Role of β1- and α2c-adrenergic receptor polymorphisms and their combination in heart failure: A case-control study

Evolution of the α2-adrenoreceptors in vertebrates: ADRA2D is absent in mammals and crocodiles

Evolutionary studies of genes that have been functionally characterized and whose variation has been associated with pathological conditions represent an opportunity to understand the genetic basis of pathologies. α₂-Adrenoreceptors (ADRA2) are a class of G protein-coupled receptors that regulate several physiological processes including blood pressure, platelet aggregation, insulin secretion, lipolysis, and neurotransmitter release. This gene family has been extensively studied from a molecular/physiological perspective, yet much less is known about its evolutionary history. Accordingly, the goal of this study was to investigate the evolutionary history of α₂-adrenoreceptors (ADRA2) in vertebrates. Our results show that in addition to the three well-recognized α₂-adrenoreceptor genes (ADRA2A, ADRA2B and ADRA2C), we recovered a clade that corresponds to the fourth member of the α₂-adrenoreceptor gene family (ADRA2D). We also recovered a clade that possesses two ADRA2 sequences found in two lamprey species. Furthermore, our results show that mammals and crocodiles are characterized by possessing three α₂-adrenoreceptor genes, whereas all other vertebrate groups possess the full repertoire of α₂-adrenoreceptor genes. Among vertebrates ADRA2D seems to be a dispensable gene, as it was lost two independent times during the evolutionary history of the group. Additionally, we found that most examined species possess the most common alleles described for humans; however, there are cases in which non-human mammals possess the alternative variant. Finally, transcript abundance profiles revealed that during the early evolutionary history of gnathostomes, the expression of ADRA2D in different taxonomic groups became specialized to different tissues, but in the ancestor of sarcopterygians this specialization would have been lost.

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.

Race, common genetic variation, and therapeutic response disparities in heart failure

Because of its comparatively recent evolution, Homo sapiens exhibit relatively little within-species genomic diversity. However, because of genome size, a proportionately small amount of variation creates ample opportunities for both rare mutations that may cause disease as well as more common genetic variations that may be important in disease modification or pharmacogenetics. Primarily because of the East African origin of modern humans, individuals of African ancestry (AA) exhibit greater degrees of genetic diversity than more recently established populations, such as those of European ancestry (EA) or Asian ancestry. Those population effects extend to differences in frequency of common gene variants that may be important in heart failure natural history or therapy. For cell-signaling mechanisms important in heart failure, we review and present new data for genetic variation between AA and EA populations. Data indicate that: 1) neurohormonal signaling mechanisms frequently (16 of the 19 investigated polymorphisms) exhibit racial differences in the allele frequencies of variants comprising key constituents; 2) some of these differences in allele frequency may differentially affect the natural history of heart failure in AA compared with EA individuals; and 3) in many cases, these differences likely play a role in observed racial differences in drug or device response.

Adrenergic receptor gene polymorphism and left ventricular reverse remodelling after cardiac resynchronization therapy: preliminary results

AIMS

Several factors can influence the extent of left ventricular (LV) reverse remodelling after cardiac resynchronization therapy (CRT) in patients with heart failure (HF). Polymorphism in genes involved in cardiac remodelling, namely beta-adrenergic receptors (ARs), may have a role. We studied the influence of beta-1 Arg389Gly, beta-2 Arg16Gly, and beta-2 Gln27Glu ARs gene polymorphisms on the magnitude of reverse remodelling response to CRT and its possible correlations with the incidence of appropriate implantable cardioverter-defibrillator (ICD) shocks.

METHODS AND RESULTS

Beta-ARs were assessed in 101 patients with HF due to idiopathic (50.5%) or ischaemic (49.5%) dilated cardiomyopathy, undergoing CRT for standard indications [left ventricular ejection fraction (LVEF) 23.5 ± 7.5%, QRS ≥ 120 ms]. Left ventricular ejection fraction was measured by echocardiography at baseline, 6 months after CRT, and periodically afterwards. The LVEF change from baseline was of 3.1 ± 11 units among Gln27Gln, 8.3 ± 10.4 units among Gln27Glu, 11 ± 6.4 units among Glu27Glu carriers (P = 0.018 for Gln27Gln vs. Glu27Glu carriers), and 8.8 ± 9.8 units among Gln27Glu + Glu27Glu carriers (P = 0.006 vs. Gln27Gln). Gln27 homozygotes had a higher incidence of appropriate ICD shocks for fast ventricular tachycardia/ventricular fibrillation.

CONCLUSION

Beta-2 Gln27Glu ARs gene polymorphism may influence LV reverse remodelling after CRT with Glu27Glu carriers showing the greatest improvement. It may also influence the incidence of malignant ventricular tachyarrhythmias.

Genetic prediction of heart failure incidence, prognosis and beta-blocker response

Heart failure (HF) is a widespread syndrome due to left ventricular dysfunction with high mortality, morbidity and health-care costs. Beta-blockers, together with diuretics and ACE-inhibitors or angiotensin receptor blockers, are a cornerstone of HF therapy, as they reduce mortality and morbidity. Nevertheless, their efficacy varies among patients, and genetics is likely to be one of the modifying factors. In this article, literature on the role of candidate genes on the development of HF, its prognosis and pharmacogenomics of β-blockers in patients with HF is reviewed. The available findings do not support, at the present time, a role for genetic tests in the treatment of HF. More large-scale genome-wide studies with adequate methodology and statistical analysis are required before considering genetic tailoring of HF therapy in patients with systolic HF.

The α(2C)-Del322-325 adrenoceptor polymorphism and the occurrence of left ventricular hypertrophy in hypertensives

OBJECTIVES

Sympathetic activation has a role in the development of left ventricular hypertrophy (LVH). The presynaptic α(2C)-adrenoceptor inhibits the release of norepinephrine from sympathetic nerve terminals in the heart. A deletion polymorphism in the α(2C)-adrenoceptor (α(2C)Del322-325) generates a hypofunctional α(2C)-adrenoceptor, which may result in chronic adrenergic signalling. This study aimed to investigate whether the α(2C)Del322-325 polymorphism was associated with an increased prevalence of LVH in patients with systemic hypertension.

METHODS

Left ventricular mass was measured in 205 patients with systemic hypertension and 60 normal volunteers using a 1.5-T Philips MRI system. Genotyping was performed using a restriction fragment length polymorphism assay.

RESULTS

No significant difference was observed between the distribution of the α(2C)Del322-325 genotypes in hypertensive patients with LVH compared with those without LVH. Adjusting for confounding variables the odds ratio (OR) of being ins/del for the α(2C)Del322-325 and having LVH was 0.49 (95% CI 0.14-1.69, p = 0.256).

CONCLUSIONS

These observations suggest that there is little evidence for an association between α(2C)Del322-325 polymorphism and an increased prevalence of LVH in patients with systemic hypertension.

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.

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.

RAAS and adrenergic genes in heart failure: Function, predisposition and survival implications

It is well appreciated that several neurohormones and signaling cascades are activated that promote long-term deterioration of cardiac function and structure. Activation of the renin-angiotensin-aldosterone system (RAAS) and the adrenergic system is closely related to heart failure. Common gene variants that encode neurohormonal, adrenergic and intracellular proteins have been demonstrated to modulate the course and consequences of heart failure. However, the literature is replete with conflicting results and it remains uncertain as to whether particular gene variants predispose heart failure. Therefore, the main purpose of this review was to discuss the effects of single nucleotide polymorphisms (SNPs) that are located in genes encoding elements of the RAAS and the adrenergic system on the predisposition to and survival from heart failure. Most studies indicate that common SNPs encoding elements of the RAAS and the adrenergic system do not predispose individuals to heart failure. Conversely, it has been demonstrated that ARB1 Arg389Gly, GRK5 Gln41Leu, ACE I/D, CYP11B2 C-344T and AGTR1 A+1166C modulate pharmacological responses and have a considerable impact on cardiac-related survival. It should not be expected, however, that a single polymorphism determines survival, given that multiple gene products and environmental factors contribute to the pathogenesis of heart failure. Therefore, future studies should consider the interaction effects of multiple genes in populations that are as homogeneous as possible with respect to environmental characteristics.

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.

Effect of the alpha2C-adrenoreceptor deletion322-325 variant on sympathetic activity and cardiovascular measures in healthy subjects

BACKGROUND

The alpha2C-adrenergic receptor plays an important role in the regulation of the sympathetic nervous system and, therefore, blood pressure and heart rate. A deletion polymorphism in its gene (ADRA2C del322-325), ten times more common in black than white Americans, has been associated with a loss of function in vitro and, under controlled study conditions, raised blood pressure and catecholamine secretion. We therefore examined the hypothesis that the ADRA2C deletion variant would alter sympathetic activity and contribute to ethnic differences in blood pressure.

METHODS

We measured resting plasma norepinephrine and epinephrine concentrations, blood pressure and heart rate in 224 healthy subjects (127 whites), and determined their ADRA2C del322-325 genotype. Additionally, we analyzed heart rate variability (HRV) in a subgroup of 50 black subjects.

RESULTS

Systolic (SBP) and diastolic blood pressure (DBP) were higher in blacks than whites [difference (95% confidence interval), 4.4 (1.5-7.4) mmHg, P = 0.003; and 2.7 (0.7-4.6) mmHg, P = 0.01, respectively]. Norepinephrine concentrations did not differ among subjects with 0, 1 and 2 copies of the deletion variant [median (interquartile range), 185.0 (147.5-269.8), 200.0 (154.9-257.0) and 173.8 (158.5-235.8) pg/ml, respectively; P = 0.54]. Similarly, none of the HRV parameters differed among the genotype groups. In multiple linear regression analyses adjusting for multiple covariates, the deletion genotype was not associated with SBP or DBP. In contrast, black ethnicity was associated with higher SBP (P = 0.001) and DBP (P = 0.005).

CONCLUSION

The ADRA2C deletion polymorphism had no effect on markers of resting sympathetic activity and cardiovascular measures, and did not account for ethnic differences in blood pressure.

Presynaptic α-2C Adrenoceptor-mediated Control of Noradrenaline Release in Humans: Genotype- or Age-Dependent?

In vitro alpha-2CDel322-325 adrenoceptor (AR) polymorphism exhibits reduced functional responsiveness. We studied whether this is true also in vivo in humans. We assessed in nine young wild-type (WT) alpha-2C AR subjects (aged 23 years), 10 elder WT alpha-2C AR subjects (aged 63 years), and nine alpha-2CDel AR subjects (aged 28 years) clonidine (1 microg/kg intravenous (i.v.) bolus)-evoked plasma noradrenaline (pNA), heart rate (HR), and blood pressure (BP) changes. Clonidine-evoked pNA decreases were comparable in young WT alpha-2C and in alpha-2CDel AR subjects, but significantly lower (P=0.033) in elder subjects. Similarly, clonidine-evoked HR decreases were significantly larger in young WT alpha-2C and in alpha-2CDel AR subjects than in elder subjects, whereas clonidine-evoked BP decreases were larger in elder subjects. In conclusion, alpha-2CDel AR appears to play only a minor role in presynaptic regulation of NA release and/or to be not hypofunctional in vivo in humans, but functional responsiveness of presynaptic alpha-2 AR declines with ageing.