Impaired Muscle Oxygen Metabolism in Uremic Children: Improved After Renal Transplantation

Reduced peripheral and respiratory muscle strength in pediatric patients after kidney transplantation

INTRODUCTION

Reduced muscle strength and low-exercise capacity are well documented in adults, but there are few studies examining those impairments in children and adolescents after kidney transplantation. The objective of this study was to evaluate peripheral and respiratory muscle strength and the association with submaximal exercise capacity in children and adolescents after kidney transplant.

METHODS

Forty-seven patients between six and 18 years of age clinically stable after transplantation were included. Peripheral muscle strength (isokinetic and hand-grip dynamometry), respiratory muscle strength (maximal inspiratory and expiratory pressure), and submaximal exercise capacity (six-minute walk test - 6MWT) were assessed.

RESULTS

Patients had a mean age of 13.1 ± 2.7 years and an average of 34 months had elapsed since the transplantation. Flexors of the knee showed a significant reduction in muscle strength (77.3% of predicted) and knee extensors had normal values (105.4% of predicted). Hand-grip strength and maximal respiratory pressures (inspiratory and expiratory) also were significantly lower than expected (p < 0.001). Although distance walked in the 6MWT was significantly lower than predicted (p < 0.001), no significant correlation was found with peripheral and respiratory muscle strength.

CONCLUSION

Children and adolescents after kidney transplantation have reduced peripheral muscle strength of knee flexors, hand-grip, and maximal respiratory pressures. No associations were found between peripheral and respiratory muscle strength and submaximal exercise capacity.

Physical performance capacity after pediatric kidney transplant and clinical parameters associated with physical performance capacity

BACKGROUND

History of chronic kidney disease and kidney transplantation is known to influence physical performance capacity. The aim of this study was to compare the physical performance of pediatric kidney transplant recipients to healthy controls and to find possible correlations between clinical parameters and physical performance capacity.

METHODS

Twenty-four pediatric kidney transplant recipients (62.5% boys) were tested at a median age of 10.8 years. Physical performance capacity was tested with a test set including six different components assessing muscle endurance, strength, speed, and flexibility. The control group consisted of 273 healthy age-matched schoolchildren. Clinical parameters were collected as part of routine follow-up protocol. The majority of patients (62.5%) had congenital nephrotic syndrome of Finnish type (CNS) as primary diagnosis, and therefore, the results of CNS recipients were compared to the other disease groups.

RESULTS

The physical performance capacity in pediatric kidney transplant recipients was lower compared to healthy controls. Surprisingly, no statistically significant correlation was found between graft function and physical performance capacity. The CNS patients scored worse than patients with other diagnoses in all test domains except for sit-and-reach and shuttle run, but the differences did not reach statistical significance.

CONCLUSION

The physical performance of pediatric kidney transplant recipients is reduced, especially in those with congenital nephrotic syndrome. Clinical parameters, including graft function, did not predict physical performance capacity, suggesting that the reduced physical performance seems to be of multivariable cause. A higher resolution version of the Graphical abstract is available as Supplementary information.

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.

Near-infrared spectroscopy for medical applications: Current status and future perspectives

The near-infrared radiation (NIR) window, also known as the "optical window" or "therapeutic window", is the range of wavelengths that has the maximum depth of penetration in tissue. Indeed, because NIR is minimally absorbed by water and hemoglobin, spectra readings can be easily collected from the body surface. Recent reports have shown the potential of NIR spectroscopy in various medical applications, including functional analysis of the brain and other tissues, as well as an analytical tool for diagnosing diseases. The broad applicability of NIR spectroscopy facilitates the diagnosis and therapy of diseases as well as elucidating their pathophysiology. This review introduces recent advances and describes new studies in NIR to demonstrate potential clinical applications of NIR spectroscopy.

Approaches to uremia

The development of dialysis was a dramatic step forward in medicine, allowing people who would soon have died because of lack of kidney function to remain alive for years. We have since found, however, that the "artificial kidney" does not live up fully to its name. Dialysis keeps patients alive but not well. Part of the residual illness that dialysis patients experience is caused by retained waste solutes that dialysis does not remove as well as native kidney function does. New means are available to identify these toxic solutes, about which we currently know remarkably little, and knowledge of these solutes would help us to improve therapy. This review summarizes our current knowledge of toxic solutes and highlights methods being explored to identify additional toxic solutes and to enhance the clearance of these solutes to improve patient outcomes.

Exercise test in pediatric renal transplant recipients and its relationship with their cardiac function

Pediatric kidney transplant recipients are at increased risk of CVD. Exercise test is a good method to evaluate exercise capacity, cardiorespiratory fitness, and risk of potential CVDs. The aim of this study was to assess the exercise capacity in this population and determine its relationship with their cardiac function using conventional and tissue Doppler echocardiography. Exercise test, conventional and tissue Doppler echocardiography were performed on 44 kidney transplant children (age ranging 11-20, 59% male) with acceptable renal function, and the results were compared with their normal healthy counterparts. Our transplant patients achieved significantly lower maximal heart rate, maximal heart rate ratio, total energy expenditure during the exercise, and maximal O2 consumption (Max VO2 ) than the normal group (p < 0.05). No correlation was found between hemoglobin (Hb) level, dialysis duration, kidney function, and the exercise test parameters. Kidney transplant patients had preserved systolic despite diminished diastolic cardiac function compared to the normal children. Our pediatric renal transplant recipients had severely impaired diastolic dysfunction and significantly reduced MaxVO2 compared with their healthy counterparts. No correlation was found between MaxVO2 and measured indices of systolic and diastolic cardiac function.

Exercise limitation following transplantation

Organ transplantation is one of the medical miracles or the 20th century. It has the capacity to substantially improve exercise performance and quality of life in patients who are severely limited with chronic organ failure. We focus on the most commonly performed solid-organ transplants and describe peak exercise performance following recovery from transplantation. Across all of the common transplants, evaluated significant reduction in VO2peak is seen (typically renal and liver 65%-80% with heart and/or lung 50%-60% of predicted). Those with the lowest VO2peak pretransplant have the lowest VO2peak posttransplant. Overall very few patients have a VO2peak in the normal range. Investigation of the cause of the reduction of VO2peak has identified many factors pre- and posttransplant that may contribute. These include organ-specific factors in the otherwise well-functioning allograft (e.g., chronotropic incompetence in heart transplantation) as well as allograft dysfunction itself (e.g., chronic lung allograft dysfunction). However, looking across all transplants, a pattern emerges. A low muscle mass with qualitative change in large exercising skeletal muscle groups is seen pretransplant. Many factor posttransplant aggravate these changes or prevent them recovering, especially calcineurin antagonist drugs which are key immunosuppressing agents. This results in the reduction of VO2peak despite restoration of near normal function of the initially failing organ system. As such organ transplantation has provided an experiment of nature that has focused our attention on an important confounder of chronic organ failure-skeletal muscle dysfunction.

Dysregulated oxygen metabolism of the kidney by uremic toxins: review

Because kidneys consume a large amount of oxygen and are relatively inefficient in oxygen uptake, they are susceptible to hypoxia, especially in patients with advanced chronic kidney disease accompanied by loss of peritubular capillaries. Accumulating evidence suggests that chronic tubulointerstitial hypoxia acts as a final common pathway leading to end-stage renal disease. Some biologically active uremic retention molecules, considered as uremic toxins, accumulate as the renal function declines, and at this moment, more than 90 bioactive uremic toxins have been identified. Uremic toxins per se have been proven to accelerate the progression of renal failure. However, the causal relationship between uremic toxin and tubulointerstitial hypoxia remains unclear. Our studies provided direct evidence that uremic toxin dysregulates oxygen metabolism in the kidney. Indoxyl sulfate (IS), a representative protein-bound uremic toxin, increased oxygen consumption in proximal renal tubules, decreased renal oxygenation, and consequently aggravated hypoxia in the remnant rat kidneys. The increase in tubular oxygen consumption by IS was dependent on sodium-potassium adenosine triphosphatase and oxidative stress. Our work also indicated a possible connection between IS and the desensitization of the oxygen-sensing mechanism in erythropoietin-producing cells, which may partly explain inadequate erythropoietin production in hypoxic kidneys of end-stage renal disease patients. Studies of uremic toxins will open a new avenue in development of novel therapeutic approaches of kidney disease.

Exercise for children with chronic kidney disease and end-stage renal disease

It is well known that adults suffering from chronic kidney disease (CKD) experience muscle wasting and excessive fatigue, which results in a reduced exercise capacity and muscle weakness compared to their healthy counterparts, but research suggests that this can be improved through exercise. There is very limited data available regarding exercise tolerance in children with CKD and even less on the effects of exercise training programs. However, the available evidence does suggest that like adults, children also suffer from poor exercise capacity and reduced muscle strength, although the reasons for these limitations remain unclear. Studies that have attempted to implement exercise training programs in pediatric CKD populations have experienced high dropout rates, suggesting that the approach used to implement such programs in children needs to be different from the approach used for adults. This review summarizes the current knowledge regarding exercise capacity and muscle strength in children with CKD, the methods used to perform these assessments, and the possible causes of physical limitations. The results of exercise training studies, and the potential reasons as to why training programs have proved relatively unsuccessful are also discussed.

Influence of physical activity on cardiorespiratory fitness in children after renal transplantation

BACKGROUND

Cardiorespiratory fitness is significantly reduced in children with end-stage renal disease. The role of renal transplantation in improving cardiorespiratory fitness has not been thoroughly investigated.

METHODS

In this work, we wanted to assess whether, in children after a successful renal transplant, the amount of weekly physical exercise affects cardiorespiratory fitness and left ventricular mass (LVM). The study was conducted on 16 children after renal transplantation and 36 matching healthy controls. Four groups were formed according to the weekly amount of physical exercise; all children received an echocardiogram and underwent a treadmill exercise test according to the Bruce protocol.

RESULTS

Cardiorespiratory fitness is worst in renal transplant children with a weekly physical exercise<3 h; renal transplant children with a physical exercise of 3-5 h per week attain a cardiorespiratory fitness comparable to controls with a sedentary lifestyle (<3-h exercise per week); healthy controls with a weekly physical exercise of 3-5 h per week show the highest levels of cardiorespiratory fitness; the LVM assessed via echocardiography follows the same pattern.

CONCLUSIONS

In children with a successful renal transplant, a weekly physical exercise of 3-5 h significantly improves the cardiorespiratory fitness and the LVM, up to the level of matching healthy controls with a sedentary lifestyle (<3 h exercise per week).

Exercise capacity and body composition in living-donor renal transplant recipients over time

BACKGROUND

Renal transplantation (RTx) restitutes the function of the failing organ and induces convalescence of the entire organism. Our study investigates whether this is accompanied by improvements in cardiovascular function and structural changes.

METHODS

A total of 25 Caucasian patients (14 male, median age 44.2 +/- 9.2 years, BMI 23.7 +/- 4.0 kg/m(2)) were assessed in a prospective trial before, 1, 3 and 12 months after RTx from living donors by clinical examination, cardiopulmonary exercise testing, dual X-ray absorptiometry (DEXA) and analysis of plasma indices.

RESULTS

Creatinine clearance improved from 8.0 +/- 3.1 to 60.9 +/- 18.1 mL/min at 1 month, but declined at 3 (51.6 +/- 16.3 mL/min) and 12 months (53.6 +/- 20.8 mL/min, P = 0.04 versus month 1). Body composition shifted from lean towards fat tissue (25.8 +/- 12.5-31.2 +/- 11.2% body fat content, P = 0.0001). Only baseline lean weight correlated with fat increase over time (r(2) = 0.28, P = 0.008). Patients with fat content above median (n = 13) had a 3-fold increased hazard ratio of infection (CI 1.04-9.41, P = 0.042) and overall hospitalization (hazard ratio 2.95, CI 1.10-7.93, P = 0.03). PeakVO(2) decreased over RTx (23.2 +/- 6.0- 17.6 +/- 5.1 mL/kg/min) and returned to baseline levels not until 1 year later (P < 0.001). After an initial decline, muscle oxidative capacity (peakVO(2)/lean mass) improved from 33.6 +/- 10.1 to 35.0 +/- 8.2 mL/kg/min at 12 months after RTx (P < 0.001).

CONCLUSIONS

After RTx, body composition shifted continuously towards fat tissue, and baseline lean weight significantly correlated with fat increase over time. Both severe infections and hospitalizations are associated with a higher fat content before RTx. Exercise capacity (peakVO(2)) worsened after RTx and restitutes during follow-up, with muscle quality (peakVO(2)/lean) even exceeding baseline levels after 12 months.

Low-volume muscular endurance and strength training during 3-week forearm immobilization was effective in preventing functional deterioration

Purpose

The purpose of this study was to determine whether endurance and strength hand grip exercises during 3-week upper limb immobilization preserve muscle oxidative capacity, endurance performance and strength.

Methods

Ten healthy adult men underwent non-dominant forearm immobilization by plaster cast for 21 days. Five healthy adult subjects were designated as the immobilization (IMM) group and five were designated as the immobilization + training (IMM+TRN) group. Grip strength, forearm circumference, dynamic handgrip endurance and muscle oxygenation response were measured before and after the 21 day immobilization period. Using near-infrared spectroscopy (NIRS), muscle oxygen consumption recovery (VO₂mus) was recorded after a submaximal exercise and the recovery time constant (TcVO₂mus) was calculated. Reactive hyperemic oxygenation recovery was evaluated after 5 minutes ischemia. Two training programs were performed by the IMM+TRN group twice a week. One exercise involved a handgrip exercise at 30% maximum voluntary contraction (MVC) at a rate of 1 repetition per 1 second until exhaustion (about 60 seconds). The other involved a handgrip exercise at 70% MVC for 2 seconds with a 2 second rest interval, repeated 10 times (40 seconds).

Results

There was a significant group-by-time interaction between the IMM and IMM+TRN groups in the TcVO₂mus (p = 0.032, F = 6.711). A significant group-by-time interaction was observed between the IMM and IMM+TRN groups in the MVC (p = 0.001, F = 30.415) and in grip endurance (p = 0.014, F = 9.791). No significant group-by-time interaction was seen in forearm circumference and reactive hyperemic oxygenation response either in IMM or IMM+TRN group.

Conclusion

The training programs during immobilization period used in this experiment were effective in preventing a decline in muscle oxidative function, endurance and strength.

Decreased maximal aerobic capacity in pediatric chronic kidney disease

Adult and pediatric patients with ESRD have impaired maximum oxygen consumption (VO(2) max), a reflection of the cardiopulmonary system's ability to meet increased metabolic demands. We sought to determine factors associated with decreased VO(2) max in pediatric patients with different stages of CKD. VO(2) max was measured using a standardized exercise testing protocol in patients with stage 2 to 4 chronic kidney disease (CKD) (n = 46), in renal transplant recipients (n = 22), in patients treated with maintenance hemodialysis (n = 12), and in age-matched healthy controls (n = 33). VO(2) max was similar between children with stage 2 CKD and controls, whereas lower VO(2) max was observed among children with stage 3 to 4 CKD, those treated with hemodialysis, and transplant recipients. In univariate analysis, VO(2) max was significantly associated with body mass index, resting heart rate, C-reactive protein, serum triglycerides, serum creatinine, and measures of diastolic function; no significant associations with left ventricular structure or systolic function were identified. In multivariate regression analysis, patient category versus control and the presence of diastolic dysfunction were independent predictors of lower VO(2) max. These results suggest that aerobic capacity is decreased in the early stages of CKD in children and that lower VO(2) max can be predicted by the presence of diastolic dysfunction, even if systolic function is normal.

Rehabilitative training program for end-stage renal disease patients

A 4–5. (vég-)stádiumú és transzplantált vesebetegek izomereje, állóképessége, cardiovascularis kockázati tényezői, életminősége és a dialízishatásfoka is jelentősen javul a heti 3 × 30–60 perces, 45–60%-os intenzitású testmozgás során, amelyet többnyire a dialízis alatt végez a beteg. A korlátozó tényezők és ellenjavallatok figyelembevételével a vesebetegek többsége számára is kínálni kellene a rehabilitációs programokat.