PlA2 Polymorphism Research Articles

Platelet PlA2 polymorphism and platelet activation are associated with increased troponin I release after cardiopulmonary bypass.

The PlA2 polymorphism of platelet glycoprotein IIIa has been identified as a prothrombotic risk factor in a number of cardiovascular settings. The aim of this study was to determine whether the PlA2 polymorphism of platelet glycoprotein IIIa and degree of platelet activation were associated with more severe myocardial injury as indicated by troponin I release following cardiopulmonary bypass. The PlA2 genotype was determined in 66 patients undergoing elective coronary artery bypass grafting requiring cardiopulmonary bypass. Troponin I concentrations and the percentage of circulating, activated (CD62P+) platelets were measured at predetermined intervals perioperatively. Forty-six patients were Pl(A1,A1), and 20 were Pl(A1,A2) or Pl(A2,A2). Patients with at least one PlA2 allele had significantly greater postoperative troponin I concentrations than PlA1 homozygotes (P = 0.006, analysis of variance). Peak troponin I concentrations also correlated significantly with the increase in circulating, activated platelets (P = 0.02, Spearman rank correlation). The PlA2 allele of platelet glycoprotein IIIa is associated with higher troponin I concentrations following cardiopulmonary bypass surgery, suggesting that this platelet polymorphism contributes to perioperative myocardial injury.

Antagonists of platelet fibrinogen receptor are less effective in carriers of Pl A2 polymorphism of β 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-α-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.

Reduced inhibition by abciximab in platelets with the PlA2 polymorphism

Background The PlA2 polymorphism of the glycoprotein IIb/IIIa (fibrinogen) receptor has been associated with increased restenosis and stent thrombosis. We postulated that this allele could alter the antiplatelet effect of abciximab in patients undergoing percutaneous coronary intervention. Methods Optical platelet aggregation assays, Ultegra (Accumetrics, San Diego) rapid platelet function assays, and radiometric abciximab binding assays were performed in 66 PlA1/A1 and 21 PlA1/A2 patients undergoing percutaneous coronary interventions. The affinity of abciximab for the PlA1 and PlA2 receptors was determined with use of transfected cells. Results Compared with PlA1/A1 homozygotes, PlA1/A2 platelets were less completely inhibited after abciximab bolus (P =.002) and at 24 hours (P =.02) as assessed by the rapid platelet function assays. Optical aggregation assays confirmed that PlA1/A2 platelets were less completely inhibited after abciximab bolus (P =.05). The radiometric abciximab binding assay demonstrated that the PlA1/A2 platelets had fewer baseline fibrinogen receptors than did the PlA1/A1 platelets (P =.04) and more free fibrinogen receptors at 24 hours (P =.008). Cells transfected to express homozygous PlA1 or PlA2 demonstrated a nonsignificant trend (P =.12) for reduced abciximab affinity for PlA2. Conclusions PlA1/A2 platelets are less completely inhibited with abciximab, contributing to the observed interindividual variability in platelet function inhibition. Because the extent of platelet inhibition is an independent predictor for the risk of major adverse coronary events after percutaneous coronary intervention, the relative resistance of PlA2-positive platelets may contribute to a less favorable outcome in these patients. (Am Heart J 2002;143:76-82.)

Effect of the PlA2 alloantigen on the function of β3-integrins in platelets

AbstractThe polymorphism responsible for the PlA2 alloantigen on the β3-component of β3-containing integrins is reported to be a risk factor for coronary thrombosis. This study examined the effect of PlA2 on the function of β3-integrins using platelets from subjects homozygous and heterozygous for PlA1 and PlA2. There was overlap in the distribution of the dissociation constant (Kd) and maximum fibrinogen binding (Bmax) values for fibrinogen binding to αIIbβ3 on platelets from PlA1 and PlA2 homozygotes and PlA1/PlA2 heterozygotes. However, whereas there was no statistical difference in these values for the PlA1homozygotes and PlA2 heterozygotes, the Kd for the PlA2 homozygotes was significantly lower than that for the PlA1/PlA2 heterozygotes, but was not statistically different from that for the PlA1 homozygotes. No differences were detected in ADP sensitivity between platelets from PlA1 homozygotes and PlA1/PlA2heterozygotes, in the IC50 for RGDS inhibition of fibrinogen binding to αIIbβ3, in the αvβ3-mediated adhesion of platelets to osteopontin and vitronectin, and in the phorbol ester-stimulated adhesion to fibrinogen of B lymphocytes expressing αIIbβ3 containing either the PlA1 or the PlA2 polymorphism. Finally, no differential effects of PlA2 on turbidometric platelet aggregation, platelet secretion, or platelet thrombus formation were found as measured in the PFA-100. Because no differences were detected in the ability of β3-integrins to interact with ligands based on the presence or absence of the PlA2 polymorphism, the results suggest that factors unrelated to β3-integrin function may account for the reported association of the PlA2 allele with coronary thrombosis.

Platelet Pl A2 polymorphism enhances risk of neurocognitive decline after cardiopulmonary bypass

Background. Neurocognitive decline, often produced by atherosclerotic plaque embolization, remains a frequent complication of cardiopulmonary bypass. Plaque fragments may initiate local thrombosis, which, in turn, aggravates the embolic insult. Prothrombotic genetic factors may exacerbate this process. We investigated whether the Pl A2 polymorphism of platelet GPIIIa, a prothrombotic risk factor in other cardiovascular settings, is associated with early neurocognitive decline after cardiopulmonary bypass. Methods. Neurocognitive changes were evaluated by the Mini-Mental State Examination administered preoperatively and on postoperative day 4 and the Pl A genotype determined in 70 patients undergoing cardiopulmonary bypass. Results. Forty-nine patients were Pl A1/A1, and 21 were Pl A1/A2 or Pl A2/A2. Fifty-two patients (74%) demonstrated post–cardiopulmonary bypass neurocognitive decline, of which 34 were Pl A1/A1 and 18 were Pl A1/A2 or Pl A2/A2. Multivariate analysis revealed that the Pl A2 genotype and baseline Mini-Mental State Examination were significantly associated with greater neurocognitive decline (decreased Mini-Mental State Examination scores, p = 0.036 and 0.024, respectively). Conclusions. This study demonstrates a link between the Pl A2 allele of platelet GPIIIa and more severe neurocognitive decline after cardiopulmonary bypass. Although the mechanism is unknown, it could represent exacerbation of platelet-dependent thrombotic processes associated with plaque embolism.

The PlA polymorphism of glycoprotein IIIa functions as a modifier for the effect of estrogen on platelet aggregation.

Although estrogen has been shown to contribute to retardation of the development of coronary heart disease in premenopausal women, the efficacy of hormone replacement therapy for coronary heart disease prevention in women with established coronary heart disease remains controversial. Hence, additional research is needed to clarify the effects of hormone replacement therapy on the cardiovascular and clotting systems. We investigated the effect of estrogen on platelet aggregation induced by standard agonists (epinephrine and adenosine diphosphate), with and without the platelet antagonist aspirin. Furthermore, we analyzed our data according to the presence or absence of a prevalent polymorphism of the glycoprotein (GP) IIIa subunit of the platelet fibrinogen receptor GPIIb-IIIa, PlA2. The effect of estrogen on aggregation of platelets was studied in healthy men (n = 20, 10 PlA1/A1 and 10 PlA1/A2) and premenopausal healthy women (n = 10, 5 PlA1/A1 and 5 PlA1/A2). The PlA1/A1 and PlA1/A2 individuals were matched for age and race. Platelet response to agonists was investigated in the presence of (1) estrogen (10(-11) to 10(-8) mol/L), (2) aspirin (0.056 to 56 micromol/L), (3) estrogen plus aspirin, and (4) estrogen plus ICI 182 780 (ICI, 10(-9) mol/L, an inhibitor of the estrogen receptor). We found that physiologic concentrations of estrogen strongly and significantly inhibited the aggregation of PlA1/A2 platelets (P<.005 for epinephrine and P<.05 for adenosine diphosphate, induced aggregation, respectively) in both men and women. Concentrations of estrogen that were 1000-fold greater were required to observe the same level of inhibition with PlA1/A1 platelets. In the presence of aspirin, estrogen failed to provide additional inhibitory effect on aggregation of both PlA1/A1 and PlA1/A2 platelets. The estrogen-specific inhibitor ICI blocked the effect of estrogen on aggregation, suggesting that this effect is mediated by the estrogen receptor. Estrogen inhibits the aggregation of platelets, but such inhibition is highly dependent on the presence or absence of the PlA2 polymorphism of GPIIIa. However, in the presence of aspirin, the inhibitory effect of estrogen on aggregation was no longer detectable.

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

This meta-analysis examined all the published reports up to October 1999 that studied the association between PlA2 polymorphism of platelet glycoprotein IIIa gene and myocardial infarction. The PlA2 polymorphism was not found to be associated with an increased risk of myocardial infarction, either overall or in selected subgroups, which were patients with premature disease onset (age < or = 60 years), first acute myocardial infarction, and patients who were men, women, and exclusively Caucasian.

Higher prevalence of GPIIIa PlA2 polymorphism in siblings of patients with premature coronary heart disease.

The Pl(A2) polymorphism of GPIIIa has been associated with unstable coronary syndromes in some studies, but the association has remained debated. None of the previous studies have focused on families at high risk. Risk factors tend to cluster within kindreds with high prevalence of premature coronary heart disease (CHD). Therefore, a heightened prevalence of the Pl(A2) polymorphism among siblings of patients with CHD would support the hypothesis that Pl(A2) is linked, directly or indirectly, to CHD. To measure the prevalence of the Pl(A2) polymorphism among siblings of patients with CHD before the age of 60 years and to seek an association between the Pl(A2) polymorphism and established atherosclerotic and thrombogenic risk factors. From January 1994 to April 1996, we genotyped 116 asymptomatic siblings (60 Caucasians, 56 Afro-Caribbeans) of patients with CHD manifestations before the age of 60 years for the Pl(A) polymorphism (also called HPA-1). A control cohort was used for comparison, consisting of individuals that were matched for race and geographic area but were free of CHD (n = 268, 168 Caucasians and 100 Afro-Caribbeans). In addition, we have characterized the sibling cohort for other atherogenic and thrombogenic risk factors. The prevalence of Pl(A2)-positive individuals (Pl(A2)[+], Pl(A1/A2) heterozygotes plus Pl(A2/A2) homozygotes) in the sibling cohort was high: 41.4%. When analyzed separately, the prevalence of Pl(A2)(+) siblings was 53.3% among Caucasians and 28.6% among Afro-Caribbeans. There was no association between Pl(A2) and other established atherogenic or thrombogenic risk factors. Interestingly, the clustering of other risk factors was lesser among Pl(A2)(+) siblings than their Pl(A1) counterparts. This study supports the hypothesis that the prevalence of Pl(A2)(+) individuals is high in kindreds with premature CHD. Hence, like the established risk factors that tend to cluster in families with premature CHD and contribute strongly to the accelerated atherosclerotic process affecting these individuals, the Pl(A2) polymorphism of GPIIIa may represent an inherited risk that promotes the thromboembolic complications of CHD. That these asymptomatic Pl(A2)(+) siblings had overall less established risk factors than their Pl(A1) counterparts might represent an explanation for why they remained asymptomatic despite their Pl(A2) positivity.

The PlA2 polymorphism of the platelet glycoprotein IIIA gene as a risk factor for acute renal allograft rejection.

Glycoprotein IIIa/IIb is a membrane receptor for fibrinogen and von Willebrand factor that plays an important role in platelet aggregation. The beta integrin chain of this receptor, GPIIIa, is polymorphic, and the allele known as PlA2 has been associated with coronary thrombosis. The GPIIIa genotype of a cohort of 119 consecutive renal allograft recipients (46.3 +/- 13 yr; 85 M/34 F; 24.4% diabetic patients) was determined by PCR-restriction fragment length polymorphism, and those patients were followed for at least 12 mo. From 119 patients with at least 1 yr of follow-up, those who suffered an acute rejection (n = 52) showed a lower proportion of HLA-DR beta1 identity with the donor (7.7% versus 23.9%; P = 0.03), a higher proportion of cytomegalovirus-positive (CMV+) donors/CMV- recipients (21% versus 7.5%; P = 0.05), and the PlA2 allele was more frequent (48.1% versus 26.9%; P = 0.02) compared with patients free of acute rejection (n = 67). No other variable was associated with acute rejection in the univariate analysis. The impact of the three above-mentioned significant variables on acute rejection was analyzed by stepwise logistic regression. The presence of the PlA2 allele yielded an odds ratio of 2.75 (95% confidence interval, 1.01 to 7.93) and an HLA-DR beta1 identity of 0.2 (95% confidence interval, 0.06 to 0.99) for suffering an acute rejection episode. In addition, the serum creatinine at discharge was higher in PlA2-positive versus PlA2-negative patients (2.2 +/- 1.6 versus 1.5 +/- 0.6 mg/dl, respectively; P = 0.01), and the prevalence of proteinuria >1.5 g/d 1 yr after transplantation was significantly higher among patients showing the PlA2 allele (16% versus 3%; P = 0.02). Finally, in the entire cohort of patients, the 2-yr graft survival was significantly lower in PlA2-positive (n = 43) compared with PlA2-negative (n = 76) patients (85.7% versus 97.2%; P = 0.015). No differences were found in patient survival (95.2% versus 98.7%, respectively). Proportional hazards regression analysis (Cox regression model) confirmed that serum creatinine level at discharge is the best predictor of allograft survival, followed by CMV status, delayed graft function, and the glycoprotein IIIa/IIb genotype. The PlA2 polymorphism is an independent risk factor for acute renal graft rejection, affecting short-term graft survival. Future studies aimed at preventing the hemostatic imbalance favoring platelet aggregation associated with this polymorphism may be important in preventing acute rejection and its impact on chronic rejection.

Pl A1/A2 polymorphism of platelet glycoprotein IIIa and risk of acute coronary syndromes in heterozygous familial hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal inherited disorder caused by different mutations in the low density lipoprotein (LDL) receptor gene. It has been demonstrated that there is an increased risk of coronary heart disease (CHD) in heterozygous FH subjects, although this excess CHD is not only explained by the LDL-cholesterol concentration or the class of the LDL-receptor mutation. To investigate if a common polymorphism at the platelet glycoprotein (GP) IIIa gene locus could be related to CHD phenotypic variation in heterozygous FH, we have carried out a case-control study. We have studied 40 cases and 40 controls matched for age, sex and genetic defect in the LDL-receptor gene. Allele frequency of Pl A2 polymorphism for cases and controls was 20 and 22.5%, respectively, and the difference was not significant. In conclusion, our data do not support any association between the GP IIIa polymorphism and the increased prevalence of acute coronary syndromes in the heterozygous FH subjects.

Platelet PlA2 polymorphism and thromboembolic events: from inherited risk to pharmacogenetics.

Platelet PlA2 polymorphism and thromboembolic events: from inherited risk to pharmacogenetics.

Lipoprotein(a) and the significance of the association between platelet glycoprotein IIIa polymorphisms and the risk of premature myocardial infarction

Platelet glycoprotein IIb/IIIa may be involved in the pathogenesis of myocardial infarction as the key element in platelet aggregation and as the binding site of lipoprotein(a) to platelets, inhibiting plasminogen binding and activation. Recently, a strong association between the Pl A2 polymorphism of the glycoprotein IIIa gene and acute coronary thrombosis has been reported, although this has not been confirmed. In an associated study, we determined plasma lipoprotein levels, the apo E genotype and the Pl A genotype in 250 males under 55 years with myocardial infarction and they were compared with 250 age- and sex-matched controls. Patients showed an over-representation of the ϵ3/4 genotype with respect to the control group. We found that there were no differences in the allelic frequency of Pl A2 between case patients and age-matched controls ( χ 2=0.05, P=0.92) and that subjects bearing the Pl A2 allele showed higher plasma lipoprotein(a) concentration than Pl A1/Pl A1 individuals. Therefore, in this population there is no association between carriage of Pl A2 allele and increased risk of myocardial infarction but the carriage of Pl A2 is associated with higher plasma Lp(a) concentration.

Pl A2 polymorphism and efficacy of aspirin

Aspirin is widely used as an antiplatelet drug to prevent arterial thromboembolic events. 1 Antiplatelet Trialists' CollaborationCollaborative overview of randomised trials of antiplatelet therapy—I: prevention of death, myocardial infarction, and stroke by prolonged antiplatelet therapy in various categories of patients. BMJ. 1994; 308: 81-106 Crossref PubMed Scopus (706) Google Scholar Aspirin acetylates irreversibly the enzyme cyclooxygenase (COX-1), and thereby inhibits the production of thromboxane A2 in platelets. However, the mechanism by which thromboxane A2 induces the expression of high-affinity receptor molecules for fibrinogen on the surface of platelets (the final common pathway of platelet activation) remains unknown.

Coronary Thrombosis and the Platelet Glycoprotein IIIA Gene PLA2 Polymorphism

Myocardial infarction results from a platelet-rich occlusive coronary thrombus. Platelet membrane glycoprotein IIb/IIIa plays an important role in platelet adhesion and aggregation. Two polymorphisms of the gene encoding the IIIa subunit. PLA1 and PLA2, have been identified. We investigated the frequency of these polymorphisms in 114 consecutive patients with a history of angina-like chest pain admitted for coronary arteriography. Forty-three of these patients had previously suffered a myocardial infarction. The PLA2 polymorphism was found in 21% of the patients with previous myocardial infarction and in 27% of the patients with angina-like chest pain but no previous myocardial infarction (p = 0.634). There was also no significant association with the extent of coronary disease. There is no evidence, therefore, from this study of an association between the PLA polymorphisms and the occurrence of myocardial infarction.

Interdonor variability of platelet response to thrombin receptor activation: influence of PlA2 polymorphism.

Considering that platelet response to thrombin receptor activation might be critical for the development of arterial thrombosis, we measured the dense granule release under stimulation by the thrombin receptor activating peptide (TRAP) in a series of 102 healthy volunteers. The threshold TRAP concentration which initiated a secretion ranged from 3 to 20 microM. A good concordance (79%, k=0.677) between two tests performed at a 1 month interval indicated that platelet response to thrombin receptor activation was characteristic of each individual donor. Since the threshold concentration required to initiate secretion corresponded to the threshold concentration which induced a biphasic aggregation, all volunteers were genotyped for the PlA2 polymorphism, the Pro33 variant of GPIIIa. Platelets from subjects with the PlA2 polymorphism required higher TRAP concentrations to aggregate than those from subjects with no PlA2 allele (P=0.0012). However, they also required a higher ADP concentration to aggregate. In order to exclude any influence of GPIIIa polymorphism on TRAP-induced secretion, we studied the variability of platelet response to TRAP among the 77 individuals with no PlA2 allele, and found the same interdonor variability with the same distribution of threshold TRAP concentrations as for the 102 individuals. The results suggest that (i) platelet secretion in response to thrombin receptor activation could be a genetically controlled phenotype independent of the GPIIIa polymorphism; (ii) the PlA2 polymorphism is associated with platelet hypoaggregability.

The PlA2 polymorphism in human platelet membrane GPIIIa is associated with increased fibrinogen binding to stimulated platelets

The PlA2 polymorphism in human platelet membrane GPIIIa is associated with increased fibrinogen binding to stimulated platelets

A polymorphism of a platelet glycoprotein receptor as an inherited risk factor for coronary thrombosis: Weiss EJ, Bray PF, Tayback M, et al. N Engl J Med 334:1090–1094, 1996

Background. Platelet glycoprotein IIb/IIIa is a membrane receptor for fibrinogen and von Willebrand factor, and it has an important role in platelet aggrega- tion. It is known to be involved in the pathogenesis of acute coronary syndromes. Previously, we found a high frequency of a particular polymorphism, Pl A2 , of the gene encoding glycoprotein IIIa in kindreds with a high preva- lence of premature myocardial infarction. Methods. To investigate the relation between the Pl A2 polymorphism and acute coronary syndromes, we con- ducted a case-control study of 71 case patients with my- ocardial infarction or unstable angina and 68 inpatient controls without known heart disease. The groups were matched for age, race, and sex. We used two methods to determine the Pl A genotype: reverse dot blot hybridiza- tion and allele-specific restriction digestion. Results. The prevalence of Pl A2 was 2.1 times higher

A polymorphism of a platelet glycoprotein receptor as an inherited risk factor for coronary thrombosis.

Platelet glycoprotein IIb/IIIa is a membrane receptor for fibrinogen and von Willebrand factor, and it has an important role in platelet aggregation. It is known to be involved in the pathogenesis of acute coronary syndromes. Previously, we found a high frequency of a particular polymorphism, PlA2, of the gene encoding glycoprotein IIIa in kindreds with a high prevalence of premature myocardial infarction. To investigate the relation between the PlA2 polymorphism and acute coronary syndromes, we conducted a case-control study of 71 case patients with myocardial infarction or unstable angina and 68 inpatient controls without known heart disease. The groups were matched for age, race, and sex. We used two methods to determine the PlA genotype: reverse dot blot hybridization and allele-specific restriction digestion. The prevalence of PlA2 was 2.1 times higher among the case patients than among the controls (39.4 percent vs. 19.1 percent, P=0.01). In a subgroup of patients whose disease began before the age of 60 years, the prevalence of PlA2 was 50 percent, a value that was 3.6 times that among control subjects under 60 years of age (13.9 percent, P=0.002). Among subjects with the PlA2 polymorphism, the odds ratio for having a coronary event was 2.8 (95 percent confidence interval, 1.2 to 6.4). In the patients less than 60 years of age at the onset of disease, the odds ratio was 6.2 (95 percent confidence interval, 1.8 to 22.4). We observed a strong association between the PlA2 polymorphism of the glycoprotein IIIa gene and acute coronary thrombosis, and this association was strongest in patients who had had coronary events before the age of 60 years.