Uremic myopathy: is oxidative stress implicated in muscle dysfunction in uremia?

Exercise for patients with chronic kidney disease: from cells to systems to function

Chronic kidney disease (CKD) is among the leading causes of death and disability, affecting an estimated 800 million adults globally. The underlying pathophysiology of CKD is complex creating challenges to its management. Primary risk factors for the development and progression of CKD include diabetes mellitus, hypertension, age, obesity, diet, inflammation, and physical inactivity. The high prevalence of diabetes and hypertension in patients with CKD increases the risk for secondary consequences such as cardiovascular disease and peripheral neuropathy. Moreover, the increased prevalence of obesity and chronic levels of systemic inflammation in CKD have downstream effects on critical cellular functions regulating homeostasis. The combination of these factors results in the deterioration of health and functional capacity in those living with CKD. Exercise offers protective benefits for the maintenance of health and function with age, even in the presence of CKD. Despite accumulating data supporting the implementation of exercise for the promotion of health and function in patients with CKD, a thorough description of the responses and adaptations to exercise at the cellular, system, and whole body levels is currently lacking. Therefore, the purpose of this review is to provide an up-to-date comprehensive review of the effects of exercise training on vascular endothelial progenitor cells at the cellular level; cardiovascular, musculoskeletal, and neural factors at the system level; and physical function, frailty, and fatigability at the whole body level in patients with CKD.

Baseline Characteristics and Outcomes for People With and Without COVID-19 Diagnoses Receiving Inpatient Rehabilitation Care Across the US in 2020-2021

Objective

To assess sociodemographic, medical complexity, and outcomes of persons receiving care at inpatient rehabilitation facilities (IRFs) with and without a diagnosis of COVID-19.

Design

A retrospective cohort study using electronic medical record (EMR) data from 138 IRFs across 34 states and Puerto Rico.

Setting

N/A.

Participants

IRF EMR data for 212,663 patients discharged between 04/01/2020 and 05/31/2021 (N=212,663), of which 16,199 (COVID-19 group) had a primary or secondary COVID-19 diagnosis based upon ICD codes set (ICD-10 codes U07.1, B94.8, Z86.19, Z86.16).

Main Outcome Measures

Four categories: (a) sociodemographic, (b) medical complexity, (c) process, that is, standard IRF processes, and clinical outcomes (collected routinely as part of administrative reporting), and (d) functional outcomes. Patients with missing functional data associated with short/incomplete stays (n=623) were excluded from analysis of functional outcomes category only. Standard descriptive analysis techniques were employed for comparing categorical and continuous variables between groups.

Results

Statistically significant differences were noted between the COVID-19 group and non-COVID groups for race (26.0% vs 19.7% non-minority, P<.001), Case Mix Index (1.49 vs 1.46, P<.001), Center for Medicare and Medicaid Services 60% rule qualification (79.0% vs 73.4%, P<.001), time to onset (24.3 vs 18.0 days, P<.001), length of stay (14.2 vs 12.9 days, P<.001), and discharge disposition (to community: 75.3% vs 81%, P<.001; to acute care facility: 15.6% vs 10.8%, P<.001). The COVID-19 group had higher frequency of respiratory and cardiovascular disease, diabetes, encephalopathy, morbid obesity, and critical illness neuropathy and myopathy. Clinically insignificant differences were noted for age, sex, depression, and cognitive assessment. Ability to participate and functional outcomes were comparable between the groups.

Conclusion

There are significant differences between the COVID-19 and non-COVID group in some sociodemographic, medical complexity, process and clinical outcomes, but not in functional outcomes. The ability to participate in the IRF-required intensity of therapy services along with attainment of comparable levels of functional outcomes supports the benefit of IRFs for persons with COVID-19.

Assessment of Functional Capacity in Patients with Nondialysis-Dependent Chronic Kidney Disease with the Glittre Activities of Daily Living Test

This study evaluated the functional capacity measured by the Glittre-ADL test (TGlittre) in patients with nondialysis-dependent chronic kidney disease (NDD-CKD) and analyzed the test's associations with muscle strength, physical activity level (PAL), and quality of life. Methods: Thirty patients with NDD-CKD underwent the following evaluations: the TGlittre; the International Physical Activity Questionnaire (IPAQ); the Short Form-36 (SF-36); and handgrip strength (HGS). The absolute value and percentage of the theoretical TGlittre time were 4.3 (3.3-5.2) min and 143.3 ± 32.7%, respectively. The main difficulties in completing the TGlittre were squatting to perform shelving and manual tasks, which were reported by 20% and 16.7% of participants, respectively. The TGlittre time correlated negatively with HGS (r = -0.513, p = 0.003). The TGlittre time was significantly different between the PALs considered "sedentary", "irregularly active", and "active" (p = 0.038). There were no significant correlations between TGlittre time and the SF-36 dimensions. Patients with NDD-CKD had a reduced functional capacity to exercise with difficulties performing squatting and manual tasks. There was a relationship between TGlittre time and both HGS and PAL. Thus, the incorporation of the TGlittre in the evaluation of these patients may improve the risk stratification and individualization of therapeutic care.

Uremic Myopathy and Mitochondrial Dysfunction in Kidney Disease

Alterations in muscle structure and function in chronic kidney disease (CKD) patients are associated with poor outcomes. As key organelles in muscle cell homeostasis, mitochondrial metabolism has been studied in the context of muscle dysfunction in CKD. We conducted a study to determine the contribution of oxidative metabolism, glycolysis and fatty acid oxidation to the muscle metabolism in CKD. Mice developed CKD by exposure to adenine in the diet. Muscle of CKD mice showed significant weight loss compared to non-CKD mice, but only extensor digitorum longus (EDL) muscle showed a decreased number of fibers. There was no difference in the proportion of the various muscle fibers in CKD and non-CKD mice. Muscle of CKD mice had decreased expression of proteins associated with oxidative phosphorylation but increased expression of enzymes and transporters associated with glycolysis. In cell culture, myotubes exposed to uremic serum demonstrated decreased oxygen consumption rates (OCR) when glucose was used as substrate, conserved OCR when fatty acids were used and increased lactate production. In conclusion, mice with adenine-induced CKD developed sarcopenia and with increased glycolytic metabolism but without gross changes in fiber structure. In vitro models of uremic myopathy suggest fatty acid utilization is preserved compared to decreased glucose utilization.

Influences of renal insufficiency and ischemia on mitochondrial bioenergetics and limb dysfunction in a novel murine iliac arteriovenous fistula model

Objective

Hand disability after hemodialysis access surgery has been common yet has remained poorly understood. Arteriovenous fistula (AVF) hemodynamic perturbations have not reliably correlated with the observed measures of hand function. Chronic kidney disease (CKD) is known to precipitate myopathy; however, the interactive influences of renal insufficiency and ischemia on limb outcomes have remained unknown. We hypothesized that CKD would contribute to access-related hand dysfunction via altered mitochondrial bioenergetics. Using a novel murine AVF model, we sought to characterize the skeletal muscle outcomes in mice with and without renal insufficiency.

Methods

Male, 8-week-old C57BL/6J mice were fed either an adenine-supplemented diet to induce renal insufficiency (CKD) or a casein-based control chow (CON). After 2 weeks of dietary intervention, the mice were randomly assigned to undergo iliac AVF surgery (n = 12/group) or a sham operation (n = 5/group). Measurements of aortoiliac hemodynamics, hindlimb perfusion, and hindlimb motor function were collected for 2 weeks. The mice were sacrificed on postoperative day 14 to assess skeletal muscle histopathologic features and mitochondrial function. To assess the late outcome trends, 20 additional mice had undergone CKD induction and sham (n = 5) or AVF (n = 15) surgery and followed up for 6 weeks postoperatively before sacrifice.

Results

The adenine-fed mice had had a significantly reduced glomerular filtration rate and elevated blood urea nitrogen, confirming the presence of CKD. The sham mice had a 100% survival rate and AVF cohorts an 82.1% survival rate with an 84.4% AVF patency rate. The aorta and inferior vena cava velocity measurements and the vessel diameter had increased after AVF creation (P < .0001 vs sham). The AVF groups had had a 78.4% deficit in paw perfusion compared with the contralateral limb after surgery (P < .0001 vs sham). Mitochondrial function was influenced by the presence of CKD. The respiratory capacity of the CKD-sham mice (8443 ± 1509 pmol/s/mg at maximal energy demand) was impaired compared with that of the CON-sham mice (12,870 ± 1203 pmol/s/mg; P = .0001). However, this difference was muted after AVF creation (CKD-AVF, 4478 ± 3685 pmol/s/mg; CON-AVF, 5407 ± 3582 pmol/s/mg; P = .198). The AVF cohorts had had impairments in grip strength (vs sham; P < .0001) and gait (vs sham; P = .012). However, the presence of CKD did not significantly alter the measurements of gross muscle function. The paw perfusion deficits had persisted 6 weeks postoperatively for the AVF mice (P < .0001 vs sham); however, the myopathy had resolved (grip strength, P = .092 vs sham; mitochondrial respiration, P = .108 vs sham).

Conclusions

CKD and AVF-induced distal limb ischemia both impaired skeletal muscle mitochondrial function. Renal insufficiency was associated with a baseline myopathy that was exacerbated by the acute ischemic injury resulting from AVF creation. However, ischemia was the primary driver of the observed phenotype of gross motor impairment. This model reliably reproduced the local and systemic influences that contribute to access-related hand dysfunction and provides a platform for further mechanistic and therapeutic investigation.

Clinical and neurophysiological characterization of early neuromuscular involvement in children and adolescents with nephropathic cystinosis

BACKGROUND

Nephropathic cystinosis is a rare autosomal recessive lysosomal storage disorder characterized by kidney and extra-renal complications due to the accumulation of cystine crystals in various tissues and organs. Herein, we describe the early neuromuscular complications in a cohort of pediatric nephropathic cystinosis patients.

METHODS

We prospectively evaluated the clinical, biochemical, and neurophysiological data of 15 cystinosis patients. Neurophysiological evaluation was performed to confirm or exclude presence of neuropathy and/or myopathy.

RESULTS

Patients' age ranged between 20 and 216 months at time of examination. Nine patients were males. Three patients had early abnormal neurophysiological features consistent with neuromuscular involvement (clinically asymptomatic proximal myopathy with a patchy distribution in one patient and isolated asymptomatic sensory nerve conduction changes in two patients). A fourth patient had mixed abnormal motor and sensory axonal neuropathic changes associated with overt clinical features (predominantly motor symptoms). Patients with abnormal neuromuscular features were significantly older in age than the unaffected group (P = 0.005) and had a diagnosis of cystinosis with subsequent cysteamine therapy at a significantly older age than the unaffected group (P = 0.027 and 0.001, respectively).

CONCLUSIONS

We expanded the recognized phenotypes of cystinosis neuromuscular complications with early proximal skeletal myopathy and symptomatic motor and sensory axonal neuropathy. Early asymptomatic neuromuscular complications could develop in pediatric patients and would require neurophysiological studies for early detection prior to development of overt clinical manifestations. Prompt diagnosis and timely initiation of cysteamine therapy with recommended dose can delay the development of neuromuscular complications. A higher resolution version of the Graphical abstract is available as Supplementary information.

Skeletal muscle energetics in patients with moderate to advanced kidney disease

Sarcopenia, defined as decrease in muscle function and mass, is common in patients with moderate to advanced chronic kidney disease (CKD) and is associated with poor clinical outcomes. Muscle mitochondrial dysfunction is proposed as one of the mechanisms underlying sarcopenia. Patients with moderate to advanced CKD have decreased muscle mitochondrial content and oxidative capacity along with suppressed activity of various mitochondrial enzymes such as mitochondrial electron transport chain complexes and pyruvate dehydrogenase, leading to impaired energy production. Other mitochondrial abnormalities found in this population include defective beta-oxidation of fatty acids and mitochondrial DNA mutations. These changes are noticeable from the early stages of CKD and correlate with severity of the disease. Damage induced by uremic toxins, oxidative stress, and systemic inflammation has been implicated in the development of mitochondrial dysfunction in CKD patients. Given that mitochondrial function is an important determinant of physical activity and performance, its modulation is a potential therapeutic target for sarcopenia in patients with kidney disease. Coenzyme Q, nicotinamide, and cardiolipin-targeted peptides have been tested as therapeutic interventions in early studies. Aerobic exercise, a well-established strategy to improve muscle function and mass in healthy adults, is not as effective in patients with advanced kidney disease. This might be due to reduced expression or impaired activation of peroxisome proliferator-activated receptor-gamma coactivator 1α, the master regulator of mitochondrial biogenesis. Further studies are needed to broaden our understanding of the pathogenesis of mitochondrial dysfunction and to develop mitochondrial-targeted therapies for prevention and treatment of sarcopenia in patients with CKD.

Diabetic kidney disease progression is associated with decreased lower-limb muscle mass and increased visceral fat area in T2DM patients

AIM

This study aimed to explore the relationship between lower-limb muscle mass/visceral fat area and diabetic kidney disease (DKD) progression in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 879 participants with T2DM were divided into 4 groups according to the prognosis of CKD classification from Kidney Disease: Improving Global Outcomes (KDIGO). Rectus femoris cross-sectional area (RFCSA) was measured through ultrasound, and visceral fat area (VFA) was evaluated with bioelectric impedance analysis (BIA).

RESULTS

T2DM patients with high to very high prognostic risk of DKD showed a reduced RFCSA (male P < 0.001; female P < 0.05), and an enlarged VFA (male P < 0.05; female P < 0.05). The prognostic risk of DKD was negatively correlated with RFCSA (P < 0.05), but positively correlated with VFA (P < 0.05). Receiver-operating characteristic analysis revealed that the cutoff points of T2DM duration combined with RFCSA and VFA were as follows: (male: 7 years, 6.60 cm2, and 111 cm2; AUC = 0.82; 95% CI: 0.78-0.88; sensitivity, 78.0%; specificity, 68.6%, P < 0.001) (female: 9 years, 5.05 cm2, and 91 cm2; AUC = 0.73; 95% CI: 0.66-0.81; sensitivity, 73.9%; specificity, 63.3%, P < 0.001).

CONCLUSION

A significant association was demonstrated between reduced RFCSA/increased VFA and high- to very high-prognostic risk of DKD. T2DM duration, RFCSA, and VFA may be valuable markers of DKD progression in patients with T2DM.

CLINICAL TRIAL REGISTRATION

http://www.chictr.org.cn, identifier ChiCTR2100042214.

Clinical Assessment of Dialysis Recovery Time and Symptom Burden: Impact of Switching Hemodialysis Therapy Mode

INTRODUCTION

Most people on hemodialysis (HD) report a high symptom burden. Fatigue and lack of energy are prominent, interfering with daily life and associated with poor outcome. Prolonged recovery time after each of the thrice weekly dialysis treatments is common. The impact of HD therapies, like expanded hemodialysis (HDx), on patient reported recovery time and symptom burden is unclear.

METHODS

A dialysis unit decided to perform regular assessments of patient-reported symptom burden, using the POS-S Renal Symptom questionnaire and the "Recovery time from last dialysis session" question as part of routine patient focused care. At a similar time, a clinical evidence-based decision was taken to switch the in-center dialysis cohort from regular high-flux dialysis membrane to medium cut-off (MCO) membrane, introducing HDx therapy.

RESULTS

Quarterly assessment of patient-reported symptom burden was well accepted. A sustained clinically relevant reduction in post-dialysis recovery time was observed following the therapy switch. In patients providing data up to 12 months (N = 58), median recovery time decreased from 210 min (IQR 7.5-600) to 60 min (0-210; p = 0.002) and 105 min (0-180; p = 0.001) at 6 and 12 months, respectively. Thirty-six percent of individuals reported a recovery time longer than 360 minutes at the initial assessment, which decreased to 9% at 12 months. The POS-S Renal total symptom score showed a decrease at 6 months but no difference from baseline at 12 months. The "fatigue/lack of energy" symptom showed a sustained improvement; the percentage of participants scoring its impact as "severe" or "overwhelming" decreased from 28% at baseline to 16% at 12 months. Changes in other symptoms were more variable.

CONCLUSION

Regular assessment of patient reported symptoms is feasible in routine dialysis practice and can help in evaluating the impact of clinical interventions. Observations suggest that HDx therapy may reduce post-dialysis recovery time and improve perceived fatigue level.

Empagliflozin restores chronic kidney disease-induced impairment of endothelial regulation of cardiomyocyte relaxation and contraction

Chronic kidney disease (CKD) promotes development of cardiac abnormalities and is highly prevalent in patients with heart failure, particularly in those with preserved ejection fraction. CKD is associated with endothelial dysfunction, however, whether CKD can induce impairment of endothelium-to-cardiomyocyte crosstalk leading to impairment of cardiomyocyte function is not known. The sodium-glucose co-transporter 2 inhibitor, empagliflozin, reduced cardiovascular events in diabetic patients with or without CKD, suggesting its potential as a new treatment for heart failure with preserved ejection fraction. We hypothesized that uremic serum from patients with CKD would impair endothelial control of cardiomyocyte relaxation and contraction, and that empagliflozin would protect against this effect. Using a co-culture system of human cardiac microvascular endothelial cells with adult rat ventricular cardiomyocytes to measure cardiomyocyte relaxation and contraction, we showed that serum from patients with CKD impaired endothelial enhancement of cardiomyocyte function which was rescued by empagliflozin. Exposure to uremic serum reduced human cardiac microvascular endothelial cell nitric oxide bioavailability, and increased mitochondrial reactive oxygen species and 3-nitrotyrosine levels, indicating nitric oxide scavenging by reactive oxygen species. Empagliflozin attenuated uremic serum-induced generation of endothelial mitochondrial reactive oxygen species, leading to restoration of nitric oxide production and endothelium-mediated enhancement of nitric oxide levels in cardiomyocytes, an effect largely independent of sodium-hydrogen exchanger-1. Thus, empagliflozin restores the beneficial effect of cardiac microvascular endothelial cells on cardiomyocyte function by reducing mitochondrial oxidative damage, leading to reduced reactive oxygen species accumulation and increased endothelial nitric oxide bioavailability.

Neurophysiological and Neuroradiological Changes in Children With Chronic Kidney Disease

Background: Patients with chronic kidney disease (CKD) on maintenance hemodialysis frequently present with neurological complications. These complications include peripheral neuropathy, encephalopathy, and stroke. Objectives: To detect the prevalence of neurological manifestations and complications in children with CKD through neurophysiological and neuro-radiological findings. Methods: The study included 50 patients with CKD admitted to a pediatric nephrology unit. Their history and complete physical and neurological examination findings had been recorded. All patients underwent nerve conduction, electromyography, electroencephalography, and magnetic resonance imaging of the brain. Results: Fifty children of both sexes (23 males and 27 females) with a mean age of (12.08 ± 3.46 year) were studied. Eleven (22%) patients with CKD developed polyneuropathy, mostly of an axonal polyneuropathy pattern, while 39 (78%) of them showed normal electrophysiological studies. No myopathy was detected. Abnormal electroencephalography findings were detected in 18% of patients, mostly generalized and focal (temporal, occipital, and frontal) epileptogenic activity. Abnormal MRI brain findings were detected in 16% of patients, mostly of encephalomalacia. Conclusion: Uremic neuropathy was highly prevalent in children with CKD on maintenance hemodialysis. They developed polyneuropathy, mostly of an axonal polyneuropathy pattern. EEG is a useful method for early recognition of subclinical uremic encephalopathy and/or epileptogenic activity. Early demonstration and management of uremic neurological conditions may decrease the physical disability of CKD patients.

Effectiveness of inspiratory muscle training on respiratory fitness and breathlessness in chronic renal failure: A randomized control trial

BACKGROUND

People with chronic renal failure (CRF) show decreased respiratory fitness and poor quality of life (QOL). Exercise during hemodialysis has been suggested to improve the cardio-respiratory fitness. However, results of effects of respiratory muscle (RM) training on respiratory fitness and QOL are inconsistent. In addition, very few studies explored the association between inspiratory muscle (IM) training and sensation of breathlessness.

OBJECTIVES

To examine the effects of IM training in hemodialysis patients on respiratory fitness QOL and breathlessness.

METHOD

A randomized control trial with 50 CRF, who underwent hemodialysis (25 individuals in each group; IM training and sham group) was designed. Pulmonary function, RM strength, QOL (measured by Kidney Disease Quality of Life-36), and sensation of breathlessness were measured before and after an 8-week intervention.

RESULTS

Compared to the sham group, the IM strength increased in the intervention group after an 8-week program (Δ25.92 ± 8.73 cmH₂ O, p = 0.005). Significantly increased IM and forced vital capacity values in training groups was observed after an 8-week intervention (Δ12.44 ± 3.07 cmH₂ O and Δ0.097 ± 0.046 L, respectively), but not the sham group. Neither, the training group, nor the sham group were significantly different in the QOL. However, feeling of shortness of breath improved after the training program among inspiratory muscle training group, but not the sham group.

CONCLUSION

IM training during hemodialysis could lead to an improvement of respiratory fitness and reduce breathlessness in people with CRF who are receiving hemodialysis. However, QOL was not different after the training program. The study suggests that after 8-week intervention program, IM training (loading exercise) could improve IM strength, pulmonary function without any complications during the intervention program within 1-2 h.

Redox modulation of muscle mass and function

Muscle mass and strength are very important for exercise performance. Training-induced musculoskeletal injuries usually require periods of complete immobilization to prevent any muscle contraction of the affected muscle groups. Disuse muscle wasting will likely affect every sport practitioner in his or her lifetime. Even short periods of disuse results in significant declines in muscle size, fiber cross sectional area, and strength. To understand the molecular signaling pathways involved in disuse muscle atrophy is of the utmost importance to develop more effective countermeasures in sport science research.

We have divided our review in four different sections. In the first one we discuss the molecular mechanisms involved in muscle atrophy including the main protein synthesis and protein breakdown signaling pathways. In the second section of the review we deal with the main cellular, animal, and human atrophy models. The sources of reactive oxygen species in disuse muscle atrophy and the mechanism through which they regulate protein synthesis and proteolysis are reviewed in the third section of this review. The last section is devoted to the potential interventions to prevent muscle disuse atrophy with especial consideration to studies on which the levels of endogenous antioxidants enzymes or dietary antioxidants have been tested.

Fatigue, anxiety, depression and quality of life in kidney transplant recipients, haemodialysis patients, patients with a haematological malignancy and healthy controls

BACKGROUND

The impact of haemodialysis (HD) and kidney transplantation on quality of life (QoL) is often underestimated due to a lack of comparative studies with other patient groups.

METHODS

We conducted a cross-sectional cohort study in 168 patients including HD patients, kidney transplant recipients (KTR), patients with a haematological malignancy either receiving chemotherapy or in remission and healthy controls. All participants completed the 36-item short form survey of health-related quality of life, the Checklist Individual Strength and the Hospital Anxiety and Depression Scale questionnaire.

RESULTS

HD patients and haematological patients undergoing chemotherapy were more frequently severely fatigued (53.3% and 50% of cases) compared with KTR (33.3%), haematological patients in remission (23.3%) and healthy controls (12.1%, P < 0.001). There were no significant differences in anxiety rates. HD patients and haematological patients undergoing chemotherapy were most likely to be depressed (33.3% and 25%), compared with 16.7% of KTR, 20% of haematological patients in remission and 8.6% of healthy controls (P = 0.066). KTR reported the largest positive health change (+27%, P < 0.001), but still had a lower overall QoL than healthy controls, comparable to haematological patients in remission. HD and chemotherapy patients reported the lowest QoL scores.

CONCLUSIONS

Fatigue and depression are common in HD patients, resulting in a low QoL, comparable to haematological patients receiving chemotherapy. KTR do better, with scores similar to patients with a haematological malignancy in remission, but still have a lower QoL than healthy controls.

Mitochondrial Activity and Skeletal Muscle Insulin Resistance in Kidney Disease

Insulin resistance is a key feature of the metabolic syndrome, a cluster of medical disorders that together increase the chance of developing type 2 diabetes and cardiovascular disease. In turn, type 2 diabetes may cause complications such as diabetic kidney disease (DKD). Obesity is a major risk factor for developing systemic insulin resistance, and skeletal muscle is the first tissue in susceptible individuals to lose its insulin responsiveness. Interestingly, lean individuals are not immune to insulin resistance either. Non-obese, non-diabetic subjects with chronic kidney disease (CKD), for example, exhibit insulin resistance at the very onset of CKD, even before clinical symptoms of renal failure are clear. This uraemic insulin resistance contributes to the muscle weakness and muscle wasting that many CKD patients face, especially during the later stages of the disease. Bioenergetic failure has been associated with the loss of skeletal muscle insulin sensitivity in obesity and uraemia, as well as in the development of kidney disease and its sarcopenic complications. In this mini review, we evaluate how mitochondrial activity of different renal cell types changes during DKD progression, and discuss the controversial role of oxidative stress and mitochondrial reactive oxygen species in DKD. We also compare the involvement of skeletal muscle mitochondria in uraemic and obesity-related muscle insulin resistance.

Are dialysis patients too frail to exercise?

Clinical manifestations of functional and morphological muscular abnormalities in dialysis patients are muscle weakness and low exercise capacity, possibly leading to a sedentary life style with low physical activity. Low cardiorespiratory fitness and muscle atrophy and weakness contribute to the development of frailty and affect patients' ability to physically navigate their environment. While many dialysis patients may appear too frail to participate in moderate-to-vigorous aerobic exercise training, those who can complete such programs appear to derive substantial benefit. Less vigorous aerobic exercise, resistance training, and alternative forms of exercise can also be beneficial. Most patients on dialysis are not too frail to perform resistance exercise of adequate intensity to achieve increases in muscle size and strength, therefore, frailty should not be considered a contraindication to exercise.

Evidence of Blood and Muscle Redox Status Imbalance in Experimentally Induced Renal Insufficiency in a Rabbit Model

Chronic kidney disease (CKD) is accompanied by a disturbed redox homeostasis, especially in end-stage patients, which is associated with pathological complications such as anemia, atherosclerosis, and muscle atrophy. However, limited evidence exists about redox disturbances before the end stage of CKD. Moreover, the available redox literature has not yet provided clear associations between circulating and tissue-specific (muscle) oxidative stress levels. The aim of the study was to evaluate commonly used redox status indices in the blood and in two different types of skeletal muscle (psoas, soleus) in the predialysis stages of CKD, using an animal model of renal insufficiency, and to investigate whether blood redox status indices could be reflecting the skeletal muscle redox status. Indices evaluated included reduced glutathione (GSH), oxidized glutathione (GSSG), glutathione reductase (GR), catalase (CAT), total antioxidant capacity (TAC), protein carbonyls (PC), and thiobarbituric acid reactive substances (TBARS). Results showed that blood GSH was higher in the uremic group compared to the control (17.50 ± 1.73 vs. 12.43 ± 1.01, p = 0.033). In both muscle types, PC levels were higher in the uremic group compared to the control (psoas: 1.086 ± 0.294 vs. 0.596 ± 0.372, soleus: 2.52 ± 0.29 vs. 0.929 ± 0.41, p < 0.05). The soleus had higher levels of TBARS, PC, GSH, CAT, and GR and lower TAC compared to the psoas in both groups. No significant correlations in redox status indices between the blood and skeletal muscles were found. However, in the uremic group, significant correlations between the psoas and soleus muscles in PC, GSSG, and CAT levels emerged, not present in the control. Even in the early stages of CKD, a disturbance in redox homeostasis was observed, which seemed to be muscle type-specific, while blood levels of redox indices did not seem to reflect the intramuscular condition. The above results highlight the need for further research in order to identify the key mechanisms driving the onset and progression of oxidative stress and its detrimental effects on CKD patients.

Indoxyl sulfate induces myotube atrophy by ROS-ERK and JNK-MAFbx cascades

Accumulations of uremic toxins has been widely recognized as the major trigger of skeletal muscle loss in chronic kidney disease (CKD), which is defined as uremic sarcopenia. Current study was aimed to examine the effects of representative uremic toxin, indoxyl sulfate (IS), on C2C12 myotubes. The incubation of IS (from 0.1 mM to 1.2 mM) exerted the reduction in myotube diameter without cell survival impairment. Elevated oxidative stress and mitogen-activated protein kinase (MAPKs) phosphorylation were observed after IS stimulation for 1 and 24 h. After N-acetylcysteine (NAC) treatment as antioxidants, the recovery in IS-induced decrease myotube diameter and ERK phosphorylation was observed. This findings were implicit the transduction of p-ERK in IS-induced ROS toxicity. Moreover, the increase of LC3β was found closely with IS treatment in C2C12 myotubes. The reverse effect of NAC on LC3β expression revealed the ROS-responsibility in autophagy regulation of CKD myopathy. The evaluation of IS-treated proteasome system showed increased phospho-myosin light chain, along with the upregulation of muscle atrophy F-box (MAFbx) mRNA and protein. This alteration in MAFbx was also identified in nephrectomy-induced CKD model. Besides, the inhibition of p-JNK was capable to attenuate IS-induced upward change in MAFbx protein expression. These findings indicated that IS-mediated myotube atrophy may manipulate through ROS-ERK axis and JNK-MAFbx regulation in C2C12 cells.

Mechanisms and Modulation of Oxidative/Nitrative Stress in Type 4 Cardio-Renal Syndrome and Renal Sarcopenia

Chronic kidney disease (CKD) is a public health problem and a recognized risk factor for cardiovascular diseases (CVD). CKD could amplify the progression of chronic heart failure leading to the development of type 4 cardio-renal syndrome (T4CRS). The severity and persistence of heart failure are strongly associated with mortality risk in T4CRS. CKD is also a catabolic state leading to renal sarcopenia which is characterized by the loss of skeletal muscle strength and physical function. Renal sarcopenia also promotes the development of CVD and increases the mortality in CKD patients. In turn, heart failure developed in T4CRS could result in chronic muscle hypoperfusion and metabolic disturbances leading to or aggravating the renal sarcopenia. The interplay of multiple factors (e.g., comorbidities, over-activated renin-angiotensin-aldosterone system [RAAS], sympathetic nervous system [SNS], oxidative/nitrative stress, inflammation, etc.) may result in the progression of T4CRS and renal sarcopenia. Among these factors, oxidative/nitrative stress plays a crucial role in the complex pathomechanism and interrelationship between T4CRS and renal sarcopenia. In the heart and skeletal muscle, mitochondria, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, uncoupled nitric oxide synthase (NOS) and xanthine oxidase are major ROS sources producing superoxide anion (O2^·−) and/or hydrogen peroxide (H₂O₂). O2^·− reacts with nitric oxide (NO) forming peroxynitrite (ONOO⁻) which is a highly reactive nitrogen species (RNS). High levels of ROS/RNS cause lipid peroxidation, DNA damage, interacts with both DNA repair enzymes and transcription factors, leads to the oxidation/nitration of key proteins involved in contractility, calcium handling, metabolism, antioxidant defense mechanisms, etc. It also activates the inflammatory response, stress signals inducing cardiac hypertrophy, fibrosis, or cell death via different mechanisms (e.g., apoptosis, necrosis) and dysregulates autophagy. Therefore, the thorough understanding of the mechanisms which lead to perturbations in oxidative/nitrative metabolism and its relationship with pro-inflammatory, hypertrophic, fibrotic, cell death and other pathways would help to develop strategies to counteract systemic and tissue oxidative/nitrative stress in T4CRS and renal sarcopenia. In this review, we also focus on the effects of some well-known and novel pharmaceuticals, nutraceuticals, and physical exercise on cardiac and skeletal muscle oxidative/nitrative stress in T4CRS and renal sarcopenia.

Evidence of functional deficits at the single muscle fiber level in experimentally-induced renal insufficiency

Chronic kidney disease patients present with metabolic and functional muscle abnormalities, called uremic myopathy, whose mechanisms have not yet been fully elucidated. We investigated whether chronic renal insufficiency (CRI) affects skeletal muscle contractile properties at the cellular level. CRI was induced surgically in New Zealand rabbits (UREM), with sham-operation for controls (CON), and samples were collected at 3 months post-surgery, following euthanasia. All protocols had University Ethics approval following national and European guidelines. Sample treatments and evaluations were blinded. Maximal isometric force was assessed in 382 permeabilized psoas fibers (CON, n = 142, UREM, n = 240) initially at pH7, 10 °C ('standard' conditions), in subsets of fibers in acidic conditions (pH6.2, 10 °C) but also at near physiological temperature (pH7, 30 °C and pH6.2, 30 °C). CRI resulted in significant smaller average cross sectional areas (CSAs) by ∼11% for UREM muscle fibers (vs CON, P < 0.01). At standard conditions, UREM fibers produced lower absolute and specific forces (i.e. normalized force per fiber CSA) (vs CON, P < 0.01); force increased in 30 °C for both groups (P < 0.01), but the disparity between UREM and CON remained significant. Acidosis significantly reduced force (vs pH7, 10 °C P < 0.01), similarly in both groups (in UREM by -48% and in CON by -43%, P > 0.05). For the first time, we give evidence that CRI can induce significant impairments in single psoas muscle fibers force generation, only partly explained by fiber atrophy, thus affecting muscle mechanics at the cellular level.

Chronic kidney disease induces a systemic microangiopathy, tissue hypoxia and dysfunctional angiogenesis

Chronic kidney disease (CKD) is associated with excessive mortality from cardiovascular disease (CVD). Endothelial dysfunction, an early manifestation of CVD, is consistently observed in CKD patients and might be linked to structural defects of the microcirculation including microvascular rarefaction. However, patterns of microvascular rarefaction in CKD and their relation to functional deficits in perfusion and oxygen delivery are currently unknown. In this in-vivo microscopy study of the cremaster muscle microcirculation in BALB/c mice with moderate to severe uremia, we show in two experimental models (adenine feeding or subtotal nephrectomy), that serum urea levels associate incrementally with a distinct microangiopathy. Structural changes were characterized by a heterogeneous pattern of focal microvascular rarefaction with loss of coherent microvascular networks resulting in large avascular areas. Corresponding microvascular dysfunction was evident by significantly diminished blood flow velocity, vascular tone, and oxygen uptake. Microvascular rarefaction in the cremaster muscle paralleled rarefaction in the myocardium, which was accompanied by a decrease in transcription levels not only of the transcriptional regulator HIF-1α, but also of its target genes Angpt-2, TIE-1 and TIE-2, Flkt-1 and MMP-9, indicating an impaired hypoxia-driven angiogenesis. Thus, experimental uremia in mice associates with systemic microvascular disease with rarefaction, tissue hypoxia and dysfunctional angiogenesis.

Whole body vibration improves maximum voluntary isometric contraction of knee extensors in patients with chronic kidney disease: A randomized controlled trial

BACKGROUND

Whole body vibration (WBV) training improves maximum voluntary isometric contraction (MVIC) of knee extensors, postural balance, functional capacity, and quality of life (QOL) in several diseases. The objective was to assess the efficacy of WBV training in patients with chronic kidney disease (CKD) on hemodialysis (HD) in the interdialytic period.

METHOD

A randomized, controlled trial study with concealed allocation, intention-to-treat analysis, and triple blinding. Sixteen patients with CKD of both genders aged over 40 years were allocated in two groups, the WBV group or the sham group, training 2 times a week for 12 weeks. The primary outcome was knee extensor muscle strength, and the secondary outcomes were quadriceps thickness, distance walked, balance, and QOL.

RESULTS

The WBV group improved MVIC of knee extensors with a difference between groups in improvement of 117.29 N (95% CI, 32.25-202.24) at the end of training. The other outcomes were not different between groups. Practical applications: The WBV program has shown to be effective and may be able to help in prescribing the appropriate training program for CKD.

CONCLUSION

WBV training improves MVIC of knee extensors in patients with CKD on HD in the interdialytic period. WBV training could be considered in the management of patients with CKD.

Chronic kidney disease, kidney transplantation and oxidative stress: a new look to successful kidney transplantation

Oxidative stress plays a key role in the pathophysiological process of uremia and its complications, particularly in cardiovascular disease. The level of oxidative stress markers is known to increase as chronic kidney disease progresses and correlates significantly with the level of renal function. Hemodialysis and peritoneal dialysis are major modes of renal replacement therapy for end-stage renal disease patients, but unfortunately they are also accompanied by increased oxidative stress. Successful kidney transplantation, however, results in near normalization of the antioxidant status and lipid metabolism by eliminating free radicals despite the surge of oxidative stress caused by the surgical procedure and ischemic injury to the organ during the operation. This success is associated with both improved renal function, reduced cardiovascular complications and overall improved morbidity and mortality. Measuring oxidative stress markers such as malondialdehyde is promising in predicting allograft survival and delayed graft function.

Role of Oxidative Stress as Key Regulator of Muscle Wasting during Cachexia

Skeletal muscle atrophy is a pathological condition mainly characterized by a loss of muscular mass and the contractile capacity of the skeletal muscle as a consequence of muscular weakness and decreased force generation. Cachexia is defined as a pathological condition secondary to illness characterized by the progressive loss of muscle mass with or without loss of fat mass and with concomitant diminution of muscle strength. The molecular mechanisms involved in cachexia include oxidative stress, protein synthesis/degradation imbalance, autophagy deregulation, increased myonuclear apoptosis, and mitochondrial dysfunction. Oxidative stress is one of the most common mechanisms of cachexia caused by different factors. It results in increased ROS levels, increased oxidation-dependent protein modification, and decreased antioxidant system functions. In this review, we will describe the importance of oxidative stress in skeletal muscles, its sources, and how it can regulate protein synthesis/degradation imbalance, autophagy deregulation, increased myonuclear apoptosis, and mitochondrial dysfunction involved in cachexia.

The spectrum of hand dysfunction after hemodialysis fistula placement

Introduction

Contemporary dogma has classically attributed hand dysfunction following hemodialysis arteriovenous fistula (AVF) placement to regional ischemia. We hypothesize that hemodynamic perturbations alone do not entirely explain the postoperative changes in hand function and, furthermore, that various elements of hand function are differentially affected following surgery.

Methods

Bilateral wrist and digital pressures and upper extremity nerve conduction tests were recorded preoperatively and at 6 weeks and 6 months following upper extremity AVF construction in 46 patients. Concurrently, biomechanical tests were administered to evaluate multiple limb functional domains, including grip strength, dexterity, sensation, and perception of hand function.

Results

Mean participant age was 59 ± 14 years (75% male), and 48% were on hemodialysis at the time of access placement. Of the participants, 69% had a brachial-based AVF, and the remainder had radial-based accesses. Six weeks following AVF placement, a significant decrease in access-side digital pressures was observed, with only partial recovery at 6 months (P < 0.0001). Grip strength was significantly worse in the access-side limb (P = 0.0003), and the Disability of Arm, Shoulder and Hand (DASH) questionnaire score substantially worsened postoperatively (P = 0.06). Digital sensation and limb dexterity did not differ between limb sides (P > 0.1) or change significantly over time (P > 0.1). Principal component analyses demonstrated that nerve conduction parameters tended to track the biomechanical parameters, yet both were relatively independent of the hemodynamic parameters.

Discussion

Our findings suggest that ischemia alone does not completely explain access-related hand dysfunction and that future study is needed to elucidate alternative mechanisms.

The Association of Daily Activity Levels and Estimated Kidney Function in Men and Women With Predialysis Chronic Kidney Disease

Introduction

Chronic kidney disease (CKD) is often accompanied by complications including poor physical activity level. However, only a few studies have objectively characterized physical activity levels in predialysis CKD. Our study sought to measure daily activity levels by accelerometry in individuals with CKD (stages III−V) and to determine the association between daily activity and kidney function.

Methods

We determined kidney function by means of the estimated glomerular filtration rate (eGFR) using the Modification of Diet and Renal Disease (MDRD) equation. Participants wore an accelerometer for 7 consecutive days, and we measured multiple physical activity outcomes including total daily activity, sedentary, light, and moderate−vigorous activity. Average durations and intensity of activity were determined according to stage of CKD. The association between kidney function and activity level was determined by regression analysis.

Results

We analyzed data from 110 individuals (60% men and 40% women) with stages III to V CKD. The mean age of our participants was 64 years, mean body mass index was 27.5 kg/m², and mean eGFR was 23.7 ± 1.2 ml/min/1.73 m². Our participants were primarily sedentary (mean duration of inactivity = 1152 ± 100 minutes per day; 79% of day). Light activity was performed 280 ± 99 minutes per day, and individuals participated in only 6 ± 9 minutes per day of moderate−vigorous activity. The eGFR did not predict physical activity level (P > 0.05 for all).

Discussion

Individuals with stages III to V CKD are sedentary, and do not meet the national recommendations of 150 minutes of moderate−vigorous activity per week. Further study is required to determine whether interventions to increase activity levels in patients with CKD are associated with improved health outcomes.

Neurological complications in chronic kidney disease

Patients with chronic kidney disease (CKD) are frequently afflicted with neurological complications. These complications can potentially affect both the central and peripheral nervous systems. Common neurological complications in CKD include stroke, cognitive dysfunction, encephalopathy, peripheral and autonomic neuropathies. These conditions have significant impact not only on patient morbidity but also on mortality risk through a variety of mechanisms. Understanding the pathophysiological mechanisms of these conditions can provide insights into effective management strategies for neurological complications. This review describes clinical management of neurological complications in CKD with reference to the contributing physiological and pathological derangements. Stroke, cognitive dysfunction and dementia share several pathological mechanisms that may contribute to vascular impairment and neurodegeneration. Cognitive dysfunction and dementia may be differentiated from encephalopathy which has similar contributing factors but presents in an acute and rapidly progressive manner and may be accompanied by tremor and asterixis. Recent evidence suggests that dietary potassium restriction may be a useful preventative measure for peripheral neuropathy. Management of painful neuropathic symptoms can be achieved by pharmacological means with careful dosing and side effect considerations for reduced renal function. Patients with autonomic neuropathy may respond to sildenafil for impotence. Neurological complications often become clinically apparent at end-stage disease, however early detection and management of these conditions in mild CKD may reduce their impact at later stages.