Induction of cyp2e-1 protein in mouse colon

The inducibility of a cytochrome P450 isoform, CYP2E1 (cyp2e-1), was compared in colonic epithelium of selected inbred mice. Mice were chosen for study on the basis of reported susceptibility to 1,2-dimethylhydrazine (DMH)-induced colorectal tumor formation. DBA/2J (resistant), C57BL/6J (intermediate) and SWR/J (susceptible) mice were exposed to acetone (1% v/v) in drinking water for 10 days. SWR/J mice sustained the largest increase in colonic cyp2e-1, although protein levels, assessed by Western analysis, were markedly increased in mucosal tissue obtained from C57BL/6J mice as well. Further evidence for colonic cyp2e-1 induction is supported by elevated (3.5-fold) chlorzoxazone 6-hydroxylase activity in response to acetone. To more fully characterize these changes in colon, the tumor-sensitive SWR/J mice were chosen for further evaluation. Mice were treated with a panel of agents established to induce this protein in liver, including isoniazid (0.1% v/v) and ethanol (10% v/v) in drinking water and pyrazole (300 mg/kg), given intraperitoneally. With the exception of ethanol, each compound produced a marked (1.5- to 3-fold) elevation of cyp2e-1 in colon and liver. Overall balance between phase I and II metabolism may be a critical factor in determining tumor susceptibility. Therefore, glutathione S-transferase (GST) activity was also examined. In liver, basal GST levels varied less than 2-fold between strains, while in colon, levels were 5-10% of corresponding hepatic levels. Although acetone treatment did not significantly alter hepatic GST, a 30-60% decline in activity was observed in colons of SWR/J and C57BL/6J mice. Further examination of colonic GST revealed compound-specific effects. Ethanol exposure markedly (60%) lowered GST levels in colon, whereas pyrazole produced a 2-fold increase. None of these agents significantly altered hepatic GST activity. These studies demonstrate the ability of mouse colon to undergo an increase in immunoreactive cyp2e-1 in response to a panel of xenobiotics known to elevate this protein in liver. Further characterization of cyp2e-1 and GSTs in inbred mice may provide important information on the role of colonocytes in direct activation of ingested procarcinogens to DNA-reactive metabolites.