Study Of Allelic and Genotypic Variants of The C60t Polymorphic Locus of The Superoxide Dismutase (SOD) Gene in The Development of The Cardiovascular Form of Diabetic Autonomic Neuropathy in Patients with Type 2 Diabetes

Abstract

Diabetic autonomic (vegetative) neuropathy (DAN) is a severe and quite common complication of diabetes mellitus (DM), which is often overlooked or diagnosed late, remaining an underestimated target in therapeutic practice [1, 6]. DAN can manifest in clinically obvious or subclinical forms in patients within two years after diagnosis. The detection rate ranges from 20% to 40%, and with disease duration of more than 10 years, it exceeds 65%. DAN is recognized as an independent risk factor that reduces both quality of life and life expectancy by 2-10 times and is associated with an increased likelihood of further complications [8]. Diabetes mellitus is a leading cause of chronic autonomic neuropathies. The prevalence of autonomic disorders depends on the type of diabetes, being 54% for type 1 and 73% for type 2. The most unfavorable prognosis is associated with cardiac diabetic autonomic neuropathy, with mortality within five to ten years ranging from 27% to 56%. According to the metabolic theory of DAN pathogenesis, chronic hyperglycemia is the primary cause of the disorder, which activates the non-enzymatic glycosylation of nerve fiber sheath proteins and increases the activity of the polyol pathway of glucose metabolism. This leads to structural and functional damage to axons, segmental demyelination, and degeneration, accompanied by impaired axonal transport and slowed nerve conduction. The activation of lipid peroxidation causes damage to mitochondrial and neuronal membranes, leading to subsequent neuron death [4]. The primary markers are superoxide dismutases. The multifactorial nature of diabetic polyneuropathy (DPN) pathogenesis is now unquestionable [3]. Chronic hyperglycemia is the triggering factor for DPN development. Under hyperglycemic conditions, transmembrane glucose transport into endothelial and nerve tissue cells is activated, increasing its intracellular concentration and activating the polyol glucose utilization pathway [2]. Other significant pathogenic mechanisms of DPN include the increased production of superoxide anion radicals, formation of reactive oxygen species, development of oxidative stress, blockade of the hexosamine glucose utilization pathway, formation and accumulation of advanced glycation end products in nerve fibers, and endoneurial blood flow deficiency [7, 9]. Oxidative stress, caused by the excessive formation of free radicals against the backdrop of insufficient activity of the endogenous antioxidant system, is responsible for glucose metabolism disruption [10, 11]. Prolonged impairment of glucose metabolism is one of the main pathogenic mechanisms of DPN development [2].

Objective: The aim of this study was to investigate the role of the C60T gene polymorphism of SOD2 in the development of the cardiovascular form of diabetic autonomic neuropathy (DAN) in patients with type 2 diabetes.

Materials and Methods: The study included 135 patients with type 2 diabetes, with an average age of 56.3 ± 2.3 years and a disease duration of 5.6 ± 1.2 years, who were receiving outpatient treatment at three clinics of the Tashkent Medical Academy. Among them, 69 were women with an average age of 52.3 ± 3.4 years, and 66 were men with an average age of 54.3 ± 2.6 years. The control group consisted of 81 individuals with an average age of 53.6 ± 2.4 years. All patients were tested for fasting blood glucose, postprandial blood glucose (2 hours after eating), and glycated hemoglobin. As a glucose-lowering medication, 88 patients received DPP-4 inhibitors and biguanides, while 47 patients received combined therapy with basal insulin. Individuals who had experienced acute cardiovascular complications were excluded from the study. To diagnose cardiovascular form diabetic autonomic neuropathy (DAN-CV) in patients with type 2 diabetes, Holter monitoring was performed. Based on Holter monitoring parameters, the patients were divided into two groups: those with DAN-CV (+) and those without DAN-CV (-). All patients underwent genetic testing for the C60T polymorphism of the SOD2 gene at the Department of Molecular Genetics of the Republican Specialized Scientific-Practical Medical Center.

Results: In patients with type 2 diabetes, the fasting blood glucose level was 7.6 ± 2.3 mmol/L, and the postprandial blood glucose level (2 hours after eating) was 9.6 ± 1.4 mmol/L. The average glycated hemoglobin level was 9.2 ± 1.2%. According to the results of Holter monitoring and standard cardiovascular tests, 82 patients (60.7%) were diagnosed with DAN-CV (+), while 53 patients (39.2%) were diagnosed with DAN-CV (-). To evaluate the role of the C60T polymorphism of the SOD2

gene in the etiopathogenesis of DAN-CV in patients with type 2 diabetes, we conducted a comparative association study in a sample of patients and conditionally healthy individuals of Uzbek nationality. According to literature sources, the presence of the unfavorable allele of SOD2 (C60T) leads to the destabilization of the α-helical region, which disrupts the transport of the enzyme from the cytoplasm to the mitochondria, resulting in reduced antioxidant activity [5]. Our results also support these findings, as we established an associative link between the functionally weakened T/T genotype of the C60T locus of the SOD2 gene and the risk of developing DAN-CV in patients with type 2 diabetes.

The results of detection and the frequency of allelic and genotypic variants of the C60T locus of the SOD2 gene in the main group and subgroups of patients with type 2 diabetes, with and without DAN-CV, as well as in the control group, are presented in Tables 8, 9, and 10.