Association of IL-10 (− 1082 A/G) and IL-6 (− 174 G/C) gene polymorphism with type 2 diabetes mellitus in Ethiopia population

Type 2 Diabetes Mellitus (T2DM) is a group of metabolic syndrome characterized by hyperglycemia associated with the defect of insulin action [1, 2]. Globally, the number of people with diabetes mellitus (DM) has been increased by four folds in the past three decades as a result of urbanization and associated lifestyle change [3]. According to international diabetes federation (IDF), there are 463 million people with diabetes in 2019 in the world, and this number is expected to increase up to 700 million by 2045 [4]. About 1 in 11 adults worldwide now has diabetes mellitus, around 90% of them have T2DM, and 75% of DM patients are living in developing countries [5]. It has been expected that the fastest increase of patients living with T2DM will found to be in Sub Saharan Africa (SSA) countries in the next two decades [6]. Although the incidence and prevalence rate of T2DM is increasing in Africa, the proportion of undiagnosed DM in Africa, which is around 69% is extremely higher than that of developed countries (37%) [7]. The profile of diseases in the African continent has changed from infectious diseases such as malaria, tuberculosis and HIV to chronic noncommunicable diseases, including T2DM. According to 2017 report, the prevalence of diabetes in Ethiopia is found to be 5.2% among adults with a total of 2.6 million cases of DM in the country; of this, T2DM accounts the highest proportion [8, 9]. A recent study finding also revealed that the proportion of hidden T2DM is high among adults who are living in the urban areas of Northwest Ethiopia which is 6.34% [10]. Furthermore, the medical expense of DM patients is about three times higher than the general population without diabetes [3].

The major threat of T2DM patients is associated with micro and macro vascular complications, which is considered as the major cause of morbidity and mortality [11]. Recently, low level of chronic inflammation has been found to have great implication on the onset and progression of T2DM [12, 13]. Studies have shown that high level of inflammatory and anti-inflammatory cytokines such as IL-6 and IL-10 are detected in plasma of patients with T2DM, and thus, associated with its complication [14‐17]. Interlikun-6 is a pleiotropic cytokine mainly produced by T cells and macrophages, mapped to human chromosome 7p15–p21 [18]. It regulates a wide range of immune activities, production of cell adhesion molecules, acute phase protein, and facilitates the release of other cytokines in response to inflammatory stimuli [19]. In addition, it affects glucose homeostasis and metabolism directly, or indirectly by acting on muscle cells, hepatocytes and pancreatic β cells [20]. In fact, different ethnic populations have different levels of variability in single nucleotide polymorphisms (SNPs). Hence, polymorphism within the coding and non-coding region of cytokine genes cause interindividual variation in their expression, leading to difference in immune responses [21] and may eventually lead to increased risk of infection and occurrence of a number of chronic diseases [22]. Recent studies revealed that there is a link between IL-6 promoter polymorphism (− 174 G/C) and circulating IL-6 levels with respect to the development of several diseases, however, the effect of IL-6 gene polymorphism with the development of T2DM is not clearly understood despite the presence of contradictory findings [23‐25]. While scholars have been found that IL-6 -174 G/C polymorphism is associated with the susceptibility and individuals are the greatest risk of developing T2DM [20], others have still assumed no association [26]. Moreover, studies also showed − 174 G/C polymorphism can serve as a predictor for the progression of complications, particularly kidney diseases in T2DM patients [27, 28] and for developing comorbidity such as tuberculosis [29]. However, few studies reported that there is no association between this polymorphism with diabetes associated kidney diseases [26, 30].

Interleukin-10 (IL-10) is a multifunctional cytokine with both immunosuppressive and anti-angiogenic functions [31]. The human IL-10 gene is located on chromosome 1q31–32, a locus genetically linked to susceptibility to a number of autoimmune diseases, including T2DM [32, 33]. The replacement of nucleotide A by G on the promoter region of the IL-10 gene (− 1082 A/G) will increase the transcription of both genes, approximately two folds, as a result it increases the production of this cytokine. Due to this fact, it is expected that the polymorphic genotype may be associated with an increased frequency of T2DM [21, 34]. Now a day, the burden of the T2DM rapidly increases worldwide, especially in middle and low-income countries including Ethiopia. With an increasing number of T2DM patients in Ethiopia, knowledge on genetic background and marker, which contribute to the etiology and progression of T2DM is important in the intervention and managements of the disease. To date, as a controversial, it has been difficult to determine the exact relationship between IL-6 and 10 genotypes and the corresponding cytokine production with respect to T2DM. Therefore, the aim of this study was to investigate the association of cytokine gene polymorphisms (IL-6 (− 174 G/C) and IL-10 (− 1082 A/G)) with T2DM.

The purpose of the present study was to investigate the relationship between IL-6 and IL-10 gene polymorphisms with T2DM. Insulin resistance is understood to be the inability of cells to use glucose, and the glucose-reducing effects of insulin are abnormal, leading to hyperglycemia, and T2DM [42, 43]. Scholars have been reported that T2DM is associated with chronic inflammation that could be attributed to dysregulation of the innate immune system and this is a potential link between metabolic syndrome and diabetes [21]. Interleukin 6 is one of the most prominent cross-taking cytokine involved between inflammation and T2DM [44] whereas, IL-10 which is an anti-inflammatory cytokine plays an important role in the regulation of immune response, leading to decreased cytokine production, lower tissue factor expression, inhibiting matrix-degrading metalloproteinase, and promoting the phenotype switching of lymphocytes to the Th2 cell [45, 46]. Moreover, IL-10 has been shown to influence both the susceptibility and course of various diseases, and the different polymorphisms in the IL-10 gene promoter have been associated with T2DM prevalence and severity [21].

In this study, we found that the G alleles of − 174 IL-6 polymorphism are more frequent in T2DM participants than apparently healthy individuals. Hereafter, individuals carrying the G allele of IL-6 (− 174) were 2.82-fold odds of developing T2DM compared to individuals carrying the C allele (OR (95% CI) =2.82 (1.78–10.54)). The evidence suggested that the allele G of IL-6 -174G/C was higher in T2DM patients than those of healthy controls. It has been shown that the -174G/C polymorphism of the IL-6 promoter region has a direct effect on gene transcription [47]. Following its expression, IL-6 can function on various immune cells to trigger and/or increase inflammatory response, macrophage activation and fibrosis contributes to end organ damage such as diabetic nephropathy and neuropathy [48, 49]. Similarly, GG genotypes of − 174 IL-6 polymorphism are more frequently observed in T2DM than apparently healthy individuals.

These findings suggested that the IL-6 -174G/C polymorphism might be a risk factor for T2DM among the Ethiopian population though, future studies required to confirm the finding in large scale. Similar observations were found from Indians [50], and Native Americans and Caucasians [51]. In contrast, finding from Brazil showed that genotype and allele frequencies of polymorphisms for cytokine gene IL-6 found no statistically difference between T2DM and control groups [16]. And again our finding was not supported by a report from Pakistan and Greece that showed IL-6174 allele C was significantly associated with IL-6 expression and T2DM development [14, 52]. Besides this, IL-6 -174 GG polymorphism is associated with increased insulin sensitivity and may protect the development of T2DM in Framingham population [53]. Therefore, the lack of agreement between different studies could be due to either the variation in ethnic origin or the interaction between the susceptible gene loci and various environmental determinants.

Interestingly, there was a significant association between IL-10 (− 1082) G/A gene polymorphism and T2DM. The GG genotype was more frequently observed in T2DM patients than in apparently healthy controls that contains AA and AG genotype (P = 0.012, OR (95%CI) = 0.30 (0.101–0.892) and 0.40 (0.198–0.808), respectively). Despite the fact, AA and AG genotypes are 0.30- and 0.40-fold odds of negatively developing T2DM. Our finding provides a clue that the IL-10 (− 1082) G/A polymorphism might be a protective for T2DM among Ethiopian population. In line with this, a study conducted in Egypt and China population showed that the IL-10 gene − 1082, GG genotype was significantly increased the risk of T2DM [54, 55]. In contrast to our finding, a Brazilian study indicated that genotype and allele frequencies of polymorphisms in cytokine IL-10 gene − 1082 G/A found no statistically significant difference between T2DM and control groups [16]. In fact, the causes of T2DM are environmental or genetic factors, the genetic polymorphism of cytokines like IL-6 and 10 caused by up/down regulation of inflammatory cytokines to trigger insulin resistance [21]. In particular, T2DM are often characterized by insulin resistance due to low production or impaired signaling cascade of IL-10 concomitant to enhanced expression of pro-inflammatory molecules.

Overall, IL-10 and IL-6 play an immense role in regulating the immune response. Single nucleotide polymorphism (SNP) at promoter region − 1082 and − 174 of IL-10 and IL-6, respectively able to facilitate binding of many more transcription factors with RNA-polymerase II (RNA-Pol II) to this target gene of interest. Therefore, enhanced gene expression is not only due reaction between promoter region and RNA Pol-II, but also with the involvements of different trans-acting proteins as basal transcription factor. Subsequently, these mutations may play a part in the reaction affinity between the DNA binding domain of the RNA-pol II and promoter, and increase its catalytic activities [56‐58]. Therefore, the IL-10 and IL-6 production may alter the concentration of these cytokines in plasma of blood circulation. Therefore, here we can understand that gene polymorphism is one of the most important biomarkers for early screening and diagnosis of both communicable and non-communicable disease. Those aspects are becoming increasingly essential preventive strategic option of T2DM.

The limitation of this study was a small sample size and did not quantify IL-6 and IL-10 in the study groups, may strongly indicate, ether the wild or mutated gene of these cytokines is associated with an increased serum cytokine level in each of the study groups. However, in the study population, the G allele is predicted to increase the expression of IL-6 and 10 in plasma, a significant mediator of insulin resistance that could lead to diabetes through inhibiting insulin receptor tyrosine kinase and interfering with its action on adipocytes, and skeletal muscle (60).

The genetic polymorphisms of IL-6 and IL-10 in T2DM patients demonstrated higher frequencies of G allele and GG genotypes. Moreover, the polymorphisms of these cytokines were significantly associated with T2DM. This finding suggested that the genetic polymorphism may be contributed to the expression of cytokine, which result insulin resistance and T2DM. Furthermore, the identification of polymorphism of IL-6 and IL-10 gene is used not only for screening purpose, but also as additional diagnostic tools for T2DM.