Context: No previous study determined monocyte- and lymphocyte-suppressing effects of levothyroxine and selenomethionine and assessed whether their coadministration is superior to treatment with only one of these drugs.
Objective: Our objective was to compare the effect of levothyroxine and selenomethionine on monocyte and lymphocyte cytokine release and systemic inflammation in patients with Hashimoto's thyroiditis.
Design, setting, participants, and intervention: We conducted a randomized clinical trial involving a group of 170 ambulatory euthyroid women with recently diagnosed and previously untreated Hashimoto's thyroiditis and 41 matched healthy subjects. Participants were randomized in a double-blind fashion to receive a 6-month treatment with levothyroxine, selenomethionine, levothyroxine plus selenomethionine, or placebo. One hundred sixty-five patients completed the study.
Main outcome measures: Monocyte and lymphocyte release of proinflammatory cytokines and plasma levels of C-reactive protein (CRP) were assessed.
Results: Compared with the control subjects, monocytes and lymphocytes of Hashimoto's thyroiditis patients released greater amounts of all cytokines studied. Levothyroxine reduced monocyte release of TNF-α, IL-1β, IL-6, and monocyte chemoattractant protein-1, whereas selenomethionine inhibited lymphocyte release of IL-2, interferon-γ, and TNF-α, which was accompanied by a reduction in plasma CRP levels. The decrease in cytokine release and in plasma CRP levels was strongest when both drugs were given together.
Conclusions: Despite affecting different types of inflammatory cells, levothyroxine and selenomethionine exhibit a similar systemic antiinflammatory effect in euthyroid females with Hashimoto's thyroiditis. This action, which correlates with a reduction in thyroid peroxidase antibody titers, may be associated with clinical benefits in the prevention and management of Hashimoto's thyroiditis, particularly in subjects receiving both agents.