Decreased Thyroid Peroxidase Antibody Titer in Response to Selenium Supplementation in Autoimmune Thyroiditis and the Influence of a Selenoprotein P Gene Polymorphism: A Prospective, Multicenter Study in China

Background: Recent intervention studies have suggested that selenium (Se) is an effective treatment for autoimmune thyroiditis (AIT). However, the exact effect of Se on AIT is unclear as well as the mechanism of action. The aim of the present study was to explore the effect of Se on thyroid peroxidase antibody (TPOAb) titers in patients with AIT and to analyze the potential impact of the genetic background on the effect of Se supplementation. Methods: This was a randomized, placebo-controlled, double-blind trial. Three hundred and sixty-four patients with elevated TPOAb (>300 IU/mL) were recruited and randomized to receive Se yeast 200 μg/day supplementation or placebo. Urinary iodine concentration, serum thyrotropin, free thyroxine, TPOAb, Se, malondialdehyde, and serum glutathione peroxidase activity were measured at baseline and follow-up. Ninety-six patients were genotyped for single nucleotide polymorphism r25191G/A in the selenoprotein P (SEPP1/SELENOP) gene. Results: The median urinary iodine concentration was 182 μg/L. Serum Se increased significantly (p < 0.001) after Se treatment. TPOAb titer decreased by 10.0% at 3 months and by 10.7% at 6 months after Se supplementation, while there was a moderate increase in TPOAb titers over the follow-up period in patients receiving placebo. Glutathione peroxidase activity significantly increased (p < 0.001), and malondialdehyde significantly decreased (p < 0.001) after 6 months of Se supplementation. TPOAb titers decreased to variable extents in patients with different genotypes of single nucleotide polymorphism r25191G/A after Se supplementation. Serum TPOAb titers in patients with the AA genotype showed a more significant decrease (by 46.2%) than those with the GA and GG genotypes (by 14.5 and 9.8% respectively) at 3 months of Se supplementation (p = 0.070). Conclusions: Se supplementation significantly reduced TPOAb titers in patients with AIT, and there may be an important genetic component influencing interindividual differences in the decrease in TPOAb titers.