Genotoxic damage after radioiodine therapy: Beneficial effect of dietary supplementation with the antioxidant ginkgo biloba extract.

Radioiodine (131I) is currently used for the treatment of hyperthyroidism and ablation of post-surgical remnants of differentiated thyroid cancer (DTC). Although it is generally advised as safe, some concern exits about the induction of genetic damage. This study was aimed to evaluate the possible effect of Ginkgo biloba extract (GBE) in reducing the genotoxic activity of 131I therapy. The micronucleus (MN) assay in peripheral blood lymphocytes was applied to assess the genotoxic potential of a single dose of 131I given to 19 patients with DTC (13 F, aged 16-68 years; 2.96-5.50 GBq) and 19 with Graves’ disease (14 F, aged 24-75 years; 185-851 MBq). Lymphocytes were taken at various intervals after 131I therapy (from 7 to 180 days), and evaluated for the presence of MN in the binucleated cells identified after blocking cytokynesis with cytochalasin B. GBE (120 mg/day for 30 days) was randomly assigned to both DTC and Graves’ patients. MN induction increased significantly (p<0.001) after 131I administration, peaking at day 7 and slowly declined thereafter in DTC while, in Graves’ patients progressively increased from 7° to 35° day. In both cases MN frequency at the peak was almost four fold that of baseline, and returned toward baseline after six-months. Supplementation with GBE modified the time course of MN induction in both groups: a slight not significant increase of MN without a peak was observed. Therefore, mean MN increment was significantly blunted (from 7.0±1.7 to 5.2±1.5, p<0.05 and from 8.5±1.3 to 4.6±1.5, p<0.01 in Graves’ and DTC patients, respectively). In conclusion, a single 131I treatment dose induced a transient significant increase in the MN frequency of peripheral blood lymphocytes in both DTC and Graves’ patients even if with different time courses. GBE supplementation significantly blunted such an increment thus reducing the genotoxic activity of 131I therapy.