Insulin resistance is a significant determinant of sarcopenia in advanced kidney disease

Intermuscular adipose tissue accumulation is associated with higher tissue sodium in healthy individuals

BACKGROUND AND AIMS

High tissue sodium accumulation and intermuscular adipose tissue (IMAT) are associated with aging, type 2 diabetes, and chronic kidney disease. In this study, we aim to investigate whether high lower-extremity tissue sodium accumulation relates to IMAT quantity and whether systemic inflammatory mediators and adipocytokines contribute to such association.

METHODS

Tissue sodium content and IMAT accumulation (percentage of IMAT area to muscle area) were measured in 83 healthy individuals using sodium imaging (23Na-MRI) and proton (1H-MRI) imaging of the calf. Insulin sensitivity was assessed by glucose disposal rate (GDR) measured with the hyperinsulinemic-euglycemic clamp.

RESULTS

Median (interquartile range) muscle and skin sodium contents were 16.6 (14.9, 19.0) and 12.6 (10.9, 16.7) mmol/L, respectively. Median IMAT was 3.69 (2.80, 5.37) %. In models adjusted for age, sex, BMI, GDR, adiponectin, and high-sensitivity C-reactive protein, increasing tissue sodium content was significantly associated with higher IMAT quantity (p = 0.018 and 0.032 for muscle and skin tissue sodium, respectively). In subgroup analysis stratified by sex, skin sodium was significantly associated with IMAT only among men. In interaction analysis, the association between skin sodium and IMAT was greater with increasing levels of high-sensitivity C-reactive protein and interleukin-6 (p for interaction = 0.022 and 0.006, respectively).

CONCLUSIONS

Leg muscle and skin sodium are associated with IMAT quantity among healthy individuals. The relationship between skin sodium and IMAT may be mediated by systemic inflammation.

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.

A randomized controlled pilot trial of anakinra and pioglitazone for protein metabolism in patients on maintenance haemodialysis

BACKGROUND

Chronic inflammation and insulin resistance are highly prevalent in patients on maintenance haemodialysis (MHD) and are strongly associated with protein energy wasting. We conducted a pilot, randomized, placebo-controlled trial of recombinant human interleukin-1 receptor antagonist (IL-1ra) and pioglitazone to explore the safety, feasibility and efficacy for insulin-mediated protein metabolism in patients undergoing MHD.

METHODS

Twenty-four patients were randomized to receive IL-1ra, pioglitazone or placebo for 12 weeks. Changes in serum inflammatory markers and insulin-mediated protein synthesis, breakdown and net balance in the whole-body and skeletal muscle compartments were assessed using hyperinsulinaemic-hyperaminoacidemic clamp technique at baseline and Week 12.

RESULTS

Among 24 patients, median (interquartile range) age was 51 (40, 61), 79% were African American and 21% had diabetes mellitus. All patients initiated on intervention completed the study, and no serious adverse events were observed. There was a statistically significant decrease in serum high-sensitivity C-reactive protein in the pioglitazone group compared with placebo, but not in the IL-1ra group. No significant differences in the changes of whole-body or skeletal muscle protein synthesis, breakdown and net balance were found between the groups.

CONCLUSIONS

In this pilot study, there were no statistically significant effects of 12 weeks of IL-1ra or pioglitazone on protein metabolism in patients on MHD.

CLINICALTRIALS

gov registration: NCT02278562.

Muscle Atrophy in CKD: A Historical Perspective of Advancements in Its Understanding

OBJECTIVE

This perspective reviews the seminal clinical and experimental observations that led to today's current mechanistic model of muscle protein loss (wasting) in patients with chronic kidney disease (CKD).

RESULTS AND CONCLUSION

Early International Society of Renal Nutrition and Metabolism (ISRNM) meetings facilitated discussions and hypotheses about the causes of muscle wasting in CKD. It became widely recognized that wasting is common and correlated with increased risks of mortality and morbidity. Although anorexia and dietary restrictions contribute to muscle loss, several features of CKD-associated wasting cannot be explained by malnutrition alone. The protein catabolism-inducing actions of metabolic acidosis, inflammation, insulin resistance, endocrine disorders and uremic toxins were progressively identified. Continued research to understand the interactions of inflammation, anabolic resistance, mitochondrial dysfunction, exercise, and nutrition on muscle protein turnover in patients with CKD will hopefully accelerate discoveries and treatments to ameliorate muscle wasting as well as the progression of CKD.

Clinical features and molecular mechanism of muscle wasting in end stage renal disease

Muscle wasting in end-stage renal disease (ESRD) is an escalating issue due to the increasing global prevalence of ESRD and its significant clinical impact, including a close association with elevated mortality risk. The phenomenon of muscle wasting in ESRD, which exceeds the rate of muscle loss observed in the normal aging process, arises from multifactorial processes. This review paper aims to provide a comprehensive understanding of muscle wasting in ESRD, covering its epidemiology, underlying molecular mechanisms, and current and emerging therapeutic interventions. It delves into the assessment techniques for muscle mass and function, before exploring the intricate metabolic and molecular pathways that lead to muscle atrophy in ESRD patients. We further discuss various strategies to mitigate muscle wasting, including nutritional, pharmacological, exercise, and physical modalities intervention. This review seeks to provide a solid foundation for future research in this area, fostering a deeper understanding of muscle wasting in ESRD, and paving the way for the development of novel strategies to improve patient outcomes. [BMB Reports 2023; 56(8): 426-438].

Exercise mitigates Dapagliflozin-induced skeletal muscle atrophy in STZ-induced diabetic rats

BACKGROUND

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) are commonly used in the management of type 2 diabetes mellitus (T2DM) and have been found to worsen the reduction of skeletal muscle mass in individuals with T2DM. This study aims to examine the potential of exercise in mitigating the skeletal muscle atrophy induced by SGLT2i treatment.

METHODS

A rat model of T2DM (40 male Sprague-Dawley rats; T2DM induced by a combination of high-fat diet and streptozotocin) was used to examine the effects of six-week treatment with Dapagliflozin (DAPA, SGLT2i) in combination with either aerobic exercise (AE) or resistance training (RT) on skeletal muscle. T2DM-eligible rats were randomized into the T2DM control group (CON, n = 6), DAPA treatment group (DAPA, n = 6), DAPA combined with aerobic exercise intervention group (DAPA + AE, n = 6), and DAPA combined with resistance training intervention group (DAPA + RT, n = 6). To assess the morphological changes in skeletal muscle, myosin ATPase and HE staining were performed. mRNA expression levels of Atrogin-1, MuRF1, and Myostatin were determined using quantitative PCR. Furthermore, protein expression levels of AKT, p70S6K, mTOR, FoXO1/3A, NF-κB, and MuRF1 were examined through western blotting.

RESULTS

Both the administration of DAPA alone and the combined exercise intervention with DAPA resulted in significant reductions in blood glucose levels and body weight in rats. However, DAPA alone administration led to a decrease in skeletal muscle mass, whereas RT significantly increased skeletal muscle mass and muscle fiber cross-sectional area. The DAPA + RT group exhibited notable increases in both total protein levels and phosphorylation levels of AKT and p70S6K in skeletal muscle. Moreover, the DAPA, DAPA + AE, and DAPA + RT groups demonstrated downregulation of protein expression (FoXO1/3A) and mRNA levels (Atrogin-1, MuRF1, and Myostatin) associated with muscle atrophy.

CONCLUSIONS

Our findings provide support for the notion that dapagliflozin may induce skeletal muscle atrophy through mechanisms unrelated to protein metabolism impairment in skeletal muscle, as it does not hinder protein metabolic pathways while reduces muscle atrophy-related genes. Additionally, our observations reveal that RT proves more effective than AE in enhancing skeletal muscle mass and muscle fiber cross-sectional area in rats with T2DM by stimulating protein anabolism within the skeletal muscle.

High tissue-sodium associates with systemic inflammation and insulin resistance in obese individuals

BACKGROUND AND AIMS

High sodium intake is associated with obesity and insulin resistance, and high extracellular sodium content may induce systemic inflammation, leading to cardiovascular disease. In this study, we aim to investigate whether high tissue sodium accumulation relates with obesity-related insulin resistance and whether the pro-inflammatory effects of excess tissue sodium accumulation may contribute to such association.

METHODS AND RESULTS

In a cross-sectional study of 30 obese and 53 non-obese subjects, we measured insulin sensitivity determined as glucose disposal rate (GDR) using hyperinsulinemic euglycemic clamp, and tissue sodium content using 23Na magnetic resonance imaging. Median age was 48 years, 68% were female and 41% were African American. Median (interquartile range) BMI was 33 (31.5, 36.3) and 25 (23.5, 27.2) kg/m2 in the obese and non-obese individuals, respectively. In obese individuals, insulin sensitivity negatively correlated with muscle (r = -0.45, p = 0.01) and skin sodium (r = -0.46, p = 0.01). In interaction analysis among obese individuals, tissue sodium had a greater effect on insulin sensitivity at higher levels of high-sensitivity C-reactive protein (p-interaction = 0.03 and 0.01 for muscle and skin Na+, respectively) and interleukin-6 (p-interaction = 0.024 and 0.003 for muscle and skin Na+, respectively). In interaction analysis of the entire cohort, the association between muscle sodium and insulin sensitivity was stronger with increasing levels of serum leptin (p-interaction = 0.01).

CONCLUSIONS

Higher muscle and skin sodium are associated with insulin resistance in obese patients. Whether high tissue sodium accumulation has a mechanistic role in the development of obesity-related insulin resistance through systemic inflammation and leptin dysregulation remains to be examined in future studies.

CLINICALTRIALS

gov registration: NCT02236520.

Organ Crosstalk Contributes to Muscle Wasting in Chronic Kidney Disease

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

Gender difference in association between low muscle mass and risk of non-alcoholic fatty liver disease among Chinese adults with visceral obesity

Background and aims

Although the association between low muscle mass and the risk of non-alcoholic fatty liver disease is well-known, it has not been explored in viscerally obese populations by gender. Besides, whether low muscle mass still increases the NAFLD risk in subjects with visceral obesity, independent of obesity, is still unknown. The aim of this study was to explore the gender-specific association between low muscle mass and the risk of non-alcoholic fatty liver disease (NAFLD) in subjects with visceral obesity.

Methods

Overall, 1,114 participants aged 19-89 years were recruited in this retrospective study. Liver disease was diagnosed by hepatic ultrasound. Skeletal muscle mass was estimated by bioimpedance analysis and defined by the appendicular skeletal muscle index (ASMI). Gender-specific differences in the ASMI value were compared between NAFLD and control groups. Restricted cubic spline and multivariate logistic regression were performed to analyze the association (stratified by gender and age) between the ASMI and the risk of NAFLD, respectively.

Results

Middle-aged females (40-60 years) and males (of any age) with NAFLD had a significantly lower ASMI compared with controls (P-value < 0.05). An inverse linear association was found between the ASMI and risk of NAFLD (all P _{fornon-linearity} > 0.05). Lower quartiles of the ASMI conferred independent risk of NAFLD compared to higher quartiles (all P for trend < 0.001). Low muscle mass conferred a higher risk of NAFLD in middle-aged females (adjusted odds ratio = 2.43, 95% confidence interval: 1.19-4.95) and males [18-39 years: 3.76 (1.79-7.91); 40-60 years: 4.50 (2.16-9.39); and >60 years: 4.10 (1.13-14.84)]. Besides, Low muscle mass and low muscle mass with obesity increase the risk of developing NAFLD, independent of obesity.

Conclusion

Among those with visceral obesity, low muscle mass increased the risk of NAFLD in males of any age, and middle-aged females, this may be explained by the postmenopausal decline in estrogen.

Muscle plasticity is influenced by renal function and caloric intake through the FGF23-vitamin D axis

Skeletal muscle, the main metabolic engine in the body of vertebrates, is endowed with great plasticity. The association between skeletal muscle plasticity and two highly prevalent health problems: renal dysfunction and obesity, which share etiologic links as well as many comorbidities, is a subject of great relevance. It is important to know how these alterations impact on the structure and function of skeletal muscle because the changes in muscle phenotype have a major influence on the quality of life of the patients. This literature review aims to discuss the influence of a nontraditional axis involving kidney, bone, and muscle on skeletal muscle plasticity. In this axis, the kidneys play a role as the main site for vitamin D activation. Renal disease leads to a direct decrease in 1,25(OH)₂-vitamin D, secondary to reduction in renal functional mass, and has an indirect effect, through phosphate retention, that contributes to stimulate fibroblast growth factor 23 (FGF23) secretion by bone cells. FGF23 downregulates the renal synthesis of 1,25(OH)₂-vitamin D and upregulates its metabolism. Skeletal production of FGF23 is also regulated by caloric intake: it is increased in obesity and decreased by caloric restriction, and these changes impact on 1,25(OH)₂-vitamin D concentrations, which are decreased in obesity and increased after caloric restriction. Thus, both phosphate retention, that develops secondary to renal failure, and caloric intake influence 1,25(OH)₂-vitamin D that in turn plays a key role in muscle anabolism.

Triglyceride-Glucose Index May Predict Renal Survival in Patients with IgA Nephropathy

Background: The triglyceride−glucose (TyG) index is a simple, novel and reliable surrogate marker of insulin resistance. However, evidence for the prognostic impact of an elevated TyG index on IgA nephropathy (IgAN) is limited. Therefore, we evaluated the relationship between the TyG index and the risk of renal progression in IgAN. Method: This cohort study involved biopsy-proven IgAN between January 2009 and December 2018 in West China Hospital, in which patients were assigned to two groups based on the cut-off value of TyG using receiver operating characteristic (ROC) curves. A 1:1 matched-pair analysis was established to optimize the bias in IgAN by propensity score matching (PSM). The TyG index was calculated as ln [fasting triglyceride (mg/dL) × fasting glucose (mg/dL)/2]. The composite endpoint was defined by eGFR decreased ≥50% of the baseline level, end-stage kidney disease (ESKD), renal transplantation and/or death. Univariable and multivariable Cox proportional hazard models were applied to confirm the predictive value of the optimal marker. Results: Before PSM, a total of 1210 participants were ultimately included. During a median follow-up period of 55.8 months (range 37.20−79.09 months), 129 participants progressed to the composite endpoint (10.7%). After PSM, 366 patients were enrolled in the matched cohort, of whom 34 (9.3%) patients reached the endpoints. Based on the cut-off value of the TyG index, patients were divided into the low TyG index group (TyG ≤ 8.72, n = 690) and the high TyG index group (TyG > 8.72, n = 520). Further analysis demonstrated that a higher TyG index was significantly associated with a higher risk of reaching composite endpoints in IgAN patients in both the unmatched and matched cohorts (before PSM: HR 2.509, 95% CI 1.396−4.511, p = 0.002; after PSM: HR 2.654, 95% CI 1.299−5.423, p = 0.007). Conclusion: A high TyG index is associated with a higher risk of renal progression.

A Novel Approach for Managing Protein-Energy Wasting in People With Kidney Failure Undergoing Maintenance Hemodialysis: Rationale and Call for Trials

Protein-energy wasting (PEW) is a unique presentation of protein-energy malnutrition in people with kidney disease that is characterized by body protein catabolism exceeding anabolism. PEW is especially common in patients undergoing maintenance hemodialysis (HD) treatment. Dietary guidelines for managing PEW in HD patients primarily focus on protein adequacy and typically promote the intake of animal-based protein foods. Although intake of protein and essential amino acids is important for protein synthesis, the emphasis on protein adequacy largely fails to address-and may actually exacerbate-many of the root causes of PEW. This perspective examines the dietary determinants of PEW in people undergoing HD treatment, with an emphasis on upstream disease-related factors that reduce dietary protein utilization and impair dietary intakes. From this, we present a theoretical diet model for managing PEW that includes etiology-based dietary strategies to address barriers to intake and treat disease-related factors, as well as supportive dietary strategies to promote adequate energy and protein intakes. Given the complexity of diet-disease interactions in the pathogenesis of PEW, and its ongoing burden in HD patients, interventional trials are urgently needed to evaluate alternative diet therapy approaches for PEW in this population.

The Effect of Nutrition and Exercise on Body Composition, Exercise Capacity, and Physical Functioning in Advanced CKD Patients

Patients with stages 4 and 5 chronic kidney disease (CKD), and particularly chronic dialysis patients, commonly are found to have substantially reduced daily physical activity in comparison to age- and sex-matched normal adults. This reduction in physical activity is associated with a major decrease in physical exercise capacity and physical performance. The CKD patients are often physically deconditioned, and protein energy wasting (PEW) and frailty are commonly present. These disorders are of major concern because physical dysfunction, muscle atrophy, and reduced muscle strength are associated with poor quality of life and increased morbidity and mortality in CKD and chronic dialysis patients. Many randomized controlled clinical trials indicate that when CKD and chronic dialysis are provided nutritional supplements or undergo exercise training their skeletal muscle mass and exercise capacity often increase. It is not known whether the rise in skeletal muscle mass and exercise capacity associated with nutritional support or exercise training will reduce morbidity or mortality rates. A limitation of these clinical trials is that the sample sizes of the different treatment groups were small. The aim of this review is to discuss the effects of nutrition and exercise on body composition, exercise capacity, and physical functioning in advanced CKD patients.

Association between Sarcopenia and Insulin-Like Growth Factor-1, Myostatin, and Insulin Resistance in Elderly Patients Undergoing Hemodialysis

Sarcopenia is common in hemodialysis patients, especially in the elderly patients undergoing hemodialysis. Various factors may contribute to the occurrence of sarcopenia, such as anabolic and catabolic imbalance. This study aims to investigate the correlation of insulin-like growth factor-1 (IGF-1) levels as an anabolic factor, myostatin levels, and insulin resistance as catabolic factors with sarcopenia in the pathogenesis of sarcopenia in elderly patients undergoing hemodialysis. A total of 40 subjects aged 60 years or more who undergoing hemodialysis in Dr. Soetomo Hospital Surabaya were included in this cross-sectional study. Sarcopenia was diagnosed according to Asian Working Group Sarcopenia 2019 criteria. IGF-1, myostatin, and insulin resistance levels were measured once before hemodialysis. Subjects with sarcopenia diagnosis were 33 (82.5%), that is, 19 (47.5%) men and 14 (35%) women. There were 28 (70%) of the subjects diagnosed with severe sarcopenia. Furthermore, there were significant differences in the characteristics and geriatric parameters between the sarcopenia and nonsarcopenia groups. There were differences between the two groups in hemoglobin levels, IGF-1 levels, myostatin levels, homeostasis model assessment-insulin resistance (HOMA-IR) levels, muscle mass, handgrip strength, body mass index status, mini nutritional assessment status, and physical activity scale for elderly status (all p < 0.05). Correlation analyses showed that IGF-1 levels negatively correlated with sarcopenia status in elderly patients undergoing hemodialysis (p < 0.05). On the contrary, myostatin and HOMA-IR levels were positively correlated with sarcopenia status in elderly patients undergoing hemodialysis (all p < 0.05). Based on this recent study, IGF-1, myostatin, and insulin resistance were significantly correlated with sarcopenia in elderly patients undergoing hemodialysis.

Elevated TyG Index Predicts Incidence of Contrast-Induced Nephropathy: A Retrospective Cohort Study in NSTE-ACS Patients Implanted With DESs

BACKGROUND

Triglyceride-glucose (TyG) index is a reliable and specific biomarker for insulin resistance and is associated with renal dysfunction. The present study sought to explore the relationship between TyG index and the incidence of contrast-induced nephropathy (CIN) in non-ST elevation acute coronary syndrome (NSTE-ACS) patients implanted with drug-eluting stents (DESs).

METHODS

A total of 1108 participants were recruited to the study and assigned to two groups based on occurrence of CIN. TyG index was calculated as ln [fasting triglycerides (mg/dL) × fasting blood glucose (mg/dL)/2]. Baseline characteristics and incidence of CIN were compared between the two groups. Logistic regression analysis was performed to evaluate the relationship between TyG index and CIN.

RESULTS

The results showed that 167 participants (15.1%) developed CIN. Subjects in the CIN group had a significantly higher TyG index compared with subjects in the non-CIN group (8.9 ± 0.7 vs. 9.3 ± 0.7, P<0.001). TyG index was significantly correlated with increased risk of CIN after adjusting for confounding factors irrespective of diabetes mellitus status and exhibited a J-shaped non-linear association. Subgroup analysis showed a significant gender difference in the relationship between TyG index and CIN. Receiver operating characteristic (ROC) curve analysis indicated that the risk assessment performance of TyG index was superior compared with other single metabolic indexes. Addition of TyG index to the baseline model increased the area under the curve from 0.713 (0.672-0.754) to 0.742 (0.702-0.782) and caused a reclassification improvement of 0.120 (0.092-0.149).

CONCLUSION

The findings from the present study show that a high TyG index is significantly and independently associated with incidence of CIN in NSTE-ACS patients firstly implanted with DESs. Routine preoperative assessment of TyG index can alleviate CIN and TyG index provides a potential target for intervention in prevention of CIN.

Effects of hormonal changes on sarcopenia in chronic kidney disease: where are we now and what can we do?

Sarcopenia or muscle wasting is a progressive and generalized skeletal muscle disorder involving the accelerated loss of muscle mass and function, often associated with muscle weakness (dynapenia) and frailty. Whereas primary sarcopenia is related to ageing, secondary sarcopenia happens independent of age in the context of chronic disease states such as chronic kidney disease (CKD). Sarcopenia has become a major focus of research and public policy debate due to its impact on patient's health-related quality of life, health-care expenditure, morbidity, and mortality. The development of sarcopenia in patients with CKD is multifactorial and it may occur independently of weight loss or cachexia including under obese sarcopenia. Hormonal imbalances can facilitate the development of sarcopenia in the general population and is a common finding in CKD. Hormones that may influence the development of sarcopenia are testosterone, growth hormone, insulin, thyroid hormones, and vitamin D. Although the relationship between free testosterone level that is low in uraemic patients and sarcopenia in CKD is not well-defined, functional improvement may be seen. Unlike testosterone, it is known that vitamin D is associated with muscle strength, muscle size, and physical performance in patients with CKD. Outcomes after vitamin D replacement therapy are still controversial. The half-life of growth hormone (GH) is prolonged in patients with CKD. Besides, IGF-1 levels are normal in patients with Stage 4 CKD-a minimal reduction is seen in the end-stage renal disease. Unresponsiveness or resistance of IGF-1 and changes in the GH/IGF-1 axis are the main causes of sarcopenia in CKD. Low serum T3 level is frequent in CKD, but the net effect on sarcopenia is not well-studied. CKD patients develop insulin resistance (IR) from the earliest period even before GFR decline begins. IR reduces glucose utilization as an energy source by hepatic gluconeogenesis, decreasing muscle glucose uptake, impairing intracellular glucose metabolism. This cascade results in muscle protein breakdown. IR and sarcopenia might also be a new pathway for targeting. Ghrelin, oestrogen, cortisol, and dehydroepiandrosterone may be other players in the setting of sarcopenia. In this review, we mainly examine the effects of hormonal changes on the occurrence of sarcopenia in patients with CKD via the available data.

Peripheral Insulin Resistance Is Associated with Copeptin in Patients with Chronic Kidney Disease

Background

Insulin resistance is associated with cardiovascular disease risk and worsened kidney function. Patients with CKD have higher levels of insulin resistance. Elevated levels of copeptin (a surrogate for vasopressin levels) have been associated with an increased incidence and progression of CKD, and with incident diabetes mellitus. The purpose of our study was to examine the relationship between insulin resistance, copeptin, and CKD.

Methods

We performed a cross-sectional study to investigate if insulin resistance was associated with higher copeptin levels in nondiabetic patients with stage 3-4 CKD versus controls. We measured plasma copeptin levels and used data from 52 patients with stage 3-4 CKD and 85 controls (eGFR ≥60 ml/min per 1.73 m²) enrolled in the Insulin Resistance in Chronic Kidney Disease (IRCKD) study. We then used a multivariable linear-regression model to assess the independent relationship between peripheral or hepatic insulin resistance and copeptin across levels of eGFR.

Results

We found that in patients with CKD (eGFR of 30-60 ml/min per 1.73 m²), but not in controls, peripheral insulin resistance was significantly correlated with higher levels of log copeptin (r=-0.21, P=0.04). In patients with CKD, when adjusted for age, sex, BMI, serum osmolality, log IL6, and log leptin/adiponectin ratio, each 1 SD decrease in insulin sensitivity was associated with a 39% increase in serum copeptin levels. The relationship between hepatic insulin resistance, copeptin, and eGFR is similar between controls and patients with reduced eGFR.

Conclusion

Peripheral insulin resistance is associated with elevated copeptin levels in nondiabetic patients with stage 3-4 CKD. Further research into how the interaction between peripheral insulin resistance and elevated vasopressin affects CKD progression could be of interest.

Nutrition in chronic heart failure patients: a systematic review

Nutrition is the primary source of energy production for myocardial contractility and to maintaining cardiac efficiency. Although many studies provided evidence of the benefits of nutritional intervention in chronic heart failure patients (CHF), these effects are not still completely understood. We searched in PubMed and Embase articles related to the following keywords: "chronic heart failure" with "diet," "nutrition," "insulin resistance," and "caloric restriction." Of the 975 retrieved articles, 20 have been selected. The primary endpoint was the left ventricular (LV) function and the secondary mortality rate in HF patients. Some studies showed that the Mediterranean diet (MedDiet) had a beneficial effect on cardiac function, while others did not find any positive impact. Nutritional supplements and hypercaloric intake had positive effects on underweight HF patients, while hypocaloric diet was beneficial in obese HF patients improving glucose control and cardiac function. The effect of MedDiet in HF patients showed conflicting results. Changes in the dietary pattern can reduce the evolution of HF, considering not only the quality of food but also the caloric intake. The discriminant factor to prescribe a diet regime in HF patients is represented by body mass index (BMI). A well-balanced caloric diet represents an effective therapy in overweight HF patients to reduce the mortality rate. Long-term studies evaluating cause-effect of energy and macronutrients intake on cardiac function in HF patients are necessary.

Glucose tolerance in patients with and without type 2 diabetes mellitus during hemodialysis

AIMS

The disposal of a glucose bolus was studied to identify glucose metabolism in patients with and without type 2 diabetes mellitus (T2DM) during their regular hemodialysis (HD) treatment.

METHODS

Plasma glucose, insulin, and c-peptide concentrations were measured during a 60 min observation phase following a rapid glucose infusion (0.5 g/kg dry weight). Glucose disposition and elimination rates were determined from kinetic analysis, and insulinogenic index was calculated. Insulin resistance (R_HOMA) was determined by homeostatic model assessment (HOMA).

RESULTS

35 HD patients (14 with T2DM) distinguished by a higher age (median: 70 vs. 55 y, p < 0.01) in T2DM patients were studied. Glucose kinetic data showed only small differences between patients with or without T2DM, but as R_HOMA measured in all patients increased, a larger fraction of glucose was removed by the extracorporeal system (r = 0.430, p = 0.01). One hour after glucose bolus injection the glucose level was not different from that before HD also in patients with T2DM (p = 0.115).

CONCLUSIONS

The larger glucose amount recovered in dialysate in patients with increasing R_HOMA indicates that impaired glucose disposal could be measured during HD using a non-invasive dialysis quantification approach without blood sampling. Glucose infusion during HD is safe also in patients with T2DM.

Effects of long-term intradialytic oral nutrition and exercise on muscle protein homeostasis and markers of mitochondrial content in patients on hemodialysis

Patients with end-stage kidney disease on maintenance hemodialysis commonly develop protein-energy wasting, a syndrome characterized by nutritional and metabolic abnormalities. Nutritional supplementation and exercise are recommended to prevent protein-energy wasting. In a 6-mo prospective randomized, open-label, clinical trial, we reported that the combination of resistance exercise and nutritional supplementation does not have an additive effect on lean body mass measured by dual-energy X-ray absorptiometry. To provide more mechanistic data, we performed a secondary analysis where we hypothesized that the combination of nutritional supplementation and resistance exercise would have additive effects on muscle protein accretion by stable isotope protein kinetic experiments, muscle mass by MRI, and mitochondrial content markers in muscle. We found that 6 mo of nutritional supplementation during hemodialysis increased muscle protein net balance [baseline: 2.5 (-17.8, 13.0) µg·100 mL-1·min-1 vs. 6 mo: 43.7 (13.0, 98.5) µg·100 mL-1·min-1, median (interquartile range), P = 0.04] and mid-thigh fat area [baseline: 162.3 (104.7, 226.6) cm2 vs. 6 mo: 181.9 (126.3, 279.2) cm2, median (interquartile range), P = 0.04]. Three months of nutritional supplementation also increased markers of mitochondrial content in muscle. Although the study is underpowered to detected differences, the combination of nutritional supplementation and exercise failed to show further benefit in protein accretion or muscle cross-sectional area. We conclude that long-term nutritional supplementation increases the skeletal muscle anabolic effect, the fat cross-sectional area of the thigh, and markers of mitochondrial content in skeletal muscle.

Muscle protein turnover and low-protein diets in patients with chronic kidney disease

Adaptation to a low-protein diet (LPD) involves a reduction in the rate of amino acid (AA) flux and oxidation, leading to more efficient use of dietary AA and reduced ureagenesis. Of note, the concept of 'adaptation' to low-protein intakes has been separated from the concept of 'accommodation', the latter term implying a decrease in protein synthesis, with development of wasting, when dietary protein intake becomes inadequate, i.e. beyond the limits of the adaptive mechanisms. Acidosis, insulin resistance and inflammation are recognized mechanisms that can increase protein degradation and can impair the ability to activate an adaptive response when an LPD is prescribed in a chronic kidney disease (CKD) patient. Current evidence shows that, in the short term, clinically stable patients with CKD Stages 3-5 can efficiently adapt their muscle protein turnover to an LPD containing 0.55-0.6 g protein/kg or a supplemented very-low-protein diet (VLPD) by decreasing muscle protein degradation and increasing the efficiency of muscle protein turnover. Recent long-term randomized clinical trials on supplemented VLPDs in patients with CKD have shown a very good safety profile, suggesting that observations shown by short-term studies on muscle protein turnover can be extrapolated to the long-term period.