Tetrabromobisphenol A (TBBPA): Possible modes of action of toxicity and carcinogenicity in rodents

Due to potential consumer exposures, the toxicity of tetrabromobisphenol A (TBBPA) has been extensively studied. Reviews of TBBPA concluded no concerns regarding human health risks. The low toxicity of TBBPA is consistent with low bioavailability. However, some oral toxicity studies in rodents with TBBPA reported changes in thyroid hormone levels and a carcinogenicity study with TBBPA showed increased incidences of uterine tumors in rats. This review analyzes several modes of action (MoA) that may account for the observed thyroxine hormone changes and the uterine tumors. It concludes that the potential modes of action for thyroid changes induced by TBBPA are expected to exhibit a threshold for adverse effects due to the ability of the mammalian organism to compensate small changes in thyroid hormone levels. Regarding MoAs for the uterine tumors, TBBPA does not exert genotoxic or estrogenic effects. Available evidence suggests that TBBPA may increase levels of circulating estrogens by a competitive inhibition of estrogen conjugation and produce uterine tumors by promoting pre-existing Tp53-mutations due to increased estrogen levels resulting in increased cell proliferation.