The genetic basis of platelet responsiveness to clopidogrel

Ticagrelor vs. clopidogrel in dual antiplatelet therapy after coronary artery bypass surgery: a meta-analysis

Background

Following coronary artery bypass grafting (CABG), the standard treatment regimen typically involves dual antiplatelet therapy (DAPT), which includes a P2Y12 receptor antagonist in combination with aspirin. There is currently no clear consensus regarding the optimal DAPT strategy after CABG. The aim of this meta-analysis was to evaluate and compare the safety and efficacy of ticagrelor vs. clopidogrel in patients post-CABG.

Methods

A meta-analysis of eligible studies of patients undergoing CABG and receiving either aspirin plus clopidogrel (A + C) or aspirin plus ticagrelor (A + T) as antiplatelet therapy, was carried out. The outcomes of interest included all-cause mortality, cardiovascular mortality, major adverse cardiovascular and cerebrovascular events (MACCEs), major bleeding, myocardial infarction, stroke, revascularization, saphenous vein occlusion and total graft occlusion.

Results

4 randomized controlled trials and 3 observational studies (n = 2,424) were eligible for final analysis. A + T was associated with a decreased risk of all-cause mortality (OR = 0.47, 95% CI 0.31-0.70, p < 0.001, p heterogeneity = 0.80, I2 = 0%) and cardiovascular mortality (OR = 0.50, 95% CI 0.31-0.82, p = 0.006, p heterogeneity = 0.71, I2 = 0%), compared with A + C group. No statistically significant difference was found in the rates of major bleeding (OR = 1.16; 95% CI 0.69-1.96; p = 0.57; p heterogeneity = 0.26; I2 = 23%) between two groups. Besides, the rates of MACCEs, myocardial infarction, stroke, total graft occlusion, revascularization and saphenous vein occlusion were comparable between two groups (p > 0.05).

Conclusions

The meta-analysis presented the evidence supporting the use of A + T post-CAVG in reducing all-cause mortality and cardiovascular mortality, with no increase in bleeding events, in comparison with A + C. Additional RCTs are needed to determine the optimal DAPT after CABG.

Cytochrome P450 2C19 Polymorphisms and Its Association With Major Adverse Cardiac Events in Post-coronary Intervention Patients on Clopidogrel in the Tertiary Care Center

Background Clopidogrel has become essential in managing coronary artery disease and other atherothrombotic diseases. It is an inactive prodrug that needs biotransformation in the liver by various cytochrome P (CYP) 450 isoenzymes for its active metabolite formation. However, 4-30% of patients on clopidogrel have shown no or decreased antiplatelet response. This condition is called 'clopidogrel non-responsiveness' or 'clopidogrel resistance.' This is attributed to genetic heterogeneity causing interindividual variation and increased risk of major adverse cardiac events (MACEs). This study aimed to assess MACEs and their association with CYP450 2C19 polymorphisms in post-coronary intervention patients on clopidogrel. Methods This prospective observational study was conducted on acute coronary syndrome patients, started on clopidogrel following coronary intervention. After considering inclusion and exclusion criteria, 72 patients were enrolled, and a genetic analysis was done. Based on genetic analysis, patients were divided into two groups, normal (CYP2C19*1) and abnormal phenotypes (CYP2C19*2 & *3). These patients were followed for two years, and the MACE during the first year and second year was compared between these two groups. Results Of 72 patients, 39 (54.1%) were normal, and 33 (45.8%) were abnormal genotypes. The mean age of patients is 67.71 ± 9.968. A total of 19 and 27 MACEs were seen during first- and second-year follow-ups. During the first-year follow-up, three (9.1%) patients with abnormal phenotypes developed ST-elevation myocardial infarction (STEMI), and none of the phenotypically normal patients developed STEMI (p-value = 0.183). Non-ST elevation myocardial infarction (NSTEMI) was seen in three (7.7%) normal and seven (21.2%) abnormal phenotype patients (p-value=0.19). Other events, such as thrombotic stroke, stent thrombosis, and cardiac death, were seen in two (6.1%) abnormal phenotypic patients (p-value=0.401). During the second-year follow-up, STEMI was seen in one (2.6%) normal and three (9.7%) abnormal phenotypic patients (p-value=0.183). NSTEMI was seen in four (10.3%) normal and nine (29%) abnormal phenotype patients (p=0.045). Comparison of total MACEs between normal and abnormal phenotypic groups at the end of the first year (p-value=0.011) and second year (p-value=<0.01) has statistical significance. Conclusion We can infer that the risk of developing a recurrent MACE in post-coronary intervention patients on clopidogrel is significantly high in the abnormal phenotypic group (CYP2C19*2 & *3) than in normal phenotypic patients.

Flavonoids as potential anti-platelet aggregation agents: from biochemistry to health promoting abilities

Cardiovascular ailments are the number one cause of mortalities throughout the globe with 17.9 million deaths per year. Platelet activation and aggregation play a crucial role in the pathogenesis of arterial diseases, including acute coronary syndrome, acute myocardial infarction, cerebrovascular transient ischemia, unstable angina, among others. Flavonoids-rich plant extracts are gaining interest for treating the heart-related problems due to safe nature of these herbal extracts. Consumption of plant-food-derived bioactives, particularly flavonoids, has shown antithrombotic, and cardiovascular protective effects due to its anti-platelet activity. Preclinical and clinical trials have proven that flavonoid-rich plant extracts are protective against the cardiac ailments through anti-platelet aggregation activity. This review aims to highlight the anti-platelet aggregation potential of flavonoids with a key emphasis on the therapeutic efficacy in humans. The mechanism of flavonoids in preventing and treating cardiovascular diseases is also highlighted based on preclinical and clinical experimental trials. Further studies are the need of time for exploring the exact molecular mechanism of flavonoids as anti-platelet aggregation agents for treating heart-related problems.

Vascular oxidative stress, nitric oxide and atherosclerosis

In the vascular wall, reactive oxygen species (ROS) are produced by several enzyme systems including NADPH oxidase, xanthine oxidase, uncoupled endothelial nitric oxide synthase (eNOS) and the mitochondrial electron transport chain. On the other hand, the vasculature is protected by antioxidant enzyme systems, including superoxide dismutases, catalase, glutathione peroxidases and paraoxonases, which detoxify ROS. Cardiovascular risk factors such as hypercholesterolemia, hypertension, and diabetes mellitus enhance ROS generation, resulting in oxidative stress. This leads to oxidative modification of lipoproteins and phospholipids, mechanisms that contribute to atherogenesis. In addition, oxidation of tetrahydrobiopterin may cause eNOS uncoupling and thus potentiation of oxidative stress and reduction of eNOS-derived NO, which is a protective principle in the vasculature. This review summarizes the latest advances in the role of ROS-producing enzymes, antioxidative enzymes as well as NO synthases in the initiation and development of atherosclerosis.

Pharmacogenomics of anti-platelet and anti-coagulation therapy

Arterial thrombosis is a major component of vascular disease, especially myocardial infarction (MI) and stroke. Current anti-thrombotic therapies such as warfarin and clopidogrel are effective in inhibiting cardiovascular events; however, there is great inter-individual variability in response to these medications. In recent years, it has been recognized that genetic factors play a significant role in drug response, and, subsequently, common variants in genes responsible for metabolism and drug action have been identified. These discoveries along with new diagnostic targets and therapeutic strategies hold promise for more effective individualized anti-coagulation and anti-platelet therapy.

Pharmacogenomics in cardiovascular disease: focus on aspirin and ADP receptor antagonists

Antiplatelet agents like aspirin and adenosine diphosphate receptor antagonists are effective in reducing recurrent ischemic events. Considerable inter-individual variability in the platelet inhibition obtained with these drugs has initiated a search for explanatory mechanisms and ways to improve treatment. In recent years, numerous genetic polymorphisms have been linked with reduced platelet inhibition and lack of clinical efficacy of antiplatelet drugs, particularly clopidogrel and aspirin. Consequently, attempts to adjust antiplatelet treatment according to genotype have been made, but the clinical benefit has been modest in studies performed so far. The progress in genome science over the last decade and the declining cost of sequencing technologies hold the promise of enabling genetically tailored antiplatelet therapy. However, more evidence is needed to clarify which polymorphisms may serve as targets to improve treatment. The present review outlines the panel of polymorphisms affecting the benefit of aspirin and adenosine diphosphate receptor antagonists, including novel and ongoing studies evaluating whether genotyping may be beneficial in tailoring antiplatelet therapy.

Platelet reactivity tests for assessing antiplatelet drug response: what the clinician needs to know

Antiplatelet therapy is a cornerstone in the treatment of cardiovascular disease to prevent ischemic events. Various tests have become clinically available to measure platelet function after antiplatelet treatment. A wide interpatient variability in the magnitude of platelet inhibition has been demonstrated in numerous studies, especially in response to clopidogrel. Several reasons including clinical, pharmacological and genetic factors have been identified. High on-clopidogrel platelet reactivity has been linked to adverse clinical outcome, in particular to stent thrombosis after percutaneous coronary interventions. New antiplatelet drugs including prasugrel and ticagrelor have been advocated to overcome the limitations of clopidogrel. Several studies addressed the concept of tailored antiplatelet treatment according to the results of platelet function testing. Within this review, we summarize the current status of personalized antiplatelet therapy for cardiovascular disease.

Network meta-analysis of prasugrel, ticagrelor, high- and standard-dose clopidogrel in patients scheduled for percutaneous coronary interventions

Since novel antiplatelet treatments (prasugrel, ticagrelor, high-dose clopidogrel) have been predominantly tested against standard-dose clopidogrel, data on direct comparisons between these therapies are scarce. We therefore indirectly compared their efficacy and safety in patients undergoing percutaneous coronary intervention. Electronic databases were searched systematically to identify head-to-head randomised controlled trials (RCTs). Network meta-analysis was performed using generalised linear mixed models with adjustment for length of follow-up. Findings were corroborated by mixed treatment comparison through Bayesian methods. Fourteen RCTs were identified and included in the analysis (high- vs. standard-dose clopidogrel: 9 trials, prasugrel vs. high-dose clopidogrel: 2 trials, prasugrel vs. standard-dose clopidogrel: 2 trials, ticagrelor vs. standard-dose clopidogrel: 1 trial). No significant differences were found for efficacy outcomes except for stent thrombosis favouring prasugrel (vs. ticagrelor: odds ratio [OR] 0.63, 95% confidence interval [CI]: 0.42, 0.94; vs. high-dose clopidogrel: OR 0.70, 95%CI: 0.48, 1.01). Prasugrel exhibited a similar bleeding risk as high-dose clopidogrel, but more major (OR 1.43, 95%CI 1.07, 1.90) and major or minor bleeding (OR 1.36, 95%CI 1.09, 1.69) compared to ticagrelor. Ticagrelor was also associated with less major or minor bleeding compared to high-dose clopidogrel (OR 0.81, 95%CI 0.69, 0.96). No differences were seen for non CABG-related major bleeding between the three strategies. Results were corroborated in a subgroup analysis comprising only patients with acute coronary syndromes. In the absence of head-to-head clinical trials, network meta-analysis suggests potentially relevant differences in efficacy and bleeding risk among novel antiplatelet treatments and may thereby advance understanding of their differential therapeutic properties.