You are here:
Genotoxicity of Brominated Trihalomethanes in Human Bladder Cells
Citation:
Pegram, R., A. Teal, Steve Simmons, T. Ross, J. Campbell, D. DeMarini, AND B. Chorley. Genotoxicity of Brominated Trihalomethanes in Human Bladder Cells. Gordon Research Conference on Drinking Water Disinfection Byproducts, South Hadley, MA, July 30 - August 04, 2017.
Impact/Purpose:
This is the first report of brominated trihalomethane (BrTHM)-induced genotoxicity in human urothelial cells, and the first demonstration of glutathione S-transferase theta (GSTT1)-dependent BrTHM genotoxicity in eukaryotic cells. These findings provide evidence toward establishment of the biological plausibility of a hypothesis linking drinking water exposures to these prevalent drinking water disinfection byproducts to the etiology of human bladder cancer.
Description:
Epidemiological studies have consistently found that greater exposure to drinking water disinfection byproducts (DBPs) is associated with an increased risk for bladder cancer. In 2010, Cantor et al. (Environ. Health Perspect. 118: 1545) reported that this increased risk was dependent upon the GSTT1+ genotype and the implied expression of the xenobiotic metabolizing enzyme, glutathione S-transferase theta (GSTT1). We previously found that GSTT1 activates the prevalent DBPs, brominated trihalomethanes (BrTHMs), to mutagenic intermediates (Pegram et al., 1997, Toxicol. Appl. Pharm. 144: 183; DeMarini et al., 1997, Environ. Molec. Mutagen. 30: 440). In the present study, we determined both cytotoxicity and the induction of micronuclei by the BrTHMs, dibromochloromethane (DBCM) and bromodichloromethane (BDCM), in a human urothelial cell line (SV-HUC1) derived from normal human uroepithelium and in a novel transgenic line (SV-HUC-T1) that we engineered to stably overexpress human GSTT1. Gene transcription analysis (RT-PCR) confirmed overexpression of GSTT1 in the SV-HUC-T1 culture used in these experiments. Cell viabilities in the SV-HUC1 and SV-HUC-T1 lines, respectively, were 88% and 80% after 24 hr exposure to DBCM at 4 mM and 86% and 74% at 6 mM. We observed dose-dependent increases in micronuclei by both BDCM and DBCM, which were greater at all doses tested in the SV-HUC-T1 cells than in the parent cells. Compared to vehicle (DMSO)-treated controls, DBCM at nominal concentrations of 3 mM and 6 mM induced 2.1- and 5.3-fold increases in micronuclei per 1000 binucleated cells in the SV-HUC1 line and 3.1- and 7.7-fold increases in the SV-HUC-T1 line. Actual media concentrations of DBCM were estimated to be ~80% lower than nominal concentrations due to volatilization to headspace and adsorption to plastic in the micronuclei experiments. This is the first report of BrTHM-induced genotoxicity in human urothelial cells, and the first demonstration of GSTT1-dependent BrTHM genotoxicity in eukaryotic cells. [This abstract does not reflect EPA policy.]