LONG-TERM EFFECTS OF QUERCETIN ON OXIDATIVE STRESS PARAMETERS AND NITRIC OXIDE METABOLISM IN PATIENTS WITH TYPE 2 DIABETES MELLITUS

Introduction. Type 2 diabetes mellitus is associated with oxidative stress, impaired antioxidant defence, and dysregulation of nitric oxide metabolism, all of which contribute to the development of vascular and metabolic complications. The use of bioflavonoids, particularly quercetin, represents a promising approach for correcting these disturbances; however, the duration of persistence of its effects after treatment completion requires further investigation.Aim. The aim of the study was to evaluate the long-term effects of quercetin on oxidative stress parameters, antioxidant defence, and nitric oxide metabolism in patients with type 2 diabetes mellitus three months after completion of treatment.Materials and methods. The study involved 29 patients with type 2 diabetes mellitus, with a mean age of 59.41 ± 1.8 years; among them, 17 were men, and 12 were women. The mean duration of diabetes mellitus was 10.07 ± 1.16 years, and the mean body mass index was 30.69 ± 0.9 kg/m². Patients received quercetin in the form of the pharmaceutical preparation “Quertin” at a dose of one tablet twice daily for 20 days. Biochemical parameters were assessed before treatment, immediately after completion of therapy and 3 months after treatment. The activity of inducible NO synthase, constitutive NO synthase isoforms, arginase, superoxide dismutase and catalase, as well as malondialdehyde concentration, were determined.Results. Following treatment, superoxide dismutase activity increased from 7.185 ± 0.174 to 15.54 ± 0.479 and remained elevated at 13.08 ± 0.381 after 3 months. Catalase activity increased from 1.538 ± 0.062 to 3.024 (2.924-3.137), while after 3 months it was 2.581 ± 0.073. The level of malondialdehyde decreased from 29.12 (26.79-32.87) to 14.03 ± 0.391 and, after 3 months, remained lower than baseline at 15.03 ± 0.549. After 3 months, the activity of constitutive NO synthase isoforms increased to 0.068 (0.055–0.189), whereas arginase activity remained below baseline values. Integral comparison of the parameters at the three time points revealed statistically significant differences (H = 45.97; p < 0.0001). Differences between the post-treatment values and those obtained after 3 months were not statistically significant (p = 0.2488). Conclusions. The use of quercetin in patients with type 2 diabetes mellitus was associated with sustained positive changes in antioxidant defence parameters, lipid peroxidation and nitric oxide metabolism 3 months after completion of treatment.