Effect of antithyroid drugs on the occurrence of antibodies against type 2 deiodinase (DIO2), which are involved in hyperthyroid Graves' disease influencing the therapeutic efficacy.

Graves' disease is an organ-specific autoimmune disease with hyperthyroidism, diffuse goiter and autoantibodies against TSH receptor, thyroid peroxidase (TPO) and/or thyroglobulin (Tg). Graves' hyperthyroidism is characterized by T3 dominance due to the conversion of T4 into T3 through type 1 and 2 deiodinase enzymes (DIO1, DIO2). Methimazole (MMI) and propylthiouracil (PTU) therapies inhibit thyroid hormone synthesis blocking the activity of deiodinase and TPO enzymes. The study investigated the occurrence of autoantibodies against DIO2 peptides (cys- and hom-peptides) with the effect of antithyroid drugs on their frequencies in 78 patients with Graves' disease and 30 controls. In hyperthyroidism, the presence of DIO2 peptide antibodies was as follows: 20 and 11 cases out of 51 for cys- and hom-peptide antibodies, respectively, of whom 8 cases possessed antibodies against both peptides. Antithyroid drugs differently influenced their frequencies, which were greater in PTU than in MMI (3/6 vs 13/45 cases, P < 0.016 for cys- and 0/6 vs 2/45 cases for hom-peptide antibodies). Antibodies against both peptides demonstrated more reduced levels of anti-TPO (P < 0.003) and anti-Tg antibodies (P < 0.002) compared with those without peptide antibodies. PTU compared with MMI increased the levels of TSH receptor antibodies (32.5 UI/l vs 2.68 IU/l, P < 0.009). MMI treatment led to more reduced FT3 levels and FT3/FT4 ratios in hyperthyroid Graves' ophthalmopathy (P < 0.028 for FT3, P < 0.007 for FT3/FT4 ratio). In conclusion, the presence of DIO2 peptide antibodies is connected to Graves' hyperthyroidism influencing the levels of antibodies against TPO, Tg and TSH receptor, as well as the therapeutic efficacy of antithyroid drugs.