Induction of DNA damage in human urothelial cells by the brominated flame retardant 2,2-bis(bromomethyl)-1,3-propanediol: Role of oxidative stress

Abstract

2,2-bis(bromomethyl)-1,3-propanediol (BMP) is an extensively used brominated flame retardant found in urethane foams and polyester resins. In a 2-year dietary study conducted by the National Toxicology Program, BMP caused neoplastic lesions at multiple sites including the urinary bladder in both rats and mice. The mechanism of its carcinogenic effect is unknown. In the present study, using SV-40 immortalized human urothelial cells (UROtsa), endpoints associated with BMP induced DNA damage and oxidative stress were investigated. The effects of time (1–24 h) and concentration (5–100 μM) on BMP induced DNA strand breaks were assessed via the alkaline comet assay. The results revealed evidence of DNA strand breaks at 1 and 3 h following incubation of cells with non-cytotoxic concentrations of BMP. Strand breaks were not present after 6 h of incubation. Evidences for BMP associated oxidative stress include: an elevation of intracellular ROS formation as well as induction of Nrf2 and HSP70 protein levels. In addition, DNA strand breaks were attenuated when cells were pre-treated with N-acetyl- l-cysteine (NAC) and oxidative base modifications were revealed when a lesion specific endonuclease, human 8-hydroxyguanine DNA glycosylase 1 (hOGG1) was introduced into the comet assay. In conclusion, these results demonstrate that BMP induces DNA strand breaks and oxidative base damage in UROtsa cells. Oxidative stress is a significant, determinant factor in mediating these DNA lesions. These early genotoxic events may, in part, contribute to BMP-induced carcinogenesis observed in rodents.