No case of COX‐1‐related aspirin resistance found in 289 patients with symptoms of stable CHD remitted for coronary angiography

Comparison of VerifyNow, thromboelastography, and PL-12 in patients with minor ischemic stroke or transient ischemic attack

High on-treatment platelet reactivity (HOPR) is associated with stroke recurrence. It is important to find a reliable method to assess HOPR. We aimed to compare the correlations between VerifyNow™ system, thromboelastography (TEG), and Aggrestar platelet function analyzer (PL-12) on platelet activity in patients with minor ischemic stroke or transient ischemic attack (TIA) after dual antiplatelet therapy for 7 days. About 276 patients were included. Spearman’s correlation coefficient and the kappa coefficient were adopted to evaluate associations among the three test methods. An obvious correlation between VerifyNow and TEG on HOPR-ADP (r=0.64, p<0.001) was found. The correlations of HOPR-ADP between PL-12 and the other two platelet function analyzers were moderate (PL-12 versus VerifyNow, r=0.47, p<0.001; PL-12 versus TEG, r=0.25, p<0.001). The correlations of HOPR-AA were limited among these three platelet function analyzers (VerifyNow versus TEG, r=0.09, p=0.14; VerifyNow versus PL-12, r=0.15, p=0.01; PL-12 versus TEG, r=0.10, p=0.09). Correlations among different platelet function analyzers were varied. VerifyNow and TEG were more correlative than PL-12 on HOPR-ADP. The consistence of HOPR-AA was limited among VerifyNow, TEG and PL-12. The proportion of stroke recurrence and composite events in patients with HOPR-ADP assessing by PL-12 was higher than VerifyNow and TEG.

A brief review on the mechanisms of aspirin resistance

Aspirin is the most widely prescribed drug for the primary and secondary prevention of cardiovascular and cerebrovascular diseases. However, a large number of patients continue to experience thromboembolic events despite aspirin therapy, a phenomenon referred to as aspirin resistance or treatment failure. Aspirin resistance is often observed along with a high incidence of unstable plaque, cardiovascular events and cerebrovascular accident. Studies have shown that aspirin reduces the production of TXA2, but not totally inhibits the activation of platelets. In this review, we analyze current and past research on aspirin resistance, presenting important summaries of results regarding the potential contributive roles of single nucleotide polymorphisms, inflammation, metabolic syndrome and miRNAs. The aim of this article is to provide a brief review on aspirin resistance and platelet function, which will provide important insights into the research of aspirin resistance.

The lack of aspirin resistance in patients with coronary artery disease

Background

Aspirin resistance established by different laboratory methods is still a debated problem. Using COX1 specific methods no aspirin resistance was detected among healthy volunteers. Here we tested the effect of chronic aspirin treatment on platelets from patients with stable coronary artery disease. The expression of COX2 mRNA in platelets and its influences on the effect of aspirin was also investigated.

Methods

One hundred and forty four patients were enrolled in the study. The direct measurement of COX1 acetylation was carried out by monoclonal antibodies specific to acetylated and non-acetylated COX1 (acCOX1 and nacCOX1) using Western blotting technique. Arachidonic acid (AA) induced TXB₂ production by platelets was measured by competitive immunoassay. AA induced platelet aggregation, ATP secretion and VerifyNow Aspirin Assay were also performed. COX2 and COX1 mRNA expression in platelets were measured in 56 patients by RT-qPCR.

Results

In 138 patients only acCOX1 was detected, in the remaining six patients nacCOX1 disappeared after a compliance period. AA induced TXB₂ production by platelets was very low in all patients including the 6 patients after compliance. AA induced platelet aggregation, secretion and with a few exceptions the VerifyNow Assay also demonstrated the effect of aspirin. Smoking, diabetes mellitus and inflammatory conditions did not influence the results. The very low amount of COX2 mRNA detected in 39 % of the investigated platelets did not influence the effect of aspirin.

Conclusions

No aspirin resistance was detected among patients with stable coronary artery disease. COX2 expression in platelets did not influence the effect of aspirin.

Next-generation re-sequencing of genes involved in increased platelet reactivity in diabetic patients on acetylsalicylic acid

The objective of this study was to investigate whether rare missense genetic variants in several genes related to platelet functions and acetylsalicylic acid (ASA) response are associated with the platelet reactivity in patients with diabetes type 2 (T2D) on ASA therapy. Fifty eight exons and corresponding introns of eight selected genes, including PTGS1, PTGS2, TXBAS1, PTGIS, ADRA2A, ADRA2B, TXBA2R, and P2RY1 were re-sequenced in 230 DNA samples from T2D patients by using a pooled PCR amplification and next-generation sequencing by Illumina HiSeq2000. The observed non-synonymous variants were confirmed by individual genotyping of 384 DNA samples comprising of the individuals from the original discovery pools and additional verification cohort of 154 ASA-treated T2DM patients. The association between investigated phenotypes (ASA induced changes in platelets reactivity by PFA-100, VerifyNow and serum thromboxane B2 level [sTxB2]), and accumulation of rare missense variants (genetic burden) in investigated genes was tested using statistical collapsing tests. We identified a total of 35 exonic variants, including 3 common missense variants, 15 rare missense variants, and 17 synonymous variants in 8 investigated genes. The rare missense variants exhibited statistically significant difference in the accumulation pattern between a group of patients with increased and normal platelet reactivity based on PFA-100 assay. Our study suggests that genetic burden of the rare functional variants in eight genes may contribute to differences in the platelet reactivity measured with the PFA-100 assay in the T2DM patients treated with ASA.

A brief review on high on-aspirin residual platelet reactivity

Although aspirin is effective in secondary prevention in coronary heart disease, new thromboembolic events in patients on aspirin are frequently seen. In trials on aspirin-treated patients, platelet function tests have revealed large variability in platelet aggregation. This phenomenon has been named aspirin resistance, aspirin non-responsiveness or high-on-aspirin residual platelet reactivity. The mechanism of aspirin antiplatelet effect is due to the inhibition of cyclooxygenase-1 enzyme in platelets. In some trials, almost all patients on aspirin have a very low level of serum thromboxane B2, indicating that the measured platelet reactivity in aspirin-treated patients might be due to platelet activation via other pathways, such as ADP or thrombin. The prevalence of real aspirin resistance seems to be very low, and probably the term "high-on-aspirin residual platelet reactivity" should be preferred to describe this phenomenon.

Younger age, higher body mass index and lower adiponectin concentration predict higher serum thromboxane B2 level in aspirin-treated patients with type 2 diabetes: an observational study

Background

Evidence from the literature suggests diminished acetylsalicylic acid (ASA) treatment efficacy in type 2 diabetes (DM2). High on-aspirin platelet reactivity (HAPR) in DM2 has been linked to poor glycemic and lipid control. However, there are no consistent data on the association between HAPR and insulin resistance or adipose tissue metabolic activity. The aim of this study was to assess the relationship between laboratory response to ASA and metabolic control, insulin resistance and adipokines in DM2.

Methods

A total of 186 DM2 patients treated with oral antidiabetic drugs and receiving 75 mg ASA daily were included in the analysis. Response to ASA was assessed by measuring serum thromboxane B₂ (TXB₂) concentration and expressed as quartiles of TXB₂ level. The achievement of treatment targets in terms of glycemic and lipid control, insulin resistance parameters (including Homeostatic Model Assessment-Insulin Resistance, HOMA-IR, index), and serum concentrations of high-molecular weight (HMW) adiponectin, leptin and resistin, were evaluated in all patients. Univariate and multivariate logistic regression analyses were performed to determine the predictive factors of serum TXB₂ concentration above the upper quartile and above the median.

Results

Significant trends in age, body mass index (BMI), HOMA-IR, HMW adiponectin concentration, C-reactive protein concentration and the frequency of achieving target triglyceride levels were observed across increasing quartiles of TXB₂. In a multivariate analysis, only younger age and higher BMI were independent predictors of TXB₂ concentration above the upper quartile, while younger age and lower HMW adiponectin concentration were predictors of TXB₂ concentration above the median.

Conclusions

These results suggest that in DM2, the most important predictor of HAPR is younger age. Younger DM2 patients may therefore require total daily ASA doses higher than 75 mg, preferably as a twice-daily regimen, to achieve full therapeutic effect. Higher BMI and lower HMW adiponectin concentration were also associated with less potent ASA effect. This is the first study to demonstrate an association of lower adiponectin concentration with higher serum TXB₂ level in patients treated with ASA.

Genetic variation of platelet function and pharmacology: an update of current knowledge

Platelets are critically involved in atherosclerosis and acute thrombosis. The platelet phenotype shows a wide variability documented by the inherited difference of platelet reactivity, platelet volume and count and function of platelet surface receptors. Several candidate genes have been put into focus and investigated for their functional and prognostic role in healthy individuals and patients with cardiovascular (CV) disease treated with antiplatelet agents. In addition to genetic variation, other clinical, disease-related and demographic factors are important so-called non-genetic factors. Due to the small effect sizes of single nucleotide polymorphisms (SNP) in candidate genes and due to the low allele frequencies of functional relevant candidate SNPs, the identification of genetic risk factors with high predictive values generally depends on the sample size of study cohorts. In the post-genome era new array and bioinformatic technologies facilitate high throughput genome-wide association studies (GWAS) for the identification of novel candidate genes in large cardiovascular cohorts. One of the crucial aspects of platelet genomic studies is the precise definition of a specific clinical phenotype (e.g. stent thrombosis) as this will impact importantly the findings of genomic studies like GWAS. Here, we provide an update on genetic variation of platelet receptors and drug metabolising enzymes under specific consideration of data derived by GWAS. The potential impact of this information and the role in personalised therapeutic concepts will be discussed.

ASPIRIN RESISTANCE CANDIDATE GENES AND THEIR ASSOCIATION WITH THE RISK OF CARDIOVASCULAR EVENTS

The review presents the current literature evidence on the most likely genetic polymorphisms of aspirin resistance, such as polymorphisms of cyclooxygenase, glycoproteins GP Ib/IIIa, GP Ibα, GP VI, and adenosine diphosphate receptors P2Y1 and P2Y12. The authors discuss the prevalence of these polymorphisms in laboratory and clinical aspirin resistance, as well as their association with the risk of cardiovascular events during aspirin treatment. 

Platelet response to aspirin in Chinese stroke patients is independent of genetic polymorphisms of COX-1 C50T and COX-2 G765C

AIM

Aspirin resistance (AR) is common in Chinese stroke patients taking antiplatelet medications; however, few studies have documented the role of cyclooxygenase (COX)-1 C50T and COX-2 G765C polymorphisms in AR. The aim of this study was to investigate the prevalence of AR in Chinese stroke patients and the relationships between AR and COX-1 C50T and COX-2 G765C polymorphisms, and to evaluate the effect of these polymorphisms on platelet response to aspirin.

METHODS

We prospectively enrolled 634 Chinese stroke patients. Platelet aggregation testing was performed before and after aspirin administration. The pre- and post-aspirin levels of 11-dehydrothromboxane B(2) (11-dTxB(2)) were determined in urine samples. COX-1 C50T and COX-2 G765C genotypes were determined by a polymerase chain reaction-allelic restriction assay.

RESULTS

AR was detected in 129 patients (20.4%), aspirin semi-resistance (ASR) was detected in 28 patients (4.4%), and aspirin sensitivity (AS) was detected in 477 patients (75.2%). There was no association between COX-1 C50T or COX-2 G765C polymorphisms and ASR+AR. Aspirin could efficiently reduce 11-dTxB(2) production by approximately 75%. In addition, platelet aggregation, both in response to arachidonic acid (AA) and adenosine 5'-diphosphate (ADP), was inhibited by more than 80% and 40%, respectively; however, the percentage reduction in platelet aggregation and 11-dTxB(2) levels was not significantly different between the COX-1 C50T and COX-2 G765C genotypes (p＞0.05).

CONCLUSIONS

There was no association between COX-1 C50T and COX-2 G765C polymorphisms and AR in Chinese stroke patients. In addition, COX-1 C50T and COX-2 G765C polymorphisms had no effect on the platelet response to aspirin.

Platelet response to aspirin and clopidogrel in patients with peripheral atherosclerosis

Aspirin and clopidogrel are important drugs in the secondary prevention of ischemic events. A considerable individual variation in platelet response to these drugs has, however, been reported, and high residual platelet reactivity despite treatment may be an independent risk factor for ischemic events. Most studies have been undertaken in patients with coronary heart disease, but patients with peripheral artery disease (PAD) may exhibit greater residual platelet reactivity, possibly because of platelet activation by a larger area of diseased endothelium. It is yet unsettled which method that best measures platelet reactivity and an eventual lack of response to aspirin. Several instruments are promoted to measure platelet response and low-response to platelet inhibitors, but it is questionable if they measure this in comparable ways. We studied the comparability of three tests of platelet reactivity for the assessment of low-response to aspirin and clopidogrel in patients with PAD. In 263 patients, platelet function was assessed twice, 3 months apart, by the Platelet Function Analyzer-100 (PFA), light transmission aggregometry (LTA), and whole blood impedance aggregometry (IA). In a subgroup of 43 patients, we studied the effect of a single dose of 600 mg clopidogrel on platelet function. Low-response to aspirin assessed by analyses targeting cyclooxygenase-1 activity (LTA, IA) was rare (≤ 8.1%). With the PFA, we found 17% with low response at both visits, and 60% who were consistently responsive, whereas 23% were categorized differently at the two visits. Low response to clopidogrel, occurred in 0-23%, depending on the method and the criteria used. A low-response to aspirin, defined by lack of COX-1 inhibition, is a rare phenomenon whereas high residual platelet reactivity as determined by PFA may be a rather frequent finding but is not consistent over time in all patients. A low-response to clopidogrel depends very much on the method and definition used.

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.

Aspirin and antiplatelet agent resistance: implications for prevention of secondary stroke

Oral antiplatelet drugs, including aspirin, clopidogrel and extended-release dipyridamole, are widely prescribed for the secondary prevention of vascular events, including stroke. Despite the benefits of antiplatelet therapy, 10−20% of patients experience a recurrent vascular event while taking antiplatelet medication. This article discusses the concept of antiplatelet resistance in general, focusing on aspirin resistance in particular, as a poorly defined cause of recurrent vascular events. Factors such as the lack of a standardized method to diagnose aspirin resistance and a poor clinical correlation with laboratory assays make the treatment of aspirin nonresponders difficult. In addition, there are confounding conditions such as diabetes mellitus that can affect aspirin resistance and determine a different course of treatment for these patients. Other antiplatelet options may also have resistant subpopulations; thus, alternative strategies for the secondary stroke patient must be explored.

Long-Term Aspirin and Clopidogrel Response Evaluated by Light Transmission Aggregometry, VerifyNow, and Thrombelastography in Patients Undergoing Percutaneous Coronary Intervention

Background: A reduced response to aspirin and clopidogrel predicts ischemic events, but reliable tests are needed to identify low responders. We compared 3 platelet-function tests during long-term dual treatment with aspirin and clopidogrel.

Methods: Patients who underwent a percutaneous coronary intervention and were receiving a combination of 325 mg/day aspirin and 75 mg/day clopidogrel were followed for 1 year. Blood was sampled 5 times during this period for 3 tests: light transmission aggregometry (LTA) assay, with 5.0 μmol/L ADP or 1.0 mmol/L arachidonic acid (AA) used as an agonist; VerifyNow™ assay, with the P2Y12 or aspirin cartridge (Accumetrics); and thrombelastography (TEG), stimulated by 2.0 μmol/L ADP or 1.0 mmol/L AA.

Results: Twenty-six of 33 patients completed all scheduled visits. A low response to clopidogrel was found in a few patients at variable frequencies and at different visits, depending on the method and criteria used. We found a moderate correlation between the LTA (ADP) and VerifyNow (P2Y12 cartridge) results, but the TEG (ADP) results correlated poorly with the LTA and VerifyNow results. A low response to aspirin was found with the VerifyNow (aspirin cartridge) and TEG (AA) methods on 6 and 2 occasions, respectively, but not with the LTA (AA) method, except for 1 occasion caused by probable noncompliance.

Conclusions: Detecting a low response to clopidogrel depends largely on the method used. Which method best predicts ischemic events remains uncertain. A low response to aspirin is rare with AA-dependent methods used at the chosen cutoffs. In some patients, the response to clopidogrel or aspirin may be classified differently at different times, even with the same method.

Pharmacogenetics of aspirin resistance: a comprehensive systematic review

AIMS

The aim was to perform a systematic review of all candidate gene association studies in aspirin resistance.

METHODS

Electronic databases were searched up until 1 December 2007 for all studies investigating any candidate gene for aspirin resistance in humans. Aspirin resistance was required to have been measured by a standardized laboratory technique to be included in the analysis.

RESULTS

Within 31 studies, 50 polymorphisms in 11 genes were investigated in 2834 subjects. The PlA1/A2 polymorphism in the GPIIIa platelet receptor was the most frequently investigated, with 19 studies in 1389 subjects. The PlA1/A2 variant was significantly associated with aspirin resistance when measured in healthy subjects [odds ratio (OR) 2.36, 95% confidence interval (CI) 1.24, 4.49; P = 0.009]. Combining genetic data from all studies (comprising both healthy subjects and those with cardiovascular disease) reduced the observed effect size (OR 1.14, 95% CI 0.84, 1.54; P = 0.40). Moreover, the observed effect of PlA1/A2 genotype varied depending on the methodology used for determining aspirin sensitivity/resistance. No significant association was found with aspirin resistance in four other investigated polymorphisms in the COX-1, GPla, P2Y1 or P2Y12 genes.

CONCLUSIONS

Our data support a genetic association between the PlA1/A2 molecular variant and aspirin resistance in healthy subjects, with the effect diminishing in the presence of cardiovascular disease. The laboratory methodology used influences the detection of aspirin resistance. However, as heterogeneity was significant and our results are based on a limited number of studies, further studies are required to confirm our findings.