Beta-adrenergic receptor polymorphisms: cardiovascular disease associations and pharmacogenetics

Pediatric Beta Blocker Therapy: A Comprehensive Review of Development and Genetic Variation to Guide Precision-Based Therapy in Children, Adolescents, and Young Adults

Beta adrenergic receptor antagonists, known as beta blockers, are one of the most prescribed medications in both pediatric and adult cardiology. Unfortunately, most of these agents utilized in the pediatric clinical setting are prescribed off-label. Despite regulatory efforts aimed at increasing pediatric drug labeling, a majority of pediatric cardiovascular drug agents continue to lack pediatric-specific data to inform precision dosing for children, adolescents, and young adults. Adding to this complexity is the contribution of development (ontogeny) and genetic variation towards the variability in drug disposition and response. In the absence of current prospective trials, the purpose of this comprehensive review is to illustrate the current knowledge gaps regarding the key drivers of variability in beta blocker drug disposition and response and the opportunities for investigations that will lead to changes in pediatric drug labeling.

β1-receptor polymorphisms and junctional ectopic tachycardia in children after cardiac surgery

Junctional ectopic tachycardia (JET) is a potentially life-threatening postoperative arrhythmia in children with specific congenital heart defects and can contribute significantly to postoperative morbidity for at-risk populations. In adults, β1-adrenergic receptor (ADRB1) and β2-adrenergic receptor (ADRB2) genotypes have been associated with increased risk for arrhythmias. However, their association with arrhythmia risk in children is unknown. We aimed to test associations between ADRB1 and ADRB2 genotypes and postoperative JET in patients with congenital heart defects. Children who underwent cardiac surgery were genotyped for the ADRB1 p.Ser49Gly (rs1801252; c.145A>G), p.Arg389Gly (rs1801253; c.1165C>G), ADRB2 p.Arg16Gly (rs1042713; c.46A>G), and p.Glu27Gln (rs1042714; c.79G>C) polymorphisms. The occurrence of postoperative JET was assessed via cardiologist-interpreted electrocardiograms. Genotype associations with JET were analyzed via logistic regression, adjusted for clinical variables associated with JET, with separate analysis in patients not on a β-blocker. Of the 343 children included (median age 8 months, 53% boys, 69% European ancestry), 45 (13%) developed JET. The Arg389Arg genotype was not significantly associated with JET in the overall population (odds ratio [OR] = 1.96, 95% confidence interval [CI] = 0.96-4.03, p = 0.064), but was nominally associated in patients not taking a β-blocker (n = 324, OR = 2.25, 95% CI = 1.05-4.80. p = 0.034). None of the other variants were associated with JET. These data suggest that the ADRB1 Arg389Arg genotype may predict risk for JET following cardiac surgery in pediatric patients in the absence of β-blockade. Whether treatment with a β-blocker ameliorates this association requires further research.

Variants in ADRB1 and CYP2C9: Association with Response to Atenolol and Losartan in Marfan Syndrome

OBJECTIVE

To test whether variants in ADRB1 and CYP2C9 genes identify subgroups of individuals with differential response to treatment for Marfan syndrome through analysis of data from a large, randomized trial.

STUDY DESIGN

In a subset of 250 white, non-Hispanic participants with Marfan syndrome in a prior randomized trial of atenolol vs losartan, the common variants rs1801252 and rs1801253 in ADRB1 and rs1799853 and rs1057910 in CYP2C9 were analyzed. The primary outcome was baseline-adjusted annual rate of change in the maximum aortic root diameter z-score over 3 years, assessed using mixed effects models.

RESULTS

Among 122 atenolol-assigned participants, the 70 with rs1801253 CC genotype had greater rate of improvement in aortic root z-score compared with 52 participants with CG or GG genotypes (Time × Genotype interaction P = .005, mean annual z-score change ± SE -0.20 ± 0.03 vs -0.09 ± 0.03). Among participants with the CC genotype in both treatment arms, those assigned to atenolol had greater rate of improvement compared with the 71 of the 121 assigned to losartan (interaction P = .002; -0.20 ± 0.02 vs -0.07 ± 0.02; P < .001). There were no differences in atenolol response by rs1801252 genotype or in losartan response by CYP2C9 metabolizer status.

CONCLUSIONS

In this exploratory study, ADRB1-rs1801253 was associated with atenolol response in children and young adults with Marfan syndrome. If these findings are confirmed in future studies, ADRB1 genotyping has the potential to guide therapy by identifying those who are likely to have greater therapeutic response to atenolol than losartan.

Adrenaline activation of the carotid body: Key to CO2 and pH homeostasis in hypoglycaemia and potential pathological implications in cardiovascular disease

Ventilatory and neuroendocrine counter-regulatory responses during hypoglycaemia are essential in order to maintain glycolysis and prevent rises in P_aCO₂ leading to systemic acidosis. The mammalian carotid body has emerged as an important driver of hyperpnoea and glucoregulation in hypoglycaemia. However, the adequate stimulus for CB stimulation in hypoglycaemia has remained controversial for over a decade. The recent finding that adrenaline is a physiological activator of CB in hypoglycaemia raises the intriguing possibility that CB stimulation and hyperpnoea may be necessary to maintain pH in other adrenaline-related hypermetabolic states such as exercise. This review will therefore focus on 1) The important functional contribution of the CB in the counter-regulatory and ventilatory response to hypoglycaemia, 2) the proposed mechanisms that cause CB stimulation in hypoglycaemia including hormonal activation by adrenaline and direct low glucose sensing and 3) the possible pathological consequences of repetitive CB activation by adrenaline that could potentially be targeted to reduce CB-mediated cardiovascular disease.

Pharmacogenomics of heart failure: a systematic review

BACKGROUND

Heart failure (HF) and multiple HF-related phenotypes are heritable. Genes implicated in the HF pathophysiology would be expected to influence the response to treatment.

METHODS

We conducted a series of systematic literature searches on the pharmacogenetics of HF therapy to assess the current knowledge on this field.

RESULTS

Existing data related to HF pharmacogenomics are still limited. The ADRB1 gene is a likely candidate to predict response to β-blockers. Moreover, the cytochrome P450 2D6 coding gene (CYP2D6) clearly affects the pharmacokinetics of metoprolol, although the clinical impact of this association remains to be established.

CONCLUSION

Given the rising prevalence of HF and related costs, a more personalized use of HF drugs could have a remarkable benefit for patients, caregivers and healthcare systems.

Bayesian modeling for genetic association in case-control studies: accounting for unknown population substructure

A two-stage parametric Bayesian method is proposed to examine the association between a candidate gene and the occurrence of a disease after accounting for population substructure. This procedure, implemented via a Markov chain Monte Carlo numerical integration technique, first estimates the posterior probability of different unknown population substructures and then integrates this information into a disease-gene association model through the technique of Bayesian model averaging. The model relaxes certain assumptions of previous analyses and provides a unified computational framework to obtain an estimate of the log odds ratio parameter corresponding to the genetic factor after allowing for the allele frequencies to vary across subpopulations. The uncertainty in estimating the population substructure is taken into account while providing credible intervals for parameters in the disease-gene association model. Simulations on unmatched case-control studies that mimic an admixed Argentinean population are performed to demonstrate the statistical properties of our model. The method is also applied to a real data set coming from a genetic association study on obesity.

Adrenergic receptor genotype influences heart failure severity and β-blocker response in children with dilated cardiomyopathy

BACKGROUND

Adrenergic receptor (ADR) genotypes are associated with heart failure (HF) and β-blocker response in adults. We assessed the influence of ADR genotypes in children with dilated cardiomyopathy (DCM).

METHODS

Ninety-one children with advanced DCM and 44 with stable DCM were genotyped for three ADR genotypes associated with HF risk in adults: α2cdel322-325, β1Arg389, and β2Arg16. Data were analyzed by genotype and β-blocker use. Mean age at enrollment was 8.5 y.

RESULTS

One-year event-free survival was 51% in advanced and 80% in stable DCM. High-risk genotypes were associated with higher left ventricular (LV) filling pressures, higher systemic and pulmonary vascular resistance, greater decline in LV ejection fraction (P < 0.05), and a higher frequency of mechanical circulatory support while awaiting transplant (P = 0.05). While β-blockers did not reduce HF severity in the overall cohort, in the subset with multiple high-risk genotypes, those receiving β-blockers showed better preservation of cardiac function and hemodynamics compared with those not receiving β-blockers (interaction P < 0.05).

CONCLUSION

Our study identifies genetic risk markers that may help in the identification of patients at risk for developing decompensated HF and who may benefit from early institution of β-blocker therapy before progression to decompensated HF.

Beta2-Adrenergic Receptor Gene Polymorphisms in Egyptian Patients with Acute Myocardial Infarction

Background. Beta2-adrenergic receptor (ADRB2) gene polymorphisms, Arg16Gly and Gln27Glu, have been implicated in the pathogenesis of cardiovascular diseases. The aim of this study was to determine the association of these two polymorphisms with the risk of myocardial infarction (MI) in the Egyptian population. Methods. Blood samples were collected from 68 MI patients and 75 healthy controls. They were assessed for the presence of cardiovascular risk factors and genotyped for the Arg16Gly (rs1042713) and Gln27Glu (rs1042714) polymorphisms using allelic-discrimination polymerase chain reaction. Results. There is no significant difference in genotype and allele frequencies at codon 16 between MI patients and controls (P=0.919). However, at codon 27, MI risk was higher in Gln27 homozygous participants than in Glu27 carriers (P=0.045). The haplotype frequency distribution showed significant difference among cases and controls (P=0.002); homozygotes for Gly16/Gln27 haplotype were more susceptible to MI than Gly16/Glu27 carriers. Patients with Arg16/Gln27 haplotype had higher serum total cholesterol levels (P<0.05) and lower frequency of diabetes in MI patients (P<0.01). However, both Glu27 genotypes and haplotype showed lower frequency of hypertension (P<0.001). Conclusions. Our findings suggested that the ADRB2 gene polymorphisms may play an important role in susceptibility of MI among Egyptian population.

β1-Adrenergic receptor blockade extends the life span of Drosophila and long-lived mice

Chronic treatment with β-adrenergic receptor (βAR) agonists increases mortality and morbidity while βAR antagonists (β-blockers) decrease all-cause mortality for those at risk of cardiac disease. Levels of sympathetic nervous system βAR agonists and βAR activity increase with age, and this increase may hasten the development of age-related mortality. Here, we show that β-blockers extend the life span of healthy metazoans. The β-blockers metoprolol and nebivolol, administered in food daily beginning at 12 months of age, significantly increase the mean and median life span of isocalorically fed, male C3B6F1 mice, by 10 and 6.4%, respectively (P < 0.05). Neither drug affected the weight or food intake of the mice, indicating that induced CR is not responsible for these effects, and that energy absorption and utilization are not altered by the drugs. Both β-blockers were investigated to control for their idiosyncratic, off-target effects. Metoprolol and nebivolol extended Drosophila life span, without affecting food intake or locomotion. Thus, βAR antagonists are capable of directly extending the life span of two widely divergent metazoans, suggesting that these effects are phylogenetically highly conserved. Thus, long-term use of β-blockers, which are generally well-tolerated, may enhance the longevity of healthy humans.

Adrenoreceptors and nitric oxide in the cardiovascular system

Nitric Oxide (NO) is a small molecule that continues to attract much attention from the scientific community. Since its discovery, it has been evident that NO has a crucial role in the modulation of vascular tone. Moreover, NO is involved in multiple signal transduction pathways thus contributing to the regulation of many cellular functions. NO effects can be either dependent or independent on cGMP, and rely also upon several mechanisms such as the amount of NO, the compartmentalization of the enzymes responsible for its biosynthesis (NOS), and the local redox conditions. Several evidences highlighted the correlation among adrenoreceptors activity, vascular redox status and NO bioavailability. It was suggested a possible crosstalk between NO and oxidative stress hallmarks in the endothelium function and adaptation, and in sympathetic vasoconstriction control. Adrenergic vasoconstriction is a balance between a direct vasoconstrictive effect on smooth muscle and an indirect vasorelaxant action caused by α₂- and β-adrenergic endothelial receptor-triggered NO release. An increased oxidative stress and a reduction of NO bioavailability shifts this equilibrium causing the enhanced vascular adrenergic responsiveness observed in hypertension. The activity of NOS contributes to manage the adrenergic pathway, thus supporting the idea that the endothelium might control or facilitate β-adrenergic effects on the vessels and the polymorphic variants in β₂-receptors and NOS isoforms could influence aging, some pathological conditions and individual responses to drugs. This seems to be dependent, almost in part, on differences in the control of vascular tone exerted by NO. Given its involvement in such important mechanisms, the NO pathway is implicated in aging process and in both cardiovascular and non-cardiovascular conditions. Thus, it is essential to pinpoint NO involvement in the regulation of vascular tone for the effective clinical/therapeutic management of cardiovascular diseases (CVD).

Education, genetic ancestry, and blood pressure in African Americans and Whites

OBJECTIVES

We assessed the relative roles of education and genetic ancestry in predicting blood pressure (BP) within African Americans and explored the association between education and BP across racial groups.

METHODS

We used t tests and linear regressions to examine the associations of genetic ancestry, estimated from a genomewide set of autosomal markers, and education with BP variation among African Americans in the Family Blood Pressure Program. We also performed linear regressions in self-identified African Americans and Whites to explore the association of education with BP across racial groups.

RESULTS

Education, but not genetic ancestry, significantly predicted BP variation in the African American subsample (b=-0.51 mm Hg per year additional education; P=.001). Although education was inversely associated with BP in the total population, within-group analyses showed that education remained a significant predictor of BP only among the African Americans. We found a significant interaction (b=3.20; P=.006) between education and self-identified race in predicting BP.

CONCLUSIONS

Racial disparities in BP may be better explained by differences in education than by genetic ancestry. Future studies of ancestry and disease should include measures of the social environment.

Role of beta-adrenergic receptor gene polymorphisms in the long-term effects of beta-blockade with carvedilol in patients with chronic heart failure

BACKGROUND

Beta-blockers are mainstay of current treatment of heart failure (HF). Beta-adrenergic receptors (AR) single nucleotide gene polymorphisms (SNPs) may influence the sensitivity and density of beta-AR. We assessed the relation between three common beta-AR SNPs and the response to carvedilol administration.

METHODS AND RESULTS

We studied 183 consecutive patients with chronic HF due to ischemic or nonischemic cardiomyopathy, a LV ejection fraction (LVEF) < or = 0.35, not previously treated with beta-blockers. Each patient underwent gated-SPECT radionuclide ventriculography, cardiopulmonary exercise testing and invasive hemodynamic monitoring at baseline and after 12 months of carvedilol administration at maintenance dosages. The beta1-AR gene Arg389Gly and the beta2-AR gene Arg16Gly SNPs were not related to the response to carvedilol administration. Homozygotes for the Glu27Glu allele showed a greater increase in the LVEF, compared to the other patients (+13.0 +/- 12.2% versus +7.1 +/- 8.1% in the Gln27Gln homozygotes, and 8.3 +/- 11.4% units in the Gln27Glu heterozygotes; p = 0.022 by ANOVA). Glu27Glu homozygotes also showed a greater decline in the pulmonary wedge pressure both at rest and at peak exercise. Gln27Glu SNP was selected amongst the determinants of the LVEF response to carvedilol at multivariable analysis, in addition to the cause of cardiomyopathy, baseline systolic blood pressure and the dose of carvedilol administered.

CONCLUSION

Beta1-AR Arg389Gly and beta2-AR Arg16Gly SNPs are not related to the response to carvedilol therapy. In contrast, the Gln27Glu SNP is a determinant of the LVEF response to this agent in patients with chronic HF.

Association between polymorphisms in the beta2-adrenoceptor gene and migraine in women

OBJECTIVE

To investigate the role of three common polymorphisms in the beta2-adrenoceptor gene in migraine.

BACKGROUND

Migraine has been associated with increased risk of cardiovascular disease and asthma in which beta2-adrenoceptors play an important role; beta-adrenoceptor antagonists are used in migraine prevention. However, the role of variants in the beta2-adrenoceptor gene in migraine is unclear.

METHODS

Association study among 23,753 white women, participating in the Women's Health Study, for whom we had information on migraine at baseline and genotype status of the polymorphisms rs1042713 (Gly16Arg), rs1042714 (Gln27Glu), rs1800888 (Thr164Ile). Migraine was self-reported and we distinguished between any history of migraine, active migraine with and without aura, and prior migraine (history of migraine but not active migraine) in our analyses.

RESULTS

At baseline 4339 women reported any history of migraine. Of these, 3041 had active migraine (1221 migraine with aura, 1820 migraine without aura) and 1298 prior migraine. No migraine was reported by 19,414 women. Genotype- and haplotype-based analyses did not show an association of any of the gene variants tested with any history of migraine. The multivariable-adjusted odds ratios (ORs) (95% confidence intervals) for any history of migraine in the additive model were 1.0 (0.96-1.05) for rs1042713, 1.0 (0.95-1.05) for rs1042714, and 0.84 (0.68-1.05) for rs1800888. In the haplotype analysis the ORs ranged from 0.83 (0.67-1.03) to 1.01 (0.94-1.07) with Gly16-Glu27-Thr164 as the reference. We also did not find associations in the genotype- and haplotype-based analyses within migraine-specific subgroups.

CONCLUSIONS

Our results do not support a role of 3 investigated polymorphisms in the beta2-adrenoceptor gene in migraine pathophysiology.

IL1 gene cluster polymorphisms and its haplotypes may predict the risk to develop invasive pulmonary aspergillosis and modulate C-reactive protein level

OBJECTIVE

The aim of this study was to determine whether interleukin-1 alpha (IL1alpha), interleukin-1 beta (IL1beta), and IL1 receptor antagonist (IL1Ra) polymorphisms are implicated in invasive pulmonary aspergillosis (IPA) pathogenesis.

MATERIALS AND METHODS

Subjects comprised 110 hematological patients and 148 healthy controls. Genotypic and allelic frequencies were similar between hematological patients and controls. IPA was diagnosed in 59 of the 110 patients according to consensus criteria published by the European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group (EORTC/IFICG).

RESULTS AND DISCUSSIONS

Individual locus analysis showed that IL1alpha and IL1Ra polymorphisms were not associated with the presence of IPA (p = 0.560 and p = 0.680, respectively). However, a trend towards a higher presence of IL1beta( - ) (511TT) genotype (or IL1beta(-511T) allele) in the IPA group than in the non-IPA patient group (p = 0.092 and p = 0.095, respectively) was found. Haplotype analysis revealed that VNTR2/-889C/-511T haplotype was strongly associated with susceptibility to develop IPA infection (p = 0.020). Haplotype analysis also showed an association between VNTR2/-889C/-511C haplotype and resistance to IPA infection (p = 0.028). Furthermore, patients with IL1Ra VNTR2/2 and IL1beta(-511)T/T genotypes had a higher positive serum galactomannan percentage versus patients with other genotypes. Finally, C-reactive protein (CRP) production was significantly associated with IL1 gene cluster polymorphisms, although CRP values were similar between IPA and non-IPA groups.

CONCLUSION

These findings indicate a critical role of IL1 gene cluster polymorphisms in the susceptibility to IPA infection and CRP production.

Population pharmacokinetics and dose simulation of carvedilol in paediatric patients with congestive heart failure

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

* Applying in silico tools such as population pharmacokinetic analysis and simulation will help to find adequate dosing strategies and increase the probability of success for a randomized controlled trial. * Up to now, for carvedilol in paediatric patients with congestive heart failure (CHF) the dose has been linearly extrapolated from adults, but the results with this dosing strategy are ambiguous. * Further trials are necessary to establish carvedilol for paediatric patients with CHF.

WHAT THIS STUDY ADDS

* Carvedilol pharmacokinetics in paediatric patients with CHF depends on the weight and age of the patient. * Therefore, the drug exposure differs substantially between patients of different ages receiving the same dose with respect to body weight. * Simulations revealed that an age-adjusted carvedilol dosing strategy with higher doses for younger patients with respect to body weight is preferable to a uniform one.

AIMS

To investigate the ontogeny of carvedilol pharmacokinetics and to develop an age-appropriate carvedilol dosing strategy for paediatric patients.

METHODS

Data were derived from a prospective, nonplacebo-controlled study of carvedilol for the treatment of paediatric patients with congestive heart failure and analysed using a nonlinear mixed-effects modelling approach (NONMEM, Version V 1.1). The population pharmacokinetic model was further utilized for simulations of different carvedilol dosing strategies.

RESULTS

Four hundred and eighty carvedilol plasma concentrations of 41 patients (0.1-19.3 years; median 3.5) were included in the analysis. A two-compartment model with first-order absorption and absorption lag served as structural model. Weight and age were the most important covariates for carvedilol pharmacokinetics. The weight-adjusted clearance was highest for the younger patients with 2.7 l h(-1) kg(-1) for a 1-year-old patient compared with 0.7 l h(-1) kg(-1) for a 19.3-year-old patient. Dose simulations revealed that the area under the plasma concentration-time curve (AUC) as a measure of drug exposure increased with age despite constant doses with respect to body weight. For infants (28 days to 23 months), children (2-11 years) and adolescents (12-15 years) daily doses of 3, 2 and 1 mg kg(-1), administered in two or three discrete doses, were necessary to reach an exposure comparable to adults receiving 0.7 mg kg(-1) day(-1).

CONCLUSION

The ontogeny of carvedilol pharmacokinetics in paediatric patients depends on age and weight. Dose simulations revealed that younger patients have to be treated with higher doses with respect to body weight to reach the same exposure as adults.

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.

In patients chronically treated with metoprolol, the demand of inotropic catecholamine support after coronary artery bypass grafting is determined by the Arg389Gly-β1-adrenoceptor polymorphism

In vitro, the Arg389Gly-beta(1)-adrenoceptor (AR) polymorphism exhibits decreased receptor signaling. In vivo, dobutamine infusion evoked smaller heart rate and/or contractility increases in subjects carrying Gly389Gly-beta(1)AR vs subjects carrying Arg389Arg-beta(1)AR. The aim of this study was to find out whether the Arg389Gly-beta(1)AR polymorphism might also determine demand of catecholamine-induced inotropic support in patients with low cardiac index (CI) after coronary artery bypass grafting (CABG) surgery with cardiopulmonary bypass (CPB). For this purpose, we assessed in 82 patients, who were preoperatively chronically treated with metoprolol, after CABG surgery with CPB, the dose and duration of adrenaline-induced inotropic support in relation to the Arg389Gly-beta(1)AR genotype. Patients homozygous for the Arg389-beta(1)AR variant (n = 45) required, in comparison to patients homozygous for the Gly389-beta(1)AR variant (n = 9), lower adrenaline doses (53 +/- 24 vs 164 +/- 39 ng/kg body weight/min, p < 0.05) to reach a stable and comparable hemodynamic status and a CI >or= 3.0 l/min/m(2). Moreover, the time necessary for inotropic support tended to be shorter in patients homozygous for the Arg389-beta(1)AR than in patients homozygous for the Gly389-beta(1)AR (10.5 +/- 6 vs 20.5 +/- 12 h). Values for patients heterozygous for the Arg389Gly-beta(1)AR (n = 28) were in between. We conclude that the Arg389Gly-beta(1)AR polymorphism appears to be a determinant of cardiac responses to catecholamine stimulation. Thus, by assessment of the Arg389Gly-beta(1)AR polymorphism, it might be possible to predict demand of and therapeutic responses to beta AR agonist treatment.

Genetic influences of beta-adrenoceptor polymorphisms on arterial functional changes and cardiac remodeling in hypertensive patients

Three subtypes of beta-adrenoceptor, beta1, beta2 and beta3, are involved in the sympathetic nervous system, which plays an important role in the development of hypertension and hypertensive complications. These complications can include left ventricular hypertrophy and arterial stiffness, which are reported risk factors for cardiovascular diseases. We designed clinical trials to clarify the association between hypertensive complications and beta-adrenoceptor single nucleotide polymorphisms in essential hypertension. Using Taqman PCR methods, we detected five polymorphisms of three beta-adrenoceptors: Ser49Gly and Arg389Gly for the beta1-adrenoceptor; Gly16Arg and Glu27Gln for the beta2-adrenoceptor; and Trp64Arg for the beta3-adrenoceptor. We included 300 subjects and measured pulse wave velocity, vasodilator response to hyperemia, left ventricular hypertrophy (by electrocardiogram and echocardiography), and cardiac enlargement (by chest X-ray). We found that pulse wave velocity and nitroglycerin-induced hyperemia were both closely associated with the Ser49Gly polymorphism (p<0.05), and Glu27Gln was found by both electrocardiogram and echocardiography to be significantly associated with left ventricular hypertrophy (p<0.05). These data suggested that two polymorphisms of different beta-adrenoreceptor subtypes are the genetic influences on the development of arterial stiffness and left ventricular hypertrophy in essential 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.

β-adrenoceptor blocker treatment and the cardiac β-adrenoceptor-G-protein(s)-adenylyl cyclase system in chronic heart failure

Recent studies showed that chronic beta-adrenoceptor (AR) blocker treatment exerts beneficial effects in patients with chronic heart failure (CHF). In CHF, sympathetic drive to the heart is increased, and this causes pathological changes in cardiac beta-AR-G-protein(s)-adenylyl cyclase system: Cardiac beta-1 AR are decreased, and amount and activity of cardiac G(i)-protein and G-protein-coupled receptor kinase (GRK) are increased resulting in diminished cardiac beta-AR functional responsiveness. One possible mechanism of beneficial effects of beta-AR blockers could be that they prevent adverse effects of increased sympathetic activity and up-regulate cardiac (and vascular) beta-AR density, and by this, enhance beta-AR-mediated effects. Another possibility could be that chronic beta-AR blocker treatment normalizes activity of G(i)-protein and may thereby restore beta-AR functional responsiveness. Moreover, failing human heart exhibits an inverse force-frequency relationship. beta-AR blockers reduce heart rate; this may, therefore, improve force of contraction. One of the strongest stimuli to activate GRK is increased sympathetic activity (as in CHF) via beta-AR stimulation. beta-AR blockers, by blocking beta-AR, can prevent GRK activation and/or can reduce the (previously enhanced) GRK activity, and this might-at least partly-contribute to beneficial effects of beta-AR blockers in CHF treatment. Finally, the "loss-of-function" Arg389Gly beta-1 AR polymorphism seems to determine heart rate and blood pressure responses to beta-1 AR blocker administration: Arg389Arg beta-1 AR subjects exhibit stronger effects than subjects with one or two Gly389 alleles. Thus, it might be predicted that patients homozygous Arg389 beta-1 AR should be good responders, whereas patients homozygous Gly389 beta-1 AR polymorphism should be poor or non-responders.

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.

Defective vasodilatory mechanisms in hypertension: a G-protein-coupled receptor perspective

PURPOSE OF REVIEW

The purpose of this article is to review recent evidence relating to the regulation of vasodilatation and alterations in these mechanisms in the hypertensive state. In particular, we will focus on signaling systems regulating nitric oxide synthase and intracellular cyclic AMP - the two principal mechanisms mediating vasodilatation.

RECENT FINDINGS

G-protein-coupled-receptor-mediated, endothelial-dependent processes are increasingly being seen as critical vasodilatory mechanisms. Impairment of endothelial responses to G-protein-coupled receptor activation is a key component of the decrease in G-protein-coupled-receptor-mediated vasodilatation in hypertension. In addition, an 'uncoupling' of the G-protein-coupled receptor/G-protein complex is the principal mechanism underlying impaired G-protein-coupled-receptor-mediated vasodilatation in hypertension. Alterations in G-protein-coupled receptor kinase function have a central role underlying this defect. Finally, the importance of the expression of genetic variants of G-protein-coupled receptors and G-proteins underlying the defect in vasodilatation in hypertension remains contentious.

SUMMARY

G-protein signaling pathways in the vasculature play an important role in both the development and the maintenance of the hypertensive state. It is unlikely, however, that any single defect in the G-protein-linked vasodilatory pathway will ever be shown to be the sole cause of hypertension.

Polymorphisms in the Advanced Glycosylation End Product–Specific Receptor Gene and Risk of Incident Myocardial Infarction or Ischemic Stroke

Background and Purpose— Recent findings of an association between polymorphisms of advanced glycosylation end product–specific receptor (AGER) and risk of diabetic vasculopathy have generated great interest. However, to date, no genetic–epidemiological data are available on risk of atherothrombotic events among nondiabetic populations.

Methods— Using DNA samples collected at baseline in a prospective cohort of 14 916 initially healthy American men, we evaluated 3 AGER genetic variants: −429T>C, −374T>A, and Gly82Ser, among 600 white individuals who subsequently developed atherothrombotic event (incident myocardial infarction or ischemic stroke) and among 600 age- and smoking-matched white individuals who remained free of reported vascular disease during follow-up (controls).

Results— Genotype distributions for the polymorphisms tested were in Hardy–Weinberg equilibrium. Haplotype-based conditional logistic regression, adjusting for other potential confounders, showed that haplotype C-T-Gly (myocardial infarction: odds ratio [OR], 0.60; 95% CI, 0.41 to 0.90; P =0.01) and haplotype T-A-Gly (ischemic stroke: OR, 0.63; 95% CI, 0.40 to 0.99; P =0.05), compared with the reference haplotype T-T-Gly, were associated with reduced risk of atherothrombosis. Prespecified analysis limited to those without baseline history of diabetes showed similar significant findings.

Conclusions— We found an association of specific AGER promoter gene haplotypes with reduced risk of incident myocardial infarction and ischemic stroke that was independent of the presence of diabetes.

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.

Cardiac adrenoceptors: physiological and pathophysiological relevance

At present, nine adrenoceptor (AR) subtypes have been identified: alpha(1A)-, alpha(1B)-, alpha(1D)-, alpha(2A)-, alpha(2B)-, alpha(2C)-, beta(1)-, beta(2)-, and beta(3)AR. In the human heart, beta(1)- and beta(2)AR are the most powerful physiologic mechanism to acutely increase cardiac performance. Changes in betaAR play an important role in chronic heart failure (CHF). Thus, due to increased sympathetic activity in CHF, betaAR are chronically (over)stimulated, and that results in beta(1)AR desensitization and alterations of down-stream mechanisms. However, several questions remain open: What is the role of beta(2)AR in CHF? What is the role of increases in cardiac G(i)-protein in CHF? Do increases in G-protein-coupled receptor kinase (GRK)s play a role in CHF? Does betaAR-blocker treatment cause its beneficial effects in CHF, at least partly, by reducing GRK-activity? In this review these aspects of cardiac AR pharmacology in CHF are discussed. In addition, new insights into the functional importance of beta(1)- and beta(2)AR gene polymorphisms are discussed. At present it seems that for cardiovascular diseases, betaAR polymorphisms do not play a role as disease-causing genes; however, they might be risk factors, might modify disease, and/or might influence progression of disease. Furthermore, betaAR polymorphisms might influence drug responses. Thus, evidence has accumulated that a beta(1)AR polymorphism (the Arg389Gly beta(1)AR) may affect the response to betaAR-blocker treatment.

The Arg389Gly β1-adrenoceptor polymorphism does not affect cardiac effects of exercise after parasympathetic inhibition by atropine

In vitro, Arg389Gly beta1-adrenoceptor (AR) polymorphism exhibits decreased beta-AR signalling. In vivo, beta1-AR-mediated cardiac effects of exercise showed no genotype-dependent differences in Arg389 vs. Gly389 beta1-AR subjects. We studied in 16 male subjects homozygous Arg389 or Gly389 beta1-AR, whether blockade of parasympathetic activity might unmask genotype-dependence of exercise effects. Subjects were infused with atropine (10 microg/kg i.v. loading dose followed by continuous i.v. infusion of 0.15 microg/kg/min throughout exercise-time); 20 min after start of atropine bicycle-exercise in supine position (25, 50, 75 and 100 W for 5 min each) was performed and heart rate, contractility, blood pressure, plasma noradrenaline and plasma-renin activity were assessed. Exercise-evoked increases in all but one parameters were not different between Arg389 and Gly389 beta1-AR subjects; only plasma noradrenaline increased slightly more in Gly389 vs. Arg389 beta1-AR subjects.

IN CONCLUSION

It appears to be unlikely that lack of Arg389Gly beta1-AR genotype-dependence of exercise-effects can be explained by influences of parasympathetic activity.

Beta2-adrenoceptor gene polymorphisms

Beta2-adrenoceptors (AR) play an important role in regulation of vascular and bronchial smooth muscle tone; functional beta2-AR, however, also exist in human heart where they can mediate positive inotropic and chronotropic effects. Recent studies have discovered that beta2-AR are polymorphic. The most common single nucleotide polymorphisms (SNPs) are: Arg16Gly, Gln27Glu, Thr164Ile in the coding region, and Arg-19Cys in the 5' upstream peptide. These SNPs affect receptor function in vitro; however, conflicting data exist on their functional relevance in vivo. This might be due to the fact that the four SNPs in the 5' upstream peptide and in the coding region, respectively, are linked and form certain haplotypes. This review gives an overview on the contribution of beta2-AR polymorphisms to cardiovascular diseases or altered drug responses. In addition, the relevance of SNPs vs. haplotypes for beta2-AR functional responsiveness is discussed.

Improving pharmacotherapy outcomes by pharmacogenomics: from expectation to reality?

The genomic era is now a reality and the extraction of genomic information with a practical value in healthcare represents the next challenge following the completion of the Human Genome Project. To this end, the first pharmacogenomics test approved by the US Food & Drug Administration for assessing cytochrome P450 (CYP)2D6 and CYP2C19 genotype in the implementation of pharmacotherapy decisions in patients, is expected to improve pharmaceutical care outcomes, at least for drugs that are substrates or inhibitors of these enzymes. Furthermore, the progress already achieved and the experience gained in the fields of pharmacogenomics and personalized medicine has clearly demonstrated that an interdisciplinary approach could better serve the target of improving pharmacotherapy outcomes in routine clinical practice. Such an approach will obviously move drug prescription towards pharmacotyping, a stage where the drug selection and dosage process carried out by medical practitioners for any given patient will be advanced by genomic knowledge and information.

Sequencing drug response with HapMap

The information about how DNA sequence varies across the human genome is crucial for unravelling the genetic basis of drug response. A haplotype map, or HapMap, intended to reveal such a variation pattern, has been recently developed by the International HapMap Consortium. Here, we present a conceptual model for directly characterizing specific DNA sequence variants that are responsible for drug response based on the haplotype structure provided by HapMap. Our model is developed in the maximum likelihood context, incorporated by clinically meaningful mathematical functions that model drug response and implemented with the EM algorithm. Our model is employed to a pharmacogenetic study of cardiovascular disease with 107 patients. We found that the haplotype constituted by allele Gly16 (G) at codon 16 and allele Glu27 (G) at codon 27 genotyped within the beta2AR candidate gene exhibits a different effect on heart rate curve from the rest haplotypes. Parents with the diplotype consisting of two copies of haplotype GG are more sensitive in heart rate to increasing dosages of dobutamine than those with other haplotypes. This model provides a powerful tool for elucidating the genetic variants of drug response and ultimately designing personalized medications based on each patient's genetic constitution.

Haplotype analysis of the beta2 adrenergic receptor gene and risk of myocardial infarction in humans

Polymorphisms in the beta2 adrenergic receptor (ADRB2), in particular G16R, Q27E, and T164I, have been implicated in the pathogenesis of cardiovascular and metabolic phenotypes. However, no prospective, genetic-epidemiological data are available on the risk of cardiovascular disease associated with these variants. Using DNA samples collected at baseline in a prospective cohort of 14,916 initially healthy American men, we evaluated the G16R, Q27E, and T164I polymorphisms among 523 individuals who subsequently developed myocardial infarction and among 2092 individuals who remained free of reported cardiovascular events during follow-up. The haplotype frequency distribution was significantly different among cases and controls (chi(2)(7d.f.) = 20.92, P = 0.0039). Haplotype-based logistic regression, adjusting for age, smoking, and randomized treatment group, indicated that G16-Q27-I164 (odds ratio 0.178, 95% C.I. 0.043-0.737, P = 0.017) and (non-G16-Q27)-T164 (odds ratio 1.235, 95% C.I. 1.031-1.480, P = 0.022) haplotypes were significantly associated with altered risk of myocardial infarction. These findings remained after further adjustment for BMI, history of hypertension, and presence or absence of diabetes. In conclusion, variation in haplotype frequencies for the beta2 adrenergic receptor gene was found to be associated with risk of myocardial infarction.

β2-adrenoceptor polymorphisms: Relation between in vitro and in vivo phenotypes

Beta2-adrenoceptors are expressed in many cell types throughout the body and play a pivotal role in the regulation of the cardiac, pulmonary, vascular, endocrine and central nervous system. Recent studies have discovered that Beta2-adrenoceptor are polymorphic. Three common polymorphisms appear to influence receptor function: Arg16Gly, Gln27Glu, and Thr164Ile. In vitro studies of agonist-stimulation have shown that the Gly16 Beta2-adrenoceptors demonstrate enhanced agonist-promoted down-regulation, while Glu27 variants seem to be resistant. The Ile164 variant, on the other hand, demonstrates decreased responsiveness to agonist stimulation in vitro. However, the functional relevance and phenotypic consequence of such Beta2-adrenoceptor variants in vivo is still unclear. The aim of this review is therefore to provide an overview about the somewhat controversy in vitro, ex vivo and in vivo studies.

Recent advances in drug action and therapeutics: relevance of novel concepts in G-protein-coupled receptor and signal transduction pharmacology

PROBLEM STATEMENT

During especially the past two decades many discoveries in biological sciences, and in particular at the molecular and genetic level, have greatly impacted on our knowledge and understanding of drug action and have helped to develop new drugs and therapeutic strategies. Furthermore, many exciting new drugs acting via novel pharmacological mechanisms are expected to be in clinical use in the not too distant future.

SCOPE AND CONTENTS OF REVIEW

In this educational review, these concepts are explained and their relevance illustrated by examples of drugs used commonly in the clinical setting, with special reference to the pharmacology of G-protein-coupled receptors. The review also addresses the basic theoretical concepts of full and partial agonism, neutral antagonism, inverse agonism and protean and ligand-selective agonism, and the relevance of these concepts in current rational drug therapy. Moreover, the mechanisms whereby receptor signalling (and eventually response to drugs) is fine-tuned, such as receptor promiscuity, agonist-directed trafficking of receptor signalling, receptor trafficking, receptor 'cross-talk' and regulators of G-protein signalling (RGSs) are discussed, from theory to proposed therapeutic implications.

CONCLUSIONS

It is concluded that the understanding of molecular receptor and signal transduction pharmacology enables clinicians to improve their effective implementation of current and future pharmacotherapy, ultimately enhancing the quality of life of their patients.

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.

Beta-adrenergic receptor polymorphism in human cardiovascular disease

Beta-adrenoceptors are polymorphic. Two common polymorphisms in the beta1-adrenoceptor (Ser49Gly and Arg389Gly) and three in the beta2-adrenoceptor (Arg16Gly, Gln27Glu, and Thr164Ile) appear to influence receptor function. In vitro studies of agonist-stimulation have shown that the Gly49 beta1-adrenoceptor and the Gly16 beta2-adrenoceptors are more susceptible to down-regulation, while the Glu27 beta2-adrenoceptor variant seems to be resistant. Whereas the Arg389 beta1-adrenoceptor demonstrates increased responsiveness to agonist stimulation in vitro, the Ile164 beta2-adrenoceptor variant, on the other hand, exhibits a decreased responsiveness. Although several studies in humans (ex vivo and in vivo) do support those functional effects, the literature on the phenotypic consequences of these beta-adrenoceptor polymorphisms in vivo is still far from being conclusive. 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.

Pharmacogenetics of hypertension treatment

The extent of blood pressure lowering by anti-hypertensive agents is difficult to predict for individual patients, even when evaluated in the context of biochemical or demographic information. Genetic predictors (mainly single nucleotide polymorphisms, SNPs) have been the focus of several recent studies and are gaining much attention. We have conducted a literature search for studies in which the lowering of ambient blood pressure by specific drugs or drug classes in humans was related to specific genotypes. Twenty-eight studies were identified, of which six had a single-dose design, and the remaining 22 studied drug effects after more than 4 weeks of drug administration. Virtually all were association studies. Prospective trials that compared the prognostic value of genetic methods to routine clinical practice were not identified. Almost all studies used a candidate-gene design, usually with a very small number of SNPs (typically one). Gene-gene and gene-environment interactions were studied only rarely. Only one study targeted genes involved in drug metabolism. Most candidate-genes were part of the renin-angiotensin system. By far the most extensively studied has been the angiotensin-converting enzyme insertion/deletion polymorphism (15 studies) but, to date, no clear picture has emerged for this or other genetic variants. Thus, the potential for utility of genetic characterization of individual patients as a predictor of anti-hypertensive response has yet to be realized.

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.