Oxidative Stress Biomarkers and Their Association with Interleukin-6 in Patients with Obstructive Sleep Apnea: A Cross-Sectional Study

Oxidative stress and systemic inflammation are considered key mechanisms linking obstructive sleep apnea (OSA) to cardiovascular disease. This study aimed to investigate the relationships among oxidative stress, nitrosative stress, inflammatory biomarkers, and echocardiographic alterations in OSA. This cross-sectional observational study included 72 adults with OSA, classified according to disease severity as mild, moderate, or severe. Clinical characteristics and echocardiographic parameters were assessed. Oxidative stress biomarkers—malondialdehyde (MDA), total oxidant status (TOS), total antioxidant capacity (TAC), nitric oxide (NO), oxidative stress index (OSI), and paraoxonase-1 (PON1); the nitrosative stress marker 3-nitrotyrosine (3-NT), inflammatory biomarkers—interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α); and N-terminal pro-B-type natriuretic peptide (NT-proBNP)—were determined using spectrophotometric and ELISA methods. Correlation and regression analyses were performed to evaluate associations between oxidative stress and inflammation. No significant differences in echocardiographic parameters, oxidative stress biomarkers, inflammatory markers, or NT-proBNP concentrations were observed across OSA severity categories (all p > 0.05). Patients with diabetes mellitus exhibited larger left and right atrial diameters and higher pulmonary artery systolic pressure values compared with non-diabetic patients (all p < 0.05). Significant positive correlations were identified between IL-6 and MDA (ρ = 0.364, p = 0.002), TOS (ρ = 0.259, p = 0.029), and OSI (ρ = 0.257, p = 0.030). The nitrosative stress marker 3-NT was also positively correlated with MDA, TOS, and OSI (all p < 0.05). In multivariable regression analyses adjusted for age, body mass index, and diabetes mellitus, MDA remained independently associated with IL-6 concentrations (B = 1.776, 95% CI 0.110–3.442, standardized β = 0.271, p = 0.037). Similarly, OSI remained independently associated with IL-6 (B = 0.043, 95% CI 0.003–0.083, standardized β = 0.277, p = 0.034). OSA severity was not associated with significant differences in oxidative stress, inflammatory, or echocardiographic parameters. However, oxidative stress biomarkers were strongly interrelated and remained significantly associated with IL-6 concentrations, suggesting a potential link between oxidative stress and systemic inflammation in patients with OSA. These findings support further investigation of oxidative stress pathways as biomarkers of disease-related biological activity in OSA.