Investigating the Relationship between rs1862513 Polymorphism of Resistin Gene and Triglycerides Levels, HOMA-IR and Non-alcoholic Fatty Liver Disease in A Population of Iranian Women

Non-alcoholic fatty liver disease is one of the most common non-communicable diseases in developed countries that affects about 20-30% of the adult population, and this rate reaches 80% in obese people (1). In Asia, the prevalence of this disease is between 12 and 24 percent according to age, gender, place of residence and race. In the Iranian female population, the prevalence of non-alcoholic fatty liver and non-alcoholic steatohepatitis varies between 2.9 and 7.1%, which is 55.6% in patients with type 2 diabetes (2). Among the molecular factors that cause the development of non-alcoholic fatty liver, we can mention obesity and metabolic disorders such as insulin resistance or dyslipidemia, which are the most well-known mechanisms that lead to excessive accumulation of triglycerides in liver cells (3). Studies conducted in several populations have shown the relationship of resistin with changes in fat levels and obesity, HDL, LDL (11, 12  ). Also, the relationship between the serum level of resistin, cholesterol and body mass index has been observed in researchers' reports (13). Research shows that the expression of resistin is increased in obesity (14), cardiovascular diseases and other diseases related to inflammation (8). Studies have shown that there is a relationship between resistin and non-alcoholic fatty liver, and there is also a relationship between resistin and liver inflammation and the degree of liver fibrosis (15), but there are conflicting reports from studies conducted on the relationship between human resistin and insulin resistance and diabetes (8). According to the conflicting reports of the association of 1862513rs polymorphism with resistin level, diabetes, non-alcoholic fatty liver, insulin resistance and metabolic parameters, the present study was conducted to investigate the association of 1862513rs polymorphism with metabolic parameters and insulin resistance for the first time in Iranian women population.

The present case-control study is to investigate the association of rs1862513 polymorphism of the resistin gene with metabolic parameters and insulin resistance. 60 women with non-alcoholic fatty liver disease and 60 healthy women were studied. Non-alcoholic fatty liver patients were selected based on ultrasound findings and confirmation of fatty liver. The condition of entering this study was not to consume alcohol and metabolic drugs. All the people participating in this study entered into informed consent and the people were given full explanations of the objectives of the project. After measuring the height and weight, 10 ml peripheral blood samples were taken from the participants, 5 ml of which was poured into a tube containing blood anticoagulant (20 mg EDTA) for DNA extraction and the rest was poured into a tube without anticoagulant. Body mass index (BMI) is a correct reflection of body fat percentage (22). Biochemical factors such as fasting blood sugar (FBS), triglycerides (TG), cholesterol (CHOL), and high molecular weight lipoproteins (HDL) were measured on the serum of the samples. In this research, the salting out method using Poroteinase K was used to extract genomic DNA. Genotypes of rs1862513 polymorphism were determined by PCR-RFLP method. For this purpose, the fragments carrying the rs1862513 polymorphism of the resistin gene were amplified by polymerase chain reaction (PCR) and evaluated using the RFLP technique and restriction enzyme BbSI.

Comparison of women in healthy and diseased groups shows a significant difference in terms of age, body mass index, resistance, HDL, triglyceride, fasting sugar and HOMA. In terms of the correlation of resistin with biochemical variables in healthy and sick people, it was shown that resistin has a positive relationship with LDL and triglycerides and a negative relationship with HDL in healthy people. Also, the frequency of the rs1862513 polymorphism of the resistin gene in insulin resistant and sensitive women was investigated and the results show that there is no significant relationship between the rs1862513 polymorphism of the resistin gene and insulin resistance. Regression analysis was performed for genotypes in healthy and sick women and the results show that rs1862513 polymorphism genotypes play a role in the occurrence of non-alcoholic fatty liver disease.

Resistin induces apoptosis and dysfunction of pancreatic beta cells and increases insulin resistance in the liver (24). The increase of resistin in inflammations has been clearly seen and studies show that there is a strong relationship between resistin and obesity, inflammation and insulin resistance (20, 24). The different and contradictory results of the studies can be the gender of the samples and the volume of the study and the type of disease under investigation. One of the limitations of this study was the small sample size, which was due to the small number of people without a history of taking metabolic drugs. There was a significant relationship between the genotypes of the rs1862513 polymorphism with non-alcoholic fatty liver disease, but there was no significant relationship with insulin resistance.