Synergistic effect of alpha-adducin and ACE genes causes blood pressure changes with body sodium and volume expansion

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.

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.

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.

Hypertension-Related Gene Polymorphisms of G-Protein-Coupled Receptor Kinase 4 Are Associated with NT-proBNP Concentration in Normotensive Healthy Adults

G protein-coupled receptor kinase 4 (GRK4) with activating polymorphisms desensitize the natriuric renal tubular D1 dopamine receptor, and these GRK4 polymorphisms are strongly associated with salt sensitivity and hypertension. Meanwhile, N-terminal pro-B-type natriuretic peptide (NT-proBNP) may be useful in detecting slight volume expansion. However, relations between hypertension-related gene polymorphisms including GRK4 and cardiovascular indices such as NT-proBNP are not clear, especially in healthy subjects. Therefore, various hypertension-related polymorphisms and cardiovascular indices were analyzed in 97 normotensive, healthy Japanese adults. NT-proBNP levels were significantly higher in subjects with two or more GRK4 polymorphic alleles. Other hypertension-related gene polymorphisms, such as those of renin-angiotensin-aldosterone system genes, did not correlate with NT-proBNP. There was no significant association between any of the hypertension-related gene polymorphisms and central systolic blood pressure, cardioankle vascular index, augmentation index, plasma aldosterone concentration, or an oxidative stress marker, urinary 8-OHdG. Normotensive individuals with GRK4 polymorphisms show increased serum NT-proBNP concentration and may be at a greater risk of developing hypertension and cardiovascular disease.

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.

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.

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.

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.

Blood pressure response to potassium supplementation is associated with genetic variation in endothelin 1 and interactions with E selectin in rural Chinese

OBJECTIVE

Although beneficial effects of potassium intake on blood pressure (BP) are well established, little is known about genetic factors that underlie interindividual variability in BP response to dietary potassium. In a previous study, we reported the first evidence for significant heritabilities for BP response in a dietary intervention study in rural Chinese. In this report, we extend our genetic studies to examine associations with polymorphisms in genes in vascular endothelial pathways.

METHODS

We genotyped study participants for 23 single nucleotide polymorphisms (SNPs) in endothelin 1 (EDN1), nitric oxide synthase 3, and E selectin (SELE). We tested 17 of these SNPs for associations with BP response to potassium supplementation in 1843 participants. Association tests used population-based [generalized estimation equation (GEE)] and family-based (quantitative transmission disequilibrium test) methods, as well as tests for gene-by-gene (GxG) interaction (generalized multifactor dimensionalilty reduction and GEE).

RESULTS

Single SNP analysis identified significant associations for several SNPs in EDN1 with multiple measures of BP response to potassium supplementation. The cumulative effects of the minor EDN1 alleles that showed significant associations were to reduce measures of BP response by 0.5-0.9 mmHg. We found significant evidence for effects of GxG interactions between EDN1 and SELE, even in the absence of individual associations with SELE variants.

CONCLUSION

Our results implicate variability in EDN1 and SELE as genetic factors that influence BP response to potassium intake. Although such epidemiological studies do not allow direct determination of physiologic mechanisms, our findings of joint effects identify EDN1 and SELE as targets for functional studies to determine their interactions in BP response to potassium intake.

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.

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.

Single nucleotide polymorphisms in genes of circulatory homeostasis in surviving pediatric intensive care patients with meningococcal infection

OBJECTIVE

In the course of a meningococcal infection, invasive and severe disease occurs in a restricted number of individuals. The predominant mechanism of death in case of meningococcal septic shock is circulatory failure. Inotropic requirements between patients vary widely. We investigated whether polymorphisms in genes regulating the hemodynamic response influence the amount of inotropics required or the susceptibility to severe meningococcal disease.

DESIGN

Retrospective case control study.

SETTING

Single-center pediatric intensive care unit (PICU).

PATIENTS

Fifty-six cases (all consecutive patients admitted to the PICU between 1993 and 2001 with a proven meningococcal infection) and 136 controls. Patients were divided into two groups according to their inotropic requirements.

INTERVENTION

DNA analysis was performed to determine the polymorphisms of the beta-adrenergic receptor gene-1, beta-adrenergic receptor gene-2, alpha-adducin, angiotensin converting enzyme, and angiotensin II type-1 receptor-1 genes.

RESULTS

For the alpha-adducin gene a significant difference of the genotype distribution was found between the cases and controls. The odds ratio for admission to the PICU with meningococcal sepsis with or without meningitis, for carriers of the variant allele (Gly460Trp or Trp460Trp) was 2.1 (95% confidence interval 1.11-4.04; p < 0.02). Cases, homozygote for the wild-type allele of the beta-1 adrenergic receptor at locus 389, were more likely to have a low pediatric risk of mortality score on admission (odds ratio 3.6, 95% confidence interval 1.11-11.76). No difference was found in the distribution of the beta-adrenergic receptor gene-1, beta-adrenergic receptor gene-2, angiotensin converting enzyme, and angiotensin II type-1 receptor-1 polymorphisms between the two groups of patients or between cases and controls.

CONCLUSIONS

Among patients admitted to the PICU with a meningococcal infection, the variant allele of the alpha-adducin gene was more prevalent compared with controls. Patients with the variant allele of the beta-adrenergic receptor gene-1 at locus 389 were more likely to have a high pediatric risk of mortality score on admission. The mechanism and clinical relevance of these findings is unclear.

Alpha-adducin polymorphism associated with increased risk of adverse cardiovascular outcomes: results from GENEtic Substudy of the INternational VErapamil SR-trandolapril STudy (INVEST-GENES)

BACKGROUND

The alpha-adducin (ADD1) Gly460Trp polymorphism has been associated with hypertension and response to diuretic therapy, but controversy exists.

METHODS

The present study was conducted to prospectively investigate the relationship among the ADD1 Gly460Trp polymorphism, diuretic use, and adverse cardiovascular outcomes among 5,979 patients with hypertensive coronary artery disease, who participated in the INVEST and provided genomic DNA. The primary outcome was defined as the first occurrence of nonfatal stroke, nonfatal myocardial infarction, or all-cause death. Secondary outcomes were the components of the primary outcome. Ancestry informative markers were used to control for population stratification.

RESULTS

In blacks, ADD1 variant carriers were at higher risk for a primary outcome event than wild-type homozygotes (adjusted hazard ratio 2.62, 95% CI 1.23-5.58, P = .012), with a similar trend in whites and Hispanics, albeit a smaller magnitude of effect (adjusted hazard ratio 1.43, 0.86-2.39 in Hispanics; 1.24, 0.90-1.71 in whites). Secondary outcome analysis showed that the all-cause death was driving the differences in primary outcomes by genotype. There was no interaction between the ADD1 polymorphism and diuretic use for either primary outcome or secondary outcomes.

CONCLUSIONS

In hypertensive patients with coronary artery disease, black ADD1 variant carriers showed a 2.6-fold excess risk for a primary outcome event and an 8-fold increase risk of death. White and Hispanic ADD1 variant carriers showed an increased but nonsignificant excess risk. However, the effect of diuretic use on risk of cardiovascular outcomes did not vary by ADD1 carrier status.

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.

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.

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.

Angiotensin-converting enzyme I/D and alpha-adducin Gly460Trp polymorphisms: from angiotensin-converting enzyme activity to cardiovascular outcome

The angiotensin-converting enzyme (ACE) I/D and the alpha-adducin (ADD1) Gly460Trp polymorphisms are associated with cardiovascular risk factors. In a prospective population study and in cell models, we investigated the combined effects of these 2 polymorphisms. We randomly recruited 1287 white subjects (women: 50.0%; mean age: 55.9 years). We obtained outcomes from registries and repeat examinations (median 3). Over 9.0 years (median), 178 fatal or nonfatal cardiovascular events occurred. In ADD1 Trp allele carriers, the multivariate-adjusted hazard ratios associated with ACE DD versus I were 1.72 (P=0.007) for total mortality, 2.35 (P=0.02) for cardiovascular mortality, 2.02 (P=0.005) for all cardiovascular events, and 2.59 (P=0.03) for heart failure. In contrast, these hazard ratios did not reach significance in ADD1 GlyGly homozygotes (0.08<or=P<or=0.90). The positive predictive value and attributable risk associated with ACE DD homozygosity combined with mutated ADD1 were 36.2% and 10.3%, respectively. To clarify our epidemiological observations, we investigated the effects of mutated human ADD1 on the membrane-bound ACE activity in fibroblasts from 51 volunteers and in transfected human embryonic kidney cells (31 experiments). In fibroblasts (5.10 versus 3.63 nanomoles of generated hippuric acid per milligram of protein per minute; P=0.0021) and human embryonic kidney cells (1.086 versus 0.081 nmol/mg per minute; P=0.017), the membrane-bound ACE activity increased in the presence but not absence of the ADD1 Trp allele. In conclusion, the combination of ACE DD homozygosity and mutated ADD1 worsened cardiovascular prognosis to a similar extent as classic risk factors, possibly because of increased membrane-bound ACE activity in subjects carrying the ADD1 Trp allele.

Interaction of angiotensin I-converting enzyme insertion-deletion polymorphism and daily salt intake influences hypertension in Japanese men

The contribution of angiotensin I-converting enzyme insertion-deletion polymorphism (ACE I/D) to salt-sensitivity hypertension has been extensively studied by means of salt-loading tests, but whether or not the interaction with daily salt intake affects blood pressure still remains to be clarified. We therefore conducted a cross-sectional study of 284 Japanese male workers (age range, 20-64 years) to examine the effect of ACE I/D genotype and daily salt intake on hypertension. Blood pressure was measured and the ACE I/D was identified by polymerase chain reaction (PCR). Daily salt intake was calculated from a food frequency questionnaire (FFQ). In multivariate analyses, we explored the interaction of ACE I/D and salt intake by means of logistic regression analysis and multiple linear regression analysis. ACE I/D per se was not associated with blood pressure levels or hypertension. ACE I/D interacted with daily salt intake and correlated with hypertension (p for interaction = 0.047). In the ID+II genotype, hypertension was increased by high salt intake (p = 0.005), while in the DD genotype it was not (p = 0.257). The interaction was more prominent in the overweight group (p = 0.039) than in non-overweight group. In the overweight group, high salt intake induced a 10.5 mmHg higher diastolic blood pressure in the ID+II genotype than in the DD genotype (p = 0.042). Our results suggest that ACE I/D and daily salt intake constitute a gene-environment interaction, which may be further modulated by overweight.

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.

α-Adducin and angiotensin-converting enzyme polymorphisms in hypertension: evidence for a joint influence on albuminuria

BACKGROUND

A single-nucleotide polymorphism (Gly460Trp) within the alpha-adducin gene (ADD1) may influence several renal phenotypes, including salt sensitivity, susceptibility to renal failure, the renal haemodynamics and confer a worse cardiovascular risks profile. However, its relationship with microalbuminuria, a marker of early renal and cardiovascular damage and an independent predictor of morbid events in hypertension, is unknown. For this reason, we related the ADD1 genetic polymorphism to urine albumin levels and other clinical variables in essential hypertensive men. The angiotensin-converting enzyme (ACE) insertion/deletion (ID) polymorphism was also evaluated because of its interactive potential with the ADD1 genotype.

METHODS

Albuminuria (three overnight collections), echocardiographic left ventricular mass index, blood pressure, body mass index, renal function, glucose and lipids were measured in 238 genetically unrelated, never treated, uncomplicated Caucasian essential hypertensive men. Polymerase chain reaction or a 5' nuclease assay were used to characterize the ACE ID and ADD1 Gly460Trp variants, respectively.

RESULTS

Microalbuminuria (albuminuria >or= 15 microg/min) was more frequent in patients with the ACE DD variant, but only in those with a ADD1 Gly460Gly background. In contrast, urine albumin did not differ by ACE ID genotype in the presence of mutated ADD1 Trp alleles. ADD1 polymorphisms per se were not associated with albuminuria. Cardiovascular, renal, metabolic parameters were homogeneously distributed among different genetic backgrounds.

CONCLUSIONS

ACE DD and ADD1 Gly460Gly polymorphisms may jointly influence albuminuria in hypertensive men, 460Gly homozygosis facilitating or, possibly, the 460Trp allele mitigating the noxious renal impact of the ACE DD genotype. The data highlight further the complex pathophysiological implications of microalbuminuria in hypertension.

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.

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.

Pharmacogenomics of blood pressure response to antihypertensive treatment

PURPOSE IDENTIFICATION: Inter-individual variability in blood pressure response to treatment is well documented, but a clinically useful means to distinguish responders from non-responders has been elusive. With the advent of new technologies and genomic knowledge, more investigators are seeking to identify genetic determinants of blood pressure response to therapy.

STUDY SELECTION

We identified studies of candidate polymorphisms from an initial PubMed search using the MESH terms 'Hypertension: Drug Therapy' and 'Genetics' or 'Pharmacogenetics', limiting results to English-language publications on studies in human adults. We further identified specific polymorphisms of interest noted in earlier reviews and performed additional PubMed searches based on these candidate genes. Pertinent studies were further extracted from the references of studies already identified. We focused on clinical trials that measured blood pressure response to a medication or class of medications over a minimum of 4 weeks.

DATA EXTRACTION

We evaluated studies looking at blood pressure response to commonly used classes of antihypertensive medications by major genetic variants. RESULTS OF ANALYSIS: Although many studies show that blood pressure response to a given class of antihypertensive medications varies by genotype for different polymorphisms, none of the genotypes identified consistently predicted blood pressure response.

CONCLUSIONS

Common variants may influence response to diuretics, beta-blockers, angiotensin-converting enzyme inhibitors, and angiotensin receptor blockers, but studies of polymorphisms have generally yielded conflicting results. The inclusion of pharmacogenomic studies in large clinical trials and other more innovative investigative methods may provide greater clarity of the potential role for genotyping in the treatment of patients with hypertension.

OASIS-HT: design of a pharmacogenomic dose-finding study

Experimental evidence and observations in humans strongly support an interactive role of mutated α-adducin, sodium (Na+)/potassium (K+)-adenosine triphosphatase (ATPase) activity and endogenous ouabain in Na+ homeostasis and the pathogenesis of hypertension. The Ouabain and Adducin for Specific Intervention on Sodium in HyperTension (OASIS-HT) trial is an early Phase II dose-finding study, which will be conducted across 39 European centers. Following a run-in period of 4 weeks without treatment, eligible patients will be randomized to one of five oral doses of rostafuroxin consisting of 0.05, 0.15, 0.5, 1.5, or 5.0 mg/day. Each dose will be compared to a placebo in a double-blind crossover experiment with balanced randomization. Treatment will be initiated with the active drug and continued with placebo or vice versa. Each double-blind period will last 5 weeks. The primary end point is the reduction in systolic blood pressure defined as the average of three clinic readings with the patient in the sitting position. Secondary end points include the reduction in diastolic blood pressure on clinic measurement, the decrease in the 24-h blood pressure, and the incidence of end points related to safety. Secondary objectives are to investigate the dependence of the blood pressure-lowering activity on the plasma concentration of endogenous ouabain and the genetic variation of the enzymes involved in the metabolism of this hormone, and the adducin cytoskeleton proteins. Eligible patients will have Grade I or II systolic hypertension without associated conditions and no more than two additional risk factors. In conclusion, OASIS-HT is a combination of five concurrent crossover studies, one for each dose of rostafuroxin to be studied. To our knowledge, OASIS-HT is the first Phase II dose-finding study in which a genetic hypothesis is driving primary and secondary end points.

Preventing end stage renal disease in diabetic patients--genetic aspect (part I)

Diabetic nephropathy is a major cause of diabetes- related morbidity and mortality; however the clinical course of the disease and the renal prognosis is highly variable among individuals. The current review will discuss the genetic influence on the development of end stage renal disease (ESRD) in diabetic patients and potential improvements to the current treatment strategy to slow the loss of kidney function in these patients. In this first part, the growing evidence that glucose-induced activation of the intra-renal and systemic renin-angiotensin systems plays an essential role in processes leading to destruction of renal function is summarised. Genetic variations, especially the angiotensin-converting enzyme (ACE)/ID polymorphisms in the gene coding for ACE, are involved in activation of the renin-angiotensin system and seem to influence the clinical course of diabetic nephropathy during treatment with ACE inhibitors. In addition, this polymorphism may interact with other polymorphisms within the renin-angiotensin system, leading to high risk of ESRD. As new genetic approaches and methods develop, further understanding of diabetic nephropathy will evolve and genotyping will help prevent ESRD in diabetic patients.

Role of the adducin family genes in human essential hypertension

OBJECTIVE

In both humans and rats, polymorphisms of the alpha adducin (ADD1) gene are involved in renal sodium handling, essential hypertension and some of its organ complications. Adducin functions within cells as a heterodimer composed of various combinations of three subunits that are coded by three genes (ADD1, 2, 3) each located on a different chromosome.

DESIGN

These characteristics provide the biochemical basis for investigating epistatic interactions among these loci.

METHODS

We examined the three adducin gene polymorphisms and their association with ambulatory blood pressure (ABPM) and with plasma levels of renin activity (PRA), endogenous ouabain (EO), in 512 newly discovered and never-treated hypertensive patients.

RESULTS

Relative to carriers of the wild type (Gly/Gly) ADD1 gene, patients carrying the mutated Trp ADD1 allele had higher blood pressure (systolic blood pressure (SBP) 143.2 +/- 1.0 versus 140.6 +/- 0.6 mmHg P = 0.027 and diastolic blood pressure (DBP) 94.2 +/- 0.77 versus 92.3 +/- 0.5 mmHg, P = 0.03), lower PRA and EO, consistent with the hypothesis of the renal sodium retaining effect of the Trp allele. Polymorphisms in the ADD2 and ADD3 genes taken alone were not associated with these variables. However, the differences in SBP and DBP between the two ADD1 genotypes were greatest in carriers of the ADD3 G allele (around + 8 mmHg). The significance of the interaction between ADD1 and ADD3 ranged between P = 0.020 to P = 0.006 according to the genetic model applied.

CONCLUSIONS

The interaction of ADD1 and ADD3 gene variants in humans is statistically associated with variation in blood pressure, suggesting the presence of epistatic effects among these loci.

Associations of baseline blood pressure levels and efficacy of Benazepril treatment with interaction of alpha-adducin and ACE gene polymorphisms in hypertensives

The molecular mechanisms underlying essential hypertension are not fully elucidated. Although Benazepril is being widely used in antihypertensive medication, the agent is efficacious in only a portion of hypertensive patients. To evaluate the interaction of alpha-adducin gene Gly460Trp and angiotensin I-converting enzyme (ACE) gene I/D polymorphisms in regard to baseline blood pressure (BP) levels and the reductions of blood pressures after Benazepril treatment, we conducted an investigation of 954 Chinese hypertensive patients in Anhui province, China. We found that compared with the baseline systolic BP (SBP) of subjects with one ACE I allele and one alpha-adducin Trp allele, the baseline SBP of those with ACE DD and alpha-adducin Gly/Gly genotypes was significantly higher [Crude: beta(SE) = 7.83(3.09), p = .01; Adjusted: beta(SE) = 5.83(2.83), p = .04]. However, no associations were found between the interaction of ACE I/D and alpha-adducin Gly460Trp polymorphisms and the baseline diastolic BP or the BP response to Benazepril treatment. Our results suggested that the interaction effect of alpha-adducin Gly460Trp and ACE I/D polymorphisms might play a significant role in regulating baseline BP but not BP response to Benazepril.

Epistatic interaction between α- and γ-adducin influences peripheral and central pulse pressures in white Europeans

BACKGROUND

Adducin is a membrane skeleton protein consisting of alpha- and beta- or alpha- and gamma-subunits. Mutations in alpha- and beta-adducin are associated with hypertension. In the European Project on Genes in Hypertension, we investigated whether polymorphisms in the genes encoding alpha-adducin (Gly460Trp), beta-adducin (C1797T) and gamma-adducin (A386G), alone or in combination, affected pulse pressure (PP), an index of vascular stiffness.

METHODS

We measured peripheral and central PP by conventional sphygmomanometry and applanation tonometry, respectively. We randomly recruited 642 subjects (162 nuclear families and 70 unrelated individuals) from three European populations. In multivariate analyses, we used generalized estimating equations and the quantitative transmission disequilibrium test.

RESULTS

Peripheral and central PP averaged 46.1 and 32.6 mmHg, respectively. Among carriers of the alpha-adducin Trp allele, peripheral and central PP were 5.8 and 4.7 mmHg higher in gamma-adducin GG homozygotes than in their AA counterparts, due to an increase in systolic pressure. gamma-Adducin GG homozygosity was associated with lower urinary Na/K ratio among alpha-adducin Trp allele carriers and with higher urinary aldosterone excretion among alpha-adducin GlyGly homozygotes. Sensitivity analyses in founders and offspring separately, and tests based on the transmission of the gamma-adducin G allele across families, confirmed the interaction between the alpha- and gamma-adducin genes.

CONCLUSIONS

In alpha-adducin Trp allele carriers, peripheral and central PP increased with the gamma-adducin G allele. This epistatic interaction is physiologically consistent with the heterodimeric structure of the protein and its influence on transmembranous sodium transport.

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.

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.

Pharmacogenetics of antihypertensive drug response

Pharmacogenetics is a discipline of molecular medicine that investigates the genetic basis of individual variation of drug responses. Before the era of the human genome project and the subsequent progress in genomic research, this field was primarily restricted to the investigation of the genetics of drug-metabolizing enzymes as they account for individual differences in pharmacokinetics and tolerability of drugs. In the current genomic era, pharmacogenetic research is applied to all fields of drug treatment in clinical medicine, including hypertension research. In contrast to the traditional approach, however, the influence of individual genetic variation on the efficacy of a drug (ie, the pharmacodynamic response) is the major focus of pharmacogenetic research and its clinical applicability. Therefore, the identification of individual genetic variation influencing the blood pressure-lowering effect of an antihypertensive compound and the implementation of this knowledge into clinical practice is the major goal of pharmacogenetic research in the field of hypertension. In this article, some important, recent research work and progress on the pharmacogenetics of antihypertensive drug responses are reviewed and evaluated.

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.

Interaction between ACE and ADD1 gene polymorphisms in the progression of IgA nephropathy in Japanese patients

An interaction effect between the angiotensin-converting enzyme insertion/deletion (ACE I/D) and alpha-adducin (ADD1) Gly460Trp polymorphisms (G460W) on blood pressure regulation has recently been suggested, although its significance in the prognosis of renal function in IgA nephropathy (IgAN) has not been fully investigated. Therefore, we evaluated the clinical manifestations and renal prognosis in 276 Japanese patients with histologically proven IgAN with respect to their ACE I/D and ADD1 G460W polymorphisms. The prognosis of renal function was analyzed by Kaplan-Meier survival curves and multivariate Cox proportional-hazards regression models. Baseline data, including blood pressures, proteinuria, renal function, and incidence of hypertension, were similar for the different genotypes of ACE and ADD1. The individual genotypes taken alone were not associated with the progression of renal dysfunction. However, renal survival of patients with the 460WW polymorphism of ADD1 was significantly worse within the group with the II genotype of ACE (Kaplan-Meier, log rank test; chi2=6.062, P=0.0138) but not for those with other ACE genotypes. In the Cox proportional-hazards regression model with adjustment for clinical risk factors, including hypertension, proteinuria, and no administration of an angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers, the 460WW variant of ADD1 was a highly significant and independent risk factor only for patients with the ACE II genotype, with a hazard ratio of 3.65 (P=0.0016), but not for those with other ACE genotypes (hazard ratio=0.65, P=0.2902). These findings suggest an interaction between ACE and ADD1 polymorphisms not only on blood pressure regulation but also on the progression of renal dysfunction in patients with IgAN.

Essential hypertension

Hypertension is a frequent, chronic, age-related disorder, which often entails debilitating cardiovascular and renal complications. Blood pressure is usually noted in combination with other cardiovascular risk factors. Diagnosis of hypertension increasingly relies on automated techniques of blood pressure measurement. The pathophysiology of essential hypertension depends on the primary or secondary inability of the kidney to excrete sodium at a normal blood pressure. The central nervous system, endocrine factors, the large arteries, and the microcirculation also have roles in the disorder. Although monogenic forms of blood pressure dysregulation exist, hypertension mostly arises as a complex quantitative trait that is affected by varying combinations of genetic and environmental factors. Non-pharmacological strategies can reduce blood pressure. Antihypertensive drug treatment diminishes the complications of hypertension. The concept that a few major genes will provide the final clue to the pathogenesis of essential hypertension is an oversimplification that contradicts the heterogeneous nature of this disorder. Further integration of genetic, molecular, clinical, and epidemiological research could disclose subsets of patients in whom specific combinations of genetic and environmental factors raise blood pressure, and might lead to more individualised treatment.

Pharmacogenomics of primary hypertension--the lessons from the past to look toward the future

A number of recent reviews have addressed the issue of the pharmacogenomics of primary hypertension and related complications by considering the data on the genotype-drug response relationship. Here we mainly discuss the methodological aspects of this issue, trying to integrate 'traditional' clinical and experimental pathophysiology and therapy-pharmacology with the 'new' genetics. Such integration is indispensable to: a). define the appropriate 'context' (genetic background, environment, age, gender, phase of hypertension, previous therapy etc.) in which a given genotype-drug response relationship should be tested (it is indeed likely that many discrepancies among published data originate from context's interference); b). assign the correct clinical meaning to the results obtained by statistics and functional genetics methodologies; c). define a novel clinical entity caused by a disease favoring allele, alone or in combination with other alleles, with a consistent clinical picture, prognosis and responsiveness to the appropriate drug; d). estimate the size of the population target amenable to benefit from a therapeutic intervention developed according to the pharmacogenomics' principles; e). develop a novel drug that selectively interferes with the sequence of events triggered by the genetic mechanism(s) underlying the clinical entity. Peculiar to this strategy is to look for consistency among findings gathered from different 'contexts' after having properly accounted for the context's dependency of the results.

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.

ACE and alpha-adducin polymorphism as markers of individual response to diuretic therapy

Renin-angiotensin system reactivity and the constitutive capacity of the renal tubule to reabsorb sodium play a role in the individual response to diuretic therapy; therefore we evaluated the blood pressure (BP) response to hydrochlorothiazide in 87 never-treated individuals with mild essential hypertension, according to ACE gene I/D and alpha-adducin Gly460Trp polymorphism. These genotypes where chosen because previous data showed their interaction in determining the BP response to salt probably was the result of their involvement in the activation of the renin-angiotensin system (ACE) and in the constitutive capacity of the kidney to reabsorb sodium (alpha-adducin) (treatment for 2 months). BP was measured after 3 run-in visits and after the first and second months of treatment by means of a standardized procedure. Data were analyzed by ANOVA, t test, and multivariate ANOVA for repeated measures (covarying for gender, age, and body mass index). Although basal mean BP (MBP) was similar in the different ACE and alpha-adducin genotypes, patients carrying at least one I allele of ACE and one 460Trp allele of alpha-adducin had the largest MBP decrease with treatment (12.7+/-1.9 mm Hg), the effect of the combination of genotypes being additive but not epistatic. These patients had an odds ratio of 15.75 of being a responder to hydrochlorothiazide compared with patients with Gly460Gly+DD, with the least MBP decrease (3.4+/-1.7 mm Hg). Alpha-adducin and ACE I/D polymorphism may be useful to predict the interindividual degree of response to hydrochlorothiazide; the analysis of the combination of the 2 genotypes increases the accuracy of the prediction of response to the drug.

Between-patient differences in the renal response to renin-angiotensin system intervention: clue to optimising renoprotective therapy?

Renin-angiotensin-aldosterone system (RAAS) blockade with angiotensin-converting enzyme inhibitors (ACE-I) or angiotensin II (Ang II), AT(1)-receptor blockers (ARB) is the cornerstone of renoprotective therapy. Still, the number of patients with end-stage renal disease is increasing worldwide, prompting the search for improved renoprotective strategies. In spite of proven efficacy at group level, the long-term renoprotective effect of RAAS blockade displays a marked between-patient heterogeneity, which is closely linked to between-patient differences in the intermediate parameters of blood pressure, proteinuria and renal haemodynamics. Of note, the between-patient differences by far exceed the between-regimen differences, and thus may provide a novel target for exploration and intervention. The responsiveness to RAAS blockade appears to be an individual characteristic as demonstrated by studies applying a rotation-schedule design. The type and severity of renal disease, obesity, insulin-resistance, glycaemic control, and genetic factors may all be involved in individual differences in responsiveness, as well as dietary factors, such as dietary sodium and protein intake. Several strategies, such as dietary sodium restriction and diuretic therapy, dose-titration for proteinuria, and dual RAAS blockade with ACE-I and ARB, can improve the response to therapy at a group level. However, when analysed for their effect in individuals, it appears that these measures do not allow poor responders to catch up with the good responders, i.e. in spite of their efficacy at group level, the available measures are usually not sufficient to overcome individual resistance to RAAS blockade. We conclude that between-patient differences in responsiveness to renoprotective intervention should get specific attention as a target for intervention. Unravelling of the underlying mechanisms may allow development of specific intervention. Based on the currently available data, we propose that response-based treatment schedules, with a multidrug approach titrated and adapted at individual responses rather than fixed treatment schedules, may provide a fruitful strategy for more effective renoprotection.