Salt-resistant Individuals Research Articles

Metabolomics signature of blood pressure salt sensitivity and its link to cardiovascular disease: A dietary salt-intervention trial.

Individuals with a high degree of salt sensitivity (SS) have a greater risk of cardiovascular disease (CVD), but whether SS fosters CVD by influencing metabolomics homeostasis remains unclear. This study aimed to reveal the role of the SS-related metabolomics signature in the development of CVDs, based on the MetaSalt study, which was a dietary salt-intervention trial conducted at four centers in China in 2019. A total of 528 participants were recruited and underwent 3 days of baseline observations, a 10-day low-salt intervention, and a 10-day high-salt intervention. Plasma untargeted metabolomics, lipidomics, and BP measurements were scheduled at each stage. Participants were grouped into extreme SS, moderate SS, and salt-resistant (SR) individuals according to their BP responses to salt. Linear mixed models were used to identify SS-related metabolites and determine the relationship between the SS-related metabolomics signature and arterial stiffness. Mendelian randomization (MR) analyses were applied to establish the causal pathways among the SS-related metabolites, BP, and CVDs. Among the 713 metabolites, 467 were significantly changed after the high-salt intervention. Among them, the changes in 30 metabolites from the low-salt to the high-salt intervention differed among the SS groups. Of the remaining nonsalt-related metabolites, the baseline levels of 11 metabolites were related to SS. These 41 metabolites explained 23% of the variance in SS. Moreover, SS and its metabolomics signature were positively correlated with arterial stiffness. MR analyses demonstrated that the SS-related metabolites may affect CVD risk by altering BP, indicating that the increase in BP was the consequence of the changes in SS-related metabolites rather than the cause. Our study revealed that the metabolomics signature of SS individuals differs from that of SR individuals and that the changes in SS-related metabolites may increase arterial stiffness and foster CVDs. This study provides insight into understanding the biology and targets of SS and its role in CVDs.

GENETIC VARIANCE IN HEPARAN SULFATION IS ASSOCIATED WITH SALT-SENSITIVITY: A GENE-ENVIRONMENT ANALYSIS

Objective: The high heritability of salt sensitivity suggests an essential role for genetic variants in the relationship between sodium intake and blood pressure (BP). Candidate gene studies have mainly focused on renal and vascular pathways, but the role of glycosaminoglycan (GAG) genes, which are crucial for salinity tolerance, remains to be elucidated. Design and method: Interactions between 54,126 variants in 130 GAG genes and daily sodium excretion on BP were explored in 20,420 EPIC-Norfolk subjects. UK Biobank (n=414,132) and the multi-ethnic HELIUS study (n=2,239) were used for validation. In HELIUS sodium intake was estimated with Food Frequency Questionnaires (FFQ). Urinary GAG composition in 57 Dutch origin HELIUS participants stratified by genotype were analyzed to assess the association between SNP and GAG difference. Also, urinary GAG composition in 12 healthy volunteers after a sodium intervention (7-day low (50 mmol Na+/day) and 7-day high (200 mmol Na+/day) diet) were studied to assess if differences in genotype are associated with different GAG expression. Results: The intron variant rs2892799, mapped to NDST3, showed the strongest interaction with sodium on mean arterial pressure (MAP) (FDR 0.03), and the intron variant rs9654628 mapped to HS3ST5 with sodium on systolic BP (FDR 0.03). These interactions were multi-ethnically validated (Fig 1A, B). When stratified for rs2892799 genotype, T-allele carriers had a significantly higher urinary expression of N-sulfated heparan sulfate epitope D0S0 (Fig1C). Conversely, upon dietary salt loading, urinary D0S0 expression differed substantially between salt-sensitive and salt-resistant individuals (Fig1D). Sodium-induced effects on this epitope were opposite in salt-sensitive in salt-resistant individuals. Conclusions: Genetic variants associated with NDST3 and HS3ST5 interact with relation between sodium consumption and BP. rs2892799 (NDST3) genotype results in a different expression of the N-sulfated D0S0 epitope. In turn, D0S0 expression is associated with salt-mediated BP increase, indicating that genetic GAG variation and metabolic GAG adaptation to a high salt environment might be important for human BP regulation.

Immune Metabolic Reprogramming by Excess Dietary Salt in Salt Sensitive Hypertension via CXCL8

Salt sensitivity of blood pressure (SSBP) is when blood pressure changes parallel to salt loading/ depletion and is an independent risk factor for cardiovascular disease. Despite its importance, there is no feasible diagnosis, which limits investigational studies to identify therapeutic targets. We have found that immune cells mediate SSBP via Epithelial Sodium Channel (ENaC). CXCL8/(IL-8), a known chemoattractant plays a well-known role in glycolysis. We hypothesize that CXCL8 mediates immune metabolic reprogramming of immune cells to glycolysis via ENaC. To test this hypothesis, we performed bulk and single cell RNA sequencing in human monocytes from individuals from a modified Weinberger inpatient salt loading/ depletion protocol. The participants were instructed to refrain from taking their blood pressure medication for 2 weeks prior to the salt loading/depletion protocol. Blood and urine samples were collected, as well as ambulatory blood pressure recording. We found that changes in immune cell activation via isolevuglandin (IsoLG) protein-adducts mirror changes in salt balance and blood pressure in salt sensitive but not salt resistant individuals. We confirmed that these in vivo changes can be recapitulated in vitro. In addition, we found that salt-loading both in vivo and in vitro increases antigen presenting cell production of IL-8, which was reversed after salt depletion in salt sensitive, but not salt resistant people. ENaC inhibition by amiloride prevented the high salt-induced production of IL-8. Moreover, high salt induced blood pressure changes of expression of CXCL8 (p = 0.01553, r = 0.8067) were significant along with varying expression of glycolytic genes, including hexokinase 1(HK1)(p = 0.04190, r = -0.7249), phosphofructokinase (PFKP)(p = 0.05932, r = 0.6879) and galactose mutarotase (GALM) (p = 0.04176, r = 0.5138). Seahorse analysis revealed increased extracellular acidification rate (ECAR) in high salt conditioned monocytes, which was associated with mitochondrial dysfunction. Our results suggest that high salt intake reprograms antigen presenting cell metabolism to glycolysis via IL-8 signaling. Furthermore, targeting IL-8 and mitochondrial switching to glycolysis may not only provide novel therapeutic approaches, but also important biomarkers for diagnosis of salt sensitivity of blood pressure. 1R03HL155041-01 (Kirabo, PI), 1R01HL144941-01A1 (Kirabo, PI), 5R01HL147818-22 (Kleyman & Kirabo), 1R01HL157584-01 (Shibao, Kirabo — MPI), R01DK135764 (Kon, Shelton, Kirabo — MPI), R21TW012635 (Kirabo, Masenga — MPI), Meharry Medical College: School of Graduate Studies T32AI007281, T32GM14492, andT32HL00773. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Abstract P177: Antigen-presenting Cell Vitamin D3 Modulates Salt-sensitive Hypertension In Humans

Salt-sensitivity of blood pressure (SSBP) is a condition in which high sodium intake causes shifts in blood pressure that are associated with cardiovascular disease and mortality. Recent studies from our lab indicate that increased sodium concentrations activate antigen-presenting cells (APCs), leading to SSBP. Vitamin D3 has been shown to attenuate inflammation, but its mechanisms and contribution to SSBP remain unknown. We hypothesized that vitamin D anti-inflammatory signaling in immune cells attenuates SSBP. To test this hypothesis, we performed bulk-RNA sequencing on monocytes after high-salt exposure and noticed an increase in vitamin D receptor (VDR) expression (NS: 1781.18 ± 222.33; HS: 2922.18 ± 371.65). Additionally, we performed single-cell CITE-Seq analysis on peripheral blood mononuclear cells isolated from hypertensive individuals after a rigorous inpatient salt-loading and salt-depletion protocol over a three-day period. On the second day when salt treatment was introduced, we observed an increase in VDR expression within APCs. Conversely, we observed a drop in VDR expression on the third day when salt was depleted from the APCs in salt-sensitive but not salt-resistant individuals. These results suggest that VDRs play an important role in modulating SSBP.

Abstract 133: Urine Derived Human Renal Proximal Tubule Cells Isolated From Inverse Salt Sensitive Participants Have Higher C-src Kinase Activity And Aminopeptidase N Expression

We have previously published that 11% of individuals in a salt sensitivity clinical trial are determined to be Inverse Salt Sensitive (ISS), and are associated with SNPs in the Dopamine D2 Receptor (D 2 R) that are shown to have decrease D 2 R expression in urine derived human renal proximal tubule cells (uRPTC) compared to salt resistant (SR) and salt sensitive (SS) individuals. We also previously have shown that ISS uRPTCs have increased expression of aminopeptidase N (APN), the enzyme capable of converting AngIII to AngIV. Inhibition of this activity in ISS may be a therapeutic strategy for ISS individuals. We previously reported that a nanobody designed to inhibit human APN activity added to cells reverses a number of adverse cell physiologic responses to low sodium conditions in ISS derived uRPTCs. Here we show evidence that the increased expression of APN in ISS uRPTCs is due to increased constitutive C-SRC activity. Three stable ISS uRPTCs, three SR uRPTCs and three SS uRPTCs were grown and lysed for analysis by Western blotting. The human homolog of the V-Src Avian Sarcoma viral oncogene tyrosine kinase (C-Src) activation state was measure using a Y-416 C-Src tyrosine phosphorylation specific antibody. There is a 266.1±21.7% increase in ISS Y416 p-Src vs SR (p<0.01 ISS vs SR, N=3) and no difference in SS vs SR. Plasma membrane localized APN was measured by In-cell Western and the increase in APN expression between ISS and SR was completely blocked by incubating cells for 4 hours with the C-Src inhibitor PP2 (ISS 49.1±8.8% increase over SR vs -14.6±11.9% with PP2, p<0.01, N=4 per group). Similarly lithium chloride (10 mM 4hrs), and D 2 R overexpression normalized the differential expression of D 2 R in ISS and completely blocked the increased APN expression found in ISS. In summary, low D 2 R expression in ISS leads to constitutively active C-Src and increased APN expression, and re-expression of D 2 R or inhibition of C-Src normalizes expression of APN. Future studies will determine if the tyrosine phosphorylation site in the intracellular domain of APN is a direct target of C-Src.

High sodium intake differentially impacts brachial artery dilation when evaluated with reactive versus active hyperemia in salt resistant individuals.

This study sought to determine if high sodium (HS) intake in salt resistant (SR) individuals attenuates upper limb arterial dilation in response to reactive (occlusion) and active (exercise) hyperemia, two stimuli with varying vasodilatory mechanisms, and the role of oxidative stress in this response. Ten young, SR participants (9 males, 1 female) consumed a 7-day HS (6,900 mg/day) and a 7-day recommended sodium intake (RI: 2,300 mg/day) diet in a randomized order. On the last day of each diet, brachial artery (BA) function was evaluated via reactive (RH-FMD: 5 min of cuff occlusion) and active [handgrip (HG) exercise] hyperemia after consumption of both placebo (PL) and antioxidants (AO). The HS diet significantly elevated sodium excretion (P < 0.05), but mean arterial blood pressure was unchanged. During the PL condition, the HS diet significantly reduced RH-FMD when compared with RI diet (P = 0.01), but this reduction was significantly restored (P = 0.01) when supplemented with AO (HS + PL: 5.9 ± 3.4; HS + AO: 8.2 ± 2.7; RI + PL: 8.9 ± 4.7; RI + AO: 7.0 ± 2.1%). BA shear-to-dilation slopes, evaluated across all HG exercise workloads, were not significantly different across sodium intervention or AO supplementation. In SR individuals, HS intake impaired BA function when assessed via RH-FMD, but was restored with acute AO consumption suggesting oxidative stress as a contributor to this dysfunction. However, exercise-induced BA dilation was unaltered, potentially implicating an inability of HS intake to influence the mechanisms responsible for effectively maintaining skeletal muscle perfusion during exercise.NEW & NOTEWORTHY This study examined if high sodium (HS) intake in salt resistant (SR) individuals attenuates brachial artery (BA) flow-mediated dilation in response to reactive (occlusion) and active (exercise) hyperemia. In SR individuals, HS intake impaired reactive hyperemia-induced BA dilation, but not exercise-induced BA dilation. This finding suggests that although brachial artery nitric oxide bioavailability may be reduced following HS intake, the redundant mechanisms associated with adequate upper limb blood flow regulation during exercise are maintained.

SALT-SENSITIVITY IN HEALTHY NORMOTENSIVE MEN IS ASSOCIATED WITH IMPAIRED BAROREFLEX SENSITIVITY

Objective: Blood pressure (BP) responses to Na+ intake show great variability, discriminating sodium sensitive (SS) from salt resistant (SR) individuals. The pathophysiology behind salt-sensitivity is still not fully elucidated. A pivotal role for the sympathetic nervous system to BP increase after sodium loading is suggested. Therefore, we aimed to investigate the effect of the sympathovagal balance on Na+-induced BP effects and if Na+-induced effects on sympathetic activation contribute to salt-sensitivity. Design and method: We performed a randomized cross-over study in 31 young healthy men with normal BMI and eGFR. Subjects followed both an 8-day low Na+ diet (LSD, &lt; 50mmol/d) and high Na+ diet (HSD, &gt; 200mmol/d), in 18 subjects the diets were extended to 14-days. SS was defined as an increase of three or more mmHg standardized measured office MAP after HSD. Cardiac-output (CO) and cross correlation baroreflex sensitivity (xBRS) were measured with continuous non-invasive finger photoplethysmography. Systemic vascular resistance (SVR) was calculated as the ratio of MAP by CO. Results: After HSD, SS men (19%) showed a mean 6.2 (±2.1 SD) mmHg increase in MAP. No absolute differences in Na+-induced effects on CO and SVR could be observed between groups. After HSD, xBRS was 34% lower in SS men compared to SR men (Fig1A). Sodium loading resulted in a mean xBRS decrease of 3.4 (±6.5 SD) ms/mmHg in SS men, whilst xBRS increased with 2.3 (±6.3 SD) ms/mmHg in SR men (p = 0.06). HSD xBRS values were significantly correlated with Na+-induced BP changes in the complete group when corrected for age and BMI (Fig1B). Conclusions: Salt-sensitivity of BP in young normotensive men seems to be predominantly driven by changes in sympathovagal balance. The significant correlation between xBRS and delta BP further suggests a continuous relation between sympathetovagal balance and salt exposure. Further studies are needed to unravel pathophysiological mechanisms underlying Na+-effects on sympathetic regulation.

7-DAYS HIGH-SALT DIET AFFECTS NO-MEDIATED MICROVASCULAR ENDOTHELIAL VASODILATION IN YOUNG HEALTHY INDIVIDUALS

Objective: We have previously reported that short-term (7-days) high-salt (HS) loading impairs microvascular endothelial function in young healthy individuals, independently of blood pressure (BP) or body composition and fluid status changes. This study aimed to functionally assess specifically nitric-oxide (NO) mediated endothelial vasodilation of skin microcirculation in response to 7-day HS diet in healthy salt-resistant individuals. Design and method: 20 young healthy individuals (10 women and 10 men), age ranged between 19–24 years, participated in the present study. All subjects adhered to a 7-day low-salt (LS) diet (3.5 g salt/day) followed by a 7-day high-salt (HS) diet (∼14.7 g salt/day) protocol. To confirm that subjects conformed to the diet protocol, daily salt intake based on 24-h urinary sodium excretion was calculated using appropriate formula before and after HS diet protocol. Blood pressure (BP) was measured before and after respective diet protocols and salt resistance was defined as a &lt; 5 mmHg change in mean arterial pressure (MAP) determined on LS versus HS diet. NO-mediated microvascular endothelial vasodilation in response to local heating (42°C) was functionally assessed using laser Doppler Flowmetry (LDF) (moorVMS-LDF, Moor Instruments, UK) and skin heater controller (moorVMS-HEAT, Moor Instruments, UK). Results: 24-hour sodium excretion significantly increased following HS diet compared to LS conditions (salt/g LS 6.6 ± 2.6 vs. HS 14.3 ± 2.5, P &lt; 0.001). Salt resistance was confirmed in all subjects undergoing study (MAP/mmHg LS 87 ± 7 vs. HS 86 ± 9, P = 0.829). 7-day HS diet significantly reduced skin microvascular flow increase in response to local heating compared to LS conditions (LDF HEAT LS 14.16 ± 6.01 vs. HS 10.67 ± 3.27, P = 0.006). Conclusions: Results of the present study have functionally demonstrated that 7-days HS diet alters specifically NO-mediated endothelium-dependent of skin microcirculation in salt-resistant young healthy individuals.

High Dietary Salt Intake Is Associated With Histone Methylation in Salt-Sensitive Individuals

BackgroundHigh salt diet is one of the important risk factors of hypertension and cardiovascular diseases. Increasingly strong evidence supports epigenetic mechanisms' significant role in hypertension. We aimed to explore associations of epigenetics with high salt diet, salt sensitivity (SS), and SS hypertension.MethodsWe conducted a dietary intervention study of chronic salt loading in 339 subjects from northern China in 2004 and divided the subjects into different salt sensitivity phenotypes. A total of 152 participants were randomly selected from the same cohort for follow-up in 2018 to explore the effect of a high-salt diet on serum monomethylation of H3K4 (H3K4me1), histone methyltransferase Set7, and lysine-specific demethylase 1 (LSD-1).ResultsAmong SS individuals, the blood pressure (SBP: 140.8 vs. 132.9 mmHg; MAP: 104.2 vs. 98.7 mmHg) and prevalence of hypertension (58.8 vs. 32.8%) were significantly higher in high salt (HS) diet group than in normal salt (NS) diet group, but not in the salt-resistant (SR) individuals (P > 0.05). Serum H3K4me1 level (287.3 vs. 179.7 pg/ml, P < 0.05) significantly increased in HS group of SS individuals, but not in SR individuals. We found daily salt intake in SS individuals was positively correlated with serum H3K4me1 (r = 0.322, P = 0.005) and Set7 (r = 0.340, P = 0.005) levels after adjusting for age and gender, but not with LSD-1 (r = −0.137, P = 0.251). In addition, positive correlation between the serum H3K4me1 level and Set7 level (r = 0.326, P = 0.007) was also found in SS individuals. These correlations were not evident in SR individuals.ConclusionOur study indicates that high salt diet increases the serum H3K4me1 and Set7 levels in SS individuals.

Abstract P276: A High Sodium Diet Reduces Cutaneous Microvascular Function In Normotensive Individuals With Salt Sensitive Blood Pressure

Impaired vascular function likely contributes to the association between dietary sodium intake and the development of cardiovascular disease. Using the cutaneous microvasculature as a model, we have previously shown that a high sodium (HS) diet blunts local heating-induced vasodilation in normotensive individuals with salt resistant (SR) blood pressure (BP). However, the effect of a HS diet on the cutaneous microvasculature in normotensive salt sensitive (SS) individuals remains unclear. Therefore, we tested the hypothesis that cutaneous microvascular function is reduced by a HS diet to a greater degree in SS compared to SR individuals. After each 7-day controlled feeding diet (low sodium (LS) = 20 mmol/day; HS = 300 mmol/day), an intradermal microdialysis fiber was inserted in the ventral forearm and perfused with Ringer’s solution. Skin blood flow (SkBF) was continuously monitored via laser Doppler flowmetry and a local heating unit was placed over the fiber and heated to 42°C until SkBF reached a stable plateau. Site-specific maximal SkBF was determined by perfusing 28mM sodium nitroprusside and heating to 43°C. Mean arterial pressure (MAP) was assessed at regular intervals on the contralateral arm and was used to calculate cutaneous vascular conductance (CVC = SkBF / MAP). Subjects wore a 24-hr ambulatory BP monitor and collected their urine on the final day of each diet. Fourteen subjects (9W / 5M, 42 ± 14 yr) whose MAP increased &gt;5 mmHg (Δ8 ± 1 mmHg) on the HS diet were defined as SS and were compared to 14 age- (43± 14 yr) and sex-matched SR subjects (Δ1 ± 3 mmHg). SS and SR had similar MAP at baseline (88 ± 9 vs. 90 ± 8 mmHg, P = 0.88) and urinary sodium excretion was increased similarly across groups by the HS diet (Δ239 ± 104 vs. Δ220 ± 66 mmol / 24 hr, P = 0.20). Cutaneous vasodilation in response to local heating was decreased on the HS diet relative to the LS diet in both SS (Δ-9 ± 9 %CVCmax, P = 0.005) and SR (Δ-9 ± 9 %CVCmax, P=0.005); however, there was not a group x diet interaction (P = 0.99). In contrast to our hypothesis, these results suggest that the deleterious effects of high sodium diets on cutaneous microvascular function are similar in normotensive salt sensitive and salt resistant individuals.

Immune Mechanisms of Dietary Salt-Induced Hypertension and Kidney Disease: Harry Goldblatt Award for Early Career Investigators 2020.

Salt sensitivity of blood pressure is an independent risk factor for cardiovascular mortality not only in hypertensive but also in normotensive adults. The diagnosis of salt sensitivity of blood pressure is not feasible in the clinic due to lack of a simple diagnostic test, making it difficult to investigate therapeutic strategies. Most research efforts to understand the mechanisms of salt sensitivity of blood pressure have focused on renal regulation of sodium. However, salt retention or plasma volume expansion is not different between salt-sensitive and salt-resistant individuals. In addition, over 70% of extracellular fluid is interstitial and, therefore, not directly controlled by renal salt and water excretion. We discuss in this review how the seminal work by Harry Goldblatt paved the way for our attempts at understanding the mechanisms that underlie immune activation by salt in hypertension. We describe our findings that sodium, entering antigen-presenting cells via an epithelial sodium channel, triggers a PKC (protein kinase C)- and SGK1 (serum/glucocorticoid kinase 1)-stimulated activation of nicotinamide adenine dinucleotide phosphate oxidase, which, in turn, enhances lipid oxidation with generation of highly reactive isolevuglandins. Isolevuglandins adduct to proteins, with the potential to generate degraded peptide neoantigens. Activated antigen-presenting cells increase production of the TH17 polarizing cytokines, IL (interleukin)-6, IL-1β, and IL-23, which leads to differentiation and proliferation of IL-17A producing T cells. Our laboratory and others have shown that this cytokine contributes to hypertension. We also discuss where this sodium activation of antigen-presenting cells may occur in vivo and describe the multiple experiments, with pharmacological antagonists and knockout mice that we used to unravel this sequence of events in rodents. Finally, we describe experiments in mononuclear cells obtained from normotensive or hypertensive volunteers, which confirm that analogous processes of salt-induced immunity take place in humans.

An exploratory analysis of comparative plasma metabolomic and lipidomic profiling in salt-sensitive and salt-resistant individuals from The Dietary Approaches to Stop Hypertension Sodium Trial.

Objective:This study conducted exploratory metabolomic and lipidomic profiling of plasma samples from the DASH (Dietary Approaches to Stop Hypertension) Sodium Trial to identify unique plasma biomarkers to identify salt-sensitive versus salt-resistant participants.Methods:Utilizing plasma samples from the DASH-Sodium Trial, we conducted untargeted metabolomic and lipidomic profiling on plasma from salt-sensitive and salt-resistant DASH-Sodium Trial participants. Study 1 analyzed plasma from 106 salt-sensitive and 85 salt-resistant participants obtained during screening when participants consumed their regular diet. Study 2 examined paired within-participant plasma samples in 20 salt-sensitive and 20 salt-resistant participants during a high-salt and low-salt dietary intervention. To investigate differences in metabolites or lipidomes that could discriminate between salt-sensitive and salt-resistant participants or the response to a dietary sodium intervention Principal Component Analysis and Orthogonal Partial Least Square Discriminant Analysis was conducted. Differential expression analysis was performed to validate observed variance and to determine the statistical significance.Results:Differential expression analysis between salt-sensitive and salt-resistant participants at screening revealed no difference in plasma metabolites or lipidomes. In contrast, three annotated plasma metabolites, tocopherol alpha, 2-ketoisocaproic acid, and citramalic acid, differed significantly between high-sodium and low-sodium dietary interventions in salt-sensitive participants.Conclusion:In DASH-Sodium Trial participants on a regular diet, plasma metabolomic or lipidomic signatures were not different between salt-sensitive and salt-resistant participants. High-sodium intake was associated with changes in specific circulating metabolites in salt-sensitive participants. Further studies are needed to validate the identified metabolites as potential biomarkers that are associated with the salt sensitivity of blood pressure.

A high salt diet induces tubular damage associated with a pro-inflammatory and pro-fibrotic response in a hypertension-independent manner

High salt diet (HSD), considered a public health problem worldwide, is associated with chronic degenerative diseases including renal diseases. However, little is known about the effects of HSD on renal function independently of the development of hypertension. To address the hypothesis that HSD induces renal injuries even without changes in blood pressure, BALB/c mice were fed for 7 days with chow with a high salt content (0.3–8%). Blood pressure did not change and there was a decrease in cortical (Na+ + K+)ATPase and NHE3 exchanger and an increase in renal fractional excretion of sodium. Positive correlations between Na+ intake or urinary sodium excretion with proteinuria were found. HSD did not change glomerular function and structure, but induced tubule-interstitial injury measured by an increase in collagen deposition, interstitial space and γ-GT activity, a marker of tubular injury. These effects were associated with a decrease in cortical albumin reabsorption and megalin expression. Similarly, the addition of NaCl 20 mM to the incubation medium of LLC-PK1 cells reduced megalin expression and albumin endocytosis indicating that HSD could have a direct effect on proximal tubule cells. Furthermore, tubule-interstitial injury was associated with pro-inflammatory and pro-fibrotic phenotypes with an increase in Th1 and Th17 phenotypes and a decrease in Tregs followed by increases in IL-6, -17, -10, TNF-α, IFN-γ and TGF-β. Our results reveal a complex network involved in renal injuries induced by HSD independently of changes in blood pressure. These findings strengthen the importance of restriction of salt intake for the general population even for salt-resistant individuals.

Effects Of Dietary Sodium Intake On Blood Flow Regulation During Exercise In Salt Resistant Individuals

PURPOSE: Dietary guidelines for sodium intake is less than 2,300 mg/day, yet 90% of Americans exceed this value. This study examined individuals resistant to salt-induced changes in blood pressure to determine the impact of a high sodium diet on blood flow regulation during upper and lower limb exercise. METHODS: Six young (25 ± 2 years) males followed recommended dietary sodium intake guidelines on two separate weeks, with one week supplemented with salt capsules (HS: 6,900 mg/day of sodium) and the other week supplemented with placebo capsules (LS: 2,300 mg/day of sodium). Resting central hemodynamic measurements [heart rate (HR), heart rate variability (HRV), and mean arterial pressure (MAP)] were evaluated the end of each diet. Peripheral hemodynamic measurements [blood flow (BF), shear rate (SR), and flow mediated dilation (FMD)/SR)] of the brachial and superficial femoral artery were taken during rhythmic (1 Hz), progressive handgrip (HG) and plantar flexion (PF) exercise, respectively. Exercise workloads were three minutes in length and increased by increments of 8 kilograms until exhaustion. RESULTS: Between each diet (LS and HS) there were no significant differences in resting MAP (82 ± 4 v 80 ± 5 mmHg; p = 0.3), HR (56 ± 6 v 59 ± 10 bpm; p = 0.4), or HRV (2.7 ± 1.9 v 8.3 ± 15.1 LF/HF; p = 0.4). During progressive HG and PF exercise the BF, SR, and FMD/SR were significantly increased by workload (p < 0.03 for all), but not different between diets (p > 0.05 for all). CONCLUSION: Despite previous evidence reporting a HS diet can impair resting vascular function, this study revealed that peripheral vascular function and blood flow regulation during exercise is not impacted by a HS diet in salt resistant individuals.

Effect of Salt Supplementation on Sympathetic Activity and Endothelial Function in Salt-Sensitive Type 2 Diabetes.

Lower sodium intake is paradoxically associated with higher mortality in type 2 diabetes (T2D). To determine whether sympathetic nervous system (SNS) activation and endothelial dysfunction contribute to these observations, we examined the effect of salt supplementation on these systems in people with T2D with habitual low sodium. We hypothesized that salt supplementation would lower SNS activity and improve endothelial function compared to placebo. We conducted a randomized, double-blinded, placebo-controlled crossover trial. The study took place in a tertiary referral diabetes outpatient clinic. Twenty-two people with T2D with habitual low sodium intake (24-hour urine sodium <150 mmol/24h) were included. Salt supplementation (100 mmol NaCl/24h) or placebo for 3 weeks was administered. The primary outcome of SNS activity and endothelial function was assessed as follows: Microneurography assessed muscle sympathetic nerve activity (MSNA), pulse amplitude tonometry assessed endothelial function via reactive hyperemic index (RHI), and arterial stiffness was assessed via augmentation index (AI). Secondary outcomes included cardiac baroreflex, serum aldosterone, ambulatory blood pressure monitoring (ABPM), heart rate variability (HRV), and salt sensitivity. Compared to placebo, salt supplementation increased MSNA (burst frequency P = .047, burst incidence P = .016); however, RHI (P = .24), AI (P = .201), ABPM (systolic P = .09, diastolic P = .14), and HRV were unaffected. Salt supplementation improved baroreflex (slope P = .026) and lowered aldosterone (P = .004), and in salt-resistant individuals there was a trend toward improved RHI (P = .07). In people with T2D and low habitual sodium intake, salt supplementation increased SNS activity without altering endothelial function or blood pressure but improved baroreflex function, a predictor of cardiac mortality. Salt-resistant individuals trended toward improved endothelial function with salt supplementation.

Effect of Salt Intake on the Serum Cardiotrophin-1 Levels in Chinese Adults

Background: Dietary sodium affects fluctuations in blood pressure (BP) and vascular function. Cardiotrophin-1 (CT-1), a stress-induced cytokine that belongs to the interleukin 6 family, is released by cells in response to potentially harmful stresses and plays a pivotal role in congestive heart failure, hypertension and arterial stiffness. In this study, we performed a randomized trial to confirm the effects of altered salt intake on the serum CT-1 levels in humans. Methods: Forty-four subjects (18–65 years of age) were selected from a rural community in northern China. All subjects initially maintained a baseline period for 3 days, transitioned to a low-salt (LS) diet for 7 days (3.0 g/day of NaCl) and then a high-salt (HS) diet for an additional 7 days (18.0 g/day of NaCl). Results: For the whole group, the serum CT-1 concentrations were significantly increased in the HS period compared to those of the LS period (293.50 ± 137.70 vs. 360.40 ± 162.83 pg/mL, p = 0.040). The serum CT-1 concentrations significantly decreased from the baseline period to the LS diet (419.91 ± 123.50 to 256.49 ± 109.75 pg/mL, p < 0.01) and significantly increased from the LS to HS diet (256.49 ± 109.75 to 414.39 ± 191.21 pg/mL, p < 0.01). These changes were observed in salt-sensitive (SS) individuals but not in salt-resistant (SR) individuals. In addition, a significant positive relationship was observed between the changes in the CT-1 concentrations and systolic BP as well as the changes in the mean arterial pressure from the LS period to the HS period (r = 0.376, p = 0.012; r = 0.311, p = 0.040). The serum CT-1 concentrations were positively correlated with the 24-h urinary sodium-to-potassium (Na/K) excretion ratios during both of the LS and HS diet intervention periods in SS subjects (r = 0.621, p < 0.01), but this correlation was not evident in SR subjects (r = 0.208, p = 0.107). Conclusions: Our study indicates that variations in dietary salt intake affect the serum CT-1 levels in Chinese adults.

Abstract P263: Renal Proximal Tubule Cells from Inverse Salt Sensitive Individuals Have Lower Basal but Higher Sodium Stimulated ENaC Compared to Salt Resistant Individuals

Our previous studies on salt sensitivity has demonstrated that approximately 11% of study participants had a paradoxical increase in blood pressure (BP) (greater than 7-mm Hg) on a low NaCl diet and an increased basal renal proximal tubule cells (RPTC) Na + transport, which we define as inverse salt sensitivity (ISS). We hypothesized that the amiloride blockable Na + channel (ENaC) could be involved in ISS, particularly in the RPTC where up to 75% of renal nephron Na + reabsorption occurs. Previous investigators have localized αENaC in the distal nephron; however, we found αENaC is also present in the human RPTCs, as confirmed by tissue and cellular immunostaining, RT-PCR, and western blot with two selective αENaC antibodies. The presence of αENaC in human kidney tissue was confirmed by the Human Protein Atlas. Urine derived RPTCs from 3 ISS and 3 salt resistance (SR) clinical study participants were treated overnight with normal salt and high salt (140mM Na + and 170mM Na + respectively). High salt increased αENaC expression to a greater extent in ISS versus SR cells; however, ISS cells have significantly less αENaC at basal level (αENaC/actin: SR 1.41±0.248 VS ISS 0.592±0.157, n=3, P&lt;0.05). Patch clamp ramp currents were recorded using a voltage ramp from -100 to +45 mV within 200 ms (N≥5 for each cell line). Na + current was measured at both 140 and 170 mM Na + with and without Bensamil (ENaC antagonist) and expressed as a ratio of current (170 mM/ 140 mM Na + ). Bensamil blocked ENaC activity in ISS cells, but not in SR cells (Bensamil ratio/primary ratio: SR 1.149±0.026 VS ISS 0.818±0.017, n=3, t-test, P&lt;0.001; final ratio/primary ratio: SR 1.088±0.022 VS 0.705±0.1, n=3, t-test, P&lt;0.05). αENaC knockdown using siRNA significantly decreased Na + current in ISS cells (0.763±0.029, n=3, t-test, P&lt;0.05) but not in SR cells (1.046±0.097, n=3, t-test, P&lt;0.05). In conclusion, RPTC from ISS study participant urine demonstrated increased Bensamil Na + current compared to SR RPTC when exposed to increased sodium. This data could provide a novel functional assay for the diagnosis of ISS in the clinical setting and allow for an appropriate personalized medical intervention.

The responses of the inflammatory marker, pentraxin 3, to dietary sodium and potassium interventions.

Pentraxin-3 is a sensitive marker of inflammation that plays dual roles, pathogenic and cardioprotective, in the progression of cardiovascular diseases. Inflammation is intimately involved in salt-induced hypertension. We investigated the responses of pentraxin-3 to sodium and potassium supplementation to elucidate the potential role of pentraxin-3 in salt-induced hypertension. A total of 48 participants from northwest China were enrolled. All participants were maintained on a 3-day normal diet, which was sequentially followed by a 7-day low-sodium diet, a 7-day high-sodium diet, and a 7-day high-sodium plus potassium diet. Plasma concentrations of pentraxin-3 were assessed using ELISA. Plasma pentraxin-3 decreased significantly during the low-salt period compared to baseline (0.57±0.19ng/mL vs 0.72±0.33ng/mL, P=.012) and increased during the high-salt period (0.68±0.26ng/mL vs 0.57±0.19ng/mL, P=.037). Potassium supplementation inhibited salt-induced increase in pentraxin-3 (0.56±0.21ng/mL vs 0.68±0.26ng/mL, P=.015). Ln-transformed pentraxin-3 at baseline was inversely correlated with BMI (r=-.349, P=.02), DBP (r=-.414, P=.005), MAP (r=-.360, P=.017). We found a positive correlation between the ln-transformed concentrations of pentraxin-3 and 24-hour urinary sodium during low and high Na+ periods (r=.269, P=.012) and a negative relationship with 24hours urinary potassium excretion during high-salt and high-salt plus potassium periods (r=-.246, P=.02). These correlations remained significant after adjusting for confounders. Pentraxin-3 responses were more prominent in salt-sensitive individuals than salt-resistant individuals. Dietary salt and potassium interventions significantly altered circulating pentraxin-3.

Effect of Salt Intervention on Serum Levels of Fibroblast Growth Factor 23 (FGF23) in Chinese Adults: An Intervention Study.

BackgroundFibroblast growth factor 23 (FGF23), a prominent regulator of phosphate and calcium metabolism, regulates sodium excretion in distal tubules through sodium-chloride cotransporter. This effect regulates blood pressure. Salt intake exerts effects on serum levels of FGF23 in mice. The aim of this study was to explore whether salt intervention affects serum concentrations of FGF23 in Chinese adults.Material/MethodsWe enrolled 44 participants from Lantian, a rural community of Shaanxi, China. All participants were maintained on a three-day normal diet, which was sequentially followed by a seven-day low-Na+ diet and seven-day high-Na+ diet. Serum FGF23 concentrations were assessed by ELISA.ResultsSerum FGF23 concentrations elevated during low-salt diet compared with levels at baseline (66.20±44.21 pg/mL versus 86.77±53.74 pg/mL, p<0.05) and remarkably decreased when changed from low to high salt intake (86.77±53.74 pg/mL versus 49.26±42.67 pg/mL, p<0.001). Responses of FGF23 to salt intervention were more prominent in normotensive, older than 60 years, BMI <24 kg/m2 and salt-resistant individuals. Furthermore, a significant inverse correlation was observed between 24-hour urinary sodium and serum concentrations of FGF23 after adjusting age, sex, BMI and hypertension status.ConclusionsDietary salt intervention significantly affects serum FGF23 in Chinese adults.

A Quantitative Systems Physiology Model of Renal Function and Blood Pressure Regulation: Application in Salt-Sensitive Hypertension.

Salt‐sensitivity (SS) refers to changes in blood pressure in response to changes in sodium intake. SS individuals are at greater risk for developing kidney disease, and also respond differently to antihypertensive therapies compared to salt‐resistant (SR) individuals. In this study we used a systems pharmacology model of renal function (presented in a companion article) to evaluate the ability of proposed mechanisms to produce salt‐sensitivity. The model reproduced previously published data on renal functional changes in response to salt‐intake, and also predicted that glomerular pressure, a variable that is not easily evaluated clinically but is a key factor in renal injury, increases with salt intake in SS hypertension. We then used the model to generate mechanistic insight into the differential blood pressure and glomerular pressure responses to angiotensin converting enzyme (ACE) inhibitors, thiazide diuretics, and calcium channel blockers observed in SS and SR hypertension.