Monocyte chemoattractant protein-1 -2518G/A gene polymorphism and the risk of nephropathy in type 2 diabetes mellitus among Asians: a meta-analysis

Abstract

The association between monocyte chemoattractant protein-1 (MCP-1) -2518G/A gene polymorphism and the risk of nephropathy in type 2 diabetes mellitus (T2DM) remains controversial. A meta-analysis was conducted to assess the association of MCP-1 -2518G/A gene polymorphism with the risk of nephropathy in T2DM. Eight studies were included in our meta-analysis by searching electronic databases according to predefined criteria. No significant association between G allele, GG genotype, or AA genotype and the onset of nephropathy in T2DM was observed among Asians. GA genotype was significantly associated with nephropathy risk in T2DM among Asians (p = 0.024). MCP-1 -2518G/A gene polymorphism was not associated with nephropathy risk in T2DM among Chinese, Koreans, and Turks. For Indians, G allele and AA genotype were not associated with nephropathy risk in T2DM, GG genotype was associated with a lower risk of nephropathy in T2DM (p = 0.017), GA genotype was associated with the susceptibility of nephropathy in T2DM (p = 0.029). In conclusions, GA genotype might be a risk factor for the onset of nephropathy in T2DM among Asians, particularly Indians; GG genotype seems to be a protective factor against the susceptibility of nephropathy in T2DM among Indians.

• Diabetes
• gene polymorphism
• meta-analysis
• monocyte chemoattractant protein-1 -2518G/A
• nephropathy

Introduction

Diabetic nephropathy (DN) is a leading cause of chronic kidney disease, and once present will be likely to progress to end-stage renal disease.1 DN complicates about 20–40% of type 2 diabetes mellitus (T2DM) cases, which suggests that certain factors predispose patients with T2DM to DN.2 Currently, hypertension, poor glycemic regulation, and albuminuria are well-accepted risk factors for the onset of DN in T2DM.3 However, the development of a number of DN cases remains unexplained.

Recently, tissue macrophage accumulation is thought to promote the development and progression of DN.4 Macrophage infiltration is observed during the moderate stage of diffuse diabetic glomerulosclerosis in the renal biopsy specimen from diabetic cases.5 Infiltrated macrophages release various inflammatory mediators that would lead to inflammation, interstitial fibrosis, and finally permanent kidney damage.6 Monocyte chemoattractant protein-1 (MCP-1) is a strong stimulator of macrophage recruitment. Hence, MCP-1 is believed to be a pathogenic mediator in the development and progression of DN. Genetic variations in the gene encoding the MCP-1 might confer susceptibility to DN.7 Several polymorphisms have been identified in the MCP-1 gene. -2518 A/G polymorphism in the distal regulatory region of MCP-1 is believed to regulate gene expression and influence plasma MCP-1 concentration.8 In this sense, it is reasonable to postulate that MCP-1 -2518 A/G gene polymorphism is associated with the risk of nephropathy in T2DM.

The past few years have witnessed an increasing interest in testing this hypothesis among Asians. However, the results were in conflict among the reported studies.6,9–15 An improved understanding of this issue may have important clinical implications provided the possibility that the MCP-1 -2518 A/G gene polymorphism may be an indicator to predict the onset of nephropathy in T2DM. Meta-analysis is a good way to summarize the available evidence to provide more robust results than the individual study. Thus, we performed this meta-analysis to investigate the association between MCP-1 -2518 A/G gene polymorphism and nephropathy risk in T2DM with the aim of providing a much more reliable finding on the significance of the association.

Materials and methods

Search strategy

We attempted to search the published literature related to the association between MCP-1 -2518G/A gene polymorphism and the risk of nephropathy in T2DM using Pub Med, Embase, Cochrane, and China National Knowledge Infrastructure (CNKI) databases through May 2013. No restriction was imposed on search language. The used search terms were as follows: (1) type 2 diabetes mellitus, T2DM, nephropathy; and (2) monocyte chemoattractant protein-1, MCP-1, -2518G/A, gene polymorphism. Bibliographies of retrieved articles and reviews were also scrutinized. If the same data was included in more than one study, we chose the study with the most complete analysis.

Inclusion criteria

1. A case-control study

2. The outcome of interest was DN.

3. At least two comparison groups (DN group vs. T2DM group)

Exclusion criteria

1. Case reports, reviews, and editorials

2. Association of other genes with DN risk

3. Multiple publications of the same data

4. Investigation of the role of MCP-1 to diseases

Data extraction and synthesis

The following characteristics from each study were extracted: first author’s surname, year of publication, region of study population, number of cases and controls for MCP-1 -2518G/A genotype. Frequencies of G allele were calculated for case and control groups, from the corresponding genotype distribution. Two authors independently performed the data extraction and synthesis with any disagreements resolved by discussion.

Statistical analysis

STATA version 12.0 (Stata Corp, College Station, TX) was used to calculate the available data from each study. Odds ratio (OR) was used to measure the association between MCP-1 -2518G/A gene polymorphism and nephropathy risk in T2DM across studies. Heterogeneity of ORs among studies was tested by using the Q statistic (significance level at p < 0.10). The I² statistic, a quantitative measure of inconsistency across studies, was also calculated. The pooled ORs were calculated using either a fixed-effects model or, in the presence of heterogeneity, a random-effects model. In addition, 95% confidence intervals (CIs) were also calculated. The OR was calculated by using four methods: method 1, allele comparison (G allele vs. A allele); method 2, comparing GG homozygous with the other two combinations (GG vs. GA + AA); method 3, comparing AA genotype with the other two combinations (AA vs. GA + GG); method 4, comparing GA genotype with the other two combinations (GA vs. GG + AA). A chi-square test using a web-based program was used to determine whether genotype distribution of the control groups reported conformed to Hardy–Weinberg equilibrium (HWE) (HWE; p < 0.05 was considered significant). Potential publication bias was assessed for overall Asians by Begg’s test and Egger’s test at the p < 0.05 level of significance. p < 0.05 was considered statistically significant, except where otherwise specified.

Results

Literature search

We firstly retrieved 106 references from the electronic databases. Of these, 98 publications were excluded according to the inclusion and exclusion criteria. Eight studies6,9–15 were identified for the analysis of the association between MCP-1 -2518G/A gene polymorphism and nephropathy risk in T2DM (Figure 1).

Figure 1. Flow chart of study selection.

Study characteristics

A total of eight studies were recruited. Four studies10,12,13,15 were conducted in China, two6,11 in Korea, one14 in India, and one9 in Turkey (Table 1). A total of 908 cases and 806 controls were included (Table 1). The average frequency of the G allele was 47.9% in Chinese patients and 51.2% in controls (Table 1). For Koreans, the average frequency of G allele was 60.5% in the case group and 65.1% for controls (Table 1). For Indians, the average frequency of G allele was 33.8% in the case group and 33.1% for controls (Table 1). For Turks, the average frequency of G allele was 22.1% in the case group and 19.8% for controls (Table 1). The ratio of cases/controls for average frequency of G allele in Turks was higher compared with that in Indians, Chinese, and Koreans (Turks: cases/controls = 1.12; Indians: cases/controls = 1.02; Chinese: cases/controls = 0.94; Koreans: cases/controls = 0.93).

Table 1. Characteristics of studies evaluating the effects of MCP-1 -2518G/A gene polymorphism on DN risk.

		DN				T2DM				G allele (%)		HWE
First author, year	Region	GG	GA	AA	Total	GG	GA	AA	Total	Case	Control	p
Moon, 2007	Korea	35	61	16	112	51	50	11	112	58.5	67.9	0.969
Joo, 2007	Korea	65	73	26	164	68	78	23	169	61.9	63.3	0.996
Cheng, 2007	China	26	44	24	94	22	40	24	86	51.1	48.8	0.814
Ahluwalia, 2009	India	16	130	94	240	36	97	122	255	33.8	33.1	0.078
Tang, 2009	China	18	39	42	99	32	7	12	51	37.9	69.6	<10^−5
Cheng, 2010	China	24	42	28	94	19	34	23	76	47.9	47.4	0.669
Karadeniz, 2010	Turkey	0	19	24	43	0	17	26	43	22.1	19.8	0.271
Wang, 2013	China	21	31	10	62	17	27	24	68	58.9	44.9	0.266

Note: MCP = monocyte chemoattractant protein, DN = diabetic nephropathy, T2DM = type 2 diabetes mellitus, HWE = Hardy–Weinberg

equilibrium.

Association between the MCP-1 -2518G/A gene polymorphism and nephropathy risk in T2DM

No significant association between G allele, GG genotype, or AA genotype and the risk of nephropathy in T2DM was observed among Asians (Table 2). GA genotype was significantly associated with nephropathy risk in T2DM among Asians (p = 0.024; Table 2; Figure 2). MCP-1 -2518G/A gene polymorphism was not associated with nephropathy risk in T2DM among Chinese, Koreans, and Turks (Table 2). For Indians, G allele and AA genotype were not associated with nephropathy risk in T2DM (Table 2), GG genotype was associated with a lower risk of nephropathy in T2DM (p = 0.017; Table 2), GA genotype was associated with the susceptibility of nephropathy in T2DM (p = 0.029; Table 2; Figure 2).

Figure 2. Association between MCP-1 -2518G/A GA genotype and DN risk for Asians.

Table 2. Meta-analysis of the association of MCP-1 -2518G/A gene polymorphism with DN risk.

Genetic variant	Region	Studies		Model selected	OR (95% CI)	p Value
G versus A	Asia	8	0.14	Fixed	0.956 (0.85–1.074)	0.449
	China	4	0.019	Random	0.933 (0.655–1.329)	0.701
	Korea	2	0.522	Fixed	0.929 (0.769–1.123)	0.446
	India	1	–	Fixed	1.018 (0.794–1.306)	0.885
	Turkey	1	–	Fixed	1.118 (0.544–2.295)	0.762
GG versus (GA + AA)	Asia	8	0.022	Random	0.759 (0.534–1.079)	0.125
	China	4	0.007	Random	0.808 (0.408–1.599)	0.541
	Korea	2	0.272	Fixed	0.855 (0.625–1.17)	0.328
	India	1	–	Fixed	0.472 (0.255–0.873)	0.017
	Turkey	1	–	Fixed	1 (0.061–16.508)	1
AA versus (GA + GG)	Asia	8	0.294	Fixed	0.944 (0.773–1.154)	0.575
	China	4	0.106	Fixed	0.964 (0.689–1.349)	0.831
	Korea	2	0.666	Fixed	1.261 (0.779–2.042)	0.346
	India	1	–	Fixed	0.819 (0.594–1.129)	0.223
	Turkey	1	–	Fixed	0.923 (0.46–1.854)	0.822
GA versus (GG + AA)	Asia	8	0.414	Fixed	1.216 (1.026–1.441)	0.024
	China	4	0.19	Fixed	1.227 (0.912–1.65)	0.177
	Korea	2	0.44	Fixed	1.063 (0.793–1.427)	0.682
	India	1	–	Fixed	1.424 (1.038–1.954)	0.029
	Turkey	1	–	Fixed	1.118 (0.513–2.436)	0.78
Sensitivity analysis
G versus A	Asia	7	0.836	Fixed	1.007 (0.891–1.138)	0.916
	China	3	0.62	Fixed	1.101 (0.883–1.373)	0.392
	Korea	2	0.522	Fixed	0.929 (0.769–1.123)	0.446
	India	1	–	Fixed	1.018 (0.794–1.306)	0.885
	Turkey	1	–	Fixed	1.118 (0.544–2.295)	0.762
GG versus (GA + AA)	Asia	7	0.31	Fixed	0.862 (0.689–1.079)	0.196
	China	3	0.842	Fixed	1.132 (0.766–1.673)	0.533
	Korea	2	0.272	Fixed	0.855 (0.625–1.17)	0.328
	India	1	–	Fixed	0.472 (0.255–0.873)	0.017
	Turkey	1	–	Fixed	1 (0.061–16.508)	1
AA versus (GA + GG)	Asia	7	0.527	Fixed	0.891 (0.722–1.098)	0.278
	China	3	0.3	Fixed	0.794 (0.539–1.17)	0.243
	Korea	2	0.666	Fixed	1.261 (0.779–2.042)	0.346
	India	1	–	Fixed	0.819 (0.594–1.129)	0.223
	Turkey	1	–	Fixed	0.923 (0.46–1.854)	0.822
GA versus (GG + AA)	Asia	7	0.784	Fixed	1.166 (0.98–1.388)	0.084
	China	3	0.827	Fixed	1.066 (0.773–1.469)	0.697
	Korea	2	0.44	Fixed	1.063 (0.793–1.427)	0.682
	India	1	–	Fixed	1.424 (1.038–1.954)	0.029
	Turkey	1	–	Fixed	1.118 (0.513–2.436)	0.78

Note: MCP = monocyte chemoattractant protein, DN = diabetic nephropathy, OR: odds ratio, CI = confidence interval.

Sensitivity analysis

The genotype distribution of the control group in one study was not in HWE. Hence, we included seven studies in the sensitivity analysis. For Asians, similar results regarding the association of G allele, GG genotype or AA genotype and nephropathy risk in T2DM were found in the sensitivity analysis compared with those in the non-sensitivity analysis (Table 2). Notably, an insignificant association was observed between GA genotype and the risk of nephropathy in T2DM (p = 0.084; Table 2) which was a little different from that in the non-sensitivity analysis. For Chinese, similar results regarding the association of MCP-1 -2518G/A gene polymorphism and nephropathy risk in T2DM were found in the sensitivity analysis compared with those in the non-sensitivity analysis (Table 2).

Evaluation of publication bias

Visual inspection of funnel plot showed no significant asymmetry (Figure 3). No evidence of significant publication bias for Asians was observed (G vs. A: Begg p = 0.621, Egger p = 0.852; GG vs. GA + AA: Begg p = 1, Egger p = 0.994; AA vs. GA + GG: Begg p = 0.37, Egger p = 0.296; GA vs. GG + AA: Begg p = 0.322, Egger p = 0.452).

Figure 3. Publication bias for the analysis of association of MCP-1 -2518G/A gene polymorphism with DN risk for Asians.

Discussion

Increasing attention has been paid to the investigation of the etiology of nephropathy in T2DM. The confirmation of possible genetic origin of DN would give an insight to early diagnosis or intervention of DN. In our meta-analysis, we found that GA genotype was associated with the onset of nephropathy in T2DM among Asians and Indians, GG genotype was associated with a lower risk of nephropathy in T2DM among Indians. No evidence of publication bias for Asians was observed. Of note, the sensitivity analysis showed that an insignificant association between GA genotype and nephropathy risk in T2DM existed among Asians, which was a little from that in non-sensitivity analysis. Nevertheless, it still has important clinical significance that GA genotype may be a possible genetic marker for the onset of nephropathy in T2DM among Asians.

The regional differences might affect the association between MCP-1 -2518 A/G gene polymorphism and nephropathy risk in T2DM. In our investigation, the ratio of cases/controls for average frequency of G allele was 1.12, 1.02, 0.94, and 0.93 in Turks, Indians, Chinese, and Koreans, respectively. Although the ratio in Turks was the highest, no significant association between MCP-1 -2518 A/G gene polymorphism and nephropathy risk in T2DM was observed. This was mainly due to the fact that only one study9 in Turks was recruited, which made the results less robust. More studies should be performed in the future. In Indians, we found that GA genotype was associated with the nephropathy onset in T2DM, GG genotype was associated with a lower risk of nephropathy in T2DM. However, only one study14 in Indians was enrolled, more studies are needed to validate our results. For Chinese and Koreans, the results from the sensitivity analysis were similar to those from the non-sensitivity analysis, which indicated the results were relatively robust.

Several facts may explain the association between MCP-1 -2518 A/G gene polymorphism and nephropathy risk in T2DM. First, MCP-1 can directly stimulate macrophages to secrete increased levels of active and total TGF-β 1, which can promote production of extracellular matrix.16 Meanwhile, TGF-β 1 can itself stimulate mesangial expression of MCP-1, which suggests a mechanism of self-amplifying cytokine-loop for promoting mesangial matrix accumulation.17 In vitro studies also indicated that MCP-1 could promote renal fibrosis during diabetes.18 MCP-1- deficient diabetic kidneys showed that a lack of MCP-1 reduces the accumulation of interstitial myofibroblasts and the deposition of glomerular and interstitial collagen type IV.19 Second, kidney MCP-1 production plays a critical role in the development of diabetic renal inflammation, which leads to progression of DN.20 Selective targeting of MCP-1 has been proven to be an effective therapy in suppressing animal models of DN.21 Finally, the polymorphism of -2518G/A in the MCP-1 gene influences MCP-1 expression in response to inflammatory stimuli.22 This polymorphism was associated with the production of MCP-1 by interleukin-1β-stimulated peripheral blood mononuclear cells.8 All the above-mentioned data indicate a possible association of MCP-1 -2518G/A gene polymorphism with nephropathy risk in T2DM.

In the past, the association between MCP-1 -2518G/A gene polymorphism and renal diseases were investigated in a number of studies. Mori et al.23 reported that AA genotype was an independent risk factor for the progression of renal disease in Japanese patients with IgA nephropathy. Malafronte et al.24 reported that GG genotype was associated with the risk of lupus nephritis in Brazilians. Piotrowski et al.25 reported that G variant was associated with renal manifestations of systemic lupus erythematous in Polishes. Kim et al.26 reported that -2518G/A gene polymorphism was associated with nephritis in systemic lupus erythematous by modulating MCP-1 expression in Koreans. All these evidences support the possibility that MCP-1 -2518G/A gene polymorphism is associated with the development and progression of renal diseases.

Although no marked publication bias for Asians was observed, several limitations should be considered in our investigation. First, heterogeneities might be present, affecting the results of our meta-analysis, although a random-effects model had been performed. Second, the reporting bias might affect the results; further studies are needed to be performed in other ethnicities than Asians. Finally, the small sample size limited the statistical power. More studies should be performed in the future.

In conclusion, the results of our study suggest that GA genotype might be a risk factor for the onset of nephropathy in T2DM among Asians, particularly Indians; GG genotype seems to be a protective factor against the susceptibility of nephropathy in T2DM among Indians. However, larger number of studies in different regions and ethnicities are needed in the future.

Declaration of interest

There is no conflict of interest for all authors.