Tissue sodium stores in peritoneal dialysis and hemodialysis patients determined by 23-sodium magnetic resonance imaging

Meta-analysis of the correlation between pulmonary hypertension and echocardiographic parameters in patients with chronic kidney disease

Objective

To investigate the correlation between pulmonary hypertension (PH) and echocardiographic parameters in patients with chronic kidney disease (CKD).

Methods

PubMed, Embase, Web of Science, Cochrane, VIP, CNKI, and Wanfang databases were systematically searched for articles published from inception to 19 May 2023. Study quality was estimated using the Quality Assessment of Case-Control Studies tool. Forest plots were drawn using R language software. The "metacor" function in the "meta" package was utilized for meta-analysis of the r-values and their standard errors. Heterogeneity and sensitivity analyses were carried out, with the main outcomes as r-value, p-value, and I2 value.

Results

Eleven studies were included, with 1,809 CKD patients. The correlations between 12 echocardiographic parameters and PH were analyzed. Except for FS and LVEF which were negatively correlated with CKD-PH, the other 10 parameters were positively correlated with CKD-PH. Among them, LA was highly correlated with CKD-PH (0.70 < r < 0.89); LVDD, RA, RV, LVMI, and LVDS were moderately correlated with CKD-PH (0.40 < r < 0.69); while PA, IVS, LVPW, SV, FS, and LVEF were lowly correlated with CKD-PH (0.20 < r < 0.39). The synthesized estimates were stable against heterogeneity.

Conclusion

CKD-PH patients may have large cardiac chambers, thickened septal tissue on both sides of the chambers, reduced pulmonary artery flow rates, and decreased left ventricular function.

Overlooked factor in the etiology of pruritus in hemodialysis patients: Ultrafiltration volume

INTRODUCTION

This study investigated the relationship between ultrafiltration (UF) volume and pruritus severity based on the idea that skin perfusion and inflammatory changes occur in dialysis patients with high UF volume.

MATERIALS AND METHODS

This observational study included 392 patients. Patients filled out the Numerical Rating Scale, Verbal Rating Scale, and Visual Analogue Scale, showing the severity of pruritis. UF volumes in the last 12 sessions were recorded and averaged.

RESULTS

The rate of patients with pruritis was between 59.4% and 67.5% in the three scales. In three pruritis scales, the severity of pruritis, age, body mass index (BMI), UF volume, and UF volume/body weight ratio were positively correlated. UF volume/body weight ratio, age, and BMI were independent predictors of pruritis severity.

CONCLUSION

Limiting interdialytic weight gain may be an important treatment approach in pruritus control.

Tangram of Sodium and Fluid Balance

Homeostasis of fluid and electrolytes is a tightly controlled physiological process. Failure of this process is a hallmark of hypertension, chronic kidney disease, heart failure, and other acute and chronic diseases. While the kidney remains the major player in the control of whole-body fluid and electrolyte homeostasis, recent discoveries point toward more peripheral mechanisms leading to sodium storage in tissues, such as skin and muscle, and a link between this sodium and a range of diseases, including the conditions above. In this review, we describe multiple facets of sodium and fluid balance from traditional concepts to novel discoveries. We examine the differences between acute disruption of sodium balance and the longer term adaptation in chronic disease, highlighting areas that cannot be explained by a kidney-centric model alone. The theoretical and methodological challenges of more recently proposed models are discussed. We acknowledge the different roles of extracellular and intracellular spaces and propose an integrated model that maintains fluid and electrolyte homeostasis and can be distilled into a few elemental players: the microvasculature, the interstitium, and tissue cells. Understanding their interplay will guide a more precise treatment of conditions characterized by sodium excess, for which primary aldosteronism is presented as a prototype.

Why should we use a low sodium dialysis solution for peritoneal dialysis?

Overhydration is highly prevalent in patients on peritoneal dialysis (PD), with inappropriately high sodium load supposedly playing a central role in the pathophysiology of the conditions. Recent studies have revealed the novel role of the interstitium as a buffer system for sodium ions, and it has been reported that patients on dialysis, including PD, present increased levels of sodium in the interstitium, such as in subcutaneous tissue and muscle. Hence, therapy for correction of overhydration should target the excess extracellular volume and the excess sodium storage in the interstitium. The ultrafiltrate obtained using the currently available PD solutions is hypo- to isonatric as compared to serum, which is disadvantageous for prompt and efficient sodium removal from the body in patients with overhydration. In contrast, use of low sodium PD solutions is characterised by iso- to hypernatric ultrafiltrate, which may beneficial for reducing sodium storage in the interstitium. Trials of low sodium PD solutions have reported possible clinical merits, for example, decreased blood pressure, reduced dryness of mouth and decreased body water content as assessed using bioimpedance methods. Given these observations and the high prevalence of overhydration in current PD populations, it makes medical sense that low sodium solutions be positioned as the new standard solution in the future. However, for medical safety, that is, to avoid hyponatremia and excessive decreases in blood pressure, further studies are needed to establish the appropriate compositions and applications of low sodium solutions.

The role of intra- and interdialytic sodium balance and restriction in dialysis therapies

The relationship between sodium, blood pressure and extracellular volume could not be more pronounced or complex than in a dialysis patient. We review the patients' sources of sodium exposure in the form of dietary salt intake, medication administration, and the dialysis treatment itself. In addition, the roles dialysis modalities, hemodialysis types, and dialysis fluid sodium concentration have on blood pressure, intradialytic symptoms, and interdialytic weight gain affect patient outcomes are discussed. We review whether sodium restriction (reduced salt intake), alteration in dialysis fluid sodium concentration and the different dialysis types have any impact on blood pressure, intradialytic symptoms, and interdialytic weight gain.

Sodium handling in pediatric patients on maintenance dialysis

The risk of cardiovascular disease remains exceedingly high in pediatric patients with chronic kidney disease stage 5 on dialysis (CKD 5D). Sodium (Na+) overload is a major cardiovascular risk factor in this population, both through volume-dependent and volume-independent toxicity. Given that compliance with a Na+-restricted diet is generally limited and urinary Na+ excretion impaired in CKD 5D, dialytic Na+ removal is critical to reduce Na+ overload. On the other hand, an excessive or too fast intradialytic Na+ removal may lead to volume depletion, hypotension, and organ hypoperfusion. This review presents current knowledge on intradialytic Na+ handling and possible strategies to optimize dialytic Na+ removal in pediatric patients on hemodialysis (HD) and peritoneal dialysis (PD). There is increasing evidence supporting the prescription of lower dialysate Na+ in salt-overloaded children on HD, while improved Na+ removal may be achieved in children on PD with an individual adaptation of dwell time and volume and with icodextrin use during the long dwell.

Muscle Sodium Accumulation in Kidney Failure: Physiological Impact and Mitigation Strategies

Skeletal muscle has recently been recognized as a nonosmotic sodium reservoir that buffers dietary sodium. The in-vivo quantification of muscle sodium is based on a novel technology, sodium magnetic resonance imaging. Studies using this technology have shown that muscle sodium accumulation may be a clinical complication of chronic kidney disease (CKD). This review aims to summarize existing evidence on muscle sodium accumulation in patients with CKD and to identify knowledge gaps and topics for further research. The literature examined in this review suggests that muscle sodium accumulation is associated with CKD progression and pathological conditions. However, the causalities between muscle sodium accumulation and its related pathological changes are still elusive mainly because it is still uncertain where and how sodium accumulates in the muscle. More research is needed to address these gaps and determine if muscle sodium is a new intervention target in CKD.

Sodium in the skin: a summary of the physiology and a scoping review of disease associations

A large and growing body of research suggests that the skin plays an important role in regulating total body sodium, challenging traditional models of sodium homeostasis that focused exclusively on blood pressure and the kidney. In addition, skin sodium may help to prevent water loss and facilitate macrophage-driven antimicrobial host defence, but may also trigger immune dysregulation via upregulation of proinflammatory markers and downregulation of anti-inflammatory processes. We performed a systematic search of PubMed for published literature on skin sodium and disease outcomes and found that skin sodium concentration is increased in patients with cardiometabolic conditions including hypertension, diabetes and end-stage renal disease; autoimmune conditions including multiple sclerosis and systemic sclerosis; and dermatological conditions including atopic dermatitis, psoriasis and lipoedema. Several patient characteristics are associated with increased skin sodium concentration including older age and male sex. Animal evidence suggests that increased salt intake results in higher skin sodium levels; however, there are conflicting results from small trials in humans. Additionally, limited data suggest that pharmaceuticals such as diuretics and sodium-glucose co-transporter-2 inhibitors approved for diabetes, as well as haemodialysis may reduce skin sodium levels. In summary, emerging research supports an important role for skin sodium in physiological processes related to osmoregulation and immunity. With the advent of new noninvasive magnetic resonance imaging measurement techniques and continued research on skin sodium, it may emerge as a marker of immune-mediated disease activity or a potential therapeutic target.

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.

Recent Advances in Sodium Magnetic Resonance Imaging and Its Future Role in Kidney Disease

Sodium imbalance is a hallmark of chronic kidney disease (CKD). Excess tissue sodium in CKD is associated with hypertension, inflammation, and cardiorenal disease. Sodium magnetic resonance imaging (23Na MRI) has been increasingly utilized in CKD clinical trials especially in the past few years. These studies have demonstrated the association of excess sodium tissue accumulation with declining renal function across whole CKD spectrum (early- to end-stage), biomarkers of systemic inflammation, and cardiovascular dysfunction. In this article, we review recent advances of 23Na MRI in CKD and discuss its future role with a focus on the skin, the heart, and the kidney itself.

Tissue Sodium Accumulation Induces Organ Inflammation and Injury in Chronic Kidney Disease

High salt intake is a primary cause of over-hydration in chronic kidney disease (CKD) patients. Inflammatory markers are predictors of CKD mortality; however, the pathogenesis of inflammation remains unclear. Sodium storage in tissues has recently emerged as an issue of concern. The binding of sodium to tissue glycosaminoglycans and its subsequent release regulates local tonicity. Many cell types express tonicity-responsive enhancer-binding protein (TonEBP), which is activated in a tonicity-dependent or tonicity-independent manner. Macrophage infiltration was observed in the heart, peritoneal wall, and para-aortic tissues in salt-loading subtotal nephrectomized mice, whereas macrophages were not prominent in tap water-loaded subtotal nephrectomized mice. TonEBP was increased in the heart and peritoneal wall, leading to the upregulation of inflammatory mediators associated with cardiac fibrosis and peritoneal membrane dysfunction, respectively. Reducing salt loading by a diuretic treatment or changing to tap water attenuated macrophage infiltration, TonEBP expression, and inflammatory marker expression. The role of TonEBP may be crucial during the cardiac fibrosis and peritoneal deterioration processes induced by sodium overload. Anti-interleukin-6 therapy improved cardiac inflammation and fibrosis and peritoneal membrane dysfunction. Further studies are necessary to establish a strategy to regulate organ dysfunction induced by TonEBP activation in CKD patients.

Assessing Tissue Hydration Dynamics Based on Water/Fat Separated MRI

BACKGROUND

Optimal fluid status is an important issue in hemodialysis. Clinical evaluation of volume status and different diagnostic tools are used to determine hydration status in these patients. However, there is still no accurate method for this assessment.

PURPOSE

To propose and evaluate relative lean water signal (LWS_rel ) as a water-fat MRI-based tissue hydration measurement.

STUDY TYPE

Prospective.

POPULATION

A total of 16 healthy subjects (56 ± 6 years, 0 male) and 11 dialysis patients (60.3 ± 12.3 years, 9 male; dialysis time per week 15 ± 3.5 hours, dialysis duration 31.4 ± 27.9 months).

FIELD STRENGTH/SEQUENCE

A 3 T; 3D spoiled gradient echo.

ASSESSMENT

LWS_rel , a measurement of the water concentration of tissue, was estimated from fat-referenced MR images. Segmentations of total adipose tissue as well as thigh and calf muscles were used to measure LWS_rel and tissue volumes. LWS_rel was compared between healthy subjects and dialysis patients, the latter before and after dialysis. Bioimpedance-based body composition monitor over hydration (BCM OH) was also measured.

STATISTICAL TESTS

T-tests were used to compare differences between the healthy subjects and dialysis patients, as well as changes between before and after dialysis. Pearson correlation was calculated between MRI and non-MRI biomarkers. A P value <0.05 was considered statistically significant.

RESULTS

The LWS_rel in adipose tissue was significantly higher in the dialysis cohort compared with the healthy cohort (246.8% ± 60.0% vs. 100.0% ± 10.8%) and decreased significantly after dialysis (246.8 ± 60.0% vs. 233.8 ± 63.4%). Thigh and calf muscle volumes also significantly decreased by 3.78% ± 1.73% and 2.02% ± 2.50% after dialysis. There was a significant correlation between changes in adipose tissue LWS_rel and ultrafiltration volume (r = 87), as well as with BCM OH (r = 0.66).

DATA CONCLUSION

MRI-based LWS_rel and tissue volume measurements are sensitive to tissue hydration changes occurring during dialysis.

EVIDENCE LEVEL

2.

TECHNICAL EFFICACY

Stage 3.

Magnetic Resonance Imaging (MRI) Analysis of Tissue Sodium Concentration in Chronic Kidney Disease

Human body sodium is regulated by the kidneys and extrarenal mechanisms. Stored skin and muscle tissue sodium accumulation is associated with kidney function decline, hypertension, and a pro-inflammatory and cardiovascular disease profile. In this chapter, we describe the use of sodium-hydrogen magnetic resonance imaging (²³Na/¹H MRI) to dynamically quantify tissue sodium concentration in the lower limb of humans. Real-time quantification of tissue sodium is calibrated against known sodium chloride aqueous concentrations. This method may be useful for investigating in vivo (patho-)physiological conditions associated with tissue sodium deposition and metabolism (including in relation to water regulation) to enlighten our understanding of sodium physiology.

Nonsteroidal Mineralocorticoid Receptor Antagonism by Finerenone—Translational Aspects and Clinical Perspectives across Multiple Organ Systems

Perception of the role of the aldosterone/mineralocorticoid receptor (MR) ensemble has been extended from a previously renal epithelial-centered focus on sodium and volume homeostasis to an understanding of their role as systemic modulators of reactive oxygen species, inflammation, and fibrosis. Steroidal MR antagonists (MRAs) are included in treatment paradigms for resistant hypertension and heart failure with reduced ejection fraction, while more recently, the nonsteroidal MRA finerenone was shown to reduce renal and cardiovascular outcomes in two large phase III trials (FIDELIO-DKD and FIGARO-DKD) in patients with chronic kidney disease and type 2 diabetes, respectively. Here, we provide an overview of the pathophysiologic role of MR overactivation and preclinical evidence with the nonsteroidal MRA finerenone in a range of different disease models with respect to major components of the aggregate mode of action, including interfering with reactive oxygen species generation, inflammation, fibrosis, and hypertrophy. We describe a time-dependent effect of these mechanistic components and the potential modification of major clinical parameters, as well as the impact on clinical renal and cardiovascular outcomes as observed in FIDELIO-DKD and FIGARO-DKD. Finally, we provide an outlook on potential future clinical indications and ongoing clinical studies with finerenone, including a combination study with a sodium–glucose cotransporter-2 inhibitor.

Outcomes and predictors of skin sodium concentration in dialysis patients

Background

Sodium-23 magnetic resonance imaging (23Na MRI) allows the measurement of skin sodium concentration ([Na+]). In patients requiring dialysis, no data are available relating to the clinical outcomes associated with skin sodium accumulation or the determinants of increasing deposition.

Methods

This was an exploratory, observational study of adult hemodialysis (HD) and peritoneal dialysis (PD) patients. Participants underwent skin [Na+] quantification with leg 23Na MRI at the study's beginning. Outcomes of interest were all-cause mortality and composite all-cause mortality plus major adverse cardiovascular events. Cumulative total and event-free survival were assessed using the Kaplan-Meier survival function after stratification into skin [Na+] quartiles. Cox proportional hazards regression was used to model the association between skin [Na+] and outcomes of interest. Multiple linear regression was used to model the predictors of skin [Na+].

Results

A total of 52 participants (42 HD and 10 PD) underwent the study procedures. The median follow-up was 529 days (interquartile range: 353-602). Increasing skin [Na+] quartiles were associated with significantly shorter overall and event-free survival (log-rank χ2(1) = 3.926, log-rank χ2(1) = 5.685; P for trend <0.05 in both instances). Skin [Na+] was associated with all-cause mortality {hazard ratio (HR) 4.013, [95% confidence interval (95% CI) 1.988-8.101]; P < 0.001} and composite events [HR 2.332 (95% CI 1.378-3.945); P < 0.01], independently of age, sex, serum [Na+] and albumin. In multiple regression models, dialysate [Na+], serum albumin and congestive heart failure were significantly associated with skin [Na+] in HD patients (R2 adj = 0.62).

Conclusions

Higher skin [Na+] was associated with worse clinical outcomes in dialysis patients and may represent a direct therapeutic target.

Tissue Sodium in Patients With Early Stage Hypertension: A Randomized Controlled Trial

Background

Sodium (Na⁺) stored in skin and muscle tissue is associated with essential hypertension. Sodium magnetic resonance imaging is a validated method of quantifying tissue stores of Na⁺. In this study, we evaluated tissue Na⁺ in patients with elevated blood pressure or stage I hypertension in response to diuretic therapy or low Na⁺ diet.

Methods and Results

In a double‐blinded, placebo‐controlled trial, patients with systolic blood pressure 120 to 139 mm Hg were randomized to low sodium diet (<2 g of sodium), chlorthalidone, spironolactone, or placebo for 8 weeks. Muscle and skin Na⁺ using sodium magnetic resonance imaging and pulse wave velocity were assessed at the beginning and end of the study. Ninety‐eight patients were enrolled to undergo baseline measurements and 54 completed randomization. Median baseline muscle and skin Na⁺ in 98 patients were 16.4 mmol/L (14.9, 18.9) and 13.1 mmol/L (11.1, 16.1), respectively. After 8 weeks, muscle Na⁺ increased in the diet and chlorthalidone arms compared with placebo. Skin sodium was decreased only in the diet arm compared with placebo. These associations remained significant after adjustment for age, sex, body mass index, systolic blood pressure, and urinary sodium. No changes were observed in pulse wave velocity among the different groups when compared with placebo.

Conclusions

Diuretic therapy for 8 weeks did not decrease muscle or skin sodium or improve pulse wave velocity in patients with elevated blood pressure or stage I hypertension.

Registration

URL: https://www.clinicaltrials.gov; Unique identifier: NCT02236520.

Salt-Sensitivity of Blood Pressure and Insulin Resistance

Salt sensitivity of blood pressure (SSBP) is an independent risk factor for cardiovascular morbidity and mortality that is seen in both hypertensive and normotensive populations. Insulin resistance (IR) strongly correlates with SSBP and affects nearly 50% of salt sensitive people. While the precise mechanism by which IR and SSBP relate remains elusive, several common pathways are involved in the genesis of both processes, including vascular dysfunction and immune activation. Vascular dysfunction associated with insulin resistance is characterized by loss of nitric oxide (NO)-mediated vasodilation and heightened endothelin-1 induced vasoconstriction, as well as capillary rarefaction. It manifests with increased blood pressure (BP) in salt sensitive murine models. Another common denominator in the pathogenesis of insulin resistance, hypertension, and salt sensitivity (SS) is immune activation involving pro-inflammatory cytokines like tumor necrosis factor (TNF)-α, IL-1β, and IL-6. In the last decade, a new understanding of interstitial sodium storage in tissues such as skin and muscle has revolutionized traditional concepts of body sodium handling and pathogenesis of SS. We have shown that interstitial Na⁺ can trigger a T cell mediated inflammatory response through formation of isolevuglandin protein adducts in antigen presenting cells (APCs), and that this response is implicated in salt sensitive hypertension. The peroxisome proliferator-activated receptor γ (PPARγ) is a transcription factor that modulates both insulin sensitivity and BP. PPARγ agonists increase insulin sensitivity and ameliorate salt sensitivity, whereas deficiency of PPARγ results in severe insulin resistance and hypertension. These findings suggest that PPARγ plays a role in the common pathogenesis of insulin sensitivity and salt sensitivity, perhaps via effects on the immune system and vascular function. The goal of this review is to discuss those mechanisms that may play a role in both SSBP and in insulin resistance.

Salt Sensitivity of Blood Pressure in Blacks and Women: A Role of Inflammation, Oxidative Stress, and Epithelial Na+ Channel

Significance: Salt sensitivity of blood pressure (SSBP) is an independent risk factor for mortality and morbidity due to cardiovascular disease, and disproportionately affects blacks and women. Several mechanisms have been proposed, including exaggerated activation of sodium transporters in the kidney leading to salt retention and water. Recent Advances: Recent studies have found that in addition to the renal epithelium, myeloid immune cells can sense sodium via the epithelial Na⁺ channel (ENaC), which leads to activation of the nicotinamide adenine dinucleotide phosphate oxidase enzyme complex, increased fatty acid oxidation, and production of isolevuglandins (IsoLGs). IsoLGs are immunogenic and contribute to salt-induced hypertension. In addition, aldosterone-mediated activation of ENaC has been attributed to the increased SSBP in women. The goal of this review is to highlight mechanisms contributing to SSBP in blacks and women, including, but not limited to increased activation of ENaC, fatty acid oxidation, and inflammation. Critical Issues: A critical barrier to progress in management of SSBP is that its diagnosis is not feasible in the clinic and is limited to expensive and laborious research protocols, which makes it difficult to investigate. Yet without understanding the underlying mechanisms, this important risk factor remains without treatment. Future Directions: Further studies are needed to understand the mechanisms that contribute to differential blood pressure responses to dietary salt and find feasible diagnostic tools. This is extremely important and may go a long way in mitigating the racial and sex disparities in cardiovascular outcomes. Antioxid. Redox Signal. 35, 1477-1493.

Volume-Independent Sodium Toxicity in Peritoneal Dialysis: New Insights from Bench to Bed

Sodium overload is common in end-stage kidney disease (ESKD) and is associated with increased cardiovascular mortality that is traditionally considered a result of extracellular volume expansion. Recently, sodium storage was detected by Na23 magnetic resonance imaging in the interstitial tissue of the skin and other tissues. This amount of sodium is osmotically active, regulated by immune cells and the lymphatic system, escapes renal control, and, more importantly, is associated with salt-sensitive hypertension. In chronic kidney disease, the interstitial sodium storage increases as the glomerular filtration rate declines and is related to cardiovascular damage, regardless of the fluid overload. This sodium accumulation in the interstitial tissues becomes more significant in ESKD, especially in older and African American patients. The possible negative effects of interstitial sodium are still under study, though a higher sodium intake might induce abnormal structural and functional changes in the peritoneal wall. Interestingly, sodium stored in the interstial tissue is not unmodifiable, since it is removable by dialysis. Nevertheless, the sodium removal by peritoneal dialysis (PD) remains challenging, and new PD solutions are desirable. In this narrative review, we carried out an update on the pathophysiological mechanisms of volume-independent sodium toxicity and possible future strategies to improve sodium removal by PD.

Total Body Sodium Balance in Chronic Kidney Disease

Excess sodium intake is a leading but modifiable risk factor for mortality, with implications on hypertension, inflammation, cardiovascular disease, and chronic kidney disease (CKD). This review will focus mainly on the limitations of current measurement methods of sodium balance particularly in patients with CKD who have complex sodium physiology. The suboptimal accuracy of sodium intake and excretion measurement is seemingly more marked with the evolving understanding of tissue (skin and muscle) sodium. Tissue sodium represents an extrarenal influence on sodium homeostasis with demonstrated clinical associations of hypertension and inflammation. Measurement of tissue sodium has been largely unexplored in patients with CKD. Development and adoption of more comprehensive and dynamic assessment of body sodium balance is needed to better understand sodium physiology in the human body and explore therapeutic strategies to improve the clinical outcomes in the CKD population.

Animal, Human, and 23Na MRI Imaging Evidence for the Negative Impact of High Dietary Salt in Children

PURPOSE OF THE REVIEW

Conditions typically prevalent in adults such as hypertension, kidney stones, osteoporosis, and chronic kidney disease are increasing among adolescents and young adults (AYA). The purpose of this review is to describe the association of these conditions to a high salt diet among pediatric patients.

RECENT FINDINGS

We present animal, human, and 23Na MRI evidence associated with the negative impact of high dietary salt in children. Special focus is placed on novel 23Na MRI imaging which reveals the important concept of a third compartment for sodium storage in soft tissue. Finally, we make recommendations on who should not be on a low salt diet.

SUMMARY

A high salt intake predisposes children and AYA to considerable morbidity. We exhort the reader to engage in advocacy efforts to curve the incidence and prevalence of high salt-related life-limiting conditions.

Reduction of Tissue Na+ Accumulation After Renal Transplantation

Introduction

Chronic kidney disease (CKD) engenders salt-sensitive hypertension. Whether or not tissue Na⁺ accumulation is increased in CKD patients remains uncertain. How tissue Na⁺ is affected after renal transplantation has not been assessed.

Methods

We measured tissue Na⁺ amount in 31 CKD patients (stage 5) and prospectively evaluated tissue Na⁺ content at 3 and 6 months, following living-donor kidney transplantation. Additionally, pre- and post-transplantation data were compared to 31 age- and sex-matched control subjects. ²³Na-magnetic resonance imaging (²³Na-MRI) was used to quantify muscle and skin Na⁺ of the lower leg and water distribution was assessed by bioimpedance spectroscopy.

Results

Compared to control subjects, CKD patients showed increased muscle (20.7 ± 5.0 vs. 15.5 ± 1.8 arbitrary units [a.u.], P < 0.001) and skin Na⁺ content (21.4 ± 7.7 vs. 15.0 ± 2.3 a.u., P < 0.001), whereas plasma Na⁺ concentration did not differ between groups. Restoration of kidney function by successful renal transplantation was accompanied by mobilization of tissue Na⁺ from muscle (20.7 ± 5.0 vs. 16.8 ± 2.8 a.u., P < 0.001) and skin tissue (21.4 ± 7.7 vs. 16.8 ± 5.2 a.u., P < 0.001). The reduction of tissue Na⁺ after transplantation was associated with improved renal function, normalization of blood pressure as well as an increase in lymphatic growth-factor concentration (vascular endothelial growth factor C [VEGF-C] 4.5 ± 1.8 vs. 6.7 ± 2.7 ng/ml, P < 0.01).

Conclusions

Tissue Na⁺ accumulation in predialysis patients with CKD was almost completely reversed to the level of healthy controls after successful kidney transplantation.

Magnetic resonance imaging determination of tissue sodium in patients with chronic kidney disease

Excess sodium is a major modifiable contributor to hypertension and cardiovascular risk. Knowledge of sodium storage and metabolism has derived mainly from indirect measurements of dietary sodium intake and urinary sodium excretion, however both attempt to measure body sodium and fluid in a two-compartment model of intracellular and extracellular spaces. Our understanding of total body sodium has recently included a storage pool in tissues. In the last two decades, sodium-23 magnetic resonance imaging (²³ Na MRI) has allowed dynamic quantification of tissue sodium in vivo. Tissue sodium is independently associated with cardiovascular dysfunction and inflammation. This review explores (i) The revolution of our understanding of sodium physiology, (ii) The development and potential clinical adoption of ²³ Na MRI to provide improved measurement of total body sodium in CKD and (iii) How we can better understand mechanistic and clinical implications of tissue sodium in hypertension, cardiovascular disease and immune dysregulation, especially in the CKD population.

Hyperkalemia in patients undergoing hemodialysis: its pathophysiology and management

Potassium is a major intracellular cation in the body, regulating membrane potential of excitable cells, such as cardiomyocytes and skeletal muscle cells. Because the kidney plays a critical role in controlling potassium balance, the elevation in serum potassium levels is one of the most common complications in patients with maintenance hemodialysis (MHD). In addition to reduced renal potassium excretion, the alteration in body potassium distribution owing to comorbid conditions may also contribute to dyskalemia. Besides potassium elimination through hemodialysis in MHD patients, accumulating data indicate the potential importance of extra‐renal elimination involving the gastrointestinal system, which can be affected by the inhibitors of the renin‐angiotensin‐aldosterone system. In this article, the literature on potassium physiology in MHD patients is reviewed with an emphasis on the changes from individuals with normal kidney function. This article also summarizes the findings of recent studies on dietary control, dialysate prescription, and pharmacological therapy.

Skin sodium is increased in male patients with multiple sclerosis and related animal models

Novel MRI techniques allow a noninvasive quantification of tissue sodium and reveal the skin as a prominent compartment of sodium storage in health and disease. Since multiple sclerosis (MS) immunopathology is initiated in the periphery and increased sodium concentrations induce proinflammatory immune cells, the skin represents a promising compartment linking high sodium concentrations and MS immunopathology. We used a 7-T sodium MRI (23Na-MRI) and inductively coupled plasma mass spectrometry to investigate the skin sodium content in two mouse models of MS. We additionally performed 3-T 23Na-MRI of calf skin and muscles in 29 male relapsing-remitting MS (RRMS) patients and 29 matched healthy controls. Demographic and clinical information was collected from interviews, and disease activity was assessed by expanded disability status scale scoring. 23Na-MRI and chemical analysis demonstrated a significantly increased sodium content in the skin during experimental autoimmune encephalomyelitis independent of active immunization. In male patients with RRMS, 23Na-MRI demonstrated a higher sodium signal in the area of the skin compared to age- and biological sex-matched healthy controls with higher sodium, predicting future disease activity in cranial MRI. In both studies, the sodium enrichment was specific to the skin, as we found no alterations of sodium signals in the muscle or other tissues. Our data add to the recently identified importance of the skin as a storage compartment of sodium and may further represent an important organ for future investigations on salt as a proinflammatory agent driving autoimmune neuroinflammation such as that in MS.