Relationship between Plasma Antioxidants and Thyroid Hormones in Chronic Obstructive Pulmonary Disease

Background: A low-T-3 syndrome is observed in chronic diseases, but its treatment is still debated. Chronic obstructive pulmonary disease (COPD) has not been conclusively studied under this aspect. COPD is a complex condition, which cannot be considered a lung-related disorder, but rather a systemic disease also associated to increased oxidative stress. We evaluated thyroid hormones and antioxidant systems, the lipophilic Coenzyme Q(10) (CoQ(10)) and total antioxidant capacity (TAC) in COPD patients to reveal the presence of a low-T3 syndrome in COPD and investigate the correlation between thyroid hormones, lung function parameters and antioxidants. Methods: We studied: 32 COPD patients and 45 controls, evaluating thyrotropin (TSH), free-triiodotyronine (fT(3)), free-tetraiodotyronine (fT(4)), CoQ(10) (also corrected for cholesterol) and TAC. CoQ(10) was assayed by HPLC; TAC by the metmyoglobin-ABTS method and expressed as latency time (LAG) in radical species appearance. Results: We found significantly lower LAG values, fT(3) and fT(4) levels and significantly higher TSH in COPD patients vs. controls. LAG values significantly correlated with fT(3) concentration. 12 out of 32 patients exhibited fT(3) levels lower than normal range. So we divided COPD patients in 2 groups on the basis of the fT(3) concentration (normal fT(3) COPD and low fT(3) COPD). We observed lower LAG values in normal fT(3)-COPD, compared to healthy subjects, with a further significant reduction in low fT(3)-COPD patients. Moreover higher TSH concentration was present in normal fT(3)-COPD, compared to healthy subjects, with a further significant increase in low fT(3)-COPD patients. CoQ(10)/cholesterol ratio was higher in low fT(3)-COPD vs. normal fT(3)-COPD, with a nearly significant difference. Conclusions: These data seem to indicate an increased oxidative stress in low fT(3)-COPD and a role of fT(3) in modulating antioxidant systems. However low fT(3) levels are joined to metabolic indexes of true hypothyroidism, suggesting that elevated CoQ(10) expresses a reduced tissue utilization. These data might suggest the need of thyroid replacement therapy in such a condition.