Pl(A2) polymorphism of beta(3) integrins is associated with enhanced thrombin generation and impaired antithrombotic action of aspirin at the site of microvascular injury

Clot Retraction and Its Correlation with the Function of Platelet Integrin αIIbβ3

Clot retraction results from retractions of platelet filopodia and fibrin fibers and requires the functional platelet αIIbβ3 integrin. This assay is widely used to test the functions of platelets and fibrinogen as well as the efficacy of fibrinolysis. Changes in clot retraction have been found in a variety of hemostatic abnormalities and, more recently, in arterial thrombosis. Despite its broad clinical use and low cost, many aspects of clot retraction are poorly understood. In the present study, we performed two clinical standard clot retraction assays using whole-blood and platelet-rich plasma (PRP) samples to determine how clot retraction correlates with platelet counts and mean volume, the density of αIIbβ3 integrin and PLA genotypes, and plasma fibrinogen levels. We found that clot retraction was affected by platelet counts, but not mean platelet volume. It correlated with the surface density of the integrin αIibβ3, but not PLA genotypes. These results indicate that clot retraction measures a unique aspect of platelet function and can serve as an additional means to detect functional changes in platelets.

An Exploratory Study Using Next-Generation Sequencing to Identify Prothrombotic Variants in Patients with Cerebral Vein Thrombosis

Prothrombotic hereditary risk factors for cerebral vein thrombosis (CVT) are of clinical interest to better understand the underlying pathophysiology and stratify patients for the risk of recurrence. This study explores prothrombotic risk factors in CVT patients. An initial screening in patients of the outpatient clinic of the Department of Transfusion Medicine and Hemostaseology of the University Hospital Erlangen, Germany, revealed 183 patients with a history of CVT. An initial screening identified a number of common prothrombic risk factors, including Factor V Leiden (rs6025) and Prothrombin G20210A (rs1799963). All patients without relevant findings (58 individuals) were invited to participate in a subsequent genetic analysis of 55 relevant genes using next-generation sequencing (NGS). Three intron variants (ADAMTS13: rs28446901, FN1: rs56380797, rs35343655) were identified to occur with a significantly higher frequency in the CVT patient cohort compared to the general European population. Furthermore, the combined prevalence of at least two of four potentially prothrombic variants (FGA (rs6050), F13A1 (rs5985), ITGB3 (rs5918), and PROCR (rs867186)) was significantly higher in the CVT subjects. The possible impact of the identified variants on CVT is discussed.

Biomarkers for Antiplatelet Therapies in Acute Ischemic Stroke: A Clinical Review

Stroke is one of the world's leading causes of disability and death. Antiplatelet agents are administered to acute ischemic stroke patients as secondary prevention. Clopidogrel involves biotransformation by cytochrome P450 (CYP) enzymes into an active metabolite, and single nucleotide polymorphisms (SNPs) can influence the efficacy of this biotransformation. Despite the therapeutic advantages of aspirin, there is significant inter-individual heterogeneity in response to this antiplatelet drug. In this clinical review, the recent advances in the biomarkers of antiplatelet agents in acute ischemic stroke are discussed. The studies reviewed herein highlight the clinical relevance of antiplatelet resistance, pharmacotherapy of antiplatelet agents predicting drug response, strategies for identifying aspirin resistance, pharmacogenetic variants of antiplatelet agents, miRNAs, and extracellular vesicles (EVs) as biomarkers toward the personalized approach in the management of acute ischemic stroke. The precise pathways contributing to antiplatelet resistance are not very well known but are presumably multi-factorial. It is essential to understand the clinical relevance of clopidogrel and aspirin-related single nucleotide polymorphism (SNPs) as potential predictive and prognostic biomarkers. Prasugrel is a next-generation antiplatelet agent that prevents ADP-platelet activation by binding irreversibly to P2Y12 receptor. There are sporadic reports of prasugrel resistance and polymorphisms in the Platelet endothelial aggregation receptor-1 (PEAR1) that may contribute to a change in the pharmacodynamics response. Ticagrelor, a direct-acting P2Y12-receptor antagonist, is easily absorbed and partly metabolized to major AR-C124910XX metabolite (ARC). Ticagrelor's primary active metabolite, ARC124910XX (ARC), is formed via the most abundant hepatic cytochrome P450 (CYP) enzyme, CYP3A4, and CYP3A5. The integration of specific biomarkers, genotype as well as phenotype-related data in antiplatelet therapy stratification in patients with acute ischemic stroke will be of great clinical significance and could be used as a guiding tool for more effective, personalized therapy.

Aspirin and the prevention of venous thromboembolism following total joint arthroplasty: commonly asked questions

The number of arthroplasties being performed increases each year. Patients undergoing an arthroplasty are at risk of venous thromboembolism (VTE) and appropriate prophylaxis has been recommended. However, the optimal protocol and the best agent to minimise VTE under these circumstances are not known. Although many agents may be used, there is a difference in their efficacy and the risk of bleeding. Thus, the selection of a particular agent relies on the balance between the desire to minimise VTE and the attempt to reduce the risk of bleeding, with its undesirable, and occasionally fatal, consequences.

Acetylsalicylic acid (aspirin) is an agent for VTE prophylaxis following arthroplasty. Many studies have shown its efficacy in minimising VTE under these circumstances. It is inexpensive and well-tolerated, and its use does not require routine blood tests. It is also a ‘milder’ agent and unlikely to result in haematoma formation, which may increase both the risk of infection and the need for further surgery. Aspirin is also unlikely to result in persistent wound drainage, which has been shown to be associated with the use of agents such as low-molecular-weight heparin (LMWH) and other more aggressive agents.

The main objective of this review was to summarise the current evidence relating to the efficacy of aspirin as a VTE prophylaxis following arthroplasty, and to address some of the common questions about its use.

There is convincing evidence that, taking all factors into account, aspirin is an effective, inexpensive, and safe form of VTE following arthroplasty in patients without a major risk factor for VTE, such as previous VTE.

Cite this article: Bone Joint J 2017;99-B:1420–30.

Molecular Mechanisms of Prothrombotic Risk Due to Genetic Variations in Platelet Genes: Enhanced Outside-In Signaling Through the Pro33 Variant of Integrin β3

In recent years inherited variations in platelet proteins have emerged as potential risk factors that could predispose individuals to arterial thrombosis. Although many studies have examined the association of platelet gene polymorphisms with particular disease states, the underlying mechanisms by which most of these polymorphisms contribute to the pathophysiology of thrombosis have remained largely unexplored. This review will focus on the cellular and molecular features by which these genetic changes affect platelet physiology. Although many genes have been investigated in this regard, only the genes encoding integrins β3 and α2, and the platelet Fc receptor, FcγRIIA, have been studied in any depth. In some cases (such as integrin α2), evidence supports a quantitative trait locus. For other genes, nonsynonymous nucleotide substitutions lead to structural and functional consequences. A large portion of this review will focus on the widely studied Leu33Pro (PIA) polymorphism of integrin β3, and will consider the potential mechanisms by which the Pro33 polymorphism could induce a prothrombotic risk. A detailed understanding of how polymorphisms modulate platelet physiology will be important for understanding individual differences in response to antiplatelet therapy.

[Prevalence and prognosis of aspirin resistance in critical limb ischemia patients]

OBJECTIVES

To assess the prevalence and the association between aspirin resistance in critical limb ischemia patients using the VerifyNow^® bed-side platelet test, and occurrence of cardiovascular morbidity and/or death at one year.

MATERIALS AND METHODS

National multicenter prospective observational study related to COPART II centers. From 2010 through 2014, 64 subjects hospitalized for critical limb ischemia and already treated by aspirin before the VerifyNow^® test were included. A VerifyNow^® test>550 ARU was defined as aspirin resistance. Critical limb ischemia was defined according to the TASC I criteria. The primary outcome was a composite including death, acute coronary syndrome, stroke and major amputation during the one-year follow-up period.

RESULTS

In all, 9/64 patients were aspirin resistant, the status was confirmed in one case. The prevalence of aspirin resistance was 14.06%. There was no significant difference between aspirin resistant and aspirin non-resistant groups in terms of cardiovascular history and glycemia status. Neither was there significant difference between the two groups in terms of survival.

CONCLUSION

Aspirin resistance was not predictive of poorer survival in critical limb ischemia patients. However, our population was limited. Considering that a clear definition of aspirin resistance and standardized diagnostic tests are lacking, complementary studies might be useful.

Sticky platelet syndrome: an important cause of life-threatening thrombotic complications

Sticky platelet syndrome (SPS) is a prothrombotic thrombocytopathy with familial occurrence, characterized by hyperaggregability of platelets in response to adenosine diphosphate (ADP), epinephrine (EPI) or both. The syndrome has been identified in approximately 21% of unexplained arterial thrombotic episodes, regarded to be the most common thrombophilia in arterial thrombosis and 13.2% of unexplained venous thromboembolism (VTE). The relatively young age at the first manifestation, relation to fertility and pregnancy, seriousness of the symptoms, easy and effective management of the disorder indicate to the necessity to take it into account in the differential diagnosis of the underlying cause of the thrombotic event. As the various localizations of the thrombosis in SPS have been reported, its management often requires a multidisciplinary approach. This review deals with the clinical aspects of thrombophilia, its etiopathogenesis, diagnosis as well as novel advances in the treatment and outlines the challenges for the further research.

Personalized antiplatelet and anticoagulation therapy: applications and significance of pharmacogenomics

In recent years, substantial effort has been made to better understand the influence of genetic factors on the efficacy and safety of numerous medications. These investigations suggest that the use of pharmacogenetic data to inform physician decision-making has great potential to enhance patient care by reducing on-treatment clinical events, adverse drug reactions, and health care-related costs. In fact, integration of such information into the clinical setting may be particularly applicable for antiplatelet and anticoagulation therapeutics, given the increasing body of evidence implicating genetic variation in variable drug response. In this review, we summarize currently available pharmacogenetic information for the most commonly used antiplatelet (ie, clopidogrel and aspirin) and anticoagulation (ie, warfarin) medications. Furthermore, we highlight the currently known role of genetic variability in response to next-generation antiplatelet (prasugrel and ticagrelor) and anticoagulant (dabigatran) agents. While compelling evidence suggests that genetic variants are important determinants of antiplatelet and anticoagulation therapy response, significant barriers to clinical implementation of pharmacogenetic testing exist and are described herein. In addition, we briefly discuss development of new diagnostic targets and therapeutic strategies as well as implications for enhanced patient care. In conclusion, pharmacogenetic testing can provide important information to assist clinicians with prescribing the most personalized and effective antiplatelet and anticoagulation therapy. However, several factors may limit its usefulness and should be considered.

Why does aspirin decrease the risk of venous thromboembolism? On old and novel antithrombotic effects of acetyl salicylic acid

It is well established that aspirin, an irreversible inhibitor of platelet cyclooxygenase activity, is effective in secondary prevention of arterial thromboembolic events. The pooled results of the recent randomized, multicenter WARFASA and ASPIRE aspirin trials showed a 32% reduction in the rate of recurrence of venous thromboembolism (VTE) in patients receiving aspirin following VTE. These clinical data support evidence that platelets contribute to the initiation and progression of venous thrombosis and aspirin inhibits thrombin formation and thrombin-mediated coagulant reactions. In addition to the known acetylation of serine 529 residue in platelet cyclooxygenase-1, the postulated mechanisms of aspirin-induced antithrombotic actions also involve the acetylation of other proteins in blood coagulation, including fibrinogen, resulting in more efficient fibrinolysis. This review summarizes current knowledge on the aspirin-induced antithrombotic effects that potentially explain clinical studies showing reduced rates of VTE events in aspirin-treated subjects.

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.

The PlA1/A2 polymorphism of glycoprotein IIIa as a risk factor for stroke: a systematic review and meta-analysis

BACKGROUND

The PlA1/A2 polymorphism of glycoprotein IIIa (GPIIIa) has been reported to be associated with risk of stroke in some studies, although other studies suggest no such association. This meta-analysis and systematic review was conducted to investigate the hypothesis that carriage of the PlA2 allele is a risk factor for stroke.

METHODS

Electronic databases (MEDLINE and EMBASE) were searched for all articles evaluating carriage of the PlA2 allele and the incidence of stroke. Pooled odds ratios (ORs) were calculated using fixed-effect and random-effect models.

FINDINGS

A total of 35 articles were eligible for inclusion, of which 25 studies were suitable for statistical analysis. For carriage of the PlA2 allele, OR 1.12 (n = 11,873; 95% CI = 1.03-1.22; p = 0.011) was observed for the incidence of stroke in adults, with subgroup analyses identifying the association driven by stroke of an ischaemic (n = 10,494; OR = 1.15, 95% CI = 1.05-1.27; p = 0.003) but not haemorrhagic aetiology (n = 2,470; OR = 0.90, 95% CI = 0.71-1.14; p = 0.398). This association with ischaemic stroke was strongest in individuals homozygous for the PlA2 allele compared to those homozygous for wild-type PlA1 (n = 5,906; OR = 1.74, 95% CI = 1.34-2.26; p<0.001). Subgroup analysis of ischaemic stroke subtypes revealed an increased association with stroke of cardioembolic (n = 1,271; OR 1.56, 95% CI 1.14-2.12; p = 0.005) and large vessel (n = 1,394; OR = 1.76, 95% CI 1.34-2.31; p<0.001) aetiology, but not those of small vessel origin (n = 1,356; OR = 0.99, 95% CI 0.74-1.33; p = 0.950). Egger's regression test suggested a low probability of publication bias for all analyses (p>0.05).

CONCLUSIONS

The totality of published data supports the hypothesis that carriage of the PlA2 polymorphism of GPIIIa is a risk factor for ischaemic strokes, and specifically those of cardioembolic and large vessel origin.

The PlA1/A2 polymorphism of glycoprotein IIIa as a risk factor for myocardial infarction: a meta-analysis

BACKGROUND

The PlA2 polymorphism of glycoprotein IIIa (GPIIIa) has been previously identified as being associated with myocardial infarction (MI), but whether this represents a true association is entirely unclear due to differences in findings from different studies. We performed a meta-analysis to evaluate whether this polymorphism is a risk factor for MI.

METHODS

Electronic databases (MEDLINE and EMBASE) were searched for all articles evaluating genetic polymorphisms of GPIIIa. For studies where acute coronary events were recorded in association with genetic analysis, pooled odds ratios (ORs) were calculated using fixed-effects and random-effects models. The primary outcome measure was MI, and a secondary analysis was also performed for acute coronary syndromes (ACS) more generally.

FINDINGS

57 studies were eligible for statistical analysis and included 17,911 cases and 24,584 controls. Carriage of the PlA2 allele was significantly associated with MI (n = 40,692; OR 1.077, 95% CI 1.024-1.132; p = 0.004) but with significant publication bias (p = 0.040). The degree of association with MI increased with decreasing age of subjects (≤45 years old: n = 9,547; OR 1.205, 95% CI 1.067-1.360; p = 0.003) and with adjustment of data for conventional cardiovascular risk factors (n = 12,001; OR 1.240, 95% CI 1.117-1.376; p<0.001). There was a low probability of publication bias for these subgroup analyses (all p<0.05).

CONCLUSIONS

The presence of significant publication bias makes it unclear whether the association between carriage of the PlA2 allele and MI is true for the total population studied. However for younger subjects, the relative absence of conventional cardiovascular risk factors results in a significant association between carriage of the PlA2 allele and MI.

Association of platelet glycoprotein receptor alpha2beta1 integrin and glycoprotein IIIa gene polymorphisms with diabetic retinopathy: evidence from 3007 subjects

PURPOSE

Many epidemiological studies have evaluated associations of platelet glycoprotein receptor alpha2beta1 integrin (ITGA2) and glycoprotein IIIa (ITGB3) gene polymorphisms with diabetic retinopathy (DR), but the published data are inconclusive. The aim of the present study was to assess the associations by using meta-analysis.

METHODS

A comprehensive electronic search (PubMed, EMBASE, Elsevier Science Direct, CNKI and Wanfang) was carried out until 31 August 2013. Odds ratios (ORs) and its 95% confidence intervals (CIs) were used to assess the strength of the associations.

RESULTS

Nine studies including 1678 cases and 1329 controls were included in the meta-analysis. Meta-analysis was performed for ITGA2 gene BgI II polymorphism (7 studies including 758 cases and 570 controls) and ITGB3 gene PlA1/A2 polymorphism (4 studies including 1047 cases and 861 controls). Significant associations were found for BgI II (+ versus -: OR = 1.42, 95% CI = 1.06-1.90, p = 0.02; +/- + +/+ versus -/-: OR = 1.46, 95% CI = 0.99-2.15, p = 0.06; +/+ versus -/- + +/-: OR = 1.90, 95% CI = 1.35-2.67, p = 0.0003) and PlA1/A2 (A2 versus A1: OR = 0.74, 95% CI = 0.52-1.07, p = 0.11; A1A2 + A2A2 versus A1A1: OR = 0.80, 95% CI = 0.64-0.99, p = 0.04; A2A2 versus A1A1 + A1A2: OR = 0.45, 95% CI = 0.27-0.75, p = 0.002) polymorphisms.

CONCLUSION

This meta-analysis demonstrates that DR is associated with ITGA2 BgI II and ITGB3 PlA1/A2 polymorphisms.

Pro32Pro33 mutations in the integrin β3 PSI domain result in αIIbβ3 priming and enhanced adhesion: reversal of the hypercoagulability phenotype by the Src inhibitor SKI-606

The plasma-membrane integrin αIIbβ3 (CD41/CD61, GPIIbIIIa) is a major functional receptor in platelets during clotting. A common isoform of integrin β3, Leu33Pro is associated with enhanced platelet function and increased risk for coronary thrombosis and stroke, although these findings remain controversial. To better understand the molecular mechanisms by which this sequence variation modifies platelet function, we produced transgenic knockin mice expressing a Pro32Pro33 integrin β3. Consistent with reports utilizing human platelets, we found significantly reduced bleeding and clotting times, as well as increased in vivo thrombosis, in Pro32Pro33 homozygous mice. These alterations paralleled increases in platelet attachment and spreading onto fibrinogen resulting from enhanced integrin αIIbβ3 function. Activation with protease-activated receptor 4- activating peptide, the main thrombin signaling receptor in mice, showed no significant difference in activation of Pro32Pro33 mice as compared with controls, suggesting that inside-out signaling remains intact. However, under unstimulated conditions, the Pro32Pro33 mutation led to elevated Src phosphorylation, facilitated by increased talin interactions with the β3 cytoplasmic domain, indicating that the αIIbβ3 intracellular domains are primed for activation while the ligand-binding domain remains unchanged. Acute dosing of animals with a Src inhibitor was sufficient to rescue the clotting phenotype in knockin mice to wild-type levels. Together, our data establish that the Pro32Pro33 structural alteration modifies the function of integrin αIIbβ3, priming the integrin for outside-in signaling, ultimately leading to hypercoagulability. Furthermore, our data may support a novel approach to antiplatelet therapy by Src inhibition where hemostasis is maintained while reducing risk for cardiovascular disease.

High on-treatment platelet reactivity in peripheral endovascular procedures

The use of aspirin is considered the "gold standard" for the decrease of major adverse cardiovascular events in patients with atherosclerosis, including peripheral arterial disease (PAD), whereas a dual-antiplatelet regimen with aspirin and clopidogrel is usually indicated for such patients after angioplasty and stent deployment. However, a substantial number of subsequent adverse events still occur, even in patients who receive double-antiplatelet therapy. The "high on-treatment platelet reactivity" (HTPR) phenomenon has been lately recognized and plays a major role in the management of patients with PAD. Greater and more rapid inhibition of platelet aggregation has become the goal for new antiplatelet agents with the expectation of further improving outcomes for percutaneous intervention for PAD. The purpose of this review article is to highlight current evidence regarding the prevalence, aetiology, and clinical implications of HTPR in PAD as well as to discuss the possibilities of novel alternative antiplatelet regiments.

ASPIRIN RESISTANCE CANDIDATE GENES AND THEIR ASSOCIATION WITH THE RISK OF CARDIOVASCULAR EVENTS

The review presents the current literature evidence on the most likely genetic polymorphisms of aspirin resistance, such as polymorphisms of cyclooxygenase, glycoproteins GP Ib/IIIa, GP Ibα, GP VI, and adenosine diphosphate receptors P2Y1 and P2Y12. The authors discuss the prevalence of these polymorphisms in laboratory and clinical aspirin resistance, as well as their association with the risk of cardiovascular events during aspirin treatment. 

Polymorphisms associated with in vitro aspirin resistance are not associated with clinical outcomes in patients with coronary artery disease who report regular aspirin use

BACKGROUND

We hypothesized that single-nucleotide polymorphisms (SNPs) associated with heightened in vitro platelet function during aspirin exposure (which we define as "laboratory aspirin resistance") would be associated with greater risk for death, myocardial infarction (MI) or stroke among patients with coronary artery disease regularly using aspirin.

METHODS

Duke Databank for Cardiovascular Disease patients with (n = 3,449, CATHeterization GENetics cohort) or without (n = 11,754, nongenetic cohort) banked DNA with ≥1 coronary stenosis >75% were followed up at 6 months, then annually for death, MI, or stroke occurring during periods of reported aspirin use. We evaluated associations of candidate SNPs from GNB3, PEAR1, ITGB3, VAV3, ITGA2, GPVI, PTGS1, F2R, THBS1, A2AR, and GP1BA with events during follow-up using Cox proportional hazards modeling adjusted for clinical characteristics associated with outcomes in the nongenetic cohort.

RESULTS

Over a median of 3.5 years, 2,762 (24%) nongenetic cohort patients and 648 (19%) CATHeterization GENetics cohort patients had the composite outcome during reported aspirin use. No candidate SNPs were significantly associated with death, MI, or stroke in either univariable or multivariable analyses. A prospective analysis demonstrated 80% to 88% power to detect a hazard ratio of ≥1.3 for minor allele carriers.

CONCLUSION

Patients with angiographically significant coronary artery disease regularly using aspirin and carrying SNPs associated with laboratory aspirin resistance were not at higher risk for death, MI, or stroke. Using these SNPs to guide more aggressive antiplatelet therapy is not justified by these results. Direct extrapolation from in vitro findings to the clinical setting should be avoided.

Mold allergen sensitization in adult asthma according to integrin β3 polymorphisms and Toll-like receptor 2/+596 genotype

BACKGROUND

Integrin β3 (ITGB3) and Toll-like receptor 2 (TLR2) are candidate genes for asthma and sensitization to mold allergens. Integrin β3 forms a complex with TLR2, and this biological interaction is required for the response of monocytes to TLR2 agonists such as fungal glucan.

OBJECTIVE

To study whether genetic interaction between single nucleotide polymorphisms (SNPs) in genes encoding the TLR2-ITGB3 complex enhances susceptibility to mold sensitization.

METHODS

Association analysis was conducted in 1243 adults (524 with asthma) who participated in the follow-up of the Epidemiological Study on the Genetics and Environment of Asthma. Allergic sensitization to mold allergens was determined by skin prick testing. Association of mold sensitization with 14 ITGB3 SNPs was tested under an additive genetic model. Interaction between ITGB3 SNPs and TLR2/+596, which was previously shown to be associated with asthma, was studied.

RESULTS

A positive skin prick test to mold was found in 115 subjects with asthma (22.0%) and in 61 subjects without asthma (8.5%). The ITGB3 rs2056131 A allele was associated with mold sensitization in subjects with asthma with an odds ratio (95% CI) of 0.60 (0.43-0.83; P = .001). Ten other ITGB3 SNPs were significantly associated with mold sensitization in TLR2/+596TT subjects with asthma (P = .03-.002), whereas much weaker associations were found in carriers of the TLR2/+596 C allele (P = .60-.04). Interaction between TLR2/+596 and these ITGB3 SNPs was statistically significant (P interaction = .05-.001).

CONCLUSION

TLR2/+596 genotype may influence the association between ITGB3 SNPs and mold sensitization in adults with asthma.

Antiplatelet drug therapy: role of pharmacodynamic and genetic testing

Antiplatelet therapy represents the cornerstone of treatment for the short- and long-term prevention of atherothrombotic disease processes, in particular in high-risk settings such as in patients with acute coronary syndrome and those undergoing percutaneous coronary intervention. Currently, dual antiplatelet therapy with aspirin and clopidogrel represents the most commonly used treatment regimen in these settings. However, a considerable number of patients continue to experience adverse outcomes, including both bleeding and recurrent ischemic events. Numerous investigations have demonstrated that this phenomenon may be, in part, attributed to the broad variability in individual response profiles to this standard antiplatelet treatment regimen, as identified by various assays of platelet function testing. In addition, recent studies have demonstrated that genetic polymorphisms may also have an important role in determining levels of platelet inhibition and may be considered as a tool to identify patients at risk of adverse events. This article provides an overview on antiplatelet drug response variability, an update on definitions, including the role of pharmacodynamic testing, underlying mechanisms – with emphasis on recent understandings on pharmacogenetics and drug–drug interactions – and current and future perspectives on individualized antiplatelet therapy.

Urinary 11-dehydro thromboxane B₂ levels in type 2 diabetic patients before and during aspirin intake

BACKGROUND

Diabetic patients commonly present an increased risk for cardiovascular events, for which aspirin is the most frequently used medication for primary prevention. Urinary 11-dehydro thromboxane (11-dhTXB₂) concentrations assess the effect of aspirin on platelets and identify patients who are at risk of cardiovascular events. The present study investigated whether or not type 2 diabetic patients who took a daily dose of 100mg of aspirin had a significant reduction in urinary 11-dhTXB₂ concentrations and whether these results were associated with clinical and laboratory variables.

METHODS

Eighty-one type 2 diabetic patients were enrolled in the study. Laboratory tests included the determination of lipidic profile, glycated hemoglobin, platelets count, molecular analysis for both GPIIbIIIa and COX-1 polymorphisms, and urinary 11-dhTXB₂.

RESULTS

Patients' median value for urinary 11-dhTXB₂ before aspirin intake was 179 pg/mg of creatinine. After 15days taking aspirin, the patients presented median of 51 pg/mg of creatinine, thus revealing a significant difference between medians (p=0.00). A reduction of 95% in urinary 11-dhTXB₂ concentrations could only be identified in 4 patients (5%). A BMI of ≥ 26 presented a significant association with a reduction of urinary 11-dhTXB₂ concentrations (p=0.010), as shown by the multiple logistic regression model. Other clinical and laboratory variables showed no association.

CONCLUSIONS

Regardless of the mechanisms related to aspirin non-responsiveness, most patients enrolled in the present study also presented a reduced or minimal response to low-dose aspirin therapy, thereby indicating a clear variability related to aspirin effectiveness. Moreover, BMI appears to be independently associated to the reduction of urinary 11-dhTXB₂ concentrations in type 2 diabetic patients taking aspirin.

A1/A2 polymorphism of the glycoprotein IIIa gene and diabetic retinopathy in Caucasians with type 2 diabetes

BACKGROUND

A PlA1/A2 polymorphism of glycoprotein IIIa is known to be involved in the pathogenesis of arterial thrombosis, myocardial infarction, stroke and type 2 diabetes, but there is no evidence of association with diabetic retinopathy. The aim of this study was to examine the role of the PlA1/A2 polymorphism of the glycoprotein IIIa gene in the development of diabetic retinopathy in Caucasians with type 2 diabetes.

DESIGN

Cross-sectional case-control study.

PARTICIPANTS

Totally 222 patients with diabetic retinopathy and 120 diabetic subjects without clinical signs of diabetic retinopathy from the Eye Clinic, University Medical Centre Ljubljana were enrolled in the study.

METHODS

Fundus examination and blood biochemical analysis were performed. The polymerase chain reaction and restriction fragment length polymorphism were used.

MAIN OUTCOME MEASURES

The total cholesterol, triglyceride, high-density lipoprotein levels, fasting blood glucose and HbA(1c) were measured, and the genotypes of the PlA1/A2 polymorphism were determined.

RESULTS

Patients with diabetic retinopathy had earlier onset, longer duration of type 2 diabetes and a higher incidence of insulin therapy compared to the diabetic patients without diabetic retinopathy. A significantly lower frequency of the A2A2 genotype of glycoprotein IIIa was found in diabetic patients with retinopathy compared to those without retinopathy (odds ratio = 0.49, 95% confidence interval = 0.28-0.89; P = 0.018).

CONCLUSIONS

The A2A2 genotype of the glycoprotein IIIa polymorphism was associated with lower risk for diabetic retinopathy in Caucasians with type 2 diabetes. Further studies are needed to elucidate its protective role in the development of diabetic retinopathy in Caucasians.

Platelet gene polymorphisms and risk of bleeding in patients undergoing elective coronary angiography: a genetic substudy of the PRAGUE-8 trial

AIM

Utilization of cardiac catheterization has increased dramatically over time. Bleeding is a major prognostic predictor after percutaneous coronary catheterization procedures. This study aimed to assess the impact of eight polymorphisms of genes encoding platelet receptors and enzymes on the risk of bleeding in patients undergoing elective coronary angiography (CAG).

METHODS

Polymorphisms of platelet receptors, GP Ia (807C>T, rs1126643), GP VI (13254T>C, rs1613662), GP IIIa (HPA-1, rs5918), PAR-1 (IVS-14A>T, rs168753), P2Y(12) (34C>T, rs6785930 and H1/H2 haplotype, rs2046934), and genetic variations of the gene coding for cyclooxygenase-1 (COX-1) (-842A>G, rs10306114 and 50C>T, rs3842787) were studied. The frequencies of gene polymorphisms carriers were investigated in 696 patients undergoing elective CAG because of suspected or proven stable coronary artery disease. Genotyping was done using PCR, followed by melting curve analysis with specific fluorescent hybridization probes.

RESULTS

In patients undergoing elective CAG (without ad hoc percutaneous coronary intervention (PCI) and without clopidogrel pretreatment) a significant association was found between bleeding risk and variations in the gene coding for COX-1 (-842A>G and 50C>T) (both p=0.013). Six other investigated polymorphisms did not show any influence on bleeding complications. After controlling for potential bleeding confounders, the association between COX-1 gene polymorphisms (-842A>G and 50C>T) and bleeding risk remained statistically significant (both odds ratios 12.1, p=0.012).

CONCLUSION

Cyclooxygenase-1 -842G and 50T alleles significantly contribute to the risk of bleeding complications in patients undergoing elective CAG. Genetic testing is able to influence the safety of diagnostic cardiac catheterization in large numbers of low risk patients with borderline indications.

Platelet aspirin resistance in ED patients with suspected acute coronary syndrome

BACKGROUND

Platelet aspirin resistance is reported to be as high as 45%. The prevalence of emergency department (ED) platelet aspirin resistance in suspected acute coronary syndrome (ACS) is not described. Our purpose was to determine the prevalence of platelet aspirin resistance.

METHODS

We determined platelet aspirin resistance in a convenience sample of ED suspected ACS patients. Eligible patients had longer than 10 minutes of chest pain or an ischemic equivalent. Two hours after receiving 325 mg of aspirin, blood was assessed for platelet function (Accumetrics, San Diego, CA). Definitions are as follows: aspirin resistance, at least 550 aspirin reaction units; positive troponin T, greater than 0.1 ng/mL; significant coronary lesion, at least 70% stenosis. The composite end point was prospectively defined as a 30-day revisit, positive cardiac catheterization, or hospital length of stay (LOS) longer than 3 days.

RESULTS

Of 200 patients, 50.5% were male, 50.0% were black, troponin T was positive in 7.5%, cardiac catheterization was done in 10.5%, and 33.3% had a significant stenosis. Final diagnoses were noncardiac in 83.4%, stable angina in 8.0%, and unstable angina in 8.5%. Overall, 6.5% were resistant to aspirin; and high-risk patients trended to more aspirin resistance than non-high-risk patients (23.1% [3] vs 9.1% [17]; P value 95% confidence interval [CI], -0.0929 to 0.373). One-month follow-up found ED revisits in 12.5% of aspirin-resistant vs 4.9% of non-aspirin-resistant patients (95% CI, -0.114 to 0.182) and rehospitalization in 12.5% of resistant patients vs 4.3% of nonresistant patients (P value 95% CI, -0.108 to 0.187). Although LOS was similar at index admission, if rehospitalized, LOS was 6.5 for aspirin-resistant patients vs 3.2 days in nonresistant patients (P < .0001).

CONCLUSION

This first report of platelet aspirin resistance in patients presenting to the ED with suggested ACS finds that it is present in 6.5% of patients.

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.

Stroke pharmacogenomics

Circulatory disease accounts for fifteen million deaths each year, of which stroke accounts for four and a half million- with an estimated nine million stroke survivors annually. The overall incidence rate of stroke is 2 to 2.5 per thousand adults with an approximate prevalence of 5 per thousand and an estimated 5-year risk of stroke recurrence of 15 to 40 percent. Conventional risk factors for stroke include: increasing age, hypertension, diabetes mellitus, smoking, increased body mass index, ischemic heart disease, heart failure, atrial fibrillation and lack of physical activity. Age is the strongest risk factor for both ischemic and haemorrhagic stroke with its incidence doubling for each successive decade after the age of fifty-five years. However, there is a substantial portion of patients with significant cerebrovascular disease who do not have any of these stroke risk-factors, leading to the speculation that there are other factors that have not been identified yet So as to improve diagnosis and treatment strategies, as well as to reduce the related public health burden, it could be helpful to successfully identify its extremely complex genetic determinants (polygenic, multiple genes play a role). Pharmacogenetics is the field of pharmacology that deals with the influence of genetic variation on drug response by correlating gene expression and gene variants with the efficacy or toxicity of drugs. The principle drugs in stroke medicine are antithrombotics. The aim of this paper was to review the most commonly used drugs for stroke such as rtPA in the acute phase as well as antiplatelets and wafarin for secondary prophylaxis.

The Leu33Pro polymorphism in the ITGB3 gene does not modify BRCA1/2-associated breast or ovarian cancer risks: results from a multicenter study among 15,542 BRCA1 and BRCA2 mutation carriers

Integrins containing the beta(3) subunit are key players in tumor growth and metastasis. A functional Leu33Pro polymorphism (rs5918) in the beta(3) subunit of the integrin gene (ITGB3) has previously been suggested to act as a modifier of ovarian cancer risk in Polish BRCA1 mutation carriers. To investigate the association further, we genotyped 9,998 BRCA1 and 5,544 BRCA2 mutation carriers from 34 studies from the Consortium of Investigators of Modifiers of BRCA1/2 for the ITGB3 Leu33Pro polymorphism. Data were analysed within a Cox-proportional hazards framework using a retrospective likelihood approach. There was marginal evidence that the ITGB3 polymorphism was associated with an increased risk of ovarian cancer for BRCA1 mutation carriers (per-allele Hazard Ratio (HR) 1.11, 95% CI 1.00-1.23, p-trend 0.05). However, when the original Polish study was excluded from the analysis, the polymorphism was no longer significantly associated with ovarian cancer risk (HR 1.07, 95% CI 0.96-1.19, p-trend 0.25). There was no evidence of an association with ovarian cancer risk for BRCA2 mutation carriers (HR 1.09, 95% CI 0.89-1.32). The polymorphism was not associated with breast cancer risk for either BRCA1 or BRCA2 mutation carriers. The ITGB3 Leu33Pro polymorphism does not modify breast or ovarian cancer risk in BRCA1 or BRCA2 mutation carriers.

Genomic view of factors leading to plaque instability

The manifestations of coronary artery disease are varied. They all arise as a consequence of the deposition of atherosclerotic plaque within the vessel wall. The most feared sequela of coronary artery disease is sudden and unexpected death in the ostensibly healthy patient. Plaque rupture of hemodynamically insignificant atherosclerotic plaques and ensuing thrombosis is likely responsible for a large proportion of such deaths. Identifying populations at increased risk for sudden death would represent a major advance. Such screening is contingent upon identification of DNA sequence variants that predispose individuals to plaque rupture. Phenotyping is not sufficiently nuanced to detect such variants on a large scale, so we are limited to end points that are crude surrogates for plaque rupture. As imaging modalities are refined and our ability to recruit large numbers of appropriate patients is facilitated by the formation of alliances, our ability to probe this conundrum via a genome-wide approach will improve.

Pharmacogenetics in cardiovascular antithrombotic therapy

Thrombosis is the most important underlying mechanism of coronary artery disease and embolic stroke. Hence, antithrombotic therapy is widely used in these scenarios. However, not all patients achieve the same degree of benefit from antithrombotic agents, and a considerable number of treated patients will continue to experience a new thrombotic event. Such lack of clinical benefit may be related to a wide variability of responses to antithrombotic treatment among individuals (i.e., interindividual heterogeneity). Several factors have been identified in this interindividual heterogeneity in response to antithrombotic treatment. Pharmacogenetics has emerged as a field that identifies specific gene variants able to explain the variability in patient response to a given drug. Polymorphisms affecting the disposition, metabolism, transporters, or targets of a drug all can be implicated in the modification of an individual's antithrombotic drug response and therefore the safety and efficacy of the aforementioned drug. The present paper reviews the modulating role of different polymorphisms on individuals' responses to antithrombotic drugs commonly used in clinical practice.

Aspirin resistance in coronary artery disease is correlated to elevated markers for oxidative stress but not to the expression of cyclooxygenase (COX) 1/2, a novel COX-1 polymorphism or the PlA1/2polymorphism

Aspirin resistance (AR) is estimated to be present in 5-75% of patients and is related to increased cardiovascular mortality. However, the underlying mechanisms are mostly unknown. In the present study, AR was detected in 14 out of 55 patients (25%) with coronary artery disease. The presence of concomitant anti-inflammatory drugs did not affect AR. Plasma levels of thromboxane B(2) as well as the markers for oxidative stress and known platelet activators 8-isoprostane and lipid peroxidation products were significantly higher in aspirin-resistant individuals (349.3 pg/ml, 53.9 pg/ml, and 538 micromol/l) compared to controls (113.7 pg/ml, 10.3 pg/ml, and 32.2 micromol/l; P < 0.05, respectively). Platelet cyclooxygenase-1 (COX-1) and COX-2 mRNA and protein expression were without significant differences between the two groups. DNA sequencing detected a novel platelet COX-1 single nucleotide polymorphism (SNP) resulting in amino acid exchange at position 8 (Arg8/Trp8). The wild-type as well as the heterozygous and homozygous SNP were present in both patient groups without significant differences. The aspirin binding (Arg120) and acetylation site (Ser529) were unaffected in the samples tested. Neither was AR related to the platelet integrin PlA(1)/A(2) polymorphism. In conclusion, AR appears to be unrelated to differences in platelet COX-1 and COX-2 expression or to a novel platelet COX-1 SNP and the PlA(1)/A(2) SNP. However, a correlation exists to elevated eicosanoids generated by oxidative stress indicating COX-1-independent pathways for the generation of platelet activating molecules represent a potential cause for AR.

Prospective, observational study of antiplatelet and coagulation biomarkers as predictors of thromboembolic events after implantation of ventricular assist devices

BACKGROUND

Long-term success in ventricular assist device (VAD) recipients is limited by thromboembolic events, the prediction of which remains elusive. We evaluated the predictive value of aspirin hyporesponsiveness and markers of coagulation and fibrinolysis.

METHODS

We prospectively enrolled patients scheduled to undergo VAD implantation between June 2004 and March 2006. Once before surgery, daily during hospitalization, and weekly after discharge we assessed platelet function, measured prothrombin activation fragment 1.2 (F1.2) and plasminogen activator inhibitor-1 (PAI-1) concentrations, and evaluated aspirin hyporesponsiveness by whole-blood aggregometry and thromboelastography. All patients received 325 mg oral aspirin daily from at least 7 days before VAD implantation. Follow-up continued until heart transplantation, death or closure of the database.

RESULTS

We included 26 patients (median follow-up 315 days, range 9-833 days). In eight (31%) patients, 14 thromboembolic events occurred at a median of 42 (interquartile range 26-131) days. Only six (43%) events based on whole-blood aggregometry and one (7%) based on thromboelastography coincided with aspirin hyporesponsiveness. Within-patient variability was high for both tests (59% and 567%, respectively). Compared with levels before surgery, PAI-1 concentrations were raised for up to 45 days (P <0.0001) and those of F1.2 for up to 3 days (P = 0.0001) after VAD implantation. PAI-1 and F1.2 levels did not rise significantly further before thromboembolic events.

CONCLUSIONS

Aspirin hyporesponsiveness was not associated with raised risk of future clinical thromboembolic events after VAD implantation. Impaired fibrinolysis, demonstrated by raised PAI-1 concentrations, might, however, indicate a predisposition to such events early after surgery.

Systemic blood coagulation activation in acute coronary syndromes

We evaluated systemic alterations to the blood coagulation system that occur during a coronary thrombotic event. Peripheral blood coagulation in patients with acute coronary thrombosis was compared with that in people with stable coronary artery disease (CAD). Blood coagulation and platelet activation at the microvascular injury site were assessed using immunochemistry in 28 non-anticoagulated patients with acute myocardial infarction (AMI) versus 28 stable CAD patients matched for age, sex, risk factors, and medications. AMI was associated with increased maximum rates of thrombin-antithrombin complex generation (by 93.8%; P< .001), thrombin B-chain formation (by 57.1%; P< .001), prothrombin consumption (by 27.9%; P= .012), fibrinogen consumption (by 27.0%; P= .02), factor (f) Va light chain generation (by 44.2%; P= .003), and accelerated fVa inactivation (by 76.1%; P< .001), and with enhanced release of platelet-derived soluble CD40 ligand (by 44.4%; P< .001). FVa heavy chain availability was similar in both groups because of enhanced formation and activated protein C (APC)-mediated destruction. The velocity of coagulant reactions in AMI patients showed positive correlations with interleukin-6. Heparin treatment led to dampening of coagulant reactions with profiles similar to those for stable CAD. AMI-induced systemic activation of blood coagulation markedly modifies the pattern of coagulant reactions at the site of injury in peripheral vessels compared with that in stable CAD patients.

Prothrombotic polymorphisms, mutations, and their association with pediatric non-cardioembolic stroke in Asian-Indian patients

Genes involved in the hemostatic mechanism are logical candidate genes for association studies in prothrombotic conditions such as stroke. Since the underlying etiology in pediatric strokes is different than adults, looking for genetic causes would be the logical thing to do in the pediatric stroke population. Fifty-eight Asian-Indian stroke patients below 15 years of age and equal number of age- and sex-matched healthy controls were the subjects for the study. The subjects were screened for 13 polymorphisms and three mutations spread across seven different candidate genes involved in the hemostatic system. Of the 13 polymorphisms and three mutations studied, four polymorphisms, HPA-I, TAFI 147Ala>Thr, methylene tetrahydrofolate reductase (MTHFR) 677 C>T, and MTHFR 1298 A>C, showed significant association with the disease phenotype. MTHFR 677 C>T showed the strongest association and therefore may have a strong predisposing role for pediatric strokes. Gene-gene interaction studies showed a strong interaction between HPA-I and MTHFR 677 C>T polymorphism. The wild type of both these polymorphisms synergistically showed a strong protective effect [p < 0.0001, O.R: 10.06(4.26-23.71)]. Polymorphisms in HPA-I and MTHFR may have important predisposing roles in the development of pediatric stroke.

Hyperglycemia is associated with enhanced thrombin formation, platelet activation, and fibrin clot resistance to lysis in patients with acute coronary syndrome

OBJECTIVE

Acute hyperglycemia on admission for acute coronary syndrome worsens the prognosis in patients with and without known diabetes. Postulated mechanisms of this observation include prothrombotic effects. The aim of this study was to evaluate the effect of elevated glucose levels on blood clotting in acute coronary syndrome patients.

RESEARCH DESIGN AND METHODS

We studied 60 acute coronary syndrome patients within the first 12 h after pain onset, including 20 subjects with type 2 diabetes, 20 subjects with no diagnosed diabetes but with glucose levels >7.0 mmol/l, and 20 subjects with glucose levels <7.0 mmol/l. We determined generation of thrombin-antithrombin complexes (TATs) and soluble CD40 ligand (sCD40L), a platelet activation marker, at the site of microvascular injury, together with ex vivo plasma fibrin clot permeability and lysis time.

RESULTS

The acute coronary syndrome patients with no prior diabetes but elevated glucose levels had increased maximum rates of formation and total production of TATs (by 42.9%, P < 0.0001, and by 25%, P < 0.0001, respectively) as well as sCD40L release (by 16.2%, P = 0.0011, and by 16.3%, P < 0.0001, respectively) compared with those with normoglycemia, whereas diabetic patients had the highest values of TATs and sCD40L variables (P < 0.0001 for all comparisons). Patients with hyperglycemia, with no previously diagnosed diabetes, had longer clot lysis time (by approximately 18%, P < 0.0001) similar to that in diabetic subjects, but not lower clot permeability compared with that in normoglycemic subjects.

CONCLUSIONS

Hyperglycemia in acute coronary syndrome is associated with enhanced local thrombin generation and platelet activation, as well as unfavorably altered clot features in patients with and without a previous history of diabetes.

Pharmacogenomics of platelet responsiveness to aspirin

Aspirin is the most widely used drug in the world for cardiovascular protection. Aspirin's ability to suppress platelet function varies widely among individuals and lesser suppression of platelet function is associated with increased risk of myocardial infarction, stroke and cardiovascular death. Platelet response to aspirin is a complex phenotype involving multiple genes and molecular pathways. Aspirin response phenotypes can be categorized as directly or indirectly related to cyclooxygenase-1 (COX-1) activity, with phenotypic variation indirectly related to COX-1 being much more prominent. Recent data indicate that variability in platelet response to aspirin is genetically determined, but the specific gene variants that contribute to phenotypic variation are not known. An understanding of the relationship between genotype, aspirin response phenotype and clinical outcome will help to bring about a personalized approach to antiplatelet therapy that maximizes antithrombotic benefit whilst minimizing bleeding risk for individual patients.

Pharmacogenetics of aspirin resistance: a comprehensive systematic review

AIMS

The aim was to perform a systematic review of all candidate gene association studies in aspirin resistance.

METHODS

Electronic databases were searched up until 1 December 2007 for all studies investigating any candidate gene for aspirin resistance in humans. Aspirin resistance was required to have been measured by a standardized laboratory technique to be included in the analysis.

RESULTS

Within 31 studies, 50 polymorphisms in 11 genes were investigated in 2834 subjects. The PlA1/A2 polymorphism in the GPIIIa platelet receptor was the most frequently investigated, with 19 studies in 1389 subjects. The PlA1/A2 variant was significantly associated with aspirin resistance when measured in healthy subjects [odds ratio (OR) 2.36, 95% confidence interval (CI) 1.24, 4.49; P = 0.009]. Combining genetic data from all studies (comprising both healthy subjects and those with cardiovascular disease) reduced the observed effect size (OR 1.14, 95% CI 0.84, 1.54; P = 0.40). Moreover, the observed effect of PlA1/A2 genotype varied depending on the methodology used for determining aspirin sensitivity/resistance. No significant association was found with aspirin resistance in four other investigated polymorphisms in the COX-1, GPla, P2Y1 or P2Y12 genes.

CONCLUSIONS

Our data support a genetic association between the PlA1/A2 molecular variant and aspirin resistance in healthy subjects, with the effect diminishing in the presence of cardiovascular disease. The laboratory methodology used influences the detection of aspirin resistance. However, as heterogeneity was significant and our results are based on a limited number of studies, further studies are required to confirm our findings.

Platelet fragmentation requires a specific structural conformation of human monoclonal antibody against beta3 integrin

We have described an autoantibody against beta3 (GPIIIa49-66), a region of platelet integrin alphaIIbbeta3 that is unique. It induces platelet fragmentation in the absence of complement via antibody activation of platelet NADPH oxidase and 12-lipoxygenase to release reactive oxygen species, which destroy platelets. To study the mechanism of anti-GPIIIa antibody-induced platelet fragmentation, we screened a human single chain Fv antibody library with the GPIIIa49-66 peptide. Nine monoclonal antibodies were identified that were capable of binding to GPIIIa49-66. Surprisingly, binding avidity for GPIIIa49-66 did not correlate with activity of induction of platelet fragmentation. We therefore investigated the requirements for platelet fragmentation. Mutations were introduced into the heavy chain complementary-determining region-3 of clones 11, 43, and 54 by site-directed mutagenesis. The capability of these clones to induce platelet fragmentation or bind to GPIIIa49-66 subsequently changed. Molecular modeling of these clones with their mutants revealed that the ability to induce platelet fragmentation is affected by the side chain orientation of positively charged amino acids in the heavy chain of residues 99-102. Thus, a structural change in the conformation of anti-GPIIIa49-66 antibody contributes to its binding to the beta3 integrin and subsequent antibody-induced platelet fragmentation and aggregate dissolution.

Prevalence and risk factors for aspirin and clopidogrel resistance in cerebrovascular stenting

BACKGROUND AND PURPOSE

The prevalence of antiplatelet drug resistance among patients who undergo cerebrovascular stent placement is unknown. We aimed to assess the feasibility of monitoring antiplatelet drug effects in a single-center cohort undergoing cerebrovascular stent placement.

MATERIALS AND METHODS

We prospectively collected medical, laboratory, and radiographic data on patients who underwent cerebrovascular stent placement. We used the rapid platelet function assay-aspirin (RPFA-ASA) to calculate aspirin reaction units (ARU) and the P2Y12 assay to calculate P2Y12 reaction units and percentage platelet inhibition. Aspirin resistance was defined as ARU > 550, whereas clopidogrel resistance was defined as percentage platelet inhibition < 40%.

RESULTS

Among 76 patients, stent indications were the following: wide-neck aneurysm (57, 75.0%), symptomatic intracranial stenosis (12, 15.7%), carotid stenosis (5, 6.6%), and vertebral stenosis (2, 2.6%). For aspirin, the median dosage per week was 1300 mg and median ARU was 410. Among 71 patients on aspirin, 3 patients (4.2%) were resistant; there was a significant inverse correlation between aspirin dose and ARU (r = -0.31, P = .01). Among 55 patients on clopidogrel, the median dosage per week was 525 mg with a mean platelet inhibition of 43.2%. Twenty-eight patients (51.9%) were clopidogrel-resistant. In a multivariable linear regression model, age older than 55 years (b = -16.3, P = .020) and diabetes (b = -26.8, P = .015) were inversely related to percentage platelet inhibition.

CONCLUSIONS

Using point-of-care tests, we found that aspirin resistance is relatively uncommon, whereas clopidogrel resistance occurred in half of patients undergoing cerebrovascular stent placement. Further studies should focus on ideal doses, timing, and duration of antiplatelet therapy for cerebrovascular stent placement.

Abnormal PFA-100 closure time is associated with increased platelet aggregation in patients presenting with chest pain

BACKGROUND

Antiplatelet therapy has been proven to be effective for both primary and secondary prevention of myocardial infarction, stroke, and cardiovascular death. However, a significant proportion of patients treated with aspirin experience ischemic events. A number of prospective studies have demonstrated that decreased responsiveness to antiplatelet therapy as measured by various methods, is strongly associated with an increase in clinical events. Our objective was to characterize platelet function in patients presenting with chest pain using a point-of-care assay, PFA-100 and correlating results to traditional platelet aggregometry to determine if patients with aspirin non-responsiveness have increased clinical sequelae.

METHODS

Platelet function was assessed using PFA-100, flow cytometry, and optical aggregometry in 94 patients presenting to the emergency department with chest pain. All patients were on aspirin 81-325 mg daily. Clinical events occurring during the index hospitalization were documented.

RESULTS

Forty-seven patients (50%) were defined as aspirin non-responders by PFA-100 (collagen-epinephrine closure time <or= 193). Compared to aspirin responders, aspirin non-responders had higher levels of mean platelet aggregation to adenosine diphosphate (ADP) (P = 0.004) and high dose epinephrine (P = 0.03). Furthermore, expression of PAC-1 was significantly increased in patients with aspirin nonresponse as compared to aspirin responders (P = 0.003 and P = 0.0006 respectively). No significant difference in clinical events during the index hospitalization was noted between aspirin non-responders and aspirin responders.

CONCLUSION

Patients presenting with chest pain who have abnormal PFA-100 closure times have increased platelet aggregation and activation however this aspirin non-responsiveness does not correlate with increased clinical events in the index hospitalization.

Genetics of coagulation: considerations for cardiac surgery

Genetic variants in the coagulation system have been known since antiquity. Today, because of modern improvements in diagnosis and medical management, the clinician is likely to encounter a spectrum of coagulation factor deficiencies and identified polymorphic variants in the surgical population. Because perioperative hemorrhagic and thrombotic complications are potentially serious, it is important to understand the role that these defects and variants may play in predicting risk and optimizing patient management. The implications of coagulation genetics on the perioperative management of the cardiac surgery patient are reviewed.

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.