Diabetes 2013 Aug-3

 

J Investig Med. 2013 Feb;61(2):265-9. doi: 10.231/JIM.0b013e31827b98c9.

Association analysis between -308G/A and -238G/A TNF-alpha gene promoter polymorphisms and insulin resistance in Mexican women with gestational diabetes mellitus.

Guzmán-Flores JM, Escalante M, Sánchez-Corona J, García-Zapién AG, Cruz-Quevedo EG, Muñoz-Valle JF, Moran-Moguel MC, Saldaña-Cruz AM, Flores-Martínez SE.

Source

División de Medicina Molecular, Centro de Investigación Biomédica de Occidente, Instituto Mexicano del Seguro Social, Guadalajara, México.

Abstract

BACKGROUND:

Gestational diabetes mellitus (GDM) is characterized by insulin resistance. It has been described that tumor necrosis factor α (TNF-α) plays a key role in the pathogenesis of insulin resistance; moreover, increased levels of this proinflammatory cytokine have been reported in women with GDM. Therefore, this study was aimed to assess the presence of associations between the -308G/A and -238G/A polymorphisms and specific haplotypes of the TNF-α gene promoter region and insulin resistance in Mexican women with GDM.

METHODS:

This study included 51 women with GDM and 44 pregnant women with normal glucose tolerance. Measurements of anthropometric parameters and biochemical estimations were performed. We genotyped the TNF-α -308G/A and -238G/A polymorphisms using polymerase chain reaction-restriction fragment length polymorphism analysis.

RESULTS:

The genotype and allele frequencies of both polymorphisms did not differ significantly between the women with GDM and the controls. However, we found that the frequency of the AG haplotype was significantly increased in the patients with GDM compared with controls (P = 0.019; odds ratio, 4.11; 95% confidence interval, 1.31-12.85). In patients with GDM, we observed that insulin levels and homeostasis model assessment of insulin resistance were significantly higher in women bearing the G/G genotype than in carriers of the G/A and A/A genotypes of the -308G/A polymorphism (P = 0.022 and P = 0.043, respectively).

CONCLUSIONS:

Our results suggest that the G/G genotype of the TNF-α -308G/A polymorphism increases insulin levels and insulin resistance in women with GDM and that the AG haplotype is a genetic risk factor for GDM in our study population.

 

Supplementary:

It has been suggested that inflammation is a central feature of the insulin resistance and evidence of inflammatory deregulation can be observed as early as the first trimester among pregnant women who later develop GDM. The tumor necrosis factor a (TNF-a), which is a proinflammatory cytokine, is synthesized and secreted from macrophages infiltrated in the adipose tissue and in the placenta. Several studies have shown that TNF-a plays a key role in the pathogenesis of insulin resistance; moreover, increased levels of TNF-a have been reported in women with GDM. Hence, TNF-a may be involved in the pathogenesis of GDM.

We analyzed the genotype and allele distributions of the TNF-a –308G/A and –238G/A gene promoter polymorphisms in genomic DNA of 51 unrelated pregnant women with GDM and 44 women with normoglycemic pregnancies, and assessed the existence of associations between insulin resistance and the presence of these polymorphisms or specific haplotypes. All women were Mexican mestizos living in western Mexico (Jalisco State).

Measurements of anthropometric parameters and biochemical estimations were performed and compared. We found that women with GDM were older than control women (33.0 ± 5.2 vs 25.6 ± 5.8 years). BMI, glucose and insulin blood levels, and HOMA-IR were also significantly higher in patients with GDM than in controls.

The polymorphisms were identified by PCR–RFLP analysis. The haplotypes formed by the TNF-a –308G/A and –238G/A polymorphisms were inferred by considering –308G/A as the first position and –238G/A as the second position. The genotypic distributions of both polymorphisms were consistent with Hardy–Weinberg equilibrium (P > 0.05).

We found that the –238G/A polymorphism of the TNF-a gene was not associated significantly with the gestational diabetes phenotype; however, it was not possible to correlate this result with those of other reports because, to date of our study, the relationship between the TNF-a –238G/A polymorphism and GDM had not been studied. In addition, we did not find an association between this polymorphic site of the TNF-a promoter and insulin resistance or other biochemical variables, as described in China and in the Danish population. The results of our study also revealed that the –308G/A polymorphism of the TNF-a gene was not significantly associated with the gestational diabetes phenotype.

Regarding the haplotype analysis, we found that GDM patients carrying the AG haplotype exhibited an increased risk of developing GDM compared with controls. The present study is of particular importance because, to the best of our knowledge, this is the first report assessing the relationship between the haplotypes formed by the TNF-a –308G/A and –238G/A polymorphisms and gestational diabetes; studies exist regarding type 1 and type 2 diabetes, but not with gestational diabetes.

In the GDM patients, anthropometric and biochemical parameters were analyzed according to the genotypes of the two polymorphisms. We observed that insulin levels and HOMA-IR were significantly higher in women carrying the G/G genotype than in carriers of the G/A and A/A genotypes of the TNF-a –308G/A polymorphism (Table; reproduced from the J Investig Med. doi: 10.231/JIM.0b013e31827b98c9 Supplemental Data file). We supposed that the –308A allele of the –308G/A polymorphism is associated with insulin resistance, as the –308A allele has been associated previously with high transcription of the gene and insulin resistance in obesity. Nevertheless, the association between the G/G genotype of the –308G/A polymorphism and high insulin levels and insulin resistance was a major, albeit unexpected finding of our study. This finding is in contrast with a study that reported association between the GDM phenotype and an insulin resistance state in relation with the AA + GA genotypes of the TNF-a –308 polymorphism. Other studies have described that individuals bearing the G/G genotype of the TNF-a –308 polymorphism have higher levels of this cytokine than carriers of the A allele, which seems to support our results if we consider that the –308G allele affects the transcription of the gene and that this, in turn, may affect the production of the cytokine. Unfortunately, we did not have the opportunity to measure the serum levels of TNF-a and provide a correlation between genotype and levels of cytokine, as well as between the levels of cytokine and insulin resistance. Our findings are also supported by the controversial results found regarding the association between the TNF-a –308G/A polymorphism and insulin resistance in several populations. Some reports show that the –308A allele is associated with insulin resistance, whereas other studies show no association. In conclusion our results suggest that the G/G genotype of the TNF-a –308G/A polymorphism increases insulin levels and insulin resistance in women with GDM, and  moreover that the AG haplotype formed by the TNF-a –308G/A and –238G/A polymorphisms is a genetic risk factor for GDM in our population. However, because the small number of subjects exhibited in the comparative groups, caution is warranted when extending these findings to other populations.

 

Table. Anthropometric and biochemical traits in patients with GDM according to TNF-a genotypes for the 308 G/A and 238 G/A polymorphisms.

Silvia Esperanza Flores-Martínez-1

BMI, body mass index; HOMA-IR, homeostasis model assessment of insulin resistance. Values are expressed as the mean ± standard deviation.

* Comparison performed using Student’s t test and the Mann–Whitney U test, when necessary

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