Biochemical Remodeling of Purine Metabolism and Lipid Peroxidation Across Thyroid Disease Phenotypes

Background and Objectives: Purine-metabolism profiles across distinct thyroid phenotypes remain poorly characterized despite the recognized redox imbalance associated with thyroid dysfunction and autoimmune thyroiditis (AIT). We compared plasma and erythrocyte purine-metabolite profiles, derived purine ratios, and their associations with lipid peroxidation across four thyroid-disease phenotypes and healthy controls. Materials and Methods: This single-center cross-sectional study included 164 participants: hypothyroidism without AIT (n = 31), AIT with hypothyroidism (n = 30), nontoxic nodular goiter with euthyroidism (n = 42), euthyroid AIT (n = 37), and healthy controls (n = 24). Purine metabolites were assessed by direct UV spectrophotometry and expressed in relative extinction units; thiobarbituric acid-reactive substances (TBARS)-derived malondialdehyde (MDA) equivalents were measured in plasma and erythrocytes.