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MEETING AT RTP, NC - COMPARATIVE CYTOTOXICITY OF TRIHALOMETHANES (THMs) AND TRIHALONITROMETHANES (THNMs) IN CULTURED NORMAL HUMAN COLON CELLS
Citation:
KHAMDY, A. A., M. P. MOYER, AND A. B. DEANGELO. MEETING AT RTP, NC - COMPARATIVE CYTOTOXICITY OF TRIHALOMETHANES (THMs) AND TRIHALONITROMETHANES (THNMs) IN CULTURED NORMAL HUMAN COLON CELLS. Presented at North Carolina Society of Toxicology Spring Meeting, Research Triangle Park, NC, February 17, 2006.
Description:
Epidemiological studies have linked the consumption of chlorinated surface waters to an increased risk of colorectal cancer. The THMs [trichloromethane, TCM, bromo'dichloromethane, BDCM, dibromochloromethane, DBCM, and tribromomethane, TBM] comprise a major class of by-products (DBPs) formed when chlorine is used to disinfect drinking water. THMs have been demonstrated to increase preneoplastic lesions and colorectal cancer in laboratory rodents. Halonitromethanes (HNMs) characterized by the presence of a nitro moiety on the central carbon have recently been identified as chlorination DBPs and have received a high priority ranking for investigation by the EPA. We have initiated studies using normal human colonocytes (NCM-460) to explore toxicological, biochemical, and molecular alterations induced by the THMs and their nitro-congeners, the trihalonitromethanes (THNMs), for comparison to those observed in vivo. The effects of the THMs and THNMs on NCM-460 cell growth were monitored in 96-well plates using the crystal violet staining assay. NCM-460 cells (7000/well) were plated and incubated for 24 hr at 37' and 5% CO2. The cells were exposed to the THMs and THNMs at concentrations between 10-6 and 10-3 M for 72-96 hr. The concentration of the chemical that induced a 50% reduction of cell density when compared to the negative control (%C?) was calculated. The THNMs decreased cell growth with %C' of 1.0610-4 M , 9.83x 10-5 M, 7.07x 10-5 M, and 2.62x 10-5 M for BDCNM, TCNM, DBCNM, and TBNM, respectively. For comparison, the dihalonitromethanes exhibited %C's of 1.56x10-5 M (dibromonitromethane), 4.45x10-5 M (bromochloronitromethane), and 4.98x10-5 M (dichloronitromethane). Toxicity was related to the degree of bromination of the halonitromethane. In contrast, none of the brominated THMs inhibited cell growth at concentrations < 1 x 10-3 M. These experiments will serve as the basis of studies designed to examine THM- and THNM-induced DNA damage (strand breaks, adduct formation), cell proliferation and apoptosis, and gene expression alterations. The in vitro results will determine the suitability of cultured normal colonocytes to aid our understanding of the mechanisms underlying colon cancer that may be induced by exposure to DBPs.