Inhibition of thyroid hormone sulfation by hydroxylated metabolites of polychlorinated biphenyls.

In this study we investigated the possible inhibitory effects of hydroxylated metabolites of polychlorinated biphenyls (OH-PCBs) on iodothyronine sulfotransferase activity. The results indicate that OH-PCBs are potent inhibitors of this activity in vitro, with IC50 concentrations in the low micro molar range. Inhibition of sulfotransferase activity towards 3,3'-diiodothyronine (T2) was similar to that towards 3,3',5-triiodothyronine (T3) in this in vitro assay, therefore, T2 can be used as the model substrate for the active hormone T3. An important structural requirement for T2 sulfotransferase inhibition is a hydroxyl group on the para or meta position of the OH-PCBs. Since T3 is the active hormone, playing a very important role in somatic and brain development and since hydroxylated PCBs can accumulate in fetuses, inhibition of T3 sulfation could be a possible mechanism for the developmental neurotoxicity of PCBs.