Muscle wasting in chronic kidney disease: the role of the ubiquitin proteasome system and its clinical impact

Irisin Ameliorates Muscle Atrophy by Inhibiting the Upregulation of the Ubiquitin‒Proteasome System in Chronic Kidney Disease

Muscle atrophy is a common complication of chronic kidney disease (CKD). Irisin, a novel muscle cytokine, protects against muscle atrophy, but its specific role in CKD-associated muscle atrophy requires further elucidation. Because the ubiquitin-proteasome system (UPS) plays an important role in CKD muscle atrophy, our study will explore whether irisin affects UPS and alleviate CKD-associated muscle atrophy. In this study, an adenine-fed mouse model of CKD and urotension II (UII)-induced C2C12 myotubes were used as in vivo and in vitro models of muscle atrophy. The results showed that renal function, mouse weight, and the cross-sectional area (CSA) of skeletal muscles were significantly improved in CKD mice treated with irisin. Moreover, irisin effectively mitigated the decreases in phosphorylated Forkhead box O 3a (p-FOXO3A) levels and increases in the levels of E3 ubiquitin ligases, such as muscle RING finger 1 (MuRF1) and muscle atrophy F-box (MAFbx/atrogin1), in both the muscles of CKD mice and UII-induced C2C12 myotubes. In addition, irisin significantly increased the expression levels of myogenic differentiation factor D (MyoD) in the muscles of CKD mice. Our study is the first to demonstrate that irisin ameliorates skeletal muscle atrophy by inhibiting UPS upregulation and improving satellite cell differentiation in CKD.

Shenshuai Yingyang Jiaonang ameliorates chronic kidney disease-associated muscle atrophy in rats by inhibiting ferroptosis mediated by the HIF-1α/SLC7A11 pathway

Objective

Shenshuai Yingyang Jiaonang (SSYYJN), a traditional Chinese medicine formula, can ameliorate muscle atrophy associated with chronic kidney disease (CKD). However, its mechanisms of action remain unclear. This study is to investigate the molecular mechanisms involved in the effects of SSYYJN in ameliorating muscle atrophy associated with CKD in rats. Methods: The chemical compounds of SSYYJN were identified by UPLC-Q-Orbitrap HRMS. Considering the dose-response relationship of the identified compounds, male SD rats were randomly divided into Sham, Model, SSYYJN, and α-Keto Acid (KA) groups. Subsequently, we assessed the therapeutic and anti-ferroptotic effects of SSYYJN. Network pharmacology studies were used to predict the molecular mechanism of SSYYJN on ferroptosis and were further verified for accuracy.

Results

A total of 42 active compounds were identified from SSYYJN. SSYYJN alleviated muscle atrophy caused by CKD, as evidenced by changes in body weight, serum biochemical indices, mass and histopathology of the skeletal muscle, and the levels of MuRF1. SSYYJN reduced the levels of iron, MDA, and ROS, increased the levels of GSH, NAPDH, and Gpx4. Network pharmacology analysis indicated that SSYYJN exerted anti-ferroptotic effects that were closely related to the HIF-1α signaling pathway. Molecular protein and genetic test results showed that SSYYJN increased HIF-1α protein and increased SLC7A11.

Conclusions

SSYYJN attenuates muscle atrophy in CKD by inhibiting ferroptosis through the activation of the HIF-1α/SLC7A11 pathway and might be a promising traditional Chinese medicine for muscle atrophy in CKD.

Cardiovascular Consequences of Uremic Metabolites: an Overview of the Involved Signaling Pathways

The crosstalk of the heart with distant organs such as the lung, liver, gut, and kidney has been intensively approached lately. The kidney is involved in (1) the production of systemic relevant products, such as renin, as part of the most essential vasoregulatory system of the human body, and (2) in the clearance of metabolites with systemic and organ effects. Metabolic residue accumulation during kidney dysfunction is known to determine cardiovascular pathologies such as endothelial activation/dysfunction, atherosclerosis, cardiomyocyte apoptosis, cardiac fibrosis, and vascular and valvular calcification, leading to hypertension, arrhythmias, myocardial infarction, and cardiomyopathies. However, this review offers an overview of the uremic metabolites and details their signaling pathways involved in cardiorenal syndrome and the development of heart failure. A holistic view of the metabolites, but more importantly, an exhaustive crosstalk of their known signaling pathways, is important for depicting new therapeutic strategies in the cardiovascular field.

Proteomic signature associated with chronic kidney disease (CKD) progression identified by data-independent acquisition mass spectrometry

BACKGROUND

Halting progression of chronic kidney disease (CKD) to established end stage kidney disease is a major goal of global health research. The mechanism of CKD progression involves pro-inflammatory, pro-fibrotic, and vascular pathways, but pathophysiological differentiation is currently lacking.

METHODS

Plasma samples of 414 non-dialysis CKD patients, 170 fast progressors (with ∂ eGFR-3 ml/min/1.73 m2/year or worse) and 244 stable patients (∂ eGFR of - 0.5 to + 1 ml/min/1.73 m2/year) with a broad range of kidney disease aetiologies, were obtained and interrogated for proteomic signals with SWATH-MS. We applied a machine learning approach to feature selection of proteins quantifiable in at least 20% of the samples, using the Boruta algorithm. Biological pathways enriched by these proteins were identified using ClueGo pathway analyses.

RESULTS

The resulting digitised proteomic maps inclusive of 626 proteins were investigated in tandem with available clinical data to identify biomarkers of progression. The machine learning model using Boruta Feature Selection identified 25 biomarkers as being important to progression type classification (Area Under the Curve = 0.81, Accuracy = 0.72). Our functional enrichment analysis revealed associations with the complement cascade pathway, which is relevant to CKD as the kidney is particularly vulnerable to complement overactivation. This provides further evidence to target complement inhibition as a potential approach to modulating the progression of diabetic nephropathy. Proteins involved in the ubiquitin-proteasome pathway, a crucial protein degradation system, were also found to be significantly enriched.

CONCLUSIONS

The in-depth proteomic characterisation of this large-scale CKD cohort is a step toward generating mechanism-based hypotheses that might lend themselves to future drug targeting. Candidate biomarkers will be validated in samples from selected patients in other large non-dialysis CKD cohorts using a targeted mass spectrometric analysis.

Combined prenatal to postnatal protein restriction augments protein quality control processes and proteolysis in the muscle of rat offspring

Several human epidemiological and animal studies suggest that a maternal low-protein (MLP) diet affects skeletal muscle (SM) health in the offspring. However, effect of combined prenatal to postnatal protein restriction (chronic PR) and prenatal to perinatal protein restriction (PR) with postnatal rehabilitation maternal protein restriction (MPR) on protein quality control (PQC) processes and proteolysis in the offspring remains poorly understood. The current study explored the impact of chronic PR and MPR on SM protein degradation rates, chaperones, unfolded protein response (UPR), ubiquitin-proteasome system (UPS), autophagy, and apoptosis, in the adult offspring. Wistar rats were randomly assigned to a normal protein (NP; 20% casein), or low-protein (LP; 8% casein) isocaloric diets from 7 weeks prior to breeding through weaning. Offspring born to NP dams received the same diet (NP offspring) while a group of LP offspring remained on LP diet and another group was rehabilitated with NP diet (LPR offspring) from weaning for 16 weeks. LP offspring displayed lower body weight, lean mass, and myofiber cross-sectional area than NP. Furthermore, LP offspring demonstrated increased total protein degradation, urinary 3-methyl histidine, ER stress, autophagy, UPS components, proteasomal activity, muscle atrophy markers, and apoptosis-related proteins than NP. However, MPR showed little or no effect on muscle proteolysis, UPR, UPS, autophagy, apoptosis, and muscle atrophy in LPR offspring. These results indicate that exposure to chronic PR diets induces muscle atrophy and accelerates SM proteolysis via augmenting PQC processes in the offspring, while MPR shows little or no effect.

Absence of ULK1 decreases AMPK activity in the kidney, leading to chronic kidney disease progression

AMP-activated protein kinase (AMPK) inactivation in chronic kidney disease (CKD) leads to energy status deterioration in the kidney, constituting the vicious cycle of CKD exacerbation. Unc-51-like kinase 1 (ULK1) is considered a downstream molecule of AMPK; however, it was recently reported that the activity of AMPK could be regulated by ULK1 conversely. We demonstrated that AMPK and ULK1 activities were decreased in the kidneys of CKD mice. However, whether and how ULK1 is involved in the underlying mechanism of CKD exacerbation remains unknown. In this study, we investigated the ULK1 involvement in CKD, using ULK1 knockout mice. The CKD model of Ulk1^-/- mice exhibited significantly exacerbated renal function and worsening renal fibrosis. In the kidneys of the CKD model of Ulk1^-/- mice, reduced AMPK and its downstream β-oxidation could be observed, leading to an energy deficit of increased AMP/ATP ratio. In addition, AMPK signaling in the kidney was reduced in control Ulk1^-/- mice with normal renal function compared to control wild-type mice, suggesting that ULK1 deficiency suppressed AMPK activity in the kidney. This study is the first to present ULK1 as a novel therapeutic target for CKD treatment, which regulates AMPK activity in the kidney.

Clinical Consequences of Metabolic Acidosis-Muscle

Metabolic acidosis is common in people with chronic kidney disease and can contribute to functional decline, morbidity, and mortality. One avenue through which metabolic acidosis can result in these adverse clinical outcomes is by negatively impacting skeletal muscle; this can occur through several pathways. First, metabolic acidosis promotes protein degradation and impairs protein synthesis, which lead to muscle breakdown. Second, metabolic acidosis hinders mitochondrial function, which decreases oxidative phosphorylation and reduces energy production. Third, metabolic acidosis directly limits muscle contraction. The purpose of this review is to examine the specific mechanisms of each pathway through which metabolic acidosis affects muscle, the impact of metabolic acidosis on physical function, and the effect of treating metabolic acidosis on functional outcomes.

Muscle Wasting in Chronic Kidney Disease: Mechanism and Clinical Implications—A Narrative Review

Muscle wasting, known to develop in patients with chronic kidney disease (CKD), is a deleterious consequence of numerous complications associated with deteriorated renal function. Muscle wasting in CKD mainly involves dysregulated muscle protein metabolism and impaired muscle cell regeneration. In this narrative review, we discuss the cardinal role of the insulin-like growth factor 1 and myostatin signaling pathways, which have been extensively investigated using animal and human studies, as well as the emerging concepts in microRNA- and gut microbiota-mediated regulation of muscle mass and myogenesis. To ameliorate muscle loss, therapeutic strategies, including nutritional support, exercise programs, pharmacological interventions, and physical modalities, are being increasingly developed based on advances in understanding its underlying pathophysiology.

Longitudinal Assessment of Body Composition and Its Association With Survival Among Participants of the ACTIVE/ADIPOSE Study

OBJECTIVES

The importance of muscle wasting as a predictor of mortality in the hemodialysis population is not clear. Lack of association of muscle mass with survival in some studies could be related to reliance on single measures or to incorporation of excess extracellular water (ECW) into estimates of muscle mass. We examined changes in body composition over a 2-year period and the association of body composition with survival.

DESIGN AND METHODS

We analyzed data from 325 adults receiving hemodialysis in the Bay Area. We estimated ECW, intracellular water (ICW), and fat mass by whole-body bioimpedance spectroscopy (BIS) at 0, 12, and 24 months from enrollment. We used linear mixed modeling to examine changes in body mass index and BIS-derived estimates of body composition and Cox modeling with BIS-derived estimates as time-varying independent variables to examine associations between body composition and survival in multivariable analyses.

RESULTS

Body mass index declined over time. Considering individual components of body composition, ICW declined (-0.09 kg/m² per year, 95% confidence interval -0.14 to -0.04), but fat mass and ECW did not change significantly. There were 120 deaths over a median of 5.2 years. The relationship between ICW and mortality was not linear such that the association was steeper at low values of ICW, whereas higher ICW was associated with better survival that was relatively stable above 9 kg/m2. Higher ECW was associated with higher mortality, and fat mass was not associated with survival. These associations were independent of markers of inflammation and nutritional status.

CONCLUSIONS

ICW declined over 2 years in this cohort, whereas fat mass and ECW remained relatively stable. Higher ICW was associated with better survival, but higher fat mass was not. Higher ECW was associated with worse survival. These results suggest that muscle mass may predict survival among patients on hemodialysis.

Comparison of Simplified Creatinine Index and Systemic Inflammatory Markers for Nutritional Evaluation of Hemodialysis Patients

Protein-energy wasting (PEW) is associated with adverse outcomes in hemodialysis patients. This study compares the simplified creatinine index (SCI) and circulating inflammatory markers as nutritional screening tools for hemodialysis patients. Maintenance hemodialysis patients (230 total patients, 34.8% women, 64.0 ± 14.3 years old) from a tertiary medical center were assessed for demographic data, body composition analysis, biochemistry tests, and circulating inflammatory biomarkers. The SCI was calculated using Canaud’s formula. Reduced fat-free mass index (FFMI), a surrogate of lean body mass, was identified according to the European Society for Clinical Nutrition and Metabolism guidelines. Nutritional status was assessed by the geriatric nutritional risk index (GNRI) and International Society of Renal Nutrition and Metabolism (ISRNM) criteria. Multivariate logistic regression revealed independent risk factors for low FFMI and malnutrition. Of the patients, 47.4% had low FFMI. Patients with a reduction in FFMI tended to be older females with lower body mass index, SCI, and GNRI scores but significantly higher levels of interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), and IL-8. SCI was found to be an independent predictor for reduced FFMI (OR 0.57, 95% CI 0.40–0.81) and presence of PEW according to ISRNM criteria (OR 0.38, 95% CI 0.21–0.68). Although a positive association between systemic inflammatory markers and low FFMI was observed, this association disappeared in multivariate analysis. Moreover, the inflammatory markers examined in this study were not associated with malnutrition after adjusting for potential confounders. Compared with markers of systemic inflammation, SCI achieved better performance in assessing the nutritional status of hemodialysis patients.

Formononetin ameliorates muscle atrophy by regulating myostatin-mediated PI3K/Akt/FoxO3a pathway and satellite cell function in chronic kidney disease

Muscle atrophy is a common complication in chronic kidney disease (CKD). Inflammation and myostatin play important roles in CKD muscle atrophy. Formononetin (FMN), which is a major bioactive isoflavone compound in Astragalus membranaceus, exerts anti‐inflammatory effects and the promotion of myogenic differentiation. Our study is based on myostatin to explore the effects and mechanisms of FMN in relation to CKD muscle atrophy. In this study, CKD rats and tumour necrosis factor α (TNF‐α)‐induced C2C12 myotubes were used for in vivo and in vitro models of muscle atrophy. The results showed that FMN significantly improved the renal function, nutritional status and inflammatory markers in CKD rats. Values for bodyweight, weight of tibialis anterior and gastrocnemius muscles, and cross‐sectional area (CSA) of skeletal muscles were significantly larger in the FMN treatment rats. Furthermore, FMN significantly suppressed the expressions of MuRF‐1, MAFbx and myostatin in the muscles of CKD rats and the TNF‐α‐induced C2C12 myotubes. Importantly, FMN significantly increased the phosphorylation of PI3K, Akt, and FoxO3a and the expressions of the myogenic proliferation and differentiation markers, myogenic differentiation factor D (MyoD) and myogenin in muscles of CKD rats and the C2C12 myotubes. Similar results were observed in TNF‐α‐induced C2C12 myotubes transfected with myostatin‐small interfering RNA (si‐myostatin). Notably, myostatin overexpression plasmid (myostatin OE) abolished the effect of FMN on the phosphorylation of the PI3K/Akt/FoxO3a pathway and the expressions of MyoD and myogenin. Our findings suggest that FMN ameliorates muscle atrophy related to myostatin‐mediated PI3K/Akt/FoxO3a pathway and satellite cell function.

How metabolic acidosis and kidney disease may accelerate the aging process

Consuming a lower acid (and particularly lower phosphate) diet and/or supplementing the diet with base precursors, such as bicarbonate, might have a number of mitigating effects on the aging process. These include: (1) slowing progression of fibrosis by reduction of high endogenous acid production to preserve net acid excretion and minimize the degree of systemic acidosis; (2) avoiding the downregulation of klotho, a membrane and soluble factor associated with aging. Klotho declines when constant high dietary phosphate intake leads to an increase in FGF23 production; and (3) increasing activity of the enzyme telomerase, an important factor in maintaining telomere length, another factor associated with longer lifespan. Current evidence is based on studies in invertebrate and small animal models. These results, and extrapolations of associated human studies, suggest that low acid-producing diets, or neutralization of the low grade metabolic acidosis seen in humans with age-related renal dysfunction could potentially lead to a longer, healthier lifespan.

Atractylenolide III Attenuates Muscle Wasting in Chronic Kidney Disease via the Oxidative Stress-Mediated PI3K/AKT/mTOR Pathway

Oxidative stress contributes to muscle wasting in advanced chronic kidney disease (CKD) patients. Atractylenolide III (ATL-III), the major active constituent of Atractylodes rhizome, has been previously reported to function as an antioxidant. This study is aimed at investigating whether ATL-III has protective effects against CKD-induced muscle wasting by alleviating oxidative stress. The results showed that the levels of serum creatinine (SCr), blood urea nitrogen (BUN), and urinary protein significantly decreased in the ATL-III treatment group compared with the 5/6 nephrectomy (5/6 Nx) model group but were higher than those in the sham operation group. Skeletal muscle weight was increased, while inflammation was alleviated in the ATL-III administration group compared with the 5/6 Nx model group. ATL-III-treated rats also showed reduced dilation of the mitochondria, increased CAT, GSH-Px, and SOD activity, and decreased levels of MDA both in skeletal muscles and serum compared with 5/6 Nx model rats, suggesting that ATL-III alleviated mitochondrial damage and increased the activity of antioxidant enzymes, thus reducing the production of ROS. Furthermore, accumulated autophagosomes (APs) and autolysosomes (ALs) were reduced in the gastrocnemius (Gastroc) muscles of ATL-III-treated rats under transmission electron microscopy (TEM) together with the downregulation of LC3-II and upregulation of p62 according to Western blotting. This evidence indicated that ATL-III improved skeletal muscle atrophy and alleviated oxidative stress and autophagy in CKD rats. Furthermore, ATL-III could also increase the protein levels of p-PI3K, p-AKT, and p-mTOR in skeletal muscles in CKD rats. To further reveal the relevant mechanism, the oxidative stress-mediated PI3K/AKT/mTOR pathway was assessed, which showed that a reduced expression of p-PI3K, p-AKT, and p-mTOR in C2C12 myoblast atrophy induced by TNF-α could be upregulated by ATL-III; however, after the overexpression of Nox2 to increase ROS production, the attenuated effect was reversed. Our findings indicated that ATL-III is a potentially protective drug against muscle wasting via activation of the oxidative stress-mediated PI3K/AKT/mTOR pathway.

Changes in expression of the autophagy-related genes microtubule-associated protein 1 light chain 3β and autophagy related 7 in skeletal muscle of fattening Japanese Black cattle: a pilot study

Objective

Autophagy is a bulk degradation system for intracellular proteins which contributes to skeletal muscle homeostasis, according to previous studies in humans and rodents. However, there is a lack of information on the physiological role of autophagy in the skeletal muscle of meat animals. This study was planned as a pilot study to investigate changes in expression of two major autophagy-related genes, microtubule-associated protein 1 light chain 3β (MAP1LC3B) and autophagy related 7 (ATG7) in fattening beef cattle, and to compare them with skeletal muscle growth.

Methods

Six castrated Japanese Black cattle (initial body weight: 503±20 kg) were enrolled in this study and fattened for 7 months. Three skeletal muscles, M. longissimus, M. gluteus medius, and M. semimembranosus, were collected by needle biopsy three times during the observation period, and mRNA levels of MAP1LC3B and ATG7 were determined by quantitative reverse-transcription polymerase chain reaction. The expression levels of genes associated with the ubiquitin-proteasome system, another proteolytic mechanism, were also analyzed for comparison with autophagy-related genes. In addition, ultrasonic scanning was repeatedly performed to measure M. longissimus area as an index of muscle growth.

Results

Our results showed that both MAP1LC3B and ATG7 expression increased over the observation period in all three skeletal muscles. Interestingly, the increase in expression of these two genes in M. longissimus was highly correlated with ultrasonic M. longissimus area and body weight. On the other hand, the expression of genes associated with the ubiquitin-proteasome system was unchanged during the same period.

Conclusion

These findings suggest that autophagy plays an important role in the growth of skeletal muscle of fattening beef cattle and imply that autophagic activity affects meat productivity.

Stressor-driven extracellular acidosis as tumor inducer via aberrant enzyme activation: A review on the mechanisms and possible prophylaxis

When the extracellular pH of human body vacillates in either direction, tissue homeostasis is compromised. Fluctuations in acidity have been linked to a wide variety of pathological conditions, including bone loss, cancer, allergies, and auto-immune diseases. Stress conditions affect oxygen tension, and the resultant hypoxia modulates the expression and/or activity of membrane-tethered transporters/pumps, transcription factors, enzymes and intercellular junctions. These modifications provoke erratic gene expression, aberrant tissue remodeling and oncogenesis. While the physiological optimization of pH in tissues is practically challenging, it is at least theoretically achievable and can be considered as a possible therapy to resolve a broad array of diseases.

Astragalus polysaccharides decrease muscle wasting through Akt/mTOR, ubiquitin proteasome and autophagy signalling in 5/6 nephrectomised rats

ETHNOPHARMACOLOGICAL RELEVANCE

Existing evidences suggest that Radix Astragali and its polysaccharides composition (APS) can improve muscle mass, but the mechanisms need more research.

AIM OF THE STUDY

In this study, we aimed to examine the effects of APS on muscle wasting at molecular level in 5/6 nephrectomised rats.

MATERIALS AND METHODS

We performed 5/6 nephrectomy or sham operation in 160 6-week-old Sprague-Dawley rats, and feed animals with or without 2% APS for 155 days. After treatment, we compared the change of weight, muscle fibre, protein metabolism, pro-inflammatory factors (TNF-α, IL-15, CRP) and oxidative factors (MDA, SOD) among each group. In addition, we detected the Akt/mTOR, ubiquitin proteasome, autophagy signalling and AA transporters in vivo and in vitro.

RESULTS

Data in vivo show 2% APS could alleviate weight loss and improve protein metabolism in nephrectomised rats. The levels of serum pro-inflammatory factors and oxidative factors were restored by APS treatment. In molecular levels, APS restored Akt/mTOR, MAFbx, MuRF1, Atg7, LC3B-II/LC3B-I and SLC38A2 which changed in nephrectomised rats. Data in vitro show the optimal dose of APS is 0.2mg/mL, and SLC38A2 siRNA attenuated the effects of 0.2mg/mL APS on atrophy and autophagy.

CONCLUSIONS

Our results suggested APS could improve muscle wasting through Akt/mTOR, ubiquitin proteasome and autophagy signalling, and SLC38A2 may be one of potential targets.

Myostatin Activates the Ubiquitin-Proteasome and Autophagy-Lysosome Systems Contributing to Muscle Wasting in Chronic Kidney Disease

Our evidence demonstrated that CKD upregulated the expression of myostatin, TNF-α, and p-IkBa and downregulated the phosphorylation of PI3K, Akt, and FoxO3a, which were also associated with protein degradation and muscle atrophy. The autophagosome formation and protein expression of autophagy-related genes were increased in muscle of CKD rats. The mRNA level and protein expression of MAFbx and MuRF-1 were also upregulated in CKD rats, as well as proteasome activity of 26S. Moreover, activation of myostatin elicited by TNF-α induces C2C12 myotube atrophy via upregulating the expression of autophagy-related genes, including MAFbx and MuRF1 and proteasome subunits. Inactivation of FoxO3a triggered by PI3K inhibitor LY294002 prevented the myostatin-induced increase of expression of MuRF1, MAFbx, and LC3-II protein in C2C12 myotubes. The findings were further consolidated by using siRNA interference and overexpression of myostatin. Additionally, expression of myostatin was activated by TNF-α via a NF-κB dependent pathway in C2C12 myotubes, while inhibition of NF-κB activity suppressed myostatin and improved myotube atrophy. Collectively, myostatin mediated CKD-induced muscle catabolism via coordinate activation of the autophagy and the ubiquitin-proteasome systems.

Effect of endurance and/or strength training on muscle fiber size, oxidative capacity, and capillarity in hemodialysis patients

We previously reported reduced limb muscle fiber succinate dehydrogenase (SDH) activity and capillarity density and increased cross-sectional areas (CSAs) of all fiber types in maintenance hemodialysis (MHD) patients compared with matched controls that may contribute to their effort intolerance and muscle weakness. This study evaluated whether endurance training (ET), strength training (ST), or their combination (EST) alters these metabolic and morphometric aberrations as a mechanism for functional improvement. Five groups were evaluated: 1) controls; 2) MHD/no training; 3) MHD/ET; 4) MHD/ST; and 5) MHD/EST. Training duration was 21.5 ± 0.7 wk. Vastus lateralis muscle biopsies were obtained after HD at baseline and at study end. Muscle fibers were classified immunohistochemically, and fiber CSAs were computed. Individual fiber SDH activity was determined by a microdensitometric assay. Capillaries were identified using antibodies against endothelial cells. Type I and IIA fiber CSAs decreased significantly (10%) with EST. In the ET group, SDH activity increased 16.3% in type IIA and 19.6% in type IIX fibers. Capillary density increased significantly by 28% in the EST group and 14.3% with ET. The number of capillaries surrounding individual fiber type increased significantly in EST and ET groups. Capillary-to-fiber ratio increased significantly by 11 and 9.6% in EST and ET groups, respectively. We conclude that increments in capillarity and possibly SDH activity in part underlie improvements in endurance of MHD patients posttraining. We speculate that improved specific force and/or neural adaptations to exercise underlie improvements in limb muscle strength of MHD patients.

Interdialytic weight gain in oligoanuric children and adolescents on chronic hemodialysis

BACKGROUND

Little is known about the clinical impact of interdialytic weight gain (IDWG) on oligoanuric children undergoing chronic hemodialysis (HD).

METHODS

We retrospectively assessed IDWG, left ventricular mass index (LVMI) and its changes (ΔLVMI), pre-HD systolic and diastolic blood pressure (DBP), residual urine output, Kt/V, the frequency of intradialytic symptoms, normalized protein catabolic rate, and the 3-month change in the dry weight of 16 hemodialyzed oligoanuric patients with a median age of 14.8 years (range 5.0-17.9).

RESULTS

There was a significant correlation between IDWG and median LVMI (r 0.55, p = 0.026), which was 27.3 g/m(2.7) (22.5-37.6) in the patients with a median IDWG of <4 %, and 44.3 g/m(2.7) (28.2-68.7) in those with a median IDWG of >4 % (p = 0.003). None of the four patients with an IDWG of <4 % showed left ventricular hypertrophy, compared with 10 of the 12 patients (83.3 %) with an IDWG of >4 % (p = 0.003); the former also had a better median ΔLVMI (-33.5 % vs -13.0 %; p = 0.02) and a lower median DBP sds (0.24 vs 1.72, p = 0.04).

CONCLUSIONS

There is a significant correlation between IDWG and LVMI in pediatric oligoanuric patients on chronic HD: those with an IDWG of >4 % are at a higher risk of left ventricular hypertrophy.

The interdialytic weight gain: a simple marker of left ventricular hypertrophy in children on chronic haemodialysis

Despite multiple advances in haemodialysis (HD) technology over the years, the morbidity and mortality of HD patients remain unacceptably high. Cardiovascular disease is the most common cause of death, and left ventricular hypertrophy (LVH), seen in two-thirds of children on dialysis, is a significant contributor. The importance of volume control is increasingly recognized by nephrologists and now considered to be as important as urea kinetics, both in the day-to-day management and the long-term outcome of dialysis patients. The results published by Paglialonga et al. ( 10.1007/s00467-014-3005-2 ) in this issue of Pediatric Nephrology clearly demonstrate that there is a significant correlation between interdialytic weight gain (IDWG) and LVH in oligoanuric children on chronic HD and that children with an IDWG of >4 % are at high risk of LVH. One common practice to achieve euvolaemia is to prescribe very high ultrafiltration rates. However, both volume overload and aggressive fluid removal can induce circulatory stress and multi-organ injury. In adults, ultrafiltration rates of >1.24 % body weight per hour, even if well tolerated, are associated with a significant increase in mortality. Nephrologists should be aware of the risk of a high ultrafiltration rate, especially if tolerance is obtained by a positive dialysate-to-plasma sodium gradient. Haemodiafiltration, which allows for higher ultrafiltration rates with greater intradialytic haemodynamic stability, or more frequent and longer dialysis sessions allow for safe and effective fluid removal.

Endotoxin-induced skeletal muscle wasting is prevented by angiotensin-(1-7) through a p38 MAPK-dependent mechanism

Skeletal muscle atrophy induced during sepsis syndrome produced by endotoxin in the form of LPS (lipopolysaccharide), is a pathological condition characterized by the loss of strength and muscle mass, an increase in MHC (myosin heavy chain) degradation, and an increase in the expression of atrogin-1 and MuRF-1 (muscle-specific RING-finger protein 1), two ubiquitin E3 ligases belonging to the ubiquitin-proteasome system. Ang-(1-7) [Angiotensin-(1-7)], through its Mas receptor, has beneficial effects in skeletal muscle. We evaluated in vivo the role of Ang-(1-7) and Mas receptor on the muscle wasting induced by LPS injection into C57BL/10J mice. In vitro studies were performed in murine C2C12 myotubes and isolated myofibres from EDL (extensor digitorum longus) muscle. In addition, the participation of p38 MAPK (mitogen-activated protein kinase) in the Ang-(1-7) effect on the LPS-induced muscle atrophy was evaluated. Our results show that Ang-(1-7) prevents the decrease in the diameter of myofibres and myotubes, the decrease in muscle strength, the diminution in MHC levels and the induction of atrogin-1 and MuRF-1 expression, all of which are induced by LPS. These effects were reversed by using A779, a Mas antagonist. Ang-(1-7) exerts these anti-atrophic effects at least in part by inhibiting the LPS-dependent activation of p38 MAPK both in vitro and in vivo. We have demonstrated for the first time that Ang-(1-7) counteracts the skeletal muscle atrophy induced by endotoxin through a mechanism dependent on the Mas receptor that involves a decrease in p38 MAPK phosphorylation. The present study indicates that Ang-(1-7) is a novel molecule with a potential therapeutic use to improve muscle wasting during endotoxin-induced sepsis syndrome.

Insulin resistance as a therapeutic target for chronic kidney disease

Insulin resistance (IR) is a prevalent metabolic feature in chronic kidney disease (CKD). Postreceptor insulin-signaling defects have been observed in uremia. A decrease in the activity of phosphatidylinositol 3-kinase appears critical in the pathophysiology of CKD-associated IR. Lipotoxicity due to ectopic accumulation of lipid moieties has recently emerged as another mechanism by which CKD and/or associated metabolic disorders may lead to IR through impairment of various insulin-signaling molecules. Metabolic acidosis, anemia, excess of fat mass, inflammation, vitamin D deficiency, adipokine imbalance, physical inactivity, and the accumulation of nitrogenous compounds of uremia all contribute to CKD-associated IR. The clinical impacts of IR in this setting are numerous, including endothelial dysfunction, increased cardiovascular mortality, muscle wasting, and possibly initiation and progression of CKD. This is why IR may be a therapeutic target in the attempt to improve outcomes in CKD. General measures to improve IR are directed to counteract causal factors. The use of pharmaceutical agents such as inhibitors of the renin-angiotensin system may improve IR in hypertensive and CKD patients. Pioglitazone appears a safe and promising therapeutic agent to reduce IR and uremic-associated abnormalities. However, interventional studies are needed to test if the reduction and/or normalization of IR may actually improve outcomes in these patients.

The effects of an ActRIIb receptor Fc fusion protein ligand trap in juvenile simian immunodeficiency virus-infected rhesus macaques

There are no approved therapies for muscle wasting in children infected with human immunodeficiency virus (HIV), which portends poor disease outcomes. To determine whether a soluble ActRIIb receptor Fc fusion protein (ActRIIB.Fc), a ligand trap for TGF-β/activin family members including myostatin, can prevent or restore loss of lean body mass and body weight in simian immunodeficiency virus (SIV)-infected juvenile rhesus macaques (Macaca mulatta). Fourteen pair-housed, juvenile male rhesus macaques were inoculated with SIVmac239 and, 4 wk postinoculation (WPI) treated with intramuscular injections of 10 mg ⋅ kg(-1) ⋅ wk(-1) ActRIIB.Fc or saline placebo. Body weight, lean body mass, SIV titers, and somatometric measurements were assessed monthly for 16 wk. Age-matched SIV-infected rhesus macaques were injected with saline. Intervention groups did not differ at baseline. Gains in lean mass were significantly greater in the ActRIIB.Fc group than in the placebo group (P < 0.001). Administration of ActRIIB.Fc was associated with greater gains in body weight (P = 0.01) and upper arm circumference than placebo. Serum CD4(+) T-lymphocyte counts and SIV copy numbers did not differ between groups. Administration of ActRIIB.Fc was associated with higher muscle expression of myostatin than placebo. ActRIIB.Fc effectively blocked and reversed loss of body weight, lean mass, and fat mass in juvenile SIV-infected rhesus macaques.

Supplementation of ketoacids contributes to the up-regulation of the Wnt7a/Akt/p70S6K pathway and the down-regulation of apoptotic and ubiquitin–proteasome systems in the muscle of 5/6 nephrectomised rats

Ketoacids (KA) are known to improve muscle mass among patients with chronic kidney disease (CKD) on a low-protein diet (CKD-LPD), but the mechanism of its preventive effects on muscle atrophy still remains unclear. Since muscle atrophy in CKD may be attributable to the down-regulation of the Wnt7a/Akt/p70S6K pathway and the activation of the ubiquitin–proteasome system (UPS) and the apoptotic signalling pathway, a hypothesis can readily be drawn that KA supplementation improves muscle mass by up-regulating the Wnt7a/Akt/p70S6K pathway and counteracting the activation of the UPS and caspase-3-dependent apoptosis in the muscle of CKD-LPD rats. Rats with 5/6 nephrectomy were randomly divided into three groups, and fed with either 22 % protein (normal-protein diet; NPD), 6 % protein (LPD) or 5 % protein plus 1 % KA for 24 weeks. Sham-operated rats with NPD intake were used as the control. The results demonstrated that KA supplementation improved protein synthesis and increased related mediators such as Wnt7a, phosphorylated Akt and p70S6K in the muscle of CKD-LPD rats. It also inhibited protein degradation, withheld the increase in ubiquitin and its ligases MAFbx (muscle atrophy F-box) and MuRF1 (muscle ring finger-1) as well as attenuated proteasome activity in the muscle of CKD-LPD rats. Moreover, KA supplementation gave rise to a reduction in DNA fragment, cleaved caspase-3 and 14 kDa actin fragment via the down-regulation of the Bax:Bcl-2 ratio in the muscle of CKD-LPD rats. The beneficial effects unveiled herein further consolidate that KA may be a better therapeutic strategy for muscle atrophy in CKD-LPD.

Skeletal muscle mitochondrial depletion and dysfunction in chronic kidney disease

Advanced chronic kidney disease (CKD) is associated with impaired exercise capacity, skeletal muscle dysfunction, and oxidative stress. Mitochondria are the primary source for energy production and generation of reactive oxygen species (ROS). Mitochondrial state 3 respiration, mitochondrial complex I enzyme activity, and tissue porin/actin ratio were determined in the gastrocnemius muscle of male SD rats 14 weeks after 5/6 nephrectomy (CKD) or sham-operation (control). The CKD group exhibited azotemia, hypertension, significant reduction (-39%) of state 3 mitochondrial respiration, and a significant increase in the mitochondrial complex I enzyme activity. The latter is the first step in oxidative phosphorylation, a process linked to production of ROS. These abnormalities were associated with a significant reduction in muscle porin/β actin ratio denoting substantial reduction of mitochondrial mass in skeletal muscle of animals with CKD. CKD results in impaired mitochondrial respiration, reduced muscle mitochondrial mass, depressed energy production and increased ROS generation in the skeletal muscle. These events can simultaneously contribute to the reduction of exercise capacity and oxidative stress in CKD.

Nutrition in infants and very young children with chronic kidney disease

Provision of adequate nutrition is a cornerstone of the management of infants and very young children with chronic kidney disease (CKD). Very young children with CKD frequently have poor spontaneous nutritional intake. Because growth depends strongly on nutrition during early childhood, growth in very young children with CKD is often suboptimal. In this review we will consider the mechanisms and manifestations of inadequate nutritional status in very young children with CKD, mechanisms mediating inadequate nutritional intake, and the optimal nutritional management of this special population. In addition, we suggest an approach to the assessment of nutritional status, including the use of body mass index in infants. Five major nutritional components are considered: energy, macronutrients, fluids and electrolytes, micronutrients, and calcium/phosphorus/vitamin D. The use of adjunctive therapies, including appetite stimulants, treatment of gastroesophageal reflux and gastric dysmotility, enhanced dialytic clearance, and growth hormone, is also briefly discussed.

Melanocortin antagonism ameliorates muscle wasting and inflammation in chronic kidney disease

Aberrant melanocortin signaling has been implicated in the pathogenesis of wasting in chronic kidney disease (CKD). Previously, we demonstrated that agouti-related peptide (AgRP), a melenocortin-4 receptor antagonist, reduced CKD-associated cachexia in CKD mice. Our previous studies with AgRP utilized dual energy X-ray (DXA) densitometry to assess the body composition in mice (Cheung W, Kuo HJ, Markison S, Chen C, Foster AC, Marks DL, Mak RH. J Am Soc Nephrol 18: 2517-2524, 2007; Cheung W, Yu PX, Little BM, Cone RD, Marks DL, Mak RH. J Clin Invest 115: 1659-1665, 2005). DXA is unable to differentiate water content in mice, and fluid retention in CKD may lead to an overestimate of lean mass. In this study, we employed quantitative magnetic resonance technique to evaluate body composition change following central administration of AgRP in a CKD mouse model. AgRP treatment improved energy expenditure, total body mass, fat mass, and lean body mass in CKD mouse. We also investigated the effect of CKD-associated cachexia on the signaling pathways leading to wasting in skeletal muscle, as well as whether these changes can be ameliorated by central administration of AgRP. AgRP treatment caused an overall decrease in proinflammatory cytokines, which may be one important mechanism of its effects. Muscle wasting in CKD may be due to the activation of proteolytic pathways as well as inhibition of myogenesis and muscle regeneration processes. Our results suggest that these aberrant pathological pathways leading to muscle wasting in CKD mice were ameliorated by central administration of AgRP.

The dose-dependent effects of endotoxin on protein metabolism in two types of rat skeletal muscle

Endotoxin administration is frequently used as a model of systemic inflammatory response which is considered the important pathogenetic factor in muscle wasting development in severe illness, such as sepsis, cancer, injury, AIDS and others. The main purpose of this study was determining the effect of various doses of endotoxin on protein and amino acid metabolism in two types of rat skeletal muscle. Sepsis was induced by intraperitoneal administration of endotoxin in a dose of 1, 3 and 5 mg/kg body weight (bw); control animals received a corresponding volume of the saline solution. After 24 h, extensor digitorum longus (EDL) and soleus (SOL) muscles were isolated and used for determination of total and myofibrillar proteolysis, protein synthesis, activity of cathepsins B and L, chymotrypsin-like activity of proteasome and amino acid release. The endotoxemia induced the body weight loss, the rise of total cholesterol and triglyceride plasma concentration and the protein catabolic state in skeletal muscle, which was caused by a higher increase in protein breakdown (due to activation of the proteasome system) than protein synthesis. The more significant effect of endotoxin was seen in EDL than SOL. The dose of 5 mg of endotoxin/kg bw induced the most significant changes in parameters of the protein and amino acid metabolism measured and could be therefore considered appropriate for studies of protein catabolism in young rat skeletal muscle at 24 h after endotoxin treatment.

Insulin alleviates degradation of skeletal muscle protein by inhibiting the ubiquitin-proteasome system in septic rats

Hypercatabolism is common under septic conditions. Skeletal muscle is the main target organ for hypercatabolism, and this phenomenon is a vital factor in the deterioration of recovery in septic patients. In skeletal muscle, activation of the ubiquitin-proteasome system plays an important role in hypercatabolism under septic status. Insulin is a vital anticatabolic hormone and previous evidence suggests that insulin administration inhibits various steps in the ubiquitin-proteasome system. However, whether insulin can alleviate the degradation of skeletal muscle protein by inhibiting the ubiquitin-proteasome system under septic condition is unclear. This paper confirmed that mRNA and protein levels of the ubiquitin-proteasome system were upregulated and molecular markers of skeletal muscle proteolysis (tyrosine and 3-methylhistidine) simultaneously increased in the skeletal muscle of septic rats. Septic rats were infused with insulin at a constant rate of 2.4 mU.kg^-1.min^-1 for 8 hours. Concentrations of mRNA and proteins of the ubiquitin-proteasome system and molecular markers of skeletal muscle proteolysis were mildly affected. When the insulin infusion dose increased to 4.8 mU.kg^-1.min^-1, mRNA for ubiquitin, E2-14 KDa, and the C2 subunit were all sharply downregulated. At the same time, the levels of ubiquitinated proteins, E2-14KDa, and the C2 subunit protein were significantly reduced. Tyrosine and 3-methylhistidine decreased significantly. We concluded that the ubiquitin-proteasome system is important skeletal muscle hypercatabolism in septic rats. Infusion of insulin can reverse the detrimental metabolism of skeletal muscle by inhibiting the ubiquitin-proteasome system, and the effect is proportional to the insulin infusion dose.

Optimal hemodialysis prescription: do children need more than a urea dialysis dose?

When prescribing hemodialysis in children, the clinician should first establish an adequate regimen, before seeking to optimize the treatment (Fischbach et al. 2005). A complete dialysis dose should consist of a urea dialysis dose and a determined convective volume. Intensified and more frequent dialysis regimens should not be considered exclusively as rescue therapy. Interestingly, a recent single-center study demonstrated that frequent on-line HDF provides an optimal dialysis prescription, both in terms of blood pressure control (and therefore avoidance of left ventricular hypertrophy), and catch-up growth, that is, no malnutrition or cachexia and less resistance to growth hormone. Nevertheless, this one-center experience would benefit from a prospective randomized study.

Dialysis strategies to improve growth in children with chronic kidney disease

Despite major advances in the understanding and management of uremic growth failure, 35% to 50% of children with chronic kidney disease still grow up to become adults of small stature. The final adult height achieved is correlated with the height deficit recorded at the time of kidney transplantation. A degree of catch-up growth does occur after kidney transplantation in childhood, but it is often limited. Growth retardation in children with chronic kidney disease causes significant difficulties in their daily lives, often limiting psychosocial integration. Additionally, growth retardation is associated with a greater number of hospital admissions and an increased risk of mortality. Growth failure is the common endpoint of a variety of pathologies, including growth hormone resistance. In children on chronic dialysis, linear growth may be improved by ensuring that optimal clinical care is provided. This includes maximizing nutritional support (e.g., tube feeding in cases of anorexia) so as to prevent malnutrition. Further management options include the administration of recombinant human growth hormone (rhGH) treatment and the use of more frequent and intensive dialysis sessions, such as daily on-line hemodiafiltration, which combines increased dialysis convective flow with ultrapure dialysate, to limit cachexia.

The role of metabolic acidosis in chronic kidney diseases

Background and objectives: This review focuses on three areas, basic acid-base physiology especially concerning hydrogen ion balance, development of acidosis in chronic kidney disease (CKD), and the consequences of acidosis. We highlight what is well established, what is less certain, and what is unknown. Method and results: The literature on acidosis in CKD were searched from 2004 to 2010 utilizing PubMed, Google Scholar, and Ovid to augment the classic work on acid base physiology over the past three decades. The original research in endogenous acid production and net acid excretion were reviewed. Touching upon the development of metabolic acidosis in CKD, we focused on the consequences of chronic metabolic acidosis on growth and other important variables. Finally, we recognize the significant issue of patients’ medical non-compliance and presented treatment strategy to counter this problem. Conclusion: The correction of acidosis in chronic kidney disease needs no advocacy. The case is made conclusively. Patient non-compliance because of the medication that needs to be taken several times a day is a problem, requiring due diligence.

Limb immobilization induces a coordinate down-regulation of mitochondrial and other metabolic pathways in men and women

Advancements in animal models and cell culture techniques have been invaluable in the elucidation of the molecular mechanisms that regulate muscle atrophy. However, few studies have examined muscle atrophy in humans using modern experimental techniques. The purpose of this study was to examine changes in global gene transcription during immobilization-induced muscle atrophy in humans and then explore the effects of the most prominent transcriptional alterations on protein expression and function. Healthy men and women (N = 24) were subjected to two weeks of unilateral limb immobilization, with muscle biopsies obtained before, after 48 hours (48 H) and 14 days (14 D) of immobilization. Muscle cross sectional area (∼5%) and strength (10–20%) were significantly reduced in men and women (∼5% and 10–20%, respectively) after 14 D of immobilization. Micro-array analyses of total RNA extracted from biopsy samples at 48 H and 14 D uncovered 575 and 3,128 probes, respectively, which were significantly altered during immobilization. As a group, genes involved in mitochondrial bioenergetics and carbohydrate metabolism were predominant features at both 48 H and 14 D, with genes involved in protein synthesis and degradation significantly down-regulated and up-regulated, respectively, at 14 D of muscle atrophy. There was also a significant decrease in the protein content of mitochondrial cytochrome c oxidase, and the enzyme activity of cytochrome c oxidase and citrate synthase after 14 D of immobilization. Furthermore, protein ubiquitination was significantly increased at 48 H but not 14 D of immobilization. These results suggest that transcriptional and post-transcriptional suppression of mitochondrial processes is sustained throughout 14 D of immobilization, while protein ubiquitination plays an early but transient role in muscle atrophy following short-term immobilization in humans.

Absence of caspase-3 protects against denervation-induced skeletal muscle atrophy

The ubiquitin-proteasome system is a key proteolytic pathway activated during skeletal muscle atrophy. The proteasome, however, cannot degrade intact myofibrils or actinomyosin complexes. In rodent models of diabetes mellitus and uremia, caspase-3 is involved in actinomyosin cleavage, generating fragments that subsequently undergo ubiquitin-proteasome-mediated degradation. Here, we demonstrate that caspase-3 also mediates denervation-induced muscle atrophy. At 2 wk after tibial nerve transection, the denervated gastrocnemius of caspase-3-knockout mice weighed more and demonstrated larger fiber-type-specific cross-sectional area than the denervated gastrocnemius of wild-type mice. However, there was no difference between caspase-3-knockout and wild-type denervated muscles in the magnitude or pattern of actinomyosin degradation, as determined by Western blotting for actin and the 14-kDa actin fragment. Similarly, there was no difference between caspase-3-knockout and wild-type denervated muscles in the magnitude of increase in proteasome activity, total protein ubiquitination, or atrogin-1 and muscle-specific ring finger protein 1 transcript levels. In contrast, there was an increase in TdT-mediated dUTP nick end label-positive nuclei in the denervated muscle of wild-type compared with caspase-3-knockout mice. Apoptotic signaling upstream of caspase-3 remained intact, with equivalent mitochondrial Bax translocation and cytochrome c release and caspase-9 activation in the denervated gastrocnemius muscle of wild-type and caspase-3-knockout mice. In contrast, diminished poly(ADP-ribose) polymerase cleavage in the denervated muscle of caspase-3-knockout compared with wild-type mice revealed that apoptotic signaling downstream of caspase-3 was impaired, suggesting that the absence of caspase-3 protects against denervation-induced muscle atrophy by suppressing apoptosis as opposed to ubiquitin-proteasome-mediated protein degradation.

Asymmetrical dimethylarginine triggers lipolysis and inflammatory response via induction of endoplasmic reticulum stress in cultured adipocytes

Protein energy wasting, a state of decreased stores of body protein and fat, is a risk factor for mortality in advanced chronic kidney disease (CKD). Little is known about the mechanism underlying loss of fat in CKD. Accumulation of asymmetric dimethylarginine (ADMA) is prevalent in advanced CKD. Here we assessed the effect of ADMA on cellular perturbation in cultured 3T3-L1 adipocytes. Exposure of adipocytes to ADMA induced lipolysis and decreased perilipin A, with no alteration of lipases expression or activity. ADMA treatment also upregulated the expression of inflammatory adipocytokines via activation of nuclear factor-kappaB (NF-kappaB). Blocking the inflammatory responses with NF-kappaB inhibitor partly inhibited the ADMA-induced lipolysis. Furthermore, ADMA treatment triggered endoplasmic reticulum (ER) stress, revealed by phosphorylation of PKR-like eukaryotic initiation factor 2alpha kinase, eukaryotic translational initiation factor 2alpha, c-Jun NH2-terminal kinase, and overexpression of glucose-regulated protein 78. Treatment with ER stress inhibitor completely abolished the ADMA-induced lipolysis and inflammatory responses. Moreover, conditioned medium from the ADMA-treated adipocytes increased protein degradation in cultured C2C12 myotubes, suggesting that the ADMA-induced adipocyte perturbation may promote skeletal muscle proteolysis. These data suggest that elevated ADMA promoted the adipocyte perturbation through induction of ER stress, which might have implication for protein energy wasting in CKD.

Regulation of muscle protein degradation, not synthesis, by dietary leucine in rats fed a protein-deficient diet

The aim of this study was to elucidate the effects of long-term intake of leucine in dietary protein malnutrition on muscle protein synthesis and degradation. A reduction in muscle mass was suppressed by leucine-supplementation (1.5% leucine) in rats fed protein-free diet for 7 days. Furthermore, the rate of muscle protein degradation was decreased without an increase in muscle protein synthesis. In addition, to elucidate the mechanism involved in the suppressive effect of leucine, we measured the activities of degradation systems in muscle. Proteinase activity (calpain and proteasome) and ubiquitin ligase mRNA (Atrogin-1 and MuRF1) expression were not suppressed in animals fed a leucine-supplemented diet, whereas the autophagy marker, protein light chain 3 active form (LC3-II), expression was significantly decreased. These results suggest that the protein-free diet supplemented with leucine suppresses muscle protein degradation through inhibition of autophagy rather than protein synthesis.

Fatigue in patients receiving maintenance dialysis: a review of definitions, measures, and contributing factors

Fatigue is a debilitating symptom or side effect experienced by many patients on long-term dialysis therapy. Fatigue has a considerable effect on patient health-related quality of life and is viewed as being more important than survival by some patients. Renal providers face many challenges when attempting to reduce fatigue in dialysis patients. The lack of a reliable, valid, and sensitive fatigue scale complicates the accurate identification of this symptom. Symptoms of daytime sleepiness and depression overlap with fatigue, making it difficult to target specific therapies. Moreover, many chronic health conditions common in the long-term dialysis population may lead to the development of fatigue and contribute to the day-to-day and diurnal variation in fatigue in patients. Key to improving the assessment and treatment of fatigue is improving our understanding of potential mediators, as well as potential therapies. Cytokines have emerged as an important mediator of fatigue and have been studied extensively in patients with cancer-related fatigue. In addition, although erythropoietin-stimulating agents have been shown to mitigate fatigue, the recent controversy regarding erythropoietin-stimulating agent dosing in patients with chronic kidney disease suggests that erythropoietin-stimulating agent therapy may not serve as the sole therapy to improve fatigue in this population. In conclusion, fatigue is an important and often underrecognized symptom in the dialysis population. Possible interventions for minimizing fatigue in patients on long-term dialysis therapy should aim at improving health care provider awareness, developing improved methods of measurement, understanding the pathogenesis better, and managing known contributing factors.