23Na magnetic resonance imaging-determined tissue sodium in healthy subjects and hypertensive patients

An observational study on intracutaneous sodium storage in intensive care patients and controls

The development of ICU-acquired sodium disturbances is not fully understood. Alterations in non-osmotic skin sodium storage, hypothetically inflammation-driven, could play a role. To investigate this in critically ill patients we conducted a patient-control study with skin punch biopsies in patients with sepsis (n = 15), after coronary artery bypass grafting (CABG, n = 15) and undergoing total hip arthroplasty (THA-controls, n = 15) respectively, together representing a range in severity of systemic inflammation. Biopsies were taken within 24 hours (sepsis) and within 2 hours (CABG) after ICU-admission, and prior to arthroplasty. Biopsies were analysed for sodium content. In addition immunostainings and quantitative real time PCR were performed. The primary aim of this study was to detect possible differences in amounts of cutaneous sodium. The secondary aims were to quantify inflammation and lymphangiogenesis with concomitant markers. The highest amounts of both water and sodium were found in patients with sepsis, with slightly lower values after CABG and the lowest amounts in THA-controls. Correlation between water and sodium was 0.5 (p<0.01). In skin biopsies in all groups comparable amounts of macrophages, T-cells and lymph vessels were found. In all groups comparable expression of inflammation markers were found. However, higher mRNA transcript expression levels of markers of lymphangiogenesis were found in patients with sepsis and after CABG. The conjoint accumulation of water and sodium points towards oedema formation. However, the correlation coefficient of 0.5 leaves room for alternative explanations, including non-osmotic sodium storage. No signs of dermal inflammation were found, but upregulation of markers of lymphangiogenesis could indicate future lymphangiogenesis.

The relationship of volume overload and its control to hypertension in hemodialysis patients

Hypertension is highly prevalent and associated with poor clinical outcomes among individuals receiving maintenance hemodialysis (HD). Volume overload is a key modifiable contributor to hypertension and cardiovascular disease in the HD population. Despite their importance, assessment and treatment of volume overload and hypertension remain major clinical challenges and have substantial implications for both clinical outcomes and patient experiences of care. This review will summarize current data on the diagnosis, epidemiology, pathophysiology, and clinical consequences of hypertension and volume overload in HD patients. We will also identify priorities for future research studies.

Acute body sodium depletion induces skin sodium mobilization in female Wistar rats

NEW FINDINGS

What is the central question of this study? Can Na⁺ depletion mobilize Na⁺ from the skin reservoir in ovariectomized rats? Does oestrogen replacement change the amount and the dynamics of skin Na⁺ storage? Is the reduced salt appetite after Na⁺ depletion in ovariectomized rats with oestrogen replacement related to changes in the skin Na⁺ ? What is the main finding and its importance? This work demonstrated that acute body Na⁺ depletion induced by frusemide mobilized the osmotically inactive skin Na⁺ reservoir to become osmotically active. Oestrogen treatment decreased the induced Na⁺ intake in ovariectomized rats but did not modulate the inactive Na⁺ reservoir in control conditions or its mobilization induced by Na⁺ depletion.

ABSTRACT

Oestradiol, which is an important hormone for water and electrolyte balance, also has a role in the inhibition of induced Na⁺ appetite. Sodium can be stored in the skin in osmotically active or inactive forms, and this skin Na⁺ reservoir may be involved in the control of body Na⁺ levels during physiopathological challenges. In this study, we investigated whether the effect of sodium depletion by frusemide can mobilize Na⁺ from the skin reservoir and whether oestradiol replacement changes or mobilizes the Na⁺ reserves in the skin. Ovariectomized Wistar rats were treated with vehicle or oestradiol for 7 days to evaluate the effects of oestrogen on the hydroelectrolyte balance, intake responses and skin Na⁺ and water content in basal conditions. Furthermore, the effects of oestrogen were evaluated after 24 h frusemide-induced whole-body Na⁺ depletion. Oestradiol-replaced rats exhibited reduced water intake without any significant changes in salt intake, Na⁺ excretion or water and Na⁺ skin content in basal conditions. After sodium depletion, both vehicle- and oestradiol-treated rats exhibited an increase in the osmotically active skin Na⁺ , which was associated with a decrease of the inactive skin Na⁺ reservoir. Oestrogen decreased the hypertonic saline intake induced by Na⁺ depletion, but it was not associated with any significant changes in the skin Na⁺ reservoir. Thus, sodium depletion is able to change the inactive-active skin Na⁺ reservoir balance. However, the oestrogenic modulation of sodium appetite after Na⁺ depletion is probably not related to the action of this hormone in the skin Na⁺ reservoir balance.

New Insights on the Role of Sodium in the Physiological Regulation of Blood Pressure and Development of Hypertension

A precise maintenance of sodium and fluid balance is an essential step in the regulation of blood pressure and alterations of this balance may lead to the development of hypertension. In recent years, several new advances were made in our understanding of the interaction between sodium and blood pressure regulation. The first is the discovery made possible with by new technology, such as ²³Na-MRI, that sodium can be stored non-osmotically in tissues including the skin and muscles particularly when subjects are on a high sodium diet or have a reduced renal capacity to excrete sodium. These observations prompted the refinement of the original model of regulation of sodium balance from a two-compartment model comprising the extracellular fluid within the intravascular and interstitial spaces to a three-compartment model that includes the intracellular space of some tissues, most prominently the skin. In this new model, the immune system plays a role, thereby supporting many previous studies indicating that the immune system is a crucial co-contributor to the maintenance of hypertension through pro-hypertensive effects in the kidney, vasculature, and brain. Lastly, there is now evidence that sodium can affect the gut microbiome, and induce pro-inflammatory and immune responses, which might contribute to the development of salt-sensitive hypertension.

Dietary reference values for sodium

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) derived dietary reference values (DRVs) for sodium. Evidence from balance studies on sodium and on the relationship between sodium intake and health outcomes, in particular cardiovascular disease (CVD)-related endpoints and bone health, was reviewed. The data were not sufficient to enable an average requirement (AR) or population reference intake (PRI) to be derived. However, by integrating the available evidence and associated uncertainties, the Panel considers that a sodium intake of 2.0 g/day represents a level of sodium for which there is sufficient confidence in a reduced risk of CVD in the general adult population. In addition, a sodium intake of 2.0 g/day is likely to allow most of the general adult population to maintain sodium balance. Therefore, the Panel considers that 2.0 g sodium/day is a safe and adequate intake for the general EU population of adults. The same value applies to pregnant and lactating women. Sodium intakes that are considered safe and adequate for children are extrapolated from the value for adults, adjusting for their respective energy requirement and including a growth factor, and are as follows: 1.1 g/day for children aged 1-3 years, 1.3 g/day for children aged 4-6 years, 1.7 g/day for children aged 7-10 years and 2.0 g/day for children aged 11-17 years, respectively. For infants aged 7-11 months, an Adequate Intake (AI) of 0.2 g/day is proposed based on upwards extrapolation of the estimated sodium intake in exclusively breast-fed infants aged 0-6 months.

High Salt Activates CD11c+ Antigen-Presenting Cells via SGK (Serum Glucocorticoid Kinase) 1 to Promote Renal Inflammation and Salt-Sensitive Hypertension

Salt-sensing mechanisms in hypertension involving the kidney, vasculature, and central nervous system have been well studied; however, recent studies suggest that immune cells can sense sodium (Na+). Antigen-presenting cells (APCs) including dendritic cells critically modulate inflammation by activating T cells and producing cytokines. We recently found that Na+ enters dendritic cells through amiloride-sensitive channels including the α and γ subunits of the epithelial sodium channel (ENaC) and mediates nicotinamide adenine dinucleotide phosphate oxidase-dependent formation of immunogenic IsoLG (isolevuglandin)-protein adducts leading to inflammation and hypertension. Here, we describe a novel pathway in which the salt-sensing kinase SGK1 (serum/glucocorticoid kinase 1) in APCs mediates salt-induced expression and assembly of ENaC-α and ENaC-γ and promotes salt-sensitive hypertension by activation of the nicotinamide adenine dinucleotide phosphate oxidase and formation of IsoLG-protein adducts. Mice lacking SGK1 in CD11c+ cells were protected from renal inflammation, endothelial dysfunction, and developed blunted hypertension during the high salt feeding phase of the N-Nitro-L-arginine methyl ester hydrochloride/high salt model of salt-sensitive hypertension. CD11c+ APCs treated with high salt exhibited increased expression of ENaC-γ which coimmunoprecipitated with ENaC-α. This was associated with increased activation and expression of various nicotinamide adenine dinucleotide phosphate oxidase subunits. Genetic deletion or pharmacological inhibition of SGK1 in CD11c+ cells prevented the high salt-induced expression of ENaC and nicotinamide adenine dinucleotide phosphate oxidase. These studies indicate that expression of SGK1 in CD11c+ APCs contributes to the pathogenesis of salt-sensitive hypertension.

Sodium Intake and Hypertension

The close relationship between hypertension and dietary sodium intake is widely recognized and supported by several studies. A reduction in dietary sodium not only decreases the blood pressure and the incidence of hypertension, but is also associated with a reduction in morbidity and mortality from cardiovascular diseases. Prolonged modest reduction in salt intake induces a relevant fall in blood pressure in both hypertensive and normotensive individuals, irrespective of sex and ethnic group, with larger falls in systolic blood pressure for larger reductions in dietary salt. The high sodium intake and the increase in blood pressure levels are related to water retention, increase in systemic peripheral resistance, alterations in the endothelial function, changes in the structure and function of large elastic arteries, modification in sympathetic activity, and in the autonomic neuronal modulation of the cardiovascular system. In this review, we have focused on the effects of sodium intake on vascular hemodynamics and their implication in the pathogenesis of hypertension.

23Na MRI of human skeletal muscle using long inversion recovery pulses

²³Na inversion recovery (IR) imaging allows for a weighting toward intracellular sodium in the human calf muscle and thus enables an improved analysis of pathophysiological changes of the muscular ion homeostasis. However, sodium signal-to-noise ratio (SNR) is low, especially when using IR sequences. ²³Na has a nuclear spin of 3/2 and therefore experiences a strong electrical quadrupolar interaction. This results in very short relaxation times as well as in possible residual quadrupolar splitting. Consequently, relaxation effects during a radiofrequency pulse can no longer be neglected and even allow for increasing SNR as has previously been shown for human brain and knee. The aim of this work was to increase the SNR in ²³Na IR imaging of the human calf muscle by using long inversion pulses instead of the usually applied short pulses. First, the influence of the inversion pulse length (1 to 20 ms) on the SNR as well as on image contrast was simulated for different model environments and verified by phantom measurements. Depending on the model environment (agarose 4% and 8%, xanthan 2% and 3%), SNR values increased by a factor of 1.15 up to 1.35, while NaCl solution was successfully suppressed. Thus, image contrast between the non-suppressed model compartments changes with IR pulse length. Finally, in vivo measurements of the human calf muscle of ten healthy volunteers were conducted at 3 Tesla. On average, a 1.4-fold increase in SNR could be achieved by increasing the inversion pulse length from 1 ms to 20 ms, leaving all other parameters - including the scan time - constant. This enables ²³Na IR MRI with improved spatial resolution or reduced acquisition time.

Exploring a new method for quantitative sodium MRI in the human upper leg with a surface coil and symmetrically arranged reference phantoms

Background

The aim of this study is to validate and evaluate the reproducibility of a new setup for the quantification of the tissue sodium concentration (TSC) in the human upper leg muscles with sodium MRI at 3 Tesla. This setup is making use of an emit and receive single loop surface coil together with a set of square, symmetrically arranged reference phantoms. As a second aim, the performances of two MRI protocols for the TSC quantification in the upper leg muscles are compared: one using an ultra-short echo time (UTE) 3-dimensional radial sequence (UTE-protocol), and the other one using standard gradient echo sequence (GRE-protocol).

Methods

A validation test of the quantification of sodium concentration is performed in phantoms. The bias of the method is estimated and compared between both protocols. The reproducibility of TSC quantification is assessed in phantoms by the coefficient of variation (CV) and compared between both protocols. The reproducibility is also assessed in 11 health volunteers. Signal to noise ratio (SNR) maps are acquired in phantoms with both protocols in order to compare the resulting SNR.

Results

The apparatus and post processing were successfully implemented. The bias of the method was smaller than 10% in phantoms (excepted for Na concentration of 10 mmol/L when using the GRE protocol). The reproducibility of the method using symmetrically arranged phantoms was high in phantoms and humans (CV <5%). The GRE-protocol leads to a better SNR than the UTE-protocol in 2D images.

Conclusions

The use of symmetrically arranged reference phantoms lead to reproducible results in phantoms and humans. Sodium imaging in the human upper leg with a single loop surface coil should be performed with a standard 2-dimensional GRE protocol if an optimal SNR is needed. However, the quantification of the fast and slow decay time constants of the sodium signal, which plays a role in the TSC quantification, still has to be done with a UTE sequence. Moreover, the quantification of sodium concentration is more accurate with the UTE protocol for small sodium concentrations (<20 mmol).

Abnormal sodium and water homeostasis in mice with defective heparan sulfate polymerization

Glycosaminoglycans in the skin interstitium and endothelial surface layer have been shown to be involved in local sodium accumulation without commensurate water retention. Dysfunction of heparan sulfate glycosaminoglycans may therefore disrupt sodium and water homeostasis. In this study, we investigated the effects of combined heterozygous loss of heparan sulfate polymerization genes (exostosin glycosyltransferase 1 and 2; Ext1^+/-Ext2^+/-) on sodium and water homeostasis. Sodium storage capacity was decreased in Ext1^+/-Ext2^+/- mice as reflected by a 77% reduction in endothelial surface layer thickness and a lower skin sodium-to-glycosaminoglycan ratio. Also, these mice were characterized by a higher heart rate, increased fluid intake, increased plasma osmolality and a decreased skin water and sodium content, suggesting volume depletion. Upon chronic high sodium intake, the initial volume depletion was restored but no blood pressure increase was observed. Acute hypertonic saline infusion resulted in a distinct blood pressure response: we observed a significant 15% decrease in control mice whereas blood pressure did not change in Ext1^+/-Ext2^+/- mice. This differential blood pressure response may be explained by the reduced capacity for sodium storage and/or the impaired vasodilation response, as measured by wire myography, which was observed in Ext1^+/-Ext2^+/- mice. Together, these data demonstrate that defective heparan sulfate glycosaminoglycan synthesis leads to abnormal sodium and water homeostasis and an abnormal response to sodium loading, most likely caused by inadequate capacity for local sodium storage.

Increased myocardial sodium signal intensity in Conn's syndrome detected by 23Na magnetic resonance imaging

AIMS

Sodium intake has been linked to left ventricular hypertrophy independently of blood pressure, but the underlying mechanisms remain unclear. Primary hyperaldosteronism (PHA), a condition characterized by tissue sodium overload due to aldosterone excess, causes accelerated left ventricular hypertrophy compared to blood pressure matched patients with essential hypertension. We therefore hypothesized that the myocardium constitutes a novel site capable of sodium storage explaining the missing link between sodium and left ventricular hypertrophy.

METHODS AND RESULTS

Using 23Na magnetic resonance imaging, we investigated relative sodium signal intensities (rSSI) in the heart, calf muscle, and skin in 8 PHA patients (6 male, median age 55 years) and 12 normotensive healthy controls (HC) (8 male, median age 61 years). PHA patients had a higher mean systolic 24 h ambulatory blood pressure [152 (140; 163) vs. 125 (122; 130) mmHg, P < 0.001] and higher left ventricular mass index [71.0 (63.5; 106.8) vs. 55.0 (50.3; 66.8) g/m2, P = 0.037] than HC. Compared to HC, PHA patients exhibited significantly higher rSSI in the myocardium [0.31 (0.26; 0.34) vs. 0.24 (0.20; 0.27); P = 0.007], calf muscle [0.19 (0.16; 0.22) vs. 0.14 (0.13; 0.15); P = 0.001] and skin [0.28 (0.25; 0.33) vs. 0.19 (0.17; 0.26); P = 0.014], reflecting a difference of +27%, +38%, and +39%, respectively. Treatment of PHA resulted in significant reductions of the rSSI in the myocardium, calf muscle and skin by -13%, -27%, and -29%, respectively.

CONCLUSION

Myocardial tissue rSSI is increased in PHA patients and treatment of aldosterone excess effectively reduces rSSI, thus establishing the myocardium as a novel site of sodium storage in addition to skeletal muscle and skin.

Dermal Interstitial Alterations in Patients With Heart Failure and Reduced Ejection Fraction: A Potential Contributor to Fluid Accumulation?

BACKGROUND

Large networks of interstitial glycosaminoglycans help to regulate water and electrolyte homeostasis. The relation between dermal interstitial alterations and occurrence of edema in heart failure patients with reduced ejection fraction (HFrEF) is unknown. We hypothesize that in HFrEF patients (1) interstitial glycosaminoglycan density is increased, (2) changes in the interstitial glycosaminoglycan network are associated with interstitial fluid accumulation, and (3) there is a link between the interstitial glycosaminoglycan network and the renin-angiotensin-aldosterone system.

METHODS AND RESULTS

Two punch biopsies of the skin were obtained in healthy subjects (n=18) and HFrEF patients (n=29). Alcian blue staining and immunostaining for the angiotensin II type 1 receptor was performed. After obtaining tissue water content, total interstitial glycosaminoglycan (uronic acid) and sulfated glycosaminoglycan were quantified. A venous blood sample, clinical examination, and echocardiography were obtained. A significantly higher interstitial glycosaminoglycan content was observed in HFrEF patients compared with healthy subjects (uronic acid: 13.0±4.2 versus 9.6±1.6 μg/mg; P=0.002; sulfated glycosaminoglycan: 14.1 [11.7; 18.1] versus 10.0 [9.1; 10.8] μg/mg; P<0.001). Uronic acid and sulfated glycosaminoglycan density were strongly associated with tissue water content and peripheral edema (uronic acid: ρ=0.66; P<0.0001 and sulfated glycosaminoglycan: τ=0.58; P<0.0001). Expression of the angiotensin II type 1 receptor was found on dermal cells, although use of angiotensin-converting enzyme inhibitors/angiotensin receptor blocker was associated with significantly lower levels of interstitial glycosaminoglycans in HFrEF patients.

CONCLUSIONS

Interstitial glycosaminoglycan concentration is significantly increased in HFrEF patients compared with healthy subjects and correlated with tissue water content and clinical signs of volume overload. A better appreciation of the interstitial compartment might improve management of volume overload in HF.

Tissue sodium content in patients with type 2 diabetes mellitus

BACKGROUND

Tissue sodium content by ²³Na magnetic resonance imaging (MRI) has been found to be increased in arterial hypertension. We analyzed whether tissue sodium content is increased in patients with type-2 diabetes (T2DM).

METHODS

Patients with T2DM were compared to those with primary hypertension. Patients with T2DM were off any antidiabetic and hypertensive patients off any antihypertensive therapy for at least 4 weeks. Skin and muscle sodium content was assessed non-invasively with a 3.0 T clinical MRI system (Magnetom Verio, Siemens Health Care, Erlangen, Germany) in each patient.

RESULTS

In patients with T2DM (N = 59) we observed significantly greater muscle sodium content (diabetes: 20.6 ± 3.5 vs hypertension: 16.3 ± 2.5 mmol/l, p < 0.001) and skin sodium content (diabetes: 24.5 ± 7.2 vs hypertension: 20.6 ± 5.7 mmol/l, p = 0.01) than in those with primary hypertension (N = 33). When potential confounders (age, body mass index, gender, systolic and diastolic blood pressure, estimated glomerular filtration rate) were entered in a covariance analysis, both skin sodium content (p = 0.037) and muscle sodium content (p < 0.001) were still clearly elevated.

CONCLUSION

Patients with T2DM have greater skin and muscle sodium content. These are the first known data to demonstrate increased tissue sodium content in patients with T2DM, measured by ²³Na magnetic resonance imaging. Since tissue sodium content is related to organ damage, therapeutic intervention should aim at reducing tissue sodium content.

The role of sodium in modulating immune cell function

Sodium intake is undoubtedly indispensable for normal body functions but can be detrimental when taken in excess of dietary requirements. The consequences of excessive salt intake are becoming increasingly clear as high salt consumption persists across the globe. Salt has long been suspected to promote the development of hypertension and cardiovascular diseases and is now also recognized as a potential modulator of inflammatory and autoimmune diseases through its direct and indirect effects on immune cells. The finding that, in addition to the kidneys, other organs such as the skin regulate sodium levels in the body prompted new hypotheses, including the concept that skin-resident macrophages might participate in tissue sodium regulation through their interactions with lymphatic vessels. Moreover, immune cells such as macrophages and different T cell subsets are found in sodium-rich interstitial microenvironments, where sodium levels modulate their function. Alterations to the intestinal bacterial community induced by excess dietary salt represent another relevant axis whereby salt indirectly modulates immune cell function. Depending on the inflammatory context, sodium might either contribute to protective immunity (for example, by enhancing host responses against cutaneous pathogens) or it might contribute to immune dysregulation and promote the development of cardiovascular and autoimmune diseases.

Multinuclear MRI at Ultrahigh Fields

In this article, an overview of the current developments and research applications for non-proton magnetic resonance imaging (MRI) at ultrahigh magnetic fields (UHFs) is given. Due to technical and methodical advances, efficient MRI of physiologically relevant nuclei, such as Na, Cl, Cl, K, O, or P has become feasible and is of interest to obtain spatially and temporally resolved information that can be used for biomedical and diagnostic applications. Sodium (Na) MRI is the most widespread multinuclear imaging method with applications ranging over all regions of the human body. Na MRI yields the second largest in vivo NMR signal after the clinically used proton signal (H). However, other nuclei such as O and P (energy metabolism) or Cl and K (cell viability) are used in an increasing number of MRI studies at UHF. One major advancement has been the increased availability of whole-body MR scanners with UHFs (B0 ≥7T) expanding the range of detectable nuclei. Nevertheless, efforts in terms of pulse sequence and post-processing developments as well as hardware designs must be made to obtain valuable information in clinically feasible measurement times. This review summarizes the available methods in the field of non-proton UHF MRI, especially for Na MRI, as well as introduces potential applications in clinical research.

Residual Renal Function and Effect of Low-Sodium Solution on Blood Pressure in Peritoneal Dialysis Patients

Background:Residual renal function (RRF) affects sodium and fluid balance. The aim of this analysis was to examine the impact of RRF on the effect of a sodium-reduced peritoneal dialysis fluid (PDF) on blood pressure (BP).Methods:This is a post-hoc analysis of a prospective, randomized, controlled double-blind clinical trial with 82 patients on continuous ambulatory PD (CAPD) treated with a low-sodium (125 mmol/L Na) or a standard-sodium (134 mmol/L Na) PDF. Subgroups according to glomerular filtration rate (GFR) at baseline (≤ / > 6 mL/min/1.73 m²) were analyzed for BP and antihypertensive medication.Results:In the low-GFR group on low-sodium PDF (N = 26), systolic BP was reduced from 152 ± 24 mmHg at baseline to 137 ± 21 mmHg at week 12, diastolic BP from 90 ± 16 mmHg to 83 ± 11 mmHg. In the low-GFR group on standard-sodium PDF and in the high-GFR group on both PDF types, only minor changes were observed. For the low-GFR subgroup, the confounder-adjusted mean study group difference in systolic BP at week 12 between low-sodium and standard-sodium PDF was -16.9 (95% confidence interval [CI] -27.2 to -6.6) mmHg, for diastolic BP, it was -7.0 (95% CI -12.6 to -1.4) mmHg. In both GFR subgroups, more patients had a reduced daily dose of antihypertensive medication and fewer patients an increased daily dose in the low-sodium compared with the standard-sodium group at week 12.Conclusions:The reduction of BP with a sodium-reduced PDF seems to be more effective in patients with no or low RRF than in patients with residual capacity of renal sodium and fluid control.

Dietary Habits Bursting into the Complex Pathogenesis of Autoimmune Diseases: The Emerging Role of Salt from Experimental and Clinical Studies

The incidence and prevalence of autoimmune diseases have increased in Western countries over the last years. The pathogenesis of these disorders is multifactorial, with a combination of genetic and environmental factors involved. Since the epidemiological changes cannot be related to genetic background, which did not change significantly in that time, the role of environmental factors has been reconsidered. Among these, dietary habits, and especially an excessive salt, typical of processed foods, has been implicated in the development of autoimmune diseases. In this review, we summarize current evidence, deriving both from experimental models and clinical studies, on the capability of excessive salt intake to exacerbate proinflammatory responses affecting the pathogenesis of immune-mediated diseases. Data on several diseases are presented, including rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, and Crohn’s disease, with many of them supporting a proinflammatory effect of salt. Likewise, a hypertonic microenvironment showed similar effects in experimental models both in vivo and in vitro. However, murine models of spontaneous autoimmune polyneuropathy exposed to high salt diet suggest opposite outcomes. These results dictate the need to further analyse the role of cooking salt in the treatment and prevention of autoimmune diseases, trying to shape a fine tuning between the possible advantages of a restricted salt intake and the changes in circulating metabolites, mediators, and hormones which come along salt consumption and could in turn influence autoimmunity.

The Influence of Dietary Salt Beyond Blood Pressure

PURPOSE OF REVIEW

Excess sodium from dietary salt (NaCl) is linked to elevations in blood pressure (BP). However, salt sensitivity of BP varies widely between individuals and there are data suggesting that salt adversely affects target organs, irrespective of BP.

RECENT FINDINGS

High dietary salt has been shown to adversely affect the vasculature, heart, kidneys, skin, brain, and bone. Common mediators of the target organ dysfunction include heightened inflammation and oxidative stress. These physiological alterations may contribute to disease development over time. Despite the adverse effects of salt on BP and several organ systems, there is controversy surrounding lower salt intakes and cardiovascular outcomes. Our goal here is to review the physiology contributing to BP-independent effects of salt and address the controversy around lower salt intakes and cardiovascular outcomes. We will also address the importance of background diet in modulating the effects of dietary salt.

Effects of Water Loading on Observed and Predicted Plasma Sodium, and Fluid and Urine Cation Excretion in Healthy Individuals

RATIONALE & OBJECTIVE

The discovery of sodium storage without concurrent water retention suggests the presence of an additional compartment for sodium distribution in the body. The osmoregulatory role of this compartment under hypotonic conditions is not known.

STUDY DESIGN

Experimental interventional study.

SETTING & PARTICIPANTS

Single-center study of 12 apparently healthy men.

INTERVENTION

To investigate whether sodium can be released from its nonosmotic stores after a hypotonic fluid load, a water-loading test (20mL water/kg in 20 minutes) was performed.

OUTCOMES

During a 240-minute follow-up, we compared the observed plasma sodium concentration ([Na⁺]) and fluid and urine cation excretion with values predicted by the Barsoum-Levine and Nguyen-Kurtz formulas. These formulas are used for guidance of fluid therapy during dysnatremia, but do not account for nonosmotic sodium stores.

RESULTS

30 minutes after water loading, mean plasma [Na⁺] decreased 3.2±1.6 (SD) mmol/L, after which plasma [Na⁺] increased gradually. 120 minutes after water loading, plasma [Na⁺] was significantly underestimated by the Barsoum-Levine (-1.3±1.4mmol/L; P=0.05) and Nguyen-Kurtz (-1.5±1.5mmol/L; P=0.03) formulas. In addition, the Barsoum-Levine and Nguyen-Kurtz formulas overestimated urine volume, while cation excretion was significantly underestimated, with a cation gap of 57±62 (P=0.009) and 63±63mmol (P=0.005), respectively. After 240 minutes, this gap was 28±59 (P=0.2) and 34±60mmol (P=0.08), respectively.

LIMITATIONS

The compartment from which the mobilized sodium originated was not identified, and heterogeneity in responses to water loading was observed across participants.

CONCLUSIONS

These data suggest that healthy individuals are able to mobilize osmotically inactivated sodium after an acute hypotonic fluid load. Further research is needed to expand knowledge about the compartment of osmotically inactivated sodium and its role in osmoregulation and therapy for dysnatremias.

FUNDING

This investigator-initiated study was partly supported by a grant from Unilever Research and Development Vlaardingen, The Netherlands B.V. (MA-2014-01914).

Dermal tissue remodeling and non-osmotic sodium storage in kidney patients

Background

Excess dietary sodium is not only excreted by the kidneys, but can also be stored by non-osmotic binding with glycosaminoglycans in dermal connective tissue. Such storage has been associated with dermal inflammation and lymphangiogenesis. We aim to investigate if skin storage of sodium is increased in kidney patients and if this storage is associated with clinical parameters of sodium homeostasis and dermal tissue remodeling.

Methods

Abdominal skin tissue of 12 kidney patients (5 on hemodialysis) and 12 healthy kidney donors was obtained during surgery. Skin biopsies were processed for dermal sodium measurement by atomic absorption spectroscopy, and evaluated for CD⁶⁸⁺ macrophages, CD³⁺ T-cells, collagen I, podoplanin + lymph vessels, and glycosaminoglycans by qRT-PCR and immunohistochemistry.

Results

Dermal sodium content of kidney patients did not differ from healthy individuals, but was inversely associated with plasma sodium values (p < 0.05). Compared to controls, kidney patients showed dermal tissue remodeling by increased CD⁶⁸⁺ macrophages, CD³⁺ T-cells and Collagen I expression (all p < 0.05). Also, both N- and O-sulfation of heparan sulfate glycosaminoglycans were increased (all p < 0.05), most outspoken in hemodialysis patients. Plasma and urinary sodium associates with dermal lymph vessel number (both p < 0.05), whereas loss of eGFR, proteinuria and high systolic blood pressure associated with dermal macrophage density (all p < 0.05).

Conclusion

Kidney patients did not show increased skin sodium storage compared to healthy individuals. Results do indicate that kidney failure associates with dermal inflammation, whereas increased sodium excretion and plasma sodium associate with dermal lymph vessel formation and loss of dermal sodium storage capacity.

Trial registration The cohort is registered at clinicaltrials.gov as NCT (September 6, 2017). NCT, NCT03272841. Registered 6 September 2017—Retrospectively registered, https://clinicaltrials.gov

Common skin bacteria protect their host from oxidative stress through secreted antioxidant RoxP

Cutibacterium acnes is an abundant skin commensal with several proposed mutualistic functions. A protein with strong antioxidant activity was recently identified from the C. acnes secretome. This protein, termed RoxP, facilitated aerobic bacterial growth in vitro and ex vivo. As reducing events naturally occurred outside of the bacterial cell, it was further hypothesized that RoxP could also serve to modulate redox status of human skin. The biological function of RoxP was here assessed in vitro and in vivo, through oxidatively stressed cell cultures and through protein quantification from skin affected by oxidative disease (actinic keratosis and basal cell carcinoma), respectively. 16S rDNA amplicon deep sequencing and single locus sequence typing was used to correlate bacterial prevalence to cutaneous RoxP abundances. We show that RoxP positively influence the viability of monocytes and keratinocytes exposed to oxidative stress, and that a congruent concentration decline of RoxP can be observed in skin affected by oxidative disease. Basal cell carcinoma was moreover associated with microbial dysbiosis, characterized by reduced C. acnes prevalence. C. acnes's secretion of RoxP, an exogenous but naturally occurring antioxidant on human skin, is likely to positively influence the human host. Results furthermore attest to its prospective usability as a biopharmaceutical.

Potential of Sodium MRI as a Biomarker for Neurodegeneration and Neuroinflammation in Multiple Sclerosis

In multiple sclerosis (MS), experimental and ex vivo studies indicate that pathologic intra- and extracellular sodium accumulation may play a pivotal role in inflammatory as well as neurodegenerative processes. Yet, in vivo assessment of sodium in the microenvironment is hard to achieve. Here, sodium magnetic resonance imaging (²³NaMRI) with its non-invasive properties offers a unique opportunity to further elucidate the effects of sodium disequilibrium in MS pathology in vivo in addition to regular proton based MRI. However, unfavorable physical properties and low in vivo concentrations of sodium ions resulting in low signal-to-noise-ratio (SNR) as well as low spatial resolution resulting in partial volume effects limited the application of ²³NaMRI. With the recent advent of high-field MRI scanners and more sophisticated sodium MRI acquisition techniques enabling better resolution and higher SNR, ²³NaMRI revived. These studies revealed pathologic total sodium concentrations in MS brains now even allowing for the (partial) differentiation of intra- and extracellular sodium accumulation. Within this review we (1) demonstrate the physical basis and imaging techniques of ²³NaMRI and (2) analyze the present and future clinical application of ²³NaMRI focusing on the field of MS thus highlighting its potential as biomarker for neuroinflammation and -degeneration.

Much Ado about N…atrium: modelling tissue sodium as a highly sensitive marker of subclinical and localized oedema

Hypertonic Na⁺ accumulation in peripheral tissues is a recently described phenomenon: it has been associated with ageing, hypertension, diabetes, chronic kidney disease and heart failure, but its clinical meaning has yet to be determined. This concept conflicts with the classic physiological paradigm of constant balance between salt intake and excretion, and its water-independent nature is still a matter of debate.

We developed a theoretical model explaining changes in the chemical composition of tissues as a function of extracellular volume fraction and excess extracellular fluid, i.e. oedema. The model suggests that the proportional increase in absolute Na⁺ content and concentration due to different degrees of oedema is higher than the parallel increase in water content, thus making Na⁺ a more sensitive index to detect this oedema.

Our model would explain some of the recent findings of high tissue Na⁺ content in pathological conditions. More importantly, it prompts the reappraisal of tissue Na⁺ analysis from being a topic of niche interest to a potential diagnostic tool with broad applicability in the investigation of subclinical systemic and localized oedema.

Regulatory T Cells: From Discovery to Autoimmunity

Multiple sclerosis (MS) is a genetically mediated autoimmune disease of the central nervous system. Allelic variants lead to lower thresholds of T-cell activation resulting in activation of autoreactive T cells. Environmental factors, including, among others, diet, vitamin D, and smoking, in combination with genetic predispositions, play a substantial role in disease development and activation of autoreactive T cells. FoxP3⁺ regulatory T cells (Tregs) have emerged as central in the control of autoreactive T cells. A consistent finding in patients with MS is defects in Treg cell function with reduced suppression of effector T cells and production of proinflammatory cytokines. Emerging data suggests that functional Tregs become effector-like T cells with loss of function associated with T-bet expression and interferon γ (IFN-γ) secretion.

Double quantum filtered 23 Na MRI with magic angle excitation of human skeletal muscle in the presence of B0 and B1 inhomogeneities

Double quantum filtered ²³ Na MRI with magic angle excitation (DQF-MA) can be used to selectively detect sodium ions located within anisotropic structures such as muscle fibers. It might therefore be a promising tool to analyze the microscopic environment of sodium ions, for example in the context of osmotically neutral sodium retention. However, DQF-MA imaging is challenging due to various signal dependences, on both measurement parameters and external influences. The aim of this work was to examine how B₀ in combination with B₁ inhomogeneities alter the DQF-MA signal intensity. We showed that, in the presence of B₀ inhomogeneities, flip angle schemes with only one 54.7° pulse can be favorable compared with the classical 90°-54.7°-54.7° scheme. DQF-MA images of the human lower leg were acquired at B₀  = 3 T with a nominal spatial resolution of 12 × 12 × 36 mm³ within an acquisition time of T_Acq  < 10 min, and compared with spin density weighted (DW), as well as triple quantum filtration (TQF) ²³ Na images. We found mean normalized signal-to-noise ratios of TQF/DW = 13.7 ± 2.3% (tibialis anterior), 11.9 ± 2.3% (soleus) and 11.4 ± 2.2% (gastrocnemius medialis), as well as DQF-MA/DW = 4.7 ± 1.1% (tibialis anterior), 3.3 ± 0.73% (soleus) and 3.4 ± 0.6% (gastrocnemius medialis). These ratios might serve as additional measures in future clinical studies of sodium retention within human skeletal muscle. However, the influence of B₀ and B₁ inhomogeneities should be considered when interpreting DQF-MA images.

Pros and cons of ultra-high-field MRI/MRS for human application

Magnetic resonance imaging and spectroscopic techniques are widely used in humans both for clinical diagnostic applications and in basic research areas such as cognitive neuroimaging. In recent years, new human MR systems have become available operating at static magnetic fields of 7 T or higher (≥300 MHz proton frequency). Imaging human-sized objects at such high frequencies presents several challenges including non-uniform radiofrequency fields, enhanced susceptibility artifacts, and higher radiofrequency energy deposition in the tissue. On the other side of the scale are gains in signal-to-noise or contrast-to-noise ratio that allow finer structures to be visualized and smaller physiological effects to be detected. This review presents an overview of some of the latest methodological developments in human ultra-high field MRI/MRS as well as associated clinical and scientific applications. Emphasis is given to techniques that particularly benefit from the changing physical characteristics at high magnetic fields, including susceptibility-weighted imaging and phase-contrast techniques, imaging with X-nuclei, MR spectroscopy, CEST imaging, as well as functional MRI. In addition, more general methodological developments such as parallel transmission and motion correction will be discussed that are required to leverage the full potential of higher magnetic fields, and an overview of relevant physiological considerations of human high magnetic field exposure is provided.

Recent advances in renal imaging

Kidney diseases can be caused by a wide range of genetic, hemodynamic, toxic, infectious, and autoimmune factors. The diagnosis of kidney disease usually involves the biochemical analysis of serum and blood, but these tests are often insufficiently sensitive or specific to make a definitive diagnosis. Although radiologic imaging currently has a limited role in the evaluation of most kidney diseases, several new imaging methods hold great promise for improving our ability to non-invasively detect structural, functional, and molecular changes within the kidney. New methods, such as dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and blood oxygen level-dependent (BOLD) MRI, allow functional imaging of the kidney. The use of novel contrast agents, such as microbubbles and nanoparticles, allows the detection of specific molecules in the kidney. These methods could greatly advance our ability to diagnose disease and also to safely monitor patients over time. This could improve the care of individual patients, and it could also facilitate the evaluation of new treatment strategies.

Mechanisms of sodium balance: total body sodium, surrogate variables, and renal sodium excretion

The classical concepts of human sodium balance include 1) a total pool of Na+ of ≈4,200 mmol (total body sodium, TBS) distributed primarily in the extracellular fluid (ECV) and bone, 2) intake variations of 0.03 to ≈6 mmol·kg body mass−1·day−1, 3) asymptotic transitions between steady states with a halftime (T½) of 21 h, 4) changes in TBS driven by sodium intake measuring ≈1.3 day [ΔTBS/Δ(Na+ intake/day)], 5) adjustment of Na+ excretion to match any diet thus providing metabolic steady state, and 6) regulation of TBS via controlled excretion (90–95% renal) mediated by surrogate variables. The present focus areas include 1) uneven, nonosmotic distribution of increments in TBS primarily in “skin,” 2) long-term instability of TBS during constant Na+ intake, and 3) physiological regulation of renal Na+ excretion primarily by neurohumoral mechanisms dependent on ECV rather than arterial pressure. Under physiological conditions 1) the nonosmotic distribution of Na+ seems conceptually important, but quantitatively ill defined; 2) long-term variations in TBS represent significant deviations from steady state, but the importance is undetermined; and 3) the neurohumoral mechanisms of sodium homeostasis competing with pressure natriuresis are essential for systematic analysis of short-term and long-term regulation of TBS. Sodium homeostasis and blood pressure regulation are intimately related. Real progress is slow and will accelerate only through recognition of the present level of ignorance. Nonosmotic distribution of sodium, pressure natriuresis, and volume-mediated regulation of renal sodium excretion are essential intertwined concepts in need of clear definitions, conscious models, and future attention.

The Contribution of Skin Glycosaminoglycans to the Regulation of Sodium Homeostasis in Rats

The glycosaminoglycan (GAG) molecules are a group of high molecular weight, negatively charged polysaccharides present abundantly in the mammalian organism. By their virtue of ion and water binding capacity, they may affect the redistribution of body fluids and ultimately the blood pressure. Data from the literature suggests that the mitogens Vascular Endothelial Growth Factor (VEGF)-A and VEGF-C are able to regulate the amount and charge density of GAGs and their detachment from the cell surface. Based on these findings we investigated the relationship between the level of dietary sodium intake, the expression levels of VEGF-A and VEGF-C, and the amount of the skin GAGs hyaluronic acid and chondroitin sulfate in an in vivo rat model. Significant correlation between dietary sodium intake, skin sodium levels and GAG content was found. We confirmed the GAG synthesizing role of VEGF-C but failed to prove that GAGs are degraded by VEGF-A. No significant difference in blood pressure was registered between the different dietary groups. A quotient calculated form the ion and water content of the skin tissue samples suggests that – in contrast to previous findings – the osmotically inactive ions and bound water fractions are proportional.

Estimation of sodium and chloride storage in critically ill patients: a balance study

BACKGROUND

Nonosmotic sodium storage has been reported in animals, healthy individuals and patients with hypertension, hyperaldosteronism and end-stage kidney disease. Sodium storage has not been studied in ICU patients, who frequently receive large amounts of sodium chloride-containing fluids. The objective of our study was to estimate sodium that cannot be accounted for by balance studies in critically ill patients. Chloride was also studied. We used multiple scenarios and assumptions for estimating sodium and chloride balances.

METHODS

We retrospectively analyzed patients admitted to the ICU after cardiothoracic surgery with complete fluid, sodium and chloride balance data for the first 4 days of ICU treatment. Balances were obtained from meticulously recorded data on intake and output. Missing extracellular osmotically active sodium (MES) was calculated by subtracting the expected change in plasma sodium from the observed change in plasma sodium derived from balance data. The same method was used to calculate missing chloride (MEC). To address considerable uncertainties on the estimated extracellular volume (ECV) and perspiration rate, various scenarios were used in which the size of the ECV and perspiration were varied.

RESULTS

A total of 38 patients with 152 consecutive ICU days were analyzed. In our default scenario, we could not account for 296 ± 35 mmol of MES in the first four ICU days. The range of observed MES in the five scenarios varied from 111 ± 27 to 566 ± 41 mmol (P < 0.001). A cumulative value of 243 ± 46 mmol was calculated for MEC in the default scenario. The range of cumulative MEC was between 62 ± 27 and 471 ± 56 mmol (P = 0.001 and P = 0.003). MES minus MEC varied from 1 ± 51 to 123 ± 33 mmol in the five scenarios.

CONCLUSIONS

Our study suggests considerable disappearance of osmotically active sodium in critically ill patients and is the first to also suggest rather similar disappearance of chloride from the extracellular space. Various scenarios for insensible water loss and estimated size for the ECV resulted in considerable MES and MEC, although these estimates showed a large variation. The mechanisms and the tissue compartments responsible for this phenomenon require further investigation.

Acute NaCl Loading Reveals a Higher Blood Pressure for a Given Serum Sodium Level in African American Compared to Caucasian Adults

Purpose: African American individuals are more prone to salt-sensitive hypertension than Caucasian individuals. Small changes in serum sodium (Na⁺) result in increased blood pressure (BP). However, it remains unclear if there are racial differences in BP responsiveness to increases in serum Na⁺. Therefore, the purpose of this investigation was to determine if African American adults have altered BP responsiveness to acute changes in serum Na⁺ compared to Caucasian adults.

Methods: We measured beat-by-beat BP, serum Na⁺, plasma renin activity (PRA), angiotensin II (Ang II), and aldosterone (Aldo) during a 60-min 3% NaCl infusion (hypertonic saline infusion, HSI) in 39 participants (19 African Americans, age: 23 ± 1, 20 Caucasians, age: 25 ± 1). Data reported as African American vs. Caucasian cohort, mean ± SEM.

Results: Baseline BP and serum Na⁺ were similar between groups and increased during HSI in both African American and Caucasian participants (p < 0.01). However, the peak change in serum Na⁺ was greater in African American participants (Δ5.8 ± 0.34 vs. Δ4.85 ± 0.38 mmol/L, p = 0.03). There was a significant group effect (p = 0.02) and an interaction between race and serum Na⁺ on systolic BP (p = 0.02). Larger categorical changes in serum Na⁺ corresponded to changes in systolic BP (p < 0.01) and African American participants demonstrated greater systolic BP responses for a given categorical serum Na⁺ increase (p < 0.01). Baseline Aldo was lower in African American adults (7.2 ± 0.6 vs. 12.0 ± 1.9 ng/dL, p = 0.03), there was a trend for lower baseline PRA (0.59 ± 0.9 vs. 1.28 ± 0.34 ng/mL/h, p = 0.07), and baseline Ang II was not different (14.2 ± 1.8 vs. 18.5 ± 1.4 pg/mL, p = 0.17). PRA and Aldo decreased during the HSI (p ≤ 0.01), with a greater decline in PRA (Δ–0.31 ± 0.07 vs. Δ–0.85 ± 0.25 ng/mL/h, p < 0.01) and Aldo (Δ–2.5 ± 0.5 vs. Δ–5.0 ± 1.1 ng/dL, p < 0.01) in Caucasian participants. However, the racial difference in PRA (p = 0.57) and Aldo (p = 0.59) reduction were no longer significant following baseline covariate analysis. Conclusion: African American individuals demonstrate augmented serum Na⁺ to an acute hypertonic saline load and greater systolic BP responsiveness to a given serum Na⁺. The altered BP response may be attributable to lower basal PRA and Aldo and a subsequently blunted RAAS response during the HSI.

Salt, water and nephron: Mechanisms of action and link to hypertension and chronic kidney disease

Our knowledge on sodium and water homeostasis and regulation continues to evolve. A considerable amount of new information in this area has emerged in recent years. This review summarizes existing and new literature and discusses complex multi-organ effects of high-salt and low-water intake and role of arginine vasopressin in this process, as well as the potential clinical significance of non-osmotic sodium storage pool and rhythmicity of urine sodium excretion. It has become clear that sodium and water dysregulation can exert profound effects on kidney and vascular health, far greater than previously recognized. Maladaptation to a combined high-salt and low-water intake can be linked to the growing epidemic of hypertension and chronic kidney disease.

Skin Sodium and Hypertension: a Paradigm Shift?

Purpose of Review

Dietary sodium is an important trigger for hypertension and humans show a heterogeneous blood pressure response to salt intake. The precise mechanisms for this have not been fully explained although renal sodium handling has traditionally been considered to play a central role.

Recent Findings

Animal studies have shown that dietary salt loading results in non-osmotic sodium accumulation via glycosaminoglycans and lymphangiogenesis in skin mediated by vascular endothelial growth factor-C, both processes attenuating the rise in BP. Studies in humans have shown that skin could be a buffer for sodium and that skin sodium could be a marker of hypertension and salt sensitivity.

Summary

Skin sodium storage could represent an additional system influencing the response to salt load and blood pressure in humans.

High-Salt Diet Causes Expansion of the Lymphatic Network and Increased Lymph Flow in Skin and Muscle of Rats

Objective—

A commonly accepted pivotal mechanism in fluid volume and blood pressure regulation is the parallel relationship between body Na + and extracellular fluid content. Several recent studies have, however, shown that a considerable amount of Na + can be retained in skin without commensurate water retention. Here, we asked whether a salt accumulation shown to result in VEGF (vascular endothelial growth factor)-C secretion and lymphangiogenesis had any influence on lymphatic function.

Approach and Results—

By optical imaging of macromolecular tracer washout in skin, we found that salt accumulation resulted in an increase in lymph flow of 26% that was noticeable only after including an overnight recording period. Surprisingly, lymph flow in skeletal muscle recorded with a new positron emission tomography/computed tomography method was also increased after salt exposure. The transcapillary filtration was unaffected by the high-salt diet and deoxycorticosterone-salt treatment, suggesting that the capillary barrier was not influenced by the salt accumulation. A significant reduction in lymph flow after depletion of macrophages/monocytes by clodronate suggests these cells are involved in the observed lymph flow response, together with collecting vessels shown here to enhance their contraction frequency as a response to extracellular Na + .

Conclusions—

The observed changes in lymph flow suggest that the lymphatics may influence long-term regulation of tissue fluid balance during salt accumulation by contributing to fluid homeostasis in skin and muscle. Our studies identify lymph clearance as a potential disease-modifying factor that might be targeted in conditions characterized by salt accumulation like chronic kidney disease and salt-sensitive hypertension.

Water Homeostasis and Cell Volume Maintenance and Regulation

From early unicellular organisms that formed in salty water environments to complex organisms that live on land away from water, cells have had to protect a homeostatic internal environment favorable to the biochemical reactions necessary for life. In this chapter, we will outline what steps were necessary to conserve the water within our cells and how mechanisms have evolved to maintain and regulate our cellular and organismal volume. We will first examine whole body water homeostasis and the relationship between kidney function, regulation of blood pressure, and blood filtration in the process of producing urine. We will then discuss how the composition of the lipid-rich bilayer affects its permeability to water and salts, and how the cell uses this differential to drive physiological and biochemical cellular functions. The capacity to maintain cell volume is vital to epithelial transport, neurotransmission, cell cycle, apoptosis, and cell migration. Finally, we will wrap up the chapter by discussing in some detail specific channels, cotransporters, and exchangers that have evolved to facilitate the movement of cations and anions otherwise unable to cross the lipid-rich bilayer and that are involved in maintaining or regulating cell volume.

Reliability and agreement of sodium (23Na) MRI in calf muscle and skin of healthy subjects from the US

PURPOSE

To quantify the reliability and agreement of sodium (²³Na) MRI in calf muscle and skin of healthy subjects and to measure the smallest real difference (SRD) in each.

SUBJECTS AND METHODS

Thirty healthy subjects underwent ²³Na MRI studies of the calf. A scan-rescan protocol was performed the same day and 1 week later. Relative sodium concentration was measured in the calf muscle and skin and compared between studies.

RESULTS

A high degree of reliability was confirmed between the scan and rescan tests using linear regression analysis. The Bland-Altman plots indicated high agreement between runs in all regions. The SRD was measured between scans taken the same day and one week later. Correlations were also reported with age, gender and race.

CONCLUSIONS

Reliability and agreement of ²³Na MRI in the calf muscle and skin show promise for accurately assessing serial changes in patients.

Evaluation of renal and cardiovascular protection mechanisms of SGLT2 inhibitors: model-based analysis of clinical data

The mechanisms of cardiovascular and renal protection observed in clinical trials of sodium-glucose cotransporter 2 (SGLT2) inhibitors (SGLT2i) are incompletely understood and likely multifactorial, including natriuretic, diuretic, and antihypertensive effects, glomerular pressure reduction, and lowering of plasma and interstitial fluid volume. To quantitatively evaluate the contribution of proposed SGLT2i mechanisms of action on changes in renal hemodynamics and volume status, we coupled a mathematical model of renal function and volume homeostasis with clinical data in healthy subjects administered 10 mg of dapagliflozin once daily. The minimum set of mechanisms necessary to reproduce observed clinical responses (urinary sodium and water excretion, serum creatinine and sodium) was determined, and important unobserved physiological variables (glomerular pressure, blood and interstitial fluid volume) were then simulated. We further simulated the response to SGLT2i in diabetic virtual patients with and without renal impairment. Multiple mechanisms were required to explain the observed response: 1) direct inhibition of sodium and glucose reabsorption through SGLT2, 2) SGLT2-driven inhibition of Na⁺/H⁺ exchanger 3 sodium reabsorption, and 3) osmotic diuresis coupled with peripheral sodium storage. The model also showed that the consequences of these mechanisms include lowering of glomerular pressure, reduction of blood and interstitial fluid volume, and mild blood pressure reduction, in agreement with clinical observations. The simulations suggest that these effects are more significant in diabetic patients than healthy subjects and that while glucose excretion may diminish with renal impairment, improvements in glomerular pressure and blood volume are not diminished at lower glomerular filtration rate, suggesting that cardiorenal benefits of SGLT2i may be sustained in renally impaired patients.

Sodium chloride triggers Th17 mediated autoimmunity

The detrimental effects of a high-salt diet on human health have received much attention in the past few years. While it has been well established that high dietary salt intake is related to cardiovascular diseases, there is growing evidence that excess salt also affects the immune system and might be considered as a risk factor in autoimmune diseases such as multiple sclerosis (MS). Several studies have implicated T helper 17 cells (Th17) in the pathogenesis of MS. We and others recently demonstrated that excessive salt enhances the differentiation of Th17 cells, inducing a highly pathogenic phenotype that aggravates experimental neuroinflammation. Moreover, a diet rich in sodium affects intestinal microbiota alongside increased intestinal Th17 cells, thus linking the detrimental effects of high salt consumption to the gut-immune axis. First human studies revealed an association of increased MS disease activity with elevated sodium chloride consumption, while more recent epidemiology studies in larger cohorts suggest no correlation between salt intake and MS. However, it is known that ordinary urinary sodium analyses and nutritional questionnaires do not necessarily correspond to the actual sodium load and more sophisticated analyses are needed. Moreover, studies revealed that sodium can temporarily be stored in the body. This review summarizes recent findings on the impact of salt on the immune system and discusses potential challenges investigating dietary salt intake as a risk factor in MS.

Dietary Influence on Body Fluid Acid-Base and Volume Balance: The Deleterious "Norm" Furthers and Cloaks Subclinical Pathophysiology

The popular modern diet, characterized by an excess of animal protein and salt but insufficient in fruits, vegetables and water, is a poor fit for human physiological and homeostatic regulatory systems. Sustained net acid and sodium retention, coupled with an insufficient intake of cardiovascular protective potassium-rich foods and hydration in the modern diet can give rise to debilitating chronic organ dysfunction and ultimately, mortality. This holds true, especially in our aging population who are already facing inevitable decline in organ functional reserve. Importantly, in most cases, despite the mismatch and adverse effects to multiple organ systems, plasma electrolyte and acid-base parameters can, on the surface, be maintained within a “normal” reference range, primarily by activating (often maximally activating) compensatory homeostatic mechanisms. These diet-induced effects can thus be clinically silent for decades. Embodied in the chronic corrective homeostatic processes, however, are real risks for multiorgan damage. According to the Dietary Guideline Advisory Committee (DGAC), half of American adults have one or more chronic diseases that are preventable with dietary modification. Here, homeostasis of body fluid acid-base, sodium, potassium and water is examined. Our current dietary habits and their required regulatory adaptation, maladaptation and relevant physiology and pathophysiology are discussed. A framework of dietary modifications to avoid a propensity for maladaptation and thus lowers the risks of common modern diseases (primary prevention) and minimizes the risk of chronic and age-related disease progression (secondary prevention) is emphasized. Although there are other variables at play, a key to restoring the all-important dietary potassium to sodium ratio is greater consumption of vegetables/fruits and adopting salt temperance. Dietary and nutritional optimization is an under-emphasized area of health care that has an enormous potential to temper the epidemics of prevalent chronic diseases in modern society and improve population health.

Salt, inflammation, IL-17 and hypertension

Traditionally, arterial hypertension and subsequent end-organ damage have been attributed to haemodynamic factors, but increasing evidence indicates that inflammation also contributes to the deleterious consequences of this disease. The immune system has evolved to prevent invasion of foreign microorganisms and to promote tissue healing after injury. However, this beneficial activity comes at a cost of collateral damage when the immune system overreacts to internal injury, such as prehypertension. Over the past few years, important findings have revolutionized hypertension research. Firstly, in 2007, a seminal paper showed that adaptive immunity is involved in the pathogenesis of hypertension. Secondly, salt storage in the skin and its consequences for cardiovascular physiology were discovered. Thirdly, after the discovery that salt promotes the differentiation of CD4⁺ T cells into T_H 17 cells, it was demonstrated that salt directly changes several cells of the innate and adaptive immune system and aggravates autoimmune disease but may improve antimicrobial defence. Herein, we will review pathways of activation of immune cells by salt in hypertension as the framework for understanding the multiple roles of salt and immunity in arterial hypertension and autoimmune disease. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Dendritic Cell Amiloride-Sensitive Channels Mediate Sodium-Induced Inflammation and Hypertension

Sodium accumulates in the interstitium and promotes inflammation through poorly defined mechanisms. We describe a pathway by which sodium enters dendritic cells (DCs) through amiloride-sensitive channels including the alpha and gamma subunits of the epithelial sodium channel and the sodium hydrogen exchanger 1. This leads to calcium influx via the sodium calcium exchanger, activation of protein kinase C (PKC), phosphorylation of p47^phox, and association of p47^phox with gp91^phox. The assembled NADPH oxidase produces superoxide with subsequent formation of immunogenic isolevuglandin (IsoLG)-protein adducts. DCs activated by excess sodium produce increased interleukin-1β (IL-1β) and promote T cell production of cytokines IL-17A and interferon gamma (IFN-γ). When adoptively transferred into naive mice, these DCs prime hypertension in response to a sub-pressor dose of angiotensin II. These findings provide a mechanistic link between salt, inflammation, and hypertension involving increased oxidative stress and IsoLG production in DCs.

Acute changes in extracellular volume fraction in skeletal muscle monitored by 23Na NMR spectroscopy

In this article, we induced acute changes in extracellular volume fraction in skeletal muscle tissue and compared the sensitivity of a standard ¹H T₂ imaging method with different ²³Na‐NMR spectroscopy parameters within acquisition times compatible with clinical investigations. First, we analyzed the effect of a short ischemia on the sodium distribution in the skeletal muscle. Then, the lower leg of 21 healthy volunteers was scanned under different vascular filling conditions (vascular draining, filling, and normal condition) expected to modify exclusively the extracellular volume. The first experiment showed no change in the total sodium content during a 15 min ischemia, but the intracellular weighted ²³Na signal slowly decreased. For the second part, significant variations of total sodium content, sodium distribution, and T₁ and T2∗ of ²³Na signal were observed between different vascular filling conditions. The measured sodium distribution correlates significantly with sodium T₁ and with the short and long T2∗ fractions. In contrast, significant changes in the proton T₂w signal were observed only in three muscles. Altogether, the mean T₂w signal intensity of all muscles as well as their mean T₂ did not vary significantly with the extracellular volume changes. In conclusion, at the expense of giving up spatial resolution, the proposed ²³Na spectroscopic method proved to be more sensitive than standard ¹H T₂ approach to monitor acute extracellular compartment changes within muscle tissue.

Using Electrolyte Free Water Balance to Rationalize and Treat Dysnatremias

Dysnatremias or abnormalities in plasma [Na+] are often termed disorders of water balance, an unclear physiologic concept often confused with changes in total fluid balance. However, most clinicians clearly recognize that hypertonic or hypotonic gains or losses alter plasma [Na+], while isotonic changes do not modify plasma [Na+]. This concept can be conceptualized as the electrolyte free water balance (EFWB), which defines the non-isotonic components of inputs and outputs to determine their effect on plasma [Na+]. EFWB is mathematically proportional to the rate of change in plasma [Na+] (dPNa/dt) and, therefore, is actively regulated to zero so that plasma [Na+] remains stable at its homeostatic set point. Dysnatremias are, therefore, disorders of EFWB and the relationship between EFWB and dPNa/dt provides a rationale for therapeutic strategies incorporating mass and volume balance. Herein, we leverage dPNa/dt as a desired rate of correction of plasma [Na+] to define a stepwise approach for the treatment of dysnatremias.

Speculations on salt and the genesis of arterial hypertension

Blood pressure salt sensitivity and salt resistance are mechanistically imperfectly explained. A prescient systems medicine approach by Guyton and colleagues-more than 50 years ago-suggested how salt intake might influence blood pressure. They proposed that a high-salt diet engenders sodium accumulation, volume expansion, cardiac output adjustments, and then autoregulation for flow maintenance. The autoregulation in all vascular beds increases systemic vascular resistance, causing the kidneys to excrete more salt and water, thus reducing systems to normal and minimizing any changes in blood pressure. This schema, which is remarkably all encompassing, included all regulatory mechanisms Guyton could identify at the time. Guyton introduced the idea that the kidney is central, particularly concerning the regulation of renal pressure natriuresis. Numerous criticisms have been subsequently raised, particularly recently. Kurtz and colleagues argue that the ability of individuals to respond with an appropriate vasodilatory response to increased salt intake is pivotal. Data exist to address that issue. Salt-resistant hypertensive models provide additional information. We identified a mendelian form of hypertension not related to sodium reabsorption in the distal nephron. The hypertension develops because of increased systemic vascular resistance. In addition, we rediscovered a third salt-storage glycose-aminoglycan-related compartment, largely in the skin. This compartment operates independently of renal function, and when perturbed, is associated with salt sensitivity. More recently, we found novel molecular mechanisms demonstrating how large salt quantities are excreted by the kidneys with minimal water losses. We introduce novel interpretations as to how the kidneys excrete salt when the intake is high. The findings could have relevance as to how blood pressure may be regulated at varying salt intakes. Our purposes are to provide the readership with a banquet of thoughts to digest, to pursue Guyton's ideas, and to adjust them accordingly.