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Background: P2Y12 is the major platelet receptor that mediates ADP-induced aggregation. P2Y12 is also expressed by vascular cells. The factors that regulate P2Y12 expression have not been determined. Since nicotine (NIC) has effects on platelet activation and vascular function, and because nicotinic and purinerigic receptors may interact, we determined whether nicotine altered P2Y12 expression., Methods: Four cell lines (human coronary artery endothelial cells, HCAEC; human umbilical vein endothelial cells, HUVEC; human aortic smooth muscle cells, HASMC; and human megakaryoblastic cells, MEG-01) were cultured in the absence or presence of nicotine. Immunoblotting for P2Y12, P2Y2, and actin was performed., Results: Nicotine, at concentrations of 0.1-1.0 microM, induced P2Y12 (but not P2Y2) expression in all the four cell lines. HASMC exhibited the greatest induction with a sixfold mean increase in P2Y12 expression in response to 0.25 microM nicotine. The induction was inhibited by nicotinic acetylcholine receptor antagonists. Healthy smokers were observed to have higher P2Y12 expression in platelet lysates compared to non-smokers., Conclusion: Nicotine induces the expression of P2Y12 in vascular cells and megakaryoblasts, and is mediated by nicotinic acetylcholine receptors. Smokers exhibit higher platelet P2Y12, possibly mediated via nicotine. These results may contribute to a better understanding of the effects of cigarette smoking on platelet activation and the vessel wall., Condensed Abstract: The factors that regulate the expression of P2Y12, the platelet ADP receptor, have not been determined. Four cell lines (human coronary artery endothelial cells, HCAEC; human umbilical vein endothelial cells, HUVEC; human aortic smooth muscle cells, HASMC; and human megakaryoblastic cells, MEG-01) were cultured in the absence or presence of nicotine. Nicotine, at concentrations of 0.1-1.0 microM, induced P2Y12 expression in all the four cell lines. HASMC exhibited the greatest induction with a sixfold mean increase in P2Y12 expression in response to 0.25 microM nicotine. The induction was inhibited by nicotinic acetylcholine receptor antagonists. Healthy smokers were observed to have higher P2Y12 expression in platelet lysates compared to non-smokers. These results may contribute to a better understanding of the effects of cigarette smoking on platelet activation and the vessel wall.

Objectives: To examine the frequency of cerebrovascular complications among patients receiving abciximab (AB) undergoing PCI with prior intracranial hemorrhage (ICH) or recent (< 2 years) ischemic strokes., Background: AB improves clinical outcomes in high-risk patients undergoing percutaneous coronary intervention (PCI); however, the safety of AB in patients with prior stroke has not been adequately studied., Methods: A database review of 7,244 consecutive PCIs, from 7/97 to 10/01, identified 6,190 PCIs performed with AB among which 515 interventions were performed in patients with prior stroke history [ICH or recent ischemic stroke, (n = 101) and remote (> 2 years) ischemic stroke, (n = 414)]., Results: The post-PCI stroke rate was significantly higher in patients with prior stroke (2.06% vs. 0.35%, p < 0.001 for all stroke; 0.38% vs. 0.03%, p = 0.023 for ICH). The incidence of ICH among the AB-treated group was 0.065%; a history of prior stroke did not increase the incidence of ICH in the AB-treated group (0.39% vs. 0.0%, p = ns). Moreover, the post-PCI stroke rate was similar between the prior ICH or recent ischemic stroke-group and remote ischemic stroke-group (2 vs. 1.9%; OR: 1.03; 95% CI: 0.21-4.90; p = ns for all strokes; 2% vs. 1.5%; OR: 1.4; 95% CI: 0.27-6.91; p = ns for ischemic stroke). Importantly, no ICH occurred in patients with recent ischemic or any prior ICH stroke., Conclusions: Abciximab, in addition to aspirin, heparin and ADP-inhibitors does not increase the risk of stroke in patients with prior stroke undergoing PCI.

Background: We postulated that antibodies to platelet factor 4/heparin complex lead to a heightened inflammatory state, contributing to an increased risk of recurrent thrombotic events., Methods: We analyzed serum from a subset of patients in the placebo/unfractionated heparin arm of the GUSTO IV-ACS trial who had prior heparin exposure. We selected 109 patients with the 30 day primary endpoint (death, MI or revascularization) and an equal number of controls, excluding patients with thrombocytopenia. Anti-platelet factor 4/heparin antibodies and inflammatory markers (sVCAM-1, sICAM-1, sE-selectin, sP-selectin, us-CRP, IL-6) were measured on serum samples., Results: Patients with anti-PF4/heparin antibodies were more likely to have death or MI (30.4% vs. 11.3%, p = 0.01), or MI (21.7% vs. 6.2%, p = 0.01) than patients who were antibody negative. In a multiple logistic regression model that included inflammatory markers and clinical risk factors, antibody to PF4/heparin was a strong predictor of 30 day MI (odds ratio: 9.0; 95% confidence intervals 2.1-38.6; p < 0.01), with IL-6 being the only other predictor (odds ratio: 1.1; 95% confidence intervals 1.0-1.2; p = 0.03). Antibody positive patients had higher levels of sVCAM-1 (892 +/- 263 microg/l versus 780 +/- 228 microg/l; p = 0.04) and sICAM-1(246 +/- 50 microg/l versus 222 +/- 71microg/l; p = 0.02) than antibody-negative patients., Conclusions: Antibodies to the platelet factor 4/heparin complex were associated with elevated levels of endothelial but not platelet activation markers, or markers of a systemic inflammatory state. Anti-PF4/heparin antibodies were associated with a 9-fold increased risk of recurrent MI at 30 days. We measured soluble cell adhesion molecules, CRP and IL-6 from 218 non-thrombocytopenic patients, 23 of whom had antibodies to PF4/heparin. Antibody positive patients had higher levels of sVCAM-1 (892 +/- 263 microg/l versus 780 +/- 228 microg/l; p = 0.04) and sICAM-1(246 +/- 50 microg/l versus 222 +/- 71 microg/l; p = 0.02). In a multiple logistic regression model, antibody to PF4/heparin was a predictor of 30 day MI (odds ratio: 9.0; 95% CI: 2.1-38.6; p < 0.01). The presence of antibodies to PF4/heparin, even in the absence of thrombocytopenia, is a stronger predictor of 30 day MI than clinical variables or inflammatory markers.

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.