β-blocker therapy and heart rate control during exercise testing in the general population: role of a common G-protein β-3 subunit variant

Severe systemic adverse reactions to ophthalmic timolol in a CYP2D6 homozygous *4 allele carrier: a case report

A woman with ocular hypertension suffered from severe bradycardia, hypotension and syncope attacks in temporal relation with ophthalmic timolol application. Topically applied timolol is nasally absorbed and has been shown to reach potentially relevant systemic concentrations. Timolol is mainly metabolized by CYP2D6, which exhibits interindividual metabolic capacity due to genetic variations. A reactive pharmacogenetic panel test identified the patient as a CYP2D6 homozygous *4 allele carrier, which has been associated with a poor metabolizer phenotype and lacking enzyme activity. Thus, the adverse drug reactions possibly resulted from increased systemic timolol exposure. This case report highlights that pharmacogenetic panel testing can contribute to safe and effective pharmacotherapy, even for topically applied drugs.

Subtype-dependent regulation of Gβγ signalling

G protein-coupled receptors (GPCRs) transmit information to the cell interior by transducing external signals to heterotrimeric G protein subunits, Gα and Gβγ subunits, localized on the inner leaflet of the plasma membrane. Though the initial focus was mainly on Gα-mediated events, Gβγ subunits were later identified as major contributors to GPCR-G protein signalling. A broad functional array of Gβγ signalling has recently been attributed to Gβ and Gγ subtype diversity, comprising 5 Gβ and 12 Gγ subtypes, respectively. In addition to displaying selectivity towards each other to form the Gβγ dimer, numerous studies have identified preferences of distinct Gβγ combinations for specific GPCRs, Gα subtypes and effector molecules. Importantly, Gβ and Gγ subtype-dependent regulation of downstream effectors, representing a diverse range of signalling pathways and physiological functions have been found. Here, we review the literature on the repercussions of Gβ and Gγ subtype diversity on direct and indirect regulation of GPCR/G protein signalling events and their physiological outcomes. Our discussion additionally provides perspective in understanding the intricacies underlying molecular regulation of subtype-specific roles of Gβγ signalling and associated diseases.

β2 -Adrenergic Receptor Gene Affects the Heart Rate Response of β-Blockers: Evidence From 3 Clinical Studies

β-Blockers' heart rate (HR)-lowering effect is an important determinant of the effectiveness for this class of drugs, yet it is variable among β-blocker-treated patients. To date, genetic studies have revealed several genetic signals associated with HR response to β-blockers. However, these genetic signals have not been consistently replicated across multiple independent cohorts. Here we sought to use data from 3 hypertension clinical trials to validate single-nucleotide polymorphisms (SNPs) previously associated with the HR response to β-blockers. Using linear regression analysis, we investigated the effects of 6 SNPs in 3 genes, including ADRB1, ADRB2, and GNB3, relative to the HR response following β-blocker used in the PEAR (n = 757), PEAR-2 (n = 368), and INVEST (n = 1401) trials, adjusting for baseline HR, age, sex, and ancestry. Atenolol was used in PEAR and INVEST, and metoprolol was used in PEAR-2. We found that rs1042714 and rs1042713 in ADRB2 were significantly associated with HR response to both β-blockers in whites (rs1042714 C-allele carriers, meta-analysis β = -0.95 beats per minute [bpm], meta-analysis P = 3×10^-4 ; rs1042713 A-allele carriers, meta-analysis β = -1.15 bpm, meta-analysis P = 2×10^-3 ). In conclusion, the results of our analyses provide strong evidence to support the hypothesis that rs1042714 and rs1042713 in the ADRB2 gene are important predictors of HR response to cardioselective β-blockade in hypertensive patient cohorts.

Adrenergic Polymorphisms and Survival in African Americans With Heart Failure: Results From A-HeFT

BACKGROUND

Polymorphisms in adrenergic signaling affect the molecular function of adrenergic receptors and related proteins. The β1 adrenergic receptor (ADRB1) Arg389Gly, G-protein receptor kinase type 5 (GRK5) Gln41Leu, G-protein β-3 subunit (GNB3) 825 C/T, and α2c deletion affect adrenergic tone, impact heart failure outcomes and differ in prevalence by ethnicity. Their combined effect within black cohorts remains unknown.

METHODS AND RESULTS

We analyzed subjects from the African American Heart Failure Trial (A-HeFT) by assessing event-free survival, quality of life, and gene coinheritance. Significant coinheritance effects on survival included GRK5 Leu41 among subjects co-inheriting GNB3 825 C alleles (n = 166, 90.4% vs 69.0%, P < 0.001). By contrast, the impact of ADRB1 Arg389Arg genotype was magnified among subjects with GNB3 825 TT genotype (n = 181, 66.3% vs 85.7%, P = .002). The lack of the α2c deletion (ie, insertion) led to a greater impact of the ARG389Arg genotype (n = 289, 76.4% vs 86.1%, P = .007).

CONCLUSIONS

Polymorphisms in adrenergic signaling affects outcomes in black subjects with heart failure. Coinheritance patterns in genetic variation may help determine heart failure survival.

Correction of the Pathogenic Alternative Splicing, Caused by the Common GNB3 c.825C>T Allele, Using a Novel, Antisense Morpholino

The very common GNB3 c.825C>T polymorphism (rs5443) is present in approximately half of all human chromosomes. Significantly, the presence of the GNB3 825T allele has been strongly associated with predisposition to essential hypertension. Paradoxically the presence of the GNB3 825T allele, in exon 10, introduces a pathogenic alternative RNA splice site into the middle of exon 9. To attempt to correct this pathogenic aberrant splicing, we, therefore, bioinformatically designed, using a Gene Tools(®) algorithm, a GNB3-specific, antisense morpholino. It was hoped that this morpholino would behave in vitro as either a potential splice blocker and/or exon skipper, to both bind and inhibit/reduce the aberrant splicing of the GNB3 825T allele. On transfecting a human lymphoblast cell line homozygous for the 825T allele, with this antisense morpholino, we encouragingly observed both a significant reduction (from ∼58% to ∼5%) in the production of the aberrant smaller GNB3 transcript, and a subsequent increase in the normal GNB3 transcript (from ∼42% to ∼95%). Our results demonstrate the potential use of a GNB3-specific antisense morpholino, as a pharmacogenetic therapy for essential hypertension.

A Physiologic Approach to the Pharmacogenomics of Hypertension

Hypertension is a multifactorial condition with diverse physiological systems contributing to its pathogenesis. Individuals exhibit significant variation in their response to antihypertensive agents. Traditional markers, such as age, gender, diet, plasma renin level, and ethnicity, aid in drug selection. However, this review explores the contribution of genetics to facilitate antihypertensive agent selection and predict treatment efficacy. The findings, reproducibility, and limitations of published studies are examined, with emphasis placed on candidate genetic variants affecting drug metabolism, the renin-angiotensin system, adrenergic signalling, and renal sodium reabsorption. Single-nucleotide polymorphisms identified and replicated in unbiased genome-wide association studies of hypertension treatment are reviewed to illustrate the evolving understanding of the disease's complex and polygenic pathophysiology. Implementation efforts at academic centers seek to overcome barriers to the broad adoption of pharmacogenomics in the treatment of hypertension. The level of evidence required to support the implementation of pharmacogenomics in clinical practice is considered.

Influence of 825 C>T polymorphism of G protein β3 subunit gene (GNB3) on hemodynamic response during dobutamine stress echocardiography

There is a wide interpersonal difference to dobutamine response during dobutamine stress echocardiography (DSE). The aim of this study was to determine an association between GNB3 825C>T gene polymorphism, encoding the β3-subunit of G protein, and heart rate (HR), systolic (SBP) and diastolic blood pressure (DBP) response to dobutamine during DSE. The study involved 119 patients with clinical indications for DSE. Genotyping of GNB3 825C>T (rs5443) polymorphism was based on PCR-RFLP method with BseDI restriction enzyme. Significantly higher levels of both resting SBP and DBP in 825T allele carriers vs. 825CC patients were revealed. HR of 825CC vs. CT + TT subjects was slower along the test period reaching marked difference at dobutamine level 30 μg/kg/min (109 ± 20 vs. 116 ± 18 bpm, respectively, p = 0.047). SBP and DBP were markedly lower in 825CC homozygotes compared to 825T allele carriers throughout DSE. It can be concluded that GNB3 825C>T polymorphism is associated with resting SBP and DBP in Polish Caucasian patients subjected for diagnostic DSE. The polymorphism also modulate HR, SBP and DBP response during DSE.