G protein beta3 subunit polymorphism and risk of thrombosis and restenosis following coronary stent placement

GNB3 gene 825 TT variant predicts hard coronary events in the population-based Heinz Nixdorf Recall study

OBJECTIVE

The C825T polymorphism of the gene encoding the human G protein beta-3 subunit (GNB3) is associated with hypertension and obesity. Moreover, genotypes of the GNB3 polymorphism have been associated with development of coronary artery disease, and the 825T allele is thought to influence the process of atherosclerosis. However, the potential of the C825T polymorphism to predict coronary events has been poorly explored in a longitudinal setting at the population level.

METHODS

In 4159 Caucasian subjects from the Heinz Nixdorf Recall study cohort (age: 45-75 years, 48% male), genotypes of the GNB3 C825T polymorphism (rs5443) were determined and associated with fatal and non-fatal myocardial infarction (hard coronary events). Established cardiovascular risk factors were used to adjust for confounders.

RESULTS

The median follow-up time was 9.9 years (1st/3rd quartiles 9.5/10.2). 148 subjects (3.6%) experienced a hard coronary event. The 10-year event-free survival rate was CC, 96.1%; CT 96.9%, TT, 93.7% (p = 0.018). Multivariable analysis showed that the TT genotype is a significant risk factor for hard coronary events (hazard ratio (HR) = 1.9 (95% confidence interval (CI) 1.2-2.9); p = 0.008) after adjustment for age, sex, diabetes, systolic blood pressure, body mass index, high-density lipoprotein, and coronary artery calcification as determined by electron beam computed tomography at baseline. While prognosis in females was independent of GNB3 genotypes, analysis in males even elevated the HR for TT versus C-allele to 2.6 (95% CI 1.6-4.2; p < 0.001).

CONCLUSION

The GNB3 825 TT genotype is a significant and independent risk factor for hard coronary events independent of other established cardiovascular risk factors at a population level in males.

SNPs in genes encoding G proteins in pharmacogenetics

Heterotrimeric guanine-binding proteins (G proteins) transmit signals from the cell surface to intracellular signal cascades and are involved in various physiological and pathophysiological processes. Polymorphisms in the genes GNB3 (encoding the Gβ3 subunit), GNAS (encoding the Gαs subunit) and GNAQ (encoding the Gαq subunit) have been the primary focus of investigation. Polymorphisms in these genes could be associated with different complex phenotypes underlining that alterations in G-protein signaling can cause multiple disorders. G proteins present a point of convergence or ‘bottleneck’ between various receptors and effectors, thus making them a sensible tool for pharmacogenetic studies. The pharmacogenetic studies performed to date mostly demonstrate an association between G-protein polymorphisms and response to therapy or occurrence of adverse drug effects. Therefore, polymorphisms in genes encoding G-protein subunits may help to individualize drug treatment in various diseases with regard to both efficacy and safety.

G-protein beta3 subunit polymorphism and bleeding in the orbofiban in patients with unstable coronary syndromes-thrombolysis in myocardial infarction 16 trial

SUMMARY BACKGROUND

Variability in platelet response to antiplatelet drugs is heritable. A common single base substitution (825C>T) in the G-protein beta polypeptide 3 (GNB3) gene leads to alternative splicing (41-amino-acid deletion) of the human G-protein beta3 (Gbeta3) subunit. This truncated protein carried by GNB3 T allele carriers is linked to coronary artery disease and implicated as a genetic marker of drug response. Large studies of Caucasians associate T allele carriage with lower platelet reactivity.

OBJECTIVES

To evaluate whether the GNB3 genotype would predispose to bleeding in patients treated with a GPIIb/IIIa receptor antagonist.

METHODS

GNB3 genotype distribution was determined in DNA samples from patients in the orbofiban in patients with unstable coronary syndromes-thrombolysis in myocardial infarction (OPUS-TIMI) 16 genetic sub-study. Impact of genotype on the bleeding endpoint and the composite primary endpoint of death, myocardial infarction (MI), re-hospitalization for ischemia and urgent revascularization was estimated in the treatment and placebo arm.

RESULTS

Out of 887 patients, 45.1% carried the GNB3 CC genotype, 44.5% CT and 10.4% TT. Interaction between T allele carriership and treatment for bleeding was significant (P = 0.008). This reflects the fact that GNB3 non-T carriers treated with orbofiban had no bleeding effect compared with placebo (RR = 0.92, 95% CI 0.55-1.55) whereas T carriers did (RR = 2.62, 95% CI 1.58-4.35, P < 0.001). Interaction between T allele carriership and treatment was not significant for the primary endpoint (P = 0.18) or MI (P = 0.69).

CONCLUSION

The GNB3 T allele significantly increased bleeding in patients treated with the platelet antagonist orbofiban. Our findings suggest that risk of bleeding associated with an antiplatelet agent is heritable and may be dissociated from risk of thrombosis.

Association of antipsychotic induced weight gain and body mass index with GNB3 gene: a meta-analysis

It has been reported that C825T variant in the gene encoding the G-protein subunit beta3 (GNB3) is associated with antipsychotic-induced weight gain and obesity. We investigated the association of the GNB3 and antipsychotic-induced weight gain as well as body mass index (BMI) using meta-analytical techniques. Our analysis of 402 schizophrenia subjects showed a trend (p=0.072) only under a fixed-model. As it was observed heterogeneity among the studies (p=0.007), we re-analyzed using a random-effects framework and no significance was found (p=0.339). No evidence for bias publication was reported (p=0.868). Our analysis of 18,903 subjects showed a trend (p=0.053) associating CC and lower BMI under a fixed model. Although no significant association was found, the same pattern (CC and lower antipsychotic-induced weight gain) was observed. Our meta-analysis indicates that firmly establishing the role of pharmacogenetics in clinical psychiatry requires much larger sample sizes that have been reported.

Present status of outcome prediction of invasive coronary treatment by using genetic markers

A growing number of studies suggest that the outcome after invasive coronary treatment may be in part genetically determined. Here, we review the present status of outcome prediction of invasive coronary treatments by using genetic markers. Although some studies found an association between one or another genetic marker with one or another clinical endpoint, many other studies found no such relations; to date, none of the genetic markers that have been investigated in association studies are used in routine clinical practice to prospectively assess the prognosis following invasive coronary treatment or to decide upon therapeutic strategies. Many associations between genetic markers and certain clinical endpoints were initially reported in small studies but could not be confirmed in larger ones. Some of these discrepancies may be explained by publication bias. Some genetic variants may have true effects on clinical endpoints, which, albeit biologically interesting, do not bear much clinical relevance. On the other hand, many-if not most-studies that have been published to date are more or less grossly underpowered and very rarely report on the results of an a priori power analysis. Thus, there is still a need for further high-quality studies designed to investigate the specific contribution of genetic factors to the outcome after invasive coronary interventions.

G Protein Polymorphisms in Hypertension, Atherosclerosis, and Diabetes

A common C825T polymorphism in the gene GNB3, which encodes the beta 3 subunit of heterotrimeric G proteins, was identified in cell lines from patients with hypertension. The 825T allele is associated with increased intracellular signal transduction. Many population-based and case-control studies in different ethnicities have investigated an association between this polymorphism and hypertension, obesity, and atherosclerosis. A critical assessment of published studies suggests that 825T allele carriers have an increased risk for hypertension combined with features of the metabolic syndrome, such as dyslipidemia, hypercholesterolemia, insulin resistance, and obesity. It is anticipated that this polymorphism will be used in clinical practice to better characterize hypertension and for individualized treatment regimens.

Genetic predictive factors in restenosis

Restenosis is still the main drawback of percutaneous transluminal coronary angioplasty (PTCA). It is thought to be a multifactorial process where recoil of the vessel, neointimal proliferation and thrombus formation are thought to play a role. Until now it has proven difficult to predict restenosis on clinical and procedural grounds, however, genetic epidemiology might provide more insights. In this review several genetic variables, i.e. polymorphisms that were determined in relation to restenosis are described. The single nucleotide polymorphisms (SNPs) described in the literature so far involve; the renin-angiotensin system, platelet aggregation, the inflammatory response, matrix metalloproteinases, smooth muscle cell proliferation, lipids and oxidative stress and nitric oxide. Nowadays DNA-microarrays have been developed which make it possible to test 50 or 60 polymorphisms at once. However, the risk of error due to multiple testing should be kept in mind. The results of the studies described should be interpreted with care. Many of the published studies are of relatively small sample size, which sometimes show more positive outcomes than the larger studies, this is possibly due to publication bias towards more positive results. The small sample size studies also exhibit wide confidence intervals. On the other hand, one must take into account that the process of restenosis is a multifactorial one and it is likely that multiple genes are involved. Thus, relatively small odds ratios relating to single gene contribution to restenosis can be of paramount importance when encompassed in the overall picture. Although still much research has to be done, stratification according to genetic make-up may enable tailoring of the interventional treatment to the individual patient.

Cooperative effect of GNB3 825C>T and GPIIIa PI(A) polymorphisms in enhanced platelet aggregation

INTRODUCTION

Platelet aggregation contributes to various thrombembolic disorders. Environmental factors affect platelet aggregability but only partially explain the interindividual variability in aggregation. While the platelet glycoprotein IIb/IIIa is involved in the pathogenesis of acute coronary syndromes whereas most platelet activating stimuli act via G Protein coupled receptors we investigated whether the 825C>T polymorphism of the gene GNB3 encoding the G protein beta3 subunit together with the platelet glycoprotein (GP) IIIa Pl(A) polymorphism are predictive of platelet aggregability on stimulation with various agonists acting via GPCRs.

MATERIALS AND METHODS

Platelet aggregation was measured by turbidometry in 150 non-smoking individuals aged 18-40 years at a density of 2 x 10(5) platelets/microl with various agonists according to the method of Born. Genotypes of the GNB3 825C>T and glycoprotein IIb/IIIa PI(A) polymorphisms were determined using Pyrosequencing technology and restriction analysis. All functional studies were completed within 3 h. The data were analysed by Student's t-test for paired data.

RESULTS

Low concentrations of agonists resulted in enhanced platelet aggregation in subjects with the GNB3 CC-genotype compared to carriers of a 825T-allele. This effect was further enhanced in carriers of the GPIIIa Pl(A2) allele (2 microM ADP: 42% vs. 19%, p=0.017; 1 microM U-46619: 51% vs. 30%, p=0.03; 5 microM epinephrine: 69% vs. 53%, p=0.025). No significant pattern of aggregation was observed on stratification by GPIIIa genotypes alone.

CONCLUSIONS

Our findings indicate that two genetic markers contribute synergistically to increased platelet aggregation. This will help to identify patients at increased risk for thrombosis.

G protein beta 3 subunit 825T allele carriage and risk of coronary artery disease

C825T polymorphism in the G protein beta3 subunit gene (GNB3) is associated with increased transmembrane signal transduction via adenylyl cyclase inhibiting G (G(i)) proteins. We tested whether GNB3 C825T is associated with an increased risk of coronary artery disease (CAD). Genotypes were determined with polymerase chain reaction and allele-specific fluorogenic probes. Angiographically examined, consecutive patients (n=998) with CAD and angiographically examined, sex- and age-matched controls (n=340) with no evidence of CAD were studied. The proportion of T allele carriers was significantly higher in the group with CAD compared with the control group (55.6 vs. 48.5; P=0.02). T allele carriage was associated with a 33% increase in the unadjusted risk (OR 1.33 [95% confidence interval, 1.04-1.70]) and a 37% increase in the adjusted risk (OR from the multivariate model 1.37 [95% CI, 1.06-1.76]) for CAD. Moreover, an increase in T allele carriage was associated with an increase in disease severity (P=0.006; test for trend). The strongest association was observed between T allele carriage and three-vessel disease (unadjusted OR 1.47 [95% CI, 1.10-1.96]). Thus, carrying this allele is associated with the presence as well as the severity of CAD.

G-protein beta3 subunit 825T allele and hypertension

The G-protein beta3 subunit (GNB3) C825T polymorphism was detected through a classical candidate gene approach using cell lines with enhanced G-protein activation from patients with essential hypertension. The 825T allele is associated with the expression of a shortened, functionally active splice variant of the G-protein beta3 subunit and enhanced intracellular signal transduction. Independent studies have confirmed an association of the 825T allele with hypertension in whites. Potential pathogenetic mechanisms comprise an increased susceptibility for obesity in 825T allele carriers and, potentially, increased responsiveness to vasoactive hormones. Both phenomena appear to be strongly influenced by lifestyle in the sense of a gene-environment interaction. Whether hypertensive 825T allele carriers are at increased risk for stroke and left ventricular hypertrophy remains controversial. Current studies try to define optimal therapy strategies for hypertensive 825T allele carriers.

G-protein beta3 subunit C825T polymorphism: no association with risk for hypertension and obesity

OBJECTIVE

Several recent studies have indicated that a C825T polymorphism in the gene encoding the G-protein beta3 subunit is a significant risk factor for hypertension and obesity. In this study, we tested whether this polymorphism is associated with hypertension and obesity in white men.

DESIGN

Population-based prospective cohort study.

METHODS

We followed a cohort of 903 men, aged 42-61 years at baseline, for an average time of 4.2 years. Genotyping was performed by polymerase chain reaction.

RESULTS

The genotype distribution was in Hardy-Weinberg equilibrium: 514 (57%) had the CC genotype, 49 (5%) had the TT genotype and 340 (38%) were heterozygous (T:C = 0.24:0.76). There was no statistically significant difference between the genotype groups in respect to baseline and end of follow-up risk for hypertension or obesity, systolic or diastolic blood pressure, or body mass index.

CONCLUSION

We conclude that the C825T polymorphism of the G-protein beta3 subunit gene does not notably contribute to the development of hypertension or obesity, and is not a significant determinant for blood pressure and body mass index in white men.