Soy extracts suppressed iodine uptake and stimulated the production of autoimmunogen in rat thyrocytes

Abstract

Soy consumption is associated with thyroid disorders such as hypothyroidism, goiter, and autoimmune thyroid disease (ATD) as well as increased iodine requirement in certain cases. However, the anti-thyroid component(s) in soy are yet to be identified and the molecular mechanism(s) involved remain unclear. This study examined the effects of soy isoflavones (ISF) on iodide uptake and expression of thyroglobulin (Tg) and sodium/iodide symporter (NIS) in thyrocytes. Fischer rat thyroid cells (FRTL) were treated with Novasoy (a soy alcohol extract containing 30% ISF) or major ISF aglycones or glycosides for 24 h. Iodide uptake was measured by a colorimetric assay. The protein level of Tg and NIS was measured by Western blotting. Cytotoxicity of tested compounds was determined by the MTT cell proliferation assay. Iodide uptake in FRTL cells was dose-dependently suppressed by Novasoy added into the cell culture (10, 25, or 50 µg/mL, P < 0.05). However, neither the major ISF aglycones nor glycosides alone or in combination had similar effects. Novasoy (up to 200 µg/mL) had no cytotoxic effect. Novasoy (1, 10, and 50 µg/mL) and genistein (1 and 10 µM) markedly increased the protein content of a 40 kDa Tg fragment (P40, a known autoimmunogen) and non-glycosylated NIS in the FRTL cells (P < 0.05). Overall, this study demonstrated that the alcohol soluble component(s) other than the major ISF in soy remarkably inhibited iodide uptake in the FRTL cells. Soy ISF, particularly genistein, induced the production of P40, which might be responsible for the higher incidence of ATD reported in soy infant formula-fed children.

Soy Reduces Bone Turnover Markers in Women During Early Menopause: A Randomized Controlled Trial

“…(29) In vitro studies have demonstrated that isoflavones inhibit thyroid peroxidase (TPO) and inhibit iodide. (30) However, other studies using different preparations for up to 3 years have not shown changes in thyroid hormones. (31) In patients with subclinical hypothyroidism, the soy protein and isoflavone combination has been shown to increase the risk of developing overt hypothyroidism.…”

The association between soya consumption and serum thyroid-stimulating hormone concentrations in the Adventist Health Study-2

“…Much more recently, soya isoflavones were shown to inhibit thyroid peroxidase in vitro and in vivo in rats although rat thyroid function remained normal (26) . Others have reported that in rats while soya isoflavones inhibit synthesis of thyroglobulin and thyroid hormones, availability of thyroid hormone in peripheral tissues may increase (27) . The observation that people living in Asian countries have consumed soya foods for centuries with no perceptible thyrotoxic effects suggests their safety in the general population.…”

Efeito Dos Nutrientes E Substâncias Alimentares Na Função Tireoidiana E No Hipotireoidismo

“…Por outro lado, a soja tem gerado preocupação sobre a função da glândula tireoide. 43 Pacientes com hipotireoidismo subclínico apresentam risco três vezes maior de desenvolver hipotireoidismo com suplementação de 16mg fitoestrógenos da soja ao dia. 44 Em estudo realizado com mulheres na menopausa, 45 75mg de isoflavonas reduziram os níveis de T3 livre, bem como aliviaram os sintomas da menopausa.…”