2-Hydroxy-4-methoxybenzophenone (HMB) and 2,4,4′-trihydroxybenzophenone (THB) Suppress Amphibian Metamorphosis

Widely used in cosmetics and plastics, the class of chemical substances known as chemical ultraviolet (UV) filters make their way into the environment, polluting rivers and lakes and eventually accumulating in tissues of wildlife and humans. The ultimate consequence of this is unknown, although an increasing number of studies have confirmed the estrogenic activities of many of these substances. In the present study we make use of T-3 induced enhancement of amphibian metamorphosis to screen HMB and THB, two commonly used UV filters, for possible effect on thyroid hormone (TH) related processes. Our findings show that both substances inhibit T-3-induced tail atrophy and apoptosis in Rana rugosa tadpoles, as well as suppress spontaneous metamorphosis in Silurana tropicalis. Using transgenic Xenopus laevis tadpoles expressing EGFP driven by TR beta Al promoter region containing TH response element (TRE), these chemicals were found to prevent the binding of T-3 to TH receptor (TR), suggesting that both HMB and THB act as T-3 antagonists.