Effect of iodine or iopanoic acid on thyroid Ca2+/NADPH-dependent H2O2-generating activity and thyroperoxidase in toxic diffuse goiters.

Objective: The aim of the present study was to compare the effects of iopanoic acid (IOP) or a saturated solution of potassium iodide (SSKI) administration to patients with toxic diffuse goiters (TDG).

Design: Patients with TDG are treated with thionamides and high doses of iodine preoperatively. In this study, two types of preoperative drug regimens were used: propylthiouracil or methimazole plus SSKI for 10-15 days (n=8) or IOP for 7 days (n=6).

Methods: Serum thyroid hormones (total and free thyroxine (T(4)), total tri-iodothyronine (T(3)) and reverse T(3) (rT(3)), were evaluated after 7 days of either SSKI or IOP treatment, and after 10-15 days of SSKI administration. During thyroidectomy, samples of thyroid gland were obtained to evaluate thyroperoxidase and thyroid H(2)O(2)-generating activities.

Results: Serum total T(3) was significantly decreased after 7 days of either treatment, and serum rT(3) was significantly increased in IOP-treated patients. Serum total and free T(4) were unaffected by 7 days of IOP treatment, but decreased after 7 days of SSKI treatment, although significantly diminished levels were only reached after a further 3-8 days of SSKI administration. During both drug regimens, serum TSH remained low (SSKI: 0.159+/-0.122; IOP: 0.400+/-0.109 microU/ml). Thyroperoxidase activity was significantly lower in thyroid samples from patients treated with SSKI for 10-15 days than in the thyroid glands from IOP-treated patients. However, thyroid H(2)O(2) generation was inhibited in samples from patients treated with either IOP or SSKI.

Conclusions: We show herein that IOP treatment can be effective in the management of hyperthyroidism and that this drug inhibits thyroid NADPH oxidase activity, just as previously described for SSKI, probably due to its iodine content.