Genetic analysis in human hypertension

Case-control association study of polymorphisms in the angiotensinogen and angiotensin-converting enzyme genes and coronary artery disease and systemic artery hypertension in African-Brazilians and Caucasian-Brazilians

The rennin-angiotensin-aldosterone system (RAAS) is a critical pathway in regulating blood pressure and salt/water homeostasis, possessing an intimate relationship with the development of systemic artery hypertension (SAH). Once hypertension is considered a risk factor for coronary artery disease (CAD), the RAAS is also related to this pathology. This investigation aimed to analyse if the frequencies of AGT M235T (rs699) and ACE I/D (rs4646994) polymorphisms are associated with CAD and SAH in African-Brazilians and Caucasian-Brazilians. In this study we analysed 714 subjects who underwent coronary angiography to detect obstructive lesions and CAD, as well as blood pressure measurement and SAH, grouped according to ethnicity: 266 African-Brazilians and 448 Caucasian-Brazilians. Among CAD and SAH cases and controls, the genotype and allele frequencies of ACE I/D polymorphism were similar in both ethnic groups. The AGT 235TT genotype and 235T allele frequencies were higher in SAH cases (32%, 54.7%) versus controls in Caucasian-Brazilians (19.8%, 46.4%; P = 0.038, P = 0.031, respectively). The AGT 235TT (OR = 1.8; P = 0.028) demonstrated to be an independent factor risk in a multivariate logistic regression increasing SAH risk in Caucasians but not in African-Brazilians. In summary, AGT M235T polymorphism was associated with SAH risk in Caucasian-Brazilians, and no association was detected with CAD. No association was also observed in ACE I/D polymorphism either in CAD or SAH in African-Brazilians and Caucasian-Brazilians.

Differences in genotype frequencies of salt-sensitive genes between fishing and nonfishing communities in Japan

PURPOSE

To identify the differences in genotype frequencies of salt-sensitive genes between residents of fishing communities (FCs) and nonfishing communities (NFCs).

METHODS

The subjects included 18,156 individuals (8,043 males [44%] and 10,113 females [56%]; average age: 57.2±16.1 years) from the general population who were registered with large-scale genome banks and resided in 30 prefectures and 78 different regions in Japan. The measurement items were age, sex, blood pressure, presence or absence of hypertension, body mass index, alcohol consumption, and smoking habit. Furthermore, to analyze the genotype frequencies of salt-sensitive genes, α-adducin 1 (ADD1), angiotensinogen (AGT), angiotensin II receptor type 1 (AT1), and guanine nucleotide-binding protein β peptide 3 (GNB3) were measured. According to the 2004 government classification of municipalities (cities, towns, and villages), communities existing in areas bordering an ocean and with an ocean port were defined as FCs (28 areas). The others were defined as NFCs (50 areas). A logistic regression model was used for comparison of genotype frequencies between subjects residing in FCs and NFCs.

RESULTS

Of the included subjects, 4,916 (27.0%) and 13,240 (73.0%) resided in FCs and NFCs, respectively. In FCs, the mean age was 59.4±16.7 years and men accounted for 41.0% of the cohort (n=2,015). In NFCs, the mean age was 56.4±15.8 years and men accounted for 45.5% of the cohort (n=6,028). The adjusted odds ratios of the AA and AG genotypes compared with the GG genotype for AGT were 0.80 (95% confidence interval [CI]: 0.68-0.95) and 0.76 (95% CI: 0.64-0.91), respectively. The adjusted odds ratio of the CC genotype compared with AA for AT1 was 0.63 (95% CI: 0.40-0.93).

CONCLUSION

The incidence of the salt-sensitive genotypes AGT and AT1 in residents of FCs were significantly lower than in NFCs.

Molecular genetics of essential hypertension

Hypertension is a major public health problem in the developing as well as in developed countries due to its high prevalence and its association with coronary heart disease, renal disease, stroke, peripheral vascular disease, and related disorders. Essential hypertension (EH) is the most common diagnosis in this disease, suggesting that a monocausal etiology has not been identified. However, a number of risk factors associated with EH have also been identified such as age, sex, demographic, environmental, genetic, and vascular factors. Recent advances in molecular biological research had achieved clarifying the molecular basis of Mendelian hypertensive disorders. Molecular genetic studies have now identified mutations in several genes that cause Mendelian forms of hypertension in humans. However, none of the single genetic variants has emerged from linkage or association analyses as consistently related to the blood pressure level in every sample and in all populations. Besides, a number of polymorphisms in candidate genes have been associated with differences in blood pressure. The most prominent candidate has been the polymorphisms in the renin-angiotensin-aldosterone system. In total, EH is likely to be a polygenic disorder that results from inheritance of a number of susceptibility genes and involves multiple environmental determinants. These determinants complicate the study of blood pressure variations in the general population. The complex nature of the hypertension phenotype makes large-scale studies indispensable, when screening of familial and genetic factors was intended. In this review, recent genetic studies exploring the molecular basis of EH, including different molecular pathways, are highlighted.

Lifestyle intervention might easily improve blood pressure in hypertensive men with the C genotype of angiotensin II type 2 receptor gene

BACKGROUND/OBJECTIVES

Recent studies have reported an association of the angiotensin II type 2 receptor (AT2R) 3123Cytosine/Adenine (3123C/A) polymorphism with essential hypertension and cardiovascular diseases. The purpose of the study was to investigate whether the AT2R 3123C/A polymorphism affects blood pressure for free-living hypertensive men during a 5-month intervention period.

SUBJECTS/METHODS

The subjects were free-living hypertensive Japanese men aged 40 to 75 years who agreed to intervention in the period from 2004 to 2011. Detection of the AT2R 3123C/A polymorphism was determined by polymerase chain reaction. The dietary intervention was designed to decrease salt level and to increase potassium level through cooking instructions and self-monitoring of the diet. The exercise session consisted of activities such as stretching, resistance training, and walking. Blood pressure, urinary sodium and potassium excretion, dietary and lifestyle data, and non-fasting venous blood sample were collected at baseline and after the intervention period.

RESULTS

Thirty nine subjects were eligible for participation and the follow-up rate was 97.4%. The C allele proportion was 57.9%. AT2R 3123C/A polymorphism was X-chromosome-linked, therefore we analyzed the C and A genotypes. At baseline, no significant differences were observed between the genotype groups. After the intervention, there were no significant differences in lifestyle habit between the groups. Nevertheless, the estimated salt excretion (g/day) was significantly decreased only in the C genotype (13.0-10.3, P = 0.031). No significant change was observed in systolic blood pressure (SBP) (mmHg) in the A genotype, but a significant decrease was observed in the C genotype (150.0-141.5, P = 0.024).

CONCLUSTIONS

In the C genotype, it might be easy to improve SBP through lifestyle intervention in free-living hypertensive Japanese men, however generalization could not be achieved by the small sample size.

Association of single nucleotide polymorphisms in the 3'UTR of ERAP1 gene with essential hypertension in the Northeastern Han Chinese

Endoplasmic reticulum aminopeptidase 1 (ERAP1) may be involved in blood pressure regulation by inactivation of angiotensin II and generation of bradykinin. Our previous study with cDNA microarray indicated that the expression of ERAP1 is down-regulated in essential hypertension (EH) patients. Since the 3'untranslated region (3'UTR) is known to play an important role in the post-transcriptional regulation by influencing the stability and translation process of mRNA, the present study aims to identify single nucleotide polymorphisms (SNPs) in the 3'UTR of ERAP1 gene in a case-control study among the Northeastern Han Chinese through PCR-sequencing, and analyze the association with EH. Our results further verified the lower expression level of ERAP1 in the peripheral blood cells in patients with EH (917.12±517.57 vs. 1506.59±1214.09pg/mL, P=0.011). Four SNPs, 3'UTR-761G>A, 3'UTR-787C>T, 3'UTR-1008A>C and 3'UTR-1055A>G, were identified in the 3'UTR of ERAP1. 3'UTR-1008A>C and 3'UTR-1055A>G were in almost complete linkage disequilibrium. Association analysis showed that the genotypic and allelic frequencies of 3'UTR-1008A>C and 3'UTR-1055A>G were significantly different between EH and the control groups. Logistic regression and haplotypic analysis indicated that alleles of E20-1037C and E20-1084G as well as haplotype of C-G were the risk factors of EH (P<0.05). Subgroup analysis performed by age suggested that the frequencies of genotype and allele of 3'UTR-1008A>C and 3'UTR-1055A>G as well as the haplotypes C-G and A-A were significantly different between EH and the control in the younger group (<50), but not in the older group (≥50). Younger population with the 3'UTR-1008CC and/or 3'UTR-1055GG genotypes also tended to have higher blood pressure, especially the diastolic blood pressure. In conclusion, the 3'UTR-1008A>C and 3'UTR-1055A>G polymorphisms of ERAP1 gene were associated with EH, especially in the younger population, and the haplotype C-G could be the independent marker of EH.

Natural variation within the neuronal nicotinic acetylcholine receptor cluster on human chromosome 15q24: influence on heritable autonomic traits in twin pairs

Nicotinic acetylcholine receptors (nAChRs) are combinations of subunits arranged as pentamers encircling a central cation channel. At least nine alpha and four beta subunits are expressed in the central and peripheral nervous systems; their presence in autonomic ganglia, the adrenal medulla, and central nervous system, with accompanying responses elicited by nicotinic agonists, point to their involvement in cardiovascular homeostasis. nAChRs formed by alpha3, alpha5, and beta4 subunits may regulate blood pressure (BP) by mediating release of catestatin, the endogenous nicotinic antagonist fragment of chromogranin A (CHGA) and potent inhibitor of catecholamine secretion. Genes encoding these subunits (CHRNA3, CHRNA5, and CHRNB4) are clustered on human chromosome 15q24. Because variation in this cluster may alter autonomic regulation of BP, we sequenced approximately 15 kilobase pairs in 15q24 containing their coding and 5'- and 3'-untranslated regions in 80 individuals. We identified 63 variants: 25 in coding regions of CHRNA3, CHRNA5, and CHRNB4 and 48 noncoding single-nucleotide polymorphisms (SNPs). Haplotype frequencies varied across ethnic populations. We assessed the contribution of six SNPs in the putative catestatin binding region of CHRNA3 and CHRNB4 to autonomic traits. In twins, catestatin and BP were heritable. CHRNA3 SNPs and haplotypes containing K95K (G285A) associated with circulating plasma catestatin, epinephrine levels, as well as systolic BP, suggesting altered coupling of the nAChRs to BP. Studies of chromaffin cells in vitro reveal that nicotinic agonist stimulation releases catecholamines and CHGA, a process augmented by overexpression of CHRNA3 and blocked by catestatin. These cellular events suggest a homeostatic mechanism underlying the pleiotropic actions of CHRNA3 genetic variation on autonomic function observed in twins.

Xylosyltransferase gene variants and their role in essential hypertension

BACKGROUND

An accumulation of extracellular matrix molecules, such as proteoglycans, is observed in the vascular wall of hypertensive patients. Xylosyltransferases I and II (XT-I and XT-II), the chain-initiating enzymes in the biosynthesis of proteoglycans, catalyze the transfer of D-xylose from UDP-D-xylose to specific serine residues of the core protein. Because associations between XYLT polymorphisms and an altered blood pressure have been observed, genetic variations in the XYLT genes might predispose to essential hypertension. The localization of the XYLT2 gene on chromosome 17q increases its attractiveness as this region has been reported to be a potential candidate locus for essential hypertension.

METHODS

Genotyping of four polymorphisms in the genes XYLT1 and XYLT2 was performed in 150 unrelated essential hypertension patients and 150 age- and sex-matched normotensive controls using restriction fragment length polymorphism analysis.

RESULTS

The allele and genotype frequencies of the XYLT variants investigated did not show any significant differences between patients and controls, among allele-carriers and nonallele-carriers and among recessive and nonrecessive allele-carriers comparing patients and controls. Systolic and diastolic blood pressures did not differ significantly between the genotypes concerning all XYLT variants analyzed. Two XYLT2 variants deviated from Hardy-Weinberg equilibrium (HWE) in the hypertensive group.

CONCLUSIONS

No statistically significant association was found between four XYLT variants and hypertension or blood pressure, suggesting that they do not play a significant role in the development of essential hypertension. The deviation from HWE of two XYLT2 variants might be due to gene-phenotype associations which remain to be explored, as well as the possibility of gene-gene interactions.

1H NMR-based metabonomic analysis of urine from young spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) and their substrains are a useful model for studying essential hypertension which is a complex, polygenic, and multifactorial disorder. Their genetic and metabolic features are of great interest because they may provide insights into the mechanism of blood pressure regulation. We have compared urinary metabolic profiles of young SHR with those of their age-matched normotensive controls, Wistar Kyoto rats, using (1)H NMR-based metabonomics. Principal components analysis was applied to the NMR spectral data after data-reduced and normalized by the total integral or the creatinine integral. Consequently, a clear separation of urine samples between the two strains was observed in the principal components scores plot. The loadings plot from the data normalized by the creatinine integral showed that many metabolites such as citrate, alpha-ketoglutarate, and hippurate contributed to the separation, and the urinary levels of most metabolites used in this study, including these three, were lower in SHR than in Wistar Kyoto rats. These metabolic changes may be concerned with blood pressure regulation in SHR, although a relation to other strain differences cannot be ruled out. The present study suggests the usefulness of a (1)H NMR-based metabonomic approach using SHR in the field of hypertension research.

Endothelin-1 gene and endothelial nitric oxide synthase gene polymorphisms in adolescents with juvenile and obesity-associated hypertension

Hypertension is an increasing public health problem all over the world. Essential hypertension accounts for more than 90% of cases of hypertension. It is a complex genetic, environmental and demographic trait. New method in molecular biology has been proposed a number of candidate genes, but the linkage or association with hypertension has been problematic (lack of gene-gene and gene-environment interaction). It is well known that genetic influences are more important in younger hypertensives, because children are relatively free from the common environmental factors contributing to essential hypertension. The association studies compare genotype ferquencies of the candidate gene between patient groups and the controls, in pathways known to be involved in blood pressure regulation. This study examined three polymorphisms of these factors encoding genes (ET-1 G+5665T (Lys198Asn), endothelial nitric oxide synthase (eNOS) T-786C promoter polymorphism and 27-bp repeat polymorphism in intron 4) in adolescents with juvenile essential and obesity-associated hypertension. Significant differences were found in the G/T genotype of the ET-1 polymorphism in the hypertensive and obese+hypertensive patients (body mass index (BMI) > 30). A strong association was detected between the BMI and the polymorphism of the ET-1 gene. It seems that ET-1 gene polymorphism plays a role in the development of juvenile hypertension associated with obesity. Although no significant differences were seen in the case of the eNOS promoter polymorphism and the eNOS 4th intron 27-bp repeat polymorphism. It seems that eNOS may play a role, but this is not the main factor in the control of blood pressure; it is rather a fine regulator in this process. This study with adolescents facilitates an understanding of the genetic factors promoting juvenile hypertension and obesity.

Mistyping of Angiotensinogen M235T Alleles

Conflicting results are to be found in the literature on the relationship between the M235T polymorphism of the angiotensinogen (AGT) gene and hypertension. The controversy may be due to insufficient numbers of subjects, the variability of the inclusion criteria and the different genotype analysis methods used. We have experienced that the most frequently used, original polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) method involves significant uncertainties when the TT genotype is determined, independently of the restriction digestion. To make the determination more accurate, we improved the PCR by designing a new antisense primer containing only one mismatch instead of the two in the original protocol and also by adding DMSO to the PCR reaction mixture. The original and our improved methods were compared by using DNA from 123 patients: parallel determinations resulted in values of 33 MM, 90 MT and 0 TT with the original method and of 33 MM, 56 MT and 34 TT with the improved RFLP protocol. In summary, a plausible explanation for some of the conflicting data published on AGT M235T polymorphism may be that inaccuracies arose during the determination of the genotype.

Protective effect of the KCNMB1 E65K genetic polymorphism against diastolic hypertension in aging women and its relevance to cardiovascular risk

The E65K polymorphism in the beta1-subunit of the large-conductance, Ca2+-dependent K+ (BK) channel, a key element in the control of arterial tone, has recently been associated with low prevalence of diastolic hypertension. We now report the modulatory effect of sex and age on the association of the E65K polymorphism with low prevalence of diastolic hypertension and the protective role of E65K polymorphism against cardiovascular disease. We analyzed the genotype frequency of the E65K polymorphism in 3924 participants selected randomly in two cross-sectional studies. A five-year follow-up of the cohort was performed to determine whether cardiovascular events had occurred since inclusion. Estrogen modulation of wild-type and mutant ion channel activity was assessed after heterologous expression and electrophysiological studies. Multivariate regression analyses showed that increasing age upmodulates the protective effect of the K allele against moderate-to-severe diastolic hypertension in the overall group of participants (odds ratio [OR], 0.35; P=0.006). The results remained significant when analyses were restricted to women (OR, 0.18; P=0.02) but not men (OR, 0.46; P=0.09). This effect was independent of the reported acute modulation of BK channels by estrogen. A five-year follow-up study also demonstrated a reduced age- and sex-adjusted hazard ratio of 0.11, 95% CI, 0.01 to 0.79 of K-carriers for "combined cardiovascular disease" (myocardial infarction and stroke) compared with EE homozygotes. Our study provides the first genetic evidence for the different impact of the BK channel in the control of human blood pressure in men and women, with particular relevance in aging women, and highlights the E65K polymorphism as one of the strongest genetic factors associated thus far to protection against myocardial infarction and stroke.

Sympathetic Hypertensive Syndrome: A Possible Surgically Curable Type of Hypertension

Poorly controlled hypertension was incidentally cured after performing an endoscopic sympathetic block (ESB) in a patient with hyperhidrosis craniofacialis (HHC). A survey of the literature indicated that 30% to 40% of essential hypertension is of sympathetic origin. Patients with facial sweating associated with hypertension were then studied to determine whether blood pressure is lowered after performing ESB. Between November 2002 and July 2003, 17 hypertensive patients (13 males and 4 females) ranging in age from 22 to 62 years underwent ESB solely for HHC at the Department of Surgery of Kaohsiung Medical University, Taiwan. Their preoperative systolic blood pressure (SBP) values ranged from 170 +/- 6 to 200.7 +/- 7.6 mmHg, and their diastolic blood pressure (DBP) values ranged from 94.7 +/- 6.1 to 120.3 +/- 5.7 mmHg. Their heart rates were between 92.67 +/- 2.28 and 119.67 +/- 5.13 beats per minute (bpm). They were refractory to aggressive medical treatment, including lifestyle modifications and antihypertensive medications. Their postoperative blood pressure, heart rate and surgical outcomes were recorded. After performing ESB, HHC was cured in all 17 patients. Based on the reductions in blood pressure and heart rate, the patients could be divided into two groups, one showing high-level reductions (Group T) and one showing low-level reductions (Group S). The blood pressure of Group T (ten patients) was reduced to the range of 120.2 +/- 6.9 to 131.6 +/- 3.5 mmHg SBP and 74.8 +/- 3.1 to 85.4 +/- 4.5 DBP, and the heart rate of this group was reduced to the range of 65.36 +/- 4.63 to 85 +/- 3.60 bpm, while the blood pressure and heart rate of Group S (seven other patients) were reduced to the ranges of 145.9 +/- 5.7 to 160.5 +/- 5.5 mmHg SBP, 90 +/- 4 to 100.7 +/- 3.2 mmHg DBP, and 80 +/- 4 to 90.83 +/- 3.53 bpm, respectively. The patients in Group S were well controlled at 119.8 +/- 5.5 to 130.6 +/- 8.0 mmHg SBP and 70.1 +/- 3.8 to 84.5 +/- 5.7 mmHg DBP with a daily low-dose of calcium channel blocker. The average follow-up periods of the two groups were 17.00 +/- 2.906 and 17.43 +/- 2.37 months, respectively. We named this surgically curable form of hypertension "Sympathetic Hypertensive Syndrome" (SHS), which we define by the presence of all three of the following: 1) stage II hypertension; 2) HHC or other sympathetic disorders; and 3) heart rate > or = 100 bpm. If the patient is male the reductions of blood pressure after the surgery will be better, which might be due to the link with Y chromosome. Finally, we recommend that ESB should be performed in patients with SHS, although the female would respond less satisfactorily in terms of the blood pressure.

Investigations into Biochemical Changes of Genetic Hypertensive Rats Using 1H Nuclear Magnetic Resonance-Based Metabonomics

Genetically hypertensive rats provide a simple and accessible model for studying essential hypertension, which is a polygenic, heterogenous and multifactorial disease. Their genetic and metabolic features are of great interest because they may provide insight into the pathophysiological processes underlying essential hypertension. We have investigated the genetic influence on metabolic balance and metabolite excretion patterns in stroke-prone spontaneously hypertensive rats (SHRSP) with established hypertension using 1H NMR-based metabonomics. Urinary metabolite profiles for SHRSP and their age-matched normotensive controls, Wistar Kyoto rats, were acquired using 1H NMR spectroscopy. Principal components analysis was applied to these complex NMR data to facilitate differentiation and determine metabolic differences between urine samples collected from the hypertensive and normotensive rats. Consequently, it was possible to distinguish urine samples between the two strains in the principal components scores plot. The loadings plot showed that taurine, creatine and some unidentified metabolites resonating at around delta 2.48, 3.10 and 3.58 predominantly contributed to the separation. In SHRSP, the urinary levels of taurine and creatine were found to be higher and the intensities of the unknown signals much lower than those in the Wistar Kyoto rats. Although the pathophysiological significance of these components remains to be elucidated, this study suggests that 1H NMR-based metabonomics is a promising approach to provide new information on metabolic changes related to the pathophysiological processes of the genetically hypertensive rats.

A Single Nucleotide Polymorphism in the Carboxylesterase Gene Is Associated with the Responsiveness to Imidapril Medication and the Promoter Activity

Imidapril is an angiotensin-converting enzyme inhibitor that is widely used in treating hypertension, although the responses vary among individuals. We investigated whether a single nucleotide polymorphism at position -816 of the carboxylesterase 1 (CES1) gene, which activates imidapril in the liver, is involved in the responsiveness to imidapril medication. A total of 105 Japanese hypertensives with systolic/diastolic blood pressures (SBP/DBP) of 140/90 mmHg or higher were prescribed 5-10 mg/day of imidapril. At baseline, blood pressure levels were not different between patients with and those without the -816C allele (AA vs. AC+ CC groups). After 8 weeks of treatment, we classified the responders and non-responders based on the decline in their blood pressures, and found that the responder rate was significantly higher in the AC+CC group than in the AA group (p=0.0331). Also, the reduction in SBP was significantly greater in the AC+CC group than in the AA group (24.7+/-11.8 vs. 17.6+/-16.8 mmHg, p=0.0184). Furthermore, an in vitro reporter assay revealed that the -816C construct had significantly higher promoter activity (p<0.0001). These findings suggest that the A(-816)C polymorphism affects the transcriptional activity, and that this may account for the responsiveness to imidapril.

Relation between the angiotensin-converting enzyme insertion/deletion polymorphism and blood pressure in Japanese male subjects

Inconsistent results have been reported regarding the association of the angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism and hypertension. Recent studies of population-based samples of three different areas in Japan presented conflicting results regarding this association. We, thus, investigated the relation between the ACE I/D polymorphism and blood pressure (BP), or the frequency of hypertension, respectively, in 706 Japanese male subjects who participated in the health check-up programme of our hospital. The ACE I/D polymorphism was determined by the polymerase chain reaction technique. Of 706 subjects, 203 were found to have hypertension and the other 503 were found to be normotensive. In all subjects, the frequencies of the DD, ID, and II genotypes were 0.123, 0.432, and 0.445, respectively, and the allelic frequency of the D allele was 0.339. In the younger subjects aged <50 years (n=264), neither systolic nor diastolic BP differed significantly among the genotypes. Conversely, in the older subjects aged > or =50 years (n=442), the systolic BP was significantly higher by 5.9 mmHg in the subjects with the ID genotype than those with the II genotype (P<0.01), and the diastolic BP was significantly higher in the subjects with the DD and ID genotypes by 5.1 and 3.3 mmHg, respectively than those with the II genotype (P<0.05 for each), although age, BMI, percentage of smoking habits, drinking habits, or the use of antihypertensive drugs did not differ significantly among the genotypes. In addition, in the older subjects, the hypertensive subjects showed significantly higher frequencies of the DD and ID genotypes and the D allele than the normotensive subjects. These results demonstrated that there was no significant association of the ACE I/D polymorphism with BP or a prevalence of hypertension in younger Japanese men aged <50 years but there was in older Japanese men aged > or =50 years.

High Sodium Intake Strengthens the Association between Angiotensinogen T174M Polymorphism and Blood Pressure Levels among Lean Men and Women: a Community-Based Study

Evidence on the effect of salt intake on the interaction between angiotensinogen (AGT) T174M polymorphism and high blood pressure is sparse. We therefore conducted a large population-based cross-sectional study of 2,823 men and women aged 30-74 in a Japanese farming community to examine associations between AGT polymorphism and blood pressure levels stratified by age (30-64 and 65-74), body mass index (BMI; median), and salt intake (median) estimated by 24-h urine collection and dietary questionnaire. Our a priori hypothesis is that individuals, particularly younger and non-overweight individuals, with the 174M allele have elevated blood pressure levels in response to higher sodium intake, and thus the association between T174M polymorphism and blood pressure is more evident among individuals with higher sodium intake than those with lower sodium intake. There were no differences in systolic or diastolic blood pressure levels (SBP or DBP) between the TT and TM+MM genotype groups overall. However, the mean difference in DBP between the TM+MM and TT groups was +1.0 mmHg in subjects of younger age (p=0.06), +1.7 mmHg in non-overweight subjects (BMI<23.5 kg/m2, p=0.01), and +2.3 mmHg in younger and non-overweight subjects (p = 0.002). Furthermore, among younger and non-overweight subjects, blood pressure differences were larger for those with higher urinary sodium excretion (+3.1 mmHg, p = 0.03), those with a higher sodium/potassium excretion ratio (+4.1 mmHg, p=0.007), those with higher present sodium intake score (+3.0 mmHg, p=0.003), and those with higher past sodium intake score (+3.4 mmHg, p<0.001). In conclusion, AGT T174M polymorphism was associated with higher DBP levels in younger and non-overweight Japanese. This association was more evident among subjects with higher sodium intake.

Association of a GNAS1 Gene Variant with Hypertension and Diabetes Mellitus

Previous studies have shown that the T allele of the GNAS1 T393C polymorphism is associated with poor responsiveness to beta-blockade and that the T393C polymorphism interacts with cigarette smoking and alcohol consumption in the pathogenesis of hypertension. Thus, the T393C polymorphism is likely to interact with beta-adrenoceptor (beta-AR) stimulation in the pathogenesis of hypertension. Although this interaction might be caused by a direct effect of Gs proteins on the cardiovascular system, it could also result from an indirect effect of Gs proteins mediated by glucose metabolism. Moreover, association studies are often irreproducible. We therefore examined the possible interaction between the T393C polymorphism and gamma-glutamyl transpeptidase (GGT), which is an established biomarker of alcohol consumption, in the association with glucose metabolism as well as with hypertension in a Japanese population. Genotyping for GNAS1 was performed by using the polymerase chain reaction-restriction fragment length polymorphism method in all 821 samples. The present study showed a significant interaction between the T393C polymorphism and GGT in the association with hypertension (p =0.033). This interaction was even more significant after adjustment for all confounding factors (p =0.0025). In contrast, analysis of the possible interaction of the T393C polymorphism with GGT in the association with diabetes mellitus or fasting plasma glucose failed to show a significant result. These results did not support the hypothesis that the interaction between the T393C polymorphism and GGT in the association with hypertension could be caused by an indirect effect of Gs proteins mediated by glucose metabolism.

Association of angiotensin II type 2 receptor gene variant with hypertension

The renin-angiotensin system plays an important role in blood pressure regulation by influencing salt-water homeostasis and vascular tone. Angiotensin II, the major biologically active component of this system, exerts its effect via two pharmacologically distinct subtypes of angiotensin II receptors, the angiotensin II type 1 receptor (AT1-R) and the angiotensin II type 2 receptor (AT2-R). Thus, the AT2-R gene may be involved in hypertension. Accordingly, our objective was to examine whether polymorphisms of the AT2-R gene are involved in hypertension. The entire AT2-R gene including the promoter region was screened to find polymorphisms. As a result, two novel single nucleotide polymorphisms (SNPs), A1818T in intron 2 and G4303A in exon 3, as well as two known SNPs, A1675G in intron 1 and C4599A in exon 3, were identified. These four SNPs had similar allele frequencies, and the A1675G and C4599A polymorphisms were in almost complete linkage disequilibrium. Because the AT2-R gene is located on the X chromosome, we analyzed the possible association between the C4599A polymorphism and hypertension in men and in women separately in two large Japanese populations. This analysis showed that the C4599A polymorphism was associated with hypertension in women (p=0.0058), but not in men. Moreover, this female-specific association was pronounced in premenopausal women. The female-specific association may be helpful in conducting further molecular and biological studies on the relationship among sex, the renin-angiotensin system, and hypertension.

Variation near the region of the lipoprotein lipase gene and hypertension or blood pressure levels in Chinese

Essential hypertension (EH) is a common late-onset disease that exhibits complex genetic heterogeneity. Human lipoprotein lipase (LPL) is a rate-limiting enzyme that regulates the catabolism of triglycerides (TG) and chylomicrons (CM). Since dyslipidemia is a common finding in hypertensive patients, the LPL gene is a logical candidate gene that could contribute to the development of hypertension. Using linkage analysis in 148 Chinese hypertensive families, we identified a region of linkage with systolic blood pressure (SBP) and diastolic blood pressure (DBP) that consisted of a 10.6-cM interval defined by markers D8S1145, D8S261, and D8S282 on chromosome 8, which maps between 31 to 41.6 cM from the 8p-telomere contained LPL gene, with statistically significant p values for the marker D8S261 (p = 0.0021 for SBP, and p = 0.0395 for DBP). In the qualitative-trait linkage analysis, evidence for linkage between the marker D8S1145 and EH was found (p = 0.0286). The transmission/disequilibrium test (TDT/S-TDT) also supported a significant linkage-disequilibrium of the allele 3 of D8S261 with EH (chi2 = 8.643, p < 0.01). Furthermore, the marker neurofilament light polypeptide (NEFL) (11 cM centromeric to the LPL gene) appeared to be in linkage with SBP and DBP (p = 0.0329 for SBP; p = 0.0319 for DBP). Additionally, two flanking markers for LPL, D8S511 (9.5 cM telomeric to the LPL gene) and D8S560 (3.2 cM centromeric to the LPL gene), also showed significant linkage with EH (p = 0.0036 for D8S511; p = 0.0115 for D8S560). Previous knowledge about the physiological involvement of LPL in blood pressure regulation and the present findings of variation near the LPL gene support the proposition that a region near the LPL gene or the LPL gene itself might contribute to the individual blood pressure variation in Chinese.

An alternative fast and convenient genotyping method for the screening of angiotensin converting enzyme gene polymorphisms

Insertion/deletion (I/D) polymorphisms in intron 16 of the angiotensin converting enzyme gene (ACE) are associated with the plasma angiotensin converting enzyme (ACE) levels, and individuals with the DD allele have been reported to be more susceptible to cardiovascular disease than those without. The conventional genotyping method for the screening of I/D polymorphisms, which involves polymerase chain reaction (PCR)-gel electrophoresis, is laborious and time-consuming. In this study, we assessed the use of TaqMan-PCR genotyping for the screening of I/D polymorphisms as a replacement for the conventional method. We genotyped seven single nucleotide polymorphisms (SNPs) in linkage disequilibrium (LD) with the I/D polymorphisms, and calculated the LD coefficients of the I/D polymorphisms. We found that three polymorphisms, rs4331, rs4334 and rs4341, exhibited the highest LD coefficients (D' = 1.000; r2 = 0.967) and that the genotyping of rs4341 by the TaqMan-PCR method yielded the best discrimination among the different genotypes. Genotyping of 511 samples took only 2 h and the amount of DNA required for each test was only 6 ng by the TaqMan-PCR method using rs4341. In the course of this study, we identified a novel additional polymorphism (a deletion of six amino acids) in exon 13, near rs4316. The deletion allele encoded the testicular ACE, but not the plasma ACE. We concluded that genotyping of the rs4341 ACE polymorphism by the TaqMan-PCR method is a fast and convenient alternative method for direct I/D genotyping. We also concluded that testicular ACE may manifest a deletion of six amino acids that may result in deleterious function of this enzyme.

Alterations in the Dimensions of Aortopulmonary Septum in Hypertensive Subjects

The neural crest origin of the aortopulmonary septum has led us to investigate the septum for a special function, and we designed the present study to assess the alteration, if any, in the dimensions of the aortopulmonary septum in hypertension. The dimensions of the aortopulmonary septum were measured by echocardiography in 36 hypertensive and 36 age- and sex-matched normotensive subjects. Echocardiographic examination included measurement of the cross-sectional area of the aortopulmonary septum with standard two-dimensional views from the parasternal windows. Standardization of this dimension with appropriate cardiac measurements such as aortic and internal left ventricular diameters was also performed to provide growth-independent estimates of septal size. The average area of the septum in the hypertensive group was 2.183 +/- 0.391 cm2, significantly lower than that in the normotensive group (2.370 +/- 0.415 cm2). There were also significant differences in the area of the aortopulmonary septum between the groups when the values were standardized with internal left ventricular diameters. In conclusion, these data confirm that the aortopulmonary septum is smaller in hypertensive than in normotensive humans. This difference might be the result of a possible function of the aortopulmonary septum in blood pressure regulation.