Background

Cardiovascular disease (CVD) is a medical term that describes any disorder, which affects the blood vessels, the heart, or both. CVDs, including stroke, coronary artery disorder, and venous thromboembolism, are usually caused by blood coagulation which blocks the vessels from supplying oxygen, glucose, minerals, and micro-minerals to the cardiac or other tissues. Patients with CVD should be subjected to antiplatelet or anticoagulant medications to avoid further blood coagulation [1, 2].

Despite the availability of various clinically effective antiplatelet drugs to prevent blood clots, some patients may have either a hyper-response or resistance to these medications owing to genetic factors. For instance, Higashi et al. reported that warfarin users who are CYP2C9*2 or CYP2C9*3 allele carriers could suffer from bleeding due to the poor metabolism of this drug [3]. Also, Wu et al. showed that dabigatran users carrying the rs2244613 allele of the CES-1 gene are at high risk of recurrent cardiovascular events (CVEs) because of a lower response to the drug [4].

Clopidogrel is an antiplatelet medication frequently used in Middle-Eastern countries as a protective agent to avoid recurrent CVEs [5]. The effect of several mutations related to the CYP2C19 gene on the prognosis of patients with CVDs treated with clopidogrel is still controversial. Most studies suggest that some CYP2C19 variants among specific ethnicities cause weak antiplatelet activity [6].

Pharmacokinetic studies showed that the clopidogrel prodrug is activated by several metabolic enzymes, which is converted to 2-oxo-clopidogrel (inactive metabolite) by CYP1A2, CYP2C19, and CYP2B6 oxidative enzymes. Moreover, 2-oxo-clopidogrel is further converted to cis-thiol-clopidogrel (active metabolite) by CYP3A4, CYP2C19, CYP2C9, and CYP2B6 oxidative enzymes [7, 8]. Therefore, some genetic mutations related to these oxidative enzymes (e.g., CYP2C19) could affect the metabolism of clopidogrel and consequently affect its plasma concentration levels and efficacy [9].

At least 30 variants of CYP2C19 have been identified [10]; however, only three variants have been described as most familiar, including CYP2C19*2, CYP2C19*3, and CYP2C19*17 alleles. CYP2C19*2 and CYP2C19*3 mutant alleles encode an inactive CYP2C19 enzyme, and the CYP2C19*17 mutant allele is known to express a more active form of CYP2C19 enzyme [11]. CYP2C19*1 is described as the wild-type allele and encodes a normal active form of the CYP2C19 enzyme.

Previous studies revealed that CYP2C19*2 and CYP2C19*3 alleles are related to poor clinical outcomes among Asian and European CVD patients treated with clopidogrel [12,13,14]. Nevertheless, few studies have discussed the efficacy of clopidogrel in preventing recurrent CVEs among Arab (as an ethnic group) carriers of CYP2C19 mutations. Therefore, this systematic review aimed to investigate the efficacy of clopidogrel as an antiplatelet drug among CYP2C19 gene mutation carriers. In addition, a qualitative assessment was conducted to determine the frequency of CYP2C19 polymorphic alleles and genotypes among the Arab population.

Methods

Search methods

Two authors (N.R. and A.K.) independently searched PubMed, Google Scholar, and EMBASE databases for studies published in any year in the English language and related to clopidogrel efficacy in Arabic CVD patients carrying CYP2C19*2, CYP2C19*3, and CYP2C19*17 alleles. Studies related to CYP2C19 gene polymorphisms frequency among Arabs were reviewed. Manuscripts that included non-Arab populations, non-clopidogrel users, or patients with any contraindication for clopidogrel (i.e., intracranial hemorrhage) were excluded. The following terms were used for the search; CYP2C19 genotypes; OR CYP2C19 polymorphic alleles; OR CYP2C19 gene mutations; AND clopidogrel response; OR antiplatelet activity; AND Arabs.

Type of participants

The qualitative section of this systematic review included Arab people genotyped to determine the frequency of CYP2C19 genotypes and alleles. For the quantitative section (meta-analysis), only patients with previous CVEs on clopidogrel as secondary prophylaxis were included. These patients were categorized into carriers of (cases) and non-carriers (controls) of CYP2C19 mutations, including CYP2C19*2, CYP2C19*3, and CYP2C19*17. Cardiovascular patients on other drugs rather than clopidogrel were excluded from the study.

Outcome measures

The outcome of the quantitative part of the study was to predict the antiplatelet efficacy of clopidogrel among CYP2C19 mutation carriers and non-carriers who previously had CVEs by measuring the frequency of the recurrent CVDs or high platelet aggregation reported. On the other hand, the qualitative part aimed to determine the frequency of genotypes and alleles related to the CYP2C19 gene among Arabs.

Data collection and extraction

Two authors (N.R. and A.K.) independently reviewed the abstracts of potential articles to determine the inclusion criteria and identify all the relevant articles. In addition, they extracted the specific characteristics from the included studies, including study setting, duration, design, participants' age, sex, and outcome measures. Disagreement or variation in judgment was resolved by discussion; thus, it is not likely that this method could introduce bias in this systematic review.

Assessment of the risk of bias

Two authors (N.R., N.M.) independently judged the risk of bias in the included studies. They graded each risk as high, low, or unclear according to The Newcastle Ottawa Scale for non-randomized Studies [15].

Assessment of the quality of evidence

According to the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach, the quality of evidence for each outcome measure was judged as high, moderate, low, or very low [16].

Measures of treatment effect

A random-effect model of the Review Manager 5.3 program [17] was used for data analysis. The prevalence of different studied alleles was determined. To assess the role of CYP2C19*2, *3, and *17 alleles on recurrent CVEs, Odds Ratio (OR) with 95% Confidence Interval (CI) was conducted between carriers (cases) and non-carriers (controls) of these different CYP2C19 variants with the level of significant was considered at < 0.05.

Dealing with heterogeneity

The I2 statistic was used to assess heterogeneity among the included studies in each analysis  [18].

Results

Results of search

The search included one hundred and eighty-eight potentially relevant articles, of which 97 were identified after the removal of duplicates. Nineteen full-text articles were assessed for eligibility; ten met the inclusion criteria (10 in the qualitative and 6 in the quantitative analysis). Details of the search are given in the PRISMA flow diagram (see Fig. 1).

Fig. 1
figure 1

PRISMA flow diagram detailing the search process and studies included

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Included studies

In the quantitative part of the study, the review included 6 observational studies (2 retrospectives, 3 prospective, and one cross-section) [13, 19,20,21,22,23], which reported data on clopidogrel antiplatelet efficacy in the presence of different CYP2C19 gene variations.

On the other hand, the qualitative part included 10 studies, four case series, and 6 observational studies. These ten studies reported the frequency of CYP2C19 polymorphisms among Arabs [24,25,26,27].

Two authors independently (N.R. and A.K.) extracted characteristics of the included studies, including study title, journal, study design, duration, setting, aim, participants' age, sex, number, and outcome measures (see Table 1).

Table 1 Characteristics of the included studies
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Trial participants

The quantitative part of the review included 878 Araba (Saudis, Egyptians, Jordanians, Tunisians, Iraqis, and Palestinians) patients who were previously diagnosed with CVDs. For the qualitative part, 1417 Arabs, either healthy or non-healthy, were included. The participants in the qualitative were from 7 different Arabic countries, including Saudi Arabia, Egypt, Jordan, Lebanon, Tunisia, Iraq, and Palestine.

Risk of bias among included studies

Overall, no high risk of bias was recorded among the included studies in this review. Regarding {adequate case definition} bias and {comparability of cases and control} bias, it was unclear in Rjoub et al. study. In addition, the {same representative rate for cases and control} bias was low risk in all included studies. While {consecutive representative of cases} bias and {independent outcome assessment} bias were unclear in most of the included studies (Additional file 1: Fig. S1).

Outcomes

Outcomes of the quantitative part

Figures 2, 3, and 4 present the forest plots of the frequency of recurrent CVD events among Arab patients who are clopidogrel users and are either carriers or non-carriers of CYP2C19*2, CYP2C19*3, and CYP2C19*17 mutations. The results showed a significantly increased risk of recurrent CVDs events by about threefold associated with CYP2C19*2 and CYP2C19*3 mutations compared to non-carriers (OR = 3.32, CI = 1.94–5.67, and OR = 3.53, CI = 1.17–10.63, respectively). However, no significant difference was recorded between both studied groups regarding the presence of CYP2C19*17 mutation (OR = 0.80, (CI = 0.44–1.44).

Fig. 2
figure 2

Forest plot showing the frequency of recurrent CVEs among carriers and non-carriers of CYP2C19*2 mutation, and results of odds ratios

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Fig. 3
figure 3

Forest plot showing the frequency of recurrent CVEs among carriers and non-carriers of CYP2C19*3 mutation

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Fig. 4
figure 4

Forest plot showing the frequency of recurrent CVEs among carriers and non-carriers of CYP2C19*17 mutation, and results of odds ratios

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Outcomes of the qualitative part

This part included 1417 Arab people, which were genotyped in order to determine the CYP2C19 gene variations and to detect the availability of any well-known mutated alleles, including CYP2C19*2, CYP2C19*3, and CYP2C19*17 alleles among Arab populations, including Saudis, Egyptians, Jordanians, Iraqis, Palestinians, Lebanese, and Tunisians people. The results revealed that 59 (4.16%) of these carried two CYP2C19*2 alleles (homozygous), and 356 (25.12%) had one CYP2C19*2 allele and one CYP2C19*1 allele (heterozygous). Moreover, 42 (2.96%) carried two CYP2C19*17 alleles (homozygous), and 262 (18.49%) carried one CYP2C19*17 allele, and one wild-type allele of CYP2C19 gene (heterozygous).

The most common CYP2C19 genotype reported among Arabs was the wild type *1/*1, of which 49.26% of them had the homozygous form of the CYP2C19*1 allele. The frequency of the CYP2C19*1 allele was 71.07%, followed by the CYP2C19*2 allele (16.73%) and CYP2C19*17 (12.21%), respectively. The CYP2C19*3 allele was rarely detected among Arabs (< 1%) compared to CYP2C19*1, *2, and *17 alleles.

Based on the frequencies of genotypes, about half of the Arab people (> 49%) could be described as CYP2C19 extensive metabolizers. Other common CYP2C19 gene phenotypes identified among Arabs were intermediate metabolizers (25%), rapid metabolizers (18%), poor metabolizers (4%), and ultra-rapid metabolizers (3%), respectively.

Discussion

Many studies genotyped the CYP2C19 gene to assess clopidogrel's efficacy among specific ethnic groups. However, few studies correlated CYP2C19 gene mutation and clopidogrel efficacy among Arab ethnic groups.

In the quantitative part, the present study recorded significant differences between carriers (cases) and non-carriers (controls) of CYP2C19*2 and CYP2C19*3 alleles regarding the number of recurrent CVEs among Arabs using clopidogrel (OR = 3.32, CI = 1.94, 5.67, and OR = 3.53, CI = 1.17, 10.63, respectively). However, there was no significant difference among carriers and non-carriers of the CYP2C19*17 allele concerning the same aspect (OR = 0.80, CI = 0.44, 1.44).

The included studies regarding the recurrent CVEs among carriers and non-carriers of CYP2C19*2 and CYP2C19*17 alleles showed low or insignificant heterogeneity. Therefore, we judged the quality of evidence of these outcomes to be high. This strong evidence indicates high confidence that the evidence reflects the actual effect. Meanwhile, we judged the quality of evidence of the pooled estimate of the included studies related to the recurrent CVEs among carriers and non-carriers of CYP2C19*3 to be moderate. We downgrade the evidence by one level due to imprecision, as indicated by a wide confidence interval due to the small sample size. Moderate evidence indicates moderate confidence that the evidence reflects the actual effect, and further research is likely to change the results.

These results indicate that carrying CYP2C19*2 and CYP2C19*3 alleles may decrease the antiplatelet activity of clopidogrel among Arab patients and could lead to recurrent CVEs. The present outcomes were consistent with more than 18 high-quality clinical trials and 6 meta-analysis studies. These revealed that CYP2C19*2 and *3 alleles have a significant role in causing recurrent CVEs among patients using clopidogrel [28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47].

On the other hand, 3 previous meta-analysis concluded that loss-of-function alleles (CYP2C19*2 and CYP2C19*3) have no significant effect in causing recurrent CVEs while using clopidogrel. However, they showed a significant effect in leading to other complications (e.g., ST-elevation and stent thrombosis) [48,49,50]. This could be explained by the presence of other genetic factors that may affect both the clopidogrel bioactivation process and recurrent CVEs, including specific CYP2C9, CYP3A4, CYP1A2, and CYP2B6 genes' mutations.

Regarding the qualitative part, the study revealed that CYP2C19 alleles including *1 (71%), *2 (17%), *17 (12%), and *3 (< 1%), respectively, are commonly distributed among Arabs. Compared with some other ethnic groups (Caucasians, Africans, and Asians), the frequency of CYP2C19*1 allele among Arabs was more or less similar to Caucasians (59%), Africans (70%), and Asians (65%). Besides, the frequency of the CYP2C19*2 allele is similar to that of Caucasians (15%) and Africans (13%) but less than Asians (35%). Concerning the frequency of the CYP2C19*17 allele among some different ethnic groups, it could be described that Caucasians were the most ethnic group to carry this allele (26%), followed by the Africans (17%), Arabs (12%), and Asians (0.5%). While the CYP2C19*3 allele was rare among all reported ethnic groups, this allele is commonly detected in Asians (9%) [23].

Conclusion and future perspective

This study revealed that the CYP2C19 genotypes including *1/*1, *1/*2, *1/*17, *2/*2, and *17/*17 are commonly distributed among Arabs. In addition, most Arab patients carrying CYP2C19*2 or CYP2C19*3 mutated alleles are at a significantly higher risk of recurrent CVEs, and could be described as non-responders to clopidogrel. However, few available studies were included in the quantitative part of the analysis, and further studies with a large sample size are recommended to confirm our results.