RESUMO
Ionizing radiation in differentiated thyroid cancer (DTC) patients treated with radioiodine (131-I) produces reactive oxygen species (ROS), which could induce oxidative stress with disturbance of redox balance. The aim of this study was to evaluate oxidative stress in DTC patients treated with 3.7 or 5.5 GBq of 131-I using values for serum malondialdehyde (MDA, a marker of oxidative stress), uric acid (to determine antioxidant status) and total antioxidative status (TAS). The study population included 20 DTC patients and 20 healthy controls. Significant differences in MDA concentrations were found between DTC patients before 131-I therapy and control subjects (p = 0.001), while TAS values were similar in both populations (p > 0.05). There was a negative correlation between MDA concentrations and TAS in the DTC group before therapy (R2 = 0.2973, p = 0.013). Three days after 131-I therapy, MDA concentrations were higher than the pretreatment values (3.36 +/- 1.69 nmol/mL vs. 2.93 +/- 1.31 nmol/mL; p = 0.006), while serum uric acid concentrations declined progressively from 341.0 +/- 80.39 micromol/L to 304.25 +/- 77.25 micromol/L (p = 0.026) in 3 days and 291.2 +/- 88.86 micromol/L (p = 0.009) in 7 days after 131-I therapy. There was no dose-dependent effect on MDA, or uric acid concentrations and TAS. Thus, 131-I therapy in DTC patients induced oxidative stress, which was accompanied by a simultaneous and extended reduction in uric acid concentration, but without significant disturbances in TAS. This is the first study that evaluated TAS capacity in DTC patients before and 7 days after 131-I therapy. The relatively stabile TAS values in these patients indicated a good protection from oxidative stress induced by high doses of ionizing radiation.
