Diabetes mellitus (DM) is one of the four priority non-infectious diseases that represent a serious medical and social problem in all countries of the world [1]. According to the results of the epidemiological study NATION, 19.2% of the Russian Federation population has preceding DM prediabetes, diagnosed by the HbA1C level [2]; however, when using the criterion of lean glycemia, the number of patients with early carbohydrate metabolism disorders (CMD) can reach 28.1% of the Russia population [3]. It is known that preventive measures already at the stage of prediabetes can prevent or slow down the development of type 2 DM, as well as its micro- and macrovascular complications [4]. These measures, in addition to normalizing the level of glycemia, should be aimed at reducing body weight and normalizing blood pressure and lipid metabolism. According to the “Algorithms of Specialized Medical Care for Patients with Diabetes Mellitus” of the 11th revision (2023), upon early detection of CMD, in addition to educating patients on the principles of nutritional therapy, metformin can be prescribed [5]. In addition to the sugar-lowering effect, this drug has a number of pleiotropic effects, such as cardioprotection, neuro- and oncoprotective effects, as well as the normalization of lipid metabolism due to the suppression of the production and activity of SREBP-1 protein and apolipoprotein V-48, which regulate fatty acid metabolism [6]. However, the therapeutic response to metformin is variable, which can be due to the genetic characteristics of the patient [7].

One of the genes that can modulate response to metformin therapy is SLC22A1. This gene encodes a cation transporter type 1 (organic cation transporter type 1, OCT1), which transports metformin from the bloodstream into liver cells [8]. Currently, more than 34 polymorphisms of this gene are known [9]; however, the greatest interest for this study is the polymorphic marker rs622342 SLC22A1.

The purpose of the work was to study the relationship of the rs622342 SLC22A1 polymorphism with short-term changes in fat and carbohydrate metabolism in various therapeutic options for early CMD.

Overweight or obese women (BMI ≥ 25 kg/m2), having also other risk factors for CMD (family history, type 2 DM, impaired fasting glycemia or history of impaired glucose tolerance, high-density lipoprotein ≤ 0.9 mmol/L and/or history of triglycerides ≥ 2.82 mmol/L, gestational DM or history of large fetal birth, cardiovascular disease, polycystic ovary syndrome) were included in the study. Residence in the Republic of Tatarstan for at least three generations, established by a questionnaire, was an important condition for inclusion in the study. The study protocol was approved by the Local Ethics Committee of FSBEI HE Kazan State Medical University of the Ministry of Health of the Russian Federation (meeting minutes No. 10 of December 18, 2018). The objectives and methods of the study were explained to all patients, on the basis of which each patient signed a voluntary informed consent to participate in the study. At the beginning of the study, all patients underwent venous blood sampling to determine the levels of fasting glucose, total cholesterol (TC), high-density lipoproteins (HDL), low-density lipoproteins (LDL), and triglycerides (TG) by the enzymatic colorimetric method (Olvex Diagnosticum reagent kit, St. Petersburg; biochemical analyzer Stat Fax 4500, USA). Glycated hemoglobin (HbA1C) was also determined by the express method (Abbott NycoCard Reader II analyzer, USA). Additionally, to detect CMD, all patients underwent an oral glucose tolerance test (OGTT) with a standard load of 75 g of anhydrous glucose dissolved in 300 ml of water. The rs622342 SLC22A1 polymorphism was determined using real-time polymerase chain reaction (PCR) (Synthol reagent kit, Moscow; amplifier CFX96, USA). DNA obtained from whole blood lymphocytes of patients by the sorbent method (DNA-sorb-B reagent kit; LLC ILS, Moscow) was the substrate for the reaction. Patients were randomized into two therapeutic groups. Participants in the first group followed the nutritional diet generally accepted at CMD, which implies the exclusion of simple carbohydrates from the diet and the restriction of the use of complex carbohydrates and fats. Participants in the second group took metformin at a therapeutic dose in addition to compliance with dietary therapy. Compliance with the recommendations was monitored by face-to-face meetings once every two weeks, with checking the diet diary. After three months, the lipid spectrum, the level of fasting glucose, and HbA1C were evaluated again in all patients. Statistical data processing was carried out using the IBM SPSS Statistics 26.0 and Microsoft Excel 2016 programs. The χ2 test was used to assess the correspondence of the genotype distribution to the Hardy-Weinberg equilibrium. When studying the relationship of rs622342 SLC22A1 with changes in the lipid profile, a recessive inheritance model was taken into account, namely, the indicators of groups of patients with the absence and presence of allele A were compared. The compliance of the studied samples with the normal distribution was previously checked using the Shapiro-Wilk test. If the distribution was different from normal, then the Mann-Whitney U test was used when comparing the groups. Statistical data are presented as M ± σ in the case of normal distribution and as Me [Q25; Q75] if the data were not subject to normal distribution. The results were considered statistically significant at p ≤ 0.05.

A total of 118 women were included in the study, but 29 patients dropped out of follow-up due to non-compliance with recommended therapy. In total, the therapy results of 89 patients aged 25 to 65 years (average age 47 ± 14 years) with excess body weight or obesity (average BMI before the study 33.67 ± 5.81 kg/m2) were analyzed. The “diet therapy” group included 53 patients; 36 patients took metformin in addition to following the diet. Although the prevalence of genotypes and allele A rs622342 SLC22A1 in the studied groups was comparable (Table 1), in the “diet therapy” group, the prevalence of genotypes and allele A did not comply with the Hardy-Weinberg law of genetic equilibrium (χ2 = 4.39; p = 0.04), which can be explained by the higher occurrence of the risk allele C in the sampling. In the group of “diet therapy and metformin”, the prevalence of genotypes and allele A corresponded to the Hardy-Weinberg law (χ2 = 0.57; p = 0.44).

The compared groups were comparable in terms of the CMD distribution, as well as the severity of body weight excess (Table 2.3).

In the absence of accounting for the method of treatment, the association of the A allele rs622342 SLC22A1 carrier with changes in the biochemical blood parameters of the patients was not revealed (Table 4).

In the “diet therapy” group, among homozygous carriers of allele C compared with carriers of allele A rs622342 SLC22A1, a more pronounced decrease in total cholesterol and triglycerides was observed three months after the follow-up start (Figs. 1, 2), while there were no differences in the decrease in HDL and LDL levels. There were no significant differences in the dynamics of glycated hemoglobin and fasting glucose levels (Table 5).

In the “diet therapy and metformin” group, no significant differences were found in the dynamics of fat and carbohydrate metabolism indicators among carriers of the A allele and CC genotype (Table 6).

During the analysis of literature data, we identified several opposing opinions of various groups of authors about the relationship of rs622342 SLC22A1 with changes in blood biochemical parameters. In the course of work conducted among representatives of the Mexican population by Res’endiz-Abarca et al., a significant decrease was revealed in the level of HbA1C among carriers of allele A relative to CC homozygotes rs622342 SLC22A1 at three and six months from the follow-up start [10]. In the study of Tkáč et al., conducted on the European population, rs622342 SLC22A1 was not associated with the dynamics of carbohydrate metabolism indicators [11]. In our study, conducted on the indigenous population of the Republic of Tatarstan, in the genetic composition of which the Caucasian component predominates [12], we also did not find an association of the polymorphic marker rs622342 SLC22A1 with changes in carbohydrate metabolism indicators.

The association of rs622342 SLC22A1 with changes in lipid fractions remains poorly understood. During the analysis of the literature, we found only one study, in which this issue was covered. In the course of a study conducted among the Indian population, there was no association of this polymorphism with changes in the levels of TC, TG, LDL, and HDL three months after the beginning of metformin administration [13], which is consistent with our results. At the same time, we found a significant decrease in the levels of TC and TG among homozygous carriers of CC who did not take metformin, which can level out the lipid-lowering effect of diet therapy when prescribing metformin in this category of patients. Further sample enlargement, in particular by including men in the study, will allow determining how applicable the results are for the European population as a whole.