Association of IL‐10‐1082A/G polymorphism with cardiovascular disease risk: Evidence from a case–control study to an updated meta‐analysis

Abstract Background Previous studies have generated controversial results about the association of interleukin 10 (IL‐10) gene polymorphisms (−1082G/A) in the progression of cardiovascular disease (CVD). Therefore, this study processed a systemic meta‐analysis to verify this association. Methods The publication studies on the IL‐10 (−1082G/A) polymorphism and CVDs risk were obtained by searching PubMed and Embase databases. We analyzed the genotype data for meta‐analysis. The results were evaluated by odds ratios (ORs) and 95% confidence intervals (CIs). Meanwhile, our meta‐analysis was also performed sensitivity analyses, heterogeneity test, and identification of publication bias. Results The present meta‐analysis suggested that the risk with allele G is lower than with allele A for CVD. The G allele of IL‐10 (−1082) could increase the risk of CVDs in the 31 case–control studies for all genetic models. (OR = 1.10, 95% CI: 1.04–1.15 for the allele model A vs. G; OR = 0.87, 95% CI: 0.72–1.04 for the dominant model GG+AG vs. AA; OR = 1.03, 95% CI: 1.02–1.05 for the recessive model GG vs. AG + AA; OR = 1.06, 95% CI = 1.03–1.10 for the homozygote comparison model GG vs. AA; and OR = 0.88, 95% CI = 0.73–1.06 for the heterozygote comparison model AG vs. AA). Conclusions In genetic models, the association between the IL‐10 (−1082G/A) polymorphism and CVDs risk was significant. This meta‐analysis proposes that the IL‐10 (−1082G/A) polymorphism may serve as a risk factor for CVDs.


| Data extraction
Primary investigators used standardization requirements to extract qualified research from the database. They organized the data into tables and submitted them to coauthors for review to ensure that data are strict and reasonable. We collected the following information from the retrieved literature: first author's name, publication year, control source, country and ethnicity of population, the methods of genotype, the number of cases and controls, the distribution of genotype in cases and controls, and the p value for HWE (Hardy-Weinberg Equilibrium) in controls. Different ethnicity was categorized as Asians, Caucasians, and Mixed.

| Statistical analyses
The IL-10 (−1082 G/A) polymorphisms and CVDs risk was assessed by OR and the corresponding 95% CI for each study. Different ORs (95% CI) were calculated using the following models: the allele model (G vs. A), the dominant model (GG + AG vs. AA), the recessive model (GG vs. AG + AA), the homozygote model (GG vs. AA), and the heterozygote model (GA vs. AA). Using the Cochran's Q statistic and I 2 test to evaluated the statistical heterogeneity between eligible studies, which was considered as significant when p Q ＜0.1 or I 2 > 50%. A fixed-effect model (the Mantel-Haenszel method) was adopted if p > .1 and I 2 < 50%, and a randomeffect model (DerSimonian-Laird method) was used if p < .1 and I 2 > 50%. Furthermore, we conducted subgroup analysis based on ethnicity (Asian, Caucasian, or Mixed) and disease subtype (CAD, stroke, and cerebral infarction) to explore the sources of heterogeneity. All statistical analyses were performed using software STATA 15.0 (StataCorp LP).

| Eligible studies
As shown in Figure 1, the process of literature retrieval and exclusion is listed. In general, the preliminary comprehensive search was identified 813 relevant articles. According to the inclusion and exclusion criteria, this meta-analysis is involving 31 case-control studies with 18,367 total sample sizes (10,502 cases and 7,865 controls).
The characteristics of the studies are listed in Table 1. IL-10 (−1082 G/A) genotype distributions in the controls from all studies has carried on HWE ( Table 2). The 31 studies identified in this meta-analysis including 14 studies of Caucasians, 15 studies of Asians, and two studies from mixed population. Among these researches, patients were mostly recruited in referral centers with CAD, stroke, cerebral infarction and myocardial infarction, and the controls have not any obvious disease.

| Meta-analysis databases
As shown in Tables 3 and 4, the results including the association of the IL-10 (−1082 G/A) polymorphism and CVDs risk, as well as homozygote test and heterogeneity test. The combined results showed that the variant genotypes were related to increase the CVDs risk in different genetic models (OR = 1.06, 95% CI = 1.03-1.10 for the homozygote comparison model GG vs. AA; OR = 0.88, 95% CI = 0.73-1.06 for the heterozygote comparison model AG vs. AA; OR = 1.10, 95% CI: 1.04-1.15 for the allele model A vs. G; OR = 0.87, 95% CI: 0.72-1.04 for the dominant model GG + AG vs. AA; and OR = 1.03, 95% CI: 1.02-1.05 for the recessive model GG vs. AG + AA). The forest plots for −1082 G/A in the allele model are shown in Figure 2. In subgroup analyses by ethnicity, our results were similar to the Caucasian population.

| Test of heterogeneity
Using the chi-square test and fixed effects model, we observed the statistically significant heterogeneity in trials (Allele model G vs. A: p = .000, I 2 > 50%; dominant model  (Tables 3 and 4). Thus, the wider CIs will be generated by the random-effect model.

| Sensitivity analysis and Bias diagnostics
To evaluate the stability of the pooled results, sensitivity analysis was performed. The result showed that there were no substantial changes in ORs after canceling each study ( Figure 3). As to the publication bias, it was estimated by the Begg's funnel plots and Egger's tests. The funnel plot shapes did not reveal obvious evidence of asymmetry ( Figure 4)

| DISCUSSION
Cardiovascular disease is broadly testified as atherosclerosis, underlying vascular aberrations, as well as formation of coronary plaques (Malik et al., 2004;Strazzullo, D'Elia, Kandala, & Cappuccio, 2009;Vasan, 2006). Many studies identified that the potential influence of inflammatory cascade in many kinds of CVD. Inflammatory responses could trigger and accelerate vascular injury and CVDs risk (Lakka et al., 2002;Malik et al., 2004). Therefore, the pathogenesis of CVDs have been deemed as both genetic and inflammatory pathways, which modulated by various inflammatory cytokines. Genetic factors are regarded as strong determinants of CVDs (Brigitta, 2007;Mckusick, 1959). According to the chromosomal location and functional relevance, IL-10 is a multifunctional cytokine that has been considered as a candidate gene for kinds of CVD (Couper, Blount, & Riley, 2008;Dopheide et al., 2015;Eskdale, Wordsworth, Bowman, Field, & Gallagher, 2010;Heeschen et al., 2003a). Therefore, this meta-analysis was performed to obtain a more precise T A B L E 3 Stratified analyses of the association between IL-10-1082A/G polymorphisms and cardiovascular disease risk

T A B L E 4 Heterogeneity and
homogeneity analyses of the association between IL-10-1082A/G polymorphisms and cardiovascular disease risk conclusion and to make a better understanding of IL-10 (−1082 G/A) SNP with CVDs risk. For this meta-analysis, we aimed to identify the dispute about the role of IL-10 (−1082 G/A) in CVD risk. The results showed that there exists a significant relationship between IL-10 (−1082 G/A) and CVDs risk. This study was conducted by critically evaluating 31 individual case-control studies involving the IL-10 (−1082 G/A) polymorphism and CVDs risk. We found that the IL-10 (−1082 G/A) was associated with an increased risk of CVDs among Asians. As far as we know, this updated meta-analysis includes the largest samples and the most cogent conclusions.
In our study, we observed that the allele and genotype frequencies of IL-10 (−1082A/G) were associated with CVDs risk, which was consistent with a present study, as reported by Yang et al. (Xuan, Wang, Zhi, Li, & Wei, 2016). One metaanalysis study observed that the allele and genotype frequencies of IL-10 (−1082A/G) were not associated with ischemic stroke risk (Liu, Hui-Min, et al., 2017). However, the powerful relationship between IL-10 (−1082A/G) and ischemic stroke has been found in the Italian population (Tuttolomondo et al., 2012a). Li et al. reported that IL-10 −1082G/A was related to increase the atherosclerotic risk (Chao, Lei, & Fei, 2014). Wang et al. observed that IL-10 (−1082A/G) polymorphism F I G U R E 2 Forest plots for the IL-10-1082A/G polymorphism and cardiovascular disease in the allele model was significantly associated with increasing the cerebral infarction risk in Asians (Fan et al., 2016). Based on the Asian population, several studies have indicated the positive or null relationship of IL-10 (−1082A/G) with CVDs, and the results remain controversial. Although previous individual studies have reported an association, the overall result of the present analysis support the relationship between IL-10 −1082G/A polymorphism and CVD risk in all genetic models. There are three potential reasons can explain the difference among these findings. First, the relatively small sample sizes of included studies might lead to false positive or negative results. Second, the inconsistent results could result from different genotype frequencies among enrolled subjects, especially in different ethnic groups. Third, due to the complicated pathogenesis of CVDs, it is difficult to explain that the SNP in a single gene could increase risk of CVD without a contribution of other polymorphic susceptibility genes.
Limitations also exist in our study. First, the study lack of detailed information in patients. Second, the studies with small sample size (<100 cases and controls) may overestimate the relationship. Third, the origins of heterogeneity may contain many factors, such as the diverse characteristics of the control group and the different methods of diverse genotyping. Finally, the human IL-10 production is regulated by the complicated interaction between gene and environment, the effect of single genetic mutation is limited. So the evidence offered by this meta-analysis should be accepted with caution. However, our study also exist some advantages: the reasonable-designed search and selection method could increase the statistical power and the accuracy of the results, at the same time, the results did not show any evidence of publication bias.
In conclusion, the results of our study indicate that the IL-10 −1082A/G polymorphism is associated with an increased risk of CVDs. In subsequent studies, we will conduct functional studies to confirm our conclusions.

ACKNOWLEDGMENT
This research was supported by Natural Science Foundation of Hainan Province grants (20168320) and International Cooperation Program of Science and Technology Department of Hainan Province (ZDYF2016223). We thank every researcher who contributed to this study.

F I G U R E 3 Sensitivity analyses of the summary odds ratio
coefficients for the allele model in the overall meta-analysis F I G U R E 4 Begg's funnel plot from the meta-analysis of cardiovascular disease risk and IL-10-1082A/G polymorphism in the allele model