Persistent Redox Imbalance in Post-COVID-19 Syndrome: Lipid Peroxidation, Antioxidant Enzyme Depletion, and Reduced Nitric Oxide Availability in an Amazonian Population.

Post-COVID-19 syndrome (PCS) can persist even after mild acute illness, and oxidative stress has been proposed as a central mechanism for this persistence, although it remains poorly studied in the Amazon. This study characterized redox imbalance in patients with PCS through a combined analysis of lipid peroxidation, antioxidant defenses, and nitric oxide bioavailability. In a cross-sectional observational design, 85 patients with PCS and 53 healthy controls were evaluated, with determination of TBARS, total antioxidant capacity (ABTS), erythrocyte SOD, CAT, and GPx activity, plasma nitric oxide levels, and subgroup analysis according to disease duration (≤6, 6-12, and >12 months). Patients with PCS showed significantly higher TBARS concentrations and lower nitric oxide, ABTS, SOD, CAT, and GPx levels than controls, with predominantly large effect sizes. Lipid peroxidation correlated positively with HDL-c levels, and none of the markers differed significantly among the symptom duration subgroups. The findings indicate that PCS is associated with a persistent redox imbalance, marked by continuous lipid oxidative damage and sustained depletion of enzymatic and non-enzymatic antioxidant defenses, with a vascular component suggested by reduced nitric oxide levels, regardless of the time elapsed since symptom onset.