Inhibition of platelet aggregation by aspirin progressively decreases in long-term treated patients

Obstructive Sleep Apnea, Platelet Aggregation, and Cardiovascular Risk

BACKGROUND

Although related, the precise mechanisms linking obstructive sleep apnea (OSA) and cardiovascular disease (CVD) are unclear. Platelets are mediators of CVD risk and thrombosis and prior studies suggested associations of OSA and platelet activity. The aim of this study is to assess the link between OSA, platelet activity, and CVD-related risk factors.

METHODS AND RESULTS

We studied the association of OSA-measures and platelet aggregation in participants dually enrolled in the SHHS (Sleep Heart and Health Study) and FHS (Framingham Heart Study). We applied linear regression models with adjustment for demographic and clinical covariates and explored interactions with OSA and CVD-related factors, including age, sex, body mass index, hypertension, OSA diagnosis (apnea-hypopnea index 4%≥5), and aspirin use. Our final sample was of 482 participants (60 years [14.00], 50.4% female). No associations were observed between apnea-hypopnea index 4% and platelet aggregation in the main sample. Stratified analysis revealed an association in aspirin users (n=65) for our primary exposure (apnea-hypopnea index 4%, β=0.523; P<0.001; n=65), and secondary exposures: hypoxic burden (β=0.358; P<0.001), minimum saturation (β=-0.519; P=0.026), and oxygen desaturation index 3% (β=74.672; P=0.002). No associations were detected in nonaspirin users (n=417).

CONCLUSIONS

No associations were detected between OSA and platelet aggregation in a community sample. Our finding that OSA associates with increased platelet aggregation in the aspirin group, most of whom use it for primary prevention of CVD, suggests that platelet aggregation may mediate the adverse impact of OSA on vascular health in individuals with existing CVD risk, supporting further investigation.

Does one size really fit all? The case for personalized antiplatelet therapy in interventional cardiology

Cardiovascular disease is the leading cause of death worldwide. Dual antiplatelet therapy (DAPT), with aspirin plus a P2Y12 inhibitor, is currently recommended as a default for patients after acute coronary syndrome (ACS) and following percutaneous coronary intervention (PCI). However, controversies arise over the role of aspirin, the optimal duration of DAPT after drug-eluting stent (DES) implantation, the choice of P2Y12 inhibitor and the variability in individual responses to antiplatelet agents. Recent data indicate that monotherapy with a P2Y12 inhibitor may have adequate anti-ischemic effects with lower bleeding risk. Additionally, discrepancies in DAPT duration recommendations and the optimal P2Y12 inhibitor, provides more uncertainty. We ask the question "does one size really fits all?" or should a more personalized strategy should be implemented.

Study on the mechanism of MDSC-platelets and their role in the breast cancer microenvironment

Myeloid-derived suppressor cells (MDSCs) are key immunosuppressive cells in the tumor microenvironment (TME) that play critical roles in promoting tumor growth and metastasis. Tumor-associated platelets (TAPs) help cancer cells evade the immune system and promote metastasis. In this paper, we describe the interaction between MDSCs and TAPs, including their generation, secretion, activation, and recruitment, as well as the effects of MDSCs and platelets on the generation and changes in the immune, metabolic, and angiogenic breast cancer (BC) microenvironments. In addition, we summarize preclinical and clinical studies, traditional Chinese medicine (TCM) therapeutic approaches, and new technologies related to targeting and preventing MDSCs from interacting with TAPs to modulate the BC TME, discuss the potential mechanisms, and provide perspectives for future development. The therapeutic strategies discussed in this review may have implications in promoting the normalization of the BC TME, reducing primary tumor growth and distant lung metastasis, and improving the efficiency of anti-tumor therapy, thereby improving the overall survival (OS) and progression-free survival (PFS) of patients. However, despite the significant advances in understanding these mechanisms and therapeutic strategies, the complexity and heterogeneity of MDSCs and side effects of antiplatelet agents remain challenging. This requires further investigation in future prospective cohort studies.

Studying the efficacy of antiplatelet drugs on atherosclerosis by optofluidic imaging on a chip

Vascular stenosis caused by atherosclerosis instigates activation and aggregation of platelets, eventually resulting in thrombus formation. Although antiplatelet drugs are commonly used to inhibit platelet activation and aggregation, they unfortunately cannot prevent recurrent thrombotic events in patients with atherosclerosis. This is partially due to the limited understanding of the efficacy of antiplatelet drugs in the complex hemodynamic environment of vascular stenosis. Conventional methods for evaluating the efficacy of antiplatelet drugs under stenosis either fail to simulate the hemodynamic environment of vascular stenosis characterized by high shear stress and recirculatory flow or lack spatial resolution in their analytical techniques to statistically identify and characterize platelet aggregates. Here we propose and experimentally demonstrate a method comprising an in vitro 3D stenosis microfluidic chip and an optical time-stretch quantitative phase imaging system for studying the efficacy of antiplatelet drugs under stenosis. Our method simulates the atherogenic flow environment of vascular stenosis while enabling high-resolution and statistical analysis of platelet aggregates. Using our method, we distinguished the efficacy of three antiplatelet drugs, acetylsalicylic acid (ASA), cangrelor, and eptifibatide, for inhibiting platelet aggregation induced by stenosis. Specifically, ASA failed to inhibit stenosis-induced platelet aggregation, while eptifibatide and cangrelor showed high and moderate efficacy, respectively. Furthermore, we demonstrated that the drugs tested also differed in their efficacy for inhibiting platelet aggregation synergistically induced by stenosis and agonists (e.g., adenosine diphosphate, and collagen). Taken together, our method is an effective tool for investigating the efficacy of antiplatelet drugs under vascular stenosis, which could assist the development of optimal pharmacologic strategies for patients with atherosclerosis.

Ticagrelor-Aspirin Versus Clopidogrel-Aspirin Among CYP2C19 Loss-of-Function Carriers With Minor Stroke or Transient Ischemic Attack in Relation to Renal Function: A Post Hoc Analysis of the CHANCE-2 Trial

BACKGROUND

Evidence on the risk-benefit ratio of dual antiplatelet therapies among patients with stroke and impaired renal function is limited and inconsistent.

OBJECTIVE

To investigate the effect of renal function on the efficacy and safety of ticagrelor-aspirin versus clopidogrel-aspirin treatment.

DESIGN

Post hoc analysis of a multicenter, randomized, double-blind, placebo-controlled trial. (ClinicalTrials.gov: NCT04078737).

SETTING

202 centers in China.

PATIENTS

CYP2C19 loss-of-function allele carriers with minor stroke or transient ischemic attack.

INTERVENTION

Ticagrelor-aspirin and clopidogrel-aspirin.

MEASUREMENTS

Renal function was evaluated by estimated glomerular filtration rate (eGFR) levels. The primary efficacy and safety outcomes were recurrent stroke and severe or moderate bleeding within 90 days, respectively.

RESULTS

Among 6378 patients, 4050 (63.5%) had normal (eGFR ≥90 mL/min/1.73 m²), 2010 (31.5%) had mildly decreased (eGFR 60 to 89 mL/min/1.73 m²), and 318 (5.0%) had moderately to severely decreased (eGFR <60 mL/min/1.73 m²) renal function. The corresponding differences in recurrent stroke between ticagrelor-aspirin and clopidogrel-aspirin for normal, mildly decreased, and moderately to severely decreased renal function was -2.8 percentage points (95% CI, -4.4 to -1.3 percentage points) (hazard ratio [HR], 0.63 [CI, 0.49 to 0.81]), -0.2 percentage point (CI, -2.4 to 2.0 percentage points) (HR, 0.98 [CI, 0.69 to 1.39]), and 3.7 percentage points (CI, -2.3 to 10.1 percentage points) (HR, 1.31 [CI, 0.48 to 3.55]), respectively. Rates of severe or moderate bleeding did not substantially differ by treatment assignments across eGFR categories.

LIMITATION

Renal function was only evaluated by using eGFR, and the proportion of patients with severely decreased renal function was low.

CONCLUSION

Patients with normal, rather than impaired, renal function received greater benefit from ticagrelor-aspirin versus clopidogrel-aspirin.

PRIMARY FUNDING SOURCE

Ministry of Science and Technology of the People's Republic of China.

Comparison of Different Laboratory Tests to Identify “Aspirin Resistance” and Risk of Vascular Events among Ischaemic Stroke Patients: A Double-Blind Study

“Aspirin resistance” (AR) is associated with increased risk of vascular events. We aimed to compare different platelet function tests used in identifying AR and assess their implications on clinical outcome. We performed platelet aggregation studies on non-cardioembolic ischaemic stroke patients taking aspirin 100 mg/day and 30 non-stroke controls. Data were collected on demographics, vascular risk factors, and concomitant medications. Cut-offs for AR were (1) light transmission aggregometry (LTA) of ≥20% using arachidonic acid (AA), ≥70% using ADP, or ≥60% using collagen; and (2) VerifyNow® assay ≥ 550 ARU. Telephone follow-ups were conducted by study staff blinded to AR status to ascertain the occurrence of vascular outcomes (stroke, myocardial infarction, amputation, death). A total of 113 patients were recruited, mean age 65 ± 8 years, 47% women, 45 ± 15 days from index stroke. 50 (44.3%, 95% CI 34.9–53.9) had AR on at least 1 test. Frequency of AR varied from 0% to 39% depending on method used and first vs. recurrent stroke. There were strong correlations between LTA AA, VerifyNow® and Multiplate® ASPItest (r = 0.7457–0.8893), but fair to poor correlation between LTA collagen and Multiplate® COLtest (r = 0.5887) and between LTA ADP and Multiplate® ADPtest (r = 0.0899). Of 103 patients with a mean follow up of 801 ± 249 days, 10 (9.7%) had vascular outcomes, of which six had AR by LTA-ADP. AR by LTA-ADP is associated with increased risk of vascular outcome (p = 0.034). Identification of AR is not consistent across different platelet function tests. LTA of ≥70% using 10 µM ADP in post-stroke patients taking aspirin is associated with increased risk of vascular outcome.

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 Inhibition by Low-Dose Acetylsalicylic Acid Reduces Neuroinflammation in an Animal Model of Multiple Sclerosis

Aside from the established immune-mediated etiology of multiple sclerosis (MS), compelling evidence implicates platelets as important players in disease pathogenesis. Specifically, numerous studies have highlighted that activated platelets promote the central nervous system (CNS)-directed adaptive immune response early in the disease course. Platelets, therefore, present a novel opportunity for modulating the neuroinflammatory process that characterizes MS. We hypothesized that the well-known antiplatelet agent acetylsalicylic acid (ASA) could inhibit neuroinflammation by affecting platelets if applied at low-dose and investigated its effect during experimental autoimmune encephalomyelitis (EAE) as a model to study MS. We found that oral administration of low-dose ASA alleviates symptoms of EAE accompanied by reduced inflammatory infiltrates and less extensive demyelination. Remarkably, the percentage of CNS-infiltrated CD4+ T cells, the major drivers of neuroinflammation, was decreased to 40.98 ± 3.28% in ASA-treated mice compared to 56.11 ± 1.46% in control animals at the disease maximum as revealed by flow cytometry. More interestingly, plasma levels of thromboxane A2 were decreased, while concentrations of platelet factor 4 and glycoprotein VI were not affected by low-dose ASA treatment. Overall, we demonstrate that low-dose ASA could ameliorate the platelet-dependent neuroinflammatory response in vivo, thus indicating a potential treatment approach for MS.

The emergent phenomenon of aspirin resistance: insights from genetic association studies

Despite the clinical benefits of aspirin, the interindividual variation in response to this antiplatelet drug is considerable. The manifestation of aspirin resistance (AR) is frequently observed, although this complex process remains poorly understood. While AR etiology is likely to be multifactorial, genetic factors appear to be preponderant. According to several genetic association studies, both genome-wide and candidate gene studies, numerous SNPs in cyclooxygenase, thromboxane and platelet receptors-related genes have been identified as capable of negatively affecting aspirin action. Thus, it is essential to understand the clinical relevance of AR-related SNPs as potential predictive and prognostic biomarkers as they may be essential to defining the AR phenotype.

Resistance to Antiplatelet Therapy Is Associated With Symptoms of Cerebral Ischemia in Carotid Artery Disease

Background:

Platelet inhibitory therapy is prescribed to prevent arterial thromboembolism in patients with atherosclerotic disease. Although taken by millions of people, around 30% are resistant to the treatment they are being prescribed.

Aims:

To determine whether symptoms of cerebral ischemia, or pre-operative cerebral emboli, in patients admitted for a carotid endarterectomy were associated with resistance to aspirin or clopidogrel.

Methods:

Venous blood from 133 patients immediately before carotid endarterectomy (CEA) was analyzed for resistance to aspirin and clopidogrel by multiplate impedance aggregometry. The number of emboli/hour entering the ipsilateral middle cerebral artery was counted by transcranial Doppler (TCD) on the day before surgery in 33 of these patients.

Results:

Resistance was found in 21 (26.3%) of 100 patients taking aspirin and 14 (42%) of 33 taking clopidogrel. Mean (sd) residual platelet aggregation was significantly higher at 41.9(32) Au in patients who had suffered recent symptoms of cerebral ischemia compared with 30.8(16) Au in asymptomatic patients (p = 0.012). Residual platelet aggregation also correlated significantly with the number of emboli/hour counted by TCD in the ipsilateral middle cerebral artery (r = 0.45, p = 0.009).

Conclusion:

Antiplatelet resistance was associated with the frequency of cerebral emboli and recent symptoms of cerebral ischemia in patients with carotid disease. Definitive clinical studies are needed to explore whether testing for antiplatelet resistance should be undertaken routinely in patients starting platelet inhibitory therapy for cardiovascular disease.

Influence of Sex on Platelet Reactivity in Response to Aspirin

Background There are sex differences in the efficacy and safety of aspirin for the prevention of myocardial infarction and stroke. Whether this is explained by underlying differences in platelet reactivity and aspirin response remains poorly understood. Methods and Results Healthy volunteers (n=378 208 women) and patients with coronary artery disease or coronary artery disease risk factors (n=217 112 women) took aspirin for 4 weeks. Light transmittance aggregometry using platelet-rich plasma was used to measure platelet reactivity in response to epinephrine, collagen, and ADP at baseline, 3 hours after the first aspirin dose, and after 4 weeks of daily aspirin therapy. A subset of patients underwent pharmacokinetic and pharmacodynamic assessment with levels of salicylate and cyclooxygenase-1-derived prostaglandin metabolites and light transmittance aggregometry in response to arachidonic acid and after ex vivo exposure to aspirin. At baseline, women had increased platelet aggregation in response to ADP and collagen. Innate platelet response to aspirin, assessed with ex vivo aspirin exposure of baseline platelets, did not differ by sex. Three hours after the first oral aspirin dose, platelet aggregation was inhibited in women to a greater degree in response to epinephrine and to a lesser degree with collagen. After 4 weeks of daily therapy, despite higher salicylate concentrations and greater cyclooxygenase-1 inhibition, women exhibited an attenuation of platelet inhibition in response to epinephrine and ADP. Conclusions We observed agonist-dependent sex differences in platelet responses to aspirin. Despite higher cyclooxygenase-1 inhibition, daily aspirin exposure resulted in a paradoxical attenuation of platelet inhibition in response to epinephrine and ADP over time in women but not in men.

Bifidobacteriumbreve Bif195 Protects Against Small-Intestinal Damage Caused by Acetylsalicylic Acid in Healthy Volunteers

BACKGROUND & AIMS

Enteropathy and small-intestinal ulcers are common adverse effects of nonsteroidal anti-inflammatory drugs such as acetylsalicylic acid (ASA). Safe, cytoprotective strategies are needed to reduce this risk. Specific bifidobacteria might have cytoprotective activities, but little is known about these effects in humans. We used serial video capsule endoscopy (VCE) to assess the efficacy of a specific Bifidobacterium strain in healthy volunteers exposed to ASA.

METHODS

We performed a single-site, double-blind, parallel-group, proof-of-concept analysis of 75 heathy volunteers given ASA (300 mg) daily for 6 weeks, from July 31 through October 24, 2017. The participants were randomly assigned (1:1) to groups given oral capsules of Bifidobacterium breve (Bif195) (≥5 × 10¹⁰ colony-forming units) or placebo daily for 8 weeks. Small-intestinal damage was analyzed by serial VCE at 6 visits. The area under the curve (AUC) for intestinal damage (Lewis score) and the AUC value for ulcers were the primary and first-ranked secondary end points of the trial, respectively.

RESULTS

Efficacy data were obtained from 35 participants given Bif195 and 31 given placebo. The AUC for Lewis score was significantly lower in the Bif195 group (3040 ± 1340 arbitrary units) than the placebo group (4351 ± 3195) (P = .0376). The AUC for ulcer number was significantly lower in the Bif195 group (50.4 ± 53.1 arbitrary units) than in the placebo group (75.2 ± 85.3 arbitrary units) (P = .0258). Twelve adverse events were reported from the Bif195 group and 20 from the placebo group. None of the events was determined to be related to Bif195 intake.

CONCLUSIONS

In a randomized, double-blind trial of healthy volunteers, we found oral Bif195 to safely reduce the risk of small-intestinal enteropathy caused by ASA. ClinicalTrials.gov no: NCT03228589.

Optimal Duration of Aspirin Plus Clopidogrel After Ischemic Stroke or Transient Ischemic Attack

Background and Purpose- The role of aspirin plus clopidogrel (A+C) therapy compared with aspirin monotherapy in patients presenting with acute ischemic stroke (IS) or transient ischemic attack remains uncertain. We conducted this study to determine the optimal period of efficacy and safety of A+C compared with aspirin monotherapy. Methods- Ten randomized controlled trials (15 434 patients) were selected using MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials (CENTRAL) (inception June 2018) comparing A+C with aspirin monotherapy in patients with transient ischemic attack or IS. The primary efficacy outcome was recurrent IS, and the primary safety outcome was major bleeding. The secondary outcomes were major adverse cardiovascular events (composite of stroke, myocardial infarction, and cardiovascular mortality) and all-cause mortality. We stratified analysis based on the short- (≤1 month), intermediate- (≤3 month), and long-term (>3 month) A+C therapy. Effects were estimated as relative risk (RR) with 95% CI. Results- A+C significantly reduced the risk of recurrent IS at short-term (RR, 0.53; 95% CI, 0.37-0.78) and intermediate-term (RR, 0.72; 95% CI, 0.58-0.90) durations. Similarly, major adverse cardiovascular event was significantly reduced by short-term (RR, 0.68; 95% CI, 0.60-0.78) and intermediate-term (RR, 0.76; 95% CI, 0.61-0.94) A+C therapy. However, long-term A+C did not yield beneficial effect in terms of recurrent IS (RR, 0.81; 95% CI, 0.63-1.04) and major adverse cardiovascular events (RR, 0.87; 95% CI, 0.71-1.07). Intermediate-term (RR, 2.58; 95% CI, 1.19-5.60) and long-term (RR, 1.87; 95% CI, 1.36-2.56) A+C regimens significantly increased the risk of major bleeding as opposed to short-term A+C (RR, 1.82; 95% CI, 0.91-3.62). Excessive all-cause mortality was limited to long-term A+C (RR, 1.45; 95% CI, 1.10-1.93). Conclusions- Short-term A+C is more effective and equally safe in comparison to aspirin alone in patients with acute IS or transient ischemic attack.

Platelet miRNA-26b down-regulates multidrug resistance protein 4 in patients on chronic aspirin treatment

BACKGROUND

Multidrug resistance protein-4 (MRP4) is an ATP binding cassette membrane transporter, actively involved in the efflux of important pharmacological and physiological molecules. Recently, its over-expression has been associated with reduced aspirin (ASA) efficacy after by-pass surgery. MicroRNAs (miRNAs) are small molecules of non-coding RNA involved in the regulation of many physiological and pathophysiological pathways, are abundant in platelets, and can be modulated by several drugs. In the present study, we assessed the role of platelet miRNAs in modulating MRP4 function in response to ASA.

METHODS

MRP4 mRNA expression has been analyzed by RealTime PCR in platelets from patients on chronic ASA treatment versus a control group. A panel of miRNAs was run on the pool of each cohort. MiRNAs validation was performed by RealTime PCR. To verify whether MRP4 is the target of miR-26b also in platelets, miR-26b was transfected in platelet and DAMI cells with miRNA mimic technology. MRP4 expression was evaluated by flow cytometry and western blotting.

RESULTS

We observed a higher MRP4 mRNA expression in platelets of patients under ASA treatment compared to the control group (p<0.005). MiR-26b was found significantly down-regulated in patients on ASA treatment as compared to control group (P < 0.005) and this was validated by RealTime PCR. MiR-26b transfection in platelets was associated to a significant down-regulation of MRP4 expression (p<0.005). MiR-26b transfection in DAMI cells was associated to a significant reduction of MRP4 mRNA and protein level (P < 0.05).

CONCLUSION

We found that miR-26b is down-regulated in platelets in patients on chronic ASA treatment. Importantly, miR-26b can specifically downregulate MRP4. Thus, miR-26b seems to be involved in MRP4 modulation and may contribute to ASA resistance.

Anticoagulant mechanism, pharmacological activity, and assessment of preclinical safety of a novel fibrin(ogen)olytic serine protease from leaves of Leucas indica

The harnessing of medicinal plants containing a plethora of bioactive molecules may lead to the discovery of novel, potent and safe therapeutic agents to treat thrombosis-associated cardiovascular diseases. A 35 kDa (m/z 34747.5230) serine protease (lunathrombase) showing fibrin(ogen)olytic activity and devoid of N- and O- linked oligosaccharides was purified from an extract of aqueous leaves from L. indica. The LC-MS/MS analysis, de novo sequencing, secondary structure, and amino acid composition determination suggested the enzyme’s novel characteristic. Lunathrombase is an αβ-fibrinogenase, demonstrating anticoagulant activity with its dual inhibition of thrombin and FXa by a non-enzymatic mechanism. Spectrofluorometric and isothermal calorimetric analyses revealed the binding of lunathrombase to fibrinogen, thrombin, and/or FXa with the generation of endothermic heat. It inhibited collagen/ADP/arachidonic acid-induced mammalian platelet aggregation, and demonstrated antiplatelet activity via COX-1 inhibition and the upregulation of the cAMP level. Lunathrombase showed in vitro thrombolytic activity and was not inhibited by endogenous protease inhibitors α₂ macroglobulin and antiplasmin. Lunathrombase was non-cytotoxic to mammalian cells, non-hemolytic, and demonstrated dose-dependent (0.125–0.5 mg/kg) in vivo anticoagulant and plasma defibrinogenation activities in a rodent model. Lunathrombase (10 mg/kg) did not show toxicity or adverse pharmacological effects in treated animals.

Platelet-related biomarkers and their response to inhibition with aspirin and p2y12-receptor antagonists in patients with acute coronary syndrome

The PLATelet inhibition and patient Outcomes (PLATO) trial showed that treatment with ticagrelor reduced the rate of death due to vascular causes, myocardial infarction and stroke when compared to clopidogrel in patients with ST-elevation or non-ST-elevation acute coronary syndrome (ACS). While the comparative benefit of ticagrelor over clopidogrel increased over time, event rates accrued in both groups during the study period. The purpose of our biomarker-based exploratory analysis was to determine whether long-term platelet inhibition may be associated with platelet adaptation. A sample of 4000 participants from the PLATO trial also consented to participate in a prospectively designed biomarker substudy. Blood samples were procured at baseline, immediately prior to hospital discharge and at 1 and 6 months. Markers of platelet activity, including platelet count, serum CD40-ligand and soluble P-selectin were analyzed. Mean levels were compared at discharge, 1 and 6 months following study drug initiation-first for all patients and subsequently stratified by treatment group. A linear mixed model was used to estimate the short-term change rate (baseline to 1 month) and long-term change rate (1-6 months) for each biomarker. A Cox proportional hazards model was used to calculate hazard ratios for each change in biomarker over the two time periods examined: baseline to 1 month and 1 to 6 months. Prior to randomized treatment (baseline), sCD40 ligand and sP-selectin levels were elevated above the normal range of the assay (0.39 and 33.5 µg/L, respectively). The mean level of each biomarker was significantly different at 1 month compared to baseline (p < 0.0001). When stratified by treatment group, at 1 month patients treated with ticagrelor had a larger increase in platelet count compared to those treated with clopidogrel (p < 0.0001). Similarly, when comparing biomarker levels for all patients at 6 months with those at 1 month, each differed significantly (p < 0.05). There was no significant difference between treatment groups during this time period. The rate of change for both platelet count and sP-selectin were significantly different between baseline and 1 month when compared to the 1 to 6-month time period (p < 0.0001). When comparing treatment groups, the rate of increase in platelets from baseline to 1 month was greater for patients treated with ticagrelor (p < 0.0001). This was no longer observed in the 1 to 6-month interval. Using a Cox proportional hazard model, the increase in platelet count from 1 to 6 months was associated with ischemic-thrombotic events, while sCD40 ligand decrease from 1 to 6 months was associated with hemorrhagic events. There were no differences between treatment groups for the associations with clinical endpoints. Dynamic changes in platelet count, sCD-40 ligand and sP-selectin occur over time among patients with ACS. Platelet-directed therapy with a P2Y₁₂ receptor inhibitor in combination with aspirin modestly impacts the expression of these biomarkers. Platelet count and sCD40 ligand may offer modest overall predictive value for future ischemic-thrombotic or hemorrhagic clinical events, respectively. The existence of a platelet adaptome and its overall clinical significance among patients at risk for thrombotic events will require a more in-depth and platelet-biology specific investigation.

Role of Aspirin in Breast Cancer Survival

Chemotherapy and hormonal therapy have significantly decreased breast cancer mortality, although with considerable side effects and financial costs. In the USA, over three million women are living after a breast cancer diagnosis and are eager for new treatments that are low in toxicity and cost. Multiple observational studies have reported improved breast cancer survival with regular aspirin use. Furthermore, pooled data from five large randomized trials of aspirin for cardiovascular disease showed that subjects on aspirin had decreased risk of cancer mortality and decreased risk of metastatic cancer. Although the potential mechanism for aspirin preventing breast cancer is not known, possible pathways may involve platelets, inflammation, cyclooxygenase (COX) 2, hormones, or PI3 kinase. This review article summarizes the current epidemiologic and clinical trial evidence as well as possible underlying mechanisms that justify current phase III randomized trials of aspirin to improve breast cancer survival.

Early time course of major bleeding on antiplatelet therapy after TIA or ischemic stroke

Objective

To study the early time course of major bleeding and its subtypes in patients with cerebral ischemia on dual and single antiplatelet therapy.

Methods

We performed a post hoc analysis on individual patient data from 6 randomized clinical trials (Clopidogrel Versus Aspirin in Patients at Risk of Ischaemic Events [CAPRIE], Second European Stroke Prevention Study [ESPS-2], Management of Atherothrombosis With Clopidogrel in High-Risk Patients [MATCH], Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization, Management, and Avoidance [CHARISMA], European/Australasian Stroke Prevention in Reversible Ischaemia Trial [ESPRIT], and Prevention Regimen for Effectively Avoiding Second Strokes [PRoFESS]) including 45,195 patients with a TIA or noncardioembolic ischemic stroke. We studied incidence rates of bleeding per antiplatelet regimen stratified by time from randomization (≤30, 31–90, 91–180, 181–365, >365 days). We calculated incidence rates per trial and pooled estimates with random-effects meta-analysis. We performed Poisson regression to assess differences between time periods with adjustment for age and sex.

Results

The incidence of major bleeding on aspirin plus clopidogrel and aspirin plus -dipyridamole was highest in the first 30 days, 5.8 and 4.9 per 100 person-years, respectively, and was significantly higher than at 31 to 90 days (rate ratio 1.98, 95% confidence interval 1.16–3.40 for aspirin plus clopidogrel; rate ratio 1.94, 95% confidence interval 1.24–3.03 for aspirin plus dipyridamole). Incidence rates on aspirin and clopidogrel monotherapy were 2.8 and 2.5 per 100 person-years, respectively, in the first 30 days, with no significant change over time. The time course was similar for gastrointestinal bleeds. There was no early excess of intracranial hemorrhage in patients on either dual or single antiplatelet therapy.

Conclusion

Dual antiplatelet therapy is associated with high early risks of major and gastrointestinal bleeding that decline after the first month in trial cohorts.

The N-terminal-truncated recombinant fibrin(ogen)olytic serine protease improves its functional property, demonstrates in vivo anticoagulant and plasma defibrinogenation activity as well as pre-clinical safety in rodent model

An N-terminal truncated fibrino(geno)lytic serine protease gene encoding a ~42kDa protein from Bacillus cereus strain AB01 was produced by error prone PCR, cloned into pET19b vector, and expressed in E5 coli BL21 DE3 cells. The deletion of 24 amino acid residues from N-terminal of wild-type Bacifrinase improves the catalytic activity of [Bacifrinase (ΔN24)]. The anticoagulant potency of [Bacifrinase (ΔN24)] was comparable to Nattokinase and Warfarin and results showed that its anticoagulant action is contributed by progressive defibrinogenation and antiplatelet activities. Nonetheless, at the tested concentration of 2.0μM [Bacifrinase (ΔN24)] did not show in vitro cytotoxicity or chromosomal aberrations on human embryonic kidney cells-293 (HEK-293) and human peripheral blood lymphocytes (HPBL) cells. [Bacifrinase (ΔN24)], at a dose of 2mg/kg, did not show toxicity, adverse pharmacological effects, tissue necrosis or hemorrhagic effect after 72h of its administration in Swiss albino mice. However, at the tested doses of 0.125 to 0.5mg/kg, it demonstrated significant in anticoagulant effect as well as defibrinogenation after 6h of administration in mice. We propose that [Bacifrinase (ΔN24)] may serve as prototype for the development of potent drug to prevent hyperfibrinogenemia related disorders.

Increased platelet aggregation and serum thromboxane levels in aspirin-treated patients with prior myocardial infarction

The antiplatelet effect of aspirin displays considerable inter-individual variability. We investigated the antiplatelet effect of aspirin in patients with coronary artery disease on aspirin mono-therapy with and without prior myocardial infarction (MI). Further, we investigated whether the effect of aspirin differed between patients with and without aspirin use at the time of MI onset. We performed a study on 231 patients, including 171 with prior MI. Among patients with only one prior MI (116 patients), 59 patients were on aspirin at the time of MI onset. All patients received 75 mg aspirin as mono-therapy. Platelet aggregation was assessed by multiple electrode aggregometry (Multiplate®) and Verify -Now®, and platelet activation was evaluated by soluble P-selectin. Furthermore, we measured serum thromboxane B2. MI patients had higher median platelet aggregation levels than patients without prior MI when evaluated by Multiplate® (parachidonic acid<0.0001, pcollagen=0.20). This was not supported by VerifyNow®. Furthermore, MI patients had higher median serum thromboxane B2 levels than patients without prior MI (p=0.01). Patients on aspirin before MI onset had significantly higher median aggregation levels compared with MI patients not on aspirin when evaluated by Multiplate® (pcollagen=0.02) and VerifyNow® (p<0.0001). In conclusion, patients with prior MI had higher platelet aggregation levels than patients without prior MI when evaluated by Multiplate®, despite same aspirin dose and optimal compliance. Serum thromboxane B2 levels were higher in MI patients than in patients without prior MI. Finally, patients on aspirin before MI onset had higher aggregation levels compared with patients not on aspirin.

High residual platelet reactivity (HRPR) for adenosine diphosphate (ADP) stimuli is a determinant factor for long-term outcomes in acute ischemic stroke with anti-platelet agents: The meaning of HRPR after ADP might be more prominent in large atherosclerotic infarction than other subtypes of AIS

High residual platelet activation (HRPA) after ADP stimuli has associated with recurrent vascular events in acute atherothrombosis with the use of antiplatelet agents (APAs). However, there has been little evidence supporting this association in acute ischemic stroke (AIS). In this study, we evaluated the influences of HRPR after ADP stimuli on the 1-year incidence of recurrent cardiovascular events and mortality in AIS with APAs. We conducted an observational, referral center cohort study on 968 AIS patients with APAs from January 2010 to December 2013 who were evaluated using optical platelet aggregometry (OPA). All patients received the dual APA combination of aspirin and clopidogrel or aspirin alone. We evaluated their platelet function 5 days after hospital admission using OPA. HRPR after ADP stimuli was defined as platelet aggregation of 70 % or greater according to OPA after 10 µM ADP stimuli. The primary endpoint was a composite of all causes of death, myocardial infarction, and stroke at the 1-year follow-up. The secondary endpoints were each component of the primary endpoint. The event rate of primary endpoint was 11.3 % (109/968). Its rate was significantly higher in the patients with HRPR (16.7 %) than in those without (9.7 %). HPRP was independently associated with the primary endpoint (OR = 1.97, CI 1.22-3.18, p < 0.01). According to the AIS subtype, the presence of HRPR was independently significant for the occurrence of the primary endpoint in the large artery atherosclerosis (LAA) subtype only (OR = 2.26, CI 1.15-4.45, p = 0.02). In this study, the presence of HRPR after ADP stimuli is associated with a poor long-term outcome after acute ischemic stroke. In particular, the influence of this factor might be more prominent in LAA compared with other types of AIS.

Platelet aggregation in response to ADP is highly variable in normal donors and patients on anti-platelet medication

BACKGROUND

P2Y12 inhibitors are indicated in patients following percutaneous coronary intervention. Several studies have demonstrated that high on treatment platelet reactivity is correlated with outcomes yet prospective studies of guided therapy have failed to show benefit. There is a paucity of studies on the platelet aggregation response to ADP before P2Y12 therapy is started. The aim of this study was to characterize platelet responses to 20 μM ADP by light transmission aggregometry (LTA) in a homogenous population.

METHODS

Platelet aggregation was assessed in 201 patients on dual antiplatelet therapy, 98 patients on aspirin alone and 47 normal, healthy volunteers free from anti-platelet medication.

RESULTS

Consensus guidelines suggest that a platelet aggregation response in response to the agonist ADP of <57% is an adequate therapeutic response to P2Y12 inhibition. Seven healthy donors and 38 patients taking aspirin only had aggregation responses below 57%.

CONCLUSIONS

The results of our study demonstrate that 15% of normal donors and 38% of patients taking aspirin only would be classified as having a therapeutic response to P2Y12 inhibition using current guidelines.

Aspirin Resistance Predicts Adverse Cardiovascular Events in Patients with Symptomatic Peripheral Artery Disease

Antiplatelet therapy reduces the risk of myocardial infarction, stroke, and vascular death in patients who have symptomatic peripheral artery disease. However, a subset of patients who take aspirin continues to have recurrent cardiovascular events. There are few data on cardiovascular outcomes in patients with peripheral artery disease who manifest aspirin resistance. Patients with peripheral artery disease on long-term aspirin therapy (≥4 wk) were tested for aspirin responsiveness by means of the VerifyNow Aspirin Assay. The mean follow-up duration was 22.6 ± 8.3 months. The primary endpoint was a composite of death, myocardial infarction, or ischemic stroke. Secondary endpoints were the incidence of vascular interventions (surgical or percutaneous), or of amputation or gangrene caused by vascular disease. Of the 120 patients enrolled in the study, 31 (25.8%) were aspirin-resistant and 89 (74.2%) were aspirin-responsive. The primary endpoint occurred in 10 (32.3%) patients in the aspirin-resistant group and in 13 (14.6%) patients in the aspirin-responsive group (hazard ratio=2.48; 95% confidence interval, 1.08-5.66; P=0.03). There was no significant difference in the secondary outcome of revascularization or tissue loss. By multivariate analysis, aspirin resistance and history of chronic kidney disease were the only independent predictors of long-term adverse cardiovascular events. Aspirin resistance is highly prevalent in patients with symptomatic peripheral artery disease and is an independent predictor of adverse cardiovascular risk. Whether intervening in these patients with additional antiplatelet therapies would improve outcomes needs to be explored.

Enhanced platelet MRP4 expression and correlation with platelet function in patients under chronic aspirin treatment

Platelet multidrug resistance protein4 (MRP4)-overexpression has a role in reducing aspirin action. Aspirin in vivo treatment enhances platelet MRP4 expression and MRP4 mediated transport inhibition reduces platelet function and delays thrombus formation. The aim of our work was to verify whether MRP4 expression is enhanced in platelets obtained from patients under chronic aspirin treatment and whether it correlates with residual platelet reactivity. We evaluated changes on mRNA and protein-MRP4 expression and platelet aggregation in four populations: healthy volunteers (HV), aspirin-free control population (CTR), patients who started the treatment less than one month ago (ASA<1 month patients) and aspirinated patients who started the treatment more than two months ago (ASA>2 months patients). In platelets obtained from ASA>2 months patients, it was found a statistically significant MRP4 enhancement of both mRNA and protein expression compared to HV, CTR and ASA<1 month patients. Platelets obtained from ASA>2 months patients that present high levels of platelet MRP4, have higher serum TxB₂ levels and collagen-induced platelet aggregation compared to patient with low levels of MRP4 in platelets. In addition collagen induced platelet aggregation is higher in in vitro aspirinated platelets obtained from patients with high levels of MRP4 patients compared to those obtained from patients with low MRP4 levels. We can assert that, in patients under chronic aspirin treatment, platelets that present high MRP4 levels have an increase of residual platelet reactivity, which is due in part to incomplete COX-1 inhibition, and in part to COX-1-independent mechanism.

The role of aspirin in colorectal cancer chemoprevention

Considerable interest has emerged over the last decade regarding the role of aspirin in prevention of colorectal cancer. This disease is one of the commonest cancers in the Western World, therefore, the existence of a simple "everyday" agent, which could have the ability to prevent the disease, represents an invaluable opportunity clinicians may be able to exploit. Evidence from case-control and cohort studies, and recent updates of randomised controlled trials have been very encouraging-indicating benefit from long term use of aspirin at low dose. Possible mechanisms of chemoprevention include inhibition of the cyclooxygenase (COX) pathway, or COX-independent mechanisms, for example, the PIK3CA pathway, or therapy-induced senescence of cancer cells. The most serious side effect of prolonged aspirin treatment is haemorrhage, especially from the GI tract. This is likely to be less of a problem with chemoprevention at lower doses. One also needs to consider the impact if aspirin resistance, an increasingly recognised clinical entity.

Aspirin influences megakaryocytic gene expression leading to up-regulation of multidrug resistance protein-4 in human platelets

Aim

The aim of the study was to investigate whether human megakaryocytic cells have an adaptive response to aspirin treatment, leading to an enhancement of multidrug resistance protein-4 (MRP4) expression in circulating platelets responsible for a reduced aspirin action. We recently found that platelet MRP4 overexpression has a role in reducing aspirin action in patients after by-pass surgery. Aspirin enhances MRP4-mRNA levels in rat liver and drug administration transcriptionally regulates MRP4 gene expression through peroxisome proliferator-activated receptor-α (PPARα).

Methods

The effects induced by aspirin or PPARα agonist (WY14643) on MRP4 modulation were evaluated in vitro in a human megakaryoblastic DAMI cell line, in megakaryocytes (MKs) and in platelets obtained from human haematopoietic progenitor cell (HPC) cultures, and in vivo platelets obtained from aspirin treated healthy volunteers (HV).

Results

In DAMI cells, aspirin and WY14643 treatment induced a significant increase in MRP4 and PPARα expression. In human MKs grown in the presence of either aspirin or WY14643, MRP4 and PPARα-mRNA were higher than in control cultures and derived platelets showed an enhancement in MRP4 protein expression. The ability of aspirin to modulate MRP4 expression in MKs and to transfer it to platelets was also confirmed in vivo. In fact, we found the highest MRP4 mRNA and protein expression in platelets obtained from HV after 15 days' aspirin treatment.

Conclusions

The present study provides evidence, for the first time, that aspirin treatment affects the platelet protein pattern through MK genomic modulation. This work represents an innovative and attractive approach, useful both to identify patients less sensitive to aspirin and to improve pharmacological treatment in cardiovascular high-risk patients.

Multidrug Resistance Protein-4 Influences Aspirin Toxicity in Human Cell Line

Overexpression of efflux transporters, in human cells, is a mechanism of resistance to drug and also to chemotherapy. We found that multidrug resistance protein-4 (MRP4) overexpression has a role in reducing aspirin action in patients after bypass surgery and, very recently, we found that aspirin enhances platelet MRP4 levels through peroxisome proliferator activated receptor-α (PPARα). In the present paper, we verified whether exposure of human embryonic kidney-293 cells (Hek-293) to aspirin modifies MRP4 gene expression and its correlation with drug elimination and cell toxicity. We first investigated the effect of high-dose aspirin in Hek-293 and we showed that aspirin is able to increase cell toxicity dose-dependently. Furthermore, aspirin effects, induced at low dose, already enhance MRP4 gene expression. Based on these findings, we compared cell viability in Hek-293, after high-dose aspirin treatment, in MRP4 overexpressing cells, either after aspirin pretreatment or in MRP4 transfected cells; in both cases, a decrease of selective aspirin cell growth inhibition was observed, in comparison with the control cultures. Altogether, these data suggest that exposing cells to low nontoxic aspirin dosages can induce gene expression alterations that may lead to the efflux transporter protein overexpression, thus increasing cellular detoxification of aspirin.

Does the response to aspirin and clopidogrel vary over 6 months in patients with ischemic heart disease?

BACKGROUND

Dual-antiplatelet therapy (DAPT) with aspirin and a P2Y12 inhibitor, mostly clopidogrel, is the default therapy in both acute coronary syndrome (ACS) and after intracoronary stents. It is well established that responses to antiplatelet therapy (APT), particularly clopidogrel, are subject to considerable interindividual variability.

OBJECTIVES

We investigated whether responses to APT in individuals vary significantly over time.

METHODS

Simultaneous assay with VerifyNow(™) and short thrombelastography (s-TEG) was performed before and at four time points over 6 months after hospital discharge in 40 patients receiving DAPT. Serum thromboxane B2 levels were also measured.

RESULTS

While aspirin response units (ARU) by VerifyNow(™) and serum thromboxane B2 levels remained stable over time, arachidonic acid (AA)-mediated platelet aggregation with s-TEG (i.e. area under the curve at 15 min in AA channel, AUC15AA ) increased at 1 week compared with predischarge (P < 0.008). In addition, platelet reactivity units (PRU) by VerifyNow(™) (P = 0.046) and adenosine diphosphate (ADP)-mediated platelet aggregation with s-TEG (i.e. AUC15ADP ) also increased at 1 week compared with predischarge (P = 0.026). There were no significant changes in either platelet reactivity or rates of high on-treatment platelet reactivity while receiving clopidogrel beyond 1 week.

CONCLUSIONS

This study demonstrates important variability in responses to APT within individuals between predischarge and 1 week but not thereafter. The use of a single early (predischarge) platelet function assay as an indicator of future response may therefore be flawed. The design of future strategies to assess individual responses for tailored therapy needs to take this into account.

Antiplatelet and antithrombotic activity of a fibrin(ogen)olytic protease from Bacillus cereus strain FF01

Fibrin(ogen)olytic enzymes offer great promise for the treatment of thrombosis associated disorders. The present study describes the characterization of an extracellular fibrin(ogen)olytic serine protease (named Bacethrombase) purified from the Bacillus cereus strain FF01. The molecular mass of the Bacethrombase was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and matrix assisted laser desorption/ionization-time-of-flight-mass spectroscopy analyses at 39.5 kDa and 38,450.51 Da, respectively. The peptide mass fingerprinting and analyses of the composition of the amino acids revealed the similarity of the Bacethrombase to the bacterial serine proteases. The secondary structure of the Bacethrombase was composed of 14% helix, 6.6% beta-sheet, and 79.4% random coil. Bacethrombase was found to contain 48% sialic acid and it preferentially degraded the Aα-chain of fibrinogen, as well as fibrin. The anticoagulant potency of the Bacethrombase was comparable with that of warfarin and heparin, and was corroborated by its fibrinogenolytic activity rather than the inhibition of thrombin, prothrombin or FXa. Bacethrombase demonstrated antiplatelet activity, and dose-dependently inhibited the ADP-induced platelet aggregation. Bacethrombase (10 mg/kg) did not show toxicity after i.v. administration in Wistar rats; however, it revealed an in vivo anticoagulant effect and significantly inhibited the carrageenan-induced in vivo thrombus formation in rats.

Does platelet count in platelet-rich plasma influence slope, maximal amplitude and lag phase in healthy individuals? Results of light transmission aggregometry

Light transmission aggregometry lacks in standardisation and normal reference values are not widely available. The aims of our study were to establish reference ranges for aggregation, slope and lag phase in healthy controls with platelet counts between 150 and 450 × 10(9)/l in platelet-rich plasma (PRP) as well as evaluate the influence of platelet count. Ninety-nine subjects were evaluated with four agonists and divided into two groups based on platelet count and the groups were compared by Student's t-test. There was no difference between the means of the two groups for amplitude and slope barring the lag phase for collagen. Platelet counts between 150 and 450 × 10(9)/l have no effects on light transmission aggregometry and hence adjustment of platelet count is not necessary.

Searching for factors associated with resistance to acetylsalicylic acid used for secondary prevention of stroke

INTRODUCTION

The aim of the study was to evaluate the prevalence of resistance to acetylsalicylic acid (ASA), used for secondary prevention of stroke, including the assessment of risk factors associated with the lack of ASA anti-aggregatory action.

MATERIAL AND METHODS

Patients after a transient ischaemic attack (TIA) or ischaemic stroke in the acute (n = 111) and chronic phase (n = 87) were enrolled in the study. The assessment of platelet function was performed by whole blood impedance aggregometry using a multi-channel platelet function analyser (Multiplate).

RESULTS

A proper response to ASA was found in 121 patients (61.1%) (ASA responders), a partial response to ASA in 59 patients (29.8%) (ASA partial responders), and ASA resistance in 18 patients (9.1%) (ASA non-responders). Acetylsalicylic acid resistance was observed more frequently in the chronic phase. The mean low-density lipoprotein (LDL) concentration was higher in ASA non-responders (p = 0.02). The mean heart rate (p = 0.03) and the mean haematocrit (p = 0.03) were higher in the group of ASA partial responders and ASA non-responders. Angiotensin II receptor antagonists were more often used in the group of ASA partial responders and ASA non-responders (p = 0.04). Diuretics were more rarely used by ASA non-responders, whereas fibrates were more rarely used by ASA partial responders.

CONCLUSIONS

The method enabled the detection of ASA resistance in some patients with cerebrovascular disease. The study revealed some possible risk factors of ASA resistance: long ASA therapy, increased heart rate, higher LDL concentration, and higher haematocrit value. The relationship between the effect of ASA and other medications (angiotensin II receptor blockers, fibrates, diuretics) requires further study. Platelet function monitoring should be considered in patients at a greater risk of ASA resistance.

Two acidic, anticoagulant PLA2 isoenzymes purified from the venom of monocled cobra Naja kaouthia exhibit different potency to inhibit thrombin and factor Xa via phospholipids independent, non-enzymatic mechanism

Background

The monocled cobra (Naja kaouthia) is responsible for snakebite fatality in Indian subcontinent and in south-western China. Phospholipase A₂ (PLA₂; EC 3.1.1.4) is one of the toxic components of snake venom. The present study explores the mechanism and rationale(s) for the differences in anticoagulant potency of two acidic PLA₂ isoenzymes, Nk-PLA₂α (13463.91 Da) and Nk-PLA₂β (13282.38 Da) purified from the venom of N. kaouthia.

Principal Findings

By LC-MS/MS analysis, these PLA₂s showed highest similarity (23.5% sequence coverage) with PLA₂ III isolated from monocled cobra venom. The catalytic activity of Nk-PLA₂β exceeds that of Nk-PLA₂α. Heparin differentially regulated the catalytic and anticoagulant activities of these Nk-PLA₂ isoenzymes. The anticoagulant potency of Nk-PLA₂α was comparable to commercial anticoagulants warfarin, and heparin/antithrombin-III albeit Nk-PLA₂β demonstrated highest anticoagulant activity. The anticoagulant action of these PLA₂s was partially contributed by a small but specific hydrolysis of plasma phospholipids. The strong anticoagulant effect of Nk-PLA₂α and Nk-PLA₂β was achieved via preferential, non-enzymatic inhibition of FXa (Ki = 43 nM) and thrombin (Ki = 8.3 nM), respectively. Kinetics study suggests that the Nk-PLA₂ isoenzymes inhibit their “pharmacological target(s)” by uncompetitive mechanism without the requirement of phospholipids/Ca²⁺. The anticoagulant potency of Nk-PLA₂β which is higher than that of Nk-PLA₂α is corroborated by its superior catalytic activity, its higher capacity for binding to phosphatidylcholine, and its greater strength of thrombin inhibition. These PLA₂ isoenzymes thus have evolved to affect haemostasis by different mechanisms. The Nk-PLA₂β partially inhibited the thrombin-induced aggregation of mammalian platelets suggesting its therapeutic application in the prevention of unwanted clot formation.

Conclusion/Significance

In order to develop peptide-based superior anticoagulant therapeutics, future application of Nk-PLA₂α and Nk-PLA₂β for the treatment and/or prevention of cardiovascular disorders are proposed.

Resistance to acetylsalicylic acid in patients with type 2 diabetes mellitus is associated with lipid disorders and history of current smoking

BACKGROUND

Diabetes mellitus (DM) is an important risk factor for stroke. Acetylsalicylic acid (ASA) is the most frequently used medication for prevention of cardio-cerebral vascular diseases. However, some patients experience ischaemic vascular events despite the use of ASA. This phenomenon is known as "aspirin resistance" (AR). The aim of this study was to assess the prevalence of AR in diabetic patients and search for factors associated with it.

MATERIALS AND METHODS

The examined group consisted of 96 subjects with diagnosed type 2 DM. Platelet function test was performed by the method of whole blood impedance aggregometry.

RESULTS

Among examined subjects, 51 patients (53.1 %) were sensitive to ASA action (ASA responders) and 45 patients (46.9 %) were resistant to ASA action (ASA non-responders). No association was found between platelet aggregation and gender, age, dose of ASA, known duration of diabetes, BMI, heart rate, mean systolic and diastolic blood pressure, and risk factors except for current smoking (p = 0.030). ASA non-responders were treated shorter with ASA than ASA responders (p = 0.010). The mean total cholesterol (p = 0.020), LDL concentration (p = 0.005), HCT (p = 0.010), WBC (p = 0.030), and PLT (p = 0.050) were significantly higher in ASA non-responders. No association was found between AR and results of other laboratory tests and medications. Multiple logistic regression analysis revealed factors associated with AR: current smoking and LDL concentration higher than 3.5 mmol/l.

CONCLUSIONS

Results of our study did not confirm the association between poor glycaemic control in the diabetic patients and AR. Resistance to ASA in diabetic patients is associated with lipid disorders and history of current smoking.

Mechanisms of aspirin resistance

Aspirin is integral to the secondary prevention of cardiovascular disease and acts to impair the development of platelet-mediated atherothromboembolic events by irreversible inhibition of platelet cyclooxygenase-1 (COX-1). Inhibition of this enzyme prevents the synthesis of the potent pro-aggregatory prostanoid thromboxane A2. A large number of patients continue to experience atherothromboembolic events despite aspirin therapy, so-called 'aspirin treatment failure', and this is multifactorial in aetiology. Approximately 10% however do not respond appropriately to aspirin in a phenomenon known as 'aspirin resistance', which is defined by various laboratory techniques. In this review we discuss the reasons for aspirin resistance in a systematic manner, starting from prescription of the drug and ending at the level of the platelet. Poor medication adherence has been shown to be a cause of apparent aspirin resistance, and may in fact be the largest contributory factor. Also important is high platelet turnover due to underlying inflammatory processes, such as atherosclerosis and its complications, leading to faster regeneration of platelets, and hence of COX-1, at a rate that diminishes the efficacy of once daily dosing. Recent developments include the identification of platelet glycoprotein IIIa as a potential biomarker (as well as possible underlying mechanism) for aspirin resistance and the discovery of an anion efflux pump that expels intracellular aspirin from platelets. The absolute as well as relative contributions of such factors to the phenomenon of aspirin resistance are the subject of continuing research.

Impact of aspirin dose on adenosine diphosphate-mediated platelet activities. Results of an in vitro pilot investigation

Different aspirin dosing regimens have been suggested to impact outcomes when used in combination with adenosine diphosphate (ADP) P2Y12 receptor antagonists. Prior investigations have shown that not only aspirin, but also potent ADP P2Y12 receptor blockade can inhibit thromboxane A2-mediated platelet activation. The impact of aspirin dosing on ADP mediated platelet activities is unknown and represents the aim of this in vitro pilot pharmacodynamic (PD) investigation. Twenty-six patients with stable coronary artery disease on aspirin 81 mg/day and P2Y12 naïve were enrolled. PD assessments were performed at baseline, while patients were on 81 mg/day aspirin and after switching to 325 mg/day for 7 ± 2 days with and without escalating concentrations (vehicle, 1, 3, and 10 μM) of prasugrel's active metabolite (P-AM). PD assays included flow cytometric assessment of VASP to define the platelet reactivity index (PRI) and the Multiplate Analyzer (MEA) using multiple agonists [ADP, ADP + prostaglandin (PGE1), arachidonic acid (AA), and collagen]. Escalating P-AM concentrations showed incremental platelet P2Y12 inhibition measured by VASP-PRI (p<0.001). However, there were no differences according to aspirin dosing regimen at any P-AM concentration (vehicle: p=0.899; 1 μM: p=0.888; 3 μM: p=0.524; 10 μM: p=0.548). Similar findings were observed in purinergic markers assessed by MEA (ADP and ADP+PGE1). P-AM addition significantly reduced AA and collagen induced platelet aggregation (p<0.001 for all measures), irrespective of aspirin dose. In conclusion, aspirin dosing does not appear to affect PD measures of ADP-mediated platelet reactivity irrespective of the degree of P2Y12 receptor blockade. P2Y12 receptor blockade modulates platelet reactivity mediated by alternative activators.

Persistent high on-treatment platelet reactivity in acute coronary syndrome

Persistent high on-treatment platelet reactivity in acute coronary syndrome (ACS) patients managed with appropriate antiplatelet therapy has been correlated with increased risk of cardiovascular events; however, the evolution of this phenomenon overtime is not well known. We investigated platelet activity at a three month follow-up after initial presentation with an ACS. We enrolled a total of 124 patients in the study, 65 were diagnosed with ACS and 59 controls who presented with non-cardiac chest pain for baseline comparisons. Of the enrolled patients, we had 25 ACS patients return, in stable condition, three months after their initial presentation for repeat platelet functional testing. Epinephrine (EPI), adenosine diphosphate (ADP), and arachidonic acid induced platelet aggregation were monitored at baseline with repeat measurement of EPI- and ADP-stimulated aggregation at follow-up. In addition, P-selectin and PAC-1 expression were monitored at presentation and at a three month follow-up period. ACS patients were maintained on aspirin therapy during the intervening period. At the three month follow-up visit, ACS patients initiated on aspirin had no significant percentage change in aggregation to submaximal concentrations of EPI and ADP. They also had no significant percentage change in PAC-1 or P-selectin expression. This study demonstrates persistent high on-treatment platelet reactivity in ACS patients at a three month follow-up, which may place these patients at increased risk of recurrent cardiovascular events.

Time-dependent changes in non-COX-1-dependent platelet function with daily aspirin therapy

To develop an integrated metric of non-COX-1-dependent platelet function (NCDPF) to measure the temporal response to aspirin in healthy volunteers and diabetics. NCDPF on aspirin demonstrates wide variability, despite suppression of COX-1. Although a variety of NCDPF assays are available, no standard exists and their reproducibility is not established. We administered 325 mg/day aspirin to two cohorts of volunteers (HV1, n = 52, and HV2, n = 96) and diabetics (DM, n = 74) and measured NCDPF using epinephrine, collagen, and ADP aggregometry and PFA100 (collagen/epi) before (Pre), after one dose (Post), and after several weeks (Final). COX-1 activity was assessed with arachidonic acid aggregometry (AAA). The primary outcome of the study, the platelet function score (PFS), was derived from a principal components analysis of NCDPF measures. The PFS strongly correlated with each measure of NCDPF in each cohort. After 2 or 4 weeks of daily aspirin the Final PFS strongly correlated (r > 0.7, P < 0.0001) and was higher (P < 0.01) than the Post PFS. The magnitude and direction of the change in PFS (Final–Post) in an individual subject was moderately inversely proportional to the Post PFS in HV1 (r = -0.45), HV2 (r = -0.54), DM (r = -0.68), P < 0.0001 for all. AAA remained suppressed during aspirin therapy. The PFS summarizes multiple measures of NCDPF. Despite suppression of COX-1 activity, NCDPF during aspirin therapy is predictably dynamic: those with heightened NCDPF continue to decline whereas those with low/normal NCDPF return to pre-aspirin levels over time.