Effects of selenium supplementation on antibodies of autoimmune thyroiditis

Abstract

To evaluate the effects of selenium (Se) supplementation on concentrations of thyroid peroxidase antibodies (TPOAb) and TPOAb IgG subclasses in autoimmune thyroiditis (AIT) patients with different thyroid functional status. A blind and placebo-controlled prospective study was performed for a total of 134 cases with AIT and thyroid peroxidase antibodies above 300 U/ml. Their mean age was 41 years (range: 15-70). All of them were recruited from Department of Endocrinology, First Affiliated Hospital of China Medical University from June 2008 to June 2009 and divided into 2 groups according to thyroid function: euthyroidism or subclinical hypothyroidism (n = 89) and hypothyroidism (n = 45). Then they were randomized into 2 groups: selenium-treated and placebo-treated. And 49 cases in subclinical autoimmune thyroiditis group and 28 cases in hypothyroidism group received 200 µg oral selenium yeast daily for 6 months while others placebo. Serum concentrations of TPOAb, TPOAb IgG subclasses, thyroid-stimulating hormone (TSH), free thyroxine (FT(4)) and Se were measured at baseline and after 3 and 6 months of follow-up. The TPOAb levels showed an overall decrease of 4.3% at 3 months and of 12.6% at 6 months (both P < 0.05) post-supplementation in subclinical autoimmune thyroiditis patients. In overt hypothyroidism patients, the overall decrease of TPOAb concentrations was 21.9% at 3 months and 20.4% at 6 months (both P < 0.05) compared with those at pre-treatment. The predominant TPOAb IgG subclasses in sera from the AIT patients were IgG1, IgG3 and IgG4 and the positive percentages 72%, 41% and 72% respectively. The positive rate and concentrations of IgG3 in the patients with hypothyroidism were significantly higher than those of subclinical autoimmune thyroiditis (P < 0.05). Significant decreases in IgG1 and IgG3 levels were noted in subclinical autoimmune thyroiditis group at 6 months post-supplementation (P < 0.05). IgG1 levels in overt hypothyroidism decreased significantly compared with those at pre-supplementation (P < 0.05). In all patients with supplementation (n = 77), the TPOAb levels decreased in 52 at 6 months while increase or no change occurred in 25. The positive percentage and concentrations of IgG1 in patients whose TPOAb levels decreased at 6 months post-supplementation were markedly higher than those whose TPOAb levels increased (P < 0.05). Se is effective in reducing TPOAb concentrations and the predominant decreasing TPOAb IgG subclasses are IgG1 and IgG3. And a high level of IgG1 subclass may explain the difficult decline of TPOAb.