Decreased platelet activation predicts hepatic decompensation and mortality in patients with cirrhosis.

BACKGROUND AND AIMS: Patients with cirrhosis show alterations in primary hemostasis, yet prognostic implications of changes in platelet activation remain controversial, and assay validity is often limited by thrombocytopenia. We aimed to study the prognostic role of platelet activation in cirrhosis, focusing on bleeding/thromboembolic events, decompensation, and mortality. APPROACH AND RESULTS: We prospectively included 107 patients with cirrhosis undergoing a same-day hepatic venous pressure gradient (HVPG) and platelet activation measurement. Platelet activation was assessed using flow cytometry after protease-activated receptor (PAR)-1, PAR-4, or epinephrine stimulation. Over a follow-up of 25.3 (IQR: 15.7-31.2) months, first/further decompensation occurred in 29 patients and 17 died. More pronounced platelet activation was associated with an improved prognosis, even after adjusting for systemic inflammation, HVPG, and disease severity. Specifically, higher PAR-4-inducible platelet activation was independently linked to a lower decompensation risk [adjusted HR per 100 MFI (median fluorescence intensity): 0.95 (95% CI: 0.90-0.99); p =0.036] and higher PAR-1-inducible platelet activation was independently linked to longer survival [adjusted HR per 100 MFI: 0.93 (95% CI: 0.87-0.99); p =0.040]. Thromboembolic events occurred in eight patients (75% nontumoral portal vein thrombosis [PVT]). Higher epinephrine-inducible platelet activation was associated with an increased risk of thrombosis [HR per 10 MFI: 1.07 (95% CI: 1.02-1.12); p =0.007] and PVT [HR per 10 MFI: 1.08 (95% CI: 1.02-1.14); p =0.004]. In contrast, of the 11 major bleedings that occurred, 9 were portal hypertension related, and HVPG thus emerged as the primary risk factor. CONCLUSIONS: Preserved PAR-1- and PAR-4-inducible platelet activation was linked to a lower risk of decompensation and death. In contrast, higher epinephrine-inducible platelet activation was a risk factor for thromboembolism and PVT.

Platelet Function Decreases with Increasing Severity of Liver Cirrhosis and Portal Hypertension-A Prospective Study.

BACKGROUND: Cirrhotic patients display an increased risk for both bleeding and thrombosis. We investigated platelet activation across Child-Pugh stages (CPSs) and portal hypertension (PH) severity. MATERIAL AND METHODS: A total of 110 cirrhotic patients were prospectively included. CPS and hepatic venous pressure gradient (HVPG) were determined. Platelet surface expression of P-selectin and activated glycoprotein (GP) IIb/IIIa were measured by flow cytometry before/after stimulation with protease-activated receptor (PAR)-1 (thrombin receptor activating peptide, TRAP) and PAR-4 (AYPGKF) agonists, epinephrine, and lipopolysaccharide (LPS). RESULTS: Platelet count was similar across CPS but lower with increasing PH severity. Expression of P-selectin and activated GPIIb/IIIa in response to TRAP and AYPGKF was significantly reduced in platelets of CPS-B/C versus CPS-A patients (all p < 0.05). Platelet P-selectin expression upon epinephrine and LPS stimulation was reduced in CPS-C patients, while activated GPIIb/IIIa in response to these agonists was lower in CPS-B/C (all p < 0.05). Regarding PH severity, P-selectin and activated GPIIb/IIIa in response to AYPGKF were lower in HVPG ≥20 mmHg patients (both p < 0.001 vs. HVPG < 10 mmHg). Similarly, activated GPIIb/IIIa was lower in HVPG ≥20 mmHg patients after TRAP stimulation (p < 0.01 vs. HVPG < 10 mmHg). The lower platelet surface expression of P-selectin and activated GPIIb/IIIa upon stimulation of thrombin receptors (PAR-1/PAR-4) in CPS-B/C and HVPG ≥20 mmHg patients was paralleled by reduced antithrombin-III levels in those patients (all p < 0.05). Overall, PAR-1- and PAR-4-mediated platelet activation correlated with antithrombin-III levels (p < 0.001). CONCLUSION: Platelet responsiveness decreases with increasing severity of liver cirrhosis and PH but is potentially counterbalanced by lower antithrombin-III levels.

Platelet function and soluble P-selectin in patients with primary immune thrombocytopenia.

BACKGROUND: The bleeding phenotype in immune thrombocytopenia (ITP) is heterogeneous, but usually mild and only partly dependent on the severity of thrombocytopenia. Platelet reactivity has previously been suggested to underly the mild phenotype. METHODS: Platelet function was assessed as basal and agonist-induced surface expression of P-selectin and activation of GPIIb/IIIa via flow cytometry, and soluble (s)P-selectin levels were assessed in plasma of 77 patients with primary ITP, 19 hemato-oncologic thrombocytopenic controls (TC) and 20 healthy controls (HC). The association of platelet function with laboratory and clinical parameters such as bleeding manifestations at inclusion and previous thrombosis was analyzed. RESULTS: ITP patients showed tendency towards increased surface P-selectin and elevated levels of activated GPIIb/IIIa. Platelet activation after stimulation with all agonists including TRAP-6, ADP, arachidonic acid and CRP was decreased compared to HC. Compared to TC, only GPIIb/IIIa activation but not surface P-selectin was higher in ITP. Levels of soluble (s)P-selectin were significantly higher in ITP patients compared to TC, but similar to HC. Higher sP-selectin levels were associated with blood group O and current therapy, with highest levels in TPO-RA treated patients. Platelet reactivity was not associated with platelet count or size, platelet antibodies, treatment regime, or blood group. No correlation between platelet activation with the bleeding phenotype or previous thrombotic events could be observed. CONCLUSION: ITP patients did not have hyper-reactive platelets compared to HC, but partly higher reactivity compared to TC. Further studies are needed to understand the underlying mechanism behind the bleeding and pro-thrombotic phenotype in ITP. 250/250.

Growth Differentiation Factor 15 Is Associated with Platelet Reactivity in Patients with Acute Coronary Syndrome.

Bleeding events in patients with acute coronary syndrome (ACS) are a risk factor for adverse outcomes, including mortality. We investigated the association of growth differentiation factor (GDF)-15, an established predictor of bleeding complications, with on-treatment platelet reactivity in ACS patients undergoing coronary stenting receiving prasugrel or ticagrelor. Platelet aggregation was measured by multiple electrode aggregometry (MEA) in response to adenosine diphosphate (ADP), arachidonic acid (AA), thrombin receptor-activating peptide (TRAP, a protease-activated receptor-1 (PAR-1) agonist), AYPGKF (a PAR-4 agonist) and collagen (COL). GDF-15 levels were measured using a commercially available assay. GDF-15 correlated inversely with MEA ADP (r = -0.202, p = 0.004), MEA AA (r = -0.139, p = 0.048) and MEA TRAP (r = -0.190, p = 0.007). After adjustment, GDF-15 was significantly associated with MEA TRAP (ß = -0.150, p = 0.044), whereas no significant associations were detectable for the other agonists. Patients with low platelet reactivity in response to ADP had significantly higher GDF-15 levels (p = 0.005). In conclusion, GDF-15 is inversely associated with TRAP-inducible platelet aggregation in ACS patients treated with state-of-the-art antiplatelet therapy and significantly elevated in patients with low platelet reactivity in response to ADP.

Impact of ABO Blood Group on Thromboembolic and Bleeding Complications in Patients with Left Ventricular Assist Devices.

BACKGROUND: The ABO blood group system is linked to hemostasis via its relationship with von Willebrand factor (VWF) and factor VIII (FVIII). In the current study, we investigated the association of the ABO system with clinical outcomes as well as VWF and platelet function in patients with left ventricular assist devices (LVADs). METHODS: Bleeding and thromboembolic complications were assessed in 111 patients during 1 year after LVAD implantation. In 67 LVAD patients, VWF antigen, VWF activity, VWF ristocetin cofactor, VWF collagen-binding, and FVIII activity were assessed. Platelet surface P-selectin and activated glycoprotein IIb/IIIa were determined by flow cytometry, and soluble P-selectin was measured with an enzyme-linked immunoassay. Platelet aggregation was assessed by light transmission and impedance aggregometry. RESULTS: Thirty-six patients (32.4%) experienced a bleeding and 22 patients (19.8%) a thromboembolic event. In univariate analyses, patients with blood group O had numerically more bleeding complications and less thromboembolic events as compared to patients with blood group non-O (both p ≥ 0.05). After multivariable adjustment, blood group O was significantly associated with a higher risk of bleeding (hazard ratio 2.42 [95% confidence interval 1.03-5.70], p = 0.044) but not linked to thromboembolic complications. CONCLUSION: Patients with blood group O had significantly lower levels of VWF and FVIII (all p < 0.05), whereas P-selectin expression in response to thrombin-receptor activating peptide and soluble P-selectin were higher as compared to patients with blood group non-O (both p < 0.05). LVAD patients with blood group O are at an increased bleeding risk, potentially due to lower VWF and FVIII levels.

Assay validity of point-of-care platelet function tests in thrombocytopenic blood samples.

Introduction: Point-of-care (POC) platelet function tests are faster and easier to perform than in-depth assessment by flow cytometry. At low platelet counts, however, POC tests are prone to assess platelet function incorrectly. Lower limits of platelet count required to obtain valid test results were defined and a testing method to facilitate comparability between different tests was established. Materials and methods: We assessed platelet function in whole blood samples of healthy volunteers at decreasing platelet counts (> 100, 80-100, 50-80, 30-50 and < 30 x109/L) using two POC tests: impedance aggregometry and in-vitro bleeding time. Flow cytometry served as the gold standard. The number of platelets needed to reach 50% of the maximum function (ED50) and the lower reference limit (EDref) were calculated to define limits of test validity. Results: The minimal platelet count required for reliable test results was 100 x109/L for impedance aggregometry and in-vitro bleeding time but only 30 x109/L for flow cytometry. Comparison of ED50 and EDref showed significantly lower values for flow cytometry than either POC test (P value < 0.05) but no difference between POC tests nor between the used platelet agonists within a test method. Conclusion: Calculating the ED50 and EDref provides an effective way to compare values from different platelet function assays. Flow cytometry enables correct platelet function testing as long as platelet count is > 30 x109/L whereas impedance aggregometry and in-vitro bleeding time are inconsistent unless platelet count is > 100 x109/L.

Growth Differentiation Factor-15 Correlates Inversely with Protease-Activated Receptor-1-Mediated Platelet Reactivity in Patients with Left Ventricular Assist Devices.

Growth differentiation factor (GDF)-15 inhibits platelet activation, prevents thrombus formation, and has been linked to bleeding events. This was a prospective study including 51 left-ventricular assist device (LVAD) patients on aspirin and phenprocoumon. Platelet surface expression of activated glycoprotein (GP) IIb/IIIa was assessed by flow cytometry, and platelet aggregation was measured by multiple electrode aggregometry (MEA) in response to arachidonic acid (AA), adenosine diphosphate (ADP), and thrombin receptor-activating peptide (TRAP), a protease-activated-receptor-1 (PAR-1) agonist. GDF-15 was determined with a commercially-available assay. There was a trend towards an inverse correlation of GDF-15 with activated GPIIb/IIIa in response to TRAP (r = -0.275, p = 0.0532) but not in response to AA and ADP. Moreover, GDF-15 correlated with MEA TRAP (r = -0.326, p = 0.0194), whereas it did not correlate with MEA ADP and MEA AA. In a second step, GDF-15 levels in the fourth quartile were defined as high GDF-15. Patients with high GDF-15 showed significantly lower TRAP-inducible platelet aggregation by MEA compared to patients in the first quartile (63 AU vs. 113 AU, p = 0.0065). In conclusion, in LVAD patients receiving state-of-the-art antithrombotic therapy, GDF-15 correlates inversely with residual platelet reactivity via PAR-1.

Platelet-to-Lymphocyte Ratio as Marker of Platelet Activation in Patients on Potent P2Y12 Inhibitors.

A high platelet-to-lymphocyte ratio (PLR) has recently been associated with ischemic outcomes in cardiovascular disease. Increased platelet reactivity and leukocyte-platelet aggregate formation are directly involved in the progress of atherosclerosis and have been linked to ischemic events following percutaneous coronary intervention (PCI). In order to understand the relation of PLR with platelet reactivity, we assessed PLR as well as agonist-inducible platelet aggregation and neutrophil-platelet aggregate (NPA) formation in 182 acute coronary syndrome (ACS) patients on dual antiplatelet therapy with aspirin and prasugrel (n = 96) or ticagrelor (n = 86) 3 days after PCI. PLR was calculated from the blood count. Platelet aggregation was measured by multiple electrode aggregometry and NPA formation was determined by flow cytometry, both in response to ADP and SFLLRN. A PLR ≥91 was considered as high PLR based on previous data showing an association of this threshold with adverse ischemic outcomes. In the overall cohort and in prasugrel-treated patients, high PLR was associated with higher SFLLRN-inducible platelet aggregation (67 AU [50-85 AU] vs 59.5 AU [44.3-71.3 AU], P = .01, and 73 AU [50-85 AU] vs 61.5 AU [46-69 AU], P = .02, respectively). Further, prasugrel-treated patients with high PLR exhibited higher ADP- (15% [11%-23%] vs 10.9% [7.6%-15.9%], P = .007) and SFLLRN-inducible NPA formation (64.3% [55.4%-73.8%] vs 53.8% [44.1%-70.1%], P = .01) as compared to patients with low PLR. These differences were not seen in ticagrelor-treated patients. In conclusion, high PLR is associated with increased on-treatment platelet reactivity in prasugrel-treated patients, but not in patients on ticagrelor.

Peripheral versus central venous blood sampling does not influence the assessment of platelet activation in cirrhosis.

Cirrhotic patients have an increased risk of bleeding and thromboembolic events, with platelets being involved as key players in both situations. The impact of peripheral versus central blood sampling on platelet activation remains unclear. In 33 cirrhotic patients, we thus analyzed platelet function in peripheral (P) and central (C) blood samples. Platelet surface expression of P-selectin, activated glycoprotein (GP) IIb/IIIa, and leukocyte-platelet aggregate formation were measured by flow cytometry in response to different agonists: thrombin receptor-activating peptide-6, adenosine diphosphate, collagen-related peptide (CrP), epinephrine, AYPGKF, Pam3CSK4, and lipopolysaccharide. Unstimulated platelet surface expression of P-selectin (p = .850) and activated GPIIb/IIIa (p = .625) were similar in peripheral and central blood samples. Stimulation with various agonists yielded similar results of platelet surface expression of P-selectin and activated GPIIb/IIIa in peripheral and central samples, except for CrP-inducible expression of activated GPIIb/IIIa (median fluorescence intensity, MFI in P: 7.61 [0.00-24.66] vs. C: 4.12 [0.00-19.04], p < .001). The formation of leukocyte-platelet aggregate was similar in central and peripheral blood samples, both unstimulated and after stimulation with all above-mentioned agonists. In conclusion, peripheral vs. central venous blood sampling does not influence the assessment of platelet activation by flow cytometry in cirrhosis.Abbreviations: ACLD: advanced chronic liver disease; ADP: adenosine diphosphate; ALD: alcoholic liver disease; AYPGKF: PAR-4 agonist AYPGKF; CrP: collagen related protein; EPI: epinephrine; FACS: fluorescence-activated cell sorting; GP: glycoprotein; HVPG: hepatic venous pressure gradient; IQR: interquartile range; LPS: lipopolysaccharide; LSM: liver stiffness measurement; MFI: median fluorescence intensity; NAFLD: nonalcoholic fatty liver disease; PAM: lipopeptide Pam3CSK4; PAR: protease-activated receptor; PBS: phosphate-buffered saline; PH: portal hypertension; TIPS: transjugular intrahepatic portosystemic stent shunt; TLR: toll-like receptor; TRAP-6: thrombin receptor-activator peptide-6; vWF: von Willebrand factor.

Platelet activation and aggregation in different centrifugal-flow left ventricular assist devices.

Left-ventricular assist devices (LVADs) improve outcomes in end-stage heart failure patients. Two centrifugal-flow LVAD systems are currently approved, HeartMate 3 (HM3) and Medtronic/Heartware HVAD (HVAD). Clinical findings suggest differences in thrombogenicity between both systems. We compared markers of platelet activation and aggregation between HM3 and HVAD. We prospectively included 59 LVAD patients (40 HM3, 19 HVAD). Platelet P-selectin expression, activated glycoprotein (GP) IIb/IIIa and monocyte-platelet aggregates (MPA) were assessed by flow-cytometry. Platelet aggregation was measured by light-transmission aggregometry (LTA) and multiple-electrode aggregometry (MEA). Von-Willebrand factor (VWF) antigen (VWF:Ag), VWF activity (VWF:Ac), and VWF multimer pattern analysis were determined. Soluble P-selectin (sP-selectin) was measured with an enzyme-linked immunoassay. P-selectin, GPIIb/IIIa and MPA levels in vivo and in response to arachidonic acid, adenosine diphosphate, and thrombin receptor activating peptide were similar between HM3 and HVAD (all p > .05). Likewise, agonist-inducible platelet aggregation by LTA and MEA did not differ between HM3 and HVAD (all p > .05). VWF:Ag levels and FVIII:C were similar between both systems (both p > .05), but patients with HVAD had significantly lower VWF:Ac (p = .011) and reduced large VWF multimers (p = .013). Finally, sP-selectin levels were similar in patients with HVAD and HM3 (p = .845). In conclusion, on-treatment platelet activation and aggregation are similar in HM3 and HVAD patients. Potential clinical implications of observed differences in VWF profiles between both LVAD systems need to be addressed in future clinical trials.

Circulating MicroRNAs and Monocyte-Platelet Aggregate Formation in Acute Coronary Syndrome.

BACKGROUND: Monocyte-platelet aggregates (MPAs) are a sensitive marker of in vivo platelet activation in acute coronary syndrome (ACS) and associated with clinical outcomes. MicroRNAs (miRs) play an important role in the regulation of platelet activation, and may influence MPA formation. Both, miRs and MPA, could be influenced by the type of P2Y12 inhibitor. AIM: To study the association of platelet-related miRs with MPA formation in ACS patients on dual antiplatelet therapy (DAPT), and to compare miRs and MPA levels between prasugrel- and ticagrelor-treated patients. METHODS AND RESULTS: We analyzed 10 circulating platelet-related miRs in 160 consecutive ACS patients on DAPT with low-dose aspirin and either prasugrel (n = 80) or ticagrelor (n = 80). MPA formation was measured by flow cytometry without addition of platelet agonists and after simulation with the toll-like receptor (TLR)-1/2 agonist Pam3CSK4, adenosine diphosphate (ADP), or arachidonic acid (AA). In multivariate regression analyses, we identified miR-21 (ß = 9.50, 95% confidence interval [CI]: 1.60-17.40, p = 0.019) and miR-126 (ß = 7.50, 95% CI: 0.55-14.44, p = 0.035) as independent predictors of increased MPA formation in vivo and after TLR-1/2 stimulation. In contrast, none of the investigated miRs was independently associated with MPA formation after stimulation with ADP or AA. Platelet-related miR expression and MPA formation did not differ significantly between prasugrel- and ticagrelor-treated patients. CONCLUSION: Platelet-related miR-21 and miR-126 are associated with MPA formation in ACS patients on DAPT. miRs and MPA levels were similar in prasugrel- and ticagrelor-treated patients.

Comparison of Light Transmission Aggregometry With Impedance Aggregometry in Patients on Potent P2Y12 Inhibitors.

Since data on the agreement between light transmission aggregometry (LTA) and multiple electrode aggregometry (MEA) in patients on the more potent P2Y12 inhibitors are missing so far, we investigated if the evaluation of the responsiveness to therapy by LTA can be replaced by MEA in 160 acute coronary syndrome (ACS) patients on dual antiplatelet therapy with aspirin and prasugrel or ticagrelor (n = 80 each). Cut-off values for high on-treatment residual platelet reactivity (HRPR) in response to adenosine diphosphate (ADP) or arachidonic acid (AA) were defined according to previous studies showing an association of HRPR with the occurrence of adverse ischemic outcomes. ADP- inducible platelet aggregation was 33% and 37% (P = 0.07) by LTA and 19 AU and 20 AU (P = 0.38) by MEA in prasugrel- and ticagrelor-treated patients, respectively. AA- inducible platelet aggregation was 2% and 3% by LTA and 15 AU and 16 AU by MEA, (all P ≥ 0.3) in patients on prasugrel and ticagrelor, respectively. By LTA, HRPR ADP and HRPR AA were seen in 5%/5% and in 4%/ 13% of patients receiving prasugrel- and ticagrelor, respectively. By MEA, HRPR ADP and HRPR AA were seen in 3%/ 25% and 0%/24% of prasugrel- and ticagrelor-treated patients, respectively. ADP-inducible platelet reactivity by MEA correlated significantly with LTA ADP in prasugrel-treated patients (r = 0.4, P < 0.001), but not in those receiving ticagrelor (r = 0.09, P = 0.45). AA-inducible platelet aggregation by LTA and MEA did not correlate in prasugrel- and ticagrelor-treated patients. Sensitivity/specificity of HRPR by MEA to detect HRPR by LTA were 25%/99% for MEA ADP and 100%/79% for MEA AA in prasugrel-treated patients, and 0%/100% for MEA ADP and 70%/83% for MEA AA in ticagrelor-treated patients. In conclusion, on-treatment residual ADP-inducible platelet reactivity by LTA and MEA shows a significant correlation in prasugrel- but not ticagrelor-treated patients. However, in both groups LTA and MEA revealed heterogeneous results regarding the classification of patients as responders or non-responders to P2Y12 inhibition.

Angiotensin-Converting Enzyme Inhibitors and Angiotensin Receptor Blockers in Acute Coronary Syndrome: Implications for Platelet Reactivity?

BACKGROUND: In patients with acute coronary syndrome (ACS), angiotensin-converting enzyme (ACE) inhibitors are preferred over angiotensin receptor blockers (ARBs). However, in a recent pilot study, treatment with ACE inhibitors was associated with increased platelet reactivity compared to ARBs. Therefore, we sought to investigate the impact of renin-angiotensin-aldosterone system (RAAS) blockade with ACE inhibitors and ARBs on platelet aggregation in patients with ACS undergoing percutaneous coronary intervention. METHODS: On-treatment residual platelet reactivity in response to arachidonic acid (AA), adenosine diphosphate (ADP), SFLLRN, AYPGKF, and collagen was assessed by multiple electrode aggregometry (MEA) in 197 ACS patients on dual antiplatelet therapy (DAPT) with aspirin and either prasugrel or ticagrelor. RESULTS: One hundred sixty-five (83.7%) patients were treated with ACE inhibitors, 32 (16.3%) with ARBs. On-treatment residual AA- and ADP-inducible platelet reactivity was significantly higher in patients with ACE inhibitors (both p < 0.05). Likewise, SFLLRN was significantly higher in patients with ACE inhibitors (p = 0.036) and there was a trend for higher AYPGKF- and collagen-inducible platelet reactivity (p = 0.053 and p = 0.082). The incidence of high on-treatment residual platelet reactivity AA was significantly higher in patients with ACE inhibitors (52 [31.5%] vs. 3 [9.4%] patients; p = 0.019). CONCLUSION: ACE inhibitors are associated with increased on-treatment residual platelet reactivity in ACS patients with potent DAPT. Further clinical trials are needed to elucidate the role of RAAS blockade with ACE inhibitors and ARBs in ACS patients treated according to current standards.

Residual platelet reactivity in low-dose aspirin-treated patients with class 1 obesity.

BACKGROUND: Recent data suggest a decreased clinical efficacy of low-dose aspirin in patients weighing ≥70 kg. We therefore investigated the impact of body weight and class 1 obesity on thromboxane generation and platelet reactivity to arachidonic acid (AA) in 316 patients on dual antiplatelet therapy following angioplasty and stenting. METHODS: Platelet surface expression of P-selectin and activated glycoprotein (GP) IIb/IIIa in response to AA were determined by flow cytometry as sensitive markers of platelet activation. Urinary 11-dehydro-thromboxane B2 (11-dehydro-TXB2) and serum TXB2 were measured by commercially-available immunoassays. On-treatment residual AA-inducible platelet aggregation was assessed by light transmission aggregometry (LTA), the VerifyNow aspirin assay and multiple electrode aggregometry (MEA). RESULTS: Class 1 obesity was independently associated with increased platelet surface expression of P-selectin and activated GPIIb/IIIa, but not with urinary 11-dehydro-TXB2, serum TXB2, and on-treatment platelet aggregation by all assays. Of all measured parameters, only MEA showed a positive albeit very weak correlation with body weight (r = 0.13, p = 0.02). Furthermore, the results of all tests did not differ significantly between patients without and with a body weight ≥ 70 kg. After adjustment for age and diabetes by multivariate logistic regression analysis, the frequency of high-on treatment residual TXB2 generation and high on-treatment residual AA-inducible platelet reactivity (HRTG/HRPR) did not differ significantly between obese and non-obese patients. CONCLUSION: Class 1 obesity is associated with enhanced platelet activation in response to AA in patients on dual antiplatelet therapy. This seems to be independent of cyclooxygenase-1 inhibition and does not translate into HRTG/HRPR.

Ticagrelor Inhibits Toll-Like and Protease-Activated Receptor Mediated Platelet Activation in Acute Coronary Syndromes.

PURPOSE: Since ticagrelor inhibits the cellular uptake of adenosine, thereby increasing extracellular adenosine concentration and biological activity, we hypothesized that ticagrelor has adenosine-dependent antiplatelet properties. In the current study, we compared the effects of ticagrelor and prasugrel on platelet activation in acute coronary syndrome (ACS). METHODS: Platelet surface expression of P-selectin and activated glycoprotein (GP) IIb/IIIa in response to adenosine diphosphate (ADP), the toll-like receptor (TLR)-1/2 agonist Pam3CSK4, the TLR-4 agonist lipopolysaccharide (LPS), the protease-activated receptor (PAR)-1 agonist SFLLRN, and the PAR-4 agonist AYPGKF were measured by flow cytometry in blood from 80 ticagrelor- and 80 prasugrel-treated ACS patients on day 3 after percutaneous coronary intervention. Residual platelet aggregation to arachidonic acid (AA) and ADP were assessed by multiple electrode aggregometry and light transmission aggregometry. RESULTS: ADP-induced platelet activation and aggregation, and AA-induced platelet aggregation were similar in patients on ticagrelor and prasugrel, respectively (all p ≥ 0.3). Further, LPS-induced platelet surface expression of P-selectin and activated GPIIb/IIIa did not differ significantly between ticagrelor- and prasugrel-treated patients (both p > 0.4). In contrast, Pam3CSK4-induced platelet surface expression of P-selectin and activated GPIIb/IIIa were significantly lower in ticagrelor-treated patients (both p ≤ 0.005). Moreover, SFLLRN-induced platelet surface expression of P-selectin and activated GPIIb/IIIa were significantly less pronounced in patients on ticagrelor therapy compared to prasugrel-treated patients (both p < 0.03). Finally, PAR-4 mediated platelet activation as assessed by platelet surface expression of activated GPIIb/IIIa following stimulation with AYPGKF was significantly lower in patients receiving ticagrelor (p = 0.02). CONCLUSION: Ticagrelor inhibits TLR-1/2 and PAR mediated platelet activation in ACS patients more strongly than prasugrel.

Association of Soluble Suppression of Tumorigenesis 2 (sST2) With Platelet Activation, Monocyte Tissue Factor and Ischemic Outcomes Following Angioplasty and Stenting.

Background: Peripheral artery disease (PAD) patients undergoing infrainguinal angioplasty with stenting suffer high rates of target lesion restenosis and ischemic events. Blood-based prognostic markers in these patients are currently limited. The IL-33/ST2-system is involved in atherothrombosis. Soluble ST2 has been proposed as a biomarker in patients with cardiovascular disease. Aim: To investigate the association of sST2 with platelet activation and monocyte tissue factor (TF) in 316 patients undergoing elective angioplasty and stenting for cardiovascular disease, and its predictive value for ischemic outcomes following infrainguinal angioplasty with stent implantation in 104 PAD patients within this cohort. Methods and Results: Circulating levels of sST2, platelet surface P-selectin, monocyte TF expression as well as soluble P-selectin were determined in 316 consecutive patients on dual antiplatelet therapy following angioplasty and stenting. sST2 was independently associated with soluble P-selectin (B = 6.4, 95% CI 2.0-10.7, p = 0.004) and TF expression (B = 0.56, 95% CI 0.02-1.1, p = 0.041) but not with platelet surface P-selectin (B = 0.1, 95% CI -0.1-0.3, p = 0.307) after adjustment for age, sex, clinical risk factors and inflammatory parameters. During the follow-up of 24 months, the primary endpoint occurred in 41 of 104 PAD patients (39.4%). However, circulating levels of sST2 did not predict the primary endpoint in PAD patients (HR 1.1, 95% CI 0.76-1.71, p = 0.527). Conclusion: sST2 is associated with soluble P-selectin and monocyte TF expression in atherosclerosis but not with ischemic outcomes following infrainguinal angioplasty with stent implantation for PAD.

Plasma Levels of snoRNAs are Associated with Platelet Activation in Patients with Peripheral Artery Disease.

In addition to supervised walking therapy, antithrombotic therapy and the management of risk factors, the treatment of peripheral artery disease (PAD) is limited to endovascular and surgical interventions, i.e., angioplasty with stent implantation and bypass surgery, respectively. Both are associated with a high restenosis rate. Furthermore, patients with PAD often suffer atherothrombotic events like myocardial infarction, transient ischemic attacks or stroke. Small ribonucleic acids (RNAs) have proven reliable biomarkers because of their remarkable stability. Small nucleolar RNAs (snoRNAs) guide modifications to small nuclear RNAs and ribosomal RNAs, enabling protein synthesis. In the current study, we measured four snoRNAs in 104 consecutive PAD patients who underwent elective infrainguinal angioplasty with stent implantation. We selected snoRNAs that showed significant overexpression in the plasma of end-stage PAD patients in a previous study. All four snoRNAs are transcribed from the 14q32 locus, which is strongly linked to human cardiovascular disease, including PAD and restenosis. We showed that the four selected 14q32 snoRNAs were abundantly expressed in the plasma of PAD patients. The plasma levels of these snoRNAs were not directly associated with target vessel restenosis, however, levels of SNORD113.2 and SNORD114.1 were strongly linked to platelet activation, which is an important determinant of long-term outcome, in PAD, and in cardiovascular disease in general.

Protease-activated receptor-mediated platelet aggregation in acute coronary syndrome patients on potent P2Y12 inhibitors.

BACKGROUND: Despite the increasing use of potent P2Y12 inhibitors, further atherothrombotic events still impair the prognosis of many acute coronary syndrome (ACS) patients. This may in part be attributable to intact platelet aggregation via the human thrombin receptors protease-activated receptor (PAR)-1 and PAR-4. OBJECTIVE: We studied PAR mediated platelet aggregation in ACS patients following percutaneous coronary intervention (PCI) with stent implantation in a cross-sectional study. METHODS: Platelet aggregation to ADP as well as to the PAR-1 agonist SFLLRN and the PAR-4 agonist AYPGKF was assessed by multiple electrode aggregometry in 194 ACS patients on dual antiplatelet therapy with aspirin and either prasugrel (n = 114) or ticagrelor (n = 80) 3 days after PCI. RESULTS: Based on the consensus cutoff value, high on-treatment residual platelet reactivity to ADP (HRPR ADP) was observed in only 2 prasugrel-treated patients. Both patients with HRPR ADP had also a normal response to SFLLRN and AYPGKF. Among the 112 prasugrel-treated patients with adequate P2Y12 inhibition, 50 patients (45%) still had a normal response to SFLLRN, and 70 patients (63%) still had a normal response to AYPGKF. Among the 80 ticagrelor-treated patients with adequate P2Y12 inhibition, 25 patients (31%) still had a normal response to SFLLRN, and 50 (63%) still had a normal response to AYPGKF. CONCLUSION: Normal platelet aggregation via PAR-1 and PAR-4 is preserved in many patients with adequate P2Y12 inhibition by prasugrel and ticagrelor. The present findings may at least in part explain adverse ischemic events despite potent P2Y12 inhibition.

Disaggregation Following Agonist-Induced Platelet Activation in Patients on Dual Antiplatelet Therapy.

Disaggregation as the difference between maximal and final platelet aggregation by light transmission aggregometry indicates the stability of platelet aggregates. We evaluated the extent of disaggregation after platelet stimulation with adenosine diphosphate (ADP), arachidonic acid (AA), collagen, epinephrine, and thrombin receptor-activating peptide (TRAP)-6 in 323 patients on dual antiplatelet therapy with daily aspirin and clopidogrel (group 1), prasugrel (group 2), or ticagrelor (group 3) therapy. All patients in group 1 underwent elective angioplasty and stenting, whereas all patients included in groups 2 and 3 suffered from acute coronary syndromes (STEMI or NSTEMI) and underwent urgent PCI. Significant differences between maximal and final platelet aggregation were observed with all agonists throughout the groups (all p<0.001). Disaggregation was highest using AA (clopidogrel 36.5%; prasugrel/ticagrelor 100%) and ADP (clopidogrel 21.7%; prasugrel/ticagrelor 100%). In contrast, low disaggregation was observed after platelet stimulation with collagen and TRAP-6 in clopidogrel-treated patients, and after platelet stimulation with collagen and epinephrine in prasugrel- and ticagrelor-treated patients. In conclusion, pathways of platelet activation that are not inhibited by standard antiplatelet therapy allow persisting platelet aggregation and may at least in part be responsible for adverse ischemic events.

Antibodies against complement-regulatory proteins on platelets in immune thrombocytopenia.

In immune thrombocytopenia (ITP), antibodies reacting with platelet membrane glycoproteins (GP) mediate premature platelet cleavage, resulting in thrombocytopenia and therefore a risk of bleeding. These antibodies may induce complement activation, thus mediating complement-induced platelet destruction. In this study, we investigated the possibility of an additional complement-related pathogenic mechanism, where antibodies against the complement-regulatory factors CD55 and CD59 may directly interfere with normal complement function. CD55 downregulates both the classic and the alternative activation pathways, while CD59 blocks the formation of the membrane attack complex; both proteins are present on platelets and may therefore be targets of autoantibodies. Using the simultaneous analysis of specific platelet antibodies (SASPA) assay, we found that in some cases of immune-mediated thrombocytopenia, anti-CD55 and -CD59 antibodies are detectable in patients' sera and/or on their autologous platelets in combination with antibodies against platelet-specific GP. Although antibodies against CD55 and CD59 seem to be a rare phenomenon, this finding may have clinical relevance due to the availability of highly effective therapeutics targeting the complement system.