Association between salt sensitivity and target organ damage in essential hypertension

Irisin mitigates salt-sensitive hypertension via regulating renal AMPK-Rac1 pathway

BACKGROUND

Irisin, as a myokine, plays a protective role against cardiovascular disease, including myocardial infarction, atherosclerosis and hypertension. However, whether irisin attenuates salt-sensitive hypertension and the related underlying mechanisms is unknown.

METHODS

Male Dahl salt-resistant (DSR) and Dahl salt-sensitive (DSS) (12 weeks) rats were fed a high salt diet (8% NaCl) with or without irisin treatment by intraperitoneal injection for 8 weeks.

RESULTS

Compared with DSR rats, DSS rats showed higher systolic blood pressure (SBP), impaired natriuresis and diuresis and renal dysfunction. In addition, it was accompanied by downregulation of renal p-AMPKα and upregulation of renal RAC1 and nuclear mineralocorticoid receptor (MR). Irisin intervention could significantly up-regulated renal p-AMPKα level and down-regulated renal RAC1-MR signal, thereby improving renal sodium excretion and renal function, and ultimately reducing blood pressure in DSS rats. Ex vivo treatment with irisin reduced the expression of RAC1 and nuclear MR in primary renal distal convoluted tubule cells from DSS rats and the effects of irisin were abolished by cotreatment of compound C (AMPK inhibitor), indicating that the regulation of RAC1-MR signals by irisin depended on the activation of AMPK.

CONCLUSIONS

Irisin administration lowered salt-sensitive hypertension through regulating RAC1-MR signaling via activation of AMPK, which may be a promising therapeutic approach for salt-sensitive hypertension.

The effects of the atrial natriuretic peptide deficiency on renal cortical mitochondrial bioenergetics in the Dahl SS rat

Atrial Natriuretic Peptide (ANP) plays an important role in blood pressure regulation. Low levels of ANP correlate with the development of salt-sensitive hypertension (SS-HTN). Our previous studies indicated that ANP deficiency exacerbated renal function decline in SS-HTN. In the heart and fat tissue, ANP was reported to affect lipid peroxidation and mitochondrial bioenergetics but the effects of ANP on mitochondrial function in the kidney are unexplored. We hypothesized that ANP deficiency in SS-HTN causes renal bioenergetic shift, leading to disruption of mitochondrial network and oxidative stress. To address the hypothesis, we placed Dahl SS wild-type (SSWT) and ANP knockout (SSNPPA-/-) rats on 4% NaCl high salt (HS) diet to induce HTN or maintained them on 0.4% NaCl normal salt (NS) diet and assessed mitochondrial bioenergetics and dynamics using spectrofluorimetry, Seahorse assay, electron paramagnetic resonance (EPR) spectroscopy, Western blotting, electron microscopy, PCR and cytokine assays. We report that under high salt conditions, associated with hypertension and renal damage, the SSNPPA-/- rats exhibit a decrease in mitochondrial membrane potential and elevation in mitochondrial ROS levels compared to SSWT. The redox shift is also evident by the presence of more pronounced medullar lipid peroxidation in the SSNPPA-/- strain. We also revealed fragmented, more damaged mitochondria in the SSNPPA-/- rats, accompanied by increased turnover and biogenesis. Overall, our data indicate that ANP deficiency causes disruptions in mitochondrial bioenergetics and dynamics which likely contributes to aggravation of the renal damage and hypertension in the Dahl SS rat; the major pathological effects are evident in the groups subjected to a combined salt and ANP deficiency-induced mitochondrial stress.

Renalase alleviates salt-induced kidney necroptosis and inflammation

Recent evidence suggests that necroptosis may contribute to the development of kidney injury. Renalase is a novel secretory protein that exerts potent prosurvival and anti-inflammatory effects. We hypothesized that renalase could protect the kidney from salt-induced injury by modulating necroptosis. High salt and renalase treatments were administered to Dahl salt-sensitive (SS) rats, renalase knockout (KO) mice, and HK-2 cells. Furthermore, a cohort of 514 eligible participants was utilized to investigate the association between single nucleotide polymorphisms (SNPs) in the genes RIPK1, RIPK3, and MLKL, and the risk of subclinical renal damage (SRD) over 14 years. A high-salt diet significantly increased the expression of key components of necroptosis, namely RIPK1, RIPK3, and MLKL, as well as the release of inflammatory factors in SS rats. Treatment with recombinant renalase reduced both necroptosis and inflammation. In renalase KO mice, salt-induced kidney injury was more severe than in wild-type mice, but supplementation with renalase attenuated the kidney injury. In vitro experiments with HK-2 cells revealed high salt increased necroptosis and inflammation. Renalase exhibited a dose-dependent decrease in salt-induced necroptosis, and this cytoprotective effect was negated by the knockdown of PMCA4b, which is the receptor of renalase. Furthermore, the cohort study showed that SNP rs3736724 in RIPK1 and rs11640974 in MLKL were significantly associated with the risk of SRD over 14 years. Our analysis shows that necroptosis plays a significant role in the development of salt-induced kidney injury and that renalase confers its cytoprotective effects by inhibiting necroptosis and inflammation.

Self-Performed Dietary Sodium Reduction and Blood Pressure in Patients With Essential Hypertension: A Randomized Clinical Trial

BACKGROUND

Hypertension is the leading risk factor for cardiovascular disease worldwide. Patients with blood pressure (BP) response to dietary sodium reduction are referred to as "salt sensitive." Salt sensitivity (SS) might be due to differences in sodium storage capacity and the erythrocyte SS examines this capacity of the red blood cells. This study aimed to test the effect of a self-performed sodium reduced diet on BP in patients with essential hypertension and examine whether erythrocyte SS predicts SS.

METHODS AND RESULTS

Seventy-two patients with hypertension were included and randomized 2:1 to either sodium reduction or a control group for 4 weeks. Blood samples, 24-hour BP measurement, and 24-hour urine collection were performed before and after. The intervention group received advice on how to lower sodium intake. Urinary sodium excretion decreased 66 mmol (95% CI, -96 to -37 mmol) in the intervention group compared with the control group. Systolic 24-hour BP decreased 9 mm Hg after low-sodium diet compared with the control group (95% CI, -13 to -4 mm Hg). Similarly, the difference in reduction in diastolic BP between the groups was 5 mm Hg (95% CI, -8 to -1 mm Hg). We found no correlation between erythrocyte SS at baseline and decrease in 24-hour BP, neither systolic nor diastolic (P=0.66 and P = 0.84).

CONCLUSIONS

Self-performed sodium reduction was feasible and led to decrease in 24-hour BP of 9/5 mm Hg compared with a control group. The erythrocyte SS did not correlate to the change in BP after lowering sodium intake.

REGISTRATION

URL: https://clinicaltrials.gov; Unique Identifier: NCT05165823.

Research trends and hotpots on the relationship between high salt and hypertension: A bibliometric and visualized analysis

INTRODUCTION

A high salt diet is a significant risk factor for hypertension, and scholarly investigations into this relationship have garnered considerable attention worldwide. However, bibliometric analyses in this field remain underdeveloped. This study aimed to conduct a bibliometric and visual analysis of research progress on the link between high salt and hypertension from 2011 to 2022 with the goal of identifying future research trends and providing valuable insights for this field.

METHODS

High salt and hypertension data were obtained from the Web of Science Core Collection database. Microsoft Excel, Scimago Graphica, CiteSpace, and VOSviewer software were employed to analyze publication output trends, the most productive countries or regions, journals, authors, co-cited references, and keywords.

RESULTS

After screening, 1470 papers met the inclusion criteria. Relevant publications increased annually by 3.66% from 2011 to 2022. The United States led in research productivity, with The Journal of Hypertension publishing the most papers, and David L. Mattson as the most prolific author. Oxidative stress has emerged as a prominent research topic, and extensive investigations have been conducted on related mechanisms. "Oxidative stress," "gut microbiota," and "kidney injury" are recent hotspots that are expected to remain so, and this study carefully characterizes the mechanism of high salt-induced hypertension based on these hotspots.

CONCLUSION

This study utilized bibliometric and visualization analysis to identify the development trends and hotspots of publications related to high salt and hypertension. The findings of this study offer valuable insights into the forefront of emerging trends and future directions in this field.

Novel mechanisms of salt-sensitive hypertension

A high dietary sodium-consumption level is considered the most important lifestyle factor that can be modified to help prevent an increase in blood pressure and the development of hypertension. Despite numerous studies over the past decades, the pathophysiology explaining why some people show a salt-sensitive blood pressure response and others do not is incompletely understood. Here, a brief overview of the latest mechanistic insights is provided, focusing on the mononuclear phagocytic system and inflammation, the gut-kidney axis, and epigenetics. The article also discusses the effects of 3 types of novel drugs on salt-sensitive hypertension-sodium-glucose cotransporter 2 inhibitors, nonsteroidal mineralocorticoid receptor antagonists, and aldosterone synthase inhibitors. The conclusion is that besides kidney-centered mechanisms, vasoconstrictor mechanisms are also relevant for both the understanding and treatment of this blood pressure phenotype.

Endothelial Glycocalyx in Aging and Age-related Diseases

The worldwide population is aging exponentially, creating burdens to patients, their families and society. Increasing age is associated with higher risk of a wide range of chronic diseases, and aging of the vascular system is closely linked to the development of many age-related diseases. Endothelial glycocalyx is a layer of proteoglycan polymers on the surface of the inner lumen of blood vessels. It plays an important role in maintaining vascular homeostasis and protecting various organ functions. Endothelial glycocalyx loss happens through the aging process and repairing the endothelial glycocalyx may alleviate the symptoms of age-related diseases. Given the important role of the glycocalyx and its regenerative properties, it is posited that the endothelial glycocalyx may be a potential therapeutic target for aging and age-related diseases and repairing endothelial glycocalyx could play a role in the promotion of healthy aging and longevity. Here, we review the composition, function, shedding, and manifestation of the endothelial glycocalyx in aging and age-related diseases, as well as regeneration of endothelial glycocalyx.

Inverse salt sensitivity in normotensive adults: role of demographic factors

BACKGROUND

Salt sensitivity and inverse salt sensitivity [ISS; a reduction in blood pressure (BP) on a high sodium diet] are each associated with increased incidence of hypertension. The purpose of this analysis was to determine the prevalence of ISS in normotensive adults and whether ISS is associated with any demographic characteristic(s).

METHODS

Healthy normotensive, nonobese adults [ n  = 84; 43 women; age = 37 ± 13 years; baseline mean arterial pressure (MAP) = 89 ± 8 mmHg] participated in a controlled feeding study, consuming 7-day low-sodium (20 mmol sodium/day) and high-sodium (300 mmol sodium/day) diets. Twenty-four-hour ambulatory BP was assessed on the last day of each diet. ISS was defined as a reduction in 24-h MAP more than 5 mmHg, salt sensitivity as an increase in MAP more than 5 mmHg and salt resistance as a change in MAP between -5 and 5 mmHg from low sodium to high sodium.

RESULTS

Using this cutoff, 10.7% were ISS, 76.2% salt resistant, and 13.1% salt sensitive. Prevalence of ISS was similar between sexes and age groups ( P  > 0.05). However, ISS was more prevalent in those with normal BMI (15.8% ISS) compared with those with overweight BMI (0% ISS; P  < 0.01). Interestingly, classification of participants using a salt sensitivity index (ΔMAP/Δ urinary sodium excretion) categorized 21.4% as ISS, 48.8% salt resistant, and 29.8% salt sensitive.

CONCLUSION

Overall, we found that the prevalence of ISS was 10.7% (5 mmHg cutoff) or 21.4% (salt sensitivity index), and that ISS was associated with lower BMI. These results highlight the importance of future work to understand the mechanisms of ISS and to standardize salt sensitivity assessment.

A pilot study to evaluate the erythrocyte glycocalyx sensitivity to sodium as a marker for cellular salt sensitivity in hypertension

Supressed plasma renin in patients with primary hypertension is thought to be an indirect marker of sodium-induced volume expansion which is associated with more severe hypertension and hypertension-mediated organ damage. A novel test for erythrocyte glycocalyx sensitivity to sodium (eGCSS) has been proposed as a direct measure of sodium-induced damage on erythrocyte surfaces and a marker of sensitivity of the endothelium to salt in humans. Here we explore if eGCSS relates to plasma renin and other clinical and biochemical characteristics in a cohort of patients with primary hypertension. Hypertensive subjects (n = 85, 54% male) were characterised by blood biochemistry (including plasma renin/aldosterone), urine analysis for albumin-creatinine ratio (ACR), 24-h urine sodium/potassium excretion. eGCSS was measured using a commercially available kit. Correlations between eGCSS and clinical and biochemical characteristics were explored using Spearman's correlation coefficient and characteristics compared across tertiles of eGCSS. eGCSS was inversely correlated with renin (p < 0.05), with renin 17.72 ± 18 µU/l in the highest tertile of eGCSS compared to 84.27 ± 146.5 µU/l in the lowest (p = 0.012). eGCSS was positively correlated with ACR (p < 0.01), with ACR 7.37 ± 15.29 vs. 1.25 ± 1.52 g/mol for the highest vs. lowest tertiles of eGCSS (p < 0.05). eGCSS was not correlated with other clinical characteristics or biochemical measures. These results suggests that sodium retention in hypertension characterised by a low-renin state is associated with cell membrane damage reflected by eGCSS. This may contribute to the hypertension-mediated organ damage and the excess mortality associated with sodium overload and "salt sensitivity".

Etiological Diagnosis and Personalized Therapy for Hypertension: A Hypothesis of the REASOH Classification

With the epidemic of risk factors such as unhealthy lifestyle, obesity and mental stress, the prevalence of hypertension continues to rise across the world. Although standardized treatment protocols simplify the selection of antihypertensive drugs and ensure therapeutic efficacy, the pathophysiological state of some patients remains, which may also lead to the development of other cardiovascular diseases. Thus, there is an urgent need to consider the pathogenesis and selection of antihypertensive drug for different type of hypertensive patients in the era of precision medicine. We proposed the REASOH classification, based on the etiology of hypertension, including renin-dependent hypertension, elderly-arteriosclerosis-based hypertension, sympathetic-active hypertension, secondary hypertension, salt-sensitive hypertension and hyperhomocysteinemia hypertension. The aim of this paper is to propose a hypothesis and provide a brief reference for the personalized treatment of hypertensive patients.

Genetically inducing renal lymphangiogenesis attenuates hypertension in mice

BACKGROUND

Hypertension (HTN) is associated with renal proinflammatory immune cell infiltration and increased sodium retention. We reported previously that renal lymphatic vessels, which are responsible for trafficking immune cells from the interstitial space to draining lymph nodes, increase in density under hypertensive conditions. We also demonstrated that augmenting renal lymphatic density can prevent HTN in mice. Whether renal lymphangiogenesis can treat HTN in mice is unknown. We hypothesized that genetically inducing renal lymphangiogenesis after the establishment of HTN would attenuate HTN in male and female mice from three different HTN models.

METHODS

Mice with inducible kidney-specific overexpression of VEGF-D (KidVD) experience renal lymphangiogenesis upon doxycycline administration. HTN was induced in KidVD+ and KidVD- mice by subcutaneous release of angiotensin II, administration of the nitric oxide synthase inhibitor L-NAME, or consumption of a 4% salt diet following a L-NAME priming and washout period. After a week of HTN stimuli treatment, doxycycline was introduced. Systolic blood pressure (SBP) readings were taken weekly. Kidney function was determined from urine and serum measures. Kidneys were processed for RT-qPCR, flow cytometry, and imaging.

RESULTS

Mice that underwent renal-specific lymphangiogenesis had significantly decreased SBP and renal proinflammatory immune cells. Additionally, renal lymphangiogenesis was associated with a decrease in sodium transporter expression and increased fractional excretion of sodium, indicating improved sodium handling efficiency.

CONCLUSIONS

These findings demonstrate that augmenting renal lymphangiogenesis can treat HTN in male and female mice by improving renal immune cell trafficking and sodium handling.

Inverse Salt Sensitivity of Blood Pressure Is Associated with an Increased Renin-Angiotensin System Activity

High and low sodium diets are associated with increased blood pressure and cardiovascular morbidity and mortality. The paradoxical response of elevated BP in low salt diets, aka inverse salt sensitivity (ISS), is an understudied vulnerable 11% of the adult population with yet undiscovered etiology. A linear relationship between the number of single nucleotide polymorphisms (SNPs) in the dopamine D2 receptor (DRD2, rs6276 and 6277), and the sodium myo-inositol cotransporter 2 (SLC5A11, rs11074656), as well as decreased expression of these two genes in urine-derived renal proximal tubule cells (uRPTCs) isolated from clinical study participants suggest involvement of these cells in ISS. Insight into this newly discovered paradoxical response to sodium is found by incubating cells in low sodium (LS) conditions that unveil cell physiologic differences that are then reversed by mir-485-5p miRNA blocker transfection and bypassing the genetic defect by DRD2 re-expression. The renin-angiotensin system (RAS) is an important counter-regulatory mechanism to prevent hyponatremia under LS conditions. Oversensitive RAS under LS conditions could partially explain the increased mortality in ISS. Angiotensin-II (AngII, 10 nmol/L) increased sodium transport in uRPTCs to a greater extent in individuals with ISS than SR. Downstream signaling of AngII is verified by identifying lowered expression of nuclear factor erythroid 2-related factor 2 (NRF2), CCCTC-binding factor (CTCF), and manganese-dependent mitochondrial superoxide dismutase (SOD2) only in ISS-derived uRPTCs and not SR-derived uRPTCs when incubated in LS conditions. We conclude that DRD2 and SLC5A11 variants in ISS may cause an increased low sodium sensitivity to AngII and renal sodium reabsorption which can contribute to inverse salt-sensitive hypertension.

Inverse salt sensitivity: an independent risk factor for cardiovascular damage in essential hypertension

OBJECTIVE

Salt sensitivity is a powerful risk factor for cardiovascular (CV) disease and mortality in both normotensive and hypertensive patients. We investigated the predictive value of the salt sensitivity phenotype in the development of CV events and hypertensive target organ damage (TOD) among essential hypertensive patients.

METHODS

Eight hundred forty-four naive hypertensive patients were recruited and underwent an acute saline test during which blood pressure (BP) displayed either no substantial variation (salt-resistant, SR individuals), an increase (salt-sensitive, SS), or a paradoxical decrease (inverse salt-sensitive, ISS). Sixty-one patients with the longest monitored follow-up (median 16 years) for blood pressure and organ damage were selected for the present study. A clinical score for TOD development based on the severity and the age of onset was set up by considering hypertensive heart disease, cerebrovascular damage, microalbuminuria, and vascular events.

RESULTS

CV events were significantly higher among SS and ISS than in SR patients. The relative risk of developing CV events was 12.67 times higher in SS than SR and 5.94 times higher in ISS than SR patients. The development of moderate to severe TOD was 10-fold higher in SS and over 15-fold higher in ISS than in SR patients. Among the three phenotypes, changes in plasma endogenous ouabain were linked with the blood pressure effects of saline.

CONCLUSIONS

Salt sensitivity and inverse salt sensitivity appear to be equivalent risk factors for CV events. The response to an acute saline test is predictive of CV damage for newly identified ISS individuals.

Salt-Sensitive Ileal Microbiota Plays a Role in Atrial Natriuretic Peptide Deficiency-Induced Cardiac Injury

Atrial natriuretic peptide (ANP) activity deficiency contributes to salt-sensitive hypertension in humans and mice. However, the role of ileal microbiota in salt sensitivity in ANP deficiency-related cardiac injury has not been investigated yet. This study used ANP^−/− mice to analyze the role of the salt-sensitive ileal microbiome on cardiac injury. ANP^−/− mice showed an increase in blood pressure (BP), the heart weight/body weight (HW/BW) ratio, and cardiac hypertrophy compared with wild-type (WT) mice. ANP deficiency did not impact the histological structure but reduced occludin expression in the ileum. Antibiotics significantly relieved BP and cardiac hypertrophy in ANP^−/− mice. A high-salt diet (HSD) increased BP, the HW/BW ratio, and cardiac hypertrophy/fibrosis in WT and ANP^−/− mice, and an HSD treatment in ANP^−/− mice exacerbated these cardiac parameters. The HSD markedly decreased muscularis layer thickening, villus length, and numbers of Paneth and goblet cells in the ileum of WT and ANP^−/− mice. Furthermore, the HSD increased the level of TLR4 and IL-1β in ANP^−/− mice ileum compared with WT mice. Antibiotics reduced the HW/BW ratio, cardiac hypertrophy/fibrosis, and the level of TLR4 and IL-1β in the ileum, and rescued the muscularis layer thickening, villus length, and numbers of Paneth and goblet cells in the ileum of HSD-ANP^−/− mice. Importantly, ANP deficiency induced the colonization of Burkholderiales bacterium YL45, Lactobacillus johnsonii, and Lactobacillus reuteri in the ileum on the NSD diet, which was only observed in HSD-induced WT mice but not in WT mice on the NSD. Besides, the HSD significantly enhanced the sum of the percentage of the colonization of Burkholderiales bacterium YL45, Lactobacillus johnsonii, and Lactobacillus reuteri in the ileum of ANP^−/− mice. Ileal microbiota transfer (IMT) from ANP^−/− mice to healthy C57BL/6J mice drove Lactobacillus johnsonii and Lactobacillus reuteri colonization in the ileum, which manifested an increase in BP, the HW/BW ratio, cardiac hypertrophy, and ileal pathology compared with IMT from WT mice. The HSD in C57BL/6J mice with IMT from ANP^−/− mice drove the colonization of Burkholderiales bacterium YL45, Lactobacillus johnsonii, and Lactobacillus reuteri in the ileum and further exacerbated the cardiac and ileal pathology. Our results suggest that salt-sensitive ileal microbiota is probably related to ANP deficiency-induced cardiac injury.

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

Background

High 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.

Methods

We 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).

Results

Among 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.

Conclusion

Our study indicates that high salt diet increases the serum H3K4me1 and Set7 levels in SS individuals.

High blood pressure in children and adolescents: current perspectives and strategies to improve future kidney and cardiovascular health

Hypertension is one of the most common causes of preventable death worldwide. The prevalence of pediatric hypertension has increased significantly in recent decades. The cause of this is likely multifactorial, related to increasing childhood obesity, high dietary sodium intake, sedentary lifestyles, perinatal factors, familial aggregation, socioeconomic factors, and ethnic blood pressure (BP) differences. Pediatric hypertension represents a major public health threat. Uncontrolled pediatric hypertension is associated with subclinical cardiovascular disease and adult-onset hypertension. In children with chronic kidney disease (CKD), hypertension is also a strong risk factor for progression to kidney failure. Despite these risks, current rates of pediatric BP screening, hypertension detection, treatment, and control remain suboptimal. Contributing to these shortcomings are the challenges of accurately measuring pediatric BP, limited access to validated pediatric equipment and hypertension specialists, complex interpretation of pediatric BP measurements, problematic normative BP data, and conflicting society guidelines for pediatric hypertension. To date, limited pediatric hypertension research has been conducted to help address these challenges. However, there are several promising signs in the field of pediatric hypertension. There is greater attention being drawn on the cardiovascular risks of pediatric hypertension, more emphasis on the need for childhood BP screening and management, new public health initiatives being implemented, and increasing research interest and funding. This article summarizes what is currently known about pediatric hypertension, the existing knowledge-practice gaps, and ongoing research aimed at improving future kidney and cardiovascular health.

From salt to hypertension, what is missed?

Excess salt intake is viewed as a major contributor to hypertension and cardiovascular disease, and dietary salt restriction is broadly recommended by public health guidelines. However, individuals can have widely varying physiological responses to salt intake, and a tailored approach to evaluation and intervention may be needed. The traditional sodium related concepts are challenging to assess clinically for two reasons: (1) spot and 24-hour urine sodium are frequently used to evaluate salt intake, but are more suitable for population study, and (2) some adverse effects of salt may be blood pressure-independent. In recent years, previously unknown mechanisms of sodium absorption and storage have been discovered. This review will outline the limitations of current methods to assess sodium balance and discuss new potential evaluation methods and treatment targets.

Metabolic syndrome and its components predict the development of arterial stiffening in a sample of adult men

BACKGROUND AND OBJECTIVE

Metabolic syndrome (MS) and its components are associated with greater cardiovascular risk. A number of studies found a positive association between MS and vascular damage, but few observational studies evaluated the predictive role of MS on arterial stiffening (AS). Therefore, the aim of this study was to estimate the ability of MS and its components to predict the risk of AS in an 8-year follow-up of a sample of adult men (Olivetti Heart Study).

METHODS

The analysis included 778 men without AS (pulse pressure >60 mmHg) at baseline. A positive diagnosis of MS was made by recognized criteria, if at least three components were present.

RESULTS

At the end of the follow-up period, there was an incidence of 11% in AS. The percentage of participants that developed AS was greater in the MS group than those without MS, also after adjustment for main confounders (odds ratio: 2.5, 95% confidence interval: 1.3-4.9). The risk of AS also increased with increase in the numbers of MS elements (p for trend <.01). In addition, the analysis of the predictive role of the single MS component showed that high blood pressure (HBP) was the strongest predictor.

CONCLUSIONS

The results of this prospective study indicate a predictive role of MS on AS, independently of main confounders. In addition, HBP seems the strongest predictor of AS among MS components.

The Effects of Short-Term Changes in Sodium Intake on Plasma Marinobufagenin Levels in Patients with Primary Salt-Sensitive and Salt-Insensitive Hypertension

Increased marinobufagenin (MBG) synthesis has been suggested in response to high dietary salt intake. The aim of this study was to determine the effects of short-term changes in sodium intake on plasma MBG levels in patients with primary salt-sensitive and salt-insensitive hypertension. In total, 51 patients with primary hypertension were evaluated during acute sodium restriction and sodium loading. Plasma or serum concentrations of MBG, natriuretic pro-peptides, aldosterone, sodium, potassium, as well as hematocrit (Hct) value, plasma renin activity (PRA) and urinary sodium and potassium excretion were measured. Ambulatory blood pressure monitoring (ABPM) and echocardiography were performed at baseline. In salt-sensitive patients with primary hypertension plasma MBG correlated positively with diastolic blood pressure (ABPM) and serum NT-proANP concentration at baseline and with serum NT-proANP concentration after dietary sodium restriction. In this subgroup plasma MBG concentration decreased during sodium restriction, and a parallel increase of PRA was observed. Acute salt loading further decreased plasma MBG concentration in salt-sensitive subjects in contrast to salt insensitive patients. No correlation was found between plasma MBG concentration and left ventricular mass index. In conclusion, in salt-sensitive hypertensive patients plasma MBG concentration correlates with 24-h diastolic blood pressure and dietary sodium restriction reduces plasma MBG levels. Decreased MBG secretion in response to acute salt loading may play an important role in the pathogenesis of salt sensitivity.

Inhibition of neprilysin with sacubitril without RAS blockage aggravates renal disease in Dahl SS rats

Salt-sensitive (SS) hypertension is accompanied with severe cardiorenal complications. In this condition, elevated blood pressure (BP) resulting from salt retention is associated with counterintuitively lower levels of atrial natriuretic peptide (ANP). In plasma, ANP is degraded by the neprilysin; therefore, pharmacological inhibition of this metalloprotease (i.e., with sacubitril) can be employed to increase ANP level. We have shown earlier that sacubitril in combination with valsartan (75 μg/day each) had beneficial effects on renal function in Dahl SS rats. The goal of this study was to evaluate the effects of a higher dose of sacubitril on renal damage in this model. To induce hypertension, male Dahl SS rats were fed a 4% NaCl diet (HS) for 21 days, and were administered sacubitril (125 μg/day) or vehicle via s.c. osmotic pumps. At the end of the HS challenge, both groups exhibited similar outcomes for GFR, heart weight, plasma electrolytes, BUN, and creatinine. Sacubitril exacerbated kidney hypertrophy, but did not affect levels of renal fibrosis. We also observed aggravated glomerular lesions and increased formation of protein casts in the sacubitril-treated animals compared to controls. Thus, in Dahl SS rats, administration of sacubitril without renin-angiotensin-system blockage had adverse effects on renal disease progression, particularly in regards to glomerular damage and protein cast formation. We can speculate that while ANP levels are increased because of neprilysin inhibition, there are off-target effects of sacubitril, which are detrimental to renal function in the SS hypertensive state.

Urinary phosphate-containing nanoparticle contributes to inflammation and kidney injury in a salt-sensitive hypertension rat model

Although disturbed phosphate metabolism frequently accompanies chronic kidney disease (CKD), its causal role in CKD progression remains unclear. It is also not fully understood how excess salt induces organ damage. We here show that urinary phosphate-containing nanoparticles promote kidney injury in salt-sensitive hypertension. In Dahl salt-sensitive rats, salt loading resulted in a significant increase in urinary phosphate excretion without altering serum phosphate levels. An intestinal phosphate binder sucroferric oxyhydroxide attenuated renal inflammation and proteinuria in this model, along with the suppression of phosphaturia. Using cultured proximal tubule cells, we confirmed direct pathogenic roles of phosphate-containing nanoparticles in renal tubules. Finally, transcriptome analysis revealed a potential role of complement C1q in renal inflammation associated with altered phosphate metabolism. These data demonstrate that increased phosphate excretion promotes renal inflammation in salt-sensitive hypertension and suggest a role of disturbed phosphate metabolism in the pathophysiology of hypertensive kidney disease and high salt-induced kidney injury.

Construction of a ceRNA coregulatory network and screening of hub biomarkers for salt-sensitive hypertension

Salt-sensitive hypertension (SSH) is an independent risk factor for cardiovascular disease. The regulation of long non-coding RNAs, mRNAs and competing endogenous RNAs (ceRNAs) in the pathogenesis of SSH is uncertain. An RNA microarray was performed to discover SSH-associated differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs), and 296 DElncRNAs and 44 DEmRNAs were identified, and 247 DElncRNAs and 44 DEmRNAs among these RNAs were included in the coexpression network. The coregulatory network included 23 ceRNA loops, and six hub RNAs (lnc-ILK-8:1, lnc-OTX1-7:1, lnc-RCAN1-6:1, GIMAP8, SUV420H1 and PIGV) were identified for further population validation. The ceRNA correlations among lnc-OTX1-7:1, hsa-miR-361-5p and GIMAP8 were confirmed in SSH and SRH patients. A larger-sample validation confirmed that GIMAP8, SUV420H1 and PIGV were differentially expressed between the SSH and SRH groups. In addition, SUV420H1 was included in the SSH screening model, and the area under the curve of the model was 0.720 (95% CI: 0.624-0.816). Our study explored the transcriptome profiles of SSH and constructed a ceRNA network to help elucidate the mechanism of SSH. In addition, SUV420H1 was identified as a hub element that participates in SSH transcriptional regulation and as a potential biomarker for the early diagnosis of SSH.

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.

Oral Fludrocortisone Test for Salt-Sensitive Screening in Hypertensive Patients: A Randomized Crossover Trial

Background

Salt sensitivity is associated with an increased cardiovascular risk, but the gold standard method (diet cycles) requires 24-h urine samples and has poor patient compliance.

Objectives

Test the hypothesis that oral fludrocortisone (0.4 mg per day for 7 days) is a good alternative in identifying salt-sensitive patients.

Methodology

We conducted a randomized crossover study with 30 hypertensive individuals comprising the following steps: (1) washout; (2) phase A (low- and high-sodium diet cycles); (3) washout 2; (4) phase B (fludrocortisone test). Phase A and B steps were performed in a random way. Consistent with the literature, we found that 53.3% were salt-sensitive according to the reference test. Using the ROC curve, the fludrocortisone test defined salt sensitivity by a median blood pressure increase of ≥3 mmHg. A good accuracy of fludrocortisone in detecting salt sensitivity was observed (AUC: 0.732±0.065; p<0.001), with 80% sensitivity and 53% specificity.

Conclusion

The fludrocortisone test is a good option for screening salt sensitivity in hypertensive patients. However, the low specificity prevents this test from being an ideal substitute to the labor-intensive diet cycles exam in the definition of salt sensitivity. This clinical trial is registered with NCT01453959.

Uncoupling Protein 2: A Key Player and a Potential Therapeutic Target in Vascular Diseases

Uncoupling protein 2 (UCP2) is an inner mitochondrial membrane protein that belongs to the uncoupling protein family and plays an important role in lowering mitochondrial membrane potential and dissipating metabolic energy with prevention of oxidative stress accumulation. In the present article, we will review the evidence that UCP2, as a consequence of its roles within the mitochondria, represents a critical player in the predisposition to vascular disease development in both animal models and in humans, particularly in relation to obesity, diabetes, and hypertension. The deletion of the UCP2 gene contributes to atherosclerosis lesion development in the knockout mice, also showing significantly shorter lifespan. The UCP2 gene downregulation is a key determinant of higher predisposition to renal and cerebrovascular damage in an animal model of spontaneous hypertension and stroke. In contrast, UCP2 overexpression improves both hyperglycemia- and high-salt diet-induced endothelial dysfunction and ameliorates hypertensive target organ damage in SHRSP. Moreover, drugs (fenofibrate and sitagliptin) and several vegetable compounds (extracts from Brassicaceae, berberine, curcumin, and capsaicin) are able to induce UCP2 expression level and to exert beneficial effects on the occurrence of vascular damage. As a consequence, UCP2 becomes an interesting therapeutic target for the treatment of common human vascular diseases.

Salt sensitivity and its implication in clinical practice

Hypertension (HTN) is a complex multi-factorial disease and is considered one of the foremost modifiable risk factors for stroke, heart failure, ischemic heart disease and renal dysfunction. Over the past century, salt and its linkage to HTN and cardiovascular (CV) mortality has been the subject of intense scientific scrutiny. There is now consensus that different individuals have different susceptibilities to blood pressure (BP)-raising effects of salt and this susceptiveness is called as salt sensitivity. Several renal and extra-renal mechanisms are believed to play a role. Blunted activity of the renin–angiotensin–aldosterone system (RAAS), adrenal Rac1-MR-Sgk1-NCC/ENaC pathway, renal SNS-GR-WNK4-NCC pathway, defect of membrane ion transportation, inflammation and abnormalities of Na⁺/Ca²⁺ exchange have all been implicated as pathophysiological basis for salt sensitive HTN. While salt restriction is definitely beneficial recent observation suggests that treatment with Azilsartan may improve salt sensitivity by selectively reducing renal proximal tubule Na⁺/H⁺ exchange. This encourages the future potential benefits of recognizing and therapeutically addressing the salt sensitive phenotype in humans.

Trans-ethnic Fine Mapping Highlights Kidney-Function Genes Linked to Salt Sensitivity

We analyzed genome-wide association studies (GWASs), including data from 71,638 individuals from four ancestries, for estimated glomerular filtration rate (eGFR), a measure of kidney function used to define chronic kidney disease (CKD). We identified 20 loci attaining genome-wide-significant evidence of association (p < 5 × 10(-8)) with kidney function and highlighted that allelic effects on eGFR at lead SNPs are homogeneous across ancestries. We leveraged differences in the pattern of linkage disequilibrium between diverse populations to fine-map the 20 loci through construction of "credible sets" of variants driving eGFR association signals. Credible variants at the 20 eGFR loci were enriched for DNase I hypersensitivity sites (DHSs) in human kidney cells. DHS credible variants were expression quantitative trait loci for NFATC1 and RGS14 (at the SLC34A1 locus) in multiple tissues. Loss-of-function mutations in ancestral orthologs of both genes in Drosophila melanogaster were associated with altered sensitivity to salt stress. Renal mRNA expression of Nfatc1 and Rgs14 in a salt-sensitive mouse model was also reduced after exposure to a high-salt diet or induced CKD. Our study (1) demonstrates the utility of trans-ethnic fine mapping through integration of GWASs involving diverse populations with genomic annotation from relevant tissues to define molecular mechanisms by which association signals exert their effect and (2) suggests that salt sensitivity might be an important marker for biological processes that affect kidney function and CKD in humans.

The blood pressure-salt sensitivity paradigm: pathophysiologically sound yet of no practical value

Sodium plays an important pathophysiological role in blood pressure (BP) values and in the development of hypertension, and epidemiological studies such as the Intersalt Study have shown that the increase in BP occurring with age is determined by salt intake. Recently, a meta-analysis of 13 prospective studies has also shown the close relationship between excess sodium intake and higher risk of stroke and total cardiovascular events. However, the BP response to changing salt intake displayed a marked variability, as first suggested by Kawasaki et al. (The effect of high-sodium and low-sodium intakes on blood pressure and other related variables in human subjects with idiopathic hypertension. Am J Med 1978; 64: 193-198) and later by Weinberger et al. (Definitions and characteristics of sodium sensitivity and blood pressure resistance. Hypertension 1986; 8: II127-II134), who recognized the heterogeneity of the BP response to salt and developed the concept of salt sensitivity. We have a large body of evidence in favour of a major role of metabolic and neuro-hormonal factors in determining BP salt sensitivity in association with the effect of genetic variation. There is evidence that salt sensitivity influences the development of organ damage, even independently-at least in part-of BP levels and the occurrence of hypertension. In addition, several observational studies indicate that salt sensitivity is clearly associated with a higher rate of cardiovascular events and mortality, independently of BP levels and hypertension. A cluster of factors with well-known atherogenic potential such as hyperinsulinaemia, dyslipidaemia and microalbuminuria-all known to be prevalent in salt-sensitive hypertension-might at least partially explain the increased cardiovascular risk observed in salt sensitive individuals. The gold standard for the evaluation of BP salt sensitivity is the BP response to a moderate reduction of salt intake for several weeks; nevertheless, these protocols often suffer of poor patient compliance to dietary instructions. To overcome this problem, short-term tests have been proposed that evaluate either large differences in salt intake for a few days or the response to intravenous administration of saline solution and short-acting diuretics. Recently, the use of ambulatory BP measurement has been proposed for the clinical assessment of BP salt sensitivity. Noteworthy, BP salt sensitivity, in whomever or however assessed, behaves as a continuous variable but salt sensitivity is used as a categorical parameter, with salt-sensitive individuals being defined as those with a difference in BP between low- and high-sodium intake >10%, and salt-resistant subjects those in whom BP does not increase or shows an increase <5% under sodium loading. The general conclusion that can and should be drawn from the above considerations is that the paradigm of salt sensitivity, despite its important pathophysiological meaning, is not helpful, so far, to the practising physician in clinical practice nor is it relevant or useful to the design and implementation of a population-based strategy of salt intake reduction; however, further studies are warranted for an accurate assessment of the salt-sensitivity phenotype in clinical practice. In the absence of a population strategy for salt intake reduction, the aim should be the generation of a 'low sodium environment' allowing for a dietary salt intake tailored on true human requirements and not on deleterious lifestyle habits.

Ambulatory blood pressure and blood pressure load responses to low sodium intervention in Han Chinese population

We aimed to illustrate ambulatory blood pressure monitoring parameters responses to low sodium intake and their differences between salt-sensitive and non-salt-sensitive individuals. A total of 186 participants were included in this analysis. Twenty-four hour, day-time and night-time blood pressure (BP) and BP load decreased during low sodium intervention, especially in salt-sensitive (SS) group. After multivariable adjustment, 24-h systolic BP, diastolic BP, mean arterial pressure and BP load responses to low sodium intervention of SS individuals were more pronounced than those of non-salt-sensitive individuals. Thus, reducing salt intake is potentially needed for the prevention of hypertension, especially in SS individuals.

Genetic variation in NEDD4L, an epithelial sodium channel regulator, is associated with cardiovascular disease and cardiovascular death

OBJECTIVES

We have previously shown that genetic variance in NEDD4L, a regulating protein of a sodium channel in the distal nephron, has been associated with marginally higher blood pressure and enhanced salt sensitivity. Here, we tested if the genetic NEDD4L variation previously associated with salt sensitivity is related to population blood pressure, incidence of cardiovascular disease (CVD) and mortality.

METHOD

We genotyped the rs4149601 A→G and rs2288774 T→C NEDD4L variants in 27,564 participants of the Malmö Diet and Cancer Study. The genotype combination previously shown to be associated with salt sensitivity (rs4149601 GG+rs2288774 CC), which was present in 9.6% of participants, was related to cross sectional blood pressure as well as to CVD incidence and mortality during a median follow-up time of 14 years using Cox regression models.

RESULTS

Carriers of the NEDD4L salt sensitivity-associated genotype had (mean ± SEM) higher systolic (142 ± 0.4 vs. 141 ± 0.1 mmHg, P = 0.002) and diastolic (86.0 ± 0.5 vs. 85.6 ± 0.2 mmHg, P = 0.025) blood pressure and multivariate adjusted hazards ratio (95% confidence interval) of CVD 1.13 (1.02-1.25, P = 0.018), coronary events 1.20 (1.06-1.37; P = 0.005) and cardiovascular mortality 1.17 (0.99-1.37; P = 0.055) than noncarriers but there was no significant difference in the incidence of stroke and total mortality.

CONCLUSION

The NEDD4L salt sensitivity-associated genotype was associated with higher blood pressure, which may translate into increased risk for CVD morbidity and mortality. Interestingly, there was no association with stroke suggesting that the association is partially blood pressure independent.

Salt-induced epithelial-to-mesenchymal transition in Dahl salt-sensitive rats is dependent on elevated blood pressure

Dietary salt intake has been linked to hypertension and cardiovascular disease. Accumulating evidence has indicated that salt-sensitive individuals on high salt intake are more likely to develop renal fibrosis. Epithelial-to-mesenchymal transition (EMT) participates in the development and progression of renal fibrosis in humans and animals. The objective of this study was to investigate the impact of a high-salt diet on EMT in Dahl salt-sensitive (SS) rats. Twenty-four male SS and consomic SS-13^BN rats were randomized to a normal diet or a high-salt diet. After 4 weeks, systolic blood pressure (SBP) and albuminuria were analyzed, and renal fibrosis was histopathologically evaluated. Tubular EMT was evaluated using immunohistochemistry and real-time PCR with E-cadherin and alpha smooth muscle actin (α-SMA). After 4 weeks, SBP and albuminuria were significantly increased in the SS high-salt group compared with the normal diet group. Dietary salt intake induced renal fibrosis and tubular EMT as identified by reduced expression of E-cadherin and enhanced expression of α-SMA in SS rats. Both blood pressure and renal interstitial fibrosis were negatively correlated with E-cadherin but positively correlated with α-SMA. Salt intake induced tubular EMT and renal injury in SS rats, and this relationship might depend on the increase in blood pressure.

Transgenic overexpression of uncoupling protein 2 attenuates salt-induced vascular dysfunction by inhibition of oxidative stress

BACKGROUND

Ablation of uncoupling protein 2 (UCP2) has been involved in the enhancement of salt sensitivity associated with increased superoxide level and decreased nitric oxide (NO) bioavailability. However, the role of overexpression of UCP2 in salt-induced vascular dysfunction remains elusive.

METHODS

UCP2 transgenic (TG) and wild-type (WT) mice were placed on either a normal-salt (NS, 0.5%) or a high-salt (HS, 8%) diet for 12 weeks. Blood pressure (BP) and hypotensive responses were measured, and the vascular tone, superoxide level, and NO bioavailability in aortas were measured in each group.

RESULTS

The TG mice had increased expression and function of UCP2 in vascular smooth muscle cells. The acetylcholine (ACh)- and nitroglycerin (NTG)-induced hypotensive responses and aortic relaxations were significantly blunted in WT mice fed with an HS diet compared with an NS diet. These harmful effects were prevented in UCP2 TG mice. The impairments of ACh- and NTG-induced relaxation in aorta were inhibited by the endothelial NO synthase (eNOS) inhibitor L-NAME and mitochondrial antioxidant MitoQ, respectively. The HS intake led to a significant increase in superoxide production and a comparable decrease in NO bioavailability in aortas, and these effects were blunted in UCP2 TG mice. The expression of UCP2 was slightly increased in the HS group. However, the expression and phosphorylation of eNOS were not affected by an HS diet and overexpression of UCP2.

CONCLUSIONS

These findings suggest that overexpression of UCP2 can ameliorate salt-induced vascular dysfunction. This beneficial effect of UCP2 is mediated by decreased superoxide and reserved NO bioavailability.

Sodium restriction in heart failure: benefit or harm?

OPINION STATEMENT

Current guidelines vary in the recommended amount of dietary sodium intake for heart failure (HF) patients. Observational studies and the hypertension literature support the concept that sodium restriction improves HF outcomes. In contrast, several randomized controlled trials imply that dietary sodium restriction can cause harm through hypovolemia and increased neurohormonal activation. Data from hypertensive animal models and humans suggest that dietary sodium intake may need to be individually tailored based on HF severity and the physiologic response to sodium loading. Future studies must assess interactions between sodium intake, fluid intake, and diuretics to match clinical practice and improve safety. More information is needed in multiple areas, including accurate measurement of sodium intake, implementation of dietary changes in HF patients, and establishment of biomarkers that predict response to changes in sodium intake. Additional research is urgently needed to determine the true impact of the most commonly recommended self-care strategy in HF.

Relation between left atrial enlargement and stroke subtypes in acute ischemic stroke patients

Objective

Increased atrial size is frequently seen in ischemic stroke patients in clinical practice. There is controversy about whether left atrial enlargement (LAE) should be regarded as a risk factor for cerebral infarction. We investigated the association between indexed left atrial volume (LAVI) and conventional stroke risk factors as well as stroke subtypes in acute ischemic stroke patients.

Methods

One hundred eighty two acute cerebral infarction patients were included in this study. Brain magnetic resonance imaging and transthoracic echocardiography were done for all patients within 30 days of diagnosis of acute cerebral infarction. Echocardiographic LAE was identified when LAVI was more than 27 mL/m². Stroke subtypes were classified by the Trial of Org 10171 in acute stroke treatment classification.

Results

There were significant differences between subjects with normal and increased LAVI in prevalence of stroke risk factors including atrial fibrillation (p = 0.001), hypertension (p = 0.000), valvular heart disease (p = 0.011) and previous stroke (p = 0.031). An increased LAVI was associated with cardioembolic subtype with an adjusted odds ratio was 6.749 (p = 0.002) compared with small vessel disease.

Conclusion

Increased LAVI was more prevalent in those who had cardiovascular risk factors, such as atrial fibrillation, hypertension, valvular heart disease and history of previous stroke. LAE influenced most patients in all subtypes of ischemic stroke but was most prevalent in the cardioembolic stroke subtype. Increased LAVI might be a risk factor of cerebral infarction, especially in patients with cardioembolic stroke subtype.

Salt sensitivity: a review with a focus on non-Hispanic blacks and Hispanics

The purpose of this review is to summarize the available information regarding salt sensitivity particularly as it relates to non-Hispanic blacks and Hispanics and to clarify possible etiologies, especially those that might shed light on potential treatment options. In non-Hispanic blacks, there is evidence that endothelial dysfunction, reduced potassium intake, decreased urinary kallikrein excretion, upregulation of sodium channel activity, dysfunction in atrial natriuretic peptide (ANP) production, and APOL1 gene nephropathy risk variants may cause or contribute to salt sensitivity. Supported treatment avenues include diets high in potassium and soybean protein, the components of which stimulate nitric oxide production. Racial heterogeneity complicates the study of salt sensitivity in Hispanic populations. Caribbean Hispanics, who have a higher proportion of African ancestry, may respond to commonly prescribed anti-hypertensive agents in a way that is characteristic of non-Hispanic black hypertensives. The low-renin hypertensive phenotype commonly seen in non-Hispanic blacks has been linked to salt sensitivity and may indicate an increased risk for salt sensitivity in a portion of the Hispanic population. In conclusion, increased morbidity and mortality associated with salt sensitivity mandates further studies evaluating the efficacy of tailored dietary and pharmacologic treatment in non-Hispanic blacks and determining the prevalence of low renin hypertension and salt sensitivity within the various subgroups of Hispanic Americans.

Regulation of the epithelial sodium channel [ENaC] in kidneys of salt-sensitive Dahl rats: insights on alternative splicing

The epithelial sodium channel [ENaC] is critical for the maintenance of sodium balance, extracellular fluid volume and long term blood pressure control. Monogenic disorders causing ENaC hyperactivity have led to a severe form of hereditary hypertension in humans, known as Liddle's syndrome. Similarly, in animal models, ENaC hyperactivity has been well documented in kidneys of salt-sensitive [S] Dahl rats [a genetic model of salt-sensitive hypertension] versus their normotensive control [Dahl salt-resistant [R] rats]. The purpose of the present review is to highlight the differential regulation of ENaC in kidneys of Dahl S versus R rats. A systematic overview of the putative role of alternative splicing of the main alpha subunit of ENaC [alpha ENaC] in modulating ENaC expression in kidneys of Dahl rats will be discussed. Finally, a better understanding of the meaningful contribution of ENaC in the pathogenesis of salt-sensitive hypertension will be achieved upon completion of this review.

Salt-induced cardiac hypertrophy is independent of blood pressure and endothelin in obese, heart failure-prone SHHF rats

The interaction of salt sensitivity and obesity in development of cardiac hypertrophy is incompletely understood. The SHHF/Mcc-fa(cp) (SHHF) rat model was used to examine the effect of high salt on cardiac hypertrophy and expression of endothelin (ET) and nitric oxide synthase (NOS) isoforms. Homozygous lean (+/+) and obese (fa(cp)/fa(cp)) SHHF were fed a low-salt diet (0.3% NaCl) for seven days followed by a high-salt diet (8.0% NaCl) for seven days. To assess the role of ET in mediating cardiac hypertrophy and gene expression with high salt, additional groups were treated with an ET(A)/ET(B) receptor antagonist (bosentan) while on high salt. Obese SHHF showed an increase in systolic blood pressure and cardiac hypertrophy in response to the high-salt diet. High salt resulted in decreased expression of preproET as well as all three NOS isoforms in the Obese, while cytokine induced NOS (iNOS) and neuronal NOS (nNOS) increased in Leans. Though the salt-sensitive component of the hypertension observed in the Obese was prevented by bosentan, cardiac hypertrophy still occurred and expression of all NOS isoforms remained lower in Obese compared to Lean. Endothelial NOS (eNOS) expression increased in the Lean with bosentan. These studies suggest that cardiac hypertrophy is independent of the level of hypertension and may be mediated by altered production of NOS isoforms in salt-sensitive, obese SHHF.

Renal response to angiotensin II is blunted in sodium-sensitive normotensive men

BACKGROUND

In hypertension, sodium sensitivity (SS) of blood pressure is associated with renal hemodynamic abnormalities related to increased activity of the renal renin-angiotensin aldosterone system (RAAS). The renal mechanisms of SS in normotensives are unknown. Therefore, we studied whether SS is related to renal hemodynamics and renal responsiveness to angiotensin II (AngII) in young healthy adults.

METHODS

Blood pressure (mean arterial pressure (MAP)) and renal function were measured in 34 healthy men after 1-week low-sodium diet (LS; 50 mmol Na(+)/24 h), 1-week high-sodium diet (HS; 200 mmol Na(+)/24h), and 1-week HS-ACEi (enalapril 20 mg/day). The responses of effective renal plasma flow (ERPF; (131)I-Hippuran clearance) to graded infusion of AngII were assessed during each condition.

RESULTS

The sodium-induced change in MAP ranged from -7 to +14 mm Hg. SS (a sodium-induced increase in MAP >3 mm Hg) was present in 13 subjects. ERPF was lower in SS subjects during LS and during HS-ACEi. The AngII-induced decrease in ERPF was blunted in SS on LS (-25 +/- 6 vs. -29 +/- 7% in sodium-resistant (SR) subjects, P < 0.05) and on HS (-30 +/- 5 vs. -35 +/- 6%, P < 0.05). The blunting was corrected by angiotensin-converting enzyme inhibitors (ACEi) (-36 +/- 6 vs. -37 +/- 7%).

CONCLUSION

SS normotensive subjects have a blunted renal response to exogenous AngII. This is ameliorated by ACEi, supporting a role for inappropriately high intrarenal RAAS activity. As these findings cannot be attributed to subclinical renal hypertensive damage, high intrarenal RAAS activity and altered renal hemodynamics may be primary phenomena underlying SS.

Genetic linkage of urinary albumin excretion in Dahl salt-sensitive rats: influence of dietary salt and confirmation using congenic strains

Previously, we reported a linkage analysis for urinary albumin excretion (UAE) from a backcross population derived from the Dahl salt-sensitive (S) rat and the spontaneously hypertensive rat (SHR) raised on a low-salt diet. The present study sought to examine the effect of salt loading on the observation of UAE quantitative trait loci (QTL) using a F1(S x SHR) x S backcross population (n = 228) raised on a 2% NaCl diet. Parental strain data demonstrated that S rats have significantly higher blood pressure (BP) and UAE compared with either F1(S x SHR) or SHR at 8 wk of age, and this difference was exacerbated by 12 wk of age in response to a high-salt diet (2% NaCl). Genome scans done at 8, 12, and 16 wk of age yielded eight QTL for UAE. At week 8 (low salt), QTL for UAE were observed on rat chromosomes (RNO) 1, 2, 6, 8, 9, 11, 13, and 19. Week 8 linkage analysis confirmed previous linkage data and provided a baseline to examine the effect of salt loading at subsequent time points. At weeks 12 and 16 (after salt- loading), QTL for UAE were observed on RNO1, -6, -8, -9, and -13. Surprisingly, UAE QTL were no longer observed on RNO2, -11, and -19 after salt loading, suggesting that these QTL are attenuated by increased salt intake. The effects of UAE QTL on RNO2, -6, -9, -11, and -13 were examined using congenic strains whereby the SHR alleles at each QTL were placed on the S background. These congenic strains demonstrated large and significant effects on UAE compared with the S rat, proving that QTL for UAE reside on these chromosomes.

Common genetic variants and haplotypes in renal CLCNKA gene are associated to salt-sensitive hypertension

Abnormal renal reabsorption of sodium (Na(+)) is likely to play a role in the pathogenesis of salt-sensitivity. In the kidney, chloride channels CLC-Ka (gene CLCNKA) and CLC-Kb (gene CLCNKB) and their subunit Barttin (gene BSND) have important effects on the control of Na(+) and water homeostasis. We investigated if single nucleotide polymorphisms (SNPs) or haplotypes within CLCNKA, CLCNKB and BSND loci affect salt-sensitivity in hypertensive subjects. Associations between blood pressure (BP) change after Na(+)-load and 15 SNPs spanning the length of CLCNKA and CLCNKB and six SNPs spanning the length of BSND were studied in 314 never treated essential hypertensives who underwent an i.v. infusion of saline (300 mm NaCl in 2 l H(2)O in 120 min). Four SNPs were significantly associated with BP change after Na-load. Rs848307 (P = 0.0026) and rs1739843 (P = 0.0023) map upstream the 5' of CLCNKA. Non-coding Rs1010069 (P = 0.0006) and non-synonymous rs1805152 (Thr447Ala; P = 0.0078) map within CLCNKA. Moreover, basal plasma renin activity and heart rate (measured before Na-load) were significantly lower in patients carrying the alleles associated with the larger mean BP increase after Na-load, indicating that such alleles are associated with chronic volume expansion. This study supports the candidacy of CLCNKA as a new susceptibility gene for salt-sensitivity.