Meta-analysis of the association of platelet glycoprotein IIIa PlA1/A2 polymorphism with myocardial infarction

Genetic polymorphisms in early-onset myocardial infarction in a sample of Iraqi patients: a pilot study

OBJECTIVES

Early-onset myocardial infarction constitutes nearly one third of cases of myocardial infarction among Iraqis, which is rather higher than the proportions reported in many Western countries. Thus this study was initiated to investigate the role of some genetic polymorphisms, as well as acquired risk factors in this condition.

RESULTS

A total of 102 Iraqi patients with first myocardial infarction aged 50 years, and 77 matched controls were enrolled. The DNAs of participants were screened for nine polymorphisms, namely: β-Fibrinogen (- 455G > A), Factor XIII (V34L), Plasminogen Activator inhibitor-1 (PAI-1, 4G/5G), Human Platelet Antigen-1 (HPA1a/b), 5,10-Methylenetetrahydrofolate Reductase MTHFR (C677T) and MTHFR (A1298C), Angiotensin-Converting Enzyme (ACE) 287 bp insertion/deletion (I/D), Apolipoprotein-B (ApoB: R3500Q), and Apolipoprotein-E (Apo E: E2/E3/E4), using PCR and reverse hybridization technique. Among traditional risk factors, univariate analysis revealed that smoking (OR 2.86 [95%CI 1.53-5.34]), hyperlipidemia (OR 5.23 [95%CI 2.66-10.29]), and diabetes mellitus (OR 4.05 [95% CI 1.57-10.41]) were significantly higher among patients compared to controls (P<0.001, <0.001 and 0.002 respectively), while none of the nine genetic polymorphisms reached significance. Multivariate Logistic regression, however, revealed that only smoking and hyperlipidemia retained significance (P of < 0.001 each). The need to initiate further studies on larger cohorts is paramount to understand the higher than expected frequency of early-onset myocardial infarction in our population.

Common rs5918 (PlA1/A2) polymorphism in the ITGB3 gene and risk of coronary artery disease

INTRODUCTION

The T to C transition at nucleotide 1565 of the human glycoprotein IIIa (ITGB3) gene represents a genetic polymorphism (PlA1/A2) that can influence both platelet activation and aggregation and that has been associated with many types of disease. Here, we present a newly designed multiplex tetra-primer amplification refractory mutation system - polymerase chain reaction (T-ARMS-PCR) for genotyping a single nucleotide polymorphism (SNP) (dbSNP ID: rs5918) in the human ITGB3 gene.

MATERIAL AND METHODS

We set up T-ARMS-PCR for the rs5918 SNP in a single-step PCR and the results were validated by the PCR-RFLP method in 132 coronary artery disease (CAD) patients and 122 unrelated healthy individuals.

RESULTS

Full accordance was found for genotype determination by the PCR-RFLP method. The multiple logistic regression analysis showed a significant association of the rs5918 polymorphism and CAD according to dominant and recessive models (dominant model OR: 2.40, 95% CI: 1.33-4.35; p = 0.003, recessive model OR: 4.71, 95% CI: 1.32-16.80; p = 0.0067).

CONCLUSIONS

Our T-ARMS-PCR in comparison with RFLP and allele-specific PCR is more advantageous because this PCR method allows the evaluation of both the wild type and the mutant allele in the same tube. Our results suggest that the rs5918 (PlA1/A2) polymorphism in the ITGB3 gene may contribute to the susceptibility of sporadic Iranian coronary artery disease (CAD) patients.

Susceptible gene polymorphisms for blood stasis syndrome of coronary heart disease

Coronary heart disease (CHD) is a typically polygenic and multi-factorial disease. Recent advances have proposed the hypothesis that multiple polymorphisms in the presence of environmental factors could act synergistically in the pathogenesis of CHD. Lots of gene polymorphisms related with CHD have been discovered by genome-wide linkage (in families) and association (in populations) studies. A key issue now is to move from mapping gene polymorphisms to pinpointing causal genes and variants, and to develop a molecular understanding of how these genes lead to CHD. New thinking needs to be brought in for resolving this problem. The benefifit of Chinese medicine (CM) in CHD has been proven by more and more clinical evidences. More importantly, linking CM syndrome differentiation and biomedical diagnosis might help further accurate stratifification of CHD patients for intervention selection. The epidemiological investigation has demonstrated that blood stasis syndrome (BSS) is the major CM syndrome type of CHD. BSS is a kind of pathological state caused by disturbance of blood circulation. Clinical studies indicate that the severity of BSS is related with the severity of CHD and BSS of CHD may be "one involved in multiple genes" with hereditary tendency. If BSS of CHD is polygenic and hereditary, gene polymorphisms may be one of the pathogens. There are some pilot researches to explore the association between gene polymorphisms and BSS of CHD. In this review, the current status of gene polymorphisms related with BSS of CHD and future perspectives are discussed.

The PlA1/A2 polymorphism of glycoprotein IIIa in relation to efficacy of antiplatelet drugs: a systematic review and meta-analysis

AIM

The PlA1/A2 polymorphism of glycoprotein IIIa (GPIIIa) has been associated with both antiplatelet drug resistance and increased cardiovascular events. The aim of this study was to conduct the first meta-analysis investigating the association between carriage of the PlA2 allele and resistance to currently licensed antiplatelet drugs.

METHODS

Electronic databases (MEDLINE and EMBASE) were searched for all articles evaluating genetic polymorphisms of GPIIIa. For studies where antiplatelet resistance was measured using validated techniques, pooled odds ratios (ORs) were calculated using fixed effects and random effects models.

RESULTS

Sixteen studies were eligible for statistical analysis and included 1650 PlA1 homozygous subjects and 668 carriers of the PlA2 allele. For carriers of the PlA2 allele, OR 0.924 (n = 2318; 95% CI 0.743, 1.151; P = 0.481) was observed for resistance to any antiplatelet drug, OR 0.862 (n = 2085; 95% CI 0.685, 1.086; P = 0.208) for resistance to aspirin and OR 1.429 (n = 233; 95% CI 0.791, 2.582; P = 0.237) for resistance to clopidogrel. In the aspirin cohort, sub-group analysis revealed no statistical association in either healthy subjects or those with cardiovascular disease. PlA2 carriage was marginally associated with aspirin sensitivity using the fixed effects model when identified by the PFA-100 assay (n = 1151; OR 0.743, 95% CI 0.558, 0.989; P = 0.041) but with significant heterogeneity (I(2) = 55%; P = 0.002). Significance was lost with analysis using a random effects model.

CONCLUSIONS

The totality of published data does not support an association between carriage of the PlA2 allele and antiplatelet drug resistance. Significant heterogeneity indicates the need for larger studies using validated and standardized assays.

PLA1A2 platelet polymorphism predicts mortality in prediabetic subjects of the population based KORA S4-Cohort

OBJECTIVE

The genetic polymorphism concerning the ß3-subunit of platelet integrin receptor glycoprotein IIIa is held responsible for enhanced binding of adhesive proteins resulting in increased thrombogenic potential. Whether it is associated with mortality, HbA1c or platelet volume is tested prospectively in an epidemiological cohort.

RESEARCH DESIGN AND METHODS

Population-based Cooperative Health Research in the Region of Augsburg (KORA) S4-Survey (N = 4,028) was investigated for prognostic value of PLA1A2-polymorphism regarding all-cause mortality, correlation with HbA1c, and mean platelet volume. Multivariate analysis was performed to investigate association between genotype and key variables.

RESULTS

Prevalence of thrombogenic allele variant PLA2 was 15.0%. Multivariate analysis revealed no association between PLA1A2 polymorphism and mortality in the KORA-cohort. HbA1c was a prognostic marker of mortality in non-diabetic persons resulting in J-shaped risk curve with dip at HbA1c = 5.5% (37 mmol/mol), confirming previous findings regarding aged KORA-S4 participants (55-75 years). PLA1A2 was significantly associated with elevated HbA1c levels in diabetic patients (N = 209) and reduced mean platelet volume in general population. In non-diabetic participants (N = 3,819), carriers of PLA2 allele variant presenting with HbA1c > 5.5% (37 mmol/mol) showed higher relative risk of mortality with increasing HbA1c.

CONCLUSION

PLA1A2 polymorphism is associated with mortality in participants with HbA1c ranging from 5.5% (37 mmol/mol) to 6.5% (48 mmol/mol). Maintenance of euglycemic control and antiplatelet therapy are therefore regarded as effective primary prevention in this group.

Platelet glycoprotein IIIA PIA1/A2 polymorphism in young patients with ST elevation myocardial infarction and idiopathic ischemic stroke

It has been identified that platelet glycoprotein IIIa PIA1/A2 polymorphism plays an important role in atherothrombotic disease such as myocardial infarction and stroke, but results remain controversial. Here, we investigated whether the PIA2 allele is associated with ST myocardial infarction or idiopathic ischemic stroke in young individuals in two independent studies. In a case-control study 275 patients with ST elevation myocardial infarction ≤45 years of age and 278 controls were recruited. In a second study, 200 patients with idiopathic ischemic stroke ≤45 years of age and 200 controls were enrolled. In both studies cases and controls were matched by age and gender. The PIA1/A2 polymorphism was determined in all participants by a polymerase chain reaction-restriction fragment length polymorphism assay. There was a significant difference in the PIA1/A2 genotype distribution (P = 0.001) and allele frequency (P = 0.001), between ST elevation myocardial infarction and control groups, but not in the PIA1/A2 genotype distribution (P = 0.61) and allele frequency (P = 0.80), between idiopathic ischemic stroke. The allele PIA2 represented an independent risk for ST elevation myocardial infarction but not for idiopathic ischemic stroke. Hypertension, smoking, and family history of atherothrombotic disease were also associated with ST elevation myocardial infarction and idiopathic ischemic stroke. Our results suggest that PA2 allele represents a risk factor for ST elevation myocardial infarction in young Mexican individuals but not for idiopathic ischemic stroke.

Integrin αIIbβ3: from discovery to efficacious therapeutic target

From the initial description of platelets in 1882, their propensity to aggregate and to contribute to thrombosis was apparent. Indeed, excessive platelet aggregation is associated with myocardial infarction and other thrombotic diseases whereas Glanzmann thrombasthenia, in which platelet aggregation is reduced, is a bleeding syndrome. Over the last half of the 20th century, many investigators have provided insights into the cellular and molecular basis for platelet aggregation. The major membrane protein on platelets, integrin αIIbβ3, mediates this response by rapidly transiting from its resting to an activated state in which it serves as a receptor for ligands that can bridge platelets together. Monoclonal antibodies, natural products, and small peptides were all shown to inhibit αIIbβ3 dependent platelet aggregation, and these inhibitors became the forerunners of antagonists that proceeded through preclinical testing and into large patient trials to treat acute coronary syndromes, particularly in the context of percutaneous coronary interventions. Three such αIIbβ3 antagonists, abciximab, eptifibatide, and tirofiban, received Food and Drug Administration approval. Over the past 15 years, millions of patients have been treated with these αIIbβ3 antagonists and many lives have been saved by their administration. With the side effect of increased bleeding and the development of new antithrombotic drugs, the use of αIIbβ3 antagonists is waning. Nevertheless, they are still widely used for the prevention of periprocedural thrombosis during percutaneous coronary interventions. This review focuses on the biology of αIIbβ3, the development of its antagonists, and some of the triumphs and shortcomings of αIIbβ3 antagonism.

Idiopathic sudden sensorineural hearing loss: classic cardiovascular and new genetic risk factors

BACKGROUND

The main causative process in idiopathic sudden sensorineural hearing loss (iSSNHL) has yet to be explained or demonstrated. The clinical picture supports vascular involvement, but obvious limitations of inner ear study make this difficult to corroborate.

OBJECTIVES

To determine the role of thrombophilic genetic variants that may affect platelet function and to assess the cardiovascular risk profile in a cohort of patients with iSSNHL.

PATIENTS AND METHODS

118 Caucasian patients with iSSNHL were recruited from the same geographical area and enrolled prospectively in this study. Clinical data were obtained for each patient. Polymorphisms of the platelet glycoprotein subunit IIIa gene, ITGB3 (PLA1/A2, rs5918), and of the platelet glycoprotein subunit Ia gene, ITGA2 (C807T, rs1126643) were analyzed. A control group of 161 age- and gender-matched healthy individuals from the same geographical area was recruited for genetic comparisons. In order to determine the cardiovascular risk profile of each patient and of our cohort, a cross-sectional assessment was performed by means of a calibrated Framingham coronary heart disease risk scale. Risk factor proportions were compared to those recommended in European guidelines for coronary prevention, which are also based on the Framingham function.

RESULTS

A significantly high prevalence of the 807T allele of platelet glycoprotein subunit Ia was found in patients compared to controls. There was a significant correlation between the 807TT homozygous genotype and a low probability of recovery. The PLA1/A2 polymorphism of platelet glycoprotein subunit IIIa was not associated with recovery, with a similar genotype prevalence being found in patients and controls. In terms of cardiovascular risk profile, patients did not present an excess of baseline coronary risk factors compared to the general population in the same geographical area.

CONCLUSIONS

Patients with iSSNHL had a higher prevalence of the 807T thrombophilic polymorphism of platelet glycoprotein Ia/IIa. Patients homozygous for this polymorphism are less likely to recover from iSSNHL. Classical cardiovascular risk factors were not related to iSSNHL.

Platelet glycoprotein IIIA PIA2 polymorphism is associated with ST elevation acute myocardial infarction in young Mexican population

Platelet membrane glycoprotein IIb/IIIa plays an important role in adhesion and platelet aggregation. Polymorphisms of genes in platelet activation and fibrinolysis have been associated with myocardial infarction (MI), however this has not been confirmed by others, and results are still controversial. The aim of this study was to determine the frequency distribution and association of polymorphism in the platelet glycoprotein GPIIIa PLA/A2 and the possible interaction with the 4G/5G in the plasminogen activator inhibitor genes with ST elevation acute myocardial infarction (STEAMI) in young Mexican subjects. A total of 254 unrelated patients with first STEAMI ≤45 years of age, who were admitted to a cardiovascular intense care unit and 254 healthy controls matched by age and gender were recruited from January 2006 and May 2011. The PIA1/A2 and 4G/5G polymorphism were determined in all participants by a PCR restriction based restriction endonuclease digestion. There was a difference in the PIA2 allele distribution between both groups (P = 0.001). Also, we found an increased percent of 4G allele in the group of patients compared to control group (P = 0.001). There was an increased risk for STEAMI in carries with the allele PIA2 and 4G (OR = 4.3, CI 95 % 1.7-6.5). The modifiable risk factors such: smoking, hypertension, family history of cardiovascular disease, and dyslipidemia were associated with myocardial infarction. This is the first study to evaluate the role of gene polymorphism in both the thrombotic and fibrinolytic pathways in young Mexican individuals with STEAMI and suggest a synergistic effect between PIA2 and 4G allele.

Association of the platelet GPIIb/IIIa polymorphism with atherosclerotic plaque morphology: the Atherosclerosis Risk in Communities (ARIC) Study

OBJECTIVES

Platelet activation and aggregation play an important role in the pathogenesis of cardiovascular disease. We examined the association of a single nucleotide polymorphism (SNP) in the GPIIIa platelet glycoprotein (Leu33Pro) with carotid artery plaque morphology and with expression of platelet markers using data from the Atherosclerosis Risk in Communities (ARIC) Carotid MRI study.

METHODS

The study sample consisted of 1202 Caucasian members of the ARIC study cohort recruited in 2004-2005 to participate in the Carotid MRI Substudy under stratified sampling based on maximum carotid artery wall thickness. The Leu33Pro polymorphism was identified as SNP rs5918 in the ITGB3 gene. Plaque visualization was accomplished with contrast enhanced MRI examination of the thickest segment of the carotid artery. Expression of platelet markers was measured using fasting whole blood flow cytometry.

RESULTS

This cross-sectional analysis based on age and gender adjusted weighted linear regression models suggests that those homozygous for the Leu33Pro risk allele (C) have decreased mean and minimum fibrous cap thickness. We did not observe differences in plaque lipid volume or maximum carotid artery wall thickness across SNP rs5918 genotypes. Carriers of the Leu33Pro polymorphism, as compared to major allele homozygotes, had greater percent of platelets expressing P-selectin, a platelet glycoprotein indicating activation status. Prevalent coronary heart disease did not affect estimates of fibrous cap thickness or of platelet activation.

CONCLUSION

Our results suggest that individuals with Leu33Pro polymorphism of the GPIIIa glycoprotein may be predisposed to increased risk of atherosclerotic plaque rupture.

Genetic regulation of platelet receptor expression and function: application in clinical practice and drug development

Understanding genetic contributions to platelet function could have profound clinical ramifications for personalizing platelet-directed pharmacotherapy, by providing insight into the risks and possible benefits associated with specific genotypes. This article represents an integrated summary of presentations related to genetic regulation of platelet receptor expression and function given at the Fifth Annual Platelet Colloquium in January 2010. It is supplemented with additional highlights from the literature covering (1) approaches to determining and evidence for the associations of genetic variants with platelet hypo- and hyperresponsive phenotypes, (2) the ramifications of these polymorphisms with regard to clinical responses to antiplatelet therapies, and (3) the role of platelet function/genetic testing in guiding antiplatelet therapy.

The GPIIIA PlA2 polymorphism is associated with an increased risk of cardiovascular adverse events

BACKGROUND

The clinical impact of PlA2 polymorphism has been investigated in several diseases, but the definition of its specific role on thrombotic cardiovascular complications has been challenging. We aimed to explore the effect of PlA2 polymorphism on outcome in patients with atherosclerosis.

METHODS

We studied 400 consecutive patients with coronary artery disease (CAD) undergoing percutaneous coronary intervention. A replication study was conducted in 74 hypertensive patients with cerebrovascular events while a group of 100 healthy subjects was included as control population. PlA genotype was determined by PCR-RFLP on genomic DNA from peripheral blood cells. Major adverse cardiac events (MACE), were considered as end points, and recorded at a mean follow up of 24 ± 4.3 months.

RESULTS

The frequencies of PlA2 polymorphism was similar between groups and genotype distribution was in Hardy-Weinberg equilibrium. In patients with CAD, the presence of PlA2 allele was associated with higher incidence of cardiac death (13.1% vs. 1.5%, p = 0.0001), myocardial infarction (10.7% vs. 2.6%, p = 0.004) and needs of new revascularization (34.8% vs. 17.7%, p = 0.010). Accordingly, the Kaplan-Meier analysis for event free survival in patients harboring the PlA2 allele showed worse long-term outcome for these patients (p = 0.015). Cox regression analysis identified the presence of PlA2 as an independent predictor of cardiac death (OR: 9.594, 95% CI: 2.6 to 35.3, p = 0.002) and overall MACE (OR: 1.829, 95% CI: 1.054 to 3.176, p = 0.032). In the replication study, the PlA2 polymorphism increased the risk of stroke (OR: 4.1, 95% CI: 1.63-12.4, p = 0.02) over TIA and was identified as an independent risk factor for stroke (B:-1.39; Wald: 7.15; p = 0.001).

CONCLUSIONS

Our study demonstrates that in patients with severe atherosclerosis the presence of PlA2 allele is associated with thrombotic cardiovascular complications.

The glycoprotein IIIa gene polymorphism and the risk of myocardial infarction

The hemostatic platelet response of an individual may be influenced by the genetic profile of the platelet membrane glycoprotein (GP) receptors. The GP IIIa, as a part of von Willebrand factor and fibrinogen receptor, plays a central role in platelet aggregation. Polymorphism in GP IIIa has been extensively studied for its association with myocardial infarction or coronary artery diseases. To date, the role of GP IIIa polymorphism in genetic susceptibility to thrombotic disease still remains controversial. The results of case-control association studies vary, even with the same ethnic background, and the association was hardly found in studies with larger sample size, suggesting publication-bias toward positive findings. In meta-analysis, the GP IIIa Pl(A2) allele carriers did not show increased risk for myocardial infarction compared with Pl(A1/A1) homozygotes. The functional studies also showed conflicting results. In conclusion, GP IIIa Pl(A1/A2) polymorphism does not seem to have a major role either in determining the individual variance of platelet function or the risk of myocardial infarction according to the currently available data. Therefore, the genotype determination of GP IIIa Pl(A1/A2 )polymorphism may not be useful for risk assessment of myocardial infarction at this time. Nevertheless, the author can not completely exclude its possible role in coronary thrombosis after angioplasty or sudden cardiac death. Thus, further evaluation in larger prospective or multicenter studies is required to elucidate the role of GPs in cardiovascular system.

Celiac artery thrombosis in a young patient with multiple platelet receptor polymorphisms and local compression syndrome

Numerous clinical and experimental studies have been published concerning platelet receptor polymorphism and their role in causing myocardial infarction at an earlier age. It is still unclear, however, whether these polymorphisms are a risk factor for other occlusive diseases such as those in visceral arteries. We report a case of a young woman with acute celiac artery thrombosis and multiple platelet receptor polymorphisms. In addition, the intraoperative exploration showed some evidence of a local vascular compression syndrome. The patient was successfully treated with a bypass procedure and combined anticoagulation. It seems that platelet receptor polymorphisms are a moderate risk factor for local artery thrombosis regardless of vascular region. The obligatory precondition is pre-existing vascular damage, such as that caused by a local compression syndrome.

Inherited Thrombophilia

Inherited thrombophilia can be defined as a genetically determined predisposition to the development of thromboembolic complications. Since the discovery of activated protein C resistance in 1993, several additional disorders have been described and, at present, it is possible to identify an inherited predisposition in about 60 to 70% of patients with such complications. These inherited prothrombotic risk factors include qualitative or quantitative defects of coagulation factor inhibitors, increased levels or function of coagulation factors, defects of the fibrinolytic system, altered platelet function, and hyperhomocysteinemia. In this review, the main inherited prothrombotic risk factors are analyzed from epidemiological, laboratory, clinical, and therapeutic points of view. Finally, we discuss the synergism between genetic and acquired prothrombotic risk factors in particular conditions such as childhood and pregnancy.

Double heterozygosity polymorphisms for platelet glycoproteins Ia/IIa and IIb/IIIa increases arterial thrombosis and arteriosclerosis in patients with the antiphospholipid syndrome or with systemic lupus erythematosus

OBJECTIVE

We analysed the genetic polymorphisms in platelet glycoproteins (GP) Ib-alpha, Ia/IIa and IIb/IIIa and their correlation with the development of arterial thrombosis and preclinical arteriosclerosis in patients with antiphospholipid syndrome (APS) or with systemic lupus erythematosus (SLE).

METHODS

We included 131 patients with APS (86 with primary APS and 45 with APS associated with SLE), 102 patients with SLE and 160 healthy controls. GP Ib-alpha VNTR polymorphism, GP Ia/IIa 807 C/T polymorphism and GP IIb/IIIa PlA1/2 polymorphism were determined by polymerase chain reaction. Thrombotic events were assessed clinically and confirmed by objective methods. The presence of preclinical arteriosclerosis was evaluated by a carotid ultrasound study in a subgroup of 70 patients with SLE measuring the intima-media wall thickness and the presence of arteriosclerotic plaque.

RESULTS

A total of 50 episodes of arterial thrombosis in 36 patients with APS have been registered. We found a significant correlation between the 807 T/T genotype of GP Ia/IIa and arterial thrombosis (22% vs 7%, p = 0.04; OR 3.59, 95% CI 1.20 to 10.79). The VNTR Ib-alpha and P1A1/2 IIb/IIIa polymorphisms were not associated with arterial thrombosis in patients with APS when individually analysed. The coexistence of both 807 T and PlA2 alleles increased the arterial thrombosis risk (28% vs 7%, p = 0.005; OR 4.84, 95% CI 1.67 to 13.96). In patients with SLE, no relationship was found between the presence of carotid arteriosclerotic plaque and separate polymorphisms of platelet GP. The coexistence of alleles 807 T of GP Ia/IIa and PlA2 of GP IIb/IIIa was associated with the presence of carotid plaque (35% vs 4%, p = 0.002; OR 12.92, 95% CI 2.39 to 69.81).

CONCLUSIONS

The T/T genotype of 807 C/T polymorphism of GP Ia/IIa may be an additional risk for the development of arterial thrombosis in APS. The coexistence of both 807 T and PlA2 alleles increased the arterial thrombosis risk in patients with APS and preclinical arteriosclerosis in patients with SLE.

Association of polymorphisms in platelet and hemostasis system genes with acute myocardial infarction

BACKGROUND

Genetic polymorphisms may affect the balance between coagulation and fibrinolysis and thereby affect individual vulnerability to acute myocardial infarction (MI) among patients with underlying coronary atherosclerosis.

METHODS

We enrolled 1375 patients with an initial clinical presentation of coronary disease. We genotyped 49 single nucleotide polymorphisms (SNPs) in 9 coagulation system genes and compared patients who had an initial acute MI with patients who presented with stable exertional angina.

RESULTS

An SNP in CD36 (rs3211956) was significantly (P = .04) more common among patients who presented with acute MI (minor allele frequency 10.5%) than patients with stable exertional angina (minor allele frequency 8.0%). This association became marginally significant, however, after adjustment for conventional cardiac risk factors in an additive genetic model (odds ratio 1.34, CI 1.00-1.88, P = .053). An SNP in ITGB3 (Leu59Pro, rs5918) was slightly, but not significantly (P = .083), more common among patients with acute MI (minor allele frequency 14.5%) than among patients with stable exertional angina (minor allele frequency 12.0%). Two linked SNPs in THBD (Ala473Val, rs1042579; and rs3176123) were slightly, but not significantly (P = .079 and 0.052, respectively), less common among patients with acute MI (minor allele frequency 16.1%) than among patients with stable exertional angina (18.7% and 19.0%, respectively).

CONCLUSIONS

Four SNPs in platelet glycoprotein and hemostatic genes were nominally associated with acute MI rather than stable exertional angina as the initial clinical presentation of coronary artery disease. These findings are suggestive but require independent confirmation in larger studies.

Effect of PlA1/A2 glycoprotein IIIa gene polymorphism on the long-term outcome after successful coronary stenting

Aim

To prospectively determine the role of platelet glycoprotein IIIa (GP IIIa) gene PlA1/PlA2 polymorphism on the long-term clinical outcome in patients with coronary artery disease undergoing coronary stenting.

Design and setting

Prospective observational study in the University Hospital of Caen (France).

Patients and methods

1 111 symptomatic consecutive Caucasian patients treated with percutaneous coronary intervention including stent implantation underwent genotyping for GP IIIa PlA1/A2.

Main outcome measures

Long-term clinical outcome in terms of the rate of major adverse cardiac events (MACE, ie death from any cause, non-fatal Q wave or non Q wave myocardial infarction, and need for coronary revascularisation) was obtained and subsequently stratified according to the GP IIIa PlA1/A2 polymorphism.

Results

Three groups of patients were determined according to the GP IIIa PlA1/A2 polymorphism (71.6% had the A1/A1, 25.8% had the A1/A2 and 2.6% had the A2/A2 genotype). These three groups were comparable for all clinical characteristics including sex ratio, mean age, vascular risk factors, previous coronary events, baseline angiographic exam, indication for the percutaneous coronary intervention and drug therapy). The incidence of MACE was similar in these 3 groups of patients during a mean follow-up period of 654+/-152 days. Independent risk factors for MACE were a left ventricular ejection fraction < 40%, absence of treatment with a beta-blocker and absence of treatment with an angiotensin converting enzyme inhibitor during follow-up.

Conclusion

The GP IIIa PlA1/A2 polymorphism does not influence the clinical long-term outcome in patients with symptomatic coronary disease undergoing percutaneous coronary intervention with stent implantation.

Role of beta3 integrin in acute renal allograft rejection in humans

BACKGROUND AND OBJECTIVES

Beta3 Integrin may play a role in the process of acute rejection by increasing leukocyte adhesion to the endothelium, cytotoxic T lymphocyte activation, and platelet aggregation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

For investigation of the role of beta3 integrin in the pathogenesis of acute rejection, this study examined the surface expression of beta3 integrin on leukocyte subsets and analyzed a common single-nucleotide polymorphism in exon 2 of the gene encoding the beta3 subunit that generates two beta3 integrin isoforms, termed Pl(A1) and Pl(A2). Pl(A) genotype was determined in blood samples from 445 renal allograft recipients at two centers. Patients were then grouped by Pl(A) genotype, and clinical outcomes as recorded in a preexisting database were analyzed.

RESULTS

Although almost all monocytes express beta3 integrin, its expression was also found on all leukocyte subsets, including T, B, and NK cells. The percentage of patients who experienced acute rejection was noted to be significantly higher in those with Pl(A1)/Pl(A1) (TT) genotype versus patients with the Pl(A1)/Pl(A2) or Pl(A2)/Pl(A2) (CT or CC) genotypes (33% for TT versus 20% for CT or CC). In a multivariate analysis, the Pl(A1)/Pl(A1) (TT) genotype remained significantly associated with acute rejection. Patients with Pl(A1)/Pl(A1) (TT) genotype also exhibited a higher number of acute rejection episodes per patient.

CONCLUSIONS

The Pl(A1)/Pl(A1) (TT) genotype is associated with an increased incidence of acute renal allograft rejection in humans, supporting a role for beta3 integrin in the pathophysiology of acute rejection.

Antithrombotic properties of aspirin and resistance to aspirin: beyond strictly antiplatelet actions

Aspirin is effective in the prevention of cardiovascular events in high-risk patients. The primary established effect of aspirin on hemostasis is to impair platelet aggregation via inhibition of platelet thromboxane A(2) synthesis, thus reducing thrombus formation on the surface of the damaged arterial wall. Growing evidence also indicates that aspirin exerts additional antithrombotic effects, which appear to some extent unrelated to platelet thromboxane A(2) production. Aspirin can reduce thrombin generation with the subsequent attenuation of thrombin-mediated coagulant reactions such as factor XIII activation. Aspirin also acetylates lysine residues in fibrinogen resulting in increased fibrin clot permeability and enhanced clot lysis as well as directly promoting fibrinolysis with high-dose aspirin. The variable effectiveness of aspirin in terms of clinical outcomes and laboratory findings, which has been termed aspirin resistance, may be related to these additional antithrombotic effects that are altered when associated with common genetic polymorphisms such as the Leu33Pro beta(3)-integrin or Val34Leu factor XIII mutations. However, the clinical relevance of these observations is still unclear. Elucidation of the actual impacts of aspirin other than antiaggregation effects could be important in view of the widespread use of this drug in the prevention of thrombotic manifestations of atherosclerosis.

Advancing the study of stroke in women: summary and recommendations for future research from an NINDS-Sponsored Multidisciplinary Working Group

BACKGROUND AND PURPOSE

Women have poorer outcomes from stroke than men. Women also have risk factors that are unique, including pregnancy and hormone therapy. Hormone therapy for postmenopausal replacement increased the risk of ischemic stroke according to results of the Women's Health Initiative clinical trials. Based on the current understanding of the mechanisms of action of estrogen, the reasons for this increased risk are uncertain. One method to better understand the reasons for this increased risk is to re-evaluate estrogen's role in the neurovascular unit, simplistically comprised of the neurons, glia, and endothelial cells, as well as the processes of inflammation, and hemostasis/thrombosis. Besides the role of estrogen there are many gaps of knowledge about issues specific to women and stroke.

SUMMARY OF REVIEW

A multidisciplinary workshop was held in August 2005 to summarize the current evidence for estrogen and, more generally, stroke in women, and to provide recommendations for future basic, preclinical, and clinical research studies.

CONCLUSIONS

These studies may ultimately change the approach to stroke prevention and treatment in women.

Platelet glycoprotein IIb/IIIa polymorphism and coronary artery disease: implications for clinical practice

Membrane glycoprotein (GP) IIb/IIIa plays a major role in platelet function; indeed it enables stimulated platelets to bind fibrinogen and related adhesive proteins, a process that is considered key in the development of thrombosis. The gene encoding GPIIIa (ITGB3, also known as GP3A) shows a common platelet antigen polymorphism [PL(A1)/PL(A2); expressed by alleles ITGB3*001 and ITGB3*002] that was variably associated with vascular disease. In 1996, the presence of the PL(A2) allele (ITGB3*001) was first reported to increase the risk of coronary heart disease. Shortly after, the interest in this study was increased by the publication of a case report on the death from myocardial infarction of an Olympic athlete who was found to be homozygous for the PL(A2) allele. Overviews of the published studies on the PL(A1)/PL(A2) polymorphism and coronary risk suggest an influence of the PL(A2) allele on the clinical phenotype and the interaction with other environmental factors. In particular, the strongest effect of the ITGB3 PL(A2) allele was expressed on the risk of occlusion after revascularization procedures, mainly after stent implantation, a condition in which platelet activation is more important as compared with other stenotic mechanisms. In the future, the identification of patients who are particularly responsive to GPIIb/IIIa antagonist therapy (e.g. those with the PL(A2) allele) might help to improve the treatment efficacy in this relatively small population. In a mechanism possibly unrelated to its effect on platelet reactivity to aggregating stimuli, the presence of the PL(A2) allele might influence the antiaggregatory effect of platelet inhibitory drugs such as aspirin (acetylsalicylic acid), clopidogrel, and GPIIb/IIIa antagonists. Although interesting, current data does not yet have direct clinical implications for patient risk identification and drug therapy tailoring. Larger studies are necessary to define the role of the PL(A2) allele in more homogeneous groups where platelet GPIIb/IIIa activation might be particularly relevant.

The impact of genetic variation in the region of the GPIIIa gene, on Pl expression bias and GPIIb/IIIa receptor density in platelets

Some studies have suggested that genetic variability in the glycoprotein (GP) IIIa gene modulates expression of platelet GPIIb/IIIa (alpha(2b)beta(3)). We sought to determine as to whether combinations of genetic variants within the GPIIIa gene (haplotypes) influenced the expression of GPIIIa RNA and protein levels in human platelets. Three promoter polymorphisms, Pl(A1/A2) genotype and platelet receptor densities were determined in 207 acute coronary syndrome (ACS) patients. Allele-specific quantitative reverse transcription-polymerase chain reaction of platelet RNA from Pl(A1/A2) heterozygotes identified a greater expression of Pl(A2) bearing transcripts among heterozygotes. Among the patients studied, the ratio of Pl(A1)/Pl(A2) RNA expression was significantly influenced by promoter haplotype (P < 0.01). However, this effect reflected carriership of rare not common haplotypes (P = 0.2). There was a threefold variation between subjects in the number of GPIIb/IIIa receptors expressed per platelet, although no association between receptor density and the Pl(A2) (P = 0.93) or promoter polymorphisms was demonstrated (-468A, P = 0.52; -425C, P = 0.59; -400A, P = 0.52). Among common haplotypes, Pl(A1)/Pl(A2) RNA expression was negatively correlated with adjusted GPIIb/IIIa receptor density (P = 0.04). The overall trend towards higher expression of Pl(A2) bearing message in Pl(A1/A2) heterozygotes, and the existence of rare haplotypes with more pronounced changes indicate the existence of cis-acting genetic factors that remain to be identified.

Seven haemostatic gene polymorphisms in coronary disease: meta-analysis of 66,155 cases and 91,307 controls

BACKGROUND

Variants of certain haemostatic genes (such as that encoding factor V Leiden) are involved in the development of venous thrombosis, but studies of such variants in coronary disease have reported apparently conflicting results. We did meta-analyses on seven such haemostatic genetic variants for which the available evidence on each comprises at least 5000 coronary disease cases and at least 5000 controls.

METHODS

Meta-analyses were done of 191 studies in relation to factor V G1691A (ie, factor V Leiden), factor VII G10976A, prothrombin G20210A, plasminogen activator inhibitor-1 (PAI-1) [-675] 4G/5G, and three platelet glycoprotein (GP) receptor variants (GPIa C807T, GPIbalpha T[-5]C, GPIIIa C1565T), involving a total of 66 155 coronary disease cases and 91 307 controls. We explored potential sources of heterogeneity.

FINDINGS

In a combined analysis of all studies, the per-allele relative risks (RR) for coronary disease of factor V 1691A and of prothrombin 20210A were 1.17 (95% CI 1.08-1.28) and 1.31 (1.12-1.52), respectively. Combined analyses of studies of the PAI-1 [-675] 4G variant yielded a per-allele relative risk for coronary disease of 1.06 (1.02-1.10), but there was an indication of publication bias in these studies. Combined analyses of the factor VII 10976A, GPIa 807T, GPIbalpha [-5]C, and GPIIIa 1565T variants showed no significant overall associations with coronary disease, yielding per-allele RRs of 0.97 (0.91-1.04), 1.02 (0.97-1.08), 1.05 (0.96-1.13), and 1.03 (0.98-1.07), respectively.

INTERPRETATION

The 1691A variant of the factor V gene and the 20210A variant of the prothrombin gene, both of which increase circulating thrombin generation, might each be moderately associated with the risk of coronary disease. Further studies are merited to assess these associations in greater detail (including any gene-gene and gene-environment interactions) and to determine any implications with regard to potential therapies designed to reverse patients' prothrombotic phenotype, such as selective plasma factor V or factor Xa inhibition.

Aspirin Resistance: An Evaluation of Current Evidence and Measurement Methods

Aspirin resistance is a poorly characterized phenomenon, whereby certain patients do not benefit from the antithrombotic effect of aspirin. The frequency of aspirin resistance is unknown, but estimates range from 5-60%. The mechanism of aspirin resistance also is unknown; proposed mechanisms are poor patient compliance, poor aspirin absorption, increased isoprostane activity, platelet hypersensitivity to agonists, increased cyclooxygenase-2 activity, a cyclooxygenase-1 polymorphism, and the platelet alloantigen 2 polymorphism of platelet glycoprotein IIIa. Aspirin resistance appears to be dose related in some patients and therefore may be overcome with high doses. Evidence indicates that aspirin resistance is a dynamic state, with significant intrapatient variability in aspirin sensitivity with time. To date, a sensitive and specific assay of aspirin effect that reliably predicts treatment failure has not emerged. However, several commercially available products are being marketed for this purpose without convincing clinical data. Despite a wealth of literature on the topic, aspirin resistance remains an enigma. Further investigation is needed regarding strategies to identify and treat patients resistant to aspirin.

Association of polymorphisms of platelet membrane integrins alpha IIb(beta)3 (HPA-1b/Pl) and alpha2(beta)1 (alpha807TT) with premature myocardial infarction

Conflicting results of an association of the human platelet antigen 1b (HPA-1b/PlA2), localized on the beta-subunit of the integrin alpha(IIb)beta3, and the alpha(2)807TT genotype of the integrin alpha2beta1 with coronary atherosclerosis and myocardial infarction have been reported. Both platelet receptor polymorphisms were genotyped in 3261 patients who had undergone coronary angiography, including 1175 survivors of a myocardial infarction, 1211 individuals with coronary artery disease but no history of myocardial infarction, and 571 control patients without angiographic coronary artery disease, and in 793 blood donors. In a case-control design, the prevalence of HPA-1b and alpha(2)807TT genotypes did not differ significantly between the patient groups with coronary artery disease or myocardial infarction and patient controls or blood donors. By contrast, using a multivariate case-only design, it was found that the median age of onset of myocardial infarction was 5.2 years earlier (P = 0.006) in carriers of the HPA-1b allele and 6.3 years earlier (P = 0.006) in carriers of the alpha(2)807TT genotype in the 264 survivors of myocardial infarction of recent onset with one- or two-vessel coronary artery disease. A significant interaction with the conventional risk factors hypercholesterolemia, smoking, diabetes, hypertension, and hyperfibrinogenemia was excluded. Human platelet antigen 1b and alpha(2)807TT are associated with premature myocardial infarction but not with coronary artery disease, suggesting a role of distinct integrin genotypes for increased platelet thrombogenicity. This association requires confirmation in follow-up studies.

Variation in ITGB3 has sex-specific associations with plasma lipoprotein(a) and whole blood serotonin levels in a population-based sample

A recent genome-scan identified the Leu33Pro polymorphism in the beta3 integrin (ITGB3) gene as a quantitative trait locus for whole blood serotonin level in a large Hutterite pedigree. Because both the Leu33Pro polymorphism and the serotonin system have been implicated in cardiovascular disease (CVD) risk and treatment response, we studied additional variation in ITGB3 and its relationship to intermediate phenotypes associated with CVD in the same population. We examined associations between 15 single nucleotide polymorphisms (SNPs) across ITGB3 and five CVD-related traits in the Hutterites: plasma levels of high density lipoprotein-cholesterol (HDL-c), triglycerides (TG), low density lipoprotein-cholesterol (LDL-c), and lipoprotein(a) [Lp(a)] and blood pressure or hypertension. Seven of these SNPs in ITGB3 were associated with whole blood serotonin. Among the intermediate CVD-related phenotypes, only Lp(a) was associated with multiple ITGB3 SNPs, five of which were also associated with serotonin. A sex-stratified analysis revealed that the association between ITGB3 and Lp(a) is present only in females, whereas the association between ITGB3 and serotonin is concentrated in males. Our results suggest that variation in ITGB3 in addition to Leu33Pro could contribute to susceptibility to CVD and serotonin in a sex-specific manner.

Genetics of platelet glycoprotein receptors: risk of thrombotic events and pharmacogenetic implications

Platelet aggregation and coronary thrombosis have a central role in the development of acute coronary syndromes and myocardial infarction (MI). Therapies aimed at inhibiting platelet aggregation have shown great benefit in individuals with coronary disease or with multiple risk factors for coronary disease. Genetic variation in platelet surface receptors mediating thrombus formation has been suggested to be associated with platelet hyperreactivity, with increased risk of MI and possibly with the benefit received from various antithrombotic drug treatments. This review focuses on discrepancies and their likely explanations in studies on platelet glycoprotein genetics. Current knowledge on important issues concerning coronary event phenotypes and pharmacogenetics is analyzed. Possible future applicability of these data to patient treatment is also discussed.

A part le fibrinogène, les facteurs/marqueurs d’hémostase ont-ils aussi une place pour évaluer le risque d’accident cardiovasculaire ischémique ?

Most cardiovascular events result from a thrombotic complication of atherosclerotic lesions. In arterial vessels such as the coronary bed, an interrelationship of haemostatic, coagulation and fibrinolytic factors is implicated. While it can be demonstrated that fibrinogen is a risk factor/marker, the role of other factors is not well established. Under arterial flow conditions, platelets are predominantly involved in the thrombotic reaction. Yet, apart from a large increase in the platelet count, the involvement of platelet parameters in cardiovascular risk is not clearly evident. The lack of definitive platelet markers is at least partly due to the difficulty of studying platelet function ex vivo. Several polymorphisms of platelet glycoproteins carrying a moderate increase in risk have been reported, but only in younger patients. One potentially important factor for coagulation is the fibrin structure, which is dependent on fibrinogen, the rate of thrombin generation, the activity of factor XIII and the interrelationship of the cells concerned, all of which act on its sensitivity to thrombosis. Coagulation factors largely affect the rate of thrombin generation. The activity of the fibrinolytic system (and principally any deficiency) has a role in the cardiovascular risk. General markers of cardiovascular risk such as D-dimers are potentially useful, but they increase with thrombin generation and are decreased by a deficiency in fibrinolysis. Furthermore, possibly because they are not indicative of the fibrin structure, they are poorly correlated with clinical events. The poor significance of the available haemostatic, coagulation and/or fibrinolytic parameters is probably due to their lack of representativeness, since haemostatic, coagulation and fibrinolytic systems are all involved in the thrombotic response (and some in atherogenesis itself). Atherogenesis is a multifactorial process and numerous moderate risk factors act in association. Better predictability of the haemostatic tests would probably result from both the design of more representative tests and the evaluation of multiple parameters, and would lead to the definition of a risk score. Technological advances will make this possible.

Effect of glycoprotein IIIa PlA2 polymorphism on outcome of patients with stable coronary artery disease and effect of smoking

A polymorphism of glycoprotein IIb/IIIa has been associated with myocardial infarction and restenosis after percutaneous coronary intervention. The influence on outcome and the interaction of the Pl(A1) genotype with classic risk factors for coronary artery disease (CAD) were characterized in patients with chronic CAD followed prospectively for 3 years. Pl(A1) genotypes were assessed in 592 patients enrolled in the Medical, Angioplasty, or Surgery Study II, a randomized trial comparing treatments for patients with CAD and preserved left ventricular function. The incidence of the composite end point of cardiac death, myocardial infarction, and refractory angina requiring revascularization were determined in each genotype group. Risk was assessed with the Cox proportional-hazards model. The clinical characteristics and treatment of each genotype were similar. Although the composite end point tended to be more common in patients with the Pl(A2) allele, only smokers with the Pl(A2) allele had a significantly increased incidence of the composite end point (p = 0.01). Moreover, a 2.2-fold increased risk was apparent in smokers with the Pl(A2) allele (p = 0.03). Thus, taken together, these data provide support for the interaction effect between smoking and the Pl(A1) gene variant. Smokers with the Pl(A2) polymorphism of platelet glycoprotein IIIa are at greater risk for subsequent cardiac events in stable coronary disease.

Role of thrombotic and fibrinolytic factors in acute coronary syndromes

There is a growing body of literature concerning the contribution of hemostatic factors to the development of cardiovascular disease. The mechanisms of the coagulation/fibrinolytic system are complicated and one factor is intimately interrelated with another; thus the contribution of each factor cannot be clearly understood, unless hemostatic factors are considered in accordance with endothelial function and vessel morphology. Although there are many clinical studies about the correlation between hemostatic factors and cardiovascular risk, the results are inconsistent and conflicting at times. Fibrinogen and D-dimer are associated with atherosclerosis or coronary events across multiple studies, even after multivariate adjustment. But the hemostatic factors are intimately correlated, so it can be said that focusing on one to the exclusion of others is inappropriate. The clinical trials with statins or angiotensin converting enzyme inhibitors have shown favorable effects on the prognosis of cardiovascular disease. The study of hemostatic factors in relation to these drugs has provided insights into understanding how these drugs produce beneficial effects.

Genetic influences on blood pressure within the Stanislas Cohort

OBJECTIVE

To investigate the association of 21 polymorphisms within 13 genes, APOE, APOB, APOC3, CETP, LPL, PON1, MTHFR, FGB, F5, GPIIIa, SELE, ACE and AGT, with inter-individual blood pressure (BP) variation.

PARTICIPANTS

Seven hundred and seventy-six men and 836 women, free of antihypertensive and lipid-lowering medications, were selected from the Stanislas Cohort.

RESULTS

ANOVA on blood pressure values after adjustment for covariates [age, body mass index (BMI), contraceptive pill, tobacco and alcohol] showed that lipoprotein lipase (LPL) Ser447Ter and glycoprotein IIIA (GpIIIa) Pl polymorphisms were significantly associated with BP in women (0.01 < or = P < or = 0.05), whereas BP levels in men were significantly different according to apolipoprotein CIII (APOC3) 3206T/G and -482C/T polymorphisms (P < or = 0.05). In women, compared to the most common allele, the GpIIIa Pl allele was associated with increased mean arterial pressure (MAP) (P < 0.05) and pulse pressure (PP) (P < 0.001), and the LPL 447Ter allele was associated with decreased systolic blood pressure (SBP) and PP levels (0.001 < or = P < or = 0.05). These two polymorphisms appeared to act independently. In men, the APOC3 3206GG genotype was related to decreased diastolic blood pressure (DBP) and MAP levels (P < or = 0.01), and the APOC3 -482T allele with decreased PP levels (P < or = 0.05). The presence of both the -482C allele and the 3206GG genotype was related to decreased DBP, suggesting that specific haplotypes might be involved.

CONCLUSION

The APOC3, LPL and GpIIIa genes were found to be associated with BP levels. The contributions of these genes, although modest, are consistent with the polygenic nature of BP levels.

Nonarteritic anterior ischemic optic neuropathy is associated with a specific platelet polymorphism located on the glycoprotein Ibalpha gene

OBJECTIVE

To evaluate the association between platelet glycoprotein polymorphisms and the risks of single and second eye involvement with nonarteritic anterior ischemic optic neuropathy (NAION).

DESIGN

Case-control study.

PARTICIPANTS

Ninety-two consecutive patients with NAION, 26 of whom had second eye involvement, and 145 controls who attended the eye clinic for nonvascular entities.

METHODS

Polymerase chain reactions and restriction enzyme analyses were performed for genotyping 5 platelet glycoprotein polymorphisms on DNA extracted from whole blood.

MAIN OUTCOME MEASURES

Frequencies of the various platelet polymorphisms.

RESULTS

One of the 5 platelet glycoprotein polymorphisms analyzed, the B allele of the glycoprotein Ibalpha variable number of tandem repeats (VNTR), was a significant independent risk factor for NAION, with an odds ratio of 4.25 and a 95% confidence interval of 1.67 to 10.82 (P = 0.0026). All other platelet glycoprotein polymorphisms were similarly distributed in patients and controls. In addition, 9 of 16 patients who bore the VNTR B allele (56.3%) had second eye involvement, whereas among patients not harboring the VNTR B allele only 17 of 72 patients (23.6%) had second eye involvement (P = 0.009). Moreover, second eye involvement occurred earlier in patients who bore the specific polymorphism.

CONCLUSIONS

The presence of the VNTR B allele of glycoprotein Ibalpha confers a significant risk for NAION and predisposes affected patients to second eye involvement.

Interaction between a genetic variant of the platelet fibrinogen receptor and fibrinogen levels in determining the risk of cardiovascular events

BACKGROUND

The PlA1A2 polymorphism of glycoprotein IIIa (GPIIIa), which affects postoccupancy signaling by the platelet fibrinogen receptor IIbIIIa, has been investigated as a potential genetic risk factor for cardiovascular events in numerous studies, without consistent results. We investigated whether the effect of this genetic variant of the platelet fibrinogen receptor on the risk of cardiovascular events is affected by fibrinogen plasma levels.

METHODS

The GPIIIa PlA1A2 polymorphism and fibrinogen levels were determined in 455 men with angiographically documented coronary atherosclerosis.

RESULTS

Neither carriership of the rare PlA2 allele nor fibrinogen plasma levels affected the time to cardiovascular event, as assessed in a proportional hazards model. However, there was a significant interaction between PlA2 carriership and fibrinogen plasma levels (P =.002). Carriership of the variant PlA2 allele significantly affected event-free survival only in individuals within the highest fibrinogen quartile (hazard ratio, 2.7; 95% CI, 1.1 to 7.1; P =.03).

CONCLUSIONS

We observed a statistically significant interaction between a genetic variant of the platelet fibrinogen receptor and fibrinogen levels in determining the risk of cardiovascular events. This interaction may account for the inconsistent results of genetic association studies investigating this genotype as a genetic risk factor in thrombotic cardiovascular events.

Failure of aspirin to prevent atherothrombosis: potential mechanisms and implications for clinical practice

Aspirin (acetylsalicylic acid) reduces the odds of serious atherothrombotic vascular events and death in a broad category of high risk patients by about one-quarter. The mechanism is believed to be inhibition of thromboxane biosynthesis by inactivation of platelet cyclo-oxygenase-1 enzyme. However, aspirin is not that effective; it still fails to prevent the majority of serious vascular events. Mechanisms that may account for the failure of aspirin to prevent vascular events include non-atherothrombotic causes of vascular disease, non-adherence to aspirin therapy, an inadequate dosage, alternative "upstream" pathways of platelet activation (e.g. via stimulation of the ADP, collagen or thrombin receptors on platelets), aspirin-insensitive thromboxane biosynthesis (e.g. via monocyte cyclo-oxygenase-2), or drugs that interfere with the antiplatelet effects of aspirin. Genetic or acquired factors may further modify the inhibitory effects of aspirin on platelets (e.g. polymorphisms involving platelet-associated proteins, increased platelet turnover states). Identification and treatment of the potential causes of aspirin failure could prevent at least another 20% of serious vascular events (i.e. over and above those that are currently prevented by aspirin). There is currently no role for routine laboratory testing to measure the antiplatelet effects of aspirin. Clinicians should ensure that patients at high risk of atherothrombosis (>3% risk over 5 years) are compliant with aspirin therapy and are taking the correct dosage (75-150 mg/day). Patients who cannot tolerate aspirin, are allergic to aspirin, or have experienced recurrent serious atherothrombotic events whilst taking aspirin, should be treated with clopidogrel, and patients with acute coronary syndromes benefit from the combination of clopidogrel plus aspirin. Future research is required to standardize and validate laboratory testing of the antiplatelet effects of aspirin and to identify treatments that can both improve these laboratory measures and reduce the risk of future atherothrombotic events.

Role of platelet glycoprotein polymorphisms in cardiovascular diseases

Atherothrombosis is the leading cause of death in western countries. Major complications of atherothrombotic disease, which are responsible for a large burden of morbidity and mortality, are acute coronary syndromes, ischemic stroke, and peripheral occlusive disease. Plaque rupture, platelet adhesion, aggregation, and thrombosis may lead to unstable angina and may progress to myocardial infarction as well as to ischemic stroke. Platelet membrane glycoprotein receptors mediate crucial reactions in acute thrombosis and chronic processes of atherogenesis. The platelet glycoprotein GP IIb/IIIa, which is the most abundant platelet receptor, also represents the drug target of a novel class of anti-platelet drugs, which includes abciximab, tirofiban, and eptifibatide. The genes encoding the three major platelet glycoprotein receptors (GP Ib/IX/V, GP Ia/IIa, and GP IIb/IIIa) are subject to considerable genetic variability. This paper reviews how polymorphisms in the platelet glycoprotein receptors affect platelet function, susceptibility to atherothrombosis and its major complications including myocardial infarction, stroke, and complications following percutaneous coronary interventions, and individual variability of drug response. Recent data on platelet glycoprotein receptor polymorphisms as modifiers of drug action and as predictors of drug response offer the perspective of individualized drug treatment. Prospective studies will show whether this approach is useful or not. As the data reviewed here show clearly, future clinical trials should routinely take into account genetic susceptibility factors and modifiers, both for study design and for predefined patient stratification.

Prothrombotic determinants of coronary atherothrombosis

An acute coronary syndrome (ACS) is the clinical manifestation of a thrombotic event occurring within a coronary artery narrowed by atherosclerosis. This atherothrombotic event is thought to occur following destabilizing changes within the atherosclerotic plaque, rendering it a surface on which thrombus can develop. The development and progression of this thrombus are determined by deleterious perturbations in the hemostatic equilibrium within the local environment of the plaque that favor thrombosis. Major risk factors for the development of atherosclerotic disease have been clearly established and are targets of aggressive modification in an effort to impede the development or slow the progression of disease. While conferring an increased risk for plaque development, these and other risk factors also establish a prothrombotic milieu within the microenvironment of the atherosclerotic plaque that favors thrombosis. This review seeks to address these traditional and emerging risk factors from the context of their pathologic effects on local hemostatic balance. Aggressive risk factor modification not only reduces atherosclerotic disease development and progression, but also ameliorates the prothrombotic state, and ultimately serves to reduce atherothrombotic events.

Increased platelet-collagen interaction associated with double homozygosity for receptor polymorphisms of platelet GPIa and GPIIIa

OBJECTIVE

There is considerable controversy regarding the clinical role of the single-nucleotide polymorphisms (SNPs) of the platelet glycoprotein receptor GPIa C807T and the Pl(A1/A2) of GPIIIa as cardiovascular risk factors. We hypothesized that two combined SNPs in their homozygous prothrombotic forms could clarify their pathophysiological impact.

METHODS AND RESULTS

We identified a family with a striking history of premature cardiovascular events and a high frequency of the prothrombotic form of the two SNPs. From this family, the platelets of a healthy, 27-year-old propositus with this double homozygosity were compared with three matched male neutral gene variant controls. The propositus had shortened PFA-100 closure times and an increased platelet aggregation response to collagen. Platelet deposition to collagen was augmented under the blood flow conditions of a high shear rate model (1600 s(-1)). Platelet adhesion on collagen monomers was induced in a static system, leading to the promotion of subsequent procoagulant activity.

CONCLUSIONS

The combined homozygous prothrombotic SNPs of GPIa and GPIIIa are associated with an increased platelet-collagen interaction and procoagulant activity that can be readily demonstrated in several independent systems. Our patient may serve as a useful model for the functional consequences of two combined, potentially procoagulant, platelet SNPs.

Antagonists of platelet fibrinogen receptor are less effective in carriers of Pl(A2) polymorphism of beta(3) integrin

The polymorphism Leu(33)-->Pro (platelet-specific antigen; Pl(A1/A2)) of platelet GPIIIa is a potential risk factor for arterial thrombosis. However, its influence on platelet function remains controversial and little is known about its impact on platelet sensitivity to GPIIb-IIIa antagonists. Our objective was to compare the effectiveness of various GPIIb-IIIa antagonists in Pl(A2)(+) and Pl(A2)(-) carriers. Platelet aggregation was monitored in healthy donors including Pl(A2)(-) (N=31) and Pl(A2)(+) subjects (N=27; 23 Pl(A1/A2), 4 Pl(A2)/(A2)) using the impedance and turbidimetric aggregation techniques. We evaluated the inhibition of ADP- and collagen-induced aggregation by disintegrins, kistrin and echistatin, and the low-molecular-weight blockers, GR144053F ((4-[4-[4-(aminoiminomethyl]-1-piperazinyl]-1-piperidineacetic acid, hydrochloride trihydrate) and eptifibatide (N(6)-(aminoiminomethyl)-N(2)-(3-mercapto-1-oxopropyl-L-lysylglycyl-L-alpha-aspartyl-L-tryptophyl-L-propyl-L-cysteinamide, cyclic (1-->6)-disulfide). Kistrin (10-30 nmol/l) inhibited ADP- and collagen-induced aggregation stronger in Pl(A2)(-) donors than in Pl(A2)(+) donors; there was a significant difference between 50% inhibitory concentrations (IC(50)). The same tendency occurred with moderate concentrations of eptifibatide (40-100 nmol/l) and also at low concentrations of GR144053F (5-10 nmol/l) and high concentrations of echistatin (80-150 nmol/l), although in the case of the two latter inhibitors, the estimated IC(50) values were not significantly different. In conclusion, GPIIb-IIIa blockers representing various classes are less effective inhibitors of platelet aggregation in Pl(A2)(+) carriers; however, the effect of the genotype is both agonist- and antagonist-dependent.

PLA1/A2 polymorphism of the platelet glycoprotein receptor IIb/IIIa in young patients with cryptogenic TIA or ischemic stroke

BACKGROUND

The relationship between the PIA2 allele of the Leu(33)Pro polymorphism of glycoprotein IIb/IIIa receptor (GPIIb/IIIa) and ischemic stroke is uncertain. The purpose of this study was to investigate a possible association between the GPIIb/IIIa PIA1/A2 polymorphism and the occurrence of cryptogenic stroke in young patients.

METHODS

From a consecutive series of 80 patients aged 45 or less with a recent ischemic stroke or TIA, we selected 45 patients with stroke due to small vessel occlusion or stroke of undetermined etiology (according to the TOAST criteria). Controls were 60 healthy blood donors with a similar age distribution. All patients underwent CT of the brain and were screened for cardiovascular risk factors, cardiac disorders and large vessel disease. The frequency of the PIA2 allele was determined by PCR and Msp1 restriction analysis.

RESULTS

Eight patients (16%) and 16 controls (27%) were heterozygous for PIA2 allele. Two patients (4%) were homozygous for PIA2. The relative risk of ischemic stroke associated with PIA2 allele was estimated at 0.8 (95% CI: 0.3-1.9).

CONCLUSION

This study does not support the association between the PIA1/A2 polymorphism and cryptogenic stroke or TIA in patients aged 45 or less.

The influence of platelet glycoprotein polymorphisms on receptor function and risk for thrombosis

With regard to hemostasis and thrombosis, collagens are among the most important physiologic components of the extracellular matrix in their role as platelet activators. Differences in the rate of platelet activation markedly influence normal hemostasis and the pathological outcome of thrombosis. Thus, collagen receptors, such as the integrin alpha2beta1 and indirectly, GPIb alpha, represent a relatively unexploited target of pharmacological control and are only recently becoming appreciated as potential factors in the generic risk for thrombosis. In general, the importance platelet glycoprotein polymorphisms as genetic risk factors for arterial thrombosis is a new area of human genomics that needs to be carefully addressed. Discrepancies in the degree to which they are reported to contribute to risk for clinical thrombosis will only be resolved once there is a universal standard for clinical study design. Most of the clinical studies differ by patient population size, ethnicity, bias in the selection of patients and controls, plurality in clinical endpoints and variation of environmental factors. Despite these differences, there is substantial evidence that the integrin beta3 PlA2 haplotype, the GPIb alpha Met145 haplotype, the GPIb alpha -5C haplotype and the integrin alpha2 haplotype 1 (807T) each contribute to the risk for and morbidity of thrombotic disease. There may remain dispute as to the extent of their contribution. However, well-designed, large, prospective, genetic and epidemiologic studies are needed to clarify the role of these and other platelet receptor polymorphisms. Most importantly, the cumulative effects of multiple platelet and plasma glycoproteins SNPs to thrombotic risk must be evaluated concurrently. Additional in vitro studies of the functional relevance underlying these polymorphisms are needed to provide a sound biological explanation for the results of clinical correlations. The opportunity now exists to make significant inroads into the development of strategies for the prevention of thrombotic disease.

[Genes and coronary heart disease]

The causes of atherosclerotic cardiovascular disease have been intensely scrutinized for the last few decades. Since the classic risk factors have been found to be incomplete predictors of the disease, additional risk factors based on molecular genetics are now being sought. Polymorphisms are gene variations that have only modest effects on the function of coded proteins or enzymes. However, they are common and may be risk factors in the presence of environmental risk factors (cholesterol, stress, tobacco). Recent advances in molecular biology have made it possible to detect numerous polymorphisms that might have a detrimental effect on vascular biology, suggesting the hypothesis that multiple polymorphisms in the presence of environmental factors could act synergistically in the pathogenesis of atherosclerosis and coronary heart disease, which are typically polygenic and multifactorial diseases. In this review, the current status of our knowledge of polymorphisms and mutations potentially implicated in the mechanisms of coronary artery disease is discussed. Genotype/phenotype, gene-gene, and gene-environmental interactions related to lipid metabolism, the renin-angiotensin-aldosterone and adrenergic systems, insulin resistance, oxidative stress and endothelial function, inflammation and thrombosis are analyzed. Individual coronary risk might be related to the presence of a critical accumulation detrimental polymorphisms.