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The Pharmacogenetics of Antiplatelet Agent: Meta-Analyses of Aspirin and Clopidogrel Loss-of-Function Alleles

Antiplatelet agents combined with aspirin have been shown to play a significant role in mitigating the effects of coronary disease, and ample research has found that distinct genetic determine patients’ response to clinically significant antiplatelet agents.
 
Platelets play a decisive role during the formation of an initial hemostatic plug through their intricate response to injury. When inappropriately activated, platelets contribute to pathological thrombus formation. Arterial thrombus formation can then lead to tissue ischemia causing potentially fatal coronary and cerebrovascular events.
 

Interindividual Genetic Variation Impacts Aspirin Antiplatelet Efficacy

 
Aspirin is regarded as “the cornerstone for secondary cardiovascular prevention,” the efficacy of which has long been established. as noted in Current Pharmaceutical Design, “Pharmacogenetics of the Antiplatelet Effect of Aspirin” (2012).
 
The researchers aver that there is considerable interindividual variation in response to aspirin, thus reducing its efficacy in treating heart disease in some patients.
 

P1A2 and P2Y1 Association with Decreased Aspirin Antiplatelet Efficacy

 
Specifically, the review conducted by Current Pharmaceutical Design examined polymorphisms of genes that contributed highly to antiplatelet responses. These were P1A2 from glycoprotein GP IIb/IIIa, and the P2Y1 polymorphism from AD receptor (ADP) genes.
 
P1A2 was characterized as having an association with coronary thrombus formation. One study showed P1A2 allele was related with a shorter baseline bleeding time in comparison to a wild type allele. After measuring bleeding after aspirin ingestion, there was a a reduced antiplatelet effect.
 
Another study supported this finding by discovering an enhanced thrombin formation in P1A2 carriers compared to P1A1/A1 homozygotes before and after aspirin ingestion. The review concluded that P1/A2 polymorphism is a prothrombotic platelet phenotype responding inadequately to aspirin.
 
Polymorphism P2Y1 was utilized in an arachidonic acid-induced optical platelet aggregometry to assess its antiplatelet effect of aspirin. The results showed that the T allele of the C893T P2Y1 polymorphism was substantially linked with a decreased antiplatelet effect of aspirin.
 

CYP2C19 Mediates Clopidogrel Non-Response

 
Evidence for association of CYP2C19 with clopidogrel response was investigated in the Journal of Human Genetics “Pharmacogenomics of Anti-Platelet Therapy: How Much Evidence is Enough for Clinical Implementation?” (June 2013).
 
The study established CYP2C19 as a genetic factor contributing to the creation of the active metabolite of clopidogrel. A corresponding analysis detailing the associations of CYP2C19 alleles and increasing residual on-treatment platelet reactivity corroborated this finding. The study concluded that patients with even one reduced function of CYP2C19 and taking clopidogrel as treatment for percutaneous coronary intervention may be “associated with increased risk of major adverse cardiovascular events as a consequence of aspirin antiplatelet inefficacy.
 
The International Journal of Environmental Research and Public Health “Pharmacokinetic and Pharmacodynamics Responses to Clopidogrel” (February 2017) also reviewed the connection between CYP2C19 and clopidogrel. The review was based on the authors’ argument that genetic polymorphisms impact the absorbtion and metabolism of clopidogrel and that the P2Y12 receptor may interfere with its antiplatelet activity.
 
In one meta-analysis, it was found there was a critical relation between CYPC219 loss-of-function in diverse patients with frequent cardiovascular events. In another meta-analysis, CYPC219 was identified as having a having a crucial part in reducing the active metabolite of clopidogrel.
 

CYP3A4/5 Mediates Clopidogrel Non-Response

 
In addition to analyzing clopidogrel, the review also analyzed CYP3A4/5. The authors found that the CYP3A5*3 allele has an influence on clopidogrel metabolism because of its possible dependence on CYP2C19 and CYP3A4 inhibitors. In the study, the patients with a CYP3A5*3/3 genotype displayed enhanced platelet reactivity compared to those with a CYP3A5*1 allele in CYP2C19 poor metabolizers. An additional study reported CYP3A5*3 on clopidogrel response is prominently in patients with the CYP2C19 loss-of-function.
 

Benefits of Individualizing Antiplatelet Therapy with Pharmacogenetic Testing

 
Research has been conclusive in identifying potential antiplatelet pharmacogenetic applications pointing to effective individualized treatments, according to the studies.
 
The review by the International Journal of Environmental Research and Public Health asserted there is an “inter-individual variability” in clopidogrel’s antiplatelet effects. They concluded inadequate platelet responsiveness to clopidogrel has a role in accumulating the risk of cardiovascular events, and therefore increasing drug dosage or switching to alternative drug medications may be more beneficial for patients. Similarly, the review published in Current Pharmaceutical Design concludes by recommending utilization of antiplatelet pharmacogenetics in clinical practice. “The promise of pharmacogenetics lies in the prospect of improving treatment efficacy and safety.”

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