Novel antiplatelet therapies for treatment of patients with ischemic heart disease: inhibitors of the platelet glycoprotein IIb/IIIa integrin receptor

Loading Gentamicin and Zn2+ on TiO2 Nanotubes to Improve Anticoagulation, Endothelial Cell Growth, and Antibacterial Activities

Titanium and its alloys are widely used in blood-contacting implantable and interventional medical devices; however, their biocompatibility is still facing great challenges. In the present study, in order to improve the biocompatibility and antibacterial activities of titanium, TiO2 nanotubes were firstly in situ prepared on the titanium surface by anodization, followed by the introduction of polyacrylic acid (PAA) and gentamicin (GS) on the nanotube surface by layer-by-layer assembly, and finally, zinc ions were loaded on the surface to further improve the bioactivities. The nanotubes displayed excellent hydrophilicity and special nanotube-like structure, which can selectively promote the albumin adsorption, enhance the blood compatibility, and promote the growth of endothelial cells to some degree. After the introduction of PAA and GS, although the superhydrophilicity cannot be achieved, the results of platelet adhesion, cyclic guanosine monophosphate (cGMP) activity, hemolysis rate, and activated partial thromboplastin time (APTT) showed that the blood compatibility was improved, and the blood compatibility was further enhanced after zinc ion loading. On the other hand, the modified surface showed good cytocompatibility to endothelial cells. The introduction of PAA and zinc ions not only promoted the adhesion and proliferation of endothelial cells but also upregulated expression of vascular endothelial growth factor (VEGF) and nitric oxide (NO). The slow and continuous release of GS and Zn2+ over 14 days can significantly improve the antibacterial properties. Therefore, the present study provides an effective method for the surface modification of titanium-based blood-contacting materials to simultaneously endow with good blood compatibility, endothelial growth behaviors, and antibacterial properties.

Oxidative pathways of arachidonic acid as targets for regulation of platelet activation

Platelet activation plays an important role in acute and chronic cardiovascular disease states. Multiple pathways contribute to platelet activation including those dependent upon arachidonic acid. Arachidonic acid is released from the platelet membrane by phospholipase A2 action and is then metabolized in the cytosol by specific arachidonic acid oxidation enzymes including prostaglandin H synthase, 12-lipoxygenase, and cytochrome P450 to produce pro- and anti-inflammatory eicosanoids. This review aims to analyze the role of arachidonic acid oxidation on platelet activation, the enzymes that use it as a substrate associated as novel therapeutics target for antiplatelet drugs.

Curcumin, hemostasis, thrombosis, and coagulation

Atherothrombotic cardiovascular disease is a major cause of mortality throughout the world. Platelet activation and aggregation play a central role in hemostasis and thrombosis. Herbal medicines have been traditionally used in the management of cardiovascular disease and can help in modifying its progression, particularly in hemostasis and the coagulation process, as well as altering platelet function tests and some coagulation parameters. Curcumin is a polyphenol derived from the Curcuma longa plant and has been used extensively in complementary and alternative medicine, as it is nontoxic and safe with various therapeutic properties. Modern scientific research has demonstrated its anti-inflammatory, antioxidant, anti-carcinogenic, antithrombotic, and cardiovascular protective effects. The present study reviewed previous studies in the literature, which support the positive activity of curcumin in hemostasis, anticoagulation, and fibrinolysis. We also presented molecular mechanisms associated with the antiplatelet and anticoagulant activities of curcumin and potential implications for the treatment of cardiovascular 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.

Progress in the research of GPIIb/IIIa antagonists

This review covers the recent advances in the development of small RGD (Arg-Gly-Asp sequence) containing peptides and their mimetics as potential antithrombotic agents. Glycoprotein IIb/IIIa (GPIIb/IIIa) antagonists include monoclonal antibodies, RGD peptides, peptide hybrids and nonpeptide mimetics. The current trend in the development of nonpeptide mimetics is clearly directed toward orally active and safe antithrombotic drug candidates. But several nonpeptide mimetics, being evaluated for their oral activity in human clinical trials, are currently not approved for clinical use due to poor safety profile. It is expected that newer and more effective nonpeptide mimetics will be developed in the near future.

Antiplatelet effects of Spatholobus suberectus via inhibition of the glycoprotein IIb/IIIa receptor

ETHNOPHARMACOLOGICAL RELEVANCE

The vine stem of Spatholobus suberectus is a widely used blood-activating and stasis-dispelling medicine for the treatment of diseases related to blood stasis syndrome in traditional medicine in Korea, Japan, and China.

AIM OF THE STUDY

To demonstrate the clinical effects of Spatholobus suberectus against blood stasis syndromes using in vitro and in vivo platelet aggregation studies and to investigate its exact mechanisms.

MATERIALS AND METHODS

We extracted vine stems of Spatholobus suberectus, using 95% EtOH (SSE) and investigated its antiplatelet activity on platelet aggregation induced by collagen and ADP in human platelet-rich plasma (PRP). For the mechanism study, a glycoprotein IIb/IIIa (GP IIb/IIIa) assay using flow cytometric analysis and a thromboxane A(2) (TXA(2)) assay were performed. In addition, we investigated the effects of SSE in a thromboembolic mouse model.

RESULTS

SSE significantly inhibited ADP- and collagen-induced platelet aggregation in human PRP concentration-dependently without affecting plasma clotting time. It also significantly inhibited fibrinogen binding to the GP IIb/IIIa receptor and partly inhibited the formation of TXA(2). In the in vivo study, oral administration of SSE dose-dependently suppressed the death of thromboembolism model mice induced by intravenous injection of collagen plus epinephrine.

CONCLUSIONS

SSE showed antiplatelet activity without anticoagulant effects mainly through the inhibition of fibrinogen binding to the GP IIb/IIIa receptor. Our current results support the clinical usage of SSE in the East Asian region treating atherothrombotic diseases and may represent a new natural source to develop antiplatelet agents.

The PFA-100R cannot detect blood group-dependent inhibition of platelet function by eptifibatide or abciximab at therapeutic plasma concentrations

Previous investigations revealed that AB0 blood groups are associated with divergent concentrations of several coagulation factors. Concentrations of von Willebrand factor (vWF) and factor VIII are lower in individuals with blood group 0 compared to subjects with blood group A, B or AB, which might in turn result in a reduced inhibition of platelet aggregation in individuals with blood group 0. The aim of the present in vitro investigation was to elucidate the impact of AB0 blood group-dependent vWF concentrations on eptifibatide and abciximab mediated inhibition of GPIIb/IIIa function. Platelet function was measured with the platelet function analyzer PFA-100(R) at baseline and at increasing concentrations of eptifibatide and abciximab. It was stratified for blood group 0 vs A. If measured with the collagen/ADP cartridge, blood group 0 was associated with a prolonged mean baseline closure time in comparison with blood group A (94.3 +/- 14.6 s vs. 74.6 +/- 9.9 s, p = 0.007) which was paralleled by reduced concentrations of vWF and factor VIII. In contrast, no statistically significant differences in closure times (167.4 +/- 83.9 s vs. 140.1 +/- 99.0 s, p = 0.562) could be found in the presence of eptifibatide (0.1 microg/ml). Higher concentrations of abciximab (1 microg/ml) than those of eptifibatide were needed to increase the closure times in both cartridges of the PFA-100, but at this concentration of abciximab differences in closure times could not be detected most probably due to higher variability at these drug concentrations. The PFA-100(R) is not suitable for monitoring abciximab or eptifibatide within the therapeutic concentration range because the highest concentrations where the PFA-100(R) had measurable closure times of below 300 s is much too low to lead to the necessary platelet inhibition and, consequently, does not resemble the in vivo situation.

Studies of tricyclic piperazine/piperidine furnished molecules as novel integrin αvβ3/αIIbβ3 dual antagonists using 3D-QSAR and molecular docking

The development of injectable integrin α(v)β(3)/α(IIb)β(3) dual antagonists attracts much attention of research for treating of acute ischemic diseases in recent years. In this work, based on a dataset composed of 102 tricyclic piperazine/piperidine furnished dual α(v)β(3) and α(IIb)β(3) antagonists, a variety of in silico modeling approaches including the comparative molecular field analysis (CoMFA), comparative similarity indices analysis (CoMSIA), and molecular docking were applied to reveal the requisite 3D structural features impacting the biological activities. Our statistical results show that the ligand-based 3D-QSAR models for both the α(v)β(3) and α(IIb)β(3) studies exhibited satisfactory internal and external predictability, i.e., for the CoMFA models, results of Q(2)=0.48, R(ncv)(2)=0.87, R(pred)(2)=0.71 for α(v)β(3) and Q(2)=0.50, R(ncv)(2)=0.85, R(pred)(2)=0.72 for α(IIb)β(3) analysis were obtained, and for the CoMSIA ones, the outcomes of Q(2)=0.55, R(ncv)(2)=0.90, R(pred)(2)=0.72 for α(v)β(3) and Q(2)=0.52, R(ncv)(2)=0.88, R(pred)(2)=0.74 for α(IIb)β(3) were achieved respectively. In addition, through a comparison between 3D-QSAR contour maps and docking results, it is revealed that that the most crucial interactions occurring between the tricyclic piperazine/piperidine derivatives and α(v)β(3)/α(IIb)β(3) receptor ligand binding pocket are H-bonding, and the key amino acids impacting the interactions are Arg214, Asn215, Ser123, and Lys253 for α(v)β(3), but Arg214, Asn215, Ser123 and Tyr190 for α(IIb)β(3) receptors, respectively. Halogen-containing groups at position 15 and 16, benzene sulfonamide substituent at position 23, and the replacement of piperazine with 4-aminopiperidine of ring B may increase the α(v)β(3)/α(IIb)β(3) antagonistic activity. The potencies for antagonists to inhibit isolated α(v)β(3) and α(IIb)β(3) are linear correlated, indicating that similar interaction mechanisms may exist for the series of molecules. To our best knowledge this is the first report on 3D-QSAR modeling of these dual α(v)β(3)/α(IIb)β(3) antagonists. The results obtained should provide information for better understanding of the mechanism of antagonism and thus be helpful in design of novel potent dual α(v)β(3)/α(IIb)β(3) antagonists.

Acute Cerebral Infarction Following Intravenous Glycoprotein IIb/IIIa Inhibitor for Acute Myocardial Infarction

Stroke is a rare but serious complication of acute myocardial infarction (AMI). Currently, glycoprotein (GP) IIb/IIIa inhibitor is used in clinical practice for acute coronary syndromes and percutaneous coronary interventions (PCIs). The incidence of stroke in patients receiving GP IIb/IIIa inhibitor during PCIs is very low. We report the case of a 47-year-old man who presented with AMI and suffered an acute cerebral infarction after infusion of a GP IIb/IIIa inhibitor following primary PCI.

Actual Role of Platelet Glycoprotein IIb/IIIa Receptor Inhibitors as Adjunctive Pharmacological Therapy to Primary Angioplasty in Acute Myocardial Infarction: In the Light of Recent Randomized Trials and Observational Studies with Bivalirudin

Strategies for preventing ischemic complications during percutaneous coronary interventions (PCI) in the setting of acute myocardial infarction (AMI) have focused on the platelet surface-membrane glycoprotein (GP) IIb/IIIa receptor. The platelet GP IIb/IIIa receptor inhibitors, by blocking the final common pathway of platelet aggregation, have become a breakthrough in the management of acute coronary syndromes. Current adjuvant pharmacological therapy of AMI with aspirin, clopidogrel, unfractionated heparin (UH), and platelet GP IIb/IIIa inhibitors provides useful therapeutic benefits. Although the use of more potent antithrombin and antiplatelet agents during PCI in AMI has reduced the rate of ischemic complications, in parallel, the rate of bleeding has increased. Several studies have reported an association between bleeding after PCI and an increase in morbidity and mortality. Therefore, investigational studies have focused in pharmacological agents that would reduce bleeding complications without compromising the rate of major adverse cardiovascular events. Based on the results of several randomized trials, abciximab with UH, aspirin and clopidogrel have become a standard adjunctive therapy with primary PCI for AMI. However, some of the trials were done before the use of stents and the widespread use of thienopyridines. In addition, GP IIb/IIIa inhibitors use have been associated with thrombocytopenia, high rates of bleeding, and the need for transfusions, which increase costs, length of hospital stay, and mortality. On the other hand, in the stent era, bivalirudin, a semi-synthetic direct thrombin inhibitor, has recently been shown to provide similar efficacy with less bleeding compared with unfractionated heparin plus platelet GP IIb/IIIa inhibitors in AMI patients treated with primary PCI. The impressive results of this recent randomized trial and other observational studies make a strong argument for the use of bivalirudin rather than heparin plus GP IIb/IIIa inhibitors for the great majority of patients with AMI treated with primary PCI. However, some controversial results and limitations in the studies with bivalirudin exert some doubts in the future widespread use of this drug.

From ATP to AZD6140: the discovery of an orally active reversible P2Y12 receptor antagonist for the prevention of thrombosis

Starting from adenosine triphosphate (ATP), the identification of a novel series of P2Y(12) receptor antagonists and exploitation of their SAR is described. Modifications of the acidic side chain and the purine core and investigation of hydrophobic substituents led to a series of neutral molecules. The leading compound, 17 (AZD6140), is currently in a large phase III clinical trial for the treatment of acute coronary syndromes and prevention of thromboembolic clinical sequelae.

Cardioprotective effects of curcumin

Curcumin, a major active component of turmeric, is extracted from the powdered dry rhizome of Curcuma longa Linn (Zingiberaceae) and it has been used for centuries in indigenous medicine. We have shown that curcumin has a protective role against myocardial necrosis in rats. The antioxidant activity of curcumin could be attributed to the phenolic and methoxy groups in conjunction with the 1,3-diketone-conjugated diene system, for scavenging of the oxygen radicals. In addition, curcumin is shown to enhance the activities of detoxifying enzymes such as glutathione-S-transferase in vivo. We have also shown that oxygen free radicals exacerbate cardiac damage and curcumin induces cardioprotective effect and it also inhibits free-radical generation in myocardial ischemia in rats. This chapter on the cardioprotective effects of curcumin covers the following aspects: (1) the history of curcumin and its discovery as a potent drug with relevance to cardiovascular diseases; (2) mechanistic role of curcumin in vitro, emphasizing the antiplatelet and anticoagulant effects; (3) cardiovascular properties of curcumin; (4) application of curcumin in different animal models (viz. myocardial ischemia, myocardial infarction, cardiomyopathy, and arrhythmia in vitro and in vivo); (5) curcumin free-radical scavenging activity, particularly against O2 radical and depletion of the oxidative stress.

Preparation, characterization and anticoagulation of curcumin-eluting controlled biodegradable coating stents

Curcumin is pharmaceutically active in many ways, having properties including anticoagulation, anti-proliferation, anti-inflammatory, and may be used to fabricate drug-eluting stents to treat in-stent restenosis after stent implantation. Here we describe our investigations of curcumin-eluting PLGA coatings formed using the biodegradable polymer PLGA (polylactic acid-co-glycolic acid) as drug carrier and uniformly fabricated on the surface of 316L stainless steel stents by an ultrasonic spray method. Three doses were explored--low dose ( approximately 140 microg per stent or 115 microg/cm(2)), moderate dose ( approximately 280 microg per stent or 230 microg/cm(2)), and high dose ( approximately 490 microg per stent or 408 microg/cm(2)). Pre- and post-expansion morphologies of the stent coating were examined by optical microscopy (OM) and scanning electron microscopy (SEM), indicating that the coating not only was very smooth and uniform but also had the ability to withstand the compressive and tensile strains imparted without cracking from the stent during the expansion process. Atomic force microscopy (AFM) images indicated the topography of the PLGA-only and moderate dose curcumin-eluting stent that showed an average roughness below 1 nm; no drug particles could be seen on the stent surface, indicating that curcumin can be mixed with PLGA at the molecular level using an ultrasonic atomization spray method. The structure of the coating films was characterized by Fourier Transform Infrared (FTIR) spectroscopy and X-ray electron spectroscopy (XPS), with results suggesting that there was no chemical reaction between curcumin and the drug. The results of in vitro measurements of drug release from curcumin-eluting stents showed that all the curcumin-eluting stents studied exhibited a nearly linear sustained-release profile with no significant burst releases within the measurement period. The in vitro anticoagulation behavior of curcumin-eluting stents was investigated by static platelet adhesion and APTT (activated partial thromboplastin time) tests, revealing that the anticoagulation properties of curcumin-eluting stents are superior to those for stainless steel stents and PLGA-only-coated stents. The anticoagulation behavior of curcumin stents improved significantly as the drug dose was increased.

Prohemorrhagic and bleeding time activities of recombinant tissue plasminogen activator, heparin, aspirin, and a glycoprotein IIb/IIIa antagonist

Intracerebral hemorrhage (ICH) is the most serious side effect of antithrombotic agents, especially in cases of cerebrovascular disease. In the present study, we compared the exacerbation of ICH and prolongation of bleeding time (BT) in guinea pigs with recombinant tissue plasminogen activator (rt-PA), heparin, aspirin, and FK419, a novel nonpeptide platelet glycoprotein (GP) IIb/IIIa receptor antagonist. ICH was induced by injection of bacterial collagenase into the caudate nucleus; BT was measured with a Simplate R device. Neither heparin nor aspirin prolonged BT. In contrast, rt-PA at the highest dose used in the study did prolong BT, and FK419 caused a dose-dependent prolongation of BT. Moreover, rt-PA and heparin increased the degree of ICH in a dose-dependent manner, leading to death in more than half of the animals treated with higher doses of these drugs. These findings show that the prohemorrhagic mechanisms underlying the prolongation of BT differ from those in collagenase-induced ICH, and that the risk of an agent with antithrombotic effects potentiating hemorrhage in the collagenase-induced model of ICH more closely parallels that in stroke patients than does the effect of the agent on BT. The findings also suggest that antiplatelet agents, including FK419, may be safer than thrombolytic or anticoagulant agents for use in patients at risk for ICH, such as those with stroke or cerebral aneurysm.

Curcumin modulates free radical quenching in myocardial ischaemia in rats

This study was designed to investigate the protective effect of curcumin (CUR) against isoprenaline induced myocardial ischaemia in rat myocardium. The effect of single oral dose of curcumin (15 mg kg(-1)), administered 30 min before and/or after the onset of ischaemia, was investigated by assessing oxidative stress related biochemical parameters in rat myocardium. Curcumin pre and post-treatment (PPT) was shown to decrease the levels of xanthine oxidase, superoxide anion, lipid peroxides (LPs) and myeloperoxidase while the levels of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) activities were significantly increased after curcumin PPT. Histopathological and transmission electron microscopical studies also confirmed the severe myocardial damage occurring as a consequence of isoprenaline induced ischaemia and they also showed the significant improvement effected by curcumin PPT. These findings provided evidence that curcumin was found to protect rat myocardium against ischaemic insult and the protective effect could be attributed to its antioxidant properties as well as its inhibitory effects on xanthine dehydrogenase/xanthine oxidase (XD/XO) conversion and resultant superoxide anion production.

Ongoing clinical trials of anti-platelet agents in the management of acute ischaemic coronary syndromes

Acute ischaemic coronary syndromes, the clinical sequelae of thrombosis over a fissured atherosclerotic plaque within the coronary circulation, are the leading cause of death and hospitalisation in Western countries. Platelets are fundamental for the initiation and continuation of thrombosis, and currently available anti-platelet agents such as aspirin significantly improve the clinical outcome of patients with these syndromes. Therapeutic success with available therapy is however not universal, and adverse clinical event rates remain high. Several new classes of agents with a variety of anti-platelet actions are currently under development. Those which inhibit the final common pathway of platelet aggregation, the glycoprotein (GP) IIb/IIIa receptor, appear to show the most promise. Much clinical trial evidence already exists supporting the use of GP IIb/IIIa receptor antagonists in the management of acute ischaemic coronary syndromes. Several clinical studies are underway to further refine this knowledge base, and to assess their efficacy in a variety of novel applications.

Rhodostomin, a disintegrin, inhibits adhesion of neutrophils to fibrinogen and attenuates superoxide production

Disintegrins are a group of Arg (or Lys)-Gly-Asp-containing snake venom proteins which inhibit platelet aggregation via the blockade of alpha(IIb)beta(3) integrin. Here, we studied the effect of rhodostomin, a disintegrin purified from the venom of Calloselasma rhodostoma, on the functions of neutrophils. By flow cytometric analysis of whole blood, we found that rhodostomin interacted with leukocytes of the myeloid and monocytic lineage as well as with platelets. The binding of rhodostomin to neutrophils could reach saturation in a dose-dependent manner, and its binding was increased in neutrophils stimulated with phorbol 12-myristate 13-acetate (PMA) and N-formyl-Met-Leu-Phe. EDTA did not inhibit the binding of rhodostomin. In addition, bound rhodostomin was not internalized. Soluble fibrinogen, a natural ligand of Mac-1 (CD11b/CD18, alpha(M)beta(2)), and the peptide, GRGDS, inhibited the binding of rhodostomin to PMA-activated neutrophils, while 7E3, a monoclonal antibody (mAb) raised against beta(3) integrin, or mAbs raised against alpha(M) and beta(2) integrin did not. Rhodostomin blocked the Mac-1-dependent adhesion of neutrophils to immobilized fibrinogen, in parallel with decreasing the production of superoxide from adherent neutrophils. Taken together, our results indicate that rhodostomin binds to activated neutrophils in an RGD-dependent manner, blocks the adhesion of activated neutrophils to fibrinogen and attenuates superoxide production, suggesting that rhodostomin may have anti-inflammatory properties.

Comparison of the effects of cellulose triacetate and polysulfone membrane on GPIIb/IIIa and platelet activation

BACKGROUND

During hemodialysis session, several adverse reactions can occur on platelets, which are attributable to bioincompatibility of the dialysis membrane. Glycoprotein IIb/IIIa (GPIIb/IIIa) is the receptor for fibrinogen, which mediates platelet aggregation and adhesion. Accordingly, we compared the influence of a cellulose triacetate (CTA) and polysulfone (PS) membrane on GPIIb/IIIa and platelet activation.

METHODS

Blood samples from 5 patients on hemodialysis were taken at 0 time, 15 min, 30 min, 60 min and 240 min, during a single hemodialysis session, by a crossover design using CTA or PS. Platelet count and plasma concentration of GPIIb/IIIa, beta-thromboglobulin (beta-TG) and platelet factor 4 (PF-4) were measured. GPIIb/IIIa was measured by flow cytometry. beta-TG and PF-4 were measured by ELISA.

RESULTS

There was no significant change in the total amount of GPIIb/IIIa during dialysis session between the CTA and PS. However, the level of bound GPIIb/IIIa was significantly (p < 0.0002) increased from 1,426 +/- 435 to 40,446 +/- 2,777 mol/PLT with PS. In contrast, there was no significant change with CTA (3,258 +/- 1,469 to 4,301 +/- 1,422 mol/PLT). The platelet counts and beta-TG and PF-4 behavior during the dialysis session did not show significant change between the PS and CTA.

CONCLUSION

The characterization of changes in platelet membrane receptor (GPIIb/IIIa) may be a useful marker for studying the biocompatibility of dialysis membranes. On platelet aggregation, CTA might be more biocompatible membrane than PS.

Long-term clinical benefits of a platelet glycoprotein IIb/IIIa receptor blocker, abciximab (ReoPro), in high-risk diabetic patients undergoing percutaneous coronary intervention

BACKGROUND

High-risk percutaneous coronary interventions (PCIs) are associated with a high complication rate, a low procedural success rate and a high restenosis rate, especially in diabetics. We sought to determine whether abciximab (ReoPro) therapy affects long-term clinical outcomes of Korean patients with diabetes undergoing high-risk PCI.

METHODS

One hundred and nineteen patients with 152 lesion sites were administered ReoPro among 2,231 patients who underwent PCI at Chonnam National University Hospital from March 1999 to Feb 2001. These 119 patients were divided into two groups, 30 were allocated to a diabetic group (Group 1, 57.7 +/- 8.2 years, 22 male), and 89 to a non-diabetic group (Group II, 59.6 +/- 10.8 years, 68 male). Early and long-term clinical outcomes after PCI were analyzed.

RESULTS

In terms of clinical diagnosis, the number of acute myocardial infarctions in Group I was 25 (83.3%) and 76 in Group II (85.4%). As for risk factors, target artery lesions, and ACC/AHA types, no differences were found between the two groups. The number of patients with total occlusion was 21 (55.3%) and 62 (53.9%), and the number with a thrombus-containing lesion was 28 (93.3%) and 88 (98.9%) in Groups I and II, respectively. The procedure was successful in 27 (90.0%) in Group I, and in 80 (89.9%) in Group II, and no differences were evident between the two groups in terms of bleeding complications. No major adverse cardiac events (MACE), including myocardial infarction, repeat revascularization or cardiac death, were observed in Group I, but 8 cases of MACE occurred in Group II during hospitalization. Clinical follow-up was performed in 116 patients (97.5%) over 18.5 +/- 6.7 (5-28) months. The number of overall MACEs was 10 (3.3%) in Group I and 14 (15.7%) in Group II (p = 0.038).

CONCLUSION

ReoPro used in high-risk PCI in diabetics was effective in terms of early clinical outcomes, but its long-term clinical benefits were not proven.

Pharmacotherapeutic considerations in anesthesia

This article focuses on new findings leading to improved understanding of the pathophysiology and mechanisms of potential drug interactions between anesthetic drugs or techniques and cardiovascular medications in patients scheduled for surgery. Only the most frequently used drugs are reviewed. Elective surgery provides the luxury to consider these risks and alter therapy accordingly. Under urgent circumstances, however, the increased risks associated with these agents should be anticipated with the goal to minimize adverse effects while maintaining optimal cardiovascular function in the perioperative period.

Occupancy of glycoprotein IIb/IIIa by B-6 vitamers inhibits human platelet aggregation

Vitamin B-6 inhibits platelet aggregation. However, the effect of the occupancy of GPIIb/IIIa, a major receptor responsible for aggregation on platelet membranes, by B-6 vitamers on platelet aggregation is unknown. This study was carried out to quantify GPIIb/IIIa occupancy in platelets treated with B-6 vitamers [pyridoxal-5-phosphate (PLP); pyridoxal (PL); pyridoxine (PN); pyridoxamine (PM)], using a monoclonal antibody-based assay, by flow cytometry. Antibody binding was compared with inhibition of platelet aggregation. PLP, PL, PN and PM occupied GPIIb/IIIa with dissociation constants of 1.83 +/- 1.15, 19.43 +/- 7.86, 3.63 +/- 1.67 and 10.89 +/- 2.93 mmol/L, respectively. Occupancy of GPIIb/IIIa by the four B-6 vitamers was negatively correlated with platelet aggregation (r = -0.90 to -0.94, P < 0.001). The concentrations of the four B-6 vitamers that inhibited maximal platelet aggregation were in the order of PLP < PN <PM < PL, the same order in which they occupied > or =80% of the GPII/IIIa receptor. Platelet aggregation was inhibited by B-6 vitamers via the occupancy of GPIIb/IIIa with the potency of PLP > PN > PM > PL.

The GP IIb/IIIa inhibitor abciximab (c7E3) inhibits the binding of various ligands to the leukocyte integrin Mac-1 (CD11b/CD18, alphaMbeta2)

Cross-reactivity with integrins other than glycoprotein IIb/IIIa (GP IIb/IIIa) is discussed as a potential reason for the overall clinical benefits of the GP IIb/IIIa-blocking antibody-fragment abciximab. We evaluated whether abciximab binds to the leukocyte integrin Mac-1, whether it inhibits binding of the distinct ligands and thereby may modulate inflammation, cell proliferation and coagulation. Binding of fluorescence-labelled abciximab to phorbolmyristate acetate-stimulated monocytes and to a monocytic cell line (THP-1) could be detected in flow cytometry. The binding of fibrinogen, the inactivated complement factor 3b (iC3b), and the coagulation factor X to Mac-1 could be inhibited by abciximab (10 microg/ml) in vitro. As a functional consequence, the conversion of factor X to factor Xa mediated by Mac-1, as detected by the chromogenic substrate SZ-2222, was impaired by abciximab. Adhesion of THP-1 cells to immobilized intercellular adhesion molecule 1 (ICAM-1) and to fibrinogen was reduced significantly by abciximab. Fibrinogen-mediated cell aggregation was also impaired. In conclusion, we describe binding of abciximab to Mac-1 on stimulated monocytes. Thereby, abciximab inhibits binding of the ligands fibrinogen, ICAM-1, iC3b and factor X. Furthermore, we demonstrated that Mac-1-dependent conversion from factor X to factor Xa is impaired by abciximab, arguing for the direct modulation of the coagulation cascade by abciximab. Overall, the inhibition of Mac-1 could provide additional clinical benefits of abciximab beyond the well-described blockade of GP IIb/IIIa.

Administration of glycoprotein IIb-IIIa inhibitors in patients with ST-segment elevation myocardial infarction

Patients with ST-segment elevation acute myocardial infarction require immediate reperfusion therapy. Reperfusion therapy can be provided by either pharmacologic or mechanical means. Pharmacologic reperfusion therapy consists of administering fibrinolytics, whereas mechanical reperfusion consists of performing percutaneous intervention, usually with stent placement. Each approach has been shown to decrease mortality, but each has disadvantages in establishing flow in the infarct-related artery. Regardless of the approach, during an acute myocardial infarction, activation and externalization of glycoprotein (GP) IIb-IIIa receptors occur on the surface of platelets. The GP IIb-IIIa inhibitors block the binding of fibrinogen to these platelet receptors. These inhibitors have been investigated in combination with both reperfusion strategies. The goal of adding GP IIb-IIIa inhibitor therapy to either reperfusion approach is to obtain better early, complete, and sustained reperfusion. Subsequently, this should lead to better clinical outcomes for patients with ST-segment elevation acute myocardial infarction. Although no mortality benefit has been seen with the addition of GP IIb-IIIa inhibitor therapy, ischemic complications have been reduced significantly.

Clinical pharmacokinetics of tirofiban, a nonpeptide glycoprotein IIb/IIIa receptor antagonist: comparison with the monoclonal antibody abciximab

Tirofiban is a nonpeptide tyrosine derivative that antagonises platelet glycoprotein IIb/IIIa (GP IIb/IIIa) receptors. It is one of three GP IIb/IIIa antagonists approved by the US Food and Drug Administration for the treatment of patients with acute coronary syndromes. The clinical effect of tirofiban has been shown in large studies such as PRISM (Platelet Receptor Inhibition for Ischemic Syndrome Management), PRISM-PLUS (PRISM - Patients Limited by Unstable Signs and Symptoms) and RESTORE (Randomised Efficacy Study of Tirofiban for Outcomes and Restenosis). Tirofiban is administered as an intravenous infusion. Volume of distribution ranges from 21 to 87 L, and binding to human plasma proteins is modest at 64%. Metabolism in humans is negligible, and most drug is excreted renally with systemic clearance ranging from 4.8 to 25.8 L/h. Renal function may influence the excretion of tirofiban, but concurrent disease or other drugs generally used in patients with ischaemia seem not to do so. This review updates what is known about the pharmacokinetics of tirofiban in humans, especially in comparison with the monoclonal antibody against the IIb/IIIa receptor, abciximab.

Antioxidant potential of a novel tetrapeptide derivative in isoproterenol-induced myocardial necrosis in rats

A novel tetrapeptide derivative Boc-Lys(Boc)-Arg-Asp-Ser(tbu)-OtBu (PEP1261) has been tested in vivo in isoproterenol (ISO) hydrochloride (HCl)-induced myocardial necrosis in rats. ISO x HCl induces myocardial necrosis in rats which is accompanied by the distinct increase in heart weight, marked electrocardiographic changes, increase in the levels of serum marker enzymes and lipid peroxides and decrease in the levels of antioxidants. PEP1261 (5 mg/kg body weight i.p.) pre- and post-treatment effectively decreases serum marker enzyme levels, while the electrocardiographic changes get restored towards normalcy. PEP1261 also inhibits the action of the free radicals toxicity by increasing the levels of antioxidants and histological studies confirm the above findings. This study shows that PEP1261 could serve as an excellent cardioprotective agent possessing membrane-stabilizing action.

Antiplatelet and antithrombotic activity of RWJ-53308, a novel orally active glycoprotein IIb/IIIa antagonist

RWJ-53308 is a novel nonpeptide glycoprotein IIb/IIIa (GPIIb/IIIa) antagonist that inhibits fibrinogen binding to GPIIb/IIIa with an IC(50) of 0.4+/-0.3 nM. RWJ-53308 inhibits thrombin-induced platelet aggregation in human gel-filtered platelets (IC(50)=60+/-12 nM) and platelet aggregation in human platelet-rich plasma (PRP) in response to collagen, arachidonic acid, ADP, and SFLLRN-NH(2) (IC(50)=60+/-10, 150+/-30, 70+/-4, and 160+/-80 nM, respectively). The potency of RWJ-53308 in dog and guinea pig PRP is similar to human PRP. RWJ-53308 inhibits ex vivo collagen- and ADP-induced platelet aggregation in conscious dogs for up to 4 h following 0.3 mg/kg iv, and through 4 and 6 h following 1 and 3 mg/kg po. Oral bioavailability is 16+/-7%. RWJ-53308 reduces thrombus weight in a canine arteriovenous (AV) shunt model following intravenous (0.01-0.1 mg/kg) and oral (3 mg/kg) administration. In a guinea pig carotid artery pinch-injury model, RWJ-53308 completely suppresses thrombus-induced cyclic flow reductions (CFR) at 0.7 mg/kg iv. RWJ-53308 also blocks thrombus formation in photoactivation- and ferric chloride-induced models of thrombosis in guinea pigs at 0.3 and 1 mg/kg iv, respectively. In summary, RWJ-53308 is a potent orally active GPIIb/IIIa antagonist that may be useful for both acute and chronic treatment of arterial thrombotic disorders.

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.

Experimental myocardial necrosis in rats: role of arjunolic acid on platelet aggregation, coagulation and antioxidant status

Arjunolic acid, a new triterpene and a potent principle from the bark of Terminalia arjuna, has been shown to provide significant cardiac protection in isoproterenol induced myocardial necrosis in rats. To further explore the mechanism of action of arjunolic acid, antiplatelet activity, anticoagulant assays, electrocardiographic changes, serum marker enzymes, antioxidant status, lipid peroxide and myeloperoxidase (MPO) have been measured and the results are compared with a potent cardioprotective drug, acetyl salicylic acid (ASA). Administration of isoproterenol produces electrocardiographic changes such as decreased R amplitude and increased ST segment elevation and has resulted in an increase in serum marker enzyme levels as well as a decrease in enzymatic and nonenzymatic antioxidant levels. Arjunolic acid at an effective dosage of 15 mg/kg body wt. (pre and post treatment), when administered intraperitoneally (i.p.), effects a decrease in serum enzyme levels and the electrocardiographic changes get restored towards normalcy. Arjunolic acid treatment is also shown to prevent the decrease in the levels of superoxide dismutase, catalase, glutathione peroxidase, ceruloplasmin, alpha-tocopherol, reduced glutathione (GSH), ascorbic acid, lipid peroxide, MPO and the cardioprotection is confirmed by the histopathological studies. This study shows that the cardioprotection of arjunolic acid pre and post treatment could possibly be due to the protective effect against the damage caused by myocardial necrosis.

Coagulation and cancer: implications for diagnosis and management

Coagulation disorders are a common problem in neoplastic patients and many factors contribute to increase the risk of thromboembolic events in these patients. An hypercoagulable state is induced by malignant cells interacting directly with hemostatic system and activating the coagulation cascade. More sensitive tests to assess an hypercoagulable state in cancer patients have been developed; even though these tests are always altered in cancer patients, none of them possess a clinical significance in terms of predictive value for the occurence of thromboembolism and disease prognosis in the individual patient. The most frequent thromboembolic complications in cancer patients are deep vein thrombosis of the lower extremities and pulmonary embolism; therefore, disseminated intravascular coagulation, thrombotic thrombocytopenic purpura or haemolytic uremic syndrome are special manifestations of neoplastic disease. Diagnosis of idiopathic deep vein thrombosis, in the absence of other risk factors, could indicate the presence of occult malignant disease; however, the need for an extensive work-up to detect malignancy is still controversial. Neoplastic patients showing a thromboembolic event should be treated with unfractioned heparin or, alternatively, with low molecular weight heparins. In order to prevent recurrence, the administration of heparin should be associated and followed by an oral anticoagulant drug. In recent years new approaches in anti-aggregation therapy have been studied, such as COX-inhibitors, cicaprost and ReoPro; further studies are needed to determine the usefulness of these molecules in treatment of malignancies.

Glycoprotein IIb/IIIa antagonists and low-molecular weight heparin in acute coronary syndromes

The glycoprotein (GP) IIb/IIIa antagonists and the low-molecular weight heparins are the newest additions to the armamentarium of antiplatelet drugs for the treatment of acute coronary syndromes. They are extremely potent inhibitors of platelet aggregation and thrombin generation, respectively. There are currently three GP IIb/IIIa inhibitors (abciximab, eptifibatide, and tirofiban) and two low-molecular weight heparins (dalteparin and enoxaparin) approved for use with acute coronary syndromes. Data continue to accumulate outlining the specific roles for these drugs in the treatment of patients with acute coronary syndromes. Clinical trials in patients with acute coronary syndromes have demonstrated that the GP IIb/IIIa antagonists and low-molecular weight heparins offer significant benefit with acceptable safety profiles. Future issues that need to be addressed include refinement of indications for administration and patient selection, comparison between existing agents, evaluation of newer agents, and optimization of dosing to maximize benefit and safety in the use of these powerful new classes of drugs.

New developments in percutaneous coronary intervention

The field of percutaneous coronary intervention continues to progress at a tremendous rate. Advances in techniques, in device technology, and in adjunctive therapy have increased significantly the number of patients who may benefit from angioplasty and have increased the early and long-term success rates of these procedures. Future progress in radiation therapy, IIb/IIIa inhibitors, stent design, and other novel approaches undoubtedly will offer further improvements in the capability of coronary interventions to help patients live longer and feel better.

The use of antiplatelet agents in acute cardiac care

Antiplatelet therapy with aspirin has long been established as standard therapy in the management of conditions such as ST-elevation myocardial infarction and the acute coronary syndromes (unstable angina and non-ST-elevation myocardial infarction). Recently, several more potent platelet inhibitors have been developed and tested in randomized clinical trials. This article reviews the current state of the art of antiplatelet therapy.

Platelet glycoprotein IIb/IIIa receptor antagonists and coronary artery disease

The importance of platelets in coronary artery disease has been better elucidated in the past 20 years with the continued understanding of their role in the development of the atherosclerotic lesion and acute coronary syndromes. The most recent therapeutic efforts have focused on blockade of the platelet glycoprotein IIb/IIIa receptor, which represents the final common pathway to platelet aggregation and arterial thrombus formation. This manuscript summarizes platelet function and pathophysiology, currently available glycoprotein IIb/IIIa inhibitors, and the important clinical trials with this new class of drugs.

Platelet GPIIb/IIIa receptor blockade reduces infarct size in a canine model of ischemia-reperfusion

OBJECTIVES

We studied the effects of N-acetyl-cys-asn-(5,5-dimethyl-4-thiazolidine-carbonyl)-4-amino-methyl-phe-gly-asp-cys, monoacetate (MK-0852) (platelet GPIIb/IIIa receptor blocker) on peak reactive hyperemia, distribution of blood flow, regional contractile function and infarct size in a canine model of acute ischemia-reperfusion injury.

BACKGROUND

Platelet activation and formation of platelet microaggregates in coronary vessels could contribute to ischemia-induced myocyte injury. Inhibition of platelet aggregation could reduce ischemia-reperfusion injury.

METHODS

Three groups of dogs (n = 10/group) were studied; group 1--heparin (HEP) (100 U/kg/h intravenously), group 2--MK-0852 (300 microg/kg intravenous bolus followed by 3 microg/kg/min for 3 h) and group 3--MK-0852 plus HEP. Infarct size after 60 min regional ischemia and 3 h reperfusion was evaluated by tetrazolium staining and normalized to risk area (Monastral blue dye).

RESULTS

Infarct size in HEP-treated controls was 32.4+/-2.8%; in MK-0852 without or with HEP groups, infarct size was 17.4+/-1.9% (p = 0.001) and 23.4+/-3.0% (p = 0.04), respectively. Cardiac hemodynamics and rate-pressure product were comparable between groups. Multivariate analysis using collateral blood flow as the independent variable confirmed the cytoprotective actions of MK-0852. Postischemic peak reactive hyperemia in the infarct-related artery was depressed in all groups; during reperfusion, transmural distribution of myocardial blood flow returned to near control levels, but severe regional hypokinesia persisted.

CONCLUSIONS

Diminished infarct size with MK-0852 treatment suggests an additional mechanism of benefit for GPIIb/IIIa blockers beyond stabilization of a "culprit" acute coronary lesion. This cytoprotective effect was unrelated to preservation of coronary vasoreactivity (assessed by reactive hyperemia), restoration of blood flow across the myocardium or acute improvement in contractility.

Increased expression of P-selectin in patients with chronic atrial fibrillation

Previous studies have shown that platelets are activated during atrial fibrillation (AF). However, prophylactic therapy with aspirin is not associated with a reduction of thromboembolic complications in patients with AF. Stimulation of platelet thrombin and ADP receptors causes a release of P-selectin, which is not affected by aspirin. The purpose of this study was to assess the influence of AF on platelet P-selectin expression. Blood samples from 30 patients were studied ex vivo. Nineteen patients had chronic AF (> 3 months), 11 patients were in sinus rhythm (SR). P-selectin expression was determined by flow cytometry (antibody binding capacity [BC]) at baseline and after platelet stimulation with adenosine diphosphate (ADP) and thrombin receptor activating peptide (TRAP). To determine the effect of heart rate and atrial pressure (RAP), measurements were repeated after 10 minutes of ventricular pacing (120 beats/min) in patients with SR. P-selectin expression was increased in patients with AF at baseline (AF: 1329 +/- 81 BC vs SR: 968 +/- 108 BC; P < 0.05) and after stimulation with ADP (AF: 1445 +/- 101 BC vs SR: 1061 +/- 109 BC; P < 0.05) and TRAP (AF: 13,783 +/- 2442 BC vs SR: 5977 +/- 800 BC; P < 0.05). RAP (2.0 +/- 0.5 vs 6.0 +/- 0.8 mmHg; P < 0.01) and atrial rate (75 +/- 5 vs 114 +/- 5 beats/min; P < 0.001) increased during ventricular pacing. However, P-selectin levels remained stable. AF was accompanied by increased P-selectin expression. In contrast, increased ventricular rate and elevated atrial pressure alone had no effect on platelet activity. Further studies are needed to determine if platelet ADP receptor inhibitors offer a therapeutic benefit in patients with AF.

Pharmacology: antiplatelet and antithrombin therapy in acute coronary syndromes

Coronary artery disease is the leading cause of death in the United States. According to estimates, 1.25 million acute myocardial infarctions (AMI) occur in the United States each year, 500,000 of which result in death (half of those resulting from sudden death within the first hour). Worldwide, the annual death toll from AMI is approximately 4 million. Inhibitors of platelet function have been associated with decreased morbidity in patients with atherosclerotic cardiovascular disease. Reperfusion of occluded coronary arteries via thrombolytic therapy has markedly reduced mortality and morbidity resulting from events of acute myocardial infarction. This article addresses several antiplatelet and antithrombin agents currently in clinical use throughout the United States.

Antiplatelet effects of MK-852, a platelet fibrinogen receptor antagonist, in healthy volunteers

MK-852, a cyclic heptapeptide, is a potent platelet fibrinogen receptor antagonist. When administered to normal healthy male subjects by 1- and 4-hour constant rate intravenous infusions, it provides a generally well-tolerated and reversible means of inhibition of platelet function. At infusion rates of 1 microgram/kg/min for 1 hour and 0.44 microgram/kg/min for 4 hours, respectively, MK-852 extended baseline bleeding time by greater than 2.2-fold and 2.6-fold, inhibited ADP-induced platelet aggregation by 76% and 69%, and inhibited collagen-induced platelet aggregation by 65% and 67%, respectively. The pharmacokinetics of MK-852 include an elimination half-life of approximately 2 hours, total clearance of about 150 ml/min, and volume of distribution of about 18 liters. Examination of the relationship between MK-852 whole-blood concentration in vitro and inhibition of platelet aggregation showed an EC50 of about 55 ng/ml and a Hill coefficient of 1.55. The infusions were generally well tolerated, with no study drug-related changes in blood counts or biochemical profiles.

Antithrombotic activity of NSP-513, a novel selective phosphodiesterase 3 inhibitor, on femoral arterial thrombosis induced by physical stenosis and electrical current: comparison of antithrombotic and hemodynamic effects

NSP-513, a novel potent and selective phosphodiesterase 3 (PDE 3) inhibitor, and cilostazol, a previously developed PDE 3 inhibitor, were compared with respect to antiplatelet, antithrombotic, and hemodynamic effects. In the in vitro antiplatelet aggregation studies, NSP-513 and cilostazol inhibited collagen-induced canine platelet aggregation with median inhibitory concentration (IC50) values of 0.093 and 3.1 miccroM, respectively, and inhibited adenosine diphosphate (ADP)-induced canine platelet aggregation with IC50 values of 0.15 and 12 microM, respectively. For ADP-induced platelet aggregation, the presence of prostaglandin E1 (PGE1; 3 and 10 nM) further decreased the IC50 values for NSP-513 to 0.11 and 0.032 microM, respectively. In ex vivo antiplatelet aggregation studies, orally administered NSP-513 (0.03-1 mg/kg) and cilostazol (50 mg/kg) inhibited collagen-induced canine platelet aggregation. In an in vivo canine femoral arterial thrombosis model, intraduodenally administered NSP-513 (0.01-0.03 mg/ kg) dose-dependently prevented thrombus formation without any changes in blood pressure, heart rate, or bleeding time. In conscious dogs, NSP-513 at oral doses of > or =0.3 mg/kg produced hemodynamic changes such as decreased blood pressure and increased heart rate and LVdP/dt(max). Thus the minimal hemodynamically effective dose of NSP-513 was 0.3 mg/kg, and the hemodynamic effects of this dose were comparable to those of 50 mg/kg of cilostazol. In conclusion, these data suggest that NSP-513 has in vivo selectivity for antiplatelet and antithrombotic activities over hemodynamic activity, and that the selectivity of NSP-513 is higher than that of cilostazol in dogs.