Inhibition Of Thromboxane Research Articles

Long-term pharmacodynamic and clinical effects of twice- versus once-daily low-dose aspirin in essential thrombocythemia: The ARES trial.

Patients with essential thrombocythemia (ET) are treated with once-daily low-dose aspirin to prevent thrombosis, but their accelerated platelet turnover shortens the antiplatelet effect. The short-term Aspirin Regimens in EsSential Thrombocythemia trial showed that twice-daily aspirin dosing restores persistent platelet thromboxane (TX) inhibition. However, the long-term pharmacodynamic efficacy, safety and tolerability of twice-daily aspirin remain untested. We performed a multicenter, randomized, open-label, blinded-endpoint, phase-2 trial in which 242 patients with ET were randomized to 100 mg aspirin twice- or once-daily and followed for 20 months. The primary endpoint was the persistence of low serum TXB2, a surrogate biomarker of antithrombotic efficacy. Secondary endpoints were major and clinically relevant non-major bleedings, serious vascular events, symptom burden assessed by validated questionnaires, and in vivo platelet activation. Serum TXB2 was consistently lower in the twice-daily versus once-daily regimen on 10 study visits over 20 months: median 3.9 ng/mL versus 19.2 ng/mL, respectively; p < .001; 80% median reduction; 95% CI, 74%-85%. No major bleeding occurred. Clinically relevant non-major bleedings were non-significantly higher (6.6% vs. 1.7%), and major thromboses lower (0.8% vs. 2.5%) in the twice-daily versus once-daily group. Patients on the twice-daily regimen had significantly lower frequencies of disease-specific symptoms and severe hand and foot microvascular pain. Upper gastrointestinal pain was comparable in the two arms. In vivo platelet activation was significantly reduced by the twice-daily regimen. In patients with ET, twice-daily was persistently superior to once-daily low-dose aspirin in suppressing thromboxane biosynthesis and reducing symptom burden, with no detectable excess of bleeding and gastrointestinal discomfort.

Optimizing aspirin dose for colorectal cancer patients through deep phenotyping using novel biomarkers of drug action.

Background: Low-dose aspirin's mechanism of action for preventing colorectal cancer (CRC) is still debated, and the optimal dose remains uncertain. We aimed to optimize the aspirin dose for cancer prevention in CRC patients through deep phenotyping using innovative biomarkers for aspirin's action. Methods: We conducted a Phase II, open-label clinical trial in 34 CRC patients of both sexes randomized to receive enteric-coated aspirin 100mg/d, 100mg/BID, or 300mg/d for 3 ± 1weeks. Biomarkers were evaluated in blood, urine, and colorectal biopsies at baseline and after dosing with aspirin. Novel biomarkers of aspirin action were assessed in platelets and colorectal tissues using liquid chromatography-mass spectrometry to quantify the extent of cyclooxygenase (COX)-1 and COX-2 acetylation at Serine 529 and Serine 516, respectively. Results: All aspirin doses caused comparable % acetylation of platelet COX-1 at Serine 529 associated with similar profound inhibition of platelet-dependent thromboxane (TX)A2 generation ex vivo (serum TXB2) and in vivo (urinary TXM). TXB2 was significantly reduced in CRC tissue by aspirin 300mg/d and 100mg/BID, associated with comparable % acetylation of COX-1. Differently, 100mg/day showed a lower % acetylation of COX-1 in CRC tissue and no significant reduction of TXB2. Prostaglandin (PG)E2 biosynthesis in colorectal tumors and in vivo (urinary PGEM) remained unaffected by any dose of aspirin associated with the variable and low extent of COX-2 acetylation at Serine 516 in tumor tissue. Increased expression of tumor-promoting genes like VIM (vimentin) and TWIST1 (Twist Family BHLH Transcription Factor 1) vs. baseline was detected with 100mg/d of aspirin but not with the other two higher doses. Conclusion: In CRC patients, aspirin 300mg/d or 100mg/BID had comparable antiplatelet effects to aspirin 100mg/d, indicating similar inhibition of the platelet's contribution to cancer. However, aspirin 300mg/d and 100mg/BID can have additional anticancer effects by inhibiting cancerous tissue's TXA2 biosynthesis associated with a restraining impact on tumor-promoting gene expression. EUDRACT number: 2018-002101-65. Clinical Trial Registration: ClinicalTrials.gov, identifier NCT03957902.

Early assessment of the pharmacokinetic and pharmacodynamic effects following acetylsalicylic acid loading: toward a definition for acute therapeutic response.

Despite decades of investigations, the optimal assessment of the "therapeutic response" to early after loading dose of acetylsalicylic acid (ASA) remains unclear. Limited information is available on the relation between pharmacodynamic (PD) and pharmacokinetic (PK) measurements assessed immediately after ASA administration. Serial PD and PK analyses were performed immediately after a single 162 or 650mg dose of chewed and swallowed ASA in ten healthy adults. ASA response was defined as > 95% inhibition of serum thromboxane (Tx)B2, < 550 aspirin reaction units (ARU) by VerifyNow Aspirin (VN) test, and ≤ 20% arachidonic acid (AA)-induced platelet aggregation (PA). Correlation analyses between PK and PD measurements and receiver operating characteristic (ROC) curve analyses were performed. ASA response measured by VN test and AA-induced PA was achieved within 30min of ASA administration. A correlation was observed between ARU and AA-induced maximum PA (r = 0.69, p < 0.001), serum TxB2 (r = 0.74 and p < 0.001), and serum TxB2 inhibition (r = 0.79, p < 0.001). In ROC curve analyses, ≤ 558 ARU and ≤ 7% AA-induced PA were associated with > 95% inhibition of TxB2. 686ng/ml plasma ASA cut-off point was associated with > 95% inhibition of serum TxB2, ≤ 7% 1mM AA-induced PA, and ≤ 585 ARU. A modest ~ 50% inhibition of TxB2 inhibition was associated with marked inhibition of 1mM AA-induced platelet aggregation by LTA. Our analyses demonstrated important relationships between pharmacodynamic, and pharmacokinetic parameters measured immediately following oral ASA and cutoff values for ARU and AA-induced PA that is associated with > 95% inhibition of serum TxB2.

Use of Glycoprotein IIb-IIIa Inhibitors in Patients Undergoing Carotid Artery Stenting in the Vascular Quality Initiative

Antiplatelet therapies with thromboxane inhibitors and adenosine 5'-diphosphate antagonists have been widely used following carotid artery stenting (CAS). However, these therapies may not apply to patients who are intolerant or present acutely. Glycoprotein IIb/IIIa inhibitors (GPI) are a proposed alternative therapy in these patients; however, their use has been limited due to concerns of increased risk for intracranial bleeding. Thus, this study aims to assess the safety profile of GPI in patients undergoing CAS. All patients undergoing CAS in the Society of Vascular Surgery - Vascular Quality Initiative database from 2012 to 2021 was included and grouped into GPI versus non-GPI therapy (control). The primary outcome was in-hospital stroke or death, and secondary outcomes included in-hospital stroke/transient ischemic attack (TIA), death, myocardial infarction, and intracranial hemorrhage (ICH)/seizure. Patients were stratified by surgical approach (Transcarotid artery revascularization using flow reversal (TCAR) and transfemoral carotid artery stenting), and stepwise backward logistic regression analysis was conducted to evaluate major primary and secondary outcomes. A total of 50,628 patients underwent carotid revascularization. Of these, 4.4% of the patients received GPI. Mean age was similar between control versus GPI (71.35(9.67) vs. 71.36(10.20) years). Compared to the control group, patients who receive GPI are less likely to be on optimal medical therapy, including aspirin (83.0% vs. 88.1%), P2Y12 inhibitor (73.0% vs. 82.7%), and statin (82.3% vs. 86.0%) (All P<0.05). In addition, patients in the GPI group were more likely to undergo TCAR for carotid revascularization (52.2% vs. 48.4%) for emergent/urgent (29.4% vs. 16.8%) and symptomatic indications (55.5% vs. 49.7%) (All P<0.001). After stratifying by surgical approach, if patients underwent TFCAS and received a GPI, they were at increased odds of developing stroke/death (1.77(1.25-2.51)), death (odds ratio (OR) (95% CI): 1.67(1.07-2.61)), stroke/TIA (OR (95% confidence interval (CI)): 1.65(1.09-2.51)), and ICH/seizure (OR (95% CI): 2.13(1.23-3.68)) (All P<0.05). No difference was seen in outcomes between the 2 groups if undergoing TCAR. Patients who receive GPI were more likely to be symptomatic at presentation and less likely to be medically optimized before their carotid revascularization. Transfemoral access in patients receiving GPI was associated with increased odds of morbidity and mortality. However, this was not observed if undergoing TCAR. TCAR can be considered for its overall favorable results in high-risk patients who are not medically optimized.

Biomarkers of Response to Low-Dose Aspirin in Familial Adenomatous Polyposis Patients.

The results of Aspirin prevention of colorectal adenomas in patients with familial adenomatous polyposis (FAP) are controversial. We conducted a biomarker-based clinical study in eight FAP patients treated with enteric-coated low-dose Aspirin (100 mg daily for three months) to explore whether the drug targets mainly platelet cyclooxygenase (COX)-1 or affects extraplatelet cellular sources expressing COX-isozymes and/or off-target effects in colorectal adenomas. In FAP patients, low-dose Aspirin-acetylated platelet COX-1 at Serine529 (>70%) was associated with an almost complete inhibition of platelet thromboxane (TX) B2 generation ex vivo (serum TXB2). However, enhanced residual urinary 11-dehydro-TXB2 and urinary PGEM, primary metabolites of TXA2 and prostaglandin (PG)E2, respectively, were detected in association with incomplete acetylation of COX-1 in normal colorectal biopsies and adenomas. Proteomics of adenomas showed that Aspirin significantly modulated only eight proteins. The upregulation of vimentin and downregulation of HBB (hemoglobin subunit beta) distinguished two groups with high vs. low residual 11-dehydro-TXB2 levels, possibly identifying the nonresponders and responders to Aspirin. Although low-dose Aspirin appropriately inhibited the platelet, persistently high systemic TXA2 and PGE2 biosynthesis were found, plausibly for a marginal inhibitory effect on prostanoid biosynthesis in the colorectum. Novel chemotherapeutic strategies in FAP can involve blocking the effects of TXA2 and PGE2 signaling with receptor antagonists.

Retracted: Poster No. 005 Platelet Thromboxane Inhibition by Low-Dose Aspirin in Polycythemia Vera:Ex Vivo and In Vivo Measurements and In Silico Simulation

This abstract has been withdrawn. Please see: https://doi.org/10.1093/cvr/cvac183

The specific deletion of cyclooxygenase-1 in megakaryocytes/platelets reduces intestinal polyposis in ApcMin/+ mice

Clinical and experimental evidence sustain the role of cyclooxygenase (COX)−1 in intestinal tumorigenesis. However, the cell type expressing the enzyme involved and molecular mechanism(s) have not been clarified yet. We aimed to elucidate the role of platelet COX-1 (the target of low-dose aspirin in humans) in intestinal tumorigenesis of ApcMin/+ mice, considered a clinically relevant model. To realize this objective, we generated an ApcMin/+ mouse with a specific deletion of Ptgs1(COX-1 gene name) in megakaryocytes/platelets (ApcMin/+;pPtgs1-/-mice) characterized by profound inhibition of thromboxane(TX)A2 biosynthesis ex vivo (serum TXB2; by 99%) and in vivo [urinary 2,3-dinor-TXB2(TXM), by 79%]. ApcMin/+ mice with the deletion of platelet COX-1 showed a significantly reduced number (67%) and size (32%) of tumors in the small intestine. The intestinal adenomas of these mice had decreased proliferative index associated with reduced COX-2 expression and systemic prostaglandin(PG)E2 biosynthesis (urinary PGEM) vs. ApcMin/+mice. Extravasated platelets were detected in the intestine of ApcMin/+mice. Thus, we explored their contribution to COX-2 induction in fibroblasts, considered the primary polyp cell type expressing the protein. In the coculture of human platelets and myofibroblasts, platelet-derived TXA2 was involved in the induction of COX-2-dependent PGE2 in myofibroblasts since it was prevented by the selective inhibition of platelet COX-1 by aspirin or by a specific antagonist of TXA2 receptors. In conclusion, our results support the platelet hypothesis of intestinal tumorigenesis and provide experimental evidence that selective inhibition of platelet COX-1 can mitigate early events of intestinal tumorigenesis by restraining COX-2 induction.

Platelet thromboxane inhibition by low-dose aspirin in polycythemia vera: Ex vivo and in vivo measurements and in silico simulation.

Low-dose aspirin is currently recommended for patients with polycythemia vera (PV), a myeloproliferative neoplasm with increased risk of arterial and venous thromboses. Based on aspirin pharmacodynamics in essential thrombocythemia, a twice-daily regimen is recommended for patients with PV deemed at particularly high thrombotic risk. We investigated the effects of low-dose aspirin on platelet cyclooxygenase activity and in vivo platelet activation in 49 patients with PV, as assessed by serum thromboxane (TX) B2 and urinary TXA2 /TXB2 metabolite (TXM) measurements, respectively. A previously described pharmacokinetic-pharmacodynamic in silico model was used to simulate the degree of platelet TXA2 inhibition by once-daily (q.d.) and twice-daily (b.i.d.) aspirin, and to predict the effect of missing an aspirin dose during q.d. and b.i.d. regimens. Serum TXB2 averaged 8.2 (1.6-54.7) ng/ml and significantly correlated with the platelet count (γ=0.39) and urinary TXM (γ=0.52) in multivariable analysis. One-third of aspirin-treated patients with PV displayed less-than-maximal platelet TXB2 inhibition, and were characterized by significantly higher platelet counts and platelet-count corrected serum TXB2 than those with adequate inhibition. Eight patients with PV were sampled again after 12 ± 4months, and had reproducible serum TXB2 and urinary TXM values. The in silico model predicted complete inhibition of platelet-derived TXB2 by b.i.d. aspirin, a prediction verified in a patient with PV with the highest TXB2 value while on aspirin q.d. and treated short-term with a b.i.d. regimen. In conclusion, one in three patients with PV on low-dose aspirin display less-than-maximal inhibition of platelet TXA2 production. Serum TXB2 measurement can be a valuable option to guide precision dosing of antiplatelet therapy in patients with PV.

A Comprehensive Literature Review on Cardioprotective Effects of Bioactive Compounds Present in Fruits of Aristotelia chilensis Stuntz (Maqui).

Some fruits and vegetables, rich in bioactive compounds such as polyphenols, flavonoids, and anthocyanins, may inhibit platelet activation pathways and therefore reduce the risk of suffering from CVD when consumed regularly. Aristotelia chilensis Stuntz (Maqui) is a shrub or tree native to Chile with outstanding antioxidant activity, associated with its high content in anthocyanins, polyphenols, and flavonoids. Previous studies reveal different pharmacological properties for this berry, but its cardioprotective potential has been little studied. Despite having an abundant composition, and being rich in bioactive products with an antiplatelet role, there are few studies linking this berry with antiplatelet activity. This review summarizes and discusses relevant information on the cardioprotective potential of Maqui, based on its composition of bioactive compounds, mainly as a nutraceutical antiplatelet agent. Articles published between 2000 and 2022 in the following bibliographic databases were selected: PubMed, ScienceDirect, and Google Scholar. Our search revealed that Maqui is a promising cardiovascular target since extracts from this berry have direct effects on the reduction in cardiovascular risk factors (glucose index, obesity, diabetes, among others). Although studies on antiplatelet activity in this fruit are recent, its rich chemical composition clearly shows that the presence of chemical compounds (anthocyanins, flavonoids, phenolic acids, among others) with high antiplatelet potential can provide this berry with antiplatelet properties. These bioactive compounds have antiplatelet effects with multiple targets in the platelet, particularly, they have been related to the inhibition of thromboxane, thrombin, ADP, and GPVI receptors, or through the pathways by which these receptors stimulate platelet aggregation. Detailed studies are needed to clarify this gap in the literature, as well as to specifically evaluate the mechanism of action of Maqui extracts, due to the presence of phenolic compounds.

Use of Glycoprotein IIb-IIIa Inhibitors in patients undergoing Carotid Artery Stenting

Antiplatelet therapies with thromboxane inhibitors and adenosine 5'-diphosphate antagonists have been widely used following carotid artery stenting (CAS). These therapies may not be applicable in patients that are intolerant or nonresponders. Glycoprotein IIb/IIIa inhibitors (GPI) are a proposed alternative therapy for these patients, however, its use has been limited due to concern of increased hemorrhage. Thus, the purpose of this study is to assess the safety profile of GPI in patient’s undergoing transfemoral CAS (TF-CAS) and transcarotid artery revascularization using flow-reversal (TCAR).

Use of Glycoprotein IIb/IIIa Inhibitors in Patients Undergoing Carotid Artery Stenting in the Vascular Quality Initiative

Antiplatelet therapies with thromboxane inhibitors and adenosine 5'-diphosphate antagonists have been widely used following carotid artery stenting (CAS). These therapies may not be applicable in patients that are intolerant or nonresponders. Glycoprotein IIb/IIIa inhibitors (GPI) are a proposed alternative therapy for these patients, however, it’s use has been limited owing to concern of increased hemorrhage. Thus, the purpose of this study is to assess the safety profile of GPI in patient’s undergoing transfemoral CAS (TF-CAS) and transcarotid artery revascularization using flow reversal (TCAR).

Screening of Synthetic Heterocyclic Compounds as Antiplatelet Drugs.

Antiplatelet drugs represent the keystone in the treatment and prevention of diseases of ischemic origin, including coronary artery disease. The current palette of drugs represents efficient modalities in most cases, but their effect can be limited in certain situations or associated with specific side effects. In this study, representatives of compounds selected from series having scaffolds with known or potential antiplatelet activity were tested. These compounds were previously synthetized by us, but their biological effects have not yet been reported. The aim of this study was to examine the antiplatelet and anticoagulation properties of selected compounds and determine their mechanism of action. Antiplatelet activity of compounds and their mechanisms of action were evaluated using human blood by impedance aggregometry and various aggregation inducers and inhibitors and compared to appropriate standards. Cytotoxicity was tested using breast adenocarcinoma cell cultures and potential anticoagulation activity was also determined. In total, four of 34 compounds tested were equally or more active than the standard antiplatelet drug Acetylsalicylic Acid (ASA). In contrast to ASA, all 4 active compounds decreased platelet aggregation triggered not only by collagen, but also partly by ADP. The major mechanism of action is based on antagonism at thromboxane receptors. In higher concentrations, inhibition of thromboxane synthase was also noted. In contrast to ASA, the tested compounds did not block cyclooxygenase- 1. The most active compound, 2-amino-4-(1H-indol-3-yl)-6-nitro-4H-chromene-3- carbonitrile (2-N), which is 4-5x times more potent than ASA, is a promising compound for the development of novel antiplatelet drugs.

ADP and Thromboxane Inhibitors Both Reduce Global Contraction of Clot Length, While Thromboxane Inhibition Attenuates Internal Aggregate Contraction.

Platelet contractility drives clot contraction to enhance clot density and stability. Clot contraction is typically studied under static conditions, with fewer studies of wall-adherent platelet clots formed under flow. We tested the effect of inhibitors of ADP and/or thromboxane A2 (TXA2) signaling on clot contraction. Using an eight-channel microfluidic device, we perfused PPACK-treated whole blood (WB) ± acetylsalicylic acid (ASA), 2-methylthioAMP (2-MeSAMP), and/or MRS-2179 over collagen (100/s) for 7.5 min, then stopped flow to observe contraction for 7.5 minutes. Two automated imaging methods scored fluorescent platelet percent contraction over the no-flow observation period: (1) “global” measurement of clot length and (2) “local” changes in surface area coverage of the numerous platelet aggregates within the clot. Total platelet fluorescence intensity (FI) decreased with concomitant decrease in global aggregate contraction when ASA, 2-MeSAMP, and/or MRS-2179 were present. Total platelet FI and global aggregate contraction were highly correlated ( R 2 = 0.87). In contrast, local aggregate contraction was more pronounced than global aggregate contraction across all inhibition conditions. However, ASA significantly reduced local aggregate contraction relative to conditions without TXA2 inhibition. P-selectin display was significantly reduced by ADP and TXA2 inhibition, but there was limited detection of global or local aggregate contraction in P-selectin-positive platelets across all conditions, as expected for densely packed “core” platelets. Our results demonstrate that global aggregate contraction is inhibited by ASA, 2-MeSAMP, and MRS-2179, while ASA more potently inhibited local aggregate contraction. These results help resolve how different platelet antagonists affect global and local clot structure and function.

Hypothermia and Cold Injury in Children.

Hypothermia and Cold Injury in Children.

Association of Platelet Thromboxane Inhibition by Low-Dose Aspirin With Platelet Count and Cytoreductive Therapy in Essential Thrombocythemia.

Essential thrombocythemia (ET) is a myeloproliferative neoplasm characterized by enhanced platelet production and thrombotic complications. The inhibition of platelet cyclooxygenase (COX) activity by the standard once‐daily aspirin is mostly incomplete due to accelerated thrombopoiesis. The phase II Aspirin Regimens in EsSential thrombocythemia (ARES) trial has recently compared the efficacy of once‐ vs. twice‐ or three‐times daily low‐dose aspirin in inhibiting platelet thromboxane (TX) A2 production, as reflected by serum (s) TXB2 measurements. The present substudy characterized the determinants of the highly variable response to the standard aspirin 100 mg once‐daily regimen in fully compliant patients with ET and the effects of the experimental dosing regimens on response variability. By multivariable analysis, the platelet count (directly) and cytoreductive treatment (inversely) were significantly associated with sTXB2 values in 218 patients with ET. However, the platelet count positively correlated with sTXB2 in patients not being treated with cytoreductive drugs (ρ = 0.51, P < 0.01, n = 84), but not in patients on cytoreduction. Patients in the lowest sTXB2 quartile were older, more often on cytoreductive drugs, had lower platelet count and Janus‐Associated Kinase2 (JAK2)‐V617F allele frequency as compared with patients in the upper sTXB2 quartiles. After 2 weeks of a twice‐ or 3‐times daily aspirin regimen, the association between the platelet count and sTXB2 became similar in cytoreduced and non‐cytoreduced patients. In conclusion, the platelet count appears the strongest determinant of TXA2 inhibition by once‐daily low‐dose aspirin in ET, with different patterns depending of cytoreductive treatment. More frequent aspirin dosing restores adequate platelet inhibition and reduces interindividual variability, independently of cytoreduction.

Core and shell platelets of a thrombus: A new microfluidic assay to study mechanics and biochemistry

BackgroundHemostatic clots have a P‐selectin positive platelet core covered with a shell of P‐selectin negative platelets. ObjectiveTo develop a new human blood microfluidic assay to interrogate core/shell mechanics. MethodsA 2‐stage assay perfused whole blood over collagen/± tissue factor (TF) for 180 seconds at 100 s−1 wall shear rate, followed by buffer perfusion at either 100 s−1 (venous) or 1000 s−1 (arterial). This microfluidic assay used an extended channel height (120 µm), allowing buffer perfusion well before occlusion. ResultsClot growth on collagen stopped immediately with buffer exchange, revealing ~10% reduction in platelet fluorescence intensity (at 100 s−1) and ~30% (at 1000 s−1) by 1200 seconds. Thrombin generation (on collagen/TF) reduced erosion at either buffer flow rate. P‐selectin–positive platelets were stable (no erosion) against 1000 s−1, in contrast to P‐selectin negative platelets. Thrombin inhibition (with D‐Phe‐Pro‐Arg‐CMK) reduced the number of P‐selectin‐positive platelets and lowered thrombus stability through the reduction of P‐selectin–positive platelets. Interestingly, fibrin inhibition (with H‐Gly‐Pro‐Arg‐Pro‐OH acetate salt) increased the number of P‐selectin–positive platelets but did not lower stability, suggesting that fibrin was only in the core region. Thromboxane inhibition reduced P‐selectin–positive platelets and caused a nearly 60% reduction of the clot at arterial buffer flow. P2Y1 antagonism reduced clot size and the number of P‐selectin–positive platelets and reduced the stability of P‐selectin–negative platelets. ConclusionThe 2‐stage assay (extended channel height plus buffer exchange) interrogated platelet stability using human blood. Under all conditions, P‐selectin–positive platelets never left the clot.

Obesity and laboratory aspirin resistance in high-risk pregnant women treated with low-dose aspirin

Low-dose aspirin is used for preeclampsia prevention in high-risk women, but the precise mechanism and optimal dose are unknown. Evidence suggests that an imbalance in prostacyclin and thromboxane A2 (TXA2) plays a key role in the pathogenesis of preeclampsia. Aspirin has a dose-dependent effect blocking production of TXA2, a potent stimulator of platelet aggregation and promoter of vasoconstriction. Incomplete inhibition of platelet aggregation, designated aspirin resistance, can be reduced by increasing the aspirin dose. Evidence in the nonobstetric literature suggests that aspirin resistance may be more common among patients with a high body mass index. To investigate the association of obesity on platelet-derived thromboxane inhibition in high-risk women treated with low-dose aspirin. This was a secondary analysis of a prospective multi-centered study investigating the effect of low-dose aspirin (60-mg) administration in women at high risk for preeclampsia. Maternal serum TXB2 (an indirect measure of TxA2) levels were drawn at 3 time points: randomization (13-26 weeks' gestation), second trimester (at least 2 weeks after randomization and 24-28 weeks' gestation), and third trimester (34-38 weeks' gestation). Patients were included in the analysis if a TXB2 level was recorded at randomization and at least 1 time point thereafter. Patients were stratified by body mass index category and treatment arm. Median TXB2 levels were calculated at each time point, as well as rates of complete TXB2 inhibition (<0.01 ng/mL). A multivariate logistic regression analysis was performed to generate odds ratios (OR) for complete TXB2 inhibition by body mass index category, adjusting for maternal age, race, high-risk group at randomization, nulliparity, and rate of randomization less than 16 weeks' gestation. A total of 1002 patients were included in the analysis, 496 (49.5%) and 506 (50.5%) in the low-dose aspirin and placebo groups respectively. There were substantial decreases in TXB2 levels among low-dose aspirin-treated women in all body mass index categories. In contrast, women assigned to placebo did not show a marked decrease in TXB2 levels after randomization, and obese women had higher median TXB2 levels in both the second (16.5, interquartile range [IQR] 8.0-31.8 vs 14.0, IQR 6.9-26.7, ng/mL; P= .032) and third (15.7, IQR 7.6-28.5 vs11.9, IQR 4.6-25.9, ng/mL; P= .043) trimesters. When comparing among stratified body mass index low-dose aspirin groups, women with class III obesity had the lowest odds of undetectable TXB2 levels in the second trimester (adjusted odds ratio [aOR], 0.33; 95% confidence interval [CI], 0.15-0.72) and third trimester (aOR, 0.30; 95% CI, 0.11-0.78) as well as at both time points (aOR, 0.09; 95% CI, 0.02-0.41). High-risk obese women receiving low-dose aspirin for the prevention of preeclampsia have lower rates of complete inhibition of TXB2. These data suggest that an increase in aspirin dosing or frequency may be necessary in this population.

Relationship of platelet thromboxane inhibition by aspirin and all-cause mortality in patients with stable coronary artery disease

Aim: Anti-platelet therapy with aspirin (ASA) reduces nonfatal myocardial infarction, stroke, and cardiovascular death by irreversibly inhibiting platelet COX-1 and TxA2 production. However, variable TxA2 inhibition is common. We studied the relationship of urinary 11dhTxB2, an inactive TxA2 metabolite, with all-cause mortality in stable coronary artery disease (CAD) patients on ASA treatment.

Abstract 525: Integration of Platelet Agonist Signaling During the Hemostatic Response in vivo

The local microenvironment within an evolving hemostatic plug shapes the distribution of soluble platelet agonists, resulting in a gradient of platelet activation emanating from the site of injury. While thrombin and ADP mediated platelet activation are clearly critical for establishment of this gradient, it remains unclear to what extent there is overlap of these and other platelet signaling pathways in time and space. In other words, does a single agonist dominate the platelet activation state within specific regions of a hemostatic plug, or do multiple agonist pathways need to be integrated to produce the gradient of platelet activation observed? Further, how do the relationships among different agonists change in the face of anti-platelet or anti-coagulant therapy and what are the consequences for hemostatic plug organization? Here, we used a combination of genetic and pharmacologic approaches coupled with real-time intravital imaging to examine how thrombin, thromboxane A 2 , P2Y 12 and epinephrine signaling are coordinated in time and space to regulate the development of platelet activation gradients at a site of vascular injury in vivo. We found that both thromboxane A 2 /TP signaling and ADP/P2Y 12 signaling are required for accumulation of minimally activated platelets in the outer shell region of hemostatic plugs. Interestingly, dual inhibition of both thromboxane and P2Y 12 signaling did not have an additive effect, but rather was similar to inhibition of either pathway alone. Epinephrine, which activates a Gi signaling pathway similar to ADP/P2Y 12 , was completely dispensable for hemostatic plug formation, even in the absence of P2Y 12 signaling. Finally, inhibition of P2Y 12 in the setting of sub-maximal thrombin activity revealed no role for P2Y 12 signaling in the development of robust platelet activation within the hemostatic plug core region. Taken together, these data shed new light on the way multiple platelet signaling pathways are integrated during the hemostatic response in vivo, and predict the outcome of therapeutically targeting specific platelet signaling pathways alone and in combination on hemostatic plug organization.

0321: In the aera of new P2Y12 inihibitors, high platelet reactivity on aspirin in patients with ST elevation myocardial infarction remains a predictor of ischemic events

Despite dual antiplatelet treatment with the new P2Y12 platelet receptor antagonists (P2Y12i), major ischemic events are common following ST elevation myocardial infarction (STEMI). To assess separately resistance to aspirin (HPR-aspirin), resistance to P2Y12i (HPR-P2Y12i) and their association during the acute phase of STEMI in relation to the occurrence of ischemic events. We included all consecutive patients admitted for STEMI in our center between January 2013 and December 2013. All patients received a loading dose followed by a maintenance dose of aspirin (75mg/day) and either clopidogrel, prasugrel or ticagrelor. Platelet reactivity was assessed 4±1 days and 75±15 days after admission using light transmission aggregometry (LTA) with arachidonic acid (AA) and serum Thromboxane-B2 concentration to assess HPR-aspirin and LTA-ADP and VASP index to assess HPR-P2Y12i. Major cardiac and cerebrovascular events (MACCE) were recorded during one year. 106 patients (61years old, 76% male, 20% with diabetes) were included. STEMI was anterior in 52% and LV ejection fraction at discharge was 51±9%. At day 4 after STEMI, HPR-aspirin measured by LTA-AA alone was found in 23% patients and was correlated with serum thromboxane inhibition, HPR-P2Y12i (VASP≥50% and LTA-ADP≥65%) was observed only in 7% and combined resistance was present in 4% of the patients. Diabetes and age were predictors of HPR-aspirin. The large use of ticagrelor (34%) and prasugrel (50%) explained the low rate of P2Y12i resistance. HPR-aspirin was persistent 75 days later in 36% patients who were resistance at day 4. At 1 year, 7.9% patients had experienced MACCE. HPR-aspirin alone and HPR for both aspirin and P2Y12i were significantly associated with MACCE. Aspirin resistance is frequent just after STEMI and is associated with MACCE especially when associated with P2Y12i resistance.