Beta1-adrenoceptor gene variations: a role in idiopathic dilated cardiomyopathy?

The Role of Personalized Medicine in Companion Animal Cardiology

Cardiomyopathies remain one of the most common inherited cardiac diseases in both human and veterinary patients. To date, well over 100 mutated genes are known to cause cardiomyopathies in humans with only a handful known in cats and dogs. This review highlights the need and use of personalized one-health approaches to cardiovascular case management and advancement in pharmacogenetic-based therapy in veterinary medicine. Personalized medicine holds promise in understanding the molecular basis of disease and ultimately will unlock the next generation of targeted novel pharmaceuticals and aid in the reversal of detrimental effects at a molecular level.

Association of Genetic Polymorphisms in the Beta-1 Adrenergic Receptor with Recovery of Left Ventricular Ejection Fraction in Patients with Heart Failure

Two common genetic polymorphisms in the beta-1 adrenergic receptor (ADRB1 Ser49Gly [rs1801252] and Arg389Gly [rs1801253]) significantly affect receptor function in vitro. The objective of this study was to determine whether ADRB1 Ser49Gly and Arg389Gly are associated with recovery of left ventricular ejection fraction (LVEF) in patients with heart failure. Patients with heart failure and baseline LVEF ≤ 40% were genotyped (n = 98), and retrospective chart review assessed the primary outcome of LVEF recovery to ≥ 40%. Un/adjusted logistic regression models revealed that Ser49Gly, but not Arg389Gly, was significantly associated with LVEF recovery in a dominant genetic model. The adjusted odds ratio for Ser49 was 8.2 (95% CI = 2.1-32.9; p = 0.003), and it was the strongest predictor of LVEF recovery among multiple clinical variables. In conclusion, patients with heart failure and reduced ejection fraction that are homozygous for ADRB1 Ser49 were significantly more likely to experience LVEF recovery than Gly49 carriers.

Effects of GRK5 and ADRB1 polymorphisms influence on systolic heart failure

BACKGROUND

G-protein receptor kinase 5 (GRK5) Gln41 > Leu and β1-adrenergic receptor (ADRB1) Arg389 > Gly polymorphisms presented the different distribution of genotype frequencies between Caucasian American and African American, and produced the difference in β-blocker treatment effect among them with systolic heart failure (SHF).

OBJECTIVE

This study sought to identify the distributed characteristics of these variant genotypes in Chinese population, and influence of GRK5 and ADRB1 polymorphisms on SHF morbidity and β-blocker treatment effect in patients with SHF.

METHODS

This study was based on cross-sectional survey data. 1794 and 1718 subjects' ADRB1 and GRK5 gene sequencing (sanger method) data were achieved respectively. Blood samples collection, clinical laboratory detection, electrocardiogram and echocardiography examinations were performed. Medication usage was confirmed at in-hospital visits or the questionnaire by personal interview.

RESULTS

GRK5 Leu41Leu genotype was not found in our Chinese population. In non-SHF population, allele frequencies of GRK5 Gln41 and Leu41 were 2782 (0.992) and 22 (0.008) (Hardy-Weinberg equilibrium test χ(2) = 0.088, P = 0.767), and allele frequencies of ADRB1 Arg389 and Gly389 were 2127 (0.715) and 849 (0.285) (χ(2) = 0.272, P = 0.602). In SHF patients, allele frequencies of Gln41 and Leu41 were 446 (0.991) and 4 (0.009) (χ(2) = 0.018, P = 0.893), and allele frequencies of Arg389 and Gly389 were 331 (0.726) and 125 (0.274) (χ(2) = 1.892, P = 0.169). Further in logistic regression model, these ADRB1 and GRK5 variants were not significantly independently associated with the risk of SHF morbidity. Those carrying genotype ADRB1 Gly389Gly did not reduce significantly the risk of SHF morbidity after β-blocker therapy.

CONCLUSIONS

GRK5 Leu41Leu genotype was not found in our Chinese population, neither ADRB1 nor GRK5 variants presented independently associated with the risk of SHF morbidity, most ADRB1 and GRK5 polymorphisms did decrease significantly the risk of SHF morbidity after β-blocker therapy except for those carrying genotype ADRB1 Gly389Gly.

IRS1, TCF7L2, ADRB1, PPARG, and HHEX polymorphisms associated with atherogenic risk in Mexican population

Objective. We aimed to explore the association between polymorphisms of IRS1 (rs1801278), TCF7L2 (rs7903146 and rs12255372), ADRB1 (rs1801253), PPARG (rs1801282), and HHEX (rs5015480) genes with atherogenic risk (AI = Total cholesterol/HDL) in MetS, T2D, and healthy populations from the Mexican Social Security Institute. Methodology and Results. Four hundred thirty-five MetS, 517 T2D, and 547 healthy individuals were selected. The association between the SNPs and the atherogenic index was evaluated by multiple linear regression and multinomial logistic regression models. The ADRB1 gene showed a statistically significant association with high-risk atherogenic index, OR = 2.94 (IC 95% 1.64-5.24; P < 0.0001) for the Arg/Gly variant, under the dominant model an OR = 2.96 (IC 95% 1.67-5.25; P < 0.0001), and under the Log additive model an OR = 2.52 (IC 95% 1.54-4.15; P < 0.0001). Conclusions. The Arg389Gly polymorphism of the ADRB1 gene may be a worthy biological marker to predict the risk of developing cardiovascular diseases given a high-risk atherogenic index.

Identification of DNA variants in the canine beta-1 adrenergic receptor gene

Beta-adrenergic receptor antagonists are utilized for the management of several cardiac diseases in the dog. In humans the beneficial effects of beta-adrenergic receptor antagonists are variable and are associated with a genetic variability in the beta one adrenergic receptor gene (ADRB1). To determine if DNA variants were present in the canine ADRB1 gene, DNA from five breeds of dogs was evaluated. Two deletions were identified within the region of the gene that encodes the cytoplasmic tail of ADRB1. The functions of this region are not well understood although it is important in differentiating subtypes of adrenergic receptors and may be associated with control of receptor downregulation. The functional consequences of these identified variants deserve further study.

β-adrenergic receptor polymorphisms in susceptibility, response to treatment and prognosis in heart failure: implication of ethnicity

Common functional polymorphisms in β-adrenergic receptor (βAR) genes have been associated with heart failure (HF) phenotypes and pharmacogenetic interactions with βAR blockers. This study evaluated the association between βAR polymorphisms and carvedilol drug response and prognosis in patients with HF. In this prospective cohort controlled study, 326 volunteers were enrolled [146 HF patients (ejection fraction (EF)<50% by Simpson) and 180 healthy controls]. Drug response was evaluated by echocardiography and outcomes were mortality and hospitalization. DNA was extracted from peripheral blood leukocytes, fragments were amplified by the polymerase reaction and genotyped by restriction fragment length polymorphism (RFLP) for Ser49Gly and Arg389Gly βAR-1 polymorphisms and Gln27Glu and Arg16Gly βAR-2 polymorphisms. The study population was in Hardy‑Weinberg equilibrium. The survival rate was adjusted using the Kaplan-Meier method. HF patients showed the following characteristics: EF 35±9%, 69.9% male, age 59±13 years, 50.7% self-identified as black, 46% had ischemic etiology. The mean follow-up of 23 months showed 18 mortalities and 46 hospitalizations. The genotypes Glu27Glu (24.7 vs. 6.1%, p=0.0004) and Arg16Arg (72.6 vs. 22.8, p<0.0001) of βAR2 polymorphisms and Gly49Gly (33.6 vs. 4.3%, p<0.0001) of the βAR1 polymorphism were higher in HF patients compared with controls. Patients with hospital admission showed a significantly higher Gly389 allelic frequency (54.9 vs. 42.1%, p=0.039), and the trend prevailed among patients who succumbed to the disease (61.1%, p=0.047). Black patients with the Ser49Ser genotype showed a reduced survival compared with the Gly49Gly or Ser49Gly genotypes (p=0.028). There was no association between improved LVEF >20% and βAR polymorphisms. HF patients with β-blocker therapy and the Gly389 allele have reduced event-free survival compared to those carrying the Arg389 allele. Additionally, systolic HF outpatients undergoing β-blocker therapy, self‑identified as black and homozygous for Ser49Ser may have reduced event-free survival, while Glu27Glu, Arg16Arg and Gly49Gly genotypes may be associated with risk for HF.

β1 adrenergic receptor polymorphisms and heart failure: a meta-analysis on susceptibility, response to β-blocker therapy and prognosis

Aims

The risk stratification of patients for heart failure (HF) remains a challenge, as well as the anticipation of the response to β-blocker therapy. Since the pivotal role of β1 adrenergic receptor (β1-AR) in HF, many publications have studied the associations between the β1-AR polymorphisms (Ser49Gly and Arg389Gly) and HF, with inconsistent results. Thus, we performed a meta-analysis of studies to evaluate the impact of β1-AR polymorphisms on susceptibility to HF, the response to β-blocker therapy and the prognosis of HF.

Methods and Results

Electronic databases were systematically searched before August 2011. We extracted data sets and performed meta-analysis with standardized methods. A total of 27 studies met our inclusion criteria. It was found that in East Asians, the Gly389 allele and Gly389 homozygotes significantly increased the HF risk, while the Gly389 allele and Gly389 homozygotes trended to decrease the risk of HF in whites. With the similar reduction of heart rate, overall, the Arg389 homozygotes showed a better response to β-blocker therapy. Furthermore, the Arg389 homozygotes were significantly associated with better LVEF improvement in East Asians and a mixed population. And in white people, the Arg389 homozygotes made a greater LVESd/v improvement and trended to be associated with better LVEDd/v improvement. However, the prognosis of Arg389 homozygotes HF patients was similar to those with Gly389 carriers. The Ser49Gly polymorphism did not impact the risk or prognosis of HF.

Conclusion

Based on our meta-analysis, the Gly389 allele and Gly389 homozygotes were risk factors in East Asians while trending to protect whites against HF. Furthermore, Arg389 homozygote is significantly associated with a favorable response to β-blocker treatment in HF patients. However, neither of the two polymorphisms is an independent predictor of the prognosis of HF.

The effect of beta1-adrenergic receptor gene polymorphism on prolongation of corrected QT interval during endotracheal intubation under sevoflurane anesthesia

Background

The hemodynamic responses to endotracheal intubation are associated with sympathoadrenal activity. Polymorphisms in the beta1-adrenergic receptor (β₁AR) gene can alter the pathophysiology of specific diseases. The aim of this study is to investigate whether the Ser49Gly and Arg389Gly polymorphism of the β₁AR gene have different cardiovascular responses during endotracheal intubation under sevoflurane anesthesia.

Methods

Ninety-one healthy patients undergoing general anesthesia were enrolled. Patients underwent slow inhalation induction of anesthesia using sevoflurane in 100% oxygen. Vecuronium 0.15 mg/kg was given for muscle relaxation. Endotracheal intubation was performed by an anesthesiologist. The mean arterial pressure (MAP), heart rate (HR), and the corrected QT (QTc) interval were measured before induction, before laryngoscopy, and immediately after tracheal intubation. Genomic DNA was isolated from the patients' peripheral blood and then evaluated for the β₁AR-49 and β₁AR-389 genes using an allele-specific polymerase chain reaction method.

Results

No differences were found in the baseline values of MAP, HR, and the QTc interval among β₁AR-49 and β₁AR-389, respectively. In the case of β₁AR-49, the QTc interval change immediately after tracheal intubation was significantly greater in Ser/Ser genotypes than in Ser/Gly genotypes. No differences were observed immediately after tracheal intubation in MAP and HR for β₁AR-49 and β₁AR-389.

Conclusions

We found an association between the Ser49 homozygote gene of β₁AR-49 polymorphism and increased QTc prolongation during endotracheal intubation with sevoflurane anesthesia. Thus, β₁AR-49 polymorphism may be useful in predicting the risk of arrhythmia during endotracheal intubation in patients with long QT syndrome.

A meta-analysis of β1-adrenergic receptor gene polymorphisms in idiopathic dilated cardiomyopathy

Published data on the association between β1-adrenergic receptor gene polymorphisms and idiopathic dilated cardiomyopathy (IDCM) risk are inconclusive. To derive a more precise estimation of the relationship, a meta-analysis was performed. A total of 12 case-control studies including 2642 cases and 3136 controls provided data on the association between β1-adrenergic receptor gene polymorphisms and susceptibility to IDCM. Overall, no significantly elevated risk was associated with Arg389Gly polymorphisms for all genetic models. In the subgroup analysis by ethnicity, no statistically increased risk was found for Gly389Gly versus Arg389Arg (OR 0.73; 95% CI 0.54-0.99; Ph=0.35) and Gly389Gly versus Arg389Arg+Arg389Gly (OR 0.75; 95% CI 0.55-1.01; Ph=0.52) among Europeans. Meanwhile, significantly increased risk was found among Asians based on the relatively small sample size. Further, significantly elevated IDCM risk was associated with Ser49Gly polymorphisms for all genetic models. When stratified by ethnicity, statistical association was found among Asians for Gly49Gly versus Ser49Ser (OR 4.56; 95% CI 1.36-15.23; Ph=0.10) and Gly49Gly versus Ser49Ser+Ser49Gly (OR 4.49; 95% CI 1.33-15.15; Ph=0.12), but not among Europeans. In summary, this meta-analysis suggests that no statistically increased risk was found between β1-adrenergic receptor gene polymorphisms and susceptibility to IDCM among Europeans.

Association of beta-1 and beta-2 adrenergic receptor gene polymorphisms with myocardial infarction

Both beta(1)- and beta2-adrenergic receptors (beta(1)- and beta(2)-AR) have important roles in heart function mainly in response to catecholamines. Some specific polymorphisms in the beta(1)- and beta(2)-AR genes, named ADRB1 and ADRB2, respectively, have been implicated in several cardiovascular and noncardiovascular phenotypes. In this study, we aimed to investigate the possible relationship between Ser49Gly and Arg389Gly polymorphisms of the ADRB1 and Arg16Gly and Gln27Glu polymorphisms of the ADRB2 gene with ST elevation myocardial infarction (MI) in a Turkish population. One hundred patients with ST elevation MI and 100 healthy control subjects were genotyped using the PCR-RFLP method. Although the Arg389 allele of the ADRB1 gene was associated with an elevated risk of MI, the Glu27 allele of the ADRB2 gene was associated with a decreased risk of MI. Carriers of the ADRB1 Arg389 allele (heterozygotes+homozygotes) had an approximately 3.5-fold increased risk for MI than Gly389 homozygotes (OR=3.59, 95% CI=0.96-13.47, P=0.045). For the ADRB2 Gln27Glu polymorphism, subjects having one or two copies of the Glu27 allele showed a decreased risk of MI compared with Gln27 homozygote subjects (OR=0.48, 95% CI=0.24-0.94, P=0.03). Haplotype analysis of these polymorphisms showed no significant differences between groups. These results suggest that the Arg389Gly and Gln27Glu polymorphisms may be associated with an altered risk of MI in this Turkish population.

Polymorphisms of beta-adrenoceptor and natriuretic peptide receptor genes influence the susceptibility to and the severity of idiopathic dilated cardiomyopathy in a Chinese cohort

BACKGROUND

This study evaluated the potential effects of beta-adrenoceptor (beta-AR) and natriuretic peptide receptor (NPR) gene polymorphisms on the susceptibility to and the severity of idiopathic dilated cardiomyopathy (IDCM) in a Chinese cohort.

METHODS AND RESULTS

Ten polymorphisms in the coding regions of beta1-AR, beta2-AR, beta3-AR, NPR1, and NPR2 were genotyped in 430 IDCM patients and 468 healthy subjects. Patients with IDCM were followed for 2 years. In multi-loci combined subtype analysis, the combined profile of beta-AR and NPR was significantly different between IDCM patients and controls (P < .0001), mainly influenced by 2 loci beta1-Ser49Gly and NPR2-C2077T, which were also associated with the severity of IDCM. In single-loci analysis, allele frequencies of beta1-Gly49, NPR1-Glu939, and NPR2-T2077 were higher in patients with IDCM than in controls. Genotypes carrying NPR2-T2077 allele showed 1.94-fold independent risk for IDCM phenotype than C2077 homozygote (P < .001). Carriers of the NPR2-T2077 or beta1-Gly49 variant had worse New York Heart Association functional class or echocardiographic results and elevated serum brain natriuretic peptide, experienced severe symptoms, and required intensive medications and frequent hospitalization for heart failure. Furthermore, synergistic interactions between NPR2-C2077T and beta1-Ser49Gly were detected by multifactor-dimensionality reduction method.

CONCLUSIONS

This study suggests that NPR2-T2077 and beta1-Gly49 polymorphisms may be genetically synergistic adverse factors for the susceptibility to or the severity of IDCM.

Clinical and genetic modifiers of long-term survival in heart failure

OBJECTIVES

This study sought to identify genetic modifiers of beta-blocker response and long-term survival in heart failure (HF).

BACKGROUND

Differences in beta-blocker treatment effect between Caucasians and African Americans with HF have been reported.

METHODS

This was a prospective cohort study of 2,460 patients (711 African American, 1,749 Caucasian) enrolled between 1999 and 2007; 2,039 patients (81.7%) were treated with a beta-blocker. Each was genotyped for beta1-adrenergic receptor (ADRB1) Arg389>Gly and G-protein receptor kinase 5 (GRK5) Gln41>Leu polymorphisms, which are more prevalent among African Americans than Caucasians. The primary end point was survival time from HF onset.

RESULTS

There were 765 deaths during follow-up (median 46 months). beta-blocker treatment increased survival in Caucasians (log-rank p = 0.00038) but not African Americans (log-rank p = 0.327). Among patients not taking beta-blockers, ADRB1 Gly389 was associated with decreased survival in Caucasians (hazard ratio [HR]: 1.98, 95% confidence interval [CI]: 1.1 to 3.7, p = 0.03) whereas GRK5 Leu41 was associated with improved survival in African Americans (HR: 0.325, CI: 0.133 to 0.796, p = 0.01). African Americans with ADRB1 Gly389Gly GRK5 Gln41Gln derived a similar survival benefit from beta-blocker therapy (HR: 0.385, 95% CI: 0.182 to 0.813, p = 0.012) as Caucasians with the same genotype (HR: 0.529, 95% CI: 0.326 to 0.858, p = 0.0098).

CONCLUSIONS

These data show that differences caused by beta-adrenergic receptor signaling pathway gene polymorphisms, rather than race, are the major factors contributing to apparent differences in the beta-blocker treatment effect between Caucasians and African Americans; proper evaluation of treatment response should account for genetic variance.

Mutation of important amino acid residue of Asp104Lys in human beta(1)-adrenergic receptor triggers functional and constitutive inactivation

Based on our previous molecular modeling and radioligand binding study, we have demonstrated that aspartic acid of 104 in transmembrane helix (TMH) II of beta(1)-adrenergic receptor (beta(1)-AR) is important for functional characteristics of these receptors. We have also showed that mutation of negatively charged aspartic acid to neutral charged alanine exhibited constitutive activity of beta(1)-AR. However, the mutation of negatively charged aspartic acid to positively charged lysine is still remained to be examined, which is very important to know for fully understanding the characteristics of beta(1)-AR. At the present study, we mutated aspartic acid to lysine (Asp104Lys) residue in human beta(1)-AR. This resultant mutant (Asp104Lys) markedly reduced the binding affinity of isoproterenol and (-)-epinephrine. On the other hand, antagonist binding with this mutant was similar to the wild type receptor. Isoproterenol at its saturation concentrations produced lower amount of intracellular cyclic adenosine-3',5' cyclic monophosphate (cAMP) in HEK-293 cells expressing Asp104Lys mutant receptor as compared to cells expressing wild type receptor. Moreover, cAMP accumulation of Asp104Lys mutant was unchanged in the presence or absence of isoproterenol. Therefore, it has been demonstrated that Asp104Lys mutation in the human beta(1)-AR differentially affects the binding of antagonist and exhibits a functional uncoupling of G-protein-coupled receptors. Thus, we may suggest that mutation of negatively charged aspartic acid to positively charged lysine as well as neutral charged alanine may help to understand the mechanism of the activation or inactivation of beta(1)-AR by its conformational changes and this finding would be helpful for clarifying the functional responses mediated by beta(1)-AR.

Mutations in the beta1 adrenergic receptor gene and massive obesity in Japanese

Catecholamines strongly promote lipolysis and thermogenesis, and play a central role in the regulation of body fat content. The beta1 adrenergic receptor (BAR-1) is a major mediator of catecholamine-induced lipolysis and thermogenesis. To explore whether mutations in the BAR-1 gene contribute to morbid obesity in Japanese, we scanned for mutations in the coding sequence of the gene in 50 morbid obese [body mass index (BMI)>==35.0kg/m(2); 99.7th percentile] Japanese subjects. Direct DNA sequencing was performed following polymerase chain reaction (PCR) amplification. Two common polymorphisms, Gly49Arg and Arg389Ser, were detected in these subjects. The frequencies of these polymorphisms, as determined by PCR-restriction fragment length polymorphism (RFLP) analysis, showed no significant difference between 180 severely obese subjects (BMI>==30.0kg/m(2); 97th percentile) and 132 control (BMI<25.0kg/m(2)) subjects. This study represents the first investigations of genetic variations of BAR-1 in relationship to morbid obesity and suggests mutations in the BAR-1 coding sequence is not likely a major cause of morbid obesity at least in Japanese.

Role of beta adrenergic receptor polymorphisms in heart failure: systematic review and meta-analysis

Heart Failure (HF) is a common disorder associated with substantial morbidity and mortality. beta adrenergic receptors (betaAR) are the primary pathway through which cardiac function is influenced. Chronic beta(1)AR activation is implicated in the pathogenesis of HF and betaAR blockade improves survival in left ventricular systolic dysfunction. Common functional polymorphisms in beta adrenergic receptor genes (ADRB) have been associated with HF phenotypes, and with pharmacogenetic interaction with beta adrenergic receptor blockers (beta blockers). However, these associations have not been consistently replicated. The evidence for ADRB variant involvement in pathogenesis, progression and response to beta blockers in HF is reviewed. In addition, a meta-analysis of three studies analysing the effect of ADRB1 Arg389Gly polymorphism on left ventricular remodelling with the use of beta blockers, demonstrating a 5% improvement in left ventricular ejection fraction in Arg389 homozygotes, is presented. There is now accumulating molecular evidence for a different functional response to beta blockers associated with this polymorphism. In the future, confirmed genotypic associations may enable patients to be identified who are either at greater risk of developing HF, whose HF may rapidly progress, or who are unlikely to benefit from beta blockers, and such patients may benefit from targeted aggressive therapy.

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.

Studies of associations between the Arg389Gly polymorphism of the beta1-adrenergic receptor gene (ADRB1) and hypertension and obesity in 7677 Danish white subjects

AIMS

Activation of the beta(1)-adrenergic receptor (ADRB1) causes increased lipolysis in adipose tissue and enhances cardiac output. Analysis of the association of the functional ADRB1 Arg389Gly variant with obesity and hypertension has given ambiguous results. To clarify the potential impact of this variant on obesity and hypertension in the general population, we examined the Arg389Gly variant in a relatively large-scale population-based study.

METHODS

Case-control studies and quantitative trait analyses were carried out in 7677 Danish Caucasians who were genotyped for the Arg389Gly variant (dbSNP rs1801253) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

RESULTS

A weak association between the Gly allele of the Arg389Gly variant and obesity was observed when comparing cases (n = 1540) defined as body mass index (BMI) > 30 kg/m(2) with control subjects (n = 6108) defined as BMI < or = 30 kg/m(2) for both allele frequencies (P = 0.05) and genotype distribution (P = 0.05). Case-control studies (cases n = 2518; control n = 3981) examining the effect on hypertension showed no association with allele frequencies (P = 0.3) or genotype distribution (P = 0.5); however, in the quantitative trait analyses, individuals carrying the Gly allele had slightly but significantly lower diastolic (Arg/Arg = 81.9 mmHg vs. Gly-allele carriers = 81.5 mmHg) and systolic (Arg/Arg = 129.4 mmHg vs. Gly-allele carriers = 128.8 mmHg) blood pressure as well as a lower mean arterial blood pressure.

CONCLUSION

Our results suggest that the Arg389Gly polymorphism does not have any clinically important impact on the pathogenesis of obesity in Danish white subjects. Furthermore, despite the observed minor influence on blood pressure, this variant is most likely not to be a major contributor to the development of hypertension.

The Emerging Pharmacogenomics of the β‐Adrenergic Receptors

Beta-adrenergic signaling mechanisms are of central importance to cardiovascular health and disease. Modulation of these pathways represents an important pharmacologic approach to the treatment of heart failure and hypertension. Advances in molecular genetics have identified genetic polymorphisms in the human beta-adrenergic receptor genes; some of this variation predicts changes in protein sequence/structure, and potentially changes in function, of the b-adrenergic receptors. This article reviews the current state of knowledge and understanding of the genetic variation present in the three human beta-adrenergic receptor genes. Already, variation in these genes has been associated with observed differences in several cardiovascular phenotypes. This work has led to the demonstration of functional differences in activity between receptors with certain known polymorphisms and "wild-type" receptors. An understanding of these polymorphisms is key to the development of studies of how differences in drug response/effects may be mediated by these polymorphisms. Such studies are anticipated to provide a foundation for the development of novel pharmacologic approaches where selection of and dosing of cardiovascular therapy is tailored to individuals on the basis of each patient's specific genetic makeup.

Neurohumoral activation in heart failure: the role of adrenergic receptors

Heart failure (HF) is a common endpoint for many forms of cardiovascular disease and a significant cause of morbidity and mortality. The development of end-stage HF often involves an initial insult to the myocardium that reduces cardiac output and leads to a compensatory increase in sympathetic nervous system activity. Acutely, the sympathetic hyperactivity through the activation of beta-adrenergic receptors increases heart rate and cardiac contractility, which compensate for decreased cardiac output. However, chronic exposure of the heart to elevated levels of catecholamines released from sympathetic nerve terminals and the adrenal gland may lead to further pathologic changes in the heart, resulting in continued elevation of sympathetic tone and a progressive deterioration in cardiac function. On a molecular level, altered beta-adrenergic receptor signaling plays a pivotal role in the genesis and progression of HF. beta-adrenergic receptor number and function are decreased, and downstream mechanisms are altered. In this review we will present an overview of the normal beta-adrenergic receptor pathway in the heart and the consequences of sustained adrenergic activation in HF. The myopathic potential of individual components of the adrenergic signaling will be discussed through the results of research performed in genetic modified animals. Finally, we will discuss the potential clinical impact of beta-adrenergic receptor gene polymorphisms for better understanding the progression of HF.

The role of adrenergic receptor polymorphisms in heart failure

The main function of the cardiac adrenergic system is to regulate cardiac work both in physiologic and pathologic states. A better understanding of this system has permitted the elucidation of its role in the development and progression of heart failure. Regardless of the initial insult, depressed cardiac output results in sympathetic activation. Adrenergic receptors provide a limiting step to this activation and their sustained recruitment in chronic heart failure has proven to be deleterious to the failing heart. This concept has been confirmed by examining the effect of beta-blockers on the progression of heart failure. Studies of adrenergic receptor polymorphisms have recently focused on their impact on the adrenergic system regarding its adaptive mechanisms, susceptibilities and pharmacological responses. In this article, we review the function of the adrenergic system and its maladaptive responses in heart failure. Next, we discuss major adrenergic receptor polymorphisms and their consequences for heart failure risk, progression and prognosis. Finally, we discuss possible therapeutic implications resulting from the understanding of polymorphisms and the identification of individual genetic characteristics.

Adrenergic Receptor Polymorphisms Associated with Resting Heart Rate: The HyperGEN Study

The association between polymorphisms in the beta1, beta2 and alpha2B adrenergic receptor (ADR) genes (ADRB1, ADRB2 and ADRA2B) and resting heart rate was examined in white and African-American participants of the HyperGEN Study. All analyses were adjusted for age, sex, body mass index, alcohol use, smoking status and daily exercise within strata of race, hypertension status and beta-blocker use. The Ser49Gly polymorphism of the beta1 ADR was associated with resting heart rate in hypertensive African-Americans and hypertensive whites taking beta-blockers, with carriers of the Gly allele having a higher mean resting heart rate by 2.7 and 4.4 beats per minute (bpm), respectively. The Arg389Gly polymorphism of the beta1 ADR was associated with lower heart rate in the normotensive African-American sample. A beta1 haplotype (Ser49Gly-Arg389Gly) was modestly associated with resting heart rate in the hypertensive African-Americans. The alpha2B C/A polymorphism was associated with heart rate in hypertensive whites, and both whites and African-Americans taking beta-blockers, with carriers of the A allele having a higher mean resting heart rate. In summary, each of the ADR gene polymorphisms was associated with heart rate in at least one stratum studied, but there was no consistent association from which one would infer a large genetic contribution to heart rate.

Pharmacogenetics of the human beta-adrenergic receptors

The beta-adrenergic receptors (ADRBs) are cell surface receptors that play central roles in the sympathetic nervous system. Pharmacological targeting of two of these receptors, ADRB1 and ADRB2, represents a widely used therapeutic approach for common and important diseases including asthma, hypertension and heart failure. Genetic variation in both ADRB1 and ADRB2 has been linked to both in vitro and clinical disease phenotypes. More recently, interest has shifted to studies that explore potential interaction between variation in ADRBs and medications directed at these important receptors. This paper reviews the current state of knowledge and understanding of ADRB genetic variation and explores the likely direction of future studies in this area.

Distributive characteristics of Ser49Gly and Gly389Arg genetic polymorphisms of beta1-adrenoceptor in Chinese Han and Dai populations

AIM

Genetic polymorphisms causing Ser49Gly and Gly389Arg mutants of beta(1)-adrenoceptor may result in significant changes in the function of this receptor. The aim of the present study was to investigate the frequencies of the Ser49Gly and Gly389Arg mutant alleles in healthy Chinese populations and to investigate the differences between 2 Chinese ethnic groups (Han and Dai populations) with respect to the frequencies of these alleles.

METHODS

A total of 225 Han Chinese and 175 Dai Chinese unrelated healthy volunteers were recruited for this study. Genomic DNA was extracted from peripheral blood leukocytes by using a standard manual chloroform-phenol extraction. Fragments spanning the 2 polymorphisms were amplified by using polymerase chain reaction with template genomic DNA and relevant primers. The DNA products including the polymorphic loci were subjected to restriction endonuclease digestion with Eco0109I and BcgI. Digested fragments were detected with an ultraviolet detector after electrophoresis (100 V for approximately 1.5 h).

RESULTS

The frequencies of the Gly49 and Arg389 alleles were, respectively, 16.2% and 76.4% in the Han population and 14.6% and 75.7% in the Dai population.

CONCLUSION

The polymorphisms causing the Ser49Gly and Gly389Arg mutations of the beta(1)-adrenoceptor existed in both healthy Han and Dai Chinese populations. The frequencies of the Ser49Gly and Gly389Arg mutant alleles were not significantly different in the Han and Dai populations. However, the frequency of the Gly389 variant seems to be significantly lower in these 2 populations than in an African-American population.

The CAREGENE study: polymorphisms of the β1-adrenoceptor gene and aerobic power in coronary artery disease

AIMS

The heritability of aerobic power and of the response to physical training has been shown in healthy subjects. beta(1)-Adrenergic receptor (beta(1)AR) function affects exercise performance. This study aims to investigate whether the Ser49Gly and Gly389Arg polymorphisms of the beta(1)AR gene or their haplotypes are associated with aerobic power or its response to physical training in coronary artery disease (CAD).

METHODS AND RESULTS

Nine hundred and thirty-five biologically unrelated Caucasian patients with CAD who had exercised until exhaustion during graded bicycle testing at baseline and after completion of 3 months of exercise training from 1990 to 2001 (n = 1095) were eligible for inclusion in the CAREGENE (CArdiac REhabilitation and GENetics of Exercise performance) study. Polymorphisms were detected using the invader assay (Third Wave Technologiestrade mark, Madison, Wisconsin, USA). Patients with the Gly49Gly genotype had significantly higher covariate-adjusted aerobic power at baseline than those with Ser49Ser and Ser49Gly (P < 0.05). Adjusted aerobic power at baseline was highest in the Ser49-Gly389/Gly49-Gly389 and Gly49-Arg389/Gly49-Arg389 haplotype combinations. Aerobic power increased significantly (P < 0.001) with physical training. There was no association with the effect of physical training.

CONCLUSION

Ser49Gly and haplotype combinations of Ser49Gly and Gly389Arg of the beta(1)AR gene are associated with aerobic power, but not with the response to physical training in patients with CAD included in the CAREGENE study.

The functional significance of genetic variation within the beta-adrenoceptor

The beta-1 adrenoceptor is an archetypal G-coupled protein receptor that controls sympathetic responses in the heart, kidney and adipocytes. It has been widely exploited as a drug target with the development of antagonists to treat cardiovascular diseases such as hypertension, angina and heart failure. Signalling through the receptor is modulated by desensitization and beta1- adrenoceptor down-regulation. It is also affected by in vitro substitution of specific amino acid residues within the beta-1 adrenoceptor. Amino acid substitutions also occur naturally due to polymorphic variation within the human beta-1 adrenoceptor gene itself. Since these variants are common (typically being present in > 5% of the population), the pharmacogenetic implications are enormous. A number of these variants have been identified, although two have been the particular focus of recent publications: a serine to glycine substitution at position 49 (49S > G) and an arginine to glycine at position 389 (389R > G). The data on the in vitro behaviour of these two receptor variants is reviewed here, along with the evidence that they may affect both the risk of cardiovascular disease and the therapeutic response to beta-1 adrenoceptor antagonists.

Genetic polymorphisms and heart failure

Heart failure is a complex clinical syndrome. There is evidence for a genetic contribution to the pathophysiology of heart failure. Considering the fundamental role of neurohormonal factors in the pathophysiology and progression of cardiac dysfunction and hypertrophy, variants of genes involved in this system are logical candidate genes in heart failure. In this report, genetic polymorphisms of the major neurohormonal systems in heart failure will be discussed. Studies on polymorphisms of the renin-angiotensin-aldosterone system (RAAS), adrenergic receptor polymorphisms, endothelin (receptor) polymorphisms, and a group of miscellaneous polymorphisms that may be involved in the development or phenotypic expression of heart failure will be reviewed. Research on left ventricular hypertrophy is also included. The majority of genetic association studies focused on the ACE I/D polymorphism. Initial genetic associations have often been difficult to replicate, mainly due to problems in study design and lack of power. Promising results have been obtained with genetic polymorphisms of the RAAS and sympathetic system. Considering the evidence so far, a modifying role for these polymorphisms seems more likely than a role of these variants as susceptibility genes. Besides the need for larger studies to examine the effects of single nucleotide polymorphisms and haplotypes, future studies also need to focus on the complexity of these systems and study gene-gene interactions and gene-environment interactions.

Pharmacogenomics of adrenoceptors

Adrenoceptors (ARs) consist of nine subtypes (alpha(1A)-, alpha(1B)-, alpha(1D)-, beta(1)-, beta(2)-, beta(3)-, alpha(2A)-, alpha(2B)- and alpha(2C)-AR), which are involved in a wide spectrum of physiological functions and are the site of action for a considerable percentage of currently prescribed therapeutics. With the exception of alpha(1D), all AR subtypes are polymorphic with genetic variations in the coding and non-coding regions. This review discusses the biochemical consequences of these genetic variations and their impact in receptor function, disease pathophysiology, and drug response. Pharmacogenomic principles that have been discovered are also discussed.

Functional responses of human beta1 adrenoceptors with defined haplotypes for the common 389R>G and 49S>G polymorphisms

OBJECTIVES

The human beta1-adrenoceptor (beta1-AR) is an important therapeutic target for cardiovascular diseases and has two common functional polymorphisms (49S>G and 389R>G). These polymorphisms have only been studied in isolation, however, and not in the context of the four haplotypes (SR, SG, GR and GG) that exist in native beta1-ARs.

METHODS

To address this, the function of each of the receptor haplotypes was studied in HEK 293 cells stably transfected with appropriately modified human beta1-adrenoceptor cDNA sequence.

RESULTS

The affinity for the beta-adrenoceptor ligand, [125I]-cyanopindolol, was not significantly different across the haplotypes, but a high affinity state for the beta1-AR could only be demonstrated for receptors carrying the 389R substitution. Both basal (GR 36.3 +/- 2.9* vs. SR 16.5 0 +/- 3.6 and GG 31.7 +/- 1.4* vs. SG 15.6 +/- 1.5 pmol/mg protein; *P < 0.001) and maximal (GR 163 +/- 7.6 vs. SR 124 +/- 8.1* and GG 75.0 +/- 1.0 vs. SG 52.4 +/- 1.1* pmol/mg protein; *P < 0.001) isoprenaline-evoked cAMP production was significantly affected by both substitutions. Incubation with isoprenaline (10 microm for 30 min or 20 h) caused increased down-regulation of beta1-ARs in cells expressing GG and GR haplotypes (at 20 h percentage fall respectively -28.1 +/- 5.2 and -38.2 +/- 3.0).

CONCLUSIONS

These data highlight important functional differences between the common beta1-AR haplotypes and the need for consideration of haplotypes and not individual genotypes in determining the in-vivo role of these polymorphisms within this important drug target.

Genetic predisposition to heart failure

This review describes the numerous and complex molecular systems that are either known players or candidates in heart failure(HF). All systems whose genetic background has been investigated to date in HF are listed and discussed. Discussion also includes functional notes and known genetic polymorphisms already investigated in HF or candidates that have not yet been investigated. Despite substantial research on HF, relatively few coordinated studies have been conducted that assign precise risk to specific genetic polymorphisms. Identification of risk associated with genetic variations and subsequent translation of genetic knowledge into clinical practice will likely progress only in cases of large coordinated studies based on identical standards. The potential result will be a more accurate definition of HF identified as an evolving complex of cardiovascular diseases.

Risk stratification and management of sudden cardiac death: a new paradigm

Risk Stratification and Management of SCD. Management of SCD is undergoing radical change in direction. It is becoming increasingly appreciated that besides depressed left ventricular systolic function and the conventional risk stratification tools, new markers for plaque vulnerability, enhanced thrombogenesis, specific genetic alterations of the autonomic nervous system, cardiac sarcolemmal and contractile proteins, and familial clustering may better segregate patients with atherosclerotic coronary artery disease who are at high risk for SCD from those who may suffer from nonfatal ischemic events. Better understanding of pathophysiologic processes, such as postmyocardial infarction remodeling, the transition from compensated hypertrophy to heart failure, and the increased cardiovascular risk of coronary artery disease in the presence of diabetes or even a prediabetic state will help to improve both risk stratification and management. The rapidly developing fields of microchips technology and proteomics may allow rapid and cost-effective mass screening of multiple risk factors for SCD. The ultimate goal is to identify novel methods for risk stratification, risk modification, and prevention of SCD that could be applied to the general public at large.

Genetic variation and pharmacogenomics: concepts, facts, and challenges

The analysis of genetic variation in candidate genes is an issue of central importance in pharmacogenomics. The specific approaches taken will have a critical impact on the successful identification of disease genes, the molecular correlates of drug response, and the establishment of meaningful relationships between genetic variants and phenotypes of biomedical and pharmaceutical importance in general. Against a historical background, this article distinguishes different approaches to candidate gene analysis, reflecting different stages in human genome research. Only recently has it become feasible to analyze genetic variation systematically at the ultimate level of resolution, ie, the DNA sequence. In this context, the importance of haplotype-based approaches to candidate gene analysis has at last been recognized; the determination of the specific combinations of variants for each of the two sequences of a gene defined as a haplotype is essential. An up-to-date summary of such maximum resolution data on the amount, nature, and structure of genetic variation in candidate genes will be given. These data demonstrate abundant gene sequence and haplotype diversity. Numerous individually different forms of a gene may exist. This presents major challenges to the analysis of relationships between genetic variation, gene function, and phenotype. First solutions seem within reach. The implications of naturally occurring variation for pharmacogenomics and “personalized” medicine are now evident. Future approaches to the identification, evaluation, and prioritization of drug targets, the optimization of clinical trials, and the development of efficient therapies must be based on in-depth knowledge of candidate gene variation as an essential prerequisite.

Autonomic Nervous System Pharmacogenomics: A Progress Report

Pharmacogenetics, the inherited basis for interindividual differences in drug response, has rapidly expanded with the advent of new molecular tools and the sequencing of the human genome, yielding pharmacogenomics. We review here recent ideas and findings regarding pharmacogenomics of components of the autonomic nervous system, in particular, neuronal nicotinic acetylcholine receptors, postsynaptic receptors with which the parasympathetic and sympathetic neurotransmitters, acetylcholine (ACh) and norepinephrine, respectively, interact. The receptor subtypes that mediate these responses, M(1-3) muscarinic cholinergic receptors (mAChRs), and alpha(1A,B,D)-, alpha(2A,B,C)-, and beta(1,2,3)-adrenergic receptors (AR), show highly variable expression of genetic variants; variants of mAChRs and alpha(1)-ARs are relatively rare, whereas alpha(2)-AR and beta-AR subtype variants are quite common. The largest amount of data is available regarding variants of the latter ARs and represents efforts to associate certain receptor genotypes, most commonly, single nucleotide polymorphisms, with particular phenotypes (e.g., cardiovascular and metabolic responses). In vitro and in vivo studies have yielded inconsistent results; definitive conclusions are limited. We identify several conceptual and methodological problems with available data: sample size, ethnicity, tissue differences, coding versus noncoding variants, limited studies of haplotypes, and interaction among variants. Thus, although progress has been made in identifying genetic variation that influences drug response fo autonomic nervous system components, we are still at the early stages of defining the most critical genetic determinants and their role in human physiology and pharmacology.

What is the role of beta-adrenergic signaling in heart failure?

This review addresses open questions about the role of beta-adrenergic receptors in cardiac function and failure. Cardiomyocytes express all three beta-adrenergic receptor subtypes-beta1, beta2, and, at least in some species, beta3. The beta1 subtype is the most prominent one and is mainly responsible for positive chronotropic and inotropic effects of catecholamines. The beta2 subtype also increases cardiac function, but its ability to activate nonclassical signaling pathways suggests a function distinct from the beta1 subtype. In heart failure, the sympathetic system is activated, cardiac beta-receptor number and function are decreased, and downstream mechanisms are altered. However, in spite of a wealth of data, we still do not know whether and to what extent these alterations are adaptive/protective or detrimental, or both. Clinically, beta-adrenergic antagonists represent the most important advance in heart failure therapy, but it is still debated whether they act by blocking or by resensitizing the beta-adrenergic receptor system. Newer experimental therapeutic strategies aim at the receptor desensitization machinery and at downstream signaling steps.

Beta-adrenoceptor polymorphisms

There can be no doubt that beta(1)-, beta(2)- and beta(3)-adrenoceptor genes have genetic polymorphisms. Two single nucleotide polymorphisms have been described for the beta(1)- (Ser49Gly; Gly389Arg), three for the beta(2)- (Arg16Gly; Gln27Glu; Thr164Ile) and one for the beta(3)-adrenoceptor subtype (Trp64Arg) that might be of functional importance. The possibility that changes in expression or properties of the beta-adrenoceptors due to single nucleotide polymorphisms might have phenotypic consequences influencing their cardiovascular or metabolic function or may contribute to the pathophysiology of several disorders like hypertension, congestive heart failure, asthma or obesity is an idea that has attracted much interest during the last 10 years. At present, it appears that these beta-adrenoceptor polymorphisms are very likely not disease-causing genes, but might be risk factors, might modify disease and/or might influence progression of disease. The aim of this review is to provide an overview of the functional consequences of such beta-adrenoceptor polymorphisms in vitro, ex vivo and in vivo.

Pharmacology and physiology of human adrenergic receptor polymorphisms

Adrenergic receptors are expressed on virtually every cell type in the body and are the receptors for epinephrine and norepinephrine within the sympathetic nervous system. They serve critical roles in maintaining homeostasis in normal physiologic settings as well as pathologic states. These receptors are also targets for therapeutically administered agonists and antagonists. Recent studies have shown that at least seven adrenergic receptor subtypes display variation in amino acid sequence in the human population due to common genetic polymorphisms. Variations in potential regulatory domains in noncoding sequence are also present. Here, we review the consequences of these polymorphisms in terms of signaling, human physiology and disease, and response to therapy.

Gender, ethnicity and genetics in cardiovascular disease: part 1: Basic principles

Prior to 1993, most drug efficacy and safety trials were conducted in white males, although gender and racial differences in pharmacodynamics and pharmacokinetics have been documented since the early 1900s. Over the last 2 decades, supported by the FDA and legislation, attempts to include more women and minorities in clinical drug trials have been made, with limited success. Yet, there are important differences in pathophysiology and pharmacogenetics, as well as pharmacotherapeutic effectiveness. This is the first of 2 articles that review the basic scientific principles of such differences. In particular, genetic polymorphisms of cardiovascular candidate genes and drug metabolism are described. The pharmacodynamic and pharmacokinetic variations among genders and ethnicities are summarized.

The Gln27Glu beta2-adrenoceptor polymorphism slows the onset of desensitization of cardiac functional responses in vivo

Studies performed have shown that the Arg16Gly allele in beta-adrenoceptors (beta2AR) enhances susceptibility to agonist-induced down-regulation, while the Gln27Glu polymorphism diminishes it. In this study, we tested whether similar phenotypes occur in vivo. We assessed 32 volunteers (mean age 25 +/- 2 years) with different genotypes (group A: wild-type beta2AR, n = 16; group B: homozygous Glu27, n = 10; group C: homozygous Gly16, n = 6) for the effect of 2 weeks treatment with 3 x 5 mg/day oral terbutaline on terbutaline infusion-induced increases in heart rate and contractility (i.e. shortening of heart rate-corrected duration of electromechanical systole, QS2c). At baseline, terbutaline infusion increased heart rate and contractility similarly among subjects in the three groups. Treatment with oral terbutaline for 14 days reduced the ability of intravenous (i.v.) terbutaline to increase heart rate and contractility. The extent of this reduction was similar but the time course of desensitization differed among the three groups. While in groups A and C terbutaline infusion-induced increases in heart rate and contractility were reduced within 24 h after oral ingestion of terbutaline, a significant effect on response to terbutaline infusion was not evident for the first 3 days of terbutaline treatment in group B. The Arg16Gly and the Gln27Glu variants of the beta2AR do not alter the extent of agonist-induced beta2AR desensitization in vivo but Glu27 homozygotes develop desensitization more slowly. This result may have implications for cardiac side-effects in patients who are Glu27 homozygotes and who receive beta2AR agonist therapy.

Greater inotropic and cyclic AMP responses evoked by noradrenaline through Arg389 beta 1-adrenoceptors versus Gly389 beta 1-adrenoceptors in isolated human atrial myocardium

1. We studied the biochemical and contractile responses of isolated human myocardial tissue expressing native receptor variants of the 389G>R beta(1)-adrenoceptor polymorphism. 2. Right atrial appendage was obtained from homozygous RR patients (n=37) and homozygous GG patients (n=17) undergoing elective cardiac surgery. The positive inotropic effect of noradrenaline in these tissues, mediated through beta(1)-adrenoceptors, was studied using electrically stimulated (1 Hz) atrial strips, as well as the effects of noradrenaline on cyclic AMP levels and cyclic AMP-dependent protein kinase. 3. Tissue from RR homozygotes (n=14) showed significantly increased inotropic potency to noradrenaline (-log EC(50), M=6.92+/-0.12) compared to GG homozygotes (n=8, -log EC(50), M=6.36+/-0.11, P<0.005). This difference was not dependent on tissue basal force. 4. Tissue cyclic AMP levels (pmol mg(-1)) were also greater in RR homozygotes (basal 34.8+/-3.7 n=12, 300 nM noradrenaline 41.4+/-7.6 n=9, 30 micro M noradrenaline 45.2+/-3.2 n=22, 0.2 mM isoprenaline 48.3+/-4.2 n=16) compared to GG homozygotes (basal 30.7+/-4.4 n=5, 300 nM noradrenaline 32.6+/-6.92 n=5, 30 micro M noradrenaline 38.1+/-3.1 n=8, 0.2 mM isoprenaline 42.6+/-5.2 n=6, P=0.007). There were no differences between the variants in terms of cyclic AMP-dependent protein kinase activity. 5. These data provide the first evidence that enhanced G-protein coupling of the R389 beta(1)-adrenoceptor variant reported in rodent fibroblast expression systems is also present in native human receptors. The functional consequence of this is to significantly alter the inotropic potency of beta(1)-adrenoceptor activation depending on its genotype at the 389 position.

Beta-adrenergic receptor polymorphisms: cardiovascular disease associations and pharmacogenetics

The beta-adrenergic receptors (betaAR) play important roles in cardiovascular function and disease, and both agonists and antagonists are widely used in various settings for treatment of cardiovascular disease. Both the beta1AR and beta2AR genes have several polymorphisms that are common in the population and result in encoding of different amino acids. More importantly, in vitro functional studies suggest that these polymorphisms have functional significance. In this review we summarize the literature on the relationship between the betaAR polymorphisms and cardiovascular disease as well as the literature on the impact of these polymorphisms on drug response. Additionally, the polymorphisms in both the beta1AR and beta2AR genes are in linkage disequilibrium; thus, the relevance of single polymorphism vs. haplotype analysis is discussed. Further study of the betaAR genetic polymorphisms is likely to enhance our understanding of cardiovascular disease and improve our use of beta-agonists and beta-antagonists in treatment of cardiovascular disease.

Conservation of the cardiostimulant effects of (-)-norepinephrine across Ser49Gly and Gly389Arg beta(1)-adrenergic receptor polymorphisms in human right atrium in vitro

OBJECTIVE

The goal of this study was to determine whether the cardiostimulant effects of the endogenous beta(1)-adrenergic receptor (AR) agonist, (-)-norepinephrine are modified by polymorphic (Serine49Glycine [Ser49Gly], Glycine389Arginine [Gly389Arg]) variants of beta(1)-ARs in the nonfailing adult human heart.

BACKGROUND

Human heart beta(1)-ARs perform a crucial role in mediating the cardiostimulant effects of (-)-norepinephrine. An understanding of the significance of Ser49Gly and Gly389Arg polymorphisms in the human heart is beginning to emerge, but not as yet in adult patients who have coronary artery disease (CAD).

METHODS

The potency and maximal effects of (-)-norepinephrine at beta(1)-ARs (in the presence of beta(2)-AR blockade with 50 nM ICI 118,551 [erythro-DL-1(7-methylindan-4-yloxy)-3-isopropylamino-butan-2-ol]) for changes in contractile force and shortening of contractile cycle duration were determined in human right atrium in vitro from 87 patients undergoing coronary artery bypass grafting who were taking beta-blockers before surgery. A smaller sample of patients (n = 20) not taking beta-blockers was also investigated. Genotyping for two beta(1)-AR polymorphisms (Ser49Gly and Gly389Arg) was determined from a sample of blood taken at the time of surgery.

RESULTS

(-)-Norepinephrine caused concentration-dependent increases in contractile force and reductions in time to reach peak force and time to reach 50% relaxation. There were no differences in the potency or maximal effects of (-)-norepinephrine in the right atrium from patients with different Ser49Gly and Gly389Arg polymorphisms.

CONCLUSIONS

The cardiostimulant effects of (-)-norepinephrine at beta(1)-ARs were conserved across Ser49Gly and Gly389Arg polymorphisms in the right atrium of nonfailing hearts from patients with CAD managed with or without beta-blockers.