NPC 15669, an Antiinflammatory Leucine Derivative, Reduces In Vitro Platelet Aggregability in Both Swine and Human Plasma

Survival in Acute Myocardial Infarction Induced by Coronary Ligation: Prognostic Relevance of Certain Hemostatic Factors During the Occlusion Phase

Alterations in various hemostatic factor have been identified as risk factors for survival after acute myocardial infarction (AMI). However, these clinical data are primarily limited to observations made during the postinfarct stage. We assessed the effects of 50 minutes of left anterior descending artery occlusion on several hemostatic factors and analyzed their changes with outcome in 18 Yorkshire swine. Blood samples were obtained from the systemic circulation at base-line and at 25 and 50 minutes of occlusion. Platelet aggregability and plasma antithrombin-III protein C, protein S, fibronectin, endothelin-1, as well as the metabolites of thromboxane and prostacyclin were measured. Of the 18 swine, 7 survived the infarct and 11 animals developed fatal ventricular fibrillation. Both groups demonstrated significant decreases in platelet aggregation, and a decline in plasma protein S when compared with baseline. Thromboxane, prostacyclin, and ondothelin-1 plasma concentrations were also markedly reduced at the end of occlusion. There were significant changes in antithrombin-III, protein C, and fibronectin levels between surviving animals and those that died of ventricular fibrillation. Acute coronary artery occlusion is associated with substantial changes in the hemostatic factors in swine. Plasma levels of fibronectin, antithrombin-111, and protein C differed between survivors and nonsurvivors and thus might serve as predictors of mortality due to fatal ventricular fibrillation during AMI. The mechanisms of these changes during the acute phase of AMI are unclear. Immediately AMI prognosis may be related to hemostatic changes not only after thrombolysis or spontaneous reperfusion, but also during the occlusion phase as well.

Crossreactivity of Human versus Swine Platelet Surface Antigens Is Similar for Glycoproteins Ib and IIIa, but Not for the Glycoprotein IIb/IIIa Complex

Swine platalets are very similar to those of humans and are therefore relevant to cardiovascular research. The swine coronary circulation mimics the human circulation and is large enough to obtain multiple blood samples in survival experiments. In swine regional ischemia similar to the human condition is easily obtainable, which makes the porcine model an ideal choice to study coronary artery disease. However, little is known about the similarity between swine and human platelet surface antigens. We tested the hypothesis that certain swine platelet antigens could crossreact with antihuman antibodies. Using FITC-conjugated monoclonal murine antihuman platelet antibodies, surface antigen expression was determined for human and Yorkshire swine platelets. Expression of CD9 (p24), CD42B (Ib), CD41b, (Ilb), CD61 (IIIa), CD41a (Ilb/IlIa), CD49b (VLA-2), CD62p, (P selectin), CD31 (PECAM-1D, and CD51/CD61 (vitronectin) was measured by flow cytometry. Significant crossreactivity with human platelets was observed consistently for swine platelet GP 1b and GP IIIa. Crossreactivity of the swine GPIb, and GP IIIa with the human receptors is evidence of receptor similarity between human and swine platelets. The implications of significant crossreactivity of these antigens and the lack of recognition of IIb/IIIa needs to be understood in cardiovascular research. Determining commercially available antihuman GP Ib and GP IIIa, rather than GP IIb/IIIa, would contribute to better elucidation of the effect of von Willebrand factor and the booming family of platelet inhibitors in the swine model of ischemia-reperfusion.

Effects of a novel Mac-1 inhibitor, NPC 15669, on hemostatic parameters during preconditioned myocardial infarction

NPC 15669, a member of the leumedins family, inhibits leukocyte adhesion to the endothelium by blockage of upregulation of a member of beta2 integrin family Mac-1 (CD11b/CD18). Inhibition of neutrophil-endothelial interactions may alter the course of myocardial reperfusion injury. However, the effects of NPC 15669 supplementation on the hemostatic profile during ischemia-reperfusion are unknown. The aim of the present study was to define changes in the certain hemostatic factors in the natural course of preconditioned myocardial infarction. Twelve consecutive Yorkshire swine underwent myocardial stunning (8 min. left anterior descending artery occlusion followed by 90 min. of reperfusion) and then preconditioned myocardial infarction (50 min. occlusion followed by 3 hours of reperfusion) experiments. NPC 15669 (10 mg/kg loading dose followed by constant infusion at 6 mg x kg(-1) x h(-1)) was administered in 6 animals; another 6 swine received saline and served as controls. Blood samples were obtained at baseline, twice during occlusion; and three times during reperfusion. The levels of antithrombin-III, Protein C, total Protein S, fibronectin, endothelin-1, as well as the stable metabolites of thromboxane (TxB2) and prostacyclin (6-keto-PGF1a), were determined. NPC 15669 treatment was associated with diminished endothelin-1, TxB2 levels and increased fibronectin, 6-keto-PGF1a, Protein C and total Protein S concentrations in the setting of preconditioned myocardial infarction. There were no changes in the plasma concentrations of antithrombin-III in NPC 15669 group when compared with controls. The increase in Protein C, total Protein S, and 6-keto-PGF1a (favoring antithrombosis), and decrease in endothelin-1 and TxB2 levels (favoring vasodilatation), following NPC 15669 may explain the reduction in infarct size previously reported with this agent.

Mild myocardial stunning affects platelet aggregation and certain hemostatic factors in swine

Myocardial stunning is characterized by transient contractile dysfunction occurring subsequent to an episode of ischemia followed by reperfusion. Platelet activation and hemostatic abnormalities have been described in patients with unstable angina and acute myocardial infarction, however, their role in the pathogenesis of myocardial stunning is unknown. The purpose of this study was to determine if platelet aggregation and certain hemostatic factors change during myocardial stunning following brief coronary arterial occlusion. Nine Yorkshire swine underwent left anterior descending coronary artery occlusion for 8 minutes followed by 90 minutes of reperfusion. Blood samples were obtained at baseline, at 4 and 8 minutes of occlusion, and at 60 and 90 minutes of reperfusion. Platelet aggregability and concentrations of antithrombin III, protein C, protein S, fibronectin, endothelin 1, and the stable metabolites of thromboxane (TxB2) and prostacyclin (6-keto-PGF1a) were measured in systemic circulation. The occlusion phase was associated with a decline of endothelin 1 (-13.6%), and TxB2 (-19.6%), and elevation of antithrombin III (+40.2%) and protein C (+22.9%). Mild myocardial stunning was associated with a significant increase in platelet aggregation (+33.7%), endothelin-1 (+24.7%), 6-keto-PGF1a (+41.5%), TxB2 (+11.9%), and protein C (+42.3%) during the reperfusion phase. There were no changes in plasma fibronectin and total protein S. Thus, mild myocardial stunning following brief coronary artery occlusion is associated with substantial dynamic changes in platelet aggregability and certain hemostatic factors. These results may be relevant to understanding the mechanisms determining myocardial stunning and coronary arterial patency following reperfusion.

Clopidogrel: the future choice for preventing platelet activation during coronary stenting?

Ticlopidine has become an established therapy in patients with stroke, and during stenting in patients with coronary artery disease. Clopidogrel, another thienopyridine, is a safe and promising alternative, that irreversibly inhibits ADP-induced platelet aggregation, and reduces formation of both arterial and venous thrombi. In a recent, large, well-controlled trial (CAPRIE), clopidogrel has been shown to be superior to aspirin in terms of prevention of ischaemic stroke, myocardial infarction and death in patients with atherosclerotic vascular disease. Clopidogrel provides a safe opportunity to enhance reperfusion when administered during stent placement, by protecting platelets from excessive activation. However, the ability of clopidogrel to be superior to ticlopidine in terms of its antiplatelet properties in the clinical setting of coronary stenting, is unknown. The effects of clopidogrel versus ticlopidine on platelet and endothelial function are yet to be determined and may strongly affect the outcome, benefits, and complications following coronary stent placement. Further clinical trials, well-designed, and carefully conducted, should elucidate possible benefits of clopidogrel during coronary interventions, especially in conjunction with new and aggressive reperfusion techniques. The benefits of clopidogrel in an expanding array of clinical conditions, including myocardial infarction, may be directly related to platelet inhibition. Moreover, marginal clinical benefits, and recently reported severe bleeding events in some patients after oral platelet glycoprotein IIb/IIIa therapy, may advance clopidogrel as a safe, and efficient alternative during coronary interventions. This review summarises the latest, and often confusing data on the effects of thienopyridines on certain haemostatic characteristics in interventional cardiology. 1999 Academic Press.

Plasma fibronectin during myocardial ischemia-reperfusion: effects of magnesium, diltiazem, and a novel Mac-1 inhibitor

The important role of fibronectin (Fn) has been recognized in patients with ischemic heart disease. However, serial changes of Fn during both brief and prolonged ischemia-reperfusion are poorly known. Plasma Fn was measured during acute myocardial infarction (AMI) and myocardial stunning (MS), and in the absence of myocardial injury. The effects of magnesium (Mg), diltiazem, and a Mac-1 inhibitor on the level of Fn were elucidated. Forty-nine swine underwent prolonged (50 min) or brief (8 min) coronary artery occlusion followed by reperfusion, while six control animals were free of ischemia. During the AMI experiments, plasma Fn underwent a significant progressive increase. Mg or diltiazem similarly affects the plasma Fn, reducing its release during the entire reperfusion period, and did not influence the plasma Fn in the absence of myocardial injury. Contrarily, Mac-1 inhibition resulted in the Fn elevation in controls, and during the occlusion phase, with no significant effect during reperfusion. There were no changes in the plasma Fn during MS, while inhibition of Mac-1 was associated with the significant increase of Fn during ischemia-reperfusion. Ability of Mg, diltiazem, and leumedins to modulate plasma Fn level may have direct clinical implications for the use of these agents in patients with coronary artery disease.

Serial changes of the plasma prostanoids during myocardial ischemia-reperfusion in swine. Effects of magnesium, diltiazem, and a novel Mac-1 inhibitor

The key role of prostanoids has been recognized in patients with ischemic heart disease. However, serial changes of thromboxane and prostacyclin during both brief and prolonged ischemia-reperfusion are poorly known. These plasma prostanoids were measured during myocardial stunning (MS) and acute myocardial infarction (AMI). The effects of magnesium (Mg), diltiazem, and a Mac-1 inhibitor on the level of the stable metabolites of thromboxane (TXB2) and prostacyclin (6-keto-PGF1 alpha) were elucidated. Forty-nine swine underwent brief (8 min) or prolonged (50 min) coronary artery occlusion followed by reperfusion. The occlusion phase was associated with a decline of plasma prostanoids, followed by a significant increase during reperfusion. Mg and diltiazem similarly affected plasma prostanoids by reducing TXB2 release at 1 h of reperfusion. There was, however, no effect on plasma 6-keto-PGF1 alpha. The Mac-1 inhibition was associated with stabilization of both antagonistic prostanoids as well. Ability of Mg, diltiazem, and leumedins to favorably modulate plasma prostanoid levels have direct clinical implications for the use of these agents in patients with coronary artery disease.