alpha-Adducin Gly460Trp polymorphism is associated with low renin hypertension in younger subjects in the Ohasama study

The adducin saga: pleiotropic genomic targets for precision medicine in human hypertension-vascular, renal, and cognitive diseases

Hypertension is a leading risk factor for stroke, heart disease, chronic kidney disease, vascular cognitive impairment, and Alzheimer's disease. Previous genetic studies have nominated hundreds of genes linked to hypertension, and renal and cognitive diseases. Some have been advanced as candidate genes by showing that they can alter blood pressure or renal and cerebral vascular function in knockout animals; however, final validation of the causal variants and underlying mechanisms has remained elusive. This review chronicles 40 years of work, from the initial identification of adducin (ADD) as an ACTIN-binding protein suggested to increase blood pressure in Milan hypertensive rats, to the discovery of a mutation in ADD1 as a candidate gene for hypertension in rats that were subsequently linked to hypertension in man. More recently, a recessive K572Q mutation in ADD3 was identified in Fawn-Hooded Hypertensive (FHH) and Milan Normotensive (MNS) rats that develop renal disease, which is absent in resistant strains. ADD3 dimerizes with ADD1 to form functional ADD protein. The mutation in ADD3 disrupts a critical ACTIN-binding site necessary for its interactions with actin and spectrin to regulate the cytoskeleton. Studies using Add3 KO and transgenic strains, as well as a genetic complementation study in FHH and MNS rats, confirmed that the K572Q mutation in ADD3 plays a causal role in altering the myogenic response and autoregulation of renal and cerebral blood flow, resulting in increased susceptibility to hypertension-induced renal disease and cerebral vascular and cognitive dysfunction.

Genetics of Human Primary Hypertension: Focus on Hormonal Mechanisms

Increasingly, primary hypertension is being considered a syndrome and not a disease, with the individual causes (diseases) having a common sign-an elevated blood pressure. To determine these causes, genetic tools are increasingly employed. This review identified 62 proposed genes. However, only 21 of them met our inclusion criteria: (i) primary hypertension, (ii) two or more supporting cohorts from different publications or within a single publication or one supporting cohort with a confirmatory genetically modified animal study, and (iii) 600 or more subjects in the primary cohort; when including our exclusion criteria: (i) meta-analyses or reviews, (ii) secondary and monogenic hypertension, (iii) only hypertensive complications, (iv) genes related to blood pressure but not hypertension per se, (v) nonsupporting studies more common than supporting ones, and (vi) studies that did not perform a Bonferroni or similar multiassessment correction. These 21 genes were organized in a four-tiered structure: distant phenotype (hypertension); intermediate phenotype [salt-sensitive (18) or salt-resistant (0)]; subintermediate phenotypes under salt-sensitive hypertension [normal renin (4), low renin (8), and unclassified renin (6)]; and proximate phenotypes (specific genetically driven hypertensive subgroup). Many proximate hypertensive phenotypes had a substantial endocrine component. In conclusion, primary hypertension is a syndrome; many proposed genes are likely to be false positives; and deep phenotyping will be required to determine the utility of genetics in the treatment of hypertension. However, to date, the positive genes are associated with nearly 50% of primary hypertensives, suggesting that in the near term precise, mechanistically driven treatment and prevention strategies for the specific primary hypertension subgroups are feasible.

A Review on Adducin from Functional to Pathological Mechanisms: Future Direction in Cancer

Adducin (ADD) is a family of membrane skeleton proteins including ADD1, ADD2, and ADD3 that are encoded by distinct genes on different chromosomes. Adducin is primarily responsible for the assembly of spectrin-actin network that provides physical support to the plasma membrane and mediates signal transduction in various cellular physiological processes upon regulation by protein kinase C-dependent and calcium/calmodulin-dependent pathways. Abnormal phosphorylation, genetic variations, and alternative splicing of adducin may contribute to alterations in cellular functions involved in pathogenic processes. These alterations are associated with a wide range of diseases including cancer. This paper begins with a discussion on how adducin partakes in the structural formation of membrane skeleton, its regulation, and related functional characteristics, followed by a review on the pathogenesis of hypertension, biliary atresia, and cancer with respect to increased disease susceptibility mediated by adducin polymorphism and/or dysregulation. Given the functional diversity of adducin in different cellular compartments, we aim to provide a knowledge base whereby its pathophysiological roles can be better understood. More importantly, we aim to provide novel insights that may be of significance in turning the adducin model to clinical application.

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.

Virtual patients and sensitivity analysis of the Guyton model of blood pressure regulation: towards individualized models of whole-body physiology

Mathematical models that integrate multi-scale physiological data can offer insight into physiological and pathophysiological function, and may eventually assist in individualized predictive medicine. We present a methodology for performing systematic analyses of multi-parameter interactions in such complex, multi-scale models. Human physiology models are often based on or inspired by Arthur Guyton's whole-body circulatory regulation model. Despite the significance of this model, it has not been the subject of a systematic and comprehensive sensitivity study. Therefore, we use this model as a case study for our methodology. Our analysis of the Guyton model reveals how the multitude of model parameters combine to affect the model dynamics, and how interesting combinations of parameters may be identified. It also includes a "virtual population" from which "virtual individuals" can be chosen, on the basis of exhibiting conditions similar to those of a real-world patient. This lays the groundwork for using the Guyton model for in silico exploration of pathophysiological states and treatment strategies. The results presented here illustrate several potential uses for the entire dataset of sensitivity results and the "virtual individuals" that we have generated, which are included in the supplementary material. More generally, the presented methodology is applicable to modern, more complex multi-scale physiological models.

Genetic variation in renin predicts the effects of thiazide diuretics

BACKGROUND

While genetic variants of renin-angiotensin-aldosterone system (RAAS) may modify the blood pressure (BP) response to thiazide diuretics, there was no evidence of genetic variations in renin (REN) playing a role. This study aimed to address the potential effects of genetic variations of RAAS on the response to initial treatment of hydrochlorothiazide (HCTZ).

MATERIALS AND METHODS

We enrolled nondiabetic hypertensive patients with a systolic blood pressure (SBP) ≥140 or a diastolic blood pressure (DBP) ≥90mmHg, who were either previously untreated or unsatisfactorily treated. After lifestyle modification and diet instruction for 2weeks, 90 patients with persistently elevated BP were given HCTZ 50 mg every morning for 2 weeks. Single nucleotide polymorphism markers were selected from genes involving in RAAS, including rs7079 and rs699 of angiotensinogen, rs4293 and rs4353 of angiotensin-converting enzyme and rs1464816 and rs11240688 of REN.

RESULTS

The patients were divided into three groups according to the SBP response after HCTZ. The upper 1/3 responders had older age (P=0·035), higher SBP (P=0·039), higher pulse pressure (P=0·006) and lower plasma REN activity (PRA) (P=0·020) when compared with the lower 1/3 responders. Renin rs11240688 CC polymorphism (β=9·931, corrected P=0·012), Log PRA (β=7·451, P=0·004) and baseline SBP (β=0·299, P=0·006) were the independent predictors for the BP lowering response.

CONCLUSIONS

In addition to PRA, renin rs11240688 CC polymorphism may also independently predict the effect of HCTZ.

Gly460Trp polymorphism of the ADD1 gene and essential hypertension in an Indian population: A meta-analysis on hypertension risk

BACKGROUND:

Essential hypertension is a complex genetic trait. Genetic variant of alpha adducin (ADD1) gene have been implicated as a risk factor for hypertension. Given its clinical significance, we investigated the association between ADD1 Gly460Trp gene polymorphism and essential hypertension in an Indian population. Further, a meta-analysis was carried out to estimate the risk of hypertension.

METHODS:

In the current study, 432 hypertensive cases and 461 healthy controls were genotyped for the Gly460Trp ADD1 gene polymorphism. Genotyping was determined by real time PCR using Taqman assay. Multiple logistic regression analysis was used to detect the association between Gly460Trp polymorphism and hypertension.

RESULTS:

No significant association was found in the genotype and allele distribution of Gly460Trp polymorphism with hypertension in our study. A total of 15 case-control studies were included in the meta-analysis. There was no evidence of the association of Gly460Trp polymorphism with hypertension in general or in any of the sub group.

CONCLUSIONS:

We found that the Gly460Trp polymorphism is not a risk factor for essential hypertension in a south Indian Tamilian population. However, the role of ADD1 polymorphism may not be excluded by a negative association study. Further, large and rigorous case-control studies that investigate gene–gene–environment interactions may generate more conclusive claims about the molecular genetics of hypertension.

Dopamine and renal function and blood pressure regulation

Dopamine is an important regulator of systemic blood pressure via multiple mechanisms. It affects fluid and electrolyte balance by its actions on renal hemodynamics and epithelial ion and water transport and by regulation of hormones and humoral agents. The kidney synthesizes dopamine from circulating or filtered L-DOPA independently from innervation. The major determinants of the renal tubular synthesis/release of dopamine are probably sodium intake and intracellular sodium. Dopamine exerts its actions via two families of cell surface receptors, D1-like receptors comprising D1R and D5R, and D2-like receptors comprising D2R, D3R, and D4R, and by interactions with other G protein-coupled receptors. D1-like receptors are linked to vasodilation, while the effect of D2-like receptors on the vasculature is variable and probably dependent upon the state of nerve activity. Dopamine secreted into the tubular lumen acts mainly via D1-like receptors in an autocrine/paracrine manner to regulate ion transport in the proximal and distal nephron. These effects are mediated mainly by tubular mechanisms and augmented by hemodynamic mechanisms. The natriuretic effect of D1-like receptors is caused by inhibition of ion transport in the apical and basolateral membranes. D2-like receptors participate in the inhibition of ion transport during conditions of euvolemia and moderate volume expansion. Dopamine also controls ion transport and blood pressure by regulating the production of reactive oxygen species and the inflammatory response. Essential hypertension is associated with abnormalities in dopamine production, receptor number, and/or posttranslational modification.

Alpha-adducin Gly460Trp polymorphism and hypertension risk: a meta-analysis of 22 studies including 14303 cases and 15961 controls

Background

No clear consensus has been reached on the alpha-adducin polymorphism (Gly460Trp) and essential hypertension risk. We performed a meta-analysis in an effort to systematically summarize the possible association.

Methodology/Principal Findings

Studies were identified by searching MEDLINE and EMBASE databases complemented with perusal of bibliographies of retrieved articles and correspondence with original authors. The fixed-effects model and the random-effects model were applied for dichotomous outcomes to combine the results of the individual studies. We selected 22 studies that met the inclusion criteria including a total of 14303 hypertensive patients and 15961 normotensive controls. Overall, the 460Trp allele showed no statistically significant association with hypertension risk compared to Gly460 allele (P = 0.69, OR = 1.02, 95% CI 0.94–1.10, P_{heterogeneity}<0.0001) in all subjects. Meta-analysis under other genetic contrasts still did not reveal any significant association in all subjects, Caucasians, East Asians and others. The results were similar but heterogeneity did not persist when sensitivity analyses were limited to these studies.

Conclusions/Significance

Our meta-analysis failed to provide evidence for the genetic association of α-adducin gene Gly460Trp polymorphism with hypertension. Further studies investigating the effect of genetic networks, environmental factors, individual biological characteristics and their mutual interactions are needed to elucidate the possible mechanism for hypertension in humans.

Genetic polymorphisms related to the renin-angiotensin-aldosterone system and response to antihypertensive drugs

IMPORTANCE OF THE FIELD

Only 23 - 41% of hypertensive patients receiving antihypertensive drugs achieve adequate blood pressure control. Multiple physiological systems regulate blood pressure and variation in genes involved in these systems may account for enhanced or diminished blood pressure lowering response to antihypertensive therapy.

AREAS COVERED IN THIS REVIEW

We explored explanations for variation in blood pressure response to antihypertensive drugs by linking genetic polymorphisms in renin-angiotensin-aldosterone system (RAAS) genes to antihypertensive drug response on intermediate parameters (e.g., potassium excretion, aldosterone levels). A MEDLINE search (1966 - 2008) was performed to identify publications reporting effects of genetic polymorphisms in the RAAS on antihypertensive drug response with regard to intermediate parameters.

WHAT THE READER WILL GAIN

With regard to the ACE insertion/deletion and the angiotensinogen -217G/A polymorphism variation in blood pressure response could be explained by effects on intermediate parameters. However, most studies that were identified with our search varied in study design, population and outcome, which complicate adequate comparisons.

TAKE HOME MESSAGE

Little evidence is available that explains these pharmacogenetic interactions. In the future, a better understanding of these mechanisms should provide a more solid evidence base for the individualized hypertension treatment based on genetic variation.

Promoter Polymorphism of RGS2 Gene Is Associated with Change of Blood Pressure in Subjects with Antihypertensive Treatment: The Azelnidipine and Temocapril in Hypertensive Patients with Type 2 Diabetes Study

We performed a prospective study to examine the genetic effect on the response to a calcium (Ca) channel blocker, azelnidipine and an ACE inhibitor, temocapril treatment in patients with hypertension, as a part of the prior clinical trial, the Azelnidipine and Temocapril in Hypertensive Patients with Type 2 Diabetes Study (ATTEST). Methods and Results. All subjects who gave informed consent for genetic research were divided into two groups: the subjects treated with azelnidipine or temocapril, for 52 weeks. We selected 18 susceptible genes for hypertension and determined their genotypes using TaqMan PCR method. RNA samples were extracted from peripheral blood, and quantitative real time PCR for all genes was performed using TaqMan method. One of the polymorphisms of the RGS2 gene was extracted as being able to influence the effect of these treatments to reduce BP. At eight weeks, BP change showed a significant interaction between the A-638G polymorphism of Regulator of G protein signaling-2 (RGS2) gene and treatment with azelnidipine or temocapril. There was no gene whose expression was associated with BP phenotypes or the polymorphisms of each gene. Conclusions. A-638G polymorphism of the RGS-2 gene could be a predictive factor for therapeutic performance of Ca channel blockers.

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.

Dopamine and G protein-coupled receptor kinase 4 in the kidney: role in blood pressure regulation

Complex interactions between genes and environment result in a sodium-induced elevation in blood pressure (salt sensitivity) and/or hypertension that lead to significant morbidity and mortality affecting up to 25% of the middle-aged adult population worldwide. Determining the etiology of genetic and/or environmentally-induced high blood pressure has been difficult because of the many interacting systems involved. Two main pathways have been implicated as principal determinants of blood pressure since they are located in the kidney (the key organ responsible for blood pressure regulation), and have profound effects on sodium balance: the dopaminergic and renin-angiotensin systems. These systems counteract or modulate each other, in concert with a host of intracellular second messenger pathways to regulate sodium and water balance. In particular, the G protein-coupled receptor kinase type 4 (GRK4) appears to play a key role in regulating dopaminergic-mediated natriuresis. Constitutively activated GRK4 gene variants (R65L, A142V, and A486V), by themselves or by their interaction with other genes involved in blood pressure regulation, are associated with essential hypertension and/or salt-sensitive hypertension in several ethnic groups. GRK4γ 142Vtransgenic mice are hypertensive on normal salt intake while GRK4γ 486V transgenic mice develop hypertension only with an increase in salt intake. GRK4 gene variants have been shown to hyperphosphorylate, desensitize, and internalize two members of the dopamine receptor family, the D(1) (D(1)R) and D(3) (D(3)R) dopamine receptors, but also increase the expression of a key receptor of the renin-angiotensin system, the angiotensin type 1 receptor (AT(1)R). Knowledge of the numerous blood pressure regulatory pathways involving angiotensin and dopamine may provide new therapeutic approaches to the pharmacological regulation of sodium excretion and ultimately blood pressure control.

Association of alpha-adducin Gly460Trp polymorphism with coronary artery disease in a Korean population

OBJECTIVE

Coronary artery disease is caused by multiple genetic and environmental factors. The disease is also closely associated with cardiovascular conditions such as hypertension. In order to investigate any possible role of hypertension candidate genes in the disease development and progression, we examined the association of the polymorphisms of 31 hypertension candidate genes with coronary artery disease.

METHODS

Genetic polymorphisms of 31 hypertension candidate genes were initially screened by resequencing DNA samples from 24 unrelated individuals in a Korean population. Association analysis was performed using 1284 unrelated Korean men, including 749 coronary artery disease subjects and 535 normal healthy controls.

RESULTS

We identified a total of 409 single nucleotide polymorphisms including 40 nonsynonymous single nucleotide polymorphisms, 32 insertions/deletions and four microsatellites. Among 40 nonsynonymous single nucleotide polymorphisms, 29 were examined for an association with coronary artery disease. A significant association with coronary artery disease was observed in a polymorphism of the ADD1 gene (Gly460Trp; +29017G/T) (odds ratio 0.71-0.81; P = 0.01-0.04). The same polymorphism was also associated with the number of arteries with significant coronary artery stenosis in the coronary artery disease patients (P = 0.01) as well as the increase in systolic blood pressure (P = 0.02).

CONCLUSIONS

The ADD1 Gly460Trp polymorphism is significantly associated with an increased risk of coronary artery disease as well as blood pressure, indicating that ADD1 plays a role in the pathogenesis of coronary artery disease as well as hypertension.

Definition of phenotype

Definition of the phenotype is crucial in designing any genetic study, especially an association study, intended to detect the disease predisposing genes. In this chapter, we review the different types of phenotypes such as discrete or continuous and discuss the issues impacting on the phenotype definition related to study design, specifically, the impact of diagnostic error (misclassification) in case-control studies and measurement error in continuous traits. We show that the power of a study depends heavily on the phenotype measured and that misclassification or measurement error can dramatically reduce the power. We also suggest some possible responses to these challenges.

Adducin polymorphisms and the treatment of hypertension

Hypertension is an important public health problem affecting more than 50 million individuals in the USA alone. The most common form, essential hypertension, results from the complex interplay between genetic predisposition and environmental influences. Epidemiological, migration, intervention and genetic studies in humans and animals provide very strong evidence of a causal link between high salt intake and high blood pressure. One of the candidate genes for salt-sensitive hypertension is adducin. Adducin is a heterodimeric cytoskeleton protein, the three subunits of which are encoded by genes (ADD1, ADD2 and ADD3) that map to three different chromosomes. A long series of parallel studies in the Milan hypertensive rat strain model of hypertension and humans indicated that an altered adducin function might cause hypertension through enhanced constitutive tubular sodium reabsorption. An example of a prospective efficacy of pharmacogenetics and pharmacogenomics is the detection and impact of adducin polymorphisms on hypertension. In particular, the selective advantages of diuretics in preventing myocardial infarction and stroke over other antihypertensive therapies that produce a similar blood pressure reduction in carriers of the mutated adducin may support new strategies aimed at optimizing the use of new antihypertensive agents for the prevention of hypertension-associated organ damage.

Single-Nucleotide Polymorphisms for Diagnosis of Salt-Sensitive Hypertension

Background: Salt-sensitive (SS) hypertension affects &gt;30 million Americans and is often associated with low plasma renin activity. We tested the diagnostic validity of several candidate genes for SS and low-renin hypertension.

Methods: In Japanese patients with newly diagnosed, untreated hypertension (n = 184), we studied polymorphisms in 10 genes, including G protein–coupled receptor kinase type 4 (GRK4), some variations of which are associated with hypertension and impair D1 receptor (D1R)-inhibited renal sodium transport. We used the multifactor dimensionality reduction method to determine the genotype associated with salt sensitivity (≥10% increase in blood pressure with high sodium intake) or low renin. To determine whether the GRK4 genotype is associated with impaired D1R function, we tested the natriuretic effect of docarpamine, a dopamine prodrug, in normotensive individuals with or without GRK4 polymorphisms (n = 18).

Results: A genetic model based on GRK4 R65L, GRK4 A142V, and GRK4 A486V was 94.4% predictive of SS hypertension, whereas the single-locus model with only GRK4 A142V was 78.4% predictive, and a 2-locus model of GRK4 A142V and CYP11B2 C-344T was 77.8% predictive of low-renin hypertension. Sodium excretion was inversely related to the number of GRK4 variants in hypertensive persons, and the natriuretic response to dopaminergic stimulation was impaired in normotensive persons having ≥3 GRK4 gene variants.

Conclusions: GRK4 gene variants are associated with SS and low-renin hypertension. However, the genetic model predicting SS hypertension is different from the model for low renin, suggesting genetic differences in these 2 phenotypes. Like low-renin testing, screening for GRK4 variants may be a useful diagnostic adjunct for detection of SS hypertension.

Combined analysis of polymorphisms in angiotensinogen and adducin genes and their effects on hypertension in a Japanese sample: The Shigaraki Study

We examined the interactions between lifestyle and polymorphisms of salt-sensitive genes and their effects on hypertension in a general Japanese sample (The Shigaraki Study). The study group consisted of 2,902 subjects who underwent a medical examination in 1999 in Shigaraki, a suburban area in Shiga. Among 1,647 subjects not receiving antihypertensive medication, in a combined analysis of angiotensinogen (AGT) and adducin (ADD1) polymorphisms, double homozygosity of 235Thr or 460Trp was not found to be associated with hypertension. A multiple logistic regression analysis showed that age (odds ratio [OR]: 1.07, 95% confidence interval [95% CI]: 1.06-1.08), body mass index (BMI) (OR: 1.18, 95% CI: 1.13-1.23), alcohol consumption (OR: 1.39, 95% CI: 1.16-1.66), family history of hypertension (OR: 1.57, 95% CI: 1.18-2.07), and combined AGT M235T Thr/Thr and ADD1 Trp/Trp polymorphisms (OR: 1.37, 95% CI: 1.03-1.82) were associated with hypertension. However, there was no interaction between eating salty food and combined AGT and ADD1 polymorphisms. Furthermore, eating salty food was not associated with hypertension in a multivariate analysis. Therefore, a combination of the AGT and ADD1 polymorphisms appears to be associated with hypertension. However, a simple questionnaire regarding salt intake was not sufficient to confirm the relationship between salt intake and hypertension and/or salt-sensitive genes.

Genetic variations of tubular sodium reabsorption leading to “primary” hypertension: from gene polymorphism to clinical symptoms

The definition of the most appropriate strategy to demonstrate causation of a given genetic-molecular mechanism in a complex multifactorial polygenic disease like hypertension is hampered by the underestimation of the complexity arising from the genetic and environmental interactions. To disentangle this complexity, we developed a strategy based on six steps: 1) isolation of a rodent model of hypertension (Milan hypertensive strain and Milan normotensive strain) that shares some pathophysiological abnormalities with human primary hypertension; 2) definition in the model of the sequence of events linking these abnormalities to a genetic molecular mechanism; 3) determination of the polymorphism of the three adducin genes discovered in the model both in rats and in humans; 4) comparison at biochemical and physiological levels between the rodent models and the hypertensive carriers of the “mutated” gene variants; 5) evaluation of the impact of the adducin genes in hypertension and its organ complications with association and linkage studies in humans, also considering the genetic and environmental interactions; and 6) development of a pharmacogenomic approach aimed at establishing the therapeutic benefit of a drug interfering with the sequence of events triggered by adducin and their effect's size. The bulk of data obtained demonstrates the importance of a multidisciplinary approach considering a variety of genetic and environmental interactions. Adducin functions within the cells as a heterodimer composed of a combination of three subunits. Each of these subunits is coded by genes mapping to different chromosomes. Therefore, the interaction among these genes, taken together with the interactions with other modulatory genes or with the environment, is indispensable to establish the adducin clinical impact. The hypothesis that adducin polymorphism favors the development of hypertension via an increased tubular sodium reabsorption is well supported by a series of consistent experimental and clinical data. Many mechanistic aspects, underlying the link between these genes and clinical symptoms, need to be clarified. The clinical effect size of adducin must be established also with the contribution of pharmacogenomics with a drug that selectively interferes with the sequence of events triggered by the mutated adducin.

The thiazide-sensitive Na(+)-Cl(-) cotransporter gene, C1784T, and adrenergic receptor-beta3 gene, T727C, may be gene polymorphisms susceptible to the antihypertensive effect of thiazide diuretics

The response of blood pressure to thiazide diuretics (TZDs) differs among individuals. The prediction of the antihypertensive effect of TZDs is important for realizing individualized therapy in the management of hypertension. The aim of this study was to identify the single nucleotide polymorphisms (SNPs) susceptible to the antihypertensive effect of TZDs, particularly focusing on genes related to water-electrolyte absorption in the kidney. Seventy-six outpatients (mean age, 65.4+/-9.0 years) with essential hypertension (EHT) taking TZDs were retrospectively assessed. We defined as responders (R) those whose mean blood pressure was lowered by more than 5 mmHg after the use of TZDs. Forty-eight SNPs in 17 genes (ADD1, GNB3, TSC [SLC12A3], MLR [NR3C2], NCX1 [SLC8A1], WNK1, WNK4, AGT, ACE, AT1 [AGTR1], CYP11B2, ADRB1, ADRB2, ADRB3, ADRA1A, ADRA1B, ADRA2A) were genotyped in the 76 patients. The SNPs in TSC, MLR, NCX1, WNK1, and WNK4 were identified by direct sequencing and those with minor frequencies of greater than 5% were genotyped in this study. The comparison of polymorphism prevalence between R and non-responders (NR) showed significant differences in TSC C1784T (C allele vs. T allele, odds ratio (OR)=3.81, p =0.016, confidence interval (CI): 1.25-11.63) and ADRB3 T727C (Trp64Arg) (T allele vs. C allele, OR=4.59, p =0.005, CI: 1.54-13.68). The blood pressure (BP) in patients homozygous for the major alleles of both TSC C1784T and ADRB3 T727C were significantly reduced by TZD treatment; however, the BP in those homozygous for the minor allele and heterozygous (TSC C1784T: TT+CT; ADRB3 T727C: CC+CT) for both SNPs were not significantly changed after TZD treatment. Both newly detected TSC C1784T and ADRB3 T727C are gene polymorphisms susceptible to the antihypertensive effect of TZDs in patients with EHT. Thus, the prediction of BP reduction by TZDs may be possible by evaluating these two SNPs.

Relationship of bradykinin B2 receptor gene polymorphism with essential hypertension and left ventricular hypertrophy

The bradykinin B2 receptor shows a protective role in the development of hypertension and renal and cardiovascular complications. It was recently reported that a polymorphism of the bradykinin B2 receptor gene (BDKRB2) is a genetic predisposing factor for hypertension and cardiovascular disease. The aim of this study was to examine the relationship of a polymorphism (-58 T/C and exon 1 +9/-9) of BDKRB2, and an insertion/deletion polymorphism (I/D) of the angiotensin converting enzyme gene (ACE) with essential hypertension and cardiovascular mortality in the Japanese population. Genotyping was carried out in 275 hypertensive and 441 normotensive subjects. Left ventricular hypertrophy (LVH) was detected by ECG in 242 untreated patients with hypertension. All participants were Japanese and gave their written informed consent. The polymorphism (-58 T/C) in the promoter region of the BDKRB2 was determined using the TaqMan-polymerase chain reaction (PCR) method, the exon 1 +9/-9 polymorphism of the BDKRB2 and I/D polymorphism of the ACE were monitored by PCR and gel electrophoresis. The genotypes and allelic frequencies were in Hardy-Weinberg equilibrium. The polymorphism (-58 T/C) in the promoter of the BDKRB2 was associated with LVH in the hypertensive group (n =242) (p =0.048; chi2 =3.9; odds ratio: 1.8; 95% confidence interval (CI): 1.0-3.3). Furthermore, the frequency of LVH in hypertensives was significantly higher in the subjects with both the BDKRB2 CC and ACE D allele than those with other genotypes (p =0.002, chi2 =9.4). However, no relationship could be found between polymorphism of the BDKRB2 (p =0.86, chi2 =0.3) or the ACE (p =0.21, chi2 =3.1) and hypertension in this group of subjects. These results suggest that the polymorphism (-58 T/C) in the promoter region of BDKRB might be a risk factor and might have a synergetic effect with the ACE for LVH in hypertensives, but it is not associated with hypertension in the Japanese population.

Genetic variations related to hypertension: a review

Hypertension is a complex multifactorial disorder with genetic, environmental and demographic factors contributing to its prevalence. The genetic element contribution to blood pressure variation ranges from 30 to 50%. Therefore, identifying hypertension susceptibility genes will help understanding the pathophysiology of the disease. In addition to the potential impact of genomic information in selecting antihypertensive drug therapy, it may also help in recognizing those at risk of developing the disease, which may lead to new preventive approaches. Several strategies and methods have been used to identify hypertension susceptibility genes. Currently, genetic analysis of such data produced complex results, which makes it difficult to draw final conclusion on the use of genomic data in management of hypertension. This review attempts to summarize present known genetic variations that may be implicated in the pathogenesis of hypertension and to discuss various research strategies used to identify them. It also highlights some of the opportunities and challenges, which may be encountered in interpreting the value of these genetic variations to improve management of hypertension.

Association between angiotensin II type 1 receptor gene polymorphism and essential hypertension: the Ohasama Study

Gene targeting approaches have suggested that the angiotensin II type 1 receptor (AT1R) is involved in blood pressure (BP) regulation and modulation of the effect of angiotensin II. The A1166C polymorphism of the AT1 receptor gene (AT1R/A1166C) is associated with hypertension in Caucasians, but not in Japanese. The goal of this study, the Ohasama Study, was to examine the association between AT1R/A1166C and hypertension, especially home BP, in the Japanese general population. The Ohasama Study was a cohort study based on Japanese rural residents of Ohasama Town in the northern part of Japan. Subjects who gave informed consent to the study protocol and genetic analysis were recruited. Home BP was measured twice in the morning within 1 h of waking up and in the evening just before going to bed. The TaqMan polimerase chain reaction (PCR) method clearly determined AT1R/A1166C genotypes (n =1,207). The genotype distribution of AT1R/A1166C was as follows: AA 84%; AC 15%; CC 1%. There was almost no difference in baseline characteristics among the AT1R genotypes (AA, AC, CC). In the subjects not receiving antihypertensive medication (n =817), both casual BP and home BP were not different among the AT1R genotypes after adjusting for confounding factors (age, sex, body mass index, current smoking habit and current alcohol consumption). The frequency of hypertension showed no difference among AT1R genotypes after adjusting for confounding factors, though the AC and CC genotypes were more frequent in hypertensives than in normotensives. Our data suggested that the AT1R/A1166C polymorphism is not a major genetic predisposing factor for hypertension in Japanese.

Adducin Polymorphism

Adducin is a heterodymeric cytoskeleton protein, the 3 subunits of which are encoded by genes ( ADD1 , ADD2 , ADD3 ) mapping to 3 different chromosomes. A long series of parallel studies in the Milan hypertensive rat strain model of hypertension and humans indicated that an altered adducin function may cause hypertension through an enhanced constitutive tubular sodium reabsorption. Six human linkage studies showed positive results when a DNA marker mapping to 30 kb from the ADD1 locus or single-nucleotide polymorphisms (SNPs) of 1 of the 3 adducin genes were considered either alone or in combination with each other or angiotensin-converting enzyme (ACE) D allele or salt intake. When DNA markers mapping at much larger distance from the ADD1 locus were used, negative results were found by 4 studies. Positive results were also obtained in 18 of 20 association studies that, in addition to blood pressure, investigated variables reflecting body sodium or the renin-angiotensin system. Mixed results regarded case-control studies or studies in predominantly normotensive populations that did not consider the above-mentioned variables. Four of 5 studies showed a selective beneficial effect of diuretics in carriers of the mutated ADD1. Twelve of 16 studies found that ADD1 polymorphism alone or in combination with that of ACE positively associates with stroke or coronary heart disease or renal or vascular dysfunctions. In conclusion, when context is taken into account, the impact of adducin in hypertension and its related disorders is clear.

G2736A polymorphism of thiazide-sensitive Na-Cl cotransporter gene predisposes to hypertension in young women

OBJECTIVE

The thiazide-sensitive Na-Cl cotransporter (TSC) is located in the distal renal tubules. Several mutations of the TSC gene cause Gitelman's syndrome, which is an autosomal recessive disease characterized by low blood pressure and hypokalemia. Recently, an association between TSC gene polymorphisms (Arg904Gln, G2736A; Thr465Thr, C1420T; Gly264Ala, G816C) and essential hypertension has been reported in Sweden. We examined the genetic involvement of the TSC gene in essential hypertension in Japanese.

DESIGN

Participants were recruited from outpatients of Osaka University Hospital. We investigated 386 hypertensive and 371 normotensive subjects.

METHODS

Genotypes of TSC polymorphisms (G2736A, C1420T, G816C) were determined by the TaqMan polymerase chain reaction (PCR) method, and statistical significance was examined using JMP 5.0.1J (SAS Institute Inc., Cary, North Carolina, USA). The allele frequency of A2736 and T1420 was 6.0 and 3.0%, respectively, whereas we could not detect the G816C polymorphism in this study. Only the G2736A polymorphism was significantly associated with the prevalence of hypertension (P <0.04), and the estimated odds ratio was 1.8 (95% confidence interval, 1.1-3.0) in A2736 allele carriers. The odds ratio for hypertension in A2736 carriers was increased to 2.2 (1.1-4.9) in women (n=413), and further to 3.3 (1.4-8.0) in women with early onset of hypertension (< or = 50 years old). In addition, all subjects with the homozygous A2736 allele in this study (n=2) and the Swedish study (n=5) were hypertensive.

CONCLUSION

G2736A polymorphism of the TSC gene is a genetic predisposing factor for essential hypertension in Japanese women.

Genetic predisposition to salt-sensitivity: a systematic review

PURPOSE

To assess the role of genetic polymorphisms in salt sensitivity of blood pressure.

DATA IDENTIFICATION

We conducted a systematic review by searching the Medline literature from March 1993 to June 2003. Each paper was scrutinized and data concerning study population, method of salt sensitivity testing, blood pressure measurement, definition of salt sensitivity, and effects were extracted.

STUDY SELECTION AND DATA EXTRACTION

A total of 23 studies met the inclusion criteria. There was considerable heterogeneity in the method of salt sensitivity testing among the studies. Due to these differences, it was impossible to perform pooled analyses by genetic variants. Detailed investigation was done on the alpha-adducin Gly460Trp, ACE I/D, angiotensinogen M235T, G protein beta 3 C825T, aldosterone synthase gene and 11 beta-hydroxysteroid dehydrogenase type 2 G534A polymorphism.

RESULTS AND CONCLUSIONS

Our analysis shows that the 460Trp variant of the alpha-adducin polymorphism is probably associated with a sodium-sensitive form of hypertension, while the polymorphisms of the angiotensin II type 1 receptor gene and the -344C/T variant of the aldosterone synthase gene are not associated with this phenotype. In view of the lack of standardization in salt sensitivity testing, we propose uniformity in study design in these type of studies.

Blood pressure in relation to three candidate genes in a Chinese population

OBJECTIVE

In a prospective analysis of a Caucasian population, we recently found that the genes encoding angiotensin-converting enzyme (ACE, I/D polymorphism), alpha-adducin (Gly460Trp) and aldosterone synthase (-344C/T) jointly influence the incidence of hypertension. We therefore investigated the association between blood pressure and these three genes in a Chinese population.

METHODS

We genotyped 479 Han Chinese from 125 nuclear families recruited in northern China via random sampling (approximately 75%) and at specialized hypertension clinics (approximately 25%). We performed population-based and family-based association analyses using generalized estimating equations (GEE) and the quantitative transmission disequilibrium test (QTDT), respectively, while controlling for covariables.

RESULTS

The participants included 239 (49.9%) women and 132 (27.6%) hypertensive patients, of whom 77 took antihypertensive drugs. The blood pressure, measured at the subjects' homes, averaged 126/80 mmHg. Mean values of urinary sodium, potassium and Na/K ratio were 226 mmol/day, 37 mmol/day and 6.31, respectively. In adjusted GEE analyses, systolic blood pressure was 9.3 mmHg (95% confidence interval 3.6-15.0 mmHg; P = 0.001) and 14.6 mmHg (95% confidence interval 3.4-25.8 mmHg; P = 0.01) higher in the ACE DD than II subjects among the alpha-adducin TrpTrp (n = 141) and aldosterone synthase CC (n = 33) homozygotes, respectively (P < or =0.05 for interactions of the ACE genotype with the alpha-adducin and aldosterone synthase polymorphisms). Among 40 informative offspring homozygous for the alpha-adducin Trp allele, systolic blood pressure was significantly associated with transmission of the ACE D allele (beta = 5.5 mmHg; P = 0.046).

CONCLUSIONS

The ACE I/D, alpha-adducin Gly460Trp and aldosterone synthase -344C/T polymorphisms interact to influence systolic blood pressure in Chinese, suggesting that these genes might indeed predispose to hypertension, especially in an ecogenetic context characterized by a high salt intake.

Alpha-adducin Gly460Trp polymorphism and essential hypertension in Korea

Previous studies have suggested that the Gly460Trp polymorphism of the alpha-adducin gene (ADD-1) is associated with salt sensitivity and primary hypertension. The results of linkage or association studies of ADD-1 of different populations are controversial. This study investigated the relationship between the Gly460Trp polymorphism of ADD-1 and essential hypertension in a Korean population. The subjects (n=903) were participants in a population-based study in Jangseong County, Korea. The Gly460Trp polymorphism of ADD-1 was determined using a polymerase chain reaction method. The frequency of the 460Trp allele was 59.4% in normotensives and 61.1% in hypertensives (p=0.523). The frequencies of the genotypes did not differ significantly between the hypertensive and normotensive groups (16.3% Gly/Gly, 45.8% Gly/Trp, and 38.0% Trp/Trp in normotensives; 16.2% Gly/Gly, 45.8% Gly/Trp, and 38.0% Trp/Trp in hypertensives; p=0.928). After adjusting for other risk factors, Gly/Trp and Trp/Trp were not associated with hypertension (OR 1.00, 95% CI 0.65-1.53, Gly/Trp vs. Gly/Gly; OR 1.22, 95% CI 0.79-1.90, Trp/Trp vs. Gly/Gly). These findings suggest that the Gly460Trp polymorphism of ADD-1 is not associated with hypertension.

Association between hypertension and the alpha-adducin, beta1-adrenoreceptor, and G-protein beta3 subunit genes in the Japanese population; the Suita study

This study focused on 3 genetic polymorphisms that have previously been implicated in hypertension: the alpha-adducin (ADD1/Gly460Trp), beta1-adrenoreceptor (ADRB1/Arg389Gly), and G-protein beta3 subunit (GNB3/C825T) gene polymorphisms. We determined genetic variants using the TaqMan system in a large cohort representing the general population in Japan (867 males, 1,013 females). Logistic analysis indicated that the ADD1/ G460W polymorphism was associated with hypertension in female subjects. The odds ratio of the WW genotype for hypertension was 1.53 (95%Cl, 1.12-2.08) over the WG+GG genotype (p=0.0070, p corrected (p(c)) =0.0420 corrected by the Bonferroni method). The ADRB1/R389G polymorphism tended to be associated with hypertensive status in male subjects (p=0.0117, p(c)=0.0702). The odds ratio of the GG genotype for hypertension was 0.38 (95%CI, 0.167-0.780) over the RR+RG genotype. The GNB3/C825T polymorphism was not associated with hypertensive status in either male or female subjects. The present results do not agree with those in previous reports. Almost all common variants may have only a modest effect on common diseases, and a single study even employing 1,880 subjects may lack the statistical power to detect a real association. Accordingly, it will be necessary to verify the association between these three genes and hypertension using a larger number of subjects from the Suita cohort or another population.

Renal function in relation to three candidate genes in a Chinese population

We recently found in a white population that the genes encoding angiotensin-converting enzyme (ACE, I/D polymorphism), alpha-adducin (Gly460Trp), and aldosterone synthase (-344C/T) jointly influence renal function. We therefore investigated in a Chinese population the associations between the serum concentrations of creatinine and uric acid and these three genetic polymorphisms. We genotyped 471 ethnic Han Chinese subjects from 125 nuclear families recruited in northern China via random population sampling (75%) and at specialized hypertension clinics (25%). We performed population-based and family-based association analyses using generalized estimating equations (GEE) and quantitative transmission disequilibrium test (QTDT), respectively, while controlling for covariables. The participants were 39.7 years old and included 235 women (49.9%). The blood pressure measured at the subjects' homes averaged 126/80 mmHg. Mean values were 71 micromol/l for serum creatinine, 111 ml min(-1) 1.73 m(-2) for calculated creatinine clearance, and 236 micromol/l for serum uric acid. With adjustment for covariables, GEE analyses of single genes demonstrated that serum uric acid, but not serum creatinine, was positively associated with the ACE D allele. Serum uric acid concentrations were 15.8 micromol/l (95% confidence interval 3.3-28.2) and 25.7 micromol/l (11.1-40.2) higher in DD homozygotes than in ID and II subjects, respectively. Further GEE analyses of the three genes combined showed that the association between serum uric acid and the ACE polymorphism was confined to carriers of the alpha-adducin Gly and/or aldosterone synthase C alleles. Sensitivity analyses in parents and offspring separately as well as QTDT analyses were confirmatory. Among 114 informative offspring carrying the alpha-adducin Gly allele serum uric acid was significantly and positively associated with the transmission of the ACE D allele (beta=20.7 micromol/l). In conclusion, the present study extends our previous findings on the combined effects of the three candidate genes and supports the concept that these genetic polymorphisms jointly influence renal function.

Alpha-adducin gene polymorphism is associated with essential hypertension in Chinese: a case-control and family-based study

OBJECTIVE

A polymorphism at position 460(G <-- W) of the alpha-adducin gene was found to be associated with essential hypertension in some but not all studies. The aim of the present study was to further investigate the association of the alpha-adducin 460W allele with essential hypertension in Chinese population.

METHODS

Individuals from a population-based sample (n = 748) and 95 nuclear families and 47 discordant sibships were studied by questionnaire as well as by physical examination and biochemical analyses. The alpha-adducin gene G460W polymorphism was determined by polymerase chain reaction and restriction enzyme digestion. Chi-square test, one-way analysis of variance, logistic regression, linear regression, haplotype-based haplotype relative risk and transmission/disequilibrium test analyses were used to determine the association between the alpha-adducin G460W polymorphism and essential hypertension.

RESULTS

In the case-control study, the prevalence of hypertension was higher in individuals with the WW genotype (40.0%) as compared with those with the GW and GG genotype (31.7%) (chi2 = 4.768, P = 0.029, odds ratio = 1.43). Adjusted for the conventional risk factors of hypertension, alpha-adducin polymorphism still plays an independent role on systolic blood pressure. We confirmed the results of our case-control study by observing a significant preferential transmission of the 460W allele of the alpha-adducin to the affected subjects in another northern Chinese population (for haplotype-based haplotype relative risk, chi2 = 6.24, P = 0.01; and for the transmission/disequilibrium test, chi2 = 4.69, P = 0.03).

CONCLUSIONS

The present findings show a positive association between the alpha-adducin G460W polymorphism and essential hypertension in a northern Chinese population. This evidence indicates that the alpha-adducin gene may be a susceptible gene to essential hypertension.

Decrease in Hypothalamic Gamma Adducin in Rat Models of Hypertension

We have previously shown that a decrease in hypothalamic gamma adducin (γ-adducin) is associated with hypertension in the spontaneously hypertensive rat (SHR). In view of many inherent issues with SHR, our objective in the present study was to provide proof of this concept with the use of 2 nongenetic rat models of hypertension. Subcutaneous angiotensin II (Ang II) infusion for 2 weeks (55 ng/kg per day) resulted in an increase in blood pressure (BP) of 18 mm Hg. This was associated with a 70% decrease in hypothalamic γ-adducin. Concomitant administration of losartan attenuated the development of hypertension and a decrease in γ-adducin. Deoxycorticosterone acetate salt-induced hypertension also caused a 70% decrease in hypothalamic γ-adducin. Finally, neuronal cultures from neonatal rat brains were incubated with 100 nmol/L Ang II for 4 hours to mimic the in vivo Ang II infusion rat model. This chronic incubation with Ang II resulted in a 60% decrease in the neuronal γ-adducin. Taken together, these observations strengthen our hypothesis that a decrease in hypothalamic γ-adducin is linked to hypertension.

Pharmacogenomics of diuretic drugs: data on rare monogenic disorders and on polymorphisms and requirements for further research

This review summarizes the current status of our knowledge about the role of pharmacogenetic variation in response to diuretics and suggests future research topics for the field. Genes with a role in the pharmacokinetics of most diuretics are renal drug transporters, especially OAT1, OAT3 and OCT2 (genes SLC22A6, SLC22A8 and SLC22A2) whereas variants in carbonic anhydrase (CA), cytochrome P450 enzymes and sulfotransferases are relevant only for specific substances. Genes on the pharmacodynamic side include the primary targets of thiazide, loop, K+-sparing and aldosterone antagonistic diuretics: NCC, NKCC2, ENaC and the mineralocorticoid receptor (genes SLC12A3, SLC12A1, SCNN1A, B, G and NR3C2). Rare variants of these proteins cause Gitelman’s syndrome, Bartter’s syndrome, Liddle’s syndrome or pregnancy-induced hypertension. Polymorphisms in these and in associated proteins such as GNB3, α-adducin and angiotensin-converting enzyme (ACE) seem to be clinically relevant. In conclusion, first knowledge has evolved that efficacy of diuretic drugs may be determined by genetic polymorphisms in genes determining pharmacokinetics and pharmacodynamics of this drug class. In the future, the selection of a diuretic drug or the dosing schedules may be individually chosen based on pharmacogenetic parameters, however, many questions remain to be answered before this fantasy becomes reality.

Expression analysis of the human adducin gene family and evidence of ADD2 beta4 multiple splicing variants

Adducin is a cytoskeleton heterodimeric protein. Its subunits are encoded by three related genes (ADD1, ADD2, and ADD3) which show alternative spliced variants. Adducin polymorphisms are involved in blood pressure regulation in humans and rats. We have analyzed mRNA distribution of ADD gene family in human tissues and cells with Real-Time TaqMan RT-PCR. Whereas ADD1 is ubiquitously distributed, ADD3 is more expressed in kidney medulla and cortex than in fetal kidney, while in adult liver it is less abundant than in fetal liver. ADD2 beta1 and beta4 variants show the same pattern of distribution with the highest expression in brain, fetal liver, and kidney. Conventional RT-PCR identified new beta4 variants. Beta4a is characterized by an in-frame insertion of 21 nucleotides upstream exon 15 predicting a 7 amino acids longer protein with a similar C-terminus region. It is coexpressed with beta1 and beta4 in several tissues. Fetal kidney shows further beta4b, beta4c and beta4d variants containing internal exon deletions that enormously modify the predicted NH(2) and central regions. Our findings could help one to understand the functional role of adducin variants in specific tissues and cells.

Salt, endogenous ouabain and blood pressure interactions in the general population

OBJECTIVE

Experimental data show that ouabain is a modulator of the sodium-potassium pump, which plays an important role in sodium homeostasis and blood pressure regulation. We investigated the distribution of plasma ouabain in the general population in relation to blood pressure and other determinants of sodium homeostasis.

METHODS

In 379 subjects enrolled in a Belgian population study, we measured plasma ouabain, clinical characteristics including blood pressure, serum and urinary electrolytes, urinary aldosterone excretion, various lifestyle factors, and the Gly460Trp polymorphism of the alpha-adducin gene. Our statistical methods included analysis of covariance and multiple linear regression.

RESULTS

Plasma ouabain (median, 140 pmol/l) correlated independently and positively with male gender (n = 182, P = 0.002), smoking (n = 116, P = 0.05), urinary potassium excretion (mean 69 mmol/day, P < 0.0001), and mutation of the alpha-adducin gene (n = 161, P < 0.0001). Both before and after adjustment for covariables, continuous as well as categorical analyses revealed a significant interaction (P < or = 0.02) between plasma ouabain and urinary sodium excretion (mean 194 mmol/day) in relation to blood pressure (mean systolic blood pressure/diastolic blood pressure, 123/76 mmHg). In individuals with plasma ouabain values below the median, blood pressure increased by 2.2 mmHg systolic and 1.4 mmHg diastolic for each 50 mmol/day increment in urinary sodium excretion (P < or = 0.01). No association between blood pressure and urinary sodium excretion was found when plasma ouabain exceeded the median.

CONCLUSIONS

Plasma ouabain behaves as a blood pressure modulating factor, possibly released in response to potassium, either inhibiting the pressor effect of an excessive salt intake or counteracting the depressor action of sodium depletion.

Salt sensitivity of Japanese from the viewpoint of gene polymorphism

Excess salt intake is an important environmental risk for the predisposition to essential hypertension. Previous physiological studies have shown that salt sensitivity is associated with insulin resistance, enhancement of sympathetic nerve activity and decrease of blood pressure decline at night. We have been examining the genetic importance of candidate gene polymorphisms of salt-sensitive hypertension using several populations. The angiotensinogen gene (AGT) is a thrifty gene which increases the risk for common disease with growth of civilization via sodium and body fluid retention. The CC genotype of the AGT/T+31C polymorphism, which is in complete linkage disequilibrium with the TT genotype of the M235T polymorphism, was associated with a decrease of blood pressure decline at night in the Ohasama Study. On the other hand, the Gly460Trp genotype of the alpha-adducin gene (ADD1) is associated with erythrocyte sodium transport and increases tubular sodium reabsorption and risk for hypertension. We also revealed in the Ohasama Study that the Trp460 allele of ADD1 is associated with hypertension in young subjects with low renin activity. In addition to these polymorphisms, the T(-344)C polymorphism in the promoter of the aldosterone synthase gene (CYP11B2) and the C825T polymorphism of the G-protein beta3 subunit gene (GNB3) are considered candidates for the genetic risk of salt-sensitive hypertension. We compared the allele frequency of five candidate genes between Japanese and Caucasians; the results showed that the frequencies of all alleles were significantly higher in Japanese than in Caucasians. This interesting finding might suggest a feasible explanation for the huge interracial differences in the frequency of salt-sensitive hypertension.

Genetics of hypertension: the adducin paradigm

The following were investigated: (1) how we became interested in studying adducin genes and what we know about adducin; (2) studies in animals and humans supporting the role of adducin polymorphisms in hypertension, including some methodological problems related to the dissection of the role of a given genetic molecular mechanism in a complex multifactorial polygenic disease like hypertension; (3) biochemical mechanisms underlying the effect of adducin and its interaction with the Na-K pump; and (4) future directions.

Dopamine and the kidney: a role in hypertension?

PURPOSE OF REVIEW

Defective transduction of the dopamine receptor signal in the kidney has been shown to be important in the pathogenesis of hypertension This review will discuss the genetic mechanism for the defective renal dopaminergic function and the interaction with other gene variant products in the pathogenesis of salt sensitivity and essential hypertension.

RECENT FINDINGS

Single nucleotide polymorphisms of G protein-coupled receptor kinase type 4 (GRK4) phosphorylate, desensitize, and diminish the inhibitory action of D receptors on sodium transport in the kidney. Inhibition of GRK4 expression normalizes renal proximal tubule D receptor function in humans and rodents and ameliorates the hypertension in genetically hypertensive rats. Expression of the GRK4 variant, GRK4gammaA142V, produces hypertension and impairs the natriuretic effect of D receptor stimulation in mice. In humans, GRK4 single nucleotide polymorphisms are associated with essential hypertension, particularly salt sensitive hypertension. The prediction of the hypertensive phenotype is most accurate when elements of the renin-angiotensin system and GRK4 are included in the analysis.

SUMMARY

GRK4 single nucleotide polymorphisms, by preventing the natriuretic function of the dopaminergic system and by allowing the antinatriuretic function of angiotensin II type 1 receptors to predominate, may be responsible for salt sensitivity. Hypertension develops with additional perturbations caused by the variants of other genes (e.g., alpha-adducin, angiotensin converting enzyme, angiotensinogen, angiotensin II type 1 receptor, aldosterone synthase, 11beta-hydroxysteroid dehydrogenase type 2), the quantitative interaction of which may vary depending upon the genetic background.