Individuality of the plasma sodium concentration

Revisiting the concept of constant tissue conductivities for volume estimation in dialysis patients using bioimpedance spectroscopy

RATIONALE

Current estimation of body fluid volumes in hemodialysis patients using bioimpedance analysis assumes constant specific electrical characteristics of biological tissues despite a large variation in plasma Na⁺ concentrations [Na⁺], ranging from 130 to 150 mmol/L. Here, we examined the potential effect of variable [Na⁺] on bioimpedance-derived volume overload.

METHOD

Volumes were calculated from published whole-body extra- and intracellular resistance data and relationships using either "standard" or "revised" specific electrical characteristics modeled as functions of [Na⁺].

RESULT

With "standard" assumptions, volumes increased with increasing [Na⁺]. The increase in volume overload was about 0.5 dm³ and 3% of extracellular volume per 10 mmol/dm³ of [Na⁺] in a 75 kg patient. This increase was abolished when the same bioimpedance data were analyzed under "revised" conditions.

DISCUSSION

The overestimation in extracellular volume overload in the range of 0.5 dm³ per 10 mmol/dm³ [Na⁺] perfectly matches the positive relationship determined in a large cohort of hemodialysis patients. The bias may be considered moderate when interpreting data of individual patients, but may become important when comparing data of larger patient groups. The bias disappears when analysis of bioimpedance data accounts for differences in tissue electrical properties, using individual [Na⁺].

Middle-age high normal serum sodium as a risk factor for accelerated biological aging, chronic diseases, and premature mortality

BACKGROUND

It is known that some people age faster than others, some people live into old age disease-free, while others develop age-related chronic diseases. With a rapidly aging population and an emerging chronic diseases epidemic, finding mechanisms and implementing preventive measures that could slow down the aging process has become a new challenge for biomedical research and public health. In mice, lifelong water restriction shortens the lifespan and promotes degenerative changes. Here, we test the hypothesis that optimal hydration may slow down the aging process in humans.

METHODS

We performed a cohort analysis of data from the Atherosclerosis Risk in Communities study with middle-age enrollment (45-66 years, n = 15,752) and 25 years follow-up. We used serum sodium, as a proxy for hydration habits. To estimate the relative speed of aging, we calculated the biological age (BA) from age-dependent biomarkers and assessed risks of chronic diseases and premature mortality.

FINDINGS

The analysis showed that middle age serum sodium >142 mmol/l is associated with a 39% increased risk to develop chronic diseases (hazard ratio [HR] = 1.39, 95% confidence interval [CI]:1.18-1.63) and >144 mmol/l with 21% elevated risk of premature mortality (HR = 1.21, 95% CI:1.02-1.45). People with serum sodium >142 mmol/l had up to 50% higher odds to be older than their chronological age (OR = 1.50, 95% CI:1.14-1.96). A higher BA was associated with an increased risk of chronic diseases (HR = 1.70, 95% CI:1.50-1.93) and premature mortality (HR = 1.59, 95% CI 1.39-1.83).

INTERPRETATION

People whose middle-age serum sodium exceeds 142 mmol/l have increased risk to be biologically older, develop chronic diseases and die at younger age. Intervention studies are needed to confirm the link between hydration and aging.

FUNDING

This work was funded by Intramural Research program of the National Heart, Lung, and Blood Institute (NHLBI). The ARIC study has been funded in whole or in part with federal funds from the NHLBI; the National Institutes of Health (NIH); and the Department of Health and Human Services.

Middle age serum sodium levels in the upper part of normal range and risk of heart failure

AIMS

With increasing prevalence of heart failure (HF) owing to the ageing population, identification of modifiable risk factors is important. In a mouse model, chronic hypohydration induced by lifelong water restriction promotes cardiac fibrosis. Hypohydration elevates serum sodium. Here, we evaluate the association of serum sodium at middle age as a measure of hydration habits with risk to develop HF.

METHODS AND RESULTS

We analysed data from Atherosclerosis Risk in Communities study with middle age enrolment (45-66 years) and 25 years of follow-up. Participants without water balance dysregulation were selected: serum sodium within normal range (135-146 mmol/L), not diabetic, not obese and free of HF at baseline (N = 11 814). In time-to-event analysis, HF risk was increased by 39% if middle age serum sodium exceeded 143 mmol/L corresponding to 1% body weight water deficit [hazard ratio 1.39, 95% confidence interval (CI) 1.14-1.70]. In a retrospective case-control analysis performed on 70- to 90-year-old attendees of Visit 5 (N = 4961), serum sodium of 142.5-143 mmol/L was associated with 62% increase in odds of left ventricular hypertrophy (LVH) diagnosis [odds ratio (OR) 1.62, 95% CI 1.03-2.55]. Serum sodium above 143 mmol/L was associated with 107% increase in odds of LVH (OR 2.07, 95% CI 1.30-3.28) and 54% increase in odds of HF (OR 1.54, 95% CI 1.06-2.23). As a result, prevalence of HF and LVH was increased among 70- to 90-year-old participants with higher middle age serum sodium.

CONCLUSION

Middle age serum sodium above 142 mmol is a risk factor for LVH and HF. Maintaining good hydration throughout life may slow down decline in cardiac function and decrease prevalence of HF.

Edelman Revisited: Concepts, Achievements, and Challenges

The key message from the 1958 Edelman study states that combinations of external gains or losses of sodium, potassium and water leading to an increase of the fraction (total body sodium plus total body potassium) over total body water will raise the serum sodium concentration ([Na]_S), while external gains or losses leading to a decrease in this fraction will lower [Na]_S. A variety of studies have supported this concept and current quantitative methods for correcting dysnatremias, including formulas calculating the volume of saline needed for a change in [Na]_S are based on it. Not accounting for external losses of sodium, potassium and water during treatment and faulty values for body water inserted in the formulas predicting the change in [Na]_S affect the accuracy of these formulas. Newly described factors potentially affecting the change in [Na]_S during treatment of dysnatremias include the following: (a) exchanges during development or correction of dysnatremias between osmotically inactive sodium stored in tissues and osmotically active sodium in solution in body fluids; (b) chemical binding of part of body water to macromolecules which would decrease the amount of body water available for osmotic exchanges; and (c) genetic influences on the determination of sodium concentration in body fluids. The effects of these newer developments on the methods of treatment of dysnatremias are not well-established and will need extensive studying. Currently, monitoring of serum sodium concentration remains a critical step during treatment of dysnatremias.

Plasma sodium, extracellular fluid volume, and blood pressure in healthy men

In the general population we recently reported a consistent association between plasma sodium and volume markers, suggesting that individuals with higher plasma sodium have higher extracellular fluid volume (ECFV). To test this hypothesis, we analyzed the association between plasma sodium and directly measured ECFV (iothalamate distribution volume) in healthy men. Second, we studied whether plasma sodium is associated with blood pressure. We analyzed data from 70 men (age 24 ± 7 years) at the end of two 7-day periods on a low-sodium diet (LS, 50 mmol Na/24 h) and a high-sodium diet (HS, 200 mmol Na/24 h), respectively. The association of plasma sodium with blood pressure was assessed in the combined data of the different sodium intakes by linear mixed effects models. A positive univariable association between plasma sodium and ECFV was found during HS (β = 0.24, p = 0.042) and LS (β = 0.23, p = 0.058), respectively. Individual values of plasma sodium on LS and HS diet were strongly correlated (β = 0.68, p < 0.001), as were values for ECFV (β = 0.54, p < 0.001). In the combined data set plasma sodium level was significantly associated with ECFV (B [SE] = 0.10 [0.04], p = 0.02), and systolic blood pressure (SBP, B [SE] = 0.73 [0.26], p = 0.006), independent of ECFV. In conclusion, plasma sodium concentration is positively associated with ECFV on both LS and HS intake. Our data confirm and extend prior data on individual regulation of plasma sodium and suggest that this is associated with individuality of the regulation of ECFV. Finally, plasma sodium level is associated with SBP, independent of ECFV and diet.

Clinical and neurohumoral associates of variations in plasma Na+in the PREVEND cohort

Plasma Na+concentration is regulated within narrow limits. Yet, substantial interindividual differences exist even in the normal range. The determinants of these differences are not well understood. We therefore investigated the clinical and neurohumoral associates of plasma Na+. We studied 2,364 men (age: 48 ± 12 yr) and 2,710 women (age: 47 ± 12 yr) from the prospective Prevention of Renal and Vascular End-Stage Disease (PREVEND) cohort study. In the present study, we investigated the neurohumoral factors NH2-terminal prohormone of brain natriuretic peptide (NT-proBNP) and aldosterone as volume markers and copeptin as a marker for osmoregulation. Clinical associating variables of plasma Na+were age, sex, and plasma glucose. Furthermore, plasma Na+levels were associated with log2copeptin (men: standardized β = 0.18, P < 0.001; women: standardized β = 0.17, P < 0.001), log2NT-proBNP (men: standardized β = 0.07, P = 0.008; women: standardized β = 0.12, P < 0.001), and log2aldosterone (men: standardized β = −0.06, P = 0.005; women: standardized β = −0.09, P < 0.001). Copeptin and NT-proBNP showed an interaction in their association with plasma Na+. Thus, our data 1) support that osmoregulation, as estimated from copeptin levels, is a main associate of plasma Na+; 2) show a consistent association with volume markers, with higher NT-proBNP and lower aldosterone in individuals with higher plasma Na+; and 3) show that the interaction between copeptin and NT-proBNP illustrates that osmoregulation and volume regulation act in concert in the regulation of plasma Na+.

Suboptimal hydration remodels metabolism, promotes degenerative diseases, and shortens life

With increased life expectancy worldwide, there is an urgent need for improving preventive measures that delay the development of age-related degenerative diseases. Here, we report evidence from mouse and human studies that this goal can be achieved by maintaining optimal hydration throughout life. We demonstrate that restricting the amount of drinking water shortens mouse lifespan with no major warning signs up to 14 months of life, followed by sharp deterioration. Mechanistically, water restriction yields stable metabolism remodeling toward metabolic water production with greater food intake and energy expenditure, an elevation of markers of inflammation and coagulation, accelerated decline of neuromuscular coordination, renal glomerular injury, and the development of cardiac fibrosis. In humans, analysis of data from the Atherosclerosis Risk in Communities (ARIC) study revealed that hydration level, assessed at middle age by serum sodium concentration, is associated with markers of coagulation and inflammation and predicts the development of many age-related degenerative diseases 24 years later. The analysis estimates that improving hydration throughout life may greatly decrease the prevalence of degenerative diseases, with the most profound effect on dementia, heart failure (HF), and chronic lung disease (CLD), translating to the development of these diseases in 3 million fewer people in the United States alone.

In mice, restricting the amount of drinking water shortens lifespan and may accelerate degenerative changes leading to age-related chronic diseases.

Heritability and individuality of the plasma sodium concentration: a twin study in the United States veteran population

Little is known about the population genetics of water balance. A recent meta-genome-wide association study on plasma sodium concentration identified novel loci of high biological plausibility, yet heritability of the phenotype has never been convincingly shown in European ancestry. The present study linked the Vietnam Era Twin Registry with the Department of Veterans Affairs VistA patient care clinical database. Participants (n = 2,370, 59.6% monozygotic twins and 40.4% dizygotic twins) had a median of seven (interquartile range: 3-14) plasma sodium determinations between October 1999 and March 2017. Heritability of the mean plasma sodium concentration among all twins was 0.41 (95% confidence interval: 0.35-0.46) and 0.49 (95% confidence interval: 0.43-0.54) after exclusion of 514 twins with only a single plasma sodium determination. Heritability among Caucasian (n = 1,958) and African-American (n = 268) twins was 0.41 (95% confidence interval: 0.34-0.47) and 0.36 (95% confidence interval: 0.17-0.52), respectively. Exclusion of data from twins who had been prescribed medications known to impact systemic water balance had no effect. The ability of the present study to newly detect substantial heritability across multiple racial groups was potentially a function of the cohort size and relatedness, exclusion of sodium determinations confounded by elevated plasma glucose and/or reduced glomerular filtration rate, transformation of plasma sodium for the independent osmotic effect of plasma glucose, and use of multiple laboratory determinations per individual over a period of years. Individual-level plasma sodium concentration exhibited longitudinal stability (i.e., individuality); the degree to which individual-level means differed from the population mean was substantial, irrespective of the number of determinations. In aggregate, these data establish the heritability of plasma sodium concentration in European ancestry and corroborate its individuality.

Low dialysate sodium levels for chronic haemodialysis

BACKGROUND

Cardiovascular (CV) disease is the leading cause of death in dialysis patients, and strongly associated with fluid overload and hypertension. It is plausible that low dialysate [Na+] may decrease total body sodium content, thereby reducing fluid overload and hypertension, and ultimately reducing CV morbidity and mortality.

OBJECTIVES

This review evaluated harms and benefits of using a low (< 138 mM) dialysate [Na+] for maintenance haemodialysis (HD) patients.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 7 August 2018 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

Randomised controlled trials (RCTs), both parallel and cross-over, of low (< 138 mM) versus neutral (138 to 140 mM) or high (> 140 mM) dialysate [Na+] for maintenance HD patients were included.

DATA COLLECTION AND ANALYSIS

Two investigators independently screened studies for inclusion and extracted data. Statistical analyses were performed using random effects models, and results expressed as risk ratios (RR) for dichotomous outcomes, and mean differences (MD) or standardised MD (SMD) for continuous outcomes, with 95% confidence intervals (CI). Confidence in the evidence was assessed using GRADE.

MAIN RESULTS

We included 12 studies randomising 310 patients, with data available for 266 patients after dropout. All but one study evaluated a fixed concentration of low dialysate [Na+], and one profiled dialysate [Na+]. Three studies were parallel group, and the remaining nine cross-over. Of the latter, only two used a washout between intervention and control periods. Most studies were short-term with a median (interquartile range) follow-up of 3 (3, 8.5) weeks. Two were of a single HD session, and two of a single week's HD. Half of the studies were conducted prior to 2000, and five reported use of obsolete HD practices. Risks of bias in the included studies were often high or unclear, lowering confidence in the results.Compared to neutral or high dialysate [Na+], low dialysate [Na+] had the following effects on "efficacy" endpoints: reduced interdialytic weight gain (10 studies: MD -0.35 kg, 95% CI -0.18 to -0.51; high certainty evidence); probably reduced predialysis mean arterial blood pressure (BP) (4 studies: MD -3.58 mmHg, 95% CI -5.46 to -1.69; moderate certainty evidence); probably reduced postdialysis mean arterial BP (MAP) (4 studies: MD -3.26 mmHg, 95% CI -1.70 to -4.82; moderate certainty evidence); probably reduced predialysis serum [Na+] (7 studies: MD -1.69 mM, 95% CI -2.36 to -1.02; moderate certainty evidence); may have reduced antihypertensive medication (2 studies: SMD -0.67 SD, 95% CI -1.07 to -0.28; low certainty evidence). Compared to neutral or high dialysate [Na+], low dialysate [Na+] had the following effects on "safety" endpoints: probably increased intradialytic hypotension events (9 studies: RR 1.56, 95% 1.17 to 2.07; moderate certainty evidence); probably increased intradialytic cramps (6 studies: RR 1.77, 95% 1.15 to 2.73; moderate certainty evidence).Compared to neutral or high dialysate [Na+], low dialysate [Na+] may make little or no difference to: intradialytic BP (2 studies: MD for systolic BP -3.99 mmHg, 95% CI -17.96 to 9.99; diastolic BP 1.33 mmHg, 95% CI -6.29 to 8.95; low certainty evidence); interdialytic BP (2 studies:, MD for systolic BP 0.17 mmHg, 95% CI -5.42 to 5.08; diastolic BP -2.00 mmHg, 95% CI -4.84 to 0.84; low certainty evidence); dietary salt intake (2 studies: MD -0.21g/d, 95% CI -0.48 to 0.06; low certainty evidence).Due to very low quality of evidence, it is uncertain whether low dialysate [Na+] changed extracellular fluid status, venous tone, arterial vascular resistance, left ventricular mass or volumes, thirst or fatigue. Studies did not examine cardiovascular or all-cause mortality, cardiovascular events, or hospitalisation.

AUTHORS' CONCLUSIONS

It is likely that low dialysate [Na+] reduces intradialytic weight gain and BP, which are effects directionally associated with improved outcomes. However, the intervention probably also increases intradialytic hypotension and reduces serum [Na+], effects that are associated with increased mortality risk. The effect of the intervention on overall patient health and well-being is unknown. Further evidence is needed in the form of longer-term studies in contemporary settings, evaluating end-organ effects in small-scale mechanistic studies using optimal methods, and clinical outcomes in large-scale multicentre RCTs.

Serum sodium concentration and the progression of established chronic kidney disease

Background

Higher serum sodium concentration has been reported to be a risk factor for the development of incident chronic kidney disease (CKD), but its relationship with the progression of established CKD has not been investigated. We hypothesised that increased serum sodium concentration is a risk factor for estimated glomerular filtration rate (eGFR) decline in CKD.

Methods

This was a retrospective cohort study using data collected over a 6-year period, with baseline data obtained during the first 2 years. We included patients known to our renal service who had had a minimum of three blood tests every 2 years and an eGFR of < 60 mL/min/1.73 m² at baseline. Exclusion criteria were renal replacement therapy, diabetes mellitus, heart failure and decompensated liver disease. A multiple linear regression model investigated the relationship between baseline serum sodium and eGFR decline after adjustment for confounding factors.

Results

7418 blood results from 326 patients were included. There was no relationship between serum sodium concentration and estimated glomerular filtration rate at baseline. After multivariable adjustment, a 1 mmol/L increase in baseline serum sodium was associated with a 1.5 mL/min/1.73 m² decline in eGFR during the study period (95% CI 0.9, 2.0). A reduction in eGFR was not associated with significant changes in serum sodium concentration over 6 years.

Conclusion

Higher serum sodium concentration is associated with the progression of CKD, independently of other established risk factors. Conversely, significant alterations in serum sodium concentration do not occur with declining kidney function.

Cross-Sectional Positive Association of Serum Lipids and Blood Pressure With Serum Sodium Within the Normal Reference Range of 135-145 mmol/L

OBJECTIVE

Serum sodium concentration is maintained by osmoregulation within normal range of 135 to 145 mmol/L. Previous analysis of data from the ARIC study (Atherosclerosis Risk in Communities) showed association of serum sodium with the 10-year risk scores of coronary heart disease and stroke. Current study evaluated the association of within-normal-range serum sodium with cardiovascular risk factors.

APPROACH AND RESULTS

Only participants who did not take cholesterol or blood pressure medications and had sodium within normal 135 to 145 mmol/L range were included (n=8615), and the cohort was stratified based on race, sex, and smoking status. Multiple linear regression analysis of data from ARIC study was performed, with adjustment for age, blood glucose, insulin, glomerular filtration rate, body mass index, waist to hip ratio, and calorie intake. The analysis showed positive associations with sodium of total cholesterol, low-density lipoprotein cholesterol, and total cholesterol to high-density lipoprotein cholesterol ratio; apolipoprotein B; and systolic and diastolic blood pressure. Increases in lipids and blood pressure associated with 10 mmol/L increase in sodium are similar to the increases associated with 7 to 10 years of aging. Analysis of sodium measurements made 3 years apart demonstrated that it is stable within 2 to 3 mmol/L, explaining its association with long-term health outcomes. Furthermore, elevated sodium promoted lipid accumulation in cultured adipocytes, suggesting direct causative effects on lipid metabolism.

CONCLUSIONS

Serum sodium concentration is a cardiovascular risk factor even within the normal reference range. Thus, decreasing sodium to the lower end of the normal range by modification of water and salt intake is a personalizable strategy for decreasing cardiovascular risks.

Effects of potassium supplementation on markers of osmoregulation and volume regulation: results of a fully controlled dietary intervention study

OBJECTIVE

Lifestyle measures including dietary sodium restriction and increased potassium intake are recognized to lower blood pressure (BP). Potassium was found to be effective in reducing BP at higher levels of sodium intake, but to have little effect when sodium intake is restricted. The humoral mechanisms underlying these sodium intake dependent effects of potassium are unknown. We investigated the effects of potassium supplementation on top of a fully controlled sodium-restricted diet on markers of osmoregulation and volume regulation.

METHODS

In this post-hoc analysis, we included 35 (pre)hypertensive individuals participating in a randomized, double-blind, placebo-controlled crossover trial. Individuals received capsules containing sodium [3.0 g (130 mmol)/day], potassium [2.8 g (72  mmol)/day], or placebo for three four-week periods. Linear mixed-effect models were used to estimate the effects of potassium supplementation compared with placebo. Skewed data were ln-transformed before analysis.

RESULTS

Increased potassium intake was associated with a significant decrease in 24-h BP (-3.6/-1.6 mmHg). Furthermore, we found a significant decrease in ln MR-proANP [-0.08 (95% confidence interval -0.15, -0.01) pmol/l, P = 0.03] and significant increases in 24-h heart rate [2.5 (0.9, 4.0) bpm, P = 0.002], ln plasma copeptin [0.11 (0.01, 0.20) pmol/l, P = 0.02], ln renin [0.34 (0.08, 0.60) μIU/ml, P = 0.01], and ln aldosterone [0.14 (0.07, 0.22) nmol/l, P < 0.001] compared with placebo.

CONCLUSIONS

We found that potassium has BP-lowering effects during sodium restriction. These BP-lowering effects, however, seem mitigated by several counter regulatory mechanisms (i.e. increased secretion of vasopressin, stimulation of RAAS, and increased heart rate) that were activated to maintain volume homeostasis and counterbalance the decrease in BP.

Determinants of water and sodium intake and output

Physiological regulation of sodium and water intake and output is required for the maintenance of homeostasis. The behavioral and neuroendocrine mechanisms that govern fluid and salt balance are highly interdependent, with acute and chronic alterations in renal output tightly balanced by appropriate changes in thirst and, to a lesser extent in humans, sodium appetite. In healthy individuals, these tightly coupled mechanisms maintain extracellular fluid volume and body tonicity within a narrow homeostatic range by initiating ingestive behaviors and the release of hormones necessary to conserve water and sodium within the body. In this review, the factors that determine output of sodium and fluid and those that determine "normal" input (i.e., matched to output) are addressed. For output, individual variability accompanied by dysregulation of homeostatic mechanisms may contribute to acute and/or chronic disease. To illustrate that point, the specific condition of salt-sensitive hypertension is discussed. For input, physical characteristics, physiological phenotypes, genetic and developmental influences, and cultural and environmental factors combine to result in a wide range of individual variability that, in humans, is compensated for by alterations in excretion.

Serum Magnesium and the Risk of Death From Coronary Heart Disease and Sudden Cardiac Death

BACKGROUND

Low serum magnesium has been implicated in cardiovascular mortality, but results are conflicting and the pathway is unclear. We studied the association of serum magnesium with coronary heart disease (CHD) mortality and sudden cardiac death (SCD) within the prospective population-based Rotterdam Study, with adjudicated end points and long-term follow-up.

METHODS AND RESULTS

Nine-thousand eight-hundred and twenty participants (mean age 65.1 years, 56.8% female) were included with a median follow-up of 8.7 years. We used multivariable Cox proportional hazard models and found that a 0.1 mmol/L increase in serum magnesium level was associated with a lower risk for CHD mortality (hazard ratio: 0.82, 95% CI 0.70-0.96). Furthermore, we divided serum magnesium in quartiles, with the second and third quartile combined as reference group (0.81-0.88 mmol/L). Low serum magnesium (≤0.80 mmol/L) was associated with an increased risk of CHD mortality (N=431, hazard ratio: 1.36, 95% CI 1.09-1.69) and SCD (N=217, hazard ratio: 1.54, 95% CI 1.12-2.11). Low serum magnesium was associated with accelerated subclinical atherosclerosis (expressed as increased carotid intima-media thickness: +0.013 mm, 95% CI 0.005-0.020) and increased QT-interval, mainly through an effect on heart rate (RR-interval: -7.1 ms, 95% CI -13.5 to -0.8). Additional adjustments for carotid intima-media thickness and heart rate did not change the associations with CHD mortality and SCD.

CONCLUSIONS

Low serum magnesium is associated with an increased risk of CHD mortality and SCD. Although low magnesium was associated with both carotid intima-media thickness and heart rate, this did not explain the relationship between serum magnesium and CHD mortality or SCD. Future studies should focus on why magnesium associates with CHD mortality and SCD and whether intervention reduces these risks.

Unique chloride-sensing properties of WNK4 permit the distal nephron to modulate potassium homeostasis

Dietary potassium deficiency activates thiazide-sensitive sodium chloride cotransport along the distal nephron. This may explain, in part, the hypertension and cardiovascular mortality observed in individuals who consume a low-potassium diet. Recent data suggest that plasma potassium affects the distal nephron directly by influencing intracellular chloride, an inhibitor of the with-no-lysine kinase (WNK)-Ste20p-related proline- and alanine-rich kinase (SPAK) pathway. As previous studies used extreme dietary manipulations, we sought to determine whether the relationship between potassium and NaCl cotransporter (NCC) is physiologically relevant and clarify the mechanisms involved. We report that modest changes in both dietary and plasma potassium affect NCC in vivo. Kinase assay studies showed that chloride inhibits WNK4 kinase activity at lower concentrations than it inhibits activity of WNK1 or WNK3. Also, chloride inhibited WNK4 within the range of distal cell chloride concentration. Mutation of a previously identified WNK chloride-binding motif converted WNK4 effects on SPAK from inhibitory to stimulatory in mammalian cells. Disruption of this motif in WNKs 1, 3, and 4 had different effects on NCC, consistent with the three WNKs having different chloride sensitivities. Thus, potassium effects on NCC are graded within the physiological range, which explains how unique chloride-sensing properties of WNK4 enable it to mediate effects of potassium on NCC in vivo.

Blood pressure and sodium: Association with MRI markers in cerebral small vessel disease

Dietary salt intake and hypertension are associated with increased risk of cardiovascular disease including stroke. We aimed to explore the influence of these factors, together with plasma sodium concentration, in cerebral small vessel disease (SVD). In all, 264 patients with nondisabling cortical or lacunar stroke were recruited. Patients were questioned about their salt intake and plasma sodium concentration was measured; brain tissue volume and white-matter hyperintensity (WMH) load were measured using structural magnetic resonance imaging (MRI) while diffusion tensor MRI and dynamic contrast-enhanced MRI were acquired to assess underlying tissue integrity. An index of added salt intake (P = 0.021), pulse pressure (P = 0.036), and diagnosis of hypertension (P = 0.0093) were positively associated with increased WMH, while plasma sodium concentration was associated with brain volume (P = 0.019) but not with WMH volume. These results are consistent with previous findings that raised blood pressure is associated with WMH burden and raise the possibility of an independent role for dietary salt in the development of cerebral SVD.

Elevated sodium and dehydration stimulate inflammatory signaling in endothelial cells and promote atherosclerosis

Cardiovascular diseases (CVDs) are a leading health problem worldwide. Epidemiologic studies link high salt intake and conditions predisposing to dehydration such as low water intake, diabetes and old age to increased risk of CVD. Previously, we demonstrated that elevation of extracellular sodium, which is a common consequence of these conditions, stimulates production by endothelial cells of clotting initiator, von Willebrand Factor, increases its level in blood and promotes thrombogenesis. In present study, by PCR array, using human umbilical vein endothelial cells (HUVECs), we analyzed the effect of high NaCl on 84 genes related to endothelial cell biology. The analysis showed that the affected genes regulate many aspects of endothelial cell biology including cell adhesion, proliferation, leukocyte and lymphocyte activation, coagulation, angiogenesis and inflammatory response. The genes whose expression increased the most were adhesion molecules VCAM1 and E-selectin and the chemoattractant MCP-1. These are key participants in the leukocyte adhesion and transmigration that play a major role in the inflammation and pathophysiology of CVD, including atherosclerosis. Indeed, high NaCl increased adhesion of mononuclear cells and their transmigration through HUVECs monolayers. In mice, mild water restriction that elevates serum sodium by 5 mmol/l, increased VCAM1, E-selectin and MCP-1 expression in mouse tissues, accelerated atherosclerotic plaque formation in aortic root and caused thickening or walls of coronary arteries. Multivariable linear regression analysis of clinical data from the Atherosclerosis Risk in Communities Study (n=12779) demonstrated that serum sodium is a significant predictor of 10 Years Risk of coronary heart disease. These findings indicate that elevation of extracellular sodium within the physiological range is accompanied by vascular changes that facilitate development of CVD. The findings bring attention to serum sodium as a risk factor for CVDs and give additional support to recommendations for dietary salt restriction and adequate water intake as preventives of CVD.