African Americans,hypertension and the renin angiotensin system

African Americans have exceptionally high rates of hypertension and hypertension related complications. It is commonly reported that the blood pressure lowering efficacy of renin angiotensin system(RAS) inhibitors is attenuated in African Americans due to a greater likelihood of having a low renin profile. Therefore these agents are often not recommended as initial therapy in African Americans with hypertension. However, the high prevalence of comorbid conditions, such as diabetes, cardiovascular and chronic kidney disease makes treatment with RAS inhibitors more compelling. Despite lower circulating renin levels and a less significant fall in blood pressure in response to RAS inhibitors in African Americans, numerous clinical trials support the efficacy of RAS inhibitors to improve clinical outcomes in this population, especially in those with hypertension and risk factors for cardiovascular and related diseases. Here, we discuss the rationale of RAS blockade as part of a comprehensive approach to attenuate the high rates of premature morbidity and mortality associated with hypertension among African Americans.     

Mutation analysis of CYP11B1 and CYP11B2 in patients with increased 18-hydroxycortisol production

BACKGROUND: In patients with glucocorticoid remediable aldosteronism (GRA), a rare hypertensive disorder caused by the presence of a chimeric aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1) gene, high level of urinary 18-hydroxycortisol (18OHF) excretion are observed. In some patients with hypertension, increased urinary 18OHF secretion is also found in the absence of the hybrid CYP11B1/CYP11B2 gene. We hypothesised that gene variants of CYP11B1 or CYP11B2 may be linked to this abnormal glucocorticoid production. METHODS: The urinary steroid profile was analysed by gas chromatography/mass spectrometry in 429 hypertensive patients and 98 (23%) thereof tested positive for increased 18OHF excretion. After correction for total cortisol excretion, 12 subjects showed an abnormally high 18OHF excretion. For genotyping DNA was obtained from six of these patients. All were tested negative for the hybrid CYP11B1/CYP11B2 gene and were further analysed for mutations in all exons and promoter regions of both CYP11B1 and CYP11B2 by single strand conformation polymorphism (SSCP) and sequencing when appropriate. RESULTS: The genetic analysis of the two genes revealed the presence of nine molecular variants in CYP11B2 and three in CYP11B1. In addition to published polymorphic sites, we identified two new variants in CYP11B2 but no new variants in CYP11B1. The newly identified CYP11B2 mutations are a C/T single nucleotide exchange located in the first intron and a double nucleotide exchange at the 3'-splice site of exon 8. The mutated sequence corresponds to the sequence of CYP11B1 indicating a gene conversion. This suggests that the mutant is not likely to affect splicing. Thus, none of the genetic variants identified explains the high urinary excretion of 18OHF. CONCLUSIONS: We present here a complete method for the genetic analysis of the CYP11B1 and CYP11B2 genes. By this method we could not identify genetic variants responsible for a GRA-like phenotype. The presence of high levels of 18OHF should not be used alone as a diagnosis tool for GRA.     

血管紧张素转换酶和醛固酮合成酶基因多态性与氢氯噻嗪降压疗效的关系

目的研究血管紧张素转换酶(ACE)基因I/D多态性和醛固酮合成酶(CYP11B2)基因-344T/C多态性与氢氯噻嗪降压疗效的关系。方法829例高血压病(EH)患者同时服用氢氯噻嗪12·5mg(1次/d),6周后资料完整的785例患者按不同ACE基因型和CYP11B2基因型分组,比较不同基因型和不同基因型组合间血压下降值有无差别。结果服用氢氯噻嗪6周后,ACE基因II、ID、DD型患者收缩压分别下降(5·1±14·8)mmHg(1mmHg=0·133kPa)、(4·8±16·3)mmHg和(9·4±15·7)mmHg,DD型患者下降值大于II、ID型患者,组间比较差异有统计学意义(P<0·00);CYP11B2基因TT、TC、CC型患者收缩压下降值分别为(5·8±16·2)mmHg、(5·5±14·9)mmHg和(7·6±16·1)mmHg,组间比较差异无统计学意义。DD+CC基因型患者收缩压下降值为(10·6±12·3)mmHg,高于其他基因型组合患者,但差异无统计学意义(P>0·05)。多因素分析结果表明DD基因型和治疗前醛固酮浓度是影响患者坐位收缩压下降的主要因素。结论ACE基因的DD型与氢氯噻嗪的降压疗效相关,CYP11B2基因CC型、DD+CC型患者对氢氯噻嗪的降压反应可能优于其他基因组合患者。     

The Prevalence of CYP2C8, 2C9, 2J2, and soluble epoxide hydrolase polymorphisms in African Americans with hypertension

BACKGROUND: The cytochrome P450 (CYP) epoxygenase pathway produces arachidonic acid metabolites that are vasoactive, that affect renal sodium handling, and that have been proposed to play a mechanistic role in hypertension. Multiple single nucleotide polymorphisms (SNP) in CYP2C8, 2C9, 2J2 and soluble epoxide hydrolase (sEH) have been identified, many of which have altered functional activity in vitro. We performed a case-control study to determine the prevalence of epoxygenase-related SNP in African American individuals and to evaluate whether these SNP are associated with increased risk of hypertension. METHODS: Normotensive African American individuals (N = 107) and African American patients with hypertension (N = 108) were recruited. DNA was extracted from a venous blood sample and genotyped for CYP2C8*2,*3, CYP2C9*2-*5,*8,*11, CYP2J2 *2-*7, L50L, R49S, V113M, N124S, sEH R287Q, and sEH 403Rins variant alleles by allelic discrimination using real-time polymerase chain reaction. Genotype and allele frequencies were calculated and associations with hypertension were estimated using unconditional logistic regression, adjusting for age and sex. RESULTS: No association was found between any of the variant alleles and hypertension. We did find that only the CYP2C8*3and CYP2C9*2 alleles were in strong linkage disequilibrium in both the hypertensive and healthy African American groups, a finding that was reported previously in healthy individuals of white ethnicity. CONCLUSIONS: These results suggest that these epoxygenase-related SNP are not associated with increased risk of hypertension in the African American population. There was significant linkage disequilibrium between CYP2C8*3 and CYP2C9*2 alleles that was not associated with hypertension.     

Haplotype analysis of aldosterone synthase gene (CYP11B2) polymorphisms shows association with essential hypertension

OBJECTIVE: The CYP11B2 locus is an important candidate region in essential hypertension (HT). We therefore investigated CYP11B2 polymorphisms T-344C, T4986C and A6547G for association with essential HT. This included haplotype analysis and measurement of plasma aldosterone levels. METHODS: The three single nucleotide polymorphisms were genotyped by polymerase chain reaction-restriction fragment length polymorphism analysis of genomic DNA from 146 HT and 291 normotensive (NT) white subjects of Anglo-Celtic descent, in whom parental blood pressure status was the same as the subjects'. Genotype and allele frequencies in HTs and NTs were compared by chi2 analysis. Linkage disequilibrium and haplotype frequencies were estimated by the program 'snphap'. Phenotype-genotype relationships were tested using one-way analysis of variance. RESULTS: The T-344C variant was associated with HT (chi2 = 7.4, P = 0.0064). This association was confined to female HTs (P = 0.0061 for genotypes, P = 0.0013 for alleles). A strong association with HT was also seen for the A6547G variant (P = 0.0015), being greatest in females (P < 0.0001). No association was seen for the T4986C variant. Haplotype analysis of the three single nucleotide polymorphisms across eight different haplotype combinations showed a significant association with HT (chi2 = 24, seven degrees of freedom, P < 0.001). No significant tracking of plasma aldosterone with genotype was observed. CONCLUSION: The T-344C and A6547G, but not the T4986C, variants of the aldosterone synthase gene are associated with HT in females of the Anglo-Celtic population studied. This was reinforced by haplotype analysis.     

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.     

ACE基因、CYP11B2基因多态性联合分析与原发性高血压合并缺血性脑血管病的相关性研究

目的探讨血管紧张素转换酶（ACE）基因I／D多态性和醛固酮合酶（CYP11B2）基因-344T／C多态性联合分析与原发性高血压（EH）及合并缺血性脑血管病（ICVD）的关系。方法运用聚合酶链反应（PCR）、限制性片段长度多态性（RFLP）等技术检测正常对照（NE）组305例、单纯高血压（SEH）组324例和高血压合并缺血性脑血管病（ICVD）组297例的ACE、CYP11B2基因型，结合临床资料统计分析。结果ACE基因DD型及D等位基因频率在ICVD组显著高于NE组和SEH组（P〈0．0125），在SEH组与NE组问无显著差异；CYP11B2三种基因型在各组分布差异无显著性；ACE基因DD型＋CYP11B2基因TC／CC型分布在三组间有显著差异（P〈0．05），DD—TC／CC频率在ICVD组显著高于NE组和SEH组（P〈0．0125），在SEH组与NE组间差异无显著性；Logistic回归分析提示，年龄、体重指数（BMI）、血清总胆固醇（CHOL）、血糖（GLU）、基因联合DD—TC／CC是EH人群发生ICVD的独立危险因素，而ACE基因DD型未进入回归方程。结论ACE基因I／D多态性和CYP11B2基因-344T／C多态性与高血压无明显关系，但在高血压人群中，年龄、BMI、CHOL、GLU、ACE基因DD型＋CYP11B2基因TC／CC型可能是其发生ICVD的独立危险因素，ACE基因与CYP11B2基因可能存在协同作用。     

Deletion hybrid genes, due to unequal crossing over between CYP11B1 (11beta-hydroxylase) and CYP11B2(aldosterone synthase) cause steroid 11beta-hydroxylase deficiency and congenital adrenal hyperplasia.

Chromosomal rearrangements are natural experiments that can provide unique insights into in vivo regulation of genes and physiological systems. We have studied a patient with congenital adrenal hyperplasia and steroid 11beta-hydroxylase deficiency who was homozygous for a deletion of the CYP11B1 and CYP11B2 genes normally required for cortisol and aldosterone synthesis, respectively. The genes were deleted by unequal recombination between the tandemly arranged CYP11B genes during a previous meiosis, leaving a single hybrid gene consisting of the promoter and exons 1-6 of CYP11B2 and exons 7-9 of CYP11B1. The hybrid gene also carried an I339T mutation formed by intracodon recombination at the chromosomal breakpoint. The mutant complementary DNA corresponding to this gene was expressed in COS-1 cells and was found to have relatively unimpaired 11beta-hydroxylase and aldosterone synthase activities. Apparently the 11beta-hydroxylase deficiency and the adrenal hyperplasia are due to the lack of expression of this gene in the adrenal zona fasciculata/reticularis resulting from replacement of the CYP11B1 promoter and regulatory sequences by those of CYP11B2.     

Variation at the aldosterone synthase (CYP11B2) locus contributes to hypertension in subjects with a raised aldosterone-to-renin ratio

The aldosterone-to-renin ratio (ARR) is a marker of aldosterone activity in hypertension. We examined the relationship of the ARR to the distribution of two biallelic polymorphisms at the CYP11B2 gene locus. One polymorphism affects a putative steroidogenic factor-1 binding site (-344 T/C) in the 5'-regulatory region, whereas the other marker reflects replacement of the intron-2 from CYP11B2 with that from the neighboring gene encoding 11beta-hydroxylase (CYP11B1; wild-type/conversion). We studied consecutive referrals to the Tayside hypertension clinic in 1998. Because the specificity of ARR (pmol/liter/ng/ml/h) for hyperaldosteronism increases with its threshold, ARRs of at least 750 and 1000 were used. A total of 375 patients were assessed; 86.9% had complete data. There were significant excesses of steroidogenic factor-1 (T) (ARR >/= 750, 0.62 vs. 0.51, P = 0.014; ARR >/= 1000, 0.63 vs. 0.51, P = 0.039) and intron-2 (conversion) (ARR >/= 750, 0.49 vs. 0.41, P = 0.205; ARR >/= 1000, 0.54 vs. 0.41, P = 0.029) alleles in patients with a raised ARR. The odds ratio for a raised ARR was 2.27 [95% confidence interval, 1.01, 5.09; P < 0.05] comparing patients with a homozygous haplotype for these alleles with those without any such alleles, and this risk increased with age. This study supports the notion that there is a genetic component that regulates aldosterone production and that hyperaldosteronism might develop over time in susceptible individuals.     

Development of test systems for the discovery of selective human aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1) inhibitors. Discovery of a new lead compound for the therapy of congestive heart failure, myocardial fibrosis and hypertension

Two key players in adrenal steroid hormone biosynthesis are the human mitochondrial cytochrome P450 enzymes CYP11B1 and CYP11B2 that catalyze the final steps in the biosynthesis of cortisol and aldosterone, respectively. Overproduction of both hormones contributes to a number of severe diseases, as illustrated by the association of elevated aldosterone levels with hypertension and higher mortality in congestive heart failure, and by Cushing's syndrome as the clinical correlate of chronic hypercortisolism. Thus, CYP11B1 and CYP11B2 comprise new targets for drug treatment and selective inhibitors of both enzymes are of high pharmacological interest. To facilitate the search for such compounds, we have established novel test procedures using recombinant fission yeast strains that stably express these enzymes. The aim of this study was to compare the inhibition profiles displayed by these enzymes in established mammalian cell culture test systems to those obtained with the new fission yeast assays, and to evaluate the usefulness of the Schizosaccharomyces pombe strains as screening systems for the identification of novel lead compounds. Using these test systems, we were able to identify a new and very selective CYP11B2 inhibitor (SIAS-1) that displayed no detectable interference with CYP11B1 activity.     

Association between aldosterone synthase (CYP11B2) polymorphism and left ventricular mass in human essential hypertension

OBJECTIVES: The aim of our study was to evaluate the relationship between aldosterone synthase gene polymorphism and cardiac dimensions in essential hypertension. BACKGROUND: Higher aldosterone synthase messenger ribonucleic acid levels in the human heart are accompanied by increased intracardiac aldosterone production, a phenomenon that is associated with cardiac fibrosis and hypertrophy. Recent evidence suggests that a polymorphism (-344C/T) in the promoter region of the aldosterone synthase gene is associated with increased constitutive aldosterone production. METHOD: Relationships between M-mode echocardiographic cardiac dimensions and aldosterone synthase -344C/T polymorphism were studied in 210 never-treated, middle-aged patients (age 41.6 +/- 1.4 years) affected by mild to moderate essential hypertension. Among these patients, 48 had the genotype -C344C, 97 had -C344T, and 65 had -T344T. Patients in the three groups were similar in terms of age, gender, body mass index, and blood pressure. RESULTS: Left ventricular (LV) mass and thickness were positively correlated with the number of T alleles: LV mass (CC, CT, and TT, respectively: 168 +/- 6.9, 179 +/- 5.2, and 193 +/- 6.9 g; p = 0.03), LV septal thickness (0.99 +/- 0.02, 1.03 +/- 0.02, and 11.08 +/- 0.03 cm, p = 0.04), PWT (0.93 +/- 0.03, 0.95 +/- 0.01, and 1.03 +/- 0.02 cm; p = 0.002), and relative wall thickness (38.3 +/- 1.2%, 38.8 +/- 0.8%, and 42.8 +/- 1.1%; p = 0.004). This trend was confirmed by linear regression, suggesting a "major gene" behavior for the T allele. Multiple regression analysis showed that this effect was independent of anthropometric and clinical factors, including adrenal aldosterone. CONCLUSIONS: Our data suggest that -344C/T polymorphism affects LV mass and thickness in essential hypertension, independent of adrenal aldosterone. A role for intracardiac aldosterone synthesis is hypothesized.     

Association between aldosterone production and variation in the 11beta-hydroxylase (CYP11B1) gene

CONTEXT: Variation in the region of chromosome 8 including the genes steroid 11beta-hydroxylase (CYP11B1) and aldosterone synthase (CYP11B2) influences mineralocorticoid and glucocorticoid metabolism. However, the relative importance of polymorphisms in CYP11B1 and CYP11B2 in determining these phenotypes is unknown. OBJECTIVE: Our objective was to investigate genetic influences of the CYP11B1 and CYP11B2 genes on mineralocorticoid metabolism. DESIGN: We measured 24-h urinary excretion of the key metabolites of the principal mineralocorticoids, glucocorticoids and androgens secreted by the adrenal cortex. We genotyped polymorphisms spanning the CYP11B1 and CYP11B2 genes, which together capture all common variations at the locus. PARTICIPANTS: Participants included 573 members of 105 British Caucasian families ascertained on a hypertensive proband. MAIN OUTCOME MEASURES: We assessed heritability of urinary tetrahydroaldosterone (THAldo) excretion and association of THAldo excretion with genotype. RESULTS: The heritability of THAldo excretion was 52% (P < 10(-6)). There was significant association between THAldo and genotype at several of the CYP11B1/B2 polymorphisms. The strongest association was observed at the rs6387 (2803A/G) polymorphism in intron 3 of CYP11B1 (P = 0.0004). Association followed a codominant model with a 21% higher THAldo excretion per G allele. Genotype at rs6387 accounted for 2.1% of the total population variability of THAldo. We found significant association between THAldo excretion and urinary total androgen excretion, urinary tetrahydrodeoxycortisol level, and urinary cortisol metabolites (all P < 0.001). CONCLUSIONS: Aldosterone synthesis is highly heritable and is affected by genotype at CYP11B1. Our findings support the hypothesis that genetically determined differences in 11-hydroxylation efficiency can have downstream effects on mineralocorticoid synthesis. Such effects may be of relevance to the development of low-renin essential hypertension.