Aspirin resistance

The dilemma of aspirin resistance in obese patients

Aspirin resistance (AR) commonly refers to the concept of reduced aspirin efficacy in preventing cardiovascular disease and platelet inhibition. Obesity increases the risk of heart disease three- to four-fold and has been associated with AR. Aspirin is used as a tool for both primary and secondary prevention, but recent studies suggest that its lack of efficacy for primary prevention is partly attributable to obesity. Several mechanisms have been described that contribute to AR in obese patients using pharmacokinetics and pharmacodynamics. AR may be attenuated through weight loss, alternative dosing regimens, and different drug formulations. With the global rise of obesity, it is imperative to find preventive therapies that adequately address atherosclerotic cardiovascular disease (ASCVD) risk in this population.

The potential of acetylsalicylic acid and vitamin E in modulating inflammatory cascades in chickens under lipopolysaccharide-induced inflammation

Distinct enzymes, including cyclooxygenase 1 and 2 (COX-1 and COX-2), lipoxygenase (LOXs), and cytochrome P450 monooxygenase (CYP450), produce different stress mediators and mediate inflammation in birds. Bioactive agents such as acetylsalicylic acid (ASA) and vitamin E (vE) may affect enzyme activities and could be used in poultry production to control the magnitude of acute phase inflammation. Here, we characterized COX, LOX, and CYP450 mRNA expression levels in chicken immune tissues in response to Escherichia coli lipopolysaccharide (LPS) challenge and investigated whether ASA and vE could alter gene expression. Additionally, for the first time in chickens, we evaluated oxygen consumption by platelet mitochondria as a biomarker of mitochondria function in response to ASA- and vE. LPS challenge compromised bird growth rates, but neither dietary ASA nor vE significantly ameliorated this effect; however, gradually increasing dietary vE levels were more effective than basal levels. ASA regulated arachidonic acid metabolism, providing an eicosanoid synthesis substrate, whereas gradually increasing vE levels evoked aspirin resistance during challenge. Gene expression in immune tissues was highly variable, indicating a complex regulatory network controlling inflammatory pathways. However, unlike COX-1, COX-2 and CYP450 exhibited increased mRNA expression in some cases, suggesting an initiation of novel anti-inflammatory and pro-resolving signals during challenge. Measuring oxygen consumption rate, we revealed that neither the ASA nor vE levels applied here exerted toxic effects on platelet mitochondria.

rs5911 and rs3842788 Genetic Polymorphism, Blood Stasis Syndrome, and Plasma TXB2 and hs-CRP Levels Are Associated with Aspirin Resistance in Chinese Chronic Stable Angina Patients

The identification of single nucleotide polymorphisms (SNPs) related to aspirin resistance (AR) is of great significance for the explanation why some individuals demonstrate an incomplete response to aspirin and for optimizing the antiplatelet therapy strategy. The study was designed to investigate the possible associated genetic markers and clinical factors of AR for Chinese patients with chronic stable angina after PCI and to analyze the association between TXA2, PGI2, hs-CRP level, AR, and gene polymorphisms. Totally 207 chronic stable angina patients who received 100 mg maintenance dose daily of aspirin for more than 7 days were enrolled. The inhibition of platelets was assessed using light transmittance aggregometry. TXB2, 6-keto-PGF1α, and hs-CRP were measured by radioimmunoassay. Genotyping was performed using Taqman probe technique (rs5787 and rs5911) and gene sequencing technology (rs3842788). By using binary logistic regression analysis, the impact of clinical and genetic determinants on AR was evaluated. The prevalence of AR and aspirin semiresistance (ASR) was 3.86% and 20.76%, respectively, in Chinese chronic stable angina patients. rs5911 A/C and C/C versus A/A genotype (OR = 5.546, 95% CI = 1.812–11.404), rs3842788 A/G versus G/G genotype (OR = 8.358, 95% CI = 2.470–28.286), and blood stasis syndrome (BSS, OR = 10.220, 95% CI = 4.242–24.621) were associated with AR, but rs5787 variants were all homozygous of G/G genotype. Plasma TXB2 and hs-CRP increased significantly in AR and ASR group, while 6-keto-PGF1α showed no difference, and TXB2 level was significantly higher in carriers of the rs3842788 A/G genotype. According to our results, rs5911 and rs3842788 are proved to be specific genetic markers of AR in Chinese chronic stable angina patients for the first time, and BSS was also proved to be a remarkable determinant for AR. The AR and ASR patients were with increased plasma TXB2 and hs-CRP levels, and the TXB2 level was influenced by the variation of rs3842788 genotype.

The Effect of Xuefuzhuyu Oral Liquid on Aspirin Resistance and Its Association with rs5911, rs5787, and rs3842788 Gene Polymorphisms

Aspirin should be continued indefinitely in patients after interventional therapy, but 10% to 40% of patients experience recurrent vascular events despite adequate aspirin therapy, a condition known as aspirin resistance (AR). Xuefuzhuyu oral liquid, derived from the classic recipe Xuefuzhuyu decoction, has been well documented to inhibit platelet aggregation and to improve hemorheology. The aims of this study were to investigate the effects of Xuefuzhuyu oral liquid on AR in patients with chronic stable angina after percutaneous coronary intervention (PCI) and the possible genetic markers related to the drug response. 43 patients diagnosed as having aspirin resistance or semi-resistance were randomly divided into control and treatment groups after screening 207 stable CHD patients. Platelet aggregation rate was determined using turbidimetry. Three single nucleotide polymorphisms in COX-1 (rs5787, rs3842788) and GP IIb (rs5911) were genotyped in whole blood samples using ABI PRISM 7900 HT Fast Real-Time instrument and ABI PRISM 3730 DNA Sequencer. The results showed that Xuefuzhuyu oral liquid could effectively improve blood stasis syndrome and AR by inhibiting ADP-induced platelet aggregation and that patients with the rs5911 genetic variant exhibited better drug response upon treatment with Xuefuzhuyu oral liquid, which suggests Xuefuzhuyu oral liquid as a new possible drug for the prevention of AR.

Effect of acetylsalicylic acid on platelet activation and oxidative profile in a set of Brazilian patients with type 2 diabetes mellitus

Type 2 diabetes mellitus (DM2) is a metabolic disorder associated with hyperactivation of platelets, increased formation of platelet microparticles (PMPs) and oxidative stress that are related to cardiovascular complications. Acetylsalicylic acid (ASA) is an antiplatelet agent used in the prevention of atherothrombosis. The aim of this study was to evaluate the effect of ASA by means of platelet activation and oxidative profile. We collected blood samples of 81 patients with DM2 before and during ASA treatment. These samples were analyzed to determine the levels of 2,3-dinor thromboxane-B2 (2,3-dinor-TXB2), PMPs, thiobarbituric acid reactive species (TBARS) and 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT). Moreover, the relationship between the levels of 2,3-dinor-TXB2 with some clinical and laboratory variables such as glycated hemoglobin, platelet count, D dimer, low-density lipoprotein cholesterol and glycoprotein IIb/IIIa and cyclooxygenase-1 polymorphisms was evaluated. ASA intake did not change the levels of PMP, TBARS and MTT. Although a significant decrease in the levels of 2,3 dinorTXB2 (P < 0.001) in patients under ASA has been observed, an equal and satisfactory response to this drug was not found. However, the presence of PIA2 allele in GPIIIa gene may be associated with a better response to ASA intake in these patients, whereas other clinical and laboratory variables showed no association with this drug use. These findings are consistent with previous reports in the literature that patients with DM2 do not benefit in an equal way from the use of ASA for primary prevention of atherothrombotic events.

Reduced aspirin responsiveness as assessed by impedance aggregometry is not associated with adverse outcome after cardiac surgery in a small low-risk cohort

Reduced aspirin responsiveness (i.e. persistent high platelet reactivity in platelet function testing) might be associated with increased risk of myocardial ischemia and cardiac mortality in patients with coronary disease. However, the impact in patients undergoing coronary artery bypass grafting (CABG) is unclear. The aim of this prospective cohort study was to evaluate the predictive value of reduced aspirin responsiveness on cardiac and thromboembolic events in patients undergoing elective isolated CABG surgery with aspirin intake until at least two days before surgery. We included 304 patients in this prospective single-center cohort study. Impedance platelet aggregometry (Multiplate®) was performed directly before and on the first day after surgery. Reduced aspirin responsiveness was defined as area under the curve in ASPItest (AUCASPI) ≥300 U. The primary outcome was a composite of all-cause mortality and/or major adverse cardiac or thromboembolic events within 1 year. Reduced aspirin responsiveness was found in 13 and 24% of patients pre and postoperatively, respectively. There was no difference in the outcomes between patients with normal and reduced aspirin responsiveness in the preoperative measurement (log-rank test, p = 0.540). Multivariate analysis including logistic EuroSCORE I and postoperative troponin T levels did not show any association of reduced aspirin responsiveness with adverse outcome (hazard ratio, 0.576; (95% CI 0.128-2.585; p = 0.471). Similarly, postoperative reduced aspirin responsiveness was not associated with adverse events. To conclude, reduced aspirin responsiveness as evaluated by Multiplate® platelet function analyzer was not associated with increased incidence of major adverse cardiac and thromboembolic events and mortality after CABG surgery.

Effects of cilostazol on the progression and regression of symptomatic intracranial artery stenosis: it reduces the risk of ischemic stroke

OBJECTIVE:

To assess the efficacy and safety of cilostazol on the progression and regression of symptomatic intracranial artery stenosis.

DATA RETRIVAL:

We searched the main databases for eligible trials including Medline (from 1966 to June 2014), Embase (from 1980 to June 2014), Cochrane Library (Issue 6, 2014), Chinese National Knowledge Infrastructure (from 1995 to June 2014), Current Controlled Trials (http://controlled-trials.com), Clinical Trials.gov (http://clinicaltrials.gov), and Chinese Clinical Trial Registry (http://www.chictr.org). All studies regarding prevention and treatment of symptomatic intracranial arterial stenosis by cilostazol were collected. The Mesh or text keywords were the English words: “cilostazol, phosphodiesterase 3 inhibitor, atherosclerosis, and ischemic stroke.” No restrictions were put on publications or publication language.

SELECTION CRITERIA:

Grade A or B randomized controlled trials were selected according to the quality of evaluation criteria from the Cochrane Collaboration, in which cilostazol and aspirin were used to evaluate the effects of cilostazol in the treatment of patients with symptomatic intracranial artery stenosis. The quality of study methodology was evaluated based on criteria described in Cochrane Reviewer's Handbook 5.0.1. RevMan 5.2 software was used for data analysis.

MAIN OUTCOME MEASURES:

Clinical efficacy and safety of cilostazol in stopping progression and promoting regression of symptomatic intracranial artery stenosis were measured by magnetic resonance angiography and transcranial Doppler.

RESULTS:

Two randomized controlled trials with a total of 203 patients were included in this study. The results showed that while cilostazol was associated with a significantly reduced progression of intracranial artery stenosis (OR = 0.21, 95%CI: 0.09–0.47, P < 0.01), it had no beneficial effect on symptom regression (OR = 1.42, 95%CI: 0.80–2.51, P = 0.24). During the follow-up period, although some adverse effects developed, including headache, gastrointestinal disturbance, and dizziness, incidences of bleeding were lower than in aspirin-treated patients.

CONCLUSION:

Cilostazol may prevent the progression of symptomatic intracranial artery stenosis, which could reduce the incidence of ischemic stroke.

Aspirin resistance in patients undergoing hemodialysis and effect of hemodialysis on aspirin resistance

The aim of this study was to evaluate the prevalence of aspirin resistance (AR) in patients undergoing hemodialysis (HD) and to assess the effect of HD on the results of the Multiplate test. A total of 54 patients undergoing HD were included in this study. Blood samples were taken just before and after the HD session. To determine AR, we used Multiplate test. Platelet aggregation values of the study population were 363.01 ± 225.69 aggregation unit (AU) × minutes before and 375.33 ± 254.05 AU × minutes after the HD (P = .597). There was strong correlation between the values before and after HD (R = .755, P < .0001). The AR status was changed in 9 (16.6%) patients after HD. Agreement of AR status before and after HD was substantial (κ coefficient = .667, P < .0001). The prevalence of AR in patients undergoing HD seems higher than in most of the studied populations, and this study has shown that the AR statuses of a significant number of patients undergoing HD change after an HD session.

Aspirin treatment failure: is this a real phenomenon? A review of the aetiology and how to treat it

Multiple clinical trials have shown that aspirin can reduce all cardiovascular events in primary and secondary prevention and yet there is a large population in whom aspirin fails. This review brings together the evidence and controversies surrounding the definition of ‘aspirin treatment failure’, its clinical significance and the possible approaches to managing such patients. Several different assays have been developed to measure the biochemical action of aspirin. At present there is no ‘gold standard’ and there is massive disparity between methods. Studies thus far have shown inconsistent results and to date the treatment of aspirin therapy failure is left to the discretion of the leading physician.

Pravastatin and simvastatin improves acetylsalicylic acid-mediated in vitro blood platelet inhibition

BACKGROUND

Insight into the pathophysiology of atherothrombosis indicates that an integrated risk factor approach, focusing particularly on the management of dyslipidaemia (with statins) and thrombosis (with ASA), may constitute an optimal therapeutic approach. We investigated whether pravastatin, simvastatin and atorvastatin may directly modulate under in vitro conditions the reactivity of blood platelets originating from healthy volunteers. In addition, we analysed the influence of statins on the platelet sensitivity to ASA under such conditions.

MATERIALS AND METHODS

We monitored collagen- or ADP-induced platelet aggregation, CD36, PAC-1 and CD62 expression on platelet surface and thromboxane generation after incubation with pravastatin, simvastatin, atorvastatin and/or ASA.

RESULTS

The incubation of whole blood with simvastatin and pravastatin significantly decreased CD36 expression. In the presence of 50 μM ASA, simvastatin and pravastatin significantly reduced the PAC-1 expression (30% reduction for simvastatin, P < 0·01, and 15% reduction for pravastatin, P < 0·01), platelet aggregation (20% reduction for both statins, P < 0·01) and thromboxane generation (35% reduction for simvastatin, P < 0·001, and 30% reduction for pravastatin, P < 0·001) compared to ASA alone. Atorvastatin changed neither baseline platelet aggregation nor ASA-mediated platelet inhibition.

CONCLUSIONS

Our results suggested that statins may directly interact with platelet membranes or may modulate a signalling pathway in platelets (the pleiotropic effects of statins). It is possible that the statin effect on CD36 and ASA-mediated protein acetylation can be reached by the modulation of a distribution or a function of membrane-associated proteins. Further studies are certainly needed to better elucidate the mechanism(s) underlying the statins' effects on platelet sensitivity to ASA.

Genetic Polymorphisms of HO-1 and COX-1 Are Associated With Aspirin Resistance Defined by Light Transmittance Aggregation in Chinese Han Patients

Background:

Cyclooxygenase 1 ( COX-1), COX-2, and HO-1 are involved in the process of aspirin’s effect. The genetic susceptibility of these enzymes to aspirin resistance (AR) is unclear. Methods: A total of 431 patients took aspirin. Using arachidonic acid-induced light transmittance aggregation combined with adenosine diphosphate-induced light transmittance aggregation, 36 participants served for AR, 164 participants for semi-AR, and 231 participants for aspirin sensitivity (AS). The AR with 9 single-nucleotide polymorphism in COX-1, COX-2, and HO-1 genes was investigated.

Results:

COX-1 rs1330344 (−1676A>G) is associated with AR. G-Allele carriers significantly increased the risk of AR. For patients with AS as control, P is .02 (odds ratio [OR] = 1.77, confidence interval [CI]: 1.07-2.92). For patients with semi-AR as control, P is .05. HO-1 rs2071746 (−413A>T) is associated with AR. T-Allele carriers significantly increased the risk of AR. For patients with AS as control, P is .04 (OR = 1.70, CI: 1.02-2.79). For patients with semi-AR as control, P is .05 (OR = 1.68, CI: 1.00-2.80).

Conclusion:

rs2071746 in HO-1 gene, rs1330344 in COX-1 gene contribute to AR.

Aging-shifted prostaglandin profile in endothelium as a factor in cardiovascular disorders

Age-associated endothelium dysfunction is a major risk factor for the development of cardiovascular diseases. Endothelium-synthesized prostaglandins and thromboxane are local hormones, which mediate vasodilation and vasoconstriction and critically maintain vascular homeostasis. Accumulating evidence indicates that the age-related changes in endothelial eicosanoids contribute to decline in endothelium function and are associated with pathological dysfunction. In this review we summarize currently available information on aging-shifted prostaglandin profiles in endothelium and how these shifts are associated with cardiovascular disorders, providing one molecular mechanism of age-associated endothelium dysfunction and cardiovascular diseases.

A systematic review on pharmacogenetics in cardiovascular disease: is it ready for clinical application?

Pharmacogenetics is the search for heritable genetic polymorphisms that influence responses to drug therapy. The most important application of pharmacogenetics is to guide choosing agents with the greatest potential of efficacy and smallest risk of adverse drug reactions. Many studies focusing on drug-gene interactions have been published in recent years, some of which led to adaptation of FDA recommendations, indicating that we are on the verge of the clinical application of genetic information in drug therapy. This systematic review provides a comprehensive overview of the current knowledge on pharmacogenetics of all major drug classes currently used in the treatment of cardiovascular diseases.

NP-313, 2-acetylamino-3-chloro-1,4-naphthoquinone, a novel antithrombotic agent with dual inhibition of thromboxane A(2) synthesis and calcium entry

BACKGROUND AND PURPOSE

1,4-Naphthoquinones exhibit antiplatelet activity both in vivo and in vitro. In the present study, we investigated the antiplatelet effect of a novel naphthoquinone derivative NP-313, 2-acetylamino-3-chloro-1,4-naphthoquinone and its mechanism of action.

EXPERIMENTAL APPROACH

We measured platelet aggregation, Ca(2+) mobilization, thromboxane B2 formation and P-selectin expression and examined several enzymatic activities. Furthermore, we used the irradiated mesenteric venules in fluorescein sodium-treated mice to monitor the antithrombotic effect of NP-313 in vivo.

KEY RESULTS

NP-313 concentration-dependently inhibited human platelet aggregation induced by collagen, arachidonic acid, thapsigargin, thrombin and A23187. NP-313 also inhibited P-selectin expression, thromboxane B(2) formation and [Ca(2+) ](i) elevation in platelets stimulated by thrombin and collagen. NP-313 at 10 µM inhibited cyclooxygenase, thromboxane A(2) synthase, and protein kinase Cα, whereas it did not affect phospholipase A(2) or phospholipase C activity. In the presence of indomethacin and an adenosine 5-diphosphate scavenger, NP-313 concentration-dependently inhibited thrombin- and A23187-induced [Ca(2+)](i) increase through its inhibitory effects on Ca(2+) influx, rather than blocking Ca(2+) release from intracellular stores. NP-313 also inhibited thapsigargin-mediated Ca(2+) influx through store-operated calcium channel but had no effect on Ca(2+) influx through store-independent calcium channel evoked by the diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol. Nevertheless, it had little effect on cyclic AMP and cyclic GMP levels. Also, intravenously administered NP-313 dose-dependently inhibited the thrombus occlusion of the irradiated mesenteric vessels of fluorescein-pretreated mice.

CONCLUSIONS AND IMPLICATIONS

Taken together, these results indicate that NP-313 exerts its antithrombotic activity through dual inhibition of thromboxane A(2) synthesis and Ca(2+) influx through SOCC.

The PPAR-Platelet Connection: Modulators of Inflammation and Potential Cardiovascular Effects

Historically, platelets were viewed as simple anucleate cells responsible for initiating thrombosis and maintaining hemostasis, but clearly they are also key mediators of inflammation and immune cell activation. An emerging body of evidence links platelet function and thrombosis to vascular inflammation. peroxisome proliferator-activated receptors (PPARs) play a major role in modulating inflammation and, interestingly, PPARs (PPARβ/δ and PPARγ) were recently identified in platelets. Additionally, PPAR agonists attenuate platelet activation; an important discovery for two reasons. First, activated platelets are formidable antagonists that initiate and prolong a cascade of events that contribute to cardiovascular disease (CVD) progression. Dampening platelet release of proinflammatory mediators, including CD40 ligand (CD40L, CD154), is essential to hinder this cascade. Second, understanding the biologic importance of platelet PPARs and the mechanism(s) by which PPARs regulate platelet activation will be imperative in designing therapeutic strategies lacking the deleterious or unwanted side effects of current treatment options.

The effect of a platelet cholesterol modulation on the acetylsalicylic acid-mediated blood platelet inhibition in hypercholesterolemic patients

Aspirin (acetylsalicylic acid, ASA) is widely used in the prevention of cardiovascular disease, but its beneficial effects may be restrained in some individuals, where the reduced ability of ASA to protect against arterial thrombotic events is observed. We analyzed the influence of the treatment with atorvastatin (10mg/day) on the platelet sensitivity to ASA monitored under in vitro conditions in hypercholesterolemic patients. The associations between plasma or platelet cholesterol parameters and the ASA-mediated inhibition of platelet reactivity or the extent of platelet protein acetylation by ASA were estimated in the patients treated with atorvastatin for 1, 3, or 6 months. Out of 27 patients, in 17 individuals platelets appeared significantly more sensitive to 50 μM ASA in arachidonic acid- or collagen-induced whole blood aggregation following 1 month atorvastatin therapy (inhibition by 60.9 ± 5.6% vs. 48.8 ± 5.4%, P<0.05 for 0.5mM arachidonic acid, 40.8 ± 2.9% vs. 27.0 ± 4.1%, P<0.05 for 1 μg/ml collagen), and this effect lasted for 3 and 6 months, remaining in a weak, although significant, relation to the reduction of platelet cholesterol content (R(S)=-0.277, P<0.002 for arachidonic acid, R(S)=-0.197, P<0.02 for collagen). It was, however, not dependent upon either antiplatelet action or plasma lipid-lowering activity of atorvastatin. In addition, in about 50% of patients, we noticed that ASA (50 μM) significantly and time-dependently diminished thromboxane B(2) concentration in atorvastatin-treated patients. The ASA-induced acetylation of platelet proteins significantly increased in the course of atorvastatin therapy and was associated with reduced platelet cholesterol (R(S)=-0.598, P<0.0001). In conclusion, statin therapy may improve platelet sensitivity to ASA in some hypercholesterolemic patients. This effect may extend beyond the action of atorvastatin as merely a lipid-lowering agent. The mechanisms of resistance of some patients to such a combined ASA-statin treatment remain to be elucidated.

Functional testing methods for the antiplatelet effects of aspirin

At antiplatelet doses of 75–325 mg/day, aspirin irreversibly inhibits the platelet cyclooxygenase (COX)-1-dependent thromboxane A2 (TXA2) formation. This is the pharmacological mode of action of aspirin, and it can be predicted that if aspirin does not inhibit COX-1 sufficiently, patients will not benefit from its antiplatelet effects. A pharmacodynamic failure of aspirin occurs in 1–2% of patients. The vast majority of atherothrombotic events in patients treated with aspirin result from mechanisms that are dependent on residual (non-COX-1-dependent) platelet reactivity. Global tests of platelet activation in vitro may identify patients with high residual platelet reactivity but are not sufficiently specific to test the pharmacological effect of aspirin. A further problem is the absence of standardized normal ranges for many assays and the fact that different equipment measures different signals, which are also influenced by the agonist and the anticoagulant used. Similar considerations apply for the determination of platelet-derived biomarkers such as circulating P-selectin, soluble CD40 ligand and others. The direct measurement of inhibition of thromboxane-forming capacity is the most specific pharmacological assay for aspirin. However, there is no linear correlation between inhibition of TXA2 formation and inhibition of platelet function. Measurement of urinary levels of the TXB2 metabolite, 11-dehydro-thromboxane B2, represents an index of TXA2 biosynthesis in vivo, but is also sensitive to other cellular sources of TXA2. One general problem of all assays is the relationship with clinical outcome, which is still unclear. Monitoring aspirin treatment by testing platelet function or measuring biomarkers in clinical practice should not be recommended until a clear relationship for the predictive value of these assays for clinical outcome has been established.

Relation of CYP2C19 loss-of-function polymorphism to the occurrence of stent thrombosis

IMPORTANCE OF THE FIELD

Major adverse cardiovascular events including stent thrombosis associated with residual platelet reactivity on antiplatelet treatment in high risk vascular patients is a hot issue that needs a strong effort to be solved. Dual antiplatelet therapy with clopidogrel and aspirin prevents ischemic events and improves outcomes following acute coronary syndromes and percutaneous coronary intervention. However, adverse cardiovascular events occur in these patients, and several studies have shown that patients who suffer cardiovascular complications have high post-treatment platelet reactivity despite antiplatelet treatment. Clopidogrel requires conversion to active metabolite by CYP isoenzymes. Recently, CYP2C19*2 polymorphism (G681A nucleotide substitution) has been shown to be associated with decreased metabolisation of clopidogrel, poor antiaggregant effect and increased adverse cardiovascular events.

AREAS COVERED IN THIS REVIEW

This review summarises the principal studies contributing to establish the relationship between CYP2C19*2 polymorphism and adverse outcomes in high risk patients on clopidogrel treatment.

TAKE HOME MESSAGE

Prospective studies are urgently needed to determine the clinical impact of a score that takes into account individual characteristics of patients - CYP2C19*2 genotypes, residual platelet reactivity, drug-drug interaction, as well as traditional and procedural risk factors - for the identification of the therapeutic strategy that provides the best benefit for the single subject.

Genomics of cardiovascular disease

As the leading cause of death worldwide and a major cause of disability, cardiovascular disease remains a central focus of basic research, pharmacological treatment, surgical interventions, and long-term care. Inherited, monogenic syndromes have provided insight into pathophysiological mechanisms across the range of cardiovascular diseases. With the advent of post-Human Genome Project resources and technology, there has been a flood of research aimed at genome-wide predisposition markers, pharmacogenetics, and genomic signatures in complex cardiovascular disorders. Genomic research has both further elucidated the impact of genes previously identified in cardiovascular disease development and progression and discovered genomic regions as yet unknown to be associated with cardiovascular outcomes. The promise of personalized medicine lies in combining this genetic information with other biomarkers to tailor preventive and therapeutic strategies to individual patients for effective management, fewer adverse events, and preventive care.

Determinants to optimize response to clopidogrel in acute coronary syndrome

The inhibition of platelet function by antiplatelet therapy determines the improvement of the survival of patients with clinically evident cardiovascular disease. Clopidogrel in combination with aspirin is the recommended standard of care for reducing the occurrence of cardiovascular events in patients with acute coronary syndromes undergoing percutaneous coronary intervention. However, major adverse cardiovascular events including stent thrombosis occur in patients taking clopidogrel and aspirin. A growing body of evidence demonstrates that high post-treatment platelet reactivity on antiplatelet treatment is associated with increased risk of adverse clinical events. Clopidogrel requires conversion to active metabolite by cytochrome P450 isoenzymes. The active metabolite inhibits ADP-stimulated platelet activation by irreversibly binding to P2Y₁₂ receptors. Recently, the loss-of-function CYP2C19*2 allele has been associated with decreased metabolization of clopidogrel, poor antiaggregant effect, and increased cardiovascular events. In high risk vascular patients, the CYP2C19*2 polymorphism is a strong predictor of adverse cardiovascular events and particularly of stent thrombosis. Prospective studies evaluating if an antiplatelet treatment tailored on individual characteristics of patients, CYP2C19*2 genotypes, platelet phenotype, drug–drug interaction, as well as traditional and procedural risk factors, are now urgently needed for the identification of therapeutic strategies providing the best benefit for the single subject.

Antiplatelet therapy in percutaneous coronary intervention: a critical review of the 2007 AHA/ACC/SCAI guidelines and beyond

Antiplatelet therapy is a mainstay in the treatment of patients who have undergone percutaneous coronary intervention (PCI). Although the 2007 PCI treatment guidelines were published by the American College of Cardiology, the American Heart Association, and the Society for Cardiovascular Angiography and Interventions, new clinical evidence has emerged, expanding our understanding of antiplatelet use and potentially affecting the treatment guidelines. For example, clinical trial results prompted a Science Advisory to recommend that dual therapy with aspirin and clopidogrel be used for longer periods-up to 1 year in patients who receive bare metal stents and at least 1 year in patients receiving drug-eluting stents. New trial results have also emerged regarding the use of glycoprotein IIb/IIIa antagonists such as abciximab, eptifibatide, and tirofiban. This article reviews the current recommendations for antiplatelet therapy in PCI patients, recent trial results, newly developed agents, ongoing clinical trials, and the future direction of antiplatelet therapy in patients who undergo PCI.

Response to aspirin and clopidogrel monitored with different platelet function methods

Laboratory non-response to aspirin or clopidogrel is defined as an inability to cause in vitro detectable platelet function inhibition. It would be beneficial to monitor response to aspirin or clopidogrel with widely available and routinely used platelet function methods, like the platelet function analyzer (PFA-100) or the fully automated coagulation analyzer BCT. The aim of this study was to assess the potential of the coagulation analyzer BCT and the platelet function analyzer PFA-100 in monitoring the response of aspirin and clopidogrel. A group of 125 consecutive patients with arterial occlusive disease treated either with aspirin 100 mg/day (82 patients) or clopidogrel 75 mg/day (43 patients) as only antiplatelet drug were investigated. For the first time platelet-enriched plasma (PRP), not adjusted to a fixed predetermined concentration of platelets, was used for aggregation studies and the effect of clopidogrel alone without combination of aspirin treatment on platelet function was investigated. Response to aspirin was observed in 85% (70/82) of patients using PFA-100, while performing the arachidonic acid-induced aggregation on the BCT showed an inhibitory effect to aspirin in 91% (75/82) of patients. Non-response to aspirin was assessed with both platelet function methods in 7% (6/82) of patients. Clopidogrel response was observed in 58% (25/43) of patients when performing ADP-induced aggregation on the BCT. On the PFA-100 the antiplatelet effect of clopidogrel could not be detected. In conclusion, measurement of platelet aggregation on the BCT using native platelet-enriched plasma allows the quantification of individual inhibitory effects to aspirin as well as to clopidogrel, while the PFA-100 seems only suitable to investigate the degree of platelet inhibition induced by aspirin but not by clopidogrel.

Variability in platelet response to the antiplatelet agents aspirin and clopidogrel: mechanisms, measurement, and clinical relevance

Platelet reactivity (eg, platelet adhesion, activation, aggregation) is the underlying pathology for atherothrombotic processes and subsequent ischemic complications. Antiplatelet drugs, including aspirin, dipyridamole, thienopyridines (clopidogrel and ticlopidine), and glycoprotein IIb/IIIa antagonists, have proven efficacy in atherothrombotic event prevention. However, variability of platelet response measured in the laboratory has been reported and is a subject of keen interest.It is unclear to what extent variability of platelet response to antiplatelet agents is associated with clinical outcomes. A better understanding of this issue requires a general consensus for a standard, preferably point-of-care, ex vivo or in vitro assay to determine the effects of antiplatelet agents on key platelet functions. Currently, results using various methods have not yielded an obvious answer. Small-scale studies have examined the correlation between ex vivo inhibition of platelet aggregation or residual platelet activity and clinical endpoints, and although evidence shows that such correlations may exist, results have not been consistent or definitive. Data from large-scale prospective trials are needed to expand our current understanding of the benefits and limitations of utilizing platelet function tests to effectively manage the balance between protection and risks associated with the antiplatelet therapies, aspirin, and clopidogrel.

Relation of cytochrome P450 2C19 loss-of-function polymorphism to occurrence of drug-eluting coronary stent thrombosis

Residual platelet reactivity (RPR) to adenosine 5' diphosphate (ADP) was an independent predictor of stent thrombosis (ST) in patients receiving drug-eluting stents on dual-antiplatelet treatment and was associated with the cytochrome P450 (CYP)2C19*2 polymorphism. The aim was to evaluate the role of the CYP2C19*2 polymorphism in the occurrence of ST or the composite end point of ST and cardiac mortality within a 6-month follow-up in patients undergoing percutaneous coronary interventions with drug-eluting stent implantation on dual-antiplatelet treatment enrolled in the RECLOSE trial. Seven hundred seventy-two patients were studied for the CYP2C19*2 polymorphism and RPR (using 10-muM ADP-induced platelet aggregation). Patients with ST or the composite of ST and cardiac mortality showed a higher prevalence of carriers of the rare allele (54.1% vs 31.3%; p = 0.025 and 51.7% vs 31.2%; p = 0.020, respectively). At multivariate logistic regression analysis with ST or ST and cardiac mortality as dependent variables and the CYP2C19*2 polymorphism, ADP RPR, and additional previously shown clinical and procedural risk factors for ST as independent variables, the CYP2C19*2 allele (ST odds ratio [OR] 3.43, 95% confidence interval [CI] 1.01 to 12.78, p = 0.047; ST and cardiac mortality OR 2.70, 95% CI 1.00 to 8.42, p = 0.049) and ADP RPR (ST OR 3.08, 95% CI 1.23 to 7.72, p = 0.016; ST and cardiac mortality OR 2.90, 95% CI 1.08 to 12.98, p = 0.019) were independent risk factors. Subjects with the contemporary presence of the CYP2C19*2 allele and ADP RPR showed a strong risk of ST or ST and cardiac mortality (OR 5.79, 95% CI 1.04 to 39.01, p = 0.033 and OR 11.45, 95% CI 1.84 to 71.27, p = 0.009, respectively). In conclusion, the CYP2C19*2 allele was associated with the occurrence of ST or ST and cardiac mortality in high-risk vascular patients on dual-antiplatelet treatment. These findings could impact on the future design of pharmacogenetic antiaggregant strategies.

Aspirin resistance is more common in lacunar strokes than embolic strokes and is related to stroke severity

The aim of this study was to investigate the relationship between aspirin resistance, ischaemic stroke subtype, stroke severity, and inflammatory cytokines. Aspirin resistance was assessed by thrombelastography in 45 people with ischaemic stroke and 25 controls. Plasma interleukin (IL)-6 was measured. Stroke severity was assessed using the modified Rankin scale and National Institute of Health Stroke Score within 72 h of stroke. Aspirin resistance was more common in the stroke than the control group (67% versus 40%, P=0.028), and within the stroke group the aspirin-resistant group had a higher Rankin score (4.0 versus 2.0, P=0.013). Aspirin resistance was greater in lacunar than embolic strokes (platelet activation 79% versus 59%, P=0.020). The stroke aspirin-resistant group had higher levels of IL-6 than the stroke aspirin-sensitive group (2.4+/-1 versus 1.8+/-0.9 ng/mL, P=0.037). Using multivariate analysis, we examined the interrelationships between aspirin resistance, IL-6, and stroke severity. These analyses showed that IL-6 was independently associated with stroke severity as the outcome (B=3.738, P=0.036), and aspirin resistance was independently associated with IL-6 (B=0.765, P=0.005) as the outcome. In conclusion, aspirin resistance is related to stroke severity and aspirin resistance is more common in lacunar strokes than embolic strokes.

Antiplatelet therapy for recurrent stroke prevention: newer perspectives based on (MATCH), (CHARISMA), and (ESPRIT)

Antiplatelet therapy is an important component of our armamentarium for recurrent stroke prevention. Aspirin is a safe and effective antiplatelet drug for recurrent stroke prevention, however, it has been challenged recently by the thienopyridine derivative, clopidogrel, and the combination agent, aspirin plus extended release dipyridamole. In this review, we discuss recent studies of thienopyridine derivatives and aspirin plus extended-release dipyridamole in stroke prevention and evidence-based guidelines for the administration of these agents in practice for recurrent stroke prevention.

The genetics of aspirin resistance

Aspirin is widely used for the prophylaxis of cardiovascular events in patients with cardiovascular risk factors or established atherosclerotic disease. However, despite aspirin treatment, a substantial number of patients experience recurrent events. Such 'aspirin resistance' is generally defined as failure of aspirin to produce an expected biological response, for example inhibition of platelet aggregation or of thromboxane A2 synthesis. Whilst its aetiology is multifactorial, genetic factors are also likely to play their part. Here we review the evidence for and against such a genetic contribution, as well as the data suggesting the involvement of specific genes.

Flavonoids inhibit the platelet TxA(2) signalling pathway and antagonize TxA(2) receptors (TP) in platelets and smooth muscle cells

AIMS

Flavonoids may affect platelet function by several mechanisms, including antagonism of TxA(2) receptors (TP). These TP are present in many tissues and modulate different signalling cascades. We explored whether flavonoids affect platelet TP signalling, and if they bind to TP expressed in other cell types.

METHODS

Platelets were treated with flavonoids, or other selected inhibitors, and then stimulated with U46619. Similar assays were performed in aspirinized platelets activated with thrombin. Effects on calcium release were analysed by fluorometry and changes in whole protein tyrosine phosphorylation and activation of ERK 1/2 by Western blot analysis. The binding of flavonoids to TP in platelets, human myometrium and TPalpha- and TPbeta-transfected HEK 293T cells was explored using binding assays and the TP antagonist (3)H-SQ29548.

RESULTS

Apigenin, genistein, luteolin and quercetin impaired U46619-induced calcium mobilization in a concentration-dependent manner (IC(50) 10-30 microm). These flavonoids caused a significant impairment of U46619-induced platelet tyrosine phosphorylation and of ERK 1/2 activation. By contrast, in aspirin-treated platelets all these flavonoids, except quercetin, displayed minor effects on thrombin-induced calcium mobilization, ERK 1/2 and total tyrosine phosphorylation. Finally, apigenin, genistein and luteolin inhibited by >50% (3)H-SQ29548 binding to different cell types.

CONCLUSIONS

These data further suggest that flavonoids may inhibit platelet function by binding to TP and by subsequent abrogation of downstream signalling. Binding of these compounds to TP occurs in human myometrium and in TP-transfected HEK 293T cells and suggests that antagonism of TP might mediate the effects of flavonoids in different tissues.

Antithrombotic effects of aspirin based on PLA1/A2 glycoprotein IIIa polymorphism in patients with coronary artery disease

OBJECTIVE

The diallelic glycoprotein IIIa polymorphism P1A1/A2 was attributed to be an inherited risk factor for coronary events. Whether this polymorphism affects response to aspirin in patients with coronary artery disease is not known.

METHODS

We assessed thrombin generation (prothrombin fragment F1+2) in consecutive blood samples collected from bleeding-time wounds in 28 men with coronary artery disease; P1A2 carriers, n=9; P1A1/A1, n=19. Thrombin generation and bleeding time were measured before and after 2 weeks of aspirin 300 mg/day.

RESULTS

Aspirin-depressed thrombin generation in A1 homozygotes (p=0.04), but not in A2 carriers. Bleeding time after aspirin was also prolonged in A1 subjects only (p=0.02).

CONCLUSION

Genotyping for glycoprotein IIIa polymorphism might be helpful in predicting antithrombotic action of aspirin in secondary prevention of coronary artery disease.

Aspirin failure course during exercise and its connection with soluble CD40L

INTRODUCTION

The aspirin failure (resistance) is a still discussed and highly studied problem. This phenomenon is observed in rest, but could be precipitated by an exercise. The aspirin resistance was also linked with the inflammatory process which is a key event for the atherosclerosis development. Platelets seem to play an important role also in that setting, probably by the CD40-CD40L axis. The aim of the study was to assess the frequency of the aspirin failure induced by the exercise and the role of sCD40L in that regard.

MATERIALS AND METHODS

The study included 40 patients with established coronary artery disease. The control group consisted of 10 patients without coronary artery disease matched for age. All patients and controls were on 75 mg of aspirin for at least 30 days and had treadmill testing and blood collected for measurement of sCD40L and optical platelet aggregation with ADP, collagen and arachidonic acid. Aspirin resistance was defined as a maximal aggregation with ADP and collagen exceeding 70%.

RESULTS

There were 15 aspirin-resistant patients in the studied group (37%). There were significantly higher concentration of sCD40L (ng/ml) in aspirin-resistant patients in comparison with aspirin-sensitive ones before testing (7,9 +/- 2,5 vs. 5,1 +/- 3,5, p < 0,05) and on the top of it (8,1 +/- 2,9 vs. 4,5 +/- 3,9, p < 0,05). There were 3 persons who become resistant on the top of the exercise which was connected with the significant increase of sCD40L concentration in that group (from 7,6 +/- 1,9 before exercise to 10,1 +/- 2,9 on the top of the exercise, p < 0,05). There was also a positive correlation between the sCD40L level before and on the top of the exercise in an aspirin-resistant group (r = 0,48 for both, p < 0,05). Patients who were aspirin-resistant at rest had also significant elevation of platelet aggregation on the top of the exercise (ADP (%) from 90,5 +/- 8,6 to 95,0 +/- 6,5, p < 0,05 and collagen (%) from 87,8 +/- 8,7 to 92,1 +/- 8,0, p < 0,05).

CONCLUSIONS

1. Aspirin resistance phenomenon is present in about 37% patients on 75 mg aspirin daily.2. Aspirin-resistant patients have higher platelet aggregation during the exercise.3. Moderate physical exercise provokes 12% increase in the aspirin resistance phenomenon occurrence.4. Aspirin resistance is connected with higher sCD40L level at rest and exercise provoked aspirin resistance is connected with the sCD40L concentration increase.

Measuring antiplatelet drug effects in the laboratory

This review discusses the advantages and disadvantages of currently available tests for the monitoring of antiplatelet therapy (especially aspirin and clopidogrel). Many tests of platelet function are now available for clinical use, and some of these tests have been shown to predict clinical outcomes after antiplatelet therapy. However, in most of these studies, the number of major adverse clinical events was low. No published studies address the clinical effectiveness of altering therapy based on the results of monitoring antiplatelet therapy. Therefore, the correct treatment, if any, of "resistance" to antiplatelet therapy is unknown and, other than in research trials, monitoring of antiplatelet therapy in patients is not generally recommended. A clinically meaningful definition of "resistance" to antiplatelet drugs needs to be developed, based on data linking drug-dependent laboratory tests to clinical outcomes in patients.

Aspirin resistance: is this term meaningful?

PURPOSE OF REVIEW

To review data for and against the existence of 'aspirin resistance', a term coined to indicate aspirin-treated patients having ex-vivo tests of platelet activation insensitive to aspirin treatment and recurrence of cardiovascular disease.

RECENT FINDINGS

'Aspirin resistance' defined by ex-vivo tests of platelet activation yielded values ranging from 21 to 78%, indicating that such tests do not provide a useful measurement. In long-term aspirin-treated patients, studies demonstrated small but functionally relevant platelet thromboxane A2 formation that was responsible for an enhanced platelet activation in response to platelet agonist. These studies, however, did not fully exclude that aspirin compliance may be implicated in such phenomena. Two trials performed in patients with coronary artery disease demonstrated that laboratory evidence of aspirin resistance was no longer detectable when aspirin compliance was accurately monitored.

SUMMARY

Given the multifactorial nature of atherothrombosis, recurrence of cardiovascular events in aspirin-treated patients does not necessarily suggest 'drug failure'. A cause-effect relationship between platelet insensitivity to aspirin and cardiovascular recurrence has not been defined overall because aspirin compliance has been scarcely considered. Until this information is taken into account, the existence of 'clinical resistance' to aspirin should be reconsidered.

Aspirin resistance: truth or dare

Acetylsalicylic acid, or aspirin (ASA), is widely used in patients with cardiovascular disease to prevent acute ischemic events. However, platelet response to ASA is not equal in all individuals, and a high variability in the prevalence of ASA resistance is reported in the literature (0.4-83%). Actually, ASA resistance is poorly understood; this stems from the fact that its definition is unclear, its presence can be evaluated by a number of assays that are not equivalent, and its prevalence may vary widely based on the population studied. This article (1) exposes the difficulties in defining ASA resistance; (2) discusses the mechanisms by which ASA resistance may occur; (3) presents the characteristics that may put patients at greater risk of exhibiting ASA resistance; and (4) discusses the clinical impact of ASA resistance in patients requiring chronic therapy.

Aspirin resistance measured by cationic propyl gallate platelet aggregometry and recurrent cardiovascular events during 4 years of follow-up

BACKGROUND

Aspirin resistance appears to be an important prognostic factor in patients with coronary artery disease, yet there is no standardized method to measure it and limited data on its correlation to clinical outcomes.

METHODS

In a prospective study we followed 103 patients (mean age 64 years) with acute coronary syndrome (ACS) without ST segment elevation who were treated with 100 mg of aspirin (ASA) daily. Optical platelet aggregometry using cationic propyl gallate (CPG) as an inductor was measured at ACS onset and after 3, 12, 24, 36, and 48 months. ASA responsiveness was defined both by the slope of the aggregation curve (<53%/min) and by spontaneous aggregation (<5%). The primary outcomes were the recurrence of ACS or stroke.

RESULTS

Patients with ACS exhibited a greater prevalence of ASA resistance (55%) than healthy volunteers (4%; p<0.01). ASA resistance occurred more often in patients with type 2 diabetes, hypertriacylglycerolemia, and decreased HDL levels, and in smokers (p<0.05). A single assessment of platelet aggregometry was sufficient to identify ASA-resistant patients. During the 4-year follow-up, the patients with ASA resistance had an 88% incidence of recurrent cardiovascular events versus 46% for the patients without ASA resistance (p<0.01). In the subgroup with recurrent cardiovascular (CV) events, significantly more patients were ASA-resistant than in the subgroup without recurrent CV events (72% vs. 8%, p<0.01).

CONCLUSION

ASA resistance measured by CPG-induced platelet aggregometry is more common among patients with ACS and some metabolic risk factors, and ASA-resistant patients have a significantly higher recurrence of cardiovascular events.

Pharmacogenetics of chronic cardiovascular drugs: applications and implications

Cardiovascular disease continues to be a tremendous worldwide problem, and drug therapy is a major modality to attenuate its burden. At present, conditions such as hypertension, dyslipidaemia and heart failure are pharmacologically managed with an empirical trial-and-error approach. However, it has been suggested that this approach fails to adequately address the therapeutic needs of many patients, and pharmacogenetics has been offered as a tool to enhance patient-specific drug therapy. This review outlines pharmacogenetic studies of common cardiovascular drugs, such as diuretics, beta-blockers, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, statins and warfarin, ultimately highlighting considerations for future research and practice.

The platelet as a therapeutic target for treating vascular diseases and the role of eicosanoid and synthetic PPARgamma ligands

The platelet was traditionally thought only to serve as the instigator of thrombus formation, but now is emerging as a pivotal player in cardiovascular disease and diabetes by inciting and maintaining inflammation. Upon activation, platelets synthesize eicosanoids such as thromboxane A2 (TXA2) and PGE2 and release pro-inflammatory mediators including CD40 ligand (CD40L). These mediators activate not only platelets, but also stimulate vascular endothelial cells and leukocytes. These autocrine and paracrine activation processes make platelets an important target for attenuating inflammation. The growing interest and recent discoveries in platelet biology has lead to the search for therapeutic platelet targets. Recently, platelets, although anucleate, were discovered to possess the transcription factor PPARgamma. Treatment with eicosanoid and synthetic PPARgamma ligands blunts platelet release of the bioactive mediators, soluble (s) CD40L and TXA2, in thrombin-activated platelets. PPARgamma ligand treatment may prove useful for dampening unwanted platelet activation and chronic inflammatory diseases such as cardiovascular disease.