Thromboxane Biosynthesis Research Articles

Determinants of thromboxane biosynthesis in rheumatoid arthritis: Role of RAGE and oxidant stress

Thromboxane (TX) biosynthesis by platelets and other cells in response to inflammatory triggers may provide a link between chronic inflammatory disease and atherothrombosis in rheumatoid arthritis (RA). In this study, we investigated the determinants of TX biosynthesis in RA, with particular reference to enhanced oxidative stress, receptor for advanced glycation end-products (RAGE) hyperactivity, and anti-tumor necrosis factor (TNF) treatment. Fifty-four patients with RA and 20 healthy subjects were recruited and a cross-sectional comparison of urinary 11-dehydro-TXB 2, 8-iso-PGF 2α, and plasma endogenous secretory RAGE (esRAGE) levels was performed between patients and controls. Urinary 11-dehydro-TXB 2 was significantly higher in RA patients than in healthy controls [425 (309–592) vs 233 (158–327) pg/mg creatinine, P < 0.0001]. Furthermore, urinary 8-iso-PGF 2α [323 (221–515) vs 172 (91–292) pg/mg creatinine, P < 0.0001] and plasma esRAGE [155 (100–240) vs 377 (195–486) pg/ml, P = 0.001] were higher and lower, respectively, in patients than in controls. A direct correlation was found between urinary 11-dehydro-TXB 2 and 8-iso-PGF 2α only in patients not on anti-TNF therapy ( r = 0.420, P = 0.021). Conversely, patients on anti-TNF therapy showed significantly lower urinary 8-iso-PGF 2α [284 (201–373) vs 404 (241–539) pg/mg creatinine, P = 0.043] but not 11-dehydro-TXB 2 than anti-TNF-treated subjects, with esRAGE as the only independent predictor of 11-dehydro-TXB 2 in this group of patients (adjusted R 2 = 0.496, β = − 0.725, SEM = 0.025, P = 0.001). In conclusion, we provide biochemical evidence of enhanced TX biosynthesis in patients with RA, driven, at least in part, by lipid peroxidation. Treatment with anti-TNF agents may blunt isoprostane generation in the absence of significant effects on TX biosynthesis. We suggest that RAGE hyperactivity may escape TNF blockade, thus contributing to persistent TX biosynthesis in this setting.

Aspirin as antiplatelet agent in diabetes. PROS-

Macrovascular complications in diabetes mellitus (DM) manifest themselves as accelerated atherosclerosis, clinically resulting in premature coronary artery disease (CAD), increased risk of cerebrovascular disease, and severe peripheral vascular disease [1]. Patients with type 2 diabetesmellitus (T2DM) have a twoto four-fold increase in the risk of CAD and patients with DM but without previous myocardial infarction (MI) carry the same level of risk for subsequent acute coronary events as non-diabetic patients with previous MI [2]. The abnormal metabolic state that accompanies diabetes is responsible for abnormalities in endothelial and platelet function, which may contribute to the cellular events that cause atherosclerosis and subsequently increase the risk of the adverse cardiovascular events. In particular, an altered platelet metabolism and changes in intraplatelet signalling pathways may contribute to the pathogenesis of atherothrombotic complications of diabetes. It is still under debate whether enhanced platelet activation is merely a consequence of more prevalent atherosclerotic lesions (relevant to a risk of thrombosis complicating plaque rupture) or reflects the influence of the accompanyingmetabolic disturbances on platelet biochemistry and function [3]. Since 1965 many studies demonstrated a variety of platelet alterations in diabetes [4]. Chronic hyperglycemia has been clearly identified as a causal factor for in vivo platelet activation in DM patients [3,5]. In 1990, Davi et al. demonstrated enhanced thromboxane (TX) biosynthesis in T2DM and provided evidence for its platelet origin [6]. Tightmetabolic control led to a reduction of TX levels in the same study [6]. We subsequently reported that the release of a platelet-derived inflammatorymolecule, soluble CD40 ligand, able to activate platelets, is largely thromboxane dependent, thus suggesting a potential mechanismof amplificationof thromboxane-dependent platelet activation [7]. Interestingly, the metabolic disorder rather than the attendant vasculardiseaseappears tobe responsible forpersistentplatelet activation in this setting [3]. This important issue has been further proven by the detection of enhanced TX biosynthesis in type 1 diabetic children and adolescents at diagnosis, presumably driven by the underlying inflammatory burden [8], as well as in newly-diagnosed type 2 diabetic subjects free of vascular disease. In the latter the biochemical abnormality is reversible by dampening postprandial glycemic spikes with acarbose treatment [9]. Consistently, acute, short-term hyperglycemia induces increased activation of platelets exposed to high shear stress conditions

A selective inhibitor of thromboxane biosynthesis (OKY-046) reduces the airway response to inhaled leukotriene D4 and acetylcholine in patients with asthma

A selective inhibitor of thromboxane biosynthesis (OKY-046) reduces the airway response to inhaled leukotriene D4 and acetylcholine in patients with asthma

The contribution of cyclooxygenase-1 and -2 to persistent thromboxane biosynthesis in aspirin-treated essential thrombocythemia: implications for antiplatelet therapy

AbstractWe tested whether cyclooxygenase 2 (COX-2) expression and unacetylated COX-1 in newly formed platelets might contribute to persistent thromboxane (TX) biosynthesis in aspirin-treated essential thrombocythemia (ET). Forty-one patients on chronic aspirin (100 mg/day) and 24 healthy subjects were studied. Platelet COX-2 expression was significantly increased in patients and correlated with thiazole orange–positive platelets (r = 0.71, P < .001). The rate of TXA2 biosynthesis in vivo, as reflected by urinary 11-dehydro-TXB2 (TXM) excretion, and the maximal biosynthetic capacity of platelets, as reflected by serum TXB2, were higher in patients compared with aspirin-treated healthy volunteers. Serum TXB2 was significantly reduced by the selective COX-2 inhibitor NS-398 added in vitro. Patients were randomized to adding the selective COX-2 inhibitor, etoricoxib, or continuing aspirin for 7 days. Etoricoxib significantly reduced by approximately 25% TXM excretion and serum TXB2. Fourteen of the 41 patients were studied again 21 (± 7) months after the first visit. Serum TXB2 was consistently reduced by approximately 30% by adding NS398 in vitro, while it was completely suppressed with 50μM aspirin. Accelerated platelet regeneration in most aspirin-treated ET patients may explain aspirin-persistent TXA2 biosynthesis through enhanced COX-2 activity and faster renewal of unacetylated COX-1. These findings may help in reassessing the optimal antiplatelet strategy in ET.

Effect of two doses of aspirin on thromboxane biosynthesis and platelet function in patients undergoing coronary surgery

Early post-operative aspirin improves survival in patients undergoing coronary artery bypass graft (CABG). However, most patients do not benefit of aspirin after CABG, still remaining at risk of thrombotic events due to insufficient platelet inhibition, specifically via the thromboxane (TX) pathway. We evaluated the effect of two aspirin doses (100 or 325 mg daily, enteric coated formulations) on platelet function and TX biosynthesis in patients after CABG and assessed whether the incidence of residual platelet reactivity could be reduced by the higher dose. Fifty-six patients undergoing CABG were randomly assigned to 100 or 325 mg aspirin daily for five days in a prospective single-centre study. Treatment effect was assessed by measuring either platelet function (light-transmission aggregometry and point-of-care PFA-100(R)) or TX biosynthesis in collagen-stimulated platelets, serum, urine, and in lipopolysaccharide (LPS)-cultured whole blood (WB). An insufficient TX inhibition was observed with 100 mg aspirin but not with the higher dose. The different effect of the two doses was, however, highlighted by either TX (platelet- or serum-derived) or by PFA-100(R) but not by the other assays. In conclusion, early after CABG, the incidence of residual platelet activity was lower in patients who received 325 mg aspirin. Moreover, evidence was provided that different methods yield different results in the detection of aspirin resistance, rendering them not interchangeable.

Response to Letter Regarding Article, “Incomplete Inhibition of Thromboxane Biosynthesis by Acetylsalicylic Acid: Determinants and Effect on Cardiovascular Risk”

To the Editor: In their article about 3261 aspirin-treated patients enrolled in the Clopidogrel for the High Atherothrombotic Risk and Ischemic Stabilization, Management and Avoidance (CHARISMA) trial,1 Eikelboom et al suggest that incomplete inhibition of platelet thromboxane biosynthesis by aspirin is associated with heightened cardiovascular risk on the basis of the finding that high urinary concentrations of the thromboxane A2 metabolite, 11-dehydrothromboxane B2, were associated with increased risk for cardiovascular events. Among the limitations of this study that have been acknowledged by the authors, the choice of urinary 11-dehydrothromboxane B2 …

Letter by Cattaneo Regarding Article, “Incomplete Inhibition of Thromboxane Biosynthesis by Acetylsalicylic Acid: Determinants and Effect on Cardiovascular Risk”

To the Editor: In their article about 3261 aspirin-treated patients enrolled in the Clopidogrel for the High Atherothrombotic Risk and Ischemic Stabilization, Management and Avoidance (CHARISMA) trial,1 Eikelboom et al suggest that incomplete inhibition of platelet thromboxane biosynthesis by aspirin is associated with heightened cardiovascular risk on the basis of the finding that high urinary concentrations of the thromboxane A2 metabolite, 11-dehydrothromboxane B2, were associated with increased risk for cardiovascular events. Among the limitations of this study that have been acknowledged by the authors, the choice of urinary 11-dehydrothromboxane B2 …

Spice active principles as the inhibitors of human platelet aggregation and thromboxane biosynthesis

Spice active principles are reported to have anti-diabetic, anti-hypercholesterolemic, antilithogenic, anti-inflammatory, anti-microbial and anti-cancer properties. In our previous report we have shown that spices and their active principles inhibit 5-lipoxygenase and also formation of leukotriene C4. In this study, we report the modulatory effect of spice active principles viz., eugenol, capsaicin, piperine, quercetin, curcumin, cinnamaldehyde and allyl sulphide on in vitro human platelet aggregation. We have demonstrated that spice active principles inhibit platelet aggregation induced by different agonists, namely ADP (50 μM), collagen (500 μg/ml), arachidonic acid (AA) (1.0 mM) and calcium ionophore A-23187 (20 μM). Spice active principles showed preferential inhibition of arachidonic acid-induced platelet aggregation compared to other agonists. Among the spice active principles tested, eugenol and capsaicin are found to be most potent inhibitors of AA-induced platelet aggregation with IC50 values of 0.5 and 14.6 μM, respectively. The order of potency of spice principles in inhibiting AA-induced platelet aggregation is eugenol>capsaicin>curcumin>cinnamaldehyde>piperine>allyl sulphide>quercetin. Eugenol is found to be 29-fold more potent than aspirin in inhibiting AA-induced human platelet aggregation. Eugenol and capsaicin inhibited thromboxane B2 (TXB2) formation in platelets in a dose-dependent manner challenged with AA apparently by the inhibition of the cyclooxygenase (COX-1). Eugenol-mediated inhibition of platelet aggregation is further confirmed by dose-dependent decrease in malondialdehyde (MDA) in platelets. Further, eugenol and capsaicin inhibited platelet aggregation induced by agonists—collagen, ADP and calcium ionophore but to a lesser degree compared to AA. These results clearly suggest that spice principles have beneficial effects in modulating human platelet aggregation.

The anti-inflammatory pharmacology of Pycnogenol ® in humans involves COX-2 and 5-LOX mRNA expression in leukocytes

We investigated the effects of Pycnogenol ® supplementation on the arachidonic acid pathway in human polymorphonuclear leukocytes (PMNL) in response to an inflammatory stimulus. Pycnogenol is a standardised extract of French maritime pine bark consisting of procyanidins and polyphenolic monomers. Healthy volunteers aged 35 to 50 years were supplemented with 150 mg Pycnogenol a day for five days. Before and after the final day of supplementation, blood was drawn and PMNL were isolated. PMNL were primed with lipopolysaccharide (LPS) and stimulated with the receptor-mediated agonist formyl-methionyl-leucyl-phenylalanine (fMLP) to activate the arachidonic acid pathway and the biosynthesis of leukotrienes, thromboxane and prostaglandins. Pycnogenol supplementation inhibited 5-lipoxygenase (5-LOX) and cyclooxygenase-2 (COX-2) gene expression and phospholipase A2 (PLA2) activity. This effect was associated with a compensatory up-regulation of COX-1 gene expression. Interestingly, Pycnogenol suspended the interdependency between 5-LOX and 5-lipoxygenase activating protein (FLAP) expression. Pycnogenol supplementation reduced leukotriene production but did not leave prostaglandins unaltered, which we attribute to a decline of COX-2 activity in favour of COX-1. Here we show for the first time that Pycnogenol supplementation simultaneously inhibits COX-2 and 5-LOX gene expression and reduces leukotriene biosynthesis in human PMNL upon pro-inflammatory stimulation ex vivo.

Aspirin and Other Non-Steroidal Anti-Inflammatory Drugs as Cyclooxygenase Inhibitors: State of the Art, Barriers and Perspectives

Non-steroidal anti-inflammatory drugs (NSAIDs) claimed during last years an increased research interest to establish their cardiovascular safety profile. Generally, NSAIDs inhibit in different degrees both isoforms of cyclooxygenase (COX). Aspirin has a unique property among NSAIDs, namely at low doses it inactivates irreversibly the COX-1 activity in platelets. It is well known that platelets are a significant source of inflammatory mediators and their activation leads to important clinical atherothrombotic vascular events. Atherosclerosis is a chronic inflammatory process. The cardioprotective effect of aspirin resides in its mechanism of action, suppressing the platelet COX-1 dependent thromboxane biosynthesis. There are patients who do not benefit from the cardioprotective effect of aspirin, being labeled as “resistant” to aspirin. The underlying mechanism of aspirin resistance is yet unclear. This review intends to detail recent advances in the field of molecular simulation applied to nonselective non-aspirin NSAIDs and other COX selective inhibitors. Binding studies were performed between the COX-2 enzyme and these molecules. Using 2D-QSAR, it was noticed that the lipophilic bulkier group width-wise is required for a significant biological activity and also, the hydrophobic interactions might be crucial for the potency of same COX inhibitors. In order to understand a meaningful comparison of both classical NSAIDs and newer COX-2 inhibitors, three-dimensional quantitative structure-activity relationships and also molecular docking techniques were applied.

Thrombin as a common downstream target blocking both platelet and monocyte activation

Thromb Haemost 2009; 101: 220–221 Platelets play a pivotal role in the pathogenesis of thrombotic complications after percutaneous coronary interventions (PCI) (1). The use of optimal antiplatelet therapy is critical in reducing adverse events in this setting. Despite the efficacy of dual antiplatelet therapy in patients undergoing PCI, thrombo-ischaemic events and, in particular, stent thrombosis are frequent complications (2). High post-treatment platelet reactivity is associated with cardiovascular outcome after PCI (3) and coronary stent implantation (4). Different agents are currently in use for adjunctive anticoagulant treatment on top of adequate antiplatelet regimen during PCI. Traditionally, unfractionated heparin (UFH) has been the standard anticoagulant administered during coronary intervention. Enhanced platelet activation in vivo and ex vivo has been shown after UFH treatment (5, 6). Moreover, heparin does not suppress the transient increase in thromboxane biosynthesis associated with coronary angioplasty (7). Low-molecular-weight heparin (LMWH), in contrast, does not affect platelet activation in vivo and ex vivo after PCI (5, 8). Recently bivalirudin, a short-acting direct thrombin inhibitor, has been shown to be effective and safe in patients undergoing PCI (9), with reduced bleeding as compared with heparin. Reduced inhibition of adenosine diphosphate (ADP)-induced platelet aggregation at the time of PCI is associated with an increased risk for adverse thrombotic complications (10). Bivalirudin, given during PCI in patients pretreated with 600 mg of clopidogrel, is unlike UFH associated with further inhibition of platelet aggregation (11). A similar effect by bivalirudin was previously described on platelet P-selectin (12). Moreover, bivalirudin alone or coupled with clopidogrel may significantly down© 2009 Schattauer GmbH, Stuttgart

Density Functional Studies on Thromboxane Biosynthesis: Mechanism and Role of the Heme‐Thiolate System

Reaction mechanisms for the isomerization of prostaglandin H(2) to thromboxane A(2), and degradation to 12-L-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and malondialdehyde (MDA), catalyzed by thromboxane synthase, were investigated using the unrestricted Becke-three-parameter plus Lee-Yang-Parr (UB3LYP) density functional level theory. In addition to the reaction pathway through Fe(IV)-porphyrin intermediates, a new reaction pathway through Fe(III)-porphyrin pi-cation radical intermediates was found. Both reactions proceed with the homolytic cleavage of endoperoxide O-O to give an alkoxy radical. This intermediate converts into an allyl radical intermediate by a C-C homolytic cleavage, followed by the formation of thromboxane A(2) having a 6-membered ring through a one electron transfer, or the degradation into HHT and MDA. The proposed mechanism shows that an iron(III)-containing system having electron acceptor ability is essential for the 6-membered ring formation leading to thromboxane A(2). Our results suggest that the step of the endoperoxide O-O homolytic bond cleavage has the highest activation energy following the binding of prostaglandin H(2) to thromboxane synthase.

Incomplete Inhibition of Thromboxane Biosynthesis by Acetylsalicylic Acid

Incomplete inhibition of platelet thromboxane generation, as measured by elevated urinary 11-dehydro thromboxane B(2) concentrations, has been associated with an increased risk of cardiovascular events. We aimed to determine the external validity of this association in aspirin-treated patients enrolled in the Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization, Management and Avoidance (CHARISMA) trial and to determine whether there are any modifiable factors or interventions that lower urinary 11-dehydro thromboxane B(2) concentrations that could thereby reduce cardiovascular risk. Urinary 11-dehydro thromboxane B(2) concentrations were measured in 3261 aspirin-treated patients at least 1 month after they had been randomly assigned to placebo or clopidogrel. Baseline urinary 11-dehydro thromboxane B(2) concentrations in the highest quartile were associated with an increased risk of stroke, myocardial infarction, or cardiovascular death compared with the lowest quartile (adjusted hazard ratio 1.66, 95% CI 1.06 to 2.61, P=0.03). Increasing age, female sex, history of peripheral artery disease, current smoking, and oral hypoglycemic or angiotensin-converting enzyme inhibitor therapy were independently associated with higher urinary concentrations of 11-dehydro thromboxane B(2), whereas aspirin dose > or =150 mg/d, history of treatment with nonsteroidal antiinflammatory drugs, history of hypercholesterolemia, and statin treatment were associated with lower concentrations. Randomization to clopidogrel (versus placebo) did not reduce the hazard of cardiovascular events in patients in the highest quartile of urinary 11-dehydro thromboxane B(2) levels. In aspirin-treated patients, urinary concentrations of 11-dehydro thromboxane B(2) are an externally valid and potentially modifiable determinant of stroke, myocardial infarction, or cardiovascular death in patients at risk for atherothrombotic events.

Circulating endothelial progenitor cells and residual in vivo thromboxane biosynthesis in low-dose aspirin-treated polycythemia vera patients

AbstractPolycythemia vera (PV) is associated with high morbidity and mortality for thrombosis. We hypothesized that in PV altered sensitivity to aspirin might be related to dysfunction of the endothelial repair and/or of the nitric oxide (NO) system. Urinary thromboxane (TX) A2 metabolite (TXM), endothelial colony-forming cells (ECFCs), plasma asymmetric dimethylarginine (ADMA) and von Willebrand factor (VWF) were measured in 37 PV patients on low-dose aspirin and 12 healthy controls. Patients showed an approximately 2-fold increase in median TXM and plasma ADMA levels (P < .001), while ECFC numbers were reduced by approximately 7-fold (P < .001) as compared with nonaspirinated control. These differences were more pronounced in patients with previous thrombosis. An 8-week course of aspirin did not affect ECFCs in 6 controls. VWF and TXM correlated directly with ADMA, and inversely with ECFCs. By multiple regression analysis, lower ECFC quartiles (beta = −0.39; SE = 0.17; P = .028) and higher VWF levels (beta = 0.338, SE = 0.002, P = .034) were independent predictors of higher TXM quartiles (R2 = 0.39). Serum TXB2, measured in 22 patients, was approximat-ly 10-fold higher than aspirin-treated controls. PV patients appear to have an unbalanced ECFC/NO axis, and an apparent altered sensitivity of platelet TXA2 production, all potentially contributing to aspirin-insensitive TXM formation. Thus, additional antithrombotic strategies may be beneficial in PV.

Molecular modeling study on chemically diverse series of cyclooxygenase-2 selective inhibitors: generation of predictive pharmacophore model using Catalyst

Cyclooxygenase (COX) enzymes catalyse the biosynthesis of prostaglandins and thromboxane from arachidonic acid (AA). We summarize in this paper, the development of pharmacophores of a dataset of inhibitors for COX-2 by using the Catalyst/Hypogen module using six chemically diverse series of compounds. Training set consisting of 24 compounds was carefully selected. The activity spread of the training set molecules was from 0.1 to 10000 nM. The most predictive pharmacophore model (hypothesis 1), consisting of four features, namely, one hydrogen bond donor, one hydrogen bond acceptor, one hydrophobic aliphatic and one ring aromatic feature, had a correlation (r) of 0.954 and a root mean square deviation of 0.894. The entropy (configuration cost) value of the hypotheses was 16.79, within the allowed range. The difference between the null hypothesis and the fixed cost and between the null hypothesis and the total cost of the best hypothesis (hypothesis 1) was 88.37 and 78.51, respectively. The model was validated on a test set consisting of six different series of structurally diverse 22 compounds and performed well in classifying active and inactive molecules correctly. This validation approach provides confidence in the utility of the predictive pharmacophore model developed in this work as a 3D query tool in the virtual screening of drug like molecules to retrieve new chemical entities as potent COX-2 inhibitors. The model can also be used to predict the biological activities of compounds prior to their costly and time-consuming synthesis.

Endothelial Progenitor Cells and Angiogenesis Join the PPARty

See related article, pages 80–88 Peroxisome proliferator-activated receptors (PPARs) are ligand-inducible transcription factors that belong to the nuclear hormone receptor superfamily.1 In mammals, the PPAR family consists of 3 subtypes of proteins encoded by separate genes: PPARα (NR1C1), PPARγ (NR1C3), and PPARδ (also known as β or NR1C2).2 They act as heterodimers with the retinoid X receptor and regulate gene transcription by binding to specific response elements in the promoter of the target genes.3 The classical biological activity of PPARα is the regulation of the rate of fatty acid uptake and their esterification into triglyceride or oxidation,4–7 whereas PPARγ is classically involved in adipocyte differentiation, regulation of fat storage, and maintenance of glucose homeostasis.5 The physiological functions of PPARδ are instead still unclear, although it is known that this receptor contributes to an inflammatory switch through its association and disassociation with transcriptional repressors.8 The clinical importance of PPARs originates with fibrates and thiazolidinediones (TZDs), which respectively act on PPARα and PPARγ and are used to ameliorate hyperlipidemia and hyperglycemia in subjects with type 2 diabetes mellitus (T2DM). Fibrates, such as gemfibrozil, clofibrate, fenofibrate, and bezofibrate, are drugs that effectively reduce triglycerides (TG) and free …

Triflusal versus Aspirin for the Prevention of Stroke

ABSTRACTAntiplatelet agents represent an important part of the therapeutic armamentarium in the prevention of stroke. Triflusal is an antiplatelet agent structurally related to salicylates but not derived from acetylsalicylic acid. Like aspirin, triflusal irreversibly acetylates cyclo-oxygenase isoform 1 (COX-1) and therefore inhibits thromboxane biosynthesis. Triflusal is rapidly absorbed after oral administration, with an absorption half life of 0.44 hours. Evidence of the efficacy and safety of triflusal is derived from clinical trials performed in patients with unstable angina, acute myocardial infarction, stroke, aortocoronary by-pass, atrial fibrillation, valve replacement, and asthmatic patients intolerant to aspirin and/or non-steroidal antiinflamatory drugs (NSAID). The Triflusal versus Aspirin for the Prevention of Infarction: A Randomized Stroke Study (TAPIRSS) study was performed to explore the efficacy and safety of triflusal versus aspirin in the prevention of vascular complications in patients with a previous TIA or ischemic stroke in a Latin American population. In this pilot study differences between triflusal and aspirin in the prevention of vascular complications after TIA or ischemic stroke were not observed. Hemorrhagic risk was lower with triflusal than with aspirin. The TAPIRSS study contributed evidence on the efficacy and safety of triflusal as a valid alternative to aspirin in the prevention of vascular events in patients with ischemic stroke or TIA.

Aspirin therapy and thromboxane biosynthesis in systemic lupus erythematosus

Incomplete suppression of thromboxane biosynthesis during aspirin therapy is associated with increased cardiovascular risk. Since systemic lupus erythematosus (SLE) is associated with platelet activation and increased cardiovascular mortality, we compared thromboxane and prostacyclin biosynthesis in patients with SLE and control subjects, and measured inhibition of thromboxane excretion in aspirin-treated subjects. We measured the urinary excretion of 11-dehydro thromboxane B( 2) (TXB(2)) and 2,3-dinor 6-ketoPGF(1alpha) (PGI-M), the stable metabolites of thromboxane A(2) and prostacyclin, respectively, in 74 patients with SLE and 70 controls. In subjects who were not receiving aspirin, TXB(2) excretion was higher in patients with SLE [0.40 ng/mg creatinine (0.26-0.64), median (interquartile range)] than controls [0.31 ng/mg creatinine (0.23-0.44)] (P = 0.04), and in these patients, TXB(2) excretion correlated with disease activity (rho = 0.28, P = 0.03) and tumor necrosis factor alpha (rho = 0.48, P < 0.001). Aspirin therapy resulted in significantly lower TXB(2) excretion in controls (P = 0.01), but not in patients with SLE (P = 0.10), compared with subjects not receiving aspirin. Prostacyclin biosynthesis did not differ among patients and controls, and was not affected by aspirin (P all >0.35). Thromboxane biosynthesis is increased in SLE and is associated with disease activity. Additionally, response to aspirin may be attenuated in some patients with SLE.

Chronic effects of oral prostacyclin analogue on thromboxane A2 and prostacyclin metabolites in pulmonary hypertension.

Abnormal biosynthesis of thromboxane and prostacyclin has been implicated in patients with primary pulmonary hypertension and secondary pulmonary hypertension associated with congenital heart disease, and could be involved in the pathogenesis of pulmonary vascular disease. The chronic effects of an oral prostacyclin analogue, beraprost sodium, on thromboxane and prostacyclin biosynthesis and on pulmonary circulation were investigated in 15 children with pulmonary hypertension. The plasma concentrations of thromboxane B2 and 6-keto-prostaglandin F1 alpha were measured, as was the urinary excretion of 11-dehydro-thromboxane B2 and 2,3-dinor-6-keto-prostaglandin F1 alpha, which are stable metabolites of thromboxane A2 and prostacyclin, respectively. In patients with pulmonary hypertension, the plasma concentration of thromboxane B2 and the ratio of thromboxane B2 to 6-keto-prostaglandin F1 alpha were greater than in healthy controls: 210 +/- 49 versus 28 +/- 4 pg/mL (P < 0.05) and 32.6 +/- 8.9 versus 5.7 +/- 1.8 (P < 0.01), respectively. After 3 months of administration of beraprost, the plasma concentration of thromboxane B2 and the ratio of thromboxane B2 to 6-keto-prostaglandin F1 alpha were reduced significantly: 210 +/- 49 to 98 +/- 26 pg/mL (P < 0.01) and 32.6 +/- 8.9 to 18.0 +/- 6.7 (P < 0.05), respectively. In contrast, the plasma concentrations of 6-keto-prostaglandin F1 alpha in patients were slightly but not significantly higher than in controls, and did not change significantly after administration of beraprost. The concentrations of 11-dehydro-thromboxane B2 and 2,3-dinor-6-keto-prostaglandin F1 alpha in urine correlated significantly with thromboxane B2 and 6-keto-prostaglandin F1 alpha, respectively, in plasma. Beraprost improved the imbalance of thromboxane and prostacyclin biosynthesis and has a potential efficacy for preventing the progressive development of pathological changes in pulmonary vasculature.

Invited commentary

Aspirin is widely used to reduce graft thrombosis after coronary artery bypass grafting. However, aspirin only prevents approximately 25% of all ischemic vascular events and there are many causes, including all the causes of aspirin resistance for the other events. Aspirin resistance is the inability of aspirin to block platelet production of thromboxane A2 and subsequent platelet activation and aggregation. Increasing degrees of aspirin resistance may correlate independently with increasing risk of cardiovascular events. The study by Lim and colleagues [1Lim E. Carballo S. Cornelissen J. et al.Dose-related efficacy of aspirin after coronary surgery in patients with PlA2 polymorphism (NCT00262275).Ann Thorac Surg. 2007; 83: 134-139Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar] analyzed a genetic polymorphism within a subgroup of a prospective randomized trial. They attempted to evaluate the role of genetic polymorphism on the aspirin response in patients after coronary artery bypass grafting. The authors postulated that several genetic polymorphisms are common and some may affect responses to aspirin. In particular, PIA2 polymorphism seems to cause aspirin resistance. As with most genetic studies, the results were not clear-cut and statistical significance was not achieved, although trends were similar to published results. The design of this study is a major weakness for determining correlation between clinical findings and genetic polymorphisms. Basically most studies on genetic polymorphism need several populations of subjects. Several different subject populations or a highly selected group can establish a correlation between clinical findings and polymorphisms. Analytic studies that investigate the association of biochemical aspirin resistance and clinical events must quantitatively account for potential confounders (eg, age, sex, ethnicity, and clinical conditions), hematologic and biochemical factors (eg, hyperlipidemia, platelet count, and hemoglobin level), and nonadherence. The analysis in this study did not consider aspirin resistance that can be diagnosed in the laboratory by measurement of platelet thromboxane A2 production or thromboxane-dependent platelet function. Potential causes of aspirin resistance include inadequate dose, drug interactions, genetic polymorphisms involved in thromboxane biosynthesis, upregulation of nonplatelet sources of thromboxane biosynthesis, and increased platelet turnover. To prove the association between the polymorphism and clinical risk, statistical exclusion of confounders is required to reach a conclusion. Differential sensitivity to aspirin may have potential clinical implications, whereby specific antiplatelet therapy is best tailored to a patient’s PIA2 genotype. A well-designed study in a larger population is necessary to confirm the association between genetic polymorphisms and aspirin resistance. Dose-Related Efficacy of Aspirin After Coronary Surgery in Patients With PlA2 Polymorphism (NCT00262275)The Annals of Thoracic SurgeryVol. 83Issue 1PreviewTo evaluate the impact of the genetic polymorphisms affecting aspirin response using platelet aggregation and the response to different aspirin doses after cardiopulmonary bypass, we performed a subanalysis of the results from a randomized trial evaluating low- and medium-dose aspirin and clopidogrel. Full-Text PDF