Beta2-adrenergic receptor polymorphisms and sudden cardiac death: a signal to follow

Beta-Adrenergic Receptor Polymorphism and Patho-Genetics of Trauma: A Transformational Frontier of Personalized Medicine in Neurotrauma

Trauma is a serious public health issue, and remains a major cause of mortality and disability worldwide. The notion that genetic factors contribute to an individual's response to traumatic injury has advanced significantly. Genetic variations in severely injured patients have been linked to mortality, morbidity, and psychological outcomes. We conducted a comprehensive review of beta-adrenergic receptor polymorphisms and their impact on the pathogenetics of traumatic injuries, which could pave the way for a transformational frontier of personalized medicine in neurotrauma. It remains unclear why some individuals are vulnerable to worse outcomes, whereas others are resilient. Although genetic factors may be significant, the intricate interplay between environmental and genetic factors may be responsible for variations in the presentation and outcome after injury. Recent advancements in genetic analysis and molecular physiology have helped to shed light on the causes of such variability. Although exposure to trauma can initiate a cascade of stress-related responses, these responses alone are insufficient to explain etiopathogenesis. Therefore, gaining insights into how trauma and genetic predispositions to adrenergic variations interact at the molecular level to affect an individual's susceptibility and recuperation could provide an essential understanding of the molecular pathogenesis of traumatic injuries. Therefore, it is imperative to identify potential genetic and physiological markers to guide early management and prognosis of trauma. Such knowledge could pave the way for the discovery of novel biomarkers that can identify a transdiagnostic subgroup that is at high risk and requires early intervention. This could lead to the adoption of personalized medical approaches in neurotrauma care.

[Molecular and genetic background of sudden cardiac death]

Despite recent findings on the functional, structural and genetic background of sudden cardiac death, the incidence is still relatively high in the entire population. A thorough knowledge on susceptibility, as well as pathophysiology behind the development of malignant arrhythmias will help us to identify individuals at risk and prevent sudden cardiac death. This article presents a review of the current literature on the role of altered intracellular Ca2+ handling, acute myocardial ischaemia, cardiac autonomic innervation, renin-angiotensin-aldosterone system, monogenic and complex heritability in the pathogenesis of sudden cardiac death.

A common β1-adrenergic receptor polymorphism predicts favorable response to rate-control therapy in atrial fibrillation

OBJECTIVES

In this study, we evaluated the impact of 2 common β1-adrenergic receptor (β1-AR) polymorphisms (G389R and S49G) in response to ventricular rate control therapy in patients with atrial fibrillation (AF).

BACKGROUND

Randomized studies have shown that ventricular rate control is an acceptable treatment strategy in patients with AF. However, identification of patients who will adequately respond to rate-control therapy remains a challenge.

METHODS

We studied 543 subjects (63% men; age 61.8 ± 14 years) prospectively enrolled in the Vanderbilt AF registry and managed with rate-control strategy. A "responder" displayed adequate ventricular rate control based on the AFFIRM (Atrial Fibrillation Follow-Up Investigation of Rhythm Management) criteria: average heart rate (HR) at rest ≤80 beats/min; and maximum HR during a 6-min walk test ≤110 beats/min or average HR during 24-h Holter ≤100 beats/min.

RESULTS

A total of 295 (54.3%) patients met the AFFIRM criteria. Baseline clinical characteristics were similar in responders and nonresponders except for mean resting HR (76 ± 20 beats/min vs. 70 ± 15 beats/min; p < 0.01) and smoking (6% vs. 1%; p < 0.01). Multiple clinical variables (age, gender, hypertension) failed to predict response to rate-control therapy. By contrast, carriers of Gly variant at 389 were more likely to respond favorably to rate-control therapy; 60% versus 51% in the Arg389Arg genotype, p = 0.04. This association persisted after correction for multiple clinical factors (odds ratio: 1.42, 95% confidence interval: 1.00 to 2.03, p < 0.05). Among responders, subjects carrying the Gly389 variant required the lowest doses of rate-control medications; atenolol: 92 mg versus 68 mg; carvedilol: 44 mg versus 20 mg; metoprolol: 80 mg versus 72 mg; diltiazem: 212 mg versus 180 mg, and verapamil: 276 mg versus 200 mg, respectively (p < 0.01 for all comparisons).

CONCLUSIONS

We have identified a common β1-AR polymorphism, G389R, that is associated with adequate response to rate-control therapy in AF patients. Gly389 is a loss-of-function variant; consequently, for the same adrenergic stimulation, it produces reduced levels of adenyl cyclase, and hence, attenuates the β-adrenergic cascade. Mechanistically, the effect of rate-control drugs will be synergistic with that of the Gly389 variant, which could possibly explain our findings. These findings represent a step forward in the development of a long-term strategy of selecting treatment options in AF based on genotype.

Single-nucleotide polymorphisms in the β-adrenergic receptor genes are associated with lung allograft utilization

BACKGROUND

Pulmonary edema and associated impaired oxygenation are a major reason for rejection of donor lung allografts offered for transplantation. Clearance of pulmonary edema can be upregulated by stimulation of β-adrenergic receptors (βARs). Single-nucleotide polymorphisms (SNPs) in βAR genes have functional effects in vitro and in vivo. We hypothesized that SNPs in βAR genes would be associated with rates of utilization of donor lung allografts offered for transplantation.

METHODS

Nine hundred fifty-one organ donors were genotyped for 4 amino-acid-coding SNPs in the βAR genes. Lung allograft utilization was compared among donors stratified by genotypes.

RESULTS

Utilization of donor lung allografts was 55% vs 35% (p = 0.02) among donors with GG vs AA/AG genotypes of the Ser49Gly SNP, 39% vs 32% (p = 0.04) with GG vs AA/AG genotype of Gly16Arg SNP and 37% vs 32% (p = 0.1) with CC vs GC/GG genotype of the Arg389Gly SNP. In the combined analysis, donors carrying 0 or 1 associated genotype had a utilization rate of 33%, whereas donors carrying 2 or 3 associated genotypes had utilization rates of 44% and 58%, respectively (p = 0.008). There was a stepwise decrease in chest radiograph infiltrates and an increase in partial pressure of oxygen/fraction of inspired oxygen (PaO(2)/FIO(2)) with an increasing number of these associated genotypes.

CONCLUSION

Genetic variants in the βAR genes among organ donors are associated with higher rates of lung allograft utilization. The increased utilization may be related to increased clearance of pulmonary edema and improved oxygenation in donors with favorable genotypes and suggests that βAR agonists may have a role in donor management.

Rescue of familial cardiomyopathies by modifications at the level of sarcomere and Ca2+ fluxes

Cardiomyopathies are a heterogeneous group of diseases of the myocardium associated with mechanical and/or electrical dysfunction that frequently show inappropriate ventricular hypertrophy or dilation. Current data suggest that numerous mutations in several genes can cause cardiomyopathies, and the severity of their phenotypes is also influenced by modifier genes. Two major types of inherited cardiomyopathies include familial hypertrophic cardiomyopathy (FHC) and dilated cardiomyopathy (DCM). FHC typically involves increased myofilament Ca(2+) sensitivity associated with diastolic dysfunction, whereas DCM often results in decreased myofilament Ca(2+) sensitivity and systolic dysfunction. Besides alterations in myofilament Ca(2+) sensitivity, alterations in the levels of Ca(2+)-handling proteins have also been described in both diseases. Recent work in animal models has attempted to rescue FHC and DCM via modifications at the myofilament level, altering Ca(2+) homeostasis by targeting Ca(2+)-handling proteins, such as the sarcoplasmic reticulum ATPase and phospholamban, or by interfering with the products of different modifiers genes. Although attempts to rescue cardiomyopathies in animal models have shown great promise, further studies are needed to validate these strategies in order to provide more effective and specific treatments.

The beta2 adrenergic receptor Gln27Glu polymorphism affects insulin resistance in patients with heart failure: possible modulation by choice of beta blocker

Insulin resistance is prevalent in heart failure (HF) patients, and beta2 adrenergic receptors (beta2-AR) are involved in glucose homeostasis. We hypothesized that beta2-AR Gln27Glu and Arg16Gly polymorphisms affect insulin resistance in HF patients, and we explored if effects of beta2-AR polymorphisms on glucose handling are modified by choice of beta blocker. We studied 30 nondiabetic adults with HF and a history of systolic dysfunction; 15 were receiving metoprolol succinate, and 15 were receiving carvedilol. We measured fasting glucose, insulin, and insulin resistance, and we determined beta2-AR genotypes at codons 27 and 16. The cohort was insulin resistant with a mean HOMA-IR score of 3.4 (95% CI, 2.3 to 4.5; normal value, 1.0). Patients with the Glu27Glu genotype exhibited higher insulin and HOMA-IR compared to individuals carrying a Gln allele (P = 0.019). Patients taking carvedilol demonstrated lower insulin resistance if also carrying a wild-type allele at codon 27 (fasting insulin, 9.8 +/- 10.5 versus 20.5 +/- 2.1 for variant, P = 0.072; HOMA-IR, 2.4 +/- 2.7 versus 5.1 +/- 0.6, P = 0.074); those on metoprolol succinate had high insulin resistance irrespective of genotype. The beta2-AR Glu27Glu genotype may be associated with higher insulin concentrations and insulin resistance in patients with HF. Future studies are needed to confirm whether treatment with carvedilol may be associated with decreased insulin and insulin resistance in beta2-AR codon 27 Gln carriers.

beta-adrenergic receptor gene polymorphisms and beta-blocker treatment outcomes in hypertension

Numerous studies have demonstrated that beta(1)- and beta(2)-adrenergic receptor gene (ADRB1 and ADRB2) variants influence cardiovascular risk and beta-blocker responses in hypertension and heart failure. We evaluated the relationship between ADRB1 and ADRB2 haplotypes, cardiovascular risk (death, nonfatal myocardial infarction (MI), and nonfatal stroke), and atenolol-based vs. verapamil sustained-release (SR)-based antihypertensive therapy in 5,895 coronary artery disease (CAD) patients. After an average of 2.8 years, death rates were higher in patients carrying the ADRB1 Ser49-Arg389 haplotype (hazard ratio (HR) 3.66, 95% confidence interval (95% CI) 1.68-7.99). This mortality risk was significant in patients randomly assigned to verapamil SR (HR 8.58, 95% CI 2.06-35.8) but not atenolol (HR 2.31, 95% CI 0.82-6.55), suggesting a protective role for the beta-blocker. ADRB2 haplotype associations were divergent within the treatment groups but did not remain significant after adjustment for multiple comparisons. ADRB1 haplotype variation is associated with mortality risk, and beta-blockers may be preferred in subgroups of patients defined by ADRB1 or ADRB2 polymorphisms.

Sudden cardiac death: influence of diabetes

This article reviews current thinking on the problem of sudden cardiac death (SCD) within community settings, highlighting progress in understanding risks and mechanisms. Information available on the influence of diabetes as a risk factor for SCD and the question of whether this disease enhances susceptibility to ventricular arrhythmias is summarized as are central strategies in risk stratification and mortality prevention.

Genomics, heart failure and sudden cardiac death

Sudden cardiac death (SCD) is among the most common causes of death in developed countries throughout the world. Despite decreased overall cardiac mortality, SCD rates appear to be increasing in concert with escalating global prevalence of coronary disease and heart failure, the two major conditions predisposing to SCD. This unfavorable trend is a consequence of our inability to identify those who will die suddenly from lethal ventricular arrhythmias and to develop effective therapies for all populations at risk. The known risk factors for SCD lack the predictive power needed to generate preventive strategies for the large number of fatal arrhythmic events that occur among lower-risk subsets of the population. Even among recognized high-risk subsets, prediction of SCD remains challenging. With the exception of the implantable cardioverter defibrillator (ICD) there are few effective strategies for the prevention and treatment of SCD. This article discusses the prospect of genomic science as an approach to the identification of patients at high-risk for SCD. While the final common pathway for SCD is malignant ventricular arrhythmias, there are many potential contributors, pathways, and mechanisms by which common genetic variants (polymorphisms) could affect initiation and propagation of life-threatening cardiac arrhythmias. Recent advances in genomic medicine now provide us with novel approaches to both identify candidate genes/pathways and relatively common polymorphisms which may predispose patients to increased risk for SCD. Improved understanding of the relationship between common polymorphisms and SCD will not only improve risk stratification such that ICDs can be targeted to those patients most likely to benefit from them but also provide new insight into the pathophysiology of SCD.