Personalized medicine and antiplatelet therapy: ready for prime time?

Anti-Anemic Effect of Antioxidant-Rich Apple Vinegar against Phenylhydrazine-Induced Hemolytic Anemia in Rats

This study aims to examine the ability of apple vinegar on phenylhydrazine (PHZ)-induced hemolytic anemia in Wistar rats. In vitro, phenolic and flavonoid content and antioxidant activity were determined. In vivo, phenylhydrazine (10 mg/kg) was injected intravenously into rats for 4 days and then treated with apple vinegar daily by gavage (1 mL/kg) for five weeks. high level of polyphenols and flavonoids (90 ± 1.66 mg GAE/100 mL and 7.29 ± 0.23 mg QE/100 mL, respectively) were found in the apple vinegar which gives it a good ability to scavenge free radicals (TAC = 4.22 ± 0.18 mg AAE/100 mL and DPPH, IC₅₀ = 0.49 ± 0.004 µL/ml). The phytochemical composition of apple vinegar revealed the presence of numerous bioactive compounds including arbutin, apigenin, sinapic, ferulic and trans-ferulic acids. The major antioxidant components in apple vinegar were ferulic and trans-ferulic acids (40% and 43%, respectively). PHZ treatment induced changes in platelets, blood cell count, mean corpuscular volume, hemoglobin concentration and mean capsulated hemoglobin. However, the co-administration of apple vinegar revealed its capacity to ameliorate the changes induced by phenylhydrazine. Therefore, apple vinegar use could have a positive impact on the prevention of hemolytic anemia induced by phenylhydrazine due to the antioxidant properties of its major components.

Electrical impedance vs. light transmission aggregometry: Testing platelet reactivity to antiplatelet drugs using the MICELI POC impedance aggregometer as compared to a commercial predecessor

BACKGROUND

Patients' responses to antiplatelet therapy significantly vary, with individuals showing high residual platelet reactivity associated with thrombosis. To personalize thrombosis management, platelet function testing has been suggested as a promising tool able to monitor the antithrombotic effect of antiplatelet agents in real-time. We have prototyped the MICELI, a miniature and easy-to-use electrical impedance aggregometer (EIA), measuring platelet aggregation in whole blood. Here, we tested the capability of the MICELI aggregometer to quantify platelet reactivity on antiplatelet agents, as compared with conventional light-transmission aggregometry (LTA).

METHODS

Platelet aggregation in ACD-anticoagulated whole blood and platelet-rich plasma of healthy donors (n = 30) was evaluated. The effect of clopidogrel, ticagrelor, cangrelor, cilostazol, and tirofiban on ADP-induced aggregation was tested, while aspirin was evaluated with arachidonic acid and collagen. Platelet aggregation was recorded using the MICELI or BioData PAP-8E (Bio/Data Corp.) aggregometers.

RESULTS

The MICELI aggregometer detected an adequate and comparable dose-dependent decrease of platelet aggregation in response to increments of drugs' concentrations, as compared to LTA (the inter-device R² = 0.79-0.93). Platelet aggregation in platelet-rich plasma recorded by LTA showed higher sensitivity to antiplatelet agents, but it couldn't distinguish between different drug doses as indicated by saturation of the aggregatory response.

CONCLUSION

Platelet aggregation in whole blood as recorded by EIA represents a better model system for evaluation of platelet reactivity as compared with platelet aggregation in platelet-rich plasma as recorded by LTA, since EIA takes into consideration the modulatory effect of other blood cells on platelet hemostatic function and pharmacodynamics of antiplatelet drugs in vivo. As such, the MICELI impedance aggregometer could be potentially employed for the point-of-care monitoring of platelet function in patients on-treatment for personalized tailoring of their antiplatelet regimen.

Effect of hydro-methanol stem bark extract of Burkea africana on erythrocyte osmotic fragility and haematological parameters in acetaminophen-poisoned rats

Background

Burkea africana is a widely used medicinal plant in folkloric medicine in many developing countries of the world. It is useful in the treatment of various ailments including hepatitis, jaundice, diarrhea, stomach aches, abscesses, oedema, epilepsy, bloody diarrhea, gonorrhea, syphilis, toothaches and poisoning. Nevertheless, there are little or no scientific evidence to substantiate this medicinal claim by traditional healers. Burkea africana stem bark was therefore, investigated for its protective or stabilizing effect on erythrocyte membrane in acetaminophen-treated rats. B. africana stem bark was extracted using 80% methanol. Erythrocyte stabilizing effect was studied using erythrocyte osmotic fragility (EOF) test. Thirty (30) male rats were randomly assigned into five (5) groups of six (6) rats each. Groups 1 and 2 served as normal control and negative control (acetaminophen-treated group) respectively. Groups 3, 4 and 5 were pretreated with methanol stem bark extract of Burkea africana (MSBEBA) at doses of 200, 400 and 600 mg/kg body weight respectively once daily for seven (7) days. Blood samples were collected from the animals in all the groups on the 8 day for evaluation of packed cell volume, haemoglobin, red blood cell, white blood cell counts, and differential white blood cell count as well as erythrocyte osmotic fragility.

Results

The erythrocyte osmotic fragility test showed that there was a significantly (p < 0.05) low percentage hemolysis in the groups pre-treated with the extract when compared with the negative control. The percentage hemolysis was least at 600 mg/kg body weight of the extract. There was also a significant (p < 0.05) increase in the packed cell volume, haemoglobin, red blood cell count at all the doses of the extract used. Neutrophils were significantly (p < 0.05) decreased while lymphocytes were significantly increased in the groups administered MSBEBA 400 and 600 mg/kg body weight.

Conclusion

Methanol stem bark extract of Burkea africana had protective effect on the red blood cells and also improved haematological parameters. This indicates that Burkea africana may be useful in the treatment of disease conditions that results in hemolytic anemia by stabilizing red erythrocyte membranes and enhancing erythropoiesis.

DAPT Plus Cilostazol is Better Than Traditional DAPT or Aspirin Plus Ticagrelor as Elective PCI for Intermediate-to-Highly Complex Cases: Prospective, Randomized, PRU-Based Study in Taiwan

PURPOSE

Current treatment guidelines do not recommend different antiplatelet treatments for patients in different coronary risk categories; nor do they consider ethnic differences in responses to individual drugs.

OBJECTIVES

We performed a prospective, single-blind, randomized, comparative study of Taiwanese patients with stable angina and scheduled stent implantation for intermediate-to-highly complex coronary lesions and compared the platelet reactivity unit (PRU) levels and 24-month outcomes of groups receiving three different antiplatelet treatments.

METHODS

Patients (N = 334) were randomized into three treatment groups (aspirin + clopidogrel, aspirin + ticagrelor, or aspirin + clopidogrel + cilostazol) for 6 months of treatment and were then switched to aspirin only. PRU levels were determined 24 h, 7 days, and 1 month after stent implantation. Clinical outcomes and adverse events were recorded over 24 months.

RESULTS

Clopidogrel treatment reached full effect after 1 month. Ticagrelor decreased PRU levels more than did clopidogrel but often to levels that increased the risk of hemorrhage. The addition of cilostazol to clopidogrel decreased PRU levels earlier and more strongly than clopidogrel alone but not as strongly as did ticagrelor. Ticagrelor treatment caused fewer major adverse cardiovascular events (MACEs) and more episodes of minor bleeding than the other two treatments.

CONCLUSIONS

Clopidogrel appears safer than ticagrelor in Taiwanese patients with stable angina after stent implantation for intermediate-to-highly complex coronary lesions. The addition of cilostazol to clopidogrel may provide a more rapid decrease in PRU to therapeutic levels without increasing the risk of hemorrhage.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02101411.

Effect of platelet receptor gene polymorphisms on outcomes in ST-elevation myocardial infarction patients after percutaneous coronary intervention

Polymorphisms in platelet receptor genes may influence platelet function. This study aimed to assess the impact of five polymorphisms of genes encoding platelet receptors on the risk of ischemic and bleeding events in ST-elevation myocardial infarction (STEMI) patients after percutaneous coronary intervention (PCI). 503 consecutive Chinese patients with STEMI after an uneventful PCI and exposed to standard dual antiplatelet therapy for 12 months were enrolled. Polymorphisms of platelet receptors, GPIa (ITGA2, 807C > T, rs1126643), GPVI (GP6, 13254T > C, rs1613662), PAR-1 (F2R, IVS-14A > T, rs168753) and P2Y12 (P2RY12, 34C > T, rs6785930 and H1/H2 haplotype, 52G > T, rs6809699) were detected by the ligase detection reaction. The follow-up period was 12 months. Overall, 34 (6.8%) ischemic events occurred and 46 (9.1%) major bleedings occurred. Multivariate Cox regression analysis showed the carriage of F2R rs168753 minor allele was an independent predictor of the composite ischemic events (HR 0.387, 95% CI 0.193-0.778, p = 0.008) after adjusted for established risk factors. Multivariate logistic regression model identified that carriage of P2RY12 rs6809699 minor allele (OR 2.71, 95% CI 1.298-5.659, p = 0.008) was an independent predictor of major bleedings. The associations were then validated in a second cohort of 483 STEMI patients. In STEMI patients after PCI, F2R rs168753 minor allele could significantly contribute to the risk of ischemic events, and P2RY12 rs6809699 minor allele could predict bleedings. The genetic testing of platelet receptors can be valuable in predicting adverse events in STEMI patients after PCI.

The potential role of anticoagulant therapy for the secondary prevention of ischemic events post-acute coronary syndrome

Abstract The use of dual antiplatelet therapy has led to a substantial reduction in ischemic events post-acute coronary syndrome (ACS). Despite this, recurrent event rates remain high. Recent research has combined antiplatelet with anticoagulant therapy to reduce recurrent event rates further. Compared with standard medical therapy, rivaroxaban demonstrated improved efficacy outcomes and significantly reduced mortality after an ACS. Although clear benefits of novel oral anticoagulants post-ACS have been proven, concerns regarding bleeding are still a barrier to widespread use. This review explores key trials of dual antiplatelet therapy and examines the latest research in anticoagulation aiming to optimize clinical outcomes post-ACS.

Relationship between ABCB1 polymorphisms, thromboelastography and risk of bleeding events in clopidogrel-treated patients with ST-elevation myocardial infarction

INTRODUCTION

This study sought to investigate the relationship of polymorphisms in ABCB1 and the predictive value of thromboelastography (TEG) on bleeding risk in clopidogrel-treated patients with ST-elevation myocardial infarction (STEMI).

METHODS

467 consecutive patients with STEMI undergoing percutaneous coronary intervention (PCI) were enrolled. Twenty tag single nucleotide polymorphisms (SNPs) selected from ABCB1 gene and CYP2C19*2, *3, *17 were detected by the ligase detection reaction. Platelet reactivity was assessed by TEG. The follow-up period was 12months.

RESULTS

By receiver operating characteristic curve analysis, the TEG platelet mapping assay value of ADP inhibition had the best predictive value of bleeding academic research consortium definition (BARC) ≥ 3b bleedings, yielding an area under the curve (AUC) of 0.707 (95% CI 0.662-0.749, p=0.009; cut-off value > 93.4%). ADP inhibition can also predict BARC ≥ 3 bleedings with an AUC of 0.594 (95% CI 0.546-0.640, p = 0.05; cut-off value > 92.5%). After adjustment for established risk factors of bleeding including the gain of function CYP2C19*17 allele, age, female gender, renal function, the multivariable logistic regression model demonstrated that ADP inhibition > 92.5% (OR 2.247, 95%CI 1.082-4.665, P=0.03), carriage of rs1045642 (OR 2.943, 95%CI 1.195-7.247, P = 0.019) and rs7779562 (OR 0.453, 95%CI 0.219-0.936, P = 0.032) were independent predictors of BARC ≥ 3 bleedings. These associations were validated in a second cohort of 504 STEMI patients.

CONCLUSIONS

In STEMI patients treated with clopidogrel after PCI, the ABCB1 tag SNP rs1045642 is associated with higher risk of bleedings while rs7779562 is associated with lower bleeding risk, and ADP inhibition in TEG has a predictive value of bleedings.

New antithrombotic drugs: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

This article focuses on new antithrombotic drugs that are in or are entering phase 3 clinical testing. Development of these new agents was prompted by the limitations of existing antiplatelet, anticoagulant, or fibrinolytic drugs. Addressing these unmet needs, this article (1) outlines the rationale for development of new antithrombotic agents; (2) describes the new antiplatelet, anticoagulant, and fibrinolytic drugs; and (3) provides clinical perspectives on the opportunities and challenges faced by these novel agents.

Clarifying the importance of CYP2C19 and PON1 in the mechanism of clopidogrel bioactivation and in vivo antiplatelet response

AIMS

It is thought that clopidogrel bioactivation and antiplatelet response are related to cytochrome P450 2C19 (CYP2C19). However, a recent study challenged this notion by proposing CYP2C19 as wholly irrelevant, while identifying paraoxonase-1 (PON1) and its Q192R polymorphism as the major driver of clopidogrel bioactivation and efficacy. The aim of this study was to systematically elucidate the mechanism and relative contribution of PON1 in comparison to CYP2C19 to clopidogrel bioactivation and antiplatelet response.

METHODS AND RESULTS

First, the influence of CYP2C19 and PON1 polymorphisms and plasma paraoxonase activity on clopidogrel active metabolite (H4) levels and antiplatelet response was assessed in a cohort of healthy subjects (n = 21) after administration of a single 75 mg dose of clopidogrel. There was a remarkably good correlation between H4 AUC (0-8 h) and antiplatelet response (r2 = 0.78). Furthermore, CYP2C19 but not PON1 genotype was predictive of H4 levels and antiplatelet response. There was no correlation between plasma paraoxonase activity and H4 levels. Secondly, metabolic profiling of clopidogrel in vitro confirmed the role of CYP2C19 in bioactivating clopidogrel to H4. However, heterologous expression of PON1 in cell-based systems revealed that PON1 cannot generate H4, but mediates the formation of another thiol metabolite, termed Endo. Importantly, Endo plasma levels in humans are nearly 20-fold lower than H4 and was not associated with any antiplatelet response.

CONCLUSION

Our results demonstrate that PON1 does not mediate clopidogrel active metabolite formation or antiplatelet action, while CYP2C19 activity and genotype remains a predictor of clopidogrel pharmacokinetics and antiplatelet response.

ABCB1 C3435T polymorphism and risk of adverse clinical events in clopidogrel treated patients: a meta-analysis

INTRODUCTION

The ABCB1 C3435T polymorphism limits oral bioavailability of clopidogrel and may influence prognosis of patients treated with clopidogrel. Several studies have examined the association between the C3435T polymorphism and risk of adverse clinical events in clopidogrel treated patients, but the results were inconsistent. To assess the role of the C3435T polymorphism in the impact on clinical outcomes, a meta-analysis was conducted.

METHODS

6 studies with 10,153 subjects were included in this meta-analysis. Fixed- or random-effects model was chosen according to heterogeneity. Publication bias was evaluated by fail-safe numbers.

RESULTS

The association of the C3435T polymorphism with risk of overall recurrent ischemic events in clopidogrel treated patients was not statistically significant for all genetic models (OR=1.13, 95%CI: 0.78-1.64, P=0.51; OR=1.15, 95%CI: 0.99-1.33, P=0.07; OR=1.19, 95%CI: 0.81-1.76, P=0.37). Significant association was identified between the C3435T polymorphism and risk of short-term recurrent ischemic events (OR=1.55, 95% CI: 1.09-2.20, P=0.01; OR=1.41, 95% CI: 1.06-1.87, P=0.02; OR=1.77, 95% CI: 1.19-2.63, P=0.005). No statistically significant association between the C3435T polymorphism and stent thrombosis (OR=0.79, 95% CI: 0.47-1.32, P=0.37) or bleeding (OR=0.98, 95% CI: 0.79-1.21, P=0.82) was identified. The results may be affected by publication bias.

CONCLUSIONS

This meta-analysis failed to show an association between the ABCB1 C3435T polymorphism and risk of overall recurrent ischemic events, stent thrombosis or bleeding in clopidogrel treated patients. However, the association between TT homozygotes of the C3435T polymorphism and risk of short-term recurrent ischemic events may exist, but needs more studies to confirm.

Platelet dysfunction in vascular pathologies and how can it be treated

Cardiovascular diseases are one of the leading causes of morbidity and mortality in industrialized countries, and although many processes play a role in the development of vascular disease, thrombosis is the primary event that precipitates stroke and acute coronary syndromes. The blood platelets are of significant importance in medicine. These cells are involved in many physiological processes, particularly haemostasis through their ability to aggregate and form clots in response to activation. In addition, these dynamic cells display activities that extend beyond thrombosis, including an important role in initiating and sustaining vascular inflammation. The expansion of knowledge from basic and clinical research has highlighted the critical position of platelets in several inflammatory diseases such as arthritis and atherosclerosis. Platelets are emerging as important mediators of inflammation and provide important signals to mediate phenotype of other blood and vascular cells. The important role of platelets in arterial thrombosis and the onset of acute myocardial infarction after atherosclerotic plaque rupture make inhibition of platelet aggregation a critical step in preventing thrombotic events associated with stroke, heart attack, and peripheral arterial thrombosis. However, the use of platelet inhibitors for thrombosis prevention must seek a delicate balance between inhibiting platelet activation and an associated increased bleeding risk. The aim of this review is to up-date the knowledge on platelets physiology and dysfunction in pathologies, such as diabetes mellitus, hypercholesterolemia, and hypertension, emphasizing the link between platelets and the inflammation-related atherosclerosis. The review evaluates the opportunities offered by the novel platelet inhibitors to efficiently alleviate the thrombotic events.

Effect of paraoxonase-1 polymorphism on clinical outcomes in patients treated with clopidogrel after an acute myocardial infarction

Paraoxonase-1 (PON1) Q192R polymorphism was recently suggested to determine per se clopidogrel response on major cardiovascular events (MACEs). We assessed the impact of PON1, CYP2C19, and ABCB1 polymorphisms on MACE in clopidogrel-treated acute myocardial infarction (AMI) patients (N = 2,210), including those undergoing percutaneous coronary intervention (PCI) (n = 1,538). PON1 polymorphism was not associated with increased risk of in-hospital death and MACEs at 1 year (adjusted hazard ratio (HR) 1.03, 95% confidence interval (CI) 0.66-1.61 and adjusted HR 0.77, 95% CI 0.42-1.41 for QQ versus RR in all and PCI patients, respectively). The presence of two CYP2C19 loss-of-function (LOF) alleles was associated with the risk of in-hospital death and MACEs at 1 year in the overall population (adjusted odds ratio (OR) 3.67, 95% CI 1.05-12.80 and adjusted HR 1.96, 95% CI 1.08-3.54) and in PCI patients (adjusted OR 6.87, 95% CI 2.52-18.72 and adjusted HR 3.06, 95% CI 1.47-6.41). Unlike CYP2C19 polymorphism, PON1 (Q192R) polymorphism is not a major pharmacogenetic contributor of clinical response to clopidogrel in AMI patients.

Impact of genetic variants on post-clopidogrel platelet reactivity in patients after elective percutaneous coronary intervention

Aim: To determine the effect of various SNPs on post-clopidogrel platelet reactivity and clinical outcome. Materials & methods: Cytochrome 2C19 (CYP2C19) loss-of-function (LOF; *2, *3) and gain-of-function (GOF; *17) allelic variants, together with ABCB1 (3435 C→T and 2677 G→T/A) and paraoxonase-1 (PON-1; 192 Q→R) SNPs were analyzed in 189 patients after elective stent implantation who participated in a randomized, placebo-controlled trial (NCT00638326). Platelet reactivity was determined with light transmission aggregometry and vasodilator stimulated phosphoprotein phosphorylation (VASP-PRI) 12–24 h after 600 mg clopidogrel. High on-treatment platelet reactivity (HTPR) was defined according to the consensus definition (ADP 5 µM >46%; VASP-PRI>50%). Results: In the case of CYP2C19 genotypes, a gene–dose effect was observed in ADP reactivity with the lowest values in GOF homozygotes and the highest degree in patients carrying two LOF alleles. The odds for HTPR also increased with the number of LOF alleles. There were no significant differences in platelet reactivity according to PON-1 or ABCB1 genotypes. In multivariate analysis, the presence of a CYP2C19 LOF allele turned out to be the independent determinant of HTPR. Although the study was not powered to clinical outcome (not LOF heterozygotes), only patients with two LOF alleles had a significantly higher risk for cardiovascular death, myocardial infarction or unplanned target vessel revascularization at 1 year compared with non-LOF carriers. Conclusion: Genetic variants in CYP2C19 have a gene–dose effect on post-clopidogrel platelet reactivity, with homozygote LOF carriers having the highest risk for HTPR and for adverse ischemic events. Neither ABCB1 nor PON-1 genotypes significantly influenced platelet reactivity or outcome.

Original submitted 28 February 2011; Revision submitted 5 May 2011

Genotypic and phenotypic assessment of platelet function and response to P2Y12 antagonists

The P2Y12-ADP receptor antagonists are the cornerstone of oral antiplatelet therapy in the secondary prevention of coronary artery disease, especially after acute coronary syndrome or percutaneous coronary intervention. Currently, the therapeutic agents available to block the receptor include clopidogrel and prasugrel; ticagrelor is not available everywhere. Clopidogrel was the gold standard, but recently it has been challenged by prasugrel and ticagrelor. One pitfall of clopidogrel is that in some patients it cannot induce optimal platelet reactivity inhibition in connection with several factors, including some genetic polymorphisms of enzymes participating in its bioabsorption or metabolism. This variability of response can be evaluated by platelet reactivity monitoring. This comprehensive review provides the available data regarding the genotypic and phenotypic interaction with the response to P2Y12-ADP receptor antagonists and discusses the concept of personalized antiplatelet therapy based on a genotypic or phenotypic profile.

Platelet function monitoring in patients on clopidogrel

Clopidogrel is essential to prevent recurrent ischemic events in patients with acute coronary syndromes and after percutaneous coronary interventions (PCIs). However, platelet reactivity after clopidogrel treatment is not uniform, and high on-treatment platelet reactivity (HTPR) persists in approximately one third of patients receiving clopidogrel. As recent observational studies suggest that HTPR is associated with higher risk of ischemic events, including cardiovascular death, myocardial infarction and stent thrombosis, it seems rational to monitor post-clopidogrel platelet reactivity for risk assessment and to tailor anti-platelet therapy for patients with HTPR. However, routine platelet function monitoring is not recommended by current clinical guidelines. The article aims to review the available evidence on the clinical relevance of platelet function monitoring, highlighting possible reasons for the conflict between guidelines and observational studies.

Clinical events as a function of proton pump inhibitor use, clopidogrel use, and cytochrome P450 2C19 genotype in a large nationwide cohort of acute myocardial infarction: results from the French Registry of Acute ST-Elevation and Non-ST-Elevation Myocardial Infarction (FAST-MI) registry

BACKGROUND

Clopidogrel requires metabolic activation by cytochrome P450 2C19 (CYP2C19). Proton pump inhibitors (PPIs) that inhibit CYP2C19 are commonly coadministered with clopidogrel to reduce the risk of gastrointestinal bleeding. This analysis compares treatment outcomes for patients in the French Registry of Acute ST-Elevation and Non-ST-Elevation Myocardial Infarction (FAST-MI) who did or did not receive clopidogrel and/or PPIs.

METHODS AND RESULTS

The FAST-MI registry included 3670 patients (2744 clopidogrel- and PPI-naïve patients) presenting with definite MI. Patients were categorized according to use of clopidogrel and/or PPI within 48 hours after hospital admission. PPI use was not associated with an increased risk for any of the main in-hospital events (in-hospital survival, reinfarction, stroke, bleeding, and transfusion). Likewise, PPI treatment was not an independent predictor of 1-year survival (hazard ratio, 0.97; 95% confidence interval [CI], 0.87 to 1.08; P=0.57) or 1-year MI, stroke, or death (hazard ratio, 0.98; 95% CI, 0.90 to 1.08; P=0.72). No differences were seen when the type of PPI or CYP2C19 genotype was taken into account. In the propensity-matched cohorts, the odds ratios for major in-hospital events in PPI versus no PPI were 0.29 (95% CI, 0.06 to 1.44) and 1.70 (95% CI, 0.10 to 30.3) for patients with 1 and 2 variant alleles, respectively. Similarly, the hazard ratio for 1-year events in hospital survivors was 0.68 (95% CI, 0.26 to 1.79) and 0.55 (95% CI, 0.06 to 5.30), respectively.

CONCLUSION

PPI use was not associated with an increased risk of cardiovascular events or mortality in patients administered clopidogrel for recent MI, whatever the CYP2C19 genotype, although harm could not be formally excluded in patients with 2 loss-of-function alleles.

Clopidogrel: a pharmacogenomic perspective on its use in coronary artery disease

The thienopyridine antiplatelet agent clopidogrel is an effective drug for the prevention of vascular events. However, data has accumulated over time to suggest it is prone to significant interpatient variability. While there are several factors that contribute to this, one of the most important is variability in forming the active metabolite necessary for clopidogrel function. Several enzymes are involved in formation of this metabolite, and two, CYP2C19 and P-glycoprotein, appear to have alleles that both occur frequently in the population and have a clinically significant impact. Patients carrying these alleles can be identified, but it remains to be determined if this information is necessary or sufficient for risk stratification. Furthermore, if patients with high-risk alleles are identified, it is unclear how treatment should be adjusted.

[Impact of genetic polymorphisms in the clinical response of oral inhibitors of the platelet P2Y12 adenosine diphosphate (ADP) receptor]

Dual antiplatelet therapy with clopidogrel combined to aspirin reduces ischemic events in a wide range of patients with cardiovascular disease. However, a large interindividual variability has been observed in the pharmacodynamics response of clopidogrel with lower platelet inhibition associated with increased risk for major adverse cardiovascular events. Multiple mechanisms have been proposed for the variable response to clopidogrel, among which the impact of pharmacogenetic seems to play an important role. This article reviews the role of genetic polymorphisms in the clinical impact of oral inhibitors of the platelet P2Y12 adenosine diphosphate (ADP) receptor.

Genetic testing for CYP450 polymorphisms to predict response to clopidogrel: current evidence and test availability. Application: pharmacogenomics

The anti-platelet agent clopidogrel bisulfate (sold under the trade name Plavix in the United States) is a widely prescribed medication for the prevention of blood clots in patients with acute coronary syndrome, in those who have suffered other cardiovascular disease-related events such as ischemic stroke, and in patients who are undergoing percutaneous coronary intervention. Response to clopidogrel varies substantially due to genetic and acquired factors. Patients who experience recurrent cardiovascular ischemic or thrombotic events while taking clopidogrel are typically described as non-responsive or resistant.

The drug's oxidation is mainly dependent on the cytochrome P450 enzyme 2C19 (CYP2C19). Patients with certain genetic variants in CYP2C19 have been found to have lower levels of the active metabolite, less platelet inhibition, and greater risk of major adverse cardiovascular events such as heart attack, stroke, and death. Testing for CYP2C19 polymorphisms may identify patients who will not respond adequately to the standard clopidogrel regimen and who should, consequently, be given an alternate treatment strategy. This article outlines the evidence concerning pharmacogenetic testing for clopidogrel response, including data on clinical validity and clinical utility, and summarizes the currently available tests marketed for this purpose.

Prognostic significance of high on-clopidogrel platelet reactivity after percutaneous coronary intervention: systematic review and meta-analysis

BACKGROUND

A growing number of observational studies suggest that high on-clopidogrel platelet reactivity (HPR) is associated with recurrent thrombotic events after percutaneous coronary intervention. We aimed to perform an updated systematic review and meta-analysis on the clinical relevance of HPR to summarize the available evidence and to define more precise effect estimates.

METHODS

Relevant observational studies published between January 2003 and February 2010 were searched that presented intent-to-treat analyses on the clinical relevance of HPR measured with an adenosine diphosphate (ADP)-specific platelet function assay. The main outcome measures were cardiovascular (CV) death, definite/probable stent thrombosis (ST), nonfatal myocardial infarction (MI), and a composite end point of reported ischemic events. The outcome parameters were pooled with the random-effect model via generic inverse variance weighting.

RESULTS

Twenty studies comprising a total number of 9,187 patients qualified. High on-clopidogrel platelet reactivity appeared to be a strong predictor of MI, ST, and the composite end point of reported ischemic events (odds ratios [95% CI]: 3.00 [2.26-3.99], 4.14 [2.74-6.25], and 4.95 [3.34-7.34], respectively; P < .00001 for all cases). According to the meta-analysis, patients with HPR had a 3.4-fold higher risk for CV death compared with patients with normal ADP reactivity (odds ratio 3.35, 95% CI 2.39-4.70, P < .00001). Although there were large differences in the methodology as well as in the definition of HPR between studies, the predicted risk for CV death, MI, or ST was not heterogeneous (I(2): 0%, 0%, and 12%, respectively; P = not significant for all cases).

CONCLUSIONS

High on-clopidogrel platelet reactivity, measured by an ADP-specific platelet function assay, is a strong predictor of CV death, MI, and ST in patients after percutaneous coronary intervention.

Emerging drugs for acute myocardial infarction

IMPORTANCE OF THE FIELD

The present review is aimed at going over the pharmacological profile (and the clinical impact) of the emerging drugs involved in the management of patients with ST-elevation myocardial infarction (STEMI) in order to provide the cardiologists who deal with these patients in the early phase with the most recent evidence on this topic.

AREAS COVERED IN THIS REVIEW

Anticoagulant and antiplatelet drugs are the main cornerstones of therapy in the treatment of STEMI patients undergoing primary percutaneous coronary intervention (PCI). The main issues that clinicians have to deal with are represented by balancing thrombotic and bleeding risks. In tailoring therapy, variables such as age, sex and previous disease should be taken into account, as well as ongoing complications (such as acute renal failure) that could affect hemostasis. Despite the well-established clinical benefits of antiplatelet agents, questions remain, mainly surrounding potential for variable platelet response, which are strictly related to non-genetic (i.e., diet, drug-drug interaction, clinical factors such as obesity, diabetes mellitus, and inflammation) and genetic determinants.

WHAT THE READER WILL GAIN

In their daily practice, cardiologists cannot abstract from the knowledge and updating on the ongoing research fields as well as the newly developed drugs, which they should frame in the very patient in the attempt to the develop a personalized medical strategy. These include also the pharmacological option(s) in the treatment of the reperfusion injury, the metabolic aspects and the stem cell therapy. TAKE HOME MASSAGE: In our opinion, the goal of ongoing research on the pharmacological approach to STEMI patients is a personalized medical strategy that relies on critical clinicians who merge newly developed acquisitions on this topic and a more complete, systemic and critical approach to the patient.