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(Circulation. 2000;101:1013.)
© 2000 American Heart Association, Inc.

Basic Science Reports

Platelet GP IIIa Pl^A Polymorphisms Display Different Sensitivities to Agonists

Alan D. Michelson, MD; Mark I. Furman, MD; Pascal Goldschmidt-Clermont, MD; Mary Ann Mascelli, PhD; Craig Hendrix, MD; Lindsay Coleman, BS; Jeanette Hamlington, BS; Marc R. Barnard, MS; Thomas Kickler, MD; Douglas J. Christie, PhD; Sourav Kundu, PhD; Paul F. Bray, MD

From the Departments of Medicine and Pathology (P.F.B, C.H., L.C., J.H., T.K.), Johns Hopkins University School of Medicine, Baltimore, Md; Departments of Pediatrics, Medicine, and Surgery (A.D.M., M.I.F, M.R.B.), University of Massachusetts, Worcester; Heart and Lung Institute, Department of Medicine (P.G.-C.), Ohio State University, Columbus; Department of Clinical Pharmacology (M.A.M.), Centocor Inc, Malvern, Pa; and Dade-Behring (D.J.C., S.K.), Miami, Fla.

Correspondence to Paul F. Bray, MD, Ross 1015, Johns Hopkins University School of Medicine, 720 Rutland Ave, Baltimore, MD 21205. E-mail pfb{at}welchlink.welch.jhu.edu

	Abstract

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Background—Both inherited predisposition and platelet hyperreactivity have been associated with ischemic coronary events, but mechanisms that support genetic differences among platelets from different subjects are generally lacking. Associations between the platelet Pl^A2 polymorphism of GP IIIa and coronary syndromes raise the question as to whether this inherited variation may contribute to platelet hyperreactivity.

Methods and Results—In this study, we characterized functional parameters in platelets from healthy donors with the Pl^A (HPA-1) polymorphism, a Leu (Pl^A1) to Pro (Pl^A2) substitution at position 33 of the GP IIIa subunit of the platelet GP IIb/IIIa receptor (integrin _IIbß₃). We studied 56 normal donors (20 Pl^A1,A1, 20 Pl^A1,A2, and 16 Pl^A2,A2). Compared with Pl^A1,A1 platelets, Pl^A2-positive platelets showed a gene dosage effect for significantly greater surface-expressed P-selectin, GP IIb/IIIa–bound fibrinogen, and activated GP IIb/IIIa in response to low-dose ADP. Surface expression of GP IIb/IIIa was similar in resting platelets of all 3 genotypes but was significantly greater on Pl^A2,A2 platelets after ADP stimulation (P=0.003 versus Pl^A1,A1; P=0.03 versus Pl^A1,A2). Pl^A1,A2 platelets were more sensitive to inhibition of aggregation by pharmacologically relevant concentrations of aspirin and abciximab.

Conclusions—Pl^A2-positive platelets displayed a lower threshold for activation, and platelets heterozygous for Pl^A alleles showed increased sensitivity to 2 antiplatelet drugs. These in vitro platelet studies may have relevance for in vivo thrombotic conditions.

Key Words: platelets • coronary disease • polymorphisms • inhibitors

	Introduction

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Most acute ischemic coronary syndromes result from the formation of a platelet-rich thrombus at the site of a ruptured atherosclerotic plaque.¹ Platelet hyperreactivity has been correlated with coronary events and mortality in patients with established coronary artery disease.² Platelet aggregation is mediated through the binding of fibrinogen or von Willebrand factor (vWF) to the activated form of the platelet glycoprotein (GP) IIb/IIIa (integrin _IIbß₃) receptor. Platelet membrane adhesive receptors are polymorphic, and recent reports of associations between the platelet Pl^A2 polymorphism of GP IIIa and ischemic coronary syndromes^{3 4} raise the question as to whether this genetic variation may contribute to platelet hyperreactivity. This is particularly important considering that 25% of individuals of Northern European ancestry are Pl^A2-positive, with only 2% being homozygous Pl^A2.⁵

Standard light transmission ("turbidimetric") platelet aggregometry is designed to detect platelet hypofunction in the evaluation of hemorrhagic conditions. This technique detects only aggregates of several hundred platelets and thus is insensitive to the early stages of platelet aggregation and may be suboptimal in discriminating platelet hyperreactivity.⁶ An additional concern regarding the use of platelet-rich plasma (PRP) in turbidimetric aggregometry is the loss of larger, high-density platelets during the centrifugation procedure. Whole-blood platelet aggregation measures electrical impedance caused by platelet thrombus formation on electrodes. However, this technique may suffer from nonreproducibility because of other causes of increased impedance, such as fibrin buildup on the electrodes. We have previously shown that a whole-blood flow cytometric analysis using epitope-dependent monoclonal antibodies is an extremely reliable measure of the platelet activation state.⁷ Using this assay and several others, we investigated whether the Pl^A2 polymorphism might contribute to the heterogeneity observed in platelet GP IIb/IIIa function by testing platelets from 56 normal donors, 16 of whom were Pl^A2,A2. We found that Pl^A2-positive platelets were hyperreactive and demonstrated an altered sensitivity to antiplatelet agents.

	Methods

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Blood Collection
After the Pl^A genotype⁵ had been determined, repeat phlebotomy on healthy individuals was performed for functional studies when the donor was in a fasting state and had not taken medications for at least 10 days. The first 2 mL was discarded, then 100 mL of blood was drawn through a 19-gauge needle into 3.2% sodium citrate. Samples were included for functional studies only if there was maximal aggregation to arachidonic acid. In a few cases, not all assays could be performed on all 56 donors, usually because of insufficient blood sample.

Monoclonal Antibodies
Monoclonal antibody F26 is directed against a conformational change in fibrinogen bound to the GP IIb/IIIa complex.⁸ Monoclonal antibody LIBS1 is directed against a conformational change in the GP IIb/IIIa complex induced by fibrinogen binding.⁹ F26 and LIBS1 were FITC-conjugated as described.⁷ Peridinin chlorophyll protein (PerCP)–conjugated CD42a (Becton Dickinson) is a GP IX–specific monoclonal antibody. Phycoerythrin-conjugated monoclonal antibody CD62P (Becton Dickinson) is directed against P-selectin.¹⁰

Whole-Blood Flow Cytometry
Two- and 3-color whole-blood flow cytometry was performed by a modification of previously described methods,⁷ with the operator blinded to the genotype of the donor. Briefly, samples were incubated with CD42a-PerCP 2.5 µg/mL, followed by saturating concentrations of antibodies, followed by buffer or agonists. Samples were fixed in 1% formaldehyde, diluted in buffer, and sent at 4°C by overnight delivery to the Center for Platelet Function Studies at the University of Massachusetts Medical Center. All samples were analyzed within 24 hours in an XL flow cytometer (Coulter) as described.⁷ In the 2-color assay, color compensation was not required because PerCP does not interfere with FITC. In the 3-color assay, stimulated or unstimulated normal donor samples labeled with test or isotype-matched control antibodies were prepared to establish appropriate color compensation.

Quantification of Platelet Fibrinogen Binding, GP IIb/IIIa, and Platelet Fibrinogen and vWF
PRP was prepared by centrifugation at 120g for 20 minutes. Functional studies were completed within 2.5 hours. We have previously described the FITC-labeled fibrinogen preparation, binding to platelets, and the method of converting fluorescence intensity data to the number of binding sites per cell.¹¹ The bivalent form (IgG) of monoclonal antibody 7E3, directed against GP IIIa, was used in a radiometric assay at a concentration of 18 µg/mL to quantify the number of receptors per platelet as previously described.¹² Fibrinogen and vWF were quantified from washed platelets by an ELISA technique from Accurate Chemical and Scientific Corp and American Diagnostica, Inc.

Platelet Aggregation
PRP was adjusted to 250 000 platelets/µL with autologous platelet-poor plasma for use in a BIO-DATA 4-channel platelet aggregometer. One hundred percent aggregation was the optical density obtained with platelet-poor plasma. The sample (450 µL) was preincubated at 37°C for 10 minutes. For the inhibition studies, aspirin was added for an additional 10 minutes. Because of variable response to epinephrine, the data for this agonist were used only if >60% aggregation was obtained with 10 µmol/L epinephrine.

IC₅₀ Determinations
The 50% inhibitory concentration (IC₅₀) of aspirin was modeled for each subject individually. A sigmoid E_max model achieved the best fit for nearly all subjects according to an accepted model diagnostic criterion.¹³

Statistics
Data were analyzed by 1-way ANOVA and repeated-measures ANOVA. A Bonferroni-Dunn test was used for post hoc comparisons of individual means. A probability of <0.05 was considered significant. The IC₅₀ model parameters were not normally distributed. Accordingly, nonparametric methods were used for comparisons among (Kruskall-Wallis) and between (Mann-Whitney U test) genotype groups to determine statistical significance (2-sided P<0.05).

	Results

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Donor Characteristics
The characteristics of the blood donors are shown in Table 1 according to Pl^A genotype. The groups were similarly matched, except that the Pl^A2 homozygote group subjects were older than the other groups. There was no difference in platelet counts among the groups.

View this table: [in this window] [in a new window]   Table 1. Donor Characteristics

Subthreshold Platelet Stimulation Studies
Resting platelets that were Pl^A2-positive bound significantly higher levels of CD62P (specific for P-selectin) than did Pl^A2-negative platelets (Pl^A1,A1 versus Pl^A1,A2, P=0.01; Pl^A1,A1 versus Pl^A2,A2, P=0.001), reflecting -granule secretion (Figure 1). The F26 antibody showed greater binding to the Pl^A2,A2 platelets than to the other genotypes. LIBS1 binding showed a trend toward greater binding to Pl^A2-positive platelets (not shown), and a larger sample size may be necessary to detect a significant difference in LIBS1 binding to resting platelets. In addition, in resting platelets, perhaps the Pl^A2 conformation favors fibrinogen and F26 binding without LIBS1 exposure.

View larger version (33K): [in this window] [in a new window]   Figure 1. Analysis of platelet activation state under resting conditions using whole-blood flow cytometry. CD62P detects P-selectin. F26 detects a conformation of fibrinogen that is bound to GP IIb/IIIa. Numbers of donors used were 19 PlA1,A1, 18 to 19 PlA1,A2, and 14 to 15 PlA2,A2. Error bars indicate SEM. Numbers above bars indicate probability value for differences between 2 means.

When blood was stimulated with low concentrations of ADP, a consistent Pl^A2-dependent increase in binding of CD62P, F26, and LIBS1 was observed (Figure 2). Compared with Pl^A1,A1 platelets, the homozygous Pl^A2,A2 platelets bound significantly more of all 3 antibodies on stimulation with both 0.5 µmol/L and 1.0 µmol/L ADP. At these same ADP concentrations, significant differences between Pl^A1,A2 and Pl^A2,A2 platelets were observed for the antibodies detecting GP IIb/IIIa activation: F26 and LIBS1. Similar variations were observed at 0.1 µmol/L ADP, although only F26 binding showed significant differences. These differences in binding of activation-dependent antibodies among the 3 genotypes were not due to differences in platelet size as assessed by forward light scatter in the flow cytometer (not shown).

View larger version (31K): [in this window] [in a new window]   Figure 2. Platelet activation state on stimulation with low-dose ADP. Whole blood was incubated with monoclonal antibodies CD62P (A), F26 (B), and LIBS1 (C) and analyzed by flow cytometry. Main effect of genotype on CD62P, F26, and LIBS1 binding was P=0.07, P=0.005, and P=0.01, respectively; there was a significant interaction (P=0.03, P=0.005, and P=0.007) between ADP concentration and genotype for CD62P, F26, and LIBS1, respectively, in a 3-way ANOVA. Numbers of donors used were 19 PlA1,A1, 18 to 19 PlA1,A2, and 14 to 15 PlA2,A2.

We considered an effect of age on these findings, but the older 8 donors (mean age, 53.6 years) in the Pl^A2,A2 group showed no significant differences from the younger 8 donors (mean age, 35.4 years) for any of the antibodies (Table 2). In addition, for every experiment in which there was a significant difference between the older half of the Pl^A2,A2 group and either Pl^A1-positive group, there was also a significant difference between the younger half of the Pl^A2,A2 group and either Pl^A1-positive group (data not shown).

View this table: [in this window] [in a new window]   Table 2. Effect of Age on ADP-Induced Platelet Activation Within the PlA2,A2 Donors

From these studies, we conclude that 2 copies of the Pl^A2 allele correlated with increased platelet reactivity, as determined by -granule secretion (indicated by surface P-selectin) and the GP IIb/IIIa activation state (indicated by F26 and LIBS1 binding). A single copy of the Pl^A2 allele showed a consistent, but not statistically significant, association with increased platelet reactivity.

GP IIb/IIIa Quantification
We used several approaches to assess whether the increased binding of activation-dependent antibodies by Pl^A2 genotype was due to a higher absolute number of GP IIb/IIIa receptors. 7E3 is a GP IIb/IIIa–specific monoclonal antibody that can be used to quantify the number of receptors.¹² No difference in the receptor density was observed by Pl^A status in nonstimulated platelets (Figure 3). When stimulated with 20 µmol/L ADP, more GP IIb/IIIa receptors were detected on the Pl^A2-positive platelets than on the Pl^A2-negative platelets. Under the static conditions of these experiments, ADP would not have been expected to cause granule release,¹⁴ consistent with the lack of change observed in the Pl^A1,A1 platelets. These results suggested a lower threshold for degranulation in the Pl^A2-positive platelets, consistent with the data in Figure 1, where a higher P-selectin expression was observed in Pl^A2-positive platelets. Age did not affect the increased 7E3 binding to Pl^A2,A2 platelets (Table 2). To confirm that -granule release was possible under the conditions of these experiments, we maximally stimulated platelets from 3 Pl^A1,A1 and 4 Pl^A1,A2 donors with 20 µmol/L thrombin receptor–activating peptide (TRAP) and observed the expected 30% increase¹² in GP IIb/IIIa receptor surface expression (maximal receptor numbers were 57 377±5486 for Pl^A1A1 and 57 510±6582 for Pl^A1,A2) compared with unstimulated platelets. We also assessed binding of a GP IIb–specific monoclonal antibody (SZ22) and observed an equivalent binding to platelets of all 3 Pl^A genotypes under both resting conditions and stimulation with 20 µmol/L TRAP (data not shown). Similar results with TRAP using 2 different antibodies make it unlikely that the difference in 7E3 binding to platelets stimulated with 20 µmol/L ADP (Figure 3) was simply due to an altered affinity of 7E3 for the Pl^A2 polymorphism. This conclusion is supported further by our findings in stable cell lines overexpressing the Pl^A1 or Pl^A2 forms of GP IIb/IIIa, which show equivalent binding of 7E3 Fab at concentrations >1 µg/mL (data not shown). We conclude that there is no difference in the total number of surface-accessible GP IIb/IIIa receptors among the 3 Pl^A genotypes and that Pl^A2-positive platelets possess a lower threshold for -granule release, with a corresponding increase in GP IIb/IIIa receptor density.

View larger version (46K): [in this window] [in a new window]   Figure 3. Quantification of GP IIb/IIIa. Buffer or 20 µmol/L ADP was added to PRP and incubated for 15 minutes. 125I-labeled 7E3 was added for 30 minutes, platelets were centrifuged through 30% sucrose, and number of binding sites was calculated. Numbers of donors used were 20 PlA1,A1, 19 PlA1,A2, and 16 PlA2,A2.

Maximal-Platelet-Stimulation Studies
The binding of exogenously added fibrinogen to maximally stimulated platelets was determined by use of 20 µmol/L ADP. Under these conditions, no significant differences were observed among the 3 genotypes (Table 3). Similarly, maximal stimulation with 20 µmol/L ADP and 20 µmol/L TRAP in platelet aggregometry studies negated any subthreshold difference (Table 3). Indeed, the only difference observed in aggregation studies was with 0.4 µmol/L epinephrine, in which Pl^A2,A2 platelets showed greater aggregation than Pl^A1-positive platelets. Finally, there were no significant differences among the Pl^A1,A1 and Pl^A1,A2 genotypes in intracellular fibrinogen or vWF (Table 3).

View this table: [in this window] [in a new window]   Table 3. Platelet Functional Characteristics by Pl3 Genotype

Influence of Pl^A Status on Aspirin and Abciximab Inhibition of ADP-Induced Platelet Aggregation
Aspirin is a mainstay in the treatment of coronary artery disease, and it inhibits epinephrine-induced platelet aggregation. We observed significant differences in platelet inhibition among Pl^A genotypes at 2.5 and 5 µmol/L aspirin (Figure 4A), concentrations that are typically obtained in vivo.¹⁵ As we have previously reported,¹⁶ the Pl^A1,A2 platelets were the most sensitive to aspirin. Interestingly, Pl^A2,A2 platelets, which were not studied previously, were less sensitive than Pl^A1,A2 platelets and only slightly less sensitive than Pl^A1,A1 platelets. Abciximab is a monovalent chimeric Fab fragment of 7E3 that blocks ligand binding to GP IIb/IIIa and has been beneficial in a number of coronary ischemic syndromes.¹⁷ As with aspirin, several concentrations of abciximab, within the range of concentrations that partially or completely block platelet aggregation,¹⁸ caused significant differences among genotypes in inhibiting aggregation (Figure 4B). There were statistically significant differences in the aspirin IC₅₀ (Table 4) among genotypes (P=0.024), with Pl^A2,A2 having the highest value relative to the other genotypes. Individual comparisons showed genotype Pl^A1,A2 to be lower than Pl^A2,A2 (P=0.015). There was a similar trend for the IC₅₀ with abciximab among genotypes (P=0.099), and Pl^A1,A2 was lower than Pl^A2,A2 (P=0.046) in pairwise comparisons.

View larger version (20K): [in this window] [in a new window]   Figure 4. Effect of aspirin and abciximab by PlA genotype. Data are normalized to 100%, defined as aggregation achieved with no inhibitor. Inset, Probability values for concentrations of inhibitors that showed significant differences; PlA1,A1 is abbreviated 1,1; PlA1,A2, 1,2; and PlA2,A2, 2,2. A, Aggregation performed with 2 µmol/L epinephrine. Numbers of donors used were 17 PlA1,A1, 13 PlA1,A2, and 14 PlA2,A2. Two PlA1,A1, 6 PlA1,A2, and 2 PlA2,A2 donors did not achieve >60% aggregation to epinephrine. B, Aggregation performed with 5 µmol/L ADP. Numbers of donors used were 20 PlA1,A1, 20 PlA1,A2, and 15 PlA2,A2.

View this table: [in this window] [in a new window]   Table 4. Effect of Inhibitors by Genotype

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
Our studies demonstrate that Pl^A2-positive platelets, compared with Pl^A1,A1 platelets, have a lower threshold for platelet activation, -granule release, GP IIb/IIIa activation, and fibrinogen binding. This "hyperreactive" state suggests that in vivo, Pl^A2-positive platelets may exert a greater thrombotic tendency than Pl^A1,A1 platelets. We also observed a greater sensitivity to therapeutic concentrations of aspirin and abciximab in Pl^A1,A2 platelets. This differential sensitivity to antiplatelet agents may have potential clinical implications whereby specific antiplatelet therapy may best be tailored according to a patient’s Pl^A genotype. On the basis of the findings in this mechanistic study, further studies are warranted to examine the in vivo effects of antiplatelet agents according to inherited variations in platelet adhesive receptors.

A panel of monoclonal antibodies reporting the activation state of platelets and GP IIb/IIIa consistently demonstrated a higher degree of activation in Pl^A2-positive platelets. Pl^A2-positive platelets had a lower threshold for -granule release, as shown by increased CD62P binding (Figures 1 and 2) and 7E3 binding observed with 20 µmol/L ADP (Figure 3). Presumably, the increased fibrinogen occupancy of Pl^A2-positive GP IIb/IIIa receptors in the resting state or on weak agonist stimulation results in greater outside-in signaling and subsequent degranulation and P-selectin expression. The F26 antibody displayed an increased binding to ADP-stimulated Pl^A2-positive platelets and showed greater sensitivity than LIBS1 at detecting these activation differences. We observed both an increased LIBS1 binding in resting Pl^A2-positive platelets and a consistently greater activation of Pl^A1,A2 platelets compared with Pl^A1,A1 platelets, but statistical significance was not reached in either case. A larger sample size may be necessary to detect true differences. Our data were consistent with an age independence of the Pl^A2 effect, but because of the relatively small numbers of subjects compared when the Pl^A2,A2 group was divided in half (Table 2), further investigation in a larger population is warranted. Nevertheless, our findings are strongly supported by Feng et al,¹⁹ who showed that age did not affect Pl^A2-induced platelet hyperreactivity among 1422 subjects.

Light transmission platelet aggregometry continues to be used as the "gold standard" of platelet function assays. However, the typical concentrations of agonists used in platelet aggregation studies may not be optimal for detecting platelet hyperreactivity. The only significant difference in aggregation by Pl^A status in our study was with low-dose epinephrine as an agonist, a finding consistent with the low-dose ADP data in our whole-blood assay (Figure 2) and observations that less epinephrine is required for aggregating Pl^A2-positive than Pl^A2-negative platelets.¹⁹ Platelets display an "all-or-none" activation response,²⁰ which may explain why strong agonists were able to bypass or overcome the Pl^A2-dependent difference seen with weak agonists (Table 3). In addition, because thrombogenesis under high shear rates typically proceeds via GP IIb/IIIa–ligand interactions after platelets have adhered to the subendothelium via vWF,²¹ differences in the activation state of GP IIb/IIIa or the threshold for granule release may not be apparent in the aggregometer, where low shear forces and repetitive interactions may provide sufficient time for bonds to form.

Interestingly, heterozygous platelets showed a greater sensitivity to 2 platelet inhibitors: aspirin and abciximab. It is not clear why the Pl^A2,A2 subjects responded to the inhibitors in a manner more like the Pl^A1,A1 group. Receptor clustering augments GP IIb/IIIa–mediated signaling,²² and perhaps such clustering may be inhibited in heterozygous platelets such that they are more susceptible to inhibition by aspirin or abciximab. For example, in studies with GP IIb/IIIa–expressing cell lines, we have found increased adhesion in Pl^A2-expressing cells compared with Pl^A1-expressing cells that is mediated through differences in outside-in signaling,²³ and perhaps the combination of both allele products dominantly inhibits this component of receptor-mediated cell activation. The concentrations of both aspirin and abciximab used in these experiments were within the therapeutic range achieved in vivo.^{15 18} Thus, the significant differences in inhibition observed at 2.5 and 5.0 µmol/L aspirin and 1.25 and 1.5 µg/mL abciximab may affect either beneficial (antithrombotic) or adverse (hemorrhagic) in vivo effects. It will be interesting to see whether other structurally different platelet or GP IIb/IIIa antagonists display variable inhibitory activity by Pl^A genotype. Nevertheless, our data should be interpreted cautiously until they are confirmed in a larger series. In the meantime, future clinical epidemiology studies of platelet genetic variations and cardiovascular disease would be wise to consider possible treatment effects.

It is difficult to extrapolate these Pl^A-dependent differences in platelet function to the clinical condition, because platelet behavior in young, healthy donors is likely to be quite different from that in older patients with coronary artery disease, in which numerous other effects (cardiovascular medications, hormonal alterations, serum lipids, tobacco use, injured vessel wall, etc) affect platelet physiology. But because GP IIb/IIIa is the most abundant receptor on human blood platelets (80 000 copies per platelet) and plays a central role in formation of a platelet thrombus, even a subtle functional alteration could have profound effects over the lifetime of a patient.

	Acknowledgments

 
This study was supported by grant HL-57488 from the National Institutes of Health and Frank Pearl. We are grateful to all volunteers who so generously gave of their time and blood and to Drs Mark H. Ginsberg and Harvey Gralnick for generously providing F26 and LIBS1.

Received May 6, 1999; revision received August 30, 1999; accepted September 15, 1999.

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				N. K.J. Oksala, M. Heikkinen, J. Mikkelsson, T. Pohjasvaara, M. Kaste, T. Erkinjuntti, and P. J. Karhunen Smoking and the Platelet Fibrinogen Receptor Glycoprotein IIb/IIIA PlA1/A2 Polymorphism Interact in the Risk of Lacunar Stroke and Midterm Survival Stroke, January 1, 2007; 38(1): 50 - 55. [Abstract] [Full Text] [PDF]

				S. T. Morozowich, B. S. Donahue, and I. J. Welsby Genetics of coagulation: considerations for cardiac surgery. Seminars in Cardiothoracic and Vascular Anesthesia, December 1, 2006; 10(4): 297 - 313. [Abstract] [PDF]

				G. Ndrepepa, A. Kastrati, J. Mehilli, F.-J. Neumann, J. ten Berg, O. Bruskina, F. Dotzer, M. Seyfarth, J. Pache, J. Dirschinger, et al. Age-Dependent Effect of Abciximab in Patients With Acute Coronary Syndromes Treated With Percutaneous Coronary Interventions Circulation, November 7, 2006; 114(19): 2040 - 2046. [Abstract] [Full Text] [PDF]

				A. D. Michelson, A. L. Frelinger, and M. I. Furman Resistance to antiplatelet drugs Eur. Heart J. Suppl., October 1, 2006; 8(suppl_G): G53 - G58. [Abstract] [Full Text] [PDF]

				K. V. Vijayan and P. F. Bray Molecular Mechanisms of Prothrombotic Risk Due to Genetic Variations in Platelet Genes: Enhanced Outside-In Signaling Through the Pro33 Variant of Integrin {beta}3. Experimental Biology and Medicine, May 1, 2006; 231(5): 505 - 513. [Abstract] [Full Text] [PDF]

				G. A. Nuttall, N. Henderson, M. Quinn, C. Blair, L. Summers, B. A. Williams, W. C. Oliver, and P. J. Santrach Excessive bleeding and transfusion in a prior cardiac surgery is associated with excessive bleeding and transfusion in the next surgery. Anesth. Analg., April 1, 2006; 102(4): 1012 - 1017. [Abstract] [Full Text] [PDF]

				G. E. Cooke, Y. Liu-Stratton, A. K. Ferketich, M. L. Moeschberger, D. J. Frid, R. D. Magorien, P. F. Bray, P. F. Binkley, and P. J. Goldschmidt-Clermont Effect of Platelet Antigen Polymorphism on Platelet Inhibition by Aspirin, Clopidogrel, or Their Combination J. Am. Coll. Cardiol., February 7, 2006; 47(3): 541 - 546. [Abstract] [Full Text] [PDF]

				P. Kubisz, J. Ivankova, P. Holly, J. Stasko, and J. Musia/l The Glycoprotein IIIa PLA1/A2 Polymorphism--A Defect Responsible for the Sticky Platelet Syndrome? Clinical and Applied Thrombosis/Hemostasis, January 1, 2006; 12(1): 117 - 119. [PDF]

				S E Bojesen, S K Kjaer, E V S Hogdall, B L Thomsen, C K Hogdall, J Blaakaer, A Tybjaerg-Hansen, and B G Nordestgaard Increased risk of ovarian cancer in integrin {beta}3 Leu33Pro homozygotes Endocr. Relat. Cancer, December 1, 2005; 12(4): 945 - 952. [Abstract] [Full Text] [PDF]

				D. L. Yee, C. W. Sun, A. L. Bergeron, J.-f. Dong, and P. F. Bray Aggregometry detects platelet hyperreactivity in healthy individuals Blood, October 15, 2005; 106(8): 2723 - 2729. [Abstract] [Full Text] [PDF]

				P. J. Mason, A. K. Jacobs, and J. E. Freedman Aspirin Resistance and Atherothrombotic Disease J. Am. Coll. Cardiol., September 20, 2005; 46(6): 986 - 993. [Abstract] [Full Text] [PDF]

				K. V. Vijayan, Y. Liu, W. Sun, M. Ito, and P. F. Bray The Pro33 Isoform of Integrin {beta}3 Enhances Outside-in Signaling in Human Platelets by Regulating the Activation of Serine/Threonine Phosphatases J. Biol. Chem., June 10, 2005; 280(23): 21756 - 21762. [Abstract] [Full Text] [PDF]

				E. Papp, V. Havasi, J. Bene, K. Komlosi, L. Czopf, E. Magyar, C. Feher, G. Feher, B. Horvath, Z. Marton, et al. Glycoprotein IIIA Gene (PlA) Polymorphism and Aspirin Resistance: Is There Any Correlation? Ann. Pharmacother., June 1, 2005; 39(6): 1013 - 1018. [Abstract] [Full Text] [PDF]

				S. Wang-Gohrke and J. Chang-Claude Re: Integrin {beta}3 Leu33Pro Homozygosity and Risk of Cancer J Natl Cancer Inst, May 18, 2005; 97(10): 778 - 779. [Full Text] [PDF]

				J. Mikkelsson, M. Perola, and P. J. Karhunen Genetics of Platelet Glycoprotein Receptors: Risk of Thrombotic Events and Pharmacogenetic Implications Clinical and Applied Thrombosis/Hemostasis, April 1, 2005; 11(2): 113 - 125. [Abstract] [PDF]

				V. L. Serebruany, S. R. Steinhubl, P. B. Berger, A. I. Malinin, D. L. Bhatt, and E. J. Topol Variability in platelet responsiveness to clopidogrel among 544 individuals J. Am. Coll. Cardiol., January 18, 2005; 45(2): 246 - 251. [Abstract] [Full Text] [PDF]

				K. V. Vijayan, Y. Liu, T.-T. Li, and P. F. Bray Protein Phosphatase 1 Associates with the Integrin {alpha}IIb Subunit and Regulates Signaling J. Biol. Chem., August 6, 2004; 279(32): 33039 - 33042. [Abstract] [Full Text] [PDF]

				E. V. Potapov, S. Ignatenko, B. A. Nasseri, M. Loebe, C. Harke, M. Bettmann, A. Doller, V. Regitz-Zagrosek, and R. Hetzer Clinical significance of PlA polymorphism of platelet GP IIb/IIIa receptors during long-term VAD support Ann. Thorac. Surg., March 1, 2004; 77(3): 869 - 874. [Abstract] [Full Text] [PDF]

				R. D. McBane II Genetically Determined Procoagulant States and Heparin Use Seminars in Cardiothoracic and Vascular Anesthesia, December 1, 2003; 7(4): 427 - 442. [Abstract] [PDF]

				D. E. Mager, M. A. Mascelli, N. S. Kleiman, D. J. Fitzgerald, and D. R. Abernethy Simultaneous Modeling of Abciximab Plasma Concentrations and ex Vivo Pharmacodynamics in Patients Undergoing Coronary Angioplasty J. Pharmacol. Exp. Ther., December 1, 2003; 307(3): 969 - 976. [Abstract] [Full Text] [PDF]

				L. Macchi, L. Christiaens, S. Brabant, N. Sorel, S. Ragot, J. Allal, G. Mauco, and A. Brizard Resistance in vitro to low-dose aspirin is associated with platelet PlA1 (GP IIIa) polymorphism but not with C807T(GP Ia/IIa) and C-5T kozak (GP Ib{alpha}) polymorphisms J. Am. Coll. Cardiol., September 17, 2003; 42(6): 1115 - 1119. [Abstract] [Full Text] [PDF]

				S. E. Bojesen, K. Juul, P. Schnohr, A. Tybjaerg-Hansen, and B.o. G. Nordestgaard Platelet glycoprotein IIb/IIIa PlA2/PlA2 homozygosity associated with risk of ischemic cardiovascular disease and myocardial infarction in young men: The Copenhagen City Heart Study J. Am. Coll. Cardiol., August 20, 2003; 42(4): 661 - 667. [Abstract] [Full Text] [PDF]

				S. E. Bojesen, A. Tybjaerg-Hansen, and B. G. Nordestgaard Integrin {beta}3 Leu33Pro Homozygosity and Risk of Cancer J Natl Cancer Inst, August 6, 2003; 95(15): 1150 - 1157. [Abstract] [Full Text] [PDF]