- Open Access
The antithrombotic profile of aspirin. Aspirin resistance, or simply failure?
© Altman et al; licensee BioMed Central Ltd. 2004
- Received: 13 November 2003
- Accepted: 14 January 2004
- Published: 14 January 2004
- Platelet Aggregation
- Aspirin Resistance
- Arterial Thrombotic Event
Cyclooxygenase-1 [COX-1, prostaglandin synthase] catalyses the transformation of arachidonic acid to the unstable intermediate prostaglandin PGH2. Subsequently, thromboxane synthase acts on PGH2 to form TXA2, a transient biological product that induces platelet aggregation and is a powerful vasoconstrictor. Aspirin acts primarily by interfering with the biosynthesis of cyclic prostanoids: TXA2, prostacyclin, and other prostaglandins. It irreversibly inhibits COX-1 by acetylation of serine-530 and induces a long-lasting functional defect in the platelets. The resultant decrease in production of prostaglandins and TXA2 probably accounts for much of aspirin's antithrombotic effect [1, 2]. The plasma half-life of aspirin is only 20 min in circulating blood. It is rapidly deacetylated and converted to salicylate in vivo. Salicylate does not affect COX-1 or COX-2 activity .
Because platelets cannot generate new COX, the effects of aspirin last for the duration of the life of the platelet [10 days]. After a single dose of aspirin, platelet COX activity recovers by 10% per day in parallel with platelet turnover. Although it may take 10 days for the total platelet population to be renewed, it has been shown that if as few as 20% of the platelets have normal COX activity, hemostasis may be normal.
TXA2 and PGI2 have opposing effects on hemostasis but the data suggest that the antithrombotic effects of TXA2 inhibition predominate over the possible prothrombotic effects of PGI2 inhibition .
The usual anti-thrombotic dose of ASA ranges from 80 to 500 mg/day. Platelet inhibition, as indicated by aggregometry, occurs very rapidly: within 5 min of ingestion of 320 mg lysine acetylsalicylate, or within 30 to 60 min of oral 320 mg acetylsalicylic acid administration .
As COX-1 inhibition by aspirin is irreversible, there is a cumulative inhibition of TXA2 generation by platelets when low doses of aspirin are administered chronically . There is a non-linear relationship between inhibition of platelet TXA2 generation and inhibition of TXA2-dependent platelet aggregation. More than 95% inhibition of TXA2 generation is necessary to influence function . With low aspirin doses, platelet thromboxane falls below 95% only after several days. Nevertheless, low-dose [40 to 60 mg] as well as high-dose [500 mg] aspirin suppresses thromboxane A2 synthesis by >95% [7, 8].
Although aspirin at high doses is anti-inflammatory due to inhibition of COX-2, it is 170-fold more potent in inhibiting COX-1 than COX-2 . Low aspirin doses that have little or no measurable anti-inflammatory effect leave vascular prostacyclin formation almost intact . Doses of aspirin in excess of 80 mg/d result in substantial inhibition of endogenous prostacyclin biosynthesis . Two hours after 150 mg aspirin intake, 81 to 100 per cent inhibition of prostacyclin synthesis was demonstrated .
Epidemiological studies have indicated that very low and very high doses of aspirin [30–1500 mg] have equivalent anti-thrombotic effects, suggesting that inhibition of platelet COX-1 is indeed the crucial target of aspirin . This supports the view that inhibition of platelet COX-1 by low doses is sufficient to explain the cardio-protective effect of aspirin observed in clinical trials . Aspirin reduces the risk of secondary events by about 25% in cardiovascular diseases  but some patients have recurrent vascular events in spite of aspirin therapy. It has been proposed that these patients are resistant to aspirin's antithrombotic effect.
Nevertheless, as published by Syrbe et al.,  individual dose of aspirin seems to be necessary to full inhibition of ex-vivo platelet aggregation. Thus adjusted dose of aspirin for individuals with cardiovascular diseases could be necessary to prevent failure (aspirin resistance?) of therapy
Failure of aspirin to produce the expected inhibition of platelet function might be attributed to several mechanisms. Many individuals treated with aspirin do not achieve the inhibitory response anticipated on the basis of laboratory measurements of platelet activation and aggregation, a phenomenon termed "aspirin resistance" . Antiplatelet drugs that are effective and safe in one individual may be ineffective in another. Aspirin is a weak platelet inhibitor, so on its own it does not provide sufficient antithrombotic therapy in some clinical or experimental circumstances. It seems that resistance to aspirin may be associated with an increase of arterial thrombotic events in spite of chronic intake. In ex vivo assays using aggregometry, with sodium arachidonate as agonist, aspirin inhibits platelet aggregation irreversibly in most people. However, in several patients, aspirin does not afford the degree of platelet inhibition needed to preclude events according to in vitro assessments [16–18].
Gum, Topol and co-workers  found a significant correlation between aspirin resistance as measured by platelet aggregation and the composite primary outcome of death, myocardial infarction, or cerebrovascular accident in patients with stable cardiovascular disease. Of the 326 patients studied, 17 [5.2%] were resistant to 325 mg/day aspirin. Insufficient inhibition of platelet aggregation by aspirin ["aspirin resistance"] has been observed in 6–24% of patients with stable coronary artery disease: by optical aggregation, 5.5% of the patients were aspirin resistant and 23.8% were aspirin semi-responders.
The PFA-100 [Platelet Function Analyzer, Dade] is a device that simulates platelet function in vitro at high shear. The test is performed by combining 2 agonists in cartridge form: collagen/ADP and collagen/epinephrine. Closure time is the time required for platelets to effect full occlusion of an aperture cut into a membrane coated with the pair of agonists. Under standardized flow conditions, platelet activation and aggregation slowly build a stable platelet plug at the aperture . The PFA-100 system allows quantitative assessment of platelet function, reporting platelet aggregability as the time required to close the small aperture in the biologically active membrane. This analyzer detects no difference between the effects of low and high-dose aspirin on platelet function . In the study by Gum and co-workers, 9.5% of patients were aspirin resistant  according to the PFA-100.
Aspirin resistance is significantly associated with an increased risk of death, myocardial infarction or cerebrovascular accident compared with aspirin-sensitive patients [24% vs. 10%, P = 0.03] . This study suggests that aspirin non-responders might obtain less benefit with respect to cardiovascular events. Aspirin non-responder status may contribute to failure of aspirin therapy in the secondary prevention of cerebrovascular incidents in as many as 30–40 % of patients .
In the paper by Eikelboom et al. , 488 patients who suffered myocardial infarction or stroke or died from cardiovascular causes were compared with 488 patients who had no cardiovascular event; all 976 patients took aspirin. The patients in the highest quartile of urinary 11-dehydrothromboxane B2 excretion levels [i.e. those who were least affected by aspirin intake] had a 3·5-fold higher risk of cardiovascular death compared with those in the lowest quartile .
With documented evidence of congestive heart failure [left ventricular ejection fraction <40% and New York Heart Association class II to IV symptoms], 88 outpatients who had been treated with aspirin 325 mg/day for ≥1 month were included in the study by Sane et al.. Platelets were stimulated with 5 μM of adenosine diphosphate [ADP], 1 μg/ml of collagen or 5 μM of epinephrine, and aggregation was assessed using a Chronolog Lumi-Aggregometer. Whole blood aggregation was determined using the Chronolog device and the sample was stimulated with 4 μg/ml of collagen. Platelet receptor expression was assessed by flow cytometry. The effect of shear stress on platelet function was analyzed using the PFA-100. Closure times were determined using collagen/epinephrine test cartridges. Patients were considered aspirin non-responsive when 4 of the 5 parameters assayed were observed. Persistent platelet activation despite aspirin therapy was detected in 50 of the 88 patients [56.8%]. Using the criterion of closure time ≤193 s with the collagen/epinephrine cartridge , 49 of 88 patients [55.7%] could be considered aspirin resistant.
Patients undergoing coronary artery bypass grafting (CABG) have a high incidence of aspirin resistance. Before CABG, 10 μmol/L aspirin inhibited more than 90% of thromboxane formation within 15 min. In aspirin-resistant PRP, the inhibition of thromboxane formation was significantly delayed .
Aspirin may not be cardioprotective in patients with hyperlipidaemia. Platelet aggregation was measured using a final collagen concentration of 1.0 μg/ml in 56 patients receiving aspirin 325 mg/day who had a history of coronary heart disease. The 14 patients with poor responsiveness to aspirin had significantly higher mean concentrations of total cholesterol and LDL cholesterol than the 42 patients with good responsiveness. In total, 9/13 [69%] patients with hyperlipidemia had poor responsiveness to aspirin .
Recent data also indicate that other nonsteroidal anti-inflammatory drugs [NSAIDs] might interfere with aspirin's effects [27, 28]. Kurth et al  suggested that regular but not intermittent use of NSAIDs inhibits the clinical benefits of aspirin.
Experimental models have also shown that aspirin fails to prevent thrombosis-related activities. Thrombin generated at an endothelial lesion induces platelet activation, an activity not affected by aspirin . Maalej and Folts  showed, in a canine model with coronary artery stenosis, that aspirin did not prevent the reduction in cyclic flow. As several potential agonists are released when the vascular endothelium is damaged, not only from platelets but also from the endothelial cells, erythrocytes and leukocytes, it may be supposed that the inhibitory effect of aspirin may also be overwhelmed in vivo. This study might explain why both platelet aggregation and platelet count are significantly lower in the coronary venous blood than in the aortic blood of patients with coronary artery disease, though not in normals; this was found many years ago by Metha et al. .
Santos and colleagues  found that the synergism between red cells and platelets in promoting thrombosis was not prevented by low-dose aspirin but only by 500 mg/day. The implication of these studies is that patients taking aspirin may not be fully protected against arterial thrombosis . In 1986 and 1988 [34, 35], through ex vivo aggregation experiments with platelet-rich plasma from volunteers taking aspirin, we showed that the inhibitory effect of aspirin on platelet aggregation induced by sodium arachidonate was overcome by the synergism between sodium arachidonate and platelet activating factor, or ADP or collagen. We employed a mixed agonist system in an attempt to better reflect the multiple stimuli that platelets encounter during in vivo activation. Under these conditions a normal platelet aggregation pattern was obtained, although the thromboxane level measured in the stimulated platelet-rich plasma was less than 5% in all aspirinated samples. Since this constitutes a "physiological effect at the site of eventual endothelial damage" it can not be called aspirin resistance.
As was also suggested by Bertele et al. , our study indicated no correlation between platelet function and thromboxane level, implying that aspirin does not prevent an agonist potentiation effect when low doses or a daily high dose are administered. These results are in line with those obtained by Cerletti et al. 
On the other hand, it is possible that in the PFA-100 device where a collagen/epinephrine or ADP/epinephrine coated cartridge is used, the synergistic effect of these two agonists has a similar outcome to that observed in our PRP aggregation studies. We suggest that this can not be called aspirin resistance and that the PFA-100 system used to define this concept, was overestimated
As pointed out by Patrono , recurrent vascular events despite the chronic use of aspirin should be defined as treatment failure instead aspirin resistance [unless we attribute treatment failure to aspirin resistance]. Aspirin resistance is a poorly defined term. It can imply a clinical inability of aspirin to protect individuals from arterial thrombotic events; or laboratory indications of the failure of aspirin to inhibit platelet activity, mainly platelet aggregation; or a close-to-normal urinary concentration of thromboxane metabolites. Possible mechanisms of aspirin resistance were detailed by Gaetano and Cerletti  and were summarized by Cambria-Kiely and Gandhi . They include: 1. Bioavailability of aspirin; 2. Platelet function; 3. Polymorphisms; 4. Platelet interactions with other blood cells and cell-derived products; 5. Several other factors i.e. stimulation of platelet aggregation by cigarette smoking; ASA resistant platelet aggregability by increased levels of norepinephrine, as seen during excessive exercise or periods of mental stress; biosynthesis of F-isoprostane 8-iso-prostaglandin [PGF2 alpha], a bioactive product of arachidonic acid peroxidation; and increased platelet sensitivity to collagen.
The urinary concentrations of the metabolite 11-dehydrothromboxane B2 indicate the level of TXA2 generation. Eikelboom et al  indicated that in aspirin-treated patients, urinary concentrations of 11-dehydrothromboxane B2 predict the future risk of myocardial infarction or cardiovascular death. These authors also support the view that failure to suppress thromboxane generation defines aspirin resistance . This hypothesis assumes a direct association between the rise of urinary 11-dehydrothromboxane B2 levels and increment of vascular events [myocardial infarction, stroke and cardiovascular death].
Poor platelet responsiveness to aspirin was defined by Friend et al.  as aggregation of ≥ 50% of platelets using the PFA-100 device. Gum et al  defined aspirin resistance on the basis of the platelet aggregation assay: aggregation of ≥ 70% with 10 μM ADP, and of ≥ 20% with 0.5 mg/ml arachidonic acid, constituted aspirin resistance. They also defined aspirin semiresponders as meeting one but not both of these criteria. There seems to be no correlation between the results obtained by aggregometry and by the PFA-100 device, as showed by Gum et al : of the 18 patients who were aspirin resistant by aggregation, only 4 were aspirin resistant by PFA-100.
Anti-aggregatory treatment with ASA was considered by Tarjan et al.  to be ineffective if typical aggregation curves were obtained above the following final inducer concentrations: ADP: > 5 μM, epinephrine: > 5 μM, arachidonic acid: > 250 μM, collagen: > 2 μg/ml. Compliance by subjects was proven by HPLC determination of urinary metabolites of ASA, performed immediately after admission .
Sane et al.  considered patients to be aspirin non-responsive when 4 of the following 5 parameters were observed: collagen-induced aggregation >70%; adenosine diphosphate-induced aggregation >60%, whole blood aggregation >18 ohms; expression of active GP IIb/IIIa >220 log mean fluorescence intensity units; and P-selectin positivity >8%. When the PFA-100 device was used, aspirin resistance was defined in terms of a normal collagen and/or epinephrine closure time [< or = 193 seconds] .
Weber et al.  proposed to classify aspirin resistance into three categories. Type 1 [pharmacokinetic type] entails the inhibition of platelet thromboxane formation in vitro but not in vivo. Type 2 [pharmacodynamic type] is characterized by the inability of aspirin to inhibit platelet thromboxane formation both in vivo and in vitro. Type 3 [pseudoresistance] involves thromboxane-independent platelet activation.
According to Koksch et al.  aspirin resistance involves, besides thromboxane formation, an impaired inhibition of platelet aggregation and an increased expression of P-selectin, a marker of α-granule secretion associated with the progression of atherosclerosis.
Aspirin resistance may be caused by an increased sensitivity of platelets to collagen. A platelet aggregation study specific for collagen dose response may be useful for strict selection of ASA responders for low-dose ASA therapy, and for identifying ASA non-responders for high-dose ASA therapy .
Using a collagen/epinephrine coated cartridge in the PFA-100 [R], a prevalence of aspirin resistance of 29.2% was determined by Macchi et al. . These authors support the view that hypersensitivity to adenosine diphosphate could provide a possible explanation for aspirin resistance.
Buchanan and Brister  used bleeding time to define responders and non-responders. Aspirin effected a dose-dependent prolongation of bleeding time in 60% of volunteers [ASA responders], which was associated with decreases in platelet TXA2 and 12-hydroxyeicosatetraenoic acid [12-HETE] synthesis and in platelet aggregation and adhesion. However, in volunteers whose bleeding time was not prolonged [ASA non-responders], platelet 12-HETE synthesis and platelet adhesion were unchanged or increased [P < 0.001] despite platelet TXA2 and aggregation being inhibited. Beside the problems of methodology, the dissociation between TXA2 and bleeding time makes this test inadequate for defining non-responsive patients.
Andersen et al.  showed that the levels of TXA2 were extremely low in both aspirin responders and non-responders. However, the levels of soluble P-selectin were significantly higher in non-responders than responders.
Resistance to other antiplatelet drugs has also been described. "Clopidogrel resistance" has been documented . Clopidogrel non-responders were defined by an inhibition of ADP [5 and 20 mol/L] induced platelet aggregation that was less than 10% of the baseline value 4 h after clopidogrel 600 mg intake. Semi-responders corresponded to patients with an inhibition of 10 to 29%; responders are patients with an inhibition over 30%. Up to 4.7% of the patients undergoing coronary stenting developed thrombotic stent occlusion, despite intensive clopidogrel treatment; the parallel with aspirin resistance seems striking. However, as there is no standard definition of aspirin resistance, comparison between the results of different studies is difficult.
We support the view that aspirin resistance cannot be defined by the level of serum thromboxane or its urinary metabolites, because these measurements do not correlate with the reduction of inhibition of platelet aggregation in response to multiple stimuli, and also because:
1. Although most of the thromboxane is believed to come from the platelets, there are additional cellular origins: monocytes/macrophages are also a rich source of thromboxane A2 .
2. Unlike the platelet, the macrophage is capable of synthesizing new COX-2 after aspirin has inhibited it. COX-2 is the enzyme responsible for most of the metabolism of arachidonic acid in the macrophage, and low dose aspirin is not sufficient to inhibit COX-2  maximally.
3. Macrophages in atheromata may contribute significantly to the pool of thromboxane A2 .
4. Aspirin only inhibits monocyte PGHS-2, which is inducible by inflammatory stimuli, transiently at very high concentrations .
In patients undergoing aspirin therapy, despite synergistic platelet aggregation at endothelial lesions in vivo and close-to-normal concentrations of thromboxane in plasma and thromboxane metabolites in the urine, aspirin still prevents arterial thrombosis to some extent. It therefore appears that aspirin exerts antithrombotic effects through mechanisms other than its weak inhibition of platelet aggregation. These other mechanisms could be at least as important .
Aspirin significantly decreases the levels of inflammatory factors in animal models . It markedly inhibits plaque growth. It inhibits vascular smooth muscle cell proliferation, and transforming growth factor β plays a significant intermediary role in this [55, 56]. It diminishes in vitro thrombin generation in platelet rich plasma activated by sodium arachidonate . Pretreatment with 1.2 g of aspirin preserves endothelial function and diminishes the increase of inflammatory markers after administration of salmonella vaccine . In a subset of healthy men in the Physicians Health Study, patients within the highest quartile of C-reactive protein elevation showed a significant benefit from aspirin treatment [325 mg/day every other day] compared with those in the lowest quartile . In patients with coronary artery disease, aspirin also seems to reduce C-reactive protein levels . Low-dose aspirin [as well as sinvastatin] decreased IL-1β levels and platelet activation after a 2-month treatment . Other effects of aspirin are: modulation of thrombolysis [62, 63]; increase in fibrin gel porosity ; effects on membrane fluidity ; modulation of the formation of lipid bodies in leukocytes from which eicosanoids may be released ; facilitation of the inhibition of platelet activation by neutrophils, an effect that appears to be mediated by a nitric oxide [NO]/cGMP-dependent process ; protection of low density lipoprotein from oxidative modification ; improvement of endothelial dysfunction in atherosclerosis ; and acetylation of platelet membrane glycoproteins IIb-IIIa, which augments the inhibitory effects of abciximab by increasing its binding to platelets . This range of effects of aspirin could be relevant to its pleiotropy; some of the effects could be more important than its anti-platelet activity. It is simplistic to suppose that suppression of aspirin's weak anti-aggregating action is the only cause for its failure to prevent arterial thrombosis.
It is not surprising that a hypercoagulable state occurs in the plasma in acute coronary syndromes, as indicated by blood prothrombotic markers or by the presence of new cardiovascular events in the face of powerful antithrombotic therapy [71–78]. Inflammation can have a prothrombotic effect through the increase of tissue factor, platelet reactivity or acute phase reactant proteins such as fibrinogen, or through a decrease in fibrinolysis by increasing the level of plasminogen activator inhibitor-1 [PAI-1] .
Locally, thrombin is not only involved in coagulation; it has pro-inflammatory activity . Thrombin can activate receptors on platelets and the vascular endothelium, leading to inflammation and tissue injury . Activated platelets express CD40L and induce endothelial cells to secrete chemokines and to express adhesion molecules, indicating that platelets could initiate an inflammatory response of the vessel wall . Interesting, it has recently been shown that besides their specific activity, lipid-lowering drugs [83, 84], the novel group of antidiabetic drugs thiazolidinediones [85, 86], and angiotensin-converting enzyme inhibitor, all exhibit anti-inflammatory properties. Their clinical benefits may to some extent derive from lowering inflammation .
The underlying inflammation of atheromata in acute coronary syndromes could be the basis of failure of intensive antithrombotic therapy . COX-2 inhibition may decrease athero-inflammation, reducing monocyte infiltration and improving vascular cell function and plaque stability, resulting in a decrease of coronary athero-thrombotic events . In our hands, the combination of a preferential COX-2 inhibitor, meloxicam, plus heparin and aspirin, proved superior to heparin and aspirin alone for reducing coronary thrombotic events in patients with acute coronary syndromes without ST-segment elevation .
In conclusion, aspirin resistance depends on circumstances independent of aspirin and could more aptly be termed aspirin failure. This is supported by the fact that increasing doses of aspirin can completely inhibit platelet aggregation in patients who are unresponsive or only partially responsive to aspirin [cited by ]. Otherwise, thrombin generated at the endothelial lesion can induce platelet activation, which is not affected by aspirin.
All these findings indicate that, in acute coronary syndromes, there is a strong pro-clotting activity in the complicated atheroma. This activity is augmented by the underlying inflammation, which in several circumstances can overwhelm the inhibitory effects of single or combined anti-thrombotic drugs, including aspirin. Thus, the underlying endothelial and/or atheroma inflammation in coronary syndromes could explain why the antiplatelet effect of aspirin fails, irrespective of its anti-aggregating capacity or the urinary levels of thromboxane metabolites.
- FitzGerald GA: Parsing an enigma: the pharmacodynamics of aspirin resistance. Lancet 2003, 361: 542-4. 10.1016/S0140-6736(03)12560-3View ArticlePubMedGoogle Scholar
- Awtry EH, Loscalzo J: Aspirin. Circulation 2000, 101: 1206-18.View ArticlePubMedGoogle Scholar
- Wu KK: Aspirin and salicylate: An old remedy with a new twist. Circulation 2000, 102: 2022-3.View ArticlePubMedGoogle Scholar
- Gurfinkel EP, Altman R, Scazziota A, Heguilen R, Mautner B: Fast platelet suppression by lysine acetylsalicylate in chronic stable coronary patients. Potential clinical impact over regular aspirin for coronary syndromes. Clin Cardiol 2000, 23(9):697-700.View ArticlePubMedGoogle Scholar
- Patrignani P, Filabozi P, Patrono C: Selective cumulative inhibition of platelet thromboxane production by low-dose aspirin in healthy subjects. J Clin Invest 1982, 69: 1366-72.PubMed CentralView ArticlePubMedGoogle Scholar
- Reilly IAG, FitzGerald GA: Inhibition of thromboxane formation in vivo and ex vivo. Blood 1987, 69: 180-6.PubMedGoogle Scholar
- Hoogendijk EMG, ten Cate JW: Aspirin and platelets. Lancet 1980, 1: 93-4. 10.1016/S0140-6736(80)90516-4View ArticlePubMedGoogle Scholar
- Jakubowski JA, Stampfer MJ, Vaillancourt R, Deykin D: Cumulative antiplatelet effect of low-dose enteric coated aspirin. Br J Haematol 1982, 60: 635-42.View ArticleGoogle Scholar
- Vane JR, Bakhle YS, Botting RM: Cyclooxygenases 1 and 2. Ann Rev Pharmacol Toxicol 1998, 38: 97-120. 10.1146/annurev.pharmtox.38.1.97View ArticleGoogle Scholar
- de Gaetano G, Donati MB, Cerletti C: Prevention on thrombosis and vascular inflammation: benefits and limitations of selective or combined COX-1, COX-2 and 5-LOX inhibitors. Trends Pharmacol Sci 2003, 24: 245-52.View ArticlePubMedGoogle Scholar
- FitzGerald GA, Oates JA, Hawiger J, Maas RL, Roberts LJ 2nd, Lawson JA, Brash AR: Endogenous biosynthesis of prostacyclin and thromboxane and platelet function during chronic administration of aspirin in man. J Clin Invest 1983, 71: 676-88.PubMed CentralView ArticlePubMedGoogle Scholar
- Preston FE, Whipps S, Jackson CA, French AJ, Wyld PJ, Stoddard CJ: Inhibition of prostacyclin and platelet thromboxane A2 after low-dose aspirin. N Engl J Med 1981, 304: 76-9.View ArticlePubMedGoogle Scholar
- Antithrombotic Trialists' Collaboration: Collaborative meta-analysis of randomized trials of antiplatelet therapy for prevention of death, myocardial infarction, and stroke in high risk patients. BMJ 2002, 324: 71-86. 10.1136/bmj.324.7336.S71View ArticleGoogle Scholar
- Syrbe G, Redlich H, Weidlich B, et al.: Individual dosing of ASA prophylaxis by controlling platelet aggregation. Clin Appl Thromb Hemost 2001, 7: 209-13.View ArticlePubMedGoogle Scholar
- Schafer AI: Genetic and Acquired Determinants of Individual Variability of Response to Antiplatelet Drugs. Circulation 2003, 108: 910-1. 10.1161/01.CIR.0000088843.52678.8AView ArticlePubMedGoogle Scholar
- Valles J, Santos MT, Aznar J, Osa A, Lago A, Cosin J, Sanchez E, Broekman MJ, Marcus AJ: Erythrocyte promotion of platelet reactivity decreases the effectiveness of aspirin as an antithrombotic therapeutic modality: the effect of low-dose aspirin is less than optimal in patients with vascular disease due to prothrombotic effects of erythrocytes on platelet reactivity. Circulation 1998, 97: 350-5.View ArticlePubMedGoogle Scholar
- Tarjan J, Salamon A, Jager R, Poor F, Barczi V, Dinnyes J, Hamvas J, Kinczel A, Pal A, Blasko G: The rate of acetylsalicylic acid non-respondents among patients hospitalized for acute coronary disease, previously undergoing secondary salicylic acid prophylaxis. Orv Hetil 1999, 140: 2339-43.PubMedGoogle Scholar
- Zimmermann N, Wenk A, Kim U, Kienzle P, Weber AA, Gams E, Schrör K, Hohlfeld T: Functional and Biochemical Evaluation of Platelet Aspirin Resistance After Coronary Artery Bypass Surgery. Circulation 2003, 108: 542-7. 10.1161/01.CIR.0000081770.51929.5AView ArticlePubMedGoogle Scholar
- Gum PA, Kottke-Marchant K, Poggio ED, Gurm H, Welsh PA, Brooks L, Sapp SK, Topol EJ: Profile and prevalence of aspirin resistance in patients with cardiovascular disease. Am J Cardiol 2001, 88: 230-5. 10.1016/S0002-9149(01)01631-9View ArticlePubMedGoogle Scholar
- Kundu SK, Heilmann EJ, Sio R, Garcia C, Davidson RM, Ostgaard RA: Description of an in vitro platelet function analyzer – PFA-100. Semin Thromb Hemost 1995, 21(Suppl 2):106-12.PubMedGoogle Scholar
- ten Berg JM, Gerritsen WB, Haas FJ, Kelder HC, Verheugt FW, Plokker HW: High-dose aspirin in addition to daily low-dose aspirin decreases platelet activation in patients before and after percutaneous coronary intervention. Thromb Res 2002, 105: 385-90. 10.1016/S0049-3848(02)00040-3View ArticlePubMedGoogle Scholar
- Gum PA, Kottke-Marchant K, Welsh PA, White J, Topol EJ: A prospective, blinded determination of the natural history of aspirin resistance among stable patients with cardiovascular disease. J Am Coll Cardiol 2003, 41: 961-5. 10.1016/S0735-1097(02)03014-0View ArticlePubMedGoogle Scholar
- Grundmann K, Jaschonek K, Kleine B, Dichgans J, Topka H: Aspirin non-responder status in patients with recurrent cerebral ischemic attacks. J Neurol 2003, 250: 63-6. 10.1007/s00415-003-0954-yView ArticlePubMedGoogle Scholar
- Eikelboom JW, Hirsh J, Weitz JI, Johnston M, Yi Q, Yusuf S: Aspirin-resistant thromboxane biosynthesis and the risk of myocardial infarction, stroke, or cardiovascular death in patients at high risk for cardiovascular events. Circulation 2002, 105: 1650-5. 10.1161/01.CIR.0000013777.21160.07View ArticlePubMedGoogle Scholar
- Sane DC, McKee SA, Malinin AI, Serebruany VL: Frequency of aspirin resistance in patients with congestive heart failure treated with antecedent aspirin. Am J Cardiol 2002, 90: 893-5. 10.1016/S0002-9149(02)02718-2View ArticlePubMedGoogle Scholar
- Friend M, Vucenik I, Miller M: Platelet responsiveness to aspirin in patients with hyperlipidaemia. BMJ 2003, 326: 82-3. 10.1136/bmj.326.7380.82PubMed CentralView ArticlePubMedGoogle Scholar
- Kurth T, Glynn RJ, Walker AM, Chan KA, Buring JE, Hennekens CH, Gaziano JM: Inhibition of Clinical Benefits of Aspirin on First Myocardial Infarction by Nonsteroidal Antiinflammatory Drugs. Circulation 2003, 108: 1191-5. 10.1161/01.CIR.0000087593.07533.9BView ArticlePubMedGoogle Scholar
- Catella-Lawson F, Reilly MP, Kapoor SC, Cucchiara AJ, DeMarco S, Tournier B, Vyas SN, FitzGerald GA: Cyclooxygenase inhibitors and the antiplatelet effects of aspirin. N Engl J Med 2001, 345: 1809-17. 10.1056/NEJMoa003199View ArticlePubMedGoogle Scholar
- Li N, Hu H, Hjemdahl P: Aspirin treatment does not alternate platelet or leukocyte activation as monitored by whole blood flow cytometry. Thromb Res 2003, 111: 165-170. 10.1046/j.1538-7836.2003.00354.xView ArticlePubMedGoogle Scholar
- Maalej N, Folts JD: Increased shear stress overcomes the antithrombotic platelet inhibitory effect of aspirin in stenosed dog coronary arteries. Circulation 1996, 93: 1201-5.View ArticlePubMedGoogle Scholar
- Mehta J, Mehta P, Burger C, Pepine CJ: Platelet aggregation studies in coronary artery disease. Past 4. Effect of aspirin. Atherosclerosis 1978, 31: 169-75.View ArticlePubMedGoogle Scholar
- Santos MT, Valles J, Aznar J, Marcus AJ, Broekman MJ, Safier LB: Prothrombotic effects of erythrocytes on platelet reactivity. Reduction by aspirin. Circulation 1997, 95: 63-8.View ArticlePubMedGoogle Scholar
- Altman R, Scazziota A: Why aspirin cannot prevent arterial thrombosis. Circulation 1996, 94: 3002-3.View ArticlePubMedGoogle Scholar
- Altman R, Scazziota A, Cordero Funes J: Why single daily dose of aspirin may not prevent platelet aggregation. Thromb Res 1988, 51: 259-66.View ArticlePubMedGoogle Scholar
- Altman R, Scazziota A: Synergistic actions of paf-acether and sodium arachidonate in human platelet aggregation. 2. Unexpected results after aspirin intake. Thromb Res 1986, 43: 113-20.View ArticlePubMedGoogle Scholar
- Bartele V, Cerletti C, Schiepatti A, di Minno G, de Gaetano G: Inhibition of thromboxane synthetase does not necessarily prevent platelet aggregation. Lancet 1981, 1: 1057-8. 10.1016/S0140-6736(81)92224-8View ArticlePubMedGoogle Scholar
- Cerletti C, Carriero MR, de Gaetano G: Platelet-aggregation response to single or paired aggregating stimuli after low-dose aspirin. N Engl J Med 1986, 314: 316-8.PubMedGoogle Scholar
- Patrono C: Aspirin resistance: definition, mechanism and clinical read-outs. J Thromb Haemost 2003, 1: 1710-13. 10.1046/j.1538-7836.2003.00284.xView ArticlePubMedGoogle Scholar
- de Gaetano G, Cerletti C: Aspirin resistance: a revival of platelet aggregation tests? J Thromb Haemost 2003, 1: 2048-50. 10.1046/j.1538-7836.2003.00354.xView ArticlePubMedGoogle Scholar
- Cambia-Kiely JA, Gandhi PJ: Possible mechanism of aspirin resistance. J Thromb Thrombolysis 2002, 13: 49-56. 10.1023/A:1015324310374View ArticleGoogle Scholar
- Weber AA, Przytulski B, Schanz A, Hohlfeld T, Schror K: Towards a definition of aspirin resistance: a typological approach. Platelets 2002, 13: 37-40. 10.1080/09537100120104890View ArticlePubMedGoogle Scholar
- Koksch M, Zeiger F, Wittig K, Siegemund A, Reininger CB, Pfeiffer D, Ruehlmann C: Coagulation, fibrinolysis and platelet P-selectin expression in peripheral vascular disease. Eur J Vasc Endovasc Surg 2001, 21: 147-54. 10.1053/ejvs.2000.1294View ArticlePubMedGoogle Scholar
- Weber AA, Zimmermann KC, Meyer-Kirchrath J, Schror K: Cyclooxygenase-2 in human platelets as a possible factor in aspirin resistance. Lancet 1999, 353: 900. 10.1016/S0140-6736(99)00498-5View ArticlePubMedGoogle Scholar
- Patrignani P, Sciulli MG, Manarini S, Santini G, Cerletti C, Evangelista V: [COX-2 is not involved in thromboxane biosynthesis by activated human platelets. J Physiol Pharmacol 1999, 50: 661-7.PubMedGoogle Scholar
- Kawasaki T, Ozeki Y, Igawa T, Kambayashi J: Increased platelet sensitivity to collagen in individuals resistant to low-dose aspirin. Stroke 2000, 31: 591-5.View ArticlePubMedGoogle Scholar
- Macchi L, Christiaens L, Brabant S, Sorel N, Allal J, Mauco G, Brizard A: Resistance to aspirin in vitro is associated with increased platelet sensitivity to adenosine diphosphate. Thromb Res 2002, 107: 45-9. 10.1016/S0049-3848(02)00210-4View ArticlePubMedGoogle Scholar
- Buchanan MR, Brister SJ: Individual variation in the effects of ASA on platelet function: implications for the use of ASA clinically. Can J Cardiol 1995, 11: 221-7.PubMedGoogle Scholar
- Andersen K, Hurlen M, Arnesen H, Seljeflot I: Aspirin non-responsiveness as measured by PFA-100 in patients with coronary artery disease. Thromb Res 2002, 108: 37-42. 10.1016/S0049-3848(02)00405-XView ArticlePubMedGoogle Scholar
- Muller I, Besta F, Schulz C, Massberg S, Schonig A, Gawaz M: Prevalence of clopidogrel non-responders among patients with stable angina pectoris scheduled for elective coronary stent placement. Thromb Haemost 2003, 89: 783-7.PubMedGoogle Scholar
- Halushka MK, Halushka PV: Why are some individuals resistant to the cardioprotective effects of aspirin? Could it be thromboxane A2? Circulation 2002, 105: 1620-2. 10.1161/01.CIR.0000015422.86569.52View ArticlePubMedGoogle Scholar
- Cipollone F, Prontera C, Pini B, Marini M, Fazia M, De Cesare D, Iezzi A, Ucchino S, Boccoli G, Saba V, Chiarelli F, Cuccurullo F, Mezzetti A: Overexpression of functionally coupled cyclooxygenase-2 and prostaglandin E synthase in symptomatic atherosclerotic plaques as a basis of prostaglandin E2-dependent plaque instability. Circulation 2001, 104: 921-7.View ArticlePubMedGoogle Scholar
- Cipollone F, Patrignani P, Greco A, Panara MR, Padovano R, Cuccurullo F, Patrono C, Rebuzzi AG, Liuzzo G, Quaranta G, Maseri A: Differential Suppression of Thromboxane Biosynthesis by Indobufen and Aspirin in Patients With Unstable Angina. Circulation 1997, 96: 1109-16.View ArticlePubMedGoogle Scholar
- Altman R: Acute coronary disease Athero-Inflammation: Therapeutic approach. Thromb J 2003, 1: 2. 10.1186/1477-9560-1-2PubMed CentralView ArticlePubMedGoogle Scholar
- Cyrus T, Sung S, Zhao L, Funk CD, Tang S, Praticò D: Effect of low-dose aspirin on vascular inflammation, plaque stability, and atherogenesis in low-density lipoprotein receptor-deficient mice. Circulation 2002, 106: 1282-7. 10.1161/01.CIR.0000027816.54430.96View ArticlePubMedGoogle Scholar
- Redondo S, Santos-Gallego CG, Ganado P, Garcia M, Rico L, Del Rio M, Tejerina T: Acetylsalicylic acid inhibits cell proliferation by involving transforming growth factor-β. Circulation 2003, 107: 626-9. 10.1161/01.CIR.0000045664.75269.A5View ArticlePubMedGoogle Scholar
- Kodama M, Yamasaki Y, Sakamoto K, Yoshioka R, Matsuhisa M, Kajimoto Y, Kosugi K, Ueda N, Hori M: Antiplatelet drugs attenuate progression of carotid intima-media thickness in subjects with type 2 diabetes. Thromb Res 2000, 97: 239-45. 10.1016/S0049-3848(99)00168-1View ArticlePubMedGoogle Scholar
- Altman R, Scazziota A, Rouvier J, Gonzalez C: Effect of sodium arachidonate on thrombin generation through platelet activation.-Inhibitory effect of aspirin. Thromb Haemostas 2000, 54: 1109-12.Google Scholar
- Kharbanda RK, Walton B, Allen M, Klein N, Hingorani AD, MacAllister RJ, Vallance P: Prevention of inflammation-induced endothelial dysfunction. A novel vasculo-protective action of aspirin. Circulation 2002, 105: 2600-4. 10.1161/01.CIR.0000017863.52347.6CView ArticlePubMedGoogle Scholar
- Ridker PM, Cushman M, Stampfer MJ, Tracy RP, Hennekens CH: Inflammation, Aspirin, and the Risk of Cardiovascular Disease in Apparently Healthy Men. N Engl J Med 1997, 336: 973-9. 10.1056/NEJM199704033361401View ArticlePubMedGoogle Scholar
- Bhatt DL, Topol EJ: Need to test the arterial inflammation hypothesis. Circulation 2002, 106: 136-140. 10.1161/01.CIR.0000021112.29409.A2View ArticlePubMedGoogle Scholar
- Patrizia Ferroni MD, Francesca Martini PhD, Cristiano M, Cardarello MD, Pier Paolo Gazzaniga MD, Giovanni Davì MD, Stefania Basili MD: Enhanced Interleukin-1β in Hypercholesterolemia. Effects of Simvastatin and Low-Dose Aspirin. Circulation 2003, 108: 1673-5. 10.1161/01.CIR.0000094732.02060.27View ArticlePubMedGoogle Scholar
- Bjornsson TD, Schneider DE, Berger H Jr: Aspirin acetylates fibrinogen and enhances fibrinolysis: fibrinolytic effect is independent of changes in plasminogen activator levels. J Pharmacol Exp Ther 1989, 250: 154-161.PubMedGoogle Scholar
- Ezratty A, Freedman JE, Simon D, Loscalzo J: The antithrombotic effects of acetylation of fibrinogen by aspirin. J Vasc Med Biol 1994, 5: 152-9.Google Scholar
- Williams S, Fatah K, Hjemdahl P, Blomback M: Better increase in fibrin gel porosity by low dose than intermediate dose acetylsalicylic acid. Eur Heart J 1998, 19: 1666-72. 10.1053/euhj.1998.1088View ArticlePubMedGoogle Scholar
- Watala C, Gwozdzinski K: Effect of aspirin on conformation and dynamics of membrane proteins in platelets and erythrocytes. Biochem Pharmacol 1993, 45: 1343-1. 10.1016/0006-2952(93)90288-8View ArticlePubMedGoogle Scholar
- Bozza PT, Payne JL, Morham SG, Langenbach R, Smithies O, Weller PF: Leukocyte lipid body formation and eicosanoid generation: cyclooxygenase-independent inhibition by aspirin. Proc Natl Acad Sci U S A 1996, 93: 11091-6. 10.1073/pnas.93.20.11091PubMed CentralView ArticlePubMedGoogle Scholar
- Lopez-Farre A, Caramelo C, Esteban A, Alberola ML, Millas I, Monton M, Casado S: Effects of aspirin on platelet-neutrophil interactions: role of nitric oxide and endothelin-1. Circulation 1995, 91: 2080-8.View ArticlePubMedGoogle Scholar
- Steer KA, Wallace TM, Bolton CH, Hartog M: Aspirin protects low density lipoprotein from oxidative modification. Heart 1997, 77: 333-7.PubMed CentralView ArticlePubMedGoogle Scholar
- Husain S, Andrews NP, Mulcahy D, Panza JA, Quyyumi AA: Aspirin improves endothelial dysfunction in atherosclerosis. Circulation 1998, 97: 716-20.View ArticlePubMedGoogle Scholar
- Schneider DJ, Baumann PQ, Holmes MB, Taatjes DJ, Sobel BE: Time and dose dependent augmentation of inhibitory effects of abciximab by aspirin. Thromb Haemost 2001, 85: 309-13.PubMedGoogle Scholar
- Merlini PA, Bauer KA, Oltrona L, Ardissino D, Cattaneo M, Belli C, Mannucci PM, Rosenberg RD: Persistent activation of coagulation mechanism in unstable angina and myocardial infarction. Circulation 1994, 90: 61-8.View ArticlePubMedGoogle Scholar
- Zoldhelyi P, Bichler J, Owen WG, Grill DE, Fuster V, Mruk JS, Chesebro JH: Persistent thrombin generation in humans during specific thrombin inhibition with hirudin. Circulation 1994, 90: 2671-8.View ArticlePubMedGoogle Scholar
- Merlini PA, Ardissino D, Bauer KA, Oltrona L, Pezzano A, Bottasso B, Rosenberg RD, Mannucci PM: Persistent thrombin generation during heparin therapy in patients with acute coronary syndromes. Arterioscler Thromb Vasc Biol 1997, 17: 1325-30.View ArticlePubMedGoogle Scholar
- Merlini PA, Ardissino D, Rosenberg RD, Colombi E, Agricola P, Oltrona L, Ottani F, Galvani M, Bauer KA, Bottasso B, Bertocchi F, Mannucci PM: In vivo thrombin generation and activity during and after intravenous infusion of heparin or recombinant hirudin in patients with unstable angina pectoris. Arterioscler Thromb Vasc Biol 2000, 20: 2162-6.View ArticlePubMedGoogle Scholar
- Ardissino D, Merlini PA, Bauer KA, Galvani M, Ottani F, Franchi F, Bertocchi F, Rosenberg RD, Mannucci PM: Coagulation activation and long-term outcome in acute coronary syndromes. Blood 2003, 102: 2731-5. 10.1182/blood-2002-03-0954View ArticlePubMedGoogle Scholar
- Linder R, Oldgren J, Egberg N, Grip L, Larson G, Siegbahn A, Wallentin L: The effect of a low molecular mass thrombin inhibitor, inogatran, and heparin on thrombin generation and fibrin turnover in patients with unstable coronary artery disease. Eur Heart J 1999, 20: 506-18. 10.1053/euhj.1998.1336View ArticlePubMedGoogle Scholar
- Invasive compared with non-invasive treatment in unstable coronary-artery disease: FRISC II prospective randomised multicentre study. FRagmin and Fast Revascularisation during InStability in Coronary artery disease Investigators. Lancet 1999, 354: 708-15. 10.1016/S0140-6736(99)07349-3View ArticleGoogle Scholar
- Neumann FJ, Kastrati A, Pogatsa-Murray G, Mehilli J, Bollwein H, Bestehorn HP, Schmitt C, Seyfarth M, Dirschinger J, Schomig A: Evaluation of prolonged antithrombotic pretreatment ["cooling-off" strategy] before intervention in patients with unstable coronary syndromes: a randomized controlled trial. JAMA 2003, 290: 1593-9. 10.1001/jama.290.12.1593View ArticlePubMedGoogle Scholar
- Esmon CT: Inflammation and thrombosis. J Thromb Haemost 2003, 1: 1343-8. 10.1046/j.1538-7836.2003.00261.xView ArticlePubMedGoogle Scholar
- Matthay MA: Severe sepsis-A new treatment with both anticoagulant and antiinflamatory properties. N Engl J Med 2001, 344: 759-762. 10.1056/NEJM200103083441009View ArticlePubMedGoogle Scholar
- Coughlin SR: Thrombin signalling and protease-activated. Nature 2000, 407: 258-264. 10.1038/35025229View ArticlePubMedGoogle Scholar
- Henn V, Slupsky JR, Grafe M, Anagnostopoulos I, Forster R, Muller-Berghaus G, Kroczek RA: CD40 ligand on activated platelets triggers an inflammatory reaction of endothelial cells. Nature 1998, 391: 591-594. 10.1038/35393View ArticlePubMedGoogle Scholar
- Blake GJ, Ridker PM: Are statins anti-inflammatory? Curr Control Trials Cardiovasc Med 2000, 1: 161-165. 10.1186/CVM-1-3-161PubMed CentralView ArticlePubMedGoogle Scholar
- Wiklund O, Mattsson-Hulten L, Hurt-Camejo E, Oscarsson J: Effects of simvastatin and atorvastatin on inflammation markers in plasma. J Intern Med 2002, 25: 338-347. 10.1046/j.1365-2796.2002.00966.xView ArticleGoogle Scholar
- Haffner SM, Greenberg AS, Weston WM, Chen H, Williams K, Freed MI: Effect of rosiglitazone treatment on nontraditional markers of cardiovascular disease in patients with type 2 diabetes mellitus. Circulation 2002, 106: 679-684. 10.1161/01.CIR.0000025403.20953.23View ArticlePubMedGoogle Scholar
- Marx N, Froehlich J, Siam L, Ittner J, Wierse G, Schmidt A, Scharnagl H, Hombach V, Koenig W: Antidiabetic PPARγ-activator rosiglitazone reduces MMP-9 serum levels in type 2 diabetic patients with coronary artery disease. Arterioscler Thromb Vasc Biol 2003, 23: 283-288. 10.1161/01.ATV.0000054195.35121.5EView ArticlePubMedGoogle Scholar
- Libby P, Ridker PM, Maseri A: Inflammation and Atherosclerosis. Circulation 2002, 105: 1135-1143. 10.1161/hc0902.104353View ArticlePubMedGoogle Scholar
- Altman R: Risk factors in coronary atherosclerosis athero-inflammation: the meeting point. Thromb J 2003, 1: 4. 10.1186/1477-9560-1-4PubMed CentralView ArticlePubMedGoogle Scholar
- Altman R, Luciardi HL, Muntaner J, Del Rio F, Berman SG, Lopez R, Gonzalez C: Efficacy assessment of meloxicam, a preferential cyclooxygenase-2 inhibitor, in acute coronary syndromes without ST-segment elevation: the Nonsteroidal Anti-Inflammatory Drugs in Unstable Angina Treatment-2 [NUT-2] pilot study. Circulation 2002, 106: 191-5. 10.1161/01.CIR.0000021599.56755.A1View ArticlePubMedGoogle Scholar
- McKee SA, Sane DC, Deliargyris EN: Aspirin resistance in Cardiovascular disease: A review of prevalence, mechanism, and clinical significance. Thromb Haemost 2002, 88: 711-5.PubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.