Porcine platelets in vitro and in vivo studies: relevance to human thrombosis research

In Vitro Thrombogenicity Testing of Biomaterials

The short- and long-term thrombogenicity of implant materials is still unpredictable, which is a significant challenge for the treatment of cardiovascular diseases. A knowledge-based approach for implementing biofunctions in materials requires a detailed understanding of the medical device in the biological system. In particular, the interplay between material and blood components/cells as well as standardized and commonly acknowledged in vitro test methods allowing a reproducible categorization of the material thrombogenicity requires further attention. Here, the status of in vitro thrombogenicity testing methods for biomaterials is reviewed, particularly taking in view the preparation of test materials and references, the selection and characterization of donors and blood samples, the prerequisites for reproducible approaches and applied test systems. Recent joint approaches in finding common standards for a reproducible testing are summarized and perspectives for a more disease oriented in vitro thrombogenicity testing are discussed.

Low-level light therapy reduces platelet destruction during extracorporeal circulation

Extracorporeal circulation causes many deleterious effects on blood cells. Low-level light therapy (LLLT) in the red/near-infrared spectral range is known for its cytoprotective properties but its use during cardiopulmonary bypass (CPB) has not yet been studied. We aimed to assess whether LLLT protects platelets during CPB. 24 pigs were connected to 1-hour-CPB and observed for the next 23 hours. In 12 animals, blood circulating through the oxygenator was treated with LLLT. Platelet count and function were monitored throughout the experiment. The decrease in platelet count was greater in the control group, especially during CPB and after 24 hours. In LLLT group CD62P expression remained quite stable up to the 12^th hour of the experiment, whereas in the control group it continuously decreased till the end of observation. Platelets in the control group were more prone to aggregation in the postoperative period than at the beginning of the experiment, whereas platelets in the LLLT group aggregated similarly or less intense. Limitation of platelet loss, pattern of aggregation and CD62P expression suggest that LLLT may stabilize platelet function during CPB and diminish the negative effects associated with the interaction of cells with an artificial surface.

Effect of Clostridium perfringens β-Toxin on Platelets

Clostridium perfringensβ-toxin (CPB) is the major virulence factor of C.perfringens type C causing a hemorrhagic enteritis in animals and humans. In experimentally infected pigs, endothelial binding of CPB was shown to be associated with early vascular lesions and hemorrhage but without obvious thrombosis of affected vessels, suggesting altered hemostasis in the early phase of the disease. The objective of the present study was to investigate the effect of CPB on platelets, with respect to primary hemostasis. Our results demonstrate that CPB binds to porcine and human platelets and forms oligomers resulting in a time- and dose-dependent cell death. Platelets showed rapid ultrastructural changes, significantly decreased aggregation and could no longer be activated by thrombin. This indicates that CPB affects the physiological function of platelets and counteracts primary hemostasis. Our results add platelets to the list of target cells of CPB and extend the current hypothesis of its role in the pathogenesis of C. perfringens type C enteritis.

The in-vitro effect of tirofiban, glycoprotein IIb/IIIa antagonist, on various responses of porcine blood platelets

The present study systematically evaluates the in-vitro effect of tirofiban, glycoprotein IIb/IIIa (integrins alphaIIbbetaIII) antagonist, on porcine blood platelets. It was found that tirofiban at concentrations up to 5,000 ng/ml did not affect the calcium signal produced by thrombin. Tirofiban, in a concentration-dependent manner reduced platelet aggregation evoked by ADP (IC50 approximately 70 ng/ml), collagen (IC50 approximately 200 ng/ml), and thrombin (IC50 approximately 5,000 ng/ml). Substantial thrombin-evoked platelet aggregation still occurred at high (5,000 ng/ml) tirofiban concentrations. The concentrations of tirofiban completely blocking the optical aggregation evoked by ADP or collagen failed to eliminate microaggregate formation totally. Tirofiban strongly inhibited the dense-granule and lysosome secretion induced by ADP (IC50 approximately 70-170 ng/ml), moderately inhibited that induced by collagen (IC50 approximately 420-500 ng/ml) and very poorly inhibited that elicited by thrombin (IC50 approximately 1,500-5,000 ng/ml). The extent of the inhibition of aggregation and secretion rose as concentrations of the stimulus lowered. Tirofiban was a moderate inhibitor (IC50 approximately 200 ng/ml) of adhesion and a poor inhibitor of platelet procoagulant response induced by collagen. Thromboelastography measurements indicate that, in whole blood, tirofiban, up to concentrations of 2,000 ng/ml, did not affect the kinetics of tissue factor induced clot formation. The obtained results reveal that in porcine platelets, the maximal concentrations of tirofiban used in human medicine (250 ng/ml), effectively block platelet responses triggered by ADP, partly block those induced by collagen and very poorly block those evoked by thrombin. The reason for this phenomenon seems to be the inability of tirofiban to reduce platelet secretion completely.

Evaluation of a porcine model to study in vivo platelet activation

INTRODUCTION

In order to investigate if decompression sickness involves platelet activation an animal model was evaluated.

MATERIALS AND METHODS

Twenty-four thiopentone-midazolam-fentanyl-anaesthetized pigs in four groups received 5-min infusions of adenosine diphosphate (25 mg/kg) or platelet activating factor (0.4 microg/kg). Groups 1 and 2 (adenosine diphosphate, n=6 and platelet activating factor, n=6) were studied for 30 min and then sacrificed. Groups 3 and 4 (adenosine diphosphate, n=6 and platelet activating factor, n=6) were sacrificed immediately afterwards to study short-term changes. Haemodynamics, platelet counts and post mortem lung platelet aggregates were registered. Groups 1 and 2 also had indium platelet labelling, lung scintigraphy and platelet accumulation index calculations performed.

RESULTS

Adenosine diphosphate induced immediate and more profound transient shocks. Platelet and leukocyte count decreases and occurrences of post mortem lung platelet aggregates were significantly more profound in the 5-min adenosine diphosphate group (Group 3) than in the platelet activating factor group (Group 4). With platelet labelling there were positive platelet accumulation index trends in the 30-min adenosine diphosphate group (Group 1). Adenosine diphosphate also produced platelet aggregation in platelet-rich porcine plasma. Only adenosine diphosphate (an intermediate platelet agonist) showed signs of platelet activation when considering all platelet parameters. The model should be further evaluated with different bolus doses of adenosine diphosphate, but may be used to evaluate if gas bubbles introduced into the circulation (as with decompression sickness), or possibly if clinical drugs, might produce platelet activation in vivo.

The influence of hemodynamics and wall biomechanics on the thrombogenicity of vein segments perfused in vitro1

This study addresses the hypothesis that exposure to peripheral arterial (ART) or coronary (COR) hemodynamics and wall biomechanics affect platelet deposition on vein segments. Intact human saphenous vein (HSV) and porcine internal jugular vein (PIJV) segments were studied under venous (VEN), ART, and COR environments using in vitro perfusion systems. Wall shear stress (tau) and circumferential wall stress (sigma(theta)) were calculated for PIJV segments. Platelet deposition was measured using a radioactive assay. PIJV ART segments exhibited a 14% increase in inner diameter over time (P < 0.05). tau, acting on PIJV ART specimens, was less at 6 h compared with time 0 (P < 0.05). sigma(theta) was lower in the VEN specimens compared with ART and COR groups (P < 0.01). Platelet deposition decreased by 40% on PIJV ART segments (P < 0.05) but increased 3.2-fold on PIJV COR segments (P < 0.05) versus VEN control segments. Platelet deposition was increased 1.75-fold in COR HSV cases versus VEN segments. These data indicate that short-term exposure to COR conditions lead to enhanced platelet deposition, whereas ART conditions decrease platelet deposition.

Differences and similarities in tyrosine phosphorylation of proteins in platelets from human and pig species

BACKGROUND

Pigs have been widely used as animal models to study hemostasis. However, there are significant differences when comparing the hemostatic behavior of pig and human platelets.

OBJECTIVE

To investigate signaling through tyrosine-phosphorylation of proteins in pig platelets after activation in suspension or by adhesion under flow conditions, in comparison with human platelets.

METHODS

Activation of platelet suspensions was performed with thrombin (T; 0.1 and 1 U mL(-1)) and type I collagen (Col-I; 20 microg mL(-1)), at two different time points (30 and 90 s). Activation by adhesion was carried out on Col-I-coated coverslips, using citrated whole blood samples perfused through a parallel-plate chamber.

RESULTS AND CONCLUSIONS

Significant differences between pig and human platelets were detected before and after activation. Activation of pig platelets required higher concentrations of thrombin, as well as increased activation times, to achieve similar levels of tyrosine phosphorylation. Proteins p160, p140, p85 and pp62, present in human platelets, were not detected in profiles corresponding to activated pig platelets. A protein of 70 kDa appeared only in pig platelet profiles, p55 was highly phosphorylated, and the phosphorylation levels of some proteins were significantly different from those found in human platelet profiles. In profiles corresponding to adhered pig platelets, p85 and p62 were absent, and p115 appeared highly phosphorylated. As observed in suspension studies, p70 and p55 appeared specifically in adhered pig platelets. Our study shows that the phosphotyrosine proteins involved in the activation of pig platelets are significantly different from those observed in activated human platelets. These findings may help to explain the differing adhesive and cohesive properties of platelets from both species, which should be considered when extrapolating results.

Coagulation assessment in healthy pigs undergoing single xenon anaesthesia and combinations with isoflurane and sevoflurane

BACKGROUND

With the introduction of new anaesthetics into clinical practice possible side effects of these novel anaesthetics have to be evaluated. This study was performed to clarify whether xenon or combinations of xenon with isoflurane or sevoflurane modify blood coagulation.

METHODS

The study was performed in 20 healthy pigs which first underwent xenon anaesthesia (65 Vol%) and were then randomly assigned to combinations of xenon and isoflurane or sevoflurane at varying concentrations. During anaesthesia the following parameters were controlled: aPTT, PT, fibrinogen concentrations and thrombelastographic measurements.

RESULTS

Xenon monoanaesthesia did not alter significantly any coagulation parameter. When isoflurane was introduced the aPTT showed a significant increase while fibrinogen concentration decreased. The introduction of sevoflurane led also to a decrease in fibrinogen concentration, while the aPTT was unchanged. These decreases in fibrinogen concentration were not accompanied by reduced maximal clot strength or elevated fibrinolysis evaluated by thrombelastography. Although the above-described changes were statistically significant, none of the parameters throughout the experiment exceeded the limits of normal values.

CONCLUSION

In our study, xenon monoanaesthesia and combinations of xenon with isoflurane and sevoflurane did not lead to pathologic alterations in the measured coagulation parameters.

Cisplatin triggers platelet activation

Clinical observations suggest that anticancer drugs could contribute to the thrombotic complications of malignancy in treated patients. Thrombotic microangiopathy, myocardial infarction, and cerebrovascular thrombotic events have been reported for cisplatin, a drug widely used in the treatment of many solid tumours. The aim of this study is to explore in vitro cisplatin effect on human platelet reactivity in order to define the potentially active role of platelets in the pathogenesis of cisplatin-induced thrombotic complications. Our results demonstrate that cisplatin increases human platelet reactivity (onset of platelet aggregation wave and thromboxane production) to non-aggregating concentrations of the agonists involving arachidonic acid metabolism. Direct or indirect activation of platelet phospholipase A(2) appears to be implicated. This finding contributes to a better understanding of the pathogenesis of thrombotic complications occurring during cisplatin-based chemotherapy.

Hemodynamic changes and systemic activation of coagulation and fibrinolysis during controlled endotoxemia in pigs

In this study, we have established a pig model that can combine extensive hemodynamic monitoring with simultaneous repetitive (serial) blood sampling for the study of multiple variables related to the hemostatic system. Sixteen healthy young pigs were studied to evaluate the influence of continuous endotoxin infusion on hemodynamic patterns and activation of coagulation and fibrinolysis. The chief aim of the study was to investigate the applicability of analytical methods primarily developed for use with human plasma samples in quantification of factors and reaction products of the porcine coagulation and fibrinolytic systems, and further, to use these methods to study the longitudinal changes in the plasma levels of these hemostatic variables as a consequence of endotoxin infusion. We found that acute, controlled endotoxemia induced a hemodynamic state of shock and reduced pulmonary gas exchange. Simultaneously, a gradual increase in peripheral blood mononuclear cell tissue factor activity was demonstrated, and increased maximally 5.5-fold 4 hours after onset of endotoxin infusion. Thrombin-antithrombin complexes increased in plasma to maximum levels after 3 hours, accompanied by an ethanol gelation test that was regularly positive after 1 to 2 hours, and fibrin monomer levels that gradually increased maximally 3.8-fold after 6 hours. These changes were followed by gradual decreases of both fibrinogen and factor VII levels, mainly due to consumption. Plasma levels of tissue type plasminogen activator activity peaked at 1.5 hours (11.3-fold increase), whereas the peak of plasminogen activator inhibitor-1 activity (14-fold increase at 4.5 hours) was delayed compared to tissue plasminogen activator and completely extinguished plasma tissue plasminogen activator activity. The sequential activation of coagulation and fibrinolysis established a procoagulant state favoring disseminated intravascular coagulation and microthrombus formation, potentially leading to multiple organ dysfunction.

The mechanisms of coronary restenosis: insights from experimental models

Since its introduction into clinical practice, more than 20 years ago, percutaneous transluminal coronary angioplasty (PTCA) has proven to be an effective, minimally invasive alternative to coronary artery bypass grafting (CABG). During this time there have been great improvements in the design of balloon catheters, operative procedures and adjuvant drug therapy, and this has resulted in low rates of primary failure and short-term complications. However, the potential benefits of angioplasty are diminished by the high rate of recurrent disease. Up to 40% of patients undergoing angioplasty develop clinically significant restenosis within a year of the procedure. Although the deployment of endovascular stents at the time of angioplasty improves the short-term outcome, 'in-stent' stenosis remains an enduring problem. In order to gain an insight into the mechanisms of restenosis, several experimental models of angioplasty have been developed. These have been used together with the tools provided by recent advances in molecular biology and catheter design to investigate restenosis in detail. It is now possible to deliver highly specific molecular antagonists, such as antisense gene sequences, to the site of injury. The knowledge provided by these studies may ultimately lead to novel forms of intervention. The present review is a synopsis of our current understanding of the pathological mechanisms of restenosis.

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.

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

Background: Leumedins inhibit cell adhesion to endothelium via blockage of integrin binding. We tested a hypothesis that the novel leucine derivate NPC 15669 will affect in vitro platelet aggregability (PA) in both human and swine plasma. Methods and Results: Platelet-rich plasma (PRP) was incubated with 200 µ g and 400 µ g of NPC 15669. Then PA was induced by ADP, collagen, thrombin, and ristocetin in the PRP without NPC 15669 and in NPC 15669-treated samples. We have found that PRP incubation with 200 µ g of NPC 15669 significantly decreases PA compared to baseline in all three experimental groups in response to all agonists tested. When PRP was treated with 400 µ g of NPC 15669, dose-dependent reduction of PA was observed only in the human control and swine groups, but not in patients with coronary atherosclerosis. Conclusions: Leumedins, known for their antiinflammatory properties, may have clinical applications related to their effect on platelet function. The mechanism of these effects is unknown, but may be related to the inhibition of platelet-endothelial binding.

Regional and Systemic Platelet Function Is Altered by Myocardial Ischemia-Reperfusion

Background: Myocardial reperfusion after short durations of ischemia causes prolonged contractile dysfunction (myocardial stunning). Recently it has also been suggested that ischemia-reperfusion results in impaired coronary endothelial function. Since platelet function is, in part, regulated by an intact functioning endothelium, platelet function could be expected to change during ischemia-reperfusion. However, the effect of ischemia and reperfusion on regional and systemic platelet function is unknown. The purpose of this study was to determine the effect of a brief period of myocardial ischemia followed by reperfusion on regional and systemic platelet function. Methods: Fourteen swine in an open-chest model underwent left anterior descending coronary artery (LAD) occlusion for 15 minutes followed by 120 minutes of reperfusion. Platelet aggregability in response to 5 µM ADP was determined simultaneously in the femoral (systemic; N = 14) and great cardiac (regional; N = 9) venous blood at baseline, during occlusion, and at 40 and 90 minutes after reperfusion. LAD blood flow and regional myocardial function were determined by standard methods. Results: Hemodynamics remained stable in all animals. During LAD occlusion platelet aggregability, increased only in the regional coronary circulation (126% of baseline, p =.0001). At 40 minutes of reperfusion systemic platelet aggregahility decreased (86% of baseline, p =.0001) and subsequently increased at 90 minutes at reperfusion in both the systemic (127% of baseline, p =.0001) and regional circula. tions (156% of baseline, p =.0001). Ischemia was evident by the absence ofdistal LAD flow during occlusion that returned during reperfusion and a typical response ofmyocardial stunning in each animal (stunning time = 47.7 +/- 5.2 minutes). Conclusions: This study demonstrates that platelet function is not static during ischemia-reperfusion. Instead, during ischemia regional platelet aggregability is increased. Systemic and regional platelet aggregability also increase during myocardial reperfusion. The mechanism of these responses is unknown but may be related to regional endathelial dysfunction created by ischernia. The response observed could also be explained by the release of proaggregatory mediators in the connary and/or systemic circulation during ischemia-reperfusion. The relative hyeraggregability observed following reperfusion may be relevant for further investigations of coronary artery reocclusion occurring after the relief of myocardial ischemia.

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.

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.

Effects of intracoronary diltiazem on certain hemostatic parameters during acute myocardial infarction in swine

Controversy currently exists regarding the use of diltiazem in the treatment of acute myocardial infarction (AMI). due to conflicting results from clinical trials and animal studies. The purpose of this project was to evaluate the changes in the hemostatic profile during AMI following low dose intracoronary diltiazem infusion. Fourteen Yorkshire swine underwent thoracotomy and 50 min LAD occlusion, followed by 3 h of reperfusion. The first group (n = 8) received 2.5 mg of diltiazem intracoronary at a rate of 5.6 micrograms kg min-1 at the onset of reperfusion. The second group (n = 6) received 0.9% saline intracoronary at the onset of reperfusion and served as the control. The dynamics of plasma antithrombin-III (AT-III), Protein C, total Protein S, fibronectin, endothelin-1 (ET-1), and the stable metabolites of thromboxane (TxB2) and prostacyclin (6-keto-PGF1a) were determined at baseline, then twice during occlusion and finally three times during reperfusion. Diltiazem infusion resulted in diminished ET-1 (34.5%), fibronectin (23.2%), and TxB2 (35.6%); and elevated Protein C (29.3%) when compared with controls. We conclude that intracoronary diltiazem favorable influences hemostasis during AMI in swine. The cardioprotective effects of diltiazem during AMI may be related to the improved hemostatic profile and the reduced incidence of thrombotic complications in such patients.

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.

Hemostatic changes after early versus late intracoronary magnesium during acute myocardial infarction in swine

There has been some debate regarding the benefit of magnesium (Mg) in the treatment of acute myocardial infarction (AMI) because of conflicting results from recent clinical trials. Several different hypotheses have been advanced to explain the cardioprotective properties of Mg, including the influence of the timing of Mg administration during AMI. This experiment was designed to assess the effect of intracoronary Mg on certain hemostatic parameters that are known to change during an AMI. Yorkshire swine underwent thoracotomy and 50 min left anterior descending artery (LAD) occlusion, followed by 3 h of reperfusion. In the early group, 250 mg of MgSO4 was delivered at the onset of reperfusion (n = 6, Mg-early group). In the second group, MgSO4 was given after 1 h of reperfusion (n = 6, Mg-late group). Six animals received saline instead of Mg and served as controls. The dynamics of plasma antithrombin-III (AT-III), protein C, total protein S, fibronectin, endothelin-1 (ET-1), as well as the stable metabolites of thromboxane (TXB2) and prostacyclin (6-keto-PGFla) were determined at baseline, twice during occlusion, and three times during reperfusion. Mg given at reperfusion onset was associated with a diminished ET-1 (32.9%), decreased fibronectin level (21.7-25.2%), and increased protein C concentrations (31.9-52.3%) when compared with both the control and late Mg group. In summary, intracoronary Mg administered at the onset of reperfusion favorably influenced hemostasis in swine. The beneficial effects of early Mg supplementation in an expanding array of clinical conditions, including AMI, may be directly related to the improved hemostatic profile in such patients.

Hemostatic changes after dietary coenzyme Q10 supplementation in swine

Improved cardiovascular morbidity and mortality have been observed in several clinical studies of dietary supplementation with coenzyme Q10 (CoQ10). We elucidated the effect of CoQ10 on certain hemostatic parameters that may influence the progression of heart disease. Twelve Yorkshire swine were randomized to receive diet supplementation with either CoQ10 or placebo for 20 days. Blood samples were obtained at baseline and at the end of the feeding period. At the end of the protocol, there were no significant differences in hemostatic parameters in the placebo group. A significant increase in total serum CoQ10 level (from 0.39 +/- 0.06 to 0.96 +/- 0.04 microgram/ml, p < 0.001) was noted after the feeding period in the CoQ10-supplemented group. We observed significant inhibition of ADP-induced platelet aggregation (-9.9%) and a decrease in plasma fibronectin (-20.2%), thromboxane B2 (TXB2, -20.6%), prostacyclin (-23.2%), and endothelin-1 (ET-1, -17.9%) level. There were no changes in the plasma concentrations of the natural antithrombotics [antithrombin-III (AT-III), protein S, and protein C] after CoQ10 supplementation. CoQ10 supplementation in a dose of 200 mg daily is associated with mild antiaggregatory changes in the hemostatic profile. Clinical beneficial effects of CoQ10 may be related in part to a diminished incidence of thrombotic complications.

Platelet functions and haemostasis parameters in pigs: absence of side effects of a procedure of general anaesthesia

Pigs are largely used as experimental animal models of thrombosis and for testing the anti thrombotic drug efficacy. Generally experiments are performed on pigs under general anaesthesia and observations can be affected by the anaesthetic drugs used. The effects of a general anaesthetic procedure were checked on pig haemostasis parameters; the pig was pre-anaesthetized with ketamine chloride, then intubated and ventilated with a mixture containing halothane, nitrous oxide and oxygen. Bleeding time, platelet aggregations, coagulation factors, coagulation inhibitors, fibrinolysis parameters and markers of activation of coagulation were determined on 30 Large White pigs before and under this anaesthesia procedure. Compared to human coagulation, pig is characterized by very high levels of factor V, VIII, IX, XI, XII activities, same levels of factor II, fibrinogen, antithrombin III (ATIII), low levels of protein C activities. Thrombin-antithrombin complex (TAT) and tissue plasminogen activator antigen (tPA) values were dispersed. With the reagents used, protein S, prothrombin fragment 1 + 2 (F1 + 2), D Dimers (D-D), plasminogen activator inhibitor (PAi) levels could not be determined. No difference was observed between results obtained before and under anaesthesia, particularly to increase of bleeding time, no modification of platelet aggregations and no activation of coagulation. This anaesthetic procedure does not induce any modification of pig haemostasis and can be used, without side effects, for experimental thrombosis studies in pigs.

Nitrogen microbubbles induce a disappearance of single platelets (aggregation) with porcine platelets: a comparative study of the effects of anticoagulants and blood collection methods

The pathogenesis of decompression illness (DCI) is uncertain. DCI involves all parts of the organism where gas bubbles are produced. They have both primary and secondary effects and have been classified as an agonist aggregating human platelets. In vitro effects of N2 bubbles on porcine platelets were investigated. Comparative studies using two different anticoagulants and three different sampling methods were performed. A disappearance of single platelets interpreted as platelet aggregation was observed in the presence of N2 bubbles in all studied groups. Aggregatory responses were more profound with platelets in heparinized plasma than in citrated plasma. In citrated plasma the aggregatory responses were more profound when blood was obtained from nonanaesthetized (awake) animals than from slaugtherhouse animals. Adrenaline (1 microM) had an inhibitory effect on N2 bubble induced platelet aggregation in vitro. The pig could be useful to investigate possible gas bubble effects in vivo.