Association between interleukin-10 -1082A/G polymorphism and risk of ischemic stroke: A meta-analysis.

The Interleukin-10 -1082A/G polymorphism has been indicated to be correlated with ischemic stroke susceptibility, but the results of studies are still debatable. Thus, a meta-analysis was carried out.Databases including PubMed, Embase, and CNKI were searched. Data were extracted and odds ratios (OR) with 95% confidence intervals (CI) were calculated.12 case-control studies with 2722 cases and 2405 controls were included in this meta-analysis. IL-10 -1082A/G polymorphism may decrease the risk of ischemic stroke (G vs A: OR = 0.72, 95% CI: 0.59-0.87; GG vs AA: OR = 0.59, 95% CI:0.48-0.74; AG vs AA: OR = 0.69, 95% CI: 0.51-0.93; GG+AG vs AA: OR = 0.65, 95% CI: 0.50-0.84; GG vs AG+AA: OR = 0.71, 95% CI: 0.55-0.93). Meanwhile, similar results were also observed in matched studies, hospital-based subgroup, Asians, and large sample-size studies.In conclusion, this meta-analysis suggested that the IL-10 -1082A/G polymorphism contributes to decreased ischemic stroke risk. Further large-scale and well-designed studies are still needed to confirm the results of our meta-analysis.

Introduction

Ischemic stroke is a major cause of adult disability and death in the world,[ which is a heterogeneous multifactorial disease associated with genetic and environmental factors.[ During the past few years, more and more evidence showed that inflammatory molecules and the genetic variation of the genes which encoded these inflammatory cytokines might take part in the pathogenesis of stroke.[ Inflammatory mechanisms may not only play important roles in the manifestation and development of ischemic stroke, but also may be vulnerable to ischemic stroke in time via accumulation of atherosclerotic disease and maintain of atrial fibrillation.[ Several candidate genes of inflammatory cytokines are implicated in the pathogenesis of ischemic stroke, one of which is interleukin-10 (IL-10).

IL-10 is a multifunctional cytokine with anti-inflammatory properties, which has been shown involving in the inflammatory process of ischemic stroke.[ IL-10 is mainly produced by macrophages, T-helper-2 cells, and B lymphocytes, which can both stimulate and suppress immune responses, such as cytokine production, antigen presentation, macrophage activation and antigen-specific T-cell proliferation.[ Several polymorphic loci have been identified and characterized in the IL-10 gene, and one of the most widely evaluated is -1082A/G (rs1800896) in the promoter region. It is believed that the A/G substitution is relevant to low/high amount of IL-10 secretion, respectively.[

Recently, many molecular epidemiological studies[ were performed to investigate the association between the IL-10 -1082A/G polymorphism and ischemic stroke; however, no definitive conclusion has yet been reached. This discrepancy might be due to studies with small sample size, ethnic differences, and publication bias. Therefore, it is necessary to conduct meta-analysis to explore this association between IL-10 -1082A/G polymorphism and ischemic stroke risk.

Methods

Publication search

The electronic databases PubMed, Embase, and CNKI were searched using the following terms: (interleukin-10 OR interleukin 10 OR IL-10 OR IL10) AND (stroke OR cerebrovascular accident OR cerebral ischemia OR cerebral infarction) AND (polymorphism OR mutation OR genotype OR allele OR variation OR variant) up to August 2019. To avoid missing relevant studies, the reference lists of some major articles and reviews were manually checked.

Inclusion and exclusion criteria

All selected studies complied with the following criteria:

case-control study on the IL-10 polymorphism and risk of ischemic stroke;

sufficient published data for estimation of the odds ratio (OR) with a 95% confidence interval (CI); and

genotype frequencies in the control group consistent with Hardy-Weinberg equilibrium (HWE) (P > .05).

Studies were excluded if one of the following existed:

not relevant to ischemic stroke or IL-10,

not designed as case-control studies,

genotype frequencies or number not specified,

animal studies,

editorials, reviews, and abstracts.

If more than one study by the same author using the same case series was published, either the studies with the largest sample size or the most recently published study was included. Ethical approval was not necessary since this study is a meta-analysis.

Data extraction

Data were extracted independently by two reviewers and entered into separate databases from each qualified study: the first author, year of publication, ethnicity, sample size, genotype distributions in cases and controls and P values for the HWE of genotype distribution of controls. We evaluated the quality of all of the studies included according to Newcastle–Ottawa scale (NOS).[ The NOS contains 3 categories which are selection (0–4 points), comparability (0–2 points), and exposure (0–3 points). The total scores ranged from 0 to 9.

Statistical analysis

The ORs with 95% CI were calculated under five genetic models: the allele model (G vs A), the homozygote model (GG vs AA), the heterozygote model (AG vs AA), the dominant model (GG+AG vs AA), and the recessive model (GG vs AG+AA). Heterogeneity was calculated by using both χ2 based Q-statistic and I2-statistic.[ When Q -test reported a P value of more than .10 and I2 < 50%, fixed effects model was used to calculate the pooled ORs,[ otherwise random effects model was used.[ Predefined subgroup analyses were conducted by ethnicity, source of controls, sample size, and case-control matched status. Sensitivity analysis was conducted to examine the effect of individual studies on pooled results and the stability of results. Publication bias was assessed with funnel plots and Egger regression test.[ All statistical tests were carried out using Stata 12.0 software (Stata Corporation, College Station, TX). A P value of less than .05 was considered significant. All of the P values were 2 sided.

Results

Study characteristics

A total of 122 studies were retrieved from PubMed, Embase, and CNKI. Finally, 12 eligible studies were included in this meta-analysis.[ A flow chart of the included and excluded studies was shown in Figure 1. The characteristics of the selected studies are summarized in Table 1.

Figure 1

Flow chart of included studies in the current meta-analysis.

Table 1

Main characteristics of eligible studies.

Meta-analysis

A summary of the meta-analysis findings on the associations between IL-10 -1082A/G polymorphism and susceptibility to ischemic stroke was provided in Table 2. The pooled analysis indicated that the significant association between IL-10 -1082A/G polymorphism and ischemic stroke under five genetic models (G vs A: OR = 0.72,95% CI:0.59–0.87, I2 = 66.9%, P < .001; GG vs AA: OR = 0.59,95% CI:0.48–0.74, I2 = 17.1%, P = .291; AG vs AA: OR = 0.69, 95% CI:0.51–0.93, I2 = 56.9%, P = .008; GG+AG vs AA: OR = 0.65, 95% CI: 0.50–0.84, I2 = 50.6%, P = .022; GG vs AG+AA: OR = 0.71,95% CI: 0.55–0.93, I2 = 64.5%, P = .004. Figs. 2–6).

Table 2

Main characteristics of relevant studies selected for meta-analysis.

Figure 2

Forest plot of the association between the IL-10 -1082A/G polymorphism (G vs A) and ischemic stroke susceptibility.

Figure 6

Forest plot of the association between the IL-10 -1082A/G polymorphism (GG vs AG+AA) and ischemic stroke susceptibility.

Forest plot of the association between the IL-10 -1082A/G polymorphism (GG vs AA) and ischemic stroke susceptibility.

Forest plot of the association between the IL-10 -1082A/G polymorphism (AG vs AA) and ischemic stroke susceptibility.

Forest plot of the association between the IL-10 -1082A/G polymorphism (GG+AG vs AA) and ischemic stroke susceptibility.

In a stratified analysis by case-control matched status, significant associations of IL-10 -1082A/G polymorphism with decreased risk of ischemic stroke were found in matched group of the four genetic models (G vs A: OR = 0.75, 95% CI:0.62–0.91; GG vs AA: OR = 0.59, 95% CI: 0.48–0.74; GG+AG vs AA: OR = 0.68, 95% CI: 0.52–0.90; GG vs AG+AA: OR = 0.72, 95% CI: 0.55–0.95).

Subgroup analysis by source of control showed significant associations of IL-10 -1082A/G polymorphism with decreased risk of ischemic stroke were found in hospital-based subgroup of all the five genetic models (G vs A: OR = 0.67, 95% CI: 0.53–0.84; GG vs AA: OR = 0.53, 95% CI: 0.40–0.72; AG vs AA: OR = 0.63, 95% CI: 0.43–0.91; GG+AG vs AA: OR = 0.59, 95% CI: 0.43–0.79; GG vs AG+AA: OR = 0.67, 95% CI: 0.47–0.94). No significant association was detected in the population-based subgroup in all genetic models.

When studies were stratified for ethnicity, significant associations of IL-10 -1082A/G polymorphism with decreased risk of ischemic stroke were found for Asian populations in all genetic models (G vs A: OR = 0.67, 95% CI: 0.53–0.85; GG vs AA: OR = 0.51, 95% CI:0.39–0.68; AG vs AA: OR = 0.68, 95% CI: 0.47–0.97; GG+AG vs AA: OR = 0.60, 95% CI: 0.44–0.83; GG vs AG+AA: OR = 0.63, 95% CI: 0.45–0.89). No significant association was detected under five genetic models in the Caucasian populations.

By sample size, significant associations of IL-10 -1082A/G polymorphism with decreased risk of ischemic stroke were found in large studies (total sample size ≥500) under all genetic models (G vs A: OR = 0.70, 95% CI: 0.56–0.88; GG vs AA: OR = 0.52, 95% CI:0.40–0.66; AG vs AA: OR = 0.74, 95% CI: 0.57–0.94; GG+AG vs AA: OR = 0.62, 95% CI: 0.49–0.78; GG vs AG+AA: OR = 0.66, 95% CI: 0.49–0.89), but not in small studies (total sample size < 500).

Sensitivity analysis

To evaluate the stability of this meta-analysis, we excluded the included studies one by one and compared the differences between the effect values before and after each elimination (Fig. 7). This analysis showed that the results were stable.

Figure 7

Sensitivity analyses of the association between the IL-10 -1082A/G polymorphism (G vs A) and ischemic stroke susceptibility.

Publication bias

No obvious visual asymmetry was observed in Begg funnel plots (Fig. 8), and the results of Egger test revealed no statistical evidence for publication bias among studies (P = .400 for G vs A; P = .972 for GG vs AA; P = .476 for AG vs AA; P = .431 for GG+AG vs AA; P = .976 for GG vs AG+AA).

Figure 8

Begg funnel plot of the association between the IL-10 -1082A/G polymorphism (G vs A) and ischemic stroke susceptibility.

Discussion

It is now accepted that genetics and environmental factors contribute to ischemic stroke susceptibility and outcome. Similarly, the inflammation reaction is also relevant to ischemic stroke. IL-10 is a potent anti-inflammatory cytokine with multiple functions taking part in inflammation reaction as well as the development of ischemic stroke. Recently, the associations between IL-10 -1082 A/G polymorphism and the risk of ischemic stroke have been intensively investigated, however, the results are inconsistent. Thus, we conducted a comprehensive meta-analysis involving published data, to assess the strength of association between the IL-10 -1082 A/G polymorphism and ischemic stroke risk. In this present meta-analysis, 12 studies with 2722 cases and 2405 controls concerning the IL-10 -1082 A/G polymorphism were included.

In the overall population, we found that IL-10 -1082 A/G polymorphism had a decreased association with ischemic stroke risk in all five genetic models (G vs A: OR = 0.72, 95% CI: 0.59–0.87; GG vs AA: OR = 0.59, 95% CI:0.48–0.74; AG vs AA: OR = 0.69, 95% CI: 0.51–0.93; GG+AG vs AA: OR = 0.65, 95% CI: 0.50–0.84; GG vs AG+AA: OR = 0.71, 95% CI: 0.55–0.93).

Significant heterogeneity among the studies was shown in our results; we performed stratified analyses in terms of case-control matched status, source of controls, ethnicity, and sample size. In a stratified analysis by case-control matched status, similar results were revealed in matched group of the four genetic models. Subgroup analysis by source of control showed significant associations of IL-10 -1082A/G polymorphism with decreased risk of ischemic stroke were found in hospital-based subgroup of all the five genetic models, but not in the population-based subgroup in all genetic models. In hospital-based studies, poor comparability between cases and controls might exert a confounding effect on the true association in light of a regional specialty for the disease under study and the differential hospitalization rates between cases and controls.[ In contrast, subjects drawn from community might be representative of the true population, leading us to believe that results from population-based studies might be more representative. In this meta-analysis, most studies have recruited subjects from hospital, and only two studies from population. So, more studies are required to confirm this result.

In the stratified analysis based on ethnicity, IL-10 -1082 A/G polymorphism had decreased ischemic stroke risk in Asian populations based on all five genetic models, but not in Caucasian populations. This discrepancy in ischemic stroke risk may be explained by geographic climate, differences in alleles and genotypes in various ethnic populations, daily lifestyle, ethnic diversity, and dietary habits. However, this finding should be interpreted with caution. Because in our meta-analysis for IL-10 -1082A/G polymorphism, only three articles were conducted in Caucasian subgroup totally.

By sample size, significant associations of IL-10 -1082A/G polymorphism with decreased risk of ischemic stroke were found in large studies (total sample size ≥500) under all genetic models, but not in small studies (total sample size < 500). The discrepancy might due to the small sample size in some studies, which are underpowered to detect a slight effect.

In order to make the conclusion more credible, we performed the publication bias analysis and sensitivity analysis. Funnel plots suggested that no obvious publication bias was observed. The sensitivity analysis by excluding studies showed that the results are robust and convincing.

Some limitations of this meta-analysis should be considered in interpreting the results. First, the included studies were published in English and Chinese, while studies published in other languages were ignored. Second, because of the high heterogeneity in our present meta-analysis, the reliability of the findings may be weakened. Despite the application of the random-effects model in our meta-analysis, the findings on the overall susceptibility should be taken cautiously. Third, the source of articles is uneven in geographical distribution, the majority of the included studies were conducted in Asians which may introduce ethnicity bias, and further studies should focus on Africans and Caucasians. Fourth, our analysis did not consider the possibility of gene-gene or SNP-SNP interactions or the possibility of linkage disequilibrium between polymorphisms. Further investigations of the haplotypic effect of a gene and the study of multiple polymorphisms in different genes are needed.

In our meta-analysis, the pooled results of our meta-analysis demonstrated that the IL-10 -1082A/G polymorphism may play an important role in decreasing ischemic stroke susceptibility. Due to limitations showed above in this analysis, it is critical that larger and well-designed studies are needed to confirm our results.

Author contributions

Data curation: Shuang Zuo.

Formal analysis: Tingting Zheng.

Investigation: Shuang Zuo.

Project administration: Haishan Li.

Software: Shuang Zuo, Haishan Li, Tingting Zheng.

Supervision: Shuang Zuo, Haishan Li

Writing – original draft: Shuang Zuo.

Writing – review & editing: Shuang Zuo, Haishan Li, Tingting Zheng.