting in patients after acute stroke during early rehabilitation

BACKGROUND

C-terminal Agrin Fragment (CAF) has been proposed as a novel biomarker for sarcopenia originating from the degeneration of the neuromuscular junctions. In patients with stroke muscle wasting is a common observation that predicts functional outcome. We aimed to evaluate agrin sub-fragment CAF22 as a marker of decreased muscle mass and physical performance in the early phase after acute stroke.

METHODS

Patients with acute ischaemic or haemorrhagic stroke (n = 123, mean age 70 ± 11 y, body mass index BMI 27.0 ± 4.9 kg/m(2)) admitted to inpatient rehabilitation were studied in comparison to 26 healthy controls of similar age and BMI. Functional assessments were performed at begin (23 ± 17 days post stroke) and at the end of the structured rehabilitation programme (49 ± 18 days post stroke) that included physical assessment, maximum hand grip strength, Rivermead motor assessment, and Barthel index. Body composition was assessed by bioelectrical impedance analysis (BIA). Serum levels of CAF22 were measured by ELISA.

RESULTS

CAF22 levels were elevated in stroke patients at admission (134.3 ± 52.3 pM) and showed incomplete recovery until discharge (118.2 ± 42.7 pM) compared to healthy controls (95.7 ± 31.8 pM, p < 0.001). Simple regression analyses revealed an association between CAF22 levels and parameters of physical performance, hand grip strength, and phase angle, a BIA derived measure of the muscle cellular integrity. Improvement of the handgrip strength of the paretic arm during rehabilitation was independently related to the recovery of CAF22 serum levels only in those patients who showed increased lean mass during the rehabilitation.

CONCLUSIONS

CAF22 serum profiles showed a dynamic elevation and recovery in the subacute phase after acute stroke. Further studies are needed to explore the potential of CAF22 as a serum marker to monitor the muscle status in patients after stroke.

Biomarkers for physical frailty and sarcopenia: state of the science and future developments

Physical frailty and sarcopenia are two common and largely overlapping geriatric conditions upstream of the disabling cascade. The lack of a unique operational definition for physical frailty and sarcopenia and the complex underlying pathophysiology make the development of biomarkers for these conditions extremely challenging. Indeed, the current definitional ambiguities of physical frailty and sarcopenia, together with their heterogeneous clinical manifestations, impact the accuracy, specificity, and sensitivity of individual biomarkers proposed so far. In this review, the current state of the art in the development of biomarkers for physical frailty and sarcopenia is presented. A novel approach for biomarker identification and validation is also introduced that moves from the 'one fits all' paradigm to a multivariate methodology.

Deranged iron status in psoriasis: the impact of low body mass

BACKGROUND

Iron deficiency (ID) frequently complicates inflammatory-mediated chronic disorders, irrespective of anaemia. Psoriasis is a chronic, immune-mediated skin disease with systemic pro-inflammatory activation; thus, these patients may be prone to develop ID. ID adversely affects immune cells function, which can further contribute to disease progression. This study investigates iron status in psoriasis.

METHODS

Serum concentrations of ferritin, transferrin saturation (Tsat), soluble transferrin receptor (sTfR), and hepcidin were assessed as the biomarkers of iron status in 39 patients with psoriasis (17 men, age: 47 ± 10 years) and 44 healthy subjects (30 men, age: 53 ± 6 years).

RESULTS

Compared with healthy controls, patients with psoriasis demonstrated similar haematologic status but deranged iron status as evidenced by decreased Tsat and elevated sTfR (negative tissue iron balance) and low levels of hepcidin (depleted iron stores) (all P < 0.05 vs. controls). In patients, the levels of interleukin-6 (level of pro-inflammatory activation) significantly correlated with hepcidin (R = 0.54), but not with ferritin, Tsat, and sTfR. Biomarkers reflecting ID were not associated with the severity of the disease (assessed with the Psoriasis Area and Severity Index) but significantly correlated low body mass index (BMI). Patients with BMI < 24 kg/m(2) compared with those with BMI ≥ 24 kg/m(2) demonstrated lower levels of ferritin (40 ± 30 vs. 186 ± 128 ng/mL, P < 0.001) and hepcidin (4.9 ± 2.3 vs. 10.7 ± 6.7 ng/mL, P = 0.03).

CONCLUSION

Psoriasis is associated with deranged iron status characterized by depleted iron stores with concomitant unmet cellular iron requirements. The magnitude of these abnormalities is particularly strong in patients with low body mass index. Whether iron deficiency may become a therapeutic target in psoriasis needs to be investigated.

Cardiac cachexia: hic et nunc: "hic et nunc" - here and now

Cardiac cachexia (CC) is the clinical entity at the end of chronic natural course of heart failure (HF). Despite the efforts, even the most recent definition of cardiac cachexia has been challenged, more precisely the addition of new criteria on top of obligatory weight loss. The pathophysiology of CC is complex and multifactorial. Better understanding of pathophysiological pathways in body wasting will contribute to establish potentially novel treatment strategies. The complex biochemical network related with CC and HF pathophysiology underlines that a single biomarker cannot reflect all of the features of the disease. Biomarkers that could pick-up the changes in body composition before they convey into clinical manifestations of CC would be of great importance. The development of preventive and therapeutic strategies against cachexia, sarcopenia and wasting disorders is perceived as an urgent need by healthcare professionals. The treatment of body wasting remains an unresolved challenge to this day. As CC is a multifactorial disorder, it is unlikely that any single agent will be completely effective in treating this condition. Among all investigated therapeutic strategies, aerobic exercise training in HF patients is the most proved to counteract skeletal muscle wasting and is recommended by treatment guidelines for HF.

Uric acid and xanthine oxidase in heart failure - Emerging data and therapeutic implications

The role of hyperuricaemia as cardiovascular risk factor has exhaustingly been debated for decades. While the association of elevated uric acid (UA) levels with increased mortality risk as convincingly been shown, the question whether UA is independently predictive of just a related effect within a more complex risk factor profile (including metabolic, inflammatory and haemodynamic risk factors) is still a matter of dispute. In heart failure the independent prognostic and functional impact of elevated UA has not only been shown but also the pathophysiologic mechanism(s) and the potential of targeted therapeutic interventions have been investigated in some detail. The emerging picture suggests the increased activity of the enzyme xanthine oxidase (XO) with corresponding increased production of free oxygen radical (ROS) as a main underlying principle with the resulting increase in UA levels being mostly a marker of this up-regulated pathway. While this concept will not diminish the value of UA as a prognostic marker, it provides the basis for a novel metabolic treatment option and the means to identify those patients most eligible for this tailored therapy. This review will summarize the recent evidence on XO as a novel and promising therapeutic target in heart failure.

Muscle wasting in ageing and chronic illness

PURPOSE

As life expectancy increases, muscle wasting is becoming a more and more important public health problem. This review summarizes the current knowledge of pathophysiological mechanisms underlying muscle loss in ageing and chronic diseases such as heart failure and discusses evolving interventional strategies.

RECENT FINDINGS

Loss of skeletal muscle mass and strength is a common phenomenon in a wide variety of disorders associated with ageing and morbidity-associated catabolic conditions such as chronic heart failure. Muscle wasting in ageing but otherwise healthy human beings is referred to as sarcopenia. Unlike cachexia in advanced stages of chronic heart failure, muscle wasting per se is not necessarily associated with weight loss. In this review, we discuss pathophysiological mechanisms underlying muscle loss in sarcopenia and cachexia, highlight similarities and differences of both conditions, and discuss therapeutic targets and possible treatments, such as exercise training, nutritional support, and drugs. Candidate drugs to treat muscle wasting disease include myostatin antagonists, ghrelin agonists, selective androgen receptor molecules, megestrol acetate, activin receptor antagonists, espindolol, and fast skeletal muscle troponin inhibitors.

SUMMARY

Present approaches to muscle wasting disease include exercise training, nutritional support, and drugs, although particularly the latter remain currently restricted to clinical studies. Optimizing skeletal muscle mass and function in ageing and chronic illness including heart failure is one of the chapters that are far from finished and gains future potential for new therapeutic interventions to come.

Emerging biomarkers in heart failure and cardiac cachexia

Biomarkers are objective tools with an important role for diagnosis, prognosis and therapy optimization in patients with heart failure (HF). To date, natriuretic peptides are closest to optimal biomarker standards for clinical implications in HF. Therefore, the efforts to identify and test new biomarkers in HF are reasonable and justified. Along the natural history of HF, cardiac cachexia may develop, and once at this stage, patient performance and prognosis is particularly poor. For these reasons, numerous biomarkers reflecting hormonal, inflammatory and oxidative stress pathways have been investigated, but only a few convey relevant information. The complex pathophysiology of HF appears far too complex to be embraced by a single biomarker; thus, a combined approach appears reasonable. With these considerations, we have reviewed the recent developments in the field to highlight key candidates with diagnostic, prognostic and therapy optimization properties, either alone or in combination.