Genetic predisposition to salt-sensitivity: a systematic review

Associations of SGLT2 genetic polymorphisms with salt sensitivity, blood pressure changes and hypertension incidence in Chinese adults

Sodium-glucose cotransporter 2 (SGLT2) inhibitors lowers blood pressure (BP) and exert a salutary effect on the salt sensitivity of BP. This study aimed to examine the associations of SGLT2 genetic variants with salt sensitivity, longitudinal BP changes and the risk of incident hypertension in Baoji Salt-Sensitive Study. A total of 514 participants were recruited when the cohort was established in 2004, and 333 participants received a dietary intervention that consisted of a 3-day usual diet followed sequentially by a 7-day low-salt diet and a 7-day high-salt diet. The cohort was then followed up for 14 years to evaluate the longitudinal BP changes and development of hypertension. We found that SGLT2 SNP rs3813007 was significantly associated with the systolic BP (SBP) responses to the low-salt diet. Over the 14 years of follow-up, SNPs rs3116149 and rs3813008 were significantly associated with the longitudinal SBP changes, and SNPs rs3116149, rs3813008, rs3813007 in SGLT2 were significantly associated with incidence of hypertension. Furthermore, gene-based analyses revealed that SGLT2 was significantly associated with hypertension incidence. Our study suggests that SGLT2 genetic polymorphisms may be involved in salt sensitivity and development of hypertension.

Examining the Individual Response to a Low-Sodium Diet in Patients with Hypertension: Protocol for a Pilot Randomized Controlled Trial

BACKGROUND

Excessive dietary sodium intake is an independent risk factor for hypertension and cardiovascular disease (CVD). Despite the large body of evidence concerning the effects of dietary interventions on blood pressure (BP) and CVD outcomes, trials have often reported low adherence to decreased sodium intake, likely due in part to heterogeneous BP responses. To address the challenges, recent clinical findings suggested a precise and personalized dietary approach that seeks to deliver more preventive and practical dietary advice than the "one-size-fits-all" guidelines and weighs the personal risk of developing specific diseases.

OBJECTIVE

The purpose of this pilot randomized controlled trial was to test the feasibility and preliminary efficacy of integrating the use of mobile technology and metabolomics with a low-sodium diet intervention in patients with hypertension to develop personalized low-sodium diet programs. Additionally, the study will examine the associations of urine metabolites with urinary sodium levels and BP control based on the hypothesis that targeted urine metabolites. In this report, we describe the design and protocol of the pilot trial.

METHODS

A total of 40 patients with hypertension will be randomly assigned to either a 8-week low-sodium diet group (n=20) or a standard care group (n=20). Each week, intervention participants went through individual sessions with an interventionist via videoconferencing to discuss low-sodium diet regimens, patients' food choices, and BP tracks on mobile apps. The control group followed their usual care for hypertension management. All participants in both groups monitored diet and BP using mobile apps for 8 weeks. A 24-hour urinary sodium excretion for the estimation of dietary sodium intake, systolic, and diastolic BPs were measured at the baseline and at 8 weeks. The primary outcomes of this study include the feasibility of conducting a randomized controlled trial (RCT) by reporting recruitment, retention, and completion statistics. The preliminary effects of intervention will be tested by a generalized estimating equation model.

RESULTS

This pilot RCT study was approved by the institutional review board at the University of Texas Health San Antonio in January 2021. The first participant was enrolled in April 2021, and currently, 26 participants were enrolled. All data collection is expected to conclude by March 2023, with data analysis and study results ready for reporting by December 2023. Findings from this pilot RCT will further guide the team in planning a future large-scale study.

CONCLUSIONS

The findings of this proposed study will establish a comprehensive knowledge base for future research and development of personalized dietary interventions to promote adherence to dietary strategies and self-management of chronic disease using the Precision Health approach for millions of Americans who are struggling with uncontrolled hypertension.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04764253; https://clinicaltrials.gov/ct2/show/NCT04764253.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/39058.

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

Corin, a transmembrane serine protease that can cleave pro‐atrial natriuretic peptide (Pro‐ANP) into smaller bioactive molecule atrial natriuretic peptide, has been shown to be involved in the pathophysiology of hypertension, cardiac hypertrophy. We sought to examine the associations of corin genetic variations with salt sensitivity, blood pressure (BP) changes and hypertension incidence. We studied participants of the original Baoji Salt‐Sensitive cohort, recruited from 124 families from seven Chinese villages in 2004 who sequentially received a usual baseline salt diet, a 7‐day low salt diet (3 g/day) and a 7‐day high salt diet (18 g/day), respectively. They were followed up for 8 years (in 2009, 2012) to evaluate the development of hypertension. Corin SNP rs3749584 was significantly associated with diastolic BP (DBP) and mean arterial pressure (MAP) response to low‐salt diet, while rs4695253, rs17654278 were associated with pulse pressure (PP) response to low‐salt diet. SNPs rs4695253, rs12509275, rs2351783, rs2271036, rs2271037 were significantly associated with systolic BP (SBP), DBP, and MAP responses to high‐salt diet. In addition, SNPs rs12641823, rs6834933, rs2271036, and rs22710367 were significantly associated with the longitudinal changes in SBP, DBP, MAP, or PP over 8 years of follow‐up. SNP rs73814824 was significantly associated with the incidence of hypertension over 8 years. Gene‐based analysis showed that corin gene was significantly associated with longitudinal BP changes and hypertension incidence after 8‐year follow‐up. This study suggests that corin may play a role in salt sensitivity, BP progression, and development of hypertension.

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.

Urinary proteomics reveals key markers of salt sensitivity in hypertensive patients during saline infusion

BACKGROUND

Hypertension is a complex disease and is the major cause of cardiovascular complications. In the vast majority of individuals, the aetiology of elevated blood pressure (BP) cannot be determined, thus impairing optimized therapies and prognosis for individual patients. A more precise understanding of the molecular pathogenesis of hypertension remains a pressing priority for both basic and translational research. Here we investigated the effect of salt on naive hypertensive patients in order to better understand the salt intake-blood pressure relationship.

METHODS

Patients underwent an acute saline infusion and were defined as salt-sensitive or salt-resistant according to mean blood pressure changes. Urinary proteome changes during the salt load test were analysed by a label-free quantitative proteomics approach.

RESULTS

Our data show that salt-sensitive patients display equal sodium reabsorption as salt-resistant patients, as major sodium transporters show the same behaviour during the salt load. However, salt-sensitive patients regulate the renin angiotensin system (RAS) differently from salt-resistant patients, and upregulate proteins, as epidermal growth factor (EGF) and plasminogen activator, urokinase (PLAU), involved in the regulation of epithelial sodium channel ENaC activity.

CONCLUSIONS

Salt-sensitive and salt-resistant subjects have similar response to a saline/volume infusion as detected by urinary proteome. However, we identified glutamyl aminopeptidase (ENPEP), PLAU, EGF and Xaa-Pro aminopeptidase 2 precursor XPNPEP2 as key molecules of salt-sensitivity, through modulation of ENaC-dependent sodium reabsorption along the distal tubule.

Genetic Risk Factors of Intracranial Atherosclerosis

PURPOSE OF REVIEW

Intracranial atherosclerosis (ICAS) is the most common cause of stroke throughout the world. It also increases the risk of recurrent stroke and dementia. As a complex and multifactorial disease, ICAS is influenced by multiple genetic, biological, and environmental factors. This review summarizes the candidate gene and genome-wide studies aimed at discovering genetic risk factors of ICAS.

RECENT FINDINGS

Numerous studies have focused on the association between single-nucleotide polymorphisms (SNPs) of atherosclerosis-related genes and the risk of ICAS. Variants in adiponectin Q (ADIPOQ), ring finger protein 213 (RNF213), apolipoprotein E (APOE), phosphodiesterase 4D (PDE4D), methylenetetrahydrofolate reductase (MTHFR), lipoprotein lipase (LPL), α-adducin (ADD1) genes, angiotensin-converting enzyme (ACE), and other genes related to renin-angiotensin-aldosterone system have been associated with ICAS. We review the available evidences on the candidate genes and SNPs associated with genetic susceptibility to ICAS, and point out future developments of this field. Genetic discoveries could have clinical implications for intracranial atherosclerotic disease.

Sodium sensitivity of blood pressure in Chinese populations

Hypertension is an enormous public-health challenge in the world due to its high prevalence and consequent increased cardiovascular disease morbidity and mortality. Observational epidemiologic studies and clinical trials have demonstrated a causal relationship between sodium intake and elevated blood pressure (BP). However, BP changes in response to sodium intervention vary among individuals-a trait called sodium sensitivity. This paper aims to review the recent advances in sodium-sensitivity research in Chinese and other populations. Older age, female gender, and black race are associated with high sodium sensitivity. Both genetic and environmental factors influence BP sodium sensitivity. Physical activity and dietary potassium intake are associated with reduced sodium sensitivity while obesity, metabolic syndrome, and elevated BP are associated with increased sodium sensitivity. Familial studies have documented a moderate heritability of sodium sensitivity. Candidate gene association studies, genome-wide association studies, whole-exome, and whole-genome sequencing studies have been conducted to elucidate the genomic mechanisms of sodium sensitivity. The Genetic Epidemiology Network of Salt Sensitivity (GenSalt) study, the largest family-based feeding study to date, was conducted among 1906 Han Chinese in rural northern China. This study showed that ~32.4% of Chinese adults were sodium sensitive. Additionally, several genetic variants were found to be associated with sodium sensitivity. Findings from the GenSalt Study and others indicate that sodium sensitivity is a reproducible trait and both lifestyle factors and genetic variants play a role in this complex trait. Discovering biomarkers and underlying mechanisms for sodium sensitivity will help to develop individualized intervention strategies for hypertension.

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.

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.

How far cardio metabolic and psychological factors affect salt sensitivity in normotensive adult population?

AIM

To evaluate the prevalence of salt sensitivity and the impact of cardiometabolic and psychological characteristics on salt sensitivity in normotensive population.

METHODS

Of all participants, anthropometric measurements and fasting venous blood samples were collected, and study questionnaires were completed. Salt Sensitivity was defined based on the difference in mean arterial pressure with infusion of 2 L of normal saline followed by a low sodium diet and administration of three doses of oral furosemide the day after.

RESULTS

Of 131 participants, 56 (42.7%) were diagnosed with salt sensitivity. Crude and age and sex adjusted regression analysis showed that low-density lipoprotein cholesterol and depression were positively associated with salt sensitivity (OR = 1.02, 95%CI: 1.01-1.04 and OR = 1.15, 95%CI: 1.00-1.34, respectively).

CONCLUSION

The high prevalence of salt sensitivity and its significant relation with prevalent risk factors necessitates considering its reduction actions at the population level and the need for further research.

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.

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.

Common variants in the Na(+)-coupled bicarbonate transporter genes and salt sensitivity of blood pressure: the GenSalt study

The current study comprehensively examined the association between common variants in the Na⁺-coupled bicarbonate transporter (NCBT) genes and blood pressure (BP) responses to dietary sodium intervention. A 7-day low-sodium followed by a 7-day high-sodium dietary intervention was conducted among 1906 Han participants from rural areas of northern China. Nine BP measurements were obtained at baseline and each intervention using a random-zero sphygmomanometer. A mixed-effect model was used to assess the additive associations of 76 common variants in five NCBT genes, including SLC4A4, SLC4A5, SLC4A7, SLC4A8 and SLC4A10, with salt-sensitivity phenotypes. The Bonferroni method was used to adjust for multiple testing. SLC4A4 marker rs4254735 was significantly associated with diastolic BP (DBP) response to low-sodium intervention (P=5.05×10⁻⁴), with mean (95% confidence interval [CI]) response of −2.91 (−3.21, −2.61) and −0.40 (−1.84, 1.05) mmHg for genotype AA and AG, respectively. In addition, BP responses to high-sodium intervention significantly increased with the number of minor C alleles of SLC4A4 marker rs10022637. Mean systolic BP (SBP) responses among those with genotypes TT, CT, and CC were 4.62 (4.29, 4.99), 5.94 (5.31, 6.58) and 6.00 (3.57, 8.43) mmHg (P=1.14×10⁻⁴); mean DBP responses were 1.72 (1.41, 2.03), 3.22 (2.52, 3.92) and 3.94 (1.88, 5.99) mmHg (P=2.26×10⁻⁵), and mean arterial pressure responses were 2.69 (2.40, 2.97), 4.13 (3.57, 4.70) and 4.61 (2.51, 6.71) mmHg (P=2.07×10⁻⁶), respectively. Briefly, the present study indicated that common variants in the SLC4A4 gene might contribute to the variation of BP responses to dietary sodium intake in Han Chinese population.

Aggregate blood pressure responses to serial dietary sodium and potassium intervention: defining responses using independent component analysis

BACKGROUND

Hypertension is a complex trait that often co-occurs with other conditions such as obesity and is affected by genetic and environmental factors. Aggregate indices such as principal components among these variables and their responses to environmental interventions may represent novel information that is potentially useful for genetic studies.

RESULTS

In this study of families participating in the Genetic Epidemiology Network of Salt Sensitivity (GenSalt) Study, blood pressure (BP) responses to dietary sodium interventions are explored. Independent component analysis (ICA) was applied to 20 variables indexing obesity and BP measured at baseline and during low sodium, high sodium and high sodium plus potassium dietary intervention periods. A "heat map" protocol that classifies subjects based on risk for hypertension is used to interpret the extracted components. ICA and heat map suggest four components best describe the data: (1) systolic hypertension, (2) general hypertension, (3) response to sodium intervention and (4) obesity. The largest heritabilities are for the systolic (64%) and general hypertension (56%) components. There is a pattern of higher heritability for the component response to intervention (40-42%) as compared to those for the traditional intervention responses computed as delta scores (24%-40%).

CONCLUSIONS

In summary, the present study provides intermediate phenotypes that are heritable. Using these derived components may prove useful in gene discovery applications.

Associations between CLCNKA_B tag SNPs with essential hypertension and interactions between genetic and environmental factors in an island population in China

OBJECTIVE

Essential hypertension (EH) is known as the result from the interaction of environmental and genetic factors. We selected tag SNPs of CLCNKA_B genes as gene markers, to elucidate the relationship between CLCNKA_B and EH, and to determine the possible interaction among tag SNPs and dietary factors in island of China.

METHODS

A case-control study was conducted in Changshan islands of China, blood samples of 806 participants were genotyped, and the general characteristics and dietary habits of them were collected. Unconditional logistic regression (ULR) was used to assess the effects of CLCNKA_B tag SNPs and dietary factors on EH. Generalized multifactor dimensionality reduction (GMDR) was used to test gene-environment interaction for EH risk.

RESULTS

Four SNPs were identified as the tag SNPs of CLCNKA_B. Recessive model for rs5253 and rs2275166 were marginal associated with the decrease risk of EH (OR = 0.36, 95% CI = 0.12-1.07 for rs5253; OR = 0.40, 95% CI = 0.16-1.05 for rs2275166). In GMDR, the five-factor interaction model of rs1010069, salt, marine products, meat and edible oil consumption was the best model, with a maximum CVC of 10/10 and a TBA of 0.638 (p = 0.001). In ULR, compared with subjects carried wild genotypes and null dietary risk factor, those with three or more dietary risk factors and mutation genotypes had 5.90-fold EH risk (95% CI:2.24-15.53).

CONCLUSION

Though the single loci of tag SNPs of CLCNKA_B are not enough to significantly increase the EH susceptibility, the combination of CLCNKA tag SNP, salt, marine products, meat and edible oil consumption is associated with elevated risk.

Association between polymorphisms in the renin-angiotensin-aldosterone system genes and essential hypertension in the Han Chinese population

BACKGROUND

Renin-angiotensin-aldosterone system (RAAS) is the most important endocrine blood pressure control mechanism in our body, genes encoding components of this system have been strong candidates for the investigation of the genetic basis of hypertension. However, previous studies mainly focused on limited polymorphisms, thus we carried out a case-control study in the Han Chinese population to systemically investigate the association between polymorphisms in the RAAS genes and essential hypertension.

METHODS

905 essential hypertensive cases and 905 normotensive controls were recruited based on stringent inclusion and exclusion criteria. All 41 tagSNPs within RAAS genes were retrieved from HapMap, and the genotyping was performed using the GenomeLab SNPstream Genotyping System. Logistic regression analysis, Multifactor dimensionality reduction (MDR), stratified analysis and crossover analysis were used to identify and characterize interactions among the SNPs and the non-genetic factors.

RESULTS

Serum levels of total cholesterol (TC) and triglyceride (TG), and body mass index (BMI) were significantly higher in the hypertensive group than in the control group. Of 41 SNPs genotyped, rs3789678 and rs2493132 within AGT, rs4305 within ACE, rs275645 within AGTR1, rs3802230 and rs10086846 within CYP11B2 were shown to associate with hypertension. The MDR analysis demonstrated that the interaction between BMI and rs4305 increased the susceptibility to hypertension. Crossover analysis and stratified analysis further indicated that BMI has a major effect, and rs4305 has a minor effect.

CONCLUSION

These novel findings indicated that together with non-genetic factors, these genetic variants in the RAAS may play an important role in determining an individual's susceptibility to hypertension in the Han Chinese.

Current evidence on healthy eating

Large nutritional epidemiology studies, with long-term follow-up to assess major clinical end points, coupled with advances in basic science and clinical trials, have led to important improvements in our understanding of nutrition in primary prevention of chronic disease. Although much work remains, sufficient evidence has accrued to provide solid advice on healthy eating. Good data now support the benefits of diets that are rich in plant sources of fats and protein, fish, nuts, whole grains, and fruits and vegetables; that avoid partially hydrogenated fats; and that limit red meat and refined carbohydrates. The simplistic advice to reduce all fat, or all carbohydrates, has not stood the test of science; strong evidence supports the need to consider fat and carbohydrate quality and different protein sources. This article briefly summarizes major findings from recent years bearing on these issues.

Genome-wide linkage and positional association study of blood pressure response to dietary sodium intervention: the GenSalt Study

The authors conducted a genome-wide linkage scan and positional association analysis to identify the genetic determinants of salt sensitivity of blood pressure (BP) in a large family-based, dietary-feeding study. The dietary intervention was conducted among 1,906 participants in rural China (2003-2005). A 7-day low-sodium intervention was followed by a 7-day high-sodium intervention. Salt sensitivity was defined as BP responses to low- and high-sodium interventions. Signals of the logarithm of the odds to the base 10 (LOD ≥ 3) were detected at 33-42 centimorgans of chromosome 2 (2p24.3-2p24.1), with a maximum LOD score of 3.33 for diastolic blood pressure responses to high-sodium intervention. LOD scores were 2.35-2.91 for mean arterial pressure (MAP) and 0.80-1.49 for systolic blood pressure responses in this region, respectively. Correcting for multiple tests, single nucleotide polymorphism (SNP) rs11674786 (2.7 kilobases upstream of the family with sequence similarity 84, member A, gene (FAM84A)) in the linkage region was significantly associated with diastolic blood pressure (P = 0.0007) and MAP responses (P = 0.0007), and SNP rs16983422 (2.8 kilobases upstream of the visinin-like 1 gene (VSNL1)) was marginally associated with diastolic blood pressure (P = 0.005) and MAP responses (P = 0.005). An additive interaction between SNPs rs11674786 and rs16983422 was observed, with P = 7.00 × 10(-5) and P = 7.23 × 10(-5) for diastolic blood pressure and MAP responses, respectively. The authors concluded that genetic region 2p24.3-2p24.1 might harbor functional variants for the salt sensitivity of BP.

Salt sensitivity of blood pressure is associated with polymorphisms in the sodium-bicarbonate cotransporter

Previous studies have demonstrated that single nucleotide polymorphisms (SNPs) of the sodium-bicarbonate co-transporter gene (SLC4A5) are associated with hypertension. We tested the hypothesis that SNPs in SLC4A5 are associated with salt sensitivity of blood pressure in 185 whites consuming an isocaloric constant diet with a randomized order of 7 days of low Na(+) (10 mmol/d) and 7 days of high Na(+) (300 mmol/d) intake. Salt sensitivity was defined as a ≥ 7-mm Hg increase in mean arterial pressure during a randomized transition between high and low Na(+) diet. A total of 35 polymorphisms in 17 candidate genes were assayed, 25 of which were tested for association. Association analyses with salt sensitivity revealed 3 variants that associated with salt sensitivity, 2 in SLC4A5 (P<0.001) and 1 in GRK4 (P=0.020). Of these, 2 SNPs in SLC4A5 (rs7571842 and rs10177833) demonstrated highly significant results and large effects sizes, using logistic regression. These 2 SNPs had P values of 1.0 × 10(-4) and 3.1 × 10(-4) with odds ratios of 0.221 and 0.221 in unadjusted regression models, respectively, with the G allele at both sites conferring protection. These SNPs remained significant after adjusting for body mass index and age (P=8.9 × 10(-5) and 2.6 × 10(-4) and odds ratios 0.210 and 0.286, respectively). Furthermore, the association of these SNPs with salt sensitivity was replicated in a second hypertensive population. Meta-analysis demonstrated significant associations of both SNPs with salt sensitivity (rs7571842 [P=1.2 × 10(-5)]; rs1017783 [P=1.1 × 10(-4)]). In conclusion, SLC4A5 variants are strongly associated with salt sensitivity of blood pressure in 2 separate white populations.

Genomic epidemiology of blood pressure salt sensitivity

High blood pressure (BP) is a complex trait determined by genetic and environmental factors, as well as their interactions. Over the past few decades, there has been substantial progress elucidating the genetic determinants underlying BP response to sodium intake, or BP salt sensitivity. Research of monogenic BP disorders has highlighted the importance of renal salt handling in BP regulation, implicating genes and biological pathways subsequently identified in candidate gene studies of salt sensitivity. Despite these advancements, certain candidate gene findings await replication evidence, and some biological pathways warrant further investigation. Furthermore, results from genome-wide association studies (GWASs) and sequencing work have yet to be reported. GWAS will be valuable for uncovering novel mechanisms underlying salt sensitivity, whereas future sequencing efforts promise the discovery of functional variants related to this complex trait. Delineating the genetic architecture of salt sensitivity will be critical to understanding how genes and dietary sodium interact to influence BP.

Gene-sodium interaction and blood pressure: findings from genomics research of blood pressure salt sensitivity

High blood pressure (BP) is a complex trait determined by both genetic and environmental factors, as well as the interactions between these factors. Over the past few decades, there has been substantial progress in elucidating the genetic determinants underlying the BP response to sodium intake, or BP salt sensitivity. Research of monogenic BP disorders has highlighted the importance of renal salt handling in BP regulation, implicating genes and biological pathways related to salt sensitivity. Candidate gene studies have contributed important information toward understanding the genomic mechanisms underlying the BP response to salt intake, identifying genes in the renin-angiotensin-aldosterone system, renal sodium channels/transporters, and the endothelial system related to this phenotype. Despite these advancements, genome-wide association studies are still needed to uncover novel mechanisms underlying salt sensitivity, while future sequencing efforts promise the discovery of functional variants related to this complex trait. Delineating the genetic architecture of salt sensitivity will be critical to understanding how genes and dietary sodium interact to influence BP.

Essential hypertension in adolescents and children: Recent advances in causative mechanisms

Essential hypertension is the most common form of hypertension in adults, and it is recognized more often in adolescents than in younger children. It is well known that the probability of a diagnosis of essential hypertension increases with age from birth onward. The initiation of high blood pressure burden starts in childhood and continues through adolescence to persist in the remaining phases of life. The genesis of essential hypertension is likely to be multifactorial. Obesity, insulin resistance, activation of sympathetic nervous system, sodium homeostasis, renin-angiotensin system, vascular smooth muscle structure and reactivity, serum uric acid levels, genetic factors and fetal programming have been implicated in this disorder. In addition, erythrocyte sodium transport, the free calcium concentration in platelets and leukocytes, urine kallikrein excretion, and sympathetic nervous system receptors have also been investigated as other possible mechanisms. Obesity in children appears to be the lead contributor of essential hypertension prevalence in children and adolescents. Suggested mechanisms of obesity-related hypertension include insulin resistance, sodium retention, increased sympathetic nervous system activity, activation of renin-angiotensin-aldosterone, and altered vascular function. The etiopathogenesis of essential hypertension in children and adolescents appears to closely resemble that of adults. The minor variations seen could probably be due to the evolving nature of this condition. Many of the established mechanisms that are confirmed in adult population need to be replicated in the pediatric age group by means of definitive research for a better understanding of this condition in future.

Common Variants in Epithelial Sodium Channel Genes Contribute to Salt Sensitivity of Blood Pressure

Background—

Rare mutations of the epithelial sodium channel (ENaC) lead to mendelian forms of salt-sensitive hypertension or salt-wasting hypotension. We aimed to examine the association between common variants in the ENaC genes and salt sensitivity of blood pressure (BP).

Methods and Results—

A total of 1906 Han Chinese participated in the Genetic Epidemiology Network of Salt Sensitivity (GenSalt) study, which includes a 7-day low-sodium intake (51.3 mmol sodium/d) followed by a 7-day high-sodium intake (307.8 mmol sodium/d). Nine BP measurements were obtained at baseline and each intervention period using a random-zero sphygmomanometer. Single-nucleotide polymorphisms, both tagging and functional, from the 3 ENaC subunits, α, β, and γ ( SCNN1A, SCNN1B , and SCNN1G ), were genotyped. Multiple common single-nucleotide polymorphisms in SCNN1G were significantly associated with BP response to low-sodium intervention (rs4073930, P =1.7×10 −5 ; rs4073291, P =1.1×10 −5 ; rs7404408, P =1.9×10 −5 ; rs5735, P =3.0×10 −4 ; rs4299163, P =0.004; and rs4499238, P =0.002) even after correcting for multiple testing. For example, under an additive model, the minor allele G of SNP rs4073291 was associated with 1.33 mm Hg lower systolic BP reduction during low-sodium intervention.

Conclusions—

This large dietary sodium intervention study indicates that common variants of ENaC subunits may contribute to the variation of BP response to dietary sodium intake. Future studies are warranted to confirm these findings in an independent population and to identify functional variants for salt sensitivity.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00721721.

Sodium sensitivity of blood pressure in Chinese populations

Clinical trials have demonstrated that a reduced intake of dietary sodium lowers blood pressure. However, blood pressure reduction in response to a decrease in dietary sodium intake varies considerably among different individuals-a phenomenon described as sodium sensitivity. The Genetic Epidemiology Network of Salt Sensitivity (GenSalt) study was a large family-based dietary-feeding study conducted in rural north China. This study indicated that approximately 39% of Chinese adults were sodium-sensitive. Sodium sensitivity was more common in women and in persons who were older and had higher usual blood pressure. Sodium sensitivity was also more common in individuals with higher responses to a cold pressor test and in individuals with the metabolic syndrome. Genetic factors may play an important role in determining sodium sensitivity in the Chinese population. A better understanding of the genetic and environmental determinants of sodium sensitivity has important public health and clinical implications.

Genetics of salt-sensitive hypertension

The assessment of salt sensitivity of blood pressure is difficult because of the lack of universal consensus on definition. Regardless of the variability in the definition of salt sensitivity, increased salt intake, independent of the actual level of blood pressure, is also a risk factor for cardiovascular morbidity and mortality and kidney disease. A modest reduction in salt intake results in an immediate decrease in blood pressure, with long-term beneficial consequences. However, some have suggested that dietary sodium restriction may not be beneficial to everyone. Thus, there is a need to distinguish salt-sensitive from salt-resistant individuals, but it has been difficult to do so with phenotypic studies. Therefore, there is a need to determine the genes that are involved in salt sensitivity. This review focuses on genes associated with salt sensitivity, with emphasis on the variants associated with salt sensitivity in humans that are not due to monogenic causes. Special emphasis is given to gene variants associated with salt sensitivity whose protein products interfere with cell function and increase blood pressure in transgenic mice.

An empirical test of the materialist framework for understanding the general population's reaction to nonpersonalized genetic health messages

Genetic health messages are increasingly prevalent in our society. The materialist framework of laypeople's genetic knowledge may provide a good basis for understanding the effects of such messages on preventive behavior and related health cognitions. This study provides an empirical test of the predictions of this framework. We presented 929 participants who were aware or unaware of the existence of genetic risk factors for salt sensitivity with either a genetic health message or a general health message about salt sensitivity. Baseline, immediate follow-up, 1-month follow-up, and 6-month follow-up questionnaires assessed risk perception, intention, and salt consumption. Compared with the general health message, previously unaware participants reported lower susceptibility to, and lower severity of, salt sensitivity and lower intentions to restrict salt intake immediately after reading the genetic health message, but not at the 1- and 6-month follow-ups. No such effects were observed for previously aware participants. In addition, the authors observed no effect of health message type on self-reported salt consumption. The authors' findings support the validity of the materialist framework for understanding laypeople's knowledge of genetics. On the basis of the results, several implications were deduced for public education of genetics.

α-adducin Gly460Trp polymorphism and essential hypertension risk in Chinese: a meta-analysis

No clear consensus has been reached on the α-adducin polymorphism (Gly460Trp) and essential hypertension (EH) risk in Chinese. We conducted a meta-analysis in an effort to systematically explore the possible association. Case-control studies in Chinese and English performed with human subjects were identified by searching the MEDLINE, EMBASE, China Biological Medicine Database, China National Knowledge Infrastructure platform, Wanfang and VIP databases. The fixed-effects model and the random-effects model for dichotomous outcomes were applied to combine the results of the individual studies. We selected 20 studies that met the inclusion criteria, including a total of 5562 patients with hypertension and 4289 controls. Overall, our findings supported the hypothesis that the ADD1 Gly460Trp polymorphism is associated with EH in the Chinese population. A borderline association was found between the tryptophan (Trp) allele of the Gly460Trp variant and hypertension (P=0.05, Odds ratio (OR)=1.08, 95% confidence interval (CI)=1.00-1.17 and P(heterogeneity)=0.02). Significantly increased risk was observed in the recessive genetic model (P=0.0009, OR=1.24, 95% CI=1.09-1.41 and P(heterogeneity)=0.04) as well as in the homozygote comparison (P=0.006, OR=1.25, 95% CI=1.07-1.46 and P(heterogeneity)=0.03). Furthermore, in the subgroup analysis, our results support a positive association among Chinese Han individuals (P=0.001, OR=1.25, 95% CI=1.09-1.42, P(heterogeneity)=0.08, recessive genetic model; P=0.009, OR=1.26, 95% CI=1.06-1.50, P(heterogeneity)=0.03, homozygote comparison). No apparent association was identified in Kazakhs. Our meta-analysis suggests that the Gly460Trp polymorphism might increase the risk of hypertension in Chinese populations, especially in Han Chinese. Further studies investigating gene-gene, gene-environment and mutual interactions are needed to better understand the role of ADD1 in hypertension.

Genetic variants in the apelin system and blood pressure responses to dietary sodium interventions: a family-based association study

OBJECTIVE

We examined the association between genetic variants in the apelin system and blood pressure (BP) responses to low-sodium and high-sodium interventions in the GenSalt Study.

METHODS

A 7-day low-sodium intervention (51.3 mmol sodium per day) followed by a 7-day high-sodium intervention (307.8 mmol sodium per day) was conducted among 1906 participants from 637 Han Chinese families. BP measurements were obtained at baseline and following each intervention using a random-zero sphygmomanometer. Twenty-three single nucleotide polymorphisms (SNPs), including both tag and functional SNPs, were selected from three candidate genes (APLN, APLNR, and ACE2). Single marker and haplotype analyses were conducted using the Family Based Association Test program. The false discovery rate method was used to correct for multiple testing.

RESULTS

SNPs rs2282623 and rs746886 of the APLNR gene were significantly associated with DBP (both P = 0.002) and mean arterial pressure (MAP) (P = 0.001 and 0.005, respectively) responses to low-sodium intervention. Six SNPs of the ACE2 gene were significantly associated with SBP, DBP, or MAP responses to low-sodium intervention. Three of them, rs1514283, rs1514282, and rs4646176, were also significantly associated with MAP response to high-sodium intervention (all P <or= 0.006). Haplotype analysis indicated the A-T-T haplotype of APLNR SNPs rs721608-rs2282623-rs746886 was associated with decreased DBP and MAP responses to low-sodium intervention (P = 0.001 and 0.003, respectively), whereas G-C-C was associated with increased SBP and MAP responses to high-sodium intervention (P = 0.004 and 0.01, respectively).

CONCLUSION

This large family-based study indicates that genetic variants in the APLNR and ACE2 genes are significantly associated with BP responses to dietary sodium intervention.

Genetic correlation of blood pressure responses to dietary sodium and potassium intervention and cold pressor test in Chinese population

We examined the genetic association between blood pressure (BP) responses to dietary sodium and potassium intervention and to cold pressor test (CPT) in a large family-based dietary feeding study. The dietary intervention and CPT were conducted among 1906 participants in rural China. The dietary intervention included three 7-day periods of low-sodium feeding (51.3 mmol per day), high-sodium feeding (307.8 mmol per day) and high-sodium feeding plus potassium supplementation (60 mmol per day). BP responses to high-sodium intervention had strong genetic correlations (ρ(G)) with both BP responses to low sodium (ρ(G)=-0.43 to -0.54, P-values=0.0005 to 0.03) and to potassium supplementation (ρ(G)=-0.41 to -0.49, P-values=0.001 to 0.005) interventions. Most environmental correlations between BP responses to various dietary interventions were significant. The ρ(G) between BP responses to CPT and to high-sodium intervention and potassium supplementation were statistically significant. For example, the ρ(G) between maximum BP responses to CPT and BP responses to high-sodium intervention was 0.37 (P=0.006) for systolic BP (SBP) and 0.41 (P=0.002) for diastolic BP (DBP). The ρ(G) between maximum BP responses to CPT and BP responses to potassium intervention was -0.42 (P=0.001) for SBP and -0.46 (P=0.001) for SBP. Our study suggests that there are common genetic determinants that influence BP responses to dietary sodium and potassium interventions and to CPT.

Epidemiology of hypertension and chronic kidney disease in China

PURPOSE OF REVIEW

Hypertension and chronic kidney disease have become major public health challenges in China.

RECENT FINDINGS

It is estimated that approximately 153 million Chinese adults had hypertension in 2002. It is also estimated that 2.33 million total cardiovascular deaths and 1.27 million premature cardiovascular deaths were attributable to increased blood pressure in 2005 in China. Approximately 39% of Chinese adult populations are highly sensitive to dietary sodium intake, a risk factor for hypertension and cardiovascular disease. The prevalence of chronic kidney disease varied greatly among studies due to differences in study populations and definitions of chronic kidney disease. A large prospective cohort study estimates that incidence and mortality of end-stage renal disease was 30.7 and 20.9 per 100,000 person-years among Chinese adults aged 40 years and older. Hypertension and the metabolic syndrome have been documented as risk factors for chronic kidney disease. In addition, a J-shaped association between body weight and incidence of end-stage renal disease and an inverse association between alcohol consumption and risk of end-stage renal disease were documented.

SUMMARY

These results underscore the urgent need to develop national strategies for the prevention, detection, and treatment of hypertension and chronic kidney disease.

Association between alpha-adducin gene polymorphism (Gly460Trp) and genetic predisposition to salt sensitivity: a meta-analysis

Linkage and association studies suggested the relationship between alpha-adducin polymorphism (Gly460Trp; rs4961) and genetic susceptibility to salt-sensitivity. However, the currently available results were inconsistent. This study aimed to define quantitatively the association between salt-sensitivity and alpha-adducin Gly460Trp polymorphism in all published case-control studies. Publications from PubMed and other databases were retrieved. The major inclusion criteria were: (1) case-control design; (2) salt-sensitivity confirmed by sodium loading tests, and (3) the distribution of genotypes given in detail. Seven case-control studies fulfilled the inclusion criteria. In total they involved 820 subjects (454 salt-sensitive and 366 non-salt-sensitive). The meta-analysis shows that Gly460Trp polymorphism in general is not significantly associated with salt-sensitivity [OR (95%CI): 1.40 (0.96, 2.04), P = 0.08]. Subgroup analysis showed that the association is statistically significant in Asian people [OR (95%CI):1.33 (1.06, 1.69), P = 0.02] but not in Caucasian people [OR (95%CI):1.98 (0.57, 6.92), P = 0.28]. This indicates that blood pressure response to sodium varies between ethnical groups. More studies based on a larger population are required to evaluate further the role of alpha-adducin Gly460Trp polymorphism in salt-sensitive hypertension.

Genetic health messages in the mass media: do the general public perceive non-personalized genetic health message as personally relevant?

OBJECTIVES

Although health messages communicating the role of genetics in health and disease development are increasingly prevalent in our society, no research has examined whether the general public perceives such messages as believable or personally relevant. We examined whether the general public accepted genetic health messages and viewed them personally relevant in promoting their preventive behaviour.

DESIGN

Experimental pre-test-post-test measurement design was employed to contrast the information acceptance and perceived personal relevance of the genetic health message with a general health message.

METHODS

We presented a randomly selected group of Dutch participants (N=1,319) with either a health message about the genetic risk factors for salt sensitivity or with a general health message about salt sensitivity without reference to genetic risk factors. Risk perception and intention to restrict salt intake was assessed before and after participants read the messages while information acceptance and perceived personal relevance was only assessed post-test.

RESULTS

Although we observed no effects of health message type on information processing, previously aware participants perceived the genetic health message as less personally relevant compared to the general health message. This difference in personal relevance resulted in lower estimates of susceptibility and a lower intention to engage in preventive behaviour among previously unaware participants.

CONCLUSIONS

Genetic health messages in the mass media may not be effective in promoting (intentions to engage in) preventive behaviour due to their low perceived personal relevance by the public. Hence, identifying strategies to increase personal relevance for genetic education is needed.

The Renin-Angiotensin System in the Development of Salt-Sensitive Hypertension in Animal Models and Humans

Hypertension is still one of the major causes of death from cardiovascular failure. Increased salt intake may aggravate the rise in blood pressure and the development of consequential damage of the heart, the vessels and other organs. The general necessity of restricted salt intake regardless of blood pressure or salt sensitivity has been a matter of debate over the past decades. This review summarizes the main pathogenic mechanisms of hypertension and salt sensitivity in rat models, particularly in the spontaneously hypertensive rat (SHR), and in patients with essential hypertension (EH). Although SHRs are commonly considered to be salt-resistant, there is much evidence that salt loading may deteriorate blood pressure and cardiovascular function even in these animals. Similarly, EH is not a homogenous disorder - some patients, but not all, exhibit pronounced salt sensitivity. The renin-angiotensin system (RAS) plays a key role in the regulation of blood pressure and salt and fluid homeostasis and thus is one of the main targets of antihypertensive therapy. This review focuses on the contribution of the RAS to the pathogenesis of salt-sensitive hypertension in SHRs and patients with EH.

Regulation of the epithelial sodium channel (ENaC) by membrane trafficking

The epithelial Na(+) channel (ENaC) is a major regulator of salt and water reabsorption in a number of epithelial tissues. Abnormalities in ENaC function have been directly linked to several human disease states including Liddle syndrome, psuedohypoaldosteronism, and cystic fibrosis and may be implicated in salt-sensitive hypertension. ENaC activity in epithelial cells is regulated both by open probability and channel number. This review focuses on the regulation of ENaC in the cells of the kidney cortical collecting duct by trafficking and recycling. The trafficking of ENaC is discussed in the broader context of epithelial cell vesicle trafficking. Well-characterized pathways and protein interactions elucidated using epithelial model cells are discussed, and the known overlap with ENaC regulation is highlighted. In following the life of ENaC in CCD epithelial cells the apical delivery, internalization, recycling, and destruction of the channel will be discussed. While a number of pathways presented still need to be linked to ENaC regulation and many details of the regulation of ENaC trafficking remain to be elucidated, knowledge of these mechanisms may provide further insights into ENaC activity in normal and disease states.

Two-dimensional, sex-specific autosomal linkage scan of the number of sodium pump sites

OBJECTIVES

The sodium pump consists of the membrane-bound enzyme sodium/potassium-ATPase, which exchanges internal sodium ions for external potassium ions. Obesity, hypertension, and diabetes associate with the activity of the sodium pump, motivating gene discovery for sodium pump number.

METHODS

Variance components linkage analysis was applied to the number of red blood cell sodium pump sites measured by ouabain-binding assays on 1375 members of 46 Utah pedigrees. Both one-dimensional (1D) and two-dimensional (2D) autosome-wide linkage analyses of pump number were performed on the combined sample as well as separately on the male and female subsets.

RESULTS

Two significant 1D linkages were identified: on chromosome 1p13 in the combined sample [1D logarithm of odds (LOD) score = 3.76] and on chromosome 17p21 in the female subset (1D LOD score = 3.24). In addition, two significant 2D linkages were identified in the female subset: on chromosome 10q22 interacting with chromosome 18q11 (2D LOD score = 7.18) and on chromosome 13q21 interacting with chromosome 4q31 (2D LOD score = 6.05). Single-nucleotide polymorphism rs17376826 in neuropeptide Y receptor Y2, an obesity-associated gene and a candidate in the chromosome 4q31 linkage region, is associated with pump number (P = 0.046 in the combined sample and P = 0.042 in the female subset).

CONCLUSION

Pump number is influenced by multiple genes, possibly including neuropeptide Y receptor Y2.

CYP3A5 polymorphism and sensitivity of blood pressure to dietary salt in Japanese men

The cytochrome P-450 3A5 (CYP3A5) gene has recently been implicated in renal sodium reabsorption and blood pressure regulation. The genetic effect of CYP3A5*1 (expressor) and *3 (reduced-expressor) variants on blood pressure has been studied in African Americans and Caucasians, but not yet in the Asian population. In this cross-sectional study, 238 Japanese male workers were examined to determine whether CYP3A5 *1*3 affects the blood pressure level, taking daily salt intake into account as a potential gene-environment interaction. The A6986G polymorphism was determined by melting curve analysis, and the salt intake level was inferred from spot urine specimen by calculating 24-h urinary sodium excretion. CYP3A5 *1*3 per se had no association with systolic blood pressure (SBP) and only a weak association was detected for diastolic blood pressure (DBP) (*1/*1 vs *3/*3, P=0.038), which was strengthened after adjustment with age and body mass index (*1/*1 vs*3/*3, P=0.007; *1/*1 vs*1/*3, P=0.045). Significant interactions between the genotype and salt intake were observed in both SBP (P=0.046) and DBP (P=0.003). SBP and DBP were significantly associated with the level of salt intake in*3/*3 (P<0.001) but not in *1 carriers. *1carrier had higher blood pressure than *3/*3, but only in those with low salt intake. These results suggest that CYP3A5 variants may be a determinant of salt sensitivity of blood pressure in Japanese men.