Resistance training increases muscle mitochondrial biogenesis in patients with chronic kidney disease

Skeletal Muscle Injury in Chronic Kidney Disease-From Histologic Changes to Molecular Mechanisms and to Novel Therapies

Chronic kidney disease (CKD) is associated with significant reductions in lean body mass and in the mass of various tissues, including skeletal muscle, which causes fatigue and contributes to high mortality rates. In CKD, the cellular protein turnover is imbalanced, with protein degradation outweighing protein synthesis, leading to a loss of protein and cell mass, which impairs tissue function. As CKD itself, skeletal muscle wasting, or sarcopenia, can have various origins and causes, and both CKD and sarcopenia share common risk factors, such as diabetes, obesity, and age. While these pathologies together with reduced physical performance and malnutrition contribute to muscle loss, they cannot explain all features of CKD-associated sarcopenia. Metabolic acidosis, systemic inflammation, insulin resistance and the accumulation of uremic toxins have been identified as additional factors that occur in CKD and that can contribute to sarcopenia. Here, we discuss the elevation of systemic phosphate levels, also called hyperphosphatemia, and the imbalance in the endocrine regulators of phosphate metabolism as another CKD-associated pathology that can directly and indirectly harm skeletal muscle tissue. To identify causes, affected cell types, and the mechanisms of sarcopenia and thereby novel targets for therapeutic interventions, it is important to first characterize the precise pathologic changes on molecular, cellular, and histologic levels, and to do so in CKD patients as well as in animal models of CKD, which we describe here in detail. We also discuss the currently known pathomechanisms and therapeutic approaches of CKD-associated sarcopenia, as well as the effects of hyperphosphatemia and the novel drug targets it could provide to protect skeletal muscle in CKD.

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.

A Comprehensive Exercise (COMEX) Intervention to Optimize Exercise Participation for Improving Patient-Centered Outcomes and Physical Functioning in Patients Receiving Hemodialysis: Development and Pilot Testing

Rationale & Objective

To address the need for an intradialytic exercise program that is easily delivered in clinical setting, engaging and scalable, we developed a novel COMprehensive EXercise (COMEX) program based on input from patients receiving hemodialysis (HD), dialysis staff members and nephrologists. The objective of this study was to determine the feasibility, safety, and acceptance of COMEX during HD.

Study Design

Single-arm prospective pilot feasibility study.

Setting & Participants

Seventeen patients receiving in-center HD.

Intervention

Three-month participation in the COMEX program, which included video-based dialysis chair exercises (aerobic and resistance) integrated with educational and motivational components.

Outcomes

Data on recruitment, adherence, safety and acceptability were collected. Additional assessments were performed to evaluate changes in physical functioning, patient-reported symptoms, and objectively measured sleep and physical activity. We also examined the feasibility of obtaining skeletal muscle biopsies and blood samples to explore molecular mechanisms of muscle atrophy and to assess platelet mitochondrial function and adaptation to exercise during HD.

Results

Thirteen of the 17 (76%) participants completed the 3-month intervention. The mean participant age was 63.6 ± 15.1 years. In total, 46% of participants were males, and 55% were White. The mean body mass index was 38.7 ± 11.6 kg/m2. There were no reported adverse effects, and the adherence rate to exercise sessions was high with 88% of the sessions completed. Patient satisfaction was high, as 100% of the patients would recommend the program to other dialysis patients. It was feasible to collect data on physical functioning, patient-reported symptoms, and objective sleep and physical activity and to obtain muscle biopsies and blood samples.

Limitations

Small sample size, lack of an onsite exercise professional, and technological issues with telemedicine behavioral motivation.

Conclusions

The COMEX intradialytic exercise intervention is safe and acceptable to patients, and outcome measures were feasible to obtain. Future studies should consider including exercise professionals to facilitate progression through a personalized exercise protocol.

Funding Source

This work is supported by pilot award from P30 DK079307 (PI, Jhamb).

Trial Registration

ClinicalTrials.gov, NCT03055299.

Plain-Language Summary

We tested a new COMprehensive EXercise (COMEX) program to deliver exercise during dialysis. This 3-month program included video-based dialysis chair exercises (aerobic and resistance) integrated with educational and motivational components. Our study shows COMEX was feasible, had high satisfaction and adherence, and was safe. It was feasible to collect data on physical functioning, patient-reported symptoms, and objective sleep and physical activity and to obtain muscle biopsies and blood samples. Future studies should consider including exercise professionals to facilitate progression through a personalized exercise protocol.

Therapeutic Exercise on Metabolic and Renal Outcomes in Patients with Chronic Kidney Disease: A Narrative Review

BACKGROUND

Chronic kidney disease (CKD) affects 11-13% of the world population. The main risk factors for CKD include diabetes, hypertension, and obesity. Metabolic syndrome (MS) is associated with the onset of CKD in the nondiabetic population. Obesity and MS are also risk factors for a worse progression of established CKD. Therapeutic exercise is an effective option to treat and manage obesity, MS, and diabetes in the general population. However, the evidence on the effect of exercise on patients with CKD, obesity, and MS is scarce.

SUMMARY

We evaluated available evidence on the effect of therapeutic exercise in patients with CKD, excluding dialysis, particularly in improving the metabolic risk factors and main renal outcomes: renal function loss and albuminuria/proteinuria. This review includes prospective studies and clinical trials. A total of 44 studies were analysed in 1,700 subjects with renal disease (2-5), including patients with renal transplantation. Most studies did not prove a major effect of exercise on albuminuria/proteinuria, glomerular filtration rate (GFR), obesity, or MS. These results are intriguing and deserve attention. The exploratory nature of most studies, including a low number of cases and short follow-up, might explain the lack of efficacy of exercise in our analysis. Specific aspects like the type of exercise, frequency, intensity, duration, accommodation during follow-up, individualization, safety, and adherence are crucial to the success of therapeutic exercise. The beneficial role of exercise in patients with CKD remains to be determined.

KEY MESSAGES

Key messages of this review are as follows. (1) The effect of therapeutic exercise on renal and metabolic outcomes in patients with CKD remains to be determined. (2) According to the evidence selected, therapeutic exercise seems to be safe to treat patients with CKD. (3) Most studies are exploratory by nature, with results that need further investigation. (4) Therapeutic exercise is a complex procedure that must be specifically designed to treat patients with CKD.

A Randomized, Double-Blind, Controlled Trial Assessing If Medium-Chain Triglycerides in Combination with Moderate-Intensity Exercise Increase Muscle Strength in Healthy Middle-Aged and Older Adults

An adequate nutritional intake is recommended for the prevention of physical frailty and sarcopenia. In particular, medium-chain fatty acids (MCFAs) are reportedly important for muscle strength in nursing home residents. However, the effects of MCFAs on healthy adults at risk for frailty remain unknown. Hence, a randomized, placebo-controlled study was conducted to investigate the effects of 12 weeks of medium-chain triglycerides (MCTs) intake and walking on muscle mass and function in healthy, sedentary, middle-aged and older adults with a low body mass index. Three MCT intake groups with different amounts of octanoic and decanoic acid intake were compared with a control group. After 12 weeks, knee extension strength increased in all groups, with the increases in all MCT intake groups being significantly higher than those in the control group (p < 0.05). Grip strength significantly increased from baseline in the MCT 6 g/day intake group (p < 0.05). The combination of aerobic exercise and MCT intake may be effective in preventing decline in muscle strength and promoting increase in muscle strength as they can improve muscle energy production, thereby contributing to the maintenance of good health for middle-aged and older adults at high risk for frailty and sarcopenia.

The Potential Influence of Uremic Toxins on the Homeostasis of Bones and Muscles in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) often experience a high accumulation of protein-bound uremic toxins (PBUTs), specifically indoxyl sulfate (IS) and p-cresyl sulfate (pCS). In the early stages of CKD, the buildup of PBUTs inhibits bone and muscle function. As CKD progresses, elevated PBUT levels further hinder bone turnover and exacerbate muscle wasting. In the late stage of CKD, hyperparathyroidism worsens PBUT-induced muscle damage but can improve low bone turnover. PBUTs play a significant role in reducing both the quantity and quality of bone by affecting osteoblast and osteoclast lineage. IS, in particular, interferes with osteoblastogenesis by activating aryl hydrocarbon receptor (AhR) signaling, which reduces the expression of Runx2 and impedes osteoblast differentiation. High PBUT levels can also reduce calcitriol production, increase the expression of Wnt antagonists (SOST, DKK1), and decrease klotho expression, all of which contribute to low bone turnover disorders. Furthermore, PBUT accumulation leads to continuous muscle protein breakdown through the excessive production of reactive oxygen species (ROS) and inflammatory cytokines. Interactions between muscles and bones, mediated by various factors released from individual tissues, play a crucial role in the mutual modulation of bone and muscle in CKD. Exercise and nutritional therapy have the potential to yield favorable outcomes. Understanding the underlying mechanisms of bone and muscle loss in CKD can aid in developing new therapies for musculoskeletal diseases, particularly those related to bone loss and muscle wasting.

Exercise and chronic kidney disease: potential mechanisms underlying the physiological benefits

Increasing evidence indicates that exercise has beneficial effects on chronic inflammation, cardiorespiratory function, muscle and bone strength and metabolic markers in adults with chronic kidney disease (CKD), kidney failure or kidney transplants. However, the mechanisms that underlie these benefits have received little attention, and the available clinical evidence is mainly from small, short-duration (<12 weeks) exercise intervention studies. The available data, mainly from patients with CKD or on dialysis, suggest that exercise-mediated shifts towards a less inflammatory immune cell profile, enhanced activity of the NRF2 pathway and reduced monocyte infiltration into adipose tissue may underlie improvements in inflammatory biomarkers. Exercise-mediated increases in nitric oxide release and bioavailability, reduced angiotensin II accumulation in the heart, left ventricular remodelling and reductions in myocardial fibrosis may contribute to improvements in left ventricular hypertrophy. Exercise stimulates an anabolic response in skeletal muscle in CKD, but increases in mitochondrial mass and satellite cell activation seem to be impaired in this population. Exercise-mediated activation of the canonical wnt pathway may lead to bone formation and improvements in the levels of the bone-derived hormones klotho and fibroblast growth factor 23 (FGF23). Longer duration studies with larger sample sizes are needed to confirm these mechanisms in CKD, kidney failure and kidney transplant populations and provide evidence for targeted exercise interventions.

Skeletal Muscle Complications in Chronic Kidney Disease

PURPOSE OF REVIEW

To provide an overview of the recent literature investigating the pathophysiology of skeletal muscle changes, interventions for skeletal muscle, and effects of exercise in chronic kidney disease (CKD).

RECENT FINDINGS

There are multiple CKD-related changes that negatively impact muscle size and function. However, the variability in the assessment of muscle size, in particular, hinders the ability to truly understand the impact it may have in CKD. Exercise interventions to improve muscle size and function demonstrate inconsistent responses that warrant further investigation to optimize exercise prescription. Despite progress in the field, there are many gaps in the knowledge of the pathophysiology of sarcopenia of CKD. Identifying these gaps will help in the design of interventions that can be tested to target muscle loss and its consequences such as impaired mobility, falls, and poor quality of life in patients with CKD.

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

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

High intramuscular triglyceride turnover rates and the link to insulin sensitivity: influence of obesity, type 2 diabetes and physical activity

Large intramuscular triglyceride (IMTG) stores in sedentary, obese individuals have been linked to insulin resistance, yet well-trained athletes exhibit high IMTG levels whilst maintaining insulin sensitivity. Contrary to previous assumptions, it is now known that IMTG content per se does not result in insulin resistance. Rather, insulin resistance is caused, at least in part, by the presence of high concentrations of harmful lipid metabolites, such as diacylglycerols and ceramides in muscle. Several mechanistic differences between obese sedentary individuals and their highly trained counterparts have been identified, which determine the differential capacity for IMTG synthesis and breakdown in these populations. In this review, we first describe the most up-to-date mechanisms by which a low IMTG turnover rate (both breakdown and synthesis) leads to the accumulation of lipid metabolites and results in skeletal muscle insulin resistance. We then explore current and potential exercise and nutritional strategies that target IMTG turnover in sedentary obese individuals, to improve insulin sensitivity. Overall, improving IMTG turnover should be an important component of successful interventions that aim to prevent the development of insulin resistance in the ever-expanding sedentary, overweight and obese populations. Novelty: A description of the most up-to-date mechanisms regulating turnover of the IMTG pool. An exploration of current and potential exercise/nutritional strategies to target and enhance IMTG turnover in obese individuals. Overall, highlights the importance of improving IMTG turnover to prevent the development of insulin resistance.

Primary skeletal muscle cells from chronic kidney disease patients retain hallmarks of cachexia in vitro

BACKGROUND

Skeletal muscle wasting and dysfunction are common characteristics noted in people who suffer from chronic kidney disease (CKD). The mechanisms by which this occurs are complex, and although progress has been made, the key underpinning mechanisms are not yet fully elucidated. With work to date primarily conducted in nephrectomy-based animal models, translational capacity to our patient population has been challenging. This could be overcome if rationale developing work could be conducted in human based models with greater translational capacity. This could be achieved using cells derived from patient biopsies, if they retain phenotypic traits noted in vivo.

METHODS

Here, we performed a systematic characterization of CKD derived muscle cells (CKD; n = 10; age: 54.40 ± 15.53 years; eGFR: 22.25 ± 13.22 ml/min/1.73 m² ) in comparison with matched controls (CON; n = 10; age: 58.66 ± 14.74 years; eGFR: 85.81 ± 8.09 ml/min/1.73 m² ). Harvested human derived muscle cells (HDMCs) were taken through proliferative and differentiation phases and investigated in the context of myogenic progression, inflammation, protein synthesis, and protein breakdown. Follow up investigations exposed HDMC myotubes from each donor type to 0, 0.4, and 100 nM of IGF-1 in order to investigate any differences in anabolic resistance.

RESULTS

Harvested human derived muscle cells isolated from CKD patients displayed higher rates of protein degradation (P = 0.044) alongside elevated expression of both TRIM63 (2.28-fold higher, P = 0.054) and fbox32 (6.4-fold higher, P < 0.001) in comparison with CONs. No differences were noted in rates of protein synthesis under basal conditions (P > 0.05); however, CKD derived cells displayed a significant degree of anabolic resistance in response to IGF-1 stimulation (both doses) in comparison with matched CONs (0.4 nm: P < 0.001; 100 nM: P < 0.001).

CONCLUSIONS

In summary, we report for the first time that HDMCs isolated from people suffering from CKD display key hallmarks of the well documented in vivo phenotype. Not only do these findings provide further mechanistic insight into CKD specific cachexia, but they also demonstrate this is a reliable and suitable model in which to perform targeted experiments to begin to develop novel therapeutic strategies targeting the CKD associated decline in skeletal muscle mass and function.

Evaluating the Effects of Increased Protein Intake on Muscle Strength, Hypertrophy and Power Adaptations with Concurrent Training: A Narrative Review

Concurrent training incorporates dual exercise modalities, typically resistance and aerobic-based exercise, either in a single session or as part of a periodized training program, that can promote muscle strength, mass, power/force and aerobic capacity adaptations for the purposes of sports performance or general health/wellbeing. Despite multiple health and exercise performance-related benefits, diminished muscle hypertrophy, strength and power have been reported with concurrent training compared to resistance training in isolation. Dietary protein is well-established to facilitate skeletal muscle growth, repair and regeneration during recovery from exercise. The degree to which increased protein intake can amplify adaptation responses with resistance exercise, and to a lesser extent aerobic exercise, has been highly studied. In contrast, much less focus has been directed toward the capacity for protein to enhance anabolic and metabolic responses with divergent contractile stimuli inherent to concurrent training and potentially negate interference in muscle strength, power and hypertrophy. This review consolidates available literature investigating increased protein intake on rates of muscle protein synthesis, hypertrophy, strength and force/power adaptations following acute and chronic concurrent training. Acute concurrent exercise studies provide evidence for the significant stimulation of myofibrillar protein synthesis with protein compared to placebo ingestion. High protein intake can also augment increases in lean mass with chronic concurrent training, although these increases do not appear to translate into further improvements in strength adaptations. Similarly, the available evidence indicates protein intake twice the recommended intake and beyond does not rescue decrements in selective aspects of muscle force and power production with concurrent training.

Effect of different physical training modalities on peak oxygen consumptions in post-acute myocardial infarction patients: systematic review and meta-analysis

Physical training can increase peak oxygen uptake (VO2peak) in people who have suffered acute myocardial infarction (AMI). However, there is still a gap in the literature in relation to the effectiveness of different types of interventions. Therefore, the aim of the present study was to evaluate the effects of different physical training modalities on VO2peak in post-AMI patients. The following databases were used: PubMed (MEDLINE), Cochrane Library, Scopus, and Pedro. Studies that evaluated aerobic exercise, strength exercise, or combined exercise were included. Six studies met eligibility criteria. Aerobic exercise increased VO2peak by 6.07 ml.kg^-1.min^-1 when compared to the control group (CG) (p = 0.013). The comparison between combined exercise and control group detected a difference of 1.84 ml.kg^-1.min^-1, but this was not significant (p = 0.312). We therefore conclude that aerobic exercise is the only modality that is effective for increasing VO2peak compared to a control group.

Differentiation of THP-1 monocytes to macrophages increased mitochondrial DNA copy number but did not increase expression of mitochondrial respiratory proteins or mitochondrial transcription factor A

Monocytes are differentiated into macrophages. In this study, mitochondrial DNA copy number (mtDNAcn) levels and downstream events such as the expression of respiratory chain mRNAs were investigated during the phorbol 12-myristate 13-acetate (PMA)-induced differentiation of monocytes. Although PMA treatment increased mtDNAcn, the expression levels of mRNAs encoded in mtDNA were decreased. The levels of mitochondrial transcription factor A mRNA and protein were also decreased. The levels of coenzyme Q10 remained unchanged. These results imply that, although mtDNAcn is considered as a health marker, the levels of mtDNAcn may not always be consistent with the parameters of mitochondrial functions.

Sarcopenia in Chronic Kidney Disease: Focus on Advanced Glycation End Products as Mediators and Markers of Oxidative Stress

Sarcopenia is common in chronic kidney disease (CKD), and it is independently associated with morbidity and mortality. Advanced glycation end products (AGE) are mainly known as aging products. In CKD, AGE accumulate due to increased production and reduced kidney excretion. The imbalance between oxidant/antioxidant capacities in CKD patients is one of the main factors leading to AGE synthesis. AGE can, in turn, promote CKD progression and CKD-related complications by increasing reactive oxygen species generation, inducing inflammation, and promoting fibrosis. All these derangements can further increase AGE and uremic toxin accumulation and promote loss of muscle mass and function. Since the link between AGE and sarcopenia in CKD is far from being fully understood, we revised hereby the data supporting the potential contribution of AGE as mediators of oxidative stress in the pathogenesis of sarcopenia. Understanding how AGE and oxidative stress impact the onset of sarcopenia in CKD may help to identify new potential markers of disease progression and/or therapeutic targets.

Effects of intradialytic resistance exercises on physical performance, nutrient intake and quality of life among haemodialysis people: A systematic review and meta-analysis

OBJECTIVES

The aim of this systematic reviews was to synthesize the current studies for the effectiveness of intradialytic resistance exercises with usual care on HD people.

DESIGN

Meta-analysis of randomized controlled studies.

METHODS

A systematic search of seven electronic databases, including PubMed, EMBASE, the Cochrane Library, Web of Science, WanFang, China National Knowledge Infrastructure (CNKI) and SINOMED, was systematically searched up to May 2018. The reference lists of previously reported systematic review were also checked. Pooled analysis was used to determine effection of intradialytic resistance exercises for haemodialysis people. Physical performance, nutrient intake and quality of life were explored, by comparing the association between effect sizes.

RESULTS

Fourteen studies of 594 people were included. Compared with control groups, intradialytic resistance exercises significantly improve physical performance included 6-min walk test, sit-to-stand 30 and grip strength. However, no significant improvements were found in nutrient intakes such as dietary protein intake and quality of life.

The Effect of Exercise on Nutritional Status and Body Composition in Hemodialysis: A Systematic Review

Chronic kidney disease (CKD) is associated with aggravating factors which can affect both body composition and nutritional status. The purpose of the present systematic review was to investigate the potential effects of any physical activity on body composition or nutritional status among patients with stage 5 CKD undergoing hemodialysis (HD). A literature search on PubMed, Scopus, Web of Science, Google Scholar, and Cochrane was conducted and 14 randomized clinical trials were included. Skeletal muscle index and mid-arm muscular circumference increased after resistance exercise, and the results on body mass index, % body fat, and lean body mass varied. Serum albumin and C-reactive protein, in most cases, showed a slight increase and decrease, respectively. An improvement was also observed in body strength and overall performance status. The results suggest that physical activity can be beneficial for both the body composition and nutritional status of patients undergoing HD and can help in the prevention of sarcopenia. However, further research is needed mainly in the field of nutritional status.

Aerobic Exercise Training in Patients With mtDNA-Related Mitochondrial Myopathy

In patients with mitochondrial DNA (mtDNA) mutation, a pathogenic mtDNA mutation is heteroplasmically distributed among tissues. The ratio between wild-type and mutated mtDNA copies determines the mtDNA mutation load of the tissue, which correlates inversively with oxidative capacity of the tissue. In patients with mtDNA mutation, the mutation load is often very high in skeletal muscle compared to other tissues. Additionally, skeletal muscle can increase its oxygen demand up to 100-fold from rest to exercise, which is unmatched by any other tissue. Thus, exercise intolerance is the most common symptom in patients with mtDNA mutation. The impaired oxidative capacity in skeletal muscle in patients with mtDNA mutation results in limitation in physical capacity that interferes with daily activities and impairs quality of life. Additionally, patients with mitochondrial disease due to mtDNA mutation often live a sedentary lifestyle, which further impair oxidative capacity and exercise tolerance. Since aerobic exercise training increase mitochondrial function and volume density in healthy individuals, studies have investigated if aerobic training could be used to counteract the progressive exercise intolerance in patients with mtDNA mutation. Overall studies investigating the effect of aerobic training in patients with mtDNA mutation have shown that aerobic training is an efficient way to improve oxidative capacity in this condition, and aerobic training seems to be safe even for patients with high mtDNA mutation in skeletal muscle.

Impact of physical exercise in patients with chronic kidney disease: Sistematic review and meta-analysis

Physical exercise may offer multiple benefits to patients with chronic kidney disease (CKD). However, it was not traditionally recommended because of the possibility of impairing renal function and increasing proteinuria. The objective of this study is to review the clinical trials on physical exercise in patients with CKD and describe its effect on the progression of kidney disease and other factors associated. Randomized clinical trials (RCT) comparing an intervention that included an exercise component with a control group without physical exercise in non-dialysis patients with CKD from 2007 to 2018 in English and Spanish were included. PubMed, Scopus, Embase, Ovid (Medline) and PEDro databases were used for the search. Effects of physical exercise were summarized by the standardized mean difference (SMD). No differences were found in glomerular filtration rate or proteinuria between the intervention group and the control group: SMD -0.3 (P=.81); SMD 26.6 (P=.82). Positive effects were obtained on peak oxygen consumption: SMD 2.5 (P<.001), functional capacity: SMD 56.6 (P<.001), upper limb strength: SMD 6.8 (P<.001) and hemoglobin: SMD 0.3 (P=.003). An improvement on the quality of life was also evident using the KDQOL-36 survey: SMD 3.56 (P=.02) and the SF-36 survey: SMD 6.66 (P=.02). In conclusion, the practice of low-intensity physical exercise routinely has no negative impact on renal function. On the contrary, it improves aerobic and functional capacity, impacting positively on the quality of life.

Sarcopenia in Chronic Kidney Disease: Factors, Mechanisms, and Therapeutic Interventions

Chronic kidney disease (CKD), a chronic catabolic condition, is characterized by muscle wasting and decreased muscle endurance. Many insights into the molecular mechanisms of muscle wasting in CKD have been obtained. A persistent imbalance between protein degradation and synthesis in muscle causes muscle wasting. During muscle wasting, high levels of reactive oxygen species (ROS) and inflammatory cytokines are detected in muscle. These increased ROS and inflammatory cytokine levels induce the expression of myostatin. The myostatin binding to its receptor activin A receptor type IIB stimulates the expression of atrogenes such as atrogin-1 and muscle ring factor 1, members of the muscle-specific ubiquitin ligase family. Impaired mitochondrial function also contributes to reducing muscle endurance. The increased protein-bound uremic toxin, parathyroid hormone, glucocorticoid, and angiotensin II levels that are observed in CKD all have a negative effect on muscle mass and endurance. Among the protein-bound uremic toxins, indoxyl sulfate, an indole-containing compound has the potential to induce muscle atrophy by stimulating ROS-mediated myostatin and atrogenes expression. Indoxyl sulfate also impairs mitochondrial function. Some potential therapeutic approaches based on the muscle wasting mechanisms in CKD are currently in the testing stages.

Is Neuronal Histamine Signaling Involved in Cancer Cachexia? Implications and Perspectives

In this paper, we present evidence in support of our hypothesis that the neuronal histaminergic system might be involved in cancer cachexia¹. To build our premise, we present the research and the reasonable inferences that can be drawn from it in a section by section approach starting from one of the key issues related to cachexia, increased resting energy expenditure (REE), and progressing to the other, anorexia. Based on an extensive survey of the literature and our own deliberations on the abovementioned topics, we investigate whether histamine signaling might be the mechanism used by a tumor to hijack the body's thermogenic machinery. Our hypothesis in short is that hypothalamic histaminergic neurons are stimulated by inputs from the parasympathetic nervous system (PSNS), which senses tumor traits early in cancer development. Histamine release in the preoptic area of the hypothalamus primarily activates brown adipose tissue (BAT), triggering a highly energy demanding mechanism. Chronic activation of BAT, which, in this context, refers to intermittent and/or low grade activation by the sympathetic nervous system, leads to browning of white adipose tissue and further enhances thermogenic potential. Aberrant histamine signaling not only triggers energy-consuming processes, but also anorexia. Moreover, since functions such as taste, smell, and sleep are governed by discrete structures of the brain, which are targeted by distinct histaminergic neuron populations even relatively minor symptoms of cachexia, such as sleep disturbances and taste and smell distortions, also might be ascribed to aberrant histamine signaling. In late stage cachexia, the sympathetic tone in skeletal muscle breaks down, which we hypothesize might be caused by a reduction in histamine signaling or by the interference of other cachexia related mechanisms. Histamine signaling thus might delineate distinct stages of cachexia progression, with the early phase marked by a PSNS-mediated increase in histamine signaling, increased sympathetic tone and symptomatic adipose tissue depletion, and the late phase characterized by reduced histamine signaling, decreased sympathetic tone and symptomatic muscle wasting. To support our hypothesis, we review the literature from across disciplines and highlight the many commonalities between the mechanisms underlying cancer cachexia and current research findings on the regulation of energy homeostasis (particularly as it relates to hypothalamic histamine signaling). Extrapolating from the current body of knowledge, we develop our hypothetical framework (based on experimentally falsifiable assumptions) about the role of a distinct neuron population in the pathophysiology of cancer cachexia. Our hope is that presenting our ideas will spark discussion about the pathophysiology of cachexia, cancer's devastating and intractable syndrome.

Testosterone therapy induces molecular programming augmenting physiological adaptations to resistance exercise in older men

BACKGROUND

The andropause is associated with declines in serum testosterone (T), loss of muscle mass (sarcopenia), and frailty. Two major interventions purported to offset sarcopenia are anabolic steroid therapies and resistance exercise training (RET). Nonetheless, the efficacy and physiological and molecular impacts of T therapy adjuvant to short-term RET remain poorly defined.

METHODS

Eighteen non-hypogonadal healthy older men, 65-75 years, were assigned in a random double-blinded fashion to receive, biweekly, either placebo (P, saline, n = 9) or T (Sustanon 250 mg, n = 9) injections over 6 week whole-body RET (three sets of 8-10 repetitions at 80% one-repetition maximum). Subjects underwent dual-energy X-ray absorptiometry, ultrasound of vastus lateralis (VL) muscle architecture, and knee extensor isometric muscle force tests; VL muscle biopsies were taken to quantify myogenic/anabolic gene expression, anabolic signalling, muscle protein synthesis (D₂ O), and breakdown (extrapolated).

RESULTS

Testosterone adjuvant to RET augmented total fat-free mass (P=0.007), legs fat-free mass (P=0.02), and appendicular fat-free mass (P=0.001) gains while decreasing total fat mass (P=0.02). Augmentations in VL muscle thickness, fascicle length, and quadriceps cross-section area with RET occured to a greater extent in T (P < 0.05). Sum strength (P=0.0009) and maximal voluntary contract (e.g. knee extension at 70°) (P=0.002) increased significantly more in the T group. Mechanistically, both muscle protein synthesis rates (T: 2.13 ± 0.21%·day^-1 vs. P: 1.34 ± 0.13%·day^-1 , P=0.0009) and absolute breakdown rates (T: 140.2 ± 15.8 g·day^-1 vs. P: 90.2 ± 11.7 g·day^-1 , P=0.02) were elevated with T therapy, which led to higher net turnover and protein accretion in the T group (T: 8.3 ± 1.4 g·day^-1 vs. P: 1.9 ± 1.2 g·day^-1 , P=0.004). Increases in ribosomal biogenesis (RNA:DNA ratio); mRNA expression relating to T metabolism (androgen receptor: 1.4-fold; Srd5a1: 1.6-fold; AKR1C3: 2.1-fold; and HSD17β3: two-fold); insulin-like growth factor (IGF)-1 signalling [IGF-1Ea (3.5-fold) and IGF-1Ec (three-fold)] and myogenic regulatory factors; and the activity of anabolic signalling (e.g. mTOR, AKT, and RPS6; P < 0.05) were all up-regulated with T therapy. Only T up-regulated mitochondrial citrate synthase activity (P=0.03) and transcription factor A (1.41 ± 0.2-fold, P=0.0002), in addition to peroxisome proliferator-activated receptor-γ co-activator 1-α mRNA (1.19 ± 0.21-fold, P=0.037).

CONCLUSIONS

Administration of T adjuvant to RET enhanced skeletal muscle mass and performance, while up-regulating myogenic gene programming, myocellular translational efficiency and capacity, collectively resulting in higher protein turnover, and net protein accretion. T coupled with RET is an effective short-term intervention to improve muscle mass/function in older non-hypogonadal men.

Impact of Endurance and Resistance Training on Skeletal Muscle Glucose Metabolism in Older Adults

Aging is associated with insulin resistance and the development of type 2 diabetes. While this process is multifaceted, age-related changes to skeletal muscle are expected to contribute to impaired glucose metabolism. Some of these changes include sarcopenia, impaired insulin signaling, and imbalances in glucose utilization. Endurance and resistance exercise training have been endorsed as interventions to improve glucose tolerance and whole-body insulin sensitivity in the elderly. While both types of exercise generally increase insulin sensitivity in older adults, the metabolic pathways through which this occurs can differ and can be dependent on preexisting conditions including obesity and type 2 diabetes. In this review, we will first highlight age-related changes to skeletal muscle which can contribute to insulin resistance, followed by a comparison of endurance and resistance training adaptations to insulin-stimulated glucose metabolism in older adults.

Adaptations in Mitochondrial Enzymatic Activity Occurs Independent of Genomic Dosage in Response to Aerobic Exercise Training and Deconditioning in Human Skeletal Muscle

Mitochondrial DNA (mtDNA) replication is thought to be an integral part of exercise-training-induced mitochondrial adaptations. Thus, mtDNA level is often used as an index of mitochondrial adaptations in training studies. We investigated the hypothesis that endurance exercise training-induced mitochondrial enzymatic changes are independent of genomic dosage by studying mtDNA content in skeletal muscle in response to six weeks of knee-extensor exercise training followed by four weeks of deconditioning in one leg, comparing results to the contralateral untrained leg, in 10 healthy, untrained male volunteers. Findings were compared to citrate synthase activity, mitochondrial complex activities, and content of mitochondrial membrane markers (porin and cardiolipin). One-legged knee-extensor exercise increased endurance performance by 120%, which was accompanied by increases in power output and peak oxygen uptake of 49% and 33%, respectively (p < 0.01). Citrate synthase and mitochondrial respiratory chain complex I–IV activities were increased by 51% and 46–61%, respectively, in the trained leg (p < 0.001). Despite a substantial training-induced increase in mitochondrial activity of TCA and ETC enzymes, there was no change in mtDNA and mitochondrial inner and outer membrane markers (i.e., cardiolipin and porin). Conversely, deconditioning reduced endurance capacity by 41%, muscle citrate synthase activity by 32%, and mitochondrial complex I–IV activities by 29–36% (p < 0.05), without any change in mtDNA and porin and cardiolipin content in the previously trained leg. The findings demonstrate that the adaptations in mitochondrial enzymatic activity after aerobic endurance exercise training and the opposite effects of deconditioning are independent of changes in the number of mitochondrial genomes, and likely relate to changes in the rate of transcription of mtDNA.

CKD autophagy activation and skeletal muscle atrophy-a preliminary study of mitophagy and inflammation

BACKGROUND/OBJECTIVES

Long-lived proteins and organelles, such as mitochondria and the sarcoplasmic reticulum, are degraded by autophagy. However, the specific role of autophagy in chronic kidney disease (CKD) muscle atrophy is still undefined.

SUBJECTS/METHODS

This was a cross-sectional study with 20 subjects and 11 controls. Autophagy induction was studied in human skeletal muscle biopsies from CKD patients and controls by comparing the cross-sectional areas of muscle fibers, protein, and mRNA expression of autophagy-related genes and the appearance of autophagosomes.

RESULTS

The cross-sectional area of muscle fibers was decreased in CKD patients as compared with the control group. CKD was associated with activated autophagy and mitophagy, as measured by the elevated mRNA and protein expression of BNIP3, (microtubule-associated proteins 1 A/1B light chain 3, also MAP1LC3) LC3, p62, PINK1, and PARKIN in the skeletal muscle and isolated mitochondria of the CKD group. Electron microscopy and immunohistofluorescence analysis showed mitochondrial engulfment by autophagosomes. Mitophagy was further demonstrated by the colocalization of LC3 and p62 puncta with the mitochondrial outer membrane protein TOM20. In addition, degradative FOXO3 (Forkhead box O3) was activated and synthetic mTOR (mammalian target of rapamycin) was inhibited, whereas the upstream mediators VPS34 (class III PI3-kinase) and AKT (protein kinase B, PKB) were activated in CKD patients.

CONCLUSIONS

Hyperactive autophagy and mitophagy may play important roles in CKD muscle atrophy. Autophagy was activated by FOXO3 translational factors in the skeletal muscle tissues of CKD patients, which maybe a new way of intervention for CKD muscle atrophy.

Bioactive food and exercise in chronic kidney disease: Targeting the mitochondria

Chronic kidney disease (CKD), which affects 10%-15% of the population, associates with a range of complications-such as cardiovascular disease, frailty, infections, muscle and bone disorders and premature ageing-that could be related to alterations of mitochondrial number, distribution, structure and function. As mitochondrial biogenesis, bioenergetics and the dynamic mitochondrial networks directly or indirectly regulate numerous intra- and extracellular functions, the mitochondria have emerged as an important target for interventions aiming at preventing or improving the treatment of complications in CKD. In this review, we discuss the possible role of bioactive food compounds and exercise in the modulation of the disturbed mitochondrial function in a uraemic milieu.

Characterising skeletal muscle haemoglobin saturation during exercise using near-infrared spectroscopy in chronic kidney disease

Background

Chronic kidney disease (CKD) patients have reduced exercise capacity. Possible contributing factors may include impaired muscle O₂ utilisation through reduced mitochondria number and/or function slowing the restoration of muscle ATP concentrations via oxidative phosphorylation. Using near-infrared spectroscopy (NIRS), we explored changes in skeletal muscle haemoglobin/myoglobin O₂ saturation (SMO₂%) during exercise.

Methods

24 CKD patients [58.3 (± 16.5) years, eGFR 56.4 (± 22.3) ml/min/1.73 m²] completed the incremental shuttle walk test (ISWT) as a marker of exercise capacity. Using NIRS, SMO₂% was measured continuously before, during, and after (recovery) exercise. Exploratory differences were investigated between exercise capacity tertiles in CKD, and compared with six healthy controls.

Results

We identified two discrete phases; a decline in SMO₂% during incremental exercise, followed by rapid increase upon cessation (recovery). Compared to patients with low exercise capacity [distance walked during ISWT, 269.0 (± 35.9) m], patients with a higher exercise capacity [727.1 (± 38.1) m] took 45% longer to reach their minimum SMO₂% (P = .038) and recovered (half-time recovery) 79% faster (P = .046). Compared to controls, CKD patients took significantly 56% longer to recover (i.e., restore SMO₂% to baseline, full recovery) (P = .014).

Conclusions

Using NIRS, we have determined for the first time in CKD, that favourable SMO₂% kinetics (slower deoxygenation rate, quicker recovery) are associated with greater exercise capacity. These dysfunctional kinetics may indicate reduced mitochondria capacity to perform oxidative phosphorylation—a process essential for carrying out even simple activities of daily living. Accordingly, NIRS may provide a simple, low cost, and non-invasive means to evaluate muscle O₂ kinetics in CKD.

Intracellular organelles in health and kidney disease

Subcellular organelles consist of smaller substructures called supramolecular assemblies and these in turn consist of macromolecules. Various subcellular organelles have critical functions that consist of genetic disorders of organelle biogenesis and several metabolic disturbances that occur during non-genetic diseases e.g. infection, intoxication and drug treatments. Mitochondrial damage can cause renal dysfunction as ischemic acute renal injury, chronic kidney disease progression. Moreover, mitochondrial dysfunction is an early event in aldosterone-induced podocyte injury and cardiovascular disease due to oxidative stress in chronic kidney disease. Elevated production of reactive oxygen species could be able to activate NLRP3 inflammasome representing new deregulated biological machinery and a novel therapeutic target in hemodialysis patients. Peroxisomes are actively involved in apoptosis and inflammation, innate immunity, aging and in the pathogenesis of age related diseases, such as diabetes mellitus and cancer. Peroxisomal catalase causes alterations of mitochondrial membrane proteins and stimulates generation of mitochondrial reactive oxygen species. High concentrations of hydrogen peroxide exacerbate organelles and cellular aging. The importance of proper peroxisomal function for the biosynthesis of bile acids has been firmly established. Endoplasmic reticulum stress-induced pathological diseases in kidney cause glomerular injury and tubulointerstitial injury. Furthermore, there is a link between oxidative stress and inflammations in pathological states are associated with endoplasmic reticulum stress. Proteinuria and hyperglycemia in diabetic nephropathy may induce endoplasmic reticulum stress in tubular cells of the kidney. Due to the accumulation in the proximal tubule lysosomes, impaired function of these organelles may be an important mechanism leading to proximal tubular toxicity.

Dietary supplementation with ketoacids protects against CKD-induced oxidative damage and mitochondrial dysfunction in skeletal muscle of 5/6 nephrectomised rats

Background

A low-protein diet supplemented with ketoacids (LPD + KA) maintains the nutritional status of patients with chronic kidney disease (CKD). Oxidative damage and mitochondrial dysfunction associated with the upregulation of p66SHC and FoxO3a have been shown to contribute to muscle atrophy. This study aimed to determine whether LPD + KA improves muscle atrophy and attenuates the oxidative stress and mitochondrial damage observed in CKD rats.

Methods

5/6 nephrectomy rats were randomly divided into three groups and fed with either 22% protein (normal-protein diet; NPD), 6% protein (low-protein diets; LPD) or 5% protein plus 1% ketoacids (LPD + KA) for 24 weeks. Sham-operated rats with NPD intake were used as the control.

Results

KA supplementation improved muscle atrophy and function in CKD + LPD rats. It also reduced the upregulation of genes related to the ubiquitin-proteasome system and 26S proteasome activity, as well as protein and mitochondrial oxidative damage in the muscles of CKD + LPD rats. Moreover, KA supplementation prevented the drastic decrease in activities of mitochondrial electron transport chain complexes, mitochondrial respiration, and content in the muscles of CKD + LPD rats. Furthermore, KA supplementation reversed the elevation in p66Shc and FoxO3a expression in the muscles of CKD + LPD rats.

Conclusions

Our results showed that KA supplementation to be beneficial to muscle atrophy in CKD + LPD, which might be associated with improvement of oxidative damage and mitochondrial dysfunction through suppression of p66Shc and FoxO3a.

Uremia induces adipose tissue inflammation and muscle mitochondrial dysfunction

Background.

End-stage renal disease (ESRD) is associated with inflammation and increased reactive oxygen species (ROS). Inflammation and oxidative stress are associated with several complications of ESRD. The aim of this study was to determine histological characteristics of adipose tissue and muscle mitochondrial function in uremia and its relationship with inflammation.

Methods.

ESRD patients ( n  = 18) and controls ( n  = 6) were enrolled for studies of adipose and muscle tissue by immunohistochemistry and western blot. In a uremic muscle cell model, C2C12 cells were exposed to uremic serum and inflammatory cytokines. Mitochondrial function was studied by MitoTracker Orange, translocase of the mitochondrial outer membrane 20 (TOMM20) and mitochondrial oxidative phosphorylation complex subunit expression.

Results.

ESRD patients had increased macrophage infiltration in subcutaneous and visceral adipose tissue compared with controls, even in nonobese ESRD patients (P < 0.05). Compared with controls, TOMM20 expression in muscle tissue was lower in ESRD, consistent with reduced mitochondrial function (P < 0.05). C2C12 exposed to uremia had decreased mitotracker intensity (P < 0.05) and the reduced mitochondrial function was rescued by N-acetyl cysteine (P < 0.01). Similarly, C2C12 cells exposed to tumor necrosis factor α (TNF-α)/interleukin-6 (IL-6) have decreased mitotracker intensity (P < 0.01) that was rescued with adiponectin (P < 0.05). C2C12 exposed to TNF-α, IL-6 and buthionine sulfoximine had decreased TOMM20 expression and cells exposed to TNF-α showed a decrease in subunits of mitochondrial complexes I and III.

Conclusion.

Our data indicate that uremia is associated with increased adipose tissue macrophage infiltration and concurrent muscle tissue mitochondrial dysfunction induced by inflammation/ROS. Adipose tissue is a potential source of inflammation in ESRD that is not due to increased adiposity and may contribute to mitochondrial dysfunction in uremia.

Muscle Atrophy in Chronic Kidney Disease

The renal damage and loss of kidney function that characterize chronic kidney disease (CKD) cause several complex systemic alterations that affect muscular homeostasis, leading to loss of muscle mass and, ultimately, to muscle atrophy. CKD-induced muscle atrophy is highly prevalent and, in association with common CKD comorbidities, is responsible for the reduction of physical capacity, functional independence, and an increase in the number of hospitalizations and mortality rates. Thus, this chapter summarizes current knowledge about the complex interactions between CKD factors and the pathophysiological mechanisms that induce muscle atrophy that, despite growing interest, are not yet fully understood. The current treatments of CKD-induced muscle atrophy are multidisciplinary, including correction of metabolic acidosis, nutritional supplementation, reducing insulin resistance, administration of androgenic steroids, resisted and aerobic exercise, neuromuscular electrical stimulation, and inspiratory muscle training. However, further studies are still needed to strengthen the comprehension of CKD-induced muscle atrophy and the better treatment strategies.

Resistance Training with Co-ingestion of Anti-inflammatory Drugs Attenuates Mitochondrial Function

Aim: The current study aimed to examine the effects of resistance exercise with concomitant consumption of high vs. low daily doses of non-steroidal anti-inflammatory drugs (NSAIDs) on mitochondrial oxidative phosphorylation in skeletal muscle. As a secondary aim, we compared the effects of eccentric overload with conventional training. Methods: Twenty participants were randomized to either a group taking high doses (3 × 400 mg/day) of ibuprofen (IBU; 27 ± 5 year; n = 11) or a group ingesting a low dose (1 × 75 mg/day) of acetylsalicylic acid (ASA; 26 ± 4 year; n = 9) during 8 weeks of supervised knee extensor resistance training. Each of the subject's legs were randomized to complete the training program using either a flywheel (FW) device emphasizing eccentric overload, or a traditional weight stack machine (WS). Maximal mitochondrial oxidative phosphorylation (CI+II_P) from permeabilized skeletal muscle bundles was assessed using high-resolution respirometry. Citrate synthase (CS) activity was assessed using spectrophotometric techniques and mitochondrial protein content using western blotting. Results: After training, CI+II_P decreased (P < 0.05) in both IBU (23%) and ASA (29%) with no difference across medical treatments. Although CI+II_P decreased in both legs, the decrease was greater (interaction p = 0.015) in WS (33%, p = 0.001) compared with FW (19%, p = 0.078). CS activity increased (p = 0.027) with resistance training, with no interactions with medical treatment or training modality. Protein expression of ULK1 increased with training in both groups (p < 0.001). The increase in quadriceps muscle volume was not correlated with changes in CI+II_P (R = 0.16). Conclusion: These results suggest that 8 weeks of resistance training with co-ingestion of anti-inflammatory drugs reduces mitochondrial function but increases mitochondrial content. The observed changes were not affected by higher doses of NSAIDs consumption, suggesting that the resistance training intervention was the prime mediator of the decreased mitochondrial phosphorylation. Finally, we noted that flywheel resistance training, emphasizing eccentric overload, rescued some of the reduction in mitochondrial function seen with conventional resistance training.

Impact of Resistance Training on Skeletal Muscle Mitochondrial Biogenesis, Content, and Function

Skeletal muscle metabolic and contractile properties are reliant on muscle mitochondrial and myofibrillar protein turnover. The turnover of these specific protein pools is compromised during disease, aging, and inactivity. Oppositely, exercise can accentuate muscle protein turnover, thereby counteracting decay in muscle function. According to a traditional consensus, endurance exercise is required to drive mitochondrial adaptations, while resistance exercise is required to drive myofibrillar adaptations. However, concurrent practice of traditional endurance exercise and resistance exercise regimens to achieve both types of muscle adaptations is time-consuming, motivationally demanding, and contended to entail practice at intensity levels, that may not comply with clinical settings. It is therefore of principle interest to identify effective, yet feasible, exercise strategies that may positively affect both mitochondrial and myofibrillar protein turnover. Recently, reports indicate that traditional high-load resistance exercise can stimulate muscle mitochondrial biogenesis and mitochondrial respiratory function. Moreover, fatiguing low-load resistance exercise has been shown capable of promoting muscle hypertrophy and expectedly entails greater metabolic stress to potentially enhance mitochondrial adaptations. Consequently, fatiguing low-load resistance exercise regimens may possess the ability to stimulate muscle mitochondrial adaptations without compromising muscle myofibrillar accretion. However, the exact ability of resistance exercise to drive mitochondrial adaptations is debatable, not least due to some methodological challenges. The current review therefore aims to address the evidence on the effects of resistance exercise on skeletal muscle mitochondrial biogenesis, content and function. In prolongation, a perspective is taken on the specific potential of low-load resistance exercise on promoting mitochondrial adaptations.

Exercise Affects Cardiopulmonary Function in Patients with Chronic Kidney Disease: A Meta-Analysis

This study aimed to comprehensively assess the effects of exercise on cardiopulmonary function indices in patients with chronic kidney disease (CKD). A literature review was performed by searching literatures in PubMed and Embase before June 2016. Studies were selected based on predefined inclusion and exclusion criteria, followed by data extraction and a quality assessment of the included studies using the Cochrane Collaboration's tool. Correlations between exercise and cardiopulmonary function indices [pulse wave velocity, respiratory exchange ratio, and peak oxygen uptake (VO₂ peak)] were then evaluated using mean differences and 95% confidence intervals. All meta-analyses were conducted using R 3.12 software. Finally, five eligible studies involving 179 CKD patients were included. After intervention, a heterogeneity test showed that the VO₂ peak values of the treatment group were greater than those of the control group, whereas no significant differences were found for the other indices. However, a sensitivity analysis showed inconsistent results both before and after intervention. Thus, we concluded that exercise might play an important role in improving the VO₂ peak values in CKD patients. Additional studies are needed to verify this conclusion.

The Effect of Resistance Exercise on Inflammatory and Myogenic Markers in Patients with Chronic Kidney Disease

Background: Muscle wasting is a common complication of Chronic Kidney Disease (CKD) and is clinically important given its strong association with morbidity and mortality in many other chronic conditions. Exercise provides physiological benefits for CKD patients, however the molecular response to exercise remains to be fully determined. We investigated the inflammatory and molecular response to resistance exercise before and after training in these patients. Methods: This is a secondary analysis of a randomized trial that investigated the effect of 8 week progressive resistance training on muscle mass and strength compared to non-exercising controls. A sub-set of the cohort consented to vastus lateralis skeletal muscle biopsies (n = 10 exercise, n = 7 control) in which the inflammatory response (IL-6, IL-15, MCP-1 TNF-α), myogenic (MyoD, myogenin, myostatin), anabolic (P-Akt, P-eEf2) and catabolic events (MuRF-1, MAFbx, 14 kDa, ubiquitin conjugates) and overall levels of oxidative stress have been studied. Results: A large inflammatory response to unaccustomed exercise was seen with IL-6, MCP-1, and TNF-α all significantly elevated from baseline by 53-fold (P < 0.001), 25-fold (P < 0.001), and 4-fold (P < 0.001), respectively. This response was reduced following training with IL-6, MCP-1, and TNF-α elevated non-significantly by 2-fold (P = 0.46), 2.4-fold (P = 0.19), and 2.5-fold (P = 0.06), respectively. In the untrained condition, an acute bout of resistance exercise did not result in increased phosphorylation of Akt (P = 0.84), but this was restored following training (P = 0.01). Neither unaccustomed nor accustomed exercise resulted in a change in myogenin or MyoD mRNA expression (P = 0.88, P = 0.90, respectively). There was no evidence that resistance exercise training created a prolonged oxidative stress response within the muscle, or increased catabolism. Conclusions: Unaccustomed exercise creates a large inflammatory response within the muscle, which is no longer present following a period of training. This indicates that resistance exercise does not provoke a detrimental on-going inflammatory response within the muscle.

Improving Strength, Power, Muscle Aerobic Capacity, and Glucose Tolerance through Short-term Progressive Strength Training Among Elderly People

This protocol describes the simultaneous use of a broad span of methods to examine muscle aerobic capacity, glucose tolerance, strength, and power in elderly people performing short-term resistance training (RET). Supervised progressive resistance training for 1 h three times a week over 8 weeks was performed by RET participants (71±1 years, range 65-80). Compared to a control group without training, the RET showed improvements on the measures used to indicate strength, power, glucose tolerance, and several parameters of muscle aerobic capacity. Strength training was performed in a gym with only robust fitness equipment. An isokinetic dynamometer for knee extensor strength permitted the measurement of concentric, eccentric, and static strength, which increased for the RET group (8-12% post- versus pre-test). The power (rate of force development, RFD) at the initial 0-30 ms also showed an increase for the RET group (52%). A glucose tolerance test with frequent blood glucose measurements showed improvements only for the RET group in terms of blood glucose values after 2 h (14%) and the area under the curve (21%). The blood lipid profile also improved (8%). From muscle biopsy samples prepared using histochemistry, the amount of fiber type IIa increased, and a trend towards a decrease in IIx in the RET group reflected a change to a more oxidative profile in terms of fiber composition. Western blot (to determine the protein content related to the signaling for muscle protein synthesis) showed a rise of 69% in both Akt and mTOR in the RET group; this also showed an increase in mitochondrial proteins for OXPHOS complex II and citrate synthase (both ~30%) and for complex IV (90%), in only the RET group. We demonstrate that this type of progressive resistance training offers various improvements (e.g., strength, power, aerobic capacity, glucose tolerance, and plasma lipid profile).

Clinical relevance of sarcopenia in chronic kidney disease

PURPOSE OF REVIEW

In this article, we review sarcopenia in chronic kidney disease (CKD). We aim to present how definitions of sarcopenia from the general population may pertain to those with CKD, its assessment by clinicians and emerging therapies for sarcopenia in CKD. For this review, we limit our description and recommendations to patients with CKD who are not on dialysis.

RECENT FINDINGS

Poorer parameters of lean mass, strength and physical function are associated with worsening patient-centered outcomes such as limiting mobility, falls and mortality in CKD; however, the magnitude of these associations are different in those with and without CKD. Sarcopenia in CKD is a balance between skeletal muscle regeneration and catabolism, which are both altered in the uremic environment. Multiple pathways are involved in these derangements, which are briefly reviewed. Differences between commonly used terms cachexia, frailty, protein-energy wasting, dynapenia and sarcopenia are described. Therapeutic options in predialysis CKD are not well studied; therefore, we review exercise options and emerging pharmacological therapies.

SUMMARY

Sarcopenia, now with its own International Classification of Diseases, 10th Revision (ICD-10) code, is of importance clinically and should be accounted for in research studies in patients with CKD. Multiple therapies for sarcopenia are in development and will hopefully be available for our patients in the future.

Exercise and CKD: Skeletal Muscle Dysfunction and Practical Application of Exercise to Prevent and Treat Physical Impairments in CKD

Patients with chronic kidney disease experience substantial loss of muscle mass, weakness, and poor physical performance. As kidney disease progresses, skeletal muscle dysfunction forms a common pathway for mobility limitation, loss of functional independence, and vulnerability to disease complications. Screening for those at high risk for mobility disability by self-reported and objective measures of function is an essential first step in developing an interdisciplinary approach to treatment that includes rehabilitative therapies and counseling on physical activity. Exercise has beneficial effects on systemic inflammation, muscle, and physical performance in chronic kidney disease. Kidney health providers need to identify patient and care delivery barriers to exercise in order to effectively counsel patients on physical activity. A thorough medical evaluation and assessment of baseline function using self-reported and objective function assessment is essential to guide an effective individualized exercise prescription to prevent function decline in persons with kidney disease. This review focuses on the impact of kidney disease on skeletal muscle dysfunction in the context of the disablement process and reviews screening and treatment strategies that kidney health professionals can use in clinical practice to prevent functional decline and disability.

Moderate-intensity resistance exercise alters skeletal muscle molecular and cellular structure and function in inactive older adults with knee osteoarthritis

High-intensity resistance exercise (REX) training increases physical capacity, in part, by improving muscle cell size and function. Moderate-intensity REX, which is more feasible for many older adults with disease and/or disability, also increases physical function, but the mechanisms underlying such improvements are not understood. Therefore, we measured skeletal muscle structure and function from the molecular to the tissue level in response to 14 wk of moderate-intensity REX in physically inactive older adults with knee osteoarthritis (n = 17; 70 ± 1 yr). Although REX training increased quadriceps muscle cross-sectional area (CSA), average single-fiber CSA was unchanged because of reciprocal changes in myosin heavy chain (MHC) I and IIA fibers. Intermyofibrillar mitochondrial content increased with training because of increases in mitochondrial size in men, but not women, with no changes in subsarcolemmal mitochondria in either sex. REX increased whole muscle contractile performance similarly in men and women. In contrast, adaptations in single-muscle fiber force production per CSA (i.e., tension) and contractile velocity varied between men and women in a fiber type-dependent manner, with adaptations being explained at the molecular level by differential changes in myosin-actin cross-bridge kinetics and mechanics and single-fiber MHC protein expression. Our results are notable compared with studies of high-intensity REX because they show that the effects of moderate-intensity REX in older adults on muscle fiber size/structure and myofilament function are absent or modest. Moreover, our data highlight unique sex-specific adaptations due to differential cellular and subcellular structural and functional changes.NEW & NOTEWORTHY Moderate-intensity resistance training causes sex-specific adaptations in skeletal muscle structure and function at the cellular and molecular levels in inactive older adult men and women with knee osteoarthritis. However, these responses were minimal compared with high-intensity resistance training. Thus adjuncts to moderate-intensity training need to be developed to correct underlying cellular and molecular structural and functional deficits that are at the root of impaired physical function in this mobility-limited population.

The effects of resistance exercise and oral nutritional supplementation during hemodialysis on indicators of nutritional status and quality of life

BACKGROUND

Protein-energy wasting (PEW) is common in patients undergoing hemodialysis (HD). Studies have assessed the positive effect of oral nutritional supplementation (ONS) or resistance exercise (RE) on nutritional status (NS) markers in patients undergoing HD.

METHODS

The aim of this study was to assess the effect of ONS and RE on NS and the quality of life (QOL) of 36 patients undergoing HD. In a randomized clinical trial, patients were divided into the following two groups: a control group (ONS) that received a can of ONS during their HD sessions and an intervention group (ONS + RE) that received a can of ONS and underwent a 40-min session of RE during their HD sessions. Both interventions lasted 12 weeks. The patients' anthropometric, biochemical, dietetic and bioelectrical impedance measurements as well as their QOL, evaluated using the Kidney Disease Quality of Life Short Form, were recorded.

RESULTS

At baseline, 55.5% of patients presented with PEW according to International Society of Renal Nutrition and Metabolism criteria (20 patients). We found statistically significant changes from baseline in both groups, such as increases in body weight, body mass index, midarm circumference, midarm muscle circumference, triceps skinfold thickness, fat mass percentage, handgrip strength, phase angle and serum albumin. A decrease in the prevalence of PEW was observed in both groups at the end of the intervention. A delta comparison between groups showed no statistically significant differences in the anthropometric and biochemical parameters. No significant improvement was observed in QOL and body composition measured by bioimpedance vector analysis. Dietary energy and protein intake increased significantly during the study period for all patients.

CONCLUSION

Oral nutritional supplementation during HD improves NS. The addition of RE during HD does not seem to augment the acute anabolic effects of intradialytic ONS on NS.

Accurate measurement of mitochondrial DNA deletion level and copy number differences in human skeletal muscle

Accurate and reliable quantification of the abundance of mitochondrial DNA (mtDNA) molecules, both wild-type and those harbouring pathogenic mutations, is important not only for understanding the progression of mtDNA disease but also for evaluating novel therapeutic approaches. A clear understanding of the sensitivity of mtDNA measurement assays under different experimental conditions is therefore critical, however it is routinely lacking for most published mtDNA quantification assays. Here, we comprehensively assess the variability of two quantitative Taqman real-time PCR assays, a widely-applied MT-ND1/MT-ND4 multiplex mtDNA deletion assay and a recently developed MT-ND1/B2M singleplex mtDNA copy number assay, across a range of DNA concentrations and mtDNA deletion/copy number levels. Uniquely, we provide a specific guide detailing necessary numbers of sample and real-time PCR plate replicates for accurately and consistently determining a given difference in mtDNA deletion levels and copy number in homogenate skeletal muscle DNA.

Exercise counselling practices for patients with chronic kidney disease in the UK: a renal multidisciplinary team perspective

BACKGROUND

Patients with chronic kidney disease (CKD) have elevated cardiovascular disease (CVD) risk. Physical activity (PA) is a strong and independent CVD risk factor, and despite the fact that current clinical practice guidelines recommend simultaneous treatment of multiple risk factors for optimum management of CKD, PA is rarely addressed by renal care teams. The aim of this observational cross-sectional survey was to document current exercise/PA practices across renal units in the UK, and capture views and experiences regarding the provision of PA/exercise options for patients with CKD.

METHODS

An 18-item online survey questionnaire regarding exercise counselling practice patterns was administered to 565 multidisciplinary renal care professionals.

RESULTS

142 individuals (25% response rate) completed the questionnaire. Overall, 42% of respondents discussed and encouraged PA, but only 18 and 11% facilitated implementation of PA for their patients. Nephrologists (p < 0.003) were more likely to prescribe or recommend PA compared to professionals with a nursing background and believed that specific renal rehabilitation services, including an active PA/exercise component, should be available to all patients (p < 0.01). The most commonly reported barriers for the development and implementation of PA/exercise options included lack of funding, time, and knowledgeable personnel, such as physiotherapists or other exercise professionals.

CONCLUSION

Beliefs and attitudes towards PA amongst members of the renal multidisciplinary team are encouraging. However there is a big gap between believing in the benefits of PA and promoting/implementing PA for patient benefit. This gap needs to be minimised by at least trying to address some of the reported barriers.

Anabolic exercise in haemodialysis patients: a randomised controlled pilot study

BACKGROUND

The anabolic response to progressive resistance exercise training (PRET) in haemodialysis patients is unclear. This pilot efficacy study aimed to determine whether high-intensity intradialytic PRET could reverse atrophy and consequently improve strength and physical function in haemodialysis patients. A second aim was to compare any anabolic response to that of healthy participants completing the same program.

METHODS

In a single blind controlled study, 23 haemodialysis patients and 9 healthy individuals were randomly allocated to PRET or an attention control (SHAM) group. PRET completed high-intensity exercise leg extensions using novel equipment. SHAM completed low-intensity lower body stretching activities using ultra light resistance bands. Exercises were completed thrice weekly for 12 weeks, during dialysis in the haemodialysis patients. Outcomes included knee extensor muscle volume by magnetic resonance imaging, knee extensor strength by isometric dynamometer and lower body tests of physical function. Data were analysed by a per protocol method using between-group comparisons.

RESULTS

PRET elicited a statistically and clinically significant anabolic response in haemodialysis patients (PRET-SHAM, mean difference [95 % CI]: 193[63 to 324] cm(3)) that was very similar to the response in healthy participants (PRET-SHAM, 169[-41 to 379] cm(3)). PRET increased strength in both haemodialysis patients and healthy participants. In contrast, PRET only enhanced lower body functional capacity in the healthy participants.

CONCLUSIONS

Intradialytic PRET elicited a normal anabolic and strength response in haemodialysis patients. The lack of a change in functional capacity was surprising and warrants further investigation.