Effect of sulphinpyrazone and aspirin on latelet adhesion to activated charcoal and dialysis membranes in vitro.

Charcoal haemoperfusion is used in the treatment of severe drug overdosage, and is potentially useful in fulminant hepatic failure and chronic uraemia. Haemo-compatibility of early devices has improved, but platelet loss and occasional associated haemorrhage still occur. During a double blind cross-over study, in 8 healthy male volunteers, aspirin 600 mg/day, sulphinpyrazone 800 mg/day, or a combination of both or placebo were administered for 2 days at 14 day or longer intervals. The effects of these agents were measured with reference to 1) forearm bleeding times using a spring loaded device, 2) platelet adsorption during 2 hrs haemoperfusion of heparinized blood through 2% acrylic hydrogel coated or uncoated activated charcoal in vitro, and 3) platelet retention from citrated blood on PT₁₅₀ and PT₂₅₀ cuprophan dialysis membranes in vitro. Aspirin and aspirin in combination with sulphinpyrazone prolonged bleeding time, but sulphinpyrazone alone had no significant effect on bleeding time. Aspirin alone, sulphinpyrazone alone, and their combination reduced platelet adsorption on coated activated charcoal, and platelet retention on cuprophan membranes. Aspirin, and aspirin in combination with sulphinpyrazone, reduce platelet adsorption on uncoated charcoal, while sulphinpyrazone alone had no significant effect. The results indicate that 2 days treatment with sulphinpyrazone or aspirin produce significant antiplatelet action and that the effects of sulphinpyrazone on platelet function should be explored in relation to clinical haemoperfusion and haemodialysis.     

Combination therapy with low-dose aspirin and ticlopidine in cerebral ischemia

We compared combination therapy with low-dose aspirin plus ticlopidine to therapy with aspirin alone or ticlopidine alone in patients suffering transient ischemic attack or cerebral infarction. In 17, 24, and 23 patients, respectively, 300 mg/day aspirin, 200 mg/day ticlopidine, and 81 mg/day aspirin plus 100 mg/day ticlopidine were administered orally. Aspirin alone markedly inhibited platelet aggregation induced by arachidonic acid, partially inhibited platelet aggregation induced by adenosine diphosphate, and did not inhibit platelet aggregation induced by platelet activating factor. Ticlopidine alone inhibited platelet aggregation induced by adenosine diphosphate and platelet activating factor, but did not inhibit platelet aggregation induced by arachidonic acid. Combination therapy with aspirin plus ticlopidine markedly inhibited platelet aggregation induced by all three agonists. Plasma concentrations of beta-thromboglobulin and platelet factor 4 remained unchanged by aspirin alone, were slightly reduced by ticlopidine alone, and were markedly reduced by aspirin plus ticlopidine. Plasma concentration of thromboxane B2 was reduced by aspirin alone or with ticlopidine, but not by ticlopidine alone. The level of 6-ketoprostaglandin F1 alpha was reduced only by aspirin alone. Bleeding time was significantly prolonged by aspirin alone and by ticlopidine alone, although the greatest prolongation was produced by aspirin plus ticlopidine. Our results indicate that the combination of aspirin plus ticlopidine is a potent antiplatelet strategy, although the clinical importance of the changes observed need to be determined by a properly designed and controlled prospective study.     

Reduced platelet response to aspirin in patients with coronary artery disease and type 2 diabetes mellitus

Introduction

Diabetes mellitus is complicated by accelerated atherosclerosis, resulting in an increased risk of coronary artery disease (CAD) and thrombosis. Despite the proven benefits of aspirin, previous studies indicate a reduced cardiovascular protection from aspirin in diabetic patients. We aimed to investigate whether diabetes mellitus influenced the platelet response to aspirin in patients with CAD.

Materials and Methods

Platelet aggregation and activation were evaluated during aspirin treatment in 85 diabetic and 92 non-diabetic patients with CAD. Adherence to aspirin was carefully controlled. All patients had CAD verified by coronary angiography and were taking 75 mg non-enteric coated aspirin daily.

Results

Diabetic patients showed significantly higher levels of platelet aggregation compared to non-diabetic patients evaluated by VerifyNow^® Aspirin (p = 0.03) and Multiplate^® aggregometry using arachidonic acid (AA) 0.5 mM (p = 0.005) and 1.0 mM (p = 0.009). In addition, platelet activation determined by soluble P-selectin was significantly higher in diabetics compared to non-diabetics (p = 0.005). The higher AA-induced aggregation was associated with higher levels of HbA_1c. Compliance was confirmed by low levels of serum thromboxane B₂ (below 7.2 ng/mL). Diabetics had significantly higher levels of serum thromboxane B₂ (p < 0.0001).

Conclusions

Diabetic patients with CAD had significantly higher levels of both platelet aggregation and activation compared to non-diabetic patients with CAD despite treatment with the same dosage of aspirin. These findings may partly explain the reduced cardiovascular protection from aspirin in diabetic patients.     

Pioglitazone inhibits platelet function and potentiates the effects of aspirin: a prospective observation study

Background

Thiazolidinediones (TZDs) are agonists of PPARγ and exert beneficial metabolic effects in patients with diabetes. They may also affect platelet function.

Objectives

To characterize potential platelet inhibitory effect of pioglitazone alone and in the presence of aspirin.

Methods

20 normal and 20 diabetic subjects were enrolled in a prospective study. On day 1, a blood sample was obtained at baseline and a second one after ingestion of 30 mg of pioglitazone. PRP was prepared and platelet aggregation and release were evaluated using ADP, collagen and arachidonic acid as agonists. Subjects returned at 6-9 days later after ingesting a single 81 mg dose of aspirin and a third blood sample was obtained. The subjects then again ingested 30 mg of pioglitazone and a fourth and final blood sample was obtained. Platelet aggregation and release were measured. PRP was incubated with thrombin to activate platelets, and the serum was separated and assayed for thromboxane B2, TGFβ and CD40L

Results

Pioglitazone alone did not affect aggregation with arachidonic acid. However, following ingestion of both aspirin and pioglitazone aggregation was significantly decreased compared to aspirin alone (P < 0.0001). Pioglitazone also potentiated aspirin-induced inhibition of ATP release using either arachidonic acid or collagen. Following pioglitazone alone, TXB₂ release was 32,719 ± 3,585 pg/ml which was significantly reduced compared to baseline (42,075 ± 4,479, P = 0.0004). Pioglitazone also potentiated the inhibition of TXB₂ release by aspirin.

Conclusion

Pioglitazone inhibits platelet function and potentiates the inhibitory effects of aspirin.     

Effect of increased aspirin dose after stenting in association with ClOpidogrel: the FIASCO randomized study

Background

Increased doses of antiplatelet therapy have been proposed to overcome the variability of response. However, the chronic dose of aspirin after DES remains controversial.

Methods and results

We assessed in a prospective and randomized study the benefit of higher dose of aspirin, in association with clopidogrel, on aspirin response and non COX-specific platelet testing in patients receiving Drug Eluting Stent (DES) for stable angina pectoris. 50 consecutive patients receiving DES for stable angina pectoris were prospectively included. They received loading dose of 250 mg aspirin and 600 mg clopidogrel and antiplatelet response was assessed with Arachidonic Acid-induced aggregation (AA-Ag) and ADP-induced aggregation (ADP-Ag) for aspirin and clopidogrel response respectively. Patients were randomized to either 75 or 160 mg of aspirin with 150 mg clopidogrel and platelet testing were repeated one month after hospital discharge. The two groups (aspirin “75 mg” or “160 mg”) had no difference for aspirin response: AA-Ag (5.2 ± 1.7% vs 6 ± 2%, p = 0.75) and non COX-specific pathway testing: ADP-Ag (47 ± 3% vs 49 ± 4%, p = 0.61).

Conclusion

The present study did not show any benefit of higher dose of aspirin neither on aspirin responsiveness, nor on inhibition of non COX-specific pathway. These data does not support use of higher dose than 75 mg of aspirin in association with clopidogrel in patients receiving DES, especially while higher doses have been associated with increased bleeding risk.     

Optical platelet aggregation versus thromboxane metabolites in healthy individuals and patients with stable coronary artery disease after low-dose aspirin administration

IntroductionAspirin reduces cardiovascular events in patients with coronary artery disease (CAD), but studies report a highly variable response to aspirin, often referred to as ‘aspirin low-responsiveness’. We investigated whether 75 mg of daily non-enteric coated aspirin would completely inhibit the platelet cyclooxygenase-1 activity to a comparable extent in healthy individuals and stable CAD patients.MethodsWe assessed serum thromboxane B₂ (S-TxB₂), urinary 11-dehydro-TxB₂ (U-TxM) and arachidonic acid-induced optical platelet aggregometry (OPA) in 44 CAD patients on aspirin and in 22 healthy individuals before and after aspirin. OPA was performed in duplicate for four consecutive days during aspirin treatment after one week of treatment. Compliance was optimized by face-to-face interviews and pill counting and confirmed by S-TxB₂ measurements.ResultsAspirin inhibited S-TxB₂ > 99% in healthy individuals (median 1.1 ng/mL, interquartile range (IQR) = 0.8;1.9 after aspirin) and in patients, S-TxB₂ was reduced to a similar level (0.9 ng/mL (0.7;1.5)). Healthy individuals had a median U-TxM of 278.5 pg/mg creatinine (229.5;380.0) before aspirin and 68.5 pg/mg creatinine (59.0;99.7) on aspirin corresponding to an average 74% inhibition of the endogenous TxA₂ biosynthesis. In patients median U-TxM was 67.5 pg/mg creatinine (54.0;85.5). Seven study participants (11%) were aspirin low-responders according to OPA, but none had S-TxB₂ in the highest quartile.ConclusionsLow-dose aspirin suppressed S-TxB₂ to comparable levels in CAD patients and healthy individuals. Despite an almost complete inhibition of S-TxB₂, some participants were low-responders according to OPA. Thorough compliance control and use of thromboxane-specific assays are important when measuring platelet response to aspirin.     

Effects of low dose aspirin on platelet function in patients with recent cerebral ischemia

We tested the antiplatelet effects of low-dose aspirin in patients with occlusive cerebrovascular disease, because conventional dosage aspirin inhibits vascular synthesis of prostacyclin at the same time that it inhibits platelets. The effects on platelet function and thromboxane A2 synthesis of 40 mg of aspirin daily or 40 mg aspirin plus dipyridamole were measured in 23 patients starting within a week after the onset of cerebral ischemia. All patients had normal baseline platelet aggregation responses to four stimuli: arachidonate, epinephrine, adenosine diphosphate and collagen. The generation of thromboxane A2 by platelets, measured as serum thromboxane B2, was also normal. After 3 to 7 days of low dose aspirin therapy, platelet aggregation responses were suppressed to the extent observed with higher dosage aspirin. Serotonin release during platelet aggregation was inhibited by more than 95% and thromboxane B2 levels in clotted blood fell by more than 95%. Responses to aspirin treatment were similar in patients with transient ischemic attacks and in those with stroke and were also similar in both sexes. No differences in platelet responses were observed between patients receiving aspirin alone and aspirin plus dipyridamole. Thus 40 mg aspirin daily inhibited platelet responses as effectively as higher doses of aspirin in patients who had recent cerebral ischemia and showed a cumulative antiplatelet effect.     

Antiplatelet effects of combination therapy with low-dose aspirin and ticlopidine in cerebral ischemia

Antiplatelet effects of combination therapy with aspirin and ticlopidine were investigated in comparison with single aspirin or ticlopidine therapy in 62 patients with cerebral thrombosis or transient ischemic attack. The 14, 21 and 27 patients were given orally daily aspirin 300mg, ticlopidine 200mg and aspirin 81mg with ticlopidine 100mg, respectively. Various platelet function tests were performed before and a week after medication. They included platelet aggregation (PA) to adenosine diphosphate (ADP), arachidonic acid (AA) and platelet activating factor (PAF) with turbidimetry, plasma beta-thromboglobulin (beta TG), platelet factor 4(PF4), thromboxane B2(TXB2) and 6keto-prostaglandin-F1 alpha(6keto PGF1 alpha) with radioimmunoassay, bleeding time with Simplate device, and platelet survival and lysis with Indium-111-tropolone-labelled platelets. Aspirin inhibited PA to ADP and AA but not to PAF, while ticlopidine inhibited PA to ADP and PAF but not to AA. In contrast, aspirin with ticlopidine inhibited PA to all of these agonists despite their smaller doses used. Aspirin reduced plasma TXB2 but not beta TG or PF4, while ticlopidine reduced beta TG and PF4 but not TXB2. On the contrary, aspirin with ticlopidine reduced TXB2 as well as beta TG and PF4. 6keto PGF1 alpha tended to be reduced by aspirin 300mg alone but not by ticlopidine with or without aspirin 81mg. Bleeding time was significantly prolonged by aspirin or ticlopidine alone, although most prolongation was produced by combination of aspirin and ticlopidine. Platelet survival and lysis remained unaltered in 4 patients treated with aspirin or ticlopidine alone, whereas platelet survival was prolonged and platelet lysis was reduced in 4 patients treated with both aspirin and ticlopidine.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of clopidogrel besylate and clopidogrel hydrogensulfate on platelet aggregation in patients with coronary artery disease: a retrospective study

Background

Recently several alternative forms of the original clopidogrel hydrogensulfate (CHS) were spread worldwide. A large amount of such drugs turned out to be clopidogrel besylate (CB). Only three studies, involving healthy volunteers, investigated the antiplatelet effect of CB, whereas its attribute remained unexplored in the case of patients with cardiovascular diseases. This retrospective study aimed to evaluate the difference between the antiplatelet effects of two clopidogrel formulas, CHS and CB, on patients with coronary artery diseases.

Methods

Data of 150 patients with previous CHS treatment were investigated. According to the documentations, the CHS therapy was shifted to CB. 94 patients of the selected population received dual antiplatelet therapy, clopidogrel and aspirin. The antiplatelet effects of CHS and CB were compared by ADP induced platelet aggregation measurements using light transmission aggregometry.

Results

Irrespective of the therapeutic combinations the performed statistical investigations failed to show significant difference (p = 0.30) between the effect of CB (AGGmax_CB: 27.6 ± 13.7%) or CHS (AGGmax_CHS: 29.0 ± 15.3%) on the ADP induced platelet aggregation. Insignificant deviations were found in both forms of clopidogrel salts, either in the lack (AGGmax_CB : 32.5 ± 14,2%; AGGmax_CHS: 34,0 ± 16,1%; p = 0,29) or in the presence of aspirin (AGGmax_CB: 24.7 ± 12,5%; AGGmax_CHS: 26,0 ± 14,1%; p = 0,31).

Conclusion

Our results indicated that both CB and CHS had an identical inhibitory effect on ADP induced platelet aggregation in patients with cardiovascular diseases. Moreover their efficiency showed no overall significant difference in the case of dual antiplatelet therapy with aspirin as well. However there might be an inter- and intraindividual variability between the two clopidogrel formulas.     

Influence of renal function and platelet turnover on the antiplatelet effect of aspirin

Introduction

Kidney disease predisposes to cardiovascular events. This study investigated the influence of renal function and platelet turnover on the antiplatelet effect of aspirin in patients with coronary artery disease.

Materials and Methods

We included 124 aspirin-treated patients with coronary artery disease and normal to moderately reduced renal function. All tests were performed one hour after aspirin ingestion. Renal function was assessed using creatinine, estimated glomerular filtration rate (eGFR), and cystatin C. The antiplatelet effect of aspirin was evaluated using the VerifyNow® Aspirin assay and multiple electrode aggregometry (MEA, Multiplate®) induced by collagen (1.0 μg/mL) and arachidonic acid (1.0 mmol/L). Von Willebrand factor was measured as a marker of endothelial dysfunction. Platelet turnover was evaluated by measurements of immature, reticulated platelets.

Results

Renal function did not influence the antiplatelet effect of aspirin evaluated by MEA (r = − 0.2-0.09, p = 0.03-0.77) or the VerifyNow® (r = − 0.12-0.11, all p-values > 0.1). In contrast, renal function correlated inversely with von Willebrand factor levels (r_creatinine = 0.48, p < 0.0001; r_eGFR = − 0.46, p < 0.001; r_{cystatin C} = 0.54, p < 0.0001). The number of immature platelets correlated with platelet aggregation according to MEA (r = 0.20-0.39, all p-values < 0.03), but not according to VerifyNow® (r = − 0.07, p = 0.50).

Conclusions

A reduced antiplatelet effect of aspirin may be explained by an increased number of immature platelets. Moderately impaired renal function was associated with high levels of von Willebrand factor, but not with a reduced antiplatelet effect of aspirin.     

The effect of aspirin on endothelial progenitor cell biology: Preliminary investigation of novel properties

Atherosclerosis develops in an environment of endothelial injury and inflammation. Circulating endothelial progenitor cells (EPCs) are required for vascular repair and restoration of normal endothelial function. We tested the hypothesis that the nonselective cyclooxygenase (COX) inhibitor aspirin (ASA) exerts an effect on circulating EPCs.

Methods

As part of a larger study evaluating the effect of aspirin dose in primary and secondary prevention, subjects (n = 32) were assigned randomly to either 81 mg or 325 mg aspirin daily for two months, and circulating mononuclear cells were enumerated at the beginning of the study and after 2 months using fluorescent antibodies against CD34 and CD133 as well as based on aldehyde dehydrogenase (ALDH) activity. Brachial artery endothelial function via flow-mediated dilation (BAFMD) and light transmittance platelet aggregometry in response to physiologic agonists was also determined.

Results

Subjects taking aspirin at the time of study entry had a lower numbers of CD133+/34+ cells compared to those not previously exposed (0.01% vs. 0.05% of MNCs, P < 0.03). After 2 months, subjects randomized to 81 vs. 325 mg of ASA had no significant differences in the median numbers of EPCs, although mean numbers trended lower in the high dose group. Patients on chronic ASA therapy continued to have lower numbers of EPCs. Similar effects were observed in CD34 and CD 133 single-positive cells, as well as ALDH^br cells. BAFMD did not differ nor change significantly over time between aspirin dose groups. All patients had decreased ex vivo platelet aggregation in response to arachidonic acid and ADP stimulation.

Conclusions

Our preliminary studies suggest that aspirin exerts a time-dependent effect on circulating EPCs. Short-term exposure to differing doses of ASA had indeterminate effects on EPCs levels, suggesting that time of ASA exposure may play a more important role than dose. Determining the responsible mechanism(s) and the overall clinical relevance of these findings will require further investigation.     

Evaluation of laboratory methods routinely used to detect the effect of aspirin against new reference methods

Background

Aspirin, a commonly used antiplatelet agent, blocks platelet thromboxane A₂ (TXA₂) formation from arachidonic acid (AA) by acetylating platelet cyclooxygenase-1 (COX-1). Laboratory methods currently used to detect this antiplatelet effect of aspirin provide variable results. We have reported three methods that assess platelet COX-1 acetylation (inactivation) by aspirin and its direct consequences. The first and second assays use monoclonal anti-human-COX-1 antibodies that only detect acetylated (inactivated) COX-1 and active (non-acetylated) COX-1, respectively. The third method measures platelet production of TXB₂ (the stable metabolite of TXA₂) in vitro in response to AA. We compared the results of these three reference methods with other routinely used methods for assessing the functional consequences aspirin treatment.

Methods

108 healthy volunteers were treated with low-dose aspirin for 7 days. On day 7 following aspirin treatment COX-1 in the platelets was fully acetylated whereas only non-acetylated COX-1 was present in the day 0 platelets. Further, TXB₂ production by day 7 platelets was completely blocked. The following tests were performed on the samples obtained from study participants before and after seven days of aspirin treatment: PFA-100 closure time with collagen/epinephrine cartridge, VerifyNow® (VN) Aspirin Assay, platelet aggregation and ATP secretion using AA, ADP, epinephrine and collagen as agonists.

Results

Comparing the pre-treatment and day 7 values, methods that use AA as platelet agonist (AA-induced platelet aggregation/secretion and VN Aspirin Assay) showed high discriminative power. In contrast, results of the other tests showed considerable overlap between day 7 and day 0 values.

Conclusions

Only assays that clearly distinguish between acetylated and non-acetylated platelet COX-1 are useful for establishing the antiplatelet effect of aspirin. The other tests are not suitable for this purpose.     

Monitoring aspirin treatment in patients with thrombocytosis: comparison of the platelet function analyzer (PFA)-100 with optical aggregometry

Aspirin provides satisfactory protection against thrombotic episodes in essential thrombocythemia (ET), but at higher platelet counts has been less effective. Our aim was to compare the platelet function analyzer (PFA)-100 with optical aggregometry in order to determine a reliable method in monitoring aspirin's influence on platelet function in patients with thrombocytosis.We studied 36 patients with thrombocytosis. Sixteen of them, receiving aspirin, composed group A, while group B consisted of 20 patients not taking aspirin. In all patients, we compared the platelet function measured by classic optical aggregation tests with closure times (CT) obtained by the PFA-100.The definition of platelet responses as normal or pathological showed that PFA-100 collagen and/or epinephrine (CEPI) CTs and epinephrine-induced aggregometry is the pair of methods with the higher agreement in monitoring of platelet dysfunction due to ASA treatment (a = 94%). Satisfactory results were also obtained for group B (a = 81%). The comparison between PFA-100 CEPI CTs and arachidonic acid-induced aggregometry exhibited moderate agreement both in the total number of patients and in group A (a = 79% and 94%, respectively). PFA-100 collagen and/or ADP (CADP) CTs and ADP-induced aggregometry were not concordant.The PFA-100 system appears to be a reliable and rapid method in the assessment of aspirin's antiplatelet effect in patients with thrombocytosis. Regarding aggregometry, the selection of the inducer, its concentration and cut-off points is crucial in defining the response to antiaggregating agents. It still remains to determine whether there is any relevance between the measurements obtained by these methods and clinical outcome in thrombocythemic patients.     

Initial experiences with Multiplate for rapid assessment of antiplatelet agent activity in neurosurgical emergencies

Objective

As the population ages, physicians encounter a growing number of patients who are treated with antiplatelet agents and present with severe conditions requiring urgent neurosurgical therapy. Standard laboratory investigations are insufficient to evaluate platelet activity and furthermore, it is difficult to evaluate effects of haemostatic measures on platelet function. In this article we report our initial experiences with the point-of-care device Multiplate^® for assessment of platelet activity in neurosurgical emergencies on patients with a reported intake of antiplatelet medication.

Methods

Multiplate^® assessment of antiplatelet activity was carried out in 21 non-consecutive patients with a reported intake of antiplatelet medication (aspirin: n = 21, clopidogrel: n = 3, ticragrelor: n = 1) and urgent admission to our hospital because of conditions such as intracranial haemorrhage requiring urgent neurosurgical therapy. Analysis was repeated in order to evaluate the effectiveness of haemostatic drugs and platelet concentrate transfusion on platelet activity in six patients.

Results

No technical difficulties occurred and in all cases, results were obtained within 15 min. On admission, patients’ arachidonic acid induced platelet activity was reduced by 44.4 ± 33.5% (range: −79.7% to +44.3%) compared to the lower reference limit. Two patients had a normal platelet activity despite a reported intake of aspirin. Haemostatic measures significantly increased arachidonic acid induced platelet activity by 100 ± 66% (p < 0.005).

Conclusion

The Multiplate^® device allowed rapid assessment of antiplatelet agent activity and evaluation of haemostatic measures on platelet activity. Further studies with larger patient numbers are needed, but this device may represent a valuable tool to improve treatment modalities in patients treated with antiplatelet medication and conditions requiring urgent neurosurgical therapy.     

Post interventional cardiology urinary thromboxane correlates with PlateletMapping® detected aspirin resistance

Introduction

We have previously defined aspirin resistance detected by TEG PlateletMapping using arachidonic acid (AA). This aspirin resistance is observed as platelet activation (> 20%) by AA in whole blood, even though the isolated platelets are inhibited by aspirin. This platelet activation in whole blood is due to a transcellular pathway mediated by platelets and leukocytes.

Methods

To determine if this PlateletMapping assay of aspirin resistance on pre-procedure blood samples correlated with an in vivo response we assayed the first voided urine samples collected 2-8 hours post interventional cardiology procedures for 11-dehydro thromboxane B2.

Results and Conclusions

We detected 27 aspirin resistant patients out of a total of 81 (33%), in agreement with our previous study. All of these patients were on aspirin therapy, confirmed by a < 20% aggregation response to AA by light transmission platelet aggregometry using isolated platelet rich plasma. Aspirin resistant patients urine samples (14 out of a total of 60 patients analyzed) contained significantly (P = 0.008) higher 11-dehydro thromboxane B2 levels than the other 46 aspirin sensitive patients urine samples. Since our previous study implicated 12- and 15-lipoxygenases in this pathway, we also assayed for polymorphisms to determine any correlation with aspirin resistance. A correlation was found in a polymorphism affecting the lipoxygenase domain of platelet 12-lipoxygenase. This result indicates that aspirin resistance detected in whole blood by the TEG PlateletMapping assay correlates with a physiological consequence in terms of thromboxane formation. This is the first report of such a correlation.     

Pharmacodynamic assessment of a novel P2Y12 receptor antagonist in Japanese patients with coronary artery disease undergoing elective percutaneous coronary intervention

Introduction

Numerous reports have shown that prasugrel shows a rapid and consistent antiplatelet effect among European and US patients. Previous studies suggest that prasugrel might be expected to achieve an adequate antiplatelet effect in healthy Asian subjects, even at lower doses than those assessed in the TRITON-TIMI 38 study. In this study, the antiplatelet effect of prasugrel was evaluated in Japanese coronary artery disease (CAD) patients undergoing percutaneous coronary intervention (PCI).

Methods and results

Eighty-four patients were randomized into four treatment groups: prasugrel 10/2.5 mg (loading dose [LD]/maintenance dose [MD]), 15/3.75 mg or 20/5 mg, and clopidogrel 300/75 mg. The LD of each regimen was administered the day before PCI, followed by 28-day MD on aspirin background therapy (81-100 mg). Antiplatelet effects were evaluated by light transmission aggregometry and VASP assay.The mean inhibition of platelet aggregation (IPA) induced by 20 μM of adenosine diphosphate at 4 hours after LD was higher among the prasugrel 10/2.5 mg, 15/3.75 mg and 20/5 mg groups compared with the clopidogrel group (12.3%, 20.9%, 29.8% vs. 8.4%, respectively). The proportion of subjects with an IPA of < 10% on Day 28 was lower among the prasugrel 15/3.75 mg, and 20/5 mg groups than in the clopidogrel group (0%, 6.3% vs. 15.8%, respectively). No “major” or “clinically relevant non-major” bleeding was observed.

Conclusions

Prasugrel 15 mg LD/3.75 mg MD or higher doses was well tolerated and achieved a more rapid, higher and consistent antiplatelet effect than clopidogrel in Japanese CAD patients undergoing PCI.     

Renal function and aspirin resistance in patients with coronary artery disease

Aspirin resistance and chronic renal failure are both potentially important clinical issues in coronary artery disease. To test the hypothesis of a relationship between the two, we recruited 169 stable outpatients with proven coronary artery disease (myocardial infarction, coronary artery bypass grafting, intra-coronary stents) taking 75 mg aspirin daily. Blood was taken for light transmission aggregometry to agonists arachidonic acid (0.5 mg/mL) and adenosine diphosphate (10 μmol/L), for platelet marker soluble P selectin (enzyme linked immunosorbent assay), resting and stimulated expression of CD62P (flow cytometry) and for renal function (estimated glomerular filtration rate). The estimated glomerular filtration rate was lower when aspirin resistance was defined by response to arachidonic acid after 3, 5 and 7 minutes (approximately 30% of patients) (p < 0.021), and when defined by response to adenosine diphosphate after 3 minutes (approximately 17% of patients)(p = 0.015) compared to those who were sensitive to aspirin. Mean [standard deviation] soluble P selectin levels were 57 [23] ng/mL in 49 patients with aspirin resistance, and 50 [15] ng/mL in the 119 aspirin sensitive patients (p = 0.02). Estimated glomerular filtration rate correlated inversely with platelet CD62P expression at rest (r = − 0.22, p = 0.004), and when stimulated by arachidonic acid (r = − 0.21, p = 0.007) and by adenosine diphosphate (r = − 0.17, p = 0.023). Aspirin resistance was more than twice as prevalent in those with the greatest renal disease (50% of patients) compared to those with the best renal function (21.4%). Our data point to a weak relationship between worsening glomerular filtration rate and aspirin resistance. Nevertheless, we suspect that failure of patients to be fully responsive to aspirin may be important in the pathophysiology of thrombosis in renal dysfunction.     

Multi-parameter assessment of platelet inhibition and its stability during aspirin and clopidogrel therapy

Introduction

Poor response to antiplatelet drugs is associated with adverse outcomes. We assessed platelet inhibition and its stability and tested correlation and agreement between platelet function assays.

Methods

Peripheral blood from 58 patients on both aspirin and clopidogrel who underwent percutaneous coronary intervention (PCI) was collected at hospital discharge (visit-1) and at 30-90 days (visit-2). Platelet function was measured using light transmission aggregometry (LTA-AA and LTA-ADP), VerifyNow® (Aspirin; ARU and P2Y12; PRU), ex vivo TxB₂, urinary 11dhTxB₂, and VASP (PRI) assays. Data were analyzed as continuous, quartiles and binary. Patients were defined as aspirin poor responder (PR) with ARU ≥ 550, LTA-AA maximum ≥ 20%, TxB₂ ≥ 1 ng/mL or 11dhTxB₂ ≥ 1,500 pg/mg of creatinine and as clopidogrel PR with PRU ≥ 240, PRU ≥ 208, LTA-ADP maximum ≥ 40%, PRI ≥ 50%, or PRI ≥ 66%.

Results

Aspirin PR was 3-33% and clopidogrel PR was 10-35% in visit-1. LTA-AA, 11dhTxB_2, and all clopidogrel-response measures showed correlation and agreement between visit-1 and visit-2. The highest agreement between two visits was revealed by PRU ≥ 240 and PRI ≥ 66% (PRU-κ = 0.7, 95% CI = 0.47, 0.93; PRI-κ = 0.69, 95% CI = 0.42, 0.95, p-values < 0.001). Comparison of platelet function assays in a single visit (visit-1) revealed a poor correlation between LTA-AA and 11dhTxB₂ assays and no agreement among aspirin-response assays. The highest correlation and agreement were obtained between VerifyNow® P2Y12 and VASP assays (rho = 0.7, p-value < 0.001 and PRU ≥ 208-PRI-κ = 0.41-0.42, 95% CI = 0.13, 0.69, p-values < 0.001).

Conclusions

Platelet inhibition is stable during aspirin and clopidogrel treatment. Clopidogrel-response assays correlate and agree with each other better than aspirin-response assays.     

Benefit/risk profile of combined antiplatelet therapy with ticlopidine and aspirin

Ticlopidine (T) and aspirin (ASA) are two antiplatelet drugs both capable of prolonging bleeding time (BT), with a different mechanism of action. A synergism in BT prolongation has been reported and is currently considered an argument for not recommending their combination. However, a profound suppression of platelet function might be a desirable counterpart of a marked prolongation of BT, with a possible use in selected clinical situations. We therefore studied ex vivo platelet function (aggregation by ADP 0.5-1-2.5 microM; adrenaline 0.75-2.5 microM; collagen 1.5-150 micrograms/ml; arachidonic acid 1 mM; PAF 1 microM; adrenaline 0.17 microM + ADP 0.62 microM; serum thromboxane [( TX]B2 generation) and BT (Mielke) in 6 patients with stable coronary artery disease receiving such combination. Patients underwent sequential laboratory evaluations at baseline, after 7 days of T 250 mg b.i.d., before and after the intravenous administration of ASA 500 mg, respectively, and, finally, after a minimum of 7 days of sole ASA oral administration (50 mg/day). The experimental design, therefore, allowed a comparison of T and ASA effects (2nd and 4th evaluation), and an assessment of the combination effect (3rd evaluation). Platelet aggregation in response to all doses of ADP was depressed more by T than by ASA. Conversely, responses to adrenaline, and arachidonate were affected more by ASA than by T. For all other agents, differences were not significant. T + ASA combination was more effective (p less than 0.05) than either treatment alone in depressing responses to high-dose collagen (% over control, mean +/- SEM: T: 95 +/- 3; ASA: 96 +/- 5; T + ASA: 89 +/- 4).(ABSTRACT TRUNCATED AT 250 WORDS)     

Combination treatment with dipyridamole, aspirin, and tPA in an embolic model of stroke in rats

Antithrombotic therapy has been shown to be effective in preventing secondary strokes. Inhibition of platelet function may reduce formation of thrombi thereby reducing the incidence of stroke. However, stronger inhibition of platelets is correlated with increased risk of bleeding events. The purpose of this study was to test the protective effects of combination therapy with dipyridamole and acetylsalicylic acid (ASA) in comparison to ASA alone, and whether such combination treatment may produce any added benefits when tissue plasminogen activator (tPA) treatment is also used. The study was divided into three parts. In part A, effect of antiplatelets on infarct volume was assessed. In part B, perfusion deficits were measured. In part C, efficacy of antiplatelet therapy in combination with tPA was assessed. In part A, dipyridamole and aspirin treatment significantly reduced infarct volume (P<0.05). In part B, treatment with dipyridamole significantly reduced the perfusion deficits as compared to control (P<0.05). In part C, dipyridamole plus tPA or dipyridamole and aspirin plus tPA significantly decreased infarct volume as compared to tPA alone (P<0.05). The present study suggests that there is significant protection with dipyridamole as both infarct volume and perfusion deficits are significantly reduced. Dipyridamole with tPA also significantly reduced infarct volume as compared to tPA alone. Our data suggests that higher doses of antithrombotic therapy with dipyridamole offer best neuroprotection.