Integrated disinfection by-products (DBP) mixtures research: gene expression alterations in primary rat hepatocyte cultures exposed to DBP mixtures formed by chlorination and ozonation/postchlorination.

Large-scale differential gene expression analysis was used to examine the biological effects of disinfected surface waters on cultured rat hepatocytes. Source water from East Fork Lake (Harsha Lake), a reservoir on the Little Miami River in Ohio, was spiked with iodide and bromide and disinfected by chlorination or ozonation/postchlorination. The chlorinated and ozonated/postchlorinated waters were concentrated, respectively, 136- and 124-fold (full strength) by reverse-osmosis membrane techniques. Volatile disinfection by-products (DBP) lost during concentration were restored to the extent possible. Primary rat hepatocytes were exposed to either full-strength or 1:10 or 1:20 dilutions of the concentrates for 24 h and assayed for cytotoxicity and gene expression alterations. The full-strength concentrates were cytotoxic, whereas the diluted samples exhibited no detectable cytotoxicity. Differential gene expression analysis provided evidence for the underlying causes of the severe cytotoxicity observed in rat hepatocytes treated with the full-strength ozonation/postchlorination concentrate (e.g., cell cycle arrest, metabolic stasis, oxidative stress). Many gene expression responses were shared among the hepatocyte cultures treated with dilutions of the ozonation/ postchlorination and chlorination concentrates. The shift in the character of the response between the full-strength concentrates and the diluted samples indicated a threshold for toxicity. A small subset of gene expression changes was identified that was observed in the response of hepatocytes to peroxisome proliferators, phthalate esters, and haloacetic acids, suggesting a peroxisome proliferative response.