Research Article

Role of IL-8 rs4073 and rs2227306 polymorphisms in the development of primary gouty arthritis in a Chinese population

Published: October 17, 2016
Genet. Mol. Res. 15(4): gmr15048511 DOI: 10.4238/gmr15048511

Abstract

In this study, we investigated the role of two single nucleotide polymorphisms in the promoter region of the interleukin-8 gene (IL-8; rs4073 and rs2227306) in the susceptibility to primary gouty arthritis in a Chinese population. Three hundred and twelve patients with primary gouty arthritis and 340 healthy controls were recruited from the Yan’an University Affiliated Hospital between January 2014 and March 2015. The IL-8 rs4073 and rs2227306 polymorphisms were genotyped by polymerase chain reaction combined with restriction fragment length polymorphism. Unconditional multiple-logistic regression analysis revealed that the TT genotype of rs4073 was correlated with primary gouty arthritis risk, compared to the AA genotype [adjusted odds ratio (OR) = 1.65, 95% confidence interval (CI) = 1.08-2.54; P = 0.02]. In addition, the IL-8 rs4073 T allele was associated with a significant elevated risk of primary gouty arthritis, in comparison to the A allele (OR = 1.34, 95%CI = 1.07-1.67; P = 0.01). However, we observed no significant relationship between the IL-8 rs2227306 polymorphism and primary gouty arthritis risk. The results of this study suggest that the IL-8 rs4073 polymorphism could be a marker for primary gouty arthritis development.

INTRODUCTION

Primary gouty arthritis is a human gouty arthritis with various clinical features, including increased uric acid salt and monosodium urate crystal deposition in the joint capsule, slippery bursa, cartilage, bone, and other tissues, which leads to arthritis, soft tissue mass, development of kidney stones, and urate nephropathy (Baker and Schumacher, 2010; Richette and Bardin, 2010). Several reports have suggested an increase in the morbidity rate of primary gouty arthritis, with a rate of 1.14% in China (Miao et al., 2008). The development of primary gouty arthritis involves multifactorial processes, and has many associated risk factors, including genetic, environmental, and lifestyle factors (Miao et al., 2008; Weaver, 2008). Recent studies have reported that genetic factors, including ABCG2, SLC2A9, NLRP3, Toll-like receptor 4, and estrogen receptor gene, play an important role in the susceptibility to gouty arthritis (Huang et al., 2006; Qing et al., 2013; Cai et al., 2014; Kim et al., 2015; Wang et al., 2015).

IL-8 is a key neutrophil chemokine and an effective angiogenic factor. Polymorphisms in IL-8 influence the structure, expression, and quantity of IL-8, ultimately affecting the function of genes. So far, no study has reported the relationship between polymorphisms in IL-8 and the development of primary gout arthritis. In this study, we investigated the effect of two promoter SNPs in IL-8 (rs4073 and rs2227306) on the susceptibility to primary gouty arthritis in a Chinese population.

MATERIAL AND METHODS

Subjects

Three hundred and twelve patients with primary gouty arthritis were recruited from the Yan’an University Affiliated Hospital between January 2014 and March 2015. Primary gouty arthritis was diagnosed according to the 1977 criteria of the American College of Rheumatology (ACR) classification (Wallace et al., 1977). Patients with a history of other endocrine diseases, or other autoimmune diseases were excluded from this study.

Data regarding the general characteristics of the study participants were collected from medical records or by a structured questionnaire filled by a face-to-face interview with trained doctors. The demographic, lifestyle, and clinical characteristics of study subjects included the age, gender, tobacco smoking, alcohol drinking, body mass index, hypertension, blood glucose level, triglyceride level, total cholesterol level, urea nitrogen level, and creatinine and uric acid levels.

A total of 340 healthy controls were recruited from the Yan’an University Affiliated Hospital during the same period of time. The control subjects were confirmed to be free of primary gouty arthritis and endocrine diseases. The study was approved by the Ethics Committee of Yan’an University Affiliated Hospital. Informed consent was obtained from all subjects.

Genotyping

Peripheral blood samples were collected from all patients in vacuum tubes containing 5% EDTA. Genomic DNA was extracted using a DNA purification kit (Tiangen Biotech, Beijing, China) according to the manufacturer instructions. The IL-8 rs4073 and rs2227306 polymorphisms were genotyped by polymerase chain reaction (PCR) combined with restriction fragment length polymorphism. The forward and reverse primers for IL-8 rs4073 were 5'-TTCTAACACCTGCCACTCTAG-3' and 5'-CACCAAATTGTGGAGCTTCAG-3', respectively, and the forward and reverse primers for IL-8 2227306 were 5'-GGTGAGCACTACCTGACTAGC-3' and 5'-CCACGTCACTGTGACCTAGG-3', respectively. The PCR conditions were set as follows: initial denaturation at 94°C for 10 min; 35 cycles of denaturation at 94°C for 60 s, annealing at 55°C for 30 s, and extension at 72°C for 30 s; and a final extension at 72°C for 10 min. The AseI and EcoRI restriction enzymes were used for IL-8 rs4073 and rs2227306, respectively. The digested PCR products of IL-8 rs4073 and rs2227306 were confirmed by 3% agarose gel electrophoresis, and were observed under ultraviolet light.

Statistical analysis

The differences in the demographic, lifestyle, and physical characteristics between patients with primary gouty arthritis and control subjects were analyzed by the chi-square test or the Student t-test. The association between the IL-8 rs4073 and rs2227306 polymorphisms and the risk of primary gouty arthritis was tested using the odds ratio (OR) and its 95% confidence intervals (95%CI), by considering the common genotype (TT for both rs4073 and rs2227306) as the reference group. The conformance of the IL-8 rs4073 and rs2227306 genotype frequencies with the Hardy-Weinberg equilibrium was determined using the goodness-of-fit chi-square test. The association was considered to be statistically significant when P values were less than 0.05. The SPSS software v.16.0 platform (SPSS Inc., Chicago, IL, USA) was used for all data analysis.

RESULTS

General information of patients with primary gouty arthritis and control subjects is summarized in Table 1. The chi-square test or the t-test revealed that patients with gouty arthritis were more likely to be males (χ2 = 11.33, P = 0.001), with a higher BMI (t = 3.98, P < 0.001) and higher blood glucose (t = 5.18, P < 0.001), triglyceride (t = 5.98, P < 0.001), urea nitrogen (t = 4.76, P < 0.001), and uric acid (t = 20.11, P < 0.001) levels, lower creatinine (t = 3.11, P = 0.001) levels, and likely to be suffering from hypertension (χ2 = 25.95, P < 0.001), compared to the control subjects. However, the age (χ2 = 1.16, P = 0.12), alcohol drinking status (χ2 = 0.98, P = 0.32), tobacco smoking status (χ2 = 1.69, P = 0.19), and total cholesterol level (t = 0.31, P = 0.38) of patients with primary gouty arthritis did not differ significantly from those of the control subjects.

General characteristics of study subjects.

Variables Patients (N = 312) % Controls (N = 340) % Chi-square test or t-test P value
Age (years) 52.34 ± 11.32 53.42 ± 12.45 1.16 0.12
Gender
Female 90 28.85 141 41.47
Male 222 71.15 199 58.53 11.33 0.001
BMI (kg/m2) 24.75 ± 2.65 23.86 ± 3.02 3.98 <0.001
Hypertension
No 176 56.41 256 75.29
Yes 136 43.59 84 24.71 25.95 <0.001
Alcohol drinking
No 246 78.85 257 75.59
Yes 66 21.15 83 24.41 0.98 0.32
Tobacco smoking
No 195 62.50 229 67.35
Yes 117 37.50 111 32.65 1.69 0.19
Blood glucose level (mM) 5.80 ± 2.45 4.87 ± 2.13 5.18 <0.001
Triglyceride level (mM) 2.24 ± 1.78 1.51 ± 1.32 5.98 <0.001
Total cholesterol level (mM) 4.67 ± 1.64 4.71 ± 1.67 0.31 0.38
Urea nitrogen level (mM) 5.84 ± 2.54 5.05 ± 1.64 4.76 <0.001
Creatinine level (μM) 90.12 ± 41.45 97.54 ± 14.26 3.11 0.001
Uric acid level (μM) 536.32 ± 151.80 341.37 ± 90.42 20.11 <0.001
The genotype frequencies of the IL-8 rs4073 and rs2227306 polymorphisms in patients with primary gouty arthritis and control subjects are presented in Table 2. The chi-square test revealed a significant difference in the genotype frequencies of the rs4073 polymorphism between primary gouty arthritis patients and control subjects (χ2 = 6.37, P = 0.04), while the genotype frequencies of rs2227306 did not differ significantly between these groups. However, the genotype distribution of IL-8 rs4073 was not in agreement with the HWE in both patients and controls, while that of rs2227306 conformed to the HWE in both groups.

Genotype distributions of IL-8 rs4073 and rs2227306 in the two study groups.

IL-8 gene Patients(N = 312) % Controls(N = 340) % χ2 test P value P for HWE MAF
Patients Controls Controls Database
rs4073
AA 76 24.36 112 32.94
AT 135 43.27 138 40.59
TT 101 32.37 90 26.47 6.37 0.04 0.02 0.001 0.4676 4.7374
rs2227306
CC 139 44.55 164 48.24
CT 134 42.95 141 41.47
TT 39 12.50 35 10.29 1.26 0.53 0.45 0.57 0.3103 0.2594

MAF = minor allele frequency.

As determined by unconditional multiple-logistic regression analysis, individuals carrying the TT genotype of rs4073 showed elevated risk of primary gouty arthritis compared to those expressing the AA genotype (adjusted OR = 1.65, 95%CI = 1.08-2.54; P = 0.02) (Table 3). In addition, the IL-8 rs4073 T allele was associated with a significantly elevated risk of primary gouty arthritis, compared to the A allele (OR = 1.34, 95%CI = 1.07-1.67; P = 0.01). However, we observed no significant relationship between the IL-8 rs2227306 polymorphism and primary gouty arthritis risk.

Relationship between IL-8 rs4073 and rs2227306 gene polymorphisms and risk of primary gouty arthritis.

IL-8 Patients(N = 312) % Controls(N = 340) % OR (95%CI)1 P value
rs4073
AA 76 24.36 112 32.94 1.0 (Ref.) -
AT 135 43.27 138 40.59 1.44 (0.97-2.14) 0.06
TT 101 32.37 90 26.47 1.65 (1.08-2.54) 0.02
Allele
A 287 91.99 362 106.47 1.0 (Ref.) -
T 337 108.01 318 93.53 1.34 (1.07-1.67) 0.01
rs2227306
CC 139 44.55 164 48.24 1.0 (Ref.) -
CT 134 42.95 141 41.47 1.12 (0.80-1.58) 0.49
TT 39 12.50 35 10.29 1.31 (0.77-2.26) 0.29
Allele
C 412 132.05 469 137.94 1.0 (Ref.) -
T 212 67.95 211 62.06 1.14 (0.90-1.45) 0.26

1Adjusted for gender, body mass index, hypertension, and blood glucose, triglyceride, urea nitrogen, creatinine, and uric acid levels.

DISCUSSION

Primary gouty arthritis is widely accepted as a multifactorial disease; generally, disease pathogenesis can be promoted by a single dominant mutation resulting in the expression of susceptibility genes. This is the first study investigating the possible impact of the rs4073 and rs2227306 polymorphic sites of IL-8 on primary gouty arthritis risk in a Chinese population. The results of our study revealed that the IL-8 rs4073 T allele was associated with an elevated risk of primary gouty arthritis.

Urate crystal is an important factor for gouty arthritis and immune response. Uric acid crystals released from the synovial tissues and articular cartilage are consumed by phagocytes in the joint fluid, thereby activating a number of defense mechanisms and triggering a strong immune inflammatory response (Shi et al., 2009). Urate crystals activate NALP3 inflammasomes and caspase-1, promote the secretion of IL-1β, induce an inflammatory response, and promote the release of many chemokines and inflammatory cytokines, such as IL-1, IL-6, IL-8, and tumor necrosis factor, into the synovial fluid, consequently resulting in the development of primary gouty arthritis (Urano et al., 2002). IL-8 is a potent recruiter of neutrophils and causes angiogenesis. Previous studies have indicated that the C-reactive protein level is significantly increased during acute inflammation. C-reactive proteins promote the nuclear transfer of nuclear factor-κB and activate the kinase pathway, thereby inducing IL-8 transcription and protein secretion (Wang et al., 2010).

Recent studies have indicated that polymorphisms in IL-8 could influence the development of various diseases, including acne vulgaris, glioma, gastric diseases, periodontitis, osteoarthritis, ovarian cancer, and oral cancer, as well as acute pancreatitis (Wang et al., 2013; He et al., 2014; Chen et al., 2015; Hussain et al., 2015; Koensgen et al., 2015; Liu et al., 2015; Ramis et al., 2015). Wang et al. (2013) observed, in a meta-analysis of 1324 patients with oral cancer and 1879 healthy controls, that the AA and AT genotypes of IL-8 rs4073 was correlated with an increased risk of oral cancer in a Caucasian population. On the other hand, He et al. (2014) reported, in a case-control study with 150 osteoarthritis patients and 150 controls, that the TT genotype and the T allele of IL-8 rs4073 and rs2227306 polymorphisms conferred an elevated risk of osteoarthritis. Chen et al. (2015) reported that the IL-8 rs407 polymorphism may be involved in periodontitis susceptibility in Brazilian and Asian populations, while Koensgen et al. (2015) reported a correlation between the TT genotype of IL-8 rs2227306 and a higher risk of ovarian cancer. Hussain et al. (2015) hypothesized that elevated IL-8 levels and the IL-8 rs4073 genetic variant may be correlated with acne vulgaris in a Pakistani population and Liu et al. (2015) reported that the AA genotype of the IL-8 rs4073 polymorphism conferred a significantly higher risk of glioma, compared to the TT genotype. On the other hand, Ramis et al. (2015), in a study comprising 151 patients infected with Helicobacter pylori and 76 uninfected individuals, reported that AA genotype of IL-8 rs4073 conferred an increased risk of peptic ulcer disease in the presence of an H. pylori infection. These studies indicate that IL-8 polymorphisms are associated with the development of autoimmune disease. This is the first report of a correlation between the IL-8 rs4073 and rs2227306 polymorphisms and susceptibility to primary gouty arthritis in a Chinese population. Further studies are required to confirm the findings of this study.

This study design has one major limitation: the sample size is relatively small, which may decrease the statistical power of any significant differences identified between groups. Further investigations with larger-scale sample sizes are warranted to verify our results.

In conclusion, the results of our study suggested that the TT genotype and T allele of the IL-8 rs4073 polymorphism are associated with increased susceptibility to primary gouty arthritis in a Chinese population, suggesting that this polymorphism could be a marker for primary gouty arthritis.

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