Alpha-adducin polymorphisms and renal sodium handling in essential hypertensive patients

ADD1 Single Nucleotide Polymorphisms Are Associated With Essential Hypertension Among Han and Mongolian Population in Inner Mongolia Area

Aldosterone synthase (CYP11B2) and α-adducing (ADD1) are candidate genes that play key roles during essential hypertension (EH) incidence. However, the association between their genetic mutations and the risk of EH is unclear. The present study investigated specific single nucleotide polymorphisms (SNPs) from CYP11B2 and ADD1, and their potential role as risk factors for EH based on 423 Mongolian and 410 Han people in Inner Mongolia province. In the allelic model, people with ADD1 rs2239728-A presented a 0.74-fold risk than rs2239728-C, whereas the ADD1 rs4961-T was associated with a 1.37-fold higher risk than allele G in the Han population. The genetic model reported that the rs2239728-A carrier (AA + AC) was 0.59-fold lower than the CC carrier, whereas the rs4961-G carrier (GG + GT) was 0.59-fold lower than the TT carrier in the dominant model. After gender adjustment, people with rs2239728-A was a 0.63-fold risk than –C in EH, but the rs4961-T carrier was associated with a 1.63-times higher risk than –G in females. Haplotype analysis showed that GCCT was associated with essential hypertension in the Han population, and it was a risk factor for EH. Our identification reported novel SNPs of ADD1 with protective significance for EH among females in the Chinese Han population, together with its haplotype GCCT as a risk factor for EH.

Klotho Gene in Human Salt-Sensitive Hypertension

BACKGROUND AND OBJECTIVES

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

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

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

RESULTS

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

CONCLUSIONS

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

Association of CYP11B2 gene polymorphism with preeclampsia in north east of Iran (Khorasan province)

PURPOSE

Identification the genetic factors in preeclampsia (PE) are useful to increase the current knowledge of the pathophysiology of the disorder. The genetic factors implicated for all cases of PE remain to be determined. This study was aimed to investigate association between ADD1 1378G > T, AGTR2 1675G > A, AGTR1 1166A > C, NOS3 894 G > T and CYP11B2 -344C > T gene polymorphisms in Iranian women with PE.

MATERIAL AND METHODS

117 pregnant women with PE and 103 healthy women without affected previous pregnancy by PE were selected. Genomic DNA was extracted from peripheral blood and real-time PCR was performed to investigate the polymorphisms using a commercial kit.

RESULTS

There was a significant difference in CYP11B2 -344C > T gene polymorphism between case and control groups (P = 0.025). The odds ratio was 0.71 (CI 95% = 0.28-1.79). There were no statistical significant differences between other genetic polymorphisms.

CONCLUSION

Our results showed a significant association between CYP11B2 -344C > T gene polymorphism with PE. This finding suggests that mentioned polymorphism may be associated with susceptibility to PE at least in IRAN.

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.

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.

Claudin-14 Gene Polymorphisms and Urine Calcium Excretion

BACKGROUND AND OBJECTIVES

Claudin-16 and -19 are proteins forming pores for the paracellular reabsorption of divalent cations in the ascending limb of Henle loop; conversely, claudin-14 decreases ion permeability of these pores. Single-nucleotide polymorphisms in gene coding for claudin-14 were associated with kidney stones and calcium excretion. This study aimed to explore the association of claudin-14, claudin-16, and claudin-19 single-nucleotide polymorphisms with calcium excretion.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed a retrospective observational study of 393 patients with hypertension who were naïve to antihypertensive drugs, in whom we measured 24-hour urine calcium excretion; history of kidney stones was ascertained by interview; 370 of these patients underwent an intravenous 0.9% sodium chloride infusion (2 L in 2 hours) to evaluate the response of calcium excretion in three different 2-hour urine samples collected before, during, and after saline infusion. Genotypes of claudin-14, claudin-16, and claudin-19 were obtained from data of a previous genome-wide association study in the same patients.

RESULTS

Thirty-one single-nucleotide polymorphisms of the 3' region of the claudin-14 gene were significantly associated with 24-hour calcium excretion and calcium excretion after saline infusion. The most significant associated single-nucleotide polymorphism was rs219755 (24-hour calcium excretion in GG, 225±124 mg/24 hours; 24-hour calcium excretion in GA, 194±100 mg/24 hours; 24-hour calcium excretion in AA, 124±73 mg/24 hours; P<0.001; calcium excretion during saline infusion in GG, 30±21 mg/2 hours; calcium excretion during saline infusion in GA, 29±18 mg/2 hours; calcium excretion during saline infusion in AA, 17±11 mg/2 hours; P=0.03). No significant associations were found among claudin-16 and claudin-19 single-nucleotide polymorphisms and calcium excretion and between claudin-14, claudin-16, and claudin-19 single-nucleotide polymorphisms and stones. Bioinformatic analysis showed that one single-nucleotide polymorphism at claudin-14 among those associated with calcium excretion may potentially influence splicing of transcript.

CONCLUSIONS

Claudin-14 genotype at the 3' region is associated with calcium excretion in 24-hour urine and after the calciuretic stimulus of saline infusion.

Alpha Adducin (ADD1) Gene Polymorphism and New Onset of Diabetes Under the Influence of Selective Antihypertensive Therapy in Essential Hypertension

BACKGROUND

Different antihypertensive therapies (especially diuretics) are reported to induce the new onset of diabetes in some hypertensive patients. α-adducin-1 (ADD1) gene is salt sensitive gene which has its role in etiology of hypertension via salt sensitivity. Therefore, the G460T polymorphism of ADD1 gene may be associated with new onset of diabetes under the influence of diuretic and other antihypertensive therapies.

AIM

To assess the correlation between genetic polymorphism (ADD1 G460T polymorphism) and glycaemic disturbance under influence of diuretic and other antihypertensive drug therapies.

MATERIALS AND METHODS

We recruited study subjects, 270 normotensive as control (150 male and 120 females), 270 hypertensive patients (95 male and 175 females) and 240 hypertensive with new onset of diabetes patients (80 male and 160 females). All study samples were genotyped for ADD1 polymorphic alleles and analyzed the relationship between different genotypes with respect to anthropometric and clinical parameters along with drug therapies.

RESULTS

Clinical and anthropometric parameters (such as age, SBP, DBP, FBG, height, weight, WC, HP, W/H ratio, and BMI) of study population were found highly statistically significant (p<0.05) at base value. Further, genotype wise comparison of all the above parameters revealed most of them as non-significant (p>0.05). Whereas, comparison between genotype and different antihypertensive drug therapy of hypertensive patients, specifically, diuretic therapy as mono in male (p=0.0227) and female (p=0.0292) and in combination with BBs in both male (p=0.0023) and female (p=0.0079) revealed a higher FBG level in variant T allele. In case of hypertensive with new onset of diabetes patients, only female population showed a slightly statistically significant (p=0.0413) difference in FBG level with diuretic mono therapy. Other antihypertensive drug therapies were safe and effective either as mono or in combination therapy.

DISCUSSION

Anthropometric parameters may be the indicative factors for hypertension and diabetes. Variant T allele of ADD1 gene may be considered as the risk factor for the development of diabetes in hypertensive patients. Diuretics as mono therapy and in combination with BBs may be considered as the risk factor for new onset of diabetes in EH patients carrying variant T allele (either as TG or TT).

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.

Relationship between ADD1 Gly460Trp gene polymorphism and essential hypertension in Madeira Island

Essential hypertension (EH) is a complex disease in which physiological, environmental, and genetic factors are involved in its genesis. The genetic variant of the alpha-adducin gene (ADD1) has been described as a risk factor for EH, but with controversial results.The objective of this study was to evaluate the association of ADD1 (Gly460Trp) gene polymorphism with the EH risk in a population from Madeira Island.A case-control study with 1614 individuals of Caucasian origin was performed, including 817 individuals with EH and 797 controls. Cases and controls were matched for sex and age, by frequency-matching method. All participants collected blood for biochemical and genotypic analysis for the Gly460Trp polymorphism. We further investigated which variables were independently associated to EH, and, consequently, analyzed their interactions.In our study, we found a significant association between the ADD1 gene polymorphism and EH (odds ratio 2.484, P = .01). This association remained statistically significant after the multivariate analysis (odds ratio 2.548, P = .02).The ADD1 Gly460Trp gene polymorphism is significantly and independently associated with EH risk in our population. The knowledge of genetic polymorphisms associated with EH is of paramount importance because it leads to a better understanding of the etiology and pathophysiology of this pathology.

Towards Precision Medicine for Hypertension: A Review of Genomic, Epigenomic, and Microbiomic Effects on Blood Pressure in Experimental Rat Models and Humans

Compelling evidence for the inherited nature of essential hypertension has led to extensive research in rats and humans. Rats have served as the primary model for research on the genetics of hypertension resulting in identification of genomic regions that are causally associated with hypertension. In more recent times, genome-wide studies in humans have also begun to improve our understanding of the inheritance of polygenic forms of hypertension. Based on the chronological progression of research into the genetics of hypertension as the "structural backbone," this review catalogs and discusses the rat and human genetic elements mapped and implicated in blood pressure regulation. Furthermore, the knowledge gained from these genetic studies that provide evidence to suggest that much of the genetic influence on hypertension residing within noncoding elements of our DNA and operating through pervasive epistasis or gene-gene interactions is highlighted. Lastly, perspectives on current thinking that the more complex "triad" of the genome, epigenome, and the microbiome operating to influence the inheritance of hypertension, is documented. Overall, the collective knowledge gained from rats and humans is disappointing in the sense that major hypertension-causing genes as targets for clinical management of essential hypertension may not be a clinical reality. On the other hand, the realization that the polygenic nature of hypertension prevents any single locus from being a relevant clinical target for all humans directs future studies on the genetics of hypertension towards an individualized genomic approach.

Potential role of gene-environment interactions in ion transport mechanisms in the etiology of renal cell cancer

We investigated the ion transport mechanism (ITM) in renal cell cancer (RCC) etiology using gene-environment interactions between candidate single nucleotide polymorphisms (SNPs) and associated environmental factors, including dietary intakes of sodium, potassium and fluid, hypertension and diuretic medication. A literature-based selection of 13 SNPs in ten ITM genes were successfully genotyped in toenail DNA of 3,048 subcohort members and 419 RCC cases from the Netherlands Cohort Study. Diet and lifestyle were measured with baseline questionnaires. Cox regression analyses were conducted for main effects and gene-environment interactions. ADD1_rs4961 was significantly associated with RCC risk, showing a Hazard Ratio (HR) of 1.24 (95% confidence intervals (CI): 1.01–1.53) for the GT + TT (versus GG) genotype. Four of 65 tested gene-environment interactions were statistically significant. Three of these interactions clustered in SLC9A3_rs4957061, including the ones with fluid and potassium intake, and diuretic medication. For fluid intake, the RCC risk was significantly lower for high versus low intake in participants with the CC genotype (HR(95% CI): 0.47(0.26–0.86)), but not for the CT + TT genotype (P-interaction = 0.002). None of the main genetic effects and gene-environment interactions remained significant after adjustment for multiple testing. Data do not support the general hypothesis that the ITM is a disease mechanism in RCC etiology.

Renal Haemodynamics are not Related to Genotypes in Offspring of Parents with Essential Hypertension

Introduction. The pathogenesis of essential hypertension (EH) has a major genetic component and is associated with renal abnormalities. Normotensive offspring of hypertensive parents are likely to develop EH and are a suitable population for identifying possible relations between genetic and renal abnormalities.

Methods. We investigated if renin-angiotensin-aldosterone system associated genotypes (angiotensinogen [M235T] and ACE [I/D]) are related to blood pressure (BP), renal haemodynamics and sodium excretion in sex and age-matched (18—35 years) healthy Caucasian offspring of either two parents with EH (n=101, EH-offspring) or two normotensive parents (n=50, controls). The alpha-adducin polymorphism (G460W) was also investigated.

Results. Compared to controls, BP, heart rate, renal vascular resistance (RVR) and urinary sodium excretion were, respectively, 5%, 7%, 15% and 20% higher in EH-offspring. In controls, the TT-genotype of the M235T angiotensinogen polymorphism was associated with higher BP and higher plasma angiotensinogen. By contrast, in EHoffspring the TT-genotype was associated with lower BP and unchanged plasma angiotensinogen. Plasma angiotensinogen correlated positively with BP in EH-offspring, with a similar tendency (p=0.08) in controls. The distributions of the three candidate polymorphisms were similar in EH-offspring and controls. There were no associations between any of the polymorphisms and any of the renal parameters measured.

Conclusion. The markedly greater RVR, proportionally larger than the greater BP, supports a role for RVR in the pathogenesis of EH. The lack of association between the candidate polymorphisms and the investigated parameters, even in this homogenous and for hypertension strongly predisposed group, suggests that the polymorphisms investigated do not play important roles in the pathogenesis of hypertension.

Lanosterol Synthase Gene Polymorphisms and Changes in Endogenous Ouabain in the Response to Low Sodium Intake

Circulating levels of endogenous ouabain (EO), a vasopressor hormone of adrenocortical origin, are increased by sodium depletion. Furthermore, lanosterol synthase, an enzyme involved in cholesterol biosynthesis, has a missense polymorphism (rs2254524 V642L) that affects EO biosynthesis in adrenocortical cells. Here, we investigated the hypothesis that lanosterol synthase rs2254524 alleles in vivo impact the blood pressure (BP) and EO responses evoked by a low dietary Na intake (<100 mEq/d, 2 weeks) among patients with mild essential hypertension. During the low salt diet, the declines in both systolic BP (SBP: -8.7±1.7 versus -3.0±1.5; P=0.013) and diastolic BP (DBP: -5.1±0.98 versus -1.4±0.94 mm Hg; P<0.05), and the slope of the long-term pressure-natriuresis relationship affected significantly the presence of the lanosterol synthase rs2254524 A variant (AA: 0.71±0.22, AC 0.09±0.13, and CC 0.04±0.11 mEq/mm Hg/24 h; P=0.028). In addition, BP rose in ≈25% of the patients in response to the low salt diet and this was associated with increased circulating EO. Lanosterol synthase gene polymorphisms influence both the salt sensitivity of BP and changes in circulating EO in response to a low salt diet. The response of BP and EO to the low salt diet is markedly heterogeneous. Approximately 25% of patients experienced adverse effects, that is, increased BP and EO when salt intake was reduced and may be at increased long-term risk. The augmented response of EO to the low salt diet further supports the view that adrenocortical function is abnormal in some essential hypertensives.

Correlation of renin angiotensin system (RAS) candidate gene polymorphisms with response to Ramipril in patients with essential hypertension

Background:

The renin-angiotensin system (RAS) is an important facet of blood pressure regulation physiology. Treatment of essential hypertension targets the RAS using Angiotensin Converting Enzyme Inhibitors (ACEIs). However, ACEIs are not uniformly effective and show inter-individual pharmacodynamic variations.

Aim:

To assess the correlation between genetic polymorphisms in the genes coding for RAS components (angiotensin converting enzyme (ACE I/D), α-adducin (ADD1) and β₁-adrenoreceptor (β1-ADR)) and response to Ramipril.

Materials and Methods:

We recruited 120 patients with essential hypertension who were administered Ramipril monotherapy initially, followed by combination therapy, if needed, based on their responses. Relationship between genotypes of the three candidate genes and decrease in the blood pressure (BP) was analyzed.

Results:

One hundred and six patients were evaluable at the end of the study period and 21 different genotypes were observed among them. Seven of them were classified as responders after 8 weeks and at the end of 12 weeks, an additional 77 (72.64%) were deemed responders. 19/22 non-responders were treated with combination therapy and 7/19 (36.84%) showed a response to the same. There was a significant difference between the proportions of responders and non-responders among the genotypes of the ADD1 and β1-ADR genes (P = 0.005 and 0.003, respectively). The best predictors of response to Ramipril 5 mg daily were the II/GG/SS, II/TG/SS, II/GG/SG, ID/GG/SS, ID/GG/SG and ID/TT/SS and DD/GG/SS; II/GG/GG, II/TT/SG, ID/TG/SG, ID/TT/SG, DD/GG/SG and DD/GG/GG were moderately predictive and II/TT/SS, II/TG/GG, ID/TG/GG, DD/TG/SG and DD/TG/GG were poorly predictive of response.

Discussion:

Variable responses to Ramipril may be the result of genetic factors.

Conclusion:

Pre-prescription genotyping may help individualize treatment.

Quantitative proteomics reveals novel therapeutic and diagnostic markers in hypertension

Hypertension is a prevalent disorder in the world representing one of the major risk factors for heart attack and stroke. These risks are increased in salt sensitive individuals. Hypertension and salt sensitivity are complex phenotypes whose pathophysiology remains poorly understood and, remarkably, salt sensitivity is still laborious to diagnose.

Here we present a urinary proteomic study specifically designed to identify urinary proteins relevant for the pathogenesis of hypertension and salt sensitivity. Despite previous studies that underlined the association of UMOD gene variants with hypertension, this work provides novel evidence showing different uromodulin protein level in the urine of hypertensive patients compared to healthy individuals. Notably, we also show that patients with higher level of uromodulin are homozygous for UMOD risk variant and display a decreased level of salt excretion, highlighting the essential role of UMOD in the regulation of salt reabsorption in hypertension. Additionally, we found that urinary nephrin 1, a marker of glomerular slit diaphragm, may predict a salt sensitive phenotype and positively correlate with increased albuminuria associated with this type of hypertension.

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We identified urinary proteins differently excreted in hypertensive patients.

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Nephrin 1 might predict salt sensitive phenotype and glomerular complications.

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Uromodulin impacts salt homeostasis in hypertension.

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We provide new insights into the pathogenesis of hypertension and salt sensitivity.

cGMP-dependent protein kinase 1 polymorphisms underlie renal sodium handling impairment

Defective pressure-natriuresis related to abnormalities in the natriuretic response has been associated with hypertension development. A major signaling pathway mediating pressure natriuresis involves the cGMP-dependent protein kinase 1 (PRKG1) that, once activated by Src kinase, inhibits renal Na(+) reabsorption via a direct action on basolateral Na-K ATPase and luminal Na-H exchanger type 3, as shown in renal tubuli of animals. Because a clear implication of PRKG1 in humans is still lacking, here we addressed whether PRKG1 polymorphisms affect pressure-natriuresis in patients. Naive hypertensive patients (n = 574), genotyped for PRKG1 rs1904694, rs7897633, and rs7905063 single nucleotide polymorphisms (SNPs), underwent an acute Na(+) loading, and the slope of the pressure-natriuresis relationship between blood pressure and Na(+) excretion was calculated. The underlying molecular mechanism was investigated by immunoblotting protein quantifications in human kidneys. The results demonstrate that the PRKG1 risk haplotype GAT (rs1904694, rs7897633, rs7905063, respectively) associates with a rightward shift of the pressure-natriuresis curve (0.017 ± 0.004 μEq/mm Hg per minute) compared with the ACC (0.0013 ± 0.003 μEq/mm Hg per minute; P = 0.001). In human kidneys, a positive correlation of protein expression levels between PRKG1 and Src (r = 0.83; P<0.001) or α1 Na-K ATPase (r = 0.557; P<0.01) and between α1 Na-K ATPase and Na-H exchanger type 3 (r = 0.584; P<0.01) or Src (r = 0.691; P<0.001) was observed in patients carrying PRKG1 risk GAT (n = 23) but not ACC (n = 14) variants. A functional signaling complex among PRKG1, α1 Na-K ATPase, and Src was shown by immunoprecipitation from human renal caveolae. These findings indicate that PRKG1 risk alleles associate with salt-sensitivity related to a loss of the inhibitory control of renal Na(+) reabsorption, suggestive of a blunt pressure-natriuresis response.

Lower ADD1 gene promoter DNA methylation increases the risk of essential hypertension

The goal of our study is to investigate the contribution of promoter DNA methylation of α-adducin (ADD1) gene to the risk of essential hypertension (EH). Using the bisulphite pyrosequencing technology, DNA methylation levels of five CpG dinucleotides on ADD1 promoter were measured among 33 EH cases and 28 healthy controls. Significantly higher ADD1 DNA methylation levels were observed in the females than in the males (CpG1: P = 0.016; CpG2-5: P = 0.021). A breakdown analysis by gender showed that lower CpG1 methylation was associated with an increased risk of EH in females (adjusted P = 0.042). A much more significant association between lower CpG2-5 methylation levels and the increased risk of EH was found in males (adjusted P = 0.008). CpG1 methylation was inversely correlated with age in females (r = -0.407, P = 0.019) but not in males. ADD1 CpG1 and CpG2-5 methylation levels were significantly lower in post-menopausal (>50 years) women than pre-menopausal (≤50 years) women (CpG1: P = 0.006; CpG2-5: P = 0.034). A significant interaction between CpG1 methylation and age was found in females (CpG1*age: P = 0.029). CpG2-5 methylation was shown as a significant predictor of EH in males [area under curve (AUC) = 0.855, P = 0.001], in contrast that CpG1 methylation was a trend toward indicator in females (AUC = 0.699, P = 0.054). In addition, significant differences were observed between males and females for alanine aminotransferase (ALT, P = 0.001), aspartate aminotransferase (AST, P = 0.005) and uric acid (P<0.001). The concentration of AST was inversely correlated with ADD1 CpG2-5 methylation levels in female controls (r = -0.644, P = 0.024). These observations may bring new hints to elaborate the pathogenesis of EH.

Association between polymorphisms of alpha-adducin gene and essential hypertension in Chinese population

The association between polymorphisms of α-adducin (ADD1) gene and essential hypertension is still unclear. Thus, we carried out a case-control study and an interaction analysis to test whether ADD1 is a common candidate gene for hypertension in the Chinese population. Blood samples and information including body mass index (BMI), smoking habit, and alcohol abuse were collected. Meanwhile, total cholesterol, high density lipoprotein, triglyceride were measured by automatic biochemistry analyzer. All 6 tag single nucleotide polymorphisms (tagSNPs) within ADD1 gene were genotyped by SNPstream genotyping system. Multifactor dimensionality reduction (MDR) was used to identify the interactions among the SNPs and the non-genetic factors. Results showed that plasma triglyceride, total cholesterol, and BMI were significantly higher in the hypertensive group than in the control group. Result from genotyping indicated that rs4963 was significantly associated with essential hypertension. After stratification by gender, rs4963 was associated with essential hypertension only in males. MDR analysis indicated that interaction among BMI, rs4963, and rs16843452 were involved in susceptibility of hypertension. The present study indicated that rs4963 within ADD1 gene was associated with essential hypertension in Chinese population, which might be related to altered exonic splicing and disrupted gene regulation.

Association between polymorphisms of alpha-adducin gene and essential hypertension in Chinese population

The association between polymorphisms of α-adducin (ADD1) gene and essential hypertension is still unclear. Thus, we carried out a case-control study and an interaction analysis to test whether ADD1 is a common candidate gene for hypertension in the Chinese population. Blood samples and information including body mass index (BMI), smoking habit, and alcohol abuse were collected. Meanwhile, total cholesterol, high density lipoprotein, triglyceride were measured by automatic biochemistry analyzer. All 6 tag single nucleotide polymorphisms (tagSNPs) within ADD1 gene were genotyped by SNPstream genotyping system. Multifactor dimensionality reduction (MDR) was used to identify the interactions among the SNPs and the non-genetic factors. Results showed that plasma triglyceride, total cholesterol, and BMI were significantly higher in the hypertensive group than in the control group. Result from genotyping indicated that rs4963 was significantly associated with essential hypertension. After stratification by gender, rs4963 was associated with essential hypertension only in males. MDR analysis indicated that interaction among BMI, rs4963, and rs16843452 were involved in susceptibility of hypertension. The present study indicated that rs4963 within ADD1 gene was associated with essential hypertension in Chinese population, which might be related to altered exonic splicing and disrupted gene regulation.

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.

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.

Polymorphisms, hypertension and thiazide diuretics

It is 10 years since the discovery of the human genome; however, the study of the influence of genetic variants on drug effect - pharmacogenomics - has so far failed to create a major impact on day-to-day prescription practices. In the present article we analyze the main findings in candidate gene variants, gene combinations and whole-genome scans in relation to diuretic treatment. A critical analysis of the main reasons for some contrasting results will be discussed. The hypertension phases, in clinical trials dealing with genes and related pathophysiological mechanisms, may account for these inconsistent findings. The use of previously untreated versus treated patients is addressed. Finally, a positive study with a new genetic molecular strategy is described.

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.

Genes involved in vasoconstriction and vasodilation system affect salt-sensitive hypertension

The importance of excess salt intake in the pathogenesis of hypertension is widely recognized. Blood pressure is controlled primarily by salt and water balance because of the infinite gain property of the kidney to rapidly eliminate excess fluid and salt. Up to fifty percent of patients with essential hypertension are salt-sensitive, as manifested by a rise in blood pressure with salt loading. We conducted a two-stage genetic analysis in hypertensive patients very accurately phenotyped for their salt-sensitivity. All newly discovered never treated before, essential hypertensives underwent an acute salt load to monitor the simultaneous changes in blood pressure and renal sodium excretion. The first stage consisted in an association analysis of genotyping data derived from genome-wide array on 329 subjects. Principal Component Analysis demonstrated that this population was homogenous. Among the strongest results, we detected a cluster of SNPs located in the first introns of PRKG1 gene (rs7897633, p = 2.34E-05) associated with variation in diastolic blood pressure after acute salt load. We further focused on two genetic loci, SLC24A3 and SLC8A1 (plasma membrane sodium/calcium exchange proteins, NCKX3 and NCX1, respectively) with a functional relationship with the previous gene and associated to variations in systolic blood pressure (the imputed rs3790261, p = 4.55E-06; and rs434082, p = 4.7E-03). In stage 2, we characterized 159 more patients for the SNPs in PRKG1, SLC24A3 and SLC8A1. Combined analysis showed an epistatic interaction of SNPs in SLC24A3 and SLC8A1 on the pressure-natriuresis (p interaction = 1.55E-04, p model = 3.35E-05), supporting their pathophysiological link in cellular calcium homeostasis. In conclusions, these findings point to a clear association between body sodium-blood pressure relations and molecules modulating the contractile state of vascular cells through an increase in cytoplasmic calcium concentration.

Endogenous ouabain and the renin-angiotensin-aldosterone system: distinct effects on Na handling and blood pressure in human hypertension

OBJECTIVE

To evaluate whether the renin-angiotensin-aldosterone system (RAAS) and endogenous ouabain system differently affect renal Na handling and blood pressure.

METHODS

Three hundred and one patients in whom we compared blood pressure, and renal Na tubular reabsorption in the basal condition and 2 h (T120) after saline infusion.

RESULTS

Following multivariate-adjusted linear and quartiles analysis, baseline mean blood pressure (MBP) was significantly higher (113.7 ± 1.33 mmHg) in the fourth versus the first endogenous ouabain quartile (103.8 ± 1.04 mmHg) and the trend across the quartiles was highly significant (β = 0.23, P = 3.53e-04). In contrast, an inverse relationship was present in the renin activity (PRA) quartiles with MBP highest in the first (112.5 ± 1.26) and lowest in the fourth PRA quartile (107.6 ± 1.48, P = 0.039). Following an acute saline load, changes in MBP and the slope of the pressure-natriuresis relationship were inversely related across the PRA quartiles. The fractional excretion of sodium (FENa) showed a negative linear trend going from the first to the third endogenous ouabain quartiles (2.35 ± 0.17 and 1.90 ± 0.14%, P = 0.05). Patients in the fourth endogenous ouabain quartile (>323 pmol/l) showed increased FENa T120 (2.78 ± 0.18%, P < 0.01) and increased Na tubular rejection fraction (P = 0.007) after Na load. After the saline load, there was a biphasic relationship between plasma endogenous ouabain and FENa favoring Na retention at low endogenous ouabain and Na excretion at high endogenous ouabain levels.

CONCLUSION

The RAAS and endogenous ouabain system are two independent and complementary systems having an inverse (RAAS) or a direct (endogenous ouabain system) relationship with hemodynamic parameters.

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.

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 architecture of complex traits predisposing to nephropathy: hypertension

Blood pressure and hypertension have significant genetic underpinnings that may be age-dependent. The age-dependency, significant contributions from environmental factors such as diet and exercise, and inherent moment-to-moment variability complicate the identification of the genes contributing to the development of hypertension. Although genetic abnormalities may have moderate effects, the physiologic pathways involving these genes have redundant compensating mechanisms to bring the system back into equilibrium. This has the effect of reducing or completely masking the initial genetic defects, one of the hypothesized reasons for the small genetic effects found by the recent genome-wide association studies. This review article discusses the concept of initiators versus compensators in the context of finding genes related to hypertension development. A brief review is provided of some key genes found to be associated with hypertension, including the genes identified from the nine genome-wide association studies published to date.

Strategies to improve detection of hypertension genes

Multiple factors contribute to the development of hypertension, including genetic factors and environmental exposures. Various pathophysiological mechanisms are at play in the pathogenesis of hypertension and this pathogenesis, by necessity, exhibits substantial variation at the level of the individual, as it depends on the relative contribution of inherited genes and individual lifetime environmental exposures. Over time, long-term compensatory mechanisms, including responses to either chronic hypertension or to therapeutic intervention, can only obscure the initiating mechanisms of disease. Acute compensating mechanisms can also mask initiating gene effects during or after an intervention, so that early phenotype assessments during the intervention may be more likely to detect the genetic initiators. Compensatory mechanisms, working over days, weeks or even years, will likely be variably effective in minimizing the expected blood pressure rise, making it difficult to detect genetic initiating mechanisms in cross-sectional, 'steady state', or 'in balance' studies. If the lifetime risk of hypertension indeed approaches 90%, the power to identify genetic factors can only decrease with duration of disease and treatment, and prediction of hypertension becomes of vanishing significance. With multiple factors at play, we cannot expect that all causes are mutually exclusive, but it is reasonable to assume that one of these mechanisms is predominant in the initiation of the disease in any one individual. Given the heterogeneity of essential hypertension argued above, it becomes evident that the chance of identifying genetic factors that contribute to disease development will be greatest if study subjects at highest genetic predisposition are observed during age ranges when heritability is at a maximum, using the correct phenotypes, measured in the correct tissues, during the correct time window. Genes found to be significant in such studies should be densely typed in clinical trials and large population studies to assess public health and clinical applications of the findings.

Novel genetic variants in the alpha-adducin and guanine nucleotide binding protein beta-polypeptide 3 genes and salt sensitivity of blood pressure

BACKGROUND

We examined the association between 12 single-nucleotide polymorphisms (SNPs) in the alpha-adducin (ADD1) and guanine nucleotide binding protein (G protein) beta-polypeptide 3 (GNB3) genes and systolic (SBP), diastolic (DBP), and mean arterial (MAP) pressure responses to salt intake.

METHODS

A 7-day low-sodium (51.3 mmol sodium/day) followed by a 7-day high-sodium intervention (307.8 mmol sodium/day) was conducted among 1,906 Han participants from rural North China. Blood pressure (BP) measurements were obtained at baseline and at the end of each intervention period using a random-zero sphygmomanometer.

RESULTS

We identified a significant association between a rare ADD1 variant rs17833172 and SBP, DBP, and MAP responses to high sodium (P values <0.0001) and DBP response to low sodium (P value = 0.002). Participants homozygous for the variant A allele of this marker had SBP, DBP, and MAP responses (95% confidence interval) to high salt of 1.6 (-1.8, 4.9), -0.8 (-5.6, 4.0), and -0.1 (-4.0, 3.9) mm Hg, respectively, vs. corresponding responses of 4.6 (2.5, 6.6), 1.7 (-0.2, 3.6), and 2.7 (0.9, 4.4) mm Hg, respectively, for those who were heterozygous or homozygous for the G allele. In addition, participants with at least one copy of the A allele of SNP rs1129649 of the GNB3 gene had significantly decreased MAP response to low salt compared to homozygotes for the C allele (P value = 0.004) with responses of -3.4 (-3.8, -3.0) vs. -4.2 (-4.6, -3.8) mm Hg, respectively.

CONCLUSIONS

These data support a role for the ADD1 and GNB3 genes in BP salt sensitivity. Future studies aimed at replicating these novel findings are warranted.

Physiological Interaction Between α-Adducin and WNK1-NEDD4L Pathways on Sodium-Related Blood Pressure Regulation

The kidney plays an important role in salt and blood pressure (BP) homeostasis. In previous studies, variants in the genes for α-adducin (ADD1), WNK1, and NEDD4L, which all regulate renal sodium absorption, have been associated with increased BP. However, findings have been inconsistent. We tested whether this is because of physiological interactions between the effects of variants in these genes. We assessed the single and combined effects of the ADD1 (Gly460Trp), WNK1 (rs880054 A/G), and NEDD4L (rs4149601 G/A) polymorphisms on renal and BP response to an acute Na load (n=344 subjects), BP decrease after 1 month of treatment with 12.5 mg of hydrochlorothiazide (n=193), and ambulatory 24-hour BP (n=690). Individually, the variants showed modest effects on some of the studied phenotypes. We found the ADD1 Trp allele to be permissive for the effects of variants of the other genes. In combination, the same variants (ADD1 Trp/WNK1 GG/Nedd4L GA+AA) showed a consistent effect on renal Na handling ( P =0.009) and acute BP response to a saline infusion ( P =0.021), BP lowering after thiazide treatment ( P =0.008), and nocturnal systolic BP ( P =0.044). Physiological interaction between the ADD1 and WNK1-NEDD4L pathways influences the effects of variants in these genes on sodium-related BP regulation. Relatively common alleles in the ADD1, WNK1, and NEDD4L genes when present in combination may have significant effects on renal sodium handling, BP, and antihypertensive response to thiazides.

Relationships among endogenous ouabain, alpha-adducin polymorphisms and renal sodium handling in primary hypertension

OBJECTIVE

The basolateral Na pump drives renotubular reabsorption. In cultured renal cells, mutant adducins, as well as sub-nanomolar ouabain concentrations, stimulate the Na-K pump.

METHODS

To determine whether these factors interact and affect Na handling and blood pressure (BP) in vivo, we studied 155 untreated hypertensive patients subdivided on the basis of their plasma endogenous ouabain or alpha-adducin genotype (ADD1 Gly460Trp-rs4961).

RESULTS

Under basal conditions, proximal tubular reabsorption and plasma Na were higher in patients with mutated Trp ADD1 or increased endogenous ouabain (P = 0.002 and 0.05, respectively). BPs were higher in the high plasma endogenous ouabain group (P = 0.001). Following volume loading, the increment in BP (7.73 vs. 4.81 mmHg) and the slopes of the relationship between BP and Na excretion were greater [0.017 +/- 0.002 vs. 0.009 +/- 0.003 mmHg/(muEq min)] in ADD1 Trp vs. ADD1 Gly carriers (P < 0.05). BP changes were similar, whereas the slopes of the relationship between BP and Na excretion were lower [0.016 +/- 0.003 vs. 0.008 +/- 0.002 mmHg/(muEq min)] in patients with low vs. high endogenous ouabain (P < 0.05). In patients with high endogenous ouabain, volume loading increased the BP in the ADD1 Trp group but not in the Gly group (P < 0.05). Thus, patients with ADD1 Trp alleles are sensitive to salt and tubular Na reabsorption remains elevated after volume expansion.

CONCLUSION

With saline loading, BP changes are similar in high and low endogenous ouabain patients, whereas tubular Na reabsorption increases in the high endogenous ouabain group. Saline loading unmasks differences in renal Na handling in patients with mutant adducin or high endogenous ouabain and exposes an interaction of endogenous ouabain and Trp alleles on BP.

Clinical and biochemical characteristics of normotensive patients with primary aldosteronism: a comparison with hypertensive cases

OBJECTIVE

It is unknown why some patients with biochemical evidence of primary aldosteronism (PA) do not develop hypertension. We aimed to compare clinical and biochemical characteristics of normotensive and hypertensive patients with PA.

DESIGN AND PATIENTS

Retrospective comparison of 10 normotensive and 168 hypertensive patients with PA for office or ambulatory blood pressure, serum potassium, plasma aldosterone and renin concentrations; the aldosterone:renin ratio, and tumour size. Comparison of initial hormonal pattern and drop in blood pressure following adrenalectomy in five normotensive and nine hypertensive patients matched for age, sex and body mass index.

RESULTS

The 10 normotensive patients were women and presented with hypokalemia or an adrenal mass. Age, plasma aldosterone and renin concentrations were similar in normotensive and hypertensive cases, but kalemia and body mass index were significantly lower in the normotensive patients. Mean tumour diameter was larger in the normotensive patients than in the hypertensive matched patients with an adenoma (P < 0.01). In normotensive patients, diastolic blood pressure and upright aldosterone correlated negatively with kalemia. Blood pressure was lowered similarly after adrenalectomy in five normotensive PA patients and in their matched hypertensive counterparts. Aldosterone synthase expression was detected in four out of five adrenal tumours.

CONCLUSIONS

Blood pressure may be normal in patients with well-documented PA. The occurrence of hypokalemia, despite a normal blood pressure profile, suggests that protective mechanisms against hypertension are present in normotensive patients.

alpha-Adducin mutations increase Na/K pump activity in renal cells by affecting constitutive endocytosis: implications for tubular Na reabsorption

Genetic variation in alpha-adducin cytoskeletal protein is implicated in the polymerization and bundling of actin and alteration of the Na/K pump, resulting in abnormal renal sodium transport and hypertension in Milan hypertensive rats and humans. To investigate the molecular involvement of alpha-adducin in controlling Na/K pump activity, wild-type or mutated rat and human alpha-adducin forms were, respectively, transfected into several renal cell lines. Through multiple experimental approaches (microscopy, enzymatic assays, coimmunoprecipitation), we showed that rat and human mutated forms increased Na/K pump activity and the number of pump units; moreover, both variants coimmunoprecipitate with Na/K pump. The increased Na/K pump activity was not due to changes in its basolateral localization, but to an alteration of Na/K pump residential time on the plasma membrane. Indeed, both rat and human mutated variants reduced constitutive Na/K pump endocytosis and similarly affected transferrin receptor trafficking and fluid-phase endocytosis. In fact, alpha-adducin was detected in clathrin-coated vesicles and coimmunoprecipitated with clathrin. These results indicate that adducin, besides its modulatory effects on actin cytoskeleton dynamics, might play a direct role in clathrin-dependent endocytosis. The constitutive reduction of the Na/K pump endocytic rate induced by mutated adducin variants may be relevant in Na-dependent hypertension.

Gly460Trp alpha-adducin gene polymorphism and endothelial function in untreated hypertensive patients

OBJECTIVES

Endothelium-dependent vasodilatation is impaired in essential hypertension. Besides traditional and emerging cardiovascular risk factors, genetic factors may also promote deleterious alterations of endothelial physiology. The aim of the present study was to investigate the relationship between the 460Trp allele of ADD1 and endothelium-dependent vasodilation in 110 never-treated hypertensive patients.

METHODS

Forearm blood flow (FBF) was measured during intra-arterial infusion of acetylcholine (ACh) and sodium nitroprusside (SNP) at increasing doses. Analysis of endothelium-dependent and endothelium-independent vasodilation was tested according to ADD1 genotype.

RESULTS

The FBF values at the three incremental doses of ACh were 5.22 +/- 0.24 (+76%), 8.64 +/- 0.45 (+193%) and 14.74 +/- 0.71 (+395%) ml/100 ml of tissue per min for Gly460Gly and 4.63 +/- 0.20 (+51%), 6.84 +/- 0.36 (+123%) and 11.22 +/- 3.8 (+269%) ml/100 ml of tissue per min for 460Trp. Thus, ACh-stimulated FBF was significantly reduced in hypertensive subjects carrying the 460Trp allele of ADD1 (P < 0.001). SNP-stimulated FBF was not affected by ADD1.

CONCLUSIONS

The main finding in this study was that in essential hypertensives the 460Trp allele of ADD1 is strongly associated with an impaired endothelium-dependent vasodilation, a powerful predictor of cardiovascular risk.

Targeting Ouabain- and Adducin-dependent mechanisms of hypertension and cardiovascular remodeling as a novel pharmacological approach

Essential hypertension is a heterogeneous multifactorial syndrome associated with a high cardiovascular risk. A multiple choice of antihypertensive drugs is available; however, a high individual variability to the antihypertensive therapy is still responsible for a modest reduction of the CV risk and not satisfactory control of blood pressure levels. The success of future hypertension treatment will depend upon the understanding of the genetic molecular mechanisms operating in subsets of patients, and the ability of new drugs to specifically correct such alterations. Two mechanisms, among others, are involved in determining the abnormalities of tubular Na(+) reabsorption observed in essential hypertension: the polymorphism of the cytoskeletal protein alpha-adducin and the increased circulating levels of endogenous ouabain (EO). Both lead to increased activity and expression of the renal Na-K pump, the driving force for tubular Na transport. Morphological and functional cardiovascular alterations have also been associated with adducin and EO. Rostafuroxin is a new oral antihypertensive agent able to selectively antagonize adducin and EO hypertensive and molecular effects. It is endowed with high potency and efficacy in reducing blood pressure and preventing organ hypertrophy in animal models representative of both adducin and EO mechanisms. At molecular level, in the kidney, Rostafuroxin normalizes the enhanced activity of the Na-K pump induced by adducin mutation and antagonizes the EO triggering of the Src-EGFr-dependent signaling pathway leading to renal Na-K pump, and ERK Tyrosin phosphorylation and activation. In the vasculature, it normalizes the increased myogenic tone caused by ouabain. A very high safety ratio and an absence of interaction with other mechanisms involved in blood pressure regulation, together with initial evidence of high tolerability and efficacy in hypertensive patients, indicate Rostafuroxin as the first example of a new class of antihypertensive agents designed to antagonize adducin and EO-hypertensive mechanisms. Currently, a phase II multicenter European clinical trial is ongoing for providing the proof of concept that such a compound is effective in the subset of patients where these two mechanisms are at work.

Diuretic-gene interaction and the risk of myocardial infarction and stroke

This study investigates whether the interaction between diuretics and alpha-adducin (ADD1) G460W or G-protein beta3-subunit (GNB3) rs2301339 polymorphism modifies the risk of myocardial infarction (MI) or stroke. Data were used from the Rotterdam Study. The drug-gene interaction was determined with a Cox proportional hazard model with adjustment for each drug class as time-dependent covariates. The risk of MI in current users of low-ceiling diuretics with one or two copies of the ADD1 W-allele (hazard ration (HR)=0.92) was similar compared to the expected joint effect of the W-allele and low-ceiling diuretics on a multiplicative scale (1.04 x 0.90=0.94) (synergy index (SI):0.99; 95% confidence interval (CI): 0.43-2.27). No drug-gene interaction was found on the risk of stroke (SI:0.66; 95% CI:0.43-1.27). In addition, a trend towards an interaction was found between current use and the GNB3 rs230119 G/A polymorphism on the risk of MI (SI: 0.51; 95% CI: 0.23-1.15), whereas no interaction on the risk of stroke was found (SI: 0.84; 95% CI: 0.46-1.56).

CYP11B2 -344T/C gene polymorphism and blood pressure in patients with acromegaly

CONTEXT

The pathogenesis of increased blood pressure (BP) in acromegaly is unclear, and the role of IGF-I levels and the renin-angiotensin-aldosterone system (RAAS) in this disease remains controversial.

OBJECTIVE AND DESIGN

The aim of this study was to investigate the role of gene polymorphisms of the RAAS and involved in sodium handling on BP in acromegaly.

SETTING AND PATIENTS

We conducted a multicentric retrospective study that included 100 consecutive patients with acromegaly referred during the period 2000-2003.

INTERVENTION

All patients were genotyped for ACE I/D, AGT M235T, CYP11B2 -344T/C, B2R -58T/C, and alpha-adducin G460W polymorphisms.

MAIN OUTCOME MEASURE

We assessed the prevalence of hypertension and BP according to the genotype.

RESULTS

Patients with the CYP11B2 -344CC genotype displayed a significant increase in the risk of hypertension compared with patients with CT/TT genotypes (odds ratio = 4.0; 95% confidence interval = 1.4-11.6; P = 0.01). Consistently, a significant proportion of patients with the CYP11B2 -344CC genotypes were under antihypertensive treatment (73.1%) compared with patients with the TT/TC genotypes (38.2%; P = 0.003). Patients with the -344CC genotype displayed a significant increase in systolic BP (10.2 +/- 4.3 mm Hg; P = 0.02) but not a significant increase in diastolic BP (2.6 +/- 2.6 mm Hg; P = 0.32) compared with patients with the CT/TT genotype.

CONCLUSIONS

We have shown an association of the -344T/C CYP11B2 gene polymorphism with BP in patients affected by acromegaly. These findings suggest that the RAAS is implicated in the pathogenesis of hypertension in acromegaly.

Alpha-adducin polymorphism, atherosclerosis, and cardiovascular and cerebrovascular risk

BACKGROUND AND PURPOSE

Carriers of the 460Trp allele of the alpha-adducin gene (ADD1) show higher rates of sodium reabsorption compared with homozygous carriers of the Gly460 allele and were found to have an increased risk of hypertension and cardiovascular disease. We studied the association between the Gly460Trp polymorphism and atherosclerosis, cardiovascular disease, and cerebrovascular disease.

METHODS

Intima-media thickness of the common carotid artery, as well as incident stroke and myocardial infarction, were studied within 6471 subjects of the Rotterdam Study. Within 1018 subjects of the Rotterdam Scan Study, prevalent silent brain infarcts and cerebral white matter lesions were studied. Subjects were grouped into 460Trp carriers (variant carriers) and homozygous carriers of the Gly460 allele (reference).

RESULTS

Intima-media thickness of the common carotid artery was 0.80 mm in variant carriers compared with 0.79 mm in the reference group (P=0.04). Variant carriers had an increased risk of any stroke (hazard ratio [HR], 1.22; 95% CI, 1.02 to 1.45), ischemic stroke (HR, 1.29; 95% CI, 1.02 to 1.63), hemorrhagic stroke (HR, 1.07; 95% CI, 0.59 to 1.92), and of myocardial infarction (HR, 1.33; 95% CI, 1.05 to 1.69). For any ischemic stroke, there was a significant interaction between the Gly460Trp polymorphism and hypertension. Variant carriers more often had a silent brain infarct (odds ratio, 1.36; 95% CI, 0.98 to 1.88) and had more subcortical white matter lesions than the reference group (1.45 vs1.24 mL; P=0.22).

CONCLUSIONS

The Gly460Trp polymorphism is associated with atherosclerosis, cardiovascular disease, and cerebrovascular disease, especially in hypertensive subjects.

Adducin and hypertension

Adducin is a heterodimeric cytoskeleton protein consisting of an alpha-subunit and either a beta- or gamma-subunit. In rats and humans, mutation of the alpha-adducin subunit leads to the stimulation of the sodium (Na(+)), potassium (K(+))-adenosine triphosphate (ATP)-ase activity in renal tubular cells, increased renal Na(+) reabsorption, and, subsequently, hypertension. Ouabain is a hormone that is released by the hypothalamus and, possibly, the adrenal glands. In renal tubular cells it modulates Na(+)/K(+)-ATPase activity and regulates natriuresis. Plasma ouabain levels increase with the number of copies of the mutated alpha-adducin allele. Rostafuroxin is a digitoxygenin derivative that selectively displaces ouabain from the Na(+)/K(+)-ATPase receptor and lowers blood pressure in rats and humans. In this short editorial review, we summarize the recent experimental, clinical and epidemiological evidence that contributed to our understanding of the pathogenetic mechanisms that lead to hypertension associated with the alpha-adducin Gly460Trp polymorphism and its interaction with ouabain. We propose that a pharmacogenomic approach, as applied in an ongoing Phase II dosage study of rostafuroxin, will be a critical step in moving the adducin hypothesis from experimental and observational studies to clinical application.