Protein turnover and amino acid transport kinetics in end-stage renal disease

Branched-chain ketoacid co-ingestion with protein lowers amino acid oxidation during hemodialysis: A randomized controlled cross-over trial

BACKGROUND & AIMS

Hemodialysis removes amino acids from the circulation, thereby stimulating muscle proteolysis. Protein ingestion during hemodialysis can compensate for amino acid removal but may also increase uremic toxin production. Branched-chain ketoacid (BCKA) co-ingestion may provide an additional anabolic stimulus without adding to uremic toxin accumulation. In the present study we assessed the impact of BCKA co-ingestion with protein on forearm amino acid balance and amino acid oxidation during hemodialysis.

METHODS

Nine patients (age: 73 ± 10 y) on chronic hemodialysis participated in this crossover trial. During two 4-h hemodialysis sessions, patients ingested 18 g protein with (PRO + BCKA) or without (PRO) 9 g BCKAs in a randomized order. Test beverages were labeled with L-[ring-¹³C₆]-phenylalanine and provided throughout the last 3 h of hemodialysis as 18 equal sips consumed with 10-min intervals. Arterial and venous plasma as well as breath samples were collected frequently throughout hemodialysis.

RESULTS

Arterial plasma total amino acid (TAA) concentrations during PRO and PRO + BCKA treatments were significantly lower after 1 h of hemodialysis (2.6 ± 0.3 and 2.6 ± 0.3 mmol/L, respectively) when compared to pre-hemodialysis concentrations (4.2 ± 1.0 and 4.0 ± 0.5 mmol/L, respectively; time effect: P < 0.001). Arterial plasma TAA concentrations increased throughout test beverage ingestion (time effect: P = 0.027) without differences between treatments (time∗treatment: P = 0.62). Forearm arteriovenous TAA balance during test beverage ingestion did not differ between timepoints (time effect: P = 0.31) or treatments (time∗treatment: P = 0.34). Whole-body phenylalanine oxidation was 33 ± 16% lower during PRO + BCKA when compared to PRO treatments (P < 0.001).

CONCLUSIONS

BCKA co-ingestion with protein during hemodialysis does not improve forearm net protein balance but lowers amino acid oxidation.

Organ Crosstalk Contributes to Muscle Wasting in Chronic Kidney Disease

Muscle wasting (ie, atrophy) is a serious consequence of chronic kidney disease (CKD) that reduces muscle strength and function. It reduces the quality of life for CKD patients and increases the risks of comorbidities and mortality. Current treatment strategies to prevent or reverse skeletal muscle loss are limited owing to the broad and systemic nature of the initiating signals and the multifaceted catabolic mechanisms that accelerate muscle protein degradation and impair protein synthesis and repair pathways. Recent evidence has shown how organs such as muscle, adipose, and kidney communicate with each other through interorgan exchange of proteins and RNAs during CKD. This crosstalk changes cell functions in the recipient organs and represents an added dimension in the complex processes that are responsible for muscle atrophy in CKD. This complexity creates challenges for the development of effective therapies to ameliorate muscle wasting and weakness in patients with CKD.

Amino acid removal during hemodialysis can be compensated for by protein ingestion and is not compromised by intradialytic exercise: a randomized controlled crossover trial

BACKGROUND

Patients with end-stage renal disease (ESRD) undergoing hemodialysis experience a rapid decline in skeletal muscle mass and strength. Hemodialysis removes amino acids (AAs) from the circulation, thereby lowering plasma AA concentrations and stimulating proteolysis.

OBJECTIVES

In the present study, we evaluate the impact of intradialytic protein ingestion at rest and following exercise on AA removal and plasma AA availability in patients with ESRD.

METHODS

Ten patients (age: 65 ± 16 y, male/female: 8/2, BMI: 24.2 ± 4.8 kg/m2, serum albumin: 3.4 ± 0.3 g/dL) with ESRD undergoing hemodialysis participated in this randomized controlled crossover trial. During 4 hemodialysis sessions, patients were assigned to ingest 40 g protein or a placebo 60 min after initiation, both at rest (PRO and PLA, respectively) and following exercise (PRO + EX and PLA + EX, respectively). Spent dialysate and blood samples were collected every 30 min throughout hemodialysis to assess AA removal and plasma AA availability.

RESULTS

Plasma AA concentrations declined by 26.1 ± 4.5% within 30 min after hemodialysis initiation during all interventions (P < 0.001, η2p > 0.79). Protein ingestion, but not intradialytic exercise, increased AA removal throughout hemodialysis (9.8 ± 2.0, 10.2 ± 1.6, 16.7 ± 2.2, and 17.3 ± 2.3 g during PLA, PLA + EX, PRO, and PRO + EX interventions, respectively; protein effect P < 0.001, η2p = 0.97; exercise effect P = 0.32, η2p = 0.11). Protein ingestion increased plasma AA concentrations until the end of hemodialysis, whereas placebo ingestion resulted in decreased plasma AA concentrations (time effect P < 0.001, η2p > 0.84). Plasma AA availability (incremental AUC) was greater during PRO and PRO + EX interventions (49 ± 87 and 70 ± 34 mmol/L/240 min, respectively) compared with PLA and PLA + EX interventions (-227 ± 54 and -208 ± 68 mmol/L/240 min, respectively; protein effect P < 0.001, η2p = 0.98; exercise effect P = 0.21, η2p = 0.16).

CONCLUSIONS

Protein ingestion during hemodialysis compensates for AA removal and increases plasma AA availability both at rest and during recovery from intradialytic exercise. Intradialytic exercise does not compromise AA removal or reduce plasma AA availability during hemodialysis in a postabsorptive or postprandial state.

How to Overcome Anabolic Resistance in Dialysis-Treated Patients?

A current hypothesis is that dialysis-treated patients are "anabolic resistant" i. e., their muscle protein synthesis (MPS) response to anabolic stimuli is blunted, an effect which leads to muscle wasting and poor physical performance in aging and in several chronic diseases. The importance of maintaining muscle mass and MPS is often neglected in dialysis-treated patients; better than to describe mechanisms leading to energy-protein wasting, the aim of this narrative review is to suggest possible strategies to overcome anabolic resistance in this patient's category. Food intake, in particular dietary protein, and physical activity, are the two major anabolic stimuli. Unfortunately, dialysis patients are often aged and have a sedentary behavior, all conditions which per se may induce a state of "anabolic resistance." In addition, patients on dialysis are exposed to amino acid or protein deprivation during the dialysis sessions. Unfortunately, the optimal amount and formula of protein/amino acid composition in supplements to maximixe MPS is still unknown in dialysis patients. In young healthy subjects, 20 g whey protein maximally stimulate MPS. However, recent observations suggest that dialysis patients need greater amounts of proteins than healthy subjects to maximally stimulate MPS. Since unneccesary amounts of amino acids could stimulate ureagenesis, toxins and acid production, it is urgent to obtain information on the optimal dose of proteins or amino acids/ketoacids to maximize MPS in this patients' population. In the meantime, the issue of maintaining muscle mass and function in dialysis-treated CKD patients needs not to be overlooked by the kidney community.

Anabolic Resistance of Muscle Protein Turnover Comes in Various Shapes and Sizes

Anabolic resistance is defined by a blunted stimulation of muscle protein synthesis rates (MPS) to common anabolic stimuli in skeletal muscle tissue such as dietary protein and exercise. Generally, MPS is the target of most exercise and feeding interventions as muscle protein breakdown rates seem to be less responsive to these stimuli. Ultimately, the blunted responsiveness of MPS to dietary protein and exercise underpins the loss of the amount and quality of skeletal muscle mass leading to decrements in physical performance in these populations. The increase of both habitual physical activity (including structured exercise that targets general fitness characteristics) and protein dense food ingestion are frontline strategies utilized to support muscle mass, performance, and health. In this paper, we discuss anabolic resistance as a common denominator underpinning muscle mass loss with aging, obesity, and other disease states. Namely, we discuss the fact that anabolic resistance exists as a dimmer switch, capable of varying from higher to lower levels of resistance, to the main anabolic stimuli of feeding and exercise depending on the population. Moreover, we review the evidence on whether increased physical activity and targeted exercise can be leveraged to restore the sensitivity of skeletal muscle tissue to dietary amino acids regardless of the population.

Amino acid losses are lower during pre-dilution on-line HDF than HD of the same Kt/V for urea

In this study, we investigated differences in amino acid losses between HD and pre-dilution on-line HDF with equal Kt/V for urea to determine which modality removes less amino acids from extravascular pools and ensures better nutrition. The subjects were patients receiving pre-dilution on-line HDF (n = 10) or HD (n = 10) at this hospital. Dialysis time was 4 h for all patients. In patients on HD, the blood flow rate was 200 mL/min and the dialysate flow rate was 463 ± 29.3 mL/min. In patients on pre-dilution on-line HDF, the blood flow rate was 240 ± 20 mL/min, the dialysate flow rate was 565.0 ± 42.5 mL/min, and the substitution flow rate (substitution volume) was 252.8 ± 26.4 mL/min (57.0 ± 6.0 L). Kt/V for urea was comparable between patients on HD and patients on pre-dilution on-line HDF (1.46 ± 0.25 vs. 1.46 ± 0.31). Amino acid loss and clear space were evaluated. Patients on pre-dilution on-line HDF lost significantly less glutamine and arginine (p < 0.01 and p = 0.032) and significantly less nonessential amino acids (NEAAs) than patients on HD (p = 0.013). They also had significantly lower clear space of total amino acids (TAAs), NEAAs, essential amino acids (EAAs), and branched-chain amino acids (BCAAs) than patients on HD (Total AA p = 0.019, NEAA p = 0.018, EAA p = 0.024, BCAA p = 0.042). When Kt/V for urea is equal, pre-dilution on-line HDF ensures better nutrition than does HD.

A Systematic Review of the Acute Effects of Hemodialysis on Skeletal Muscle Perfusion, Metabolism, and Function

Introduction

The underlying mechanisms of skeletal muscle wasting in hemodialysis patients are complex. We performed a systematic review to summarize evidence on whether hemodialysis has acute effects on skeletal muscle perfusion, metabolism, and function.

Methods

The protocol was registered on PROSPERO (Registration number CRD42018103682). A systematic search was performed in MEDLINE, PubMed, Cochrane, Embase, Scopus, and Web of Science. Citation, reference list, and gray literature searches were also performed. Studies were selected in 2 stages: title and abstract review, then full-text review.

Results

A total of 65 full-text articles were reviewed, and 14 studies were eligible for inclusion. No studies were identified that assessed muscle perfusion during dialysis. Two studies used near-infrared spectroscopy to indirectly measure skeletal muscle oxygen consumption, which increased during dialysis in 1 study but only in patients with diabetes in the second. Metabolism was examined in 9 studies. A number of acute metabolic changes were reported (e.g., caspase-3 activity, polyubiquitin, and interleukin-6 protein increased in response to hemodialysis) as was a net negative protein balance over the dialysis session. Three studies examining muscle function did not produce consistent findings.

Conclusion

Gaps remain in understanding the acute effects of hemodialysis on skeletal muscle, particularly for changes in perfusion and function, although there does appear to be an acute effect on muscle metabolism.

Dysregulated Handling of Dietary Protein and Muscle Protein Synthesis After Mixed-Meal Ingestion in Maintenance Hemodialysis Patients

Introduction

Skeletal muscle loss is common in patients with renal failure who receive maintenance hemodialysis (MHD) therapy. Regular ingestion of protein-rich meals are recommended to help offset muscle protein loss in MHD patients, but little is known about the anabolic potential of this strategy.

Methods

Eight MHD patients (age: 56 ± 5 years; body mass index [BMI]: 32 ± 2 kg/m²) and 8 nonuremic control subjects (age: 50 ± 2 years: BMI: 31 ± 1 kg/m²) received primed continuous L-[ring-²H₅]phenylalanine and L-[1-¹³C]leucine infusions with blood and muscle biopsy sampling on a nondialysis day. Participants consumed a mixed meal (546 kcal; 20-g protein, 59-g carbohydrates, 26-g fat) with protein provided as L-[5,5,5-²H₃]leucine-labeled eggs.

Results

Circulating dietary amino acid availability was reduced in MHD patients (41 ± 5%) versus control subjects (61 ± 4%; P = 0.03). Basal muscle caspase-3 protein content was elevated (P = 0.03) and large neutral amino acid transporter 1 (LAT1) protein content was reduced (P = 0.02) in MHD patients versus control subjects. Basal muscle protein synthesis (MPS) was ∼2-fold higher in MHD patients (0.030 ± 0.005%/h) versus control subjects (0.014 ± 0.003%/h) (P = 0.01). Meal ingestion failed to increase MPS in MHD patients (absolute change from basal: 0.0003 ± 0.007%/h), but stimulated MPS in control subjects (0.009 ± 0.002%/h; P = 0.004).

Conclusions

MHD patients demonstrated muscle anabolic resistance to meal ingestion. This blunted postprandial MPS response in MHD patients might be related to high basal MPS, which results in a stimulatory ceiling effect and/or reduced plasma dietary amino acid availability after mixed-meal ingestion.

Sex Differences in Muscle Wasting

With aging and other muscle wasting diseases, men and women undergo similar pathological changes in skeletal muscle: increased inflammation, enhanced oxidative stress, mitochondrial dysfunction, satellite cell senescence, elevated apoptosis and proteasome activity, and suppressed protein synthesis and myocyte regeneration. Decreased food intake and physical activity also indirectly contribute to muscle wasting. Sex hormones also play important roles in maintaining skeletal muscle homeostasis. Testosterone is a potent anabolic factor promoting muscle protein synthesis and muscular regeneration. Estrogens have a protective effect on skeletal muscle by attenuating inflammation; however, the mechanisms of estrogen action in skeletal muscle are less well characterized than those of testosterone. Age- and/or disease-induced alterations in sex hormones are major contributors to muscle wasting. Hence, men and women may respond differently to catabolic conditions because of their hormonal profiles. Here we review the similarities and differences between men and women with common wasting conditions including sarcopenia and cachexia due to cancer, end-stage renal disease/chronic kidney disease, liver disease, chronic heart failure, and chronic obstructive pulmonary disease based on the literature in clinical studies. In addition, the responses in men and women to the commonly used therapeutic agents and their efficacy to improve muscle mass and function are also reviewed.

Nutritional Status in Nocturnal Hemodialysis Patients - A Systematic Review with Meta-Analysis

Background

Hemodialysis patients experience an elevated risk of malnutrition associated with increased morbidity and mortality. Nocturnal hemodialysis (NHD) results in more effective removal of waste products and fluids. Therefore, diet and fluid restrictions are less restricted in NHD patients. However, it is ambiguous whether transition from conventional hemodialysis (CHD) to NHD leads to improved intake and nutritional status. We studied the effect of NHD on protein intake, laboratory indices of nutritional status, and body composition.

Study design

Systematic review with meta-analysis.

Population

NHD patients.

Search strategy

Systematic literature search from databases, Medline, Cinahl, EMBASE and The Cochrane Library, to identify studies reporting on nutritional status post-transition from CHD to NHD.

Intervention

Transition from CHD to NHD.

Outcomes

Albumin, normalized protein catabolic rate (nPCR), dry body weight (DBW), body mass index (BMI), phase angle, protein intake, and energy intake.

Results

Systematic literature search revealed 13 studies comprising 282 patients that made the transition from CHD to NHD. Meta-analysis included nine studies in 229 patients. In control group controlled studies (n = 4), serum albumin increased significantly from baseline to 4–6 months in NHD patients compared with patients that remained on CHD (mean difference 1.3 g/l, 95% CI 0.02; 2.58, p = 0.05). In baseline controlled studies, from baseline to 4–6 months of NHD treatment, significant increases were ascertained in serum albumin (mean difference (MD) 1.63 g/l, 95% CI 0.73–2.53, p<0.001); nPCR (MD 0.16 g/kg/day; 95% CI 0.04–0.29, p = 0.01); protein intake (MD 18.9 g, 95% CI 9.7–28.2, p<0.001); and energy intake (MD 183.2 kcal, 95% CI 16.8–349.7, p = 0.03). Homogeneity was rejected only for nPCR (baseline versus 4–6 months). DBW, BMI, and phase angle did not significantly change. Similar results were obtained for comparison between baseline and 8–12 months of NHD treatment.

Limitations

Most studies had moderate sample sizes; some had incomplete dietary records and relatively brief follow-up period. Studies markedly differed with regard to study design.

Conclusions

NHD is associated with significantly higher protein and energy intake as well as increases in serum albumin and nPCR. However, the data on body composition are inconclusive.

Effect of progressive resistance training on measures of skeletal muscle hypertrophy, muscular strength and health-related quality of life in patients with chronic kidney disease: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

Skeletal muscle wasting resulting in reduced muscular strength and health-related quality of life (HR-QOL) is common in chronic kidney disease (CKD) and may be reversed with progressive resistance training (PRT). Therefore, we systematically assessed the effect of PRT on measures of skeletal muscle hypertrophy, muscular strength and HR-QOL in this cohort to inform clinical practice and guidelines.

DESIGN

We performed a systematic review and meta-analysis.

INCLUSION CRITERIA

We included randomised controlled trials (RCTs) that investigated the independent effect of PRT (>6 weeks) on measures of skeletal muscle hypertrophy [muscle mass or cross-sectional area (CSA)], muscular strength and/or HR-QOL in adults with CKD.

DATA EXTRACTION AND ANALYSIS

The standardised mean difference (SMD) from each study was pooled to produce an overall estimate of effect and associated 95% confidence interval (95% CI) between treatment and control groups on primary outcomes.

RESULTS

Seven RCTs in 271 patients with Stage 3-5 CKD yielded seven studies on muscular strength (N = 249), six studies on total body muscle mass (N = 200) and six studies on HR-QOL (N = 223). PRT significantly improved standardised muscular strength [SMD 1.15 (95% CI 0.80-1.49)] and HR-QOL [SMD 0.83 (95% CI 0.51-1.16)], but not total body muscle mass [SMD 0.29 (95% CI -0.27 to 0.86)] in our primary analysis. However, secondary analysis of six studies showed that PRT induced significant muscle hypertrophy of the lower extremities (leg mass, or mid-thigh or quadriceps CSA) [SMD 0.43 (95% CI 0.11-0.76)], a pertinent analysis given that most studies implemented lower-body PRT only.

CONCLUSIONS

Robust evidence from RCTs indicates that PRT can induce skeletal muscle hypertrophy and increase muscular strength and HR-QOL outcomes in men and women with CKD. Therefore, clinical practice guidelines should be updated to inform clinicians on the benefits of PRT in this cohort.

The Effects of Parenteral Amino Acid Therapy on Protein Carbamylation in Maintenance Hemodialysis Patients

OBJECTIVE

Protein carbamylation is a urea-driven post-translational protein modification associated with mortality in dialysis patients. Free amino acids (AAs) are competitive inhibitors of protein carbamylation and animal studies suggest increasing AA concentrations reduces carbamylation burden. We hypothesized that AA therapy in maintenance hemodialysis patients would reduce carbamylation, carrying the potential to improve clinical outcomes.

DESIGN

Prospective pilot clinical trial (NCT1612429).

SETTING

The study was conducted from March 2013 to March 2014 in outpatient dialysis facilities in the Boston metropolitan area.

SUBJECTS AND INTERVENTION

We enrolled 23 consecutively consenting hemodialysis subjects, infusing the first 12 individuals with 250 cc of AAs 3 times per week postdialysis over 8 weeks. The remaining 11 subjects served as controls.

MAIN OUTCOME MEASURE

Change in carbamylated albumin (C-Alb), a measure of total body carbamylation burden, between baseline and 8 weeks was the primary outcome.

RESULTS

The treated and control groups had similar clinical characteristics and similar baseline C-Alb levels (mean ± SE 9.5 ± 2.4 and 9.3 ± 1.3 mmol/mol, respectively; P = .61). The treated arm showed a significant reduction in C-Alb compared with controls at 4 weeks (8.4% reduction in the treated arm vs. 4.3% increase in controls; P = .03) and the effect was greater by 8 weeks (15% reduction in the treated vs. 1% decrease in controls; P = .01).

CONCLUSION

In this pilot study, AA therapy appeared safe and effective at reducing C-Alb levels in hemodialysis patients compared with no treatment. The impact of reduced protein carbamylation on clinical outcomes should be further investigated.

Protein carbamylation in kidney disease: pathogenesis and clinical implications

Carbamylation describes a nonenzymatic posttranslational protein modification mediated by cyanate, a dissociation product of urea. When kidney function declines and urea accumulates, the burden of carbamylation naturally increases. Free amino acids may protect proteins from carbamylation, and protein carbamylation has been shown to increase in uremic patients with amino acid deficiencies. Carbamylation reactions are capable of altering the structure and functional properties of certain proteins and have been implicated directly in the underlying mechanisms of various disease conditions. A broad range of studies has demonstrated how the irreversible binding of urea-derived cyanate to proteins in the human body causes inappropriate cellular responses leading to adverse outcomes such as accelerated atherosclerosis and inflammation. Given carbamylation's relationship to urea and the evidence that it contributes to disease pathogenesis, measurements of carbamylated proteins may serve as useful quantitative biomarkers of time-averaged urea concentrations while also offering risk assessment in patients with kidney disease. Moreover, the link between carbamylated proteins and disease pathophysiology creates an enticing therapeutic target for reducing the rate of carbamylation. This article reviews the biochemistry of the carbamylation reaction, its role in specific diseases, and the potential diagnostic and therapeutic implications of these findings based on recent advances.

Relationship between lower extremity muscle strength and all-cause mortality in Japanese patients undergoing dialysis

BACKGROUND

Skeletal muscle wasting is common and insidious in patients who are undergoing hemodialysis. However, the association between lower extremity muscle strength and all-cause mortality remains unclear in this population.

OBJECTIVE

The purpose of this study was to investigate the prognostic significance of lower extremity muscle strength on 7-year survival in a cohort of patients who were clinically stable and undergoing hemodialysis.

DESIGN

A prospective cohort study was conducted.

METHODS

A total of 190 Japanese outpatients who were undergoing maintenance hemodialysis 3 times per week at a hemodialysis center were followed for up to 7 years. Lower extremity muscle strength was evaluated using a handheld dynamometer at the time of patient enrollment in the study. Muscle strength data were divided by dry weight and expressed as a percentage. A Cox proportional hazards regression model was used to assess the contribution of lower extremity muscle strength to all-cause mortality.

RESULTS

The median age (25th and 75th percentiles) of this study population was 64 years (57 and 72 years), 53.2% of the patients were women, and the time on hemodialysis was 39.0 months (15.9 and 110.5 months) at baseline. During a median follow-up of 36.0 months, there were 30 deaths. With a multivariate Cox model, the hazard ratio in the group with a knee extensor strength of <40% was 2.73 (95% confidence interval=1.14-6.52) compared with that in the ≥40% group.

LIMITATIONS

This was a small-scale observational study, and the mechanisms underlying the higher mortality risk in patients with poor muscle strength undergoing hemodialysis than in other patients undergoing hemodialysis remain to be elucidated.

CONCLUSIONS

Decreased lower extremity muscle strength was strongly associated with increased mortality risk in patients undergoing hemodialysis.

Mechanisms of muscle wasting in chronic kidney disease

In patients with chronic kidney disease (CKD), loss of cellular proteins increases the risks of morbidity and mortality. Persistence of muscle protein catabolism in CKD results in striking losses of muscle proteins as whole-body protein turnover is great; even small but persistent imbalances between protein synthesis and degradation cause substantial protein loss. No reliable methods to prevent CKD-induced muscle wasting currently exist, but mechanisms that control cellular protein turnover have been identified, suggesting that therapeutic strategies will be developed to suppress or block protein loss. Catabolic pathways that cause protein wasting include activation of the ubiquitin-proteasome system (UPS), caspase-3, lysosomes and myostatin (a negative regulator of skeletal muscle growth). These pathways can be initiated by complications associated with CKD, such as metabolic acidosis, defective insulin signalling, inflammation, increased angiotensin II levels, abnormal appetite regulation and impaired microRNA responses. Inflammation stimulates cellular signalling pathways that activate myostatin, which accelerates UPS-mediated catabolism. Blocking this pathway can prevent loss of muscle proteins. Myostatin inhibition could yield new therapeutic directions for blocking muscle protein wasting in CKD or disorders associated with its complications.

Natural history of skeletal muscle mass changes in chronic kidney disease stage 4 and 5 patients: an observational study

Cross-sectional studies in dialysis demonstrate muscle wasting associated with loss of function, increased morbidity and mortality. The relative drivers are poorly understood. There is a paucity of data regarding interval change in muscle in pre-dialysis and dialysis-dependant patients. This study aimed to examine muscle and fat mass change and elucidate associations with muscle wasting in advanced CKD. 134 patients were studied (60 HD, 28 PD, 46 CKD 4-5) and followed up for two years. Groups were similar in age, sex and diabetes prevalence. Soft tissue cross-sectional area (CSA) was measured annually on 3 occasions by a standardised multi-slice CT thigh. Potential determinants of muscle and fat CSA were assessed. Functional ability was assessed by sit-to-stand testing. 88 patients completed follow-up (40 HD, 16 PD, 32 CKD). There was a significant difference in percentage change in muscle CSA (MCSA) over year 1, dependant on treatment modality (χ(2) = 6.46; p = 0.039). Muscle loss was most pronounced in pre-dialysis patients. Muscle loss during year 1 was partially reversed in year 2 in 39%. Incident dialysis patients significantly lost MCSA during the year which they commenced dialysis, but not the subsequent year. Baseline MCSA, change in MCSA during year 1 and dialysis modality predicted year 2 change in MCSA (adjusted R(2) = 0.77, p<0.001). There was no correlation between muscle or fat CSA change and any other factors. MCSA correlated with functional testing, although MCSA change correlated poorly with change in functional ability. These data demonstrate marked variability in MCSA over 2 years. Loss of MCSA in both pre-dialysis and established dialysis patients is reversible. Factors previously cross-sectionally shown to correlate with MCSA did not correlate with wasting progression. The higher rate of muscle loss in undialysed CKD patients, and its reversal after dialysis commencement, suggests that conventional indicators may not result in optimal timing of dialysis initiation.

Effect of hyperinsulinemia during hemodialysis on the insulin-like growth factor system and inflammatory biomarkers: a randomized open-label crossover study

Background

A marked reduction in serum levels of bioactive insulin-like growth factor-I (IGF-I) has been observed in fasting hemodialysis (HD) patients during a 4-h HD session. The aim of the present study was to investigate the beneficial effect of hyperinsulinemia during HD on bioactive IGF-I and inflammatory biomarkers.

Methods

In a randomized cross-over study, 11 non-diabetic HD patients received a standardised HD session with either: 1) no treatment, 2) glucose infusion (10% glucose, 2.5 mL/kg/h), or 3) glucose-insulin infusion (10% glucose added 30 IU NovoRapid® per litre, 2.5 mL/kg/h). Each experiment consisted of three periods: pre-HD (−120 to 0 min), HD (0 to 240 min), and post-HD (240 to 360 min). A meal was served at baseline (−120 min); infusions were administered from baseline to 240 min. The primary outcome was change in bioactive IGF-I during the experiment. Secondary outcomes were changes in high-sensitivity C-reactive protein, interleukin-1β, interleukin-6, and tumor necrosis factor α. Comparisons were performed using mixed-model analysis of variance for repeated measures.

Results

From baseline to the end of study, no significant differences were observed in the changes in either serum bioactive IGF-I or total IGF-I between study days. Overall, serum bioactive IGF-I levels rose above baseline at 120 to 300 min with a maximum increase of 20% at 120 min (95% confidence interval (CI), 9 to 31%; p < 0.001), whereas total IGF-I levels rose above baseline at 180 to 300 min with a maximum increase of 5% at 240 min (95% CI, 2 to 9%; p = 0.004). A significant difference was observed in the changes in serum IGF-binding protein-1 (IGFBP-1) between study days (p = 0.008), but differences were only significant in the post-HD period. From baseline to the end of HD, no significant difference was observed in the changes in serum IGFBP-1 levels between study days, and in this time period overall serum IGFBP-1 levels were below baseline at all time points with a maximum decrease of 51% at 180 min (95% CI, 45 to 57%; p < 0.001). None of the investigated inflammatory biomarkers showed any differences in the changes over time between study days.

Conclusions

Postprandial insulin secretion stimulated the IGF-system during HD with no further effect of adding glucose or glucose-insulin infusion. Hyperinsulinemia during HD had no effect on biomarkers of inflammation.

Trial registration

ClinicalTrials.gov registry: NCT01209403

Nutrition support for the chronically wasted or acutely catabolic chronic kidney disease patient

Because of the number of factors affecting the nutritional and metabolic status in patients with advanced chronic kidney disease or who are on maintenance dialysis, the prevention and treatment of protein-energy wasting (PEW) of chronic kidney disease should involve a comprehensive combination of maneuvers to diminish protein and energy depletion, in addition to therapies that will avoid further losses. The available evidence suggests that nutritional supplementation, administered orally or parenterally, is effective in the treatment of maintenance dialysis patients with PEW in whom oral dietary intake from regular meals cannot maintain adequate nutritional status. Increased oral nutrient intake during dialysis and at home is the ideal choice for this intervention. In clinical practice, the advantages of intradialytic oral nutritional supplements include proven efficacy and compliance. Therefore, at a minimum, oral nutritional supplementation given intradialytically should be attempted in maintenance dialysis patients with PEW, accompanied by individualized dietary advice for appropriate intake at home. In ones who cannot tolerate oral feeding, other forms of nutritional supplementation including intradialytic parenteral nutritional are a reasonable strategy. Although not proven conclusively, nutritional interventions in the form of supplementation may lead to considerable improvements in mortality, hospitalization, and treatment costs.

Review article: Tackling the survival issue in end-stage renal disease: time to get physical on haemodialysis

Life expectancy in haemodialysis patients is reduced fourfold on average versus healthy age-matched individuals. The purpose of this review is to present empirical evidence that intradialytic exercise can mitigate primary independent risk factors for early mortality in end-stage renal disease. These risk factors include measures of skeletal muscle wasting, systemic inflammation, cardiovascular functioning and dialysis adequacy. Overall, the available literature provides support for the integration of exercise within the conventional outpatient haemodialysis unit. The amelioration of various physiological risk factors through an appropriate exercise prescription may enhance survival in this vulnerable cohort. Investigations are required to determine the effects of various doses of intradialytic exercise on a broad range of clinical outcomes, and more thoroughly elucidate the relationship between exercise-induced adaptations and survival advantage in end-stage renal disease.

Genetics and reverse epidemiology among patients on chronic hemodialysis

A reversal in the association between traditional and nontraditional risk factors and clinical outcomes is often encountered in patients with chronic illness, including among those with advanced chronic kidney disease (CKD) on maintenance hemodialysis (MHD). The effects of the malnutrition-inflammation complex syndrome (MICS) may play a significant role in the reversal of this risk factor-outcomes association. the MICS, this syndrome complex is not universal in its prevalence among MHD patients. The significant inter- and intra-individual differences in the prevalence of inflammation, oxidative stress, and malnutrition, indicates the influence of genetic factors in this variability. In recent years, enormous advancement in the field of molecular genetics, genomics and bioinformatics, have revolutionized studies of the genetic epidemiology of several diseases. However, genetic association studies are at a preliminary stage in the population with advanced CKD (Table 1). Preliminary studies of the impact of polyphisms in inflammation and oxidative stress-related genes and genes affecting body composition and metabolism suggest that genetic variation may indeed affect the phenotype of the MHD population. Further, some of these gene polymorphisms may also contribute to a reversal of the association between traditional risk factors, such as BMI, blood pressure, and cholesterol and clinical outcomes in this vulnerable patient population. Genetic studies in patients with advanced CKD pose enormous challenges, including recruitment of sufficient numbers of patients to achieve adequate statistical power, resolution of immense genotypic and phenotypic heterogeneity, and gene-environment and gene-gene interactions. However, well-designed adequately powered studies with carefully defined phenotypes may potentially allow definition of risk profiles characterized by combinations of relevant Single nucleotide polymorphisms in the setting of given environmental factors. Accurate risk stratification that takes into account genetic information would allow more informed targeting of pharmacologic intervention and better refined clinical trial methodologies.

Randomized Controlled Trial of Intradialytic Resistance Training to Target Muscle Wasting in ESRD: The Progressive Exercise for Anabolism in Kidney Disease (PEAK) Study

BACKGROUND

To determine whether prolonged (24 weeks) intradialytic progressive resistance training (PRT) could counteract muscle wasting more effectively than short-duration training (12 weeks) in patients with end-stage renal disease.

STUDY DESIGN

Randomized controlled trial.

SETTING & PARTICIPANTS

49 patients (age, 62.6 +/- 14.2 years; 0.3 to 16.7 years on hemodialysis therapy) were randomly assigned to PRT plus usual care for 24 weeks (24WK group) or a crossover control group that received usual care for the first 12 weeks, then PRT plus usual care for the latter 12 weeks (12WK group).

INTERVENTION

Two sets of 10 free-weight PRT exercises were performed at a high intensity during routine thrice-weekly hemodialysis treatment under direct supervision.

OUTCOMES & MEASUREMENTS

Primary outcomes include thigh muscle cross-sectional area by means of computed tomography and intramuscular lipid content estimated through attenuation. Secondary outcomes include muscular strength, exercise capacity, and C-reactive protein level.

RESULTS

The 24WK group increased muscle cross-sectional area (+1.82 +/- 3.25 cm(2)) compared with losses in the 12WK group (-1.37 +/- 6.87 cm(2); relative effect size, 0.59; 95% confidence interval [CI], -0.27 to 6.65; P = 0.04). However, this outcome did not achieve the level of statistical significance required (P = 0.025) after Bonferroni correction for multiple primary outcomes. There was no significant change in intramuscular lipid content between groups (+0.19 +/- 1.32 versus +0.16 +/- 1.69 Hounsfield units in the 24WK and 12WK groups, respectively; P = 0.31). Log C-reactive protein level tended to decrease in the 24WK group compared with the 12WK group (relative effect size, -0.63; 95% CI, -0.27 [-0.54 to 0.00]; P = 0.05). The 24WK group improved muscular strength measures and exercise capacity throughout the trial.

LIMITATIONS

Single geographic site used; no control group without exercise exposure; unblinded assessment of some secondary outcome measures.

CONCLUSIONS

Prolonged intradialytic PRT did not significantly improve muscle cross-sectional area or intramuscular lipid content compared with a shorter duration of exercise. Future trials are required to more thoroughly investigate the clinical importance and magnitude of myogenic adaptations to PRT in this cohort.

Amino acid repletion does not decrease muscle protein catabolism during hemodialysis

Intradialytic protein catabolism is attributed to loss of amino acids in the dialysate. We investigated the effect of amino acid infusion during hemodialysis (HD) on muscle protein turnover and amino acid transport kinetics by using stable isotopes of phenylalanine, leucine, and lysine in eight patients with end-stage renal disease (ESRD). Subjects were studied at baseline (pre-HD), 2 h of HD without amino acid infusion (HD-O), and 2 h of HD with amino acid infusion (HD+AA). Amino acid depletion during HD-O augmented the outward transport of amino acids from muscle into the vein. Increased delivery of amino acids to the leg during HD+AA facilitated the transport of amino acids from the artery into the intracellular compartment. Increase in muscle protein breakdown was more than the increase in synthesis during HD-O (46.7 vs. 22.3%, P < 0.001). Net balance (nmol.min(-1).100 ml (-1)) was more negative during HD-O compared with pre-HD (-33.7 +/- 1.5 vs. -6.0 +/- 2.3, P < 0.001). Despite an abundant supply of amino acids, the net balance (-16.9 +/- 1.8) did not switch from net release to net uptake. HD+AA induced a proportional increase in muscle protein synthesis and catabolism. Branched chain amino acid catabolism increased significantly from baseline during HD-O and did not decrease during HD+AA. Protein synthesis efficiency, the fraction of amino acid in the intracellular pool that is utilized for muscle protein synthesis decreased from 42.1% pre-HD to 33.7 and 32.6% during HD-O and HD+AA, respectively (P < 0.01). Thus amino acid repletion during HD increased muscle protein synthesis but did not decrease muscle protein breakdown.

Progressive Exercise for Anabolism in Kidney Disease (PEAK): A Randomized, Controlled Trial of Resistance Training during Hemodialysis

Skeletal muscle wasting is common and insidious in patients who receive maintenance hemodialysis treatment for the management of ESRD. The objective of this study was to determine whether 12 wk of high-intensity, progressive resistance training (PRT) administered during routine hemodialysis treatment could improve skeletal muscle quantity and quality versus usual care. Forty-nine patients (62.6 +/- 14.2 yr; 0.3 to 16.7 yr on dialysis) were recruited from the outpatient hemodialysis unit of the St. George Public Hospital (Sydney, Australia). Patients were randomized to PRT + usual care (n = 24) or usual care control only (n = 25). The PRT group performed two sets of 10 exercises at a high intensity (15 to 17/20 on the Borg Scale) using free weights, three times per week for 12 wk during routine hemodialysis treatment. Primary outcomes included thigh muscle quantity (cross-sectional area [CSA]) and quality (intramuscular lipid content via attenuation) evaluated by computed tomography scan. Secondary outcomes included muscle strength, exercise capacity, body circumference measures, proinflammatory cytokine C-reactive protein, and quality of life. There was no statistically significant difference in muscle CSA change between groups. However, there were statistically significant improvements in muscle attenuation, muscle strength, mid-thigh and mid-arm circumference, body weight, and C-reactive protein in the PRT group relative to the nonexercising control group. These findings suggest that patients with ESRD can improve skeletal muscle quality and derive other health-related adaptations solely by engaging in a 12-wk high-intensity PRT regimen during routine hemodialysis treatment sessions. Longer training durations or more sensitive analysis techniques may be required to document alterations in muscle CSA.

Protein and energy intake in advanced chronic kidney disease: how much is too much?

Uremic wasting is strongly associated with increased risk of death and hospitalization events in patients with advanced chronic kidney disease (CKD). Recent evidence indicates that patients with advanced chronic kidney disease are prone to uremic wasting due to several factors, which include the dialysis procedure and certain comorbid conditions, especially chronic inflammation and insulin resistance or deficiency. While the catabolic effects of dialysis can be readily avoided with intradialytic nutritional supplementation, there are no established alternative strategies to avoid the catabolic consequences of comorbid conditions other than treatment of their primary etiology. To this end, there is no indication that simply increasing dietary protein and energy intake above the required levels based on level of kidney disease is beneficial in patients with advanced chronic kidney disease. However, aside from the potential adverse effects such as uremic toxin production, dietary protein and energy intake in excess of actual needs might be beneficial in maintenance dialysis patients as it may lead to weight gain over time. Clearly, the role of obesity in advanced uremia needs to be examined in detail prior to making any clinically applicable recommendations, both in terms of ''low'' and ''high'' dietary protein and energy intake.

An update on nutrition in chronic kidney disease

The prevalence of malnutrition in the course of chronic kidney disease has not changed recently and is still between 30 and 50%. About 10% of patients on maintenance dialysis show signs of severe malnutrition. Recent progress has been made on protein metabolism, the validation of new diagnostic tools, and the use of anabolic compounds. Large clinical trials have characterized the use of medications for renutrition, and international guidelines are currently updated. Neverthless, physicians will be mostly efficient at the stage of malnutrition prevention, by implementing an early, interactive dietary and nutritional care programs in close collaboration with specialized dietitians.

Development of a diagnostic method for detecting increased muscle protein degradation in patients with catabolic conditions

Muscle atrophy in catabolic illnesses is due largely to accelerated protein degradation. Unfortunately, methods for detecting accelerated muscle proteolysis are cumbersome. The goal of this study was to develop a method for detecting muscle protein breakdown and assess the effectiveness of anticatabolic therapy. In rodent models of catabolic conditions, it was found that accelerated muscle protein degradation is triggered by activation of caspase-3. Caspase-3 cleaves actomyosin/myofibrils to form substrates for the ubiquitin-proteasome system and leaves a characteristic 14-kD actin fragment in the insoluble fraction of a muscle lysate. Muscle biopsies were obtained from normal adults and three groups of patients: 14 who were undergoing hip arthroplasty, 28 hemodialysis patients who were participating in exercise programs, and seven severely burned patients. In muscle of patients who were undergoing hip arthroplasty, the 14-kD actin fragment level was correlated (r = 0.787, P < 0.01) with the fractional rate of protein degradation. In muscle of hemodialysis patients who were undergoing endurance exercise training, the 14-kD actin fragment decreased to values similar to levels in normal adults; strength training did not significantly decrease the actin fragment. Severely burned patients had increased muscle protein degradation and actin fragment levels, but the two measures were not significantly correlated. The experimental results suggest that the 14-kD actin fragment in muscle biopsies is increased in catabolic states and could be used in conjunction with other methods to detect and monitor changes in muscle proteolysis that occur in patients with mild or sustained increases in muscle proteolysis.

Plasma free amino acids and their metabolites in Taiwanese patients on hemodialysis and continuous ambulatory peritoneal dialysis

BACKGROUND

The high prevalence of protein-energy malnutrition is a critical issue for patients with end stage renal disease (ESRD) on hemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD). Levels of plasma and intracellular amino acids are significant indicators of protein metabolism and nutritional status assessment. We measured plasma FAAs in patients on maintenance dialysis and to provide information in monitoring the therapeutic strategy, particularly in AA supplementary therapy or protein restriction.

METHODS

Fifty-five patients with ESRD were investigated, 25 on HD (male : female=14 : 11; 48-67 y) and 30 on CAPD (male : female=17 : 13; 45-64 y). The subjects had been on dialysis for an average of 13 months (range, 9 to 22 months). Their plasma FAAs (including their intermediate metabolites) were measured by ion exchange chromatography before and after HD or during CAPD and were compared with data obtained from 20 age- and sex-matched healthy controls.

RESULTS

The total plasma FAA levels (urea and free ammonia, NH3 were excluded) in pre-HD samples (3911 +/- 709 micromol/l) was significantly higher than in the other groups (2570 +/- 378 in control, 3210 +/- 640 in post-HD, and 3468 +/- 271 in CAPD samples). The mean plasma FAA concentrations differed significantly between pre-HD and controls and between pre-HD and CAPD samples (p<0.05). No significant differences were found among the other group comparisons. Comparing individual FAA concentrations, only citrulline differed significantly among all groups (p<0.05), whereas serine, glutamine, beta-alanine, beta-aminoisobutyric acid, and gamma-aminobutyric acid were not different. Concentrations of some FAAs involved in the urea cycle, e.g., arginine, aspartic acid, citrulline, and ornithines, and solutes urea and NH3, were significantly increased. Ratios of tyrosine/phenylalanine and valine/glycine ratios were markedly reduced in all patients on dialysis compared with controls.

CONCLUSION

FAAs either from dietary uptake or protein catabolism are substantially retained in the plasma of patients with ESRD, possibly producing higher levels of the waste products (urea and NH3) through the urea cycle and ammonia metabolism in liver. Maintenance dialysis can effectively eliminate excess FAAs in plasma, as there was a 17.9% reduction post-HD. The abnormalities in FAA metabolism found in patients with ESRD necessitate careful consideration of dialysis and dietary measures.

Renin-angiotensin polymorphisms and QTc interval prolongation in end-stage renal disease

BACKGROUND

Polymorphisms of renin-angiotensin system (RAS) genes in patients with end-stage renal disease (ESRD) on chronic hemodialysis may be associated with QTc interval prolongation, leading to fatal arrhythmias. The objective of this study was to determine (1) the prevalence of QTc prolongation in hemodialysis patients, and (2) the association of a prolonged QTc in these patients with RAS polymorphisms [angiotensin-converting enzyme-insertion/deletion (ACE-I/D), angiotensin type 1 receptor-A1166C (AT1R-A1166C), and angiotensinogen-M235T (AGT-M235T)].

METHODS

Twelve-lead electrocardiograms (ECGs), serum electrolytes (sodium, potassium, and calcium), and ACE and angiotensin II levels were obtained 10 to 12 hours after a hemodialysis session in 43 patients with ESRD on chronic hemodialysis [mean age (+/-SD), 55 +/- 14 years]. Using polymerase chain reaction (PCR), the presence of polymorphisms of the ACE-I/D, AT1R-A1166C, and AGT-M235T genes was determined from the buccal cells. A maximum QT interval in patients with sinus rhythm and normal QRS duration was corrected for heart rate using Hodges' formula.

RESULTS

Fifty-eight percent of the patients had QTc interval prolongation (>440 msec). The ACE-DD genotype (P = 0.002) and the C allele of the AT1R-A1166C gene (P = 0.004), but not the AGT-M235T gene, contributed to QTc prolongation.

CONCLUSION

Polymorphisms of ACE and AT1R genes additively contribute to QTc prolongation found in a great majority of ESRD patients. Therefore, ESRD patients with both or one of these polymorphisms may be at a higher risk for sudden cardiac death.

Muscle Protein Metabolism During Hemodialysis

Despite improvement in many aspects of the care of maintenance hemodialysis (HD) patients, protein-calorie malnutrition, which is characterized by an insidious loss of somatic protein, is common and is a major risk factor for increased morbidity and mortality. We present here an overview of the current knowledge on protein metabolism in uremic patients with the expectation of providing insights into the mechanisms involved in HD-associated catabolism and outlining the rationale underlying intradialytic nutrition. We concentrate on the discussion of muscle protein metabolism because muscle is the predominant site of protein storage, and its integrity is mandatory for the maintenance of a good quality of life.

Protein and energy: recommended intake and nutrient supplementation in chronic dialysis patients

Nutritional status is an important predictor of clinical outcome in end-stage renal disease (ESRD) patients, especially in patients on chronic hemodialysis. Uremic malnutrition is strongly associated with increased risk of death and hospitalization events in this patient population, and decreased muscle mass is the most significant predictor of these outcomes. Several factors that influence protein metabolism predispose chronic hemodialysis patients to increased catabolism and loss of lean body mass. The available evidence suggests that low protein and energy intake associated with advanced uremia along with catabolic consequences of dialytic therapies can lead to the development of uremic malnutrition. Recent studies show that the hemodialysis procedure induces a net protein catabolic state at the whole-body level as well as skeletal muscle. There is evidence to suggest that these undesirable effects are due to decreased protein synthesis and increased proteolysis. Provision of nutrients, either in the form of intradialytic parenteral nutrition or oral feeding during hemodialysis, can adequately compensate for the catabolic effects of the hemodialysis procedure. While the mechanisms of these effects are not studied in detail, changes in extracellular amino acid concentrations, along with certain anabolic hormones such as insulin, are important mediators of these actions.

Does Hemodialysis Increase Protein Breakdown? Dissociation between Whole-Body Amino Acid Turnover and Regional Muscle Kinetics

Hemodialysis (HD) is a protein catabolic procedure. Whole-body amino acid turnover studies identify dialysate amino acid loss and reduced protein synthesis as the catabolic events; proteolysis is not increased. Regional amino acid kinetics, however, document enhanced muscle protein breakdown as the cause of the catabolism; muscle protein synthesis also increased but to a lesser magnitude than the increment in protein breakdown. This discordance between whole-body and regional kinetics is best explained by the contrasting physiology between the muscle and the liver. During HD, muscle releases amino acids, which then are taken up by the liver for de novo protein synthesis. There seems to be a somatic to visceral recycling of amino acids. Evidence supporting this concept includes the increased fractional synthesis of albumin and fibrinogen during HD. It should be emphasized that region- or organ-specific kinetics vary, and whole-body turnover is a composite of all of the visceral and somatic compartments taken together. Reduced whole-body protein synthesis may be a compensatory adaptation to dialysate amino acid loss with a consequent reduction in plasma amino acid concentration. Notwithstanding the protein catabolic nature of HD, evidence is accumulating that intradialytic nutritional supplementation may blunt its catabolic effect.

Glutamine kinetics and protein turnover in end-stage renal disease

Alanine and glutamine constitute the two most important nitrogen carriers released from the muscle. We studied the intracellular amino acid transport kinetics and protein turnover in nine end-stage renal disease (ESRD) patients and eight controls by use of stable isotopes of phenylalanine, alanine, and glutamine. The amino acid transport kinetics and protein turnover were calculated with a three-pool model from the amino acid concentrations and enrichment in the artery, vein, and muscle compartments. Muscle protein breakdown was more than synthesis (nmol.min(-1).100 ml leg(-1)) during hemodialysis (HD) (169.8 +/- 20.0 vs. 125.9 +/- 21.8, P < 0.05) and in controls (126.9 +/- 6.9 vs. 98.4 +/- 7.5, P < 0.05), but synthesis and catabolism were comparable pre-HD (100.7 +/- 15.7 vs. 103.4 +/- 14.8). Whole body protein catabolism decreased by 15% during HD. The intracellular appearance of alanine (399.0 +/- 47.1 vs. 243.0 +/- 34.689) and glutamine (369.7 +/- 40.6 vs. 235.6 +/- 27.5) from muscle protein breakdown increased during dialysis (nmol.min(-1).100 ml leg(-1), P < 0.01). However, the de novo synthesis of alanine (3,468.9 +/- 572.2 vs. 3,140.5 +/- 467.7) and glutamine (1,751.4 +/- 82.6 vs. 1,782.2 +/- 86.4) did not change significantly intradialysis (nmol.min(-1).100 ml leg(-1)). Branched-chain amino acid catabolism (191.8 +/- 63.4 vs. -59.1 +/- 42.9) and nonprotein glutamate disposal (347.0 +/- 46.3 vs. 222.3 +/- 43.6) increased intradialysis compared with pre-HD (nmol.min(-1).100 ml leg(-1), P < 0.01). The mRNA levels of glutamine synthase (1.45 +/- 0.14 vs. 0.33 +/- 0.08, P < 0.001) and branched-chain keto acid dehydrogenase-E2 (3.86 +/- 0.48 vs. 2.14 +/- 0.27, P < 0.05) in the muscle increased during HD. Thus intracellular concentrations of alanine and glutamine are maintained during HD by augmented release of the amino acids from muscle protein catabolism. Although muscle protein breakdown increased intradialysis, the whole body protein catabolism decreased, suggesting central utilization of amino acids released from skeletal muscle.

Effects of hemodialysis on protein metabolism

Uremic malnutrition, as evidenced by decreased muscle mass, is strongly associated with increased risk of death and hospitalization events in chronic hemodialysis (CHD) patients. Several factors that influence protein metabolism predispose CHD patients to increased catabolism and loss of lean body mass. It has been long suspected that the hemodialysis (HD) procedure is a net catabolic event. Recent studies show that the HD procedure indeed induces a net protein catabolic state at the whole-body level as well as in skeletal muscle. There is evidence to suggest that these undesirable effects are caused by decreased protein synthesis and increased proteolysis. Animal studies suggest that decreased protein synthesis is likely mediated by the significant decrease in plasma amino acid concentrations during HD. On the other hand, increased protein degradation is, at least in part, mediated by the HD-associated inflammatory response.

Markers of inflammation, proteolysis, and apoptosis in ESRD

BACKGROUND

Hemodialysis (HD) is associated with protein catabolism and augmented apoptosis. Although the effect of metabolic acidosis and inflammatory cytokines on activation of the ubiquitin-proteasome pathway and branched-chain keto acid dehydrogenase (BCKAD) is well known, the effect of HD on these pathways remains unexplored.

METHODS

Twelve patients with end-stage renal disease were studied before and during HD. Eight controls also were studied. Plasma levels of complement components and cytokines, interleukin-1 (IL-1), IL-6, and tumor necrosis factor-alpha (TNF-alpha) were measured. Messenger RNA (mRNA) levels of caspase-3, a mediator of apoptosis; ubiquitin, a marker of proteolysis; and BCKAD-E2, an enzyme regulating branched-chain amino acid oxidation, were estimated in skeletal muscle biopsy specimens by means of reverse-transcriptase polymerase chain reaction. Annexin-V expression was quantified by DNA array. Before the study, participants were placed on a 1.2-g/kg/d protein diet, and metabolic acidosis was corrected.

RESULTS

During HD, plasma IL-6 levels increased from 7.54 +/- 2.24 to 27.86 +/- 4.94 pg/dL (P < 0.001). Complement component, IL-1, and TNF-alpha levels did not change significantly during HD. mRNA levels of caspase-3 (0.50 +/- 0.01 versus 0.81 +/- 0.04), annexin-V (0.94 +/- 0.06 versus 1.48 +/- 0.05; P < 0.001), ubiquitin (1.10 +/- 0.03 versus 1.44 +/- 0.03), and BCKAD-E2 (0.47 +/- 0.01 versus 0.81 +/- 0.04) increased in muscle during HD compared with pre-HD values (P < 0.001). mRNA levels of ubiquitin (0.62 +/- 0.03) and BCKAD-E2 (0.58 +/- 0.02) were greater in controls than pre-HD values (P < 0.05). There were significant positive correlations between plasma IL-6 levels and expression of caspase-3, ubiquitin, and BCKAD-E2 genes.

CONCLUSION

HD causes activation of cytokines, which may mediate the increase in gene expression of caspase-3, ubiquitin, and BCKAD-E2 in skeletal muscles.

Coordinated increase in albumin, fibrinogen, and muscle protein synthesis during hemodialysis: role of cytokines

Serum albumin, fibrinogen levels, and lean body mass are important predictors of outcome in end-stage renal disease (ESRD). We estimated the fractional synthesis rates of albumin (FSR-A), fibrinogen (FSR-F), and muscle protein (FSR-M) in nine ESRD patients and eight controls, using primed constant infusion of l-[ring-(13)C(6)]phenylalanine. Cytokine profile and arteriovenous balance of amino acids were also measured. ESRD patients were studied before (Pre-HD) and during hemodialysis (HD). Plasma IL-6, IL-10, and C-reactive protein increased significantly during HD. Despite a decrease in the delivery of amino acids to the leg, the outflow of the amino acids increased during HD. The net balance of amino acids became more negative during HD, indicating release from the muscle. HD increased leg muscle protein synthesis (45%) and catabolism (108%) but decreased whole body proteolysis (15%). FSR-A during HD (9.7 +/- 0.9%/day) was higher than pre-HD (6.5 +/- 0.9%/day) and controls (5.8 +/- 0.5%/day, P < 0.01). FSR-F increased during HD (19.7 +/- 2.6%/day vs. 11.8 +/- 0.6%/day, P < 0.01), but it was not significantly different from that of controls (14.4 +/- 1.4%/day). FSR-M intradialysis (1.77 +/- 0.19%/day) was higher than pre-HD (1.21 +/- 0.25%/day) and controls (1.30 +/- 0.32%/day, P < 0.001). Pre-HD FSR-A, FSR-F, and FSR-M values were comparable to those of controls. There was a significant and positive correlation between plasma IL-6 and the FSRs. Thus, in ESRD patients without metabolic acidosis, the fractional synthesis rates of albumin, fibrinogen, and muscle protein are not decreased pre-HD. However, HD increases the synthesis of albumin, fibrinogen, and muscle protein. The coordinated increase in the FSRs is facilitated by constant delivery of amino acids derived from the muscle catabolism and intradialytic increase in IL-6.