CYTOCHEMICAL-LOCALIZATION OF THE ACETONE-INDUCIBLE CYTOCHROME-P-450 ISOFORM, CYP2E1, IN MURINE COLONIC EPITHELIUM

Immunolocalization of a toxicologically important cytochrome P-450 iso form, the alcohol-inducible CYP2E1, was examined in mouse colon. Male CD-1 mice (30-40 g) were exposed to acetone (1% v/v), a potent inducer of hepatic CYP2E1, in drinking water for 14 days. Tissue sections wer e fixed in 1% paraformaldehyde and incubated with anti-rat CYP2E1 poly clonal antibody. Immunohistochemical staining on tissue sections was p erformed using the indirect peroxidase-antiperoxidase method. In aceto ne-exposed mice, immunoreactivity was localized exclusively within the cytoplasm of surface epithelial cells of the proximal colon. Infreque ntly, only very faint staining was evident in colons of untreated cont rol mice. Using the same monospecific antibody, the presence of CYP2E1 was confirmed by Western blot analysis. A 2- to 3-fold elevation in i mmunoreactivity corresponding to cytochrome P-4502E1 was found in colo n microsomes isolated from acetone-exposed mice. Further evidence for colonic CYP2E1 is provided by elevation (up to 2.5-fold) in levels of chlorzoxazone 6-hydroxylase, a CYP2E1 substrate, after acetone treatme nt. The significance of these finding is discussed in terms of the pot ential for proximal colonic epithelial cells to participate directly i n bioactivation of dietary promutagenic substances.