Thyroid Hormone Understanding Branches Out: Insights into PBDE Impacts on Brain Development

Understanding Branches Out Insights into PBDE Impacts on Brain Development Polybrominated diphenyl ether (PBDE) flame retardants and their hydroxylated metabolites are structurally similar to thyroid hormone. A detailed study now provides one of the most insightful assessments to date of how environmentally relevant levels of PBDEs may impair brain development by interfering with thyroid hormone receptor (TR)–mediated transcription [EHP 119(2):168–175; Ibhazehiebo et al.]. PBDEs were used for decades as f lame retardants in a wide variety of consumer and household goods, and U.S. citizens are widely exposed to them. Scientists know that PBDEs can cross the blood–brain barrier and accumulate in the central nervous system, and a growing body of evidence implicates these chemicals as developmental neurotoxicants. PBDEs and their metabolites have been detected in fetal blood, liver, and placenta, and in human milk. Thyroid hormone deficiency in the perinatal period can cause abnormal brain development. The study authors studied how PBDEs affected the mechanisms underlying thyroid hormone action in the developing brain using an established rodent cerebellum model. The experiments were designed to distinguish between effects on TR-mediated gene transcription due to 1) altered interactions between thyroid hormone and the TR and 2) altered interactions between the TR and short DNA sequences known as thyroid hormone response elements (TREs).