Impact of pharmacogenetics on aspirin resistance: a systematic review

Background  Pharmacogenetics promises better control of diseases such as cardiovascular disease (CVD). Acetylsalicylic acid, aspirin, prevents the formation of an activating agent of platelet aggregation and vasoconstriction, and it is used to prevent CVD. Nevertheless, patients may have treatment failure due to genetic variants that modify the metabolism of the drug causing aspirin resistance (AR). Objectives  To realize a systematic literature review to determine the impact of genetic variants on AR. Methods  Articles published in the MEDLINE/PubMed, Cochrane, Scopus, LILACS, and SCIELO databases were systematically screened. A total of 290 articles were identified and 269 articles were excluded because they did not comply with the previously established inclusion criteria. A total of 20 case-control studies and 1 cohort was included. Results  The genetic variants rs1126643 ( ITGA2 ), rs3842787 ( PTGS1 ), rs20417 ( PTGS2 ), and rs5918 ( ITGB3 ) were the most studied. As for relevance, of the 64 genetic variants evaluated by the articles, 14 had statistical significance ( p  < 0.05; 95% confidence interval [CI]) in at least one article. Among them, the following have had unanimous results: rs1371097 ( P2RY1 ), rs1045642 ( MDR1 ), rs1051931 and rs7756935 ( PLA2G7 ), rs2071746 ( HO1 ), rs1131882 and rs4523 ( TBXA2R ), rs434473 ( ALOX12 ), rs9315042 ( ALOX5AP ), and rs662 ( PON1 ), while these differ in real interference in AR: rs5918 ( ITGB3 ), rs2243093 ( GP1BA ), rs1330344 ( PTGS1 ), and rs20417 ( PTGS2 ). As study limitations, we highlight the nonuniform methodologies of the analyzed articles and population differences. Conclusion  It is noteworthy that pharmacogenetics is an expanding area. Therefore, further studies are needed to better understand the association between genetic variants and AR.


INTRODUCTION
Cardiovascular disease (CVD) is the first cause of mortality worldwide, with all the healthcare systems facing this very challenging issue. The World Health Organization (WHO) estimates that 31% of deaths worldwide are due to CVD, with $ 17.7 million CVD-related deaths in 2015. Approximately 7.4 million of these deaths were due to heart disease and 6.7 million deaths were due to stroke. 1 Platelet activation plays an important role in the development of CVD. Acetylsalicylic acid (ASA), commonly known as aspirin, is an irreversible inhibitor of platelet cyclooxygenase (COX), which prevents the formation of thromboxane A2 by arachidonic acid and, therefore, prevents the formation of this activating agent of platelet aggregation and vasoconstriction. 2 Aspirin is a widely used antiplatelet for primary and secondary prevention of CVD, such as stroke and heart attacks. 3 Nevertheless, several patients may still experience treatment failure with ASA and an increased risk in recurrent stroke events. 4 There are several contributing factors for treatment failure including medication adherence, drugdrug interactions, aspirin-independent thromboxane A2 synthesis and also genetic variations. 2 Even low daily aspirin doses (in the range between 75 and 150 mg) are able to suppress biosynthesis of thromboxane, inhibiting the accumulation of platelets, and reducing the risk of CVD. 5 Howev-er, aspirin does not always prevent the formation of thromboxane A2 due to failure to inhibit platelet COX. 6 Because of that, all individuals do not respond to antiplatelet therapy in a similar way. In this sense, the genetic mutations have been related with aspirin resistance (AR) and may cause reduction or increase in drug absorption and metabolism, contributing to AR. 6,7 Aspirin resistance can be diagnosed by clinical criteria or by laboratory tests. Clinically, the patient has a new episode of CVD, despite the regular use of aspirin. While the failure of aspirin to inhibit a platelet function test can be seen by Platelet Function Analyser (PFA-100) or light transmission aggregometry (LTA), for example. 3 The field of pharmacogenetics, which aims to implement specific pharmacological therapies to genetic characteristics with the intention to provide greater efficiency, is a constant target of research. 8 Therefore, several studies have been published about candidate genes associated with the genetic predisposition of resistance to AAS, such as COX-2, GPIIIA, and P2Y1. 9 Resistance to antiplatelet therapy and the indiscriminate use of ASA can increase rates of recurrence and mortality from cardiovascular diseases, such as stroke. 10 Hence, the aim of the present study was to perform a systematic literature review to determine the impact of genetic variants on AR.  12 Scopus, 13 LILACS, 14 and SCIELO. 15 The research was restricted to a period of 10 years (December 2009 to December 2019) and the following search terms were applied: Aspirin AND Resistance AND Polymorphism and Aspirin AND Resistance AND Genetic variation.

Eligibility criteria
Only articles published in English were included in this search. Also, only articles describing the relation between AR, proven by laboratory tests or a new case of CVD, and polymorphisms or genetic variations were included in the present systematic review. The final articles included (n ¼ 21) in the present review were 20 case-controls and 1 cohort.

Assessment of risk of bias
The authors, using the combined search terms and based on the inclusion criteria, conducted the primary literature search. In that first moment, titles and abstracts were screened. All reports that appeared in accordance with the inclusion criteria were full-text screened. All studies that did not comply with pre-established eligibility and inclusion requirements were excluded. In a second step, the research-ers independently evaluated whether the full-texts previously selected followed the inclusion criteria. In case of disagreement between two authors, a third author was consulted, and a consensus was reached by a meeting between them.
Furthermore, to assess and minimize the presence of potential biases, the Risk of Bias in Systematic Reviews (ROBIS) method was used as a reference. 16

Data extraction and synthesis
In the primary literature search, a total of 290 articles were found: 178 in SCOPUS, 104 in MEDLINE/Pubmed, 5 in Cochrane, 2 articles in LILACS, and 1 in SCIELO. Of those, 19 were duplicated. Hence, 271 articles were screened for reading of title and abstract, 216 of which were excluded for not meeting our inclusion criteria.
In the next step, the authors independently reviewed 65 full-text articles. Then, 44 articles were excluded for not meeting our inclusion criteria. So, in the end, 21 articles were included in the present systematic review (►Figure 1).

RESULTS
In the 21 final articles selected, a total of 10,873 patients were analyzed, of which 3,014 were aspirin resistant and 6,882 were aspirin sensitive (some articles brought semiresistance values and were disregarded, and another 2 articles did not classify their patients as sensitive and not sensitive). Of the 21 articles studied, 11 included patients with a cerebrovascular event, totaling 4,835 patients. The other 10 articles mostly analyzed cardiac outcomes. We also emphasize that the clinical conditions of the evaluated patients were varied among the articles, with some articles evaluating patients with > 1 disease: ischemic stroke (10 articles), coronary artery disease (9), peripheral arterial disease (3), acute vascular event (1), age > 80 years old (1), adults (1), and hypertension (1). Most of the patients in the selected articles are from the Asian continent (9 from China, 4 from India, 2 from Turkey, and 1 from Jordan), and regarding the other works, 3 articles are from the American continent (all from the United States of America), 1 from the European continent (Belgium), and 1 from the African continent (Tunisia).
In ►Table 1, we detail the following information from the 21 final articles included in the present review: Type of article, country, clinical condition, sample number, number of aspirin resistant patients, number of aspirin sensitive patients, gene, risk allele, protective allele, genetic variant, p-value, Odds Ratio (OR), CI, resistance assessment method, and daily aspirin dose.
Despite the heterogeneity of the findings in terms of methodology and results, it is clear that some polymorphisms are more studied than others. Among them, rs1126643 (ITGA2), rs3842787 (PTGS1), rs20417 (PTGS2), and rs 5918 (ITGB3) were the most studied.
In conclusion, pharmacogenetics is an expanding area that promises a therapy aimed at the individualities of each patient, personalized medicine, for better control of diseases, including cardiovascular diseases, such as stroke.
Finally, further studies are needed to better understand the association between genetic variants and AR and, therefore, the practical application of the findings.