Prevention of ischemia-induced myocardial platelet deposition by exogenous prostacyclin

What do we know about platelets in myocardial ischemia-reperfusion injury and why is it important?

Myocardial ischemia-reperfusion injury (MIRI), the joint result of ischemic injury and reperfusion injury, is associated with poor outcomes in patients with acute myocardial infarction undergoing primary percutaneous coronary intervention. Accumulating evidence demonstrates that activated platelets directly contribute to the pathogenesis of MIRI through participating in the formation of microthrombi, interaction with leukocytes, secretion of active substances, constriction of microvasculature, and activation of spinal afferent nerves. The molecular mechanisms underlying the above detrimental effects of activated platelets include the homotypic and heterotypic interactions through surface receptors, transduction of intracellular signals, and secretion of active substances. Revealing the roles of platelet activation in MIRI and the associated mechanisms would provide potential targets/strategies for the clinical evaluation and treatment of MIRI. Further studies are needed to characterize the temporal (ischemia phase vs. reperfusion phase) and spatial (systemic vs. local) distributions of platelet activation in MIRI by multi-omics strategies. To improve the likelihood of translating novel cardioprotective interventions into clinical practice, basic researches maximally replicating the complexity of clinical scenarios would be necessary.

Prostacyclin Analogue-Loaded Nanoparticles Attenuate Myocardial Ischemia/Reperfusion Injury in Rats

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Intravenously injected ONO-1301–containing nanoparticles selectively accumulated in the ischemic border area of the myocardium.

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Prominent up-regulation occurred of proangiogenic cytokines such as vascular endothelial growth factor and angiopoietin-1 in the ischemic myocardium, which may have contributed to the preservation of the native vascular and capillary networks, thus preserving regional myocardial blood flow.

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Down-regulation of the proinflammatory cytokines interleukin-1β, interleukin-6, and tumor necrosis factor-α in the ischemic myocardium might have led to the attenuation of myocyte swelling and the suppression of the endothelial bleb formation, also contributing to the preservation of myocardial blood flow or the reduced infarct size.

Intravenously injected ONO-1301–containing nanoparticles (ONO-1301NPs), unlike an ONO-1301 solution, selectively accumulated in the ischemia/reperfusion (I/R)-injured myocardium of rats and contributed to the prolonged retention of ONO-1301 in the targeted myocardial tissue. In the ischemic area, proangiogenic cytokines were up-regulated and inflammatory cytokines were down-regulated upon ONO-1301NP administration. Consequently, ONO-1301NP–injected rats exhibited a smaller infarct size, better-preserved capillary networks, and a better-preserved myocardial blood flow at 24 h after I/R injury, compared with those in vehicle-injected or ONO-1301 solution–injected rats. ONO-1301NPs attenuate the myocardial I/R injury via proangiogenic and anti-inflammatory effects of the drug.

Effects of Prostacyclin on Heparin Reversal with Protamine

This study was planned to show the beneficial effects of prostacyclin (PGI2) utilization on adverse effects of protamine. PGI2 was administered at a rate of 5 ng/kg/min. Twenty patients entered this study. Half of them received PGI2 whereas the others did not.

Right ventricular end-diastolic volume index and right ventricular stroke work index were 72 mL/m2 and 2.2 g.m/m2, respectively, after patients were weaned off the bypass and 79 and 1.5, respectively, at five minutes after pro tamine administration in the control group; these values were 88 and 3.2, re spectively, and 86 and 3, respectively, in the PGI2 group. Left ventricular stroke work index (g.m/m2) was 27.9 in the control group and 36.7 in the PGI2 group (p < 0.05) after protamine administration.

Thromboxane B2 levels (pmoL/mL) in coronary sinus (CS) blood were 251 in the control group and 90 in the PGI2 group at five minutes after protamine administration (p < 0.05). Myocardial blood flow was 174 mL in the control group and 245 mL in the PGI2 group at five minutes after protamine adminis tration (p < 0.05). Cyclic adenosine monophosphate (cAMP) and cyclic guano- sine monophosphate (cGMP) levels in CS blood were 17 pmoL/mL and 2.1 pmoL/mL, respectively, in the control group and 36 and 0.3, respectively, in the PGI2 group at five minutes after protamine administration. Leukotriene B4 level was 129 and 57 pmoL/mL in the control and PGI2 groups, respectively (at the same time as the cAMP measurement) (p < 0.05).

From the results of this study the authors conclude that adverse effects of heparin reversal with protamine can be reduced with the use of PGI2.

Effects of high dose ascorbic acid on haemostasis during and after cardiopulmonary bypass

Observations were made on the changes in platelets, bleeding time and clot retraction and the protective effects of high dose ascorbic acid in 31 patients undergoing cardiopulmonary bypass (CPB). Platelet counts in Group B (receiving ascorbic acid) were higher ( p<0.05) and platelet adhesion and aggregation were significantly lower than in Group A (no ascorbic acid) during perfusion. Platelet numbers and function rose much faster, bleeding time was significantly shorter and clot retraction better in Group B than in Group A postoperatively. These results suggest that ascorbic acid may reduce platelet destruction and depletion during CPB and promote the recovery of the haemostatic mechanism postoperatively.

Prostacyclin Reduces Incidence of Myocardial Damage After Coronary Endarterectomy

BACKGROUND

After coronary endarterectomy, patients have an increased incidence of perioperative myocardial infarction. This study was undertaken to evaluate the possible reduction of perioperative myocardial damage after coronary endarterectomy by intravenous utilization of prostacyclin.

METHODS

Elective coronary artery bypass grafting was performed in 1,190 patients with diffuse and distal coronary artery disease, in whom endarterectomy of one or more vessels was used as a treatment. All procedures were done with cardiopulmonary bypass. There were 584 patients in the prostacyclin-treated group, and 606 patients in the control group. Prostacyclin (10 ng x kg(-1) x min(-1)) was started 20 minutes before the cross-clamp removal, or at the time of rewarming, and was continued during the first 24 hours after surgery. The incidence of perioperative myocardial damage was detected by creatine kinase-MB enzyme measurement, and electrocardiographic and left ventricular function changes.

RESULTS

A significant decrease in perioperative myocardial damage was detected in the group treated with prostacyclin with respect to the control group.

CONCLUSIONS

Prostacyclin infusion initiated during revascularization and continued in the early postoperative course could be successfully employed for the prevention of thrombocyte aggregation and potentially decrease the overall incidence of significant myocardial damage after coronary endarterectomy.

Roles of prostaglandin I(2) and thromboxane A(2) in cardiac ischemia-reperfusion injury: a study using mice lacking their respective receptors

BACKGROUND

Prostaglandin (PG) I(2) and thromboxane (TX) A(2), the most common prostanoids in the cardiovascular system, are produced abundantly during cardiac ischemia/reperfusion (I/R); their roles in I/R injury, however, remain undetermined. We intended to clarify these roles of PGI(2) and TXA(2) using mice lacking the PGI(2) receptor, IP(-/-) mice, or the TXA(2) receptor, TP(-/-) mice.

METHODS AND RESULTS

The left anterior descending coronary artery was occluded for 1 hour and then reperfused for 24 hours. The size of myocardial infarct in IP(-/-) mice was significantly larger than that in wild-type mice, although the size of the area at risk was similar between the 2 groups of mice. In contrast, there was no such difference between TP(-/-) and wild-type mice. To further determine whether PGI(2) and TXA(2) act directly on the cardiac tissue or indirectly through their action on blood constituents, we perfused excised heart according to the Langendorff technique. The isolated heart was then subjected to global ischemia followed by reperfusion. In IP(-/-) mice, developed tension and coronary flow rate during reperfusion were significantly lower and release of creatine kinase was significantly higher than those in wild-type mice. There were no such differences, however, between TP(-/-) and wild-type mice.

CONCLUSIONS

PGI(2), which was produced endogenously during cardiac I/R, exerts a protective effect on cardiomyocytes independent of its effects on platelets and neutrophils. In contrast, TXA(2) has little role in the cardiac I/R injury.

Role of TGF-beta1 in platelet-mediated cardioprotection during ischemia-reperfusion in isolated rat hearts

Platelets protect myocardium against ischemia-reperfusion injury. This study examined the role of platelet-derived TGF-beta1 in cardioprotection during ischemia-reperfusion. Isolated Sprague Dawley rat hearts were perfused with K-H buffer and subjected to 25 min of global ischemia followed by 30 min of reperfusion. Ischemia-reperfusion resulted in myocardial dysfunction indicated by increase in CPP and LVEDP, and decrease in dLVP. Perfusion of hearts with washed platelets or supernatant of aggregated platelets attenuated (P < 0.01) of myocardial dysfunction following ischemia-reperfusion. Ischemia-reperfusion resulted in a decrease in myocardial TGF-beta1 determined by immunohistochemistry. ELISA showed an increase in latent TGF-beta1, but a decrease in active TGF-beta1. Perfusion of hearts with platelets or aggregated platelet supernatant preserved myocardial TGF-beta1 content upon ischemia-reperfusion. Perfusion of hearts with recombinant TGF-beta1 also resulted in cardioprotection following ischemia-reperfusion qualitatively similar to that observed with platelets or aggregated platelet supernatants. RT-PCR analysis showed an increase in myocardial TGF-beta1 mRNA following ischemia-reperfusion. These observations indicate that platelets protect the myocardium against ischemia-reperfusion-mediated dysfunction at least in part by releasing TGF-beta1. Increase in both TGF-beta1 mRNA and latent TGF-beta1 does not indicate a defect in the translation of mRNA. Reduction in myocardial TGF-beta1 following ischemia-reperfusion suggests a defect in the conversion of latent TGF-beta1 to active TGF-beta1.

Platelet-Mediated Cardioprotective Effect Against Ischemia-Reperfusion Injury in Isolated Rat Hearts: Role of Platelet Number and Contribution of Supernatant of Aggregated Platelets

BACKGROUND: Previous studies have documented cardioprotective effects of circulating platelets after reperfusion injury. The present study was designed to examine the role of platelet number and contribution of platelet-released mediators in the platelet supernatant in cardioprotection against ischemia-reperfusion-induced myocardial dysfunction. METHODS AND RESULTS: Isolated buffer-perfused (constant volume) Sprage-Dawley rat hearts were subjected to 25 minutes of global ischemia followed by 30 minutes of reperfusion. Ischemia-reperfusion resulted in myocardial dysfunction, indicated by an increase in coronary perfusion pressure and left ventricular end-diastolic pressure, and a decrease in developed left ventricular pressure. Perfusion of hearts with washed rat platelets (10(3)-2.2 x 10(7) cells/mL) significantly (P <.01) attenuated these indices of myocardial dysfunction upon ischemia-reperfusion in a concentration-dependent manner. A cardioprotective effect of platelets was observed at a concentration as low as 10(5) platelets/mL. Similar cardioprotection was seen in hearts perfused with the supernatant of aggregated platelets. CONCLUSIONS: These observations indicate that the platelet-mediated cardioprotective effect against ischemia-reperfusion in vitro is concentration dependent, and platelet-released mediators in the platelet supernatant are protective against ischemia-reperfusion injury.

Prostacyclin and thromboxane levels in pleural space fluid during cardiopulmonary bypass

Prostaglandins exhibit a variety of cardiovascular actions that may affect the hemodynamic recovery of the ischemic myocardium after cardiopulmonary bypass. We have observed a decrease in the mean arterial pressure on autotransfusion of the accumulated pleural cavity fluid during operation. One aim of this study was to determine the concentrations of prostacyclin and thromboxane A2 in the pleural cavity fluid by measuring their stable metabolites, 6-keto-PGF1 alpha and thromboxane B2, respectively, in 8 consecutive patients undergoing myocardial revascularization, and to compare them with the arterial levels. A second aim was to quantify the hemodynamic effect of the pleural cavity fluid during operation. The concentration of 6-keto-PGF1 alpha in the pleural cavity fluid was significantly higher than the arterial concentration (mean, 21.6 +/- 18.2 ng/mL; p < 0.01). The concentration of thromboxane B2 was also raised compared with the arterial concentration (mean, 3.62 +/- 5.96 ng/mL; p < 0.2). The percentage fall in the mean arterial pressure was 29.7% +/- 8.86% (p < 0.02), which was transient and lasted 1 to 3.5 minutes. The hemoglobin concentration, potassium level, and pH were also measured. This study shows that the pleural cavity fluid during cardiac operations contains significant amounts of endogenous prostacyclin. Considering the potential benefit of prostacyclin on the recovering myocardium, we believe that this fluid should be transfused as a volume replacement, keeping in mind the transient phase of hemodynamic instability.

Elevation of thromboxane in pressure wounds

Arachidonic acid metabolites have been implicated as mediators of progressive dermal ischemia. Decubitus ulcer formation results from chronic mechanical pressure on the skin which results in a diminished blood supply to the skin and underlying tissues. To evaluate the role of thromboxanes in pressure wounds, we measured TxB2, a stable metabolite of TxA2, in spontaneously occurring pressure wounds on Greyhound dogs. In pressure wounds in which the skin was showing early signs of pressure necrosis but was still intact, elevated TxB2 concentrations were found in healthy appearing tissues immediately adjacent to the pressure wounds, in the inner edge of the wounds, and in the center of the wounds. Significantly greater TxB2 concentrations (P less than 0.05) were found in the center of the intact wounds versus the TxB2 concentrations in the inner edge of the wounds or in healthy appearing tissues adjacent to the wounds. In pressure wounds in which the center of the wound had ulcerated or had an eschar, elevated TxB2 concentrations were found in tissues in the inner edge of the wounds and in healthy appearing tissues immediately adjacent to the pressure wounds. These results demonstrate the occurrence of elevated thromboxane concentrations in and around spontaneously occurring pressure wounds.

Preservation of the ischemic canine myocardium: A comparison of hypothermia, lidoflazine, and ketanserin

The purpose of this study was to determine whether ketanserin protects the globally ischemic canine heart and whether such protection, if present, is independent of that provided by hypothermia or calcium channel blockade with lidoflazine. Forty mongrel dogs, anesthetized with halothane, were divided into eight groups of five and subjected to one hour of global myocardial ischemia during hypothermic (30 degrees C; groups 1 to 4) or normothermic (37 degrees C; groups 5 to 8) cardiopulmonary bypass (CPB). Dogs in groups 1 and 5 served as controls with respect to prebypass myocardial protective therapy, and received only placebo (a normal saline bolus) prior to CPB. Before bypass, dogs in groups 2 and 6 received lidoflazine, 1.25 mg/kg intravenously (IV); those in groups 3 and 7 received ketanserin, 5 mg IV bolus, followed by a continuous infusion at 33 microg/min during bypass. Animals in groups 4 and 8 were given both lidoflazine and ketanserin according to the dosing schedules above. No type of pharmacologic or mechanical cardiovascular support was provided after termination of CPB. Postbypass hemodynamic performance and survival of the unsupported animal were assumed to reflect the degree of myocardial protection during CPB. One minute after bypass, mean arterial pressure and cardiac output were decreased in all groups. Cardiac output was lower in groups 5 to 8 (normothermic CPB) than in groups 1 to 4 (hypothermic CPB). After CPB, left ventricular filling pressures were elevated in all groups kept normothermic and in group 3 (hypothermic CPB plus ketanserin). By 15 minutes after CPB, there were no survivors in groups 5, 7, and 8. Sixty percent of animals in group 6 (normothermic CPB plus lidoflazine) survived to the end of the study. Relative odds of survival were increased 110-fold by hypothermia and sevenfold by lidoflazine. Conversely, treatment with ketanserin was associated with an increased likelihood of nonsurvival. It is concluded that, at the doses studied, ketanserin does not protect the canine myocardium against ischemic injury and may exert a detrimental effect when combined with calcium channel blockade in this setting.

Dipyridamole reduced myocardial platelet and leukocyte deposition following ischemia and cardioplegia

Urgent coronary revascularization for acute myocardial ischemia results in an increased mortality and morbidity. Deposition of activated platelets and leukocytes into the ischemic myocardium during reperfusion may augment perioperative ischemic injury. Dipyridamole reduces platelet activation and may reduce myocardial deposition and prevent ischemic injury during reperfusion. The effects of dipyridamole on myocardial platelet and leukocyte deposition were evaluated in a canine model of acute regional myocardial ischemia with reperfusion during cardioplegia on cardiopulmonary bypass. Eight dogs underwent left anterior descending (LAD) coronary artery ligation for 45 min followed by cardiopulmonary bypass and release of the ligature during 60 min of cold crystalloid cardioplegic arrest to simulate urgent revascularization. Four dogs were randomized to receive an infusion of dipyridamole perioperatively (50 mg/hr) and 4 dogs served as controls. Autologous platelets were labeled with 111In, leukocytes with 99mTc, and erythrocytes with 51Cr. The labeled cells were infused immediately after cross-clamp release and myocardial biopsies were obtained at 10, 20, 30, and 60 min of reperfusion. Platelets were deposited in the myocardium during reperfusion and four times more platelets were found in the LAD region than the circumflex region. Leukocyte deposition was similar in the LAD and circumflex regions. Dipyridamole reduced both platelet and leukocyte deposition and the reduction was greater in the LAD than in the circumflex region. Myocardial platelet and leukocyte deposition was found after regional ischemia, cardioplegia, and cardiopulmonary bypass. Dipyridamole reduced myocardial platelet and leukocyte deposition and may reduce perioperative ischemic injury.

Intracoronary platelet aggregation: pattern of deposition after ischemia, cardioplegia, and reperfusion

Platelet deposition in the coronary microvasculature has not been completely defined in the temporal relationship to acute myocardial ischemia, the application of crystalloid cardioplegia, and during reperfusion on heart bypass. Twenty-two canine hearts were serially biopsied for the analysis of radioactively tagged platelets. Eleven hearts underwent an isolated heart support preparation with seven followed by potassium cardioplegic arrest and reperfusion while the remaining 4 were maintained on continuous bypass. All 11 hearts undergoing bypass experienced transient (less than 90 sec) ischemia during bypass preparation and produced platelet aggregation in the myocardium (51.12 +/- 24.0 as compared to nonischemic control group 12.3 +/- 4.7; P = 0.005). Potassium cardioplegia did not completely wash out these platelets to the nonischemic control levels (27.8 +/- 14.9; P = 0.04). With the onset of reperfusion after 1 hr of cardioplegic arrest, platelet radioactivity profoundly increased (133.3 +/- 72.8; P = 0.0101) and remained high throughout the hour of reperfusion (324.7 +/- 269.3; P = 0.0369). In summary, intracoronary platelets are activated after transient ischemic episodes during initiation of heart bypass. These ischemia-activated platelet aggregations persist despite the application of cardioplegia during the arrest period. This deposition, in turn, allowed an ongoing pattern of platelet aggregation during the early and subsequent reperfusion. This pattern of ischemia-activated platelet aggregations probably accounts for the progressive reperfusion injury and support of an antiplatelet treatment for coronary microvasculature protection.