Effects of abciximab, ticlopidine, and combined Abciximab/Ticlopidine therapy on platelet and leukocyte function in patients undergoing coronary angioplasty

Interactions Between Therapeutic Proteins and Small Molecules: The Shared Role of Perpetrators and Victims

Therapeutic proteins (TPs) are becoming increasingly important as therapeutic agents. A consequence of expanding their clinical indications is coadministration with well-established small-molecule drugs (sMDs), which could lead to unpredictable effects. According to the existing regulatory guidance, the development of an sMD includes the evaluation of potential drug-drug interactions (DDIs). For TPs, only a few drug interaction studies have been published. Limited clinically relevant models, long half-lives, and complex elimination pathways are among the associated difficulties.

Differential platelet deposition onto collagen in cone-and-plate and parallel plate flow chambers

To routinely test the formation of thrombi and the effect of drugs modifying it, proper test systems are needed. Their design should rely on the laws of rheology and the physiology of laminar flow. To best model physiological or pathological shear conditions, parallel/linear and rotational type flow chambers are developed. We have compared the initial phase of platelet thrombus formation in a parallel plate flow chamber (PPC) and a cone-and-plate chamber (CPC) under von Willebrand dependent shear conditions. Blood was allowed to flow through human collagen type III surfaces at a shear rate of 1000 s(-1) for 150 s. Thrombus deposition was characterized by surface coverage, average area and height of thrombi. VWF distribution within thrombi was analyzed with confocal laser scanning microscopy. Reduced surface-specific platelet adhesion and aggregation (surface coverage and average thrombus size) were observed in CPC along with a significant increase in single platelet disappearance from the circulating blood. Our data suggest that the higher rate of platelet consumption in this device, as opposed to PPC, is limiting the adhesion to the surface. Consequently, surface-specific processes and aggregation in the flowing blood are both assessed using CPC, while comprehensive evaluation of surface-specific processes is best achieved with PPC. Therefore, the choice of chamber type as a diagnostic tool is purpose-dependent.

Platelets and tissue factor

Tissue factor (TF) is the most important initiator of intravascular coagulation. This article will review published evidence on the contribution of platelets to TF exposure to the circulating blood. The following mechanisms will be discussed: decryption of monocyte TF by platelets, contribution of platelets to TF expression in leukocytes, platelet-derived TF and its procoagulant activity, and activation of circulating TF by platelets.

Effects of escalating doses of tirofiban on platelet aggregation and major receptor expression in diabetic patients: Hitting the TARGET in the TENACITY trial?

INTRODUCTION

Ongoing search for the optimal dosing regimens, and valid concerns that some GPIIb/IIIa inhibitors may cause rebound platelet activation are limiting the use of these agents in patients with acute vascular events.

MATERIALS AND METHODS

We assessed the in vitro effects of preincubation with escalating (12.5-200 ng/mL) concentrations of tirofiban on platelet biomarkers in 20 diabetic patients. Platelet activity was assessed by ADP-, and collagen-induced conventional plasma aggregometry, and by whole blood flow cytometry measuring expression of PECAM-1, GPIb, GP IIb/IIIa antigen and activity, vitronectin, P-selectin, LAMP-1, GP 37, LAMP-3, activated and intact PAR-1 thrombin receptors, GPIV, and platelet-monocyte formation. All patients were treated with aspirin (at least 81 mg daily for 1 month); other antiplatelet agents were not allowed.

RESULTS

Significant decrease of ADP-induced platelet aggregation was observed starting at the low 12.5 ng/mL concentration (p=0.0001), with total inhibition occurring at 50 ng/mL of tirofiban dose. Inhibition of collagen-induced platelet aggregability requires 25 ng/ml of tirofiban (p=0.002), and was complete at 100 ng/mL. Dose-dependent blockade of GP IIb/IIIa activity was observed with tirofiban concentrations over 50 ng/mL (p=0.003). Other receptors were unaffected even with the high doses of tirofiban (100-200 ng/mL).

CONCLUSION

Tirofiban completely inhibits ADP- and, with the higher dose, collagen-induced platelet aggregation. Higher loading dose of tirofiban used in the ongoing TENACITY trial (100 ng/mL) may be superior with regard to clinical outcomes to the regimens used in PRISM-PLUS (25 ng/mL), or TARGET (50 ng/mL). Selective inhibition of GPIIb/IIIa activity, and lack of alternative platelet activation beyond the GP IIb/IIIa blockade may represent the therapeutic advantage of tirofiban over other agents.

Effect of doxazosin gastrointestinal therapeutic system on platelet degranulation and platelet-leukocyte microaggregate formation induced by physiologic shear stress in hypertension

INTRODUCTION

In this prospective, ex vivo, single-blind study, the effect of doxazosin on platelet function was studied in patients with hypertension.

MATERIALS AND METHODS

Platelet activation by shear stress was measured in whole blood samples of 22 hypertensive patients and 22 normotensive controls, using flow cytometry. Sheared samples were evaluated for CD62 expression, microaggregate formation, and Ca2+ mobilization. Results were collected at baseline and after 1 and 2 months of single-dose (4 mg/d) extended-release doxazosin gastrointestinal therapeutic system therapy.

RESULTS

Doxazosin normalized blood pressure in hypertensive patients after 1 and 2 months of treatment. Hypertensive patients had a higher baseline percentage (mean+/-SD) of degranulated platelets (CD62+) than the normotensive control group (4.14+/-1.05 vs. 2.47+/-0.68, P<0.01). After 2 months of doxazosin gastrointestinal therapeutic system treatment, the percentage of CD62+ in the experimental group significantly decreased (P<0.05). At baseline, the number of platelet-leukocyte aggregates in vivo was greater in hypertensive patients (P<0.01); doxazosin did not normalize this measurement. Following shearing, platelet expression of CD62 increased significantly in the hypertensive group (P<0.001 vs. control). Shear stress-induced platelet activation and microaggregate formation were also greater in hypertensive patients. Intraplatelet-free calcium concentration was higher in hypertensive patients at baseline than in the normotensive group (P<0.001). At 2 months, doxazosin significantly reduced thrombin-stimulated Ca2+ mobilization in hypertensive patients (P<0.01 vs. baseline).

CONCLUSIONS

Platelets from hypertensive patients are more readily activated by shear stress and demonstrate significant alterations in cytoplasmic-free calcium mobilization. Doxazosin treatment reduced blood pressure and normalized alterations in platelet function.

A randomized trial comparing clopidogrel versus ticlopidine therapy in patients undergoing infarct artery stenting for acute myocardial infarction with abciximab as adjunctive therapy

AIM

To evaluate the impact of a clopidogrel therapy on the effectiveness of myocardial reperfusion in patients with ST-segment elevation acute myocardial infarction (AMI) undergoing routine infarct-related artery (IRA) stent implantation and receiving routine abciximab therapy.

BACKGROUND

Inflammatory processes after mechanical restoration of flow in AMI play a central role in decreasing the effectiveness of reperfusion at microcirculatory level. Several studies suggest that clopidogrel may exert a protective effect against adverse cardiovascular events by virtue of its anti-inflammatory properties.

METHODS

A total of 133 patients with a first ST-elevation AMI were randomized to clopidogrel (600-mg loading dose before IRA stenting followed by 75 mg daily, n = 66) or ticlopidine (500 mg before IRA stenting followed by 250 mg twice daily, n = 67). The primary end point was scintigraphic infarct size at 1 month. The secondary end points were ST-segment elevation resolution within 3 hours of procedure and 1-month clinical outcome, as a composite of death, reinfarction, target vessel revascularization, and stroke within 1 month of the index procedure.

RESULTS

The 1-month technetium 99m sestamibi scintigraphy revealed similar infarct size (16.2% +/- 14.6% vs 15.0% +/- 14.1%, P = .703) and severity (0.48 +/- 0.18 vs 0.49 +/- 0.15, P = .592) in the clopidogrel group as compared with the ticlopidine group. Three-hour ST-segment resolution rate was similar in the 2 study groups (86% vs 89%, P = .642). At 1 month, there was no difference in major cardiovascular adverse event rate (3% vs 3%, P = .988). Discontinuation of thienopiridine therapy within the first month occurred in no patient randomized to clopidogrel and in 3 (4.5%) patients randomized to ticlopidine (P = .082).

CONCLUSION

Clopidogrel has no impact on the effectiveness of myocardial reperfusion in patients with AMI treated routinely with stenting and abciximab. However, clopidogrel, administered as a 600-mg loading dose followed by 75 mg daily, is safe and at least as effective as the standard ticlopidine therapy in this subgroup of patients.

P-selectin in haemostasis

During the past decade, interrelationships between inflammation and thrombosis have been the subject of extensive works, and it is now commonly recognized that inflammation (notably leucocyte recruitment) directly affects thrombosis, and that thrombosis also constitutes a pro-inflammatory event. This tight link is partly attributable to P-selectin, which is functional not only when expressed on the surface of activated platelets and endothelial cells, but also when shed, generating its soluble form, termed sP-selectin. In this review, we will provide an overview of the relative roles of the different compartments of P-selectin (platelet, endothelial cell, plasma) in haemostasis and vascular pathologies, and the potential therapeutic benefits achievable in targeting this molecule.

The anti-leukemic Bruton's tyrosine kinase inhibitor alpha-cyano-beta-hydroxy-beta-methyl-N-(2,5-dibromophenyl) propenamide (LFM-A13) prevents fatal thromboembolism

The leflunomide metabolite analog alpha-cyano-beta-hydroxy-beta-methyl-N-(2,5-dibromophenyl)-propenamide (LFM-A13) is a rationally-designed specific inhibitor of the TEC family protein tyrosine kinase, Bruton's tyrosine kinase (BTK) which plays an important role in platelet physiology by regulating the glycoprotein GPVI-FcRgamma-coupled collagen receptor signaling pathway. At low micromolar concentrations, LFM-A13 inhibited collagen-induced ultrastructural changes indicative of activation. LFM-A13 inhibited collagen (but not thrombin, TRAP-6, or ADP)-induced platelet aggregation in a concentration-dependent fashion with an IC50 value of 2.8 microM. LFM-A13 was not toxic to mice when administered systemically at dose levels ranging from 1 to 100 mg/kg. At nontoxic dose levels, LFM-A13 prolonged the tail bleeding times of mice and improved event-free survival in two mouse models of agonist-induced invariably fatal pulmonary thromboembolism. To our knowledge, LFM-A13 is the first anti-thrombotic agent which prevents platelet aggregation by inhibiting BTK.

Effect of clopidogrel pretreatment on inflammatory marker expression in patients undergoing percutaneous coronary intervention

Platelets play an important role in the inflammatory response. In a nonrandomized comparison, we examined the effect of clopidogrel pretreatment on platelet inflammatory marker expression in patients undergoing percutaneous coronary intervention (PCI). Platelet expression of the inflammatory markers CD40 ligand (L) and CD62 P-selectin (P) and serum levels of interleukin-6 and CD40L were compared in patients pretreated (>24 hours before PCI) or not pretreated with clopidogrel. Blood samples were obtained before and after the procedure, and from 18 to 24 hours later. Marker expression in resting and adenosine diphosphate (ADP) (50 micromol/L) and thrombin receptor activating peptide (TRAP) (10 micromol/L) activated samples was quantified by flow cytometry. Serum CD40L and interleukin (IL)-6 levels were determined by enzyme-linked immunosorbent assay. Seventy-nine patients were recruited into the study. Forty-two percent were pretreated with clopidogrel for a median of 5 days (range 1 to 1,325). Clopidogrel pretreatment was associated with lower ADP-activated platelet CD40L expression in baseline and postprocedural samples. Similarly, platelet CD62P expression at all time points in ADP-activated and in baseline and postprocedural TRAP-activated samples was lower in patients pretreated with clopidogrel. These differences remained after multivariate adjustment between the groups. Serum CD40L levels increased from 2.13 +/- 2.37 ng/ml at baseline to 4.77 +/- 3.86 ng/ml at 18 to 24 hours after the procedure (p <0.0001). Similarly, serum IL-6 levels increased at 18 to 24 hours after the procedure (14.8 +/- 42.0 pg/ml before vs 25.5 +/- 36.0 pg/ml at 18 to 24 hours after the procedure, p <0.0001). Clopidogrel pretreatment did not affect serum IL-6 or CD40L levels. Thus, clopidogrel pretreatment reduces platelet inflammatory marker expression in patients undergoing PCI.

Effects of diltiazem on platelet activation and cytosolic calcium during percutaneous transluminal coronary angioplasty

AIMS

To evaluate effects of diltiazem on platelet hyper-reactivity in situations associated with endothelial injury and their possible relationship to cytosolic calcium concentration.

METHODS

Blood samples were collected at seven time points from 35 patients undergoing percutaneous transluminal coronary angioplasty (PTCA) who received combined diltiazem and aspirin/ticlopidine therapy or aspirin/ticlopidine therapy alone. Platelet expression of glycoprotein IIb/IIIa and P-selectin, production of thromboxane B(2), and cytosolic calcium concentration were measured, respectively, by whole blood flow cytometry, radioimmunoassay, and fluorospectrophotometry. The effects of diltiazem of different concentrations on expression of glycoprotein IIb/IIIa and P-selectin were also studied in vitro in blood samples from patients with chronic stable angina.

RESULTS

Of the two treatments, aspirin/ticlopidine therapy did not prevent an acute increase of expression of glycoprotein IIb/IIIa and P-selectin and plasma thromboxane B(2) five minutes and 10 minutes after first inflation and 10 minutes after PTCA, whereas combined diltiazem and aspirin/ticlopidine therapy had a significant inhibitory effect. In the group receiving aspirin/ticlopidine therapy, there was a short term increase of platelet [Ca(2+)](i) immediately after PTCA which was significantly reduced by diltiazem treatment. Expression of glycoprotein IIb/IIIa and P-selectin was significantly inhibited in vitro by diltiazem in the concentration of 200 ng/ml or higher, but not 50 ng/ml.

CONCLUSIONS

Combined diltiazem and aspirin/ticlopidine therapy significantly inhibited platelet activation that continued in the presence of conventional aspirin/ticlopidine treatment. Antiplatelet effects of diltiazem were probably a consequence of reduction of platelet [Ca(2+)](i) and may only be achieved in higher than therapeutic concentrations.

Abciximab: an updated review of its therapeutic use in patients with ischaemic heart disease undergoing percutaneous coronary revascularisation

Abciximab (Reopro) is an antibody fragment that dose-dependently inhibits platelet aggregation and leucocyte adhesion by binding to the glycoprotein (GP) IIb/IIIa, vitronectin and Mac-1 receptors. Abciximab (0.25 mg/kg bolus plus infusion of 0.125 micro g/kg/min for 12 hours) showed greater efficacy than tirofiban in reducing the 30-day composite endpoint of death, nonfatal myocardial infarction (MI) or urgent target-vessel revascularisation in the randomised, double-blind TARGET study in patients scheduled for stent placement. In addition, the beneficial effects of treatment with abciximab previously observed in the randomised, multicentre, placebo-controlled EPILOG and EPISTENT studies have been maintained to 1 year, with a significantly reduced incidence of ischaemic complications relative to placebo consistently observed across a range of subgroups including age, sex, bodyweight and indication for revascularisation. The incidence of the composite endpoint was reduced in patients presenting with acute MI of <48 hours' duration in comparison with either fibrinolytic therapy or stenting alone in the randomised STOPAMI and ADMIRAL trials, primarily because of a reduced requirement for urgent repeat revascularisation and reduced incidence of mortality. In the randomised, nonblind, multicentre CADILLAC trial in patients with acute myocardial infarction (MI), stenting alone was superior to percutaneous transluminal coronary angioplasty (PTCA) and stenting alone was not inferior to PTCA plus abciximab. Recent large randomised, multicentre studies (ASSENT-3 and GUSTO-V) have shown higher efficacy (on various ischaemic endpoints) of abciximab in combination with either a reduced dose of tenecteplase or reteplase compared with the fibrinolytic drug alone. TIMI grade 3 flow rates at 60 and 90 minutes in the TIMI-14 and SPEED trials were higher in patients who received abciximab in combination with either alteplase or reteplase than abciximab alone and were similar to that seen with the full-dose fibrinolytic alone. In the randomised, multicentre GUSTO IV-ACS study, no significant differences in any of the ischaemic endpoints at either 7 or 30 days in patients with acute coronary syndromes who were not scheduled to undergo early revascularisation (within 12 hours of end of infusion) were apparent between those who received abciximab (bolus and either 24- or 48-hour infusion) and those who received placebo in addition to aspirin and heparin. The most common adverse events associated with the use of abciximab are bleeding complications and thrombocytopenia, although the risk of major bleeding can be limited through adhering to current administration protocols. Treatment costs are generally higher in both stent plus abciximab and angioplasty plus abciximab groups than stent plus placebo, primarily because of the acquisition cost of abciximab. Abciximab appeared most cost beneficial in high-risk patients undergoing elective percutaneous coronary revascularisation; among lower risk patients, abciximab therapy has been associated with higher total in-hospital and 6-month medical costs than eptifibatide.

CONCLUSION

The GP IIb/IIIa receptor antagonist abciximab, when used with aspirin and heparin, has demonstrated efficacy in reducing the short- and long-term risk of ischaemic complications in patients with ischaemic heart disease undergoing percutaneous coronary intervention, when used with aspirin and heparin. High-risk patients (including those with diabetes mellitus) derive particular benefits from abciximab treatment. Abciximab remains an important therapeutic option for the prevention of complications in patients with ischaemic heart disease.

Comparison of shear stress-induced platelet microparticle formation and phosphatidylserine expression in presence of alphaIIbbeta3 antagonists

The use of platelet glycoprotein IIb-IIIa (alphaIIbbeta3) antagonists is an accepted practice in the treatment of acute coronary syndromes. Recent studies have demonstrated that alpha beta receptor antagonists are effective in inhibiting the procoagulant activity of platelets under static conditions. No investigation, however, has compared the ability of these platelet antagonists to inhibit platelet procoagulant activity, defined as an increase in phosphatidylserine (PS) expression, under conditions of shear stress. Thus, the goal of this study was to quantify the amount of microparticle formation and PS expression of platelets exposed to physiologic and pathophysiologic levels of shear stress in the absence and presence of three clinically approved parenteral alpha beta antagonists (abciximab, eptifibatide, and tirofiban). Flow cytometric results demonstrated that although microparticle formation was significantly inhibited by all three antagonists, PS expression by sheared platelets was affected differently depending on the antagonist present. Specifically, abciximab suppressed PS expression compared with the saline control; both abciximab and eptifibatide significantly reduced PS expression compared with tirofiban; and tirofiban potentiated PS expression relative to the saline control at the highest shear stress. This is the first demonstration of differential regulation of platelet PS expression and, by inference, procoagulant activity in the presence of alpha receptor antagonists under shear stress. The current results may have future importance in improving the design of platelet antagonists as well as defining the general role of fluid shear stress in platelet thrombus formation.

Purinergic P2Y12 receptor blockade inhibits shear-induced platelet phosphatidylinositol 3-kinase activation

Pathologically elevated shear stress triggers aspirin-insensitive platelet thrombosis. Signaling mechanisms involved in shear-induced platelet thrombosis are not well understood. To investigate these, we examined the hypothesis that functionally important platelet phosphatidylinositol 3-kinase (PI3-K) activity is stimulated by an in vitro shear stress of 120 dynes/cm(2) (shear rate of 6,000 sec(-1)). Phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) production was examined in washed human platelets subjected to pathological shear stress in a cone-plate viscometer. PIP(3) production peaks 30 s after shear begins and is initiated by von Willebrand factor (VWF) binding to the glycoprotein (Gp) Ib-IX-V complex. Inhibiting PI3-K with wortmannin or 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) results in the inhibition of shear-induced platelet aggregation. In resting platelets, class IA PI3-K associates with the tyrosine kinase Syk. Within 30 s of beginning shear, PI3-K-associated Syk becomes tyrosine phosphorylated. Inhibiting Syk activation with piceatannol results in the inhibition of PIP(3) production and aggregation. Selective blockade of the P2Y(12) receptor results in the inhibition of Syk phosphorylation, PIP(3) production, and aggregation. These results indicate that shear-induced VWF binding to platelet GpIb-IX-V stimulates functionally important PI3-K activity. PI3-K activation is signaled by rapid feedback amplification that involves P2Y(12) receptor-mediated activation of Syk.

The effects of GPIIb-IIIa antagonists and a combination of three other antiplatelet agents on platelet-leukocyte interactions

The effects of the GPIIb-IIIa antagonists abciximab and MK-852 on platelet-leukocyte interactions in vitro were studied and the results compared with those obtained with a combination of aspirin, dipyridamole and AR-C69931 (Asp/Dip/AR-C). Platelet-monocyte (P/M) and platelet-neutrophil (P/N) conjugate formation increased when blood was stirred or a platelet agonist was added. Leukocyte activation also occurred as judged by expression of surface tissue factor antigen and CD11b. Abciximab and MK-852 potentiated P/M, especially when collagen was used. They also increased the amount of tissue factor on the monocytes, but not CD11b. The Asp/Dip/AR-C did not enhance P/M or tissue factor exposure. Augmented tissue factor expression on monocytes in the presence of a GPIIb-IIIa antagonist may be relevant to the increased mortality associated with trials of such antagonists when given orally in patients with vascular disease. The Asp/Dip/AR-C was superior to abciximab and MK-852 in inhibiting platelet and leukocyte function.

Platelet–monocyte complex formation: effect of blocking PSGL-1 alone, and in combination with αIIbβ3 and αMβ2, in coronary stenting

BACKGROUND

Binding of platelet P-selectin to P-selectin glycoprotein ligand 1 (PSGL-1) is an initial event in the interactions between platelets and monocytes. Platelet-monocyte complexes (PMCs) have been implicated in several vascular disease processes, including acute coronary syndromes (ACS) and complications after percutaneous coronary intervention (PCI). We investigated the effect of ex vivo blockade of PSGL-1, alone and in combination with blockade of the alphaMbeta(2) (Mac-1) and alpha(IIb)beta(3) (GP IIb/IIIa) integrins, on PMC formation.

METHODS AND RESULTS

Dual-label flow cytometry was used to detect PMCs in the blood of 10 volunteers and 10 patients undergoing PCI who received intravenous GP IIb/IIIa antagonists. PSGL-1 blockade, both prior to and after platelet stimulation, markedly reduced the formation of PMCs. Concomitant ex vivo blockade of the alphaMbeta(2) and alpha(IIb)beta(3) integrins did not result in further decreases of PMCs compared to PSGL-1 blockade alone. Antagonism of PSGL-1 also led to near elimination of leukocyte-platelet interactions under flowing conditions.

CONCLUSION

Blockade of PSGL-1 alone is sufficient to inhibit and reverse the formation of PMCs following platelet stimulation. Concurrent antagonism of PSGL-1 and the alpha(IIb)beta(3) and alphaMbeta(2) integrins was not more effective than inhibition of PSGL-1 alone. These results suggest that platelet-monocyte complex formation is mostly dependent on PSGL-1.

Effects of different thrombolytic treatment regimen with abciximab and tirofiban on platelet aggregation and platelet-leukocyte interactions: a subgroup analysis from the GUSTO V and FASTER trials

BACKGROUND

Due to considerably high rates of reocclusion under standard thrombolytic therapy GP IIb/IIIa inhibitors have been combined with thrombolytics to improve therapeutic outcomes. Potential reasons for arterial reocclusion may be increased platelet activation, interaction of platelets with other cell types such as leukocytes and inadequate drug dosing due to lack of ideal platelet monitoring. We compared combination therapy regimens consisting of GP IIb/IIIa inhibitors and thrombolytics with respect to platelet inhibition and platelet-leukocyte interactions.

METHODS AND RESULTS

From the GUSTO V trial (standard rPA vs. reduced dose rPA and abciximab) and the FASTER trial (standard TNK-tPA vs. reduced dose TNK-tPA and tirofiban) 15 patients were monitored by platelet aggregometry, rapid platelet function assay (RPFA) and flow cytometry (FC). rPA alone (n = 5) caused initial increases in platelet aggregation. However, platelet aggregation was significantly (p < 0.05) and sufficiently (>80%) inhibited by abciximab/rPA (n = 5) and tirofiban/TNK-tPA (n = 5). The platelet inhibitory effect of tirofiban/TNK-tPA was more pronounced compared to abciximab/rPA with a significant difference after 2 h (p < 0.05). Tirofiban/TNK-tPA and abciximab/rPA caused decreases in platelet-leukocyte aggregates as well as in binding of specific antibodies to the platelet vitronectin receptor and P-selectin (p < 0.05, respect.). No differences among the treatment groups were seen with respect to antibody binding to MAC-1 and CD154/CD40 ligand.

CONCLUSIONS

Taken together, GP IIb/IIIa inhibitors overcome the platelet activating effect of thrombolytics resulting in sufficient platelet inhibition. RPFA is a suitable monitoring tool to accurately assess platelet inhibition. Within the given combination treatment regimen tirofiban appears to be more effective compared to abciximab and to exert effects beyond the inhibition of GP IIb/IIIa.

Effect of eptifibatide for acute coronary syndromes: rapid versus late administration--therapeutic yield on platelets (The EARLY Platelet Substudy)

BACKGROUND

Receptors other than GP IIb/IIIa may mediate leukocyte-platelet-endothelial interactions that obstruct the microvasculature in acute coronary syndromes (ACS) and cause microinfarcts. The effect of eptifibatide on these receptors was investigated in a substudy of the EARLY Trial.

METHODS

Patients received early (in the Emergency Department, n = 27) or late (12-24 h, n = 28) eptifibatide. Ten platelet receptors by flow cytometry and platelet aggregation (10 micromol/L ADP) were measured serially at baseline, and at 3, 6, 12 and 24 h after randomization.

RESULTS

Platelet aggregation was rapidly inhibited by early eptifibatide therapy (baseline, 72 +/- 20%; 3 h post, 7 +/- 9%; p < 0.001). No significant differences were seen in either group for CD 31, CD 63, CD 107a, CD 107b, CD 41 (GPIIb/IIIa expression), or CD 62p. Leukocyte-platelet aggregate formation (mean fluorescense intensity) trended upward after presentation (early baseline, 43.1 +/- 26.0 versus 65.8 +/- 35.6, p =.09). PAC-1 (GP IIb/IIIa activity), CD 51/61 (vitronectin receptor) and CD 42b (GP Ib) were inhibited by eptifibatide (p <.05).

CONCLUSIONS

In Emergency Department patients with unstable angina, early eptifibatide rapidly and profoundly inhibits platelet aggregation and reduces GP IIb/IIIa activity and the expression of CD51/61 and CD 42b; the latter two effects may also contribute to the drug's anti-thrombotic effect. However, platelet-leukocyte aggregate formation, a marker of platelet activity rises within 24 h after presentation despite eptifibatide therapy and is a potential mechanism for microvascular obstruction.

Noninvasive measurement of shear rate in autologous and prosthetic bypass grafts

There is a major difference in thrombogenicity between lower extremity prosthetic and autologous vein bypass grafts, and arterial blood flow shear rate is known to influence thrombus formation. Despite this association, there has been little direct clinical observation of shear rates in bypass grafts. The authors developed a new noninvasive method to quantitate human arterial shear rate and used it in a pilot study to characterize differences in lower extremity bypasses. Shear rates were measured in 10 prosthetic and 14 autologous vein femoropopliteal bypass grafts. With CVI-M-mode color flow ultrasonography in resting supine patients, a velocity profile was recorded from a midgraft longitudinal section in the ultrasound beam direction. Shear rates were calculated by using a mathematical-graphic computer program at the anteromedial (near) and posterolateral (far) graft walls by averaging values immediately before and after peak systolic velocity (PSV). Comparison between prosthetic and autologous graft groups respectively revealed that differences in age (67 +/- 12 [SD] vs 71 +/- 10 yr), male gender (60% vs 43%), prevalence of hypertension (50% vs 71%), diabetes (40% vs 64%), smoking (50% vs 50%), hypercholesterolemia (30% vs 29%), coronary artery disease (60% vs 50%), and critical ischemia (60% vs 86%) did not reach statistical significance (p>0.19). Median PSVs were significantly less in prosthetic than in autologous vein bypasses (37 +/- 13 vs 57 +/- 22 cm/s, p=0.018). Prosthetic and autologous graft diameters were not statistically significantly different (6.3 +/- 1.1 vs 5.6 +/- 1.3 mm, p = 0.18). Shear rates were significantly less in prosthetic than in autologous vein bypasses both at the near wall (382 +/- 146 vs 698 +/- 271 s(-1), p=0.003) and at the far wall (551+/-235 vs 827+/-339 s(-1), p-0.037). This mathematical model can be used to calculate shear rate from observed ultrasound flow patterns. Prosthetic bypass grafts had lower shear rates than autologous vein grafts.

TARGET versus GUSTO-IV: appropriate use of glycoprotein IIb/IIIa inhibitors in acute coronary syndromes and percutaneous coronary intervention

Until recently, the selection of which glycoprotein IIb/IIIa inhibitor to use for patients with acute coronary syndromes or those undergoing percutaneous coronary intervention largely reflected physician preference, costs, and any evidence supporting the clinical indication. Clinicians often assumed a class effect for these agents: a benefit observed for one agent in one clinical setting (such as percutaneous coronary intervention) would confer benefit in another (such as non-ST-elevation acute coronary syndromes). The need for evidence to guide treatment selection motivated the design of the Do Tirofiban and ReoPro Give Similar Efficacy Trial (TARGET) and the Global Use of Strategies to Open occluded arteries (GUSTO-IV) trials with abciximab. This review examines the results from these and other recent trials of glycoprotein IIb/IIIa inhibition in acute coronary syndromes and percutaneous coronary intervention, presents a rationale for the lack of a consistent benefit with abciximab, and describes future directions for clinical investigation.

The failure of orally administered glycoprotein IIb/IIIa inhibitors to prevent recurrent cardiac events

PURPOSE

Despite the success of intravenous glycoprotein IIb/IIIa antagonists, oral formulations have failed to show benefit and have been associated with increased mortality. To understand these findings, we performed a meta-analysis of results from four phase 3 trials.

SUBJECTS AND METHODS

Trials were identified by MEDLINE search; review of abstracts from American College of Cardiology, European Society of Cardiology, and American Heart Association scientific sessions; or querying investigators in the field. Published, phase 3, randomized, placebo-controlled trials involving more than 1000 patients with coronary artery disease that compared an oral glycoprotein IIb/IIIa antagonist with or without background aspirin versus aspirin, and that had a planned follow-up of > or =30 days, were included. Four trials met these criteria. Odds ratios (ORs) and 95% confidence intervals (CIs) were generated from results, and combined using an empirical Bayes random-effects model.

RESULTS

Among 33,326 patients, oral glycoprotein IIb/IIIa agents were associated with 31% increased mortality (OR = 1.31; 95% CI: 1.12 to 1.53; P= 0.0001). Results were similar whether the agent was added to (OR = 1.38; 95% CI: 1.15 to 1.67) or substituted for (OR = 1.37; 95% CI: 1.00 to 1.86) aspirin. Ischemic events or sudden death (OR = 1.22; 95% CI: 0.91 to 1.63) were also more common. Among patients with acute coronary syndromes, the incidence of myocardial infarction was increased (OR = 1.16; 95% CI: 1.03 to 1.29).

CONCLUSION

Oral glycoprotein IIb/IIIa inhibitor therapy is associated with increased mortality and myocardial infarction. No single explanation for these findings is satisfactory; the problem is likely to be multifactorial.

Mechanisms of platelet-neutrophil interactions and effects on cell filtration in septic shock

ABSTRACT-We examined the mechanisms and the adhesive molecules mediating platelet-neutrophil adhesion in patients with septic shock. Neutrophils, platelets, and platelet poor plasma (NPPP) were isolated from 12 normal volunteers. Platelets and neutrophils were stimulated with platelet poor plasma (SPPP) removed from 12 patients in septic shock. Cell adhesion was assessed by filtration through 5-microm pore filters and by flow cytometry. Blocking monoclonal antibodies were used against the platelet and neutrophil surface receptors glycoprotein complex IIb/IIla, P-selectin, ICAM-2, CD11a, CD11b, and CD18. The filtration pressure (Pi) of cells suspended in SPPP was significantly greater than that of cells suspended in NPPP (24 +/- 1.0 mmHg vs. 14 +/- 1.0 mmHg; P< 0.05). The difference between the Pi of cells suspended in SPPP or NPPP (deltaPi SPPP-NPPP) in the presence of monoclonal antibodies anti-CD41, anti-CD62P, abciximab, anti-CD11a, anti-CD11b, and anti-CD18 was significantly less than the APi SPPP-NPPP of cell suspensions without the addition of these monoclonal antibodies (P < 0.01). The greatest reduction in Pi occurred when platelet receptor P-selectin was blocked simultaneously with the CD11b receptor on the neutrophil as compared to all other single blocking monoclonal antibodies or combinations of monoclonal antibodies. The mean fluorescence of activated platelet CD63-PE binding to neutrophils suspended in SPPP was significantly greater than that of cells suspended in NPPP (780 +/- 130 Ifu vs. 295 +/- 35 Ifu; P < 0.05). The greatest attenuation in mean fluorescence occurred by blocking the P-selectin receptor on the platelet simultaneously with CD11b receptor on the neutrophil. We conclude that platelet-neutrophil aggregation is increased in septic shock. This aggregation is mediated by the interaction of multiple platelet and neutrophil surface receptors. The platelet receptor P-selectin and the neutrophil receptor CD11b/CD18 appear to play the most important role in these interactions.

Antithrombotic agents: implications in dentistry

Thrombosis and the complicating emboli that can result are important causes of illness and death. Thrombosis is of greater overall clinical importance in terms of morbidity and mortality than all of the hemorrhagic disorders combined. Agents such as heparin, low-molecular weight heparin, warfarin, aspirin, ticlopidine, clopidogrel, and tirofiban are used to prevent venous or arterial thrombosis. Patients taking these antithrombotic agents may be at risk for excessive bleeding after invasive dental procedures. The current antithrombotic agents used in medicine are reviewed, and the dental management of patients taking these agents is discussed.

Close relationship between the platelet activation marker CD62 and the granular release of platelet-derived growth factor

The expression of CD62 on the surface of platelets is considered to be an indicator of platelet degranulation and secretion. We characterized the relationship between CD62 expression and platelet-derived growth factor (PDGF)(AB) and PDGF(BB) secretion in response to thrombin-receptor activating peptide (TRAP). The principal findings were 1) expression of CD62 as a constituent of platelet alpha-granule membrane and secretion of PDGF, an important ingredient of alpha-granules, can be stimulated by TRAP-induced activation in a dose-dependent fashion; 2) the activation marker and secretion product are closely correlated with each other; and 3) changes in the CD62 expression induced by a drug, namely clopidogrel, or by a disease, namely diabetes, are paralleled by changes in PDGF secretion. Although CD62 is perceived as an activation marker of platelets indicating enhanced aggregability and secretion of alpha-granular content, the proof that the CD62 status and its modifications reflect directly the actual secretion of the most important platelet mitogen, PDGF, has so far not been given. This ex vivo-in vitro study shows that at least for the activation pathway provided by the PAR-1 receptor for which TRAP is the selective agonist, CD62 expression on platelets could be a surrogate for their secretory activity.

Blockade of adenosine diphosphate receptors P2Y(12) and P2Y(1) is required to inhibit platelet aggregation in whole blood under flow

Using heparinized whole blood and flow conditions, it was shown that adenosine 5'-diphosphate (ADP) receptors P2Y(12) and P2Y(1) are both important in direct shear-induced platelet aggregation and platelet aggregation subsequent to initial adhesion onto von Willebrand factor (vWf)-collagen. In the viscometer, whole blood was subjected to shear rates of 750, 1500, and 3000 s(-1) for 30 seconds at room temperature. The extent of aggregation was determined by flow cytometry. The P2Y(12) antagonist AR-C69 931MX (ARMX) reduced shear-induced aggregation at these rates by 56%, 54%, and 16%, respectively, compared to control samples. Adenosine 3',5'-diphosphate (A3P5P; P2Y(1) antagonist) inhibited shear-induced aggregation by 40%, 30% and 29%, respectively, compared to control samples. Blockade of both ADP receptors at 3000 s(-1) with ARMX plus A3P5P further reduced the platelet aggregation by 41% compared to the addition of ARMX alone (57% compared to control samples). Using a parallel-plate flow chamber, whole blood was perfused over bovine collagen type 1 at a wall shear rate of 3000 s(-1) for 60 seconds. Platelet deposition was quantified with epifluorescence video microscopy and digital image processing. Blockade of P2Y(12) alone or blockade of P2Y(1) alone did not reduce thrombus formation on vWf-collagen. In contrast, blockade of both P2Y(12) and P2Y(1) reduced platelet deposition by 72%. These results indicate that combinations of antagonists of the ADP receptors P2Y(12) and P2Y(1) are effective inhibitors of direct shear-induced platelet aggregation and of platelet aggregation subsequent to initial adhesion under flow conditions. Inhibitors of these pathways are potentially useful as antiarterial thrombotic agents.

Fluorescence spectroscopic analysis of circulating platelet activation during coronary angioplasty

BACKGROUND AND OBJECTIVE

Platelet activation during percutaneous transluminal coronary angioplasty (PTCA) initiates thrombus formation and plaque regrowth at sites of arterial injury, limiting procedure efficacy. We have developed a simple assay for circulating platelet activation based on fluorescence analysis of membrane fluidity and intracellular calcium concentration and light scattering analysis of platelet aggregation.

STUDY DESIGN/MATERIALS AND METHODS

Platelet activation state was measured in 45 patients undergoing angioplasty, before and after treatment with platelet inhibitors.

RESULTS

PTCA alone produced a decrease in pyrene dimer formation (P0.0083) and an increase in light scattering at 650 nm (P0.0128). Treatment with ADP and GPIIb/IIIa receptor antagonists reduced PTCA induced changes in pyrene dimer formation. An unexpected decrease in pyrene dimer formation (P0.05) was detected when the GPIIb/IIIa receptor antagonist was given together with an ADP receptor antagonist.

CONCLUSIONS

1) Analysis of membrane fluidity provides a sensitive marker for platelet activation state. 2) Reduced membrane fluidity after combined platelet inhibitor treatments suggests reduced antiplatelet efficacy.

Effect of glycoprotein IIb/IIIa receptor blocker abciximab on outcome in patients with acute coronary syndromes without early coronary revascularisation: the GUSTO IV-ACS randomised trial

BACKGROUND

Glycoprotein IIb/IIIa blockers reduce procedure-related thrombotic complications of percutaneous coronary intervention, and the risk of death and myocardial infarction in patients with acute coronary syndromes. The effect on risk of death and myocardial infarction is particularly apparent in patients undergoing early percutaneous coronary interventions. We did a randomised, multicentre trial to study the effect of the glycoprotein IIb/IIIa blocker abciximab on patients with acute coronary syndromes who were not undergoing early revascularisation.

METHODS

We enrolled 7800 patients who were admitted to hospital with chest pain and either ST-segment depression or raised troponin T or I concentrations. 2598 were randomly assigned placebo, 2590 an abciximab bolus and 24 h infusion, and 2612 an abciximab bolus and 48 h infusion; all patients received aspirin and either unfractionated or low-molecular-weight heparin. The primary endpoint was death or myocardial infarction at 30 days after randomisation. Analysis was by intention to treat.

FINDINGS

There were no drop-outs. 209 (8.0%) patients on placebo, 212 (8.2%) on 24 h abciximab, and 238 (9.1%) on 48 h abciximab died or had a myocardial infarction before day 30 (odds ratio 1.0 [95% CI 0.83-1.24], for difference between placebo and 24 h abciximab, and 1.1 [0.94-1.39] for difference between placebo and 48 h abciximab). The lack of benefit from treatment with abciximab was consistent in most subgroups investigated; in particular, no benefit was seen in patients with raised cardiac troponin T or I concentrations at enrolment, although these patients did have a strongly increased risk of subsequent events. Bleeding rates were low, but increased with abciximab, particularly when continued for 48 h. Additionally, thrombocytopenia was more frequent with abciximab than with placebo.

INTERPRETATIONS

Although the explanations for our findings are unclear, this study indicates that abciximab is not beneficial as first-line medical treatment in patients admitted with acute coronary syndromes.

Antithrombotic therapy in the cardiac catheterization laboratory: focus on antiplatelet agents

Pharmacologic advances in the use of antithrombotic agents have paralleled the technologic innovations used in patients undergoing coronary interventions. The recognition of the central role of platelets in the development of complications related to coronary interventions led to the investigation and subsequent routine use of several antiplatelet agents as adjuvants to coronary intervention. Thus, the oral agents aspirin and either ticlopidine or clopidogrel are routinely administered after coronary stenting. Intravenous glycoprotein (GP) IIb/IIIa antagonists have been extensively studied and reduce adverse cardiac events in patients undergoing coronary interventions, especially those receiving intracoronary stents. Despite the growing use of GP IIb/IIIa antagonists, much information remains unknown as to the proper dosing and the effects these agents have on other elements of the hemostatic and vascular systems.