Summary. Background: Platelets release the immune-modulating lipid sphingosine-1-phosphate (S1P). However, the mechanisms of platelet S1P secretion are not fully understood.Objectives: The present study investigates the function of thromboxane (TX) for platelet S1P secretion during platelet activation and the consequences for monocyte chemotaxis. Methods: S1P was detected using thin-layer chromatography in [ 3 H]sphingosine-labeled platelets and by mass spectrometry. Monocyte migration was measured in modified Boyden chamber chemotaxis assays. Results: Release of S1P from platelets was stimulated with protease-activated receptor-1-activating peptide (PAR-1-AP, 100 lM). Acetylsalicylic acid (ASA) and two structurally unrelated reversible cyclooxygenase inhibitors diclofenac and ibuprofen suppressed S1P release. Oral ASA (500-mg single dose or 100 mg over 3 days) attenuated S1P release from platelets in healthy human volunteers ex vivo. This was paralleled by inhibition of TX formation. S1P release was increased by the TX receptor (TP) agonist U-46619, and inhibited by the TP antagonist ramatroban and by inhibitors of ABC-transport. Furthermore, thrombin-induced release of S1P was attenuated in platelets from TP-deficient mice. Supernatants from PAR-1-AP-stimulated human platelets increased the chemotactic capacity of human peripheral monocytes in a S1P-dependent manner via S1P receptors-1 and -3. These effects were inhibited by ASA-pretreatment of platelets. Conclusions: TX synthesis and TP activation mediate S1P release after thrombin receptor activation. Inhibition of this pathway may contribute to the anti-inflammatory actions of ASA, for example by affecting activity of monocytes at sites of vascular injury.

The diagnostic significance of procalcitonin concentrations in lower respiratory tract infections and tuberculosis is not known. A prospective analysis was, therefore, performed in patients with acute exacerbation of chronic bronchitis (AECB), community-acquired pneumonia (CAP), hospital-acquired pneumonia (HAP) and tuberculosis and their procalcitonin levels compared with those of patients with noninfectious lung diseases (controls). In addition, standard inflammatory parameter data were collected.A prospective clinical study was performed with four different groups of patients and a control group that consisted of patients with noninfectious lung diseases. A total of 129 patients were included: 25 with HAP, 26 CAP, 26 AECB, 27 tuberculosis, and 25 controls. C-reactive protein level, blood cell counts and procalcitonin concentration were evaluated on the first day after onset of clinical and inflammatory symptoms prior to treatment.The median procalcitonin concentrations in HAP, CAP, AECB and tuberculosis were not elevated in relation to the cut-off level of 0.5 ng?mL -1 . In the HAP group, in four of five patients who subsequently died, procalcitonin concentrations ofw0.5 ng?mL -1 were found. In acute lower respiratory infections, such as HAP, CAP and AECB, significantly elevated levels were found in comparison to the control group, but below the usual cut-off level. No differences were observed between tuberculosis and the control group.Relative to the current cut-off level of 0.5 ng?mL -1 , procalcitonin concentration is not a useful parameter for diagnosis of lower respiratory tract infections. However, compared to the control group, there were significantly elevated levels in patients with hospital-acquired pneumonia, community-acquired pneumonia and acute exacerbation of chronic bronchitis below the current cut-off level, which should be further investigated. Eur Respir J 2003; 21: 939-943.

Rationale: A reduced rate of myocardial infarction has been reported in patients with atrial fibrillation treated with FXa (factor Xa) inhibitors including rivaroxaban compared with vitamin K antagonists. At the same time, low-dose rivaroxaban has been shown to reduce mortality and atherothrombotic events in patients with coronary artery disease. Yet, the mechanisms underlying this reduction remain unknown. Objective: In this study, we hypothesized that rivaroxaban’s antithrombotic potential is linked to a hitherto unknown rivaroxaban effect that impacts on platelet reactivity and arterial thrombosis. Methods and Results: In this study, we identified FXa as potent, direct agonist of the PAR-1 (protease-activated receptor 1), leading to platelet activation and thrombus formation, which can be inhibited by rivaroxaban. We found that rivaroxaban reduced arterial thrombus stability in a mouse model of arterial thrombosis using intravital microscopy. For in vitro studies, atrial fibrillation patients on permanent rivaroxaban treatment for stroke prevention, respective controls, and patients with new-onset atrial fibrillation before and after first intake of rivaroxaban (time series analysis) were recruited. Platelet aggregation responses, as well as thrombus formation under arterial flow conditions on collagen and atherosclerotic plaque material, were attenuated by rivaroxaban. We show that rivaroxaban’s antiplatelet effect is plasma dependent but independent of thrombin and rivaroxaban’s anticoagulatory capacity. Conclusions: Here, we identified FXa as potent platelet agonist that acts through PAR-1. Therefore, rivaroxaban exerts an antiplatelet effect that together with its well-known potent anticoagulatory capacity might lead to reduced frequency of atherothrombotic events and improved outcome in patients.

EssentialsChronic kidney disease (CKD) patients have a high risk of cardiovascular events. A pharmacodynamic evaluation of the effects of aspirin in 116 patients was carried out. The antiplatelet effects of aspirin are associated with impaired renal function. The optimal antithrombotic regimen in CKD patients must be investigated on a larger scale. Summary. Background:The pharmacodynamic response to aspirin varies significantly between individuals. Insufficient antiplatelet effects of aspirin are associated with increased risk of ischemic events. Chronic kidney disease (CKD) is suggested to affect the pharmacodynamic response to antiplatelet medication. High on-treatment platelet reactivity (HTPR) to clopidogrel has been reported to partially account for the enhanced risk of death and cardiovascular events in CKD patients. Objective: To investigate the antiplatelet effects of aspirin in patients with CKD. Methods: We conducted a crosssectional study in 116 patients on permanent aspirin medication. The pharmacodynamic response to aspirin was determined by arachidonic acid-induced thromboxane formation. Results: HTPR to aspirin was more frequent in patients with impaired renal function (47% vs. 22%; odds ratio, 3.16; 95% confidence interval [CI], 1.34-7.41; P = 0.008). The pharmacodynamic response to aspirin was impaired in patients with moderate/severe CKD (92; interquartile range [IQR], 282 ng mL À1) as compared to patients with normal/mildly reduced renal function (36; IQR, 100 ng mL À1; difference in medians, 57; CI, 5-110 ng mL À1; P = 0.013). Bivariate Pearson analysis showed residual thromboxane formation to be correlated with glomerular filtration rate (R = À0.303; R 2 = 0.092; P = 0.001). Patients with CKD were older and more frequently female. Multivariate linear regression analysis revealed that the correlation was independent of age (R = À0.314; R 2 = 0.082; P = 0.002) and gender (R = À0.305; R 2 = 0.077; P = 0.006). Conclusion: Renal function is correlated with pharmacodynamic response to aspirin. Patients with CKD have an increased risk of impaired antiplatelet effects of aspirin. Larger trials are needed to assess the clinical impact of this finding and investigate the optimal antithrombotic regimen in CKD patients.

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