Muscle mass, muscle strength and mortality in kidney transplant recipients: results of the TransplantLines Biobank and Cohort Study

Thresholds of handgrip strength for all-cause mortality in patients with chronic kidney disease: a secondary systematic review with dose-response meta-analysis

BACKGROUND

Although handgrip strength is associated with all-cause mortality in patients with chronic kidney disease (CKD), whether this relationship is dose-related is unknown. Therefore, we examined dose-response relationships between handgrip strength and all-cause mortality in CKD patients based on previous studies by meta-analysis.

METHODS

Data sources included three electronic databases (PubMed, Web of Science, and Embase) from inception through October 2023. The included cohort was a CKD population not limited to disease stage, and their handgrip strength was objectively measured. Two researchers independently screened studies, extracted data, and assessed the risk of bias. We utilized estimates of handgrip strength categories using robust-error meta-regression (REMR), pooled study-specific estimates, and established dose-response relationships. Outcomes of interest included only all-cause mortality.

RESULTS

A total of 18 studies with 4810 participants (aged 47-71 years) were included. REMR modeling showed a U-shaped trend of association between handgrip strength and all-cause mortality in patients with CKD. Higher handgrip strength values, from 10 kg to approximately 28 kg, were associated with lower mortality risk. After that, the risk of death increased slightly.

CONCLUSION

A U-shaped association exists between handgrip strength and all-cause mortality risk in CKD patients. Future studies with quantitative measurements for each CKD stage will help to determine precise relative risk estimates between handgrip strength and mortality risk in patients with different stages of CKD.

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.

Myosteatosis is associated with poor survival after kidney transplantation: a large retrospective cohort validation

PURPOSE

We aim to establish diagnostic thresholds of sarcopenia and myosteatosis based on CT measurements, and to validate their prognostic value in a large cohort of kidney transplant recipients.

METHODS

Local healthy population with abdominal CT between 2010 and 2022, and patients underwent kidney transplantation between 2015 and 2019 at our center were retrospectively included. The skeletal muscle index and muscle attenuation of abdominal muscles were calculated based on CT image at the middle of the third lumbar vertebra. Primary endpoints included all-cause mortality and death censored allograft survival.

RESULTS

Age- and sex-specific thresholds for sarcopenia and myosteatosis were established based on 1598 healthy local population. The final patient cohort consisted of 992 kidney transplant recipients (median age 34 years, interquartile range 28-44 years; 694 males), including 33 (3.3%) with sarcopenia and 95 (9.5%) with myosteatosis. Multivariate analysis revealed myosteatosis (adjusted hazard ratio = 3.08, p = 0.022) was an independent baseline risk factor of mortality after adjusting for age, the history of cancer, and the history of cardiovascular event. Multivariate analysis found preemptive transplantation (adjusted hazard ratio = 0.36, p = 0.037) was an independent protective factor of allograft loss. No difference was found in the prognosis between kidney transplant recipients with and without sarcopenia.

CONCLUSION

Myosteatosis was an independent risk factor of mortality after kidney transplantation, but sarcopenia was not. Neither sarcopenia nor myosteatosis was associated with graft loss.

Assessing nutrition status, sarcopenia, and frailty in adult transplant recipients

The assessment of nutrition status, sarcopenia, and frailty holds significant relevance in the context of adult transplantation, as these factors are associated with an unfavorable prognosis; thus, transplant candidates must undergo a full nutrition assessment. Screening tools may be used to prioritize patients, this can be done using the Nutrition Risk Screening 2002 or Royal Free Hospital-Nutritional Prioritizing Tool. Subsequently, a thorough nutrition-focused physical examination should be conducted to evaluate clinical signs of nutrition deficiencies, fat and muscle loss, and fluid overload; dietary history and current intake must also be assessed. Apart from physical examination, specific testing for sarcopenia and frailty are recommended. For sarcopenia assessment, specifically for muscle quantification, the gold standard is the cross-sectional measurement of the muscle at L3 obtained from a computed tomography scan or magnetic resonance imaging; dual-energy x-ray absorptiometry is also a good tool especially when appendicular skeletal muscle index is calculated. Other more readily available options include phase angle from bioelectrical impedance or bioimpedance spectroscopy. In the sarcopenia assessment, muscle function evaluation is required, handgrip strength stands as the primary test for this purpose; this test is also part of the subjective global assessment and is included in some frailty scores. Finally, for frailty assessment, the Short Physical Performance Battery is useful for evaluating physical frailty, and for a multidimensional evaluation, the Fried frailty phenotype can be used. Specifically for liver transplant candidates, the use of Liver Frailty Index is recommended.

Handgrip strength and all-cause mortality in patients with chronic kidney disease: an updated systematic review and meta-analysis of cohort studies

OBJECTIVES

In observational studies, handgrip strength (HGS), a prognostic marker for healthy aging, has been associated with several chronic disease outcomes. The present systematic review and meta-analysis aimed to determine the quantitative relationship between HGS and the risk of all-cause mortality in patients with chronic kidney disease (CKD).

METHODS

Search PubMed, Embase, and Web of Science databases. The search was performed from inception to July 20, 2022, and the search was updated in February 2023. Cohort studies were included exploring the relationship between handgrip strength and the risk of all-cause mortality in patients with chronic kidney disease. Effect estimates and 95% confidence intervals (95% CI) were extracted from the studies to perform pooling. The quality of included studies was assessed using the Newcastle-Ottawa scale. We evaluated the overall certainty of evidence using Grades of Recommendation, Assessment, Development, and Evaluation (GRADE).

RESULTS

This systematic review included 28 articles. A random-effects meta-analysis that included 16,106 patients with CKD showed that participants with lower HGS had an increased mortality risk of 96.1% compared to higher HGS (HR: 1.961; 95% CI 1.591-2.415) (GRADE: very low). Moreover, this association was independent of baseline mean age and follow-up time. In 2,967 patients with CKD, a random-effects model-based meta-analysis showed that for each 1-unit increase in HGS, the risk of death in patients with CKD was reduced by 3.9% (HR: 0.961; 95% CI 0.949-0.974) (GRADE: moderate).

CONCLUSIONS

In patients with CKD, better HGS is associated with a lower risk of all-cause mortality. This study supports using HGS as a strong predictor of mortality in this population.

Iron deficiency is related to lower muscle mass in community-dwelling individuals and impairs myoblast proliferation

BACKGROUND

Loss of muscle mass is linked with impaired quality of life and an increased risk of morbidity and premature mortality. Iron is essential for cellular processes such as energy metabolism, nucleotide synthesis and numerous enzymatic reactions. As the effects of iron deficiency (ID) on muscle mass and function are largely unknown, we aimed to assess the relation between ID and muscle mass in a large population-based cohort, and subsequently studied effects of ID on cultured skeletal myoblasts and differentiated myocytes.

METHODS

In a population-based cohort of 8592 adults, iron status was assessed by plasma ferritin and transferrin saturation, and muscle mass was estimated using 24-h urinary creatinine excretion rate (CER). The relationships of ferritin and transferrin saturation with CER were assessed by multivariable logistic regression. Furthermore, mouse C2C12 skeletal myoblasts and differentiated myocytes were subjected to deferoxamine with or without ferric citrate. Myoblast proliferation was measured with a colorimetric 5-bromo-2'-deoxy-uridine ELISA assay. Myocyte differentiation was assessed using Myh7-stainings. Myocyte energy metabolism, oxygen consumption rate and extracellular acidification rate were assessed using Seahorse mitochondrial flux analysis, and apoptosis rate with fluorescence-activated cell sorting. RNA sequencing (RNAseq) was used to identify ID-related gene and pathway enrichment in myoblasts and myocytes.

RESULTS

Participants in the lowest age- and sex-specific quintile of plasma ferritin (OR vs middle quintile 1.62, 95% CI 1.25-2.10, P < 0.001) or transferrin saturation (OR 1.34, 95% CI 1.03-1.75, P = 0.03) had a significantly higher risk of being in the lowest age- and sex-specific quintile of CER, independent of body mass index, estimated GFR, haemoglobin, hs-CRP, urinary urea excretion, alcohol consumption and smoking status. In C2C12 myoblasts, deferoxamine-induced ID reduced myoblast proliferation rate (P-trend <0.001) but did not affect differentiation. In myocytes, deferoxamine reduced myoglobin protein expression (-52%, P < 0.001) and tended to reduce mitochondrial oxygen consumption capacity (-28%, P = 0.10). Deferoxamine induced gene expression of cellular atrophy markers Trim63 (+20%, P = 0.002) and Fbxo32 (+27%, P = 0.048), which was reversed by ferric citrate (-31%, P = 0.04 and -26%, P = 0.004, respectively). RNAseq indicated that both in myoblasts and myocytes, ID predominantly affected genes involved in glycolytic energy metabolism, cell cycle regulation and apoptosis; co-treatment with ferric citrate reversed these effects.

CONCLUSIONS

In population-dwelling individuals, ID is related to lower muscle mass, independent of haemoglobin levels and potential confounders. ID impaired myoblast proliferation and aerobic glycolytic capacity, and induced markers of myocyte atrophy and apoptosis. These findings suggest that ID contributes to loss of muscle mass.

Creatine and creatinine quantified using nuclear magnetic resonance: A method validation study and clinical associations between circulating creatine and fatigue in kidney transplant recipients

BACKGROUND

A potential contributor to fatigue in kidney transplant recipients (KTR) may be impaired creatine homeostasis. We developed and validated a high-throughput NMR assay allowing for simultaneous measurement of circulating creatine and creatinine, and determined plasma creatine and estimated intramuscular creatine concentrations in KTRs, delineated their determinants and explored their associations with self-reported fatigue.

METHODS

An NMR assay was developed and validated for measurement of circulating creatinine and creatine concentrations. Plasma creatine and creatinine concentrations were measured in 618 KTR. Fatigue was assessed using the checklist individual strength. Associations of creatine parameters with fatigue was assessed using linear mixed effect models.

RESULTS

The NMR-based assay had good sensitivity, precision and demonstrated linearity across a large range of values. Among KTR, the mean age was 56 ± 13 years, 62% were men and eGFR was 54 ± 18 ml/min/1.73 m2. Plasma creatine concentration was 27 [19-39] µmol/L. Estimated intramuscular creatine concentration was 27 ± 7 mmol/kg. Higher plasma creatine concentration and higher estimated intramuscular creatine concentration were independently associated with a lower total fatigue score and less motivation problems.

CONCLUSION

An NMR method for measurement of circulating creatine and creatinine which offers the potential for accurate and efficient quantification was developed. The found associations suggest that improving creatine status may play a beneficial role in mitigating fatigue.