Abstract

1,2-Dimethylhydrazine (DMH) is an organotropic colon carcinogen that undergoes metabolic activation to DNA-reactive metabolites. Twenty hours after parenteral treatment of AKR/J (colon tumor resistant) and SWR/J (susceptible) mice with DMH.2HCl (70 mg/kg), functional levels of Cyp1a1 and Cyp2e1 were examined by measuring O-deethylation of ethoxyresorufin (EROD) and hydroxylation of p-nitrophenol, respectively. In control animals, SWR/J mice exhibited higher hepatic EROD activity (1.4-fold) when compared with AKR/J mice. In carcinogen-treated animals, EROD activity was decreased 20-30% in both mouse lines. Hepatic p-nitrophenol hydroxylase activity, similar in control animals of both strains, was reduced comparably (45-50% of control) after DMH administration. In liver, a decrease in immunoreactive Cyp2e1 protein paralleled the decline in enzyme activity, whereas in the colon, no significant treatment-related differences were detected in either strain. In liver and colon cytosols, alcohol dehydrogenase activity was not significantly different in either mouse line, both in control and DMH-treated animals. Glutathione levels were elevated (1.7-fold) in livers of AKR/J mice after DMH administration. Total glutathione-S-transferase (GST) activity was significantly increased (1.8-fold) in the colons of SWR/J mice and in the livers (1.4-fold) of AKR/J mice. Furthermore, the GST isoform, GST-Yp, was reduced 40% in the SWR/J colon. These data demonstrate the importance of metabolic capacity as a factor in conferring differential tumor susceptibility in a murine cancer model to the indirect-acting colon carcinogen, DMH.