Differential impact of cytochrome 2C9 allelic variants on clopidogrel-mediated platelet inhibition determined by five different platelet function tests

Micro- and Macrovascular Effects of Inflammation in Peripheral Artery Disease-Pathophysiology and Translational Therapeutic Approaches

Inflammation has a critical role in the development and progression of atherosclerosis. On the molecular level, inflammatory pathways negatively impact endothelial barrier properties and thus, tissue homeostasis. Conformational changes and destruction of the glycocalyx further promote pro-inflammatory pathways also contributing to pro-coagulability and a prothrombotic state. In addition, changes in the extracellular matrix composition lead to (peri-)vascular remodelling and alterations of the vessel wall, e.g., aneurysm formation. Moreover, progressive fibrosis leads to reduced tissue perfusion due to loss of functional capillaries. The present review aims at discussing the molecular and clinical effects of inflammatory processes on the micro- and macrovasculature with a focus on peripheral artery disease.

Growth Differentiation Factor 15 Is Associated with Platelet Reactivity in Patients with Acute Coronary Syndrome

Bleeding events in patients with acute coronary syndrome (ACS) are a risk factor for adverse outcomes, including mortality. We investigated the association of growth differentiation factor (GDF)-15, an established predictor of bleeding complications, with on-treatment platelet reactivity in ACS patients undergoing coronary stenting receiving prasugrel or ticagrelor. Platelet aggregation was measured by multiple electrode aggregometry (MEA) in response to adenosine diphosphate (ADP), arachidonic acid (AA), thrombin receptor-activating peptide (TRAP, a protease-activated receptor-1 (PAR-1) agonist), AYPGKF (a PAR-4 agonist) and collagen (COL). GDF-15 levels were measured using a commercially available assay. GDF-15 correlated inversely with MEA ADP (r = -0.202, p = 0.004), MEA AA (r = -0.139, p = 0.048) and MEA TRAP (r = -0.190, p = 0.007). After adjustment, GDF-15 was significantly associated with MEA TRAP (β = -0.150, p = 0.044), whereas no significant associations were detectable for the other agonists. Patients with low platelet reactivity in response to ADP had significantly higher GDF-15 levels (p = 0.005). In conclusion, GDF-15 is inversely associated with TRAP-inducible platelet aggregation in ACS patients treated with state-of-the-art antiplatelet therapy and significantly elevated in patients with low platelet reactivity in response to ADP.

Peripheral versus central venous blood sampling does not influence the assessment of platelet activation in cirrhosis

Cirrhotic patients have an increased risk of bleeding and thromboembolic events, with platelets being involved as key players in both situations. The impact of peripheral versus central blood sampling on platelet activation remains unclear. In 33 cirrhotic patients, we thus analyzed platelet function in peripheral (P) and central (C) blood samples. Platelet surface expression of P-selectin, activated glycoprotein (GP) IIb/IIIa, and leukocyte-platelet aggregate formation were measured by flow cytometry in response to different agonists: thrombin receptor-activating peptide-6, adenosine diphosphate, collagen-related peptide (CrP), epinephrine, AYPGKF, Pam3CSK4, and lipopolysaccharide. Unstimulated platelet surface expression of P-selectin (p = .850) and activated GPIIb/IIIa (p = .625) were similar in peripheral and central blood samples. Stimulation with various agonists yielded similar results of platelet surface expression of P-selectin and activated GPIIb/IIIa in peripheral and central samples, except for CrP-inducible expression of activated GPIIb/IIIa (median fluorescence intensity, MFI in P: 7.61 [0.00-24.66] vs. C: 4.12 [0.00-19.04], p < .001). The formation of leukocyte-platelet aggregate was similar in central and peripheral blood samples, both unstimulated and after stimulation with all above-mentioned agonists. In conclusion, peripheral vs. central venous blood sampling does not influence the assessment of platelet activation by flow cytometry in cirrhosis.Abbreviations: ACLD: advanced chronic liver disease; ADP: adenosine diphosphate; ALD: alcoholic liver disease; AYPGKF: PAR-4 agonist AYPGKF; CrP: collagen related protein; EPI: epinephrine; FACS: fluorescence-activated cell sorting; GP: glycoprotein; HVPG: hepatic venous pressure gradient; IQR: interquartile range; LPS: lipopolysaccharide; LSM: liver stiffness measurement; MFI: median fluorescence intensity; NAFLD: nonalcoholic fatty liver disease; PAM: lipopeptide Pam3CSK4; PAR: protease-activated receptor; PBS: phosphate-buffered saline; PH: portal hypertension; TIPS: transjugular intrahepatic portosystemic stent shunt; TLR: toll-like receptor; TRAP-6: thrombin receptor-activator peptide-6; vWF: von Willebrand factor.

Impact of body size on platelet function in patients with acute coronary syndrome on dual antiplatelet therapy

INTRODUCTION

Patients undergoing acute percutaneous coronary intervention receive dual antiplatelet therapy for secondary prevention. Recurrent myocardial infarction or bleedings are possibly due to under- or overdosing of antiplatelet therapy in relation to body size.

METHODS

We correlated residual platelet aggregation with body mass index, body surface area, lean body mass and blood volume in 220 patients on prasugrel (n = 121) or ticagrelor (n = 99).

RESULTS

Platelet aggregation outside the recommended window was recorded in 85 patients, but not correlated with any of the body indices.

CONCLUSION

Body size does not affect platelet response to prasugrel or ticagrelor at the guideline-recommended fixed dosages.

Platelet-to-Lymphocyte Ratio as Marker of Platelet Activation in Patients on Potent P2Y12 Inhibitors

A high platelet-to-lymphocyte ratio (PLR) has recently been associated with ischemic outcomes in cardiovascular disease. Increased platelet reactivity and leukocyte-platelet aggregate formation are directly involved in the progress of atherosclerosis and have been linked to ischemic events following percutaneous coronary intervention (PCI). In order to understand the relation of PLR with platelet reactivity, we assessed PLR as well as agonist-inducible platelet aggregation and neutrophil-platelet aggregate (NPA) formation in 182 acute coronary syndrome (ACS) patients on dual antiplatelet therapy with aspirin and prasugrel (n = 96) or ticagrelor (n = 86) 3 days after PCI. PLR was calculated from the blood count. Platelet aggregation was measured by multiple electrode aggregometry and NPA formation was determined by flow cytometry, both in response to ADP and SFLLRN. A PLR ≥91 was considered as high PLR based on previous data showing an association of this threshold with adverse ischemic outcomes. In the overall cohort and in prasugrel-treated patients, high PLR was associated with higher SFLLRN-inducible platelet aggregation (67 AU [50-85 AU] vs 59.5 AU [44.3-71.3 AU], P = .01, and 73 AU [50-85 AU] vs 61.5 AU [46-69 AU], P = .02, respectively). Further, prasugrel-treated patients with high PLR exhibited higher ADP- (15% [11%-23%] vs 10.9% [7.6%-15.9%], P = .007) and SFLLRN-inducible NPA formation (64.3% [55.4%-73.8%] vs 53.8% [44.1%-70.1%], P = .01) as compared to patients with low PLR. These differences were not seen in ticagrelor-treated patients. In conclusion, high PLR is associated with increased on-treatment platelet reactivity in prasugrel-treated patients, but not in patients on ticagrelor.

Targeted temperature management after cardiac arrest is associated with reduced metabolism of pantoprazole - A probe drug of CYP2C19 metabolism

OBJECTIVE

Targeted temperature management (TTM) is part of standard post-resuscitation care. TTM may downregulate cytochrome enzyme activity and thus impact drug metabolism. This study compared the pharmacokinetics (PK) of pantoprazole, a probe drug of CYP2C19-dependent metabolism, at different stages of TTM following cardiac arrest.

METHODS

This prospective controlled study was performed at the Medical University of Vienna and enrolled 16 patients following cardiac arrest. The patients completed up to three study periods (each lasting 24 h) in which plasma concentrations of pantoprazole were quantified: (P1) hypothermia (33 °C) after admission, (P2) normothermia after rewarming (36 °C, intensive care), and (P3) normothermia during recovery (normal ward, control group). PK was analysed using non-compartmental analysis and nonlinear mixed-effects modelling.

RESULTS

16 patients completed periods P1 and P2; ten completed P3. The median half-life of pantoprazole was 2.4 h (quartiles: 1.8-4.8 h) in P1, 2.8 h (2.1-6.8 h, p = 0.046 vs. P1, p = 0.005 vs. P3) in P2 and 1.2 h (0.9 - 2.3 h, p = 0.007 vs. P1) in P3. A two-compartment model described the PK data best. Typical values for clearance were estimated separately for each study period, indicating 40% and 29% reductions during P1 and P2, respectively, compared to P3. The central volume of distribution was estimated separately for P2, indicating a 64% increase compared to P1 and P3.

CONCLUSION

CYP2C19-dependent drug metabolism is downregulated during TTM following cardiac arrest. These results may influence drug choice and dosing of similarly metabolized drugs and may be helpful for designing studies in similar clinical situations.

Differential Impact of Cytochrome 2C19 Allelic Variants on Three Different Platelet Function Tests in Clopidogrel-Treated Patients

On-treatment platelet reactivity in clopidogrel-treated patients can be measured with several platelet function tests (PFTs). However, the agreement between different PFTs is only slight to moderate. Polymorphisms of the CYP2C19 gene have an impact on the metabolization of clopidogrel and, thereby, have an impact on on-treatment platelet reactivity. The aim of the current study is to evaluate the differential effects of the CYP2C19 genotype on three different PFTs.

METHODS

From a prospective cohort study, we included patients treated with clopidogrel following percutaneous coronary intervention (PCI). One month after PCI, we simultaneously performed three different PFTs; light transmission aggregometry (LTA), VerifyNow P2Y12, and Multiplate. In whole EDTA blood, genotyping of the CYP2C19 polymorphisms was performed.

RESULTS

We included 308 patients treated with clopidogrel in combination with aspirin (69.5%) and/or anticoagulants (33.8%) and, based on CYP2C19 genotyping, classified them as either extensive (36.4%), rapid (34.7%), intermediate (26.0%), or poor metabolizers (2.9%). On-treatment platelet reactivity as measured by LTA and VerifyNow is significantly affected by CYP2C19 metabolizer status (p < 0.01); as metabolizer status changes from rapid, via extensive and intermediate, to poor, the mean platelet reactivity increases accordingly (p < 0.01). On the contrary, for Multiplate, no such ordering of metabolizer groups was found (p = 0.10).

CONCLUSIONS

For VerifyNow and LTA, the on-treatment platelet reactivity in clopidogrel-treated patients correlates well with the underlying CYP2C19 polymorphism. For Multiplate, no major effect of genetic background could be shown, and effects of other (patient-related) variables prevail. Thus, besides differences in test principles and the influence of patient-related factors, the disagreement between PFTs is partly explained by differential effects of the CYP2C19 genotype.

Decreased Platelet Inhibition by Thienopyridines in Hyperuricemia

PURPOSE

Hyperuricemia carries an increased risk of atherothrombotic events in acute coronary syndrome (ACS) patients undergoing percutaneous coronary intervention (PCI). This may at least in part be due to inadequate P2Y12 inhibition. The aim of this study was to prospectively investigate the potential association between hyperuricemia and decreased platelet inhibition by P2Y12 antagonists.

METHODS

Levels of uric acid as well as on-treatment residual platelet reactivity in response to adenosine diphosphate (ADP) were assessed in 301 clopidogrel-treated patients undergoing elective angioplasty and stenting, and in 206 prasugrel- (n = 118) or ticagrelor-treated (n = 88) ACS patients following acute PCI. Cut-off values for high on-treatment residual ADP-inducible platelet reactivity (HRPR) were based on previous studies showing an association of test results with clinical outcomes.

RESULTS

Hyperuricemia was significantly associated with increased on-treatment residual ADP-inducible platelet reactivity in clopidogrel- and prasugrel-treated patients in univariate analyses and after adjustment for differences in patient characteristics by multivariate regression analyses. In contrast, ticagrelor-treated patients without and with hyperuricemia showed similar levels of on-treatment residual platelet reactivity to ADP. HRPR occurred more frequently in clopidogrel- and prasugrel-treated patients with hyperuricemia than in those with normal uric acid levels. In contrast, hyperuricemic patients receiving ticagrelor did not have a higher risk of HRPR compared with those with normal uric acid levels.

CONCLUSION

Hyperuricemia is associated with decreased platelet inhibition by thienopyridines but a normal response to ticagrelor. It remains to be established if lowering uric acid increases the antiplatelet effects of clopidogrel and prasugrel in hyperuricemic patients with HRPR.

Genetic polymorphisms of high platelet reactivity in Chinese patients with coronary heart disease under clopidogrel therapy

BACKGROUND

The variability in the clinical response to clopidogrel treatment has been attributed to genetic factors, but the specific genes and other risk factors remain unclear.

OBJECTIVE

To investigate the incidence of high on-treatment platelet reactivity in coronary heart disease patients following clopidogrel therapy by analyzing the correlation between genetic polymorphisms and high on-treatment platelet reactivity.

SETTING

This study was conducted in the Chinese People's Liberation Army (PLA) general hospital.

METHOD

578 patients with coronary heart disease undergoing percutaneous transluminal coronary intervention treatment were enrolled. They received dual antiplatelet therapy with aspirin (300 mg) plus clopidogrel (300 mg) over 24 h, or aspirin (100 mg/day) and clopidogrel (75 mg/day) over 3 days. Patients were divided into two groups according to the adenosine diphosphate inhibition rate. The follow-up lasted at least 12 months and adverse endpoint events were recorded.

MAIN OUTCOME MEASURE

The single nucleotide polymorphisms were detected by MassArray genotyping system.

RESULTS

The incidence of HTPR was 15.74% in total, being higher in females than in males (24.29% vs. 13.01%, P < 0.01). Diabetes mellitus, homocysteine and high sensitivity C-reactive protein (hs-CRP) levels were significantly higher in the HTPR group than those in the non-HTPR group (P < 0.05). Polymorphisms of rs1057910 (OR 2.90, P = 0.003), rs2246709 (OR 0.69, P = 0.039), and rs776746 (OR 0.66, P = 0.034) were associated with the incidence of high on-treatment platelet reactivity. Female patients were prone to polymorphisms of rs1057910 (OR 3.24, P = 0.004) and rs776746 (OR 0.57, P = 0.025). Compared to non-high on-treatment platelet reactivity group, no differences in high reactivity group were observed with coexisting single nucleotide polymorphisms (14.6% vs. 14.8%, P > 0.05). The adverse endpoint events were significantly higher in the high on-treatment platelet reactivity group than in the non-treatment reactivity group. The survival analysis showed that high on-treatment platelet reactivity was significantly associated with the risk of the endpoint events (P = 0.0219).

CONCLUSION

Gender (female), diabetes mellitus, high levels of homocysteine and hs-CRP were risk factors for high on-treatment platelet reactivity, and high reactivity was a strong predictor for adverse endpoint events in the coronary heart disease patients. The polymorphism of rs1057910 was a risk factor of high on-treatment platelet reactivity while rs2246709 and rs776746 polymorphisms were protective factors, and coexisting single nucleotide polymorphisms didn't increase the incidence of high on-treatment platelet reactivity.

A Review of Danshen Combined with Clopidogrel in the Treatment of Coronary Heart Disease

OBJECTIVE

Danshen, the root of Salvia miltiorrhiza Bunge, is a traditional herbal medicine in China, which has been used to treat irregular menstruation, cold hernia, and abdominal pain for thousands of years. Danshen is frequently used in combination with drugs to treat cardiovascular diseases. Clopidogrel is a commonly used drug for treating coronary heart disease, but clopidogrel resistance restricts its development. Therefore, the clinical efficacy of Danshen combined with clopidogrel treats coronary heart disease and the relationship between Danshen and clopidogrel metabolism enzymes is suggested for future investigations.

MATERIALS AND METHODS

The information was collected by searching online databases, and the RevMan 5.3 software was used to perform meta-analysis.

RESULTS

Twenty-two articles, including 2587 patients, were enrolled after the evaluation. Meta-analysis showed that Danshen combined with clopidogrel was more effective than clopidogrel alone in treating coronary heart disease by improving clinical curative effect, reducing the frequency of angina pectoris, improving electrocardiogram results, shortening the duration of angina pectoris, and easing adverse reactions. Danshen inhibited carboxylesterase 1 and most enzyme of cytochrome P450, especially cytochrome P450 1A2, which may affect the metabolism of clopidogrel.

CONCLUSION

Danshen combined with clopidogrel may compensate for individual differences of clopidogrel resistance among individuals in the treatment of coronary heart disease. Meanwhile, the inhibitory effect of Danshen on cytochrome P450 and carboxylesterase 1 could be partly responsible for the synergistic and attenuating effects of Danshen combined with clopidogrel.

Oral antiplatelet agents in cardiovascular disease

Antiplatelet agents significantly reduce mortality and morbidity in ischemic heart disease, cerebrovascular disease and peripheral artery disease (PAD), and are therefore part of guideline-driven daily medical treatment in these patients. Due to its beneficial effects in the secondary prevention of atherothrombotic events, aspirin remains the most frequently prescribed antiplatelet agent in cardiovascular disease. In patients with acute coronary syndromes (ACS) and in those undergoing angioplasty with stent implantation dual antiplatelet therapy with aspirin and an adenosine diphosphate (ADP) receptor antagonist is indicated. The development of the newer ADP P2Y₁₂ inhibitors prasugrel and ticagrelor has further improved prognosis in ACS patients compared to clopidogrel. Moreover, vorapaxar allows the inhibition of platelet activation by thrombin via protease-activated receptor-1 and has been approved for the use in patients with PAD and in those with a history of myocardial infarction. This review article summarizes the current evidence on oral antiplatelet agents in cardiovascular disease. Keywords: Aspirin, clopidogrel, prasugrel, ticagrelor, vorapaxar, cardiovascular disease.

Low Levels of High-Density Lipoprotein Cholesterol Are Linked to Impaired Clopidogrel-Mediated Platelet Inhibition

Low high-density lipoprotein cholesterol (HDL-C) levels are an independent predictor of ischemic events in patients with atherosclerotic cardiovascular disease. This may in part be due to decreased clopidogrel-mediated platelet inhibition in patients with low HDL-C. We investigated the association of HDL-C with on-treatment platelet reactivity to adenosine diphosphate (ADP) in 314 patients on dual antiplatelet therapy with clopidogrel and aspirin undergoing angioplasty and stenting. Platelet P-selectin expression was assessed by flow cytometry, and platelet aggregation was determined by the VerifyNow P2Y₁₂ assay and the Impact-R. High-density lipoprotein cholesterol levels were inversely associated with P-selectin expression and the VerifyNow P2Y₁₂ assay (both P ≤ .01). Moreover, we found a positive correlation of HDL-C with surface coverage by the Impact-R ( P = .003). Patients with low HDL-C (≤35 mg/dL) exhibited a significantly higher P-selectin expression in response to ADP and higher platelet aggregation by the VerifyNow P2Y₁₂ assay and the Impact-R than patients with normal HDL-C (>35 mg/dL; all P < .05). High on-treatment residual platelet reactivity by the VerifyNow P2Y₁₂ assay occurred significantly more frequently in patients with low HDL-C levels than in those with normal HDL-C (47.4% vs 30.1%, P = .01). In conclusion, low HDL-C is linked to impaired clopidogrel-mediated platelet inhibition after angioplasty and stenting.

Clopidogrel in Critically Ill Patients

Only limited data are available regarding the treatment of critically ill patients with clopidogrel. This trial investigated the effects and the drug concentrations of the cytochrome P450 (CYP450) activated prodrug clopidogrel (n = 43) and the half‐life of the similarly metabolized pantoprazole (n = 16) in critically ill patients. ADP‐induced aggregometry in whole blood classified 74% (95% confidence intervals 59–87%) of critically ill patients as poor responders (n = 43), and 65% (49–79%) responded poorly according to the vasodilator‐stimulated phosphoprotein phosphorylation (VASP‐P) assay. Although the plasma levels of clopidogrel active metabolite normally exceed the inactive prodrug ∼30‐fold, the parent drug levels even exceeded those of the metabolite 2‐fold in critically ill patients. The half‐life of pantoprazole was several‐fold longer in these patients compared with reference populations. The inverse ratio of prodrug/active metabolite indicates insufficient metabolization of clopidogrel, which is independently confirmed by the ∼5‐fold increase in half‐life of pantoprazole. Thus, high‐risk patients may benefit from treatment with alternative platelet inhibitors.

The Antiplatelet Effect of Clopidogrel Decreases With Patient Age

Recent data suggest that clopidogrel-mediated platelet inhibition is age dependent. However, so far the effect of age on adenosine diphosphate (ADP)-inducible platelet reactivity has only been investigated by test systems measuring surrogate markers of platelet aggregation. We therefore sought to study the impact of age on platelet inhibition by clopidogrel by whole-blood flow cytometry. Platelet surface P-selectin expression, activated glycoprotein (GP) IIb/IIIa, and monocyte-platelet aggregate (MPA) formation were determined by flow cytometry in 302 patients with dual antiplatelet therapy after successful angioplasty and stenting. Patient age was independently associated with ADP-inducible P-selectin expression, GPIIb/IIIa, and MPA formation (all P < .05). Moreover, platelet surface expressions of P-selectin and activated GPIIb/IIIa were significantly higher in patients ≥75 years compared with younger patients (both P ≤ .004). Likewise, MPA formation was significantly more pronounced in patients ≥75 years ( P = .02). Finally, high P-selectin and high GPIIb/IIIa were significantly more frequent in patients ≥75 years compared with younger patients (both P < .001). Further, high MPA ADP occurred more frequently in patients ≥75 years compared to younger patients ( P < .05). In conclusion, the antiplatelet effect of clopidogrel decreases with patient age.

Calcium-Channel Blockers Attenuate the Antiplatelet Effect of Clopidogrel

AIMS

Dihydropyridine calcium-channel blockers (CCBs) inhibit cytochrome 3A4 and could therefore interfere with the conversion of clopidogrel to its active form. The impact of CCBs on the antiplatelet effect of clopidogrel has not been studied with assays directly capturing platelet activation to adenosine diphosphate (ADP), so far. We therefore sought to investigate platelet activation in response to ADP by flow cytometry in clopidogrel-treated patients without and with CCBs.

METHODS

Platelet surface P-selectin expression and activated glycoprotein (GP) IIb/IIIa in response to ADP were determined by flow cytometry in 302 patients on dual antiplatelet therapy with aspirin and clopidogrel after successful angioplasty with stent implantation.

RESULTS

Ninety-two patients (30.5%) received CCBs. Patients with concomitant CCB therapy showed significantly higher platelet surface expressions of P-selectin and activated GPIIb/IIIa in response to ADP than patients without CCBs (both P ≤ 0.03). Moreover, the fold increase of P-selectin and activated GPIIb/IIIa in response to ADP was significantly more pronounced in patients taking CCBs (both P ≤ 0.03). The associations of ADP-inducible activated GPIIb/IIIa and fold increase of activated GPIIb/IIIa after the addition of ADP with CCB therapy remained significant after adjustment for differences in patient characteristics and factors that were previously associated with clopidogrel response by multivariate regression analyses (both P < 0.05). High levels of ADP-inducible P-selectin and activated GPIIb/IIIa were seen significantly more frequent in patients with CCBs than in patients without CCB therapy (both P ≤ 0.01).

CONCLUSION

Dihydropyridine CCBs attenuate the effect of clopidogrel on ADP-inducible platelet activation in patients undergoing angioplasty and stenting for cardiovascular disease.

Liver Function is Associated With Response to Clopidogrel Therapy in Patients Undergoing Angioplasty and Stenting

The relationship between liver function and clopidogrel response has not been studied so far. We therefore sought to investigate the associations between 3 parameters of liver synthesis and on-treatment platelet reactivity to adenosine diphosphate in patients on dual antiplatelet therapy. On-treatment platelet reactivity was determined by the VerifyNow P2Y12 assay in 316 patients undergoing angioplasty with stent implantation for cardiovascular disease. Cholinesterase, serum albumin, and total cholesterol levels were measured by internationally standardized assays in the hospital's central laboratory. On-treatment platelet reactivity by the VerifyNow P2Y12 assay correlated inversely with cholinesterase, serum albumin, and total cholesterol levels (all P ≤ .02). The inverse associations of cholinesterase and serum albumin levels with platelet reactivity remained significant after adjustment for cytochrome P450 loss-of-function polymorphisms and other factors that were previously associated with high on-treatment residual platelet reactivity (HRPR; both P < .05). Patients without HRPR by the VerifyNow P2Y12 assay had significantly higher levels of serum albumin and total cholesterol than patients with HRPR (both P = .008). In conclusion, liver function is associated with response to clopidogrel therapy in patients undergoing angioplasty and stenting for cardiovascular disease.

The pharmacogenetic control of antiplatelet response: candidate genes and CYP2C19

INTRODUCTION

Aspirin, clopidogrel, prasugrel and ticagrelor are antiplatelet agents for the prevention of ischemic events in patients with acute coronary syndromes (ACS), percutaneous coronary intervention (PCI) and other indications. Variability in response is observed to different degrees with these agents, which can translate to increased risks for adverse cardiovascular events. As such, potential pharmacogenetic determinants of antiplatelet pharmacokinetics, pharmacodynamics and clinical outcomes have been actively studied.

AREAS COVERED

This article provides an overview of the available antiplatelet pharmacogenetics literature. Evidence supporting the significance of candidate genes and their potential influence on antiplatelet response and clinical outcomes are summarized and evaluated. Additional focus is directed at CYP2C19 and clopidogrel response, including the availability of clinical testing and genotype-directed antiplatelet therapy.

EXPERT OPINION

The reported aspirin response candidate genes have not been adequately replicated and few candidate genes have thus far been implicated in prasugrel or ticagrelor response. However, abundant data support the clinical validity of CYP2C19 and clopidogrel response variability among ACS/PCI patients. Although limited prospective trial data are available to support the utility of routine CYP2C19 testing, the increased risks for reduced clopidogrel efficacy among ACS/PCI patients that carry CYP2C19 loss-of-function alleles should be considered when genotype results are available.

Obesity is associated with poor response to clopidogrel and an increased susceptibility to protease activated receptor-1 mediated platelet activation

Obesity is associated with a prothrombotic state resulting from increased thrombin generation, platelet hyper-reactivity, and decreased fibrinolysis. Data on the influence of obesity on clopidogrel-mediated platelet inhibition are conflicting and limited to platelet function tests. Moreover, there are no data on thrombin-inducible platelet activation in obese patients. We therefore investigated response to clopidogrel therapy and protease activated receptor (PAR)-1 mediated platelet activation in obese and nonobese patients undergoing angioplasty and stenting for cardiovascular disease. The vasodilator-stimulated phosphoprotein (VASP) phosphorylation assay, multiple electrode aggregometry (MEA) with adenosine diphosphate (ADP), and surface expressions of P-selectin and activated glycoprotein (GP) IIb/IIIa in response to ADP and thrombin receptor activating peptide (TRAP)-6 were assessed in 71 obese and 245 nonobese patients. Obesity was independently associated with higher residual platelet reactivity by the VASP assay and MEA ADP, and with platelet surface expressions of P-selectin and activated GPIIb/IIIa in response to ADP (all P ≤ 0.04). Further, high on-treatment residual ADP-inducible platelet reactivity by the VASP assay and by MEA ADP were significantly more frequent in obese patients compared with nonobese patients (both P ≤ 0.04). Finally, PAR-1 mediated platelet activation as assessed by expression of P-selectin and activated GPIIb/IIIa in response to TRAP-6 was significantly more pronounced in obese patients than in patients without obesity (both P ≤ 0.02). In conclusion, obese patients undergoing angioplasty and stenting exhibit a diminished response to clopidogrel and an increased susceptibility to TRAP-6 inducible platelet activation.