Unique patterns of gene expression changes in liver after treatment of mice for 2 weeks with different known carcinogens and non-carcinogens

Previously we demonstrated that the mouse liver tumor response to the non-genotoxic carcinogens oxazepam and Wyeth-14,643 involved more differences than similarities in changes in early gene expression. In this study we used quantitative real-time PCR and oligonucleotide microarray analysis to identify genes that were up- or down-regulated in mouse liver early after treatment with different known carcinogens, including oxazepam (125 and 2500 p.p.m.), o-nitrotoluene (1250 and 5000 p.p.m.) and methyleugenol (75 mg/kg/day), or the non-carcinogens p-nitrotoluene (5000 p.p.m.), eugenol (75 mg/kg/day) and acetaminophen (6000 p.p.m.). Starting at 6 weeks of age, mice were treated with the different compounds for 2 weeks in the diet, at which time the livers were collected. First, expression of 12 genes found previously to be altered in liver after 2 weeks treatment with oxazepam and/or Wyeth-14,643 was examined in livers from the various chemical treatment groups. These gene expression changes were confirmed for the livers from the oxazepam-treated mice in the present study, but were not good early markers for all the carcinogens in this study. In addition, expression of 20 842 genes was assessed by oligonucleotide microarray [n = 4 livers/group, 2 hybridizations/liver (with fluor reversals)] and the results were analyzed using the Rosetta Resolver System and GeneSpring software. The analyses revealed that several cancer-related genes, including Fhit, Wwox, Tsc-22 and Gadd45b, were induced or repressed in unique patterns for specific carcinogens and not altered by the non-carcinogens. The data indicate that even if the tumor response, including molecular alterations, is similar, such as for oxazepam and methyleugenol, early gene expression changes appear to be carcinogen specific and seem to involve apoptosis and cell cycle-related genes.