Introduction

The use of statins to correct cholesterol metabolism disorders has significantly reduced the risk of complications such as acute coronary syndrome and, to a lesser extent, cerebrovascular disorders and other atherosclerotic lesions of peripheral arteries [1, 2]. The beneficial effects of statins, not only on cholesterol metabolism but also on the complex pathogenetic mechanisms underlying atherosclerosis and its complications, confer a distinct advantage over other drugs used to treat hypercholesterolemia [3]. Thus, statins are an essential component of therapy for patients at high risk of atherosclerotic vascular lesions and are included in treatment standards for coronary artery disease and arterial hypertension in most countries with advanced healthcare systems [4].

In contemporary Kazakhstan, statins prescribed according to indications are included in the guaranteed volume of free medical care. However, in cardiological practice, the proportion of prescriptions involving undesirable drug combinations remains considerably high [5].

The widespread use of statins by millions of people worldwide has generated significant interest in their safety profile [6]. Their substantial impact on metabolism is a factor contributing to the likelihood of adverse effects [7]. Several studies involving large patient cohorts have identified a hereditary basis for the increased risk of adverse effects during statin therapy [8]. Candidate genes considered in this context include liver cytochrome genes involved in drug metabolism [9] and genes encoding membrane transport proteins [10].

Furthermore, changes in statin efficacy associated with the presence of specific allelic variants of the corresponding genes have been identified [11].

Population-specific genomic characteristics are one of the reasons for the variability in therapeutic drug effects and the risk of adverse reactions and complications [12]. Our study is aimed at investigating the factors determining the pharmacogenetic characteristics of statin therapy in the Kazakh population.

Objective

To determine the frequency of the SLCO1B1 gene polymorphism in patients with coronary artery disease (CAD) from the Kazakh population of Eastern Kazakhstan and its association with the efficacy and safety of atorvastatin therapy.

Materials and Methods

A cross-sectional comparative clinical-genetic study was conducted.

The study included 178 individuals, comprising 108 men and 70 women aged 40 to 70 years (mean age 61.1 ± 7.8 years).

Inclusion criteria:

Exclusion criteria:

The study involved the clinical base of the Semey Emergency Hospital, the University Hospital of the Semey Medical University (Non-Commercial Joint-Stock Company), as well as primary healthcare (PHC) facilities where outpatient follow-up and treatment of patients included in the study were conducted.

The study did not involve active intervention into the ongoing treatment structure provided by family physicians, local practitioners, or cardiologists at the PHC level.

Data on the use of atorvastatin and other medications were obtained from inpatient medication charts, discharge summaries with treatment recommendations, and outpatient records containing prescriptions made by PHC physicians.

Genetic analyses were performed at the PCR Laboratory of the University Hospital, Semey Medical University (Non-Commercial Joint-Stock Company). Allelic variants of the OATP1B1 transporter protein gene SLCO1B1 (c.521T>C) were determined using polymerase chain reaction (PCR) on a BioRad instrument (USA) with SNP-Screen reagent kits in real-time PCR (RealTimePCR) according to the manufacturer's protocol (Sintol, Moscow).

Measurement of total cholesterol, lipoprotein fractions, and creatine phosphokinase (CPK) was performed on a PD 303S spectrophotometer at the Joint Educational and Scientific Laboratory of the Semey Medical University. Analyses were conducted before the start of statin therapy, at 2 months, and at 6 months.

The study employed descriptive statistical methods to determine the distribution structure of alleles and genotypes, as well as to describe the combinations of polymorphisms and prescribed drugs. Analysis of the significance of differences in numerical series was performed using the Mann-Whitney U test. The significance level for rejecting the null hypothesis was set at p < 0.05 [13].

Statistical data processing was performed using the STATISTICA Enterprise software package (StatSoft Inc., USA).

Results

Table 1 presents the distribution of the studied alleles and genotypes.

Table 1. Frequency of alleles and genotypes of the SLCO1B1 gene (polymorphism 521T>C)

Alleles and GenotypesAbsolute NumberFrequency (%)T29282.0C6418.0TT13173.6CT3016.9CC179.6

The frequency of the SLCO1B1 C allele was 18.0%. The total number of genotypes containing the C allele was 26.5%. No significant deviations from the expected equilibrium distribution were observed.

Table 2 presents data on the dynamics of cholesterol levels and CPK activity in the examined patients depending on the allelic forms of the studied gene.

Table 2. Biochemical parameters in patients depending on the SLCO1B1 genotype (polymorphism 521T>C)

ParameterTime of AssessmentGenotype  TT (n=131)TC (n=30)CC (n=17)  MeanSDMeanSDMeanSDTotal serum cholesterol (mmol/L)Before statin prescription7.711.447.921.387.731.09 At 2 months4.880.815.310.666.120.99 At 6 months4.32*0.774.87*0.706.101.03Serum LDL cholesterol (mmol/L)Before statin prescription4.180.694.270.654.250.87 At 2 months2.200.542.310.542.590.55 At 6 months2.02*0.482.20*0.472.51*0.52Serum CPK activity (U/L)Before statin prescription85.312.686.311.980.711.5 At 2 months120.514.5134.916.3196.8*#32.9 At 6 months119.617.1177.623.8406.0*#@85.0Notes: Mean; SD — standard deviation; * — differences from levels before statin prescription are significant (p < 0.05); # — differences from the indicator in the TT genotype group are significant; @ — differences from the indicator in the TC genotype group are significant.  

At baseline, the studied biochemical parameters showed no differences between the groups. Subsequently, total cholesterol levels were found to depend substantially on the genotype. Differences from patients carrying the TT genotype amounted to 25.4% at 2 months and 41.2% at 6 months (p = 0.047 for the latter). However, LDL cholesterol levels differed non-significantly across all groups (24.3% between TT and CC genotypes at 6 months).

Differences in serum CPK activity between groups were maximal when stratified by this criterion. The highest values were observed in the CC genotype group. Differences from the homozygous TT genotype were 63.3% at 2 months and 239.5% at 6 months (p = 0.043 and p < 0.001, respectively). Differences between the TC heterozygous and CC homozygous genotype groups at 6 months were also significant (128.6%, p = 0.015).

Analysis of the distribution of subjective muscular symptoms related to therapy revealed certain differences. Thus, at 2 months, among 14 patients reporting myalgia and/or muscle weakness, only 5 carried the TT genotype (3.8% of this subgroup), 2 carried the TC genotype (6.6%), whereas 7 out of 17 patients in the CC homozygous subgroup reported such symptoms (41.2%, χ² = 14.45, p = 0.005), which correlates well with the increase in serum CPK activity. At 6 months, the corresponding distribution was 6 (4.6%) for TT, 3 (10.0%) for TC, and 10 (58.8%) for CC (χ² = 23.31, p < 0.001).

Discussion

The genetic components of the risk of adverse effects from various drug combinations are a current priority in pharmacological research. The identified mechanisms of influence involve both the terminal catabolism of drugs (terminating their action) and the regulation of intracellular transport and cellular response to the active substance, which determines the features of pharmacodynamics [14].

Our study identified genetic factors that, according to current data, influence the transport of atorvastatin in hepatocytes. The polymorphism of the studied gene is a major factor determining the statin concentration at the site of primary pharmacological activity [12].

Analysis of the allele distribution frequency of the studied gene among the examined individuals revealed no deviations from the Hardy-Weinberg equilibrium.

According to several authors, the frequency of the "slow" SLCO1B15 allele (i.e., the C allele of the 521T>C polymorphism) in the European population ranges from 15.0% to 21.6% [15]. Research results indicate that the presence of one "slow" allele increases the probability of developing statin-induced myopathy by 4.5 times, while homozygous carriage increases it by more than 16 times. The frequency of various SLCO1B15 genotypes in Russia has also been determined (TT — 61.0%, TC — 32.5%, CC — 6.5%) [16].

In a study conducted by Uzbek scientists [17], the frequency of the C allele (521T>C polymorphism) in a group of CAD patients with good statin tolerance was 0.150. In a group of patients with complications during statin therapy, the frequency of this allele was 0.385 (χ² = 5.7; p = 0.017).

An important aspect is the analysis of the risk of statin therapy complications, the most significant of which is skeletal muscle damage [18].

In our study, a number of patients developed myalgias and muscle weakness during treatment. These cases corresponded to elevated serum CPK activity levels. The genetic factor demonstrating the greatest significance regarding these manifestations was the homozygous presence of the SLCO1B1 transporter protein gene polymorphism (521T>C). Other genetic variants had substantially less influence on the risk of this adverse effect or none at all. Simultaneously, this genotype was associated with a reduced lipid-lowering effect of atorvastatin.

The management of patients with cardiovascular diseases currently exhibits two characteristic features. On one hand, modern treatment technologies offer enormous potential for preventing and correcting established disorders. On the other hand, there is a clear deficiency in the systemic approach to individual patients, which would require strict monitoring of intervention efficacy and safety, as well as continuity of patient care. Genetic studies allow the assessment of population-level risk and the need for determining specific genetic variants in various clinical situations. The identification of a pronounced negative impact of the SLCO1B1 transporter protein gene polymorphism on the risk profile during atorvastatin use in the Kazakh population provides a clear indication for applying this analysis both when prescribing statins and when insufficient efficacy or signs of adverse effects on muscle tissue are detected.

Conclusion

Thus, in the examined group of patients receiving statin therapy, a high prevalence of genetic variants determining the risk of adverse drug reactions was identified. Statistically significant differences in the frequency of clinical manifestations of statin-induced myopathy were associated exclusively with the homozygous CC genotype of the SLCO1B1 gene (521T>C polymorphism). The obtained data allow considering this genotype as a prognostic marker of high risk for complications of lipid-lowering therapy (specifically atorvastatin) in the studied ethnic group, thereby justifying its utility in treatment personalization.