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

Protein kinases are involved in the cardioprotective effects activated by platelet glycoprotein IIb/IIIa inhibitor tirofiban at reperfusion in rats in vivo

The thrombolytic effect of platelet glycoprotein IIb/IIIa inhibitors (GP IIb/IIIa inhibitors) in myocardial infarction has been well established. Nevertheless, data on the mechanism of the cardioprotective effect of GP IIb/IIIa inhibitors in ischemic-reperfusion injury (IR) are lacking. Sprague-Dawley rats received 120 min of coronary ischemia and 180 min of reperfusion. A GP IIb/IIIa inhibitor was given via continuous intravenous infusion at a rate of 2 μg/kg/min 30 min prior to reperfusion with/without inhibitors of PKCε (chelerythrine), PI3 kinase and Akt (wortmannin), p38 MAPK (SB203582), p42/44 MAPK (PD98059) and ERK1/2 (u0126) 15 min prior to the GP IIb/IIIa inhibitor. Protein isolation and analysis were performed by Western blot analysis. The cardioprotective effects were measured as the ratio of myocardial necrotic area to the area at risk (AAR) and the apoptotic index (AI) calculated as the percentage of myocytes positive for terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling of all myocytes stained by 4', 6-diamidino-2-phenylindole. The GP IIb/IIIa inhibitor reduced the ratio of myocardial necrotic area to AAR and AI, and also exerted an immediate cardioprotective effect by activating multiple signaling pathways including phosphorylation and activation of PKCε, PI3 kinase, Akt, p38 MAPK, p42/44 MAPK and ERK1/2. However, there were no significant increases in the phosphorylation of Raf and MEK1/2. We concluded that the GP IIb/IIIa inhibitor reduced the extent of cardiac IR and significantly ameliorate the apoptosis of myocytes in the rats. In addition, the cardioprotective effect was mediated through the activation of multiple signal transduction pathways.

Platelet Glycoprotein IIb/IIIa Inhibitor Tirofiban Ameliorates Cardiac Reperfusion Injury

There are many published articles on the effects of the antithrombolytic function of platelet glycoprotein IIb/IIIa inhibitors (GP IIb/IIIa inhibitors) in myocardial infarction. However, few studies have explored the effects and optimal concentration of tirofibans in diminishing the extent of myocardial reperfusion injury (RI).Rats received 120 minutes of coronary ligation and 180 minutes of reperfusion. The rats were then divided into 7 groups based on the concentration of tirofiban administered intravenously 30 minutes prior to coronary reperfusion to the end of reperfusion. The ratio of myocardial necrotic area to area at risk (AAR), and myocardial malondialdehyde (MDA) and plasma myeloperoxidase (MPO) activities were measured. The apoptotic index (AI) was the percentage of myocytes positive for terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) out of all myocytes stained by 4', 6-diamidino-2-phenylindole (DAPI).The ratio of myocardial necrotic area to AAR significantly decreased in all tirofiban subgroups. The MDA activity for tirofiban concentrations of 2 and 5 ug/kg/minute showed a slight reduction. MPO activity was significantly decreased at a tirofiban concentration of 2 ug/kg/minute. The AI was significantly decreased at a tirofiban concentration of ≥ 0.4 ug/kg/minute.The results indicate that a tirofiban can significantly ameliorate the cardiac RI and myocyte apoptosis in rats.

Baseline platelet reactivity in acute myocardial infarction treated with primary angioplasty--influence on myocardial reperfusion, left ventricular performance, and clinical events

BACKGROUND

Platelet reactivity is believed to play a key role in the pathophysiology of ST-segment elevation myocardial infarction (STEMI). We sought to determine whether platelet reactivity predicts impaired myocardial reperfusion, left ventricular (LV) dysfunction, and clinical events in an unselected group of patients with STEMI.

METHODS

Platelet reactivity was measured before primary angioplasty in 125 consecutive patients with the use of Platelet Function Analyzer-100. Six-month follow-up was performed.

RESULTS

Patients were stratified into 4 quartiles according to the collagen adenosine diphosphate closure time (CADP-CT), with the fourth quartile (CADP-CT < or = 55 seconds; n = 32) defined as high reactivity. There was an increasing rate of diabetes across quartiles: 6% in the first and 38% in fourth (P < .0001). Myocardial Blush Grade 0 or 1 and the absence of ST-segment resolution (< or = 50%) were observed more often in the fourth quartile than in quartiles 1 through 3 (84% vs 22%, 27%, 35% and 81% vs 16%, 17%, 26%, respectively; P < .0001 for all). In logistic regression, high reactivity was an independent predictor of Myocardial Blush Grade 0 or 1 (odds ratio [OR], 22.7; 95% confidence interval [CI], 6.5-78.8; P < .0001), ST-segment resolution < or = 50% (OR, 28.6; 95% CI, 8.6-95.2; P < .0001), LV remodeling (OR, 10.4; 95% CI, 3.3-32.7; P < .0001), lack of early (OR, 7.9; 95% CI, 2.8-22.3; P < .0001) and late LV functional recovery (OR, 7.3; 95% CI, 2.9-18.8; P < .0001), and clinical events (OR, 7.8; 95% CI, 2.5-24.9; P = .0005).

CONCLUSIONS

Platelet reactivity is an independent predictor of myocardial reperfusion. Moreover, CADP-CT being a marker of myocardial reflow may also provide early prognostic information concerning LV performance and adverse clinical events after STEMI.

Activated platelets contribute importantly to myocardial reperfusion injury

Platelets become activated during myocardial infarction (MI), but the direct contribution of activated platelets to myocardial reperfusion injury in vivo has yet to be reported. We tested the hypothesis that activated platelets contribute importantly to reperfusion injury during MI in mice. After 30 min of ischemia and 60 min of reperfusion, P-selectin knockout mice had a significantly smaller infarct size than that of wild-type mice (P < 0.05). Platelets were detected by P-selectin antibody in the previously ischemic region of wild-type mice as early as 2 min postreperfusion after 45 min, but not 20 min, of ischemia. The appearance of neutrophils in the heart was delayed when compared with platelets. Flow cytometry showed that the number of activated platelets more than doubled after 45 min of ischemia when compared with 20 min of ischemia or sham treatment (P < 0.05). Platelet-rich or platelet-poor plasma was then transfused from either sham-operated or infarcted mice after 45 and 10 min of ischemia-reperfusion to mice undergoing 20 and 60 min of ischemia-reperfusion. Infarct size was increased by threefold and platelet accumulation was remarkably enhanced in mice treated with wild-type, MI-activated platelet-rich plasma but not in mice receiving either platelet-poor plasma from wild types or MI-activated platelet-rich plasma from P-selectin knockout mice. In conclusion, circulating platelets become activated early during reperfusion and their activation depends on the duration of the preceding coronary occlusion and is proportional to the extent of myocardial injury. Activated platelets play an important role in the process of myocardial ischemia-reperfusion injury, and platelet-derived P-selectin is a critical mediator.