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MEETING IN ATLANTA, GA - 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 IN ATLANTA, GA - COMPARATIVE CYTOTOXICITY OF TRIHALOMETHANES (THMs) AND TRIHALONITROMETHANES (THNMs) IN CULTURED NORMAL HUMAN COLON CELLS. Presented at Annual Biomedical Conference for Research for Minority Students, Atlanta, GA, November 03 - 05, 2005.
Description:
Epidemiological studies have linked the consumption of chlorinated surface waters to an increased risk of colorectal cancer. The THMs [trichloromethane, TCM, bromodichloromethane, 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) we're 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 (%C½) was calculated. The THNMs decreased cell growth with %C½ of 1x10-4 M, 1.5x10-4 M, 7.5x105 M, and 2.3x10-5 M for BDCNM, TCNM, DBCNM, and TBNM, respectively. Toxicity was related to the degree of bromination of the THNM. In contrast, the THMs exhibited no inhibition of cell growth (TCM) but increased the cell density 10-50% above the control value at concentrations between 1.5x10-4 M and 3x10-3 M, with the highly brominated species, DBCM and TBM, being the most active. 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 induced by exposure to DBPs.