beta2-adrenoceptor gene polymorphisms and blood pressure variations in East Anglian Caucasians

Association study of the β2-adrenergic receptor gene polymorphisms and hypertension in the Northern Han Chinese

Background

The β2-adrenergic receptor (ADRB2) gene has been widely researched as a candidate gene for essential hypertension (EH), but no consensus has been reached in different ethnicities. The aim of the present study was to evaluate the possible association between the ADRB2 gene polymorphisms and the EH risk in the Northern Han Chinese population.

Methodology/Principal Findings

This study included 747 hypertensive subjects and 390 healthy volunteers as control subjects in the Northern Han Chinese. Genotyping was performed to identify the C-47T, A46G and C79G polymorphisms of the ADRB2 gene. G allelic frequency of A46G polymorphism was significantly higher in hypertensive subjects (P = 0.011, OR = 1.287, 95%CI [1.059–1.565]) than that in controls. Significant association could also be found in dominant genetic model (GG+AG vs. AA, P = 0.006, OR = 1.497, 95%CI [1.121–1.998]), in homozygote comparison (GG vs. AA, P = 0.025, OR = 1.568, 95%CI [1.059–2.322]), and in additive genetic model (GG vs. AG vs. AA, P = 0.012, OR = 1.282, 95%CI [1.056–1.555]). Subgroup analyses performed by gender suggested that this association could be found in male, but not in female. Stratification analyses by obesity showed that A46G polymorphism was related to the prevalence of hypertension in the obese population (GG vs. AG vs. AA, P<0.001, OR = 1.645, 95%CI [1.258–2.151]). Significant interaction was found between A46G genotypes and body mass index on EH risk. No significant association could be found between C-47T or C79G polymorphism and EH risk. Linkage disequilibrium was detected between the C-47T, A46G and C79G polymorphisms. Haplotype analyses observed that the T-47-A46-C79 haplotype was a protective haplotype for EH, while the T-47-G46-C79 haplotype increased the risk.

Conclusions/Significances

We revealed that the ADRB2 A46G polymorphism might increase the risk for EH in the Northern Han Chinese population.

Roles of beta2- and beta3-adrenoceptor polymorphisms in hypertension and metabolic syndrome

Hypertension, diabetes mellitus (especially type 2 diabetes mellitus), metabolic syndrome and obesity are rapidly growing public health problems. Sympathetic nerve activation is observed in obesity, hypertension and diabetes mellitus, which have strong genetic as well as environmental determinants. Reduced energy expenditure and resting metabolic rate are predictive of weight gain, and the sympathetic nervous system participates in regulating energy balance through thermogenesis. The thermogenic effects of catecholamines in obesity have been mainly mediated via the β2- and β3-adrenergic receptors in humans. Further, β2-adrenoceptors importantly influence vascular reactivity and may regulate blood pressure. Genetic polymorphistns of the β-adrenoceptor gene have been shown to alter the function of several adrenoceptor subtypes and thus to modify the response to catecholamine. β2-adrenoceptor polymorphisms (Arg16Gly, Gln27Glu, and Thr164Ile) have been studied in relation to hypertension. Genetic variations in the β3-adrenoceptor (i.e. Try64Arg variant) are also associated with both obesity and hypertension. However, the precise relationships of the polymorphisms of β2- and β3-adrenoceptor genes with sympathetic nervous system activity, hypertension, and metabolic syndrome have not been fully clarified. This paper will discuss the current topics involving the influence of the sympathetic nervous system and β2- and β3- adrenoceptor polymorphisms in hypertension and metabolic syndrome.

A46G and C79G polymorphisms in the β2-adrenergic receptor gene (ADRB2) and essential hypertension risk: a meta-analysis

No consensus has been reached on the association between the β2-adrenergic receptor polymorphisms A46G and C79G and essential hypertension risk. We performed a meta-analysis to confirm the possible association. After reviewing 303 reports in PubMed and 359 reports in Embase, we included in our meta-analysis 18 articles (20 studies) that met our inclusion criteria. The fixed-effects model and the random-effects model were applied for dichotomous outcomes to combine the results of the individual studies. There was no statistical association between A46G and hypertension risk in all subjects, Asians or Caucasians. However, an association was observed in the dominant genetic model (AA vs. (AG+GG)) (P=0.04, odds ratio (OR)=1.38, 95% confidence interval (CI) 1.01-1.87, P(heterogeneity)=0.98, fixed-effects model) in the subgroup of mixed Africans. No overall statistical association could be found between C79G and hypertension risk or any ethnic subgroup. In the research conducted on severe hypertension (systolic blood pressure ≥160 mm Hg and/or diastolic blood pressure ≥95 mm Hg hypertensive population), significant association was found in the dominant genetic model (CC vs. (CG+GG)) (P=0.04, OR=1.38, 95% CI 1.02-1.86, P(heterogeneity)=0.03, random-effects model), and there was also a borderline significance between the C79 allele and severe hypertension (P=0.05, OR=1.26, 95% CI 1.00-1.57, P(heterogeneity)=0.04, random-effects model). No association could be found in this study between the two polymorphisms and stage 2 hypertension. More studies stratified for different ethnicities and different stages of hypertension should be performed in the future.

Haplotypes of the adrenergic system predict the blood pressure response to beta-blockers in women with essential hypertension

AIMS

To analyze the association of haplotypes of the adrenergic system with essential hypertension and with the blood pressure response to beta-blockers.

MATERIALS & METHODS

In 1112 never-treated essential hypertension patients and 203 normotensive controls, tightly linked SNPs of beta-adrenergic receptors (ADRB1 - Ser49Gly and Arg389Gly; ADRB2 - Cys19Arg, Gly16Arg and Gln27Glu) and the G-protein beta3-subunit (GNB3 - A3882C, G5249A and C825T) were genotyped. Association of haplotypes with essential hypertension and with the blood pressure response to atenolol 50 mg twice daily in a subgroup of essential hypertension patients (n = 340) was evaluated (Haploview 3.2).

RESULTS

No SNPs or haplotypes were associated with essential hypertension. In females only, GNB3 SNPs and haplotypes were associated with the blood pressure response (p < 0.05).

CONCLUSION

Our study confirmed the sex-specific association of GNB3 with the blood pressure response to atenolol with no substantial advantage of the analysis of haplotypes over SNPs.

Synopsis and data synthesis of genetic association studies in hypertension for the adrenergic receptor family genes: the CUMAGAS-HYPERT database

BACKGROUND

The adrenergic receptor (adrenoceptor) family genes have been extensively studied as candidate genes in hypertension but the results of individual genetic association studies (GAS) are controversial and inconclusive. To clarify these data, a systematic assessment of GAS for adrenoceptor family genes in hypertension was conducted.

METHODS

Data from 163 GAS involving 7 genes and 37 distinct genetic variants were analyzed and cataloged in CUMAGAS-HYPERT (Cumulative Meta-analysis of Genetic Association Studies-HYPERTension; a web-based information system, which allows the retrieval and synthesis of data from GAS in hypertension, available at http://biomath.med.uth.gr). Data from genome-wide association studies involving the adrenoceptor family genes were also systematically searched.

RESULTS

Individual GAS reported inconsistent associations and had limited power to detect modest genetic effects, with only 1.2% having power >80%. Thirteen variants were investigated by three or more studies and their results were subject to meta-analysis. In the main meta-analyses, significant results were shown for five variants (ADRB1 p.Arg389Gly, ADRB1 p.Ser49Gly, ADRB2 g.9368308A>G, ADRB3 p.Trp64Arg, and ADRA1A p.Cys347Arg) under the allelic contrast and/or the dominant model. Subgroup analyses by ethnicity and gender detected significant associations for three variants (ADRB1 p.Arg389Gly in east Asians, ADRB2 p.Gln27Glu in whites, and ADRB3 p.Trp64Arg in whites and in males). Heterogeneity ranged from none to high. No significant associations were recorded from genome-wide studies.

CONCLUSIONS

There is evidence to implicate adrenoceptor genes in hypertension, although future studies designed to investigate epistatic and gene-environment interactions would allow more solid conclusions to be drawn about the role of these genes in hypertension.

Combination of polymorphisms in the beta2-adrenergic receptor and nitric oxide synthase 3 genes increases the risk for hypertension

OBJECTIVE

Hypertension is a major risk factor for cardiovascular disease. Polymorphism in the beta2-adrenergic receptor (ADRB2) and nitric oxide synthase 3 (NOS3) genes is associated with clinical cardiovascular phenotypes. The Arg16Gly and Glu298Asp polymorphisms of ADRB2 and NOS3 genes, respectively, have been reported to be associated with hypertension. We hypothesized that a combination of these two polymorphisms increases the risk for hypertension. Hence, we examined the effect of this combination of single-nucleotide polymorphisms on the risk for hypertension.

METHODS

Our cross-sectional study comprised 402 middle-aged and elderly human participants. We determined the genotypes of Arg16Gly and Glu298Asp single-nucleotide polymorphisms in ADRB2 and NOS3, respectively, by TaqMan PCR method; we also measured the resting blood pressure.

RESULTS

The odds ratio for the presence of hypertension in individuals having the Gly/Gly genotype of ADRB2 compared with those having the other genotypes (Arg/Arg and Arg/Gly) was 2.87. With regard to the Glu298Asp polymorphism in NOS3, the odds ratio for the presence of hypertension in individuals having the Glu/Glu genotype of NOS3 when compared with those having the other genotypes (Asp/Asp and Asp/Glu) was 2.79. Interestingly, the odds ratio was 7.64 for individuals having a combination of the Gly/Gly genotype of ADRB2 and Glu/Glu genotype of NOS3 when compared with those having a combination of Arg/Arg and Arg/Gly genotypes of ADRB2 and Asp/Asp and Asp/Glu genotypes of NOS3.

CONCLUSION

We revealed that a combination of the Arg16Gly and Glu298Asp polymorphisms in ADRB2 and NOS3, respectively, remarkably increased the risk for hypertension in middle-aged and elderly humans.

Beta-1 and beta-2 adrenoceptor polymorphisms: functional importance, impact on cardiovascular diseases and drug responses

Beta-1 and beta-2 adrenoceptors (AR) play a pivotal role in regulation of the activity of the sympathetic nervous system and agonists and antagonists at both beta AR subtypes are frequently used in treatment of cardiovascular diseases. Both beta-1 and beta-2 AR genes have several polymorphisms that encode different amino acids. This review summarizes new insights into the functional importance of these polymorphisms, as well as their relationship to cardiovascular diseases and their impact on responses to adrenergic drug treatment. At present, it seems that, for cardiovascular diseases, beta-1 and beta-2 AR polymorphisms do not play a role as disease-causing genes; they might, however, be associated with disease-related phenotypes. In addition they could influence adrenergic drug responses. Thus, the Arg389Gly beta-1 AR polymorphism might predict responsiveness to beta-1 AR agonist and blocker treatment: patients homozygous for the Arg389 beta-1 AR polymorphism should be good responders, while patients homozygous for the Gly389 beta-1 AR polymorphism should be poor or nonresponders. Furthermore, the Arg16Gln27 beta-2 AR seems to have strong impact on long-term agonist-induced beta-2 AR desensitization. Thus, patients carrying this haplotype appear to suffer from rapid loss of therapeutic efficacy of chronic agonist treatment, as has been demonstrated in asthma patients. Moreover, the Arg16Gln27 beta-2 AR haplotype might have some predictive value for poor outcome of heart failure. Future large prospective studies have to replicate these findings in order to reach the final goal of pharmacogenomic research: to optimize and individualize drug therapy based on the patient's genetic determinants of drug efficacy.

Pharmacogenetics of beta-blockers

Beta-blockers are an important cardiovascular drug class, recommended as first-line treatment of numerous diseases such as heart failure, hypertension, and angina, as well as treatment after myocardial infarction. However, responses to a beta-blocker are variable among patients. Results of numerous studies now suggest that genetic polymorphisms may contribute to variability in responses to beta-blockers. This review summarizes the pharmacogenetic data for beta-blockers in patients with various diseases and discusses the potential implications of beta-blocker pharmacogenetics in clinical practice.

β-2 Adrenergic Receptor Diplotype Defines a Subset of Salt-Sensitive Hypertension

Two genetic variants of the beta-2 adrenergic receptor, 46G>A and 79C>G, affect agonist-mediated receptor downregulation and vascular reactivity. We determined whether these variants were associated with hypertension, per se, blood pressure response to dietary sodium, 2 forms of salt-sensitive hypertension (low renin and nonmodulation), and the activity of the renin-angiotensin-aldosterone system. Included are 280 hypertensive and 65 normotensive white subjects who had the 2 beta-2 adrenergic receptor genotypes available. Of all subjects, 171 hypertensive and 48 normotensive subjects had complete data for intermediate phenotyping and blood pressure evaluation on high- and low-sodium balance. The beta-2 adrenergic receptor variants were not associated with hypertension per se. However, among hypertensive subjects, the change (from low to high sodium balance) in mean arterial pressure differed significantly by genotype and by diplotype. Compared with all of the other diplotypes combined, 46AA/79CC was associated with a greater change in blood pressure. Furthermore, this diplotype was associated with low-renin (LR) hypertension (identifying 32% of the LR hypertensives), higher plasma aldosterone, and lower plasma renin and serum potassium levels. In conclusion, the 46AA/79CC diplotype is associated with greater blood pressure response to dietary sodium and higher odds of LR hypertension. We propose that the mechanism for the observed association is inadequate suppression of aldosterone with salt intake, implicating the beta-2 adrenergic receptor in the regulation of aldosterone secretion. This hypothesis was confirmed in isolated glomerulosa cells, where beta-2 adrenergic receptor stimulation increased aldosterone secretion, whereas blockade reduced the stimulated aldosterone response. Importantly, this association could only be detected with an intermediate and not a distant phenotype.

The Glu27 genotypes of the beta2-adrenergic receptor are predictors for severe coronary artery disease

Background

The role of the Beta2-adrenoceptor (beta2-AR) Gln27Glu polymorphism in the manifestation of cardiovascular diseases is still unclear.

Methods

In the present study, we evaluated the potential relevance of the c.79 C>G (p.Gln27Glu) polymorphism of this receptor gene for coronary artery disease (CAD) and its associated risk factors in Saudi Arabs. Genotyping was performed by PCR using the confronting two-pair primer (PCR-CTPP) method.

Results

In the general population group (BD) (n = 895), 68.5% were homozygous wild-type C/C, 28.3% were heterozygous C/G and 3.2% were homozygous mutant G/G. Among the CAD patients (n = 773), 50.6% were homozygous wild-type C/C, 43.6% were heterozygous C/G and 5.8% were homozygous mutant G/G, while in the angiographed control group (CON) (n = 528), 71.8% were C/C, 24.4% C/G and 3.8% G/G genotypes. These results indicate that both the C/G (p = < .001) and G/G (p = .005) genotypes are significantly associated with CAD, when compared to the CON group. In addition, C/G (p = < .001) and G/G (p = < .001) were significantly associated with CAD, when compared to the BD group. Furthermore, stepwise logistic regression showed that the genotype [C/G (p < .001) and G/G (p < .001)] increase the risk of CAD.

Conclusion

These results shows that the Gln27Glu genotypes (homo- or heterozygous) of the beta2-AR may be independent predictors of severe CAD.

Anger suppression and adiposity modulate association between ADRB2 haplotype and cardiovascular stress reactivity

OBJECTIVES

The purpose of this study was to examine how variation in the beta-2 adrenergic receptor gene (ADRB2), in combination with the moderating influences of race, body mass index (BMI), and anger expression style (anger-in, anger-out), affects blood pressure (BP) at rest and in response to acute laboratory stress.

METHODS

Four hundred fifty adolescents (mean age = 18.5 +/- 2.7 years; 228 [124 males] whites and 222 [110 males] blacks completed two stressors (video game challenge, forehead cold pressor). Hemodynamic measures were taken before, during, and after each stressor. Stressors were separated by a 20-minute rest period.

RESULTS

Frequency of detrimental haplotype (Gly16/Glu27) carrier status was greater among whites than blacks (p < .05). A significant three-way interaction among haplotype, BMI, and race for resting systolic blood pressure (SBP) found the highest BP level to be among high BMI carriers, but only for whites. A separate three-way interaction was found to be significant for haplotype, anger-in and race such that high anger-in carriers showed the highest level of resting SBP (p < .05) and total peripheral resistance (TPR) (p < .05) and the greatest TPR reactivity to the cold pressor task (p < .01). Post hoc analyses revealed these interactions with anger-in were only present among blacks. No significant interactions with anger-out for either ethnic group were observed.

CONCLUSIONS

This study demonstrates modulating influences of BMI and anger expression styles on ADRB2 gene associations with hemodynamic function at rest and in response to laboratory stress. These findings support the hypothesis that consideration of gene-environment interactions may better characterize the role of ADRB2 variation in the development of stress-induced essential hypertension.

Pharmacogenomics and cardiovascular drugs: need for integrated biological system with phenotypes and proteomic markers

Personalized medicine is based on a better knowledge of biological variability, considering the important part due to genetics. When trying to identify involved genes and their products in differential cardiovascular drug responses, a five-step strategy is to be followed: 1) Pharmacokinetic-related genes and phenotypes (2) Pharmacodynamic targets, genes and products (3) Cardiovascular diseases and risks depending on specific or large metabolic cycles (4) Physiological variations of previously identified genes and proteins (5) Environment influences on them. After summarizing the most well-known genes involved in drug metabolism, we will take as example of drugs, the statins, considered as very important drugs from a Public-Health standpoint, but also for economical reasons. These drugs respond differently in human depending on multiple polymorphisms. We will give examples with common ApoE polymorphisms influencing the hypolipemic effects of statins. These drugs also have pleiotropic effects and decrease inflammatory markers. This illustrates the need to separate clinical diseases phenotypes in specific metabolic pathways, which could propose other classifications, of diseases and related genes. Hypertension is also a good example of clinical phenotype which should be followed after various therapeutic approaches by genes polymorphisms and proteins markers. Gene products are under clear environmental expression variations such as age, body mass index and obesity, alcohol, tobacco and dietary interventions which are the first therapeutical actions taken in cardiovascular diseases. But at each of the five steps, within a pharmacoproteomic strategy, we also need to use available information from peptides, proteins and metabolites, which usually are the gene products. A profiling approach, i.e., dealing with genomics, but now also with proteomics, is to be used. In conclusion, the profiling, as well as the large amount of data, will more than before render necessary an organized interpretation of DNA, RNA as well as proteins variations, both at individual and population level.

Gene markers and antihypertensive therapy

Increasingly, detailed characterization of human molecular genetic variation will facilitate the use of genetic information in preventing, diagnosing, and treating common diseases. One promising application is the identification of genetic variants influencing responses to drugs used to lower blood pressure (BP) and prevent target-organ complications of hypertension. This update on gene markers to guide antihypertensive therapy highlights polymorphisms recently reported to predict interindividual differences in response to antihypertensive medications. However, single-site variation in most genes makes only a small contribution to differences in BP response, and, after all known genetic and environmental predictors have been considered, most variation in responses still remains unexplained. Advancing beyond our current "trial-and-error" approach to selecting drug therapy in individual patients will undoubtedly require whole-genome approaches to discover additional, novel genetic pathways influencing drug response. In addition, larger samples will be required to more fully characterize genetic variation within candidate genes and to consider the joint effects of gene-gene and gene-environment interactions. Eventually, knowledge of genetic variants that influence BP responses may allow more individualized tailoring of therapy to optimally reduce BP and target-organ damage.

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.

Beta2 adrenoceptor functional gene variants, obesity, and blood pressure level interactions in the general population

We investigated the association of beta2 adrenoceptor functional gene variants (Arg16Gly, Gln27Glu, and Thr164Ile polymorphisms), obesity phenotypes, and blood pressure levels in a large, ethnically mixed urban population. The individuals (n=1576) were randomly selected for a cross-sectional study of cardiovascular risk factors in Vitória, Brazil. Statistically significant associations among systolic blood pressure and the Arg16Gly and Thr164Ile variants were identified in univariate analysis. The Gly16/Gly16 genotype was still associated with systolic blood pressure (SBP) in multivariate analysis adjusting for age, gender, ethnicity, total cholesterol, diabetes, and body mass index (BMI) (P=0.01). The Arg16 allele was the only genotypic variable associated with BMI, and, in a dominant model, it remained associated with an increased BMI even after adjustment for age, gender, ethnicity, triglycerides, HDL cholesterol, LDL cholesterol, diabetes, and hypertension status (P=0.02). Although the different polymorphisms did not interact in the determination of SBP, a significant interaction with BMI (P=0.02), not through linkage disequilibrium, was identified between the Gln27Glu and the Thr164Ile variants. Furthermore, a significant interaction among the Arg16Gly polymorphism and BMI (P=0.036) and waist-hip ratio (P=0.003) in determining SBP was disclosed by ANOVA factorial modeling, with SBP used as the dependent variable. An interaction between the Thr164Ile polymorphism and waist-hip ratio was also identified (P=0.018). Finally, multiple logistic regression models showed a 1.48-fold increase in the risk of hypertension in individuals harboring the Gly16/Gly16 genotype and a 1.31-fold (P=0.01) and a 1.49-fold (P=0.003) increased risk of obesity in individuals harboring the Gln27/Gln27 genotype or the presence of the Arg16 allele, respectively. Taken together, these data provide evidence for a strong but complex relation between beta-adrenoceptor gene variants, hypertension, and obesity.

Beta(2)-adrenergic receptor gene polymorphism, age, and cardiovascular phenotypes

Previous studies suggest that variants of the beta(2)-adrenergic receptor (ADRB2) may differently affect functional responses to adrenergic stimulation, thereby possibly modulating cardiovascular and metabolic phenotypes. We examined the hypothesis that G/R16 and Q/E27 polymorphism of ADRB2, or their haplotypes, may modulate blood pressure, cardiovascular structure, and function or metabolic cardiovascular risk factors in the general population. We examined a random sample of the general population (n=571; age, 35 to 64 years). Neither clinic nor 24-hour ambulatory blood pressure was significantly associated with ADRB2 genotypes in the overall population. Cardiac structure and function were also not influenced by ADRB2 polymorphism. After adjustment for potential confounders, association of the R16 allele with higher systolic blood pressure was observed in the subgroup of younger people (below age of 50 years). Haplotype analysis showed that higher blood pressure values were more specifically associated with the presence of R16-Q27. Younger people carrying the R16-Q27 haplotype also showed a trend toward lower heart rate, higher BMI, lower glycemia, and higher trygliceridemia, which is consistent with the hypothesis of a genetic predisposition to reduced cardiovascular and metabolic response to ADRB2 stimulation. This study does not provide evidence of a major role of ADRB2 gene variability in blood pressure modulation. However, association of ADRB2 polymorphism with cardiovascular and metabolic effects can be observed in younger subjects, before the development of age-related decline of ADRB2-mediated activity. Our study emphasizes the necessity of taking into account (patho)-physiological changes related to aging (in this case, decreased efficiency of ADRB2 signaling) when analyzing phenotypic effects of genetic variants.

Beta(2)-adrenergic receptor polymorphism and nitric oxide-dependent forearm blood flow responses to isoproterenol in humans

Polymorphisms in the gene encoding the beta(2)-adrenoceptor have been associated with interindividual differences in blood pressure and the diagnosis of hypertension. A common polymorphism resulting in a change from arginine to glycine at amino acid 16 (Arg16-->Gly) enhances agonist-promoted downregulation of receptor expression in vitro. It is unknown whether genotype-dependent differences in nitric oxide generation contribute to differences in vasodilator responses to beta(2)-agonists in vivo. To address this question, venous occlusion plethysmography was used to measure forearm blood flow responses to graded brachial artery infusions of the beta-agonist isoproterenol in 41 healthy normotensive Caucasian adults (mean age (+/- S.D.) = 29 +/- 6 years), who were either Arg16 (n = 18) or Gly16 (n = 23) homozygotes. Compared to Arg16 homozygotes, Gly16 homozygotes demonstrated significantly greater blood flow responses to isoproterenol (P = 0.02). After inhibition of nitric oxide synthase by N(gamma)-monomethyl-L-arginine, blood flow responses did not differ significantly between genotype groups (P = 0.27). Consequently, effects of the Arg16 Gly polymorphism on forearm blood flow responses to isoproterenol appear to be dependent on differences in endothelial generation of nitric oxide. In contrast to previous reports based on systemic infusions of beta(2)-agonists, our findings indicate that regional blood flow responses to locally infused isoproterenol are significantly greater in Gly16 than in Arg16 homozygotes.

Essential hypertension and beta2-adrenergic receptor gene: linkage and association analysis

A region on human chromosome 5 (5q31.1-qter) contains several genes that encode important blood pressure regulators and thus is a good candidate for analysis of linkage and association with hypertension. We recruited 638 individuals from 212 Polish pedigrees with clustering of essential hypertension. These subjects were genotyped for 11 microsatellite markers that span this region to test for linkage to essential hypertension and systolic and diastolic blood pressures. The segment of this region of approximately 7 cM delineated by D5S1480 and D5S500 markers was linked to blood pressures in multipoint analysis. In 2-point analysis, D5S1480--the marker in close proximity to beta2-adrenergic receptor gene--reached the maximal linkage to essential hypertension and adjusted systolic and diastolic blood pressures, implicating this gene as a positional candidate for further association studies. Arg16Gly, Gln27Glu, and Thr164Ile--3 functional single nucleotide polymorphisms within the beta2-adrenergic receptor gene--were tested for association with essential hypertension. None of these polymorphisms showed a significant association with essential hypertension, separately or in the haplotype analysis. This study provided evidence of linkage of 5q31.1-5qter region to essential hypertension in the European population. Moreover, it implicated the chromosomal segment in close proximity to D5S1480 and D5S500. The detailed analysis of 3 single nucleotide polymorphisms does not support the role of the beta2-adrenergic receptor gene as a major causative gene for the detected linkage.

A maximal effort trial in obese women carrying the beta2-adrenoceptor Gln27Glu polymorphism

The aim of this study was to observe the relationship of the beta2-adrenoceptor (ADRB2) gene polymorphism Gln27Glu in a group of obese female subjects submitted to an acute physical activity test. Six Glu27/Glu27 obese women were compared with six Gln27/Gln27 obese women (coupled by age, BMI, waist circumference, percentage of fat mass and absence of smoking). These groups were selected after having genotyped 91 obese subjects (BMI>30 kg/m2, age 20-60). Polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) were used to genotype the obese population. The physical activity challenge consisted of a Maximal effort trial (VO2 max) following the Bruce protocol on a walking treadmill. The frequency for the Glu allele was 0.42, which is similar to other Caucasian populations. In basal conditions, subjects with the Glu27/Glu27 genotype showed a higher value of plasma insulin, while circulating glucose levels were similar in both groups. Also, diastolic arterial pressure was higher in the Glu27/Glu27 obese women. After the VO2 max trial, the Glu27 group had a significantly higher respiratory exchange ratio than the Gln27 group suggesting a lower post- exercise fat oxidation. These results provide evidence about a possible impact of the Gln27Glu polymorphism in the ADRB2 gene concerning a better response to exercise in obese Gln27 female subjects, in which basal insulinemia may play a role.

Peripheral blood mononuclear cell CD62L and CD11a expression and soluble interstitial cell adhesion molecule-1 levels following infused isoproterenol in hypertension

OBJECTIVES

Increasingly, studies indicate that alterations in leukocyte and endothelial cell adhesion molecules may enhance atherosclerotic processes in human hypertension. beta-adrenergic receptor activation has long been implicated in the aetiology and/or maintenance of hypertension and also has significant effects on leukocyte and endothelial adhesion molecules. This study therefore examined the effects of hypertension on peripheral blood mononuclear cell CD62L and CD11a expression and circulating soluble interstitial cell adhesion molecule (ICAM)-1 (sCD54) levels following infusion of the non-specific beta-adrenergic agonist isoproterenol.

DESIGN

In the setting of a General Clinical Research Center, 15 hypertensive and 20 normotensive subjects underwent an infusion of isoproterenol consisting of two sequential 15 min fixed-order doses of 20 and 40 ng/kg per min. Flow cytometry was used to quantify lymphocyte and monocyte populations and adhesion molecules, and ELISA was used to quantify sCD54 levels.

RESULTS

As expected, isoproterenol led to a significant increase in the number of circulating lymphocytes (P < 0.001) and monocytes (P < 0.01). The number of circulating CD3+CD8+CD62Llow T cytotoxic cells increased following isoproterenol (P < 0.001) and this increase was greater in hypertensives than in normotensives (P < 0.05). Isoproterenol led to a decrease in surface density of CD62L (P < 0.001) and an increase in surface density of CD11a (P < 0.001) in all subjects. Hypertensives had a significantly lower CD62L density (P = 0.01) and higher CD11a density on lymphocytes (P = 0.002) compared to normotensives. sCD54 levels were unchanged following isoproterenol but were elevated in hypertensives (P < 0.05).

CONCLUSIONS

A beta-adrenergic-induced environment of increased CD62Llow/CD11ahigh leukocytes, coupled with existing endothelial CD54 activation, could support basic atherosclerotic processes of increased peripheral blood mononuclear cell-endothelial adhesion in hypertension.

Genetic polymorphisms of adrenergic receptors

Recent advances in molecular biology have enhanced the understanding of adrenergic receptors. They have allowed the characterization of the several subtypes of adrenergic receptors expressed and have expanded the research about the potential physiologic functions they mediate. Furthermore, variant forms, or polymorphims, of the genes that code for these receptors are being identified. These genetic variants may or may not result in functional differences in the receptors they encode. There is obvious interest in determining the physiologic and clinical relevance of these polymorphisms. The purpose of this review is to describe these polymorphisms and the often contradictory literature pertaining to their clinical significance. Progress in this area is being made at a rapid pace. As the allele-disease relations become less equivocal, it might be possible to predict individual differences in susceptibility to a disease, disease prognosis, and response to treatment.