Elevated beta thromboglobulin in peripheral venous blood of patients with acute myocardial ischemia: direct evidence for enhanced platelet reactivity in vivo

Individual variations in platelet reactivity towards ADP, epinephrine, collagen and nitric oxide, and the association to arterial function in young, healthy adults

INTRODUCTION

Platelet aggregation and secretion can be induced by a large number of endogenous activators, such as collagen, adenosine diphosphate (ADP) and epinephrine. Conversely, the blood vessel endothelium constitutively release platelet inhibitors including nitric oxide (NO) and prostacyclin. NO and prostacyclin are also well-known vasodilators and contribute to alterations in local blood flow and systemic blood pressure.

MATERIALS AND METHODS

In this study we investigated individual variations in platelet reactivity and arterial functions including blood pressure and flow-mediated vasodilation (FMD) in 43 young, healthy individuals participating in the Lifestyle, Biomarkers and Atherosclerosis (LBA) study. Platelet aggregation and dense granule secretion were measured simultaneously by light transmission and luminescence. FMD was measured with ultrasound.

RESULTS

The platelet function assay showed inter-individual differences in platelet reactivity. Specifically, a sub-group of individuals had platelets with an increased response to low concentrations of ADP and epinephrine, but not collagen. When the NO-donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) was combined with high doses of these platelet activators, the results indicated for sub-groups of NO-sensitive and NO-insensitive platelets. The individuals with NO-sensitive platelets in response to SNAP in combination with collagen had a higher capacity of FMD of the arteria brachialis.

CONCLUSIONS

Platelet reactivity towards ADP, epinephrine and NO differs between young, healthy individuals. Some individuals have a more effective response towards NO, both in the aspect of platelet inhibition ex vivo, as well as vasodilation in vivo.

The utility of inflammation and platelet biomarkers in patients with acute coronary syndromes

Introduction

Thrombotic and inflammatory mechanisms are involved in the pathophysiology of acute coronary syndrome (ACS). The aim of the study was the evaluation of inflammation (white blood cells count/WBC, C-reactive protein/CRP, interleukin-6/IL-6) and platelet (platelet count/PLT, mean platelet volume/MPV, large platelet/LPLT, beta-thromboglobulin/β-TG) biomarkers in the groups of ACS patients depending on the severity of signs and symptoms and compared to controls without coronary artery disease.

Materials and methods

The study group included 93 patients categorized into 3 subgroups depending on the severity of signs and symptoms of ACS. PLT, MPV, LPLT, and WBC were determined on hematological analyzer, IL-6 and β-TG were measured using the ELISA method.

Results

In the whole group of ACS patients WBC, CRP, IL-6, MPV, and β-TG were significantly higher as compared to controls. Analyzing the inflammation and platelet biomarkers depending on the severity of signs and symptoms in comparison to controls, statistically significant differences for above-mentioned parameters were also found. There were no significant differences between the advancement of coronary artery changes and inflammation as well as platelet parameters, except for CRP concentrations. The AUCs for all inflammation parameters tested were similar, however the highest AUCs showed WBC and CRP. Among platelet parameters the highest AUC revealed β-TG.

Conclusion

Markers of inflammation and platelet activation may be associated to myocardial ischemia and myocardial injury. WBC, CRP and IL-6 as inflammation parameters and MPV and β-TG as platelet biomarkers may be useful indicators of the presence of coronary artery disease.

Platelets and Cardiovascular Disease

Platelets play an important, but often under-recognized role in cardiovascular disease. For example, the normal response of the platelet can be altered, either by increased pro-aggregatory stimuli or by diminished anti-aggregatory substances to produce conditions of increased platelet activation/aggregation and occur in active cardiovascular disease states both on a chronic (e.g. stable angina pectoris) and acute basis (e.g. acute myocardial infarction). In addition, platelet hyperaggregability is also associated with the risk factors for coronary artery disease (e.g. smoking, hypertension, and hypercholesterolaemia). Finally, the utility of an increasing range of anti-platelet therapies in the management of the above disease states further emphasizes the pivotal role platelets play in the pathogenesis of cardiovascular disease. This paper provides a comprehensive overview of the normal physiologic role of platelets in maintain homeostasis, the pathophysiologic processes that contribute to platelet dysfunction in cardiovascular disease and the associated role and benefits of anti-platelet therapies.

Protein kinase C ε expression in platelets from patients with acute myocardial infarction

Objective

Platelets play crucial roles in the pathophysiology of thrombosis and myocardial infarction. Protein kinase C ε (PKCε) is virtually absent in human platelets and its expression is precisely regulated during human megakaryocytic differentiation. On the basis of what is known on the role of platelet PKCε in other species, we hypothesized that platelets from myocardial infarction patients might ectopically express PKCε with a pathophysiological role in the disease.

Methods and Results

We therefore studied platelet PKCε expression from 24 patients with myocardial infarction, 24 patients with stable coronary artery disease and 24 healthy subjects. Indeed, platelets from myocardial infarction patients expressed PKCε with a significant frequency as compared to both stable coronary artery disease and healthy subjects. PKCε returned negative during patient follow-up. The forced expression of PKCε in normal donor platelets significantly increased their response to adenosine diphosphate-induced activation and adhesion to subendothelial collagen.

Conclusions

Our data suggest that platelet generations produced before the acute event retain PKCε-mRNA that is not down-regulated during terminal megakaryocyte differentiation. Results are discussed in the perspective of peri-infarctual megakaryocytopoiesis as a critical component of myocardial infarction pathophysiology.

Non-conventional hemostatic risk factors for coronary heart disease in individuals with spinal cord injury

STUDY DESIGN

Review.

OBJECTIVES

In subjects with spinal cord injury (SCI), there is strong evidence for platelet hyperactivity, which may stimulate atherosclerosis and coronary heart disease (CHD). The literature was reviewed.

BACKGROUND

Individuals with SCI develop premature CHD. In addition to the conventional risk factors associated with CHD, there are pathologic hematological factors involved in atherogenesis that are similar to those that have been demonstrated in individuals with diabetes, and these hematological factors might affect individuals with SCI. One such hematological factor, platelet aggregation, is essential for the development of CHD, which results from thrombus formation in the coronary vasculature. Prostacyclin (PGI(2)) is a potent inhibitor of platelet aggregation and is thought to have a beneficial role in inhibiting atherogenesis; therefore, it is possible that individuals with SCI have impaired PGI(2) receptor function.

METHODS

We reviewed the literature by conducting a search using PubMed (1970-2007).

RESULTS

Acute thrombosis is emerging as an important factor in the etiology of CHD and therefore could mediate the risk of CHD in persons with SCI, in addition to previously known risk factors such as hyperlipidemia, hypertension, hyperlipidemia, diabetes mellitus and hyperinsulinemia. Because PGI(2) may retard atherogenesis through its inhibitory effects on platelet function, we discuss the effects of PGI(2) on platelets in persons with SCI in this review.

CONCLUSIONS

Subjects with chronic SCI develop abnormal platelet function, resulting in the production of atherogenic and thrombogenic factors for the following reasons: (1) the PGI(2) and insulin receptors on their platelets are impaired; (2) thrombin generation and platelet-derived growth factor release are elevated; (3) insulin-induced nitric oxide production by platelets is markedly impaired; and (4) a circulating antibody (immunoglobulin G (IgG)) blocks the antithrombotic effect of both insulin and PGI(2) receptors. Thus, this IgG molecule is thought to be one of the pathological mediators of the increased incidence of CHD in individuals with SCI.

High platelet reactivity is associated with myocardial infarction in premenopausal women: a population-based case-control study

SUMMARY BACKGROUND

Platelets are involved in the occlusion of coronary arteries after rupture of an atherosclerotic plaque. Furthermore, activated platelets release large quantities of growth factors, chemokines and interleukins that regulate inflammatory reactions. Therefore, we hypothesized that high basal platelet reactivity may contribute to an increased risk of myocardial infarction (MI) in premenopausal women.

METHODS

We assessed the relation between high platelet reactivity and MI in a population-based case-control study among premenopausal women (aged < 50 years). We used multivariable logistic regression to quantify the effect of high platelet reactivity, adjusted for potential confounders. Platelet reactivity was estimated by plasma levels of neutrophil activating peptide 2 (NAP-2), CXC chemokine ligand (CXCL)4, soluble glycoprotein 1b (sGPIb) and soluble P-selectin.

RESULTS

High platelet reactivity (i.e. levels >or= 90th percentile control subjects) was associated with a 2- to 3-fold increased incidence of MI: the adjusted odds ratios (ORs) were 3.0 [95% confidence interval (CI) 1.4-6.4] for NAP-2, 2.2 (0.9-5.1) for CXCL4, 1.9 (0.7-4.6) for sP-selectin and 2.5 (1.1-5.7) for sGPIb. The incidence of MI dose-dependently increased when more markers were elevated. High platelet reactivity according to both NAP-2 and sGPIb was associated with an up to tenfold increased incidence (9.9, 95% confidence interval 2.0-48.3).

CONCLUSIONS

High basal platelet reactivity was associated with a 2- to 3-fold higher incidence of MI compared with normal platelet reactivity in premenopausal women. Our results suggest that high basal platelet reactivity may contribute to a higher risk of MI.

Beta-thromboglobulin and platelet factor 4 levels in post-myocardial infarction patients with major depression

Platelet factor 4 (PF 4) and beta-thromboglobulin (beta-TG) were studied in 12 depressed post-myocardial infarction (MI) patients and 12 matched non-depressed post-MI patients. PF4 was significantly higher in the depressed group than in the non-depressed group. beta-TG was increased in the depressed subgroup, but the difference was not statistically significant.

Human platelet alphaIIbeta3 integrin binding affinity and specificity of SJ874: antiplatelet efficacy versus aspirin

OBJECTIVE

To define the affinity and specificity of SJ874, a nonpeptide antiplatelet agent for platelet glycoprotein Ilb/IIIa integrin, and to determine the antiplatelet efficacy of SJ874 relative to those of glycoprotein IIbIIIa antagonists and aspirin.

METHODS

Binding affinity and specificity of SJ874 for platelet glycoprotein IIb/IIIa integrin were determined using integrin-mediated binding and adhesion assays with human cells. Additionally, the antiplatelet efficacy of SJ874 was determined and compared with those of other glycoprotein IIb/IIIa antagonists and aspirin using light-transmittance and laser-scattering aggregometry.

RESULTS

SJ874 inhibited aggregation of human platelets induced by 10 micromol/l adenosine diphosphate (ADP) with a concentration for half-maximal effect of 0.046 +/- 0.005 micromol/l using light-transmittance aggregometry. Using laser-scattering aggregometry, SJ874 was found to totally inhibit formation both of micro-aggregates and of macro-aggregates induced either by ADP or by epinephrine. In contrast, administration of 325 mg aspirin to normal healthy volunteers attenuated formation of macro-aggregates but not micro-aggregates. SJ874 inhibited binding of [125I]-fibrinogen to activated (by ADP, epinephrine, and arachidonic acid at concentrations of 100 micromol/l each) gel-filtered human platelets with a concentration for half-maximal effect of 0.0012 +/- 0.0005 micromol/l. SJ874 was demonstrated to associate more tightly with resting human platelets than did DMP754 [1] and slightly less tightly than did DMP802 [2]. SJ874 was demonstrated to exhibit a high degree of specificity for platelet glycoprotein IIb/IIIa (alphaIIb/beta3) integrin compared with other known integrins, including alphavbeta3, alphavbeta5, and alpha5beta1 (concentration for half-maximal effect > 100 micromol/l).

CONCLUSION

SJ874 is a potent and specific platelet glycoprotein IIb/IIIa antagonist with high affinity for and tight association with human platelets. These data suggest that SJ874 might have good antiplatelet utility for inhibiting formation both of platelet micro-aggregates and of macro-aggregates of platelets and a long duration of action in humans due to its slow dissociation from human platelets.

Antiplatelet and antithrombotic effects of a novel selective phosphodiesterase 3 inhibitor, NSP-513, in mice and rats

We investigated the effects of NSP-513, (R)-4,5-dihydro-5-methyl-6-[4-(2-propyl-3-oxo-1-cyclohexenyl)amino] phenyl-3(2H)-pyridazinone, on phosphodiesterase (PDE) isozyme activities, in vitro platelet aggregation and in vivo thrombus formation. NSP-513 selectively inhibited human platelet PDE 3 isozyme with an IC50 value of 0.039 microM. In an in vitro human platelet aggregation assay, the IC50 values (microM) of NSP-513 for platelet aggregation induced by collagen, U-46619, arachidonic acid, adenosine diphosphate (ADP), epinephrine and thrombin were 0.31, 0.25, 0.082, 0.66, 0.23 and 0.73, respectively. In a mouse pulmonary thromboembolism model, orally administered NSP-513 showed in vivo antithrombotic effects that were 320 to 470 times more potent than those of cilostazol. In a rat carotid arterial thrombosis model, intraduodenally administered NSP-513 (0.1 mg/kg), cilostazol (30 mg/kg) and aspirin (30 mg/kg) reduced thrombus formation by 75%, 66% and 48%, respectively. However, intravenously administered dipyridamole (10 mg/kg) did not significantly prevent thrombus formation. These results demonstrate that NSP-513 has the potential to prevent not only in vitro platelet aggregation but also in vivo thrombus formation and indicate that the highly selective PDE 3 inhibitory effect of NSP-513 may make this compound useful for assessing the physiological role of PDE 3.

Antiplatelet therapies: from aspirin to GPIIb/IIIa-receptor antagonists and beyond

This review discusses recent advances in antiplatelet therapies, comparative analysis between the antiplatelet/ antithrombotic efficacy of various antiplatelet strategies and that of platelet glycoprotein GPIIb/IIIa-receptor antagonists, issues in the development of chronic anti-GPIIb/IIIa-receptor therapy and potential adjunct strategies using GPIIb/IIIa-receptor antagonists. Acute coronary syndromes are secondary to unstable angina, ST-segment elevation, and acute myocardial infarction. These involve the rupture of a vulnerable atherosclerotic plaque, leading to platelet adhesion, activation and aggregation at the site of rupture. Several studies suggest that complex or ulcerated plaques, which might promote further thrombotic events, can persist for more than one month after the acute event. These data suggest the potential added benefit of chronic oral therapy with antiplatelet drugs beyond the well-documented benefit of acute intravenous use of various GPIIb/IIIa-receptor antagonists. However the efficacy-safety ratio or the risk-benefit ratio for chronic oral antiplatelet therapy needs to be defined. Both aspirin and clopidogrel are available for chronic oral use. By contrast, there are tremendous challenges ahead with the oral GPIIb/IIIa-receptor antagonists because of their lack of expected benefit over aspirin. However, much still remains to be defined with regard to the optimization of current and future antiplatelet therapies or their optimized combinations.

Differences between activation thresholds for platelet P-selectin glycoprotein IIb-IIIa expression and their clinical implications

Increased platelet reactivity is a descriptor of the risk of cardiovascular events in healthy men and in patients with overt coronary artery disease. We sought to determine if differential thresholds exist for activation of platelets with respect to alpha-granule degranulation and fibrinogen binding in healthy volunteers and in patients with acute coronary syndromes. We also sought to characterize the effect of aspirin on activation. Platelet activation was assessed with flow cytometry in whole blood anticoagulated with corn trypsin inhibitor and incubated with fluorescein isothiocyanate conjugated fibrinogen (to define activation of glycoprotein IIb-IIIa), a phycoerythrin conjugated antibody to P-selectin (a marker of alpha-granule degranulation), and selected concentrations of adenosine diphosphate (ADP) or thrombin receptor agonist peptide. ADP-induced fibrinogen binding was found to be a low threshold activation event (40% of platelets bound fibrinogen in response to 0.2 microM ADP). Alpha-granule degranulation was a higher threshold event (33% of platelets expressed P-selectin in response to 1.0 microM ADP). Intra- and interindividual variability were most apparent with low concentrations of agonist (0.2 microM ADP). Patients with acute coronary syndromes (on aspirin) had significantly increased P-selectin expression in response to ADP compared with healthy subjects (on aspirin), but no difference in ADP-induced fibrinogen binding was observed. Daily ingestion of 325 mg of aspirin had no effect on either P-selectin expression or fibrinogen binding in healthy subjects. Analysis of platelet reactivity with flow cytometry characterizes activation with respect to specific components of the process and should facilitate development and optimal titration of antiplatelet therapy.

Intranasal antiplatelet/antithrombotic efficacy of a novel platelet GPIIB/IIIA receptor antagonist DMP755

This article describes the equivalent antiplatelet/antithrombotic effects of DMP755 at comparable doses by intranasal and i.v. administration but required substantially higher doses with the oral administration route. Antiplatelet and antithrombotic efficacy of DMP755 or its free acid form XV459 were determined in dogs. Arterial thrombosis models were induced either electrolytically (200 microA anodal current) in the carotid artery or mechanically by external clamping of femoral artery along with stenosis, which result in either total occlusive thrombus formation or cyclic flow reduction (CFR), respectively. Either DMP755 or its free acid form, XV459 demonstrated maximal and comparable antiplatelet efficacy at 0.025-0.1 mg/kg, intravenous (i.v.) or intranasal but not oral (PO) in mongrel dogs. The antiplatelet efficacy of DMP755 at 0.1 mg/kg, intranasal, or i.v. was determined in a cross-over design (n=8 in each group). In this study, a comparable and maximal antiplatelet efficacy for DMP755 after intranasal or i.v. was demonstrated suggesting 100% intranasal bioavailability as compared with the modest antiplatelet efficacy at 0.1 mg/kg, p.o. DMP755 administered at 0.1 mg/kg, intranasally or i.v. or at 0.3 mg/kg, p.o. prevented the incidence of electrolytic injury-induced arterial thrombosis in the carotid artery thrombosis model and prevented the incidence of cyclic flow reduction in mechanically injured and stenosed femoral artery. In conclusion, DMP755 has a comparable intranasal and intravenous antiplatelet/antithrombotic profiles along with a significant improvement over its oral profiles. These data also suggest the potential utility of intranasal DMP755 in various acute and chronic thromboembolic disorders. This is the first report of intranasal bioavailability of a glycoprotein receptor antagonist.

XV454, a novel nonpeptide small-molecule platelet GIIb/IIIa antagonist with comparable platelet alpha(IIb)beta3-binding kinetics to c7E3

XV454 demonstrated high potency (IC50 = 14-25 nM) in inhibiting human platelet aggregation induced by adenosine diphosphate (ADP, 10 microM), thrombin receptor agonist peptide (TRAP) (10 microM), or collagen (20 microg/ml). XV454 exhibited a high degree of selectivity for platelet alpha(IIb)beta3 in comparison with c7E3, which is a nonspecific antagonist for both alpha(IIb)beta3 and alpha(v)beta3. Both XV454 and c7E3 bind with high affinity to either activated (A) or unactivated (U) human, baboon, or canine platelets. XV454 binds with a relatively higher affinity [Kd = 0.5 nM (A), 0.6 nM (U)] as compared with c7E3 [Kd = 9.1 nM (A), 9.2 (U) nM]. XV454 demonstrated a tight association with human, baboon, and, to a lesser extent, with canine platelets (t(1/2) of dissociation = 110 +/- 6, 80 +/- 10, and 23 +/- 2 min, respectively). Both c7E3 and XV454 associate tightly with a slower dissociation rate with unactivated human platelets: t(1/2) of 42 and 116 min, respectively. In non-human primates, oral (0.1 mg/kg, p.o.) and intravenous (0.05 mg/kg, i.v. bolus administration of XV454 methyl ester pro-drug resulted a long-lasting maximal antiplatelet efficacy for < or = 72 h with significant but reversible prolongation of bleeding time and without effects on platelet count, clinical chemistry, or hemodynamic profile. In conclusion, XV454 represents a potent antiplatelet agent in inhibiting platelet aggregation along with a high affinity and relatively slow dissociation rate from human platelet GPIIb/IIIa receptors that allow a long-lasting antiplatelet efficacy after single i.v. or oral administration.

Hostility is associated with increased platelet activation in coronary heart disease

OBJECTIVE

To determine whether Potential for Hostility is related to platelet activation (PA) among patients with coronary heart disease (CHD) and healthy controls. Increased PA has been associated with adverse secondary events after myocardial infarction or coronary angioplasty.

METHODS

We tested 32 CHD patients and 23 healthy men and women, aged 45 to 73 years, for PA by using whole blood flow cytometry. PA was measured in blood exiting a bleeding time wound (wound-induced platelet activation) and also in venous blood stimulated in vitro with collagen. Monoclonal antibodies were used to test for fibrinogen receptor activation and fibrinogen receptor binding. All subjects refrained from taking aspirin for at least 14 days before testing; CHD patients stopped nitrates and calcium channel blockers for 24 hours, while continuing to take lipid-lowering medications. Potential for Hostility was assessed, using the Type A Structured Interview.

RESULTS

Among the CHD patients only, all four of the wound-induced fibrinogen receptor activation indicators (activation and binding) were related to hostility; the relationships were significant for receptor activation at 2 minutes, and for receptor binding at 1 minute (r values = .46, p values = .02). Subjects on lipid-lowering medications had lower PA for most measures. Healthy subjects had higher wound-induced fibrinogen receptor activation at 2 minutes and fibrinogen receptor activation in vitro than the CHD patients (p = .04), but after statistical adjustment for lipid-lowering medications, there were no significant differences between the patients and controls.

CONCLUSIONS

PA was related to hostility among CHD patients, consistent with previous studies indicating a relationship between PA and psychological factors among CHD patients. However, PA was not increased in nonsmoking, nondepressed CHD patients relative to controls.

Oral antiplatelet efficacy and specificity of a novel nonpeptide platelet GPIIb/IIIa receptor antagonist, DMP 802

This study was undertaken to define the platelet glycoprotein alphaIIb beta3 integrin (GPII/IIIa) affinity, specificity, and oral antiplatelet efficacy of DMP 802, a small-molecule nonpeptide antiplatelet agent. Platelet GPIIb/IIIa integrin binding affinity and specificity for DMP 802 were determined by using binding and adhesion assays with cells from various species, including human. DMP 802 demonstrated a potent antiplatelet efficacy [median inhibitory concentration (IC50), 0.029 +/- 0.0042 microM] in inhibiting human platelet aggregation induced by 10 microM adenosine diphosphate (ADP), as assessed by light-transmittance aggregometry. DMP 802 inhibited 125I-fibrinogen binding to activated (ADP, epinephrine, and arachidonic acid at 100 microM each) gel purified human platelets with an IC50 of 0.012 +/- 0.003 microM. DMP 802 demonstrated tight association with unactivated human, baboon, or canine platelets (t(1/2) of dissociation, 32 +/- 2, 32 +/- 13, and 11 +/- 1 min, respectively). DMP 802 binds with high affinity to both unactivated and activated human platelets (Kd = 0.61 +/- 0.17, 0.57 +/- 0.21 nM, respectively). DMP 802 demonstrated species specificity in inhibiting platelet aggregation with IC50 values ranging from 0.025 to 0.092 microM (human, guinea pig, dog, swine, hamster) and 0.88-1.0 microM (rabbit and rat) in platelets obtained from these various species. DMP 802 demonstrated a high degree of specificity for platelet GPIIb/IIIa (alphaIIb/beta3) as compared with other integrins including alpha(v)beta3 (IC50, >10 microM), alpha(v)beta5 (IC50, >100 microM), alpha4beta1 (IC50, >100 microM), and alpha5beta1 (IC50, >10 microM). Oral antiplatelet efficacy of DMP 802 was examined after single oral (0.05-0.20 mg/kg) and after repeated oral dosing at 0.05 mg/kg daily for 5 days in mongrel dogs. Dose-dependent antiplatelet efficacy with an extended duration of antiplatelet efficacy was demonstrated based on ex vivo inhibition of platelet aggregation induced by 100 microM ADP. DMP 802 has an oral bioavailability of 14.9% in dogs. In conclusion, the alpha sulfonamide isoxazoline analog, DMP 802, is a novel oral antiplatelet agent with high affinity, relatively slow dissociation rate and specificity for human platelet GPIIb/IIIa receptors.

Inhibition of platelet-mediated clot retraction by integrin antagonists

The effects of the platelet alphaIIb beta3 integrin (GPIIb/IIIa) antagonists XV459 (non-peptide), c7E3 (Fab monoclonal antibody) and DMP728 (cyclic peptide) as well as the alpha(v)beta3 integrin antagonists, LM609 (monoclonal antibody) and XT199 (non-peptide) on clotting and platelet-mediated clot retraction were examined. While 30 nM of XV459 had no significant effect on the kinetics of coagulation, platelet-mediated clot retraction was nearly fully inhibited at this concentration (Relative Retraction Rate = 0.09). XV459 resulted in a concentration related-response curve. Other experiments demonstrated that platelet aggregation was maximally inhibited at XV459 concentrations ranging from 30-50 nM. Similarly, c7E3 demonstrated comparable inhibitory efficacy in inhibiting either clot retraction or platelet aggregation. In contrast, DMP728, an equally potent anti-aggregatory agent with an IC50 of 20-50 nM in inhibiting platelet aggregation induced by various agonists, was found to be a less potent inhibitor of platelet-mediated clot retraction with a half-maximal inhibition of clot retraction at approximately 0.7 microM, and maximum effects at concentrations of 10 microM. The alpha(v)beta3 integrin antagonists, LM609 or XT199 were without any significant effects on either platelet-mediated clot retraction or platelet aggregation. In conclusion, these data suggest a differential efficacy among different GPIIb/IIIa antagonists in inhibiting platelet-mediated clot retraction in spite of the equivalent anti-aggregatory potency. Additionally, the alpha(v)beta3 integrin antagonists do not affect platelet-mediated clot retraction or aggregation. Further studies with the previously described alphaIIb beta3 integrin antagonists as well as others revealed a distinct correlation between the Kd to resting and activated platelets and the efficacy in inhibiting platelet-mediated clot retraction.

Intravenous and oral antiplatelet/antithrombotic efficacy and specificity of XR300, a novel nonpeptide platelet GPIIb/IIIa antagonist

Currently used antiplatelet drugs including aspirin, ticlopidine, and others are effective against certain but not all of the many endogenous platelet activators. Because of their limited efficacy, a significant number of serious thromboembolic complications still occur, highlighting the need for a more effective therapy. Thus our study was undertaken to define the antiplatelet efficacy, specificity, and the intravenous and oral antiplatelet/antithrombotic effects of a nonpeptide glycoprotein alphaIIb beta3 integrin (GPIIb/IIIa) antagonist XR300, an ethyl ester prodrug of XR299. XR300, on its conversion to the active form XR299, inhibited human platelet aggregation induced by 100 microM adenosine diphosphate (ADP) with a median inhibitory concentration (IC50) of 0.09 microM. Similarly, XR299 inhibited 125I-fibrinogen binding to human gel-purified platelets (IC50, 0.01 microM) regardless of the agonist used. In purified human GPIIb/IIIa, XR299 demonstrated a competitive high-affinity binding with an IC50 of 1.2 nM. XR299 demonstrated a high degree of specificity for platelet GPIIb/IIIa (alphaIIb beta3) as compared with other integrins including alpha(v)beta3, alpha(v)beta5, and alpha4beta1, where IC50 values were >10 microM. XR300 administered to mongrel dogs either intravenously (0.5-1.0 mg/kg, i.v.) or orally at 1.0-2.0 mg/kg, demonstrated maximal antiplatelet effects with rapid onset and extended duration. XR300 demonstrated maximal antithrombotic efficacy in preventing the incidence of occlusive thrombosis or cyclic flow reduction (CFR) in the carotid or femoral artery thrombosis models induced either electrolytically or by mechanical injury along with stenosis. In conclusion, XR300 is a novel intravenous and oral antiplatelet/antithrombotic agent with high affinity and specificity for platelet GPIIb/IIIa receptors.

Pharmacodynamics and pharmacokinetics of DMP 728, a platelet GPIIb/IIIa antagonist, in healthy subjects

DMP 728 showed a dose-dependent inhibition of platelet aggregation at doses of 0.05 to 0.9 mg per subject, with a maximal inhibition (> 90%) of platelet aggregation at doses of 0.9 mg per subject and higher. Minimal changes in bleeding time from baseline were observed at doses up to 0.6 mg per subject. At the 0.9 mg/subject dose level, bleeding time was prolonged by approximately twofold to threefold above the baseline. At higher doses (1.5 mg/subject to 3.9 mg/subject), bleeding time prolongation was > 30 minutes during the infusion. In all dose groups, bleeding times returned to the control value within 8 hours after cessation of the infusion. Maximum plasma concentration and area under the curve of DMP 728 increased linearly and proportionally to the dose. No clinical changes in vital signs, 12-lead electrocardiograms, physical examinations, coagulation tests, or stool hemoccult tests were observed at any of the doses. In conclusion, DMP 728 is a potent antiplatelet agent and well tolerated at doses ranging from 0.05 to 3.0 mg/subject.

Oral antiplatelet efficacy of the platelet GPIIb/IIIa antagonist, DMP754 in non-human primates

Binding kinetic studies with XV459, the active form of DMP754, demonstrated comparable binding kinetics (Kd and Koff) with platelets obtained from either human or baboons which were different from that with platelets obtained from dogs. Therefore, the present study was undertaken to evaluate the antiplatelet efficacy of DMP754 following oral administration in baboons. The dose levels evaluated were 0.1 and 1.0 mg/kg, IV and 0.1, 0.3, 1.0, and 3.0 mg/kg, oral of DMP754. Oral doses of DMP754 resulted in dose- and time-related inhibition of platelet aggregation along with a modest effect on bleeding time prolongation. DMP754 at similar oral doses had 24 hours of antiplatelet effects in baboon as compared to 8-12 hours duration of antiplatelet efficacy in dogs. At maximal antiplatelet doses DMP754 demonstrated no significant effects on platelet count, clinical chemistry or hemodynamic profiles in baboons. These data suggest that DMP754 is a potent orally active antiplatelet agent with extended duration after once a day oral administration in non-human primate.

Effects of ionic and non-ionic contrast media on platelet function as evaluated by plasma concentration of beta-thromboglobulin

The aim of the study was to evaluate the effects of ionic and non-ionic contrast media on platelet function. In 44 patients who underwent angiography, the plasma concentration of beta-thromboglobulin (beta TG) was measured before and after ionic contrast medium (diatrizoate) administration in 22 patients and non-ionic contrast medium (iopromide) in the other 22 patients. A significant decrease in the plasma beta TG levels after intraarterial contrast medium injection occurred in both groups of patients. No significant beta TG level changes occurred in patients with normal pre-examination beta TG levels in both groups. In patients with elevated beta TG levels before arteriography, beta TG returned to normal values after contrast medium injection in both groups. There was no significant correlation between the amount of administered contrast medium and beta TG concentration after angiography. These results suggest that platelet function is not affected by either ionic or non-ionic contrast medium in patients with normal platelet activation. In patients with enhanced platelet activation, the activation became normal after contrast medium administration.

Intranasal absorption of the platelet glycoprotein IIb/IIIa receptor antagonist, DMP 755, and the effect of anesthesia on nasal bioavailability

Intranasal absorption and bioavailability of DMP 755, a peptidomimetic, platelet glycoprotein IIb/IIIa receptor antagonist, were examined in anesthetized and lightly sedated dogs. Nasal bioavailability was determined by measuring plasma concentrations relative to those after intravenous dosing. DMP 755 is an ester prodrug, and bioavailability reflects concentrations of the acid hydrolysis product. Nasal bioavailability in dogs anesthetized with pentobarbital was 85 +/- 4%, whereas in dogs anesthetized with the short-acting anesthetic propofol, bioavailability was 32 +/- 7%. Nasal bioavailability was greater than the reported oral bioavailability of DMP 755 in dogs, and was quite consistent. Because anesthesia affects nasal bioavailability, an effect that may depend on the absorption half-life of the test compound, a conscious or lightly sedated animal model is preferred.

Differential effects of anticoagulants on the activation of platelets ex vivo

BACKGROUND

Because activation of platelets and of the coagulation system are interdependent mediators of thrombosis, platelet activation was characterized in whole blood in the presence of anticoagulants used to assess platelet function in vitro or as treatment for patients with occlusive arterial disease.

METHODS AND RESULTS

Blood was anticoagulated alone or in combination with citrate, ethylenediaminetetraacetatic acid, corn trypsin inhibitor (CTI, an inhibitor of activated factor XII), heparin, enoxaparin, recombinant tick anticoagulant peptide (rTAP), or recombinant hirudin. Platelet activation in response to adenosine diphosphate (ADP) or collagen was detected by assay of P-selectin on the platelet surface delineated by flow cytometry. Although minimal activation was seen without ADP, the fraction of platelets expressing P-selectin in response to ADP was greatest in blood anticoagulated with citrate compared with CTI and all other anticoagulants. ADP-induced platelet activation was greater in blood anticoagulated with heparin compared with an equipotent anti-Xa concentration of enoxaparin. More variable results were seen with collagen, but platelet activation in the presence of citrate was greater than that with CTI.

CONCLUSIONS

Interpretation of assays of inhibition of platelet activation by potentially therapeutic agents in vitro requires consideration of the effects of anticoagulants used. In addition, anticoagulants other than standard heparin may potentiate efficacy of antiplatelet drugs.

Use of conformationally restricted benzamidines as arginine surrogates in the design of platelet GPIIb-IIIa receptor antagonists

The use of 5,6-bicyclic amidines as arginine surrogates in the design of a novel class of potent platelet glycoprotein IIb-IIIa receptor (GPIIb-IIIa) antagonists is described. The additional conformational restriction offered by the bicyclic nucleus results in 20-400-fold increases in potency compared to the freely flexible, acyclic benzamidine counterpart. The design, synthesis, structure-activity relationships (SAR), and in vitro activity of this novel class of GPIIb-IIIa antagonists are presented.

Elevated platelet factor 4 and beta-thromboglobulin plasma levels in depressed patients with ischemic heart disease

Clinical depression has recently been recognized as an independent risk factor for cardiac mortality in patients after myocardial infarction. The underlying mechanisms of this increased mortality remain unclear. This study investigated the hypothesis that patients suffering from ischemic heart disease (IHD) and depression concurrently may have abnormal platelet activation resulting in an increased risk of thrombosis. Platelet factor 4 (PF4) and beta-thromboglobulin (beta-TG) were measured in young healthy control subjects, in nondepressed patients with IHD, and in depressed patients with IHD. Mean PF4 and beta-TG plasma levels in the IHD group with depression were found to be significantly higher than those of the control and IHD groups. This increase was not related to age, gender, racial difference, aspirin use, or severity of cardiac disease. This finding suggests that in depressed patients with IHD there is greater platelet activation, and may indicate an increased risk of thrombotic complications.

Prevention of carotid artery thrombosis by oral platelet GPIIb/IIIa antagonist in dogs

BACKGROUND AND PURPOSE

Current antithrombotic therapy in acute ischemic stroke and myocardial infarction in which a combination of antiplatelet agents (aspirin) and anticoagulants (heparin) was used led to partial reduction of acute thrombotic complications. Recent advances in antiplatelet research led to the discovery of the platelet glycoprotein IIb/IIIa complex (GPIIb/IIIa), the final common pathway for platelet aggregation. The present study was undertaken to determine the oral antithrombotic efficacy of a potent and specific platelet GPIIb/ IIIa antagonist, DMP728, in an electrically induced carotid artery thrombosis model in dogs. Based on the powerful antiplatelet efficacy of this mechanism in inhibiting all agonist-induced platelet aggregation as well as in inhibiting platelet procoagulant activity (thrombin generation and hence fibrin formation), an orally active antagonist for this integrin receptor might have potential benefits in stroke.

METHODS

Anesthetized dogs were instrumented for monitoring of arterial blood pressure, heart rate, and carotid artery flow velocity. Animals were treated with saline or DMP728 (0.1 to 1.0 mg/kg PO). Thrombus formation (platelet-rich aggregate with fibrous coating and a few erythrocytes) by anodal electrolytic stimulation (300 microA) to the intimal surface of the right carotid artery was initiated 120 minutes after oral DMP728 administration and continued for 180 minutes. Whole blood cell counts, ex vivo platelet aggregation, and template bleeding time were determined at different time points throughout the study.

RESULTS

DMP728 administered at 0.1 to 1.0 mg/kg PO exhibited dose-dependent antithrombotic efficacy in this model. DMP728 was shown to be significantly effective in inhibiting ex vivo platelet aggregation and in inhibiting thrombosis at 0.3 to 1.0 mg/kg PO. The antiplatelet, antithrombotic effects of DMP728 were demonstrated without any significant changes in the different hemodynamic or coagulation parameters. These data demonstrated the oral antithrombotic efficacy of DMP728 in dogs.

CONCLUSIONS

Platelet GPIIb/IIIa blockade with an orally active antagonist was shown to be safe and effective in the prevention of carotid artery occlusive thrombosis.

Changes in hemostatic function at times of cyclic variation in occupational stress

In this study we demonstrated, in the same healthy subjects, a significant elevation in coagulation factors VII and VIII, fibrinogen, thrombocyte count, and thrombin and adenosine diphosphate-induced platelet aggregation during a period of increased workload compared with a calm work period. These findings may add to the understanding of the mechanism that links mental stress to coronary disease.

Oral antiplatelet, antithrombotic efficacy of DMP 728, a novel platelet GPIIb/IIIa antagonist

BACKGROUND

Currently used antiplatelet drugs, including aspirin and ticlopidine, are effective against certain but not all of the many endogenous platelet activators. Because of their limited efficacy, a significant number of serious thromboembolic complications still occur, highlighting the need for a more effective therapy. DMP 728 has been characterized as a potent and specific platelet glycoprotein IIb/IIIa complex (GPIIb/IIIa) antagonist. The goals of the present study were to determine the oral antiplatelet and antithrombotic efficacies of DMP 728 in various arterial thrombosis models in dogs.

METHODS AND RESULTS

In conscious and anesthetized mongrel dogs, DMP 728 at 0.02 to 1.0 mg/kg PO in gelatin capsules produced dose-dependent antiplatelet effects in inhibiting ex vivo platelet aggregation induced by ADP and prolonging template bleeding time. DMP 728 effects on bleeding time prolongation could be reversed more rapidly than those on platelet aggregation inhibition. A maximal antiplatelet effect for DMP 728 was demonstrated at 1.0 mg/kg PO. DMP 728 demonstrated dose-dependent oral antiplatelet effects with an absolute oral bioavailability of 8% to 12% in dogs. Additionally, the antithrombotic efficacy of DMP 728 was examined after intravenous and oral administration at different doses in various models of arterial thrombosis. In the coronary artery Folts' model in dogs, DMP 728 demonstrated maximal antithrombotic efficacy at 0.01 mg/kg IV and < 0.6 mg/kg PO. Additionally, DMP 728 at 0.1 and 1.0 mg/kg IV or PO demonstrated 60% to 100% prevention of primary thrombosis (P < .01) in an electrolytically induced carotid artery thrombosis model in dogs.

CONCLUSIONS

These data suggest that DMP 728, a low-molecular-weight GPIIb/IIIa receptor antagonist, may have therapeutic potential as an oral antithrombotic agent in coronary and carotid artery thromboembolic disorders.

Loss of high-affinity prostacyclin receptors in platelets and the lack of prostaglandin-induced inhibition of platelet-stimulated thrombin generation in subjects with spinal cord injury

Coronary artery disease is a leading cause of death in individuals with chronic spinal cord injury (SCI). However, platelets of those with SCI (n = 30) showed neither increased aggregation nor resistance to the antiaggregatory effects of prostacyclin when compared with normal controls (n = 30). Prostanoid-induced cAMP synthesis was similar in both groups. In contrast, prostacyclin, which completely inhibited the platelet-stimulated thrombin generation in normal controls, failed to do so in those with SCI. Scatchard analysis of the binding of [3H]prostaglandin E1, used as a prostacyclin receptor probe, showed the presence of one high-affinity (Kd1 = 8.11 +/- 2.80 nM; n1 = 172 +/- 32 sites per cell) and one low-affinity (Kd2 = 1.01 +/- 0.3 microM; n2 = 1772 +/- 226 sites per cell) prostacyclin receptor in normal platelets. In contrast, the same analysis in subjects with SCI showed significant loss (P < 0.001) of high-affinity receptor sites (Kd1 = 6.34 +/- 1.91 nM; n1 = 43 +/- 10 sites per cell) with no significant change in the low affinity-receptors (Kd2 = 1.22 +/- 0.23; n2 = 1820 +/- 421). Treatment of these platelets with insulin, which has been demonstrated to restore both of the high- and low-affinity prostaglandin receptor numbers to within normal ranges in coronary artery disease, increased high-affinity receptor numbers and restored the prostacyclin effect on thrombin generation. These results demonstrate that the loss of the inhibitory effect of prostacyclin on the stimulation of thrombin generation was due to the loss of platelet high-affinity prostanoid receptors, which may contribute to atherogenesis in individuals with chronic SCI.

The protective dose of the potent GPIIb/IIIa antagonist SC-54701A is reduced when used in combination with aspirin and heparin in a canine model of coronary artery thrombosis

BACKGROUND

Fibrinogen receptor antagonists block the fibrinogen-platelet interaction at the GPIIb/IIIa receptors and inhibit thrombus formation. SC-54701 is the active metabolite of SC-54684A, an orally fibrinogen receptor antagonist. We compared the efficacy of SC-54701A (SCa, hydrochloride salt) with that of aspirin (ASA) or heparin and with combination therapy in a canine model of continuous current injury.

METHODS AND RESULTS

Sixty-six dogs were used (6 per treatment). SCa (15-minute loading dose followed by [//] infusion [microgram/kg per minute]: (0.87//0.39=1 X SCa; 0.52//0.23=0.6 X SCa; and 0.425//0.20= 0.5 X SCa), ASA (2.8 mg/kg), heparin (200 U/kg plus 1000 U/h), or saline (0.1 mL/kg) was administered intravenously. Experimental time was 180 minutes of current. Time to occlusion was increased (P < .05) by SCa (T=incidence of thrombosis) (1 X SCa, >180 minutes [T=0]; 0.6 X SCa, 158 +/- 15 minutes [T=2]; 0.5 X SCa, 130 +/- 22 minutes [T=4]), heparin (114 +/- 16 minutes [T=5]), and ASA plus heparin (130 +/- 11 minutes [T=5]) relative to saline (58 +/- 7 minutes [T=6]). Time to occlusion for the SCa treatments was increased compared with ASA (64 +/- 7 minutes [T=6]). When 0.5 X SCa was administered with ASA plus heparin, time to occlusion was >180 minutes [T=0]. SCa provided complete protection at > or = 90% inhibition of ex vivo collagen-induced platelet aggregation. Cyclic flow variations were minimal with SCa or any treatment involving 0.5 X SCa and ASA.

CONCLUSIONS

SCa has dose-dependent antithrombotic efficacy and inhibits ex vivo platelet aggregation. ASA, heparin, or saline was ineffective in this model. SCa (0.5X) plus ASA and heparin maximized the antithrombotic effect of this lower dose of SCa.

Platelet activation during myocardial ischaemia: a contributory arrhythmogenic mechanism

Experimental and clinical observations of the involvement of platelets in the pathophysiology of myocardial ischaemia indicate the importance of interactions between these formed elements and the heart. The aim of this review is to outline evidence linking platelet activation, myocardial ischaemia and infarction, and to present evidence for a link between platelet activation, arrhythmogenesis and sudden death. A brief review of platelet physiology and pharmacology is provided, with a review of the cardiac electrophysiological effects of ischaemia and the electrophysiological effects of platelet-derived substances. The concept that platelet activation during myocardial ischaemia is a contributory arrhythmogenic mechanism is discussed.

Platelet activation in acute myocardial infarction and unstable angina is inhibited by nitric oxide donors

Platelet activation and thrombus formation within the coronary artery are major factors in acute myocardial infarction (AMI) and unstable angina (UA), and continuing platelet activation is associated with an adverse prognosis. We assessed platelet activation by using flow cytometry to measure platelet surface expression of P-selectin and glycoprotein IIb/IIIa in 20 patients with AMI and 20 with UA, all of whom were treated with aspirin. Platelet studies were repeated after the infusion of a nitric oxide donor (glyceryl trinitrate or S-nitrosoglutathione) that produced a fall in mean arterial pressure of no more than 10 mm Hg. P-selectin was expressed on 2.5% (range, 1.4% to 6.3%) of platelets from AMI and 2.3% (range, 1.6% to 3.3%) from UA subjects compared with 1.0% (range, 0.6% to 1.9%) of platelets from 20 control volunteers without angina (P < .001). Glycoprotein IIb/IIIa expression was 101.6 +/- 2.7 arbitrary units of relative fluorescence in AMI and 100.2 +/- 3.3 in UA compared with 87.8 +/- 2.5 in control subjects (P < .01). In both AMI and UA, S-nitrosoglutathione reduced P-selectin (P < .001) and glycoprotein IIb/IIIa (P < .05) expression, as did glyceryl trinitrate (P < .02 and P < .01, respectively). In 3 of 20 patients receiving glyceryl trinitrate the lowest dose was not tolerated due to headache or hypotension. These findings show that platelet activation persists in AMI and UA despite aspirin treatment and that this can be inhibited by using glyceryl trinitrate or S-nitrosoglutathione. S-nitrosoglutathione is better tolerated at the doses required.

A monoclonal antibody that recognizes the GPIIb/IIIa antagonist DMP 728. Reversal of the effects of DMP 728 on platelet aggregation and bleeding time in the dog

Since hemorrhagic events represent a major safety concern associated with the use of new antithrombotic therapies such as glycoprotein (GP) IIb/IIIa receptor blockade, we evaluated the ability of a monoclonal antibody recognizing DMP 728 (cyclic [D-2-aminobutyryl-N2-methyl-L-argininyl-glycyl-L-aspartyl-3- aminomethyl-benzoic acid] methanesulfonic acid salt), a potent GPIIb/IIIa receptor antagonist, to reverse the pharmacological actions of DMP 728 in the dog. DC11 was chosen for in vivo evaluation based on its ability to inhibit the binding of [3H]DMP 728 to activated platelets and to attenuate the inhibition of ADP-induced aggregation on platelet-rich plasma ex vivo by DMP 728. After anesthesia mongrel dogs were given DMP 728 (20 micrograms/kg body wt IV) infused into the femoral vein, bleeding times were determined using a Simplate device from incisions on the backside of the tongue, and platelet aggregation was determined ex vivo. Nearly complete inhibition of platelet aggregation was observed for the dogs treated with DMP 728 (20 ug/kg IV) for up to 210 minutes, and bleeding times were prolonged > 15 minutes for 2 hours and remained elevated for more than 4 hours. DC11 (0.2 or 1.0 mg/kg body wt IV) given to dogs 10 minutes after DMP 728 resulted in 50% attenuation of the effect of DMP 728 on aggregation at 3 hours. Approximately 34% inhibition of the DMP 728-mediated bleeding time was achieved at 1 hour with the 0.2 mg/kg dose, whereas approximately 50% inhibition of the bleeding time was observed for the 1 mg/kg dose at 1 hour.(ABSTRACT TRUNCATED AT 250 WORDS)

Prothrombotic effects of environmental stress: changes in platelet function, hematocrit, and total plasma protein

Mental stress can affect a range of variables relevant to hemostasis and thrombosis. However, research has not clarified whether these effects occur as part of a generalized sympathoadrenal response or whether stress-induced increases in catecholamines and blood pressure have selective and independent effects on hematologic variables. This study assessed the effects of mental and cold pressor stress on platelet activation, hematocrit, and total plasma protein and the relationship of these changes to sympathoadrenal and hemodynamic mechanisms. Platelet factor 4, beta-thromboglobulin, total plasma protein, hematocrit values, and hemoglobin were measured in 22 healthy men (32 +/- 7 years) during rest, mental arithmetic, and cold pressor task. A no-stress control group of five male subjects was used to rule out the possible effects of blood withdrawal in producing these changes. Significant increases to mental arithmetic and cold pressor (p < .001) were observed in platelet factor 4 and beta-thromboglobulin. Increases (p < .002) in hematocrit values and total plasma protein also occurred with mental arithmetic and cold pressor. Correlational analyses revealed that changes in hematocrit and total plasma protein concentrations were related to increased mean arterial pressure during stress, and platelet activation correlated positively with norepinephrine and negatively with epinephrine. The present results indicate that acute psychologic and cold stress cause concurrent changes in several hemostatic factors (increased platelet activation, hematocrit, and total plasma protein) that may play key roles in thrombosis and ischemia. The relationships of hematocrit and total plasma protein to blood pressure increases and the associations between platelet activation and catecholamines support the notion that stress-induced increases in catecholamines and blood pressure have selective effects on specific hemostatic variables.

Increased heparin-releasable platelet factor 4 and D dimer in patients one month after the onset of acute myocardial infarction: persistent activation of platelets and the coagulation/fibrinolytic system

To evaluate the activity of platelets and the coagulation/fibrinolytic system 1 month after the onset of acute myocardial infarction, we measured the plasma levels of molecular markers, i.e. beta-thromboglobulin, platelet factor 4, thrombin-antithrombin III complex and D dimer, in 16 patients with acute myocardial infarction and in 11 normal subjects. Blood was drawn through a catheter placed in the pulmonary artery before heparin injection. The heparin-releasable platelet factor 4 was calculated by subtracting the level before the injection of 5000 U of heparin, from the level 5 min after injection. The plasma beta-thromboglobulin, thrombin-antithrombin III complex and the D dimer levels in the acute phase of myocardial infarction were 134.9 +/- 121.2, 11.2 +/- 7.1 and 164.4 +/- 115.3 ng/ml, respectively. These values were significantly higher than those in the normal subjects. The plasma levels of beta-thromboglobulin and thrombin-antithrombin III complex, 1 month after the onset (36.6 +/- 16.4 and 4.6 +/- 2.3 ng/ml, respectively) were not significantly different from those of the normal subjects. In contrast, D dimer and heparin-releasable platelet factor 4 were 216.9 +/- 176.9 and 80.5 +/- 29.3 ng/ml, respectively, and significantly higher than in the normal subjects. These findings suggest a latent but persistent activation of the platelets and the coagulation/fibrinolytic system 1 month after the onset of acute myocardial infarction.

Intravenous antiplatelet efficacy and safety of the platelet GPIIb/IIIa antagonist, DMP 728 in anesthetized dogs

DMP 728, cyclo (D-2-aminobutyrate-N-Methyl-L-Arginyl-Glycyl-L-Aspartyl- 3-amino-methyl-benzoic acid) methanesulfonate salt, is a novel antiplatelet agent with high affinity and specificity for human and canine platelet GPIIb/IIIa (alpha 2/beta 3) receptors. DMP 728 demonstrated a potent antiplatelet efficacy in inhibiting ADP-induced platelet aggregation in either human or canine PRP with an IC50 of 0.046 and 0.015 microM, respectively. The IC50 of DMP 728 in inhibiting human platelet aggregation in PRP ranged from 0.02-0.05 microM regardless of the agonist used or even their combinations. Additionally, DMP 728 displayed a much greater affinity in inhibiting 125I-fibrinogen binding to stimulated human platelets as compared to the linear peptide RGDS or fibrinogen. The present study was undertaken to examine the i.v. antiplatelet efficacy and safety of DMP 728 in anesthetized dogs. In anesthetized mongrel dogs, DMP 728 (0.001-1.0 mg/kg, i.v. bolus) produced a dose-dependent inhibition of ex vivo platelet aggregation induced by ADP. The onset of inhibition was immediate, and the duration of antiplatelet effects was dose-dependent. A maximal inhibition of platelet aggregation and a reversible prolongation of bleeding time at 0.01 mg/kg were shown. Additionally, the antiplatelet efficacy/safety of DMP 728 was examined after i.v. administration at different infusion rates ranging from 0.008 to 0.833 micrograms/kg/min for 2 hours. A minimal antiplatelet effect was observed at the 0.008 micrograms/kg/min for 2 hours, while a maximal inhibition of platelet aggregation along with a reversible prolongation of bleeding time was achieved at 45-60 min post-infusion of 0.08 micrograms/kg/min x 2 hours. Prolongation of bleeding time was significantly reduced upon the cessation of the infusion while maximal inhibition of platelet aggregation was maintained longer. At all of the above regimens, DMP 728 did not result in any significant effects on platelet counts. Furthermore, DMP 728 did not elicit any other platelet unrelated adverse effects over wide range of doses. These data suggest that DMP 728, a low molecular weight platelet GPIIb/IIIa receptor antagonist, is a potent and systemically active antiplatelet agent with reversible effects on bleeding time.

Antithrombotic properties of transdermal nitroglycerin in stable angina pectoris

Nitroglycerin provides an external source of nitric oxide which stimulates guanylate cyclase and produces vasodilatation and inhibition of platelet function. The antithrombotic effects of intravenous nitroglycerin were recently documented in various experimental models and in patients with unstable angina. This protocol was designed to evaluate whether these effects could also be detected with transdermal nitroglycerin in patients with stable angina. In a randomized, double-blind, controlled parallel trial, 22 patients received transdermal nitroglycerin, 0.6 mg/hour (11 patients), or placebo (11 patients). Platelet aggregation to adenosine diphosphate (ADP) and to thrombin was measured in whole blood. Thrombus formation was assessed on porcine aortic media exposed to the patient's venous blood for 3 minutes at shear rates of 2,546 and 754 s-1. Platelet aggregation to ADP decreased from 7.7 +/- 0.8 to 5.3 +/- 0.8 ohms (p < 0.05) with nitroglycerin, and to thrombin from 15.6 +/- 1.2 to 12 +/- 1.2 ohms (p < 0.05). Thrombus size at the high-shear rate decreased from 2.8 +/- 0.7 to 1.0 +/- 0.3 microns 2 (p < 0.05), and at the low-shear rate from 2.5 +/- 0.5 to 1.0 +/- 0.2 microns 2 (p < 0.05). Placebo had no significant effect on platelet aggregation and platelet thrombus deposition. These parameters were all reduced by > or = 20% in 8 patients taking nitroglycerin but only in 3 patients taking placebo (p < 0.05). Transdermal nitroglycerin significantly inhibits platelet aggregation and mural thrombus formation in patients with angina pectoris.

Antiplatelet and antithrombotic efficacy of DMP 728, a novel platelet GPIIb/IIIa receptor antagonist

BACKGROUND

Currently used antiplatelet drugs, including aspirin, ticlopidine, and others, are effective against certain but not all of the many endogenous platelet activators. Because of their limited efficacy, a significant number of serious thromboembolic complications still occur, highlighting the need for a more effective therapy. Thus, we have identified a systemically active peptide analogue (DMP 728) of the arginine-glycine-aspartic acid (RGD) recognition sequence that mediates the binding of ligands such as fibrinogen to the platelet glycoprotein (GP) IIb/IIIa receptors. The goals of the present study were to determine the antiplatelet and antithrombotic efficacies of DMP 728 in various arterial thrombosis models.

METHODS AND RESULTS

DMP 728 demonstrated antiplatelet efficacy in vitro in inhibiting ADP-induced human platelet aggregation (IC50, 46 +/- 2 nmol/L) and fibrinogen binding to human platelets (IC50, 2.3 +/- 0.8 nmol/L) or purified human GPIIb/IIIa receptors (IC50, 0.6 +/- 0.1 nmol/L). DMP 728 demonstrated high affinity and specificity for human platelet GPIIb/IIIa over other adhesion molecules. In anesthetized mongrel dogs, DMP 728 at 0.001 to 1.0 mg/kg IV produced dose-dependent antiplatelet effects in inhibiting ex vivo platelet aggregation induced by ADP and in prolonging template bleeding time. DMP 728 effects on bleeding time prolongation were more rapidly reversible than those on platelet aggregation inhibition. A maximal antiplatelet effect for DMP 728 was demonstrated at 0.01 mg/kg IV bolus. The antithrombotic efficacy of DMP 728 was examined in vitro and in vivo after IV administration at different doses in various models of arterial thrombosis. In the coronary artery Folts model in dogs, DMP 728 demonstrated maximal antithrombotic efficacy at 0.01 mg/kg IV bolus with an ED50 of 0.005 mg/kg IV bolus in inhibiting cyclic flow reductions. Additionally, DMP 728 demonstrated 100% prevention of primary thrombosis and rethrombosis (P < .01) after treatment with different thrombolytics, including tissue plasminogen activator and streptokinase, in an electrolytically induced femoral artery thrombosis model in dogs.

CONCLUSIONS

Acute intravenous DMP 728 administration (0.001 to 1.0 mg/kg) has dose-dependent antiplatelet and antithrombotic effects in different arterial thrombosis models. These data suggest that DMP 728, a low-molecular-weight GPIIb/IIIa receptor antagonist, may have therapeutic potential as an effective antithrombotic agent in coronary and peripheral artery thromboembolic disorders.

Platelet adhesion is related to heart rhythm disturbances in the acute phase of myocardial infarction

This study examines the relationship between platelet adhesion, aggregation and the occurrence of heart rhythm disturbances in 43 consecutive patients (mean age 58) admitted to a coronary care unit with acute myocardial infarction. Blood for platelet studies was taken prior to institution of any medication and heart rhythm was monitored (Holter) for 24 h after admission. The control group consisted of 22 healthy subjects (mean age 55 yr). Platelet adhesion to collagen was measured in EDTA-platelet rich plasma by recording the changes in light transmission in an optical aggregometer. Platelet aggregation was measured by the Born method. Platelet adhesion was increased in the group of patients with acute myocardial infarction as compared to controls and was significantly higher in the patients with complex ventricular arrhythmias (Lown 3-4b, n = 18) than in the patients with stable rhythm. Platelet aggregation in the patients with acute myocardial infarction did not differ significantly from the controls and was not related to heart rhythm disturbances. The causal relationship of increased platelet adhesiveness to collagen and heart rhythm disturbances in acute myocardial infarction remains to be established.