Treatment of Hyperthyroidism Reduces Systemic Oxidative Stress, as Measured by Markers of RNA and DNA Damage.

BACKGROUND

Whole-body oxidative stress can be estimated by the urine excretion of oxidized guanosine species, 8-oxo-7,8-dihydroguanosine (8-oxoGuo) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), derived from RNA and DNA, respectively. These oxidative stress markers are not well explored in thyroid disorders.

OBJECTIVE

We aimed to determine whether treatment of hyperthyroid patients affects the levels of these oxidative stress markers.

METHODS

Urinary excretion of 8-oxoGuo and 8-oxodG was measured in 51 hyperthyroid patients (toxic nodular goiter [TNG], n = 30; Graves disease [GD], n = 21) before or shortly after initiation of therapy and when stable euthyroidism had been achieved for at least 12 months.

RESULTS

Adjusting for age, the baseline urinary excretion of oxidative stress markers correlated positively with plasma thyroxine (8-oxoGuo, P = 0.002; 8-oxodG, P = 0.021) and was significantly higher in GD than in TNG patients (P = 0.001 for both oxidative stress markers). Restoration of euthyroidism significantly affected the excretion of the oxidative stress markers. In TNG, 8-oxoGuo decreased from geometric mean 2.11 nmol/mmol creatinine (95% CI, 1.85-2.39) to 1.91 nmol/mmol (95% CI, 1.67-2.19; P = 0.001), while 8-oxodG decreased from 1.65 nmol/mmol (95% CI, 1.41-1.93) to 1.48 nmol/mmol (95% CI, 1.27-1.74; P = 0.026). In GD, 8-oxoGuo decreased from 2.25 nmol/mmol (95% CI, 1.95-2.59) to 1.79 nmol/mmol (95% CI, 1.63-1.97; P = 0.0003), while 8-oxodG decreased from 2.02 nmol/mmol (95% CI, 1.73-2.38) to 1.54 nmol/mmol (95% CI, 1.31-1.81; P = 0.001). In the euthyroid state, there were no differences between groups.

CONCLUSION

Restoration of euthyroidism in patients with hyperthyroidism significantly decreased the systemic oxidative stress load by 10% to 25%. Our findings may help to explain the higher morbidity and mortality linked to hyperthyroid diseases, as shown in observational studies.