CYP11B2 Polymorphisms and Home Blood Pressure in a Population-Based Cohort in Japanese: the Ohasama Study

CYP11B2 gene polymorphism and essential hypertension among Tibetan, Dongxiang and Han populations from northwest of China

Essential hypertension (EH) is a complex multifactorial condition influenced by both genetic and environmental factors; aldosterone synthase (CYP11B2) is a key enzyme which involves in the terminal steps of aldosterone synthesis. The result of relationship between C-344T of CYP11B2 polymorphism and EH was controversial. This study was undertaken to investigate the association of C-344T polymorphism with EH in the populations of Tibetan, Dongxiang and Han from northwest of China. A total of 2115 participants aged 18-70 years were enrolled in this study. In total, 1776 blood samples, including 545 Tibetan (305 hypertensive and 240 normotensive), 530 Dongxiang (254 hypertensive and 276 normotensive) and 701 Han (338 hypertensive and 363 normotensive), were analyzed successfully by using Snapshot minisequencing method, 30 samples were also performed by direct sequencing (5 hypertensive and 5 normotensive in each population, respectively). The frequencies of genotype and allele of CYP11B2 (C-344T) were not significantly different between EH group and control group in every ethnic population (p > 0.05). However, in female population of Tibetan, the frequencies of CC and CT genotype and C allele in EH group were higher than in control (p < 0.05) group. The frequencies of CC genotype and C allele in both the normotensive controls and EH patients in Tibetan population were higher than in Dongxiang and Han populations. Our study suggests that there is lack of association between C-344T polymorphism of CYP11B2 gene and EH in Dongxiang and Han populations, whereas the polymorphism was correlated with EH in female population of Tibetan.

Recent Advances in the Genetics of Hypertension

Hypertension is a silent killer worldwide, caused by both genetic and environmental factors. Until now, genetic and genomic association studies of hypertension are reporting different degree of association on hypertension. Hence, it is essential to gather all the available information on the reported genetic loci and to determine if any biomarker(s) is/are significantly associated with hypertension. Current review concluded the potential biomarkers for hypertension, with regards to electrolyte and fluid transports, as well as sodium/potassium ions homeostasis, which are supported by the results of case-controls and meta-analyses.

Relationship of Genetic Polymorphisms of Aldosterone Synthase Gene Cytochrome P450 11B2 and Mineralocorticoid Receptors with Coronary Artery Disease in Taiwan

The aldosterone synthase gene, cytochrome P450 11B2 (CYP11B2), and mineralocorticoid receptor (MR) genes have been reported to be associated with coronary artery disease (CAD). In this study, we investigated the association of single nucleotide polymorphisms (SNPs) of CYP11B2 (CYP11B2 T-344C) and MR (MR C3514G and MR C4582A) with CAD in Taiwanese. Six hundred and nine unrelated male and female subjects who received elective coronary angiography were recruited from Chung Shan Medical University Hospital. The enrolled subjects were those who had a positive noninvasive test. CYP11B2 T-344C, MR C3514G and MR C4582A were determined by polymerase chain reaction-restriction fragment length polymorphism. We found that women with CYP11B2 C/C had a higher risk of developing CAD. However, there were no significant differences in the genotype distributions of MR C3514G and MR C4582A between the women with and without CAD. In multivariate analysis, CYP11B2 T-344C was most significantly associated with CAD in Taiwanese women. In conclusions, CYP11B2 C/C was more significantly associated with the development of CAD than diabetes mellitus or hypertension. This implies that CYP11B2 C/C plays a more important role than some conventional risk factors in the development of CAD in Taiwanese women.

Association between cytochrome P450 promoter polymorphisms and ischemic stroke

The human cytochrome P450 (CYP) superfamily includes at least 57 genes that encode enzymes with diverse metabolic and biosynthetic functions. This study was conducted in order to investigate the associations between polymorphisms in CYP superfamily genes (CYP11B2, CYP17A1, CYP2B6, CYP2C9, CYP2E1 and CYP7A1) and ischemic stroke (IS). Six single nucleotide polymorphisms (SNPs) of CYP superfamily genes were selected and genotyped by direct sequencing in 121 patients with IS and 321 control subjects. The genetic data were analyzed using SNPStats and SPSS 18.0. Multiple logistic regression models (codominant 1, codominant 2, dominant, recessive and log-additive) were used to evaluate odds ratios (ORs), 95% confidence intervals (CIs) and p-values. The rs179998 SNP of CYP11B2 was significantly associated with IS (p=0.0336 in a log-additive model). The rs3813867 SNP of CYP2E1 was significantly associated with smoking in IS (p=0.0336 in a log-additive model). The rs1799998 SNP of CYP11B2 and rs3808607 of CYP7A1 were related to diabetes mellitus in IS (p<0.05). CYP11B2, CYP2E1 and CYP7A1 SNPs were associated with IS in the population studied. Further study is required to confirm these associations and to determine their biological significance.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

CYP11B2 gene haplotypes independently and in concurrence with aldosterone and aldosterone to renin ratio increase the risk of hypertension

OBJECTIVES

Aldosterone synthase produces aldosterone, which regulates electrolytes and thereby blood pressure. Polymorphisms in aldosterone-synthase gene (CYP11B2) may associate with heterogeneous aldosterone production and hypertension. Hence, we investigated -344T/C, Iw/Ic polymorphisms of CYP11B2, plasma renin activity (PRA) and aldosterone concentration (PAC).

DESIGN AND METHODS

Consecutive ethnically-matched 450 hypertensive patients and 360 controls were screened by PCR-RFLP for genotypes and haplotypes; PRA and PAC were measured.

RESULTS

The Iw/Ic polymorphism distribution differed significantly between the two groups (LRT chi(2)=15.8, df=2, P=0.000). The mutant allele-Ic and genotype-Ic/Ic were overrepresented in patients (35% versus 27% and 13% versus 7%). Overrepresentation of T-Ic haplotype in patients was identified as risk haplotype (P=0.000). Patients had significantly higher PAC and aldosterone-to-renin ratio (ARR; P=0.000), which was Ic-allele dependent.

CONCLUSIONS

The haplotype T-Ic associated with hypertension susceptibility. Correlation between Ic-allele and raised ARR likely serve in hypertension management.

Investigation of Major Genetic Polymorphisms in the Renin-Angiotensin-Aldosterone System in Subjects with Young-Onset Hypertension Selected by a Targeted-Screening System at University

Although polymorphisms in renin-angiotensin-aldosterone (RAA) system genes for angiotensinogen (AGT M235T), angiotensin-converting enzyme (ACE I/D), angiotensin II type 1 receptor (AT1 A/C1166), and aldosterone synthase (CYP11B2-344T/C) have been major targets for genetic investigation in association with essential hypertension (EH), the influence of these genetic factors is still to be determined. Because patients with young-onset EH are thought to possess a stronger genetic background than EH patients who show elevated BP relatively late in life, the targeted screening of hypertensive students in Tohoku University was completed for the selection of subjects for genetic investigation. Out of 16,434 students (12,794 males and 3,670 females) younger than 30, 22 students showed a high blood pressure (BP) (systolic and diastolic BP of 140 and/or 90 mmHg or greater, respectively, on two occasions and more than 135 and/or 85 mmHg, respectively, at a third measurement during casual BP measurements at the Tohoku University Health Center. These 22 students were asked to measure their BP at home (HBP). Six of the students had a systolic HBP of more than 135 mmHg and/or a diastolic HBP of more than 85 mmHg, and these students subsequently received medical examinations at Tohoku University Hospital and were diagnosed with EH. Genotyping for the four major genetic polymorphisms mentioned above was performed on the six students with EH and on 12 of the remaining 16 students whose HBP was within the normal range (white coat hypertension: WCH). Neither the EH nor the WCH students showed a different distribution of genotypes and allelic frequencies, compared to those found in the general Japanese population. Hence, the present study suggests that none of the major genetic polymorphisms in the RAA system strongly influence the onset of EH.

Hypertension in the elderly and the very old

High systolic blood pressure represents a challenge for the modern world. Epidemiologists are in the best position to appreciate the importance of systolic hypertension and its cardiovascular consequences. Although the label of hypertension seems to have lower importance in the elderly, and above all in the very old, than in younger people, high systolic and high pulse pressure are risk factors for cardiovascular events and necessitates treatment. Unfortunately, due to indolence and lack of aggressiveness, only a limited fraction of elderly hypertensive patients receives adequate therapy.

The renin-angiotensin-aldosterone system in cerebral small vessel disease

INTRODUCTION

Cerebral small vessel disease (SVD) appears on magnetic resonance imaging (MRI) as leukoaraiosis (LA), état criblé (EC), and multiple lacunar infarctions (MLI). Although the pathophysiology of SVD is poorly understood, there is evidence of a genetic contribution. We sought to analyze the influence of the renin-angiotensin-aldosterone system (RAAS) on SVD in symptomatic patients from the Génétique de l'Infarctus Cérébral (GENIC) study, including RAAS polymorphisms and circulating angiotensin converting enzyme (ACE).

METHODS

Caucasian patients (n=510) with acute brain infarction (BI) were recruited and MRIs were evaluated for SVD, including LA, EC, and MLI. We considered ACE levels and several polymorphisms, including ACE, angiotensinogen, aldosterone synthase CYP11B2, and angiotensin II receptor type I.

RESULTS

Among the polymorphisms, there were marginal negative associations between aldosterone synthase CYP11B2 -344C against severe EC (adjusted OR, 0.57; 95% CI, 0.31-1.05) and severe LA (adjusted OR, 0.54; 95% CI, 0.30-0.95), both considering -344C dominant. In addition, the frequency of -344C decreased with the number of SVD abnormalities (p=0.016). Mean plasma ACE was elevated in patients with MLI, but not with LA or EC. The risk of MLI increased gradually with increasing plasma ACE (adjusted OR, 1.25; 95% CI, 1.02-1.53).

CONCLUSIONS

This exploratory study found no strong evidence for RAAS involvement in severe SVD in this population. The whole spectrum of SVD, including EC, MLI, and LA, can be considered as phenotypes for genetic studies.

The Future of Antihypertensive Treatment

Despite progress in recent years in the prevention, detection, and treatment of high blood pressure (BP), hypertension remains an important public health challenge. Hypertension affects approximately 1 billion individuals worldwide. High BP is associated with an increased risk of mortality and morbidity from stroke, coronary heart disease, congestive heart failure, and end-stage renal disease; it also has a negative impact on the quality of life. Hypertension cannot be eliminated because there are no vaccines to prevent the development of hypertension, but, its incidence can be decreased by reducing the risk factors for its development, which include obesity, high dietary intake of fat and sodium and low intake of potassium, physical inactivity, smoking, and excessive alcohol intake. For established hypertension, efforts are to be directed to control BP by lifestyle modification (LSM). However, if BP cannot be adequately controlled with LSM, then pharmacotherapy can be instituted along with LSM. Normalization of BP reduces cardiovascular risk (for cardiovascular death, myocardial infarction, and cardiac arrest), provides renoprotection (prevention of the onset or slowing of proteinuria and progression of renal dysfunction to end-stage renal disease in patients with hypertension, diabetes mellitus types 1 and 2, and chronic renal disease), and decreases the risk of cerebrovascular events (stroke and cognition impairment), as has been amply demonstrated by a large number of randomized clinical trials. In spite of the availability of more than 75 antihypertensive agents in 9 classes, BP control in the general population is at best inadequate. Therefore, antihypertensive therapy in the future or near future should be directed toward improving BP control in treated hypertensive patients with the available drugs by using the right combinations at optimum doses, individually tailored gene-polymorphism directed therapy, or development of new modalities such as gene therapy and vaccines. Several studies have shown that BP can be reduced by lifestyle/behavior modification. Although, the reductions appear to be trivial, even small reductions in systolic BP (for example, 3-5 mm Hg) produce dramatic reduction in adverse cardiac events and stroke. On the basis of the results of clinical and clinical/observational studies, it has been recommended that more emphasis be placed on lifestyle/behavior modification (obesity, high dietary intake of fat and sodium, physical inactivity, smoking, excessive alcohol intake, low dietary potassium intake) to control BP and also to improve the efficacy of pharmacologic treatment of high BP. New classes of antihypertensive drugs and new compounds in the established drug classes are likely to widen the armamentarium available to combat hypertension. These include the aldosterone receptor blockers, vasodilator beta-blockers, renin inhibitors, endothelin receptor antagonists, and dual endopeptidase inhibitors. The use of fixed-dose combination drug therapy is likely to increase. There is a conceptual possibility that gene therapy may yield long-lasting antihypertensive effects by influencing the genes associated with hypertension. But, the treatment of human essential hypertension requires sustained over-expression of genes. Some of the challenging tasks for successful gene therapy that need to be mastered include identification of target genes, ideal gene transfer vector, precise delivery of genes into the required site (target), efficient transfer of genes into the cells of the target, and prompt assessment of gene expression over time. Targeting the RAS by antisense gene therapy appears to be a viable strategy for the long-term control of hypertension. Several problems that are encountered in the delivery of gene therapy include 1) low efficiency for gene transfer into vascular cells; 2) a lack of selectivity; 3) problem in determining how to prolong and control transgene expression or antisense inhibition; and 4) difficulty in minimizing the adverse effects of viral or nonviral vectors. In spite of the hurdles that face gene therapy administration in humans, studies in animals indicate that gene therapy may be feasible in treating human hypertension, albeit not in the near future. DNA testing for genetic polymorphism and determining the genotype of a patient may predict response to a certain class of antihypertensive agent and thus optimize therapy in individual patients. In this regard, there are some studies that report the effectiveness of antihypertensive therapy based upon the genotype of selected patients. Treatment of human hypertension with vaccines is feasible but is not likely to be available in the near future.

Association of the C−344T aldosterone synthase gene variant with essential hypertension: a meta-analysis

BACKGROUND

The CYP11B2 gene (CYP11B2) encoding aldosterone synthase has been associated with essential hypertension and some, but not all, studies have reported that the C-344T variant may influence the risk of the disease.

OBJECTIVE

We performed a systematic review of the literature by means of a meta-analysis to evaluate the influence of the C-344T CYP11B2 polymorphism on arterial hypertension and intermediate phenotypes.

METHODS

From 485 reports, we included 42 observational studies, case-control and cohort at baseline. Fixed and random effect models were used to pool data from individual studies.

RESULTS

From 19 heterogeneous studies including 5343 essential hypertensive and 5882 control subjects, we found a significant association between hypertension and the C-344T variant in fixed but not in random effect models [for homozygous CC: odds ratio (OR), 0.834; 95% confidence interval (CI), 0.760-0.914; P < 0.0001, n = 11 225]. Besides, homozygous CC subjects had lower plasma renin activity (D, -0.161; 95% CI, -0.279 to -0.043; P < 0.01, n = 1428) but no difference in plasma aldosterone levels (D, -0.006; 95% CI, -0.081 to 0.07; P = 0.88, n = 2872). Limiting the quantitative analysis of blood pressure to 13 studies including only untreated individuals, no significant association was found for systolic arterial blood pressure (D, 0.042; 95% CI, -0.057 to 0.141; P = 0.41, n = 1775) and diastolic arterial blood pressure (D, 0.026; 95% CI, -0.073 to 0.125; P = 0.61, n = 1775).

CONCLUSION

Homozygous individuals for the -344C CYP11B2 allele are at 17% lower risk of hypertension with respect to homozygous TT subjects.

Prevalence of Primary Aldosteronism among Unselected Hypertensive Patients: A Prospective Study Based on the Use of an Aldosterone/Renin Ratio above 25 as a Screening Test

Primary aldosteronism (PA) has been considered a rare cause of hypertension. The introduction of the aldosterone/renin ratio (ARR) as a screening test has led to an increase in the detection rate. The aim of this study was to evaluate the prevalence of PA among unselected hypertensive patients by using an ARR >25 as a screening test. We studied 3,000 consecutive unselected hypertensive patients. Blood samples for the determination of plasma renin activity (PRA), aldosterone (ALD) and electrolytes were drawn in the morning, and patients with an ARR >25 underwent intravenous saline infusion as a confirmatory test. Adrenal CT and a dexamethasone suppression test were performed in patients with confirmed PA. Patients with a positive dexamethasone test underwent genetic testing for glucocorticoid-remediable aldosteronism (GRA). Out of 3,000 hypertensives, 684 (22.8%) showed an ARR >25 and 177 of them (5.9% of the whole population) had a positive saline loading test. Only 44 of them (24.8%) were hypokalemic. CT was performed in all the patients with confirmed PA and 53 of them (29.9%) had a solitary adrenal macroadenoma, 112 (63.3%) had bilateral adrenal enlargement and 12 (6.8%) had normal appearing adrenal glands. Of 177 patients given dexamethasone to identify GRA, 8 (4.5%) showed aldosterone suppression but only one (0.1%) tested positive for the chimeric gene. In conclusion, our findings indicate that standardized application of an ARR >25 to unselected hypertensive patients, followed by i.v. saline loading as a confirmatory test, can result in the detection of a large number of patients with PA (5.9% of the studied population), most of whom are normokalemic. Bilateral adrenal hypertrophy represents the more common form of PA.

C-344T polymorphism of the aldosterone synthase gene and blood pressure in the elderly: a population-based study

OBJECTIVES

Whether the C-344T polymorphism of the aldosterone synthase gene is important for blood pressure control remains controversial. It has been proposed that an association between this polymorphism and blood pressure might be evident in elderly subjects. The aim of the present study was to test this hypothesis in an epidemiological context.

DESIGN

A cross-sectional epidemiological evaluation of a highly homogeneous unselected general population of elderly Caucasians.

METHODS

Lifestyle, medical history, anthropometrics, skinfold thickness, supine blood pressure, heart rate and biochemical measures were recorded in 437 subjects aged > or = 65 years living in a secluded valley. All were genotyped for C-344T allele status and underwent measurements of plasma aldosterone and renin.

RESULTS

The C-344T genotypic frequency did not deviate from Hardy-Weinberg equilibrium. The aldosterone to renin ratio was 19% lower in the CC than in the TT genotype. Systolic blood pressure was significantly lower in subjects with the CC genotype, higher in the TT (+9.6 mmHg versus CC) and intermediate in the CT (+7.9 mmHg versus CC). Adjustment for age, gender, smoking and antihypertensive treatment did not affect this association. Diastolic blood pressure did not differ across genotypes. A significant increase of systolic blood pressure with increasing age and with increasing skinfold thickness was observed in the TT homozygotes but not in the C-carriers.

CONCLUSIONS

These data support the concept that the C-344T polymorphism plays a role in controlling systolic blood pressure and the age-related increase in systolic blood pressure in response to age and to body fat, possibly through differences in modulation of aldosterone synthesis.

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

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

Characteristics of Young-Onset Hypertension Identified by Targeted Screening Performed at a University Health Check-Up

Since the prevalence and clinical characteristics of young-onset hypertension are still to be elucidated, we performed targeted-screening at an annual university health check-up for two consecutive years. Out of 16,464 subjects in 2003 and 17,032 in 2004 that were aged less than 30 years, 22 and 26 students (all males) exhibited high blood pressure (BP), respectively, on three occasions during casual BP measurements at the Tohoku University Health Center (systolic and diastolic BP of 140 and/or 90 mmHg or greater, respectively). These students were asked to measure their BP at home, and 9 subjects in total were diagnosed as having essential hypertension (EH). The remaining students were diagnosed as having white coat hypertension (WCH). In 8 out of 9 EH students, their father and/or mother had also been treated with antihypertensive medication. Adjustment by attendance ratio for each BP measurement suggested that the incidence of EH was around 0.1% and that of hypertension (EH and WCH) was around 0.5% in university students aged less than 25 years, since most of the subjects and hypertensive students were between 18 and 24 years old. Body mass index of the EH, which was more than 25 kg/m2 (overweight), was significantly higher than that with WCH. In conclusion, the combination of repeated casual BP measurements and home BP effectively identified young-onset EH. The clinical parameters indicated that male gender, genetic background, and excessive weight were risk factors for young-onset hypertension.

Correlation between left ventricular mass and urinary sodium excretion in specific genotypes of CYP11B2

BACKGROUND

Aldosterone has essential roles in regulating intravascular volume and blood pressure, and is suggested to influence cardiac structure. However, the association of polymorphisms in the aldosterone synthase gene (CYP11B2) with hypertension or cardiac hypertrophy remains controversial.

OBJECTIVE

To evaluate the distribution of polymorphisms in the CYP11B2 gene and the possible associations between genotypes and blood pressure, urinary excretion of aldosterone or electrolytes and echocardiographic measurements, in a Japanese population.

METHODS AND RESULTS

We examined the association of two common diallelic polymorphisms within CYP11B2, one in the promoter -344T/C and the other an intron 2 gene conversion, with blood pressure, 24-h urinary excretion of aldosterone and electrolytes, and echocardiographic measurements, in a Japanese population. We confirmed significant linkage disequilibrium between these polymorphic loci and ethnic differences in frequency of the alleles. The -344C and -344T haplotypes apparently diverged before the intron conversion polymorphism was generated on the latter haplotype. Allele frequencies did not differ between 535 normotensive and 360 hypertensive individuals or between hypertensive individuals with higher and lower concentrations of renin. The only significant correlation was a positive correlation of left ventricular mass with 24-h urinary excretion of sodium, which occurred only in individuals with the -344CC genotype or the intron 2 conversion (-/-) genotype.

CONCLUSIONS

The -344CC or intron 2 conversion (-/-) genotype in CYP11B2 may be a risk factor for developing sodium-sensitive cardiac hypertrophy. Ethnic differences in the distribution of CYP11B2 genotypes combined with differences in salt intake might account for inconsistencies between previous reports.

Systolic and pulse hypertension

Epidemiology, genetic analysis and clinical studies are of help in understanding how, to what extent and why systolic blood pressure increases with age (at least in Western societies), while diastolic blood pressure increases only until the age of 60–65 years. Systolic blood pressure is a predictor of outcome in humans, but pulse pressure (systolic minus diastolic) is a better predictor, particularly in the elderly. Although the cardiovascular risk pattern is different in older patients, antihypertensive treatment remains useful in the elderly and even in the very old. Nevertheless, excessive reduction of diastolic blood pressure should be avoided in order to prevent increasing pulse pressure. Although all therapeutic regimens tend to reduce systolic more than diastolic blood pressure (reducing pulse pressure), the need for antihypertensive drugs acting selectively on systolic values remains very strong.

CYP11B2 gene polymorphisms and hypertension in highlanders accustomed to high salt intake

BACKGROUND

High salt intake is the main determinant of hypertension. The alleles, which once had adaptive value in the salt-poor environment, by promoting salt retention, now induce hypertension. It would be interesting to determine whether the variant alleles of the aldosterone synthase gene (CYP11B2), if related to exaggerated expression/altered activity, are associated with hypertension when combined with a salt-rich diet.

OBJECTIVE

To investigate the -344T/C, K173R and intron-2 conversion polymorphisms of CYP11B2 for an association with hypertension in highlanders accustomed to a high salt intake.

DESIGN AND METHODS

Three CYP11B2 polymorphisms were compared with respect to frequencies and clinical characteristics in 190 normotensive highlanders (NHLs) and 100 hypertensive highlanders (HHLs). One-way ANOVA, chi2 test and logistic regression analysis were carried out to investigate the association of these polymorphisms with hypertension.

RESULTS

The HHLs had significantly higher systolic blood pressure (SBP), diastolic blood pressure (DBP) (P < 0.0001), body mass index (BMI) (P = 0.0002), plasma aldosterone levels (P = 0.03) and aldosterone to plasma renin ratio (ARR) (P < 0.0001) and lower plasma renin activity (PRA) (P = 0.007). The -344T/C and K173R polymorphisms were in complete linkage disequilibrium with each other and the intron-2 conversion allele was in absolute association with the T allele. The TC/CC genotypes correlated with higher BMI when compared with TT genotype in the NHLs and the HHLs (P = 0.002 and 0.004, respectively). The intron-2 conversion heterozygotes/homozygotes correlated with higher SBP in the HHLs (P = 0.03) and significantly higher ARR when compared to IwIw (P = 0.02). Genotype combinations between the -344T/C and intron-2 conversion polymorphisms revealed that combinations with TC or CC genotypes inclined towards higher BMI in both the groups (P < 0.05).

CONCLUSIONS

Our findings showed a correlation of C allele with high BMI, suggesting that -344T/C polymorphism is in linkage disequilibrium with a functional polymorphism on the adjacent 11-beta hydroxylase gene. The correlation of the intron-2 conversion allele with high SBP and ARR associates it with hypertension. The intron-2 conversion could be a functional variant, since it has been suggested to lead to overexpression of the gene; however, the presence of another functional variant in linkage disequilibrium within the gene cannot be ruled out.

Genetics of human hypertension

Hypertension is a complex genetic disorder caused by interplay between several "risk" genes and environmental factors (genetic heritability approximately 30%). Most genetic studies of hypertension use a candidate gene approach and two conclusions have been made: there is no association or linkage with the genes studied, or the hypertension phenotype is heterogeneous and subgroups with hypertension related to certain polymorphisms cannot be identified because of background noise. Studies using intermediate phenotypes suggest the latter is most likely. Another problem is the reliability of gene structure assessment: usually only one or two gene polymorphisms are assessed. The use of intermediate phenotypes and dense mapping of candidate genes would provide a better approach for identifying genotype-phenotype correlations, which might enable the use of genotypes to identify more-specific therapeutic and preventative measures for hypertensives.

Strong Association of a Renin Intronic Dimorphism with Essential Hypertension

The objectives of this project were two-fold: to identify the genetic mutation that has been detected as an MboI dimorphism in intron 9 of the human renin (REN) gene and to confirm a previously reported, putative association between the REN MboI dimorphism and clinical diagnosis of essential hypertension (EHT) in a population of Gulf Arabs from the United Arab Emirates. Sequencing of the MboI dimorphic site was carried out on DNA of randomly chosen cases and controls. A retrospective case-control study was carried out in 689 unrelated subjects (326 first-time, clinically diagnosed hypertensives and 363 age- and gender-matched normotensive subjects), selected from the resident population of the Abu Dhabi Emirate. A polymerase chain reaction/MboI-RFLP based method was employed to compare genotype and allele distributions. Nucleotide sequences at the MboI site of the cut and uncut alleles were determined to be GATC and GGTC, respectively. This A>G mutation is located 10,631 base pairs (bp) 3' to the start of the REN gene, and 79 bp 3' to the end of exon 9. The genotype distributions of the REN 10631A>G dimorphism were found to be significantly different between hypertensive and normotensive subjects (x2= 42.29, df=2, p<0.001). Frequencies of A alleles were 0.54 in EHT vs. 0.37 in normotensive subjects, which is even more demarcated than what was found previously. The frequency of AA genotypes was higher in the hypertensive group than in the normotensive group (34.7% vs. 14.0%). The quantification of the association of A alleles with increased risk of EHT was assessed with corresponding odds ratios (OR), which gave the following values: OR of GG vs. AG genotypes, 1.3 (95% confidence interval [CI]: 0.90-1.88); OR of GG vs. AA, 3.75 (95% CI: 2.41-5.86). In conclusion, REN 10631A alleles are significantly associated with EHT in the Emirati population. This has now been found in two different and therefore independent sample populations from the Abu Dhabi Emirate. Moreover, this genetic effect seems to be acting in a recessive fashion. Hence, either the REN gene itself, or another gene that is in linkage disequilibrium with REN 10631A>G, is implicated in the pathogenesis of EHT in Emirati.

T1198C Polymorphism of the Angiotensinogen Gene and Antihypertensive Response to Angiotensin-Converting Enzyme Inhibitors

This study examined the association between T1198C polymorphism of the angiotensinogen (AGT) gene and the blood pressure response to ACE inhibitors in a Chinese hypertensive cohort. After a 2-week single-blind placebo run-in period, benazepril (10-20 mg/day) or imidapril (5-10 mg/day) was administered for 6 weeks to 509 patients with mild-to-moderate essential hypertension. Polymerase chain reaction combined with restriction enzyme digestion was used to detect the polymorphism, and the patients were classified as having the TT, TC, or CC genotype. The achieved changes in systolic and diastolic blood pressure (SBP and DBP) were analyzed to determine their association with genotypes at the AGT gene locus. In the total 509 patients, the TT genotype was observed in 44 patients (8.7%), the TC genotype in 214 patients (42.0%), and the CC genotype in 251 patients (49.3%). The SBP reductions in patients with the TT genotype, TC genotype, and CC genotype were -15.3+/-12.7 mmHg, -14.0+/-12.7 mmHg, and -14.4+/-12.4 mmHg, respectively (p=0.809). The DBP reductions in patients with the TT genotype, TC genotype, and CC genotype were -8.5+/-8.1 mmHg, -8.3+/-7.5 mmHg, and -8.9+/-6.6 mmHg, respectively (p=0.638). There were no significant differences in the changes in SBP or DBP after treatment among the three genotype groups. In conclusion, these results suggest that the AGT genotype does not predict the blood pressure-lowering response to antihypertensive treatment with ACE inhibitors in Chinese hypertensive patients.

Association of Dopamine .BETA.-Hydroxylase Polymorphism with Hypertension through Interaction with Fasting Plasma Glucose in Japanese

Dopamine-beta-hydroxylase (DBH) catalyzes the conversion of dopamine to norepinephrine and is released from sympathetic neurons into the circulation. Several lines of evidence, including the finding of elevated plasma DBH activity in essential hypertension, suggest an important role of DBH in hypertension. Recently, a novel polymorphism (-1021C/T) in the 5' flanking region of the DBH gene has been shown to account for 35-52% of the variation in plasma DBH activity. We therefore investigated the possible association between the DBH -1021C/T polymorphism and hypertension in a large Japanese population. Moreover, because the development of hypertension is considered to be due at least partly to gene-environmental interactions, we also investigated the possible interactions between the DBH -1021C/T polymorphism and environmental factors. Consequently, we found a significant interaction between the DBH -1021C/T polymorphism and fasting plasma glucose (FPG) in the association with hypertension. CC homozygotes showed a steeper increase in probability of hypertension with FPG than T allele carriers. We also found a marginally significant trend suggesting the presence of an interaction between the DBH -1021C/T polymorphism and FPG in the association with blood pressure. Consistent with the presence of the interaction, we found that a 19 bp sequence containing the DBH -1021C/T polymorphism includes two palindromic non-canonical E boxes separated by 5 bps, and closely resembles the glucose response element of the L-type pyruvate kinase gene. These findings could be helpful in conducting further molecular and biological studies on the relationship among glucose metabolism, the sympathetic nervous system, and hypertension.

Haplotypic analyses of the aldosterone synthase gene CYP11B2 associated with stage-2 hypertension in northern Han Chinese

The objective of this study was to investigate the association of polymorphisms in the aldosterone synthase gene CYP11B2 (-344T/C, Lys173/Arg, and an intronic conversion [IC]) with stage-2 hypertension in northern Han Chinese. A total of 503 hypertensives and their age-, gender-, and area-matched controls were included in this study. The female hypertensives had significantly higher frequencies of the -344T, 173Lys, and IC-conversion alleles (p = 0.002, 0.002, and 0.014, respectively). The estimated frequency of haplotype composed of the -344T, 173Lys, and IC-conversion alleles (haplotype 4) was significantly higher in the female hypertensives compared with their controls (p = 0.007). Using a multivariate score test, we found that haplotype 4 remained associated with female hypertension after the adjustment for covariates (p = 0.003), while the haplotype 3 of T-Arg-WT showed a protective effect both in the males and in the females (p = 0.03 and 0.006, respectively). The odds ratio for haplotype phase of 4-4 was 2.60 (95% CI, 1.21-5.58) and for 3-3, 0.20 (95% CI, 0.03-0.77). These results indicate that the Lys173 and the IC-conversion allele of the CYP11B2 gene confer an increased risk for stage-2 hypertension in northern Han Chinese women.

Renal Sodium Handling for Body Fluid Maintenance and Blood Pressure Regulation

Renal sodium handling is an essential physiologic function in mammal for body fluid maintenance and blood pressure regulation. Recent advances in molecular biology have led to the identification of kidney-specific sodium transporters in the renal tubule, thereby supplying vast information for renal physiology as well as systemic physiology. Renal urinary concentration for body fluid maintenance is accomplished by counter current multiplication in the distal tubule. Sodium transport in the thick ascending limb of Henle (TAL) is the initial process of this system. We have demonstrated that renal urinary concentration is regulated in part by the expression of the Na(+)-K(+)-2Cl(-) co-transporter (BSC1) in TAL, by showing two mechanisms of BSC1 expression: pitressin vasopressin (AVP)-dependent and AVP-independent mechanisms. Two additional findings, namely, a lack of the ability to increase BSC1 expression leads to urinary concentrating defect and an enhanced BSC1 expression underlies the edema-forming condition, confirm the close association between sodium handling in TAL and body fluid accumulation. The lines of evidence from our genetic studies of the general Japanese population suggest the importance of mendelian hypertension genes in the genetic investigation of essential hypertension. Because those genes directly or indirectly regulate sodium transport by the Na-Cl co-transporter or the epithelial sodium channel in the distal convoluted tubule to the collecting duct (distal tubular segments after TAL), sodium handling in this part of the renal tubule may be, at least in part, involved in blood pressure regulation. The unveiling of such physiologic roles of sodium handling based on the sodium transporters or on the tubular segments may lead to a better understanding of systemic physiology as well as to the development of novel therapy for body fluid or blood pressure disorders.

A Serine Protease Inhibitor, Nafamostat Mesilate, Suppresses Aldosterone Secretions In Vivo

To examine the role of serine proteases in the control of aldosterone (Ald) secretion, we studied the effects of nafamostat mesilate (Naf), a serine protease inhibitor, on in vivo Ald secretion and Ald content in the rat adrenal gland. Either Naf (2 mg/kg/h; n=10) or saline (2 ml/h; n=10) was administered intravenously for 30 min to anesthetized Wistar rats whose left adrenal vein was cannulated selectively via the inferior vena cava. Naf caused a significant decrease in Ald secretion rate compared to saline (1.99+/-0.32 vs. 3.42+/-0.56 ng/min, p <0.001), while adrenal blood flow, mean arterial pressure and plasma renin activity in the adrenal venous blood did not differ between the two groups. In a separate trial, adrenal Ald content, adrenal renin content, plasma adrenocorticotropic hormone (ACTH) and plasma potassium did not differ between rats treated with Naf (n=7) and those administered saline (n=7). These data suggested that Naf-inhibitable serine proteases may participate in the control of Ald secretion through mechanism(s) other than hemodynamic changes, adrenal renin, ACTH, and/or plasma potassium.