Genomic epidemiology of blood pressure salt sensitivity

Insulin resistance is associated to future hypertension in normotensive salt-sensitive individuals: a 10-year follow-up study

BACKGROUND

Salt-sensitive hypertension is associated with insulin resistance in nonobese individuals. However, no data have been reported for normotensive offspring of hypertensive salt-sensitive parents.

AIMS

To evaluate in normotensive salt-sensitive or salt-resistant offspring of hypertensive parents (offSS-HT and offSR-HT, respectively): the possible association between insulin resistance and endothelial dysfunction, and the risk of developing hypertension in a 10-year follow-up.

DESIGN AND METHODS

Forty-one offSS-HT (29 ± 2 years; 20 female) and 36 offSR-HT (25 ± 3 years; 16 female) were followed up for 10 years. Both groups were considered lean. At baseline, creatinine clearance (CrCl), 24 h urinary albumin excretion (UAE), glycemia, and insulinemia were measured before and after 60 and 120 min of glucose overload (75 g). HOMA Index and the area under the curve (AUC) were calculated. Blood pressure (BP) and 24 h urine sodium excretion was measured annually. Postischemic minimum vascular resistance (forearm plethysmography) was assessed at baseline.

RESULTS

In offSS-HT, UAE (53 ± 3 mg/min) and CrCl (136 ± 8 ml/min) were higher in offSS-HT than in offSR-HT. (UAE: 12 ± 4 mg.min; p,0.01 and CrCl 107 ± 6 ml.min; P  < 0.01). An impaired vasodilatory postischemic response was observed in offSS-HT compared with offSR-HT ( P  < 0.01). In offSS-HT glycemia, insulin, AUC at 69 and 120 min post OTG were greater than in offSR-HT, p  < 0.02. In offSS-HT, blood pressure rose ( P  < 0.01) the 10 years follow-up compared with offSR-HT.

CONCLUSION

Salt sensitivity in the offspring of hypertensive salt-sensitive individuals is associated with insulin resistance and endothelial dysfunction and is prone to hypertension over a short period of time.

A neural perspective on the treatment of hypertension: the neurological network excitation and inhibition (E/I) imbalance in hypertension

Despite the increasing number of anti-hypertensive drugs have been developed and used in the clinical setting, persistent deficiencies persist, including issues such as lifelong dosage, combination therapy. Notwithstanding receiving the treatment under enduring these deficiencies, approximately 4 in 5 patients still fail to achieve reliable blood pressure (BP) control. The application of neuromodulation in the context of hypertension presents a pioneering strategy for addressing this condition, con-currently implying a potential central nervous mechanism underlying hypertension onset. We hypothesize that neurological networks, an essential component of maintaining appropriate neurological function, are involved in hypertension. Drawing on both peer-reviewed research and our laboratory investigations, we endeavor to investigate the underlying neural mechanisms involved in hypertension by identifying a close relationship between its onset of hypertension and an excitation and inhibition (E/I) imbalance. In addition to the involvement of excitatory glutamatergic and GABAergic inhibitory system, the pathogenesis of hypertension is also associated with Voltage-gated sodium channels (VGSCs, Nav)-mediated E/I balance. The overloading of glutamate or enhancement of glutamate receptors may be attributed to the E/I imbalance, ultimately triggering hypertension. GABA loss and GABA receptor dysfunction have also proven to be involved. Furthermore, we have identified that abnormalities in sodium channel expression and function alter neural excitability, thereby disturbing E/I balance and potentially serving as a mechanism underlying hypertension. These insights are expected to furnish potential strategies for the advancement of innovative anti-hypertensive therapies and a meaningful reference for the exploration of central nervous system (CNS) targets of anti-hypertensives.

Epithelial Transport in Disease: An Overview of Pathophysiology and Treatment

Epithelial transport is a multifaceted process crucial for maintaining normal physiological functions in the human body. This comprehensive review delves into the pathophysiological mechanisms underlying epithelial transport and its significance in disease pathogenesis. Beginning with an introduction to epithelial transport, it covers various forms, including ion, water, and nutrient transfer, followed by an exploration of the processes governing ion transport and hormonal regulation. The review then addresses genetic disorders, like cystic fibrosis and Bartter syndrome, that affect epithelial transport. Furthermore, it investigates the involvement of epithelial transport in the pathophysiology of conditions such as diarrhea, hypertension, and edema. Finally, the review analyzes the impact of renal disease on epithelial transport and highlights the potential for future research to uncover novel therapeutic interventions for conditions like cystic fibrosis, hypertension, and renal failure.

Association between salt sensitivity of blood pressure and the risk of hypertension in a Chinese Tibetan population

Epidemiological studies have confirmed salt sensitivity as a crucial risk factor for the development of hypertension. However, few studies have investigated the association between salt sensitivity of blood pressure (SSBP) and hypertension in Chinese Tibetan population. Therefore, we conducted a cross-sectional study based on a Tibetan population to evaluate the association between SSBP and the risk of hypertension. Seven hundred and eighty-four participants with hypertension and 645 participants without hypertension were included from five villages in Tibetan Autonomous Region of Gannan during 2013-2014. The assessment of salt sensitivity (SS) and non-salt sensitivity (NSS) was performed according to mean arterial pressure (MAP) changes by the modified Sullivan's acute oral saline load and diuresis shrinkage test (MSAOSL-DST). Logistic regression models and restricted cubic models were used to examine the association between SSBP and hypertension. There were 554 (70.5%) salt-sensitive participants with hypertension and 412 (63.9%) salt-sensitive participants without hypertension in this study. Compared with individuals with NSS, individuals with SS had a significantly increased risk of hypertension, and the multiple-adjusted odds ratios were 2.582 with 95% confidence interval of 1.357-4.912. Furthermore, a significant linear trend was found between MAP changes and hypertension. Subgroup analyses showed significant and stronger associations between SSBP and the risk of hypertension in the older (age ≥ 55 years old), males and participants who took exercise less than 1 time per week. Our results suggest that SS is associated with an increased risk of hypertension in Tibetan population, indicating a need for clinicians dealing with SSBP to decrease the risk of hypertension.

SNPs in lncRNA KCNQ1OT1 Modulate Its Expression and Confer Susceptibility to Salt Sensitivity of Blood Pressure in a Chinese Han Population

Long noncoding RNA (lncRNA) plays an important role in cardiovascular diseases, but the involvement of lncRNA in salt sensitivity of blood pressure (SSBP) is not well-known. We aimed to explore the association of sixteen single-nucleotide polymorphisms (SNPs) in five lncRNA genes (KCNQOT1, lnc-AGAP1-8:1, lnc-IGSF3-1:1, etc.) with their expression and susceptibility to SSBP. A two-stage association study was conducted among 2057 individuals. Quantified expression of the lncRNA was detected using real-time PCR. Genotyping was accomplished using the MassARRAY System. The expression quantitative tra2it loci test and the generalized linear model were utilized to explore the function of SNPs. One-sample Mendelian randomization was used to study the causal relationship between KCNQOT1 and SSBP. Significant effects were observed in KCNQ1OT1 expressions on the SSBP phenotype (p < 0.05). Rs10832417 and rs3782064 in KCNQ1OT1 may influence the secondary structure, miRNA binding, and expression of KCNQ1OT1. Rs10832417 and rs3782064 in KCNQ1OT1 were identified to be associated with one SSBP phenotype after multiple testing corrections and may be mediated by KCNQ1OT1. One-sample Mendelian randomization analyses showed a causal association between KCNQ1OT1 and SSBP. Our findings suggest that rs10832417 and rs3782064 might be associated with a lower risk of SSBP through influencing the KCNQ1OT1 secondary structure and miRNA binding, resulting in changes in KCNQ1OT1 expression.

Associations of genetic variations in NEDD4L with salt sensitivity, blood pressure changes and hypertension incidence in Chinese adults

Neural precursor cell expressed developmentally downregulated 4-like (NEDD4L), a member of the E3 ubiquitin-protein ligases, encoded by NEDD4L gene, was found to be involved in in salt sensitivity by regulating sodium reabsorption in salt-sensitive rats. The authors aimed to explore the associations of NEDD4L genetic variants with salt sensitivity, blood pressure (BP) changes and hypertension incidence in Chinese adults. Participants from 124 families in Northern China in the Baoji Salt-Sensitive Study Cohort in 2004, who received the chronic salt intake intervention, including a 7-day low-salt diet (3.0 g/day) and a 7-day high-salt diet (18 g/day), were analyzed. Besides, the development of hypertension over 14 years was evaluated. NEDD4L single nucleotide polymorphism (SNP) rs74408486 was shown to be significantly associated with systolic BP (SBP), diastolic BP (DBP) and mean arterial pressure (MAP) responses to low-salt diet, while SNPs rs292449 and rs2288775 were significantly associated with pulse pressure (PP) response to high-salt diet. In addition, SNP rs4149605, rs73450471, and rs482805 were significantly associated with the longitudinal changes in SBP, DBP, MAP, or PP at 14 years of follow-up. SNP rs292449 was significantly associated with hypertension incidence over the 14-year follow-up. Finally, this gene-based analysis found that NEDD4L was significantly associated with longitudinal BP changes and the incidence of hypertension over the 14-year follow-up. This study indicated that gene polymorphism in NEDD4L serve an important function in salt sensitivity, longitudinal BP change and development of hypertension in the Chinese population.

Association of Circulating Biomarkers of lnc-IGSF3-1:1, SCOC-AS1, and SLC8A1-AS1 with Salt Sensitivity of Blood Pressure in Chinese Population

Accumulating evidence suggested that long non-coding RNAs (lncRNAs) could play biological roles in cardiovascular diseases. We investigated whether lncRNAs can serve as biomarkers for salt sensitivity of blood pressure (SSBP). Participants were divided into salt-sensitive (SS) and salt-resistant (SR) ones by oral saline test. LncRNAs were tested by microarray (N = 20) and two-stage qRT-PCR (N = 89 and 228). We identified five differently expressed lncRNAs (lnc-IGSF3-1:1, SCOC-AS1, SLC8A1-AS1, KCNQ1OT1, and lnc-GNG-10-3:1) between SS and SR. In single-lncRNA analyses, lnc-IGSF3-1:1 displayed better diagnostic performance in hypertensive patients (AUC = 0.840), while SCOC-AS1 in normotensive (AUC = 0.810). In multi-lncRNA analyses, lnc-IGSF3-1:1 + SCOC-AS1 + SLC8A1-AS1 combination showed the best diagnostic performance in hypertensive (AUC = 0.853) and normotensive groups (AUC = 0.873). We constructed a lncRNA-mRNA-GO-KEGG-disease network by bioinformatic analysis; lnc-IGSF3-1:1 and SLC8A1-AS1 were identified as hub biomarkers. Our findings suggest that lnc-IGSF3-1:1, SCOC-AS1, and SLC8A1-AS1 may represent as genetic susceptible biomarkers for SSBP, and had different SS diagnostic performance in hypertensive patients and normotensive individuals.

Advances in Genomics Research of Blood Pressure Responses to Dietary Sodium and Potassium Intakes

More than half of US adults have hypertension by 40 years of age and a subsequent increase in atherosclerotic cardiovascular disease risk. Dietary sodium and potassium are intricately linked to the pathophysiology of hypertension. However, blood pressure responses to dietary sodium and potassium, phenomena known as salt and potassium sensitivity of blood pressure, respectively, are heterogenous and normally distributed in the general population. Like blood pressure, salt and potassium sensitivity are complex phenotypes, and previous research has shown that up to 75% of individuals experience a blood pressure change in response to such dietary minerals. Previous research has also implicated both high salt sensitivity and low salt sensitivity (or salt resistance) of blood pressure to an increased risk of hypertension and potentially atherosclerotic cardiovascular disease risk. Given the clinical challenges required to accurately measure the sodium and potassium response phenotypes, genomic characterization of these traits has become of interest for hypertension prevention initiatives on both the individual and population levels. Here, we review advances in human genomics research of blood pressure responses to dietary sodium and potassium by focusing on 3 main areas, including the phenotypic characterization of salt sensitivity and resistance, clinical challenges in diagnosing such phenotypes, and the genomic mechanisms that may help to explain salt and potassium sensitivity and resistance. Through this process, we hope to further underline the value of leveraging genomics and broader multiomics for characterizing the blood pressure response to sodium and potassium to improve precision in lifestyle approaches for primordial and primary atherosclerotic cardiovascular disease prevention.

No evidence of racial disparities in blood pressure salt sensitivity when potassium intake exceeds levels recommended in the US dietary guidelines

On average, black individuals are widely believed to be more sensitive than white individuals to blood pressure (BP) effects of changes in salt intake. However, few studies have directly compared the BP effects of changing salt intake in black versus white individuals. In this narrative review, we analyze those studies and note that when potassium intake substantially exceeds the recently recommended US dietary goal of 87 mmol/day, black adults do not appear more sensitive than white adults to BP effects of short-term or long-term increases in salt intake (from an intake ≤50 mmol/day up to 150 mmol/day or more). However, with lower potassium intakes, racial differences in salt sensitivity are observed. Mechanistic studies suggest that racial differences in salt sensitivity are related to differences in vascular resistance responses to changes in salt intake mediated by vasodilator and vasoconstrictor pathways. With respect to cause and prevention of racial disparities in salt sensitivity, it is noteworthy that 1) on average, black individuals consume less potassium than white individuals and 2) consuming supplemental potassium bicarbonate, or potassium rich foods can prevent racial disparities in salt sensitivity. However, the new US dietary guidelines reduced the dietary potassium goal well below the amount associated with preventing racial disparities in salt sensitivity. These observations should motivate research on the impact of the new dietary potassium guidelines on racial disparities in salt sensitivity, the risks and benefits of potassium-containing salt substitutes or supplements, and methods for increasing consumption of foods rich in nutrients that protect against salt-induced hypertension.

Epithelial Sodium Channel and Salt-Sensitive Hypertension

The development of high blood pressure is influenced by genetic and environmental factors, with high salt intake being a known environmental contributor. Humans display a spectrum of sodium-sensitivity, with some individuals displaying a significant blood pressure rise in response to increased sodium intake while others experience almost no change. These differences are, in part, attributable to genetic variation in pathways involved in sodium handling and excretion. ENaC (epithelial sodium channel) is one of the key transporters responsible for the reabsorption of sodium in the distal nephron. This channel has an important role in the regulation of extracellular fluid volume and consequently blood pressure. Herein, we review the role of ENaC in the development of salt-sensitive hypertension, and present mechanistic insights into the regulation of ENaC activity and how it may accelerate sodium-induced damage and dysfunction. We discuss the traditional role of ENaC in renal sodium reabsorption and review work addressing ENaC expression and function in the brain, vasculature, and immune cells, and how this has expanded the implications for its role in the initiation and progression of salt-sensitive hypertension.

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.

Drinking frequency modifies an association between salt intake and blood pressure: A cohort study

Salt sensitivity is one of the crucial risk factors of hypertension. The aim of the present prospective cohort study was to assess the clinical impact of alcohol drinking on an association between salt intake and blood pressure. The present study included 451 employees at a pharmaceutical company in Japan who underwent annual health checkups in both 2017 and 2018. The main exposure of interest was self-reported drinking frequency at their first checkups: rarely, occasionally, and daily. To assess the association between the change of salt intake estimated from single-spot urine specimens and that of blood pressure, the differences in systolic/diastolic blood pressure and salt intake between 2017 and 2018 were calculated for each subject. Multivariable-adjusted linear regression models adjusting for clinically relevant factors clarified a drinking frequency-dependent association between Δsalt intake and Δsystolic blood pressure (per 1 g/d of Δsalt intake adjusted β [95% confidence interval] 0.19 [-0.73, 1.12], 0.84 [0.14, 1.53], and 1.78 [0.86, 2.69] in rare, occasional, and daily drinkers). A similar association between Δsalt intake and Δdiastolic blood pressure was also observed (-0.24 [-1.02, 0.54], 0.67 (0.18, 1.16), 0.95 [0.38, 1.51], in rare, occasional, and daily drinkers). The interactions between drinking frequency and Δsalt intake were found to be statistically significant (P for interaction = .028 and .006 for ∆systolic blood pressure and ∆diastolic blood pressure, respectively). The present study identified enhanced salt sensitivity in the subjects who drink at a higher frequency, suggesting that the reduction in alcohol consumption may improve salt sensitivity in higher frequency drinkers.

Klotho Gene in Human Salt-Sensitive Hypertension

BACKGROUND AND OBJECTIVES

Hypertension is a common aging-related disorder. Salt intake is one of the main environmental factors contributing to the development of hypertension. Transgenic mice with one-half Klotho deficiency displayed a spontaneous BP increase and salt-sensitive hypertension in response to high sodium intake. Usually circulating levels of α-Klotho decrease with age, and this reduction may be stronger in patients with several aging-related diseases. This study aimed at exploring the association of Klotho with salt sensitivity in humans.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The role of Klotho polymorphisms and α-Klotho serum levels was evaluated in patients with hypertension who were treatment naive and underwent an acute salt-sensitivity test (discovery n=673, intravenous 2 L of 0.9% saline in 2 hours). Salt sensitivity was defined as a mean BP increase of >4 mm Hg at the end of the infusion. A total of 32 single nucleotide polymorphisms in the Klotho gene (KL), previously identified with a genome-wide association study, were used in the genetic analysis and studied for a pressure-natriuresis relationship.

RESULTS

Of the patients with hypertension, 35% were classified as salt sensitive. The most relevant polymorphism associated with pressure natriuresis was the common missense single nucleotide polymorphism rs9536314, and the GG and GT genotypes were more represented among patients who were salt sensitive (P=0.001). Those carrying the G allele showed a less steep pressure-natriuresis relationship, meaning that a significant increase in mean BP was needed to excrete the same quantity of salt compared with patients who were salt resistant. KL rs9536314 also replicated the pressure-natriuresis association in an independent replication cohort (n=193) and in the combined analysis (n=866). There was an inverse relationship between circulating Klotho and mean BP changes after the saline infusion (r=-0.14, P=0.03). Moreover, circulating α-Klotho was directly related to kidney function at baseline eGFR (r=0.22, P<0.001).

CONCLUSIONS

KL rs9536314 is associated with salt-sensitive hypertension in patients with hypertension who are treatment naive. Moreover, circulating α-Klotho levels were mainly related to diastolic BP changes at the end of a salt load and to eGFR as an expression of kidney aging.

Epigenetic Modifications in T Cells: The Role of DNA Methylation in Salt-Sensitive Hypertension

The SS (Dahl salt sensitive) rat is an established model of hypertension and renal damage that is accompanied with immune system activation in response to a high-salt diet. Investigations into the effects of sodium-independent and dependent components of the diet were shown to affect the disease phenotype with SS/MCW (JrHsdMcwi) rats maintained on a purified diet (AIN-76A) presenting with a more severe phenotype relative to grain-fed SS/CRL (JrHsdMcwiCrl) rats. Since contributions of the immune system, environment, and diet are documented to alter this phenotype, this present study examined the epigenetic profile of T cells isolated from the periphery and the kidney from these colonies. T cells isolated from kidneys of the 2 colonies revealed that transcriptomic and functional differences may contribute to the susceptibility of hypertension and renal damage. In response to high-salt challenge, the methylome of T cells isolated from the kidney of SS/MCW exhibit a significant increase in differentially methylated regions with a preference for hypermethylation compared with the SS/CRL kidney T cells. Circulating T cells exhibited similar methylation profiles between colonies. Utilizing transcriptomic data from T cells isolated from the same animals upon which the DNA methylation analysis was performed, a predominant negative correlation was observed between gene expression and DNA methylation in all groups. Lastly, inhibition of DNA methyltransferases blunted salt-induced hypertension and renal damage in the SS/MCW rats providing a functional role for methylation. This study demonstrated the influence of epigenetic modifications to immune cell function, highlighting the need for further investigations.

Transcriptome Sequencing to Detect the Potential Role of Long Noncoding RNAs in Salt-Sensitive Hypertensive Rats

Backgrounds

Long noncoding RNAs (lncRNAs) play an important role in various biological processes. However, their functions in salt-sensitive hypertension are largely unknown. In this study, the lncRNA-seq technique was employed to compare the expression profiles of lncRNAs and mRNAs in salt-sensitive hypertensive rats.

Methods

Blood pressure, serum sodium, and urinary creatinine were texted in salt-sensitive and salt-insensitive rats fed with different salt concentrations. High-throughput sequencing was used to detect the expression of lncRNAs and mRNA in the renal medulla of the two groups.

Results

Blood pressure and urinary sodium/creatinine of high-salt diets of the sensitive group were significantly higher than that in the control group. Serum sodium has no significant difference between the two groups in high-salt diets. NONRATG007131.2 and NONRATG012674.2 were the most different lncRNAs in the high salt-sensitive group. Correlation analysis reveals that Matn1, Serpinb12, Anxa8, and Hspa5 may play an important role in salt-sensitive hypertension.

Conclusion

This study analyzed the difference in lncRNA and mRNA between salt-sensitive and salt-insensitive rats with different salt diets by high-throughput sequencing. Salt sensitivity and salt concentration were two key factors for the induction of hypertension. We found some potential genes that play an important role in salt-sensitive hypertension.

CeRNA network analysis and functional enrichment of salt sensitivity of blood pressure by weighted-gene co-expression analysis

Background

Salt sensitivity of blood pressure (SSBP) is an independent risk factor for cardiovascular disease. The pathogenic mechanisms of SSBP are still uncertain. This study aimed to construct the co-regulatory network of SSBP and data mining strategy based on the competitive endogenous RNA (ceRNA) theory.

Methods

LncRNA and mRNA microarray was performed to screen for candidate RNAs. Four criteria were used to select the potential differently expressed RNAs. The weighted correlation network analysis (WGCNA) package of R software and target miRNA and mRNA prediction online databases were used to construct the ceRNA co-regulatory network and discover the pathways related to SSBP. Gene ontology enrichment, gene set enrichment analysis (GSEA) and KEGG pathway analysis were performed to explore the functions of hub genes in networks.

Results

There were 274 lncRNAs and 36 mRNAs that differently expressed between salt-sensitive and salt-resistant groups (P < 0.05). Using WGCNA analysis, two modules were identified (blue and turquoise). The blue module had a positive relationship with salt-sensitivity (R = 0.7, P < 0.01), high-density lipoprotein (HDL) (R = 0.53, P = 0.02), and total cholesterol (TC) (R = 0.55, P = 0.01). The turquoise module was positively related with triglyceride (TG) (R = 0.8, P < 0.01) and low-density lipoprotein (LDL) (R = 0.54, P = 0.01). Furthermore, 84 ceRNA loops were identified and one loop may be of great importance for involving in pathogenesis of SSBP. KEGG analysis showed that differently expressed mRNAs were mostly enriched in the SSBP-related pathways. However, the enrichment results of GSEA were mainly focused on basic physical metabolic processes.

Conclusion

The microarray data mining process based on WGCNA co-expression analysis had identified 84 ceRNA loops that closely related with known SSBP pathogenesis. The results of our study provide implications for further understanding of the pathogenesis of SSBP and facilitate the precise diagnosis and therapeutics.

Effects of environmental and genetic risk factors for salt sensitivity on blood pressure in northern China: the systemic epidemiology of salt sensitivity (EpiSS) cohort study

PURPOSE

The systemic epidemiology of salt sensitivity (EpiSS) study aims to combine molecular biology, epidemiology and bioinformatics methods to discover the potential causes of salt sensitivity of blood pressure (SSBP) using single-nucleotide polymorphisms in the genome and non-coding RNAs in the transcriptome to uncover both the genetic and environmental factors of SSBP.

PARTICIPANTS

Between July 2014 and July 2016, we enrolled adults from 11 study centres in Beijing and Liaoning Province; participants were of the Han population and were 35-70 years of age. We collected blood samples, spot urine samples and 24-hour urine samples, in addition to baseline data on demographics, health-related lifestyle factors, chronic diseases, family history of illness and anthropometric information through face-to-face interviews using a standardised questionnaire. EpiSS uses the modified Sullivan's acute oral saline load and diuresis shrinkage test (MSAOSL-DST) to evaluate the effects of salt on blood pressure.

FINDINGS TO DATE

In total, 2163 participants were included in the EpiSS, of which 2144 participants completed the questionnaire, 2120 (98.0%) completed the MSAOSL-DST and 2083 (96.3%) provided a 24-hour urine sample. A total of 2057 participants (1501 women and 556 men) completed all the steps of the investigation and were included in the analysis. Among them, 583 (28.3%) subjects were classified as having salt sensitivity of blood pressure, and 1061 (51.6%) had hypertension.

FUTURE PLANS

The next step of our study is to evaluate the incidence of cardiovascular disease in the participants. Biennial follow-up, including face-to-face questionnaire surveys, laboratory measurements of blood, urinary creatinine, glomerular filtration rate and anthropometric measurements, will occur two additional times. DNA and RNA will be collected for subsequent genetic biomarker studies. We plan on screening the salt-sensitive-related gene loci and non-coding RNAs based on relative environmental risk factors.

TRIAL REGISTRATION NUMBER

ChiCTR-EOC-16009980; Pre-results.

Interactions of Genes and Sodium Intake on the Development of Hypertension: A Cohort-Based Case-Control Study

There have been few studies investigating interactions of G-protein beta3 subunit (GNB3) C825T (rs5443) and dietary sodium intake on the risk of hypertension, i.e., BP salt sensitivity. The study aims to evaluate joint effects of GNB3 polymorphisms and sodium consumption on the development of hypertension. A cohort-based case-control study was conducted in 2014. There are 233 participants with newly diagnosed hypertension in the case group and 699 participants in the gender-matched control group. The primary outcome is the development of hypertension over a 10-year period. The determinants of hypertension were three genotypes of SNP in GNB3 (TT; CT; and CC) and two dietary salt categories on the basis of the level of sodium consumption representing high (>4800 mg/day) and low-sodium (<2400 mg/day) diets. The development of hypertension increased with participants carrying TT genotype and high-sodium diets comparing with those carrying TC or CC genotype with low-sodium diets (adjusted OR 3.23, 95% CI 1.52–6.83) (Rothman synergy index = 3.79). The study suggests that GNB3 C825T polymorphism may influence the response of the renin-angiotensin system to high-sodium diet. It implies that GNB3 can be served as an easy, inexpensive, and early genetic marker of salt sensitivity to blood pressure. Salt-sensitive individuals should pay more attention to salt intake to reduce cardiovascular morbidity or mortality.

The mutation of Trp64Arg in β3-adrenoreceptor-encoding gene is significantly associated with increased hypertension risk and elevated blood pressure: a meta-analysis

This meta-analysis was implemented to test the association of a missense mutation, Trp64Arg, in β3-adrenoreceptor-encoding gene (ADRB3) with both hypertension risk and blood pressure (BP) changes. A systematic search of three publicly-available databases was launched to look for articles published as of December 2016. Qualification appraisal and data extraction were independently done by two researchers. Pooled estimates were expressed as odds ratio (OR) or weighted mean difference (WMD), and their 95% confidence intervals (95% CIs). There were separately 21 (3750/4225 patients/controls) and 17 (6100 subjects) individual studies for hypertension risk and BP changes. Integral analyses revealed that Trp64Arg mutation was associated with the significantly increased risk of hypertension, and particularly, the 64Trp/64Arg heterozygote carriers were 1.23-times more likely to develop hypertension compared with the 64Trp/64Trp homozygote carriers (OR = 1.23, 95% CI: 1.02∼1.46, P = 0.021). Publication bias was extremely low for all integral comparisons. In stratified analyses, significance was spotted in populations of Chinese descent, in retrospective studies, in hospital-based studies, in age-matched case-control studies, in studies enrolling patients with mean body mass index < 25 kg/m² and in studies with total sample size ≥ 240. Heterogeneity was improved for most stratified comparisons. Further in hypertensive patients, the 64Trp/64Arg heterozygote carriers had significantly higher systolic (WMD = 0.87 mmHg, 95% CI: 0.39∼1.35, P < 0.001) and diastolic (WMD = 0.88 mmHg, 95% CI: 0.59∼1.17, P < 0.001) BP than 64Trp/64Trp homozygote carriers. Altogether, ADRB3 gene Trp64Arg mutation was significantly associated with an increased predisposition toward hypertension and elevated systolic/diastolic BP in hypertensive patients, suggesting that Trp64Arg is an important hypertension-susceptibility marker.

Resequencing Epithelial Sodium Channel Genes Identifies Rare Variants Associated With Blood Pressure Salt-Sensitivity: The GenSalt Study

BACKGROUND

A resequencing study of renal epithelial sodium channel (ENaC) genes was conducted to identify rare variants associated with blood pressure (BP) salt-sensitivity.

METHODS

The Genetic Epidemiology Network of Salt-Sensitivity (GenSalt) study was conducted among 1,906 participants who underwent a 7-day low-sodium followed by a 7-day high-sodium feeding-study. The 300 most salt-sensitive and 300 most salt-resistant GenSalt participants were selected for the resequencing study. Three ENaC genes (SCNN1A, SCNN1B, and SCNN1G) were resequenced using capillary-based sequencing methods. Traditional burden tests were utilized to examine association between rare variants and BP salt-sensitivity. Associations of low-frequency and common variants were tested using single-marker analyses.

RESULTS

Carriers of SCNN1A rare variants had a 0.52 [95% confidence interval (CI): 0.32-0.85] decreased odds of BP salt-sensitivity compared with noncarriers. Neither SCNN1B nor SCNN1G associated with salt-sensitivity of BP in rare variant analyses (P = 0.65 and 0.48, respectively). In single-marker analyses, 3 independent common variants in SCNN1A, rs11614164, rs4764586, and rs3741914, associated with salt-sensitivity after Bonferroni correction (P = 4.4 × 10-4, 1.1 × 10-8, and 1.3 × 10-3). Each copy of the minor allele of rs4764586 was associated with a 1.36-fold (95% CI: 1.23-1.52) increased odds of salt-sensitivity, whereas each copy of the minor allele of rs11614164 and rs3741914 was associated with 0.68-fold (95% CI: 0.55-0.84) and 0.69-fold (95% CI: 0.54-0.86) decreased odds of salt-sensitivity, respectively.

CONCLUSIONS

This study demonstrated for the first time a relationship between rare variants in the ENaC pathway and BP salt-sensitivity. Future replication and functional studies are needed to confirm the findings in this study.

CLINICAL TRIAL REGISTRY

Trial Number NCT00721721.

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.

Blood Pressure Genetic Risk Score Predicts Blood Pressure Responses to Dietary Sodium and Potassium: The GenSalt Study (Genetic Epidemiology Network of Salt Sensitivity)

We examined the association between genetic risk score (GRS) for blood pressure (BP), based on single nucleotide polymorphisms identified in previous BP genome-wide association study meta-analyses, and salt and potassium sensitivity of BP among participants of the GenSalt study (Genetic Epidemiology Network of Salt Sensitivity). The GenSalt study was conducted among 1906 participants who underwent a 7-day low-sodium (51.3 mmol sodium/d), 7-day high-sodium (307.8 mmol sodium/d), and 7-day high-sodium plus potassium (60 mmol potassium/d) intervention. BP was measured 9× at baseline and at the end of each intervention period using a random zero sphygmomanometer. Associations between systolic BP (SBP), diastolic BP, and mean arterial pressure GRS and respective SBP, diastolic BP, and mean arterial pressure responses to the dietary interventions were assessed using mixed linear regression models that accounted for familial dependencies and adjusted for age, sex, field center, body mass index, and baseline BP. As expected, baseline SBP, diastolic BP, and mean arterial pressure significantly increased per quartile increase in GRS (P=2.7×10^-8, 9.8×10^-8, and 6.4×10^-6, respectively). In contrast, increasing GRS quartile conferred smaller SBP, diastolic BP, and mean arterial pressure responses to the low-sodium intervention (P=1.4×10^-3, 0.02, and 0.06, respectively) and smaller SBP responses to the high-sodium and potassium interventions (P=0.10 and 0.05). In addition, overall findings were similar when examining GRS as a continuous measure. Contrary to our initial hypothesis, we identified an inverse relationship between BP GRS and salt and potassium sensitivity of BP. These data may provide novel implications on the relationship between BP responses to dietary sodium and potassium and hypertension.

A Systematic Review of Fatalities Related to Acute Ingestion of Salt. A Need for Warning Labels?

There are sporadic cases of fatalities from acutely eating salt. Yet, on social media, there are "challenges to" and examples of children and some adults acutely eating salt, and recently a charity advocated eating small amounts of salt to empathize with Syrian refugees. We performed a systematic review of fatalities from ingesting salt to assess if relatively moderate doses of salt could be fatal. In 27 reports, there were 35 fatalities documented (19 in adults and 16 in children). The lethal dose was estimated to be less than 10 g of sodium (<5 teaspoons of salt) in two children, and less than 25 g sodium in four adults (<4 tablespoons of salt). The frequency of fatal ingestion of salt is not able to be discerned from our review. If investigation of the causes of hypernatremia in hospital records indicates salt overdose is relatively common, consideration could be given to placing warning labels on salt containers and shakers. Such warning labels can have the added advantage of reducing dietary salt consumption.

Resequencing Study Identifies Rare Renin-Angiotensin-Aldosterone System Variants Associated With Blood Pressure Salt-Sensitivity: The GenSalt Study

BACKGROUND

The role of rare variants in blood pressure (BP) salt-sensitivity is unknown. We conducted a resequencing study of the renin-angiotensin-aldosterone system (RAAS) to identify rare variants associated with BP salt-sensitivity among participants of the Genetic Epidemiology Network of Salt-Sensitivity (GenSalt) study.

METHODS

The GenSalt study was conducted among 1,906 participants who underwent a 7-day low-sodium (51.3 mmol sodium/day) followed by a 7-day high-sodium feeding study (307.8 mmol sodium/day). The 300 most salt-sensitive and 300 most salt-resistant GenSalt participants were selected for the resequencing study. Seven RAAS genes were resequenced using capillary-based sequencing methods. Rare variants were tested for association with BP salt-sensitivity using traditional burden tests. Single-marker analyses were employed to test associations of low-frequency and common variants.

RESULTS

Aggregate rare variant analysis revealed an association of the RAAS pathway with BP salt-sensitivity. Carriers of rare RAAS variants had a 1.55-fold [95% confidence interval (CI): 1.15, 2.10] higher odds of salt-sensitivity compared to noncarriers (P = 0.004), a finding which was significant after Bonferroni correction. A nominal association of the APLN gene with salt-sensitivity was also identified, with rare APLN variants conferring a 2.22-fold (95% CI: 1.05, 6.58) higher odds of salt-sensitivity (P = 0.03). Single-marker analyses did not identify variant-BP salt-sensitivity associations after Bonferroni adjustment. A nominal association of a low-frequency, missense RENBP variant was identified. Each minor allele of rs78377269 conferred a 2.21-fold (95% CI: 1.10, 4.42) increased odds of salt-sensitivity (P = 0.03).

CONCLUSIONS

This study presents of the first evidence of a contribution of rare RAAS variants to BP salt-sensitivity. Clinical Trial RegistryTrial Number: NCT00721721.

Genetic susceptibility to salt-sensitive hypertension in a Han Chinese population: a validation study of candidate genes

Salt-sensitive hypertension is a complex disease associated with genetic factors. This study aimed to identify the association between 29 candidate single-nucleotide polymorphisms and salt-sensitive hypertension in a Han Chinese population. Sixty-three participants with salt-sensitive hypertension and 279 controls with salt-resistant hypertension were recruited. A modified Sullivan's acute oral saline load and diuresis shrinkage test was used to detect blood pressure salt sensitivity. Lifestyle risk factors were obtained via a questionnaire. We used the Sequenom Mass ARRAY Platform to genotype the 29 candidate single-nucleotide polymorphisms, and the cumulative genetic risk score was used to evaluate the joint genetic effect. The frequencies of eight genotypes and five alleles in CYP11B2, PRKG1, ADRB2, FGF5, SLC8A1 and BCAT1 genes differed significantly between the salt-sensitive and salt-resistant hypertension groups. Multiple logistic regression adjusted for age and sex showed that subjects carrying rs7897633-A (PRKG1), rs434082-A (SLC8A1) and rs1042714-G (ADRB2) risk alleles had 1.83-, 2.84- and 2.40-fold increased risk for salt-sensitive hypertension, respectively. Combined risk allele analysis using the cumulative genetic risk score showed that subjects carrying one risk had 2.30-fold increased risk, and those carrying 2-4 risks had 3.32-fold increased risk for salt-sensitive hypertension. Among 29 candidate single-nucleotide polymorphisms, rs7897633-A in PRKG1, rs434082-A in SLC8A1 and rs1042714-G in ADRB2 were significantly associated with salt-sensitive hypertension. A joint effect of single-nucleotide polymorphisms from different pathways contributed to a high risk of salt-sensitive hypertension.

micro-RNA screening and prediction model construction for diagnosis of salt-sensitive essential hypertension

Commonly used tests for diagnosis of salt-sensitive hypertension (SSH) are complex and time-consuming, so new methods are required. Many studies have demonstrated roles for miRNAs in hypertension; however, the diagnostic value of miRNAs has yet to be determined for human SSH. In this study, we examined miRNA expression profiles by initial high-throughput miRNA sequencing of samples from patients with salt-sensitive and salt-resistant hypertension (SSH and SRH, respectively; n = 6, both groups), followed by validation by quantitative real-time polymerase chain reaction (qRT-PCR) in a larger cohort (n = 91). We also evaluated differences in baseline characteristics (e.g., age, sex, body mass index, consumption of specific foods) between the SSH and SRH groups. Of 36 miRNAs identified as differentially expressed between SSH and SRH groups by RNA-Seq, 8 were analyzed by qRT-PCR. There were significant differences in the expression levels of hsa-miR-361-5p and hsa-miR-362-5p between the 2 groups (P = .023 and.049, respectively). In addition, there were significant differences in sauce and poultry consumption between the 2 groups (P = .004 and.001, respectively). The areas under the curve (AUC) determined by receptor operating characteristic (ROC) analysis for hsa-miR-361-5p and all 8 miRNAs were 0.793 (95% CI, 0.698-0.888; sensitivity = 73.9%, specificity = 74.4%; P < .001) and 0.836 (95% CI, 0.749-0.922; sensitivity = 80.4%, specificity = 81.4%; P < .001), respectively, when sauce and poultry consumption were included in the models. Assay feasibility and economic considerations make hsa-miR-361-5p combined with the dietary factors the preferred markers for diagnosis of SSH.

Human epithelial Na+ channel missense variants identified in the GenSalt study alter channel activity

Mutations in genes encoding subunits of the epithelial Na⁺ channel (ENaC) can cause early onset familial hypertension, demonstrating the importance of this channel in modulating blood pressure. It remains unclear whether other genetic variants resulting in subtler alterations of channel function result in hypertension or altered sensitivity of blood pressure to dietary salt. This study sought to identify functional human ENaC variants to examine how these variants alter channel activity and to explore whether these variants are associated with altered sensitivity of blood pressure to dietary salt. Six-hundred participants of the Genetic Epidemiology Network of Salt Sensitivity (GenSalt) study with salt-sensitive or salt-resistant blood pressure underwent sequencing of the genes encoding ENaC subunits. Functional effects of identified variants were examined in a Xenopus oocyte expression system. Variants that increased channel activity included three in the gene encoding the α-subunit (αS115N, αR476W, and αV481M), one in the β-subunit (βS635N), and one in the γ-subunit (γL438Q). One α-subunit variant (αA334T) and one γ-subunit variant (βD31N) decreased channel activity. Several α-subunit extracellular domain variants altered channel inhibition by extracellular Na⁺ (Na⁺ self-inhibition). One variant (αA334T) decreased and one (αV481M) increased cell surface expression. Association between these variants and salt sensitivity did not reach statistical significance. This study identifies novel functional human ENaC variants and demonstrates that some variants alter channel cell surface expression and/or Na⁺ self-inhibition.

Association of interactions between dietary salt consumption and hypertension-susceptibility genetic polymorphisms with blood pressure among Japanese male workers

BACKGROUND

Blood pressure is influenced by hereditary factors and dietary habits. The objective of this study was to examine the effect of dietary salt consumption and single-nucleotide polymorphisms (SNPs) on blood pressure (BP).

METHODS

This was a cross-sectional analysis of 2728 male participants who participated in a health examination in 2009. Average dietary salt consumption was estimated using electronically collected meal purchase data from cafeteria. A multivariate analysis, adjusting for clinically relevant factors, was conducted to examine whether the effect on BP of salt consumption, SNPs, and interaction between salt consumption and each SNP. This study examined the SNPs AGT rs699 (Met235Thr), ADD1 rs4961 (Gly460Trp), NPPA rs5063 (Val32Met), GPX1 rs1050450 (Pro198Leu), and AGTR1 rs5186 (A1166C) in relation to hypertension and salt sensitivity.

RESULTS

BP was not significantly associated with SNPs or salt consumption. The interaction between salt consumption and SNPs with systolic BP showed a significant association in NPPA rs5063 (Val32Met) (P = 0.023) and a marginal trend toward significance in rs4961 and rs1050450 (P = 0.060 and 0.067, respectively).

CONCLUSION

The effect of salt consumption on BP differed by genotype. Dietary salt consumption and genetic variation can predict a high risk of hypertension.

Genome-Wide Gene-Sodium Interaction Analyses on Blood Pressure: The Genetic Epidemiology Network of Salt-Sensitivity Study

We performed genome-wide analyses to identify genomic loci that interact with sodium to influence blood pressure (BP) using single-marker-based (1 and 2 df joint tests) and gene-based tests among 1876 Chinese participants of the Genetic Epidemiology Network of Salt-Sensitivity (GenSalt) study. Among GenSalt participants, the average of 3 urine samples was used to estimate sodium excretion. Nine BP measurements were taken using a random zero sphygmomanometer. A total of 2.05 million single-nucleotide polymorphisms were imputed using Affymetrix 6.0 genotype data and the Chinese Han of Beijing and Japanese of Tokyo HapMap reference panel. Promising findings (P<1.00×10(-4)) from GenSalt were evaluated for replication among 775 Chinese participants of the Multi-Ethnic Study of Atherosclerosis (MESA). Single-nucleotide polymorphism and gene-based results were meta-analyzed across the GenSalt and MESA studies to determine genome-wide significance. The 1 df tests identified interactions for UST rs13211840 on diastolic BP (P=3.13×10(-9)). The 2 df tests additionally identified associations for CLGN rs2567241 (P=3.90×10(-12)) and LOC105369882 rs11104632 (P=4.51×10(-8)) with systolic BP. The CLGN variant rs2567241 was also associated with diastolic BP (P=3.11×10(-22)) and mean arterial pressure (P=2.86×10(-15)). Genome-wide gene-based analysis identified MKNK1 (P=6.70×10(-7)), C2orf80 (P<1.00×10(-12)), EPHA6 (P=2.88×10(-7)), SCOC-AS1 (P=4.35×10(-14)), SCOC (P=6.46×10(-11)), CLGN (P=3.68×10(-13)), MGAT4D (P=4.73×10(-11)), ARHGAP42 (P≤1.00×10(-12)), CASP4 (P=1.31×10(-8)), and LINC01478 (P=6.75×10(-10)) that were associated with at least 1 BP phenotype. In summary, we identified 8 novel and 1 previously reported BP loci through the examination of single-nucleotide polymorphism and gene-based interactions with sodium.

Gut microbiota in hypertension

PURPOSE OF REVIEW

Hypertension, which is present in about one quarter of the world's population, is responsible for about 41% of the number one cause of death - cardiovascular disease. Not included in these statistics is the effect of sodium intake on blood pressure, even though an increase or a marked decrease in sodium intake can increase blood pressure. This review deals with the interaction of gut microbiota and the kidney with genetics and epigenetics in the regulation of blood pressure and salt sensitivity.

RECENT FINDINGS

The abundance of the gut microbes, Firmicutes and Bacteroidetes, is associated with increased blood pressure in several models of hypertension, including the spontaneously hypertensive and Dahl salt-sensitive rats. Decreasing gut microbiota by antibiotics can increase or decrease blood pressure that is influenced by genotype. The biological function of probiotics may also be a consequence of epigenetic modification, related, in part, to microRNA. Products of the fermentation of nutrients by gut microbiota can influence blood pressure by regulating expenditure of energy, intestinal metabolism of catecholamines, and gastrointestinal and renal ion transport, and thus, salt sensitivity.

SUMMARY

The beneficial or deleterious effect of gut microbiota on blood pressure is a consequence of several variables, including genetics, epigenetics, lifestyle, and intake of antibiotics. These variables may influence the ultimate level of blood pressure and control of hypertension.

Polymorphisms of three genes (ACE, AGT and CYP11B2) in the renin-angiotensin-aldosterone system are not associated with blood pressure salt sensitivity: A systematic meta-analysis

Many studies have suggested that polymorphisms of three key genes (ACE, AGT and CYP11B2) in the renin-angiotensin-aldosterone system (RAAS) play important roles in the development of blood pressure (BP) salt sensitivity, but they have revealed inconsistent results. Thus, we performed a meta-analysis to clarify the association. PubMed and Embase databases were searched for eligible published articles. Fixed- or random-effect models were used to pool odds ratios and 95% confidence intervals based on whether there was significant heterogeneity between studies. In total, seven studies [237 salt-sensitive (SS) cases and 251 salt-resistant (SR) controls] for ACE gene I/D polymorphism, three studies (130 SS cases and 221 SR controls) for AGT gene M235T polymorphism and three studies (113 SS cases and 218 SR controls) for CYP11B2 gene C344T polymorphism were included in this meta-analysis. The results showed that there was no significant association between polymorphisms of these three polymorphisms in the RAAS and BP salt sensitivity under three genetic models (all p > 0.05). The meta-analysis suggested that three polymorphisms (ACE gene I/D, AGT gene M235T, CYP11B2 gene C344T) in the RAAS have no significant effect on BP salt sensitivity.

Associations of Renin-Angiotensin-Aldosterone System Genes With Blood Pressure Changes and Hypertension Incidence

BACKGROUND

The renin-angiotensin-aldosterone system (RAAS) plays an important role in blood pressure (BP) regulation. The current study uses single-marker and gene-based analyses to examine the association between RAAS genes and longitudinal BP phenotypes in a Han Chinese population.

METHODS

A total of 1,768 participants from the Genetic Epidemiology Network of Salt Sensitivity (GenSalt) follow-up study were included in the current study. Twenty-seven BP measurements were taken using random-zero sphygmomanometers at baseline and 2 follow-up visits. Mixed-effect models were used to assess the additive associations of 106 single-nucleotide polymorphisms (SNPs) in 10 RAAS genes with longitudinal BP changes and hypertension incidence. Gene-based analyses were conducted using the truncated product method. Attempts were made to replicate significant findings among Asian participants of the Multi-ethnic Study of Atherosclerosis (MESA). False discovery rate procedures were used to adjust for multiple testing.

RESULTS

During an average of 7.2 years of follow-up, average systolic and diastolic BP increased, and 32.1% (512) of participants free from hypertension at baseline developed hypertension. NR3C2 SNPs rs7694064 and rs6856803 were significantly associated with longitudinal changes in systolic BP (P interaction = 6.9×10(-5) and 8.2×10(-4), respectively). Through gene-based analysis, NR3C2 was found to be significantly associated with longitudinal systolic BP change (P value of 1.00×10(-7)), even after removal of significant markers rs7694064 and rs6856803 from the analysis. The association between NR3C2 and longitudinal systolic BP change was replicated in Asian MESA participants (P value of 1.00×10(-4)).

CONCLUSIONS

These findings indicate that NR3C2 may play an important role in BP progression and development of hypertension.

Individual response to exercise training - a statistical perspective

In the era of personalized medicine, interindividual differences in the magnitude of response to an exercise training program (subject-by-training interaction; “individual response”) have received increasing scientific interest. However, standard approaches for quantification and prediction remain to be established, probably due to the specific considerations associated with interactive effects, in particular on the individual level, compared with the prevailing investigation of main effects. Regarding the quantification of subject-by-training interaction in terms of variance components, confounding sources of variability have to be considered. Clearly, measurement error limits the accuracy of response estimates and thereby contributes to variation. This problem is of particular importance for analyses on the individual level, because a low signal-to-noise ratio may not be compensated by increasing sample size (1 case). Moreover, within-subject variation in training efficacy may contribute to gross response variability. This largely unstudied source of variation may not be disclosed by comparison to a control group but calls for repeated interventions. A second critical point concerns the prediction of response. There is little doubt that exercise training response is influenced by a multitude of determinants. Moreover, indications of interaction between influencing factors of training efficacy lead to the hypothesis that optimal predictive accuracy may be attained using an interactive rather than additive approach. Taken together, aiming at conclusive inference and optimal predictive accuracy in the investigation of subject-by-training interaction entails specific requirements that are deducibly based on statistical principles but beset with many practical difficulties. Therefore, pragmatic alternatives are warranted.

Role of the vascular wall in sodium homeostasis and salt sensitivity

Excessive sodium intake is associated with both hypertension and an increased risk of cardiovascular events, presumably because of an increase in extracellular volume. The extent to which sodium intake affects extracellular volume and BP varies considerably among individuals, discriminating subjects who are salt-sensitive from those who are salt-resistant. Recent experiments have shown that, other than regulation by the kidney, sodium homeostasis is also regulated by negatively charged glycosaminoglycans in the skin interstitium, where sodium is bound to glycosaminoglycans without commensurate effects on extracellular volume. The endothelial surface layer is a dynamic layer on the luminal side of the endothelium that is in continuous exchange with flowing blood. Because negatively charged glycosaminoglycans are abundantly present in this layer, it may act as an intravascular buffer compartment that allows sodium to be transiently stored. This review focuses on the putative role of the endothelial surface layer as a contributor to salt sensitivity, the consequences of a perturbed endothelial surface layer on sodium homeostasis, and the endothelial surface layer as a possible target for the treatment of hypertension and an expanded extracellular volume.

A gene-based analysis of variants in the serum/glucocorticoid regulated kinase (SGK) genes with blood pressure responses to sodium intake: the GenSalt Study

BACKGROUND

Serum and glucocorticoid regulated kinase (SGK) plays a critical role in the regulation of renal sodium transport. We examined the association between SGK genes and salt sensitivity of blood pressure (BP) using single-marker and gene-based association analysis.

METHODS

A 7-day low-sodium (51.3 mmol sodium/day) followed by a 7-day high-sodium intervention (307.8 mmol sodium/day) was conducted among 1,906 Chinese participants. BP measurements were obtained at baseline and each intervention using a random-zero sphygmomanometer. Additive associations between each SNP and salt-sensitivity phenotypes were assessed using a mixed linear regression model to account for family dependencies. Gene-based analyses were conducted using the truncated p-value method. The Bonferroni-method was used to adjust for multiple testing in all analyses.

RESULTS

In single-marker association analyses, SGK1 marker rs2758151 was significantly associated with diastolic BP (DBP) response to high-sodium intervention (P = 0.0010). DBP responses (95% confidence interval) to high-sodium intervention for genotypes C/C, C/T, and T/T were 2.04 (1.57 to 2.52), 1.79 (1.42 to 2.16), and 0.85 (0.30 to 1.41) mmHg, respectively. Similar trends were observed for SBP and MAP responses although not significant (P = 0.15 and 0.0026, respectively). In addition, gene-based analyses demonstrated significant associations between SGK1 and SBP, DBP and MAP responses to high sodium intervention (P = 0.0002, 0.0076, and 0.00001, respectively). Neither SGK2 nor SGK3 were associated with the salt-sensitivity phenotypes in single-maker or gene-based analyses.

CONCLUSIONS

The current study identified association of the SGK1 gene and BP salt-sensitivity in the Han Chinese population. Further studies are warranted to identify causal SGK1 gene variants.

Blood pressure responses to dietary sodium and potassium interventions and the cold pressor test: the GenSalt replication study in rural North China

BACKGROUND

In the Genetic Epidemiology Network of Salt Sensitivity (GenSalt) study, we observed that blood pressure (BP) responses to dietary sodium and potassium interventions and the cold pressor test (CPT) varied greatly among individuals. We conducted a replication study to confirm our previous findings among 695 study participants.

METHODS

The dietary intervention included a 7-day low sodium (51.3 mmol/day), a 7-day high sodium (307.8 mmol/day), and a 7-day high sodium with potassium supplementation (307.8 mmol sodium and 60 mmol potassium/day). BP measurements were obtained during the baseline and each intervention phase. During the CPT, BP was measured before and at 0, 1, 2, and 4 minutes after the participants immersed their right hand in ice water for 1 minute.

RESULTS

Systolic and diastolic BP responses (mean ± SD (range), mm Hg) were 8.1±8.4 (-39.1 to 18.2) and -3.5±5.1 (-25.1 to 11.1) to low sodium, 9.1±8.4 (-13.3 to 33.1) and 4.0±5.4 (-16.0 to 20.7) to high sodium, and -4.6±5.8 (-31.8 to 11.6) and -1.9±4.3 (-16.9 to 14.2) to potassium supplementation, respectively (all P < 0.0001 for comparison with each former phase). The mean maximum systolic and diastolic BP responses to the CPT were 16.5±10.5 (-15.3 to 63.3) and 7.6±6.1 (-8.7 to 39.3), respectively (all P < 0.0001).

CONCLUSIONS

Our study indicates that there are large variations in BP responses to dietary sodium and potassium interventions and to the CPT among individuals.

Genome-wide association study identifies 8 novel loci associated with blood pressure responses to interventions in Han Chinese

BACKGROUND

Blood pressure (BP) responses to dietary sodium and potassium intervention and cold pressor test vary considerably among individuals. We aimed to identify novel genetic variants influencing individuals' BP responses to dietary intervention and cold pressor test.

METHODS AND RESULTS

We conducted a genome-wide association study of BP responses in 1881 Han Chinese and de novo genotyped top findings in 698 Han Chinese. Diet-feeding study included a 7-day low-sodium (51.3 mmol/d), a 7-day high-sodium (307.8 mmol/d), and a 7-day high-sodium plus potassium supplementation (60 mmol/d). Nine BP measurements were obtained during baseline observation and each intervention period. The meta-analyses identified 8 novel loci for BP phenotypes, which physically mapped in or near PRMT6 (P=7.29 × 10(-9)), CDCA7 (P=3.57 × 10(-8)), PIBF1 (P=1.78 × 10(-9)), ARL4C (P=1.86 × 10(-8)), IRAK1BP1 (P=1.44 × 10(-10)), SALL1 (P=7.01 × 10(-13)), TRPM8 (P=2.68 × 10(-8)), and FBXL13 (P=3.74 × 10(-9)). There was a strong dose-response relationship between the number of risk alleles of these independent single-nucleotide polymorphisms and the risk of developing hypertension during the 7.5-year follow-up in the study participants. Compared with those in the lowest quartile of risk alleles, odds ratios (95% confidence intervals) for those in the second, third, and fourth quartiles were 1.39 (0.97, 1.99), 1.72 (1.19, 2.47), and 1.84 (1.29, 2.62), respectively (P=0.0003 for trend).

CONCLUSIONS

Our study identified 8 novel loci for BP responses to dietary sodium and potassium intervention and cold pressor test. The effect size of these novel loci on BP phenotypes is much larger than those reported by the previously published studies. Furthermore, these variants predict the risk of developing hypertension among individuals with normal BP at baseline.

Role of interactions in pharmacogenetic studies: leukotrienes in asthma

Researchers have identified thousands of loci involved in complex traits and drug response. However, in most cases they only explain a small proportion of the heritability of the trait. Among different strategies conducted to identify this 'missing heritability', here we illustrate the importance of complex gene-environment interactions using findings regarding the role of leukotrienes on the bronchodilator response to albuterol in Latino asthmatics. Patients managing their asthma with leukotriene-modifying medication presented higher increases in the bronchodilator response to albuterol. Moreover, interactions between genes responsible for leukotriene production were associated with a decreased risk of asthma. Combining genetic and pharmacologic effects, leukotriene-modifying users carrying certain combinations of alleles presented higher improvements in lung function after bronchodilator administration. Genes and drugs act at different orders of interaction (from individual effects to gene-gene-drug-drug interactions) and population-specific effects have to be considered. These results may be extrapolated to other complex phenotypes.

Two genomic regions of chromosomes 1 and 18 explain most of the stroke susceptibility under salt loading in stroke-prone spontaneously hypertensive rat/Izm

To clarify the genetic mechanisms of stroke susceptibility in the stroke-prone spontaneously hypertensive rat (SHRSP), a quantitative trait locus (QTL) analysis was performed. Using 295 F2 rats of a cross between SHRSP/Izm and SHR/Izm, 2 major QTLs for stroke latency under salt loading were identified on chromosomes (chr) 1 and 18. Evaluation of 6 reciprocal single and double congenic rats for these QTLs showed that substitution of the SHRSP for the SHR fragment at the chr 1 and 18 QTLs increased the relative risk for stroke by 8.4 and 5.0, respectively. The combined effect of the 2 QTLs was 10× greater than that of the background genome (by Cox hazard model). Blood pressure monitoring by radio telemetry indicated that the combination of the 2 QTLs had a clear effect on the salt-dependent blood pressure increase, suggesting an important role for the salt-sensitive blood pressure increase in the susceptibility of SHRSP to stroke. A haplotype analysis of 11 substrains of SHRSP and SHR using 340 simple sequence repeat markers in the chr 1 QTL suggested that the 7-Mbp fragment between D1Rat260 and D1Rat178 was most likely to harbor the responsible gene(s), which was confirmed by a study of additional subcongenic strains. This study indicated a major role for 2 QTLs on chr 1 and 18 in stroke susceptibility in SHRSP under salt loading. The salt-sensitive blood pressure increase was implied to play a key role in the stroke susceptibility.

Relationships between selected gene polymorphisms and blood pressure sensitivity to weight loss in elderly persons with hypertension

Salt sensitivity, the heterogeneity in the response of blood pressure (BP) to alterations in sodium intake, has been studied extensively, whereas weight sensitivity, the heterogeneity in BP response to weight change, has received scant attention. We examined the relationship of 21 gene polymorphisms previously found to be associated with hypertension, diabetes mellitus, or obesity, with weight sensitivity in the Trial of Nonpharmacologic Interventions in the Elderly, where participants with hypertension were randomized to receive intensive dietary intervention of sodium reduction, weight loss, both, or attention control, whereas pharmacological therapy was kept constant. After correcting for multiplicity, we identified significant associations of 3 polymorphisms with weight sensitivity of systolic BP (rs4646994, rs2820037, and rs1800629) and 3 polymorphisms for diastolic BP (rs4646994, rs2820037, and rs5744292). A recursive partitioning algorithm selected the combination of rs4646994, rs1800629, rs1982073, and rs1800896 as the set associated with the highest weight sensitivity. Polymorphisms related to hypertension, obesity, and diabetes mellitus are associated with weight sensitivity of BP.