Cytochemical localization of the acetone-inducible cytochrome P-450 isoform, CYP2E1, in murine colonic epithelium.

Immunolocalization of a toxicologically important cytochrome P-450 isoform, 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 were fixed in 1% paraformaldehyde and incubated with anti-rat CYP2E1 polyclonal antibody. Immunohistochemical staining on tissue sections was performed using the indirect peroxidase-antiperoxidase method. In acetone-exposed mice, immunoreactivity was localized exclusively within the cytoplasm of surface epithelial cells of the proximal colon. Infrequently, only very faint staining was evident in colons of untreated control mice. Using the same monospecific antibody, the presence of CYP2E1 was confirmed by Western blot analysis. A 2-to 3-fold elevation in immunoreactivity corresponding to cytochrome P-4502E1 was found in colon microsomes isolated from acetone-exposed form 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 treatment. The significance of these finding is discussed in terms of the potential for proximal colonic epithelial cells to participate directly in bioactivation of dietary promutagenic substances.