UV filters are produced in high amounts for multiple uses. Their main application is in sun lotions for skin protection against accelerated ageing or cancer, but they are also found in many other cosmetics or in plastic materials to prevent their radiation-induced damage. Regardless of these protective properties, UV filters seem to interfere with both the reproductive and the thyroid endocrine axis. We here screened for effects of the UV filter benzophenone 2 (BP2) on thyroid hormone biosynthesis and serum levels. Possible inhibition of iodide uptake was examined using the sodium iodide symporter-expressing rat thyroid cell line FRTL-5, but inhibition was not observed. Effects on human thyroperoxidase (TPO) were measured using extracts prepared from human FTC-238 cells stably transfected with human TPO. BP2 inhibited TPO activity with IC50 values of 0.45 and 0.37 μmol H2O2 reduced per min and per mg protein in the guaiacol and the iodide oxidation assay, respectively. The values for the well known TPO inhibitor, genistein, were 61.1 and 2.06 μmol H2O2 × min−1 × mg−1, respectively. BP2 in combination with H2O2 inactivated TPO, an effect that was prevented by adequate iodide concentrations in the reaction mixture. To examine in vivo effects of BP2, adult female ovariectomized rats were treated via gavage for 5 days with olive oil (control) or with 10, 33, 100, 333 and 1000 mg/kg body weight BP2 (12 animals per group). Serum total T4 was reduced and TSH was increased; differences were significant for 333 and 1000 mg/kg BP2. The observed decrease in serum total T3 was not significant. Our data indicate that BP2 interferes with thyroid hormone biosynthesis, thereby disturbing thyroid hormone homeostasis. This may have consequences for human health, especially in the context of a still prevailing iodide deficiency in many parts of the world. Supported by EU grants.
01 - 05 Apr 2006
European Society of Endocrinology