Oxidative DNA Damage and DNA Binding Induced by 2, 2-Bis (Bromomethyl)-1, 3-Propanediol: Possible Mode of Action Implicated in its Carcinogenicity

Abstract

The studies in this dissertation research were conducted to investigate the possible mode of action by which a brominated flame retardant, 2, 2-Bis (bromomethyl)-1, 3-propanediol (BMP) causes genotoxicity. Binding of BMP to DNA and BMP induced DNA strand breaks were investigated in SV-40 immortalized human uroepithelial cells (UROtsa) as an in vitro model for the bladder (a tissue that developed cancer after two year exposure to BMP in rodents). Results showed binding of [¹⁴C]-BMP equivalents to DNA increased with increased exposure time and concentration of [¹⁴C]-BMP. Comet analysis indicated BMP significantly increased the extent of DNA strand breaks at 1 and 3 h of incubation. However, strand breaks were repaired by 6 h of incubation. The DNA damaging effects of BMP at 1 h was concentration dependent. Compared with the parent compound, BMP-glucuronide (the predominant metabolite of BMP) bound less to DNA and produced less DNA strand breaks in UROtsa cells. Evidences that the BMP induced strand breaks were the result of an oxidative stress include: a concentration and time dependent increase in ROS generation; increased expression of Nrf2 and HSP70; complete attenuation of BMP induced DNA strand breaks by the antioxidant, NAC; and the presence of the oxidized base 8-OHguanine. UROtsa cells appear to be target cells for BMP because, as compared to rat hepatocytes (non-target cells), these cells lack the ability to detoxify BMP via glucuronidation and also because they are deficient in glutathione, a major intracellular antioxidant molecule. Both of these genotoxic events, DNA binding and oxidative DNA damage may, in part, contribute to BMP carcinogenicity observed in rodents. The relevance of current results to humans is remained to be established.