Thyroid hormone-disrupting activity of brominated retardants and hydroxylated PCBs

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The thyroid hormone-disrupting activity of bisphenol A derivatives and some PCBs was estimated by the reporter assay using a rat pituitary cell line (GH3) and a Chinese hamster ovary cell line (CHO-K1). Tetrabromobisphenol A (TBBPA), tetrachlorobisphenol A, 4-hydroxy-2,2',3,4',5,5'-hexachiorobiphenyl, 4-hydroxy-3,3',4',5-tetrachlorobiphenyl and 4,4'-dihydroxy-3,3',5,5'-tetrachlorobiphenyl showed thyroid hormonal effect on GH3 cells. However, 4-hydroxy-2,2',5,5'-tetrachlorobiphenyl, 4-hydroxy-2',4',6'-trichlorobiphenyl, 3-hydroxy-2,2',5,5'-tetrachlorobiphenyl, 2,3',5,5'-tetrachlorobiphenyl and bisphenol A did not exhibit the activity. Especially, TBBPA, a flame retardant, exhibited the highest thyroid hormonal activity. In contrast, these chemicals showed anti-thyroid hormone effects on the activity of triiodothyronine (T3) in CHO-K1 cells transfected with thyroid hormone receptor (TR). 3,5-Substituted bromide or chlorine is an essential factor for the thyroid hormone-disrupting activity. The action of these chemicals was also estimated by amphibian metamorphosis using tadpole. The tail of tadpole was shortened by the addition of T3. These chemicals showed antagonistic effect on the T3-induced tadpole tail regression. These facts suggest that a brominated flame retardant, TBBPA, and hydroxylated PCBs exhibit endocrine-disrupting action in the wildlife.